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  • temperature  (59)
  • modeling  (50)
  • climate change  (49)
  • Springer  (156)
  • American Institute of Physics (AIP)
  • 2000-2004  (156)
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  • 1
    Digitale Medien
    Digitale Medien
    Effect of host density, temperature, and photoperiod on the fitness of Anagyrus kamali, a parasitoid of the hibiscus mealybug Maconellicoccus hirsutus (2000)
    Springer
    Entomologia experimentalis et applicata 96 (2000), S. 141-147 
    Details
    ISSN: 1570-7458
    Schlagwort(e): Anagyrus kamali ; Encyrtidae ; parasitoid ; Maconellicoccus hirsutus ; Pseudococcidae ; host density ; functional response ; temperature ; photoperiod
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The peformance of the parasitoid Anagyrus kamali Moursi [Hymenoptera: Encyrtidae], as a function of host density, temperature, and photoperiod was investigated with the objective to optimize a mass-rearing system in the context of a biological control program. The number of hosts parasitized at densities varying from 2–100 hibiscus mealybug (HMB), Maconellicoccus hirsutus Green [Homoptera: Pseudococcidae], corresponded to a type II-III functional response in fixed-time conditions and a type III in variable-time conditions. Twenty-six percent of the oviposited eggs led to progeny emergence with a sex ratio of 0.49±0.102 (M/F), regardless of host density. Fecundity and oviposition period under six abiotic combinations (i.e., two temperatures (26±2 °C and 32±2 °C) and three photoperiods (L0:D24, L12:D12, L24:D0)) were measured. Lifetime fecundity and reproductive life were significantly affected by temperature and photoperiod conditions. Optimum female parasitoid lifetime fecundity was attained at 26±2 °C, L0:D24 with an average of 116.1±17.43 eggs. At 32±2 °C, L24:D0 and L12:D12, an average of 79.4±34.57 and 85.8±35.81 eggs were laid, respectively. Reproductive longevity was maximal at 26±2 °C, L0:D24 with 12±4.85 days of oviposition. Because the parasite A. kamali can be reared optimally without light, this may save tremendous energy costs.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004021800991
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  • 2
    Digitale Medien
    Digitale Medien
    The temperature-dependent duration of development and parasitism of three cereal aphid parasitoids, Aphidius ervi, A. rhopalosiphi, and Praon volucre (2000)
    Springer
    Entomologia experimentalis et applicata 95 (2000), S. 173-184 
    Details
    ISSN: 1570-7458
    Schlagwort(e): Aphidius ervi ; Aphidius rhopalosiphi ; Praon volucre ; Sitobion avenae ; temperature ; development time ; parasitization ; superparasitization ; lower temperature thresholds ; immature mortality ; sex ratio
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Temperature dependencies were established for the egg-to-mummy and mummy-to-adult phases, for mummy mortality, and for parasitism of Aphidius ervi Haliday, Aphidius rhopalosiphi De Stefani-Perez, and Praon volucre (Haliday) (Hymenoptera, Aphidiidae), three parasitoids of Sitobion avenae (Fabricius) (Homoptera, Aphididae), at 8 °C, 12 °C, 16 °C, 20 °C, and 25 °C on winter wheat (cv. Haven). A physiological model described temperature-dependent development over the full temperature range, whereas a linear model was fitted for data above 8 °C and used to estimate the lower temperature thresholds and day-degrees (° D) required for development. The thresholds for A. ervi were 2.2 °C for egg-mummy development and 6.6 °C for mummy-adult development, those for A. rhopalosiphi were 4.5 °C and 7.2 °C, and those for P. volucre were 3.8 °C and 5.5 °C. The time to develop into mummies and adults differed significantly between the three species: A. ervi development into mummies required an average of 159 ° D, while development into adults took an average of 73 ° D. The corresponding average times required for A. rhopalosiphi and P. volucre to develop mummies were 124° D and 126° D, while their development into adults required an average of 70° D and 150° D, respectively. Mummy mortality was 25–35% at 8 °C and less at the higher temperatures tested, but began to increase again at 25 °C, showing a quadratic relationship between mortality and temperature. Parasitization was very low or, in the case of P. volucre, absent up to 12 °C and thereafter increased with increasing temperature. The relationship between parasitization, recorded as percent aphids mummified, and temperature was linear at the temperatures tested and depended on species. A. ervisuperparasitized 11.1% aphids at 20 °C and 16.6% aphids at 25 °C, whereas superparasitism was low in A. rhopalosiphi and absent in P. volucre. From 16 °C to 25 °C the P. volucre sex ratio increased. For A. ervi and A. rhopalosiphi there was no trend with temperature, but at 20 °C and 25 °C it was close to even. Field data for 1996 and 1997 allowed for a comparison of actual and expected emergence of overwintering mummies. In both years, parasitoids were predicted to have emerged from overwintering mummies well in advance of the onset of aphid infestation, and more than a month earlier than the first parasitized aphids were found in winter wheat. Observations from trap plants in other crops supported the predictions of the models. Other factors that can affect biological control by cereal aphid parasitoids are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1003993719952
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  • 3
    Digitale Medien
    Digitale Medien
    Transient Thermal Study of an Adsorption Refrigerating Machine (2000)
    Springer
    Adsorption 6 (2000), S. 93-104 
    Details
    ISSN: 1572-8757
    Schlagwort(e): adsorption refrigerator ; transient operation ; activated carbon ; methanol ; modeling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Physik , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008907518073
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  • 4
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): irrigated system ; modeling ; multi‐agent system ; simulation ; social networks ; coordination
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Wirtschaftswissenschaften
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1018908931155
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  • 5
    Digitale Medien
    Digitale Medien
    Studies on the Complexation Behavior of Thorium(IV). 1. Hydrolysis Equilibria (2000)
    Springer
    Journal of solution chemistry 29 (2000), S. 63-86 
    Details
    ISSN: 1572-8927
    Schlagwort(e): Thorium ; hydrolysis ; potentiometry ; solvent extraction ; temperature ; thermodynamics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The stability constants of thorium(IV) hydrolysis species have been measured at15, 25, and 35°C (in 1.0 mol dm−3 NaClO4) using both potentiometry and solventextraction. The results indicate the presence of the monomeric speciesTh(OH)3+, Th(OH)2+ 2, Th(OH)+ 3, and Th(OH)4, in addition to the polymericspecies Th4(OH)8+ 8 and Th6(OH)9+ 15. The polymeric species were found to beimportant, although the total thorium concentration was limited to 0.01–0.1mmol-dm−3. The solvent extraction measurements required the use of acetylacetone.As such, the stability constants of thorium(IV) with acetylacetone were alsomeasured using both potentiometry and solvent extraction. All logarithms of thestability constants were found to be linear functions of the reciprocal absolutetemperature indicating that ΔH o and ΔSo of reaction are both independent oftemperature (over the temperature range examined in the study).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1005166517699
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  • 6
    Digitale Medien
    Digitale Medien
    Conductivity of Dilute Aqueous Electrolyte Solutions at High Temperatures and Pressures Using a Flow Cell (2000)
    Springer
    Journal of solution chemistry 29 (2000), S. 217-235 
    Details
    ISSN: 1572-8927
    Schlagwort(e): Flow-through cell ; conductivity ; electrolyte ; ion association ; temperature ; pressure ; LiCl ; NaCl ; KCl
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract A flow-through electrical conductance cell was assembled in order to measuremolar conductances of dilute aqueous electrolytes with a high degree of accuracyat high temperatures and pressures. The design of the cell is based on the conceptdeveloped at the University of Delaware and built in 1995, with modificationsthat will allow the cell to operate at much higher temperatures (to 600°C) andpressures (to 300 MPa). At present, the cell has been tested successfully bymeasuring aqueous (10−4-10−3 mol-kg−1) solutions of LiCl, NaCl, and KCl attemperatures 25–410°C and pressures 9.8–33 MPa. The results are in goodagreement with reported values, including those measured with the Delawareflow-through cell. These new results are also complementary to our previousresults, which were measured with a static high-pressure cell. Measurements attemperatures near the critical point of water (374°C, 22.1 MPa) require the useof lower solution concentrations that were unachievable in the past with thestatic cell.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1005146332605
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  • 7
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): inventory ; modeling ; postponement ; supply chain management
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008191530004
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  • 8
    Digitale Medien
    Digitale Medien
    Theoretical chemistry as a tool for interpreting catalysts selectivities (2000)
    Springer
    Topics in catalysis 13 (2000), S. 213-219 
    Details
    ISSN: 1572-9028
    Schlagwort(e): heterogeneous catalysis ; selectivity ; quantum chemistry ; modeling ; butadiene ; α–β unsaturated aldehydes ; enantioselectivity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009002921067
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  • 9
    Digitale Medien
    Digitale Medien
    Late-glacial and early-Holocene Trichoptera (Insecta) from Kråkenes Lake, western Norway (2000)
    Springer
    Journal of paleolimnology 23 (2000), S. 49-56 
    Details
    ISSN: 1573-0417
    Schlagwort(e): Trichoptera ; caddisflies ; late glacial ; Allerød ; Younger Dryas ; early Holocene ; Kråkenes ; palaeolimnology ; climate change
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie
    Notizen: Abstract Fossil Trichoptera (caddisfly) remains have been identified and quantitatively recorded in the late-glacial and early-Holocene sediments from Kråkenes Lake, western Norway. The sediment sequence was deposited between 12,300 and 8850 14C BP, covering the Allerød, Younger Dryas, and early-Holocene periods. The first Trichoptera were recorded at 12,000 14C BP, and during the Allerod a diverse assemblage of Limnephilidae taxa developed in the lake. By about 11,400 14C BP the relatively thermophilous Polycentropus flavomaculatus and Limnephilus rhombicus were present, suggesting that the summer water temperature was at least 17 °C. This temperature fell by 5-8 °C at the start of the Younger Dryas, and the thermophilous taxa were replaced within 20-40 14C yrs by Apatania spp., including the arctic-alpine A. zonella, suggesting a maximum summer water temperature of 10-12 °C. The Trichoptera assemblage was impoverished in numbers and in diversity over the next 200 yrs as the severe conditions of the Younger Dryas developed. As soon as temperatures rose and glacial meltwater and silt input ended about 700 14C yrs later, the resident Apatania assemblage expanded immediately, within 10 yrs. About 130 yrs later, thermophilous taxa replaced Apatania, and a much more diverse assemblage than in the Allerod occupied the varied habitats made available by the development of the Holocene lake ecosystem. The 130 yr delay may have been caused by a gradual temperature increase crossing a critical threshold, or by the time taken for thermophilous taxa to migrate from their Younger Dryas refugia.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008064831048
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  • 10
    Digitale Medien
    Digitale Medien
    Evidence for mid-Eemian cooling in continental climatic record from Lake Baikal (2000)
    Springer
    Journal of paleolimnology 23 (2000), S. 365-371 
    Details
    ISSN: 1573-0417
    Schlagwort(e): Lake Baikal ; diatoms ; biogenic silica ; Eemian ; climate change ; Siberia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie
    Notizen: Abstract The discussion on climatic instability observed in Greenland ice cores during the Eemian period (substage 5e) resulted in discovery of a pronounced mid-Eemian cooling event. We report that the mid-Eemian cooling is found for the first time in the biogenic silica climatic record and microfossil abundance record of Lake Baikal. Timing of this event in Lake Baikal correlates well with timing of the European pollen records and marine sedimentary records. The presence of the mid-Eemian cooling signal in the Lake Baikal record suggests a much closer link between Asian climate influenced by strong pressure fields over the vast land masses and the climate-controlling processes in the North Atlantic during interglacial periods, than what was generally believed. Furthermore, the Lake Baikal record suggests that after the mid-Eemian cooling, the climatic conditions returned close to the warmth of the 5e optimum and thus argues that the warm conditions of the last interglacial persisted in Siberia throughout 5e, and did not end with the mid-Eemian cooling as suggested by several published marine records.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008188100542
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  • 11
    Digitale Medien
    Digitale Medien
    Holocene lake sediment records of Arctic hydrology (2000)
    Springer
    Journal of paleolimnology 24 (2000), S. 1-13 
    Details
    ISSN: 1573-0417
    Schlagwort(e): Arctic ; Holocene ; paleohydrology ; paleolimnology ; climate change
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie
    Notizen: Abstract Although paleoclimatic research in the Arctic has most often focused on variations in temperature, the Arctic has also experienced changes in hydrologic balance. Changes in Arctic precipitation and evaporation rates affects soils, permafrost, lakes, wetlands, rivers, ice and vegetation. Changes in Arctic soils, permafrost, runoff, and vegetation can influence global climate by changing atmospheric methane and carbon dioxide concentrations, thermohaline circulation, and high latitude albedo. Documenting past variations in Arctic hydrological conditions is important for understanding Arctic climate and the potential response and role of the Arctic in regards to future climate change. Methods for reconstructing past changes in Arctic hydrology from the stratigraphic, isotopic, geochemical and fossil records of lake sediments are being developed, refined and applied in a number of regions. These records suggest that hydrological variations in the Arctic have been regionally asynchronous, reflecting the impacts of different forcing factors including orbitally controlled insolation changes, changes in geography related to coastal emergence, ocean currents, sea ice extent, and atmospheric circulation. Despite considerable progress, much work remains to be done on the development of paleohydrological proxies and their application to the Arctic.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008100714795
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  • 12
    Digitale Medien
    Digitale Medien
    Diatom transfer-functions for quantifying past air temperature, pH and total organic carbon concentration from lakes in northern Sweden (2000)
    Springer
    Journal of paleolimnology 24 (2000), S. 109-123 
    Details
    ISSN: 1573-0417
    Schlagwort(e): diatoms ; climate change ; temperature ; pH ; transfer functions ; lake sediments
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie
