The dynamic vectorial model for assemblies of acicular particles

We use the Landau-Lifshitz equations to construct a dynamic model for describing a system of interacting particles. The dynamic model will produce results different from the static model for a finite line of particles with weak interaction strength and parallel anisotropy axes at a large angle to the line. Small two and three dimensional clusters of particles are also discussed. All the results indicate that increasing the angular distribution of the particles will reduce the difference between the static and dynamic simulations. The dynamic switching model is necessary for perpendicular recording because of the alignment of the switching units in the perpendicular media.     

Micromagnetic study of the switching fields in polycrystalline magnetic thin-film media

In this paper, we use micromagnetic simulation to study the switching field reduction and the switching field distribution in polycrystalline thin-film media. We first show that, for the coupled magnetic particles, the switching field of the high-anisotropy particle is reduced as a result of the exchange coupling with the low-anisotropy particle. The switching field reduction increases almost linearly with the anisotropy difference between the coupled particles. An optimal exchange exists that gives a maximum switching field reduction. This switching field reduction is more severe for a small applied field angle; therefore, the angular sensitivity of the switching field is reduced compared to the Stoner-Wohlfarth relation. Detailed micromagnetic simulations also show that in polycrystalline thin-film media, because of the variation and the reduction of the magnetic properties at the grain boundaries, the media coercivity can be reduced significantly. The primary reason for this switching field reduction is the exchange interaction between the grain boundary and the grain center region.     

Switching between 3D Surface Topographies in Liquid Crystal Elastomer Coatings Using Two-Step Imprint Lithography

While dynamic surface topographies are fabricated using liquid crystal (LC) polymers, switching between two distinct 3D topographies remains challenging. In this work, two switchable 3D surface topographies are created in LC elastomer (LCE) coatings using a two-step imprint lithography process. A first imprinting creates a surface microstructure on the LCE coating which is polymerized by a base catalyzed partial thiol-acrylate crosslinking step. The structured coating is then imprinted with a second mold to program the second topography, which is subsequently fully polymerized by light. The resulting LCE coatings display reversible surface switching between the two programmed 3D states. By varying the molds used during the two imprinting steps, diverse dynamic topographies can be achieved. For example, by using grating and rough molds sequentially, switchable surface topographies between a random scatterer and an ordered diffractor are achieved. Additionally, by using negative and positive triangular prism molds consecutively, dynamic surface topographies switching between two 3D structural states are achieved, driven by differential order/disorder transitions in the different areas of the film. It is anticipated that this platform of dynamic 3D topological switching can be used for many applications, including antifouling and biomedical surfaces, switchable friction elements, tunable optics, and beyond.     

Fixation in finite populations evolving in fluctuating environments

The environment in which a population evolves can have a crucial impact on selection. We study evolutionary dynamics in finite populations of fixed size in a changing environment. The population dynamics are driven by birth and death events. The rates of these events may vary in time depending on the state of the environment, which follows an independent Markov process. We develop a general theory for the fixation probability of a mutant in a population of wild-types, and for mean unconditional and conditional fixation times. We apply our theory to evolutionary games for which the payoff structure varies in time. The mutant can exploit the environmental noise; a dynamic environment that switches between two states can lead to a probability of fixation that is higher than in any of the individual environmental states. We provide an intuitive interpretation of this surprising effect. We also investigate stationary distributions when mutations are present in the dynamics. In this regime, we find two approximations of the stationary measure. One works well for rapid switching, the other for slowly fluctuating environments.     

Spin Torque Induced Magnetization Switching Variations

Spin torque induced magnetization switching variations are studied using experimental measurement and theoretical modeling. The study covers a wide time range, from the short time dynamic switching (10 ns) to the long time thermal switching (0.1 s). The modeling results agree well with the measurement data on switching mean and variation. Both data and model show different scaling behaviors of switching current variation and switching time variation as time scales down from the second to the nanosecond region. This study not only provides understanding of the physics involved, but also tools for making design tradeoffs between current switching magnitude, switching variation, switching speed, and thermal stability.      

Dynamic guided-mode resonant grating filter with quadratic electro-optic effect

We propose a novel and simple concept of dynamic switching of guided-mode resonant grating filters with quadratic electro-optic effect within a waveguide layer modulated by external fields due to comb-shaped electrodes that also behave as a grating. As the device has subwavelength structure, the performance must be analyzed electromagnetically. We describe numerical simulation with the finite-difference time-domain method specially modified so that it can treat inhomogeneous anisotropic media such as lead lanthanum zirconate titanate.     

