Current-voltage behavior of AlGaAs/InGaAs pHEMT structures and the effect of optical illumination

Various pseudomorphic High Electron Mobility Transistor (pHEMT) structures of AlGaAs/InGaAs alloys have been observed their current-voltage behavior. The tungsten probes were used for a measurement the structures by ramping the voltage from −5 to 5 V and measure the electrical current. Measurement was carried out at room temperature and also under optical illumination. From the measurement, the electrical current was found to increase as the increase of Al content in the AlGaAs alloys layer in the pHEMT structure. This phenomenon was supported by the decrease of sheet resistance as obtained from Hall effect measurement. Under visible light illumination, the current-voltage behavior of pHEMT structure was observed to vary as the light power density was varied for 0, 25 and 55 μW/cm.     

海面波浪坡度场光学测量装置的光源设计(英文)

在海面波浪坡度场光学测量系统中,光源是一个非常重要的照明元件。合理的设计和选用光源,是保证系统精度和布局的重要因素之一。比较传统光源短弧氙灯的明显优势,如低能耗,寿命长,更好的安全性和稳定性等,本文提出了采用LED作为本系统光源的设想,确定了所需LED个数和LED阵列方式,并经过计算和光学软件模拟,验证了本设想的可行性。     

眼底相机的均匀照明及消杂光干扰设计

给出了一种新型眼底相机照明系统的设计方案。针对现行眼底相机照明系统复杂的问题,对经典的柯勒照明光路进行改良设计,得到了一个结构简单的眼底照明系统。结构中除网膜物镜外,只需用到4片透镜,且眼底照明区域直径连续可调,充分利用了光能。通过在照明光路中添加黑点板和环形光阑,屏蔽了系统99%以上的杂散光,使眼底相机成像画面的信噪比达到20dB以上,提高了对比度。同时在Gullstrand_Le标准眼模型上,得到一个均匀度达95%以上的照明区域。     

基于图像亮度特性统计的水下距离选通成像自动增益控制方法

对水下激光距离选通成像质量与系统增益的关系进行了分析,提出了一种基于图像亮度特性统计的普适性自动增益控制方案。该方案通过设定不同灰度统计阈值,甄别目标图像的亮度特性,并以此作为控制系统增益的主要依据。在对水下大动态范围照度目标或慢速运动目标等进行成像的特殊场合,该方案也具备较强的适用性,能实时反馈控制系统增益,使成像质量优化。     

The illumination conjecture and its extensions

Summary The Illumination Conjecture was raised independently by Boltyanski and Hadwiger in 1960. According to this conjecture any <InlineEquation ID=IE"1"><EquationSource Format="TEX"><![CDATA[<InlineEquation ID=IE"2"><EquationSource Format="TEX"><![CDATA[<InlineEquation ID=IE"3"><EquationSource Format="TEX"><![CDATA[$]]></EquationSource></InlineEquation>]]></EquationSource></InlineEquation>]]></EquationSource></InlineEquation>d$-dimensional convex body can be illuminated by at most $2^d$ light sources. This is an important fundamental problem. The paper surveys the state of the art of the Illumination Conjecture.     

Characterization on titanium surfaces and its effect on photocatalytic bactericidal activity

Many studies have been published on the use of TiO₂ as a photocatalyst, which decomposes various organic compounds under UV illumination by generating various radicals. The purpose of the present study was to evaluate the photocatalytic bactericidal effects of variously treated titanium surfaces on Escherichia coli K-12. The specimens were fabricated from grade 4 commercially pure titanium, 12 mm in diameter and 1 mm in thickness. Five different surfaces were prepared (MA: machined surface; AO: anodized at 300 V; NO: NaOH-treated; NW: NaOH- and water-treated; and HT: heat-treated). Surface analysis was performed using scanning electron microscopy, optical interferometer, and thin-film X-ray diffractometry. Photocatalytic activity of each group was confirmed by degradation of methylene blue (MB). The antibacterial activity was assessed by calculating the survival ratio in a drop of a culture of E. coli placed on the surface under UV illumination. Significant photocatalytic activity and bactericidal effects were observed on the titanium surfaces of AO and NW, regardless of the surface roughness (P < 0.01). The group with anatase was the most susceptible to the photocatalytic effect, while the surface without anatase showed the least susceptibility. Based on this in vitro study, the crystallography of the oxide layer on its titanium surfaces is an important factor affecting the photocatalytic bactericidal activity.     

光照鲁棒的人脸识别

传统的人脸识别方法对待识别人脸图像的质量要求较高,而且要求所采集的人脸图像的光照情况与人脸训练库的光照情况的差异不能太大,这就限制了人脸识别系统运行的环境条件,从而限制了人脸识别的应用。为了降低人脸识别对环境条件的要求,真服光照对人脸识别的影响。本文分析了人脸图像的幅频特性和相频特性,提出了频域光照归一化的人脸识别方法,使得对任何光照条件下采集的图像经过归一化后,光照情况与训练库中的图像完全相同,同时保留了人脸的可区分性。因为人脸之间差异的信息量一般较少,故本文运用最小非零特征向量作为人脸特征,通过实验仿真,与传统方法相比本文人脸识别方法对光照变化具有鲁棒性。     

太阳能照明系统光源的选择

为了探究太阳能照明系统光源,验证LED用于太阳能照明的可行性,文章对不同批次的大功率白光LED进行了相关测试,并介绍了太阳能照明系统的组成,对不同使用场合的光源进行了比较,为太阳能照明系统光源的选择及进一步研究提供了参考。     

光学元件损伤在线检测图像处理技术

针对光学元件损伤图像中损伤区域的高精度检测问题,对内全反射照明下光学元件损伤图像的处理技术进行了研究。根据在线检测图像中损伤区域中心峰值的信号强度高于局部背景的信号强度这一特点,利用高斯滤波器生成待检测图像的局部信号强度比图像,实现了对损伤区域的低漏检率自动定位;根据CCD的成像原理,利用辐射标定的方法建立起损伤区域的尺寸与其在图像中总灰度的关系方程,实现了损伤区域的亚像素高精度尺寸测量。实验结果表明,与传统的光学元件损伤图像处理算法相比,本文提出的算法在保持低漏检率的同时大大提高了损伤区域的测量精度。     

点阵合成体视动感全息图

首先获取三维物体不同视角的透视图,并对这些视图上的不同单元的光强信息用计算机分别收集、编码,得到一组编码片,依次在同一张全息片的不同点区域上记录编码片的信息.当普通灯光照明全息片时,双眼能同时分别接收到反映物体两个侧面的清晰再现像,构成体视像,而且像会随着人眼的移动而产生动感效应.本方法的优点是利用计算机对信息处理的精确性,再结合全息记录、再现的准确性,制作了一张点阵合成动感全息图样品,能看见清晰立体再现像,观察方便,人眼移动时再现像的动态效果逼真.