100 research outputs found
Model of Electrostatic Actuated Deformable Mirror Using Strongly Coupled Electro-Mechanical Finite Element
The aim of this paper is to deal with multi-physics simulation of
micro-electro-mechanical systems (MEMS) based on an advanced numerical
methodology. MEMS are very small devices in which electric as well as
mechanical and fluid phenomena appear and interact. Because of their
microscopic scale, strong coupling effects arise between the different physical
fields, and some forces, which were negligible at macroscopic scale, have to be
taken into account. In order to accurately design such micro-electro-mechanical
systems, it is of primary importance to be able to handle the strong coupling
between the electric and the mechanical fields. In this paper, the finite
element method (FEM) is used to model the strong coupled electro-mechanical
interactions and to perform static and transient analyses taking into account
large mesh displacements. These analyses will be used to study the behaviour of
electrostatically actuated micro-mirrors.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Decoherence of encoded quantum registers
In order to eliminate disturbing effects of decoherence, encoding of quantum
information in decoherence-free subspaces has been suggested. We analyze the
benefits of this concept for a quantum register that is realized in a spin
chain in contact with a common bosonic bath. Within a dissipation-less model we
provide explicit analytical results for the average fidelity of plain and
encoded quantum registers. For the investigation of dissipative spin-boson
couplings we employ a master equation of Bloch-Redfield type.Comment: 13 pages, 9 figure
Spectral Compressibility at the Metal-Insulator Transition of the Quantum Hall Effect
The spectral properties of a disordered electronic system at the
metal-insulator transition point are investigated numerically. A recently
derived relation between the anomalous diffusion exponent and the
spectral compressibility at the mobility edge, , is
confirmed for the integer quantum Hall delocalization transition. Our
calculations are performed within the framework of an unitary network-model and
represent a new method to investigate spectral properties of disordered
systems.Comment: 5 pages, RevTeX, 3 figures, Postscript, strongly revised version to
be published in PR
Wave-packet dynamics at the mobility edge in two- and three-dimensional systems
We study the time evolution of wave packets at the mobility edge of
disordered non-interacting electrons in two and three spatial dimensions. The
results of numerical calculations are found to agree with the predictions of
scaling theory. In particular, we find that the -th moment of the
probability density scales like in dimensions. The
return probability scales like , with the generalized
dimension of the participation ratio . For long times and short distances
the probability density of the wave packet shows power law scaling
. The numerical calculations were performed
on network models defined by a unitary time evolution operator providing an
efficient model for the study of the wave packet dynamics.Comment: 4 pages, RevTeX, 4 figures included, published versio
Quantum Graphs: A simple model for Chaotic Scattering
We connect quantum graphs with infinite leads, and turn them to scattering
systems. We show that they display all the features which characterize quantum
scattering systems with an underlying classical chaotic dynamics: typical
poles, delay time and conductance distributions, Ericson fluctuations, and when
considered statistically, the ensemble of scattering matrices reproduce quite
well the predictions of appropriately defined Random Matrix ensembles. The
underlying classical dynamics can be defined, and it provides important
parameters which are needed for the quantum theory. In particular, we derive
exact expressions for the scattering matrix, and an exact trace formula for the
density of resonances, in terms of classical orbits, analogous to the
semiclassical theory of chaotic scattering. We use this in order to investigate
the origin of the connection between Random Matrix Theory and the underlying
classical chaotic dynamics. Being an exact theory, and due to its relative
simplicity, it offers new insights into this problem which is at the fore-front
of the research in chaotic scattering and related fields.Comment: 28 pages, 13 figures, submitted to J. Phys. A Special Issue -- Random
Matrix Theor
Beyond the disk: EUV coronagraphic observations of the Extreme Ultraviolet Imager on board Solar Orbiter
Context. Most observations of the solar corona beyond 2 R consist of broadband visible light imagery carried out with coronagraphs. The associated diagnostics mainly consist of kinematics and derivations of the electron number density. While the measurement of the properties of emission lines can provide crucial additional diagnostics of the coronal plasma (temperatures, velocities, abundances, etc.), these types of observations are comparatively rare. In visible wavelengths, observations at these heights are limited to total eclipses. In the ultraviolet (UV) to extreme UV (EUV) range, very few additional observations have been achieved since the pioneering results of the Ultraviolet Coronagraph Spectrometer (UVCS). Aims. One of the objectives of the Full Sun Imager (FSI) channel of the Extreme Ultraviolet Imager (EUI) on board the Solar Orbiter mission has been to provide very wide field-of-view EUV diagnostics of the morphology and dynamics of the solar atmosphere in temperature regimes that are typical of the lower transition region and of the corona. Methods. FSI carries out observations in two narrowbands of the EUV spectrum centered on 17.4 nm and 30.4 nm that are dominated, respectively, by lines of FeIX/X (formed in the corona around 1 MK) and by the resonance line of HeII (formed around 80 kK in the lower transition region). Unlike previous EUV imagers, FSI includes a moveable occulting disk that can be inserted in the optical path to reduce the amount of instrumental stray light to a minimum. Results. FSI detects signals at 17.4 nm up to the edge of its field of view (7 R), which is about twice further than was previously possible. Operation at 30.4 nm are for the moment compromised by an as-yet unidentified source of stray light. Comparisons with observations by the LASCO and Metis coronagraphs confirm the presence of morphological similarities and differences between the broadband visible light and EUV emissions, as documented on the basis of prior eclipse and space-based observations. Conclusions. The very-wide-field observations of FSI out to about 3 and 7 R, without and with the occulting disk, respectively, are paving the way for future dedicated instruments
