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971.
Messenger S. Stadermann F.J. Floss C. Nittler L.R. Mukhopadhyay S. 《Space Science Reviews》2003,106(1-4):155-172
Interplanetary dust particles collected in the stratosphere frequently exhibit enrichments in deuterium (D) and 15N relative to terrestrial materials. These effects are most likely due to the preservation of presolar interstellar materials.
While the elevated D/H ratios probably resulted from mass fractionation during chemical reactions at very low < 100 K temperatures,
the origin of the N isotopic anomalies remains unresolved. The bulk of the N-bearing material may have obtained its isotopic
signatures from low temperature chemistry, but a nucleosynthetic origin is also possible.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
972.
Contrary to the often stated view, an enrichment of organic material in the light isotope is not a conclusive evidence of
its life-related origin. The β13C - σ13C correlation is a special feature of biological systems. Therefore it can be used as a criterion for identification of organic
carbon. A survey of the available isotopic data for organic compounds in meteorites shows that they do not comply with the
β13C - σ13C correlation. The prevalence of amino and hydroxy acids in purines and sugars found in carbonaceous meteorites indicates
that condensation of HCN and HCHO passed through cyanohydrin reaction, while biological evolution proceeds through formation
of adenosine triphosphate (ATP). This, in addition to the isotope criterion, indicates that the organic compounds in carbonaceous
chondrites are not life-related substances.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
973.
With a precise geoid, GOCE will allow an estimation of absolute dynamic topography from altimetry. The projected benefits
to operational oceanography and its applications are analyzed herein. After a brief overview of operational oceanography,
we explain how the new geoids will be used in the future to improve real time altimeter products and to better constrain modelling
and data assimilation systems. A significant impact is expected both for mesoscale (e.g. better estimations and forecasts of currents for pollution monitoring, marine safety, offshore industry) and climate (better
initialization of coupled ocean/atmosphere models) applications.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
974.
Terrestrial technology is now, and increasingly, sensitive to space weather. Most space weather is caused by solar storms
and the resulting changes to the Earth's radiation environment and the magnetosphere. The Sun as the driver of space weather
is under intense observation but remains to be adequately modelled. Recent spacecraft measurements are greatly improving models
of solar activity, the interaction of the solar wind with the magnetosphere, and models of the radiation belts. In-situ data
updates the basic magnetospheric model to provide specific details of high-energy electron flux at satellite orbits. Shock
wave effects at the magnetopause can also be coarsely predicted. However, the specific geomagnetic effects at ground level
depend on the calculation of magnetic and electric fields and further improvements are needed. New work on physical models
is showing promise of raising geomagnetic and ionospheric predictability above the synoptic climatological level.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
975.
Recent data and theory for type II solar radio bursts are reviewed, focusing on a recent analytic quantitative theory for
interplanetary type II bursts. The theory addresses electron reflection and acceleration at the type II shock, formation of
electron beams in the foreshock, and generation of Langmuir waves and the type II radiation there. The theory's predictions
as functions of the shock and plasma parameters are summarized and discussed in terms of space weather events. The theory
is consistent with available data, has explanations for radio-loud/quiet coronal mass ejections (CMEs) and why type IIs are
bursty, and can account for empirical correlations between type IIs, CMEs, and interplanetary disturbances.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
976.
Neugebauer M. Steinberg J.T. Tokar R.L. Barraclough B.L. Dors E.E. Wiens R.C. Gingerich D.E. Luckey D. Whiteaker D.B. 《Space Science Reviews》2003,105(3-4):661-679
Some of the objectives of the Genesis mission require the separate collection of solar wind originating in different types
of solar sources. Measurements of the solar wind protons, alpha particles, and electrons are used on-board the spacecraft
to determine whether the solar-wind source is most likely a coronal hole, interstream flow, or a coronal mass ejection. A
simple fuzzy logic scheme operating on measurements of the proton temperature, the alpha-particle abundance, and the presence
of bidirectional streaming of suprathermal electrons was developed for this purpose. Additional requirements on the algorithm
include the ability to identify the passage of forward shocks, reasonable levels of hysteresis and persistence, and the ability
to modify the algorithm by changes in stored constants rather than changes in the software. After a few minor adjustments,
the algorithm performed well during the initial portion of the mission.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
977.
