4,085 research outputs found
Spectral evolution of two-dimensional kinetic plasma turbulence in the wavenumber-frequency domain
We present a method for studying the evolution of plasma turbulence by
tracking dispersion relations in the energy spectrum in the
wavenumber-frequency domain. We apply hybrid plasma simulations in a simplified
two-dimensional geometry to demonstrate our method and its applicability to
plasma turbulence in the ion kinetic regime. We identify four dispersion
relations: ion-Bernstein waves, oblique whistler waves, oblique
Alfv\'en/ion-cyclotron waves, and a zero-frequency mode. The energy partition
and frequency broadening are evaluated for these modes. The method allows us to
determine the evolution of decaying plasma turbulence in our restricted
geometry and shows that it cascades along the dispersion relations during the
early phase with an increasing broadening around the dispersion relations.Comment: 11 pages, 4 figure
Detailed Studies of Pixelated CZT Detectors Grown with the Modified Horizontal Bridgman Method
The detector material Cadmium Zinc Telluride (CZT), known for its high
resolution over a broad energy range, is produced mainly by two methods: the
Modified High-Pressure Bridgman (MHB) and the High-Pressure Bridgman (HPB)
process. This study is based on MHB CZT substrates from the company Orbotech
Medical Solutions Ltd. with a detector size of 2.0x2.0x0.5 cm^3, 8x8 pixels and
a pitch of 2.46 mm. Former studies have emphasized only on the cathode material
showing that high-work-function improve the energy resolution at lower
energies. Therfore, we studied the influence of the anode material while
keeping the cathode material constant. We used four different materials:
Indium, Titanium, Chromium and Gold with work-functions between 4.1 eV and 5.1
eV. The low work-function materials Indium and Titanium achieved the best
performance with energy resolutions: 2.0 keV (at 59 keV) and 1.9 keV (at 122
keV) for Titanium; 2.1 keV (at 59 keV) and 2.9 keV (at 122 keV) for Indium.
These detectors are very competitive compared with the more expensive ones
based on HPB material if one takes the large pixel pitch of 2.46 mm into
account. We present a detailed comparison of our detector response with 3-D
simulations, from which we determined the mobility-lifetime-products for
electrons and holes. Finally, we evaluated the temperature dependency of the
detector performance and mobility-lifetime-products, which is important for
many applications. With decreasing temperature down to -30C the breakdown
voltage increases and the electron mobility-lifetime-product decreases by about
30% over a range from 20C to -30C. This causes the energy resolution to
deteriorate, but the concomitantly increasing breakdown voltage makes it
possible to increase the applied bias voltage and restore the full performance.Comment: Accepted for publication in Astroparticle Physics, 25 pages, 13
figure
Methylation landscape in the genome of higher plants of agronomical interest
In eukaryotic cells the methylation of cytosines in DNA is an essential mechanism which is implied in the dynamic organization of the genome structure, in relation to genes expression. Plant genomes contain a significant proportion and variable according to the species, of sequences which are likely to be methylated during the life of the plant. It is known that the establishment and the maintenance of methylation profiles in both genomic areas and specific sequences constitute a crucial mediator in the modulation of genes expression during development. Recent studies have evidenced the implication of epimutations in the adaptation of plants to their environment particularly in response to biotic and abiotic stresses. Recently, the complete mapping of methylation in the genomes of Arabidopsis thaliana and rice provided invaluable information on the distribution of methylation within genes in relation to their expression. The impact of changes in the methylation profiles on the characters of agronomic importance has not been intensively studied yet, whereas this question takes a considerable importance in the context of an increasing food demand and foreseen global climate changes. The METHYLANDSCAPE project proposes to isolate genomic DNA sequences on the basis of their degree of methylation and to connect the variation of their methylation profiles with, on the one hand, the expression of the corresponding genes and, on the other hand, with environmental or developmental processes. Thus, it should be possible to identify genes which expression is differentially controlled by methylation during development and/or in situation of stress, and likely to have an influence on the agronomic value of the plant. The METHYLANDSCAPE partners thus propose to bring signification advances in plant genomics on four original species, by integrating DNA methylation mapping and the relationship between epigenome and transcriptome, up to the generation of methylation-sensitive markers linked with characters of agronomic importance. (Texte intégral
An explicit construction of non-tempered cusp forms on
