The mechanisms by which magnetisation changes occur in magnetic materials may be investigated by a variety of hysteresis measurements. During this study both alternating and rotational hysteresis measurements were used to characterise the mechanisms of magnetisation change in a number of permanent magnet materials. Studies of the time dependence of magnetisation, remanent magnetisations and the dependence of the reversible magnetisation on the irreversible magnetisation were undertaken. These studies revealed that in sintered rare-earth iron magnets the magnetisation change is predominately controlled by domain nucleation, with a lesser contribution from domain wall pinning within the boundary regions of the grains. Similar mechanisms control the magnetisation change in the larger grains of melt-quenched rare-earth iron magnets. In the single domain grains of the melt-quenched materials incoherent rotation mechanisms control the changes of magnetisation. Magnetisation change in MnAlC and sintered AlNiCo was found to be controlled by domain wall pinning within the interior of the grains of the materials. Two devices were constructed for the measurement of rotational hysteresis. The first measures the angular acceleration of a sample set spinning in a magnetic field, from which the rotational hysteresis loss may be determined. The second employs rotating search coils to make direct measurements of the component of magnetisation that contributes to rotational hysteresis loss during the rotation of a sample in a field. Both devices were found to produce data consistent with that in the literature and to be useful for the characterisation of rotational hysteresis in permanent magnet materials. A simple model was used to examine the dependence of rotational hysteresis loss on various material parameters. It was found that the value of the rotational hysteresis integral is dependent on interactions and to a lesser extent distributions in anisotropy. This is contrary to assumptions commonly made in the literature but consistent with published experimental data, which has been reinterpreted. Measurements of rotational hysteresis losses in the materials studied were found to be effected by geometric demagnetisation effects. A method by which such data may be corrected for these effects is proposed. Following correction and consideration of the interactions within the materials, the rotational hysteresis data was found to be consistent with the characterisations performed in linearly alternating fields.

Thesis (Ph. D.)--State University of New York at Binghamton, Mechanical Engineering Department, 2006. / Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 189-198).

Thesis (MSc Food Sc)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The relationship between malt fermentability and rheological variables, measured by means of the Rapid Visco Analyser (RVA) and application of multivariate data analysis, was investigated. The RVA Kilned Malt method was optimised to achieve maximum rheological discrimination between malt samples, differing in fermentability. Five concentrations and two particle sizes were used to investigate each malt sample. Data were analysed by two different data analysis techniques, namely principal component analysis (PCA) and analysis of variance (ANOVA). Rheological variables for peak-height, -width, -area and time occurrence, were able to discriminate between high (Metcalfe, Flagship), intermediate (SSG 585, PUMA) and low malt fermentability (SSG 506, SSG 564). Variation in particle size showed insignificant (P>0.05) fermentability discrimination. The malt to water ratio of 1:1.5 provided the best discrimination in fermentability. PCA applied to the entire dataset was the superior data analysis technique. Partial least squares (PLS) regression and Soft Independent Modeling of Class Analogy (SIMCA) were applied to predict malt fermentability. Recorded RVA data was regressed with both apparent attenuation limit (AAL) and free amino nitrogen (FAN), independently. Developed PLS calibration models were validated by test set and segmented crossvalidation for AAL and FAN, respectively. The SIMCA classification model developed was based on different malt fermentability classes, each PCA validated independently by test set validation. A strong correlation between RVA analysis and AAL was obtained (r=0.92), while FAN delivered a weak correlation (r=0.59). Regarding the SIMCA model; the proportion of test set samples correctly classified in terms of malt fermentability was 83%. South African malt blends were predicted to have low malt fermentability. Simulated blends were predicted to have high fermentability when using a minimum of 80% Metcalfe blended with SSG 506. Blends containing higher percentages of the low malt fermentability cultivar (SSG 506) were predicted to have an overall intermediate fermentability. Different experimental conditions were investigated during RVA analysis (i.e. instrument model; time/temperature profile, enzyme activity and heating/cooling