1,639 research outputs found
Chiral charge dynamics in Abelian gauge theories at finite temperature
We study fermion number non-conservation (or chirality breaking) in Abelian
gauge theories at finite temperature. We consider the presence of a chemical
potential for the fermionic charge, and monitor its evolution with
real-time classical lattice simulations. This method accounts for short-scale
fluctuations not included in the usual effective magneto-hydrodynamics (MHD)
treatment. We observe a self-similar decay of the chemical potential,
accompanied by an inverse cascade process in the gauge field that leads to a
production of long-range helical magnetic fields. We also study the chiral
charge dynamics in the presence of an external magnetic field , and extract
its decay rate . We provide in this way a
new determination of the gauge coupling and magnetic field dependence of the
chiral rate, which exhibits a best fit scaling as . We confirm numerically the fluctuation-dissipation relation
between and , the Chern-Simons diffusion rate,
which was obtained in a previous study. Remarkably, even though we are outside
the MHD range of validity, the dynamics observed are in qualitative agreement
with MHD predictions. The magnitude of the chiral/diffusion rate is however a
factor times larger than expected in MHD, signaling that we are in
reality exploring a different regime accounting for short scale fluctuations.
This discrepancy calls for a revision of the implications of fermion number and
chirality non-conservation in finite temperature Abelian gauge theories, though
not definite conclusion can be made at this point until hard-thermal-loops
(HTL) are included in the lattice simulations.Comment: 32 pages, 11 figures. V2: Improved introduction, added some
discussions and references. Corrected typos. Corresponds to published versio
Development and Application of a Statistically-Based Quality Control for Crowdsourced Air Temperature Data
In urban areas, dense atmospheric observational networks with high-quality data are still a challenge due to high costs for installation and maintenance over time. Citizen weather stations (CWS) could be one answer to that issue. Since more and more owners of CWS share their measurement data publicly, crowdsourcing, i.e., the automated collection of large amounts of data from an undefined crowd of citizens, opens new pathways for atmospheric research. However, the most critical issue is found to be the quality of data from such networks. In this study, a statistically-based quality control (QC) is developed to identify suspicious air temperature (T) measurements from crowdsourced data sets. The newly developed QC exploits the combined knowledge of the dense network of CWS to statistically identify implausible measurements, independent of external reference data. The evaluation of the QC is performed using data from Netatmo CWS in Toulouse, France, and Berlin, Germany, over a 1-year period (July 2016 to June 2017), comparing the quality-controlled data with data from two networks of reference stations. The new QC efficiently identifies erroneous data due to solar exposition and siting issues, which are common error sources of CWS. Estimation of T is improved when averaging data from a group of stations within a restricted area rather than relying on data of individual CWS. However, a positive deviation in CWS data compared to reference data is identified, particularly for daily minimum T. To illustrate the transferability of the newly developed QC and the applicability of CWS data, a mapping of T is performed over the city of Paris, France, where spatial density of CWS is especially high.DFG, 322579844, Hitzewellen in Berlin, Deutschland - StadtklimamodifkationenBMBF, 01LP1602A, Verbundprojekt Stadtklima: Evaluierung von Stadtklimamodellen (Modul B), 3DO Teilprojekt 1: Dreidimensionales Monitoring atmosphÀrischer Prozesse in Berli
Microbial carbon use efficiency predicted from genome-scale metabolic models
Respiration by soil bacteria and fungi is one of the largest fluxes of carbon (C) from the land surface. Although this flux is a direct product of microbial metabolism, controls over metabolism and their responses to global change are a major uncertainty in the global C cycle. Here, we explore an in silico approach to predict bacterial C-use efficiency (CUE) for over 200 species using genome-specific constraint-based metabolic modeling. We find that potential CUE averages 0.62â±â0.17 with a range of 0.22 to 0.98 across taxa and phylogenetic structuring at the subphylum levels. Potential CUE is negatively correlated with genome size, while taxa with larger genomes are able to access a wider variety of C substrates. Incorporating the range of CUE values reported here into a next-generation model of soil biogeochemistry suggests that these differences in physiology across microbial taxa can feed back on soil-C cycling.Published versio
Flauncher and DVMS -- Deploying and Scheduling Thousands of Virtual Machines on Hundreds of Nodes Distributed Geographically
International audienceAlthough live migration of virtual machines has been an active area of research over the past decade, it has been mainly evaluated by means of simulations and small scale deployments. Proving the relevance of live migration at larger scales is a technical challenge that requires to be able to deploy and schedule virtual machines. In the last year, we succeeded to tackle such a challenge by conducting experiments with Flauncher and DVMS, two frameworks that can respectively deploy and schedule thousands of virtual machines over hundreds of nodes distributed geographically across the Grid'5000 testbed
Shape-from-Template dans Flatland
