4,057 research outputs found
Generalized scattering-matrix approach for magneto-optics in periodically patterned multilayer systems
We present here a generalization of the scattering-matrix approach for the
description of the propagation of electromagnetic waves in nanostructured
magneto-optical systems. Our formalism allows us to describe all the key
magneto-optical effects in any configuration in periodically patterned
multilayer structures. The method can also be applied to describe periodic
multilayer systems comprising materials with any type of optical anisotropy. We
illustrate the method with the analysis of a recent experiment in which the
transverse magneto-optical Kerr effect was measured in a Fe film with a
periodic array of subwavelength circular holes. We show, in agreement with the
experiments, that the excitation of surface plasmon polaritons in this system
leads to a resonant enhancement of the transverse magneto-optical Kerr effect.Comment: 12 pages, 6 figures, submitted to Physical Review
Procedure for evaluating and refurbishing envelopes of obsolete buildings in warm regions
This research develops a procedure to evaluate and refurbish obsolete buildings obliged to comply with the Spanish Technical Building Code. This procedure matches the building typologies selected to the optimal solution for each case. The analysis focuses on buildings constructed between the 1960s and the 1980s in Castellón, Spain. The buildings selected are representative of the period, of compact cities, and of the Mediterranean climate region. Three types of intervention on the envelope have been considered. The analysis for the most appropriate intervention in each case was based on economic, environmental, technical, and social factors. It shows that the best solution for Terraced Houses (TH) and Multi-family Houses (MH) is exterior refurbishment with additional insulation on the façade. This solution is achieved at reasonable cost by reducing one-third of the primary energy consumed. The best solution for Apartment Blocks (AB) is exterior retrofitting with ventilated façades, which offers the best performance from a technical, environmental, and economic perspective. In all cases, interior retrofitting is ruled out given that exterior retrofitting with additional insulation provides greater energy savings at a similar cost.This study was funded by the project: Study of existing building envelopes and analysis of retrofit solutions, conventional and innovative, by means of multi-criteria analysis, from Jaume I University (Castellón de la Plana, Spain) [grant number P1·1A2013-08]
Generation of high-confinement step-like optical waveguides in LiNbO3 by swift heavy ion-beam irradiation
3 pages, 4 figures, 1 table.We demonstrate a swift ion-beam irradiation procedure based on electronic (not nuclear) excitation to generate a large index jump step-like optical waveguide (Δn0 ≈ 0.2, Δne ≈ 0.1) in LiNbO3. The method uses medium-mass ions with a kinetic energy high enough to assure that their electronic stopping power Se(z) reaches a maximum value close to the amorphous (latent) track threshold inside the crystal. Fluorine ions of 20 and 22 MeV and fluences in the range (1–30)×1014 are used for this work. A buried amorphous layer having a low refractive index (2.10 at a wavelength of 633 nm) is then generated at a controlled depth in LiNbO3, whose thickness is also tuned by irradiation fluence. The layer left at the surface remains crystalline and constitutes the core of the optical waveguide which, moreover, is several microns far from the end of the ion range. The waveguides show, after annealing at 300 °C, low propagation losses ( ≈ 1 dB/cm) and a high second-harmonic generation coefficient (50%–80% of that for bulk unirradiated LiNbO3, depending on the fluence). The formation and structure of the amorphous layer has been monitored by additional Rutherford backscattering/channeling experiments.We acknowledge the funding of the project MAT2002–
03220 (MEC). A. García-Navarro acknowledges the financial
support of the MEC through a FPU Fellowship and of
the Madrid City Hall-Residencia de Estudiantes.Peer reviewe
Teaching mathematical modeling software for multiobjective optimization in chemical engineering courses
