519 research outputs found
Teleparallel Gravity and Dimensional Reductions of Noncommutative Gauge Theory
We study dimensional reductions of noncommutative electrodynamics on flat
space which lead to gauge theories of gravitation. For a general class of such
reductions, we show that the noncommutative gauge fields naturally yield a
Weitzenbock geometry on spacetime and that the induced diffeomorphism invariant
field theory can be made equivalent to a teleparallel formulation of gravity
which macroscopically describes general relativity. The Planck length is
determined in this setting by the Yang-Mills coupling constant and the
noncommutativity scale. The effective field theory can also contain
higher-curvature and non-local terms which are characteristic of string theory.
Some applications to D-brane dynamics and generalizations to include the
coupling of ordinary Yang-Mills theory to gravity are also described.Comment: 31 pages LaTeX; References adde
Stochastic emergence of inflaton fluctuations in a SdS primordial universe with large-scale repulsive gravity from a 5D vacuum
We develop a stochastic approach to study scalar field fluctuations of the
inflaton field in an early inflationary universe with a black-hole (BH), which
is described by an effective 4D SdS metric. Considering a 5D Ricci-flat SdS
static metric, we implement a planar coordinate transformation, in order to
obtain a 5D cosmological metric, from which the effective 4D SdS metric can be
induced on a 4D hypersurface. We found that at the end of inflation, the
squared fluctuations of the inflaton field are not exactly scale independent
and becomes sensitive with the mass of the BH.Comment: version accepted in European Physical Journal Plu
Broken-Symmetry States in Quantum Hall Superlattices
We argue that broken-symmetry states with either spatially diagonal or
spatially off-diagonal order are likely in the quantum Hall regime, for clean
multiple quantum well (MQW) systems with small layer separations. We find that
for MQW systems, unlike bilayers, charge order tends to be favored over
spontaneous interlayer coherence. We estimate the size of the interlayer
tunneling amplitude needed to stabilize superlattice Bloch minibands by
comparing the variational energies of interlayer-coherent superlattice miniband
states with those of states with charge order and states with no broken
symmetries. We predict that when coherent miniband ground states are stable,
strong interlayer electronic correlations will strongly enhance the
growth-direction tunneling conductance and promote the possibility of Bloch
oscillations.Comment: 9 pages LaTeX, 4 figures EPS, to be published in PR
Thermodynamic and gravitational instability on hyperbolic spaces
We study the properties of anti--de Sitter black holes with a Gauss-Bonnet
term for various horizon topologies (k=0, \pm 1) and for various dimensions,
with emphasis on the less well understood k=-1 solution. We find that the zero
temperature (and zero energy density) extremal states are the local minima of
the energy for AdS black holes with hyperbolic event horizons. The hyperbolic
AdS black hole may be stable thermodynamically if the background is defined by
an extremal solution and the extremal entropy is non-negative. We also
investigate the gravitational stability of AdS spacetimes of dimensions D>4
against linear perturbations and find that the extremal states are still the
local minima of the energy. For a spherically symmetric AdS black hole
solution, the gravitational potential is positive and bounded, with or without
the Gauss-Bonnet type corrections, while, when k=-1, a small Gauss-Bonnet
coupling, namely, \alpha << {l}^2 (where l is the curvature radius of AdS
space), is found useful to keep the potential bounded from below, as required
for stability of the extremal background.Comment: Shortened to match published (PRD) version, 18 pages, several eps
figure
Monopole Inflation in Brans-Dicke Theory
According to previous work, topological defects expand exponentially without
an end if the vacuum expectation value of the Higgs field is of the order of
the Planck mass. We extend the study of inflating topological defects to the
Brans-Dicke gravity. With the help of numerical simulation we investigate the
dynamics and spacetime structure of a global monopole. Contrary to the case of
the Einstein gravity, any inflating monopole eventually shrinks and takes a
stable configuration. We also discuss cosmological constraints on the model
parameters.Comment: 17 pages, revtex, including figures, discussions in more general
theories are added, to appear in Phys. Rev.
Gravitational hedgehog, stringy hedgehog and stringy sphere
We investigate the solutions of Einstein equations such that a hedgehog
solution is matched to different exterior or interior solutions via a spherical
shell. In the case where both the exterior and the interior regions are
hedgehog solutions or one of them is flat, the resulting spherical shell
becomes a stringy shell. We also consider more general matchings and see that
in this case the shell deviates from its stringy character.Comment: 11 page
Magnetic Branes in Gauss-Bonnet Gravity
We present two new classes of magnetic brane solutions in
Einstein-Maxwell-Gauss-Bonnet gravity with a negative cosmological constant.
The first class of solutions yields an -dimensional spacetime with a
longitudinal magnetic field generated by a static magnetic brane. We also
generalize this solution to the case of spinning magnetic branes with one or
more rotation parameters. We find that these solutions have no curvature
singularity and no horizons, but have a conic geometry. In these spacetimes,
when all the rotation parameters are zero, the electric field vanishes, and
therefore the brane has no net electric charge. For the spinning brane, when
one or more rotation parameters are non zero, the brane has a net electric
charge which is proportional to the magnitude of the rotation parameter. The
second class of solutions yields a spacetime with an angular magnetic field.
