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21.
We establish a link between rational homotopy theory and the problem which vector bundles admit a complete Riemannian metric of nonnegative sectional curvature. As an application, we show for a large class of simply-connected nonnegatively curved manifolds that, if lies in the class and is a torus of positive dimension, then ``most' vector bundles over admit no complete nonnegatively curved metrics.
22.
M.A. Schneider P. Wahl L. Vitali L. Diekhöner R. Vogelgesang K. Kern 《Applied Physics A: Materials Science & Processing》2007,88(3):443-447
We use scanning tunneling microscopy and spectroscopy to study the energy dependence of hot-electron scattering processes
on metal surfaces via the determination of the energy-dependent phase-coherence length. From this an electron lifetime can
be determined, which in the case of electrons in the surface state of Ag(111) and in the case of the n=1 image-potential state
on Cu(100) shows good agreement with theoretical modeling and other experimental data. The method is based on the quantitative
analysis of electron interference patterns. A theoretical analysis shows that the phase-coherence length can be determined
in confining nanostructures of a characteristic length scale smaller than the phase-coherence length.
PACS 73.20.At; 73.50.Gr; 72.10.Fk; 68.37.Ef 相似文献
23.
Pettinari C Marchetti F Lupidi G Quassinti L Bramucci M Petrelli D Vitali LA da Silva MF Martins LM Smoleński P Pombeiro AJ 《Inorganic chemistry》2011,50(21):11173-11183
Five new silver(I) complexes of formulas [Ag(Tpms)] (1), [Ag(Tpms)(PPh(3))] (2), [Ag(Tpms)(PCy(3))] (3), [Ag(PTA)][BF(4)] (4), and [Ag(Tpms)(PTA)] (5) {Tpms = tris(pyrazol-1-yl)methanesulfonate, PPh(3) = triphenylphosphane, PCy(3) = tricyclohexylphosphane, PTA = 1,3,5-triaza-7-phosphaadamantane} have been synthesized and fully characterized by elemental analyses, (1)H, (13)C, and (31)P NMR, electrospray ionization mass spectrometry (ESI-MS), and IR spectroscopic techniques. The single crystal X-ray diffraction study of 3 shows the Tpms ligand acting in the N(3)-facially coordinating mode, while in 2 and 5 a N(2)O-coordination is found, with the SO(3) group bonded to silver and a pendant free pyrazolyl ring. Features of the tilting in the coordinated pyrazolyl rings in these cases suggest that this inequivalence is related with the cone angles of the phosphanes. A detailed study of antimycobacterial and antiproliferative properties of all compounds has been carried out. They were screened for their in vitro antimicrobial activities against the standard strains Enterococcus faecalis (ATCC 29922), Staphylococcus aureus (ATCC 25923), Streptococcus pneumoniae (ATCC 49619), Streptococcus pyogenes (SF37), Streptococcus sanguinis (SK36), Streptococcus mutans (UA159), Escherichia coli (ATCC 25922), and the fungus Candida albicans (ATCC 24443). Complexes 1-5 have been found to display effective antimicrobial activity against the series of bacteria and fungi, and some of them are potential candidates for antiseptic or disinfectant drugs. Interaction of Ag complexes with deoxyribonucleic acid (DNA) has been studied by fluorescence spectroscopic techniques, using ethidium bromide (EB) as a fluorescence probe of DNA. The decrease in the fluorescence of DNA-EB system on addition of Ag complexes shows that the fluorescence quenching of DNA-EB complex occurs and compound 3 is particularly active. Complexes 1-5 exhibit pronounced antiproliferative activity against human malignant melanoma (A375) with an activity often higher than that of AgNO(3), which has been used as a control, following the same order of activity inhibition on DNA, i.e., 3 > 2 > 1 > 5 > AgNO(3)? 4. 相似文献
24.
We verify, up to a logarithmic factor, the duality conjecture for entropy numbers in the case where one of the bodies is an ellipsoid. To cite this article: S. Artstein et al., C. R. Acad. Sci. Paris, Ser. I 336 (2003). 相似文献
25.
Crystallization and vapor condensation are considered as the processes of sequential penetration of single atoms/molecules into condensate. In the course of these transitions the transitive radiation must be generated, which would carry away the liberated latent heat by photons of characteristic frequencies. The transient radiation is examined by the general Ginzburg-Frank theory. The emission of defined frequencies determined by the values of liberated latent heat is confirmed by analyses of several experiments of authors and other researchers. 相似文献
26.
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28.
We study the existence and non-existence of positive singular solutions of second-order non-divergence type elliptic inequalities of the form $\sum\limits_{i,j = 1}^N {a_{ij} (x)\frac{{\partial ^2 u}} {{\partial x_i \partial x_j }}} + \sum\limits_{i = 1}^N {b_i (x)\frac{{\partial u}} {{\partial x_i }} \geqslant K(x)u^p ,} - \infty < p - \infty , $ with measurable coefficients in a punctured ball B R \{0} of ? N , N ≥ 1. We prove the existence of a critical value p* which separates the existence region from the non-existence region. We show that in the critical case p = p*, the existence of a singular solution depends on the rate at which the coefficients (a i j ) and (b i ) stabilize at zero, and we provide some optimal conditions in this setting. 相似文献
29.
Anna Goldberg Vitali Grinberg Irina Utepova Oleg Chupakhin Igor Eremenko 《Journal of organometallic chemistry》2011,696(13):2607-2610
New ionic complexes [ML2(MeCN)2]?2Otf (M = Co or Ni; L = 6-ferrocenyl-2,2′-bipyridyl) were synthesized and characterized by single-crystal X-ray diffraction. Cyclic voltammograms of the compounds [ML2(MeCN)2]?2Otf in CH2Cl2 show good cycle stability over 100 cycles in the quasi-reversible oxidation potential range (from −0.25 to 0.5 V). 相似文献
30.
Summary In the present paper we develop a systematic analysis of the dispersion and dissipation effects on internal gravity waves
in fluids of geophysical interest. Dissipation induces a cut-off in the short wavelengths, leading to an admissible range
of waves. Defining a suitable criterion for detection of waves, an observable wave range results, in which the frequency dispersion
is nearly the same as for the inviscid case, whereas the amplitude is damped. The peculiar behaviour displayed by the dispersion
relationship for Prandtl number equal to one is discussed. 相似文献