Mismatched filtering of periodic and odd-periodic binary arrays

Arrays with good correlation properties are required for coded-aperture imaging, as well as for other applications of two-dimensional signal processing. Since binary arrays with perfect periodic autocorrelation functions exist for only a few sizes, mismatched filtering is discussed. Mismatched filtering entirely suppresses any sidelobes of the periodic autocorrelation function at the expense of a slightly reduced signal-to-noise ratio. New construction methods for binary arrays are presented for which this loss, with respect to periodic or odd-periodic correlation, converges to zero with an increasing array size.     

Hexagonal binary arrays with perfect correlation

Two-dimensional binary signals (arrays) with good autocorrelation properties are needed for coded-aperture imaging systems. In many astrophysical instruments, circular detectors with hexagonally packed detector elements are used, such that hexagonal coded apertures are often preferable to rectangular ones. A general method for folding a one-dimensional sequence into a hexagonal array is presented, by which the periodic or odd-periodic correlation properties of the original sequence are preserved. This method is applied to a known family of sequences with perfect odd-periodic correlation, yielding a new family of almost-binary and odd-perfect-or binary and almost odd-perfect-hexagonal arrays with optimum properties for coded-aperture imaging. The new odd-perfect arrays have near-uniform side lengths and exist for many more sizes than known families of even-periodic hexagonal arrays with good imaging properties.     

New Design of Quaternary Sequences

 We construct new families of quaternary periodic sequences having good autocorrelation properties that are useful for the synchronisation of messages in multiple access communications systems. The design of these quaternary periodic sequences makes use of a general construction based on the Gray map starting from couples of binary words with particular weight or correlation properties. Received: June 26, 2000; revised version: January 21, 2002     

Bent互补函数族的构造及推广

对Bent互补二元函数族和并元互补二元序列族的等价关系做了新的刻画,简化了一个已有结果的证明,并把Bent互补函数族推广到了Zq上。同时利用Khoo等给出的Plateaued函数,构造了新的Bent互补函数族。     

戈尔德(gold)序列在声学多输入多输出系统测量中的应用

在多输入输出声学系统中,任意一对输入输出之间的脉冲响应在很多情况下需要同步测量。伪随机序列由于具有优良的相关特性从而在多输入、输出系统测量中得到了应用。运用具有优良相关特性的互逆最大长度线性移位寄存器序列对(m序列对)分别作为输入激励,然后计算两输出和输入m序列的相关,可以同步获得双输入输出系统的四个脉冲响应。当被测系统的输入多于两个时,互为优选的m序列对数目限制了它的应用。由互逆特征m序列对逐次经过τ倍间隔移位、模二加可以生成一个大的戈尔德(gold)序列集。该gold序列集中的序列除了具有和m序列相似的相关特性,即每一序列具有近似尖脉冲的自相关和两两序列间较小的互相关值外,还具有比m序列集多得多的独立优选对数。这些特性使gold序列成为同步多输入输出系统测量的首选激励信号。大量的仿真实验验证了gold序列用于声学多通道测量的可行性和有效性。     

Adaptive binary joint transform correlator for image recognition

Our research has shown that the autocorrelation peaks of a binary joint transform correlator are affected by input scenes' backgrounds. An adaptive method is proposed to overcome this problem. The image of interest is first extracted from the background based on the position of the highest correlation peak of the input and reference images. The extracted image is then correlated with the reference to obtain the final correlation peak. Numerical simulations showed that the final autocorrelation peak is the maximum constant for a specified reference image.     

Gold Binary‐Structured Arrays Based on Monolayer Colloidal Crystals and Their Optical Properties

A simple and flexible route is presented to fabricate a gold binary‐structured ordered array by one step based on non‐shadow deposition on a plasma etching‐induced dualistic monolayer colloidal crystal. Such a Au binary‐structure array is built of hexagonally arranged nanoshells and nanorings which stand between two adjacent nanoshells. Six gold nanorings surround each nanoshell. The obtained arrays exhibit both the controllable surface‐plasmon‐resonance (SPR) properties of Au nanoshells and the strong electromagnetic‐field‐enhancement effects of Au nanorings, with the high structural stability of ordered arrays, and show promising potential as the substrate of surface‐enhanced Raman scattering (SERS)‐based devices. The method could also be suitable for fabrication of other material binary‐structured arrays. This study is important in designing and fabricating basal materials for the next generation of multifunctional nanostructured devices.     

