127 research outputs found
Modulational instability of ion-acoustic wave packets in quantum pair-ion plasmas
Amplitude modulation of quantum ion-acoustic waves (QIAWs) in a quantum
electron-pair-ion plasma is studied. It is shown that the quantum coupling
parameter (being the ratio of the plasmonic energy density to the Fermi
energy) is ultimate responsible for the modulational stability of QIAW packets,
without which the wave becomes modulational unstable. New regimes for the
modulational stability (MS) and instability (MI) are obtained in terms of
and the positive to negative ion density ratio . The growth rate of MI
is obtained, the maximum value of which increases with and decreases
with . The results could be important for understanding the origin of
modulated QIAW packets in the environments of dense astrophysical objects,
laboratory negative ion plasmas as well as for the next generation laser solid
density plasma experiments.Comment: 4 pages, 2 figures (to appear in Astrophysics and Space Science
Spin magnetosonic shocks in quantum plasmas
The one-dimensional shock structures of magnetosonic waves (MSWs) propagating
in a dissipative quantum plasma medium is studied. A quantum
magnetohydrodynamic (QMHD) model is used to take into account the quantum force
term due to Bohm potential and the pressure-like spin force term for electrons.
The nonlinear evolution (Korteweg de-Vries-Burger) equation, derived to
describe the dynamics of small amplitude MSWs, where the dissipation is
provided by the plasma resistivity, is solved numerically to obtain both
oscillatory and monotonic shock structures. The shock strength decreases with
increasing the effects of collective tunneling and increases with increasing
the effects of spin alignment. The theoretical results could be of importance
for astrophysical (e.g., magnetars) as well as for ultracold laboratory plasmas
(e.g., Rydberg plasmas).Comment: 8 pages, 4 figure
Synchronization of spatiotemporal semiconductor lasers and its application in color image encryption
Optical chaos is a topic of current research characterized by
high-dimensional nonlinearity which is attributed to the delay-induced
dynamics, high bandwidth and easy modular implementation of optical feedback.
In light of these facts, which adds enough confusion and diffusion properties
for secure communications, we explore the synchronization phenomena in
spatiotemporal semiconductor laser systems. The novel system is used in a
two-phase colored image encryption process. The high-dimensional chaotic
attractor generated by the system produces a completely randomized chaotic time
series, which is ideal in the secure encoding of messages. The scheme thus
illustrated is a two-phase encryption method, which provides sufficiently high
confusion and diffusion properties of chaotic cryptosystem employed with unique
data sets of processed chaotic sequences. In this novel method of cryptography,
the chaotic phase masks are represented as images using the chaotic sequences
as the elements of the image. The scheme drastically permutes the positions of
the picture elements. The next additional layer of security further alters the
statistical information of the original image to a great extent along the
three-color planes. The intermediate results during encryption demonstrate the
infeasibility for an unauthorized user to decipher the cipher image. Exhaustive
statistical tests conducted validate that the scheme is robust against noise
and resistant to common attacks due to the double shield of encryption and the
infinite dimensionality of the relevant system of partial differential
equations.Comment: 20 pages, 11 figures; Article in press, Optics Communications (2011
Amplitude modulated drift wave packets in a nonuniform magnetoplasma
We consider the amplitude modulation of low-frequency, long wavelength
electrostatic drift wave packets in a nonuniform magnetoplasma with the effects
of equilibrium density, electron temperature and magnetic field
inhomogeneities. The dynamics of the modulated drift wave packet is governed by
a nonlinear Schr\"odinger equation. The latter is used to study the
modulational instability of a Stoke's wave train to a small longitudinal
perturbation. It is shown that the drift wave packet is stable (unstable)
against the modulation when the drift wave number lies in
. Thus, the modulated drift wave packet can propagate in the
form of bright and dark envelope solitons or as a drift wave rogon.Comment: 4 pages, 4figure
Entangled state preparation via dissipation-assisted adiabatic passages
The main obstacle for coherent control of open quantum systems is decoherence
due to different dissipation channels and the inability to precisely control
experimental parameters. To overcome these problems we propose to use
dissipation-assisted adiabatic passages. These are relatively fast processes
where the presence of spontaneous decay rates corrects for errors due to
non-adiabaticity while the system remains in a decoherence-free state and
behaves as predicted for an adiabatic passage. As a concrete example we present
a scheme to entangle atoms by moving them in and out of an optical cavity.Comment: 11 pages, 7 figures, minor changes, accepted for publication in Phys.
