Experiments and Simulations of Laminar Forced Convection With Water–Alumina Nanofluids in Circular Tubes

This work reports fundamental experimental-theoretical research related to heat transfer enhancement in laminar channel flow with nanofluids, which are essentially modifications of the base fluid with the dispersion of metal oxide nanoparticles. The nanofluids were synthesized by a two-step approach, using a dispersant and an ultrasound probe or a ball mill for alumina nanoparticles dispersion within the aqueous media. The theoretical work involves the proposition of an extension of the thermally developing flow model that accounts for the temperature variation of all the thermophysical properties, including viscosity and the consequent variation of the velocity profiles along the thermal entry region. The simulation was performed by making use of mixed symbolic-numerical computation on the Mathematica 7.0 platform and a hybrid numerical-analytical methodology (generalized integral transform technique, GITT) in accurately handling the governing partial differential equations for the heat and fluid flow problem formulation with temperature dependency in the thermophysical properties. Experimental work was also undertaken based on a thermohydraulic circuit built for this purpose, and sample results are presented to verify the proposed model. The aim is to confirm that both the constant properties and temperature-dependent properties models, besides available correlations previously established for ordinary fluids, provide adequate prediction of the heat transfer enhancement observed in laminar forced convection with such nanofluids and within the experimented Reynolds number range.Indisponível

Unraveling structural and compositional information in 3D FinFET electronic devices

Non-planar Fin Field Effect Transistors (FinFET) are already present in modern devices. The evolution from the well-established 2D planar technology to the design of 3D nanostructures rose new fabrication processes, but a technique capable of full characterization, particularly their dopant distribution, in a representative (high statistics) way is still lacking. Here we propose a methodology based on Medium Energy Ion Scattering (MEIS) to address this query, allowing structural and compositional quantification of advanced 3D FinFET devices with nanometer spatial resolution. When ions are backscattered, their energy losses unfold the chemistry of the different 3D compounds present in the structure. The FinFET periodicity generates oscillatory features as a function of backscattered ion energy and, in fact, these features allow a complete description of the device dimensions. Additionally, each measurement is performed over more than thousand structures, being highly representative in a statistical meaning. Finally, independent measurements using electron microscopy corroborate the proposed methodolog

Uso da Espectroscopia Raman e FT-IR na caracterização do biocarvão em Latossolo Amarelo da Amazônia Central

The Amazonian Latosols are acidic soils shows low activity in clay minerals. However, it is also found anthropogenic soils known as Amazonian Dark Earth (EAD) that provides a potential to develop a sustainable system in agriculture. The majority of TPI soils show fragments of black carbon stemming from an anthropic activity. The presence of these fragments endows the improvements in the physic and chemical characteristics of the soil. In order to reproduce some characteristics of these anthropogenic soils, it is proposed to apply biochar (BC) in a dystrophic Yellow Oxisol in increasing doses from 0; 40; 80 and 120 t.ha-1. The use of Spectroscopy FT-IR and Raman tools and technics can elucidate on the nature of the pyrolised biomass and likewise interfere on the fertility of the soil. Furthermore, it could clarify how the BC contributes to the increase of cation exchange capacity (CEC), the elucidation of its chemical characteristics and how it can act in the development of a sustainable agriculture model for the humid tropics. It was possible to observe that he FT-IR spectra were similar between the treatments and that the BC exhibits similar crystallinity to the carbons of Amazonian Dark Earth

Immobilized TiO2 on glass spheres applied to heterogeneous photocatalysis: photoactivity, leaching and regeneration process

Heterogeneous photocatalysis using titanium dioxide as catalyst is an attractive advanced oxidation process due to its high chemical stability, good performance and low cost. When immobilized in a supporting material, additional benefits are achieved in the treatment. The purpose of this study was to develop a simple protocol for impregnation of TiO2-P25 on borosilicate glass spheres and evaluate its efficiency in the photocatalytic degradation using an oxidizable substrate (methylene blue), in a Compound Parabolic Concentrator (CPC) reactor. The assays were conducted at lab-scale using radiation, which simulated the solar spectrum. TiO2 leaching from the glass and the catalyst regeneration were both demonstrated. A very low leaching ratio (0.03%) was observed after 24 h of treatment, suggesting that deposition of TiO2 resulted in good adhesion and stability of the photocatalyst on the surface of borosilicate. This deposition was successfully achieved after calcination of the photocatalyst at 400 °C (TiO2-400 °C). The TiO2 film was immobilized on glass spheres and the powder was characterized by scanning electron microscopy (SEM), X-ray diffraction and BET. This characterization suggested that thermal treatment did not introduce substantial changes in the measured microstructural characteristics of the photocatalyst. The immobilized photocatalyst degraded more than 96% of the MB in up to 90 min of reaction. The photocatalytic activity decreased after four photocatalytic cycles, but it was recovered by the removal of contaminants adsorbed on the active sites after washing in water under UV-Vis irradiation. Based on these results, the TiO2-400 °C coated on glass spheres is potentially a very attractive option for removal of persistent contaminants present in the environment

