658 research outputs found
Classical orbital paramagnetism in non-equilibrium steady state
We report the results of our numerical simulation of classical-dissipative
dynamics of a charged particle subjected to a non-markovian stochastic forcing.
We find that the system develops a steady-state orbital magnetic moment in the
presence of a static magnetic field. Very significantly, the sign of the
orbital magnetic moment turns out to be {\it paramagnetic} for our choice of
parameters, varied over a wide range. This is shown specifically for the case
of classical dynamics driven by a Kubo-Anderson type non-markovian noise.
Natural spatial boundary condition was imposed through (1) a soft (harmonic)
confining potential, and (2) a hard potential, approximating a reflecting wall.
There was no noticeable qualitative difference. What appears to be crucial to
the orbital magnetic effect noticed here is the non-markovian property of the
driving noise chosen. Experimental realization of this effect on the laboratory
scale, and its possible implications are briefly discussed. We would like to
emphasize that the above steady-state classical orbital paramagnetic moment
complements, rather than contradicts the Bohr-van Leeuwen (BvL) theorem on the
absence of classical orbital diamagnetism in thermodynamic equilibrium.Comment: 6 pages, 4 figures, Has appeared in Journal of Astrophysics and
Astronomy special issue on 'Physics of Neutron Stars and Related Objects',
celebrating the 75th birth-year of G. Srinivasa
Residual stress analysis and finite element modelling of repair-welded titanium sheets
An innovative FE modelling approach has been tested to investigate the effects of weld repair thin sheets of titanium alloy, taking into account pre-existing stress field in the components. In the case study analysed, the residual stress fields due to the original welds are introduced by means of a preliminary sequentially-coupled thermo-mechanical analysis and considered as pre-existing stress in the sheets for the subsequent weld simulation. Comparisons are presented between residual stress predictions and experimental measurements available from the literature with the aim of validating the numerical procedure. As a destructive sectioning technique was used in the reference experimental measurements, an investigation is also presented on the use of the element deactivation strategy when adopted to simulate material removal. Although the numerical tool is an approximate approach to simulate the actual material removal, the strategy appears to compute a physical strain relaxation and stress redistribution in the remaining part of the component. The weld repair modelling strategy and the element deactivation tool adopted to simulate the residual stress measurement technique are shown to predict residual stress trends which are very well correlated with experimental findings from the literature
Obtaining Statistics of Turbulent Velocity from Astrophysical Spectral Line Data
Turbulence is a crucial component of dynamics of astrophysical fluids
dynamics, including those of ISM, clusters of galaxies and circumstellar
regions. Doppler shifted spectral lines provide a unique source of information
on turbulent velocities. We discuss Velocity-Channel Analysis (VCA) and its
offspring Velocity Coordinate Spectrum (VCS) that are based on the analytical
description of the spectral line statistics. Those techniques are well suited
for studies of supersonic turbulence. We stress that a great advantage of VCS
is that it does not necessary require good spatial resolution. Addressing the
studies of mildly supersonic and subsonic turbulence we discuss the criterion
that allows to determine whether a traditional tool for such a research,
namely, Velocity Centroids are dominated by density or velocity. We briefly
discuss the use of higher order correlations as the means to study
intermittency of turbulence. We discuss observational data available and
prospects of the field.Comment: 12 pages, Invited Talk, Penetrating Bars Through Masks of Cosmic
Dust, Pilanesberg National Park, South Afrika, 7 June-12 June 200
Production of phi mesons at mid-rapidity in sqrt(s_NN) = 200 GeV Au+Au collisions at RHIC
We present the first results of meson production in the K^+K^- decay channel
from Au+Au collisions at sqrt(s_NN) = 200 GeV as measured at mid-rapidity by
the PHENIX detector at RHIC. Precision resonance centroid and width values are
extracted as a function of collision centrality. No significant variation from
the PDG accepted values is observed. The transverse mass spectra are fitted
with a linear exponential function for which the derived inverse slope
parameter is seen to be constant as a function of centrality. These data are
also fitted by a hydrodynamic model with the result that the freeze-out
temperature and the expansion velocity values are consistent with the values
previously derived from fitting single hadron inclusive data. As a function of
transverse momentum the collisions scaled peripheral.to.central yield ratio RCP
for the is comparable to that of pions rather than that of protons. This result
lends support to theoretical models which distinguish between baryons and
mesons instead of particle mass for explaining the anomalous proton yield.Comment: 326 authors, 24 pages text, 23 figures, 6 tables, RevTeX 4. To be
submitted to Physical Review C as a regular article. Plain text data tables
for the points plotted in figures for this and previous PHENIX publications
are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm
Beauty photoproduction measured using decays into muons in dijet events in ep collisions at =318 GeV
The photoproduction of beauty quarks in events with two jets and a muon has
been measured with the ZEUS detector at HERA using an integrated luminosity of
110 pb. The fraction of jets containing b quarks was extracted from the
transverse momentum distribution of the muon relative to the closest jet.
Differential cross sections for beauty production as a function of the
transverse momentum and pseudorapidity of the muon, of the associated jet and
of , the fraction of the photon's momentum participating in
the hard process, are compared with MC models and QCD predictions made at
next-to-leading order. The latter give a good description of the data.Comment: 32 pages, 6 tables, 7 figures Table 6 and Figure 7 revised September
200
Angular and Current-Target Correlations in Deep Inelastic Scattering at HERA
Correlations between charged particles in deep inelastic ep scattering have
been studied in the Breit frame with the ZEUS detector at HERA using an
integrated luminosity of 6.4 pb-1. Short-range correlations are analysed in
terms of the angular separation between current-region particles within a cone
centred around the virtual photon axis. Long-range correlations between the
current and target regions have also been measured. The data support
predictions for the scaling behaviour of the angular correlations at high Q2
and for anti-correlations between the current and target regions over a large
range in Q2 and in the Bjorken scaling variable x. Analytic QCD calculations
and Monte Carlo models correctly describe the trends of the data at high Q2,
but show quantitative discrepancies. The data show differences between the
correlations in deep inelastic scattering and e+e- annihilation.Comment: 26 pages including 10 figures (submitted to Eur. J. Phys. C
Plastisol Foaming Process. Decomposition of the Foaming Agent, Polymer Behavior in the Corresponding Temperature Range and Resulting Foam Properties
The decomposition of azodicarbonamide, used as foaming agent in PVC - plasticizer (1/1) plastisols was studied by DSC. Nineteen different plasticizers, all belonging to the ester family, two being polymeric (polyadipates), were compared. The temperature of maximum decomposition rate (in anisothermal regime at 5 K min-1 scanning rate), ranges between 434 and 452 K. The heat of decomposition ranges between 8.7 and 12.5 J g -1. Some trends of variation of these parameters appear significant and are discussed in terms of solvent (matrix) and viscosity effects on the decomposition reactions. The shear modulus at 1 Hz frequency was determined at the temperature of maximum rate of foaming agent decomposition, and differs significantly from a sample to another. The foam density was determined at ambient temperature and the volume fraction of bubbles was used as criterion to judge the efficiency of the foaming process. The results reveal the existence of an optimal shear modulus of the order of 2 kPa that corresponds roughly to plasticizer molar masses of the order of 450 ± 50 g mol-1. Heavier plasticizers, especially polymeric ones are too difficult to deform. Lighter plasticizers such as diethyl phthalate (DEP) deform too easily and presumably facilitate bubble collapse
The Spin Structure of the Nucleon
We present an overview of recent experimental and theoretical advances in our
understanding of the spin structure of protons and neutrons.Comment: 84 pages, 29 figure
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