3,235 research outputs found
Subcellular heterogeneity of ryanodine receptor properties in ventricular myocytes with low T-tubule density
Rationale:
In ventricular myocytes of large mammals, not all ryanodine receptor (RyR) clusters are associated with T-tubules (TTs); this fraction increases with cellular remodeling after myocardial infarction (MI).
Objective:
To characterize RyR functional properties in relation to TT proximity, at baseline and after MI.
Methods:
Myocytes were isolated from left ventricle of healthy pigs (CTRL) or from the area adjacent to a myocardial infarction (MI). Ca2+ transients were measured under whole-cell voltage clamp during confocal linescan imaging (fluo-3) and segmented according to proximity of TTs (sites of early Ca2+ release, F>F50 within 20 ms) or their absence (delayed areas). Spontaneous Ca2+ release events during diastole, Ca2+ sparks, reflecting RyR activity and properties, were subsequently assigned to either category.
Results:
In CTRL, spark frequency was higher in proximity of TTs, but spark duration was significantly shorter. Block of Na+/Ca2+ exchanger (NCX) prolonged spark duration selectively near TTs, while block of Ca2+ influx via Ca2+ channels did not affect sparks properties. In MI, total spark mass was increased in line with higher SR Ca2+ content. Extremely long sparks (>47.6 ms) occurred more frequently. The fraction of near-TT sparks was reduced; frequency increased mainly in delayed sites. Increased duration was seen in near-TT sparks only; Ca2+ removal by NCX at the membrane was significantly lower in MI.
Conclusion:
TT proximity modulates RyR cluster properties resulting in intracellular heterogeneity of diastolic spark activity. Remodeling in the area adjacent to MI differentially affects these RyR subpopulations. Reduction of the number of sparks near TTs and reduced local NCX removal limit cellular Ca2+ loss and raise SR Ca2+ content, but may promote Ca2+ waves
A Tale of Two Current Sheets
I outline a new model of particle acceleration in the current sheet
separating the closed from the open field lines in the force-free model of
pulsar magnetospheres, based on reconnection at the light cylinder and
"auroral" acceleration occurring in the return current channel that connects
the light cylinder to the neutron star surface. I discuss recent studies of
Pulsar Wind Nebulae, which find that pair outflow rates in excess of those
predicted by existing theories of pair creation occur, and use those results to
point out that dissipation of the magnetic field in a pulsar's wind upstream of
the termination shock is restored to life as a viable model for the solution of
the "" problem as a consequence of the lower wind 4-velocity implied by
the larger mass loading.Comment: 17 pages, 6 figures, Invited Review, Proceedings of the "ICREA
Workshop on The High-Energy Emission from Pulsars and their Systems", Sant
Cugat, Spain, April 12-16, 201
Solvability of boundary value problems for a class of partial difference equations on the combinatorial domain
Comparative efficacy and acceptability of methylphenidate and atomoxetine in treatment of attention deficit hyperactivity disorder in children and adolescents: a meta-analysis
Asymptotic Regge Trajectories of Non-strange Mesons
We analyze the asymptotic behavior of Regge trajectories of non-strange
mesons. In contrast to an existing belief, it is demonstrated that for the
asymptotically linear Regge trajectories the width of heavy hadrons cannot
linearly depend on their mass. Using the data on masses and widths of rho_J,
omega_J, a_J and f_J mesons for the spin values J \leq 6, we extract the
parameters of the asymptotically linear Regge trajectory predicted by the
finite width model of quark gluon bags. As it is shown the obtained parameters
for the data set B correspond to the cross-over temperature lying in the
interval 170.9-175.3 MeV which is consistent with the kinetic freeze-out
temperature of early hadronizing particles found in relativistic heavy ion
collisions at and above the highest SPS energy.Comment: 14 pages, 3 figure
Rare B Decays with a HyperCP Particle of Spin One
In light of recent experimental information from the CLEO, BaBar, KTeV, and
Belle collaborations, we investigate some consequences of the possibility that
a light spin-one particle is responsible for the three Sigma^+ -> p mu^+ mu^-
events observed by the HyperCP experiment. In particular, allowing the new
particle to have both vector and axial-vector couplings to ordinary fermions,
we systematically study its contributions to various processes involving
b-flavored mesons, including B-Bbar mixing as well as leptonic, inclusive, and
exclusive B decays. Using the latest experimental data, we extract bounds on
its couplings and subsequently estimate upper limits for the branching ratios
of a number of B decays with the new particle. This can serve to guide
experimental searches for the particle in order to help confirm or refute its
existence.Comment: 17 pages, 3 figures; discussion on spin-0 case modified, few errors
corrected, main conclusions unchange
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Improved Constraints on Sterile Neutrino Mixing from Disappearance Searches in the MINOS, MINOS+, Daya Bay, and Bugey-3 Experiments.
