9,688 research outputs found
Charged polytropic compact stars
In this work, we analyze the effect of charge in compact stars considering
the limit of the maximum amount of charge they can hold. We find that the
global balance of the forces allows a huge charge (~ 10^{20} Coulomb) to be
present in a neutron star producing a very high electric field (~ 10^{21} V/m).
We have studied the particular case of a polytropic equation of state and
assumed that the charge distribution is proportional to the mass density. The
charged stars have large mass and radius as we should expect due to the effect
of the repulsive Coulomb force with the M/R ratio increasing with charge. In
the limit of the maximum charge the mass goes up to ~ 10 M_sun which is much
higher than the maximum mass allowed for a neutral compact star. However, the
local effect of the forces experienced by a single charged particle, makes it
to discharge quickly. This creates a global force imbalance and the system
collapses to a charged black hole
Simulated evaluation of faceted browsing based on feature selection
In this paper we explore the limitations of facet based browsing which uses sub-needs of an information need for querying and organising the search process in video retrieval. The underlying assumption of this approach is that the search effectiveness will be enhanced if such an approach is employed for interactive video retrieval using textual and visual features. We explore the performance bounds of a faceted system by carrying out a simulated user evaluation on TRECVid data sets, and also on the logs of a prior user experiment with the system. We first present a methodology to reduce the dimensionality of features by selecting the most important ones. Then, we discuss the simulated evaluation strategies employed in our evaluation and the effect on the use of both textual and visual features. Facets created by users are simulated by clustering video shots using textual and visual features. The experimental results of our study demonstrate that the faceted browser can potentially improve the search effectiveness
The University of Glasgow at ImageClefPhoto 2009
In this paper we describe the approaches adopted to generate the five runs submitted to ImageClefPhoto 2009 by the University of Glasgow. The aim of our methods is to exploit document diversity in the rankings. All our runs used text statistics extracted from the captions associated to each image in the collection, except one run which combines the textual statistics with visual features extracted from the provided images.
The results suggest that our methods based on text captions significantly improve the performance of the respective baselines, while the approach that combines visual features with text statistics shows lower levels of improvements
Influence of Mathematical and Astronomical Developments in Medieval Kerala on VÄstuĆÄstra
The contribution in the field of mathematics is unparalleled. The concept of zero and the place value system is alone sufficed to place India in a high pedestal. Historians were generally under the impression that Indian supremacy in Mathematics came to an end with Bhaskaracharya (1114â1185) who is also known as Bhaskara II.Recent researches and publications of books like âCrest of the peacockâ written by George Gheverghese Joseph, has brought out the marvelous achievements of Southern India, especially Kerala region after the period of Bhaskaracharya which produced many results surpassing the Europeans in its indigenous style till the advent of Western Education system in early 19th Cent. This medieval contribution includes mathematical analysis and first steps in Calculus and many outstanding discoveries in astronomy. These contributions in Mathematics as well as in Astronomy are now grouped and studied under the title âKerala Schoolâ. Accordingly, Sangamagrama Madhava (14th Cent.), doyen of Kerala School, is recognized as the âFather of infinitesimal Analysisâ.In this paper the attempt is made to analyse the influence of Kerala School in the development of traditional building science and architecture. This branch of knowledge is generally categorized under the term âVÄstuĆÄstraâ.
Current-induced vortex dynamics in Josephson-junction arrays: Imaging experiments and model simulations
We study the dynamics of current-biased Josephson-junction arrays with a
magnetic penetration depth smaller than the lattice spacing. We compare the
dynamics imaged by low-temperature scanning electron microscopy to the vortex
dynamics obtained from model calculations based on the resistively-shunted
junction model, in combination with Maxwell's equations. We find three bias
current regions with fundamentally different array dynamics. The first region
is the subcritical region, i.e. below the array critical current I_c. The
second, for currents I above I_c, is a "vortex region", in which the response
is determined by the vortex degrees of freedom. In this region, the dynamics is
characterized by spatial domains where vortices and antivortices move across
the array in opposite directions in adjacent rows and by transverse voltage
fluctuations. In the third, for still higher currents, the dynamics is
dominated by coherent-phase motion, and the current-voltage characteristics are
linear.Comment: 10 pages, with eps figures. To appear in Phys. Rev.
Nonlocality of Majorana modes in hybrid nanowires
Spatial separation of Majorana zero modes distinguishes trivial from topological midgap states and is key to topological protection in quantum computing applications. Although signatures of Majorana zero modes in tunneling spectroscopy have been reported in numerous studies, a quantitative measure of the degree of separation, or nonlocality, of the emergent zero modes has not been reported. Here, we present results of an experimental study of nonlocality of emergent zero modes in superconductor-semiconductor hybrid nanowire devices. The approach takes advantage of recent theory showing that nonlocality can be measured from splitting due to hybridization of the zero mode in resonance with a quantum dot state at one end of the nanowire. From these splittings as well as anticrossing of the dot states, measured for even and odd occupied quantum dot states, we extract both the degree of nonlocality of the emergent zero mode, as well as the spin canting angles of the nonlocal zero mode. Depending on the device measured, we obtain either a moderate degree of nonlocality, suggesting a partially separated Andreev subgap state, or a highly nonlocal state consistent with a well-developed Majorana modeThis research was supported by Microsoft, the Danish National Research Foundation, the European Commission, and the Spanish Ministry of Economy and Competitiveness through Grants No. FIS2015-65706-P, No. FIS2015-64654-P, and No. FIS2016-80434-P (AEI/FEDER, EU), the RamĂłn y Cajal programme Grant No. RYC-2011-09345, and the MarĂa de Maeztu Programme for Units of Excellence in R&D (Grant No. MDM-2014-0377). C.M.M. acknowledges support from the Villum Foundation. M.-T.D. acknowledges support from State Key Laboratory of High Performance Computing, Chin
BoWFire: Detection of Fire in Still Images by Integrating Pixel Color and Texture Analysis
Emergency events involving fire are potentially harmful, demanding a fast and
precise decision making. The use of crowdsourcing image and videos on crisis
management systems can aid in these situations by providing more information
than verbal/textual descriptions. Due to the usual high volume of data,
automatic solutions need to discard non-relevant content without losing
relevant information. There are several methods for fire detection on video
using color-based models. However, they are not adequate for still image
processing, because they can suffer on high false-positive results. These
methods also suffer from parameters with little physical meaning, which makes
fine tuning a difficult task. In this context, we propose a novel fire
detection method for still images that uses classification based on color
features combined with texture classification on superpixel regions. Our method
uses a reduced number of parameters if compared to previous works, easing the
process of fine tuning the method. Results show the effectiveness of our method
of reducing false-positives while its precision remains compatible with the
state-of-the-art methods.Comment: 8 pages, Proceedings of the 28th SIBGRAPI Conference on Graphics,
Patterns and Images, IEEE Pres
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