Mechanical and structural characterizations of simultaneously aligned and heat treated PAN nanofibers

A simple and nonconventional electrospinning technique was employed for producing aligned polyacrylonitrile (PAN) nanofibers. A thermal zone was placed between syringe needles and collector in the electrospinning set up to obtain aligned and heat treated nanofibers. Suitable temperatures for heat treat process of PAN nanofibers was determined using differential scanning spectroscopy (DSC) technique. The influence of treatment temperature was investigated on morphology, internal structure and mechanical properties of collected PAN nanofibers. The average fiber diameter measured from SEM images exhibited decreasing trend at higher temperatures. FTIR spectra indicated no considerable difference between chemical structure of untreated and treated PAN nanofibers. Crystallization degree of PAN nanofibers calculated from WAXD patterns showed relatively low change with treatment temperature. Tenacity values of nanofiber bundles increased with increasing temperature while the extension values had an inverse trend. However, the modulus did not show a regular manner, but treated nanofibers had more modulus than untreated ones. The stress and modulus of PAN nanofibers increased to 112.9 MPa and 7.25 GPa at 270°C, respectively. Nanofibers treated at the highest temperature had the largest amount of crystallinity and strength. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

蜂窝夹芯结构的电磁、重量多目标优化设计

用射线追踪法和有限元法计算蜂窝夹心结构的电磁特性和力学特性，用多目标优化方法求解考虑电磁特性及重量特性的复合材料蜂窝夹心结构最优结构参数。这对现代飞行器雷达罩的设计有重要意义。     

Corrosion behaviour of Ti–Ta–Sn alloy systems in 0.9% NaCl solution

Two alloys of varying contents of tantalum (Ta) and tin (Sn) were prepared and homogenized to evaluate their microstructural and electrochemical characteristics. The microstructural features were revealed through optical microscopy and X‐ray diffraction methods. The formation and stability of passive film was studied by open circuit potential, potentiodynamic polarization and electrochemical scratch tests. The electrochemical impedance spectroscopy results simulated with equivalent electrical circuit suggested bilayer structure of outer porous and inner barrier oxide films. The quantitative data showed thick inner barrier oxide film retarded electrochemical reactions at low ‘Ta’ and ‘Sn’ concentration. The increased percentage of ‘Ta’ and ‘Sn’ deteriorated barrier properties by agglomeration of Ta₂Sn₃ and Ta_0.15Ti_0.85 precipitates within grains and at the grain boundaries.     

Massively Parallel Hierarchical Scene Processing with Applications in Rendering

We present a novel method for massively parallel hierarchical scene processing on the GPU, which is based on sequential decomposition of the given hierarchical algorithm into small functional blocks. The computation is fully managed by the GPU using a specialized task pool which facilitates synchronization and communication of processing units. We present two applications of the proposed approach: construction of the bounding volume hierarchies and collision detection based on divide‐and‐conquer ray tracing. The results indicate that using our approach we achieve high utilization of the GPU even for complex hierarchical problems which pose a challenge for massive parallelization. The results indicate that using our approach we achieve high utilization of the GPU even for complex hierarchical problems which pose a challenge for massive parallelization.     

Integration of Multidimensional Interaction Devices in Real-Time Computer Graphics Applications

Modern CAD/CAM and Virtual Reality applications cannot be imagined without the new class of interaction devices allowing the user direct interaction with computer generated scenes. Integrating such devices into existing or newly developed software is a complex task for a number of reasons. The set of devices is very heterogeneous in functionality and data formats. Most devices are difficult to handle by inexperienced users or need careful handling and calibration. After reviewing a number of existing systems, a novel approach to this problem is presented. A device interface that allows the flexible, hardware independent configuration and error robust operation, even reconfiguration and exchanges of interaction devices during operation, will be introduced. The system structure is discussed and novel communication protocols reducing latency are invented.     

碱金属碳酸盐对假板钛矿碳热还原反应的催化研究

本文通过X－衍射实验，电子显微镜观察得出碱金属碳酸盐对假板钛矿热还原反应有催化作用，采用热重分析法分析了碱金属碳酸盐对假板钛碳热还原反应催化能力。     

Large-area scintillating-fiber time-of-flight/hodoscope detectors for particle astrophysics experiments

A new generation of detectors of ultra-heavy (UH) cosmic rays is being built which require the use of large-area, light-weight detector elements. In this paper, we present the design and operation of a new type of scintillating optical fiber detector, which can serve as both a time-of-flight (TOF) detector and coded hodoscope (i.e. trajectory detector). We demonstrate that this type of detector can make TOF measurements with a time resolution of 48 ps. We also present results of position measurements from a large area TOF/hodoscope that was flown on a high-altitude balloon flight in August, 1995. Finally, we discuss areas of modification and improvements that can be made to these detectors to enable them to be more useful for making UH cosmic ray measurements.     

用双晶X射线衍射研究Si液相外延层

以Ｉｎ作溶剂，使用石墨滑动舟在硅衬底上液相法生成了硅外延层。双晶Ｘ射线衍射表明，对不同的生长条件，一些样品显示出具有双峰的摇摆曲线，另外一些则只有单峰，对于前者，ＸＰＳ测不出Ｉｎ的存在，而对后者，ＸＰＳ却显示硅外延层含有Ｉｎ，由此得出结论，只用双晶Ｘ射线衍射难以确定外延层的掺杂情况。     

The fractional Talbot effect in differential x‐ray phase‐contrast imaging for extended and polychromatic x‐ray sources

The influence of different physical parameters, such as the source size and the energy spectrum, on the functional capability of a grating interferometer applied for phase‐contrast imaging is discussed using numerical simulations based on Fresnel diffraction theory. The presented simulation results explain why the interferometer could be well combined with polychromatic laboratory x‐ray sources in recent experiments. Furthermore, it is shown that the distance between the two gratings of the interferometer is not in general limited by the width of the photon energy spectrum. This implies that interferometers that give a further improved image quality for phase measurements can be designed, because the primary measurement signal for phase measurements can be increased by enlargement of this distance. Finally, the mathematical background and practical instructions for the quantitative evaluation of measurement data acquired with a polychromatic x‐ray source are given.     

多维波动方程逆散射的基础理论研究

探讨了多维（包括二维和三维）波动方程逆散射基础理论。通过对前人研究成果的综合分析，指出多维波动方程逆散射解法的整体框架类似于一维波动方程反问题。三维波动方程逆散射的关键环节可类比于一维波动方程反问题，一维波动方程逆散射中的时深转换、z变换、一维谱分解和反射与透射系数等环节，在多维波动方程逆散射或速度横向变化介质逆散射的研究中，被替换为射线坐标系、单程波算子、基于Witt积的多维谱分解和反射与透射算子的平面波响应。单程波算子积分表示的有效化、射线坐标系上波动方程的微分形式化、Witt积的深入应用和多维谱分解的现代发展，是多维波动方程逆散射关键基础问题研究的重要组成部分。理论和数值实例表明，散射数据的谱分解结果有更好的聚焦效果，这对于进一步速度分析和反射系数的求取十分有益。