rate). Rheological measurement using different RVA models gave similar PCA results, indicating adequate sensitivity of the older instrument for discrimination purposes. Matching the time/temperature profile used in the commercial brewery mashing process was rejected due to increased analysis time and rheological noise while reducing fermentability discrimination. Inactivating malt enzymes prior to RVA analysis provided useful sample information, such as the large starch granule’s mean diameter, extract and starch content, by measuring peak height and iv time to peak. The amount of starch damage inflicted on a malt sample increased after repeated centrifugal milling, but was unaffected by the sieve size used. Multivariate data analysis is a suitable statistical technique applied to rheological data and provided more relevant information than traditional univariate techniques. The RVA can be considered an ideal instrument within a grain laboratory as it allowed the investigation of different operating conditions. It is beneficial to use an inexpensive, routine method of analysis to measure various interacting factors. RVA rheological measurement demonstrated to be a decisive monitor of malt fermentability and is highly recommended to be incorporated within the barley breeding, malting and brewing industries. / AFRIKAANSE OPSOMMING: Die verwantskap tussen mout fermenteerbaarheid en reologie-veranderlikes, gemeet met die “Rapid Visco Analyser” (RVA) en toepassing van meerveranderlike data analise is ondersoek. Die RVA “Kilned Malt” metode is geoptimeer om maksimum reologiese diskriminasie, tussen gars kultivars van verskillende fermenteerbaarheid, te lewer. Vyf konsentrasies en twee partikel groottes is gebruik in die ondersoek vir elke mout monster. Data is deur beide hoof komponent analise (HKA) en variansie-analise (ANOVA) ondersoek om die verskillende data analise metodes met mekaar te vergelyk. Reologiese veranderlikes vir piek-hoogte, - wydte, -area en -vormingstyd, kon diskrimineer tussen hoë (Metcalfe, Flagship), intermediêre (SSG 585, PUMA) en lae (SSG 506, SSG 564) mout fermenteerbaarheid. Variasie in partikel grootte kon nie beduidende diskriminasie in fermenteerbaarheid aantoon nie. Die mout-totwater konsentrasie van 1:1.5 het die beste diskriminasie in fermenteerbaarheid gelewer. Die toepassing van HKA op die hele datastel was die beter analitiese tegniek. Parsiële kleinste kwadrate (PKK) regressie en Sagte Onafhanklike Modellering van Klas Analogie (SIMCA) is toegepas om mout fermenteerbaarheid te voorspel. Regressie tussen RVA data en skynbare attenuasie limiet (AAL), sowel as vrye amino stikstof (FAN) inhoud, is afsonderlik uitgevoer. Die geldigheid van regressie modelle is deur middel van toets stel en gesegmenteerde kruis-validasie vir AAL en FAN onderskeidelik uitgevoer. SIMCA klassifikasie modelle is gebaseer op verskillende mout fermenteerbaarheids-klasse, waarvan elke HKA klas individueel geldig is. RVA analise het ‘n sterk korrelasie met AAL (r=0.92), maar ‘n swak korrelasie met FAN (r=0.59) getoon. Die SIMCA model het 83% van toets stel monsters as korrek geklassifiseer in terme van mout fermenteerbaarheid. Suid Afrikaanse mout mengsels is voorspel as swak fermenteerbaar. Nagebootste mengsels is voorspel as hoogs fermenteerbaar wanneer minimum 80% Metcalfe met SSG 506 vermeng word. Sodra ‘n hoër persentasie van die swakker fermenteerbaarheids-kultivar (SSG 506) bygevoeg is, word intermediêre fermenteerbaarheid voorspel. Tydens RVA analise is verskillende eksperimentele toestande ondersoek (byvoorbeeld instrument model; tyd/temperatuur profiel; ensiem aktiwiteit en verhittings/verkoelings tempo). Die gebruik van verskillende RVA modelle het soortgelyke HKA resultate gelewer. Dus bevat die ouer instrument aanvaarbare sensitiwiteit vir diskriminasie doeleindes. Nabootsing van die tyd/temperatuur profiel in die kommersiële brouproses is verwerp, aangesien analise tyd en reologiese geraas toegeneem het, terwyl fermenteerbaarheidsdiskriminasie verminder het. Inaktivering van mout ensieme voor RVA analise lewer nuttige monster inligting; deur veranderlikes soos piek-hoogte en piek-tyd te meet, kan die groot stysel korrel se gemiddelde deursnit, ekstrakwaarde en stysel inhoud verkry word. Herhaalde sentrifugale maling van ‘n mout monster lei tot beskadiging van stysel, maar dit word nie deur sif grootte beïnvloed nie. Die toepassing van meerveranderlike data analise op reologiese data is waardevol en lewer meer relevante inligting in vergelyking met tradisionele eenveranderlike data analise. Die RVA is ‘n ideale instrument vir gebruik in ‘n graan laboratorium aangesien dit verskillende operatiewe kondisies kan ondersoek. Die gebruik van ‘n enkele, goedkoop, roetine analitiese metode is voordelig en het die potensiaal om ‘n magdom interaktiewe faktore te meet. RVA reologiese meting demonstreer die vermoë as ‘n deurslaggewende tegniek vir die bepaling van mout fermenteerbaarheid, gevolglik word toepassing sterk aanbeveel binne die gars teëlings-, vermoutings- en brouers-industrieë.

