透射式变掺杂GaAs光电阴极研究

为了将变掺杂GaAs材料应用于微光像增强器,开展了透射式变掺杂GaAs光电阴极实验研究,制备了2种反转结构透射式变掺杂GaAs光电阴极。测试了玻璃粘接前后GaAs光电阴极载流子浓度变化,发现高温粘接后载流子浓度增加现象。通过测试高温激活的透射式变掺杂GaAs光电阴极发现,在450 nm～550 nm波段内,变掺杂GaAs光电阴极仍然具有较高的光谱响应。     

玻璃与GaAs外延片热压粘结工艺研究

本文报道制备GaAs透射式光阴极过程中窗玻璃与大面积GaAs外延片热压粘结工艺的原理和过程,并重点分析抗反射膜的淀积、粘结温度控制和压力大小对粘结结果的影响。     

GaAs-玻璃粘接阴极组件热辐射放气成份质谱分析

为解决负电子亲合势GaAs光电阴极电子发射灵敏度低的问题,运用质谱计对GaAs-玻璃粘接阴极组件在高温热辐射除气时的放气成份进行了分析, 获得了GaAs电子发射层原子级表面。结果表明：组件150℃为表面放气,450℃为材料体内放气,580℃为洁净表面获得温度,大于650℃ 时GaAs发射层面有As蒸发。这说明严格控制发射层表面洁净温度,是保证制备高性能阴极灵敏度的关键。     

GaAs/Ge的MOCVD生长研究

用常压MOCVD在Ge衬底上外延生长了GaAs单晶层,研究了GaAs和6e的极性与非极性材料异质外延生长,获得了质量优良的GaAs/Ge外延片,GaAs外延层X射线双晶衍射回摆曲线半高宽达16弧秒.10K下PL谱半峰宽为7meV.讨论了极性与非极性外延的界面反相畴问题和GaAs-Ge界面的Ga、Ge原子互扩散问题.     

透射式GaAs光电阴极的X射线衍射研究

本文介绍了高精度多晶多反射X射线衍射仪的一种新的应用.首次将其应用于研究高灵敏度第三代微光象增强器中由掺Zn的p型GaAs/GaAlAs、玻璃组成的光电阴极的材料特性；发展了用倒格子空间衍射图方法评价光电阴级组件晶体质量的方法.通过分析得知,衍射强度在倒格子空间沿。方向展宽主要起因于晶体中的嵌镶效应的增强.文中采用衍射动力学理论的计算方法并忽略初始条件,模拟后得到的曲线与衍射强度沿ω/θ方向的投影强度曲线符合的比较好.粘接良好的阴极样品表明,GaAs/GaAlAs晶格常数的变化基本上可以消除,但粘接引起的嵌镶效应的增强却不能完全消除.     

透射式GaAs光电阴极研究

本文叙述了透射式GaAs光电阴极的原理和制作过程,详细地研究了透射式GaAs光阴极的激活工艺,获得了500μA/1m的积分灵敏度.     

钛合金和碳纤维的粘接技术

简述了某空间遥感相机中碳纤维桁架杆与钛合金接头的粘接工艺,通过对粘接剂的选择、粘接表面处理、胶层厚度等粘接强度影响的分析和破坏性力学试验表明,J133胶粘剂适用于钛合金和碳纤维材料的粘接;适当提高粘接表面的粗糙度、用化学法对粘接表面进行处理均可提高粘接强度;对该例的套接形式胶层厚度控制在0.15mm—0.2mm可保证得到好的力学性能和粘接质量。     

透镜的粘接固定技术

本文对透镜固定技术作了分析,提出了以透镜粘接固定法代替传统的包边法和压圈固定法。对粘接剂的选择、粘接固定形式、粘接工艺及质量验证等问题均作了较详细的介绍,并列举了有关试验结果。     

GaAs阴极光电发射特性北大核心CSCD

采用氧过量YOYO激活工艺对经高温清洁的砷化镓(GaAs)晶片进行激活,测量其量子效率和在激光及背景光照射下的使用寿命,得到了4.66%的量子效率;在电子枪中的实验获得了平均流强大于1mA的束流。分析了真空度、高温清洁温度、铯氧激活工艺等因素对GaAs光阴极初始量子效率和使用寿命的影响。     

超声换能器粘接工艺的球压法研究

在检测用超声换能器的制作工艺中,粘接层是影响换能器性能的一个重要因素.为寻求最佳粘接条件,我们设计了一套加压装置,并采用非均匀加压方法,对陶瓷片几何尺寸(厚度、直径),加压橡胶球参量(直径、硬度)以及施加压力大小三者之间的关系作了一些实验研究,得出了一些有益的实用结果.文中给出了采用非均匀加压方法与一般的均匀加压法制作的换能器性能比较.     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.     

Real-time restoration of rotational blurred image using gradient-loading

The key to the restoration of rotational motion blurred image is how to restore the image under a low cost and to correct the irreversibility of the degradation function matrix.Based on the special qualities of degradation function matrix and precise deduction in space-domain, we present a new approach using gradient-loading for restoration of rotational blurred image.By easily adding a gradient operator, the irreversibility of the original matrix is corrected and can be applied for inverse filtering then.Gradientloading is the optimized approach which combines the advantages of both the approaches using constrained least square filtering and traditional diagonal-loading.Compared with the approach using least square filtering, its peak signal-to-noise ratio (PSNR) is improved from 3.18 to 6.46dB, while the computing time is reduced to 1/2-1/3.Experimental results demonstrate the effectiveness, noise-resistibility, robustness, and low complexity of this approach, which make it more suitable for real-time environment.     

All-Optical Logic Device Using Bent Nonlinear Tapered Y-Junction Waveguide Structure

We propose an all-optical logic device made of a bent tapered Y-junction waveguide with a Kerr-type nonlinear interface. It could provide an AND gate, OR gate, and exclusive-OR (XOR) gate. We could obtain different transmission results by adjusting the bending angle. The numerical simulation results show that the device functions as AND, OR, and XOR gates.     

Real-time, continuous-wave terahertz imaging by a pyroelectric camera

Real-time, continuous-wave terahertz (THz) imaging is demonstrated. A 1.89-THz optically-pumped farinfrared laser is used as the illumination source, and a 124 × 124 element room-temperature pyroelectric camera is adopted as the detector. With this setup, THz images through various wrapping materials are shown. The results show that this imaging system has the potential applications in real-time mail and security inspection.