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1.
前一工作基础上,对经一次循环后应力值不能完全恢复的现象进行了进一步研究。结果表明是因碎球引起。这不仅圆满地解释了实验现象,而且对该方法的科学性,实用性作了进一步考察。  相似文献   

2.
在前一工作基础上,对经一次循环后应力值不能完全恢复的现象进行了进一步研究。结果表明是因碎球引起。这不仅圆满地解释了实验现象,而且对该方法的科学性,实用性作了进一步考察。  相似文献   

3.
采用HV-21型碳硫自动分析仪测定碳、硫时,经常出现空白值偏高,碳含量突然偏低或无检测信号等现象,对这些现象进行了分析并提出了解决办法。  相似文献   

4.
早在本世纪初物理化学家们就已观察到,某些物质从其熔融态或溶液中结晶出来时,在某些条件下可形成周期性的宏观结晶条纹[1,2],这就是周期结晶现象,由于这种现象和晶体生长、材料物性以及成矿过程等重要问题紧密相关,很早就引起了人们的重视.近年来有关非平衡非线性系统中自发产生各种时空有序现象(自组织现象)的各种理论(如耗散结构理论)[3]的兴起,重新引起了人们对这类现象的兴趣.八十年代,Iwamoto等先后报道了甲基苄基氨基甲酸酯(MethylMesitylcarbamate)从氯仿溶液[4]和抗坏血酸(AscorbicAcid)从甲醇溶液[5]…  相似文献   

5.
指导了发生在异丁醇、硝基乙烷和水三组分两相体系中的多因素复合界面不稳定现象,文中通过对一个滴加在异丁醇水溶液表面的硝基乙烷液滴的运动特征的分析,揭示了该现象的规律,在体系趋于热力学平衡的过程中,硝基乙烷液滴先表现出周期性的振荡运动,然后转变为螺旋线和圆周运动,提出了一个溶质迁移和相间溶解的双因素自耦合机理,认为该现象的根本起因是表面活性剂溶质相间迁移所导致的溶质Marangni效应,但由于丁醇的相  相似文献   

6.
陆妙琴  龙耀庭 《色谱》1991,9(1):14-20
 〕本文较系统地观察了毛细管气相色谱中出现的“双峰现象”即单一纯组分在某些气相色谱条件下,会出现两个类似独立组分的双峰。本工作研究了柱温、柱子固定相极性、样品溶剂种类、仪器结构以及操作等因素对双峰出现的影响。实验结果表明,在柱温较低、溶剂蒸发潜热较大的情况下,容易引起双峰的事实可能说明,毛细管气相色谱中的双峰现象是一种溶剂效应。事实上,通过更换合适的溶剂,可以消除这种现象。本文对有关实验结果进行了讨论。  相似文献   

7.
〕本文较系统地观察了毛细管气相色谱中出现的“双峰现象”即单一纯组分在某些气相色谱条件下,会出现两个类似独立组分的双峰。本工作研究了柱温、柱子固定相极性、样品溶剂种类、仪器结构以及操作等因素对双峰出现的影响。实验结果表明,在柱温较低、溶剂蒸发潜热较大的情况下,容易引起双峰的事实可能说明,毛细管气相色谱中的双峰现象是一种溶剂效应。事实上,通过更换合适的溶剂,可以消除这种现象。本文对有关实验结果进行了讨论。  相似文献   

8.
温敏水凝胶   总被引:21,自引:2,他引:21  
概述了近十多年来对温敏水凝胶的研究及近期的发展,对有关现象进行了解释和说明,并提及了有关方面的应用。  相似文献   

9.
通过改变观察方式来实现实验过程和现象的可视化。通过在手机后置摄像头夹上手机微距镜头来实现微距摄影功能,通过录像捕获试管内硅酸钠溶液与绿豆大的金属盐反应画面,用"拍大师"视频编辑软件按需设置"播放倍数",以及使用教学多媒体展示来观察实验现象。结果表明,此方法能够捕获反应全过程,得到清晰、放大的画面,实验现象明显。对实验细节现象做出了更准确的描述,了解到更丰富的细节信息。  相似文献   

10.
高效液相色谱中同系物保留值收敛现象的研究   总被引:2,自引:0,他引:2  
在讨论影响溶质保留行为因素的基础上,建立了描述同系物保留值收敛现象的一般模型,对12种同系物(共38组数据)在6种不同组成的二元流动相和8种固定相中的保留值进行了回归分析,相关系数r≥0.974,标准偏差SD≤0.05.绘制了这些同系物的三维保留图形及投影图,并据此对同系物收敛现象及其物理意义进行了讨论,建立了计算收敛点坐标的简便方法.  相似文献   

11.
Hartree-Fock and Kohn-Sham orbital energies, the latter computed with several different exchange/correlation functionals, are compared and analyzed for 12 molecules. The Kohn-Sham energies differ significantly from experimental ionization energies, but by amounts that are, for a given molecule and exchange/correlation functional, roughly the same for all of the valence orbitals. With the exchange/correlation functionals used, the energy of the highest occupied Kohn-Sham orbital does not approximate the corresponding ionization potential any better than do the other orbital energies. Received: 24 October 1997 / Accepted 31 October 1997  相似文献   

