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  • Springer  (284)
  • Institute of Physics  (94)
  • EDP Sciences  (17)
  • 2000-2004  (222)
  • 1980-1984  (113)
  • 1950-1954  (60)
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  • 1
    ISSN: 1572-9540
    Keywords: nuclear β-decay ; correlations ; right-handed currents ; scalar and tensor currents ; polarized nuclei ; Penning traps
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Two experiments to search for new physics beyond the standard model for electroweak interactions by measuring correlations between different spin and momentum vectors in nuclear β-decay are discussed. In the first experiment the correlation between the emission asymmetry and the longitudinal polarisation of positrons emitted by polarised nuclei is determined. This type of measurement is sensitive to the presence of right-handed currents but also to possible scalar and tensor-type currents in the weak interaction. The aim of the second experiment is to determine the βν-correlation in β-decay by measuring the energy spectrum of the recoil ions, using a Penning trap and a retardation spectrometer. In this case the focus is on the search for scalar currents in the weak interaction. The results of the experiments presented here are complementary to results from experiments in muon decay and at high-energy colliders.
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  • 2
  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Radiation and environmental biophysics 19 (1981), S. 289-289 
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Semigroup forum 92 (2000), S. 316-320 
    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Zea mays L.) plants express unexpected K-deficiency symptoms when grown under certain conservation tillage production systems on high-K-testing soils. This field study was conducted to determine if K fertilizer treatments interact with P and N planting-time fertilizer placement treatments to affect crop growth, nutrient composition, and yield in an irrigated no-till corn production system on high-K-testing soil. The 3-yr study was conducted on Lowry silt loam soils (coarse-silty, mixed, superactive, mesic Typic Haplustolls) near Pierre, SD. Fertilizer placement (main plot) treatments consisted of P and N fertilizers that were applied with the corn planter to (i) the soil surface, (ii) the seed furrow, or (iii) a band 5 cm to the side of the seed furrow and 5 cm deep. Fertilizer products containing K, also applied at planting time, provided a with-K subplot comparison with subplots that received no added K fertilizer. Corn plants were sampled for root pull resistance, shoot dry weight, and shoot mineral nutrient composition at the tassel stage of development and grain yield. Data combined over the 3 yr of the study revealed that added K fertilizer had no effect on grain yield and did not interact with P and N fertilizer placement treatments to affect grain yield. When P fertilizer was placed with the seed and N fertilizer was placed in a 5- by 5-cm band, corn plants had 185 kg root−1 pull resistance, 0.26 g shoot−1 P accumulation, and 10.5 Mg ha−1 grain yield. However, when P and N fertilizers were applied to the soil surface, corn plants had significantly less root pull resistance (151 kg root−1), P accumulation (0.22 g P shoot−1) and grain yield (10.1 Mg ha−1). Added K fertilizer decreased shoot dry weight (added K = 97 g shoot−1, no K = 103 g), decreased P accumulation (added K = 0.22 g P plant−1, no K = 0.25 g), increased shoot N concentration (added K = 19.3 mg N g−1, no K = 19.0 mg), and had no significant effect on K concentration or accumulation. We conclude that, although planting-time fertilizer placement was important for optimum corn growth and yield production in irrigated no-till systems, added K fertilizer did not interact with fertilizer placement to improve yield on the high-K-testing soils used in this study.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of mathematical biology 19 (1984), S. 63-77 
    ISSN: 1432-1416
    Keywords: Slow coevolution ; singular perturbations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract An S→I→S epidemic transmitted by two similar strains of parasite acting on a host population of three genotypes which differ in their reaction to the disease is modelled and analyzed. Singular perturbation techniques are used to reduce the original system of nine differential equations to a coupled system of two equations describing the slowtime coevolution of gene frequency and parasite strain frequency.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of mathematical biology 19 (1984), S. 79-94 
    ISSN: 1432-1416
    Keywords: Epidemics ; slow-genetic evolution ; singular perturbations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Mathematical models of a vector-borne infectious disease acting on a host population consisting of three genotypes which differ in susceptibility to, recovery from, and death due to the disease are presented and analyzed. Singular perturbation techniques are used to obtain a single differential equation describing the slow time evolution of gene frequencies.
