11,286 research outputs found
Extreme Supernova Models for the Superluminous Transient ASASSN-15lh
The recent discovery of the unprecedentedly superluminous transient
ASASSN-15lh (or SN 2015L) with its UV-bright secondary peak challenges all the
power-input models that have been proposed for superluminous supernovae. Here
we examine some of the few viable interpretations of ASASSN-15lh in the context
of a stellar explosion, involving combinations of one or more power inputs. We
model the lightcurve of ASASSN-15lh with a hybrid model that includes
contributions from magnetar spin-down energy and hydrogen-poor circumstellar
interaction. We also investigate models of pure circumstellar interaction with
a massive hydrogen-deficient shell and discuss the lack of interaction features
in the observed spectra. We find that, as a supernova ASASSN-15lh can be best
modeled by the energetic core-collapse of a ~40 Msun star interacting with a
hydrogen-poor shell of ~20 Msun. The circumstellar shell and progenitor mass
are consistent with a rapidly rotating pulsational pair-instability supernova
progenitor as required for strong interaction following the final supernova
explosion. Additional energy injection by a magnetar with initial period of 1-2
ms and magnetic field of 0.1-1 x 10^14 G may supply the excess luminosity
required to overcome the deficit in single-component models, but this requires
more fine-tuning and extreme parameters for the magnetar, as well as the
assumption of efficient conversion of magnetar energy into radiation. We thus
favor a single-input model where the reverse shock formed in a strong SN
ejecta-CSM interaction following a very powerful core-collapse SN explosion can
supply the luminosity needed to reproduce the late-time UV-bright plateau.Comment: 8 pages, 3 figure
Differing calcification processes in cultured vascular smooth muscle cells and osteoblasts
© 2019 Published by Elsevier Inc.Arterial medial calcification (AMC) is the deposition of calcium phosphate mineral, often as hydroxyapatite, inthe medial layer of the arteries. AMC shares some similarities to skeletal mineralisation and has been associatedwith the transdifferentiation of vascular smooth muscle cells (VSMCs) towards an osteoblast-like phenotype. Thisstudy used primary mouse VSMCs and calvarial osteoblasts to directly compare the established and widely usedin vitromodels of AMC and bone formation. Significant differences were identified between osteoblasts andcalcifying VSMCs. First, osteoblasts formed large mineralised bone nodules that were associated with widespreaddeposition of an extracellular collagenous matrix. In contrast, VSMCs formed small discrete regions of calcifi-cation that were not associated with collagen deposition and did not resemble bone. Second, calcifying VSMCsdisplayed a progressive reduction in cell viability over time (≤7-fold), with a 50% increase in apoptosis,whereas osteoblast and control VSMCs viability remained unchanged. Third, osteoblasts expressed high levels ofalkaline phosphatase (TNAP) activity and TNAP inhibition reduced bone formation by to 90%. TNAP activity incalcifying VSMCs was∼100-fold lower than that of bone-forming osteoblasts and cultures treated withβ-gly-cerophosphate, a TNAP substrate, did not calcify. Furthermore, TNAP inhibition had no effect on VSMC calci-fication. Although, VSMC calcification was associated with increased mRNA expression of osteoblast-relatedgenes (e.g. Runx2, osterix, osteocalcin, osteopontin), the relative expression of these genes was up to 40-foldlower in calcifying VSMCs versus bone-forming osteoblasts. In summary, calcifying VSMCsin vitrodisplay somelimited osteoblast-like characteristics but also differ in several key respects: 1) their inability to form collagen-containing bone; 2) their lack of reliance on TNAP to promote mineral deposition; and, 3) the deleterious effectof calcification on their viability.Peer reviewedFinal Published versio
Exact relativistic stellar models with liquid surface. I. Generalizing Buchdahl's polytrope
A family of exact relativistic stellar models is described. The family
generalizes Buchdahl's n=1 polytropic solution. The matter content is a perfect
fluid and, excluding Buchdahl's original model, it behaves as a liquid at low
pressures in the sense that the energy density is non-zero in the zero pressure
limit. The equation of state has two free parameters, a scaling and a stiffness
parameter. Depending on the value of the stiffness parameter the fluid
behaviour can be divided in four different types. Physical quantities such as
masses, radii and surface redshifts as well as density and pressure profiles
are calculated and displayed graphically. Leaving the details to a later
publication, it is noted that one of the equation of state types can quite
accurately approximate the equation of state of real cold matter in the outer
regions of neutron stars. Finally, it is observed that the given equation of
state does not admit models with a conical singularity at the center.Comment: 19 pages, 12 figures (16 eps files), LaTeX2e with the standard
packages amssymb, amsmath, graphicx, subfigure, psfra
Self-tuning of the cosmological constant
Here, I discuss the cosmological constant (CC) problems, in particular paying
attention to the vanishing cosmological constant. There are three cosmological
constant problems in particle physics. Hawking's idea of calculating the
probability amplitude for our Universe is peaked at CC = 0 which I try to
obtain after the initial inflationary period using a self-tuning model. I
review what has been discussed on the Hawking type calculation, and present a
(probably) correct way to calculate the amplitude, and show that the
Kim-Kyae-Lee self-tuning model allows a finite range of parameters for the CC =
0 to have a singularly large probability, approached from the AdS side.Comment: 12 pages with 8 figure
Curie-Weiss model of the quantum measurement process
A hamiltonian model is solved, which satisfies all requirements for a
realistic ideal quantum measurement. The system S is a spin-\half, whose
-component is measured through coupling with an apparatus A=M+B, consisting
of a magnet \RM formed by a set of spins with quartic infinite-range
Ising interactions, and a phonon bath \RB at temperature . Initially A is
in a metastable paramagnetic phase. The process involves several time-scales.
