268 research outputs found
Back reaction of a long range force on a Friedmann-Robertson-Walker background
It is possible that there may exist long-range forces in addition to gravity.
In this paper we construct a simple model for such a force based on exchange of
a massless scalar field and analyze its effect on the evolution of a
homogeneous Friedmann-Robertson-Walker cosmology. The presence of such an
interaction leads to an equation of state characterized by positive pressure
and to resonant particle production similar to that observed in preheating
scenarios.Comment: 14 pages, 6 color Postscript figures, LaTe
Motion of Quantized Vortices as Elementary Objects
The general local, nondissipative equations of motion for a quantized vortex
moving in an uncharged laboratory superfluid are derived from a relativistic,
co-ordinate invariant framework, having vortices as its elementary objects in
the form of stable topological excitations. This derivation is carried out for
a pure superfluid with isotropic gap at the absolute zero of temperature, on
the level of a hydrodynamic, collective co-ordinate description. In the
formalism, we use as fundamental ingredients that particle number as well as
vorticity are conserved, and that the fluid is perfect. No assumptions are
involved as regards the dynamical behaviour of the order parameter. The
interaction of the vortex with the background fluid, representing the Magnus
force, and with itself via phonons, giving rise to the hydrodynamic vortex
mass, are separated. For a description of the motion of the vortex in a dense
laboratory superfluid like helium II, two limits have to be considered: The
nonrelativistic limit for the superfluid background is taken, and the motion of
the vortex is restricted to velocities much less than the speed of sound. The
canonical structure of vortex motion in terms of the collective co-ordinate is
used for the quantization of this motion.Comment: 25 pages, 4 figures, published versio
Fault-Tolerant Hotelling Games
The -player Hotelling game calls for each player to choose a point on the
line segment, so as to maximize the size of his Voronoi cell. This paper
studies fault-tolerant versions of the Hotelling game. Two fault models are
studied: line faults and player faults. The first model assumes that the
environment is prone to failure: with some probability, a disconnection occurs
at a random point on the line, splitting it into two separate segments and
modifying each player's Voronoi cell accordingly. A complete characterization
of the Nash equilibria of this variant is provided for every . Additionally,
a one to one correspondence is shown between equilibria of this variant and of
the Hotelling game with no faults. The second fault model assumes the players
are prone to failure: each player is removed from the game with i.i.d.
probability, changing the payoffs of the remaining players accordingly. It is
shown that for this variant of the game has no Nash equilibria
Observational evidence for self-interacting cold dark matter
Cosmological models with cold dark matter composed of weakly interacting
particles predict overly dense cores in the centers of galaxies and clusters
and an overly large number of halos within the Local Group compared to actual
observations. We propose that the conflict can be resolved if the cold dark
matter particles are self-interacting with a large scattering cross-section but
negligible annihilation or dissipation. In this scenario, astronomical
observations may enable us to study dark matter properties that are
inaccessible in the laboratoryComment: 4 pages, no figures; added references, pedagogical improvements, to
appear in PR
Linear and non-linear perturbations in dark energy models
I review the linear and second-order perturbation theory in dark energy
models with explicit interaction to matter in view of applications to N-body
simulations and non-linear phenomena. Several new or generalized results are
obtained: the general equations for the linear perturbation growth; an
analytical expression for the bias induced by a species-dependent interaction;
the Yukawa correction to the gravitational potential due to dark energy
interaction; the second-order perturbation equations in coupled dark energy and
their Newtonian limit. I also show that a density-dependent effective dark
energy mass arises if the dark energy coupling is varying.Comment: 12 pages, submitted to Phys. Rev; v2: added a ref. and corrected a
typ
Mouse Pancreatic Endocrine Cell Transcriptome Defined in the Embryonic Ngn3-Null Mouse
OBJECTIVE—To document the transcriptome of the pancreatic islet during the early and late development of the mouse pancreas and highlight the qualitative and quantitative features of gene expression that contribute to the specification, growth, and differentiation of the major endocrine cell types. A further objective was to identify endocrine cell biomarkers, targets of diabetic autoimmunity, and regulatory pathways underlying islet responses to physiological and pathological stimuli
β-Cell Proliferation, but Not Neogenesis, Following 60% Partial Pancreatectomy Is Impaired in the Absence of FoxM1
OBJECTIVE—This study was designed to determine whether the transcription factor FoxM1 was required for regeneration of β-cell mass via proliferation and/or neogenesis in the adult after 60% partial pancreatectomy (PPx)
Sleep/wake movement velocities, trajectories and micro-arousals during maturation in rats
PARP1 suppresses homologous recombination events in mice in vivo
Recent studies suggest that PARP1 inhibitors, several of which are currently in clinical trial, may selectively kill BRCA1/2 mutant cancers cells. It is thought that the success of this therapy is based on immitigable lethal DNA damage in the cancer cells resultant from the concurrent loss or inhibition of two DNA damage repair pathways: single-strand break (SSB) repair and homologous recombination repair (HRR). Presumably, inhibition of PARP1 activity obstructs the repair of SSBs and during DNA replication, these lesions cause replication fork collapse and are transformed into substrates for HRR. In fact, several previous studies have indicated a hyper-recombinogenic phenotype in the absence of active PARP1 in vitro or in response to DNA damaging agents. In this study, we demonstrate an increased frequency of spontaneous HRR in vivo in the absence of PARP1 using the pun assay. Furthermore, we found that the HRR events that occur in Parp1 nullizygous mice are associated with a significant increase in large, clonal events, as opposed to the usually more frequent single cell events, suggesting an effect in replicating cells. In conclusion, our data demonstrates that PARP1 inhibits spontaneous HRR events, and supports the model of DNA replication transformation of SSBs into HRR substrates
- …