Astrophysical limits on gauge invariance breaking in electrodynamics with torsion     

C. Sivaram  L. C. Garica de Andrade 《Astrophysics and Space Science》1993,201(1):121-123

General relativistic electrodynamics in a torsion background can give rise to a situation where the photons can ahve a non-zero rest mass and magnetic moment. Astrophysical limits are used to constrain these parameters.  相似文献   

Elementary flare bursts explained by explosive coalescence     

Cornelis de Jager  Jun-ichi Sakai 《Solar physics》1991,133(2):395-398

The observed burst durations of Elementary Flare Bursts (5–25 s), as well as the related other flare characteristics, such as the temperature (30–50 MK), the electron density (log ne = 10 to 11) and the magnetic field strengths (100 G to 200 G) can be explained quantitatively by the mechanism of explosive coalescence.  相似文献   

An observational program for a unified optical-radio reference frame     

C. de Vegt  J. A. Hughes  D. Jauncey  G. White  K. J. Johnston  J. Russell  G. Nicholson 《Astrophysics and Space Science》1991,177(1-2):199-202

An observational pilot program is described which provides a first step towards the construction of an inertial extragalactic reference frame from optical and radio measurements. Candidate objects will be selected from extragalactic compact radio sources which display optical counterparts. Galactic radio stars will be secondary reference objects. The reference frame will be defined by the radio positions of the extragalactic objects. Based on a coordinated effort in both hemispheres, a global homogeneous net of about 400 quasars and 100 radio stars is expected to result from a five year campaign.  相似文献   

The dynamics of velocity fluctuations in the solar wind – I. Coronal mass ejections     

J. Cantó  R. F. González  A. C. Raga  E. M. de Gouveia Dal Pino  A. Lara  J. A. González-Esparza 《Monthly notices of the Royal Astronomical Society》2005,357(2):572-578

In this paper we present a simple, analytic model for the dynamical evolution of supersonic velocity fluctuations at the base of the ambient solar wind. These fluctuations result in the formation of dense working surfaces that travel down the wind. It is shown how the initial parameters of the fluctuations (velocity, density and duration) are related to the characteristics of the working surfaces far from the Sun (for instance at the Earth). We apply the model to the evolution of the coronal mass ejections in the IP medium, finding that the model is in good agreement with satellite observations of these phenomena, thus providing physical insight into their dynamical evolution. Our model may contribute to future 'space weather forecasting' on the Earth, based on detailed satellite monitoring of the solar corona.  相似文献   

A bar signature and central disc in the gaseous and stellar velocity fields of NGC 5448     

Kambiz Fathi  Glenn van de Ven  Reynier F. Peletier  Eric Emsellem  Jesús Falcón-Barroso  Michele Cappellari  Tim de Zeeuw 《Monthly notices of the Royal Astronomical Society》2005,364(3):773-782

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Particulate matter exchange across a Rjord sill     

J.C. Therriault  R. de Ladurantaye  R.G. Ingram 《Estuarine, Coastal and Shelf Science》1984,18(1):51-64

Recent studies have indicated the existence of a considerably higher planktonic biomass in the deep waters of the Saguenay Fjord as compared to corresponding depths in the adjacent St Lawrence Estuary on the other side of a shallow sill. The hypothesis that has been put forward to explain this phenomenon is related to the advection of near surface estuarine waters, at times very rich in particulate matter, over the entrance sill into the deeper waters of the fjord. Mixing processes associated with the development of a density flow, the presence of a hydraulic jump or other mechanisms are assumed to be responsible for the common occurrence of lower density subsurface water within the basin as compared to that penetrating over the sill.The exchange processes between the estuary and the fjord are described and an estimate made of the estuarine water volume that penetrates into the lower layer of the fjord over a semidiurnal tide cycle. From these calculations, the replacement time for the outer basin was estimated to range between one and four days. The biological characteristics of this water were used to establish a budget for particulate matter exchange which showed, in early August, a typical net input of ? 188 t of particulate organic carbon into the deep waters of the fjord over one tide cycle.  相似文献   

The Ca II triplet lines in Starburst and AGN     

María Luisa García Vargas  Angeles I. Díaz  Elena Terlevich  Roberto Terlevich 《Astrophysics and Space Science》1993,205(1):85-89

In the frame of the Starburst Model for AGN, we show that the evolution of a massive stellar cluster in a high metallicity environment can reproduce the observed equivalent widths of Ca II triplet lines in absorption in Starburst and active galactic nuclei. In the case of Starburst galaxies, this strength, together with the emission-line ratio [O II]/[O III], can be used to determine the age of the cluster. The strength of the Ca II lines is mainly governed by the age of the stellar cluster through the presence of red supergiant stars.  相似文献   

Differential phase estimation with the SeaMARCII bathymetricsidescan sonar system     

Masnadi-Shirazi  M.A. de Moustier  C. Cervenka  P. Zisk  S.H. 《Oceanic Engineering, IEEE Journal of》1992,17(3):239-251

A maximum-likelihood estimator is used to extract differential phase measurements from noisy seafloor echoes received at pairs of transducers mounted on either side of the SeaMARC II bathymetric sidescan sonar system. Carrier frequencies for each side are about 1 kHz apart, and echoes from a transmitted pulse 2 ms long are analyzed. For each side, phase difference sequences are derived from the full complex data consisting of base-banded and digitized quadrature components of the received echoes. With less bias and a lower variance, this method is shown to be more efficient than a uniform mean estimator. It also does not exhibit the angular or time ambiguities commonly found in the histogram method used in the SeaMARC II system. A figure for the estimation uncertainty of the phase difference is presented, and results are obtained for both real and simulated data. Based on this error estimate and an empirical verification derived through coherent ping stacking, a single filter length of 100 ms is chosen for data processing applications  相似文献   

Improving reservoir description by using geostatistical and multivariate data analysis techniques     

Henrique Garcia Pereira  António Costa e Silva  Amilcar Soares  Luis Ribeiro  Justino de Carvalho 《Mathematical Geosciences》1990,22(8):879-913

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A population synthesis model for the ultraviolet spectrum of the peculiar galaxy NGC 1672     

M. L. García-Vargas  A. I. Díaz  R. J. Terlevich  E. Terlevich 《Astrophysics and Space Science》1990,171(1-2):65-69

We present a stellar population synthesis model for the UV spectrum of the peculiar galaxy NGC 1672, computed with the use of theIUE Atlas Library of Stellar Spectra.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.  相似文献