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1
Boks, Niels P. "Bacterial interaction forces in adhesion dynamics". [S.l. : [Groningen : s.n.] ; University Library Groningen] [Host], 2009. http://irs.ub.rug.nl/ppn/.
Testo completo
2
Hunt, Geoffrey A. "Dynamic analysis of railway vehicle/track interaction forces". Thesis, Loughborough University, 1986. https://dspace.lboro.ac.uk/2134/7492.
Testo completoAbstract (sommario):
Methods of predicting the dynamic forces are developed for the cases of vehicles negotiating vertical and lateral track irregularities. The bounds of validity of various models of the track are evaluated, from single degree of freedom, lumped parameter models to the case of a two layered beam on elastic foundation with a moving dynamic load. For the case of the lateral response of a vehicle negotiating a track switch, a finite element model of the track is also developed. The vehicle model developed for-the vertical case contains all the rigid body modes of a four axle vehicle for which primary and secondary suspension can be included with viscous or friction suspension damping. Solution of the vehicle/track interaction problem for these non-linear models is obtained by numerical integration, vehicle and track being connected by the non-linear wheel/rail contact stiffness. The most significant forces are shown to arise from the interaction of the unsprung mass and track resilience, with the vehicle modes also making a significant contribution, particularly in friction damped cases. For the lateral case use is made of an existing model of transient vehicle behaviour containing the wheel/rail contact non-linearities, to which track resilience is added in order to predict the track forces. The model is used to predict the forces which would be anticipated at discrete lateral irregularities such as those to be found at track switches. Once again the interaction with the track introduces modes of vibration which are significant in terms of wheel/rail forces. Comparison is made with experimental results obtained from full scale tests in the field. In one experiment the vertical track forces due to a range of vehicles negotiating a series of dipped welds in the track were measured, and in a second the lateral forces were recorded at the site of an artificially introduced lateral kink. A particular application of the results is in the prediction of the rate of deterioration of vertical and lateral geometry due to dynamic forces. This is to offer an improved understanding of the deterioration mechanism in order to influence the future design of vehicles and track to reduce maintenance costs.
3
Tha, Susan P. L. "Interaction forces between human red cells aggutinated by antibody". Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75421.
Testo completoAbstract (sommario):
A theoretical and experimental method is described whereby the hydrodynamic forces, both normal and shear, acting on the spheres of a doublet can be calculated. This is applied to a system of sphered human red blood cells agglutinated by human hyperimmune anti-B antiserum undergoing Poiseuille flow and observed using the traveling microtube technique. The mean forces separating the cells of individual doublets were found to be proportional to antiserum concentration from 0.73 to 3.56% v/v, normal forces increasing from 0.060 to 0.197 nN and shear forces from 0.023 to 0.072 nN. It was impossible to determine which force was responsible for break-up. Measurements of the doublets' mean dimensionless period of rotation indicated that doublets were rigidly linked.Micropipet aspiration was applied to the same red cell-antibody system. Separation forces were $ sim2{1 over2}$ fold greater than for normal forces of the traveling microtube technique. Non-uniformity of red cell adhesiveness was also demonstrated.
4
Arai, Nozomi. "Self-Assembly of Colloidal Particles with Controlled Interaction Forces". Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263693.
Testo completo
5
Hansson, Petra M. "Hydrophobic surfaces: Effect of surface structure on wetting and interaction forces". Doctoral thesis, KTH, Yt- och korrosionsvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-103409.
Testo completoAbstract (sommario):
The use of hydrophobic surfaces is important for many processes both in nature and industry. Interactions between hydrophobic species play a key role in industrial applications such as water-cleaning procedures and pitch control during papermaking but they also give information on how to design surfaces like hydrophobic mineral pigments. In this thesis, the influence of surface properties on wetting and interaction forces has been studied. Surfaces with close-packed particles, pore arrays, randomly deposited nanoparticles as well as reference surfaces were prepared. The atomic force microscope (AFM) was utilized for force and friction measurements while contact angles and confocal Raman microscopy experiments were mainly used for wetting studies. The deposition of silica particles in the size range of nano- to micrometers using the Langmuir-Blodgett (LB) technique resulted in particle coated surfaces exhibiting hexagonal close-packing and close to Wenzel state wetting after hydrophobization. Force measurements displayed long-range interaction forces assigned to be a consequence of air cavitation. Smaller roughness features provided larger forces and interaction distances interpreted as being due to fewer restrictions of capillary growth. Friction measurements proved both the surface structure and chemistry to be important for the observed forces. On hydrophobic pore array surfaces, the three-phase contact line of water droplets avoided the pores which created a jagged interface. The influence of the pores was evident in the force curves, both in terms of the shape, in which the three-phase contact line movements around the pores could be detected, as well as the depth of the pores providing different access and amount of air. When water/ethanol mixtures were used, the interactions were concluded to be due to ethanol condensation. Confocal Raman microscopy experiments with water and water/ethanol mixtures on superhydrophobic surfaces gave evidence for water depletion and ethanol/air accumulation close to the surface. Force measurements using superhydrophobic surfaces showed extremely long-range interaction distances. This work has provided evidence for air cavitation between hydrophobic surfaces in aqueous solution. It was also shown that the range and magnitude of interaction forces could, to some extent, be predicted by looking at certain surface features like structure,roughness and the overall length scales.QC 20121011
6
Fitzpatrick, Helen. "Direct measurement of the forces of interaction between adsorbed protein layers". Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/46769.
Testo completo
7
Dean, Delphine Marguerite Denise 1978. "Modeling and measurement of intermolecular interaction forces between cartilage ECM macromolecules". Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/30153.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. 143-151).
The mechanical properties of cartilage tissue depend largely on the macromolecules that make up its extracellular matrix (ECM). Aggrecan is the most abundant proteoglycan in articular cartilage. It is composed of a core protein with highly charged, densely packed glycosaminoglycan (GAG) side chains, which are responsible for [approximately] 50% of the equilibrium compressive stiffness of the tissue. Using atomic force microscopy (AFM) and high resolution force spectroscopy (HRFS), it is now possible to directly measure nanoscale interactions between ECM macromolecules in physiologically relevant aqueous solution conditions. In order to interpret these data and compare them to macroscopic tissue measurements, a combination of experiments and theoretical modeling must be used. In this thesis, a new molecular-scale continuum Poisson-Boltzmann (PB)-based model was developed to predict the intermolecular interactions between GAG macromolecules by taking into account nanoscale space varying electric potential and fields between neighboring GAGs. A rod-like charge density distribution describing the time averaged space occupied by a single GAG chain was formulated. The spacing and size of the rods greatly influenced the calculated force even when the total charge was kept constant. The theoretical simulations described HRFS experimental data of the normal interaction force between two surfaces chemically end-grafted with an array of GAGs ("brushes") more accurately than simpler models which approximate the GAG charge as a homogeneous volume or planar surface charge. Taken together, these results highlight the importance of nonuniform molecular-level charge distribution on the measured GAG interaction forces. Normal interaction forces between aggrecan macromolecules were measured using contact mode AFM imaging and by HRFS.
(cont.) The aggrecan molecules were end-grafted to gold-coated substrates and probe tips to achieve brush-like layers at physiologically relevant densities. Both colloidal probe tips (2.5[micro]m radius) and sharper probe tips ([approximately] 25-50nm radius) were used. The measured normal forces were predominantly repulsive and showed a strong ionic strength dependence reflecting the importance of repulsive electrostatic interactions. These aggrecan-aggrecan forces were much larger than those previously measured between brushes composed only of a single layer of GAG chains isolated from aggrecan molecules. The measured aggrecan normal force interactions were then compared to the predictions of the PB charged rod model for GAG electrostatic interactions and to measurements of the equilibrium compressive modulus of intact cartilage tissue. At near physiological bath conditions (0.1M NaCl), the PB electrostatic model closely predicted the values of the measured force for nanomechanical strains < 0.4, using model parameter values that were all fixed to their known values from the literature. At higher strains, the measured normal forces were higher than those predicted by the model, qualitatively consistent with the likelihood that other nonelectrostatic interactions were becoming more important. A compressive stiffness was also calculated from the measured aggrecan-aggrecan nanomechanical force data, and was found to be [approximately] 50% of the modulus of native intact cartilage. This is consistent with previous reports suggesting that aggrecan-associated electrostatic interactions account for approximately half of the tissue modulus.
by Delphine Marguerite Denise Dean.
Ph.D.
8
Marla, Krishna Tej. "Molecular Thermodynamics of Nanoscale Colloid-Polymer Mixtures: Chemical Potentials and Interaction Forces". Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/7604.
Testo completoAbstract (sommario):
Nanoscale colloidal particles display fascinating electronic, optical and reinforcement properties as a consequence of their dimensions. Stable dispersions of nanoscale colloids find applications in drug delivery, biodiagnostics, photonic and electronic devices, and polymer nanocomposites. Most nanoparticles are unstable in dispersions and polymeric surfactants are added generally to improve dispersability and control self-assembly. However, the effect of polymeric modifiers on nanocolloid properties is poorly understood and design of modifiers is guided usually by empirical approaches. Monte Carlo simulations are used to gain a fundamental molecular-level understanding of the effect of modifiers properties on the thermodynamics and interaction forces of nanoscale colloidal particles. A novel method based on the expanded ensemble Monte Carlo technique has been developed for calculation of the chemical potential of colloidal particles in colloid-polymer mixtures (CPM). Using this method, the effect of molecular parameters like colloid diameter, polymer chain length, colloid-polymer interaction strength, and colloid and polymer concentrations, on the colloid chemical potential is investigated for both hard-sphere and attractive Lennard-Jones CPM. The presence of short-chain polymeric modifiers reduces the colloid chemical potential in attractive as well as athermal systems. In attractive CPM, there is a strong correlation between polymer adsorption and colloid chemical potential, as both show a similar dependence on the polymer molecular weight. Based on the simulation results, simple scaling relationships are proposed that capture the functional dependence of the thermodynamic properties on the molecular parameters. The polymer-induced interaction forces between the nanoparticles have been calculated as a function of the above parameters for freely-adsorbing and end-grafted homopolymer modifiers. The polymer-induced force profiles are used to identify design criteria for effective modifiers. Adsorbing modifiers give rise to attractive interactions between the nanoparticles over the whole parameter range explored in this study. Grafted surface modifiers lead to attraction or repulsion based on the polymer chain length and grafting density. The polymer-induced attraction in both adsorbing and grafted modifiers is attributed primarily to polymer intersegmental interactions and bridging. The location of the thermodynamic minimum corresponding to the equilibrium particle spacing in nanoparticle-polymer mixtures can be controlled by tuning the modifier properties.
9
Marla, Krishna Tej. "Molecular thermodynamics of nanoscale colloid-polymer mixures: chemical potentials and interaction forces". Available online, Georgia Institute of Technology, 2004, 2004. http://etd.gatech.edu/theses/available/etd-08102004-105655/.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Chemical Engineering, Georgia Institute of Technology, 2006.Dr. J. Carson Meredith, Committee Chair ; Dr. Charles A. Eckert, Committee Member ; Dr. Clifford L. Henderson, Committee Member ; Dr. Rigoberto Hernandez, Committee Member ; Dr. Peter J. Ludovice, Committee Member. Vita. Includes bibliographical references.
10
Camesano, Terri Anne. "An investigation of bacterial interaction forces and bacterial adhesion to porous media". Adobe Acrobat reader required to view the full dissertation, 2000. http://www.etda.libraries.psu.edu/theses/approved/PSUonlyIndex/ETD-19/index.html.
