IRAS observations of cometary dust

The large beam size of the Infrared Astronomy Satellite (IRAS) focal plane detector array is well suited to measuring the low level thermal emission from cometary dust. Eight comets discovered in 1983 and nine previously known periodic comets were observed by IRAS during its ten month active lifetime. Dust production rates are derived for a wide range of heliocentric distances. Grain properties are inferred from application of simple models to the long wavelength spectral energy distribution.     

Core collapse,bounce aid shock propagation

Recent developments in the physics input for iron core collapse models of type II supernovae are reviewed. The effect of these developments on collapse calculations is also discussed. The inner core collapses homologously, with little change in specific entropy, bounces in the neighborhood of nuclear density, and sets up an outward moving shock. In adiabatic models an explosion may result. The Inclusion of neutrino effects may produce substantial shock damping. Current results indicate that core collapse, bounce and shock propagation does not produce an explosion when neutrino effects are included.     

Design Rules for Adaptive Arrays

The concepts of "equivalent linear arrays" and "minimum effective spacing" can be used to simplify the analysis of planar adaptive arrays. The resulting design rules permit the rapid determination of array configurations without the need for computer modeling.     

A Performance Measure for Evaluating Aircraft Landing Trajectories

A general performance index is developed for evaluating aircraft landing trajectories. The primary term in the index is the effect of noise on people residing near the air terminal. Other terms included are passenger comfort, fuel consumed, and the time spent in the near-terminal area. Models are developed for aircraft engine noise, passenger comfort, the population distribution about a specific airport, and the aircraft flight behavior. While this performance index may be used in computing optimal trajectories, it is also useful for comparing nonoptimal trajectories which, for one reason or another, may be worthy of consideration. Some examples of such comparisons are included through simulations of landing. The aircraft considered is a Boeing 737.     

Application of Endfire Arrays at Contemporary Glide-Slope Problem Sites

The application of the endfire-type, compatible instrument landing system (ILS) glide slope is discussed in the context of providing increased capability to install facilities without requirements for extensive terrain modification. Costs of preparing a site for glide-slope operation can be reduced many times by eliminating the requirement for the usual image-forming ground plane. An example is given where the first endfire glide slope has been installed at an airdrome on a mesa giving a high quality path in space in spite of the limited real estate. Recent flight data from this glide slope are presented.     

Exploration of the solar corona by high resolution solar decametric observations

In this review, current state of knowledge of high resolution observations at decameter wavelengths of the quiet Sun, the slowly varying component (SVC), type I to V bursts and noise storms is summarized. These observations have been interpreted to yield important physical parameters of the solar corona and the dynamical processes around 2R from the photosphere where transition from closed to open field lines takes places and the solar wind builds up. The decametric noise bursts have been classified into (i) BF type bursts which show variation of intensity with frequency and time and (ii) decametric type III bursts. The angular sizes of noise storm sources taking into account refraction and scattering effects are discussed. An attempt has been made to give phenomenology of all the known varieties of decametric bursts in this review. Available polarization information of decametric continuum and bursts has been summarized. Recent simultaneous satellite and ground-based observations of decametric solar bursts show that their intensities are deeply modulated by scintillations in the Earth's ionosphere. Salient features of various models and theories of the metric and decametric noise storms proposed so far are examined and a more satisfactory model is suggested which explains the BF type bursts as well as conventional noise storm bursts at decametric wavelengths invoking induced scattering process for 1 t conversion. Some suggestions for further solar decametric studies from the ground-based and satellite-borne experiments have been made.     

Performance of Digital Implementations of an Adaptive Processor

The performance of a digital implementation of an Applebaum-Howells type adaptive processor is analyzed for both a limiter and nonlimiter configuration. The performance is evaluated in terms of steady-state residue power, using either a single-pole filter or a perfect integrator to smooth the output of the correlation mixer. The latter filter is the more commonly used for digital implementations. It is shown that when using the perfect integrator filter for both the limiter and linear digital implementations, the steady-state average weight vector equals the optimum weight vector. Thus, for this filter, the steady-state residue power is the minimum possible for either implementation. When using the single-pole filter, neither implementation achieves the minimum possible steady-state residue power. The relative performance of the two implementations depends upon the relative gain settings. When the gains are adjusted to give comparable servo stability for the design maximum jammer power, a reasonable criterion for digital implementations because of analog to digital saturation, the limiter configuration always has smaller steady-state residue power.     

Absolute IR-spectra from the measurement of Fourier-spectrometers aboard Meteor 25 and 28

It is well known that temperature- and watervapour-profiles, ozone concentration, other atmospheric constituents and the surface-radiation of the Earth can be determined by remote sensing in the IR radiation range with the aid of a satellite.

The narrow-band radiation measurements for remote sensing of the atmosphere and the Earth-surface can be realized either by various radiometers working in selected frequency channels or, continuously in a given frequency range, by spectrometers with fixed spectral resolution.

Fourier-spectrometers (FS) have been used in Earth-orbit only four times up to now: Nimbus 3, Nimbus 4, Meteor 25 and Meteor 28.

The most important technical parameters, the working regime and some aspects of date processing of the FSs working aboard of Meteor 25 and Meteor 28 are given. For the determination of calibrated absolute spectra a method is used that is based on the experience of the first experiment and on the long time stability of the spectrometers. The results obtained in laboratory calibration tests and in the orbit are described.     

Optical observations of the X-ray source 2S0921-630

We report photometric observations of the optical counterpart of the X-ray source 2S0921-630. The data, obtained at the South African Astronomical Observatory during 3 weeks in 1980 and 1981, are consistent with a 17.9 day periodic modulation of the flux in the B band. Correlated variability of the (B-V) and (U-B) colour indices with the B mag. is demonstrated and quantified. The observed B mag. and colours at maximum and minimum light are used to compute some of the system parameters. A model of 2S0921-630 is proposed in terms of a binary system in which the variable inclination of a luminous accretion disc produces the long-term modulation of the optical flux.