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  • nitrogen  (60)
  • modeling  (50)
  • Textbook of geodesy
  • Springer  (116)
  • Irkutsk : Ross. Akad. Nauk, Sibirskoe Otd., Inst. Zemnoj Kory
  • Krefeld : Geologischer Dienst Nordhein-Westfalen
  • 2005-2009  (3)
  • 2000-2004  (113)
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Publisher
Years
Year
  • 1
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    Iceland Geodynamics - Crustal Deformation and Divergent Plate Tectonics (2006)
    Springer
    In:  Corporate, Florida, Springer, vol. Developments in Petroleum Science vol. 15B, no. Publ. No. 12, pp. 9, (3-540-24165-5, XXVI + 228 p.)
    Details
    Publication Date: 2006
    Description: This book provides a summary of geodynamic results from Iceland that presently are found in a great number of scientific articles, but have not been collected before in a book
    Keywords: Textbook of geodesy ; Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Geodesy ; Plate tectonics ; GeodesyY
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    BIBLIOGRAPHY SEISMOLOGY
  • 2
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    Volcano Deformation - New Geodetic Monitoring Techniques (2006)
    Springer
    In:  Cambridge, Springer, vol. LXXVIII, no. 2, pp. 125-169, (ISBN: 3-540-42642-6, Approx. 620 p. 30 illus., Hardcover)
    Details
    Publication Date: 2006
    Keywords: Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Volcanology ; Geodesy ; Global Positioning System ; InSAR ; Textbook of geodesy
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    BIBLIOGRAPHY SEISMOLOGY
  • 3
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    Physical Geodesy (2005)
    Springer
    In:  New York, 390 pp., Springer, vol. 36, no. XVI:, pp. 1-14, (ISBN 3-211-23584-1)
    Details
    Publication Date: 2005
    Description: Motivation, Fundamentals of potential theory The gravity field of the earth, Gravity reduction, Heights The geometry of the earth, Gravity field outside the earth, Space methods Modern views on the determination of the figure of the earth Statistical methods in physical geodesy, Least-squares collocation Computational methods, References, Subject index
    Keywords: Textbook of geodesy ; Global Positioning System ; Geoid ; Gravimetry ; Potential ; Theory ; Reference ; Systems ; collocation ; geodetic ; satellite ; techniques ; heights
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    BIBLIOGRAPHY SEISMOLOGY
  • 4
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    Geodesy: The Challenge of the Third Millennium (2003)
    Springer
    In:  New York, 473 pp., Springer, vol. 10, no. Subvol. b, pp. 220, (ISBN 3-540-43160-8)
    Details
    Publication Date: 2003
    Keywords: Geodesy ; Textbook of geodesy ; methods ; Data analysis / ~ processing ; Instruments ; Global Positioning System ; Very Long Baseline Interferometry ; InSAR ; geoid ; Gravimetry, Gravitation ; Earth rotation ; Strain ; visions ; for ; the ; future ; state ; of ; the ; science
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    BIBLIOGRAPHY SEISMOLOGY
  • 5
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    Global Positioning System - Theory, Algorithms and Applications (2003)
    Springer
    In:  Berlin, Springer, vol. 4, no. 1, pp. 1-40, (ISBN 0-06-057199-3)
    Details
    Publication Date: 2003
    Keywords: Geodesy ; Textbook of geodesy ; Handbook of geodesy ; Data analysis / ~ processing ; KSGSoft ; program ; software ; Filter- ; Error analysis
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    BIBLIOGRAPHY SEISMOLOGY
  • 6
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    Global Positioning System, Theory and Practice, 5th Edition (2000)
    Springer
    In:  New York, 390 pp., Springer, vol. 36, no. XVI:, pp. 1-14, (ISBN 0-89871-521-0)
    Details
    Publication Date: 2000
    Keywords: Global Positioning System ; Geodesy ; Handbook of geophysics ; Textbook of geodesy ; 1243 ; Geodesy ; and ; gravity ; Space ; geodetic ; surveys ; 1294 ; Instruments ; and ; techniques ; 1241 ; Satellite ; orbits
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    BIBLIOGRAPHY SEISMOLOGY
  • 7
    Electronic Resource
    Electronic Resource
    Difficulties in location and acceptance of phloem sap combined with reduced concentration of phloem amino acids explain lowered performance of the aphid Rhopalosiphum padi on nitrogen deficient barley (Hordeum vulgare) seedlings (2000)
    Springer
    Entomologia experimentalis et applicata 97 (2000), S. 203-210 
    Details
    ISSN: 1570-7458
    Keywords: EPG ; stylectomy ; phloem amino acids ; nitrogen ; aphid-plant interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Effects of nitrogen deficiency in hydroponically grown barley seedlings (Hordeum vulgare L.) on the development and reproduction of the aphid Rhopalosiphum padi (L.) (Hemiptera: Aphididae) were investigated. Plant growth was significantly reduced in seedlings grown without nitrogen. Aphid intrinsic rate of increase (r m) was also significantly lower on these plants compared with that on plants grown with 8 mol m−3 nitrogen. Phloem sap was collected from seedling stems by aphid stylectomy and amino acids quantified by HPLC. There was a significant reduction in the concentration of non-essential amino acids as a group, but not of essential amino acids. Electrical penetration graphs (EPG) indicated that aphids reached the phloem more quickly and fed for longer on plants grown with nitrogen. This is the first reported study in which this combination of techniques has been used to understand the interactions of an aphid and plant under different environmental conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004022608401
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  • 8
    Electronic Resource
    Electronic Resource
    Nutrient flows and land use change in a rural catchment: a modelling approach (2000)
    Springer
    Landscape ecology 15 (2000), S. 187-199 
    Details
    ISSN: 1572-9761
    Keywords: BOD5 ; catchment ; empirical model ; land use change ; land use scenarios ; nitrogen ; phosphorus ; runoff ; SO4
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Due largely to unprecedented land-use changes in the Porijõgi River catchment (southern Estonia) losses of nutrients and organic matter have decreased significantly. During the period 1987–1997 abandoned lands increased from 1.7 to 10.5% and arable lands decreased from 41.8 to 23.9%. At the same time, the runoff of total-N, total-P, SO4 and organic matter (after BOD5) decreased from 25.9 to 5.1, 0.32 to 0.13, 78 to 48, and 7.4 to 3.5 kg ha−1 yr−1, respectively. The most significant decreases occurred in agricultural subcatchments while the changes were insignificant in the forested upper course catchment. A simple empirical model which incorporates land-use pattern, fertilization intensity, soil parameters and water discharge accurately described the variations of total-N and total-P runoff in both the whole catchment and its agricultural subcatchments (R 2 varies from 0.95–0.99 for N to 0.49–0.93 for P). In small agricultural subcatchments the rate of fertilization is found the most important factor for nitrogen runoff, whereas in larger mosaic watersheds land use pattern plays the main role. Seven alternative scenarios compiled on the base of the empirical model allow to forecast potential nitrogen and phosphorus losses from the catchment. This information can be used in further landscape and regional planning of the whole region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008181811552
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  • 9
    Electronic Resource
    Electronic Resource
    Tithonia diversifolia as a green manure for soil fertility improvement in western Kenya: A review (2000)
    Springer
    Agroforestry systems 49 (2000), S. 201-221 
    Details
    ISSN: 1572-9680
    Keywords: biomass transfer ; integrated nutrient management ; nitrogen ; nutrient cycling ; phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Tithonia diversifolia, a shrub in the family Asteraceae, is widely distributed along farm boundaries in the humid and subhumid tropics of Africa. Green biomass of tithonia has been recognized as an effective source of nutrients for lowland rice (Oryza sativa) in Asia and more recently for maize (Zea mays) and vegetables in eastern and southern Africa. This paper reviews the potential of tithonia green biomass for soil fertility improvement based on recent research in western Kenya. Green leaf biomass of tithonia is high in nutrients, averaging about 3.5% N, 0.37% P and 4.1% K on a dry matter basis. Boundary hedges of sole tithonia can produce about 1 kg biomass (tender stems + leaves) m−1 yr−1 on a dry weight basis. Tithonia biomass decomposes rapidly after application to soil, and incorporated biomass can be an effective source of N, P and K for crops. In some cases, maize yields were even higher with incorporation of tithonia biomass than with commercial mineral fertilizer at equivalent rates of N, P and K. In addition to providing nutrients, tithonia incorporated at 5 t dry matter ha−1 can reduce P sorption and increase soil microbial biomass. Because of high labor requirements for cutting and carrying the biomass to fields, the use of tithonia biomass as a nutrient source is more profitable with high-value crops such as vegetables than with relatively low-valued maize. The transfer of tithonia biomass to fields constitutes the redistribution of nutrients within the landscape rather than a net input of nutrients. External inputs of nutrients would eventually be required to sustain production of tithonia when biomass is continually cut and transferred to agricultural land.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006339025728
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  • 10
    Electronic Resource
    Electronic Resource
    An Improved Greenspan Acoustic Viscometer (2000)
    Springer
    International journal of thermophysics 21 (2000), S. 983-997 
    Details
    ISSN: 1572-9567
    Keywords: acoustic resonator ; argon ; Greenspan viscometer ; helium ; helium-xenon mixture ; methane ; nitrogen ; speed of sound ; viscosity of gases ; xenon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An improved Greenspan acoustic viscometer (double Helmholtz resonator) was used to measure the viscosity of gases at temperatures from 250 to 400 K and at pressures up to 3.4 MPa. The improvements include a vibration damping suspension and the relocation of the fill duct. The fill duct, which is needed to supply gas to the resonator, was connected to the center of the resonator to eliminate acoustic coupling between the resonator and the manifold. In anticipation of handling corrosive gases, all surfaces of the apparatus that are exposed to the test gas are made of metal. The viscometer was tested with argon, helium, xenon, nitrogen, and methane. Isothermal measurements were carried out at 298.15 and 348.15 K and at pressures up to 3.2 MPa. Without calibration, the results differed from published viscosity data by −0.8% to +0.3% (0.47% r.m.s.). These results are significantly better than previous results from Greenspan viscometers. The measurements also yielded the speed of sound, which differed from literature data by +0.16% to +0.20% (0.18% r.m.s.). Adding empirical effective-area and effective-volume corrections to the data analysis decreased the r.m.s. deviations to 0.12% for the viscosity and to 0.006% for the speed of sound. No unusual phenomena were encountered when the viscometer was tested with a helium-xenon mixture between 250 and 375 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026471901657
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  • 11
    Electronic Resource
    Electronic Resource
    SHADOC: a multi‐agent model to tackle viability of irrigated systems (2000)
    Springer
    Annals of operations research 94 (2000), S. 139-162 
    Details
    ISSN: 1572-9338
    Keywords: irrigated system ; modeling ; multi‐agent system ; simulation ; social networks ; coordination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract The viability of irrigated systems in the Senegal River Valley is being brought into question today due to their under‐utilization. We assume that their viability depends largely on the way their different components behave and interact. We therefore sought to examine in greater depth today's knowledge of the structure of these systems and activities performed within them. This led to the development of a multi‐agent system model, a kind of virtual irrigated system, with a special focus on rules in use for access to credit, water allocation and cropping season assessment as well as organization and coordination of farmers. The purpose of this paper is to show how this kind of tool is relevant to the study of irrigated systems' viability. As an example it is used to examine the influence of existing social networks on the viability of irrigated systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018908931155
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  • 12
    Electronic Resource
    Electronic Resource
    Product Hardware Complexity and Its Impact on Inventory and Customer On-Time Delivery (2000)
    Springer
    International journal of flexible manufacturing systems 12 (2000), S. 145-163 
    Details
    ISSN: 1572-9370
    Keywords: inventory ; modeling ; postponement ; supply chain management
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This paper studies the impact of a reduction in hardware complexity on the supply-chain inventory against various customer on-time delivery alternatives and manufacturing environments. Different methods of reducing hardware complexity are proposed, and their impact on total supply-chain inventory and customer serviceability quantified. An analytical inventory optimization scheme taking into account multistage supply networks, product structure, forecast accuracy, lead-time variability, and supplier reliability is used to determine optimal inventory levels in a stochastic modeling environment. The analysis is based on a business case for an IBM midrange computer family consisting of more than 200 models and upgrades with hundreds of features. We investigate different hardware complexity reduction strategies, including low-usage feature reduction, low-volume feature reduction, and feature substitution, as well as quick response and postponement mechanisms. Our computational results show that, in a fabrication-fulfillment center environment, reducing hardware complexity results in significantly higher inventory savings than in an integrated manufacturing environment. The results presented in this paper were used to reduce hardware complexity in IBM's midrange computer division.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008191530004
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  • 13
    Electronic Resource
    Electronic Resource
    Acoustic and Volumetric Virial Coefficients of Nitrogen (2000)
    Springer
    International journal of thermophysics 21 (2000), S. 1033-1044 
    Details
    ISSN: 1572-9567
    Keywords: intermolecular potential ; nitrogen ; speed of sound ; virial coefficients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Speeds of sound in nitrogen were measured at temperatures between 170 and 400 K at amount-of-substance densities between 40 and 400 mol·m−3. From these measurements, second and third acoustic virial coefficients were obtained. The parameters of two- and three-body isotropic intermolecular potential-energy models were optimized in a simultaneous fit to the second and third acoustic virial coefficients and the ordinary second and third virial coefficients of nitrogen reported by Nowak et al. The results, which shows that the acoustic and ordinary virial coefficients are mutually consistent, may be used to predict second and third virial coefficients, and their acoustic counterparts, over a wide range of temperatures. The parameters of an anisotropic site-site potential-energy model were also obtained from a fit to the acoustic and ordinary second virial coefficients alone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026489719404
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  • 14
    Electronic Resource
    Electronic Resource
    Transient Thermal Study of an Adsorption Refrigerating Machine (2000)
    Springer
    Adsorption 6 (2000), S. 93-104 
    Details
    ISSN: 1572-8757
    Keywords: adsorption refrigerator ; transient operation ; activated carbon ; methanol ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Adsorption refrigerators are a particular type of refrigerator in which compression is avoided, and in a sense replaced by adsorption. No mobile parts are needed; the energy input, instead of being mechanical, is thermal and is used to achieve desorption. Such machines have a cyclic operation, made of successive adsorption/evaporation and of desorption/condensation steps. The transient operation of adsorption refrigerators is a relatively recent subject of research. The modeling of the adsorber is the key point of such studies, because of the complex coupled heat and mass transfer phenomena that occur during the cycle. The present work therefore presents a study of an annular type adsorber which is intended to account for transient temperatures observed experimentally. The equipment in which the experiments were performed and which uses alcohol adsorption on activated carbon is briefly described, and its operating cycle described, along with typical experimental observations of pressure and temperature transients. A model of the adsorber unit is proposed which accounts for the coupling of adsorption and heat transfer, and describes mass-transfer in the annular adsorbent layer as a global diffusional mechanism with temperature dependent parameters. This model correctly predicts, qualitatively and semi-quantitatively, the observed trends of the temperature changes. Finally, various aspects of the performances are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008907518073
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  • 15
    Electronic Resource
    Electronic Resource
    Theoretical chemistry as a tool for interpreting catalysts selectivities (2000)
    Springer
    Topics in catalysis 13 (2000), S. 213-219 
    Details
    ISSN: 1572-9028
    Keywords: heterogeneous catalysis ; selectivity ; quantum chemistry ; modeling ; butadiene ; α–β unsaturated aldehydes ; enantioselectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Reaching high selectivities is an important concern for heterogeneous catalysis. Insights in the factors which control the reaction selectivity can be obtained from theoretical approaches, also a full computational description of the reaction is not yet possible, due to the great complexity of the molecules generally involved in fine chemical catalysis. Some theoritical works related to the interpretation of chemical selectivity are rewieved in this paper, with a focus on the various types of selectivity: chemoselectivity, regioselectivity and enantioselectivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009002921067
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  • 16
    Electronic Resource
    Electronic Resource
    Short- versus Long-Term Effects of Elevated CO2 on Night-Time Respiration of Needles of Scots Pine (Pinus sylvestris L.) (2000)
    Springer
    Photosynthetica 38 (2000), S. 57-67 
    Details
    ISSN: 1573-9058
    Keywords: carbon ; C/N ; direct and indirect effects ; nitrogen ; soluble sugars ; starch ; specific leaf area
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Dark respiration rate in the night (R D) was measured in five-year-old Scots pine (Pinus sylvestris L.) trees grown for two years under ambient (AC) and elevated (AC + 400 µmol mol−1 = EC) CO2 concentrations in open top chambers. Two needle age classes (i.e., current-year and one-year-old) were measured at AC and EC in both AC- and EC-grown pines. Additionally different chemical characteristics were determined on the needles, such as nitrogen (N), carbon (C), starch, and soluble sugar concentrations as well as specific leaf area. The direct, short-term and indirect, long-term effects of EC on R D for the two needle age classes were examined. R D was expressed on a per needle area, needle mass, N, C, and C/N bases. Direct effects were only pronounced in the AC treatment where inhibition of R D was found at EC in both current- and one-year-old needles. Indirect effects were only significant in one-year-old needles where a decrease was found in the EC grown trees as compared with AC ones when R D was expressed per unit needle mass, C, or C/N. R D per unit needle area and needle N were not sensitive to long-term EC, in any needle age class. Long-term EC treatment also influenced the response of the two needle age classes. One-year-old needles from the EC treatment had significantly lower R D than current-year needles, but no such response was observed in the AC treatment. Our experiment re-emphasised the importance of expressing R D on different bases for a correct interpretation of the responses to EC. Moreover, we showed that different needle age classes can respond differently to a CO2 enrichment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026743907621
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  • 17
    Electronic Resource
    Electronic Resource
    The Role of Plant Size and Nutrient Concentrations in Associations between Medicago, and Rhizobium and/or Glomus (2000)
    Springer
    Biologia plantarum 43 (2000), S. 221-226 
    Details
    ISSN: 1573-8264
    Keywords: alfalfa ; arbuscular mycorrhizal fungi ; nitrogen ; nitrogen-fixing bacteria ; phosphorus ; plant growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The aim of this research was to carry out a critical study of the method of obtaining size equivalence between non-symbiotic alfalfa and alfalfa associated with Glomus and/or Rhizobium by applying fixed addition rates of nutrients to the non-symbiotic controls. The experimental design included three nutrient response curves in which the levels of added phosphorus and/or nitrogen were constant during the whole plant growth process: 1) a phosphorus response curve, in order to compare the growth of double symbiotic plants with that of only-Rhizobium inoculated ones; 2) a nitrogen response curve, that consisted of a comparison between the growth of double symbiotic alfalfa and four treatments associated only with Glomus; 3) a phosphorus and nitrogen response curve, to compare the growth of non-inoculated alfalfa with that of double symbiotic plants. Although similar size was achieved among some treatments at harvest, shoot growth over time and nutrient concentrations in tissues differed, indicating that growth equivalence did not mean functional equivalence. A second experimental design was performed taking into account the establishment of microsymbionts for determining the adequate moment to add supplemental phosphorus and/or nitrogen. It included four treatments: a) double symbiotic plants (MR); b) plants inoculated with Rhizobium only (R); c) plants inoculated with Glomus only (M), and d) non-inoculated plants (N). Great similarity in terms of plant growth and nutrient contents in tissues were obtained. Moreover, symbiotic plants were able to produce similar dry matter than non-symbiotic ones under P and N limitations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002700226167
