6,534 research outputs found
Axions and SN1987A
The effect of free-streaming axion emission on numerical models for the cooling of the newly born neutron star associated with SN1987A is considered. It is found that for an axion mass of greater than approximately 10 to the -3 eV, axion emission shortens the duration of the expected neutrino burst so significantly that it would be inconsistent with the neutrino observations made by the Kamiokande II and Irvine-Michigan-Brookhaven detectors. However, the possibility has not been investigated that axion trapping (which should occur for masses greater than or equal to 0.02 eV) sufficiently reduces axion emission so that axion masses greater than approximately 2 eV would be consistent with the neutrino observations
Arrest stress of uniformly sheared wet granular matter
We conduct extensive independent numerical experiments considering
frictionless disks without internal degrees of freedom (rotation etc.) in two
dimensions. We report here that for a large range of the packing fractions
below random-close packing, all components of the stress tensor of wet granular
materials remain finite in the limit of zero shear rate. This is direct
evidence for a fluid-to-solid arrest transition. The offset value of the shear
stress characterizes plastic deformation of the arrested state {which
corresponds to {\em dynamic yield stress} of the system}. {Based on an
analytical line of argument, we propose that the mean number of capillary
bridges per particle, , follows a non-trivial dependence on the packing
fraction, , and the capillary energy, \vareps. Most noticeably, we show
that is a generic and universal quantity which does not depend on the
driving protocol.} Using this universal quantity, we calculate the arrest
stress, , analytically based on a balance of the energy injection
rate due to the external force driving the flow and the dissipation rate
accounting for the rupture of capillary bridges. The resulting prediction of
is a non-linear function of the packing fraction , and the
capillary energy \vareps. This formula provides an excellent, parameter-free
prediction of the numerical data. Corrections to the theory for small and large
packing fractions are connected to the emergence of shear bands and of
contributions to the stress from repulsive particle interactions, respectively.Comment: 7 pages, g figure
How Saturated are Absorption Lines in the Broad Absorption Line Quasar PG 1411+442 ?
Recently, convincing evidence was found for extremely large X-ray absorption
by column densities in broad absorption line quasars. One
consequence of this is that any soft X-ray emission from these QSOs would be
the scattered light or leaked light from partially covering absorbing material.
A detection of the unabsorbed soft X-ray and absorbed hard X-ray compo nent
will allow to determine the total column density as well as the effective
covering factor of the absorbing material, which can be hardly obtained from
the UV absorption lines. Brinkmann et al. (1999) showed that both the
unabsorbed and absorbed components are detected in the nearby very bright broad
absorption line quasar PG 1411+442. In this letter, we make a further analysis
of the broad band X-ray spectrum and the UV spectrum from HST, and demonstrate
that broad absorption lines are completely saturated at the bottom of
absorption troughs.Comment: 6 pages, 3 postscript figures. to appear in Astrophy. J. Letter
Recent X-ray observations of intermediate BL Lac objects
We present recent ROSAT, ASCA and SAX observations of intermediate BL Lac
objects (IBLs), i.e. BL Lacs which are located between high-energy and
low-energy peaked BL Lac objects with respect to alpha_rx. Both the statistical
properties of IBLs from the RGB sample and a detailed broad band X-ray spectral
analysis of two objects (1424+2401, 1055+5644) point towards a continuous
distribution of synchrotron emission peak frequencies among BL Lac objects.Comment: 4 pages, 4 figures; to appear in the proceedings of the conference
"BL Lac Phenomenon" held in Turku, Finland, June 22-26, 199
Contact line stability of ridges and drops
Within the framework of a semi-microscopic interface displacement model we
analyze the linear stability of sessile ridges and drops of a non-volatile
liquid on a homogeneous, partially wet substrate, for both signs and arbitrary
amplitudes of the three-phase contact line tension. Focusing on perturbations
which correspond to deformations of the three-phase contact line, we find that
drops are generally stable while ridges are subject only to the long-wavelength
Rayleigh-Plateau instability leading to a breakup into droplets, in contrast to
the predictions of capillary models which take line tension into account. We
argue that the short-wavelength instabilities predicted within the framework of
the latter macroscopic capillary theory occur outside its range of validity and
thus are spurious.Comment: 6 pages, 1 figur
XMM-Newton observations of the eastern jet of SS433
The radio supernova remnant W50 hosts at its center the peculiar galactic
X-ray binary SS 433. It shows a central spherical structure with two `ears'
which are supposed to be formed by the interaction of the precessing jets of SS
433 with the supernova shell. In two pointings in September/October 2004 for 30
ks each the eastern jet of SS 433 was observed with XMM-Newton to study the
outermost parts of the `ear' and the X-ray bright emission region about 35
arcmin from SS 433. The spectra consist of two components: a non-thermal power
law with photon index \Gamma ~ 2.17+/-0.02 and a thermal component at a typical
temperature of kT ~ 0.3 keV. The X-ray emission seems to fill the whole
interior region of the radio remnant W50. The jet terminates in the eastern
`ear' in a ring-like terminal shock which indicates a flow with a kind of
hollow-cone morphology. The spatial coincidence of X-ray and radio emission
suggests physical conditions similar to those found at the outer shocks of
ordinary supernova remnants. The bright emission region closer to SS 433
radiates non-thermally in a spatially well confined geometry at higher X-ray
energies. At soft X-rays the shape of the region gets blurred, centered on the
hard lenticular emission. The shape of this region and the bend in the jet
propagation direction might be caused by the interaction of a re-collimated jet
with the outer, non homogeneous interstellar matter distribution. The physical
conditions leading to the re-collimation of the jet and the peculiar emission
morphology are far from being understood and require deeper observations as
well as a detailed modeling of the interaction of a jet with its surroundings.Comment: 10 pages, 8 figures, to appear in A&
Production and Decay of Sneutrino and Squarks at Lepton-Hadron Colliders
We investigate the potentials of future high energy lepton-proton colliders
to detect supersymmetric particles in the charged current type
, , reactions. We also study their decays
by using the mass spectrum given in the Technical Design Report of ATLAS
Collaboration (SUGRA Point 6 corresponding to large ).Comment: 6 pages, 1 eps figure, REVTEX
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