11,005 research outputs found
The dynamics of condensate shells: collective modes and expansion
We explore the physics of three-dimensional shell-shaped condensates,
relevant to cold atoms in "bubble traps" and to Mott insulator-superfluid
systems in optical lattices. We study the ground state of the condensate
wavefunction, spherically-symmetric collective modes, and expansion properties
of such a shell using a combination of analytical and numerical techniques. We
find two breathing-type modes with frequencies that are distinct from that of
the filled spherical condensate. Upon trap release and subsequent expansion, we
find that the system displays self-interference fringes. We estimate
characteristic time scales, degree of mass accumulation, three-body loss, and
kinetic energy release during expansion for a typical system of Rb87
Generalized Jarzynski Equality under Nonequilibrium Feedback Control
The Jarzynski equality is generalized to situations in which nonequilibrium
systems are subject to a feedback control. The new terms that arise as a
consequence of the feedback describe the mutual information content obtained by
measurement and the efficacy of the feedback control. Our results lead to a
generalized fluctuation-dissipation theorem that reflects the readout
information, and can be experimentally tested using small thermodynamic
systems. We illustrate our general results by an introducing "information
ratchet," which can transport a Brownian particle in one direction and extract
a positive work from the particle
Spin Fluctuation Induced Superconductivity Controlled by Orbital Fluctuation
A microscopic Hamiltonian reflecting the correct symmetry of -orbitals is
proposed to discuss superconductivity in heavy fermion systems. In the
orbitally degenerate region in which not only spin fluctuations but also
orbital fluctuations develop considerably, cancellation between spin and
orbital fluctuations destabilizes -wave superconductivity.
Entering the non-degenerate region by increasing the crystalline electric
field, -wave superconductivity mediated by antiferromagnetic
spin fluctuations emerges out of the suppression of orbital fluctuations. We
argue that the present scenario can be applied to recently discovered
superconductors CeTIn (T=Ir, Rh, and Co).Comment: 4 pages, 3 figure
Magnetic field-induced phase transitions in a weakly coupled s = 1/2 quantum spin dimer system BaCrO
By using bulk magnetization, electron spin resonance (ESR), heat capacity,
and neutron scattering techniques, we characterize the thermodynamic and
quantum phase diagrams of BaCrO. Our ESR measurements indicate that
the low field paramagnetic ground state is a mixed state of the singlet and the
S = 0 triplet for . This suggests the presence of an intra-dimer
Dzyaloshinsky-Moriya (DM) interaction with a DM vector perpendicular to the
c-axis
Fluctuation Theorem with Information Exchange: Role of Correlations in Stochastic Thermodynamics
We establish the fluctuation theorem in the presence of information exchange
between a nonequilibrium system and other degrees of freedom such as an
observer and a feedback controller, where the amount of information exchange is
added to the entropy production. The resulting generalized second law sets the
fundamental limit of energy dissipation and energy cost during the information
exchange. Our results apply not only to feedback-controlled processes but also
to a much broader class of information exchanges, and provides a unified
framework of nonequilibrium thermodynamics of measurement and feedback control.Comment: To appear in PR
Local spin and charge properties of beta-Ag0.33V2O5 studied by 51V NMR
Local spin and charge properties were studied on beta-Ag0.33V2O5, a
pressure-induced superconductor, at ambient pressure using 51V-NMR and
zero-field-resonance (ZFR) techniques. Three inequivalent Vi sites (i=1, 2, and
3) were identified from 51V-NMR spectra and the principal axes of the
electric-field-gradient (EFG) tensor were determined in a metallic phase and
the following charge-ordering phase. We found from the EFG analysis that the V1
sites are in a similar local environment to the V3 sites. This was also
observed in ZFR spectra as pairs of signals closely located with each other.
These results are well explained by a charge-sharing model where a 3d1 electron
is shared within a rung in both V1-V3 and V2-V2 two-leg ladders.Comment: 12pages, 16figure
Spectral Statistics and Local Luminosity Function of a Hard X-ray Complete Sample of Brightest AGNs
We have measured the X-ray spectral properties of a complete flux-limited
sample of bright AGNs from HEAO-1 all-sky catalogs to investigate their
statistics and provide greater constraints on the bright-end of the hard X-ray
luminosity function (HXLF) of AGNs and the AGN population synthesis model of
the X-ray background. Spectral studies using data from ASCA, XMM-Newton and/or
Beppo-SAX observations have been made for almost all AGNs in this sample.
