1,017 research outputs found
Properties of galactic B[e] supergiants. IV. Hen3-298 and Hen3-303
We present the results of optical and near-IR spectroscopic and near-IR
photometric observations of the emission-line stars Hen3-298 and Hen3-303.
Strong emission in the H-alpha line is found in both objects. The presence of
Fe II and [O I] emission lines in the spectrum of Hen3-298 indicates that it is
a B[e] star. The double-peaked CO line profiles, found in the infrared spectrum
of Hen3-298, along with the optical line profiles suggest that the star is
surrounded by a rotating circumstellar disk. Both objects also show infrared
excesses, similar to those of B[e] stars. The radial velocities of the
absorption and emission lines as well as a high reddening level suggest that
the objects are located in the Norma spiral arm at a distance of 3-4.5 kpc. We
estimated a luminosity of log (L/L_sun) ~ 5.1 and a spectral type of no earlier
than B3 for Hen3-298. Hen3-303 seems to be a less luminous B-type object (log
(L/L_sun) ~ 4.3), located in the same spiral arm.Comment: 8 pages, 5 figures, accepted by Astronomy and Astrophysic
Giant In-Particle Field Concentration and Fano Resonances at Light Scattering by High-Refractive Index Particles
A detailed analytical inspection of light scattering by a particle with high
refractive index m+i\kappa and small dissipative constant \kappa is presented.
We have shown that there is a dramatic difference in the behavior of the
electromagnetic field within the particle (inner problem) and the scattered
field outside it (outer problem). With an increase in m at fix values of the
other parameters, the field within the particle asymptotically converges to a
periodic function of m. The electric and magnetic type Mie resonances of
different orders overlap substantially. It may lead to a giant concentration of
the electromagnetic energy within the particle. At the same time, we
demonstrate that identical transformations of the solution for the outer
problem allow to present each partial scattered wave as a sum of two
partitions. One of them corresponds to the m-independent wave, scattered by a
perfectly reflecting particle and plays the role of a background, while the
other is associated with the excitation of a sharply-m-dependent resonant Mie
mode. The interference of the partitions brings about a typical asymmetric Fano
profile. The explicit expressions for the parameters of the Fano profile have
been obtained "from the first principles" without any additional assumptions
and/or fitting. In contrast to the inner problem, at an increase in m the
resonant modes of the outer problem die out, and the scattered field converges
to the universal, m-independent profile of the perfectly reflecting sphere.
Numerical estimates of the discussed effects for a gallium phosphide particle
are presented.Comment: 18 pages, 10 figure
AC field induced quantum rectification effect in tunnel junctions
We study the appearance of directed current in tunnel junctions, quantum
ratchet effect, in the presence of an external ac field f(t). The current is
established in a one-dimensional discrete inhomogeneous "tight-binding model".
By making use of a symmetry analysis we predict the right choice of f(t) and
obtain the directed current as a difference between electron transmission
coefficients in opposite directions, . Numerical
simulations confirm the predictions of the symmetry analysis and moreover, show
that the directed current can be drastically increased by a proper choice of
frequency and amplitudes of the ac field f(t).Comment: 4 pages, 3 figures, to be published in Physical Review
Radiation Pressure Quantization
Kepler's observation of comets tails initiated the research on the radiation
pressure of celestial objects and 250 years later they found new incarnation
after the Maxwell's equations were formulated to describe a plethora of
light-matter coupling phenomena. Further, quantum mechanics gave birth to the
photon drag effect. Here, we predict a novel universal phenomenon which can be
referred to as quantization of the radiation pressure. We develop a microscopic
theory of this effect which can be applied to a general system containing
Bose-Einstein-condensed particles, which possess an internal structure of
quantum states. By analyzing the response of the system to an external
electromagnetic field we find that such drag results in a flux of particles
constituting both the condensate and the excited states. We show that in the
presence of the condensed phase, the response of the system becomes quantized
which manifests itself in a step-like behavior of the particle flux as a
function of electromagnetic field frequency with the elementary quantum
determined by the internal energy structure of the particles.Comment: Manuscript: 4 pages, 3 figure
Spin filters with Fano dots
We compute the zero bias conductance of electrons through a single ballistic
channel weakly coupled to a side quantum dot with Coulomb interaction. In
contrast to the standard setup which is designed to measure the transport
through the dot, the channel conductance reveals Coulomb blockade dips rather
then peaks due to the Fano-like backscattering. At zero temperature the Kondo
effect leads to the formation of broad valleys of small conductance
corresponding to an odd number of electrons on the dot. By applying a magnetic
field in the dot region we find two dips corresponding to a total suppression
in the conductance of spins up and down separated by an energy of the order of
the Coulomb interaction. This provides a possibility of a perfect spin filter.Comment: 5 pages, 4 figures, to be published in European Physical Journal
Bacteria in our lives
Bacteria are an integral part of our lives. They don’t only surround us externally, but also live inside us. Most people think that the bacteria are harmful micro-organisms, but they are wrong. Along with the pathogenicity, they play an important role in ensuring the normal functioning of our body. Microbial colonies found on or in the body are normally benign or beneficial. Bacteria are the basis of the normal microflora of many systems, especially of the digestive tract. These microbial colonies carry out a series of helpful and necessary functions, such as aiding in digestion. They also protect the body from the penetration of pathogenic microbes. These beneficial microbial colonies compete with each other for space and resources
Incommensurate dynamics of resonant breathers in Josephson junction ladders
We present theoretical and experimental studies of resonant localized
resistive states in a Josephson junction ladder. These complex breather states
are obtained by tuning the breather frequency into the upper band of linear
electromagnetic oscillations of the ladder. Their prominent feature is the
appearance of resonant steps in the current-voltage (I-V) characteristics. We
have found the resonant breather-like states displaying incommensurate
dynamics. Numerical simulations show that these incommensurate resonant
breathers persist for very low values of damping. Qualitatively similar
incommensurate breather states are observed in experiments performed with
Nb-based Josephson ladders. We explain the appearance of these states with the
help of resonance-induced hysteresis features in the I-V dependence.Comment: 5 pages, 6 figure
Fano resonance in quadratic waveguide arrays
We study resonant light scattering in arrays of channel optical waveguides
where tunable quadratic nonlinearity is introduced as nonlinear defects by
periodic poling of single (or several) waveguides in the array. We describe
novel features of wave scattering that can be observed in this structure and
show that it is a good candidate for the first observation of Fano resonance in
nonlinear optics.Comment: 3 pages, 3 figures, submitted to Optics Letters, slightly revise
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