Light-induced electron emission from polymethylphenyl siloxane oils

Light-induced electron emission from tetramethyl tetraphenyl trisiloxane, (Dow-Corning silicone oil DC704) and trimethyl pentaphenyl siloxane (Wacker Chemie silicone oil AN175) has been measured as a function of photon energy. Absolute quantum yield and threshold energy were determined. The threshold energy of 7.5 eV for both siloxanes is comparable to the thresholds of other polymethylphenyl siloxanes with phenyl/methyl ratios of 1/3 and 1/18, which have been investigated by the authors. The quantum yield as a function of photon energy shows a systematic change with variation of the phenyl/methyl ratio. This dependence on the molecular structure is ascribed to a change of the initial ionization quantum yield     

A Low-Power CMOS Front-End for Photoplethysmographic Signal Acquisition With Robust DC Photocurrent Rejection

A micro-power CMOS front-end, consisting of a transimpedance amplifier (TIA) and an ultralow cutoff frequency lowpass filter for the acquisition of photoplethysmographic signal (PPG) is presented. Robust dc photocurrent rejection for the pulsed signal source is achieved through a sample-and-hold stage in the feed-forward signal path and an error amplifier in the feedback path. Ultra-low cutoff frequency of the filter is achieved with a proposed technique that incorporates a pair of current-steering transistors that increases the effective filter capacitance. The design was realized in a 0.35-$mu{hbox {m}}$ CMOS technology. It consumes 600 $mu {hbox {W}}$ at 2.5 V, rejects dc photocurrent ranged from 100 nA to 53.6 $mu{hbox {A}}$, and achieves lower-band and upper-band ${-{hbox { 3-dB}}}$ cutoff frequencies of 0.46 and 2.8 Hz, respectively.      

大气压下流注放电光电离过程的数值仿真

将光电离模型引入气体流注放电的流体模型中,针对光电离数值仿真计算需要对空间任意两点建立联系,导致方程求解计算量增大、计算较困难的问题,提出了光电离模型的简化计算方法。然后求解流注放电流体模型,仿真棒–板空气间隙放电过程,并比较了有和没有光电离2种情况,结果表明光电离提供了流注放电所必须的二次电子崩的种子电子,在没有光电离时,不能形成流注放电。在考虑光电离情况下仿真了流注发展过程,得到各时刻电子、光电子、电场空间分布,并从流注发展速度、通道半径、电场强度多方面与实验结果比较,验证了模型和算法的正确性。     

AC and DC conductivity studies in pulsed laser ablated (Ba,Sr)TiO3 thin films

Abstract

A comparison of the ac conductivity of laser ablated (Ba, Sr)TiO₃ thin films was made for films grown at different substrate temperatures. The ac conductivity was studied as a function of frequency and ambient temperature ranging from room temperature to 460°C. Conductivity results from ac and dc measurements were compared in their an respective Arrhenius plots revealing interesting coincidences. The value of the activation energies computed from the Arrhenius plot of à _ac with 1000/T ranged from 0.97 to 1.3 eV in the high temperature region to 0.36 to 0.54 eV in the low temperature region for different samples. The activation energies obtained from pure dc measurement for fields greater than 100 kV/cm across the samples were in the range of 1.06 to 1.32 eV for different samples. The similarity in results suggests a common origin in the de conduction process in the concerned temperature range and was attributed to ionic conduction resulting from oxygen vacancy motion which has been observed to be significant at high temperatures and high fields. For high temperature grown samples the value of activation energy computed from the Arrhenius plots was comparatively less than those grown at lower substrate temperatures. The difference was attributed to the microstructure and the effect of grain boundaries on the motion of oxygen vacancies leading to the conduction process.     