These solutions have no curvature singularity, no horizon, and no conical
singularity. Again we find that the net electric charge of the branes in these
spacetimes is proportional to the magnitude of the velocity of the brane.
Finally, we use the counterterm method in the Gauss-Bonnet gravity and compute
the conserved quantities of these spacetimes.Comment: 17 pages, No figure, The version to be published in Phys. Rev.
Paraspeckle subnuclear bodies depend on dynamic heterodimerisation of DBHS RNA-binding proteins via their structured domains
RNA-binding proteins of the DBHS (Drosophila Behavior Human Splicing) family, NONO, SFPQ, and PSPC1 have numerous roles in genome stability and transcriptional and posttranscriptional regulation. Critical to DBHS activity is their recruitment to distinct subnuclear locations, for example, paraspeckle condensates, where DBHS proteins bind to the long noncoding RNA NEAT1 in the first essential step in paraspeckle formation. To carry out their diverse roles, DBHS proteins form homodimers and heterodimers, but how this dimerization influences DBHS localization and function is unknown. Here, we present an inducible GFP-NONO stable cell line and use it for live-cell 3D-structured illumination microscopy, revealing paraspeckles with dynamic, twisted elongated structures. Using siRNA knockdowns, we show these labeled paraspeckles consist of GFP-NONO/endogenous SFPQ dimers and that GFP-NONO localization to paraspeckles depends on endogenous SFPQ. Using purified proteins, we confirm that partner swapping between NONO and SFPQ occurs readily in vitro. Crystallographic analysis of the NONOSFPQ heterodimer reveals conformational differences to the other DBHS dimer structures, which may contribute to partner preference, RNA specificity, and subnuclear localization. Thus overall, our study suggests heterodimer partner availability is crucial for NONO subnuclear distribution and helps explain the complexity of both DBHS protein and paraspeckle dynamics through imaging and structural approaches.Pei Wen Lee, Andrew C. Marshall, Gavin J. Knott, Simon Kobelke, Luciano Martelotto, Ellie Cho, Paul J. McMillan, Mihwa Lee, Charles S. Bond, and Archa H. Fo
The DWORF micropeptide enhances contractility and prevents heart failure in a mouse model of dilated cardiomyopathy
Calcium (Ca(2+)) dysregulation is a hallmark of heart failure and is characterized by impaired Ca(2+) sequestration into the sarcoplasmic reticulum (SR) by the SR-Ca(2+)-ATPase (SERCA). We recently discovered a micropeptide named DWORF (DWarf Open Reading Frame) that enhances SERCA activity by displacing phospholamban (PLN), a potent SERCA inhibitor. Here we show that DWORF has a higher apparent binding affinity for SERCA than PLN and that DWORF overexpression mitigates the contractile dysfunction associated with PLN overexpression, substantiating its role as a potent activator of SERCA. Additionally, using a well-characterized mouse model of dilated cardiomyopathy (DCM) due to genetic deletion of the muscle-specific LIM domain protein (MLP), we show that DWORF overexpression restores cardiac function and prevents the pathological remodeling and Ca(2+) dysregulation classically exhibited by MLP knockout mice. Our results establish DWORF as a potent activator of SERCA within the heart and as an attractive candidate for a heart failure therapeutic
Dupilumab reduces systemic corticosteroid use and sinonasal surgery rate in CRSwNP
BACKGROUND: Chronic rhinosinusitis with nasal polyps (CRSwNP) is a type 2 inflammatory disease with a high symptom burden and poor quality of life. Treatment options include recurrent surgeries and/or frequent systemic corticosteroids (SCS). Dupilumab, a fully human monoclonal antibody, blocks the shared receptor component for interleukin-4 and interleukin-13, key drivers of type 2-mediated inflammation. We report results of pooled analyses from 2 randomised, double-blind, placebo-controlled phase 3 studies (SINUS 24 [NCT02912468]; SINUS-52 [NCT02898454]) to evaluate dupilumab effect versus placebo in adults with CRSwNP with/without SCS use and sinonasal surgery.
METHODOLOGY: SINUS-24 patients were randomised 1:1 to subcutaneous dupilumab 300 mg (n=143) or placebo (n=133) every 2 weeks (q2w) for 24 weeks. SINUS-52 patients were randomised 1:1:1 to 52 weeks of subcutaneous dupilumab 300 mg q2w (n=150), 24 weeks q2w followed by 28 weeks of dupilumab 300 mg every 4 weeks (n=145) or 52 weeks of placebo q2w (n=153).
RESULTS: Dupilumab reduced the number of patients undergoing sinonasal surgery (82.6%), the need for in-study SCS use (73.9%), and SCS courses (75.3%). Significant improvements were observed with dupilumab vs placebo regardless of prior sinonasal surgery or SCS use in nasal polyp, nasal congestion, Lund-MacKay, and Sinonasal Outcome Test (22-items) scores, and the University of Pennsylvania Smell Identification Test.
CONCLUSIONS: Dupilumab demonstrated significant improvements in disease signs and symptoms and reduced the need for sino-nasal surgery and SCS use versus placebo in patients with severe CRSwNP, regardless of SCS use in the previous 2 years, or prior sinonasal surgery
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