Folding of Continuous Fibre Thermoplastic Composites

Thermoplastic composites with continuous fibres are attractive construction materials because of their good specific mechanical properties and their possibility to be processed very rapidly. An extremely fast processing method is folding of sheet material. Folding can be performed by local heating of a sheet along a line. Heating is done to a temperature, well above the softening or melting point of the thermoplastic polymer. Subsequent folding along the heated line requires very low forces. The folded geometry becomes permanent after cooling below the softening point of the polymer. Unfortunately, folding causes microbuckling of the reinforcing fibres at the compression side of the fold causing a severe reduction in the local strength. The present report describes a method for the folding of thermoplastic composites, which controls the direction of fibre microbuckling. The method results in a smaller strength reduction. The folding equipment is designed in such a way that microbuckling of the fibres occurs in a direction in the local plane of the sheet rather than being perpendicular to that plane. The result is a folded sheet with a reduction of about half of the original strength, as compared to a strength of only 15% of the original strength, which is typical for folds produced with more conventional means. In other words, the remaining strength is more then doubled using the new folding technology.     

选择逻辑函数的密码学性质

通过计算选择逻辑函数的Walsh循环谱和自相关函数，系统分析了选择逻辑函数的密码学性质。所得结论表明选择逻辑函数在变元个数较大的情况下具有理想的稳定性，能够抵抗最佳仿射（BAA）攻击，但是其“扩散”特性不够理想，在一定意义下不能有效地抗击差分攻击。讨论了与选择逻辑函数线性等价意义下满足严格雪崩准则或具有相关免疫性的逻辑函数构造问题。     

低信噪比环境下语音端点检测改进方法

针对语音端点检测在低信噪比环境下普遍存在检测性能急剧下降的问题,提出一种将调制域(时间-频率域)谱减法和自相关函数相结合的语音端点检测算法。该算法首先利用调制域谱减法较好的消噪能力来提高含噪语音的信噪比;然后根据语音和噪声的自相关函数的主峰最大值和次大值之比差异较大的特性,结合基于对数能量和自相关函数的端点检测方法对消噪后的语音进行端点检测。实验结果表明,该算法在低信噪比的环境下能取得较好的端点检测效果,并具有较好的稳健性。     

A New Thermodynamic Calculation Method for Binary Alloys：Part I：Statistical Calculation of Excess Functions

The improved form of calculation formula for the activities of the components in binary liquids and solid alloys has been derived based on the free volume theory considering excess entropy and Miedemaˊs model for calculating the formation heat of binary alloys.A calculation method of excess thermodynamic functions for binary alloys,the formulas of intregral molar excess properties and partial molar excess properties for solid ordered or disordered binary alloys have been developed.The calculated results are in good agreement with the experimental values.     

Generalized GMW Quadriphase Sequences Satisfying the Welch Bound with Equality

This paper gives new families of quadriphase sequences obtained from large linear complexity sequences over Z ₄ by making use of generalized permutation monomials over Galois rings. The construction of these sequences can be seen as a generalization of the binary GMW sequence construction and hence they are referred to as GGMW sequences over Z ₄. The GGMW families satisfy the Welch bound on inner products with equality and it is shown that the root mean square of all the crosscorrelations and out-of-phase autocorrelations (θ_rms), is approximately equal to the quantity ; L being the period of the sequences. However, θ_max, the maximum magnitude of periodic crosscorrelation and out-of-phase autocorrelation, deviates from the optimal value of . Computer results suggest that the number of crosscorrelation values which deviate from the optimal value of is small. The weight structure of these sequences is the same as those of m-sequences over Z ₄. The linear complexity (LC) of the sequences is computed using a generalized Blahuts theorem on the LC of sequences over Z ₄. Received: January 18, 1999; revised version: October 20, 1999     

Design and evaluation of a high data rate optical wireless system for the diffuse indoor channel using barker spreading codes and RAKE reception [optical wireless communications]

The performance of a high data rate optical wireless system (OWS) over the diffuse indoor infrared channel based on direct sequence spread spectrum (DSSS) techniques is highly sensitive to the properties of the aperiodic autocorrelation function and the spreading factor of the spreading sequence used. Ideally, the aperiodic autocorrelation function should have zero sidelobes in order to eliminate intersymbol interference caused by multipath propagation. In practice, such an ideal sequence does not exist in the binary field when data modulation is applied. For high data rates, a small spreading factor is desired in order to avoid an excessive system bandwidth. The family of Barker sequences is investigated in a DSSS-OWS. The Barker sequences are binary spreading sequences which exhibit small aperiodic autocorrelation values and short spreading factors. The system bit error rate (BER) performance is characterized on the diffuse indoor infrared channel when using RAKE reception. Results of BER against Eh/NQ are presented with data rate and spreading factor as parameters. The results demonstrate that of the seven Barker sequences existing, the length three Barker sequence {0 0 1} provides the best system design trade-off in respect of good BER performance and low implementation complexity.     

一种基于广义互相关的水声直扩信号检测方法

直扩信号因其低功率谱密度特性使得检测十分困难,针对传统自相关法在低信噪比条件下检测性能急剧下降的问题,在分析了直扩信号自相关特性的前提下,提出一种基于广义互相关估计的直扩信号检测方法.首先对接收信号分段并对相邻信号段分别进行广义互相关估计,估计结果采用二阶矩非相干积累,提取相关峰获得检测统计量,将检测统计量与门限比较,...     