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  • 18
    Electronic Resource
    Electronic Resource
    Respiration Rate and Chemical Composition of Karwinskia Roots as Affected by Temperature (2000)
    Springer
    Biologia plantarum 43 (2000), S. 611-613 
    Details
    ISSN: 1573-8264
    Keywords: carbon ; hydrogen ; nitrogen ; reducing sugars ; starch ; summer and winter temperature regime
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two-year-old plants of Karwinskia humboldtiana Zucc. and Karwinskia parvifolia Rose grown from the seeds in greenhouse were transferred to the growth cabinet and cultivated for two months under different temperature regimes (35/20 °C - the summer temperature regime, SR, and 20/5 °C - the winter temperature regime, WR). These temperatures were similar to the temperature conditions in the natural areas of the species studied (Nuevo León, Mexico). The root respiration rate was higher in the plants cultivated under SR than in those under WR. Roots of K. parvifolia res faster in both temperature regimes than roots of K. humboldtiana. Starch content in roots was higher in the plan cultivated under SR, however, concentrations of the other investigated organic and inorganic compounds were higher in the plants cultivated under WR. In K. humboldtiana roots, higher concentration of reducing sugars, carbon and hydrogen were found than in K. parvifolia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002808201124
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  • 19
    Electronic Resource
    Electronic Resource
    Population Dynamics of Biocontrol Agents and Pathogens in Soils and Rhizospheres (2000)
    Springer
    European journal of plant pathology 106 (2000), S. 401-413 
    Details
    ISSN: 1573-8469
    Keywords: inoculum density–disease incidence ; biological control agents ; pathogen detection and quantification with molecular and serological techniques ; polymerase chain reaction ; marker and reporter genes ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Understanding the dynamics between a pathogen and a biocontrol agent (BCA) in soil or in an infection court such as the rhizosphere is crucial for predicting the success of biological control. This is especially true for biological control using the strategy of reduction of initial inoculum prior to infection. By studying the population density fluxes over time, one can observe how the BCA and pathogen influence each other's population and life cycles, and how the biological and physical environment influence this relationship. Methods for quantifying fungi and bacteria in soil, including classical (dilution plating, baiting, bioassays), immunological (ELISA, IFC, immunomagnetic) and molecular (DNA hybridization, PCR, marker and reporter genes) methods, are discussed and critiqued. Finally, the value of mathematical modeling of population dynamics as a means of providing important information about the tripartite relationship between the pathogen, BCA, and host plant is reviewed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008733927515
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  • 20
    Electronic Resource
    Electronic Resource
    Automatic Guided Vehicles: Robust Controller Design in Image Space (2000)
    Springer
    Autonomous robots 8 (2000), S. 25-42 
    Details
    ISSN: 1573-7527
    Keywords: visual servoing ; robust control ; mobile robot ; vehicles ; modeling ; vision
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We have been interested in Automatic Guided Vehicles (AGV) for several years. In this paper, we synthesize controllers for AGV applications using monocular vision. In particular, we are interested in road following and direction change tasks, and in analyzing the influence of extrinsic camera parameter perturbations on vehicle behavior. We use the bicycle as the kinematic vehicle model, and we choose the position of the white band on the road as the sensor signal. We define an interaction between the camera, which is mounted inside the vehicle, and the white band detected in the image space. Using this kind of interaction, we present how to use a pole assignment technique to solve the servoing task. We show the simulation and experimental results (1/10 scale demonstrator) with and without perturbations. We then investigate the use of a robust controller to slow down the effect of perturbations on the behavior of the vehicle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008936817917
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  • 21
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    Grain-Scale Modeling of CVD of Polycrystalline Diamond Films (2000)
    Springer
    Journal of materials synthesis and processing 8 (2000), S. 73-85 
    Details
    ISSN: 1573-4870
    Keywords: Chemical vapor deposition (CVD) ; diamond films ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The evolution of grain size, grain-size distribution, morphological and crystallographic texture, surface roughness, and the contribution of various surface facets to the growth of polycrystalline diamond films is performed by carrying out a series of two-dimensional computer simulations. The films are assumed to grow from a set of randomly oriented, {100}- and {111}-faceted nuclei by the motion of their vertices (the points where the adjoining facets of the same or neighboring grains meet). The vertex velocities are found to be a function of the orientation and the growth rate of the adjoining facets. To quantify the latter, a {100} to {111} growth-rate parameter is used. The results show that the evolution of the grain size and its distribution, surface roughness, morphological and crystallographic texture, and the portion of the film grown from different surface facets are all mutually linked and governed by the magnitude of the growth-rate parameter. The latter can be controlled by the CVD processing conditions, such as the substrate temperature, reactor pressure, mole fraction of carbon-source gas (e.g., CH4, C2H2).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026517919085
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  • 22
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    A Population Density Approach That Facilitates Large-Scale Modeling of Neural Networks: Analysis and an Application to Orientation Tuning (2000)
    Springer
    Journal of computational neuroscience 8 (2000), S. 19-50 
    Details
    ISSN: 1573-6873
    Keywords: neural networks ; modeling ; population density ; orientation tuning ; visual cortex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Medicine , Physics
    Notes: Abstract We explore a computationally efficient method of simulating realistic networks of neurons introduced by Knight, Manin, and Sirovich (1996) in which integrate-and-fire neurons are grouped into large populations of similar neurons. For each population, we form a probability density that represents the distribution of neurons over all possible states. The populations are coupled via stochastic synapses in which the conductance of a neuron is modulated according to the firing rates of its presynaptic populations. The evolution equation for each of these probability densities is a partial differential-integral equation, which we solve numerically. Results obtained for several example networks are tested against conventional computations for groups of individual neurons. We apply this approach to modeling orientation tuning in the visual cortex. Our population density model is based on the recurrent feedback model of a hypercolumn in cat visual cortex of Somers et al. (1995). We simulate the response to oriented flashed bars. As in the Somers model, a weak orientation bias provided by feed-forward lateral geniculate input is transformed by intracortical circuitry into sharper orientation tuning that is independent of stimulus contrast. The population density approach appears to be a viable method for simulating large neural networks. Its computational efficiency overcomes some of the restrictions imposed by computation time in individual neuron simulations, allowing one to build more complex networks and to explore parameter space more easily. The method produces smooth rate functions with one pass of the stimulus and does not require signal averaging. At the same time, this model captures the dynamics of single-neuron activity that are missed in simple firing-rate models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008912914816
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    Co-development of wetland soils and benthic invertebrate communities following salt marsh creation (2000)
    Springer
    Wetlands ecology and management 8 (2000), S. 197-207 
    Details
    ISSN: 1572-9834
    Keywords: benthic invertebrates ; mitigation ; nitrogen ; organic matter ; pedogenesis ; phosphorus ; plant productivity ; restoration and rehabilitation ; salt marsh ; wetland creation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The development of wetland soil characteristics andbenthic invertebrate communities were evaluated increated Spartina alterniflorasalt marshes inNorth Carolina ranging in age from 1 to 25 years-old.A combination of measurements from different-agecreated marshes as well as periodic measurements overtime on two marshes were used to (1) document rates ofwetland pedogenesis, especially soil organic matter,and, (2) explore relationships between soil andbenthic invertebrate community development. Soilmacro-organic matter (MOM, the living and dead rootand rhizome mat), organic C and N increased and bulkdensity decreased during the 25 years following marshestablishment. The most dramatic changes in bulkdensity, MOM, C and N occurred within the upper 10 cmof the soil with lesser changes below this depth.Created marshes were sinks for organic C (90–140g·m-2·yr-1) and N (7–11g·m-2·yr-1) but not for P (0–1g·m-2·yr-1). The density of benthicinvertebrates (〉250 μm) and subsurface-depositfeeding oligochaetes also increased over time oncreated salt marshes. Invertebrate and oligochaetedensity were strongly related to MOM content(r2= 0.83–0.87) and soil organic C(r2= 0.52–0.82) and N (r2= 0.62–0.84). Thesefindings suggest that, in created salt marshes,development of the benthic invertebrate community istied to marsh soil formation, especially accumulationof organic matter as MOM and soil. Field studies thatmanipulate the quantity and quality of soil organicmatter are needed to elucidate the relationshipbetween salt marsh pedogenesis and benthicinvertebrate community development.
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    URL: http://dx.doi.org/10.1023/A:1008448620605
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    An Approach to Estimating Hydro Power System Income Gain from Computerized Water Scheduling (2000)
    Springer
    Natural resources research 9 (2000), S. 215-222 
    Details
    ISSN: 1573-8981
    Keywords: market ; electricity ; regression ; calibration ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Hydro power schemes operating in a free electricity market seek to maximize profits by differing generation rates to take best advantage of fluctuating selling prices, subject to the constraints of keeping storage lakes within their operational bounds and avoiding spillage losses. Various computer algorithms can be used in place of manual scheme operation to aid this maximization process, so it is desirable to quantify any profit gained from a given algorithm. A standard approach involves applying the algorithm to a period of past river flow records to see how much additional scheme income might have been obtained. This process requires the use of a hydro power scheme model, which inevitably can only approximate operational details, so the anticipated income gains are likely to be biased estimates of actual income gained from implementation of the algorithm. In addition to preliminary algorithm evaluation, it is desirable that hydro scheme managers have methodology to confirm anticipated income gain. Such confirmation can be difficult because true income gains are typically in the order of a few percentage and may not be easily distinguishable from background noise. We develop an approach, which allows estimation of true income gain for the situation where a change is made from manual to computer control of hydro power scheme operations, or upgrading from one maximization algorithm to another. The method uses a regression model to describe the former period of scheme operation. Postimplementation residuals from the regression predictions then provide estimates of actual income gain. The method can be sensitive to small but consistent income gains. Also, there is no requirement to construct any hydro scheme simulation model so bias effects should be considerably reduced. The approach was developed in the context of evaluating an income-maximization algorithm applied to a small hydro power scheme in the Kaimai Ranges of New Zealand. However, the methodology seems sufficiently simple and general to be applicable, with modification, to other power schemes moving toward increasing income through operational changes.
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    URL: http://dx.doi.org/10.1023/A:1010143717898
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    Hydrophilic Matrices for Controlled Drug Delivery: An Improved Mathematical Model to Predict the Resulting Drug Release Kinetics (the “sequential Layer” Model) (2000)
    Springer
    Pharmaceutical research 17 (2000), S. 1290-1298 
    Details
    ISSN: 1573-904X
    Keywords: controlled release ; diffusion ; hydrophilic matrix ; hydroxypropyl methylcellulose (HPMC) ; modeling ; swelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The aims of this study were (i) to elucidate the transport mechanisms involved in drug release from hydrophilic matrices; and (ii) to develop an improved mathematical model allowing quantitative predictions of the resulting release kinetics. Methods. Our previously presented model has been substantially modified, by adding: (i) inhomogeneous swelling; (ii) poorly water-soluble drugs; and (iii) high initial drug loadings. The validity of the improved model has been tested experimentally using hydroxypropyl methylcellulose (HPMC)-matrices, containing either a poorly or a freely water-soluble drug (theophylline or chlorpheniramine maleate) at various initial loadings in phosphate buffer pH 7.4 and 0.1 N HCl, respectively. Results. By overcoming the assumption of homogeneous swelling we show that the agreement between theory and experiment could be significantly improved. Among others, the model could describe quantitatively even the very complex effect on the resulting relative release rates (first slowing down, then accelerating drug release) observed when increasing the initial loading of poorly water-soluble drugs. Conclusions. The practical benefit of this work is an improved design model that can be used to predict accurately the required composition and dimensions of drug-loaded hydrophilic matrices in order to achieve desired release profiles, thus facilitating the development of new pharmaceutical products.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026455822595
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    A Human Physiologically-Based Model for Glycyrrhzic Acid, A Compound Subject to Presystemic Metabolism and Enterohepatic Cycling (2000)
    Springer
    Pharmaceutical research 17 (2000), S. 1516-1525 
    Details
    ISSN: 1573-904X
    Keywords: glycyrrhizic acid ; modeling ; enterohepatic cycling ; PBPK ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To analyze the role of the kinetics of glycyrrhizic acid (GD) in its toxicity. A physiologically-based pharmacokinetic (PBPK) model that has been developed for humans. Methods. The kinetics of GD, which is absorbed as glycyrrhetic acid (GA), were described by a human PBPK model, which is based on a rat model. After rat to human extrapolation, the model was validated on plasma concentration data after ingestion of GA and GD solutions or licorice confectionery, and an additional data derived from the literature. Observed interindividual variability in kinetics was quantified by deriving an optimal set of parameters for each individual. Results. The a-priori defined model successfully forecasted GA kinetics in humans, which is characterized by a second absorption peak in the terminal elimination phase. This peak is subscribed to enterohepatic cycling of GA metabolites. The optimized model explained most of the interindividual variance, observed in the clinical study, and adequately described data from the literature. Conclusions. Preclinical information on GD kinetics could be incorporated in the human PBPK model. Model simulations demonstrate that especially in subjects with prolonged gastrointestinal residence times, GA may accumulate after repeated licorice consumption, thus increasing the health risk of this specific subgroup of individuals.
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    URL: http://dx.doi.org/10.1023/A:1007661209921
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    Pharmacokinetic Variability and Therapeutic Drug Monitoring Actions at Steady State (2000)
    Springer
    Pharmaceutical research 17 (2000), S. 589-592 
    Details
    ISSN: 1573-904X
    Keywords: modeling ; stochastic ; Log-normal ; distributions ; pharmacodynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To develop a mathematical model for therapeutic drugmonitoring and to assess the kinetic relationships between the intensity ofcorrective action and the approach of drug concentrations to targetvalues. Methods. A mathematical model that succinctly accounts for thecorrective actions and the variability inherent in the pharmacokineticswas used. Results. The validity of the variability term was tested usingexperimental data for steady state concentrations of the drug procainamide.The approach of the monitored process to the target value followedexponential kinetics and an analytical expression for dependence thevariance with time and various dosing parameters was derived. Thevariance of the drug concentration depends critically on a singlenon-dimensional parameter containing the rate constant for the therapeuticcorrective actions and a coefficient describing the variance rate. Whenthe rate constant for the therapeutic corrective actions was less thanthis critical value, the variance increased indefinitely. Conclusions. From a dosing standpoint, large variances in drugconcentrations are undesirable because some patients will be overdosedor underdosed. Since deterministic models cannot provide analyticalsolutions for the moments of drug concentration distribution functions,stochastic models can be used to provide useful insights into the designof therapeutic regimens.
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    URL: http://dx.doi.org/10.1023/A:1007573001055
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    Clinical Trial Simulation in Drug Development (2000)
    Springer
    Pharmaceutical research 17 (2000), S. 252-256 
    Details
    ISSN: 1573-904X
    Keywords: Monte Carlo ; computer assisted trial design ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Clinical trial simulation is the application of old technologies, e.g., Monte Carlo simulation, to a newproblem, that problem being how to maximize the information content obtained during the drugdevelopment process with an intent to have the greatest chance of “success” in a clinical trial. When the informationcontent of the drug is high, then simulation provides a method to synthesize that information into acoherent package that indicates the sponsor has good control over the pharmacology of the drug. Froma purely financial point of view, what simulation offers pharmaceutical companies is the possibility ofreducing the number of required studies, maximizing the chances for success in a clinical trial, andpossibly shortening development time; all outcomes which will reduce drug development costs. Thepurpose of this paper is to introduce clinical trial simulation to the reader by discussing its potential indrug development, to briefly review the literature, and to make recommendations and caveats regardingits use.
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    URL: http://dx.doi.org/10.1023/A:1007548719885
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    Short-term Cover Crop Decomposition in Organic and Conventional Soils: Characterization of Soil C, N, Microbial and Plant Pathogen Dynamics (2000)
    Springer
    European journal of plant pathology 106 (2000), S. 37-50 
    Details
    ISSN: 1573-8469
    Keywords: carbon ; cellulose ; cover crop ; damping-off ; discriminant analysis ; lignin ; nitrogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Stages of oat–vetch cover crop decomposition were characterized over time in terms of carbon and nitrogen cycling, microbial activity and damping-off pathogen dynamics in organically and conventionally managed soils in a field and a controlled incubation experiment. A measurement of relative growth consisting of radial growth of a fungal colony over non-sterilized soil divided by that over sterilized soil was used as an assay of suppressiveness. No differences in relative growth of Pythium aphanidermatum and Rhizoctonia solani were detected between organic and conventionally managed soils amended with cover crop residue. Significant effects of cover crop decomposition stage on the relative growth of both pathogens were obtained. Relative growth of P. aphanidermatum was highest just after incorporation and decreased 3 weeks after incorporation. Relative growth of R. solani was highest about 20 days after incorporation, and decreased 2 weeks later in the organic system, but continued to increase in the conventional system. In both experiments, the N or C content, C:N ratio or dry weight of retrieved debris were significantly correlated with relative growth of P. aphanidermatum. Relative growth of R. solani was significantly correlated with the C:N ratio of soil or the C or N content of debris. Microbial activity was not consistently associated with relative growth of either pathogen.
