Estimators of Log-Normal Distribution Parameters

The maximum likelihood estimates of the median m and mean-to-median ratio ? for a log-normally distributed variate are derived, together with the asymptotic variances of these estimates. Using a Monte Carlo simulation, it is shown that these asymptotic variances of the estimates are reasonable when the number of sample points is N ? 50forp ? 8.     

Thermodynamic transport properties in dense stars

The thermodynamic transport properties of special relativistic imperfect fluids, as found in dense stars, are investigated. These properties, which include thermal. and electrical conductivities, electrothermal coefficients, and bulk and shear viscosities may be formulated in terms of the momentum distribution functions obtained from the solution of the Boltzmann transport equation. Spherical harmonic solutions of the relaxation form of the relativistic magnetic Boltzmann transport equation have also been obtained which give the non-equilibrium momentum distribution function perturbation f-f⁽⁰⁾ = f(p) in terms of electromagnetic and thermal fields.     

Effect of gravity on coupled convective and interfacial instabilities during directional solidification

We investigate the role of gravity in a linear stability analysis of the onset of coupled convective and morphological instabilities during directional solidification at constant velocity of a dilute alloy of tin in lead. For solidification vertically upwards, the temperature gradient alone would cause a negative density gradient and the solute gradient alone would cause a positive density gradient. Two types of instability are found, a convective type that occurs for long wavelengths and a morphological type that occurs for short wavelengths. In general, these are coupled but the morphological instabilities are practically independent of gravity and thus correspond to the predictions of previous morphological stability theory in which density changes and convection are neglected. The convective instabilities depend strongly on gravity; for a growth velocity of V = 1 μm/s and a temperature gradient in the liquid of G_L = 200 K/cm, the critical concentrations for convective instabilities are 3.1 × 10^?4, 3.1 × 10^?2 and 2.39 wt. % for g_e = 980 cm/s², 10^?4 g_e and 10^?6 g_e, respectively. For low velocities, the convective instabilities occur at much lower solute concentrations than the morphological instabilities whereas at high velocities, the reverse is true. At intermediate velocities where the changeover takes place, there are oscillitory instabilities of mixed character whose periods range from 60 s at g_e to 6 × 10⁴ s at 10^?6 g_e.     

A numerical model to calculate the wake structure of a spacecraft under ionospheric conditions

A spacecraft, that travels at mesothermal speeds, disturbs the plasma in its surroundings. Due to the fade out of the ions an extended negative potential structure is formed behind the probe. A numerical model based on the Vlasov-Poisson system to describe the wake structure of a spacecraft under ionospheric conditions is presented. The dependence of the wake structure on the streaming velocity of the plasma and on the ratio of electron to ion temperature is discussed.     

Mass and heat exchange in liquids enclosed in containing walls at zero gravity

The dominant phenomena in miscible binary mixtures of melts are the four transport processes (thermal diffusion, heat transfer, concentration diffusion and diffusive heat transfer). In binary melts with no perfect solubility of the components in solid and liquid phase also internal Marangoni convections driven by interfacial forces seem to be possible.     

Extragalactic and galactic U.V. observations owing to the balloon borne scap telescope at the wavelength 2000 Å

The use of the 2 000 Å transmission window of the atmosphere permitted to observe for the first time from a balloon gondola the nearest galaxies ; 30 arc/sec. resolution images were obtained for M 31, spiral arms and nucleus, M 33, M 101, with their external spiral structure, M 82 and NGC 3 077. Nearly three hundred more distant galaxies have been detected up to the magnitude V = 13. Several HII regions of the Galaxy have been observed, chiefly NGC 7 000 and the Cyghus Loop. Numerous blue stars of the halo have been identified.     

Extreme ultraviolet observations of the solar corona: First results from the coronal diagnostic spectrometer on SOHO

We present first results from the Coronal Diagnostic Spectrometer (CDS) aboard the ESA/NASA Solar and Heliospheric Observatory (SOHO). CDS is a double spectrometer operating in the 151–785 Å range. This region of the solar spectrum is rich in emission lines from trace elements in the solar atmosphere, which can be used to derive diagnostic information on coronal and transition region plasmas. Early spectra are presented and well identified lines are listed. In addition, examples of images in selected wavelength ranges are shown, for a prominence, a loop system and a bright point, demonstrating well the power of such extreme ultraviolet observations.     

Raman scattering as a probe of planetary atmospheres

The observable effects of Raman scattering on the spectra of the giant planets may provide new information on the composition and structure of these atmospheres. Satellite observations have already shown the influence of Raman scattering on the UV continuum albedo. A cross correlation technique is presented for detecting rotational and vibrational transitions of the Raman active gases in the atmosphere. This technique has been applied to ground-based visible spectra of Venus, Jupiter, Saturn and Uranus. Extension of this method into the UV would improve the detectability of the Raman lines because the ratio of Raman to Rayleigh cross section increases with decreasing wavelength. The technology currently exists to efficiently obtain high signal-to-noise ratio UV spectra through the use of silicon diode array detectors. Application of the cross-correlation technique to UV spectra obtained from space vehicles would give us a new important probe of the structure and composition of planetary atmospheres by enabling us to use the UV spectra of a planet to observe that would normally be an infrared molecular transition.     

A Comparison of Complementary and Kalman Filtering

A technique used in the flight control industry for estimation when combining measurements is the complementary filter. This filter is usually designed without any reference to Wiener or Kalman filters, although it is related to them. This paper, which is mainly tutorial, reviews complementary filtering and shows its relationship to Kalman and Wiener filtering.