    Notizen: Abstract The relationships between diatoms (Bacillariophyceae) in surface sediments of lakes and summer air temperature, pH and total organic carbon concentration (TOC) were explored along a steep climatic gradient in northern Sweden to provide a tool to infer past climate conditions from sediment cores. The study sites are in an area with low human impact and range from boreal forest to alpine tundra. Canonical correspondence analysis (CCA) constrained to mean July air temperature and pH clearly showed that diatom community composition was different between lakes situated in conifer-, mountain birch- and alpine-vegetation zones. As a consequence, diatoms and multivariate ordination methods can be used to infer past changes in treeline position and dominant forest type. Quantitative inference models were developed to estimate mean July air temperature, pH and TOC from sedimentary diatom assemblages using weighted averaging (WA) and weighted averaging partial least squares (WA-PLS) regression. Relationships between diatoms and mean July air temperature were independent of lake-water pH, TOC, alkalinity and maximum depth. The results demonstrated that diatoms in lake sediments can provide useful and independent quantitative information for estimating past changes in mean July air temperature (R2 jack = 0.62, RMSEP = 0.86 °C; R2 and root mean squared error of prediction (RMSEP) based on jack-knifing), pH (R2 jack = 0.61, RMSEP = 0.30) and TOC (R2 jack = 0.49, RMSEP = 1.33 mg l-1). The paper focuses mainly on the relationship between diatom community composition and mean July air temperature, but the relationships to pH and TOC are also discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008128014721
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  • 13
    Digitale Medien
    Digitale Medien
    A first estimate of organic carbon storage in Holocene lake sediments in Alberta, Canada (2000)
    Springer
    Journal of paleolimnology 24 (2000), S. 395-400 
    Details
    ISSN: 1573-0417
    Schlagwort(e): carbon storage ; lake sediment ; Holocene ; Canada ; climate change ; organic matter
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie
    Notizen: Abstract This paper reports a first estimate of the Holocene lake sediment carbon pool in Alberta, Canada. The organic matter content of lake sediment does not appear to depend strongly on lake size or other limnological parameters, allowing a simple first estimate in which we assume all Alberta lake sediment to have the same organic matter content. Alberta lake sediments sequester about 15 g C m-2 yr-1, for a provincial total of 0.23 Tg C yr-1, or 2.3 Pg C over the Holocene. Alberta lakes may represent as much as 1/1700 of total global, annual permanent carbon sequestration.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008103605817
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  • 14
    Digitale Medien
    Digitale Medien
    Using a Crop/Soil Simulation Model and GIS Techniques to Assess Methane Emissions from Rice Fields in Asia. III. Databases (2000)
    Springer
    Nutrient cycling in agroecosystems 58 (2000), S. 179-199 
    Details
    ISSN: 1573-0867
    Schlagwort(e): climate change ; databases ; GIS ; methane ; rice ; soils ; weather
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract As part of a series of papers describing the use of a simulation model to extrapolate experimental measurements of methane (CH4) emissions from rice fields in Asia and to evaluate the large-scale effect of various mitigation strategies, the collation and derivation of the spatial databases used are described. Daily weather data, including solar radiation, minimum and maximum temperatures, and rainfall were collated from 46 weather stations from the five countries in the study, namely China, India, Indonesia, Philippines, and Thailand. Quantitative soil data relevant to the input requirements of the model were derived by combining data from the World Inventory of Soil Emissions (WISE) database, the ISIS database, and the FAO Digital Soil Map of the World (FAO-DSMW). These data included soil pH; organic carbon content; sand, silt, and clay fractions; and iron content for top and subsoil layers, and average values of bulk density and available water capacity for the whole profile. Data on the areas allocated to irrigated, rainfed, upland, and deepwater rice at the province or district level were derived from the Huke & Huke (1997) database developed at IRRI. Using a geographical information system (GIS), a series of georeferenced data sets on climate, soils, and land use were derived for each country, at the province or district level. A summary of the soil-related derived databases is presented and their applicationn for use in global change modeling discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009898720354
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  • 15
    Digitale Medien
    Digitale Medien
    Issues related to the detection of boundaries (2000)
    Springer
    Landscape ecology 15 (2000), S. 453-466 
    Details
    ISSN: 1572-9761
    Schlagwort(e): environmental change ; GIS ; landscape ecology ; modeling ; remote sensing ; riparian ; statistics ; wetland
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008194205292
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  • 16
    Digitale Medien
    Digitale Medien
    A Fiber Optic Wavelength Modulation Sensor Based on Tantalum Pentoxide Coatings for Absolute Temperature Measurements (2000)
    Springer
    Optical review 7 (2000), S. 205-208 
    Details
    ISSN: 1349-9432
    Schlagwort(e): optical fibres ; temperature ; sensors ; tantalum pentoxide ; thermal optic ; thermal expansion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract A fiber optic low-coherence sensor based on the spectral shift of tantalum pentoxide thin films for absolute temperature sensing up to 650°C is described. A tantalum pentoxide single layer was deposited directly onto the cleaved end-face of a single mode optical fibre and was illuminated with an super luminescence diode (SLD) source through a directional coupler. Interference fringes of the film on reflection were obtained within the optical bandwidth of the SLD using an optical spectrum analyser. The spectral shift versus temperature rise showed no turning points and the output was unambiguous, linear, monotonic and gave about 0.016 nm wavelength shift in the spectrum per°C. A semi-empirical calibration procedure based on the refractive index (n) and thickness (l) of the tantalum pentoxide film for absolute thermometric measurements is described.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s10043-000-0205-8
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  • 17
    Digitale Medien
    Digitale Medien
    Ultraviolet Rayleigh Lidar for Wind and Temperature Measurements (2000)
    Springer
    Optical review 7 (2000), S. 555-560 
    Details
    ISSN: 1349-9432
    Schlagwort(e): lidar ; remote sensing ; Rayleigh scattering ; wind ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract A new method of simultaneous remote sensing of atmospheric wind and temperature by a ultraviolet Rayleigh lidar is described. This technique uses two narrowband filters located at either side of the wings of the Rayleigh backscatter spectrum to analyze Rayleigh backscattering signals. These filters are selected to be greatly sensitive to both velocity and temperature. By measuring the ratio and the sum of the two normalized filtered signals, the line-of-sight wind velocity and temperature profiles can be retrieved. A lidar system is proposed for the wind velocity and temperature measurements in the middle atmosphere, and the simulation results show that the accuracies of velocity and temperature are about 1 m/s and 2 K at the height of 30 km, respectively. The influence of aerosol component has been estimated for clear weather conditions, and with an uncertainty of aerosol component of 15% the errors are about 0.1 m/s and 2 K above the troposphere, respectively.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s10043-000-0555-2
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  • 18
    Digitale Medien
    Digitale Medien
    Temperature Modulated DSC. Theoretical interpretation (2000)
    Springer
    Journal of thermal analysis and calorimetry 60 (2000), S. 333-343 
    Details
    ISSN: 1572-8943
    Schlagwort(e): base line ; DSC ; kinetics ; modeling ; thermodynamics ; TMDSC
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1010148200201
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  • 19
    Digitale Medien
    Digitale Medien
    On the Development of the Temperature Concept (2000)
    Springer
    Journal of thermal analysis and calorimetry 60 (2000), S. 1081-1091 
    Details
    ISSN: 1572-8943
    Schlagwort(e): second law of thermodynamics ; temperature ; thermometry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract A brief outline of the history of development of the temperature concept in physics is given. Simultaneously, some persisting imperfections in the conceptual basis of classical thermodynamics closely related to the first and the second law of thermodynamics are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1010196716770
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  • 20
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): derivative thermogravimetry ; diffusion-induced stress ; modeling ; molybdenum ferrite ; oxidation kinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1010118207582
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  • 21
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): thermal plasma ; waste processing ; fly-ash vitrification ; optical emission spectroscopy ; volatilization ; lead ; modeling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006921927249
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  • 22
    Digitale Medien
    Digitale Medien
    Mathematical Modeling of Silica Anode Decomposition (2000)
    Springer
    Plasma chemistry and plasma processing 20 (2000), S. 521-553 
    Details
    ISSN: 1572-8986
    Schlagwort(e): thermal plasma ; transferred arc ; fumed silica ; modeling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007083923427
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  • 23
    Digitale Medien
    Digitale Medien
    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 
    Details
    ISSN: 1573-4870
    Schlagwort(e): TiO2 ; phase transformations ; mechanical alloying ; kinetics ; modeling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1011351807629
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  • 24
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): FeCrAl ; α Al2O3 ; high-temperature resistance ; residual stresses ; thermal stresses ; X-ray diffraction ; relaxation ; modeling ; elasto-viscoplastic model
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004530729859
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  • 25
    Digitale Medien
    Digitale Medien
    Computationally Efficient SH-Wave Modeling in Transversely Isotropic Media (2000)
    Springer
    Journal of nondestructive evaluation 19 (2000), S. 43-54 
    Details
    ISSN: 1573-4862
    Schlagwort(e): Ultrasonic testing ; modeling ; anisotropy ; shear horizontal wave ; field profile ; electromagnetic acoustic transducer
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Mathematik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006645224237
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  • 26
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): Chemical vapor deposition (CVD) ; diamond films ; modeling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1026517919085
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  • 27
    Digitale Medien
    Digitale Medien
    Global climate change and regional sustainable development: the case of Mackenzie Basin in Canada (2000)
    Springer
    Integrated assessment 1 (2000), S. 21-36 
    Details
    ISSN: 1573-1545
    Schlagwort(e): integrated assessment ; climate change ; regional sustainability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract Cohen et al. [16] suggest that in order to explore ways to bring climate change (CC) and sustainable development (SD) research together, it is necessary to develop more heuristic tools that can involve resource users and other stakeholders. In this respect, this paper focuses on methodological development in research to study climate change impacts and regional sustainable development (RSD). It starts with an introduction of an integrated land assessment framework (ILAF) which is part of the integrated phase of the Mackenzie Basin Impact Study (MBIS) in Canada. The paper then provides some articulation on how the integrated approach was applied in the Mackenzie Basin to show implications of climate change for RSD.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019167412598
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  • 28
    Digitale Medien
    Digitale Medien
    Models at the interface between science and society: impacts and options (2000)
    Springer
    Integrated assessment 1 (2000), S. 267-280 
    Details
    ISSN: 1573-1545
    Schlagwort(e): participatory integrated assessment ; climate change ; low energy society
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract Within the CLEAR project a new approach to integrated assessment modelling has been developed for the participatory integrated assessment of regional climate change involving citizens' focus groups. The climate change decision problem was structured by focusing separately on climate impacts and mitigation options. The attempt was made to link the different scales of the problem from the individual to the global level. The abstract topic of climate change was related to options on the level of a citizen's individual lifestyle. The option of a low energy society was emphasised in order to embed the climate change decision problem in a wider range of societal concerns. Special emphasis was given to the characterisation and communication of uncertainties. The chosen approach allows different kinds of uncertainties in one framework to be addressed. The paper concludes with a summary of the experience made, and recommendations for the use of models in participatory integrated assessments.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1018927120883
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  • 29
    Digitale Medien
    Digitale Medien
    Natural climate variability and climate change in the North-Atlantic European region; chance for surprise? (2000)
    Springer
    Integrated assessment 1 (2000), S. 301-306 
    Details
    ISSN: 1573-1545
    Schlagwort(e): CLEAR ; natural climate variability ; climate change ; atmosphere ; ocean
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract Long-term variability in the North Atlantic Oscillation (NAO) and the Atlantic thermohaline ocean circulation (THC) are both shaping the European climate on time scales of decades and longer. Possible linear and non-linear changes in the characteristics of these natural climate modes due to global warming are an important source of uncertainty in long-term regional projections of future climate changes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1018908027243
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  • 30
    Digitale Medien
    Digitale Medien
    Assessing alpine plant vulnerability to climate change: a modeling perspective (2000)
    Springer
    Integrated assessment 1 (2000), S. 307-320 
    Details
    ISSN: 1573-1545
    Schlagwort(e): climate change ; ecological impact assessment ; alpine and subalpine belts ; plant distribution ; statistical modeling ; local scale ; GIS ; GLM ; Swiss Alps