The spectral measurements enable us to construct the neutral absorbing column
density (Log nH) distribution and separate HXLFs for absorbed (Log nH[cm-2]>
21.5) and unabsorbed AGNs in the local universe. Our results show evidence for
a difference in the shapes of HXLFs of absorbed and unabsorbed AGNs in that
absorbed AGN HXLF drops more rapidly at higher luminosities than that of
unabsorbed AGNs, which is similar to that previously reported. In the Lx - nH
plot, we found no AGN in the high-luminosity high-intrinsic absorption regime
(Log Lx[erg/s]> 44.5, Log nH[cm-2]> 21.5) in our sample, where we expect about
5 AGNs if we assume that absorbed and unabsorbed having identical AGN HXLF
shapes. We also find that the observed flux with ASCA or XMM-Newton is smaller
than that with HEAO-1 by a factor of 0.29 on average, which is expected for
re-observation of sources with a factor 2.5 variability amplitude scale.Comment: 43 pages(one column), 10 figures(5 electronic only figures have been
included in the preprint source (tar.gz file)), accepted by The Astronomical
Journal, 9. Mar 200
Proton Spin Relaxation Induced by Quantum Tunneling in Fe8 Molecular Nanomagnet
The spin-lattice relaxation rate and NMR spectra of H in
single crystal molecular magnets of Fe8 have been measured down to 15 mK. The
relaxation rate shows a strong temperature dependence down to 400
mK. The relaxation is well explained in terms of the thermal transition of the
iron state between the discreet energy levels of the total spin S=10. The
relaxation time becomes temperature independent below 300 mK and is
longer than 100 s. In this temperature region stepwise recovery of the
H-NMR signal after saturation was observed depending on the return field of
the sweep field. This phenomenon is attributed to resonant quantum tunneling at
the fields where levels cross and is discussed in terms of the Landau-Zener
transition.Comment: 13 pages, 5 figure
Chandra survey in the AKARI North Ecliptic Pole Deep Field. I. X-ray data, point-like source catalog, sensitivity maps, and number counts
We present data products from the 300 ks Chandra survey in the AKARI North
Ecliptic Pole (NEP) deep field. This field has a unique set of 9-band infrared
photometry covering 2-24 micron from the AKARI Infrared Camera, including
mid-infrared (MIR) bands not covered by Spitzer. The survey is one of the
deepest ever achieved at ~15 micron, and is by far the widest among those with
similar depths in the MIR. This makes this field unique for the MIR-selection
of AGN at z~1. We design a source detection procedure, which performs joint
Maximum Likelihood PSF fits on all of our 15 mosaicked Chandra pointings
covering an area of 0.34 square degree. The procedure has been highly optimized
and tested by simulations. We provide a point source catalog with photometry
and Bayesian-based 90 per cent confidence upper limits in the 0.5-7, 0.5-2,
2-7, 2-4, and 4-7 keV bands. The catalog contains 457 X-ray sources and the
spurious fraction is estimated to be ~1.7 per cent. Sensitivity and 90 per cent
confidence upper flux limits maps in all bands are provided as well. We search
for optical MIR counterparts in the central 0.25 square degree, where deep
Subaru Suprime-Cam multiband images exist. Among the 377 X-ray sources detected
there, ~80 per cent have optical counterparts and ~60 per cent also have AKARI
mid-IR counterparts. We cross-match our X-ray sources with MIR-selected AGN
from Hanami et al. (2012). Around 30 per cent of all AGN that have MID-IR SEDs
purely explainable by AGN activity are strong Compton-thick AGN candidates.Comment: 23 pages, 20 figures; catalogs, sensitivity maps, and upper limit
flux maps are available from the VizieR Servic
Secure Grouping Protocol Using a Deck of Cards
We consider a problem, which we call secure grouping, of dividing a number of
parties into some subsets (groups) in the following manner: Each party has to
know the other members of his/her group, while he/she may not know anything
about how the remaining parties are divided (except for certain public
predetermined constraints, such as the number of parties in each group). In
this paper, we construct an information-theoretically secure protocol using a
deck of physical cards to solve the problem, which is jointly executable by the
parties themselves without a trusted third party. Despite the non-triviality
and the potential usefulness of the secure grouping, our proposed protocol is
fairly simple to describe and execute. Our protocol is based on algebraic
properties of conjugate permutations. A key ingredient of our protocol is our
new techniques to apply multiplication and inverse operations to hidden
permutations (i.e., those encoded by using face-down cards), which would be of
independent interest and would have various potential applications
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