Made available in DSpace on 2014-06-11T19:27:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-12-11Bitstream added on 2014-06-13T20:35:22Z : No. of bitstreams: 1 reis_jfa_me_ilha.pdf: 4095503 bytes, checksum: 7b68949931b17d9ea9723fac44c2e518 (MD5) / As propriedades reológicas do concreto no seu estado fresco são importantes principalmente no período em que o material é lançado nas fôrmas e podem ser determinadas em qualquer momento durante o período de indução da hidratação do cimento. Entretanto, o uso da reologia para estudar a taxa de fluidez ou trabalhabilidade do concreto não é muito comum. Geralmente, o abatimento de tronco de cone é o único parâmetro medido e, mesmo em laboratório, os estudos raramente fornecem informações adicionais sobre o comportamento ao escoamento desses materiais. O ensaio do tronco de cone modificado proposto de LARRARD permite avaliar a tensão crítica e a viscosidade plástica do concreto, de maneira simples e sem grandes custos, uma vez que reômetros de laboratórios são aparelhos sofisticados e relativamente com custos elevados. Este estudo avalia a tensão de escoamento e a viscosidade plástica obtida pelo teste de abatimento de tronco de cone modificado para dois tipos distintos de concreto, a saber: o concreto fresco convencional e o concreto de alto desempenho (CAD), elaborados com cimento CPV ARI-Plus. E também foi realizado correlações entre o ensaio de abatimento de tronco de cone modificado e o ensaio de reometria clássica. Os resultados obtidos mostraram-se bastante satisfatórios para o cálculo da tensão e da viscosidade dos concretos avaliados. / The concrete rheological properties in fresh state are mainly important in the period that the material is thrown in the molds and it can be certain in any moment during the induction period of the cement hydration. However, the use of the rheology to study the fluidity rate or concrete workability is not very common. Usually, the slump is just an unique measured parameter and, even in laboratory, the studies rarely supply additional information about the flow behavior of those materials. The slump modified test proposed by LARRARD it allows to evaluate the critical tension and concrete plastic viscosity so simply and without significant costs, because rheometers of the laboratories are very sophisticated and relatively expensive apparels. This study evaluates the yield stress and the viscosity obtained by the slump modified test for two different types of concrete, like to: the conventional fresh concrete and the concrete of high acting (CAD), elaborated with cement CPV ARIPlus. And it was done to test the correlation between slump modified test and test classical rheometer. For the concretes of high performed starting from the specific line the addictive volume addition superplastificante was varied obtaining initial slumps that varied between 100mm and 260mm. The initial results obtained have proved very satisfactory in tension and viscosity calculus of the evaluated concretes.

Made available in DSpace on 2014-10-09T12:27:13Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:01Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

abstract: Micro-electro-mechanical systems (MEMS) film bulk acoustic resonator (FBAR) demonstrates label-free biosensing capabilities and is considered to be a promising alternative of quartz crystal microbalance (QCM). FBARs achieve great success in vacuum, or in the air, but find limited applications in liquid media because squeeze damping significantly degrades quality factor (Q) and results in poor frequency resolution. A transmission-line model shows that by confining the liquid in a thickness comparable to the acoustic wavelength of the resonator, Q can be considerably improved. The devices exhibit damped oscillatory patterns of Q as the liquid thickness varies. Q assumes its maxima and minima when the channel thickness is an odd and even multiple of the quarter-wavelength of the resonance, respectively. Microfluidic channels are integrated with longitudinal-mode FBARs (L-FBARs) to realize this design; a tenfold improvement of Q over fully-immersed devices is experimentally verified. Microfluidic integrated FBAR sensors have been demonstrated for detecting protein binding in liquid and monitoring the Vroman effect (the competitive protein adsorption behavior), showing their potential as a promising bio-analytical tool. A contour-mode FBAR (C-FBAR) is developed to further improve Q and to alleviate the need for complex integration of microfluidic channels. The C-FBAR consists of a suspended piezoelectric ring made of aluminum nitride and is excited in the fundamental radial-extensional mode. By replacing the squeeze damping with shear damping, high Qs (189 in water and 77 in human whole blood) are obtained in semi-infinite depth liquids. The C-FBAR sensors are characterized by aptamer - thrombin binding pairs and aqueous glycerine solutions for mass and viscosity sensing schemes, respectively. The C-FBAR sensor demonstrates accurate viscosity measurement from 1 to 10 centipoise, and can be deployed to monitor in-vitro blood coagulation processes in real time. Results show that its resonant frequency decreases as the viscosity of the blood increases during the fibrin generation process after the coagulation cascade. The coagulation time and the start/end of the fibrin generation are quantitatively determined, showing the C-FBAR can be a low-cost, portable yet reliable tool for hemostasis diagnostics. / Dissertation/Thesis / Ph.D. Electrical Engineering 2011