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract The potential ecological impact of ongoing climate change has been much discussed. High mountain ecosystems were identified early on as potentially very sensitive areas. Scenarios of upward species movement and vegetation shift are commonly discussed in the literature. Mountains being characteristically conic in shape, impact scenarios usually assume that a smaller surface area will be available as species move up. However, as the frequency distribution of additional physiographic factors (e.g., slope angle) changes with increasing elevation (e.g., with few gentle slopes available at higher elevation), species migrating upslope may encounter increasingly unsuitable conditions. As a result, many species could suffer severe reduction of their habitat surface, which could in turn affect patterns of biodiversity. In this paper, results from static plant distribution modeling are used to derive climate change impact scenarios in a high mountain environment. Models are adjusted with presence/absence of species. Environmental predictors used are: annual mean air temperature, slope, indices of topographic position, geology, rock cover, modeled permafrost and several indices of solar radiation and snow cover duration. Potential Habitat Distribution maps were drawn for 62 higher plant species, from which three separate climate change impact scenarios were derived. These scenarios show a great range of response, depending on the species and the degree of warming. Alpine species would be at greatest risk of local extinction, whereas species with a large elevation range would run the lowest risk. Limitations of the models and scenarios are further discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1018912114948
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  • 31
    Digitale Medien
    Digitale Medien
    Effects of Temperature and Photoperiod on Phytotoxic Root Exudates of Cucumber (Cucumis sativus) in Hydroponic Culture (2000)
    Springer
    Journal of chemical ecology 26 (2000), S. 1953-1967 
    Details
    ISSN: 1573-1561
    Schlagwort(e): Allelopathy ; autotoxicity ; activated charcoal ; cucumber ; Cucumis sativus L ; 2,4-dichlorobenzoic acid ; organic acids ; photoperiod ; temperature ; root exudates
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract In order to elucidate the effects of temperature and photoperiod on the quality and quantity of plant root exudates, a Japanese cucumber (Cucumis sativus, cv. Shougoin-Aonaga-Fushinari) was grown hydroponically in growth chambers under controlled temperature and photoperiod conditions with or without the addition of activated charcoal (AC) to the nutrient solutions. Fresh AC was used to trap the organic compounds exuded from cucumber roots every two weeks. Cucumber plants without AC were severely retarded in root growth and in the accumulation of dry matter, especially at high temperature and long photoperiod, compared to those with AC. The growth inhibitors, adsorbed on the AC or accumulated in the nutrient solution without AC, were extracted by organic solvents and analyzed by GC-MS. Benzoic acid and its derivatives, cinnamic acid derivatives, and fatty acids were identified. The rate of root exudation in vegetative and reproductive stages for some of these organic acids increased with the elevation of temperature and the elongation of photoperiod, and the mean rate was two or more times higher than the minimum exudation at low temperature with short photoperiod. Some of the identified compounds significantly inhibited the germination and/or root growth of lettuce and cucumber.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1005509110317
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  • 32
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): Serum transferrin ; modeling ; accessible surface area ; surface charge ; molecular recognition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007059820834
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  • 33
    Digitale Medien
    Digitale Medien
    Differences in the Denaturation Behavior of Ribonuclease A Induced by Temperature and Guanidine Hydrochloride (2000)
    Springer
    The protein journal 19 (2000), S. 345-352 
    Details
    ISSN: 1573-4943
    Schlagwort(e): Ribonuclease A ; limited proteolysis ; temperature ; guanidine hydrochloride ; unfolding
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Moderate temperatures or low concentrations of denaturants diminish the catalytic activity of some enzymes before spectroscopic methods indicate protein unfolding. To discriminate between possible reasons for the inactivation of ribonuclease A, we investigated the influence of temperature and guanidine hydrochloride on its proteolytic susceptibility to proteinase K by determining the proteolytic rate constants and fragment patterns. The results were related to changes of activity and spectroscopic properties of ribonuclease A. With thermal denaturation, the changes in activity and in the rate constants of proteolytic degradation coincide and occur slightly before the spectroscopically observable transition. In the case of guanidine hydrochloride-induced denaturation, however, proteolytic resistance of ribonuclease A initially increases accompanied by a drastic activity decrease far before unfolding of the protein is detected by spectroscopy or proteolysis. In addition to ionic effects, a tightening of the protein structure at low guanidine hydrochloride concentrations is suggested to be responsible for ribonuclease A inactivation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1026479212350
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  • 34
    Digitale Medien
    Digitale Medien
    A SWACROP-based potato root water-uptake function as determined under tropical conditions (2000)
    Springer
    Potato research 43 (2000), S. 19-29 
    Details
    ISSN: 1871-4528
    Schlagwort(e): root-water uptake ; modeling ; SWACROP ; Ferralsols ; tropics ; Cuba ; Solanum tuberosum L.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Summary The SWACROP root-water uptake function for potatoes was determined in the 1994–95 crop season on a Ferralsol in Havana province, west Cuba. The maximum pressure-heads under which water is optimally extracted by potato roots were very similar to the original Feddes function. Nevertheless, the anaerobiosis point and the wilting point pressure-head in both functions were not in agreement. However, the simulated values of soil water contents in the 0–40 cm soil depth by performing SWACROP runs in the 1995–96 potato crop season using both functions were very similar. The original Feddes function seems to be good enough for predicting soil water contents in the tropics and no specific other functions need to be developed for any particular soil or climate condition.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02358510
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  • 35
    Digitale Medien
    Digitale Medien
    Metabolism of Poly-β-Hydroxybutyric Acid in Yersinia pseudotuberculosis and Listeria monocytogenes Cultivated at Different Temperatures (2000)
    Springer
    Microbiology 69 (2000), S. 652-654 
    Details
    ISSN: 1608-3237
    Schlagwort(e): poly-β-hydroxybutyric acid ; Yersinia pseudotuberculosis ; Listeria monocytogenes ; temperature ; growth
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract A comparative investigation of the intracellular content of poly-β-hydroxybutyric acid showed that Yersinia pseudotuberculosis strains accumulated, on the average, lower amounts of this reserve substance than Listeria monocytogenes strains. The intracellular pool of poly-β-hydroxybutyric acid was responsible for the growth of the bacteria at low temperatures (4–6°C) in the absence of any exogenous carbon and energy source.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1026645922491
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  • 36
    Digitale Medien
    Digitale Medien
    Optimization of Maintenance Conditions for Some Microforms of Red Algae in Collections (2000)
    Springer
    Russian journal of plant physiology 47 (2000), S. 779-785 
    Details
    ISSN: 1608-3407
    Schlagwort(e): red microalgae ; collection of algae ; maintenance conditions ; darkness ; temperature ; chlorophyll fluorescence ; phycobiliproteins ; viability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The effects of light and temperature conditions on the maintenance of some red microalgae (order Porphyridiales) in collections were studied. Periodical subculturing on solid and liquid media was used for maintenance. Halophilic species P. aeruginosa, P. cruentum, and P. sordidum were lost in 2.5 months if kept in darkness. The viability of algae in the dim light slightly declined in 4–5 months and was species-dependent. The results were compared with earlier obtained data on mesophilic Chlorococcales. For the green algae, darkness proved to be the optimal condition, while their viability markedly decreased at light. It was suggested that this discrepancy was caused by the presence of phycobiliproteins in the cells of red algae. Dim light conditions are optimal for the synthesis of phycobiliproteins, which are rapidly destroyed in darkness, thus leading to cell death.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1026611312844
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  • 37
    Digitale Medien
    Digitale Medien
    Factors influencing the induction of diapausing egg production in the calanoid copepod Diaptomus leptopus (2000)
    Springer
    Aquatic ecology 34 (2000), S. 9-17 
    Details
    ISSN: 1573-5125
    Schlagwort(e): diapause ; Diaptomus ; permanent environment ; photoperiod ; pond chemistry ; proximate cues ; temperature ; temporary environment
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Field and laboratory studies were carried out between 1995 and 1997 on four populations of Diaptomus leptopus found in seasonally temporary, occasionally temporary, and a permanent environment to assess the relative importance of photoperiod and temperature regimes versus other proximate local cues in inducing diapause egg production. Patterns of diapausing and subitaneous egg production were determined by observation of individual females bearing clutches that were produced in the field. A laboratory common-garden experiment was performed to assess the effects of four different regimes of temperature and photoperiod on the induction of diapause. Patterns of diapausing egg production differed among ponds: diapause occurred early in the seasonally temporary environment and occurred rarely in the permanent environment. In the common-garden experiment, populations exhibited substantial changes in the onset of diapause when compared to patterns found under field conditions. These results provide indirect evidence that the different populations respond to available cues of environmental change in different ways in nature, or that environmental cues vary among habitats.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009970719969
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  • 38
    Digitale Medien
    Digitale Medien
    Seasonal variations in copepod body length: a comparison between different species in the Lagoon of Venice (2000)
    Springer
    Aquatic ecology 34 (2000), S. 243-252 
    Details
    ISSN: 1573-5125
    Schlagwort(e): body size ; chlorophyll concentration ; salinity ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The seasonal variation in length of the most abundant copepod species in the lagoon of Venice were compared and the relative influence of temperature, chlorophyll concentration and salinity examined. Temperature seems to be the primary factor influencing copepod body length in the lagoon of Venice, but the different species vary markedly in their response. Calanoid copepods (Acartia clausi, A. tonsa, Paracalanus parvus and Centropages ponticus) showed a more definite trend of size variation with temperature than the cyclopoids (Oithona nana and O. similis) and the harpacticoid Euterpina acutifrons. The size of the poecilostomatoids Oncaea media and O. subtilis was not affected by temperature, and was almost constant over time. Differences in the metabolic rates, longevity and specialization of calanoid, cyclopoid and harpacticoid copepods could explain their different responses to temperature.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009971507797
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  • 39
    Digitale Medien
    Digitale Medien
    Socio-Ecological Webs and Sites of Sociality:Levins' Strategy of Model Building Revisited (2000)
    Springer
    Biology and philosophy 15 (2000), S. 197-210 
    Details
    ISSN: 1572-8404
    Schlagwort(e): ecology ; Levins ; modeling ; provisionality ; sociality
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Philosophie
    Notizen: Abstract This essay extends Levins' 1966 analysis of modelbuilding in ecology and evolutionary biology. Amodel, as the product of modeling, might bevalued according to its correspondence to reality. Yet Levins' emphasis on provisionality and changeredirects attention to the processes ofmodeling, through which scientists select and generatetheir problems, define their categories, collect theirdata, compare competing models, and present theirfindings. I identify several points where decisionsare required that are not determined by nature. Thisinvites examination of the social considerationsmodelers are reacting to at the “sites of sociality”.Modelers must weave “socio-ecological webs” so thatthe models can be seen to represent their subjectmatter at the same time as the modelers secure thesupport of colleagues, collaborators and institutions,and enjoin others to act upon their conclusions. Notonly do theory justification and theory generationmerge, but the joint project becomes simultaneouslyphilosophical and sociological.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006684801878
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  • 40
    Digitale Medien
    Digitale Medien
    Responses of rotifers and cladocerans to Microcystis aeruginosa (Cyanophyceae): A demographic study (2000)
    Springer
    Aquatic ecology 34 (2000), S. 227-242 
    Details
    ISSN: 1573-5125
    Schlagwort(e): cladocerans ; demography ; Microcystis aeruginosa ; rotifers ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The response of selected rotifers and cladocerans to Microcystis aeruginosa, offered as colonies and single cells, was compared to that on a diet of Chlorella vulgaris using the life table demography approach. The test zooplankton species were Simocephalus vetulus, Daphnia carinata, Moina macrocopa, Scapholeberis kingi, Ceriodaphnia cornuta, Brachionus calyciflorus and Hexarthra mira. To detect the development of resistance to toxins from Microcystis in zooplankton, in addition to the laboratory cultured strain of Ceriodaphnia cornuta, another strain of the same species was also used (designated as C. cornuta 2, this was collected from a pond containing Microcystis and cultured in the laboratory on Chlorella for a few weeks prior to experimentation). Experiments were conducted at 20 °C and 30 °C. Survivorship was high on Chlorella in most species but low on diets of Microcystis. Except for C. cornuta 2, S. kingi and S. vetulus, all other test species were adversely affected by Microcystis. The ability to utilise Microcystis improved at 30 °C in M. macrocopa, D. carinata and H. mira. The longest mean lifespan was recorded for C. cornuta 2 (25.3 ± 4.86 d) and the lowest for B. calyciflorus (0.58 ± 0.05 d). The highest net reproductive rate was observed for C. cornuta 1 (44.9 ± 4.88) and the longest generation time of 26.6 ± 2.13 d for S. vetulus. Among the cladocerans that showed positive values of population growth rate (r), M. macrocopa had the highest of 0.96 ± 0.04 per day.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009986928706
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  • 41
    Digitale Medien
    Digitale Medien
    Responses of Porphyra linearis (Rhodophyta) to environmental factors under controlled culture conditions (2000)
    Springer
    Journal of applied phycology 12 (2000), S. 535-542 
    Details
    ISSN: 1573-5176
    Schlagwort(e): desiccation ; growth ; growth model ; inorganic carbon ; nutrients ; photoperiod ; photosynthesis ; pigments ; Porphyra linearis ; PPF ; respiration ; temperature ; water velocity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The effect of environmental parameters on the growthof Porphyra linearis gametophytes was examinedunder controlled conditions, and related to themultilinear regression growth model recently developedfor this seaweed under coastal conditions in theeastern Mediterranean. Growth chambers, a gradienttable, special culture devices and analytical methodswere combined for this culture study.The major factors significantly controlling thegrowth rate of the P. linearis gametophytein glass dishes were: photoperiod, temperature, agein culture, photosynthetic photon flux (PPF), salinityand water dynamics. Maximal growth occurred underdaylength of 12 h, medium temperature (15–20 °C), low PPF (70–140 μmol photon m-2s-1), ambient salinity (30–40 ppt), 1–3 h ofdaily air exposure, and water velocity of 4 cm s-1.Photosynthesis and respiration rates weredominantly affected by daylength and temperature,while the concentration of pigments was dominantlyaffected by PPF and temperature.These conditions correspond well to the optimalnatural growth environment of this local species andare in agreement with the optimum estimated throughthe recently developed outdoor mathematical growthmodel.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008138227520
