Role of interactions of triplets of atoms in the formation of elastic properties of cubic crystals

It is widely known that the interaction of triplets of particles (which are not reducible to the sum of pair interactions) play an important role in formation the nonlinear and anisotropic properties of crystals. The aim of this work is to establish a general form of the dependence of these properties on interactions of triplets of atoms that is dependent only on the structure of the crystals. To separate the interactions of triplets of atoms from those of quadruples, we assume that the energy of triplets of interacting atoms depends only on the characteristics of a triangle whose vertices are the centers of gravity of interacting atoms. In this model, the internal energy must therefore be invariant upon rearrangement of the numbers of interacting atoms and any rotation of the triangle in isotropic space, P(3) × O(3). To specify the form of energy dependence on characteristics of selected triangles, we constructed an integral rational basis of invariants in dependence on the components of the vectors connecting the vertices of each triangle. Using the example of a simple dependence of the energy on basic invariants, we show how to move from the assumed energy dependence on invariants to the dependence of energy on lattice sums.     

Simulation of detection and scattering of sound waves by the lateral line of a fish

A solvable model of lateral line of a fish based on a wave equation with additional boundary conditions on a set of isolated points is proposed.Within the framework of this model it is shown that the ratio of pressures on lateral lines on different fish flanks,as well as the cross section of sound scattering on both the lines,strongly depends on angles of incidence of incoming sound waves.The strong angular dependence of the pressure ratio seems to be sufficient for the fish to determine the directions from which the sound is coming.     

Transverse Strain and Nonlinearity of the Force of Interatomic Interaction of Solids

Doklady Physics - New data on the effect of small concentrations of zirconium-oxide nanoparticles on the structural behavior of cold-pressed powder matrices based on aluminum (or aluminum with 1.5%...     

催化裂解CH4制备碳纳米管的影响因素

以柠檬酸法制备的Fe MgO、Co MgO和Ni MgO为催化剂 ,CH4 为碳源气 ,H2 为还原气 ,在 873、973和 10 73K制备出碳纳米管 ,通过TEM和拉曼光谱表征 ,讨论了催化剂、制备温度、反应时间等因素对碳纳米管形貌、产率和内部结构的影响 .结果表明 :不同的催化剂在相同的温度下制备的碳纳米管的形态和内部结构有很大的差异 .其中Fe MgO催化剂制备的碳纳米管管径粗 ,且大小不均匀 ,而Ni MgO催化剂制备的碳纳米管管径较细、较均匀 .碳纳米管的产率随着裂解温度的变化而改变 .Fe MgO催化剂制备碳纳米管的产率随制备温度的升高而提高 ,而Ni MgO催化剂制备碳纳米管的产率随制备温度的升高而降低 .Fe MgO催化剂制备碳纳米管 ,在10 73K甚至更高的制备温度才能达到其最高产率 .Co MgO催化剂制备碳纳米管的产率在 973K左右产率较高 ,而用Ni MgO催化剂制备碳纳米管 ,则在 873K甚至更低的制备温度就能达到最高产率 .反应时间与碳纳米管的产率不成正比 ,有一最佳反应时间 ,如Ni MgO催化剂的最佳反应时间为 2h .     

Assembly of single-walled carbon nanotubes on patterns of Au nanoparticles

We report on the assembly of single-walled carbon nanotubes (SWNTs) and gold nanoparticles (NPs) hybrid structure without any surface modification of SWNTs on patterns of Au nanoparticles (NPs). Microscale Au NP patterns were created on composite self-assembled monolayer (SAM) templates of octadecanethiol (ODT) and octanedithiol (OD) through self-assembly of Au NPs via the thiol-Au chemical bond onto the OD region. On such templates, we observed extensive adhesion and strong affinity of SWNTs on the Au NPs and no SWNT on ODT. We also examined systematically the adhesion of SWNTs on ODT with varying coverage of vapour-deposited Au. We observed little SWNT attachment even when there are high-density of Au clusters on the ODT SAM. Extensive adhesion of SWNTs is observed only when the coverage of ODT by Au is almost complete. Dynamic contact angle measurements of dichlorobenzene on the ODT/Au substrates revealed a direct correlation between the surface wettability and the SWNT assembly on a molecular template.     

Continuity of state functions of the Bose gas

In this paper we show that some state functions of the Bose gas, especially the entropy, depend continuously on the energy levels for the free Hamiltonian and on perturbations of the free Hamiltonian by operators of degree 0. The method used here is to introduce an appropriate topology on the density matrices and on the perturbations of the free Hamiltonian.     

