1,579 research outputs found
Analysis and modeling of CLBG using the transfer matrix
Gratings in optical fibers have been increasingly used in a variety of applications such as sensors and Telecomm. Depending on perturbation separation, they are classified as: fiber Bragg gratings (FBG), and long period gratings (LPG), whose each spectral output offer advantages for certain applications. Nowadays there is a great interest in the study of arrays formed by the combination of long period gratings and Bragg gratings in cascade (CLBG), where the propagation modes of the core and the cladding propagate in the Bragg grating after they propagate in the LPG. In this work, analysis and modeling of Cascaded Long Bragg Gratings using the Transfer Matrix method was performed for the case of two gratings in series along one fiber. We analyzed the variation of the FWHM of the reflectance and transmittance spectra for different values of the difference of the refractive indexes of the core and the perturbation of the grating, using the typical core refractive index of an SMF-28 as reference value. For smaller index difference a narrow intensity peak was observed. After the number of perturbations was varied, when there is a greater number of perturbations in the grating, there is greater intensity in reflectance. However, as our results show, this dependence is not a linear function. The results were obtained under the maximum-reflectivity condition (tuned) for each single grating. The development of the mathematical model, the results of the simulation and the analysis of results are part of the development of the present work11103SPIE Optical engineering + applications - Optical modeling and system alignmentAuthors are grateful to UAM-Azcapotzalco, CONACYT, University of Twente and UNICAMP for their suppor
Analysis and modeling of high temporal resolution spectroscopic observations of flares on AD Leo
We report the results of a high temporal resolution spectroscopic monitoring
of the flare star AD Leo. During 4 nights, more than 600 spectra were taken in
the optical range using the Isaac Newton Telescope (INT) and the Intermediate
Dispersion Spectrograph (IDS). We have observed a large number of short and
weak flares occurring very frequently (flare activity > 0.71 hours-1). This is
in favour of the very important role that flares can play in stellar coronal
heating. The detected flares are non white-light flares and, though most of
solar flares belong to this kind, very few such events had been previously
observed on stars. The behaviour of different chromospheric lines (Balmer
series from H_alpha to H_11, Ca II H & K, Na I D_1 & D_2, He I 4026 AA and He I
D_3) has been studied in detail for a total of 14 flares. We have also
estimated the physical parameters of the flaring plasma by using a procedure
which assumes a simplified slab model of flares. All the obtained physical
parameters are consistent with previously derived values for stellar flares,
and the areas - less than 2.3% of the stellar surface - are comparable with the
size inferred for other solar and stellar flares. Finally, we have studied the
relationships between the physical parameters and the area, duration, maximum
flux and energy released during the detected flares.Comment: Latex file with 17 pages, 11 figures. Available at
http://www.ucm.es/info/Astrof/invest/actividad/actividad_pub.html Accepted
for publication in: Astronomy & Astrophysics (A&A
Morphological evolution of pulsed laser deposited ZrO2 thin films
Morphological evolution of ZrO2 thin films deposited during pulsed laser deposition of Zr in O2
atmosphere has been experimentally studied at two different film deposition temperatures, 300 and
873 K. The roughness exponent, , the growth exponent, , the coarsening exponent, 1/z, and the
exponent defining the evolution of the characteristic wavelength of the surface, p, for depositions at
300 K amounted to = 1.00.1, = 0.40.1, 1/z= 0.340.03, and p= 0.490.03, whereas for
depositions carried out at 873 K amounted to = 0.30.3, = 0.40.2, and 1/z= 0.00.2.
Experimental error becomes important due to the flat morphology of the films inherent to the
deposition technique. The change in the surface topography with the film temperature has been
studied with the help of a simple Monte Carlo model which indicates the existence of two different
growth regimes: a shadowing dominated growth, occurring at low temperatures, characterized by
calculated values = 1.000.04, = 0.500.04, p= 0.460.01, and 1/z= 0.350.02 and a
diffusion dominated growth that takes place at high temperatures as well as at low deposition rates,
characterized by calculated values = 0.150.08, = 0.330.04, and 1/z= 0.330.07. The good
agreement obtained between the experimental and simulated parameters is discussed within the
frame of the general characteristics of the deposition method.Universidad Nacional Autónoma de México-PAPIIT-IN107808Consejo Nacional de Ciencia y Tecnología de México-CONACyT-50203-FMinisterio de Ciencia, Innovación y Universidades de España-MAT 2007-65764, PIE 200960I132 y CONSOLIDER INGENIO 2010-CSD2008-00023Junta de Andalucía-TEP2275 y P07-FQM-0329
J-PLUS: analysis of the intracluster light in the Coma cluster
The intracluster light (ICL) is a luminous component of galaxy clusters
composed of stars that are gravitationally bound to the cluster potential but
do not belong to the individual galaxies. Previous studies of the ICL have
shown that its formation and evolution are intimately linked to the
evolutionary stage of the cluster. Thus, the analysis of the ICL in the Coma
cluster will give insights into the main processes driving the dynamics in this
highly complex system. Using a recently developed technique, we measure the ICL
fraction in Coma at several wavelengths, using the J-PLUS unique filter system.
