51,957 research outputs found
The Radio and Gamma-Ray Luminosities of Blazars
Based on the -ray data of blazars in the third EGRET catalog and
radio data at 5 GHz, we studied the correlation between the radio and
-ray luminosities using two statistical methods. The first method was
the partial correlation analysis method, which indicates that there exist
correlations between the radio and -ray luminosities in both high and
low states as well as in the average case.
The second method involved a comparison of expected -ray luminosity
distribution with the observed data using the Kolmogorov--
Smirnov (KS) test. In the second method, we assumed that there is a
correlation between the radio and -ray luminosities and that the
-ray luminosity function is proportional to the radio luminosity
function. The KS test indicates that the expected gamma-ray luminosity
distributions are consistent with the observed data in a reasonable parameter
range. Finally, we used different -ray luminosity functions to estimate
the possible 'observed'
-ray luminosity distributions by GLAST.Comment: 8 pages, 4 figures, one table, PASJ, 53 (2001
Cue validity and object-based attention
In a previous study, Egly, Driver, and Rafal (1994) observed both space- and object-based components of visual selective attention. However, the mechanisms underlying these two components and the relationship between them are not well understood. In the present research, with a similar paradigm, these issues were addressed by manipulating cue validity. Behavioral results indicated the presence of both space- and object-based components under high cue validity, similar to the results of Egly et al.'s study. In addition, under low cue validity, the space-based component was absent, whereas the object-based component was maintained. Further event-related potential results demonstrated an object-based effect at a sensory level over the posterior areas of brain, and a space-based effect over the anterior region. The present data suggest that the space- and object-based components reflect mainly voluntary and reflexive mechanisms, respectively
Polarization and Variations of BL Lacertae Objects
BL Lacertae objects are an extreme subclass of AGNs showing rapid and
large-amplitude variability, high and variable polarization, and core-dominated
radio emissions. If a strong beaming effect is the cause of the extreme
observation properties, one would expect that these properties would be
correlated with each other. Based on the relativistic beaming model,
relationships between the polarization and the magnitude variation in
brightness, as well as the core- dominance parameter are derived and used
statistically to compare with the observational data of a BL Lacertae object
sample. The statistical results are consistent with these correlations, which
suggests that the polarization, the variation, and the core-dominance parameter
are possible indications of the beaming effect.Comment: 6 pages, two figures, one table, some revisions. PASJ, 53 (2001
Basic properties of Gamma-ray loud blazars
In this paper, a method is proposed to determine the basic properties of
-ray loud blazars, among them the central black hole mass, M, the
Doppler factor, , the propagation angle of the -rays with
respect to the symmetric axis of a two-temperature accretion disk, , and
the distance (i.e. the height above the accretion disk), d at which the
-rays are created, for seven -ray loud blazars with available
GeV variability timescales and in which the absorption effect of a -ray
and the beaming effect have been taken into account. Our results indicate that,
if we take the intrinsic -ray luminosity to be times the
Eddington luminosity, , the masses of the
blazars are in the range of , the Doppler
factors () lie in the range of 0.57 to 5.33 the angle () is in
the range of to 43 and the distance (d) is in the range
of 26R_{g} to 411R_{g}. Our model results are independent of -ray
emission mechanisms but they do depend on the X-ray emission mechanism of the
accretion disk.Comment: 14 pages, 3 tables, A&A accepte
Characterization of the residual stresses in spray-formed steels using neutron diffraction
Neutron diffraction was used to characterize the residual stresses in an as-sprayed tube-shaped steel preform. The measured residual stress distributions were compared with those simulated using finite element method by taking into account the effects of the thermal history, porosity and different phases of the sprayed preform. The porosity was measured using X-ray microcomputed tomography. The study revealed for the first time the correlation between the distribution of porosity and residual stress developed in the as-sprayed preform
Non-linear enhancement of laser generated ultrasonic Rayleigh waves by cracks
Laser generated ultrasound has been widely used for detecting cracks, surface and sub-surface defects in
many different materials. It provides a non-contact wideband excitation source which can be focused into
different geometries. Previous workers have reported enhancement of the laser generated Rayleigh wave
when a crack is illuminated by pulsed laser beam irradiation. We demonstrate that the enhancement
observed is due to a combination of source truncation, the free boundary condition at the edge of the crack
and interference effects. Generating a Rayleigh wave over a crack can lead to enhancement of the
amplitude of the Rayleigh wave signal, a shift in the dominant frequency of the wideband Rayleigh wave
and strong enhancement of the high frequency components of the Rayleigh wave
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