This dissertation is devoted to the finite element (FE) approximation of equations describing the motion of a class of non-Newtonian fluids. The main focus is on incompressible fluids whose viscosity nonlinearly depends on the shear rate and pressure. The equations of motion are discretized with equal-order d-linear finite elements, which fail to satisfy the inf-sup stability condition. In this thesis a stabilization technique for the pressure-gradient is proposed that is based on the well-known local projection stabilization (LPS) method. If the viscosity solely depends on the shear rate, the well-posedness of the stabilized discrete systems is shown and a priori error estimates quantifying the convergence of the method are proven. In the shear thinning case, the derived error estimates provide optimal rates of convergence with respect to the regularity of the solution. As is well-known, the Galerkin FE method may suffer from instabilities resulting not only from lacking inf-sup stability but also from dominating convection. The proposed LPS approach is then extended in order to cope with both instability phenomena. Finally, shear-rate- and pressure-dependent viscosities are considered. The Galerkin discretization of the governing equations is analyzed and the convergence of discrete solutions is...

Les propriétés viscoélastiques des fluides déterminent leur écoulement. L’étude de ces propriétés a de nombreuses applications industrielles et académiques qui concernent la matière dite « molle » (polymères, colloïdes, tensioactifs, protéines, ...). L’approche proposée permet d'étudier ces propriétés sur une gamme de fréquence allant de 1 à 100 kHz. La méthode utilise la mesure de la vibration d’une microstructure actionnée électromagnétiquement et immergée dans le fluide à caractériser. La réponse en fréquence du système mécanique, mesurée optiquement ou électriquement, est caractéristique du milieu dans lequel la structure est immergée. Une méthode analytique dédiée aux micropoutres, pour l’extraction des propriétés rhéologiques du milieu, a été améliorée tout au long de la thèse.La méthode analytique développée, pour être appliquée, nécessite la précision d’un système optique complexe pour mesurer sans artefact les propriétés mécaniques de l’interaction micropoutre-liquide. Ainsi les liquides opaques ne peuvent être caractérisés avec cette approche. De plus la mesure peut difficilement être intégrée dans un dispositif portable tout-électronique. Afin de pallier ces difficultés et de proposer une mesure de la viscoélasticité en milieu opaque, la stratégie de mesure du capteur jusqu’au traitement des signaux ont été réévalués : (1) des microstructures en « U » ont été fabriquées, (2) une méthode de mesure intégrée a été mise en place et (3) une méthode de traitement à fréquence unique a été utilisée. Finalement, un liquide opaque viscoélastique, le yaourt, a pu être caractérisé in-situ tout au long de la fermentation lactique permettant de démontrer la validité et l’applicabilité de la méthode mise en œuvre pour le suivi en temps réel de la viscoélasticité. / The study of viscoelastic properties has many industrial and academic applications related to "soft matter" like polymers, colloids, surfactants or proteins. The present approach measures these properties in a frequency range from 1 to 100 kHz. The method uses the measurement of the vibration of a microstructure actuated electromagnetically and immersed in the fluid that has to be characterized. The frequency response of the mechanical system, which is measured optically or electrically, is characteristic of the environment in which the structure is immersed in. An analytical method dedicated to microcantilevers for the extraction of the rheological properties has been improved during this PhD thesis.The analytical method developed requires the accuracy of a complex optical system for measuring without artifact the mechanical properties of microcantilever-liquid interaction. Thus opaque liquids cannot be characterized with this sytem. In addition, the measurement cannot easily be integrated. To overcome these difficulties and provide the measurement of viscoelasticity into opaque medium, some strategy was reassessed: (1) “U” shaped microstructures were fabricated; (2) an integrated measurement method was developed and (3) a single frequency method was used to calculate the viscoelasticity.Finally, a viscoelastic and opaque liquid, such as yogurt, has been characterized in situ during the lactic fermentation to demonstrate the validity and the applicability of the method for the real-time monitoring of viscoelasticity.

