1,883 research outputs found
Killing vectors in asymptotically flat space-times: I. Asymptotically translational Killing vectors and the rigid positive energy theorem
We study Killing vector fields in asymptotically flat space-times. We prove
the following result, implicitly assumed in the uniqueness theory of stationary
black holes. If the conditions of the rigidity part of the positive energy
theorem are met, then in such space-times there are no asymptotically null
Killing vector fields except if the initial data set can be embedded in
Minkowski space-time. We also give a proof of the non-existence of non-singular
(in an appropriate sense) asymptotically flat space-times which satisfy an
energy condition and which have a null ADM four-momentum, under conditions
weaker than previously considered.Comment: 30 page
Relativistic Acoustic Geometry
Sound wave propagation in a relativistic perfect fluid with a non-homogeneous
isentropic flow is studied in terms of acoustic geometry. The sound wave
equation turns out to be equivalent to the equation of motion for a massless
scalar field propagating in a curved space-time geometry. The geometry is
described by the acoustic metric tensor that depends locally on the equation of
state and the four-velocity of the fluid. For a relativistic supersonic flow in
curved space-time the ergosphere and acoustic horizon may be defined in a way
analogous the non-relativistic case. A general-relativistic expression for the
acoustic analog of surface gravity has been found.Comment: 14 pages, LaTe
On parameters of the Levi-Civita solution
The Levi-Civita (LC) solution is matched to a cylindrical shell of an
anisotropic fluid. The fluid satisfies the energy conditions when the mass
parameter is in the range . The mass per unit
length of the shell is given explicitly in terms of , which has a
finite maximum. The relevance of the results to the non-existence of horizons
in the LC solution and to gauge cosmic strings is pointed out.Comment: Latex, no figure
Phase Transitions in Hexane Monolayers Physisorbed onto Graphite
We report the results of molecular dynamics (MD) simulations of a complete
monolayer of hexane physisorbed onto the basal plane of graphite. At low
temperatures the system forms a herringbone solid. With increasing temperature,
a solid to nematic liquid crystal transition takes place at K
followed by another transition at K into an isotropic fluid.
We characterize the different phases by calculating various order parameters,
coordinate distributions, energetics, spreading pressure and correlation
functions, most of which are in reasonable agreement with available
experimental evidence. In addition, we perform simulations where the
Lennard-Jones interaction strength, corrugation potential strength and dihedral
rigidity are varied in order to better characterize the nature of the two
transitions through. We find that both phase transitions are facilitated by a
``footprint reduction'' of the molecules via tilting, and to a lesser degree
via creation of gauche defects in the molecules.Comment: 18 pages, eps figures embedded, submitted to Phys. Rev.
Large enhancement from freeze out
Freeze out of particles across three dimensional space-time hypersurface is
discussed in a simple kinetic model. The final momentum distribution of emitted
particles, for freeze out surfaces with space-like normal, shows a
non-exponential transverse momentum spectrum. The slope parameter of the
distribution increases with increasing , in agreement with recently
measured SPS pion and spectra.Comment: 8 pages, 1 figure. Accepted for publication in Physics Letters
Lensing Properties of Lightlike Current Carrying Cosmic Strings
The lensing properties of superconducting cosmic strings endowed with a time
dependent pulse of lightlike current are investigated. The metric outside the
core of the string belongs to the --wave class, with a deficit angle. We
study the field theoretic bosonic Witten model coupled to gravity, and we show
that the full metric (both outside and inside the core) is a Taub-Kerr-Shild
generalization of that for the static string with no current. It is shown that
the double image due to the deficit angle evolves in an unambiguous way as a
pulse of lightlike current passes between the source and the observer.
Observational consequences of this signature of the existence of cosmic strings
are briefly discussed.Comment: 21 pages, LaTeX-REVTeX, 7 figures available upon request, preprint #
DAMTP-R94/1
Area Regge Calculus and Discontinuous Metrics
Taking the triangle areas as independent variables in the theory of Regge
calculus can lead to ambiguities in the edge lengths, which can be interpreted
as discontinuities in the metric. We construct solutions to area Regge calculus
using a triangulated lattice and find that on a spacelike hypersurface no such
discontinuity can arise. On a null hypersurface however, we can have such a
situation and the resulting metric can be interpreted as a so-called refractive
wave.Comment: 18 pages, 1 figur
Colliding axisymmetric pp-waves
An exact solution is found describing the collision of axisymmetric pp-waves
with M=0. They are impulsive in character and their coordinate singularities
become point curvature singularities at the boundaries of the interaction
region. The solution is conformally flat. Concrete examples are given,
involving an ultrarelativistic black hole against a burst of pure radiation or
two colliding beam- like waves.Comment: 6 pages, REVTeX, some misprints are correcte
Excess mortality among 10âyear survivors of classical Hodgkin lymphoma in adolescents and young adults
Adolescents and young adults (AYA) surviving classical Hodgkin lymphoma (cHL) risk long term fatal treatmentârelated toxicities. We utilized the Surveillance, Epidemiology and End Results (SEER) program to compare excess mortality rate (EMRâobserved minus expected mortality) for 10âyear survivors of AYA cHL diagnosed in 1973â1992 and 1993â2003 eras. The 15âyear EMR reduced from 4.88% to 2.19% while the 20âyear EMR reduced from 9.46% to 4.07% between eras. Survivors of stages 1â2 had lower EMR than survivors of stages 3â4 cHL in the 1993â2003 but not in the 1973â1992 era. There was an overall decline in risk of death between 10 and 15 years from diagnosis, driven mostly by second neoplasms and cardiovascular mortality. Despite reduction in fatal second neoplasms and cardiovascular disease with more current therapy, long term survivors of AYA cHL still have a higher risk of death than the general population highlighting the need for safer therapies.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142133/1/ajh24964_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142133/2/ajh24964.pd
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