Effect of passive plates on vertical instability in the EAST tokamak

The effect of passive plates on vertical displacement control in the EAST tokamak is investigated by open loop experiments and numerical simulations based on a rigid displacement model.The experiments and simulations indicate that the vertical instability growth rate is reduced by a factor of about 2 in the presence of the passive plates,where the adjacent segments are not connected to each other.The simulations also show that the vertical instability growth rate is reduced by a factor of about 10 if all adjacent segments on each passive plate loop are connected to each other.The operational window is greatly enlarged with the passive plates.     

Band structure and chemical bonding in Cu2O and Ag2O oxides

The band structure, total and projected densities of states, and distributions of the valence and difference electron densities for copper and silver oxides are calculated in the framework of the density functional theory in the local approximation with ab initio norm-conserving pseudopotentials in the basis set of pseudoatomic orbitals. The results obtained are compared with the experimental data and calculations performed by other authors. The energy spectrum and spatial distribution of electrons in crystals are similar to each other. Metal ions are bonded to each other through charge density channels with a weakly pronounced maximum at the center of the empty tetrahedron.     

Experimental study of multilayer interferometers (or resonators)

The interferograms of two-layer and three-layer interferometers were recorded by a photoelectric method. The fringes corresponding to each layer appear in the same form and in the same position as they would for the separate layer. The fringes of the constituent layers modulate each other in such a manner that the maxima of each layer are intensified when they coincide with maxima of other layers, but suppressed when they coincide with minima of other layers.Translated from Izvestiya VUZ. Fizika, No. 4, pp. 35–40, April, 1970.In conclusion the author thanks professor F. A. Korolev for interest in and valuable comments offered during this study.     

Creation of an entangled state between two NV centers in a single-photon interferometric scheme

We study a method for creating an entangled state between two NV centers in diamond that do not directly interact with each other. The method is based on excitation of centers with a single photon via a half divider with subsequent coherent inversion of the spin of the excited center by a microwave pulse and on the detection of a photon that was emitted by the excited center and that passed through the divider. We consider the general case in which the transition frequencies of the centers are shifted with respect to each other and the control pulses are detuned with respect to these transitions. We find the probability of creating an entangled state and its fidelity in relation to the parameters of the method and transition frequencies of the centers. Optimal values of these parameters are determined.     

Theorems connecting surface energies and electrostatic potentials of finite and semi-infinite jellia and cavities

A Pauli-Hellmann-Feynman theorem for finite neutral jellia derived in an earlier paper by the authors and connecting energy and electrostatic potential with each other is generalized to the case of non-neutral systems and is shown to split into two theorems. For an arbitrary cavity in an otherwise homogeneous jellium a general theorem is derived. Theorems for cavities with special symmetry (void, tube, slit) are compared with each other and with theorems for corresponding jellia (sphere, wire, slab).     

Observation of interaction forces between one-dimensional spatial solitons in photorefractive crystals

We propagate two coherent and parallel beams of a He-Ne laser through a Bi(12)TiO(20) photorefractive crystal in the presence of drift nonlinearity. Our experimental results demonstrate that the beams attract or repel each other according to their initial phase difference. They attract each other when they are initially in phase and they repel each other when they are initially out of phase. These experimental results agree with numerical predictions recently published.     

Numerical modeling of ultrasonic cavitation by dividing coated microbubbles into groups

Homogeneous cavitation models usually use an average radius to predict the dynamics of all bubbles. However, bubbles with different sizes may have quite different dynamic characteristics. In this study, the bubbles are divided into several groups by size, and the volume-weighted average radius is used to separately calculate the dynamics of each group using a modified bubble dynamics equation. In the validation part, the oscillations of bubbles with two sizes are simulated by dividing them into 2 groups. Comparing with the predictions by the Volume of Fluid (VOF) method, the bubble dynamics of each size are precisely predicted by the proposed model. Then coated microbubbles with numerous sizes are divided into several groups in equal quantity, and the influence of the group number is analyzed. For bubble oscillations at f = 0.1 MHz and 1 MHz without ruptures, the oscillation amplitude is obviously under-estimated by the 1-group model, while they are close to each other after the group number increases to 9. For bubble ruptures triggered by Gaussian pulses, the predictions are close to each other when more than 5 groups are used.     

