788 research outputs found
Oscillations above sunspots from the temperature minimum to the corona
Context. An analysis of the oscillations above sunspots was carried out using
simultaneous ground-based and Solar Dynamics Observatory (SDO) observations
(SiI 10827A, HeI 10830A, FeI 6173A, 1700A, HeII 304A, FeIX 171A).
Aims. Investigation of the spatial distribution of oscillation power in the
frequency range 1-8 mHz for the different height levels of the solar
atmosphere. Measuring the time lags between the oscillations at the different
layers.
Methods. We used frequency filtration of the intensity and Doppler velocity
variations with Morlet wavelet to trace the wave propagation from the
photosphere to the chromosphere and the corona.
Results. The 15 min oscillations are concentrated near the outer penumbra in
the upper photosphere (1700 A), forming a ring, that expands in the transition
zone. These oscillations propagate upward and reach the corona level, where
their spatial distribution resembles a fan structure. The spatial distribution
of the 5 min oscillation power looks like a circle-shape structure matching the
sunspot umbra border at the photospheric level. The circle expands at the
higher levels (HeII 304A and FeIX 171A). This indicates that the low-frequency
oscillations propagate along the inclined magnetic tubes in the spot. We found
that the inclination of the tubes reaches 50--60 degrees in the upper
chromosphere and the transition zone. The main oscillation power in the 5-8 mHz
range concentrates within the umbra boundaries at all the levels. The highest
frequency oscillations (8 mHz) are located in the peculiar points inside the
umbra. These points probably coincide with umbral dots. We deduced the
propagation velocities to be 28+-15 km/s, 26+-15 km/s, and 55+-10 km/s for the
SiI 10827A-HeI 10830A, 1700A-HeII 304A, and HeII 304A-FeIX 171A height levels,
respectively
Kinetic Solvers with Adaptive Mesh in Phase Space
An Adaptive Mesh in Phase Space (AMPS) methodology has been developed for
solving multi-dimensional kinetic equations by the discrete velocity method. A
Cartesian mesh for both configuration (r) and velocity (v) spaces is produced
using a tree of trees data structure. The mesh in r-space is automatically
generated around embedded boundaries and dynamically adapted to local solution
properties. The mesh in v-space is created on-the-fly for each cell in r-space.
Mappings between neighboring v-space trees implemented for the advection
operator in configuration space. We have developed new algorithms for solving
the full Boltzmann and linear Boltzmann equations with AMPS. Several recent
innovations were used to calculate the discrete Boltzmann collision integral
with dynamically adaptive mesh in velocity space: importance sampling,
multi-point projection method, and the variance reduction method. We have
developed an efficient algorithm for calculating the linear Boltzmann collision
integral for elastic and inelastic collisions in a Lorentz gas. New AMPS
technique has been demonstrated for simulations of hypersonic rarefied gas
flows, ion and electron kinetics in weakly ionized plasma, radiation and light
particle transport through thin films, and electron streaming in
semiconductors. We have shown that AMPS allows minimizing the number of cells
in phase space to reduce computational cost and memory usage for solving
challenging kinetic problems
Quantum limits of super-resolution in reconstruction of optical objects
We investigate analytically and numerically the role of quantum fluctuations
in reconstruction of optical objects from diffraction-limited images. Taking as
example of an input object two closely spaced Gaussian peaks we demonstrate
that one can improve the resolution in the reconstructed object over the
classical Rayleigh limit. We show that the ultimate quantum limit of resolution
in such reconstruction procedure is determined not by diffraction but by the
signal-to-noise ratio in the input object. We formulate a quantitative measure
of super-resolution in terms of the optical point-spread function of the
system.Comment: 23 pages, 7 figures. Submitted to Physical Review A e-mail:
[email protected]
Quantum teleportation of optical images with frequency conversion
We describe a new version of continuous variables quantum holographic
teleportation of optical images. Unlike the previously proposed scheme, it is
based on the continuous variables quantum entanglement between the light fields
of different frequencies and allows for the wavelength conversion between the
original and the teleported images. The frequency tunable holographic
teleportation protocol can be used as a part of light-matter interface in
parallel quantum information processing and parallel quantum memoryComment: 4 pages, 3 Postscript figures, RevTeX
Sub-wavelength lithography over extended areas
We demonstrate a systematic approach to sub-wavelength resolution
lithographic image formation on films covering areas larger than a wavelength
squared. For example, it is possible to make a lithographic pattern with a
feature size resolution of by using a particular -photon, multi-mode entangled state, where , and banks of birefringent
plates. By preparing a statistically mixed such a state one can form any pixel
pattern on a pixel grid occupying a square
with a side of wavelengths. Hence, there is a trade-off between
the exposed area, the minimum lithographic feature size resolution, and the
number of photons used for the exposure. We also show that the proposed method
will work even under non-ideal conditions, albeit with somewhat poorer
performance.Comment: 8 pages, 8 figures, 1 table. Written in RevTe
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