Modélisation des structures sandwiches avec un amortissement viscoélastique intégré par une méthode hybride FEM-TMM

Cette thèse traite de la modélisation numérique de la réponse vibro-acoustique de structures sandwiches-composites avec matériaux viscoélastiques intégrés soumises à différents types d’excitations mécaniques et acoustiques. Dans une première phase, nous avons utilisé une approche de synthèse modale pour calculer les principaux indicateurs vibro-acoustiques de la structure : la vitesse quadratique, la puissance rayonnée, la perte par transmission…Ensuite, l’intégrale de Rayleigh a été exploitée pour calculer la puissance rayonnée de chaque structure. L’obstacle majeur que nous avons alors surmonté, était de gérer efficacement la dépendance en fréquence des propriétés de la couche viscoélastique dans l’approche de synthèse modale. Dans une second phase, en partant du champ vibratoire calculé dans la première étape, nous avons développé une méthode hybride FEM-TMM (méthode des éléments finis – méthode de matrices de transfert) pour prédire avec précision et en un temps de calcul acceptable, et jusqu’en hautes fréquences, les principaux paramètres de conception vibro-acoustique de ces structures, notamment l’amortissement équivalent et les nombres d’ondes suivant les deux directions spatiales x et y de propagation de l’onde acoustique. Les validations numériques que nous avons effectuées, montrent bien la robustesse de l'algorithme que nous avons développé. Ce dernier reste toutefois limité à des structures planes. Dans une troisième phase de ce travail, une étude paramétrique sur l’effet de l’emplacement et de la forme de la couche viscoélastique a été réalisée. Cette étude a été faite en se servant de la méthode hybride FEM-TMM pour calculer la réponse acoustique (puissance transmise et perte par transmission).

Rapid detection and quantification of the marine toxic algae, Alexandrium minutum, using a super-paramagnetic immunochromatographic strip test

The dinoflagellates of Alexandrium genus are known to be producers of paralytic shellfish toxins that regularly impact the shellfish aquaculture industry and fisheries. Accurate detection of Alexandrium including A. minutum is crucial for environmental monitoring and sanitary issues. In this study, we firstly developed a quantitative lateral flow immunoassay (LFIA) using super-paramagnetic nanobeads for A. minutum whole cells. This dipstick assay relies on two distinct monoclonal antibodies used in a sandwich format and directed against surface antigens of this organism. No sample preparation is required. Either frozen or live cells can be detected and quantified. The specificity and sensitivity are assessed by using phytoplankton culture and field samples spiked with a known amount of cultured A. minutum cells. This LFIA is shown to be highly specific for A. minutum and able to detect reproducibly 105 cells/L within 30 min. The test is applied to environmental samples already characterized by light microscopy counting. No significant difference is observed between the cell densities obtained by these two methods. This handy super-paramagnetic lateral flow immnunoassay biosensor can greatly assist water quality monitoring programs as well as ecological research.

Avaliação de hábitos de consumo e adequação nutricional de refeições rápidas cuja base é o pão

