76,071 research outputs found
Displaying 3D images: algorithms for single-image random-dot
A new, simple, and symmetric algorithm can be implemented that results in higher levels of detail in solid objects than previously possible with autostereograms. In a stereoscope, an optical instrument similar to binoculars, each eye views a different picture and thereby receives the specific image that would have arisen naturally. An early suggestion for a color stereo computer display involved a rotating filter wheel held in front of the eyes. In contrast, this article describes a method for viewing on paper or on an ordinary computer screen without special equipment, although it is limited to the display of 3D monochromatic objects. (The image can be colored, say, for artistic reasons, but the method we describe does not allow colors to be allocated in a way that corresponds to an arbitrary coloring of the solid object depicted.) The image can easily be constructed by computer from any 3D scene or solid object description
A Neural Network Gravitational Arc Finder based on the Mediatrix filamentation Method
Automated arc detection methods are needed to scan the ongoing and
next-generation wide-field imaging surveys, which are expected to contain
thousands of strong lensing systems. Arc finders are also required for a
quantitative comparison between predictions and observations of arc abundance.
Several algorithms have been proposed to this end, but machine learning methods
have remained as a relatively unexplored step in the arc finding process. In
this work we introduce a new arc finder based on pattern recognition, which
uses a set of morphological measurements derived from the Mediatrix
Filamentation Method as entries to an Artificial Neural Network (ANN). We show
a full example of the application of the arc finder, first training and
validating the ANN on simulated arcs and then applying the code on four Hubble
Space Telescope (HST) images of strong lensing systems. The simulated arcs use
simple prescriptions for the lens and the source, while mimicking HST
observational conditions. We also consider a sample of objects from HST images
with no arcs in the training of the ANN classification. We use the training and
validation process to determine a suitable set of ANN configurations, including
the combination of inputs from the Mediatrix method, so as to maximize the
completeness while keeping the false positives low. In the simulations the
method was able to achieve a completeness of about 90% with respect to the arcs
that are input to the ANN after a preselection. However, this completeness
drops to 70% on the HST images. The false detections are of the order of
3% of the objects detected in these images. The combination of Mediatrix
measurements with an ANN is a promising tool for the pattern recognition phase
of arc finding. More realistic simulations and a larger set of real systems are
needed for a better training and assessment of the efficiency of the method.Comment: Updated to match published versio
Cleaning sky survey databases using Hough Transform and Renewal String approaches
Large astronomical databases obtained from sky surveys such as the
SuperCOSMOS Sky Survey (SSS) invariably suffer from spurious records coming
from artefactual effects of the telescope, satellites and junk objects in orbit
around earth and physical defects on the photographic plate or CCD. Though
relatively small in number these spurious records present a significant problem
in many situations where they can become a large proportion of the records
potentially of interest to a given astronomer. Accurate and robust techniques
are needed for locating and flagging such spurious objects, and we are
undertaking a programme investigating the use of machine learning techniques in
this context. In this paper we focus on the four most common causes of unwanted
records in the SSS: satellite or aeroplane tracks, scratches, fibres and other
linear phenomena introduced to the plate, circular halos around bright stars
due to internal reflections within the telescope and diffraction spikes near to
bright stars. Appropriate techniques are developed for the detection of each of
these. The methods are applied to the SSS data to develop a dataset of spurious
object detections, along with confidence measures, which can allow these
unwanted data to be removed from consideration. These methods are general and
can be adapted to other astronomical survey data.Comment: Accepted for MNRAS. 17 pages, latex2e, uses mn2e.bst, mn2e.cls,
md706.bbl, shortbold.sty (all included). All figures included here as low
resolution jpegs. A version of this paper including the figures can be
downloaded from http://www.anc.ed.ac.uk/~amos/publications.html and more
details on this project can be found at
http://www.anc.ed.ac.uk/~amos/sattrackres.htm
Supporting Focus and Context Awareness in 3D Modelling Tasks Using Multi-Layered Displays
