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Congresos, Seminarios y Cursos

Structure and phason energetics of Al-Co decagonal phases

We develop a model for Al-Co decagonal quasicrystals and approximants. Our model defines a large number of potential atomic positions. These sites are populated by two atomic that interact with each other through electronic-structure-based pair potentials. Monte Carlo simulation of the model produces realistic atomic…

Oxygen Consumption byDesulfovibrioStrains with and without Polyglucose

The kinetics of oxygen reduction by Desulfovibrio salexigens Mast1 and the role of polyglucose in this activity were examined and compared with those of strains of D. desulfuricans and D. gigas. Oxidation rates were highest at air saturation (up to 40 nmol of O(2) min mg of protein) and declined with decreasing oxygen…

Coalescence and overgrowth of diamond grains for improved heteroepitaxy on silicon (001)

Heteroepitaxial [001]-oriented diamond films with considerably increased lateral grain size and strongly improved orientational perfection could be prepared by microwave plasma-assisted chemical vapor deposition using a [001]-textured growth process on Si (001) substrates followed by a [110] step-flow growth process.…

Numerical Simulation of Zener Pinning with Growing Second‐Phase Particles

The Zener pinning effect with growing second‐phase particles in Al 2 O 3 ‐ZrO 2 composite systems were studied by two‐dimensional (2‐D) computer simulations using a diffuse‐interface field model. In these systems, all second‐phase particles are distributed at grain corners and boundaries. The second‐phase particles gr…

Increased glass transition temperature in motionally constrained semicrystalline polymers

A large number of experimental results in the literature support and illuminate a model of behavior of chains and chain segments in the amorphous phase of semicrystalline polymers connecting the elevation of the glass transition temperature (Tg) above its normal value to several kinds of motional restrictions imposed…

Self-polarization effect in Pb(Zr,Ti)O3 thin films

The self-polarization effect is investigated in Pb(Zr,Ti)O3 (PZT) thin films deposited by sol-gel and magnetron sputtering techniques. The effective piezoelectric coefficient of as-grown films, which is proportional to their initial polarization (self-polarization), is measured by a sensitive interferometric technique…

Multivariate analysis of statistically poor EDXRD spectra for the detection of concealed explosives

Energy dispersive x-ray diffraction (EDXRD) has been developed as a tool for the detection of explosives in passenger baggage. The measured spectra result from the combined diffraction from each of the materials within a scattering volume. Multivariate regression was used to identify known components within very noisy…

Fluid particle model

We present a mechanistic model for a Newtonian fluid called fluid particle hydrodynamics. By analyzing the concept of ``fluid particle'' from the point of view of a Voronoi tessellation of a molecular fluid, we propose a heuristic derivation of a dissipative particle dynamics algorithm that incorporates shear forces b…

Emulsion Polymerization Process for Organically Soluble and Electrically Conducting Polyaniline

An emulsion process has been developed for the direct synthesis of the emeraldine salt of polyaniline (PANI) that is soluble in organic solvents. The process entails formation of emulsion particles with a mean hydrodynamic diameter of 150 nm and consisting of a water-soluble organic solvent (e.g., 2-butoxyethanol), a…

Transparent conducting ZnO thin films prepared by XeCl excimer laser ablation

Highly conductive and transparent aluminum- and gallium-doped zinc oxide (ZnO:Al and ZnO:Ga) thin films in place of indium tin oxide films have been prepared by using XeCl excimer laser ablation at relatively low temperatures. The impurity content of Al or Ga in the ZnO target was optimized on the basis of the measure…

Three‐Dimensional Computer Simulation of Ferroelectric Domain Formation

Three‐dimensional (3‐D) computer simulations of ferroelectric domain formation and evolution were performed, using a computer simulation model based on the time‐dependent Ginsburg‐Landau equations. A cubic‐to‐tetragonal ferroelectric phase transition is considered. It is shown that the initial stage of the transition…

Electronic Structure and Elastic Properties of Strongly Correlated Metal Oxides from First Principles: LSDA + U, SIC-LSDA and EELS Study of UO2 and NiO

We compare experimentally observed electron energy loss spectra (EELS) of uranium dioxide UO2 and nickel monoxide NiO with the results of ab-initio calculations carried out by using a method combining the local spin density approximation and the Hubbard U term (the LSDA + U method). We show that by taking better accou…

Role of Conductive Corrosion Products in the Protectiveness of Corrosion Layers

In carbon dioxide (CO2) corrosion of steels, the bicarbonate ion (HCO3–) is simultaneously the buffer for carbonic acid (H2CO3), the source of iron carbonate (FeCO3) precipitation, and the product of the cathodic reaction. In addition to spatial separation of the production of Fe2+ and HCO3–, galvanic coupling between…

Wear‐Accelerated Corrosion of Passive Metals in Tribocorrosion Systems

A model is presented which describes the effect of mechanical and materials parameters on the wear‐assisted corrosion rate of passive metals under sliding wear conditions. The model is based on a consideration of contact between the sliding surfaces at multiple asperities and it takes into account the passivation beha…

From VO 2 ( B ) to VO 2 ( R ) : Theoretical structures of VO 2 polymorphs and in situ electron microscopy

The intermediate steps of the phase transition between the metastable monoclinic ${\mathrm{VO}}_{2}(B)$ phase and the stable tetragonal rutile ${\mathrm{VO}}_{2}(R)$ phase have been studied by in situ electron microscopy. A crystallographic interpretation based on the static concentration waves theory is proposed: as…

Domain patterns in epitaxial rhombohedral ferroelectric films. I. Geometry and experiments

Possible domain patterns are developed for (001) oriented (pseudocubic indexing) epitaxial rhombohedral perovskite ferroelectric (FR) films. We assume that the films are grown above their Curie temperature (TC) in a cubic paraelectric (PC) state. The rhombohedral distortion consists of a “stretch” along one of the fou…

Upconversion-pumped luminescence efficiency of rare-earth-doped hosts sensitized with trivalent ytterbium

We discuss the upconversion luminescence efficiencies of phosphors that generate red, green, and blue light. The phosphors studied are single crystals and powders codoped with Er3+ and Yb3+ and with Tm3+ and Yb3+. The Yb ions are pumped near 980 nm; transfers of two or three quanta to the codoped rare-earth ion genera…

Development of Low‐Toxicity Gelcasting Systems

A series of low‐toxicity gelcasting systems has been developed. The reagents used in these systems have very low acute toxicity. The new systems perform at least as well as, and in some cases better than, the original acrylamide‐based system. The development of these systems is described herein, including the search f…

Clay mineral diagenesis in sedimentary basins — a key to the prediction of rock properties. Examples from the North Sea Basin

Abstract Dissolution of feldspar and mica and precipitation of kaolinite require a through flow of meteoric water to remove cations such as Na + and K + and silica. Compaction driven pore-water flow is in most cases too slow to be significant in terms of transport of solids. The very low solubility of A1 suggests that…