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<p>An experimental investigation has been carried out in order to investigate the effect of surface initial conditions, concentration, nanoparticles size and deposition pattern on pool boiling and jet impingement boiling of nanofluids. A flat copper surface with initial conditions of Ra = 420 nm, Ra = 80 nm and Ra = 20 nm has been used as the boiling surface. Al₂O₃ and CuO nanoparticles have been used with de-ionized water to prepare the nanofluids. At 0.01 vol. % concentration of Al₂O_3, the rate of heat transfer enhanced by 41% and 34% for the Ra = 80 nm and Ra = 20 nm, respectively. While, in the case of Ra = 420 nm, the rate of heat transfer deteriorated by 49%. At 0.005 vol. % concentration the rate of heat transfer deteriorated for all three surfaces. It is believed that the deterioration was due to the uniformity of the deposition. Using 0.01 vol. % concentration of CuO nanofluids resulted in the same trend, however, the rate of heat transfer is less compared to using Al₂O₃nanofluids. For example, in the case of Ra = 80 nm, the rate of heat transfer was reduced by 14%.</p> <p>The effect of nanoparticles size has been investigated by changing the nanoparticles size from 50 nm to 10 nm. The change in nanoparticles size resulted in a significant deterioration in the rate of heat transfer for all three surfaces. It is believed that the deterioration was due to the deposition uniformity. As the deposition uniformity has been found to be a major factor that affects the rate of heat transfer, new approach was introduced to quantify the effect of the rate of deposition on the pool boiling of nanofluids.</p> <p>An experimental investigation has been carried out in order to investigate using submerged impingement jet on the rate of heat transfer using nanofluids. At of 0.005 vol. % concentration of Al₂O₃, surface with Ra = 80 nm, jet to surface vertical distance of 3 mm and Reynolds number of 101311, the rate of heat transfer deteriorated by 19%.</p> <p>Comparing the pool boiling and jet impingement boiling of nanofluids showed that, in the case of jet impingement boiling, the rate of heat transfer was enhanced compared to the case of pool boiling and the deposition was less. However, jet impingement boiling experiments showed deterioration in the rate of heat transfer by 19% compared with pure water.</p> / Master of Applied Science (MASc)

El objetivo de esta investigación fue comparar in vitro los cambios en la rugosidad superficial de la estructura dentaria, generados por los diferentes agentes blanqueadores que contienen peróxido de hidrógeno (HP). El estudio consideró 50 especímenes obtenidos de dientes de bovino, seccionados en bloques dentales (7mm x 7mm x 7mm) y preparados para realizar una lectura inicial de rugosidad superficial (Ra), utilizando un perfilómetro. Las muestras fueron divididas aleatoriamente en 5 grupos (n= 10) según el agente blanqueador al que fueron expuestos: grupo1: Whiteness HP Maxx al 35%, grupo 2: Opalescence Boost 40% de HP, grupo 3: Opalescence Go 10% de HP, el grupo 4: Whiteness Perfect al 10% de peróxido de carbamida (CP) como control positivo y, el grupo 5: control negativo, con suero fisiológico. Al finalizar la etapa del blanqueamiento, las muestras se mantuvieron en suero fisiológico; finalmente, fueron sometidas al perfilómetro para determinar los parámetros de rugosidad superficial post blanqueamiento. Para el análisis estadístico se utilizó el paquete estadístico SPSS® 27.0. Para identificar si los datos siguen una distribución normal, se utilizó la prueba Shapiro Wilk (p > 0.05), luego se aplicó la prueba no paramétrica Prueba de Wilcoxon para muestras relacionadas (Inicial – final). Se concluyó que al aplicar los diferentes agentes blanqueadores que contienen peróxido de hidrogeno no se encontraron diferencias estadísticamente significativas entre los grupos; sin embargo, todos los grupos experimentales presentaron diferencias antes y después de la aplicación de los agentes blanqueadores. / The objective of this research was to compare in vitro the changes in the surface roughness of the tooth structure, generated by different bleaching agents containing hydrogen peroxide (HP). The study detected 50 specimens obtained from bovine teeth, sectioned into dental blocks (7 mm x 7 mm x 7 mm) and prepared to perform an initial reading of surface roughness (Ra), using a profilometer. The samples were randomly divided into 5 groups (n= 10) according to the whitening agent to which they were exposed: group 1: Whiteness HP Maxx 35%, group 2: Opalescent Boost 40% HP, group 3: Opalescent Go 10% HP, group 4: Whiteness Perfect with 10% carbamide peroxide (CP) as positive control and group 5: negative control, with physiological saline. At the end of the bleaching stage, the samples were kept in physiological saline solution; Finally, some profilometric measurements were performed to determine the postbleaching surface roughness parameters. The SPSS® 27.0 statistical package was used for statistical analysis. To identify whether the data follow a normal distribution, the Shapiro Wilk test was used (p > 0.05), then the non-parametric Wilcoxon test was applied for related samples (Initial – final). It is concluded that when applying the different whitening agents containing hydrogen peroxide, no statistically significant differences were found between the groups; however, all experimental groups presented differences before and after the application of the whitening agents.