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  • 42
    Digitale Medien
    Digitale Medien
    Stromatolitic communities in Mediterranean streams: adaptations to a changing environment (2000)
    Springer
    Biodiversity and conservation 9 (2000), S. 379-392 
    Details
    ISSN: 1572-9710
    Schlagwort(e): climate change ; cyanobacteria ; ectoenzymes ; Mediterranean ; nutrient limitation ; photosynthesis ; stromatolite
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract A stromatolitic microbial mat extensively covers La Solana streambed, a calcareous Mediterranean stream. This stromatolite shows remarkable biological and physiological diversity. It is mainly composed by cyanobacteria, with Rivularia and Schizothrix as the most abundant taxa. The stromatolite is photosynthetically adaptated to the high irradiances reaching the streambed. Photosynthetically active chlorophyll is present even in the lowest layers of the stromatolite, indicating the presence of well-preserved cyanobacteria in that part. Diffusion of gases and nutrients within the stromatolite can be possible because of the high porosity of the crust. It has been experimentally established that the stromatolite recovers heterotrophic and autotrophic activities in a few hours, after being desiccated for long periods. Recovery after desiccation is indicative of the high resilience of this community to environmental extremes, which are common in Mediterranean climatic regimes. The stromatolitic community is adapted to nutrient limitation, both to low availability of inorganic phosphorus and nitrogen (that constrain growth of primary producers), and to low dissolved organic carbon (mainly affecting heterotrophs). Stromatolitic heterotrophs mainly rely on the organic carbon stored in the crust as the main organic carbon source. These strategies are the direct response of the stromatolite to oligotrophy, and justify the restricted occurrence in stream systems affected by organic pollution.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008954801397
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  • 43
    Digitale Medien
    Digitale Medien
    Heathlands functioning in a perspective of climate warming – Estimation of parameters, elements for discrete event simulation (2000)
    Springer
    Plant ecology 149 (2000), S. 107-118 
    Details
    ISSN: 1573-5052
    Schlagwort(e): Calluna vulgaris ; demography ; nitrogen cycle ; climate change ; modelling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Three Calluna vulgaris (L.) Hull heathlands (1100, 1500 and 1780 m altitude) are studied in order to establish and estimate parameters which will be integrated in a discrete event simulation of heathland functioning in the case of a 2 °C climate warming. The sites, situated in the Chaîne des Puys and the Massif du Sancy (France), present similar conditions for Calluna growth: bedrock (trachyt), exposure and slope, so that they can be compared on a climatic basis. Main parameters sampled are: age distributions, life expectancies, layering probabilities, annual growths, biomasses (standing crop), C/N rates and potential respiratory of soils. In addition, experiments were carried out on germination, hypocotyle elongation and growth of mycorrhizal fungi in order to estimate the inhibitory-to-growth action against the substitution process. On one stand (exhibiting gaps) the patch structure of Calluna plants was recorded and mapped. The rising of biomass expected is calculated according to the Aerts's model, as a function of nitrogen availability which would increase under a scenario of climate warming. From a similar point of view, layering probabilities, life expectancies and inhibition of seedlings survival modelling – under a linear model assumption – are proposed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009805112857
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  • 44
    Digitale Medien
    Digitale Medien
    Physics of Atoll Groundwater Flow (2000)
    Springer
    Mathematical geology 32 (2000), S. 301-317 
    Details
    ISSN: 1573-8868
    Schlagwort(e): hydrogeology ; modeling ; atoll ; coral reef ; carbonate platform
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Mathematik
    Notizen: Abstract Large-scale steady-state groundwater flow in atoll carbonate platforms results from temperature and salinity-induced density gradients. Atolls are built on top of a basaltic substrate that provides geothermal heating from beneath. Moreover, they are immersed in the tropical ocean where temperature decreases rapidly with depth. Groundwater circulation in these platforms has long been associated with the geothermal heat flux because it is capable of generating inward and upward flow of oceanic origin water by buoyancy effects. This study shows that hydraulic circulation occurs even in the absence of a geothermal flux because the combination of the cold subsurface ocean waters with the warm surface conditions is sufficient to maintain a convection cell within the carbonate platform. Using a one-dimensional analytical model, validated by more sophisticated two-dimensional simulations, we can investigate the interaction between these two driving forces. The flow rate inside the platform is, in fact, a function of the ratio of the geothermal flux to the temperature gradient in the ocean. It increases with the geothermal flux but decreases with the oceanic temperature gradient. This one-dimensional model also shows that taking salinity effects on density into account increases the flow rates transiting through the platform by a third.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007533827210
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  • 45
    Digitale Medien
    Digitale Medien
    Automatic Guided Vehicles: Robust Controller Design in Image Space (2000)
    Springer
    Autonomous robots 8 (2000), S. 25-42 
    Details
    ISSN: 1573-7527
    Schlagwort(e): visual servoing ; robust control ; mobile robot ; vehicles ; modeling ; vision
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008936817917
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  • 46
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): market ; electricity ; regression ; calibration ; modeling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1010143717898
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  • 47
    Digitale Medien
    Digitale Medien
    Principles of Integrated Flow Modeling (2000)
    Springer
    Transport in porous media 41 (2000), S. 105-116 
    Details
    ISSN: 1573-1634
    Schlagwort(e): flow ; integration ; Gassmann ; acoustics ; reservoir ; characterization ; modeling ; simulation ; Newton–Raphson
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract Integrated flow modeling is the combination of a traditional flow simulator with a petrophysical model. By combining a petrophysical model with a traditional flow model, it is possible to perform calculations that improve our ability to monitor fluid movement in porous media. This paper outlines the formulation of an integrated flow model IFLO and its multi-variable, Newton–Raphson IMPES solution procedure. The benefits of integrated flow modeling and the underlying principles involved in the integration of a flow model with a petrophysical model are presented. Results from the IFLO model are used to illustrate the principles.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006658900240
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  • 48
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): achievement ; attendance ; modeling ; motivation ; problem-based learning
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Wissenschaftskunde und Wissenschaftsorganisation, Hochschul- und Universitätswesen, Museumswissenschaft
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004022116365
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  • 49
    Digitale Medien
    Digitale Medien
    The effect of seawater flow and temperature on metamorphosis and postlarval development in great scallop (2000)
    Springer
    Aquaculture international 8 (2000), S. 513-530 
    Details
    ISSN: 1573-143X
    Schlagwort(e): great scallop (Pecten maximus) ; hatchery ; metamorphosis ; seawater flow ; spat development ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Variations in growth and survival of hatchery-reared post-metamorphicjuveniles of great scallop Pecten maximus prompted anexamination of settlement and postlarval development. The effects ofseawater flow and temperature on great scallop metamorphosis andpostlarvae were studied over a 4–5 week period. In allexperiments, and regardless of environmental conditions, great scallopmetamorphosed after a 2–3 week period with values of 35 to70%. Subsequently, spat numbers increased slightly. Spatmortality generally occurred from the third week onward and reachedlevels as high as 30% by the fifth week under standardconditions. At 20 °C, however, 60% mortality levels wererecorded. Differences in spat growth rate, ranging from 37 to 45 μmday−1, were noticed at different seawater flow ratesbut no clear tendency could be discerned. Temperature affected spatgrowth with an increase in size from 24 μm day−1 at15 °C to 35 μm day−1 at 18 °C. Conversely,growth was suppressed at 20 °C (14 μm day−1).For optimal metamorphosis and postlarval development in great scallop, aseawater flow of 4.3 L h−1 per sieve and a temperatureof 15 °C are recommended.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009274707986
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  • 50
    Digitale Medien
    Digitale Medien
    Laboratory, Field and Modeling Studies of Radon‐222 as a Natural Tracer for Monitoring NAPL Contamination (2000)
    Springer
    Transport in porous media 38 (2000), S. 223-240 
    Details
    ISSN: 1573-1634
    Schlagwort(e): NAPLs ; radon ; modeling ; monitoring ; partitioning ; tracer ; emanation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract The recently developed natural radon tracer method has potential as a rapid, low‐cost, nondestructive, and noninvasive method for quantifying NAPL contamination. In the subsurface, radon‐222 (radon) is produced by the decay of naturally occurring radium‐226 contained in the mineral fraction of aquifer solids. In groundwater radon occurs as a dissolved gas, with a half‐life of 3.83 days. In the absence of NAPL, the radon concentration in groundwater quickly reaches a maximum value that is determined by the mineral composition of the aquifer solids, which controls the rate of radon emanation. In the presence of NAPL, however, the radon concentration in the groundwater is substantially reduced due to the preferential partitioning of radon into the organic NAPL phase. A simple equilibrium model and supporting laboratory studies show the reduction in radon concentration can be quantitatively correlated with residual NAPL saturation. Thus, by measuring the spatial distribution in radon it may be possible to identify locations where residual NAPL is present and to quantify the NAPL saturation. When the basic processes of partitioning, radon emanation from the aquifer solids, and first‐order decay are incorporated into an advective/dispersive transport model, good agreement is obtained with the results of laboratory and field experiments. Model sensitivity analyses shows many factors can contribute to the radon concentration response, including the length of the NAPL zone, NAPL saturation, groundwater velocity, porosity, and radon emanation. Thus, care must be taken when applying the radon method to locate and quantify NAPL contamination in the subsurface.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006671519143
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  • 51
    Digitale Medien
    Digitale Medien
    Hydraulics of Peat Filters Treating Septic Tank Effluent (2000)
    Springer
    Transport in porous media 41 (2000), S. 47-60 
    Details
    ISSN: 1573-1634
    Schlagwort(e): unsaturated flow ; peat ; filters ; septic ; modeling ; hydraulics ; soil moisture retention curve
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract Peat is an alternative filter medium for the treatment of various waste streams including septic tank effluent. The water holding capacity and adsorption capacity of peat make it a favorable filter medium over sand or gravel which are commonly used as the filter medium for the drainage field of septic systems. This paper presents the results of a field study to evaluate the hydraulics of a peat filter used to treat the septic tank effluent from a public school west of Ottawa, Canada. An experimental box was placed within the filter during its construction to provide access to the vertical profile of the peat layer. The filter is periodically pulsed with septic tank effluent, which is distributed over the top of the filter and flows vertically through the peat. The filter was instrumented with tensiometers and transducers to monitor the pore water pressures in response to a pulse of septic tank effluent. An in-depth study of the hydraulics of the system was completed. The soil moisture retention curve and the hydraulic conductivity as a function of density were determined in laboratory experiments. A one-dimensional unsaturated flow model was used to predict the pressure response due to a pulse. A comparison of the field and model results illustrates the impact of the density variations, and the corresponding hydraulic conductivity variations, on the model predictions. The compaction of the peat is an important design consideration for the filter since it directly impacts the flow characteristics and the hydraulic retention time within the filter.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006796827147
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  • 52
    Digitale Medien
    Digitale Medien
    Ecosystem Management: A Review of a New Concept and Methodology (2000)
    Springer
    Water resources management 14 (2000), S. 257-283 
    Details
    ISSN: 1573-1650
    Schlagwort(e): decision-making ; ecosystem management ; ecosystem protection ; ecosystem restoration ; modeling ; sustainable development
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008139011867
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  • 53
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): Sediment transport ; modeling ; Upper Hudson River
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1013942801354
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  • 54
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): zebra mussels ; modeling ; water quality ; Seneca River ; dissolved oxygen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1013951003172
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  • 55
    Digitale Medien
    Digitale Medien
    Climate Change Adaptation in the U.K. Water Industry: Managers' Perceptions of Past Variability and Future Scenarios (2000)
    Springer
    Water resources management 14 (2000), S. 137-156 
    Details
    ISSN: 1573-1650
    Schlagwort(e): climate adaptation ; climate change ; droughtmanagement ; England and Wales water supply
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie
