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591.
J. B. Blake B. H. Mauk D. N. Baker P. Carranza J. H. Clemmons J. Craft W. R. Crain A. Crew Y. Dotan J. F. Fennell R. H. Friedel L. M. Friesen F. Fuentes R. Galvan C. Ibscher A. Jaynes N. Katz M. Lalic A. Y. Lin D. M. Mabry T. Nguyen C. Pancratz M. Redding G. D. Reeves S. Smith H. E. Spence J. Westlake 《Space Science Reviews》2016,199(1-4):309-329
592.
Probing the first stars and black holes in the early Universe with the Dark Ages Radio Explorer (DARE) 总被引:1,自引:0,他引:1
Jack O. Burns J. Lazio S. Bale J. Bowman R. Bradley C. Carilli S. Furlanetto G. Harker A. Loeb J. Pritchard 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
A concept for a new space-based cosmology mission called the Dark Ages Radio Explorer (DARE) is presented in this paper. DARE’s science objectives include: (1) When did the first stars form? (2) When did the first accreting black holes form? (3) When did Reionization begin? (4) What surprises does the end of the Dark Ages hold (e.g., Dark Matter decay)? DARE will use the highly-redshifted hyperfine 21-cm transition from neutral hydrogen to track the formation of the first luminous objects by their impact on the intergalactic medium during the end of the Dark Ages and during Cosmic Dawn (redshifts z = 11–35). It will measure the sky-averaged spin temperature of neutral hydrogen at the unexplored epoch 80–420 million years after the Big Bang, providing the first evidence of the earliest stars and galaxies to illuminate the cosmos and testing our models of galaxy formation. DARE’s approach is to measure the expected spectral features in the sky-averaged, redshifted 21-cm signal over a radio bandpass of 40–120 MHz. DARE orbits the Moon for a mission lifetime of 3 years and takes data above the lunar farside, the only location in the inner solar system proven to be free of human-generated radio frequency interference and any significant ionosphere. The science instrument is composed of a low frequency radiometer, including electrically-short, tapered, bi-conical dipole antennas, a receiver, and a digital spectrometer. The smooth frequency response of the antennas and the differential spectral calibration approach using a Markov Chain Monte Carlo technique will be applied to detect the weak cosmic 21-cm signal in the presence of the intense solar system and Galactic foreground emissions. 相似文献
593.
F. Dalla Vedova H. Henrion M. Leipold Th. Girot R. Vaudemont Th. Belmonte K. Fleury O. Le Couls 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
SSM (Solar Sail Materials) is an on-going project for the European Space Agency (ESA) relying on past and recent European solar sail design projects. It aims at developing and testing future technologies suitable for large, operational solar sailcrafts. 相似文献
594.
Gupta Someshwar C. Hall Thomas G. 《IEEE transactions on aerospace and electronic systems》1968,(4):499-504
This paper considers the design of PCM signals with system constraints using Pontryagin's maximum principle. The transmitter signal as well as the correlation signal are determined while maximizing the output signal-to-noise ratio. Both the single and three-pole transmitter filters are considered. An upper bound has been obtained on the performance of PCM signals with constraints. 相似文献
595.
With the arrival of private entrepreneurs and the appearance of such things as prizes to stimulate space initiatives, the space economy is changing rapidly from its initial government-driven character. A number of countries and territories, such as the Isle of Man, have understood the growing role of this new space economy and are preparing the appropriate boundary conditions to support its further development. This article shows why the Isle of Man may be uniquely placed to take advantage of recent developments in the space economy, thanks to its business-friendly tax and regulatory regime, and discusses the island’s strategy to attract space businesses. The establishment of the International Institute of Space Commerce, a recently formed think-tank, is an integral part of this strategy. 相似文献
596.
T. Blöcker H. Holweger B. Freytag F. Herwig H.-G. Ludwig M. Steffen 《Space Science Reviews》1998,85(1-2):105-112
Based on radiation hydrodynamics modeling of stellar convection zones, a diffusion scheme has been devised describing the
downward penetration of convective motions beyond the Schwarzschild boundary (overshoot) into the radiative interior. This
scheme of exponential diffusive overshoot has already been successfully applied to AGB stars. Here we present an application
to the Sun in order to determine the time scale and depth extent of this additional mixing, i.e. diffusive overshoot at the
base of the convective envelope. We calculated the associated destruction of lithium during the evolution towards and on the
main-sequence. We found that the slow-mixing processes induced by the diffusive overshoot may lead to a substantial depletion
of lithium during the Sun's main-sequence evolution.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
597.
Jao J.K. Lee C.F. Ayasli S. Haywiser E.J. 《Aerospace and Electronic Systems Magazine, IEEE》1999,14(6):5-9
In July and October 1995, a large-scale airborne SAR experiment was conducted in the Yuma Proving Ground, Yuma, Arizona, to investigate ground penetration radar phenomenology and buried target detection. This paper describes the Yuma experiment and measurement results for many tactical, utility, and environmental targets deployed in the test 相似文献
598.
A new structure for the separation and tracking of uncorrelated sources through the use of a 2-dimensional adaptive array is proposed and investigated. The structure consists of a matrix preprocessing beamformer designed to result in outputs which are due to individual sources in the steady state. The preprocessing weights of the beamformer are calculated using the estimated locations of the sources and are updated periodically. Continuous estimation of the source locations is accomplished by using the beamformer outputs to adaptively eliminate correlated components in a reference element of the array while the structure proposed may have rather erratic initial convergence behavior, it has the advantages of being simple to be implemented, fast in tracking, and well suited for applications in mobile communication systems for increasing system capacity 相似文献
599.
Active Spacecraft Potential Control Investigation 总被引:1,自引:0,他引:1
K. Torkar R. Nakamura M. Tajmar C. Scharlemann H. Jeszenszky G. Laky G. Fremuth C. P. Escoubet K. Svenes 《Space Science Reviews》2016,199(1-4):515-544
600.