No / This study aimed at examining the biophysical characteristics of human derived keratinocytes (HaCaT) cultured on cholesteryl ester liquid crystals (CELC). CELC was previously shown to improve sensitivity in sensing cell contractions. Characteristics of the cell integrin expressions and presence of extracellular matrix (ECM) proteins on the liquid crystals were interrogated using various immunocytochemical techniques. The investigation was followed by characterization of the chemical properties of the liquid crystals (LC) after immersion in cell culture media using Fourier transform infrared spectroscopy (FTIR). The surface morphology of cells adhered to the LC was studied using atomic force microscopy (AFM). Consistent with the expressions of the integrins α2, α3 and β1, extracellular matrix proteins (laminin, collagen type IV and fibronectin) were found secreted by the HaCaT onto CELC and these proteins were also secreted by cells cultured on the glass substrates. FTIR analysis of the LC revealed the existence of spectrum assigned to cholesterol and ester moieties that are essential compounds for the metabolizing activities of keratinocytes. The immunostainings indicated that cell adhesion on the LC is mediated by self-secreted ECM proteins. As revealed by the AFM imaging, the constraint in cell membrane spread on the LC leads to the increase in cell surface roughness and thickness of cell membrane. The biophysical expressions of cells on biocompatible CELC suggested that CELC could be a new class of biological relevant material.

The main objective of the project was to establish a fracture-mechanics energy-based approach for the design of structural adhesive joints under cyclic loading. This required understanding how an adhesive system behaved near its fatigue threshold, and how the key factors affected this behavior in a fresh undegraded joint. The investigated factors were mode ratio (phase angle), substrate material, surface treatment and surface roughness (both affecting the bond strength), bondline thickness and load ratio. It was first required to understand how the adhesive system behaved under quasi-static loading by examining a fracture mechanics-based design approach for adhesive systems with different substrate materials and geometries. Experiments were initially performed to characterize the strength of aluminum and steel adhesive systems based on the fracture envelope, critical strain energy release rate as a function of the mode ratio. Ultimate failure loads of aluminum and steel adhesive joints, having different overlap end conditions and different geometries were then experimentally measured. These values were compared with the failure loads extracted from the fracture envelope. Considering the toughening behavior of the adhesive in the fracture mechanics analyses, a very good agreement (average of 6%) was achieved between the predictions and experiments for all types of overlap end conditions and geometries. Different fatigue threshold testing approaches, which are commonly used in the literature or suggested by the ASTM standard, were evaluated for the cracked and intact fillet joints. Based on the experimental and analytical studies, the most appropriate technique for fatigue testing and characterization of adhesive systems was suggested. Comparing the mixed-mode near-threshold behavior of different adhesive systems with the fracture behavior and fatigue mode-I and mixed-mode high crack growth rates showed the high sensitivity of the mixed-mode near-threshold fatigue to the subtle changes in the interfacial bond strength. In order to make a baseline for the design of adhesive joints under cyclic loading, similar to the previous fracture tests and following the energy-based approach, fatigue behavior was characterized as a function of the loading mode ratio for aluminum and steel adhesive joints. The effect of substrate material, surface treatment, bondline thickness, surface roughness and fatigue testing load ratio on the near-threshold fatigue behavior of adhesives joints was evaluated experimentally. The experimental observations were then explained using finite element modeling. To generalize the conclusions, the majority of experiments and studies covered a broad range of crack growth rates, as low as fatigue threshold and as high as 10-2 mm/cycle. Having understood the significant testing and design parameters, an adhesive system can be designed based on a safe cyclic load that produces an insignificant (for automotive industry) or reasonably low but known crack growth rate (for aerospace industry).