Testo completo
11
Zhang, Ying. "Dynamic spatio-temporal interaction of morphogens, forces and growth in embryonic morphogenesis". [Bloomington, Ind.] : Indiana University, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3297105.
Testo completoAbstract (sommario):
Thesis (Ph.D.)--Indiana University, Dept. of Physics, 2007.Title from dissertation home page (viewed Sept. 29, 2008). Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 0881. Adviser: James A. Glazier.
12
Schimmoller, Brian Keith. "A bubble-particle interaction model for flotation combining hydrodynamic and surface forces". Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-09192009-040332/.
Testo completo
13
Lee, Rhonda Joy. "Studies of solid-solid interaction forces and the pneumatic handling of powders /". The Ohio State University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487848078451112.
Testo completo
14
Musoke, Michael. "Direct measurement of polymer interaction forces in good and poor solvents by using a modified atomic force microscope (AFM)". Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391121.
Testo completo
15
Vincent, Abhilash. "Probing the Nanoscale Interaction Forces and Elastic Properties of Organic and Inorganic Materials Using Force-Distance (F-D) Spectroscopy". Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4251.
Testo completoAbstract (sommario):
Due to their therapeutic applications such as radical scavenging, MRI contrast imaging, Photoluminescence imaging, drug delivery, etc., nanoparticles (NPs) have a significant importance in bio-nanotechnology. The reason that prevents the utilizing NPs for drug delivery in medical field is mostly due to their biocompatibility issues (incompatibility can lead to toxicity and cell death). Changes in the surface conditions of NPs often lead to NP cytotoxicity. Investigating the role of NP surface properties (surface charges and surface chemistry) on their interactions with biomolecules (Cells, protein and DNA) could enhance the current understanding of NP cytotoxicity. Hence, it is highly beneficial to the nanotechnology community to bring more attention towards the enhancement of surface properties of NPs to make them more biocompatible and less toxic to biological systems. Surface functionalization of NPs using specific ligand biomolecules have shown to enhance the protein adsorption and cellular uptake through more favorable interaction pathways. Cerium oxide NPs (CNPs also known as nanoceria) are potential antioxidants in cell culture models and understanding the nature of interaction between cerium oxide NPs and biological proteins and cells are important due to their therapeutic application (especially in site specific drug delivery systems). The surface charges and surface chemistry of CNPs play a major role in protein adsorption and cellular uptake. Hence, by tuning the surface charges and by selecting proper functional molecules on the surface, CNPs exhibiting strong adhesion to biological materials can be prepared. By probing the nanoscale interaction forces acting between CNPs and protein molecules using Atomic Force Microscopy (AFM) based force-distance (F-D) spectroscopy, the mechanism of CNP-protein adsorption and CNP cellular uptake can be understood more quantitatively. The work presented in this dissertation is based on the application of AFM in studying the interaction forces as well as the mechanical properties of nanobiomaterials. The research protocol employed in the earlier part of the dissertation is specifically aimed to understand the operation of F-D spectroscopy technique. The elastic properties of thin films of silicon dioxide NPs were investigated using F-D spectroscopy in the high force regime of few 100 nN to 1 µN. Here, sol-gel derived porous nanosilica thin films of varying surface morphology, particle size and porosity were prepared through acid and base catalyzed process. AFM nanoindentation experiments were conducted on these films using the F-D spectroscopy mode and the nanoscale elastic properties of these films were evaluated. The major contribution of this dissertation is a study exploring the interaction forces acting between CNPs and transferrin proteins in picoNewton scale regime using the force-distance spectroscopy technique. This study projects the importance of obtaining appropriate surface charges and surface chemistry so that the NP can exhibit enhanced protein adsorption and NP cellular uptake.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science & Engr PhD
16
Oral, Hasan Giray. "Modeling time-resolved interaction force mode AFM imaging". Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/43691.
Testo completoAbstract (sommario):
Intermittent contact mode atomic force microscopy has been widely employed for simultaneous topography imaging and material characterization. The work in the literature includes both qualitative and quantitative methods. Regular AFM cantilevers are generally used in these methods, yet these cantilevers come with certain limitations. These limitations result from the very nature of cantilever probes. They are passive force sensors with insufficient damping. This prevents having active and complete control on tip-sample forces, causing sample damage and inaccurate topography measurement. Ideally, an AFM probe should offer high bandwidth to resolve interaction forces, active control capability for small interaction force and stable operation, and sufficient damping to avoid transient ringing which causes undesired forces on the sample. Force sensing integrated readout and active tip (FIRAT) probe offers these properties. A special imaging mode, time-resolved interaction force (TRIF) mode imaging can be performed using FIRAT probe for simultaneous topography and material property imaging. The accuracy of topography measurement of samples with variations in elastic and adhesive properties is investigated via numerical simulations and experiments. Results indicate that employing FIRAT probe's active tip control (ATC) capability during TRIF mode imaging provides significant level of control over the tip-sample forces. This improves the accuracy of topography measurement during simultaneous material property imaging, compared to conventional methods. Moreover, Active tip control (ATC) preserves constant contact time during force control for stable contact while preventing loss of material property information such as elasticity and adhesive forces.
17
Wong, Jason. "Simulation of realistic leaf behavior and interaction with external forces for virtual reality landscapes". University of Western Australia. School of Computer Science and Software Engineering, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0123.
Testo completoAbstract (sommario):
[Truncated abstract] Currently, one of the active areas of research in computer graphics is related to creating realistic images and animations that mimic the world we see around us. There has been significant work in modeling and simulating natural phenomena such as fire, clouds, water, and vegetation. Some of these works are employed in the entertainment industry, especially as special effects in cinematic films. Of particular interest is the area of vegetation, given the possible structural complexity and variation in different types of plants. This provides a challenge to develop methods and techniques that effectively and realistically model the movement and behavior of plants. In response to this challenge, there has been significant work in the area of modeling plant structure, as well as modeling of the dynamics and wind interaction of tree branches. However, there is a distinct lack of approaches involved with modeling the dynamics and behavior of individual leaves. Most of the previous approaches focus on the modeling of the branches of a tree, and rarely consider the movement of the leaves in detail. This makes it particularly hard to model the interactions of plants with relatively large leaves, where the dynamics of the leaves are important. In other words, there is no method that could effectively simulate the lower canopy of a forest or jungle, where there are many ferns, saplings, and other broad-leafed plants. Therefore, I present in this thesis a leaf animation system that is designed specifically for simulating and animating plants with relatively large leaves with realistic dynamics in real-time. .... These interactions illustrate the flexibility and robustness of the leaf movement model. In particular, I present a novel approach in modeling volumetric wind through the wind cube that approximates wind behavior such as obstruction by leaves, and constructive and destructive interference. This unique approach is based on modeling wind as a spatial collection of wind vectors and the interaction of the vectors is governed by the rules of each cube-shaped cell of the wind cube. In the end, this wind cube allows for convincing behavior of wind and the subsequent interaction with the leaves of a plant. The leaf animation system is also suitable for simulating a number of plants in a landscape. This is possible through another novel method of reducing the rendering time to allow for more plants to be simulated. This method involves using an animated texture in place of plants that are far from the camera, when the difference visually is not blatantly noticeable. This is a form of the commonly used levels of detail to reduce the complexity of the landscape, but my method is novel in that it has not been implemented in a way where the texture itself is animated in place of the plant. I investigate the strengths and limitations of this approach in reducing rendering time for a landscape of plants. Thus, the leaf animation system is suitable for realistic and interactive virtual reality environments. These virtual environments feature heavily in current video games that involve realistic and believable worlds. In addition to the film and video game industry, these virtual environments are also integral in the application of virtual reality as psychological therapies.
18
PEREIRA, Paulo César do Nascimento. "Energy and interaction forces in classical two-dimensional crystals with inhomogeneous goarse-grained density". Universidade Federal de Pernambuco, 2016. https://repositorio.ufpe.br/handle/123456789/24738.
Testo completoAbstract (sommario):
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CNPQ
In this M.Sc. thesis, we concentrate on classical two-dimensional crystals with soft pairwise interactions at low temperatures. Typically, the triangular lattice is the configuration which minimizes the interaction potential energy. Such energy is calculated through a lattice sum and we show some analytical approximations to it. We will be interested in cases where the coarse-grained density slightly depends on position. This can be caused by an external force on particles. Then the softness of interactions will determine how the coarse-grained density must vary. At equilibrium, the density gradient generates an equal and opposite force, resultant from interactions. In the limit of small gradients, the system has few defects and locally conserves the triangular lattice symmetry. Although the system’s configuration has a huge number of freedom degrees, only the position dependence of coarse-grained density is our relevant information at scales much greater than the nearest-neighbors’ distance. We then investigate the calculation of the resultant interaction force due to such density variations with position. A simple and intuitive, but not rigorous, way to obtain the Dynamical Density Functional Theory (DDFT) force is showed. Also, a microscopic approach giving the same result is proposed. In equilibrium, this force gives a minimization of the total free energy and it has been successful in many nonequilibrium systems. We show that this force fails in the case of long wavelength longitudinal waves, giving a smaller result for the sound speed. Also, in recent computer simulations, we obtained equilibrium configurations where the same correction in the force is needed. We show that such correction can be obtained by adding a correction term in the free energy, calculated as a functional of coarse-grained density.
Nesta tese de mestrado, nós nos concentramos em cristais clássicos bidimensionais com interações suaves entre pares e a baixas temperaturas. Tipicamente, a rede triangular é a configuração que minimiza a energia potencial de interação. Tal energia é calculada através de um somatório de rede e nós mostramos algumas aproximações analíticas para ela. Nós estaremos interessados nos casos onde a densidade coarse-grained (a densidade "olhada de longe", abordada como contínua) depende levemente da posição. Isto pode ser causado por uma força externa nas partículas e, então, a suavidade das interações determinará como a densidade coarsegrained deve variar. No equilíbrio, este gradiente de densidade gerará uma força igual e oposta, resultante das interações. No limite de pequenos gradientes, o sistema tem poucos defeitos e conserva localmente a simetria de rede triangular. Embora a configuração do sistema tenha um enorme número de graus de liberdade, apenas a dependência da densidade coarse-grained com a posição é nossa informação relevante em escalas muito maiores que a distância entre primeiros vizinhos. Portanto, nós investigamos o cálculo da força resultante de interação devido a tais variações da densidade com a posição. Uma forma simples e intutitiva, mas não rigorosa, de obter a força da Teoria Dinâmica do Funcional de Densidade é mostrada. Além disso, uma abordagem microscópica que fornece o mesmo resultado é proposta. Vemos que, no equilíbrio, esta força fornece a minimização da energia livre total e tem sido bem sucedida em vários sistemas de não-equilíbrio. Mostramos que esta força falha no caso das ondas longitudinais de longo comprimento de onda, fornecendo um resultado menor para a velocidade do som. Em recentes simulações computacionais, nós obtivemos configurações de equilíbrio onde a mesma correção na força é necessária. Nós mostramos que tal correção pode ser obtida adicionando um termo de correção na energia livre, calculada como um funcional da densidade coarse-grained.
19
Powell, Alexander Frank. "An investigation into the relationship between vertical and lateral forces, speed and superelevation in railway curves". Diss., University of Pretoria, 2016. http://hdl.handle.net/2263/59440.
