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  • Articles  (165)
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  • Springer  (165)
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  • Articles  (165)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Biogeochemistry 49 (2000), S. 37-51 
    ISSN: 1573-515X
    Keywords: Arbuscular mycorrhizae/Vesicular-arbuscular mycorrhizae (AM/VAM) ; annual grasslands ; benomyl ; nitrogen limitation ; phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Nutrient availability limits plant production acrossa wide range of terrestrial ecosystems. In this studyof a Californian annual grassland community, theinfluence of arbuscular mycorrhizal (AM) associationson plant nutrient acquisition was investigated usingfactorial combinations of nitrogen (N), phosphorus (P)and benomyl fungicide. N additions resulted in asignificant increase in shoot biomass demonstratingthat plant productivity in these soils was N-limited. The effect of P additions consistently depended onfungicide treatment. In the absence of benomyl, shootP accumulation was unaltered by P addition. In thepresence of benomyl, P addition significantlyincreased shoot P accumulation and was associated witha consistent trend towards enhanced shoot biomass.The induction of P-deficiency with benomylapplication suggests that effective P acquisition byAM may contribute to the strong N-limitation ofproduction observed in many terrestrial ecosystems.
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  • 2
    ISSN: 1573-515X
    Keywords: Bouteloua eriopoda ; Chihuahuan Desert ; desertification ; hydrology ; Larrea tridentata ; nitrogen ; nutrient budgets ; phosphorus ; runoff
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Losses of dissolved nutrients (N, P, K, Ca, Mg, Na,Cl, and SO4) in runoff were measured on grasslandand shrubland plots in the Chihuahuan desert ofsouthern New Mexico. Runoff began at a lowerthreshold of rainfall in shrublands than ingrasslands, and the runoff coefficient averaged 18.6%in shrubland plots over a 7-year period. In contrast,grassland plots lost 5.0 to 6.3% of incidentprecipitation in runoff during a 5.5-year period. Nutrient losses from shrubland plots were greater thanfrom grassland plots, with nitrogen losses averaging0.33 kg ha−1 yr−1 vs0.15 kg ha−1 yr−1, respectively, during a 3-year period. Thegreater nutrient losses in shrublands were due tohigher runoff, rather than higher nutrientconcentrations in runoff. In spite of these nutrientlosses in runoff, all plots showed net accumulationsof most elements due to inputs from atmosphericdeposition. Therefore, loss of soil nutrients byhillslope runoff cannot, by itself, account for thedepletion of soil fertility associated withdesertification in the Chihuahuan desert.
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  • 3
    ISSN: 1573-515X
    Keywords: gaseous ; kinetics ; mercury ; methods ; speciation ; waters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Mercury evasion from water is commonly modeled using measurements of dissolved gaseous mercury (DGM). We developed a method using a recently available automated field-ready mercury vapor analyzer to rapidly measure the concentrations of DGM in surface waters. We summarize here results of laboratory tests of the method, field intercomparisons with a manual method, and selected data from recent sampling campaigns in Florida and Michigan. The method uses the 1.5 lpm flow of a Tekran® Model 2537A mercury analyzer to purge and analyze discrete water samples, generating near real time (5-min) data on DGM in samples and blanks. Application of the Tekran allowed for detailed analysis of DGM removal kinetics and short-term diel studies characterizing the influence of sunlight and precipitation on DGM production in surface waters. Gas removal kinetics for dozens of samples indicates a first-order rate constant, and supports a 20-min. purge time for surface water samples from Florida (40-min for Michigan samples). Blanks are measured during a second such purge. Our results indicate that DGMs determined by both automated and manual methods are generally comparable, and that DGM in Florida samples is unstable during storage (loss rate constant ∼0.1--0.2 h-1), probably due to oxidation. This suggests that rapid in-field analysis is preferred to storage with delayed analysis. Our data indicate that DGM at the Florida site is influenced by inputs of reactive Hg in rainwater, and by production of surface DGM during photoreduction of oxidized Hg in the water column.
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  • 4
    ISSN: 1573-2614
    Keywords: Neuromuscular relaxants ; rocuronium ; kinetics ; distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Medicine
    Notes: Abstract Objective.To determine the relationship between the rate ofrocuronium injection and the onset time of neuromuscular block. Methods.After intravenous induction, 60 female patients (ASA I–II) wereassigned randomly into 3 groups for rocuronium administration within1–15, 15–30 or 30–60 seconds. Acceleromyography of the thumbwas performed using train-of-four (TOF) stimulation. Times to 50% and 90%twitch depression of the first twitch of the TOF stimulation (T1) wererecorded. Results.Injection time significantly influences time to 50%relaxation, but not time to 90% relaxation. Body mass index is negativelycorrelated with time to 50% and 90% relaxation. Conclusions.Weconclude that rate of injection influences only the initial phase ofdevelopment of the block and that slower injection times do not significantlyaffect time to 90% relaxation at the adductor pollicis muscle.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of clinical monitoring and computing 16 (2000), S. 351-360 
    ISSN: 1573-2614
    Keywords: carbon dioxide ; oxygen ; kinetics ; non-steady state ; cardiac output ; PEEP ; pulmonary embolism ; pulmonary gas exchange monitoring
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Medicine
    Notes: Abstract Traditionally, the study of CO2 and O2 kinetics in the body has been mostly confined to equilibrium conditions. However, the peri-anesthesia period and the critical care arena often involve conditions of non-steady state. The detection and explanation of CO2 kinetics during non-steady state pathophysiology have required the development of new methodologies, including the CO2 expirogram, average alveolar expired PCO2, and CO2 volume exhaled per breath. Several clinically relevant examples of non-steady state CO2 kinetics perturbations are examined, including abrupt decrease in cardiac output, application of positive end-expiratory pressure during mechanical ventilation, and occurrence of pulmonary embolism. The lesser known area of non-steady state O2 kinetics is introduced, including the measurement of pulmonary O2 uptake per breath. Future directions include the study of the respiratory quotient per breath, where the anaerobic threshold during anesthesia is identified by increasing respiratory quotient.
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  • 6
    ISSN: 1573-515X
    Keywords: aquatic plants ; dissolved organic carbon ; nutrient cycling ; phosphorus ; sediments ; wetlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Release of oxygen from the roots ofaquatic macrophytes into anaerobic sediments canaffect the quantity of interstitial dissolved organicmatter and nutrients that are available to bacteria. Nutrient and dissolved organic carbon (DOC)concentrations were compared between subsurface(interstitial) waters of unvegetated sediments andsediments among stands of the emergent herbaceousmacrophyte Juncus effusus L. in a lotic wetlandecosystem. Concentrations of inorganic nitrogen(NH4 +, NO3 -, and NO2 -)were greater from sediments of the unvegetatedcompared to the vegetated zone. DOC concentrations ofinterstitial waters were greater in sediments of theunvegetated zone both in the winter and springcompared to those from the vegetated zone. AlthoughDOC concentrations in hydrosoils collected from bothzones increased from winter to spring, bacterialproductivity per mg DOC in spring decreased comparedto winter. Greater initial bacterial productivityoccurred on DOM collected from the vegetated comparedto the unvegetated zone in winter samples (days 1 and4), with increased bacterial productivity on samplescollected from the unvegetated zone at the end of thestudy (day 20). Bacterial productivity wassignificantly greater on all sampling days on DOM fromvegetated samples compared to unvegetated samples. In nutrient enrichment experiments, bacterialproductivity was significantly increased (p 〈 0.05)with phosphorus but not nitrogen only amendments.
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  • 7
    ISSN: 1573-515X
    Keywords: carbon ; landscape geochemical flows ; model ; nitrogen ; phosphorus ; wetland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The importance of landscape geochemical flows wasinvestigated using a dynamic model simulating carbon,nitrogen and phosphorus cycling in riverine wetlands,which has been described in a previous paper. Thehydro-geomorphic unit (HGMU) concept was incorporatedin the model by defining a separate, completeunit-model for each unit (HGMU) within the wetland.These unit-models were connected by defining the flowsof nitrogen and phosphorus between them. These flows,also called landscape geochemical flows, usuallyconsist of flows of water containing N and P. The model was applied to a site at Kismeldon Meadows,in south-western England. This site consists of twounits, a slope and a floodplain, separated by a ditch,which catches most of the run off and shallowgroundwater flows from the slope. Only an estimated1% of the N and P that leaves the slope unit in thewater outflow reaches the floodplain unit; the rest iscaught in the system of ditches, which prevent thegeochemical flows taking their natural course. Toexamine the influence of this system of ditches, themodel was run for the same site, but without theditches. This is comparable to a situation of arestored site, where run off and shallow groundwaterflows containing nutrients, can freely get from theslope to the floodplain. The computer simulation experiment reconnecting theslope and floodplain showed that this (1) increasedthe nutrient input into the floodplain, causing ahigher biomass production, and (2) increased thewetness of the floodplain, causing slowerdecomposition, which together (3) led to a faster soilorganic matter accumulation in the floodplain.Nutrient inflows became relatively more importantcompared to atmospheric deposition, especially forphosphorus. By connecting the slope and the floodplainmore nitrogen and less phosphorus flowed into theriver.
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  • 8
    ISSN: 1573-515X
    Keywords: chloride ; internal eutrophication ; nitrogen ; peat soil ; phosphorus ; phytometer ; sulphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Inputs of surface waters high in chloride and sulphateincreased the availability of nutrients in fenpeatlands. This `internal eutrophication' wasdemonstrated with test plants (`phytometers') andthrough water and soil analysis. Three experiments arepresented in which the level of chloride and/orsulphate was increased to 3 mmolc l−1. Inexperiment 1 chloride levels were increased from 0.5to 3 mmolc l−1 as CaCl2 or NaCl. Inexperiment 2 and 3 similar increased levels forchloride and sulphate (3 mmolc l−1; as NaCland Na2SO4) were used. The following resultswere found: (i) No differences in soil total-N and total-P werefound before and after the treatments in any of thethree experiments. (ii) Experiment 1 showed a significant increase inBio-Available P (BAP) in pots planted with Anthoxanthum odoratum as well as in bare pots for theNaCl and CaCl2 treatments. The plants in thesetreatments had taken up much more P. (iii) Experiment 2 showed an increase in soil BAPafter treatment with chloride and sulphate in potsplanted with Anthoxanthum odoratum. The chloridetreatment had no effect on plant biomass, whereas thesulphate treatment resulted in a reduction in rootbiomass and root N and P content. The shoots showedan increase in P content in the sulphate and chloridetreatments, while N content remained the same. (iv) In experiment 3, treatments with chloride andsulphate led to significantly increased biomass and Puptake of Anthoxanthum odoratum. Again, noeffects on N uptake were found. These experiments provide evidence for distinctlyincreased availability of phosphate in peat soils whenthese come into contact with water with evenmoderately increased sulphate or chloride levels.Surface water originating from the Rhine river, whichis enriched in chloride and sulphate, is oftensupplied to fen reserves in The Netherlands, tocompensate for water losses due to agriculturaldrainage in the region. The results of this study showthat phosphate availability to the vegetation may risedrastically, with detrimental effects on the speciesdensity and the occurrence of rare species in thevegetation. Hence, supply of this water should beavoided.
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  • 9
    Electronic Resource
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    Springer
    Biogeochemistry 51 (2000), S. 1-32 
    ISSN: 1573-515X
    Keywords: aluminum ; floodplain forests ; iron ; organic matter ; P sorption capacity ; phosphorus ; soil ; wetlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We examined spatial and temporal variationsin soil chemistry in a floodplain forest landscape todetermine the effects of flooding on aluminum (Al) andiron (Fe) oxide biogeochemistry and inorganicphosphorus (Pi) sorption capacity. Whenpreviously sorbed Pi was considered, the sorptioncapacities of floodplain and adjacent upland soilswere comparable, suggesting that floodplain soilsrepresent a second line of defense protectingdownstream aquatic ecosystems from agriculturalrun-off. Pi sorption capacity was highlycorrelated with oxalate-extractable Al (Alo)(rs = 0.78); Alo and percent organic matter(OM) were also highly correlated (rs = 0.72),suggesting the importance of OM-Al complexes in thesesoils. The correlation of oxalate-extractable Fe(Feo) with OM (rs = 0.64) was improved(rs = 0.80) by removing lower elevation (swale)soils, suggesting that flooding inhibits theassociation of Feo with OM. Fe oxidecrystallinity decreased during seasonal flooding, buttotal extractable Fe did not change significantly. Fesolubilized during flooding was either replaced bysediment deposition (252 ± 3 mmol kg−1yr−1), and/or reprecipitated locally. Al oxidecrystallinity also decreased during flooding due to asignificant decline in NaOH-extractable Al (AlN). AlN concentrations subsequently returned topre-flooding levels, but sediment Al inputs (57 ±3 mmol kg−1 yr−1), were insufficient to account for this recovery. Observed Fetransformations suggest the importance offlooding-induced declines in soil redox potential toFe biogeochemistry; observed Al transformationssuggest the importance of complexation reactions withsoil OM to Al biogeochemistry in this floodplainforest.
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  • 10
    ISSN: 1432-0789
    Keywords: Key words Phosphorus dynamics ; Olsen ; phosphorus ; Soil phosphorus fractions ; Manure ; Soybean-wheat rotation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Soil P availability and efficiency of applied P may be improved through an understanding of soil P dynamics in relation to management practices in a cropping system. Our objectives in this study were to evaluate changes in plant-available (Olsen) P and in different inorganic P (Pi) and organic P (P0) fractions in soil as related to repeated additions of manure and fertilizer P under a soybean-wheat rotation. A field experiment on a Typic Haplustert was conducted from 1992 to 1995 wherein the annual treatments included four rates of fertilizer P (0, 11, 22 and 44 kg ha–1 applied to both soybean and wheat) in the absence and presence of 16 t ha–1 of manure (applied to soybean only). With regular application of fertilizer P to each crop the level of Olsen P increased significantly and linearly through the years in both manured and unmanured plots. The mean P balance required to raise Olsen P by 1 mg kg–1 was 17.9 kg ha–1 of fertilizer P in unmanured plots and 5.6 kg ha–1 of manure plus fertilizer P in manured plots. The relative sizes of labile [NaHCO3-extractable Pi (NaHCO3-Pi) and NaHCO3-extractable P0 (NaHCO3-P0)], moderately labile [NaOH-extractable Pi (NaOH-Pi) and NaOH-extractable P0 (NaOH-P0)] and stable [HCl-extractable P (HCl-P) and H2SO4/H2O2-extractable P (resisual-P)] P pools were in a 1 : 2.9 : 7.6 ratio. Application of fertilizer P and manure significantly increased NaHCO3-Pi and -P0 and NaOH-Pi, and -P0 fractions and also total P. However, HCl-P and residual-P were not affected. The changes in NaHCO3-Pi, NaOH-Pi and NaOH-P0 fractions were significantly correlated with the apparent P balance and were thought to represent biologically dynamic soil P and act as major sources and sinks of plant-available P.
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  • 11
    ISSN: 1573-0417
    Keywords: carbon isotopes ; diatoms ; lake management ; nitrogen isotopes ; phosphorus ; radium-226 ; sediments ; trophic state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract We explored the use of carbon and nitrogen isotopes (δ13C and δ15N) in sedimented organic matter (OM) as proxy indicators of trophic state change in Florida lakes. Stable isotope data from four 210Pb-dated sediment cores were compared stratigraphically with established proxies for historical trophic state (diatom-inferred limnetic total phosphorus, sediment C/N ratio) and indicators of cultural disturbance (sediment total P and 226Ra activity). Diatom-based limnetic total P inferences indicate a transition from oligo-mesotrophy to meso-eutrophy in Clear Lake, and from eutrophy to hypereutrophy in Lakes Parker, Hollingsworth and Griffin. In cores from all four lakes, the carbon isotopic signature of accumulated OM generally tracks trophic state inferences and cultural impact assessments based on other variables. Oldest sediments in the records yield lower diatom-inferred total limnetic P concentrations and display relatively low δ13C values. In the Clear, Hollingsworth and Parker records, diatom-inferred nutrient concentrations increase after ca. AD 1900, and are associated stratigraphically with higher δ13C values in sediment OM. In the Lake Griffin core, both proxies display slight increases before ~1900, but highest values occur over the last ~100 years. As Lakes Clear, Hollingsworth and Parker became increasingly nutrient-enriched over the past century, the δ15N of sedimented organic matter decreased. This reflects, in part, the increasing relative contribution of nitrogen-fixing cyanobacteria to sedimented organic matter as primary productivity increased in these waterbodies. The Lake Griffin core displays a narrow range of both δ13C and δ15N values. Despite the complexity of carbon and nitrogen cycles in lakes, stratigraphic agreement between diatom-inferred changes in limnetic total P and the stable isotope signatures of sedimented OM suggests that δ13C and δ15N reflect shifts in historic lake trophic state.
