Second-order recursive digital-filter element for poles near the unit circle and the real z axis

An arrangement of a 2nd-order element for recursive digital filters is described which is particularly suitable when the desired poles are close to the unit circle and the real z axis in the z plane. Details are given for implementing the element using a single `multiply-and-add? arithmetic unit.     

Faster image template matching in the sum of the absolute value ofdifferences measure

Given an mxm image I and a smaller nxn image P, the computation of an (m-n+1)x(m-n+1) matrix C where C(i, j) is of the form C(i,j)=Sigma(k=0)(n-1)Sigma(k'=0) (n-1)f(I(i+k,j+k'), P(k,k')), 0=/相似文献   

Stability Criteria for Tunnel-Diode Amplifiers (Correspondence)

A tunnel-diode amplifier is stable when the amplifier network is reduced to an arbitrary single loop and the equation given by the sum of the impedances around this loop equal to zero [/spl Sigma/Z(P)=0 where p= /spl gamma/ +j/spl omega/ ] has no solution in the right-half plane (/spl gamma/>0). This is equivalent to the requirement that the system determinant shall have no zeros in the right-half plane. Several authors have used this criterion. To determine analytically whether /spl Sigma/Z(p) has any positive zeros is very laborious if at all possible for many practical amplifier configurations.     

高速光纤通信系统中PMDE的设计与应用

文章用琼斯传输矩阵法研究了"偏振控制器+保偏光纤"模型仿真器的一阶偏振模色散(PMD)、二阶平行分量、二阶垂直分量及二阶PMD合矢量的统计特性.仿真器的段数越多,其一阶、二阶PMD的统计特性就越接近理论曲线,综合经济因素得出:实验室仿真一阶、二阶PMD特性时采用"3PC+3PMF"模型最为合适.这一结论给下一步的PMD补偿提供了基础.     

On the refractive properties of media with poles or zeros in the index of refraction

The refractive properties of inhomogeneous fibers are examined with emphasis being placed on the limiting situation where the index of refraction possesses poles or zeros. If, e.g., the index of refraction isn(xi) = xi^{m}, xi = r/a, whereais the radius of the fiber andman arbitrary constant, it is found that energy integrability is satisfied ifm > -1. Whenm leq -1energy infinities occur. The ray behavior of such media is examined in terms of geometrical optics, and corrections to geometrical optics are obtained by an asymptotic analysis of the exact solution. Form > 0, the lens is of the diverging type, and when the angle of incidence isalpha = 0, geometrical optics predicts that rays "reflect" at various angles from the origin (depending on the value ofm). Whenm < 0, rays "wrap" around the origin several times with a zero radius of curvature before they leave the lens (alpha = 0). For-1 < m < -frac{1}{2}, it is found that whenalpha= [(2m + 1)/2m] picaustics occur (alpha = 0, pi/2excluded). Pictorial diagrams show the behavior of these caustics and the correction coefficients to geometrical optics are obtained.     

非对称多模量子叠加态光场的等幂高次和压缩

根据量子力学中的态叠加原理,构造了由多模复共轭相干态|{zj(a)*}>q和多模复共轭相干态|{zj(b)*}>q的相反态|{-zj(b)*}>q的线性叠加所组成的非对称两态叠加多模量子叠加态光场|ψ(2)>q,利用多模压缩态理论研究了态|ψ1f(2)>q的等幂高次和压缩特性,结果表明: 1)当Rj(a)=Rj(b)和ψj(a)-ψj(b)=±(2k 1)π(k=0,1,2,3……),态|ψ1f(2)>q的两个正交相位分量均处于N-H最小测不准态的结果;2)当Rj(a)=Rj(b)=Rj和ψj(a)=ψj(b)=ψj,ψ态|1f(2)>q的等幂高次和压缩与文献3的结果相似; 3)当Rj(a)≠Rj(b)=Rj和ψj(a)=ψj(b)=ψj,且和满足一定条件时,无论qN为奇数还是偶数,态|ψ1f(2)>q的两个正交相位分量均可分别呈现周期性变化的等幂高次和压缩效应,但qN为奇数时的压缩深度大于qN为偶数时的压缩深度。     

Weight enumerator for second-order Reed-Muller codes

In this paper, we establish the following result. Theorem:A_i, the number of codewords of weightiin the second-order binary Reed-Muller code of length2^mis given byA_i = 0unlessi = 2^{m-1}or2^{m-1} pm 2^{m-l-j}, for somej, 0 leq j leq [m/2], A_0 = A_{2^m} = 1, and begin{equation} begin{split} A_{2^{m-1} pm 2^{m-1-j}} = 2^{j(j+1)} &{frac{(2^m - 1) (2^{m-1} - 1 )}{4-1} } \ .&{frac{(2^{m-2} - 1)(2^{m-3} -1)}{4^2 - 1} } cdots \ .&{frac{(2^{m-2j+2} -1)(2^{m-2j+1} -1)}{4^j -1} } , \ & 1 leq j leq [m/2] \ end{split} end{equation} begin{equation} A_{2^{m-1}} = 2 { 2^{m(m+1)/2} - sum_{j=0}^{[m/2]} A_{2^{m-1} - 2^{m-1-j}} }. end{equation}     

