4,498 research outputs found
Devasthal Fast Optical Telescope observations of Wolf-Rayet dwarf galaxy Mrk 996
The Devasthal Fast Optical Telescope (DFOT) is a 1.3 meter aperture optical
telescope, recently installed at Devasthal, Nainital. We present here the first
results using an \Ha filter with this telescope on a Wolf-Rayet dwarf galaxy
Mrk 996. The instrumental response and the \Ha sensitivity obtained with the
telescope are and respectively.
The \Ha flux and the equivalent width for Mrk~996 are estimated as and 96
respectively. The star formation rate is estimated as yr. Mrk~996 deviates from the radio-FIR correlation known for
normal star forming galaxies with a deficiency in its radio continuum. The
ionized gas as traced by \Ha emission is found in a disk shape which is
misaligned with respect to the old stellar disk. This misalignment is
indicative of a recent tidal interaction in the galaxy. We believe that
galaxy-galaxy tidal interaction is the main cause of the WR phase in Mrk~996.Comment: 13 pages, 2 figures Accepted for publication in "Journal of
Astrophysics and Astronomy
Four Generations, Higgs Physics, and the MSSM
We consider the effects of a fourth generation of chiral fermions within the
MSSM. Such a model offers the possibility of having the lightest neutral Higgs
boson significantly heavier than in the three generation MSSM. The model is
highly constrained by precision electroweak data, along with Higgs searches at
the Tevatron. In addition, the requirements of perturbative unitarity and
direct searches for heavy quarks imply that the four generation MSSM is only
consistent for tan beta ~ 1 and highly tuned 4th generation fermion masses.Comment: References added and minor typographical errors correcte
Dusty Plasma Experimental (DPEx) device for complex plasma experiments with flow
A versatile table-top dusty plasma experimental (DPEx) device to study flow
induced excitations of linear and nonlinear waves/structures in a complex
plasma is presented. In this {}-shaped apparatus a DC glow discharge
plasma is produced between a disc shaped anode and a grounded long cathode
{tray} by applying a high voltage DC in the background of a neutral gas
{(Argon)} and subsequently a dusty plasma is created by introducing micron
sized dust particles that get charged and levitated in the sheath region. A
flow of the dust particles is induced in a controlled manner by adjusting the
pumping speed and the gas flow rate into the device. A full characterisation of
the plasma, using Langmuir and emissive probe data, and that of the dusty
plasma using particle tracking data with the help of an idl based (super)
Particle Identification and Tracking (sPIT) code is reported. Experimental
results on the variation of the dust flow velocity as a function of the neutral
pressure and the gas flow rate are given. {The neutral drag force acting on the
particles and the Epstein coefficient are estimated from the initial
acceleration of the particles}. The potential experimental capabilities of the
device for conducting fundamental studies of flow induced instabilities are
discussed.Comment: 7 pages, 6 figure
Experimental investigation of flow induced dust acoustic shock waves in a complex plasma
We report on experimental observations of flow induced large amplitude
dust-acoustic shock waves (DASW) in a complex plasma. The experiments have been
carried out in a shaped DC glow discharge experimental device using
kaolin particles as the dust component in a background of Argon plasma. A
strong supersonic flow of the dust fluid is induced by adjusting the pumping
speed and neutral gas flow into the device. An isolated copper wire mounted on
the cathode acts as a potential barrier to the flow of dust particles. A sudden
change of gas flow rate is used to trigger the onset of high velocity dust
acoustic shocks whose dynamics are captured by fast video pictures of the
evolving structures. The physical characteristics of these shocks are
delineated through a parametric scan of their dynamical properties over a range
of flow speeds and potential hill heights. The observed evolution of the shock
waves and their propagation characteristics are found to compare well with
model numerical results based on a modified Korteweg-de-Vries-Burgers type
equation
Flowing dusty plasma experiments: Generation of flow and measurement techniques
A variety of experimental techniques for the generation of
subsonic/supersonic dust fluid flows and means of measuring such flow
velocities are presented. The experiments have been carried out in a
shaped Dusty Plasma Experimental (DPEx) device with micron size
kaolin/Melamine Formaldehyde (MF) particles embedded in a background of Argon
plasma created by a direct current (DC) glow discharge. A stationary dust cloud
is formed over the cathode region by precisely balancing the pumping speed and
gas flow rate. A flow of dust particles/fluid is generated by additional gas
injection from a single or dual locations or by altering the dust confining
potential. The flow velocity is then estimated by three different techniques,
namely, by super Particle Identification (sPIT) code, Particle Image
Velocimetry (PIV) analysis and the excitation of Dust Acoustic Waves (DAWs).
