Variable-Volume Engine

A description is given of an engine using the expansion-contraction of bodies subjected to controlled thermal variations and making use of free natural heat sources

Paleoenvironment Reconstruction of the Eocene Southeastern Tethys Using Geochemistry of Sedimentary Rocks

The Early Eocene hyperthermals are a series of transient global warming events that occurred between 54.09 and 52.63 Ma, and are considered as ancient analogues for future climate change. These hyperthermal events are well studied in the deep sea sites, but have not been investigated in the eastern Tethys Ocean. Here, we report new major and trace element geochemistry and stable carbon isotope data of the Early Eocene strata deposited in a shallow marine foreland basin prior to the main stage of India-Asian continent collision at Qumiba section in the Tingri County, southern Tibet. These geochemical data are used to reconstruct the paleoenvironment and past carbon cycle dynamics in the Early Eocene. The collision of India with Asia continent led to the formation of the Himalayas and the demise of the Tethys Ocean. This tectonic event played a significant role in the paleotopography, paleoceanography and paleoclimate of the southeastern Tethys. The youngest marine sediments (Enba Formation and Zhaguo Formation) represent the closure of the Tethys Ocean, and suggest an age of 53.67 to 52.63 Ma. Major element geochemistry and weathering indices indicate that the Eocene southeastern Tethys may have experienced periodic pulses of nutrient-rich detrital sediments, weathering supplies and the development of hypoxia in the water column, consistent with the warm and humid climate in the Early Eocene

Etude par STM de la déposition d'agrégats d'or sur TiO2 et mesure de l'émission électronique secondaire induite par l'impact d'agrégats sur une surface

This thesis work focuses on impact and diffusion processes as well as equilibrium positions of a metal deposited on a surface. The metal is deposited in the form of clusters containing n atoms in a controlled way. Gold or silver clusters cations (Au+n and Ag+n ) are used. Their size (n &#x2208; [1, 9]), charge state and deposition energy (E = 10 - 4500 eV) are well defined. The surface being at room temperature during the deposition, can be annealed and transferred in a scanning tunnelling microscope (STM) after deposition. The variable temperature microscope was developed during this thesis. The approach of the tip is carried out by an axial motor, which renders the microscope very stable. The first part of this work treats of the evolution of gold deposited on a TiO2(110) surface. Position and size of gold islands created by cluster or atomic depositions are determined by STM. Compared to atomic deposition at the same energy (10 < E < 100 eV), the cluster deposition produces smaller islands with a large islands density after annealing at 800 K. Regardless the deposition conditions, gold atoms diffuse on the surface already at 300 K. The impact energy is the key parameter to reduce the diffusion by cluster or atomic implantation or defect creation. Upon a high energy deposition, part of the deposited gold is invisible to the STM. The fate of these gold atoms is unclear : they are either buried under the surface or ejected in vacuum at the impact. The control of the islands size should permit the creation of a stable system with an optimum catalytic activity (i. e. CO combustion). Research groups have shown that this activity is strongly influenced by the islands size. It is equal to zero if the diameter is greater than 5 nm. The second part of this work is devoted to the electron emission γ induced by the impact of silver clusters Ag+n on a Pt and HOPG surface. Measurements are made by varying the impact energy (and so the speed v) of size-selected clusters on a defined surface. Impact velocity ranges from 104 to 105 m/s, which is lower than the classical threshold. Nevertheless every cluster size produces an electron emission. A potential emission (γ(v=0) ≠ 0) is observed for the monomer on both surfaces, which is caused by excited ions in a metastable state. The γ(v) curves are increasing, and no mesurable oscillation are observed. This does not confirm earlier work by Meiwes-Broer et al. These authors found oscillations in γ on similar systems relating them to the electronic structure of the clusters and the surface. A model based on heating of the electron gas is developed. This model gives good agreements with the γ(v) curves. The electronic temperature is estimated to 3000-8000 K. Similar behavior on both surfaces (Pt and HOPG) depending of the cluster size is shown. This behavior is probably related to the geometrical structure of the clusters. Finally, a more pronounced molecular effect is observed for the HOPG : the number of electrons emitted by the impact of a Ag+n is up to 7 times higher than the number of electrons emitted by impacts of n independent atoms. This value is smaller than 2 for the Pt surface

Factores de Riesgo Psicosocial Asociados al Maltrato Infantil

77 Páginas.La presente investigación tuvo como objetivo identificar los factores de riesgo psicosociales asociados al maltrato infantil en un grupo de niñas y adolescentes entre los 5 y 17 años, quienes se encuentran actualmente en un semi-internado de una fundación del municipio de Cajicá - Colombia. Para cumplir el objetivo anterior, se tuvo como base el modelo ecológico expuesto por Belsky (1980). Se realizó un análisis estadístico descriptivo, la unidad de análisis estuvo conformada por 50 historias clínicas de las niñas y adolescentes. Entre los factores de riesgo psicosocial asociados al maltrato infantil se encontraron las familias de tipo monoparental, las madres adolescentes y la historia de malos tratos en los padres.Especialización en Psicología Clínica de la Niñez y Adolescencia Especialist

El examen radiológico en los abscesos amibianos del hígado

En Colombia la amibiasis es una de las endemias capitales y por esto los abscesos del hígado de este origen son muy frecuentes

Estudio descriptivo de los estereotipos que causan discriminación en la Facultad de Comunicación y Lenguaje de la Pontificia Universidad Javeriana

Licenciado (a) en Lenguas ModernasPregrad

Doctor carlos m. pava

Con inmensa pesadumbre escribo estas líneas, para añorar al compañero de profesorado doctor Carlos M. Pava: quien por más de quince años me acompaño en  la Cátedra de Histología, luchando por unos mismos ideales