To identify the dynamic model of the treadmill, this study uses the piezoelectricity material (Po1yviny-lidene fluoride, PVDF) to measure the force under treadmill. With this dynamic model, the ground reaction force (GRF) can be derived from the PVDF sensors. The reliability and precision of the GRF results are verified by replacing the PVDF with the traditional load cell (Force measurement devices). To verify the accuracy of treadmill model, this study acquires three different types of GRF signals (marking time, walking and running) from ten subjects. For the marking time case, the correlation coefficients between the actual and predicated GRF signals are approximately 0.98. This study also demonstrates that the proposed model can provide sufficient bandwidth for the walking and running GRF signals. Finally, via comparing the average GRF profile, inter-personal differences of the GRF signal can be observed. Among the three tested locomotion patterns, the marking time GRF has the highest similarity whereas the running GRF signals has the largest variability.

Many proteins are known to actively interact with biological, as well as inorganic and synthetic surfaces that are widely used in nano- and bio-technology as biosensing platforms and in tissue engineering. Amyloid fibrils are insoluble protein aggregates in beta-sheet conformation that are implicated in at least 20 diseases for which no cure is currently available. The molecular mechanism of fibril formation, as well as the mechanism of fibril clusters interacting with lipid membrane surfaces is currently unknown. The lipid membrane surface has a complex biochemical composition and is also electrostatically non-homogeneous. Currently, the experimental data available for amyloid fibril formation both on lipid and artificial surfaces is limited. The goal of our study is to investigate how the physical properties of the surfaces affect binding of amyloid peptides and affect the fibril formation. We seek to elucidate the effect of electrostatic interactions of amyloid peptides with surfaces using Atomic Force Microscopy (AFM) and Kelvin probe force microscopy (KPFM). We show using KPFM that electrostatic domains readily form within biological systems such as lung surfactant and lipid monolayers. We compared three different implementations of KPFM to demonstrate that frequency modulated (FM-) KPFM provides significant advantages over other modes. We also present a study of Amyloid beta (1-42) fibril formation on model surfaces, which are uniformly charged or possess periodicity of charges and hydrophobic functionality based on thiol self-assembly. Effect of membrane composition, surface charge, and presence of steroids will be discussed.

Epitaxial growth, or the oriented growth of a crystalline monolayer on an ordered substrate, appears in a wide range of systems and applications, from novel device fabrication to freshwater remediation. Despite this, methodical studies of the phenomenon are rare, and the mechanisms governing epitaxial growth are poorly understood. This investigation employs AFM techniques to monitor the epitaxial growth of ion crystal systems at the initial stages of growth. By using systems with well-known physical properties, we are able to relate growth modes to two key parameters, crystal lattice mismatch, Δr/r₀, and affinity between the overgrowth and the substrate ions, ξ. We found wetting growth occurs for systems in which Δr/r₀ is expansive (overgrowth lattice must expand to accommodate substrate) or mildly compressive (overgrowth compresses to accommodate substrate). Additionally, a strong affinity between the substrate and overgrowth ions, in combination with an expansive system, allows for epitaxial growth from undersaturated solutions. We also have observed several instances where the lateral force contrast on the growing film exhibits a strong dependence on the time of exposure to the growth solution and on the driving force for growth (solute concentration). We present results for three epitaxial growth systems in aqueous solutions: CaSO₃ on CaCO₃, PbSO₄ on BaSO₄, and BaSO₃ on BaSO₄. Chemically and topographically identical regions grown at higher concentrations exhibit higher friction than regions grown at lower concentrations. These observations suggest that epitaxial growth occurs by a fast condensation step incorporating a high defect density.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

