Full-vector analysis of a realistic photonic crystal fiber

We analyze the guiding problem in a realistic photonic crystal fiber using a novel full-vector modal technique, a biorthogonal modal method based on the nonselfadjoint character of the electromagnetic propagation in a fiber. Dispersion curves of guided modes for different fiber structural parameters are calculated along with the 2D transverse intensity distribution of the fundamental mode. Our results match those achieved in recent experiments, where the feasibility of this type of fiber was shown.Comment: 3 figures, submitted to Optics Letter

Synthesis and properties of Co-doped titanate nanotubes and their optical sensitization with methylene blue

Here we report on a novel chemical route to synthesize homogenous cobalt doped titanate nanotubes (CoTNT), using an amorphous Co-doped precursor. The influence of the synthesis temperature, autoclave dwell time and metal doping on the structural and microstructural as well as on the optical properties of the synthesized titanate nanotubes is studied and discussed. The optical band gaps of the CoTNT samples are red shifted in comparison with the values determined for the undoped samples, such red shifts bringing the absorption edge of the CoTNT samples into the visible region. CoTNT materials also demonstrate particular high adsorption ability for methylene blue, the amount of the adsorbed dye being higher than the one predictable for a monolayer formation. This suggests the possibility of intercalation of the dye molecule between the TiO6 layers of the TNT structure. It is also shown that the methylene blue sensitized Co-doped nanostructures are highly stable under UV radiation and present a strong and broad absorption in the visible region.Comment: 31 pages, 3 tables, 7 figure

Emigrating to depopulated regions in Mediterranean Europe: demographic impact and choice of destination in a case study in north-east Spain (Aragon)

International migration to depopulated areas is a growing field of research; even more so in Spain, one of the European countries most affected by depopulation. This paper analyses, first, the demographic impact of immigration from other countries in Aragon, which has undergone an intense and long process of depopulation throughout most of its territory. Second, we examine the factors that explain the immigrants'' choice of destination. The analysis focuses on the period 2000-2016. The basic territorial units of the analysis are the municipality (NUTS 5) and the county (NUTS 4). © 2022 Adrián Palacios et al., published by Sciendo

Una actividad ctsa que favorece que el alumnado hable de ciencia : ¿hay fraude en las ciencias?

En esta comunicación se presenta una secuencia de actividades CTSA sobre el fraude en las ciencias, experimentadas con alumnos de 4º curso de secundaria obligatoria y 1º de bachillerato. Se investigan los resultados de la misma con una metodología cualitativa mediante grabación en audio, para analizar si se ha mejorado la comprensión de la ciencia, de su funcionamiento y sus valores, así como el interés por la misma

Modified Newton's law, braneworlds, and the gravitational quantum well

Most of the theories involving extra dimensions assume that only the gravitational interaction can propagate in them. In such approaches, called brane world models, the effective, 4-dimensional, Newton's law is modified at short as well as at large distances. Usually, the deformation of Newton's law at large distances is parametrized by a Yukawa potential, which arises mainly from theories with compactified extra dimensions. In many other models however, the extra dimensions are infinite. These approaches lead to a large distance power-law deformation of the gravitational newtonian potential $V_N(r)$, namely $V(r)=(1+k_b/r^b)V_N(r)$, which is less studied in the literature. We investigate here the dynamics of a particle in a gravitational quantum well with such a power-law deformation. The effects of the deformation on the energy spectrum are discussed. We also compare our modified spectrum to the results obtained with the GRANIT experiment, where the effects of the Earth's gravitational field on quantum states of ultra cold neutrons moving above a mirror are studied. This comparison leads to upper bounds on $b$ and $k_b$.Comment: 11 pages, 1 figur

Pentaquarks in the Jaffe-Wilczek approximation

The masses of $uudd\bar s$, $uudd\bar d$ and $uuss\bar d$ pentaquarks are evaluated in a framework of both the Effective Hamiltonian approach to QCD and spinless Salpeter using the Jaffe--Wilczek diquark approximation and the string interaction for the diquark--diquark--antiquark system. The pentaquark masses are found to be in the region above 2 GeV. That indicates that the Goldstone boson exchange effects may play an important role in the light pentaquarks. The same calculations yield the mass of $[ud]^2\bar c$ pentaquark $\sim$ 3250 MeV and $[ud]^2\bar b$ pentaquark $\sim$ 6509 MeV.Comment: 14 pages, 2 tables, LaTeX2e. References correcte

Reducing depopulation in rural Spain: The impact of immigration

The attraction of foreign-born immigrants to rural areas in developed countries has aroused growing interest in recent years. The central issue in this study is the demographic impact of immigration in rural Spain, focusing on depopulated areas. The economic and demographic consequences of depopulation have become major concerns, and the arrival of international migrants has come to be seen as a possible solution. The aim of this study is to add to a literature in which qualitative research and local or regional perspectives predominate. The present research draws on quantitative findings for a significant part of Spain. The evidence in this study is principally based on population figures for the last years of the 20th century, a period of low immigration to Spain, and the early years of the 21st century, when the inflow of foreign migrants gathered intensity. We also explore the early consequences of the present economic crisis, which began in 2008. The analysis is based on estimates of native and foreign-born population growth for a range of territorial aggregations. Counterfactual techniques are also used. The results show that the arrival of immigrants has so far contributed substantially to reducing and even halting or reversing depopulation. A further series of analyses concentrates on the potential of rural areas to retain immigrants in the long run. The study also recommends a comprehensive policy approach in this regard

Human immunodeficiency virus type 1 recombinant B/G subtypes circulating in Coimbra, Portugal.

An increasing prevalence of HIV-1 non-B variants is being noticed in several European regions, particularly in countries such as Portugal, which have closer contacts with African endemic areas, where multiple HIV subtypes cocirculate. HIV-1 subtyping by phylogenetic analyses of reverse transcriptase, protease and env (C2-V3) genomic regions was carried out in plasma collected from 18 HIV-1-infected subjects living in Coimbra, Portugal, and suspected to be infected with non-B variants. Three (16.7%) subjects carried recombinant B/G viruses (BV3/BRT/Gpro; GV3/URT/Bpro; AV3/GRT/Bpro), whereas all the remaining individuals were infected with HIV-1 subtype B. This is the first report of recombinant B/G subtypes in Portugal