Searches for electron antineutrino, muon neutrino, and muon antineutrino disappearance driven by sterile neutrino mixing have been carried out by the Daya Bay and MINOS+ collaborations. This Letter presents the combined results of these searches, along with exclusion results from the Bugey-3 reactor experiment, framed in a minimally extended four-neutrino scenario. Significantly improved constraints on the θ_{μe} mixing angle are derived that constitute the most constraining limits to date over five orders of magnitude in the mass-squared splitting Δm_{41}^{2}, excluding the 90% C.L. sterile-neutrino parameter space allowed by the LSND and MiniBooNE observations at 90% CL_{s} for Δm_{41}^{2}<13 eV^{2}. Furthermore, the LSND and MiniBooNE 99% C.L. allowed regions are excluded at 99% CL_{s} for Δm_{41}^{2}<1.6 eV^{2}
Morphology and photoluminescence study of titania nanoparticles
Titania nanoparticles are prepared by sol–gel chemistry with a poly(ethylene oxide) methyl ether methacrylate-block-poly(dimethylsiloxane)-block-poly(ethylene oxide) methyl ether methacrylate triblock copolymer acting as the templating agent. The sol–gel components—hydrochloric acid, titanium tetraisopropoxide, and triblock copolymer—are varied to investigate their effect on the resulting titania morphology. An increased titania precursor or polymer content yields smaller primary titania structures. Microbeam grazing incidence small-angle X-ray scattering measurements, which are analyzed with a unified fit model, reveal information about the titania structure sizes. These small structures could not be observed via the used microscopy techniques. The interplay among the sol–gel components via our triblock copolymer results in different sized titania nanoparticles with higher packing densities. Smaller sized titania particles, (∼13–20 nm in diameter) in the range of exciton diffusion length, are formed by 2% by weight polymer and show good crystallinity with less surface defects and high oxygen vacancies
Application of Graphene within Optoelectronic Devices and Transistors
Scientists are always yearning for new and exciting ways to unlock graphene's
true potential. However, recent reports suggest this two-dimensional material
may harbor some unique properties, making it a viable candidate for use in
optoelectronic and semiconducting devices. Whereas on one hand, graphene is
highly transparent due to its atomic thickness, the material does exhibit a
strong interaction with photons. This has clear advantages over existing
materials used in photonic devices such as Indium-based compounds. Moreover,
the material can be used to 'trap' light and alter the incident wavelength,
forming the basis of the plasmonic devices. We also highlight upon graphene's
nonlinear optical response to an applied electric field, and the phenomenon of
saturable absorption. Within the context of logical devices, graphene has no
discernible band-gap. Therefore, generating one will be of utmost importance.
Amongst many others, some existing methods to open this band-gap include
chemical doping, deformation of the honeycomb structure, or the use of carbon
nanotubes (CNTs). We shall also discuss various designs of transistors,
including those which incorporate CNTs, and others which exploit the idea of
quantum tunneling. A key advantage of the CNT transistor is that ballistic
transport occurs throughout the CNT channel, with short channel effects being
minimized. We shall also discuss recent developments of the graphene tunneling
transistor, with emphasis being placed upon its operational mechanism. Finally,
we provide perspective for incorporating graphene within high frequency
devices, which do not require a pre-defined band-gap.Comment: Due to be published in "Current Topics in Applied Spectroscopy and
the Science of Nanomaterials" - Springer (Fall 2014). (17 pages, 19 figures
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