Electronic relaxation of deep bulk trap and interface state in ZnO ceramics

This paper investigates the electronic relaxation of deep bulk trap and interface state in ZnO ceramics based on dielectric spectra measured in a wide range of temperature, frequency and bias, in addition to the steady state response. It discusses the nature of net current flowing over the barrier affected by interface state, and then obtains temperature-dependent barrier height by approximate calculation from steady I--V (current--voltage) characteristics. Additional conductance and capacitance arising from deep bulk trap relaxation are calculated based on the displacement of the cross point between deep bulk trap and Fermi level under small AC signal. From the resonances due to deep bulk trap relaxation on dielectric spectra, the activation energies are obtained as 0.22 eV and 0.35 eV, which are consistent with the electronic levels of the main defect interstitial Zn and vacancy oxygen in the depletion layer. Under moderate bias, another resonance due to interface relaxation is shown on the dielectric spectra. The DC-like conductance is also observed in high temperature region on dielectric spectra, and the activation energy is much smaller than the barrier height in steady state condition, which is attributed to the displacement current coming from the shallow bulk trap relaxation or other factors.     

Auto‐barrier‐thinning effect under rapid anodization of nanoporous alumina membrane

We have developed a rapid non‐steady anodization technique that leads to an in‐situ auto‐thinning of the barrier layer due to a space charge limited condition that modifies the local fields at the interfaces of the Al‐Al₂O₃‐electrolyte ternary system. Unlike steady‐state growth, in this non‐steady case an unequal movement of the boundaries of barrier takes place which etches the electrolyte‐oxide interface more than the oxide grows at the oxide‐metal interface, leading to a thinner barrier layer and favouring its complete removal via wet‐etching process. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mdm2生成速率调控的p53-Mdm2振子的全局动力学和稳定性

肿瘤抑制蛋白p53的动力学在一定程度上可以决定DNA损伤后的细胞命运.p53的动力学行为与p53信号通路中p53-Mdm2振子模块密切相关.然而,p53的负调控子Mdm2的生成速率的增加使其在一些癌细胞中过表达.因此探讨Mdm2生成速率对p53动力学的影响有重要意义.同时,PDCD5作为p53的激活子也调控p53的表达.因此,本文针对PDCD5调控的p53-Mdm2振子模型,通过分岔分析获得了Mdm2生成速率所调控的p53的单稳态、振荡以及单稳态与振荡共存的动力学行为,且稳定性通过能量面进行了分析.此外,噪声强度对p53动力学的稳定性有重要的影响.因此,针对p53的振荡行为,探讨了噪声强度对势垒高度和周期的影响.本文所获得的结果对理解DNA损伤后的p53信号通路调控起到一定的指导作用.     

Steady state and relaxation spectrum of the Oslo rice-pile model

We show that the one-dimensional Oslo rice-pile model is a special case of the abelian distributed processors model. The exact steady state of the model is determined. We show that the time evolution operator for the system satisfies the equation where n=L(L+1)/2 for a pile with L sites. This implies that has only one eigenvalue 1 corresponding to the steady state, and all other eigenvalues are exactly zero. Also, all connected time-dependent correlation functions in the steady state of the pile are exactly zero for time difference greater than n. Generalization to other abelian critical height models where the critical thresholds are randomly reset after each toppling is briefly discussed.     

Stability of continuously pumped atom lasers

A multimode model of a continuously pumped atom laser is shown to be unstable below a critical value of the scattering length. Above the critical scattering length, the atom laser reaches a steady state, the stability of which increases with pumping. Below this limit the laser does not reach a steady state. This instability results from the competition between gain and loss for the excited states of the lasing mode. It will determine a fundamental limit for the linewidth of an atom laser beam.     

Directed percolation phase transition at the onset of STI in an inhomogeneous coupled map lattice

A model for inhomogeneously coupled logistic maps is considered to find some critical exponents in the transition from inhomogeneous steady state to spatiotemporal chaos through spatiotemporal intermittency. The laminar state in the model is described by inhomogeneous steady state with spatial period two. We obtain a complete set of static exponents which match with the corresponding directed percolation (DP) values in (1+1) dimension. We also find four nonuniversal spreading exponents in which three exponents are in agreement with DP values. The model in which absorbing state is inhomogeneous steady state, contributes a new example in evidence of Pomeau's [18] conjecture that the onset of STI in a deterministic system belongs to DP universality class.     

