1,946 research outputs found
Power law tails of time correlations in a mesoscopic fluid model
In a quenched mesoscopic fluid, modelling transport processes at high
densities, we perform computer simulations of the single particle energy
autocorrelation function C_e(t), which is essentially a return probability.
This is done to test the predictions for power law tails, obtained from mode
coupling theory. We study both off and on-lattice systems in one- and
two-dimensions. The predicted long time tail ~ t^{-d/2} is in excellent
agreement with the results of computer simulations. We also account for finite
size effects, such that smaller systems are fully covered by the present theory
as well.Comment: 11 pages, 12 figure
Microwave Photon Detector in Circuit QED
Quantum optical photodetection has occupied a central role in understanding
radiation-matter interactions. It has also contributed to the development of
atomic physics and quantum optics, including applications to metrology,
spectroscopy, and quantum information processing. The quantum microwave regime,
originally explored using cavities and atoms, is seeing a novel boost with the
generation of nonclassical propagating fields in circuit quantum
electrodynamics (QED). This promising field, involving potential developments
in quantum information with microwave photons, suffers from the absence of
photodetectors. Here, we design a metamaterial composed of discrete
superconducting elements that implements a high-efficiency microwave photon
detector. Our design consists of a microwave guide coupled to an array of
metastable quantum circuits, whose internal states are irreversibly changed due
to the absorption of photons. This proposal can be widely applied to different
physical systems and can be generalized to implement a microwave photon
counter.Comment: accepted in Phys. Rev. Let
Limits to the analogue Hawking temperature in a Bose-Einstein condensate
Quasi-one dimensional outflow from a dilute gas Bose-Einstein condensate
reservoir is a promising system for the creation of analogue Hawking radiation.
We use numerical modeling to show that stable sonic horizons exist in such a
system under realistic conditions, taking into account the transverse
dimensions and three-body loss. We find that loss limits the analogue Hawking
temperatures achievable in the hydrodynamic regime, with sodium condensates
allowing the highest temperatures. A condensate of 30,000 atoms, with
transverse confinement frequency omega_perp=6800*2*pi Hz, yields horizon
temperatures of about 20 nK over a period of 50 ms. This is at least four times
higher than for other atoms commonly used for Bose-Einstein condensates.Comment: 9 pages, 4 figures, replaced with published versio
Split vortices in optically coupled Bose-Einstein condensates
We study a rotating two-component Bose-Einstein condensate in which an
optically induced Josephson coupling allows for population transfer between the
two species. In a regime where separation of species is favored, the ground
state of the rotating system displays domain walls with velocity fields normal
to them. Such a configuration looks like a vortex split into two halves, with
atoms circulating around the vortex and changing their internal state in a
continuous way.Comment: 4 EPS pictures, 4 pages; Some errata have been corrected and thep
resentation has been slightly revise
Quantitative performance characterization of three-dimensional noncontact fluorescence molecular tomography
© 2016 The Authors.Fluorescent proteins and dyes are routine tools for biological research to describe the behavior of genes, proteins, and cells, as well as more complex physiological dynamics such as vessel permeability and pharmacokinetics. The use of these probes in whole body in vivo imaging would allow extending the range and scope of current biomedical applications and would be of great interest. In order to comply with a wide variety of application demands, in vivo imaging platform requirements span from wide spectral coverage to precise quantification capabilities. Fluorescence molecular tomography (FMT) detects and reconstructs in three dimensions the distribution of a fluorophore in vivo. Noncontact FMT allows fast scanning of an excitation source and noninvasive measurement of emitted fluorescent light using a virtual array detector operating in free space. Here, a rigorous process is defined that fully characterizes the performance of a custom-built horizontal noncontact FMT setup. Dynamic range, sensitivity, and quantitative accuracy across the visible spectrum were evaluated using fluorophores with emissions between 520 and 660 nm. These results demonstrate that high-performance quantitative three-dimensional visible light FMT allowed the detection of challenging mesenteric lymph nodes in vivo and the comparison of spectrally distinct fluorescent reporters in cell culture
Use of visible and near infrared reflectance spectra to predict lipid peroxidation of light lamb meat and discriminate dam's feeding systems
Measurement of thiobarbituric acid reactive substances (TBARS) is a well-established method for determine lipid oxidation in meat. This assay, however, is time-consuming and generates undesired chemical waste. Dam''s milk is the principal source of vitamins and provitamins that delay lipid oxidation of light lamb meat; these compounds are stored in the lamb''s muscle tissue. Hence, lamb meat could be used to determine the origin of the dam''s diet. The aim of this study is to evaluate Near-infrared reflectance spectroscopy (NIRS) as a tool for determining the lipid peroxidation of light lamb meat and differentiate the meat of light lambs according the diet of their dams during lactation (grazing alfalfa, lucerne, or fed a total mixed ration). NIRS using select wavelengths was able to detect the lipid oxidation of meat (TBARS method). NIRS can detect analytes at concentrations of parts per million. Moreover, the feed diets were discriminated successfully
Split Instability of a Vortex in an Attractive Bose-Einstein Condensate
An attractive Bose-Einstein condensate with a vortex splits into two pieces
via the quadrupole dynamical instability, which arises at a weaker strength of
interaction than the monopole and the dipole instabilities. The split pieces
subsequently unite to restore the original vortex or collapse.Comment: 4 pages, 4 figures, added figures and references, revised tex
Structural instability of vortices in Bose-Einstein condensates
In this paper we study a gaseous Bose-Einstein condensate (BEC) and show
that: (i) A minimum value of the interaction is needed for the existence of
stable persistent currents. (ii) Vorticity is not a fundamental invariant of
the system, as there exists a conservative mechanism which can destroy a vortex
and change its sign. (iii) This mechanism is suppressed by strong interactions.Comment: 4 pages with 3 figures. Submitted to Phys. Rev. Let
Nonadiabatic resonances in a noisy Fitzhugh-Nagumo neuron model
We have analyzed the response of a noisy Fitzhugh-Nagumo neuronlike model (FN) to subthreshold external stimuli. In contrast to previous studies we have focused our attention on high-frequency signals which could be of interest for real systems such as nervous fibers in the auditory system. We show that the noisy FN behaves as a stochastic oscillator with a characteristic time scale whose effects remain in a wide range of situations. In the nonadiabatic regime of frequencies considered in this work we report several resonant behaviors which resemble those of classical deterministic oscillators but never the typical stochastic resonance phenomenon so often observed for low-frequency signals
Lyashko-Looijenga morphisms and submaximal factorisations of a Coxeter element
When W is a finite reflection group, the noncrossing partition lattice NCP_W
of type W is a rich combinatorial object, extending the notion of noncrossing
partitions of an n-gon. A formula (for which the only known proofs are
case-by-case) expresses the number of multichains of a given length in NCP_W as
a generalised Fuss-Catalan number, depending on the invariant degrees of W. We
describe how to understand some specifications of this formula in a case-free
way, using an interpretation of the chains of NCP_W as fibers of a
Lyashko-Looijenga covering (LL), constructed from the geometry of the
discriminant hypersurface of W. We study algebraically the map LL, describing
the factorisations of its discriminant and its Jacobian. As byproducts, we
generalise a formula stated by K. Saito for real reflection groups, and we
deduce new enumeration formulas for certain factorisations of a Coxeter element
of W.Comment: 18 pages. Version 2 : corrected typos and improved presentation.
Version 3 : corrected typos, added illustrated example. To appear in Journal
of Algebraic Combinatoric
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