Comportamiento mecánico de nuevas aleaciones de wolframio en función de la temperatura

La presente memoria de tesis tiene como objetivo principal la caracterización mecánica en función de la temperatura de nueve aleaciones de wolframio con contenidos diferentes en titanio, vanadio, itria y lantana. Las aleaciones estudiadas son las siguientes: W-0.5%Y2O3, W-2%Ti, W-2% Ti-0.5% Y2O3, W-4% Ti-0.5% Y2O3, W-2%V, W- 2%Vmix, W-4%V, W-1%La2O3 and W-4%V-1%La2O3. Todos ellos, además del wolframio puro se fabrican mediante compresión isostática en caliente (HIP) y son suministradas por la Universidad Carlos III de Madrid. La investigación se desarrolla a través de un estudio sistemático basado en ensayos físicos y mecánicos, así como el análisis post mortem de las muestras ensayadas. Para realizar dicha caracterización mecánica se aplican diferentes ensayos mecánicos, la mayoría de ellos realizados en el intervalo de temperatura de 25 a 1000 º C. Los ensayos de caracterización que se llevan a cabo son: • Densidad • Dureza Vicker • Módulo de elasticidad y su evolución con la temperatura • Límite elástico o resistencia a la flexión máxima, y su evolución con la temperatura • Resistencia a la fractura y su comportamiento con la temperatura. • Análisis microestructural • Análisis fractográfico • Análisis de la relación microestructura-comportamiento macroscópico. El estudio comienza con una introducción acerca de los sistemas en los que estos materiales son candidatos para su aplicación, para comprender las condiciones a las que los materiales serán expuestos. En este caso, el componente que determina las condiciones es el Divertor del reactor de energía de fusión por confinamiento magnético. Parece obvio que su uso en los componentes del reactor de fusión, más exactamente como materiales de cara al plasma (Plasma Facing Components o PFC), hace que estas aleaciones trabajen bajo condiciones de irradiación de neutrones. Además, el hecho de que sean materiales nuevos hace necesario un estudio previo de las características básicas que garantice los requisitos mínimos antes de realizar un estudio más complejo. Esto constituye la principal motivación de la presente investigación. La actual crisis energética ha llevado a aunar esfuerzos en el desarrollo de nuevos materiales, técnicas y dispositivos para la aplicación en la industria de la energía nuclear. El desarrollo de las técnicas de producción de aleaciones de wolframio, con un punto de fusión muy alto, requiere el uso de precursores de sinterizado para lograr densificaciones más altas y por lo tanto mejores propiedades mecánicas. Este es el propósito de la adición de titanio y vanadio en estas aleaciones. Sin embargo, uno de los principales problemas de la utilización de wolframio como material estructural es su alta temperatura de transición dúctil-frágil. Esta temperatura es característica de materiales metálicos con estructura cúbica centrada en el cuerpo y depende de varios factores metalúrgicos. El proceso de recristalización aumenta esta temperatura de transición. Los PFC tienen temperaturas muy altas de servicio, lo que facilita la recristalización del metal. Con el fin de retrasar este proceso, se dispersan partículas insolubles en el material permitiendo temperaturas de servicio más altas. Hasta ahora se ha utilizado óxidos de torio, lantano e itrio como partículas dispersas. Para entender cómo los contenidos en algunos elementos y partículas de óxido afectan a las propiedades de wolframio se estudian las aleaciones binarias de wolframio en comparación con el wolframio puro. A su vez estas aleaciones binarias se utilizan como material de referencia para entender el comportamiento de las aleaciones ternarias. Dada la estrecha relación entre las propiedades del material, la estructura y proceso de fabricación, el estudio se completa con un análisis fractográfico y micrográfico. El análisis fractográfico puede mostrar los mecanismos que están implicados en el proceso de fractura del material. Por otro lado, el estudio micrográfico ayudará a entender este comportamiento a través de la identificación de las posibles fases presentes. La medida del tamaño de grano es una parte de la caracterización microestructural. En esta investigación, la medida del tamaño de grano se llevó a cabo por ataque químico selectivo para revelar el límite de grano en las muestras preparadas. Posteriormente las micrografías fueron sometidas a tratamiento y análisis de imágenes. El documento termina con una discusión de los resultados y la compilación de las conclusiones más importantes que se alcanzan