Scaling of the elastic contribution to the surface free energy of a nematic liquid crystal on a sawtoothed substrate

We characterize the elastic contribution to the surface free energy of a nematic liquid crystal in the presence of a sawtooth substrate. Our findings are based on numerical minimization of the Landau-de Gennes model and analytical calculations on the Frank-Oseen theory. The nucleation of disclination lines (characterized by non-half-integer winding numbers) in the wedges and apexes of the substrate induces a leading order proportional to q ln q to the elastic contribution to the surface free-energy density, with q being the wave number associated with the substrate periodicity.

Die Surface Designer System

This paper defines Die Surface Designer (DSD) System for fast draw die in the product development feasibility phase on surfaces coming from styling. We propose a CAD integration, for better support the design process in industry, particularly on the development of new products in automotive sector. The DSD system intends to reduce the lead time by providing and integrating flexible and efficient capabilities for testing early concepts from surface analysis points of view in automotive product development.

Eliminação do Cr(VI) na fase de neutralização de um efluente industrial proveniente de processos de galvanoplastia

A presente tese teve por base a identificação e resolução de um problema existente no tratamento de efluentes provenientes dos processos de tratamento de superfícies por galvanoplastia, na OGMA – Indústria Aeronáutica de Portugal S.A.. Observou-se a ocorrência, esporádica, de crómio hexavalente, (Cr (VI)), em valor superior ao valor limite de emissão (VLE). Os resultados foram monitorizados e os dados recolhidos no decorrer da actividade de tratamento de efluentes, durante o período de, aproximadamente, 5 anos (2006 a 2011). A recolha de resultados decorreu no âmbito da actividade profissional da mestranda, que, para além da responsabilidade técnica dos processos de galvanoplastia na empresa, é também responsável pelo suporte técnico ao processo de tratamento de efluentes resultantes da actividade de tratamento de superficies por processos de galvanoplastia. A empresa OGMA – Indústria Aeronáutica de Portugal S.A., é uma empresa de actividade aeronáutica dedicada à Fabricação e Manutenção de aeronaves, nomeadamente a prestação de serviços de Manutenção, Revisão e Modernização de, Aeronaves, Motores e Componentes, bem como Fabricação e Montagem de Aeroestruturas. Integrada na OGMA, S.A. encontra-se a área de tratamentos electroquímicos, onde são realizados processos de tratamento de materiais metálicos por electrodeposição, deposição química e conversão química. Desta actividade resulta uma quantidade considerável de efluentes líquidos que necessitam de tratamento adequado previamente à sua descarga em cursos de água. Devido ao tipo de contaminantes que estes efluentes possuem, o tratamento dos mesmos é realizado em várias etapas, passando pela oxidação de cianetos, a redução de cromatos e a neutralização. Posteriormente segue-se uma sedimentação e a remoção de lamas. De modo a garantir um controlo dos parâmetros de descarga dos efluentes tratados, de acordo com a legislação ambiental em vigor, o efluente obtido é analisado periodicamente em laboratório acreditado. Na perspectiva de solucionar o problema em questão, procedeu-se à realização de ensaios experimentais utilizando os efluentes provenientes dos tanques de reacção da redução de cromatos e da oxidação de cianetos da linha com cádmio, com especial incidência na variação dos intervalos de pH recomendados para cada uma das fases do tratamento de efluentes, e observação do comportamento das misturas em termos de presença de Cr (VI), quando sujeitos a variações de pH. Após análise dos dados disponíveis e realização de todos os ensaios, conclui-se que, o processo de oxidação de cianeto da linha com cádmio e o processo de redução de cromatos na mesma linha estão a funcionar adequadamente. Concluiu-se que o reaparecimento de Cr (VI) ocorre devido à existência de hipoclorito de sódio, em excesso, no tanque de oxidação de cianeto que, quando passa para o tanque de neutralização e entra em contacto com o efluente proveniente do tanque de redução de cromatos, oxida parte do crómio trivalente, (Cr (III)), existente, a Cr (VI). Para impedir a ocorrência deste fenómeno separou-se todo o efluente contendo crómio que passou a ser tratado na linha de tratamento de efluentes isenta de cádmio, não entrando assim em contacto com o efluente que contém hipoclorito não reagido, evitando a oxidação do Cr (III) a Cr (VI).

