17,068 research outputs found
Oblique amplitude modulation of dust-acoustic plasma waves
Theoretical and numerical studies are presented of the nonlinear amplitude
modulation of dust-acoustic (DA) waves propagating in an unmagnetized three
component, weakly-coupled, fully ionized plasma consisting of electrons,
positive ions and charged dust particles, considering perturbations oblique to
the carrier wave propagation direction. The stability analysis, based on a
nonlinear Schroedinger-type equation (NLSE), shows that the wave may become
unstable; the stability criteria depend on the angle between the
modulation and propagation directions. Explicit expressions for the instability
rate and threshold have been obtained in terms of the dispersion laws of the
system. The possibility and conditions for the existence of different types of
localized excitations have also been discussed.Comment: 21 pages, 6 figures, to appear in Physica Script
Shape transition and oblate-prolate coexistence in N=Z fpg-shell nuclei
Nuclear shape transition and oblate-prolate coexistence in nuclei are
investigated within the configuration space (, ,
, and ). We perform shell model calculations for Zn,
Ge, and Se and constrained Hartree-Fock (CHF) calculations for
Zn, Ge, Se, and Kr, employing an effective pairing
plus quadrupole residual interaction with monopole interactions. The shell
model calculations reproduce well the experimental energy levels of these
nuclei. From the analysis of potential energy surface in the CHF calculations,
we found shape transition from prolate to oblate deformation in these
nuclei and oblate-prolate coexistence at Se. The ground state of
Se has oblate shape, while the shape of Zn and Ge are
prolate. It is shown that the isovector matrix elements between and
orbits cause the oblate deformation for Se, and four-particle
four-hole () excitations are important for the oblate configuration.Comment: 6 pages, 5 figures, accepted for publication in Phys. Rev.
The Spin Mass of an Electron Liquid
We show that in order to calculate correctly the {\it spin current} carried
by a quasiparticle in an electron liquid one must use an effective "spin mass"
, that is larger than both the band mass, , which determines the
charge current, and the quasiparticle effective mass , which determines
the heat capacity. We present microscopic calculations of in a
paramagnetic electron liquid in three and two dimensions, showing that the mass
enhancement can be a very significant effect.Comment: 10 pages, 1 figur
Temperature dependence of the ohmic conductivity and activation energy of Pb1+y(Zr0.3Ti0.7)O3 thin films
The ohmic conductivity of the sol-gel derived Pb1+y(Zr0.3Ti0.7)O3 thin films
(with the excess lead y=0.0 to 0.4) are investigated using low frequency small
signal alternate current (AC) and direct current (DC) methods. Its temperature
dependence shows two activation energies of 0.26 and 0.12 eV depending on
temperature range and excess Pb levels. The former is associated with Pb3+
acceptor centers, while the latter could be due to a different defect level yet
to be identified.Comment: 13 pages, 3 figures, PostScript. Submitted to Applied Physics Letter
Spontaneous soliton formation and modulational instability in Bose-Einstein condensates
The dynamics of an elongated attractive Bose-Einstein condensate in an
axisymmetric harmonic trap is studied. It is shown that density fringes caused
by self-interference of the condensate order parameter seed modulational
instability. The latter has novel features in contradistinction to the usual
homogeneous case known from nonlinear fiber optics. Several open questions in
the interpretation of the recent creation of the first matter-wave bright
soliton train [Strecker {\it et al.} Nature {\bf 417} 150 (2002)] are
addressed. It is shown that primary transverse collapse, followed by secondary
collapse induced by soliton--soliton interactions, produce bursts of hot atoms
at different time scales.Comment: 4 pages, 3 figures. Phys. Rev. Lett. in pres
On the characterisation of paired monotone metrics
Hasegawa and Petz introduced the notion of dual statistically monotone
metrics. They also gave a characterisation theorem showing that
Wigner-Yanase-Dyson metrics are the only members of the dual family. In this
paper we show that the characterisation theorem holds true under more general
hypotheses.Comment: 12 pages, to appear on Ann. Inst. Stat. Math.; v2: changes made to
conform to accepted version, title changed as wel
Planetesimal disk evolution driven by embryo-planetesimal gravitational scattering
The process of gravitational scattering of planetesimals by a massive
protoplanetary embryo is explored theoretically. We propose a method to
describe the evolution of the disk surface density, eccentricity, and
inclination caused by the embryo-planetesimal interaction. It relies on the
analytical treatment of the scattering in two extreme regimes of the
planetesimal epicyclic velocities: shear-dominated (dynamically ``cold'') and
dispersion-dominated (dynamically ``hot''). In the former, planetesimal
scattering can be treated as a deterministic process. In the latter, scattering
is mostly weak because of the large relative velocities of interacting bodies.
