Results on thermal conditions of crystal growth processes in space and on earth

A special measurement technique allows to determine the stationary and dynamic temperature profiles, acting on a material sample during a Bridgman crystal growth process. It turns out that the thermal field of the furnaces at the place of the sample is modified by a number of device-related factors and by regular correlations. The investigations refer to the execution of experiments in the field of materials sciences in space in furnaces on board Salyut-stations.     

Properties of the neutral density and composition in the thermosphere

Measurements of the density and composition of the thermosphere between 150 and 500 km, which were obtained by the S3-1 satellite, have been compared with the Jacchia and MSIS models. The measurements of the densities of O, N₂, N and Ar show some differences from the current models which should be considered during the preparation of the next CIRA model. The Ar measurements are particularly useful in examining the response of the neutral atmosphere to geomagnetic heating. These results are useful in establishing the appropriate lower boundary conditions for modeling of the thermosphere.     

Quasi-Complementary Sequences

A method of constructing digital phase reversal codes which have few nonzero sidelobes and which are available in frequent lengths is given. This is particularly important in the area of longer codes. The codes are a form of combined sequence and, hence, have the desirable property of bandwidth reduction for the outer code. However, only two member codes are required. A major usage of these codes may be in addressing.     

The Infrared Space Observatory (ISO)

The Infrared Space Observatory (ISO), a fully approved and funded project of ESA, will operate at wavelengths from 3–200 microns. The satellite essentially consists of a large cryostat containing about 2300 litres of superfluid helium to maintain the telescope (primary mirror diameter of 60 cm) and the scientific instruments at temperatures between 2K and 8K. A pointing accuracy of a few arc seconds is provided by a three-axis-stabilisation system. ISO's instrument complement consists of four instruments, namely: an imaging photo-polarimeter (3–200 microns), a camera (3–17 microns), a short wavelength spectrometer (3–45 microns) and a long wavelength spectrometer (45–180 microns). ISO's scheduled launch date is May 1993 and it will be operational for at least 18 months. In keeping with ISO's role as an observatory, two-thirds of its observing time will be made available to the general astronomical community via several Calls for Observing Proposals.     

New maximum entropy spectrum using uncertain eigenstructureconstraints

A number of modern spectral estimators are shown to have a common generic formulation. These include minimum variance, MUSIC, and maximum entropy. A new maximum entropy spectral estimator is derived using constraints on the modal powers or the expected-square projections of the data onto the eigenvectors of the data covariance matrix. The formulation incorporates uncertainty in the modal power constraints and the signal-versus-noise subspace separation. The resulting estimators have forms which incorporate all other modern estimators, including maximum entropy and minimum norm. The new estimators allow further development when a priori information is used in the constraints. Comparison of one version of the estimator with the minimum norm verifies the greater probability of resolution of the minimum norm but indicates in some instances the value of the incorporated uncertainties. Another version uses complex constraints and reduces to conventional maximum entropy or minimum norm under certain conditions     

Measurements of the earth radiation budget from satellites during the first garp global experiment

Two special measurements of the energy exchange between earth and space were made in connection with the FGGE. A global monitoring program using wide-field-of-view and scanner detectors from NASA's NIMBUS-7 satellite successfully returned measurements during the entire FGGE. This experiment system also used a black cavity detector to measure the total energy output of the sun to very high precision. A second set of high frequency time and space estimates of the radiation budget were determined from selected geostationary satellite data. Preliminary results from both radiation budget data sets and the solar “constant” measurements will be presented.     

Physical determinants of radiation sensitivity in bacterial spores.

Several factors modifying radiation sensitivity in dry bacterial spores are described and discussed. Vacuum inducing the loss of critical structural water, very low dose rates of radiation from which the cell may recover, radiations of high linear energy transfer, and the action of temperature over long periods of time on previously irradiated cells are recognized from extensive laboratory work as important in determining survival of spores exposed to low radiation doses at low temperatures for long periods of time. Some extensions of laboratory work are proposed.     

Beam-plasma discharge in near rocket region

The model of beam-plasma discharge near the rocket following electron beam injection into the ionosphere is presented. The dependence of discharge plasma density on neutral atmosphere concentration and beam parameters is found. Radioemission and luminiscence intensities from discharge are estimated. The model is consistent with the data of ARAKS and “Zarnitsa-2” experiments.     

Determination of basic constants of satellite-atmosphere interaction from the analysis of motion of 1974-70A

The atmospheric drag and lift effects are studied on the orbital data of the satellite 1974-70A. The values of the thermal accomodation coefficient and of the drag coefficient are determined.     

Exact Detection Performance for Broadband Correlators

The detection of a broadband plane wave in an isotropic noise field is considered. The detection statistic used is the cross correlation of the sampled output from two sensors where the sampling rate equals the Nyquist rate and the time delay is an integer multiple of the sampling period. By restricting the number of points in the cross correlation to be even, the detection and false-alarm probbilities are obtained in closed form. Numerical results are presented for several special cases.