7,214 research outputs found
Shear band formation in granular media as a variational problem
Strain in sheared dense granular material is often localized in a narrow
region called shear band. Recent experiments in a modified Couette cell
provided localized shear flow in the bulk away from the confining walls. The
non-trivial shape of the shear band was measured as the function of the cell
geometry. First we present a geometric argument for narrow shear bands which
connects the function of their surface position with the shape in the bulk.
Assuming a simple dissipation mechanism we show that the principle of minimum
dissipation of energy provides a good description of the shape function.
Furthermore, we discuss the possibility and behavior of shear bands which are
detached from the free surface and are entirely covered in the bulk.Comment: 4 pages, 5 figures; minor changes, typos and journal-ref adde
The morphology of Sersic-Pastoriza galaxies
The authors present the preliminary results of their radio-continuum and neutral hydrogen observations of Sersic-Pastoriza (S-P) galaxies. They show that the central regions contain a population of compact features thought to be young supernova remnants (SNRs) and discuss the overall morphology of the nuclei
Models relating the radio emission and ionised gas in Seyfert nuclei
Possible models are discussed in which the radio emitting components in Seyfert II nuclei can compress and accelerate the ambient nuclear medium to produce the characteristics of the narrow line region. A first order model, which considers only the expansion of the radio components, is briefly described. However, in many Seyfert nuclei it appears that the linear motion of the radio components is also important. This can result in shock heating of the ambient medium, and if the cooling time is long enough, can lead to a displacement between the radio component and the associated emission lines. This effect may be present in NGC 1068 and NGC 5929 and by considering ram pressure balance and the cooling length it is possible to estimate lobe velocities and ambient densities
Resonant continuum in the Hartree-Fock+BCS approximation
A method for incorporating the effect of the resonant continuum into
Hartree-Fock+BCS equations is proposed. The method is applied for the case of
a neutron-rich nucleus calculated with a Skyrme-type force plus a zero-range
pairing interaction and the results are compared with
Hartree-Fock-Bogoliubov calculations. It is shown that the widths of resonant
states have an important effect on the pairing properties of nuclei close to
the drip line.Comment: 9 pages, 2 figures, comparison with HFB adde
Probing the Kinematics of the Narrow-Line Region in Seyfert Galaxies with Slitless Spectroscopy: Observational Results
We present slitless spectra of 10 Seyfert galaxies observed with the Space
Telescope Imaging Spectrograph on the Hubble Space Telescope. The spectra cover
the [OIII] 4959, 5007 emission lines at a spectral resolving power of ~9000 and
a spatial resolution of 0.1". We compare the slitless spectra with previous HST
narrow-band images to determine the velocity shifts and dispersions of the
bright emission-line knots in the narrow-line regions (NLRs) of these Seyferts.
Many knots are spatially resolved with sizes of tenths of arcsecs,
corresponding to tens of pcs, and yet they appear to move coherently with
radial velocities between zero and +/- 1200 km/s with respect to the systemic
velocities of their hostgalaxies. The knots also show a broad range in velocity
dispersion, ranging from ~30 km/s (the velocity resolution) to ~1000 km/s FWHM.
Most of the Seyfert galaxies in this sample show an organized flow pattern,
with radial velocities near zero at the nucleus (defined by the optical
continuum peak) and increasing to maximum blueshifts and redshifts within ~1''
of the nucleus, followed by a decline to the systemic velocity. The
emission-line knots also follow a general trend of decreasing velocity
dispersion with increasing distance. In the Seyfert 2 galaxies, the presence of
blueshifts and redshifts on either side of the nucleus indicates that rotation
alone cannot explain the observed radial velocities, and that radial outflow
plays an important role. Each of the Seyfert galaxies in this sample (with the
exception of Mrk 3) shows a bright, compact (FWHM < 0.5") [O III] knot at the
position of its optical nucleus. These nuclear emission-line knots have
radial-velocity centroids near zero, but they typically have the highest
velocity dispersions.Comment: 28 pages, 5 figures (on 9 pages), accepted for A
Report of the Working Group on the Composition of Ultra High Energy Cosmic Rays
For the first time a proper comparison of the average depth of shower maximum
() published by the Pierre Auger and Telescope Array Observatories
is presented. The distributions measured by the Pierre Auger
Observatory were fit using simulated events initiated by four primaries
(proton, helium, nitrogen and iron). The primary abundances which best describe
the Auger data were simulated through the Telescope Array (TA) Middle Drum (MD)
fluorescence and surface detector array. The simulated events were analyzed by
the TA Collaboration using the same procedure as applied to their data. The
result is a simulated version of the Auger data as it would be observed by TA.
This analysis allows a direct comparison of the evolution of with energy of both data sets. The
measured by TA-MD is consistent with a preliminary simulation of the Auger data
through the TA detector and the average difference between the two data sets
was found to be .Comment: To appear in the Proceedings of the UHECR workshop, Springdale USA,
201
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