1,140 research outputs found
Evolution of spiral and scroll waves of excitation in a mathematical model of ischaemic border zone
Abnormal electrical activity from the boundaries of ischemic cardiac tissue
is recognized as one of the major causes in generation of ischemia-reperfusion
arrhythmias. Here we present theoretical analysis of the waves of electrical
activity that can rise on the boundary of cardiac cell network upon its
recovery from ischaemia-like conditions. The main factors included in our
analysis are macroscopic gradients of the cell-to-cell coupling and cell
excitability and microscopic heterogeneity of individual cells. The interplay
between these factors allows one to explain how spirals form, drift together
with the moving boundary, get transiently pinned to local inhomogeneities, and
finally penetrate into the bulk of the well-coupled tissue where they reach
macroscopic scale. The asymptotic theory of the drift of spiral and scroll
waves based on response functions provides explanation of the drifts involved
in this mechanism, with the exception of effects due to the discreteness of
cardiac tissue. In particular, this asymptotic theory allows an extrapolation
of 2D events into 3D, which has shown that cells within the border zone can
give rise to 3D analogues of spirals, the scroll waves. When and if such scroll
waves escape into a better coupled tissue, they are likely to collapse due to
the positive filament tension. However, our simulations have shown that such
collapse of newly generated scrolls is not inevitable and that under certain
conditions filament tension becomes negative, leading to scroll filaments to
expand and multiply leading to a fibrillation-like state within small areas of
cardiac tissue.Comment: 26 pages, 13 figures, appendix and 2 movies, as accepted to PLoS ONE
2011/08/0
Calibration of photomultiplier arrays
A method is described that allows calibration and assessment of the linearity of response of an array of photomultiplier tubes. The method does not require knowledge of the photomultiplier single photoelectron response model and uses science data directly, thus eliminating the need for dedicated data sets. In this manner all photomultiplier working conditions (e.g. temperature, external fields, etc.) are exactly matched between calibration and science acquisitions. This is of particular importance in low background experiments such as ZEPLIN-III, where methods involving the use of external light sources for calibration are severely constrained
Smooth interface effects on the Raman scattering in zinc-blende AlN/GaN superlattices
Raman spectra of (AlN)(8-delta)/(AlxGa1-xN)(delta)/(GaN)(8-delta)/(AlxGa1-xN)(delta) superlattices with interface thickness varying between delta = 0 and delta = 3 are calculated. The influence of the nonabrupt interface related broadening is described in the complete range of scattering, with special attention to the modes giving stronger contribution to the Raman intensity. It is shown that the dispersion of folded acoustic phonons does not change appreciably with the interface smoothing. For delta = 0 the Raman spectra display new peaks due to the enhancement of some confined optic modes.6119130601306
Limits on the spin-dependent WIMP-nucleon cross-sections from the first science run of the ZEPLIN-III experiment
We present new experimental constraints on the WIMP-nucleon spin-dependent elastic cross-sections using data from the first science run of ZEPLIN-III, a two-phase xenon experiment searching for galactic dark matter WIMPs based at the Boulby mine. Analysis of 450 kgdays fiducial exposure revealed a most likely signal of zero events, leading to a 90%-confidence upper limit on the pure WIMP-neutron cross-section of pb at 55 GeV/ WIMP mass. Recent calculations of the nuclear spin structure based on the Bonn CD nucleon-nucleon potential were used for the odd-neutron isotopes Xe and Xe. These indicate that the sensitivity of xenon targets to the spin-dependent WIMP-proton interaction is much lower than implied by previous calculations, whereas the WIMP-neutron sensitivity is impaired only by a factor of 2
Measurement and simulation of the muon-induced neutron yield in lead
A measurement is presented of the neutron production rate in lead by high energy cosmic-ray muons at a depth of 2850 m water equivalent (w.e.) and a mean muon energy of 260 GeV. The measurement exploits the delayed coincidences between muons and the radiative capture of induced neutrons in a highly segmented tonne scale plastic scintillator detector. Detailed Monte Carlo simulations reproduce well the measured capture times and multiplicities and, within the dynamic range of the instrumentation, the spectrum of energy deposits. By comparing measurements with simulations of neutron capture rates a neutron yield in lead of (View the MathML source) ×10-3 neutrons/muon/(g/cm2) has been obtained. Absolute agreement between simulation and data is of order 25%. Consequences for deep underground rare event searches are discussed
Phylogenetic and functional diversity of metagenomic libraries of phenol degrading sludge from petroleum refinery wastewater treatment system
