Study of the modification of spherical melamine-formaldehyde particles levitating in complex plasma

The surface modification of spherical melamine-formaldehyde particles during their levitation in a dusty plasma as a part of plasma–dust structures in a trap formed in strata in a neon glow discharge has been investigated using scanning electron microscopy. The dependence of the particle size on the time of plasma exposure has been found and measured, and the modification of the surface structure has been studied. The source of the observed modification has been interpreted.     

The effect of a longitudinal magnetic field on the plasma-dust structures in strata in a glow discharge

The plasma-dust structures in strata in a glow discharge exposed to a longitudinal magnetic field are studied in detail. In a weakly ordered structure, the angular velocity has a vertical gradient. A reversal of rotation of the structure in a magnetic field corresponding to the magnetization of electrons is found. With the help of the pair distribution function of particles, changes in the degree of order of the structure in the magnetic field are revealed. These changes correlate with changes in the angular velocity of rotation. To explain this effect, it is assumed that the dust structure is subjected to the action of ions in crossed electric and magnetic fields.     

Ion drag as a mechanism of plasma dust structure rotation in a strata in a magnetic field

In experiments on complex plasmas, afixed strata region in which the levitation of dust structures is observed is investigated using the method of probing by calibrated dust particles of different sizes in an applied magnetic field under elevated pressures. The measured azimuthal velocity of the probing particles corresponds to the action of the ion drag force for 4 μm-size particles and to the entrainment by the rotating gas owing to the electron vortex flow inside the strata for 1 μm-size particles. Extrapolation to pressures and magnetic fields in which the rotation inversion of dust structures is observed in experiments shows that the ion drag is the dominating force causing rotation with a negative projection of the angular velocity onto the magnetic induction.     

Fast yet accurate computation of the complete radiance distribution in the coupled atmosphere-ocean system

The iteration of the source-function technique is used in conjunction with the discrete ordinate radiative transfer (DISORT) method to derive analytic solutions for the radiances at arbitrary polar angles and arbitrary levels in a multiple scattering (random) medium consisting of two strata with a change in the index of refraction across the interface between them. The atmosphere overlying a body of water (the ocean) serves as a prime example of such a system consisting of two adjacent strata with different indices of refraction. The accuracy of the solutions is tested by considering the coupled atmosphere-ocean system where absorption and scattering by molecules and particles are included. The tests show that these analytic solutions are superior to a spline interpolation that has been used previously in connection with the DISORT method applied to a random medium consisting of two strata with different indices of refraction.     

Analysis of the size and shape of polydisperse dust particles in a complex glow discharge plasma

The size and shape factor distribution of levitating particles is studied by the method of extraction of dust particles from the discharge chamber. Two dust traps existing in a glow discharge in the strata and above the lower wall of the tube near the bend in the current channel are investigated separately. It is found that the size distribution of polydisperse particles of an arbitrary shape is of the bimodal type due to simultaneous levitation of particles with two shape factors. Polydisperse spherical particles of any size exhibit levitation due to the separation of particles over the wall thickness. For identical parameters of the discharge, the size of the particle in neon is slightly larger than in krypton; the particle size in the trap located in a stratum is substantially larger than the particle size in the trap above the wall of the discharge tube. Precision determination of the shape and size of particles makes it possible to estimate the electric field strength for dust traps. It is shown that the glow discharge can be used as a tool for separation of dust particles in a wide range of their sizes.     

A Gauge Model for Quantum Mechanics on a Stratified Space

In the Hamiltonian approach on a single spatial plaquette, we construct a quantum (lattice) gauge theory which incorporates the classical singularities. The reduced phase space is a stratified Kähler space, and we make explicit the requisite singular holomorphic quantization procedure on this space. On the quantum level, this procedure yields a costratified Hilbert space, that is, a Hilbert space together with a system which consists of the subspaces associated with the strata of the reduced phase space and of the corresponding orthoprojectors. The costratified Hilbert space structure reflects the stratification of the reduced phase space. For the special case where the structure group is SU(2), we discuss the tunneling probabilities between the strata, determine the energy eigenstates and study the corresponding expectation values of the orthoprojectors onto the subspaces associated with the strata in the strong and weak coupling approximations.     

