840 research outputs found
Chiral Magnetic Effect and Chiral Phase Transition
We study the influence of the chiral phase transition on the chiral magnetic
effect. The azimuthal charge-particle correlations as functions of the
temperature are calculated. It is found that there is a pronounced cusp in the
correlations as the temperature reaches its critical value for the QCD phase
transition. It is predicted that there will be a drastic suppression of the
charge-particle correlations as the collision energy in RHIC decreases to below
a critical value. We show then the azimuthal charge-particle correlations can
be the signal to identify the occurrence of the QCD phase transitions in RHIC
energy scan experiments.Comment: 4 pages, 1 figur
The Iso-regularization Descent Algorithm for the LASSO
International audienceFollowing the introduction by Tibshirani of the LASSO technique for feature selection in regression, two algorithms were proposed by Osborne et al. for solving the associated problem. One is an homotopy method that gained popularity as the LASSO modification of the LARS algorithm. The other is a finite-step descent method that follows a path on the constraint polytope, and seems to have been largely ignored. One of the reason may be that it solves the constrained formulation of the LASSO, as opposed to the more practical regularized formulation. We give here an adaptation of this algorithm that solves the regularized problem, has a simpler formulation, and outperforms state-of-the-art algorithms in terms of speed
<sup>129</sup>I record in the Taal Lake sediment, Philippines: Implication for global fallout of <sup>129</sup>I in low latitude
Interatomic potentials for atomistic simulations of the Ti-Al system
Semi-empirical interatomic potentials have been developed for Al, alpha-Ti,
and gamma-TiAl within the embedded atomic method (EAM) by fitting to a large
database of experimental as well as ab-initio data. The ab-initio calculations
were performed by the linear augmented plane wave (LAPW) method within the
density functional theory to obtain the equations of state for a number of
crystal structures of the Ti-Al system. Some of the calculated LAPW energies
were used for fitting the potentials while others for examining their quality.
The potentials correctly predict the equilibrium crystal structures of the
phases and accurately reproduce their basic lattice properties. The potentials
are applied to calculate the energies of point defects, surfaces, planar faults
in the equilibrium structures. Unlike earlier EAM potentials for the Ti-Al
system, the proposed potentials provide reasonable description of the lattice
thermal expansion, demonstrating their usefulness in the molecular dynamics or
Monte Carlo studies at high temperatures. The energy along the tetragonal
deformation path (Bain transformation) in gamma-TiAl calculated with the EAM
potential is in a fairly good agreement with LAPW calculations. Equilibrium
point defect concentrations in gamma-TiAl are studied using the EAM potential.
It is found that antisite defects strongly dominate over vacancies at all
compositions around stoichiometry, indicating that gamm-TiAl is an antisite
disorder compound in agreement with experimental data.Comment: 46 pages, 6 figures (Physical Review B, in press
2D Mathematical Modeling For Fluvial Processes Considering The Influence Of Vegetation And Bank Erosion
A 2D mathematical model for fluvial processes capable of considering the influence of vegetation and non-cohesive bank erosion is established based on a body-fitted coordinate system in this paper. The authors have improved a previously developed simulation model by taking into account the impact of vegetation with a vegetation stress term in the momentum conservation equation. A simple simulation method is adopted in the bank erosion model. Simulation runs were performed for a conceptual alluvial channel, the results of channel plan-form and cross section changes suggest that the 2D model predictions agree acceptable with the classic theories of channel pattern formation considering the effect of vegetation
Transpolar arc observation after solar wind entry into the high-latitude magnetosphere
Recently, Cluster observations have revealed the presence of new regions of solar wind plasma entry at the high-latitude magnetospheric lobes tailward of the cusp region, mostly during periods of northward interplanetary magnetic field. In this study, observations from the Global Ultraviolet Imager (GUVI) experiment on board the TIMED spacecraft and Wideband Imaging Camera imager on board the IMAGE satellite are used to investigate a possible link between solar wind entry and the formation of transpolar arcs in the polar cap. We focus on a case when transpolar arc formation was observed twice right after the two solar wind entry events were detected by the Cluster spacecraft. In addition, GUVI and IMAGE observations show a simultaneous occurrence of auroral activity at low and high latitudes after the second entry event, possibly indicating a two-part structure of the continuous band of the transpolar arc
Mass measurements of neutron-deficient Y, Zr, and Nb isotopes and their impact on rp and νp nucleosynthesis processes
© 2018 The Authors. Published by Elsevier B.V. This manuscript is made available under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International licence (CC BY-NC-ND 4.0). For further details please see: https://creativecommons.org/licenses/by-nc-nd/4.0/Using isochronous mass spectrometry at the experimental storage ring CSRe in Lanzhou, the masses of 82Zr and 84Nb were measured for the first time with an uncertainty of ∼10 keV, and the masses of 79Y, 81Zr, and 83Nb were re-determined with a higher precision. The latter are significantly less bound than their literature values. Our new and accurate masses remove the irregularities of the mass surface in this region of the nuclear chart. Our results do not support the predicted island of pronounced low α separation energies for neutron-deficient Mo and Tc isotopes, making the formation of Zr–Nb cycle in the rp-process unlikely. The new proton separation energy of 83Nb was determined to be 490(400) keV smaller than that in the Atomic Mass Evaluation 2012. This partly removes the overproduction of the p-nucleus 84Sr relative to the neutron-deficient molybdenum isotopes in the previous νp-process simulations.Peer reviewe
The effect of spontaneous collapses on neutrino oscillations
We compute the effect of collapse models on neutrino oscillations. The effect
of the collapse is to modify the evolution of the `spatial' part of the wave
function, which indirectly amounts to a change on the flavor components. In
many respects, this phenomenon is similar to neutrino propagation through
matter. For the analysis we use the mass proportional CSL model, and perform
the calculation to second order perturbation theory. As we will show, the CSL
prediction is very small - mainly due to the very small mass of neutrinos - and
practically undetectable.Comment: 24 pages, RevTeX. Updated versio
Entropy Analysis in \pi^{+}\rp and \rK^{+}\rp Collisions at GeV
The entropy properties are analyzed by Ma's coincidence method in
\pi^{+}\rp and \rK^{+}\rp collisions of the NA22 experiment at 250 GeV/
incident momentum. By using the R\'{e}nyi entropies, we test the scaling law
and additivity properties in rapidity space. The behavior of the R\'{e}nyi
entropies as a function of the average number of particles is investigated. The
results are compared with those from the {\sc Pythia} Monte Carlo event
generator.Comment: LaTeX, 11 pages, 5 figure to be appeared in Acta Phys. Pol.
Wear and damage transitions of wheel and rail materials under various contact conditions
This study discusses a Tγ/A method of plotting wear data from a twin-disc machine for identifying the wear and damage transitions of wheel and rail materials. As found in previous work, three wear regimes (mild wear, severe wear and catastrophic wear) of U71Mn rail material were identified in dry rolling-sliding contact tests. It was determined that the damage mechanism transforms in the different wear regimes. Here earlier studies were extended to establish wear behavior for the presence of a number of third body materials (oil, water, friction enhancers) and a rail cladding process designed to make wheels and rails more durable. This has provided much needed data for Multi-Body Dynamics (MBD) simulations, and will allow better predictions of profile evolution of wheel and rail over a wider range of conditions
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