8,849 research outputs found
Modeling Vocal Fold Motion with a New Hydrodynamic Semi-Continuum Model
Vocal fold (VF) motion is a fundamental process in voice production, and is
also a challenging problem for direct numerical computation because the VF
dynamics depend on nonlinear coupling of air flow with the response of elastic
channels (VF), which undergo opening and closing, and induce internal flow
separation. A traditional modeling approach makes use of steady flow
approximation or Bernoulli's law which is known to be invalid during VF
opening. We present a new hydrodynamic semi-continuum system for VF motion. The
airflow is modeled by a quasi-one dimensional continuum aerodynamic system, and
the VF by a classical lumped two mass system. The reduced flow system contains
the Bernoulli's law as a special case, and is derivable from the two
dimensional compressible Navier-Stokes equations. Since we do not make steady
flow approximation, we are able to capture transients and rapid changes of
solutions, e.g. the double pressure peaks at opening and closing stages of VF
motion consistent with experimental data. We demonstrate numerically that our
system is robust, and models in-vivo VF oscillation more physically. It is also
much simpler than a full two-dimensional Navier-Stokes system.Comment: 27 pages,6 figure
Attosecond Precision Multi-km Laser-Microwave Network
Synchronous laser-microwave networks delivering attosecond timing precision
are highly desirable in many advanced applications, such as geodesy,
very-long-baseline interferometry, high-precision navigation and
multi-telescope arrays. In particular, rapidly expanding photon science
facilities like X-ray free-electron lasers and intense laser beamlines require
system-wide attosecond-level synchronization of dozens of optical and microwave
signals up to kilometer distances. Once equipped with such precision, these
facilities will initiate radically new science by shedding light on molecular
and atomic processes happening on the attosecond timescale, such as
intramolecular charge transfer, Auger processes and their impact on X-ray
imaging. Here, we present for the first time a complete synchronous
laser-microwave network with attosecond precision, which is achieved through
new metrological devices and careful balancing of fiber nonlinearities and
fundamental noise contributions. We demonstrate timing stabilization of a
4.7-km fiber network and remote optical-optical synchronization across a 3.5-km
fiber link with an overall timing jitter of 580 and 680 attoseconds RMS,
respectively, for over 40 hours. Ultimately we realize a complete
laser-microwave network with 950-attosecond timing jitter for 18 hours. This
work can enable next-generation attosecond photon-science facilities to
revolutionize many research fields from structural biology to material science
and chemistry to fundamental physics.Comment: 42 pages, 13 figure
Transition Dependency: A Gene-Gene Interaction Measure for Times Series Microarray Data
Gene-Gene dependency plays a very important role in system biology as it pertains to the crucial understanding of different biological mechanisms. Time-course microarray data provides a new platform useful to reveal the dynamic mechanism of gene-gene dependencies. Existing interaction measures are mostly based on association measures, such as Pearson or Spearman correlations. However, it is well known that such interaction measures can only capture linear or monotonic dependency relationships but not for nonlinear combinatorial dependency relationships. With the invocation of hidden Markov models, we propose a new measure of pairwise dependency based on transition probabilities. The new dynamic interaction measure checks whether or not the joint transition kernel of the bivariate state variables is the product of two marginal transition kernels. This new measure enables us not only to evaluate the strength, but also to infer the details of gene dependencies. It reveals nonlinear combinatorial dependency structure in two aspects: between two genes and across adjacent time points. We conduct a bootstrap-based Ç2 test for presence/absence of the dependency between every pair of genes. Simulation studies and real biological data analysis demonstrate the application of the proposed method. The software package is available under request
Calculating Dilepton Rates from Monte Carlo Simulations of Parton Production
To calculate dilepton rates in a Monte Carlo simulation of ultrarelativistic
heavy ion collisions, one usually scales the number of similar QCD processes by
a ratio of the corresponding differential probabilities. We derive the formula
for such a ratio especially for dilepton bremsstrahlung processes. We also
discuss the non-triviality of including higher order corrections to direct
Drell-Yan process. The resultant mass spectra from our Monte Carlo simulation