Testo completoAbstract (sommario):
The Gautrain Rapid Rail Link (GRRL) is a rail transit system in South Africa that links Johannesburg and Pretoria, as well as Johannesburg and the O.R. Tambo International Airport. Travelling at speeds of up to 160 km/h, the Gautrain system is the first of its kind on the African continent. This dissertation covers an investigation into the relationship between the vertical and lateral forces, speed and superelevation in a GRRL curve. The research described in this dissertation is based on an experiment which involved running a test train through a curve at various speeds, changing the cant of the curve by tamping and repeating the train runs. The cant was changed due to high wheel wear rates. The curve already had a cant deficiency, and this cant deficiency was subsequently increased by reducing the curve’s cant. Assessing the before and after tamping test data validated the existence of the expected relationships between the vertical and lateral rail forces, the speed and the cant. The change in cant had a minimal effect on the magnitude of the vertical forces, although a transfer of loading between the high and low legs did occur. The theory indicates that the 14 % reduction in cant in this curve given all of the other curve characteristics should have resulted in an increase in the lateral forces. There was however a roughly 50 % reduction in the maximum lateral forces after the cant was reduced that can be explained from a train dynamics point of view. In addition, there was an increase in safety due to a reduced derailment ratio at this curve’s normal operating speed of 85 km/h. It is not unreasonable to presume that a 50 % reduction in the maximum lateral forces could lead to a halving of the wear rate of the rail and wheels in this curve with similar results to be expected in other curves on the rail network.Dissertation (MEng)--University of Pretoria, 2016.
The Chair in Railway Engineering at the University of Pretoria
Civil Engineering
MEng
Unrestricted
20
Desormeaux, Kevin. "Temporal models of motions and forces for Human-Robot Interactive manipulation". Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30221.
Testo completoAbstract (sommario):
L'intérêt pour la robotique a débuté dans les années 70 et depuis les robots n'ont cessé de remplacer les humains dans l'industrie. L'automatisation à outrance n'apporte cependant pas que des avantages, car elle nécessite des environnements parfaitement contrôlés et la reprogrammation d'une tâche est longue et fastidieuse. Le besoin accru d'adaptabilité et de ré-utilisabilité des systèmes d'assemblage force la robotique à se révolutionner en amenant notamment l'homme et le robot à interagir. Ce nouveau type de collaboration permet de combiner les forces respectives des humains et des robots. Cependant l'homme ne pourra être inclus en tant qu'agent actif dans ces nouveaux espaces de travail collaboratifs que si l'on dispose de robots sûrs, intuitifs et facilement reprogrammables. C'est à la lumière de ce constat qu'on peut deviner le rôle crucial de la génération de mouvement pour les robots de demain. Pour que les humains et les robots puissent collaborer, ces derniers doivent générer des mouvements sûrs afin de garantir la sécurité de l'homme tant physique que psychologique. Les trajectoires sont un excellent modèle pour la génération de mouvements adaptés aux robots collaboratifs, car elles offrent une description simple et précise de l'évolution du mouvement. Les trajectoires dîtes souples sont bien connues pour générer des mouvements sûrs et confortables pour l'homme. Dans cette thèse nous proposons un algorithme de génération de trajectoires temps-réel basé sur des séquences de segments de fonctions polynomiales de degré trois pour construire des trajectoires souples. Ces trajectoires sont construites à partir de conditions initiales et finales arbitraires, une condition nécessaire pour que les robots soient capables de réagir instantanément à des événements imprévus. L'approche basée sur un modèle à jerk-contraint offre des solutions orientées performance: les trajectoires sont optimales en temps sous contraintes de sécurité. Ces contraintes de sécurité sont des contraintes cinématiques qui dépendent de la tâche et du contexte et doivent être spécifiées. Pour guider le choix de ces contraintes, nous avons étudié le rôle de la cinématique dans la définition des propriétés ergonomiques du mouvement.[...]It was in the 70s when the interest for robotics really emerged. It was barely half a century ago, and since then robots have been replacing humans in the industry. This robot-oriented solution doesn't come without drawbacks as full automation requires time-consuming programming as well as rigid environments. With the increased need for adaptability and reusability of assembly systems, robotics is undergoing major changes and see the emergence of a new type of collaboration between humans and robots. Human-Robot collaboration get the best of both world by combining the respective strengths of humans and robots. But, to include the human as an active agent in these new collaborative workspaces, safe and flexible robots are required. It is in this context that we can apprehend the crucial role of motion generation in tomorrow's robotics. For the emergence of human-robot cooperation, robots have to generate motions ensuring the safety of humans, both physical and physchological. For this reason motion generation has been a restricting factor to the growth of robotics in the past. Trajectories are excellent candidates in the making of desirable motions designed for collaborative robots, because they allow to simply and precisely describe the motions. Smooth trajectories are well known to provide safe motions with good ergonomic properties. In this thesis we propose an Online Trajectory Generation algorithm based on sequences of segment of third degree polynomial functions to build smooth trajectories. These trajectories are built from arbitrary initial and final conditions, a requirement for robots to be able to react instantaneously to unforeseen events. Our approach built on a constrained-jerk model offers performance-oriented solutions : the trajectories are time-optimal under safety constraints. These safety constraints are kinematic constraints that are task and context dependent and must be specified. To guide the choice of these constraints we investigated the role of kinematics in the definition of ergonomics properties of motions. We also extended our algorithm to cope with non-admissible initial configurations, opening the way to trajectory generation under non-constant motion constraints. [...]
21
Widarda, Dina Rubiana. "Longitudinal forces in continuously welded rails due to nonlinear track-bridge interaction for loading sequences". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1238081328011-05497.
Testo completoAbstract (sommario):
The use of continuously welded rails (CWR) governs the longitudinal stress caused by seasonal temperature changes, bending of supporting structure and braking/accelerating due to passing trains. Those three loads have been regulated in Eurocode1 and accomplished by the national codes like DIN Fb-101 in Germany. An additional loading case identified and treated in this thesis is the load due to a change of the coupling stiffness in longitudinal direction between the track and bridge. This additional load occurs as a consequence of the employment of a nonlinear stiffness law which increases the restoring force by a factor of 3 when the situation of the track changes from ‘unloaded’ to ‘loaded’ due to a passing train. This particular phenomenon has not been mentioned in the codes so far though it is a natural consequence of fundamental conditions in those codes. For CWR the longitudinal coupling between the rail and bridge plays an important role. This coupling interface is created either by a ballast, for a ballasted track, or by a fastening system in the case of slab track. The deformation state of the coupling interface characterizes the behaviour of the system, whether elastic or plastic. Therefore, the nonlinear behaviour is valid for the system. To accommodate the nonlinear nature, a sequential loading analysis is used, taking into account the loading history. As the change situation due to a passing train happens in a short time, the influence of the mass acceleration should be taken into account in the system’s equilibrium. This aspect is investigated by treating the dynamic load as an impulse-like load. However, a realistic load needs some time to affect the whole bridge, thus the continuous change of stiffness is used to simulate the dynamic analysis. There is a lack of information on determining the value of coupling stiffness in longitudinal direction caused by a passing train. Therefore, it is important to evaluate the coupling stiffness from field measurements in order to find reliable values. The implementation of the load onto several typical bridges shows that the change of the coupling stiffness increases the stresses and it should not be neglected. The evaluation of the load due to a change of the coupling stiffness accompanied by bending of the supporting structure gives satisfactory results by using the static analysis only. Thus, a dynamic analysis can be avoided. Multiple cycles of passing trains occurring after seasonal temperature change indicate a significant increase of elastic parts along the track-bridge coupling interface and a decrease in stresses in the rails. Thus the danger of deterioration is reduced significantlyDie Verwendung von durchgehend geschweißten Schienen auf Brücken führt zu zusätzlichen Längsspannungen infolge der Lastfälle jahreszeitliche Temperaturänderung, Brückendurchbiegung und Bremsen/Anfahren. Diese drei Lasten sind durch den Eurocode 1 vorgegeben und in die nationale deutsche Norm DIN Fb-101 integriert. In dieser Arbeit wird erstmals ein weiterer Lastfall identifiziert und behandelt, der durch den Wechsel der Koppelsteifigkeit in Längsrichtung zwischen Gleis und Tragwerk bei der Zugüberfahrt begründet wird. Dieser Lastfall wird hier mit „Ruck“ bezeichnet und ist eine zwangsläufige Konsequenz des nichtlinearen Längsverschiebewiderstandes, wie er im EC 1 und im DIN Fb-101 vorgegeben ist. Dennoch wurden die Auswirkungen auf das Systemverhalten bisher nicht untersucht. Bei einem Wechsel vom unbelasteten Gleis zum belasteten Gleis während einer Zugüberfahrt erhöht sich zum Beispiel der Längsverschiebewiderstand für ein Schottergleis um den Faktor 3! Die dadurch bedingte Veränderung des Zusammenwirkens zwischen Gleis und Tragwerk führt zu einer Veränderung des Systemzustandes und damit zu veränderten Schienenspannungen. Für durchgehend geschweißte Schienen spielt die Längskopplung zwischen Schiene und Brücke eine wesentliche Rolle. Beim Schottergleis wird sie dargestellt durch die Einbettung des Gleisrostes im Schotterbett im Zusammenwirken mit der Schienenbefestigung. Bei der festen Fahrbahn durch das Befestigungssystem. Für kleine Deformationen ist die Koppelsteifigkeit proportional zur Relativverschiebung zwischen Gleis und Brücke. Darüberhinaus geht das linear elastische Verhalten in ein quasi plastisches Verhalten mit konstanter Koppelkraft über. Folgerichtig ist die Behandlung einer Lastenfolge nur in inkrementeller Weise unter Einbeziehung der Verformungsgeschichte mechanisch korrekt. Die Lastfälle Bremsen/Anfahren, Brückendurchbiegung und Ruck ereignen sich nur während der Zugüberfahrt; also in relativ kurzer Zeit, dann allerdings mit einem erheblichen Lastgradienten. Somit stellt sich die Frage nach dem Einfluss der Massenbeschleunigungen, die in dieser Arbeit geklärt wird. Die im Fachbericht genanntenWerte für den Längsverschiebewiderstand des belasteten Gleises basieren auf einer relativ geringen Datenmenge. Aus diesem Grund werden die Messdaten einer umfangreichen Feldmessung mit Zugüberfahrten zu Aussagen über den Längsverschiebewiederstand herangezogen und die Problematik derartiger Messungen beleuchtet. Die unterschiedlichen Modellierungen des Lastfalls „Ruck“, einmal rein statisch und zum anderen dynamisch, ergeben übereinstimmende Schienenlängsspannungen für die statische und die kontinuierliche dynamische Variante. Somit kann auf die aufwändige dynamische Analyse verzichtet werden. Mehrere Zyklen von Zugüberfahrten im Anschluss an eine jahreszeitliche Temperaturänderung bewirken einen signifikanten Abbau der Durchrutschbereiche, also eine Erhöhung der elastischen Abschnitte in der Koppelfuge zwischen Bauwerk und Gleis verbunden mit einer Abnahme der Schienendruckspannungen. Somit hilft dieser Effekt dem System, der jahreszeitlichen Temperaturänderung zu widerstehen
22
Widarda, Dina Rubiana. "Longitudinal forces in continuously welded rails due to nonlinear track-bridge interaction for loading sequences". Doctoral thesis, Technische Universität Dresden, 2008. https://tud.qucosa.de/id/qucosa%3A23616.
