8,666 research outputs found
Radio and X-ray nebulae associated with PSR J1509-5850
We have discovered a long radio trail at 843 MHz which is apparently
associated with middle age pulsar PSR J1509-5850. The radio trail has a length
of ~7 arcmin. In X-rays, Chandra observations of PSR J1509-5850 reveal an
associated X-ray trail which extends in the same orientation as the radio
trail. Moreover, two clumpy structures are observed along the radio trail. The
larger one is proposed to be the supernova remnant (SNR) candidate MSC
319.9-0.7. Faint X-ray enhancement at the position of the SNR candidate is
found in the Chandra data.Comment: Accepted by A&A, 5 pages, 4 figures, 1 tabl
Influence of the r-mode instability on hypercritically accreting neutron stars
We have investigated an influence of the r-mode instability on
hypercritically accreting () neutron stars in
close binary systems during their common envelope phases based on the scenario
proposed by Bethe et al. \shortcite{bethe-brown-lee}. On the one hand neutron
stars are heated by the accreted matter at the stellar surface, but on the
other hand they are also cooled down by the neutrino radiation. At the same
time, the accreted matter transports its angular momentum and mass to the star.
We have studied the evolution of the stellar mass, temperature and rotational
frequency.
The gravitational-wave-driven instability of the r-mode oscillation strongly
suppresses spinning-up of the star, whose final rotational frequency is well
below the mass-shedding limit, typically as small as 10% of that of the
mass-shedding state. On a very short time scale the rotational frequency tends
to approach a certain constant value and saturates there as far as the amount
of the accreted mass does not exceed a certain limit to collapse to a black
hole. This implies that the similar mechanism of gravitational radiation as the
so-called Wagoner star may work in this process. The star is spun up by
accretion until the angular momentum loss by gravitational radiation balances
the accretion torque. The time-integrated dimensionless strain of the radiated
gravitational wave may be large enough to be detectable by the gravitational
wave detectors such as LIGO II.Comment: 6 pages, 3 figure
Angular Momentum Conservation Law for Randall-Sundrum Models
In Randall-Sundrum models, by the use of general Noether theorem, the
covariant angular momentum conservation law is obtained with the respect to the
local Lorentz transformations. The angular momentum current has also
superpotential and is therefore identically conserved. The space-like
components of the angular momentum for Randall-Sundrum models are
zero. But the component is infinite.Comment: 10 pages, no figures, accepted by Mod. Phys. Lett.
Unilateral ureteral obstruction in neonatal rats leads to renal insufficiency in adulthood
Unilateral ureteral obstruction in neonatal rats leads to renal insufficiency in adulthood.BackgroundAlthough unilateral ureteropelvic junction obstruction is the most common cause of congenital obstructive nephropathy in infants and children, management remains controversial, and follow-up after pyeloplasty is generally limited to the pediatric ages. We have developed a model of temporary unilateral ureteral obstruction (UUO) in the neonatal rat: One month following the relief of five-day UUO, the glomerular filtration rate (GFR) of the postobstructed kidney was normal despite a 40% reduction in the number of glomeruli and residual vascular, glomerular, tubular, and interstitial injury.MethodsTo determine whether hyperfiltration and residual injury of remaining nephrons leads to progression of renal insufficiency in later life, 31 rats were sham operated or subjected to left UUO at one day of age, with relief of UUO five days later, and were studied at one year of age. GFR was measured by inulin clearance, and the number of glomeruli, tubular atrophy, glomerular sclerosis, and interstitial fibrosis were measured by histomorphometry in sham, obstructed (UUO), and intact opposite kidneys. Intrarenal macrophages and α-smooth muscle actin were identified by immunohistochemistry.ResultsDespite relief of UUO, ultimate growth of the postobstructed kidney was impaired. The number of glomeruli was reduced by 40%, and GFR was decreased by 80%. However, despite significant compensatory growth of the opposite kidney, there was no compensatory increase in GFR, and proteinuria was increased. Moreover, glomerular sclerosis, tubular atrophy, macrophage infiltration, and interstitial fibrosis were significantly increased not only in the postobstructed kidney, but also in the opposite kidney.ConclusionsAlthough GFR is initially maintained following relief of five-day UUO in the neonatal rat, there is eventual profound loss of function of the postobstructed and opposite kidneys because of progressive tubulointerstitial and glomerular damage. These findings suggest that despite normal postoperative GFR in infancy, children undergoing pyeloplasty for ureteropelvic junction obstruction should be followed into adulthood. Elucidation of the cellular response to temporary UUO may lead to improved methods to assess renal growth, injury, and functional reserve in patients with congenital obstructive nephropathy
