A virtual element method for the vibration problem of Kirchhoff plates

The aim of this paper is to develop a virtual element method (VEM) for the vibration problem of thin plates on polygonal meshes. We consider a variational formulation relying only on the transverse displacement of the plate and propose an $H^2(\Omega)$ conforming discretization by means of the VEM which is simple in terms of degrees of freedom and coding aspects. Under standard assumptions on the computational domain, we establish that the resulting schemeprovides a correct approximation of the spectrum and prove optimal order error estimates for the eigenfunctions and a double order for the eigenvalues. The analysis restricts to simply connected polygonal clamped plates, not necessarily convex. Finally, we report several numerical experiments illustrating the behaviour of the proposed scheme and confirming our theoretical results on different families of meshes. Additional examples of cases not covered by our theory are also presented

Capturing coevolutionary signals in repeat proteins

The analysis of correlations of amino acid occurrences in globular proteins has led to the development of statistical tools that can identify native contacts -- portions of the chains that come to close distance in folded structural ensembles. Here we introduce a statistical coupling analysis for repeat proteins -- natural systems for which the identification of domains remains challenging. We show that the inherent translational symmetry of repeat protein sequences introduces a strong bias in the pair correlations at precisely the length scale of the repeat-unit. Equalizing for this bias reveals true co-evolutionary signals from which local native-contacts can be identified. Importantly, parameter values obtained for all other interactions are not significantly affected by the equalization. We quantify the robustness of the procedure and assign confidence levels to the interactions, identifying the minimum number of sequences needed to extract evolutionary information in several repeat protein families. The overall procedure can be used to reconstruct the interactions at long distances, identifying the characteristics of the strongest couplings in each family, and can be applied to any system that appears translationally symmetric

Fatigue crack initiation and growth on a steel in the very high cycle regime with sea water corrosion

The authors acknowledge Arts et Métiers ParisTech and Foundation Arts et Métiers for the financial support of P.C. Paris’ stay at LAMEFIP. They acknowledge Vicinay Cadenas S.A. for its financial support, and both the PCP France-Mexique and the CONACYT for their financial support too.This paper is devoted to the effect of corrosion on the gigacycle fatigue strength of a martensitic–bainitic hot rolled steel used for manufacturing offshore mooring chains for petroleum platforms. Smooth specimens were tested under fully reversed tension between 1E6 and 1E10 cycles in three testing conditions and environments: (i) in air, (ii) in air after precorrosion and (iii) in air under real time artificial sea water flow. The fatigue strength at greater than 108 cycles is reduced by a factor more than five compared with non-corroded specimens. Fatigue cracks initiate at corrosion pits due to pre-corrosion, if any, or pits resulting from corrosion in real time during the cyclic loading. It is shown that under sea water flow, the fatigue life in the gigacycle regime is mainly governed by the corrosion process. Furthermore, the calculation of the mode I stress intensity factor at hemispherical surface defects (pits) combined with the Paris–Hertzberg–Mc Clintock crack growth rate model shows that fatigue crack initiation regime represents most of the fatigue life.PCP France Mexique, Conacyt, Arts et Métiers ParisTech (professeur invité Paul C Paris

Profiles based on attitudes toward public support programs of rural micro entrepreneurs of central Chile