    Notizen: Abstract In this article, the relationship between U.K. watercompanies' perceptions of past climatic extremes andtheir effect on resilience to future climatic changeis explored. Perceptions and activities related topast and future dry periods was investigated throughinterviews with managers at the ten major English andWelsh water supply/sewerage companies, and severalsmaller, water-only companies. Several of thecompanies report that they have observed a trendtowards drier summers in their regions, and a number of companies say that they have observed a changetowards more intensive rainfall of shorter duration. Recent supply measures in a number of regions havebeen aimed at improving storage and distributionrelated to the perceived change in rainfall intensity.A new requirement to incorporate regional climatechange scenarios in future supply assumptions appearsto have had little impact on planning in the region todate. Many water resource planners believe that thescenarios generated are too aggregated and do notencourage a precautionary approach to planning. Somemanagers believe that records of historical droughtconditions, such as experienced in 1933/1934 or 1995/1996,as worst-case scenarios provide a better basis for planning.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008114231502
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  • 56
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): inoculum density–disease incidence ; biological control agents ; pathogen detection and quantification with molecular and serological techniques ; polymerase chain reaction ; marker and reporter genes ; modeling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008733927515
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  • 57
    Digitale Medien
    Digitale Medien
    Temperature effects on egg size and their fitness consequences in the yellow dung fly Scathophaga stercoraria (2000)
    Springer
    Evolutionary ecology 14 (2000), S. 627-643 
    Details
    ISSN: 1573-8477
    Schlagwort(e): adaptation ; Bergmann's rule ; clutch size ; egg size ; physiological constraint ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Organisms and parts of an organism like eggs or individual cells developing in colder environments tend to grow bigger. A unifying explanation for this Bergmann's rule extended to ectotherms has not been found, and whether this is an adaptive response or a physiological constraint is debated. The dependence of egg and clutch size on the mother's temperature environment were investigated in the yellow dung fly Scathophaga stercoraria. Smaller eggs were laid at warmer temperatures in the field and the laboratory, where possible confounding variables were controlled for. As clutch size at the same time was unaffected by temperature, this effect was not due to a trade-off between egg size and number. Temperature-dependent egg sizes even persisted within individuals: when females were transferred to a cooler (warmer) environment, they laid third-clutch eggs that were larger (smaller) than their first-clutch eggs. The fitness consequences of these temperature-mediated egg sizes were further investigated in two laboratory experiments. Neither egg and pre-adult survivorship nor larval growth rate were maximized, nor was development time minimized, at the ambient temperature corresponding to the mother's temperature environment. This does not support the beneficial acclimation hypothesis. Instead, this study yielded some, but by no means conclusive indications of best performance by offspring from eggs laid at intermediate temperatures, weakly supporting the optimal temperature hypothesis. In one experiment the smaller eggs laid at 24°C had reduced survivorship at all ambient temperatures tested. Smaller eggs thus generally performed poorly. The most parsimonious interpretation of these results is that temperature-mediated variation in egg size is a maternal physiological response (perhaps even a constraint) of unclear adaptive value.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1010911017700
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  • 58
    Digitale Medien
    Digitale Medien
    Simulations of Composite Electrodes in Fuel Cells (2000)
    Springer
    Journal of electroceramics 5 (2000), S. 153-182 
    Details
    ISSN: 1573-8663
    Schlagwort(e): modeling ; SOFC ; internal reforming ; cermet
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Notizen: Abstract Approaches to models and computer simulations of conductivity, polarization resistance, and impedance of composite electrodes in solid oxide fuel cells (SOFC) are reviewed with respect to the more important experimental findings. The approaches are classified according to how they model the highly disordered structure of composite SOFC electrodes: As corrugated layers of electrode material covered by a thin film of electrolyte or vice versa (thin film model), as a random packing of particles (Monte Carlo calculations), or using a macroscopic, averaged description of the disordered electrode structure (macroscopic porous-electrode model). Thin film models appear to be useful rationalizations of some experimental measurements of polarization resistance, but in the stricter sense fail to predict a number of important electrode characteristics. The Monte Carlo method, on the other hand, apparently meets with most of the more prominent experimental results reported so far, although some issues concerning parameter choices, among other things, remain to be resolved. The macroscopic porous-electrode theory may serve as a useful simplification of the Monte Carlo method, but with a more limited scope. Modeling of composite electrodes for SOFC thus appears to have reached a level where it can be used for practical engineering applications. As an example of this, the rate of methane reforming at Ni-YSZ cermet anodes under current load is calculated using the framework of the macroscopic porous-electrode theory, modified to include non-linear kinetics and gas-phase diffusion. The reforming reaction is quite evenly distributed in the anode, and its overall rate is therefore strongly dependent on thickness. However, most of the electrochemical reaction is likely to occur in a region closer than 10 μm to the bulk electrolyte. For an anode thickness larger than this, the current-collector potential at a given current is by and large independent of thickness. The ratio between the rates of the reforming and the electrochemical reactions can therefore be balanced to a certain degree by optimizing thickness, without significant loss in cell power. In addition, cermet porosity, volume fraction of Ni and Ni-particle size, appears to have a moderate effect in controlling the rate balance, which will have to be manipulated within the constraints set by the requirement of percolation in the gas-phase and the Ni- and YSZ-networks.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009962319168
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  • 59
    Digitale Medien
    Digitale Medien
    Pharmacokinetic Variability and Therapeutic Drug Monitoring Actions at Steady State (2000)
    Springer
    Pharmaceutical research 17 (2000), S. 589-592 
    Details
    ISSN: 1573-904X
    Schlagwort(e): modeling ; stochastic ; Log-normal ; distributions ; pharmacodynamics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007573001055
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  • 60
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): controlled release ; diffusion ; hydrophilic matrix ; hydroxypropyl methylcellulose (HPMC) ; modeling ; swelling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1026455822595
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  • 61
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): glycyrrhizic acid ; modeling ; enterohepatic cycling ; PBPK ; pharmacokinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007661209921
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  • 62
    Digitale Medien
    Digitale Medien
    Effect of Boron on the Structure and Composition of Cobalt Silicides (2000)
    Springer
    Powder metallurgy and metal ceramics 39 (2000), S. 599-602 
    Details
    ISSN: 1573-9066
    Schlagwort(e): solid-phase reaction ; solubility ; temperature ; cobalt silicides ; boron
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The system Co ― Si ― B is promising for development of new soft magnetic materials. We studied the effect of boron on the structure and composition of cobalt silicides during solid-phase reaction of powders of the starting components under a 3·10−3 Pa vacuum in the temperature range 200°C to 1300°C for boron content from 0.5 mass% to 7.7 mass% by differential thermal analysis, metallographic analysis, x-ray analysis, and electron-probe microanalysis. We established that boron is not soluble in cobalt silicides. Formation of ternary chemical compounds is typical for the Co ― Si ― B system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1011384332153
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  • 63
    Digitale Medien
    Digitale Medien
    The effects of elevated [CO2] on the C:N and C:P mass ratios of plant tissues (2000)
    Springer
    Plant and soil 224 (2000), S. 1-14 
    Details
    ISSN: 1573-5036
    Schlagwort(e): climate change ; CO2 ; decomposition ; leaf ; root ; litter ; nutrient concentration ; nutrient cycle
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The influence of elevated CO2 concentration ([CO2]) during plant growth on the carbon:nutrient ratios of tissues depends in part on the time and space scales considered. Most evidence relates to individual plants examined over weeks to just a few years. The C:N ratio of live tissues is found to increase, decrease or remain the same under elevated [CO2]. On average it increases by about 15% under a doubled [CO2]. A testable hypothesis is proposed to explain why it increases in some situations and decreases in others. It includes the notion that only in the intermediate range of N-availability will C:N of live tissues increase under elevated [CO2]. Five hypotheses to explain the mechanism of such increase in C:N are discussed; none of these options explains all the published results. Where elevated [CO2] did increase the C:N of green leaves, that response was not necessarily expressed as a higher C:N of senesced leaves. An hypothesis is explored to explain the observed range in the degree of propogation of a CO2 effect on live tissues through to the litter derived from them. Data on C:P ratios under elevated [CO2] are sparse and also variable. They do not yet suggest a generalising-hypothesis of responses. Although, unlike for C:N, there is no theoretical expectation that C:P of plants would increase under elevated [CO2], the average trend in the data is of such an increase. The processes determining the C:P response to elevated [CO2] seem to be largely independent of those for C:N. Research to advance the topic should be structured to examine the components of the hypotheses to explain effects on C:N. This involves experiments in which plants are grown over the full range of N and of P availability from extreme limitation to beyond saturation. Measurements need to: distinguish structural from non-structural dry matter; organic from inorganic forms of the nutrient in the tissues; involve all parts of the plant to evaluate nutrient and C allocation changes with treatments; determine resorption factors during tissue senescence; and be made with cognisance of the temporal and spatial aspects of the phenomena involved.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004790612630
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  • 64
    Digitale Medien
    Digitale Medien
    The influence of temperature and nitrogen source on growth and nitrogen uptake of two polar-desert species, Saxifraga caespitosa and Cerastium alpinum (2000)
    Springer
    Plant and soil 227 (2000), S. 139-148 
    Details
    ISSN: 1573-5036
    Schlagwort(e): Arctic ; Cerastium alpinum ; nitrogen source ; nitrogen-uptake ; organic N ; polar-desert plants ; Saxifraga caespitosa ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Polar-desert plants experience low average air temperatures during their short growing season (4–8 °C mean July temperature). In addition, low availability of inorganic nitrogen in the soil may also limit plant growth. Our goals were to elucidate which N sources can be acquired by polar-desert plants, and how growth and N-uptake are affected by low growth temperatures. We compared rates of N-uptake and increases in mass and leaf area of two polar-desert species (Cerastium alpinum L. and Saxifraga caespitosa L.) over a period of 3 weeks when grown at two temperatures (6 °C vs. 15 °C) and supplied with either glycine, NH4 + or NO3 −. At 15 °C, plants at least doubled their leaf area, whereas there was no change in leaf area at 6 °C. Measured mean N-uptake rates varied between 0.5 nmol g−1 root DM s−1 on glycine at 15 °C and 7.5 nmol g−1 root DM s−1 on NH4 + at 15 °C. Uptake rates based upon increases in mass and tissue N concentrations showed that plants had a lower N-uptake rate at 6 °C, regardless of N source or species. We conclude that these polar-desert plants can use all three N sources to increase their leaf area and support flowering when grown at 15 °C. Based upon short-term (8 h) uptake experiments, we also conclude that the short-term capacity to take up inorganic or organic N is not reduced by low temperature (6 °C). However, net N-uptake integrated over a three-week period is severely reduced at 6 °C.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1026528830228
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  • 65
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): climate change ; immobilisation ; mineralisation ; N-turnover ; nitrogen ; soil organic matter
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004640327512
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  • 66
    Digitale Medien
    Digitale Medien
    Acclimation response of spring wheat in a free-air CO2 enrichment (FACE) atmosphere with variable soil nitrogen regimes. 2. Net assimilation and stomatal conductance of leaves (2000)
    Springer
    Photosynthesis research 66 (2000), S. 79-95 
    Details
    ISSN: 1573-5079
    Schlagwort(e): acclimation ; climate change ; CO2 ; down-regulation ; global change ; photosynthesis ; stomatal conductance
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Atmospheric CO2 concentration continues to rise. It is important, therefore, to determine what acclimatory changes will occur within the photosynthetic apparatus of wheat (Triticum aestivum L. cv. Yecora Rojo) grown in a future high-CO2 world at ample and limited soil N contents. Wheat was grown in an open field exposed to the CO2 concentration of ambient air [370 μmol (CO2) mol−1; Control] and air enriched to ∼200 μmol (CO2) mol−1 above ambient using a Free-Air CO2 Enrichment (FACE) apparatus (main plot). A High (35 g m−2) or Low (7 and 1.5 g m−2 for 1996 and 1997, respectfully) level of N was applied to each half of the main CO2 treatment plots (split-plot). Under High-N, FACE reduced stomatal conductance (g s) by 30% at mid-morning (2 h prior to solar noon), 36% at midday (solar noon) and 27% at mid-afternoon (2.5 h after solar noon), whereas under Low-N, g s was reduced by as much as 31% at mid-morning, 44% at midday and 28% at mid-afternoon compared with Control. But, no significant CO2 × N interaction effects occurred. Across seasons and growth stages, daily accumulation of carbon (A′) was 27% greater in FACE than Control. High-N increased A′ by 18% compared with Low-N. In contrast to results for g s, however, significant CO2 × N interaction effects occurred because FACE increased A′ by 30% at High-N, but by only 23% at Low-N. FACE enhanced the seasonal accumulation of carbon (A′′) by 29% during 1996 (moderate N-stress), but by only 21% during 1997 (severe N-stress). These results support the premise that in a future high-CO2 world an acclimatory (down-regulation) response in the photosynthetic apparatus of field-grown wheat is anticipated. They also demonstrate, however, that the stimulatory effect of a rise in atmospheric CO2 on carbon gain in wheat can be maintained if nutrients such as nitrogen are in ample supply.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1010646225929
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  • 67
    Digitale Medien
    Digitale Medien
    The effect of temperature on shell size and growth rate in Krithe praetexta praetexta (Sars) (2000)
    Springer
    Hydrobiologia 419 (2000), S. 141-148 
    Details
    ISSN: 1573-5117
