Optically Activated Charge Domain Model for High-Gain GaAs Photoconductive Switches

A model for theoretical analysis of nonlinear (or high gain) mode of photoconductive semiconductor switches (PCSS's) is proposed.The switching transition of high gain PCSS's can be described with an optically activated charge domain. The switching characteristics including rise time,delay and their relationship to electric field strength,optical trigger energies are discussed.The formation and radiation transit,accumulation of the charge domain are related with the triggering and sustaining phases of PCSS's,respectively.The results of the mathematical model on this mechanism agree with experimental results.

Numerical simulation of domain switching in multilayer ferroelectric actuators

Micromechanical finite element methods are developed based on a nonlinear constitutive model of ferroelectric polycrystals. Electromechanical behaviors ahead of an internal electrode tip are numerically simulated in multilayer ferroelectric actuators. Around the electrode edge, the nonuniform electric field generates a concentration of stress due to the incompatible strain as well as spontaneous strain. The preferred domain switching enhances the concentration of residual stress and may cause the actuators to crack. An electrically permeable crack emanating from an internal electrode is analyzed. A large scale domain switching zone is found in the vicinity of crack tips. The larger the actuating strain and electric field are, the larger the switching zone will be. The size of switching zone even reaches the scale of crack length with increasing electromechanical loading.

Coalescence of pore columns by domain switching

The present paper studies the coalescence of pore columns in ferroelectric ceramics driven by back and forth domain switching under cyclic electric field. A finite element method that incorporates mass transfer capacity is formulated to simulate the evolution of point defects subjected to the kinetics of pore surface diffusion and domain wall migration. The merge of point defects provides a mechanism for the vacancy agglomeration that leads to the formation of large pores or microcracks.

Phase field simulation of the 180°domain-switching process in PbTiO_3 single crystal under an antiparallel electric field

The process of 180°domain switching in PbTiO_3 single crystal under an antiparallel electric field was investigated by the three-dimensional phase field simulation,especially the effect of electric field on the type and duration of domain switching.It is found that the polarization reversal of domains takes place under an antiparallel electric field in PbTiO_3 single crystal.The results of the phase field simulation indicate that there is only 90°domain switching under a weak electric field.With the rise of the electric field,180°domain switching appears.If the electric field is strengthened further,90°domain switching disappears and the duration of domain switching is shortened.

A SIMPLIFIED MODEL FOR DOMAIN SWITCHING OF FERROELECTRIC CRYSTAL

Domain switching is the main source of nonlinear characteristics in ferroelectrics. According to crystal plasticity theory, the domains and domain switching systems for perovskite- type structure ferroelectrics are de?ned. Considering the traverse motion performance of domain wall, a rather simpli?ed form of evolution law about incremental of volume fraction during domain switching has been developed. The main factors, which exert an in?uence on domain switching, such as material parameters, domain wall motion history, kind of domain switching (180? or 90?) and volume fraction, could be addressed. The hysteresis loops of spontaneous electric polarization as a function of electric ?eld, the butter?y shaped strain versus electric ?eld curve and the platform relations between spontaneous polarization and stress, as well as the longitudinal strain and stress, are well simulated and discussed.

In-situ observation on domain switching of PLZT via Raman spectroscopy

An in-situ and nondestructive technique was proposed and established for the study of domain switching in PLZT ceramics via observation of Raman spectrum changes based on the Raman light scattering principle and the soft mode theory. A Vickers indent was introduced into the polarized PLZT specimen so that the Raman spectrum change associated with the domain switching as induced either by an applied electric field or by a stress field surrounding the tip of the Vickers indent crack was in-situ measured and studied using this established technique. The relation between the domain switching and the measured Raman spectrum was discussed. It is well demonstrated that this technique can sensitively detect and measure the domain switching via the observation of Raman spectrum changes. The results confirm that Raman spectrum intensity is directly attributed to the change of the polarization direction of the incidence and scattered lights with respect to the direction of the average polarization direction of the domain in the polarized specimen. When the two directions are parallel, the induced polarizability tensor of the specimen would be enhanced and give rise to a higher intensity for Raman scattering light.

