5,543 research outputs found
A new sample of X-ray selected narrow emission-line galaxies. I. The nature of optically elusive AGN
Using the 3XMM catalogue of serendipitous X-ray sources, and the SDSS-DR9
spectroscopic catalogue, we have obtained a new sample of X-ray selected narrow
emission line galaxies. The standard optical diagnostic diagram and selection
by hard X-ray luminosity expose a mismatch between the optically-based and
X-ray-based classifications. The nature of these misclassified elusive AGN can
be understood in terms of their broader X-ray and optical properties and leads
to a division of this sub-sample into two groups. A little more than half are
likely to be narrow-line Seyfert 1s (NLS1s), so misclassified because of the
contribution of the Broad Line Region (BLR) to their optical spectra. The
remainder have some of the properties of Seyfert 2 (Sy2) AGN; their optical
elusiveness can be explained by optical dilution from the host galaxy plus a
star-formation contribution and by their underluminous optical emission due to
low accretion rates. Because some of the Sy2 sources have very low accretion
rates, are unabsorbed, plus the fact that they lack broad optical emission
lines, they are good candidates to be True Sy2 AGN.Comment: 13 pages, 13 figues, accepted for publication in A&
Non-radial oscillation modes as a probe of density discontinuities in neutron stars
A phase transition occurring in the inner core of a neutron star could be
associated to a density discontinuity that would affect the frequency spectrum
of the non-radial oscillation modes in two ways. Firstly, it would produce a
softening of the equation of state, leading to more compact equilibrium
configurations and changing the frequency of the fundamental and pressure modes
of the neutron star. Secondly, a new non-zero frequency g-- mode would appear,
associated to each discontinuity. These discontinuity g--modes have typical
frequencies larger than those of g--modes previously studied in the literature
(thermal, core g-- modes, or g--modes due to chemical inhomogeneities in the
outer layers), and smaller than that of the fundamental mode; therefore they
should be distinguishable from the other modes of non radial oscillation. In
this paper we investigate how high density discontinuities change the frequency
spectrum of the non-radial oscillations, in the framework of the general
relativistic theory of stellar perturbations. Our purpose is to understand
whether a gravitational signal, emitted at the frequencies of the quasi normal
modes, may give some clear information on the equation of state of the neutron
star and, in particular, on the parameters that characterize the density
discontinuity. We discuss some astrophysical processes that may be associated
to the excitation of these modes, and estimate how much gravitational energy
should the modes convey to produce a signal detectable by high frequency
gravitational detectors.Comment: submitted to MNRA
Tex2Shape: Detailed Full Human Body Geometry From a Single Image
We present a simple yet effective method to infer detailed full human body shape from only a single photograph. Our model can infer full-body shape including face, hair, and clothing including wrinkles at interactive frame-rates. Results feature details even on parts that are occluded in the input image. Our main idea is to turn shape regression into an aligned image-to-image translation problem. The input to our method is a partial texture map of the visible region obtained from off-the-shelf methods. From a partial texture, we estimate detailed normal and vector displacement maps, which can be applied to a low-resolution smooth body model to add detail and clothing. Despite being trained purely with synthetic data, our model generalizes well to real-world photographs. Numerous results demonstrate the versatility and robustness of our method
Hall drift in the crust of neutron stars - necessary for radio pulsar activity?
The radio pulsar models based on the existence of an inner accelerating gap
located above the polar cap rely on the existence of a small scale, strong
surface magnetic field . This field exceeds the dipolar field ,
responsible for the braking of the pulsar rotation, by at least one order of
magnitude. Neither magnetospheric currents nor small scale field components
generated during neutron star's birth can provide such field structures in old
pulsars. While the former are too weak to create G, the ohmic decay time of the latter is much shorter than
years. We suggest that a large amount of magnetic energy is stored in a
toroidal field component that is confined in deeper layers of the crust, where
the ohmic decay time exceeds years. This toroidal field may be created
by various processes acting early in a neutron star's life. The Hall drift is a
non-linear mechanism that, due to the coupling between different components and
scales, may be able to create the demanded strong, small scale, magnetic spots.
Taking into account both realistic crustal microphysics and a minimal cooling
scenario, we show that, in axial symmetry, these field structures are created
on a Hall time scale of - years. These magnetic spots can be
long-lived, thereby fulfilling the pre-conditions for the appearance of the
radio pulsar activity. Such magnetic structures created by the Hall drift are
not static, and dynamical variations on the Hall time scale are expected in the
polar cap region.Comment: 4 pages, 5 figures, contribution to the ERPM conferences, Zielona
Gora, April 201
Learning to Reconstruct People in Clothing from a Single RGB Camera
We present a learning-based model to infer the personalized 3D shape of people from a few frames (1-8) of a monocular video in which the person is moving, in less than 10 seconds with a reconstruction accuracy of 5mm. Our model learns to predict the parameters of a statistical body model and instance displacements that add clothing and hair to the shape. The model achieves fast and accurate predictions based on two key design choices. First, by predicting shape in a canonical T-pose space, the network learns to encode the images of the person into pose-invariant latent codes, where the information is fused. Second, based on the observation that feed-forward predictions are fast but do not always align with the input images, we predict using both, bottom-up and top-down streams (one per view) allowing information to flow in both directions. Learning relies only on synthetic 3D data. Once learned, the model can take a variable number of frames as input, and is able to reconstruct shapes even from a single image with an accuracy of 6mm. Results on 3 different datasets demonstrate the efficacy and accuracy of our approach
In the Wild Human Pose Estimation Using Explicit 2D Features and Intermediate 3D Representations
Convolutional Neural Network based approaches for monocular 3D human pose estimation usually require a large amount of training images with 3D pose annotations. While it is feasible to provide 2D joint annotations for large corpora of in-the-wild images with humans, providing accurate 3D annotations to such in-the-wild corpora is hardly feasible in practice. Most existing 3D labelled data sets are either synthetically created or feature in-studio images. 3D pose estimation algorithms trained on such data often have limited ability to generalize to real world scene diversity. We therefore propose a new deep learning based method for monocular 3D human pose estimation that shows high accuracy and generalizes better to in-the-wild scenes. It has a network architecture that comprises a new disentangled hidden space encoding of explicit 2D and 3D features, and uses supervision by a new learned projection model from predicted 3D pose. Our algorithm can be jointly trained on image data with 3D labels and image data with only 2D labels. It achieves state-of-the-art accuracy on challenging in-the-wild data
Local rectification of heat flux
We present a chain-of-atoms model where heat is rectified, with different
fluxes from the hot to the cold baths located at the chain boundaries when the
temperature bias is reversed. The chain is homogeneous except for boundary
effects and a local modification of the interactions at one site, the
"impurity". The rectification mechanism is due here to the localized impurity,
the only asymmetrical element of the structure, apart from the externally
imposed temperature bias, and does not rely on putting in contact different
materials or other known mechanisms such as grading or long-range interactions.
The effect survives if all interaction forces are linear except the ones for
the impurity.Comment: 5 pages, 5 figure
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