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    URL: http://dx.doi.org/10.1023/A:1008720731062
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    Kinetics of the Electrons in Striations of Spherical Glow Discharges (2000)
    Springer
    Plasma chemistry and plasma processing 20 (2000), S. 87-110 
    Details
    ISSN: 1572-8986
    Keywords: striations ; nitrogen ; spherical discharge ; spatially inhomogeneous Boltzmann equation ; electron velocity distribution function ; dc glow discharge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Recent observations of spherical striations in large-volume nitrogen dcdischarges with a central anode have stimulated investigations of thenonlocal electron kinetics in these striations by solving the spatiallyinhomogeneous Boltzmann equation adapted to spherical geometry. Becausethe radial course of the electric potential is largely unknown in thisdischarge, different models concerning its radial course have been developedand used. These models are based on the measured radii of the striationsand the assumption that the potential drop between successive striationsdoes not change. As a consequence, with decreasing distance between thestriations the electric field strongly increases toward the centralanode. It has been found that spherical striations are only obtained ifthe electric field is strongly modulated. In this case, a highly nonlocalbehavior of the velocity distribution function and strongly modulatedradial courses of the macroscopic quantities have been obtained.
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    URL: http://dx.doi.org/10.1023/A:1006973911319
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    OES Use and Vaporization Modeling for Fly-Ash Plasma Vitrification (2000)
    Springer
    Plasma chemistry and plasma processing 20 (2000), S. 65-86 
    Details
    ISSN: 1572-8986
    Keywords: thermal plasma ; waste processing ; fly-ash vitrification ; optical emission spectroscopy ; volatilization ; lead ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Results are presented of optical emission spectroscopy (OES) application asa control tool to improve fly-ash plasma vitrification. A twin-torch plasmasystem has been used for the fly-ash processing, and a new OES method hasexamined metallic vapors above the melt. The method allows the study ofnonhomogeneous optically thin plasmas exhibiting a symmetry plane withoutsophisticated tomographic systems. The dc arc torches are mounted above acold crucible filled with a synthetic glass. The arc intensity is from200 to 400 Å. Argon is introduced into the torches along the cathodeand the anode, while argon, oxygen or hydrogen are injected through thelance between the torches. Local plasma temperatures above the melt havebeen evaluated using measured relative intensities of spectral lines ofthe plasma-forming gas. Metallic vapor concentration in the plasma isdeduced from the intensity ratio of the metal–gas spectral lines. Leadoxide has been used to study heavy-metal behavior at the fly-ash plasmavitrification. Distribution of the lead along the crucible surface,depending on the plasma-forming gas composition as well as the concentrationevolution with time, have been examined. The elemental analysis of theresultant glass has been measured by scanning electron microscopy (SEM)with energy-dispersive spectrometry (EDS). A predictive model has beenadapted to simulate the noncongruent vaporization of heavy metals from themelt. According to the data obtained, steep variations of the volatility ofthe elements depend strongly on reducing properties of gases controllingthe plasma composition near the melted surface. In addition, the melttemperature and the redox potential of the gas phase are found to be themost critical parameters.
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    URL: http://dx.doi.org/10.1023/A:1006921927249
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    Mathematical Modeling of Silica Anode Decomposition (2000)
    Springer
    Plasma chemistry and plasma processing 20 (2000), S. 521-553 
    Details
    ISSN: 1572-8986
    Keywords: thermal plasma ; transferred arc ; fumed silica ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The volatilization of quartz in a transferred arc plasma followed byquench and recondensation is a promising route to the production offumed silica. In this work, an existing model of a transferred arcwas modified and combined with a newly developed model of a moltensilica anode to predict the behavior of a transferred arc evaporatoras a function of current and plasma gas flow rate. The model predictstemperature, current, and flow fields in both the plasma and anode aswell as evaporation rates. Although quantitative agreement withexperimental results was not possible because of insufficient propertydata for silica at high temperature, the results were within an orderof magnitude of those measured experimentally. The model developed isuseful for the design and scaleup of this type of reactor.
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    URL: http://dx.doi.org/10.1023/A:1007083923427
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    Pruning effects on root distribution and nutrient dynamics in an acacia hedgerow planting in northern Kenya (2000)
    Springer
    Agroforestry systems 50 (2000), S. 59-75 
    Details
    ISSN: 1572-9680
    Keywords: below-ground competition ; carbohydrates ; nitrogen ; nutrient leaching ; resin cores
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Tree pruning is a common management practice in agroforestry for mulching and reducing competition between the annual and perennial crop. The below-ground effects of pruning, however, are poorly understood. Therefore, nutrient dynamics and root distribution were assessed in hedgerow plantings of Acacia saligna (Labill.) H.L. Wendl. after tree pruning. Pruning to a height of 1.5 m was carried out in March and September 1996. In July and October 1996, the fine root distribution (〈 2 mm) and their carbohydrate contents were determined at three distances to the tree row by soil coring. At the same time, foliar nutrient contents were assessed, whereas nutrient leaching was measured continuously. The highest root length density (RLD) was always found in the topsoil (0–0.15 m) directly under the hedgerow (0–0.25 m distance to trees). Pruning diminished the RLD in the acacia plots at all depths and positions. The relative vertical distribution of total roots did not differ between trees with or without pruning, but live root abundance in the subsoil was comparatively lower when trees were pruned than without pruning. In the dry season, the proportion of dead roots of pruned acacias was higher than of unpruned ones, while the fine roots of unpruned trees contained more glucose than those of pruned trees. Pruning effectively reduced root development and may decrease potential below-ground competition with intercropped plants, but the reduction in subsoil roots also increased the danger of nutrient losses by leaching. Leaching losses of such mobile nutrients as NO3− were likely to occur especially in the alley between pruned hedgerows and tended to be higher after pruning. The reduced size of the root system of pruned acacias negatively affected their P and Mn nutrition. Pruning also reduced the function of the trees as a safety net against the leaching of nutrients for both NO3− and Mn, though not for other studied elements. If nutrient capture is an important aim of an agroforestry system, the concept of alley cropping with pruning should be revised for a more efficient nutrient recycling in the system described here.
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    URL: http://dx.doi.org/10.1023/A:1006498709454
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    Issues related to the detection of boundaries (2000)
    Springer
    Landscape ecology 15 (2000), S. 453-466 
    Details
    ISSN: 1572-9761
    Keywords: environmental change ; GIS ; landscape ecology ; modeling ; remote sensing ; riparian ; statistics ; wetland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Ecotones are inherent features of landscapes, transitional zones, and play more than one functional role in ecosystem dynamics. The delineation of ecotones and environmental boundaries is therefore an important step in land-use management planning. The delineation of ecotones depends on the phenomenon of interest and the statistical methods used as well as the associated spatial and temporal resolution of the data available. In the context of delineating wetland and riparian ecosystems, various data types (field data, remotely sensed data) can be used to delineate ecotones. Methodological issues related to their detection need to be addressed, however, so that their management and monitoring can yield useful information about their dynamics and functional roles in ecosystems. The aim of this paper is to review boundary detection methods. Because the most appropriate methods to detect and characterize boundaries depend of the spatial resolution and the measurement type of the data, a wide range of approaches are presented: GIS, remote sensing and statistical ones.
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    Conversion of Nitrogen to Protein and Amino Acids in Wild Fruits (2000)
    Springer
    Journal of chemical ecology 26 (2000), S. 1749-1763 
    Details
    ISSN: 1573-1561
    Keywords: Conversion factor ; free amino acids ; fruits ; Kjeldahl ; nitrogen ; nutrition ; protein ; pulp ; secondary metabolites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Protein content of plant tissues is usually estimated by multiplying total nitrogen by a conversion factor of 6.25. This technique assumes that all nitrogen originates from protein. When applied to fruit pulp, it overestimates protein content because pulp typically contains free amino acids and many nitrogenous secondary metabolites. At issue is the extent of error and, consequently, what the conversion factor between nitrogen and protein should be. We calculated a conversion factor based on pulp samples from 18 species collected in the southeastern United States. We also report a new and simple method of estimating protein and free amino acids in fruit pulp. Because previous studies have found high variation in protein and secondary metabolite content among fruit species, use of a single conversion factor for all species will generate error. In an attempt to reduce such error, we calculated protein contents and conversion factors separately for two common fruit types: lipid-rich/carbohydrate-poor and lipid-poor/carbohydrate-rich. We found no difference between these types of fruit and hence combined results in calculating an average conversion factor of 5.64. Use of an accurate conversion factor is important in estimating protein consumption by wild animals and in formulating diets of captive animals. It can also reveal whether loss of body mass in captive animals on fruit diets is due to insufficient protein consumption, secondary metabolite toxicity, or an imbalance of amino acids.
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    Allelopathic Effects of Volatile Cineoles on Two Weedy Plant Species (2000)
    Springer
    Journal of chemical ecology 26 (2000), S. 303-313 
    Details
    ISSN: 1573-1561
    Keywords: Eucalyptol ; essential oils ; cineole ; monoterpenes ; chlorophyll fluorescence ; Echinochloa crusgalli ; Cassia obtusifolia ; natural products ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The volatile monoterpene analogs, 1,4-cineole and 1,8-cineole, have been identified as components of many plant essential oils, but relatively little is known about their biological activities. We compared the effects of 1,4- and 1,8-cineole on two weedy plant species by monitoring germination, mitosis, root and shoot growth, chlorophyll content, and photosynthetic efficiency. 1,4-Cineole severely inhibited growth of roots and shoots, causing cork-screw shaped morphological distortion, whereas 1,8-cineole caused a decrease in root growth and germination rates. Chlorophyll fluorescence data (yield and F v / F m) indicated that 1,4-cineole caused significantly higher stress (P ≤ 0.001) to photosynthesis when compared to controls. Mitotic index data showed that 1,8-cineole severely decreased (P ≤ 0.001) all stages of mitosis when compared with controls, while 1,4-cineole only caused a decrease in the prophase stage (P ≤ 0.05). Although superficially similar in structure, these two cineoles appear to have different modes of action.
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    The Replacement Value of Wetlands in Sweden (2000)
    Springer
    Environmental and resource economics 16 (2000), S. 347-362 
    Details
    ISSN: 1573-1502
    Keywords: cost-effectiveness ; nitrogen ; nonpoint ; policy ; value ; wetlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Economics
    Notes: Abstract Wetlands, in Sweden and elsewhere, have been suggestedas effective and low-cost sinks for agriculturalpollution. This paper estimates the value of usingwetlands for abatement of agricultural nitrogen loadon the Baltic Sea. A replacement value of wetlands isestimated for Sweden. The replacement value is definedand estimated as the difference between twocost-effective reductions of agricultural nitrogenpollution: one that uses wetlands for nitrogenabatement, and one that does not. It is shown that theuse of wetlands as nitrogen sinks can reduce the totalabatement costs of nitrogen emissions by 30% forSwedish agricultural sources of nitrogen pollution.
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    URL: http://dx.doi.org/10.1023/A:1008316619355
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    Jasmonate-Induced Responses of Nicotiana sylvestris Results in Fitness Costs Due to Impaired Competitive Ability for Nitrogen (2000)
    Springer
    Journal of chemical ecology 26 (2000), S. 915-952 
    Details
    ISSN: 1573-1561
    Keywords: Nicotiana sylvestris ; nitrogen ; nicotine ; allocation ; growth ; reproduction ; induced defenses ; costs of defense
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract We present the first evidence for a fitness cost of an inducible response that is detectable in a nitrogen (N) currency. Nicotine is an induced defense in Nicotiana sylvestris that can utilize 5–8% of the plant's total N, an investment that apparently cannot be recouped by metabolism. Induced nicotine production is endogenously regulated by jasmonic acid (JA), and we treated leaves with the methyl ester of this wound hormone (MeJA) in quantities (0, 25, 250 μg) known to elicit changes in endogenous JA and subsequent nicotine responses comparable to those elicited by mechanical wounding and herbivory in this species. We grew plants in competition chambers (CCs) in which three same-sized plants could compete for a communal but fixed pool of 15NO3 to quantify the outcome of competition for this fitness-limiting resource that is used both in defense and seed production. Competition profoundly increased all measures of growth and reproductive performance measured per milligram of N acquired. While plants acquired all the N supplied to them in the hydroponic solution, plants grown in CCs (as compared those grown in individual chambers—ICs) retained more of this N and produced more biomass, had larger nicotine contents, allocated less of their N to nicotine, produced larger floral stalks with more flowers, aborted fewer flowers, matured more capsules, and produced a greater mass of seed. Plants grown in ICs produced heavier seed, but this difference did not translate into a difference in seed viability. MeJA treatment increased nicotine concentrations in proportion to the amount applied and significantly reduced growth (13–23%) and reproductive (31–44%) performance for plants grown with uninduced competitors, reflecting a large opportunity cost of induction. The effects of MeJA treatment on growth and reproduction were significantly less pronounced for plants grown in ICs. MeJA treatment significantly reduced the ability of plants to compete for [15N]KNO3 (reducing uptake by 9.5% and 23.7% for 25- and 250-μg MeJA-treated plants, respectively); no reductions in N acquisition were found in IC grown plants treated with MeJA. This impairment of competitive ability could account for 41–47% of the jasmonate-induced reductions in biomass by the day 15 harvest and 12–20% of the reductions in seed set and, in addition, created by "opportunity benefit" for neighboring uninduced plants, which grew larger, aborted fewer flowers, and matured more seed (a 28% increase) than did uninduced plants competing with similarly uninduced plants. Competition dramatically increased plant growth and reproductive performance, and MeJA treatment of these high-performing plants significantly reduced their competitive ability, which translated into opportunity costs for induced plants and opportunity benefits for neighboring uninduced plants. Induced plants minimized these fitness costs by reducing their use of recently acquired N for nicotine biosynthesis when growing with competitors. MeJA treatments also altered stalk length, flower production, flower abortion, and allocation to seed mass. In spite of all this plasticity, induced responses incur large fitness costs, costs that could be in part attributed to reductions in competitive ability for N. We conclude that inducibility functions to minimize these costs.
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    An Ab Initio Study of the Complexes Formed by the Positive Acetylene Ion with the Hydrogen and Nitrogen Molecules and the Argon Atom (2000)
    Springer
    Journal of cluster science 11 (2000), S. 381-389 
    Details
    ISSN: 1572-8862
    Keywords: acetylene ion ; complex ; hydrogen ; nitrogen ; argon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The complexes formed by the positive acetylene ion with the hydrogen molecule, the nitrogen molecule, and the argon atom are investigated with ab initio calculations using the 6-311G** and the 6-31+G(2df,2pd) basis sets. MP2/6-311G** energies and optimum geometries are obtained, as well as single-point MP3, MP4, and QCISD(T) energies with the MP2/6-311G** optimized geometries. Single-point calculations are performed with the 6-31+G(2df,2pd) basis set at MP2/6-311G** optimized geometries.
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    URL: http://dx.doi.org/10.1023/A:1009053924254
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    Temperature Modulated DSC. Theoretical interpretation (2000)
    Springer
    Journal of thermal analysis and calorimetry 60 (2000), S. 333-343 
    Details
    ISSN: 1572-8943
    Keywords: base line ; DSC ; kinetics ; modeling ; thermodynamics ; TMDSC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The application of non-linear heating program to a heat-flux DSC apparatus has attracted much attention. From thermodynamics viewpoint, it is shown that the variation of enthalpy of a sample changing with temperature change is due, to both the true heat capacity of the sample and the enthalpy of some transformations occurring in the sample, characterized by its degree of advance. Using the simple assumption that the rate of the transformation is proportional to the distance from the thermodynamic equilibrium, an electrical model of the thermal event is given. Using the coupled cell model of the DSC apparatus, we show how to obtain the rate of transformation of the sample and heat capacity, which is directly related to the base line of the experiment.
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    Modeling of the DTG Curves for Oxidation of a Nanosized Molybdenum Ferrite Coupling Mechanics and Diffusion (2000)
    Springer
    Journal of thermal analysis and calorimetry 59 (2000), S. 847-858 
    Details
    ISSN: 1572-8943
    Keywords: derivative thermogravimetry ; diffusion-induced stress ; modeling ; molybdenum ferrite ; oxidation kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract From a model for isothermal oxidation kinetics in nanosized ferrite spinels based on a diffusion-induced stress effect, the authors present a modeling of the DTG curves for the oxidation of Fe2+ and Mo3+ cations on octahedral sites of a molybdenum ferrite. This has been made by considering that the chemical diffusion coefficient is given by the relation $$\tilde D = D_o \exp \left( {\frac{{E'_{\text{a}} + pV_{\text{a}} }}{{RT}}} \right)$$ , when D o is a pre-exponential factor, E a ′ an activation energy and V a an activation energy induced by the oxidation.
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    Evaluating Drainage Design Parameters for the Fourth Drainage Project, Pakistan by using SWAP Model: Part II – Modeling Results (2000)
    Springer
    Irrigation and drainage systems 14 (2000), S. 281-299 
    Details
    ISSN: 1573-0654
    Keywords: drainage design ; modeling ; steady-state criteria ; subsurface drainage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract This paper presents the results of modelsimulations to evaluate drainage designparameters for the Fourth Drainage Project(FDP), Punjab, Pakistan. The SWAP model wasapplied to compute the effects of landdrainage (12 combinations of drain depthand spacing) on soil moisture conditions inthe root zone and their effect on cropyield and soil salinization. For theconditions considered, the selection ofdrain depth is found to be more criticalthan that of drain spacing. Deeper drainsperform technically better in relation tocrop growth and soil salinization. Theoptimum drain depth for the multiplecropping system of the FDP-area was foundto be 2.2 m. This drain depth will producereasonably good crop yields at rather lowdrainage intensity while keeping the rootzone salinity within acceptable limits.This drainage design also maintained thegroundwater table depth below the root zonethroughout the growing season. The outcomeof this study reveals that the drainagedesign criteria applied for the FDP israther conservative with high drainageintensity. The FDP-area can effectively bedrained with a 25 percent lower drainageintensity (q drain/Δh)provided no operational or maintenanceconstraints are present. However, the finaldecision on the optimum combination ofdrain depth and drain spacing would requirea thorough economical analysis. Thenon-steady state approach proved successfulin analyzing the complex interactionsbetween irrigation and drainage components.It is a valuable tool to optimize thedesign of drainage systems against cropyields and soil salinization.
