8,850 research outputs found
Diffeomorphisms from higher dimensional W-algebras
Classical W-algebras in higher dimensions have been recently constructed. In
this letter we show that there is a finitely generated subalgebra which is
isomorphic to the algebra of local diffeomorphisms in D dimensions. Moreover,
there is a tower of infinitely many fields transforming under this subalgebra
as symmetric tensorial one-densities. We also unravel a structure isomorphic to
the Schouten symmetric bracket, providing a natural generalization of w_\infty
in higher dimensions.Comment: 10 page
On the stability of circular orbits in galactic dynamics: Newtonian thin disks
The study of off-equatorial orbits in razor-thin disks is still in its
beginnings. Contrary to what was presented in the literature in recent
publications, the vertical stability criterion for equatorial circular orbits
cannot be based on the vertical epicyclic frequency, because of the
discontinuity in the gravitational field on the equatorial plane. We present a
rigorous criterion for the vertical stability of circular orbits in systems
composed by a razor-thin disk surrounded by a smooth axially symmetric
distribution of matter, the latter representing additional structures such as
thick disk, bulge and (dark matter) halo. This criterion is satisfied once the
mass surface density of the thin disk is positive. Qualitative and quantitative
analyses of nearly equatorial orbits are presented. In particular, the analysis
of nearly equatorial orbits allows us to construct an approximate analytical
third integral of motion in this region of phase-space, which describes the
shape of these orbits in the meridional plane.Comment: 3 pages, 1 figure. In Proceedings of the MG13 Meeting on General
Relativity, Stockholm University, Sweden, 1-7 July 2012. World Scientific,
Singapore. Based on arXiv:1206.6501. in The Thirteenth Marcel Grossmann
Meeting: On Recent Developments in Theoretical and Experimental General
Relativity, Astrophysics, and Relativistic Field Theories (In 3 Volumes),
chap. 438, pages 2346-2348 (2015
System dynamics modelling in systems biology and applications in pharmacology
El modelado matemático de sistemas biológicos complejos es uno de los temas clave en la Biología de Sistemas y varios métodos computacionales basados en la simulación computarizada han sido aplicados hasta ahora para determinar el comportamiento de los sistemas no lineales. La Dinamica de Sistemas es una metodología de modelado intuitivo basada en el razonamiento cualitativo por el cual un modelo conceptual se puede describir como un conjunto de relaciones de causa y efecto entre las variables de un sistema. A partir de esta estructura, es posible obtener un conjunto de ecuaciones dinámicas que describan cuantitativamente el comportamiento del sistema. Centrándose en los sistemas farmacológicos, el modelado compartimental a menudo se utiliza para resolver un amplio espectro de problemas relacionados con la distribución de materiales en los sistemas vivos en la investigación, el diagnóstico y la terapia en todo el cuerpo, los órganos y los niveles celulares.
En este artículo presentamos la metodología de modelado de Dinámica del Sistema y su aplicación al modelado de un modelo compartimental farmacocinético-farmacodinámico del efecto de profundidad anestésica en pacientes sometidos a intervenciones quirúrgicas, derivando un modelo de simulación en el entorno de simulación orientada a objetos OpenModelica. La Dinamica de Sistemas se puede ver como una herramienta educativa poderosa y fácil de usar y en la enseñanza de Biología de Sistemas.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
Influence of atomic polarization and horizontal illumination on the Stokes profiles of the He I 10830 multiplet
The polarization observed in the spectral lines of the He I 10830 multiplet
carries valuable information on the dynamical and magnetic properties of plasma
structures in the solar chromosphere and corona, such as spicules, prominences,
filaments, emerging magnetic flux regions, etc. Here we investigate the
influence of atomic level polarization on the emergent Stokes profiles for a
broad range of magnetic field strengths, in both 90 degree and forward
scattering geometry. We show that, contrary to a widespread belief, the
selective emission and absorption processes caused by the presence of atomic
level polarization may have an important influence on the emergent linear
polarization, even for magnetic field strengths as large as 1000 G.
Consequently, the modeling of the Stokes Q and U profiles should not be done by
taking only into account the contribution of the transverse Zeeman effect
within the framework of the Paschen-Back effect theory, unless the magnetic
field intensity of the observed plasma structure is sensibly larger than 1000
G. We point out also that in low-lying optically thick plasma structures, such
as those of active region filaments, the (horizontal) radiation field generated
by the structure itself may substantially reduce the positive contribution to
the anisotropy factor caused by the (vertical) radiation field coming from the
underlying solar photosphere, so that the amount of atomic level polarization
may turn out to be negligible. Only under such circumstances may the emergent
linear polarization of the He I 10830 multiplet in such regions of the solar
atmosphere be dominated by the contribution caused by the transverse Zeeman
effect.Comment: Accepted for publication in The Astrophysical Journal (It is
tentatively scheduled for the ApJ January 20, 2007 issue
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