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91.
92.
93.
M. Schulze R. Reißner K. Bolwin W. Kuch 《Fresenius' Journal of Analytical Chemistry》1995,353(5-8):661-665
The adsorption of water on a Ni(111) single crystal surface, clean as well as precovered with oxygen, has been investigated with thermal desorption spectroscopy (TDS) and measurements of the adsorption-desorption equilibrium combined with XPS (X-ray photoelectron spectroscopy). The measurements have been carried out with water pressures up to 10–5 mbar on surfaces, which have been either clean or precovered with oxygen. On the clean Ni(111) surface the first adsorbate layer with a maximum coverage of 0.42 ML (monolayers) has a desorption energy of 52 kJ/mol and a preexponential factor of desorption of 1016s–1. A second water layer adsorbs with the desorption energy of the ice multilayer but with first order kinetics. On Ni(111) precovered with chemisorbed oxygen an additional state of molecular, more strongly bound water is found, but no dissociation. For higher oxygen precoverages where NiO islands are formed on the surface, also the water dissociation product OH is found adsorbed. On a sample covered with a closed NiO layer, adsorbed OH and molecular water in an energetically not well-defined state are found. High doses of water on oxygen-precovered Ni(111) induce a slow surface modification leading to water dissociation. 相似文献
94.
95.
In this paper, we study the blow-up theory for the L 2-critical coupled nonlinear Schrödinger system in the Euclidean plane ${\mathbb{R}^{2}}In this paper, we study the blow-up theory for the L
2-critical coupled nonlinear Schr?dinger system in the Euclidean plane
\mathbbR2{\mathbb{R}^{2}} .We show that at the finite time blow-up, similar results of Weinstein, Merle-Tsutsumi for scalar Schrodinger equations are
true for the system. 相似文献
96.
Bernd Schulze 《Discrete and Computational Geometry》2010,44(4):946-972
Recent work has shown that if an isostatic bar-and-joint framework possesses nontrivial symmetries, then it must satisfy some
very simply stated restrictions on the number of joints and bars that are “fixed” by various symmetry operations of the framework. 相似文献
97.
J. Bös M. Bär G. Hübner J. Schmidt H. W. Schulze 《Isotopes in environmental and health studies》2013,49(4):115-116
An efficient potential for radiation research has been developed at the Central Institute of Isotope and Radiation Research in Leipzig since 1969. 2Iany problems in the field of basic and applied research of radiation chemistry and biology have been studied. Ten gamma plants and two electron accelerators have been designed and established for scientific, industrial and agricultural application. 相似文献
98.
D. Koppisch E.-D. Schulze G. Gebauer 《Isotopes in environmental and health studies》2013,49(1-2):77-84
Abstract Calamagrostis villosa dominates the understory vegetation in declining spruce forests at higher elevations of the Central European mountain areas which show symptoms of needle yellowing and associated magnesium (Mg) deficiency. It was hypothesized that grasses would preferentially take up nitrate-nitrogen (NO3-N) over ammonium-nitrogen (NH4-N) which would support the cation balance in Mg deficient soils. In order to test this hypothesis, growth experiments were carried out in the greenhouse using plants which were cultivated in sand for nine weeks with full nutrient solution containing 0.2 or 2 mmol of N with different NH4 + to NO3 ? ratios (1:0, 0.5:0.5, 0:1). In a short term experiment with labelled 15NH4 + and 15NO3 ?, uptake of NH4 + and NO3 ? was measured. When NO3 ? was the only N source it was taken up at similar rate per g dry mass as in the experiment in which NH4 + was the only N source. However, at high supply pure NO3 ? nutrition resulted in higher biomass. In contrast, supply of only NH4 + caused accumulation of N in the roots but growth remained restricted. If NH4 + and NO3 ? were supplied at equal amounts, NH4 + was the preferred form for N uptake. Biomass of the plants with mixed supply did not differ from the plants with pure NO3 ? nutrition. The results point to an interesting interaction of carbon and nitrogen relation, but they do not support the initial hypothesis that grasses may prefer NO3 ? over NH4 +. 相似文献
99.
J. Stadler G. Gebauer E.-D. Schulze 《Isotopes in environmental and health studies》2013,49(1-2):85-92
Abstract Interactions between ammonium and nitrate as competitive N sources depend on various biotic and abiotic factors. The preference for one of these N sources and the influence of ammonium on nitrate uptake and nitrate reductase activity was investigated in a 15N labelling experiment using 2-year-old potted plants of ash (Fraxinus excelsior L.) and oak (Quercus robur L.) under greenhouse conditions. Seedlings of both tree species use ammonium and nitrate in equal amounts when both N forms are supplied in a 1:1 ratio (1.5 mM NH4 + + 1.5 mM NO3 ?), although there is a slight tendency that ammonium is preferred. In both species total N uptake is higher if ammonium and nitrate are supplied simultaneously when compared with uptake of nitrate alone (3 mM nitrate). If nitrate is the sole N source N uptake is only half as high as if ammonium and nitrate are supplied in a ratio of 1:1. The distribution of nitrate reductase between shoot and roots is not influenced by the N-form: nitrate reductase activity is always highest in the roots of both species under the conditions of this experiment. Xylem sap analyses showed that both species transport higher concentrations of amino acids than of nitrate from the roots to the shoot. The amino acid composition is independent of the type of N source. Furthermore, ash trees contain more nitrate in the xylem sap than oak trees, reflecting the higher N uptake and the higher nitrate reductase activity in the leaves of this species. 相似文献
100.
Abstract Naturally produced methane shows different δ13C-values with respect to its origin, e.g., geological or biological. Methane-production of ruminants is considered to be the dominant source from the animal kingdom. Isotopic values of rumen methane—given in literature—range between ?80‰ and -50‰ and are related to feed composition and also sampling techniques. Keeping cows, camels and sheep under identical feed conditions and sampling rumen gases via implanted fistulae we compared δPDB 13C-values of methane and CO2 between the species. Referring to mean values obtained from 4 or 5 samples at different times of 11 animals (n = 47) we calculated δPDB 13C-medians resulting in small but not significant differences within and significant differences between the species for CO2 and methane. The δPDB 13C-differences between methane and CO2 were statistically equal within and also between the species. Therefore a linear regression of methane values on CO2 is appropriate and leads to: δPDB 13C(methane)‰ = 1,57 * δPDB 13C(CO2)‰-47‰ with a correlation coefficient of r = 0,87. 相似文献