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    URL: http://dx.doi.org/10.1023/A:1006416921124
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    Rotational Properties of Cometary Nuclei (2000)
    Springer
    Earth, moon and planets 89 (2000), S. 135-160 
    Details
    ISSN: 1573-0794
    Keywords: C/1995 O1 (Hale-Bopp) ; 19P/Borrelly ; 46P/Wirtanen ; comets ; modeling ; nucleus ; observations ; rotation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We review several techniques used to retrieve rotational parameters from observations. The spin period of a dozen of comets retrieved with these techniques are summarized. We describe how the spin period of comet Hale-Bopp (C/1995 O1) has been calculated with a high accuracy (11.30–11.34 h). Although several authors converged to a spin axis orientation at (α,δ) = (275 ± 15°, -55 ± 5°), detailed studies indicate that the dust jets morphology in 1996–1997 may be incompatible with this orientation. Comet 19P/Borrelly has been recently observed by the Deep Space 1 spacecraft. At the same time, its spin axis orientation and period have been determined by several authors to be respectively (α,δ) = (225 ± 15°, -10 ± 10°)and 26h. These two comets are likely to be in (or close to) a principal axis spin state. We discuss new modeling of the spin state of comet 46P/Wirtanen, the target of the Rosetta mission. The model involves a three-dimensional shape and thermal model, from which the torque of the non gravitational force is calculated at each time step. The moments of inertia are computed for each irregular shape. The results from numerical integrations show that this comet can remain in a principal axis spin state during more than 10 orbits if the spin period does not get above∼6 h. If the spin period increases, its nucleus gets rapidly into excited spin states. It shows that even small and very active short-period comets are not necessarily in non principal axis spin states. In the last section, the consequences of recent observations and modeling of the rotational parameters of comet nuclei are discussed, and unsolved problems are presented.
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    URL: http://dx.doi.org/10.1023/A:1021598404115
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    Nitrogen in percolation water in paddy fields with a rice/wheat rotation (2000)
    Springer
    Nutrient cycling in agroecosystems 57 (2000), S. 75-82 
    Details
    ISSN: 1573-0867
    Keywords: nitrogen ; leaching ; paddy soil ; wheat ; rice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Nitrogen in percolation water was observed in paddy field soil under rice/wheat rotation. Different N-application rates were designed. Porous pipes were installed in triplicate at depths of 30, 60 and 90 cm to collect the water in the period of wheat growth. Suction cups were installed in triplicate at the same depths to collect the water during the period of rice growth. NH4 +, NO3 - and total N in the water were analysed with a continuous-flow nitrogen analyzer. Results showed that nitrate was the predominant form of nitrogen in percolation water during the period of wheat growth. Nitrate leaching was high in early spring after the `tillering fertilisation'. More than 50 mg l-1 of nitrate concentration in percolation water was observed for 30 and 60 cm in depth and more than 15 mg l-1 were observed for 90 cm. The concentration decreased quickly and was very low, less than 2 mg l-1 usually, in the earring stage of wheat. Nitrate in water was low, less than 1.5 mg l-1 usually, when the field was flooded during the period of rice growth. Some soluble organic N existed in the water. Nitrate in percolation water increased when the field was drained. The leaching loss of nitrogen during winter wheat growth period was estimated to be about 3.4% of the N-fertiliser applied at the normal application rate of farmers; for the rice growth period it was around 1.8%. Although a reduced N-application decreased N leaching, it caused a marked decrease in crop yield.
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    URL: http://dx.doi.org/10.1023/A:1009712404335
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    Modeling Trace Gas Emissions from Agricultural Ecosystems (2000)
    Springer
    Nutrient cycling in agroecosystems 58 (2000), S. 259-276 
    Details
    ISSN: 1573-0867
    Keywords: agroecosystem ; trace gas ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A computer simulation model was developed for predicting trace gas emissions from agricultural ecosystems. The denitrification-decomposition (DNDC) model consists of two components. The first component, consisting of the soil climate, crop growth, and decomposition submodels, predicts soil temperature, moisture, pH, Eh, and substrate concentration profiles based on ecological drivers (e.g., climate, soil, vegetation, and anthropogenic activity). The second component, consisting of the nitrification, denitrification, and fermentation submodels, predicts NH3, NO, N2O, and CH4 fluxes based on the soil environmental variables. Classical laws of physics, chemistry, or biology or empirical equations generated from laboratory observations were used in the model to parameterize each specific reaction. The entire model links trace gas emissions to basic ecological drivers. Through validation against data sets of NO, N2O, CH4, and NH3 emissions measured at four agricultural sites, the model showed its ability to capture patterns and magnitudes of trace gas emissions.
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    URL: http://dx.doi.org/10.1023/A:1009859006242
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    Effects of excreta return on properties of a grazed pasture soil (2000)
    Springer
    Nutrient cycling in agroecosystems 56 (2000), S. 79-85 
    Details
    ISSN: 1573-0867
    Keywords: exchangeable cations ; nitrogen ; soil carbon ; soil quality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The long term impact of excreta return on some chemical and biological properties of a pasture soil fertilised with sulphur and phosphate was studied in a system that had been with or without excreta for 23 years. Excreta free areas that had developed under electric fencelines, and parallel transects in the paddocks, were sampled to provide this comparison. Sampling was to 300 mm depth in 0–75, 75–150 and 150–300 mm sections. Total carbon and nitrogen were 20% higher in the 0–150 mm soil layer of areas receiving excreta but did not differ in the 150–300 mm layer. Carbon:nitrogen ratios were similar in both systems as was mineralisable nitrogen, both absolutely and as a percentage of total in the 0–75 mm layer. Significantly more N was mineralised in the 75–150 mm layers of the areas receiving excreta but this was reversed in the 150–300 mm layer. Nitrification rate was higher in all layers of the excreta areas. Inorganic and organic P fractions did not differ significantly. Total P was significantly higher in the 0–75 mm layer and significantly lower in the 150–300 mm layer of the excreta areas. Exchangeable potassium was much higher throughout the excreta areas while this was offset by calcium. The sum of the cations was similar in both areas. Excreta affected most of the diagnostic soil tests used for fertiliser recommendations. The soil properties measured did not reflect clearly the differences in productivity that were obvious in the two areas. It is concluded that excreta return has a impact resulting in increased organic matter storage. Short-term effects of urine have a greater impact on productivity. The major effect is on the disposition of cations and available P.
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    URL: http://dx.doi.org/10.1023/A:1009842727493
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    Nitrogen leaching and crop availability in manured catch crop systems in Sweden (2000)
    Springer
    Nutrient cycling in agroecosystems 56 (2000), S. 139-152 
    Details
    ISSN: 1573-0867
    Keywords: nitrogen ; N leaching ; liquid manure ; catch crops ; N mineralization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Results are presented from five years (1990–1995) of a field leaching experiment on a sandy soil in south-west Sweden. The aim was to study N leaching, change in soil organic N and N mineralization in cropping systems with continuous use of liquid manure (two application rates) and catch crops. N leaching from drains, N uptake in crops and mineral N in the soil were measured. Simulation models were used to calculate the N budget and N mineralization in the soil and to make predictions of improved fertilization strategies in relation to manure applications and changing the time for incorporation of catch crops. In treatments without catch crops, a normal and a double application of manure increased average N leaching by 15 and 34%, respectively, compared to treatment with commercial fertilizer. Catch crops reduced N leaching by, on average, 60% in treatments with a normal application of manure and commercial fertilizer, but only by 35% in the treatment with double the normal application rate of manure. Incorporation of catch crops in spring increased simulated net N mineralization during the crop vegetation period, and also during early autumn. In conclusion, manured systems resulted in larger N leaching than those receiving commercial fertilizer, mainly due to larger applications of mineral N in spring. More careful adaptation of commercial N fertilization with respect to the amounts of NH4-N applied with manure could, according to the simulations, reduce N leaching. Under-sown ryegrass catch crops effectively reduced N leaching in manured systems. Incorporating catch crop residues in late autumn instead of spring might be preferable with respect to N availability in the soil for the next crop, and would not increase N leaching.
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    URL: http://dx.doi.org/10.1023/A:1009821519042
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    Nitrogen (N) management in the ‘De Marke’ dairy farming system (2000)
    Springer
    Nutrient cycling in agroecosystems 56 (2000), S. 231-240 
    Details
    ISSN: 1573-0867
    Keywords: nitrogen ; N ; nitrate ; ammonia ; dairy farming ; systems research ; environment ; sandy soils ; groundwater ; leaching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In the sandy regions of The Netherlands, high losses of N from intensified dairy farms are threatening the environment. Therefore, government defined decreasing maximum levy-free N surplusses for the period 1998–2008. On most dairy farms, the current N surplus has to be reduced by half at least. Farmers fear that realizing these surplusses will be expensive, because it limits application of animal manure, which then has to be exported or additional land has to be bought. Moreover, farmers are worried about the impact on soil fertility. To explore the possibilities for reducing surplusses of average intensive farms by improved nutrient management, farming systems research is carried out at prototype farm ‘De Marke’. Results are compared with results of a commercial farm in the mid-1980s, the moment that systems research started and introduction of the milk quota system put a halt to further intensification. Results indicate that average intensive farms can realise a reduction in N surplus to a level below the defined final maximum, without the need to buy land or to export slurry. Inputs of N in purchased feeds and fertilisers decreased by 56 and 78%, respectively. Important factors are reduced feed intake per unit milk, as a result of a higher milk yield per cow, less young stock and judicious feeding, an improved utilization of ‘home-made’ manure and a considered balance between the grassland and maize area. Changed soil fertility status did not constrain crop production. Nitrate concentration in the upper groundwater decreased from 200 to 50 mg l-1, within a few years.
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    Transport of dissolved inorganic nitrogen from the major rivers to estuaries in China (2000)
    Springer
    Nutrient cycling in agroecosystems 57 (2000), S. 13-22 
    Details
    ISSN: 1573-0867
    Keywords: biogeochemistry ; estuary ; nitrogen ; river ; transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Long-term results of the monthly measurement of dissolved inorganic nitrogen (DIN) concentrations in three major rivers in China are presented. These data are combined with river discharge data to calculate the DIN loads discharged into the ocean. About 774.90 × 103, 55.38 × 103and 144.55 × 103tons of DIN were transported to their respective estuaries each year by the Changjiang, the Huanghe and the Zhujiang in 1980–1989, mainly in the form of nitrate (〉 80 percent). The annual transport of DIN and mean concentration of nitrate in the Changjiang had increased drastically (four-fold) in the last 29 years, especially during the 1980s. Although nitrate concentrations of the Zhujiang and the Huanghe had also increased in the 1980s, their total annual loads of DIN varied mainly with annual runoff volumes, showing no obvious uptrends. Our results also demonstrate that the majority of the DIN load of each river was transported in the high-flow period (70–80 percent). A positive relationship is observed between the annual DIN transport of the Changjiang and the annual application of chemical fertilizers in its catchment. The annual DIN loads of the Huanghe and the Zhujiang were influenced mainly by runoff volume, and also by application of chemical fertilizers.
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    Nitrogen mobilization in Asia (2000)
    Springer
    Nutrient cycling in agroecosystems 57 (2000), S. 1-12 
    Details
    ISSN: 1573-0867
    Keywords: Asia ; fertilizer ; ammonia ; food ; greenhouse effect ; nitrogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The addition of anthropogenic N by food and energy production to the global environment contributes to the greenhouse effect, acid deposition, photochemical smog, stratospheric ozone depletion and eutrophication of fresh and marine waters. On a global basis, anthropogenic N mobilization is greater then natural sources of bio-reactive N. Currently, Asia is a hotspot of N mobilization and distribution to downwind and downstream environments, primarily due to food production. Asia's contribution will continue to increase, not only due to population growth, but also to increases in the per capita consumption of food and energy. This paper provides an overview of the global N cycle, presents an analysis of N dynamics within agroecosystems, examines N mobilization in Asia and discusses possible rates of N mobilization in the future.
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    URL: http://dx.doi.org/10.1023/A:1009832221034
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    Analysis of Equilibria in the Extraction of Cesium Nitrate by Calix[4]arene-bis(t-Octylbenzo- Crown-6) in 1,2-Dichloroethane (2000)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 36 (2000), S. 21-37 
    Details
    ISSN: 1573-1111
    Keywords: Calixarene-crown ether ; Cs+ complexation ; solvent extraction ; SXLSQI ; equilibrium constants ; partition ratio ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The extraction of CsNO3 by the highly lipophilic calixarene-crown ether calix[4]arene-bis(t-octylbenzo-crown-6) (CABOBC6) in 1,2-dichloroethane (1,2-DCE) at 25 °C has been shown to be consistent with the formation of both 1 : 1 and 2 : 1 metal : ligand species. Variation of the aqueous-phase CsNO concentration up to 1.0 M and variation of the organic-phase calixarene concentration up to 0.10∼M was modeled by the program SXLSQI. Formation of the organic-phase species CsBNO3 (B = calixarene) was confirmed as well as the organic-phase dissociation products CsB+ and NO3 -. Good evidence for the 2 : 1 metal : ligand organic-phase species Cs2B(NO3)2 was also found, although the dissociation of nitrate from this complex was not observed. Binding of the second Cs+ cation by the ligand is approximately two orders of magnitude weaker than binding of the first Cs+ cation. The logarithm of the apparent partition ratio (log PB) of the calixarene between water and 1,2-DCE was found by 1H-NMR techniques to be 〉 5.1.
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    Nutrient losses in runoff from grasslandand shrubland habitats in southern New Mexico: II. Field plots (2000)
    Springer
    Biogeochemistry 49 (2000), S. 69-86 
    Details
    ISSN: 1573-515X
    Keywords: Bouteloua eriopoda ; Chihuahuan Desert ; desertification ; hydrology ; Larrea tridentata ; nitrogen ; nutrient budgets ; phosphorus ; runoff
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Losses of dissolved nutrients (N, P, K, Ca, Mg, Na,Cl, and SO4) in runoff were measured on grasslandand shrubland plots in the Chihuahuan desert ofsouthern New Mexico. Runoff began at a lowerthreshold of rainfall in shrublands than ingrasslands, and the runoff coefficient averaged 18.6%in shrubland plots over a 7-year period. In contrast,grassland plots lost 5.0 to 6.3% of incidentprecipitation in runoff during a 5.5-year period. Nutrient losses from shrubland plots were greater thanfrom grassland plots, with nitrogen losses averaging0.33 kg ha−1 yr−1 vs0.15 kg ha−1 yr−1, respectively, during a 3-year period. Thegreater nutrient losses in shrublands were due tohigher runoff, rather than higher nutrientconcentrations in runoff. In spite of these nutrientlosses in runoff, all plots showed net accumulationsof most elements due to inputs from atmosphericdeposition. Therefore, loss of soil nutrients byhillslope runoff cannot, by itself, account for thedepletion of soil fertility associated withdesertification in the Chihuahuan desert.
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    Dissolved organic nitrogen budgets for upland, forested ecosystems in New England (2000)
    Springer
    Biogeochemistry 49 (2000), S. 123-142 
    Details
    ISSN: 1573-515X
    Keywords: C:N ratio ; dissolved organic carbon ; dissolved organic nitrogen ; nitrogen ; stream chemistry ; watershed
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Relatively high deposition ofnitrogen (N) in the northeastern United States hascaused concern because sites could become N saturated.In the past, mass-balance studies have been used tomonitor the N status of sites and to investigate theimpact of increased N deposition. Typically, theseefforts have focused on dissolved inorganic forms ofN (DIN = NH4-N + NO3-N) and have largelyignored dissolved organic nitrogen (DON) due todifficulties in its analysis. Recent advances in themeasurement of total dissolved nitrogen (TDN) havefacilitated measurement of DON as the residual of TDN− DIN. We calculated DON and DIN budgets using data onprecipitation and streamwater chemistry collected from9 forested watersheds at 4 sites in New England. TDNin precipitation was composed primarily of DIN. Netretention of TDN ranged from 62 to 89% (4.7 to 10 kghaminus 1 yrminus 1) of annual inputs. DON made up themajority of TDN in stream exports, suggesting thatinclusion of DON is critical to assessing N dynamicseven in areas with large anthropogenic inputs of DIN.Despite the dominance of DON in streamwater,precipitation inputs of DON were approximately equalto outputs. DON concentrations in streamwater did notappear significantly influenced by seasonal biologicalcontrols, but did increase with discharge on somewatersheds. Streamwater NO3-N was the onlyfraction of N that exhibited a seasonal pattern, withconcentrations increasing during the winter months andpeaking during snowmelt runoff. Concentrations ofNO3-N varied considerably among watersheds andare related to DOC:DON ratios in streamwater. AnnualDIN exports were negatively correlated withstreamwater DOC:DON ratios, indicating that theseratios might be a useful index of N status of uplandforests.
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    The effects of slash burning on ecosystem nutrients during the land preparation phase of shifting cultivation (2000)
    Springer
    Plant and soil 220 (2000), S. 247-260 
    Details
    ISSN: 1573-5036
    Keywords: cations ; fire ; nitrogen ; nutrients ; phosphorus ; slash-and-burn ; soil ; tropical forests
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The most commonly observed change in soil following slash-and-burn clearing of tropical forest is a short-term increase in nutrient availability. Studies of shifting cultivation commonly cite the incorporation of nutrient-rich ash from consumed aboveground biomass into soil as the reason for this change. The effects of soil heating on nutrient availability have been examined only rarely in field studies of slash-and-burn, and soil heating as a mechanism of nutrient release is most often assumed to be of minor importance in the field. Few budgets for above and belowground nutrient flux have been developed in the tropics, and a survey of results from field and laboratory studies indicates that soils are sufficiently heated during most slash-and-burn events, particularly in dry and monsoonal climates, to cause significant, even substantial release of nutrients from non-plant-available into plant-available forms in soil. Conversely, large aboveground losses of nutrients during and after burning often result in low quantities of nutrients that are released to soil. Assessing the biophysical sustainability of an agricultural practice requires detailed information about nutrient flux and loss incurred during management. To this end, current conceptual models of shifting cultivation should be revised to more accurately describe these fluxes and losses.