después del estudio. Actualmente, el desarrollo de nuevos materiales para aplicación en los componentes de cara al plasma continúa. El estudio de estos materiales ayudará a completar una base de datos de características que permita hacer una selección de ellos más fiable. The main goal of this dissertation is the mechanical characterization as a function of temperature of nine tungsten alloys containing different amounts of titanium, vanadium and yttrium and lanthanum oxide. The alloys under study were the following ones: W-0.5%Y2O3, W-2%Ti, W-2% Ti-0.5% Y2O3, W-4% Ti-0.5% Y2O3, W-2%V, W- 2%Vmix, W-4%V, W-1%La2O3 and W-4%V-1%La2O3. All of them, besides pure tungsten, were manufactured using a Hot Isostatic Pressing (HIP) process and they were supplied by the Universidad Carlos III de Madrid. The research was carried out through a systematic study based on physical and mechanical tests as well as the post mortem analysis of tested samples. Diverse mechanical tests were applied to perform this characterization; most of them were conducted at temperatures in the range 25-1000 ºC. The following characterization tests were performed: • Density • Vickers hardness • Elastic modulus • Yield strength or ultimate bending strength, and their evolution with temperature • Fracture toughness and its temperature behavior • Microstructural analysis • Fractographical analysis • Microstructure-macroscopic relationship analysis This study begins with an introduction regarding the systems where these materials could be applied, in order to establish and understand their service conditions. In this case, the component that defines the conditions is the Divertor of magnetic-confinement fusion reactors. It seems obvious that their use as fusion reactor components, more exactly as plasma facing components (PFCs), makes these alloys work under conditions of neutron irradiation. In addition to this, the fact that they are novel materials demands a preliminary study of the basic characteristics which will guarantee their minimum requirements prior to a more complex study. This constitutes the motivation of the present research. The current energy crisis has driven to join forces so as to develop new materials, techniques and devices for their application in the nuclear energy industry. The development of production techniques for tungsten-based alloys, with a very high melting point, requires the use of precursors for sintering to achieve higher densifications and, accordingly, better mechanical properties. This is the purpose of the addition of titanium and vanadium to these alloys. Nevertheless, one of the main problems of using tungsten as structural material is its high ductile-brittle transition temperature. This temperature is characteristic of metallic materials with body centered cubic structure and depends on several metallurgical factors. The recrystallization process increases their transition temperature. Since PFCs have a very high service temperature, this facilitates the metal recrystallization. In order to inhibit this process, insoluble particles are dispersed in the material allowing higher service temperatures. So far, oxides of thorium, lanthanum and yttrium have been used as dispersed particles. Tungsten binary alloys are studied in comparison with pure tungsten to understand how the contents of some elements and oxide particles affect tungsten properties. In turn, these binary alloys are used as reference materials to understand the behavior of ternary alloys. Given the close relationship between the material properties, structure and manufacturing process, this research is completed with a fractographical and micrographic analysis. The fractographical analysis is aimed to show the mechanisms that are involved in the process of the material fracture. Besides, the micrographic study will help to understand this behavior through the identification of present phases. The grain size measurement is a crucial part of the microstructural characterization. In this work, the measurement of grain size was carried out by chemical selective etching to reveal the boundary grain on prepared samples. Afterwards, micrographs were subjected to both treatment and image analysis. The dissertation ends with a discussion of results and the compilation of the most important conclusions reached through this work. The development of new materials for plasma facing components application is still under study. The analysis of these materials will help to complete a database of the features that will allow a more reliable materials selection.