As rápidas alterações sociais, económicas, culturais e ambientais determinaram mudanças significativas nos estilos de vida e contribuíram para o crescimento e generalização do consumo de alimentos e refeições fora de casa. Portugal acompanha a tendência de aumento do consumo alimentar fora de casa, assim, as refeições fora de casa, que há uns anos eram um acontecimento fortuito, são hoje uma prática habitual das famílias portuguesas, não só durante a semana de trabalho, mas também nos fins-de-semana. As, visitas aos centros comerciais que se tornaram um hábito no nosso país incluem uma paragem nas Praças de Alimentação, espaços de excelência pela diversidade alimentar onde predominam as refeições de fast-food. Porém é fundamental a escolha adequada/equilibrada dos alimentos que se vão consumir. O presente trabalho procurou avaliar os hábitos e percepção dos consumidores de refeições rápidas com base numa ementa específica cujo alimento principal é o pão. Posteriormente e de acordo com as preferências de consumo procedeu-se à avaliação nutricional das escolhas. Neste estudo participaram 150 indivíduos que frequentaram as instalações de um restaurante de comida rápida situada na praça de alimentação de um centro comercial situado em Viseu. Foi aplicado um questionário de autopreenchimento, por nós elaborado dividido em 4 partes: caracterização sociodemográfica; hábitos de consumo dos inquiridos; produtos escolhidos pelos inquiridos; grau de satisfação face aos produtos escolhidos. As análises estatísticas foram efectuadas com recurso ao Programa informático Statistical Package for the Social Sciences - SPSS® for Windows, versão 22. Realizam-se testes de Qui-quadrado com simulação de Monte Carlo, considerando o nível de significância de 0,05. Com base nas escolhas mais frequentes feitas pelos inquiridos procedeu-se à avaliação nutricional dos menus recorrendo ao programa DIAL 1.19 versão 1 e quando não se encontrou informação neste utilizou-se a tabela de composição de alimentos portugueses on line (INSA, 2010). Compararam-se os valores obtidos para o Valor Calórico Total, os macronutrientes, a fibra, o colesterol e o sódio com as Doses Diárias Recomendadas. A amostra era composta por 68,7% mulheres e 31,3% homens, com uma média de idades de 29,9 ± 3 anos e, maioritariamente empregados (64,7%). O grau de instrução da maioria dos inquiridos (54,7%) era o ensino superior. Grande parte da amostra não se considera consumidora habitual de fast-food,referindo ainda efectuar frequentemente uma alimentação equilibrada. Sendo que apenas 5 % frequenta as instalações mais de uma vez por semana. De entre os produtos disponíveis, a preferência fez-se pela sandes e batata-frita, sendo o momento de maior consumo o almoçoA avaliação nutricional das escolhas preferenciais dos inquiridos mostrou que o VCT do menu que inclui água como bebida está dentro dos limites calóricos preconizados para o almoço excepção feita ao menu que inclui sandes quente de frango em pão de orégãos e sandes fria de queijo fresco que se destacam por apresentar um valor inferior ao limite mínimo recomendado. Pelo contrário, a inclusão no menu do refrigerante faz com que haja um aumento do VCT, independentemente da sandes considerada, em 18%. Uma análise detalhada mostra que estas ementas são desequilibradas, apresentando 33,3% delas valores de proteínas superiores à DDR enquanto que os valores de HC e lípidos se encontram maioritariamente dentro dos limites havendo apenas 13,3% das ementas fora desses valores. Relativamente ao aporte de fibra e de sódio 86,7% das ementas aparecem desenquadradas com valores excessivos de sódio e valores de fibra 33% abaixo do limite mínimo recomendado. Tratando-se de um estudo de caso em que apenas se inclui um único restaurante de uma praça de alimentação, que fornece ementas à base de pão (sandes) os resultados são interpretados de forma cautelosa e sem generalização. Podemos no entanto concluir, face aos resultados obtidos a necessidade de redução do teor de sal das ementas. Para além disso parece-nos fundamental, para que o consumidor possa comparar opções alimentares e tomar decisões informadas, a disponibilização da informação nutricional das ementas propostas.

MICROFLUIDIC ASSAY PERFORMANCE ENHANCEMENT USING POROUS VOLUMETRIC DETECTION ELEMENTS FOR IMPEDEMETRIC AND OPTICAL SENSING

Microfluidic technologies have great potential to help create automated, cost-effective, portable devices for rapid point of care (POC) diagnostics in diverse patient settings. Unfortunately commercialization is currently constrained by the materials, reagents, and instrumentation required and detection element performance. While most microfluidic studies utilize planar detection elements, this dissertation demonstrates the utility of porous volumetric detection elements to improve detection sensitivity and reduce assay times. Impedemetric immunoassays were performed utilizing silver enhanced gold nanoparticle immunoconjugates (AuIgGs) and porous polymer monolith or silica bead bed detection elements within a thermoplastic microchannel. For a direct assay with 10 µm spaced electrodes the detection limit was 0.13 fM AuIgG with a 3 log dynamic range. The same assay was performed with electrode spacing of 15, 40, and 100 µm with no significant difference between configurations. For a sandwich assay the detection limit was10 ng/mL with a 4 log dynamic range. While most impedemetric assays rely on expensive high resolution electrodes to enhance planar senor performance, this study demonstrates the employment of porous volumetric detection elements to achieve similar performance using lower resolution electrodes and shorter incubation times. Optical immunoassays were performed using porous volumetric capture elements perfused with refractive index matching solutions to limit light scattering and enhance signal. First, fluorescence signal enhancement was demonstrated with a porous polymer monolith within a silica capillary. Next, transmission enhancement of a direct assay was demonstrated by infusing aqueous sucrose solutions through silica bead beds with captured silver enhanced AuIgGs yielding a detection limit of 0.1 ng/mL and a 5 log dynamic range. Finally, ex situ functionalized porous silica monolith segments were integrated into thermoplastic channels for a reflectance based sandwich assay yielding a detection limit of 1 ng/mL and a 5 log dynamic range. The simple techniques for optical signal enhancement and ex situ element integration enable development of sensitive, multiplexed microfluidic sensors. Collectively the demonstrated experiments validate the use of porous volumetric detection elements to enhance impedemetric and optical microfluidic assays. The techniques rely on commercial reagents, materials compatible with manufacturing, and measurement instrumentation adaptable to POC diagnostics.

