基于CPLD的超低频/超大脉宽信号源的电路设计

介绍了一种基于复杂可编程逻辑器件(Complexprogrammablelogicdevice,CPLD)设计的超低频/超大脉宽脉冲信号产生器。它的主要功能是产生低频、超低频/超大脉宽脉冲信号,其最大周期Tmax>1000s,最小周期Tmin=1ms。其脉宽可在1/1000T—999/1000T范围内以T/1000步进调节。输出脉冲f/T的精确度<0.02‰,输出脉冲f/T的稳定性<±0.01‰。输出脉冲分连续输出和单次手动触发输出。该电路可以输出TTL/TTL和NIM/NIM信号。NIM快信号的上升时间tr<4ns,下降时间tf<4ns。我们用复杂可编程逻辑器件CPLD来构建主要部分电路,和常规逻辑器件相比其突出特点是:元件少、成本低、功耗低。

Kondo Effect in Carbon Nanotube Quantum Dots with Spin-Orbit Coupling

Motivated by recent experimental observation of spin-orbit coupling in carbon nanotube quantum dots [F. Kuemmeth , Nature (London) 452, 448 (2008)], we investigate in detail its influence on the Kondo effect. The spin-orbit coupling intrinsically lifts out the fourfold degeneracy of a single electron in the dot, thereby breaking the SU(4) symmetry and splitting the Kondo resonance even at zero magnetic field. When the field is applied, the Kondo resonance further splits and exhibits fine multipeak structures resulting from the interplay of spin-orbit coupling and the Zeeman effect. A microscopic cotunneling process for each peak can be uniquely identified. Finally, a purely orbital Kondo effect in the two-electron regime is also predicted.

Fano effect on shot noise through a Kondo-correlated quantum dot

Transport in a semiopen Kondo- correlated quantum dot is mediated through more than one quantum state. Using the Keldysh technique and the equation of motion method, we study the shot noise S for a wide range of source- drain voltages V-sd within a model incorporating the additional states as a background continuum, demonstrating the importance of the Fano interference. In the absence of the interference, the noise is revealed to be a probe of the second moment of the local density of states, and our theory reproduces the well- known peak structure around the Kondo temperature in the S-V-sd curve. More significantly, it is found that taking account of the background transmission, the voltage dependence of the noise exhibits rich peak- dip line shapes, indicating the presence of the Fano effect. We further demonstrate that due to its two- particle nature, the noise is more sensitive to the quantum interference effect than the simple current.

Flux-dependent shot noise through an Aharonov-Bohm interferometer with an embedded quantum dot

Shot noise through a closed Aharonov-Bohm interferometer carrying a quantum dot in one of its two current paths is investigated. It is found that the shot noise can be modulated by the magnetic flux Phi, the dot level, and the direct tunneling. Due to the interference between the two transmission channels, the Kondo correlation manifests itself in the flux dependence of the shot noise, which exhibits oscillation behavior with a period of Phi(0)/2 (Phi(0) is the flux quantum) for small voltages below the Kondo temperature T-K. At voltages well above T-K or outside the Kondo regime, the shot noise is determined by high-energy Coulomb and hybridization processes, and its Aharonov-Bohm oscillations restore the fundamental period of Phi(0). As a result of its two-particle nature, the shot noise contains higher-order harmonics absent in the current, demonstrating the fact that the noise is more sensitive to the effects of quantum interference than the current.

薄罗藓科和羽藓科某些属分类位置的探讨

Herpetineurontoccoae(Sull.et.Lesq.)Card.〕、(ThuidiumkanedaeSak.)、〔Claopodiumpellucinerve(Mitt.)Best.〕、〔Anomodonrugelii(C.Mｌｌ.)Keissl.〕、Haplohymeniumtriste(Ces.)Kindb.〕〔Lescuraeapatens(Lindb.)Arn.etJens〕、(LeskeapolycarpaEhrh.exHedw.)、〔Bryohaplocladiummicrophyllum(Hedw.)R.WatanabeetIwats〕、(FauriellatenerrimaBroth.)Bryohaplocladiumangustifolium(HampeetC.M櫣ｌｌ.)R.WatanabeetIwats.〕HaplohymeniumDoz.etMolk.)、(AnomodonHook.etTayl.)、属〔Herpetineuron(C.M櫣ｌｌ.)Card.〕(Anomodontaceae)是合理的;小羽藓属(BryohaplocladiumR.WatanabeetIwats.)Claopodium(Lesq.etJam.)RenetCard.〕Leskeaceae)。

