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211.
X. Zou Z. Deng M. Ge G. Dick W. Jiang J. Liu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
In order to obtain crustal deformations of higher spatial resolution, existing GPS networks must be densified. This densification can be carried out using single-frequency receivers at moderate costs. However, ionospheric delay handling is required in the data processing. We adapt the Satellite-specific Epoch-differenced Ionospheric Delay model (SEID) for GPS networks with mixed single- and dual-frequency receivers. The SEID model is modified to utilize the observations from the three nearest dual-frequency reference stations in order to avoid contaminations from more remote stations. As data of only three stations are used, an efficient missing data constructing approach with polynomial fitting is implemented to minimize data losses. Data from large scale reference networks extended with single-frequency receivers can now be processed, based on the adapted SEID model. A new data processing scheme is developed in order to make use of existing GPS data processing software packages without any modifications. This processing scheme is evaluated using a sub-network of the German SAPOS network. The results verify that the new scheme provides an efficient way to densify existing GPS networks with single-frequency receivers. 相似文献
212.
A. Nathues H. Boehnhardt A.W. Harris C. Jentsch S. Schaeff F. Weischede A. Wiegand N. Schmitz W. Goetz Z. Kachri 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
ASTEX (ASTeroid EXplorer) is a concept study of an in situ exploration mission to two Near-Earth-Asteroids (NEAs), which consists of an orbiting element and two individual lander units. The target candidates have different mineralogical compositions, i.e. one asteroid is chosen to be of “primitive’’ nature, the other to be a fragment of a differentiated asteroid. The main scientific goals of the ASTEX mission are the exploration of the physical, geological, and mineralogical nature of the NEAs. The higher level goal is the provision of information and constraints on the formation and evolution of our planetary system. The study identified realistic mission scenarios, defined the strawman payload as well as the requirements and options for the spacecraft bus including the propulsion system, the landers, the launcher, and assessed and defined the requirements for the mission’s operational ground segment. 相似文献
213.
L.H. Deng Z.Q. Qu T. Liu W.J. Huang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
We investigate the north–south (N–S) asynchrony of the polar faculae and compare it with the hemispheric asynchrony of solar activity at low latitudes. We find that, (1) both the solar activity at high and low latitudes do not synchronously occur in the northern and southern hemispheres, there is phase shifts between the two hemispheres; (2) the N–S asynchrony of the polar faculae is a function of latitudes, implying that the asynchrony of the polar faculae between the two hemispheres is related to the hemispheric asymmetry and latitudinal distribution of the polar faculae. 相似文献
214.
Prediction of Boundary Layer Transition Based on Modeling of Laminar Fluctuations Using RANS Approach 总被引:1,自引:0,他引:1
This article presents a linear eddy-viscosity turbulence model for predicting bypass and natural transition in boundary layers by using Reynolds-averaged Navier-Stokes (RANS) equations. The model includes three transport equations, separately, to compute laminar kinetic energy, turbulent kinetic energy, and dissipation rate in a flow field. It needs neither correlations of intermittency factors nor knowledge of the transition onset. Two transition tests are carried out: flat plate boundary layer under zero ... 相似文献
215.
M. A. Allodi R. A. Baragiola G. A. Baratta M. A. Barucci G. A. Blake P. Boduch J. R. Brucato C. Contreras S. H. Cuylle D. Fulvio M. S. Gudipati S. Ioppolo Z. Kaňuchová A. Lignell H. Linnartz M. E. Palumbo U. Raut H. Rothard F. Salama E. V. Savchenko E. Sciamma-O’Brien G. Strazzulla 《Space Science Reviews》2013,180(1-4):101-175
216.
