排序方式: 共有176条查询结果,搜索用时 62 毫秒
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M. Van Der Klis 《Space Science Reviews》1993,62(1-2):173-202
The observational information on X-ray binaries that was collected with the 80 cm2 auxiliary X-ray detector onboard the COS-B gamma-ray satellite is reviewed. The results illustrate that in the study of X-ray binaries observations of long duration are extremely effective, even when using a small instrument. 相似文献
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David H. Rodgers Patricia M. Beauchamp Laurence A. Soderblom Robert H. Brown Gun-Shing Chen Meemong Lee Bill R. Sandel David A. Thomas Robert T. Benoit Roger V. Yelle 《Space Science Reviews》2007,129(4):309-326
MICAS is an integrated multi-channel instrument that includes an ultraviolet imaging spectrometer (80–185 nm), two high-resolution
visible imagers (10–20 μrad/pixel, 400–900 nm), and a short-wavelength infrared imaging spectrometer (1250–2600 nm). The wavelength ranges were chosen
to maximize the science data that could be collected using existing semiconductor technologies and avoiding the need for multi-octave
spectrometers. It was flown on DS1 to validate technologies derived from the development of PICS (Planetary Imaging Camera
Spectrometer). These technologies provided a novel systems approach enabling the miniaturization and integration of four instruments
into one entity, spanning a wavelength range from the UV to IR, and from ambient to cryogenic temperatures with optical performance
at a fraction of a wavelength. The specific technologies incorporated were: a built-in fly-by sequence; lightweight and ultra-stable,
monolithic silicon-carbide construction, which enabled room-temperature alignment for cryogenic (85–140 K) performance, and
provided superb optical performance and immunity to thermal distortion; diffraction-limited, shared optics operating from
80 to 2600 nm; advanced detector technologies for the UV, visible and short-wavelength IR; high-performance thermal radiators
coupled directly to the short-wave infrared (SWIR) detector optical bench, providing an instrument with a mass less than 10
kg, instrument power less than 10 W, and total instrument cost of less than ten million dollars. The design allows the wavelength
range to be extended by at least an octave at the short wavelength end and to ∼50 microns at the long wavelength end. Testing
of the completed instrument demonstrated excellent optical performance down to 77 K, which would enable a greatly reduced
background for longer wavelength detectors. During the Deep Space 1 Mission, MICAS successfully collected images and spectra
for asteroid 9969 Braille, Mars, and comet 19/P Borrelly. The Borrelly encounter was a scientific hallmark providing the first
clear, high resolution images and excellent, short-wavelength infrared spectra of the surface of an active comet’s nucleus. 相似文献
165.
James E. Richardson H. Jay Melosh Natasha A. Artemeiva Elisabetta Pierazzo 《Space Science Reviews》2005,117(1-2):241-267
The cratering event produced by the Deep Impact mission is a unique experimental opportunity, beyond the capability of Earth-based
laboratories with regard to the impacting energy, target material, space environment, and extremely low-gravity field. Consequently,
impact cratering theory and modeling play an important role in this mission, from initial inception to final data analysis.
Experimentally derived impact cratering scaling laws provide us with our best estimates for the crater diameter, depth, and
formation time: critical in the mission planning stage for producing the flight plan and instrument specifications. Cratering
theory has strongly influenced the impactor design, producing a probe that should produce the largest possible crater on the
surface of Tempel 1 under a wide range of scenarios. Numerical hydrocode modeling allows us to estimate the volume and thermodynamic
characteristics of the material vaporized in the early stages of the impact. Hydrocode modeling will also aid us in understanding
the observed crater excavation process, especially in the area of impacts into porous materials. Finally, experimentally derived
ejecta scaling laws and modeling provide us with a means to predict and analyze the observed behavior of the material launched
from the comet during crater excavation, and may provide us with a unique means of estimating the magnitude of the comet’s
gravity field and by extension the mass and density of comet Tempel 1. 相似文献
166.
José F. Valdés-Galicia 《Space Science Reviews》1993,62(1-2):67-93
It is the purpose of this review to summarize and discuss recent research done in the field of particle propagation in the heliosphere. Several lines of approach have been followed to treat this problem. As a starting point the different forms of the transport equation are discussed. Quasi-Linear Theory (QLT) relates the power contained in fluctuations of the Interplanetary Magnetic Field (IMF) to the transport coefficients of energetic particles, an outline of the basic results of this theory is presented followed by a discussion of subsequent corrections made to the original formulation with an emphasis in recent developments where the effects of wave polarization, its propagation respect to the solar wind and the dissipation of power at large frequencies have been taken into account. The numerical approach using test particle trajectory integrations to obtain transport coefficients based on in situ satellite measureents is also discussed. It is well known that the determination of the particles mean free path for solar particle events by alternative methods leads to conflicting results, corrections made to original QLT are attempts to bridge the gap. Determination of the transport parameters from different lines of approach in a comparative basis have been done recently by calculating power spectra of IMF measured at the time solar particles were detected on the same spaceprobe, and performing numerical simulations with equivalent IMF data. Some of the results of such studies point to the solution of the conflicting determinations of the mean free path which has existed for nearly 30 years. An assesment of the present situation in this respect is given. Numerical determinations of transport parameters in the outer heliosphere are also reviewed and its consequences for solar modulation of galactic cosmic rays discussed. Space Science Reviews 62: Printed in Belgium. 相似文献
167.
