89 research outputs found
Ewald sum for hydrodynamic interactions with periodicity in two dimensions
We carry out the Ewald summation for the Rotne-Prager-Yamakawa mobility
tensor, the Oseen mobility tensor and further variations of both, relevant for
the hydrodynamic interactions in colloidal suspensions, where all interacting
particles are within a single plane, i.e., adsorbed at a fluid interface or
other quasi two-dimensional systems. We use the Poisson summation formula for
systems periodic in two dimensions and finite in the third dimension in order
to obtain simple formulae for applications, such as molecular dynamics or
Brownian dynamics simulations. We show, that for such systems, as soon as noise
is taken into account, a commonly used approximate three-dimensional Ewald
summation leads to a spurious system size dependence, which may considerably
affect the interpretation of simulation results and will be cured within our
approach. Additionally, the resulting formulae are found to be computationally
much less expensive than the approximate three-dimensional Ewald summation.Comment: 24 pages, 3 figure
Shock waves in capillary collapse of colloids: a model system for two--dimensional screened Newtonian gravity
Using Brownian dynamics simulations, density functional theory, and
analytical perturbation theory we study the collapse of a patch of
interfacially trapped, micrometer-sized colloidal particles, driven by
long-ranged capillary attraction. This attraction {is formally analogous} to
two--dimensional (2D) screened Newtonian gravity with the capillary length
\hat{\lambda} as the screening length. Whereas the limit \hat{\lambda} \to
\infty corresponds to the global collapse of a self--gravitating fluid, for
finite \hat{\lambda} we predict theoretically and observe in simulations a
ringlike density peak at the outer rim of a disclike patch, moving as an
inbound shock wave. Possible experimental realizations are discussed.Comment: 5 pages, 3 figures, revised version with new Refs. added, matches
version accepted for publication in PR
Pseudorapidity shape of elliptic flow as signature for fast equilibration in relativistic heavy-ion collisions at energies up to sqrt(s) = 200 GeV
The implications of parton recombination processes on the dynamics of
ultrarelativistic heavy-ion reactions are investigated. To do so, the
quark-gluon string transport model has been extended for partonic recombination
and fusion processes. Parton recombination leads to short equilibration times
and improves significantly on the theoretical description of measured directed
and elliptic flow, i.e., v_1 and v_2, distributions in Au+Au collisions at
sqrt(s) = 200 GeV, in particular what concerns their pseudorapidity dependence.
The shape of v_2(eta) is found to be closely related to fast thermalization.Comment: 7 pages (revtex4) with 4 figures, v3: substantially extended
description and discussion of the model and its results, accepted for
publication in Phys. Rev.
Hydrodynamic interactions induce anomalous diffusion under partial confinement
Under partial confinement, the motion of colloidal particles is restricted to a plane or a line but their dynamics is influenced by hydrodynamic interactions mediated by the unconfined, three-dimensional flow of the embedding fluid. We demonstrate that this dimensionality mismatch induces a characteristic divergence in the collective diffusion coefficient of the colloidal subsystem. This result, independent of the specific interparticle forces in the colloid, is solely due to the kinematical constraint on the colloidal particles, and it is different from the known divergence of transport coefficients in purely one or two-dimensional fluids.Spanish Government AIB2010DE-00263 and FIS2011-24460 (partially financed by FEDER funds)European Commission 22839
Anisotropic flow of charged and identified hadrons in the quark-gluon string model for Au+Au collisions at sqrt(s) = 200 GeV
The pseudorapidity behaviour of the azimuthal anisotropy parameters v_1 and
v_2 of inclusive charged hadrons and their dependence on the centrality has
been studied in Au+Au collisions at full RHIC energy of sqrt(s) = 200 GeV
within the microscopic quark-gluon string model. The QGSM simulation results
for the directed flow v_1 show antiflow alignment within the pseudorapidity
range |eta| < 2 in a fair agreement with the experimental v_1(eta) data, but
cannot reproduce the further development of the antiflow up to |eta| around
3.5. The eta dependence of the elliptic flow v_2 extracted from the simulations
agrees well with the experimental data in the whole pseudorapidity range for
different centrality classes. The centrality dependence of the integrated
elliptic flow of charged hadrons in the QGSM almost coincides with the PHOBOS
experimental distribution. The transverse momentum dependence of the elliptic
flow of identified and inclusive charged hadrons is studied also. The model
reproduces quantitatively the low p_T part of the distributions rather good,
but underestimates the measured elliptic flow for transverse momenta p_T > 1
GeV/c. Qualitatively, however, the model is able to reproduce the saturation of
the v_2(p_T) spectra with rising p_T as well as the crossing of the elliptic
flow for mesons and baryons.Comment: REVTeX, 10 pages, 10 figures, v2: extended discussion of the model
results, accepted for publication in Phys. Rev.
