Eutectic solidification of Al-Cu alloys influenced by convection

Directional solidification of eutectic Al-Cu alloys has been studied to demonstrate the influence of both impurity concentration and convective conditions. The λ/R relations show that higher iron concentration and intensive stirring coarsen the microstructure. The formation and growth of new iron-containing phases at the solidification front restrict impurity influence. Kinetic data follow a dependence λ.Rⁿ=const with n-value close to 0,5.     

Sporadic emission of ultra high energy gamma rays from crab pulsar

In a further study of sporadic emission from pulsars we find evidence for short lived intense emission from the Crab pulsar.     

ROSAT PSPC observations of two starburst galaxies

We present results from ROSAT observations of NGC 1808 and NGC 2903. Exposures of 10 ksec each with the PSPC detector show X-ray sources at the central positions of both galaxies which are classified as nuclear starburst galaxies. Both targets, NGC 1808 and NGC 2903 appear slightly extended in X-ray maps in the energy band 0.1–2.4 keV. The X-ray spectrum of NGC 1808 shows almost complete absorption below 0.5 keV, indicating an extremely high hydrogen column density towards that source (N_H ≈ 8 × 10²¹cm⁻² resulting from model fits on the PSPC spectrum). In case of NGC 2903, the number of counts in the ROSAT band is significantly lower than expected from a previous EINSTEIN investigation of the source.     

Reduction of aliasing ambiguities through phase relations

A method for digital determination of a single frequency from a sine wave sampled at less than the Nyquist rate is discussed. The method makes use of phase shift information to eliminate the aliasing ambiguity. Multiple sampled data are required to eliminate ambiguity completely. Computer modeling using simulated data corrupted by uncorrelated Gaussian noise was used to verify the approach. The results demonstrate that the frequency of an input sine wave can be correctly identified. This approach can be applied to electronic warfare (EW) receivers to increase their input bandwidth     

Modeling of liquid encapsulated gallium melts

Liquid encapsulation crystal growth from the melt plays an important role in space processing. Use of an encapsulant may avoid evaporation of volatile components and may control thermocapillary flow, which becomes important in microgravity. In the present work the fluid physics of encapsulated liquid gallium is studied analytically and numerically in preparation to forthcoming experiments. It is shown that flow in the viscous encapsulant is essentially negligible and that liquid encapsulation reduces flow velocities in the encapsulated electronic melt. Flow velocity in the gallium is the main parameter in the studies.     

Sharp Boundaries of Solar Wind Plasma Structures and an Analysis of Their Pressure Balance

This work is devoted to studying the sharp boundaries of small-scale structures of the solar wind according to the data of measurements with high time resolution onboard the INTERBALL-1 satellite and simultaneous measurements of the WIND spacecraft. Such issues as the character of change of various plasma and magnetic field parameters on these boundaries, the duration of boundary passage and the balance of the total (thermal plus magnetic) pressure on the boundaries of the structures are considered. On the basis of the vast statistical material available, the typical conditions in the solar wind are investigated, in which such sharp boundaries are observed.__________Translated from Kosmicheskie Issledovaniya, Vol. 43, No. 3, 2005, pp. 163–170.Original Russian Text Copyright © 2005 by Riazantseva, Khabarova, Zastenker, Richardson.     

Ion composition behaviour in low and mid-latitudes during high solar activity

In the present analysis, the mass spectrometer data from the ISS-b satellite, available in the form of contour plots at an average height of 1100 km for every alternate hour, is used. This analysis showed some interesting results in terms of the diurnal variation of the transition heights; at times dominance of He⁺ over the other ions, and the seasonal variations of different constituents. In the development of ion composition models, it is suggested that this type of result should be taken into consideration.     

Trigonometric Approximations for Bessel Functions

Bessel functions, used extensively in mathematical physics, electromagnetics, and communication-system theory, must often be approximated by appropriate formulas. The functions J?(x) and I?(x) for integer values of p are well approximated by the sum of a small number of circular and hyperbolic sines or cosines, respectively, when x is not too large, e.g., less than 10, and convenient expressions are obtained for their errors. These approximations are especially convenient for use on personal computers (PCs) and pocket calculators and in analytically evaluating integrals.     

On the generation of the stimulated electromagnetic emission. The computer simulation results

Results of computer simulations of the broad continuum (BC) feature of stimulated electromagnetic emissions (SEE) of the ionosphere are presented. The simulations were performed using the model of BC generation based on the double transformation of electromagnetic waves to upper hybrid (UH) waves and back with artificial small scale irregularities (ASI) of plasma density. An induced scattering of the UH waves by thermal ions provided a wide spectrum of SEE. For the simulations an empirical model of the ASI spectrum, development and decay was used.