2,738 research outputs found
How to Find Suitable Ontologies Using an Ontology-based WWW Broker
Knowledge reuse by means of outologies now faces three important problems: (1) there are no standardized identifying features that characterize ontologies from the user point of view; (2) there are no web sites using the same logical organization, presenting relevant information about ontologies; and (3) the search for appropriate ontologies is hard, time-consuming and usually fruitless. To solve the above problems, we present: (1) a living set of features that allow us to characterize ontologies from the user point of view and have the same logical organization; (2) a living domain ontology about ontologies (called ReferenceOntology) that gathers, describes and has links to existing ontologies; and (3) (ONTO)2Agent, the ontology-based www broker about ontologies that uses the Reference Ontology as a source of its knowledge and retrieves descriptions of ontologies that satisfy a given set of constraints. (ONTO)~Agent is available at http://delicias.dia.fi.upm.es/REFERENCE ONTOLOGY
A generalized Finch-Skea class one static solution
In the present article, we discuss relativistic anisotropic solutions of the
Einstein field equation for the spherically symmetric line element under the
class I condition. To do so we apply the embedding class one technique using
Eisland condition. Within this approach, one arrives at a particular
differential equation that links the two metric components and
. In order to obtain the full space-time description inside the
stellar configuration we ansatz the generalized form of metric component
corresponding to the Finch-Skea solution. Once the space-time geometry
is specified we obtain the complete thermodynamic description i.e. the matter
density , the radial, and tangential pressures and ,
respectively. Graphical analysis shows that the obtained model respects the
physical and mathematical requirements that all ultra-high dense collapsed
structures must obey. The diagram suggests that the solution yields
stiffer EoS as parameter increases. The graph is in agreement with
the concepts of Bejgar et al. \cite{bej} that the mass at is lesser
by few percent (for this solution ) from . This suggests
that the EoSs is without any strong high-density softening due to
hyperonization or phase transition to an exotic state.Comment: 14 figures, Accepted in European Physical Journal
Playing with Casimir in the vacuum sandbox
The Casimir effect continues to be a subject of discussion regarding its
relationship, or the lack of it, with the vacuum energy of fluctuating quantum
fields. In this note, we propose a Gedankenexperiment considering an imaginary
process similar to a vacuum fluctuation in a typical static Casimir set up. The
thought experiment leads to intriguing conclusions regarding the minimum
distance between the plates when approaching the Planck scale. More
specifically, it is found that distance between the plates cannot reach a value
below Planck lengths, being the Planck length and the
typical lateral extension of the plates. Additional findings allow the
conclusion that the approach between the two plates towards this minimum
separation distance is asymptotic
Extrinsic and intrinsic effects setting viscosity in life processes: implications for fundamental physical constants
Understanding the values and origin of fundamental physical constants, one of
the grandest challenges in modern science, has been discussed in particle
physics, astronomy and cosmology. More recently, it was realised that
fundamental constants have a bio-friendly window set by life processes
involving motion and flow. This window is related to intrinsic fluid properties
such as energy and length scales in condensed matter set by fundamental
constants. Here, we discuss important extrinsic factors governing the viscosity
of complex fluids operating in life processes due to collective effects. We
show that both extrinsic and intrinsic factors affecting viscosity need to be
taken into account when estimating the bio-friendly range of fundamental
constants from life processes, and our discussion provides a straightforward
recipe for doing this. We also find that the relative role of extrinsic and
intrinsic factors depends on the range of variability of these intrinsic and
extrinsic factors. Remarkably, the viscosity of a complex fluid such as blood
with significant extrinsic effects is not far from the intrinsic viscosity
calculated using the fundamental constants only, and we discuss the reason for
this in terms of dynamics of contact points between cells.Comment: arXiv admin note: text overlap with arXiv:2307.0527
Spillover and diffraction sidelobe contamination in a double-shielded experiment for mapping Galactic synchrotron emission
We have analyzed observations from a radioastronomical experiment to survey
the sky at decimetric wavelengths along with feed pattern measurements in order
to account for the level of ground contamination entering the sidelobes. A
major asset of the experiment is the use of a wire mesh fence around the
rim-halo shielded antenna with the purpose of levelling out and reducing this
source of stray radiation for zenith-centered 1-rpm circular scans. We
investigate the shielding performance of the experiment by means of a geometric
diffraction model in order to predict the level of the spillover and
diffraction sidelobes in the direction of the ground. Using 408 MHz and 1465
MHz feed measurements, the model shows how a weakly-diffracting and unshielded
antenna configuration becomes strongly-diffracting and double-shielded as
far-field diffraction effects give way to near-field ones. Due to the
asymmetric response of the feeds, the orientation of their radiation fields
with respect to the secondary must be known a priori before comparing model
predictions with observational data. By adjusting the attenuation coefficient
of the wire mesh the model is able to reproduce the amount of differential
ground pick-up observed during test measurements at 1465 MHz.Comment: 14 pages, 17 eps + 1 gif figures and 4 Tables. Accepted for
publication in A&AS. Fig.7 available at full resolution from
http://www.das.inpe.br/~tello/publications.ht
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