14,433 research outputs found
Superfluid and Fermi liquid phases of Bose-Fermi mixtures in optical lattices
We describe interacting mixtures of ultracold bosonic and fermionic atoms in
harmonically confined optical lattices. For a suitable choice of parameters we
study the emergence of superfluid and Fermi liquid (non-insulating) regions out
of Bose-Mott and Fermi-band insulators, due to finite Boson and Fermion
hopping. We obtain the shell structure for the system and show that angular
momentum can be transferred to the non-insulating regions from
Laguerre-Gaussian beams, which combined with Bragg spectroscopy can reveal all
superfluid and Fermi liquid shells.Comment: 4 pages, 2 figure
On Simulating Liouvillian Flow From Quantum Mechanics Via Wigner Functions
The interconnection between quantum mechanics and probabilistic classical
mechanics for a free relativistic particle is derived in terms of Wigner
functions (WF) for both Dirac and Klein-Gordon (K-G) equations. Construction of
WF is achieved by first defining a bilocal 4-current and then taking its
Fourier transform w.r.t. the relative 4-coordinate. The K-G and Proca cases
also lend themselves to a closely parallel treatment provided the Kemmer-
Duffin beta-matrix formalism is employed for the former. Calculation of WF is
carried out in a Lorentz-covariant fashion by standard `trace' techniques. The
results are compared with a recent derivation due to Bosanac.Comment: 9 pages, Latex; email: [email protected]
Comments on the paper ``Bare Quark Surfacees of Strange Stars and Electron-Positron Pair Emission''
In a recent paper (Ushov, PRL, 80, 230, 1998), it has been claimed that the
bare surface of a strange star can emit electron-positron pairs of luminosity
\~10^{51} ergs/s for about 10s. If true, obviously, this mechanism may explain
the origin of cosmic Gamma Ray Bursts. However, we point out that such a
mechanism is does not work because (i) if pair production really occurs the
supposed pre-existing supercritical electric field will be quenched and this
discharge process may at best release ~10^{24} ergs of electromagnetic energy,
and (ii) there is no way by which the trapped core thermal energy of few
10^{52} ergs can be transmitted electromagnetically on a time scale of ~10s or
even on a much larger time scale. The only way the hot core can cool on a time
scale of ~10 s or much shorter is by the well known process of emission of
nu-antinu pairs.Comment: Final version accepted in Phy. Rev. Lett. Main conclusion that the
mechanism by Usov does not work remains unchanged,
[email protected]
Meanings in motion and faces: Developmental associations between the processing of intention from geometrical animations and gaze detection accuracy
Aspects of face processing, on the one hand, and theory of mind (ToM) tasks, on the other hand, show specific impairment in autism. We aimed to discover whether a correlation between tasks tapping these abilities was evident in typically developing children at two developmental stages. One hundred fifty-four normal children (6-8 years and 16-18 years) and 13 high-IQ autistic children (11-17 years) were tested on a range of face-processing and IQ tasks, and a ToM test based oil the attribution of intentional movement to abstract shapes in a cartoon. By midchildhood, the ability accurately and spontaneously to infer the locus of attention of a face with direct or averted gaze was specifically associated with the ability to describe geometrical animations using mental state terms. Other face-processing and animation descriptions failed to show the association. Autistic adolescents were impaired at both gaze processing and ToM descriptions. using these tests. Mentalizing and gaze perception accuracy are associated in typically developing children and adolescents. The findings are congruent with the possibility that common neural Circuitry underlies, at least in part, processing implicated in these tasks. They are also congruent with the possibility that autism may lie at one end of a developmental continuum with respect to these skills, and to the factor(s) underpinning them
Superfluid and Mott Insulating shells of bosons in harmonically confined optical lattices
Weakly interacting atomic or molecular bosons in quantum degenerate regime
and trapped in harmonically confined optical lattices, exhibit a wedding cake
structure consisting of insulating (Mott) shells. It is shown that superfluid
regions emerge between Mott shells as a result of fluctuations due to finite
hopping. It is found that the order parameter equation in the superfluid
regions is not of the Gross-Pitaeviskii type except near the insulator to
superfluid boundaries. The excitation spectra in the Mott and superfluid
regions are obtained, and it is shown that the superfluid shells posses low
energy sound modes with spatially dependent sound velocity described by a local
index of refraction directly related to the local superfluid density. Lastly,
the Berezinskii-Kosterlitz-Thouless transition and vortex-antivortex pairs are
discussed in thin (wide) superfluid shells (rings) limited by three (two)
dimensional Mott regions.Comment: 11 pages, 9 figures
A 'p-n' diode with hole and electron-doped lanthanum manganite
The hole-doped manganite La0.7Ca0.3MnO3 and the electron-doped manganite
La0.7Ce0.3MnO3 undergo an insulator to metal transition at around 250 K, above
which both behave as a polaronic semiconductor. We have successfully fabricated
an epitaxial trilayer (La0.7Ca0.3MnO3/SrTiO3/La0.7Ce0.3MnO3), where SrTiO3 is
an insulator. At room temperature, i.e. in the semiconducting regime, it
exhibits asymmetric current-voltage (I-V) characteristics akin to a p-n diode.
The observed asymmetry in the I-V characteristics disappears at low
temperatures where both the manganite layers are metallic. To the best of our
knowledge, this is the first report of such a p-n diode, using the polaronic
semiconducting regime of doped manganites.Comment: PostScript text and 2 figures, to be published in Appl. Phys. Lett
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