Rapid thermal characterization of graphene oxide-nanocalorimetry as a pathway for novel insights in tribology

The use of solid lubricants such as graphene, graphene oxide, and other nanoparticles have gained notable attention in the tribological community to reduce friction and wear thus aiming at improved energy efficiency and sustainability. Tribological experiments unify rather extreme conditions such as high contact pressures, small contact areas, relative sliding motion, and rapid heating. This combination leads to mechanically- and/or thermally induced chemical, structural and microstructural modifications of the lubricating nanoparticles during rubbing thus altering their material’s properties. Due to the high sensitivity, we propose nanocalorimetry as the method of choice to shed more light on the thermally-induced processes and changes. As a model material for solid lubricants, we explore the transitions of graphene oxide under heating with 1000 °C/s up to 600 °C using quasi-adiabatic nanocalorimetry. We identify a strong exothermic runaway reaction at 317 °C. This runaway is preceded by exothermic reactions between 75–125 °C, which are correlated with the release of intercalated species and the formation of CO and CO$_{2}$

First-Principles Calculations of Thermoelectric Properties of IV–VI Chalcogenides 2D Materials

A first-principles study using density functional theory and Boltzmann transport theory has been performed to evaluate the thermoelectric (TE) properties of a series of single-layer 2D materials. The compounds studied are SnSe, SnS, GeS, GeSe, SnSe2, and SnS2, all of which belong to the IV–VI chalcogenides family. The first four compounds have orthorhombic crystal structures, and the last two have hexagonal crystal structures. Solving a semi-empirical Boltzmann transport model through the BoltzTraP software, we compute the electrical properties, including Seebeck coefficient, electrical conductivity, power factor, and the electronic thermal conductivity, at three doping levels corresponding to 300 K carrier concentrations of 1018, 1019, and 1020 cm−3. The spin orbit coupling effect on these properties is evaluated and is found not to influence the results significantly. First-principles lattice dynamics combined with the iterative solution of phonon Boltzmann transport equations are used to compute the lattice thermal conductivity of these materials. It is found that these materials have narrow band gaps in the range of 0.75–1.58 eV. Based on the highest values of figure-of-merit ZT of all the materials studied, we notice that the best TE material at the temperature range studied here (300–800 K) is SnSe

Rapid Thermal Characterization of Graphene Oxide—Nanocalorimetry as a Pathway for Novel Insights in Tribology

The use of solid lubricants such as graphene, graphene oxide, and other nanoparticles have gained notable attention in the tribological community to reduce friction and wear thus aiming at improved energy efficiency and sustainability. Tribological experiments unify rather extreme conditions such as high contact pressures, small contact areas, relative sliding motion, and rapid heating. This combination leads to mechanically- and/or thermally induced chemical, structural and microstructural modifications of the lubricating nanoparticles during rubbing thus altering their material’s properties. Due to the high sensitivity, we propose nanocalorimetry as the method of choice to shed more light on the thermally-induced processes and changes. As a model material for solid lubricants, we explore the transitions of graphene oxide under heating with 1000 °C/s up to 600 °C using quasi-adiabatic nanocalorimetry. We identify a strong exothermic runaway reaction at 317 °C. This runaway is preceded by exothermic reactions between 75–125 °C, which are correlated with the release of intercalated species and the formation of CO and CO2

Photoluminescence in silicon/silicon oxide films produced by the Pulsed Electron Beam Ablation technique

In this work we report studies of the photoluminescence emission in samples based on Si/SiOx films deposited by the Pulsed Electron Beam Ablation (PEBA) technique. The samples were prepared at room temperature using targets with different Si/SiO2 concentrations. The samples were characterized using X-ray Absorption Edge Spectroscopy (XANES) at the Si-K edge, Raman spectroscopy, Photoluminescence (PL) and X-ray Photoelectron Spectroscopy (XPS). The concentration of a-Si and nc-Si in the film was dependent on the silicon concentration in the target. It was also observed that the PL is strongly dependent on the structural amorphous/crystalline arrangement. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.Chilean agency CONICYT [11085026]Chilean agency CONICY

BIOPSIA ESTEREOTAXICA MAMARIA: 2 AÑOS DE EXPERIENCIA DIRECTIONAL VACUUM-ASSISTED STEREOTACTIC BREAST BIOPSY: A 2-YEAR EXPERIENCE

Introducción: La biopsia estereotáxica digital mamaria (BED), representa un excelente método para obtener diagnóstico histológico, siendo alternativa de elección frente a la cirugía en muchos casos. Objetivo: Presentar nuestra experiencia en la aplicación de la BED en el Hospital Clínico de Universidad de Chile. Material y método: Estudio descriptivo, retrospectivo de BED realizadas en el Hospital Clínico de la Universidad de Chile (marzo 2005-noviembre 2007). Se registró morfología de las lesiones, clasificación BI-RADS, informes de anatomía patológica, complicaciones y datos epidemiológicos. Resultados: Se incluyó a 79 pacientes con 95 lesiones. Edad promedio 55 años. De las 95 biopsias, 95,7% correspondieron a microcalcificaciones. La sensibilidad fue 92,8% y la especificidad 100%. El valor predictivo positivo fue 100%o y negativo 98,7%. La subestimación fue de 8% y la tasa de complicaciones 3,1%. Conclusiones: Nuestros resultados confirman las ventajas del procedimiento en nuestro Centro, demostrando la BED como altamente confiable, con buena correlación histológica y mínimas complicaciones.Introduction: Directional vacuum-assisted stereotactic breast biopsy (DVAB), represents an ex-cellent method for obtaining pathological diagnosis, being in many cases an alternative to surgery. Objec-tives: To present our 2-year experience in DVAB at the University of Chile's Clinical Hospital. Materials and methods: a descriptive retrospective study of DVAB was conducted in our Hospital from March 2005 to November 2007. Morphology of lesions, BI-RADS classification, pathology reports, complications as well as epidemiológica! data were recorded. Results: We included 79 patients with 95 lesions. Mean age 55 years. Of the 95 biopsies, 95.7% were microcal-cifications. The sensitivity was 92.8% and specificity 100%. The positive predictive valué was 100%, while negative PVwas 98.7%, with 8% of subestimation and complication rate of 3,1%. Conclusions: Our results confirm the advantages of said procedure in ourCenter, proving DVAB as highly reliable, with good histological correlation and minimal complications

Directional vacuum-assisted stereotactic breast biopsy: A 2-year experience Biopsia estereotaxica mamaria: 2 Años de experiencia

Introduction: Directional vacuum-assisted stereotactic breast biopsy (DVAB), represents an excellent method for obtaining pathological diagnosis, being in many cases an alternative to surgery. Objectives: To present our 2-year experience in DVAB at the University of Chile's Clinical Hospital. Materials and methods: a descriptive retrospective study of DVAB was conducted in our Hospital from March 2005 to November 2007. Morphology of lesions, BI-RADS classification, pathology reports, complications as well as epidemiological data were recorded. Results: We included 79 patients with 95 lesions. Mean age 55 years. Of the 95 biopsies, 95.7% were microcalcifications. The sensitivity was 92.8% and specificity 100%. The positive predictive value was 100%, while negative PV was 98.7%, with 8% of subestimation and complication rate of 3,1%. Conclusions: Our results confirm the advantages of said procedure in our Center, proving DVAB as highly reliable, with good histological correlation and mi