Geochemistry of Chixulub ejecta in ODP Leg 207 holes

An up to 2-cm thick Chicxulub ejecta deposit marking the Cretaceous-Paleogene (K-Pg) boundary (the "K-T" boundary) was recovered in six holes drilled during ODP Leg 207 (Demerara Rise, tropical western Atlantic). Stunning features of this deposit are its uniformity over an area of 30 km2 and the total absence of bioturbation, allowing documentation of the original sedimentary sequence. High-resolution mineralogical, petrological, elemental, isotopic (Sr-Nd), and rock magnetic data reveal a distinct microstratigraphy and a range of ejecta components. The deposit is normally graded and composed predominantly of rounded, 0.1- to max. 1-mm sized spherules. Spherules are altered to dioctahedral aluminous smectite, though occasionally relict Si-Al-rich hydrated glass is also present, suggesting acidic precursor lithologies. Spherule textures vary from hollow to vesicle-rich to massive; some show in situ collapse, others include distinct Fe-Mg-Ca-Ti-rich melt globules and lath-shaped Al-rich quench crystals. Both altered glass spherules and the clay matrix (Site 1259B) display strongly negative epsilon-Nd (T=65Ma) values (-17) indicating uptake of Nd from contemporaneous ocean water during alteration. Finally, Fe-Mg-rich spherules, shocked quartz and feldspar grains, few lithic clasts, as well as abundant accretionary and porous carbonate clasts are concentrated in the uppermost 0.5-0.7 mm of the deposit. The carbonate clasts display in part very unusual textures, which are interpreted to be of shock-metamorphic origin. The preservation of delicate spherule textures, normal grading with lack of evidence for traction transport, and sub-millimeter scale compositional trends provide evidence for this spherule deposit representing a primary air-fall deposit not affected by significant reworking. The ODP Leg 207 spherule deposit is the first known dual-layer K-Pg boundary in marine settings; it incorporates compositional and stratigraphic aspects of both proximal and distal marine sites. Its stratigraphy strongly resembles the dual-layer K-Pg boundary deposits in the terrestrial Western Interior of North America (although there carbonate phases are not preserved). The occurrence of a dual ejecta layer in these quite different sedimentary environments - separated by several thousands of kilometers - provides additional evidence for an original sedimentary sequence. Therefore, the layered nature of the deposit may document compositional differences between ballistic Chicxulub ejecta forming the majority of the spherule deposit, and material falling out from the vapor (ejecta) plume, which is concentrated in the uppermost part.

X-Ray Diffraction of Highway Materials, HR-128, 1969

X-ray diffraction data during adsorption of water vapor on Na- and Ca-montmorillonites show that interlayer expansion is continuous but nonuniform. X-ray and adsorption isotherm data indicate an ice-like configuration of water molecules is completed with the fourth layer of interlayer water for the Ca-clay; a fifth layer intrudes to give a less ordered structure. Data for the Na-clay indicate a laminar stacking arrangement for up to three layers of interlayer water. The Na-clay adsorbs more than twice as much water and undergoes four times as large a volume change than the Ca-clay. The free energy change during adsorption of water vapor on the Ca-clay is nearly twice that for the Na-clay. Free energy changes with increasing relative pressure reflect interlayer expansion increments.

Estudo da intercalação de fontes de potássio em caulinita pura, com tratamento térmico e ativação ácida

The chemical changes in clay minerals has been widely studied in order to improve its properties for use in various applications. However kaolinite has strong hydrogen bonds between their adjacent layers hindering the process changes in its structure. With the objective to facilitate the process of intercalation monobasic potassium phosphate, bibasic potassium phosphate and potassium acetate we was performed on kaolinite heat treatment at 600 °C and activated acidic with phosphoric acid and 5 to 10 mol L-1. The samples they were characterized by energy dispersive spectroscopy (EDS), X-Ray Diffraction (XRD), Infrared Spectroscopy Fourier Transform (FTIR) and Thermogravimetric Analysis (TG) and Differential Thermal Analysis (DTG) and the superficial and textural changes the samples with heat treatment and acid activation they were characterized by scanning electron microscopy (SEM) and Textural Analysis of Adsorption/desorption N2. With the help of the techniques found that, the heat treatment becomes more susceptible to acid activation kaolinite making the samples with two treatments show larger amounts of phosphorus. It was also found that bibasic potassium phosphate binds more strongly the structure of kaolinite by having a structure with two-coordinating oxygens and intercalation with potassium acetate in acid-activated kaolin increases the interlayer distance of the kaolinite and the intercalation occurs with higher response index (RI) for samples with acid activation to 5 mol /L.