Characterization of the basic statistical properties of very rough surfaces of transparent solids by immersion shearing interferometry

A new shearing-interferometry method is used to characterize the basic statistical properties of very rough surfaces of transparent solids. The mean level of these rough surfaces can be curved or flat. Using this method, one evaluates the root-mean-square values (standard deviations) of the heights and slopes of the surface irregularities. Moreover the values of autocorrelation lengths, autocorrelation functions, and one-dimensional height-distribution functions are also determined. The method is applied to a statistical analysis of rough flat or curved glass surfaces. The results from this method agree very well with those obtained with a stylus-type surface instrument and speckle contrast method.     

振动调频信号的循环平稳解调原理与实现方法

含有齿轮、滚动轴承等零部件的机械故障振动信号中，有一类信号称为频率调制信号（或称调相信号）。运用循环平稳分析理论，推导调频信号的循环自相关函数结果，并从理论上推导和分析了运用平方解调（或广义检波滤波解调）的方法实现对循环自相关函数的低频切片函数和高频切片函数进行解调的原理和方法，仿真验证理论推导正确，解调效果很好。最后通过对齿轮箱实测故障信号进行分析，验证该方法有很好的解调效果。     

Theory of Sample Surveys

Orthogonal arrays are used widely in manufacturing and high-technology industries for quality and productivity improvement experiments. For reasons of run size economy or flexibility, nearly-orthogonal arrays are also used. The construction of orthogonal or nearly-orthogonal arrays can be quite challenging. Most existing methods are complex and produce limited types of arrays. This article describes a simple and effective algorithm for constructing mixed-level orthogonal and nearly-orthogonal arrays that can construct a variety of small-run designs with good statistical properties efficiently.     

Flexible Photodetector Arrays Based on Patterned CH3NH3PbI3−xClx Perovskite Film for Real‐Time Photosensing and Imaging

The quest for novel deformable image sensors with outstanding optoelectronic properties and large‐scale integration becomes a great impetus to exploit more advanced flexible photodetector (PD) arrays. Here, 10 × 10 flexible PD arrays with a resolution of 63.5 dpi are demonstrated based on as‐prepared perovskite arrays for photosensing and imaging. Large‐scale growth controllable CH₃NH₃PbI_3?xCl_x arrays are synthesized on a poly(ethylene terephthalate) substrate by using a two‐step sequential deposition method with the developed Al₂O₃‐assisted hydrophilic–hydrophobic surface treatment process. The flexible PD arrays with high detectivity (9.4 × 10¹¹ Jones), large on/off current ratio (up to 1.2 × 10³), and broad spectral response exhibit excellent electrical stability under large bending angle (θ = 150°) and superior folding endurance after hundreds of bending cycles. In addition, the device can execute the functions of capturing a real‐time light trajectory and detecting a multipoint light distribution, indicating that it has widespread potential in photosensing and imaging for optical communication, digital display, and artificial electronic skin applications.     

Fiber-based multispeckle detection for time-resolved diffusing-wave spectroscopy: characterization and application to blood flow detection in deep tissue

We present a technique for the measurement of temporal field autocorrelation functions of multiply scattered light with subsecond acquisition time. The setup is based on the parallel detection and autocorrelation of intensity fluctuations from statistically equivalent but independent speckles using a fiber bundle, an array of avalanche photodiodes, and a multichannel autocorrelator with variable integration times between 6.5 and 104 ms. Averaging the autocorrelation functions from the different speckles reduces the integration time in diffusing-wave spectroscopy experiments drastically, thus allowing us to resolve nonstationary scatterer dynamics with single-trial measurements. We present applications of the technique to the measurement of arterial and venous blood flow in deep tissue. We find strong deviations both of the shape and characteristic decay time of autocorrelation functions recorded at different phases of the pulsation cycle from time-averaged autocorrelation functions.     

Gas sensing characteristics of MEMS gas sensor arrays in binary mixed-gas system

MOS gas sensor arrays based on MEMS gas sensor platforms were developed for the detection of carbon monoxide (CO), nitrogen oxides (NO_x) and ammonia (NH₃), and their gas sensing characteristics in binary mixed-gas system were investigated. Three gas sensing materials with nano-sized particles for these target gases, Pd–SnO₂ for CO, In₂O₃ for NO_x and Ru–WO₃ for NH₃ were synthesized using a sol–gel method. All the sensors showed good properties for their target gases at the optimum points for micro-heater operation. From the experimental data in MEMS gas sensor arrays in a binary mixed system, the gas sensing behavior and sensor response in mixed gas systems were scrutinized. The gas sensing behaviors to the mixed gas systems suggested that specific adsorption and selective activation of adsorption sites might occur in gas mixtures and offer the priority for the adsorption of specific gas. Thorough analysis of the sensing performance of the sensor arrays will make it possible to discriminate the components in gas mixtures as well as their concentrations.