Properties of ground state and anomalous quantum fluctuations in one-dimensional polaron-soliton systems-the effects of electron-two-phonon interaction and non-adiabatic quantum correlations

Based on the Holstein model Hamiltonian of one-dimensional molecular crystals, by making use of the expansion approach of the correlated squeezed-coherent states of phonon instead of the two-phonon coherent state expansion scheme, the properties of the ground state and the anomalous quantum fluctuations are investigated in a strongly coupled electron-phonon system with special consideration of the electron-two-phonon interaction. The effective renormalization （ai） of the displacement of the squeezed phonons with the effect of the squeezed-coherent states of phonon and both the electron-displaced pbonon and the polaron-squeezed phonon correlations have been combined to obtain the anomalous quantum fluctuations for the corrections of the coherent state. Due to these non-adiabatic correlations, the effective displacement parameter ai is larger than the ordinary parameter ai （0） In comparison with the electron-one-phonon interaction （g） corrected as oig, we have found the electron-two-phonon interaction （gl） corrected as ai2gi is enhanced significantly. For this reason, the ground state energy （E（2）） contributed by the electron-two-phonon interaction is more negative than the single-phonon case （E01）） and the soliton solution is more stable. At the same time, the effects of the electron-two-phonon interaction greatly increase the polaron energy and the quantum fluctuations. Furthermore, in a deeper level, we have considered the effect of the polaron-squeezed phonon correlation （f-correlation）. Since this correlation parameter f 〉 1, this effect will strengthen the electron-one and two-phonon interactions by fai9 and f2ai2g1, respectively. The final results show that the ground state energy and the polaron energy will appear more negative further and the quantum fluctuations will gain further improvement.

论文化扩张主义与文化自治主义

文章论述了美国文化霸权扩张主义的历史基础和理论基础,着重探讨了美国通过经济技术援助、教育文化交流及大众传播媒介等基本方式进行文化霸权扩张的行径。文章还分析了文化自治主义的历史根源、理论基础和基本方式。

美国的使命意识与外交政策

"天赋使命"观是影响美国外交的重要功能性因素,它发源于17世纪盎格鲁-撒克逊白人清教徒的宿命论思想,其基本含义是:美国受上帝委托,对人类社会的发展和人类自身的命运负有一种特殊的责任与使命。美国对其自身价值观和政治制度的迷恋、向外输出民主和推广自由的热衷以及拯救"落后"国家和救赎世界的冲动等,皆源自于这种使命感。通过解读"天赋使命"观的内涵及其思想渊源,来进一步理解美国的使命意识,有助于人们考察美国的外交政策。

First-Principles Study of the High-Temperature Behaviors of the Willemite-Ⅱ and Post-Phenacite Phases of Silicon Nitride

The structural and elastic properties of the recently-discovered wⅡ- and δ-Si3N4 are investigated through the plane-wave pseudo-potential method within ultrasoft pseudopotentials.The elastic constants show that wⅡ- and δ-Si3N4 are mechanically stable in the pressure ranges of 0-50 GPa and 40-50 GPa,respectively.The α→wⅡ phase transition can be observed at 18.6 GPa and 300 K.The β→δ phase transformation occurs at pressures of 29.6,32.1,35.9,39.6,41.8,and 44.1 GPa when the temperatures are100,200,300,400,500,and 600 K,respectively.The results show that the interactions among the N-2s,Si-3s,3p bands（lower valence band） and the Si-3p,N-2p bands（upper valence band） play an important role in the stabilities of the wⅡ and S phases.Moreover,several thermodynamic parameters（thermal expansion,free energy,bulk modulus and heat capacity） of δ-Si3N4 are also obtained.Some interesting features are found in these properties.δ-Si3N4 is predicted to be a negative thermal expansion material.The adiabatic bulk modulus decreases with applied pressure,but a majority of materials show the opposite trend.Further experimental investigations with higher precisions may be required to determine the fundamental properties of wⅡ- andδ-Si3N4.

美国历史上的“反帝国主义同盟”初探

反帝国主义同盟的成立有着深刻的政治哲学背景和现实背景,而美西战争无疑是触发反帝国主义同盟成立的有力催化剂。同盟成立后经历了从地区性组织到全国性组织的发展,同盟的代表人物也有着各种不同的的社会背景。同盟者们在具体主张上虽不尽相同,但他们都强调尊重自由、民主、平等等政治原则的重要性,强调《独立宣言》和宪法所确立的政治原则对美国自身行为的自我约束性。尽管同盟的活动持续了20年左右,在美国社会中形成一股反帝国主义的浪潮,但由于当时的国际形势和国内的扩张主义思潮沉渣泛起,反帝国主义同盟逐渐被扩张主义的洪流所淹没。反帝国主义同盟虽然解体了,但它对美国政治和外交的影响是不可小视的。

“博弈”视角下的美国国家公园发展理念对中国的启示--评National Parks:The American Experience

目前,我国正处于国家公园体制稳步推进,自然保护地体系转型重构的关键时期,明确国家公园的发展思路与理念是我们亟待解决的关键问题。National Parks:The American Experience一书较为全面地探讨了美国国家公园体系的发展历程及发展理念变迁,讲述了联邦政府、铁路公司和环保组织等利益团体围绕"国家公园该如何发展"这条主线展开的一系列博弈过程,涵盖了重要的历史事件、关键的推动性人物及相关开创性法案等内容。书中对推动美国国家公园发展的思潮和理念做了总结回顾,尤其是国家公园应该"保护什么"以及"如何保护"的思考,对完善我国国家公园体制、重构自然保护地体系具有一定的借鉴和启示意义。

Trajectory tracking control based on linear active disturbance rejection controller for 6-DOF robot manipulator

The trajectory tracking control for a 6-DOF robot manipulator with multiple inputs and outputs,non-linearity and strong coupling is studied.Firstly,a dynamical model for the 6-DOF robot manipulator is designed.From the view point of practical engineering,considering the model uncertainties and external disturbances,the robot manipulator is divided into 6 independent joint subsystems,and a linear active disturbance rejection controller(LADRC)is developed to track trajectory for each subsystem respectively.LADRC has few parameters that are easy to be adjusted in engineering.Linear expansion state observer(LESO)as the uncertainty observer is able to estimate the general uncertainties effectively.Eventually,the validity and robustness of the proposed method adopted in 6-DOF robot manipulator are demonstrated via numerical simulations and 6-DOF robot manipulator experiments,which is of practical value in engineering application.