Solar magnetism eXplorer (SolmeX)
The magnetic field plays a pivotal role in many fields of Astrophysics. This is especially true for the physics of the solar atmosphere. Measuring the magnetic field in the upper solar atmosphere is crucial to understand the nature of the underlying physical processes that drive the violent dynamics of the solar corona—that can also affect life on Earth. SolmeX, a fully equipped solar space observatory for remote-sensing observations, will provide the first comprehensive measurements of the strength and direction of the magnetic field in the upper solar atmosphere. The mission consists of two spacecraft, one carrying the instruments, and another one in formation flight at a distance of about 200 m carrying the occulter to provide an artificial total solar eclipse. This will ensure high-quality coronagraphic observations above the solar limb. SolmeX integrates two spectro-polarimetric coronagraphs for off-limb observations, one in the EUV and one in the IR, and three instruments for observations on the disk. The latter comprises one imaging polarimeter in the EUV for coronal studies, a spectro-polarimeter in the EUV to investigate the low corona, and an imaging spectro-polarimeter in the UV for chromospheric studies. SOHO and other existing missions have investigated the emission of the upper atmosphere in detail (not considering polarization), and as this will be the case also for missions planned for the near future. Therefore it is timely that SolmeX provides the final piece of the observational quest by measuring the magnetic field in the upper atmosphere through polarimetric observations
Beyond the disk: EUV coronagraphic observations of the Extreme Ultraviolet Imager on board Solar Orbiter
Most observations of the solar corona beyond 2 Rs consist of broadband
visible light imagery from coronagraphs. The associated diagnostics mainly
consist of kinematics and derivations of the electron number density. While the
measurement of the properties of emission lines can provide crucial additional
diagnostics of the coronal plasma (temperatures, velocities, abundances, etc.),
these observations are comparatively rare. In visible wavelengths, observations
at these heights are limited to total eclipses. In the VUV range, very few
additional observations have been achieved since the pioneering results of
UVCS. One of the objectives of the Full Sun Imager (FSI) channel of the EUI
telescope on board the Solar Orbiter mission has been to provide very wide
field-of-view EUV diagnostics of the morphology and dynamics of the solar
atmosphere in temperature regimes that are typical of the lower transition
region and of the corona. FSI carries out observations in two narrowbands of
the EUV spectrum centered on 17.4 nm and 30.4 nm that are dominated,
respectively, by lines of Fe IX/X (formed in the corona around 1 MK) and by the
resonance line of He II (formed around 80 kK in the lower transition region).
Unlike previous EUV imagers, FSI includes a moveable occulting disk that can be
inserted in the optical path to reduce the amount of instrumental stray light
to a minimum. FSI detects signals at 17.4 nm up to the edge of its FOV (7~Rs),
which is about twice further than was previously possible. Comparisons with
observations by the LASCO and Metis coronagraphs confirm the presence of
morphological similarities and differences between the broadband visible light
and EUV emissions, as documented on the basis of prior eclipse and space-based
observations. The very-wide-field observations of FSI are paving the way for
future dedicated instruments
Microwave assisted solvent free synthesis of 1,3-diphenylpropenones
<p>Abstract</p> <p>Background</p> <p>1,3-Diphenylpropenones (chalcones) are well known for their diverse array of bioactivities. Hydroxyl group substituted chalcones are the main precursor in the synthesis of flavonoids. Till date various methods have been developed for the synthesis of these very interesting molecules. Continuing our efforts for the development of simple, eco-friendly and cost-effective methodologies, we report here a solvent free condensation of aryl ketones and aldehydes using iodine impregnated alumina under microwave activation. This new protocol has been applied to a variety of substituted aryl carbonyls with excellent yield of substituted 1,3-diphenylpropenones.</p> <p>Results</p> <p>Differently substituted chalcones were synthesized using iodine impregnated neutral alumina as catalyst in 79-95% yield in less than 2 minutes time under microwave activation without using any solvent. The reaction was studied under different catalytic conditions and it was found that molecular iodine supported over neutral alumina gives the best yield. The otherwise difficult single step condensation of hydroxy substituted aryl carbonyls is an attractive feature of this protocol to obtain polyhydroxychalcones in excellent yields. In order to find out the general applicability of this new endeavor it was successfully applied for the synthesis of 15 different chalcones including highly bioactive prenylated hydroxychalcone xanthohumol.</p> <p>Conclusion</p> <p>A new, simple and solvent free method was developed for the synthesis of substituted chalcones in environmentally benign way. The mild reaction conditions, easy work-up, clean reaction profiles render this approach as an interesting alternative to the existing methods.</p
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