104,905 research outputs found
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 , \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 with 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 = 200 GeV
We study the collective flow of open charm mesons and charmonia in Au+Au
collisions at = 200 GeV within the hadron-string-dynamics (HSD)
transport approach. The detailed studies show that the coupling of
mesons to the light hadrons leads to comparable directed and elliptic flow as
for the light mesons. This also holds approximately for mesons since
more than 50% of the final charmonia for central and mid-central collisions
stem from induced reactions in the transport calculations. The
transverse momentum spectra of mesons and '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 and 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
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