Evaluación técnica de las vías de concreto hidráulico del barrio El Centro del municipio de Antiguo Cuscatlán

La presente investigación consistió en la evaluación técnica de las vías de concreto hidráulico del barrio El Centro de Antiguo Cuscatlán, basada en la evaluación de parámetros estructurales y funcionales, evaluados por medio de afores vehiculares, levantamiento de deterioros y extracciones de núcleos, lo que permitió conocer la condición del pavimento tanto estructural como funcional, con la finalidad de proveer a la alcaldía del municipio de Antiguo Cuscatlán información de las condiciones actuales del pavimento, para que tomen las medidas necesarias para su conservación

Programa Opinión Universitaria (9 mayo 2016) : Investigaciones realizadas por el Centro de Investigaciones y Desarrollo en Salud, CENSALUD.

El investigador y director de CENSALUD Saúl Díaz, las investigadoras Amy Morán y Karla Castillo hablan de las investigaciones realizadas por el Centro de Investigaciones y Desarrollo en Salud, CENSALUD, sobre la enfermedad del Chagas y la inocuidad en los alimentos.

Determinación del comportamiento al hinchamiento y retracción de suelos que tienen plasticidad, en algunos puntos de la Carretera Longitudinal del Norte, en el tramo comprendido entre Metapán (Dpto. Santa Ana) y Sensuntepeque (Dpto. Cabañas)

En la presente investigación se llevó a cabo el estudio de los suelos plásticos. El interés primordial ha sido la determinación del comportamiento al hinchamiento y retracción de materiales obtenidos en un tramo de la Carretera Longitudinal del Norte, entre Metapán (departamento Santa Ana) y Sensuntepeque (departamento de Cabañas). El documento contiene un marco teórico, el cual establece las propiedades de los diferentes materiales que componen el suelo y específicamente las propiedades de las arcillas que son las que poseen propiedades plásticas y de hinchamiento. Para su análisis se llevaron a cabo diversos ensayos, como son: Humedad natural, límites de Altlerberg, granulometría, gravedad específica, hinchamiento libre, presión de hinchamiento (a volumen constante) y ensayo Lambe. En base a sus resultados se cuantifico la expansión de cada uno y se propusieron alternativas, para evitar el daño de estructuras cuando se tiene este tipo de materiales bajo la cimentación

Superlattice structures in twisted bilayers of folded graphene

The electronic properties of bilayer graphene strongly depend on relative orientation of the two atomic lattices. Whereas Bernal-stacked graphene is most commonly studied, a rotational mismatch between layers opens up a whole new field of rich physics, especially at small interlayer twist. Here we report on magnetotransport measurements on twisted graphene bilayers, prepared by folding of single layers. These reveal a strong dependence on the twist angle, which can be estimated by means of sample geometry. At small rotation, superlattices with a wavelength in the order of 10 nm arise and are observed by friction atomic force microscopy. Magnetotransport measurements in this small-angle regime show the formation of satellite Landau fans. These are attributed to additional Dirac singularities in the band structure and discussed with respect to the wide range of interlayer coupling models.

Proton conductivity and luminiscence properties of lanthanide aminotriphosphonates

Metal phosphonates are multifunctional solids with tunable properties, such as internal H-bond networks, and high chemical and thermal stability [1]. In the present work, we describe the synthesis, structural characterization, luminescent properties and proton conduction performance of a new family of isostructural cationic compounds with general formula [Ln(H4NMP)(H2O)2]Cl·2H2O [Ln = La3+, Pr3+, Sm3+, Gd3+, Tb3+, Dy3+, Ho3+, H6NMP = nitrilotris(methylphosphonic acid)]. These solids are formed by positively charge layers, which consist of isolated LnO8 polyhedra and bridge chelating NMP2- ligands, held apart by chloride ions and water molecules. This arrangement result in extended interlayer hydrogen networks with possible proton transfer pathways. The proton conductivity of Gd3+ sample, selected as prototype of the series, was measured. In the range between range 25º and 80 ºC, the conductivity increase with the temperature up to a maximum value of 3.10-4 S·cm-1, at relative humidity of 95 %. The activation energy obtained from the Arrhenius plot (Figure 1) is in the range corresponding to a Grotthuss transfer mechanism.

