Degradación del comportamiento a flexión de perfiles tubulares de acero expuestos a la intemperie utilizados como protecciones colectivas y medios auxiliares en edificación

Los perfiles tubulares de acero (PTA) son más habitualmente empleados el ámbito de las protecciones colectivas (PC) y medios auxiliares de edificación (MAE), al ser usados en ámbitos de seguridad, adquieren una importancia tal que motiva el estudio de la fiabilidad de su comportamiento mecánico. Por ello se motiva este trabajo estudiando a flexión PTA con las mismas calidades que los que habitualmente se emplean en PC y MAE. Han sido ensayadas a flexión un total de 150 secciones de PTA, utilizando como variables la velocidad del ensayo, la distancia entre los apoyos, la influencia del dispositivo de apoyo y la comparativa entre el comportamiento de PTA expuestos a la intemperie durante 3 años en la Sierra de Guadarrama (en servicio como postes en sistemas de protección de borde) con PTA adquiridos. En este trabajo se ha evaluado en todos los casos las diferencias existentes entre los espesores de cada PTA medido con calibre, su espesor nominal y su espesor medio de cada tubo. El esquema de solicitaciones y tensiones resultante del ensayo de flexión es muy similar en la mayoría de los casos a los esquemas de solicitaciones y tensiones reales a los que trabajan los PTA utilizados como PC y MAE. En este caso, la sección más desfavorable esta solicitada por el máximo momento flector y el máximo cortante y la variación del flector a lo largo de las barras es lineal. Documentos técnicos como el CTE-SE-A o el EC3, establecen una clasificación para determinar el método de cálculo de las secciones de acero, y en la que la mayoría de las secciones de los PTA son clase 1(aquella que permite la formación de una rótula plástica con capacidad de rotación suficiente para la redistribución de momentos) con lo que es posible utilizar el cálculo plástico o el elástico para la determinación de las solicitaciones. Esta clasificación indica directamente la capacidad de aprovechamiento de la sección antes de que se produzca la abolladura y depende de las dimensiones de las secciones de los PTA. Estudios anteriores desvelan que los PTA no llegan a plastificarse ya que antes de que se produzca este fenómeno se abollan, lo que motiva el colapso. Como resultado de este trabajo de investigación se pretende estudiar, como ya predijo en su tesis González García, M.N. [1] que la clasificación de secciones indicada por EC3 o CTE para PTA queda del lado de la inseguridad porque predice comportamientos plásticos en secciones que no tienen posibilidad de plastificación

Impacto de la producción piñera en la población de la zona de amortiguamiento de la Reserva de Biosfera La Amistad, Costa Rica

En Costa Rica, con la incursión de la compañía Del Monte en el municipio Buenos Aires de la provincia de Puntarenas, en la zona sur del país, se inició en 1979 el avance intensivo del monocultivo de piña (Ananas comosus). Los distritos Volcán y Brunca y la cabecera del municipio, denominada también Buenos Aires, han sido los territorios en los que se ha concentrado la mayor extensión piñera. Los pobladores de estos distritos, desde tiempos coloniales, se dedicaban a la actividad ganadera (Bonatti y otros, 2005). Este municipio presenta índices de desarrollo humano catalogados entre los más bajos del país. Según el ranking del Índice de Desarrollo Humano por municipio para el año 2016, Buenos Aires ocupa la posición 70 de un total de 81 municipio

Wilderness Network Conservation in the Cantabrian Region of Northern Spain

Natura 2000 is a pan-European network whose principal aim is to conserve the European spaces of greatest natural interest. Its effectiveness is analyzed in a specific sector in Spain, namely the Atlantic Region, through an exhaustive division and assessment by area. This article considers questions related to the impact on the spaces included within the network, providing specific examples associated with the fauna, flora, and the territorial agroecostructures. Alternatives and communication possibilities are suggested for those spaces excluded from the network, but which have a key role as nodes for interchange and connection of biodiversity

Variaciones estacionales de tierras raras en la materia en suspensión y el agua del estuario del río Odiel (SO de España)

Seasonally distribution of the lanthanides in the suspended matter and dissolved phasehas been studied during a hydrological year in the estuary of the Odiel River. In his system affected by acid mine drainage take place the coexistence of two water mixture processes; a process salt-induced mixture typical in an estuary and a process of acid water neutralization. In the mixing zone of the estuary there is a removal of the dissolved phase to the suspended matter out of the system. REEs concentrations are controlled by the volume of discharge of the river and degree of neutralization process. Thus, during first rains after a dry period, the gradient in concentration of these elements in the mixing zone ismore pronounced in this system.Versión de edito