Without being much affected, A first acts on S, whose state collapses in a very
brief time. The mechanism differs from the usual decoherence. Soon after its
irreversibility is achieved. Finally the field induced by S on M, which may
take two opposite values with probabilities given by Born's rule, drives A into
its up or down ferromagnetic phase. The overall final state involves the
expected correlations between the result registered in M and the state of S.
The measurement is thus accounted for by standard quantum statistical mechanics
and its specific features arise from the macroscopic size of the apparatus.Comment: 5 pages Revte
Disseminated bacillus Calmette-Guérin (BCG): a cause of delirium in an older adult
Intra-vesical Bacillus Calmette-Guérin (BCG) immunotherapy is an effective treatment for high-risk bladder cancer. Less well known is that fewer than 1% of patients receiving BCG treatment can develop disseminated BCG. The reaction can range from a mild flu-like illness to a systemic disorder with a fulminant course which in the most severe cases can lead to death. The diagnostic yield is low and diagnosis is often made after a comprehensive exclusion of more common causes of pyrexia of unknown origin. A high level of suspicion is therefore required in those who may be at risk. We report a case of disseminated BCG in an older patient for whom early involvement of his family was pertinent to determining the precipitant for delirium
Information preserving structures: A general framework for quantum zero-error information
Quantum systems carry information. Quantum theory supports at least two
distinct kinds of information (classical and quantum), and a variety of
different ways to encode and preserve information in physical systems. A
system's ability to carry information is constrained and defined by the noise
in its dynamics. This paper introduces an operational framework, using
information-preserving structures to classify all the kinds of information that
can be perfectly (i.e., with zero error) preserved by quantum dynamics. We
prove that every perfectly preserved code has the same structure as a matrix
algebra, and that preserved information can always be corrected. We also
classify distinct operational criteria for preservation (e.g., "noiseless",
"unitarily correctible", etc.) and introduce two new and natural criteria for
measurement-stabilized and unconditionally preserved codes. Finally, for
several of these operational critera, we present efficient (polynomial in the
state-space dimension) algorithms to find all of a channel's
information-preserving structures.Comment: 29 pages, 19 examples. Contains complete proofs for all the theorems
in arXiv:0705.428
Consequences of critical interchain couplings and anisotropy on a Haldane chain
Effects of interchain couplings and anisotropy on a Haldane chain have been
investigated by single crystal inelastic neutron scattering and density
functional theory (DFT) calculations on the model compound SrNiVO.
Significant effects on low energy excitation spectra are found where the
Haldane gap (; where is the intrachain exchange
interaction) is replaced by three energy minima at different antiferromagnetic
zone centers due to the complex interchain couplings. Further, the triplet
states are split into two branches by single-ion anisotropy. Quantitative
information on the intrachain and interchain interactions as well as on the
single-ion anisotropy are obtained from the analyses of the neutron scattering
spectra by the random phase approximation (RPA) method. The presence of
multiple competing interchain interactions is found from the analysis of the
experimental spectra and is also confirmed by the DFT calculations. The
interchain interactions are two orders of magnitude weaker than the
nearest-neighbour intrachain interaction = 8.7~meV. The DFT calculations
reveal that the dominant intrachain nearest-neighbor interaction occurs via
nontrivial extended superexchange pathways Ni--O--V--O--Ni involving the empty
orbital of V ions. The present single crystal study also allows us to
correctly position SrNiVO in the theoretical - phase
diagram [T. Sakai and M. Takahashi, Phys. Rev. B 42, 4537 (1990)] showing where
it lies within the spin-liquid phase.Comment: 12 pages, 12 figures, 3 tables PRB (accepted). in Phys. Rev. B (2015
The Constraints in Spherically Symmetric General Relativity II --- Identifying the Configuration Space: A Moment of Time Symmetry
We continue our investigation of the configuration space of general
relativity begun in I (gr-qc/9411009). Here we examine the Hamiltonian
constraint when the spatial geometry is momentarily static (MS). We show that
MS configurations satisfy both the positive quasi-local mass (QLM) theorem and
its converse. We derive an analytical expression for the spatial metric in the
neighborhood of a generic singularity. The corresponding curvature singularity
shows up in the traceless component of the Ricci tensor. We show that if the
energy density of matter is monotonically decreasing, the geometry cannot be
singular. A supermetric on the configuration space which distinguishes between
singular geometries and non-singular ones is constructed explicitly. Global
necessary and sufficient criteria for the formation of trapped surfaces and
singularities are framed in terms of inequalities which relate appropriate
measures of the material energy content on a given support to a measure of its
volume. The strength of these inequalities is gauged by exploiting the exactly
solvable piece-wise constant density star as a template.Comment: 50 pages, Plain Tex, 1 figure available from the authors
Quasinormal Modes, the Area Spectrum, and Black Hole Entropy
The results of canonical quantum gravity concerning geometric operators and
black hole entropy are beset by an ambiguity labelled by the Immirzi parameter.
We use a result from classical gravity concerning the quasinormal mode spectrum
of a black hole to fix this parameter in a new way. As a result we arrive at
the Bekenstein - Hawking expression of for the entropy of a black
hole and in addition see an indication that the appropriate gauge group of
quantum gravity is SO(3) and not its covering group SU(2).Comment: 4 pages, 2 figure
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