CVD of CrO(2): Towards a lower temperature deposition process

The deposition of highly oriented a-axis CrO(2) films onto Al(2)O(3)(0001) by atmospheric pressure (AP)CVD at temperatures as low as 330 C is reported. Deposition rates strongly depend on the substrate temperature, whereas for film surface microstructures the dependence is mainly on film thickness. For the experimental conditions used in this work, CrO(2) growth kinetics are dominated by a surface reaction mechanism with an apparent activation energy of (121.0 +/- 4.3) kJ mol(-1). The magnitude and temperature dependence of the saturation magnetization, up to room temperature, is consistent with bulk measurements.

Influence of growth temperature and carrier flux on the structure and transport properties of highly oriented CrO2 on Al2O3 (0001)

In this work we report on the structure and magnetic and electrical transport properties of CrO2 films deposited onto (0001) sapphire by atmospheric pressure (AP)CVD from a CrO3 precursor. Films are grown within a broad range of deposition temperatures, from 320 to 410 degrees C, and oxygen carrier gas flow rates of 50-500 seem, showing that it is viable to grow highly oriented a-axis CrO2 films at temperatures as low as 330 degrees C i.e., 60-70 degrees C lower than is reported in published data for the same chemical system. Depending on the experimental conditions, growth kinetic regimes dominated either by surface reaction or by mass-transport mechanisms are identified. The growth of a Cr2O3 interfacial layer as an intrinsic feature of the deposition process is studied and discussed. Films synthesized at 330 degrees C keep the same high quality magnetic and transport properties as those deposited at higher temperatures.

Structural and Microanalytical Studies of CrO2 Thin Films on c-Sapphire by High Resolution Electron Microscopy Methods

Chromium dioxide (CrO2) has been extensively used in the magnetic recording industry. However, it is its ferromagnetic half-metallic nature that has more recently attracted much attention, primarily for the development of spintronic devices. CrO2 is the only stoichiometric binary oxide theoretically predicted to be fully spin polarized at the Fermi level. It presents a Curie temperature of ∼ 396 K, i.e. well above room temperature, and a magnetic moment of 2 mB per formula unit. However an antiferromagnetic native insulating layer of Cr2O3 is always present on the CrO2 surface which enhances the CrO2 magnetoresistance and might be used as a barrier in magnetic tunnel junctions.

Comparison of deposited surface area of airborne ultrafine particles generated from two welding processes

This article describes work performed on the assessment of the levels of airborne ultrafine particles emitted in two welding processes metal-active gas (MAG) of carbon steel and friction-stir welding (FSW) of aluminium in terms of deposited area in alveolar tract of the lung using a nanoparticle surface area monitor analyser. The obtained results showed the dependence from process parameters on emitted ultrafine particles and clearly demonstrated the presence of ultrafine particles, when compared with background levels. The obtained results showed that the process that results on the lower levels of alveolar-deposited surface area is FSW, unlike MAG. Nevertheless, all the tested processes resulted in important doses of ultrafine particles that are to be deposited in the human lung of exposed workers.

