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841.
S. Bowyer J. Clarke K. Mason F. Walter J. Henry J. Halpern J. Grindlay 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(9):93
Most, but not all, theoretical models of X-ray bursters require a binary system consisting of a mass donating star and a neutron star. The observational evidence in support of this model, however, is both indirect and meager. We have detected absorption dips in the X-ray spectrum of the Burster MXB 1916-05 with the IPC and the MPC on the Einstein Observatory which occur with a binary period of 2985 seconds. These dips are shown to be the result of a gas stream emanating from a companion star and hence this data represents the first direct evidence of the binary nature of X-ray bursters. Detailed models of the interaction of the gas stream with the accretion disk are presented. A 22nd mag. optical candidate for the system has been found. 相似文献
842.
D.F. McGinnis J.D. Tarpley 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(6):359-369
The visible and near infrared channels, Ch1 and CH2 respectively, on the Advanced Very High Resolution Radiometer (AVHRR) provide daily information for monitoring changes in vegetation and crops. Data from these channels are used to create a normalized vegetation index (NVI) that is sensitive to changes in green leaf biomass and is represented mathematically by: Operational products generated at NOAA include full-scale 1-km resolution images of the NVI covering areas viewed in a single swath of the polar-orbiting NOAA satellite. Global scale NVI images are also produced by compositing over a seven-day period, saving the maximum NVI created daily for each local array (resolution of 15 km at the equator to 30 km at the poles). Such seven-day mapping reduces the effect of cloud contamination. The global vegetation indices are used by foreign and U.S. government agencies for operational and experimental purposes such as assessment of crop conditions, monitoring potential desert locust breeding grounds, forest fire danger models, and monitoring range lands for forage availability. Examples include changes in the NVI in the Lake Chad vicinity, 1981–1982 and 1984; western United States NVI; and seasonal variations of the NVI in the Sahel using the global operational data base, 1982–1983. 相似文献
843.
The optimum (maximum likelihood criterion) bit synchronizer for phase-noncoherent reception of binary FSK signals is found and a suboptimum implementation of it is derived. The performance of this circuit is analyzed in the presence of thermal noise, and the expression of the timing jitter variance is obtained in the case of relatively large signal-to-noise ratios. 相似文献
844.
LORAN, which stands for long range navigation, was first brought into service during World War II. Its earliest form, LORAN-A, served us well up to the time the last station was taken off the air in December 1980. It was succeeded by LORAN-C as part of the Department of Defense's program to develop a new generation of radionavigation aids. LORAN-C not only has a greater range than LORAN-A but also provides better accuracy. With the declining cost of integrated circuits, LORAN-C receivers are becoming more affordable. This, along with good repeatable accuracy and excellent coverage, is increasing the worldwide popularity of navigation with LORAN-C. Fishermen, recreational boaters and the general aviation community make up a good percentage of this dramatic increase (an additional 75,000 marine and 10,000 aviation users the past year alone). 相似文献
845.
H. O. Funsten R. M. Skoug A. A. Guthrie E. A. MacDonald J. R. Baldonado R. W. Harper K. C. Henderson K. H. Kihara J. E. Lake B. A. Larsen A. D. Puckett V. J. Vigil R. H. Friedel M. G. Henderson J. T. Niehof G. D. Reeves M. F. Thomsen J. J. Hanley D. E. George J.-M. Jahn S. Cortinas A. De Los Santos G. Dunn E. Edlund M. Ferris M. Freeman M. Maple C. Nunez T. Taylor W. Toczynski C. Urdiales H. E. Spence J. A. Cravens L. L. Suther J. Chen 《Space Science Reviews》2013,179(1-4):423-484
The HOPE mass spectrometer of the Radiation Belt Storm Probes (RBSP) mission (renamed the Van Allen Probes) is designed to measure the in situ plasma ion and electron fluxes over 4π sr at each RBSP spacecraft within the terrestrial radiation belts. The scientific goal is to understand the underlying physical processes that govern the radiation belt structure and dynamics. Spectral measurements for both ions and electrons are acquired over 1 eV to 50 keV in 36 log-spaced steps at an energy resolution ΔE FWHM/E≈15 %. The dominant ion species (H+, He+, and O+) of the magnetosphere are identified using foil-based time-of-flight (TOF) mass spectrometry with channel electron multiplier (CEM) detectors. Angular measurements are derived using five polar pixels coplanar with the spacecraft spin axis, and up to 16 azimuthal bins are acquired for each polar pixel over time as the spacecraft spins. Ion and electron measurements are acquired on alternate spacecraft spins. HOPE incorporates several new methods to minimize and monitor the background induced by penetrating particles in the harsh environment of the radiation belts. The absolute efficiencies of detection are continuously monitored, enabling precise, quantitative measurements of electron and ion fluxes and ion species abundances throughout the mission. We describe the engineering approaches for plasma measurements in the radiation belts and present summaries of HOPE measurement strategy and performance. 相似文献
846.
