436 research outputs found
Lambda and Lambda-bar Polarization in Lepton Induced Processes
The study of the longitudinal polarization of Lambda and Lambda-bar hyperons
produced in polarized deep inelastic scattering, neutrino scattering, and in Z0
decays allows to access the spin dynamics of the quark fragmentation process.
Different phenomenological spin transfer mechanisms are considered and
predictions for the Lambda and Lambda-bar longitudinal polarization in various
processes using unpolarized and polarized targets are made. Current and future
semi-inclusive deep inelastic scattering experiments will provide soon accurate
enough data to study these phenomena and distinguish between various models for
the spin transfer mechanisms.Comment: 17 pages, LaTex with epsfig.sty, including 10 figures One reference
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Gluon Polarization from Correlated High-p_T Hadron Pairs in Polarized l - N Scattering
We propose to access the gluon polarization by measuring the cross
section spin-asymmetry in semi-inclusive polarized lepton -- nucleon
scattering. The photon-gluon fusion sub-process will be tagged by detecting
high- correlated hadron pairs in the forward hemisphere. Selecting
oppositely charged kaon pairs will allow to suppress the background coming from
gluon radiation.Comment: 6 pages, 3 eps figures, aipproc.cls and aipproc.sty include
Monotonicity and enclosure methods for the p-Laplace equation
We show that the convex hull of a monotone perturbation of a homogeneous
background conductivity in the -conductivity equation is determined by
knowledge of the nonlinear Dirichlet-Neumann operator. We give two independent
proofs, one of which is based on the monotonicity method and the other on the
enclosure method. Our results are constructive and require no jump or
smoothness properties on the conductivity perturbation or its support.Comment: 18 page
The quest for stable circumbinary companions to post-common envelope sdB eclipsing binaries Does the observational evidence support their existence?
Context. Period variations have been detected in a number of eclipsing close
compact binary subdwarf B stars (sdBs) and these have often been interpreted as
caused by circumbinary massive planets or brown dwarfs. Various evolutionary
scenarios have been proposed for these stars, but a definite mechanism remains
to be established. Equally puzzling is the formation of these putative
circumbinary objects which must have formed either from the remaining post
common envelope circumbinary disk or survived its evolution. Aims. In this
paper we review the eclipse time variations (ETVs) exhibited by seven such
systems and explore if there is conclusive evidence that the ETVs observed over
the last two decades can reliably predict the presence of circumbinary bodies.
Methods. We report 246 new observations of the seven sdB systems made between
2013 September and 2017 July using a worldwide network of telescopes. We
combined our new data with previously published measurements to analyse the
ETVs of these systems. Results. Our data shows that period variations cannot be
modelled simply on the basis of circumbinary objects. This implies that more
complex processes may be taking place in these systems. From eclipse time
variations, it has historically been suggested that five of the seven binary
systems reported herein had circumbinary objects. Based on our recent
observations and analysis only three systems remain serious contenders. We find
agreement with other observers that at least a decade of observations is
required to establish reliable ephemeris. With longer observational baselines
it is quite conceivable that the data will support the circumbinary object
hypothesis of these binary systems. Also we generally agree with other
observers that larger values of (O-C) residuals are found with secondary
companions of spectral type M5/6 or earlier as a result of an Applegate type
mechanismComment: 15 pages, 13 figures, 4 tables. 3 tables archived on CD
Gluon polarization from correlated high-pT hadron pairs in polarized electro-production
We propose to measure the gluon distribution function Delta G(eta) at eta <
0.2 via pseudo jet production in polarized fixed target lepton nucleon
scattering at typical lepton beam energies of 200 GeV. The measurement of the
spin-asymmetry for the production of correlated charge conjugated hadrons of
opposite transverse momentum can be directly related to Delta G(eta) through
the photo-gluon fusion process. Wa also present a numerical analysis of the
accuracy which can be obtained for different flavors and kinematics of the
observed hadron pair.Comment: 18 pages, 6 eps figure
Noise and conversion properties of Y-Ba-Cu-O Josephson mixers at operating temperatures above 20 K
We have measured the noise performance and conversion efficiency of Y-Ba-Cu-O bicrystal Josephson mixers at operating temperatures between 20 and 60 K and at operating frequencies around 90 GHz. A double-sideband mixer noise temperature of about 1600 K and a conversion efficiency of -10 dB at 20 K operating temperature has been measured using the Y-factor method. The absorbed local oscillator power was in the range of 10 nW. The dependence of the mixer performance on the normalized frequency Omega and the fluctuation parameter Gamma has been studied. In accordance with the resistively shunted junction model, the experimental data show the presence of excess noise. The temperature dependence of the mixer noise temperature can be explained by the variation of the linewidth of the Josephson oscillations with the operating temperature. (C) 2000 American Institute of Physics. [S0003-6951(00)00113-3]
3D Reconstruction for Partial Data Electrical Impedance Tomography Using a Sparsity Prior
In electrical impedance tomography the electrical conductivity inside a
physical body is computed from electro-static boundary measurements. The focus
of this paper is to extend recent result for the 2D problem to 3D. Prior
information about the sparsity and spatial distribution of the conductivity is
used to improve reconstructions for the partial data problem with Cauchy data
measured only on a subset of the boundary. A sparsity prior is enforced using
the norm in the penalty term of a Tikhonov functional, and spatial
prior information is incorporated by applying a spatially distributed
regularization parameter. The optimization problem is solved numerically using
a generalized conditional gradient method with soft thresholding. Numerical
examples show the effectiveness of the suggested method even for the partial
data problem with measurements affected by noise.Comment: 10 pages, 3 figures. arXiv admin note: substantial text overlap with
arXiv:1405.655
Parity violation in quasifree electron scattering off the deuteron
For deuteron electroweak disintegration, parity violating effects are
investigated which arise from the interference of and exchange as
well as from the hadronic sector via a small parity violating component in the
deuteron. The general formalism for the differential cross section and
polarization observables of electromagnetic deuteron disintegration is extended
to incorporate parity violating contributions. Formal expressions for the
additional structure functions are derived. Results are presented for these
parity violating structure functions for quasifree kinematics neglecting final
state interaction and two-body effects. Both types of parity violating
contributions to the asymmetry of the inclusive reaction with respect to
longitudinally polarized electrons are evaluated. The one from parity violating
deuteron components is negligible over the whole range of momentum transfers
considered.Comment: 21 pages revtex including 12 postscript figures, revised version,
accepted for publication in Nucl. Phys.
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