Crystallization measurements via ultrasonic velocity: Study of poly(lactic acid) parts

Crystallization has significant effects on the physical and mechanical properties of polymer products; therefore, crystallization measurements are important for understanding and predicting polymer products' properties. However, traditional crystallization measurement methods have disadvantages in practical applications because they can be destructive, offline, unsafe, and expensive. Recently, ultrasonic technology has shown great potential as a nondestructive, online, real‐time, and environmentally friendly measurement method for polymer characterization. In this study, a novel measurement method based on ultrasonic technology was proposed to study the crystallization characteristics of poly(lactic acid) (PLA) parts. An annealing process was employed to produce PLA parts with different degrees of crystallinity. A new ultrasonic water immersion method was used to measure the ultrasonic velocities of these annealed PLA parts. It has been found that the plot of the inverse ultrasonic velocity versus the degree of crystallinity shows good linearity over the whole crystallinity range for all three annealing temperatures. The linear relationship between the inverse of the ultrasonic velocity and the crystallinity observed in this study could provide a nondestructive method for investigating the degree of crystallinity of polymers, which can be implemented both offline and online. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 700–708     

Stress analysis of extensively and partially soldered optical components

Resistance soldering of optical components is an upcoming technology following the trends towards automation and miniaturization with particularly high relevance for high optical power applications. A stress analysis is necessary in order to qualify this technology with regard to the component's optical behavior and its long-term stability. Analytical and FEM-simulative calculations are used to estimate the stresses within the optical element and the solder layer for extensively soldered components. Furthermore partially soldered components are being simulated and optically evaluated using polarization microscopy. To evaluate the long-term stability of the compound multiple series of thermal cycling were performed.     

The pre-stack migration imaging technique for damages identification in concrete structures

Pre-stack migration imaging (PMI) method, which is used in geophysical exploration by the performance of single side detection and visually display, can be used to identify the location, orientation, and severity of damages in concrete structure. In particular, this letter focuses on the experimental study by using a finite number of sensors for further practical applications. A concrete structure with a surface-mounted linear PZT transducers array is illustrated. Three types of damages, horizontal, dipping and V-shaped crack damage, have been studied. A pre-stack reverse time migration technique is used to back-propagate the scattering waves and to image damages in concrete structure. The migration results from the scattering waves of an artificial damage are presented. It is shown that the existence of the damage in concrete structure is correctly revealed through migration process.     

利用手持技术探究铜锌双液原电池中电解质溶液对电流的影响

利用手持技术探究了铜锌双液原电池中电解质溶液的浓度和种类对电流的影响。得出正、负极电解质溶液的浓度与原电池的电流在一定范围内呈正相关，浓度越大，电流越大，负极电解质溶液种类的改变对原电池的电流影响有限。     

授之工具、传之方法建立在教师指导下的学生自主学习模式—介绍华中科技大学非线性物理教学的改革之二

以非线性物理教学为例介绍了授之工具，传之方法建立教师指导下的学生自主学习模式及其教学思想和具体做法。     

Ultrasonic extraction of anthocyanin from Clitoria ternatea flowers using response surface methodology

The ultrasonic extraction (UE) method of anthocyanin from Clitoria ternatea flowers using response surface methodology (RSM) was performed in this study. By using RSM, the objective is to optimise the extraction yield of anthocyanin from C. ternatea which is influenced by various factors, including the extraction temperature, time, ratio of solvent to solid and ultrasonic power. The empirical model was investigated by performing first-level optimisation in a two-level factorial design with Design Expert 7 software. In comparison with the conventional solvent extraction, UE showed a 246.48% better extraction yield and produced an anthocyanin extract with a radical scavenging activity of 68.48% at the optimised factors of 50°C, 150 min, 15 mL/g and 240 W.     

Fracture mechanics analysis on Smart-Cut~ technology.Part 1:Effects of stiffening wafer and defect interaction

In the present paper,continuum fracture mecha-nics is used to analyze the Smart-Cut process,a recentlyestablished ion cut technology which enables highly efficientfabrication of various silicon-on-insulator(SOI)wafers ofhigh uniformity in thickness.Using integral transform andCauchy singular integral equation methods,the mode-I andmode-Ⅱ stress intensity factors,energy release rate,and crackopening displacements are derived in order to examine seve-ral important fracture mechanisms involved in the Smart...     

Interface features of ultrasonic flip chip bonding and reflow soldering in microelectronic packaging

Ultrasonic features in the bonding area are of interest for researchers in the field of microelectronic packaging. In this study, the interface characteristics of bonding were examined using an XD7100 X‐ray instrument and a transmission electron microscope (TEM). It was seen that bubbles were usually detected at the interfaces of the reflow‐soldered flip chip (FC), but they were not found at the interfaces of ultrasonically formed FC, and so ultrasonic FC bonding is more reliable than reflow soldering. The strong mechanical effect of ultrasonic vibration activates the dislocations in the crystalline metal lattice. Dislocation diffusion is more prominent than crystal diffusion when the temperature is relatively low during ultrasonic bonding, and therefore the processes of ultrasonic bonding enhance by several orders of magnitude. This indicates that the mechanism of ultrasonic bonding is different from the melting mechanism of reflow soldering. Copyright © 2007 John Wiley & Sons, Ltd.     

光电技术在轻武器中的新应用

分析了信息技术的发展和在反恐作战需求不断增长情况下，光电技术在轻武器中的应用现状。简述了在信息技术等高新技术引发的新军事变革下各国军队作战理念的变化带来的武器装备的发展。根据轻武器发展领域中光电技术的基本作用，即通过配备光学系统、光电瞄准具等来提高传统轻武器射击精度，总结了新的军事需求下，轻武器与光电技术的密切关系。着重描述了具有拐弯结构设计的步枪、手臂安装设计的未来小武器、集成光电瞄准具的遥控轻武器站、由感知装置控制的灵巧弹药、新概念发射方式的金属风暴武器系统等的设计特点。指出光电技术在目标获取、发射控制、弹道修正等方面所起的作用。     

Modeling of optimal investment in science and technology

The latest achievements in science and technology lead to the development of new and more productive capital that can essentially increase a company’s profit. On the other hand, companies should invest not only in the productive capital, but also in science and technology.

The optimal control of an economic system that divides its output among the production of consumption goods, the accumulation of new capital, and the contribution to science and technology is considered. The model is expressed as nonlinear integral equations with unknowns in the integrands and lower limits of integration. An optimization problem for the profit maximization is suggested. The necessary condition for an extremum and the second variation of the functional are derived. The structure of optimal solutions is analyzed. Interpretation of all results is provided.