International audienceLe Shape-from-template (SfT) consiste en la reconstruction d'un objet dĂ©formable observĂ© sur une image grĂące Ă sa forme de rĂ©fĂ©rence. Le 2DSfT est le cas usuel du SfT oĂč la forme de rĂ©fĂ©rence est une surface plongĂ©e dans un espace 3D et l'image une projection 2D. Nous prĂ©sentons le 1DSfT, un nouveau cas du SfT oĂč la forme de rĂ©fĂ©rence est une courbe plongĂ©e dans un espace 2D et l'image une projection 1D. Nous nous concentrons sur les dĂ©formations isomĂ©triques, pour lesquelles le 2DSfT est un problĂšme bien posĂ©. Ă travers une Ă©tude thĂ©orique du 1DSfT avec projection perspective, nous montrons que ce cas est liĂ© au 2DSfT, mais qu'il possĂšde des propriĂ©tĂ©s diffĂ©rentes : (i) le 1DSfT ne possĂšde pas de solution Ă la fois exacte et locale et (ii) le 1DSfT ne possĂšde pas de solution unique, mais un nombre fini d'au moins deux solutions. Ensuite, nous proposons deux mĂ©thodes d'initialisation convexes: une solution locale et analytique basĂ©e sur la linĂ©aritĂ© infinitĂ©simale et une solution globale basĂ©e sur l'inextensibilitĂ©. Nous montrons comment le raffinement non-convexe peut ĂȘtre implĂ©mentĂ© et comment l'isomĂ©trie peut ĂȘtre contrainte avec une nouvelle paramĂ©trisation basĂ©e sur l'angle. Enfin, notre mĂ©thode est testĂ©e sur des donnĂ©es simulĂ©es et rĂ©elles
On Testing Persistent-Memory-Based Software
Leveraging Storage Class Memory (SCM) as a universal memory--i.e. as memory and storage at the same time--has deep implications on database architectures. It becomes possible to store a single copy of the data in SCM and directly operate on it at a fine granularity. However, exposing the whole database with direct access to the application dramatically increases the risk of data corruption. In this paper we propose a lightweight on-line testing framework that helps find and debug SCM-related errors that can occur upon software or power failures. Our testing framework simulates failures in critical code paths and achieves fast code coverage by leveraging call stack information to limit duplicate testing. It also partially covers the errors that might arise as a result of reordered memory operations. We show through an experimental evaluation that our testing framework is fast enough to be used with large software systems and discuss its use during the development of our in-house persistent SCM allocator
Frequency cavity pulling induced by a single semiconductor quantum dot
We investigate the emission properties of a single semiconductor quantum dot
deterministically coupled to a confined optical mode in the weak coupling
regime. A strong pulling, broadening and narrowing of the cavity mode emission
is evidenced when changing the spectral detuning between the emitter and the
cavity. These features are theoretically accounted for by considering the
phonon assisted emission of the quantum dot transition. These observations
highlight a new situation for cavity quantum electrodynamics involving
spectrally broad emitters
Visible spectrum extended-focus optical coherence microscopy for label-free sub-cellular tomography
We present a novel extended-focus optical coherence microscope (OCM)
attaining 0.7 {\mu}m axial and 0.4 {\mu}m lateral resolution maintained over a
depth of 40 {\mu}m, while preserving the advantages of Fourier domain OCM. Our
method uses an ultra-broad spectrum from a super- continuum laser source. As
the spectrum spans from near-infrared to visible wavelengths (240 nm in
bandwidth), we call the method visOCM. The combination of such a broad spectrum
with a high-NA objective creates an almost isotropic 3D submicron resolution.
We analyze the imaging performance of visOCM on microbead samples and
demonstrate its image quality on cell cultures and ex-vivo mouse brain tissue.Comment: 15 pages, 7 figure
The art of simulating the early Universe -- Part I
We present a comprehensive discussion on lattice techniques for the
simulation of scalar and gauge field dynamics in an expanding universe. After
reviewing the continuum formulation of scalar and gauge field interactions in
Minkowski and FLRW backgrounds, we introduce basic tools for the discretization
of field theories, including lattice gauge invariant techniques. Following, we
discuss and classify numerical algorithms, ranging from methods of
accuracy like and integration, to
methods up to accuracy, and the and
higher-order integrators, accurate up to . We adapt these methods
for their use in classical lattice simulations of the non-linear dynamics of
scalar and gauge fields in an expanding grid in dimensions, including the
case of `self-consistent' expansion sourced by the volume average of the
fields' energy and pressure densities. We present lattice formulations of
canonical cases of: Interacting scalar fields, Abelian gauge
theories, and Non-Abelian gauge theories. In all three cases we
provide symplectic integrators, with accuracy ranging from up to
. For each algorithm we provide the form of relevant observables,
such as energy density components, field spectra and the Hubble constraint.
Remarkably, all our algorithms for gauge theories respect the Gauss constraint
to machine precision, including when `self-consistent' expansion is considered.
As a numerical example we analyze the post-inflationary dynamics of an
oscillating inflaton charged under . The present manuscript
is meant as part of the theoretical basis for , a modern C++
MPI-based package for simulating the non-linear dynamics of scalar-gauge field
theories in an expanding universe, publicly available at www.cosmolattice.netComment: Minor corrections to match published version, and one more algorithm
added. Still 79 pages, 8 figures, 1 appendix, and many algorithm
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