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71.
Hensel V Godt A Popovitz-Biro R Cohen H Jensen TR Kjaer K Weissbuch I Lifshitz E Lahav M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(6):1413-1423
Composite materials of quantum particles (Q-particles) arranged in layers within crystalline powders of pi-conjugated, rodlike dicarboxylic acids are reported. The synthesis of the composites, either as three-dimensional crystals or as thin films at the air-water interface, comprises a two-step process: 1) The preparation of the Cd salts 6 (Cd), 8 (Cd) or Pb salts 6 (Pb), 8 (Pb) of the oligo(p-phenyleneethynylene)dicarboxylic acids 6 (H), 8 (H), in which the metal ions are arranged in ribbons and are separated by the long axis of the organic molecules, as demonstrated by X-ray powder diffraction analysis of the solids and grazing incidence X-ray diffraction analysis of the films on water. 2) Topotactic solid/gas reaction of these salts with H(2)S to convert the metal ions into Q-particles of CdS or PbS embedded in the organic matrix that consists of the acids 6 (H) and 8 (H). These hybrid materials have been characterized by X-ray photoelectron spectroscopy and transmission electron microscopy. 相似文献
72.
Peter C. Burgers Chava Lifshitz Paul J. A. Ruttink Gijs Schaftenaar Johan K. Terlouw 《Journal of mass spectrometry : JMS》1989,24(8):579-590
By combining results from a variety of mass spectrometric techniques (metastable ion, collisional activation, collision-induced dissociative ionization, neutralization-reionization spectrometry, 2H, 13C and 18O isotopic labelling and appearance energy measurements) and high-level ab initio molecular orbital calculations, the potential energy surface of the [CH5NO]+ ˙ system has been explored. The calculations show that at least nine stable isomers exist. These include the conventional species [CH3ONH2]+ ˙ and [HO? CH2? NH2]+ ˙, the distonic ions [O? CH2? NH3]+ ˙, [O? NH2? CH3]+ ˙, [CH2? O(H)? NH2]+ ˙, [HO? NH2? CH2]+ ˙, and the ion-dipole complex CH2?NH2+ …? OH˙. Surprisingly the distonic ion [CH2? O? NH3]+ ˙ was found not to be a stable species but to dissociate spontaneously to CH2?O + NH3+ ˙. The most stable isomer is the hydrogen-bridged radical cation [H? C?O …? H …? NH3]+ ˙ which is best viewed as an immonium cation interacting with the formyl dipole. The related species [CH2?O …? H …? NH2]+ ˙, in which an ammonium radical cation interacts with the formaldehyde dipole is also a very stable ion. It is generated by loss of CO from ionized methyl carbamate, H2N? C(?O)? OCH3 and the proposed mechanism involves a 1,4-H shift followed by intramolecular ‘dictation’ and CO extrusion. The [CH2?O …? H …? NH2]+ ˙ product ions fragment exothermically, but via a barrier, to NH4+ ˙ HCO…? and to H3N? C(H)?O+ ˙ H˙. Metastable ions [CH3ONH2]+…? dissociate, via a large barrier, to CH2?O + NH3+ + and to [CH2NH2]+ + OH˙ but not to CH2?O+ ˙ + NH3. The former reaction proceeds via a 1,3-H shift after which dissociation takes place immediately. Loss of OH˙ proceeds formally via a 1,2-CH3 shift to produce excited [O? NH2? CH3]+ ˙, which rearranges to excited [HO? NH2? CH2]+ ˙ via a 1,3-H shift after which dissociation follows. 相似文献
73.
C. Lifshitz M. Iraqi T. Peres J. E. Fischer 《Rapid communications in mass spectrometry : RCM》1991,5(5):238-239
Measurements of the translational energy loss accompanying the charge-stripping reactions M++N→M2++N+e− and M2++N→M3++N+e− have been performed for C, C and C, C respectively. The energy nesessary to remove the second electron from Buckminsterfullerene was determined, Q=IE(C→C=12.25±0.5 eV. 相似文献
74.
