硅碳双键化合物的合成及反应活性研究进展

不饱和硅碳双键化合物(硅碳烯)结构复杂,既有与烯烃相似的平面结构,又有重烯烃同系物相似的非平面结构.自1967年第一个不稳定硅碳双键中间体被发现以来,不饱和硅碳双键化合物的合成及其反应活性研究进展很快.硅碳双键化合物反应活性高,在有机合成和有机硅高分子材料等领域具有广阔的应用前景.本文对近年来不饱和硅碳双键化合物合成及其反应活性研究的最新进展进行综述.     

锂离子电池负极中一步球磨硅碳材料的应用

近年来,硅基类材料的高理论比容量使其在能源存储尤其锂离子电池电极材料的应用受到了广泛的关注。通过简单的高能球磨法制备了硅碳(Si/C)复合材料,同时对比了采用不同硅碳比例进行球磨后的复合材料的形貌及性能情况。球磨Si/C复合材料在作为锂离子电池负极时展现了较好的电化学性能,与碳的复合有效抑制了合金硅材料在充放电过程中由于体积膨胀导致的容量快速衰减,同时,碳硅的混合比例对其电化学性能也起到了较大的影响。通过简单一步球磨方法和调控硅碳比例制备高循环稳定性和高容量的改进方式为硅基类材料在锂离子电池中的实际应用拓展了更大的空间。     

基于透射光谱确定硅碳氧薄膜的光学常数

硅碳氧薄膜是一种含有Si、C和O三种元素的玻璃状化合物材料,同时拥有碳化硅薄膜及氧化硅薄膜多种优异的特性,如热稳定性好、能带宽、折射率大、硬度高和热导率高等,是一种具有潜在应用价值的新颖光学薄膜.基于硅碳氧薄膜的紫外/可见/近红外透射光谱,采用Swanepoel极值包络线法,结合WDD色散模型,建立了一套精确、方便并适合于计算硅碳氧薄膜光学常数的方法.方便地获得了硅碳氧薄膜折射率、厚度等光学常数.并将厚度计算结果与实际测量值进行了比较.结果表明,试验中研究硅碳氧薄膜光学常数所采用的方法是合理的,能够准确地获得硅碳氧薄膜的折射率及厚度等光学常数.     

硅碳双键稳定性的CNDO／2法研究

本文用CNDO／2法研究了硅碳双键Si=C不稳定的原因。通过分析SiH2CH2的烷基和苯基取代物的计算结果，对有大基团连接硅碳双键的化合物之所以能稳定存在做了合理的说明。     

浅谈碳烯和硅烯的同异

碳烯和硅烯是分属于碳化物和硅化物中的两类反应活性中间体。两者甚为相似。本文主要通过碳烯和硅烯的结构、制备、性质等三方面来阐明它们之间的同和异。     

丁硅烯双键转移异构化反应机理的研究

利用从头计算法(6-31G)对丁硅烯的双键转移异构化反应进行了研究,采用Berny能量梯度法优化出了产物、过渡态、中间体和反应物的几何构型,并对过渡态进行了振动分析确认.计算结果表明:丁硅烯的双键转移异构化反应的机理是:一个氢原子先从1号硅原子迁移至2号氢原子,然后再形成一个五元环,另一个氢原子从4号硅原子迁移至1号硅原子,这样,2,3双键转移为3,4双键.     

锂离子电池硅/碳负极材料的制备与应用

对锂离子电池中硅/碳负极材料的纳米结构、掺杂改性以及三元复合等制备工艺及其电化学性能、相关机理进行了总结。通过研究不同改性方法对硅/碳负极材料电化学性能的影响,以找到较为优异的改性路径。经过对比发现,通过采用纳米结构、原子掺杂以及三元复合的方法均可显著提升硅/碳负极材料的电化学性能。最后对硅/碳负极材料发展现状进行了简要分析,并对其研究前景进行了展望。     

中国陆地生态系统植硅体碳汇潜力估算研究进展

植硅体封存有机碳作为长期稳定的碳汇机制之一,近年来在全球碳汇研究领域备受关注.分析植硅体在陆地生态系统植被-凋落物-土壤连续体的周转,计算其封存的有机碳含量,是进一步准确估算整个陆地生态系统植硅体碳封存潜力的基础,对陆地生态系统碳稳定固存和碳中和具有重要意义.通过全面回顾中国陆地生态系统植硅体碳封存潜力研究成果,系统论...     

多元有机酸自组装硅碳复合材料用于高效储锂

相比于传统物理打浆式简易硅碳材料的复合，本工作利用自组装的方式让有机酸碳源材料与纳米硅粉进行内部结合，羧酸碳源保护层在抑制硅材料膨胀的同时，通过相互间串联起的网络增加导电性，得到稳定性更好的硅碳复合负极材料。该方法首先在纳米硅粉表面进行修饰，使其表面带上氨基，通过酰胺化反应，让柠檬酸与纳米硅键合。此外过量的碳源材料包附于外层，形成多个单纳米硅颗粒聚集的微米级多核卵壳型颗粒。这种结构使得该电极材料在电流密度500 mA/g下，经过600圈的长循环下具有1 073.4 mAh/g的比容量。在2 A/g的电流密度下，初始比容量为751.2 mAh/g,在300圈循环后比容量维持在573.0 mAh/g,容量保持率为76.3%。该实验工作为锂离子电池硅碳负极材料的合成提供了一种简单低成本的实用性合成思路。     

钯碳催化剂在硝基还原和碳碳双键加氢反应中的应用

对常温常压下钯碳催化剂在精细有机合成中的硝基还原和碳碳双键加氢两大类加氢反应进行了初步的探索，２－氯－６－硝基甲苯在钯碳催化剂存在下催化还原，除目的产物外，不生成脱氯副产物。这是一个连串反应，控制反应条件可获得较高的反应选择性。     

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.     

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.     

Jane Eyre——A Feminist In The 19th Century

In the 19th century the society was controlled by men, and women were just appendants of them, they had not any rights and freedom. But Jane was an exception, she showed some characteristics of early feminist. Jane showed her characteristics of feminism in three aspects: rebellion, equality, and independence. These characteristics were helpful to her success, and feminism is the only way out for women of that time.     

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