OMCVD-grown In0.4Al0.6As/InP quantum-wellHEMT

The transport properties and device characteristics of pseudomorphic In_0.4Al_0.6As/InP modulation-doped heterostructures are investigated. The existence of a two-dimensional electron gas at the heterojunction was confirmed by Shubnikov-de Haas measurements. A high electron mobility transistor (HEMT) having a gate length of 1.5 μm showed extrinsic transconductances and drain current densities as high as 160 mS/mm and 300 mA/mm, respectively. The HEMT also showed a very small output conductance of less than 2 mS/mm and high gate-drain breakdown voltage of larger than 15 V. These results show the great potential of this HEMT for high-voltage gain and high-power microwave applications     

In0.52Al0.48As/In0.53Ga0.47As MSM photodetectors and HEMT's grown by MOCVD on GaAs substrates

The authors report the first demonstration of In_0.52Al _0.48As/In_0.53Ga_0.47As metal-semiconductor-metal (MSM) photodetectors and high-electron-mobility transistors (HEMTs) grown on GaAs substrates by organometallic chemical vapor deposition. Both photodetectors and transistors showed no degradation in performance compared to devices simultaneously grown on InP substrates. The photodetectors exhibited a responsivity of 0.45 A/W and leakage current of 10 to 50 nA. The HEMTs with a gate length of 1.0 μm showed a transconductance as high as 250 mS/mm, and f_T and f_max of 25 and 70 GHz, respectively     

High speed performance of 1.5 mu m compressive-strained multiquantum-well gain-coupled distributed-feedback lasers

1.5 mu m compressive-strained multiquantum-well gain-coupled distributed-feedback lasers have been fabricated on semi-insulating InP substrates with very low parasitic capacitance for studying the laser dynamic characteristics. A maximum 3 dB bandwidth of 12.8 GHz under small signal modulation, a 20 dB down chirping width of 0.33 nm under modulation, a 20 dB down chirping width of 0.33 nm under 5 Gbit/s NRZ pseudorandom modulation, and a low chirping short pulse of 20 ps under gain switching are obtained.<>     

Analysis and design of a series-parallel resonant converter

A high-frequency link series-parallel resonant power converter is analyzed using the state-space approach. Analysis is presented for both the continuous capacitor voltage mode and the discontinuous capacitor voltage mode. Steady-state solutions are derived. Design curves for the converter gain and other component stresses are obtained. A method of optimizing the converter under certain constraints is presented and a simple design procedure is illustrated by a design example. Experimental results are presented to verify the theory     

Nonrandom Parameter Estimation Using Min-Max Theory

A decision-theoretic approach is proposed for bad-data elimination in parameter estimation. A linear measurement model with unknown additive noise having zero mean is considered and the noise distribution is assumed to be symmetrical and absolutely continuous. The partial covariance of the measurement random variable is considered to be constrained, and its minimum covariance and unbiasedness are chosen as criteria of goodness for the estimator. Using game-theory, a soft-limiter is shown to be optimal. It is also established that in the presence of bad data, performance of the proposed scheme is superior, and in its absence comparable, to that of linear estimators.     

Processing map for hot working of powder

The constitutive flow behavior of a metal matrix composite (MMC) with 2124 aluminum containing 20 vol pct silicon carbide particulates under hot-working conditions in the temperature range of 300 °C to 550 °C and strain-rate range of 0.001 to 1 s^-1 has been studied using hot compression testing. Processing maps depicting the variation of the efficiency of power dissipation given by [2m/(m + 1)] (wherem is the strain-rate sensitivity of flow stress) with temperature and strain rate have been established for the MMC as well as for the matrix material. The maps have been interpreted on the basis of the Dynamic Materials Model (DMM). [3] The MMC exhibited a domain of superplasticity in the temperature range of 450 °C to 550 °C and at strain rates less than 0.1 s^-1. At 500 °C and 1 s^-1 strain rate, the MMC undergoes dynamic recrystallization (DRX), resulting in a reconstitution of microstructure. In comparison with the map for the matrix material, the DRX domain occurred at a strain rate higher by three orders of magnitude. At temperatures lower than 400 °C, the MMC exhibited dynamic recovery, while at 550 °C and 1 s^-1, cracking occurred at the prior particle boundaries (representing surfaces of the initial powder particles). The optimum temperature and strain-rate combination for billet conditioning of the MMC is 500 °C and 1 s^-1, while secondary metalworking may be done in the super- plasticity domain. The MMC undergoes microstructural instability at temperatures lower than 400 °C and strain rates higher than 0.1 s^-1.     

Isothermal studies of bainitic and martensitic transformations in some low alloy steels

Ohne Zusammenfassung     

An inclined porous slider bearing with a transverse magnetic field

A hydromagnetic inclined porous slider bearing with a transverse magnetic field is analysed. Expressions for various bearing characteristics are obtained for large and small Hartmann numbers. The dimensionless load capacity, friction and centre of pressure are computed for large Hartmann numbers in the open-circuit case; the load capacity and friction increase markedly with increasing Hartmann number.     

Orbit computations

Orbital information forAryabhata was computed and made available for telemetry and tracking schedules and for mission analysis. Taking an available statevector once in a week from USSR, the orbital computations were made for the first four months using a numerical integration procedure. During the later period of the mission, an analytical method was adopted to reduce the computer time.Aryabhata, in a near circular orbit at 600 km and having an inclination of 50.68°, experienced a constant atmospheric drag due to which the semi-major axis decayed by about 0.5 km in one year. The nodal regression rate, due to asphericity of the earth, was almost constant at 4.632°/day. The inclination remained constant throughout the year.     

End effects in coupled rectangular resonators in unilateral fin line

Spectral domain analysis is used to determine the end effects in coupled rectangular slot resonators in unilateral fin lines. End corrections computed as a function of the structural parameters are reported.