Effect of ionization of condensing flux and transverse electric field on nucleation of metal films on ionic crystals

Experimental data on the effect of ions in the flux of condensing metal on the orientation of island metal films on alkali halide crystals are given. The effect of ionization of the condensing flux and the transverse electric field is explained on the basis of a previously proposed model of nucleation and oriented growth on point defects on the crystalline substrate.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 35–39, November, 1979.     

Calculation of geometries and chemisorption energies of adatoms on simple metals

We report results of calculations with a formalism that in principle applies quite generally for chemisorption on a real metallic substrate. Including the substrate structure within perturbation theory on a self-consistent jellium-plus-adatom calculation, we have computed the dependence of the binding energy of an adatom on the surface geometry. Specifically, in the case of hydrogen on Al, our model calculation predicts that the stable positions are bridge configurations on the (100) and (110) surfaces and atop positions on the (111) surface, and that they have almost the same heats of chemisorption (1.8–2.0 eV). For geometrical reasons the bridge configuration seems to be a reasonable result while the atop result for the (111) surface is more uncertain. Thus, chemisorption of H on Al should require predissociation of the H₂ gas. In addition, the predicted values for hydrogen desorption imply that measurements on H on Al surfaces should be performed at low temperatures to avoid desorption. Results for H on a jellium of Na density indicates that hydrogen should be absorbed in rather than adsorbed on Na metal.     

Numerical analysis of the dynamics of vapor bubbles

The nonlinear dynamics of vapor bubbles for the external pressure changing in steps is numerically analyzed based on a complete system of hydrodynamic equations without regard to the internal heat problem. Primary attention is focused on analyzing the applied numerical algorithms and on determining the conditions of complete vapor cavity collapse during first oscillation periods, depending on three parameters: Peclet number, Jacob number, and wave intensity.     

Analysis of the features of meniscus profile curves during growth of base-faceted sapphire ribbons

The dependence of the step parameters on the surface of base-faceted sapphire ribbons on the angle of deviation of crystallographic orientation has been measured. A model of step formation on the lateral ribbon surface is proposed. Hysteretic character of the dependence of the lateral ribbon surface inclination on the meniscus angle at the triple point is shown. The shapes of the lateral surfaces are calculated and the range of variation in the meniscus angle is determined.     

小液滴撞击壁面传热特性数值分析

小液滴撞击壁面现象在喷雾冷却等领域都有广泛应用.为研究小液滴(微米)撞击热壁面(非沸腾区)传热过程,建立了二维液滴撞壁瞬态模型,并采用相场方法对小液滴换热过程中对流热通量和导热热通量的大小进行了对比.研究结果表明:液滴撞击壁面初期形成“冷斑”,有利于小液滴与壁面的传热;小液滴撞击壁面过程中热通量峰值存在于三相接触点附近,数量级在105—106 W/m²;小液滴撞击壁面过程中受壁面浸润性和液滴尺寸对传导热通量的影响较为显著,而速度和液滴尺寸对对流热通量的影响较为显著;大多数情况下,小液滴撞击壁面传导热通量数量级在103—105 W/m²,对流热通量数量级在104—106 W/m²,对流热通量大于传导热通量,在整个换热过程中占据主导地位.     

湿颗粒堆力学特性的离散元法模拟研究

利用基于线性黏聚接触模型的离散元法对不同颗粒系统的堆积过程进行了数值模拟研究,分析了颗粒形状和湿颗粒间液桥力对颗粒堆积形态的影响机理,获得了球形和块状湿颗粒堆基底表面所受的法向力以及堆中颗粒间的法向力和切向力"中心凹陷"式的分布规律,讨论了颗粒形状和黏聚能量密度对基底表面作用力和颗粒间作用力的影响.研究结果表明,颗粒形状和液桥力对颗粒堆的堆积形态具有显著的影响.堆积角随着黏聚能量密度的增加而增大,并且相同条件下的块状颗粒堆积角大于球形颗粒.颗粒形状和黏聚能量密度对基底表面所受作用力和堆中颗粒间的作用力变化及最大幅值均有影响作用.当黏聚能量密度值逐渐增大时,颗粒堆的作用力最大幅值均逐渐增大,并且块状颗粒堆的作用力最大幅值大于球形颗粒堆.当黏聚能量密度值过大时,颗粒堆力学特性更加复杂,液桥力对颗粒堆积特性的影响作用大于颗粒形状的影响.     