An experimental study was designed to investigate the effect of different parameters on the development and structure of turbulent 3D offset jets. The present investigation considered the effects of offset height ratio, expansion ratio, surface roughness and rib placement on the flow dynamics of a turbulent 3D offset jet. The velocity measurements were performed using an acoustic Doppler velocimetry (ADV) and particle image velocimetry (PIV). Measurements were conducted within the symmetry and lateral planes. For the PIV technique, the measurements in the symmetry and lateral planes were conducted over a streamwise range of 0 ≤ x/bo ≤ 80 and 12 ≤ x/bo ≤ 60, respectively (where bo is the nozzle height). Likewise, velocity measurements using the ADV technique were conducted over a range of 4 ≤ x/bo ≤ 45 in both the symmetry and lateral planes. The velocity measurements were analyzed using both one-point and multi-point statistics. The one-point statistics included profiles of the mean velocities, Reynolds stresses and some of the budget terms in the turbulent kinetic energy transport equation. The quadrant analysis technique was used to investigate the dominant events that contribute towards the Reynolds shear stress. The two-point correlation analysis was used to investigate how the turbulence quantities are correlated. Information obtained from the two-point correlation analysis was also used to investigate the inclination of vortical structures within the inner and outer shear layers of the 3D offset jet. The direction of the positive mean shear gradient played an active role in the inclination of these vortical structures within the inner and outer shear layers. The reattachment process resulted in the breakdown of these structures within the developing region. Similarly, various length scales were estimated from these structures. The proper orthogonal decomposition was used to examine the distribution of the turbulent kinetic energy within the offset jet flow. Also, the dynamic role of the large scale structures towards the turbulent intensities, turbulent kinetic energy and Reynolds shear stress was investigated. / October 2016

<p>Disertacija daje pregled novih i relevantnih istraživanja i stavova<br />u naučnoj zajednici na temu štamparskih formi i uticaja procesa<br />štampe na trošenje neštampajućih elemenata. U disertaciji je<br />ukazano na kontinualno praćenje topografskih promena<br />neštampajućih elemenata štamparskih formi kako bi se kontrolisao<br />period eksploatacije a time i proces reprodukcije. Takođe daje<br />prilog novim istraživanjima sa analizom velikog broja<br />eksperimentalnih uzoraka sa dobijenim izmerenim podacima i<br />odgovarajućim korelacijama i predstavlja napredak u shvatanju<br />mehanizma trošenja neštampajućih površina štamparskih formi i<br />njihov uticaj na tribološke promene u odnosu na strukturu osnove<br />aluminijuma i sloja aluminijum oksida.</p> / <p>Dissertation gives an overview of the current state, research and theories of<br />printing forms and influence of printing process on wearing of non-printing<br />elements within the science community. The dissertation points out the continuous<br />monitoring of topographic changes of printing form non-printing elements to control<br />the exploitation of a period of time and the process of reproduction. This work<br />contributes to new research with the analysis of large number of experimental<br />samples and calculated correlations and represents an advance in the<br />comprehension of the surface wear mechanism of printing form non-printing<br />elements and their influence on the tribological changes to the structure of the<br />base layer of aluminium and aluminium oxide.</p>

This thesis is devoted to the study of some homogenization problems with applications in lubrication theory. It consists of an introduction, five research papers (I–V) and a complementary appendix.Homogenization is a mathematical theory for studying differential equations with rapidly oscillating coefficients. Many important problems in physics with one or several microscopic scales give rise to this kind of equations, whence the need for methods that enable an efficient treatment of such problems. To this end several mathematical techniques have been devised. The main homogenization method used in this thesis is called multiscale convergence. It is a notion of weak convergence in &nbsp;Lp&nbsp;spaces which is designed to take oscillations into account. In paper II we extend some previously obtained results in multiscale convergence that enable us to homogenize a nonlinear problem with a finite number of microscopic scales. The main idea in the proof is closely related to a decomposition of vector fields due to Hermann Weyl. The Weyl decomposition is further explored in paper III.Lubrication theory is devoted to the study of fluid flows in thin domains. More generally, tribology is the