709 research outputs found
Understanding interference experiments with polarized light through photon trajectories
Bohmian mechanics allows to visualize and understand the quantum-mechanical
behavior of massive particles in terms of trajectories. As shown by
Bialynicki-Birula, Electromagnetism also admits a hydrodynamical formulation
when the existence of a wave function for photons (properly defined) is
assumed. This formulation thus provides an alternative interpretation of
optical phenomena in terms of photon trajectories, whose flow yields a
pictorial view of the evolution of the electromagnetic energy density in
configuration space. This trajectory-based theoretical framework is considered
here to study and analyze the outcome from Young-type diffraction experiments
within the context of the Arago-Fresnel laws. More specifically, photon
trajectories in the region behind the two slits are obtained in the case where
the slits are illuminated by a polarized monochromatic plane wave. Expressions
to determine electromagnetic energy flow lines and photon trajectories within
this scenario are provided, as well as a procedure to compute them in the
particular case of gratings totally transparent inside the slits and completely
absorbing outside them. As is shown, the electromagnetic energy flow lines
obtained allow to monitor at each point of space the behavior of the
electromagnetic energy flow and, therefore, to evaluate the effects caused on
it by the presence (right behind each slit) of polarizers with the same or
different polarization axes. This leads to a trajectory-based picture of the
Arago-Fresnel laws for the interference of polarized light.Comment: 36 pages, 6 figure
Should particle trajectories comply with the transverse momentum distribution?
The momentum distributions associated with both the wave function of a
particle behind a grating and the corresponding Bohmian trajectories are
investigated and compared. Near the grating, it is observed that the former
does not depend on the distance from the grating, while the latter changes with
this distance. However, as one moves further apart from the grating, in the far
field, both distributions become identical.Comment: 10 pages, 7 figure
La Biblioteca de la Memoria
La Biblioteca de la Memòria és un projecte de la Biblioteca Central d'Igualadaque es presenta com una experiència de cerca, recollida, conservació i divulgació de testimonis personals duta a terme per la biblioteca pública. Com a característiques principals cal remarcar-ne la implicació d'entitats i persones en aquesta idea comuna de promoure la cerca i de recollir testimonis de memòria popular. Se n'explica la metodologia i els resultats, de manera que pugui servir com a pauta de treball per a d'altres biblioteques públiques que vulguin endegar projectes semblants per tal de preservar la història oral de Catalunya.The Library of Memory is a project of the Central Library of Igualada. Described is this public library’s experience in searching for, collecting, conserving and disseminating personal testimony. One of the key features has been the involvement of both organisations and individuals in this communal idea to encourage that memories of townspeople be sought out and gathered. The fact that the project has been organised by a public library may encourage other libraries to carry out similar projects. Given the size and integration among the inhabitants of the Catalan library network, collecting oral history is seen as an important task that it can perform.La Biblioteca de la Memòria es un proyecto de la Biblioteca Central d’Igualada que se presenta como una experiencia de búsqueda, recopilación, conservación y divulgación de testimonios personales, llevada a cabo por la biblioteca pública. Como características principales hay que remarcar la implicación de entidades y personas en esta idea, con el fin de promover la búsqueda y recoger testimonios de memoria popular. Se explica la metodología de trabajo y los resultados, de forma que puedan servir como pauta para otras bibliotecas públicas interesadas en iniciar proyectos similares, contribuyendo así a la preservación de la historia oral de Cataluña
Oblique surface waves at an interface of metal-dielectric superlattice and isotropic dielectric
We investigate the existence and the dispersion characteristics of surface
waves that propagate at an interface between metal-dielectric superlattice and
isotropic dielectric. Within the long wavelength limit, when the
effective-medium approximation is valid, the superlattice behaves like a
uniaxial plasmonic crystal with the main optical axes perpendicular to the
metal-dielectric interfaces. We demonstrate that if such a semi-infinite
plasmonic crystal is cut normally to the layer interfaces and brought into the
contact with semi-infinite dielectric, a new type of surface modes can appear.
