389 research outputs found
Polarization operator in the 2+1 dimensional quantum electrodynamics with a nonzero fermion density in a constant uniform magnetic field
The polarization operator (tensor) for planar charged fermions in constant
uniform magnetic field is calculated in the one-loop approximation of the 2+1
dimensional quantum electrodynamics (QED) with a nonzero fermion
density. We construct the Green function of the Dirac equation with a constant
uniform external magnetic field in the QED at the finite chemical
potential, find the imaginary part of this Green function and then obtain the
polarization tensor related to the combined contribution from real particles
occupying the finite number of energy levels and magnetic field. We expect that
some physical effects under consideration seem to be likely to be revealed in a
monolayer graphene sample in the presence of external constant uniform magnetic
field perpendicular to it.Comment: 9 pages, 2 references are delete
Plane density of induced vacuum charge in a supercritical Coulomb potential
An expression for the density of a planar induced vacuum charge is obtained
in a strong Coulomb potential in coordinate space. Treatment is based on a
self-adjoint extension approach for constructing of the Green's function of a
charged fermion in this potential. Induced vacuum charge density is calculated
and analyzed at the subcritical and supercritical Coulomb potentials for
massless and massive fermions. The behavior of the obtained vacuum charge
density is investigated at long and short distances from the Coulomb center.
The induced vacuum charge has a screening sign. Screening of a Coulomb impurity
in graphene is briefly discussed. We calculate the real vacuum polarization
charge density that acquires the quantum electrodynamics vacuum in the
supercritical Coulomb potential due to the so-called real vacuum polarization.
It is shown that the vacuum charge densities essentially differ in massive and
massless cases. We expect that our results can, as a matter of principle, be
tested in graphene with a supercritical Coulomb impurity.Comment: 12 pages. arXiv admin note: substantial text overlap with
arXiv:1601.0766
Induced current in the presence of magnetic flux tube of small radius
The induced current density, corresponding to the massless Dirac equation in
(2+1) dimensions in a magnetic flux tube of small radius is considered. This
problem is important for graphene. In the case, when an electron can not
penetrate the region of nonzero magnetic field, this current is the odd
periodical function of the magnetic flux. If the region inside the magnetic
tube is not forbidden for penetration of electron, the induced current is not a
periodical function of the magnetic flux. However in the limit , where
is the radius of magnetic flux tube, this function has the universal form
which is independent of the magnetic field distribution inside the magnetic
tube at fixed value of the magnetic flux.Comment: 5 pages, 1 figur
Vortex Interferometric Microscopy with Laguerre-Gaussian Beams
In the present research, we discuss the results of analysis of coherent light beams carrying an optical vortex and propagating through the isotropic medium with a complex surface microrelief and its application to super resolution microscopy. It was shown, that phase analysis of singular beam with single charged centered optical vortex allow to retrieve information about sample surface relief. High spatial resolution caused by vortex helical phase sensitivity to disturbances in wave front after reflection or spreading through studying sample, which can be optically transparent or have a reflecting surface. This method applicable for non-destructive testing of live cells and biological tissues in real-time regime with exceeding optical diffraction limit. Vertical resolution of a microscope based on the phase singularity of Laguerre-Gaussian beams of low order can be achieved down to 5,27 nm for helium-neon laser source for optically transparent and reflecting surfaces.
Keywords: optical vortex, phase, microscopy, singularit
Effects of pyrocatechol on neuromuscular transmission
Effects of pyrocatechol on neuromuscular transmission were studied both in the frog pectoral-cutaneous muscle and in the mouse phrenic-diaphragmatic preparation by means of extracellular microelectrode recording of synaptic signals. Pyrocatechol applied in a concentration of 0.05 mM increased the frequency of miniature end-plate currents (MEPC) and the amplitude of end-plate current (EPC) by increasing its quantum content. Pyrocatechol also increased the duration of presynaptic response. When voltage-dependent potassium channels had been blocked, pyrocatechol affected neither the EPC quantum content nor the duration of presynaptic response. It is suggested that the pyrocatechol-induced enhancement of transmitter release results from modulatory effects of pyrocatechol on voltage-dependent potassium current in the membrane of a nerve terminal. © 1995 Plenum Publishing Corporation
Simulation of thermophysical processes in residential storey buildings
© Research India Publications.Performing thermophysical modeling of processes of heatwind conditions in urban design allows setting the amount of convective-radiative heat flow, which comes from heating of the active surface and goes into the air. Knowing these values allows the possibility of taking appropriate design considerations in the human breathing zone for creating conditions for thermal comfort
Depolarizing GABA and developmental epilepsies
© 2014 John Wiley & Sons Ltd. Early in development, GABA, which is the main inhibitory neurotransmitter in adult brain, depolarizes immature neurons and exerts dual-excitatory and shunting/inhibitory-effects in the developing neuronal networks. The present review discusses some general questions, including the properties of excitation at depolarizing GABAergic synapse and shunting inhibition by depolarizing GABA; technical issues in exploration of depolarizing GABA using various techniques and preparations, including the developmental aspects of traumatic injury and what is known (or rather unknown) on the actions of GABA in vivo; complex roles of depolarizing GABA in developmental epilepsies, including a contribution of depolarizing GABA to enhanced excitability in the immature networks, caused by repetitive seizures accumulation of intracellular chloride concentration that increases excitatory GABA power and its synchronizing proconvulsive effects, and correction of chloride homeostasis as a potential strategy to treat neonatal seizures
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