32,909 research outputs found
Lamellar phase separation and dynamic competition in La0.23Ca0.77MnO3
We report the coexistence of lamellar charge-ordered (CO) and
charge-disordered (CD) domains, and their dynamical behavior, in
La0.23Ca0.77MnO3. Using high resolution transmission electron microscopy (TEM),
we show that below Tcd~170K a CD-monoclinic phase forms within the established
CO-orthorhombic matrix. The CD phase has a sheet-like morphology, perpendicular
to the q vector of the CO superlattice (a axis of the Pnma structure). For
temperatures between 64K and 130K, both the TEM and resistivity experiments
show a dynamic competition between the two phases: at constant T, the CD phase
slowly advances over the CO one. This slow dynamics appears to be linked to the
magnetic transitions occurring in this compound, suggesting important
magnetoelastic effects.Comment: 4 pages, 4 figure
Heavy Color-Octet Particles at the LHC
Many new-physics models, especially those with a color-triplet top-quark
partner, contain a heavy color-octet state. The "naturalness" argument for a
light Higgs boson requires that the color-octet state be not much heavier than
a TeV, and thus it can be pair-produced with large cross sections at
high-energy hadron colliders. It may decay preferentially to a top quark plus a
top-partner, which subsequently decays to a top quark plus a color-singlet
state. This singlet can serve as a WIMP dark-matter candidate. Such decay
chains lead to a spectacular signal of four top quarks plus missing energy. We
pursue a general categorization of the color-octet states and their decay
products according to their spin and gauge quantum numbers. We review the
current bounds on the new states at the LHC and study the expected discovery
reach at the 8-TeV and 14-TeV runs. We also present the production rates at a
future 100-TeV hadron collider, where the cross sections will be many orders of
magnitude greater than at the 14-TeV LHC. Furthermore, we explore the extent to
which one can determine the color octet's mass, spin, and chiral couplings.
Finally, we propose a test to determine whether the fermionic color octet is a
Majorana particle.Comment: 20 pages, 9 figures; journal versio
Dynamics of the two-dimensional S=1/2 dimer system (C5H6N2F)2CuCl4
Inelastic neutron scattering was used to study a quantum S=1/2
antiferromagnetic Heisenberg system-Bis(2-amino-5-fluoropyridinium)
Tetrachlorocuprate(II). The magnetic excitation spectrum was shown to be
dominated by long-lived excitations with an energy gap as 1.07(3) meV. The
measured dispersion relation is consistent with a simple two-dimensional square
lattice of weakly-coupled spin dimers. Comparing the data to a random phase
approximation treatment of this model gives the intra-dimer and inter-dimer
exchange constants J=1.45(2) meV and J'=0.31(3) meV, respectively.Comment: 4 pages, 4 figure
Information on the Pion Distribution Amplitude from the Pion-Photon Transition Form Factor with the Belle and BaBar Data
The pion-photon transition form factor (TFF) provides strong constraints on
the pion distribution amplitude (DA). We perform an analysis of all existing
data (CELLO, CLEO, BaBar, Belle) on the pion-photon TFF by means of light-cone
pQCD approach in which we include the next-to-leading order correction to the
valence-quark contribution and estimate the non-valence-quark contribution by a
phenomenological model based on the TFF's limiting behavior at both
and . At present, the pion DA is not definitely determined, it is
helpful to have a pion DA model that can mimic all the suggested behaviors,
especially to agree with the constraints from the pion-photon TFF in whole
measured region within a consistent way. For the purpose, we adopt the
conventional model for pion wavefunction/DA that has been constructed in our
previous paper \cite{hw1}, whose broadness is controlled by a parameter . We
fix the DA parameters by using the CELLO, CLEO, BABAR and Belle data within the
smaller region ( GeV), where all the data are consistent
with each other. And then the pion-photon TFF is extrapolated into larger
region. We observe that the BABAR favors which has the behavior close
to the Chernyak-Zhitnitsky DA, whereas the recent Belle favors which
is close to the asymptotic DA. We need more accurate data at large region
to determine the precise value of , and the definite behavior of pion DA can
be concluded finally by the consistent data in the coming future.Comment: 6 pages, 5 figures. Slightly changed and references update
Zero-shot keyword spotting for visual speech recognition in-the-wild
Visual keyword spotting (KWS) is the problem of estimating whether a text
