Dynamics of quantum dissipation systems interacting with fermion and boson grand canonical bath ensembles: Hierarchical equations of motion approach

A hierarchical equations of motion formalism for a quantum dissipation system in a grand canonical bath ensemble surrounding is constructed on the basis of the calculus-on-path-integral algorithm, together with the parametrization of arbitrary non-Markovian bath that satisfies fluctuation-dissipation theorem. The influence functionals for both the fermion or boson bath interaction are found to be of the same path integral expression as the canonical bath, assuming they all satisfy the Gaussian statistics. However, the equation of motion formalism is different due to the fluctuation-dissipation theories that are distinct and used explicitly. The implications of the present work to quantum transport through molecular wires and electron transfer in complex molecular systems are discussed. (c) 2007 American Institute of Physics.

Quantum transport from the perspective of quantum open systems

By viewing the non-equilibrium transport setup as a quantum open system, we propose a reduced-density-matrix based quantum transport formalism. At the level of self-consistent Born approximation, it can precisely account for the correlation between tunneling and the system internal many-body interaction, leading to certain novel behavior such as the non-equilibrium Kondo effect. It also opens a new way to construct time-dependent density functional theory for transport through large-scale complex systems. (c) 2006 Elsevier B.V. All rights reserved.

Coherent transport through a quantum dot embedded in a double-slit-like Aharonov-Bohm ring

Coherent transport through a quantum dot embedded in one arm of a double-slit-like Aharonov-Bohm (AB) ring is studied using the Green's function approach. We obtain experimental observations such as continuous phase shift along a single resonance peak and sharp inter-resonance phase drop. The AB oscillations of the differential conductance of the whole device are calculated by using the nonequilibrium Keldysh formalism. It is shown that the oscillating conductance has a continuous bias-voltage-dependent phase shift and is asymmetric in both linear and nonlinear response regimes.

Interplay between partial incoherence, partial inelasticity, resonance, and heterogeneity in long-range electron transfer and transport

A generalized scattering matrix formalism is constructed to elucidate the interplay of electron resonance, coherence, dephasing, inelastic scattering, and heterogeneity, which play important roles in the physics of long-range electron transfer/transport. The theory consists of an extension of the standard Buttiker phase-breaking model and an analytical expression of the electron transmission coefficient for donor-bridge-acceptor systems with arbitrary length and sequence. The theory incorporates the following features: Dephasing-assisted off-resonance enhancement, inelasticity-induced turnover, resonance enhancement and its dephasing-induced suppression, dephasing-induced smooth superexchange-hopping transition, and heterogeneity effects. (C) 2002 American Institute of Physics.

A density-functional study of small titanium clusters

The atomic structures and electronic properties of small Ti-N (N=2-10) clusters have been studied by using the density-functional theory with a local spin density approximation. We find that the inner-shells (3s3p) of the titanium atom plays an important role in the formation of the small clusters. We have obtained the ground state of titanium clusters, Ti-7 is found to be a magic cluster, which is in good agreement with the experimental results. Starting with Ti-8 cluster some features of the electronic structure of the titanium bulk have been developed. The ionization potentials and magnetic moments for these small titanium clusters are also presented. (C) 2000 American Institute of Physics. [S0021- 9606(00)30544-X].

Landauer-Buttiker formula for time-dependent transport through resonant-tunneling structures: A nonequilibrium Green's function approach

A nonequilibrium Green's-function formalism is employed to study the time-dependent transport through resonant-tunneling structures. With this formalism, we derive a time-dependent Landauer-Buttiker formula that guarantees current conservation and gauge invariance. Furthermore, we apply the formula to calculate the response behaviors of the resonant-tunneling structures in the presence of rectangular-pulse and harmonic-modulation fields. The results show that the displacement current plays the role of retarding the tunneling current.

Dielectric relaxation of poled polymer DCNP/PMMA

We have prepared the polymer thin films of a 3-(1,1-dicyanothenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DChTP)/poly (methyl methacrylate) (PMMA) guest-host system by spin coating. In order to investigate their temporal and temperature stability, we have measured their dielectric relaxation spectra including the frequency dependence of the real and imaginary parts of dielectric constants. The investigated frequency ranged from 50 Hz to 10 MHz. The measured temperature range above the glass transition temperature T-g (95 degrees C) of the DCNP/PMMA system was from 95 degrees C to 1250C. By using the Adam-Gibbs model, the temperature dependence of the characteristic time tau above T-g was fitted, and the values of the characteristic times tau below T-g were estimated. The lifetimes of the polymer were evaluated by the Kohlrausch-Williams Watts (KWW) empirical decay model. (C) 2000 Elsevier Science B.V. All rights reserved.

