Partial adaptivity for the large array

Most studies and experimental work in the past on the subject of adaptive arrays have been concerned with systems with, at most, a few tens of adaptive elements. In the study of the problems facing the next generation of ballistic missile defense radars, it has become clear that jamming poses a very serious threat. These radar systems typically contain as many as 3000 to 5000 elements per array face. The adaptive array technique is a likely candidate to aid in countering this threat. This paper examines the problem of configuring such a large array to provide partial adaptivity. A method of analysis is presented and the results of simulations and analysis are presented showing the effects of configuration, the effects of practical component tolerances, and the transient response characteristics of several candidate systems.     

Design of two-dimensional rectangular array beamformers withpartial adaptivity

This paper considers the problem of designing a two-dimensional (2-D) rectangular array beamformer with partial adaptivity. Using the eigenstructure of the signal data received by a 2-D rectangular array beamformer, we first show that the optimal weight matrix when using full adaptivity can be obtained from a set of singular vectors. Then the design problem of using partial adaptivity is formulated. As a result, the optimal solution for the partially adaptive weight matrix can be found by solving two basic problems, namely determining the proper dimension of the partially adaptive weight matrix and the set of the singular vectors. We develop the detection formulas for the information theoretic criteria AIC and MDL to find the proper dimension. Next, an efficient method is presented so that the optimal solution for the set of the singular vectors can be found analytically. We also investigate the required computational complexity. It is shown that 2-D partially adaptive beamforming using the proposed technique requires less computational complexity than 2-D fully adaptive beamforming using conventional techniques. Moreover, computer simulations demonstrate that the proposed 2-D partially adaptive technique provides satisfactory array performance when compared with conventional fully adaptive techniques     

Wavelet-based neural network with fuzzy-logic adaptivity fornuclear image restoration

A novel wavelet-based neural network with fuzzy-logic adaptivity (WNNFA) is proposed for image restoration using a nuclear medicine gamma camera based on the measured system point spread function. The objective is to restore image degradation due to photon scattering and collimator photon penetration with the gamma camera and allow improved quantitative external measurements of radionuclides in vivo. The specific clinical model proposed is the imaging of bremsstrahlung radiation using ³² P and ⁹⁰Y. The theoretical basis for four-channel multiresolution wavelet decomposition of the nuclear image into different subimages is developed with the objective of isolating the signal from noise. A fuzzy rule is generated to train a membership function using least mean squares to obtain an optimal balance between image restoration and the stability of the neural network, while maintaining a linear response for the camera to radioactivity dose. A multichannel modified Hopfield neural network architecture is then proposed for multichannel image restoration using the dominant signal subimages     

Signal enhancement in a near-field MIMO environment through adaptivity on transmit

A technique is presented on how to enhance the received signals in a near field multi-input multi-output (MIMO) environment where beam forming is not possible. This is done through the use of adaptivity on transmit. This technique is based on the principle of reciprocity, is independent of the material medium in which it is transmitting, and incorporates near-field environments and multipath. The objective here is to select a set of weights adapted to each receiver to be applied to each transmitting antenna, which is a function of the user location, so that the transmitted signal at the carrier frequency may be directed to a particular receiver location while simultaneously minimizing the received signal strengths at other receiver locations. Numerical simulations have been made to illustrate the novelty of the proposed approach.     

The structural reliability of cable television

The simultaneous structure of cable television (CATV) as the distribution network. The new topology of CATV as the interactive information net. The structure reliability of CATV.     

带通滤波器的结构和工艺设计

介绍了一种新型滤波器的结构、工艺设计,分析了该滤波器的结构特点和加工工艺。试验结果表明,该滤波器达到了设计要求。     

The structural features and the deliberative quality of online discussions

This paper examines the quality of online political discussions from the perspective of deliberative democracy. Reason-giving and mutual respect are two important principles of deliberative democracy and, therefore, deemed indicators of the deliberative quality of online discussions. A content analysis of discussion threads about the 2004 US presidential election randomly selected from eight online spaces during the last month of the election was conducted to assess the relationships between the structural features of the spaces—diversity and moderation—and the deliberative quality of the discussions. The results showed that the relationship between moderation and the discussion quality was conditioned on the diversity of the spaces. The finding indicates that the structural features of online spaces may shape the deliberative quality of political discussions and, thus, deserve further scholarly attention.     

一种折叠反射面天线的结构设计

针对机动雷达反射面天线结构尺寸运输超限问题,介绍了在结构设计过程中依据载荷分析计算结果,应用三维建模技术,虚拟装配技术,优化结构布局,完成自动展开/折叠反射面天线的结构设计。该天线在工作状态展开,在运输状态收缩到规定运输界限范围内,满足了雷达机动要求。     

某车载雷达天线结构分析

车载雷达天线是车载雷达工作的核心部件。本文选用UG对某天线进行三维建模,用ANSYS软件对天线进行静力分析以及振动模态分析,对不同的反射面厚度、天线背架上不同梁的横截面尺寸进行天线模态分析。根据有限元分析结果,对某天线进行结构优化设计,提高固有频率。     

