Effect of Spatial Frequency on Equal-Luminance Point for the Mechanism of Shape from Shading

We examined 1) whether the perception of shape from shading is based on luminance or brightness by testing the additivity law, and 2) whether the spatial frequency contents in the stimulus affect on the spectral sensitivity. We measured the relative radiance at which shading disappeared in a simple shading figure. Results showed that 1) the additivity law holds for shading disappearance settings and that 2) the sensitivity for green to white decreased as higher spatial frequencies in the figure decreases. These results suggest that the perception of shape from shading is based on a luminance type additive mechanism and that the spectral sensitivity of the mechanism varies depending on spatial frequency.Presented at the International Commission of Optics Topical Meeting, Kyoto, 1994.     

由光影明暗度获得物体表面形状的快速算法

由Netwon Raphson迭代方法,提出了一种新的由光影明暗度恢复物体表面形状的快速算法此算法的思路为先将表面梯度(p,q)离散近似,然后再对深度Z(x,y)基础上的反射函数实施线性化,从而大大降低了传统算法的复杂性,提高了速度,同时又保持了所恢复的物体表面形状的准确性实验证明此算法是有效的.     

A statistical‐mechanical analysis of group additivity. Calculation of thermochemical values from frequency distributions

Molecular vibrational frequencies of homologous series plotted as cumulative frequency distributions are very similar, and the fine structure of the distributions exhibit identical features. An obvious explanation is that the changes in the molecular frequency distributions (MFDs) from one homologue to the next is independent of the chain length and of the functional groups in the molecule. Since group additivity is valid for the chosen homologous series there is here an explanation for the linearity of thermochemical values expressed by group additivity. For these properties the following hypothesis is proposed: group additivity is observed when the MFD is a sum of group frequency distributions (GFDs). This leads to additivity for the zero‐point vibrational energy which is confirmed by analysis of the frequencies of 126 organic molecules from 11 homologous series. The frequency distribution for a methylene group is estimated from that of octadecane. From this GFD combined with 11 different MFD it is possible to calculate model frequencies for the homologous series which are in good agreement with frequencies from ab initio calculations. For three thermochemical parameters (the logarithm of the vibrational partition function, the vibrational excitation energy and the vibrational heat capacity), the combination of the estimated methylene GFD with 11 different MFDs lead to group additivity values for a methylene group which are identical over a wide temperature range. The derivation of Benson additivity for thermochemical functions from frequency distributions is at step towards a better understanding of Benson additivity. Copyright © 2008 John Wiley & Sons, Ltd.     

利用曲面逼近进行三维形状恢复

通过对表面形状的平滑性约束，给出了一个关于表面深度和图像亮度的能量函数。并通过对预先给曲面进行调速使得这个能量函数达到极小值，来逼近实际的表面，从而恢复表面形状。这一方法同时利用了图像的局部和全局阴影，避免了只利用局部或全局阴影所带来的误差。通过对合成图像以及实际图像进行的实验，证明该方法是行之有效的。     

基于球扩展光源模型的物体三维形状的恢复

计算机视觉中传统的物体三维形状恢复方法大都基于光源是无穷远点光源的假设，如由单幅图像恢复三维形状（ｓｈａｐｅｆｒｏｍｓｈａｄｉｎｇ）光度立体视觉（ｐｈｏｔｏｍｅｔｒｉｃｓｔｅｒｅｏ）方法等。实际环境中的光源往往不能满足这个假设，因此大大限制了这些方法的应用，本文提出了一种更加实用的球扩光源模型，并推导出此光源下反射物体表面的反射图，此模型在三维坐标系中描述了球光源位置，亮度，漫反射物体表面反射度与     

Analysis of visual perception of light emitting diode brightness in dense fog with various droplet sizes

Road signs must provide a conspicuous signal to a wide variety of drivers over a broad range of environmental and geometric conditions. Recently, there are an increasing number of applications in which light emitting diodes (LEDs) are used as the light source, including critical transportation signaling. In the presence of fog, the resulting visual signal is disturbed due to light scattering by airborne water droplets. By measuring LED brightness with human spectral sensitivity in various densities and various droplet sizes (10, 30, 50, and 100 μm), it is understood that the particle size distribution (fog droplet size) and density of fog does affect visibility in fog. The colored LEDs that contain a yellow component had high brightness evaluation, blue component had low brightness evaluation in all densities and different droplet sizes. The result in this paper can contribute to air and land traffic safety and the prevention of accidents.     

