1,948 research outputs found
The generalized identification of truly interfacial molecules (ITIM) algorithm for nonplanar interfaces
We present a generalized version of the ITIM algorithm for the identification of interfacial molecules, which is able to treat arbitrarily shaped interfaces. The algorithm exploits the similarities between the concept of probe sphere used in ITIM and the circumsphere criterion used in the α-shapes approach, and can be regarded either as a reference-frame independent version of the former, or as an extended version of the latter that includes the atomic excluded volume. The new algorithm is applied to compute the intrinsic orientational order parameters of water around a dodecylphosphocholine and a cholic acid micelle in aqueous environment, and to the identification of solvent-reachable sites in four model structures for soot. The additional algorithm introduced for the calculation of intrinsic density profiles in arbitrary geometries proved to be extremely useful also for planar interfaces, as it allows to solve the paradox of smeared intrinsic profiles far from the interface. © 2013 American Institute of Physics
Random parking, Euclidean functionals, and rubber elasticity
We study subadditive functions of the random parking model previously
analyzed by the second author. In particular, we consider local functions
of subsets of and of point sets that are (almost) subadditive in
their first variable. Denoting by the random parking measure in
, and by the random parking measure in the cube
, we show, under some natural assumptions on , that there
exists a constant such that % % almost surely. If is the counting measure of in , then we
retrieve the result by the second author on the existence of the jamming limit.
The present work generalizes this result to a wide class of (almost)
subadditive functions. In particular, classical Euclidean optimization problems
as well as the discrete model for rubber previously studied by Alicandro,
Cicalese, and the first author enter this class of functions. In the case of
rubber elasticity, this yields an approximation result for the continuous
energy density associated with the discrete model at the thermodynamic limit,
as well as a generalization to stochastic networks generated on bounded sets.Comment: 28 page
Bounding wide composite vector resonances at the LHC
In composite Higgs models (CHMs), electroweak precision data generically push
colourless composite vector resonances to a regime where they dominantly decay
into pairs of light top partners. This greatly attenuates their traces in
canonical collider searches, tailored for narrow resonances promptly decaying
into Standard Model final states. By reinterpreting the CMS same-sign dilepton
(SS2) analysis at the Large Hadron Collider (LHC), originally designed to
search for top partners with electric charge , we demonstrate its
significant coverage over this kinematical regime. We also show the reach of
the 13 TeV run of the LHC, with various integrated luminosity options, for a
possible upgrade of the SS2 search. The top sector of CHMs is found to be
more fine-tuned in the presence of colourless composite resonances in the few
TeV range.Comment: 9 pages, 5 figures. Minor corrections for publication in JHE
Predictions from Heavy New Physics Interpretation of the Top Forward-Backward Asymmetry
We derive generic predictions at hadron colliders from the large
forward-backward asymmetry observed at the Tevatron, assuming the latter arises
from heavy new physics beyond the Standard Model. We use an effective field
theory approach to characterize the associated unknown dynamics. By fitting the
Tevatron t \bar t data we derive constraints on the form of the new physics.
Furthermore, we show that heavy new physics explaining the Tevatron data
generically enhances at high invariant masses both the top pair production
cross section and the charge asymmetry at the LHC. This enhancement can be
within the sensitivity of the 8 TeV run, such that the 2012 LHC data should be
able to exclude a large class of models of heavy new physics or provide hints
for its presence. The same new physics implies a contribution to the
forward-backward asymmetry in bottom pair production at low invariant masses of
order a permil at most.Comment: 11 pages, 6 figures. v2: added remarks on EFT validity range, dijet
bounds and UV completions; matches published versio
Tests of a cooling system for thin targets submitted to intense ion beams for the numen experiment
The NUMEN experiment, hosted at LNS (Catania, Italy), aims to determine the Nuclear Matrix Elements (NMEs) involved in 0β β decay via heavy-ion induced Double Charge Exchange (DCE) reactions. High intensity beams of about 50 μA and of energies ranging from 15 to 60 MeV/u are necessary, due to the low DCE cross sections and the use of very thin targets (several hundreds of nm) needed to reach the required energy resolution. These intense beams produce a considerable amount of heat inside the target, which can be dissipated by depositing the targets on a highly thermally conductive substrate, HOPG (Highly Oriented Pyrolytic Graphite), and coupling it with a suitable designed target-cooler system. The heat transfer from the beam spot to the cold region has been studied by solving numerically the heat equation to determine the evolution in space and time of the temperature inside the target. According to calculations, the temperatures of most of the target isotopes remain under the melting points. Experimental tests with a laser were initiated to validate the whole cooling system and the calculations
Thickness and uniformity characterization of thin targets for intense ion beam experiments
The NUMEN Experiment aims to get information on the Nuclear Matrix Elements of the Neutrinoless Double Beta Decay, by measuring heavyion induced Double Charge Exchange (DCE) reactions cross sections. A good energy resolution is needed to clearly distinguish energy states of DCE products. To measure the energy of reaction products with the required resolution, the target must be thin and uniform to minimise dispersion and straggling effects on the ejectile energy. Few hundreds of nanometers of the target isotope are deposited on a Highly Oriented Pyrolytic Graphite substrate a few micrometers thick. The results of the characterisation of the first target prototypes of tin and tellurium are presented. The Scanning Electron Microscopy was used to qualitatively analyse the samples surface. A setup to study Alpha Particle Transmission has been assembled to measure thickness and uniformity of the targets; the thickness results have been verified by the Rutherford Backscattering measurements. To evaluate the effects of the thickness on the resolution of the DCE products energy, a Monte Carlo code has been implemented, using the measured thickness and uniformity as input data for the simulation
Étude comparative et validation de modèles prédictifs de résistance thermique de contact dans le cas solide-liquide avec prise en compte de la tension superficielle
La plupart des modèles prédictifs de résistance thermique de contact portent sur les contacts solides-solides. La nature des contacts (glissant ou statique), la complexité de la description des rugosités de surface ou les niveaux de pressions de contact mises en jeu, ont conduit au développement d'un nombre important de modèles prédictifs. Cependant, ceux portant sur l’étude des contacts solides-liquides sont très rares bien que l’étude des transferts thermiques dans ce type de contacts soit d’un intérêt majeur dans de nombreuses applications: contact polymère fondu et surface métallique au cours de la mise en forme de composites, contact bitume liquide et granulat au cours de la fabrication d'enrobé bitumineux, contact solide-solide avec matériau d'interface en microélectronique. Toutefois, ces modèles nécessitent la prise en compte de propriétés adhésives des liquides sur les surfaces solides contribuant à modifier les résistances de contacts. La validation de ces modèles prédictifs nécessite des tests sur un grand nombre de matériaux de textures et de caractéristiques chimiques de surface différentes (tension superficielle, angle de contact). Dans cette étude nous présentons et comparons deux modèles prédictifs de résistance thermique de contact récemment mis au point pour les contacts solides-liquides et mettant en évidence l'influence des caractéristiques chimiques de surface ainsi que la structure topographique de l'interface solide-liquide. Ces modèles ont été confrontés à des résultats expérimentaux obtenus par mesure de résistance de contact entre un granulat très rugueux et du bitume liquide pour différentes températures de contact et pour une pression de contact modérée correspondant aux conditions d’élaboration de nouveaux procédés d'enrobés bitumineux économes en énergie. Les résultats obtenus montrent un bon accord entre les prédictions et les résultats expérimentaux obtenus
- …