The object proposed in this study is to consider both the activities and the importance of the Pathfinder Force, Royal Air Force, in the Second World War. Their story has a much earlier beginning than 15 August 1942 when the founder squadrons gathered on various R.A.F. stations in the vicinity of the cathedral city of Ely in Cambridgeshire. Some form of target finding and marking became inevitable from the moment it was acknowledged that the preparations that had been made for war during the 1930s were less than adequate. The arguments that ensued pior to August 1942 were much less concerned with the need, than with the form, such a force should take. Unfortunately, while the administrative in-fighting surged back and forth, R.A.F. aircrews went to war not only insufficiently trained but also poorly equipped. Necessity and duty drove these men to attempt to combat weather conditions and enemy defensive measures in aircraft, that all too frequently, were unfitted for the roles they were expected to fulfil. To their credit they pressed on despite the hazards of weather, the fury of enemy defences and the deficiencies of their aircraft and equipment. Regardless of the forces of nature and man ranged against them, the crews of Bomber Command and the Pathfinder Force pressed on. It is therefore fitting that 'Press on Regardless' became the unofficial motto of the Pathfinder Force. It would also provide a singularly apt epitaph for the 3,727 men of the Pathfinder Force who were killed on operations. This work has been written in tribute to all who served in the Pathfinder Force but particularly to those who failed to return.

The Atomic Force Microscope (AFM) is a tool for imaging surfaces at the microand nano meter scale. The microscope senses the force acting between a surfaceand a tip positioned at the end of a micro-cantilever, forming an image of the surface topography. Image contrast however, arises not only from surface topography, but also from variation in material composition. Improved material contrast, and improved interpretation of that contrast are two issues central to the further development of AFM. This thesis studies dynamic AFM where the cantilever is driven at multiple frequencies simultaneously. Due to the nonlinear dependence of the tip-surface force on the tip’s position, the cantilever will oscillate not only at the driven frequencies, but also at harmonics and at mixing frequencies of the drives, so-called intermodulation products. A mode of AFM called Intermodulation AFM (ImAFM) is primarily studied, which aims to make use of intermodulation products centered around the resonance frequency of the cantilever. With proper excitation many intermodulation products are generated near resonance where they can be measured with large signal-to-noise ratio. ImAFM is performed on samples containing two distinct domains of different material composition and a contrast metric is introduced to quantitatively evaluate images obtained at each response frequency. Although force sensitivity is highest on resonance, we found that weak intermodulation response off resonance can show larger material contrast. This result shows that the intermodulation images can be used to improve discrimination of materials. We develop a method to obtain material parameters from multifrequency AFM spectra by fitting a tip-surface force model. Together with ImAFM, this method allows high resolution imaging of material parameters. The method is very generalas it is not limited to a specific force model or particular mode of multifrequency AFM. Several models are discussed and applied to different samples. The parameter images have a direct physical interpretation and, if the model is appropriate, they can be used to relate the measurement to material properties such as the Young’s modulus. Force reconstruction is tested with simulations and on measured data. We use the reconstructed force to define the location of the surface so that we can address the issue of separating topographic contrast and material contrast. / Svepkraftmikroskop (eller atomkraftmikroskop från engelskans atomic forcemicroscope, AFM) är ett instrument för att avbilda ytor på mikro- och nanometer skalan. Mikroskopet känner av kraften som verkar mellan en yta och en spetsplacerad längst ut på ett mikrometerstort fjäderblad och kan därigenom skapa en topografisk bild av ytans form. Bildkontrast uppstår dock inte bara från ytans form utan även från variation i material. Förbättrad materialkontrast och förbättrad tolkning av denna kontrast är två centrala mål i vidareutvecklingen av AFM. Denna avhandling berör dynamisk AFM där fjädern drivs med flera frekvensersamtidigt. På grund av det ickelinjära förhållandet i yt-spets-kraften som funktion av spetsens position så kommer fjädern inte bara att svänga på de drivna frekvenserna utan också på övertoner och blandfrekvenser, så kallade intermodulationsprodukter. Vi undersöker primärt Intermodulation AFM (ImAFM) som ämnar att utnyttja intermodulationsprodukter nära fjäderns resonansfrekvens. Med en lämplig drivsignal genereras många intermodulationsprodukter nära resonansen, där de kan mätas med bra signal till brus förhållande. ImAFM utförs på ytor bestående av två distinkta domäner av olika material ochen kontrastmetrik introduceras för att kvantitativt utvärdera bilderna som skapas vid varje frekvens. Trots att känsligheten för kraftmätningen är högst på resonans-frekvensen, så fann vi att svaga intermodulationsprodukter bortanför resonansen kan visa hög materialkontrast. Detta resultat visar att intermodulationsbilderna kan användas för att bättre särskilja olika material. Vi har utvecklat en metod för att rekonstruera yt-spets-kraften från multifrekventa AFM spektra genom modellanpassning i frekvensrymden. Tillsammans med ImAFM leder detta till högupplösta bilder av materialparametrar. Metoden är generell och är applicerbar för olika kraftmodeller och AFM-varianter. Parametrarna har en direkt fysikalisk tolkning och, om lämpliga modeller används, kan egenskaper så som materialets elasticitetsmodul mätas. Metoden har testats på simulerat såvälsom experimentellt data, och den har också används för att särskilja topografisk kontrast från materialkontrast. / <p>QC 20150209</p>