空气/甲醇界面和频振动光谱的定量偏振分析

对空气／甲醇液体界面的和频振动光谱进行了定量的理论分析．虽然甲醇的红外和Raman光谱中都具有明显的反对称伸缩振动峰,但该光谱峰在界面和频振动光谱中却从未被观测到．利用已知的甲醇液体的红外和Raman光谱对和频振动光谱的键极化模型进行了修正,从而对此实验现象进行了定量的解释．此修正可以广泛地应用于界面和频振动光谱的研究中．     

CuBr激光充氢机理研究

详细研究了ＣｕＢｒ激光充氢后的激光动力学过程,解释了实验中观测到的两个现象：１）充氢后功率增大,其主要原因是：充氢使中心气体温度和ＣｕＢｒ分子蒸汽密度降低,从而减少了电子碰撞离解ＣｕＢｒ的有量损耗,导致电子温度上升。同时,脉冲期间的电子密度增加,电子密度的趋肤效应减弱,激光的“黑心”现象被改善。２）存在一个最佳充氢范围,其原因是：充氢后,随着气体温度的进一步降低,电子温度和铜原子度也将下降,它们与     

H$lt;em$gt;T$lt;/em$gt;$lt;sub$gt;c$lt;/sub$gt;SQUID低频通信接收机和穿墙通信接收实验

试验了一种能够在含水的岩层、土壤甚至海水中建立起无线通信的系统和方法.该系统的关键部件,高灵敏接收前端和接收机使用的是商品级高温超导量子干涉仪（high critical temperature superconducting quantum interference device,HT_cSQUID）磁强计和商用高速、高精度数据采集处理系统. 目前在从30 Hz到100 kHz频段内,商品级HT_cSQUID磁强计可以提供优于100 fT/Hz^1/2的内秉磁场噪声谱密度,同时商用数据采集处理系统可通过软件实现对传输信息的调制、采集、解调和分析. 利用低频电磁波在导电介质中有较大穿透深度以及HT_cSQUID磁强计低频磁场灵敏度高、体积小的特点,对于一种能在地下（岩石和土壤）和水下（海水）环境中使用的可移动式低频无线电通讯系统实现的可行性,进行了初步讨论. 使用面积等于1 m²的方形线圈作为测试信号的辐射体（发射天线）,将SQUID磁强计的传感器封闭在一个能对超低频测试信号提供较大衰减的电磁屏蔽体中,成功地接收到了发射线圈辐射的99 Hz调幅信号.因此证明,采用HT_cSQUID技术,可以在地面与数百米深的地下建立起有实用价值的无线电通信. 关键词： T_cSQUID磁强计')" href="#">HT_cSQUID磁强计 低频电磁波 低频无线电通讯     

带宽对平顶高斯宽带激光传输特性的影响

研究了横向分布为平顶高斯模式的宽带激光在自由空间的传输特性,分析了频带宽度对其强度分布的影响。首先推导了平顶高斯模式宽带激光的每一频率分量在自由空间的传输公式,然后将频率域的传输公式通过傅里叶变换得到时间域的传输公式。基于推导的公式通过数值算例给出了不同频带宽度激光光束的强度分布结果,详细分析了空间模式的变化和时空耦合现象。研究结果表明:随着传输距离增大,平顶高斯空间模式趋于高斯分布。同时随着带宽增大,平顶高斯模式宽带激光表现出更强的时空耦合现象,并导致其空间横向分布发生明显变化。变化的主要特征为波前的强度分布随带宽增大而变窄,波后的强度分布则随带宽增大而远离轴中心向外扩展。     

Transverse coupling and dynamics of patterns in a photorefractive oscillator

The effect of transverse coupling in a photorefractive oscillator is studied. From the study the condition for stable optical patterns of multimode oscillation is given analytically and verified by numerical simulation. Under the stable condition, the period-doubling route to spatiotemporal chaos is observed.     

微波低通高阻复合材料构件的设计与性能验证

随着海洋环境武器装备隐身发展的需要, 开展具有微波低通高阻特性的复合材料构件设计与研究显得重要而迫切. 文章首先设计了一种中空六边形周期性结构, 以此为基础设计了一个由面层、中空六边形环周期层1、中间层、中空六边形环周期层2、面层组成的新型复合双层频率选择表面(FSS)结构件. 其上层FSS的结构参数为中空六边形环边长3.0 mm, 线宽度0.5 mm, 缝隙宽度0.4 mm; 下层FSS的结构参数为中空六边形环的边长3.2 mm, 线宽度0.5 mm, 缝隙宽度1.0 mm. 模拟结果表明: 该复合材料构件具备优良的低频透过性与高频屏蔽性快速转换的特性, 能够获得优异的低通高阻性能, 同时在45°范围内具备优良的角度不敏感性. 最后制备和实验验证得到了0–2 GHz低频段具有95.6%高透过性、同时在7.05–18 GHz高频段具有10 dB 以上屏蔽性能的复合材料构件, 对具有隐身特性的新型滤波电磁功能构件的研制具有重要价值.     