Nanofiltration of surface water for the removal of endocrine disruptors

The assessment of surface water nanofiltration (NF) for the removal of endocrine disruptors (EDs) Nonylphenol Ethoxylate (IGEPAL), 4-Nonylphenol (NP) and 4-Octylphenol (OP) was carried out with three commercial NF membranes - NF90, NF200, NF270. The permeation experiments were conducted in laboratory flat-cell units of 13.2 x 10(-4) m(2) of surface area and in a DSS Lab-unit M20 with a membrane surface area of 0.036 m2. The membranes hydraulic permeabilities ranged from 3.7 to 15.6 kg/h/m(2)/bar and the rejection coefficients to NaCl, Na2SO4 and Glucose are for NF90: 97%, 99% and 97%, respectively; for NF200: 66%, 98% and 90%, respectively and for NF270: 48%, 94% and 84%, respectively. Three sets of nanofiltration experiments were carried out: i) NF of aqueous model solutions of NP, IGEPAL and OP running in total recirculation mode; ii) NF of surface water from Rio Sado (Settibal, Portugal) running in concentration mode; iii) NF of surface water from Rio Sado inoculated with NP, IGEPAL and OP running in concentration mode. The results of model solutions experiments showed that the EDs rejection coefficients are approximately 100% for all the membranes. The results obtained for the surface water showed that the rejection coefficients to natural organic Matter (NOM) are 94%, 82% and 78% for NF90, NF200 and NF 270 membranes respectively, with and without inoculation of EDs. The rejection coefficients to EDs in surface water with and without inoculation of EDs are 100%, showing that there is a fraction of NOM of high molecular weight that retains the EDs in the concentrate and that there is a fraction of NOM of low molecular weight that permeates through the NF membranes free of EDs.

Diffuse liver disease classification from ultrasound surface characterization, clinical and laboratorial data

In this work liver contour is semi-automatically segmented and quantified in order to help the identification and diagnosis of diffuse liver disease. The features extracted from the liver contour are jointly used with clinical and laboratorial data in the staging process. The classification results of a support vector machine, a Bayesian and a k-nearest neighbor classifier are compared. A population of 88 patients at five different stages of diffuse liver disease and a leave-one-out cross-validation strategy are used in the classification process. The best results are obtained using the k-nearest neighbor classifier, with an overall accuracy of 80.68%. The good performance of the proposed method shows a reliable indicator that can improve the information in the staging of diffuse liver disease.

Nanotech thin film photovoltaics

Trabalho Final de Mestrado para obtenção do grau de Mestre em Engenharia de Electrónica e Telecomunicações

Monitorization of alveolar deposited surface area of nanoparticles and ultrafine particles in different environments

Nanotechnology is an important emerging industry with a projected annual market of around one trillion dollars by 2015. It involves the control of atoms and molecules to create new materials with a variety of useful functions. Although there are advantages on the utilization of these nano-scale materials, questions related with its impact over the environment and human health must be addressed too, so that potential risks can be limited at early stages of development. At this time, occupational health risks associated with manufacturing and use of nanoparticles are not yet clearly understood. However, workers may be exposed to nanoparticles through inhalation at levels that can greatly exceed ambient concentrations. Current workplace exposure limits are based on particle mass, but this criteria could not be adequate in this case as nanoparticles are characterized by very large surface area, which has been pointed out as the distinctive characteristic that could even turn out an inert substance into another substance exhibiting very different interactions with biological fluids and cells. Therefore, it seems that, when assessing human exposure based on the mass concentration of particles, which is widely adopted for particles over 1 μm, would not work in this particular case. In fact, nanoparticles have far more surface area for the equivalent mass of larger particles, which increases the chance they may react with body tissues. Thus, it has been claimed that surface area should be used for nanoparticle exposure and dosing. As a result, assessing exposure based on the measurement of particle surface area is of increasing interest. It is well known that lung deposition is the most efficient way for airborne particles to enter the body and cause adverse health effects. If nanoparticles can deposit in the lung and remain there, have an active surface chemistry and interact with the body, then, there is potential for exposure. It was showed that surface area plays an important role in the toxicity of nanoparticles and this is the metric that best correlates with particle-induced adverse health effects. The potential for adverse health effects seems to be directly proportional to particle surface area. The objective of the study is to identify and validate methods and tools for measuring nanoparticles during production, manipulation and use of nanomaterials.