漫谈物理学的过去、现在与未来

文章试图对物理学的发展历史作一透视，从而理解其现状，并进而窥测其未来的前景，我们希望这一看法对于当今从事物理学教学与科研的人士有所助益，由于物理世界的层次化，诸层次之间既可能存在耦合，又可能出现脱耦，因而大量粒子所构成的复杂体系中所涌现的各种层展性质就不能简单地还原成个别粒子所服从的规律，我们根据这一观点并结合物理学的未来前景，讨论了当今物理学研究的若干前沿问题，一切迹象预示着物理学将有光明的前景     

地层静温预测的非牛顿流体数学模型

根据热力学参数、泥浆参数及井筒结构参数等，先选定一个地层温度梯度进行计算，得出泥浆出口温度.将此计算值与实测温度值比较，按照比较结果再修正所选的地层温度梯度.如此反复，直到得出合理的地层温度梯度.在此基础上，从热力学及流体力学等有关方程出发， 经过推演得到井壁上温度随深度变化以及地层温度分布的数学模型.由于钻井过程中泥浆、 岩石及其温度场间是相互作用、相互影响的，这为研究热 流 固耦合渗流过程的理论与应 用提供了一种新的方法. 关键词： 温度梯度 非牛顿流体 数学模型     

The onset of rotational motion of dusty plasma structures in strata of a glow discharge in a magnetic field

An interpretation is given to the previously observed action of a magnetic field on the state of a dusty plasma structure in strata of a glow discharge. The conditions of previous experiments are analyzed, in which a nonuniform rotation and a change in the degree of order of a dusty plasma structure (the translational order), as well as a correlation between them, were revealed. Based on this analysis and on data in the literature on dusty plasmas in a magnetic field, a hypothesis is made that the reason for the rotation of the structure is the ion drag force. Additional experiments on the observation of the onset of rotational motion of a structure in “weak” and “strong” magnetic fields are conducted. It is shown that rotation reversal (and rearrangement of the order of the structure) is caused by changes in the direction of ionic flows—from internal regions of the structure to its periphery and vice versa—in the weak and strong magnetic fields. The results obtained agree qualitatively with the hypothesis adopted, as well as with the data of the two-dimensional theory of strata.     

Optical scanning of dusty 3D-structures formed in a glow discharge

3D-quasi-crystals formed in strata of a glow discharge are scanned in the optical range with the help of a moving laser knife and high-speed videorecording. The spatial positions of dusty grains are determined. The ordering of structures and the type of arrangement of particles are determined from a comparison of pair correlation functions constructed for the structures under study with correlation functions corresponding to ideal crystalline structures. Several types of unit cells are found through the visual collation of separate parts of structures. As compared to data from the literature on experiments in a high-frequency discharge, the structures under study have a clearly pronounced anisotropy.     

Fluctuating velocity and momentum transfer in dense granular flows

We show experimentally that in a free-surface granular flow the fluctuating velocity brings about momentum transfer at a considerable rate only very close to the free surface. Away from the free surface, where the flow is dense and stratified (or laminar), the fluctuating velocity plays no prominent dynamic role and stems passively from a kinematic constraint: The strata of particles must shake laterally as they slip past one another in the direction of the mean flow. Based on this insight, we formulate a simple model for the fluctuating velocity of dense granular flows. The predictions of the model agree well with our experimental measurements.     

生物体内的磁铁矿（Fe3O4）粒子

磁铁矿(Fe3O4)粒子是具有反尖晶石结构的立方晶系亚铁磁性矿物,在生命科学和生物技术领域有着重要的应用价值,可以在生物体内自然合成.文章介绍了生物体内的磁铁矿粒子,并从晶体结构等角度较详细地介绍了多种生物体内的磁铁矿粒子的情况.文章最后给出了趋磁细菌、人类大脑以及石鳖体内自然合成的纳米Fe3O4粒子的晶貌、磁畴分布等     

Ordered structures in a nonideal dusty glow-discharge plasma

The formation of ordered structures of charged macroparticles in a constant-current neon glow-discharge plasma is investigated. Experiments were performed with two types of particles: thin-walled glass spheres 50–63 μm in diameter and particles of Al₂O₃, 3–5 μm in diameter. Formation of quasicrystalline structures is observed in the standing strata and in an artificially created double electric layer. The formation of extended filamentary structures of macroparticles in the absence of visible stratification of the positive column has been observed for the first time. The influence of the discharge parameters on the formation of the ordered structures and their melting is examined. The form of the interaction potential between the charged macroparticles is considered, as well as changes in the conditions for maintaining the discharge in the presence of high concentrations of dust particles. Zh. éksp. Teor. Fiz. 112, 2030–2044 (December 1997)     

Structure of small metallic particles

This is a short review of some crystallographical anomalies or specific behaviour in thin metallic films. We give information about the structure of microparticles which do not have bulk-like symmetries. Their structure has been investigated by electron diffraction and electron microscopy. It is concluded that for the early stage of growth, the particles have five-fold symmetries and icosahedral structure. The growth mechanism is discussed and evidence for a layer- by-layer growth with respect to the pentagonal symmetry is emphasized. It is suggested that the substrate has much influence on the very early stages of growth of icosahedral particles. Beyond a certain size (about 80 Å), icosahedral particles transform into polytetrahedral particles which growth with the same shape and with a pseudo-pentagonal structure.     