query occurs in a given recording using only video information. This paper
focuses on visual KWS for words unseen during training, a real-world, practical
setting which so far has received no attention by the community. To this end,
we devise an end-to-end architecture comprising (a) a state-of-the-art visual
feature extractor based on spatiotemporal Residual Networks, (b) a
grapheme-to-phoneme model based on sequence-to-sequence neural networks, and
(c) a stack of recurrent neural networks which learn how to correlate visual
features with the keyword representation. Different to prior works on KWS,
which try to learn word representations merely from sequences of graphemes
(i.e. letters), we propose the use of a grapheme-to-phoneme encoder-decoder
model which learns how to map words to their pronunciation. We demonstrate that
our system obtains very promising visual-only KWS results on the challenging
LRS2 database, for keywords unseen during training. We also show that our
system outperforms a baseline which addresses KWS via automatic speech
recognition (ASR), while it drastically improves over other recently proposed
ASR-free KWS methods.Comment: Accepted at ECCV-201
Kinetics of viral self-assembly: the role of ss RNA antenna
A big class of viruses self-assemble from a large number of identical capsid
proteins with long flexible N-terminal tails and ss RNA. We study the role of
the strong Coulomb interaction of positive N-terminal tails with ss RNA in the
kinetics of the in vitro virus self-assembly. Capsid proteins stick to
unassembled chain of ss RNA (which we call "antenna") and slide on it towards
the assembly site. We show that at excess of capsid proteins such
one-dimensional diffusion accelerates self-assembly more than ten times. On the
other hand at excess of ss RNA, antenna slows self-assembly down. Several
experiments are proposed to verify the role of ss RNA antenna.Comment: 4 pages, 3 figures, several experiments are proposed, a new idea of
experiment is adde
The fidelity of general bosonic channels with pure state input
We first derive for the general form of the fidelity for various bosonic
channels. Thereby we give the fidelity of different quantum bosonic channel,
possibly with product input and entangled input respectively, as examples. The
properties of the fidelity are carefully examined.Comment: 3 pages, comments welcom
Small ball probability, Inverse theorems, and applications
Let be a real random variable with mean zero and variance one and
be a multi-set in . The random sum
where are iid copies of
is of fundamental importance in probability and its applications.
We discuss the small ball problem, the aim of which is to estimate the
maximum probability that belongs to a ball with given small radius,
following the discovery made by Littlewood-Offord and Erdos almost 70 years
ago. We will mainly focus on recent developments that characterize the
structure of those sets where the small ball probability is relatively
large. Applications of these results include full solutions or significant
progresses of many open problems in different areas.Comment: 47 page
Langevin Dynamics of the vortex matter two-stage melting transition in Bi_2Sr_2CaCu_2O in the presence of straight and of tilted columnar defects
In this paper we use London Langevin molecular dynamics simulations to
investigate the vortex matter melting transition in the highly anisotropic
high-temperature superconductor material Bi_2Sr_2CaCu_2O in the
presence of low concentration of columnar defects (CDs). We reproduce with
further details our previous results obtained by using Multilevel Monte Carlo
simulations that showed that the melting of the nanocrystalline vortex matter
occurs in two stages: a first stage melting into nanoliquid vortex matter and a
second stage delocalization transition into a homogeneous liquid. Furthermore,
we report on new dynamical measurements in the presence of a current that
identifies clearly the irreversibility line and the second stage delocalization
transition. In addition to CDs aligned along the c-axis we also simulate the
case of tilted CDs which are aligned at an angle with respect to the applied
magnetic field. Results for CDs tilted by with respect to c-axis
show that the locations of the melting and delocalization transitions are not
affected by the tilt when the ratio of flux lines to CDs remains constant. On
the other hand we argue that some dynamical properties and in particular the
position of the irreversibility line should be affected.Comment: 13 pages, 11 figure
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