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  • 12
    ISSN: 1573-0417
    Keywords: diatoms ; Everglades ; phosphorus ; wetland ; calibration ; multivariate ; Florida
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The relationship between diatom taxa preserved in surface soils and environmental variables at 31 sites in Water Conservation Area 2A (WCA-2A) of the Florida Everglades was explored using multivariate analyses. Surface soils were collected along a phosphorus (P) gradient and analyzed for diatoms, total P, % nitrogen (N), %carbon (C), calcium (Ca), and biogenic silica (BSi). Phosphorus varied from 315-1781 μg g-1, and was not found to be correlated with the other geochemical variables. Canonical correspondence analysis (CCA) was used to examine which environmental variables correlated most closely with the distributions in diatom taxa. Canonical correspondence analysis with forward selection, constrained and partial CCA, and Monte Carlo permutation tests of significance show the most significant changes in diatom assemblages along the P gradient (p 〈 0.01), with additional species differences correlated with soil C, N, Ca, and BSi. Weighted-averaging (WA) regression and calibration models of diatom assemblages to P and BSi were developed. The diatom-based inference model for soil [P] had a high apparent r2 (0.86) with RMSEboot = 218 μg g-1. Indicator diatom species identified by assessing species WA optima and WA tolerance to [P], such as Nitzschia amphibia and N. palea for high [P] (~1300-1400 μ g-1) and Achnanthes minutissima var. scotica and Mastogloia smithii for low [P] (~400-600 μg g-1), may be useful as monitoring tools for eutrophication in WCA-2A as well as other areas of the Everglades. Diatom assemblages analyzed by cluster analysis were related to location within WCA-2A, and dominant taxa within clusters are discussed in relation to the geochemical variables measured as well as hydrology and pH. Diversity of diatom assemblages and a ‘Disturbance Index’ based on diatom data are discussed in relation to the historically P-limited Everglades ecosystem. Diatom assemblages should be very useful for reconstructions of [P] through time in the Florida Everglades, provided diatoms are well preserved in soil cores.
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  • 13
    Electronic Resource
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    Molecular and cellular biochemistry 197 (1999), S. 195-201 
    ISSN: 1573-4919
    Keywords: phospholipase D ; phosphatidylinositol 4,5-bisphosphate ; neomycin ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The kinetics of phosphatidylcholine-specific phospholipase D activated by phosphatidylinositol 4,5-bisphosphate (PIP2) and inhibition by neomycin were studied in an enzyme preparation partially purified from human hepatocarcinoma cell line. It was found that phospholipase D was marginally activated by phosphatidyl-4-phosphate (PIP) and phosphatidylethanolamine (PE). In contrast, it was considerably activated by PIP2 in different concentration of phosphatidylcholine (PC). Sphingomyelin (SM), lysophosphatidylcholine (LPC) and phosphatidylserine (PS) were neither substrates nor inhibitors of the phospholipase D. PIP2 induced an allosteric effect on phospholipase D and a negative cooperative effect with respect to phosphatidylcholine as indicated in the Lineweaver-Burk plot. In the absence of PIP2, a straight line was obtained, whereas a downward concave curve was observed in the presence of 25 μM of PIP2. The Hill coefficient and the apparent Km of phosphatidylcholine in the presence of 25 μM PIP2 were calculated to be 0.631 and 10.79 mM, respectively. PIP2 also increased the maximal velocity (Vmax) of the phospholipase D reaction, suggesting that the affinity of substrate to enzyme was decreased, and the turnover number of the enzyme (kcat) was increased by PIP2. The activation of phospholipase D by PIP2 was dose dependent up to 50 μM of PIP2. The Ka of PIP2 was 15.8 mM. Neomycin, a polycationic glycoside, was shown to be an uncompetitive inhibitor of phospholipase D, and revealed the formation of a neomycin-PIP2 complex. The Ki of neomycin was estimated to be 8.7 mM.
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  • 14
    Electronic Resource
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    Molecular and cellular biochemistry 193 (1999), S. 19-22 
    ISSN: 1573-4919
    Keywords: poly(ADP-ribose)polymerase ; kinetics ; allosterism ; regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Here, we describe the latest developments on the mechanistic characterization of poly(ADP-ribose) polymerase (PARP) [EC 2.4.2.30], a DNA-dependent enzyme that catalyzes the synthesis of protein-bound ADP-ribose polymers in eucaryotic chromatin. A detailed kinetic analysis of the automodification reaction of PARP in the presence of nicked dsDNA indicates that protein-poly(ADP-ribosyl)ation probably occurs via a sequential mechanism since enzyme-bound ADP-ribose chains are not reaction intermediates. The multiple enzymatic activities catalyzed by PARP (initiation, elongation, branching and self-modification) are the subject of a very complex regulatory mechanism that may involve allosterism. For instance, while the NAD+ concentration determines the average ADP-ribose polymer size (polymerization reaction), the frequency of DNA strand breaks determines the total number of ADP-ribose chains synthesized (initiation reaction). A general discussion of some of the mechanisms that regulate these multiple catalytic activities of PARP is presented below.
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  • 15
    ISSN: 1573-515X
    Keywords: acidification ; anthropogenic nitrogen ; cations ; nitrate leaching ; nitric oxide ; nitrous oxide ; nutrient limitation ; phosphorus ; productivity ; tropical ecosystems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Human activities have more than doubled the inputs of nitrogen (N) into terrestrial systems globally. The sources and distribution of anthropogenic N, including N fertilization and N fixed during fossil fuel combustion, are rapidly shifting from the temperate zone to a more global distribution. The consequences of anthropogenic N deposition for ecosystem processes and N losses have been studied primarily in N-limited ecosystems in the temperate zone; there is reason to expect that tropical ecosystems, where plant growth is most often limited by some other resource, will respond differently to increasing deposition. In this paper, we assess the likely direct and indirect effects of increasing anthropogenic N inputs on tropical ecosytem processes. We conclude that anthropogenic inputs of N into tropical forests are unlikely to increase productivity and may even decrease it due to indirect effects on acidity and the availability of phosphorus and cations. We also suggest that the direct effects of anthropogenic N deposition on N cycling processes will lead to increased fluxes at the soilwater and soil-air interfaces, with little or no lag in response time. Finally, we discuss the uncertainties inherent in this analysis, and outline future research that is needed to address those uncertainties.
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  • 16
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    Biogeochemistry 46 (1999), S. 179-202 
    ISSN: 1573-515X
    Keywords: carbon dioxide ; grazing ; nitrogen fixation ; nitrogen limitation ; phosphorus ; shade
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The widespread occurrence ofN limitation to net primary production (NPP) and other ecosystem processes, despite the ubiquitous occurrence ofN-fixing symbioses, remains a significant puzzle in terrestrial ecology. We describe a simple simulation model for an ecosystem containing a generic nonfixer and a symbioticN fixer, based on: (1) a higher cost forN acquisition byN fixers than nonfixers; (2) growth of fixers and fixation ofN only when lowN availability limits the growth of nonfixers, and other resources are available; and (3) losses of fixedN from the system only when the quantity of availableN exceeds plant and microbial demands. Despite the disadvantages faced by theN fixer under these conditions,N fixation and loss adjustN availability close to the availability of other resources, and biomass and NPP in this simple model can be substantially but only transientlyN limited. We then modify the model by adding: (1) losses ofN in forms other than excess availableN (e.g., dissolved organicN, trace gases produced by nitrification); and (2) constraints to the growth and activity ofN fixers imposed by differential effects of shading,P limitation, and grazing. The combination of these processes is sufficient to describe an open system, with input from both precipitation andN fixation, that is nevertheless stronglyN-limited at equilibrium. This model is useful for exploring causes and consequences of constraints toN fixation, and hence ofN limitation, and we believe it will also be useful for evaluating howN fixation and limitation interact with elevatedCO 2 and other components of global enviromental change.
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  • 17
    ISSN: 1573-515X
    Keywords: estuaries ; lakes ; marine ; nitrogen ; phosphorus ; rivers ; streams ; temperate ; tropics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Published data and analyses from temperate and tropical aquatic systems are used to summarize knowledge about the potential impact of land-use alteration on the nitrogen biogeochemistry of tropical aquatic ecosystems, identify important patterns and recommend key needs for research. The tropical N-cycle is traced from pre-disturbance conditions through the phases of disturbance, highlighting major differences between tropical and temperate systems that might influence development strategies in the tropics. Analyses suggest that tropical freshwaters are more frequently N-limited than temperate zones, while tropical marine systems may show more frequent P limitation. These analyses indicate that disturbances to pristine tropical lands will lead to greatly increased primary production in freshwaters and large changes in tropical freshwater communities. Increased freshwater nutrient flux will also lead to an expansion of the high production, N- and light-limited zones around river deltas, a switch from P- to N-limitation in calcareous marine systems, with large changes in the community composition of fragile mangrove and reef systems. Key information gaps are highlighted, including data on mechanisms of nutrient transport and atmospheric deposition in the tropics, nutrient and material retention capacities of tropical impoundments, and N/P coupling and stoichiometric impacts of nutrient supplies on tropical aquatic communities. The current base of biogeochemical data suggests that alterations in the N-cycle will have greater impacts on tropical aquatic ecosystems than those already observed in the temperate zone.
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  • 18
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    Biogeochemistry 44 (1999), S. 93-118 
    ISSN: 1573-515X
    Keywords: Everglades National Park ; mangrove soils ; organic matter ; nitrogen ; phosphorus ; sedimentation ; simulation model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The distribution and accumulation of organic matter, nitrogen (N) and phosphorus (P) in mangrove soils at four sites along the Shark River estuary of south Florida were investigated with empirical measures and a process-based model. The mangrove nutrient model (NUMAN) was developed from the SEMIDEC marsh organic matter model and parameterized with data from mangrove wetlands. The soil characteristics in the four mangrove sites varied greatly in both concentrations and profiles of soil carbon, N and P. Organic matter decreased from 82% in the upstream locations to 30% in the marine sites. Comparisons of simulated and observed results demonstrated that landscape gradients of soil characteristics along the estuary can be adequately modeled by accounting for plant production, litter decomposition and export, and allochthonous input of mineral sediments. Model sensitivity analyses suggest that root production has a more significant effect on soil composition than litter fall. Model simulations showed that the greatest change in organic matter, N, and P occurred from the soil surface to 5 cm depth. The rapid decomposition of labile organic matter was responsible for this decrease in organic matter. Simulated N mineralization rates decreased quickly with depth, which corresponded with the decrease of labile organic matter. The increase in organic matter content and decrease in soil bulk density from mangrove sites at downstream locations compared to those at upstream locations was controlled mainly by variation in allochthonous inputs of mineral matter at the mouth of the estuary, along with gradients in mangrove root production. Research on allochthonouns sediment input and in situ root production of mangroves is limited compared to their significance to understanding nutrient biogeochemistry of these wetlands. More accurate simulations of temporal patterns of nutrient characteristics with depth will depend on including the effects of disturbance such as hurricanes on sediment redistribution and biomass production.
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  • 19
    ISSN: 1573-515X
    Keywords: Chaohu Lake ; chemical fertilizer ; cycling ; denitrification ; multipond system ; nitrogen ; nutrient budget ; phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract During a two-year field study, an annual nutrient budget and cycles were developed for a small agricultural watershed. The study emphasized the integrated unit of the watershed in understanding the biogeochemistry. It was found that the total nutrient input was 39.1× 104 kg nitrogen and 3.91×104 kg phosphorus in the year 1995, of which the greatest input of nutrients to the watershed was chemical fertilizer application, reaching 34.7×104 kg (676 kg/ha) nitrogen and 3.88×104 kg (76 kg/ha) phosphorus. The total nutrient output from the watershed was 13.55×104 kg nitrogen and 0.40×104 kg phosphorus, while the largest output of nitrogen was denitrification, accounting for 44.1% of N output; the largest output of phosphorus was sale of crops, accounting for 99.4% of P output. The results show that the nutrient input is larger than output, demonstrating that there is nutrient surplus within the watershed, a surplus which may become a potential source of nonpoint pollution to area waters. The research showed that both denitrification and volatilization of nitrogen are key ways of nitrogen loss from the watershed. This suggests that careful management of fertilizer application will be important for the sustainable development of agriculture. The research demonstrated that a multipond system within the watershed had high retention rate for both water and nutrients, benefiting the water, nutrient and sediment recycling in the terrestrial ecosystem and helping to reduce agricultural nonpoint pollution at its source. Therefore, this unique watershed system should be recommended due to its great potential relevance for sustainable agricultural development.
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  • 20
    ISSN: 1573-515X
    Keywords: Chihuahuan desert ; desert ; desertification ; grassland ; nitrogen ; nutrient budgets ; phosphorus ; runoff
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Rainfall simulation experiments were performed in areas of semiarid grassland (Bouteloua eriopoda) and arid shrubland (Larrea tridentata) in the Chihuahuan desert of New Mexico. The objective was to compare the runoff of nitrogen (N) and phosphorus (P) from these habitats to assess whether losses of soil nutrients are associated with the invasion of grasslands by shrubs. Runoff losses from grass- and shrub-dominated plots were similar, and much less than from bare plots located in the shrubland. Weighted average concentrations of total dissolved N compounds in runoff were greatest in the grassland (1.72 mg/1) and lowest in bare plots in the shrubland (0.55 mg/1). More than half of the N transported in runoff was carried in dissolved organic compounds. In grassland and shrub plots, the total N loss was highly correlated to the total volume of discharge. We estimate that the total annual loss of N in runoff is 0.25 kg/ha/yr in grasslands and 0.43 kg/ha/yr in shrublands — consistent with the depletion of soil N during desertification of these habitats. Losses of P from both habitats were very small.
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  • 21
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    Biogeochemistry 44 (1999), S. 93-118 
    ISSN: 1573-515X
    Keywords: Everglades National Park ; mangrove soils ; organic matter ; nitrogen ; phosphorus ; sedimentation ; simulation model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The distribution and accumulation of organic matter, nitrogen (N) and phosphorus (P) in mangrove soils at four sites along the Shark River estuary of south Florida were investigated with empirical measures and a process-based model. The mangrove nutrient model (NUMAN) was developed from the SEMIDEC marsh organic matter model and parameterized with data from mangrove wetlands. The soil characteristics in the four mangrove sites varied greatly in both concentrations and profiles of soil carbon, N and P. Organic matter decreased from 82% in the upstream locations to 30% in the marine sites. Comparisons of simulated and observed results demonstrated that landscape gradients of soil characteristics along the estuary can be adequately modeled by accounting for plant production, litter decomposition and export, and allochthonous input of mineral sediments. Model sensitivity analyses suggest that root production has a more significant effect on soil composition than litter fall. Model simulations showed that the greatest change in organic matter, N, and P occurred from the soil surface to 5 cm depth. The rapid decomposition of labile organic matter was responsible for this decrease in organic matter. Simulated N mineralization rates decreased quickly with depth, which corresponded with the decrease of labile organic matter. The increase in organic matter content and decrease in soil bulk density from mangrove sites at downstream locations compared to those at upstream locations was controlled mainly by variation in allochthonous inputs of mineral matter at the mouth of the estuary, along with gradients in mangrove root production. Research on allochthonouns sediment input and in situ root production of mangroves is limited compared to their significance to understanding nutrient biogeochemistry of these wetlands. More accurate simulations of temporal patterns of nutrient characteristics with depth will depend on including the effects of disturbance such as hurricanes on sediment redistribution and biomass production.