航天器空间静电效应研究进展

航天器在轨运行过程中面临的空间环境复杂多变,高能电子、等离子体环境、低气压、大温差等环境因素会引起航天器发生静电带电和放电效应,对航天器的安全运行造成严重影响。基于国内外试验数据和案例分析了空间环境引起的航天器故障,从数值仿真软件、地面模拟技术、强场诱发放电以及防护技术等方面介绍了空间环境作用下航天器充放电效应研究进展,对我国目前研究差距和未来研究方向进行了展望。研究表明:我国航天器充放电效应防护技术研究取得了进步,下一步重点针对空间站、深空探测、探月工程等新任务,进一步拓展空间环境作用下航天器充放电效应机理和防护新技术研究,为提升我国航天器的安全性和可靠性提供技术支撑。     

面形误差对亚波长金属光栅偏振器性能的影响

基于严格耦合波理论分析了光栅面形误差对亚波长金属光栅偏振器偏振性能的影响.通过对数值结果的分析发现,光栅圆角误差、光栅侧壁倾斜误差和光栅表面粗糙误差对光栅的TM透射效率影响不大,但它们使得光栅的消光比明显降低.因此,面形误差使得光栅的偏振性能明显降低.理论分析表明,顶角为直角、侧壁垂直和表面光滑的理想矩形光栅结构的偏振性能最好.     

Effect of the stabilizing coating and the presence of free polymer on the rate of crystallization of colloidal systems

Visual observations and preliminary light scattering experiments on the crystallization process in various colloidal systems are reported. In the first place we studied the influence of the stabilizing coating of the colloidal particles on the rate of crystallization. The various coatings give rise to different ranges of the repulsive interaction. This is found to have a pronounced effect on the rate of crystallization. Furthermore we investigated the effect of free polymer added to the dispersion. It appears that addition of free polymer has a dramatic effect on the crystallization phenomena.     

Information analysis of the problem of extrapolation of stochastic processes in the case of continuously-discrete observations with memory

Information analysis of the problem of extrapolation (prediction, forecast) of stochastic processes based on an ensemble of their continuously-discrete realizations, which depend not only on the running but also on the preceding values of the signal process, is considered. An equation has been derived for the Shannon amount of information, based on which the efficiency of observations with memory has been investigated in comparison with observations without memory for the Ornstein-Uhlenbeck process. Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 135–140, March, 1999.     

Effect of microscopic inhomogeneity of the medium on reaction-diffusion front velocity

A model of random walks on an inhomogeneous lattice is used to analyze the effect of microscopic inhomogeneity of the medium on reaction-diffusion front velocity. It is shown that the front velocity can be substantially higher on an inhomogeneous lattice as compared to that on a homogeneous one with the same onsite waiting time. The increase in velocity is due to a bias in the particle distribution between sites of different types toward those with shorter waiting times. The amount of bias depends on the rate of chemical reaction: the higher the rate, the stronger the bias. The front velocity also strongly depends on the reaction mechanism, more precisely, on how product particles are distributed between sites of different types.     

Analysis of the dependence of the microwave generation power of a low-voltage vircator on controlling parameters

The results of experimental and theoretical analysis of the dependence of the generation power of a low-voltage vircator, viz., a nonrelativistic electrovacuum device based on a high-intensity electron beam with a virtual cathode, on the values of controlling parameters are considered. The dependences of the generation power on the decelerating potential and on the beam current are analyzed.     

菁染料J-聚集体的微观结构研究

用原子力显微镜观察了阴阳离子菁染料及对应的阴离子菁染料和阳离子菁染料吸附在立方体(100)和八面体(111)溴碘化银乳剂颗粒表面形成的J-聚集体的微观结构,得到了3种不同排列的J-聚集体结构。研究结果表明,菁染料分子在溴碘化银颗粒表面不是单层吸附,而是以一定的形状聚集在溴碘化银表面。阴阳离子菁染料形成的J-聚集体为"鱼骨"状;阴离子菁染料的J-聚集体以"卡片堆积"式排列;阳离子菁染料J-聚集体为"磁砖"式结构。     

Fine structure of faces and imperfection of surface layers of shaped sapphire crystals

The development of faces on cylindrical and ribbon-shaped sapphire single crystals grown from a melt using the Stepanov method is investigated by optical and electronic microscopy. The crystallographic indices on the detected faces are established, and the microstructure of the growth layers is studied. The X-ray spectral microanalysis of foreign particles on the sapphire surface confirms the presence of molybdenum single crystals on it. Cathodoluminescence spectra of surface layers of sapphire single crystals are obtained.