Thermodynamic Analysis of the Wilson Model Using Partial Excess Functions

An approach to thermodynamic analysis of models of liquid solutions is developed. The approach is based on studying local characteristics of the concentration dependences of the partial excess molar functions. The applicability region is established, and constraints on the parameters of the Wilson equation are found.     

High-performance surface-micromachined inchworm actuator

This work demonstrates a polycrystalline silicon surface-micromachined inchworm actuator that exhibits high-performance characteristics such as large force (/spl plusmn/0.5 millinewtons), large velocity range (0 to /spl plusmn/4.4 mm/sec), large displacement range (/spl plusmn/100 microns), small step size (/spl plusmn/10, /spl plusmn/40 or /spl plusmn/100 nanometers), low power consumption (nanojoules per cycle), continuous bidirectional operation and relatively small area (600 /spl times/ 200/spl mu/m/sup 2/). An in situ load spring calibrated on a logarithmic scale from micronewtons to millinewtons, optical microscopy and Michelson interferometry are used to characterize its performance. The actuator consists of a force-amplifying plate that spans two voltage-controlled clamps, and walking is achieved by appropriately sequencing signals to these three components. In the clamps, normal force is borne by equipotential rubbing counterfaces, enabling friction to be measured against load. Using different monolayer coatings, we show that the static coefficient of friction can be changed from 0.14 to 1.04, and that it is load-independent over a broad range. We further find that the static coefficient of friction does not accurately predict the force generated by the actuator and attribute this to nanometer-scale presliding tangential deflections.     

Wavelength stabilizer for telecommunication lasers: design and optimization

We introduce a novel method for the wavelength stabilization of semiconductor lasers for telecommunications. The approach is based on a wavelength-sensitive photodetector which, in a feedback system, generates an error signal apt to tune the source to the desired value. We extensively investigate the influence of various design parameters on performance figures such as tunability, steady-state error, and temperature dependence, as well as fabrication tolerances. The results are compared with standard specifications for wavelength-division-multiplexed optical communications with various channel spacings.     

Performance failure analysis of EDFA cascades in optical DWDM packet-switched networks

A simple and comprehensive technique to determine the probability that a cascade of erbium-doped fiber amplifiers (EDFAs) may be driven into unacceptable regimes of bit error rate (BER) and/or gain levels is presented. This technique allows network designers to determine the tolerances by which the signal power levels may deviate from their predesigned average values and still give acceptable gain variances and BERs at the receiver. We show that even in the signal power range well above the receiver sensitivities (-38 dBm/ch) where the gain spread is not significant, the corresponding spread in BER due to random arrival of packets might result in unacceptable performance. We show for typical levels of operation, the BER temporarily (for about 3 /spl mu/s) deviates to below 10/sup -9/ (10/sup -15/) with a probability of 10/sup -3/ (10/sup -2/), for 100 (64) channels. We show that the gain spread for a single EDFA can be negligible for a range of signal and pump powers at a given average gain.     

QoS enhancement for adaptive streaming services over WCDMA

This paper presents a new method to adapt the quality-of-service (QoS) in a wideband code-division multiple-access (WCDMA) system, called radio network feedback (RNF). The concept of RNF is in general applicable to all the services requiring a minimum quality (i.e., non best effort) and in this paper, the focus is on streaming. In this context, RNF makes it possible for a streaming server to adapt its source bit rate to a WCDMA radio link, whose bandwidth may vary in time due, for example, to decongestion/congestion situations over the air interface or to handover. This is very beneficial for the end user as it allows to increase the bandwidth (i.e., the quality) when possible and to decrease it (instead of just dropping the service) when needed. RNF was compared with Client-based adaptation solutions. Simulation results show that RNF is fast and accurate and performs better than Client-based adaptation. For example, rebuffering occurs only with Client-based method. Moreover, with RNF the up-switch is performed only when needed, whereas the up-switch performed by means of the Client-based method is often erroneous and may annoy the end user.     

High voltage (>1kV) and high current gain (32) 4H-SiC power BJTs using Al-free ohmic contact to the base

This letter reports the design and fabrication of 4H-SiC bipolar junction transistors with both high voltage (>1kV) and high dc current gain (/spl beta/=32) at a collector current level of I/sub c/=3.83A (J/sub c/=319 A/cm/sup 2/). An Al-free base ohmic contact has been used which, when compared with BJTs fabricated with Al-based base contact, shows clearly improved blocking voltage. A specific on-resistance of 17 m/spl Omega//spl middot/cm/sup 2/ has been achieved for collector current densities up to 289 A/cm/sup 2/.     

Design of radiation-emission measurements of an air-traffic surveillance radar

The current work presents the procedure of designing and carrying out measurements of radiation emission from an air-traffic surveillance radar. The system requirements are first given, and then the equipment used is described. The steps to determine the operating characteristics of the radar are specified in detail. The necessary methods for manual power measurements and calculations are next explained. Since the final measurement system was fully automated, its main features (topology, protocol of operation) are also given. Finally, some measurement results taken during the initial phase of system operation are presented and discussed.