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21.
Let Q be a convex solid in
n
, partitioned into two volumes u and v by an area s. We show that s>min(u,v)/diam Q, and use this inequality to obtain the lower bound n
-5/2 on the conductance of order Markov chains, which describe nearly uniform generators of linear extensions for posets of size n. We also discuss an application of the above results to the problem of sorting of posets.Computing Center of the USSR Academy of Sciences USSR 相似文献
22.
Leonid Brevdo 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1991,42(6):911-942
A formalism for absolute and convective instabilities in parallel shear flows is extended to the three-dimensional case. Assuming that the dispersion relation function is given byD(k, l, ), wherek andl are wave numbers, and is a frequency, the analytic criterion is formulated by which a point (k
0,l
0,
0) with Im
0>0 contributes to the absolute instability if and only if one of the two equivalent conditions is satisfied:
Consequently, the causality condition for spatially amplifying 3-D waves in absolutely stable, but convectively unstable flow is derived as follows. We denote by (, ) a unit vector on the (x, y) plane. The contributions to amplification in the direction of this vector come from the end points of the trajectories that consist of the coalescence roots on thel
1-plane, given byl
1,=–k+l, of the systemD=0,–D
k
+gaD
1=0. Thek
1-components of these trajectories have to pass from above to below the real axis on ak
1-plane, given byk
1=k+l, as moves down to
0. Here
0 is the real frequency of excitation. At each point of such trajectories the group velocity vector (D
k
,D
l
) is collinear with the direction vector (, ). There exists a direction for which the spatial amplification rate reaches its maximum. 相似文献
(i) | At least two roots inl of the systemD(k, l, )=0,D k (k, l, )=0, originating on opposite sides of the reall-axis, collide on thel-plane for the parameter valuesk 0,l 0, 0, as is brought down to 0. Every point on thek-plane, that corresponds to a point on the collision paths on thel-plane, is itself a coalescence point ofk-roots for a fixedl ofD(k, l, )=0, that originate on opposite sides of the realk-axis. |
(ii) | At least two roots ink of the systemD(k, l, )=0,D l ,(k, l, )=0, originating on opposite sides of the realk-axis, collide on thek-plane for the parameter valuesk 0,l 0, 0, as is brought down to 0. Every point on thel-plane, that corresponds to a point on the collision paths on thek-plane, is itself a coalescence point ofl-roots for a fixedk ofD(k, l, )=0, that originate on opposite sides of the reall-axis. |
23.
H. G. Stern 《Nachrichten aus der Chemie》1979,27(6):330-332
24.
25.
26.
Leonid G. Sokoletsky Olga V. Nikolaeva Leonid P. Bass Victor S. Kuznetsov 《Journal of Quantitative Spectroscopy & Radiative Transfer》2009,110(13):1132-5779
Several numerical and analytical solutions of the radiative transfer equation (RTE) were compared for plane albedo in a problem of solar light reflection by sea water. The study incorporated the simplest case—a semi-infinite one-dimensional plane—parallel absorbing and scattering homogeneous layer illuminated by a monodirectional light beam. Inelastic processes (such as Raman scattering and fluorescence), polarization and air-water surface refraction-reflection effects, were not considered. Algorithms were based on the invariant imbedding method and two different variants of the discrete ordinate method (DOM). Calculations were performed using parameters across all possible ranges (single-scattering albedo ω0 and refracted solar zenith angle θ1), but with a special emphasis on natural waters. All computations were made for two scattering phase functions, which included an almost isotropic Rayleigh phase function and strongly anisotropic double-peaked Fournier-Forand-Mobley phase function. Models were validated using quasi-single-scattering (QSSA) and exponential approximations, which represent the extreme cases of ω0→0 and ω0→1, respectively. All methods yielded relative differences within 1.8% for modeled natural waters. An analysis of plane albedo behavior resulted in the development of a new extended QSSA approximation, which when applied in conjunction with the extended Hapke approximation developed earlier, resulted in a maximum relative error of 2.7%. The study results demonstrated that for practical applications, the estimation of inherent optical properties from observed reflectance can best be achieved using an extended Hapke approximation. 相似文献
27.
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29.
The new ternary carbodiimide LiY(CN2)2 was synthesized by solid state metathesis reaction between YF3 and Li2(CN2) in a silica tube at 550 °C. The X‐ray single‐crystal structure determination yielded an orthorhombic crystal system (Pbcn, Z = 4, a = 982.0(3), b = 698.5(2), c = 613.4(2) pm). The crystal structure can be considered related to the NiAs structure. The carbodiimide ions are arranged in layers following the motif of a hexagonal closest packing of sticks. Lithium and yttrium cations occupy all octahedral voids in an ordered fashion, alternating on top of each other along the hcp stacking direction. 相似文献
30.
Decomposition of N2O on modified zeolites, crystalline titanosilicalites, and related amorphous systems is studied by the catalytic and spectroscopic methods. Zinc-containing HZSM-5 zeolites and titanosilicalites with moderate Ti/Si ratios are shown to exhibit a better catalytic performance in N2O decomposition as compared with conventionally used Cu/HZSM-5 zeolites and amorphous Cu-containing catalysts. Dehydroxylation of the HZSM-5 zeolite by calcination at 1120 K results in an enhancement of the N2O conversion. The mechanism of the reaction and the role of coordinatively unsaturated cations and Lewis acid sites in N2O decomposition are discussed on the basis of the spectroscopic data. 相似文献