28,483 research outputs found
Characterization of Acoustic Streaming in Gradients of Density and Compressibility
Suppression of boundary-driven Rayleigh streaming has recently been
demonstrated for fluids of spatial inhomogeneity in density and compressibility
owing to the competition between the boundary-layer-induced streaming stress
and the inhomogeneity-induced acoustic body force. Here we characterize
acoustic streaming by general defocusing particle tracking inside a
half-wavelength acoustic resonator filled with two miscible aqueous solutions
of different density and speed of sound controlled by the mass fraction of
solute molecules. We follow the temporal evolution of the system as the solute
molecules become homogenized by diffusion and advection. Acoustic streaming
rolls is suppressed in the bulk of the microchannel for 70-200 seconds
dependent on the choice of inhomogeneous solutions. From confocal measurements
of the concentration field of fluorescently labelled Ficoll solute molecules,
we conclude that the temporal evolution of the acoustic streaming depends on
the diffusivity and the initial distribution of these molecules. Suppression
and deformation of the streaming rolls are observed for inhomogeneities in the
solute mass fraction down to 0.1 %.Comment: RevTex, pdfLaTex, 10 pages, 10 pdf figure
Acoustic streaming and its suppression in inhomogeneous fluids
We present a theoretical and experimental study of boundary-driven acoustic
streaming in an inhomogeneous fluid with variations in density and
compressibility. In a homogeneous fluid this streaming results from dissipation
in the boundary layers (Rayleigh streaming). We show that in an inhomogeneous
fluid, an additional non-dissipative force density acts on the fluid to
stabilize particular inhomogeneity configurations, which markedly alters and
even suppresses the streaming flows. Our theoretical and numerical analysis of
the phenomenon is supported by ultrasound experiments performed with
inhomogeneous aqueous iodixanol solutions in a glass-silicon microchip.Comment: 6 pages, 3 pdf figures, RevTex 4-
Nuclear effects on open charm production in p+A reactions
We calculate and resum the nuclear enhanced power corrections from the final
state partonic scattering in nuclear matter to open charm production and
correlations. In p+A reactions, we find that single and double inclusive D
mesons can be suppressed as much as the neutral pions from the dynamical high
twist shadowing. Effects of initial state energy loss in p+A collisions are
also investigated and may lead to significantly weaker transverse momentum
dependence of the nuclear suppression.Comment: Poster proceedings for Quark Matter 2005. As published in Heavy Ion
Physics. 5 pages, 2 figure
Open charm tomography of cold nuclear matter
We study the relative contribution of partonic sub-processes to D meson
production and D meson-triggered inclusive di-hadrons to lowest order in
perturbative QCD. While gluon fusion dominates the creation of large angle
DD-bar pairs, charm on light parton scattering determines the yield of single
inclusive D mesons. The distinctly different non-perturbative fragmentation of
c quarks into D mesons versus the fragmentation of quarks and gluons into light
hadrons results in a strong transverse momentum dependence of anticharm content
of the away-side charm-triggered jet. In p+A reactions, we calculate and resum
the coherent nuclear-enhanced power corrections from the final state partonic
scattering in the medium. We find that single and double inclusive open charm
production can be suppressed as much as the yield of neutral pions from
dynamical high-twist shadowing. Effects of energy loss in p+A collisions are
also investigated phenomenologically and may lead to significantly weaker
transverse momentum dependence of the nuclear attenuation.Comment: 24 pages, 21 figure
Ion-beam-enhanced adhesion in the electronic stopping region
The use of ion beams in the electronic stopping region to improve the adhesion of insulators to other materials is described. In particular, the bonding of Au films to Teflon, ferrite, and SiO2 was improved by bombarding them with He and Cl, respectively. Improvements in bonding were also observed for Au on glass, Au and Cu on sapphire, and Si3N4 on Si. The mechanism is apparently associated with sputtering and track forming processes occurring in the electronic stopping region. Some applications are discussed
Single transverse-spin asymmetry in Drell-Yan lepton angular distribution
We calculate a single transverse-spin asymmetry for the Drell-Yan
lepton-pair's angular distribution in perturbative QCD. At leading order in the
strong coupling constant, the asymmetry is expressed in terms of a twist-3
quark-gluon correlation function T_F^{(V)}(x_1,x_2). In our calculation, the
same result was obtained in both light-cone and covariant gauge in QCD, while
keeping explicit electromagnetic current conservation for the virtual photon
that decays into the lepton pair. We also present a numerical estimate of the
asymmetry and compare the result to an existing other prediction.Comment: 15 pages, Revtex, 5 Postscript figures, uses aps.sty, epsfig.st
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