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371.
We report the results of a 1.4 104s observation of the region of 4U 1323-62 with the EXOSAT ME. The source has a flux of 7–8 10-11 erg/cm2s (2–10 keV) and a power-law spectrum with 1.1 < < 1.8. During our observation, the source showed a symmetric 60% dip in its X-ray flux of R~1 hr. The spectrum hardens during the dip. Inside the dip we observed an X-ray burst with a 2–10 keV peak flux of 7 10-10 erg/cm2s. The burst spectrum is black-body, and shows evidence of cooling during the burst decay. The discovery of a burst from 4U 1323-62 settles the classification of the source; the observation of a dip suggests that we may be able to measure its orbital period in the near future. 相似文献
372.
The results of a previous discrete-time model of the series resonant dc-dc converter are reviewed and from these a small signal dynamic model is derived. This model is valid for low frequencies and is based on the modulation of the diode conduction angle for control. The basic converter is modeled separately from its output filter to facilitate the use of these results for design purposes. Experimental results are presented. 相似文献
373.
Lazarus A. J. Belcher J. W. Paularena K. I. Richardson J. D. 《Space Science Reviews》1998,83(1-2):87-92
We discuss the solar wind parameters measured in the distant heliosphere from the Voyager 2 spacecraft. Periodic variations in the speed of the wind observed at roughly the solar rotation period may correspond to interaction regions between slower and faster streams of wind. Since the interplanetary magnetic field is enhanced in such regions, they are important for the study of modulation of cosmic rays. Unfortunately, direct observation of the enhanced magnetic field from Voyager 2 has been made difficult by spacecraft-associated noise since 1989. 相似文献
374.
Beers T.C. Rossi S. Norris J.E. Ryan S.G. Molaro P. Rebolo R. 《Space Science Reviews》1998,84(1-2):139-144
Ongoing spectroscopy and photometry of stars selected in the HK objective-prism/interference-filter survey of Beers and colleagues has resulted in the identification of many hundreds of additional stars in the halo (and possibly the thick disk) of the Galaxy with abundances [Fe/H] -2.0. A new calibration of the technique for estimation of metal abundance based on a CaII K index as a function of broadband B - V color is applied to obtain metallicities for stars observed with the SSO 2.3m and INT 2.5m telescopes. This new data is combined with other samples of extremely metal-deficient stars (Ryan and Norris, 1991a; Beers et al., 1992; Carney et al., 1994) to form a large database of objects of low metallicity. The combined sample is examined and compared with expectations derived from a Simple Model of Galactic chemical evolution. There appears to be a statistically-significant deficit of stars more metal-weak than [Fe/H] = -3.0. An abundance of [Fe/H] -4.0 can be taken as the low-metallicity limit for presently-observable stars in the Galaxy. 相似文献
375.
Spilker James J. Luby Donald D. 《IEEE transactions on aerospace and electronic systems》1967,(1):71-82
A special-purpose adaptive machine is described which carries out estimation in real time of an unknown binary waveform which is perturbed with additive Gaussian noise. Unknown waveforms of over 103 samples in duration can be recovered. The unknown waveforms are of unknown epoch and can reappear at either random or periodic time intervals. The observed signal is received at moderate or low signal-to-noise ratios so that a single observation of the received data (even if one knew the precise signal arrival time) is not sufficient to provide a good estimate of the signal waveshape. Experimental results are described which show transient behavior waveform estimate. The transient behavior is expressed as the number of errors in the current estimate of the signal plotted vs. time. In a noisy environment, each ``learning' transient is a random time function. These learning transients are shown for several different signal-to-noise ratios and indicate the threshold noise levels for various types of initial states of the machine memory. 相似文献
376.
377.
The synodic recurrence of the Mt. Wilson plage index (MPSI) and the Calgary cosmic ray (CR) intensity is investigated, using
the wavelet power spectra in the range of 18–38 days, during the last three solar cycles. The unique temporal coincidence
between the quasi–synodic MPSI and the CR periods is detected in 1978–1982 (the 21st solar cycle). In the 22nd cycle there
is a very strong MPSI synodic recurrence, from 1989.5 to 1990.5, but it is absent in the CR data. In 1992.5–1993.5 the MPSI
and CR recurrence phenomenon is in good accordance with the solar wind speed and cosmic ray modulation as measured during
the first Ulysses passage around the Sun. The Gnevyshev gap is present in the 27-day recurrence of CR, in agreement with Kudela
et al. (1999).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
378.
Klumpar D.M. Möbius E. Kistler L.M. Popecki M. Hertzberg E. Crocker K. Granoff M. Tang Li Carlson C.W. McFadden J. Klecker B. Eberl F. Künneth E. Kästle H. Ertl M. Peterson W.K. Shelly E.G. Hovestadt D. 《Space Science Reviews》2001,98(1-2):197-219
The Time-of-flight Energy Angle Mass Spectrograph (TEAMS) is being flown on the FAST Small Explorer mission to measure the 3-dimensional distribution function of the major ion species present in the lower magnetosphere. The instrument is similar to time-of-flight plasma analyzer systems that have been designed and planned for flight as CODIF (COmposition and DIstribution Function analyzer) on the four European Space Agency Cluster-II spacecraft and, as ESIC (Equator-S Ion Composition instrument) on Equator-S. This instrument allows the 3-dimensional distribution functions of individual ion species to be determined within
spin period (2.5 s). Two-dimensional distributions are measured in 80 ms. These capabilities are crucial for the study of selective energization processes in the auroral regions of the magnetosphere. The design, operational characteristics, and test and calibration results for this instrument are presented. The sensor consists of a toroidal top-hat electrostatic analyzer with instantaneous acceptance of ions over 360° in polar angle. After post-acceleration of the incoming ions by up to 25 kV, a time-of-flight mass spectrograph discriminates the individual species. It has been demonstrated through calibration that the instrument can easily separate H+, He2+, He+, O+ and, for energies after post-acceleration of > 20 keV, even O2
+ molecules. On-board mass discrimination and the internal accumulation of several distinct data quantities combined with the spacecraft's flexible telemetry formatting allow for instrument data rates from 7.8 kb s–1 to 315 kb s–1 to be telemetered to ground through the FAST centralized Instrument Data Processor. 相似文献
379.
We study the solar cycle, radial, and latitudinal dependence of the characteristics of magnetic field irregularities in the
Heliosphere. The frequency of magnetic field discontinuities is determined, using high time resolution magnetic field observations
by Ulysses, covering the time interval from 1992 to 2000. The quasi-linear scattering mean free path of particles is also calculated.
These investigations aim at understanding/exploring transport properties of energetic charged particles in the Heliosphere.
We find that the travel time of solar wind plasma from the Sun to the observer is the key parameter of the process, by controling
the decay of the irregularities.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
380.
The simple tilted dipole picture of Corotating Interaction Regions which prevailed during the first polar pass of Ulysses no longer applies since the Sun entered a more active phase. Recent observations show that CIRs still persist, though the
large polar coronal holes of solar minimum shrink to smaller areas and move to lower latitudes. We present 3-D simulations
for the cosmic-ray intensity variations in a model with non-polar high speed streams. Latitudinal and recurrent time-variations
are discussed, but more detailed and realistic simulations are required before quantitative comparisons with observations
can be made.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献