Testo completoAbstract (sommario):
The use of continuously welded rails (CWR) governs the longitudinal stress caused by seasonal temperature changes, bending of supporting structure and braking/accelerating due to passing trains. Those three loads have been regulated in Eurocode1 and accomplished by the national codes like DIN Fb-101 in Germany. An additional loading case identified and treated in this thesis is the load due to a change of the coupling stiffness in longitudinal direction between the track and bridge. This additional load occurs as a consequence of the employment of a nonlinear stiffness law which increases the restoring force by a factor of 3 when the situation of the track changes from ‘unloaded’ to ‘loaded’ due to a passing train. This particular phenomenon has not been mentioned in the codes so far though it is a natural consequence of fundamental conditions in those codes. For CWR the longitudinal coupling between the rail and bridge plays an important role. This coupling interface is created either by a ballast, for a ballasted track, or by a fastening system in the case of slab track. The deformation state of the coupling interface characterizes the behaviour of the system, whether elastic or plastic. Therefore, the nonlinear behaviour is valid for the system. To accommodate the nonlinear nature, a sequential loading analysis is used, taking into account the loading history. As the change situation due to a passing train happens in a short time, the influence of the mass acceleration should be taken into account in the system’s equilibrium. This aspect is investigated by treating the dynamic load as an impulse-like load. However, a realistic load needs some time to affect the whole bridge, thus the continuous change of stiffness is used to simulate the dynamic analysis. There is a lack of information on determining the value of coupling stiffness in longitudinal direction caused by a passing train. Therefore, it is important to evaluate the coupling stiffness from field measurements in order to find reliable values. The implementation of the load onto several typical bridges shows that the change of the coupling stiffness increases the stresses and it should not be neglected. The evaluation of the load due to a change of the coupling stiffness accompanied by bending of the supporting structure gives satisfactory results by using the static analysis only. Thus, a dynamic analysis can be avoided. Multiple cycles of passing trains occurring after seasonal temperature change indicate a significant increase of elastic parts along the track-bridge coupling interface and a decrease in stresses in the rails. Thus the danger of deterioration is reduced significantly.Die Verwendung von durchgehend geschweißten Schienen auf Brücken führt zu zusätzlichen Längsspannungen infolge der Lastfälle jahreszeitliche Temperaturänderung, Brückendurchbiegung und Bremsen/Anfahren. Diese drei Lasten sind durch den Eurocode 1 vorgegeben und in die nationale deutsche Norm DIN Fb-101 integriert. In dieser Arbeit wird erstmals ein weiterer Lastfall identifiziert und behandelt, der durch den Wechsel der Koppelsteifigkeit in Längsrichtung zwischen Gleis und Tragwerk bei der Zugüberfahrt begründet wird. Dieser Lastfall wird hier mit „Ruck“ bezeichnet und ist eine zwangsläufige Konsequenz des nichtlinearen Längsverschiebewiderstandes, wie er im EC 1 und im DIN Fb-101 vorgegeben ist. Dennoch wurden die Auswirkungen auf das Systemverhalten bisher nicht untersucht. Bei einem Wechsel vom unbelasteten Gleis zum belasteten Gleis während einer Zugüberfahrt erhöht sich zum Beispiel der Längsverschiebewiderstand für ein Schottergleis um den Faktor 3! Die dadurch bedingte Veränderung des Zusammenwirkens zwischen Gleis und Tragwerk führt zu einer Veränderung des Systemzustandes und damit zu veränderten Schienenspannungen. Für durchgehend geschweißte Schienen spielt die Längskopplung zwischen Schiene und Brücke eine wesentliche Rolle. Beim Schottergleis wird sie dargestellt durch die Einbettung des Gleisrostes im Schotterbett im Zusammenwirken mit der Schienenbefestigung. Bei der festen Fahrbahn durch das Befestigungssystem. Für kleine Deformationen ist die Koppelsteifigkeit proportional zur Relativverschiebung zwischen Gleis und Brücke. Darüberhinaus geht das linear elastische Verhalten in ein quasi plastisches Verhalten mit konstanter Koppelkraft über. Folgerichtig ist die Behandlung einer Lastenfolge nur in inkrementeller Weise unter Einbeziehung der Verformungsgeschichte mechanisch korrekt. Die Lastfälle Bremsen/Anfahren, Brückendurchbiegung und Ruck ereignen sich nur während der Zugüberfahrt; also in relativ kurzer Zeit, dann allerdings mit einem erheblichen Lastgradienten. Somit stellt sich die Frage nach dem Einfluss der Massenbeschleunigungen, die in dieser Arbeit geklärt wird. Die im Fachbericht genanntenWerte für den Längsverschiebewiderstand des belasteten Gleises basieren auf einer relativ geringen Datenmenge. Aus diesem Grund werden die Messdaten einer umfangreichen Feldmessung mit Zugüberfahrten zu Aussagen über den Längsverschiebewiederstand herangezogen und die Problematik derartiger Messungen beleuchtet. Die unterschiedlichen Modellierungen des Lastfalls „Ruck“, einmal rein statisch und zum anderen dynamisch, ergeben übereinstimmende Schienenlängsspannungen für die statische und die kontinuierliche dynamische Variante. Somit kann auf die aufwändige dynamische Analyse verzichtet werden. Mehrere Zyklen von Zugüberfahrten im Anschluss an eine jahreszeitliche Temperaturänderung bewirken einen signifikanten Abbau der Durchrutschbereiche, also eine Erhöhung der elastischen Abschnitte in der Koppelfuge zwischen Bauwerk und Gleis verbunden mit einer Abnahme der Schienendruckspannungen. Somit hilft dieser Effekt dem System, der jahreszeitlichen Temperaturänderung zu widerstehen.
23
Dobryden, Illia. "Scanning probe microscopy studies of interaction forces between particles: emphasis on magnetite, bentonite and silica". Doctoral thesis, Luleå tekniska universitet, Materialvetenskap, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-25691.
Testo completoAbstract (sommario):
Scanning probe microscopy (SPM), such as the atomic force microscope (AFM), using colloidal probes is a highly suitable technique to probe single particle-particle interactions in aqueous solution. The interaction force between a colloidal probe on the AFM cantilever and sample surface is measured. Ultrasmall intermolecular and surface forces, down to the piconewton level, can reliably be measured under controlled experimental conditions with AFM. The interaction between magnetite, bentonite and silica particles plays an important role in many different applications. One important application is in the steel production process where high-quality iron ore pellets are used. Moreover, the interaction between magnetite nanoparticles with Ca2+ ions and with silica particles has high importance in several medical applications and for nanoelectronics. It is known and widely studied that particle surface properties significantly affect the particle dispersion and aggregation. Also, the particles are often treated in aqueous suspensions or in moist conditions prior to the final aggregation, for instance in a pelletizing processes. Thus, different dissolved chemical species may modify the magnetite, bentonite and silica surfaces, which causes the surface properties to change. However, the exact mechanism how the dissolved chemical species influence the direct particle-particle interaction and particle adhesion is not well known.The main focus of this thesis was the study of magnetite particle force interaction with natural and synthetic magnetite, silica and bentonite particles in aqueous solution with SPM. In addition, complimentary methods, such as scanning electron microscopy (SEM), vertical scanning interferometry (VSI), energy dispersive spectroscopy (SEM-EDS), x-ray diffraction (XRD) and electrophoresis techniques were used for surface morphology investigation, chemical characterization, determination of atomic structure and measurements of zeta-potential. The particle interaction forces were examined in solutions with various Ca2+ ion concentrations and in NaCl solution to determine the effect of Ca2+ ions on the surface properties. Also, the effect of pH at various concentrations was studied. The colloidal probes in the studies were natural magnetite and bentonite particles, micrometer-sized spherical silica particles. Sample surfaces were natural magnetite particles, smooth layers of synthetic magnetite nanoparticles and bentonite flakes.Qualitative changes in adhesion forces, i.e. interaction trends, and forces on approach for magnetite-magnetite, magnetite-silica, magnetite-bentonite and bentonite-silica interaction systems with an increase of Ca2+ ion concentration and pH were measured and evaluated. The interaction trends were consistent in most cases with zeta-potential measurements. Possible surface modification and formation of calcium silicates and calcium carbonates at pH 10 on the magnetite surfaces was discussed. The long-range repulsive interaction, similar to a steric-like interaction, was observed in the interactions for bentonite-silica and magnetite-silica systems, likely due to the swelling of bentonite layers and rising of bentonite flakes from the surface. The rising of bentonite flakes in water was verified with cryo-scanning electron microcopy investigation. Furthermore, the measured adhesion forces were compared with calculated adhesion forces, which were evaluated with the use of a few contact mechanics models. The comparison revealed discrepancies, which could be explained by the particle surface roughness. Additionally, a comparison of VSI and AFM techniques for surface characterization was performed on samples possessing sharp periodic surface structures and three stage plateaux honed cast iron surface. This comparison is of high relevance to the accurate calculation of tribological surface roughness parameters. Moreover, force measurements on biological samples and between magnetic particles are also briefly discussed in the thesis.The work within this thesis shows that SPM methods can be successfully applied to measure and predict forces between natural particles, such as magnetite and bentonite, in solution. The obtained and presented results are new and of high interest in applications where the knowledge of the dispersion and aggregation of studied particle interaction is important.Godkänd; 2014; 20140422 (illdob); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Illia Dobryden Ämne: Fysik/Physics Avhandling: Scanning Probe Microscopy Studies of Interaction Forces Between Particles: Emphasis on Magnetite, Bentonite and Silica Opponent: Associate Professor/Reader Neil Thomson, Department of Oral Biology, Leeds Dental Institute/School of Physics and Astronomy, University of Leeds, UK, Ordförande: Biträdande professor Nils Almqvist, Avd för materialvetenskap, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Tid: Onsdag den 18 juni 2014, kl 10.00 Plats: E632, Luleå tekniska universitet
24
Ocampo, Minette C. "Protein-Lipid Interactions with Pulmonary Surfactant Using Atomic Force Microscopy". The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1395050693.
Testo completo
25
Shinto, Hiroyui. "Interfacial Microstructures and Interaction Forces between Colloidal Particles in Simple and complex Fluids-Molecular Dynamics Simulation-". Kyoto University, 1999. http://hdl.handle.net/2433/77943.
Testo completo
26
Arjmandi-Tash, Omid. "Interaction of droplets and foams with solid/porous substrates". Thesis, Loughborough University, 2017. https://dspace.lboro.ac.uk/2134/24889.
Testo completoAbstract (sommario):
Current problems on the interaction of complex liquids (i.e. droplets or foams) with complex surfaces (i.e. soft deformable or porous surfaces) are addressed in the following areas: (1) wetting of deformable substrates and surface forces, (2) kinetics of wetting and spreading of non-Newtonian liquids over porous substrates, (3) kinetics of spreading of non-Newtonian solutions over hair, (4) free drainage of foams produced from non-Newtonian solutions, and (5) foam drainage placed on porous substrates. Equilibrium of liquid droplets on deformable substrates was investigated and the effect of disjoining pressure action in the vicinity of the apparent three phase contact line was taken into account. It was proven that the deformation of soft solids is determined by the action of surface forces inside the transition zone. Spreading/imbibition of blood, which is a power law shear thinning non-Newtonian liquid, over a dry porous layer was investigated from both theoretical and experimental points of view. It was found that blood droplet spreading/imbibition over porous substrates shows two different behaviours: (i) partial wetting case with three subsequent stages: initial fast spreading, constant maximum droplet base and the shrinkage of the droplet base; (ii) complete wetting case with only two stages: initial fast spreading and the shrinkage of the droplet base. The wetting of hair tresses by aqueous solutions of two commercially available polymers, AculynTM 22 (A22) and AculynTM 33 (A33) was investigated experimentally. Both A22 and A33 solutions demonstrate well pronounced shear thinning behaviour. Initial contact angle of the A22 and A33 solutions on hair tresses was about 100o. The A22 droplets remained on the hair tress after spreading for at least half an hour. However, a fast penetration of the A33 droplets inside the hair tresses was observed when advancing contact angle in the course of spreading reached a critical value of about 60o. This could be explained by Cassie-Wenzel wetting transition which is caused by filling the pores inside the porous media by liquid. The influence of non-Newtonian rheology of A22 and A33 solutions on foam drainage was also investigated experimentally and a new theory of foam drainage was presented for the case of free drainage. For lowly viscous polymeric solutions and under the assumption of rigid surface of the Plateau border, the predicted values of the time evolution of the foam height and liquid content were in good agreement with the experimental data. However, in the case of highly viscous solutions an interfacial mobility at the surface of the Plateau border has to be taken into account. A completely new theory of foam drainage placed on porous substrate was developed. It was found that there are three different regimes of the process: (i) a rapid imbibition, the imbibition into the porous substrate dominates as compared with the foam drainage; (ii) an intermediate imbibition, that is, the imbibition into the porous substrate and the rate of drainage are comparable; (iii) a slow imbibition, the rate of drainage inside the foam is higher than the imbibition into the porous substrate for a period of time and a free liquid layer is formed over the porous substrate.
