排序方式： 共有11条查询结果，搜索用时 31 毫秒
1.
2.
G. Berthomieu 《Solar physics》1974,38(2):311-319
The response of a one dimensional isothermal atmosphere with rigid lower boundary and bounded upward by a very hot isothermal atmosphere to an applied random source is studied. It is shown that a concentrated white noise source merely excites the damped eigen-modes of the model and that the enhanced response at the cut-off frequency found in semi-infinite isothermal model is removed by the reflections. We believe that this rules out the attempts to relate the photospheric and chromospheric oscillations to the singular response of an excited semi-infinite isothermal atmosphere. 相似文献
3.
FIRST RESULTS FROM VIRGO,THE EXPERIMENT FOR HELIOSEISMOLOGY AND SOLAR IRRADIANCE MONITORING ON SOHO 总被引：1，自引：0，他引：1
Fröhlich Claus Andersen Bo N. Appourchaux Thierry Berthomieu Gabrielle Crommelynck Dominique A. Domingo Vicente Fichot Alain Finsterle Wolfgang Gómez Maria F. Gough Douglas Jiménez Antonio Leifsen Torben Lombaerts Marc Pap Judit M. Provost Janine Roca Cortés Teodoro Romero José Roth Hansjörg Sekii Takashi Telljohann Udo Toutain Thierry Wehrli Christoph 《Solar physics》1997,170(1):1-25
First results from the VIRGO experiment (Variability of solar IRradiance and Gravity Oscillations) on the ESA/NASA Mission SOHO (Solar and Heliospheric Observatory) are reported. The observations started mid-January 1996 for the radiometers and sunphotometers and near the end of March for the luminosity oscillation imager. The performance of all the instruments is very good, and the time series of the first 4–6 months are evaluated in terms of solar irradiance variability, solar background noise characteristics and p-mode oscillations. The solar irradiance is modulated by the passage of active regions across the disk, but not all of the modulation is straightforwardly explained in terms of sunspot flux blocking and facular enhancement. Helioseismic inversions of the observed p-mode frequencies are more-or-less in agreement with the latest standard solar models. The comparison of VIRGO results with earlier ones shows evidence that magnetic activity plays a significant role in the dynamics of the oscillations beyond its modulation of the resonant frequencies. Moreover, by comparing the amplitudes of different components ofp -mode multiplets, each of which are influenced differently by spatial inhomogeneity, we have found that activity enhances excitation. 相似文献
4.
Helioseismology requires solar models computed with great accuracy. Results of investigations about the incidence in ZAMS models of one solar mass of the numerical errors arising from the interpolation of opacity tables and from the integration of the atmosphere are reported.Though the numerical accuracy reached by some actual codes is of the order of 10–4 (Christensen-Dalsgaard, 1989), it looks optimistic to expect a numerical accuracy better than few percent for models without mesh refinements in opacity tables and more consistency between atmospheric and internal structure models.Since most of the calculations were made with a new code based on spline/collocation, the numerical method used is outlined in an Appendix. 相似文献
5.
Virginie Chapon Laurie Piette Marie-Hélène Vesvres Frédéric Coppin Claire Le Marrec Richard Christen Nicolas Theodorakopoulos Laureline Février Sviatoslav Levchuk Arnaud Martin-Garin Catherine Berthomieu Claire Sergeant 《Applied Geochemistry》2012
The diversity of bacterial communities exposed to radioactive contamination in Chernobyl soils was examined by a combination of molecular and culture-based approaches. A set of six radioactive soil samples, exhibiting high levels of 137Cs contamination, were collected from the T22 trench. Three samples were also collected in nearby soils with low contamination. Complex bacterial community structures were observed in both highly and weakly contaminated samples, using a molecular approach targeting the 16S rRNA gene. However, the presence of specific populations within samples from highly contaminated soils could not be revealed by statistical analysis of the DGGE profiles. More than 200 culturable isolates, representative of dominant morphotypes, were grouped into 83 Operational Taxonomic Units (OTUs) and affiliated to Firmicutes, Actinobacteria, Alpha-, Beta-, Gamma-Proteobacteria and Bacteroïdetes. No specific pattern linked to contamination was observed for these culturable bacteria. The results show that both highly and weakly contaminated soils host a wide diversity of bacteria, suggesting that long term exposure to radionuclides does not lead to the extinction of bacterial diversity. 相似文献
6.