This paper expects to give undergraduate students some guidelines about how to incorporate environmental considerations in a chemical supply chain and how the introduction of these concerns have an important effect on the results obtained in the multiobjective optimization problem where both economic and environmental aspects are considered simultaneously. To extend the economic and environmental assessment outside the chemical plant and to identify the tradeoffs associated with the reality of chemical and petrochemical industries, a simplified problem of a chemical supply chain is proposed as a case study. The inclusion of environmental concerns to this economic problem make this new case study a good example for undergraduate students interested in implementing simultaneous economic and environmental considerations in the chemical process design incorporating mathematical modeling software for solving this multiobjective problem. Thus, the final objective of this paper is to show to undergraduate students how environmental together with economic considerations could have an important impact in the logistics of a supply chain and how multiobjective optimization could be used to make better decisions in the design of chemical processes including its supply chain. To reach our purpose, the Pareto curve of the supply chain is obtained using the ɛ-constraint method. In addition, the tradeoffs of this multiobjective optimization have been identified and analyzed and ultimately a good decision based on the set of ‘equivalent’ optimal solutions for this chemical supply chain problem determined.Spanish Ministry of Education and Science (CTQ2009-14420)
The occultation events of the Herbig Ae/Be star V1247 Ori
Aims: I study new deep (DeltaV ~ 1.20-1.65 mag) occultation events of the
delta Scuti, Herbig Ae/Be star V1247 Ori in the Ori OB1 b association. Methods:
I use the V-band ASAS light curve of V1247 Ori, which covers the last nine
years, together with photometric data in the near-ultraviolet, visible, near-,
and far-infrared taken from the literature. I carry out a periodogram analysis
of the "cleaned" light curve and construct the spectral energy distribution of
the star. Results: The star V1247 Ori is interesting for the study of the UX
Orionis phenomenon, in which Herbig Ae/Be stars are occulted by their
protoplanetary discs, for three reasons: brightness (V ~ 9.85 mag), large
infrared excess at 20-100 mum (F_60 ~ 10 Jy), and photometric stability out of
occultation (sigma(V) ~ 0.02 mag), which may help to determine the location and
spatial structure of the occulting disc clumps.Comment: A&A Letters, in pres
Simultaneous environmental and economic process synthesis of Isobutane Alkylation
This multidisciplinary study concerns the optimal design of processes with a view to both maximizing profit and minimizing environmental impacts. This can be achieved by a combination of traditional chemical process design methods, measurements of environmental impacts and advanced mathematical optimization techniques. More to the point, this paper presents a hybrid simulation-multiobjective optimization approach that at once optimizes the production cost and minimizes the associated environmental impacts of isobutane alkylation. This approach has also made it possible to obtain the flowsheet configurations and process variables that are needed to manufacture isooctane in a way that satisfies the above-stated double aim. The problem is formulated as a Generalized Disjunctive Programming problem and solved using state-of-the-art logic-based algorithms. It is shown, starting from existing alternatives for the process, that it is possible to systematically generate a superstructure that includes alternatives not previously considered. The optimal solution, in the form a Pareto curve, includes different structural alternatives from which the most suitable design can be selected. To evaluate the environmental impact, Life Cycle Assessment based on two different indicators is employed: Ecoindicator 99 and Global Warming Potential.Spanish Ministry of Science and Innovation (CTQ2012-37039-C02-02)
Study of the effects of magnetic braking on the lithium abundances of the Sun and solar-type stars
The study of lithium (Li) surface abundance in the Sun and young stellar
globular clusters which are seemingly anomalous in present-day scenarios, as
well as the influence of rotation and magnetic braking (MB) on its depletion
during pre-main sequence (PMS) and main sequence (MS). In this work, the
effects of rotational mixing and of the rotational hydrostatic effects on Li
abundances are studied by simulating several grids of PMS and MS rotating and
non-rotating models. Those effects are combined with the additional impact of
the MB (with magnetic field intensities ranging between 3.0 and 5.0 G). The
data obtained from simulations are confronted by comparing different stellar
parameters. The results show that the surface Li abundance for the Sun like
models at the end of the PMS and throughout the MS decreases when rotational
effects are included, i.e. the Li depletion rate for rotating models is higher
than for non-rotating ones. This effect is attenuated when the MB produced by a
magnetic field is present. This physical phenomena impacts also the star
effective temperature () and its location in the HR diagram.
