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891.
The decrease of the magnetic saturation moment of superparamagnetic nickel particles of 30 Å radius by hydrogenation was investigated, and proved to be?=0.72 Bohr magnetons per hydrogen atom chemisorbed. This is the same amount that has been reported byDietz andSelwood for 64 Å particles. From this the conclusion may be drawn that most probably the effect does not depend on particle size. Interpreting the result in Pauling’s model of the covalent bond, one may conclude the Ni-H-chemisorption bond to have about 14% ionic character. This seems reasonable in view of the difference in electronegativity between hydrogen and nickel surface, but one of the assumptions of the model seems to be not safely fulfilled as will be discussed. On the other hand one may conceive chemisorption to be the first step towards formation of nickel hydride at the particle surface. Doing so, the comparison of the found result for? with recent experiments on thick nickel films electrolytically loaded with hydrogen yields a satisfactory result. 相似文献
892.
893.
The mass of gamma-globulin fouling an Anodisc alumina membrane with a nominal pore diameter of 0.1 μm has been measured at several concentrations and pHs. This fouling resulted from filtering through the membrane in a continuous recirculation device. The low-concentration fouling can be attributed mainly to adsorption. The complete concentration dependence of fouling mass has been obtained and fitted to a Freundlich heterogeneous isotherm, from which the pH dependence of active fouling sites and energies has been also obtained. Adsorption is studied as a function of the electrostatic forces between the solute and the membrane. A sharp maximum in the adsorbed mass for zero electrostatic force is observed. At high concentrations, accumulation plays a relevant role at alkaline pH, as confirmed by flux decay experiments, retention measurements, and AFM (atomic force microscopy) pictures. Copyright 2000 Academic Press. 相似文献
894.
ZnO nanocombs have been fabricated in high yield via a thermal evaporation process on Si(1 1 1) substrate by using metallic zinc powder and oxygen as source materials for zinc and oxygen, respectively, without the use of catalyst or additives at low-temperature. Morphological investigations revealed that the nanocombs were grown in high density over the whole substrate surface. The branches (teeth) of the nanocombs are uniform and nicely attached along one side of the ribbon-like stem and are arranged in a proper manner. X-ray diffraction patterns confirmed that the grown nanostructures were single-crystalline and possessed a wurtzite hexagonal phase. Room-temperature photoluminescence (PL) spectrum of the grown nanostructures is exhibit a dominant, sharp and strong UV emission with a suppressed deep-level emission indicating good crystallinity and optical properties for the as-grown ZnO nanocombs. 相似文献
895.
We present a calculation of the cross section for the process e+e-→W±H∓ in the minimal supersymmetric standard model (MSSM) and the two Higgs doublet model (THDM). We study the basic features of
the MSSM prediction for some distinctive parameter scenarios. We find large effects from virtual third-generation squarks
for scenarios with large mixing, which can lead to a cross section vastly different from a THDM with identical Higgs sector
parameters. We investigate this interesting behaviour in more detail by thoroughly scanning the MSSM parameter space for regions
of large cross section. For a charged Higgs boson too heavy to be pair produced at a future high-energy electron–positron
collider it turns out that a large MSSM cross section with a good chance of observation is linked to a squark mass scale below
600 GeV and a considerable amount of mixing in either the stop and sbottom sector. 相似文献
896.
S. Barcikowski A. Hahn A.V. Kabashin B.N. Chichkov 《Applied Physics A: Materials Science & Processing》2007,87(1):47-55
Femtosecond laser ablation is used to generate nanoparticle aerosols and colloids from solid targets of various materials
(Ti, Ag, Au, Co, etc.) in air and water ambience. We determine the influence of different laser parameters (pulse energy,
pulse overlap) and properties of media (air, airbrush, water) on the rate of production and size distribution of the laser-generated
nanoparticles. It is shown that the pulse overlap and laser fluence are the parameters determining the nanoparticle size.
At optimum conditions the nanoparticle productivity can be increased by 150–300%. The generation of multimaterial nanoparticle
dispersions is demonstrated. Being free of toxic impurities, the laser-produced nanoparticles may be promising for biomedical
applications.
PACS 79.20.Ds; 81.16.Mk; 81.16.-c; 52.38.Ph; 06.60.Jn 相似文献
897.
17O-Labelled aminyloxides 1–8 (dialkyl-, alkylaryl-, diaryl-, acylaminyloxides and amidinyloxides) have been prepared by various methods. The ESR spectra of 1a and 4 have been measured in various solvents, showing a very good correlation between aN respectively aO and the ET-values of solvents. From the solvent-dependence of the coupling constants of 1a Q-values have been evaluated for the simplified equation ai = Qiii × pi (QNNN = 33.1 G; Qooo = 35.3 G). These values were used to calculate the spin density ?N and ?o of the aminyloxides 1–8. The Q-values are shown to be reasonable by summation of the spin density of all positions for the radicals 4–7. which gives one with only small deviations. In most of these radicals in which the unpaired electron is delocalized into the conjugated π-system ?N is reduced significantly, as compared to dialkyl-ammyloxides, whereas ?0 is only lowered to a small extent. 相似文献
898.
F. L. Hahn 《Fresenius' Journal of Analytical Chemistry》1960,177(2):113-121
Ohne Zusammenfassung 相似文献
899.
900.
The charge dependence of the nucleon-nucleon force can be derived from the low-energy scattering parameters. The p-p and n-p parameters were measured in direct scattering experiments. The n-n parameters ann = (-16.70 ± 0.38) fm and rnn = (2.78 ± 0.13) fm have been determined from few particle reactions. The difference of the scattering lengths (ann - ann) ≈ 7 fm demonstrates the violation of the charge independence. Information on the charge symmetry is still doubtful due to the inaccuracy of the charge correction for the p-p parameters. Whereas the n-n and the charge corrected p-p parameters known at present yield a weaker n-n force than the p-p force, the opposite result follows from the binding energy difference for 3He and 3H and the meson theory of the nuclear forces. 相似文献