This allows one to use the Fokker-Planck approximation and the two-body
approximation to explore the disk evolution. We compare the results obtained by
this method with the outcomes of the direct numerical integrations of
planetesimal orbits and they agree quite well. In the intermediate velocity
regime an approximate treatment of the disk evolution is proposed based on
interpolation between the two extreme regimes. We also calculate the rate of
embryo's mass growth in an inhomogeneous planetesimal disk and demonstrate that
it is in agreement with both the simulations and earlier calculations. Finally
we discuss the question of the direction of the embryo-planetesimal interaction
in the dispersion-dominated regime and demonstrate that it is repulsive. This
means that the embryo always forms a gap in the disk around it, which is in
contrast with the results of other authors. The machinery developed here will
be applied to realistic protoplanetary systems in future papers.Comment: 40 pages, 9 figures, submitted to A
Laboratory Measurement of the Pure Rotational Transitions of the HCNH+ and its Isotopic Species
The pure rotational transitions of the protonated hydrogen cyanide ion,
HCNH+, and its isotopic species, HCND+ and DCND+, were measured in the 107 -
482 GHz region with a source modulated microwave spectrometer. The ions were
generated in the cell with a magnetically confined dc-glow discharge of HCN
and/or DCN. The rotational constant B0 and the centrifugal distortion constant
D0 for each ion were precisely determined by a least-squares fitting to the
observed spectral lines. The observed rotational transition frequencies by
laboratory spectroscopy and the predicted ones are accurate in about 30 to 40
kHz and are useful as rest frequencies for astronomical searches of HCNH+ and
HCND+.Comment: 14 pages in TeX, 1 figures in JPE
Possible spin triplet superconductivity in NaCoOH0
Combining symmetry based considerations with inputs from available
experimental results, we make the case that a novel spin-triplet
superconductivity triggered by antiferromagnetic fluctuations may be realized
in the newly discovered layered cobaltide NaCoOHO. In the
proposed picture, unaccessable via resonating-valence-bond physics extrapolated
from half-filling, the pairing process is similar to that advanced for
SrRuO, but enjoys a further advantage coming from the hexagonal
structure of the Fermi-surface which gives a stronger pairing tendency.Comment: 4 page
Theory of multiwave mixing and decoherence control in qubit array system
We develop a theory to analyze the decoherence effect in a charged qubit
array system with photon echo signals in the multiwave mixing configuration. We
present how the decoherence suppression effect by the {\it bang-bang} control
with the pulses can be demonstrated in laboratory by using a bulk
ensemble of exciton qubits and optical pulses whose pulse area is even smaller
than . Analysis is made on the time-integated multiwave mixing signals
diffracted into certain phase matching directions from a bulk ensemble.
Depending on the pulse interval conditions, the cross over from the decoherence
acceleration regime to the decoherence suppression regime, which is a peculiar
feature of the coherent interaction between a qubit and the reservoir bosons,
may be observed in the time-integated multiwave mixing signals in the realistic
case including inhomogeneous broadening effect. Our analysis will successfully
be applied to precise estimation of the reservoir parameters from experimental
data of the direction resolved signal intensities obtained in the multiwave
mixing technique.Comment: 19 pages, 11 figure
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