6,341 research outputs found
Nonlinear wave-wave interactions in quantum plasmas
Wave-wave interaction in plasmas is a topic of important research since the
16th century. The formation of Langmuir solitons through the coupling of
high-frequency (hf) Langmuir and low-frequency (lf) ion-acoustic waves, is one
of the most interesting features in the context of turbulence in modern plasma
physics. Moreover, quantum plasmas, which are ubiquitous in ultrasmall
electronic devices, micromechanical systems as well as in dense astrophysical
environments are a topic of current research. In the light of notable interests
in such quantum plasmas, we present here a theoretical investigation on the
nonlinear interaction of quantum Langmuir waves (QLWs) and quantum ion-acoustic
waves (QIAWs), which are governed by the one-dimensional quantum Zakharov
equations (QZEs). It is shown that a transition to spatiotemporal chaos (STC)
occurs when the length scale of excitation of linear modes is larger than that
of the most unstable ones. Such length scale is, however, to be larger
(compared to the classical one) in presence of the quantum tunneling effect.
The latter induces strong QIAW emission leading to the occurrence of collision
and fusion among the patterns at an earlier time than the classical case.
Moreover, numerical simulation of the QZEs reveals that many solitary patterns
can be excited and saturated through the modulational instability (MI) of
unstable harmonic modes. In a longer time, these solitons are seen to appear in
the state of STC due to strong QIAW emission as well as by the collision and
fusion in stochastic motion. The energy in the system is thus strongly
redistributed, which may switch on the onset of Langmuir turbulence in quantum
plasmas.Comment: 6 pages, 6 figures (To appear in AIP Conf. Proceedings 2010
Rossby rogons in atmosphere and in the solar photosphere
The generation of Rossby rogue waves (Rossby rogons), as well as the
excitation of bright and dark Rossby envelpe solitons are demonstrated on the
basis of the modulational instability (MI) of a coherent Rossby wave packet.
The evolution of an amplitude modulated Rossby wave packet is governed by
one-dimensional (1D) nonlinear Schr\"odinger equation (NLSE). The latter is
used to study the amplitude modulation of Rossby wave packets for fluids in
Earth's atmosphere and in the solar photosphere. It is found that an ampitude
modulated Rossby wave packet becomes stable (unstable) against
quasi-stationary, long wavelength (in comparision with the Rossby wave length)
perturbations, when the carrier Rossby wave number satisfies or
or ). It is also shown that a
Rossby rogon or a bright Rossby envelope soliton may be excited in the shallow
water approximation for the Rossby waves in solar photosphere. However, the
excitation of small or large scale perturbations may be possible for magnetized
plasmas in the ionosphereic layer.Comment: 6 pages, 5 figures; To appear in Europhysics Letter
Hot Nuclear Matter : A Variational Approach
We develop a nonperturbative technique in field theory to study properties of
infinite nuclear matter at zero temperature as well as at finite temperatures.
Here we dress the nuclear matter with off-mass shell pions. The techniques of
thermofield dynamics are used for finite temperature calculations. Equation of
state is derived from the dynamics of the interacting system in a self
consistent manner. The transition temperature for nuclear matter appears to be
around 15 MeV.Comment: 16 pages, IP/BBSR/91-3
Neutron matter - Quark matter phase transition and Quark star
We consider the neutron matter quark matter phase transition along with
possible existence of hybrid quark stars. The equation of state for neutron
matter is obtained using a nonperturbative method with pion dressing of the
neutron matter and an analysis similar to that of symmetric nuclear matter. The
quark matter sector is treated perturbatively in the small distance domain. For
bag constant =148 MeV, a first order phase transition is seen. In the
context of neutron quark hybrid stars, Tolman-Oppenheimer-Volkoff equations are
solved using the equations of state for quark matter and for neutron matter
with a phase transition as noted earlier. Stable solutions for such stars are
obtained with the Chandrasekhar limit as 1.58 and radius around 10
km. The bulk of the star is quark matter with a thin crust of neutron matter of
less than a kilometer.Comment: 28 pages including 9 figures, Revtex, IP/BBSR/92-8
Flux enhancement in the inner region of a geometrically and optically thick accretion disk
The surface flux (and the corresponding observed flux) of a geometrically
thick ``funnel'' shaped disk is computed taking into account the radiation
impinging on the surface from other parts of the disk. It is found that the
ratio of the maximum apparent luminosity to the real luminosity of the disk is
only a factor even when the opening angle of the disk is small
(). Thus, geometrically beamed emission from ``funnel'' shaped
sub-Eddington disks around stellar mass black holes, cannot explain the
Ultra-Luminous X-ray sources detected in nearby galaxies.Comment: accepted for publication in Ap
Generation of wakefields by whistlers in spin quantum magnetoplasmas
The excitation of electrostatic wakefields in a magnetized spin quantum
plasma by the classical as well as the spin-induced ponderomotive force (CPF
and SPF, respectively) due to whistler waves is reported. The nonlinear
dynamics of the whistlers and the wakefields is shown to be governed by a
coupled set of nonlinear Schr\"{o}dinger (NLS) and driven Boussinesq-like
equations. It is found that the quantum force associated with the Bohm
potential introduces two characteristic length scales, which lead to the
excitation of multiple wakefields in a strongly magnetized dense plasma (with a
typical magnetic field strength T and particle density
m), where the SPF strongly dominates over the CPF.
In other regimes, namely T and
m, where the SPF is comparable to the CPF, a plasma wakefield can also
be excited self-consistently with one characteristic length scale. Numerical
results reveal that the wakefield amplitude is enhanced by the quantum
tunneling effect, however it is lowered by the external magnetic field. Under
appropriate conditions, the wakefields can maintain high coherence over
multiple plasma wavelengths and thereby accelerate electrons to extremely high
energies. The results could be useful for particle acceleration at short
scales, i.e. at nano- and micrometer scales, in magnetized dense plasmas where
the driver is the whistler wave instead of a laser or a particle beam.Comment: 8 pages, 2 figures; Revised version to appear in Physics of Plasmas
(Dec. 2010 issue
Supernovae as Probes of Extra Dimensions
Since the dawn of the new millennium, there has been a revived interest in
the concept of extra dimensions.In this scenario all the standard model matter
and gauge fields are confined to the 4 dimensions and only gravity can escape
to higher dimensions of the universe.This idea can be tested using table-top
experiments, collider experiments, astrophysical or cosmological observations.
The main astrophysical constraints come from the cooling rate of supernovae,
neutron stars, red giants and the sun. In this article, we consider the energy
loss mechanism of SN1987A and study the constraints it places on the number and
size of extra dimensions and the higher dimensional Planck scale.Comment: 5 pages, no figures, new references are adde
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