纳米磁性颗粒小点阵体系的动力学响应

通过数值解Landau Lifshitz Gilbert(LLG)方程,来研究一个具有垂直各向异性的N×N平方点阵结构的单畴铁磁颗粒体系的动力学响应.由于磁性颗粒间的偶极相互作用,我们发现存在三种不同的典型磁矩构形分布.这些构形由磁晶各向异性和磁偶相互作用之间的竞争所决定.磁性粒子的点阵几何构形是影响磁矩翻转的重要因素,偶极相互作用的增强,引起不同位置的颗粒磁矩发生先后顺序的翻转.当初态所有颗粒磁矩都平行于 z方向,且颗粒间的偶极相互作用不足以使磁矩发生耦合翻转,反转某个磁矩所需的最小翻转场将比反转单个(即无偶极相互作用)磁矩时所需的最小翻转场小得多.该种效应随着颗粒间距的增加,将明显地减弱,最小翻转场很快地增加且趋于反转单个磁矩时所需的最小翻转场.当所有颗粒磁矩处于各种不同初态时,弱偶极相互作用加宽了翻转场的取值范围.     

纳米磁性颗粒点阵的磁电阻效应

纳米颗粒高密度排列体系有其独特的磁学和电输运性质.主要研究了具有单轴各向异性的单畴磁性颗粒二维正方点阵的磁性和隧穿磁电阻效应.纳米磁性颗粒规则地浸在绝缘基质中.自旋电子在点阵中的输运主要来源于隧穿磁电阻.颗粒磁矩的取向与隧穿磁电阻的大小直接相关.我们发现磁偶极矩相互作用的强弱及温度对该种纳米颗粒点阵系统中的磁学和电输运性质有重要的影响.弱偶极相互作用下,系统的磁化强度和隧穿磁电阻随温度的增加而减小.在给定温度时,偶极相互作用强度的增加,使系统出现由低电阻状态向高电阻状态的转变.强偶极相互作用使系统出现明显的磁电阻各向异性.     

磁性超晶格的静磁能和磁相图的唯像理论研究

计算了包含不同自旋取向的单畴粒子具有短程交换相互作用能,各向异性能及长程偶极相互作用能的磁性超晶格的静磁能,利用能面图和局域能量极小模型得到了磁相图和磁滞回线,研究了有限尺寸和温度效应,计算结果较好解释了在超薄磁性薄膜中观察到的两种磁相（磁化强度平行和垂直于薄膜平面）的转变行为。     

磁性颗粒材料磁化率的研究

作者分析了磁性颗粒系统的磁化率在晶粒间传导电子和偶极相互作用下的效应．在磁性颗粒间通过传导电子的RKKY相互作用,发现了不像多层膜系统那样的非振荡的反铁磁性现象．由偶极相互作用的退磁效应显示出与简单超顺磁行为的偏差．关于71和温度的线性关系,仅适用于阻挡温度T6以上．作者还利用导出的关系实际计算了Co20Cu80和Co26Ag74的磁化率,计算结果与瓦以上的实验点的实验值吻合较好,这正表明由于颗粒偶极相互作用,使非朗之万磁化率得以显现,     

量子点磁化动力学行为的研究

利用Monte-Carlo方法研究磁性量子点阵列在不同交换耦合常数Jex、偶极相互作用常数D和磁各向异性常数K下的磁化曲线及自旋组态.模拟结果表明,对于不同的Jex和D,系统表现出不同的磁化行为和自旋组态;当Jex=0.0,D取小值时,量子点阵列的磁性基本保持了孤立原子团的磁特性,矫顽力随温度变化关系与单个的磁性原子团的相似,在低温区,矫顽力随温度的增加急剧减少;在中间温区,出现矫顽力极小;在更高温区,矫顽力随温度的增加而减少.     

偶极流体相行为的研究

偶极流体具有很强的方向性,并且是长程的。近年的理论和实验表明,它还具有强偶极相互作用。偶极流体相行为得到了广泛的研究,分子间的势能形式、多分散性、外场、浓度、温度、压强和容积率等众多因素对偶极流体相行为都有影响。回顾偶极流体相行为发展历程,明确偶极流体相行为的计算模型、模拟方法T理论方法。     

ZnxFe3-xO4磁性液体的制备及性能研究

利用改进的化学共沉淀法制备ZnxFe3-xO4(x＝0.1～0.3)纳米颗粒,研究了Z2+n的摩尔比对ZnxFe3-xO4纳米颗粒比饱和磁化强度的影响;选择饱和磁化强度最大的Zn0.2Fe2.8O4纳米粉体,制备了煤油基磁性液体,对其饱和磁化强度、黏度等性质进行研究;结果表明当x为0.2时,饱和磁化强度达到最大,为63.07Am2/kg;合成的磁性液体在外磁场作用下显出超顺磁性,其比饱和磁化强度随密度的增大而增大,最大可达29.93 Am2/kg;随着温度的升高,磁性液体的黏度下降,质量浓度越大,其下降速度越快,在30℃时,当质量浓度小于0.28g/mL时,磁性液体呈现牛顿流体特性,当质量浓度大于0.28g/mL时,牛顿流体特性消失.     

光晶格中偶极BEC偶极——偶极相互作用极限的讨论

在GP方程和离散Schrodinger方程的基础上,根据对光晶格中偶极玻色——爱因斯坦凝聚体(BEC)的调制不稳定性的研究,如果频率出现虚值,则光晶格中的偶极BEC将出现调制不稳定性,而偶极——偶极相互作用对光晶格中偶极BEC的非线性激发和稳定性有很大的影响。由于偶极——偶极相互作用可以通过外场很方便地进行调节,本文中,我们对光晶格中偶极BEC偶极——偶极相互作用的极限进行了必要的讨论,这可为实际应用中如何操控偶极BEC提供有用的信息。     

硬磁CoFe2O4/软磁CoFe2复合物的磁性研究

采用金属有机盐热分解方法制备出均匀、分散的硬磁CoFe_2O_4纳米颗粒,在H2环境、低温条件下进行还原,合成硬磁CoFe_2O_4/软磁CoFe_2复合磁体.采用低温还原,目的在于尽可能减少粒子的聚集.制备出的样品具有较好的磁性能:有较高的剩磁比Mr/Ms,其值为0.64;随着还原时间延长,饱和磁化强度增加至124emu·g~(-1),同时保持较高的矫顽力.分析认为,可以通过减弱粒子间的偶极相互作用来有效提高硬磁/软磁复合磁体的矫顽力和剩磁比.     

基于计算经典辐射功率的量子偶极-偶极相互作用求解

提出了一种通用的严格求解任意微纳结构中2个二能级“原子”间量子偶极-偶极相互作用的方法.量子偶极-偶极相互作用传输率用2个经典电偶极子同时存在时的辐射功率减去它们单独存在时的辐射功率来表达,辐射功率通过经典的时域有限差分方法获得.将该方法应用到偶极子处于真空和平板金属腔中的情况,其数值结果与解析结果符合得很好,验证了该方法的可行性.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

An affordable accurate evaluation of the binding conformations predicted by molecular docking studies in bio-system

Franck-Condon factors bridge the gap between theoretical modeling and experimental observations for molecular electronic spectroscopy and electron transfer.Under the displaced harmonic oscillator approximation,multidimensional Franck-Condon factors are decomposed into a product of many one-dimensional(1D)Franck-Condon(FC)factors,and each 1D-FC factor is associated with one Huang-Rhys factor that determines the leading contribution of     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

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