We introduce a sensor which uses phase shifted dual diffraction gratings in order to increase the detectable range of motion when using phase sensitive diffraction for optical detection of displacement in probe microscopy. The modified FIRAT structure is comprised of a micro-machined bridge structure with integrated diffraction gratings for use in optical detection. With this new design and modified geometry/fabrication process, we will demonstrate force sensing structures with improved displacement detection range and dynamic response. The structure is based upon a previous implementation of force sensor modified for use in AFM imaging. It is built upon a transparent substrate and the bridge / grating serve as an integrated electrostatic actuator. The previously introduced an AFM sensor structure, with integrated actuator, can feasibly obtain Pico Newton force resolution along with increased bandwidth. The advantages of the integrated phase-sensitive diffraction grating and electrostatic actuator over other cantilever based implementations are well developed, yet the FIRAT structure suffered from limited displacement detection range of about ë/4 (167.5 nm for ë = 670 nm), its dynamics were dominated by squeeze film damping and the stiffness was not suitable for many imaging applications. This limitation in range was not due to the device physical structure or actuator, but was inherent to the optical detection scheme used. Modifications to the previous structure design, and sensor detection scheme, are implemented in order to increase the detectable range of the sensor implementation, reduce damping and stiffness, and custom tailor our devices to imaging applications

Thesis (Ph. D.).--Catholic University of America, 1939. / Includes bibliographical references (p. 117-120).

