Ferroelectric and piezoelectric properties of a quenched poly(vinylidene fluoride-trifluoroethylene) copolymer

The ferroelectric and piezoelectric properties of melt-quenched unoriented poly(vinylidene fluoride-trifluoroethylene) (73 : 27) copolymer films as a function of the number of poling cycles have been studied. The investigation revealed that quenched films exhibit a decrease in D-E hysteresis behavior as the number of poling cycles increases when the samples are poled at room temperature. Corresponding decreases in remanent polarization, Pr, as well as small increases in the coercive field, Ec, were observed as the material was subjected to successive poling cycles. The piezoelectric coefficients, d₃₁ and e₃₁, also decreased as the number of poling cycles increased. In addition, a clear reduction in the “apparent” Curie transition temperature between unpoled and poled material was observed. Preliminary evidence indicates that films quenched from the melt to below T_c do not form a stable ferroelectric crystal phase as previously believed. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2671–2679, 1997     

Cd13−xInySb10 (x≈2.7, y≈1.5): An Interstitial‐Free Variant of Thermoelectric β‐Zn4Sb3

Although free from structural disorder , the new intermetallic compound Cd_13?xIn_ySb₁₀ (see figure) displays similarly low thermal conductivity values as disordered thermoelectric β‐Zn₄Sb₃ with an isostructural framework.

     

Calculation of the streaming potential near a rotating disk

A corrected theory of the streaming potential in the vicinity of a disk-shaped sample rotating in an electrolytic solution is presented. When streaming-potential measurements on a variety of materials were reduced to a zeta potential according to a prior theory, the results exceeded expected values by a factor of approximately 2, even though other aspects of the same experiments seemed to confirm the theory. Investigation of the source of the discrepancy revealed a flaw in the prior theory. The crucial understanding is that the surface current produced by the rotation of the disk emerges from the diffuse layer and enters the bulk solution at the periphery of the disk. The new treatment accounts entirely for the discrepancy between literature data and results based on the prior theory.     

A Continuum of Pure States in the Ising Model on a Halfplane

We study the homogeneous nearest–neighbor Ising ferromagnet on the right half plane with a Dobrushin type boundary condition—say plus on the top part of the boundary and minus on the bottom. For sufficiently low temperature T, we completely characterize the pure (i.e., extremal) Gibbs states, as follows. There is exactly one for each angle \(\theta \in [-\pi /2,+\pi /2]\); here \(\theta \) specifies the asymptotic angle of the interface separating regions where the spin configuration looks like that of the plus (respectively, minus) full-plane state. Some of these conclusions are extended all the way to \(T=T_{c}\) by developing new Ising exact solution results—in particular, there is at least one pure state for each \(\theta \).     

Random graph models for dynamic networks

Recent theoretical work on the modeling of network structure has focused primarily on networks that are static and unchanging, but many real-world networks change their structure over time. There exist natural generalizations to the dynamic case of many static network models, including the classic random graph, the configuration model, and the stochastic block model, where one assumes that the appearance and disappearance of edges are governed by continuous-time Markov processes with rate parameters that can depend on properties of the nodes. Here we give an introduction to this class of models, showing for instance how one can compute their equilibrium properties. We also demonstrate their use in data analysis and statistical inference, giving efficient algorithms for fitting them to observed network data using the method of maximum likelihood. This allows us, for example, to estimate the time constants of network evolution or infer community structure from temporal network data using cues embedded both in the probabilities over time that node pairs are connected by edges and in the characteristic dynamics of edge appearance and disappearance. We illustrate these methods with a selection of applications, both to computer-generated test networks and real-world examples.     

2D FDTD simulation of low loss small angle bend and Y branch configurations in a photonic crystal waveguide layout with a Mach–Zehnder device design configuration

A technique to produce low loss small angle bends in photonic crystal waveguides is presented. The technique consists of bridging parallel input and output waveguide segments with an inclined waveguide region of the same basic design that has a lateral dielectric shift. Results are presented for waveguides produced by enlarging the silicon gap along the central line, separating air holes in a square array photonic crystal for the TE polarization and an operating wavelength of λ_o = 1.55 μm. This low loss waveguide bending technique is applied to the design of Y branch and Mach–Zehnder photonic crystal structures. Simulation of the performance of the dielectric structures is achieved using 2-D FDTD, similar results are anticipated when applied to 3-D waveguide configurations and for other photonic crystal layouts.     

Nonlinear analytical multi-dimensional convolution solution of the second order system

In this paper, a procedure to analytically develop an approximate solution for the prototypical nonlinear mass–spring–damper system based on multi-dimensional convolution expansion theory is offered. The nonlinearity herein is mathematically considered in quadratic and bilinear terms. A variational expansion methodology, one of the most efficient analytical Volterra techniques, is used to develop an analytical two-term Volterra series. The resultant model is given in the form of first and second kernels. This analytical solution is visualized in the time domain followed by a parametric study for understanding the influence of each nonlinear/linear term appearing in the kernel structure. An analytical nonlinear step response is also conducted to characterize the overall system response from the fundamental components. The developed analytical step response provides an illumination for the source of differences between nonlinear and linear responses such as initial departure time, settling time, and steady value. Feasibility of the proposed implementation is assessed by numerical examples. The developed kernel-based model shows the ability to predict, understand, and analyze the system behavior beyond that attainable by the linear-based model.