science of bodies in relative motion interacting through a mechanical contact. An important aspect of tribology is to explain the principles of friction, lubrication and wear. The mathematical foundations of lubrication theory are given by the Navier–Stokes equation which describes the motion of a viscous fluid. In thin domains several simplifications are possible, as shown in the introduction of this thesis. The resulting equation is named after Osborne Reynolds and is much simpler to analyze than the Navier--Stokes equation.The Reynolds equation is widely used by engineers today. For extremely thin films, it is well-known that the surface micro-topography is an important factor in hydrodynamic performance. Hence it is important to understand the influence of surface roughness with small characteristic wavelengths upon the solution of the Reynolds equation. Since the 1980s such problems have been increasingly studied by homogenization theory. The idea is to replace the original equation with a homogenized equation where the roughness effects are “averaged out”. One problem consists of finding an algorithm for computing the solution of the homogenized equation. Another problem consists of showing, on introducing the appropriate mathematical definitions, that the homogenized equation is the correct method of averaging. Papers I, II, IV and V investigate the effects of surface roughness by homogenization techniques in various situations of hydrodynamic lubrication. To compare the homogenized solution with the solution of the deterministic Reynolds equation, some numerical examples are also included. / Godkänd; 2011; 20110408 (johfab); DISPUTATION Ämnesområde: Matematik/Mathematics Opponent: Professor Guy Bayada, Institut National des Sciences Appliquées de Lyon (INSA-LYON), Lyon, France, Ordförande: Professor Lars-Erik Persson, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Tid: Tisdag den 7 juni 2011, kl 10.00 Plats: D2214/15, Luleå tekniska universitet

Este estudo avaliou os efeitos de pastilhas efervescentes na superfície de liga de cobalto cromo (Co-Cr) e resina termopolimerizável, simulando um período de até 5 anos de imersão, como também analisar sua ação antimicrobiana. A partir de uma matriz metálica, padrões de cera circulares (12 x 3 mm) foram obtidos e fundidos em liga de Co-Cr (DeguDent®). As amostras foram imersas em: Polident 3 minutes® (P3M), Steradent® (St), Polident for Partials® (PP), Efferdent® (Ef), Corega Tabs® (CT), Nitradine® (Ni), Fixodent® (Fi) e Kukident® (K). Foi avaliada a resistência à corrosão (Ecorr, Ipass) (n=5) por meio do Potenciostato/Galvanostato. Foram realizadas análises qualitativas complementares com Microscópio Eletrônico de Varredura (MEV) e Espectrometria de Energia Dispersiva de Raios-X (EDS). Após o ensaio de corrosão, cada disco metálico foi incluído em mufla preparada por matrizes circulares de cera (20 x 5 mm), incorporando-o à resina acrílica termopolimerizável (Clássico Ltda®). Os grupos das 4 pastilhas que apresentaram a menor taxa de corrosão e da água destilada (controle) (n=9) foram analisados quanto à rugosidade da superfície metálica e da resina acrílica (Sa, &micro;m) por meio de microscopia confocal a laser. Foram avaliadas a alteração de cor (&Delta;E) da resina por meio de espectrocolorímetro no início e após a simulação de ½, 1, 2, 3, 4 e 5 anos e alteração de massa (g), no início e final, em balança de alta precisão. Para avaliação antimicrobiana, por meio da contagem de Unidades Formadoras de Colônia (UFC/mL), os espécimes mistos foram contaminados com biofilme misto composto por: S. mutans (Sm), S. aureus (Sa), C. albicans (Ca) e C. glabrata (Cg) e, posteriormente, imersos nas soluções higienizadoras, onde foram semeados em meios específicos para contagem das UFC. De acordo com os resultados obtidos (&alpha;=0,05), P3M causou a menor taxa de corrosão e Ni, o menor potencial de corrosão. Com o MEV, verificou-se evidenciação da microestrutura da liga metálica. Quanto à rugosidade superficial do metal, CT (p=0,009) e Ni (p=0,036) causaram aumento na rugosidade em relação ao tempo (Friedman). Na resina, houve aumento da rugosidade após 5 anos (p<0,01). Entre as soluções (Kruskal-Wallis), não houve diferença para ambos os materiais. Não houve diferença na cor da resina acrílica, tanto em relação às soluções (Kruskal Wallis) quanto aos tempos (Friedman). Não foram observadas alterações de massa (Kruskal-Wallis). Quanto à ação antimicrobiana (Kruskal-Wallis), Ni propiciou redução de UFC de Sm (p=0,001). Conclui-se que, embora todas as pastilhas efervescentes não tenham alterado a superfície do metal e da resina acrílica de maneira significativa, nenhuma apresentou ação antimicrobiana contra os microrganismos avaliados do biofilme misto; somente Ni reduziu a quantidade de S. mutans / The aim of this study were: to evaluate the effects of denture cleansers on the surface of cobalt chromium (Co-Cr) and