利用干涉光场的相位涡旋测量拉盖尔-高斯光束的轨道角动量

对拉盖尔-高斯光束经多圆孔衍射屏在远场平面上形成的干涉光场的相位和零值线进行了计算模拟.当入射光束的轨道角动量量子数为零时,实部零值线与虚部零值线在干涉光场中心点不相交,因而在该点上不能形成相位涡旋.当入射光束的轨道角动量量子数为+1和-1时,实部零值线与虚部零值线在干涉光场中心垂直并相交,干涉光场相应位置处的相位涡旋的符号相反.当入射光束的轨道角动量量子数为±2和±3时,有四条零值线相交于干涉光场的中心点上,并且实部零值线和虚部零值线交替分布,该交点处形成的相位涡旋的拓扑荷的值恰好与拉盖尔-高斯光束的轨道角动量量子数相等.这种结果可以用来测量涡旋光束的轨道角动量.     

Interference in electron-positron creation

We explore the mutual coherence properties of electrons that are created by a subcritical time-dependent force field. We compare the spatial evolution of the quantum field theoretical density with that of a relativistic classical mechanical ensemble. We find that portions of the electron cloud that were created sufficiently far from each other are not able to show interference patterns as they pass each other. The corresponding classical phase-space density reveals interesting spiral-shaped gaps, which have their manifestation in the corresponding quantum field theoretical data.     

Ice tessellation on a hydroxylated silica surface

The adsorption of water on a fully hydroxylated silica surface is studied by using density-functional total-energy and molecular dynamics calculations. The (100) surface of beta(alpha)-cristobalite covered by geminal hydroxyls has been taken as the substrate. A well-ordered and stable two-dimensional ice with quadrangular and octagonal patterns of hydrogen bond (H-bond) networks-an ice tessellation-is found on the surface for the first time. With the vibrational recognition, the four water molecules in the quadrangle are found to be bonded by strong H bonds while the quadrangles are connected to each other by weak H bonds. This configuration is the most stable, because all the water molecules are fully saturated with H bonds either to each other or to the surface hydroxyl groups.     

二维云母界面对晶体定向生长的诱导作用研究

利用原子力显微镜(AFM)研究了云母衬底对氯化钠晶体定向生长的诱导作用,发现云母表面的氯化钠按照夹角60°左右的方向或者相互平行、相互垂直的方向生长,此角度分布规律与文献中生物分子在云母表面诱导下组装的纳米结构的夹角相互一致。说明云母表面不但可以用于诱导生物分子按照一定的方向进行自组装,还可以用于诱导无机晶体按照特定的方向进行组装生长。     

左手材料薄板波导中模式之间的正交关系

基于电磁场理论,采用直接计算的方法证明了左手材料薄板波导中各个模式是相互正交的,即不同传播模之间、传播模与辐射模以及不同辐射模之间是相互正交的.这为研究左手材料薄板波导中的模式耦合奠定了基础. 关键词： 左手材料 薄板波导 模式 正交关系     

核磁共振技术在生物组织中的应用

在生物组织内部存在大量的生化、生理反应以及分子的扩散运动,它们相互独立, 又相互关联,共同构成一个生化反应网络. 在病理条件下,某些生化反应过程会发生改变,代谢中间体可能会出现质和量的变化. 核磁共振 (NMR)可以对这些过程的研究提供非常有用的信息. 目前,有3种核磁共振波谱技术可以用于生物组织的研究：① 活体组织定域波谱技术;② 生物组织提取物的液体高分辨核磁共振技术;③ 离体组织的高分辨魔角旋转技术. 这些方法各有优劣,互为补充. 介绍了在生物组织的NMR研究方面的最新进展.     