Analysis of the effect of stiffener profile on buckling strength in composite isogrid stiffened shell under axial loading 总被引:1,自引:0,他引:1
In this paper, the buckling behavior of thin-walled GFRP cylindrical shells with triangular lattice patterned reinforcements formed by helical and circumferential ribs under axial force is analyzed. In this analysis, various models of composite isogrid stiffened cylindrical shells with outer diameter of 150 millimeters, shell thickness of 0.5 millimeters and height of 280 millimeters, stiffened with 6 helical and 2 circumferential ribs and all with the same material properties of shell and ribs are used. Ribs have constant section areas but different shapes and cross section profiles. The effects of these differences on buckling strengths of structures under axial load are studied. For analysis and modeling of structures, Finite Element Analysis method and ANSYS software were used. The results (elastic buckling load) for each model were derived and based on these results, ratio of buckling strengths to weight parameters were calculated for each model and were compared to results obtained from other models. The effect of profile of the ribs on the buckling of shells under axial loading can be concluded from the results. Results showed that stiffening the shells increased the buckling load from 10% up to 36% while decreased the buckling load to weight ratio to 42% up to 52% of an unstiffened shell. 相似文献
847.
I.F. Shaikhislamov V.M. AntonovYu.P. Zakharov E.L. BoyarintsevA.V. Melekhov V.G. PosukhA.G. Ponomarenko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Magnetosphere with a size comparable to the ion kinetic scales is investigated by means of laboratory experiment, analytical analysis and Hall MHD simulation. In experiment a specific magnetic field was observed which is non-coplanar to dipole field, does not change sign at dipole moment inversion and could be generated only via the quadratic Hall term. Magnetopause position and plasma stand off distance were found to be profoundly different between the experimental regimes with small and large ion inertia length. In the previous studies of a mini-magnetosphere by kinetic codes such novel features were observed as absence of the bow shock and plasma stopping at the Stoermer particle limit instead of the pressure balance distance. Proposed analytical model explains these features by Hall currents which tend to cancel magnetic field convection by ions. Performed numerical simulation shows a good agreement with experiment and analytical model. It gives detailed spatial structure of the Hall field and reveals that while ions penetrate deep inside mini-magnetosphere electrons overflow around it along magnetopause boundary. 相似文献
848.
Atmospheric gaseous constituents play an important role in determining the surface temperatures and habitability of a planet. Using a global climate model and a parameterization of the carbonate-silicate cycle, we explored the effect of the location of the substellar point on the atmospheric CO(2) concentration and temperatures of a tidally locked terrestrial planet, using the present Earth continental distribution as an example. We found that the substellar point's location relative to the continents is an important factor in determining weathering and the equilibrium atmospheric CO(2) level. Placing the substellar point over the Atlantic Ocean results in an atmospheric CO(2) concentration of 7 ppmv and a global mean surface air temperature of 247 K, making ~30% of the planet's surface habitable, whereas placing it over the Pacific Ocean results in a CO(2) concentration of 60,311 ppmv and a global temperature of 282 K, making ~55% of the surface habitable. 相似文献
849.
Abstract The survival strategies of one cyanobacteria colony and three terricolous lichen species from the hot subdesert of Tabernas, Spain, were studied along with topographical attributes of the area to investigate whether the protective strategies adopted by these pioneer soil colonizers are related to the environmental stressors under which they survive. A handheld Raman spectrometer was used for biomolecular characterization, while the microclimatic and topographic parameters were estimated with a Geographic Information System (GIS). We found that the survival strategies adopted by those organisms are based on different combinations of protective biomolecules, each with diverse ecophysiological functions, such as UV-radiation screening, free-energy quenching, antioxidants, and the production of different types and amounts of calcium oxalates. Our results show that the cyanobacteria community and each lichen species preferentially colonized a particular microhabitat with specific moisture and incident solar radiation levels and exhibited different adaptive mechanisms. In recent years, a number of studies have provided consistent results that suggest a link between the strategies adopted by those extremophile organisms and the microclimatic environmental parameters. To date, however, far too little attention has been paid to results from Raman analyses on dry specimens. Therefore, the results of the present study, produced with the use of our miniaturized instrument, will be of interest to future studies in astrobiology, especially due to the likely use of Raman spectroscopy at the surface of Mars. Key Words: Hot desert-Raman spectroscopy-Topography-Terricolous lichens-Cyanobacteria-Planetary exploration. Astrobiology 12, 743-753. 相似文献
850.
G. F. Putin A. F. Glukhov I. A. Babushkin D. A. Zavalishin M. Yu. Belyaev A. I. Ivanov V. V. Sazonov 《Cosmic Research》2012,50(5):346-352
The results of experiments with the DAKON-M convection sensor onboard the Russian orbital segment of the International Space Station are described. A comparison of the sensor measurements with the results of calculation of the quasistatic microacceleration component at the point of installation is made. For this comparison we have used three measurement intervals of the experiments in 2009, during which spacecraft were docked with the station, undocked from it, and actuation of jet engines of the attitude control system took place. When calculating microacceleration, we use the measurement data of the low-frequency MAMS accelerometer, installed on the American segment, and the telemetry data on the ISS rotational motion. This information allowed one to convert the MAMS measurements to the point of installation of the DAKON-M convection sensor. A comparison of sensor measurements with calculated microaccelerations showed sufficiently accurate coincidence between the calculated and measured data. 相似文献