Fabrication of material-independent morphology gradients for high-throughput applications

Gradient surfaces allow rapid, high-throughput investigations and systematic studies in many disparate fields, including biology, tribology and adhesion. We describe a novel method for the fabrication of material-independent morphology gradients, involving a two-step process of particle erosion followed by a chemical polishing procedure that preferentially removes features with a small radius of curvature as a function of time. Gradients are fabricated on aluminium surfaces, but they may be readily transferred to other materials via a replication technique, which allows for the production of identical roughness gradient samples with any chosen surface chemistry. The gradients have been characterized by means of scanning electron microscopy and optical profilometry. Standard roughness parameters (Ra, Rq, Rz, Sm and Sk) were calculated from optical profilometry data. The roughness has also been assessed over different wavelength windows by means of a fast Fourier transformation approach.     

Constraint incorporation in optimization

Numerical methods for solving constrained optimization problems need to incorporate the constraints in a manner that satisfies essentially competing interests; the incorporation needs to be simple enough that the solution method is tractable, yet complex enough to ensure the validity of the ultimate solution. We introduce a framework for constraint incorporation that identifies a minimal acceptable level of complexity and defines two basic types of constraint incorporation which (with combinations) cover nearly all popular numerical methods for constrained optimization, including trust region methods, penalty methods, barrier methods, penalty-multiplier methods, and sequential quadratic programming methods. The broad application of our framework relies on addition and chain rules for constraint incorporation which we develop here.     

保险管理决策中的两个问题

本文运用风险决策理论建立了分保限额与红利分派两个保险管理决策问题的数学模型,从理论和实践两个方面讨论了最优管理策略,并给出了计算实例。     

X-ray damage characterization in BaLiF3,KMgF3 and LiCaAlF6 complex fluorides

Two-inch sized KMgF₃,BaLiF₃ and LiCaAlF₆ (LiCAF) single crystals were grown by the Czochralski method under a CF₄ atmosphere. X-ray irradiation was used to carry out a comparative study of induced optical absorption phenomena and colour centre creation in the ultra-violet and visible spectral regions. The integral of the induced absorption spectra is significantly lower in LiCAF with respect to the other studied materials. It is found that the amplitude of the F-absorption band is suppressed more than a factor of 3 by Mg-doping. For Mg-doped crystals, the optimum doping concentration is about 0.2 mol% of Mg²⁺.     

Performance of noise barriers with various edge shapes and acoustical conditions

The performances of barriers having different shapes and surface conditions were tested using the boundary element method in a well-controlled environment. The heights and widths of the barriers were standardized and the insertion losses for six receiver positions were averaged and compared. Figures displaying the results allow for straightforward barrier performance estimation. It was shown that absorbing and soft edges significantly improve the efficiency of the barrier, but configuration modifications provide only a slight improvement. The soft T-shaped barrier produces the highest performance. A 3 m high T-shaped barrier provides the same performance as a 10 m high plain barrier. The spectral efficiency was also investigated. The insertion loss spectra for the absorbing and the soft barriers exhibit a similar shape, but the rigid barrier differs from these two.     

Time-domain simulations of sound propagation through screen-induced turbulence

A flow model in combination with a statistical-dynamical turbulence generator and a linearised Euler time-domain model for sound waves were used to simulate the effect of screen-induced turbulence on the noise level in the acoustical shadow of a screen in wind. Instead of simulating a great number of different frozen turbulence realisations, the concept of transient turbulence was successfully tested and applied. This concept is adequate to the time-domain model and reduces the computational demands. Several two-dimensional simulations allowed to isolate the individual effects of wind and screen on the propagation of 500 Hz sound waves over a 4-m high noise barrier. At a distance of 250 m from the source (240 m behind the screen) the sheltering effect of the screen and the refraction effect of the wind are in the order of 6 and 4 dB, respectively. The screen-induced turbulence leads to fluctuations in the noise level with a standard deviation of 1.2 dB and a maximum amplitude of 3 dB. However, the time averaged effect turned out to be in the order of merely 0.2 dB. The effect of the screen-induced turbulence on the average noise level behind the screen is therefore negligible.     

价格波动对进出初级产品行业的影响

初级产品生产行业有两大特点：一是其初级投资有较大的不可逆转性，二是其产品价格具有较大的随机性（不确定性）。这两点的同时存在，给进入和退出初级产品行业造成壁垒。     

Modeling Studies of the Formation and Destruction of NO in Pulsed Barrier Discharges in Nitrogen and Air

This paper presents the results of modeling studies on the formation and destruction of NO in pulsed barrier discharges in nitrogen and air. The goals of this work are to identify the major processes involved in the formation and destruction of NO in air discharges, to distinguish between oxidative and reductive paths for NO destruction, to explore the potential importance of excited state reactions, to evaluate the role of water in such systems, and to identify the final products in the absence of heterogeneous processes. In all cases, the systems were modeled with 100×10^–4% (100 ppm) of added NO, with and without 3% added water. The focus in all of this work is chemistry in the post-pulse regime.     

高阻隔材料——偏氯乙烯悬浮共聚树脂

本文介绍偏氯乙烯悬浮共聚树脂的优异阻隔性能、合成配方与工艺。     

Characterization of the barrier properties of composites of HDPE and purified cellulose fibers

The present work presents and discusses the interrelation between composition, morphology, thermal history, mechanical and barrier properties to oxygen and limonene of composites of HDPE/MA-PE/cellulose fibers of significant interest in, among others, food packaging applications. From the overall results, it was observed that increasing the loading of purified alpha-cellulose fibers in the polyethylene matrix beyond 10 wt.% led to a decrease in the permeability coefficient of d-limonene, effect which was found to be primarily related to a decrease in the overall solubility of this strongly plasticizing aroma component. On the other hand, the oxygen permeability was found to decrease to a significant extend with increasing fiber content beyond 5 wt.%, but this effect was more strongly ascribed to a significant decrease in the diffusion coefficient. Therefore, the fibers are thought to generate a more tortuous path for the non-interacting gas molecules to travel across the composites thickness, even when tested at high relative humidity conditions. Optimum fiber loading levels in terms of overall property balance were found to be around 20 wt.%.