17,467 research outputs found
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
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
Small atom diffusion and breakdown of the StokesâEinstein relation in the supercooled liquid state of the Zr46.7Ti8.3Cu7.5Ni10Be27.5 alloy
Be diffusivity data in the bulk metallic glass forming alloy Zr46.7Ti8.3Cu7.5Ni10Be27.5 are reported for temperatures between 530 and 710 K, extending 85 K into the supercooled liquid state of the alloy. At the glass transition temperature Tg, a change in temperature dependence of the data is observed, and above Tg the diffusivity increases more quickly with temperature than below. The data in the supercooled liquid can be described by a modified Arrhenius expression based on a diffusion mechanism suggested earlier. The comparison with viscosity data in the supercooled liquid state of Zr46.7Ti8.3Cu7.5Ni10Be27.5 reveals a breakdown of the StokesâEinstein relation, indicating a cooperative diffusion mechanism in the supercooled liquid state of Zr46.7Ti8.3Cu7.5Ni10Be27.5
Nonlocal magnon-polaron transport in yttrium iron garnet
The spin Seebeck effect (SSE) is observed in magnetic insulator|heavy metal
bilayers as an inverse spin Hall effect voltage under a temperature gradient.
The SSE can be detected nonlocally as well, viz. in terms of the voltage in a
second metallic contact (detector) on the magnetic film, spatially separated
from the first contact that is used to apply the temperature bias (injector).
Magnon-polarons are hybridized lattice and spin waves in magnetic materials,
generated by the magnetoelastic interaction. Kikkawa et al. [Phys. Rev. Lett.
\textbf{117}, 207203 (2016)] interpreted a resonant enhancement of the local
SSE in yttrium iron garnet (YIG) as a function of the magnetic field in terms
of magnon-polaron formation. Here we report the observation of magnon-polarons
in \emph{nonlocal} magnon spin injection/detection devices for various
injector-detector spacings and sample temperatures. Unexpectedly, we find that
the magnon-polaron resonances can suppress rather than enhance the nonlocal
SSE. Using finite element modelling we explain our observations as a
competition between the SSE and spin diffusion in YIG. These results give
unprecedented insights into the magnon-phonon interaction in a key magnetic
material.Comment: 5 pages, 6 figure
Virtual photon fragmentation functions
We introduce operator definitions for virtual photon fragmentation functions,
which are needed for reliable calculations of Drell-Yan transverse momentum
() distributions when is much larger than the invariant mass . We
derive the evolution equations for these fragmentation functions. We calculate
the leading order evolution kernels for partons to fragment into a unpolarized
as well as a polarized virtual photon. We find that fragmentation functions to
a longitudinally polarized virtual photon are most important at small , and
the fragmentation functions to a transversely polarized virtual photon dominate
the large region. We discuss the implications of this finding to the
J/ mesons' polarization at large transverse momentum.Comment: Latex, 19 pages including 6 figures. An error in the first version
has been corrected, and references update
Origin of intrinsic dark count in superconducting nanowire single-photon detectors
The origin of the decoherence in superconducting nanowire single-photon
detectors, the so-called dark count, was investigated. We measured the
direct-current characteristics and bias-current dependencies of the dark count
rate in a wide range of temperatures from 0.5 K to 4 K, and analyzed the
results by theoretical models of thermal fluctuations of vortices. Our results
indicate that the current-assisted unbinding of vortex-antivortex pairs is the
dominant origin of the dark count.Comment: 10 pages, 2 figure
Responses of Vascular Endothelial Cells to Photoembossed Topographies on Poly(Methyl Methacrylate) Films.
Failures of vascular grafts are normally caused by the lack of a durable and adherent endothelium covering the graft which leads to thrombus and neointima formation. A promising approach to overcome these issues is to create a functional, quiescent monolayer of endothelial cells on the surface of implants. The present study reports for the first time on the use of photoembossing as a technique to create polymer films with different topographical features for improved cell interaction in biomedical applications. For this, a photopolymer is created by mixing poly(methyl methacrylate) (PMMA) and trimethylolpropane ethoxylate triacrylate (TPETA) at a 1:1 ratio. This photopolymer demonstrated an improvement in biocompatibility over PMMA which is already known to be biocompatible and has been extensively used in the biomedical field. Additionally, photoembossed films showed significantly improved cell attachment and proliferation compared to their non-embossed counterparts. Surface texturing consisted of grooves of different pitches (6, 10, and 20 ”m) and heights (1 ”m and 2.5 ”m). The 20 ”m pitch photoembossed films significantly accelerated cell migration in a wound-healing assay, while films with a 6 ”m pitch inhibited cells from detaching. Additionally, the relief structure obtained by photoembossing also changed the surface wettability of the substrates. Photoembossed PMMA-TPETA systems benefited from this change as it improved their water contact angle to around 70°, making it well suited for cell adhesion.This project was supported in part by MRC/EPSRC grant G0502256-77947. Lin Qiu was supported by a joint PhD studentship from Queen Mary University of London and the China Scholarship Council (CSC) between 2010 and 2014
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