Dynamic evolution of transverse energy flow in focused asymmetric optical vector-vortex beams

We present here controlled generation of asymmetric optical vector-vortex beams using a two-mode optical fiber and study the dynamic evolution of the transverse energy flow (TEF) when focused through a spherical lens. The dependence of the TEF on various factors such as the vortex charge, vortex anisotropy and polarization structure around the vortex core is explored. It is found that the TEF is directly proportional to the phase gradient and its direction is governed by the vortex charge. The presence of C-point polarization singularity in the beam and the polarization structure around it results in vibrational phase gradient which is the major factor deciding the TEF in vector-vortex beams.     

Potential-energy surfaces for asymmetric heavy-ion reactions

We calculate the macroscopic potential energy of deformation as a function of mass asymmetry and distance between mass centers for shape configurations of interest in heavy-ion reactions. For the system³⁰⁰120 we also study the effect of adding microscopic shell and pairing corrections to the macroscopic potential energy. The shape configurations are generated by bringing together two separated spheres of unequal size. After the spheres touch the shapes are constructed by filling in the neck while keeping constant the radii of the end spheres, the nuclear density and the total nuclear volume. The macroscopic energy is calculated as the sum of a Coulomb energy and a nuclear macroscopic energy that takes into account the finite range of the nuclear force. For systems throughout the periodic table we display the calculated energy as a function of distance between mass centers and mass asymmetry in the form of contour maps. Some important features of the contour maps are the stationary points of the potential energy and how they change in character and location as functions of the nuclear system considered. For example, for light systems there is a maximum in the potential energy for symmetric shapes. As we move to heavier systems this peak in the potential-energy surface splits into two asymmetric peaks that are separated by a symmetric saddle point. This occurs when Z²/A ≈ 30 for the total system. As the systems become still heavier the peaks become more and more asymmetric. In heavy-ion reactions for which the asymmetry of the system is smaller than that corresponding to the peak, the smaller nucleus tends to suck up the larger one. For larger asymmetries the larger nucleus tends to suck up the smaller one. For heavy systems the binary fission saddle point is lower than the maximum in the one-dimensional interaction barrier. The penetrability calculated for the multidimensional potential-energy surface is therefore increased relative to that for the one-dimensional barrier. The microscopic shell and pairing corrections lower the potential energy for configurations in which the target and/or projectile are magic or nearly magic. This effect persists to somewhat inside the point of touching. These corrections also lower the energy near the ground state.     

Directed flow in nonadiabatic stochastic pumps

We analyze the operation of a molecular machine driven by the nonadiabatic variation of external parameters. We derive a formula for the integrated flow from one configuration to another, obtain a "no-pumping theorem" for cyclic processes with thermally activated transitions, and show that in the adiabatic limit the pumped current is given by a geometric expression.     

Search for collective transverse flow using particle transverse momentum spectra in relativistic heavy-ion collisions

The particle transverse momentum spectra recently measured in relativistic heavy-ion collisions at CERN and BNL are analysed within an expanding fireball model. All the particle spectra at a given beam energy can be reproduced simultaneously with a single set of intensive parameters for the initial state of the fireball. As typical freeze-out parameters in this beam energy region we find a freeze-out temperatureT _f?110 MeV for most hadrons, and an average transverse expansion velocity at freeze-out of 〈v/c〉?0.4–0.45. The striking enhancement at transverse momentap _T<200 MeV/c in the CERN pion data cannot be fully explained by the existence of transverse flow.     

Collective mechanism for nuclear stopping and transverse flow in heavy-ion collisions

The role of filamentation instability of quark-gluon plasma, in explaining collective phenomena in relativistic heavy-ion collisions, has been analyzed. Using equations of SU(2) two fluid color hydrodynamics it is shown that this instability can significantly enhance nuclear stopping and might contribute to collective sideward flows.     

Directed flow at midrapidity in heavy-ion collisions

It was recently shown that fluctuations in the initial geometry of a heavy-ion collision generally result in a dipole asymmetry of the distribution of outgoing particles. This asymmetry, unlike the usual directed flow, is expected to be present at a wide range of rapidity--including midrapidity. The first evidence of this phenomenon can be seen in recent two-particle correlation data by the STAR Collaboration, providing the last element necessary to quantitatively describe long-range dihadron correlations. We extract differential directed flow from these data and propose a new direct measurement.     

Steady flow through asymmetric membranes

For the two special cases that the permeability of the membrane is (1) an exponential and (2) a power function of location and pressure, the pressure dependence of the current, the average permeability, and the asymmetry of permeability Δ = <P_>/ <P+> — 1 were calculated on the basis of irreversible thermodynamics. The asymmetry is small in both cases. It increases rather fast for small pressure but reaches soon a slightly inclined plateau in the former case and a maximum with a small subsequent drop in the latter case. The maximum value is close to 0.5 in case 1 and about 0.2 in case 2. It is also shown that Fick's law cannot be applied to inhomogeneous or nonideal membranes.     