Efecto del drenaje ácido sobre el fraccionamiento de tierras raras ligeras en sedimentos: un caso de estudio en el estuario de los ríos Tinto y Odiel

The effect of acid drainage on light rare earth elements (LREE) has been studied in the estuarine sediment of the Tinto and Odiel system, where the fluvial and marine water mixing cause an important pH and chlorinity gradient inside. Due to the high influence of pH over the LREE partitioning from dissolved toparticulate phases, an anomalous behaviour has been found on La content in these sediments. Large removal of LREE takes place at low chlorinity zones in unaffected estuaries, but in the studied system this natural process is moved out the outer zones of the estuary. So, the relative La depletion in the estuarine mixing zone is due to the low pH values (< 6) that prevents LREE removal in low chlorinity zones. Once the acid neutralization (pH ~ 7) occurs, some La enrichment can be observed in sediments of the marine estuary.Versión de edito

The correlation between leader–member exchange and organisational commitment among spanish registered nurses: The moderating role of sex and hospital size

The role of the supervisor in hospitals is to oversee and encourage the active work participation of registered nurses. In this context, leadership should be focused on the creation of a positive environment for the generation of high-quality care and the development of attitudes that have a beneficial influence on the work of the registered nurse. The aims of this study have been: (i) To verify if the quality of the supervisor–nurse interpersonal relationship was correlated with organisational commitment; (ii) to establish if the correlation could be moderated by empowerment, perceived organisational support, and leader–leader exchange. A cross-sectional survey with self-report questionnaires was performed. A total of 2541 registered nurses from nine public hospitals participated in the study. They completed scales measuring leader–member exchange, commitment, empowerment, perceived organisational support, and leader–leader exchange. There was a positive correlation between the quality of the leader–member exchange and commitment. Leader–leader exchange has a moderating effect on this relationship. The moderating effects of empowerment, perceived organisational support, and leader–member exchange on the supervisor–nurse interpersonal relationship and the nurse’s organisational commitment are influenced by sex and/or hospital size. Organisations should design supervisor training strategies aimed at establishing high-quality supervisor–nurse interpersonal relationships

Multi-Proxy Approach for Identifying Heinrich Events in Sediment Cores from Hatton Bank (NE Atlantic Ocean)

A series of six gravity cores has been used to reconstruct the depositional history of Hatton Bank (Rockall Plateau, NE Atlantic Ocean). The cores have been studied for magnetic susceptibility (MS), geochemical composition, grain size distribution, and a semi-quantitative foraminiferal association. Two main interbedded facies have been described: (i) calcareous ooze; and (ii) lithogenous silt. The study reveals prominent peaks from the MS signal, silt, Mg/Ca, Fe/Ca, Al/Ca, and Rare Earth Elements normalised by Continental Crust (REE/CC), which are sensitive indicators for Heinrich events (H1, H2, H3, H4, and H5) and ash layers. These peaks may relate to alternations in dominance of the calcareous and lithogenic facies. The sediment displays a high percentage of carbonate in interglacial layers but is lithogenic-dominated in glacial stages. The layers with prominent lithic-rich and foraminifera-poor sediments (established as Heinrich layers) may be related to a possible palaeoclimatic effect, where freshwater discharged during iceberg melting may have reduced the formation of North Atlantic Deep Water (NADW). In the study area, the mean sedimentation rates for the last glacial as ~4.2 cm ka−1 and ~1.4 cm ka−1 for the last ~18 ka (interglacial period) have been estimated. Besides this evidence, Fe/Ca and MS peaks may reflect the presence of basalt, either introduced through ice-rafting or transported and redistributed by bottom currents in the study area. Certain indices, including MS and Fe/Ca, are proposed as good proxies for detecting Heinrich events and ash layers in the Hatton Bank sediments and, in consequence, are parameters that can be used to infer strengthened/weakened NADW formation, according to stadials/interstadials. Moreover, we suggest that the northernmost boundary of the area with evidence of Heinrich events may be situated around 57°38′ N in the Hatton–Rockall area, at least for H4, based on the variation of the Mg/Ca and Fe/Ca curves