27
Paljic, Alexis. "Interaction en environnements immersifs et retours d'effort passifs". Paris 6, 2004. https://hal-mines-paristech.archives-ouvertes.fr/tel-01479203.
Testo completo
28
Antonopoulos, Theodoros C. Yiazitzis John T. "The constitutional and legal status of the Hellenic Armed Forces and their interaction with the Hellenic Society /". Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1997. http://handle.dtic.mil/100.2/ADA342026.
Testo completoAbstract (sommario):
Thesis (M.A. in National Security Affairs) Naval Postgraduate School, December 1997."December 1997." Thesis advisor(s): Cynthia Levy. Includes bibliographical references (p. 93-94). Also available online.
29
Antonopoulos, Theodoros C., e John T. Yiazitzis. "The constitutional and legal status of the Hellenic Armed Forces and their interaction with the Hellenic Society". Thesis, Monterey, California. Naval Postgraduate School, 1997. http://hdl.handle.net/10945/8145.
Testo completoAbstract (sommario):
Approved for public release; distribution is unlimitedHellas was officially declared an independent State in 1828, after a seven-year struggle against the conquerors. Despite the young age, however, she demonstrated a rich, and often turbulent, political life. The followed pattern was not unique by itself: it reflected the parliamentary transformations that swept all over Europe during the last three hundred years. Its uniqueness lies on the rapidity with which these transformations took place, until the finalization of stable republican governance in 1974. What makes this Thesis interesting for the foreign reader is the degree of influence exerted by the armed forces over the political developments. Covertly in the beginning, but with ever increasing determination as the years passed, the armed forces assumed leading role and even dominated the political scene. Inadequately institutionalized civilian control over the army and political immaturity combined to form this behavioral pattern. By the beginning of the last quarter of the century, however, it was realized that Hellas could not claim a reputable position among the community of civilized nations unless by abolishing antiquated institutions. The 1975 Constitution, and the way civilian authorities consolidated control over the armed forces, are textbook examples of a successful transition to a fully developed democratic regime
30
Economides, Spyridon. "The international implications of the Greek Civil War : the interaction of domestic and external forces, 1946-1949". Thesis, London School of Economics and Political Science (University of London), 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307701.
Testo completo
31
Lardon, Isabelle. "Interaction d'une dislocation vis avec une interface cohérente : étude des forces images par simulation à l'échelle atomique". Poitiers, 1994. http://www.theses.fr/1994POIT2316.
Testo completoAbstract (sommario):
Les forces d'interaction entre les dislocations et les interfaces sont d'origines diverses. Cette etude est consacree a l'interaction d'une dislocation vis avec une interface coherente separant deux phases de modules elastiques differents. La principale difficulte de ce probleme est qu'en elasticite les dislocations et les interfaces sont des singularites, ce qui conduit a la divergence des forces d'interaction. A l'echelle atomique, les curs de dislocations et les interfaces ayant une extension non nulle, ces problemes inherents a l'elasticite disparaissent. Dans le cas de faibles differences de modules elastiques, la contrainte de peierls est partout superieure a celle exercee par l'interface. Nous avons alors pu deduire une courbe de contrainte par differences finies de l'energie elastique calculee en chaque vallee. Dans le cas de grandes differences de modules elastiques, nous avons determine l'intervalle de contrainte appliquee qui maintient la dislocation dans chaque vallee de peierls. Nous avons montre que la structure de cur des dislocations evolue au voisinage de l'interface: l'extension de cur se reduit du cote mou et augmente du cote dur. Ce phenomene est du au fait que l'action de l'interface est plus importante sur les parties proches de la dislocation que sur celles plus eloignees. Dans le milieu dur, cet effet va jusqu'a une veritable dissociation en deux partielles de composantes vis b/2 separees par une faute d'empilement. Pour verifier que cette dissociation est une propriete generale, nous avons developpe une analyse tenant compte des interactions entre partielles, de l'energie de faute et de la contrainte appliquee: il apparait alors que le franchissement de l'interface est favorise par la dissociation. L'ensemble de ces resultats est generalise sous la forme d'une loi simple dans laquelle un parametre important est la largeur de cur des dislocations en milieu homogene
32
Tarasova, Anna Optometry UNSW. "Fabrication and characterisation of affinity-bound liposomes". Awarded by:University of New South Wales. Optometry, 2007. http://handle.unsw.edu.au/1959.4/29114.
Testo completoAbstract (sommario):
In considering the concept of surface-immobilised liposomes as a drug release system, two factors need to addressed, the interfacial surface density of the liposomes for maximum drug loading and the stability of these liposomes to allow for controlled drug release. This thesis investigates a multilayer system for the affinity immobilisation of liposomes and their stability to various applied stresses. In the work presented here an allylamine monomer was used to create plasma coatings that were stable, thin and amine-rich. The aging studies using AFM showed these films to rapidly oxidise on exposure to water. The freshly deposited films were used for further surface modifications, by the covalent grafting of PEG layers of different interfacial densities under the conditions of varying polymer solvation. The AFM was used to measure the interaction forces between the grafted PEG layers and modified silica interfaces. It was found that the polydispersity of the PEG species resulted in bridging interactions of ???brush???-like PEG layers with the silica surface. These interactions were screened minimised by increasing the ionic strength of the solution. Although the densely grafted PEG layers were found to be highly protein-resistant by the XPS and QCM-D some minor protein-polymer adhesions were observed by the AFM. The densely anchored biotinylated PEG chains served as an optimum affinity platform for affinity-docking of NeutrAvidinTM molecules, which assembled in a rigid, 2-D layer as confirmed by the QCM-D. The submonolayer surface density of NeutrAvidin, as determined by Europium-labelling, was attributed to steric hindrance of the immobilised molecules. The final protein layer enabled specific binding of biotin-PEG-liposomes as a highly dissipative, dense and stable layer verified by tapping mode AFM and QCM-D. We found that these liposomes were also stable under a range of stresses induced by the shearing effects of water, silica probe and HSA layer at increased loads and velocities. The frictional response of the liposome layer also demonstrated the viscoelasticity and stability of these surface immobilised liposomes. Finally, the minimal adhesive interaction forces, as measured by the AFM, demonstrated the repellency of these liposomes to commonly found proteins, such as HSA.
33
Smee, Delbert Lee. "The Ecology of Yikes! Environmental Forces Alter Prey Perception of Predators". Diss., Connect to this title online, 2006. http://etd.gatech.edu/theses/available/etd-05082006-213823/.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Georgia Institute of Technology, 2006.Title from PDF t.p. (viewed on Oct. 28, 2006). Marc Weissburg, Committee Chair ; Mark Hay, Committee Member ; Lin Jiang, Committee Member ; David Dusenbery, Committee Member ; Don Webster, Committee Member. Includes bibliographical references (p. 115-122).
34
Gambin, Yann. "Dynamique en milieux confinés : peptides et protéines en interaction avec des bicouches modèles". Paris 6, 2006. http://www.theses.fr/2006PA066609.
Testo completo
35
Passerat, de Silans Thierry. "Interaction atome-surface : Interaction de Van der Waals entre un atome exité et une surface diélectrique thermiquement émissive : Oscillations de Bloch pour un atome adsorbé". Paris 13, 2009. http://scbd-sto.univ-paris13.fr/secure/edgalilee_th_2009_passerat_de_silans.pdf.
Testo completoAbstract (sommario):
Dans cette thèse nous avons étudié différents aspects de l’interaction entre un atome et une surface diélectrique. Nous avons notamment recherché expérimentalement des situations où l’interaction de van der Waals à longue portée varie avec la population thermique de photons du vide, telle qu’imposée par un équilibre avec l’environnement. Une variation avec la température est prévue lorsqu’il y a un couplage virtuel résonnant en champ proche entre l’émission thermique de la surface (dans l’IR) et une absorption atomique. Notre recherche a porté sur l’interaction entre Cs(8P) et une surface de CaF2 en utilisant la spectroscopie de réflexion sélective. Jusqu’à présent, les valeurs expérimentales du coefficient C3 de l’interaction de van der Waals sont en contradiction avec les prédictions théoriques. Nous avons pourtant raffiné les prédictions théoriques en introduisant dans les calculs la dépendance en température de la constante diélectrique, à partir de nouvelles mesures de la réflectance sur des surfaces de saphir, CaF2 et BaF2 effectués à différentes températures. Nous avons, en outre, observé, sur une expérience auxiliaire d’absorption saturée, des raies inédites autour de la transition 6S1/2→8P, que nous avons attribuées à des dimères spécifiquement formés par nos faisceaux lasers. Ces raies apparaissent pour des densités de vapeur inhabituellement faibles. A un régime de plus faible distance de l’interaction atome-surface, où le potentiel combine attraction van der Waals et répulsion au voisinage immédiat de la surface, nous avons analysé la possibilité d’observer des oscillations de Bloch, en considérant le cas d’un atome d’Helium adsorbé sur une surface de LiF et soumis à une force externeIn this thesis we have studied different aspects of the interaction between an atom and a dielectric surface. We have experimentally searched situations where the long range van der Waals interaction changes with the vacuum temperature as governed by its surrounding environnement. Such a situation occurs when the thermal surface emission resonantly couples in the near field to an atomic absorption. Our research deals with the interaction between a Cs(8P) atom and a CaF2 surface, and was performed through selective reflection spectroscopy. Until now, experimental values for C3 coefficient of the van der Waals interaction are in contradiction with the theoretical predictions. We have nevertheless refined our theoretical predictions by introducing in the calculations the temperature evolution of the dielectric constant, as obtained from new temperature dependent measurements of the surface reflectivity for CaF2, BaF2 and sapphire. We have also observed, in an auxiliary saturated absorption experiment, new lines around the 6S1/2→8P transitions, that we have attributed to dimers specifically formed by our lasers beams. Such lines appear for unusually low vapour densities. At a shorter distance range of atom-surface interaction, where the interaction potential combines van der Waals attraction and repulsion in the immediate vicinity of the surface, we have analysed the possibility of observing Bloch oscillations, on the basis of calculations for a He atom adsorbed on a LiF surface and submitted to an external force
36
Saunders, Daniel Curtis. "Wind Turbine Wake Interactions - Characterization of Unsteady Blade Forces and the Role of Wake Interactions in Power Variability Control". ScholarWorks @ UVM, 2017. http://scholarworks.uvm.edu/graddis/745.
