488 research outputs found
A useful form of the recurrence relation between relativistic atomic matrix elements of radial powers
Recently obtained recurrence formulae for relativistic hydrogenic radial
matrix elements are cast in a simpler and perhaps more useful form. This is
achieved with the help of a new relation between the and the
terms ( is a Dirac matrix and are constants) in the
atomic matrix elements.Comment: 7 pages, no figure
NGC 6705 a young -enhanced Open Cluster from OCCASO data
The stellar [/Fe] abundance is sometimes used as a proxy for stellar
age, following standard chemical evolution models for the Galaxy, as seen by
different observational results. In this work we show that the Open Cluster
NGC6705/M11 has a significant -enhancement [/Fe] dex,
despite its young age (300 Myr), challenging the current paradigm. We use
high resolution (R) high signal-to-noise (70) spectra of 8 Red
Clump stars, acquired within the OCCASO survey. We determine very accurate
chemical abundances of several elements, using an equivalent width
methodology (Si, Ca and Ti), and spectral synthesis fits (Mg and O). We obtain
[Si/Fe]=, [Mg/Fe]=, [O/Fe]=,
[Ca/Fe]= and [Ti/Fe]=. Our results place these
cluster within the group of young [/Fe]-enhanced field stars recently
found by several authors in the literature. The ages of our stars have an
uncertainty of around 50 Myr, much more precise than for field stars. By
integrating the cluster's orbit in several non-axisymmetric Galactic
potentials, we establish the M11's most likely birth radius to lie between
6.8-7.5 kpc from the Galactic center, not far from its current position. With
the robust Open Cluster age scale, our results prove that a moderate
[/Fe]-enhancement is no guarantee for a star to be old, and that not
all -enhanced stars can be explained with an evolved blue straggler
scenario. Based on our orbit calculations, we further argue against a Galactic
bar origin of M11.Comment: 10 pages, 6 figures, accepted in A&
Relativistic quantum mechanics of a Dirac oscillator
The Dirac oscillator is an exactly soluble model recently introduced in the
context of many particle models in relativistic quantum mechanics. The model
has been also considered as an interaction term for modelling quark confinement
in quantum chromodynamics. These considerations should be enough for
demonstrating that the Dirac oscillator can be an excellent example in
relativistic quantum mechanics. In this paper we offer a solution to the
problem and discuss some of its properties. We also discuss a physical picture
for the Dirac oscillator's non-standard interaction, showing how it arises on
describing the behaviour of a neutral particle carrying an anomalous magnetic
moment and moving inside an uniformly charged sphere.Comment: 19 pages, 1 figur
From circular paths to elliptic orbits: A geometric approach to Kepler's motion
The hodograph, i.e. the path traced by a body in velocity space, was
introduced by Hamilton in 1846 as an alternative for studying certain dynamical
problems. The hodograph of the Kepler problem was then investigated and shown
to be a circle, it was next used to investigate some other properties of the
motion. We here propose a new method for tracing the hodograph and the
corresponding configuration space orbit in Kepler's problem starting from the
initial conditions given and trying to use no more than the methods of
synthetic geometry in a sort of Newtonian approach. All of our geometric
constructions require straight edge and compass only.Comment: 9 pages, 4 figure
Limitations on the superposition principle: superselection rules in non-relativistic quantum mechanics
The superposition principle is a very basic ingredient of quantum theory.
What may come as a surprise to many students, and even to many practitioners of
the quantum craft, is tha superposition has limitations imposed by certain
requirements of the theory. The discussion of such limitations arising from the
so-called superselection rules is the main purpose of this paper. Some of their
principal consequences are also discussed. The univalence, mass and particle
number superselection rules of non-relativistic quantum mechanics are also
derived using rather simple methods.Comment: 22 pages, no figure
Simulador de negocios CAPSTONE: Análisis de la empresa Digby
El primer capÃtulo de este trabajo presenta el
marco teóric,o que permite explicar la definición de estrategia y su importancia en el
desarrollo de las empresas; se ejemplifica a través de análisis de casos las principales
teorÃas y herramientas para la aplicación de esta.
El capÃtulo dos, es una explicación detallada de la competencia de CAPSTONE, en
las que se discutirán las estrategias genéricas, desarrollo de toma de decisiones,
preferencias de mercado y accesibilidad con los clientes. Además, se definirá la estrategia a
seguir por parte de la compañÃa Digby para los siguientes ocho años de operación.
En los capÃtulos tres al seis se detallará un análisis de los resultados y las
condiciones del mercado de la industria de los sensores, asà como las oportunidades de
mejorar de la estrategia establecida por los ejecutivos para ser una empresa lÃder en el
mercado.
Por último, en el capÃtulo siete, se realizan las conclusiones del simulador, análisis
del curso y reflexión del posgrado
Exposición de curvas y superficies: una experiencia extraacadémica universitaria
En este artÃculo se comenta una experiencia extraacadémica realizada
por un grupo de alumnos universitarios de Matemáticas, juntamente con
su profesor, en el marco de la Semana de las Matemáticas organizada por
la Facultad de Matemáticas de Sevilla para conmemorar el Año Mundial de las Matemáticas (Año 2000). La citada experiencia consistió en la realización y montaje de una Exposición de Curvas y Superficies, cuyos objetivos generales, desarrollo y conclusiones finales constituyen la base de este trabajo
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