    Schlagwort(e): Crustacea ; Ostracoda ; Krithe praetexta praetexta ; life cycle ; ontogeny ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The effect of temperature on growth rate, shell size and shell shape in Krithe praetexta praetexta (Sars) was studied in four thermocultures. From July 1995 to June 1996, the cultures were kept in a continuously flowing open system pumping water from the intermediate watermass of the Gullmarn fjord, west coast of Sweden. Three cultures were kept at constant temperatures of 5, 10 and 14 °C, respectively. The fourth (reference) culture largely followed the natural variation in temperature. At the termination of the experiment, all living ostracods from a 125 μm sieve were sampled from the cultures. Population age structures were analysed for the various thermocultures of K. praetexta praetexta. These were more shifted towards later ontogenetic stages with higher temperature, i.e. the ontogenetic development was more rapid in the warmer cultures. An alternative explanation is due to diapause causing cohorts to accumulate in some ontogenetic stages only when the temperature is constant. The differences in shell size of K. praetexta praetexta among the thermoconstant cultures were not statistically significant.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1003943617431
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  • 68
    Digitale Medien
    Digitale Medien
    Energy exploitation in Chirocephalus croaticus (Steuer, 1899) (Crustacea: Anostraca): survival strategy in an intermittent lake (2000)
    Springer
    Hydrobiologia 437 (2000), S. 157-163 
    Details
    ISSN: 1573-5117
    Schlagwort(e): Chirocephalus ; metabolic potential ; intermittent lake ; ecology ; physiology ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Electron transport system (ETS) activity was measured in Chirocephalus croaticus from the intermittent lake, Petelinjsko Jezero. The ETS activities were measured at 5, 10, 15, 20, and 25 °C, and were studied separately in juveniles, females and males. Juveniles had significantly higher activity than adults at a standard temperature of 20 °C. The mass-specific ETS activity decreased with increasing size of the animals; the value b was 0.787. Respiration rates (R) were determined at 20 °C and the ratio ETS/R (±standard deviation) for C. croaticus was 1.43±0.46 (n=38). ETS activity increased with temperature. Females had higher Q10 than males in higher temperature range (t-test; t=2.50; d.f.=8; p〈0.05). Activation energy Ea was higher for females than males (t-test; t=2.35; d.f.=8; p〈0.05). Females exhibited lower ETS activity than males over the lower temperature range, but their ETS could function more efficient at higher temperature.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1026507024238
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  • 69
    Digitale Medien
    Digitale Medien
    Reproduction of the Endangered Killifish Aphanius iberus at Different Salinities (2000)
    Springer
    Environmental biology of fishes 57 (2000), S. 113-115 
    Details
    ISSN: 1573-5133
    Schlagwort(e): photoperiod ; temperature ; spawning ; larva rearing ; larva food
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Adult fish of a freshwater population of the Iberian endangered cyprinodontid Aphanius iberus, were induced to reproduce at salinities of 5, 15, 30, 45 and 60 ppt. For each salinity five 30 l aquaria were used, each one including a male and two females. Maturity and spawning outside the natural season, were obtained at conditions of 22 to 28°C and a photoperiod of 14L:10D. The larvae were fed with rotifers Brachionus plicatilis and Synchaeta cecilia valentina. Experiment lasted 40 days. The first spawning occurred on the 17th day at 45 ppt of salinity and the first embryos hatched on the 34th day at 5 and 15 ppt salinity. The final average number of larvae per aquarium ranged from 5.2 (45 ppt salinity) to 10.8 (15 ppt salinity). No significant differences were found between the average values at different salinities (p〈0.01).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007579527064
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  • 70
    Digitale Medien
    Digitale Medien
    Seasonal and Diel Changes in Behaviour, Microhabitat use and Preferences by Young Pool-dwelling Atlantic Salmon, Salmo salar, and Brown Trout, Salmo trutta (2000)
    Springer
    Environmental biology of fishes 59 (2000), S. 163-179 
    Details
    ISSN: 1573-5133
    Schlagwort(e): deep pools ; young salmonids ; habitat use ; habitat availability ; temporal variation ; temperature ; winter
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract There was a pronounced decline in activity of young pool-dwelling Atlantic salmon, Salmo salar, and brown trout, Salmo trutta, as the water temperatures dropped in the autumn and early winter, and the fish switched from a predominantly diurnal towards a nocturnal activity pattern. Such a switch in activity pattern has previously been observed in young brown trout, but the present study is the first documentation for juvenile Atlantic salmon under natural conditions. Juvenile fish fed actively even when water temperatures were below 0°C, although foraging behaviour at near-freezing temperatures was recorded exclusively during night surveys. This indicates that other proximate factors, in addition to water temperature, affect the activity of young salmon and trout in rivers. Trout kept feeding positions significantly higher above bottom than salmon in August and September, but both species reduced the height above bottom at the onset of winter, possibly due to reduced swimming performance and lowered food availability in the upper part of the water column.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007691316864
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  • 71
    Digitale Medien
    Digitale Medien
    The influence of climate change scenarios on populations of the mayfly Cloeon dipterum (2000)
    Springer
    Hydrobiologia 441 (2000), S. 55-62 
    Details
    ISSN: 1573-5117
    Schlagwort(e): climate change ; temperature ; mayflies ; Cloeon dipterum
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Populations of the mayfly Cloeon dipterum from 48 ponds (3000 l fibre-glass tanks of 1 m depth) were monitored over the course of 1 year. To simulate possible patterns of climatic change, the ponds were subject to three temperature treatments: continuous heating to 3 °C above ambient; heating to 3 °C above ambient during the summer only; and no heating. Further experimental complexity included enhanced nutrient input into the ponds and the presence or absence of fish, giving a factorial combination of 3 temperature regimes × 2 nutrient levels × presence/absence of fish predation. Few nymphs were found in the presence of fish. Where fish were absent, the temperature treatments did not significantly affect nymph abundances, and only marginally influenced mean nymph body-lengths. In contrast, the nutrient treatment had significant effects on both nymph abundance and size, with greater numbers of generally larger nymphs occurring in those fish-free ponds receiving additional nutrients. Adult emergence began earlier in the year from the heated ponds, particularly those ponds receiving additional nutrients. Adult body-length differed between temperature treatments, but consistent patterns were difficult to ascertain because of interactions with nutrient treatment and seasonal effects. Our results show that during the short term at least, elevated temperature as a simulation of climate change does not have an overwhelming influence on either mayfly abundance or size. The influence of temperature is subtle and subject to complex interaction with other habitat variables. We therefore suggest that the direct consequences of small changes in temperature will likely be of little significance to C. dipterum, relative to indirect effects operating through interactions with predation and nutrient input.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1017595223819
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  • 72
    Digitale Medien
    Digitale Medien
    The physiological response of Northern krill (Meganyctiphanes norvegica) to temperature gradients in the Kattegat (2000)
    Springer
    Hydrobiologia 426 (2000), S. 157-160 
    Details
    ISSN: 1573-5117
    Schlagwort(e): Meganyctiphanes norvegica ; respiration ; temperature ; vertical migration ; Kattegat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The Alkor-Deep (140 m), which forms part of a depression system in the northern Kattegat channel east of the island of Læsø (Denmark), is the location of a self sustaining population of Northern krill, Meganyctiphanes norvegica (Euphausiacea). This population is exposed to one of the most pronounced thermal gradients within the distributional range of this pelagic crustacean. During summer, the temperature of the water column ranges between 4 and 6 in the deep to 16 °C near the surface which results in the krill being exposed to temperature differences of 8–10 °C during diel vertical migration. Oxygen consumption rates were used to investigate the physiological adaptation of the animal to such gradients in temperature. The rates were found to increase exponentially from 31 μmol O2 h-1 gdw -1 at 4 °C to 72 μmol O2 h-1 gdw -1 at 16 °C, giving a Q 10-value of 2.0, and indicating that physiological adaptation to varying thermal conditions does not take place. Behavioural adaptations are discussed which may help the krill to cope with large temperature gradients in their environment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1003974613473
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  • 73
    Digitale Medien
    Digitale Medien
    Further expansion of the genus Cercopagis (Crustacea, Branchiopoda, Onychopoda) in the Baltic Sea, with notes on the taxa present and their ecology (2000)
    Springer
    Hydrobiologia 429 (2000), S. 207-218 
    Details
    ISSN: 1573-5117
    Schlagwort(e): Cercopagis ; invasion ; Baltic Sea ; depth ; temperature ; salinity ; morphological variations
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The onychopod cladoceran Cercopagis that recently invaded the Baltic Sea is reported from new zones of the northern Baltic proper. Because of successful survival and an expanding distribution range, the addition of Cercopagis to the Baltic fauna is considered to be permanent. What has previously been cited as Cercopagis pengoi encompasses the morphology of several other species, subspecies and forms. Either a number of morphologically similar species is present, or there is a number of spurious species in Cercopagis. The last hypothesis is favoured. The spatial distribution pattern of Cercopagis, as well as that of total zooplankton, was correlated with depth. Deep (〉100 m) and shallow (〈10 m) stations had significantly lower abundance than stations of intermediate depth (〈100 m). An overview of the distribution of C. pengoi group in fresh and brackish waters suggests a high tolerance to environmental factors, but with differences among taxa. Due to this ecological flexibility, the colonization of the Baltic is not unexpected. Increasing salinity may restrict dispersal of cercopagids to the southern areas of the Baltic and to the North Sea, but inland lakes (e.g. in Sweden) present an ecological profile suitable for colonization.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004004504571
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  • 74
    Digitale Medien
    Digitale Medien
    Can zebra mussels change stratification patterns in a small reservoir? (2000)
    Springer
    Hydrobiologia 431 (2000), S. 175-184 
    Details
    ISSN: 1573-5117
    Schlagwort(e): Dreissena ; lake stratification ; water clarity ; temperature ; oxygen ; metalimnion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Colonization and proliferation of zebra mussel (Dreissena polymorpha) population in Hargus lake, a small thermally stratified reservoir in Ohio, U.S.A., caused a significant increase in water clarity and a remarkable decrease in phytoplankton biomass during the period from 1993 to 1995. Increased light penetration and reduced organic matter loading to the meta-and hypolimnion were reflected in the lake stratification patterns, particularly in the temperature and oxygen profiles in the metalimnion. The meta- and hypolimnetic water temperature increased significantly over three years, irrespective of variation in surface water temperature. The epilimnion depth (mixing depth) increased by about the same magnitude as did the average Secchi depth. However, the total heat content of the lake did not show a consistent trend to increasing zebra mussel abundance, as it was largely influenced by the temperature of the large water volumes near the surface, which were in turn affected by weather conditions. Concurrent with the thermal structure change, the dissolved oxygen structure also changed over three years, though to a lesser extent. The changes in oxygen stratification pattern were reflected by increased oxygen concentrations in the metalimnion and a lowered depth of 3 mg l−1 DO isopleth. These observed changes were likely attributed to increased water mixing depth, metalimnion photosynthesis and reduced oxygen consumption by organic matter. With increased epilimnion thickness and improved oxygen conditions in the metalimnion, the habitable space for aquatic macro-organisms (including fish) expanded substantially. Our results suggest that the indirect impacts of zebra mussels on small lake stratification patterns may have much broader implications than do the direct trophic interactions to the whole ecosystem.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004092229180
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  • 75
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): nutrient flux ; nitrogen ; phosphate ; tidal flats ; temperature ; geographical comparison
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1026542621512
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  • 76
    Digitale Medien
    Digitale Medien
    Will changes in soil organic carbon act as a positive or negative feedback on global warming? (2000)
    Springer
    Biogeochemistry 48 (2000), S. 21-51 
    Details
    ISSN: 1573-515X
    Schlagwort(e): carbon cycle ; decomposition ; global change ; soil organic matter ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie
    Notizen: Abstract The world's soils contain about 1500 Gt of organic carbon to a depth of 1m and a further 900 Gt from 1--2m. A change of total soil organic carbon by just 10% would thus be equivalent to all the anthropogenic CO2 emitted over 30 years. Warming is likely to increase both the rate of decomposition and net primary production (NPP), with a fraction of NPP forming new organic carbon. Evidence from various sources can be used to assess whether NPP or the rate of decomposition has the greater temperature sensitivity, and, hence, whether warming is likely to lead to an increase or decrease in soil organic carbon. Evidence is reviewed from laboratory-based incubations, field measurements of organic carbon storage, carbon isotope ratios and soil respiration with either naturally varying temperatures or after experimentally increasing soil temperatures. Estimates of terrestrial carbon stored at the Last Glacial Maximum are also reviewed. The review concludes that the temperature dependence of organic matter decomposition can be best described as: d(T) = exp[3.36 (T − 40)/(T + 31.79)] where d(T) is the normalised decomposition rate at temperature T (in °C). In this equation, decomposition rate is normalised to ‘1’ at 40 °C. The review concludes by simulating the likely changes in soil organic carbon with warming. In summary, it appears likely that warming will have the effect of reducing soil organic carbon by stimulating decomposition rates more than NPP. However, increasing CO2 is likely to simultaneously have the effect of increasing soil organic carbon through increases in NPP. Any changes are also likely to be very slow. The net effect of changes in soil organic carbon on atmospheric CO2 loading over the next decades to centuries is, therefore, likely to be small.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006238902976
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  • 77
    Digitale Medien
    Digitale Medien
    Quantitative analysis of cell division in leaves: methods, developmental patterns and effects of environmental conditions (2000)