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  • 22
    ISSN: 1573-515X
    Keywords: Chaohu Lake ; chemical fertilizer ; cycling ; denitrification ; multipond system ; nitrogen ; nutrient budget ; phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract During a two-year field study, an annual nutrient budget and cycles were developed for a small agricultural watershed. The study emphasized the integrated unit of the watershed in understanding the biogeochemistry. It was found that the total nutrient input was 39.1 × 104 kg nitrogen and 3.91 × 104 kg phosphorus in the year 1995, of which the greatest input of nutrients to the watershed was chemical fertilizer application, reaching 34.7 × 104 kg (676 kg/ha) nitrogen and 3.88 × 104 kg (76 kg/ha) phosphorus. The total nutrient output from the watershed was 13.55 × 104 kg nitrogen and 0.40 × 104 kg phosphorus, while the largest output of nitrogen was denitrification, accounting for 44.1% of N output; the largest output of phosphorus was sale of crops, accounting for 99.4% of P output. The results show that the nutrient input is larger than output, demonstrating that there is nutrient surplus within the watershed, a surplus which may become a potential source of nonpoint pollution to area waters. The research showed that both denitrification and volatilization of nitrogen are key ways of nitrogen loss from the watershed. This suggests that careful management of fertilizer application will be important for the sustainable development of agriculture. The research demonstrated that a multipond system within the watershed had high retention rate for both water and nutrients, benefiting the water, nutrient and sediment recycling in the terrestrial ecosystem and helping to reduce agricultural nonpoint pollution at its source. Therefore, this unique watershed system should be recommended due to its great potential relevance for sustainable agricultural development.
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  • 23
    ISSN: 1573-515X
    Keywords: atmospheric deposition ; moss ; bog ; nitrogen ; phosphorus ; water table
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Nitrogen additions as NH4NO3 corresponding to 0 (N0), 1 (N1), 3 (N3) and 10 (N10) g N m−2 yr−1 were made toSphagnum magellanicurn cores at two-week intervalsin situ at four sites across Europe, i.e. Lakkasuo (Finland). Männikjärve (Estonia), Moidach More (UK) and Côte de Braveix (France). The same treatments were applied in a glasshouse experiment in Neuchâtel (Switzerland) in which the water table depth was artificially maintained at 7, 17 and 37 cm below the moss surface. In the field, N assimilation in excess of values in wet deposition occurred in the absence of growth, but varied widely between sites, being absent in Lakkasuo (moss N∶P ratio 68) and greatest in Moidach More (N∶P 21). In the glasshouse, growth was reduced by lowering the water table without any apparent effect on N assimilation. Total N content of the moss in field sites increased as the mean depth of water table increased indicating growth limitation leading to increased N concentrations which could reduce the capacity for N retention. Greater contents of NH4 + in the underlying peat at 30 cm depth, both in response to NH4NO3 addition and in the unamended cores confirmed poor retention of inorganic N by the moss at Lakkasuo. Nitrate contents in the profiles at Lakkasuo, Moidach More, and Côte de Braveix were extremely low, even in the N10 treatment, but in Männikjärve, where the mean depth of water table was greatest and retention absent, appreciable amounts of NO3 − were detected in all cores. It is concluded that peatland drainage would reduce the capture of inorganic N in atmospheric deposition bySphagnum mosses.
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  • 24
    ISSN: 1573-515X
    Keywords: estuaries ; lakes ; marine ; nitrogen ; phosphorus ; rivers ; streams ; temperate ; tropics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Published data and analyses from temperate and tropical aquatic systems are used to summarize knowledge about the potential impact of land-use alteration on the nitrogen biogeochemistry of tropical aquatic ecosystems, identify important patterns and recommend key needs for research. The tropical N-cycle is traced from pre-disturbance conditions through the phases of disturbance, highlighting major differences between tropical and temperate systems that might influence development strategies in the tropics. Analyses suggest that tropical freshwaters are more frequently N-limited than temperate zones, while tropical marine systems may show more frequent P limitation. These analyses indicate that disturbances to pristine tropical lands will lead to greatly increased primary production in freshwaters and large changes in tropical freshwater communities. Increased freshwater nutrient flux will also lead to an expansion of the high production, N- and light-limited zones around river deltas, a switch from P- to N-limitation in calcareous marine systems, with large changes in the community composition of fragile mangrove and reef systems. Key information gaps are highlighted, including data on mechanisms of nutrient transport and atmospheric deposition in the tropics, nutrient and material retention capacities of tropical impoundments, and N/P coupling and stoichiometric impacts of nutrient supplies on tropical aquatic communities. The current base of biogeochemical data suggests that alterations in the N-cycle will have greater impacts on tropical aquatic ecosystems than those already observed in the temperate zone.
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  • 25
    ISSN: 1573-515X
    Keywords: acidification ; anthropogenic nitrogen ; cations ; nitrate leaching ; nitric oxide ; nitrous oxide ; nutrient limitation ; phosphorus ; productivity ; tropical ecosystems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Human activities have more than doubled the inputs of nitrogen (N) into terrestrial systems globally. The sources and distribution of anthropogenic N, including N fertilization and N fixed during fossil fuel combustion, are rapidly shifting from the temperate zone to a more global distribution. The consequences of anthropogenic N deposition for ecosystem processes and N losses have been studied primarily in N-limited ecosystems in the temperate zone; there is reason to expect that tropical ecosystems, where plant growth is most often limited by some other resource, will respond differently to increasing deposition. In this paper, we assess the likely direct and indirect effects of increasing anthropogenic N inputs on tropical ecosytem processes. We conclude that anthropogenic inputs of N into tropical forests are unlikely to increase productivity and may even decrease it due to indirect effects on acidity and the availability of phosphorus and cations. We also suggest that the direct effects of anthropogenic N deposition on N cycling processes will lead to increased fluxes at the soil-water and soil-air interfaces, with little or no lag in response time. Finally, we discuss the uncertainties inherent in this analysis, and outline future research that is needed to address those uncertainties.
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  • 26
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    Biogeochemistry 46 (1999), S. 179-202 
    ISSN: 1573-515X
    Keywords: carbon dioxide ; grazing ; nitrogen fixation ; nitrogen limitation ; phosphorus ; shade
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The widespread occurrence of N limitation to net primary production (NPP) and other ecosystem processes, despite the ubiquitous occurrence of N-fixing symbioses, remains a significant puzzle in terrestrial ecology. We describe a simple simulation model for an ecosystem containing a generic nonfixer and a symbiotic N fixer, based on: (1) a higher cost for N acquisition by N fixers than nonfixers; (2) growth of fixers and fixation of N only when low N availability limits the growth of nonfixers, and other resources are available; and (3) losses of fixed N from the system only when the quantity of available N exceeds plant and microbial demands. Despite the disadvantages faced by the N fixer under these conditions, N fixation and loss adjust N availability close to the availability of other resources, and biomass and NPP in this simple model can be substantially but only transiently N limited. We then modify the model by adding: (1) losses of N in forms other than excess available N (e.g., dissolved organic N, trace gases produced by nitrification); and (2) constraints to the growth and activity of N fixers imposed by differential effects of shading, P limitation, and grazing. The combination of these processes is sufficient to describe an open system, with input from both precipitation and N fixation, that is nevertheless strongly N-limited at equilibrium. This model is useful for exploring causes and consequences of constraints to N fixation, and hence of N limitation, and we believe it will also be useful for evaluating how N fixation and limitation interact with elevated CO2 and other components of global enviromental change.
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  • 27
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    Biogeochemistry 47 (1999), S. 25-38 
    ISSN: 1573-515X
    Keywords: Hedley fractionation ; phosphorus ; Ruttenberg fractionation ; soil phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We used l6 soils to compare the Hedley method for soil phosphorus fractionation to an alternative method recently developed by Ruttenberg to differentiate among P fractions in marine sediments. For forms of labile and Fe-bound P in soils, these methods were poorly correlated, with the Hedley fractionation showing a greater ability to discriminate among variations in plant-available P. For Ca-bound P, total organic P, and total P, the methods were well correlated (r2 = 0.93, 0.48, 0.74, respectively), although the sum of P measured in the Ruttenberg extractions is only 45% of the total P recovered by the Hedley fractionation. The Hedley fractionation seems superior when an index of plant-available phosphorus and a separation of organic and inorganic forms is needed, whereas the Ruttenberg method allows a separation of CaCO3-bound P from apatite-P, which is potentially useful in calcareous soils.
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  • 28
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    Biogeochemistry 47 (1999), S. 25-38 
    ISSN: 1573-515X
    Keywords: Hedley fractionation ; phosphorus ; Ruttenberg fractionation ; soil phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We used 16 soils to compare the Hedley method for soil phosphorus fractionation to an alternative method recently developed by Ruttenberg to differentiate among P fractions in marine sediments. For forms of labile and Fe-bound P in soils, these methods were poorly correlated, with the Hedley fractionation showing a greater ability to discriminate among variations in plant-available P. For Ca-bound P, total organic P, and total P, the methods were well correlated (r2=0.93, 0.48, 0.74, respectively), although the sum of P measured in the Ruttenberg extractions is only 45% of the total P recovered by the Hedley fractionation. The Hedley fractionation seems superior when an index of plant-available phosphorus and a separation of organic and inorganic forms is needed, whereas the Ruttenberg method allows a separation of CaCO3-bound P from apatite-P, which is potentially useful in calcareous soils.
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  • 29
    ISSN: 1573-0662
    Keywords: atmosphere ; kinetics ; nitrate radical ; monoterpenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The aim of this work is to study the reactivity of some naturally emitted terpenes, 2-carene, sabinene, myrcene, α-phellandrene, d-limonene, terpinolene and γ-terpinene, towards NO3 radical to evaluate the importance of these reactions in the atmosphere and their atmospheric impact. The experiments with these monoterpenes have been carried out under second-order kinetic conditions over the range of temperature 298–433 K, using a discharge flow system and monitoring the NO3 radical by Laser Induced Fluorescence (LIF). This work is the first temperature dependence study for the reactions of the nitrate radical with the above-mentioned monoterpenes. The measured rate constants at 298 K for the reaction of NO3 with such terpenes are as follows: 2-carene, 16.6 ± 1.8, sabinene 10.7 ± 1.6, myrcene 12.8 ± 1.1, α-phellandrene 42 ± 10, d-limonene 9.4 ± 0.9, terpinolene 52 ± 9 and γ-terpinene 24 ± 7, in units of 10-12 cm3 molecule-1 s-1. The proposed Arrhenius expressions, for the reactions of NO3 with 2-carene, sabinene, myrcene and α-phellandrene are, respectively k1 = (1.4 ± 0.7) × 10-12 exp[(741 ± 190/T)] (cm3 molecule-1 s-1), k2=(2.3 ± 1.3) × 10-10 exp[−(940 ± 200/T)] (cm3 molecule-1 s-1), k3 = (2.2 ± 0.2) × 10-12 exp[(523 ± 35/T)] (cm3 molecule1 s-1) and k4 = (1.9 ± 1.3) × 10-9 exp[−(1158 ± 270/T)] (cm3 molecule-1 s-1). A decrease in the rate constants when raising the temperature has also been found for the reaction of d-limonene with NO3 while an increase in the rate constant with temperature has been observed for the reactions of terpinolene and γ-terpinene with NO3. Tropospheric half-lives for these terpenes have been calculated at night and during the day for typical NO3 and OH concentrations showing that both radicals provide an effective tropospheric sink for these compounds and that the night-time reaction with NO3 radical can be an important, if not dominant, loss process for these naturally emitted organics and for NO3 radicals.
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  • 30
    ISSN: 1573-0662
    Keywords: δ3-carene ; chlorine atoms ; isoprene ; kinetics ; methacrolein and methyl vinyl ketone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The rate coefficients for the reaction between atomic chlorine and a number of naturally occurring species have been measured at ambient temperature and atmospheric pressure using the relative rate technique. The values obtained were (4.0 ± 0.8) × 10-10, (2.1 ± 0.5) × 10-10, (3.2 ± 0.5) × 10-10, and (4.9 ± 0.5) × 10-10 cm3 molecule-1 s-1, for reactions with isoprene, methyl vinyl ketone, methacrolein and δ3-carene, respectively. The value obtained for isoprene compares favourably with previously reported values. No values have been reported to date for the rate constants of the other reactions.
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  • 31
    ISSN: 1573-515X
    Keywords: atmospheric deposition ; moss ; bog ; nitrogen ; phosphorus ; water table
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Nitrogen additions as NH4NO3 corresponding to 0 (N0), 1 (N1), 3 (N3) and 10 (N10) g N m-2 yr-1 were made to Sphagnum magellanicum cores at two-week intervals in situ at four sites across Europe, i.e. Lakkasuo (Finland), Männikjärve (Estonia), Moidach More (UK) and Côte de Braveix (France). The same treatments were applied in a glasshouse experiment in Neuchâtel (Switzerland) in which the water table depth was artificially maintained at 7, 17 and 37 cm below the moss surface. In the field, N assimilation in excess of values in wet deposition occurred in the absence of growth, but varied widely between sites, being absent in Lakkasuo (moss N:P ratio 68) and greatest in Moidach More (N:P 21). In the glasshouse, growth was reduced by lowering the water table without any apparent effect on N assimilation. Total N content of the moss in field sites increased as the mean depth of water table increased indicating growth limitation leading to increased N concentrations which could reduce the capacity for N retention. Greater contents of NH4+ in the underlying peat at 30 cm depth, both in response to NH4NO3 addition and in the unamended cores confirmed poor retention of inorganic N by the moss at Lakkasuo. Nitrate contents in the profiles at Lakkasuo, Moidach More, and Côte de Braveix were extremely low, even in the N10 treatment, but in Männikjärve, where the mean depth of water table was greatest and retention absent, appreciable amounts of NO3- were detected in all cores. It is concluded that peatland drainage would reduce the capture of inorganic N in atmospheric deposition by Sphagnum mosses.
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  • 32
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    Biogeochemistry 45 (1999), S. 197-221 
    ISSN: 1573-515X
    Keywords: intertidal marshes ; phosphorus ; sediments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We examined forms of solid phosphorus fractions in intertidal marsh sediments along a salinity (0–22‰) gradient in a river-dominated estuary and in a marine-dominated salt marsh with insignificant freshwater input. Freshwater marsh sediments had the highest ratio of organic N:P of between 28:1 and 47:1 mol:mol, compared to 21:1 to 31:1 mol:mol in the saltmarshes, which is consistent with a trend toward P-limitation of primary production in freshwater and N-limitation in salt marshes. However, total P concentration, 24.7 ± 11.1 µmol P g dw-1 (±1 SD) averaged over the upper meter of sediment, was greatest in the freshwater marsh where bioavailablity of P is apparently limited. In the freshwater marsh the greatest fraction of total P (24–51%) was associated with humic acids, while the importance of humic-P decreased with increasing salinity to 1–23% in the salt marshes. Inorganic P contributed considerably less to total sediment P in the freshwater marsh (15–40%) than in the salt marshes (33–85%). In reduced sediments at all sites, phosphate bound to aluminum oxides and clays was an important inorganic P pool irrespective of salinity. Inorganic P associated with ferric iron [Fe(III)] phases was most abundant in surface sediments of freshwater and brackish marshes, while Ca-bound P dominated inorganic P pools in the salt marshes. Thus, our results showed that particle-bound P in marsh sediments exhibited changes in chemical association along the salinity gradient of an estuarine system, which is a likely consequence of changes in ionic strength and the availability of iron and calcium.
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  • 33
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    Biogeochemistry 45 (1999), S. 197-221 
    ISSN: 1573-515X
    Keywords: intertidal marshes ; phosphorus ; sediments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We examined forms of solid phosphorus fractions in intertidal marsh sediments along a salinity (0–22%.) gradient in a river-dominated estuary and in a marine-dominated salt marsh with insignificant freshwater input. Freshwater marsh sediments had the highest ratio of organic N:P of between 28:1 and 47:1 mol:mol, compared to 21∶1 to 31∶1 mol∶mol in the saltmarshes, which is consistent with a trend toward P-limitation of primary production in freshwater and N-limitation in salt marshes. However, total P concentration, 24.7±11.1μmol P g dw−1 (±1 SD) averaged over the upper meter of sediment, was greatest in the freshwater marsh where bioavailablity of P is apparently limited. In the freshwater marsh the greatest fraction of total P (24–51%.) was associated with humic acids, while the importance of humic-P decreased with increasing salinity to 1–23%. in the salt marshes. Inorganic P contributed considerably less to total sediment P in the freshwater marsh (15–40%.) than in the salt marshes (33–85%.). In reduced sediments at all sites, phosphate bound to aluminum oxides and clays was an important inorganic P pool irrespective of salinity. Inorganic P associated with ferric iron [Fe(III)] phases was most abundant in surface sediments of freshwater and brackish marshes, while Ca-bound P dominated inorganic P pools in the salt marshes. Thus, our results showed that particle-bound P in marsh sediments exhibited changes in chemical association along the salinity gradient of an estuarine system, which is a likely consequence of changes in ionic strength and the availability of iron and calcium.
