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Freeze casting is a colloidal processing technique that shows great promise for development of nanostructured materials. A ceramic nanopowder is dispersed with a polymer in water, under carefully controlled pH. The suspension is cast into a suitable mold and frozen, then de-molded and exposed to a vacuum to sublimate and remove the water. Polymer adsorption and rheology were studied to optimize and characterize a colloidal suspension of a 38 nm Al2O3 powder. The dispersant, dispersant amount, pH and solids loading were examined to determine the best conditions for freeze casting. Based on adsorption and viscosity data, optimal conditions for freeze casting were found with Poly(acrylic acid) (PAA) dispersant, at 2.00 wt% (of Al2O3), pH of 9.5, and a solids loading of 40 vol%. Carbon nanotubes (CNTs) were added to that suspension in increments of 0.14, 0.28, 0.53, 1.30 and 2.60 vol%. The viscosity increased dramatically upon addition of 1.30 vol% CNTs. The colloidal CNT-Al2O3 suspension was successfully freeze cast and the microstructure showed a very smooth fracture surface. It was determined that upon resting, the suspension undergoes a physical change which must be completed to obtain advantageous microstructure. Freeze cast Al2O3 discs with and without CNTs were measured using a concentric ring test, with strengths on the order of one MPa. The freeze cast sample was successfully debinded, but the heating profile attempted was not effective in obtaining full density. / Master of Science

Yes / In this work, a novel concept in freeze desalination (FD) was introduced. Nowadays the total liquefied natural gas (LNG) production capacity has reached 290 Megatons per year. Its enormous cold energy released from re-gasification can be used in the freeze desalination process to minimize the overall energy consumption. A process of FD on flake ice maker utilizing LNG cold energy was designed and simulated by HYSYS software. An ice bucket on flake ice maker was chosen as seawater crystallizer mainly due to its continuous ice making and removing ice without heat source. A dynamic model of the freezing section has been developed and simulated through gPROMS software. The results show that the consumption of 1 kg equivalent LNG cold energy can obtain about 2 kg of ice melt water. In addition, it is shown that the power consumption of this LNG/FD hybrid process is negligible.

Background: Adequate adaptation of the autonomic nervous system (ANS) is crucial in potentially life-threatening situations. The defence cascade provides a descriptive model of progressing dominant physiological reactions in such situations, including cardiovascular parameters and body mobility. The empirical evidence for this model is scarce, and the influence of physiological reactions in this model for predicting trauma-induced intrusions is unresolved. Objectives: Using a trauma-film paradigm, we aimed to test physiological reactions to a highly stressful film as an analogue to a traumatic event along the defence cascade model. We also aimed to examine the predictive power of physiological activity for subsequent intrusive symptoms. Method: Forty-seven healthy female participants watched a stressful and a neutral film in randomized order. Heart rate (HR), heart rate variability (HRV), and body sway were measured. Participants tracked frequency, distress, and quality of subsequent intrusions in a diary for 7 consecutive days. Results: For the stressful film, we observed an initial decrease in HR, followed by an increase, before the HR stabilized at a high level, which was not found during the neutral film. No differences in HRV were observed between the two films. Body sway and trembling frequency were heightened during the stressful film. Neither HR nor HRV predicted subsequent intrusions, whereas perceived distress during the stressful film did. Conclusions: Our results suggest that the physiological trauma-analogue response is characterized by an orientation response and subsequent hyperarousal, reaching a high physiological plateau. In contrast to the assumptions of the defence cascade model, the hyperarousal was not followed by downregulation. Potential explanations are discussed. For trauma-associated intrusions in the subsequent week, psychological distress during the film seems to be more important than physiological distress. Understanding the interaction between physiological and psychological responses during threat informs the study of ANS imbalances in mental disorders such as post-traumatic stress disorder.

