On the stereoselective aminoacylation of RNA

Aminoacylation of the “internal” 2′-hydroxyl groups of poly(A) with the imidazolide of racemic DL-leucine resulted in the formation of an enantiomeric excess of the D-ester, whereas aminoacylation with the imidazolide of racemic N-3,5-dinitrobenzoyl-DL-leucine gave an enantiomeric excess of the L-ester. Comparison of these results with those obtained earlier for alanine shows that the larger side chain tends to favor the formation of the D-ester. High resolution proton magnetic resonance spectroscopy was performed on the D- and L-alanyl “internal” 2′-esters of 3′,5′-ApA. The resonance of the side chain methyl group of the D-ester is upfield from that of the L-ester, and the separation of the peaks increases with a decrease in temperature.     

Nonlinear analysis of hydrodynamic instability in laminar flames—II. Numerical experiments

We consider a nonstationary nonlinear integrodifferential equation describing the evolution of a disturbed plane flame front. The following two-dimensional problems are solved numerically: (i) The formation of a wrinkled noncellular laminar flame front under conditions of spontaneous hydrodynamic instability. (ii) The formation of a turbulent cellular flame front under conditions of spontaneous diffusional-thermal instability. (iii) The formation of a turbulent wrinkled-cellular flame front under conditions of spontaneous hydrodynamic and diffusional-thermal instability. We compute the flame front velocity in laminar and turbulent propagation.     

Lightweight (AlGaAs)GaAs/CuInSe2 tandem junction solarcells for space applications

Mechanically stacked tandem cells consisting of GaAs thin-film upper cells and CuInSe₂ thin-film lower cells have been developed to meet the increasing power needs projected for future spacecraft. The authors report the fabrication of the first highly efficient lightweight GaAs/CuInSe₂ tandem cell on a 2-mil thick substrate, update recent performance improvements in thin-film GaAs/CuInSe₂ tandem cells, and discuss their application to space power systems. The efficiency of 4-cm² cells has improved to 21.6% AM0, the highest ever reported for a thin-film photovoltaic cell. Lightweight 4-cm² tandem cells have been successfully fabricated with efficiencies as high as 20.8%. These cells weighed about 180 mg without optimized substrate trimming. Radiation and operating temperature effects on GaAs/CuInSe₂ tandem cells are also discussed, and an interconnect scheme to form a voltage-matched string is described     

Determining rotation rates from light curves: RW Mon and RW Tau

We present light curve solutions for the non-synchronously rotating Algols RW Mon and RW Tau, and we illustrate how rotation rates are determined from light curves. We find RW Mon's primary component to spin at about 5 times the synchronous rate, which confirms the indication of fast rotation from reported emission line activity. RW Tau turns out to be only a mildly rapidly rotating Algol system, and our light curve solutions do not yield any firm value for the rotation rate of the primary component. It is suggested that continued efforts should be made to do good quality line broadening studies in order to find rotation rates for systems with only modest degrees of rapid rotation, and in order to further test photometric rotation rates against those of line broadening studies.     

LIPS III-a solar cell test bed in space

The LIPS III satellite, which was launched into a 1100-km circular orbit of 60° inclination in the spring of 1987, is discussed. LIPS III is a member of the living-plume-shield class of spacecraft, all of which were built around a simple sheet metal plume deflector. The purpose of LIPS III was to provide a testbed for space power sources. An overview of the LIPS III system is given, and the experiments submitted for it, all but one of which were photovoltaic in nature, are described     

PAVE PACE: system avionics for the 21st century

The PAVE PACE Initiative has been established to validate system avionics concepts for advanced military aircraft. The author presents the rationale of why the advanced architecture established by the PAVE PILLAR program should be continued under PAVE PACE to achieve: practical and affordable airborne versions of modular parallel processing network architectures for many applications currently beyond real-time implementation, readily available avionics for use in all avionics and, greatly improved techniques to reduce the cost of software development and support. An approach to the overall design structure for future avionics is also presented that entails: the use of CAD (computer-aided design) tools to assist in the development of system, hardware and software requirements, the use of replicated hardware modules (some at the wafer level), the use of reuseable software modules and the use of CAD tools to tailor hardware/software modules for specific application requirements. Continued use of the PAVE PILLAR high-speed data bus and operating system is recommended as the means to integrate and control the data input and output of physically and functionally separate parallel networks     

International participation and the space station : A contractor's perspective

This article presents the views of the Boeing company on the benefits and disadvantages of international participation in the space station. The author outlines the company's goals within the project, and makes some recommendations on how to reduce the concerns which arise from international cooperation, in order to maximize the benefits which could be achieved.     

Radar auroral observations and ionospheric electric fields

The ground-based systems STARE and SABRE utilize radar auroral phenomena to estimate ionospheric electric fields. Some of the assumptions underlying these systems have been tested and general agreement with expectations have been found. However, as the results have been analysed in detail, it has become clear that the error in the irregularity drift velocity can at times amount to 100 ms^?1. Direct comparisons with other E-field measurements, as well as assessments of the results of applications of the Stare data clearly demonstrate that the electric field, calculated on the basis of the irregularity drift velocity, is a useful estimate of the actual horizontal electric field in the ionosphere and is sufficiently accurate for a great variety of geophysical studies.     

Frequency Domain Interpolation

A formula is derived for interpolation between output samples of a fast Fourier transform (FFT), i.e., in the frequency domain. Such a formula is useful for obtaining greater frequency resolution when two coarse FFT outputs are available. Consideration is also given to the effect of such interpolation on a weighted FFT.     

Limiting Performance of Generalized Sign Test Detector

The limiting performance of the generalized sign test detector as the number M of target returns becomes infinite has been derived by Hansen and Olsen [1]. Simple expressions are derived herein for the limiting performance for finite M as K, the number of noise samples in the reference set, becomes infinite. Curves are presented which indicate how this limiting performance is approached as K is increased for both constant target returns and fluctuating target returns.