1,310 research outputs found
Extensional rheology and elastic instabilities of a wormlike micellar solution in a microfluidic cross-slot device
Wormlike micellar surfactant solutions are encountered in a wide variety of important applications, including enhanced oil recovery and ink-jet printing, in which the fluids are subjected to high extensional strain rates. In this contribution we present an experimental investigation of the flow of a model wormlike micellar solution (cetyl pyridinium chloride and sodium salicylate in deionised water) in a well-defined stagnation point extensional flow field generated within a microfluidic cross-slot device. We use micro-particle image velocimetry (m-PIV) and full-field birefringence microscopy coupled with macroscopic measurements of the bulk pressure drop to make a quantitative characterization of the fluidâs rheological response over a wide range of deformation rates. The flow field in the micromachined cross-slot is first characterized for viscous flow of a Newtonian fluid, and m-PIV measurements show the flow field remains symmetric and stable up to moderately high Reynolds number, Re z 20, and nominal strain rate, _3nom z 635 s1. By contrast, in the viscoelastic micellar solution the flow field remains symmetric only for low values of the strain rate such that _3nom # lM1, where lM ÂŒ 2.5 s is the Maxwell relaxation time of the fluid. In this stable flow regime the fluid displays a localized and elongated birefringent strand extending along the outflow streamline from the stagnation point, and estimates of the apparent extensional viscosity can be obtained using the stressoptical rule and from the total pressure drop measured across the cross-slot channel. For moderate deformation rates (_3nom $ lM1) the flow remains steady, but becomes increasingly asymmetric with increasing flow rate, eventually achieving a steady state of complete anti-symmetry characterized by a dividing streamline and birefringent strand connecting diagonally opposite corners of the cross-slot. Eventually, as the nominal imposed deformation rate is increased further, the asymmetric divided flow becomes time dependent. These purely elastic instabilities are reminiscent of those observed in crossslot flows of polymer solutions, but seem to be strongly influenced by the effects of shear localization of the micellar fluid within the microchannels and around the re-entrant corners of the cross-slot
Thermal Field Theory and Generalized Light Front Coordinates
The dependence of thermal field theory on the surface of quantization and on
the velocity of the heat bath is investigated by working in general coordinates
that are arbitrary linear combinations of the Minkowski coordinates. In the
general coordinates the metric tensor is non-diagonal. The
Kubo, Martin, Schwinger condition requires periodicity in thermal correlation
functions when the temporal variable changes by an amount
. Light front quantization fails since
, however various related quantizations are possible.Comment: 10 page
ON THE INTRINSIC CHARM COMPONENT OF THE NUCLEON
Using a meson cloud model we calculate the squared charm radius
of the nucleon . The ratio between this squared radius and the ordinary baryon
squared radius is identified with the probability of ``seeing'' the intrinsic
charm component of the nucleon. Our estimate is compatible with those used to
successfully describe the charm production phenomenology.Comment: 9 pages, 2 figures not included, avaiable from the author
Intrinsic Charm Contribution to Double Quarkonium Hadroproduction
Double production has been observed by the NA3 collaboration in and collisions with a cross section of the order of 20-30 pb. The
pairs measured in nucleus interactions at 150 and 280
GeV are observed to carry an anomalously large fraction of the projectile
momentum in the laboratory frame, at 150 GeV and
at 280 GeV. We postulate that these forward pairs
are created by the materialization of Fock states in the projectile containing
two pairs of intrinsic quarks. We calculate the overlap of the
charmonium states with the
Fock state as described by the intrinsic charm model and find that the longitudinal momentum and invariant mass distributions
are both well reproduced. We also discuss double production in
interactions and the implications for other heavy quarkonium production
channels in QCD.Comment: Revtex, APS style, 7 pages, 3 figures in uuencoded fil
Contact-induced spin polarization in carbon nanotubes
Motivated by the possibility of combining spintronics with molecular
structures, we investigate the conditions for the appearance of
spin-polarization in low-dimensional tubular systems by contacting them to a
magnetic substrate. We derive a set of general expressions describing the
charge transfer between the tube and the substrate and the relative energy
costs. The mean-field solution of the general expressions provides an
insightful formula for the induced spin-polarization. Using a tight-binding
model for the electronic structure we are able to estimate the magnitude and
the stability of the induced moment. This indicates that a significant magnetic
moment in carbon nanotubes can be observed.Comment: To appear in Phys. Rev. B (2003
Equivalence of light-front and conventional thermal field theory
ONE PHYSICS ELLIPSE, COLLEGE PK, USA, MD,
20740-384
Density Perturbations in the Brans-Dicke Theory
We analyse the fate of density perturbation in the Brans-Dicke Theory, giving
a general classification of the solutions of the perturbed equations when the
scale factor of the background evolves as a power law. We study with details
the cases of vacuum, inflation, radiation and incoherent matter. We find, for
the a negative Brans-Dicke parameter, a significant amplification of
perturbations.Comment: 26 pages, latex fil
QCD and Intrinsic Heavy Quark Predictions for Leading Charm and Beauty Hadroproduction
Recent experiments at Fermilab and CERN have observed a strong asymmetry
between the hadroproduction cross sections of leading mesons, containing
projectile valence quarks, and nonleading charmed mesons, without projectile
valence quarks. The observed correlations of the
cross section with the projectile charge violates the usual assumption that
heavy quark jet fragmentation factorizes. We examine the asymmetry between
leading and nonleading charm production as a function of and
assuming a two-component model combining leading-twist fusion subprocesses and
charm production from intrinsic heavy quark Fock states. We predict a sizable
asymmetry at low and high from coalescence of the charm quarks
with the comoving spectator quarks of the projectile. An intrinsic production cross section of 0.5 b is sufficient to explain both the
magnitude and kinematic dependence of the asymmetry. In contrast, the charm jet
hadronization mechanisms contained in PYTHIA predict a sizeable leading charm
asymmetry even at low The two-component model is extended to predict the
asymmetry in meson production in proton-proton and pion-proton
interactions.Comment: 16 pages LaTeX with 6 postscript figures available upon request,
LBL-35380, SLAC-PUB-646
Quark initiated coherent diffractive production of muon pair and W boson at hadron colliders
The large transverse momentum muon pair and W boson productions in the quark
initiated coherent diffractive processes at hadron colliders are discussed
under the framework of the two-gluon exchange parametrization of the Pomeron
model. In this approach, the production cross sections are related to the
small-x off-diagonal gluon distribution and the large-x quark distribution in
the proton (antiproton). By approximating the off-diagonal gluon distribution
by the usual gluon distribution function, we estimate the production rates of
these processes at the Fermilab Tevatron.Comment: 11pages, 6 PS figures, to appear in PR
The leading particle effect from light quark fragmentation in charm hadroproduction
The asymmetry of and meson production in scattering
observed by the E791 experiment is a typical phenomenon known as the leading
particle effect in charm hadroproducton. We show that the phenomenon can be
explained by the effect of light quark fragmentation into charmed hadrons
(LQF). Meanwhile, the size of the LQF effect is estimated from data of the E791
experiment.
A comparison is made with the estimate of the LQF effect from prompt
like-sign dimuon rate in neutrino experiments. The influence of the LQF effect
on the measurement of nucleon strange distribution asymmetry from charged
current charm production processes is briefly discussed.Comment: 6 latex pages, 1 figure, to appear in EPJ
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