S. Turck-Chièze S. Basu A. S. Brun J. Christensen-Dalsgaard A. Eff-Darwich I. Lopes F. Pérez Hernández G. Berthomieu J. Provost R. K. Ulrich F. Baudin P. Boumier J. Charra A. H. Gabriel R. A. Garcia G. Grec C. Renaud J. M. Robillot T. Roca Cortés 《Solar physics》1997,175(2):247-265
After 8 months of nearly continuous measurements the GOLF instrument, aboard SOHO, has detected acoustic mode frequencies
of more than 100 modes, extending from 1.4 mHz to 4.9 mHz. In this paper, we compare these results with the best available
predictions coming from solar models. To verify the quality of the data, we examine the asymptotic seismic parameters; this
confirms the improvements achieved in solar models during the last decade.
Using the GOLF set of frequencies for l=0, 1, 2, 3 combined with the LOWL second year data set for l > 3 we then carry out
inversions to infer properties of the solar core.
This largely confirms the previous results down to around 0.1 R⊙, while there remain differences, even closer to the centre,
where the present study shows an extreme sensitivity of the inversion results to the values of the frequencies. We finally
consider physical processes which may influence directly or indirectly the solar core structure. 相似文献
7.
By applying the theory of slowly rotating stars to the Sun, the solar quadrupole and octopole moments J
2 and J
4 were computed using a solar model obtained from CESAM stellar evolution code (Morel, 1997) combined with a recent model of solar differential rotation deduced from helioseismology (Corbard et al., 2002). This model takes into account a near-surface radial gradient of rotation which was inferred and quantified from MDI f-mode observations by Corbard and Thompson (2002). The effect of this observational near-surface gradient on the theoretical values of the surface parameters J
2, J
4 is investigated. The results show that the octopole moment J
4 is much more sensitive than the quadrupole moment J
2 to the subsurface radial gradient of rotation. 相似文献
8.
Some results are given on the properties of the second-order asymptotic expression of the periods of low-degree gravity modes and on their rotational splitting. These could be of some help for the detection of these modes in the signal. 相似文献
9.
The asymptotic properties of the gravity modes of solar models with a mixed core have been investigated. In this model, the Brunt-Väissälä frequency has a strong enhancement in the region of variable chemical composition at the boundary of the mixed core, giving rise to a non-equidistant spectrum of gravity modes periods. An asymptotic expression for the periods is derived, which relates the main feature of the departure from period equidistance to the stratification of the model. Qualitative agreement with the numerical periods of the model is obtained. 相似文献
10.
Claus Fröhlich José Romero Hansjörg Roth Christoph Wehrli Bo N. Andersen Thierry Appourchaux Vicente Domingo Udo Telljohann Gabrielle Berthomieu Philippe Delache Janine Provost Thierry Toutain Dominique A. Crommelynck André Chevalier Alain Fichot Werner Däppen Douglas Gough Todd Hoeksema Antonio Jiménez Maria F. Gómez José M. Herreros Teodoro Roca Cortés Andrew R. Jones Judit M. Pap Richard C. Willson 《Solar physics》1995,162(1-2):101-128
The scientific objective of the VIRGO experiment (Variability of solar IRradiance and Gravity Oscillations) is to determine the characteristics of pressure and internal gravity oscillations by observing irradiance and radiance variations, to measure the solar total and spectral irradiance and to quantify their variability over periods of days to the duration of the mission. With these data helioseismological methods can be used to probe the solar interior. Certain characteristics of convection and its interaction with magnetic fields, related to, for example, activity, will be studied from the results of the irradiance monitoring and from the comparison of amplitudes and phases of the oscillations as manifest in brightness from VIRGO, in velocity from GOLF, and in both velocity and continuum intensity from SOI/MDI. The VIRGO experiment contains two different active-cavity radiometers for monitoring the solar constant, two three-channel sunphotometers (SPM) for the measurement of the spectral irradiance at 402, 500 and 862 nm, and a low-resolution imager (LOI) with 12 pixels, for the measurement of the radiance distribution over the solar disk at 500 um. In this paper the scientific objectives of VIRGO are presented, the instruments and the data acquisition and control system are described in detail, and their measured performance is given.died 13 October 1994 相似文献