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  • 34
    ISSN: 1573-515X
    Keywords: Chihuahuan desert ; desert ; desertification ; grassland ; nitrogen ; nutrient budgets ; phosphorus ; runoff
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Rainfall simulation experiments were performed in areas of semiarid grassland (Bouteloua eriopoda) and arid shrubland (Larrea tridentata) in the Chihuahuan desert of New Mexico. The objective was to compare the runoff of nitrogen (N) and phosphorus (P) from these habitats to assess whether losses of soil nutrients are associated with the invasion of grasslands by shrubs. Runoff losses from grass- and shrub-dominated plots were similar, and much less than from bare plots located in the shrubland. Weighted average concentrations of total dissolved N compounds in runoff were greatest in the grassland (1.72 mg/l) and lowest in bare plots in the shrubland (0.55 mg/l). More than half of the N transported in runoff was carried in dissolved organic compounds. In grassland and shrub plots, the total N loss was highly correlated to the total volume of discharge. We estimate that the total annual loss of N in runoff is 0.25 kg/ha/yr in grasslands and 0.43 kg/ha/yr in shrublands – consistent with the depletion of soil N during desertification of these habitats. Losses of P from both habitats were very small.
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  • 35
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    Journal of chemical crystallography 28 (1998), S. 69-72 
    ISSN: 1572-8854
    Keywords: Co(III) complex ; crystal structure ; kinetics ; steric effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallizes in the orthorhombic space group Pnma, with a = 7.9209(5), b = 9.818(1), c = 16.867(2) Å, and Z = 4. The structure was solved employing 1864 independent x-ray reflections with I〉2σ(I) by Patterson and difference Fourier techniques and refined by full-matrix least-squares to R = 0.036. The trans-[CO(NH3)4(NH2CH3)Cl](ClO4)2 molecule is on a crystallographic mirror plane. The cobalt ion is in an elongated octahedral coordination with four equatorial ammonia ligands [average Co–N distance equal to 1.966(2) Å], an axial methylamine [Co–N=1.965(3)Å], and an axial chlorine ion [Co–Cl=2.2771(9)Å]. Kinetic steric effects of the complex are interpreted in terms of structural results.
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  • 36
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    Journal of paleolimnology 20 (1998), S. 47-55 
    ISSN: 1573-0417
    Keywords: diatoms ; spatial variability ; canonical correspondence analysis ; lake eutrophication ; transfer functions ; phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Diatom analyses were undertaken of sediment cores covering a range of water depths in a small eutrophic lake (Lough Augher, Co. Tyrone, N. Ireland). The significance of between-core variability in diatom relative frequency stratigraphy was assessed by Canonical Correspondence Analysis (CCA) where the ordination axes were constrained to external environmental variables (sediment depth, core location coordinates, water depth, effective fetch, distance-from-shore and distance-from-inflow). After the removal of the effect of sediment age by partialling it out, the resultant first two axes from the partial-CCA were significantly correlated with water depth and distance-from-shore, indicating non-uniform diatom stratigraphies across the lake. Despite this variability, all cores show the same succession of species and, therefore, record the eutrophication of the lake. Diatom-inferred total phosphorus (DI-TP) was inferred for six cores using weighted averaging regression and calibration. Apart from considerable differences of DI-TP in surficial sediment samples, there was good between-core repeatability of DI-TP profiles. These data support the use of DI-TP for establishing background nutrient concentrations for lakes, and associated implications for lake restoration schemes using single cores. Comparisons of DI-TP profiles and total diatom accumulation rate data for the individual cores indicate that diatom production peaked prior to the maximum TP concentrations in the lake.
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  • 37
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    Journal of paleolimnology 20 (1998), S. 31-46 
    ISSN: 1573-0417
    Keywords: phosphorus ; Lake Okeechobee ; lead-210 dating ; eutrophication ; phosphorus loading
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Phosphorus accumulation rates in depositional zone sediments of Lake Okeechobee were determined in 11 mud-zone cores and two peat-zone cores dated by 210Pb. Although difficulties were encountered in interpreting 210Pb data from some sites, reliable dating of sediments from the mud zone of this shallow lake is possible. Sediment accumulation rates in this zone have increased during the present century by an average of about twofold, and accumulation of organic sediments in the lake during pre-settlement times apparently was much slower than during the past century. Concentrations of all forms of sedimentary P but especially nonapatite inorganic-P and organic-P also have increased since pre-settlement times and especially since about 1940. Annual P accumulation rates in the lake's sediments have increased about fourfold during the 1900s, with most of the increase occurring in the past 40–50 years. The recent accumulation rate of sedimentary P (past ~ 10 years) agrees within a factor of 1.5 with the net retention of P in the lake calculated from published input-output mass balances.
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  • 38
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    Molecular and cellular biochemistry 189 (1998), S. 201-205 
    ISSN: 1573-4919
    Keywords: brain ; P450 ; PB ; PROD ; induction ; inhibition ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract O-dealkylation of 7-pentoxyresorufin (PR) was studied in rat brain to characterise the functional activity specific for cytochrome P450 2B1/2B2 isoenzymes in brain microsomes. Brain microsomes catalyzed the O-dealkylation of PR in the presence of NADPH. Pretreatment with phenobarbital (PB; 80 mg/kg body wt, i.p.× 5 days) resulted in 3-4 fold induction of pentoxyresorufin-O-dealkylase (PROD) activity while 3-methylcholanthrene (MC; 30 mg/kg body wt, i.p. × 5 days) did not produce any significant increase in enzyme activity. Kinetic studies revealed that the rate of velocity (Vmax) for the O-dealkylation of PR was significantly increased to 2.9 times higher in brain microsomes isolated from PB pretreated rats. In vitro studies using metyrapone, an inhibitor of P450 2B1/2B2 catalyzed reactions and antibody for hepatic PB inducible P450s (P450 2B1/2B2) significantly inhibited the activity of PROD in cerebral microsomes prepared from PB pretreated animals. These studies suggest that PB inducible isoenzymes of P450, i.e. P450 2B1/2B2 specifically catalyze the O-dealkylation of PR in brain microsomes.
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  • 39
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    Biogeochemistry 42 (1998), S. 169-187 
    ISSN: 1573-515X
    Keywords: aridisols ; desertification ; erosion ; geostatistics ; Larrea tridentata ; nitrogen ; phosphorus ; Prosopis glandulosa ; soil heterogeneity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Geostatistical analyses show that the distribution of soil N, P and K is strongly associated with the presence of shrubs in desert habitats. Shrubs concentrate the biogeochemical cycle of these elements in ‘islands of fertility’ that are localized beneath their canopies, while adjacent barren, intershrub spaces are comparatively devoid of biotic activity. Both physical and biological processes are involved in the formation of shrub islands. Losses of semiarid grassland in favor of invading shrubs initiate these changes in the distribution of soil nutrients, which may promote the further invasion and persistence of shrubs and cause potential feedbacks between desertification and the Earth's climate system.
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  • 40
    ISSN: 1573-0662
    Keywords: peroxy radicals ; kinetics ; conjugateddienes ; biogenic VOC ; degradation mechanisms ; tropospheric ozone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The laser flash photolysis/UV absorption spectrometry technique has been used to investigate the kinetics of the peroxy radical permutation reactions (i.e. self and cross reactions) arising from the OH-initiated oxidation of isoprene (2-methyl-1,3-butadiene), and of the simpler, but related conjugated dienes, 1,3-butadiene and 2,3-dimethyl-1,3-butadiene. The results of the two simpler systems are analysed to provide values of the rate coefficients for the 6 peroxy radical permutation reactions of the three types of isomeric peroxy radical produced in each system (T = 298 K, P = 760 Torr). The rate coefficients are all significantly larger than values estimated previously by extrapolation of structure-reactivity relationships based on the kinetics of a limited dataset of simpler radicals containing similar structural features. The results are discussed in terms of trends in self and cross reaction reactivity of primary, secondary and tertiary peroxy radicals containing combinations of allyl, β-hydroxy and δ-hydroxy functionalities. Since the peroxy radicals formed in these systems are structurally very similar to those formed in the isoprene system, the kinetic parameters derived from the results of the simpler systems are used to assist the assignment of kinetic parameters to the 21 permutation reactions of the six types of isomeric peroxy radical generated in the isoprene system. Kinetic models describing the OH-initiated degradation of all three conjugated dienes to first generation products in the absence of NOx are recommended, which are also consistent with available end product studies. The model for isoprene is considered to be a further improvement on that suggested previously for its OH-initiated oxidation in the absence of NOx. The mechanism is further extended to include chemistry applicable to ‘NOx-present’ conditions, and calculated product yields are compared with those reported in the literature.
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  • 41
    ISSN: 1573-0662
    Keywords: hydroxyl radical ; nitrate radical ; ozone ; pinonaldehyde ; caronaldehyde ; sabinaketone ; kinetics
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    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Using a relative rate method, rate constants have been measured for the gas-phase reactions of OH and NO3 radicals with pinonaldehyde, caronaldehyde and sabinaketone at 296 ± 2 K. The OH radical reaction rate constants obtained are (in units of 10−12 cm3 molecule−1 s−1): pinonaldehyde, 48 ± 8; caronaldehyde, 48 ± 8; and sabinaketone, 5.1 ± 1.4, and the NO3 radical reaction rate constants are (in units of 10−14 cm3 molecule−1 s−1): pinonaldehyde, 2.0 ± 0.9; caronaldehyde, 2.5 ± 1.1; and sabinaketone, 0.036 ± 0.023, where the error limits include the estimated overall uncertainties in the rate constants for the reference compounds. Upper limits to the O3 reaction rate constants were also obtained, of 〈2 × 10−20 cm3 molecule−1 s−1 for pinonaldehyde and caronaldehyde, and 〈5 × 10−20 cm3 molecule−1 s−1 for sabinaketone. These reaction rate constants are combined with estimated ambient tropospheric concentrations of OH radicals, NO3 radicals and O3 to calculate tropospheric lifetimes and dominant transformation process(es) of these and other monoterpene reaction products.
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  • 42
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    Cell biology and toxicology 14 (1998), S. 167-174 
    ISSN: 1573-6822
    Keywords: acetylcholinesterase ; cycloheximide ; inhibition ; kinetics ; retina
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The kinetic parameters of inhibition of camel retinal acetylcholinesterase (AChE) activity by cycloheximide (CH) were investigated. For the control system, the Michaelis–Menten constant (K m)for the hydrolysis of acetylthiocholine iodide was found to be 0.076 mmol/L and the V max was 0.547 μmol/min per mg protein. In contrast, these parameters were decreased in the CH-treated systems. Dixon and Lineweaver–Burk plots, and their secondary replots, indicated that the inhibition was of the linear mixed type, which seems to be a combination of partial competitive and pure noncompetitive inhibition. The values of K′i(slope) and K I(intercept) were estimated to be 3.50 and 5.68 mmol/L, respectively. K i was greater than K′i, indicating that CH has a greater binding affinity for the peripheral site than the active site.
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  • 43
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    Environmental geology 30 (1997), S. 224-230 
    ISSN: 1432-0495
    Keywords: Key words Sediment ; Washington ; DC ; Pollution ; phosphorus ; nutrients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Sediments in the rivers and basins around Washington, DC, have high concentrations of phosphorus, which, based on geographic distributions, is largely derived from urban runoff and municipal sewage. Dissolved-particulate phosphate exchange reactions and biological uptake of dissolved phosphorus from the water column may be an added source of phosphorus to the sediments. Concentrations of total sedimentary phosphorus ranged from 24 to 56 μm P/g-dw, and were highest in areas near combined sewer outfalls. As a part of this study, sedimentary phosphorus was fractionated into Fe-P, Ca-P, Al-P, and organic phases using a selective-sequential leaching procedure. The distribution of the phases in all sediments analyzed follow the order , Fe-P〉Ca-P〉Al-P. Spatial variations in the amounts of phosphorus in the different phases is related to the sources of phosphorus to the area. The proportions of occluded Al-P and organic P are 10–20% of the total P, respectively. This suggests that phosphorus from natural sources is small compared to anthropogenic inputs in this area. The high leachable Fe-P and Ca-P in these sediments might contribute a substantial amount of P to the water column under conditions of remobilization.
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  • 44
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    European journal of clinical pharmacology 52 (1997), S. 505-506 
    ISSN: 1432-1041
    Keywords: Key words Ibuprofen; effervescent tablets ; kinetics ; bioavailability
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    Topics: Chemistry and Pharmacology , Medicine
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  • 45
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    Biogeochemistry 37 (1997), S. 237-252 
    ISSN: 1573-515X
    Keywords: freshwater ; limitation ; marine ; nitrogen ; phosphorus ; ratio ; stoichiometry ; trace elements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Nitrogen supply is often assumed to limitmarine primary production. A global analysis of totalnitrogen (N) to phosphorus (P) molar ratios shows thattotal N:P is low (〈16:1) in some estuarine andcoastal ecosystems, but up to 100:1 in open oceans.This implies that elements other than N may limitmarine production, except in human impacted, estuarineor coastal ecosystems. This pattern may reconcileconflicting enrichment studies, because N additionfrequently increases phytoplankton growth where totalN:P is expected to be low, but P, Fe, or Si augmentphytoplankton growth in waters where total N:P ishigh. Comparison of total N:P stoichiometry betweenmarine and freshwaters yields a model of the form ofthe aquatic N:P cycle.
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  • 46
    ISSN: 1573-515X
    Keywords: carbon ; nitrogen ; Ohio River ; phosphorus ; Red field ratios ; dissolved organic matter ; rivers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract A 12-month study was conducted to measure the concentrations ofdissolved organic matter (DOC, TDN, TDP) in four sites within a119 km long reach of the Ohio River, near Louisville, KY. In thisstudy we test whether specific geomorphological and biologicalfactors influenced variations in dissolved organic matter.Concentrations of DOC in the river averaged ≈1200μmol/L, and varied by nearly two orders of magnitudeseasonally (mean DOC during base flow ≈620 μmol/L).Peak periods for DOC at all sites were during April–May. Thesite nearest a navigation dam (deeper, lower current velocities)had significantly lower concentrations of TDN and greater C:Nratios than upstream sites. The largest tributary entering thisreach (Kentucky River) had no significant effect on levels of DOMin the main river, despite having significantly greaterconcentrations of TDN and lower levels of DOC during most monthsof the year. Concentrations of DOC, TDN, and TDP were notsignificantly different in littoral and pelagic habitats at allsites studied, suggesting little floodplain influence on DOM inthis constricted-channel section of the Ohio River. C:N ratios ofDOM in the Ohio were significantly different among seasons; C:Nexceeded or equaled Redfield ratios in summer and fall (6 to 10),but were below Redfield (1.8 to 3.0) during winter and spring.Regression models suggest that total phytoplankton densities andflow conditions are the two most important factors regulating DOMin this very large river.
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  • 47
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    Biogeochemistry 37 (1997), S. 63-75 
    ISSN: 1573-515X
    Keywords: nutrient limitation ; soil development ; nitrogen ; phosphorus ; chronosequence ; Hawai'i
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Walker & Syers (1976) proposed a conceptual model that describesthe pattern and regulation of soil nutrient pools and availability during long-term soil and ecosystem development. Their model implies that plantproduction generally should be limited by N on young soils and by P on oldsoils; N and P supply should more or less equilibrate onintermediate-aged soils. We tested the application of this model to nutrientlimitation, using a well characterized substrate age sequence in Hawaiianmontane rain forest. Earlier experiments had evaluated nutrient limitationin forests on a young (300 y) and an old (4,100,000 y) substrate on the samedevelopmental sequence; N alone limited tree growth on the youngsubstrate, while P alone did so on the old one. An additional fertilizerexperiment based on replicated treatments with N, P, and all othernutrients combined, applied in individually and in all factorialcombinations, was established in an intermediate-aged site in theLaupahoehoe Forest Reserve, Hawaii. Here, diameter increments of thedominant tree Metrosideros polymorpha increased slightly with Nadditions, and nearly doubled when N and P were added together.Additions of elements other than N and P had no significant effecton growth. These results show that N and P had equilibrated (relativeto plant requirements) in the intermediate aged site. Together withthe earlier experiments, these results suggest that the Walker and Syersmodel provides a useful starting point for explaining the nature anddistribution of nutrient limitation in forest ecosystems.