心肌组织T-管结构的扫描电镜研究

心肌兴奋 收缩偶联由于其明显的理论和临床意义一直受到关注。肌浆网 (ｓａｒｃｏｐｌａｓｍｉｃｒｅｔｉｃｕｌｕｍＳＲ)及肌浆网内Ｃａ2 +释放在心肌兴奋 收缩偶联机制中起着重要作用。在肌兴奋 收缩偶联机制中起重要作用的单元为三联管即Ｔ 管、肌浆网。由透射电镜观察得出 ,Ｔ 管是肌细胞膜凹陷垂直伸向细胞浆的横管。我们采用扫描电镜对心肌纤维与Ｔ 管的关系进行了研究 ,取得了有意义的结果。材料与方法正常豚鼠 (体重 30 0ｇ,由第二军医大学动物中心提供 ) ,颈椎脱位。取其心室部位的心肌组织 ,用玻璃分针小心的将心组织分离为长约 …     

新型功率MOS器件的结构与性能特点

电力电子器件的结构决定其性能,而器件的性能又决定电路的性能。根据此原理,分析比较了近十年来10种实用的具有新结构的功率MOS器件的结构与性能特点。     

风廓线雷达天线系统结构设计

介绍了对流层风廓线雷达天线系统的结构设计,着重介绍了Co－Co线源、天线骨架的商品化、模块化结构设计及应用。     

一种舰载雷达机柜结构设计

为了适应海上恶劣环境,本文介绍了一种舰载雷达密闭机柜结构设计,其中包括电磁兼容设计、热设计和三防设计。     

The osteoblastic phenotype in calcium-depleted and calcium-repleted rats: a structural and histomorphometric study

In a previous report we showed that young rats fed a calcium-free diet for 28 days developed severe hypocalcaemia and showed a significant increase in serum alkaline phosphatase activity. The main histological and cytochemical changes exhibited by these animals in bone of the metaphyseal primary spongiosa were: (1) hyperplasia of osteoblasts, (2) an increase in the frequency of tartrate-resistant acid phosphatase (TRAP)-positive osteoblasts apposed to osteoid, and (3) an excessive amount of osteoid tissue. In addition to typical osteoblasts, there was a subpopulation of osteoblast-like cells with coated pits, lysosome-like bodies and large cytoplasmic processes. In the present study, we investigated how the above parameters change when calcium-depleted rats are placed on a normal diet for 7 days. Such a regimen normalized calcium concentration and alkaline phosphatase activity in the serum. The osteoid thickness returned to normal and, in some areas, was fully calcified. Most osteoblasts no longer showed TRAP activity and their ultrastructure was similar to that found in controls. Despite an intense alkaline phosphatase activity, some of them still exhibited a number of macrophagic characteristics. They were TRAP-positive, and showed electron-dense bodies in the cytoplasm facing bone, an abundance of coated pits, calcified spicules impinging on the cell membrane and large processes extending into the mineralized matrix. We concluded that calcium deficiency causes hyperplasia of osteoblasts in primary spongiosa and an increase in expression of TRAP. It also induces changes in their phenotype characterized by the acquisition of macrophagic cellular features. While TRAP activity is normalized by calcium repletion, macrophagic characteristics persist. These results suggest that the osteoblast can modulate its phenotype according to its physiological status.     

The chemical and structural origin of efficient p-type doping in P3HT

We investigate the chemical and structural properties of solution-processed thin films of P3HT blended with p-type dopant F4TCNQ. The maximum in-plane electrical conductivity of doped films is observed at a molar doping fraction of 0.17, in agreement with the binding mechanism of F4TCNQ:P3HT complexes. Through the use of X-ray diffraction, a previously unreported crystalline phase is observed for P3HT films doped above a critical threshold concentration. This crystalline phase involves the incorporation of F4TCNQ molecules into ordered polymer regions and ultimately improves charge dissociation, leading to higher carrier density in thin film. Finally, optical absorption and X-ray diffraction reveal that the chemical state of P3HT in solution has a dramatic impact on the electrical and structural properties of the blended films.     

The structural changes in CdS-CdTe thin films due to annealing

Thin film solar cells based upon CdS-CdTe heterojunctions have become an important alternative to silicon based devices. The film structures formed during fabrication are critical to cell efficiency and thus their study is fundamental to improving device performance. We have used synchrotron x-ray diffraction to investigate the effect of a post deposition anneal upon the film structures and, in particular, have examined the dynamic formation of intermixed regions adjacent to the original, metallurgical interface. Our results have enabled us to produce a dynamic model for the structural changes which includes the extent of interdiffusion. We show that, for a 400 nm CdTe film in the presence of chlorine, the original CdS and CdTe layers are completely transformed into layers with average compositions CdS_0.93Te_0.07 and CdTe_0.94S_0.06, respectively. We present evidence that the interdiffusion occurs during or following a recrystallization and that, to a limited extent, these changes also occur without chlorine.     

The structural property of network bottlenecks in maxmin fair flowcontrol

In this letter we introduce a new conceptual framework to investigate into the underlying structure of network bottlenecks in maxmin fair flow control. It is shown that a network has a hierarchical structure with regard to its bottlenecks. The number H of network bottleneck levels is proved to be no greater than the number K of network bottleneck rates. It is also shown that there can be many bottleneck rates on each hierarchical level. So H can be much smaller than K