Two-dimensional NMR of velocity exchange: VEXSY and SERPENT

Two different multidimensional pulsed field gradient sequences are compared which have the purpose of correlating spin displacements in different time intervals with each other. The simplest possible sequence, three-pulse SERPENT, measures displacements in two interleaved time intervals, while in VEXSY, consisting of two independent pairs of gradient pulses separated by a mixing time, displacements during the two encoding intervals are compared to each other. The formalism for both sequences is discussed in q space and in displacement space and common features as well as differences between the two types of experiments are highlighted, employing the particular case of the concurrent VEXSY scheme which allows treatment according to both formalisms.     

Phase Transition of Triangulated Spherical Surfaces with Elastic Skeletons

A first-order transition is numerically found in a spherical surface model with skeletons, which are linked to each other at junctions. The shape of the triangulated surfaces is maintained by skeletons, which have a one-dimensional bending elasticity characterized by the bending rigidity b, and the surfaces have no two-dimensional bending elasticity except at the junctions. The surfaces swell and become spherical at large b and collapse and crumple at small b. These two phases are separated from each other by the first-order transition. Although both of the surfaces and the skeleton are allowed to self-intersect and, hence, phantom, our results indicate a possible phase transition in biological or artificial membranes whose shape is maintained by cytoskeletons.     

Interactions of flame balls

Flame ball interactions are numerically investigated in a reaction–diffusion system characterized by single-step Arrhenius kinetics and radiative heat losses. It is found that the interactions of two neighbouring flame balls are characterized by two distinct regimes – a repulsion regime and an attraction regime, depending upon the separation distance. The two regimes join at a critical separation distance, which corresponds to an unstable equilibrium state. For supercritical separation distances, the two flame balls repel and drift apart from each other; whereas for sub-critical separation distances, they move towards each other and eventually merge into a single stationary flame ball. In this connection, flame ball interactions are found to exhibit a qualitatively reverse character in comparison with the well-known van der Waals curve which characterizes intermolecular forces.     

Topological structures of boundary value problems in block elements

Block structures are considered; a boundary value problem for a system of inhomogeneous partial differential equations with constant coefficients is formulated in each block of a structure. The problem of matching solutions to boundary value problems in blocks with each other by topological study of the properties of solutions in the block structure is examined in the conditions of correct solvability of boundary value problems in blocks of the block structure. Some new properties of solutions to boundary value problems in block structures are found that are important for applications.     

The excluded-volume effect in microscopic pedestrian simulations

We propose a pedestrian position update rule, which is added to a microscopic pedestrian model to avoid pedestrian overlap. In the rule, the step size of a pedestrian moving in a selected direction at each update is in inverse proportion to the repulsive actions imposed by other pedestrians moving in a direction with an exponential rate. The positions of the pedestrians are then updated in each small time interval. In this way, a barrier between the pedestrians can be generated, and after updating their positions the pedestrians do not overlap with each other. The modified model is compared to the original model through a simulation of the evacuation process of pedestrians in a closed area. The simulation results indicate that the modified model is superior to the original model in several aspects.     

Manifestation of Three-Body Forces in Three-Body Bethe–Salpeter and Light-Front Equations

Bethe–Salpeter and light-front bound state equations for three scalar particles interacting by scalar exchange-bosons are solved in ladder truncation. In contrast to two-body systems, the three-body binding energies obtained in these two approaches differ significantly from each other: the ladder kernel in light-front dynamics underbinds by approximately a factor of two compared to the ladder Bethe–Salpeter equation. By taking into account three-body forces in the light-front approach, generated by two exchange-bosons in flight, we find that most of this difference disappears; for small exchange masses, the obtained binding energies coincide with each other.     

Trust in the CODA model: Opinion dynamics and the reliability of other agents

A model for the joint evolution of opinions and how much the agents trust each other is presented, using the framework of the Continuous Opinions and Discrete Actions (CODA) model. Instead of a fixed probability that the other agents will decide in the favor of the best choice, each agent considers that other agents might be one of two types: trustworthy or untrustworthy. Each agent its opinion and also the probability for each one of the other agents it interacts with being trustworthy. The dynamics of opinions and the evolution of the trust between the agents are studied. Clear evidences of the existence of two phases, one with strong polarization and the other tending to agreement, are observed. The transition shows signs of being a first-order transition. This happens despite the fact that the trust network evolves much slower than the opinion on the central issue.