1,343 research outputs found
Algorithmic construction of static perfect fluid spheres
Perfect fluid spheres, both Newtonian and relativistic, have attracted
considerable attention as the first step in developing realistic stellar models
(or models for fluid planets). Whereas there have been some early hints on how
one might find general solutions to the perfect fluid constraint in the absence
of a specific equation of state, explicit and fully general solutions of the
perfect fluid constraint have only very recently been developed. In this
article we present a version of Lake's algorithm [Phys. Rev. D 67 (2003)
104015; gr-qc/0209104] wherein: (1) we re-cast the algorithm in terms of
variables with a clear physical meaning -- the average density and the locally
measured acceleration due to gravity, (2) we present explicit and fully general
formulae for the mass profile and pressure profile, and (3) we present an
explicit closed-form expression for the central pressure. Furthermore we can
then use the formalism to easily understand the pattern of inter-relationships
among many of the previously known exact solutions, and generate several new
exact solutions.Comment: Uses revtex4. V2: Minor clarifications, plus an additional section on
how to turn the algorithm into a solution generalization technique. This
version accepted for publication in Physical Review D. Now 7 page
Timed Multiparty Session Types
We propose a typing theory, based on multiparty session types, for modular verification of real-time choreographic interactions. To model real-time implementations, we introduce a simple calculus with delays and a decidable static proof system. The proof system ensures type safety and time-error freedom, namely processes respect the prescribed timing and causalities between interactions. A decidable condition on timed global types guarantees time-progress for validated processes with delays, and gives a sound and complete characterisation of a new class of CTAs with general topologies that enjoys progress and liveness
Spherically Symmetric Gravity as a Completely Integrable System
It is shown - in Ashtekar's canonical framework of General Relativity - that
spherically symmetric (Schwarzschild) gravity in 4 dimensional space-time
constitutes a finite dimensional completely integrable system. Canonically
conjugate observables for asymptotically flat space-times are masses as action
variables and - surprisingly - time variables as angle variables, each of which
is associated with an asymptotic "end" of the Cauchy surfaces. The emergence of
the time observable is a consequence of the Hamiltonian formulation and its
subtleties concerning the slicing of space and time and is not in contradiction
to Birkhoff's theorem. The results are of interest as to the concept of time in
General Relativity. They can be formulated within the ADM formalism, too.
Quantization of the system and the associated Schr\"odinger equation depend on
the allowed spectrum of the masses.Comment: 20.p., Latex, PITHA 93-3
Thermally assisted magnetization reversal in the presence of a spin-transfer torque
We propose a generalized stochastic Landau-Lifshitz equation and its
corresponding Fokker-Planck equation for the magnetization dynamics in the
presence of spin transfer torques. Since the spin transfer torque can pump a
magnetic energy into the magnetic system, the equilibrium temperature of the
magnetic system is ill-defined. We introduce an effective temperature based on
a stationary solution of the Fokker-Planck equation. In the limit of high
energy barriers, the law of thermal agitation is derived. We find that the
N\'{e}el-Brown relaxation formula remains valid as long as we replace the
temperature by an effective one that is linearly dependent of the spin torque.
We carry out the numerical integration of the stochastic Landau-Lifshitz
equation to support our theory. Our results agree with existing experimental
data.Comment: 5 figure
Flux transitions in a superconducting ring
We perform a numeric study of the flux transitions in a superconducting ring
at fixed temperature, while the applied field is swept at an ideally slow rate.
The current around the ring and its free energy are evaluated. We partially
explain some of the known experimental features, and predict a considerably
large new feature: in the vicinity of a critical field, giant jumps are
expected
An absolute polarimeter for high energy protons
A study of the spin asymmetries for polarized elastic proton proton
collisions in the electromagnetic hadronic interference (CNI) region of
momentum transfer provides a method of self calibration of proton polarization.