12.
陈鸿章  王文峰  李俊汉 《化学学报》2007,65(22):2577-2582
根据三轨道作用法重点讨论了Diels-Alder反应中反应物轨道演变成产物轨道的过程, 演变结果与轨道对称守恒原理的结果基本相同. 量子化学计算证实了演变过程的合理性, 这表明在解释D-A反应方面轨道对称守恒原理比前线轨道理论更加合理可靠.  相似文献   

13.
Maximum bond order hybrid orbitals   总被引:1,自引:0,他引:1  
Summary Based on the simplified calculation scheme of the maximum bond order principle and the basic idea of the maximum overlap symmetry orbital method, a simple procedure is suggested for constructing systematically the bonding hybrid orbitals, called maximum bond order hybrid orbitals, for a given molecule from the first-order density matrix obtained from a molecular orbital calculation. As an example, the proposed procedure is performed for some typical small molecules by use of the density matrix obtained from CNDO/2 calculation. It is shown that the bonding hybrid orbitals constructed by using the procedure are extremely close to those by using the natural hybrid orbital procedure and in good agreement with chemical intuition, and that the proposed procedure can be performed more easily than the natural hybrid orbital procedure and can given simultaneously the values of the maximum bond order for all bonds in molecules.The project was supported by National Natural Science Foundation of China and also supported partly by Foundation of Hubei Education Commission  相似文献   

14.
Optimal Gaussian-type orbital (GTO) basis sets of positron and electron in positron-molecule complexes are proposed by using the full variational treatment of molecular orbital (FVMO) method. The analytical expression for the energy gradient with respect to parameters of positronic and electronic GTO such as the orbital exponents, the orbital centers, and the linear combination of atomic orbital (LCAO) coefficients, is derived. Wave functions obtained by the FVMO method include the effect of electronic or positronic orbital relaxation explicitly and satisfy the virial and Hellmann–Feynman theorems completely. We have demonstrated the optimization of each orbital exponent in various positron-atomic and anion systems, and estimated the positron affinity (PA) as the difference between their energies. Our PA obtained with small basis set is in good agreement with the numerical Hartree–Fock result. We have calculated the OH and [OH; e+] species as the positron-molecular system by the FVMO method. This result shows that the positronic basis set not only becomes more diffuse but also moves toward the oxygen atom. Moreover, we have applied this method to determine both the nuclear and electronic wave functions of LiH and LiD molecules simultaneously, and obtained the isotopic effect directly. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 491–501, 1998  相似文献   

15.
16.
Fukui提出的前线轨道理论在预测反应活性方面获得了极大的成功。在某些情况下,除了前线轨道之外,还必须考虑其它轨道之间的相互作用。本文提出赝轨道的概念,将所有内层轨道的作用包括在赝轨道参数之内。扩展了前线轨道理论的适用范围。并用硝基苯和苯睛的硝化反应的定位效应为例说明了赝轨道指数的应用。  相似文献   

17.
In the course of frontier orbital theory, the teacher and students discussed the conditions for the nitric oxide formation reaction, by using this theory. In an extracurricular practice, students testified the reaction mechanism obtained from the course by molecular orbital calculations. The course practice improved students' understanding of these theories and their abilities to apply them to exploration of chemical problems.  相似文献   

18.
The orbital invariance problem is analyzed from the tensor theory point of view, with an emphasis on multireference coupled cluster methods. Using the transformation properties of second‐quantized operators, we discuss the orbital invariance properties of various methods by examining the tensor properties of the residual equations. A simple self‐consistency‐checking algorithm is proposed. We first establish the orbital invariance properties for the Hartree–Fock, single reference configuration interaction, single reference coupled cluster, complete‐active‐space self‐consistent‐field, and multireference configuration interaction methods, and then discuss the invariance properties of the complete‐active‐space coupled cluster and CCSDt methods. Finally, we demonstrate theoretically the lack of orbital invariance for Jeziorski–Monkhorst ansatz based methods. It appears necessary to modify the ansatz to achieve orbital invariance, and internal contraction serves as one possible solution. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010  相似文献   

19.
介绍了Dirac,Desclaux等人发展的相对论多电子原子自洽场Dirac-Fock(MCDF)方法,并用相对论多电子原子MERECC-94程序计算了元素Au,Fr的电子结构。结果表明:尽管Fr的1s轨道相对论收缩效应比Au大,但因外壳层电子结构的不同,使Au的6s轨道的相对论收缩和稳定化效应比Fr和7s更明显。  相似文献   

20.
The utility and importance of predictive, rather than correlative, molecular orbital calculations in organic chemistry are discussed. Examples of the predictive approach to organic synthesis and the study of organic reaction mechanisms are presented.  相似文献   

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