排序方式: 共有162条查询结果,搜索用时 0 毫秒
91.
M.R. Bakhtiari P. Vignolo M.P. Tosi 《Physica E: Low-dimensional Systems and Nanostructures》2005,28(4):385-392
We evaluate the phase-coherent transport of electrons along linear structures of varying length, which are made from two types of potential wells set in either a periodic or a Fibonacci quasi-periodic sequence. The array is described by a tight-binding Hamiltonian and is reduced to an effective dimer by means of a decimation-renormalization method, extended to allow for connection to external metallic leads, and the transmission coefficient is evaluated in a T-matrix-scattering approach. Parallel behaviors are found for the energy dependence of the density of electron states and of the transmittivity of the array. In particular, we explicitly show that on increasing its length the periodic array undergoes a metal–insulator transition near single occupancy per dot, whereas prominent pseudo-gaps emerge away from the band center in the Fibonacci-ordered array. 相似文献
92.
Majid M. Heravi Shima Taheri Khadijeh Bakhtiari Hossein A. Oskooie 《Monatshefte für Chemie / Chemical Monthly》2006,12(2):1075-1078
Cupric sulfate pentahydrate was found to be an efficient catalyst for the protection of aldehydes as 1,1-diacetates in high
yields in a solvent-free system at room temperature. Ketones are not affected under these reaction conditions. 相似文献
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Let (L,∧, ∨) be a finite lattice with a least element 0. AG(L) is an annihilating-ideal graph of L in which the vertex set is the set of all nontrivial ideals of L, and two distinct vertices I and J are adjacent if and only if I ∧ J = 0. We completely characterize all finite lattices L whose line graph associated to an annihilating-ideal graph, denoted by L(AG(L)), is a planar or projective graph. 相似文献
97.
Khadijeh Bagheri Mohammad-Reza Sadeghi Daniel Panario 《Designs, Codes and Cryptography》2018,86(10):2345-2377
We propose BQTRU, a non-commutative NTRU-like cryptosystem over quaternion algebras. This cryptosystem uses bivariate polynomials as the underling ring. The multiplication operation in our cryptosystem can be performed with high speed using quaternions algebras over finite rings. As a consequence, the key generation and encryption process of our cryptosystem is faster than NTRU in comparable parameters. Typically using Strassen’s method, the key generation and encryption process is approximately 16 / 7 times faster than NTRU for an equivalent parameter set. Moreover, the BQTRU lattice has a hybrid structure that makes inefficient standard lattice attacks on the private key. This entails a higher computational complexity for attackers providing the opportunity of having smaller key sizes. Consequently, in this sense, BQTRU is more resistant than NTRU against known attacks at an equivalent parameter set. Moreover, message protection is feasible through larger polynomials and this allows us to obtain the same security level as other NTRU-like cryptosystems but using lower dimensions. 相似文献
98.
A Simple Primal-Dual Feasible Interior-Point Method for Nonlinear Programming with Monotone Descent 总被引:1,自引:0,他引:1
We propose and analyze a primal-dual interior point method of the feasible type, with the additional property that the objective function decreases at each iteration. A distinctive feature of the method is the use of different barrier parameter values for each constraint, with the purpose of better steering the constructed sequence away from non-KKT stationary points. Assets of the proposed scheme include relative simplicity of the algorithm and of the convergence analysis, strong global and local convergence properties, and good performance in preliminary tests. In addition, the initial point is allowed to lie on the boundary of the feasible set. 相似文献
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'Decoking' of a 'coked' zeolite catalyst in a glow discharge in oxygen is investigated. The 'decoking' process involves reactions of atomic oxygen (O atoms) with 'coke' and yields gases such as CO, CO2 as well as other gaseous products that could be easily pumped out.Three different modes of discharge were investigated including a static mode, a flowing-gas mode, and a periodic-purge mode where the oxygen and other gaseous products of the discharge were replaced by fresh O2 gas after short but regular intervals of time. In some cases, additional heating was also used to provide base temperatures of the order of 100 °C to facilitate penetration of oxygen atoms into the inner layers and cages of the zeolite catalyst.This paper presents some results of spectroscopic analytical techniques used to monitor the atomization of oxygen, oxidation of 'coke', and to confirm the process of 'decoking'. More specifically, radiation emission on the 3 s 5S– 3p 5P transitions of O around 777.2–777.5 nm were selected for monitoring the atomization of O2. On the other hand, X-ray photo-electron spectroscopy (XPS) was used to determine the amount of residual carbon and extent of 'decoking'. Furthermore, evolution of CO and CO2 gases as a function of time was systematically monitored in real time. For CO, the 451.1 nm band head belonging to the B1 - A1 bands of the Angstrom system of the CO spectrum was used, while for CO2, the band head at 353.4 nm belonging to the CO2+ spectrum was used. The rates of evolution of CO and CO2 were related to the rate of 'decoking' of the catalyst. It is noted that in the periodic-purge mode, about 63% of the total yield of CO from a given sample of the catalyst appears in the first 3-min exposure to discharge whereas it takes up to 15 min to remove nearly 94% of the removable carbon under our experimental conditions. 相似文献
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Hossein A. Oskooie Negar M. Javadi Khadijeh Bakhtiari Fatemeh F. Bamoharram 《合成通讯》2013,43(17):2864-2869
Condensation of a variety of β-dicarbonyl compounds with primary and secondary amines carried out in the presence of catalytic amounts of K7[PW11CoO40]. From this reaction N-substituted β-enamino esters and ketones were obtained in high yields. 相似文献