岩层变形检测的光纤光栅多点传感理论与工程应用

为了监测松散地层沉降变形,提出了一种用于钻孔中植入式光纤Bragg光栅传感器(FBG)的结构和传感网络系统.基于室内实验结果,给出了用于岩层变形检测的传感光栅波长带宽为6 nm,分析了多点传感信号分辨因子,山光源带宽决定的测试系统最大实际复用能力为6个传感器.设计并实现了一个由18个光纤光栅组成的具有特色的光纤Bragg光栅波分复用/空分复用混合阵列.工程实践表明,光纤光栅传感系统采用双同路布置.可提高系统下放后光纤光栅传感器的成活率.     

不对称二聚物粒子在两嵌段共聚物形成的支撑膜上的自组装

结合自洽场理论和密度泛函理论,研究了不对称的二聚物粒子在AB两嵌段共聚物形成的支撑膜上的自组装行为. 不对称的二聚物粒子是由两个不同的球组成的两性分子. 其中一个球与A嵌段相亲,另外一个喜欢B嵌段. 不对称粒子能在支撑膜上形成一个双层结构. 由于衬底的存在,所形成的支撑膜上下两叶的对称性被破坏,导致了二聚物粒子在膜上形成的结构也变的不对称. 随着二聚物粒子浓度的增加,在膜上的二聚物粒子的结构将发生变化,从稀四方、六角、密四方再到圆柱结构. 在一个高浓度的密堆积下,二聚物粒子将形成弯曲的圆柱结构. 在支撑膜     

Indentation behaviour of superelastic hard carbon

Superelastic hard carbon particles widely varying in structure and properties have been studied by instrumented microindentation technique. The carbon particles up to 200 μm in size were produced by fullerene collapse upon high-pressure high-temperature treatment of metal–fullerene powder mixture with simultaneous sintering of metal matrix composite materials (CM) reinforced by the particles. The structure and properties of the carbon particles were controlled by changing synthesis parameters and the state (composition and structure) of the parent fullerite crystals. The specific features of the instrumented indentation behaviour of the particles were studied as a function of their hardness. Mechanical properties of the particles tested at loads of up to 1970 mN exhibit an indentation size effect, which becomes more pronounced with increasing hardness of the carbon particles. Upon holding at a constant load, the fullerene-derived carbon particles undergo unrecoverable deformation, and the indentation creep C_IT increases with increasing particle hardness. An increase in hardness of the reinforcing carbon particles substantially improves the wear resistance of the CM and decreases their friction coefficient.     

Structure of the space of reducible connections for Yang-Mills theories

The geometrical structure of the gauge equivalence classes of reducible connections are investigated. The general procedure to determine the set of orbit types (strata) generated by the action of the gauge group on the space of gauge potentials is given. In the so obtained classification, a stratum, containing generically certain reducible connections, corresponds to a class of isomorphic subbundles given by an orbit of the structure and gauge group. The structure of every stratum is completely clarified. A nonmain stratum can be understood in terms of the main stratum corresponding to a stratification at the level of a subbundle.     

Effect of the lattice structure of nickel nanoparticles on their practical magnetization

Magnetization of nickel nanoparticles with various lattice structures is studied. Nickel particles with the fcc structure are shown to be magnetically harder than the particles with the icosahedron structure. Easy magnetization axes in the particles are found.     

Synthesis and microwave magnetic properties of a-Fe/ferrite composites with sandwich structure

A new kind of a-Fe/ferrite composites with sandwich structure was realized by chemical reduction method, where the as-prepared W-type barium hexaferrite flake particles were subjected to a reduction treatment in hydrogen atmosphere at different temperatures. X-ray diffractometer reveals that a-Fe/Co particles precipitate in the ferrite matrix, when the reduction temperature is higher than 230 °C. With the temperature increased, the particles morphology changed into sandwich structure in hexagonal flake particles and the barium hexaferrite phase was decomposed gradually, when were completely decomposed at T=450 °C. Results show that the composites particles with sandwich structure (T=270 °C) have higher microwave complex permeability than the others.