Inertial effects on two-particle relative dispersion in turbulent flows

We report experimental results on the relative motion of pairs of solid spheric particles with initial separations in the inertial range of fully developed turbulence in water. The particle densities were in the range of $1 \lessapprox \rho_{p}/\rho_{f} \lessapprox 8$, \textit{i.e.}, from neutrally buoyant to highly inertial; and their sizes were of the Kolmogorov scale. For all particles, we observed a Batchelor like regime, in which particles separated ballistically. Similar to the Batchelor regime for tracers, this regime was observed in the early stages of the relative separation for times $t \lessapprox 0.1 t_0$ with $t_0$ determined by the turbulence energy dissipation rate and the initial separation between particle pairs. In this time interval heavier particles separated faster than fluid tracers. The second order Eulerian velocity structure functions was found to increase with density. In other words, both observations show that the relative velocity between inertial particles was larger than that between tracers. Based on the widely used, simplified equation of motion for inertial point-particles, we derived a model that shows an increase in relative velocity between inertial particles. In its scale dependence, however, it disagrees quantitatively with the experimental results. This we attribute to the preferential sampling of the flow field by inertial particles, which is not captured by the model.Comment: 6 pages, 5 figures, 2 tables, epl2.cls, submitted to EP

The nature of symmetric instability and its similarity to convective and inertial instability

It is shown that there exists a local similarity among SI (Symmetric Instability), BI (Buoyancy or Convective Instability), and II (Inertial Instability) even for fully nonlinear viscous motion. The most unstable slope angles for SI and Moist SI motions are analyzed based on parcel energetics. These considerations also suggest qualitatively that CSI (Conditional SI) circulations will be slantwise and lie between the moist most unstable slope and dry least stable slope of the basic state

Collective flow of open and hidden charm in Au+Au collisions at s\sqrt{s} = 200 GeV

We study the collective flow of open charm mesons and charmonia in Au+Au collisions at $\sqrt{s}$ = 200 GeV within the hadron-string-dynamics (HSD) transport approach. The detailed studies show that the coupling of $D,\bar{D}$ mesons to the light hadrons leads to comparable directed and elliptic flow as for the light mesons. This also holds approximately for $J/\Psi$ mesons since more than 50% of the final charmonia for central and mid-central collisions stem from $D+\bar{D}$ induced reactions in the transport calculations. The transverse momentum spectra of $D,\bar{D}$ mesons and $J/\Psi$'s are only very moderately changed by the (pre-)hadronic interactions in HSD which can be traced back to the collective flow generated by elastic interactions with the light hadrons.Comment: 9 pages, 8 figures, Phys. Rev. C, in pres

Multichannel cold collisions between metastable Sr atoms

We present a multichannel scattering calculation of elastic and inelastic cold collisions between two low-field seeking, metastable ^{88}Sr [(5s5p) ^3P_2] atoms in the presence of an external magnetic field. The scattering physics is governed by strong anisotropic long-range interactions, which lead to pronounced coupling among the partial waves of relative motion. As a result, nonadiabatic transitions are shown to trigger a high rate of inelastic losses. At relatively high energies, T > 100 mkK, the total inelastic collision rate is comparable with the elastic rate. However, at lower collisional energy, the elastic rate decreases, and at T ~ 1mkK, it becomes substantially smaller than the inelastic rate. Our study suggests that magnetic trapping and evaporative cooling of ^{88}Sr [(5s5p) ^3P_2] atoms, as well as ^{40}Ca [(4s4p) ^3P_2], in low-field seeking states will prove difficult to achieve experimentally.Comment: 4 pages, Latex, Submitte

An interactive and multi-level framework for summarising user generated videos

We present an interactive and multi-level abstraction framework for user-generated video (UGV) summarisation, allowing a user the flexibility to select a summarisation criterion out of a number of methods provided by the system. First, a given raw video is segmented into shots, and each shot is further decomposed into sub-shots in line with the change in dominant camera motion. Secondly, principal component analysis (PCA) is applied to the colour representation of the collection of sub-shots, and a content map is created using the first few components. Each sub-shot is represented with a ``footprint'' on the content map, which reveals its content significance (coverage) and the most dynamic segment. The final stage of abstraction is devised in a user-assisted manner whereby a user is able to specify a desired summary length, with options to interactively perform abstraction at different granularity of visual comprehension. The results obtained show the potential benefit in significantly alleviating the burden of laborious user intervention associated with conventional video editing/browsing

Correspondence Between DGP Brane Cosmology and 5D Ricci-flat Cosmology

We discuss the correspondence between the DGP brane cosmology and 5D Ricci-flat cosmology by letting their metrics equal each other. By this correspondence, a specific geometrical property of the arbitrary integral constant I in DGP metric is given and it is related to the curvature of 5D bulk. At the same time, the relation of arbitrary functions $\mu$ and $\nu$ in a class of Ricci-flat solutions is obtained from DGP brane metric.Comment: 8 pages, 1 figure, accepted by MPLA, added referenc

Thermalization of gluons in ultrarelativistic heavy ion collisions by including three-body interactions in a parton cascade

We develop a new 3+1 dimensional Monte Carlo cascade solving the kinetic on-shell Boltzmann equations for partons including the inelastic gg ggg pQCD processes. The back reaction channel is treated -- for the first time -- fully consistently within this scheme. An extended stochastic method is used to solve the collision integral. The frame dependence and convergency are studied for a fixed tube with thermal initial conditions. The detailed numerical analysis shows that the stochastic method is fully covariant and that convergency is achieved more efficiently than within a standard geometrical formulation of the collision term, especially for high gluon interaction rates. The cascade is then applied to simulate parton evolution and to investigate thermalization of gluons for a central Au+Au collision at RHIC energy. For this study the initial conditions are assumed to be generated by independent minijets with p_T > p_0=2 GeV. With that choice it is demonstrated that overall kinetic equilibration is driven mainly by the inelastic processes and is achieved on a scale of 1 fm/c. The further evolution of the expanding gluonic matter in the central region then shows almost an ideal hydrodynamical behavior. In addition, full chemical equilibration of the gluons follows on a longer timescale of about 3 fm/c.Comment: 121 pages with 55 figures, revised version. Two eps-figures and comments are added. Formula (54) which has typo in journal version is given correctl