Study of Annealed Indium Tin Oxide-Films prepared by RF Reactive Magnetron Sputtering

Tin doped indium oxide (ITO) films were deposited on glass substrates by rf reactive magnetron sputtering using a metallic alloy target (In-Sn, 90-10). The post-deposition annealing has been done for ITO films in air and the effect of annealing temperature on the electrical, optical and structural properties of ITO films was studied. It has been found that the increase of the annealing temperature will improve the film electrical properties. The resistivity of as deposited film is about 1.3 x 10(-1) Omega*cm and decreases down to 6.9 x 10(-3) Omega*cm as the annealing temperature is increased up to 500 degrees C. In addition, the annealing will also increase the film surface roughness which can improve the efficiency of amorphous silicon solar cells by increasing the amount of light trapping.

Electrodeposition and characterization of nickel–copper metallic foams for application as electrodes for supercapacitors

Nickel-copper metallic foams were electrodeposited from an acidic electrolyte, using hydrogen bubble evolution as a dynamic template. Their morphology and chemical composition was studied by scanning electron microscopy and related to the deposition parameters (applied current density and deposition time). For high currents densities (above 1 A cm(-2)) the nickel-copper deposits have a three-dimensional foam-like morphology with randomly distributed nearly-circular pores whose walls present an open dendritic structure. The nickel-copper foams are crystalline and composed of pure nickel and a copper-rich phase containing nickel in solid solution. The electrochemical behaviour of the material was studied by cyclic voltammetry and chronopotentiometry (charge-discharge curves) aiming at its application as a positive electrode for supercapacitors. Cyclic voltammograms showed that the Ni-Cu foams have a pseudocapacitive behaviour. The specific capacitance was calculated from charge-discharge data and the best value (105 F g(-1) at 1 mA cm(-2)) was obtained for nickel-copper foams deposited at 1.8 A cm(-2) for 180 s. Cycling stability of these foams was also assessed and they present a 90 % capacitance retention after 10,000 cycles at 10 mA cm(-2).

Electrodeposition and characterization of nikel-copper metallic foams for application as electrodes for supercapacitors

Nickel-copper metallic foams were electrodeposited from an acidic electrolyte, using hydrogen bubble evolution as a dynamic template. Their morphology and chemical composition was studied by scanning electron microscopy and related to the deposition parameters (applied current density and deposition time). For high currents densities (above 1 A cm(-2)) the nickel-copper deposits have a three-dimensional foam-like morphology with randomly distributed nearly-circular pores whose walls present an open dendritic structure. The nickel-copper foams are crystalline and composed of pure nickel and a copper-rich phase containing nickel in solid solution. The electrochemical behaviour of the material was studied by cyclic voltammetry and chronopotentiometry (charge-discharge curves) aiming at its application as a positive electrode for supercapacitors. Cyclic voltammograms showed that the Ni-Cu foams have a pseudocapacitive behaviour. The specific capacitance was calculated from charge-discharge data and the best value (105 F g(-1) at 1 mA cm(-2)) was obtained for nickel-copper foams deposited at 1.8 A cm(-2) for 180 s. Cycling stability of these foams was also assessed and they present a 90 % capacitance retention after 10,000 cycles at 10 mA cm(-2).

Emissions of nanoparticles during friction stir welding (FSW) of aluminium alloys

Friction stir welding (FSW) is now well established as a welding process capable of joining some different types of metallic materials, as it was (1) found to be a reliable and economical way of producing high quality welds, and (2) considered a "clean" welding process that does not involve fusion of metal, as is the case with other traditional welding processes. The aim of this study was to determine whether the emission of particles during FSW in the nanorange of the most commonly used aluminum (Al) alloys, AA 5083 and AA 6082, originated from the Al alloy itself due to friction of the welding tool against the item that was being welded. Another goal was to measure Al alloys in the alveolar deposited surface area during FSW. Nanoparticles dimensions were predominantly in the 40- and 70-nm range. This study demonstrated that microparticles were also emitted during FSW but due to tool wear. However, the biological relevance and toxic manifestations of these microparticles remain to be determined.