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    Soil patchiness in juniper-sagebrush-grass communities of central Oregon (2000)
    Springer
    Plant and soil 223 (2000), S. 47-61 
    Details
    ISSN: 1573-5036
    Keywords: correlograms ; nitrogen ; soil arthropods ; soil resource islands ; variograms ; vesicular-arbuscular mycorrhizae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract This study compared the sizes, spacings and properties (soil moisture, pH, nitrogen, soil arthropods and VAM) of soil resource islands and bare patches in sagebrush-grass communities invaded by western juniper versus those without juniper. We analyzed 1000 surface soil samples taken from nine 50-m radius circular plots sampled in December of 1991 and May of 1992 on ‘The Island’, one of the few undisturbed areas of sagebrush-grass shrubland in Oregon. Spatial structure was interpreted from correlograms (Moran's I) and standardized semivariograms. The presence of juniper was associated with increased bare area and smaller, more widely spaced grass and sagebrush plants. Soil arthropod numbers and biomass in plots with juniper were only roughly one-fifth of those in sagebrush-grass plots in December. The dominant soil pattern in both sagebrush-grass and juniper-sagebrush-grass plots was regularly-distributed patches spanning a range of sizes and spacings. Plots with juniper had greater patchiness at shorter lags (〈3 m), and patchiness was more developed for soil moisture, net nitrification, and net N mineralization, whereas sagebrush-grass plots had greater patchiness at longer lags (3 – 9 m) and patchiness was more developed for NO3–N, arthropod numbers and biomass. These differences in soil patterns with and without juniper indicate that juniper responds to, or causes, changes in the size of resource islands under sage and grass when it invades sage-grass communities.
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    Spatial heterogeneity of soil respiration and related properties at the plant scale (2000)
    Springer
    Plant and soil 222 (2000), S. 203-214 
    Details
    ISSN: 1573-5036
    Keywords: carbon ; geostatistics ; nitrification potential ; nitrogen ; pH ; root biomass ; soil respiration ; spatial Heterogeneity ; variability scale
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Geostatistical techniques were used to quantify the scale and degree of soil heterogeneity in 2 m2 plots around 9-year-old poplar trees and within a wheat field. Samples were taken during two years, on an unaligned grid, for analysis of soil respiration, C and N content, available P, gravimetric moisture, pH, nitrification potential, and root biomass. Kriged maps of soil respiration, moisture, and C content showed strong spatial structure associated with poplar trees but not with wheat rows. All soil properties showed higher autocorrelation in June than in April. Isopleth patchiness for all variates was less in June. This was associated with lower respiration rates due to lower litter decomposition. From the degree and scale of heterogeneity seen in this study, we conclude that the main causes of soil heterogeneity at this scale (2 m2) are likely to be found at micro scales controlled in part by plant root and plant residue patterns. These must be understood in the evaluation of ecosystem processes.
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    Estimating crop N uptake from organic residues using a new approach to the 15N isotope dilution technique (2000)
    Springer
    Plant and soil 223 (2000), S. 33-46 
    Details
    ISSN: 1573-5036
    Keywords: crop residues ; nitrogen ; organic residues
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Experiments were conducted to test a new approach to the 15N isotope dilution technique for estimating crop N uptake from organic inputs. Soils were pre-labelled with 15N fertiliser and a carbon source. These were then incubated until there was stabilisation of the 15N abundance of the inorganic N pool and resumption of inorganic N concentrations. Residues were then applied to the soils and planted with ryegrass (Lolium perenneL.) to determine the nitrogen derived from the residue (Ndfr) using the isotope dilution equations. This method was compared with the direct method, i.e. where 15N-labelled residues were added to the soil and Ndfr in the ryegrass calculated directly. Estimates of percentage nitrogen derived from the residue (%Ndfr) alfalfa (Medicago sativaL.) in the ryegrass, were similar, 22 and 23% for the direct and soil pre-labelling methods, respectively, in the Wechsel sandy loam. Also, estimates of the %Ndfr from soybean (Glycine max (L.) Merr) residues in the Krumbach sandy loam were similar 34% (direct) and 36% (soil pre-labelling approach). However, in the Seibersdorf clay loam, the %Ndfr from soybean was 49% using the direct method and 61% using the soil pre-labelling method; yet Ndfr from common bean residue was 46% using the direct approach and 40% using the pre-labelling, not significantly different (P 〉 0.05). The soil pre-labelling approach appears to give realistic values for Ndfr. It was not possible to obtain an estimate of Ndfr using the soil pre-labelling method from the maize residues (Zea mays L.) in two of the soils, as there was no increase in the total N of the ryegrass over the growing period. This was probably due to microbial immobilisation of inorganic N, as a result of the wide C:N ratio of the residue added. The results suggest that the new soil pre-labelling method is feasible and that it is a potentially useful technique for measuring N release from a wide range or organic residues, but it requires further field-testing.
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    URL: http://dx.doi.org/10.1023/A:1004789103949
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    Influence of light and nitrogen on the phlorotannin content of the brown seaweeds Ascophyllum nodosum and Fucus vesiculosus (2000)
    Springer
    Hydrobiologia 440 (2000), S. 299-305 
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    ISSN: 1573-5117
    Keywords: Ascophyllum ; Fucus ; CNBM ; light ; nitrogen ; phlorotannins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Phlorotannins, C-based defence compounds in brown seaweeds, show a high degree of spatial and temporal variation within seaweed species. One important model explaining this variation is the Carbon Nutrient Balance Model (CNBM), which states that the relative supply of carbon and limiting nutrients will determine the level of defence compounds in plants. Nitrogen is often considered to be the limiting nutrient for marine macroalgal growth and the CNBM thus predicts that when the carbon:nitrogen ratio is high, photosynthetically fixed carbon will be allocated to production of phlorotannins. In the present study, we evaluated the effects of light (i.e. carbon) and nitrogen on the phlorotannin content of two intertidal brown seaweeds, Ascophyllum nodosum and Fucus vesiculosus. This was done in an observational field study, as well as in a manipulative experiment where plants from habitats with different light regimes were subjected to different nitrogen and light treatments, and their phlorotannin content was measured after 14 days. The results showed that there was a negative relationship between tissue nitrogen and phlorotannin content in natural populations of F. vesiculosus, but not in A. nodosum. In the short term, the phlorotannin content in both algal species was not affected by changes in nitrogen availability. Exposure to sunlight had a positive effect on the phlorotannin content in natural populations of both algal species but, in the manipulative experiment, only F. vesiculosus showed a rapid response to changes in light intensities. Plants subjected to sunlight contained higher phlorotannin content than shaded plants. In conclusion, the results imply that nitrogen availability explains some of the natural variation in the phlorotannin content of F. vesiculosus, but the light environment has greater importance than nitrogen availability in predicting the phlorotannin content of each species.
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    URL: http://dx.doi.org/10.1023/A:1004152001370
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    Light- and nutrient-limited periphyton in low order streams of Oahu, Hawaii (2000)
    Springer
    Hydrobiologia 432 (2000), S. 101-111 
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    ISSN: 1573-5117
    Keywords: Hawaii ; light ; nitrogen ; nutrients ; periphyton ; phosphorus ; spate ; stream
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To date, most studies of light- and nutrient-limited primary productivity in forested streams have been carried out in deciduous forests of temperate, continental regions. Conceptual models of light and nutrient limitation have been developed from these studies, but their restricted geographic range reduces the generality of such models. Unlike temperate continental streams, streams on tropical high islands are characterized by flashy, unpredictable discharge and riparian canopies that do not vary seasonally. These contrasting conditions suggest that patterns of light and nutrient limitation in tropical streams may differ from those in temperate streams. The effects of light, and nitrogen and phosphorus availability on periphyton accrual (measured as chlorophyll a per unit area) were investigated using field experiments in 4 low-order streams on the island of Oahu, Hawaii. Levels of chlorophyll a in partially-shaded stream pools were significantly greater than in heavily-shaded pools, and nutrient-enrichment increased the level of chlorophyll a in partially-shaded pools but not in heavily-shaded pools. In each stream, phosphate enrichment resulted in an increase in the level of chlorophyll a, but nitrate enrichment had no effect. Spates following rainstorms occur frequently in these streams, and may increase periphyton productivity by increasing the flux of nutrients to algal cells. However, differences in inorganic nitrogen and phosphorus concentrations measured during spates and baseflow were small, and during some spates, concentrations of these two nutrients declined relative to baseflow concentrations. These observations suggest that phosphorus limitation was not alleviated by spates.
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    URL: http://dx.doi.org/10.1023/A:1004074004416
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    Atmospheric deposition and watershed nitrogen export along an elevational gradient in the Catskill Mountains, New York (2000)
    Springer
    Biogeochemistry 50 (2000), S. 21-43 
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    ISSN: 1573-515X
    Keywords: acid deposition ; atmospheric deposition ; nitrate ; nitrification ; nitrogen ; soil carbon ; soil chemistry ; stream water acidification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Cumulative effects of atmospheric N deposition mayincrease N export from watersheds and contribute tothe acidification of surface waters, but naturalfactors (such as forest productivity and soildrainage) that affect forest N cycling can alsocontrol watershed N export. To identify factors thatare related to stream-water export of N, elevationalgradients in atmospheric deposition and naturalprocesses were evaluated in a steep, first-orderwatershed in the Catskill Mountains of New York, from1991 to 1994. Atmospheric deposition of SO 4 2− , andprobably N, increased with increasing elevation withinthis watershed. Stream-water concentrations ofSO 4 2− increased with increasing elevationthroughout the year, whereas stream-waterconcentrations of NO 3 − decreased withincreasing elevation during the winter and springsnowmelt period, and showed no relation with elevationduring the growing season or the fall. Annual exportof N in stream water for the overall watershed equaled12% to 17% of the total atmospheric input on thebasis of two methods of estimation. This percentagedecreased with increasing elevation, from about 25%in the lowest subwatershed to 7% in the highestsubwatershed; a probable result of an upslope increasein the thickness of the surface organic horizon,attributable to an elevational gradient in temperaturethat slows decomposition rates at upper elevations. Balsam fir stands, more prevalent at upper elevationsthan lower elevations, may also affect the gradient ofsubwatershed N export by altering nitrification ratesin the soil. Variations in climate and vegetationmust be considered to determine how future trends inatmospheric deposition will effect watershed export ofnitrogen.
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    Carbon, nitrogen and phosphorus cycling in rivermarginal wetlands; a model examination of landscapegeochemical flows (2000)
    Springer
    Biogeochemistry 50 (2000), S. 45-71 
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    ISSN: 1573-515X
    Keywords: carbon ; landscape geochemical flows ; model ; nitrogen ; phosphorus ; wetland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The importance of landscape geochemical flows wasinvestigated using a dynamic model simulating carbon,nitrogen and phosphorus cycling in riverine wetlands,which has been described in a previous paper. Thehydro-geomorphic unit (HGMU) concept was incorporatedin the model by defining a separate, completeunit-model for each unit (HGMU) within the wetland.These unit-models were connected by defining the flowsof nitrogen and phosphorus between them. These flows,also called landscape geochemical flows, usuallyconsist of flows of water containing N and P. The model was applied to a site at Kismeldon Meadows,in south-western England. This site consists of twounits, a slope and a floodplain, separated by a ditch,which catches most of the run off and shallowgroundwater flows from the slope. Only an estimated1% of the N and P that leaves the slope unit in thewater outflow reaches the floodplain unit; the rest iscaught in the system of ditches, which prevent thegeochemical flows taking their natural course. Toexamine the influence of this system of ditches, themodel was run for the same site, but without theditches. This is comparable to a situation of arestored site, where run off and shallow groundwaterflows containing nutrients, can freely get from theslope to the floodplain. The computer simulation experiment reconnecting theslope and floodplain showed that this (1) increasedthe nutrient input into the floodplain, causing ahigher biomass production, and (2) increased thewetness of the floodplain, causing slowerdecomposition, which together (3) led to a faster soilorganic matter accumulation in the floodplain.Nutrient inflows became relatively more importantcompared to atmospheric deposition, especially forphosphorus. By connecting the slope and the floodplainmore nitrogen and less phosphorus flowed into theriver.
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    URL: http://dx.doi.org/10.1023/A:1006360315792
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    Internal eutrophication in peat soils through competition between chloride and sulphate with phosphate for binding sites (2000)
    Springer
    Biogeochemistry 50 (2000), S. 183-194 
    Details
    ISSN: 1573-515X
    Keywords: chloride ; internal eutrophication ; nitrogen ; peat soil ; phosphorus ; phytometer ; sulphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Inputs of surface waters high in chloride and sulphateincreased the availability of nutrients in fenpeatlands. This `internal eutrophication' wasdemonstrated with test plants (`phytometers') andthrough water and soil analysis. Three experiments arepresented in which the level of chloride and/orsulphate was increased to 3 mmolc l−1. Inexperiment 1 chloride levels were increased from 0.5to 3 mmolc l−1 as CaCl2 or NaCl. Inexperiment 2 and 3 similar increased levels forchloride and sulphate (3 mmolc l−1; as NaCland Na2SO4) were used. The following resultswere found: (i) No differences in soil total-N and total-P werefound before and after the treatments in any of thethree experiments. (ii) Experiment 1 showed a significant increase inBio-Available P (BAP) in pots planted with Anthoxanthum odoratum as well as in bare pots for theNaCl and CaCl2 treatments. The plants in thesetreatments had taken up much more P. (iii) Experiment 2 showed an increase in soil BAPafter treatment with chloride and sulphate in potsplanted with Anthoxanthum odoratum. The chloridetreatment had no effect on plant biomass, whereas thesulphate treatment resulted in a reduction in rootbiomass and root N and P content. The shoots showedan increase in P content in the sulphate and chloridetreatments, while N content remained the same. (iv) In experiment 3, treatments with chloride andsulphate led to significantly increased biomass and Puptake of Anthoxanthum odoratum. Again, noeffects on N uptake were found. These experiments provide evidence for distinctlyincreased availability of phosphate in peat soils whenthese come into contact with water with evenmoderately increased sulphate or chloride levels.Surface water originating from the Rhine river, whichis enriched in chloride and sulphate, is oftensupplied to fen reserves in The Netherlands, tocompensate for water losses due to agriculturaldrainage in the region. The results of this study showthat phosphate availability to the vegetation may risedrastically, with detrimental effects on the speciesdensity and the occurrence of rare species in thevegetation. Hence, supply of this water should beavoided.
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    Effect of continuous nutrient enrichment on microalgae colonizing hard substrates (2000)
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    Hydrobiologia 426 (2000), S. 185-192 
    Details
    ISSN: 1573-5117
    Keywords: nutrient competition ; periphyton ; nitrogen ; silicate ; eutrophication ; benthic microalgae ; hard substrates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In order to understand the effect of changing nutrient conditions on benthic microalgae on hard substrates, in-situ experiments with artificial substrates were conducted in Kiel Fjord, Western Baltic Sea. As an extension of previous investigations, we used artificial substrates without silicate and thus were able to supply nutrient media with different Si:N ratios to porous substrates, from where they trickled out continuously. The biofilm developing on these substrates showed a significant increase in biovolume due to N + P enrichment, while Si alone had only minor effects. The stoichiometric composition of the biomass indicated nitrogen limitation during most of the year. The C:N ratios were lowered by the N + P addition. The algae were dominated by diatoms in most cases, but rhodophytes and chlorophytes also became important. The nutrient treatment affected the taxonomic composition mostly at the species level. The significance of the results with regard to coastal eutrophication is discussed.
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    Tracing mangrove carbon in suspended matter and aquatic fauna of the Gautami–Godavari Delta, Bay of Bengal (India) (2000)
    Springer
    Hydrobiologia 431 (2000), S. 225-241 
    Details
    ISSN: 1573-5117
    Keywords: Stable isotope tracers ; carbon ; nitrogen ; mangroves ; litterfall ; suspended matter ; zooplankton ; macrobenthos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Stable carbon isotopic composition and C/N ratio were used to trace the input of carbon associated with mangrove litter into the estuary of the Godavari–Gautami delta system and Kakinada bay (Andhra Pradesh, India). Suspended organic matter in the mangrove channels was more depleted in 13C (average δ13C = −24.5‰) than in Kakinada bay which showed δ13C values for suspended matter (average δ13C = −22.7‰) closer to those expected for marine phytoplankton. Suspended organic matter from mangrove channels was enriched in nitrogen (average C/N atom ratio ≤ 12.7) and 13C (average δ13C = −24.5‰) relative to mangrove leaf litter, which had a C/N ratio of 75 and a δ13C value of −28‰. Lowest C/N ratios for suspended matter were observed during southwest monsoon when rainfall was highest. Although in general, mangrove litter fall was also lower during this period, no clear correlation was observed between litter fall and C/N ratio of suspended matter. In general, the composition of suspended matter pointed towards phytoplankton as a major component. Isotopic composition of zooplankton suggested selective feeding on 13C-enriched, marine phytoplankton in open Kakinada bay and on 13C-depleted organic matter, such as estuarine phytoplankton and mangrove litter, in the mangrove channels. From the δ13C signature, it appeared that mangrove carbon was present to some extent in zooplankton and macrofauna from the mangrove mudflats and channels, but the signal rapidly decreased in Kakinada bay. Nitrogen isotopic composition of zooplankton and macrofauna indicated a progressive enrichment of 15N away from the mangrove forest towards the northern part of Kakinada bay, in approach of Kakinada city. This is thought to reflect input of anthropogenic nitrogen enriched in 15N and subsequent uptake of this enriched nitrogen into the aquatic food chain.
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    Nutrient fluxes in intertidal communities of a South European lagoon (Ria Formosa) – similarities and differences with a northern Wadden Sea bay (Sylt-Rømø Bay) (2000)
    Springer
    Hydrobiologia 436 (2000), S. 217-235 
    Details
    ISSN: 1573-5117
    Keywords: nutrient flux ; nitrogen ; phosphate ; tidal flats ; temperature ; geographical comparison
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract During an annual cycle, flux rates of oxygen, nitrate, nitrite, ammonium, phosphate and silicate were measured in light and dark bell jars at three sites in Ria Formosa (Algarve, Portugal) enclosing either a natural macrophytic community (macroalgae on sand or mud, a seagrass bed of Zostera noltii) or bare sediments. The results are compared with a preceeding study in which the same bell jar technique has been applied in the Sylt-Rømø Bay of the northern Wadden Sea. Nitrate flux was mainly directed from the water column to the benthic communities in Ria Formosa, as well as in the Sylt-Rømø Bay. However, nitrate uptake was higher in the northern, more eutrophic study area. In Ria Formosa, nutrient concentrations were lower than in the Sylt-Rømø Bay possibly due to strong water exchange with Atlantic waters. High temperatures and strong insolation had a greater impact on nitrate fluxes in Ria Formosa than in the Sylt-Rømø Bay. Bioturbating macrofauna increased ammonium efflux in the Sylt- Rømø Bay while this effect was not as pronounced in the Ria Formosa study sites. Benthic phosphate uptake dominated in the Ria Formosa and was correlated to initial phosphate concentrations in incoming waters. At both study sites, oxygen and nutrient fluxes were correlated with temperature. Additionally, flux rates were strongly influenced by biotic components and levels of eutrophication. A literature survey showed that mainly in temperate regions, material fluxes increase with temperature, whereas in warmer areas, ammonium and phosphate fluxes between sediment and water were generally lower.
