74 research outputs found
CPT and Lorentz violation effects in hydrogen-like atoms
Within the framework of Lorentz-violating extended electrodynamics, the Dirac
equation for a bound electron in an external electromagnetic field is
considered assuming the interaction with a CPT-odd axial vector background
. The quasi-relativistic Hamiltonian is obtained using a -series
expansion. Relativistic Dirac eigenstates in a spherically-symmetric potential
are found accurate up to the second order in . -induced CPT-odd
corrections to the electromagnetic dipole moment operators of a bound electron
are calculated that contribute to the anapole moment of the atomic orbital and
may cause a specific asymmetry of the angular distribution of the radiation of
a hydrogen atom.Comment: 13 pages, 1 figure; (5.14) is corrected to conform to the
normalization convention for Laguerre polynomials adopted at present; minor
grammatical change
Competition of Color Ferromagnetic and Superconductive States in a Quark-Gluon System
The possibility of color ferromagnetism in an SU(2) gauge field model is
investigated. The conditions allowing a stable color ferromagnetic state of the
quark system in the chromomagnetic field occupying small domains are
considered. A phase transition between this state and the color superconducting
state is considered. The effect of finite temperature is analyzed.Comment: 21 pages, 4 Postscript figure
Free Energy of an SU(2) Model of (2+1)-dimensional QCD in the Constant Condensate Background
Gluon and quark contributions to the thermodynamic potential (free energy) of
a (2+1)-dimensional QCD model at finite temperature in the background of a
constant homogeneous chromomagnetic field H combined with A_0 condensate are
calculated. The role of the tachyonic mode in the gluon energy spectrum is
discussed. A possibility of the free energy global minimum generation at
nonzero values of H and A_0 condensates is investigated.Comment: LaTeX 2e, 14 pages, 6 eps figures, some miscalculations were
correcte
Plasmonic nanoparticle monomers and dimers: From nano-antennas to chiral metamaterials
We review the basic physics behind light interaction with plasmonic
nanoparticles. The theoretical foundations of light scattering on one metallic
particle (a plasmonic monomer) and two interacting particles (a plasmonic
dimer) are systematically investigated. Expressions for effective particle
susceptibility (polarizability) are derived, and applications of these results
to plasmonic nanoantennas are outlined. In the long-wavelength limit, the
effective macroscopic parameters of an array of plasmonic dimers are
calculated. These parameters are attributable to an effective medium
corresponding to a dilute arrangement of nanoparticles, i.e., a metamaterial
where plasmonic monomers or dimers have the function of "meta-atoms". It is
shown that planar dimers consisting of rod-like particles generally possess
elliptical dichroism and function as atoms for planar chiral metamaterials. The
fabricational simplicity of the proposed rod-dimer geometry can be used in the
design of more cost-effective chiral metamaterials in the optical domain.Comment: submitted to Appl. Phys.
Gauge field theory for Poincar\'{e}-Weyl group
On the basis of the general principles of a gauge field theory the gauge
theory for the Poincar\'{e}-Weyl group is constructed. It is shown that tetrads
are not true gauge fields, but represent functions from true gauge fields:
Lorentzian, translational and dilatational ones. The equations of gauge fields
which sources are an energy-momentum tensor, orbital and spin momemta, and also
a dilatational current of an external field are obtained. A new direct
interaction of the Lorentzian gauge field with the orbital momentum of an
external field appears, which describes some new effects. Geometrical
interpretation of the theory is developed and it is shown that as a result of
localization of the Poincar\'{e}-Weyl group spacetime becomes a Weyl-Cartan
space. Also the geometrical interpretation of a dilaton field as a component of
the metric tensor of a tangent space in Weyl-Cartan geometry is proposed.Comment: LaTex, 27 pages, no figure
Quark zero modes in intersecting center vortex gauge fields
The zero modes of the Dirac operator in the background of center vortex gauge
field configurations in and are examined. If the net flux in D=2
is larger than 1 we obtain normalizable zero modes which are mainly localized
at the vortices. In D=4 quasi-normalizable zero modes exist for intersecting
flat vortex sheets with the Pontryagin index equal to 2. These zero modes are