In situ atomic force microscopy study of Alzheimer’s β-amyloid peptide on different substrates: New insights into mechanism of β-sheet formation

We have applied in situ atomic force microscopy to directly observe the aggregation of Alzheimer’s β-amyloid peptide (Aβ) in contact with two model solid surfaces: hydrophilic mica and hydrophobic graphite. The time course of aggregation was followed by continuous imaging of surfaces remaining in contact with 10–500 μM solutions of Aβ in PBS (pH 7.4). Visualization of fragile nanoscale aggregates of Aβ was made possible by the application of a tapping mode of imaging, which minimizes the lateral forces between the probe tip and the sample. The size and the shape of Aβ aggregates, as well as the kinetics of their formation, exhibited pronounced dependence on the physicochemical nature of the surface. On hydrophilic mica, Aβ formed particulate, pseudomicellar aggregates, which at higher Aβ concentration had the tendency to form linear assemblies, reminiscent of protofibrillar species described recently in the literature. In contrast, on hydrophobic graphite Aβ formed uniform, elongated sheets. The dimensions of those sheets were consistent with the dimensions of β-sheets with extended peptide chains perpendicular to the long axis of the aggregate. The sheets of Aβ were oriented along three directions at 120° to each other, resembling the crystallographic symmetry of a graphite surface. Such substrate-templated self-assembly may be the distinguishing feature of β-sheets in comparison with α-helices. These studies show that in situ atomic force microscopy enables direct assessment of amyloid aggregation in physiological fluids and suggest that Aβ fibril formation may be driven by interactions at the interface of aqueous solutions and hydrophobic substrates, as occurs in membranes and lipoprotein particles in vivo.

Polpa de guavira (Campomanesia cambessedeana Berg) desidratada em spray dryer: efeitos das condições de processo e composição da alimentação nas propriedades físico químicas e atividade antioxidante

O objetivo desse trabalho foi obter polpa de guavira desidratada por atomização, utilizando maltodextrina ou goma arábica como agentes carreadores. Inicialmente, avaliou-se a influência das condições de processo, temperatura do ar de secagem (130, 155 e 180) °C e vazão volumétrica da mistura (20 e 40) mL/min, o tipo e concentração de agente carreador (10 e 20) % nas características físicas, físico-químicas e atividade antioxidante do produto obtido. As propriedades analisadas foram umidade, atividade de água, higroscopicidade, solubilidade, cor, distribuição e tamanho médio de partículas, morfologia, compostos fenólicos totais e atividade antioxidante. A temperatura do ar de secagem e a vazão volumétrica de alimentação influenciaram significativamente todas as propriedades da guavira em pó. A umidade e atividade de água apresentaram os menores valores na temperatura intermediária, independentemente do tipo e concentração do carreador usado. A solubilidade das amostras adicionadas de maltodextrina foram superiores às amostras com goma arábica. O aumento da concentração de agente carreador, em geral, proporcionou um aumento no parâmetro L* e diminuição dos parâmetros a* e b*, tornando as amostras mais claras e reduzindo as tonalidades vermelha e amarela. A guavira em pó apresentou coloração próxima do amarelo e marrom, com grande variação nos parâmetros de cor C* e H* em função das diferentes condições de secagem. A distribuição do tamanho de partículas não teve um padrão definido e o tamanho médio das amostras com maltodextrina foram maiores do que as com goma arábica para a temperatura do ar a 130 °C. No entanto, para as outras temperaturas (155 e 180) °C não houve um comportamento específico do tamanho das partículas em função da vazão de alimentação, tipo e ou concentração de agente carreador. A análise de microscopia eletrônica de varredura permitiu observar que as partículas obtidas tanto com maltodextrina como goma arábica apresentaram formato esférico, superfície rugosa e com adesão de partículas menores nas de maior tamanho, sendo que a superfície das partículas com goma arábica também apresentaram concavidades. A atividade antioxidante foi superior quando utilizada a temperatura de secagem intermediária. A partir das condições selecionadas na primeira etapa (temperatura do ar de 155 °C, vazão volumétrica da mistura de 40 mL/min e 10% de maltodextrina ou goma arábica) a polpa de guavira em pó foi caracterizada quanto a temperatura de transição vítrea, as isotermas de adsorção e a estabilidade à estocagem do ácido ascórbico, compostos fenólicos totais e da atividade antioxidante da polpa de guavira em pó produzida por spray drying ao longo de 120 dias. As temperaturas de transição vítrea foram de (25,2 ± 2,7 °C e 31,4 ± 0,4) °C para os pós produzidos com goma arábica e maltodextrina, respectivamente. O modelo de BET apresentou ajuste muito bom (R2>0,99) para descrever o comportamento de sorção de água das amostras nas temperaturas de (20, 30 e 40) °C. A polpa de guavira em pó produzida com goma arábica apresentou maior adsorção de água do que as amostras obtidas com maltodextrina. No estudo da estabilidade, as amostras foram acondicionadas em embalagem de polietileno laminado e armazenadas a 25 °C e umidade relativa de 75%. A embalagem de polietileno laminado foi eficiente na manutenção do teor de ácido ascórbico e atividade antioxidante da guavira em pó por um período de 120 dias, independente do carreador adicionado. O teor de compostos fenólicos para a guavira em pó com goma arábica apresentou uma redução nos primeiros 22 dias, contudo a amostra com maltodextrina manteve-se estável durante 120 dias de armazenamento.