heat-polymerized acrylic resin, simulating a period until 5 years of immersion, as well as to analyze its antimicrobial action. From a metal matrix, disc-shaped wax patterns (12 x 3 mm) were made and later were casting in Co-Cr alloy (DeguDent&trade;). The specimes were immersed in: Polident 3 minutes&trade; (P3M), Steradent&trade; (St), Polident for Partials&trade; (PP), Efferdent&trade; (Ef), Corega Tabs&trade; (CT), Nitradine&trade; (Ni), Fixodent&trade; (Fi) and Kukident&trade; (K). The corrosion resistance (Ecorr, Ipass) (n = 5) was evaluated by Potentiostat / Galvanostat. Further qualitative analyzes were performed with scanning electronic microscopy (SEM) and energy dispersive x-ray spectrometry (EDS). After the corrosion test, each metal disk was included in heat-cured acrylic resin (Clássico Ltda&trade;) using moulds previously prepared from circular wax matrices (20 x 5 mm). The four dentures cleansers with the lowest corrosive potential were analyzed for surface roughness of the metal and acrylic resin (Sa, &micro;m) by laser confocal microscopy. The color change (&Delta;E) of the resin was evaluated by means of a spectrocolorimeter at the beginning and after the simulation of ½, 1, 2, 3, 4 and 5 years and mass change (g), at the beginning and end, in high-precision balance. For antimicrobial evaluation, the mixed specimens (n = 9) were contaminated with multispecies biofilm [S. mutans (Sm), S. aureus (Sa), C. albicans (Ca) and C. glabrata (Cg)] and subsquently immersed in denture cleansers, where they were seeded in specific CFU / mL media. According to the results obtained (&alpha;=0.05), there was a significant difference: P3M presented the lowest corrosion rate and Ni, the lowest corrosion potential. According to SEM, the tablets effervescent provided evidence of the microstructure of the alloy. As for the surface roughness in the metal surface, CT (p = 0.009) and Ni (p = 0.036) showed increase in roughness in relation to time (Friedman). At the resin surface, the roughness growed after 5 years. Among the solutions (Kruskal-Wallis), there was no difference for both materials. There was no difference in the color of the acrylic resin (&delta;E), both for solution (Kruskal-Wallis), and for time (Friedman). Differences in weight weren\'t observed (Kruskal-Wallis). In antimicrobial action (Kruskal-Wallis), Ni group showed significant reduction for Sm (p=0.001). It\'s concluded that, although all the denture cleansers didn\'t significantly changed the surface of the metal and acrylic resin, none showed antimicrobial action against the evaluated microorganisms of the mixed biofilm; only Ni reduced the amount of S. mutans

I det här arbetet har tätningsmetoder för aluminiumhus undersökts. Arbetet avgränsades mot fordonsindustrin och statiska packningar. Examensarbetet tar upp flänskonstruktionens inver-kan på tätheten och packningen, packningstyper, ytjämnhetens inverkan på packningsmateri-al, porositet, relativ materialkostnad och fästelement.Arbetet grundar sig på en litteraturstudie och intervjuer med berörda personer på företaget. Även praktiska prover genomfördes på ett urval av material från leverantörer där material exponerades för olika kemikalier och därefter dragprovades.Materialet som insamlats genom intervjuer och litteraturstudien vittnar om att många paramet-rar påverkar vilka tätningsmetoder som är möjliga att använda. Det är inte bara materialval som det behövs tas hänsyn till. Faktorer som flänskonstruktioner, materialkostnader, ytdefek-ter, fästelement samt porositet har en stor påverkan. De praktiska proverna vittnar om att olika kemikalier har olika stor inverkan på materialens mekaniska egenskaper och svullnad.Slutligen föreslås ett par packningsmaterial som är lämpliga för företaget att använda i deras produkter. / In this work sealing methods for aluminum housing have been investigated. The work was delimited to the automotive industry and static gaskets. The thesis brings up how the flange impacts on the sealing capability and the gasket, sealing types, the surface impact on gasket materials, porosity, relative material cost and fasteners.The work is based on a literature study and interviews with concerned people at the company. Practical samples were carried out on a number of materials from suppliers and the materials where exposed to different chemicals and then tensile tested.The materials that were collected through interviews and the literature study testify that many parameters influence the possible sealing methods. It’s not just the material itself that needs to be taken into account. Factors like flange design, material cost, surface defects, fasteners and porosity have a great impact. The practical sample testifies that different chemicals have dif-ferent impact on the mechanical properties and swelling of the material.Finally, a couple of sealing materials are suggested that are suitable for the company to use in their products.