The impact of MB in Li depletion is sensitive to the magnetic field intensity:
the higher it is, the lower the Li destruction. A direct link between the
magnetic fields and the convective zone (CZ) size is observed: stronger
magnetic fields produce shallower CZ's. This result suggests that MB effect
must be taken into consideration during PMS if we aim to reproduce Li
abundances in young clusters
Low-resolution spectroscopy and spectral energy distributions of selected sources towards sigma Orionis
Aims: We investigated in detail nine sources in the direction of the young
sigma Orionis cluster, which is considered a unique site for studying stellar
and substellar formation. The nine sources were selected because of some
peculiar properties, such as extremely red infrared colours or too strong
Halpha emission for their blue optical colours. Methods: We took high-quality,
low-resolution spectroscopy (R ~ 500) of the nine targets with ALFOSC at the
Nordic Optical Telescope. We also re-analyzed [24]-band photometry from
MIPS/Spitzer and compiled the best photometry available at the ViJHKs passbands
and the four IRAC/Spitzer channels for constructing accurate spectral energy
distributions covering from 0.55 to 24 mum. Results: The nine targets were
classified into: one Herbig Ae/Be star with a scatterer edge-on disc, two
G-type stars, one X-ray flaring, early-M, young star with chromospheric Halpha
emission, one very low-mass, accreting, young spectroscopic binary, two young
objects at the brown dwarf boundary with the characteristics of classical T
Tauri stars, and two emission-line galaxies, one undergoing star formation, and
another one whose spectral energy distribution is dominated by an active
galactic nucleus. Besides, we discover three infrared sources associated to
overdensities in a cold cloud in the cluster centre. Conclusions:
Low-resolution spectroscopy and spectral energy distributions are a vital tool
for measuring the physical properties and the evolution of young stars and
candidates in the sigma Orionis cluster.Comment: Accepted for publication in A&
Desarrollo de la representación espacial
Planteamos el desarrollo de la representación espacial comenzando por una delimitación del concepto de espacio, en la que distinguimos el espacio corporal del espacio de apresamiento y del de acción. Tras abordar el estudio de la representación espacial, nos centramos en los dos enfoques teóricos desde los que se ha planteado este tema: la cognición fundamental y la cognición ambiental. Terminamos el artículo abordando la utilidad del mapa cognitivo como estrategia de enseñanza y aprendizaje, tras una breve referencia sobre cómo ha sido estudiado, su definición, características y funciones, y comentando los efectos que algunas variables ejercen sobre él (familiaridad con el entorno, vida en un medio urbano o rural, sexo, normas parentales y vinculación emocional con el entorno)
Stars and brown dwarfs in the sigma Orionis cluster: the Mayrit catalogue
The young sigma Orionis cluster is an indispensable basis for understanding
the formation and evolution of stars, brown dwarfs and planetary-mass objects.
Our knowledge of its stellar population is, however, incomplete. I present the
Mayrit catalogue, that comprises most of the stars and high-mass brown dwarfs
of the cluster. The basis of this work is an optical-near infrared correlation
between the 2MASS and DENIS catalogues in a circular area of radius 30 arcmin
centred on the OB-type binary sigma Ori AB. The analysis is supported on a
bibliographic search of confirmed cluster members with features of youth and on
additional X-ray, mid-infrared and astrometric data. I list 241 sigma Orionis
stars and brown dwarfs with known features of youth, 97 candidate cluster
members (40 are new) and 115 back- and foreground sources in the survey area.
The 338 cluster members and member candidates constitute the Mayrit catalogue.
This catalogue is a suitable input for studying the spatial ditribution,
multiplicity, properties and frequency of discs and the complete mass function
of sigma Orionis.Comment: accepted for publication in A&A, section 14. Online catalogs and dat
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