<p dir="ltr">Air-entraining agents (AEA) were introduced in the 1930s to improve concrete's resistance to cyclic freezing-thawing exposure. Over the past 90 years, there has been extensive discussion about how traditional AEAs contribute to durability improvements. However, the issue of strength loss associated with conventional AEA use remains unresolved unless the cement is overdosed. Moreover, the effectiveness of traditional AEAs in entraining air voids has proven inconsistent, as it is influenced by various factors. As a result, the increased costs and carbon footprint associated with AEA use continue to be ongoing concerns for the industry.</p><p dir="ltr">Hollow polymeric microspheres have emerged as a promising solution for enhancing concrete's cyclic freezing-thawing resistance by providing encapsulated air without compromising mechanical performance or durability. In this study, the hydration, fresh properties, hardening performance, and freezing-thawing resistance of air-entrained cement mortar and concrete were investigated using the novel hollow polymeric microspheres and a traditional aqueous AEA, respectively. Additionally, the dynamic modulus of elasticity change and surface spalling damage of concrete beams following cyclic freezing-thawing exposure were evaluated. The air-void system and capillary pore structure of cement mortar and concrete, air-entrained with the traditional AEA and microspheres, respectively, were examined through various characterization methods, including optical microscopy (OM), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and 3D X-ray microscopy (micro-CT, or XCT). The properties of mortar and concrete with varying dosages of AEA and microspheres were assessed, and the mechanisms behind the enhanced freezing-thawing resistance were explored.</p><p dir="ltr">The microspheres used in this study were found to have a 'curing' effect, enhancing the hydration, workability, and mechanical strength of the mortar compared to both plain mortar without air entrainment and mortar air-entrained with the traditional aqueous AEA. Evaluating the mechanical strength changes and mass loss of mortar specimens demonstrated that the freezing-thawing resistance of mortar air-entrained with microspheres was superior to that achieved with aqueous AEA. The small size and compressibility of the microspheres resulted in a fine and well-distributed air void system, offering improved freezing-thawing resistance in the mortar specimens.</p><p dir="ltr">Additionally, due to the potential 'curing' and nucleation effects of the microspheres, the strength of air-entrained concrete with microspheres was slightly higher than that of plain concrete without air entrainment. In contrast, the traditional air-entraining method led to a 7.0% to 8.4% strength loss in concrete with 1% entrained air. Furthermore, concrete air-entrained with microspheres exhibited significantly less surface spalling damage compared to plain concrete, thanks to its well-distributed air void system and enhanced strength. On the other hand, although traditionally air-entrained concrete maintained its dynamic modulus throughout the 300 cycles of freezing-thawing exposure, it still suffered severe surface spalling damage, likely due to its reduced strength.</p><p dir="ltr">This study provides valuable insights into the practical application of polymeric microspheres for enhancing the freezing-thawing resistance of concrete.</p>

Magnetic field-assisted freeze-casting was used to create porous B4C ceramic preforms. An optimum slurry consisted of a mixture of B4C powders with 6 wt.% Er2O3 powder in an H2O-PVA solution and was cooled at a rate of 1 °C/min from room temperature to -30 °C resulting in porous green state ceramic preform with vertical channels. The Er2O3 powder was added to improve the magnetic response of the slurry. The preform was then sublimated to remove H2O and then sintered. The sintered ceramic preform was then infiltrated in the most vertically aligned channel direction with molten Al (A356) metal through a vacuum-assisted pump to create the metal matrix composite (MMC). Finite element analysis simulations were used to analyze and predict the anisotropic effect of B4C channel alignment on mechanical properties. The mechanical properties of the composite were then experimentally found via compression testing, which was compared with rule-of-mixtures and finite element modeling simulations, to analyze the effect of anisotropy due to magnetic field-assisted freeze-casting. This study reinforces the viability of cost-effective magnetic field-assisted freeze-casting as a method to create highly directional ceramic preforms, which can be subsequently metal infiltrated to produce MMCs with highly anisotropic toughness.

Submitted by Angela Maria de Oliveira (amolivei@uepg.br) on 2019-02-27T11:49:16Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Gustavo Antoniacomi de Carvalho.pdf: 6310308 bytes, checksum: 8e1efd9d86bc5a1adf80b45bba2a3985 (MD5) / Made available in DSpace on 2019-02-27T11:49:16Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Gustavo Antoniacomi de Carvalho.pdf: 6310308 bytes, checksum: 8e1efd9d86bc5a1adf80b45bba2a3985 (MD5) Previous issue date: 2018-01-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Cerâmicas porosas vêm ganhando visibilidade devido a algumas aplicações tecnológicas interessantes, tais como a utilização em eletrólitos sólidos, ânodos de células a combustível, filtros cerâmicos e reposição óssea e dental. Dentre elas, há especial atenção ao estudo de materiais porosos com porosidade graduada, nos quais a quantidade de poros e a morfologia dos mesmos se alteram pelo volume do material. Nesse trabalho foi realizado o processamento e caracterização de materiais cerâmicos de alumina com porosidade graduada a partir das técnicas de freeze casting e colagem de barbotina, utilizando hidróxido de alumínio e amido de arroz como fases de sacrifício. Após a conformação das amostras por esses métodos, a porosidade foi caracterizada por microscopia eletrônica de varredura, pelas medidas de porosidade aparente feita pelo Princípio de Arquimedes e pela distribuição de tamanho de poros feita pela técnica de porosimetria de mercúrio. Foi avaliada também a resistência mecânica das amostras a partir de ensaio de compressão. Foi confirmada a relação entre as amostras processados isoladamente e suas respectivas camadas nas amostras graduadas. Foi observada também uma boa interação interfacial entre cada uma das camadas das amostras graduadas. A porosidade das amostras com porosidade graduada se manteve próxima do esperado, o valor esperado foi determinado a partir da média das amostras processadas isoladamente em relação às camadas do material com porosidade graduada. O ensaio mecânico demonstrou que não houve influência das interfaces dos materiais graduados na sua resistência à compressão. / Porous ceramics have been gaining visibility due to some interesting technological applications, such as its use as solid electrolytes, fuel cell anodes, ceramic filters and bone and dental reposition. Among them, there is special care in studying graded porosity materials, where the quantity of pores and pore morphology changes through the material volume. In this work the processing and characterization of alumina ceramic materials with functionally graded porosity by freeze casting and slip casting techniques using aluminum hydroxide and rice starch as sacrificial template was performed. After conformation, the porosity was characterized through electron scanning microscopy, apparent porosity through Archimedes method and median pore size through mercury porosimetry. The mechanical resistance was also obtained by compression testing. The analysis allowed to confirm the relation between each of the isolated samples’ microstructure and its respective layer in each of the graded materials, also, the graded materials shown good interfacial interaction between each of the layers. The porosity in graded materials kept close to the expected value, which was determined by the medium value of the porosities of the isolated samples respective to the graded material. Mechanical testing shown that there was no influence of the graded material interfaces in its compressive strength.

