基于Durbin与Burg算法的AR SαS有色噪声α谱估计

稳定分布可更好地描述实际中所遇到的具有显著脉冲特性的随机噪声。在简要介绍稳定分布统计特性的基础上,描述了稳定分布的谱表示。为了对AR SαS过程进行α谱估值,通过对广义Yule-Walker方程进行分析,借鉴杜宾推算法和Burg算法推导了一种求解广义Yule-Walker方程的新方法。仿真结果表明,该方法能够较为准确地估计出AR模型参数,且能准确地估计出AR SαS过程的α谱。     

基于FLOC的ARMA SαS模型α谱估计方法

分析了基于分数低阶矩（FLOM）估计ARMA SαS模型参数的不足,根据分数低阶协方差（FLOC）的概念,提出了一种基于分数低阶协方差系数估计ARMA SαS模型参数的方法。在此基础上,给出了ARMA SαS模型的α谱估计。通过对给定ARMA SαS模型的α谱估计、α稳定分布噪声中正弦信号的估计与分辨进行仿真,详细比较了基于FLOM的ARMA SαS模型α谱估计和基于FLOC的ARMA SαS模型α谱估计的性能。结果表明,α值较小时,基于FLOC的ARMA SαS模型α谱估计的性能明显优于基于FLOM的ARMA SαS模型α谱估计。     

基于分数低阶协方差的AR SαS模型α谱估计

根据自回归(AR) SαS模型的α谱,分析了基于分数低阶矩(FLOM)法估计AR SαS模型参数的不足.提出了一种基于分数低阶协方差(FLOC)的AR SαS模型参数估计方法,并给出了基于FLOC的AR SαS模型α谱方法.分别对AR SαS模型参数的估计、α稳定分布噪声中单一正弦信号的估计和两个正弦信号的分辨进行了仿真.仿真结果表明,基于FLOC的AR SαS模型α谱估计方法对于不同的α值均具有较好的韧性.特别是在α值较小,即α稳定分布噪声概率密度函数(PDF)拖尾比较严重时,本文所提出的基于FLOC的AR SαS模型α谱估计方法,其性能明显优于基于FLOM的AR SαS模型α谱估计方法.     

α-SiO_xN_y薄膜中分立能级的光发射

采用 PECVD法制备了 α- Si Ox Ny 薄膜 ,观察到两组分立能级的强荧光发射 ,一组位于紫外光波段 ,由三个可分辨的发射峰组成 ,波长分别为 330、340和 345nm;另一组位于红光波段 ,由两个发射峰组成 ,波长分别为 735nm和 745nm.发射峰依赖于薄膜中氧和氮的同时存在 ,其强度首先随薄膜中其含量的增加而增强 ,达到饱和值后 ,随着其含量的进一步增加而下降 .这表明发射峰可能起源于 O- Si- N结合而形成的发光中心 .     

α-SiOxNy薄膜中分立能级的光发射

采用PECVD法制备了α-SiOxNy薄膜,观察到两组分立能级的强荧光发射,一组位于紫外光波段,由三个可分辨的发射峰组成,波长分别为330、340和345nm;另一组位于红光波段,由两个发射峰组成,波长分别为735nm和745nm.发射峰依赖于薄膜中氧和氮的同时存在,其强度首先随薄膜中其含量的增加而增强,达到饱和值后,随着其含量的进一步增加而下降.这表明发射峰可能起源于O-Si-N结合而形成的发光中心.     

Hg_(1-x)Cd_xTe光电二极管反向漏电机制分析

分析了可能导致Hg_(1-x)Cd_xTe P-N结反向软击穿的若干漏电机制。位于结区中的深能级和沉淀及混晶材料中的组份涨落和杂质浓度涨落等都可能产生过量隧道电流。用一些理论模型对实验数据进行了拟合和比较。对于我们的离子注入N~+-P结,P型材料的高补偿度可能是导致漏电的主要原因。     

低阶α稳定分布噪声下诱发电位潜伏期变化估计的一种新方法

本文提出了一种低阶α稳定分布噪声下诱发电位潜伏期变化估计的新算法.新算法克服了原有算法需估计伴随噪声的特征指数α的缺点,并且将现有算法的适用范围加以扩展到伴随噪声的特征指数为0＜α≤2的场合.本文在理论上对新算法的收敛性进行了证明,计算机仿真也表明新算法对于原有算法具有更好的鲁棒性.     

