2,761 research outputs found
Correlations in Hot Asymmetric Nuclear Matter
The single-particle spectral functions in asymmetric nuclear matter are
computed using the ladder approximation within the theory of finite temperature
Green's functions. The internal energy and the momentum distributions of
protons and neutrons are studied as a function of the density and the asymmetry
of the system. The proton states are more strongly depleted when the asymmetry
increases while the occupation of the neutron states is enhanced as compared to
the symmetric case. The self-consistent Green's function approach leads to
slightly smaller energies as compared to the Brueckner Hartree Fock approach.
This effect increases with density and thereby modifies the saturation density
and leads to smaller symmetry energies.Comment: 7 pages, 7 figure
Nanofriction behavior of cluster-assembled carbon films
We have characterized the frictional properties of nanostructured (ns) carbon
films grown by Supersonic Cluster Beam Deposition (SCBD) via an Atomic
Force-Friction Force Microscope (AFM-FFM). The experimental data are discussed
on the basis of a modified Amonton's law for friction, stating a linear
dependence of friction on load plus an adhesive offset accounting for a finite
friction force in the limit of null total applied load. Molecular Dynamics
simulations of the interaction of the AFM tip with the nanostructured carbon
confirm the validity of the friction model used for this system. Experimental
results show that the friction coefficient is not influenced by the
nanostructure of the films nor by the relative humidity. On the other hand the
adhesion coefficient depends on these parameters.Comment: 22 pages, 6 figures, RevTex
Properties of asymmetric nuclear matter in different approaches
Properties of asymmetric nuclear matter are derived from various many-body
approaches. This includes phenomenological ones like the Skyrme Hartree-Fock
and relativistic mean field approaches, which are adjusted to fit properties of
nuclei, as well as more microscopic attempts like the Brueckner-Hartree-Fock
approximation, a self-consistent Greens function method and the so-called
approach, which are based on realistic nucleon-nucleon interactions
which reproduce the nucleon-nucleon phase shifts. These microscopic approaches
are supplemented by a density-dependent contact interaction to achieve the
empirical saturation property of symmetric nuclear matter. The predictions of
all these approaches are discussed for nuclear matter at high densities in
-equilibrium. Special attention is paid to behavior of the isovector
component of the effective mass in neutron-rich matter.Comment: 16 pages, 7 figure
Momentum distribution of liquid helium
We have obtained the one--body density matrix and the momentum distribution
of liquid He at K from Diffusion Monte Carlo (DMC)
simulations, using trial functions optimized via the Euler Monte Carlo (EMC)
method. We find a condensate fraction smaller than in previous calculations.
Though we do not explicitly include long--range correlations in our
calculations, we get a momentum distribution at long wavelength which is
compatible with the presence of long--range correlations in the exact wave
function. We have also studied He, using fixed--node DMC, with nodes and
trial functions provided by the EMC. In particular, we analyze the momentum
distribution with respect to the discontinuity as well as the
singular behavior, at the Fermi surface. We also show that an approximate
factorization of the one-body density matrix
holds, with and respectively the density matrix of the
ideal Fermi gas and the density matrix of a Bose He.Comment: 10 pages, REVTeX, 12 figure
Quenching of Weak Interactions in Nucleon Matter
We have calculated the one-body Fermi and Gamow-Teller charge-current, and
vector and axial-vector neutral-current nuclear matrix elements in nucleon
matter at densities of 0.08, 0.16 and 0.24 fm and proton fractions
ranging from 0.2 to 0.5. The correlated states for nucleon matter are obtained
by operating on Fermi-gas states by a symmetrized product of pair correlation
operators determined from variational calculations with the Argonne v18 and
Urbana IX two- and three-nucleon interactions. The squares of the charge
current matrix elements are found to be quenched by 20 to 25 % by the
short-range correlations in nucleon matter. Most of the quenching is due to
spin-isospin correlations induced by the pion exchange interactions which
change the isospins and spins of the nucleons. A large part of it can be
related to the probability for a spin up proton quasi-particle to be a bare
spin up/down proton/neutron. We also calculate the matrix elements of the
nuclear Hamiltonian in the same correlated basis. These provide relatively mild
effective interactions which give the variational energies in the Hartree-Fock
approximation. The calculated two-nucleon effective interaction describes the
spin-isospin susceptibilities of nuclear and neutron matter fairly accurately.