Rev.
The rms-flux relations in different branches in Cyg X-2
In this paper, the rms-flux (root mean square-flux) relation along the
Z-track of the bright Z-Source Cyg X-2 is analyzed using the observational data
of Rossi X-ray Timing Explorer (RXTE). Three types of rms-flux relations, i.e.
positive, negative, and 'arch'-like correlations are found in different
branches. The rms is positively correlated with flux in normal branch (NB), but
anti-correlated in the vertical horizontal branch (VHB). The rms-flux relation
shows an 'arch'-like shape in the horizontal branch (HB). We also try to
explain this phenomenon using existing models.Comment: Accepted for publication in Astrophysics & Space Scienc
Monitoring Effect of Spatial Growth on Land Surface Temperature in Dhaka
Spatial urban growth and its impact on land surface temperature (LST) is a high priority environmental issue for urban policy. Although the impact of horizontal spatial growth of cities on LST is well studied, the impact of the vertical spatial distribution of buildings on LST is under-investigated. This is particularly true for cities in sub-tropical developing countries. In this study, TerraSAR-X add-on for Digital Elevation Measurement (TanDEM-XDEM), Advanced Spaceborne Thermal Emission and Reflection (ASTER)-Global Digital Elevation Model (GDEM), and ALOS World 3D-30m (AW3D30) based Digital Surface Model (DSM) data were used to investigate the vertical growth of the Dhaka Metropolitan Area (DMA) in Bangladesh. Thermal Infrared (TIR) data (10.6-11.2µm) of Landsat-8 were used to investigate the seasonal variations in LST. Thereafter, the impact of horizontal and vertical spatial growth on LST was studied. The result showed that: (a) TanDEM-X DSM derived building height had a higher accuracy as compared to other existing DSM that reveals mean building height of the Dhaka city is approximately 10 m, (b) built-up areas were estimated to cover approximately 94%, 88%, and 44% in Dhaka South City Corporation (DSCC), Dhaka North City Corporation (DNCC), and Fringe areas, respectively, of DMA using a Support Vector Machine (SVM) classification method, (c) the built-up showed a strong relationship with LST (Kendall tau coefficient of 0.625 in summer and 0.483 in winter) in comparison to vertical growth (Kendall tau coefficient of 0.156 in the summer and 0.059 in the winter), and (d) the ‘low height-high density’ areas showed high LST in both seasons. This study suggests that vertical development is better than horizontal development for providing enough open spaces, green spaces, and preserving natural features. This study provides city planners with a better understating of sustainable urban planning and can promote the formulation of action plans for appropriate urban development policies
Nonlinear gravito-electrostatic waves in self-gravitating complex plasma in presence of ion-drag effects
Non-exponential decay in quantum field theory and in quantum mechanics: the case of two (or more) decay channels
We study the deviations from the exponential decay law, both in quantum field
theory (QFT) and quantum mechanics (QM), for an unstable particle which can
decay in (at least) two decay channels. After a review of general properties of
non-exponential decay in QFT and QM, we evaluate in both cases the decay
probability that the unstable particle decays in a given channel in the time
interval between and An important quantity is the ratio of the
probability of decay into the first and the second channel: this ratio is
constant in the Breit-Wigner limit (in which the decay law is exponential) and
equals the quantity , where and
are the respective tree-level decay widths. However, in the full
treatment (both for QFT and QM) it is an oscillating function around the mean
value and the deviations from this mean value can be
sizable. Technically, we study the decay properties in QFT in the context of a
superrenormalizable Lagrangian with scalar particles and in QM in the context
of Lee Hamiltonians, which deliver formally analogous expressions to the QFT
case.Comment: 32 pages, 10 figures. To appear in "Foundations of Physics
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