基于语义的Web服务匹配及其框架模型研究

随着Internet上异构应用系统的大量增加和SOA技术的空前发展，Web服务技术变得越来越重要，已经成为了学术界和工业界关注的热点。在Web服务技术中，服务发现为Web服务消费者调用Web服务提供者提供的服务提供了桥梁，起到非常重要的承接作用，成为了Web服务技术中的重点。目前的Web服务发现机制主要有两种，第一种是传统的Web服务发现方式，主要基于UDDI（Universal Description， Discovery and Integration）的纯粹关键字查找；第二种是基于Web服务的语义信息，进行Web服务间的语义匹配。 第一种方法的基础UDDI是国际标准，而且应用也最为广泛，但UDDI中对于Web服务的描述是基于语法的，而且缺乏Web服务所特有的I/O属性和服务质量属性等信息。第二种方法基于Web服务的语义信息，包括Web服务所特有的I/O属性，但因为缺乏灵活有效的Web服务匹配方法和与之对应的Web服务匹配框架，限制了其应用。 基于此，本文在对当前语义Web服务匹配技术分析和研究的基础上，对当前的语义Web服务匹配方法进行了改进，同时提出了基于过滤器（filter）的语义Web服务匹配框架模型。本文的主要工作有： 1）对目前的语义Web服务匹配技术进行了较为全面深入的探讨和综述。 2）对当前的语义Web服务匹配的各个阶段进行了详细的分析，对其中的匹配方法进行了改进。提出了基于向量空间模型(VSM)和TF-IDF(Term Frequency–Inverse Document Frequency)思想的本体权重的计算方法，本体层次关系图中边的权重的计算方法和本体之间相似度的计算方法。 3）提出了基于web服务黑盒属性的语义。 4）语义Web服务匹配框架方面，本文提出了基于filter的语义Web服务匹配框架，并将其延伸到非语义Web服务系统中。

Enhancements of the simulation method on the edge effect in resin transfer molding processes

In resin transfer molding processes, small clearances exist between the fiber preform and the mold edges, which result in a preferential resin flow in the edge channel and then disrupt the flow patterns during the mold filling stage. A mathematical model including the effect of cavity thickness on resin flow was developed for flow behavior involving the interface between an edge channel and a porous medium. According to the mathematical analysis of momentum equations in a fully developed rectangular duct and formulations of the equivalent edge permeability, comparing with three-dimensional Navier-Stokes equations, the governing equations were modified in the edge channel. The volume of fluid (VOF) method was applied to track the flow front. A simple case is numerically simulated using the modified governing equations. The effects of edge channel width and cavity thickness on flow front and inlet pressure are analyzed, and the evolution characteristics of simulated results are in agreement with the experimental results. (c) 2007 Elsevier B.V. All rights reserved

Self-Assembly of Rod-Terminally Tethered Three-Armed Star-Shaped Coil Block Copolymer: Investigation of the Presence of the Branching in the Coil to the Self-Assembled Behavior

Self-assembled behavior of rod-terminally tethered three-armed star-shaped coil block copolymer melts was studied by applying self-consistent-field lattice techniques in three-dimensional (3D) space. Similar to rod-coil diblock copolymers, five morphologies were observed, i.e., lamellar, perforated lamellar, gyroidlike, cylindrical and sphericallike structures, while the distribution of the morphologies in the phase diagram was dramatically changed with respect to that Of rod-coil diblock copolymers.