W.J. Heikkila T. Chen Z.X. Liu Z.Y. Pu R.J. Pellinen T.I. Pulkkinen 《Space Science Reviews》2001,95(1-2):399-414
We propose that the appropriate instability to trigger a substorm is a tailward meander (in the equatorial plane) of the strong current filament that develops during the growth phase. From this single assumption follows the entire sequence of events for a substorm. The main particle acceleration mechanism in the plasma sheet is curvature drift with a dawn-dusk electric field, leading to the production of auroral arcs. Eventually the curvature becomes so high that the ions cannot negotiate the sharp turn at the field-reversal region, locally, at a certain time. The particle motion becomes chaotic, causing a local outward meander of the cross-tail current. An induction electric field is produced by Lenz's law, E
ind=–A/t. An outward meander with B
z>0 will cause E×B flow everywhere out from the disturbance; this reaction is a macroscopic instability which we designate the electromotive instability. The response of the plasma is through charge separation and a scalar potential, E
es=–. Both types of electric fields have components parallel to B in a realistic magnetic field. For MHD theory to hold the net E
must be small; this usually seems to happen (because MHD often does hold), but not always. Part of the response is the formation of field-aligned currents producing the well-known substorm current diversion. This is a direct result of a strong E
ind (the cause) needed to overcome the mirror force of the current carriers; this enables charge separation to produce an opposing electrostatic field E
es (the effect). Satellite data confirm the reality of a strong E
in the plasma sheet by counter-streaming of electrons and ions, and by the inverse ion time dispersion, up to several 100 keV. The electron precipitation is associated with the westward traveling surge (WTS) and the ion with omega () bands, respectively. However, with zero curl, E
es cannot modify the emf =Edl=–dM/dt of the inductive electric field E
ind (a property of vector fields); the charge separation that produces a reduction of E
must enhance the transverse component E
. The new plasma flow becomes a switch for access to the free energy of the stressed magnetotail. On the tailward side the dusk-dawn electric field with EJ<0 will cause tailward motion of the plasma and a plasmoid may be created; it will move in the direction of least magnetic pressure, tailward. On the earthward side the enhanced dawn-dusk induction electric field with EJ>0 will cause injection into the inner plasma sheet, repeatedly observed at moderate energies of 1–50 keV. This same electric field near the emerging X-line will accelerate particles non-adiabatically to moderate energies. With high magnetic moments in a weak magnetic field, electrons (ions) can benefit from gradient and curvature drift to attain high energies (by the ratio of the magnetic field magnitude) in seconds (minutes). 相似文献
217.
T.E. Gergely M.R. Kundu S.T. Wu M. Dryer Z. Smith R.T. Stewart 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(7):283-286
A large coronal transient took place on 8 May 1981. The transient was related to an M7.7/2B flare and was associated with at least two coronal type II bursts. The velocities of the type II bursts were in the range 1100–1800 kms?1, in excess of the transient velocity of 500–1000 kms?1. Two dimensional positions of the type II radio sources are available from both the Clark Lake and the Culgoora Radio Observatories. We carry out two dimensional MHD simulations of the event, taking into account the observed velocity, position, and size of the type II bursts. We simulate the multiple shocks observed during the event and their interaction, and discuss some results of the simulation. 相似文献
218.
S. Savin L. Zelenyi N. Maynard I. Sandahl H. Kawano C. T. Russell S. Romanov E. Amata L. Avanov J. Blecki J. Buechner G. Consolini G. Gustafsson S. Klimov F. Marcucci Z. Nemecek B. Nikutowski J. Pickett J. L. Rauch J. Safrankova A. Skalsky V. Smirnov K. Stasiewicz P. Song J. G. Trotignon Yu. Yermolaev 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(12):2821-2830
Multi-spacecraft tracing of the high latitude magnetopause (MP) and boundary layers and Interball-1 statistics indicate that:
- 1. (a) The turbulent boundary layer (TBL) is a persistent feature in the region of the cusp and ‘sash’, a noticeable part of the disturbances weakly depends on the interplanetary magnetic field By component; TBL is a major site for magnetosheath (MSH) plasma penetration inside the magnetosphere through percolation and local reconnection.
- 2. (b) The TBL disturbances are mainly inherent with the characteristic kinked double-slope spectra and, most probably, 3-wave cascading. The bi-spectral phase coupling indicates self-organization of the TBL as the entire region with features of the non-equilibrium multi-scale and multi-phase system in the near-critical state.
- 3. (c) We've found the different outer cusp topologies in summer/winter periods: the summer cusp throat is open for the decelerated MSH flows, the winter one is closed by the distant MP with a large-scale (several Re) diamagnetic ‘plasma ball’ inside the MP; the ‘ball’ is filled from MSH through patchy merging rather than large-scale reconnection.
- 4. (d) A mechanism for the energy release and mass inflow is the local TBL reconnection, which operates at the larger scales for the average anti-parallel fields and at the smaller scales for the nonlinear fluctuating fields; the latter is operative throughout the TBL. The remote from TBL anti-parallel reconnection seems to happen independently.
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相似文献
219.
H. Rothkaehl Z. K
os V. S. Dokukin P. Triska 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,15(12):25-28
In the Apex project the modulated electron beam (pulses of 2 micro sec duration, E=8 keV, I=0.1 A and 25 micro sec repetition) was emitted from a main satellite. The RF emissions were observed in parallel on the mother satellite as well as on Magion-3 subsatellite. The paper discusses the case when the subsatellite was separated about 200 km from the main object and the electron gun was operated. Together with strong electrostatic emission at the upper hybrid plasma frequency on the main spacecraft, selected spikes in RF frequency range on Magion-3, were simultaneously detected, which can be related to pulse electron beam emission. 相似文献
220.
M. Popova V. Popov A. Antov Z. Kraicheva 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
The results from the photometric observations of the x-ray source KR Aur for the period Oct. 1979 – Mai 1983 obtained at the National Astronomical Observatory, Bulgarian Acedemy of Sciences, are presented. The 1981 – 1982 minimum of the light curve is discussed. 相似文献