On the theory of photoionization of deep-level impurity centers in a parabolic quantum well

The localized state of a deep-level impurity in a quantum well (QW) with a parabolic potential profile is investigated within the context of a zero-range impurity potential model. It is demonstrated that, if the well is sufficiently thin, an effect of positional disorder exists: the binding energy of a deep-level impurity center is a decreasing function of the center transverse coordinate. It is found that the positional disorder effect is enhanced in the parabolic potential well in comparison with the rectangular well of finite depth. The spectral dependence of the photoionization cross section of deep-level impurity centers is examined. It is shown that the spectral dependence of the photoionization cross section is not monotonic, and the position of the impurity-absorption edge depends strongly on the impurity center coordinate and the QW parameters.     

Effects of carrier frequency accuracy on quasi-synchronous,multicarrier DS-CDMA communications using optimized sequences

It is known that the multiple access interference (MAI) of a quasi-synchronous (QS) multicarrier direct signal code division multiple access (DS-CDMA) system can be substantially reduced by using signature sequences having optimized cross correlation at small shifts around the origin. This paper shows that the time-frequency cross correlation function rather than the usual (time-domain) cross correlation determines the MAI when the system is operated in the presence of carrier frequency offset (CFO), which arises due to the frequency-accuracy limit of the oscillator. Several known sets of sequences having optimized time-domain cross correlation are investigated for their MAI-minimization capabilities in the presence of CFO. It is found that: (i) a system using Walsh codes or Suehiro-Hatori (1985) polyphase sequences can be driven into outage as a result of significant worst-case MAI and (ii) it is possible to minimize the MAI for systems using preferentially phased Gold codes cyclic-shift m-sequences or Lin-Chang 9see ibid., vol.45, p.221-6, 1997) sequences only if the product of chip period and maximum frequency deviation is less than around 0.01. Implications of these findings to practical implementation of systems are discussed     

A theoretical study to improve wire sag of ultra-long wire bond loops for 3D/MCM packaging

An innovative theoretical model by altering cross section of gold wire is proposed to reinforce the wire sag stiffness of a wire bond that suffered low yield for the applications of 3-dimensional and multi-chip module (MCM) packaging. The flexural rigidity of a wire bond is found to be a function of the material properties in the moment of inertia of a bond wire. Suffice to say, if the moment of inertia of the bond wire can be raised, the associated sag deflection will be diminished. By manipulating the moment of inertia of the bond wire, the sag deflection of the wire bond can be regulated appropriately to avoid wire sag and even the wire sweep enigma. The ellipse-like cross section of a wire bond is applied as a numerical example to improve the wire sweep stiffness or wire sag stiffness in this study. The results show the sag deflection of a wire bond can be reduced significantly if the ellipse-like cross section is oriented in the preferred direction of flexural rigidity of a wire bond. Furthermore, a systematic study of matching design is performed to control wire sag and wire sweep for the wire bonding applications of overhang cross-stacked and step-stacked packaging. It shows that to use a single diameter of bonding wire in these complicate bonding environments of overhang stacked configurations is a favored possibility. The advantages shown from the theoretical study need to be implemented in further work in a production environment on current wire bonding equipment.     

混合进制复制生成序列的相关函数

介绍了以混合进制码为复制信息,用平移复制生成多复数值序列的方法,讨论了复制生成序列的性质和复制生成序列的相关函数,给出了两个生成序列的互相关函数值恒为零的条件,最后给出了一个复制信息的选取准则,根据这个准则可以得到一个两两之间互相关函数值恒为零的序列族.     

Bandpass correlator analysis for general input assumptions (Corresp.)

For general assumptions concerning bandpass signal and noise inputs, previous analyses of analog cross correlators have yielded very complicated expressions for the probability density function (pdf) of the correlator output. The inherent computational difficulties, therefore, limited the application of these pdf's almost exclusively to special cases of equal noise powers and noise spectrums symmetric about the signal's frequency. In this correspondence it is shown that for general bandpass inputs, the correlator output can always be expressed as the difference of two scaled independent noncentral chi-squared variables if a certain matrix transformation of variables is employed. The characteristic function method is then used to derive the pdf, which is as readily computed as for the case of special assumptions.     

Calculation of the local cross-correlation function on the basis ofthe Laguerre transform

A simple and computationally efficient mechanism for calculating a running or local cross-correlation function of two time-domain signals is presented. In order to obtain a running cross-correlation function, the signals must be windowed. It is argued that an appropriate window for a local cross correlation is an exponential function. To obtain a computationally efficient mechanism, the windowed functions are decomposed in a series of orthogonal functions. The set or orthogonal functions is matched to the chosen window and is a Laguerre-Fourier series. The cross correlation of the windowed functions is equal to a weighted summation of cross-correlated pattern functions. The weights are determined by cross correlating the Laguerre coefficients     

