78,109 research outputs found
Speeding up active mesh segmentation by local termination of nodes.
This article outlines a procedure for speeding up segmentation of images using active mesh systems. Active meshes and other deformable models are very popular in image segmentation due to their ability to capture weak or missing boundary information; however, where strong edges exist, computations are still done after mesh nodes have settled on the boundary. This can lead to extra computational time whilst the system continues to deform completed regions of the mesh. We propose a local termination procedure, reducing these unnecessary computations and speeding up segmentation time with minimal loss of quality
Probing New Physics Models of Neutrinoless Double Beta Decay with SuperNEMO
The possibility to probe new physics scenarios of light Majorana neutrino
exchange and right-handed currents at the planned next generation neutrinoless
double beta decay experiment SuperNEMO is discussed. Its ability to study
different isotopes and track the outgoing electrons provides the means to
discriminate different underlying mechanisms for the neutrinoless double beta
decay by measuring the decay half-life and the electron angular and energy
distributions.Comment: 17 pages, 14 figures, to be published in E.P.J.
GMRT observations of X-shaped radio sources
We present results from a study of X-shaped sources based on observations
using the Giant Metrewave Radio Telescope (GMRT). These observations were
motivated by our low frequency study of 3C 223.1 (Lal & Rao 2005), an X-shaped
radio source, which showed that the wings (or low-surface-brightness jets) have
flatter spectral indices than the active lobes (or high-surface-brightness
jets), a result not easily explained by most models. We have now obtained GMRT
data at 240 and 610 MHz for almost all the known X-shaped radio sources and
have studied the distribution of the spectral index across the sources. While
the radio morphologies of all the sources at 240 and 610 MHz show the
characteristic X-shape, the spectral characteristics of the X-shaped radio
sources, seem to fall into three categories, namely, sources in which (A) the
wings have flatter spectral indices than the active lobes, (B) the wings and
the active lobes have comparable spectral indices, and (C) the wings have
steeper spectral indices than the active lobes. We discuss the implications of
the new observational results on the various formation models that have been
proposed for X-shaped sources.Comment: The paper contains 12 figures and 3 tables, accepted for publication
in MNRAS Main Journal, please note, some figures are of lower qualit
Binocular fusion and invariant category learning due to predictive remapping during scanning of a depthful scene with eye movements
How does the brain maintain stable fusion of 3D scenes when the eyes move? Every eye movement causes each retinal position to process a different set of scenic features, and thus the brain needs to binocularly fuse new combinations of features at each position after an eye movement. Despite these breaks in retinotopic fusion due to each movement, previously fused representations of a scene in depth often appear stable. The 3D ARTSCAN neural model proposes how the brain does this by unifying concepts about how multiple cortical areas in the What and Where cortical streams interact to coordinate processes of 3D boundary and surface perception, spatial attention, invariant object category learning, predictive remapping, eye movement control, and learned coordinate transformations. The model explains data from single neuron and psychophysical studies of covert visual attention shifts prior to eye movements. The model further clarifies how perceptual, attentional, and cognitive interactions among multiple brain regions (LGN, V1, V2, V3A, V4, MT, MST, PPC, LIP, ITp, ITa, SC) may accomplish predictive remapping as part of the process whereby view-invariant object categories are learned. These results build upon earlier neural models of 3D vision and figure-ground separation and the learning of invariant object categories as the eyes freely scan a scene. A key process concerns how an object's surface representation generates a form-fitting distribution of spatial attention, or attentional shroud, in parietal cortex that helps maintain the stability of multiple perceptual and cognitive processes. Predictive eye movement signals maintain the stability of the shroud, as well as of binocularly fused perceptual boundaries and surface representations.Published versio
Rotating Disks and Non-Kinematic Double Peaks
Double-peaked line profiles are commonly considered a hallmark of rotating
disks, with the distance between the peaks a measure of the rotation velocity.
