344 research outputs found
Bound states of scalar particles in the presence of a short range potential
We analyze the behavior of the energy spectrum of the Klein-Gordon equation
in the presence of a truncated hyperbolic tangent potential. From our analysis
we obtain that, for some values of the potential there is embedding of the
bound states into the negative energy continuum, showing that, in opposition to
the general belief, relativistic scalar particles in one-dimensional short
range potentials can exhibit resonant behavior and not only the Schiff-Snyder
effect.Comment: To appear in Modern Physics Letters
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
Planar Dirac Electron in Coulomb and Magnetic Fields
The Dirac equation for an electron in two spatial dimensions in the Coulomb
and homogeneous magnetic fields is discussed. For weak magnetic fields, the
approximate energy values are obtained by semiclassical method. In the case
with strong magnetic fields, we present the exact recursion relations that
determine the coefficients of the series expansion of wave functions, the
possible energies and the magnetic fields. It is found that analytic solutions
are possible for a denumerably infinite set of magnetic field strengths. This
system thus furnishes an example of the so-called quasi-exactly solvable
models. A distinctive feature in the Dirac case is that, depending on the
strength of the Coulomb field, not all total angular momentum quantum number
allow exact solutions with wavefunctions in reasonable polynomial forms.
Solutions in the nonrelativistic limit with both attractive and repulsive
Coulomb fields are briefly discussed by means of the method of factorization.Comment: 18 pages, RevTex, no figure
Induced Current and Aharonov-Bohm Effect in Graphene
The effect of vacuum polarization in the field of an infinitesimally thin
solenoid at distances much larger than the radius of solenoid is investigated.
The induced charge density and induced current are calculated. Though the
induced charge density turned out to be zero, the induced current is finite
periodical function of the magnetic flux . The expression for this
function is found exactly in a value of the flux. The induced current is equal
to zero at the integer values of as well as at half-integer
values of this ratio, where is the elementary magnetic
flux. The latter is a consequence of the Furry theorem and periodicity of the
induced current with respect to magnetic flux. As an example we consider the
graphene in the field of solenoid perpendicular to the plane of a sample.Comment: 3 pages, 1 figure, version accepted to Phys. Rev.
Hydrogen sulfide inhibits giant depolarizing potentials and abolishes epileptiform activity of neonatal rat hippocampal slices
© 2016 IBROHydrogen sulfide (H2S) is an endogenous gasotransmitter with neuroprotective properties that participates in the regulation of transmitter release and neuronal excitability in various brain structures. The role of H2S in the growth and maturation of neural networks however remains unclear. The aim of the present study is to reveal the effects of H2S on neuronal spontaneous activity relevant to neuronal maturation in hippocampal slices of neonatal rats. Sodium hydrosulfide (NaHS) (100 ΌM), a classical donor of H2S produced a biphasic effect with initial activation and subsequent concentration-dependent suppression of network-driven giant depolarizing potentials (GDPs) and neuronal spiking activity. Likewise, the substrate of H2S synthesis L-cysteine (1 mM) induced an initial increase followed by an inhibition of GDPs and spiking activity. Our experiments indicate that the increase in initial discharge activity by NaHS is evoked by neuronal depolarization which is partially mediated by a reduction of outward K+ currents. The subsequent decrease in the neuronal activity by H2S appears to be due to the rightward shift of activation and inactivation of voltage-gated Na+ currents, thus preventing network activity. NaHS also reduced N-methyl-D-aspartate (NMDA)-mediated currents, without essential effect on AMPA/kainate or GABAA-mediated currents. Finally, H2S abolished the interictal-like events induced by bicuculline. In summary, our results suggest that through the inhibitory action on voltage-gated Na+ channels and NMDA receptors, H2S prevents the enhanced neuronal excitability typical to early hippocampal networks
Spectrum of the Relativistic Particles in Various Potentials
We extend the notion of Dirac oscillator in two dimensions, to construct a
set of potentials. These potentials becomes exactly and quasi-exactly solvable
potentials of non-relativistic quantum mechanics when they are transformed into
a Schr\"{o}dinger-like equation. For the exactly solvable potentials,
eigenvalues are calculated and eigenfunctions are given by confluent
hypergeometric functions. It is shown that, our formulation also leads to the
study of those potentials in the framework of the supersymmetric quantum
mechanics
Anisotropic Pressures in Very Dense Magnetized Matter
The problem of anisotropic pressures arising as a consequence of the spatial
symmetry breaking introduced by an external magnetic field in quantum systems
is discussed. The role of the conservation of energy and momentum of external
fields as well as of systems providing boundary conditions in quantum
statistics is considered. The vanishing of the average transverse momentum for
an electron-positron system in its Landau ground state is shown, which means
the vanishing of its transverse pressure. The situation for neutron case and
Strange Quark Matter (SQM) in -equilibrium is also briefly discussed.
Thermodynamical relations in external fields as well as the form of the stress
tensor in a quantum relativistic medium are also discussed. The ferromagnetic
symmetry breaking is briefly discussed.Comment: 10 page
Theoretical evaluation of rheological state of sand cement composite systems with polyoxyethylene additive using topological dynamics concept
© 2016 Trans Tech Publications, Switzerland.Presents the results of studies of contemporary materials in the field of rheological state. The topological mortar structure has been provided by theoretical evaluation of the rheological state of the cross-linked solutions and the experimental viscosity data of the sand cement mortar which has been modified by water-soluble additive â polyoxyethylene. The general model has been made for the structure of non-Newtonian liquideous systems including dilatant, pseudoplastic bodies with two main rheological active components in their structure â rigid and viscous phases. It is shown that in pseudoplastic systems, as the shear stress increases, the viscous phase grows because of the reduction of rigid phase content. In dilatant systems the converse situation has been observed. Furthermore, these phases are not clearly distinguishable, but to the contrary they are spatially interconnected in a complex way. The structure modeling has been made for non-Newtonian bodies using the Shklovskii-de Gennes model. The studies have found that the construction composite sand cement system is defined as the pseudoplastic body where cement and sand act as the rigid phase, water solution of polyoxyethylene â as the viscous phase. These findings can be used to prove the influence of polymer powder on the workability of dry mortar
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