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  • 48
    ISSN: 1573-6822
    Keywords: diabetes ; rat ; cell culture ; antidepressant ; kinetics ; biotransformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Biotransformation of amitriptyline (AMI) was studied at different intervals in freshly isolated hepatocytes from healthy or streptozocin-induced diabetic rats in order to investigate the influence of the diabetic state. Levels of free and conjugated AMI, demethylated and hydroxylated metabolites, were assessed by HPLC analysis. In hepatocytes isolated from diabetic rats, AMI was less completely metabolized and the demethylation reaction became more important than in non-diabetic rat hepatocytes. Although the proportions of hydroxylated metabolites decreased in diabetic rats, it always remained predominant. Furthermore, glucuronidation of metabolites was greater, especially for (Z)-10-hydroxynortriptyline in diabetic animals.
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  • 49
    ISSN: 1573-0778
    Keywords: hypoxia ; recombinant protein ; animal cells ; erythropoietin ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Expression of specific genes is a strategy of animal cells for adaptation to oxygen deficiency and the mechanism underlying the hypoxic activation of gene expression may be useful for efficient production of recombinant proteins by animal cells, because oxygen is a limiting factor in animal cell cultures. We prepared an animal cell line harboring the plasmid in which expression of a reporter gene, β-galactosidase, is controlled by an enhancer responsible for the hypoxic activation of gene transcription. The purpose of this paper is to understand this hypoxic production of recombinant proteins quantitatively by a mathematical model originally developed based on the following hypotheses; 1 lacZ (the reporter gene) is transcribed after HIF-1 protein complex is bound to the hypoxic enhancer, 2. β-galactosidase synthesis rate is limited at the transcription of lacZ, 3. HIF-1 is an inactive form under a normal oxygen concentration, 4. Oxygen works as a repressor in the synthesis of HIF-1 protein, 5. Both β-galactosidase and HIF-1 are decomposed according to the first order reaction. The effects of hypoxic duration as well as oxygen concentration on the β-galactosidase production were successfully predicated by the model.
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  • 50
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    Pure and applied geophysics 147 (1996), S. 367-375 
    ISSN: 1420-9136
    Keywords: Induced seismicity ; kinetics ; rock fracture ; rockburst ; earthquake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Powerful seismic events, such as earthquakes and rockbursts, are caused by the accumulation of energy in rocks and loss of rock mass stability. Usually methods of their forecasting are based on the registration of anomalous behavior of geophysical fields. However an efficiency of this approach is low. The present paper proposes a kinetic approach to the description of rock fracture process, which can be used for the forecasting of seismic events and an investigation of structure and energy distributions in rock. 3-D and 1-D kinetic equations describing a process of cluster formation in rock were obtained. The equations are invariant to deformation conditions and to the scale level of events. They showed a good agreement with the results of field observations and laboratory experiments. It was also shown that these equations well describe the processes of earthquake, rockburst and rock sample failure preparation. Catalogues of rockbursts in mines were analyzed with the use of the kinetic equations to find out evidence of induced seismic events. The proposed approach makes it possible to reveal trends in rock behavior and thus predict the rock failure at different scale levels.
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  • 51
    ISSN: 1432-1041
    Keywords: Key words Diphemanil methylsulphate ; Neonate; antimuscarinic agent ; kinetics
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    Topics: Chemistry and Pharmacology , Medicine
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  • 52
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    Molecular and cellular biochemistry 156 (1996), S. 93-100 
    ISSN: 1573-4919
    Keywords: rat liver nucleus ; oxalate binding protein ; histone III ; purification ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The rat liver nuclear oxalate binding protein was isolated, purified by anion and cation exchange column chromatography using Diethyl Amino Ethyl Sephadex, Carboxy Methyl Cellulose and Carboxy Methyl Sephadex C-50 ion exchangers. The purified oxalate binding protein was found to be H1B of H1 fraction of histories. Kinetic analysis of oxalate binding showed the presence of two affinity sites, one with Kd of 133.5 nM and Bmax of 40 pmoles and another with Kd of 262.5 nM and Bmax of 210 pmoles. The optimal oxalate binding was at pH 4.2 and at 28°C. The oxalate binding was specific and reversible and not due to ionic charge interaction. The IC50 of other dicarboxylates was higher than that of oxalate. EGTA had no effect on oxalate binding but di- and tri-carboxylate carrier inhibitors and thiol modifying agents significantly lowered the binding activity. Oxalate binding to histones was significantly reduced in the presence of DNA or nucleotides, but RNA had no effect. ATP completely inhibited the oxalate binding activity at 1 mM concentration. Different tissues exhibited oxalate binding showing ubiquitous nature. Calf thymus H1 showed maximal binding similar to liver histones.
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  • 53
    ISSN: 1573-4919
    Keywords: acetylcholinesterase ; kinetics ; inhibition ; methotrexate ; anticancer drugs ; human erythrocyte
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract This work addresses the kinetic analysis of the interaction of methotrexate (MTX) with human erythrocyte membrane-bound acetylcholinesterase (AChE, EC 3.1. 1.7). It was found that the MTX effect was independent of time of incubation with AChE before the addition of substrate which proves its reversible action. The IC50 was determined, by three methods, to be 0.73 mM. The Michaelis-Menten constant (Ks) for the hydrolysis of acetylthiocholine iodide (ASCh) by AChE was 0.13 mM in the control system, a value decreased by 30–61% in the MTX treated systems. The Vmax was 1.27μtmole/min/mg protein for the control system while it was decreased by 44–77% in the MTX treated systems. The Linexveaver-Buck plot, Dixon plot, and their secondary replots indicated that the nature of the inhibition was of the linear mixed type, i.e. uncompetitive and noncompetitive. The values of Ki(slope) and KI(tntecept) were estimated as 1.67 and 0.34 mM, respectively.
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  • 54
    ISSN: 1573-0778
    Keywords: hybridomas ; serum-free medium ; monoclonal antibodies ; reactor series ; kinetics ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Hybridomas were cultured under steady-state conditions in a series of two continuous stirred-tank reactors (CSTRs), using a serum-free medium. The substrate not completely converted in the first CSTR, was transported with the cells to the second one and very low growth rates, high death rates, and lysis of viable cells were observed in this second CSTR. These conditions are hardly accessible in a single vessel, because such experiments would be extremely time-consuming and unstable due to a low viability. In contrast to what is often observed in literature, kinetic parameters could thus be derived without the neccessity for extrapolation to lower growth rates. Good agreement with literature averages for other hybridomas was found. Furthermore, showing that the reactor series is a valuable research tool for kinetic studies under extreme conditions, the possibility to observe cell death under stable and defined steady-state conditions offers interesting opportunities to investigate apoptosis and necrosis. Additionally, a model was developed that describes hybridoma growth and monoclonal antibody production in the bioreactor cascade on the basis of glutamine metabolism. Good agreement between the model and the experiments was found.
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  • 55
    ISSN: 1573-515X
    Keywords: lacustrine sediment ; organic matter ; sedimentation rates ; recycling ; burial ; carbon ; nitrogen ; silicon ; phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The areal distribution of organic C contents, δ13C values, total N and P and biogenic Si contents in surficial sediments were used to study the distribution, origin and diagenetic transformations of sedimented biogenic debris in the eutrophic subalpine Lake Bled (Slovenia), which for most of the yearhas an anoxic hypolimnion. The influence of an allochthonous input, restricted to the western basin, was clearly traced by higher organic C and total N and P contents, higher δ13C values, and higher sedimentation rate in comparison to the eastern basin. The low δ13C values of sedimentary organic matter in the major part of the lake, lower than the δ13C values of different types of organic matter, suggest that this sedimentary organic matter is most probably the product of a microbial community and not a residue of primary production. The temporal variation of benthic diffusive fluxes of NH4, Si and PO4, derived from modelling the pore water profiles, was related to sedimentation of phytoplanktonic blooms, while the PO4 fluxes were also dependent on changing redox conditions at the sediment-water interface in the period of the winter-spring overtum. The removal of PO4 in pore waters is probably due to the adsorption of phosphate and precipitation of apatite and vivianite. The budget of C, N and P at the sediment-water interface revealed a high recycling efficiency (〉70%), also confirmed by the rather uniform (or only slightly decreasing) vertical profiles of organic C, total N and P in sediment cores and C/N and C/P ratios. The percentage of biogenic Si recycling is low (〈10%), suggesting its removal in sediments.
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  • 56
    ISSN: 1573-515X
    Keywords: continental shelf ; estuaries ; mass balance ; nitrogen ; North Atlantic ; nutrient budget ; phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Five large rivers that discharge on the western North Atlantic continental shelf carry about 45% of the nitrogen (N) and 70% of the phosphorus (P) that others estimate to be the total flux of these elements from the entire North Atlantic watershed, including North, Central and South America, Europe, and Northwest Africa. We estimate that 61 · 109 moles y−1 of N and 20 · 109 moles y−1 of P from the large rivers are buried with sediments in their deltas, and that an equal amount of N and P from the large rivers is lost to the shelf through burial of river sediments that are deposited directly on the continental slope. The effective transport of active N and P from land to the shelf through the very large rivers is thus reduced to 292 · 109 moles y−1 of N and 13 · 109 moles y−1 of P. The remaining riverine fluxes from land must pass through estuaries. An analysis of annual total N and total P budgets for various estuaries around the North Atlantic revealed that the net fractional transport of these nutrients through estuaries to the continental shelf is inversely correlated with the log mean residence time of water in the system. This is consistent with numerous observations of nutrient retention and loss in temperate lakes. Denitrification is the major process responsible for removing N in most estuaries, and the fraction of total N input that is denitrified appears to be directly proportional to the log mean water residence time. In general, we estimate that estuarine processes retain and remove 30–65% of the total N and 10–55% of the total P that would otherwise pass into the coastal ocean. The resulting transport through estuaries to the shelf amounts to 172–335 · 109 moles y−1 of N and 11–19 · 109 moles y−1 of P. These values are similar to the effective contribution from the large rivers that discharge directly on the shelf. For the North Atlantic shelf as a whole, N fluxes from major rivers and estuaries exceed atmospheric deposition by a factor of 3.5–4.7, but this varies widely among regions of the shelf. For example, on the U.S. Atlantic shelf and on the northwest European shelf, atmospheric deposition of N may exceed estuarine exports. Denitrification in shelf sediments exceeds the combined N input from land and atmosphere by a factor of 1.4–2.2. This deficit must be met by a flux of N from the deeper ocean. Burial of organic matter fixed on the shelf removes only a small fraction of the total N and P input (2–12% of N from land and atmosphere; 1–17% of P), but it may be a significant loss for P in the North Sea and some other regions. The removal of N and P in fisheries landings is very small. The gross exchange of N and P between the shelf and the open ocean is much larger than inputs from land and, for the North Atlantic shelf as a whole, it may be much larger than the N and P removed through denitrification, burial, and fisheries. Overall, the North Atlantic continental shelf appears to remove some 700–950· 109 moles of N each year from the deep ocean and to transport somewhere between 18 and 30 · 109 moles of P to the open sea. If the N and P associated with riverine sediments deposited on the continental slope are included in the total balance, the net flux of N to the shelf is reduced by 60 · 109 moles y−1 and the P flux to the ocean is increased by 20 · 109 moles y−1. These conclusions are quite tentative, however, because of large uncertainties in our estimates of some important terms in the shelf mass balance.
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  • 57
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    Biogeochemistry 35 (1996), S. 419-432 
    ISSN: 1573-515X
    Keywords: phosphorus ; sequential extraction ; soils ; riparian forest ; seasonal pattern
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract This study addresses the temporal distribution of forms of phosphorus in the soil of a temporarily flooded riparian forest of the valley of the river Garonne (Southwest of France). A sequential extraction for forms of phosphorus of increasing chemical stability was used. During the study period (13 months), the forest was flooded a few days during March and May. In winter, resin-Pi concentration was high (26 μg g−1) in comparison to spring values (〈9 μg g−1). NaHCO3-Po, NaHCO3-Pi or NaOH-Pi concentrations increased during winter (up to 74, 124 and 78 μg g−1 respectively) and decreased significantly during spring (32, 44 and 32 μg g−1 respectively). This pattern was attributed to simultaneous mineralization and plant uptake during the growing season and to the flood events (erosional processes and P-release). During summer and fall, resin-Pi concentration increased significantly (up to 26 μg g−1 in October). NaHCO3-Po concentrations remained low during spring and summer (〈33 μg g−1), and increased significantly in fall (〉45 μg g−1 NaHCO3-Pi or NaOH-Pi increased in late spring or summer (90 μg g−1 and 68 μg g−1 respectively). Increasing concentrations of the labile forms during late spring or summer were ascribed to the warm temperature and soil dryness that limited plant growth. HCl-Pi increased regularly after the floods (174 μg g−1 before the flood events to 254 μg g−1 after the floods). Residual P presented a similar pattern i.e. 214 μg g−1 and 279 μg g−1 respectively before and after the flood events. This pattern was attributed to a progressive incorporation of flood deposits to the soil.
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  • 58
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    Journal of atmospheric chemistry 24 (1996), S. 23-37 
    ISSN: 1573-0662
    Keywords: hydroxyl radical ; dimethylsulfoxide ; kinetics ; sulfur cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We have employed a pulsed laser photolysis-pulsed laser induced fluorescence technique to study the kinetics and mechanism of the reaction of OH with dimethylsulfoxide and its deuterated analogue. A rate coefficient of (1.0±0.3)×10-10 cm3 molecule-1 s-1 was obtained ar room temperature. The rate coefficient was independent of pressure over the range 25–700 Torr, showed no dependence on the nature of the buffer gas and showed no kinetic isotope effect. A limited study of the temperature dependence indicated that the reaction displays a negative activation energy. The gas phase ultraviolet absorption spectrum was obtained at room temperature and showed a strong absorption feature in the far ultraviolet. The absolute absorption cross-section at 205 nm, the absorption peak, is (1.0±0.3)×10-17 cm2, where the large uncertainty results from experimental difficulties associated with the low vapor pressure and ‘stickiness’ of DMSO.
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  • 59
    ISSN: 1573-515X
    Keywords: fertilizer study ; Hawaii ; montane tropical forest ; nitrogen ; phosphorus ; primary succession
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We applied fertilizers in a 23complete factorial design to determine the effects of nutrient amendments on plant growth in Hawaiian montane forests growing on two different volcanic substrates: ‘a‘ā and pāhoehoe lava. Both sites were about 140 years old and their overstories were nearly monospecific stands of Metrosideros polymorpha. Fertilizer applications included N, P, a mixture of essential macro- and micronutrients excepting P and N, and all combinations thereof in each of four blocks. Additions of nutrients other than N or P had no significant effects on measured plant-growth variables. In contrast, additions of either N or P significantly increased tree height growth, diameter increments, biomass growth, and height growth of the understory fern Dicranopteris linearis in both sites. The effect of N was greater than that of P. Greatest growth rates occurred in plots receiving both N and P, and signficant N*P interactions occurred in several cases, suggesting a synergistic effect between these two elements. Plant growth on these young, poorly weathered, basaltic lavas is colimited by N and P availability. Growth in a similar-aged stand growing on a mixture of volcanic ash and cinders is N but not P limited, indicating that the texture of the parent material influences nutrient-availability patterns during early primary succession.
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  • 60
    ISSN: 1573-515X
    Keywords: anthropogenic ; atmospheric deposition ; eutrophication ; fertilizer ; nitrogen ; nitrogen budget ; nitrogen fixation ; N:P ratio ; phosphorus ; pristine ; rivers ; temperate ; tropical
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We present estimates of total nitrogen and total phosphorus fluxes in rivers to the North Atlantic Ocean from 14 regions in North America, South America, Europe, and Africa which collectively comprise the drainage basins to the North Atlantic. The Amazon basin dominates the overall phosphorus flux and has the highest phosphorus flux per area. The total nitrogen flux from the Amazon is also large, contributing 3.3 Tg yr−1 out of a total for the entire North Atlantic region of 13.1 Tg yr−1 . On a per area basis, however, the largest nitrogen fluxes are found in the highly disturbed watersheds around the North Sea, in northwestern Europe, and in the northeastern U.S., all of which have riverine nitrogen fluxes greater than 1,000 kg N km−2 yr−1. Non-point sources of nitrogen dominate riverine fluxes to the coast in all regions. River fluxes of total nitrogen from the temperate regions of the North Atlantic basin are correlated with population density, as has been observed previously for fluxes of nitrate in the world's major rivers. However, more striking is a strong linear correlation between river fluxes of total nitrogen and the sum of anthropogenically-derived nitrogen inputs to the temperate regions (fertilizer application, human-induced increases in atmospheric deposition of oxidized forms of nitrogen, fixation by leguminous crops, and the import/export of nitrogen in agricultural products). On average, regional nitrogen fluxes in rivers are only 25% of these anthropogenically derived nitrogen inputs. Denitrification in wetlands and aquatic ecosystems is probably the dominant sink, with storage in forests perhaps also of importance. Storage of nitrogen in groundwater, although of importance in some localities, is a very small sink for nitrogen inputs in all regions. Agricultural sources of nitrogen dominate inputs in many regions, particularly the Mississippi basin and the North Sea drainages. Deposition of oxidized nitrogen, primarily of industrial origin, is the major control over river nitrogen export in some regions such as the northeastern U.S. Using data from relatively pristine areas as an index of change, we estimate that riverine nitrogen fluxes in many of the temperate regions have increased from pre-industrial times by 2 to 20 fold, although some regions such as northern Canada are relatively unchanged. Fluxes from the most disturbed region, the North Sea drainages, have increased by 6 to 20 fold. Fluxes from the Amazon basin are also at least 2 to 5 fold greater than estimated fluxes from undisturbed temperate-zone regions, despite low population density and low inputs of anthropogenic nitrogen to the region. This suggests that natural riverine nitrogen fluxes in the tropics may be significantly greater than in the temperate zone. However, deforestation may be contributing to the tropical fluxes. In either case, projected increases in fertilizer use and atmospheric deposition in the coming decades are likely to cause dramatic increases in nitrogen loading to many tropical river systems.