Refractive index dispersion measurement on nonlinear optical polymer using V-prism refractometer

By using V-prism refractometer, the refractive indices of a polyetherketone (PEK-c) guest-host polymer system were measured with the polymer in solutions. The Lorenz-Lorentz local field formalism was used in the calculation of the refractive indices of the polymers from the measured indices of the polymer solutions and the pure solvent by using V-prism refractometer. The refractive index dispersions of the polymers were obtained by fitting the measured indices of the polymers to Sellmeyer equation. The method allows for an accuracy in index of 0.7% in the determination of the polymer indices. In addition, a large difference between the indices of the polymer and the solvent, and a higher polymer volume fraction in the measured polymer solution are favorable for a high accuracy. (C) 2000 Elsevier Science Ltd. All rights reserved.

Electron transport through a double-quantum-dot structure with intradot and interdot Coulomb interactions

Electron transport through a double-quantum-dot structure with intradot and interdot Coulomb interactions is studied by a Green's function (GF) approach. The conductance is calculated by a Landauer-Buttiker formula for the interacting systems derived using the nonequilibrium Keldysh formalism and the GF's are solved by the equation-of-motion method. It is shown that the interdot-coupling dependence of the conductance peak splitting matches the recent experimental observations. Also, the breaking of the electron-hole symmetry is numerically demonstrated by the presence of the interdot repulsion. [S0163-1829(99)01640-9].

Resonant magnetopolaron effects in GaAs/AlGaAs multiple quantum well structures

A detailed experimental study of electron cyclotron resonance (CR) has been carried out at 4.2 K in three modulation-doped GaAs/Al0.3Ga0.7As multiple quantum well samples in fields up to 30 T. A strong avoided-level-crossing splitting of the CR energies due to resonant magnetopolaron effects is observed for all samples near the GaAs reststrahlen region. Resonant splittings in the region of AlAs-like interface phonon modes of the barriers are observed in two samples with narrower well width and smaller doping concentration. The interaction between electrons and the AlAs interface optical phonon modes has been calculated for our specific sample structures in the framework of the memory-function formalism. The calculated results are in good agreement with the experimental results, which confirms our assignment of the observed splitting near the AlAs-like phonon region is due to the resonant magnetopolaron interaction of electrons in the wells with AlAs-like interface phonons. (C) 1998 Elsevier Science B.V. All rights reserved.

yet another meta-language for programming language processing

The formal specification language LFC was designed to support formal specification acquisition. However, it is yet suited to be used as a meta-language for specifying programming language processing. This paper introduces LFC as a meta-language, and compares it with ASF+SDF, an algebraic specification formalism that can also be used to programming languages.

基于LDA模型的文本分割

文本分割在信息提取、文摘自动生成、语言建模、首语消解等诸多领域都有极为重要的应用.基于LDA模型的文本分割以LDA为语料库及文本建模,利用MCMC中的Gibbs抽样进行推理,间接计算模型参数,获取词汇的概率分布,使隐藏于片段内的不同主题与文本表面的字词建立联系.实验以汉语的整句作为基本块,尝试多种相似性度量手段及边界估计策略,其最佳结果表明二者的恰当结合可以使片段边界的识别错误率远远低于其它同类算法.

Species transformation of trace elements and their distribution prediction in dyestuff residue incineration

The release of heavy metals from the combustion of hazardous wastes is an environmental issue of increasing concern. The species transformation characteristics of toxic heavy metals and their distribution are considered to be a complex problem of mechanism. The behavior of hazardous dyestuff residue is investigated in a tubular furnace under the general condition of hazardous waste pyrolysis and gasfication. Data interpretation has been aided by parallel theoretical study based on a thermodynamic equilibrium model based on the principle of Gibbs free energy minimization. The results show that Ni, Zn, Mn, and Cr are more enriched in dyestuff residue incineration than other heavy metals (Hg, As, and Se) subjected to volatilization. The thermodynamic model calculation is used for explaining the experiment data at 800 degrees C and analyzing species transformation of heavy metals. These results of species transformation are used to predict the distribution and emission characteristics of trace elements. Although most trace element predictions are validated by the measurements, cautions are in order due to the complexity of incineration systems.

Free radial oscillation of a sphere in relativistic elasticity theory

The spherically symmetric free radial oscillation in the first post-Newtonian approximation for a homogeneous and isotropic elastic sphere with a constant density is studied. Based on the Xu, Wu, and Soffel formalism, the relation of the oscillation frequency of the sphere with the radius, mass density, and elastic constants of the sphere is derived by using the successive approximation method.

