Adaptive Multiuser Detection Based on RBF Networks in Impulsive Noise CDMA Channels

With increasing need for capacity in mobilecellular communications, code division multiple accesshas been viewed as the technique to meet this goal.However, the conventional receiver suffers frommultiuser interference and the near-far effect. Toalleviate this problem, various multiuser receivers havebeen proposed. They have been shown to enhance theperformance of the conventional receiver with respect to capacity and interference rejection. Butthese receivers, intended for Gaussian noise channels,can fail in other environments such as impulsive noiseconditions. A possible solution is to exploit the advantages of neural networks. A neuralnetwork's ability to reject non-Gaussian noise can beutilized to implement multiuser receivers that rejectboth impulsive noise and multiuser interference.Following this logic, this paper considers nonadaptivemultiuser receiver and adaptive multiuser receiver basedon radial basis function neural networks. Simulations ofthese receivers show results that are superior to previously studied multiuser receivers, withrespect to practicality and performance.     

Monitoring localised corrosion in inhibited solutions using wire beam electrode–noise signatures method

Abstract

The objective of this work is to determine the nature of localised corrosion in inhibited solutions by establishing possible relationships between characteristic features in electrochemical noise and corrosion processes using an electrochemically integrated multielectrode system, namely the wire beam electrode (WBE) in combination with noise signatures method. Experiments have been carried out to simultaneously measure electrode potential noise and WBE current distribution maps from stainless steel (SS316L) WBE exposed to inhibited solutions containing 6%FeCl₃ solution with inorganic inhibitors including 2 wt-% sodium chromate (Na₂CrO₄), cerium chloride (CeCl₃) and lanthanum chloride (LaCl₃). Characteristic electrochemical noise signatures were found to correlate with characteristic changes in WBE current distribution maps that show corrosion rates distributions and the degree of localised corrosion. A new concept namely localisation parameter (LP) has been proposed to identify the degree of inhibition. Na₂CrO₄ effectively inhibited the pitting corrosion process and the LP successively decreased through out the corrosion process. With the presence of CeCl₃ and LaCl₃, pits on stainless steel in 6%FeCl₃ solution were not repassivated and an increase in the LP was observed for both inhibitors. The results suggest that the WBE method could be used in combination with the noise signatures as a sensitive technique for monitoring inhibiting effect on localised corrosion.     

浅谈活塞式压缩机运转条件的改善

通过对管路振动及噪声这两个主要影响活塞式压缩机运转条件的因素进行分析，提出了相应的改善措施。     

Monitoring of stress corrosion cracking of sensitised 304H stainless steel in nuclear applications by electrochemical methods and acoustic emission

Abstract

A hybrid monitoring technique for stress corrosion cracking (SCC) has been developed that employs simultaneously localised corrosion monitoring, electrochemical noise and acoustic emission (AE) techniques. The application of the hybrid technique for detection of SCC initiation and propagation in sensitised 304H stainless steel in dilute tetrathionate solutions at ambient temperature is reported. Initial result shows that SCC initiation and its early stage propagation can be detected by the localised corrosion monitoring and electrochemical noise methods. The dimensions of the crack can be estimated from the charge values derived from the detected transients. The locations of AE events determined using two sensors are in good agreement with the locations of cracks observed in the specimen. The AE technique is sensitive to rapid crack propagation, but does not appear to be sensitive to SCC initiation and early stage propagation for the present material environment load combination. It is postulated that AE is sensitive to SCC propagation involving a relatively large volume of plastic deformation. On the basis of test results and on information from the literature, it is suggested that in this material environment system SCC cracks initiate via slow anodic dissolution at the chromium depleted grain boundaries. Subsequently, elemental sulphur adsorbed on the surface around the crack tip catalyses the entry of hydrogen atoms produced by the hydrogen reduction reaction into the steel matrix ahead of the crack tip; this hydrogen accumulates gradually over a relatively long period of time and preferentially at carbide/matrix interfaces, eventually causing hydrogen induced brittle fracture along grain boundaries.     

