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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-8744
    Keywords: carrier-mediated transport ; organic cations ; cationic drugs ; hepatobiliary elimination ; hepatic distribution ; drug interactions ; structure-pharmacokinetic relationship ; multiplicity in carrier proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Carrier-mediated transport of drugs occurs in various tissues in the body and may largely affect the rate of distribution and elimination. Saturable translocation mechanisms allowing competitive interactions have been identified in the kidneys (tubular secretion), mucosal cells in the gut (intestinal absorption and secretion), choroid plexus (removal of drug from the cerebrospinal fluid), and liver (hepatobiliary excretion). Drugs with quaternary and tertiary amine groups represent the large category of organic cations that can be transported via such mechanisms. The hepatic and to a lesser extent the intestinal cation carrier systems preferentially recognize relatively large molecular weight amphipathic compounds. In the case of multivalent cationic drugs, efficient transport only occurs if large hydrophobic ring structures provide a sufficient lipophilicity-hydrophilicity balance within the drug molecule. At least two separate carrier systems for hepatic uptake of organic cations have been identified through kinetic and photoaffinity labeling studies. In addition absorptive endocytosis may play a role that along with proton-antiport systems and membrane potential driven transport may lead to intracellular sequestration in lysosomes and mitochondria. Concentration gradients of inorganic ions may represent the driving forces for hepatic uptake and biliary excretion of drugs. Recent studies that aim to the identification of potential membrane carrier proteins indicate multiple carriers for organic anions, cations, and uncharged compounds with molecular weights around 50,000 Da. They may represent a family of closely related proteins exhibiting overlapping substrate specificity or, alternatively, an aspecific transport system that mediates translocation of various forms of drugs coupled with inorganic ions. Consequently, extensive pharmacokinetic interactions can be anticipated at the level of uptake and secretion of drugs regardless of their charge.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Polymer bulletin 24 (1990), S. 421-427 
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The thermal conductivity at low temperatures (between 0.5 K and 100 K) was measured for diolmodified epoxies. Diglycidyl ether of bisphenol A (DGEBA) was modified for this purpose by aliphatic diols with the structure HO-(-CH2-)n-OH in the presence of catalyst (either N,N-dimethyl benzylamine or magnesium perchlorate). Sample series with diols of n=4,8 and 12 were synthesized and measured. The results at T〈20K shows a clear dependence of the thermal conductivity values on the chain length of the diols. The increasing amount of diol in the epoxies cause a larger change on these values in the same temperature range.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 111 (1988), S. 121-126 
    ISSN: 1573-5036
    Keywords: barley ; decomposition ; fertilization ; green manure ; liming ; N-budget ; N-release ; 15N ; red clover
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Red clover material labelled with15N was confined in mesh bags and buried into microplots in October at two field sites in Sourthern Finland. The soils (Kettula silt loam and Långvik loam) contained in the microplots were previously limed and fertilized with PK (N was given in next May) in different combinations. The following May the microplots were sown with barley and after the barley had been harvested (that August) soil samples and the mesh bags were removed. The crop, mesh bags and soil were then analysed for15N content. The soil treatments did not affect the release of clover N from the mesh bags and only slightly its retention in Kettula silt loam. The dry mass of barley obtained responded strongly to the different soil treatments. In comparison, the uptake of clover N by the barley varied much less; in Kettula silt loam a 1.6 fold increase in barley dry mass did not affect its content of clover N (12–13% of input) and in Långvik loam a ten fold increase in barley dry mass yield corresponded to a three fold increase of the content of clover N (5–16%). The total recovery of clover N (clover N in soil+mesh bags+barley harvest) was almost independent of the soil treatment; in Kettula silt loam and Långvik loam being respectively 52–56% and 71–85% of the input.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 105 (1988), S. 133-139 
    ISSN: 1573-5036
    Keywords: field bean ; green manure ; mesh bag ; N cycling ; N loss ; N-15 ; red clover ; subterranean clover ; timothy ; white clover
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Release of N, retention in soil, availability to a subsequent crop and total recovery of N derived from different15N-labelled plant materials decomposing in soil was investigated in two field experiments. In the first experiment five different plant species (white clover, red clover, subterranean clover, field bean and timothy) and in the second subterranean clover of different maturity (2,3 and 4 months old) were buried in mesh bags in the soil and allowed to decompose for 10 and 4 months, respectively. Most of the N released from the decaying plant materials was retained in the soil (27–46% of input). The subsequent crop (barley) took up 6–25% of input. The uptake correlated with the amount of N released from the decomposing material (r=0.936*, I experiment). Similar amounts of subterranean clover N were taken up by barley regardless to whether the material was buried in soil in the previous autumn or just before sowing of the crop. At the end of the experiments, the total recovery of the introduced plant-derived N varied between 89 and 102%. The results present evidence that the ability of the soil to retain plant-derived N is strong in comparison with the ability of the subsequent crop and different loss mechanisms to remove it.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 105 (1988), S. 141-147 
