Interference effects on Space Station Freedom and Space Shuttleorbiter Ku-band downlinks

The Space Shuttle orbiter (SSO) Ku-band single access return (KSAR) link and the Space Station Freedom (SSF) KSAR link via the tracking and data relay satellite system (TDRSS) use the same carrier frequency. The interference between spacecraft is minimized by opposite antenna polarizations and by TDRSS antenna beam pointing, but if the SSF and SSO are in close proximity, it is expected that mutual interference will be significant. It is shown that a simplified analytical approach will yield adequate accuracy for the expected range of operating conditions. Relative degradation in bit-energy-to-thermal-noise power spectral density ratio to achieve a 10^-5 coded bit-error probability is determined to be 4 dB for the Ku-band SSO-to-TDRS I-channel return link with a 4.5-dB effective signal-to-interference total power ratio (S/I) when the Ku-band SSF-to-TDRS return link interferes. For the Ku -band SSF-to-TDRS return link, both analysis and simulation results yield a relative signal degradation of 0.4 dB at the effective S/I=21.6 dB     

Optimal regulators using time-weighted quadratic performance index with prespecified closed-loop eigenvalues

Optimization of linear time-invariant systems, using a given time-weighted quadratic performance index, is investigated for the prespecified closed-loop eigenvalues. The necessary conditions have simple forms and this algorithm gives a considerable amount of computational time savings compared to the previous algorithms [1]-[2].     

Constrained densification in boehmite–alumina mixtures for the fabrication of porous alumina ceramics

It is demonstrated that inherent constrained densification characteristics of the bimodal size distributed powders can be utilized to fabricate porous alpha alumina. Seeded boehmite was mixed with coarse alpha alumina particles to produce various compositions of bimodal mixtures. The densification behaviour of the mixtures was correlated with shrinkage and microstructural evolution. The mixtures sintered at 1200 °C contained more than 30% porosity and the mechanical strength of the mixtures was increased by 2–4 fold relative to the coarse particles alone with similar porosity (<5 MPa). © 1998 Chapman & Hall     

Experimental investigation on low energy impact behavior of foam cored sandwich composites

This study focuses on an experimental investigation of damage tolerance of the foam cored sandwich composite subjected to low energy impact. Tests are performed to correlate delamination length with failure loads and loss of damage tolerance of the sandwich composite. The impact force history is used to determine momentum imparted to the specimen, the work done on the specimen, and the kinetic energy in order to gain an understanding of the mechanisms involved in damage due to impact loading.     

Parallel computational geometry of rectangles

Rectangles in a plane provide a very useful abstraction for a number of problems in diverse fields. In this paper we consider the problem of computing geometric properties of a set of rectangles in the plane. We give parallel algorithms for a number of problems usingn processors wheren is the number of upright rectangles. Specifically, we present algorithms for computing the area, perimeter, eccentricity, and moment of inertia of the region covered by the rectangles inO(logn) time. We also present algorithms for computing the maximum clique and connected components of the rectangles inO(logn) time. Finally, we give algorithms for finding the entire contour of the rectangles and the medial axis representation of a givenn × n binary image inO(n) time. Our results are faster than previous results and optimal (to within a constant factor).The work of Sung Kwan Kim was supported by NSF Grant CCR-87-03196 and the work of D. M. Mount was partially supported by National Science Foundation Grant CCR-89-08901.     

An electrically saturated anti-plane shear crack in a piezoelectric layer constrained between two elastic layers

Within the framework of linear elasticity and nonlinear electroelasticity, the electrical nonlinear behavior of an anti-plane shear crack in a piezoelectric ceramic layer constrained between two orthotropic layers is examined by using an electrical strip saturation model. The analysis is performed based on the electrical unified crack surface condition, which can describe all of the permeable, the impermeable, and the limited permeable ones. Fourier transforms are used to reduce the problem to the solutions of two pairs of dual integral equations, which are then expressed to two Fredholm integral equations of the second kind. Some numerical results for the energy release rates are presented to show the effects of the electrical crack condition parameter relating with elliptic flaw shape parameters and permittivity inside the crack, the electric field, the crack length, the electromechanical coupling coefficient, the crack position, and the bonded elastic materials.     

Novel Current Driving Circuit for Active Matrix Organic Light Emitting Diode

This paper describes a novel current driving circuit for an active matrix organic light emitting diode (AMOLED). The proposed current driving circuit has a lower power consumption and higher chip density for the AMOLED display compared with the conventional one because all elements operate at a normal voltage and are shielded from the high voltage of the panel. The chip size and power consumption of the current driving circuit for an AMOLED can be improved by about 30 to 40% and 10 to 20%, respectively, compared with the conventional one.     

V-band harmonic injection-locked frequency divider using cross-coupled FETs

A V-band 1/2 frequency divider is developed using harmonic injection-locked oscillator. The cross-coupled field effect transistors (FETs) and low quality-factor microstrip resonator are employed as a wide-band oscillator to extend the locking bandwidth. The second harmonic of free-running oscillation signal is injected to the gates of cross-coupled FETs for high-sensitivity superharmonic injection locking. The fabricated microwave monolithic integrated circuit frequency divider using 0.15-/spl mu/m GaAs pHEMT process showed a maximum locking range of 7.4 GHz (from 65.1 to 72.5 GHz) under a low power dissipation of 100 mW. The maximum single-ended output power was as high as -3 dBm.     

Actinomycin D, C2 and VII, inhibitors of Grb2-SHC interaction produced by Streptomyces

Actinomycin D, C2 and VII, cyclic peptides, inhibited Grb2 SH2 domain association (IC50 5-7 microM) with a phosphotyrosine containing peptide derived from the Shc protein (pTyr317). Actinomycins are the first examples of nonphosphorylated natural ligands of SH2 domain.