    Springer
    Plant molecular biology 43 (2000), S. 555-567 
    Details
    ISSN: 1573-5028
    Schlagwort(e): cell cycle ; kinematic analysis ; leaf development ; light ; temperature ; water deficit
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract In planta quantitative studies of cell cycle are necessary for examining the role of cell division in the response of plants to environmental conditions and to analyse the behaviour of transformed plants in this context. We present and discuss non-intrusive kinematic methods which allow estimating the duration of cell cycle with a high spatial resolution in the leaf. Different methods are proposed and discussed for monocotyledons and dicotyledons, and compared with methods involving the use of chemicals. In monocotyledon leaves, cell division is restricted to a limited zone near the leaf insertion point, twice as long in the mesophyll as in the epidermis. In dicotyledons, cell division occurs in the whole leaf with a uniform and constant cell cycle duration for a determinate number of cell cycles, representing about half of leaf development. Over several experiments, this number is well conserved in a given leaf zone in the absence of stresses, but larger near the leaf base than near the leaf tip. After that, cell cycle duration increases because cells are progressively blocked in G1 while the durations of S-G2-M phases do not change with time. Leaf temperature affects neither the distribution of nuclei in each phase of the cycle nor the number of cell cycles in a leaf. Water or light deficits both cause a partial blockage of nuclei in G1 during the stress only, thereby increasing cell cycle duration and decreasing final cell number. These results suggest that a strong developmental programme drives cell division in leaves, so a simple framework allows analysis of temporal patterns, of spatial gradients and of the effect of environmental conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006438321386
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  • 78
    Digitale Medien
    Digitale Medien
    Changes in Na+,K+-ATPase activity and gill chloride cell morphology in the grouper Epinephelus coioides larvae and juveniles in response to salinity and temperature (2000)
    Springer
    Fish physiology and biochemistry 23 (2000), S. 83-94 
    Details
    ISSN: 1573-5168
    Schlagwort(e): chloride cells ; Epinephelus coioides ; grouper ; Na+,K+-ATPase activity ; salinity ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The activity of the enzyme Na+,K+-ATPase and morphological changes of gill chloride cells in grouper, Epinephelus coioides larvae and juveniles were determined 6–48 h after abrupt transfer from ambient rearing conditions (30–32 ppt, 26.5–30 °C) to different salinity (8, 18, 32, 40 ppt) and temperature (25, 30 °C) combinations. Na+,K+-ATPase activity in day 20 larvae did not change at salinities 8–32 ppt. Activity decreased significantly (P 〈0.01) after exposure to 40 ppt at 25–30 °C, which was accompanied by an increase (P 〈0.05) in density and fractional area of chloride cells. Enzyme activity in 40 ppt did not reach a stable level and larvae failed to recover from an osmotic imbalance that produced a low survival at 25 °C and death of all larvae at 30 °C. Enzyme activity and chloride cell morphology in day 40 groupers did not change in 8–40 ppt at 25 °C and 8–32 ppt at 30 °C. A significant decrease and a subsequent increase in Na+,K+-ATPase activity in 40 ppt at 30 °C was associated with the increase in chloride cell density resulting in an increased fractional area but a decreased cell size. Enzyme activity and chloride cells of day 60 grouper were unaffected by abrupt transfer to test salinities and temperatures. These results demonstrate that grouper larvae and juveniles are efficient osmoregulators over a wide range of salinities. Salinity adaptation showed an ontogenetic shift as the larvae grew and reached the juvenile stage. This development of tolerance limits may reflect their response to actual conditions existing in the natural environment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007827331137
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  • 79
    Digitale Medien
    Digitale Medien
    Environmental influences on melatonin secretion in Atlantic cod (Gadus morhua L.) and their relevance to commercial culture (2000)
    Springer
    Fish physiology and biochemistry 23 (2000), S. 191-200 
    Details
    ISSN: 1573-5168
    Schlagwort(e): Atlantic cod ; temperature ; melatonin ; photoperiod
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract This study investigated the effects of photoperiod and temperature on plasma melatonin secretion in Atlantic cod (Gadus morhua L.). Initial work confirmed the presence of a diel profile of melatonin synthesis, with elevated levels during the dark phase. Unusually for fish, the peak in plasma melatonin occurred towards the end of the dark phase, which is indicative of a type `A' melatonin profile. When exposed to 60 hours of continuous darkness a clear endogenous rhythm of melatonin synthesis was observed, which continued for 4 cycles with a periodicity which, approximated to 24 h. When acclimated to varying temperatures (4, 8, 12 or 16 °C) no variation in melatonin production was seen, however, body size appeared to be an important influence, with the smallest fish exhibiting significantly higher levels of dark phase melatonin. Finally, the application of additional night-time illumination to cod maintained in sea cages i.e. without blackout, did not significantly reduce dark phase plasma melatonin, suggesting that cod are less sensitive to photoperiod manipulation in cages than salmonids.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007816426509
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  • 80
    Digitale Medien
    Digitale Medien
    A drop in ambient temperature results in a transient reduction of interrenal ACTH responsiveness in the gilthead sea bream (Sparus aurata, L.) (2000)
    Springer
    Fish physiology and biochemistry 23 (2000), S. 265-273 
    Details
    ISSN: 1573-5168
    Schlagwort(e): cortisol ; ACTH ; α-MSH ; GH ; head kidney ; pituitary ; temperature ; stress ; Sparus aurata
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract This study investigated the effects of a drop in water temperature (18 °C to 9 °C in 24 h) on the pituitary and interrenal hormones of the gilthead sea bream Sparus aurata. The in vitro sensitivity of the interrenal tissue to ACTH, plasma levels of cortisol, ACTH, α-MSH, GH, glucose, lactate and ions were determined. In vitro ACTH, stimulated the release of cortisol from isolated interrenal glands from control gilthead sea bream in a concentration dependent fashion. However, the interrenal cells were less sensitive to ACTH as soon as 24 h following the onset of the temperature drop. At this time, plasma cortisol and ACTH levels were raised, and plasma GH concentrations were decreased, whereas no significant changes were found in plasma α-MSH. After 96 h plasma ACTH levels had recovered whereas plasma cortisol levels were still higher than controls after 8 days of the beginning of the experiment. Interrenal sensitivity had recovered after 8 days. The results may help to clarify the relationship between the stress response and the aetiology of the winter syndrome in sea bream.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007873811975
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  • 81
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): neural networks ; modeling ; population density ; orientation tuning ; visual cortex
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Medizin , Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008912914816
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  • 82
    Digitale Medien
    Digitale Medien
    Geographical Clines for Quantitative Traits in Natural Populations of a Tropical Drosophilid: Zaprionus Indianus (2000)
    Springer
    Genetica 108 (2000), S. 91-100 
    Details
    ISSN: 1573-6857
    Schlagwort(e): altitude ; clines ; latitude ; phenotypic variability ; temperature ; Zaprionus indianus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract We analyzed natural populations of Zaprionus indianusin 10 Indian localities along a south-north transect (latitude: 10–31°3 N). Size traits (body weight, wing length and thorax length) as well as a reproductive trait (ovariole number) followed a pattern of clinal variation, that is, trait value increased with latitude. Wing/thorax ratio, which is inversely related to wing loading, also had a positive, but non-significant correlation with latitude. By contrast, bristle numbers (sternopleural and abdominal) exhibited a non-significant but negative correlation with latitude. Sex dimorphism, estimated as the female/male ratio, was very low in Z. indianus, contrasting with results already published in other species. Genetic variations among populations were also analyzed according to other geographic parameters (altitude and longitude) and to climatic conditions from each locality. A significant effect of altitude was found for size traits. For abdominal bristles, a multiple regression technique evidenced a significant effect of both latitude and altitude, but in opposite directions. Genetic variations were also correlated to climate, and mainly with average year temperature. Taking seasonal variations into account failed however to improve the predictability of morphometrical variations. The geographic differentiation of Z.indianusfor quantitative traits suggests adaptive response to local conditions, especially to temperature, but also reveals a complex situation according to traits investigated and to environmental parameters, which does not match results on other drosophilid species.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004090517967
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  • 83
    Digitale Medien
    Digitale Medien
    Climate Change and the Representative Agent (2000)
    Springer
    Environmental and resource economics 15 (2000), S. 135-148 
    Details
    ISSN: 1573-1502
    Schlagwort(e): climate change ; overlapping generations models
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik , Wirtschaftswissenschaften
    Notizen: Abstract The artifice of an infinitely-lived representative agent iscommonly invoked to balance the present costs and future benefitsof climate stabilization policies. Since actual economies arepopulated by overlapping generations of finite-lived persons,this approach begs important questions of welfare aggregation.This paper compares the results of representative agent andoverlapping generations models that are numerically calibratedbased on standard assumptions regarding climate--economyinteractions. Under two social choice rules -- Pareto efficiencyand classical utilitarianism -- the models generate closelysimilar simulation results. In the absence of policies toredistribute income between present and future generations,efficient rates of carbon dioxide emissions abatement rise from15 to 20% between the years 2000 and 2105. Under classicalutilitarianism, in contrast, optimal control rates rise from 48 to 79% this same period.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008361812597
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  • 84
    Digitale Medien
    Digitale Medien
    Participatory integrated assessment of adaptation to climate change in Alpine tourism and mountain agriculture (2000)
    Springer
    Integrated assessment 1 (2000), S. 331-338 
    Details
    ISSN: 1573-1545
    Schlagwort(e): climate change ; mountain agriculture ; tourism ; participatory integrated assessment ; focus groups
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract Winter tourism and mountain agriculture are the most important economic sectors in a major part of the Swiss Alps. Both are highly sensitive to changing climatic conditions. In the framework of the CLEAR project, results from climate impact research in the field of tourism and agricultural production were used to investigate the perception of climatic change by stakeholders and to assess possible adaptations. We used a participatory integrated assessment (PIA) to involve the knowledge, values and experiences of the various social actors in tourism and agriculture (e.g., skiers, tourism managers, farmers) in the research process. Whereas climate change may have various severe direct impacts on the tourism industry, depending on the region, agricultural production may generally benefit from changed climatic conditions. But because of the dependence of farmers on “off-farm” income, the loss due to declining winter tourism in specific areas may cause more important indirect effects. However, the two sectors may adapt actively by choosing from a variety of strategies, and the loss of income from the tourism industry may support the re-evaluation of the various functions agriculture plays in mountain regions, beyond the production of food. The study demonstrates the suitability of the PIA approach to elucidate the interactions between different stakeholders and their perception of the climate change phenomena. A similar participatory approach could be a useful tool to transfer research results and expert knowledge to the political process addressing adaptations to climate change.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1018940901744
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  • 85
    Digitale Medien
    Digitale Medien
    Studies on anaerobic proteolytic bacteria of Leh, India (2000)
    Springer
    World journal of microbiology and biotechnology 16 (2000), S. 297-301 
    Details
    ISSN: 1573-0972
    Schlagwort(e): Anaerobic bacteria ; growth ; protease ; psychrotrophs ; temperature ; volatile fatty acids
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract Five anaerobic proteolytic bacteria were isolated from water bodies of Leh, India, where the ambient temperature varies from −25 to 25 °C. Isolates showed growth at all temperatures ranging from 5 to 37 °C except SPL-4 and SPL-5 which showed no growth at 5 °C. The cultures could grow and produce proteases on various protein substrates and the yield varied with the substrates. Two of the cultures showed the presence of spores. Acetate was the dominant VFA during hydrolysis of protein substrates.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008935425175
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  • 86
    Digitale Medien
    Digitale Medien
    Rubber stoppers used with sulphidic media: a note of caution (2000)
    Springer
    World journal of microbiology and biotechnology 16 (2000), S. 571-572 
    Details
    ISSN: 1573-0972
    Schlagwort(e): Anaerobes ; hydrogen sulphide ; rubber stoppers ; sulphate reduction ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract Common black rubber stoppers, made from natural rubber and styrene–butadiene, may cause a loss of hydrogen sulphide from aqueous media and impede the growth of sulphate-reducing bacteria under thermophilic conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008909530445
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  • 87
    Digitale Medien
    Digitale Medien
    Effects of temperature, water activity and gas atmosphere on mycelial growth of tempe fungi Rhizopus microsporus var. microsporus and R. microsporus var. oligosporus (2000)
    Springer
    World journal of microbiology and biotechnology 16 (2000), S. 853-858 
    Details
    ISSN: 1573-0972
    Schlagwort(e): Carbondioxide ; fungi ; oxygen ; Rhizopus ; solid-substrate fermentation SSF ; tempe modelling ; temperature ; water activity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract Rhizopus microsporus var. microsporus and var. oligosporus are used in the manufacture of various Asian fermented foods (tempe, black oncom, sufu). In view of solid-substrate fermentation (SSF) control, mycelial growth of strains of both varieties was tested for sensitivity to fluctuations of temperature, water activity and interstitial gas composition. This was achieved by measuring radial growth as well as biomass dry weight of pre-germinated microcolonies on defined media. The optimum conditions were temperature 40 °C, a w 0.995 and a gas composition of air for the growth of both strains on a model medium. Whereas radial growth rates of var. microsporus and var. oligosporus were similar, biomass growth rates of var. oligosporus were higher than those of var. microsporus under optimum conditions. The temperature-dependent growth of Rhizopus spp. at a w 〉 0.98 could be described by the Ratkowsky Equation. Carbon dioxide (5–10% v/v) inhibited the growth of Rhizopus spp. at non-limiting levels of oxygen. The two strains were able to grow at low (0.5% v/v) oxygen levels, but the mycelial density was rather low. No interrelation of water activity and gas composition was observed, but at high water activity the fungi were more sensitive to changes of temperature. The implications for process control are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008974621698
