Performance analysis of SSC diversity receiver over correlated Ricean fading channels in presence of co-channel interference

A novel infinite-series-based approach for the performance analysis of a dual-branch switched-and-stay combining (SSC) diversity receiver operating over Ricean correlated fading channels in the presence of correlated Nakagami-m distributed co-channel interference (CCI) is presented. The performance analysis is based on outage probability (P_out) and average bit error probability (ABEP) criteria.     

Effects of the presence of probiotic bacteria in the aging medium on the surface roughness and chemical composition of two dental alloys

The aims of this study were: (a) to determine if the presence of probiotic bacteria in an aging medium, that is, artificial saliva in this study, has relevant effects on the surface roughness and the chemical composition of two main alloys used in dentistry (NiTi and stainless steel [SS]) and (b) in the case of NiTi, if these effects are influenced by the coating of the alloy (rhodium and titanium nitride). Atomic force microscopy and Raman spectroscopy were used to study the surface morphology and identify metal oxides formed on the surface of the alloys. Experiments demonstrated that the probiotic bacteria Lactobacillus reuteri can induce processes that alter some features of the surface such as roughness and chemical composition. The effect is dependent on the type of alloy and coating. The bacteria increased roughness in the case of uncoated NiTi more than saliva alone (pH = 4.8). Probiotic bacteria tend to decrease the corrosive influence of saliva on NiTi when the alloy is coated with rhodium or titanium nitride and this effect was also evidenced on SS. Raman spectroscopy confirmed that only SS samples are prone to oxidation processes, predominantly associated with exposure to saliva rather than probiotic bacteria.     

Finite-element model-based fault diagnosis, a case study of a ceramic pressure sensor structure

Finite-element (FE) analysis is an efficient aid in the design optimisation of modern electronic devices. Simulation tools have dramatically reduced the product design cycle. The model validated with actual prototypes can also be used for other purposes such as failure analysis, fatigue prediction, reliability studies, etc. In this paper we present a case study of application of FE model in fault localisation in ceramic pressure sensor structures. The sensing elements are thick-film resistors acting as strain gauges, which translate the strain into an electrical signal. In the design phase, FE analysis was used to analyse the sensitivity of the thick-film resistors to the applied pressure. The same model was used for non-destructive fault diagnosis and troubleshooting of the prototype series. Selected examples illustrate the approach. FE model can also be used in the production test process. Since simulations are rather time consuming, quick fault localisation can be performed by a fault dictionary while in-depth diagnosis is performed by FE analysis.     

Analyzing the Uses of a Software Modeling Tool

While a lot of progress has been made in improving analyses and tools that aid software development, less effort has been spent on studying how such tools are commonly used in practice. A study into a tool's usage is important not only because it can help improve the tool's usability but also because it can help improve the tool's underlying analysis technology in a common usage scenario. This paper presents a study that explores how (beginner) users work with the Alloy Analyzer, a tool for automatic analysis of software models written in Alloy, a first-order, declarative language. Alloy has been successfully used in research and teaching for several years, but there has been no study of how users interact with the analyzer. We have modified the analyzer to log (some of) its interactions with the user. Using this modified analyzer, 11 students in two graduate classes formulated their Alloy models to solve a problem set (involving two problems, each with one model). Our analysis of the resulting logs (total of 68 analyzer sessions) shows several interesting observations; based on them, we propose how to improve the analyzer, both the performance of analyses and the user interaction. Specifically, we show that: (i) users often perform consecutive analyses with slightly different models, and thus incremental analysis can speed up the interaction; (ii) users' interaction with the analyzer is sometimes predictable, and akin to continuous compilation, the analyzer can precompute the result of a future action while the user is editing the model; and (iii) (beginner) users can naturally develop semantically equivalent models that have significantly different analysis time, so it is useful to study manual and automatic model transformations that can improve performance.     

A Novel Bilateral Power Conversion Scheme for Variable Frequency Static Power Supplies

PWM voltage source inverters (VSI's) supplied from diode rectifiers are employed with most of today's static power supplies for variable frequency ac type loads. This method generates nonsinusoidal input and output voltage/current waveforms and yields poor system reliability. An upgraded method of power conversion is presented that eliminates both problems. In addition, it allows bidirectional power flow which improves efficiency and simplifies cooling requirements. The subject method requires a PWM rectifier and a PWM current source inverter. Advanced PWM techniques employed with both static Converters allow the minimization of all associated passive components.     

A Lyapunov-Krasovskii stability analysis for game-theoretic based power control in optical links

We analyze the stability of a game-theoretic based power control algorithm for optical links in the presence of time-delays. The control objective is to achieve optimal optical signal to noise ratio (OSNR) values for the signal channels. The control algorithms regularly adjust the signal powers entering the link based on a game-theoretic model. Each signal power is modeled as a player, whose goal is to maximize its own utility function. The utility function increases with an increasing OSNR value, and hence requires an increasing signal power. The trade-off is that if one player increases its OSNR value, this adversely affects the OSNR values of all of the other players. In addition to the signal powers, a dynamic price parameter is fed back to the power control algorithms. Time-delay is present for both the channel pricing parameter and the OSNR feedbacks in the link. We study the stability of the closed-loop, time-delay system. The work utilizes singular perturbation theory modified to handle Lyapunov-Krasovskii techniques.     

Performance analysis of dual switched diversity over correlated Weibull fading channels with co‐channel interference

This paper studies the performance of switch and stay combining (SSC) diversity in the presence of co‐channel interference over correlated Weibull fading channels. SSC diversity based on signal‐to‐interference ratio (SIR) is a low‐complexity and a very efficient technique that reduces fading and co‐channel interference influence. New closed‐form expressions for the probability density function and cumulative distribution function of the output SIR's are derived. These formulas are used in a detailed analysis of the average output SIR and outage probability. The influence of fading severity and correlation coefficient on the optimum switching threshold and system performance is investigated. Monte Carlo simulations are performed to verify obtained theoretical results and determine average bit error rate in detecting binary phase‐shift keying (BPSK), differential BPSK and quadrature amplitude modulation signals. Copyright © 2011 John Wiley & Sons, Ltd.     

Ghana’s nuclear power and its potential to curtail carbon dioxide emission

Clean Technologies and Environmental Policy - The Ghana Nuclear Power Agenda is a program laid out by the Ghana Atomic Energy Commission in collaboration with the government of Ghana to guide and...     

Application Areas of Ionic Hydraulic Fluids

Ionic liquids, as high-tech technical fluids, have been in practical application in various fields of technology for several years. The search for ionic liquids suitable for use within hydraulic systems, as another new very important field of technology, has taken more than a decade. The development included the identification of material properties important for usage as a hydraulic fluid, an extensive preselection process and laboratory testing of suitable ionic liquids, as well as long-term testing using real hydraulic components under real operating conditions. Based on the findings, potential areas of industrial application of ionic liquids as hydraulic fluids are presented, which arise from their extraordinary physicochemical properties.