一种改进的Focal Loss在语义分割上的应用

传统基于深度学习的语义分割方法使用的损失函数为交叉熵,而交叉熵并不能解决训练数据中的样本非均衡性问题。语义分割任务属于像素级分类,样本的非均衡性问题在其中体现得十分突出。文章提出了一种改进的Focal Loss作为损失函数来自动解决训练样本的非均衡性。该损失函数等同于在标准交叉熵上加上一个权重,该权重能够自动增加困难样本的交叉熵损失值,同时保持简单样本的交叉熵损失值。将Focal Loss作为DeepLabv3+的损失函数,并将DeepLabv3+的Backbone替换为ResNet-18,再使用Cityscapes数据集作为训练样本,分别使用交叉熵和Focal Loss作为损失函数来对模型进行训练。实验结果表明,改进的Focal Loss损失函数相比于交叉熵获得的语义分割精度更高,且能够有效缓解训练样本的非均衡性问题。     

FIFO技术在SDH数字交叉连接芯片设计中的应用

首先介绍了数字交叉设备中SDH数字交叉连接芯片的位置及作用，简要介绍了SDH数字交叉芯片的基本结构，并讨论了采用FIFO技术来解决该结构中多条高速链路之间交叉所面临的问题，对FIFO基本电路给予描述，重点讨论了FIFO技术在SDH数字交叉连接芯片中的应用，最后给出了数字交叉连接芯片中FIFO技术的设计实现。     

RF Characteristics of thin dipoles

This paper considers the average bistatic scattering cross section of thin cylindrical dipoles as a function of frequency, bistatic angle, and transmitting and receiving polarization. The averaging is over all orientations of the dipole with all orientations equally likely. Section II is essentially tutorial, approaching the problem of scattering cross section from the equivalent circuit point of view. Using this approach, the maximum scattering cross sections of lossless dipoles in the Rayleigh region and at the first and second resonances are derived. Section III presents a novel method of predicting cross section at the first resonance with the effect of loss included. Numerous measurements indicate that this method is widely applicable. Section IV describes our microwave scattering range and the results of measurements made on dipoles resonant at X band. In Section V the averaging of cross sections is considered. The average bistatic cross sections for resonant half-wave and full-wave dipoles are plotted vs bistatic angle for various transmitting and receiving polarizations. These results, which are new, were obtained using a digital computer. The average cross section for short (Rayleigh region) dipoles is also obtained as a function of bistatic angle for various polarizations. Section VI is a summary of parameters of the West Ford dipoles.     

基于互模糊函数的快速时差频差联合估计

针对无源定位中的时差频差联合估计问题,利用内积公式推导出了基于互模糊函数的时差频差联合估计公式,并提出了相应的快速实现算法。其中通过适当变换互模糊函数计算公式,将传统的二维时差频差搜索算法变为对信号内积进行快速傅里叶变换,然后对变换后的数据进行二维搜索,大大提高了时差频差联合估计的速度,降低了运算量。通过重构离散傅里叶变换项,并进行近似,进一步降低了运算量。仿真结果说明,两种算法都能得出准确的结果,改进的算法计算时间更少。     

Measuring radar cross section at short distance

Radar cross sections (RCS) must be measured at large distance. We exclude here the special near-field methods. The distance (R) must be so large that different RCS contributions are added in the same way as at infinite distance. This leads to the ruleR > 2D^{2}/lambdaif the target cross range is confined withinpm D/2and a phase error ofpi /4is tolerated. It is shown, however, that if the RCS is measured as a function of an angle and is low-pass filtered with a cut off period ofphi_{c}(radians), the distance requirement could be changed toR > 4Dphi^{-1}_{c}(1 - lambda/2phi_{c}D)). All RCS measurements at such distances give approximately the same result after low-pass filtering. We assume that a set of isotropic point scatterers, accurately describes the target.     

扩频码速率异步时直扩系统码分多址能力

直接序列扩频码分多址系统是目前应用最广泛的扩频系统,影响系统容量的主要因素是系统内多址信号的干扰。分析了采用Gold码的码速率异步直扩系统多址干扰,对扩展积分周期和单一积分周期均进行了数值仿真。仿真结果表明,码速率异步的Gold序列互相关函数不再具有三值特性;随着积分长度的扩展,互相关函数的统计值逐渐递减,即多址干扰减小;多址干扰与码偏移量大小有关,在某些特定码偏移量,积分长度为最小公倍数周期时,互相关函数接近为单值,而这些码偏移量正负对称出现;积分长度为单一周期时,多址干扰随码偏移量的变化趋势与扩频码长度无关;在相同码偏移量的情况下,随着扩频码的长度增加而减小。     

The scattering cross section of a composite cylinder, geometric optics

The optical analogue of the scattering cross section of a composite cylinder is developed from a representation of the forward scattered amplitude as a continuous spectrum of radial eigenfunctions. The Debye approximation for the Hankel functions, which is valid when their arguments are large compared to the order, leads to a series of integrals which can be evaluated asymptotically by the method of stationary phase. The final result, for a certain range of parameters, is a diffraction correction plus a double sum of terms, each of which can be interpreted as an optical ray. It is shown that if the angular displacement between the incoming and scattered ray directions is(2m + 1)pi, the ray must have been reflected at the conducting core of the cylinder at least2m + 1times. After the parameter ranges to which these results apply were determined, the nonlinear equations for the ray angles were solved on a large-scale digital computer and the scattering cross section of a number of composite cylinders was calculated as a function of frequency. The results are presented graphically.     

