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931.
T. Muoz-Darias I.G. Martínez-Pais J. Casares T.R. Marsh R. Cornelisse D. Steeghs V.S. Dhillon P.A. Charles 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2762-2764
We present preliminary results of a simultaneous X-ray/optical campaign of the prototypical LMXB Sco X-1 at 1–10 Hz time resolution. Lightcurves of the high excitation Bowen/HeII emission lines and a red continuum at λc 6000 Å were obtained through narrow interference filters with ULTRACAM, and these were cross-correlated with simultaneous RXTE X-ray lightcurves. We find evidence for correlated variability, in particular when Sco X-1 enters the Flaring branch. The Bowen/HeII lightcurves lag the X-ray lightcurves with a light travel time which is consistent with reprocessing in the companion star while the continuum lightcurves have shorter delays consistent with reprocessing in the accretion disc. 相似文献
932.
933.
The problem of stability of a rotating spacecraft with a cavity partially filled with liquid to a small depth is considered with regard to the distinction in angular velocities of spacecraft and liquid rotation and their variability (the modes of the spacecraft’s stationary rotation, spin-up, and rotation deceleration). The regions of stability (in space of the characteristic parameters of an object) are found, and mathematical simulating of the disturbed motion is carried out. 相似文献
934.
An approach to knowledge-aided covariance estimation 总被引:1,自引:0,他引:1
Melvin W.L. Showman G.A. 《IEEE transactions on aerospace and electronic systems》2006,42(3):1021-1042
This paper introduces a parametric covariance estimation scheme for use with space-time adaptive processing (STAP) methods operating in heterogeneous clutter environments. The approach blends both a priori knowledge and data observations within a parameterized model to capture instantaneous characteristics of the cell under test (CUT) and reduce covariance errors leading to detection performance loss. We justify this method using both measured and synthetic data. Performance potential for the specific operating conditions examined herein include: 1) averaged behavior within roughly 2 dB of the optimal filter, 2) 1 dB improvement in exceedance characteristic relative to the optimal filter, highlighting improved instantaneous capability, and 3) impervious ness to corruptive target-like signals in the secondary data (no additional signal-to-interference-plus-noise ratio (SINK) loss, compared with 10 dB or greater loss for the standard STAP implementation), with corresponding detections comparable to the optimal filter case 相似文献
935.
N. F. Blagoveshchenskaya A. D. Andreev V. A. Kornienko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,15(12):45-48
Effects of ionospheric modification produced by powerful high frequency radio waves are studied using the method of field-aligned scattering of diagnostic HF radio signals. Observations of scattered HF signals have been made by the Doppler spectrum method. Analysis of the experimental data shows the appearance of quasiperiodic variations in Doppler frequency shift fd, with periods 30–60 s during the heating cycles. Powerful HF waves are assumed to excite the Alfvén resonator generating oscillations of the magnetic field lines in the heated region and giving rise to fd artificial variations and magnetic pulsations. In the case of continuous action of the powerful HF transmitter ionospheric waves are sometimes observed with periods 12–25 min, typical of medium-scale travelling ionospheric disturbances. 相似文献
936.
Suresh M.S. Subrahmanyam A. Sathyanarayana P. Seth R. 《Aerospace and Electronic Systems Magazine, IEEE》1995,10(4):26-29
There has been a debate about the need for reconditioning nickel/hydrogen batteries in geosynchronous satellites. A study was done as part of life cycling, to determine the necessity of reconditioning and its effect on the cell performance. A 36 Ah nickel/hydrogen cell was put on a GEO simulated cycling at 15°C without reconditioning up to four eclipse seasons. The effect of reconditioning on the fifth and sixth eclipse seasons was studied. The study has conclusively proven the need for reconditioning and has shown the benefits of a high rate reconditioning. It has also been possible to draw some conclusions about the effect of a long duration trickle charge on the positive electrode 相似文献
937.
W. J. Raitt G. A. Berg D. C. Thompson S. Sazykin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,15(12):79-82
During the initial period of high voltage biasing of the SPEAR-3 sounding rocket payload, it was observed that electrical breakdown occurred in the gas surrounding the rocket. The breakdown occurred almost all the way to apogee of 289 km on the upleg, but did not recur on the downleg until the payload reached an altitude of 100 km. It is suggested that this behavior can be attributed to payload outgassing on the upleg leading to abnormally high gas pressure near the payload skin. Consideration of a modified Paschen discharge process with varying pressure along the discharge path was found to be consistent with the results. 相似文献
938.
W A Schutte 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,16(2):53-60
An absorption feature at 3.4 micrometers has been observed in various lines-of-sight through the diffuse interstellar medium. Its position and width lead to an identification with the C-H stretching mode of solid organic material. A possible mechanism for the production of organic solids in the interstellar medium is UV photoprocessing of icy mantles which accrete on dust grains in dense clouds. Furthermore, thermally induced reactions involving formaldehyde molecules in the mantles could be an important source of organics. Laboratory simulation of these processes shows that a large variety of oxygen- and nitrogen-rich species may be produced. It is shown that the occurrence of periodic transient heating events plays an important role in the production of organic material in the ice mantles. Finally, it is pointed out how future missions like the Infrared Space Observatory (ISO) as well as analysis of comet material by Rosetta may be able to clarify the nature and evolution of interstellar organics. 相似文献
939.
940.
A V Shafirkin V M Petrov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(4):995-998
This paper presents a new concept of radiation hazard assessment for spacecraft crew members during long term space missions on the basis of a generalized dosimetric function. This new dosimetric function enables a complicated nature of space radiation exposure to be reduced to the conditions of a standard irradiation. It can be obtained on the basis of mean-tissue equivalent dose values calculated for each space radiation source and transmission coefficients describing the influence of the complex spatial and temporal distribution of the absorbed dose in the cosmonaut's body on the radiobiological effects. The combination of cosmic ionizing radiation with other non-radiation nature factors in flight can also be accounted for. In terms of the generalized dose, it is possible to assess the nature and extent of lowering a crew working capacity, as well as radiation risk, both during a flight and post flight period. 相似文献