mainly localized at the vortex intersection points, which carry a topological
charge of . To circumvent the problem of normalizability the
space-time manifold is chosen to be the (compact) torus \T^2 and \T^4,
respectively. According to the index theorem there are normalizable zero modes
on \T^2 if the net flux is non-zero. These zero modes are localized at the
vortices. On \T^4 zero modes exist for a non-vanishing Pontryagin index. As
in these zero modes are localized at the vortex intersection points.Comment: 20 pages, 4 figures, LaTeX2e, references added, treatment of ideal
vortices on the torus shortene
Роль МРТ у діагностиці м'язово-неінвазивного раку cечового міхура
Рак сечового міхура (РСМ) залишається актуальною проблемою сучасної урології у зв’язку з широкою поширеністю захворювання, тривалістю та складністю лікування, високим відсотком інвалідизації, неухильним ростом захворюваності та смертності. В Україні щороку реєструється близько 5 тис. нових випадків і 2,3 тис. смертей від даної патології. Приблизно 90% пухлин сечового міхура
(СМ) представлені уротеліальною карциномою, яку також називають перехідно-клітинним раком. Водночас своєчасна інформативна діагностика пухлин сечового міхура на ранній стадії та лікування хворих із даною патологією залишаються складними проблемами сучасної онкоурології
Large N dynamics in QED in a magnetic field
The expression for the dynamical mass of fermions in QED in a magnetic field
is obtained for a large number of the fermion flavor N in the framework of 1/N
expansion. The existence of a threshold value N_{thr}, dividing the theories
with essentially different dynamics, is established. For the number of flavors
N << N_{thr}, the dynamical mass is very sensitive to the value of the coupling
constant \alpha_b, related to the magnetic scale \mu = |eB|. For N of order
N_{thr} or larger, a dynamics similar to that in the Nambu-Jona-Lasinio model
with cutoff of order |eB| and the dimensional coupling constant G \sim
1/(N|eB|) takes place. In this case, the value of the dynamical mass is
essentially \alpha_b independent (the dynamics with an infrared stable fixed
point). The value of N_{thr} separates a weak coupling dynamics (with
\tilde{\alpha}_b \equiv N\alpha_b << 1) from a strong coupling one (with
\tilde{\alpha}_b \gtrsim 1) and is of order 1/\alpha_b.Comment: 4 pages, REVTe
Radiative Effects in the Standard Model Extension
The possibility of radiative effects induced by the Lorentz and CPT
non-invariant interaction term for fermions in the Standard Model Extension is
investigated. In particular, electron-positron photo-production and photon
emission by electrons and positrons are studied. The rates of these processes
are calculated in the Furry picture. It is demonstrated that the rates obtained
in the framework of the model adopted strongly depend on the polarization
states of the particles involved. As a result, ultra-relativistic particles
produced should occupy states with a preferred spin orientation, i.e., photons
have the sign of polarization opposite to the sign of the effective potential,
while charged particle are preferably in the state with the helicity coinciding
with the sign of the effective potential. This leads to evident spatial
asymmetries which may have certain consequences observable at high energy
accelerators, and in astrophysical and cosmological studies.Comment: 10 pages, 2 figures, Revtex4, to appear in Phys.Rev.D, misprints are
correcte
Helix movement is coupled to displacement of the second extracellular loop in rhodopsin activation
The second extracellular loop (EL2) of rhodopsin forms a cap over the binding site of its photoreactive 11-cis retinylidene chromophore. A crucial question has been whether EL2 forms a reversible gate that opens upon activation or acts as a rigid barrier. Distance measurements using solid-state 13C NMR spectroscopy between the retinal chromophore and the β4 strand of EL2 show that the loop is displaced from the retinal binding site upon activation, and there is a rearrangement in the hydrogen-bonding networks connecting EL2 with the extracellular ends of transmembrane helices H4, H5 and H6. NMR measurements further reveal that structural changes in EL2 are coupled to the motion of helix H5 and breaking of the ionic lock that regulates activation. These results provide a comprehensive view of how retinal isomerization triggers helix motion and activation in this prototypical G protein-coupled receptor. © 2009 Nature America, Inc. All rights reserved
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