    ISSN: 1573-5036
    Keywords: barley ; decomposition ; green manure ; N-budget ; N-release ; N-15 ; soil type ; subterranean clover
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Seven soils were collected from different field sites in Southern Finland and placed into microplots confined in PVC-cylinders (30 cm i.d. × 50 cm). Subterranean clover material labelled with15N, contained in mesh bags, was buried into the microplots in October, and the plots were sown with barley the following May. The mesh bags were removed and soil samples taken immediately after the barley harvest. The crop, mesh bags and soil were then analysed for15N content. The soil type affected release of clover N from the mesh bags and its retention in soil only slightly; at the end of the experiment the mesh bags contained 30–38% and the soil (0–45 cm) 28–37% of the clover N input. The uptake of clover N by the barley crop varied from 11 to 20% and correlated best with the soil electrical conductivity (r=0.820*). The total recovery of clover-derived N varied from 72 to 92%.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 105 (1988), S. 149-152 
    ISSN: 1573-5036
    Keywords: C release ; liming ; mesh bag ; Nitrogen ; N release ; red clover
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Red clover root material confined in mesh bags was buried in three different limed and unlimed soils and incubated for 196 days at room temperature. Remaining amounts of organic matter, as well as concentrations of C and N of the decomposing material were determined three times during the incubation and finally the concentration of soil mineral N and pH of remaining roots was also assessed. Liming only temporarily affected the decomposition rate of organic matter and N release, and at the end of the incubation no effects could be observed due to liming. A possible explanation is that the decomposing root residues provide a well buffered micro-environment for the decomposing microflora. Liming did not change the pH of the root residues even when 97–98% of dry mass had disappeared from the mesh bags. Concentrations of mineral N were higher in limed than in unlimed soils.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 102 (1987), S. 185-191 
    ISSN: 1573-5036
    Keywords: green manure ; leaching ; loam ; nitrogen ; nitrogen budget ; N-15 ; subterranean clover
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The leaching of subterranean clover-derived N (15N) was investigated in a laboratory and a field experiment. In both experiments 30 cm i.d. ×50cm soil columns were used. In the laboratory experiment the clover material was buried in the soil in mesh bags, and leaching of clover-derived N was compared to leaching of added NH 4 + −N and NO 3 − −N over a period of 75 days at 20°C. During that time 75% of the clover-N was released from the mesh bags and 17% of the clover-N, 50% of the NH 4 + −N and 70% of the NO 3 − −N was leached through the soil column. In the field experiment 6 lysimeters and 7 control microplots were constructed. The clover material was buried in soil (to the soil of two control microplots within mesh bags) in October. During one year 2% of the added clover-N was leached. This was despite a release of 65% of the N from the mesh bag contents and despite a 26% loss of the clover-derived N in total from the controls.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    BIT 31 (1991), S. 314-320 
    ISSN: 1572-9125
    Keywords: 65L20 ; Implicit Runge-Kutta methods ; I-stability ; generalized positive function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Well-known stability concepts for Runge-Kutta methods areA-stability andB-stability. These stability properties can be characterized by algebraic conditions related to the generating matrix of the method. In this note we show, thatI-stable methods can be characterized similarly, yielding aunified description ofB-,A- andI-stability in terms of a matrixR.I-stability, although a weaker concept thanA-stability, is of some relevance in parallelizing Runge-Kutta methods.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Review of industrial organization 5 (1990), S. 25-43 
    ISSN: 1573-7160
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract The survivor test to determine scale economies in an industry is applied to the U.S. petroleum refining industry. A time series covering every refinery for the period 1947–1984 is used. The results support Stigler's original conclusion of a saucer-shaped long-run average cost curve when his technique is duplicated on the full time series. However, we argue that the technique is misleading and try an alternative method which concludes that costs are decreasing for large scale refineries.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Ethik in der Medizin 10 (1998), S. 189-194 
    ISSN: 1437-1618
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Philosophy
    Type of Medium: Electronic Resource
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