981 research outputs found
A Remark on Smoothing Out Higher Codimension Branes
We discuss some issues arising in studying (linearized) gravity on non-BPS
higher codimension branes in an infinite-volume bulk. In particular, such
backgrounds are badly singular for codimension-3 and higher delta-function-like
branes with non-zero tension. As we discuss in this note, non-trivial issues
arise in smoothing out such singularities. Thus, adding higher curvature terms
might be necessary in this context.Comment: 8 pages, revtex, a minor misprint corrected (to appear in Mod. Phys.
Lett. A
Gravitational Higgs Mechanism
We discuss the gravitational Higgs mechanism in domain wall background
solutions that arise in the theory of 5-dimensional Einstein-Hilbert gravity
coupled to a scalar field with a non-trivial potential. The scalar fluctuations
in such backgrounds can be completely gauged away, and so can be the
graviphoton fluctuations. On the other hand, we show that the graviscalar
fluctuations do not have normalizable modes. As to the 4-dimensional graviton
fluctuations, in the case where the volume of the transverse dimension is
finite the massive modes are plane-wave normalizable, while the zero mode is
quadratically normalizable. We then discuss the coupling of domain wall gravity
to localized 4-dimensional matter. In particular, we point out that this
coupling is consistent only if the matter is conformal. This is different from
the Randall-Sundrum case as there is a discontinuity in the delta-function-like
limit of such a smooth domain wall - the latter breaks diffeomorphisms only
spontaneously, while the Randall-Sundrum brane breaks diffeomorphisms
explicitly. Finally, at the quantum level both the domain wall as well as the
Randall-Sundrum setups suffer from inconsistencies in the coupling between
gravity and localized matter, as well as the fact that gravity is generically
expected to be delocalized in such backgrounds due to higher curvature terms.Comment: 16 pages, revtex; a minor correctio
Effect of stators geometry on the resonance sensitivity of capacitive MEMS
open4openFrangi, A.; Laghi, G.; Minotti, P.; Langfelder, G.Frangi, ATTILIO ALBERTO; Laghi, Giacomo; Minotti, Paolo; Langfelder, Giacom
In-Plane and Out-of-Plane MEMS Motion Sensors Based on Fringe Capacitances
Abstract New MEMS motion sensors have been developed. These prototypes are based on a sensing technique that exploits the fringe capacitance between two co-planar electrodes designed over a thin oxide layer covering a grounded wafer substrate. A relevant fraction of the electric-field streamlines, generated by the readout voltage applied between the electrodes, develops in the air (or vacuum) volume over the electrodes. A grounded suspended mass moving within this volume modifies the streamlines configuration, causing relative changes in the capacitance between the electrodes as large as the ∼80% of the initial value. Two types of devices based on the described concept have been designed and built in an industrial surface micromachining process, to sense acceleration in the direction both parallel and orthogonal to the substrate surface. The realized devices have been tested and a sensitivity of ∼0.9 fF/g and ∼0.2 fF/g has been obtained for the in plane and for the out-of-plane structures respectively
A note on spherically symmetric naked singularities in general dimension
We discuss generalizations of the recent theorem by Dafermos (hep-th/0403033)
forbidding a certain class of naked singularities in the spherical collapse of
a scalar field. Employing techniques similar to the ones Dafermos used, we
consider extending the theorem (1) to higher dimensions, (2) by including more
general matter represented by a stress-energy tensor satisfying certain
assumptions, and (3) by replacing the spherical geometry by a toroidal or
higher genus (locally hyperbolic) one. We show that the extension to higher
dimensions and a more general topology is straightforward; on the other hand,
replacing the scalar field by a more general matter content forces us to shrink
the class of naked singularities we are able to exclude. We then show that the
most common matter theories (scalar field interacting with a non-abelian gauge
field and a perfect fluid satisfying certain conditions) obey the assumptions
of our weaker theorem, and we end by commenting on the applicability of our
results to the five-dimensional AdS scenarii considered recently in the
literature.Comment: 16 pages, no figures, typos fixe
A Remark on Non-conformal Non-supersymmetric Theories with Vanishing Vacuum Energy Density
We discuss non-conformal non-supersymmetric large N gauge theories with
vanishing vacuum energy density to all orders in perturbation theory. These
gauge theories can be obtained via a field theory limit of Type IIB D3-branes
embedded in orbifolded space-times. We also discuss gravity in this setup.Comment: 13 pages, revtex; a minor change in wordin
Integrated genomics and proteomics define huntingtin CAG length-dependent networks in mice.