The results obtained from these three different techniques along with their
merits and demerits are discussed. An estimation of the neutral drag force
responsible for the generation as well as the attenuation of the dust fluid
flow is made. These techniques can be usefully employed in laboratory devices
to investigate linear and non-linear collective excitations in a flowing dusty
plasma.Comment: 8 pages, 10 figure
Theoretical study of head-on collision of dust acoustic solitary waves in a strongly coupled complex plasma
We investigate the propagation characteristics of two counter propagating
dust acoustic solitary waves (DASWs) undergoing a head-on collision, in the
presence of strong coupling between micron sized charged dust particles in a
complex plasma. A coupled set of nonlinear dynamical equations describing the
evolution of the two DASWs using the extended Poincar\'e-Lighthill-Kuo
perturbation technique is derived. The nature and extent of post collision
phase-shifts of these solitary waves are studied over a wide range of dusty
plasma parameters in a strongly and a weakly coupled medium. We find a
significant change in the nature and amount of phase delay in the strongly
coupled regime as compared to a weakly coupled regime. The phase shift is seen
to change its sign beyond a threshold value of compressibility of the medium
for a given set of dusty plasma parameters.Comment: 8 pages, 5 figure
Optical spectroscopy of star-forming regions in dwarf Wolf-Rayet galaxies
We present here spatially-resolved optical spectroscopic observations of four
nearby dwarf Wolf-Rayet (WR) galaxies. The ages of the most recent starburst
events in these galaxies are found between 3 and 10 Myr. The gas-phase
metallicities [12+log(O/H)] for the spatially-resolved star-forming regions are
derived using several indicators. The star-forming regions within the galaxies
are found chemically homogeneous within the uncertainties in the estimates.
Nitrogen-enrichment as expected in the WR regions is not detected. This implies
that metal-enrichment due to supernovae explosions in the most recent
star-forming episode is not being detected here. It is suggested that the newly
synthesized metals still reside in hot gas-phase. The metals from the previous
episodes, cooled by now and well mixed across the whole extent of galaxies, are
making galaxies chemically homogeneous with normal N/O ratio. These galaxies
are residing in dense environments with galaxy density in the range of
Mpc.Comment: 24 pages, 14 figures, Accepted for publication in MNRA
Boltzmann equation with a nonlocal collision term and the resultant dissipative fluid dynamics
Starting with the relativistic Boltzmann equation where the collision term
was generalized to include gradients of the phase-space distribution function,
we recently presented a new derivation of the equations for the relativistic
dissipative fluid dynamics. We compared them with the corresponding equations
obtained in the standard Israel-Stewart and related approaches. Our method
generates all the second-order terms that are allowed by symmetry, some of
which have been missed by the traditional approaches, and the coefficients of
other terms are altered. The first-order or Navier-Stokes equation too receives
a small correction. Here we outline this work for the general audience.Comment: Invited talk given by Rajeev Bhalerao at Rencontres du Vietnam,
International Conference on 'Heavy Ion Collisions in the LHC Era', 15-21 July
2012, Quy Nhon, Vietna
Complete relativistic second-order dissipative hydrodynamics from the entropy principle
We present a new derivation of relativistic dissipative hydrodynamic
equations, which invokes the second law of thermodynamics for the entropy
four-current expressed in terms of the single-particle phase-space distribution
function obtained from Grad's 14-moment approximation. This derivation is
complete in the sense that all the second-order transport coefficients are
uniquely determined within a single theoretical framework. In particular, this
removes the long-standing ambiguity in the relaxation time for bulk viscosity
thereby eliminating one of the uncertainties in the extraction of the shear
viscosity to entropy density ratio from confrontation with the anisotropic flow
data in relativistic heavy-ion collisions. We find that in the one-dimensional
scaling expansion, these transport coefficients prevent the occurrence of
cavitation even for rather large values of the bulk viscosity estimated in
lattice QCD.Comment: 5 pages, 2 figures, version to appear in PRC (Rapid Comm
Associated b-Quark Higgs Boson Production at the LHC
The associated production of a Higgs boson with a b quark is a discovery mode
for an MSSM Higgs boson at large tan beta. We present updates on the production
rate at the LHC, along with a discussion of the importance of the SQCD
corrections from squark and gluino loops. We also discuss the purely
electroweak contributions.Comment: 35th International Conference of High Energy Physics - ICHEP2010,
July 22-28, 2010, Paris Franc
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