Da tradução ou não de pronomes e partículas pronominais do Italiano ao Português: algumas escolhas feitas por dois tradutores

Este estudo é movido pela curiosidade quanto a como se resolvem, nas traduções do italiano para o português, questões de colocação pronominal. Encontramos, normal e frequentemente, na língua italiana, principalmente na língua falada, pronomes cujos equivalentes em português existem em gramáticas normativas da língua portuguesa, mas que, na prática, não são utilizados pelos falantes e escritores brasileiros. Encontramos, também, na língua italiana, um significativo número de verbos pronominais (como esserci, volerci, averne etc.) e um considerável número de verbos pronominais múltiplos (como andarsene, farcela, fregarsene etc.) que, juntamente com esses pronomes, constituem, para os professores brasileiros de italiano língua estrangeira (LE), elementos difíceis de trabalhar na sala de aula. Além disso, tais elementos também podem dificultar o trabalho dos tradutores, que devem fazer determinadas escolhas ao traduzi-los para o português. Como são traduzidos os pronomes combinados do italiano nas versões brasileiras? Será que os portugueses, que possuem, por exemplo, tais pronomes utilizam-nos em todos os casos em que os encontramos nos textos de partida? E as partículas pronominais são simplesmente eliminadas no texto de chegada ou são substituídas? Tais aspectos, se observados e organizados, podem levar a uma melhor compreensão das duas línguas em contato e dar subsídios a estudantes, professores e tradutores. Pensando nessa dificuldade, esta pesquisa buscou e listou alguns autores e obras disponíveis para consulta e analisou um corpus com cento e sessenta e três ocorrências de pronomes no italiano, mais sete acréscimos de pronomes no português brasileiro (PB) e/ou português europeu (PE), partindo do romance Uno, nessuno e centomila de Luigi Pirandello e suas respectivas traduções em PB e PE. Nosso objetivo consiste em encontrar respostas úteis à diminuição do estranhamento, por parte de um italiano, que escuta, de um brasileiro, frases sem pronomes (ainda que o italiano as entenda) e/ou a sensação de inadequação e, até mesmo, de desconforto, por parte de um brasileiro, ao produzir frases com todos os pronomes. No corpus analisado, temos uma amostra das escolhas e respectivas traduções propostas pelos tradutores para casos de pronomes reflexivos, de pronomes pessoais do caso reto, de pronomes pessoais do caso oblíquo, de pronomes combinados e de partículas pronominais ne, ci e vi, com manutenções, omissões, trocas por outros pronomes (possessivos, retos, oblíquos, demonstrativos) e, até mesmo, uma espécie de compensação numérica com a inclusão de palavra inexistente no texto de partida.

