块状纳米材料的设计理论研究

在二元共晶Spinodal系统中 ,Spinodal波长的大小随过冷度的增加而减少 ,并存在一个最小的波长 ,此时合金的生长速度最快 .提出当过冷度足够大时 ,液态Spinodal的波长进入到纳米尺度 ,形成块状纳米材料 .由于液态的扩散较易发生 ,当波长为纳米量级时 ,Spinodal的转变时间为微秒量级 .由于液体表面张力等的影响 ,液态Spinodal的组织由网状变成微粒形态 .     

块状纳米材料的制备实验研究

提出的块状纳米材料的形成模型可以预测和解释共晶合金的液态Ｓｐｉｎｏｄａｌ相分离，以及发生的区域和组织。当液态Ｓｐｉｎｏｄａｌ相分离在瞬间发生后。形成一种纳米材料，其晶界粒结合较紧密，具有较好的性能。对合金Ｆｅ９０Ｂ１０而言，当过冷度大于４１６℃时，液态Ｓｐｉｎｏｄａｌ相分离发生，并出现多重Ｓｐｉｎｏｄａｌ分解。晶粒尺寸为２～３ｎｍ，软磁性能为Ｂｒ＝１．３０Ｔ，Ｈｃ＝０．０１Ａ／ｃｍ。     

块状纳米材料的设计理论研究

在二元共晶Ｓｐｉｎｏｄａｌ系统中，Ｓｐｉｎｏｄａｌ波长的大小随过冷度的增加而减少，并存在一个最小的波长，此时合金的生长速度最快。提出当过冷度足够大时，液态Ｓｐｉｎｏｄａｌ的波长进入到纳米尺度，形成块状纳米材料。由于液态的扩散较易发生，当波长为纳米量级时，Ｓｐｉｎｏｄａｌ的转变时间为微秒量级。由于液体表面张力等的影响，液态Ｓｐｉｎｏｄａｌ的组织由网状变成微粒形态。     

δ′相(Al3Li) 早期沉淀过程的计算机模拟

通过计算二元铝锂合金中锂原子的占位几率,得出δ′相(Al3Li) 早期沉淀的长程序参数和成分偏离序参数,并对原子有序化和成分相分离过程进行了研究.结果表明:当合金在相图上处在失稳区时,有序化过程首先完成,而后进行成分相分离,即先发生等成分有序化,后进行失稳分解;在失稳区同一温度下,随浓度减小,有序化和成分相分离的孕育期变长.当合金位置处于亚稳区时,合金有序化与成分相分离耦合两过程同时进行.研究还发现:随合金在相图上的位置由失稳区向亚稳区过渡,有序化速度变慢.     

Cu-Ni-Al-Ti合金时效早期的Spinodal分解

本文用TEM研究了Cu-Ni-Al-Ti合金时效早期的转变方式和时效特性,推出用δ条纹的衬度变化及其间距不变等特征,作为时效早期Spinodal分解的一个判据,证实了该合金时效早期就发生了Spinodal分解,以及观察到了Spinodal有序现象。     

大晶粒Ni-Al合金的超塑性

研究了原始晶粒尺寸为 2 2 0μm的 Ni- 40 % Al(原子分数 )单相合金的高温变形行为 .结果表明 ,该合金在 1 0 0 0～ 1 1 0 0°C温区 ,5× 1 0 -4～ 5× 1 0 -5s-1的应变速率范围内呈现超塑性变形 ,在1 0 5 0°C应变速率为 2 .5× 1 0 -4s-1时 ,最大延伸率可达 340 % ,相应的应变速率敏感指数为 0 .3,表观激活能为 2 89k J/mol.原始大晶粒组织经超塑性变形后显著细化 ,而大晶粒超塑性是由高温变形过程中发生连续回复和再结晶所致 .     

纳米钨合金粉末常压烧结的致密化和晶粒长大

高密度合金由于具有密度和强度高、延性好等一系列优异的性能,在军工上被用作动能穿甲弹材料.纳米材料被认为是21世纪应用前景非常广阔的新型材料,采用纳米粉末可望大大细化钨合金晶粒,显著提高合金的强度、延性和硬度等力学性能,因而是制备新型高强韧高密度钨合金的很重要的研究方向.作者采用机械合金化(MA)工艺制备了纳米钨合金复合粉末,研究了纳米钨合金粉末在常压氢气气氛中的烧结致密化和在烧结过程中的W晶粒长大行为.同时,指出了在液相烧结时存在的问题,即W晶粒加速重排、产生晶粒聚集与合并,迅速发生W晶粒长大,在较短时间内液相烧结时,W晶粒尺寸又长大到接近传统高密度合金水平.研究结果表明,MA纳米粉末促进了致密化,使致密化温度降低100～200℃;在一般固相烧结温度时可以得到晶粒粒径为3～5μm的细晶高强度合金.     

Mg_2Si_(1-x)Sn_x合金的组织和性能

采用机械合金化+热压烧结制备Mg_2Si_(1-x)Sn_x(x=0、0.2、0.4、0.6、0.8)合金,对合金的组织性能进行了研究.结果表明:Mg2Si中的部分Si被Sn替代,晶体结构并不发生改变.随Sn替代量的增加,合金的点阵常数逐渐增大,整个XRD衍射峰向低角偏移增大,致密度先增大后减小,晶粒得到细化.随Sn替代量的增加,合金的抗压强度、抗弯强度先增大后减小,断裂方式由解理断裂向准解理断裂转变;引入Sn元素,Mg2Si1-xSnx的力学性能和热电性能得到提高,当x=0.4时,合金具有最佳的综合性能.合金的强化是由细晶强化、固溶强化和第二相强化3种机制共同作用的结果.     

Mg65Cu25Y10-xLax块体非晶合金的玻璃形成能力

传统的非晶合金多为粉末或者薄带，这样就大大限制了非晶合金的许多优异性能的发挥以及在工业中的应用，因此研究开发块体非晶合金有重要的理论与应用价值．用真空吹铸法制备了直径2mm的Mg65Cu25Y10-xLax（x=0、0．35、1、2）块体非晶合金梓，采用X射线衍射（XRD）、差热分析（DTA）分别对非晶合金的结构和形成能力进行了研究．研究结果表明，x=2时，合金具有最高的玻璃形成能力（k=0．5872）；当x=0．35时，也就是当原子半径参数λ=0．18时，不但没得到共晶点的成分，反而其玻璃形成能力比Mg65Cu25Y10还差；当x=3、4时，此时在非晶基体中已经出现晶体相，说明其玻璃形成能力显著降低．     

通过添加Dy和Ga改善纳米复合永磁合金的磁性能

采用快淬及热处理工艺 ,通过复合添加Dy和Ga ,制备了高磁性能的NdFeB纳米复合永磁合金。最佳条件下 ,添加Dy和Ga的合金磁性能为Jr =1.16T、Hci =5 80 .92kA/m和 (BH) max=16 2 .74kJ/m3;而不含Dy和Ga的NdFeB合金为Jr =1.18T、Hci =379.5kA/m和 (BH) max =119.5kJ/m3。X射线衍射和透射电子显微分析表明两种合金均由 2 :14 :1硬磁相和α -Fe软磁相组成。 2 :14 :1相晶粒尺寸在两合金中相当 ,但添加Dy和Ga的合金的α -Fe相晶粒尺寸和含量分别小于和低于不含Dy和Ga的NdFeB合金     

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.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

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     

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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