MANIPULATION OF IONS, ELECTRONS, AND PHOTONS IN 2D MATERIALS BY ION INTERCALATION

2D materials have attracted tremendous attention due to their unique physical and chemical properties since the discovery of graphene. Despite these intrinsic properties, various modification methods have been applied to 2D materials that yield even more exciting results. Among all modification methods, the intercalation of 2D materials provides the highest possible doping and/or phase change to the pristine 2D materials. This doping effect highly modifies 2D materials, with extraordinary electrical transport as well as optical, thermal, magnetic, and catalytic properties, which are advantageous for optoelectronics, superconductors, thermoelectronics, catalysis and energy storage applications. To study the property changes of 2D materials, we designed and built a planar nanobattery that allows electrochemical ion intercalation in 2D materials. More importantly, this planar nanobattery enables characterization of electrical, optical and structural properties of 2D materials in situ and real time upon ion intercalation. With this device, we successfully intercalated Li-ions into few layer graphene (FLG) and ultrathin graphite, heavily dopes the graphene to 0.6 x 10^15 /cm2, which simultaneously increased its conductivity and transmittance in the visible range. The intercalated LiC6 single crystallite achieved extraordinary optoelectronic properties, in which an eight-layered Li intercalated FLG achieved transmittance of 91.7% (at 550 nm) and sheet resistance of 3 ohm/sq. We extend the research to obtain scalable, printable graphene based transparent conductors with ion intercalation. Surfactant free, printed reduced graphene oxide transparent conductor thin film with Na-ion intercalation is obtained with transmittance of 79% and sheet resistance of 300 ohm/sq (at 550 nm). The figure of merit is calculated as the best pure rGO based transparent conductors. We further improved the tunability of the reduced graphene oxide film by using two layers of CNT films to sandwich it. The tunable range of rGO film is demonstrated from 0.9 um to 10 um in wavelength. Other ions such as K-ion is also studied of its intercalation chemistry and optical properties in graphitic materials. We also used the in situ characterization tools to understand the fundamental properties and improve the performance of battery electrode materials. We investigated the Na-ion interaction with rGO by in situ Transmission electron microscopy (TEM). For the first time, we observed reversible Na metal cluster (with diameter larger than 10 nm) deposition on rGO surface, which we evidenced with atom-resolved HRTEM image of Na metal and electron diffraction pattern. This discovery leads to a porous reduced graphene oxide sodium ion battery anode with record high reversible specific capacity around 450 mAh/g at 25mA/g, a high rate performance of 200 mAh/g at 250 mA/g, and stable cycling performance up to 750 cycles. In addition, direct observation of irreversible formation of Na2O on rGO unveils the origin of commonly observed low 1st Columbic Efficiency of rGO containing electrodes. Another example for in situ characterization for battery electrode is using the planar nanobattery for 2D MoS2 crystallite. Planar nanobattery allows the intrinsic electrical conductivity measurement with single crystalline 2D battery electrode upon ion intercalation and deintercalation process, which is lacking in conventional battery characterization techniques. We discovered that with a “rapid-charging” process at the first cycle, the lithiated MoS2 undergoes a drastic resistance decrease, which in a regular lithiation process, the resistance always increases after lithiation at its final stage. This discovery leads to a 2- fold increase in specific capacity with with rapid first lithiated MoS2 composite electrode material, compare with the regular first lithiated MoS2 composite electrode material, at current density of 250 mA/g.