We explicitly construct cusp forms on the orthogonal group of signature for an arbitrary natural number as liftings from Maass cusp forms of level one. In our previous works, the fundamental tool to show the automorphy of the lifting was the converse theorem by Maass. In this paper, we use the Fourier expansion of the theta lifts by Borcherds instead. We also study cuspidal representations generated by such cusp forms and show that they are irreducible and that all of their non-archimedean local components are non-tempered while the archimedean component is tempered, if the Maass cusp forms are Hecke eigenforms. The standard -functions of the cusp forms are proved to be products of symmetric square -functions of the Hecke-eigen Maass cusp forms with shifted Riemann zeta functions
Measurements of Stellar Inclinations for Kepler Planet Candidates II: Candidate Spin-Orbit Misalignments in Single and Multiple-Transiting Systems
We present a test for spin-orbit alignment for the host stars of 25 candidate
planetary systems detected by the {\it Kepler} spacecraft. The inclination
angle of each star's rotation axis was estimated from its rotation period,
rotational line broadening, and radius. The rotation periods were determined
using the {\it Kepler} photometric time series. The rotational line broadening
was determined from high-resolution optical spectra with Subaru/HDS. Those same
spectra were used to determine the star's photospheric parameters (effective
temperature, surface gravity, metallicity) which were then interpreted with
stellar-evolutionary models to determine stellar radii. We combine the new
sample with the 7 stars from our previous work on this subject, finding that
the stars show a statistical tendency to have inclinations near 90, in
alignment with the planetary orbits. Possible spin-orbit misalignments are seen
in several systems, including three multiple-planet systems (KOI-304, 988,
2261). Ideally these systems should be scrutinized with complementary
techniques---such as the Rossiter-McLaughlin effect, starspot-crossing
anomalies or asteroseismology---but the measurements will be difficult owing to
the relatively faint apparent magnitudes and small transit signals in these
systems.Comment: 11 pages, 9 figures, accepted for publication in Ap
Using Abandoned Paddy Fields for Grazing in Northern Japan
The number of abandoned paddy fields is increasing in Japan, because the government has been regulating rice production. It has been recommended that the abandoned paddy fields be used for stock raising. However, there is sometimes a lack of information about the land on the abandoned paddy fields and farmers want to know the cost of fencing and the best grass species to use. This paper seeks to provide farmers with information on how to begin to use the abandoned paddy fields as pastures in hilly rural areas in Japan
Global existence problem in -Gowdy symmetric IIB superstring cosmology
We show global existence theorems for Gowdy symmetric spacetimes with type
IIB stringy matter. The areal and constant mean curvature time coordinates are
used. Before coming to that, it is shown that a wave map describes the
evolution of this system
Evaluation of magnetic helicity density in the wave number domain using multi-point measurements in space
We develop an estimator for the magnetic helicity density, a measure of the spiral geometry of magnetic field lines, in the wave number domain as a wave diagnostic tool based on multi-point measurements in space. The estimator is numerically tested with a synthetic data set and then applied to an observation of magnetic field fluctuations in the Earth foreshock region provided by the four-point measurements of the Cluster spacecraft. The energy and the magnetic helicity density are determined in the frequency and the wave number domain, which allows us to identify the wave properties in the plasma rest frame correcting for the Doppler shift. In the analyzed time interval, dominant wave components have parallel propagation to the mean magnetic field, away from the shock at about Alfvén speed and a left-hand spatial rotation sense of helicity with respect to the propagation direction, which means a right-hand temporal rotation sense of polarization. These wave properties are well explained by the right-hand resonant beam instability as the driving mechanism in the foreshock. Cluster observations allow therefore detailed comparisons with various theories of waves and instabilities
On the area of the symmetry orbits in symmetric spacetimes with Vlasov matter
This paper treats the global existence question for a collection of general
relativistic collisionless particles, all having the same mass. The spacetimes
considered are globally hyperbolic, with Cauchy surface a 3-torus. Furthermore,
the spacetimes considered are isometrically invariant under a two-dimensional
group action, the orbits of which are spacelike 2-tori. It is known from
previous work that the area of the group orbits serves as a global time
coordinate. In the present work it is shown that the area takes on all positive
values in the maximal Cauchy development.Comment: 27 pages, version 2 minor changes and correction
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