Agglomeration Economies in the Presence of an Informal Sector The Colombian Case

Este trabajo analiza la relación entre las economías de aglomeración y la productividad en el contexto de un país en desarrollo, teniendo en cuenta la presencia marcada de un sector informal. Utilizando datos de Colombia, investigamos el efecto de las economías de aglomeración en la productividad formal e informal. Examinamos si el sector informal obtiene beneficios de las economías de aglomeración, así como si existen diferencias entre los sectores formal e informal en términos de los rendimientos de la aglomeración. Encontramos que las economías de aglomeración, medidas por la densidad del empleo local, tienen un efecto significativamente positivo en la productividad en el sector informal, mientras que hay poco efecto en el sector formal. Estimamos una elasticidad de los salarios con respecto a la densidad de empleo de aproximadamente 2% para el sector informal, lo que implica que los trabajadores informales en áreas más densas ganarán aproximadamente un 11% más que aquellos en áreas menos densas.This paper analyzes the relationship between agglomeration economies and productivity in the context of a developing country while taking into account the marked presence of an informal sector. Using data from Colombia, we investigate the effect of agglomeration economies on formal and informal productivity. We examine whether the informal sector achieves benefits from agglomeration economies as well as whether there are differences between the formal and informal sectors in terms of agglomeration returns. We find that agglomeration economies, measured by the density of local employment, have a significantly positive effect on productivity in the informal sector, while there is little effect in the formal sector. We estimate an elasticity of wages with respect to employment density of approximately 2% for the informal sector, which implies that informal workers in denser areas will earn approximately 11% more than those in less dense areas

On the origin of two unidentified radio/X-ray sources discovered with XMM-Newton

We aim at clarifying the nature of the emission of two spatially related unidentified X-ray sources detected with XMM-Newton telescope at intermediate-low Galactic latitude. Observations reveal a point-like source aligned with elongated diffuse emission. The X-ray spectra are best-fitted by absorbed power laws with photon indices ~1.7 for the point-like and ~2.0 for the extended one. Both sources show nonthermal radio-continuum counterparts that might indicate a physical association. From the available data, we did not detect variability on the point-like source in several timescales. Two possible scenarios are analyzed: first, based on HI line absorption, assuming a Galactic origin, we infer a distance upper bound of <2 kpc, which poses a constraint on the height over the Galactic plane of <200 pc and on the linear size of the system of 10^32 erg/s and >7.5 x 10^32 erg/s, for the point-like and extended sources, respectively; second, an extra-Galactic nature is discussed, where the point-like source might be the core of a radio galaxy and the extended source its lobe. In this case, we compare derived fluxes, spectral indices, and spatial correlation with those typical from the radio galaxy population, showing the feasibility of this alternative astrophysical scenario. From the available observational evidence, we suggest that the most promising scenario to explain the nature of these sources is a system consisting of a one-sided radio galaxy, where the point-like source is an active galactic nucleus and the extended source corresponds to the emission from its lobe. Other possibilities include a PSR/PWN origin, where the radio/X-ray emission originates from the synchrotron cooling of relativistic particles in the PSR magnetic field or a casual alignment between two unrelated sources, such as an AGN core and a Galactic X-ray blob.Comment: 6 pages, 2 figures. Accepted for publication in Astronomy and Astrophysics (A&A

Monte Carlo simulation of damage and amorphization induced by swift-ion irradiation in LiNbO3

This paper presents a Monte Carlo (MC) simulation tool which is applied to describe the ion beam induced damage generated by electronic excitation in LiNbO3. Based on a previously published thermal spike based analytical model, the MC technique allows for a more flexible and accurate treatment of the problem. A main advantage of this approach with respect to the analytical one is the possibility of studying the role of statistical fluctuations, relevant at low fluences. The paper recalls the main features of the physical model, describes the MC algorithm, and compares simulation results to experimental data (irradiations of LiNbO3 using silicon ions at 5 and 7.5 MeV and oxygen ions at 5 MeV). © 2006 American Institute of Physics.Peer Reviewe

Optical determination of three-dimensional nanotrack profiles generated by single swift-heavy ion impacts in lithium niobate

Three-dimensional (3D) profiles of single nanotracks generated by a low impact density of Cl ions at 46 MeV have been determined by optical methods, using an effective-medium approach. The buried location of the maximum stopping power induces a surface optical waveguiding layer even at ultralow fluences (1011-1013 at./cm2) that allows to obtain the effective refractive index profiles (from dark-mode measurements). Combining the optical information with Rutherford backscattering spectroscopy/channeling experiments, the existence of a surrounding defective halo around the amorphous track core has been ascertained. The 3D profile of the halo has also been determined. © 2006 American Institute of Physics.Peer Reviewe

Optical determination of three-dimensional nanotrack profiles generated by single swift-heavy ion impacts in lithium niobate

Three-dimensional (3D) profiles of single nanotracks generated by a low impact density of Cl ions at 46 MeV have been determined by optical methods, using an effective-medium approach. The buried location of the maximum stopping power induces a surface optical waveguiding layer even at ultralow fluences (1011-1013 at./cm2) that allows to obtain the effective refractive index profiles (from dark-mode measurements). Combining the optical information with Rutherford backscattering spectroscopy/channeling experiments, the existence of a surrounding defective halo around the amorphous track core has been ascertained. The 3D profile of the halo has also been determined. © 2006 American Institute of Physics.Peer Reviewe

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