An optimal control approach to the optical flow problem

The optical flow problem is reduced to an optimal control problem governed by a linear parabolic equation having the unknown velocity field (the optical flow) as drift term. This model is derived from a new assumption, that is, the brightness intensity is conserved on a moving pattern driven by a Gaussian stochastic process. The optimality conditions are deduced by a passage to the limit technique in an approximating optimal control problem introduced for a regularization purpose. Finally, the controller uniqueness is addressed.     

DFT study of the oxygen reduction reaction on iron,cobalt and manganese macrocycle active sites

The best performing non-precious metal based catalysts for polymer electrolyte membrane fuel cells are manufactured by incorporation of nitrogen into a carbon structure in the presence of iron and cobalt. Herein, density functional theory (DFT) calculations have been performed to investigate the oxygen reduction reaction on catalyst active sites modelled as transition metal macrocycles with iron, cobalt or manganese central atoms. The effects of the transition metal and macrocycle structure have been investigated. The structure of the most promising active sites has been proposed, and the detailed potential energy profiles of the oxygen reduction reaction have been obtained over the active sites, including all intermediate steps with corresponding activation barriers. The efficiency of the active sites depends primarily on the transition metal nature, and the central iron atom accounts for the higher catalytic activity than cobalt and manganese. The central manganese atom can favour the two-electron oxygen reduction pathway and thus yielding hydrogen peroxide.     

Evaluation of gluing of CFRP onto concrete structures by infrared thermography coupled with thermal impedance

Carbon Fiber Reinforced Polymers (CFRPs) have been increasingly employed for structural strengthening, and are attached to structures using bonding adhesives. The aim of this work is to characterize defects in the bond between CFRP and concrete (after they are located by pulse infrared thermography), and assign the defects a “numerical value” (ranging from 0 for a complete air–gap to 1 for a fully glued bond). Quantitative characterization is performed by measuring the thermal impedance, and then identifying the thermophysical parameters of the system through fitting the measured impedance to a theoretical model. An inversion procedure is carried out to estimate the unknown parameters, without prior knowledge of sample properties. In particular, it is possible to estimate more accurately both the amount of glue within a defect and the thermal contact resistance.     

基于城市形象传播的吉祥物创新设计研究

目的 针对目前国内城市吉祥物形象直线的传播方式以及造型设计雷同，缺乏个性化表达等问题,创新城市吉祥物设计，推动城市经济文化产业向前发展。方法 深入发掘城市内涵，并且将城市地域特征与历史文化相结合，让吉祥物成为一个城市的代表。在造型设计上注重赋予吉祥物灵魂，注重五官的传神与内心状态的传达，利用三维表现方法，借助VR技术，在吉祥物与观众之间搭建网上交流平台，多角度多层次地将直线的吉祥物形象传播形式转变成互动循环传播模式。通过这一创新理念设计出的吉祥物既具备鲜明的个性特征，又能传达城市文化精神内涵。结论 只有创新吉祥物造型设计与设计传播方式，才能使吉祥物具备独特的吸引力，更好地被大众接受，从侧面有效地传播城市文化理念，推动城市经济发展，提升城市在国际上的知名度。     

Thermo-optical characterization of CdZnS nanoparticle colloids

Thermo-optical properties of cadmium zinc sulfide (CdZnS) nanoparticle colloids are investigated by interferometry technique. The nanoparticle colloids are synthesized by an improved co-precipitation method. Transmission electron microscopy, UV–vis spectrometry and X-ray diffraction analysis are used to characterize the CdZnS nanocrystals. The thermo-optic coefficient of the colloids has been determined using a Fizeau interferometer. For this purpose, the interference patterns are deformed by a photothermal phase shift which is locally induced in the sample by the focused pump laser beam. The change in the refractive index at this region imposes a shift on the phase of the fringe patterns. Fourier analysis performed on the interference patterns allows us to estimate the values of the thermo-optic coefficient and nonlinear refractive index of the sample. It is shown that the CdZnS nanoparticle colloids enhance the absorption of the laser light and induce high rise in the temperature of the sample, which leads to the nonlinear phase shift.     

