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排序方式: 共有221条查询结果,搜索用时 46 毫秒
41.
Cover Picture: Coordination Chemistry of N‐Heterocyclic Nitrenium‐Based Ligands (Chem. Eur. J. 19/2015) 下载免费PDF全文
42.
Dynamic sampling utilizes the option of varying the sampling rates according to the situation of the systems, thus obtaining procedures with improved efficiencies. In this paper, the technique is applied to a typical problem in optimal control theory, that of tracking and controlling the position of an object. It is shown that the dynamic sampling results in a significantly improved procedure for this case, even when applying a suboptimal policy which can be analyzed in closed form. 相似文献
43.
Assaf Libman 《Topology》2003,42(3):555-568
For a coaugmented functor J on spaces, we consider J-modules and finite J-limits. The former are spaces X which are retracts of JX via the natural map. The latter are homotopy limits of J-modules arranged in diagrams whose shape is finite dimensional. Familiar examples are generalised Eilenberg MacLane spaces, which are the SP∞-modules. Finite SP∞-limits are nilpotent spaces with a very strong finiteness property. We show that the cofacial Bousfield-Kan construction of the functors Jn is universal for finite J-limits in the sense that every map X→Y where Y is a finite J-limit, factors through such natural map X→JnX, for some n<∞. 相似文献
44.
Dori Gal Eli Sone R Cohen G Hodes J Libman A Shanzer H-W Schock David Cahen 《Journal of Chemical Sciences》1997,109(6):487-496
The electronic properties of semiconductor surfaces can be controlled by binding tailor-made ligands to them. Here we demonstrate
that deposition of a conducting phase on the treated surface enables control of the performance of the resulting device. We
describe the characteristics of the free surface of single crystals and of polycrystalline thin films of semiconductors that
serve as absorbers in thin film polycrystalline, heterojunction solar cells, and report first data for actual cell structures
obtained by chemical bath deposition of CdS as the window semiconductor. The trend of the characteristics observed by systematically
varying the ligands suggests changes in work function rather than in band bending at the free surface, and implies that changes
in band line-up, which appear to cause changes in band bending, rather than direct, ligand-induced band bending changes, dominate. 相似文献
45.
The performance of La2−xCexCu1−yZnyO4 perovskites as catalysts for the high temperature water-gas shift reaction (HT-WGSR) was investigated. The catalysts were characterized by EDS, XRD, BET surface area, TPR, and XANES. The results showed that all the perovskites exhibited the La2CuO4 orthorhombic structure, so the Pechini method is suitable for the preparation of pure perovskite. However, the La1.90Ce0.10CuO4 perovskite alone, when calcined at 350/700 °C, also showed a (La0.935Ce0.065)2CuO4 perovskite with tetragonal structure, which produced a surface area higher than the other perovskites. The perovskites that exhibited the best catalytic performance were those calcined at 350/700 °C and, among these, La1.90Ce0.10CuO4 was outstanding, probably because of the high surface area associated with the presence of the (La0.935Ce0.065)2CuO4 perovskite with tetragonal structure and orthorhombic La2CuO4 phase. 相似文献
46.
High throughput production of single core double emulsions in a parallelized microfluidic device 总被引:1,自引:0,他引:1
Double emulsions are useful templates for microcapsules and complex particles, but no method yet exists for making double emulsions with both high uniformity and high throughput. We present a parallel numbering-up design for microfluidic double emulsion devices, which combines the excellent control of microfluidics with throughput suitable for mass production. We demonstrate the design with devices incorporating up to 15 dropmaker units in a two-dimensional or three-dimensional array, producing single-core double emulsion drops at rates over 1 kg day(-1) and with diameter variation less than 6%. This design provides a route to integrating hundreds of dropmakers or more in a single chip, facilitating industrial-scale production rates of many tons per year. 相似文献
47.
48.
Assaf Rinot 《Archive for Mathematical Logic》2007,46(5-6):457-464
In their paper from 1981, Milner and Sauer conjectured that for any poset , if , then P must contain an antichain of size κ. We prove that for λ > cf(λ) = κ, if there exists a cardinal μ < λ such that cov(λ, μ, κ, 2) = λ, then any poset of cofinality λ contains λ
κ
antichains of size κ. The hypothesis of our theorem is very weak and is a consequence of many well-known axioms such as GCH, SSH and PFA. The
consistency of the negation of this hypothesis is unknown.
相似文献
49.
We show that an infinite weighted tree admits a bi-Lipschitz embedding into Hilbert space if and only if it does not contain
arbitrarily large complete binary trees with uniformly bounded distortion. We also introduce a new metric invariant called
Markov convexity, and show how it can be used to compute the Euclidean distortion of any metric tree up to universal factors.
The research of the first author was conducted while he was at U. C. Berkeley and the Institute for Advanced Study. 相似文献
50.
We present two applications of Ball's extension theorem. First we observe that Ball's extension theorem, together with the recent solution of Ball's Markov type problem due to Naor, Peres, Schramm and Sheffield, imply a generalization, and an alternative proof of, the Johnson-Lindenstrauss extension theorem. Second, we prove that the distortion required to embed the integer lattice , equipped with the metric, in any -uniformly convex Banach space is of order .