用计算机显示和记录超低频信号

介绍用ＡＰＰＬＥ—Ⅱ计算机来显示和记录超低频信号的一种方法。     

双稳调参高频共振机理

针对双稳系统的高频信号响应,探讨了双稳调参的高频共振机理.研究表明,二次采样频率变换并不改变双稳结构直接在原系统结构上在与高频映射对应的低频处实现共振,而双稳系统参数调节是调参改变双稳结构并直接在高频处实现共振.双稳系统参数调节之所以能够实现高频随机共振,是因为同时调节双稳系统两参数可使Kramers逃逸速率不存在极限值,突破了随机共振信号频率必须在小频率范围内的限制. 关键词： 双稳系统 高频共振 二次采样频率变换 系统参数调节     

A Basic Predator‐Prey Type Model for Low Frequency Discharge Oscilations in Hall Thrusters

The mechanism of low frequency oscillations in Hall thrusters is usually explained using the predator‐prey type model, but the reasonable boundary conditions for the model have not been given. Analyses on thrusters' model equations show that besides the processes of neutral replenishment and ionization avalanche, the effects of dynamic electric field are also necessary for low frequency oscillations. The dynamic electric field reflects the interaction of ionization zone with acceleration zone, and is embodied in boundary conditions of the predator‐prey type model. Furthermore, a basic predator‐prey type model with reasonable boundary conditions and complete physical mechanism is proposed. And the effects of electric field on low frequency oscillations are verified by experiment (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

低对称性非线性光学晶体BIBO的倍频性质

测量了BIBO晶体的主轴折射率.对BIBO晶体在整个空间内的倍频性质进行了系统讨论.当基频 光为Nd:YAG激光时（λ=1064nm），发现最大的有效非线性光学系数位于（168.9°，90°） 的Ⅰ类相位匹配方向上.测量了BIBO晶体的容限角、容限温度、光损伤阈值，以及1064nm的 腔外、腔内倍频性质.实验中，最大腔外倍频转换效率达到68%，腔内倍频输出达到1.06W. 关键词： 低对称性 BIBO晶体 倍频     

光纤阵与压电阵的海试比较

为了检验光纤水听器阵在低频(100Hz~1kHz)/甚低频段(100Hz)的测量性能,在南海海试中,我们将一16元光纤阵与16元常规压电水听器阵平行安装在同一基阵框架上并沿舷侧布放,使得两阵受到基本相同的振动干扰。通过单频和宽带脉冲信号的传播实验,对双阵接收信号进行比较。试验结果表明,光纤阵具有更好的抗振动加速度性能,因此在甚低频段检测中具有明显的优势。     

The Relationship Between Vocal Pitch-Matching Skills and Pitch Discrimination Skills in Untrained Accurate and Inaccurate Singers

Few studies have compared the relationship between pitch discrimination accuracy and the accuracy of fundamental frequency (F(o)) control. This study investigated the relationship between vocal pitch-matching skills, which is one method of testing F(o) control, and pitch discrimination skills in untrained accurate and inaccurate singers, and the effect of timbre on their pitch discrimination accuracy. Data showed that accurate singers had more precise discrimination and pitch-matching abilities compared with their inaccurate counterparts. Pitch discrimination was differentially affected by the timbre (eg, spectral differences) of comparison tones. In addition, results showed a significant relationship between pitch discrimination abilities and pitch-matching accuracy. The results suggest that accurate F(o) control is at least partially dependent on pitch discrimination abilities, which are important for accurate singing.     

添加剂对LiBr溶液吸收蒸汽过程中的强化机理

利用吊板法测量了加有正辛醇和异辛醇这两种添加剂的溴化锂溶液的表面张力 ,利用激光照相的可视化方法研究了在静池吸收过程中添加剂对溴化锂溶液吸收水蒸汽的强化影响 .实验结果显示液体添加剂和蒸汽添加剂都能显著地降低溴化锂溶液的表面张力 ;蒸汽添加剂不仅和液体添加剂一样可以在吸收表面引起马拉戈尼对流 ,而且对吸收具有更好的强化效果 .根据对实验现象的分析 ,得出了添加剂对吸收的强化机理 :由于溶液表面层对液体添加剂或蒸汽添加剂的表面吸附作用 ,造成吸收界面处表面张力分布不均匀 ,从而在吸收界面引起马拉戈尼对流现象 ,强化了吸收过程中的传热、传质性能     

ZnO: Cu,Sn electroluminescent phosphor

The a.c. electroluminescent characteristics of ZnO:Cu, Sn powder phosphor have been investigated in audio frequency range. A simple preparative method for this phosphor has been described. The detailed variation of light output during one cycle of the applied sinusoidal voltage has been studied and discussed. In addition to the two primary peaks, the two secondary peaks have also been observed in each cycle of the applied field. The voltage and frequency dependence of the time-averaged electroluminescent brightness have been found to follow the Alfrey-Taylor relation over a wide range of frequencies. The constants of this relation have been determined. The spectral energy distribution of this phosphor shows that the peak-shift depends upon the a.c. frequency and is independent of the magnitude of applied field.