1,775 research outputs found
Spectral Density on the Lattice
Spectral density in the pseudoscalar and vector channels is extracted from
the SU(2) lattice quenched data. It is shown to consist of three sharp poles
within the energy range accessible on the lattice.Comment: 38 pages, uuencoded tar-compressed ps-fil
Expansion Aspect of Color Transparency on the Lattice
The opportunity to observe color transparency (CT) is determined by how
rapidly a small-sized hadronic wave packet expands. Here we use SU(2) lattice
gauge theory with Wilson fermions in the quenched approximation to investigate
the expansion. The wave packet is modeled by a point hadronic source, often
used as an interpolating field in lattice calculations. The procedure is to
determine the Euclidean time (t), pion channel, Bethe-Salpeter amplitude
, and then evaluate . This quantity represents the soft interaction of a small-sized
wave packet with a pion. The time dependence of is fit as a
superposition of three states, which is found sufficient to reproduce a reduced
size wave packet. Using this superposition allows us to make the analytic
continuation required to study the wave packet expansion in real time. We find
that the matrix elements of the soft interaction between the excited
and ground state decrease rapidly with the energy of the excited state.Comment: 19 pages, latex, 4 figure
The use of ratiometric fluorescence measurements of the voltage sensitive dye Di-4-ANEPPS to examine action potential characteristics and drug effects on human induced pluripotent stem cell-derived cardiomyocytes
Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) and higher throughput platforms have emerged as potential tools to advance cardiac drug safety screening. This study evaluated the use of high bandwidth photometry applied to voltage-sensitive fluorescent dyes (VSDs) to assess drug-induced changes in action potential characteristics of spontaneously active hiPSC-CM. Human iPSC-CM from 2 commercial sources (Cor.4U and iCell Cardiomyocytes) were stained with the VSD di-4-ANEPPS and placed in a specialized photometry system that simultaneously monitors 2 wavebands of emitted fluorescence, allowing ratiometric measurement of membrane voltage. Signals were acquired at 10 kHz and analyzed using custom software. Action potential duration (APD) values were normally distributed in cardiomyocytes (CMC) from both sources though the mean and variance differed significantly (APD90: 229 ± 15 ms vs 427 ± 49 ms [mean ± SD, P < 0.01]; average spontaneous cycle length: 0.99 ± 0.02 s vs 1.47 ± 0.35 s [mean ± SD, P < 0.01], Cor.4U vs iCell CMC, respectively). The 10–90% rise time of the AP (Trise) was ∼6 ms and was normally distributed when expressed as 1/T2riseTrise2 in both cell preparations. Both cell types showed a rate dependence analogous to that of adult human cardiac cells. Furthermore, nifedipine, ranolazine, and E4031 had similar effects on cardiomyocyte electrophysiology in both cell types. However, ranolazine and E4031 induced early after depolarization-like events and high intrinsic firing rates at lower concentrations in iCell CMC. These data show that VSDs provide a minimally invasive, quantitative, and accurate method to assess hiPSC-CM electrophysiology and detect subtle drug-induced effects for drug safety screening while highlighting a need to standardize experimental protocols across preparations
The issue of Dark Energy in String Theory
Recent astrophysical observations, pertaining to either high-redshift
supernovae or cosmic microwave background temperature fluctuations, as those
measured recently by the WMAP satellite, provide us with data of unprecedented
accuracy, pointing towards two (related) facts: (i) our Universe is accelerated
at present, and (ii) more than 70 % of its energy content consists of an
unknown substance, termed dark energy, which is believed responsible for its
current acceleration. Both of these facts are a challenge to String theory. In
this review I outline briefly the challenges, the problems and possible avenues
for research towards a resolution of the Dark Energy issue in string theory.Comment: Based on Invited lecture at the ``Third Aegean Summer School on: The
Invisible Universe: Dark matter and Dark energy'', Karfas, Chios Island
(Greece) September 26-October 1 200
Asymptotic description of solitary wave trains in fully nonlinear shallow-water theory
We derive an asymptotic formula for the amplitude distribution in a fully
nonlinear shallow-water solitary wave train which is formed as the long-time
outcome of the initial-value problem for the Su-Gardner (or one-dimensional
Green-Naghdi) system. Our analysis is based on the properties of the
characteristics of the associated Whitham modulation system which describes an
intermediate "undular bore" stage of the evolution. The resulting formula
represents a "non-integrable" analogue of the well-known semi-classical
distribution for the Korteweg-de Vries equation, which is usually obtained
through the inverse scattering transform. Our analytical results are shown to
agree with the results of direct numerical simulations of the Su-Gardner
system. Our analysis can be generalised to other weakly dispersive, fully
nonlinear systems which are not necessarily completely integrable.Comment: 25 pages, 7 figure
Detecting Features from Confusion Matrices using Generalized Formal Concept Analysis
We claim that the confusion matrices of multiclass problems can be analyzed by means of a generalization of Formal Concept Analysis to obtain symbolic information about the feature sets of the underlying classification task.We prove our claims by analyzing the confusion matrices of human speech perception experiments and comparing our results to those elicited by experts.This work has been supported by Spanish Government-Comisión Interministerial de Ciencia y Tecnología TEC2008-02473/TEC y TEC2008-06382/TEC.Publicad
Multibeam Maser Survey of methanol and excited OH in the Magellanic clouds: new detections and maser abundance estimates
‘The definitive version is available at www.blackwell-synergy.com.’ Copyright Blackwell Publishing DOI: 10.1111/j.1365-2966.2008.12888.xPeer reviewe
Dissipative Liouville Cosmology: A Case Study
We consider solutions of the cosmological equations pertaining to a
dissipative, dilaton-driven off-equilibrium Liouville Cosmological model, which
may describe the effective field theoretic limit of a non-critical string model
of the Universe. The non-criticality may be the result of an early-era
catastrophic cosmic event, such as a big-bang, brane-world collision etc. The
evolution of the various cosmological parameters of the model are obtained, and
the effects of the dilaton and off-shell Liouville terms, including briefly
those on relic densities, which distinguish the model from conventional
cosmologies, are emphasised.Comment: 19 pages latex, 11 eps figures incorporate
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