Janus MSiGeN4 (M =Zr and Hf) monolayers derived from centrosymmetric β-MA2Z4:A first-principles study

A two-dimensional (2D) MA2Z4 family with α andβ phases has been attracting tremendous interest,the MoSi2N4 and WSi2N4 of which have been successfully fabricated (Science 369,670 (2020)).Janus monolayers have been achieved in many 2D families,so it is interesting to construct a Janus monolayer from the MA2Z4 family.In this work,Janus MSiGeN4 (M =Zr and Hf)monolayers are predicted fromβ-MA2Z4,which exhibit dynamic,mechanical and thermal stabilities.It is found that they are in-direct band-gap semiconductors by using generalized gradient approximation (GGA) plus spin-orbit coupling (SOC).With biaxi-al strain a/a0 from 0.90 to 1.10,the energy band gap shows a nonmonotonic behavior due to a change of conduction band min-imum (CBM).A semiconductor to metal transition can be induced by both compressive and tensile strains,and the phase trans-formation point is about 0.96 for compressive strain and 1.10 for tensile strain.The tensile strain can change the positions of CBM and valence band maximum (VBM),and can also induce the weak Rashba-type spin splitting near CBM.For MSiGeN4 (M =Zr and Hf) monolayers,both an in-plane and out-of-plane piezoelectric response can be produced,when a uniaxial strain in the basal plane is applied,which reveals the potential as piezoelectric 2D materials.The high absorption coefficients in the visible light region suggest that MSiGeN4 (M =Zr and Hf) monolayers have potential photocatalytic applications.Our works provide an idea to achieve a Janus structure from the MA2Z4 family,and can hopefully inspire further research exploring Janus MA2Z4 monolayers.     

掺钪AlN材料特性及HBAR器件性能研究

该文基于掺钪AlN薄膜制备了高次谐波体声波谐振器(HBAR),研究了钪(Sc)掺杂浓度对AlN压电薄膜材料特性及器件性能的影响。研究表明,当掺入Sc的摩尔分数从0增加到25%时,压电应力系数e₃₃增加、刚度 下降,导致Al₁-_xSc_xN压电薄膜的机电耦合系数 从5.6%提升至15.8%,从而使HBAR器件的有效机电耦合系数 提升了3倍。同时,当Sc掺杂摩尔分数达25%时,Al₁-_xSc_xN(x为Sc掺杂摩尔分数)压电薄膜的声速下降13%,声学损耗提高,导致HBAR器件的谐振频率和品质因数降低。     

An interior point iterative maximum-likelihood reconstruction algorithm incorporating upper and lower bounds with application to SPECT transmission imaging

The algorithm we consider here is a block-iterative (or ordered subset) version of the interior point algorithm for transmission reconstruction. Our algorithm is an interior point method because each vector of the iterative sequence [x(k)], k = 0, 1, 2, ... satisfies the constraints a(j) < x(j)k < b(j), j = 1, ..., J. Because it is a block-iterative algorithm that reconstructs the transmission attenuation map and places constraints above and below the pixel values of the reconstructed image, we call it the BITAB method. Computer simulations using the three-dimensional mathematical cardiac and torso phantom, reveal that the BITAB algorithm in conjunction with reasonably selected prior upper and lower bounds has the potential to improve the accuracy of the reconstructed attenuation coefficients from truncated fan beam transmission projections. By suitably selecting the bounds, it is possible to restrict the over estimation of coefficients outside the fully sampled region, that results from reconstructing truncated fan beam projections with iterative transmission algorithms such as the maximum-likelihood gradient type algorithm.     

