8,287 research outputs found
Modeling and removal of optical ghosts in the PROBA-3/ASPIICS externally occulted solar coronagraph
Context: ASPIICS is a novel externally occulted solar coronagraph, which will
be launched onboard the PROBA-3 mission of the European Space Agency. The
external occulter will be placed on the first satellite approximately 150 m
ahead of the second satellite that will carry an optical instrument. During 6
hours per orbit, the satellites will fly in a precise formation, constituting a
giant externally occulted coronagraph. Large distance between the external
occulter and the primary objective will allow observations of the white-light
solar corona starting from extremely low heights 1.1RSun. Aims: To analyze
influence of optical ghost images formed inside the telescope and develop an
algorithm for their removal. Methods: We implement the optical layout of
ASPIICS in Zemax and study the ghost behaviour in sequential and non-sequential
regimes. We identify sources of the ghost contributions and analyze their
geometrical behaviour. Finally we develop a mathematical model and software to
calculate ghost images for any given input image. Results: We show that ghost
light can be important in the outer part of the field of view, where the
coronal signal is weak, since the energy of bright inner corona is
redistributed to the outer corona. However the model allows to remove the ghost
contribution. Due to a large distance between the external occulter and the
primary objective, the primary objective does not produce a significant ghost.
The use of the Lyot spot in ASPIICS is not necessary.Comment: 14 pages, 13 figure
Low polarized emission from the core of coronal mass ejections
In white-light coronagraph images, cool prominence material is sometimes
observed as bright patches in the core of coronal mass ejections (CMEs). If, as
generally assumed, this emission is caused by Thomson-scattered light from the
solar surface, it should be strongly polarised tangentially to the solar limb.
However, the observations of a CME made with the SECCHI/STEREO coronagraphs on
31 August 2007 show that the emission from these bright core patches is
exceptionally low polarised. We used the polarisation ratio method of Moran and
Davila (2004) to localise the barycentre of the CME cloud. By analysing the
data from both STEREO spacecraft we could resolve the plane-of-the-sky
ambiguity this method usually suffers from. Stereoscopic triangulation was used
to independently localise the low-polarisation patch relative to the cloud. We
demonstrated for the first time that the bright core material is located close
to the centre of the CME cloud. We show that the major part of the CME core
emission, more than 85% in our case, is H radiation and only a small
fraction is Thomson-scattered light. Recent calculations also imply that the
plasma density in the patch is 8 10 cm or more compared to 2.6
10 cm for the Thomson-scattering CME environment surrounding the
core material.Comment: 5 pages, 3 figure
Current perpendicular to plane Giant Magnetoresistance (GMR) in laminated nanostructures
We theoretically studied spin dependent electron transport
perpendicular-to-plain (CPP) in magnetic laminated multilayered structures by
using Kubo formalism. We took into account not only bulk scattering, but the
interface resistance due to both specular and diffuse reflection and also spin
conserving and spin-flip processes. It was shown that spin-flip scattering at
interfaces substantially reduces the value of GMR. This can explain the
experimental observations that the CPP GMR ratio for laminated structures only
slightly increases as compared to non-laminated ones despite lamination induces
a significant increase in CPP resistance.Comment: 4 pages, 2 figure
Observation of the fine structure for rovibronic spectral lines in visible part of emission spectra of
For the first time in visible part of the emission spectrum the pseudo
doublets representing partly resolved fine structure of rovibronic lines have
been observed. They are characterized by splitting values about 0.2 cm
and relative intensity of the doublet components close to 2.0. It is shown that
they are determined by triplet splitting in lower rovibronic levels of various
electronic transitions. It is proposed to use
an existence of such partly resolved fine structure patterns for identification
of numerous unassigned spectral lines of the molecule coming from great
variety of triplet "gerade" electronic states to vibro-rotational levels of the
state.Comment: 6 pages, including 2 figures and 1 table; submitted to Phys.Rev.Let
From Coulomb excitation cross sections to non-resonant astrophysical rates in three-body systems: Ne case
Coulomb and nuclear dissociation of Ne on light and heavy targets are
studied theoretically. The dipole E1 strength function is determined in a broad
energy range including energies of astrophysical interest. Dependence of the
strength function on different parameters of the Ne ground state
structure and continuum dynamics is analyzed in a three-body model. The
discovered dependence plays an important role for studies of the strength
functions for the three-body E1 dissociation and radiative capture. The
constraints on the configuration mixing in Ne and on
-wave interaction in the O+ channel are imposed based on
experimental data for Ne Coulomb dissociation on heavy target.Comment: 12 pages, 13 figure
Self-propagating high-temperature synthesis of energetic borides
A promising way to synthesize new energy materials based on refactory inorganic compounds is self-propagating high-temperature synthesis of compositions based on boron compounds. This paper describes a laboratory technology of production of aluminum borides. The experimental results of thermogravimetric analysis and particle size analysis obtained for synthesized powders are given. According to thermogravimetric analysis data the degree of oxidation of obtained powders exceeds 95 %. The experimental data have shown that the development of new compositions of high-energy fuel cells using borides can yield high-quality results in the sphere of solid hypersonic engines
On the possibility to fabricate ceramics using fused deposition modeling
The paper presents a uniquely designed device that enables controlled manufacturing of semi-fabricated products from thermoplastic ceramic suspensions by fused deposition modeling. Sintering of the products yields ceramics with high strength and hardness. We use ceramic aluminum oxide (Al2O3) as an example to prove that additive ceramic structures can be produced without noticeable boundaries between layers of the material
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