Pulse switching in thin magnetic films

The main results of the investigations of pulse switching in thin magnetic films with uniaxial anisotropy which have been obtained in Moscow State University are reviewed. Simultaneous investigation of integral switching properties, inner effective field, and dynamic domains produced during pulse switching has increased our understanding of bi-directional incoherent rotation mechanism and found new peculiarities of the pulse switching by domain boundary propagation. A new variety of incoherent rotation which manifests itself at strong fields has been found. It has been also found that the curve representing the pulse field dependence of an inverse switching time in the general case consists of five distinct regions. The relation between these regions and the switching mechanisms are discussed.     

Fast Transient Current Response to Switching Events in Short Chains of Molecular Islands

We consider current flow between two metallic leads joined by tunneling junctions to a molecular island. The junctions are assumed to be “wiggly,” that is, switching on and off intermittently. The resulting sequence of current transients overlaps in dependence on the interplay between the switching times and the decay time of “initial” correlations induced by each switching event. The process is described in terms of nonequilibrium Green’s functions.     

异步切换下切换系统的动态输出反馈保成本控制

作为一类重要的混杂系统,切换系统由若干个子系统以及一个协调各子系统之间切换的切换信号构成,在自然科学、工程控制和社会系统等方面有着广泛的应用。在对切换系统的控制问题进行研究时,一般假设子系统和控制器同步运行。然而,在实际工程控制中,控制器的切换相对于子系统的切换存在切换时延,从而产生异步切换。因此,对异步切换下的切换系统研究是十分必要的。针对一类异步切换下切换系统的动态输出反馈保成本控制问题进行了研究。报告了切换系统的研究现状以及异步切换下切换系统的最新研究成果。利用分段李雅普诺夫函数法和平均驻留时间法,得到了使得异步切换下的闭环切换系统稳定的动态输出反馈控制器存在的充分条件。从线性矩阵不等式的角度,提出了异步切换动态输出反馈保成本控制器设计方案,并给出成本上界的优化方法。最后,通过一个数值算例说明了提出的方法的有效性。     

Switching time of single magnetic particle and maximum recording frequency of perpendicular magnetic recording

We investigated the switching time of a magnetic particle-which may impose limits on magnetic recording frequency-by computer simulation. We found that the difference in switching time between low and high temperatures decreases with increasing the angle /spl xi/ between the applied field and the easy direction, and scarcely changes with temperature if the angle is larger than a few degrees. This can be explained by considering the energy contour and locus of magnetization in switching. The switching times derived by using divided models, in which the particle is divided into 2/spl times/2/spl times/2 or 4/spl times/4/spl times/4 cells, are smaller than those derived by using an undivided model. But the difference between the switching times derived with the divided and undivided models is less than 1% if the angle /spl xi/ is larger than 1/spl deg/. We derived equations to express the switching times of the particle for the divided models at /spl xi/=0, and we used the equations to estimate the maximum recording frequency in perpendicular recording.     

Interval estimators of coupling between switched systems

We describe a method for detecting the presence and evaluating the character of interactions between two systems which exhibit a chaotic dynamics involving sharp changes (switching) of their motion at various equilibrium states (in different regions of the phase space). Interval estimators of the coupling are proposed based on the known exact point estimators, which use an analysis of intervals between close switching events. We also propose new interval estimators based on an analysis of the conditional probabilities of switching. The efficiency of both approaches is illustrated using the results of numerical experiments.     

The Influence of Switching between Chaotic Regimes on the Correlation Characteristics of Nonlinear Systems

Technical Physics Letters - The problem of dynamic regime diagnostics in nonlinear systems using their experimental time series is studied in the presence of switching between various oscillatory...     

Simple way for achieving passive all-optical switching of continuous waves lasers using pure nematic liquid crystal

We have examined pure nematic liquid crystal (LC), 4'-pentyl-4-biphenylcarbonitrile (5-CB), with a 90° twisted alignment within a cell made of two cross-polarized absorptive plastic polarizers, and investigated the nonlinear transmission properties using cw (532 nm) lasers. We observed optically self-activated polarization switching with a factor of three lower switching power than a dye-doped LC cell with similar linear transmittance using glass substrates. We also studied the dynamics of the switching processes and observed millisecond switching time. These studies have demonstrated a simpler but more efficient way for fabricating broadband, low switching power, millisecond time scale switching, and optical limiting devices.     

Switching windows for a nanostructured cell of synthetic ferrimagnets

The magnetization switching window of nanostructured synthetic ferrimagnets with lateral dimension of 160 nm x 80 nm under combined in-plane magnetic fields along the longitudinal and transverse directions is investigated by numerical calculation using an analytical equation for the total energy. The considered total energy equation precisely accounts for the magnetostatic energy, which is significantly large in nanostructured magnetic cells. Due to the complex magnetization alignment of synthetic ferrimagnets, a different switching criterion based on the reversibility of magnetization process is used, instead of the simple criterion frequently used for single magnetic layers. Synthetic ferrimagnets with various thickness asymmetries are considered, and switching windows are calculated both in static and dynamic conditions. The static switching windows show a smaller dependence on the thickness asymmetry than the dynamic switching windows do. The dynamic switching window at a large thickness asymmetry resembles that of a single magnetic layer. The results are discussed in terms of energy profiles that can be obtained by locating the lowest energy path linking the two stable states from the total energy surface.     