Post-CMOS compatible high-throughput fabrication of AIN-based piezoelectric microcantilevers

A post-complementary metal oxide semiconductor (CMOS) compatible microfabrication process of piezoelectric cantilevers has been developed. The fabrication process is suitable for standard silicon technology and provides low-cost and high-throughput manufacturing. This work reports design, fabrication and characterization of piezoelectric cantilevers based on aluminum nitride (AlN) thin films synthesized at room temperature. The proposed microcantilever system is a sandwich structure composed of chromium (Cr) electrodes and a sputtered AlN film. The key issue for cantilever fabrication is the growth at room temperature of the AlN layer by reactive sputtering, making possible the innovative compatibility of piezoelectric MEMS devices with CMOS circuits already processed. AlN and Cr have been etched by inductively coupled plasma (ICP) dry etching using a BCl3–Cl2–Ar plasma chemistry. As part of the novelty of the post-CMOS micromachining process presented here, a silicon Si (1 0 0) wafer has been used as substrate as well as the sacrificial layer used to release the microcantilevers. In order to achieve this, the Si surface underneath the structure has been wet etched using an HNA (hydrofluoric acid + nitric acid + acetic acid) based solution. X-ray diffraction (XRD) characterization indicated the high crystalline quality of the AlN film. An atomic force microscope (AFM) has been used to determine the Cr electrode surface roughness. The morphology of the fabricated devices has been studied by scanning electron microscope (SEM). The cantilevers have been piezoelectrically actuated and their out-of-plane vibration modes were detected by vibrometry.

Dynamic mechanical-thermal, microstructural and mechanical analysis of ultra-light polymer-metal composites: influence of forming

A really particular and innovative metal-polymer sandwich material is Hybrix. Hybrix is a product developed and manufactured by Lamera AB, Gothenburg, Sweden. This innovative hybrid material is composed by two relatively thin metal layers if compared to the core thickness. The most used metals are aluminum and stainless steel and are separated by a core of nylon fibres oriented perpendicularly to the metal plates. The core is then completed by adhesive layers applied at the PA66-metal interface that once cured maintain the nylon fibres in position. This special material is very light and formable. Moreover Hybrix, depending on the specific metal which is used, can achieve a good corrosion resistance and it can be cut and punched easily. Hybrix architecture itself provides extremely good bending stiffness, damping properties, insulation capability, etc., which again, of course, change in magnitude depending in the metal alloy which is used, its thickness and core thickness. For these reasons nowadays it shows potential for all the applications which have the above mentioned characteristic as a requirement. Finally Hybrix can be processed with tools used in regular metal sheet industry and can be handled as solid metal sheets. In this master thesis project, pre-formed parts of Hybrix were studied and characterized. Previous work on Hybrix was focused on analyze its market potential and different adhesive to be used in the core. All the tests were carried out on flat unformed specimens. However, in order to have a complete description of this material also the effect of the forming process must be taken into account. Thus the main activities of the present master thesis are the following: Dynamic Mechanical-Thermal Analysis (DMTA) on unformed Hybrix samples of different thickness and on pre-strained Hybrix samples, pure epoxy adhesive samples analysis and finally moisture effects evaluation on Hybrix composite structure.

Involvement of cell surface TG2 in the aggregation of K562 cells triggered by gluten

Gluten-induced aggregation of K562 cells represents an in vitro model reproducing the early steps occurring in the small bowel of celiac patients exposed to gliadin. Despite the clear involvement of TG2 in the activation of the antigen-presenting cells, it is not yet clear in which compartment it occurs. Herein we study the calcium-dependent aggregation of these cells, using either cell-permeable or cell-impermeable TG2 inhibitors. Gluten induces efficient aggregation when calcium is absent in the extracellular environment, while TG2 inhibitors do not restore the full aggregating potential of gluten in the presence of calcium. These findings suggest that TG2 activity is not essential in the cellular aggregation mechanism. We demonstrate that gluten contacts the cells and provokes their aggregation through a mechanism involving the A-gliadin peptide 31-43. This peptide also activates the cell surface associated extracellular TG2 in the absence of calcium. Using a bioinformatics approach, we identify the possible docking sites of this peptide on the open and closed TG2 structures. Peptide docks with the closed TG2 structure near to the GTP/GDP site, by establishing molecular interactions with the same amino acids involved in stabilization of GTP binding. We suggest that it may occur through the displacement of GTP, switching the TG2 structure from the closed to the active open conformation. Furthermore, docking analysis shows peptide binding with the β-sandwich domain of the closed TG2 structure, suggesting that this region could be responsible for the different aggregating effects of gluten shown in the presence or absence of calcium. We deduce from these data a possible mechanism of action by which gluten makes contact with the cell surface, which could have possible implications in the celiac disease onset.

