27,467 research outputs found
Depth map compression via 3D region-based representation
In 3D video, view synthesis is used to create new virtual views between
encoded camera views. Errors in the coding of the depth maps introduce
geometry inconsistencies in synthesized views. In this paper, a new 3D plane
representation of the scene is presented which improves the performance of
current standard video codecs in the view synthesis domain. Two image segmentation
algorithms are proposed for generating a color and depth segmentation.
Using both partitions, depth maps are segmented into regions without
sharp discontinuities without having to explicitly signal all depth edges. The
resulting regions are represented using a planar model in the 3D world scene.
This 3D representation allows an efficient encoding while preserving the 3D
characteristics of the scene. The 3D planes open up the possibility to code
multiview images with a unique representation.Postprint (author's final draft
Exploring the Kibble-Zurek mechanism with homogeneous Bose gases
Out-of-equilibrium phenomena is a subject of considerable interest in many
fields of physics. Ultracold quantum gases, which are extremely clean,
well-isolated and highly controllable systems, offer ideal platforms to
investigate this topic. The recent progress in tailoring trapping potentials
now allows the experimental production of homogeneous samples in custom
geometries, which is a key advance for studies of the emergence of coherence in
interacting quantum systems. Here we review recent experiments in which
temperature quenches have been performed across the Bose-Einstein condensation
(BEC) phase transition in an annular geometry and in homogeneous 3D and
quasi-2D gases. Combined, these experiments give a comprehensive picture of the
Kibble-Zurek (KZ) scenario through complementary measurements of correlation
functions and topological defects density. They also allow the measurement of
KZ scaling laws, the direct confirmation of the "freeze-out" hypothesis that
underlies the KZ theory, and the extraction of critical exponents of the
Bose-Einstein condensation transition.Comment: 11 pages, 6 figures; topical revie
Flexible system of multiple RGB-D sensors for measuring and classifying fruits in agri-food Industry
The productivity of the agri-food sector experiences continuous and growing challenges that make the use of innovative technologies to maintain and even improve their competitiveness a priority. In this context, this paper presents the foundations and validation of a flexible and portable system capable of obtaining 3D measurements and classifying objects based on color and depth images taken from multiple Kinect v1 sensors. The developed system is applied to the selection and classification of fruits, a common activity in the agri-food industry. Being able to obtain complete and accurate information of the environment, as it integrates the depth information obtained from multiple sensors, this system is capable of self-location and self-calibration of the sensors to then start detecting, classifying and measuring fruits in real time. Unlike other systems that use specific set-up or need a previous calibration, it does not require a predetermined positioning of the sensors, so that it can be adapted to different scenarios. The characterization process considers: classification of fruits, estimation of its volume and the number of assets per each kind of fruit. A requirement for the system is that each sensor must partially share its field of view with at least another sensor. The sensors localize themselves by estimating the rotation and translation matrices that allow to transform the coordinate system of one sensor to the other. To achieve this, Iterative Closest Point (ICP) algorithm is used and subsequently validated with a 6 degree of freedom KUKA robotic arm. Also, a method is implemented to estimate the movement of objects based on the Kalman Filter. A relevant contribution of this work is the detailed analysis and propagation of the errors that affect both the proposed methods and hardware. To determine the performance of the proposed system the passage of different types of fruits on a conveyor belt is emulated by a mobile robot carrying a surface where the fruits were placed. Both the perimeter and volume are measured and classified according to the type of fruit. The system was able to distinguish and classify the 95% of fruits and to estimate their volume with a 85% of accuracy in worst cases (fruits whose shape is not symmetrical) and 94% of accuracy in best cases (fruits whose shape is more symmetrical), showing that the proposed approach can become a useful tool in the agri-food industry.This project has been supported by the National Commission for Science and Technology Research of Chile (Conicyt) under FONDECYT grant 1140575 and the Advanced Center of Electrical and Electronic Engineering - AC3E (CONICYT/FB0008)
Critical Point of an Interacting Two-Dimensional Atomic Bose Gas
We have measured the critical atom number in an array of harmonically trapped
two-dimensional (2D) Bose gases of rubidium atoms at different temperatures. We
found this number to be about five times higher than predicted by the
semi-classical theory of Bose-Einstein condensation (BEC) in the ideal gas.
This demonstrates that the conventional BEC picture is inapplicable in an
interacting 2D atomic gas, in sharp contrast to the three-dimensional case. A
simple heuristic model based on the Berezinskii-Kosterlitz-Thouless theory of
2D superfluidity and the local density approximation accounts well for our
experimental results
The Chemical Evolution Carousel of Spiral Galaxies : Azimuthal Variations of Oxygen Abundance in NGC1365
19 pages, 13 figures. Accepted to ApJThe spatial distribution of oxygen in the interstellar medium of galaxies is the key to understanding how efficiently metals that are synthesized in massive stars can be redistributed across a galaxy. We present here a case study in the nearby spiral galaxy NGC1365 using 3D optical data obtained in the TYPHOON Program. We find systematic azimuthal variations of the HII region oxygen abundance imprinted on a negative radial gradient. The 0.2 dex azimuthal variations occur over a wide radial range of 0.3 to 0.7 R25 and peak at the two spiral arms in NGC1365. We show that the azimuthal variations can be explained by two physical processes: gas undergoes localized, sub-kpc scale self-enrichment when orbiting in the inter-arm region, and experiences efficient, kpc scale mixing-induced dilution when spiral density waves pass through. We construct a simple chemical evolution model to quantitatively test this picture and find that our toy model can reproduce the observations. This result suggests that the observed abundance variations in NGC1365 are a snapshot of the dynamical local enrichment of oxygen modulated by spiral-driven, periodic mixing and dilution.Peer reviewedFinal Published versio
Magnetization of cloud cores and envelopes and other observational consequences of reconnection diffusion
Recent observational results for magnetic fields in molecular clouds reviewed
by Crutcher (2012) seem to be inconsistent with the predictions of the
ambipolar diffusion theory of star formation. These include the measured
decrease in mass to flux ratio between envelopes and cores, the failure to
detect any self-gravitating magnetically subcritical clouds, the determination
of the flat PDF of the total magnetic field strengths implying that there are
many clouds with very weak magnetic fields, and the observed scaling that implies gravitational contraction with weak magnetic fields.
We consider the problem of magnetic field evolution in turbulent molecular
clouds and discuss the process of magnetic field diffusion mediated by magnetic
reconnection. For this process that we termed "reconnection diffusion" we
provide a simple physical model and explain that this process is inevitable in
view of the present day understanding of MHD turbulence. We address the issue
of the expected magnetization of cores and envelopes in the process of star
formation and show that reconnection diffusion provides an efficient removal of
magnetic flux that depends only on the properties of MHD turbulence in the core
and the envelope. As a result, the magnetic flux trapped during the collapse in
the envelope is being released faster than the flux trapped in the core,
resulting in much weaker fields in envelopes than in cores, as observed. We
provide simple semi-analytical model calculations which support this conclusion
and qualitatively agree with the observational results. We argue that magnetic
reconnection provides a solution to the magnetic flux problem of star formation
that agrees better with observations than the long-standing ambipolar diffusion
paradigm.Comment: 22 pages, 11 figures, submitted to ApJ, revised version. arXiv admin
note: substantial text overlap with arXiv:1111.069
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