排序方式: 共有22条查询结果,搜索用时 15 毫秒
1.
Sigmund Fritz 《Space Science Reviews》1964,3(4):541-580
Summary It can thus be seen that organization in various stages of tropical storm development are frequently seen in satellite pictures. And it appears that further work will establish relationships between the size and organization of the cloud masses with the coarse magnitude of the wind speed in the storm area. 相似文献
2.
Yann Alibert Christoph Mordasini Olivier Mousis Willy Benz 《Space Science Reviews》2005,116(1-2):77-95
We present models of giant planet formation, taking into account migration and disk viscous evolution. We show that migration
can significantly reduce the formation timescale bringing it in good agreement with typical observed disk lifetimes. We then
present a model that produces a planet whose current location, core mass and total mass are comparable with the one of Jupiter.
For this model, we calculate the enrichments in volatiles and compare them with the one measured by the Galileo probe. We
show that our models can reproduce both the measured atmosphere enrichments and the constraints derived by Guillot et al. (2004), if we assume the accretion of planetesimals with ices/rocks ratio equal to 4, and that a substantial amount of CO2 was present in vapor phase in the solar nebula, in agreement with ISM measurements. 相似文献
3.
Willy Benz 《Space Science Reviews》2000,92(1-2):279-294
The physics of low velocity collisions (5 m/s to 40 m/s) between basalt bodies ranging in size from 1 m to 10 km is studied
in an effort to investigate the early phases of planetesimal accretions. To assess the importance of the internal structure
of planetesimals on the outcome of the collisions, we model them either as solid spheres or as rubble piles with a filling
factor of 0.5.
The collisions are simulated using a three dimensional Smooth Particle Hydrodynamics (SPH) code that incorporates the combined
effects of material strength and a brittle fragmentation model. This approach allows the determination not only of the mass
of the largest fragments surviving the collisions but also their dynamical characteristics.
We find that low velocity collisions are for equal incoming kinetic energy per gram of target material considerably more efficient
in destroying and dispersing bodies than their high velocity counterparts. Furthermore, planetesimals modeled as rubble piles
are found to be characterized by a disruption threshold about 5 times smaller than solid bodies. Both results are a consequence
of a more efficient momentum transfer between projectile and fragments in collisions involving bodies of comparable sizes.
Size and shape dependent gas drag is shown to provide relative collision velocities between similar meter-sized objects well
in excess of the critical disruption threshold of either rubble piles or solid bodies. Unless accretion can proceed avoiding
collisions between bodies of similar masses, the relative weakness of bodies in this size range creates a serious bottleneck
for planetesimal growth.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
4.
Terrestrial planets are accreted in a disk orbiting a central star. The basic challenge of their formation consists of assembling
micron-sized or smaller dust grains to bodies with over 104 km in diameter. This formation process, ultimately based on collisions, occurs in three very different physical regimes depending
upon the size of the bodies present: 1) Early on, micron- to mm-sized dust grains, chondrules and chondrites are strongly
coupled to the gas. 2) As they grow larger, gravity increases the collisional cross section allowing runaway growth to occur.
3) After this runaway phase stops from exhaustion of matter in the immediate surroundings of the protoplanets, further growth
occurs on timescales typical of mutual gravitational perturbations. The emphasis of this book is on the timescales corresponding
to these formation phases as well as the characteristic chemical and isotopic composition of the bodies involved.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
5.
6.
Energetic ion measurements of GEOS-1 and ATS-6 are analysed for the period of geomagnetic activity following the arrival of a solar wind shock at 0027 UT on July 29, 1977. GEOS crossed the magnetopause at 6.9 R
E and 0027 UT (1312 LT). Although the difference in local time to ATS at 6.6 R
E is only 2 h ATS seems to remain well inside the magnetopause. During the second orbital pass on this day GEOS crossed the geostationary orbit at the onset time of a major substorm developing at 1120 UT. At this time the local time difference of GEOS and ATS was 12 h. The considerably different energy dispersions are discussed. An azimuthal anisotropy of approximately 20% observed in the GEOS data is interpreted to be the result of a particle density gradient.NOAA-SEL, Boulder, Colo., U.S.A. 相似文献
7.
Electromagnetic induction is a powerful technique to study the electrical conductivity of the interior of the Earth and other solar system bodies. Information about the electrical conductivity structure can provide strong constraints on the associated internal composition of planetary bodies. Here we give a review of the basic principles of the electromagnetic induction technique and discuss its application to various bodies of our solar system. We also show that the plasma environment, in which the bodies are embedded, generates in addition to the induced magnetic fields competing plasma magnetic fields. These fields need to be treated appropriately to reliably interpret magnetic field measurements in the vicinity of solar system bodies. Induction measurements are particularly important in the search for liquid water outside of Earth. Magnetic field measurements by the Galileo spacecraft provide strong evidence for a subsurface ocean on Europa and Callisto. The induction technique will provide additional important constraints on the possible subsurface water, when used on future Europa and Ganymede orbiters. It can also be applied to probe Enceladus and Titan with Cassini and future spacecraft. 相似文献
8.
T M Seed T E Fritz D V Tolle W E Jackson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(4):945-955
In attempting to evaluate the possible health consequences of chronic ionizing radiation exposure during extended space travel (e.g., Mars Mission), ground-based experimental studies of the clinical and pathological responses of canines under low daily doses of 60Co gamma irradiation (0.3-26.3 cGy d-1) have been examined. Specific reference was given to responses of the blood forming system. Results suggest that the daily dose rate of 7.5 cGy d-1 represents a threshold below which the hematopoietic system can retain either partial or full trilineal cell-producing capacity (erythropoiesis, myelopoiesis, and megakaryopoiesis) for extended periods of exposure (>1 yr). Trilineal capacity was fully retained for several years of exposure at the lowest dose-rate tested (0.3 cGy d-1) but was completely lost within several hundred days at the highest dose-rate (26.3 cGy d-1). Retention of hematopoietic capacity under chronic exposure has been demonstrated to be mediated by hematopoietic progenitors with acquired radioresistance and repair functions, altered cytogenetics, and cell-cycle characteristics. Radiological, biological, and temporal parameters responsible for these vital acquisitions by hematopoietic progenitors have been partially characterized. These parameters, along with threshold responses, are described and discussed in relation to potential health risks of the space traveler under chronic stress of low-dose irradiation. 相似文献
9.
10.
M. Taraba H. Fauland T. Turetschek W. Stumptner V. Kudielka D. Scheer B. Sattler A. Fritz B. Stingl H. Fuchs B. Gubo S. Hettrich A. Hirtl E. Unger A. Soucek N. Frischauf G. Grömer 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
The Passepartout sounding balloon transportation system for low-mass (<1200 g) experiments or hardware for validation to an altitude of 35 km is described. We present the general flight configuration, set-up of the flight control system, environmental and position sensors, power system, buoyancy considerations as well as the ground control infrastructure including recovery operations. In the telemetry and command module the integrated airborne computer is able to control the experiment, transmit telemetry and environmental data and allows for a duplex communication to a control centre for tele-commanding. The experiment module is mounted below the telemetry and command module and can either work as a standalone system or be controlled by the airborne computer. This spacing between experiment- and control unit allows for a high flexibility in the experiment design. After a parachute landing, the on-board satellite based recovery subsystems allow for a rapid tracking and recovery of the telemetry and command module and the experiment. We discuss flight data and lessons learned from two representative flights with research payloads. 相似文献