9,971 research outputs found
The Cosmological Slingshot Scenario: a Stringy Proposal for the Early Time Cosmology
In the Cosmological Slingshot Scenario, our Universe is a D3-brane that
extends in the 4d noncompact directions of a warped Calabi-Yau compactification
of IIB Supergravity. Early time cosmology corresponds to a period in which the
brane moves inside a warped throat where a non-vanishing angular momentum
ensures that the trajectory of the brane has a turning point. The corresponding
induced metric on the D3-brane experiences a cosmological evolution with a
bounce. In this framework, the homogeneity, flatness, and isotropy problems of
standard cosmology might be avoided. The power spectrum of primordial
perturbations of the brane embedding can be found and it is shown to be in
agreement to WMAP data.Comment: Presented at "Ten Years of AdS/CFT: A Workshop Celebrating the Tenth
Anniversary of the Maldacena Conjecture", Buenos Aires, Argentina, 19-21 Dec
200
Discovery of a FR0 radio galaxy emitting at -ray energies
We present supporting evidence for the first association of a Fermi source,
3FGLJ1330.0-3818, with the FR0 radio galaxy Tol1326-379. FR0s represent the
majority of the local radio loud AGN population but their nature is still
unclear. They share the same properties of FRIs from the point of view of the
nuclear and host properties, but they show a large deficit of extended radio
emission. Here we show that FR0s can emit photons at very high energies.
Tol1326-379 has a GeV luminosity of erg
s, typical of FRIs, but with a steeper -ray spectrum
(). This could be related to the intrinsic jet properties
but also to a different viewing angle.Comment: 7 pages, 5 figures , accepted for publication on MNRA
X-ray study of a sample of FR0 radio galaxies: unveiling the nature of the central engine
FR0s are compact radio sources that represent the bulk of the Radio-Loud (RL)
AGN population, but they are still poorly understood. Pilot studies on these
sources have been already performed at radio and optical wavelengths: here we
present the first X-ray study of a sample of 19 FR0 radio galaxies selected
from the SDSS/NVSS/FIRST sample of Best & Heckman (2012), with redshift
0.15, radio size 10 kpc and optically classified as low-excitation
galaxies (LEG). The X-ray spectra are modeled with a power-law component
absorbed by Galactic column density with, in some cases, a contribution from
thermal extended gas. The X-ray photons are likely produced by the jet as
attested by the observed correlation between X-ray (2-10 keV) and radio (5 GHz)
luminosities, similar to FRIs. The estimated Eddington-scaled luminosities
indicate a low accretion rate. Overall, we find that the X-ray properties of
FR0s are indistinguishable from those of FRIs, thus adding another similarity
between AGN associated with compact and extended radio sources. A comparison
between FR0s and low luminosity BL Lacs, rules out important beaming effects in
the X-ray emission of the compact radio galaxies. FR0s have different X-ray
properties with respect to young radio sources (e.g. GPS/CSS sources),
generally characterized by higher X-ray luminosities and more complex spectra.
In conclusion, the paucity of extended radio emission in FR0s is probably
related to the intrinsic properties of their jets that prevent the formation of
extended structures, and/or to intermittent activity of their engines.Comment: Accepted for publication in MNRAS (18 pages, 4 figures
Aggregating Dependency Graphs into Voting Agendas in Multi-Issue Elections
Many collective decision making problems have a
combinatorial structure: the agents involved must
decide on multiple issues and their preferences over
one issue may depend on the choices adopted for
some of the others. Voting is an attractive method
for making collective decisions, but conducting a
multi-issue election is challenging. On the one hand,
requiring agents to vote by expressing their preferences
over all combinations of issues is computationally
infeasible; on the other, decomposing the
problem into several elections on smaller sets of
issues can lead to paradoxical outcomes. Any pragmatic
method for running a multi-issue election will
have to balance these two concerns. We identify
and analyse the problem of generating an agenda
for a given election, specifying which issues to vote
on together in local elections and in which order to
schedule those local elections
Generalized Pomeranchuk instabilities in graphene
We study the presence of Pomeranchuk instabilities induced by interactions on
a Fermi liquid description of a graphene layer. Using a recently developed
generalization of Pomeranchuk method we present a phase diagram in the space of
fillings versus on-site and nearest neighbors interactions. Interestingly, we
find that for both interactions being repulsive an instability region exists
near the Van Hove filling, in agreement with earlier theoretical work. In
contrast, near half filling, the Fermi liquid behavior appears to be stable, in
agreement with theoretical results and experimental findings using ARPES. The
method allows for a description of the complete phase diagram for arbitrary
filling.Comment: 9 pages, 3 figure
A stable, single-photon emitter in a thin organic crystal for application to quantum-photonic devices
Single organic molecules offer great promise as bright, reliable sources of
identical single photons on demand, capable of integration into solid-state
devices. It has been proposed that such molecules in a crystalline organic
matrix might be placed close to an optical waveguide for this purpose, but so
far there have been no demonstrations of sufficiently thin crystals, with a
controlled concentration of suitable dopant molecules. Here we present a method
for growing very thin anthracene crystals from super-saturated vapour, which
produces crystals of extreme flatness and controlled thickness. We show how
this crystal can be doped with a widely adjustable concentration of
dibenzoterrylene (DBT) molecules and we examine the optical properties of these
molecules to demonstrate their suitability as quantum emitters in nanophotonic
devices. Our measurements show that the molecules are available in the crystal
as single quantum emitters, with a well-defined polarisation relative to the
crystal axes, making them amenable to alignment with optical nanostructures. We
find that the radiative lifetime and saturation intensity vary little within
the crystal and are not in any way compromised by the unusual matrix
environment. We show that a large fraction of these emitters are able to
deliver more than photons without photo-bleaching, making them
suitable for real applications.Comment: 12 pages, 10 figures, comments welcom
The Conserved G-Protein Coupled Receptor FSHR-1 Regulates Protective Host Responses to Infection and Oxidative Stress
The innate immune system’s ability to sense an infection is critical so that it can rapidly respond if pathogenic microorganisms threaten the host, but otherwise maintain a quiescent baseline state to avoid causing damage to the host or to commensal microorganisms. One important mechanism for discriminating between pathogenic and non-pathogenic bacteria is the recognition of cellular damage caused by a pathogen during the course of infection. InCaenorhabditis elegans, the conserved G-protein coupled receptor FSHR-1 is an important constituent of the innate immune response. FSHR-1 activates the expression of antimicrobial infection response genes in infected worms and delays accumulation of the ingested pathogenPseudomonas aeruginosa. FSHR-1 is central not only to the worm’s survival of infection by multiple pathogens, but also to the worm’s survival of xenobiotic cadmium and oxidative stresses. Infected worms produce reactive oxygen species to fight off the pathogens; FSHR-1 is required at the site of infection for the expression of detoxifying genes that protect the host from collateral damage caused by this defense response. Finally, the FSHR-1 pathway is important for the ability of worms to discriminate pathogenic from benign bacteria and subsequently initiate an aversive learning program that promotes selective pathogen avoidance
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