Consider the GPS for biomedical applications

One important field of research in biology is the study of the mechanisms that govern orientation and navigation of living objects in a natural environment. For this purpose, experimental techniques for localization and reconstructing a given path as a function of time are of fundamental importance. The most attractive of these techniques is certainly satellite-based. Recent developments in the Navigation System Time and Range (NAVSTAR) for the Global Positioning System (GPS) have given rise to some very interesting applications for biology and medicine. Global Positioning Systems are space-based radio positioning systems that provide 24 hour, three-dimensional position, velocity and time information to suitably equipped users anywhere on or near the surface of the earth. Here we refer to NAVSTAR GPS, operated by the U.S. Department of Defense, which is the first GPS widely available to civilian users. A system could be designed that reconstructs the path of a free ranging animal using a GPS receiver carried by the animal itself. The receiver would be operated in a continous navigation mode and record successive position data, which are then analyzed at the end of the experiment. Such an experimental technique would not suffer from the typical constraints of visual, radio, and radar techniques, where the required "electromagnetic" link between the observer and the animal limits the monitoring range and may be heavily impaired by the nature of the surrounding environment     

Photovoltaic effect in rhombohedral and tetragonal phase BiFeO3 ferroelectric thin films

The in-plane photovoltaic effect of epitaxially grown rhombohedral and tetragonal BiFeO₃ thin film were studied. The absorption spectrum of tetragonal BiFeO₃ is overall blue shifted compared with that of rhombohedral one, with an absorption onset near 2.5?eV and direct band gap of 3.1?eV. The photocurrent is measured with symmetric platinum electrodes in the plane to eliminate the interfacial energy barriers in rhombohedral and the effect of the depolarization field in tetragonal film. Except for the different sign and magnitude, the photo-current of both rhombohedral and tetragonal films depends on the linearly polarized light onto the plane of the sample along X and Y directions, showing evidence of a strong bulk photovoltaic effect (BPVE). These results indicate that the BPVE in both rhombohedral and tetragonal BiFeO₃ thin films could be further explored for the next generation of solar photovoltaic applications.     

A novel and effective multi-constrained QoS routing scheme in WMNs

Multi-constrained quality of service (QoS) routing aims at finding an optimal path that satisfies a set of QoS parameters, as an NP complete problem, which is also a big challenge for wireless mesh networks (WMNs). Heuristic algorithms with polynomial and pseudo-polynomial-time complexities are often used to deal with this problem. However, existing solutions, most of which suffered either from excessive computational complexities or from low performance, were proposed only for wired networks and cannot be used directly in wireless mesh networks. In this paper, we propose a novel routing scheme based on mean field annealing (MFA-RS) to solve this problem. MFA-RS first uses a function of two QoS parameters, wireless link’s delay and transmission success rate as the cost function, and then seeks to find a feasible path by MFA. Because MFA-RS uses a set of deterministic equations to replace the stochastic process in simulated annealing (SA) and uses saddle point approximation in the calculation of the stationary probability distribution at equilibrium, the convergence time is much less than the routing scheme based on SA (SA-RS). Simulation results demonstrate that MFA-RS is an effective algorithm and is very fit for WMNs.     

Simulation of corona discharge. Positive corona in SF6

Positive coronas in SF₆ under three voltage levels, 3.0, 3.5 and 4.0 kV, are studied for a 0.5 cm gap between a hyperboloid needle and a plane electrode at a gas number density N=2.12×10¹⁸ cm³. The current in the form of a burst of pulses is found to increase with increasing voltage. The initiation and development of successive avalanches are traced as function of time after voltage increases. The development of electron avalanches and streamers are due to ionization and photoionization and quenching of avalanches is due to space charge. The simulation provides a detailed structure of avalanches from which essential differences between positive and negative corona with regard to total field distribution, propagation of successive avalanches and ion distribution can be discerned     

A self-consistent model of electron emission from metals

We present a model of electron emission from metals, which takes into account deviation of the electron distribution function from the Fermi equilibrium form inside the cathode under the emission effect. Using the Grad method electron distribution function, the emission boundary is expressed consecutively in terms of its hydrodynamic moments: temperature, average velocity, heat flux density. These hydrodynamic moments are caused by the emission itself and thus need a self-consistent determination. New easy-to-use equations for the emission current density, emission heat flux, and total energy distribution function of the emitted electrons are proposed. Consideration was made for a wide range of temperatures (⩽3500 K), field strengths (⩽1.5×10⁸ V/cm) and work function (3.0 to 4.5 eV) of the emitter. A considerable deviation from the Fowler-Nordheim (FN) theory was found at high current density (>10 ⁹ A/cm²)     