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  • 61
    ISSN: 1573-2983
    Keywords: Zinc ; copper ; manganese ; iron ; lead ; cadmium ; nickel ; phosphorus ; limestone ; fertilizer ; sewage sludge compost
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Medicine
    Notes: Abstract Previous research has demonstrated that many urban soils are enriched in Pb, Cd and Zn. Culture of vegetable crops in these soils could allow transfer of potentially toxic metals to foods. ‘Tanya’ lettuce (Lactuca sativa L.) was grown in pots of five urban garden soils and one control agricultural soil to assess the effect of urban-soil metal enrichment, and the effect of soil amendments, on heavy metal uptake by garden vegetables. The amendments included NPK fertilizer, limestone, Ca(H2PO4)2, and two rates of limed sewage sludge compost. Soil Cd ranged from 0.08 to 9.6 mg kg−1; soil Zn from 38 to 3490 mg kg−1; and soil Pb from 12 to 5210 mg kg−1. Lettuce yield on the urban garden soils was as great as or greater than that on the control soil. Lettuce Cd, Zn and Pb concentrations increased from 0.65, 23, and 2.2 mg kg−1 dry matter in the control soil to as high as 3.53, 422 and 37.0 mg kg−1 on the metal-rich urban garden soils. Adding limestone or limed sewage sludge compost raised soil pH and significantly reduced lettuce Cd and Zn, while phosphate fertilizer lowered soil pH and had little effect on Zn but increased Cd concentration in lettuce. Urban garden soils caused a significant increase in lettuce leaf Pb concentration, especially on the highest Pb soil. Adding NPK fertilizer, phosphate, or sludge compost to two high Pb soils lowered lettuce Pb concentration, but adding limestone generally did not. On normally fertilized soils, Pb uptake by lettuce was not exceptionally high until soil Pb substantially exceeded 500 mg kg−1. Comparing garden vegetables and soil as potential sources of Pb risk to children, it is clear that the risk is greater through ingestion of soil or dust than through ingestion of garden vegetables grown on the soil. Urban dwellers should obtain soil metal analyses before selecting garden locations to reduce Pb risk to their children.
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  • 62
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    Bulletin of experimental biology and medicine 121 (1996), S. 329-330 
    ISSN: 1573-8221
    Keywords: erythropoiesis ; kinetics ; cell death
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The fundamental patterns of influence of the localization of erythroid cell death on cell kinetics are defined with the aid of mathematical modeling. It is established that the kinetic picture is mainly dictated by the region where the death is localized.
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  • 63
    ISSN: 1572-8854
    Keywords: Octahedral ; phosphorus ; chloride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound [P(tpp)Cl2]+Cl− crystallizes in the space group P21/n witha=10.701(2),b=24.860(2),c=14.799(2), β=94.24(2)°,Z=4. The phosphorus atom has an octahedral coordination geometry formed by the four nitrogen atoms (Np) of the porphyrinato group and the two chloride ions. The average phosphorus-chloride distance is 2.150(1) Å, with phosphorus situated 0.006 Å below the porphyrin ring.
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  • 64
    ISSN: 1573-0417
    Keywords: diatoms ; eutrophication ; lake management ; paleolimnology ; British Columbia ; lakes ; phosphorus ; training sets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Eighteen lakes were added to a published training set of 46 British Columbia (BC) lakes in order to expand the original range of total phosphorus (TP) concentrations. Canonical correspondence analysis (CCA) was used to analyze the relationship between diatom assemblages and environmental variables. Specific conductivity and [TP] each explained significant (P≤0.05) directions of variance in the distribution of the diatoms. The relationship between diatom assemblages and [TP] was sufficiently strong to warrant the development of a weighted-averaging (WA) regression and calibration model that can be used to infer past trophic status from fossil diatom assemblages. The relationship between observed and inferred [TP] was not improved by the addition of more eutrophic lakes, however the [TP] range and the number of taxa used in the transfer function are now superior to the original model. Diatom species assemblages changed very little in lakes with TP concentrations greater than 85 µg 1−1, so we document the development of a model containing lakes with TP≤85 µg 1−1. The updated model uses 59 training lakes and covers a range of species optima from 6 to 41.9 µg 1−1 TP, and a total of 150 diatom taxa. The updated inference model provided a more realistic reconstruction of the anthropogenic history of a highly eutrophic BC lake. The model can now be used to infer past nutrient conditions in other BC lakes in order to assess changes in trophic status.
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  • 65
    ISSN: 1573-1421
    Keywords: calcite ; precipitation ; dissolution ; kinetics ; reaction mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Calcite dissolution rates were measured using a free-drift technique at 25°C, 1 atm total pressure, and various $$P_{CO_2 } $$ in deionized water. The data were corrected for gas phase disequilibrium and fitted to a kinetic expression derived by coupling the mechanistic models of Plummeret al. (1987a) and Chouet al. (1989) to the surface complexation model of Van Cappellenet al. (1993). Corrected dissolution and precipitation rate measurements from previous investigations were combined to our data set and fitted to the same expression. The following reactions provide an adequate description of the calcite dissolution and precipitation mechanism in dilute solutions: for which the overall reaction rate is given by where 〉i are the densities of surface complexes (mol/m2),a i are the activities of dissolved species and,k i are the rate constants corresponding to the above reactions. This rate equation satisfies the principle of microscopic reversibility and applies to both dissolution and precipitation reactions over a wide range of $$P_{CO_2 } $$ , pH and saturation states. The rate constants obtained from fitting the data set to Equation (3) are compatible with values reported by Plummeret al. and Chouet al., as well as yielding a very good estimate of the thermodynamic solubility constant of calcite, K 0 sp .
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  • 66
    ISSN: 1573-4919
    Keywords: acetylcholinesterase ; optimization ; kinetics ; venom ; turnover number
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Acetylcholinesterase (AChE) was investigated inWalterinnesia aegyptia venom and characterized with respect to its kinetic properties. It was found that 4.0 ug of crude venom protein and an incubation time of 4.0 min were suitable conditions for linearity of AChE activity at 25°C. The optimum strength of the sodium phosphate buffer was 0.05 M, and the optimum pH was 7.75. The optimum temperature was 30°C. The activation energy and the heat of activation were observed to be 6510 and 5922 cal/mole. The AChE was specific for acetylthiocholine but it did not hydrolyse butyrylthiocholine. The optimum substrate concentration was 3.0 mM but at higher substrate concentrations, the AChE activity declined. The ASCh concentration ranges for different orders of the reactions were determined and kinetic parameters (Km, Vmax, kcat, and ksp) were established at each order of the reaction.
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  • 67
    ISSN: 1573-515X
    Keywords: budget ; carbon ; mass balance ; Narragansett Bay ; nitrogen ; nutrients ; phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Narragansett Bay is a relatively well-mixed, high salinity coastal embayment and estuary complex in southern New England (USA). Much of the shoreline is urban and the watershed is densely developed. We have combined our data on C, N, and P inputs to this system, on C, N, and P accumulation in the sediments, and on denitrification with extensive work by others to develop approximate annual mass balances for these elements. The results show that primary production within the bay is the major source of organic carbon (4 times greater than other sources), that land drainage and upstream sewage and fertilizer are the major sources of N, and that landward flowing bottom water from offshore may be a major source of dissolved inorganic phosphorus. Most of the nutrients entering the bay arrive in dissolved inorganic form, though DON is a significant component of the N carried by the rivers. About 40% of the DIN in the rivers is in the form of ammonia. Sedimentation rates are low in most of Narragansett Bay, and it appears that less than 20% of the total annual input of each of these elements is retained within the system. A very small amount of C, N, and P is removed in fisheries landings, denitrification in the sediments removes perhaps 10–25% of the N input, and most of the carbon fixed in the system is respired within it. Stoichiometric calculations suggest that some 10–20% of the organic matter formed in the bay is exported to offshore and that Narragansett Bay is an autotrophic system. Most of the N and P that enters the bay is, however, exported to offshore waters in dissolved inorganic form. This assessment of the overall biogeochemical behavior of C, N, and P in the bay is consistent with more rigorously constrained mass balances obtained using large living models or mesocosms of the bay at the Marine Ecosystem Research Laboratory (MERL).
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  • 68
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    Biogeochemistry 29 (1995), S. 223-235 
    ISSN: 1573-515X
    Keywords: chronosequence ; montane tropical forest ; nitrogen ; nutrient limitation ; phosphorus ; productivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We tested the hypothesis that P was the nutrient limiting net primary production of a nativeMetrosideros polymorpha forest on a highly weathered montane tropical soil in Hawaii. A factorial experiment used all combinations of three fertilizer treatments: nitrogen (N), phosphorus (P) and a mix of other essential nutrients (OE), consisting primarily of mineral derived cations and excluding N and P. P addition, but not N or OE, increased leaf area index within 12 months, foliar P concentration measured at 18 months, and stem diameter increment within 18 months. Stem growth at 18 months was even greater when trees fertilized with P also received the OE treatment. N and P additions increased leaf litterfall and N and P in combination further increased litterfall. The sequence of responses suggests that increased available P promoted an increase in photosynthetic area which led to increased wood production. P was the essential element most limiting to primary production on old volcanic soil in contrast to the N limitation found on young volcanic soils.
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  • 69
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    Aquatic geochemistry 1 (1995), S. 399-426 
    ISSN: 1573-1421
    Keywords: manganese reduction ; manganese oxidation ; organic matter oxidation ; kinetics ; bacteria ; alkalinity ; lake chemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The redox processes regulating transport of Mn in the water column of a eutrophic, dimictic lake (Lake Norrviken, Sweden) are interpreted based on a one-dimensional diffusion-reaction model for Mn(II). It is found that rates and rate constants for oxidation and reduction vary greatly with depth and also with time during the season of stratification. Calculated rates show that Mn(II) oxidation and reduction generally occur in narrow depth intervals (25–50 cm). This is in good agreement with measured profiles of particulate Mn (MnO x ). Maximum oxidation rate constants (assuming first order kinetics) at each date are in the first half of the season 〈1 d−1, but then increases to a rather constant value of about 25 d−1. These high rate constants are indicative of microbiological involvement in the Mn(II) oxidation. This is further evidenced by SEM-EDS analysis showing Mn enriched particles morphologically similar toMetallogenium. Reductive dissolution of Mn oxides occurs mainly in the zone just below the zone of maximum oxidation rate. The release of Mn(II) is accompanied by production of alkalinity and ΣCO2. The relation between production rates of Mn(II) and alkalinity indicates that Mn oxides act as terminal electron acceptors in the bacterially mediated oxidation of organic matter. However, the ΔMn2+/ΔΣCO2 ratio is significantly lower than what is expected from this process. It is suggested that the Mn reduction is coupled to fermentation. Close coexistence of Mn reduction and oxidation at high rates, such as found in the water column of this lake, facilitates rapid and continuous regeneration of reducible Mn oxides. This gives rise to a quantitatively important mechanism of organic matter oxidation in the water column.
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  • 70
    ISSN: 1573-0417
    Keywords: Great Basin ; climatic variations ; productivity ; organic matter ; nitrogen ; phosphorus ; hardwater lake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Sediment cores from the shallow and deep basins of Pyramid Lake, Nevada, revealed variations in composition with depth reflecting changes in lake level, river inflow, and lake productivity. Recent sediments from the period of historical record indicate: (1) CaCO3 and organic content of sediment in the shallow basin decrease at lower lake level, (2) CaCO3 content of deep basin sediments increases when lake level decreases rapidly, and (3) the inorganic P content of sediments increases with decreasing lake volume. Variations in sediment composition also indicate several periods for which productivity in Pyramid Lake may have been elevated over the past 1000 years. Our data provide strong evidence for increased productivity during the first half of the 20th Century, although the typical pattern for cultural eutrophication was not observed. The organic content of sediments also suggests periods of increased productivity in the lake prior to the discovery and development of the region by white settlers. Indeed, a broad peak in organic fractions during the 1800's originates as an increase starting around 1600. However, periods of changing organic content of sediments also correspond to periods when inflow to the lake was probably at extremes (e.g. drought or flood) indicating that fluctuations in river inflow may be an important factor affecting sediment composition in Pyramid Lake.
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  • 71
    ISSN: 1432-0495
    Keywords: Nitrogen ; phosphorus ; Precipitation collector ; Nutrients rates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The contribution of nitrogen and phosphorus due to precipitation constitutes the second most important route after superficial runoff. The sampling carried out during a two-year period by means of a precipitation collector allows us to determine the contribution of this route both qualitatively and quantitatively. Nitrogen is mainly supplied in an inorganic form, while phosphorus is principally supplied as orthophosphate. During the period of this study (March 1986–February 1988) it was found that in the Santillana Reservoir Watershed the level of nitrogen supplied by precipitation constitutes an average of 4.87% and the level of phosphorus constitutes 8.01%. The contribution of nitrogen varies in inverse ratio to precipitation and the contribution of phosphorus varies in direct ratio.
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  • 72
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    Molecular and cellular biochemistry 131 (1994), S. 43-47 
    ISSN: 1573-4919
    Keywords: angiotensinogen ; kinetics ; recombinant protein ; renin ; species specificity ; transgenic mouse
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The renin-angiotensin system (RAS) is the most important regulator of electrolyte homeostasis and blood pressure. Our recently generated transgenic mice carrying either the human renin (hREN) or human angiotensinogen (hANG) genes did not develop hypertension but dual gene strains obtained by cross-mating separate lines of mice exhibited a chronically sustained increase in blood pressure, suggesting the presence of species-specific reactivity between renin and angiotensinogen. In order to examine this specificity, the present study was designed to perform a strictly comparative study on hydrolysis of hANG by hREN and mouse submandibular renin (mREN)in vitro by using pure proteins. The recombinant hANG (rhANG) and the synthetic human-type tridecapeptide (hTDP), Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu-Val-Ile-His, corresponding to the N-terminal sequences of hANG, were used to determine the species specificity of recombinant hREN (rhREN) and mREN. While hTDP was cleaved by both rhREN with similar Km and with the same order of kcat, rhANG was cleaved by mREN with 16.7-fold higher Km and with 28.2-fold lower kcat than by rhREN. These results showed that kcat/Km value of mREN for rhANG was 468-fold lower than that for rhREN acting on rhANG.
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  • 73
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    Molecular and cellular biochemistry 138 (1994), S. 33-37 
    ISSN: 1573-4919
    Keywords: poly(ADP-ribose) polymerase ; structure ; chemistry ; kinetics ; automodification ; mechanism(s)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract In this minireview, we summarize recent advances on the enzymology of ADP-ribose polymer synthesis. First, a short discussion of the primary structure and cloning of poly(ADP-ribose) polymerase (PARP) [EC 2.4.2.30], the enzyme that catalyzes, the synthesis of poly(ADP-ribose), is presented. A catalytic distinction between the multiple enzymatic activities of PARP is established. The direction of ADP-ribose chain growth as well as the molecular mechanism of the automodification reaction catalyzed by PARP are described. Current approaches to dissect ADP-ribose polymer synthesis into individual reactions of initiation, elongation and branching, as well as a partial mechanistic characterization of the ADP-ribose elongation reaction at he chemical level are also presented. Finally, recent developments in the catalytic characterization of PARP by site-directed mutagensis are also briefly summarized.