To gain insight into how mutant huntingtin (mHtt) CAG repeat length modifies Huntington's disease (HD) pathogenesis, we profiled mRNA in over 600 brain and peripheral tissue samples from HD knock-in mice with increasing CAG repeat lengths. We found repeat length-dependent transcriptional signatures to be prominent in the striatum, less so in cortex, and minimal in the liver. Coexpression network analyses revealed 13 striatal and 5 cortical modules that correlated highly with CAG length and age, and that were preserved in HD models and sometimes in patients. Top striatal modules implicated mHtt CAG length and age in graded impairment in the expression of identity genes for striatal medium spiny neurons and in dysregulation of cyclic AMP signaling, cell death and protocadherin genes. We used proteomics to confirm 790 genes and 5 striatal modules with CAG length-dependent dysregulation at the protein level, and validated 22 striatal module genes as modifiers of mHtt toxicities in vivo
Reverse Engineering Gene Networks with ANN: Variability in Network Inference Algorithms
Motivation :Reconstructing the topology of a gene regulatory network is one
of the key tasks in systems biology. Despite of the wide variety of proposed
methods, very little work has been dedicated to the assessment of their
stability properties. Here we present a methodical comparison of the
performance of a novel method (RegnANN) for gene network inference based on
multilayer perceptrons with three reference algorithms (ARACNE, CLR, KELLER),
focussing our analysis on the prediction variability induced by both the
network intrinsic structure and the available data.
Results: The extensive evaluation on both synthetic data and a selection of
gene modules of "Escherichia coli" indicates that all the algorithms suffer of
instability and variability issues with regards to the reconstruction of the
topology of the network. This instability makes objectively very hard the task
of establishing which method performs best. Nevertheless, RegnANN shows MCC
scores that compare very favorably with all the other inference methods tested.
Availability: The software for the RegnANN inference algorithm is distributed
under GPL3 and it is available at the corresponding author home page
(http://mpba.fbk.eu/grimaldi/regnann-supmat
Cosmic Super-Strings and Kaluza-Klein Modes
Cosmic super-strings interact generically with a tower of relatively light
and/or strongly coupled Kaluza-Klein (KK) modes associated with the geometry of
the internal space. In this paper, we study the production of spin-2 KK
particles by cusps on loops of cosmic F- and D-strings. We consider cosmic
super-strings localized either at the bottom of a warped throat or in a flat
internal space with large volume. The total energy emitted by cusps in KK modes
is comparable in both cases, although the number of produced KK modes may
differ significantly. We then show that KK emission is constrained by the
photo-dissociation of light elements and by observations of the diffuse gamma
ray background. We show that this rules out regions of the parameter space of
cosmic super-strings that are complementary to the regions that can be probed
by current and upcoming gravitational wave experiments. KK modes are also
expected to play an important role in the friction-dominated epoch of cosmic
super-string evolution.Comment: 35pp, 5 figs, v2: minor modifications and Refs. added, matches
published versio
Large-scale associations between the leukocyte transcriptome and BOLD responses to speech differ in autism early language outcome subtypes.
Heterogeneity in early language development in autism spectrum disorder (ASD) is clinically important and may reflect neurobiologically distinct subtypes. Here, we identified a large-scale association between multiple coordinated blood leukocyte gene coexpression modules and the multivariate functional neuroimaging (fMRI) response to speech. Gene coexpression modules associated with the multivariate fMRI response to speech were different for all pairwise comparisons between typically developing toddlers and toddlers with ASD and poor versus good early language outcome. Associated coexpression modules were enriched in genes that are broadly expressed in the brain and many other tissues. These coexpression modules were also enriched in ASD-associated, prenatal, human-specific, and language-relevant genes. This work highlights distinctive neurobiology in ASD subtypes with different early language outcomes that is present well before such outcomes are known. Associations between neuroimaging measures and gene expression levels in blood leukocytes may offer a unique in vivo window into identifying brain-relevant molecular mechanisms in ASD
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