Advanced frequency hopping modulation for spread spectrum WLAN

A wireless LAN standard developed by IEEE committee P802.11 operates in the unlicensed 2.4 GHz ISM band. This band is a very hostile environment due to many unpredictable interference sources, such as microwave ovens, utilizing the same frequency bands. At the same time the allowed signal power density that can be used is limited in order to minimize the interference to other users in the same band. In order to avoid these interference and keep a low signal power density the standard supports both direct sequence (DS) and frequency hopping (FH) modulation for these applications. The new test beds for multimedia wireless (WLANs) also use FH modulation. We analyze the performance of a modification of the FH multiple frequency shift keying (MFSK) system that includes a multitone multiamplitude MFSK signal, designated as amMFSK modulation. In this case, in order to meet the transmitted power density limits imposed in the ISM band, the signal energy is split into m separate tones. This makes the system more vulnerable to noise and fading, but still the overall flow of useful information will be increased. The results demonstrate that under the large range of the signal, channel and interference parameters this system offers better performance     

Light-emitting-diode-based light source for calibration of an intensified charge-coupled device detection system intended for galvanoluminescence measurements

A spectrally tunable light source utilizing three light-emitting diodes (LEDs) for calibration of a highly sensitive intensified charge-coupled device (ICCD) optical detection system intended for time-resolved galvanoluminescence (GL) measurements is described. The source has been conceived as a low-cost substitute for standard tungsten lamps usually used for relative and absolute calibration of optical detection systems. Three LEDs with different spectral characteristics in conjunction with a system of two integrating spheres as light mixers and light reducers are used. This construction provides control over the source spectrum by changing individual LED contributions. The use of integration spheres eliminated angular distribution of light intensities of LEDs as well as angular dependence of their spectral contributions. Moreover, by using the source we have avoided the problem of stray and diffuse light of higher wavelengths, as well as different light intensities for different wavelengths (up to three orders of magnitude in the range from 400 nm to 750 nm), which we have with standard tungsten lamps. A complete calibration procedure for the LED source and ICCD detection system is described. Finally, for the first time, we have performed time-resolved spectral GL measurements during aluminum anodization in porous film-forming electrolyte phosphoric acid in a transient regime. Two peaks at 425 nm and 595 nm are recognized, confirming the same mechanism of GL in both transient and steady-state regimes of anodization.     

CO2 Conversion Enhancement in a Periodically Operated Sabatier Reactor: Nonlinear Frequency Response Analysis and Simulation-based Study

Conversion of CO₂ into synthetic CH₄ via thermocatalytic hydrogenation (the Sabatier reaction), has recently gained increasing interest as a possible route for CO₂ utilization and energy storage pathway. Herein, we analyze the possibility of increasing the CO₂ conversion through periodic operation of the reactor. The analysis is performed by using the Nonlinear Frequency Response (NFR) method, a recently developed analytical technique, suitable for fast evaluation of periodic reactor operations. The NFR analysis predicts a significant conversion gain (up to 50 %) for certain frequencies of the feed flow rate modulation. This prediction is validated by numerical simulations with a reaction rate expression obtained by CO₂ conversion experiments using a Ni/Al₂O₃ catalysts. Both the NFR analysis and numerical simulations predict that it is possible to obtain 70 % CO₂ conversion at 500 K, 5 bar, and average space velocity of 7600 h⁻¹ by a periodic modulation of the feed flow rate, as compared to the corresponding steady state CO₂ conversion of 43 %.     

Closed‐Form Expressions for Selection Combining System Statistics over Correlated Generalized‐K Fading Channels in the Presence of Interference

This paper considers the effects of simultaneous correlated multipath fading and shadowing on the performances of a signal‐to‐interference ratio (SIR)‐based dual‐branch selection combining (SC) diversity receiver. This analysis includes the presence of cochannel interference. A generalized fading/shadowing channel model in an interference‐limited correlated fading environment is modeled by generalized‐K distribution. Closed‐form expressions are obtained for probability density function and cumulative distribution function of the SC output SIR, as well as for the outage probability. Based on this, the influence of various fading and shadowing parameter values and the correlation level on the outage probability is examined.     

An Approach to Estimating Building Layouts Using Radar and Jump-Diffusion Algorithm

Estimating building layouts using exterior radar measurements is a challenging task involving electromagnetic modeling, many unknown parameters, and a limited number of sensors. We propose using the jump-diffusion algorithm as a powerful stochastic tool that can be used to estimate the number of walls, their unknown positions and other parameters. We develop an efficient iterative procedure that first uses low-frequency transmissions to obtain rough estimates of the building layout. These estimates are then used to initialize the estimation at higher frequencies, thus obtaining more accurate results. We show that with proper frequency selection, the building layout can be estimated using radar measurements at only a few frequencies. Numerical examples are used to illustrate the performance of the proposed algorithm in practical situations.     

Design in the Power-Limited Scaling Regime

Technology scaling has entered a new era, where chip performance is constrained by power dissipation. Power limits vary with the application domain; however, they dictate the choices of technology and architecture and necessitate implementation techniques that tradeoff performance for power savings. This paper examines technology options in the power-limited-scaling regime and reviews sensitivity-based analysis that can be used for the optimal selection of optimal architectures and circuit implementations to achieve the best performance under power constraints. These tradeoffs are examined in the context of power minimization at the technology, circuit, logic, and architecture levels, both at the design and run times.     

Densification rate and phase structure changes during sintering of zinc titanate ceramics

Densification rate and phase structure changes during sintering of nanosized ZnTiO₃ were studied. Sintering was performed in a dilatometer in two regimes: the first to 900 °C (heating rates 5, 10 and 15 °C/min) and the second to 1200 °C (heating rates 3, 5 and 10 °C/min). XRD analysis of samples sintered at both temperatures combined with Rietveld structure refinement enabled determination of all phases present and their structure parameters. Samples sintered to 900 °C contained ZnTiO₃ and Zn₂TiO₄ with traces of r-TiO₂ (rutile) and Zn₂Ti₃O₈, while samples sintered to1200 °C contained only r-TiO₂ and Zn₂TiO₄. A master sintering curve was defined for sintering to 900 °C enabling determination of the sintering process activation energy as 313 kJ/mol.     

X-ray photoemission analysis of passivated Cd(1 − x)ZnxTe surfaces for improved radiation detectors

Surface passivation of device-grade CdZnTe was investigated using X-ray photoelectron spectroscopy in combination with transport property measurements after Br-MeOH (2% Br) and KOH/NH₄F/H₂O₂ solutions were used to etch and oxidize the surface. High-resolution photoemission measurements on the valence band electronic structure and core lines were used to evaluate the surface chemistry of the chemically treated surfaces. Metal overlayers were then deposited on these chemically treated surfaces and the I-V characteristics measured. The measurements were correlated to understand the effect of interface chemistry on the electronic structure at these interfaces with the goal of optimizing the Schottky barrier height for radiation detector devices.     

Extended Arc Furnace

A new development in plasma furnace technology in which by relatively simple modifications a more or less conventional arc furnace can be made to produce a long stable plasma flame is described. A very promising application of this technique is in the steel melting as well as in direct reduction of fine iron ore, waste oxides, flotation concentrates, blast furnace dust, fly ash, mill scale, etc.