The autoresonant peniotron with a quadrupole interaction circuit

In the autoresonant peniotron interaction, all of the electrons will be able to give almost all of their kinetic energy to an electromagnetic wave, resulting in a conversion efficiency of nearly 100%, if the condition of V_p=C is satisfied in an interaction circuit and the initial velocity ratio of electrons is correctly given as a function of the electron kinetic energy. A quadrupole circuit is proposed in which the above circuit condition is usually satisfied and the RF electric field distribution in a cross section is suitable for the peniotron interaction at the fundamental cyclotron frequency. The design procedure for the test tube with the circuit and some simulation results concerned with the tube's operation are described     

掺镱光纤激光器温度特性分析

温度对于光纤激光器的影响是多方面的,着重对光纤吸收截面、发射截面及激光器激射波长的温度特性进行了深入的研究,更加精确、全面地描述温度对光纤激光器系统的影响。当温度变化时,掺镱光纤各子能级上的粒子数分布发生变化,从而导致相应的吸收截面和发射截面发生变化。通过拟合方法可以得到光纤吸收截面与温度的关系。并利用任意温度下,吸收截面与发射截面的特定关系式,得到发射截面在各温度点上的取值。进一步推导出了激射波长与工作温度、光纤长度、腔的损耗、掺杂浓度等系统参数的关系;并将不同工作温度下激射波长的计算结果与实验结果比较,得到两种方法下的相似结论。     

不同衬底材料对光刻胶剖面的影响

文章研究了在127mm硅片上分别生长金属铝和二氧化硅氮化硅叠两种IC常用材料作为衬底对光刻胶形貌的影响,其造成光刻胶形貌差的原因是金属底部反射率高导致光刻胶侧面曝光和入射光通过二氧化硅氮化硅叠层厚度的光程差正好为光源波长的整数倍,从而导致光刻胶底部干涉光同相位。通过增加底部抗反射层和调整最佳膜层厚度解决了在这两种衬底材料下光刻胶形貌差的问题。     

Synthesis of an in-line prototype filter with two transmission zeros without cross couplings

This letter describes a method for synthesizing a general in-line prototype filter presenting one or two transmission zeros without using cross couplings; the basic topology is constituted by resonators coupled through inverters, with input and/or output taken at the second and/or last but one resonators. In this case, the first and last resonators, tuned at frequencies in the stopband, produce two zeros in the transfer function. It is shown that, even if it is not possible to exactly synthesize this structure with extracted poles techniques, an approximated design procedure can be derived; the procedure is based on the synthesis of a low pass prototype with multiple couplings starting from source and/or load, followed by suitable network transformations. This design technique can be easily implemented in case of classical combline or interdigital filters.     

Axial cross polarization in reflector antennas with surface imperfections

Expressions for the probability density function and mean of boresight cross polarization field intensity in terms of the rms surface errorepsilonare derived. It is shown that for small errors the mean on-axis cross polarization field intensity is directly proportional to the rms surface error. For relatively large errors (epsilon > 0.04 lambda) forward cross polarization is proportional to the square root of (1 - exp (-2sigma^{2})) wheresigmais the rms phase error. It is also shown that forward cross polarization is proportional to the correlation diameter and is a function of the polarization efficiency. Experimental measurements are revealed and results are compared with theoretical findings.     

平顶光谱响应的光学交叉复用滤波器

提出了一种设计光学交叉复用滤波器interleaver的新结构。该结构采用具有环形波导的单级MZ干涉仪设计而成。比较3级、5级及7级interleaver的功率透射谱发现,级次越高平顶效果越好;同时通带和阻带越陡,越接近方波。结果表明,只要给出期望得到的这种结构的椭圆半谱带滤波器交叉口的传递函数．便可以得到相应的设计参数;随着级数的增加其功率透射谱具有接近方波的平顶效果,适宜设计interleaver。     

The potential performance gain in using spectral information inpassive detection/localization of wideband sources

We address the problem of detecting the presence of wideband point sources and/or estimating their location using data collected by an array of sensors. This passive localization problem is typical to applications where the radiated signals do not carry information and are of no interest. However, knowledge of their waveshape, or their cross spectral matrix, is essential for applying optimal/sub-optimal detection/localization algorithms. In this paper, we present results of a study in which we compare the optimal procedures for detection/localization and their performance to suboptimal procedures that use no spectral information or only partial spectral information. We show that if the number of sensors in the array is larger than the number of sources to be localized (or detected), then the performance gain of the optimal procedures is potentially significant mainly in conditions of small separation and/or high correlation between sources. The performance gain is also a function of the spectrum: it is potentially higher if the sources are known to be correlated and if their spectra is not smooth. If, however, the number of sources is smaller than the number of sensors, then the role of the spectral information in improving detection/localization performance becomes major: only the use of spectral prior enables reliable localization of more sources than sensors