Fuensanta Zertuche Terán (1945-2015)

La hija de Francisco M. Zertuche, abogada, actriz de cine y teatro, que fue dirigida por Juan José Gurrola y Alejandro Jodorowsky, y que cobró fama como vedette, fue un personaje incomprendido al que la UANL le rindió un homenaje a través de la Feria Universitaria del Libro UANLeer 2016

Estudo da influência da temperatura de brasagem nas uniões zircônia/aço inox 304 utilizando metalização mecânica

Metal-Ceramic (M/C) Zirconia-stainless steel interfaces have been processed through brazing techniques due to the excellent combination of properties such as high temperature stability, high corrosion resistance and good mechanical properties. However, some M/C interfaces show some defects, like porosity and cracks results in the degradation of the interfaces, leading even to its total rupture. Most of time, those defects are associated with an improper brazing parameters selection to the M/C system. In this work, ZrO2 Y-TZP and ZrO2 Mg - PSZ were joint with the stainless steel grade 304 by brazing using a eutectic silver-copper (Ag28Cu) interlayer alloy with different thermal cycles. Ceramic surfaces were previous mechanically metallized with titanium to improve adhesion of the system. The effect of temperature on the M/C interface was studied. SEM-EDS and 3 point flexural bend test were performed to evaluate morphology, chemical composition and mechanical resistance of the M/C interfaces. Lower thermal cycle temperatures produced better results of mechanical resistance, and more regular/ homogeneous reaction layers between braze alloy and metal-ceramic surfaces. Also was proved the AgCu braze alloy activation in situ by titanium

Decisiones de inversión en el sertor vitivinícola de las Rías Baixas: Análisis mediante opciones reales

En este estudio analiza las decisiones de inversión de un proyecto vitivinícola, es decir, un viñedo, bajo dos variables con incertidumbre, producción y precio. La valoración mediante opciones reales identifica los niveles óptimos de ingresos para la entrada y salida al negocio considerando factores económicos como costes hundidos y de estructura, economías de escala, volatilidad de precio y producción y valor deliquidación. Los resultados obtenidos explican el lento ajuste de la producción de vino a la demanda del sector de las Rías Baixas. Asimismo, se discute como las características de la región hacen que el tamaño de la zona histéresis lleve a los cultivadores a esperar en lugar de ejercer la opción de entrada o salida.

Fonctionnalisation covalente de monocouches et bicouches de graphène

Le graphène est une nanostructure de carbone hybridé sp2 dont les propriétés électroniques et optiques en font un matériau novateur avec un très large potentiel d’application. Cependant, la production à large échelle de ce matériau reste encore un défi et de nombreuses propriétés physiques et chimiques doivent être étudiées plus en profondeur pour mieux les exploiter. La fonctionnalisation covalente est une réaction chimique qui a un impact important dans l’étude de ces propriétés, car celle-ci a pour conséquence une perte de la structure cristalline des carbones sp2. Néanmoins, la réaction a été très peu explorée pour ce qui est du graphène déposé sur des surfaces, car la réactivité chimique de ce dernier est grandement dépendante de l’environnement chimique. Il est donc important d’étudier la fonctionnalisation de ce type de graphène pour bien comprendre à la fois la réactivité chimique et la modification des propriétés électroniques et optiques pour pouvoir exploiter les retombées. D’un autre côté, les bicouches de graphène sont connues pour avoir des propriétés très différentes comparées à la monocouche à cause d’un empilement des structures électroniques, mais la croissance contrôlée de ceux-ci est encore très difficile, car la cinétique de croissance n’est pas encore maîtrisée. Ainsi, ce mémoire de maîtrise va porter sur l’étude de la réactivité chimique du graphène à la fonctionnalisation covalente et de l’étude des propriétés optiques du graphène. Dans un premier temps, nous avons effectué des croissances de graphène en utilisant la technique de dépôt chimique en phase vapeur. Après avoir réussi à obtenir du graphène monocouche, nous faisons varier les paramètres de croissance et nous nous rendons compte que les bicouches apparaissent lorsque le gaz carboné nécessaire à la croissance reste présent durant l’étape de refroidissement. À partir de cette observation, nous proposons un modèle cinétique de croissance des bicouches. Ensuite, nous effectuons une étude approfondie de la fonctionnalisation du graphène monocouche et bicouche. Tout d’abord, nous démontrons qu’il y a une interaction avec le substrat qui inhibe grandement le greffage covalent sur la surface du graphène. Cet effet peut cependant être contré de plusieurs façons différentes : 1) en dopant chimiquement le graphène avec des molécules réductrices, il est possible de modifier le potentiel électrochimique afin de favoriser la réaction; 2) en utilisant un substrat affectant peu les propriétés électroniques du graphène; 3) en utilisant la méthode d’électrogreffage avec une cellule électrochimique, car elle permet une modulation contrôlée du potentiel électrochimique du graphène. De plus, nous nous rendons compte que la réactivité chimique des bicouches est moindre dû à la rigidité de structure due à l’interaction entre les couches. En dernier lieu, nous démontrons la pertinence de la spectroscopie infrarouge pour étudier l’effet de la fonctionnalisation et l’effet des bicouches sur les propriétés optiques du graphène. Nous réussissons à observer des bandes du graphène bicouche dans la région du moyen infrarouge qui dépendent du dopage. Normalement interdites selon les règles de sélection pour la monocouche, ces bandes apparaissent néanmoins lorsque fonctionnalisée et changent grandement en amplitude dépendamment des niveaux de dopage et de fonctionnalisation.