Resistência à abrasão de aço Hadfield para britadores: efeito do tamanho do abrasivo e do pH do meio.

Neste trabalho, foi investigado o efeito do tamanho do abrasivo e do pH do meio na resistência ao desgaste abrasivo do aço H-13 com matriz martensítica e do aço Hadfield com matriz austenítica. Ensaios de abrasão foram realizados utilizando o equipamento roda de borracha a úmido, variando o tamanho do abrasivo entre 0,15 e 2,40 mm e o pH do meio entre 5,5 e 12,8. As microestruturas dos materiais estudados foram analisadas utilizando microscopia óptica, as superfícies de desgaste e as partículas de desgaste foram analisadas em microscópio eletrônico de varredura. A macrodureza e a microdureza, antes e após os ensaios, foram obtidas utilizando durômetro Vickers. A topografia da região central da superfície de desgaste foi obtida utilizando Perfilometria 3D, visando obter valores de profundidade de penetração do abrasivo. Os resultados mostraram que o aço Hadfield é mais resistente do que o aço H-13 em todos os valores de pH e tamanhos de abrasivo utilizados. Para os dois materiais, a perda de massa aumenta linearmente até um tamanho crítico de abrasivo (TCA) e, após este, a mesma continua a aumentar, mas com uma intensidade menor. Para os dois materiais e para todos os tamanhos de abrasivo, o aumento do pH do meio resultou em menores perdas de massa, sendo este efeito maior para os dois menores tamanhos de abrasivo. Para maiores valores de pH, foram observadas menores profundidades de penetração do abrasivo. A microdureza da superfície de desgaste do aço H-13 sofreu um pequeno aumento com o aumento do tamanho do abrasivo enquanto que para o aço Hadfield esse aumento foi mais intenso. A análise das partículas de desgaste mostraram que, para todas as condições ensaiadas, os debris do aço H-13 tinham duas morfologias, contínuas e descontínuas enquanto que os cavacos do aço Hadfield foram sempre descontínuos. Para os dois materiais, foram observados dois micromecanismos de desgaste, sendo eles microcorte e microsulcamento. Por fim, os resultados apresentados neste trabalho sugerem que a análise de desempenho do aço Hadfield em serviço deve considerar o pH do meio bem como a granulometria do abrasivo em contato.

Behavior of different soot combustion catalysts under NOx/O2. Importance of the catalyst–soot contact

Four different catalysts (Pt/Al2O3, Ce0.8Zr0.2O2, PrO2−x and SrTiCuO3) have been investigated on a laboratory scale to evaluate their potential as diesel soot combustion catalysts under different experimental conditions, which simulate the situation found in a continuous regeneration technology trap (dual-bed configuration of catalyst and soot) or a catalyst-coated filter system (single-bed configuration, both catalyst and soot particles mixed under loose-contact mode). Under dual-bed configuration, the behavior of the catalysts towards soot combustion are very similar, despite the differences observed in the NO2 production profiles. However, under single-bed configuration, there are important differences in the soot combustion activities and in the NO2 slip profiles. The configurations chosen have an enormous impact on CO/(CO + CO2) ratios of combustion products as well. The most active catalyst under NOx + O2 is PrO2−x combining a high contribution of active oxygen-assisted soot combustion as well as high NO2 production activity along the catalytic bed.

