1,692 research outputs found
Flow tracing fidelity of scattering aerosol in laser Doppler velocimetry
An experimental method for determinating the flow tracing fidelity of a scattering aerosol used in laser Doppler velocimeters was developed with particular reference to the subsonic turbulence measurements. The method employs the measurement of the dynamic response of a flow seeding aerosol excited by acoustic waves. The amplitude and frequency of excitation were controlled to simulate the corresponding values of fluid turbulence components. Experimental results are presented on the dynamic response of aerosols over the size range from 0.1 to 2.0 microns in diameter and over the frequency range 100 Hz to 100 kHz. It was observed that unit density spherical scatterers with diameters of 0.2 microns followed subsonic air turbulence frequency components up to 100 kHz with 98 percent fidelity
Directional acoustic measurements by laser Doppler velocimeters
Laser Doppler velocimeters (LDVs) were used as velocity microphones to measure sound pressure level in the range of 90-130 db, spectral components, and two-point cross correlation functions for acoustic noise source identification. Close agreement between LDV and microphone data is observed. It was concluded that directional sensitivity and the ability to measure remotely make LDVs useful tools for acoustic measurement where placement of any physical probe is difficult or undesirable, as in the diagnosis of jet aircraft noise
A symmetrical laser Doppler velocity meter and its application to turbulence characterization
A symmetrical method of optical heterodyning of the Doppler shifted scattered laser radiation developed for velocity measurements with a minimal instrumental spectral broadening and a high signal-to-noise ratio. The method employs two laser beams incident on the moving scatterer and does not use any reference beam for heterodyning. The Doppler signal frequency is independent of the scattering angle and the signal possesses no receiving aperture broadening. Optical alignment is simple. Typical values of the instrumental spectral broadening were approximately 0.8 percent of the center frequency of the Doppler signal, and the signal-to-noise ratio was approximately 25 dB, obtained from an air flow system using submicron dioctylphthalate scattering aerosol. Experimental and theoretical studies were made on the characteristics of the Doppler signal and the effect of system parameters in turbulent flow measurement. The optimization process involved in the beam optics and in the use of a spatial filter is described. For localized flow measurement in any direction of the three-dimensional orthogonal coordinates, the system, using uncorrected optical components, had a sensing volume which can be described by a sensitive length of 600 microns and a diameter of 100 microns
Baryonic contributions to the dilepton spectra in relativistic heavy ion collisions
We investigate the baryonic contributions to the dilepton yield in high
energy heavy ion collisions within the context of a transport model. The
relative contribution of the baryonic and mesonic sources are examined. It is
observed that most dominant among the baryonic channels is the decay of
N*(1520) and mostly confined in the region below the rho peak. In a transport
theory implementation we find the baryonic contribution to the lepton pair
yield to be small.Comment: 11 pages, 8 figure
Validity of the Generalized Second Law of Thermodynamics of the Universe Bounded by the Event Horizon in Brane Scenario
In this paper, we examine the validity of the generalized second law of
thermodynamics (GSLT) of the universe bounded by the event horizon in
brane-world gravity. Here we consider homogeneous and isotropic model of the
universe filled with perfect fluid in one case and in another case holographic
dark energy model of the universe has been considered. The conclusions are
presented point wise.Comment: 8 pages, the paper has been accepted in EPJC for publication.
Conclusion has been modified an some references have been adde
Momentum dependence of drag coefficients and heavy flavour suppression in quark gluon plasma
The momentum dependence of the drag coefficient of heavy quarks propagating
through quark gluon plasma (QGP) has been evaluated. The results have been used
to estimate the nuclear suppression factor of charm and bottom quarks in QGP.
We observe that the momentum dependence of the transport coefficients plays
crucial role in the suppression of the heavy quarks and consequently in
discerning the properties of QGP using heavy flavours as a probe. We show that
the large suppression of the heavy quarks observed at RHIC and LHC is
predominantly due to the radiative losses. The suppression of in Pb+Pb
collisions at LHC energy - recently measured by the ALICE collaboration has
also been studied.Comment: Minor changes in the tex
Symmetric and anti-symmetric Landau parameters and magnetic properties of dense quark matter
We calculate the dimensionless Fermi liquid parameters (FLPs),
and , for spin asymmetric dense quark matter.
In general, the FLPs are infrared divergent due to the exchange of massless
gluons. To remove such divergences, the Hard Density Loop (HDL) corrected gluon
propagator is used. The FLPs so determined are then invoked to calculate
magnetic properties such as magnetization and magnetic
susceptibility of spin polarized quark matter. Finally, we investigate
the possibility of magnetic instability by studying the density dependence of
and .Comment: 14 pages, 5 figures, abstract and introduction modifified. Published
in Phys. Rev. C. 81, 054906 (2010
Energy and momentum relaxation of heavy fermion in dense and warm plasma
We determine the drag and the momentum diffusion coefficients of heavy
fermion in dense plasma. It is seen that in degenerate matter drag coefficient
at the leading order mediated by transverse photon is proportional to
while for the longitudinal exchange this goes as . We
also calculate the longitudinal diffusion coefficient to obtain the Einstein
relation in a relativistic degenerate plasma. Finally, finite temperature
corrections are included both for the drag and the diffusion coefficients.Comment: 8 pages, 1 eps figure, typos corrected and paragraphs rearranged.
Accepted for publication in Physical Review
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