Preparation and characterization of well-ordered MoOx films on Cu3Au(1 0 0)–oxygen substrate (CAOS)

5 p. : il.The goal of this work is to prepare well-ordered molybdenum oxide films using oxygen implanted Cu3Au(1 0 0) substrate (CAOS, Cu3Au– Oxygen Substrate) and identify the structure of the different oxide phases. Those films were grown on an UHV chamber (2 x 10=¹º mbar background pressure) and prepared by electron beam deposition. The structure of the films was studied using low energy electron diffraction (LEED), scanning tunnelling microscopy (STM), and X-ray photoelectron spectroscopy (XPS). The ultra thin molybdenum film shows the formation of an oxide layer with hexagonal symmetry plus a square lattice. The hexagonal mesh units are rotated by 908 (or 308) with respect to one another. Based on XPS data, the Mo cations are in an oxidation state that ranges from 4+ to 6+. STM results show the presence of hexagonal islands formed over a square symmetry phase

Early stages of vanadium deposition on Si(111)-7 x 7

4 p. : il.We investigate the low-coverage regime of vanadium deposition on the Si(111)-7 x 7 surface using a combination of scanning tunnelling microscopy (STM) and density-functional theory (DFT) adsorption energy calculations. We theoretically identify the most stable structures in this system: (i) substitutional vanadium atoms at silicon adatom positions; (ii) interstitial vanadium atoms between silicon adatoms and rest atoms; and (iii) interstitial vanadium – silicon adatom vacancy complexes. STM images reveal two simple vanadium-related features near the Si adatom positions: bright spots at both polarities (BB) and dark spots for empty and bright spots for filled states (DB). We relate the BB spots to the interstitial structures and the DB spots to substitutional structures

Electrochemical Analysis of Free Glycerol in Biodiesel Using Reduced Graphene Oxide and Gold/Palladium Core-Shell Nanoparticles Modified Glassy Carbon Electrode

Glycerol is a major byproduct obtained in the production of biodiesel, an important renewable fuel. The presence of free glycerol in fuel can have structural and performance consequences with respect to the engine, making fuel quality control important. The standard method to analyze glycerol in biodiesel is gas chromatography, a time-consuming and expensive technique. In this context, an electrode based on glassy carbon electrodes (GCEs) modified with reduced graphene oxide and core-shell gold@palladium nanoparticles was developed for the determination of glycerol in biodiesel. The free glycerol analysis was performed in the aqueous phase obtained by liquid–liquid extraction from a biodiesel sample. Cyclic voltammetry was chosen as the method for glycerol electrochemical analysis to regenerate active sites and promote greater sensor stability. The modified Au@Pd/rGO/GCE electrode showed an excellent performance, obtaining a linear range of 18.2 to 109 µmol L−1 with a correlation coefficient of 0.9895, limits of detection and quantification of 5.33 and 17.6 µmol L−1, respectively, high stability during 1000 cycles, and recovery values of 86% and 87% in the quantification of glycerol in biodiesel samples. The proposed method proved to be a great alternative for the analysis of glycerol in biodiesel, being a fast, sensitive, and low-cost technique due to its high stability and the use of small quantities of reagents

Measuring the strength of interaction between the Ebola fusion peptide and lipid rafts: implications for membrane fusion and virus infection.

The Ebola fusion peptide (EBO₁₆) is a hydrophobic domain that belongs to the GP2 membrane fusion protein of the Ebola virus. It adopts a helical structure in the presence of mimetic membranes that is stabilized by the presence of an aromatic-aromatic interaction established by Trp8 and Phe12. In spite of its infectious cycle becoming better understood recently, several steps still remain unclear, a lacuna that makes it difficult to develop strategies to block infection. In order to gain insight into the mechanism of membrane fusion, we probed the structure, function and energetics of EBO₁₆ and its mutant W8A, in the absence or presence of different lipid membranes, including isolated domain-resistant membranes (DRM), a good experimental model for lipid rafts. The depletion of cholesterol from living mammalian cells reduced the ability of EBO₁₆ to induce lipid mixing. On the other hand, EBO₁₆ was structurally sensitive to interaction with lipid rafts (DRMs), but the same was not observed for W8A mutant. In agreement with these data, W8A showed a poor ability to promote membrane aggregation in comparison to EBO₁₆. Single molecule AFM experiments showed a high affinity force pattern for the interaction of EBO₁₆ and DRM, which seems to be a complex energetic event as observed by the calorimetric profile. Our study is the first to show a strong correlation between the initial step of Ebola virus infection and cholesterol, thus providing a rationale for Ebola virus proteins being co-localized with lipid-raft domains. In all, the results show how small fusion peptide sequences have evolved to adopt highly specific and strong interactions with membrane domains. Such features suggest these processes are excellent targets for therapeutic and vaccine approaches to viral diseases

Electron Microscopy and Spectroscopy Analysis of Carbon Nanostructures in Highly Fertile Amazonian Anthrosoils

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012. © 2012, Microscopy Society of America. All rights reserved

Residual stress measurements by x-ray diffraction : critical evaluation of error sources [Slides]

24 slidesNacional round robin for residual stress measurements