Effect of enclosure shape on natural convection velocities in microgravity

A numerical analysis was performed to compare natural convection velocities in two-dimensional enclosures of various shape. The following shapes were investigated: circle, square, horizontal and upright 2 × 1 aspect ratio rectangles, horizontal and upright half-circles, diamond (square oriented with diagonal vertical) and triangle (equilateral and horizontal base). In all cases, the length scale in the various dimensionless parameters, such as Rayleigh number, is defined as the diameter of the equal area circle. Natural convection velocities were calculated for Rayleigh numbers of 100 and 500 with the temperature difference taken to be across (a) the maximum horizontal dimension, (b) the median horizontal line (line through centroid) and (c) the horizontal distance such that the temperature gradient is the same for shapes of equal area. A Rayleigh number of 1000 is within the “low Rayleigh number” range for agreement with first order theory for circular enclosures. A Rayleigh number of 5000 is slightly out of this range. For the class of shapes including the square, upright half-circle and upright rectangle, the computed velocities were found to agree very closely with that of the equal area circle when the temperature difference is taken to be across the maximum horizontal dimension [condition (a)]. The velocities for the horizontal rectangle and half circle were found to be approximately one-half that of the equal area circle for the same condition. Better overall agreement among all shapes was obtained by setting the temperature difference across a distance such that the temperature gradients were equal for shapes of equal area.     

Adaptive Estimation for a System with Unknown Measu rement Bias

An adaptive state estimator for passive underwater tracking of maneuvering targets is developed. The state estimator is designed specifically for a system containing unknown or randomly switching biased measurements. In modeling the stochastic system, it is assumed that the bias sequence dynamics can be modeled by a semi-Markov process. By incorporating the semi-Markovian concept into a Bayesian estimation technique, an estimator consisting of a bank of parallel, adaptively weighted, Kalman filters has been developed. Despite the large and randomly varying measurement biases, the proposed estimator, provides an accurate estimate of the system states.     

Generalized Problem of Two Fixed Centers or the Darboux-Gredeaks Problem

A brief review of publications on the problem of two fixed centers is given, including its generalizations and astronomical applications. A comparison of the Darboux potential with that of Eve Gredeaks is made. An account of the basic points of development of modern high-precision theories of the motion of planetary satellites, based on the Gredeaks’ intermediate orbit, is given.__________Translated from Kosmicheskie Issledovaniya, Vol. 43, No. 3, 2005, pp. 194–200.Original Russian Text Copyright © 2005 by Lukyanov, Emeljanov, Shirmin.Dedicated to the memory of Professor Evgenii Petrovich Aksenov     

1E 1740.7-2942 revisited: Confirmation of its identification with the core of a double sided radio jet structure

After more than two years of successful in-orbit operations, the γ-ray coded aperture SIGMA telescope has accumulated 800 hours of live-time observations of the Galactic Center region, including the remarkable hard source identified with the X-ray source 1E 1740.7–2942. The long-term behavior of the soft γ-ray emission of 1E 1740.7–2942, as determined from the SIGMA survey, supplemented with previously available soft γ-ray data, leads to its identification with a singular radio source, which consists of a double sided radio jet emanating from a compact variable core whose variability is correlated with that of the soft γ-ray source. The compact radio core, which lies well inside the improved soft γ-ray (40–150 keV) error circle (27″ radius) derived from the high-resolution SIGMA survey, is also inside the ROSAT and TTM error circle derived respectively in the soft and hard X-ray bands.     

"SYMBIOSE" SYstem for Microgravity BIOregenerative Support of Experiments.

SYMBIOSE is an ESA supported research and development program which aims at establishing a first pilot model of a closed ecological system, compatible with operation in weightlessness conditions, and dedicated to scientific investigations in the microgravity environment. It integrates microalgal photosynthesis within an artificial ecosystem featuring a symbiotic strain of Chlorella (241 .80, Gottingen), which synthesizes and excretes substantial amounts of maltose, and is further looped on a consumer compartment. A technological concept has been developed. It is presently being integrated in order to gain knowledge on the system dynamics, and ultimately demonstrate the feasibility of such a biotechnology. Preliminary work on the photosynthetic metabolism of this microalga is being undertaken in order 1) to support later a mathematical formalisation of the dynamics of this artificial ecosystem, and, on this basis, 2) to compensate for its lack of stability with model-based external control. The most recent results are presented, along with a new design of the photobioreactor which integrates efficient light energy capture, microgravity compatible gas transfer and reduced shear stress.     

