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791.
Sublethal abnormalities were examined in developing embryos of the winter flounder,Pseudopleuronectes americanus, as part of a study of its early reproductive success in Long Island Sound and two sites in Boston Harbor. These sites represented varying levels of anthropogenic contamination that were possibly affecting reproduction, as ascertained by chromosomal abnormalities and lowered developmental rates in the embryos. Effort was focused on examination of blastula and tail-bund embryos from field-captured females spawned at the laboratory. Abnormalities observed included evidence of cytotoxicity and chromosome damage. Embryos of fish from New Haven were usually the most aberrant, while embryos from other sites, notably Hempstead, Shoreham, and both Boston Harbor stations, showed subtle indications of abnormality. 相似文献
792.
The influence of compressibility of media on both the statistical acceleration and the turbulent diffusion of cosmic-ray particles is investigated. The averaging over an ensemble of random velocity fields of the medium was performed in the kinetic equation. The kinetic coefficients, which are responsible for the particle acceleration, were obtained in the cases of weak and strong scattering due inhomogeneous magnetic fields. 相似文献
793.
G. M. Petrov 《Astrophysics and Space Science》1991,177(1-2):269-270
The classical method of determination of the absolute azimuth (or Bessel's parameter n) can secure sufficiently precision for RA from observations of stars at high geographical latitudes during polar night only. 相似文献
794.
The 5-dimensional Jordan-Brans-Dicke cosmologies in vacuum are found for the Bianchi type I metric, their relation with general relativity cosmologies is studied. Two solutions are possible, both produce effective pressure and energy density in the 4-dimensional G.R.-universes. One is a power-law relation, with two cases, the first one is forp
eff=eff and the other forp
eff=eff(– 1 < < 1) has a behaviour as the open flat universe. The second solution is an exponential only valid forp
eff=–eff. In all cases the three-space expansion reaches infinity ast and the fifth dimension can be made to decrease approaching zero. The scalar field can increase or decrease with time. 相似文献
795.
G. Z. Xie F. K. Liu Y. Y. Zhu J. H. Fan R. W. Lu 《Astrophysics and Space Science》1991,179(2):321-329
It has become clear in recent years that relativistic beaming is a good explanation for the BL Lac phenomenon. Of studies based on the relativistic beaming model of BL Lac objects, we note that the orientation of jet's axis to the line-of-sight is very small and, therefore, the observed flux emitted from a rapidly moving source is orders of magnitude higher than the flux in its rest-frame:F
obs = 3 +
F
intr, where is the bulk relativistic Doppler factor. Then the observed apparent magnitudem
v
must be corrected for this effect. For our 39 samples, the corrected apparent magnitudem
v
corr
and logZ have a good correlation. 相似文献
796.
E. F. Arias C. Boucher M. Feissel J. -F. Lestrade 《Astrophysics and Space Science》1991,177(1-2):187-192
The relative orientations of various VLBI celestial reference frames are evaluated on the basis of coordinate differences of common sources. It is shown that an accuracy better than 0.001 can be achieved. Possible regional deformations in the different catalogues are investigated; they are found to reach a few 0.001 in some restricted zones. The application of these studies to the realisation of a combined celestial reference frame consistent with the BIH Terrestrial System is outlined. 相似文献
797.
Glenn M. Frye Jr. Philip P. Dunphy Edward L. Chupp Paul Evenson 《Solar physics》1988,118(1-2):321-346
798.
The surface distribution of M stars is studied by differentiating them according to whether they show a circumstellar dust shell (CS) or not. Analysis shows that galactic latitudinal and longitudinal distributions are not determined by spectral subclasses alone. The study also indicates that M-type stars with CS have higher luminosities in the K band than those without CS. The M stars used in the study are obtained from theTwo-Micron Sky-Survey Catalogue (IRC) which is a most unbiased sample with respect to the interstellar extinction. The CS feature is identified by the ratio of flux densities at 12 and 25 m in the IRAS point source catalog. 相似文献
799.
M. J. Hagyard 《Solar physics》1988,115(1):107-124
We have analyzed the vector magnetic field of an active region at a location of repeated flaring to determine the nature of the currents flowing in the areas where the flares initiated. The component of electric current density crossing the photosphere along the line-of-sight was derived from the observed transverse component of the magnetic field. The maximum concentrations of these currents occurred exactly at the sites of flare initiation and where the photospheric field was sheared the most. The calculated distribution of current density at the flare sites suggested that currents were flowing out of an area of positive magnetic polarity and across the magnetic inversion line into two areas of negative polarity. This interpretation was reinforced by a calculation of the source field, the magnetic field produced in the photosphere by the electric currents above the photosphere. In the vicinity of the flare sites, the calculated source field exhibited three particular characteristics: (1) maximum magnitudes at the sites of flare initiation, (2) a rotational direction where the vertical current density was concentrated, and (3) a fairly constant angular orientation with the magnetic inversion line. The source field was thus very similar to the field produced by two arcades of currents crossing the inversion line at the locations of greatest magnetic shear with orientations of about 60° to the inversion line. With this orientation, the inferred arcades would be aligned with the observed chromospheric fibrils seen in the H data so that the currents were field-aligned above the photosphere. The field thus exhibited a vertical gradient of magnetic shear with the shear decreasing upward from the photosphere. We estimated the currents in the two arcades by matching the source field derived from observations with that produced by a model of parallel loops of currents. We found that the loops of the model would each have a radius of 4500 km, a separation of 1830 km, and carry a current of 0.15 × 1012 A. Values of vertical current densities and source fields appearing in the umbrae of the two large sunspots away from the flare sites were shown to lie at or below the level of uncertainty in the data. The main source of this uncertainty lay in the method by which the 180° ambiguity in the azimuth of the transverse field is resolved in umbral areas. We thus concluded that these quantities in large umbrae should be treated with a healthy skepticism. Finally, we found that the source field at the flare sites was produced almost entirely by the angular difference between the observed and potential field and not by the difference in field intensity. 相似文献
800.
J. P. Vallée 《Astrophysics and Space Science》1988,149(2):225-231
Recent observations of the longest known head-tail galaxy IC 711, at long wavelengths have shown it to extend farther than previously known. At δ 74 cm, Vallée and Roger (1987) found it to stretch 17′ (930 kpc) behind the optical nucleus of this elliptical galaxy. At δ92 cm, Vallée and Strom (1988) found it to stretch 18.3′ (1 Mpc) behind the optical nucleus. What new physics can be learned from it? To that end, a theoretical simulation in 3 dimensions of the longest head-tail galaxy has been performed, building the radio trail cell by cell inside a volume of space composed of 8 million cells, with each cell being assigned a proper radio emissivity. Matching ram pressure theory and recent observations yields a primary fast decrease of the radio luminosity with time or distance from the optical nucleus of the galaxy, and a secondary periodic variation of the radio luminosity every 500 kpc. Near the end of the tail, a sudden and unpredicted flare-up of the observed width of the tail requires a sudden change in the jet's physical conditions about 2 Gyr earlier, or that of the surroundings. These simulations provide some additional constraints on the ram pressure theory. Along the tail ridge, particle aging and particle acceleration must combine to give a luminosity function that mimics an exponential decrease with time. Across the tail ridge, no edge brightening is necessary, suggesting that particle aging and particle acceleration must combine via central turbulences and central instabilities (not by edge effects). The disappearance of the radio trail at two points along the radio ridge is unexpected from the ram pressure theory. Thus particle aging and particle acceleration must combine once more to mimic a sinusoidal modulation with time of the radio luminosity, perhaps near the nucleus inside the optical galaxy. 相似文献