Collective dynamics of colloids at fluid interfaces
The evolution of an initially prepared distribution of micron sized colloidal
particles, trapped at a fluid interface and under the action of their mutual
capillary attraction, is analyzed by using Brownian dynamics simulations. At a
separation \lambda\ given by the capillary length of typically 1 mm, the
distance dependence of this attraction exhibits a crossover from a logarithmic
decay, formally analogous to two-dimensional gravity, to an exponential decay.
We discuss in detail the adaption of a particle-mesh algorithm, as used in
cosmological simulations to study structure formation due to gravitational
collapse, to the present colloidal problem. These simulations confirm the
predictions, as far as available, of a mean-field theory developed previously
for this problem. The evolution is monitored by quantitative characteristics
which are particularly sensitive to the formation of highly inhomogeneous
structures. Upon increasing \lambda\ the dynamics show a smooth transition from
the spinodal decomposition expected for a simple fluid with short-ranged
attraction to the self-gravitational collapse scenario.Comment: 13 pages, 12 figures, revised, matches version accepted for
publication in the European Physical Journal
How many of the scaling trends in collisions will be violated at sqrt{s_NN} = 14 TeV ? - Predictions from Monte Carlo quark-gluon string model
Multiplicity, rapidity and transverse momentum distributions of hadrons
produced both in inelastic and nondiffractive collisions at energies from
\,GeV to 14\,TeV are studied within the Monte Carlo quark-gluon
string model (QGSM). Good agreement with the available experimental data up to
\,TeV is obtained, and predictions are made for the collisions
at top LHC energy \,TeV. The model indicates that Feynman
scaling and extended longitudinal scaling remain valid in the fragmentation
regions, whereas strong violation of Feynman scaling is observed at
midrapidity. The Koba-Nielsen-Olesen (KNO) scaling in multiplicity
distributions is violated at LHC also. The origin of both maintenance and
violation of the scaling trends is traced to short range correlations of
particles in the strings and interplay between the multistring processes at
ultrarelativistic energies
Anisotropic flow in Pb+Pb collisions at LHC from the quark gluon string model with parton rearrangement
We present predictions for the pseudorapidity dependence of the azimuthal
anisotropy parameters v_1 and v_2 of baryons and inclusive charged hadrons in
Pb+Pb collisions at a LHC energy of sqrt(s) = 5.5 TeV applying a microscopic
transport model, namely the quark gluon string model (QGSM) which has been
recently extended for parton rearrangement and fusion processes. Pb+Pb
collisions with impact parameters b = 2.3 fm and b = 8 fm have been simulated
in order to investigate additionally the difference between central and
semiperipheral configurations. In contrast to v_1(eta) at RHIC, the directed
flow of charged hadrons shows a small normal flow alignment. The elliptic flow
v_2(eta) turns out to be rather similar in shape for RHIC and LHC conditions,
the magnitude however increases about 10-20 % at the LHC, leading to the
conclusion that the hydrodynamical limit will be reached.Comment: 6 pages, 4 figures, accepted for publication in Phys. Lett.
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