Electronic properties of SnO2-based ceramics with double function of varistor and humidity sensor

This is the post-print version of the article. The official published version can be obtained from the link below - Copyright @ 2010 AD-Tech.Tin dioxide based varistor ceramics SnO2-Co3O4-Nb2O5-Cr2O3-xCuO (x=0; 0.05; 0.1 and 0.5) were made and their electrical properties were studied. The highest nonlinearity coefficient and electric field (at current density 10-3 A cm-2) were obtained for 0.1 mol.% CuO addition. It was observed that low-field electrical conductivity is increased with relative humidity, therefore, materials obtained exhibit double function of varistor and humidity sensor. The highest humidity sensitivity coefficient is found for SnO2-Co3O4-Nb2O5-Cr2O3 ceramics (without CuO). Observed varistor and humidity-sensitive properties are explained in the frames of grain-boundary double Schottky barrier concept as a decrease of the barrier height with electric field or relative humidity. Using suggested simple theory and data obtained on isothermal capacitance relaxation, the energy of the grain-boundary monoenergetic trapping states were estimated. These values are less than found for activation energy of electrical conduction (as a measure of the barrier height). These observations confirm the barrier concept.This work is funded by the Royal Society, United Kingdom (2007R1/R26999)

The Simple Non-degenerate Relativistic Gas: Statistical Properties and Brownian Motion

This paper shows a novel calculation of the mean square displacement of a classical Brownian particle in a relativistic thermal bath. The result is compared with the expressions obtained by other authors. Also, the thermodynamic properties of a non-degenerate simple relativistic gas are reviewed in terms of a treatment performed in velocity space.Comment: 6 pages, 2 figure

On the inertia of heat

Does heat have inertia? This question is at the core of a long-standing controversy on Eckart's dissipative relativistic hydrodynamics. Here I show that the troublesome inertial term in Eckart's heat flux arises only if one insists on defining thermal diffusivity as a spacetime constant. I argue that this is the most natural definition, and that all confusion disappears if one considers instead the space-dependent comoving diffusivity, in line with the fact that, in the presence of gravity, space is an inhomogeneous medium.Comment: 3 page

Tumor de colisión de cérvix uterino: presentación de 17 casos

El tumor de colisión es una variante poco frecuente de tumores del cérvix uterino, originados de las células de reserva de la unión escamocelular y que debe ser diferenciado de los carcinomas adenoescamosos. El objetivo del presente artículo es determinar las características morfológicas de 17 casos de tumor de colisión de cérvix uterino. La edad promedio de presentación fue 48,7 años (rango: 34-87 años). Los 4 casos con metástasis ganglionares correspondieron al componente de adenocarcinoma

Implementation of AMI Systems in CFE-Distribution, Mexico

The Smart Grid concept has been conceived as the integration of the electrical grid (generation, transmission and distribution) and the communications network of an electric utility. Although, traditional communications interfaces, protocols and standards has been used in the electrical grid in an isolated manner, modern communications networks are considered as the fundamental enabling technologies within a Smart Grid environment. Emerging communications technologies, protocol architectures and standards can help to build a common communications network infrastructure for data transport between customer premises, power substations, power distribution systems, utility control centers and utility data centers. The Smart Grid will support traditional applications such as supervisory control and data acquisition (SCADA), distribution automation (DA), energy management systems (EMS), demand site management (DSM) and automated meter reading (AMR), etc., as well as new applications like advanced metering infrastructure (AMI), substation automation (SA), microgrids, distributed generation (DG), grid monitoring and control, data storage and analysis, among others. To make this possible, the Smart Grid requires a two-way wide area communications network between different dispersed areas, from generation to consumer premises. An AMI system uses communication technologies for smart meter reading several times a day to get data consumption of electricity, as well as sending outage alarm information and meter tampering almost in real time, from the meter to the control center. Currently, there are various communication technologies to implement AMI systems. This paper presents an overview of the most relevant communications technologies that can be used to implement AMI communications infrastructure such as neighborhood area networks (NAN), field area networks (FAN) and wide area networks (WAN) using different transmission media such as fiber optics, spread spectrum radio frequency, microwave, WiMax, Wi-Fi, ZigBee, cellular, and power line carrier. In addition, a review of the current state of various AMI projects around the world, including the progress in the implementation of AMI systems in Mexico, besides the evaluation performance of CFE´s AMI networks

Spread of the invasive alga Caulerpa racemosa var. cylindracea (Caulerpales, Chlorophyta) along the Mediterranean Coast of the Murcia region (SE Spain)