The isotope composition of selenium in chondrites constrains the depletion mechanism of volatile elements in solar system materials

Solar nebula processes led to a depletion of volatile elements in different chondrite groups when compared to the bulk chemical composition of the solar system deduced from the Sun's photosphere. For moderately-volatile elements, this depletion primarily correlates with the element condensation temperature and is possibly caused by incomplete condensation from a hot solar nebula, evaporative loss from the precursor dust, and/or inherited from the interstellar medium. Element concentrations and interelement ratios of volatile elements do not provide a clear picture about responsible mechanisms. Here, the abundance and stable isotope composition of the moderately- to highly-volatile element Se are investigated in carbonaceous, ordinary, and enstatite chondrites to constrain the mechanism responsible for the depletion of volatile elements in planetary bodies of the inner solar system and to define a δ(82/78)Se value for the bulk solar system. The δ(82/78)Se of the studied chondrite falls are identical within their measurement uncertainties with a mean of −0.20±0.26‰ (2 s.d., n=14n=14, relative to NIST SRM 3149) despite Se abundance depletions of up to a factor of 2.5 with respect to the CI group. The absence of resolvable Se isotope fractionation rules out a kinetic Rayleigh-type incomplete condensation of Se from the hot solar nebula or partial kinetic evaporative loss on the precursor material and/or the parent bodies. The Se depletion, if acquired during partial condensation or evaporative loss, therefore must have occurred under near equilibrium conditions to prevent measurable isotope fractionation. Alternatively, the depletion and cooling of the nebula could have occurred simultaneously due to the continuous removal of gas and fine particles by the solar wind accompanied by the quantitative condensation of elements from the pre-depleted gas. In this scenario the condensation of elements does not require equilibrium conditions to avoid isotope fractionation. The results further suggest that the processes causing the high variability of Se concentrations and depletions in ordinary and enstatite chondrites did not involve any measurable isotope fractionation. Different degrees of element depletions and isotope fractionations of the moderately-volatile elements Zn, S, and Se in ordinary and enstatite chondrites indicate that their volatility is controlled by the thermal stabilities of their host phases and not by the condensation temperature under canonical nebular conditions.

A grammar of late modern English : for the use of continental, especially Dutch, students /

Includes bibliographical references and indexes.

A liberation model for comminution based on probability theory

Mineral processing plants use two main processes; these are comminution and separation. The objective of the comminution process is to break complex particles consisting of numerous minerals into smaller simpler particles where individual particles consist primarily of only one mineral. The process in which the mineral composition distribution in particles changes due to breakage is called 'liberation'. The purpose of separation is to separate particles consisting of valuable mineral from those containing nonvaluable mineral. The energy required to break particles to fine sizes is expensive, and therefore the mineral processing engineer must design the circuit so that the breakage of liberated particles is reduced in favour of breaking composite particles. In order to effectively optimize a circuit through simulation it is necessary to predict how the mineral composition distributions change due to comminution. Such a model is called a 'liberation model for comminution'. It was generally considered that such a model should incorporate information about the ore, such as the texture. However, the relationship between the feed and product particles can be estimated using a probability method, with the probability being defined as the probability that a feed particle of a particular composition and size will form a particular product particle of a particular size and composition. The model is based on maximizing the entropy of the probability subject to mass constraints and composition constraint. Not only does this methodology allow a liberation model to be developed for binary particles, but also for particles consisting of many minerals. Results from applying the model to real plant ore are presented. A laboratory ball mill was used to break particles. The results from this experiment were used to estimate the kernel which represents the relationship between parent and progeny particles. A second feed, consisting primarily of heavy particles subsampled from the main ore was then ground through the same mill. The results from the first experiment were used to predict the product of the second experiment. The agreement between the predicted results and the actual results are very good. It is therefore recommended that more extensive validation is needed to fully evaluate the substance of the method. (C) 2003 Elsevier Ltd. All rights reserved.