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    Contaminant sources, distribution and fate in the Athabasca, Peace and Slave River Basins, Canada (2000)
    Springer
    Journal of aquatic ecosystem stress and recovery 8 (2000), S. 39-51 
    Details
    ISSN: 1573-5141
    Keywords: broad spectrum analysis ; contaminants ; distribution ; fate ; metals ; modeling ; persistent organic pollutants ; pulp-mill effluents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Northern river ecosystems worldwide are under increasing environmental stress from degrading developments that influence water quality and associated ecological integrity. In particular, contaminant-related threats to these systems are rising from enhanced industrial and municipal effluent discharges along with elevated non-point source inputs related to land-use activities such as forestry, agriculture, mining and long-range atmospheric transport. In this regard, the contaminants program of the Northern River Basins Study (NRBS) in western Canada identified key contaminant sources to the Athabasca, Slave and Peace river basins (particularly related to pulp-mill developments) and assessed their environmental fate and distribution in water and sediments. The study also developed and employed new analytical approaches and generated improved models to predict contaminant transport and fate in the aquatic environment and related food webs. Consequently the study focused on those contaminant families identified in characterization studies as arising from key point- and non-point sources within the basins or as being of greatest toxicological significance. These included resin acids, polychlorinated dioxins and furans, polychlorinated biphenyls, chlorinated phenolics, polyaromatic hydrocarbons and selected heavy metals such as mercury. Low or non-detectable concentrations of a number of contaminant groups were found in the ambient water phase including chlorinated phenolics, some chlorinated dioxins and furans and some resin acids. For both suspended and depositional sediments, significant declines were observed over the study period for the major chlorinated contaminant groups tested, correlating directly with the implementation of improved effluent treatment in many of the pulp mills located in the basins. In general, the environmental levels of chlorinated organic and metal contaminants in water or sediments were low and within Canadian health or environmental guidelines. It is hoped that the approaches used and lessons learned from the NRBS will be of use to others assessing contaminant and multiple stressor issues in other large river ecosystems.
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    Nutrient enrichment of northern rivers in response to pulp mill and municipal discharges (2000)
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    Journal of aquatic ecosystem stress and recovery 8 (2000), S. 53-66 
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    ISSN: 1573-5141
    Keywords: Canada ; nitrogen ; periphyton ; phosphorus ; pulp mill effluent ; rivers ; sewage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To evaluate the effects of pulp mill and municipal sewageeffluents on the nitrogen (N) and phosphorus (P) status of northernCanadian rivers, the Northern River Basins Study required an integratedresearch and assessment program consisting of field observation andexperimentation. Analysis of monitoring data collected over 3–13 yshowed that on an annual basis, pulp mills contributed 22% of theP and 20% of the N load discharged from the Wapiti to the Smokyriver, and 6 to 16% of the P load and 4 to 10% of the Nload in the Athabasca River. Despite these low contributions, N and Pconcentrations were elevated below pulp mill discharges on all threerivers during the low discharge period of September to April. Insitu experiments conducted with nutrient diffusing substrata showedthat periphyton biomass was maintained at low levels by insufficient Pin the upper reaches of the Athabasca River and insufficient N+P inthe Wapiti River upstream of point-source discharges. In contrast,effluent loading from pulp mill and sewage inputs alleviated nutrientlimitation downstream of major discharges on both rivers. Experimentsconducted in artificial streams located beside the Athabasca Riverupstream of the first pulp mill showed that P addition increasedperiphyton biomass (expressed as chlorophyll a content) suchthat biomass increased sharply at low P concentrations (2–5µg/L soluble reactive P) and approached saturation at 35µg/L soluble reactive P. As a result of recommendations fromthis integrated program of river monitoring and experimentation,nutrient loading has been reduced to the most affected river(Wapiti-Smoky) and federal and provincial departments of environment arereviewing loading limits for other river reaches.
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    The history of fruit thinning (2000)
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    Plant growth regulation 31 (2000), S. 1-16 
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    ISSN: 1573-5087
    Keywords: apple ; application methods ; caustic sprays ; economics ; flowering ; growth regulators ; Malus xdomestics Borkh. ; modeling ; photosynthesis ; review
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The history of fruit thinning is reviewed, beginning with hand removalof fruits, the effects upon subsequent flowering, and current attemptsto develop mechanical methods of fruit removal. Early experiments withcaustic compounds and growth regulators and their subsequent developmentas commercial practices are discussed, as well as the modes of action ofgrowth regulators. Brief reviews of methods of application, factorsaffecting response, modeling to improve efficiency, and the economicvalue of thinning to the grower are also included.
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    Effects of in vitro treatments on leaf area growth of potato transplants during acclimatisation (2000)
    Springer
    Plant cell, tissue and organ culture 61 (2000), S. 59-67 
    Details
    ISSN: 1573-5044
    Keywords: alar ; in vitro plantlet ; mannitol ; nitrogen ; rooting ; temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The importance of leaf area of in vitro propagated potato (Solanum tuberosum L.) plantlets for further growth during acclimatisation and the after-effects of in vitro treatments on growth were examined. The in vitro treatments included different levels of alar, nitrogen or mannitol or different temperatures during the last in vitro phase, the rooting phase. Leaf area or ground cover was recorded one day after planting to soil and at the end of the first phase of ex vitro growth, the acclimatisation phase. Regression analysis showed that leaf area of a transplant at the end of acclimatisation phase was positively influenced by leaf area of the same plantlet at the beginning of the phase. The relative increase in leaf area during acclimatisation (increase/early leaf area) was linearly related to the inverse of the early leaf area, indicating almost comparable relative increases for plantlets having larger early leaf areas, but more variable responses for plantlets having smaller early leaf areas. In vitro treatments mainly affected leaf area of transplants through their effects on early leaf area. Adding alar, reducing nitrogen and reducing temperature increased leaf area. Reducing mannitol increased ground cover. A lower nitrogen concentration and higher temperature in some cultivars had slight negative effects on the relative increase in leaf area after acclimatisation. For nitrogen these negative effects were less significant than the positive effects through early leaf area. Results stress the importance of manipulation of leaf area in vitro to enhance plant performance in later stages of growth.
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    A mathematical model of C4 photosynthesis: The mechanism of concentrating CO2 in NADP-malic enzyme type species (2000)
    Springer
    Photosynthesis research 66 (2000), S. 199-224 
    Details
    ISSN: 1573-5079
    Keywords: C4 photosynthesis ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A computer model comprising light reactions in PS II and PS I, electron-proton transport reactions in mesophyll and bundle sheath chloroplasts, all enzymatic reactions and most of the known regulatory functions of NADP-ME type C4 photosynthesis has been developed as a system of differential budget equations for intermediate compounds. Rate-equations were designed on principles of multisubstrate-multiproduct enzyme kinetics. Some of the 275 constants needed (ΔG0′ and K m values) were available from literature and others (V m) were estimated from reported rates and pool sizes. The model provided good simulations for rates of photosynthesis and pool sizes of intermediates under varying light, CO2 and O2. A basic novelty of the model is coupling of NADPH production via NADP-ME with ATP production and regulation of the C3 cycle in bundle sheath chloroplasts. The functional range of the ATP/NADPH ratio in bundle sheath chloroplasts extends from 1.5 to 2.1, being energetically most efficient around 2. In the presence of such stoichiometry, the CO2 concentrating function can be explained on the basis of two processes: (a) extra ATP consumption for starch and protein synthesis in bundle sheath leads to a faster NADPH and CO2 import compared with CO2 fixation in bundle sheath, and (b) the residual photorespiratory activity consumes RuBP by oxygenation, NADPH and ATP and causes the imported CO2 to accumulate in bundle sheath cells. As a wider application, the model may be used for predicting results of genetic engineering of plants.
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    URL: http://dx.doi.org/10.1023/A:1010695402963
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    Dynamics of biomass and N accumulation of alfalfa under three N fertilization rates (2000)
    Springer
    Plant and soil 219 (2000), S. 177-185 
    Details
    ISSN: 1573-5036
    Keywords: alfalfa ; growth ; Medicago sativa L. ; nitrogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The dynamics of biomass and N accumulation following defoliation of alfalfa and the application of N fertilization has rarely been studied under field conditions, particularly in the seeding year. Our objectives were to determine the effect of N fertilization on the dynamics of biomass and N accumulation during the first regrowth of alfalfa in the seeding year, and to determine if a model describing critical N concentration developed for established stands could be used in the seeding year. In two separate experiments conducted in 1992 and 1993, the biomass and N accumulation of alfalfa grown with three N rates (0, 40 and 80 kg N ha-1) were determined weekly. Maximum shoot growth was reached with 40 kg N ha-1 in 1992, and maximum shoot growth was not reached with the highest N fertilization rate in 1993. Nitrogen fixation, root N reserves and soil inorganic N uptake when no N was applied were, therefore, not sufficient to ensure non-limiting N conditions, particularly when growth rates were the highest between 14 to 21 d after defoliation. Nitrogen fertilization increased shoot biomass accumulation in the first 21 d of regrowth, biomass partitioning to the shoots and shoot and taproot N concentrations. The model parameters of critical N concentration developed by Lemaire et al. (1985) for established stands of alfalfa were not adequate in the seeding year. The N requirements per unit of shoot biomass produced are greater in the seeding year than on established stands, and this was attributed to a greater proportion of leaves in the seeding year.
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    13C NMR study of pine needle decomposition (2000)
    Springer
    Plant and soil 219 (2000), S. 273-278 
    Details
    ISSN: 1573-5036
    Keywords: cellulose ; lignin ; litter ; nitrogen ; Pinus radiata ; tannins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The quality of substrates in plantation forest litter, and their chemistry, can influence decomposition and N cycling. We studied the decomposition of Pinus radiata D. Don needles suspended on branches in windrows, for 3 yr after clear-cutting, using improved solid-state 13C NMR and chemical analysis. The NMR spectra suggested that the concentration of condensed tannins was 12–22%, and showed they were chemically altered during the period 4–12 months after clear-cutting. The spectra showed no evidence for further chemical modification of the tannins during the second or third years. Data for P. radiata needle decomposition in New Zealand indicated rapid loss of mass in the first 3 months, and condensed tannins did not appear to prevent mineralization of C or N. The tannin and lignin concentrations increased with decomposition of the needles, which was consistent with the early mineralization of readily available C compounds.
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    Temporal changes in C, P and N concentrations in soil solution following application of synthetic sheep urine to a soil under grass (2000)
    Springer
    Plant and soil 222 (2000), S. 1-13 
    Details
    ISSN: 1573-5036
    Keywords: carbon ; defoliation ; nitrogen ; phosphorus ; sheep urine ; soil solution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract We have determined the temporal changes in the concentration of dissolved organic carbon (DOC) and P and N components in soil solution following application of synthetic sheep urine (500 kg N ha-1) to a brown forest soil in boxes sown with Agrostis capillaris. Three contrasting defoliation treatments (no cutting, single cut before urine application and regular cutting twice per week) plus a fallow soil were studied. The synthetic urine contained 15N labelled urea and was P-free. Intact soil cores were taken after 2, 7, 14, 21 and 56 d and centrifuged to obtain soil solution. The urea in the synthetic urine was rapidly hydrolysed in the soil, increasing soil solution pH, DOC and total dissolved phosphorus (TDP) concentrations. For the regularly defoliated sward, DOC and P reached maximum concentrations (4000 mg DOC L-1 and 59 mg TDP L-1) on day 7. From their peak values, pH and DOC and P concentrations generally decreased with time and at day 56 were near those of the control. Concentrations of NH4 + and NO3 - in the no-urine treatments fluctuated and the greatest treatment differences were between the fallow soil and the soil sown with grass. Adding synthetic urine increased NH4 + concentrations during the first week, but NO3 - concentrations decreased. This was consistent with the 15N labelling of the NO3 - pool which required 3 weeks to reach that of 15NH4 +. Dissolved organic nitrogen (DON) reached a maximum value at day 7 with a concentration of 409 mg N L-1. The DON in soil solution contained no detectable amounts of 15N label indicating that it was derived from sources in the soil. Differences in soil solution composition related to the effect of the other cutting treatments and the fallow treatment were small compared to the effect of synthetic urine addition.
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    URL: http://dx.doi.org/10.1023/A:1004799323646
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    Dynamics of mineral N availability in grassland ecosystems under increased [CO2]: hypotheses evaluated using the Hurley Pasture Model (2000)
    Springer
    Plant and soil 224 (2000), S. 153-170 
    Details
    ISSN: 1573-5036
    Keywords: climate change ; immobilisation ; mineralisation ; N-turnover ; nitrogen ; soil organic matter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The following arguments are outlined and then illustrated by the response of the Hurley Pasture Model to [CO2] doubling in the climate of southern Britain. 1. The growth of N-limited vegetation is determined by the concentration of N in the soil mineral N pools and high turnover rates of these pools (i.e., large input and output fluxes) contribute positively to growth. 2. The size and turnover rates of the soil mineral N pools are determined overwhelmingly by N cycling into all forms of organic matter (plants, animals, soil biomass and soil organic matter — `immobilisation' in a broad sense) and back again by mineralisation. Annual system N gains (by N2 fixation and atmospheric deposition) and losses (by leaching, volatilisation, nitrification and denitrification) are small by comparison. 3. Elevated [CO2] enriches the organic matter in plants and soils with C, which leads directly to increased removal of N from the soil mineral N pools into plant biomass, soil biomass and soil organic matter (SOM). ‘Immobilisation’ in the broad sense then exceeds mineralisation. This is a transient state and as long as it exists the soil mineral N pools are depleted, N gaseous and leaching losses are reduced and the ecosystem gains N. Thus, net immobilisation gradually increases the N status of the ecosystem. 4. At the same time, elevated [CO2] increases symbiotic and non-symbiotic N2 fixation. Thus, more N is gained each year as well as less lost. Effectively, the extra C fixed in elevated [CO2] is used to capture and retain more N and so the N cycle tracks the C cycle. 5. However, the amount of extra N fixed and retained by the ecosystem each year will always be small (ca. 5–10 kg N ha-1 yr-1) compared with amount of N in the immobilisation-mineralisation cycle (ca. 1000 kg N ha-1 yr-1). Consequently, the ecosystem can take decades to centuries to gear up to a new equilibrium higher-N state. 6. The extent and timescale of the depletion of the mineral N pools in elevated [CO2] depends on the N status of the system and the magnitude of the overall system N gains and losses. Small changes in the large immobilisation—mineralisation cycle have large effects on the small mineral N pools. Consequently, it is possible to obtain a variety of growth responses within 1–10 year experiments. Ironically, ecosystem models — artificial constructs — may be the best or only way of determining what is happening in the real world.
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    Modeling of the Phase Transformation Induced by Ball Milling in Anatase TiO2 (2000)
    Springer
    Journal of materials synthesis and processing 8 (2000), S. 139-144 
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    ISSN: 1573-4870
    Keywords: TiO2 ; phase transformations ; mechanical alloying ; kinetics ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A high-pressure and high-temperature phase of TiO2 : TiO2 II is formed transiently during room-temperature high-energy ball milling of anatase TiO2 : TiO2 anatase → TiO2 II → TiO2 rutile. Rutile is the only phase present after prolonged ball milling. The present paper focuses on the influences of physical and chemical processing conditions on the transformation kinetics. The effects of two milling parameters on the kinetics of phase transformation of anatase TiO2 were investigated: the nature of milling tools and the powder-to-ball weight ratio R. Granulometric characterizations and TEM observations have demonstrated that the transformation of TiO2 anatase into TiO2 II occurs without fracturing of particles and that TiO2 II nanograins form at the surface of anatase particles. The parameter R affects only the transformation rate. For a given R, the transformation rate is the largest with alumina grinding tools, intermediate with zirconia tools, and the smallest with steel tools. The parameters involved in current models of the mechanical alloying process do not suffice to explain the differences in transformation rates observed here. A parameter, which takes into account the influence of the mechanical properties of grinding materials, is considered.
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    URL: http://dx.doi.org/10.1023/A:1011351807629
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    Physiological regulation of plant-atmosphere ammonia exchange (2000)
    Springer
    Plant and soil 221 (2000), S. 95-102 
    Details
    ISSN: 1573-5036
    Keywords: ammonia exchange ; apoplast ; atmosphere ; glutamine synthetase ; nitrogen ; photorespiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Plants have a compensation point for NH3 which ranges from 0.1 to 20 nmol mol-1, and may be several-fold higher or lower than naturally occurring atmospheric NH3 concentrations. This implies that NH3 fluxes over vegetated surfaces are bi-directional and that ammonia exchange with the atmosphere in many cases contributes significantly to the nitrogen economy of vegetation. Physiological regulation of plant–atmosphere NH3 fluxes is mediated via processes involved in nitrogen uptake, transport and metabolism. A rapid turnover of NH3 + in plant leaves leads to the establishment of a finite NH3 + concentration in the leaf apoplastic solution. This concentration determines, together with that of H+, the size of the NH3 compensation point. Barley and oilseed rape plants with access to NH3 + in the root medium have higher apoplastic NH3 + concentrations than plants absorbing NO3 -. Furthermore, the apoplastic NH3 + concentration increases with the external NH3 + concentration. Inhibition of GS leads to a rapid and substantial increase in apoplastic NH3 + and barley mutants with reduced GS activity have higher apoplastic NH3 + than wild-type plants. Increasing rates of photorespiration do not affect the steady-state NH3 + or H+ concentration in tissue or apoplast of oilseed rape, indicating that the NH3 + produced is assimilated efficiently. Nevertheless, NH3 emission increases due to a temperature-mediated displacement of the chemical equilibrium between gaseous and aqueous NH3 in the apoplast. Sugarbeet plants grown with NO3 - seem to be temporarily C-limited in the light due to a repression of respiration. As a consequence, the activity of chloroplastic GS declines during the day causing a major part of NH3 + liberated in photorespiration to be assimilated during darkness when 2-oxoglutarate is supplied in high rates by respiration.