一种新的包装机电机算法切换系统设计

目的 研究不同工况下包装机生产线中异步电机控制算法的在线灵活切换。方法 选用2种异步电机高性能控制策略FOC和DTC作为包装机电机算法的切换对象,研究2种算法的共同基础,得出新的FOC_DTC算法作为切换系统的过渡算法,有效解决2种控制策略在线相互切换带来的转矩、电流突变等问题,并且在硬件平台上与直接切换方案、重置PI切换方案进行对比。结果 在满足包装机各个工况要求的前提下,混合FOC_DTC切换系统在切换响应时间、切换平滑度和切换效率上比上述2种方案更优越,切换响应时间提高了2%,切换转矩尖峰降低了30%。结论 通过使用混合FOC_DTC切换系统,包装机在不同工况下可以在线实时切换动力系统电机的控制算法,在平滑度和响应时间上比其他方案有明显的优势。     

Field-effect-transistor self-electro-optic-effect-device (FET-SEED) electrically addressed differential modulator array

We describe a 6 × 6 array of electrically addressed field-effect-transistor self-electro-optic-effect-device differential modulators in which each element has a single-stage amplifier to permit an input voltage of less than 1 V to control the output modulators, which can operate at as high as 10 V. The variations in the switching voltages across the array are less than ±70 mV, and the individual array elements are operated at as high as 2 Gbits/s. We also measure cross talk between adjacent elements within the array, measure the dependence of the switching time on the input voltage swing, and calculate the dependence of the switching time that is due to the photocurrent of the modulators.     

Comparative study on orthotropic solid waves by time-domain BEM and dynamic photoelasticity

Experimental research and numerical analysis are two basic tools in the study of wave propagation problems in orthotropic media. In this paper, an experimental method, namely dynamic orthotropic photoelasticity, which studies the dynamic behavior of orthotropic materials on a macroscopic scale by employing orthotropic birefringent materials, is established. Meanwhile, a numerical method, namely time domain boundary element method (BEM) for wave propagation in orthotropic media, is also presented. The two methods are used together in the analysis of semi-infinite orthotropic plates with and without a circular hole modeled by a unidirectional fiber-reinforced composite under impact loading. The propagation, reflection and diffraction of stress waves in the orthotropic media are recorded experimentally and investigated. Time histories of birefringent fringe orders or stresses for specific points of the plates are obtained, respectively, from the two methods and compared with each other. The comparative study demonstrates the applicability and accuracy of the two methods for wave propagation problems in orthotropic media.     

Long memory retention time and high contrast ratio in a tristate liquid crystal display device

We propose a method to obtain long memory retention time and high contrast ratio in a tristate liquid crystal display device. The proposed device has three unique liquid crystal (LC) states that are known as splay, π twist, and bend, with different operating schemes for the two modes of operation, which are the memory (M) mode or dynamic (D) mode. A form of selective vertical or horizontal switching changes the optically compensated π twist LC as a common black state in both the M and D modes into a bend LC state for the D mode or into the splay LC state for the M mode, respectively.     

Electrical switching and memory phenomena observed in redox dendrimer thin films

This article reports on the fabrication of dendrimer molecular thin film sandwich devices with electrical switching and memory properties. The storage media consists of a redox-gradient N,N?-(1,4-phenylene)bis(N,N′N′N″,N″-pentakis(4-methoxyphenyl)-1,3,5-benzenetriamine) (4AAPD) dendrimer layer sandwiched between two N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD) thin films. The TPD thin films are used as potential barriers. The 4AAPD layer acts as a potential well where redox-state changes and consequent electrical transitions of the embedded 4AAPD molecules can be effectively triggered. Experimental results indicate that electrical switching could be reproducibly obtained in the dendrimer sandwiches upon crossing a threshold bias voltage. After switching, the device conductivity can be increased more than three orders of magnitude, which is stable for several days in ambient conditions. This work demonstrates the possibility of using solid-state redox-gradient dendrimer layer as information storage media.     

Nanoelectromechanical switch operating by tunneling of an entire C60 molecule

We present a solid state single molecule electronic device where switching between two states with different conductance happens predominantly by tunneling of an entire C60 molecule. This conclusion is based on a novel statistical analysis of approximately 10(5) switching events. The analysis yields (i) the relative contribution of tunneling, current induced heating and thermal fluctuations to the switching mechanism, (ii) the voltage dependent energy barrier (approximately 100-200 meV) separating the two states of the switch and (iii) the switching attempt frequency, omega0, corresponding to a 2.8 meV mode, which is most likely rotational.