The propagation of such modes obliquely to the optical axes occurs under
favorable conditions that regard thicknesses of the layers, as well as the
proper choice of dielectric permittivity of the constituent materials. We show
that losses within the metallic layers can be substantially reduced by making
the layers sufficiently thin. At the same time, a dramatic enlargement of the
range of angles for oblique propagation of the new surface modes is observed.
This can lead, however, to the field non-locality and consequently to the
failure of the effective-medium approximation.Comment: 4 pages, 3 figure
The electron-phonon coupling strength at metal surfaces directly determined from the Helium atom scattering Debye-Waller factor
A new quantum-theoretical derivation of the elastic and inelastic scattering
probability of He atoms from a metal surface, where the energy and momentum
exchange with the phonon gas can only occur through the mediation of the
surface free-electron density, shows that the Debye-Waller exponent is directly
proportional to the electron-phonon mass coupling constant . The
comparison between the values of extracted from existing data on the
Debye-Waller factor for various metal surfaces and the values known
from literature indicates a substantial agreement, which opens the possibility
of directly extracting the electron-phonon coupling strength in quasi-2D
conducting systems from the temperature or incident energy dependence of the
elastic Helium atom scattering intensities.Comment: 14 pages, 2 figures, 1 tabl
Generalization of Vélu's formulae
Given an elliptic curve and a finite subgroup , Vélu's formulae concern to a separable isogeny with kernel . In particular, for a point these formulae express the first elementary symmetric polynomial on the abscissas of the points in the set as the
difference between the abscissa of and the first elementary symmetric polynomial on the abscissas of the nontrivial points of the kernel . On the other hand, they express Weierstrass coefficients of as polynomials in the coefficients of and two additional parameters: and . We generalize this by defining parameters for all and giving analogous formulae for all the elementary
symmetric polynomials and the power sums on the abscissas of the
points in . Simultaneously, we obtain an efficient way of
performing computations concerning the isogeny when is a
rational group
Modelización contextual y lingüística del abstract del artículo de investigación científica, y desarrollo de un sistema de escritura asistida – RedACTe : informe de avance
El proyecto, que es continuación de RedACTe I-III, tiene como objeto de estudio el Abstract del artículo de investigación científica en inglés (AbAICI). Como objetivo teórico-descriptivo, se propone elaborar una modelización sistémico-funcional formal, orientada a la generación de textos, de correlaciones sistemáticas entre las propiedades contextuales y las propiedades lingüísticas del AbAICI, y, como objetivo aplicado, la construcción de un sistema de principios de escritura asistida de AbAICIs basado en dicha modelización.La aplicación resultante tendrá las características distintivas de (i) captar, tanto a nivel de estratos superiores cuanto a nivel de estratos inferiores, la unidad y la diversidad de las disciplinas objeto de la modelización, (ii) adaptar e instrumentar pedagógicamente la imprescindible conceptualización retórico-lingüística, y (iii) asistir a investigadores locales en la redacción de AbAICIs bien formados, apropiados y altamente competitivos, y contribuir así a superar la desventaja comparativa que, por problemas de idiomaticidad, tienen nuestros científicos para publicar en revistas especializadas.This project, which is a continuation of Projects RedACTe I-III, focuses on the research article abstract (RAA). Its theoretical-descriptive aim is to provide a formal systemic-functional text generation-oriented modeling of regular correlations between the contextual and linguistic features of the RAA. Its applied aim is to build a system of principles for assisted writing of RAAs based on such a modeling.The resulting application will (i) capture the unity and diversity of RAA features of various disciplines at both the higher and the lower strata, (ii) adapt and implement pedagogically the necessary rhetorical and linguistic conceptualization, and (iii) assist local researchers in the writing of well-formed, appropriate and competitive RAAs, and thus help them to overcome the comparative disadvantage that emerges, due to idiomaticity problems, when local Spanish speaking researchers write RAAs to be submitted for publication in prestigious international scientific journals
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