5,225 research outputs found
Spectral and localization properties of the Dirichlet wave guide with two concentric Neumann discs
Bound states of the Hamiltonian describing a quantum particle living on three
dimensional straight strip of width are investigated. We impose the Neumann
boundary condition on the two concentric windows of the radii and
located on the opposite walls and the Dirichlet boundary condition on the
remaining part of the boundary of the strip. We prove that such a system
exhibits discrete eigenvalues below the essential spectrum for any .
When and tend to the infinity, the asymptotic of the eigenvalue is
derived. A comparative analysis with the one-window case reveals that due to
the additional possibility of the regulating energy spectrum the anticrossing
structure builds up as a function of the inner radius with its sharpness
increasing for the larger outer radius. Mathematical and physical
interpretation of the obtained results is presented; namely, it is derived that
the anticrossings are accompanied by the drastic changes of the wave function
localization. Parallels are drawn to the other structures exhibiting similar
phenomena; in particular, it is proved that, contrary to the two-dimensional
geometry, at the critical Neumann radii true bound states exist.Comment: 25 pages, 7 figure
Propagation of axions in a strongly magnetized medium
The polarization operator of an axion in a degenerate gas of electrons
occupying the ground-state Landau level in a superstrong magnetic field G is investigated in a model with a
tree-level axion-electron coupling. It is shown that a dynamic axion mass,
which can fall within the allowed range of values , is generated under the conditions of strongly
magnetized neutron stars. As a result, the dispersion relation for axions is
appreciably different from that in a vacuum.Comment: RevTex, no figures, 13 pages, Revised version of the paper published
in J. Exp. Theor. Phys. {\bf 88}, 1 (1999
On the motion of a heavy rigid body in an ideal fluid with circulation
Chaplygin's equations describing the planar motion of a rigid body in an
unbounded volume of an ideal fluid involved in a circular flow around the body
are considered. Hamiltonian structures, new integrable cases, and partial
solutions are revealed, and their stability is examined. The problems of
non-integrability of the equations of motion because of a chaotic behavior of
the system are discussed.Comment: 25 pages, 4 figure
Photometric and Spectroscopic Investigation of the Dwarf Nova HS 0218+3229: A Short Review
This paper is devoted to the study of the cataclysmic variable HS 0218+3229 using the photometric and spectroscopic observations
Coherent control of injection currents in high-quality films of Bi2Se3
Films of the topological insulator Bi2Se3 are grown by molecular beam epitaxy
with in-situ reflection high-energy electron diffraction. The films are shown
to be high-quality by X-ray reflectivity and diffraction and atomic-force
microscopy. Quantum interference control of photocurrents is observed by
excitation with harmonically related pulses and detected by terahertz
radiation. The injection current obeys the expected excitation irradiance
dependence, showing linear dependence on the fundamental pulse irradiance and
square-root irradiance dependence of the frequency-doubled optical pulses. The
injection current also follows a sinusoidal relative-phase dependence between
the two excitation pulses. These results confirm the third-order nonlinear
optical origins of the coherently controlled injection current. Experiments are
compared to a tight-binding band structure to illustrate the possible optical
transitions that occur in creating the injection current.Comment: 11 pages, 3 figure, journal articl
On the full, strongly exceptional collections on toric varieties with Picard number three
We investigate full strongly exceptional collections on smooth, com- plete
toric varieties. We obtain explicit results for a large family of varieties
with Picard number three, containing many of the families already known. We
also describe the relations between the collections and the split of the push
forward of the trivial line bundle by the toric Frobenius morphism
Microsecond Time-Resolved Absorption Spectroscopy Used to Study CO Compounds of Cytochrome bd from Escherichia coli
Cytochrome bd is a tri-heme (b558, b595, d) respiratory oxygen reductase that is found in many bacteria including pathogenic
species. It couples the electron transfer from quinol to O2 with generation of an electrochemical proton gradient. We
examined photolysis and subsequent recombination of CO with isolated cytochrome bd from Escherichia coli in oneelectron
reduced (MV) and fully reduced (R) states by microsecond time-resolved absorption spectroscopy at 532-nm
excitation. Both Soret and visible band regions were examined. CO photodissociation from MV enzyme possibly causes fast
(t,1.5 ms) electron transfer from heme d to heme b595 in a small fraction of the protein, not reported earlier. Then the
electron migrates to heme b558 (t,16 ms). It returns from the b-hemes to heme d with t,180 ms. Unlike cytochrome bd in
the R state, in MV enzyme the apparent contribution of absorbance changes associated with CO dissociation from heme d is
small, if any. Photodissociation of CO from heme d in MV enzyme is suggested to be accompanied by the binding of an
internal ligand (L) at the opposite side of the heme. CO recombines with heme d (t,16 ms) yielding a transient
hexacoordinate state (CO-Fe2+
-L). Then the ligand slowly (t,30 ms) dissociates from heme d. Recombination of CO with a
reduced heme b in a fraction of the MV sample may also contribute to the 30-ms phase. In R enzyme, CO recombines to
heme d (t,20 ms), some heme b558 (t,0.2–3 ms), and finally migrates from heme d to heme b595 (t,24 ms) in ,5% of the
enzyme population. Data are consistent with the recent nanosecond study of Rappaport et al. conducted on the
membranes at 640-nm excitation but limited to the Soret band. The additional phases were revealed due to differences in
excitation and other experimental conditions
Chaplygin ball over a fixed sphere: explicit integration
We consider a nonholonomic system describing a rolling of a dynamically
non-symmetric sphere over a fixed sphere without slipping. The system
generalizes the classical nonholonomic Chaplygin sphere problem and it is shown
to be integrable for one special ratio of radii of the spheres. After a time
reparameterization the system becomes a Hamiltonian one and admits a separation
of variables and reduction to Abel--Jacobi quadratures. The separating
variables that we found appear to be a non-trivial generalization of
ellipsoidal (spheroconical) coordinates on the Poisson sphere, which can be
useful in other integrable problems.
Using the quadratures we also perform an explicit integration of the problem
in theta-functions of the new time.Comment: This is an extended version of the paper to be published in Regular
and Chaotic Dynamics, Vol. 13 (2008), No. 6. Contains 20 pages and 2 figure
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