Evaluación en época seca de ecosistemas acuáticos y terrestres: componentes de vegetación y faunación. Sector Centro Administrativo PNN El Tuparro (Cumaribo, Vichada)

La asignatura Ecología Regional Continental tiene como objetivo el análisis de los procesos ecológicos a escala de paisaje y bioma. A lo largo de su existencia dentro del programa curricular de Biología de la Universidad Nacional de Colombia se han realizado distintos estudios ecológicos en distintas regiones del país, ampliando cada vez más el conocimiento de los estudiantes que toman la asignatura y aportando al conocimiento de zonas poco estudiadas. Durante los últimos periodos, la fase de campo se ha realizado en zonas pertenecientes al Sistema de Parques Nacionales Naturales de Colombia. Es así como se realizó un estudio preliminar durante el segundo semestre de 2010 en el PNN Cueva de Los Guacharos en el departamento del Huila, cumpliendo con el objetivo de una evaluación ecológica rápida a nivel de vegetación y limnología de manera dirigida, además de proyectos de distintos temas sobre aspectos ecológicos de la región. Para este periodo, primer semestre de 2011, la fase de campo se desarrolló en el PNN El Tuparro, ubicado en el departamento del Vichada y se incluyó adicionalmente el componente de faunación. Esta zona del país es poco conocida dado su difícil acceso, por lo que la información obtenida es de gran valor

In-situ shear modulus determination by pressuremeter tests in opalinus clay and reconciliation with laboratory tests

Opalinus Clay is the designated host rock for a deep geological repository of radioactive waste in Switzerland. The determination of its geo-mechanical properties relies heavily on laboratory tests on small specimens. To assess the in-situ elastic stiffness at a larger scale, pressuremeter tests were performed in Opalinus Clay at the Mont Terri Rock Laboratory, with the testing probe oriented both perpendicular and parallel to the bedding planes. The shear modulus of the Opalinus Clay is determined using the unload data of the pressuremeter tests in different lithofacies and at multiple expansion pressure levels. The measured shear modulus is dependent on the expansion pressure at the initial stage of the test but approaches a relatively constant value when a pressure magnitude of about 5 MPa is reached. The stiffness anisotropy of the Opalinus Clay, the rock mass disturbance, and the local fractures at test intervals can affect the measured moduli. In this test program, the impact of lithofacies was not evident at low expansion pressures and could not be evaluated at a greater expansion pressure. The shear modulus of the Opalinus Clay exhibits a nonlinear dependence on strain increment, which can be interpreted using a power-law stress–strain relationship. The small-strain nonlinearity is also dependent on the expansion pressures for the Opalinus Clay. At expansion pressures greater than 5 MPa, the strain-dependent shear moduli obtained from pressuremeter tests are comparable with those determined by triaxial tests on intact core specimens. At the shear strain increment of 0.1%, a secant shear modulus (parallel to bedding) of approximately 3 GPa for the intact Opalinus Clay can be concluded from both the pressuremeter and triaxial tests

Study of the permanent deformation of asphalt mixtures in the field: A multiscale approach

Rutting in asphalt concrete layers is a longitudinal depression in wheel paths caused by traffic load repetitions. Different tests and analysis have been proposed to investigate the phenomenon, although few studies of resistance to rutting can be found regarding a multiscale approach from binder to field in literature. Thus, the main objective of this study is to evaluate the behavior of the different scales against the phenomenon of permanent deformation for different binders, mixtures and in-service pavements, verifying the performance relationship between them and how the properties can be correlated. For this, eight monitored asphalt pavements were chosen during road rehabilitation. They consisted of conventional, SBS modified and rubber binders, evaluated in the laboratory for linear viscoelastic characterization and permanent deformation tests. Track rutting was also observed in the field during the first year for comparison with laboratory results. The experimental segments monitored in this research showed that mixtures with SBS and rubber-modified binders returned lower Rutting/N ratios. It was possible to conclude that binders modified using SBS polymer and rubber have greater stiffness and lower phase angles at high temperatures. Asphalt mixtures showed greater stiffness and lower phase angles at high temperatures for mixtures consisting of binders modified by SBS polymer. Flow Number (FN) results were also higher for these mixtures, suggesting better performance in the field. In the mixture scale, the |E*|/sinφ (54 °C; 1 Hz) show the best correlated-with-field rutting in this research, to binder scale, the Jnr parameter was the one that best represented the behavior observed in the field

Nanoscale electrical investigation of layer-by-layer grown molecular wires

Nanoscopic metal-molecule-metal junctions consisting of Fe-bis(terpyridine)-based ordered nanostructures are grown in layer-by-layer fashion on a solid support. Hopping is demonstrated as the main charge-transport mechanism both experimentally and theoretically