The combination of narrow- and broadband filters provides valuable information
on the dynamical state of the cluster, the ICL stellar types, and the
morphology of the diffuse light. We use the Chebyshev-Fourier Intracluster
Light Estimator (CICLE) to disentangle the ICL from the light of the galaxies,
and to robustly measure the ICL fraction in seven J-PLUS filters. We obtain the
ICL fraction distribution of the Coma cluster at different optical wavelengths,
which varies from , showing the highest values in the narrowband
filters J0395, J0410, and J0430. This ICL fraction excess is distinctive
pattern recently observed in dynamically active clusters (mergers), indicating
a higher amount of bluer stars in the ICL compared to the cluster galaxies.
Both the high ICL fractions and the excess in the bluer filters are indicative
of a merging state. The presence of younger/lower-metallicity stars the ICL
suggests that the main mechanism of ICL formation for the Coma cluster is the
stripping of the stars in the outskirts of infalling galaxies and, possibly,
the disruption of dwarf galaxies during past/ongoing mergers.Comment: 10 pages, 3 figures, 1 table. Accepted for publication in A&
Exploring the Potential of Integral Field Spectroscopy Observing Extrasolar Planet Transits: Ground Based Observations of the Atmospheric Na in HD209458b
We explore the use of Integral Field Spectroscopy (IFS) to observe extrasolar
planet transits. Although this technique should find its full potential in
space observations (e.g. JWST, TPF), we have tested its basics with ground
based time series observations of HD209458b obtained with WHT+INTEGRAL during a
transit. For this analysis we used 5550 spectra, obtained in 150 exposures
during a period of >7 hours. We found that IFS offers 3 fundamental advantages
with respect to previously used methods. (i) It improves the effective S/N in
photon limited observations by distributing the light coming from the star into
the 2 dimensions of the detector. (ii) This type of IFS data allows to
'auto-calibrate' instrumental and background effects. (iii) Since the star
image characteristics as well as its photometric properties are extracted from
the same data-cube, it is possible to decorrelate photometric instabilities
induced by PSF variations. These data have also allowed us to explore the
accuracy limits of ground based 'relative' spectrophotometry. This was done
using a photometric index that probes the NaD lines, for which we obtained a
nominal 1-sigma error of ~1.0x10^-4. This result, based on observations of only
1 transit, indicates that this type of ground observation can constrain the
characterization of the transmission spectrum of extrasolar planets. The
present observations are compatible with no extra NaD depression during the
transit. Though this result seems to be inconsistent with the recently reported
HST-STIS findings we point out its limited statistical meaning: the results
disagree within 1-sigma, but agree within 2-sigma. We also give some
recommenda-tions to instrument developers in order to enhance the efficiency of
the method.Comment: 15 pages, 2 tables, 10 figures. To appear in PASP (January 2006
The bird species diversity in the wintering season is negatively associated with precipitation, tree species diversity and stand density in the Sierra Madre Occidental, Durango, Mexico
Bird migration constitutes a redistribution of bird diversity that radically changes the composition of the bird community worldwide. It comprises about 19% of the world’s bird species. Several studies have indicated that changes in avian community structure and differences in bird richness in different seasons are mainly driven by seasonality and by winter harshness, and that the associated costs increase with the distance involved. Western Mexico is an important wintering area for most passerines that breed in western North America, and that travel long on the long-distance Central and Pacific migration routes. In this study, we examined bird species richness and diversity during the breeding and wintering seasons in the Central Sierra Madre Occidental (SMO), North Durango (Mexico) in relation to i) tree species diversity, ii) tree dimension, iii) forest stand density and site quality, iv) density and dimension of snag trees, and v) various climate variables. The overall aim of the study was to determine how the observed associations between bird species diversity and variables i-v are affected by the season considered (breeding or wintering). The diversity of bird species in the breeding season was not affected by any of the climate and forest stand variables considered. In contrast, bird species diversity in the wintering season was significantly and weakly to moderately associated with climate variables, tree species diversity and stand density, although not with density or dimension of snag trees. Bird species diversity was higher at lower elevations and in drier and warmer locations of the SMO. The association detected is therefore mainly a local migratory phenomenon.
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Supporting Information
Supporting Information
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MADERA: A standardized Pan-Amazonian dataset for tropical timber species
We compiled and presented a dataset for all timber species reported in the Amazon region from all nine South American Amazonian countries. This was based on official information from every country, as well as from two substantial scientific references. We verified the standard taxonomic names from each individual source, using the Taxonomic Name Resolution Service (TNRS) and considered all Amazonian tree species with diameter at breast height (DBH) ≥10 cm. We also obtained estimates of the current population size for most species from a published approach based on data from 1900 tree inventory plots (1-ha each) distributed across the Amazon region and part from the Amazon Tree Diversity Network (ATDN). We then identified the hyperdominant timber species. In addition, we overlapped our timber species list with data for species that are used for commercial purposes, according to the International Tropical Timber Organization (ITTO), the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and the International Union for Conservation of Nature (IUCN) taxa assessment and Red List categories. Finally, we also included IUCN Red List categories based on combined deforestation, and climate change scenarios for these species. Our final Amazonian timber species dataset contains 1112 unique species records, which belong to 337 genera and 72 families from the lowland Amazonian rainforest, with associated information related to population, conservation, and trade status of each species. The authors of this research expect that the information provided will be useful to strengthen the public forestry policies of the Amazon countries, inform ecological studies, as well for forest management purposes. The data are released under the Creative Commons Attribution 4.0 International license
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