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  • 88
    Digitale Medien
    Digitale Medien
    Future Inequality in CO2 Emissions and the Impact of Abatement Proposals (2000)
    Springer
    Environmental and resource economics 17 (2000), S. 163-181 
    Details
    ISSN: 1573-1502
    Schlagwort(e): carbon emissions inequality ; climate change ; global warming
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik , Wirtschaftswissenschaften
    Notizen: Abstract This paper analyzes future carbon emissions inequality using a group decomposition of the Gini index. Business-as-usual projections to the year 2100 for 135 countries show inequality in per capita emissions declines slowly. Next, the impact on emissions levels and inequality of the Kyoto Protocol and other abatement proposals for Annex II countries in 2010 are measured, with a focus on the gap-narrowing and reranking effects. Substantial reranking of per capita emissions between Annex II and non-Annex II countries will not occur unless the former reduce their emissions by at least 50% (versus 1990 levels) and the latter continue growing unabated.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008326515058
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  • 89
    Digitale Medien
    Digitale Medien
    Intergenerational equity and discounting (2000)
    Springer
    Integrated assessment 1 (2000), S. 127-136 
    Details
    ISSN: 1573-1545
    Schlagwort(e): integrated assessments ; climate change ; discounting ; equity ; climate policy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract A standard framework is presented as an underlying model for the discounting debate. Views and proposals for the techniques and rates of discounting are assessed. Alternative modeling frameworks for studying intergenerational equity issues are evaluated with the result that the basic insights they provide do not differ very much. Results from model experiments involving different discount rate proposals show that fudging the discount rate does not lead to efficient climate policy. Three major clusters of opinions are identified regarding the applicability of cost-benefit analysis to the climate change problem and the appropriate discount rate to use. It is concluded that under some very special circumstances the cost-benefit rule should be abandoned and cost-effective strategies implying standard discount rates should be sought to reach clearly defined and justified environmental targets.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019123630345
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  • 90
    Digitale Medien
    Digitale Medien
    A New Approach for SOI Devices Small-Signal Parameters Extraction (2000)
    Springer
    Analog integrated circuits and signal processing 25 (2000), S. 157-169 
    Details
    ISSN: 1573-1979
    Schlagwort(e): microwave measurements ; SOI technology ; small-signal parameters ; modeling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract SOI devices are frequently used nowadays in the RF and HF field. Design of complex SOI integrated circuits involves a prior detailed analog simulation, that can only be performed through accurate SOI active components models. We are interested here in linear operation modeling; we test new methods for small-signal parameters determination, suitable for a conventional MOSFET high-frequency model and somewhat inspired from methods applied to MESFET technology. In this paper, we deal mainly with extrinsic parameters, for which we obtain reliable estimation on a large frequency range. Our finally adopted extraction procedure takes closely into account the model topology, which reflects the device electrical behavior. We completely describe the procedure, from measurements to the extracted equivalent circuit simulation, without having to optimize parameters and with a straightforward extrinsic elements extraction.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008332732738
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  • 91
    Digitale Medien
    Digitale Medien
    A Length-Scale Equation (2000)
    Springer
    Flow, turbulence and combustion 63 (2000), S. 1-21 
    Details
    ISSN: 1573-1987
    Schlagwort(e): turbulence ; RANS ; modeling ; length-scale
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009957503000
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  • 92
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): Kyoto Protocol ; GHG ; mitigation strategies ; economiccosts ; modeling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik , Geographie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009697416321
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  • 93
    Digitale Medien
    Digitale Medien
    Desertification, and climate change: the case for greater convergence (2000)
    Springer
    Mitigation and adaptation strategies for global change 5 (2000), S. 361-377 
    Details
    ISSN: 1573-1596
    Schlagwort(e): carbon budget ; climate change ; desertification ; international environmental institutions ; land degradation ; research convergence ; science policy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik , Geographie
    Notizen: Abstract Poor knowledge of links between desertification and globalclimate change is limiting funding from the Global Environment Facility foranti-desertification projects and realization of synergies between theConvention to Combat Desertification (CCD) and the FrameworkConvention on Climate Change (FCCC). Greater convergence betweenresearch in the two fields could overcome these limitations, improve ourknowledge of desertification, and benefit four areas of global climate changestudies: mitigation assessment; accounting for land cover change in thecarbon budget; land surface-atmosphere interactions; and climate changeimpact forecasting. Convergence would be assisted if desertification weretreated more as a special case in dry areas of the global process of landdegradation, and stimulated by: (a) closer cooperation between the FCCCand CCD; (b) better informal networking between desertification and globalclimate change scientists, e.g. within the framework of theIntergovernmental Panel on Climate Change (IPCC). Both strategies wouldbe facilitated if the FCCC and CCD requested the IPCC to provide ascientific framework for realizing the synergies between them.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1026537621437
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  • 94
    Digitale Medien
    Digitale Medien
    Migration caused by climate change: how vulnerable are people inn dryland areas? (2000)
    Springer
    Mitigation and adaptation strategies for global change 5 (2000), S. 379-406 
    Details
    ISSN: 1573-1596
    Schlagwort(e): climate change ; Ethiopia ; historical analogy ; migration ; vulnerability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik , Geographie
    Notizen: Abstract Climate change has been presented as a likely trigger formigration of people, especially in dryland areas of less developed countries.The underlying research questions focus on the strength of adaptationcapacity of subsistence farmers in Northern Ethiopia, and evaluate historicalexperiences gained from drought-induced migration. Through a survey of104 peasants who had to migrant due to persistent drought, vulnerabilityto climate change has shown to be a complex issue, including themultiplicity of factors comprising a household environment. Still, to bevulnerable does not make someone a potential climate migrant, as peoplein marginal regions have developed a great variety of adaptationmechanisms, which strengthen their ability to cope with both, slow climaticchanges and extreme climatic events.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1026570529614
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  • 95
    Digitale Medien
    Digitale Medien
    Changes in patterns of fertilizer nitrogen use in Asia and its consequences for N2O emissions from agricultural systems (2000)
    Springer
    Nutrient cycling in agroecosystems 57 (2000), S. 107-117 
    Details
    ISSN: 1573-0867
    Schlagwort(e): N-fertilizer ; nitrous oxide ; climate change
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract In most soils, formation and emissions of N2O to the atmosphere are enhanced by an increase in available mineral nitrogen (N) through increased rates of nitrification and denitrification. Therefore, addition of N, whether in the form of organic or inorganic compounds eventually leads to enhanced N2O emissions. Global N2O emissions from agricultural systems have previously been related primarily to fertilizer N input from synthetic sources. Little attention has been paid to N input from other N sources or to the N2O produced from N that has moved through agricultural systems. In a new methodology used to estimate N2O emissions on the country or regional scale, that is briefly described in this paper, the anthropogenic N input data used include synthetic fertilizer, animal waste (feces and urine) used as fertilizer, N derived from enhanced biological N-fixation through N2 fixing crops and crop residue returned to the field. Using FAO database information which includes data on synthetic fertilizer consumption, live animal production and crop production and estimates of N input from recycling of animal and crop N, estimates of total N into Asian agricultural systems and resulting N2O emissions are described over the time period 1961 through 1994. During this time the quantity and relative amounts of different types of materials applied to agricultural soils in Asia as nitrogen (N) fertilizer have changed dramatically. In 1961, using the earliest entry from the FAO database, of the approximately 15.7 Tg of fertilizer N applied to agricultural fields 2.1 Tg N (13.5% of total N applied) was from synthetic sources, approximately 6.9 Tg N from animal wastes, 1.7 Tg N from biological N-fixation, and another 5 Tg N from reutilization of crop residue. In 1994, 40.2 Tg from synthetic fertilizer N (57.8% of total), 14.2 Tg from animal wastes, 2.5 Tg from biological N-fixation and 12.6 Tg from crop residue totalling 69.5 Tg N were utilized within agricultural soils in all Asian countries. The increases in N utilization have increased the emission of nitrous oxide from agricultural systems. Estimated N2O from agricultural systems in Asia increased from about 0.8 Tg N2O-N in 1961 to about 2.1 in 1994. The period of time when increases in N input and resulting N2O emissions were greatest was during 1970–1990. This evaluation of N input into Asian agricultural systems and the resulting N2O emissions demonstrates the large change in global agriculture that has occurred in recent decades. Because of the increased need for food production increases in N input are likely. Although the rate of increase of N input and N2O emissions during the 1990s appears to have declined, we ask if this slowed rate of increase is a general long term trend or if global food production pressures will tend to accelerate N input demand and resulting N2O emissions as we move into the 21st century.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009716505244
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  • 96
    Digitale Medien
    Digitale Medien
    Modeling Trace Gas Emissions from Agricultural Ecosystems (2000)
    Springer
    Nutrient cycling in agroecosystems 58 (2000), S. 259-276 
    Details
    ISSN: 1573-0867
    Schlagwort(e): agroecosystem ; trace gas ; modeling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009859006242
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  • 97
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): drainage design ; modeling ; steady-state criteria ; subsurface drainage
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006416921124
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  • 98
    Digitale Medien
    Digitale Medien
    Rotational Properties of Cometary Nuclei (2000)
    Springer
    Earth, moon and planets 89 (2000), S. 135-160 
    Details
    ISSN: 1573-0794
    Schlagwort(e): C/1995 O1 (Hale-Bopp) ; 19P/Borrelly ; 46P/Wirtanen ; comets ; modeling ; nucleus ; observations ; rotation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1021598404115
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  • 99
    Digitale Medien
    Digitale Medien
    Modelling the Effects of Climate Change on Water Resources in Central Sweden (2000)
    Springer
    Water resources management 14 (2000), S. 177-189 
    Details
    ISSN: 1573-1650
    Schlagwort(e): climate change ; Sweden ; water balance models ; water resources
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie
    Notizen: Abstract This article describes investigationsinto the effects of climate change on flow regimes oftwenty-five catchments (from 6 to 1293 km2) incentral Sweden. Hydrological responses of fifteenhypothetical climate change scenarios (e.g.combinations of ΔT = +1, +2 and +4 °C andΔP = 0, ± 10%, ± 20%) were simulated by a conceptual monthly water balance model. The results suggest thatall the hypothetical climate change scenarios wouldcause major decreases in winter snow accumulation.Significant increase of winter flow and decrease ofspring and summer runoff were resulted from mostscenarios. Attendant changes in actualevapotranspiration were also examined for all climatechange scenarios. Despite the changes in seasonaldistribution of evapotranspiration, the change inannual total evapotranspiration was relatively smallwith the maximum change of 23% compared with the 76%for mean annual snow water equivalent changes and 52%for mean annual runoff changes. Such hydrologicresults would have significant implications on futurewater resources design and management.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1026502114663
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  • 100
    Digitale Medien
    Digitale Medien
    Virtual Solar System Project: Learning Through a Technology-Rich, Inquiry-Based, Participatory Learning Environment (2000)
    Springer
    Journal of science education and technology 9 (2000), S. 7-25 
    Details
    ISSN: 1573-1839
    Schlagwort(e): virtual reality ; modeling ; constructionism ; astronomy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Allgemeine Naturwissenschaft , Technik allgemein
    Notizen: Abstract In this manuscript we describe an introductory astronomy course for undergraduate students in which we moved from the large-lecture format to one in which students were immersed in a technologically-rich, inquiry-based, participatory learning environment. Specifically, undergraduate students used 3-D modeling tools to construct virtual reality models of the solar system, and in the process, build rich understandings of various astronomical phenomena. For this study, primarily naturalistic inquiry was used to gain a holistic view of this semester-long course. These data are presented as two case studies focusing on: (1) the role of the teacher in this participatory learning environment; (2) the particular dynamics that formed in each group; (3) the modeling process; (4) the resources used, specifically student-developed inscriptions; and (5) the role of technology and whether learning the technology interfered with learning astronomy. Results indicated that VR can be used effectively in regular undergraduate university courses as a tool through which students can develop rich understandings of various astronomical phenomena.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009416822783
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