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    URL: http://dx.doi.org/10.1023/A:1004761931558
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    Chemistry and toughness predict leaf litter decomposition rates over a wide spectrum of functional types and taxa in central Argentina (2000)
    Springer
    Plant and soil 218 (2000), S. 21-30 
    Details
    ISSN: 1573-5036
    Keywords: carbon ; functional types ; leaf tensile strength ; litter quality ; mass loss ; nitrogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Litter decomposition, a major determinant of ecosystem functioning, is strongly influenced by the litter quality of different species. We aimed at (1) relating interspecific variation in leaf litter decomposition rate to the functional types different species belong to; and (2) understanding the chemical and/or physical basis for such variation and its robustness to environmental factors. We selected 52 Angiosperms from a climatic gradient in central-western Argentina, representing the widest range of functional types and habitats published so far. Ten litter samples of each species were simultaneously buried for 9 weeks during the 1996 summer in an experimental decomposition bed. Decomposition rate was defined as the percentage of dry mass loss after incubation. Chemical litter quality was measured as carbon (C) content, nitrogen (N) content, and C-to-N ratio. Since tensile strength of litter and living leaves were strongly correlated, the latter was chosen as an indicator of physical litter quality. A subset of 15 species representing different functional types was also incubated in England for 15 weeks, following a similar experimental procedure. Litter C-to-N and leaf tensile strength of the leaves showed the strongest negative associations with decomposition rate, both at the species and at the functional-type level. Decomposition rates of the same species in Argentina and in England were strongly correlated. This reinforces previous evidence that species rankings in terms of litter decomposition rates are robust to methodological and environmental factors. This paper has shown new evidence of plant control over the turnover of organic matter through litter quality, and confirms, over a broad spectrum of functional types, general models of resource allocation. The strong correlations between leaf tensile strength – a trait that is easy and quick to measure in a large number of species – decomposition rate, and C-to-N ratio indicate that leaf tensile strength can be useful in linking plant quality to decomposition patterns at the ecosystem level.
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    URL: http://dx.doi.org/10.1023/A:1014981715532
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    On variation in forest floor thickness across four red pine plantations in Pennsylvania, USA (2000)
    Springer
    Plant and soil 219 (2000), S. 57-69 
    Details
    ISSN: 1573-5036
    Keywords: decomposition ; litter quality ; mycorrhiza ; nitrogen ; phosphorus ; saprotrophic microorganisms ; tannins ; forest soils ; acidification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract We studied variation in forest floor thickness in four plantations of red pine (Pinus resinosa Ait.) which were similar in age, soil type and associated vegetation. The plantations were located (west to east) in the Clear Creek, Moshannon, Sproul and Tiadaghton State Forests of Pennsylvania, USA. A gradient in forest floor thickness exists across these plantations; the forest floor is thickest in the west and it becomes progressively thinner toward the east. Decomposition of imported litter increased from west to east, suggesting that the variation in forest floor thickness is related to variation in the rate of decomposition. Decomposition rates were related to saprotroph abundance. Variation in forest floor N and phenolic concentrations, in overall mycorrhiza density and in the relative proportions of three common mycorrhiza morphotypes could not explain the variation in decomposition rate. The P concentrations and pH of the forest floor were significantly lower at Clear Creek and Moshannon, where decomposition rates were lowest, compared to Sproul and Tiadaghton, where decomposition rates were most rapid. This suggests that P concentration and pH may have exerted some control on decomposition.
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    URL: http://dx.doi.org/10.1023/A:1004748220856
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    Molecular Modeling of Human Serum Transferrin for Rationalizing the Changes in Its Physicochemical Properties Induced by Iron Binding. Implication of the Mechanism of Binding to Its Receptor (2000)
    Springer
    The protein journal 19 (2000), S. 215-223 
    Details
    ISSN: 1573-4943
    Keywords: Serum transferrin ; modeling ; accessible surface area ; surface charge ; molecular recognition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In order to rationalize the physicochemical properties of human serum-transferrin (STf) and the STf-receptor (TfR) recognition process, we have tried to predict the 3D structures of apo- and iron-loaded STf using a homology modeling technique to study the changes in the structural characteristics that take place upon the uptake of iron by STf in solution. The crystal structures of both forms for ovotransferrin were used as templates for the STf modeling. The modeled structure of STf gave a satisfactory interpretation for the typical physicochemical properties such that (1) STf has a negative electrophoretic mobility and its value increases with iron uptake, and (2) the radius of gyration Rg of Tf decreases with iron uptake. It was found that upon iron binding, interdomain closures take place with large movements of the NII and CII subdomains comprising the N- and C-lobes in STf through a hinge-bending motion, accompanied by the opening of the bridge region with a displacement of more than 15 Å. Moreover, in view of the findings from our capillary electrophoresis experiments that the electrostatic interactions significantly contribute to a specific binding of Fe2-STf with TfR, it is inferred that the connecting (bridge) and its neighboring region associated with a surface exposure of negative charge play an important role in the STf-receptor recognition process.
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    Carbon dioxide enrichment and nitrogen fertilization effects on cotton (Gossypium hirsutum L.) plant residue chemistry and decomposition (2000)
    Springer
    Plant and soil 220 (2000), S. 89-98 
    Details
    ISSN: 1573-5036
    Keywords: Carbohydrates ; CO2 ; lignin ; nitrogen ; proanthocyanidins ; soil respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Increased atmospheric carbon dioxide (CO2) concentration will likely cause changes in plant productivity and composition that might affect soil decomposition processes. The objective of this study was to test to what extent elevated CO2 and N fertility-induced changes in residue quality controlled decomposition rates. Cotton (Gossypium hirsutum L.) was grown in 8-l pots and exposed to two concentrations of CO2 (390 or 722 μmol mol-1) and two levels of N fertilization (1.0 or 0.25 g l-1 soil) within greenhouse chambers for 8 wks. Plants were then chemically defoliated and air-dried. Leaf, stem and root residues were assayed for total non-structural carbohydrates (TNC), lignin (LTGA), proanthocyanidins (PA), C and N. Respiration rates of an unsterilized sandy soil (Lakeland Sand) mixed with residues from the various treatments were determined using a soda lime trap to measure CO2 release. At harvest, TNC and PA concentrations were 17 to 45% higher in residues previously treated with elevated CO2 compared with controls. Leaf and stem residue LTGA concentrations were not significantly affected by either the elevated CO2 or N fertilization treatments, although root residue LTGA concentration was 30% greater in plants treated with elevated CO2. The concentration of TNC in leaf residues from the low N fertilization treatment was 2.3 times greater than that in the high N fertilization treatment, although TNC concentration in root and stem residues was suppressed 13 to 23% by the low soil N treatment. PA and LTGA concentrations in leaf, root and stem residues were affected by less than 10% by the low N fertilization treatment. N concentration was 14 to 44% lower in residues obtained from the elevated CO2 and low N fertilization treatments. In the soil microbial respiration assay, cumulative CO2 release was 10 to 14% lower in soils amended with residues from the elevated CO2 and low N fertility treatments, although treatment differences diminished as the experiment progressed. Treatment effects on residue N concentration and C:N ratios appeared to be the most important factors affecting soil microbial respiration. The results of our study strongly suggest that, although elevated CO2 and N fertility may have significant impact on post-harvest plant residue quality of cotton, neither factor is likely to substantially affect decomposition. Thus, C cycling might not be affected in this way, but via simple increases in plant biomass production.
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    Nutrient limitations in wet, drained and rewetted fen meadows: evaluation of methods and results (2000)
    Springer
    Plant and soil 220 (2000), S. 35-47 
    Details
    ISSN: 1573-5036
    Keywords: drainage ; fertilisation ; nature management ; nitrogen ; nutrient contents ; nutrients ; peat ; phosphate ; potassium ; restoration ; rewetting ; shoot biomass ; species richness ; wetlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Restoration of wet grassland communities on peat soils involves management of nutrient supply and hydrology. The concept of nutrient limitation was discussed as well as its interaction with drainage and rewetting of severely drained peat soils. Different methods of assessing nutrient limitation were compared and the type and extent of nutrient limitation were determined for several wet grassland communities. It was concluded that a full-factorial field fertilisation experiment is the most preferable method. Plant tissue analyses and soil chemical analyses were considered less suitable, although they may provide helpful additional information. Fertilisation experiments in the laboratory using sods or using test plants appear to be the proper means to study mechanisms or processes, but have a restricted predictive value for field situations. Generalising the results, it seems that many relativily undisturbed grassland plant communities on peaty soils are characterised by N limitation. Phosphate limitation for vegetation on peat soils is mainly observed in specific circumstances such as extreme calcium richness, high concentrations of Fe or as a result of drainage or long-term hay cropping. The latter two may also cause K limitation. Rewetting is regarded as a prerequisite in restoring wet grassland communities. Further restoration measures to influence nutrient availability depend on aims of the management and the individual site conditions.
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    URL: http://dx.doi.org/10.1023/A:1004735618905
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    Long-term effects of elevated atmospheric CO2 on below-ground biomass and transformations to soil organic matter in grassland (2000)
    Springer
    Plant and soil 224 (2000), S. 85-97 
    Details
    ISSN: 1573-5036
    Keywords: carbon ; CO2 enrichment ; nitrogen ; particulate organic matter ; roots ; tallgrass prairie
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract We determined the effects of elevated [CO2] on the quantity and quality of below-ground biomass and several soil organic matter pools at the conclusion of an eight-year CO2 enrichment experiment on native tallgrass prairie. Plots in open-top chambers were exposed continuously to ambient and twice-ambient [CO2] from early April through late October of each year. Soil was sampled to a depth of 30 cm beneath and next to the crowns of C4 grasses in these plots and in unchambered plots. Elevated [CO2] increased the standing crops of rhizomes (87%), coarse roots (46%), and fibrous roots (40%) but had no effect on root litter (mostly fine root fragments and sloughed cortex material 〉500 μm). Soil C and N stocks also increased under elevated [CO2], with accumulations in the silt/clay fraction over twice that of particulate organic matter (POM; 〉53 μm). The mostly root-like, light POM (density ≤1.8 Mg m-3) appeared to turn over more rapidly, while the more amorphous and rendered heavy POM (density 〉1.8 Mg m-3) accumulated under elevated [CO2]. Overall, rhizome and root C:N ratios were not greatly affected by CO2 enrichment. However, elevated [CO2] increased the C:N ratios of root litter and POM in the surface 5 cm and induced a small but significant increase in the C:N ratio of the silt/clay fraction to a depth of 15 cm. Our data suggest that 8 years of CO2 enrichment may have affected elements of the N cycle (including mineralization, immobilization, and asymbiotic fixation) but that any changes in N dynamics were insufficient to prevent significant plant growth responses.
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    URL: http://dx.doi.org/10.1023/A:1004771805022
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    Autumn leaf colours as indicators of decomposition rate in sycamore (Acer pseudoplatanus L.) (2000)
    Springer
    Plant and soil 225 (2000), S. 33-38 
    Details
    ISSN: 1573-5036
    Keywords: deciduous tree ; foliar pigmentation ; fungus ; litter mass loss ; nitrogen ; phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract We tested the hypothesis that there is a causal connection between autumn colour, nutrient concentration and decomposibility of fresh leaf litter. Samples from patches of different autumn colours within the leaves of the deciduous tree sycamore (Acer pseudoplatanus) were sealed into litter bags and incubated for one winter in an outdoor leaf mould bed. Green leaf patches were decomposed faster than yellow or brown patches and this corresponded with the higher N and P concentrations in the former. Black patches, indicating colonisation by the tar spot fungus Rhytisma acerinum, were particularly high in P, but were decomposed very slowly, owing probably to resource immobilisation by the fungus. The results supported the hypothesis and were consistent with a previous study reporting an interspecific link between autumn coloration and decomposition rate. Autumn leaf colour of deciduous woody plants may serve as a useful predictor of litter decomposibility in ecosystem or biome scale studies where extensive direct measurements of litter chemistry and decomposition are not feasible.
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    URL: http://dx.doi.org/10.1023/A:1026530214258
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    Influence of decomposer food web structure and nitrogen availability on plant growth (2000)
    Springer
    Plant and soil 225 (2000), S. 153-165 
    Details
    ISSN: 1573-5036
    Keywords: carbon ; decomposer food web ; indirect effects ; microbes ; nitrogen ; plant growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract We studied the sensitivity of soil microbial communities and ecosystem processes to variation in the vertical and horizontal structure of decomposer food web under nitrogen poor and N-enriched conditions. Microcosms with humus and litter layer of boreal forest floor, birch seedlings infected with mycorrhizal fungi, and decomposer food webs with differing trophic group and species composition of soil fauna were constructed. During the second growing period for the birch, we irrigated half of the microcosms with urea solution, and the other half with de-ionised water to create two levels of N concentration in the substrate. During the experiment night time respirations of the microcosms were measured, and the water leached through the microcosms was analysed for concentration of mineral N, and nematode numbers. The microcosms were destructively sampled after 37 weeks for plant biomass and N uptake, structure of soil animal and microbial community (indicated by PLFA profiles), and physical and chemical properties of the humus and litter materials. Predatory mites and nematodes had a negative influence on the biomass of their microbivorous and microbi-detritivorous prey, and microbi-detritivores affected the biomass and community structure of microbes (indicated by PLFA-analysis). Moreover, predatory mites and nematodes increased microbial biomass and changed the microbial community structure. The decomposer food web structure affected also N uptake and growth of plants. Microbi-detritivorous fauna had a positive effect, whereas predators of microbial and detritus feeding fauna exerted a negative influence on plant N uptake and biomass production. The impact of a trophic group on the microbes and plant was also strongly dependent on species composition within the group. Nitrogen addition magnified the influence of food web structure on microbial biomass and plant N uptake. We suggest that addition of urea-N to the soil modified the animal-microbe interaction by increasing microbial growth and altering community structure of microbes. The presence of microbi-detritivores and predators reduced loss of carbon from the microcosms, and the food web structure influenced also water holding capacity of the materials. The changes in plant growth, nutrient cycling, size of N and C pools, and in the physical properties of the soil emphasize the importance and diversity of indirect consequences of decomposer food web structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026534812422
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    The effect of three or five years of set-aside on the husbandry and grain yield of subsequent cereal crops in the UK (2000)
    Springer
    Plant and soil 225 (2000), S. 279-297 
    Details
    ISSN: 1573-5036
    Keywords: cereal ; cereal quality ; cereal yields ; natural regeneration ; nitrogen ; nitrogen uptake ; rye-grass ; set-aside ; white clover
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract During the period 1993–1997, at six contrasting sites located throughout England, two successive cereal test crops were grown both with and without nitrogen fertiliser after three or five years of set-aside or after continuous arable cropping. Vegetation during set-aside included natural regeneration and perennial rye-grass (Lolium perenne) with or without white clover (Trifolium repens), managed by mowing on one or more occasions per year. Establishment of the successive cereal test crops after destruction of the set-aside was generally not a problem. Fertile tiller numbers were increased by inclusion of clover in the set-aside cover or application of inorganic nitrogen. The presence of couch grass (Elytrigia repens) or volunteer cereals in the set-aside covers provided alternative hosts for take-all (Gaeumanomyces graminis) and eyespot (Pseudocercosporella herpotrichoides) and take-all caused some yield reductions in following cereal crops. Management during the set-aside period significantly affected grain yields of the subsequent cereal crops in the majority of the site-year combinations. However, these effects were not as large as would be expected after traditional break crops and were frequently masked by the application of nitrogen fertiliser. Mean yields increased by 80% due to the application nitrogen at the optimum rate compared to nil nitrogen. Most of the effects of set-aside treatment on grain yield were shown to be attributable to soil mineral nitrogen content, but at some sites, infections by take-all or eyespot also accounted for some of the variation. There were no effects of pests that could be related to treatment. The presence of sown clover during the set-aside period had the most consistent effect across sites, affecting tiller populations, grain yield and grain quality of cereal crops. At some sites, establishing a sown cover during the set-aside period, or cutting the cover more than once a year, improved grain yield and quality, and reduced the incidence of some specific weeds and disease.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026531528082
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    Root-shoot interactions in mineral nutrition (2000)
    Springer
    Plant and soil 226 (2000), S. 57-69 
    Details
    ISSN: 1573-5036
    Keywords: ABA ; K/Na selectivity ; nitrate reduction ; nitrogen ; phloem ; phosphate ; root-shoot interactions ; salinity ; xylem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In this paper four classes of co-operative root-shoot interations are addressed. (I) Nitrogen concentrations in the xylem sap originating from the root and in the phloem sap as exported from source leaves are much lower than those required for growth by apices and developing organs. Enrichment of xylem sap N is achieved by xylem to xylem (X-X) transfer, by which reduced N, but not nitrate, is abstracted from the xylem of leaf traces and loaded into xylem vessels serving the shoot apex. Nitrogen enrichment of phloem sap from source leaves is enacted by transfer of reduced N from xylem to phloem (X-P transfer). Quantitative data for the extent of the contribution of X-X and X-P transfer to the nutrition of young organs of Ricinus communis L. and for their change with time are presented. (II) Shoot and root cooperate in nitrate reduction and assimilation. The partitioning of this process between shoot and root is shifted towards the root under conditions of nitrate- and K-deficiency and under salt stress, while P deficiency shifts nitrate reduction almost totally to the shoot. All four changes in partitioning can be attributed to the need for cation-anion balance during xylem transport and the change in electrical charge occurring with nitrate reduction. (III) Even maintenance of the specificity of ion uptake by the root may – in addition to its need for energy – require a shoot-root interaction. This is shown to be needed in the case of the maintenance of K/Na selectivity under the highly adverse condition of salt stress and absence of K supply from the soil. (IV) Hormonal root to shoot interactions are required in the whole plant for sensing mineral imbalances in the soil. This is shown and addressed for conditions of salt stress and of P deficiency, both of which lead to a strong ABA signalling from root to shoot but result in different patterns of response in the shoot.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026431408238
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    Computationally Efficient SH-Wave Modeling in Transversely Isotropic Media (2000)
    Springer
    Journal of nondestructive evaluation 19 (2000), S. 43-54 
    Details
    ISSN: 1573-4862
    Keywords: Ultrasonic testing ; modeling ; anisotropy ; shear horizontal wave ; field profile ; electromagnetic acoustic transducer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Based on the description of shear horizontal (SH) wave propagation in arbitrarily oriented transversely isotropic media, radiation characteristics of ultrasonic transducers for this wave type are determined. The radiated wavefields are obtained by point source superposition, making use of an analytical relationship for the wave propagation direction as a function of the spatial coordinates. Approximate formulae are given for the radiation characteristics of circular and rectangular transducers in the far-field, which are in a form similar to the isotropic material case. Focusing on transversely isotropic weld metal specimens and unidirectional composites, numerical evaluation is performed for normal-incidence probes as well as for electromagnetic acoustic transducers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006645224237
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    Residual Stresses in Alumina Scales. Experiments, Modeling, and Stress-Relaxation Phenomena (2000)
    Springer
    Oxidation of metals 53 (2000), S. 49-75 
    Details
    ISSN: 1573-4889
    Keywords: FeCrAl ; α Al2O3 ; high-temperature resistance ; residual stresses ; thermal stresses ; X-ray diffraction ; relaxation ; modeling ; elasto-viscoplastic model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The stresses generated in alumina scales during different oxidation stepscontrol the protective character of such scales and their lifetime. Laboratoryand industrial Fe–Cr–Al alloys, differing by their impuritycontent and preparation, and for which the oxidation kinetics werepreviously characterized, were studied here to experimentally determine ortheoretically calculate the stress level in the alumina scales. Theexperiments were performed by X-ray diffraction (XRD) at room temperature,using the sin2psi method. The oxide-stress level wascorrelated with many parameters, such as the scale microstructure andmorphology, the nature of the substrate, the substrate and oxide thickness,the oxide grain size, the cooling rate, etc. A numerical elasto-viscoplasticmodel was developed to calculate the thermal stresses and to point out theeffect of the relaxation phenomena either during cooling or duringisothermal treatment after oxidation. The results obtained by theelasto-viscoplastic model are in good agreement with the experimental ones.