Testo completoAbstract (sommario):
Growing concerns about the environmental impact of fossil fuel energy and
improvements in both the cost and performance of wind turbine technologies has spurred
a sharp expansion in wind energy generation. However, both the increasing size of wind
farms and the increased contribution of wind energy to the overall electricity generation
market has created new challenges. As wind farms grow in size and power density, the
aerodynamic wake interactions that occur between neighboring turbines become
increasingly important in characterizing the unsteady turbine loads and power output of
the farm. Turbine wake interactions also impact variability of farm power generation,
acting either to increase variability or decrease variability depending on the wind farm
control algorithm. In this dissertation, both the unsteady vortex wake loading and the
effect of wake interaction on farm power variability are investigated in order to better
understand the fundamental physics that govern these processes and to better control
wind farm operations to mitigate negative effects of wake interaction.
The first part of the dissertation examines the effect of wake interactions between
neighboring turbines on the variability in power output of a wind farm, demonstrating
that turbine wake interactions can have a beneficial effect on reducing wind farm
variability if the farm is properly controlled. In order to balance multiple objectives, such
as maximizing farm power generation while reducing power variability, a model
predictive control (MPC) technique with a novel farm power variability minimization
objective function is utilized. The controller operation is influenced by a number of
different time scales, including the MPC time horizon, the delay time between turbines,
and the fluctuation time scales inherent in the incident wind. In the current research, a
non-linear MPC technique is developed and used to investigate the effect of three time
scales on wind farm operation and on variability in farm power output. The goal of the
proposed controller is to explore the behavior of an "ideal" farm-level MPC controller
with different wind, delay and horizon time scales and to examine the reduction of
system power variability that is possible in such a controller by effective use of wake
interactions.
The second part of the dissertation addresses the unsteady vortex loading on a
downstream turbine caused by the interaction of the turbine blades with coherent vortex
structures found within the upstream turbine wake. Periodic, stochastic, and transient
loads all have an impact on the lifetime of the wind turbine blades and drivetrain. Vortex
cutting (or vortex chopping) is a type of stochastic load that is commonly observed when
a propeller or blade passes through a vortex structure and the blade width is of the same
order of magnitude as the vortex core diameter. A series of Navier-Stokes simulations of
vortex cutting with and without axial flow are presented. The goal of this research is to
better understand the challenging physics of vortex cutting by the blade rotor, as well as
to develop a simple, physics-based, validated expression to characterize the unsteady
force induced by vortex
37
Lundberg, Oskar. "On the influence of surface roughness on rolling contact forces". Doctoral thesis, KTH, MWL Marcus Wallenberg Laboratoriet, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-193935.
Testo completoAbstract (sommario):
Road vehicle tyres, railway wheels and ball bearings all generate rolling contact forces which are transferred within a finite area of contact between the rolling element and the substrate. Either it is visible or not for the human eye, a certain degree of roughness is always present on the contacting surfaces and it influences the generation of both vertical and lateral contactforces. The purpose of this investigation is to enhance the understanding and modelling of the influence from small-scale surface roughness on the generation of rolling contact forces. To this end, a computationally efficient method to include roughness-induced contact nonlinearities in the dynamic modelling of rolling contacts is proposed. The method is implemented in a time domain model for vertical wheel–track interaction to model rolling-induced rail vibrations, showing good agreement with measurements. Furthermore, a test rig is developed and used for the investigation of tyre–road rolling contact forces. Detailed studies are performed on the influence of substrate roughness on the resulting contact forces for a tyre tread block which is rolling at different operating conditions. The choice of substrate as well as the rolling velocity and the slip ratio is observed to have significant influence on the resulting friction coefficient. For high slip ratios, stick–slip oscillations appear, exhibiting frequency content which is largely dependent on the choice of substrate. The outcomes of this study can potentially be used to improve future tyre–road contacts with respect to wear, traction and noise generation.QC 20161013
Centre for Eco2 Vehicle Design
38
Schiefele, Jürgen. "Casimir-Polder interaction in second quantization". Phd thesis, Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2011/5417/.
Testo completoAbstract (sommario):
The Casimir-Polder interaction between a single neutral atom and a nearby surface, arising from the (quantum and thermal) fluctuations of the electromagnetic field, is a cornerstone of cavity quantum electrodynamics (cQED), and theoretically well established. Recently, Bose-Einstein condensates (BECs) of ultracold atoms have been used to test the predictions of cQED. The purpose of the present thesis is to upgrade single-atom cQED with the many-body theory needed to describe trapped atomic BECs. Tools and methods are developed in a second-quantized picture that treats atom and photon fields on the same footing. We formulate a diagrammatic expansion using correlation functions for both the electromagnetic field and the atomic system.
The formalism is applied to investigate, for BECs trapped near surfaces, dispersion interactions of the van der Waals-Casimir-Polder type, and the Bosonic stimulation in spontaneous decay of excited atomic states. We also discuss a phononic Casimir effect, which arises from the quantum fluctuations in
an interacting BEC.Die durch (quantenmechanische und thermische) Fluktuationen des elektromagnetischen Feldes hervorgerufene Casimir-Polder-Wechselwirkung zwischen einem elektrisch neutralen Atom und einer benachbarten Oberfläche stellt einen theoretisch gut untersuchten Aspekt der Resonator-Quantenelektrodynamik (cavity quantum electrodynamics, cQED) dar. Seit kurzem werden atomare Bose-Einstein-Kondensate (BECs) verwendet, um die theoretischen Vorhersagen der cQED zu überprüfen. Das Ziel der vorliegenden Arbeit ist es, die bestehende cQED Theorie für einzelne Atome mit den Techniken der Vielteilchenphysik zur Beschreibung von BECs zu verbinden. Es werden Werkzeuge und Methoden entwickelt, um sowohl Photon- als auch Atom-Felder gleichwertig in zweiter Quantisierung zu beschreiben. Wir formulieren eine diagrammatische Störungstheorie, die Korrelationsfunktionen des elektromagnetischen Feldes und des Atomsystems benutzt. Der Formalismus wird anschließend verwendet, um für in Fallen nahe einer Oberfläche gehaltene BECs Atom-Oberflächen-Wechselwirkungen vom Casimir-Polder-Typ und die bosonische Stimulation des spontanen Zerfalls angeregter Atome zu untersuchen. Außerdem untersuchen wir einen phononischen Casimir-Effekt, der durch die quantenmechanischen Fluktuationen in einem wechselwirkenden BEC entsteht.
39
Divaret, Lise. "U-RANS Simulation of fluid forces exerted upon an oscillating tube array". Thesis, KTH, Farkost och flyg, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-32747.
Testo completoAbstract (sommario):
The aim of this master thesis is to characterize the fluid forces applied to a fuel assembly inthe core of a nuclear power plant in case of seism. The forces are studied with a simplifiedtwo-dimensional model constituted of an array of 3 by 3 infinite cylinders oscillating in aclosed box. The axial flow of water, which convects the heat in the core of a nuclear powerplant, is also taken into account. The velocity of the axial flow reaches 4m/s in the middle ofthe assembly and modifies the forces features when the cylinders move laterally.The seism is modeled as a lateral displacement with high amplitude (several cylinderdiameters) and low frequencies (below 20 Hz). In order to study the effects of the amplitudeand of the frequency of the displacement, the displacement taken is a sine function withboth controlled amplitude and frequency. Four degrees of freedom of the system will bestudied: the amplitude of the displacement, its frequency, the axial velocity amplitude andthe confinement (due to the closed box).The fluid forces exerted on the cylinders can be seen as a combination of three terms: anadded mass, related to the acceleration of cylinders, a drift force, related to the damping ofthe fluid and a force due to the interaction of the cylinder with residual vortices. The firsttwo components will be characterized through the Morison expansion, and their evolutionwith the variation of the degree of freedom of the system will be quantified. The effect ofthe interaction with the residual vortices will be observed in the plots of the forces vs. timebut also in the velocity and vorticity map of the fluid.The fluid forces are calculated with the CFD code Code_Saturne, which uses a second orderaccurate finite volume method. Unsteady Reynolds Averaged Navier Stokes simulations arerealized with a k-epsilon turbulence model. The Arbitrary Lagrange Euler model is used todescribe the structure displacement. The domain is meshed with hexahedra with thesoftware gmsh [1] and the flow is visualized with Paraview [2]. The modeling techniquesused for the simulations are described in the first part of this master thesis.
40
Langer, Sebastian. "Expenditure Interactions between Municipalities and the Role of Agglomeration Forces: A spatial analysis for North Rhine-Westphalia". Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-236245.
Testo completoAbstract (sommario):
This paper analyzes municipal expenditures in the light of horizontal fiscal interactions. I investigate total expenditures and a set of non-earmarked expenditure subcategories in the largest German federal state, North Rhine-Westphalia (NRW). The empirical analysis is based on a Spatial Durbin Model in a panel for the years 2009-2015. Using a two-regime spatial matrix, I also examine the impact of agglomeration on the intensity of public expenditure interactions, thus testing the hypothesis that an agglomerated region can decrease the amount of public goods without losing mobile factors to the periphery.
The findings indicate that significant municipal expenditure interaction effects do exist. The reaction functions also vary for different expenditure subcategories. Unlike spillover effects and fiscal competition, yardstick competition is an insignificant source of potential interactions. Expenditure interaction is fiercer if there is less agglomeration in a municipality. Urbanized and populous municipalities appear to benefit from agglomeration economies, a fact that enables them to spend less. Robustness checks confirm the findings.
41
Anderson, Carl 1943. "Motions driven by buoyancy forces and atmospheric stresses in the Avalon Channel, Newfoundland, Canada". Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=72098.
Testo completoAbstract (sommario):
Currents and sea level fluctuations in the Avalon Channel, driven over a broad range of time scales by buoyancy forces, atmospheric pressure, and wind stress, are described and compared with dynamical theory.Seasonal fluctuations in adjusted coastal sea level at St. John's are shown to be consistent with steric height and bottom pressure variations 3 km offshore in a depth of 180 m.
Low frequency fluctuations (periods of 7-50 d) in observed Avalon Channel currents and water properties suggest the presence of a baroclinically-unstable, buoyancy-driven coastal current. A kinematic analysis of the current fluctuations reveals an eddy structure resembling that predicted for baroclinically-unstable waves on a longshore current with the density stratification and vertical shear observed in the fall.
Cross-spectral analysis of St. John's sea level and meteorological records, and Avalon Channel steric height estimates, shows that sea level responds isostatically to atmospheric pressure forcing at periods longer than 2 days, and to seasonal changes in steric height. Adjusted sea level responds 180 degrees out-of-phase to forcing by longshore wind stress at periods longer than 2 days. Longshore current responds in-phase to longshore wind stress forcing, with surface intensification of the response close to shore.
Frequency response functions are derived from the shallow water equations of motion for the response of sea level and current to atmospheric pressure and wind stress forcing in homogeneous and two-layer, uniform-depth coastal ocean models, and in a homogeneous, step-shelf model. Linear bottom friction is assumed in the homogeneous ocean models. The phases of the observed sea level and current responses to wind stress suggest that the response is due to the existence of continental shelf waves originating at the northern edge of the Grand Banks, about 150 km away from the study site. The near-shore surface intensification of the current and sea level responses are consistent with the predictions of the two-layer uniform-depth model.
42
Semin, Benoît. "Interaction d'une fibre et d'un écoulement en géométrie confinée". Phd thesis, Ecole Polytechnique X, 2010. http://pastel.archives-ouvertes.fr/pastel-00006340.