However 3-body terms are necessary to reproduce the compressibility. All
presented results use the simple 2-body cluster approximation to calculate the
correlated basis matrix elements.Comment: submitted to PR
Nanotribological characterization of industrial Polytetrafluorethylene-based coatings by atomic force microscopy
We present the result of a systematic study of the tribological properties of
industrial Polytetrafluorethylene (PTFE)-based coatings carried out with an
atomic force microscope. A new characterization protocol allowed the reliable
and quantitative assessment of the friction coefficient and adhesion forces at
the sub-micrometer scale even for highly corrugated industrial samples. We have
studied and compared PTFE coatings charged with different additives in dry and
humid environment. The influence of additives and humidity on the friction
coefficient and on adhesion forces has been investigated using standard silicon
nitride tips as sliders in the low-load regime.Comment: to be published in Thin Solid Films 18 pages, 2 tables, 3 figure
Three Transducers Embedded into One Single SiC Photodetector: LSP Direct Image Sensor, Optical Amplifier and Demux Device
Bose-Einstein Condensates in the Large Gas Parameter Regime
Bose-Einstein condensates of 10 Rb atoms in a cylindrical trap are
studied using a recently proposed modified Gross-Pitaevskii equation. The
existence of a Feshbach resonance allows for widely tuning the scattering
length of the atoms, and values of the peak gas parameter, , of the
order of 10 can be attained. We find large differences between the
results of the modified Gross-Pitaevskii and of the standard Thomas-Fermi, and
Gross-Pitaevskii equations in this region. The column densities at may
differ by as much as and the half maximum radius by . The
scattering lengths estimated by fitting the half maximum radius within
different approaches can differ by .Comment: 4 LaTeX pages, 2 figure
Quantitative Nanofriction Characterization of Corrugated Surfaces by Atomic Force Microscopy
Atomic Force Microscopy (AFM) is a suitable tool to perform tribological
characterization of materials down to the nanometer scale. An important aspect
in nanofriction measurements of corrugated samples is the local tilt of the
surface, which affects the lateral force maps acquired with the AFM. This is
one of the most important problems of state-of-the-art nanotribology, making
difficult a reliable and quantitative characterization of real corrugated
surfaces. A correction of topographic spurious contributions to lateral force
maps is thus needed for corrugated samples. In this paper we present a general
approach to the topographic correction of AFM lateral force maps and we apply
it in the case of multi-asperity adhesive contact. We describe a complete
protocol for the quantitative characterization of the frictional properties of
corrugated systems in the presence of surface adhesion using the AFM.Comment: 33 pages, 9 figures, RevTex 4, submitted to Journal of Applied
Physic
Bilateral osteoma of the internal auditory canal: Case report and literature review
Osteomas of the external auditory canal tend to be rather common; those of the internal auditory canal (IAC) are much rarer, though, with less than twenty cases reported in literature up to this very day. Bilateral IAC osteomas, as in this case, are extremely unusual.These benign bone tumors grow very slowly and this implies that the patient is very often asymptomatic. The diagnosis is generally made relatively late and it is, in many cases, absolutely incidental, with Computed Thomography (CT) scans of the temporal bones performed for other reasons. The manuscript describe the case of a patient complaining with progressive bilateral hearing impairment, worsening in the course of many years; we would like to point out the benefits brought by CT in the diagnosis and therapeutic choice, which is, still today, not yet subject to unanimous consensus. (C) 2014 The College of Radiographers. Published by Elsevier Ltd. All rights reserved
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