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关键词： 强迫症   动脉自旋标记   脑血流   磁共振成像  

摘要： 目的 探究首发未治疗强迫症患者的静息态脑血流灌注特点.方法 采用GE 3.0T MR扫描仪对32例强迫症患者(患者组)和34例健康志愿者(对照组)行三维伪连续式动脉自旋标记(3D-pCASL)序列扫描,采用基于体素的方法,分析2组全脑水平的血流灌注,并将有统计学差异的区域脑血流值与临床量表评分进行相关分析.结果 与对照组相比,患者组右侧扣带回灌注减低[t=-3.588,P<0.05,簇≥30,高斯随机场(GRF)校正],左侧颞中下回灌注增加(t=3.714,P<0.05,簇≥30,GRF校正);患者组左侧颞中下回平均脑血流值与强迫行为因子分呈正相关(r=0.411).结论 首发未治疗强迫症患者存在静息态脑血流的异常,脑区的灌注异常与临床症状密切相关.

摘要： 本文采用双时格林函数方法研究了自旋为1的双层平方晶格阻挫模型的相变行为.详细探讨了层间耦合相互作用J;和单离子各向异性参数D对奈尔态（AF1）和共线态（AF2）之间相转换的影响.结果显示：只要参数J;和D不同时为零，奈尔态（AF1）和共线态（AF2）在J;=J;/2(这里J;和J;分别描述的是系统自旋间最近邻和次近邻交换作用)时的相变温度相等，两个态共存.在低于相变点的温度范围内，AF1-AF2态之间可以发生相转换，其相变类型为一阶相变.当J;≠J;/2时，尽管AF1-AF2态有不同相变温度，但它们也可以共存.如果AF1（AF2）态的相变温度大，在低温，AF1（AF2）态更稳定；在高温，AF2（AF1）态更稳定；在中间温度范围内，AF1-AF2态之间也可以发生一阶相转换.

关键词： Public policy and governance   Probability theory   Statistical thermodynamics   Chemical dynamics   Quantum mechanical systems and processes  

摘要： We study analytically and numerically the non-equilibrium dynamics of an isolated interacting many-body quantum system following a random quench. We model the system Hamiltonian by Embedded Gaussian Orthogonal Ensemble (EGOE) of random matrices with one plus few-body interactions for fermions. EGOE are paradigmatic models to study the crossover from integrability to chaos in interacting many-body quantum systems. We obtain a generic formulation, based on spectral variances, for describing relaxation dynamics of survival probabilities as a function of rank of interactions. Our analytical results are in good agreement with numerics.

关键词： Potential energy  

摘要： Nonadiabatic dynamics, which goes beyond the Born-Oppenheimer approximation, has increasingly been shown to play an important role in chemical processes, particularly those involving electronically excited states. Understanding multistate dynamics requires rigorous quantum characterization of both electronic and nuclear motion. However, such first principles treatments of multi-dimensional systems have so far been rather limited due to the lack of accurate coupled potential energy surfaces and difficulties associated with quantum dynamics. In this Perspective, we review recent advances in developing high-fidelity analytical diabatic potential energy matrices for quantum dynamical investigations of polyatomic uni- and bi-molecular nonadiabatic processes, by machine learning of high-level ab initio data. Special attention is paid to methods of diabatization, high fidelity construction of multi-state coupled potential energy surfaces and property surfaces, as well as quantum mechanical characterization of nonadiabatic nuclear dynamics. To illustrate the tremendous progress made by these new developments, several examples are discussed, in which direct comparison with quantum state resolved measurements led to either confirmation of the observation or sometimes reinterpretation of the experimental data. The insights gained in these prototypical systems greatly advance our understanding of nonadiabatic dynamics in chemical systems.

关键词： Applied and Technical Physics   Theoretical   Mathematical and Computational Physics   Complex Systems   Condensed Matter Physics   Atomic   Molecular   Optical and Plasma Physics  

摘要： In this study, using the path integral formalism, the quantum thermodynamic properties of an open quantum system consisting of a vector field in the presence of a moving environment are investigated. The environment is modeled as a continuum of the Klein-Gordon field, and the environment velocity is added in the coupling tensor. Starting from a covariant Lagrangian and using functional integrals, series expansions of Green's function are obtained. Series expansions for free energy in finite temperature are derived. Using Matsubara formalism, a new definition of the first law of thermodynamics, heat and work of the quantum system is defined.

关键词： Three solutions   Time scales   Sturm-Liouville boundary value problem   Critical point theory   Variational methods  

摘要： In this paper, we give conditions guaranteeing the existence of at least three solutions for a second-order dynamic Sturm-Liouville boundary value problem involving two parameters. In the proofs of the results, we utilize critical point theory and variational methods. In addition, an example is given in order to illustrate our results. (C) 2020 Elsevier Inc. All rights reserved.

关键词： Oriented hypergraphs   Laplace operator   Spectrum   Independence number   Coloring number  

摘要： The independence number, coloring number and related parameters are investigated in the setting of oriented hypergraphs using the spectrum of the normalized Laplace operator. For the independence number, both an inertia-like bound and a ratio-like bound are shown. A Sandwich Theorem involving the clique number, the vector chromatic number and the coloring number is proved, as well as a lower bound for the vector chromatic number in terms of the smallest and the largest eigenvalue of the normalized Laplacian. In addition, spectral partition numbers are studied in relation to the coloring number. (C) 2021 Elsevier Inc. All rights reserved.

关键词： Signless Laplacian matrix   Split graph   Bidegreed graph   Eigenvalues   Combinatorial design  

摘要： It is a well-known fact that a graph of diameter d has at least d+1 eigenvalues (A.E. Brouwer, W.H. Haemers (2012) [2]). A graph is d-extremal (resp. dsL-extremal) if it has diameter d and exactly d+ 1 distinct eigenvalues (resp. signless Laplacian eigenvalues), and a graph is split if its vertex set can be partitioned into a clique and a stable set. Such graphs have diameter at most three. If all vertex degrees in a split graph are either (d) over cap or (d) over cap, then we say it is ((d) over cap, (d) over cap)-bidegreed. In this paper, we present a complete classification of the connected bidegreed 3(SL)-extremal split graphs using the association of split graphs with combinatorial designs. (C) 2021 Elsevier Inc. All rights reserved.

关键词： bistable systems   Fokker‐   Planck equation   quantum equilibrium statistical mechanics   quantum field theory   related classical field theories   solitons   transition in quantum tunneling  

摘要： A model for one-dimensional bistable systems characterized by a deformable double-well energy landscape is introduced in order to investigate the effect of shape deformability on the order of phase transition in quantum tunneling and on the quasi-exact integrability of the classical statistical mechanics of these systems. The deformable double-well energy landscape is modeled by a parameterized double-well potential possessing two fixed degenerate minima and a constant barrier height, but a tunable shape of its walls which affects the confinement of the two wells. It is found that unlike bistable models involving the standard phi(4)-field model for which the transition in quantum tunneling is predicted to be strictly of second order, a parameterization of the double-well potential also favors a first-order transition occurring above a universal critical value of the shape deformability parameter. The partition function of the model is constructed within the framework of the transfer integral formalism, with emphasis on low-lying eigenstates of the transfer integral operator. Criteria for quasi-exact integrability of the partition function were formulated, in terms of the condition for possible existence of exact eigenstates of the transfer integral operator. The quasi-exact solvability condition is obtained analytically, and from this, some exact eigenstates are derived at several temperatures. The exact probability densities obtained from the analytical expressions of the ground state wavefunctions at different temperatures are found to be in excellent agreement with the probability density obtained from numerical simulations of the Fokker-Planck equation.