628 research outputs found
Low-Temperature Dynamical Structure Factor of the Two-Leg Spin-1/2 Heisenberg Ladder
We determine the dynamical structure factor of the two-leg spin-1/2
Heisenberg ladder at low temperatures in the regime of strong rung coupling.
The dominant feature at zero temperature is the coherent triplon mode. We show
that the lineshape of this mode broadens in a non-symmetric way at finite
temperatures and that the degree of asymmetry increases with temperature. We
also show that at low frequencies a temperature induced resonance akin to the
Villain mode in the spin-1/2 Heisenberg Ising chain emerges.Comment: 13 pages, 7 figures, revte
Smoluchowski dynamics and the ergodic-nonergodic transition
We use the recently introduced theory for the kinetics of systems of
classical particles to investigate systems driven by Smoluchowski dynamics. We
investigate the existence of ergodic-nonergodic (ENE) transitions near the
liquid-glass transition. We develop a self-consistent perturbation theory in
terms of an effective two-body potential. We work to second order in this
potential. At second order we have an explicit relationship between the static
structure factor and the effective potential. We choose the static structure
factor in the case of hard spheres to be given by the solution of the
Percus-Yevick approximation for hard spheres. Then using the analytically
determined ENE equation for the ergodicity function we find an ENE transition
for packing fraction, eta, greater than a critical value eta*=0.76 which is
physically unaccessible. The existence of a linear fluctuation-dissipation
theorem in the problem is shown and used to great advantage.Comment: 51 pages, 6 figure
Efficacy of carprofen on conception rates in lactating dairy cows after subcutaneous or intrauterine administration at the time of breeding
Manipulation of the reproductive tract can cause inflammatory processes in the
endometrium and release of cytokines and prostaglandins. It has been shown
that PGF2α has direct negative effects on embryonic survival and development.
Treatment with nonsteroidal antiinflammatory drugs (e.g., ibuprofen lysinate,
flunixin meglumine) might improve pregnancy rates after embryo transfer in
recipient heifers. The primary objective of this study was to evaluate the
effect of a nonsteroidal antiinflammatory drug on reproductive performance in
lactating dairy cows when administered at the time of first-service artificial
insemination (AI) based on the hypothesis that uterine manipulation during AI
might be similarly intense compared with embryo transfer in its effect on
prostaglandin release. A total of 970 cows (333 primiparous and 637
multiparous) from 17 Holstein dairy farms were enrolled. On the day of first
AI, cows were randomly allocated to 1 of 3 treatment groups. Cows of group 1
received 1.4 mg/kg of body weight (BW) of carprofen subcutaneously immediately
after AI (SC group). In group 2, 1.4 mg/kg of BW of carprofen was administered
into the uterus using a sterile disposable catheter 12 to 24 h after AI (IU
group). Animals of group 3 remained as untreated controls. First AI conception
rate was similar for the SC group (42.2%) compared with the untreated control
group (45.1%). A binary logistic regression model for the odds of conception
at first AI revealed a negative effect of an intrauterine administration of
carprofen on conception rate (38.3%). Cows allocated to the IU group had a
lower likelihood of being pregnant within 200 d in milk than cows in the
control group. In summary, subcutaneous treatment with the nonsteroidal
antiinflammatory drug carprofen at the time of AI did not influence conception
rate, whereas an intrauterine administration of carprofen 12 to 24 h after
first AI had a negative effect on first-service conception rate in lactating
dairy cows
Do current-density nonlinearities cut off the glass transition?
Extended mode coupling theories for dense fluids predict that nonlinear
current-density couplings cut off the singular `ideal glass transition',
present in the standard mode coupling theory where such couplings are ignored.
We suggest here that, rather than allowing for activated processes as sometimes
supposed, contributions from current-density couplings are always negligible
close to a glass transition. We discuss in schematic terms how activated
processes can nonetheless cut off the transition, by causing the memory
function to become linear in correlators at late times.Comment: 4 page
Finite Temperature Dynamical Structure Factor of the Heisenberg-Ising Chain
We consider the spin-1/2 Heisenberg XXZ chain in the regime of large
Ising-like anisotropy . By a combination of duality and Jordan-Wigner
transformations we derive a mapping to weakly interacting spinless fermions,
which represent domain walls between the two degenerate ground states. We
develop a perturbative expansion in for the transverse dynamical spin
structure factor at finite temperatures and in an applied transverse magnetic
field. We present a unified description for both the low-energy
temperature-activated response and the temperature evolution of the T=0
two-spinon continuum. We find that the two-spinon continuum narrows in energy
with increasing temperature. At the same time spectral weight is transferred
from the two-spinon continuum to the low energy intraband scattering continuum,
which is strongly peaked around the position of the (single) spinon dispersion
(`Villain mode').Comment: 23 pages, 19 eps figures (now improved), uses feynm
Are there localized saddles behind the heterogeneous dynamics of supercooled liquids?
We numerically study the interplay between heterogeneous dynamics and
properties of negatively curved regions of the potential energy surface in a
model glassy system. We find that the unstable modes of saddles and
quasi-saddles undergo a localization transition close to the Mode-Coupling
critical temperature. We also find evidence of a positive spatial correlation
between clusters of particles having large displacements in the unstable modes
and dynamical heterogeneities.Comment: 7 pages, 3 figures, submitted to Europhys. Let
Att-TasNet: attending to encodings in time-domain audio speech separation of noisy, reverberant speech mixtures
Separation of speech mixtures in noisy and reverberant environments remains a challenging task for state-of-the-art speech separation systems. Time-domain audio speech separation networks (TasNets) are among the most commonly used network architectures for this task. TasNet models have demonstrated strong performance on typical speech separation baselines where speech is not contaminated with noise. When additive or convolutive noise is present, performance of speech separation degrades significantly. TasNets are typically constructed of an encoder network, a mask estimation network and a decoder network. The design of these networks puts the majority of the onus for enhancing the signal on the mask estimation network when used without any pre-processing of the input data or post processing of the separation network output data. Use of multihead attention (MHA) is proposed in this work as an additional layer in the encoder and decoder to help the separation network attend to encoded features that are relevant to the target speakers and conversely suppress noisy disturbances in the encoded features. As shown in this work, incorporating MHA mechanisms into the encoder network in particular leads to a consistent performance improvement across numerous quality and intelligibility metrics on a variety of acoustic conditions using the WHAMR corpus, a data-set of noisy reverberant speech mixtures. The use of MHA is also investigated in the decoder network where it is demonstrated that smaller performance improvements are consistently gained within specific model configurations. The best performing MHA models yield a mean 0.6 dB scale invariant signal-to-distortion (SISDR) improvement on noisy reverberant mixtures over a baseline 1D convolution encoder. A mean 1 dB SISDR improvement is observed on clean speech mixtures
On the relationship between structure and dynamics in a supercooled liquid
We present the dynamic propensity distribution as an explicit measure of the
degree to which the dynamics in a liquid over the time scale of structural
relaxation is determined by the initial configuration. We then examine, for a
binary mixture of soft discs in two dimensions, the correlation between the
spatial distribution of propensity and that of two localmeasures of
configuration structure: the local composition and local free volume. While the
small particles dominate the high propensity population,we find no strong
correlation between either the local composition or the local free volume and
the propensity. It is argued that this is a generic failure of purely local
structural measures to capture the inherently non-local character of collective
behaviour.Comment: Published, see below or
http://www.iop.org/EJ/abstract/0953-8984/17/49/001/ Editing comments have
been remove
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