A newly formed neutron star in a supernova finds itself in a dense environment, in which the gravitational energy of accreting matter can be lost to neutrinos. For the conditions in SN 1987A, 0.1M may have fallen back onto the central neutron star on a timescale of hours after the explosion, after which the accretion rate is expected to drop sharply. Radiation is trapped in the flow until the mass accretion rate drops to 2×10–4M yr–1 at which point radiation can begin to escape from the shocked envelope at an Eddington limit luminosity. Between this neutrino limit and the Eddington limit, 3×10–8M yr–1, there are no steady, spherical solutions for neutron star accretion. SN 1987A should have reached the neutrino limit within a year of the explosion; the current lack of an Eddington luminosity can be attributed to black hole formation or to a clearing of the neutron star envelope. There is no evidence for newly formed neutron stars in supernovae. Radio supernovae, which were initially interpreted as pulsar activity, probably involve circumstellar interaction; SN 1993J shows especially good evidence for outer shock phenomena. 相似文献
The effects of a finite correlation length of a turbulent velocity field on the line formation process are considered for hydrogen absorption lines observed in quasar spectra. It is shown that both thermal and large-scale stochastic motions with a finite correlation length (0<l<) lead in general tosmaller equivalent widths of hydrogen lines than in the case when macroscopic motions are assumed to be completely uncorrelated (l0). Different influence of this effect on optically thin and thick absorption lines allows us to measure eventually turbulent characteristics of the gas in the Ly forest clouds. It is emphasized that possible measurements of the deuterium abundance in the early Universe could yield systematically higher ratios of D/H if the finite-correlation-length effects are ignored. 相似文献
To investigate changes in spatial orientation ability and walking performance following space flight, 7 astronaut subjects were asked pre- and post-flight to perform a goal directed locomotion paradigm which consisted of walking a triangular path with and without vision. This new paradigm, involving inputs from different sensory systems, allows quantification of several critical parameters, like orientation performance, walking velocities and postural stability, in a natural walking task. The paper presented here mainly focusses on spatial orientation performance quantified by the errors in walking the previously seen path without vision. Errors in length and reaching the corners did not change significantly from pre- to post-flight, while absolute angular errors slightly increased post-flight. The significant decrease in walking velocity and a change in head-trunk coordination while walking around the corners of the path observed post-flight may suggest that during re-adaptation to gravity the mechanisms which are necessary to perform the task have to be re-accomplished. 相似文献
We evaluated the influence of prolonged weightlessness on the performance of visual tasks in the course of the Russian-French missions ANTARES, Post-ANTARES and ALTAIR aboard the MIR station. Eight cosmonauts were subjects in two experiments executed pre-flight, in-flight and post-flight sessions.
In the first experiment, cosmonauts performed a task of symmetry detection in 2-D polygons. The results indicate that this detection is locked in a head retinal reference frame rather than in an environmentally defined one as meridional orientations of symmetry axis (vertical and horizontal) elicited faster response times than oblique ones. However, in weightlessness the saliency of a retinally vertical axis of symmetry is no longer significantly different from an horizontal axis. In the second experiment, cosmonauts performed a mental rotation task in which they judged whether two 3-D objects presented in different orientations were identical. Performance on this task is basically identical in weightlessness and normal gravity. 相似文献
To study the possible effect of simulated weightlessness on brain function state, the brain event-related potentials (ERPs) in a simple visual selective response task were compared between HDT and HUT in 9 normal subjects. The results were: The Target(T) and non-Target(NT) flash signals both induced significant slow positive potentials which were supposed to related to the attention state; the amplitude of the positive potentials in frontal regions decreased significantly especially for NT-ERPs during HDT comprared with that during HUT. The data reported provide new evidence indicating that more attention should be paid on the brain function study during space flight. 相似文献
This paper discusses the factors that control the flexibility of fabric space suit elements by examining a bending model of a pressurized fabric tube. Results from the model are used to evaluate the current direction in highly mobile EVA glove research and suggest that changes are necessary in the suit and glove fabric selection methodology. 相似文献
The current state of space life sciences knowledge and research is described. Findings about the health of astronauts in space are reviewed and a plea is made by some former astronauts to increase the amount of research being conducted. Longitudinal studies of the long term effects of space travel, especially radiation exposure, are being conducted and have yet to show any ill effects. Current research focuses are discussed, including Neurolab, an upcoming shuttle mission devoted to neurological and vestibular research. Experiment and spacecraft hardware is discussed, as are future directions in research. Partnership with Russian space life sciences investigators is also underway. 相似文献
A physical and a mathematical model of a working process in the pulsejet engine based on the analysis of the thermodynamic cycle are proposed. The process of self-sustained periodic combustion is connected with special features of elementary processes comprising the cycle, influencing the engine operation and depending on its design parameters. The calculation method is based on the use of fundamental laws of conservation and basic equations of gas dynamics 相似文献
We review the results obtained in the frequency range of Pc3 (22-100 mHz) and Pc4 (7-22 mHz) pulsations at Italian Antarctic
stations in the southern polar cap (“Mario Zucchelli”, at Terra Nova Bay, TNB, 80˚.S; “Concordia”, the Italian/French base at Dome C, DMC, 89˚.S). The absence of a midnight enhancement in the pulsation power suggests a negligible substorm influence at extreme latitudes,
while the sharp noon enhancement, which appears only at TNB, is determined by the closer proximity of the station to cusp
related phenomena. The relationship between the frequency of the band-limited signals and the interplanetary magnetic field
strength, the cone angle influence, and the higher correlation of the Pc3 power with the solar wind speed in the morning hours
suggest a global scenario in which upstream waves would be mainly responsible for the mid-frequency activity in the polar
cap. However, the polarization pattern is odd with respect to the predictions for tailward propagating modes. 相似文献