Les racines des plantes jouent un rôle important dans la croissance et le développement des plantes, et il est bien connu que les interactions mécaniques entre une croissance racinaire et le sol environnant peuvent avoir un impact majeur sur la croissance des racines et par conséquent sur la production de biomasse végétale. Ces interactions mécaniques sont l'un des nombreux facteurs qui peuvent expliquent la variabilité de l'architecture des racines, y compris les facteurs génétiques, environnementaux et l'instabilité du développement. Mais ce facteur a souvent été sous-estimé. Nous supposons que la structure hétérogène du sol à l'échelle des grains, démontrée par la large répartition des forces, peut influencer d'une manière significative sur les trajectoires de croissance des racines. Ce travail de thèse vise à déterminer comment les grains dans les sols granulaires se réorganisent sous l'action de la croissance des racines, et en retour, comment les forces résultantes agissant sur les apex des racines modifient leur développement, y compris la cinématique de leurs trajectoires. Nous avons développé un modèle numérique 2D de la croissance des racines dans un milieu granulaire en utilisant la méthode des éléments discrets (DEM). Le modèle est capable de calculer les forces de contacts grain-grain et racine-grain dans un milieu granulaire. Le système racinaire est modélisé en utilisant des chaînes d'éléments de spheroline connectés. L'orientation de la croissance des racines, à chaque étape de croissance est déterminée par la dynamique de la racine entière sous l'action des forces élastiques internes et des forces de réaction exercées par les grains, ces sont les interactions mécaniques qui contrôlent la croissance numérique dans le modèle.Des études paramétriques ont été réalisées afin (i) d'estimer l'influence de la structure granulaire (distribution de grains de diamètre, la cohésion, la fraction volumique ...) et les propriétés mécaniques des racines (la rigidité à la flexion) sur le signal de force axiale agissant sur la pointe de la racine, et sur les trajectoires et (ii) de définir les lois physiques générales qui peuvent être utilisées en outre pour analyser des données expérimentales. Les courbes de distribution des forces axiales calculées normalisées par leurs moyens au cours d'une période donnée de la croissance, sont caractérisées par une loi de puissance décroissante pour les forces en dessous de la force moyenne, et une décroissance exponentielle pour les forces ci-dessus de la force moyenne, reflétant ainsi la large répartition des forces à l'intérieur d'un matériau granulaire. Une analyse de l'écart-type des déformations locales des trajectoires des racines, résulte deux régimes en fonction la rigidité de la racine. Une première lorsque le sol contrôle les déformations des racines, et une deuxième lorsque la racine est trop rigide, et se déplace plus les grains environnants durant la croissance. / Plant roots play an important role in the growth and development of plants, and it is well known that the mechanical interactions between a growing root and the surrounding soil can have a major impact on root growth and consequently on plant biomass production. These mechanical interactions are one of numerous factors that explain the variability of root architecture, including genetics, environment and developmental instability. But this factor has often been under-estimated. I hypothesize that the heterogeneous structure of soil at the particle scale, demonstrated by the broad distribution of forces, can significantly influence root growth trajectories. This thesis aims at determining how grains in granular soils are reorganized under the action of growing roots, and in return how the resulting forces acting on root tips modify their development, including the kinematics of their trajectories, in order to develop a general biophysical law of root-soil mechanical interactions. I developed a 2D numerical model of root growth in a granular medium using a Discrete Element Model (DEM). The model is able to compute grain-grain and root-grain contact forces within a granular medium. The root system is modelled using chains of connected spheroline elements. The orientation of root growth at every growth step is determined by the dynamics of the whole root under the action of its internal elastic forces and reaction forces exerted by the grains, which are the mechanical interactions that control numerical growth in the model.Parametric studies were carried out in order to (i) estimate the influence of granular structure (grain diameter distribution, cohesion, volume fraction) and root mechanical properties (root bending stiffness) on the axial force signal acting on the root tip, and on the root trajectories and (ii) define general physical laws that can be used further to analyze experimental data. The distribution curves of computed root tip-grain forces normalized by the mean force during a given period of growth were characterized by a decreasing power law for forces below the mean force, and an exponential fall-off for forces above the mean force, thus reflecting the broad distribution of forces inside the granular material. An analysis of the standard deviation of the local deformations of root trajectories resulted in two different regimes with regard root stiffness. In the first regime, soil controlled the root deformation and in the second, the root trajectory was straighter and displaced more significantly the surrounding grains during growth.

Background: Age-related changes in pelvic floor muscle (PFM) biomechanics may contribute to urinary incontinence in older women; however, empirical evidence is scant. Purpose: This study aimed to understand the age-related changes in the biomechanical properties of the PFMs in women with no major risk factors for urinary incontinence. Methods: Thirty-three nulliparous women (20-64 years) were recruited to study active force, rate of force development, endurance, resistance to passive stretch and stiffness properties of the PFMs using an automated dynamometer. Separate regression analyses were performed to investigate the relationship between age and each outcome measure. Results: No significant relationships were observed between age and any of the outcome measures. Conclusion: The findings from this study do not support the presence of any age-related changes in PFM mechanics among women aged 20-64. Recruiting women over the age of 65 may be essential to detect age-related changes in PFM biomechanics in nulliparous women.