Advanced Luminescent Materials for Technological Applications

This thesis focusses on the study of several luminescent materials and investigates some related technological applications. It is made of six chapters. Chapter 1 introduces a brief history, basic principles and applications of photoluminescence. Chapter 2 presents the photophysical properties of five benzoheterodiazole dyes. These molecules were incorporated in PMMA- and PDMS-based LSC-PV devices to determine the emission quantum yields, transmission, re-absorption and IPCE properties. DFT calculations were performed to investigate the structures and energy levels of these dyes. Chapter 3 concerns the preparation of a luminescent film to calibrate an ESA satellite that will monitor the fluorescence of terrestrial vegetation. ZnPc was selected as suitable dye to make the film. Ferrocene was selected as quencher to control the emission intensity. An industrial printing technology was used to produce large-area calibration sheets coated with green pigment that simulates the NIR reflectance of green plants in which the ZnPc is embedded. Photophysical properties of a series of alkynyl gold NHC complexes containing naphthalimide chromophore were studied in Chapter 4. All the compounds were studied in solution and solid state. Further investigations were carried out by incorporating these compounds in PMMA matrix to make films. XRD and DFT calculations were made to determine the structures and energy levels of the complexes. In chapter 5 we studied the photophysical properties of star-shaped molecular systems which can operate as molecular motors when attached onto surface, along with those of their related ligands/moieties in tetrahydrofuran solution. The photophysical properties of these molecular systems can show if they are suitable to operate as light-triggered molecular machines. Finally, chapter 6 concerns the photoluminescence behavior of three NHC half-sandwich Ir/Rh metal complexes. The photophysical properties of these compounds were examined in CH2Cl2 solutions and PMMA films. These complexes may prove potential candidates for organic phosphorescent materials.

Vibro-acoustic analysis of additively manufactured acoustic metamaterials

In the last decade it emerged the interest in new types of acoustic insulating materials, called acoustic metamaterials. These materials are composed by a host and inclusions and are arranged periodically or non-periodically in sub-wavelength elements called meta-atoms. Their inclusions and internal geometries can be manipulated to tailor the acoustic properties, reducing weight, and increasing at the same time their efficiency. Thanks to the high absorbing characteristics that they can achieve, their usage is of particularly interest as material of the core in sandwich panels of aerospace structures to reduce vibrations and noise inside passengers aircraft’s cabin. In addition, since the low frequency signals are difficult to be damped with conventional materials, their usage can guarantee a high transmission loss at low frequencies, obtaining a positive benefit on passengers’ comfort. The performances and efficiency of these materials are enhanced thanks to the new additive manufacturing techniques opposed to the conventional ones uncapable to pro- duce such complex internal geometries. The aim of this work is to study, produce and redesign micro-perforated sandwich panels of a literature case study to achieve high performances in the low frequency range, e.g., below 2000 Hz. Some geometrical parameters, such as perforation ratio and diameter of holes, were considered to realize different models and see the differences in the sound transmission loss. The models were produced by means of Fused Deposition Modelling using an Acrylonitrile Butadiene Styrene (ABS Plus p430) material on a commercial additive manufacturing system. Finally, the frequency response analysis was carried out with Mul2 software, based on the Carrera’s Unified Formulation (CUF) to understand the acoustic and structural properties of the material employed, analyzing the plates’ displacements and the TL results.

Indagine biomeccanica del dispositivo di fissazione esterna Rekrea per l'allungamento degli arti

L'allungamento controllato monofocale viene eseguito nel caso di discrepanze della lunghezza degli arti. Il dispositivo Rekrea, ideato e realizzato dall'azienda Citieffe, viene utilizzato per lo svolgimento di tale trattamento. La stabilità del sistema di fissazione esterna è un fattore cruciale per il successo di un trattamento di allungamento osseo ma difficile da raggiungere in quanto dipendente da numerose variabili. Nello specifico, questo lavoro di tesi verte sullo studio del comportamento meccanico dei singoli morsetti Small e Standard e dell'innovativa configurazione Tandem impiegati in due contesti clinici particolari: i pazienti acondroplasici ed il trattamento di allungamento di tibia. A seguito di una iniziale ricerca bibliografica, sono state pianificate e svolte delle prove meccaniche di diverse configurazioni per caratterizzare il comportamento di tali dispositivi. Attraverso un'analisi dei risultati ottenuti è stato evidenziato quanto il singolo morsetto Small conferisca un'elevata rigidezza del costrutto e permetta di ridurre la distanza morsetto - analogo osseo. In più è stato evidenziato come la configurazione Tandem sia risultata un buon sostituto del morsetto Sandwich ed in particolare, come l'utilizzo di tre viti ossee conferisca una maggiore rigidezza del costrutto.