The method can be extended to non-identical spin half scattering so that, in
principle, the polarization of a proton may be obtained through an analysis of
its elastic collision with a different polarized particle, helium 3 for
instance. Sufficiently large CNI spin asymmetries provide enough information to
facilitate the evaluation of nearly all the helicity amplitudes at small t as
well as the polarization of both initial spin half fermions. Thus it can serve
equally well as a polarimeter for helium 3
Alarming signs and symptoms in febrile children in primary care: An observational cohort study in The Netherlands
__Abstract__
Context: Febrile children in primary care have a low risk for serious infection. Although several alarming signs and symptoms are proposed to have predictive value for serious infections, most are based on research in secondary care. The frequency of alarming signs/symptoms has not been established in primary care; however, in this setting differences in occurrence may influence their predictive value for serious infections. Objective: To determine the frequency of alarming signs/symptoms in febrile children in primary care. Design: Observational cohort study. Clinical information was registered in a semi-structured way and manually recoded. Setting: General practitioners' out-of-hours service. Subjects: Face-to-face patient contacts concerning children (aged â€16 years) with fever were eligible for inclusion. Main outcome measures: Frequency of 18 alarming signs and symptoms as reported in the literature. Results: A total of 10,476 patient contacts were included. The frequency of alarming signs/symptoms ranged from n = 1 (ABC instability; 40°C as reported by the parents; 12.9%) to 8,647 contacts (parental concern; 82.5%). Conclusion: Although the prevalence of specific alarming signs/symptoms is low in primary care, â„50% of children have one or more alarming signs/symptoms. There is a need to determine the predictive value of alarming signs/symptoms not only for serious infections in primary care, but as well for increased risk of a complicated course of the illness
Probing the Nature of Short Swift Bursts via Deep INTEGRAL Monitoring of GRB 050925
We present results from Swift, XMM-Newton, and deep INTEGRAL monitoring in
the region of GRB 050925. This short Swift burst is a candidate for a newly
discovered soft gamma-ray repeater (SGR) with the following observational burst
properties: 1) galactic plane (b=-0.1 deg) localization, 2) 150 msec duration,
and 3) a blackbody rather than a simple power-law spectral shape (with a
significance level of 97%). We found two possible X-ray counterparts of GRB
050925 by comparing the X-ray images from Swift XRT and XMM-Newton. Both X-ray
sources show the transient behavior with a power-law decay index shallower than
-1. We found no hard X-ray emission nor any additional burst from the location
of GRB 050925 in ~5 Ms of INTEGRAL data. We discuss about the three BATSE short
bursts which might be associated with GRB 050925, based on their location and
the duration. Assuming GRB 050925 is associated with the H II regions (W 58) at
the galactic longitude of l=70 deg, we also discuss the source frame properties
of GRB 050925.Comment: 13 pages, 13 figures, accepted for publication in ASR special issue
on Neutron Stars and Gamma Ray Bursts, full resolution of Fig 5 is available
at
http://asd.gsfc.nasa.gov/Takanori.Sakamoto/GRB050925/integral_ibis_images.ep
Human Bocavirus in Febrile Children Consulting a GP Service in the Netherlands
Human bocavirus (HBoV) was detected in nasopharyngeal swabs of 1.6% (95% CI 0.4% to 3.9%) of 257 febrile children presented to a GP center. Symptoms of respiratory tract infection, gastrointestinal symptoms and skin rash were reported. Our results suggest HBoV as a pathogen causing mild disease in non-hospitalized febrile children
Displaying the Heterogeneity of the SN 2002cx-like Subclass of Type Ia Supernovae with Observations of the Pan-STARRS-1 Discovered SN2009ku
SN2009ku, discovered by Pan-STARRS-1, is a Type Ia supernova (SNIa), and a
member of the distinct SN2002cx-like class of SNeIa. Its light curves are
similar to the prototypical SN2002cx, but are slightly broader and have a later
rise to maximum in g. SN2009ku is brighter (~0.6 mag) than other SN2002cx-like
objects, peaking at M_V = -18.4 mag - which is still significantly fainter than
typical SNeIa. SN2009ku, which had an ejecta velocity of ~2000 kms^-1 at 18
days after maximum brightness is spectroscopically most similar to SN2008ha,
which also had extremely low-velocity ejecta. However, SN2008ha had an
exceedingly low luminosity, peaking at M_V = -14.2 mag, ~4 mag fainter than
SN2009ku. The contrast of high luminosity and low ejecta velocity for SN2009ku
is contrary to an emerging trend seen for the SN2002cx class. SN2009ku is a
counter-example of a previously held belief that the class was more homogeneous
than typical SNeIa, indicating that the class has a diverse progenitor
population and/or complicated explosion physics. As the first example of a
member of this class of objects from the new generation of transient surveys,
SN2009ku is an indication of the potential for these surveys to find rare and
interesting objects.Comment: 7 pages, 3 figure
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