Multicolor carbon dots with concentration-tunable fluorescence and solvent-affected aggregation states for white light-emitting diodes

Multicolor emissive carbon dots (M-CDs) have tremendous potential applications in manifold fields of bioimaging, biomedicine and light-emitting devices. Until now, it is still difficult to produce fluorescence tunable CDs with high quantum yield across the entire visible spectra. In this work, a type of M-CDs with concentration-tunable fluorescence and solvent-affected aggregation states was synthesized by solvothermal treatment of citric acid (CA) and 1-(2-pyridylazo)-2-naphthol (PAN) and the formation mechanism was monitored by different reaction time and raw material ratio. The fluorescence spectra of M-CDs in organic solvents can range from 350 to 750 nm by adjusting the concentration. M-CDs possess different aggregation states in water and organic solvents, accompanied by different fluorescence emission, which is attributed to the different surface states of various component CDs in M-CDs. Moreover, the obtained products can be uniformly dispersed into polymethylmethacrylate (PMMA) solutions as well as epoxy resins to fabricate transparent CDs/PMMA films and CDs/epoxy composites, which can effectively prevent the aggregation and produce multicolor and white light-emitting diodes (WLED). In addition, the prepared WLED with Commission Internationale de L’Eclairage (CIE) of (0.29, 0.31) by using M-CDs/epoxy resin as packages, demonstrating the M-CDs exhibit potential applications for light-emitting devices.

     

高速纺纱锭子弹性管减振机制与振动特性

为探究锭子弹性管的减振机制,将其开螺旋槽部分作为矩形弹簧模型处理,建立了减振弹性管的抗弯刚度及底部振幅的理论数学模型,并利用MatLab仿真分析了减振弹性管关键结构参教与其抗弯刚度和底部振动特性的耦合关系,同时结合有限元仿真及模态测试得到弹性管各阶固有频率。研究结果表明:随着槽宽和圈数的增大,刚度降低,底部振幅增加;随着壁厚、螺距、螺旋升角、弹性模量的增大,刚度增加,底部振幅降低;弹性管固有频率和锭子系统共振频率区间一致,且工作频率有效避开了共振频率。     

Entrapment in food-grade transglutaminase cross-linked gelatin–maltodextrin microspheres protects Lactobacillus spp. during exposure to simulated gastro-intestinal juices

Dietary intake of probiotic bacteria has been shown to impart health effects, however, maintaining viable cells in foods and during passage of the adverse conditions in the upper gastro-intestinal tract is often a problem. The objective of this research was to develop and characterize novel food-grade phase-separated gelatin–maltodextrin (G-MD) microspheres, where the gelatin was cross-linked with transglutaminase (TGase), to determine if encapsulated probiotic lactic acid bacteria were protected during exposure to simulated upper gastro-intestinal tract conditions. The stability, size, structure and protective ability of G-MD microspheres as a function of different TGase concentrations and gelatin bloom strengths were tested. The G-MD microspheres made with gelatin A 300 bloom and a TGase concentration of 10 U/g prevented pepsin-induced degradation of the microspheres in simulated gastric juice (pH 2.0, 2 h, 37 °C), resulting in significantly (p < 0.05) higher numbers of survivors due to the buffering effect of intact microspheres (average diameter 46 μm). After sequential incubation in simulated gastric (1 h) and intestinal juices (pH 7.4, 4 h, 37 °C), survivor levels of each of the three encapsulated Lactobacillus sp. (3C2–10, 21C2–10 and 21C2–12) were reduced by 0.2–1 log(CFU/g) as compared to 3–4 log(CFU/g) for the free non-encapsulated cells. This study presents a new protein based microencapsulation method, which using all food-grade ingredients protects probiotic lactic acid bacteria during exposure to adverse environmental conditions.     

牦牛绒过氧化氢/过硫酸铵脱色体系工艺优化及其机制

针对现有商业化牦牛绒脱色过程复杂、脱色时间长等问题,提出新型过氧化氢/过硫酸铵体系牦牛绒脱色工艺。在尽可能提高纤维白度的前提下尽量减少纤维损伤,通过单因素试验确定了脱色时间、过硫酸铵用量和试剂pH值,对脱色工艺进行探讨并与商业化脱色牦牛绒进行比较。结果表明:采用过硫酸铵质量浓度为400 g/L,试剂pH值为9,在室温下脱色为180 min可达到商业脱色牦牛绒的效果,脱色时间节省至原来的1/8;脱色机制分析发现,脱色过程中硫酸根自由基起主要作用,羟基自由基起次要作用。该脱色工艺简单,为牦牛绒高值化利用提供了新的解决方案。     

我国食品安全问题的社会学分析

以近几年来我国频发的食品安全事件为鉴，从社会学视角分析了其产生的原因，并提出了相应的预防和解决问题的对策。