Reliability index algorithm of a sub-domain interconnection large communication network

The normalized weighted capacity reliability index of a sub-domain interconnection large scale communication network is defined and a new algorithm to calculate the reliability index is proposed, The proposed algorithm can be performed using logical or algebraic operation by means of computer-aided programming and the correctness of each key step is validated in detail. This paper takes the sub-domain interconnection symmetrical topologi- cal network for a typical example to calculate the network reliability index and verifies the correctness of the proposed algorithm us- ing the real measured statistical data. The real measured results are well in accordance with the results obtained by the proposed algorithm. The result shows that the proposed algorithm is a valid means to estimate the reliability index of a sub-domain intercon- nection large-scale communication network.

A MICROMECHANICS METHOD TO STUDY THE EFFECT OF DOMAIN SWITCHING ON FRACTURE BEHAVIOR OF POLYCRYSTALLINE FERROELECTRIC CERAMICS

The effect of domain switching on anisotropic fracture behavior of polycrystalline ferroelectric ceramics was revealed on the basis of the micromechanics method. Firstly, the electroelastic field inside and outside an inclusion in an infinite ferroelectric ceramics is carried out by the way of Eshelby-Mori-Tanaka's theory and a statistical model, which accounts for the influence of domain switching. Further, the crack extension force (energy-release rate) G(ext) for a penny-shape crack inside an effective polycrystalline ferroelectric ceramics is derived to estimate the averaged effect of domain switching on the fracture behavior of polycrystalline ferroelectric ceramics. The simulations of the crack extension force for a crack in a BaTiO3 ceramics are shown that the effect of domain switching must be taken into consideration while analyzing the fracture behavior of polycrystalline ferroelectric ceramics. These results also demonstrate that the influence of the applied electric field on the crack propagation is more profound at smaller mechanical loading and the applied electric field may enhance the crack extension in a sense, which are consistent with the experimental results.

Nanoscale domain switching mechanism of Bi_(3.15)Eu_(0.85)Ti_3O_(12) thin film under the different mechanical forces

The switching process of ferroelectric thin films in electronic devices is one of the most important requirements for their application. Especially for the different external fields acting on the film surface, the mechanism of domain switching is more complicated. Here we observe the nanoscale domain switchings of Bi3.15Eu0.85Ti3O12 thin film under different mechanical forces at a fast scan rate. As the force increases from initial state to 247.5 n N, the original bright or grey contrasts within the selected grains are all changed into dark contrasts corresponding to the polarization vectors reversed from the up state to the down state, except for the clusters. As the mechanical force increases to 495 n N, the color contrasts in all of the selected grains further turn into grey contrasts and some are even changed into grey contrasts completely showing the typical 90° domain switching. When another stronger loading force 742.5 n N is applied, the phase image becomes unclear and it indicates that the piezoelectric signal can be suppressed under a sufficiently high force, which is coincident with previous experimental results. Furthermore, we adopt the domain switching criterion from the perspective of equilibrium state free energy of ferroelectric nanodomain to explain the mechanisms of force-generated domain switchings.

Large and Recoverable Electrostrain in Strained Ferroelectric Superlattices due to Domain Switching

The ferroelectric superlattices have been widely studied due to their distinguished electromechanical coupling properties.Under different biaxial mismatch strains,ferroelectric superlattices exhibit different domain structures and electromechanical coupling properties.A three-dimensional phase field model is employed to investigate the detailed domain evolution and electromechanical properties of the PbTiO_(3)/SrTiO_(3)(PTO/STO)superlattices with different biaxial mismatch strains.The phase field simulations show that the ferroelectric superlattice exhibits large electrostrain in the stacking direction when an external field is applied.Under a large compressive mismatch strain,vortex domains appear in ferroelectric layers with the thickness of 4 nm.The vortex domains become stable cdomain under a large external electric field,which remains when the electric field is removed.When the initial compressive mismatch strain decreases gradually,the waved or a1/a2 domains replaces the initial vortex domains in the absence of electric field.The fully polarized c-domain by a large electric field switches to diagonal direction domain or a/c domain when the electric field is small.Furthermore,when a biaxial tensile strain is applied to the superlattice,ferroelectric domains switch back to the initial a1/a2 twin-like domain structure,resulting in the recoverable and large electrostrain.This provides an effective way to obtain the large and recoverable electrostrain for the engineering application.

