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201.
202.
203.
We present observations of electric and magnetic field variations from proton (about few Hz) to electron cyclotron frequencies
(about few kHz) obtained by STAFF instrument on Cluster satellites during two cusp crossings, at ∼6 R
E
altitude, in September 2002. The cusp was identified by the presence of intensive fluxes of counter streaming electrons with
low energies and broadband wave activity which is typical for this region.
Special attention is given for the interval of measurements when the waveform of the magnetic field fluctuations was taken
in this region by CLUSTER satellites. The wave has been processed using the wavelet and bispectral analysis. Results showing
the cascade of turbulence and wave-wave interactions are presented in this paper. A three wave process can be responsible
for the broadening of the wave spectra in the polar cusp. 相似文献
204.
A methodology has been proposed which can be used to reduce the number of ground motion records needed for the reliable prediction of the median seismic response of structures by means of incremental dynamic analysis (IDA). This methodology is presently limited to predictions of the median IDA curve only. The reduction in the number of ground motion records needed to predict the median IDA curve is achieved by introducing a precedence list of ground motion records. The determination of such a list is an optimization problem, which is solved in the paper by means of (1) a genetic algorithm and (2) a proposed simple procedure. The seismic response of a simple, computationally non‐demanding structural model has been used as input data for the optimization problem. The presented example is a three‐storey‐reinforced concrete building, subjected to two sets of ground motion records, one a free‐field set and the other a near‐field set. It is shown that the median IDA curves can be predicted with acceptable accuracy by employing only four ground motion records instead of the 24 or 30 records, which are the total number of ground motion records for the free‐field and near‐field sets, respectively. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
205.
206.
Jan Kouba 《GPS Solutions》2002,5(3):88-90
The GPS Toolbox is dedicated to highlighting algorithms and source code utilized by GPS engineers and scientists. If you have
an interesting subroutine or program you would like to share with our readers, please pass it along so that we might continue
to bring you this column; e-mail it to us at gps-toolbox@ngs.noaa.gov. To comment on any of the source code discussed here,
or to leave a request for a piece of source code you may be looking for, visit our web site at http:/www.ngs.noaa.gov/gps-toolbox.
This column is edited by Stephen Hilla, National Geodetic Survey, NOAA, Silver Spring, Maryland, and Mike Craymer, Geodetic
Survey Division, Natural Resources Canada, Ottawa, Ontario, Canada. ? 2002 Wiley Periodicals, Inc. 相似文献
207.
Robustness analysis of geodetic horizontal networks 总被引:2,自引:1,他引:2
208.
Progress in Carrier Phase Time Transfer 总被引:1,自引:0,他引:1
Jim Ray Felicitas Arias Gérard Petit Tim Springer Thomas Schildknecht Jon Clarke Jan Johansson 《GPS Solutions》2001,4(4):47-54
The progress of the joint Pilot Project for time transfer, formed by the International GPS Service (IGS) and the Bureal International
des Poids et Mesures (BIPM), was recently reviewed. Three notable milestones were set. (1) The IGS will implement, at least
in a test mode, an internally realized time scale based on an integration of combined frequency standards within the IGS network.
This will eventually become the reference time scale for all IGS clock products (instead of the current GPS broadcast time).
(2) A new procedure for combined receiver and satellite clock products will be implemented officially in November 2000. Receiver
clocks are an entirely new product of the IGS. (3) The BIPM will coordinate an effort to calibrate all Ashtech Z12-T (and
possibly other) receivers suitable for time transfer applications, either differentially or absolutely. Progress reports will
be presented publicly in the spring 2001. ? 2001 John Wiley & Sons, Inc. 相似文献
209.
Geoid, topography, and the Bouguer plate or shell 总被引:1,自引:1,他引:1
Topography plays an important role in solving many geodetic and geophysical problems. In the evaluation of a topographical
effect, a planar model, a spherical model or an even more sophisticated model can be used. In most applications, the planar
model is considered appropriate: recall the evaluation of gravity reductions of the free-air, Poincaré–Prey or Bouguer kind.
For some applications, such as the evaluation of topographical effects in gravimetric geoid computations, it is preferable
or even necessary to use at least the spherical model of topography. In modelling the topographical effect, the bulk of the
effect comes from the Bouguer plate, in the case of the planar model, or from the Bouguer shell, in the case of the spherical
model. The difference between the effects of the Bouguer plate and the Bouguer shell is studied, while the effect of the rest
of topography, the terrain, is discussed elsewhere. It is argued that the classical Bouguer plate gravity reduction should
be considered as a mathematical construction with unclear physical meaning. It is shown that if the reduction is understood
to be reducing observed gravity onto the geoid through the Bouguer plate/shell then both models give practically identical
answers, as associated with Poincaré's and Prey's work. It is shown why only the spherical model should be used in the evaluation
of topographical effects in the Stokes–Helmert solution of Stokes' boundary-value problem. The reason for this is that the
Bouguer plate model does not allow for a physically acceptable condensation scheme for the topography.
Received: 24 December 1999 / Accepted: 11 December 2000 相似文献
210.
Effects of the spherical terrain on gravity and the geoid 总被引:3,自引:0,他引:3