Prolonged weightlessness, reference frames and visual symmetry detection

We evaluated the influence of prolonged weightlessness on the performance of three cosmonauts to bilateral symmetry detection in the course of a 15-day-long Russian-French mission CASSIOPEE 96 aboard the MIR station. We tested the influence of weightlessness on subjects' performance as a function of the retinal orientation of axis of symmetry. as a function of type of stimuli (closed versus multi-elements shapes) and as a function of visual field presentation (at fixation, left visual field. right visual field). The results indicate firstly a difference between presentation at fixation versus away of fixation. Away of fixation, no effect of microgravity on performance was shown. A hypothesis of hemispheric specialization for symmetry detection was not supported as well. At fixation, an effect of micro-gravity was shown and more interestingly, the effect was quite different as a function of type of shapes used. suggesting that symmetry detection is a multiple-stage process.     

Vertical motions in Thailand after the 2004 Sumatra–Andaman Earthquake from GPS observations and its geophysical modelling

Following previous findings from ongoing GPS research in Thailand since 2004 we continue to exploit the GPS technique to monitor and model land motions induced by the Sumatra–Andaman Earthquake. Our latest results show that up to the end of 2010, Thailand has been co-seismically displaced and is subsequently undergoing a post-seismic horizontal deformation with total displacements (co-seismic plus post-seismic) ranging from 10.5 to 74.7 cm. We observed the largest horizontal displacements in the southern part of Thailand and moderate and small displacements in the central and northern parts. In addition to horizontal displacements throughout Thailand, continuous GPS measurements show that large parts of Thailand are subsiding at rates up to 1 cm/yr. It is the first time that such vertical post-seismic deformations at large distances (650–1500 km away from the Earthquake’s epicentre) have been recorded. We have investigated the physical processes leading to the observed subsidence. While after-slip on the subduction interface induces negligible or even slightly positive vertical motions, relaxation in the asthenosphere is associated with a sizable subsidence. Predictions from a 3D finite element model feature an asthenosphere with an effective viscosity of the order of 3 * 10¹⁸ Pas, fit the horizontal post-seismic data and the observed subsidence well. This model is then used to predict the subsidence over the whole seismic cycle. The subsidence should go on with a diminishing rate through the next two decades and its final magnitude should not exceed 10 cm in the Bangkok area.     

Delay-Doppler Ambiguity Function for Wideband Signals

The conventional ambiguity function is extended to include the Doppler distortions of the modulation function. The distinctive features of the extension are the use of the complex notation for wideband signals, and inclusion of the Doppler effect on the signal amplitude. The result is an ambiguity function from which Woodward's form can be found by inspection. It is shown that the well-known volume constraint also applies, in unchanged form, to the generalized ambiguity function. For the volume to be constant, it is not required that the distortions of the modulation function be neglected. Rather, the volume constancy is related to the sinusoidal fluctuations of a modulated carrier-type signal and thus is strictly a matter of the percentage bandwidth of the signal.     

Planetary Accumulation with a Continuous Supply of Planetesimals

Previous calculations of the accumulation of small (∼10 km) planetesimals at ∼1 AU to form Mars-sized bodies assumed that the initial assemblage of planetesimals were all present at the outset. This is an obviously reasonable assumption in systems in which the time scale for growth time of ∼10²⁶ g planetary bodies is long compared to estimates of the evolutionary time scale of a protosolar disk, as was the case in the pioneering work of Safronov (1969). It is now found that as a result of the preplanetary assemblage being unstable with respect to the runaway growth of the largest bodies, this is unlikely to be the case. The more realistic alternative of adding the initial planetesimals on a ∼10⁵ year time scale is considered here, as well as the consequences of the initial planetesimals being considerably smaller than those assumed previously. It is found that although the time scale for runaway growth is now actually controlled by the availability of planetesimals, for planetesimal production time scales of ∼10⁵ yrs, the final consequences are very similar. These calculations do show, however, that as a consequence of continuous infall during the runaway growth process, the late initial planetesimals are likely to be catastrophically disrupted by mutual collisions. For this reason, a more detailed treatment of the growth of planetesimals into planetary embryos will require a better understanding of the difficult problem of formation of the initial planetesimals themselves. This revised version was published online in June 2006 with corrections to the Cover Date.     

