10,237 research outputs found
The Near-Infrared Photometric Properties of Bright Giants in the Central Regions of the Galactic Bulge
Images recorded through broad (J, H, K), and narrow (CO, and 2.2micron
continuum) band filters are used to investigate the photometric properties of
bright (K < 13.5) stars in a 6 x 6 arcmin field centered on the SgrA complex.
The giant branch ridgelines in the (K, J-K) and (K, H-K) color-magnitude
diagrams are well matched by the Baade's Window (BW) M giant sequence if the
mean extinction is A_K ~ 2.8 mag. Extinction measurements for individual stars
are estimated using the M_K versus infrared color relations defined by M giants
in BW, and the majority of stars have A_K between 2.0 and 3.5 mag. The
extinction is locally high in the SgrA complex, where A_K ~ 3.1 mag.
Reddening-corrected CO indices, CO_o, are derived for over 1300 stars with J,
H, and K brightnesses, and over 5300 stars with H and K brightnesses. The
distribution of CO_o values for stars with K_o between 11.25 and 7.25 can be
reproduced using the M_K versus CO_o relation defined by M giants in BW. The
data thus suggest that the most metal-rich giants in the central regions of the
bulge and in BW have similar photometric properties and 2.3micron CO strengths.
Hence, it appears that the central region of the bulge does not contain a
population of stars that are significantly more metal-rich than what is seen in
BW.Comment: 29 pages, including 14 figure
Chiral properties of hematite ({\alpha}-Fe2O3) inferred from resonant Bragg diffraction using circularly polarized x-rays
Chiral properties of the two phases - collinear motif (below Morin transition
temperature, TM=250 K) and canted motif (above TM) - of magnetically ordered
hematite ({\alpha}-Fe2O3) have been identified in single crystal resonant x-ray
Bragg diffraction, using circular polarized incident x-rays tuned near the iron
K-edge. Magneto-electric multipoles, including an anapole, fully characterize
the high-temperature canted phase, whereas the low-temperature collinear phase
supports both parity-odd and parity-even multipoles that are time-odd. Orbital
angular momentum accompanies the collinear motif, while it is conspicuously
absent with the canted motif. Intensities have been successfully confronted
with analytic expressions derived from an atomic model fully compliant with
chemical and magnetic structures. Values of Fe atomic multipoles previously
derived from independent experimental data, are shown to be completely
trustworthy
Fermions and Kaluza-Klein vacuum decay: a toy model
We address the question of whether or not fermions with twisted periodicity
condition suppress the semiclassical decay of M^4xS^1 Kaluza--Klein vacuum. We
consider a toy (1+1)-dimensional model with twisted fermions in cigar-shaped
Euclidean background geometry and calculate the fermion determinant. We find
that contrary to expectations, the determinant is finite. We consider this as
an indication that twisted fermions do not stabilize the Kaluza--Klein vacuum.Comment: 13 pages, 2 figure
Volume modulus inflation and a low scale of SUSY breaking
The relation between the Hubble constant and the scale of supersymmetry
breaking is investigated in models of inflation dominated by a string modulus.
Usually in this kind of models the gravitino mass is of the same order of
magnitude as the Hubble constant which is not desirable from the
phenomenological point of view. It is shown that slow-roll saddle point
inflation may be compatible with a low scale of supersymmetry breaking only if
some corrections to the lowest order Kahler potential are taken into account.
However, choosing an appropriate Kahler potential is not enough. There are also
conditions for the superpotential, and e.g. the popular racetrack
superpotential turns out to be not suitable. A model is proposed in which
slow-roll inflation and a light gravitino are compatible. It is based on a
superpotential with a triple gaugino condensation and the Kahler potential with
the leading string corrections. The problem of fine tuning and experimental
constraints are discussed for that model.Comment: 28 pages, 8 figures, comments and references added, minor change in
notation, version to be publishe
Sparse 3D Point-cloud Map Upsampling and Noise Removal as a vSLAM Post-processing Step: Experimental Evaluation
The monocular vision-based simultaneous localization and mapping (vSLAM) is
one of the most challenging problem in mobile robotics and computer vision. In
this work we study the post-processing techniques applied to sparse 3D
point-cloud maps, obtained by feature-based vSLAM algorithms. Map
post-processing is split into 2 major steps: 1) noise and outlier removal and
2) upsampling. We evaluate different combinations of known algorithms for
outlier removing and upsampling on datasets of real indoor and outdoor
environments and identify the most promising combination. We further use it to
convert a point-cloud map, obtained by the real UAV performing indoor flight to
3D voxel grid (octo-map) potentially suitable for path planning.Comment: 10 pages, 4 figures, camera-ready version of paper for "The 3rd
International Conference on Interactive Collaborative Robotics (ICR 2018)
Tunneling mechanism of light transmission through metallic films
A mechanism of light transmission through metallic films is proposed,
assisted by tunnelling between resonating buried dielectric inclusions. This is
illustrated by arrays of Si spheres embedded in Ag. Strong transmission peaks
are observed near the Mie resonances of the spheres. The interaction among
various planes of spheres and interference effects between these resonances and
the surface plasmons of Ag lead to mixing and splitting of the resonances.
Transmission is proved to be limited only by absorption. For small spheres, the
effective dielectric constant can be tuned to values close to unity and a
method is proposed to turn the resulting materials invisible.Comment: 4 papges, 5 figure
Enhanced dimerization of TiOCl under pressure: spin-Peierls - to - Peierls transition
We report high-pressure x-ray diffraction and magnetization measurements
combined with ab-initio calculations to demonstrate that the high-pressure
optical and transport transitions recently reported in TiOCl, correspond in
fact to an enhanced Ti3+-Ti3+ dimerization existing already at room
temperature. Our results confirm the formation of a metal-metal bond between
Ti3+ ions along the b-axis of TiOCl, accompanied by a strong reduction of the
electronic gap. The evolution of the dimerization with pressure suggests a
crossover from the spin-Peierls to a conventional Peierls situation at high
pressures.Comment: 9pages, 4 figure
Maximum Entropy Limit of Small-scale Magnetic Field Fluctuations in the Quiet Sun
The observed magnetic field on the solar surface is characterized by a very
complex spatial and temporal behavior. Although feature-tracking algorithms
have allowed us to deepen our understanding of this behavior, subjectivity
plays an important role in the identification and tracking of such features. In
this paper, we continue studies Gorobets, A. Y., Borrero, J. M., & Berdyugina,
S. 2016, ApJL, 825, L18 of the temporal stochasticity of the magnetic field on
the solar surface without relying either on the concept of magnetic features or
on subjective assumptions about their identification and interaction. We
propose a data analysis method to quantify fluctuations of the line-of-sight
magnetic field by means of reducing the temporal field's evolution to the
regular Markov process. We build a representative model of fluctuations
converging to the unique stationary (equilibrium) distribution in the long time
limit with maximum entropy. We obtained different rates of convergence to the
equilibrium at fixed noise cutoff for two sets of data. This indicates a strong
influence of the data spatial resolution and mixing-polarity fluctuations on
the relaxation process. The analysis is applied to observations of magnetic
fields of the relatively quiet areas around an active region carried out during
the second flight of the Sunrise/IMaX and quiet Sun areas at the disk center
from the Helioseismic and Magnetic Imager on board the Solar Dynamics
Observatory satellite.Comment: 11 pages, 5 figures, The Astrophysical Journal Supplement Series
(accepted
- …