Global convergence toward traveling fronts in nonlinear parabolic systems with a gradient structure

We consider nonlinear parabolic systems of the form ut=−∇V(u)+u_xx$u_t=-\mathrm{\nabla }V(u)+u_{xx}$, where u∈Rn$u\in {\mathbb{R}}^n$, n?1$n?1$, x∈R$x\in \mathbb{R}$, and the potential V   is coercive at infinity. For such systems, we prove a result of global convergence toward bistable fronts which states that invasion of a stable homogeneous equilibrium (a local minimum of the potential) necessarily occurs via a traveling front connecting to another (lower) equilibrium. This provides, for instance, a generalization of the global convergence result obtained by Fife and McLeod [P. Fife, J.B. McLeod, The approach of solutions of nonlinear diffusion equations to traveling front solutions, Arch. Rat. Mech. Anal. 65 (1977) 335–361] in the case n=1$n=1$. The proof is based purely on energy methods, it does not make use of comparison principles, which do not hold any more when n>1$n>1$.     

Microlocal analysis of quasianalytic Gelfand-Shilov type ultradistributions

We introduce a global wave front set suitable for the analysis of tempered ultradistributions of quasi-analytic Gelfand–Shilov type. We study the transformation properties of the wave front set and use them to give microlocal existence results for pullbacks and products. We further study quasi-analytic microlocality for classes of localization and ultradifferential operators, and prove microellipticity for differential operators with polynomial coefficients.     

Hybrid paper sheets with improved barrier properties

Hybrid paper sheets were prepared by applying a thin coating layer of cross-linked polydimethylsiloxane (PDMS) and inorganic particles onto Whatman Grade 1 filter paper substrates. Several coatings with different inorganic particle contents and types were applied onto the paper substrates to investigate the effect of the variation in the coating formulation on the (i) wetting, (ii) water barrier properties, (iii) air barrier properties, (iv) surface roughness, and (v) mechanical properties of the samples. It was revealed that the superhydrophobic hybrid paper sheets with significantly low air permeability and high water barrier properties could be prepared which is an indication that the method proposed can be used for the preparation of packaging materials.     

Enhanced Terahertz Phonon Polariton in Lithium Niobate Chip

Terahertz (THz) phonon polaritons, fundamental quasi-particles that couple lattice vibrations with electromagnetic fields at THz frequencies, are found in a variety of materials that offer the potential for a wide range of THz optoelectronic devices and on-chip integrated systems. However, these compact devices and on-chip systems are hampered by the absence of on-chip powerful THz phonon polariton sources. In this study, the efficient generation and amplification of THz phonon polaritons are proposed and directly visualized on a lithium niobate (LN) chip via a tilted pulsefront phase matching technique. By combining lateral pumping and phase matching schemes, two orders of magnitude are successfully attained in the interaction distance between the pump light and the LN chip, accompanied by a substantial amplification of generated THz phonon polariton. The results of this study may lead to abundant potential applications in chip scale THz photonic devices and systems based on LN materials and its integrated heterostructures.     

Synthesis and characterization of semifluorinated polymers and block copolymers

The goal of the investigation presented here was to evaluate the influence of semifluorinated side chains on the bulk structure and the surface properties of polysulfones with different chain structure. Thus, segmented block copolymers consisting of polysulfone and semifluorinated aromatic polyester segments as well as polysulfones having semifluorinated side chains randomly distributed over the polymer backbone were synthesized and characterized. Oxydecylperfluorodecyl side chains were used because of their strong tendency for self-organization. The influence of the chain architecture on the self-organization as well as on the surface properties, particularly the wetting behavior, was examined. It could be shown that despite of the higher self-organizing tendency of block copolymers the surface properties of both polymer types are comparable and depend only on the concentration of side chains.     

Traveling fronts of a real supercritical quintic Ginzburg-Landau equation coupled by a slow diffusion mode

In this paper, we investigate the existence of traveling front solutions for a class of quintic Ginzburg-Landau equations coupled with a slow diffusion mode. By employing the theory of geometric singular perturbations, we turn the problem into a geometric perturbation problem. We demonstrate the intersection property of the critical manifold and further validate the existence of heteroclinic orbits by computing the zeros of the Melnikov function on the critical manifold. The results demonstrate that under certain parameters, there is 1 or 2 heteroclinic solutions, confirming the existence of traveling front solutions for the considered quintic Ginzburg-Landau equation coupled with a slow diffusion mode.     

岩心表面润湿性与化学选堵剂对油水的封堵能力

选择阳离子聚丙烯酰胺类选堵剂,进行岩心模拟实验,研究不同岩心表面润湿性与化学选堵剂封堵能力之间的关系.表面润湿性强烈影响对水的堵塞率,水润湿性越强,对水的堵塞率越高,典型的亲水表面和亲油表面对水的堵塞率相差20%左右;使用水基凝胶,水驱后的残余阻力系数(RRF)大于油驱后的RRF,水基凝胶使水相渗透率的降低比油相渗透率的降低多.对于润湿性相同,渗透率不同的天然岩心,选堵剂的堵水率大于85%,堵油率在20%左右,表现出良好的选择性.     

飞秒啁啾脉冲放大系统中折叠反射式望远镜对脉冲波前的影响

推导出飞秒激光啁啾脉冲放大系统中使用的折叠反射式望远镜对脉冲波前的影响. 分析和计 算了波前倾斜与反射式望远镜参数之间的关系.结果发现：当脉冲宽度小于100 fs时，波前 倾斜对光束质量的影响不可忽略，并提出了抑制这种脉冲波前倾斜的有效方法. 关键词： 飞秒激光啁啾脉冲放大 波前倾斜 反射式望远镜     

具有InAlAs浸润层的InGaAs量子点的制备和特性研究

采用自组装方法生长了一种新型的InGaAs量子点/InAlAs浸润层结构.通过选取合适的In组分 ，使InAlAs浸润层的能级与GaAs势垒相当，从而使浸润层的量子阱特征消失.通过低温光致 发光（PL）谱的测试分析得到InGaAs量子点/InAlAs浸润层在样品中的确切位置.变温PL谱的 研究显示，具有这种结构的量子点发光峰的半高全宽随温度上升出现展宽，这明显区别于普 通InGaAs量子点半高全宽变窄的行为.这是因为采用了InAlAs浸润层后，不仅增强了对InGaA s量子点的限制作用，同时切断了载流子的 关键词： InGaAs量子点 InAlAs浸润层 PL谱     

A well‐balanced explicit/semi‐implicit finite element scheme for shallow water equations in drying–wetting areas

Numerical solutions of the shallow water equations can be used to reproduce flow hydrodynamics occurring in a wide range of regions. In hydraulic engineering, the objectives include the prediction of dam break wave propagation, fluvial floods and other catastrophic flooding phenomena, the modeling of estuarine and coastal circulations, and the design and optimization of hydraulic structures. In this paper, a well‐balanced explicit and semi‐implicit finite element scheme for shallow water equations over complex domains involving wetting and drying is proposed. The governing equations are discretized by a fractional finite element method using a two‐step Taylor–Galerkin scheme. First, the intermediate increment of conserved variable is obtained explicitly neglecting the pressure gradient term. This is then corrected for the effects of pressure once the pressure increment has been obtained from the Poisson equation. In order to maintain the ‘well‐balanced’ property, the pressure gradient term and bed slope terms are incorporated into the Poisson equation. Moreover, a local bed slope modification technique is employed in drying–wetting interface treatments. The proposed model is well validated against several theoretical benchmark tests. Copyright © 2014 John Wiley & Sons, Ltd.