Biologically weighted measurement of UV radiation in space and on Earth with the biofilm technique.

Biological dosimetry has provided experimental proof of the high sensitivity of the biologically effective UVB doses to changes in atmospheric ozone and has thereby confirmed the predictions from model calculations. The biological UV dosimeter 'biofilm' whose sensitivity is based on dried spores of B. subtilis as UV target weights the incident UV radiation according to its DNA damaging potential. Biofilm dosimetry was applicated in space experiments as well as in use in remote areas on Earth. Examples are long-term UV measurements in Antarctica, measurements of diurnal UV profiles parallel in time at different locations in Europe, continuous UV measurements in the frame of the German UV measurement network and personal UV dosimetry. In space biofilms were used to determine the biological efficiency of the extraterrestrial solar UV, to simulate the effects of decreasing ozone concentrations and to determine the interaction of UVB and vitamin D production of cosmonauts in the MIR station.     

The human cardiovascular system during space flight

Purpose of the work is to analyze and to summarize the data of investigations into human hemodynamics performed over 20 years aboard orbital stations Salyut-7 and Mir with participation of 26 cosmonauts on space flights (SF) from 8 to 438 days in duration. The ultrasonic techniques and occlusive plethysmography demonstrated dynamics of changes in the cardiovascular system during SF of various durations. The parameters of general hemodynamics, the pumping function of the heart and arterial circulation in the brain remained stable in all the space flights; however, there were alterations in peripheral circulation associated with blood redistribution and hypovolemie in microgravity. The anti-gravity distribution of the vascular tone decayed gradually as unneeded. The most considerable changes were observed in leg vessels, equally in arteries (decrease in resistance) and veins (increase in maximum capacity). The lower body negative pressure test (LBNP) revealed deterioration of the gravity-dependent reactions that changed for the worse as SF duration extended. The cardiovascular deconditioning showed itself as loss of descent acceleration tolerance and orthostatic instability in the postflight period.     

Ship-mounted satellite tracking antenna with fuzzy logic control

A robust satellite tracking antenna is designed to cope with the sensor imprecision and the highly noisy sea environment. Fuzzy logic is utilized for the controller imprecision and the highly noisy sea environment. Fuzzy logic is utilized for the controller design as well as inaccurate data interpretation. The fuzzy-rule based controller eliminates the need to model the nonlinear and noisy ship-mounted antenna system. With Global Positioning System and the tracking controller the antenna can be brought to a neighborhood of the desired orientation. Spiral search with signal power feedback can then servo the antenna to the true orientation. Computer simulations and antenna experiments verify our design is indeed robust and effective     

A Test of the Effect of Satellite Spin on Two-Way Doppler Range-Rate Measurements

Analysis indicates that the rotation of a satellite can cause an error in the range-rate measurements of a two-way Doppler tracking system. The error is proportional to the rotation rate, and the constant of proportionality depends on the polarization of the satellite transponder antennas. Measurements made by ground-based simulation confirmed the analytical prediction.     

Effect of Dimensions on the Efficiency of Radiant Energy Cells

This paper deals with the enhancement of the quantum efficiency and photovoltaic energy conversion efficiency of a p-n semiconducting cell by optimizing the dimensions of the cell. Based on the Shockley-Read statistics a general expression for the quantum efficiency of monochromatic incident radiant energy photons has been derived in terms of the absorption coefficient of the incident photons, the minority carrier diffusion length, the built-in electrostatic field appearing in diffused cells, and the surface recombination velocity in the exposed layer of the cell. Although the expressions derived may be used for all semiconducting p-n cells, special efforts have been made in the analysis and computations of the germanium p-n cell. The germanium cells show a great potential for photovoltaic energy conversion from radiant sources other than the sun. The results for germanium indicate that the quantum efficiency strongly depends upon the thicknesses of the exposed and base layers. The built-in electrostatic field and the surface recombination velocity in the exposed layer influence the quantum efficiency greatly. Optimization studies for the thicknesses of the exposed and base layers of an n-p type germanium for different values of minority carrier diffusion length, built-in electrostatic field, and surface recombination velocity have been worked out.