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971.
The sodium emissions have been observed in several new and long-period comets, but only for comet Mrkos 1957d (Nguyen-Huu-Doan,
1960) was a sodium tail detected on a Schmidt plate obtained with a objective prism. Comet Hale-Bopp 1995 O1 offered the first
great opportunity to get an image of a long sodium tail. It was more than 3 × 107 km long, defined as a third type of tail, as it was composed only of neutral atoms (Cremonese, 1997a). After the discovery
of the sodium tail another team announced it had observed it (Wilson et al., 1998), but it was soon realized they had seen a different sodium tail. The image of Wilson et al. (1998) showed a very diffuse sodium tail superimposed on the dust tail, most likely due to the release of sodium atoms from
dust particles. It was different from the narrow tail found in the image obtained by the European Hale-Bopp Team and its position
angle was 15-20 degrees lower. Spectroscopic observations have been performed on the dust tail, at different beta values,
and along the narrow sodium tail showing that the sodium emissions had very different line profiles. The analysis of these
profiles will yield important insights into the sources in the inner coma and in the dust tail. This work will report on preliminary
analysis of both sodium tails and emphasize the high-resolution spectroscopy performed on the dust tail.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
972.
P.R. Gazis F.B. McDonald R.A. Burger S. Chalov R.B. Decker J. Dwyer D.S. Intriligator J.R. Jokipii A.J. Lazarus G.M. Mason V.J. Pizzo M.S. Potgieter I.G. Richardson L.J. Lanzerotti 《Space Science Reviews》1999,89(1-2):269-305
We discuss the structure and evolution of CIRs and their successors in the outer heliosphere. These structures undergo significant
evolution as they are convected to greater heliocentric distances. A progression of different types of structure are observed
at increasing distance from the Sun. Similar structures are observed at similar heliocentric distance at different portions
of the solar cycle. CIRs and their successors are associated with many important physical processes in the outer heliosphere.
We discuss the relationship between these structures and recurrent phenomena such as cosmic ray variations, and review some
of the associated theoretical models on the role of corotating structures and global merged interaction regions (GMIRs) in
global cosmic ray modulation. We also discuss some outstanding questions related to the origin of non-dispersive quasi-periodic
particle enhancements associated with CIRs and their successors in the outer heliosphere.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
973.
Thermal drill sampling system onboard high-velocity impactors for exploring the subsurface of Europa
P. Weiss K.L. Yung N. Kömle S.M. Ko E. Kaufmann G. Kargl 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The planned Europa Jupiter System Mission (EJSM) will provide a unique opportunity to place scientific instruments onto the surface of Jupiter’s moon Europa in the late 2020s. After the Galileo mission, this will be a long awaited chance to have a close glimpse into some of the mysteries of this moon. Care must be taken in the choice of in-situ science that will be undertaken on the surface. 相似文献
974.
Bela G. Fejer 《Space Science Reviews》2011,158(1):145-166
The low latitude ionosphere is strongly affected by several highly variable electrodynamic processes. Over the last two decades
ground-based and satellite measurements and global numerical models have been extensively used to study the longitude-dependent
climatology of low latitude electric fields and currents. These electrodynamic processes and their ionospheric effects exhibit
large ranges of temporal and spatial variations during both geomagnetic quiet and disturbed conditions. Numerous recent studies
have investigated the short term response of equatorial electric fields and currents to lower atmospheric transport processes
and solar wind-magnetosphere driving mechanisms. This includes the large electric field and current perturbations associated
with arctic sudden stratospheric warming events during geomagnetic quiet times and highly variable storm time prompt penetration
and ionospheric disturbance dynamo effects. In this review, we initially describe recent experimental and numerical modeling
results of the global climatology and short term variability of quiet time low latitude electrodynamic plasma drifts. Then,
we examine the present understanding of equatorial electric field and current perturbation fields during periods of enhanced
geomagnetic activity. 相似文献
975.
976.
A technological process of removing a complex-shaped ceramic core from the interior of GTE thin-walled blade castings is considered. We propose an aluminium oxide-based method for removing a core by leaching accompanied by process intensification with a carboxylic acid additive. 相似文献
977.
R.B. Dahlburg L. Rudakov C. Crabtree G. Ganguli 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
The evolution of a magnetized conducting medium suspended in magnetic and gravitational fields is examined. In this paper some effects of the influence of velocity fields on the linear stability properties of such layers are investigated. A fully compressible, three-dimensional analysis of the layer is described. The relevant equations are derived and then solved by the MagnetoHydroDynamic SPEctral Compressible Linear Stability (MHDSPECLS) algorithm, a Chebyshev collocation code. The code allows for the computation of magnetic and thermal effects. A complete stabilization of the system is found above a critical velocity of approximately 2500 m/s. 相似文献
978.
N Munakata K Makita D Bolsee D Gillotay G Horneck 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2000,26(12):1995-2003
Environmental UV radiation can be quantified using spore dosimetry, which measures the inactivation of repair-deficient Bacillus subtilis spores dried on a membrane filter. The system exhibits highly selective sensitivity to UV radiation, not being affected by various environmental adversities, such as high and low temperature and humidity. Biologically-effective dose rate and cumulative dose of ambient radiation are measurable under various conditions at various places on the earth, including tropical, temperate, and polar sites. Applications to monitor the exposure at the surface of organisms including humans and plants have also been advanced. 相似文献
979.
Svigelj A. Mohorcic M. Kandus G. 《IEEE transactions on aerospace and electronic systems》2007,43(1):187-196
Adaptive per-hop routing in the intersatellite link (ISL) network of a packet-switched, nongeostationary satellite system is addressed. In particular, a traffic class dependent (TCD) routing is proposed with different optimization criteria for different traffic classes. Furthermore, for delay sensitive traffic, performance is enhanced by an exponential smoothing link-cost function, which reduces traffic load oscillations in the network. The performance of the proposed procedures is evaluated in two different traffic scenarios using an appropriate simulation model 相似文献
980.
G.P. Wu G.L. Huang Y. Huang D.Y. Wang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(6):984-987
Based upon the most efficient electron acceleration near the midplane of 3D non-neutral driven reconnecting current sheet (RCS) and the electrostatic wave excitation by the drift Maxwellian distribution of electrons in Vlasov simulation, we assume that the electrostatic waves mainly propagate opposite to the reconnecting electric field and investigated how these waves affect the electron acceleration. The main results are: (1) when the electron’s velocity equals to the phase speed of the waves, they will be trapped and have the different accelerating characteristics from the untrapped electrons through solving the momentum equations of electrons analytically; (2) the test particle simulations further prove that the number of the energetic electrons decreases with the increasing intensity of unstable waves, and the distribution of the energetic electrons takes on the double power-law. 相似文献