The aim of this paper was to document the appearance and spread of the green alga Caulerpa racemosa along the coast of Murcia in south–eastern Spain. It was found for the first time in the area in 2005 and over the next two years the number of new sightings increased almost exponentially. In the period 2005–2007 the total surface area colonised by the alga in the region was estimated to be at least 265 ha. Benthic assemblages colonised by the alga were rocky bottoms with photophilic algae, dead P. oceanica rhizomes, infralittoral and circalittoral soft bottoms and maerl beds. No penetration of the alga was observed in P. oceanica meadows, except in one locality. Biometric analysis indicated high vegetative development in the established colonies in comparison to those described in other Mediterranean areas. Rapid spreading dynamics observed in the Murcia region is a potential threat for native benthic communities. Key words: Biological invasions, Caulerpa racemosa var. cylindracea, Colonised surface area, Distribution, Mediterranean Sea, Spain.En el presente trabajo se documenta la aparición y dispersión del alga verde Caulerpa racemosa a lo largo de la costa de Murcia, región situada en el sureste español. El alga fue detectada por primera vez en el año 2005 y durante los dos años consecutivos se observó un crecimiento casi exponencial en el número de áreas colonizadas. La superficie total colonizada por el alga en Murcia durante el periodo 2005–2007 ha sido estimada en 265 ha., siendo las comunidades bentónicas afectadas algas fotófilas sobre sustrato rocoso, "mata muerta" de P. oceanica, fondos blandos infralitorales y circalitorales y fondos con comunidades de maërl. La presencia del alga dentro de praderas de P. oceanica solamente fue detectada en una localidad. Los estudios biométricos realizados muestran un elevado desarrollo vegetativo de las poblaciones de C. racemosa en Murcia en comparación con colonias de otras áreas del Mediterráneo, siendo esta rápida dinámica de expansión una amenaza potencial para las comunidades bentonicas nativas. Palabras clave: Invasiones biológicas, Caulerpa racemosa var. cylindracea, Superficie colonizada, Mar Mediterraneo, España.The aim of this paper was to document the appearance and spread of the green alga Caulerpa racemosa along the coast of Murcia in south–eastern Spain. It was found for the first time in the area in 2005 and over the next two years the number of new sightings increased almost exponentially. In the period 2005–2007 the total surface area colonised by the alga in the region was estimated to be at least 265 ha. Benthic assemblages colonised by the alga were rocky bottoms with photophilic algae, dead P. oceanica rhizomes, infralittoral and circalittoral soft bottoms and maerl beds. No penetration of the alga was observed in P. oceanica meadows, except in one locality. Biometric analysis indicated high vegetative development in the established colonies in comparison to those described in other Mediterranean areas. Rapid spreading dynamics observed in the Murcia region is a potential threat for native benthic communities. Key words: Biological invasions, Caulerpa racemosa var. cylindracea, Colonised surface area, Distribution, Mediterranean Sea, Spain

Síntesis y caracterización fisicoquímica de circonia promovida con ácido tungstofosfórico y ácido bórico utilizada como catalizador en la isomerización de n-pentano

En este trabajo se muestra la preparación, caracterización y evaluación de la actividad catalítica de materiales del tipo ZrO2 promovida con ácido tungstofosfórico y ácido bórico. El Zr(OH)4 se sintetizó por el método sol-gel utilizando como precursores al n-butóxido de circonio y 1-butanol, manteniendo un pH = 8 durante la síntesis. El Zr(OH)4 se impregnó con un 15% en pesodel agente ácido, calcinado a 600 ºC e impregnado  posteriormente con 0,5% en peso de platino. Se observó que los iones [PW12O40]3– y [BO3]3– permanecen fuertementeenlazados a la superficie de la ZrO2 inhibiendo el crecimiento de la partícula, retardando la sinterización del material y la aparición de la fase monoclínica.Además, con la incorporación de estos dopantes se incrementó la acidez total del material, específicamente la población de sitios ácidos fuertes, siendo este tipo de sitios los predominantes en las muestras acidificadas.La acidez desarrollada por los materiales fue la adecuada para lograr catalizar la reacción de isomerización de n-pentano con conversiones superiores al 20% y selectividades hacia el isopentano que fluctuaron alrededor del 90%

The thermal and kinematic Sunyaev-Zel'dovich effects revisited

This paper shows that a simple convolution integral expression based on the mean value of the isotropic frequency distribution corresponding to photon scattering off electrons leads to useful analytical expressions describing the thermal Sunyaev-Zel'dovich effect. The approach, to first order in the Compton parameter is able to reproduce the Kompaneets equation describing the effect. Second order effects in the parameter $z=\frac{kT_{e}}{mc^{2}}$ induce a slight increase in the crossover frequency.Comment: 7 pages, 2 figure

Un análisis transversal del ecoturismo: Arte místico y riesgo alternativo

En el marco de promoción del emprendimiento local para el desarrollo regional sustentable, los estudios del turismo se han centrado en el análisis de la experiencia vital como antecedente de la satisfacción turística y el retorno vacacional, pero sin considerarlos como parte de un ciclo de recreación y esparcimiento que podría ser explicado desde las representaciones sociales. En tal sentido, se llevó a cabo un trabajo exploratorio, transversal y cualitativo con una selección de informantes, considerando sus recorridos a un museo natural surrealista del centro de México. Las interpretaciones en torno a las respuestas a preguntas derivadas de las categorías de núcleo de esparcimiento, periferia recreativa y experiencia vacacional muestran similitudes en cuanto a la búsqueda de un significado del recorrido y el escenario, pero también diferencias en cuanto a la integración con el escenario, orientando futuras líneas de investigación hacia las diferencias entre generacione