Tetragonal Domain Switching via Reversible tm Phase Transformation

Grinding-induced tm phase transformation and the resultant texture in ceria-yttria-doped tetragonal zirconia polycrystals with varied tetragonality have been studied by XRD. It is observed that the reversible tm phase transformation occurs during grinding and the intensity ratio of I(002)t/I(200)t increases with the transformability. The author proposes that the texture induced by grinding at low temperatures is due to the tetragonal variant reorientation via cyclic,reversible tm phase transformation, termed 'transformational domain switching', instead of the ferroelastic one

Structural and functional consequences of switching carboxy terminal domains in mouse CD200 receptors

CD200:CD200R interactions regulate immune responses. Since CD200Rs show extensive homology in their extracellular region, generating anti-CD200R specific antibodies is a challenge. We report below on the generation of mAbs specific for murine (m)R1/R2 and evidence that mR2 is expressed on the cell surface in the absence of the adaptor protein Dap12. Despite homology between mR1 and mR4, the unexpected reduction in the molecular mass (i.e. 90kDa vs 48kDa) between the two receptors suggested that the TM and cytoplasmic region of mR4 regulated glycosylation. Substitution of the TM and cytoplasmic region of mR1 and mR2 with that of mR4 reduced glycosylation of the chimeric receptors mR1r4 and mR2r4 implying that these regions regulated the glycosylation of mCD200Rs. In activation experiments, phosphorylation of Dap12 following interaction with CD200 occurred on cells expressing mR2V5 but not mR4V5. Similar experiments with the chimeric receptors mR1r2 and mR1r4 also produced phosphorylation of Dap12. Our data suggest that the TM and cytoplasmic region of mCD200Rs dictate their state of glycosylation and provide further evidence that both mCD200R1 and mCD200R2 bind CD200 as ligand with functional consequences for down-stream signaling.

Survey of Mechanisms for Inter-Domain SDN

Software defined networking(SDN) has been applied increasingly in practical networks. Currently, SDN is mainly used to improvethe flexibility and efficiency of datacenter networks, enterprise networks and wide-area networks(WAN). There also emerge somestudies that try to deploy SDN to inter-domain settings. In this article, we introduce the progress stages of inter-domain SDN andstudies related to each stage. Finally, we discuss the applications and challenges of inter-domain SDN.

Optical simulation of in-plane-switching blue phase liquid crystal display using the finite-difference time-domain method

The finite-difference time-domain method is used to simulate the optical characteristics of an in-plane switching blue phase liquid crystal display.Compared with the matrix optic methods and the refractive method,the finite-difference timedomain method,which is used to directly solve Maxwell＇s equations,can consider the lateral variation of the refractive index and obtain an accurate convergence effect.The simulation results show that e-rays and o-rays bend in different directions when the in-plane switching blue phase liquid crystal display is driven by the operating voltage.The finitedifference time-domain method should be used when the distribution of the liquid crystal in the liquid crystal display has a large lateral change.

Resolution for Conflicts of Inter-Operation in Multi-Domain Environment

This paper proposes a method to formalize the interoperation in multi-domain environment. Through employing the algebra method, we conclude four types of the conflicts for the interoperation, and analyzes the cause of the policy conflicts. For each type of conflicts, we formalize it and proposes the method of detection and resolution. Finally, the method is illuminated be effective through comparing our work with others.