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  • 7
    ISSN: 1432-1424
    Keywords: transepithelial Na transport ; intracellular electrolytes ; electron microprobe analysis ; vasopressin ; amiloride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The intracellular electrolyte concentrations of the frog skin epithelium have been determined in thin freeze-dried cryosections using the technique of electron microprobe analysis. Stimulation of the transepithelial Na transport by arginine vasopressin (AVP) resulted in a marked increase in the Na concentration and a reciprocal drop in the K concentration in all epithelial cell layers. The effects of AVP were cancelled by addition of amiloride. It is concluded from these results that the primary mechanism by which AVP stimulates transepithelial Na transport is an increase in the Na permeability of the apical membrane. However, also some evidence has been obtained for an additional stimulatory effect of AVP on the Na pump. In mitochondria-rich cells and in gland cells no significant concentration changes were detected, supporting the view that these cells do not share in transepithelial Na transport. Furthermore, the dependence of the intracellular electrolyte concentrations upon the Na concentration in the outer and inner bathing solution was evaluated. Both in control and AVP-stimulated skins the intracellular Na concentration showed saturation already at low external Na concentrations, indicating that the self-inhibition of transepithelial Na transport is due to a reduction of the permeability of the apical membrane. After lowering the Na concentration in the internal bath frequently a Na increase in the outermost and a drop in the deeper epithelial layers was observed. It is concluded that partial uncoupling of the transport syncytium occurs, which may explain the inhibition of the transepithelial Na transport and blunting of the AVP response under this condition.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Physics and chemistry of minerals 8 (1982), S. 146-147 
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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  • 9
    ISSN: 1432-2048
    Keywords: Key words: Chlamydomonas ; Gametogenesis ; Nitrate reductase mutants ; Nitrate signal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract.  The effect of nitrate on gamete differentiation as well as on the expression of genes involved in gametogenesis, nitrogen scavenging, and nitrate assimilation has been analyzed in wild-type and mutant strains of Chlamydomonas reinhardtii. Nitrate prevented gamete formation from wild-type strains and caused a strong reduction in the number of zygotes recovered in genetic crosses between nitrate-assimilation-deficient mutants, thus suggesting that nitrate by itself is providing a negative regulatory signal for the sexual differentiation of the alga. Addition of nitrate at low concentrations to wild-type cells, after an initial period of nitrogen starvation, resulted in a drastic decrease in transcript levels of both nitrate-assimilation genes (NIA1 and NRT2;1) and genes induced after N-starvation (NCG2 and NCG4). This strong effect of nitrate was due to its assimilation products since it was not evident in nitrate-assimilation mutants. A slight negative effect of nitrate on NCG4 expression was only observed in the mutant. Nitrate by itself was also found to provide a negative signal for the expression of gamete-specific genes (GAS3 and GAS18) in mutants incapable of assimilating nitrate.
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  • 10
    ISSN: 1432-2048
    Keywords: Equilibrium freezing ; Freezing tolerance ; Leaf (water potential) ; Rosette plant (Afroalpine) ; Water potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The water potentials of frozen leaves of Afroalpine plants were measured psychrometrically in the field. Comparison of these potentials with the osmotic potentials of an expressed cellular sap and the water potentials of ice indicated almost ideal freezing behaviour and suggested equilibrium freezing. On the basis of the osmotic potentials of expressed cellular sap, the fractions of frozen cellular water which correspond to the measured water potentials of the frozen leaves could be determined (e.g. 74% at -3.0° C). The freezing points of leaves were found to be in the range between 0° C and -0.5° C, rendering evidence for freezing of almost pure water and thus confirming the conclusions drawn from the water-potential measurements. The leaves proved to be frost resistant down to temperatures between -5° C and -15° C, as depending on the species. They tolerated short supercooling periods which were necessary in order to start ice nucleation. Extracellular ice caps and ice crystals in the intercellular space were observed when cross sections of frozen leaves were investigated microscopically at subfreezing temperatures.
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