Testo completoAbstract (sommario):
Le déplacement d'objets allongés dans un fluide se retrouve dans de nombreux domaines tels que la récupération du pétrole, la production du papier ou la nage de micro-organismes. Dans ce travail, nous étudions le comportement d'une fibre cylindrique longue dans un écoulement en géométrie confinée (fracture, canal microfluidique). Dans un premier temps, les forces de trainée exercées sur la fibre ont été déterminées expérimentalement et numériquement en fonction de son orientation et de sa position dans l'ouverture. Lorsque la fibre est parallèle à l'écoulement, elle le perturbe faiblement et une modélisation 2D est suffisante ; au contraire, lorsqu'elle est perpendiculaire, l'écoulement devient 3D quand le blocage est incomplet. Pour cette orientation, la portance est suffisante pour maintenir l'objet au centre de l'écoulement. Pour un nombre de Reynolds de l'ordre de 20, cette position devient instable : le cylindre oscille entre les deux parois. Le seuil de l'instabilité est inférieur au seuil d'émission des tourbillons de Bénard-Von Kármán. La position du cylindre est modélisée par une équation de Van der Pol qui prédit quantitativement la bifurcation de Hopf du système. Une interprétation hydrodynamique des coefficients de cette équation est présentée. Nous présentons et validons ensuite une méthode de traitement d'image, qui détermine de manière analytique la forme d'une fibre avec une précision sub-pixel. De plus, l'angle du vecteur tangent et la courbure de la fibre - essentielle car reliée à son moment fléchissant - sont mesurés avec précision.
43
Ibargüen, becerra César. "Effet des forces de van der Waals sur la dynamique de l'azote et de l'hydrogène en interaction avec la surface de W(100)". Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0261.
Testo completoAbstract (sommario):
Une littérature scientifique nourrie est consacrée aux processus élémentaires hétérogènes se produisant à l’interface gaz-solide en raison de leur rôle clé dans de nombreux domaines. Ainsi, l’interaction d’atomes et de molécules avec les surfaces revêt une importance primordiale dans l’étude de la catalyse hétérogène, la combustion, la corrosion, le stockage de l’hydrogène, l’industrie automobile et pétrolière, les interactions plasma/paroi dans le contexte du réacteur expérimental thermonucléaire (ITER), les technologies du spatial, la chimie atmosphérique et l’astrochimie, pour citer quelques exemples. Lorsqu'un atome ou une molécule entre en collision avec une surface, de nombreux processus élémentaires peuvent avoir lieu. Ils dépendent de nombreux facteurs tels que : l'énergie de collision du projectile, l'angle d'incidence sur la surface, la température de surface, l'état initial le des molécules, le transfert d'énergie entre la surface des projectiles, etc… Tous ces facteurs influencent fortement les mécanismes réactionnels et la dynamique de ces processus. Les expériences de faisceaux moléculaires permettent un contrôle toujours plus précis de l'état initial des réactifs associé à un caractérisation fine des produits de réactions. Cependant, dans la plupart des cas, ces observations expérimentales ne fournissent pas tous les détails qui nous permettent de décrire finement les mécanismes gouvernant les processus élémentaires étudiés. Par conséquent, l'élaboration de modèles théoriques devient essentielle pour en rationaliser la description. L'objectif principal de ce travail de thèse est de proposer une analyse de la dynamique de plusieurs processus élémentaires pouvant se produire sur une surface de W(100) en contact avec de l'hydrogène et de l'azote (diffusion inélastique de N2 et H2, l'adsorption dissociative et non dissociative de H2 et l'adsorption et l'absorption de H et N). Par rapport aux études antérieures, la nouveauté de ce travail réside dans la prise en compte des interactions à longue distance de type van der Waals, qui s’avèrent essentielles lorsqu'on souhaite atteindre un bon accord théorie expérience dans le régime des faibles énergies de collision. Les résultats sont comparés aux données expérimentales disponibles et aux résultats théoriques antérieurs. Des simulations de dynamique moléculaire quasi-classique sont réalisés à l'aide de surfaces d'énergie potentielle (PES) basées sur la théorie de la fonctionnelle de la densité, tenant compte d’interactions non locales, telles que les forces de van der Waals. La dissipation de l’énergie aux vibrations du réseau et aux excitations électroniques est prise en compte au moyen de modèles effectifsAn important part of scientific literature is devoted to the heterogeneous elementary processes occurring at gas-solid interface due to their great importance and key role in many different domains and applications. Thus, interaction of gas atoms/molecules with surface reactions are of primary importance in the study of: heterogeneous catalysis, combustion of solid fuel and coal gasification, processes of corrosion, hydrogen storage in solid material, automotive and oil industry, plasma-wall interactions in the context of thermonuclear experimental reactor (ITER), atmospheric re-entries technologies and astrochemistry, to name some examples. When an atom or molecule impinges on a surface many different elementary processes can take place, which depends on factors such as: the collision energy of the projectile, the angle of incidence to the surface, the surface temperature, the initial state of the molecules, the transference of energy projectiles-surface, etc. All these factors determines the mechanisms of reaction and the dynamics of the processes. Experimental molecular beams (MB) and other experimental techniques are able to accurately control the initial state of the reactive and characterizing products of gas-surface reactions. However, in most of the case experimental techniques do not provide enough details about the mechanisms through which elementary processes occur. Consequently, theoretical models becomes essential to rationalize the description that in certain cases the experiments do not reach.The main goal of this thesis work is to propose an analyze of the dynamics of several elementary processes occurring on a W(100) surface, such as: the inelastic scattering of N2 and H2, the dissociative and non-dissociative adsorption of of H2 and the adsorption and absorption of H and N. Compared to previous studies, the novelty of this work resides in the taking into account of van der Waals long-distance interactions, which are essential to reach a good agreement between theoretical and experiment results, especially at low collision energy regime. To rationalize the non-adiabatic effects, the energy dissipation to lattice vibrations and electronic excitation are taken in to account by means of GLO and LDFA models respectively
44
Hawari, Haitham M. "Minimising track degradation through managing vehicle/track interaction". Queensland University of Technology, 2007. http://eprints.qut.edu.au/16366/.
Testo completoAbstract (sommario):
The rate at which a railway track deteriorates depends on the response of the track under different static and repeated dynamic forces. These wheel/rail forces lead to imperfections in the rail surface and deviation in track geometry alignment. The wheel/rail forces are dependent upon the quality of maintenance of the characteristics of both train and track. If train components such as wheelsets and suspensions are maintained to a high standard, less dynamic forces are generated at the wheel/rail interface and less damage is caused over time. Therefore, the amount and cost of maintenance of track are reduced. However, there is little known about how the characteristics of train components affect time-dependent track degradation. Track degradation through deviation of track from its ideal position has the most effect on maintenance costs. Therefore, the present research aims to investigate this track degradation and improve understanding of the effects of train characteristics (such as train mass and speed, suspension stiffness and damping) on railway tracks. The research is conducted by looking into the relationship between wheel/rail forces and track degradation on one hand and between wheel/rail forces and train characteristics on the other hand, with the objective of assisting in managing vehicle/track interaction in order to minimise track degradation. This aim is achieved by investigating the above two relationships to attain the desired relationship between track degradation and train characteristics. The research focuses on wheel/rail vertical forces (both amplitudes and frequencies), vertical track alignment (longitudinal vertical profile), and rail head defects. The study started by collecting wheel/rail vertical forces data in addition to data on vertical track degradation under sustained traffic loads on a heavy haul railway section of track in Central Queensland. Also, five years of degradation and maintenance history data were collected on three other test sections of railway track under variety of traffic conditions and loads in Central Queensland. There were four main analyses of this data employed to probe the study. The first analysis was performed by examining the track degradation history data. The standard deviation method was used in this first analysis to acquire the rate of deterioration in terms of its relationship to track profile (roughness). The second analysis was accomplished by correlating the vertical wheel/rail forces to both vertical track profile and rail roughness using signal processing principles and a function know as coherence. The third analysis was carried out by using the computer simulation software NUCARS to obtain the link between wheel/rail forces and the deterioration of the vertical track profile. The fourth analysis was achieved by combining the results obtained from the above three analyses to acquire the rate of track deterioration in terms of its relationship to varying train characteristics. The first analysis mentioned above quantified the relationship between the level of roughness of the track and rate at which that roughness deteriorated. An important outcome of this relationship is that there is a threshold of roughness below which track deterioration is minimal. The track maintenance planners can now use that threshold for cost effective targeting of tamping activities. The correlation study between track roughness and wheel/rail forces using the coherence function found, surprisingly, that the overall deterioration of the track roughness, in the absence of frequencies of forces above 30 Hz, is due to the so-called quasi-static lower frequency oscillations of dynamic forces. This conclusion together with the relationship between vehicle characteristics and track forces, established in the analyses above, has significant implications for the design of wagon bogies and for charges track owners might levy on trains using their tracks. This research is part of a larger Rail CRC project 11/4 called 'Enhancing the Optimisation of Maintenance/Renewal' being carried out in the School of Urban Development in Queensland University of Technology.
45
Senechal, Annie. "Initial stages of adhesion of enterococcus faecalis responsible for biofilm formation on medical devices : quantification of bacterial adhesion and measurement of cell-surface interaction forces". Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=80142.
Testo completoAbstract (sommario):
The presence of a microbial biofilm on medical implants and devices remains a serious clinical problem since it can increase the risk of infection. To prevent biofilm formation, it is important to study the initial stages of bacterial adhesion. The aim of this study was to compare the initial interactions of the uropathogen Enterococcus faecalis with different medical grade polymers. To accomplish this, kinetics of E. faecalis adhesion were followed using a DNA quantification assay. The influence of biomaterial surface properties, including surface wettability and roughness, was investigated. Moreover, the distribution and morphology of the adhered bacteria were studied. Finally, quantification of bacterial adhesion forces was achieved using AFM through cell detachment measurements.The results showed significant differences in E. faecalis adhesion between the studied polymers suggesting that precautions should be made for the choice of polymers in the design of medical applications in order to prevent subsequent biofilm formation.
46
Essig, Marie. "Interaction entre le cytosquelette et le systeme fibrinolytique : modulation par les inhibiteurs de la 3-hydroxy 3-methylglutaryl coenzyme a reductase et les forces de cisaillement". Paris 7, 1998. http://www.theses.fr/1998PA077207.
Testo completoAbstract (sommario):
Le systeme fibrinolytique est une cascade proteolytique qui a pour but la degradation de la fibrine et le remodelage de la matrice extracellulaire. Dans le rein, ces deux elements sont impliques dans la progression des lesions renales et a la formation d'une fibrose. La fibrose interstitielle resulte d'un desequilibre entre la synthese et la degradation de la matrice et est un facteur pronostic majeur de la deterioration de la fonction renale. Les mecanismes qui initient ce desequilibre sont un point fondamental a eclaircir pour prevenir la destruction du parenchyme renal. Le cytosquelette participe a la regulation du systeme fibrinolytique. Le stress mecanique endothelial induit par les forces de cisaillement, qui provoque une reorganisation du cytosquelette, modifie plusieurs molecules du systeme fibrinolytique. D'autre part, le fait que des medicaments hypocholesterolemiants, les inhibiteurs de l'hmg coa reductase ou statines, qui ont la propriete de desorganiser le cytosquelette, ralentissent la progression de lesions vasculaires ou renales, suggere que ces agents modulent le systeme fibrinolytique. Cette etude a cherche a preciser les interactions entre le systeme fibrinolytique tubulaire renal et le cytosquelette, particulierement les effets respectifs des modifications du cytosquelette induites par les statines ou par un stress mecanique. Nous montrons que les statines induisent in vivo et in vitro, le systeme fibrinolytique de cellules endotheliales aortiques. Cet effet resulte d'une inhibition de proteines isoprenylees geranylgeranylees, les proteines rho, et est associe a une desorganisation des filaments d'actine. Ces resultats sont reproduits dans les cellules tubulaires proximales, in vivo, ex vivo et in vitro. A l'inverse, nous montrons que les contraintes de cisaillement exercees sur des cellules tubulaires proximales, in vivo lors de modification du flux urinaire, ou in vitro dans une chambre de flux, induisent une inhibition du systeme fibrinolytique et un renforcement du cytosquelette. Ce travail permet d'etablir de nouveaux mecanismes physiopathologiques de la deterioration du parenchyme renal et ainsi de developper des approches pharmacologiques qui pourraient ralentir la progression de l'insuffisance renale terminale
47
Sweetman, Adam. "Forces at the nanoscale : interactions in atomic force microscopy and dielectrophoresis". Thesis, University of Nottingham, 2010. http://eprints.nottingham.ac.uk/11213/.