Directed transport of an asymmetric particle pair induced by non-equilibrium conditions

The hopping motion of a classical bounded pair of two particles along a chain is investigated. It is shown that in the asymmetric case of the system dynamics including excited states which differ from the respective ground states by the barrier to be overcome by one of the two particles, the over- and underpopulation of these excited states leads to a directed motion of the particle pair. Thereby, overpopulation results in one direction of motion, whereas underpopulation results in the opposite direction, and the mean velocity is determined by the amount of over-resp. underpopulation. For small deviations from equilibrium, the system exhibits linear response well known from other ratchet-type models. Possible generalizations and applications are discussed. Received 17 August 2001 and Received in final form 11 October 2001     

Phenomenology of flow disappearance in intermediate-energy heavy ion collisions

The disappearance of collective flow effects in heavy ion collisions is investigated using a microscopic optical model formalism for estimating collision momentum transfers. Phenomenological expressions for the balance energy are obtained which agree very well with measurements for various experimental collision pairs and with results obtained from Boltzmann-Uehling-Uhlenbeck simulations.     

Directed flow from global symmetry and initial state Fluctuations

Collective flow is studied in a 3+1D fluid dynamical model with globally symmetric, peripheral initial conditions, taking into account the shear flow. At $\sqrt {s_{NN} } $ = 2.76 TeV in semi-peripheral Pb+Pb collisions this leads to rotation, while at more peripheral collisions with high resolution and low numerical viscosity, the initial development of a Kelvin-Helmholz instability is observed. This effect provides a precision tool for studying the viscosity of Quark-Gluon Plasma.     

Transport of microscopic objects using asymmetric transverse optical gradient force

We report an efficient technique based on an optical tweezers setup for optically controlled transport of microscopic objects. The technique makes use of an elliptically profiled trap beam that has an asymmetric intensity distribution about the center of its long axis. Microscopic objects pulled into the trap from the side having the larger intensity gradient become accelerated along the major axis of the focus and are ejected from the lower-stiffness end. The speed of transport is determined by the laser-beam power and the degree of asymmetry in the intensity profile. The approach could be used to simultaneously trap and transport hundreds of particles, varying in sizes from sub-micrometer to a few micrometers. Further, transport of red blood cells using this method is demonstrated.     

Directed flow of baryons from high-energy heavy-ion collisions

The collective motion of nucleons from high-energy heavy-ion collisions is analyzed within a relativistic two-fluid model for different equations of state (EoS). As function of beam energy the theoretical slope parameter F _y of the differential directed flow is in good agreement with experimental data, when calculated for the QCD-consistent EoS described by the statistical mixed-phase model. Within this model, which takes the deconfinement phase transition into account, the excitation function of the directed flow (P _x ) turns out to be a smooth function in the whole range from SIS till SPS energies. This function is close to that for pure hadronic EoS and exhibits no minimum predicted earlier for a two-phase bag-model EoS. Attention is also called to a possible formation of nucleon antiflow (F _y < 0) at energies ? 100 A·GeV.     

Ray delay in gradient waveguides with asymmetric transverse refractive index profiles

Former investigations of symmetric refractive index profiles in gradient waveguides are extended to include also asymmetric profile curves. The generalized delay expression is derived and illustrated by means of various examples. Possibilities of compensating symmetric by asymmetric components of the refractive index in the delay formula lead to a number of optimum profiles for low-dispersion transmission.The pulse broadening in a waveguide with a gradient profile being distributed in a ring-shaped form over its cross section, which is to serve as an example of a guide with an asymmetric profile, is assessed.     

Evolution of kinematic structure of the flow behind a transverse rib for transitional flow regimes

Results are presented on visualization of a separated flow behind two kinds of transverse ribs in a channel for a range of Reynolds numbers covering the different stages of laminar-turbulent flow transition. The data was obtained on dynamics of kinematic structure of flow and on evolution of large-scale transverse vortex structures which were generated in the mixing layer during late stages of laminar-turbulent transition. The qualitative estimates were obtained for the vortex generation frequency and velocity of their convective transfer. The features of flow structure were identified for flow behind tested shapes of ribs.     

Transverse radius dependence for transverse velocity and elliptic flow in intermediate energy HIC

The mean transverse velocity and elliptic flow of light fragments (A≤2) as a function of transverse radius are studied for 25 MeV/nucleon <'64>Cu+<'64>Cu collisions with impact parameters 3-5 fm by the isospin- dependent quantum molecular dynamics model. By comparison between the in-plane and the out-of-plane transverse velocities, the elliptic flow dependence on the transverse radius can be understood qualitatively, and variation of the direction of the resultant force on the fragments can be investigated qualitatively.     

Transverse radius dependence for transverse velocity and elliptic flow in intermediate energy HIC

The mean transverse velocity and elliptic flow of light fragments (A ≤ 2) as a function of transverse radius are studied for 25 MeV/nucleon ⁶⁴Cu+⁶⁴Cu collisions with impact parameters 3--5 fm by the isospin-dependent quantum molecular dynamics model. By comparison between the in-plane and the out-of-plane transverse velocities, the elliptic flow dependence on the transverse radius can be understood qualitatively, and variation of the direction of the resultant force on the fragments can be investigated qualitatively.     

Analytical study of an asymmetric 1D statistical model for chemical reactions

An analytical study is presented for the asymmetric FGZ reaction model, involving two different species A and B (only B can spontaneously desorb) in contact with a bath containing A and B with the same concentration. The expected values of the density and the pair correlation functions are calculated and their time behaviour is analysed in detail. This also allows to define an average time-dependent fragmentation index describing quantitatively the evolution of the topology (connectivity) of the clusters. In addition, when the system is doomed to end its evolution in the A-poisoned state, the distribution law P(T) of the times T_k at which this occurs is investigated numerically. It turns out that, in the case where a single isolated B is present in the initial state, this law is well enough represented by a stretched exponential in the log variable: P(T) = C^ste exp[− α(1n T)^ß].