J. Bleibel

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 λ as the screening length. Whereas the limit λ→∞ corresponds to the global collapse of a self-gravitating fluid, for finite λ[over ^] 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.

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

Microscopic models and effective equation of state in nuclear collisions in the vicinity of

\lambda

E_{\rm lab} = 30A

given by the capillary length of typically 1mm, 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 adaptation 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

GeV at the GSI Facility for Antiproton and Ion Research (FAIR) and beyond

\lambda

Elliptic flow at RHIC : Where and when was it formed?

the dynamics shows a smooth transition from the spinodal decomposition expected for a simple fluid with short-ranged attraction to the self-gravitational collapse scenario.

How many of the scaling trends in

Two microscopic models, UrQMD and QGSM, were employed to study the formation of locally equilibrated hot and dense nuclear matter in heavy-ion collisions at energies from 11.6A GeV to 160A GeV. Analysis was performed for the fixed central cubic cell of volume V = 125 fm and for the expanding cell which followed the growth of the central area with uniformly distributed energy. To decide whether or not the equilibrium was reached, results of the microscopic calculations were compared to that of the statistical thermal model. Both dynamical models indicate that the state of kinetic, thermal and chemical equilibrium is nearly approached at any bombarding energy after a certain relaxation period. The higher the energy, the shorter the relaxation time. Equation of state has a simple linear dependence P = a( √ s)ε, where a ≡ c2s is the sound velocity squared. It varies from 0.12± 0.01 at Elab = 11.6A GeV to 0.145± 0.005 at Elab = 160A GeV. Change of the slope in a( √ s) behavior occurs at Elab = 40A GeV and can be assigned to the transition from baryon-rich to meson-dominated matter. The phase diagrams in the T − μB plane show the presence of kinks along the lines of constant entropy per baryon. These kinks are linked to the inelastic (i.e. chemical) freeze-out in the system.

pp

Abstract Evolution of the elliptic flow of hadrons in heavy-ion collisions at RHIC energies is studied within the microscopic quark–gluon string model. The elliptic flow is shown to have a multi-component structure caused by (i) rescattering and (ii) absorption processes in spatially asymmetric medium. Together with different freeze-out dynamics of mesons and baryons, these processes lead to the following trend in the flow formation: the later the mesons are frozen, the weaker their elliptic flow, whereas baryon fraction develops stronger elliptic flow during the late stages of the fireball evolution. The phase-space distributions of the emitted particles are studied as well. The flow is shown to be formed both in the central and in the fragmentation regions of the reaction. Comparison with the PHOBOS data demonstrates the model ability to reproduce the v 2 ch ( η ) signal in different centrality bins.

collisions will be violated at sqrt{s_NN} = 14 TeV ? - Predictions from Monte Carlo quark-gluon string model

tic and non-diffractive pp collisions at energies from p s = 200GeV to 14TeV are studied within the Monte Carlo quark-gluon string model. Good agreement with the available experimental data is obtained and predictions are made for the collisions at top LHC energy p s = 14TeV. 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 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 multi-string processes at ultra-relativistic energies.

3D hydrodynamic interactions lead to divergences in 2D diffusion.

We investigate the influence of 3D hydrodynamic interactions on confined colloidal suspensions, where only the colloids are restricted to one or two dimensions. In the absence of static interactions among the colloids, i.e., an ideal gas of colloidal particles with a finite hydrodynamic radius, we find a divergent collective diffusion coefficient. The origin of the divergence is traced back to the dimensional mismatch of 3D hydrodynamic interactions and the colloidal particles moving only in 1D or 2D. Our results from theory are confirmed by Stokesian dynamics simulations and supported by light scattering observational data for particles at a fluid interface.