The Quantum-Mechanical Position Operator in Extended Systems

The position operator (defined within the Schroedinger representation in the standard way) becomes meaningless when periodic boundary conditions are adopted for the wavefunction, as usual in condensed matter physics. We show how to define the position expectation value by means of a simple many-body operator acting on the wavefunction of the extended system. The relationships of the present findings to the Berry-phase theory of polarization are discussed.Comment: Four pages in RevTe

El rezo del pescado, ritual de pubertad femenina entre los sikuani y cuiba

El rezo del pescado es un ritual generalizado en los grupos llaneros, el cual se desarrolla con ocasión del comienzo del destete de los bebés antes de su primer año y con ocasión de la primera menstruación femenina. En este trabajo se presenta una descripción del ritual de acuerdo a nuestras observaciones en las comunidades Cuiba de Mochuelo y Sikuani de Tsamani en Casanare. Se incluyen igualmente los textos de los rezos que aunque hasta el momento sólo han sido parcialmente traducidos, presentan un interés especial para la comprensión del simbolismo y el ritual

Electron Localization in the Insulating State

The insulating state of matter is characterized by the excitation spectrum, but also by qualitative features of the electronic ground state. The insulating ground wavefunction in fact: (i) sustains macroscopic polarization, and (ii) is localized. We give a sharp definition of the latter concept, and we show how the two basic features stem from essentially the same formalism. Our approach to localization is exemplified by means of a two--band Hubbard model in one dimension. In the noninteracting limit the wavefunction localization is measured by the spread of the Wannier orbitals.Comment: 5 pages including 3 figures, submitted to PR

Failure analysis of the fasten system of wheels used in mining pickup trucks

Regardless of their specific applications, all the vehicles used in mining operations are subjected to severe working conditions that reduce in a considerable amount, their active in-service life. In this work, the causes that promote failure of the fasten system and subsequent ejection of the wheels of passenger pickup trucks used in open-pit mines are analysed. By means of scanning electron microscopy, optical microscopy analyses and hardness tests, it was found that failure of the fasten system is characterised by a series of synergetic steps that include, the plastic deformation of the lug nuts caused by deficient tightening practices, fatigue and plastic deformation of the bolts. When combined, these phenomena leaded to the formation of cracks that propagated in the radial direction of these elements. The reasons that promote the development of this kind of failure are presented and discussed in this investigation. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Background studies and shielding effects for the TPC detector of the CAST experiment

Sunset solar axions traversing the intense magnetic field of the CERN Axion Solar Telescope (CAST) experiment may be detected in a Time Projection Chamber (TPC) detector, as X-rays signals. These signals could be masked, however, by the inhomogeneous background of materials in the experimental site. A detailed analysis, based on the detector characteristics, the background radiation at the CAST site, simulations and experimental results, has allowed us to design a shielding which reduces the background level by a factor of ~4 compared to the detector without shielding, depending on its position, in the energy range between 1 and 10 keV. Moreover, this shielding has improved the homogeneity of background measured by the TPC.Comment: 14 pages, 5 figures, accepted in New Journal of Physic

Plan Nacional de Transferencia de Tecnología Agropecuaria PLANTRA para 1990-1994: resumen consolidado nacional.

Se tratan aspectos generales relacionados con la transferencia de tecnología en Colombia y se menciona el objetivo general y los específicos del Plan Nacional de Transferencia de Tecnología Agropecuaria (PLANTRA) para el período 1990-94. Se describe la metodología utilizada para la obtención de la información en los aspectos de diagnóstico (necesidades tecnológicas y circunstancias cindicionantes de los productores, oferta tecnológica disponible y situación actual de la transferencia de tecnología), confrontación de las necesidades tecnológicas con la oferta tecnológica disponible y los productos resultantes del proceso (perfiles de proyectos). Se resumen los principales resultados obtenidos y una lista de documentos generados en la reformulación del PLANTR

Capital social como fator de sucesso nas cooperativas mexicanas Caso: Cooperativa "Las chiquihuitecas" produtor de grana cochinilla

The main objective of this work is to reflect the importance of social capital in the establishment and growth of cooperatives in Mexico, specifically the cooperative "Las Chiquihuitecas", producer of cochineal insect (Dactylopius coccus Costa). The research method used was totally qualitative applying the documentary analysis and the interview in depth as an instrument for the collection of the information. As a result, it was obtained that social capital has been the key element in the formation and development of the cooperative.O principal objetivo deste trabalho é refletir a importância do capital social no estabelecimento e crescimento das cooperativas no México, caso específico do "Os Chiquihuitecas" cochonilha cooperativa produtora de grana (Dactylopius coccus Costa). O método de pesquisa utilizado foi aplicando plenamente análise documental qualitativa e entrevista em profundidade como uma ferramenta para coleta de informações. Como foi obtido um resultado que a capital tem sido o elemento chave na formação e desenvolvimento da cooperativa

Nematodos asociados con el cultivo del plátano (Musa AAB o ABB) en el Valle del Cauca.

Se realizó un reconocimiento cualitativo y cuantitativo de los principales nemátodos fitoparásitos asociados con el cultivo de plátano. El estudio se llevó a cabo en fincas de agricultores minifundistas localizadas en los municipios vallecaucanos de El Bolo, Rozo y Cerrito. Se analizaron 87 muestras tanto de suelo como de raíces, discriminados así: 31 en El Bolo, 25 en Rozo y 31 en Cerrito, para un área total de 88.7 ha, aproximadamente. Se encontró que los géneros más importantes por su incidencia, población y distribución observada fueron: Meloidogyne, Helicotylenchus, Pratylenchus, Rotylenchulus y Radopholus. El género Meloidogyne se encontró ampliamente distribuído en las 3 zonas. Otros nemátodos que se encontraron asociados con este cultivo fueron: Trophurus sp, Paratylenchus sp. Hoplotylus sp. Criconemoides sp. Trichodorus sp. Ditylenchus sp. Tylenchorhynchus sp. Psilenchus sp. y Xiphinema sp. Las plantaciones donde se registraron altas poblaciones de nemátodos en general, presentaron síntomas de amarillamiento y clorosis del área foliar, racimos pequeños y raquíticos, tallos delgados en su parte inferior, necrosis y muerte de raíces, ausencia de raicillas y embalconamiento de la plantaPlátano-Musa sapientu

Usutu Virus in Migratory Song Thrushes, Spain

Our data imply that introduction of USUV (and potentially other flaviviruses such as West Nile virus lineage 2, which has not yet been detected in Spain) from Northern Europe, in addition to local endemicity and introduction from Africa, occurs, and that the zoonotic European USUV strain may be co-circulating with strains of African origin. At this time, it is not clear whether USUV strains of Spanish/African lineage differ in virulence for humans from strains from the European/African lineage. However, virus introduction by northern migrants, in combination with locally favorable conditions for vector populations, implies a risk for virus amplification and transmission and disease outbreaks in humans and horses outside the currently established mosquito-trapping period (May-October) of targeted flavivirus surveillance programs.Fil: Höfle, Ursula. Consejo Superior de Investigaciones Cientificas; España;Fil: Gamino, Virginia. Consejo Superior de Investigaciones Cientificas; España;Fil: Fernández de Mera, Isabel G.. Consejo Superior de Investigaciones Cientificas; España;Fil: Mangold, Atilio Jose. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Santa Fe. Estación Experimental Agropecuaria, Rafaela; Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina;Fil: Ortíz, José Antonio. Consejo Superior de Investigaciones Cientificas; España;Fil: de la Fuente, José. Oklahoma State University; Estados Unidos de América