365 research outputs found
Lattice fringe signatures of epitaxy on nanotubes
Carbon nanotubes are of potential interest as heterogeneous catalysis
supports, in part because they offer a high surface area hexagonal array of
carbon atoms for columnar or epitaxial attachment. Fringe visibility modeling
of electron microscope lattice images allows one to investigate the
relationship between individual nanoparticles and such nanotube supports. We
show specifically how (111) columnar or epitaxial growth of FCC metal lattices,
on carbon nanotubes viewed side-on, results in well-defined patterns of
(111)-fringe orientations with respect to the tube axis. In the epitaxial case,
the observations also provide information on chirality of the nanotube's
outermost graphene sheet.Comment: 4 pages, 5 figures, 9 refs, cf.
http://newton.umsl.edu/~run/nano/epitaxy.htm
Heavy quark dynamics in a strongly magnetized quark-gluon plasma
We present a calculation of the heavy quark momentum diffusion coefficients
in a quark-gluon plasma under the presence of a strong external magnetic field,
within the Lowest Landau Level (LLL) approximation. In particular, we apply the
Hard Thermal Loop (HTL) technique for the resummed effective gluon propagator,
generalized for a hot and magnetized medium. Using the derived effective HTL
gluon propagator and the LLL quark propagator we analytically derive the full
results for the longitudinal and transverse momentum diffusion coefficients as
well as the energy losses for charm and bottom quarks beyond the static limit.
We also show numerical results for these coefficients in two special cases
where the heavy quark is moving either parallel or perpendicular to the
external magnetic field.Comment: 21 pages, 8 figures; Version published in Phys Rev D 10
Medium-Assisted Enhancement of Production from Small to Large Colliding Systems
Studies of exotic hadrons such as the state provide
crucial insights into the fundamental force governing the strong interaction
dynamics, with an emerging new frontier to investigate their production in high
energy collisions where a partonic medium is present. Latest experimental
measurements from the Large Hadron Collider show an intriguing evolution
pattern of the -to- yield ratio from proton-proton
collisions with increasing multiplicities toward proton-lead and lead-lead
collisions. Here we propose a novel mechanism of medium-assisted enhancement
for the production, which competes with the more
conventional absorption-induced suppression and results in a non-monotonic
trend from small to large colliding systems. Realistic simulations from this
model offer the first quantitative description of all available data.
Predictions are made for the centrality dependence of this observable in PbPb
collisions as well as for its system size dependence from OO and ArAr to XeXe
and PbPb collisions. In both cases, a non-monotonic behavior emerges as the
imprint of the competition between enhancement and suppression and can be
readily tested by future data.Comment: 7 pages, 4 figure
Heavy quark dynamics in a strongly magnetized medium
We present a calculation of the heavy quark momentum diffusion coefficients in a strongly magnetized medium, within the Lowest Landau Level (LLL) approximation. In particular, we use the Hard Thermal Loop (HTL) resummed effective gluon propagator, generalized for a hot and magnetized medium. Using this effective HTL gluon propagator along with the LLL quark propagator we analytically derive the full results for the longitudinal and transverse momentum diffusion coefficients for charm and bottom quarks beyond the static limit. Going beyond the static limit of the heavy quark, we also show numerical results for these coefficients in two special cases where the heavy quark is moving either parallel or perpendicular to the external magnetic field
Unraveling Gluon Jet Quenching through Production in Heavy-Ion Collisions
Jet quenching has long been regarded as one of the key signatures for the
formation of quark-gluon plasma in heavy-ion collisions. Despite significant
efforts, the separate identification of quark and gluon jet quenching has
remained as a challenge. Here we show that in high transverse momentum
() region provides a uniquely sensitive probe of in-medium gluon
energy loss since its production at high is particularly dominated
by gluon fragmentation. Such gluon-dominance is first demonstrated for the
baseline of proton-proton collisions within the framework of leading power
NRQCD factorization formalism. We then use the linear Boltzmann transport model
combined with hydrodynamics for the simulation of jet-medium interaction in
nucleus-nucleus collisions. The satisfactory description of experimental data
on both nuclear modification factor and elliptic flow
reveals, for the first time, that the gluon jet quenching is the driving force
for high suppression. This novel finding is further
confirmed by the data-driven Bayesian analyses of relevant experimental
measurements, from which we also obtain the first quantitative extraction of
the gluon energy loss distribution in the quark-gluon plasma.Comment: 7 pages, 5 figures, version published in Science Bulleti
Numerical investigations on scour and flow around two crossing pipelines on a sandy seabed
When a pipeline is laid on the seabed, local scour often occurs below it due to sea currents. In practical engineering, there are some cases that two pipelines laid on the seabed need to cross with each other. The complex flow structures around two crossing pipelines make the scour characteristics different from that of an isolated single pipeline. In this study, scour below two crossing pipelines was simulated numerically using the CFD software Flow-3D. The study is focused on the effect of the intersecting angle on the equilibrium depth and time scale of scour below the crossing position. Five intersecting angles, i.e., α = 0◦ , 15◦ , 30◦ , 45◦ and 90◦ , are considered, where α = 0◦ and 90◦ represent two pipelines parallel and perpendicular to each other, respectively. The results show that the equilibrium depth and the time scale of scour below the two crossing pipelines are greater than those of an isolated single pipeline. The equilibrium depth and time scale of scour have the largest values at α = 0◦ and decrease with the increase of the intersecting angle. Finally, the flow structures around the crossing pipelines are presented to explain the scour process
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