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  • 74
    ISSN: 1573-515X
    Keywords: carbonate sediments ; phosphate adsorption ; phosphorus ; phosphorus limitation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We determined phosphate uptake by calcareous sediments at two locations within a shallow lagoon in Bermuda that varied in trophic status, with one site being mesotrophic and the other being more eutrophic. Phosphate adsorption over a six hour period was significantly faster in sediments from the mesotrophic site. Uptake at both sites was significantly less than that reported for a similar experiment on calcareous sediments in an oligotrophic lagoon in the Bahamas. The difference in phosphorus adsorption between our sites did not appear to be related to sediment characteristics often cited as important, such as differences in surface area (as inferred from grain size distributions), total organic matter content, or iron content. However, the sediment total phosphorus contents were inversely related to phosphorus uptake at our sites in Bermuda, and at the previously studied Bahamas site. We hypothesize that phosphate uptake in these calcareous sediments is a multi-step process, as previously described for fluvial sediments or pure calcium carbonate solids, with rapid initial surface chemisorption followed by a slower incorporation into the carbonate solid-phase matrix. Accordingly, sediments already richer in solid phase phosphorus take up additional phosphate more slowly since the slower incorporation of surface-adsorbed phosphate into the carbonate matrix limits the rate of renewal of surface-reactive adsorption sites. Although carbonate sediments are a sink for phosphate, and thereby reduce the availability of phosphorus for benthic macrophytes and phytoplankton in the shallow overlying water, phosphate uptake by these sediments appears to decrease along a gradient from oligotrophic to eutrophic sites. If our result is general, it implies a positive feedback in phosphorus availability, with a proportionately greater percentage of phosphorus loading being biologically available longer as phosphorus loading increases. This pattern is supported by the significantly higher tissue phosphorus content of the seagrass,Thalassia testudinum, collected from the eutrophic inner bay site. Over time, this effect may tend to cause a shift from phosphorus to nitrogen limitation in some calcareous marine environments.
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  • 75
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    Transport in porous media 16 (1994), S. 237-251 
    ISSN: 1573-1634
    Keywords: phosphate ; soil ; adsorption ; leaching ; kinetics ; computer simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Effects of flow rate and distance travelled on average mobilities of phosphate in a soil are estimated from breakthrough curves of phosphate at the outlets of small columns of soil, following step increases in the concentration at the inlets. Experimental results are compared with results from a computer simulation model of leached columns of soil. Average mobilities of phosphate in columns of soil, following a step increase in the input concentration, decrease with decreasing rate of flow and with increasing distance travelled and appear to be linearly correlated on a logarithmic scale with both flow rate and distance travelled. An empirical equation, describing these relationships, is fitted to data from leaching experiments at flow rates between 30 and 600 cm/day in ≈ 10 cm long columns of soil. Coefficients are obtained by curve fitting breakthrough curves, calculated with a numerical computer simulation model, to experimental breakthrough curves. The fitted equation enables extrapolation to flow rates and travel distances that are more relevant to a field situation.
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  • 76
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    Cellular and molecular life sciences 49 (1993), S. 110-117 
    ISSN: 1420-9071
    Keywords: Polymerization ; sickle hemoglobin ; sickle cell disease ; kinetics ; thermodynamics ; polymer domains ; nucleation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The polymerization of sickle hemoglobin occurs by the same mechanisms in solutions and in cells, and involves the formation of 14 stranded fibers from hemoglobin molecules which have assumed a deoxy quaternary structure. The fibers form via two types of highly concentration-dependent nucleation processes: homogeneous nucleation in solutions with hemoglobin activity above a critical activity, and heterogeneous nucleation in similarly supersaturated solutions which also contain hemoglobin polymers. The latter pathway is dominant, and creates polymer arrays called domains. The individual polymers bend, but also cross-link, and the resulting mass behaves as a solid. The concentration of polymerized hemoglobin increases exponentially unless clamped by rate limiting effects such as oxygen delivery.
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  • 77
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    European journal of clinical pharmacology 44 (1993), S. 231-235 
    ISSN: 1432-1041
    Keywords: Carbamazepine ; kinetics ; population pharmacokinetics ; bioavailability ; controlled release ; non-linear model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The absorption properties of a conventional tablet of carbamazepine (T) and a controlled release form of carbamazepine (TCR) have been compared using a nonlinear mixed effect model (NONMEM). Plasma carbamazepine concentration data were obtained from an open, steady-state, crossover bioavailability study in which 494 measurements were obtained from 13 patients, with an equal number of samples per patient for each dosage form. The pharmacokinetic model used was a one-compartment open model with first-order absorption and elimination. The objective function was used as a measure of the goodness of fit of the model to the data. Body weight was an important determinant of carbamazepine clearance (CL) but not volume of distribution (V). Accounting for the interindividual variability in volume of distribution did not significantly influence the objective function. Including different rates of absorption (ka) for the two dosage forms resulted in a significant improvement in the objective function, as well as reducing the interindividual variability in the rate of absorption. Adding a parameter for relative bioavailability (f) of TCR improved the objective function statistically, but an unrealistic value for V was obtained, and the absorption and elimination rates appeared to be transposed in the classical “flip-flop” manner. Fixing V to the value obtained before introducing f did not change the objective function and permitted estimation of f without the confounding influence of excessive parameters. The final population parameter estimates (standard error of estimate) were: CL, 0.0522 (0.0019) l·h−1·kg−1; V, 63.7 (FIXED)l; kaT, 0.312 (0.064) h−1; kaTCR, 0.149 (0.016) h−1; f, 1.01 (0.0326); variance (additive) in CL, 0.291 (0.083) (l·h−1·kg−1)2; residual intrasubject error variance (additive), 0.572 (0.082) (mg·l−1)2. The 95% confidence interval of the extent of absorption (f) of 93.6%–107.4% was well within the generally accepted range of ±20%, while the rate of absorption of Tegretol CR was significantly slower than that of Tegretol, as expected for a controlled release product.
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    Biogeochemistry 21 (1993), S. 141-166 
    ISSN: 1573-515X
    Keywords: acetylene reduction ; agroecology ; natural abundance15N ; nitrogen fixation ; phosphorus ; sustainable agriculture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Although nitrogen is considered to be the nutrient that most commonly limits production of natural and managed terrestrial ecosystems, I propose that phosphorus may regulate productivity in many continuously cultivated agroecosystems that do not receive applications of synthetic fertilizers. One way P may limit agroecosystem productivity is by controlling nitrogen fixation of legume crops, thus affecting nitrogen availability in the overall agroecosystem. I tested this hypothesis in two studies by examining the effect of phosphorus nutrition on nitrogen fixation of alfalfa in traditional Mexican agroecosystems. All farms used in the research relied on alfalfa as the primary nitrogen source for maize cultivation and other crops, and had minimal or no reliance on synthetic fertilizers. In one study, I used the natural abundance of15N to estimate nitrogen fixation in five alfalfa plots with soils representing a wide range of P fertility. I found a correlation of r = 0.85 between foliage P concentrations and nitrogen fixation in the alfalfa plots. Mean nitrogen fixation in alfalfa plots ranged between 232–555 kg ha−1 yr−1 as estimated by the15N-natural abundance method. In a second study, I sampled soils from alfalfa plots on traditional farms located in 5 different physiographic regions of Mexico. Half of each soil sample was augmented with phosphorus in a greenhouse experiment. I grew alfalfa on the fertilized and unfertilized soils from each site and then determined nitrogenase activity (acetylene reduction) of the Rhizobium on the plant roots. Nitrogenase activity increased in the alfalfa grown on all soils with added phosphorus, with two of the five differences being statistically significant at P 〈 0.01, 0 and one at P 〈 0.05. Foliage P concentrations and nitrogenase activity were 0 positively correlated (r = 0.81,P 〈 0.01).0
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  • 79
    ISSN: 1573-515X
    Keywords: chronosequence ; montane tropical forest ; nitrogen ; soil development ; phosphorus ; tropical forest
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We determined the effects of nutrient amendments on plant growth in three tropical montane rainforest sites representing a sequence of soil ages (〈 30, 200, and ≈ 2000 y). Factorial fertilization with nitrogen, phosphorus, and all other essential nutrients (combined) was applied to the two younger sites; only nitrogen was applied to the oldest one. Nitrogen supply represented the most important limitation to plant growth in the two younger sites; additions of nitrogen caused significant increases in tree diameter increment, height growth, litterfall, and most other growth-related parameters. In contrast, nitrogen additions had no significant effect on plant growth in the oldest site. Phosphorus additions increased extractable soil phosphorus and plant tissue phosphorus, but did not increase plant growth at the young sites. The results are consistent with Walker & Syers' (1976) model for the control of nutrient limitation during soil development.
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  • 80
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    Magnetic resonance materials in physics, biology and medicine 1 (1993), S. 65-76 
    ISSN: 1352-8661
    Keywords: nuclear magnetic resonance spectroscopy ; phosphorus ; brain ; curve fitting ; NMR1™
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics
    Notes: Abstract A procedure is presented for the computerized automated curve fitting ofin vivo 31P NMR data. This procedure was implemented in the form of three C shell scripts (Appendix) which automatically execute commands from the commercial software program, NMR1™. The accuracy and limitations of curve fitting was tested using simulated data designed to representin vivo 31P NMR spectra obtained from brain. For isolated peaks, the predicted areas for 140 test spectra were in good agreement with the noise free or ‘true’ values, with variations on the order of that expected for the calculated S/N of the simulated peaks. However, when the S/N was less than 2:1, predicted areas were systemically overestimated; this error was traced to a bias for linewidth overestimates. For peaks that overlap, a second systematic error was noted in predicted areas for adjacent peaks, where one peak area was overestimated and the other was underestimated. Furthermore, these systematic errors show partial inverse co-linearity with each other, increasing in proportion to the extent of peak overlap. The curve fitting procedure and tests described here provide guidelines and cautions to investigators who endeavour to use computerized procedures for the analysis ofin vivo NMR spectroscopic data using NMR1 or other software programs.
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  • 81
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    European journal of clinical pharmacology 42 (1992), S. 107-110 
    ISSN: 1432-1041
    Keywords: Phenobarbitone ; Cerebral malaria ; P.falciparum ; kinetics ; drug absorption ; children
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The absorption of intramuscular phenobarbitone 7 mg·kg−1 was studied in 11 Karen children aged between 1.7 and 11 y with severe falciparum malaria. Eight of the children were comatose. Clinical findings were compared with those in 9 further children with severe malaria of similar age range (four of whom were unconscious), who received an identical placebo. One child, who had received placebo, had repeated convulsions and died 1 h after admission to hospital. The remainder made an uncomplicated recovery. There were no convulsions subsequent to treatment, although the study was too small to assess anticonvulsant efficacy. There was no observable toxicity, but phenobarbitone recipients had a significant tendency to deepen in their level of coma or to become sleepy within the 4 h after drug administration. Phenobarbitone was rapidly absorbed, reaching a mean (range) peak concentration of 34.2 [29.3–42.6] μmol·l−1 in a median (range) of 4 (2.5–12) h. These values are comparable to those previously reported in healthy children and in children with febrile convulsions. Intramuscular phenobarbitone is well absorbed in children with severe malaria; the optimum prophylactic anticonvulsant dose remains to be determined.
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  • 82
    ISSN: 1432-1041
    Keywords: Atrial natriuretic peptide ; kinetics ; ageing
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    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary To study the influence of age on the kinetics of atrial natriuretic peptide (ANP) in man, human (99–126) ANP 2.0 μg·min−1 was infused IV for 60 min in 8 healthy young (18 to 25 y) and 9 healthy elderly (71 to 84 y) subjects. Both baseline ANP values and the levels at the end of infusion were higher in the elderly subjects. The mean residence time of ANP in the two age groups was not significantly different, whereas total body clearance (CL) was markedly diminished in the elderly as compared to the young subjects (mean±SD 3.1±1.0 l·min−1 and 6.2±4.1 l·min−1, respectively). The apparent volume of distribution at steady state was lower in the elderly than in the young, but the difference was not significant (mean±SD 44±19 and 103±111, respectively. The decrease in CL largely explained the higher ANP levels found in the elderly subjects. The MRT and the plasma half-life of the terminal phase did not differ between the two groups. In the elderly but not in the young subjects the calculated endogenous creatinine clearance was closely correlated with the CL (r=0.90, P〈0.001), thereby emphasizing the importance of the kidney in the metabolic clearance of ANP in the elderly.
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  • 83
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    European journal of clinical pharmacology 42 (1992), S. 461-462 
    ISSN: 1432-1041
    Keywords: Talinolol ; Sulfasalazine ; β-adrenoceptor-blocking drugs ; absorption ; drug interaction ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The absorption of talinolol (TA) 50 mg was investigated without and together with the co-administration of sulfasalazine (SASP) 4 g in 11 healthy young volunteers, in order to clarify gastrointestinal transit of TA. Without SASP, the tmax of TA was 2.8 h, Cmax was 112 ng·ml−1 and the half life was 12 h; the AUCo-t was 958 ng·ml−1·h. In the case of concomitant administration of SASP, TA was found only in serum from 3 individuals, with a Cmax of 23 ng·ml−1 and a mean AUCo-t of 84 ng·ml−1·h. TA was not detectable in 5 subjects and it was at the limit of detection (2 ng·ml−1) in 3 subjects. Pharmacokinetic analysis was not possible in any of those individuals. The reason for the interaction appears to be the adsorption of TA by SASP. An interval of 2–3 h should elapse between giving SASP and other drugs.
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  • 84
    ISSN: 1573-515X
    Keywords: nitrogen fixation ; phosphorus ; internal loading ; water hyacinth ; floodplain ; Paraná ; flood-pulse hypothesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Some aspects of nutrient status and dynamics prevailing during low and high water conditions in the fringing floodplain ponds of the Paraná River dominated by the floating macrophyte Eichhornia crassipes are described. During summertime low water conditions, low DIN:DRP ratios (0.16–1.0) and low DIN (0.5–4.8 μmol.liter−1) in the root-zone of the floating meadows suggest that macrophyte growth is limited by nitrogen. DRP concentrations appear to be controlled more by abiotic sorption-dissolution than by biological reactions. Preflood nutrient fluxes from the sediments, as estimated from porewater profiles, show that a minimum of 1.19 and 0.38 mmol.m−2.d−1 of DIN and DRP were regenerated from the sediments, respectively. Heterotrophic N2 fixation is primarily associated with decaying litter (0.4 to 3.2 μmolN2.g−1.d−1). Nutrient recycling from sediments and meadow-litter, and heterotrophic N2 fixation (1.4 mmolN.m−2.d−1) appear sufficient to sustain high floating macrophyte productivity for long periods of time, without invoking large inputs from the river. The high water and early isolation periods are characterized by a very dynamic behavior of DIN, reflecting marked imbalances between N supply and demand by the biota. After hydrologic isolation of the ponds, DIN rapidly decreases to undetectable levels and stays low for the following 3 weeks, presumably as a result of high demand by phytoplankton and sediment bacteria. DIN increases again to high values 3–8 weeks after the flood, following the re-establishment of NH4 + fluxes from the sediments. Compared to DIN, DRP concentrations remain relatively high and change little during and after the flood. Because of their small amplitude and short duration, floods do not appear to stimulate floating macrophyte production in the Paraná.
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    Biogeochemistry 18 (1992), S. 19-35 
    ISSN: 1573-515X
    Keywords: Dinitrogen fixation ; nitrogen ; phosphorus ; competition ; legumes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract An analysis of data compiled from the literature confirms a strong inverse relationship between annual rates of nitrogen fixation and the soil nitrogen content in agricultural and pastoral ecosystems. However, this inverse relationship is strongly modified by the rate of application of phosphorus fertilizer, which strongly influences the activities of both symbiotic and non-symbiotic nitrogen fixing organisms. In the case of symbiotic legumes, the response of N-fixation to N and P is in part a result of changes in legume dominance within the plant community. These results, as well as supporting data presented from a review of experiments on nitrogen fixation in a variety of other terrestrial and aquatic ecosystems, provide important support for the hypothesis that phosphorus availability is a key regulator of nitrogen biogeochemistry.