Zhang RQ Lifshitz Y Ma DD Zhao YL Frauenheim T Lee ST Tong SY 《The Journal of chemical physics》2005,123(14):144703
The analysis and density-functional tight-binding simulations of possible configurations of silicon nanowires (SiNWs) enclosed by low-index surfaces reveal a number of remarkable features. For wires along <100>, <110>, and <111> directions, many low-index facet configurations and cross sections are possible, making their controlled growth difficult. The 112 wires are the most attractive for research and applications because they have only one configuration of enclosing low-index facets with a rectangular cross section, enclosed with the most stable (111) facet and the (110) facet next to it. In general, the stability of the SiNWs is determined by a balance between (1) minimization of the surface energy gamma(111)svr(rectangular)>svr(triangular)]. The energy band gaps follow the order of <100>wires > <112>wires > <111>wires > <110>wires. The results are compared with our recent scanning tunneling microscopy and transmission electron microscopy data. 相似文献
75.
Ido Efrat 《Israel Journal of Mathematics》2009,172(1):75-92
Given a field F and a subgroup S of F
x containing −1, we define a graph on F
x/S associated with the relative Milnor K-ring K
*
M
(F)/S. We prove that if the diameter of this graph is at least 4, then there exists a valuation v on F such that S is v-open. This is done by adopting to our setting a construction in a noncommutative setting due to Rapinchuk, Segev and Seitz.
We study the behavior of the diameter under important K-theoretic constructions, and relate it to the elementary type conjecture. Finally, we provide an example showing that the
above bound 4 is sharp. 相似文献
76.
The stopping powers (SP) for 10 solid organic materials and water have been calculated in the range of proton energies 50–500 keV. Most of the presented results are new and are in good agreement with existing experimental data. The calculated data might be useful for applications in radiobiology and space research. 相似文献
77.
Let \C be a collection of n Jordan regions in the plane in general position, such that each pair of their boundaries intersect in at most s points, where s is a constant. If the boundaries of two sets in \C cross exactly twice, then their intersection points are called regular vertices of the arrangement \A(\C) . Let R(\C) denote the set of regular vertices on the boundary of the union of \C . We present several bounds on |R(\C)| , depending on the type of the sets of \C . (i) If each set of \C is convex, then |R(\C)|=O(n
1.5+\eps
) for any \eps>0 . (ii) If no further assumptions are made on the sets of \C , then we show that there is a positive integer r that depends only on s such that |R(\C)|=O(n
2-1/r
) . (iii) If \C consists of two collections \C
1
and \C
2
where \C
1
is a collection of m convex pseudo-disks in the plane (closed Jordan regions with the property that the boundaries of any two of them intersect at most twice), and
\C
2
is a collection of polygons with a total of n sides, then |R(\C)|=O(m
2/3
n
2/3
+m +n) , and this bound is tight in the worst case.
Received December 4, 1998, and in revised form June 3, 2000. Online publication Feburary 1, 2001. 相似文献
78.
79.
Annals of Operations Research - Exact analysis of a multi-server Markovian queueing system with cross selling in steady-state is presented. Cross selling attempt is initiated at the end of a... 相似文献
80.
We consider a system comprised of two connected M/M/?/? type queues, where customers of one queue act as servers for the other queue. One queue, Q 1, operates as a limited-buffer M/M/1/N?1 system. The other queue, Q 2, has an unlimited-buffer and receives service from the customers of Q 1. Such analytic models may represent applications like SETI@home, where idle computers of users are used to process data collected by space radio telescopes. Let L 1 denote the number of customers in Q 1. Then, two models are studied, distinguished by their service discipline in Q 2: In Model 1, Q 2 operates as an unlimited-buffer, single-server M/M/1/∞ queue with Poisson arrival rate λ 2 and dynamically changing service rate μ 2 L 1. In Model 2, Q 2 operates as a multi-server M/M/L 1/∞ queue with varying number of servers, L 1, each serving at a Poisson rate of μ 2. We analyze both models and derive the Probability Generating Functions of the system’s steady-state probabilities. We then calculate the mean total number of customers present in each queue. Extreme cases are indicated. 相似文献