Effects of Deformation Rate on the Necking of an Amorphous Copolyester Studied by Modulated DSC

The tensile loading-induced necking in notched specimens of an amorphous copolyester (aCOP) was studied by modulated differential scanning calorimetry (MDSC). It was shown that necking occurred by cold drawing since the enthalpy of cold crystallization and that of the subsequent melting agreed fairly with each other. Increasing deformation in the necking zone and increasing deformation rate of the specimens shifted the onset of cold crystallization toward lower temperatures and yielded a slightly higher glass transition temperature (T_g). This was attributed to the molecular orientation caused by mechanical loading. The finding that the melting contained a non-reversing part was considered as appearance of possible microcrystallinity. The T_g range was strongly influenced by the deformation rate and reflects the thermomechanical history of the samples accordingly. This revised version was published online in August 2006 with corrections to the Cover Date.     

Determination of trapping–detrapping events,recombination processes and gap-state parameters by modulated photocurrent measurements on amorphous silicon

Analysis of the out-of-phase modulated photocurrent (MPC) signal, the so-called Y signal, is proposed for determining the trapping–detrapping events, recombination processes and gap-state parameters in amorphous silicon. This is demonstrated by analysing experimental Y spectra obtained on this material from different laboratories including our own. Model simulations are also employed in which the amphoteric nature of the dangling bonds and their distribution according to the defect-pool model are taken into account. From the reconstruction of the Y signal, phase shift and MPC amplitude spectra, several contributions resolved from the frequency dependence of the experimental Y spectra are identified. Two electron trapping–detrapping processes are resolved. These are attributed to hydrogen-related positive defects and to transitions involving the D^+/0 level of the normal dangling bonds from the defect-pool distribution. At lower frequencies a residual contribution is resolved that is attributed to a term related to recombination through the D^+/0 and D^0/? levels. Between 300 and 150?K the above recombination contribution is essentially from the D^0/? and dominates the Y signal at lower frequencies. In this region a characteristic phase lead appears, which is attributed to the existence of safe hole traps in the valence band tail. Around 150?K, trapping–detrapping events in the conduction band tail dominate.     

瞄准制导仪中的调制盘光学系统分析

瞄准制导仪中的调制盘光学系统包含有光束投射系统、光束投影系统和旋转调制盘。基于旋转调制盘图案设计的原理,分析了瞄准制导仪中内、外调制图案与光学系统的配合问题。较详细地分析了激光束投射系统和投影系统。     

Modulated‐temperature differential scanning calorimetry study of temperature‐induced mixing and demixing in poly(vinylmethylether)/water

The heat capacity or reversing heat flow signal from modulated‐temperature differential scanning calorimetry can be used to measure the onset of phase separation in a poly(vinylmethylether)/water mixture, clearly showing the special type III lower critical solution temperature demixing behavior. Characteristic of this demixing behavior is a three‐phase region, which is detected in the nonreversing heat flow signal. Stepwise quasi‐isothermal measurements through the phase transition show large excess contributions in the (apparent) heat capacity signal, caused by demixing/remixing heat effects on the timescale of the modulation (fast process). These excess contributions and their time‐dependent evolutions (slow process) are useful in understanding the kinetics of phase separation and the morphology (interphase) development. Care has to be taken, however, in interpreting the heat capacity signal derived from the amplitude of the modulated heat flow because nonlinear effects lead to the occurrence of higher harmonics. Therefore, the raw heat flow signal for quasi‐isothermal demixing and remixing measurements is also examined in the time domain. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1824–1836, 2003     

具有周期信号调制噪声的线性模型的随机共振

研究了具有周期信号调制噪声的过阻尼线性系统的随机共振现象.当采用非对称的分段噪声 时，可以得到系统响应的一、二阶矩和信噪比的精确表达式.通过对信噪比的分析, 发现了 “真实的"随机共振和传统的随机共振现象，讨论了乘性噪声的非对称性、自相关时间和噪 声之间的相关强度对信噪比的影响. 关键词： 随机共振 信噪比 周期信号调制噪声 线性模型     

非均匀调制随机激励下系统的非平稳响应分析

基于时域复模态分析，提出一种非均匀调制随机激励下系统非平稳响应特性的解析解法，用Ｎｉｉｇａｔａ地震激励模型作了说明．算例与仿真结果吻合良好．     

QUASI-NEUTRAL LIMIT OF THE BIPOLAR NAVIER-STOKES-POISSON SYSTEM

This paper is concerned with the quasi-neutral limit of the bipolar NavierStokes-Poisson system. It is rigorously proved, by introducing the new modulated energy functional and using the refined energy analysis, that the strong solutions of the bipolar Navier-Stokes-Poisson system converge to the strong solution of the compressible NavierStokes equations as the Debye length goes to zero. Moreover, if we let the viscous coefficients and the Debye length go to zero simultaneously, then we obtain the convergence of the strong solutions of bipolar Navier-Stokes-Poisson system to the strong solution of the compressible Euler equations.     

Local asymptotics of a Markov modulated random walk with heavy-tailed increments

In this paper, we obtain sufficient and necessary conditions for local asymptotics for the maximum of a Markov modulated random walk with long-tailed increments and negative drifts, where the local asymptotics means asymptotic behaviour of P(· ∈ (x, x + z]) for each z > 0, as x→∞. Our results extend and improve the existing ones in the literature.     

Piecewise linear processes with Poisson‐modulated exponential switching times

We consider the jump telegraph process when switching intensities depend on external shocks also accompanying with jumps. The incomplete financial market model based on this process is studied. The Esscher transform, which changes only unobservable parameters, is considered in detail. The financial market model based on this transform can price switching risks as well as jump risks of the model.     

On the interplay between inertial and viscoelastic effects for the flow in weakly modulated channels

The flow inside a spatially modulated channel is examined for viscoelastic fluids of the Oldroyd‐B type. The lower wall is flat and the upper wall is sinusoidally modulated. The modulation amplitude is assumed to be small. Thus, a regular perturbation expansion of the flow field coupled to a variable‐step finite‐difference scheme is used to solve the problem. Convergence and accuracy assessment against earlier experimental results indicate that there is a significant range of validity of the perturbation approach. The influences of wall geometry, inertia and viscoelasticity on the flow kinematics and stresses are investigated systematically. In particular, the interplay between the flow and fluid parameters effects on the conditions for the onset of backflow, number of vortices, their size and location is revealed. The distance between the flow separation and reattachment locations identifies the vortex size. Non‐monotonic dependence of the vortex size on elasticity is reported. The critical conditions for the onset of negative elasticity effects on vortex size are identified. The critical Reynolds number for the onset of backflow initially decreases then levels off or even increases as elasticity increases. For highly elastic fluid and large enough Reynolds number, more than one vortex appear near the lower wall. Copyright © 2005 John Wiley & Sons, Ltd.