Gain-coupled strained layer MQW-DFB lasers with an essentiallysimplified fabrication process for λ=1.55 μm

A gain-coupled (GC) strained-layer (SL) multi-quantum-well (MQW) distributed-feedback (DFB) laser with a metallized surface grating and a substantially simplified fabrication process made by single-step epitaxy without corrugation overgrowth is described. The complex coupling coefficient can be adjusted by the contact metallization. Room-temperature single-mode continuous-wave (CW) operation with a threshold current of 22 mA, an output power of 20 mW, and a linewidth of 2.5 MHz is demonstrated     

Epitaxial lift-off GaAs HEMT's

An extensive study of epitaxial lift-off (ELO) Al_0.3Ga _0.7As/GaAs modulation doped heterostructure high electron mobility field-effect transistors (HEMT's) is presented. Effects of ELO on electron transport properties of two-dimensional electron gas at AlGaAs/GaAs interface are investigated. An ELO HEMT with 1.5 μm gate length had a maximum extrinsic transconductance g_m-max=125 mS/mm, a unity current gain cut-off frequency f_t=10.5 GHz, and a maximum frequency of oscillation f_max=12 GHz. Statistical distributions of maximum intrinsic transconductance of ELO HEMT's are presented and compared with their on-wafer counterparts. Stability of the ELO HEMT's has also been evaluated by continuous operation at room temperature under dc bias     

New cubane MOCVD precursors for gallium sulphide and gallium selenide: Synthesis of [(Et2MeC)GaS]4 and [(Me2EtC)GaS]4: Structural determinations of [(Et2MeC)GaS]4 by X-ray diffraction and [(tBu)GaSe]4 by electron diffraction

The gallium sulphide cubane compounds [(Me₂EtC)GaS]₄ and [(Et₂MeC)GaS]₄, have been synthesised, and their potential as MOCVD precursors for GaS is discussed. The molecular structure of [(Et₂MeC)GaS]₄ has been determined by X-ray diffraction. In addition, the vapour phase structure of the GaSe precursor, [(^tBu)GaSe]₄ has been determined by gas phase electron diffraction and is compared with that previously determined in the solid state by X-ray diffraction.     

The electrode system in impedance-based ventilation measurement

In this paper, we determined which electrode types, sizes, and locations were best suited for impedance-based ventilation measurement. Optimal electrodes provide high signal-to-(motion) artifact ratio (SAR) and reliability by meeting the following criteria: 1) low baseline impedance, 2) high adhesion, 3) good physical stability, 4) large effective area, 5) thin with high flexibility. We compared 14 electrodes from two main groups: adhesive-gel and conductive rubber electrodes. Adhesive-gel electrodes are easy to apply, make good body contact, and do not slip during the course of an experiment. We found that higher SAR's are obtained when electrode area is increased by connecting several small electrodes together rather than by using a single electrode with a larger area. The peak SAR is achieved when two electrode arrays (area = 70 cm2) are centered at the 8th intercostal spaces on opposite midaxillary lines. To determine the optimal electrode locations, we placed 32 electrodes on the trunk and recorded impedance between 171 electrode combinations on ten normal adult subjects. Based on these data, we conclude that the SAR's are highest when one electrode is placed on the midpoint between the left and right second intercostal spaces on the sternum and the other electrode is placed in the opposite position on the back.     

A power-efficient channel coder/decoder chip for GSM terminals

A compact power- and computing-delay-efficient channel codec chip for the Pan-European digital cellular radio (GSM) system is presented. This key component for the hand-portable mobile station, mainly implementing GSM Recommendation 5.03 on a full duplex basis, is accomplished through a dedicated architecture and application tailored memories. An important effort was made to increase the testability of the design; the sequentiality, the low pin count, and the presence of embedded macro functions implied the need for internal scan and BIST techniques. Full scan design and self-test facilities, supported by automatic test pattern generating software, resulted in time- and coverage-efficient testing. The chip is fabricated in a double-metal 1.2-μm CMOS technology, using a cell-based design approach incorporating memory and programmable array macro blocks. A full-rate speech channel block is decoded in less than 1.8 ms and typical average in-system power consumption does not exceed 10 mW     

Scattering from a thin perfectly-conducting square plate

Extensive numerical experiments on the scattering from a thin perfectly conducting square plate have been carried out to assess the performance of the exact analytical expressions for the electromagnetic field of a rectangular patch with uniform and linear distributions of current, in connection with the method of moments. Two solution schemes, employing pulses and roof-top functions for approximating the surface current on the plate, have been used. Convergence rates and results for the two solution schemes are compared with each other, as well as with an efficient solution by A.W. Glisson and D.R. Wilton (1980). The overall performance indicated by the numerical experiments suggests that it would be useful to use the exact numerical expressions in the solution of problems where accurate computation of the field radiated by such current sources is required     

Terminal-pair reliability of three-type computer communicationnetworks

The terminal-pair reliabilities, between the root and a leaf, of the two-center binary tree, the X-tree, and the ring-tree are computed; the beheaded binary tree is used as a benchmark. A building block is identified in the two-center binary tree from which a decomposition method is formulated. Another building block is identified for the X-tree and ring-tree from which a truss-transformation method is obtained. Computation has been carried out using algorithms based on the analysis. Although the ring-tree is the most reliable at all practical ranges of link and mode reliabilities, the X-tree and two-center binary tree are also good candidates because link reliability over 0.95 is quite common, and node reliability can be kept very high. The X-tree in particular is quite desirable due to its lower connectivity at each node and hence a lower implementation complexity. Three computational methods are presented. The simplicity of the two-center binary-tree algorithm blends with the hierarchical structure of the network itself because the states directly show that the level of computation can be summarized by some reliability subcomponents     

Error probability for reduced-state sequence estimation

The performance of ideal reduced-state sequence estimation (RSSE) (without error propagation) is known as a good approximation to the performance of real RSSE. In the literature, the minimum distance of ideal RSSE has been employed for approximating the error probability of real RSSE. However, this approximation can be very poor, even though the system has a large signal-to-noise ratio. In this work, a union upper bound on the error probability for ideal RSSE is used to approximate the true error probability. This union bound provides a better approximation than the minimum distance. A new method based on a stack algorithm and a subset-error state diagram is proposed for calculating this union bound. The stack algorithm is employed because it provides a good tradeoff between computer memory and computing time