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    URL: http://dx.doi.org/10.1023/A:1004530729859
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    Incidence of bacteria involved in nitrogen and sulphur cycles in tropical shrimp culture ponds (2000)
    Springer
    Aquaculture international 8 (2000), S. 463-472 
    Details
    ISSN: 1573-143X
    Keywords: nitrogen ; organic matter ; shrimp culture ; sulphur cycle bacteria ; water quality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009250004999
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    Achieving the Kyoto Protocol in the U.S.: How Great are the Needed Changes? (2000)
    Springer
    Mitigation and adaptation strategies for global change 5 (2000), S. 123-142 
    Details
    ISSN: 1573-1596
    Keywords: Kyoto Protocol ; GHG ; mitigation strategies ; economiccosts ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Abstract The Kyoto Protocol requires the U.S.to reduce the rate of emissions of six greenhousegases (GHG) to 93% of their 1990 rate and to achievethis target by the 2008 to 2012 commitment period. This study assesses the magnitude of change needed inthe U.S. economy and, specifically, in the U.S. energysector, to achieve and maintain the target establishedby the Kyoto Protocol. A simple carbon (C)emissions-energy model is explained in this analysisusing four key variables. Current and future trendsin C emissions are explained by: the carbon/energy(C/E) ratio, Gross Domestic Product growth, energyprices and an energy trend variable. Potential GHGmitigation policy actions affect C emissionsindirectly by affecting at least one of these keyvariables. The analysis concludes that reducingfossil energy use in the U.S. to meet the Kyoto GHGemissions reduction target would be very costly. Technological progress that reduces C emissions wouldnot be fully sufficient without prematurely abandoningproductive capital equipment. Energy price increasesof about 14% per year, or declines in economic growthof almost 5% per year, could reduce energy demand andassociated C emissions enough to achieve the terms ofthe Kyoto Protocol.
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    URL: http://dx.doi.org/10.1023/A:1009697416321
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    Soil Acidification in Loess and Clay Soils in The Netherlands (2000)
    Springer
    Water, air & soil pollution 120 (2000), S. 139-167 
    Details
    ISSN: 1573-2932
    Keywords: base saturation ; clay soils ; loess soils ; modeling ; nutrient uptake ; soil acidification ; weathering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract To assess the impact of acid deposition on forestedloess and clay soils in the Netherlands, changes inbase saturation and soil solution concentrations weresimulated with the dynamic soil acidification modelReSAM for 38 loess soils and 16 clay soils. Theselected locations represent the range in geographicalposition and diversity in parent material occurring inforested loess and clay soils in the Netherlands. Twodeposition scenarios were used for the period1992–2050: a business as usual scenario (BAU) and ascenario in which deposition was reduced according topresent Dutch policy plans (MV-3). A comparison ofsimulated and measured soil solution concentrationsand base saturation in 1992/1993 showed that the modelsimulated concentrations and base saturation in theloess soils quite good. However, the model tended tooverestimate acidification in the top (0–10 cm) of theclay soils. Despite the reasonable agreement betweenmeasured and simulated data some uncertainty in thevalidity of the model predictions remains because timetrends to validate the model were not available. Themodel predicted a small but ongoing acidificationduring the BAU scenario in the loess soils asindicated by a decline in median base saturation andpH in the topsoil in 2050. Present policy plans (MV-3)lead to a slight recovery of the base saturation in2050 and a decline in Al concentrations. In the claysoils a strong decline in base saturation is simulatedin the topsoil, whereas an increase in base saturationis predicted for the subsoil.
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    URL: http://dx.doi.org/10.1023/A:1005254304043
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    Nitrogen and Phosphorus Levels in Sediments from Tropical Catatumbo River (Venezuela) (2000)
    Springer
    Water, air & soil pollution 117 (2000), S. 27-37 
    Details
    ISSN: 1573-2932
    Keywords: eutrophication ; nitrogen ; phosphorus ; river ; sediment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Nitrogen (N) and phosphorus (P) concentrations were determined in sediment samples along the bed of Catatumbo river in both Colombian and Venezuelan territories until the river outlet in Maracaibo lake. Total phosphorus was determined by digestion with HCl followed by analysis using the ascorbic acid method and total nitrogen was done using the standard microkjeldahl method plus nitrate-nitrite. Ammonium, orthophosphate and nitrate were determined using standard methods after extraction steps. The mean concentrations along the river bed were found in an interval of 0.035 and 1.492 mg g-1 dry sed. for nitrogen and 0.027 and 1.039 mg g-1 dry sed. for phosphorus at 95% confidence level. The mean molar ratio N/P in the river bed was 4.42 and 3.46 for river outlet zones in the lake, which indicates that nitrogen is the limiting nutrient. For comparison with previous results of lake sediments from sites near the river outlet it was concluded that Catatumbo river is a significant source of nutrients to the Maracaibo Lake system because sediment nutrients concentrations from Catatumbo river were higher than the ones in Maracaibo Lake. Statistic studies showed significant differences between countries, zones and similar behaviour in the river bed as related to the affluent rivers.
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    URL: http://dx.doi.org/10.1023/A:1005189710803
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    Copper, Chromium, and Arsenic Adsorption and Equilibrium Modeling in An Iron-Oxide-Coated Sand, Background Electrolyte System (2000)
    Springer
    Water, air & soil pollution 119 (2000), S. 105-120 
    Details
    ISSN: 1573-2932
    Keywords: adsorption ; arsenic ; chromium ; copper ; iron-oxide-coated sand ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The adsorption of copper, chromate, and arsenate (CCA)onto iron-oxide-coated sand (IOCS) was examined insingle-metal and mixed-metal systems. Copper andarsenate were strongly adsorbed or formed inner-spheresurface complexes with the IOCS surface while chromatewas weakly adsorbed or formed an outer-sphere surfacecomplex with the IOCS surface. Copper adsorption byIOCS slightly increased in the presence of arsenatebut was not affected by the presence of chromate. Arsenate adsorption was not affected by the presenceof copper and/or chromate. Chromate adsorptionincreased in the presence of copper by the combinationof electrostatic effects and possiblesurface-copper-chromate ternary complex formation. The presence of arsenate significantly decreasedchromate adsorption due to competition for adsorptionsites and electrostatic effects. Using inner-spheresurface complexation constants for copper and arsenateand outer-sphere surface complexation constants forchromate, the triple-layer model (TLM) was successfulin describing adsorption of copper, chromate, andarsenate in single-solute systems. The modelindicated that each metal uses a different number ofadsorption sites. For CCA metals-IOCS systems, theequilibrium constants determined from single-solutesystems were not able to predict adsorption frommulti-solute systems. The TLM does not currentlyaccount for the heterogeneity of oxide surface sitesand the formation of ternary complexes and/or solidphases that do not exist in single-solute systems.
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    URL: http://dx.doi.org/10.1023/A:1005109325539
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    Analysis of Nitrogen Dynamics in the Lye Brook Wilderness Area, Vermont, USA (2000)
    Springer
    Water, air & soil pollution 122 (2000), S. 63-75 
    Details
    ISSN: 1573-2932
    Keywords: nitrification ; nitrogen ; nitrogen mineralization ; soil water ; stream chemistry ; wilderness area
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Nitrogen (N) deposition and its impact on terrestrial and aquatic ecosystems is a concern facing federal land managers at the Lye Brook Wilderness in Vermont and other protected aras throughout the northeastern United States. In this study, we compared N production in soils with N concentrations and outputs in leachates to determine how forest cover types differ in regulating N losses. Also, precipitation inputs and modeled estimates of streamwater outputs were used to calculate a watershed N budget. Most ammonium and nitrate were produced in organic soils with deciduous cover. Softwood stands had low net nitrification rates and minimal N leaching. A comparison of watershed inputs and outputs showed a net gain in total dissolved N (5.5 kg ha-1 yr-1) due to an accumulation of dissolved inorganic N. The Lye Brook Wilderness ecosystem has N budgets similar to other forested ecosystems in the region, and appears to be assimilating the accumulating N. However seasonal losses of nitrate observed in mineral soils and streamwater may be early warnings of the initial stages of N saturation.
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    URL: http://dx.doi.org/10.1023/A:1005258814565
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    Using Bacterial Growth on Insects to Assess Nutrient Impacts in Streams (2000)
    Springer
    Environmental monitoring and assessment 63 (2000), S. 431-446 
    Details
    ISSN: 1573-2959
    Keywords: aquatic bacteria ; benthic macroinvertebrates ; bioindicator ; eutrophication ; nitrogen ; phosphorus ; stream pollution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract A combination field and laboratorystudy was conducted to evaluate the ability of arecently developed bioindicator to detect detrimentalnutrient conditions in streams. The method utilizesbacterial growth on aquatic insects to determinenutrient impacts. Field investigations indicated thatelevated concentrations of nitrate and phosphate wereassociated with growth of filamentous bacteria oninsect body surfaces, and that there was a significantreduction in the density of major insect taxa in thenutrient-enriched stream reaches. Laboratoryinvestigations confirmed a strong linkage betweenbacterial growth and reduced survival of insects. Survival was examined for insects with bacterialinfestation ranging from 0% to greater than 50%coverage of the body surface. A threshold forcatastrophic mortality occurred at about 25% bodycoverage; there were few survivors above that amount. Based on these findings, the diagnostic endpoint forthe bioindicator is 25% body coverage by bacterialgrowth, a level that signifies major impacts and isalso easy to detect visually. This study providesadditional evidence that the insect-bacteriabioindicator is a reliable tool for assessing nutrientimpacts on stream macroinvertebrate communities. Thebioindicator should prove useful for identifyingnutrient-impacted sites as well as monitoring thesuccess of management actions to improve water quality.
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    URL: http://dx.doi.org/10.1023/A:1006211929599
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    A Length-Scale Equation (2000)
    Springer
    Flow, turbulence and combustion 63 (2000), S. 1-21 
    Details
    ISSN: 1573-1987
    Keywords: turbulence ; RANS ; modeling ; length-scale
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We derive an equation for the average length-scale in a turbulent flow from a simple physical model. This is a tensorial length-scale. We use as a model the evolution of a blob of turbulent kinetic energy under the influence of production, dissipation, and transport, as well as distortion by the mean motion. A single length-scale is defined which is biased toward the smallest of the scales in the various directions. Constants are estimated by consideration of homogeneous decay. Preliminary computations are carried out in a mixing layer and a two-dimensional jet, using the new length-scale equation and the equation for the turbulent kinetic energy. The results are compared with data and with the predictions of the classical k-epsilon equations; the new results are quite satisfactory. In particular, the plane jet/round jet anomaly is approximately resolved.
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    URL: http://dx.doi.org/10.1023/A:1009957503000
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    Ecosystem Management: A Review of a New Concept and Methodology (2000)
    Springer
    Water resources management 14 (2000), S. 257-283 
    Details
    ISSN: 1573-1650
    Keywords: decision-making ; ecosystem management ; ecosystem protection ; ecosystem restoration ; modeling ; sustainable development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract Ecosystem Management (EM) is a new holistic approach to the management of natural resources. It integrates the scientificknowledge on ecological interrelationships and the complex socioeconomic and political frame of values, aiming at the long-term sustainability of a region, i.e., the ecosystem. Itincludes the human, biological and natural dimensions, and canregulate the internal structures and functions of the ecosystem,and the inputs and outputs from it, so that solutions to development and protection problems can be achieved and be socially well-accepted. It has been given attention since 1991,mainly in the U.S.A., where the existing legal framework formeda basis for EM. The former experience of programs based on the traditional methods of management, the goal of sustainable development stated by many governmental, public or private agencies, and the advent of scientific knowledge, permitted the development of a theoretical basis for EM. Today, a significant number of EM programs have been established and are in progressin the U.S.A. Here the concept, general principles and methodology of EM are reviewed, and the EM program in the Stateof Florida in the U.S.A. is presented, which is considered a successful case study. In addition, the examples of managementof two very important ecosystems in Northern Greece are critically presented for comparison, in order to evaluate if they have EM characteristics.
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    URL: http://dx.doi.org/10.1023/A:1008139011867
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    Modeling Sediment Transport Dynamics in Thompson Island Pool, Upper Hudson River (2000)
    Springer
    Water quality and ecosystem modeling 1 (2000), S. 193-222 
    Details
    ISSN: 1573-1669
    Keywords: Sediment transport ; modeling ; Upper Hudson River
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Two-dimensional, vertically-averaged hydrodynamic and sediment transport models were developed and applied as part of a PCB fate and transport modeling study of Thompson Island Pool (TIP), Upper Hudson River. Mechanistic formulations were used to simulate cohesive and non-cohesive suspended load transport; site-specific data were extensively used to determine model inputs. This modeling approach is compared and contrasted to non-mechanistic solids transport sub-models used in other contaminant fate studies. A minimum number of model parameters were adjusted to calibrate the sediment transport model using data collected during the 1994 spring flood. The model was validated during the 1997 spring flood and for a 22-year (1977–1998) period. Successful calibration and validation of the model showed that: (1) deposition and resuspension processes were realistically and accurately formulated in the model; (2) the model is an effective diagnostic tool for quantitatively evaluating net deposition and erosion from various areas of TIP; and (3) sediment transport results can be coupled with a PCB fate model with a high degree of confidence.
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    URL: http://dx.doi.org/10.1023/A:1013942801354
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    A River Water Quality Model for Chlorophyll and Dissolved Oxygen that Accommodates Zebra Mussel Metabolism (2000)
    Springer
    Water quality and ecosystem modeling 1 (2000), S. 271-309 
    Details
    ISSN: 1573-1669
    Keywords: zebra mussels ; modeling ; water quality ; Seneca River ; dissolved oxygen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The development, testing and application of a dynamic two-dimensional (longitudinal-vertical) mass balance model for dissolved oxygen (DO) and chlorophyll (Chl) for rivers is documented that for the first time accommodates both the oxygen demand and filtering effects of zebra mussels. The test system is a phytoplankton-rich section (∼ 15 km long) of the Seneca River, NY, that is believed to represent an upper bound of the impact of this exotic invader. Changes in common measures of water quality of the river brought about by the zebra mussel invasion are reviewed and related longitudinal patterns in DO, Chl, and Secchi disc transparency are documented. Model testing is supported by comprehensive measurements of DO, Chl, and various forcing conditions over a three-month period, and independent determinations of several model coefficients. Wide variations in the areal consumption rate of DO (ZOD; g·m−2·d−1) and filtering rate (m3·m−2·d−1) of zebra mussels, as determined through model calibration, occurred over the study period. Values of ZOD in areas with dense zebra mussel populations at times (e.g., 〉 50 g·m−2·d−1) were an order of magnitude greater than the sediment oxygen demand associated with organically enriched deposits. The value of determinations of these fluxes from model calibration procedures is evaluated within the context of the limitations of protocols presently available to support independent specification of these rates. Model analyses are conducted to evaluate the relative magnitude of source and sink processes for DO and Chl, the potential operation and implications of feedback from low DO levels on oxygen consumption by zebra mussels, and the sensitivity of model simulations to selected sources of uncertainty and variability. Model projections of oxygen resources of the river are presented in a probabilistic format in evaluating reductions in zebra mussel biomass that would be necessary to eliminate violations of standards and regain assimilative capacity.
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    URL: http://dx.doi.org/10.1023/A:1013951003172
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    Motivation to commit oneself as a determinant of achievement in problem-based learning (2000)
    Springer
    Higher education 40 (2000), S. 231-242 
    Details
    ISSN: 1573-174X
    Keywords: achievement ; attendance ; modeling ; motivation ; problem-based learning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Nature of Science, Research, Systems of Higher Education, Museum Science
    Notes: Abstract Problem-based learning is a constructivist approach toprofessional education stressing the use of real lifeproblems in education. Several previous attempts tounderstand the intricacies of learning in theproblem-based context have led to a causal model,elements of which were tested in the present study.The focus of the investigation was on the students' motivation to committhemselves to studying in a problem-based healthsciences curriculum, expressed in term of levels ofattendance at tutorial meetings. Data were collectedregarding functioning of the tutorial group, tutorfunctioning, level of prior knowledge, quality of theinstructional problems, time spent on individualstudy, academic achievement and increased interest.These data were analyzed using a structural equationsmodeling approach. As hypothesized, commitment appears to bea potent determinant of achievement. In fact, itrepresents one of the strongest determinants oflearning in the model tested.
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    URL: http://dx.doi.org/10.1023/A:1004022116365
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