Image understanding research for automatic target recognition

Automatic target recognition (ATR) is an important capability for defense applications. Many aspects of image understanding (IU) research are traditionally used to solve ATR problems. The authors discuss ATR applications and problems in developing real-world ATR systems and present the status of technology for these systems. They identify several IU problems that need to be resolved in order to enhance the effectiveness of ATR-based weapon systems. They conclude that technological gains in developing robust ATR systems will lead to significant advances in many other areas of applications of image understanding     

Changes of contractile responses due to simulated weightlessness in rat soleus muscle.

Some contractile and electrophysiological properties of muscle fibers isolated from the slow-twitch soleus (SOL) and fast-twitch extensor digitorum longus (EDL) muscles of rats were compared with those measured in SOL muscles from suspended rats. In suspended SOL (21 days of tail-suspension) membrane potential (Em), intracellular sodium activity (aiNa) and the slope of the relationship between Em and log [K]o were typical of fast-twitch muscles. The relation between the maximal amplitude of K-contractures vs Em was steeper for control SOL than for EDL and suspended SOL muscles. After suspension, in SOL muscles the contractile threshold and the inactivation curves for K-contractures were shifted to more positive Em. Repriming of K-contractures was unaffected by suspension. The exposure of isolated fibers to perchlorate (ClO4-)-containing (6-40 mM) solutions resulted in a similar concentration-dependent shift to more negative Em of activation curves for EDL and suspended SOL muscles. On exposure to a Na-free TEA solution, SOL from control and suspended rats, in contrast to EDL muscles, generated slow contractile responses. Suspended SOL showed a reduced sensitivity to the contracture-producing effect of caffeine compared to control muscles. These results suggested that the modifications observed due to suspension could be encounted by changes in the characteristics of muscle fibers from slow to fast-twitch type.     

Heating of the solar corona by Alfvén wave envelopes

Alfvén waves are investigated including dissipation and dispersion (Hall effect). The latter leads to a modulational instability and to a soliton envelope so that the temperature may increase by an order of magnitude. Applications are the heating of the solar corona, a possible triggering of flares and maybe tokamak heating.     

Balloon-borne far-infrared spectrophotometry of the galactic center region

Far-infrared observations of the Galactic Center have been carried through with the MPE Im balloon-borne telescope “Golden Dragon”. The measurements are composed of photometric scanning (33–95 μm) of the inner 4′×4′ and low resolution spectroscopy (δ^ν = 10 cm^?1) of the center and of a position approximately 1.5′ to the north. A Mars spectrum has been obtained for calibration. The spatial resolution of the photometry map is increased using the Maximum Entropy Method and the resulting map is compared to other observations in the same and other spectral regions. A clear asymmetry in the ring-like structure around the center indicates the presence of noncircular motions. The shape of the spectra is fairly smooth with at least no prominent dust features. A simple modelling shows a drastic increase of column density within 2 pc from the center and a modest drop over the next 3 pc to the north.     

The role of scientific ballooning for exploration of the magnetosphere

The magnetosphere is explored in situ by satellites, but measurements near the low altitude magnetospheric boundary by rockets, balloons and groundbased instruments play a very significant role. The geomagnetic field provides a frame with anisotropic wave and particle propagation effects, enabling remote sensing of the distant magnetosphere by means of balloon-borne and groundbased instruments. Examples will be given of successful studies, with coordinated satellite and balloon observations, of substorm, pulsation and other phenomena propagating both along and across the geomagnetic field. Continued efforts with sophisticated balloon-borne instrumentations should contribute substantially to our understanding of magnetospheric physics.