基于LabVIEW的激光加工路径识别算法

激光加工应用于各行各业,其作用不可忽视,而且功能越来越丰富.传统的激光加工往往是由上位机生成矢量图导入下位机后控制激光头移动.这种方式局限性在于不能自由的对加工平面上规划好的路径进行加工.为了解决这个问题提出了基于LabVIEW机器视觉的路径识别算法,通过不断改变ROI即感兴趣区域来获取所需的点,将这些点连起来便是所要加工的路径,并将这些点转换成世界坐标传输到控制器来控制激光头的运动,在不断改变ROI的同时必须严格保证ROI不偏离规定路径也不能同时包含其他路径而造成干扰,实验结果显示路径可以被有效识别验证了该算法的可行性.     

短光程下差分吸收光谱法测量低浓度污染气体的反演算法

传统差分吸收光谱(differential optical absorption spectroscopy,DOAS)技术对长光程或高浓度烟气污染物可以实现准确、快速和在线测量,但是对于短光程、低浓度污染气体测量却存在较大的浓度反演误差。该文提出了一种新的光谱数据处理方法,并对信噪比较低的实测光谱数据进行了浓度反演。研究结果表明：气体浓度在0~150 mg/m3范围内,新算法的反演精度明显优于传统算法,反演误差都在10%以内;在150~4 000 mg/m3范围内与传统算法相当;超过4 000 mg/m3后新算法的反演误差较大。新算法具有良好的抗烟尘干扰能力,其零点误差较传统算法减小了95%以上。与传统DOAS算法相结合可以获得较宽的动态测量范围。     

Experimental analysis of lightning overvoltages induced on low-voltage distribution lines

Problems have often been caused in low-voltage distribution lines such as single-phase 100/200 V and three-phase 200-V systems. For instance, the burning of low-voltage devices and the unnecessary operation of ground fault interrupters have occurred, which are caused possibly by lightning overvoltages. Experimental analysis was performed on the generation modes of lightning overvoltages on low-voltage distribution lines. A scale model line, one-fourth the size of an actual power distribution line of Tokyo Electric Power Company (TEPCO), was installed for experimental analysis on the lightning protection of an overhead ground wire, an overhead common grounding wire (system neutral conductor), surge arresters and pole transformers against the overvoltages induced on low-voltage distribution lines due to a nearby lightning stroke. A balloon was flown at a location 30 km away from the scale model line in a normal direction to it. A 200-m long wire is suspended from the balloon to simulate a lightning path. Pulse current is applied to the simulated path using a pulse generator and the voltages induced on the line conductors are measured. This paper analyzes those overvoltages by means of the experimental and the theoretical methods.     

Integrated GaInAsP laser diodes with monitoring photodiodes throughsemiconductor/air Bragg reflector (SABAR)

A 1.3-μm GaInAsP laser diode (LD) is integrated with a monitoring photodiode (M-PD) through a semiconductor/air Bragg reflector (SABAR). Instead of conventional cleavage, the SABAR can provide not only Fabry-Perot resonance with high reflectivity, but also possibility of integration of laser with other functional devices. The design, fabrication, and some characteristics including threshold current, monitoring photocurrent, SABAR reflectivity as a function of the number of semiconductor/air pairs N are reported. The threshold current of ridge waveguide laser with SABAR (cavity length L=160 μm, ridge width W=7 μm, SABAR pairs N=3) is 20 mA. The threshold current is reduced by improving butt-coupled interface between active and passive waveguides employed in this laser and is expected 2 mA/μm. The monitoring photocurrent responds linearly with output power from the laser and 0.024 mA at laser output power of 5 mW. From the threshold characteristics, SABAR reflectivity is determined to >80%. The increase of photocurrent can be achieved by optimizing the number of SABAR pairs to N=1. We have obtained threshold current of 22 mA in the followed laser structure (L=270 μm, W=7 μm, N=1), and detector photocurrent of 1.13 mA (@5 mW). The experimental SABAR reflectivity is ~50%, which is estimated by threshold characteristics and efficiency of light output power. The laser has a mode field converter section, resulting in narrow beam divergence 11° along vertical axis. This integrated laser is very promising candidate for coming optical module in low-power consumption and low-cost access network systems     

