排序方式： 共有10条查询结果，搜索用时 31 毫秒
1
1.
G. Le Chat A. Zaslavsky N. Meyer-Vernet K. Issautier S. Belheouane F. Pantellini M. Maksimovic I. Zouganelis S. D. Bale J. C. Kasper 《Solar physics》2013,286(2):549-559
New measurements using radio and plasma-wave instruments in interplanetary space have shown that nanometer-scale dust, or nanodust, is a significant contributor to the total mass in interplanetary space. Better measurements of nanodust will allow us to determine where it comes from and the extent to which it interacts with the solar wind. When one of these nanodust grains impacts a spacecraft, it creates an expanding plasma cloud, which perturbs the photoelectron currents. This leads to a voltage pulse between the spacecraft body and the antenna. Nanodust has a high charge/mass ratio, and therefore can be accelerated by the interplanetary magnetic field to the speed of the solar wind: significantly faster than the Keplerian orbital speeds of heavier dust. The amplitude of the signal induced by a dust grain grows much more strongly with speed than with mass of the dust particle. As a result, nanodust can produce a strong signal despite its low mass. The WAVES instruments on the twin Solar TErrestrial RElations Observatory spacecraft have observed interplanetary nanodust particles since shortly after their launch in 2006. After describing a new and improved analysis of the last five years of STEREO/WAVES Low Frequency Receiver data, we present a statistical survey of the nanodust characteristics, namely the rise time of the pulse voltage and the flux of nanodust. We show that previous measurements and interplanetary dust models agree with this survey. The temporal variations of the nanodust flux are also discussed. 相似文献
2.
Empirical site response evaluations: case studies in Israel 总被引：1，自引：0，他引：1
Y. Gitterman Y. Zaslavsky A. Shapira V. Shtivelman 《Soil Dynamics and Earthquake Engineering》1996,15(7):447-463
A closed-loop, time-efficient technique for site effect evaluation for seismic microzonation in urban areas is developed and implemented. It includes the following successive steps: microtremor measurements using a triangular array of three-component seismometers; estimation of the Nakamura horizontal-vertical spectral ratio, calculation of Rayleigh wave dispersion using the Aki spatial correlation method; inversion of the dispersion curve to determine a shear wave velocity model of the shallow subsurface; analytical computation of Rayleigh wave spectral ellipticity and 1-D SH transfer function for this model; and a comparison of empirical and analytical ratios and correction of the model if required. The technique has been tested at several locations in a number of towns near the active Jordan Rift valley. A reasonable agreement is obtained when comparing empirical spectral ratios and analytical transfer functions. 相似文献
3.
Belheouane S. Zaslavsky A. Meyer-Vernet N. Issautier K. Mann I. Maksimovic M. 《Solar physics》2012,281(1):501-506
Most in situ measurements of cosmic dust have been carried out with dedicated dust instruments. However, dust particles can also be detected with radio and plasma wave instruments. The high velocity impact of a dust particle generates a small crater on the spacecraft, and the dust particle and the crater material are vaporised and partly ionised. The resulting electric charge can be detected with plasma instruments designed to measure electric waves. Since 2007 the STEREO/WAVES instrument has recorded a large number of events due to dust impacts. Here we will concentrate on the study of those impacts produced by dust grains originating from the local interstellar cloud. We present these fluxes during five years of the STEREO mission. Based on model calculations, we determine the direction of arrival of interstellar dust. We find that the interstellar dust direction of arrival is ～260°, in agreement with previous studies.
相似文献4.
E. L. Akim G. S. Zaslavsky I. M. Morskoy E. G. Ruzsky V. A. Stepaniants A. G. Tuchin 《Solar System Research》2010,44(1):26-37
This paper is concerned with the problems of ballistics, navigation, and flight control of the space craft (SC) in the Phobos-Grunt
mission. We consider an insertion into the Earth-Mars transfer trajectory, the Earth-Mars transfer, the strategy of corrections,
and the accuracy of the insertion of the SC into Martian orbit. During the orbital maneuvering stage in the sphere of influence
of Mars, we set up a scheme that allows for the insertion of the SC, with the prescribed accuracy, into a point 80-km above
the Phobos surface over the theoretical landing area. We specify the sequence for a controlled landing and provide methods
for solving the problems of navigation and control during a self-c ontained landing. We also consider the liftoff from Phobos,
insertion into the parking orbit, and the Mars-Earth transfer. 相似文献
5.
When applied to a sea surface, shortcomings are noted for the ordinary classification of drag conditions at rigid underlying surfaces according to the Reynolds roughness number Re
s
. It is shown that in the case of mobile underlying surfaces, it would be more natural to use the dynamical classification of drag conditions according to the order of magnitude of the ratio ( = /) of the momentum flux toward the waves (
w) to the viscous momentum flux through the surface (
w). The relevant estimates of for the main stages of development of the wind waves indicate that the observed values of the drag coefficient of the sea surface correspond to the case of underdeveloped roughness. 相似文献
6.