are consistent with the semi-analytical calculation using dilepton
fragmentation functions.Comment: 14 pages in RevTex, 3 figures in uuencoded files, LBL-3466
Negative permittivity derived from inductive characteristic in the percolating Cu/EP metacomposites
Recently, increasing attention has been concentrated on negative permittivity with the development of the emerging metamaterials composed of periodic array structures. However, taking facile preparation into consideration, it is important to achieve negative permittivity behavior based on materials’ intrinsic properties rather than their artificially periodic structures. In this paper, we proposed to fabricate the percolating composites with copper dispersed in epoxy (EP) resin by a polymerization method to realize the negative permittivity behavior. When Cu content in the composites reached to 80 wt%, the conductivity abruptly went up by three orders of magnitudes, suggesting a percolation behavior. Below the percolation threshold, the conductivity spectra conform to Jonscher’s power law; when the Cu/EP composites reached to percolating state, the conductivity gradually reduced in high frequency region due to the skin effect. It is indicated that the conductive mechanism changed from hopping conduction to electron conduction. In addition, the permittivity did not increase monotonously with the increase of Cu content in the vicinity of percolation threshold, due to the presence of leakage current. Meanwhile, the negative permittivity conforming to Drude model was observed above the percolation threshold. Further investigation revealed that there was a constitutive relationship between the permittivity and the reactance. When conductive fillers are slightly above the percolation threshold, the inductive characteristic derived from conductive percolating network leads to the negative permittivity. Such epsilon-negative materials can potentially be applied in novel electrical devices, such as high-power microwave filters, stacked capacitors, negative capacitance field effect transistors and coil-free resonators. In addition, the design strategy based on percolating composites provides an approach to epsilon-negative materials
Terahertz metamaterials on free-standing highly-flexible polyimide substrates
We have fabricated resonant terahertz metamaterials on free standing
polyimide substrates. The low-loss polyimide substrates can be as thin as 5.5
micron yielding robust large-area metamaterials which are easily wrapped into
cylinders with a radius of a few millimeters. Our results provide a path
forward for creating multi-layer non-planar metamaterials at terahertz
frequencies.Comment: 4 pages, higher resolution figures available upon reques
Primordial Black Hole Formation from Inflaton
Measurements of the distances to SNe Ia have produced strong evidence that
the Universe is really accelarating, implying the existence of a nearly uniform
component of dark energy with the simplest explanation as a cosmological
constant. In this paper a small changing cosmological term is proposed, which
is a function of a slow-rolling scalar field, by which the de Sitter primordial
black holes' properties, for both charged and uncharged cases, are carefully
examined and the relationship between the black hole formation and the energy
transfer of the inflaton within this cosmological term is eluciatedComment: 6 pages, Late
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Elucidating the Limit of Li Insertion into the Spinel Li4Ti5O12
In this work, we show that the well-known lithium-ion anode material, Li4Ti5O12, exhibits exceptionally high initial capacity of 310 mAh g-1 when it is discharged to 0.01 V. It maintains a reversible capacity of 230 mAh g-1, far exceeding the "theoretical" capacity of 175 mAh g-1 when this anode is lithiated to the composition Li7Ti5O12. Neutron diffraction analyses identify that additional Li reversibly enters into the Li7Ti5O12 to form Li8Ti5O12. density functional theory (DFT) calculations reveal the average potentials of the Li4Ti5O12 to Li7Ti5O12 step and the Li7Ti5O12 to Li8Ti5O12 step are 1.57 and 0.19 V, respectively, which are in excellent agreement with experimental results. Transmission electron microscopy (TEM) studies confirm that the irreversible capacity of Li4Ti5O12 during its first cycle originates from the formation of a solid electrolyte interface (SEI) layer. This work clarifies the fundamental lithiation mechanism of the Li4Ti5O12, when lithiated to 0.01 V vs Li
A genuine maximally seven-qubit entangled state
Contrary to A.Borras et al.'s [1] conjecture, a genuine maximally seven-qubit
entangled state is presented. We find a seven-qubit state whose marginal
density matrices for subsystems of 1,2- qubits are all completely mixed and for
subsystems of 3-qubits is almost completely mixed
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