Existence of dual solutions and three-dimensional instability in helical pipe flow

Three-dimensional (3D) direct numerical simulations (DNS) of the viscous incompressible fluid flow through a helical pipe with circular cross section were performed. The flow is governed by three parameters: the Dean number (or the Reynolds number), curvature, and torsion. First, we obtained steady solutions by steady 3D calculations, where dual solutions were found, one was uniform in the pipe axial direction and the other varied very slowly, if torsion exceeded a critical value. Then, the instability of the steady solutions obtained was studied by unsteady 3D calculations. We obtained critical Reynolds numbers of steady to unsteady transition by observing the behaviors of the unsteady solutions. The present results of the critical Reynolds number nearly agreed with those by the 2D linear stability analysis (Yamamoto et al. [9]) except for the lowest critical Reynolds number region, where the present study gave the critical Reynolds number much less than that obtained by the 2D linear stability analysis. We found the vortical structures in the form of a standing wave slightly above the marginal instability state, which is a trigger of explosive 3D instability.     

Alpha-channeling simulation experiment in the DIII-D tokamak

Alfvén instabilities can reduce the central magnetic shear via redistribution of energetic ions. They can sustain a steady state internal transport barrier as demonstrated in this DIII-D tokamak experiment. Improvement in burning plasma performance based on this mechanism is discussed.     

Effect of nano-SiO2 films on the electron radiation induced conductivity of polyimide

The radiation induced conductivity (RIC) behaviors in nano-SiO2 deposited polyimide (PI) were investigated using the in situ measurement technique. The results indicate that, by comparison with the case of virgin polyimide, the RIC in nano-SiO2/polyimide shows low steady state values. Moreover, the steady state RIC is a power function of the dose rate with a power index of 0.659, lower than that of 0.76 in the virgin polyimide. The interfacial barrier and trapping effects are the main reasons for the change. Meanwhile, both of the interfacial effects also result in a unipolar carrier transportation mechanism in nano-SiO2 deposited PI from the dipolar one in the virgin PI. The mechanisms of the RIC behaviors are discussed in the paper.     

Abrupt transition from viscoelastic solidlike to liquidlike behavior in jammed materials

Using a new rheometrical technique, which makes it possible to determine both the velocity field in steady state and the strain field in the very first instants of the flow, we show that, beyond a critical deformation, typical pasty materials (a foam and a polymeric gel) turn abruptly from a viscoelastic solidlike behavior to a steady liquidlike behavior at a shear rate larger than a critical value.     

Lattice wave emission from moving cracks

Antiplane shear cracks moving in square lattices have been studied in a molecular dynamics simulation. They become unstable when a critical stress intensity at the tip is reached. Within picoseconds they accelerate to steady state velocity, which can be supersonic or not, depending on the interatomic potential. If the surface energy is low, they become supersonic; if the surface energy is high, they reach only subsonic speeds before the crystal reaches the theoretical shear strength. A simple modification of the interatomic potential switches the crystal behaviour from brittle to ductile, substituting dislocations to daughter cracks. The steady state velocities are the same, whether the model crystal is brittle or ductile. The steady state velocity is a function of the applied stress, not the stress intensity.     

Crack propagation as a free boundary problem

A sharp interface model of crack propagation as a phase transition process is discussed. We develop a multipole expansion technique to solve this free boundary problem numerically. We obtain steady state solutions with a self-consistently selected propagation velocity and shape of the crack, provided that elastodynamic effects are taken into account. Also, we find a saturation of the steady state crack velocity below the Rayleigh speed, tip blunting with increasing driving force, and a tip splitting instability above a critical driving force.     

Dynamical vanishing of the order parameter in a fermionic condensate

We analyze the dynamics of a condensate of ultracold atomic fermions following an abrupt change of the pairing strength. At long times, the system goes to a nonstationary steady state, which we determine exactly. The superfluid order parameter asymptotes to a constant value. We show that the order parameter vanishes when the pairing strength is decreased below a certain critical value. In this case, the steady state of the system combines properties of normal and superfluid states -- the gap and the condensate fraction vanish, while the superfluid density is nonzero.     