In petrochemical refinery wastewater treatment plants (WWTP), different concentrations of pollutant compounds are received daily in the influent stream, including significant amounts of phenolic compounds, creating propitious conditions for the development of particular microorganisms that can rapidly adapt to such environment. In the present work, the microbial sludge from a refinery WWTP was enriched for phenol, cloned into fosmid vectors and pyrosequenced. The fosmid libraries yielded 13,200 clones and a comprehensive bioinformatic analysis of the sequence data set revealed a complex and diverse bacterial community in the phenol degrading sludge. The phylogenetic analyses using MEGAN in combination with RDP classifier showed a massive predominance of Proteobacteria, represented mostly by the genera Diaphorobacter, Pseudomonas, Thauera and Comamonas. The functional classification of phenol degrading sludge sequence data set generated by MG-RAST showed the wide metabolic diversity of the microbial sludge, with a high percentage of genes involved in the aerobic and anaerobic degradation of phenol and derivatives. In addition, genes related to the metabolism of many other organic and xenobiotic compounds, such as toluene, biphenyl, naphthalene and benzoate, were found. Results gathered herein demonstrated that the phenol degrading sludge has complex phylogenetic and functional diversities, showing the potential of such community to degrade several pollutant compounds. This microbiota is likely to represent a rich resource of versatile and unknown enzymes which may be exploited for biotechnological processes such as bioremediation
Dispersive charge density wave excitations and temperature dependent commensuration in Bi2Sr2CaCu2O8+{\delta}
Experimental evidence on high-Tc cuprates reveals ubiquitous charge density
wave (CDW) modulations, which coexist with superconductivity. Although the CDW
had been predicted by theory, important questions remain about the extent to
which the CDW influences lattice and charge degrees of freedom and its
characteristics as functions of doping and temperature. These questions are
intimately connected to the origin of the CDW and its relation to the
mysterious cuprate pseudogap. Here, we use ultrahigh resolution resonant
inelastic x-ray scattering (RIXS) to reveal new CDW character in underdoped
Bi2Sr2CaCu2O8+{\delta} (Bi2212). At low temperature, we observe dispersive
excitations from an incommensurate CDW that induces anomalously enhanced phonon
intensity, unseen using other techniques. Near the pseudogap temperature T*,
the CDW persists, but the associated excitations significantly weaken and the
CDW wavevector shifts, becoming nearly commensurate with a periodicity of four
lattice constants. The dispersive CDW excitations, phonon anomaly, and
temperature dependent commensuration provide a comprehensive momentum space
picture of complex CDW behavior and point to a closer relationship with the
pseudogap state
On the gauge boson's properties in a candidate technicolor theory
The technicolor scenario replaces the Higgs sector of the standard model with
a strongly interacting sector. One candidate for a realization of such a sector
is two-technicolor Yang-Mills theory coupled to two degenerate flavors of
adjoint, massless techniquarks. Using lattice gauge theory the properties of
the technigluons in this scenario are investigated as a function of the
techniquark mass towards the massless limit. For that purpose the minimal
Landau gauge two-point and three-point correlation functions are determined,
including a detailed systematic error analysis. The results are, within the
relatively large systematic uncertainties, compatible with a behavior very
similar to QCD at finite techniquark mass. However, the limit of massless
techniquarks exhibits features which could be compatible with a
(quasi-)conformal behavior.Comment: 27 pages, 17 figures, 1 table; v2: persistent notational error
corrected, some minor modification
Activity of arginine-phenylalanine and arginine-tryptophan-based surfactants against Staphylococcus aureus
Aims: This study aimed to evaluate the antibacterial effect of two new cationic surfactants based on phenylalanine-arginine (LPAM) and tryptophan-arginine (LTAM). Materials & methods: Antibacterial activity, mechanism of action and interactions with Staphylococcus aureus enzymes were measured through microbiological, flow cytometry and molecular docking assays, respectively. Results & conclusion: These compounds showed antibacterial activity in the range of 4.06-16.24 μg/ml against planktonic cells and no activity against mature biofilms, since they caused a loss of membrane integrity and increased DNA damage, as revealed by flow cytometry analysis. In silico assays revealed the existence of molecular bonds such as hydrogen bonds, mainly with DNA. Therefore, these compounds have promising pharmacological activity against MRSA strains.The authors would like to thank Central Analítica-UFC/CT-INFRA/MCTI- SISANO/Pró-Equipamentos CAPES for the support.Peer reviewe
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