Gastrointestinal transit in the common brushtail possum measured by gamma scintigraphy

This paper reports an example of the application of pharmaceutical technology to wildlife management, specifically the design of an oral delivery system for the common brushtail possum in New Zealand. Designing an oral delivery system requires a knowledge of the time taken for particulates to reach target sites within the gastrointestinal tract (GIT). The transit time for fluid and indigestible particles of two different size ranges was determined in the common brushtail possum (Trichosurus vulpecula). Technetium-labelled (Tc-99m) anion exchange resin particles (75-125 or 500-700 mu m diameter) or solution (Tc-99m-labelled diethylenetriamine pentaacetic acid, Tc-99m-DTPA) was administered orally. At predetermined times after dosing (3, 6, 12, 24 or 32 h), the distribution of radioactivity throughout excised gastrointestinal tracts was determined by gamma scintigraphy. The transit profile was similar for the three formulations investigated. Unlike other closely related hindgut fermenting marsupials, there was no evidence to support the presence of a colonic separating mechanism in the common brushtail possum. Gastrointestinal transit was independent of body mass, gender and time of day that the dose is given. To target the hindgut for oral delivery of protein and peptide biocontrol agents, the formulation Would need to protect the bioactive for approximately 12 h prior to release. (c) 2005 Elsevier B.V. All rights reserved.

Preparation of immuno-stimulating complexes (ISCOMs) by ether injection

preparation of liposomes, as a new, continuous and potentially scaleable method for the preparation of ISCOMs. Phosphatidylcholine (PC) and cholesterol (Chol) were dissolved in ether, which was injected into an aqueous solution, maintained at 55 degrees C, containing Quil A. The influences of the following variables on ISCOM formation were investigated: ratio of PC:Quil A:Chol used, pumping rate, total lipid mass and concentration of buffer salts and Quil A in the aqueous phase. All samples were characterized by negative stain transmission electron microscopy, photon correlation spectroscopy and sucrose ultracentrifugation gradient. It was demonstrated that ISCOMs could be produced by this method but the homogeneity of the preparation was influenced by the conditions used. Homogeneous ISCOM preparations were consistently produced only when the weight ratio of PC:Quil A:Chol was 5:3:2 with a total lipid mass of 20 mg, the Quil A dissolved in a 0.01 M phosphate buffer at a concentration of 6 mg in 4 ml, and the ether solution injected into the warmed buffer solution at a rate of 0.2 ml/min. Changing any of these variables resulted in more heterogeneous preparations in which ISCOMs typically co-existed with other colloidal structures such as worm-like and helical micelles, liposomes, lamellae and lipidic particles. (C) 2005 Elsevier B.V. All rights reserved.

Optical trapping of a cube

The successful development and optimisation of optically-driven micromachines will be greatly enhanced by the ability to computationally model the optical forces and torques applied to such devices. In principle, this can be done by calculating the light-scattering properties of such devices. However, while fast methods exist for scattering calculations for spheres and axisymmetric particles, optically-driven micromachines will almost always be more geometrically complex. Fortunately, such micromachines will typically possess a high degree of symmetry, typically discrete rotational symmetry. Many current designs for optically-driven micromachines are also mirror-symmetric about a plane. We show how such symmetries can be used to reduce the computational time required by orders of magnitude. Similar improvements are also possible for other highly-symmetric objects such as crystals. We demonstrate the efficacy of such methods by modelling the optical trapping of a cube, and show that even simple shapes can function as optically-driven micromachines.

Bio-inspired carbon electro-catalysis for the oxygen reduction reaction

We report the synthesis, characterisation and catalytic performance of two nature-inspired biomass-derived electro-catalysts for the oxygen reduction reaction in fuel cells. The catalysts were prepared via pyrolysis of a real food waste (lobster shells) or by mimicking the composition of lobster shells using chitin and CaCO3 particles followed by acid washing. The simplified model of artificial lobster was prepared for better reproducibility. The calcium carbonate in both samples acts as a pore agent, creating increased surface area and pore volume, though considerably higher in artificial lobster samples due to the better homogeneity of the components. Various characterisation techniques revealed the presence of a considerable amount of hydroxyapatite left in the real lobster samples after acid washing and a low content of carbon (23%), nitrogen and sulphur (<1%), limiting the surface area to 23 m2/g, and consequently resulting in rather poor catalytic activity. However, artificial lobster samples, with a surface area of ≈200 m2/g and a nitrogen doping of 2%, showed a promising onset potential, very similar to a commercially available platinum catalyst, with better methanol tolerance, though with lower stability in long time testing over 10,000 s.