Kamide Y. Kihn E.A. Ridley A.J. Cliver E.W. Kadowaki Y. 《Space Science Reviews》2003,107(1-2):307-316
We report the recent progress in our joint program of real-time mapping of ionospheric electric fields and currents and field-aligned
currents through the Geospace Environment Data Analysis System (GEDAS) at the Solar-Terrestrial Environment Laboratory and
similar computer systems in the world. Data from individual ground magnetometers as well as from the solar wind are collected
by these systems and are used as input for the KRM and AMIE magnetogram-inversion algorithms, which calculate the two-dimensional
distribution of the ionospheric parameters. One of the goals of this program is to specify the solar-terrestrial environment
in terms of ionospheric processes, providing the scientific community with more than what geomagnetic activity indices and
statistical models provide.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
978.
Alexeev Igor I. Belenkaya Elena S. Bobrovnikov Sergey Yu. Kalegaev Vladimir V. 《Space Science Reviews》2003,107(1-2):7-26
A magnetohydrodynamic model of the solar wind flow is constructed using a kinematic approach. It is shown that a phenomenological
conductivity of the solar wind plasma plays a key role in the forming of the interplanetary magnetic field (IMF) component
normal to the ecliptic plane. This component is mostly important for the magnetospheric dynamics which is controlled by the
solar wind electric field. A simple analytical solution for the problem of the solar wind flow past the magnetosphere is presented.
In this approach the magnetopause and the Earth's bow shock are approximated by the paraboloids of revolution. Superposition
of the effects of the bulk solar wind plasma motion and the magnetic field diffusion results in an incomplete screening of
the IMF by the magnetopause. It is shown that the normal to the magnetopause component of the solar wind magnetic field and
the tangential component of the electric field penetrated into the magnetosphere are determined by the quarter square of the
magnetic Reynolds number. In final, a dynamic model of the magnetospheric magnetic field is constructed. This model can describe
the magnetosphere in the course of the severe magnetic storm. The conditions under which the magnetospheric magnetic flux
structure is unstable and can drive the magnetospheric substorm are discussed. The model calculations are compared with the
observational data for September 24–26, 1998 magnetic storm (Dst
min=−205 nT) and substorm occurred at 02:30 UT on January 10, 1997.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
979.
This paper reviews our present knowledge about elemental and isotopic ratios in the Giant Planets and Titan. These parameters
can provide key information about the formation and evolution of these objects. Element abundances, especially after the results
of the Galileo Probe Mass Spectrometer in Jupiter, strongly support the formation model invoking an initial core formation
(Mizuno, 1980; Pollack et al., 1996). They also suggest that solar composition icy planetesimals (SCIPs) brought the heavy elements to Jupiter. The Jupiter
value of D/H appears to be representative of the protosolar value, while the D/H enrichment observed on Uranus and Neptune
is consistent with the formation scenario of these planets. The 15N/14N measurement in Jupiter seems to be representative of its protosolar value. Future measurements are expected to come from
the Cassini and Herschel space mission, as well as the ALMA submillimeter observatory.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
980.
Novel wideband multimode hybrid interferometer system 总被引:3,自引:0,他引:3
Pasala K. Penno R. Schneider S. 《IEEE transactions on aerospace and electronic systems》2003,39(4):1396-1406
In this paper, a novel hybrid of a three-element interferometer comprised of multimode antennas is analyzed. The phase ambiguities associated with the long baselines of the interferometer are resolved using the "coarse" angle estimates provided by the multimode antenna. This results in the elimination of the short baseline interferometers of the conventional five-element interferometer. It is shown here that the signal-to-noise ratio (SNR) must be above a threshold value to resolve the phase ambiguities with a high degree of probability. An expression that shows the dependence of this threshold SNR on the interferometer spacing and the variance of the angle estimates provided by the multimode antenna is derived. A single three-element wideband multimode antenna interferometer can replace several five-element conventional interferometers, each covering a separate frequency band. 相似文献