中波HgCdTe双色红外探测器优化模拟计算

针对光伏型中波HgCdTe双色红外探测器作了优化模拟计算，器件采用典型n-p-p-p-n结构和同时工作模式，建立的二维模型考虑了辐射复合、俄歇复合和Shockley-Read-Hall(SRH)复合三种复合机理，以及深能级辅助隧穿和带间直接隧穿效应，载流子穿过阻挡层势垒的隧道效应采用传递矩阵法计算.分析了双色器件光谱响应随吸收区SRH复合少子(电子)寿命的变化关系，以及串音与阻挡层组分的关系.模拟结果显示，随吸收区少子寿命变短，量子效率迅速下降；为了使器件有较高的量子效率，HgCdTe材料的SRH复合电子寿命应该至少在10ns以上.随阻挡层组分增大，势垒增高，串音迅速减小，大约在阻挡层组分差为0.03时下降到光学串音决定的稳定值，得出了抑制电学串音，阻挡层组分差的临界值为0.03. 关键词： HgCdTe中波双色红外探测器 光谱响应 光谱串音 少子寿命     

Magnetic field effect on the binding energy of a hydrogenic impurity in coaxial GaAs/ AlxGa1−xAs quantum well wires

We propose a coaxial cylindrical quantum well wire (QWW) system, in which two conducting cylindrical layers are separated by an insulating layer. The ground state binding energy of a hydrogenic impurity subjected to uniform magnetic field applied parallel to the wire axis is studied within a variational scheme as a function of the inner barrier thickness for two different impurity positions and various barrier potentials. The ground state energy and wave function in the presence of a magnetic field is directly calculated using the fourth-order Runge–Kutta method. It is found that the binding energy in critical barrier thickness shows a sharp increase or decrease depending on the impurity position and magnetic field strength. The main result is that a sharp variation in the binding energy, which may be important in device applications, depends strongly not only on the location of the impurity but also on the magnetic field and the geometry of the wire.     

Chemotaxis driven instability of a confined bacterial suspension

A suspension of bacteria in a thin channel or film subject to a gradient in the concentration of a chemoattractant, will develop, in the absence of an imposed fluid flow, a steady bacteria concentration field that depends exponentially on cross-stream position. Above a critical bacteria concentration, this quiescent base state is unstable to a steady convective motion driven by the active stresses induced by the bacteria's swimming. Unlike previously identified long-wavelength instabilities of active fluids, this instability results from coupling of the bacteria concentration field with the disturbance flow.     

Stability of Bose-Einstein condensates in a double-well potential

We investigate the stability of the first excited state, the so-called “π-state,” of Bose-Einstein condensates in a double-well potential. From the condition of complex excitation energies, we determine the critical barrier height, above which the π-state is dynamically unstable. We find that the critical barrier height decreases monotonically as the number of condensate atoms increases. We also simulate the dynamics of the π-state by solving the time-dependent Gross-Pitaevskii equation. Our simulation results show that the π-state in the dynamically unstable region exhibits distinctively different behavior from that in the dynamically stable region.     

Fokker-Planck equation approach to fluctuations about nonequilibrium steady states

We examine the properties of steady states in systems which interact at the boundary with a nonequilibrium environment. The examination is based on a nonlinear Fokker-Planck equation, the structure of which is determined by the fact that it also governs the time evolution of the equilibrium fluctuations of the system. The nonlinearities in the Fokker-Planck equation may have two origins: thermodynamic nonlinearities which arise if the thermodynamic potential is not a bilinear function of the state variables, and nonlinear mode coupling which arises if the transport coefficients depend on the state. While these nonlinearities have only a small effect on the equilibrium fluctuations of a system away from critical points, they are shown to be important for the determination of fluctuations about nonequilibrium steady states. In particular the state dependence of the transport coefficients may lead to deviations from local equilibrium and to a breakdown of detail balance. An explicit formula for the time correlations of fluctuations about the nonequilibrium steady state is obtained. The formula leads to long-range correlations in fluids in the presence of a temperature gradient. The result is compared with earlier approaches to the same problem. Finally, we study the linear response to external forces and obtain a generalization of the fluctuation-dissipation formula relating the response functions with the nonequilibrium correlation functions.     

Dynamically driven renormalization group

We present a detailed discussion of a novel dynamical renormalization group scheme: the dynamically driven renormalization group (DDRG). This is a general renormalization method developed for dynamical systems with non-equilibrium critical steady state. The method is based on a real-space renormalization scheme driven by a dynamical steady-state condition which acts as a feedback on the transformation equations. This approach has been applied to open nonlinear systems such as self-organized critical phenomena, and it allows the analytical evaluation of scalling dimensions and critical exponents. Equilibrium models at the critical point can also be considered. The explicit application to some models and the corresponding results are discussed.     

Self-Organization in a Granular Medium by Internal Avalanches

Internal avalanches of grain displacements can be created inside a granular material kept in a bin in two ways: (i) by removing a randomly selected grain at the bottom of the bin; and (ii) by breaking a stable arch of grains clogging a hole at the bottom of the bin. Repeated generation of such avalanches leads the system to a steady state. It is relevant to ask whether this state is a critical state, as in self-organized criticality (SOC). We review here some recent studies of this problem using cellular automata and hard-disc models.