Administration routes affect the quality of immune responses:a cross-sectional evaluation of particulate antigen-delivery systems

Particulate delivery systems such as liposomes and polymeric nano- and microparticles are attracting great interest for developing new vaccines. Materials and formulation properties essential for this purpose have been extensively studied, but relatively little is known about the influence of the administration route of such delivery systems on the type and strength of immune response elicited. Thus, the present study aimed at elucidating the influence on the immune response when of immunising mice by different routes, such as the subcutaneous, intradermal, intramuscular, and intralymphatic routes with ovalbumin-loaded liposomes, N-trimethyl chitosan (TMC) nanoparticles, and poly(lactide-co-glycolide) (PLGA) microparticles, all with and without specifically selected immune-response modifiers. The results showed that the route of administration caused only minor differences in inducing an antibody response of the IgG1 subclass, and any such differences were abolished upon booster immunisation with the various adjuvanted and non-adjuvanted delivery systems. In contrast, the administration route strongly affected both the kinetics and magnitude of the IgG2a response. A single intralymphatic administration of all evaluated delivery systems induced a robust IgG2a response, whereas subcutaneous administration failed to elicit a substantial IgG2a response even after boosting, except with the adjuvanted nanoparticles. The intradermal and intramuscular routes generated intermediate IgG2a titers. The benefit of the intralymphatic administration route for eliciting a Th1-type response was confirmed in terms of IFN-gamma production of isolated and re-stimulated splenocytes from animals previously immunised with adjuvanted and non-adjuvanted liposomes as well as with adjuvanted microparticles. Altogether the results show that the IgG2a associated with Th1-type immune responses are sensitive to the route of administration, whereas IgG1 response associated with Th2-type immune responses were relatively insensitive to the administration route of the particulate delivery systems. The route of administration should therefore be considered when planning and interpreting pre-clinical research or development on vaccine delivery systems.

A study of the drying of single droplets in free-flight

The literature relating to evaporation from single droplets of pure liquids and the drying of solution and slurry droplets, and of droplet sprays has been reviewed. The heat and mass transfer rates for individual droplets suspended in free-flight, were investigated using a specially-designed vertical wind tunnel, to simulate conditions in a spray drier. The technique represented a unique alternative method for investigating evaporation from unrestrained single droplets with variable residence times. The experiments covered droplets of pure liquid allowbreak (water, isopropanol) allowbreak and of significantly different solutions (sucrose, potassium sulphate) over a range of temperatures of 37oC to 97oC, initial concentrations of 5 to 40wt/wt% , and initial drop sizes of 2.8 to 4.6mm. Drop behaviour was recorded photographically and dried particles were examined by Scanning Electron Microscopy. Correlations were developed for mass transfer coefficients for pure water droplets in free-flight; (i) experiencing oscillations, rotation and deformation, Sh = -105 + 3.9 [Ta - Td/Tamb]0.18Re0.5Sc033 for Re approx. > 1380 (ii) when these movements had ceased or diminished, Sh = 2.0 + 0.71 [Ta - Td/Tamb]0.18Re0.5Sc033 for Re approx. < 1060. Data for isopropanol drops were correlated resonably well by these equations. The heat transfer data showed a similar transition range. The drying rate curves for drops of sucrose and potassium sulphate solution exhibited three distinct stages; an initial increase in the drying rate as drop temperature reduced to the wet-bulb temperature, a short constant-rate period and a falling-rate period characterised by formation of a crust which controlled the mass transfer rate. Due to drop perturbation the rates in the high Re number region were up to 5 times greater than predicted from theory for spherical droplets. In the case of sucrose solution a `skin' formed over the drop surface prior to crust formation. This provided an additional resistance to mass transfer and resulted in extended drying times and a smooth crust of low porosity. The relevance of the results to practical spray drying operations is discussed.