5,290 research outputs found
Quark core impact on hybrid star cooling
In this paper we investigate the thermal evolution of hybrid stars, objects
composed of a quark matter core, enveloped by ordinary hadronic matter. Our
purpose is to investigate how important are the microscopic properties of the
quark core to the thermal evolution of the star. In order to do that we use a
simple MIT bag model for the quark core, and a relativistic mean field model
for the hadronic envelope. By choosing different values for the microscopic
parameters (bag constant, strange quark mass, strong coupling constant) we
obtain hybrid stars with different quark core properties. We also consider the
possibility of color superconductivity in the quark core. With this simple
approach, we have found a set of microscopic parameters that lead to a good
agreement with observed cooling neutron stars. Our results can be used to
obtain clues regarding the properties of the quark core in hybrid stars, and
can be used to refine more sophisticated models for the equation of state of
quark matter.Comment: 8 pages, 10 figures. Accepted for publication in Physical Review
Rotating Neutron Stars in a Chiral SU(3) Model
We study the properties of rotating neutron stars within a generalized chiral
SU(3)-flavor model. The influence of the rotation on the inner structure and
the hyperon matter content of the star is discussed. We calculate the Kepler
frequency and moments of inertia of the neutron star sequences. An estimate for
the braking index of the associated pulsars is given.Comment: 14 pages, 9 figure
Fractal dimension of domain walls in the Edwards-Anderson spin glass model
We study directly the length of the domain walls (DW) obtained by comparing
the ground states of the Edwards-Anderson spin glass model subject to periodic
and antiperiodic boundary conditions. For the bimodal and Gaussian bond
distributions, we have isolated the DW and have calculated directly its fractal
dimension . Our results show that, even though in three dimensions
is the same for both distributions of bonds, this is clearly not the case for
two-dimensional (2D) systems. In addition, contrary to what happens in the case
of the 2D Edwards-Anderson spin glass with Gaussian distribution of bonds, we
find no evidence that the DW for the bimodal distribution of bonds can be
described as a Schramm-Loewner evolution processes.Comment: 6 pages, 5 figures. Accepted for publication in PR
Hybrid Stars in an SU(3) Parity Doublet Model
We apply an extended version of the SU(3) parity model, containing quark
degrees of freedom, to study neutron stars. The model successfully reproduces
the main thermodynamic features of QCD which allows us to describe the
composition of dense matter. Chiral symmetry restoration is realized inside the
star and the chiral partners of the baryons appear, their masses becoming
degenerate. Furthermore, quark degrees of freedom appear in a transition to a
deconfined state. Performing an investigation of the macroscopic properties of
neutron stars, we show that observational constraints, like mass and thermal
evolution, are satisfied and new predictions can be made
Estimating novel potential drug targets of Plasmodium falciparum by analysing the metabolic network of knock-out strains in silico
Malaria is one of the world’s most common and serious diseases causing death of about 3 million people
each year. Its most severe occurrence is caused by the protozoan Plasmodium falciparum. Biomedical
research could enable treating the disease by effectively and specifically targeting essential enzymes of
this parasite. However, the parasite has developed resistance to existing drugsmaking it indispensable to
discover new drugs. We have established a simple computational tool which analyses the topology of the
metabolic network of P. falciparum to identify essential enzymes as possible drug targets.Weinvestigated
the essentiality of a reaction in the metabolic network by deleting (knocking-out) such a reaction in silico.
The algorithmselected neighbouring compounds of the investigated reaction that had to be produced by
alternative biochemical pathways. Using breadth first searches, we tested qualitatively if these products
could be generated by reactions that serve as potential deviations of the metabolic flux. With this we
identified 70 essential reactions. Our results were compared with a comprehensive list of 38 targets of
approved malaria drugs. When combining our approach with an in silico analysis performed recently
[Yeh, I., Hanekamp, T., Tsoka, S., Karp, P.D., Altman, R.B., 2004. Computational analysis of Plasmodium
falciparum metabolism: organizing genomic information to facilitate drug discovery. Genome Res. 14,
917–924] we could improve the precision of the prediction results. Finally we present a refined list of 22
new potential candidate targets for P. falciparum, half of which have reasonable evidence to be valid
targets against micro-organisms and cancer
SLE local martingales in logarithmic representations
A space of local martingales of SLE type growth processes forms a
representation of Virasoro algebra, but apart from a few simplest cases not
much is known about this representation. The purpose of this article is to
exhibit examples of representations where L_0 is not diagonalizable - a
phenomenon characteristic of logarithmic conformal field theory. Furthermore,
we observe that the local martingales bear a close relation with the fusion
product of the boundary changing fields.
Our examples reproduce first of all many familiar logarithmic representations
at certain rational values of the central charge. In particular we discuss the
case of SLE(kappa=6) describing the exploration path in critical percolation,
and its relation with the question of operator content of the appropriate
conformal field theory of zero central charge. In this case one encounters
logarithms in a probabilistically transparent way, through conditioning on a
crossing event. But we also observe that some quite natural SLE variants
exhibit logarithmic behavior at all values of kappa, thus at all central
charges and not only at specific rational values.Comment: 40 pages, 7 figures. v3: completely rewritten, new title, new result
Calogero-Sutherland eigenfunctions with mixed boundary conditions and conformal field theory correlators
We construct certain eigenfunctions of the Calogero-Sutherland hamiltonian
for particles on a circle, with mixed boundary conditions. That is, the
behavior of the eigenfunction, as neighbouring particles collide, depend on the
pair of colliding particles. This behavior is generically a linear combination
of two types of power laws, depending on the statistics of the particles
involved. For fixed ratio of each type at each pair of neighboring particles,
there is an eigenfunction, the ground state, with lowest energy, and there is a
discrete set of eigenstates and eigenvalues, the excited states and the
energies above this ground state. We find the ground state and special excited
states along with their energies in a certain class of mixed boundary
conditions, interpreted as having pairs of neighboring bosons and other
particles being fermions. These particular eigenfunctions are characterised by
the fact that they are in direct correspondence with correlation functions in
boundary conformal field theory. We expect that they have applications to
measures on certain configurations of curves in the statistical O(n) loop
model. The derivation, although completely independent from results of
conformal field theory, uses ideas from the "Coulomb gas" formulation.Comment: 35 pages, 9 figure
Ultra-Transparent Antarctic Ice as a Supernova Detector
We have simulated the response of a high energy neutrino telescope in deep
Antarctic ice to the stream of low energy neutrinos produced by a supernova.
The passage of a large flux of MeV-energy neutrinos during a period of seconds
will be detected as an excess of single counting rates in all individual
optical modules. We update here a previous estimate of the performance of such
an instrument taking into account the recent discovery of absorption lengths of
several hundred meters for near-UV photons in natural deep ice. The existing
AMANDA detector can, even by the most conservative estimates, act as a galactic
supernova watch.Comment: 9 pages, Revtex file, no figures. Postscript file also available from
http://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-888.ps.Z or from
ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-888.ps.
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