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91.
92.
Chubb Elliott Grindon John R. Venters David C. 《IEEE transactions on aerospace and electronic systems》1967,(2):250-256
A system for providing near-instantaneous determination of the azimuthal angle of arrival of a received signal has been designed and fabricated at L band. Direction is determined by phase measurement of the outputs of a multimode antenna, which has no moving parts. Effects of multipath interference are reduced to a minimum through a combination of signal processing techniques. The position of the transmitting source is presented on a PPI display. 相似文献
93.
Bieber John W. Eroshenko Eugenia Evenson Paul Flückiger Erwin O. Kallenbach Reinald 《Space Science Reviews》2000,93(1-2):1-9
Cosmic rays provide a diagnostic tool to analyze processes in interplanetary space and at the Sun. Cosmic rays also directly
affect the terrestrial environment and serve as indicators of solar variability and non anthropogenic climatic changes on
Earth at present and in the distant past.
After the invention of the neutron monitor by John A. Simpson in 1948, an international network of cosmic ray detectors developed
in a cooperative effort to examine temporal and spatial variations in our space environment. The resulting datasets represent
the longest continuous, high time resolution series of particle radiation measurement in space science. At present, the neutron
monitor network is complemented by spacecraft instrumentation to study solar-terrestrial correlated phenomena.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
94.
The invention of the neutron monitor pile for the study of cosmic-ray intensity-time and energy changes began with the discovery
in 1948 that the nucleonic component cascade in the atmosphere had a huge geomagnetic latitude dependence. For example, between
0° and 60° this dependence was a ∼ 200–400% effect – depending on altitude – thus opening the opportunity to measure the intensity
changes in the arriving cosmic-ray nuclei down to ∼1–2 GeV nucl−1 for the first time. In these measurements the fast (high energy) neutron intensity was shown to be a surrogate for the nuclear
cascade intensity in the atmosphere.
The development of the neutron monitor in 1948–1951 and the first geomagnetic latitude network will be discussed. Among its
early applications were:
(1) to prove that there exists interplanetary solar modulation of galactic cosmic-rays (1952), and;
(2) to provide the evidence for a dynamical heliosphere (1956).
With the world-wide distribution of neutron monitor stations that are presently operating (∼ 50) many novel investigations
are still to be carried out, especially in collaborations with spacecraft experiments.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
95.
John A. Wood 《Space Science Reviews》2000,92(1-2):97-112
Radiometric dating shows that the earliest steps in forming the substance of meteorites and assembling it into planetesimals
occurred in a very short interval of time, 1–2 Ma. This study shows that rapid formation is also dictated by the need to use
short-lived 26Al (half-life T
1/2=0.74 Ma) as a heat source to metamorphose and in some cases melt the meteorite parent bodies after they accreted. The earliest
events in solar system history dated by cosmochemists, formation at high temperatures of the Ca,Al-rich inclusions that occur
in chondritic meteorites, probably occurred during the most energetic stage of protosolar disk evolution, as the protosun
neared its present mass and infall drew to a close.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
96.
97.
Margarita Karovska Brian E. Wood John W. Cook Russell A. Howard Guenter E. Brueckner 《Space Science Reviews》1999,87(1-2):219-222
We present the results from a study of the dynamical properties of polar jets in the Sun's polar regions using LASCO C2 coronagraph
and EIT observations. In the simplest impulsive acceleration scenarios for jets, gravity is expected to be the dominant force
on the jet following the initial acceleration, especially in the Sun's polar regions where the open magnetic fields should
not significantly impede the jet's motion. Our analysis shows that although at low heights the kinematics of the jets could
be consistent with a gravitational deceleration of the ejected plasma, at higher heights their motions may simply follow the
ambient solar wind outflow. If so, the polar jets can be used as tracers of the solar wind in coronal holes.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
98.
John M. Logsdon 《Space Policy》2011,27(3):153-156
A newly released tape of a 18 September 1963 conversation between President Kennedy and NASA Administrator James Webb has been interpreted by some as showing that the president was looking for a way out of his Apollo commitment. This commentary analyses the meeting – in which Webb did most of the talking – and concludes instead that Kennedy was concerned about how to keep the program going in the face of growing criticism of its cost and goals. In particular there was discussion of how to ensure that his support for Apollo did not harm his chances of re-election. To Kennedy, giving Apollo a military rationale seemed the best way to ensure its support. 相似文献
99.
James R. Drummond Jiansheng Zou Florian Nichitiu Jayanta Kar Robert Deschambaut John Hackett 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
The MOPITT (Measurements of Pollution in the Troposphere) instrument has provided more than nine years of global carbon monoxide (CO) measurements on a continuous basis since its launch aboard the Terra Spacecraft on December 18th, 1999. This paper gives an overview of the core sub-system performance and major issues of the in-flight instrument over the mission period. Some of the instrument anomalies are also discussed. The major successes are: (1) the concept of using a combination of correlation systems such as Length Modulated Cells (LMCs) and Pressure Modulated Cells (PMCs) to retrieve CO profiles in the troposphere; (2) the redundant design in the instrumentation which was crucial for coping with unexpected in-flight anomalies and for continuing the mission in the case of component failure; (3) the thermal environment on orbit that is so stable that some calibration procedures are not necessary; and (4) the recent production of CO total column retrieved from the MOPITT 2.3 μm channel. 相似文献
100.
The discovery of evidence indicative of life in a Martian meteorite has led to an increase in interest in astrobiology. As a result of this discovery, and the ensuing controversy, it has become apparent that our knowledge of the early development of life on Earth is limited. Archean stratigraphic successions containing evidence of Earth's early biosphere are well preserved in the Pilbara Craton of Western Australia. The craton includes part of a protocontinent consisting of granitoid complexes that were emplaced into, and overlain by, a 3.51-2.94 Ga volcanigenic carapace - the Pilbara Supergroup. The craton is overlain by younger supracrustal basins that form a time series recording Earth history from approximately 2.8 Ga to approximately 1.9 Ga. It is proposed that a well-documented suite of these ancient rocks be collected as reference material for Archean and astrobiological research. All samples would be collected in a well-defined geological context in order to build a framework to test models for the early evolution of life on Earth and to develop protocols for the search for life on other planets. 相似文献