Abstract Modern ecological niches are teeming with an astonishing diversity of microbial life in biofilms closely associated with mineral surfaces, which highlights the remarkable success of microorganisms in conquering the challenges and capitalizing on the benefits presented by the mineral-water interface. Biofilm formation capability likely evolved on early Earth because biofilms provide crucial cell survival functions. The potential toxicity of mineral surfaces toward cells and the complexities of the mineral-water-cell interface in determining the toxicity mechanisms, however, have not been fully appreciated. Here, we report a previously unrecognized role for extracellular polymeric substances (EPS), which form biofilms in shielding cells against the toxicity of mineral surfaces. Using colony plating and LIVE/DEAD staining methods in oxide suspensions versus oxide-free controls, we found greater viability of wild-type, EPS-producing strains of Pseudomonas aeruginosa PAO1 compared to their isogenic knockout mutant with defective biofilm-producing capacity. Oxide toxicity was specific to its surface charge and particle size. High resolution transmission electron microscopy (HRTEM) images and assays for highly reactive oxygen species (hROS) on mineral surfaces suggested that EPS shield via both physical and chemical mechanisms. Intriguingly, qualitative as well as quantitative measures of EPS production showed that toxic minerals induced EPS production in bacteria. By determining the specific toxicity mechanisms, we provide insight into the potential impact of mineral surfaces in promoting increased complexity of cell surfaces, including EPS and biofilm formation, on early Earth. Key Words: Mineral toxicity-Bacteria-EPS evolution-Biofilms-Cytotoxicity-Silica-Anatase-Alumina. Astrobiology 12, 785-798. 相似文献
168.
Junliang He Yong Zha Jiahua Zhang Jay Gao Qiang Wang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Aerosol optical depth (AOD) is one of the most important indicators of atmospheric pollution. It can be retrieved from satellite imagery using several established methods, such as the dark dense vegetation method and the deep blue algorithm. All of these methods require estimation of surface reflectance prior to retrieval, and are applicable to a certain pre-designated type of surface cover. Such limitations can be overcome by using a synergetic method of retrieval proposed in this study. This innovative method is based on the fact that the ratio K of surface reflectance at different angles/geometries is independent of wavelength as reported by Flowerdew and Haigh (1995). An atmospheric radiative transfer model was then established and resolved with the assistance of the ratio K obtained from two Moderate Resolution Imaging Spectroradiometer (MODIS) spectral bands acquired from the twin satellites of Terra and Aqua whose overpass is separated by three hours. This synergetic method of retrieval was tested with 20 pairs of MODIS images. The retrieved AOD was validated against the ground observed AOD at the Taihu station of the AErosol RObotic NETwork (AERONET). It is found that they are correlated with the observations at a coefficient of 0.828 at 0.47 μm and 0.921 at 0.66 μm wavelengths. The retrieved AOD has a mean relative error of 25.47% at 0.47 μm and 24.3% at 0.66 μm. Of the 20 samples, 15 and 17 fall within two standard error of the line based observed AOD data on the ground at the 0.47 μm and 0.66 μm, respectively. These results indicate that this synergetic method can be used to reliably retrieve AOD from the twin satellites MODIS images, namely Terra and Aqua. It is not necessary to determine surface reflectance first. 相似文献
169.
T. Beuselinck C. Van Bavinchove V. I. Abrashkin A. E. Kazakova V. V. Sazonov 《Cosmic Research》2010,48(3):246-259
The results of reconstruction of rotational motion of the Foton M-3 satellite during its uncontrolled flight in September 2007 are presented. The reconstruction was performed by processing
the data of onboard measurements of the Earth’s magnetic field obtained by the DIMAC instruments. The measurements were carried
out continuously throughout the flight, but the processing technique dealt with the data portions covering time intervals
of a few orbital revolutions. The data obtained on each such interval were processed jointly by the least squares method with
using integration of the equations of satellite motion relative to its center of mass. When processing, the initial conditions
of motion and the used mathematical model’s parameters were estimated. The results of processing 16 data sets gave us complete
information about the satellite motion. This motion, which began at a low angular velocity, had gradually accelerated and
in five days became close to the regular Euler precession of an axisymmetric solid body. At the end of uncontrolled flight
the angular velocity of the satellite relative to its lengthwise axis was 0.5 deg/s; the angular velocity projection onto
the plane perpendicular to this axis had a magnitude of about 0.18 deg/s. 相似文献
170.