Radio Supernova SN 1998bw and Its Relation to GRB 980425
SN 1998bw is an unusual Type Ic supernova that may be associated with the
-ray burst GRB 980425. We use a synchrotron self-absorption model for
its radio emission to deduce that the synchrotron-emitting gas is expanding
into a circumstellar medium of approximately density profile, at a
speed comparable to the speed of light. We assume that the efficiencies of
production of relativistic electrons and magnetic field are constant through
the evolution. The circumstellar density is consistent with that expected
around the massive star core thought to be the progenitor of SN 1998bw. The
explosion energy in material moving with velocity is ergs, with some preference for the high values. The rise in
the radio light curves observed at days 20-40 is inferred to be the result of a
rise in the energy of the blast wave by a factor . Interaction with a
jump in the ambient density is not consistent with the observed evolution. We
infer that the boost in energy is from a shell of matter from the explosion
that catches up with the decelerating shock front. Both the high explosion
energy and the nature of the energy input to the blast wave are difficult to
reconcile with energy input from the shock-accelerated high velocity ejecta
from a supernova. The implication is that there is irregular energy input from
a central engine, which is the type of model invoked for normal -ray
bursts. The link between SN 1998bw and GRB 980425 is thus strengthened.Comment: 21 pages, 9 figures, revised version to appear in Ap
YAPA: A generic tool for computing intruder knowledge
Reasoning about the knowledge of an attacker is a necessary step in many
formal analyses of security protocols. In the framework of the applied pi
calculus, as in similar languages based on equational logics, knowledge is
typically expressed by two relations: deducibility and static equivalence.
Several decision procedures have been proposed for these relations under a
variety of equational theories. However, each theory has its particular
algorithm, and none has been implemented so far. We provide a generic procedure
for deducibility and static equivalence that takes as input any convergent
rewrite system. We show that our algorithm covers most of the existing decision
procedures for convergent theories. We also provide an efficient
implementation, and compare it briefly with the tools ProVerif and KiSs
A Possible Explanation of the Radio Afterglow of GRB980519: The Dense Medium Effect
GRB{980519} is characterized by its rapidly declining optical and X-ray
afterglows. Explanations of this behavior include models invoking a dense
medium environment which makes the shock wave evolve quickly into the
sub-relativistic phase, a jet-like outflow, and a wind-shaped circumburst
medium environment. Recently, Frail {et al}. (1999a) found that the latter two
cases are consistent with the radio afterglow of this burst. Here, by
considering the trans-relativistic shock hydrodynamics, we show that the dense
medium model can also account for the radio light curve quite well. The
potential virtue of the dense medium model for GRB{980519} is that it implies a
smaller angular size of the afterglow, which is essential for interpreting the
strong modulation of the radio light curve. Optical extinction due to the dense
medium is not important if the prompt optical-UV flash accompanying the
-ray emission can destroy dust by sublimation out to an appreciable
distance. Comparisons with some other radio afterglows are also discussed.Comment: 5 pages, 1 figure, a few minor changes made and references up dated,
MNRAS, in pres
Deduction with XOR Constraints in Security API Modelling
We introduce XOR constraints, and show how they enable a theorem prover to reason effectively about security critical subsystems which employ bitwise XOR. Our primary case study is the API of the IBM 4758 hardware security module. We also show how our technique can be applied to standard security protocols
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