Most 3D modelling software have been developed for conventional 2D displays, and as such, lack support for true depth perception. This contributes to making polygonal 3D modelling tasks challenging, particularly when models are complex and consist of a large number of overlapping components (e.g. vertices, edges) and objects (i.e. parts). Research has shown that users of 3D modelling software often encounter a range of difficulties, which collectively can be defined as focus and context awareness problems. These include maintaining position and orientation awarenesses, as well as recognizing distance between individual components and objects in 3D spaces. In this paper, we present five visualization and interaction techniques we have developed for multi-layered displays, to better support focus and context awareness in 3D modelling tasks. The results of a user study we conducted shows that three of these five techniques improve users' 3D modelling task performance
A Peculiar Family of Jupiter Trojans: the Eurybates
The Eurybates family is a compact core inside the Menelaus clan, located in
the L4 swarm of Jupiter Trojans. Fornasier et al. (2007) found that this family
exhibits a peculiar abundance of spectrally flat objects, similar to
Chiron-like Centaurs and C-type main belt asteroids. On the basis of the
visible spectra available in literature, Eurybates family's members seemed to
be good candidates for having on their surfaces water/water ice or aqueous
altered materials. To improve our knowledge of the surface composition of this
peculiar family, we carried out an observational campaign at the Telescopio
Nazionale Galileo (TNG), obtaining near-infrared spectra of 7 members. Our data
show a surprisingly absence of any spectral feature referable to the presence
of water, ices or aqueous altered materials on the surface of the observed
objects. Models of the surface composition are attempted, evidencing that
amorphous carbon seems to dominate the surface composition of the observed
bodies and some amount of silicates (olivine) could be present.Comment: 23 pages, 2 figures, paper accepted for publication in Icaru
The bulk of the black hole growth since z ~ 1 occurs in a secular universe: no major merger-AGN connection
What is the relevance of major mergers and interactions as triggering mechanisms for active galactic nuclei (AGNs)
activity? To answer this long-standing question, we analyze 140 XMM-Newton-selected AGN host galaxies and
a matched control sample of 1264 inactive galaxies over z ~ 0.3â1.0 and M_â < 10^(11.7) M_â with high-resolution
Hubble Space Telescope/Advanced Camera for Surveys imaging from the COSMOS field. The visual analysis of
their morphologies by 10 independent human classifiers yields a measure of the fraction of distorted morphologies
in the AGN and control samples, i.e., quantifying the signature of recent mergers which might potentially be
responsible for fueling/triggering the AGN. We find that (1) the vast majority (>85%) of the AGN host galaxies
do not show strong distortions and (2) there is no significant difference in the distortion fractions between active
and inactive galaxies. Our findings provide the best direct evidence that, since z ~ 1, the bulk of black hole (BH)
accretion has not been triggered by major galaxy mergers, therefore arguing that the alternative mechanisms, i.e.,
internal secular processes and minor interactions, are the leading triggers for the episodes of major BH growth.We
also exclude an alternative interpretation of our results: a substantial time lag between merging and the observability
of the AGN phase could wash out the most significant merging signatures, explaining the lack of enhancement
of strong distortions on the AGN hosts. We show that this alternative scenario is unlikely due to (1) recent major
mergers being ruled out for the majority of sources due to the high fraction of disk-hosted AGNs, (2) the lack of
a significant X-ray signal in merging inactive galaxies as a signature of a potential buried AGN, and (3) the low
levels of soft X-ray obscuration for AGNs hosted by interacting galaxies, in contrast to model predictions
Digital technologies for virtual recomposition : the case study of Serpotta stuccoes
The matter that lies beneath the smooth
and shining surface of stuccoes of the Serpotta family, who used to work in Sicily from 1670 to 1730, has
been thoroughly studied in previous papers, disclosing
the deep, even if empirical, knowledge of materials science that guided the artists in creating their master-
works. In this work the attention is focused on the solid
perspective and on the scenographic sculpture by Giacomo Serpotta, who is acknowledged as the leading exponent of the School. The study deals with some particular works of the artist, the so-called "teatrini" (Toy
Theater), made by him for the San Lorenzo Oratory in
Palermo. On the basis of archive documents and previous analogical photogrammetric plotting, integrated
with digital solutions and methodologies of computer-
based technologies, the study investigates and interprets
the geometric-formal genesis of the examined works of
art, until the prototyping of the whole scenic apparatus.peer-reviewe
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