Noise deconvolution for area fraction measurements

Abstract

A novel approach to area fraction measurement is developed to deal with the limitations of the segmentation method. The new approach takes advantage of the statistical nature of the noise within an image to deconvolute the image histogram and calculate, by means of fitting, the area fractions. Both segmentation and noise deconvolution approaches are critically discussed, and their limitations and advantages tested using two extreme backscattered electron images of a metal matrix composite. The deconvolution approach is shown to produce accurate results in a situation in which the segmentation approach fails.     

Angle Diversity to Combat the Ambient Noise in Indoor Optical Wireless Communication Systems

We propose and study the use of angle diversityto combat the ambient noise in indoor optical wirelesscommunication systems. Models for the radiation patternof spot lamps and for the spatial distribution of the ambient light based on an isotropic anda directional noise component are derived. Performanceevaluation of receivers using angle diversity is carriedout and significant optical power gains are demonstrated. The optical gains are seen toincrease with the relative weight of the directionalnoise within the cell, with the sharpness of thedirectional noise source beam width, and in environments where there are noise sources positionedoutside the cell. Also, the signal-to-noise ratio (SNR)of a sectored receiver is seen to be much less sensitiveto the position and beam width of the noise sources than the SNR of a nonsectored receiver,allowing for more universal transceiverdesigns.     

Process parameter selection for optimising weld bead geometry in stainless steel cladding using Taguchi's approach

Abstract

In the present study, the Taguchi method, a tool to design optimisation for quality, is used to find the optimal welding process parameters for cladding of austenitic stainless steel. An orthogonal array, the signal to noise (S/N) ratio, and the analysis of variance (ANOVA) are employed to investigate the effect of process parameters on weld bead characteristics. The present study was conducted by depositing AISI 317L onto an IS : 2062 structural steel substrate by the flux cored arc welding (FCAW) process under the shield of 95%Ar and 5%CO₂ gas mixture. The weld bead parameters are optimised individually (single objective) as well as collectively (multiobjective) to get the desired quality characteristics. The results show that these techniques can be used effectively to control the process parameters in cladding with certain limitations.     

数字存储示波器噪声特性的分析

以TektronixTDS2 10为研究对象 ,对数字存储示波器噪声进行了多次时域采样和频域分析 ,结果表明 ,示波器噪声是一种非零均值的带限白噪声 ,频谱很宽 ,对示波器测量误差和谱分析影响显著 ,应在高电压测试和信号数字处理时采取措施     

Carbon recycling for zero-emission carbon-neutral transportation

Abstract

Converting current internal combustion engines to operate in closed-cycle, lean-burn mode with pure oxygen could generate an exhaust stream of >99% carbon dioxide. The ease of capture of this carbon, relative to the dilute CO₂ in current exhaust gases, points the way to a feasible route to zero-emission transportation. Prospects for implementing such an approach, which would include re-synthesis of fuel from the captured CO₂ and water using renewable power, are considered.     

Accumulation of coincidence site lattice boundaries during grain growth

Abstract

Monte Carlo simulations were used to investigate the effect of grain growth on the coincidence site lattice (CSL) boundary content of randomly textured polycrystals. Each grain was assigned an orientation, and grain boundary properties were dependent on both the boundary misorientation and the CSL character. While low misorientation angle boundaries (LABs) increase during growth, the fraction of CSL boundaries does not change with time. Decreasing CSL boundary energy and mobility did not alter these results. In contrast with LABs, which are characterised by a scalar misorientation angle, a particular combination of three independent rotation variables is required to create a low energy CSL boundary; thus, these boundaries are unlikely to form or to persist in a random polycrystal. While texture influences boundary formation, a texture that can enhance CSL boundaries is not apparent. Boundary plane effects should not increase CSL fraction during grain growth.