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  • 86
    ISSN: 1573-515X
    Keywords: nitrogen ; phosphorus ; soil fertility ; tropical forest
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We measured concentrations of soil nutrients (0–15 and 30–35 cm depths) before and after the dry season in control and dry-season irrigated plots of mature tropical moist forest on Barro Colorado Island (BCI) in central Panama to determine how soil moisture affects availability of plant nutrients. Dry-season irrigation (January through April in 1986, 1987, and 1988) enhanced gravimetric soil water contents to wet-season levels (ca. 400 g kg−1 but did not cause leaching beyond 0.8 m depth in the soil. Irrigation increased concentrations of exchangeable base cations (Ca2+, Mg2+, K+, Na+), but it had little effect on concentrations of inorganic N (NH4 +C, NO3 − and S (SO4 2−). These BCI soils had particularly low concentrations of extractable P especially at the end of the dry season in April, and concentrations increased in response to irrigation and the onset of the rainy season. We also measured the response of soil processes (nitrification and S mineralization) to irrigation and found that they responded positively to increased soil moisture in laboratory incubations, but irrigation had little effect on rates in the field. Other processes (plant uptake, soil organic matter dynamics) must compensate in the field and keep soil nutrient concentrations at relatively low levels.
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  • 87
    ISSN: 1573-515X
    Keywords: algae ; nitrogen ; nutrient ; phosphorus ; regeneration ; zooplankton
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Most ecosystem models consolidate members of food-webs, e.g. species, into a small number of functional components. Each of these is then described by a single state variable such as biomass. When a multivariate approach incorporating multiple substances within components is substituted for this univariate one, a ‘stoichiometric’ model is formed. Here we show that the Nitrogen:Phosphorus ratio within zooplankton herbivores varies substantially intraspecifically but not intraspecifically. By using stoichiometric theory and recent measurements of the N:P ratio within different zooplankton taxa, we calculate large differences in ratios of nutrients recycled by different zooplankton species. Finally, we demonstrate that N:P stoichiometry can successfully account for shifts in N- and P-limitation previously observed in whole-lake experiments. Species stoichiometry merges food-web dynamics with biogeochemical cycles to yield new insights.
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  • 88
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    Cytotechnology 10 (1992), S. 147-155 
    ISSN: 1573-0778
    Keywords: batch culture ; continuous culture ; hybridoma ; kinetics ; specific rates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract For the mouse hybridoma cell line VO 208, kinetics of growth, consumption of glucose and glutamine, and production of lactate, ammonia and antibodies were compared in batch and continuous cultures. At a given specific growth rate, different metabolic activities were observed: a 40% lower glucose and glutamine consumption rate, but a 70% higher antibody production rate in continuous than in batch culture. Much higher metabolic rates were also measured during the initial lag phase of the batch culture. When representing the variation of the specific antibody production rate as a function of the specific growth rate, there was a positive association between growth and antibody production in the batch culture, but a negative association during the transient phase of the continuous culture. The kinetic differences between cellular metabolism in batch and continuous cultures may be result of modifications in the physiology and metabolism of cells which, in continuous cultures, were extensively exposed to glucose limitations.
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  • 89
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    Cellular and molecular life sciences 47 (1991), S. 1104-1118 
    ISSN: 1420-9071
    Keywords: Transaminase ; decarboxylase ; serine hydroxymethyltransferase ; pyridoxal 5′-phosphate ; enzyme mechanism ; stereochemistry ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Pyridoxal 5′-phosphate is a coenzyme for a number of enzymes which catalyse reactions at Cα of amino acid substrates including transaminases, decarboxylases and serine hydroxymethyltransferase. Using the X-ray coordinates for a transaminase, aspartate aminotransferase, and the results of stereochemical and mechanistic studies for decarboxylases and serine hydroxymethyltransferase, an active-site structure for the decarboxylase group is constructed. The structure of the active-site is further refined through active-site pyridoxyllysine peptide sequence comparison and a 3-D catalytic mechanism for the L-α-amino acid decarboxylases is proposed. The chemistry of serine hydroxymethyltransferase is re-examined in the light of the proposed decarboxylase mechanism.
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  • 90
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    European journal of clinical pharmacology 40 (1991), S. 181-185 
    ISSN: 1432-1041
    Keywords: Etizolam ; α-hydroxyetizolam ; healthy subjects ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The pharmacokinetics of etizolam, a new thienodiazepine derivative, has been examined after single and multiple (0.5 mg tablet) (0.5 mg b.d for 1 week) oral therapeutic doses in healthy volunteers. The single-dose kinetic profile of etizolam suggested that absorption after oral dosage was reasonably rapid, the maximum plasma concentration (Cmax) being attained within 0.5–2 h in all subjects. The mean elimination half-life (t1/2) averaged 3.4 h. Consistent with this, steady-state concentration were rapidly achieved and accumulation was extremely limited. Predicted average plasma concentrations (Cp) did not differ significantly from those actually measured at steady-state, suggesting that the kinetics of etizolam was linear, at least at therapeutic doses. The mean wash-out t1/2 was comparable to the elimination t1/2 of the single dose, which means that the drug probably has no effect on hepatic microsomal enzymes and other kinetic variables after repeated dosing. At steady state plasma concentrations of the main metabolite, α-hydroxyetizolam, were higher and disappeared more slowly (mean t1/2 8.2 h) than those of the parent compound. Taken with the fact that in animals the metabolite shows almost the same potency of pharmacological action as etizolam, this suggests that it may contribute significantly to the clinical effects of the parent compound. Based on the kinetic characteristics of the parent drug and its metabolite, etizolam can be regarded as a short-acting benzodiazepine, with elimination kinetics between those of short-intermediate derivatives and ultra-rapidly eliminated benzodiazepines.
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  • 91
    ISSN: 1573-4919
    Keywords: phosphate-dependent glutaminase ; acute metabolic acidosis ; kinetics ; kidney tubules ; enterocytes ; hepatocytes ; brain tissue
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary We describe the kinetic modifications to mitochondrial-membrane-bound phosphate-dependent glutaminase in various types of rat tissue brought about by acute metabolic acidosis. The activity response of phosphate-dependent glutaminase to glutamine was sigmoidal, showing positive co-operativity, the Hill coefficients always being higher than 2. The enzyme from acidotic rats showed increased activity at subsaturating concentrations of glutamine in kidney tubules, as might be expected, but not in brain, intestine or liver tissues. Nevertheless, when brain and intestine from control rats were incubated in plasma from acutely acidotic rats enzyme activity increased at 1 mM glutamine in the same way as in kidney cortex. The enzyme from liver tissue remained unaltered. S0.5 and nH values decreased significantly in kidney tubules, enterocytes and brain slices preincubated in plasma from acidotic rats. The sigmoidal curves of phosphate-dependent glutaminase shifted to the left without any significant changes in Vmax. The similar response of phosphate-dependent glutaminase to acute acidosis in the kidney, brain and intestine confirms the fact that enzymes from these tissues are kinetically identical and reaffirms the presence of an ammoniagenic factor in plasma, either produced or concentrated in the kidneys of rats with acute acidosis.
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  • 92
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    Mathematical geology 23 (1991), S. 325-347 
    ISSN: 1573-8868
    Keywords: hydrocarbons ; kinetics ; inverse methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract From a determination of the transformation matrix for three pyrolysis product experimental data sets, an examination is given of both the applicability of the laboratory experimental data to the modeling of oil cracking in a sedimentary basin, and of the appropriateness of an inverse model. The results of the laboratory experimental data sets, which were done under different thermodynamic conditions and using different sources, show that the transformation matrix varies over each data set and also with time. Therefore, it is necessary to check the data sets before applying them to a basin for hydrocarbon modeling. The laboratory experimental data taken at lower temperature and over longer times appear more pertinent for the construction of an oil-cracking kinetic model suitable for geologic conditions.
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  • 93
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    Biogeochemistry 12 (1991), S. 135-148 
    ISSN: 1573-515X
    Keywords: fens ; management ; nitrogen ; phosphorus ; productivity ; vegetation ; wetlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract A fertilization experiment was carried out in 3 mesotrophic fens to investigate whether plant growth in these systems is controlled by the availability of N, P or K. The fens are located in an area with high N inputs from precipitation. They are annually mown in the summer to prevent succession to woodland. Above-ground plant biomass increased significantly upon N fertilization in the two “mid”-succession fens studied. In the “late”-succession fen that had been mown for at least 60 years, however, plant biomass increased significantly upon P fertilization. The mowing regime depletes the P pool in the soil, while it keeps N inputs and outputs in balance. A long-term shift occurs from limitation of plant production by N toward limitation by P. Hence, mowing is a suitable management tool to conserve the mesothrophic character of the fens.
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  • 94
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    Journal of atmospheric chemistry 12 (1991), S. 137-151 
    ISSN: 1573-0662
    Keywords: Soot particles ; polycyclic aromatic hydrocarbons ; NO2 ; HNO3 ; heterogeneous reactions ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract An experimental technique for studying atmospheric heterogeneous reactions of polyaromatic hydrocarbons (PAH) on particle surfaces is reported. Particle bound organics were reacted in a 200 liter Teflon continuous stirred tank reactor (CSTR), with vapor phase oxidants. To provide a source of chemically stable particles for the CSTR, soot particles from a residential wood stove were first introduced during under darkness into a 25 m3 outdoor Teflon chamber. Air containing the particles was then added at a constant flow to the CSTR. The rates of heterogeneous reactions were obtained by comparing reacted particle samples with unreacted ones. The derivation of rate expressions for heterogeneous reactions in the CSTR is described. The use of the technique for a study of the nitration of selected soot particle bound PAH species by NO2 and HNO3 is demonstrated.
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  • 95
    ISSN: 1573-0662
    Keywords: Organic nitrates ; kinetics ; OH radical ; atmosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Rate coefficients for the reactions of difunctional nitrates with atmospherically important OH radicals are not currently available in the literature. This study represents the first determination of rate coefficients for a number of C(3) and C(4) carbonyl nitrates and dinitrates with OH radicals in a 38 l glass reaction chamber at 1000 mbar total pressure of synthetic air by 298±2 K using a relative kinetic technique. The following rate coefficients (in units of 10-12 cm3 molecule-1 s-1) were obtained: 1,2-propandiol dinitrate, 〈0.31; 1,2-butandiol dinitrate, 1.70±0.32; 2,3-butandiol dinitrate, 1.07±0.26; α-nitrooxyacetone, 〈0.43; 1-nitrooxy-2-butanone, 0.91±0.16; 3-nitrooxy-2-butanone, 1.27±0.14; 1,4-dinitrooxy-2-butene, 15.10±1.45; 3,4-dinitrooxy-1-butene, 10.10±0.50. The possible importance of reaction of OH as an atmospheric sink for the compounds compared to other loss processes is considered.
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  • 96
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    Biogeochemistry 13 (1991), S. 87-115 
    ISSN: 1573-515X
    Keywords: biogeochemistry ; energetic constraints ; nitrogen fixation ; phosphorus ; succession ; trace elements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The widespread occurrence of nitrogen limitation to net primary production in terrestrial and marine ecosystems is something of a puzzle; it would seem that nitrogen fixers should have a substantial competitive advantage wherever nitrogen is limiting, and that their activity in turn should reverse limitation. Nevertheless, there is substantial evidence that nitrogen limits net primary production much of the time in most terrestrial biomes and many marine ecosystems. We examine both how the biogeochemistry of the nitrogen cycle could cause limitation to develop, and how nitrogen limitation could persist as a consequence of processes that prevent or reduce nitrogen fixation. Biogeochemical mechansism that favor nitrogen limitation include: the substantial mobility of nitrogen across ecosystem boundaries, which favors nitogen limitation in the “source” ecosystem — especially where denitrification is important in sediments and soils, or in terrestrial ecosystems where fire is frequent; differences in the biochemistry of nitrogen as opposed to phosphorus (with detrital N mostly carbon-bonded and detrital P mostly ester-bonded), which favor the development of nitrogen limitation where decomposition is slow, and allow the development of a positive feedback from nitrogen limitation to producers, to reduced decomposition of their detritus, and on to reduced nitrogen availability; and other more specialized, but perhaps no less important, processes. A number of mechanisms could keep nitrogen fixation from reversing nitrogen limitation. These include: energetic constraints on the colonization or activity of nitrogen fixers; limitation of nitrogen fixers or fixation by another nutrient (phosphorus, molybdenum, or iron) — which would then represent the ultimate factor limiting net primary production; other physical and ecological mechanisms. The possible importance of these and other processes is discussed for a wide range of terrestrial, freshwater, and marine ecosystems.
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  • 97
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    Cytotechnology 5 (1991), S. 165-171 
    ISSN: 1573-0778
    Keywords: growth ; hybridoma ; inoculum age ; kinetics ; production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract To determine the influence of the inoculum age on the kinetics of hybridoma growth and metabolism, spinner flasks have been inoculated with cells previously propagated in T flasks for 43, 52, 62 and 71 hr respectively. Increasing the age of the inoculum is found to result in a longer lag phase, in a lower maximum specific growth rate and in a reduced maximal cell density. During the growth phase specific rates of glucose and glutamine uptake and of ammonia and lactate production are similar. However, with the older inoculum, much higher metabolic activities are observed during the lag phase. The production of antibodies is delayed with increasing inoculum age, but the final antibody concentrations are similar, which indicates a higher specific antibody production rate when inoculating with older cells.
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  • 98
    ISSN: 1573-0778
    Keywords: cell culture ; kinetics ; Ig promoter/enhancer ; plasmacytoma ; recombinant protein production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A model mammalian cell system for the production of recombinant proteins was investigated. Murine myeloma cells which had lost the ability to produce both heavy and light chain immunoglobulin molecules were transfected with a vector containing the immunoglobulin heavy chain promoter and enhancer elements linked to the human growth hormone gene. The growth kinetics of G32, a clonal isolate, were found to be similar to both the parent myeloma and hybridomas. However, production of hGH by G32 was growth associated, rather than as a secondary metabolite as is the case for hybridomas. In addition, G32 produced hGH at molar levels greater than most hybridomas.
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  • 99
    ISSN: 1435-232X
    Keywords: G6PD ; electrophoresis ; deficiency ; new variants ; kinetics ; inhibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Biochemical characteristics of one non-deficient fast G6PD variant (Gd Singapore) and six different deficient variants (three new, two Mahidol, one each of Indonesian and Mediterranean) were studied among the Malays of Singapore. TheGd Singapore variant had normal enzyme activity (82%) and fast electrophoretic mobilities (140% in TEB buffer, 160% in phosphate and 140% in Tris-HCl buffer systems respectively). This variant is further characterized by normalK m for G6P; utilization of analogues (Gal6P, 2dG6P; dAmNADP), heat stability and pH optimum. The other six deficient G6PD variants had normal electrophoretic mobility in TEB buffer with enzyme activities ranging from 1 to 12% ofGd B+. The biochemical characteristics identity them to be 2 Mahidol, 1 Indonesian and 1 Mediterranean variants and three new deficient variants.
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  • 100
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    European journal of clinical pharmacology 39 (1990), S. 155-159 
    ISSN: 1432-1041
    Keywords: Gentamicin ; Dosage ; kinetics ; dose individualization ; dose prediction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary A prospective study was carried out in 40 acutely ill patients to compare the non-kinetic and kinetic approaches to individualization of the dosage regimen of gentamicin. The patients were divided into two equal groups. For the non-kinetic group, the doses were derived from the physician's personal experience, on a mg/kg basis, and by use of nomograms. The total daily dose ranged from 1.43 to 4.5 mg/kg. Based on serum concentration measurements, the dosage regimen for individual patient was calculated by Sawchuk-Zaske's method. The calculated doses were compared to the prescribed doses in each patient. Of the patients on empirically prescribed doses 65% received 36% more drug than the calculated dose and 20% received 36% less than the calculated dose. The calculated dosing intervals were greater than the recommended intervals in 60% of the patients. The gentamicin trough concentration was 〉 2 μg/ml in 70% of the patients. There was a significant tendency to overdosage of the patients. For the kinetic group, following administration of the calculated dose, the steady-state peak and trough concentrations in each patient were measured. The correlation of measured to predicted steady-state serum concentrations was excellent (r=0.9968, p〈0.05). About 85% of the served trough concentrations and 90% of the peak values fell within the therapeutic range. The mean of the prediction error (ME), mean absolute error (MAE), mean squared error (MSE), and root mean squared error (RMSE) of the trough and peak concentrations were calculated. The 95% confidence interval of the ME for the trough and peak concentrations included zero, which shows that the prediction was not significantly biased. A significant relationship between gentamicin clearance and the ratio of the peak and trough concentrations achieved to the administered dose (r=0.873, 0.916 for trough and peak, respectively) was found. The findings suggest that the individualized approach to dosage determination using pharmacokinetic principles, in conjunction with daily monitoring of serum gentamicin concentrations, may provide safe and effective therapy.
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