Amplification effects from earthquakes and ambient noise in the Dead Sea rift (Israel) 总被引：1，自引：0，他引：1
Seven sites were instrumented in the Parsa area located in the seismically active Dead Sea rift system. Moderate and weak motions generated by earthquakes and ambient noise were used to identify amplifications due to geological and topographic effects.Three observation methods were applied to estimate site effects: (1) conventional soil–bedrock station-pair spectral ratios for earthquake motions and microtremors; (2) horizontal-to-vertical component spectral ratios for shear-waves observed simultaneously at a site (receiver function estimates) and (3) horizontal-to-vertical spectral ratios of microtremor measurements (Nakamura estimate). The site response spectra of soil sites exhibited significant peaks between 1 and 3 Hz with amplification factors typically within the range of 2.5–4.0. A bedrock site on the high plateau near the escarpment top showed a peak between 2 and 3 Hz, mainly due to an EW oscillation of the NS topographic feature. Our observations indicated that seismograms recorded in the tunnel were either enriched or depleted at certain frequencies owing to interference of incident and surface-reflected waves. 相似文献
7.
Filippo Pantellini Soraya Belheouane Nicole Meyer-Vernet Arnaud Zaslavsky 《Astrophysics and Space Science》2012,341(2):309-314
High rate sampling detectors measuring the potential difference between the main body and boom antennas of interplanetary spacecraft have been shown to be efficient means to measure the voltage pulses induced by nano dust impacts on the spacecraft body itself (see Meyer-Vernet et al. in Sol. Phys. 256:463, 2009). However, rough estimates of the free charge liberated in post impact expanding plasma cloud indicate that the cloud’s own internal electrostatic field is too weak to account for measured pulses as the ones from the TDS instrument on the STEREO spacecraft frequently exceeding 0.1 V/m. In this paper we argue that the detected pulses are not a direct measure of the potential structure of the plasma cloud, but are rather the consequence of a transitional interruption of the photoelectron return current towards the portion of the antenna located within the expanding cloud. 相似文献
8.
Michael S. Zhdanov Vjacheslav V. Spichak Leonid Yu. Zaslavsky 《Physics of the Earth and Planetary Interiors》1990,60(1-4):53-61
A method for numerical modeling of quasi-stationary electromagnetic fields in axially symmetric media is proposed. It is based on the direct finite-element method and the use of special basis functions. Assuming cylindrical coordinates r, φ, z, the three-dimensional solution is presented as a superposition of fields with the azimuthal dependence exp(inφ). For each case this results in a system of two equations of elliptical type in two scalar functions in the (r, z) plane.
The discretization leads to the conservative nine-points difference scheme. The system of linear equations is solved by means of the LU-decomposition technique, the band structure of the matrix being taken into account.
The program is tested using analytical results (DC asymptote) for a near-surface inhomogeneity. Comparison also is made with 2D results (H-polarization) for the model of a local well conducting inclusion in a three-layered Earth. 相似文献
9.
Alexander Lopatnikov Leonid Marochnik Lev Mukhin Roald Sagdeev Daniel Usikov Georgy Zaslavsky 《Astrophysics and Space Science》1991,186(2):225-243
This paper considers the evolution of a flat svarm of cometary bodies (under the effect of the passage of stars), initially moving in one direction along the circular orbits with radii 1.4×104<r<2×104 AU and along elliptic orbits with semi-major axes 5×103<a<1×104 AU and with perihelia within 50<q<100 AU. Numerical simulation shows that the original flat belt of comets is thermalizing. Its root-mean-squarez-coordinate grows withr. A cometary cloud forms with a dense flattened inner core and a rarefied halo (the Oort cloud proper). The value =N
core/N
halo varies within a wide range (up to the order of magnitude) depending on the model used (N
core andN
halo are the numbers of comets in the core and the halo, respectively).The hypothesis of a massive Oort cloud (Marochniket al., 1988) implies that the Oort cloud should have a large angular momentum. This paper employs numerical simulation to calculate Oort cloud models to which the initially flat located at the periphery of the solar nebula rotating cometary swarms is evolving in time. The loss of the initial angular momentum over the time of the Oort cloud evolution is not large. 相似文献
10.
V. Krupar M. Maksimovic O. Santolik E. P. Kontar B. Cecconi S. Hoang O. Kruparova J. Soucek H. Reid A. Zaslavsky 《Solar physics》2014,289(8):3121-3135
We have performed a statistical study of 152 Type III radio bursts observed by Solar TErrestrial RElations Observatory (STEREO)/Waves between May 2007 and February 2013. We investigated the flux density between 125 kHz and 16 MHz. Both high- and low-frequency cutoffs were observed in 60 % of events, suggesting an important role of propagation. As already reported by previous authors, we observed that the highest flux density occurs at 1 MHz on both spacecraft. We developed a simplified analytical model of the flux density as a function of radial distance and compared it with the STEREO/Waves data. 相似文献
1