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361.
Scientific and policy developments in the field of Near-Earth Objects (NEOs) since the UN NEO conference in 1995 are briefly outlined. Some areas of research and discovery have exhibited considerable progress while others have languished. In particular, facilities in the southern hemisphere for discovery and tracking of NEOs are inadequate. Suggestions are made both at the scientific and technical levels as well as at the policy level to provide coordinated and coherent progress in developing a long-term approach to NEO hazard mitigation. The next step should be the establishment of a panel of international scientific experts on the subject. 相似文献
362.
The observational and theoretical arguments for spatial fragmentation of the bulk of the thermal and non-thermal components of solar flare plasma are summarised. Observational aspects considered include XUV filling factors, EUV centre to limb variations, andH impact polarisation. Theoretical points addressed are the high flare inductance and beam/return current closure at the acceleration site.A high degree of beam/plasma filamentation implies strong transverse temperature gradients so that cross-field conduction must be included in energy transport modelling. Preliminary results are described for a simple two-component model. 相似文献
363.
John E. Moores Raymond Francis Marianne Mader G.R. Osinski T. Barfoot N. Barry G. Basic M. Battler M. Beauchamp S. Blain M. Bondy R-D. Capitan A. Chanou J. Clayton E. Cloutis M. Daly C. Dickinson H. Dong R. Flemming P. Furgale J. Gammel N. Gharfoor M. Hussein R. Grieve H. Henrys P. Jaziobedski A. Lambert K. Leung C. Marion E. McCullough C. McManus C.D. Neish H.K. Ng A. Ozaruk A. Pickersgill L.J. Preston D. Redman H. Sapers B. Shankar A. Singleton K. Souders B. Stenning P. Stooke P. Sylvester L. Tornabene 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
364.
The geomagnetic signal contains an enormous temporal range—from geomagnetic jerks on time scales of less than a year to the evolution of Earth’s dipole moment over billions of years. This review compares observations and numerical models of the long-term range of that signal, for periods much larger than the typical overturn time of Earth’s core. On time scales of 105–109 years, the geomagnetic field reveals the control of mantle thermodynamic conditions on core dynamics. We first briefly describe the general formalism of numerical dynamo simulations and available paleomagnetic data sets that provide insight into paleofield behavior. Models for the morphology of the time-averaged geomagnetic field over the last 5 million years are presented, with emphasis on the possible departures from the geocentric axial dipole hypothesis and interpretations in terms of core dynamics. We discuss the power spectrum of the dipole moment, as it is a well-constrained aspect of the geomagnetic field on the million year time scale. We then summarize paleosecular variation and intensity over the past 200 million years, with emphasis on the possible dynamical causes for the occurrence of superchrons. Finally, we highlight the geological evolution of the geodynamo in light of the oldest paleomagnetic records available. A summary is given in the form of a tentative classification of well-constrained observations and robust numerical modeling results. 相似文献
365.
Blinn John C. Campbell James P. 《IEEE transactions on aerospace and electronic systems》1966,(5):585-590
This paper discusses the results of an analytic study of the feasibility of using microwave radiometry as a technique for navigation data sensing in Army aircraft. The study included a review of Army aircraft characteristics and navigation requirements. Various means of sensing passively aircraft velocity, altitude, and velocity-altitude ratio were considered. While there appears to be no practical method for direct measurement of either velocity or altitude separately, it does appear possible to measure velocity-altitude ratio by comparing radiometric signals received from the terrain along the aircraft ground track. When combined with a radar altimeter, such a sensor could yield navigation data compatible with Army aircraft requirements. Microwave radiometry may also be the basis for direction sensing (to known landmarks) in high-flying aircraft or satellites. 相似文献
367.
John B. Rogerson Jr. 《Space Science Reviews》1963,2(5):621-652
A review is presented of the Orbiting Astronomical Observatories Program together with a detailed of the OAO spacecraft and the four astronomical instruments currently being developed for the first three observations. 相似文献
368.
D'Antonio R. A. Gaffney John E. 《IEEE transactions on aerospace and electronic systems》1968,(5):728-732
This paper describes a radio interferometer that can be employed for beaming and attitude determination. It differs from conventional interferometers in that it employs a carrier modulated by a pseudonoise sequence. This enables it to provide an unambiguous angular resolution of the signal source. 相似文献
369.
Robert C. Singleterry Steve R. Blattnig Martha S. Clowdsley Garry D. Qualls Chris A. Sandridge Lisa C. Simonsen Tony C. Slaba Steven A. Walker Francis F. Badavi Jan L. Spangler Aric R. Aumann E. Neal Zapp Robert D. Rutledge Kerry T. Lee Ryan B. Norman John W. Norbury 《Acta Astronautica》2011,68(7-8):1086-1097
OLTARIS (On-Line Tool for the Assessment of Radiation In Space) is a space radiation analysis tool available on the World Wide Web. It can be used to study the effects of space radiation for various spacecraft and mission scenarios involving humans and electronics. The transport is based on the HZETRN transport code and the input nuclear physics model is NUCFRG. This paper describes the tools behind the web interface and the types of inputs required to obtain results. Typical inputs are mission parameters and slab definitions or vehicle thickness distributions. Radiation environments can be chosen by the user. This paper describes these inputs as well as the output response functions including dose, dose equivalent, whole body effective dose equivalent, LET spectra and detector response models. 相似文献
370.