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The photolysis of C2H5I in a glassy salt matrix (5M, 7.5M, 10M) of aqueous LiCl at 77 K with light of λ = 254 nm has been conducted, product analysis being by ESR and UV spectroscopy. The electrolytic medium causes the ionization of product HI, and I? concentrations can be continuously determined. During photolysis [I?] is less than the amount of C2H5I decomposed. But after photolysis thaw-freeze cycling is accompanied by progressive growth in [I?] until the yield matches the C2H5I loss, the quantum yields being 0.26, 0.20, and 0.17 for the three LiCl solutions, respectively. The quantum yield of unionized HI is unchanged, however, at around 0.36, the overall change being due to a fall in the extent to which the HI is ionized in the direct photolysis (ø = 0.22, 0.16, and 0.11). It is proposed that this is a consequence of the density increase of matrix packing as the LiCl concentration is increased so that fewer HI are in contact with the aqueous medium and cage recombination is favored. The results establish that the primary reaction is essentially exclusive: and that substantial aggregates of C2H5I exist within which HI are caged and cannot be ionized. The direct reaction occurs only to a trivial extent, ø; = 10?4, C2H5 arising virtually totally via 相似文献
23.
We have calculated the surface state density on the (001) surface (assumed to consist of nickel atoms) of the antiferromagnetic phase of hexagonal nickel sulphide. We find that a surface state only exists for one spin and we style it a ferromagnetic surface state. The density of surface states has been calculated and is compared to the bulk density of states. Some possible effects of the surface state band are considered. 相似文献
24.
In real systems, inelastic processes remove photoelectrons from the elastic scattering channel. This reduces the amplitude of the EXAFS. Traditionally the discrepancies between experimental and theoretical amplitudes were treated by including two semi-empirical reduction factors in the data analysis. Some inelastic effects may, however, be modelled more rigorously using a complex exchange and correlation potential, for example the Hedin-Lundqvist (HL) potential used in most EXAFS data-analysis programs. In this paper a systematic study of the effects of the HL potential on the calculated EXAFS amplitudes is presented. Expressions are derived whereby the EXAFS amplitudes may be examined in the presence of an arbitrary complex potential independently to the rest of the EXAFS signal. These results are used to study the effects of the HL potential on EXAFS data analysis in detail. 相似文献
25.
Electromigration of hydrogen in YH(3-delta) is studied by exploiting the H concentration dependence of the optical transmission of YH(3-delta). We find the effective valence Z* of H in YH(3-delta) to be negative. Its value is dominated by a huge wind-force-like term, i.e., Z* approximately K/rho, with K approximately -60 mOmega cm. This value is 3 orders of magnitude larger than typical for H in metals. In an Arrhenius plot, the ratio of hydrogen and electron fluxes extrapolates to unity at infinite temperature, suggesting a one-to-one correlation of hydrogen and electron hopping. We discuss our results in the light of strong electron correlation theories which predict each proton to bind two electrons in a sort of Zhang-Rice singlet. 相似文献
26.
IA Simpson R Bol ID Bull RP Evershed K Petzke SJ Dockrill 《Rapid communications in mass spectrometry : RCM》1999,13(13):1315-1319
Compound specific stable isotope analyses of managed soils using isotope ratio mass spectrometry have been undertaken as a means of determining early land use practices. delta (15)N amino acid signals demonstrate differences between manured grassland, unmanured grassland and continuous cereal cultivation under long-term experimental land use control conditions, with delta (15)N in hydrophobic amino acids providing the most distinctive signals. Analysis of early modern/medieval and of Bronze age anthropogenic soils from Orkney demonstrates that such signals are retained in archaeological contexts. delta (13)C analyses of n- alkanoic acid components of the fossil, Bronze Age, anthropogenic soils suggest a major terrestrial input to these soils, with uniform composition of formation materials. Surficial soils demonstrate the assimilation of isotopically lighter carbon, providing a means of assessing the mobility of the n- alkanoic acids within soils and sediments. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
27.
We have performed extensive small-angle neutron scattering (SANS) diffraction studies of the vortex lattice in single crystal
YNi2B2C for B‖c. High-resolution SANS, combined with a field-oscillation vortex lattice preparation technique, allows us to separate Bragg
scattered intensities from two orthogonal domains and accurately determine the unit cell angle, β. The data suggest that upon increasing field there is a finite transition width where both low- and high-field distorted
hexagonal vortex lattice phases, mutually rotated by 45°, coexist. The smooth variation of diffracted intensity from each
phase through the transition corresponds to a redistribution of populations between the two types of domains. 相似文献
28.
New first- and high-order centred methods for conservation lawsare presented. Convenient TVD conditions for constructing centredTVD schemes are then formulated and some useful results areproved. Two families of centred TVD schemes are constructedand extended to nonlinear systems. Some numerical results arealso presented. 相似文献
29.
We consider an approach to the estimation of attainability sets of a control system for solving various control problems.
The approach is based on two types of extension of the system, by weakening the finite constraints describing the set of velocities
and by diminishing the order of the differential constraint. By combining extensions of both types, one can obtain a sufficiently
wide class of estimates from which one can then choose the most effective estimates from the viewpoint of accuracy or simplicity. 相似文献
30.
Experimental ESR spectra of the 2,2,6,6-tetramethyl-4-oxopiperidinoxyl (TEMPON) radical probe in the glycerol, polystyrene,
and polyvinylbutyral matrices measured in the temperature range 77–373 K were quantitatively compared with the ESR spectra
calculated using the known theoretical models of rotational mobility. It was shown that simulation of ESR spectra by the nonlinear
least-squares method is an efficient procedure for discriminating between theoretical models. The temperature ranges were
determined in which it is possible to achieve quantitative agreement between experimental and theoretical spectra as well
as the ranges in which theoretical models are insufficient to quantitatively describe the experimental results. It was established
that the widely used model of Brownian diffusion in isotropic medium is inadequate to describe the ESR spectra in the case
of slow motions of small probe molecules. It was found that specific interactions (formation of weak complexes) between the
probe molecules and the molecules of the medium results in strongly anisotropic molecular rotational motions.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1065–1073, June, 2000. 相似文献