Dysprosium transport in Nd-Fe-B pellets

The addition of heavy rare earth (RE) elements to Nd2Fe14B based magnets to form (Nd,Dy)2Fe14B is known to increase the coercivity and high temperature performance required for hybrid vehicle electric motors and other extreme temperature applications. Attempts to conserve heavy rare earth elements for high temperature (RE)2Fe14B based magnets have led to the development of a grain boundary diffusion process for bulk magnets. This process relies on transport of a heavy rare earth, such as Dy, into a bulk Nd2Fe14B magnet along pores, a low volume fraction of eutectic liquid along grain boundary grain triple junctions and grain boundaries. This enriches the grain surfaces in Dy through the thickness of the bulk magnet, leading to larger increases coercivity with a smaller Dy concentration than can be achieved with homogeneous alloys. Attempts to carry out the same process during sintering require significant control of Dy transport efficiency. The macroscopic transport of Dy in Nd2.7Fe14B1.4 based powder packs is studied using a 'layered' pellet, where Nd2.7Fe14B1.4powder is an interlayer and Dy source as a center layer. The sintering of this layered pellet provided evidence for very large effective diffusion lengths aided by Dy rich liquid flow through connected porosity. Approaches to controlling Dy transportation include decreasing the liquid phase transport capability of the powder pack by increasing the melting point of the Dy source and the decreasing amount of RE rich liquid in the powder packs. The solid-liquid reaction is studied in which melt spun Nd2.7Fe14B1.4 ribbons are PVD coated with Dy-Fe eutectic composition and then thermally treated. The resulting microstructure from the reaction between Dy-Fe eutectic coating and Nd2.7Fe14B1.4 ribbon is interpreted as support for a proposed dissolution/reprecipitation process between solid and liquid phases. The estimate the diffusion coefficient and the effective diffusion length of Dy sources in Nd2.7Fe14B1.4 layered pellets and melt spun ribbons were obtained from the calculation of Fick's second law combined with EDS results from the experiment. The results indicate that the effective diffusion coefficient of Dy in the layered pellets is higher than the diffusion in ribbons due to its higher porosity than ribbons.

ELECTRON TRANSPORT IN LOW-DIMENSIONAL NANOSTRUCTURES - THEORETICAL STUDY WITH APPLICATION

Graphene as a carbon monolayer has attracted extensive research interest in recent years. My research work within the frame of density functional theory has suggested that positioning graphene in proximity to h-BN may induce a finite energy gap in graphene, which is important for device applications. For an AB-stacked graphene/BN bilayer, a finite gap is induced at the equilibrium configuration. This induced gap shows a linear relationship with the applied strain. For a graphene/BN/graphene trilayer, a negligible gap is predicted in the ground state due to the overall symmetry of the system. When an electric field is applied, a tunable gap can be obtained for both AAA and ABA stackings. Enhanced tunneling current in the AA-stacked bilayer nanoribbons is predicted compared to either single-layer or AB-stacked bilayer nanoribbons. Interlayer separation between the nanoribbons is shown to have a profound impact on the conducting features. The effect of boron or nitrogen doping on the electronic transport properties of C60 fullerene is studied. The BC59 fullerene exhibits a considerably higher current than the pristine or nitrogen doped fullerenes beyond the applied bias of 1 V, suggesting it can be an effective semiconductor in p-type devices. The interaction between nucleic acid bases - adenine (A), guanine (G), cytosine (C), thymine (T) and uracil (U) - and a hydrogen-passivated silicon nanowire (SiNW) is investigated. The binding energy of the bases with the SiNW shows the order: G > A~C~T~U. This suggests that the interaction strength of a hydrogen passivated SiNW with the nucleic acid bases is nearly the same-G being an exception. The nature of the interaction is suggested to be electrostatic.