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1.
通过分子动力学模拟,考查并分析了(KI)108离子簇的结构、能量和相变的动力学行为.在加热和冷却过程中,离子簇再现了熔化和凝固现象,而且熔化起始于立方体的其一顶点,熔化的离子簇不是球形的,说明了离子簇的非湿特征.根据结晶的成核速率,讨论了电子衍射实验中观察KI凝固的可能性  相似文献   
2.
编写红外光谱检索程序“IRS-NSI”旨在直接根据未知物的红外光谱图确定其结构。该程序分数据库程序和检索程序两大部分。数据库程序是根据Sadtler标准红外光栅光谱将强峰位置进行数字编码建立的。从4000cm~(-1)到400cm~(-1)范围内将谱图分为13格,每格选取两个最强峰,将强峰在每格中的位置进行编码,这样每张谱图均用一个26位数表示,连同谱图顺序号共占27个存贮单元。  相似文献   
3.
用气相电子衍射法和质谱相联合,分析了二元混合超声气流的剖面和质量分布情况。证明质谱利于确定气流剖面和气流中粒子的质量分布,而电子衍射则可以给出气流剖面和气流中生成了何种固相的信息。  相似文献   
4.
李小华  黄锦凡 《中国化学》2003,21(12):1543-1552
Molecular dynamics computer simulation based on the Born-Mayer-Huggins potential function has been carried out to study the effects of duster size and temperature on the nucleation rate of sodium chloride dusters in the temperature range of 580 K to 630 K. Clusters with 256 and 500 NaCl molecules have been studied and the results have been compared with those obtained from 108 molecule dusters. The melting point (MP) of the clusters were observed to increase with the size of the clusters and can be well described by a linear equation MP =1107(37)-1229(23)N^-1/3(N is the number of molecules in the duster).The nucleation rate was found to decrease with increasing the duster size or temperature. Various nucleation theories have been used to interpret the nucleation rates obtained from this molecular dynamics simulation. It is possible to use a constant diffuse interface thickness to interpret the nucleation rate from the diffuse interface theory in the temperature range of this study. However, the interfacinl free energy estimated from classical nucleation theory and diffuse interface theory increases too fast with increasing the temperature while that from Gran-Gunton theory does not change with changing temperatures.The sizes of critical nuclei estimated from all the theories are smaller than those estimated from our simulations.  相似文献   
5.
Molecular dynamics computer simulation has been carded out to study the structure and physical properties of iron nanoparticles with 331 to 2133 Fe atoms or with diameter from 2.3 to 4.3 nm. The core of liquid nanodroplets has the similar structure of the bulk molten iron liquid that has an average coordination number around 10.5 and the packing density around 0.45, although the closest Fe-Fe distance is slightly longer in the bulk liquid. Most of the iron nanoparticles formed from the cooling of molten nanodroplets have the same body center cubic crystal structure as it was observed in the bulk under the normal temperature and pressure. Lattice contraction was observed for iron nanoparticles. An amorphous solid and an HCP like solid were obtained accidentally during the quenching runs on Fe331 nanoparticles. The physical properties of iron nanoparticles such as molar volume, density, thermal expansion coefficient, melting point, heat of fusion, heat capacity and diffusion coefficient were estimated based on the results obtained from this simulation. The dependence of physical properties on the nanoparticle sizes was addressed.  相似文献   
6.
Molecular dynamics (MD) computer simulations have been carried out to study the structures, properties and crystal nucleation of nanoparticles with 453 Cu atoms. Structure information was analyzed from the MD simulations, while properties of nanoparticles of Cu453, such as melting point, freezing temperature, heat capacity and mo- lar volumes, have been estimated. The face center cubic (FCC) phase and icosahedron (Ih) phase were observed during the quenching process, and nucleation rates of crystallization to FCC crystal of Cu453 at temperatures of 650, 700, 750, and 800 K were analyzed. Both classical nucleation theory (CNT) and diffuse interface theory (DIT) were used to interpret our observed nucleation rates. The free energy and diffuse interface thickness between the liquid and the FCC crystal phases were estimated by the CNT and DIT respectively, and the results show that the DIT does not work properly to the system.  相似文献   
7.
用气相电子衍射法和质谱法相联合,分析了二元混合超声气流的剖面和质量分布情况。证明质谱利于确定气流剖面和气流中粒子的质量分布,而电子衍射则可以给出气流剖面和气流中生成了何种固相的信息。  相似文献   
8.
通过分子动力学模拟研究了覆盖较高熔点的原子的氩原子簇.原子族由177个氩原子和72个覆盖原子组成.覆盖原子的势能参数ε比氩原子大50%,该原子簇比纯氩原子簇熔点过热2K.模拟结果表明,覆盖的原子簇过热的原因是:在达到熔点之前,体系缺少氩原子构成的自由表面,仍然是覆盖原子的有序表面.  相似文献   
9.
通过超声膨胀产生了直径约为4.3nm的SiF4纳米粒子,并用电子衍射表征其结构.在选择的射流部分中,粒子大小的分布是很窄的,因而可以用541个分子构成的分子簇进行结构精化.在SiF4的纳米粒子中,分子的堆积可用大块物质的立方晶体结构来模拟.还谈到纳米粒子表面上由于平动和转动运动引起的分子混乱.  相似文献   
10.
2,2,3-三甲基丁烷(C7H16)晶体的成核动力学   总被引:1,自引:0,他引:1  
High temperature solid phase I of 2,2,3-trimethylbutane(C7H16)(TMB) was investigated by X-ray powder diffraction. The electron diffraction technique for observing the kinetics of phase transitions in the condensed matter has been applied to study the freezing of TMB clusters with diameter of~13nm. Cluster beams were generated from the supersonically expanded TMB vapor with mole fraction of 0.01 in neon carrier gas. The freezing evolution was monitored by electron diffraction in interval of 7-9 μs. Clusters with an average size of ~5,500 molecules were observed to freeze into the solid phase I at a nucleation rate of 3.5 × 1028 m-3•s- 1 at the freezing temperature of clusters, ~170K. The estimated growth rate of postcritical nuclei indicates that the observed nucleation in the present experiment corresponds to mononuclear freezing of the clusters into single crystals of solid phase I.  相似文献   
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