Reliability of linear consecutively-connected systems withmultistate components

A linear consecutively-connected system with multistate components (LCCSMC) consists of n+2 linear ordered statistically independent multistate components C_i, i∈[0,n], and the sink C_n+1 (which is absolutely reliable in a certain sense). System failure is caused by the C_i. If C_i is in state 0 then it is failed, if it is in the state j (1⩽j⩽k_j for a given k_j) then there are paths from C_i to the next min(j,n-i+1) components. The system fails if there is no path from C₀ to C_n+1. This system generalizes the linear consecutive-k-out-of-n:F system and the consecutively-connected system of Shanthikumar (1987). The paper gives recursive algorithms for determining the LCCSMC reliability     

环Fq+uFq+…+uk-1Fq上一类重根常循环码

记R=Fq+uFq++uk-1Fq,G=R[x]/,且是R中可逆元。定义了从Gn到Rtn的新的Gray映射,证明了J是G上长为n的线性的x-常循环码当且仅当(J)是R上长为tn的线性的-常循环码。使用有限环理论,获得了环R上长为pe的所有的(u-1)-常循环码的结构及其码字个数。特别地,获得了环F2m+uF上长为2e的(u-1)-常循环码的对偶码的结构及其码字个数。推广了环Z2a根负循环码的若干结果。     

Scattering Coefficients for Wall Impedance Changes in Waveguides

The Wiener-Hopf tectilque is used to obtain an exact solution to a two-dimensional scattering problem. In the problem solved, an incident TE/sub 10/ mode, traveling from z= -/spl infin/ in the positive z direction, is confined by infinite bounding planes; these planes have infinite conductivity for z<0 and an impedance Z/sub 1/, for z>0. The scattering from the junction at z=0 gives rise to reflection and transmission coefficients that are exactly determined. An approximate solution for the reflection coefficients is also given when the TE/sub 10/ mode is incident from the opposite direction. Finally, a table is presented which lists some transmission and reflection coefficients for rectangular and circular waveguides with discontinuities in the wall impedances.     

On generalizations of the maximum power transfer problem

The necessary conditions for maximum power transfer to the outputs of a multiport are discussed. The condition Z = Z0^*is sufficient. A solution to this problem is not generally unique, because the matrix Z must satisfy the matrix equation Z(Z0+ Z0^*)^-1E0= - Z0(Z0+ Z0^*)^-1E0+ E0. When the power transfer is maximum, only the total power of the equivalent sources is equally divided between the "passive" multiport and the ports.     

Conservative Input–State–Output Systems with Evolution on a Multidimensional Integer Lattice

A fundamental object of study in both operator theory and system theory is a discrete-time conservative system (variously also referred to as a unitary system or unitary colligation). In this paper we introduce three equivalent multidimensional analogues of a unitary system where the time axis , d>1, is multidimensional. These multidimensional formalisms are associated with the names of Roesser, Fornasini and Marchesini, and Kalyuzhniy–Verbovetzky. We indicate explicitly how these three formalisms generate the same behaviors. In addition, we show how the initial-value problem (including the possibility of initial conditions at infinity) can be solved for such systems with respect to an arbitrary shift-invariant sublattice as the analogue of the positive-time axis. Some of our results are new even for the d=1 case.First online version published in May 2005*The authors were supported in part by a grant from the US-Israel Binational Science Foundation.     

A universal chart for use in relating ionospheric absorption to phase path and group path

The absorption of a radio wave in the ionosphere can be approximated byA = frac{omega}{c}frac{1}{2}intfrac{Z(mu' - mu)}{1 + g} cos alpha ds, where the integral is along the ray that exists when the normalized collision frequencyZ = 0, mu'andmuare the group and phase refractive indices, respectively, andalphathe angle between the wave normal and ray direction. Graphs are presented from whichgcan be obtained for any values of the ionospheric plasma parametersXandY.     

基于遗传算法的非对称多波束反射阵天线设计

针对传统方法设计的多波束反射阵天线增益低、波束偏移大、要求波束对称等问题,通过引入全局优化算法中的遗传算法对反射阵相位分布进行优化,以完成非对称多波束反射阵天线设计。为验证其有效性,设计并制作了一副Ku频段,波束指向分别为θ1=25°,1=0°和θ2=15°,2=180°的非对称双波束反射阵天线。测试和仿真结果较吻合,天线在中心频点的增益为26.03dBi,效率达到28.04%,1dB增益带宽和3dB轴比带宽均能覆盖11.3~12.3GHz(8.3%),实测波束指向为θ1=24.3°,1=0°和θ2=15°,2=180°,波束偏移0.7°。结果表明遗传算法能有效完成非对称多波束反射阵天线设计。     

An equivalent circuit for microwave noise at the potential minimum

It has been suggested that an inductive element should be added to Watkins RC equivalent circuit for the microwave noise current fluctuations at the potential minimum of a diode, and that this added element gives closer agreement with more recent work which shows a pronounced peak in noise current near the plasma resonance,a = frac{1}{2}. This paper presents an approximate analytical argument for the inclusion of an inductive element, based on the density-function method of analysis, which predicts the proper value for the inductance and yields a curve of reduction factor vs frequency in agreement with more detailed theories. The value of the inductance is such as to resonate with the capacitance of the potential minimum ata = frac{1}{2}. A discussion of the linearity of the potential minimum and of the idealized potential-minimum model is also included.