基于分数阶谱的频域广义白化滤波方法

在简要介绍稳定分布统计特性的基础上,描述了稳定分布的谱表示,提出了一种不同于二阶过程功率谱的共变谱密度概念及基于共变函数与共变谱密度的稳定分布白噪声的概念及其判断标准,对传统意义上的白噪声进行了广义化,并依据稳定分布的参数模型,论述了一种基于α谱的频域广义白化滤波方法。仿真实验表明,这种算法是一种在高斯和分数低阶α稳定分布噪声条件下具有良好韧性的白化滤波方法,是对传统的二阶统计量基础上的白化滤波方法的改造与推广。     

缺氧诱导因子1α对大鼠骨髓间充质干细胞核心结合因子α1表达的影响

目的：研究体外低氧实验中缺氧诱导因子1α（HIF-1α）对大鼠骨髓间充质干细胞核心结合因子α1（Cbfα1）表达的影响。方法：将体外培养的大鼠骨髓间充质干细胞分别置于常氧（含有5％c02的培养箱中）和低氧（含4％02、5％CO2和91％N2的三气培养箱中）中培养,分别于1d、3d、5d和7d用实时荧光定量PCR检测细胞内HIF-1α和CbfalmRNA的表达水平：用siRNA抑制细胞HIF-1αmRNA表达后用Westernblot法检测HIF-1α和Cbfal蛋白表达。结果：与常氧组相比,低氧组细胞HIF-1αanRNA的表达均增加（1d、3d、5d和7d：P〈0．05）,且3d达到最高峰;细胞CbfalmRNA的表达明显下降,3d尤为明显（P〈0．05）：低氧组细胞转染siRNA干扰HIF-1α表达后,能促进细胞内Cbfcd蛋白的表达（P〈0．05）。结论：低氧微环境抑制骨髓间充质千细胞的成骨向分化,细胞内HIF-1α反向调节Cbfal的表达。     

α稳定分布综述

介绍了a稳定分布的基本理论、理论发展动因以及它的主要应用,并着重对几种主要的参数估计方法进行了论述,介绍了几种典型的参数估计方法.     

The Zak transform and some counterexamples in time-frequencyanalysis

It is shown how the Zak transform can be used to find nontrivial examples of functions f, g∈L²(R) with f×g≡0≡F×G, where F, G are the Fourier transforms of f, g, respectively. This is then used to exhibit a nontrivial pair of functions h, k∈L²(R), h≠k, such that |h|=|k|, |H |=|K|. A similar construction is used to find an abundance of nontrivial pairs of functions h, k∈L² (R), h≠k, with |A_h |=|A_k| or with |W_h|=|W _k| where A_h, A_k and W_h, W_k are the ambiguity functions and Wigner distributions of h, k, respectively. One of the examples of a pair of h, k∈L²(R), h≠k , with |A_h|=|A_k| is F.A. Grunbaum's (1981) example. In addition, nontrivial examples of functions g and signals f₁≠f₂ such that f₁ and f₂ have the same spectrogram when using g as window have been found     

Bounds for abnormal binary codes with covering radius one

The normality of binary codes is studied. The minimum cardinality of a binary code of length n with covering radius R is denoted by K(n,R). It is assumed that C is an (n,M)R code, that is, a binary code of length n with M codewords and covering radius R. It is shown that if C is an (n,M)1 code, then it is easy to find a normal (n ,M)1 code by changing C in a suitable way, and that all the optimal (n,M)1 codes (i.e. those for which M=K(n,1)) are normal and their every coordinate is acceptable. It is shown that if C is an abnormal (n,M) code, then n⩾9, and an abnormal (9118)1 code which is the smallest abnormal code known at present, is constructed. Lower bounds on the minimum cardinality of a binary abnormal code of length n with covering radius 1 are derived, and it is shown that if an (n,M)1 code is abnormal, then M⩾96     

Maximum-rank array codes and their application to crisscross errorcorrection

A μ-[n×n,k] array code C over a field F is a k-dimensional linear space of n×n matrices over F such that every nonzero matrix in C has rank ⩾μ. It is first shown that the dimension of such array codes must satisfy the Singleton-like bound k⩽n(n-μ+1). A family of so-called maximum-rank μ-[n×n,k=n ( n-μ+1)] array codes is then constructed over every finite field F and for every n and μ, 1⩽μ⩽n . A decoding algorithm is presented for retrieving every Γ∈C, given a received array Γ+E, where rank (E)+1⩽(μ-1)/2. Maximum-rank array codes can be used for decoding crisscross errors in n×n bit arrays, where the erroneous bits are confined to a number t of rows or columns (or both). This construction proves to be optimal also for this model of errors. It is shown that the behavior of linear spaces of matrices is quite unique compared with the more general case of linear spaces of n×n. . .×n hyper-arrays     

