Wideband chirp measurement technique for high bit rate sources

A Mach Zehnder (MZ) interferometer has been used as an optical discriminator to measure the time-resolved frequency chirp of an optical source     

Mathematical analysis of dynamic channel selection in indoor mobilewireless communication systems

Dynamic channel selection (DCS) is an algorithm for flexible resource sharing in mobile radio systems. The digital enhanced cordless telecommunications (DECT) standard implements a version of DCS based on time as well as frequency multiplexing. In this paper, mathematical models are developed to evaluate the probabilities of channel availability, desired carrier power, and the carrier-to-interference ratio (CIR) for a constant traffic load. These results can be used to compute the call setup blocking probability. The models reported in this study are based on a decentralized DCS according to the DECT standard specifications. The results show that blocking due to availability of a channel (resource blocking), not interference blocking, generally is the most important factor in overall call blocking. Furthermore, it is seen that resource blocking is sensitive to the implementation of portable sets. Also, with homogeneous static traffic, this type of DCS ran be as good as fixed channel allocation (FCA) with respect to resource blocking     

The effect of multiple time scales and subexponentiality in MPEGvideo streams on queueing behavior

Guided by the empirical observation that real-time MPEG video streams exhibit both multiple time scale and subexponential characteristics, we construct a video model that captures both of these characteristics and is amenable to queueing analysis. We investigate two fundamental approaches for extracting the model parameters: using sample path and second-order statistics-based methods. The model exhibits the following two canonical queueing behaviors. When strict stability conditions are satisfied, i.e., the conditional mean of each scene is smaller than the capacity of the server, precise modeling of the interscene dynamics (long-term dependency) is not essential for the accurate prediction of small to moderately large queue sizes. In this case, the queue length distribution is determined using quasistationary (perturbation theory) analysis. When weak stability conditions are satisfied, i.e., the conditional mean of at least one scene type is greater than the capacity of the server, the dominant effect for building a large queue size is the subexponential (long-tailed) scene length distribution. In this case, precise modeling of intrascene statistics is of secondary importance for predicting the large queueing behavior. A fluid model, whose arrival process is obtained from the video data by replacing scene statistics with their means, is shown to asymptotically converge to the exact queue distribution. Using the transition scenario of moving from one stability region to the other by a change in the value of the server capacity, we synthesize recent queueing theoretic advances and ad hoc results in video modeling, and unify a broad range of seemingly contradictory experimental observations found in the literature. As a word of caution for the widespread usage of second-order statistics modeling methods, we construct two processes with the same second-order statistics that produce distinctly different queueing behaviors     

Kinetics of benzonitrile nitration with mixed acid under homogeneous conditions

Chemical kinetics of benzonitrile nitration with mixed acid is investigated in the temperature range 283–299 K. Pseudo-first-order rate constants are evaluated by means of rate experiments on homogeneous reacting mixtures having large stoichiometric excesses of nitric acid. The second-order kinetic constants for nitronium ion attack to the aromatic substrate are derived on the basis of the assessed nitration mechanism. An activation energy of 604 ± 37 kJ mol^?1 is calculated for this reaction step. © 1993 John Wiley & Sons, Inc.     

AN ALTERNATIVE SPECIFICATION FOR MODELING GROUNDWATER DYNAMICS

This research extends previous work with dynamic models to manage groundwater quality by using the consumptive nitrate use rate instead of the nitrate application rate. The analysis indicates that misspecification results in overestimation of economic benefits, and supra-optimum nitrogen fertilizer application rates and groundwater nitrate stocks at a steady state.     

PLATOP: a novel planarized trench isolation and field oxideformation using poly-silicon

A novel isolation scheme named planarized trench isolation and field oxide formation using poly-silicon (PLATOP) Is described. PLATOP is applicable to high-performance submicron VLSI since it results in encroachment-free shallow trenches, and planarized field oxide. The process offers poly silicon-filled deep trenches. The process also relies on noncritical lithography and novel etch processes to planarize the deposited poly-silicon from the top of the active areas, and oxidation to consume the poly-silicon in the field regions. Electrical results are presented proving the viability of the isolation scheme     

Electro-optic sampling system for the testing of high-speedintegrated circuits using a free running solid-state laser

This paper deals with the indirect electro-optic sampling technique for the low-invasive detection of periodical voltage waveforms on lines in high-speed integrated circuits. The system introduced here is based on a passive mode-coupled Ti:Sapphire-Laser as light source for generating optical pulses in the subpicosecond regime. Therefore, we have to synchronize the resulting electric measurement signal and its external trigger onto the pulse repetition rate of this free running solid-state laser. The multi user function of the laser system forces us to transmit the pulses via a single-mode fiber into the measurement setup. For that purpose we developed a special optical arrangement to minimize the widening of the pulses in the time domain. The system's high-temporal resolution of nearly 10 ps in combination with its high-voltage sensitivity of about 800 μV/√(Hz) is demonstrated by measurements of an integrated microwave frequency divider     

Selective saturation and inversion of multiple resonances in high-resolution solid-state 13C experiments using slow spinning CP/MAS and tailored DANTE pulse sequences.

Taking advantage of the long 13C T1 values generally encountered in solids, selective saturation and inversion of more than one resonance in 13C CP/MAS experiments can be achieved by sequentially applying several DANTE pulse sequences centered at different transmitter frequency offsets. A new selective saturation pulse sequence is introduced composed of a series of 90 degrees DANTE sequences separated by interrupted decoupling periods during which the selected resonance is destroyed. Applications of this method, including the simplification of the measurement of the principal values of the 13C chemical shift tensor under slow MAS conditions, are described. The determination of the aromaticity of coal using a relatively slow MAS rate is also described.     

Analysis of a resonant-cavity enhanced GaAs/AlGaAs MSMphotodetector

The authors have developed a 2-D device simulator for heterostructure metal-semiconductor-metal (MSM) photodetectors. They have incorporated a model of multilayer optics into the simulator and used it to analyze the temporal response of a resonant-cavity enhanced heterostructure with a confining buffer layer and a distributed Bragg reflector (DBR). The authors show that through fine tuning the layer thicknesses, optical resonance enhancement of the light absorption can be obtained