La presente investigación tiene como propósito contribuir a la comprensión de las actitudes de micro y pequeños productores agrícolas de la zona central de Chile ante los programas públicos de apoyo enfocados en el fomento sectorial. Para lo anterior, se llevó a cabo una encuesta a 126 empresarios de la Comuna de Cauquenes, Región del Maule, los cuales participan de un programa de apoyo coordinado por la Municipalidad junto con el Instituto de Desarrollo Agropecuario (Indap). Dicha encuesta se centró en los siguientes temas: identificación de los encuestados, características socio demográficas, métodos productivos y de gestión empresarial, acceso a tecnologías y actitudes sobre los programas de apoyo público sectorial. A los datos obtenidos se les aplicó un análisis descriptivo y de conglomerados no jerárquicos. Mediante lo anterior se identificó la existencia de dos grupos de empresarios, los cuales se denominaron: "escépticos" (30,15%) y "receptivos" (69,85%), con relevantes diferencias tanto en sus actitudes hacia los programas de apoyo público, como en su nivel educativo, productividad predial y acceso a tecnologías. Lo señalado lleva a concluir que, incluso entre productores en condiciones de vulnerabilidad, existen importantes contrastes que deben ser recogidos en el diseño, ejecución y evaluación de los programas.This research aims to contribute to the understanding of the attitudes related to public support programs of micro and small farmers in the central zone of Chile. For this, it was conducted a survey of 126 entrepreneurs in the Commune of Cauquenes, Maule Region, which participate in a support program coordinated by the Municipality together with the Institute of Agricultural Development (Indap). The survey focused on the following issues: respondents’ identification, sociodemographic characteristics, production and business management methods, access to technologies and attitudes about public support programs. It was applied a non-hierarchical cluster analysis to data obtained. The existence of two groups of entrepreneurs was identified: "skeptics" (30.15%) and "receptive" (69.85%), with important differences in their attitudes toward support programs and also in their education level, farm productivity and access to technologies. This leads to the conclusion that, even among producers in vulnerable situations, there are important contrasts that should be incorporated in the design, implementation and evaluation of programs.Fil: Boza, Sofía. Universidad de Chile. Facultad de Ciencias Agronómicas. Departamento de Economía Agraria.Fil: Marcos, Gonzalo. Universidad de Chile. Facultad de Ciencias Agronómicas. Departamento de Economía Agraria.Fil: Cortés, Maruja. Universidad de Chile. Facultad de Ciencias Agronómicas. Departamento de Economía Agraria.Fil: Mora, Marcos. Universidad de Chile. Facultad de Ciencias Agronómicas. Departamento de Economía Agraria

Characterization of Rhizobium grahamii extrachromosomal replicons and their transfer among rhizobia

Background Rhizobium grahamii belongs to a new phylogenetic group of rhizobia together with Rhizobium mesoamericanum and other species. R. grahamii has a broad-host-range that includes Leucaena leucocephala and Phaseolus vulgaris, although it is a poor competitor for P. vulgaris nodulation in the presence of Rhizobium etli or Rhizobium phaseoli strains. This work analyzed the genome sequence and transfer properties of R. grahamii plasmids. Results Genome sequence was obtained from R. grahamii CCGE502 type strain isolated from Dalea leporina in Mexico. The CCGE502 genome comprises one chromosome and two extrachromosomal replicons (ERs), pRgrCCGE502a and pRgrCCGE502b. Additionally, a plasmid integrated in the CCGE502 chromosome was found. The genomic comparison of ERs from this group showed that gene content is more variable than average nucleotide identity (ANI). Well conserved nod and nif genes were found in R. grahamii and R. mesoamericanum with some differences. R. phaseoli Ch24-10 genes expressed in bacterial cells in roots were found to be conserved in pRgrCCGE502b. Regarding conjugative transfer we were unable to transfer the R. grahamii CCGE502 symbiotic plasmid and its megaplasmid to other rhizobial hosts but we could transfer the symbiotic plasmid to Agrobacterium tumefaciens with transfer dependent on homoserine lactones. Conclusion Variable degrees of nucleotide identity and gene content conservation were found among the different R. grahamii CCGE502 replicons in comparison to R. mesoamericanum genomes. The extrachromosomal replicons from R. grahamii were more similar to those found in phylogenetically related Rhizobium species. However, limited similarities of R. grahamii CCGE502 symbiotic plasmid and megaplasmid were observed in other more distant Rhizobium species. The set of conserved genes in R. grahamii comprises some of those that are highly expressed in R. phaseoli on plant roots, suggesting that they play an important role in root colonization.Fil: Althabegoiti, Maria Julia. Universidad Nacional Autónoma de México; México. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ormeño Orrillo, Ernesto. Universidad Nacional Autónoma de México; MéxicoFil: Lozano, Luis. Universidad Nacional Autónoma de México; MéxicoFil: Torres Tejerizo, Gonzalo Arturo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional Autónoma de México; MéxicoFil: Rogel, Marco Antonio. Universidad Nacional Autónoma de México; MéxicoFil: Mora, Jaime. Universidad Nacional Autónoma de México; MéxicoFil: Martinez Romero, Esperanza. Universidad Nacional Autónoma de México; Méxic