L’étude des écoulements compressibles, notamment supersoniques, traversant les chambres de combustion de certains moteurs ramjet et scramjet, requiert la prise en compte de différents dispositifs complexes pour l’amélioration du processus de combustion et en particulier de leur stabilisation. La connaissance des interactions entre la turbulence, les effets de compressibilité, et les interaction fluide-solide dans ce type d’écoulement reste imparfaite. Ce travail de thèse est dédié à l’amélioration de notre compréhension de ce type d’écoulement dans un certain nombre de configurations canoniques par la biais de la simulation numérique directe. L’ensemble des simulations conduites s’appuie sur l’emploi d’un outil de simulation numérique haute fidélité : CREAMS (Compressible REActive Multi-species Solver) développé à l’Institut Pprime. Ce code de calcul met en oeuvre des schémas numériques d’ordre élevé : schéma Runge–Kutta d’ordre 3 pour l’intégration temporelle combiné à un schéma WENO d’ordre 7 et centré d’ordre 8 pour la discrétisation spatiale. Dans un premier temps, nous présentons une nouvelle méthode de frontières immergées pour le calcul d’écoulement d’un fluide visqueux compressible dans des géométries irrégulières. La méthode développée dans le cadre de cette thèse est basée sur la combinaison de l’approche appelée "Direct forcing" et celle de "Ghost-Point-Forcing". L’originalité de cette méthode réside dans sa capacité à simuler des écoulements subsoniques et supersoniques à différents nombres de Reynolds. L’examen de précision de cette méthode a permis d’établir un ordre supérieur à deux et sa robustesse est éprouvée par l’étude d’un bon nombre de cas tests. Dans un second temps, une configuration canonique idéalisée d’interaction choc-turbulence est étudiée pour mettre en lumière les mécanismes physiques fondamentaux caractéristiques du phénomène d’interaction entre une turbulence homogène isotrope et une onde de choc droite. Cette étude est complétée par une étude d’interaction choc-mélange scalaire pour étudier l’impact du choc normal sur le processus du mélange. Ce travail permet de mettre en place une base de données de résultats susceptibles d’être confrontés ultérieurement à des calculs basés sur l’emploi de modèles de turbulence. Enfin, nous nous sommes intéressés à l’effet des propriétés de transport moléculaire, en particulier celles de la viscosité volumique, sur le développement d’une couche de mélange impactée par un choc oblique. Les simulations réalisées dans cette configuration ont permis d’étudier la validité de l’hypothèse de Stokes consistant à négliger l’effet de la viscosité volumique. / The study of compressible flows, especially supersonic, passing through the combustion chambers of ramjet and scramjet engines, requires the consideration of various complex devices for improving the combustion processand in particular its stabilization. Indeed, the knowledge of the interactions between turbulence, compressibility effects, and fluid-solid interactions in this type of flow still remains imperfect. This thesis is dedicated to improving our understanding of this type of flow in a number of canonical flow configurations through direct numerical simulation. All the simulations that have been conducted are based on the use of a high-precision numerical simulations tool, called CREAMS (Compressible REActive Multi-species Solver), developed at the Pprime Institute. This computational solver makes use of high precision numerical schemes: a 3rd order Runge–Kutta scheme for time integration combined with a 7th order WENO and 8th order centered scheme for spatial discretization. In a first step of this study, we present a new immersed boundary method for calculating the flow of compressible viscous fluids in irregular geometries. The method developed in this thesis is based on the combination of the "Directforcing" approach with the "Ghost-Point-Forcing" strategy. The originality of this method lies in its ability to simulate subsonic and supersonic flows at different Reynolds numbers. The accuracy of this method is found to be slightly larger than second order and its robustness is investigated by considering a large set of benchmarks. Ina second step, an idealized canonical configuration of shock-turbulence interaction is studied to highlight the fundamental physical mechanisms that are characteristic of the interaction between an isotropic homogeneous turbulence and a normal shock wave. This analysis is complemented by a scalar shock-mixing interaction study to investigate the impact of normal shock on the mixing process properties. Through this work, a database is made available. It can be used to assess and improve turbulence models. Finally, we investigated the effect of molecular transport properties, more specifically the volume viscosity, on the development of a mixture layer impacted by an oblique shock. The simulations performed in this configuration allow to scrutinize the validity of the Stokes hypothesis that is based on the neglection of the volume viscosity.