Testo completoAbstract (sommario):
Interactions at the nanoscale are governed almost exclusively by electromagnetic forces, but the interplay between different scaling laws produces a vast array of behaviours. We investigate radically different systems spanning almost three orders of magnitude of length scales, and use a variety of experimental techniques to determine the forces present in each regime, and the interplay between them. An important prototypical surface in SPM science has been the Si(100) surface, which due to it’s unstable buckling and complex electronic structure has fostered considerable debate in the surface science community. We have used small amplitude, high sensitivity combined qPlus STM/AFM to investigate tip -- sample interactions on the Si(100) surface at low-temperature in UHV, with a focus on the chemical, and electronic properties of the system and how these are modified by the probe. We present the first atomic resolution combined force/tunnel current results on the surface and show that great care must be taken in interpreting either pure AFM or pure STM data. We also examine tip -- sample interactions on arrays of thiol passivated spin-cast nanoparticles in both UHV and ambient conditions and show for the first time how minor modifications to the experimental parameters can radically alter the data collected, most likely due to the thiol -- surface -- tip interaction. We also present SKPM and voltage spectroscopy of the same samples and show the importance of electrostatic interactions in correct height determination of these network arrays, in parallel with the caution that must be maintained in interpreting CPD data. A key mechanism for the manipulation of meso-scale objects in solution is Dielelectrophoresis, which offers strong material and size specificity and a high degree of spatial control. In the final experimental chapter we investigate the effect of inhomogenous electric fields on nanoparticles in aqueous solution, and reveal how previously uninvestigated electrochemical effects can become important even at high frequencies, and may offer a new and exciting route for the control of self organised nanowires in solution.
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Hamamda, Mehdi. "Perspectives nouvelles pour l’optique atomique en jets : Interaction de van der Waals-Zeeman et milieux d’indice négatif pour les ondes de matière". Paris 13, 2011. http://www.theses.fr/2011PA132008.
Testo completoAbstract (sommario):
Dans la première partie de cette thèse, nous développons l’étude expérimentale et théorique d’un type d’interactions à très courte portée (moins de 10nm), dites de van der Waals-Zeeman, entre un atome de gaz rare et une surface métallique. Il s’agit d’utiliser d’une part un jet supersonique d’atomes métastables pour diverse espèces (Ne*, Ar*, Kr*) et, d’autre part, un jet d’argon métastable Ar*(3P2) décéléré par un ralentisseur Zeeman standard. Dans le premier cas, on observe un accroissement de la portée de l’interaction de van der Waals-Zeeman en fonction de l’augmentation de la constante d’anisotropie . Dans le second cas, l’augmentation de la portée est observée lors d’une diminution de la vitesse d’un atome d’argon métastable de 560 à 170m/s. La combinaison de ces méthodes nous a permis de mesurer la portée de l’interaction (dont l’efficacité est de quelques 10-4) avec une résolution spatiale de 2 à 3nm. Dans la seconde partie de ce travail, nous introduisons la thématique nouvelle des milieux d’indice négatif pour l’optique atomique. Ces milieux consistent en des potentiels dits comobiles agissant dans le vide. Deux effets majeurs de ces milieux d’indice négatif sont démontrés : la réfraction négative pour des ondes de matière et le rétrécissement du paquet d’onde atomique. Enfin, nous montrons que l’application de milieux d’indice négatif aux ondes évanescentes de matière (créées à l’aide d’une barrière de potentiel magnétique statique) permet de les localiser sur une épaisseur de quelques micromètres de part et d’autre du bord de la barrière de potentielIn the first part of this thesis, we develop both theoretical and experimental studies of a type of short range atom-surface interaction (less than 10nm) called van der Waals-Zeeman transitions. To perform this study, we first use a supersonic beam of various metastable gaz rare atoms (Ne*, Ar*, Kr*), then we use a metastable argon beam Ar*(3P2) decelerated using a standard Zeeman slower. In the first case, we observe an increase of the range of the van der Waals-Zeeman interaction with respect to the raise of the anisotropy constant . In the second case, the increase of the range is observed as a function of the velocity decrease of a metastable argon atom from 560 to 170m/s. The combination of these two methods allows us to measure the range of the interaction (the yield of which is of a few 10-4) with a spatial resolution between 2 and 3 nm. In the second part of this work, we introduce the new field of negative index media for atom optics. These media consist of potentials called comoving potentials acting in vacuum. The two major demonstrated effects produced by this type of media are: the negative refraction effect for atomic waves and the spatial narrowing of the atomic wave-packet. Finally, the application of the negative index media to evanescent waves (produced by a static magnetic potential barrier) allows a localization of these waves within a few micrometers thick zone on both sides of the potential barrier
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Ramond, Céline. "Probing the femtosecond dynamics of laser-cluster interaction via X-ray and electron spectroscopy : = Sonder la dynamique sub picoseconde de l'interaction laser agrégats par spectroscopie X et d'électrons énergétiques". Paris 6, 2012. http://www.theses.fr/2012PA066272.
Testo completoAbstract (sommario):
Ce travail de thèse a consisté en l’étude de la dynamique sub-picoseconde de l’interaction laser-agrégats d’argon par spectroscopie X et d’électrons énergétiques. Une attention particulière à été portée à la mesure précise de l’intensité seuil en éclairement laser nécessaire pour la production de lacune en couche interne. L’évolution de ce paramètre clé avec la durée d’impulsion doit en effet permettre de révéler la compétition temporelle entre les mécanismes de chauffage des électrons et l’expansion de l’agrégat. Ces mesures, réalisées pour deux longueurs d’onde du laser, 400 et 800 nm, ont permis de confirmer des résultats expérimentaux précédents: des valeurs extrêmement basses ont été trouvées, de l’ordre de 1014W/cm2, mais ici pour des durées d’impulsion supérieures à 800 fs en lumière IR et 600 fs pour le bleu. Pour cette valeur d’intensité laser, seul l’ionisation des premiers électrons des atomes d’argon est possible par effet tunnel, démontrant ainsi que la production d’Ar1+ est le processus d’allumage pour la production de rayonnement X issu de la désexcitation d’ions multichargés Arq+. Il a aussi été possible, pour la première fois, d’étudier l’influence unique de la longueur d’onde sur l’efficacité des mécanismes de chauffage des électrons. Nous avons montré que sur la gamme de durées d’impulsion étudiée, i. E. Jusqu’à 735 fs, la probabilité d’ionisation en couche interne est toujours 10 fois supérieur en IR qu’en bleu, mettant en défaut les résultats présents dans la littérature. Enfin, nous avons démontré expérimentalement une forte corrélation entre l’émission X et la partie haute énergie de la distribution énergétique des électronsThe work performed during my thesis aims to study the sub-picosecond dynamics of laser- argon cluster interaction using X-ray and energetic electron spectroscopy. One of the key parameter to reveal the temporal competition between the electron heating mechanisms and the cluster expansion is the laser intensity threshold needed to create inner-shell vacancy in cluster atoms. Its evolution with pulse duration has been measured very accurately for two wavelengths, 400 and 800 nm. For long pulse durations, typically more than 800 fs in IR light and 600 fs in blue light, this intensity threshold is a low as 1014 W/cm2, confirming previous results at 610 fs. At this laser intensity, only ionization of the least bound electrons of the argon atom is possible via tunnel effect. This demonstrates that the production of Ar1+ is the ignition process for production of K-shell vacancy in highly charged Arq+. It has also been possible to compare, for the first time, the efficiency of the electron heating mechanisms between both wavelengths (400 and 800 nm) under similar experimental conditions. The mid- IR light is found to be always 10 times more efficient than blue light to create inner-shell vacancies, whatever the pulse duration up to 635 fs. This finding is in clear disagreement with the results present in the literature, as a -6 scaling law was found. Finally, by recording electron energy distribution under the same experimental conditions than the X-ray yield, we demonstrated a strong correlation between the high energy tail of the electron distribution (for energy typically higher than the inner-shell binding energy of the argon atom) and the X-ray emission
50
Semin, Benoît. "Intercation d'une fibre et d'un écoulement en géométrie confinée". Palaiseau, Ecole polytechnique, 2010. http://pastel.archives-ouvertes.fr/docs/00/55/93/59/PDF/these_BSemin.pdf.
Testo completoAbstract (sommario):
Le déplacement d'objets allongés dans un fluide se retrouve dans de nombreux domaines tels que la récupération du pétrole, la production du papier ou la nage de micro-organismes. Dans ce travail, nous étudions le comportement d'une fibre cylindrique longue dans un écoulement en géométrie confinée (fracture, canal microfluidique). Dans un premier temps, les forces de trainée exercées sur la fibre ont été déterminées expérimentalement et numériquement en fonction de son orientation et de sa position dans l'ouverture. Lorsque la fibre est parallèle à l'écoulement, elle le perturbe faiblement et une modélisation 2D est suffisante ; au contraire, lorsqu'elle est perpendiculaire, l'écoulement devient 3D quand le blocage est incomplet. Pour cette orientation, la portance est suffisante pour maintenir l'objet au centre de l'écoulement. Pour un nombre de Reynolds de l'ordre de 20, cette position devient instable : le cylindre oscille entre les deux parois. Le seuil de l'instabilité est inférieur au seuil d'émission des tourbillons de Bénard-Von Kármán. La position du cylindre est modélisée par une équation de Van der Pol qui prédit quantitativement la bifurcation de Hopf du système. Une interprétation hydrodynamique des coefficients de cette équation est présentée. Nous présentons et validons ensuite une méthode de traitement d'image, qui détermine de manière analytique la forme d'une fibre avec une précision sub-pixel. De plus, l'angle du vecteur tangent et la courbure de la fibre - essentielle car reliée à son moment fléchissant - sont mesurés avec précisionThe motion of elongated objects in a fluid is encountered in many scientific fields, ranging from oil recovery and paper production to microorganism swimming. In the present thesis we study the behavior of a long cylindrical fiber in a confined flow (fracture, microfluidic channel). We first determine both experimentally and numerically the drag on this object as a function of its orientation and position in the aperture. A fiber parallel to the flow only slightly perturbs the flow, and the force on it can be estimated using 2D models. On the contrary, if it is perpendicular to the flow, the latter becomes 3D if blockage is partial. In this configuration, the lift is sufficient to keep the cylinder in the middle of the flow. For Reynolds numbers higher than 20, this position becomes unstable and the cylinder oscillates between the walls. The threshold of this instability is lower than that of Bénard-Von Kármán vortex shedding. The position of the cylinder satisfies a Van der Pol equation, which allows for a quantitative prediction of the Hopf bifurcation of the system. A hydrodynamic interpretation of the coefficients of this equation is given. We also develop and validate a new image processing method, which give the shape of the fiber with a sub-pixel precision. Moreover, the tangent vector angle and the curvature, of interest because it is related to the bending moment, are accurately measured