Improving Inter-Domain Fast Handover Using MIH Services in Mobile WiMAX

Recently, the IP connectivity during the Mobile Node (MN) movement between Base Stations (BSs) belonging to different Internet Service Providers (ISPs) is still a key issue to be tackled. In this paper, therefore, we develop a new scheme to improve the performance of inter-domain fast handover over mobile WiMAX networks. The framework basically relies on the Fast Handover for Mobile IPv6 protocol (FMIPv6) when the Media Independent Information Services (MIIS) as defined in IEEE802.21 standard is applied to enable the Mobile Node in storing the information of the neighboring networks. A Fully Qualified Domain Name (FQDN) is also used to identify the IP address of the previous network operator and the MN during its movements. Since both MIIS and FQDN can support the node mobility between multiple domains, our proposed scheme can also be called P-FMIPv6. The numerical results show that the latency of IP connectivity of this proposed handover can be significantly reduced in addition to less service disruption time during handovers as compared to the existing FMIPv6 when IEEE802.16e network is considered.

基于Internet阶层结构的域间路由聚合增强算法

提出了一种域间路由聚合的增强算法,它利用Internet阶层结构特性,以自治系统间关系为依据,强化路由聚合行为并约束可聚合路由的通告范围,给出了原形系统的实现算法·算法所需数据全部来自自治系统内部,没有全局协调数据,并有效回避了聚合行为对负载均衡和链路冗余的负面影响·数据实测和分析显示,算法能有效降低路由表规模,从而缓解当前Internet域间路由表高速增长的局面,加强了Internet的可扩展性·

Internet域间路由系统:问题与挑战

作为Internet的核心基础设施,基于BGP协议的域间路由系统目前在扩展性、端到端性能、安全性与可信性等方面存在问题。由于部署的广域性、AS的自治性以及ISP之间交互的复杂性、域间路由行为的动态性,使得人们对域间路由系统的结构和行为规律尚未充分理解,缺乏全面有效的解决方案,大规模的系统的网络实验难以开展。理想的域间路由系统及其支撑的Internet在性能上应具有快速恢复和全局优化的能力,在安全上应具有自主防范和协同控制能力,在运营上应具有自主配置和协同管理能力。

Energy principle of ferroelectric ceramics and single domain mechanical model

Many physical experiments have shown that the domain switching in a ferroelectric material is a complicated evolution process of the domain wall with the variation of stress and electric field. According to this mechanism, the volume fraction of the domain switching is introduced in the constitutive law of ferroelectric ceramic and used to study the nonlinear constitutive behavior of ferroelectric body in this paper. The principle of stationary total energy is put forward in which the basic unknown quantities are the displacement ui, electric displacement Di and volume fraction pI of the domain switching for the variant I. Mechanical field equation and a new domain switching criterion are obtained from the principle of stationary total energy. The domain switching criterion proposed in this paper is an expansion and development of the energy criterion. On the basis of the domain switching criterion, a set of linear algebraic equations for the volume fraction PI of domain switching is obtained, in which the coefficients of the linear algebraic equations only contain the unknown strain and electric fields. Then a single domain mechanical model is proposed in this paper. The poled ferroelectric specimen is considered as a transversely isotropic single domain. By using the partial experimental results, the hardening relation between the driving force of domain switching and the volume fraction of domain switching can be calibrated. Then the electromechanical response can be calculated on the basis of the calibrated hardening relation. The results involve the electric butterfly shaped curves of axial strain versus axial electric field, the hysteresis loops of electric displacement versus electric filed and the evo- lution process of the domain switching in the ferroelectric specimens under uniaxial coupled stress and electric field loading. The present theoretic prediction agrees reasonably with the experimental results given by Lynch.

Internet扁平化趋势测量与分析

目前对Internet拓扑结构的扁平化趋势的研究多集中在定性描述上,没有大规模的测量数据支撑。从域间路由的角度,分析了Internet层级结构和互连策略的演变趋势。发现Internet扁平化的主要原因是绕过Tier-1ISP以及peer-to-peer链路比例的增加。测量了路由基础设施的变化情况,发现IXP在数量和地理位置上都快速增长,极大地方便了内容提供商和内容分发网络的扩张。测量结果能够加深对Internet生态系统的理解,有助于未来互联网架构的设计。最后分析了Internet扁平化的原因和影响。