反式1，4-聚丁二烯的形态和结构研究

高分子材料一般都具有某种特定的结构，这种结构将直接决定着材料的性能。当高聚物从一种结构变为另一种结构时，其材料的性能将发生改变。近来，M.Hikosaka根据聚乙烯结晶的特点，提出了“链滑移扩散理论”，认为对聚合物热处理时，其晶体片层增厚快慢与分子链的滑移扩散能力有关。反式1,4-聚丁二烯(TPBD)在常压下能以六方相稳定存在，是少有的几种具有六方相结构的聚合物。因为其六方相分子链具有较高的构象数，而各个构象之间由于能垒相差不大，构象之间很容易发生转变；因而分子链运动时相对容易，决定了六方相分子链之间的滑移扩散能力较强。为了验证M.Hikosaka的理论，特对样品在六方相温度范围进行热处理。另外由于TPBD在不同的温度下能以两种晶型稳定存在，这两种晶型之间是怎样转变的也是我们关心的问题，而且通过电镜第一次摄得了单斜相和六方相共存的电子衍射。针对上述问题我们进行了下列研究。(1)以三氯化钒体系，稀土催化剂体系合成了两种分子量的反式1,4-聚丁二烯，用IR，NMR分析高分子量样品的反式1,4结构含量为96.2%，低分子量样品反式l,4结构含量为91.2%。对两种分子量样品进行DSC研究，结果表明低分子量样品的转变温度。熔融温度均比高分子量样品低；用Thomoson-Gibbs方程计算了该样品的片层厚度，并与样品的SAXS实验结果对照，认为这种转变温度和熔点的差异除了与1,2-结构的含量有关外，也与不同分子量具有不同的片层厚度有很大关系。(2)对不同分子量的TPBD进行WAXD实验，研究了其在不同温度下的相行为及单斜相向六方相的相转变过程。以PLM为手段跟踪观察了低分子量样品的相态转变，发现许多晶粒在相转变时从视场中消失。用电镜观察到了单斜相电子衍射，六方相电子衍射及单斜相和六方相共存的电子衍射， 并发现两相结构的形貌没有大的差别。(3)用Cerius~2软件模拟了单斜相结构和六方相结构的分子链堆砌，认为单斜相向六方相发生转变时，六方相分子链构象与单斜相分子链构象相比，有序度较低，从而使其堆砌结构变得松散。同时也模拟了单斜相和六方相在晶带轴为[001]方向的电子衍射，实验观察只能得到计算机模拟所得的单斜相和六方相内层的几个电子衍射点。(4)对低分子量样品在64 ℃热处理1小时后进行的DSC，WAXD，SAXS研究表明，样品的片层厚度显著增大，结晶度也相应提高。(5)研究了高分子量样品在85 ℃和低分子量样品在53 ℃热处理不同时间后，所得的DSC曲线。结果表明随时间增加，TPBD的转变峰温度值明显增加；而且发现在前5分钟内处理样品时，结晶度都有明显增加，处理样品5分钟以后结晶度增长缓慢。对高分子量样品四次升降温时，发现降温曲线有肩峰出现，但升温曲线没有肩峰出现，把肩峰的出现归结于有小尺寸亚稳定晶体的形成。(6)对高分子量样品的六方相等温结晶数据及对由熔体快速冷却到一定温度生成单斜相的等温结晶数据进行处理，得到平衡熔点为476K，比文献值高。并利用Thomoson-Gibbs方程，得到了单斜相和六方相的温度对尺寸倒数的相图，确定了在一定尺寸下单斜相和六方相稳定存在的温度范围。(7)用电镜观察了在70 ℃热处理不同时间后所得形貌图，并讨论了样品在六方相中热处理时，样品聚集体的聚集方式。(8)研究了两种分子量样品溶液结晶时所得的球晶形貌，发现其结晶形貌与分子量有关，而且发现摄得的电子衍射是六方相电子衍射，而不是室温下稳定存在的单斜相电子衍射，认为是由于电子辐照使样品升温而发生了晶型转变。(9)用修饰后的Avrami方程，Ozawa，方程分别处理了TPBD非等温结晶数据，由Jeziorny修饰的Avrami方程分析显示TPBD的非等温结晶明显地分为一次结晶和二次结晶两个阶段，指数值n意味着一次结晶和二次结晶的成核种类，Ozawa方程分析不能很好地适用于TPBD的六方相非等温结晶数据，主要是由于Ozawa理论的不精确假定，如二次结晶，结晶温度对片层厚度相关性及整个结晶过程中恒定的冷却函数等。并由Kissinger方程得到六方相的结晶活化能为167.9kJ/mol。