Simulated morphological landscape of polymer single crystals by phase-field model

The novel phase field model with the "polymer characteristic" was established based on a nonconserved spatiotemporal Ginzburg-Landau equation (TDGL model A). Especially, we relate the diffusion equation with the crystal growth faces of polymer single crystals. Namely, the diffusion equations are discretized according to the diffusion coefficient of every lattice site in various crystal growth faces and the shape of lattice is selected based on the real proportion of the unit cell dimensions.

Temperature Dependence of Surface Composition and Morphology in Polymer Blend Film

Thin films of poly(methyl methacrylate) (PMMA) and poly(styrene-ran-acrylonitrile) (SAN) blend can phase separate upon heating to above its critical temperature. Temperature dependence of the surface composition and morphology in the blend thin film upon thermal treatment was studied using in situ X-ray photoelectron spectroscopy (XPS) and in situ atomic force microscopy (AFM). It was found that in addition to phase separation, the blend component preferentially diffused to and aggregated at the surface of the blend film, leading to the variation of surface composition with temperature. At 185 degrees C, above the critical temperature, the amounts of PMMA and SAN phases were comparable.

Rigidity effect on phase behavior of symmetric ABA triblock copolymers: A Monte Carlo simulation

The phase behavior of symmetric ABA triblock copolymers containing a semiflexible midblock is studied by lattice Monte Carlo simulation. As the midblock evolves from a fully flexible state to a semiflexible state in terms of increase in its persistence length, different phase behaviors are observed while cooling the system from an infinite high temperature to a temperature below T-ODT (order-disorder transition temperature). Within the midblock flexibility range we studied (l(p)/N-c <= 0.105), a lamellar structure is formed at equilibrium state as the situation for fully flexible chains. The fraction of bridge chain is evaluated for the lamellar structures. We find that the increase in midblock rigidity indeed results in the increase in bridge chain fraction within the range from 44.9% to 51.8%.

The dewetting dynamics of the polymer thin film by solvent annealing

The slippage effect of the polymer chains is investigated in the dewetting process of the polymer solution film. The solvent-induced dewetting is used in our experiments to study the dynamics of hole growth in the dewetting process of the polymer solution film. Our results show that in the case of the low molecular weight polystyrene (PS) film, the slippage effect of the polymer chains is not displayed and the radius of the holes is R similar to exp(t/tau); in the case of the higher molecular weight PS film, the slippage effect of the polymer chain is not valid in the case of the thin film and that is valid in the case of the thick film, and the dynamic process of hole growth divides into three stages (R similar to t, and then R similar to t(x) (2/3 < x < 1), finally, R similar to t). Besides, the solvent and substrate properties also influence the dewetting dynamics of the polymer solution film.

Self-assembly of T-shaped rod-coil block copolymer melts

Self-assembled behavior of T-shaped rod-coil block copolymer melts is studied by applying self-consistent-field lattice techniques in three-dimensional space. Compared with rod-coil diblock copolymers with the anchor point positioned at one end, the copolymers with the anchor point at the middle of the rod exhibit significantly different phase behaviors. When the rod volume fraction is low, the steric hindrance of the lateral coils prevents the rods stacking into strip or micelle as that in rod-coil diblock copolymers. The competition between interfacial energy and entropy results in the formation of lamellar structures and the increasing thickness of the lamellar layer with increasing rod volume fraction.

Composition effect on dewetting of ultrathin films of miscible polymer blend

Two kinds of dewetting and their transition induced by composition fluctuation due to different composition in blend [poly(methyl methacrylate) (PMMA) and poly(styrene-ran-acrylonitrile) (SAN)] films on SiOx substrate at 145 degrees C have been studied by in-situ atomic force microscopy (AFM). The results showed that morphology and pathway of dewetting depended crucially on the composition. Possible reason is the variation in intensity of composition fluctuation resulted from the change of components in polymer blend. Based on the discussion of this fluctuation due to the composition gradient, parameter of U-q0/E, which describes the initial amplitude of the surface undulation and original thickness of film respectively, has been employed to distinguish the morphologies of spontaneous dewetting including bicontinuous structures and holes.