12,554 research outputs found
Heat conduction of single-walled carbon nanotube isotope-superlattice structures: A molecular dynamics study
Heat conduction of single-walled carbon nanotubes (SWNTs)
isotope-superlattice is investigated by means of classical molecular dynamics
simulations. Superlattice structures were formed by alternately connecting
SWNTs with different masses. On varying the superlattice period, the critical
value with minimum effective thermal conductivity was identified, where
dominant physics switches from zone-folding effect to thermal boundary
resistance of lattice interface. The crossover mechanism is explained with the
energy density spectra where zone-folding effects can be clearly observed. The
results suggest that the critical superlattice period thickness depends on the
mean free path distribution of diffusive-ballistic phonons. The reduction of
the thermal conductivity with superlattice structures beats that of the
one-dimensional alloy structure, though the minimum thermal conductivity is
still slightly higher than the value obtained by two-dimensional random mixing
of isotopes.Comment: 7 Pages, 5 figures, accepted to Phys. Rev.
Multi-antikaonic nuclei in the relativistic mean-field theory
Properties of multi-antikaonic nuclei (MKN), where several numbers of
mesons are bound, are studied in the relativistic mean-field model, combined
with chiral dynamics for kaonic part of the thermodynamic potential. The
density profiles for nucleons and mesons, the single particle energy of
the mesons, and binding energy of the MKN are obtained. The effects of
the interactions on these quantities are discussed in
comparison with other meson (, , and )-exchange models.
It is shown that the interactions originate from two
contributions: One is the contact interaction between antikaons inherent in
chiral symmetry, and the other is the one generated through coupling between
the and meson mean fields. Both effects of the repulsive
interactions become large on the ground state properties of the MKN as the
number of the embedded mesons increases. A relation between the
multi-antikaonic nuclei and kaon condensation in infinite and uniform matter is
mentioned.Comment: 27 pages, 13 figure
Breathing Oscillations in Bose - Fermi Mixing Gases with Yb atoms in the Largely Prolate Deformed Traps
We study the breathing oscillations in bose-fermi mixtures with Yb isotopes
in the largely prolate deformed trap, which are realized by Kyoto group. We
choose the three combinations of the Yb isotopes, Yb170-Yb171, Yb170-Yb173 and
Yb174-Yb173, whose boson-fermion interactions are weakly repulsive, strongly
attractive and strongly repulsive. The collective oscillations in the deformed
trap are calculated in the dynamical time-development approach, which is
formulated with the time-dependent Gross-Pitaevskii and the Vlasov equations.
We analyze the results in the time-development approach with the intrinsic
oscillation modes of the deformed system, which are obtained using the scaling
method, and show that the damping and forced-oscillation effects of the
intrinsic modes give time-variation of oscillations, especially, in the fermion
transverse mode.Comment: 27 pages, 12 figure
Electron-Hole Asymmetry in Single-Walled Carbon Nanotubes Probed by Direct Observation of Transverse Quasi-Dark Excitons
We studied the asymmetry between valence and conduction bands in
single-walled carbon nanotubes (SWNTs) through the direct observation of
spin-singlet transverse dark excitons using polarized photoluminescence
excitation spectroscopy. The intrinsic electron-hole (e-h) asymmetry lifts the
degeneracy of the transverse exciton wavefunctions at two equivalent K and K'
valleys in momentum space, which gives finite oscillator strength to transverse
dark exciton states. Chirality-dependent spectral weight transfer to transverse
dark states was clearly observed, indicating that the degree of the e-h
asymmetry depends on the specific nanotube structure. Based on comparison
between theoretical and experimental results, we evaluated the band asymmetry
parameters in graphene and various carbon nanotube structures.Comment: 11 pages, 4 figure
Hidden symmetry and quantum phases in spin-3/2 cold atomic systems
Optical traps and lattices provide a new opportunity to study strongly
correlated high spin systems with cold atoms. In this article, we review the
recent progress on the hidden symmetry properties in the simplest high spin
fermionic systems with hyperfine spin , which may be realized with atoms
of Cs, Be, Ba, Ba, and Hg. A {\it generic}
SO(5) or isomorphically, ) symmetry is proved in such systems with the
s-wave scattering interactions in optical traps, or with the on-site Hubbard
interactions in optical lattices. Various important features from this high
symmetry are studied in the Fermi liquid theory, the mean field phase diagram,
and the sign problem in quantum Monte-Carlo simulations. In the s-wave quintet
Cooper pairing phase, the half-quantum vortex exhibits the global analogue of
the Alice string and non-Abelian Cheshire charge properties in gauge theories.
