13,333 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
Electron Correlations and Two-Photon States in Polycyclic Aromatic Hydrocarbon Molecules: A Peculiar Role of Geometry
We present numerical studies of one- and two-photon excited states ordering
in a number of polycyclic aromatic hydrocarbon molecules: coronene,
hexa-peri-hexabenzocoronene and circumcoronene, all possessing point
group symmetry versus ovalene with symmetry, within the
Pariser-Parr-Pople model of interacting -electrons. The calculated
energies of the two-photon states as well as their relative two-photon
absorption cross-sections within the interacting model are qualitatively
different from single-particle descriptions. More remarkably, a peculiar role
of molecular geometry is found. The consequence of electron correlations is far
stronger for ovalene, where the lowest spin-singlet two-photon state is a
quantum superposition of pairs of lowest spin triplet states, as in the linear
polyenes. The same is not true for group hydrocarbons. Our work
indicates significant covalent character, in valence bond language, of the
ground state, the lowest spin triplet state and a few of the lowest two-photon
states in ovalene but not in those with symmetry.Comment: 11 pages, 3 figures, 3 table
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
Spinodal decomposition: An alternate mechanism of phase conversion
The scenario of homogeneous nucleation is investigated for a first order
quark-hadron phase transition in a rapidly expanding background of quark gluon
plasma. It is found that significant supercooling is possible before
hadronization begins. This study also suggests that spinodal decomposition
competes with nucleation and may provide an alternative mechanism for phase
conversion.Comment: LaTeX, 4 pages with 3 Postscript figures. Talk given at International
Conference on Physics and Astrophysics of Quark Gluon Plasma (ICPAQGP 2001),
Nov. 26-30, 2001, Jaipur, Indi
Nonlinear dynamics of large amplitude dust acoustic shocks and solitary pulses in dusty plasmas
We present a fully nonlinear theory for dust acoustic (DA) shocks and DA
solitary pulses in a strongly coupled dusty plasma, which have been recently
observed experimentally by Heinrich et al. [Phys. Rev. Lett. 103, 115002
(2009)], Teng et al. [Phys. Rev. Lett. 103, 245005 (2009)], and Bandyopadhyay
et al. [Phys. Rev. Lett. 101, 065006 (2008)]. For this purpose, we use a
generalized hydrodynamic model for the strongly coupled dust grains, accounting
for arbitrary large amplitude dust number density compressions and potential
distributions associated with fully nonlinear nonstationary DA waves.
Time-dependent numerical solutions of our nonlinear model compare favorably
well with the recent experimental works (mentioned above) that have reported
the formation of large amplitude non-stationary DA shocks and DA solitary
pulses in low-temperature dusty plasma discharges.Comment: 9 pages, 4 figures. To be published in Physical Review
Theory of nonlinear optical properties of phenyl-substituted polyacetylenes
In this paper we present a theoretical study of the third-order nonlinear
optical properties of poly(diphenyl)polyacetylene (PDPA) pertaining to the
third-harmonic-generation (THG) process. We study the aforesaid process in
PDPA's using both the independent electron Hueckel model, as well as
correlated-electron Pariser-Parr-Pople (P-P-P) model. The P-P-P model based
calculations were performed using various configuration interaction (CI)
methods such as the the multi-reference-singles-doubles CI (MRSDCI), and the
quadruples-CI (QCI) methods, and the both longitudinal and the transverse
components of third-order susceptibilities were computed. The Hueckel model
calculations were performed on oligo-PDPA's containing up to fifty repeat
units, while correlated calculations were performed for oligomers containing up
to ten unit cells. At all levels of theory, the material exhibits highly
anisotropic nonlinear optical response, in keeping with its structural
anisotropy. We argue that the aforesaid anisotropy can be divided over two
natural energy scales: (a) the low-energy response is predominantly
longitudinal and is qualitatively similar to that of polyenes, while (b) the
high-energy response is mainly transverse, and is qualitatively similar to that
of trans-stilbene.Comment: 13 pages, 7 figures (included), to appear in Physical Review B (April
15, 2004
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