6,059 research outputs found
Ballistic heat transport of quantum spin excitations as seen in SrCuO2
Fundamental conservation laws predict ballistic, i.e., dissipationless
transport behaviour in one-dimensional quantum magnets. Experimental evidence,
however, for such anomalous transport has been lacking ever since. Here we
provide experimental evidence for ballistic heat transport in a S=1/2
Heisenberg chain. In particular, we investigate high purity samples of the
chain cuprate SrCuO2 and observe a huge magnetic heat conductivity
. An extremely large spinon mean free path of more than a
micrometer demonstrates that is only limited by extrinsic
scattering processes which is a clear signature of ballistic transport in the
underlying spin model
Untying the Gordian Knot of Cytokinesis: Role of Small G Proteins and Their Regulators
© The Rockefeller University PressSergei N. Prokopenko, Robert Saint, and Hugo J. Belle
Accurate mass measurements of Ne, Na, Mg performed with the {\sc Mistral} spectrometer
The minuteness of the nuclear binding energy requires that mass measurements
be highly precise and accurate. Here we report on new measurements Mg
and Na performed with the {\sc Mistral} mass spectrometer at {\sc
Cern}'s {\sc Isolde} facility. Since mass measurements are prone to systematic
errors, considerable effort has been devoted to their evaluation and
elimination in order to achieve accuracy and not only precision. We have
therefore conducted a campaign of measurements for calibration and error
evaluation. As a result, we now have a satisfactory description of the {\sc
Mistral} calibration laws and error budget. We have applied our new
understanding to previous measurements of Ne, Na and
Mg for which re-evaluated values are reported.Comment: submitted to Nuclear Physics
Configurational entropy of Wigner crystals
We present a theoretical study of classical Wigner crystals in two- and
three-dimensional isotropic parabolic traps aiming at understanding and
quantifying the configurational uncertainty due to the presence of multiple
stable configurations. Strongly interacting systems of classical charged
particles confined in traps are known to form regular structures. The number of
distinct arrangements grows very rapidly with the number of particles, many of
these arrangements have quite low occurrence probabilities and often the
lowest-energy structure is not the most probable one. We perform numerical
simulations on systems containing up to 100 particles interacting through
Coulomb and Yukawa forces, and show that the total number of metastable
configurations is not a well defined and representative quantity. Instead, we
propose to rely on the configurational entropy as a robust and objective
measure of uncertainty. The configurational entropy can be understood as the
logarithm of the effective number of states; it is insensitive to the presence
of overlooked low-probability states and can be reliably determined even within
a limited time of a simulation or an experiment.Comment: 12 pages, 8 figures. This is an author-created, un-copyedited version
of an article accepted for publication in J. Phys.: Condens. Matter. IOP
Publishing Ltd is not responsible for any errors or omissions in this version
of the manuscript or any version derived from it. The definitive
publisher-authenticated version is available online at
10.1088/0953-8984/23/7/075302.
Study of phonon transport across several Si/Ge interfaces using full-band phonon Monte Carlo simulation
A Full Band Monte Carlo simulator has been developed to consider phonon
transmission across interfaces that are perpendicular to the heat flux. This
solver of the Boltzmann transport equation which does not require any
assumption on the shape the phonon distribution can naturally consider all
phonon transport regimes from the diffusive to the fully ballistic regime.
Hence, this simulator is used to study single and double Si/Ge heterostructures
from the micrometer scale down to the nanometer scale i.e. in all phonon
transport regime from ballistic to fully diffusive. A methodology to estimate
the thermal conductivities and the thermal interfaces is presented
An experimental approach for investigating many-body phenomena in Rydberg-interacting quantum systems
Recent developments in the study of ultracold Rydberg gases demand an
advanced level of experimental sophistication, in which high atomic and optical
densities must be combined with excellent control of external fields and
sensitive Rydberg atom detection. We describe a tailored experimental system
used to produce and study Rydberg-interacting atoms excited from dense
ultracold atomic gases. The experiment has been optimized for fast duty cycles
using a high flux cold atom source and a three beam optical dipole trap. The
latter enables tuning of the atomic density and temperature over several orders
of magnitude, all the way to the Bose-Einstein condensation transition. An
electrode structure surrounding the atoms allows for precise control over
electric fields and single-particle sensitive field ionization detection of
Rydberg atoms. We review two experiments which highlight the influence of
strong Rydberg--Rydberg interactions on different many-body systems. First, the
Rydberg blockade effect is used to pre-structure an atomic gas prior to its
spontaneous evolution into an ultracold plasma. Second, hybrid states of
photons and atoms called dark-state polaritons are studied. By looking at the
statistical distribution of Rydberg excited atoms we reveal correlations
between dark-state polaritons. These experiments will ultimately provide a