However, double-peaks can arise also from radiative transfer effects in
optically thick non-rotating sources. Utilizing exact solutions of the line
transfer problem we present a detailed study of line emission from
geometrically thin Keplerian disks. We derive the conditions for emergence of
kinematic double peaks in optically thin and thick disks, and find that it is
generally impossible to disentangle the effects of kinematics and line opacity
in observed double-peaked profiles. Unless supplemented by additional
information, a double-peaked profile alone is not a reliable indicator of a
rotating disk. In certain circumstances, triple and quadruple profiles might be
better indicators of rotation in optically thick disks.Comment: MNRAS, to be publishe
A Framework for Image Segmentation Using Shape Models and Kernel Space Shape Priors
©2008 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or distribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.DOI: 10.1109/TPAMI.2007.70774Segmentation involves separating an object from the background in a given image. The use of image information alone often leads to poor segmentation results due to the presence of noise, clutter or occlusion. The introduction of shape priors in the geometric active contour (GAC) framework has proved to be an effective way to ameliorate some of these problems. In this work, we propose a novel segmentation method combining image information with prior shape knowledge, using level-sets. Following the work of Leventon et al., we propose to revisit the use of PCA to introduce prior knowledge about shapes in a more robust manner. We utilize kernel PCA (KPCA) and show that this method outperforms linear PCA by allowing only those shapes that are close enough to the training data. In our segmentation framework, shape knowledge and image information are encoded into two energy functionals entirely described in terms of shapes. This consistent description permits to fully take advantage of the Kernel PCA methodology and leads to promising segmentation results. In particular, our shape-driven segmentation technique allows for the simultaneous encoding of multiple types of shapes, and offers a convincing level of robustness with respect to noise, occlusions, or smearing
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Shape-driven segmentation of the arterial wall in intravascular ultrasound images
Segmentation of arterial wall boundaries from intravascular images is an important problem for many applications in the study of plaque characteristics, mechanical properties of the arterial wall, its 3D reconstruction,
and its measurements such as lumen size, lumen radius, and wall radius. We present a shape-driven approach to segmentation of the arterial wall from intravascular ultrasound images in the rectangular domain. In a properly built
shape space using training data, we constrain the lumen and media-adventitia contours to a smooth, closed geometry, which increases the segmentation quality without any tradeoff with a regularizer term. In addition to a shape prior,
we utilize an intensity prior through a non-parametric probability density based image energy, with global image measurements rather than pointwise measurements used in previous methods. Furthermore, a detection step is included to address the challenges introduced to the segmentation process by side branches and calcifications. All these features greatly enhance our segmentation method. The tests of our algorithm on a large dataset demonstrate the effectiveness of our approach
Inhomogeneous exponential jump model
We introduce and study the inhomogeneous exponential jump model - an
integrable stochastic interacting particle system on the continuous half line
evolving in continuous time. An important feature of the system is the presence
of arbitrary spatial inhomogeneity on the half line which does not break the
integrability. We completely characterize the macroscopic limit shape and
asymptotic fluctuations of the height function (= integrated current) in the
model. In particular, we explain how the presence of inhomogeneity may lead to
macroscopic phase transitions in the limit shape such as shocks or traffic
jams. Away from these singularities the asymptotic fluctuations of the height
function around its macroscopic limit shape are governed by the GUE Tracy-Widom
distribution. A surprising result is that while the limit shape is
discontinuous at a traffic jam caused by a macroscopic slowdown in the
inhomogeneity, fluctuations on both sides of such a traffic jam still have the
GUE Tracy-Widom distribution (but with different non-universal normalizations).
The integrability of the model comes from the fact that it is a degeneration
of the inhomogeneous stochastic higher spin six vertex models studied earlier
in arXiv:1601.05770 [math.PR]. Our results on fluctuations are obtained via an
asymptotic analysis of Fredholm determinantal formulas arising from contour
integral expressions for the q-moments in the stochastic higher spin six vertex
model. We also discuss "product-form" translation invariant stationary
distributions of the exponential jump model which lead to an alternative
hydrodynamic-type heuristic derivation of the macroscopic limit shape.Comment: 52 pages, 12 figure
ROAM: a Rich Object Appearance Model with Application to Rotoscoping
Rotoscoping, the detailed delineation of scene elements through a video shot,
is a painstaking task of tremendous importance in professional post-production
pipelines. While pixel-wise segmentation techniques can help for this task,
professional rotoscoping tools rely on parametric curves that offer the artists
a much better interactive control on the definition, editing and manipulation
of the segments of interest. Sticking to this prevalent rotoscoping paradigm,
we propose a novel framework to capture and track the visual aspect of an
arbitrary object in a scene, given a first closed outline of this object. This
model combines a collection of local foreground/background appearance models
spread along the outline, a global appearance model of the enclosed object and
a set of distinctive foreground landmarks. The structure of this rich
appearance model allows simple initialization, efficient iterative optimization
with exact minimization at each step, and on-line adaptation in videos. We
demonstrate qualitatively and quantitatively the merit of this framework
through comparisons with tools based on either dynamic segmentation with a
closed curve or pixel-wise binary labelling
Flow characteristics of various three-dimensional rounded contour bumps in a Mach 1.3 freestream
Streamwise and spanwise flow pattern over three rounded contour bumps with different flow control strategies employed have been experimentally investigated in a Mach 1.3 freestream. Surface oil flow visualisation, Schlieren photography and particle image velocimetry measurements were used for flow diagnostics. Experimental data showed that in a Mach 1.3 freestream over the baseline plain bump, significant flow separation appeared at the bump crest that led to the formation of a large wake region downstream. In addition, two large counter-rotating spanwise vortices were formed in the bump valley. It was observed that the use of the passive by-pass blowing jet in the bump valley showed no obvious effects in reducing the sizes of both the wake region and the spanwise vortices in the bump valley. In contrast, it was found that the size of the wake region and the spanwise vortices could be reduced by blowing sonic jet in the bump valley. This approach of flow control found to be the most effective when the total pressure of the blowing jet was 2 bar. It is deduced that the active blowing jet hindered the formation of the spanwise vortices in the bump valley as well as deflected the shear layer downwards so that a smaller re-circulating bubble was formed downstream of the bump crest
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