Evaluación de los impactos al recurso agua derivados de la operación de una central termoeléctrica “Termogas Machala”

Una de las principales formas de energía es la electricidad, la cual se consume en el mundo y constituye parte integral de los seres humanos. Sin embargo, lo que enmarca a esta actividad provoca contaminación del aire y el agua. La empresa Termoeléctrica Termogas Machala ha recibido quejas de ser una posible fuente de contaminación del agua de la playa de Bajo Alto, parroquia Tendales, Provincia de El Oro. Esta investigación se desarrolló desde el 2012 al 2015. Con la finalidad de evaluar los impactos al recurso agua derivados de la operación de la Central Termoeléctrica se determinaron i) los parámetros físico-químicos del agua de descarga: Temperatura, pH, Demanda Química de Oxígeno (DQO), Sólidos Suspendidos Totales (SST), ii) la concentración de contaminantes químicos: Hidrocarburos Totales de Petróleo (HTP), Aceites y Grasas (AyG), Metales Pesados, Sulfuros y Fenoles, y iii) contaminantes biológicos: Coliformes Totales (CT) y Fecales (CF), para compararlos con los Límites Máximos Permisibles de descarga desde centrales termoeléctricas (2007) y las normas generales para descarga de aguas residuales domésticas e industriales TULSMA (2015) y evidenciar si existe contaminación por parte de la Termoeléctrica al cuerpo receptor de agua marina. En las aguas de descarga, los parámetros físico-químicos se encontraron dentro de los límites permisibles, al igual que los contaminantes químicos. No se detectaron metales pesados, Cu, Cr+6, Pb ni Zn. Se observó contaminación de tipo biológica por Coliformes Fecales en el año 2015 donde se registraron valores máximos en el Límite Máximo Permisible de 2000 NMP/100 mL. Finalmente se realizó un análisis de componentes principales y una correlación de Pearson donde se observó correlación entre HTP y AyG (r=0,673; p=0,000); CT y CF (r=0,885; p=0,000) y SST vs DQO (r=0,791; p=0,000). Se concluye que la contaminación química como biológica del sector procede de fuentes externas a este proceso industrial de generación eléctrica.One of the main forms of energy is electricity, which is consumed in the world and is an integral part of human beings. However, what part to this activity causes pollution of air and water. The thermoelectric company Termogas Machala has received complaints of being a possible source of water pollution from the beach of Bajo Alto, parish Tendales, El Oro Province. This research was conducted from 2012 to 2015. With the purpose of evaluating the impacts to water resources derived from the operation of the thermoelectric power plant were determined (i) the physical and chemical parameters of the water of download: Temperature, pH, Chemical Oxygen Demand (COD), Total Suspended Solids (TSS), (ii) the concentration of chemical contaminants: Total Petroleum Hydrocarbons (TPH), Oils and Fats (O&F), Heavy Metals, Sulphides and Phenols, and (iii) biological contaminants: Total Coliforms (CT) and Fecal Coliforms (CF), in order to compare them with the maximum permissible limits of download from thermoelectric plants (2007) and the general standards for wastewater discharge of domestic and industrial TULSMA (2015), and evidence if there is contamination by the thermoelectric plant to the body receiver marine water. In the waters of download, the physical and chemical parameters were within the permissible limits, as well as the chemical contaminants. Heavy metals were not detected, Cu, Cr 6, Pb or Zn. It was noted contamination of biological type for Fecal Coliforms in the year 2015 where maximum values were recorded in the maximum permissible limit of 2000 NMP/100 mL. Was finally carried out an analysis of principal components and a Pearson correlation where correlation was observed between TPH and O&F (r=0,673; p=0.000); TC and FC (r=0.885; p=0.000) and TSS vs COD (r=0,791; p=0.000). It is concluded that the chemical pollution as biological the sector comes from external sources to this industrial process of electricity generation