Le monoxyde d'azote est exclusivement synthétisé chez les mammifères par une famille d’hémoprotéines, les NO-Synthases. Le cœur de l’activité des NO-Synthases est l’activation de l’oxygène c'est-à-dire l’activation de l’intermédiaire réactionnel FeIIO2. Cette étape est contrôlée par la réactivité intrinsèque du fer, par les transferts de proton et les transferts d’électron. Elle doit être parfaitement maîtrisée car elle contrôle le chemin catalytique emprunté et la nature du produit final. Comprendre l’étape d’activation de l’oxygène est essentiel à la compréhension du rôle biologique et/ou pathologique de la NO-Synthase de mammifère. Cette question s'étend aux NO-Synthases bactériennes pour lesquelles on ne connait ni le mécanisme moléculaire ni la fonction biologique. Ce manuscrit propose une analyse approfondie de l’étape d’activation de l’oxygène de la NO-Synthase. Dans un premier temps, nous avons étudié l’influence de l’environnement proximal sur la réactivité intrinsèque du fer et l’activation de l’oxygène. Nous avons généré des protéines mutées qui modifient les propriétés électroniques de la liaison proximale de l’hème. Ces protéines mutées ont été caractérisées par différentes spectroscopies (résonance paramagnétique électronique, Raman de résonance). Dans un second temps nous avons directement étudié le complexe FeIIO2, en présence d’analogues de substrat, grâce à des analyses de cinétique rapide en flux continu et en flux arrêté (stopped-flow). Dans un troisième temps, le rôle du cofacteur tetrahydrobioptérine dans le transfert de proton et d’électron a été étudié par une méthode de piégeage à des temps très courts : le freeze-quench. L'ensemble de nos résultats montrent que l’activation de l’oxygène est régulée par les propriétés électro-donneuses du ligand proximal et par le réseau de liaisons H distal. Nous mettons en évidence des différences dans le rôle redox du cofacteur tetrahydrobioptérine entre la NO-Synthase de mammifère et la NO-Synthase bactérienne. La difficulté majeure pour comprendre l’étape d’activation de l’oxygène de la NO-Synthase réside dans la complexité et la rapidité de la réaction catalytique. Dans ce contexte, nous avons cherché à adapter une méthodologie qui a prouvé son efficacité dans le cas des cytochromes P450 : la cryo-réduction couplée à des sauts en température. / Nitric oxide is exclusively synthesized by NO-Synthases in mammals. The heart of the NO-synthase activity is oxygen activation, which corresponds to the activation of the FeIIO2 intermediate. This step depends on the heme electronic properties and on the electron and proton transfers. Oxygen activation has to be well mastered to control exactly the nature of the end-product. Understanding the oxygen activation step is necessary to better understand the biological/pathological role of the mammalian NO-Synthases. Furthermore, bacterial NO-Synthases function and oxygen activation mechanism are unknown. This PhD work proposes a deep analysis of the oxygen activation step in NO-Synthases. First, proximal environment has been studied with mutated proteins. These mutations impact the electronic properties of the heme proximal bond. Spectroscopic analyses of these mutants have been done by electron paramagnetic resonance and resonance Raman. Then, we have studied the FeIIO2 intermediate with substrate analogs which has necessitated continuous flow and stopped-flow analyses. Finally, the role of the tetrahydrobiopterin cofactor in the electron and proton transfer has been studied and clarified thanks to a very fast trapping method : the freeze-quench. Our results show that the oxygen activation step is elaborately controlled by the proximal bond electron donation and the distal H bond network. At the same time we show some differences between mammalian and bacterial NO-Synthases concerning the redox role of the tetrahydrobiopterin cofactor. The major obstacle to understand the oxygen activation step resides in the complexity of the active site chemistry and the rate of catalytic reactions. For this reason, we propose to adapt an already successful protocol to trap some intermediates in the cytochromes P450 mechanism : cryo-reduction coupled with temperature jumps.