Limiting efficiencies of burst-correcting array codes

The author evaluates the limiting efficiencies e(-S ) of burst-correcting array codes A(n₁,n₂, -s) for all negative readouts -s as n₂ tends to infinity and n₁ is properly chosen to maximize the efficiency. Specializing the result to the products of the first i primes donated by s_i (1⩽i<∞), which are optimal choices for readouts, gives the expression e(-s_i)=(2p_i+1 -2)/(2p_i+1-1) where p_i+1 is the next prime. Previously, it was known only that e(-2)⩾4/5 and e(-1)⩾2/3. This result reveals the existence of burst-correcting array codes with efficiencies arbitrarily close to 1 and with rates also arbitrarily close to 1     

New minimum distance bounds for certain binary linear codes

Let an [n, k, d]-code denote a binary linear code of length n, dimension k, and minimum distance at least d. Define d(n, k) as the maximum value of d for which there exists a binary linear [n, k, d]-code. T. Verhoeff (1989) has provided an updated table of bounds on d(n, k) for 1⩽k⩽n⩽127. The authors improve on some of the upper bounds given in that table by proving the nonexistence of codes with certain parameters     

On the competitive optimality of Huffman codes

Let X be a discrete random variable drawn according to a probability mass function p(x), and suppose p(x), is dyadic, i.e., log(1/p(x)) is an integer for each x. It is shown that the binary code length assignment l(x)=log(1/p(x)) dominates any other uniquely decodable assignment l'(x) in expected length in the sense that El(X)<El'(X), indicating optimality in long run performance (which is well known), and competitively dominates l'(x), in the sense that Pr{ l (X)<l'(X)}>Pr{l ( X)>l'(X)}, which indicates l is also optimal in the short run. In general, if p is not dyadic then l=[log 1/p] dominates l'+1 in expected length and competitivity dominates l'+1, where l' is any other uniquely decodable code     

Balancing sets of vectors

For n>0, d⩾0, n≡d (mod 2), let K(n, d) denote the minimal cardinality of a family V of ±1 vectors of dimension n, such that for any ±1 vector w of dimension n there is a v∈V such that |v- w|⩽d, where v-w is the usual scalar product of v and w. A generalization of a simple construction due to D.E. Knuth (1986) shows that K(n , d)⩽[n/(d+1)]. A linear algebra proof is given here that this construction is optimal, so that K(n, d)-[n/(d+1)] for all n≡d (mod 2). This construction and its extensions have applications to communication theory, especially to the construction of signal sets for optical data links     

Asymptotic performance of M-ary orthogonal modulation ingeneralized fading channels

The asymptotic (M→∞) probability of symbol error P_e,_m for M-ary orthogonal modulation in a Nakagami-m fading channel is given by the incomplete gamma function P(m, mx) where x=In 2/(E_b/N₀) and E_b is the average energy per bit. For large signal-to-noise ratio this leads to a channel where the probability of symbol error varies as the inverse mth power of E_b/N₀. These channels exist for all m⩾1/2. The special case of m=1 corresponds to Rayleigh fading, an inverse linear channel     

On the Hamming distance properties of group codes

Under certain mild conditions, the minimum Hamming distance D of an (N, K, D) group code C over a non-abelian group G is bounded by D⩽N -2K+2 if K⩽N/2, and is equal to 1 if K>N/2. Consequently, there exists no (N, K, N-K+1) group code C over an non-abelian group G if 1<K<N. Moreover, any normal code C with a non-abelian output space has minimum Hamming distance equal to D=1. These results follow from the fact that non-abelian groups have nontrivial commutator subgroups. Finally, if C is an (N, K, D) group code over an abelian group G that is not elementary abelian, then there exists an (N, K, D) group code over a smaller elementary abelian group G'. Thus, a group code over a general group G cannot have better parameters than a conventional linear code over a field of the same size as G     

A storage-efficient method for solving banded Toeplitz systems

A method is presented for solving the banded Toeplitz system Tx=y by decomposing T into its asymptotic upper and lower triangular factors (which are banded and Toeplitz) and a rank-p correction matrix, where p is the bandwidth of T. This way of representing T requires only O(p²) words of storage and allows computation of x in O(2Np) operations. A similar method is presented for the case in which T is bi-infinite and y is zero outside a finite region