The existence of the quartetting phase, a four-fermion counterpart of the
Cooper pairing phase, and its competition with other orders are studied in one
dimensional spin-3/2 systems. We also show that counter-intuitively quantum
fluctuations in spin-3/2 magnetic systems are even stronger than those in
spin-1/2 systems
Finite-size effects at the hadron-quark transition and heavy hybrid stars
We study the role of finite-size effects at the hadron-quark phase transition
in a new hybrid equation of state constructed from an ab-initio
Br\"uckner-Hartree-Fock equation of state with the realistic Bonn-B potential
for the hadronic phase and a covariant non-local Nambu--Jona-Lasinio model for
the quark phase. We construct static hybrid star sequences and find that our
model can support stable hybrid stars with an onset of quark matter below and a maximum mass above in agreement with recent
observations. If the finite-size effects are taken into account the core is
composed of pure quark matter. Provided that the quark vector channel
interaction is small, and the finite size effects are taken into account, quark
matter appears at densities 2-3 times the nuclear saturation density. In that
case the proton fraction in the hadronic phase remains below the value required
by the onset of the direct URCA process, so that the early onset of quark
matter shall affect on the rapid cooling of the star.Comment: version to match the one published in PR
Topological quantum phase transition in the BEC-BCS crossover phenomena
A crossover between the Bose Einstein condensation (BEC) and BCS
superconducting state is described topologically in the chiral symmetric
fermion system with attractive interaction. Using a local Z_2 Berry phase, we
found a quantum phase transition between the BEC and BCS phases without
accompanying the bulk gap closing.Comment: 4 pages, 5 figure
Thermodynamical Detection of Entanglement by Maxwell's Demons
Quantum correlation, or entanglement, is now believed to be an indispensable
physical resource for certain tasks in quantum information processing, for
which classically correlated states cannot be useful. Besides information
processing, what kind of physical processes can exploit entanglement? In this
paper, we show that there is indeed a more basic relationship between
entanglement and its usefulness in thermodynamics. We derive an inequality
showing that we can extract more work out of a heat bath via entangled systems
than via classically correlated ones. We also analyze the work balance of the
process as a heat engine, in connection with the Second Law of thermodynamics.Comment: 5 pages, 4 figures. v3: a figure added, a few refs added, & typos
correcte
Finite Element Integration on GPUs
We present a novel finite element integration method for low order elements
on GPUs. We achieve more than 100GF for element integration on first order
discretizations of both the Laplacian and Elasticity operators.Comment: 16 pages, 3 figure
Fast, Simple Calcium Imaging Segmentation with Fully Convolutional Networks
Calcium imaging is a technique for observing neuron activity as a series of
images showing indicator fluorescence over time. Manually segmenting neurons is
time-consuming, leading to research on automated calcium imaging segmentation
(ACIS). We evaluated several deep learning models for ACIS on the Neurofinder
competition datasets and report our best model: U-Net2DS, a fully convolutional
network that operates on 2D mean summary images. U-Net2DS requires minimal
domain-specific pre/post-processing and parameter adjustment, and predictions
are made on full images at 9K images per minute. It
ranks third in the Neurofinder competition () and is the best model
to exclusively use deep learning. We also demonstrate useful segmentations on
data from outside the competition. The model's simplicity, speed, and quality
results make it a practical choice for ACIS and a strong baseline for more
complex models in the future.Comment: Accepted to 3rd Workshop on Deep Learning in Medical Image Analysis
(http://cs.adelaide.edu.au/~dlmia3/
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