3,990 research outputs found
Turbulent thermal diffusion of aerosols in geophysics and laboratory experiments
We discuss a new phenomenon of turbulent thermal diffusion associated with
turbulent transport of aerosols in the atmosphere and in laboratory
experiments. The essence of this phenomenon is the appearance of a nondiffusive
mean flux of particles in the direction of the mean heat flux, which results in
the formation of large-scale inhomogeneities in the spatial distribution of
aerosols that accumulate in regions of minimum mean temperature of the
surrounding fluid. This effect of turbulent thermal diffusion was detected
experimentally. In experiments turbulence was generated by two oscillating
grids in two directions of the imposed vertical mean temperature gradient. We
used Particle Image Velocimetry to determine the turbulent velocity field, and
an Image Processing Technique based on an analysis of the intensity of Mie
scattering to determine the spatial distribution of aerosols. Analysis of the
intensity of laser light Mie scattering by aerosols showed that aerosols
accumulate in the vicinity of the minimum mean temperature due to the effect of
turbulent thermal diffusion. Geophysical applications of the obtained results
are discussed.Comment: 9 pages, 6 figures, revtex
decays
Effective chiral theory of mesons is applied to study the four decay modes of
. Theoretical values of the branching ratios are in
agreement with the data. The theory predicts that the resonance plays a
dominant role in these decays. There is no new parameter in this study.Comment: 12 pages and one figur
Turbulent thermal diffusion in a multi-fan turbulence generator with the imposed mean temperature gradient
We studied experimentally the effect of turbulent thermal diffusion in a
multi-fan turbulence generator which produces a nearly homogeneous and
isotropic flow with a small mean velocity. Using Particle Image Velocimetry and
Image Processing techniques we showed that in a turbulent flow with an imposed
mean vertical temperature gradient (stably stratified flow) particles
accumulate in the regions with the mean temperature minimum. These experiments
detected the effect of turbulent thermal diffusion in a multi-fan turbulence
generator for relatively high Reynolds numbers. The experimental results are in
compliance with the results of the previous experimental studies of turbulent
thermal diffusion in oscillating grids turbulence (Buchholz et al. 2004;
Eidelman et al. 2004). We demonstrated that turbulent thermal diffusion is an
universal phenomenon. It occurs independently of the method of turbulence
generation, and the qualitative behavior of particle spatial distribution in
these very different turbulent flows is similar. Competition between turbulent
fluxes caused by turbulent thermal diffusion and turbulent diffusion determines
the formation of particle inhomogeneities.Comment: 9 pages, 9 figure, REVTEX4, Experiments in Fluids, in pres
Transition phenomena in unstably stratified turbulent flows
We study experimentally and theoretically transition phenomena caused by the
external forcing from Rayleigh-Benard convection with the large-scale
circulation (LSC) to the limiting regime of unstably stratified turbulent flow
without LSC whereby the temperature field behaves like a passive scalar. In the
experiments we use the Rayleigh-B\'enard apparatus with an additional source of
turbulence produced by two oscillating grids located nearby the side walls of
the chamber. When the frequency of the grid oscillations is larger than 2 Hz,
the large-scale circulation (LSC) in turbulent convection is destroyed, and the
destruction of the LSC is accompanied by a strong change of the mean
temperature distribution. However, in all regimes of the unstably stratified
turbulent flow the ratio varies slightly (even in the range
of parameters whereby the behaviour of the temperature field is different from
that of the passive scalar). Here are the integral scales of
turbulence along x, y, z directions, T and \theta are the mean and fluctuating
parts of the fluid temperature. At all frequencies of the grid oscillations we
have detected the long-term nonlinear oscillations of the mean temperature. The
theoretical predictions based on the budget equations for turbulent kinetic
energy, turbulent temperature fluctuations and turbulent heat flux, are in
agreement with the experimental results.Comment: 14 pages, 14 figures, REVTEX4-1, revised versio
Parton distribution functions from the precise NNLO QCD fit
We report the parton distribution functions (PDFs) determined from the NNLO
QCD analysis of the world inclusive DIS data with account of the precise NNLO
QCD corrections to the evolution equations kernel. The value of strong coupling
constant \alpha_s^{NNLO}(M_Z)=0.1141(14), in fair agreement with one obtained
using the earlier approximate NNLO kernel by van Neerven-Vogt. The intermediate
bosons rates calculated in the NNLO using obtained PDFs are in agreement to the
latest Run II results.Comment: 8 pages, LATEX, 2 figures (EPS
Pion pole contribution to hadronic light-by-light scattering and muon anomalous magnetic moment
We derive an analytic result for the pion pole contribution to the
light-by-light scattering correction to the anomalous magnetic moment of the
muon, . Using the vector meson dominance model (VMD) for
the pion transition form factor, we obtain .Comment: 4 pages, revte
Constraints on narrow exotic states from K+p and K0_Lp scattering data
We consider the effect of exotic S=+1 resonances Theta+ and Theta++ on K+p
elastic scattering data (total cross section) and the process K0_Lp-->K0_Sp.
Data near the observed Theta+(1540) are examined for evidence of additional
states. The width limit for a Theta++ state is reconsidered and shown to be
much less than 1 MeV.Comment: 4 pages, 3 eps figures; minor corrections, one fig adde
Hadronic Contributions to the Photon Vacuum Polarization and their Role in Precision Physics
I review recent evaluations of the hadronic contribution to the shift in the
fine structure constant and to the anomalous magnetic moment of the muon.
Substantial progress in a precise determination of these important observables
is a consequence of substantially improved total cross section measurement by
the CMD-2 and BES II collaborations and an improved theoretical understanding.
Prospects for further possible progress is discussed.Comment: 17 pages 7 figures 2 tables, update: incl. CMD-2 data, reference
Hysteresis phenomenon in turbulent convection
Coherent large-scale circulations of turbulent thermal convection in air have
been studied experimentally in a rectangular box heated from below and cooled
from above using Particle Image Velocimetry. The hysteresis phenomenon in
turbulent convection was found by varying the temperature difference between
the bottom and the top walls of the chamber (the Rayleigh number was changed
within the range of ). The hysteresis loop comprises the one-cell
and two-cells flow patterns while the aspect ratio is kept constant (). We found that the change of the sign of the degree of the anisotropy of
turbulence was accompanied by the change of the flow pattern. The developed
theory of coherent structures in turbulent convection (Elperin et al. 2002;
2005) is in agreement with the experimental observations. The observed coherent
structures are superimposed on a small-scale turbulent convection. The
redistribution of the turbulent heat flux plays a crucial role in the formation
of coherent large-scale circulations in turbulent convection.Comment: 10 pages, 9 figures, REVTEX4, Experiments in Fluids, 2006, in pres
New high order relations between physical observables in perturbative QCD
We exploit the fact that within massless perturbative QCD the same Green's
function determines the hadronic contribution to the decay width and the
moments of the cross section. This allows one to obtain relations
between physical observables in the two processes up to an unprecedented high
order of perturbative QCD. A precision measurement of the decay width
allows one then to predict the first few moments of the spectral density in
annihilations integrated up to with high accuracy.
The proposed tests are in reach of present experimental capabilities.Comment: 7 pages, Latex, no figure
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