1,466 research outputs found
Evaluating kernels on Xeon Phi to accelerate Gysela application
This work describes the challenges presented by porting parts ofthe Gysela
code to the Intel Xeon Phi coprocessor, as well as techniques used for
optimization, vectorization and tuning that can be applied to other
applications. We evaluate the performance of somegeneric micro-benchmark on Phi
versus Intel Sandy Bridge. Several interpolation kernels useful for the Gysela
application are analyzed and the performance are shown. Some memory-bound and
compute-bound kernels are accelerated by a factor 2 on the Phi device compared
to Sandy architecture. Nevertheless, it is hard, if not impossible, to reach a
large fraction of the peek performance on the Phi device,especially for
real-life applications as Gysela. A collateral benefit of this optimization and
tuning work is that the execution time of Gysela (using 4D advections) has
decreased on a standard architecture such as Intel Sandy Bridge.Comment: submitted to ESAIM proceedings for CEMRACS 2014 summer school version
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Operations on integral lifts of K(n)
This very rough sketch is a sequel to arXiv:1808.08587; it presents evidence
that operations on lifts of the functors K(n) to cohomology theories with
values in modules over valuation rings of local number fields, indexed by
Lubin-Tate groups of such fields, are extensions of the groups of automorphisms
of the indexing group laws, by the exterior algebras on the normal bundle to
the orbits of the group laws in the space of lifts.Comment: \S 2.0 hopefully less cryptic. To appear in the proceedings of the
2015 Nagoya conference honoring T Ohkawa. Comments very welcome
Low-energy graceful exit in anisotropic string cosmology backgrounds
We discuss the possibility of a smooth transition from the pre- to the
post-big bang regime, in the context of the lowest-order string effective
action (without higher-derivative corrections), taking into account with a
phenomenological model of source the repulsive gravitational effects due to the
back-reaction of the quantum fluctuations outside the horizon. We determine a
set of necessary conditions for a successful and realistic transition, and we
find that such conditions can be satisfied (by an appropriate model of source),
provided the background is higher-dimensional and anisotropic.Comment: 13 pages, latex, 2 figures included using epsfi
Cosmological perturbations across a curvature bounce
String-inspired cosmologies, whereby a non-singular curvature bounce is
induced by a general-covariant, -duality-invariant, non-local dilaton
potential, are used to study numerically how inhomogeneities evolve and to
compare the outcome with analytic expressions obtained through different
matching conditions across the bounce. Good agreement is found if continuity
across the bounce is assumed to hold for , the curvature perturbation
on comoving hypersurfaces, rather than for the Bardeen potential.Comment: 36 pages, 5 included figure
Tachyonic perturbations in AdS orbifolds
We show that scalar as well as vector and tensor metric perturbations in the
Randall-Sundrum II braneworld allow normalizable tachyonic modes, i.e.,
possible instabilities. These instabilities require nonvanishing initial
anisotropic stresses on the brane. We show with a specific example that within
the Randall-Sundrum II model, even though the tachyonic modes are excited, no
instability develops. We argue, however, that in the cosmological context
instabilities might in principle be present. We conjecture that the tachyonic
modes are due to the singularity of the orbifold construction. We illustrate
this with a simple but explicit toy model.Comment: 11 pages, matches published versio
On graviton production in braneworld cosmology
We study braneworlds in a five dimensional bulk, where cosmological expansion
is mimicked by motion through AdS. We show that the five dimensional
graviton reduces to the four dimensional one in the late time approximation of
such braneworlds. Inserting a fixed regulator brane far from the physical
brane, we investigate quantum graviton production due to the motion of the
brane. We show that the massive Kaluza-Klein modes decouple completely from the
massless mode and they are not generated at all in the limit where the
regulator brane position goes to infinity. In the low energy limit, the
massless four dimensional graviton obeys the usual 4d equation and is therefore
also not generated in a radiation-dominated universe.Comment: 9 pages, minor changes, references correcte
Uniform generation in trace monoids
We consider the problem of random uniform generation of traces (the elements
of a free partially commutative monoid) in light of the uniform measure on the
boundary at infinity of the associated monoid. We obtain a product
decomposition of the uniform measure at infinity if the trace monoid has
several irreducible components-a case where other notions such as Parry
measures, are not defined. Random generation algorithms are then examined.Comment: Full version of the paper in MFCS 2015 with the same titl
The cholesterol 24-hydroxylase activates autophagy and decreases mutant huntingtin build-up in a neuroblastoma culture model of Huntington’s disease
Objective
Compromised brain cholesterol turnover and altered regulation of brain cholesterol metabolism have been allied with some neurodegenerative diseases, including Huntington’s disease (HD). Following our previous studies in HD, in this study we aim to investigate in vitro in a neuroblastoma cellular model of HD, the effect of CYP46A1 overexpression, an essential enzyme in cholesterol metabolism, on huntingtin aggregation and levels.
Results
We found that CYP46A1 reduces the quantity and size of mutant huntingtin aggregates in cells, as well as the levels of mutant huntingtin protein. Additionally, our results suggest that the observed beneficial effects of CYP46A1 in HD cells are linked to the activation of autophagy. Taken together, our results further demonstrate that CYP46A1 is a pertinent target to counteract HD progression.This work was supported by Brainvectis and E.rare: E-Rare Joint Transnational Call for Proposals 2017 “Transnational Research Projects for Innovative Therapeutic Approaches for Rare Diseases”. CN laboratory is supported by the French Muscular Dystrophy Association (AFM-Téléthon), the Ataxia UK, and the Fundação para a Ciência e Tecnologia (project ALG-01-0145-FEDER-29480 “SeGrPolyQ”). AM is supported by a Ph.D. fellowship from FCT (SFRH/BD/133192/2017)info:eu-repo/semantics/publishedVersio
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