UN-MUSIC and UN-CLE: an application of generalized correlationanalysis to the estimation of the direction of arrival of signals inunknown correlated noise

A new approach is proposed for the consistent estimation of the directions of arrival (DOA) of signals in an unknown spatially-correlated noise environment. The signal and noise model used is based on the assumption that the data are received by two arrays well separated so that their noise outputs are uncorrelated. The generalized correlation decomposition of the cross-correlation matrix between the two arrays is then introduced. Of particular interest is the canonical correlation decomposition. The analysis of the generalized correlation leads to various interesting geometric and asymptotic properties of the eigenspace structure. Two algorithms, UN-MUSIC and UN-CLE, are developed to estimate the DOA of signals in unknown spatially correlated noise based on the utilization of these properties. Computer simulations show that these methods are superior in performance compared to conventional methods. Furthermore, it is demonstrated that the new methods are equally effective even when only one sensor array is employed     

Measurement of the thermal expansion coefficient of an all-sapphireoptical cavity

We present measurements of the frequency-temperature dependence of an all-sapphire Fabry-Perot optical cavity to be used as an optical frequency reference. Measurements were made by tracking the frequency of the cavity relative to a second high-stability cryogenic sapphire-spaced cavity-a technique with impressive resolution for measurements of the coefficient of thermal expansion (CTE). Measurements presented here cover the temperature range of 11 K to 26 K. We find that the CTE of the all-sapphire cavity for these temperatures is given by α_cavity=(7.7±0.9)×10^$ -¹³ T/sup (3.23±0.05/)     

TiB_2基烧结材料的研究现状与进展

TiB_2基烧结材料再度受到材料研究者的关注,是因为它有一系列优异性能,并将成为新一代的陶瓷和硬质合金。本文报导了近几年国外对TiB_2基烧结材料研究现状和进展。     

Treatment of wastewaters containing propellants and explosives

Studies were conducted at Radford Army Ammunition Plant (RAAP) to compare selected wastewater treatment methods, to define the treatment parameters and to prepare the design criteria for facilities to treat wastewater containing dissolved nitroguanidine (NGu), nitroglycerin (NG) and other nitrate esters and colloidal nitrocellulose (NC).The design criteria for two pretreatment facilities were prepared based on the results of the pilot plant evaluation and transmitted to the Army Corps of Engineers who constructed the facilities at RAAP.     

Constrained identification of virtual CNC drives using a genetic algorithm

This paper presents a genetic algorithm (GA) for identifying virtual models of machine tool drives with minimal intervention to the production machine. The proposed solution builds on the “rapid identification” concept reported earlier in literature, in which a short series of motion data is captured from the Computer Numerical Control (CNC) and used for closed-loop transfer function identification subject to stability constraints. Compared to the Lagrange multipliers solution that was used in the original implementation of rapid identification, the proposed GA is both significantly faster and better suited for industrial use. The novel contributions in the paper include the reduction of the search space from eight unknown variables down to three, which also enables stability constraints to be incorporated in a natural manner, and the re-formulation of the objective function, which streamlines the convergence of the GA by two to three orders of magnitude. Following initial verification in simulations, the GA has been used to identify the closed-loop dynamics of a stand-alone ball screw drive and the x- and y-axes of a five-axis machining center. In experimental results, it is shown that drive models constructed using the GA can be successfully used to predict the tracking and contouring errors for different part programs in a virtual process planning environment.     

Interferometry Measurement of Lubricating Films in Slider-On-Disc Contacts

Interferometry proves to be an efficient way to measure thin lubricant film thickness. However, there are very few reports on the film thickness measurement of conformal lubricated contacts using optical interferometry due to experimental difficulties. In this article, a custom-built test apparatus is introduced, in which a lubricated conformal contact is made between a stationary fixed-incline slider and a moving transparent disc. With a flexible holder, the slider can be positioned in such a way that a specified inclination with respect to the flat disc plane can be obtained. When the disc rotates and the slider is loaded against it, lubricating films are generated. The minimum film thickness h _m at the exit can be determined by interference intensity changes. Measurement error correction in the film thickness was discussed. Case experiments were carried out using the new test apparatus. The credibility of the measurement system is validated by good correlation between the experiments and the theoretical results. The applicability is demonstrated by the film thickness measurement under different inclinations, loads, velocities, lubricants and slider materials. Amongst those case experiments, it is highlighted that the influences of solid/liquid interface properties on the lubrication behaviours can be clearly identified in terms of film thickness.     

Byte-Level Parametric Wavelength Exchange for Narrow Pulsewidth Return-to-Zero Signal

We investigate the feasibility of switching return-to-zero signals with 3-ps pulsewidth by byte-level parametric wavelength exchange (PWE) numerically and experimentally. Square-wave modulated pumps are used in PWE for pump gating. Simultaneous bit swapping for two signals at the same time slot is achieved. Error-free operation is achieved for both signal channels with ap3.5-dB power penalty at 10^-9 bit-error rate.     

Robust Collaborative-Relay Beamforming

Relay communications is a promising technique to extend the range of wireless communications by forwarding the message from the sender to the intended destination. While fixed or variable-power relays have been previously investigated, this paper addresses the collaborative use of variable-phase variable-power amplify-and-forward (AF) relays for robust beamforming, with the aid of imperfect channel state information (CSI) at the sender. In particular, the maximization of the worst-case signal-to-noise ratio (SNR) at the destination terminal is studied under a bounded spherical region for the norm of the CSI error vector from the relays to the destination. Our main contribution is that we prove, under a condition on the quality of the estimated CSI, the robust-optimal collaborative-relay beamforming (CRBF) can be obtained by S-procedure and rank relaxation techniques. In addition, a distributed algorithm is developed by examining the structure of the optimal CRBF solution. Results demonstrate a significant gain of CRBF over non-robust approaches.     

Effects of periphery encapsulation material on the characteristics of micro vacuum dielectric capacitor

The effects of the periphery sealant on the electrical characteristics of vacuum dielectric capacitors (VDCs) are modeled. For the square shape VDCs, their characteristics are predominantly determined by the ratio of capacitor side length versus the width of boundary sealant layer, r. The smaller of the r value, the smaller of the dissipation factor, and the better frequency response of the VDCs are found. To achieve a dissipation factor of less than 10⁻⁵ at 1 GHz, the dimension parameter, r, should be smaller than 0.05 which has been achieved based on the present technology for a capacitor with size larger than 4 mm × 4 mm. The leakage current can also be reduced significantly in the VDCs. We found that the leakage current is mainly governed by the Poole-Frenkel emission of electrons over the periphery region. The present results have demonstrated that the VDC structure is a promising technology option for making high-frequency micro capacitors.     

Design and performance evaluation of an adaptive FPGA for network applications

This paper presents the design, implementation and performance evaluation of a coarse-grain dynamically reconfigurable FPGA platform for multi-service edge and access network devices. The platform consists of two MicroBlaze RISC processors and a number of hardware co-processors used for the processing of packet payloads (Data Encryption Standard (DES) and Lempel-Ziv Compression). The co-processors can be connected either directly to the processors or using a shared bus. The functionality of the co-processors is dynamically reconfigured to meet the requirements of the network workload. The system has been implemented on the Xilinx Virtex II Pro platform and the network traces from real passive measurements have been used for performance evaluation. The use of dynamically reconfigurable co-processors for network applications shows that the performance speedup versus a static version varies from 12% to 35% in the best case and from 10% to 15% on average, depending on the network traffic fluctuation.