基于动态阈值的AGV路径识别算法

针对基于视觉引导自动引导车(AGV)系统的引导路径识别技术,易受光照强度,路面反光,阴影等因素的影响的问题.采用了一种基于路径预判的图像动态阈值获取方法.它通过已识别的路径点,利用线性插值所得函数预估当前路径点所在图像区域,在此区域内找出最优阈值,依据阈值对当前区域内图像进行二值化,找出当前区域的引导线,依据引导线本身特征来判断此阈值是否有效,以获取到适应当前环境下的阈值,并根据此阈值提取出引导线.通过此种方法对路径信息进行采集、识别、处理,从而使AGV能在跑道上较快较稳的前行.     

考虑分子碰撞时理想气体内部压强公式的推导

根据分子按自由程的分布律和麦克斯韦速率分布律 ,给出了推导气体压强的一种比较严格的方法     

Variations of interface potential barrier height and leakage current of (Ba,Sr)TiO3 thin films deposited by sputtering process

Abstract

Variations of the leakage current behaviors and interface potential barrier height (Φ_B) of rf-sputter deposited (Ba, Sr)TiO₃ (BST) thin films with thicknesses ranging from 20 nm to 150 nm are investigated as a function of the thickness and bias voltages. The top and bottom electrodes are dc-sputter-deposited Pt films. Φ_B critically depends on the BST film deposition temperature, postannealing atmosphere and time after the annealing. The postannealing under N₂ atmosphere results in a high interface potential barrier height and low leakage current. Maintaining the BST capacitor in air for a long time reduces the Φ_B from about 2.4 eV to 1.6 eV due to the oxidation. Φ_B is not so dependent on the film thickness in this experimental range. The leakage conduction mechanism is very dependent on the BST film thickness; the 20 nm thick film shows tunneling current, 30 and 40 nm thick films show Schottky emission current.     

基于改进蚁群算法的无人机三维航迹规划

针对传统蚁群算法在无人机三维航迹规划中，存在早期盲目搜索、收敛速度慢、易陷入局部最优等问题，本文提出了一种改进蚁群算法。该算法利用空间位置初始化信息素分布并设定浓度阈值，增强了蚁群早期搜索的方向性，避免了算法陷入局部最优；设计兼顾距离因素和方向因素的启发函数，改善了航迹规划质量；采用自适应挥发因子控制信息素的挥发，提高了算法的收敛速度。通过两组实验表明，该算法相比传统算法规划的航迹平均长度均减少18.6%，平均迭代次数分别减少63.3%和78.7%，平均拐角次数分别减少62.5%和42.3%。     

An incremental analysis of spark paths in air using 3-dimensionalimage processing

A video camera has been used to record the path of spark breakdowns across a positive point/plane air-gap. By using a prism as a mirror, two images were obtained from which the path could be determined in three dimensions by subsequent computer processing and analysis. Images were analyzed for each of five angular positions of the point electrode's axis, the gap remaining constant. The fractal dimension of each path was determined and found to increase slightly with the inclination of the pointed electrode. Each spark appeared to have propagated semi-randomly in a direction which included a `memory' factor, that is, it tended to follow the previous direction while moving monotonically towards the opposite electrode. This was confirmed by an analysis of 400 spark paths which showed that each section has a specific relationship to the previous section, but that there is a wide variation around this mean which leads to the characteristic shape of a spark path. Simulations based on these results yield spark tracks which look similar to those measured and have similar fractal dimensions. These analyses strongly suggest that the development of spark paths in air is by successive steps and in a direction suggested by an angular probability distribution which is related to the field at the tip of the propagating leader