232 research outputs found
Channeling 5-min photospheric oscillations into the solar outer atmosphere through small-scale vertical magnetic flux tubes
We report two-dimensional MHD simulations which demonstrate that photospheric
5-min oscillations can leak into the chromosphere inside small-scale vertical
magnetic flux tubes. The results of our numerical experiments are compatible
with those inferred from simultaneous spectropolarimetric observations of the
photosphere and chromosphere obtained with the Tenerife Infrared Polarimeter
(TIP) at 10830 A. We conclude that the efficiency of energy exchange by
radiation in the solar photosphere can lead to a significant reduction of the
cut-off frequency and may allow for the propagation of the 5 minutes waves
vertically into the chromosphere.Comment: accepted by ApJ
de-Broglie Wave-Front Engineering
We propose a simple method for the deterministic generation of an arbitrary
continuous quantum state of the center-of-mass of an atom. The method's spatial
resolution gradually increases with the interaction time with no apparent
fundamental limitations. Such de-Broglie Wave-Front Engineering of the atomic
density can find applications in Atom Lithography, and we discuss possible
implementations of our scheme in atomic beam experiments.Comment: The figures' quality was improved, the text remains intact. 5 pages,
3 figures; submitted to PR
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Cortical hot spots and labyrinths: Why cortical neuromodulation for episodic migraine with aura should be personalized
Quantum synthesis of arbitrary unitary operators
Nature provides us with a restricted set of microscopic interactions. The
question is whether we can synthesize out of these fundamental interactions an
arbitrary unitary operator. In this paper we present a constructive algorithm
for realization of any unitary operator which acts on a (truncated) Hilbert
space of a single bosonic mode. In particular, we consider a physical
implementation of unitary transformations acting on 1-dimensional vibrational
states of a trapped ion. As an example we present an algorithm which realizes
the discrete Fourier transform.Comment: 6 RevTeX pages with 3 figures, submitted to Phys.Rev.A, see also
http://nic.savba.sk/sav/inst/fyzi/qo
Quantum carpet interferometry for trapped atomic Bose-Einstein condensates
We propose an ``interferometric'' scheme for Bose-Einstein condensates using
near-field diffraction. The scheme is based on the phenomenon of intermode
traces or quantum carpets; we show how it may be used in the detection of weak
forces.Comment: 4 figures. Submitted to Phys. Rev.
Effective Thermal Conductivity of Composite Materials Based on Open Cell Foams
Open cell metal foams increasingly find lots of applications in modern energy systems. For example, they improve the efficiency of low-energy modules based on paraffin wax. In this work, the effective thermal conductivity of selected composite materials based on open cell foam solids is calculated by means of computer simulations. The results are compared with appropriate experimental values with a very good agreement. The characteristic constants for three material laws (Bhattacharya, Ashby and Maxwell) are found. The range of validity of these laws is narrowed to enable the well-directed use of them in the future
Quantum-state synthesis of multi-mode bosonic fields: Preparation of arbitrary states of 2-D vibrational motion of trapped ions
We present a universal algorithm for an efficient deterministic preparation
of an arbitrary two--mode bosonic state. In particular, we discuss in detail
preparation of entangled states of a two-dimensional vibrational motion of a
trapped ion via a sequence of laser stimulated Raman transitions. Our formalism
can be generalized for multi-mode bosonic fields. We examine stability of our
algorithm with respect to a technical noise.Comment: 8 pages, revtex, including 2 ps-figures, section about physical
implementation added, references updated, submitted to Phys. Rev. A, computer
program available at http://www.savba.sk/sav/inst/fyzi/qo
Spectropolarimetric investigation of the propagation of magnetoacoustic waves and shock formation in sunspot atmospheres
Velocity oscillations in sunspot umbrae have been measured simultaneously in
two spectral lines: the photospheric Silicon I 10827 A line and the
chromospheric Helium I 10830 A multiplet. From the full Stokes inversion of
temporal series of spectropolarimetric observations we retrieved, among other
parameters, the line of sight velocity temporal variations at photospheric and
chromospheric heights. Chromospheric velocity oscillations show a three minute
period with a clear sawtooth shape typical of propagating shock wave fronts.
Photospheric velocity oscillations have basically a five minute period,
although the power spectrum also shows a secondary peak in the three minute
band which has proven to be predecessor for its chromospheric counterpart. The
derived phase spectra yield a value of the atmospheric cut-off frequency around
4 mHz and give evidence for the upward propagation of higher frequency
oscillation modes. The phase spectrum has been reproduced with a simple model
of linear vertical propagation of slow magneto-acoustic waves in a stratified
magnetized atmosphere that accounts for radiative losses through Newton's
cooling law. The model explains the main features in the phase spectrum, and
allows us to compute the theoretical time delay between the photospheric and
chromospheric signals, which happens to have a strong dependence on frequency.
We find a very good agreement between this and the time delay obtained directly
from the cross-correlation of photospheric and chromospheric velocity maps
filtered around the 6 mHz band. This allows us to infer that the 3-minute power
observed at chromospheric heights comes directly from the photosphere by means
of linear wave propagation, rather than from non-linear interaction of 5-minute
(and/or higher frequency) modes.Comment: aastex preprint, 32 pages, 12 figure
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