deeper understanding of many-body phenomena in strongly-interacting regimes,
including the study of strongly-coupled plasmas and interfaces between atoms
and light at the quantum level.Comment: 14 pages, 11 figures; submitted to a special issue of 'Frontiers of
Physics' dedicated to 'Quantum Foundation and Technology: Frontiers and
Future
Analyse de sensibilité globale d'un modÚle spatialisé pour l'évaluation économique du risque d'inondation
L'analyse de sensibilitĂ© globale peine Ă se dĂ©velopper dans le champ de la modĂ©lisation environnementale. Dans sa formulation initiale, elle est limitĂ©e Ă l'Ă©tude de modĂšles Y = f (X1; : : : ;Xp) oĂč les variables d'entrĂ©e Xj et la sortie Y sont scalaires, alors que nombre de modĂšles environnementaux incluent une dimension spatiale marquĂ©e, soit qu'ils fassent appel Ă des cartes comme variables d'entrĂ©e, soit que leurs sorties soient distribuĂ©es spatialement. Au travers d'une Ă©tude de cas dĂ©taillĂ©e, nous prĂ©sentons dans cet article une extension de l'analyse de sensibilitĂ© globale Ă l'Ă©tude de modĂšles spatialisĂ©s. Le modĂšle Ă©tudiĂ©, nommĂ© ACB-DE, est un outil d'Ă©valuation Ă©conomique du risque d'inondation. Il est ici appliquĂ© sur la basse-vallĂ©e de l'Orb (HĂ©rault). Des spĂ©cifications spatialisĂ©es de l'incertitude sont utilisĂ©es pour gĂ©nĂ©rer un nombre fini de rĂ©alisations alĂ©atoires Ă©quiprobables des variables d'entrĂ©e qui sont des cartes : les effets de structure spatiale ou d'auto-corrĂ©lation dans ces cartes peuvent ainsi ĂȘtre pris en compte. La rĂ©alisation de cartes d'indices de sensibilitĂ© permet ensuite d'Ă©tudier les sorties spatialisĂ©es du modĂšle ACB-DE et de rendre compte de la variabilitĂ© spatiale des indices de Sobol. L'influence relative des variables d'entrĂ©e Ă diffĂ©rentes Ă©chelles d'Ă©tude est analysĂ©e par la rĂ©alisation de cartes d'indices de sensibilitĂ© de rĂ©solution croissante. L'analyse rĂ©alisĂ©e permet d'identifier les variables d'entrĂ©e incertaines qui expliquent la plus grande part de la variabilitĂ© de l'indicateur Ă©conomique fourni par le modĂšle ACB-DE ; elle apporte un Ă©clairage nouveau sur le choix de l'Ă©chelle adĂ©quate de reprĂ©sentation spatialisĂ©e de cet indicateur selon la prĂ©cision des variables d'entrĂ©e. L'approche proposĂ©e pourrait ĂȘtre aisĂ©ment appliquĂ©e Ă d'autres modĂšles spatialisĂ©s peu coĂ»teux en temps de calcul. / Variance-based Sobol' global sensitivity analysis (GSA) was initially designed for the study of models with scalar inputs and outputs, while many models in the environmental field are spatially explicit. As a result, GSA is not a common practise in environmental modelling. In this paper we describe a detailed case study where GSA is performed on a spatially dependent model for flood risk economic assessment on the Orb valley (southeast France). Spatial input factors are handled by associating randomly generated map realizations to scalar values sampled from discrete uniform distributions. The realisations of random input maps can be generated by any method including geostatistical simulation techniques, allowing for spatial structure and auto-correlation to be taken into account. The estimation of sensitivity indices on ACB-DE spatial outputs makes it possible to produce maps of sensitivity indices. These maps describe the spatial variability of Sobol' indices. Sensitivity maps of different resolutions are then compared to discuss the relative influence of uncertain input factors at different scales
Spin Gap in the Single Spin-1/2 Chain Cuprate SrCaCuO
We report Cu nuclear magnetic resonance and muon spin rotation
measurements on the S=1/2 antiferromagnetic Heisenberg spin chain compound
SrCaCuO. An exponentially decreasing spin-lattice
relaxation rate 1/T indicates the opening of a spin gap. This behavior is
very similar to what has been observed for the cognate zigzag spin chain
compound SrCaCuO, and confirms that the occurrence of a
spin gap upon Ca doping is independent of the interchain exchange coupling
. Our results therefore generally prove the appearance of a spin gap in an
antiferromagnetic Heisenberg spin chain induced by a local bond disorder of the
intrachain exchange coupling . A low temperature upturn of 1/T evidences
growing magnetic correlations. However, zero field muon spin rotation
measurements down to 1.5 K confirm the absence of magnetic order in this
compound which is most likely suppressed by the opening of the spin gap.Comment: 5 pages, 4 figure
On the theory of the vortex state in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase
We demonstrate that the vortex state in the Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) phase may be very different depending on the field orientation relative
to the crystalline axes. We calculate numerically the upper critical field near
the tricritical point taking into account the modulation of the order parameter
along the magnetic field as well as the higher Landau levels. For s-wave
superconductors with the anisotropy described by an elliptical Fermi surface we
propose a general scheme of the analysis of the angular dependence of upper
critical field at all temperatures on the basis of the exact solution for the
order parameter. Our results show that the transitions (with tilting magnetic
field) between different types of mixed states may be a salient feature of the
FFLO phase. Moreover we discuss the reasons for the first-order phase
transition into the FFLO state in the case of CeCoIn5 compound.Comment: 7 figure
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