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1
Snow, Edward Ramsey. "The load/deflection behavior of pretensioned cable-pulley transmission mechanisms." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/36477.
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Yazicioglu, Faruk. "Design And Implementation Of A Two-axes Linear Positioning System For Rapid Prototyping Applications." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608835/index.pdf.
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In this study, a two axes linear positioning system for testing and applying different rapid prototyping techniques was designed and manufactured. A cable/ pulley mechanism is utilized in the system for transmitting motion from motors into linear motion. Use of a cable/ pulley mechanism overcomes the problems resulting from the utilization of conventional drive systems like ball screws and decreases the
overall cost of the system.
The carriage elements of both axes were designed and manufactured by using investment casting. The molds used in casting were also designed and manufactured within this study. The designed system is controlled by a servo motion control system composed of a motion controller, DC servo motors and linear encoders. All elements of the motion control system were selected, integrated and programmed
within the scope of the study.
3
Kong, Lingyuan. "Coupled belt-pulley mechanics in serpentine belt drives." The Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1069789616.
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Adam, Petr. "Pomocná jeřábová kočka licího jeřábu." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-241179.
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This master thesis deals with issue design of crab trolley. Concretely is acted about auxiliary crab trolley with required capacity 65 000 kg. This crab is on overhead crane, which is situated at hall of foundry. In particular chapters is processed design of lifting mechanism and travelling mechanism, which is amended to strength control of frame. This whole leads to output solutions, which is drawing documentation.
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Albagli, D. (Douglas). "Fundamental mechanisms of pulsed laser ablation of biological tissue." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/33521.
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Castera, Philippe. "Energy coupling mechanisms in pulsed surface discharges for flow control." Thesis, Châtenay-Malabry, Ecole centrale de Paris, 2015. http://www.theses.fr/2015ECAP0041/document.
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Ce travail s'intéresse aux effets mécaniques créés par les décharges de surface et à leur efficacité comme actionneur. Une géométrie particulière d'électrodes permet de créer de manière pulsée un filament linéaire de plasma et de le chauffer très rapidement par effet Joule (à raison de plusieurs Joules en moins d'une microseconde). Ce chauffage rapide entraîne la formation d'ondes de choc qui peuvent interagir avec l'écoulement ambiant.Nous étudions le comportement électrique de la décharge de surface afin d'évaluer l'énergie déposée dans le filament de plasma par effet Joule. Pour ce faire, nous réalisons une étude paramétrique sur la configuration du circuit et nous déterminons les principaux paramètres qui pilotent la dynamique de la décharge. Différents modèles de résistance sont utilisés dans un code de simulation du circuit électrique, et leurs prédictions du courant et du dépôt d'énergie sont confrontées aux mesures expérimentales.Des mesures spectroscopiques dans différentes configurations de circuit donnent accès à certaines propriétés de la décharge comme la densité électronique, qui atteint des valeurs de 2x1018 cm-3. Le rayon du canal est également mesuré par imagerie rapide. Les ondes de chocs créées par la décharge de surface sont visualisées en imagerie Schlieren pour plusieurs configurations de circuit. Ces ondes de chocs créent une impulsion proportionnelle à l'énergie déposée dans la décharge. Nos développons un modèle de choc pour décrire la trajectoire du choc et pour calculer l'impulsion communiquée par la décharge de surface. Le modèle est en bon accord avec les mesures expérimentales et la décharge de surface a une efficacité mécanique de 0.12mNs/J pour notre configuration d'étude. Nous terminons cette étude en comparant cet actionneur potentiel avec d'autres actionneurs courants et proposons plusieurs pistes pour de futurs travauxIn this study, we investigate the mechanical effects generated by pulsed surface discharges and their efficiency as an actuator. Using a specific electrode configuration, it is possible to create a short-lived, pulsed, rectilinear plasma channel and to heat it up rapidly (several Joules in less than a microsecond) through Joule heating. This fast energy deposition causes the formation of shock waves that can then interact with the surrounding flow.We study the electrical behavior of the pulsed surface discharge to assess the energy deposited in the plasma channel through Joule heating. To do so, we perform a parametric study on the circuit configuration and identify the main parameters driving the discharge dynamics. Several resistance models are implemented in a numerical description of the electrical circuit and their predictions of the current and deposited energy are compared with experimental measurements.Spectroscopic measurements in different circuit configurations give access to some of the plasma properties such as the electron number density that can reach values up to 2x1018 cm-3. Fast imaging also gives insight into the plasma channel radius. The shock waves generated by the pulsed surface discharge in different circuit configurations are visualized through Schlieren imaging. These shock waves generate an impulse that increases linearly with the energy deposited in the discharge. We develop a shock model to describe the shock trajectory and to compute the impulse imparted by the pulsed surface discharge. The model is in good agreement with our measurements and the pulsed surface discharge is found to have a mechanical efficiency of 0.12 mNs/J for our setup configuration. We conclude this study by comparing the proposed pulsed surface discharge actuator with other common designs and offer some directions for future studies
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Kubánek, Jan. "Lanový drapák." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2009. http://www.nusl.cz/ntk/nusl-228815.
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When soluting the contruction of a grab dredger we will deal with suitable solution with reference to its using and capacity, possibilites of its setting in low temperatures and incidental aplication of the exchangeable abrasion - resistant mouldings. There will be made a calculation of forces taking effect on a grab dredger and a check calculation of the chosen structural parts.
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Yalukova, Olga. "Interaction mechanisms of pulsed laser beams at different wavelengths with matter." Licentiate thesis, Luleå, 2004. http://epubl.luth.se/1402-1757/2004/029.
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Scharlemann, Carsten A. "Investigation of thrust mechanisms in a water fed pulsed plasma thruster." The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1070354149.
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Ladogana, Santino. "Kinetics and Mechanisms of Metal Carbonyls." Thesis, University of North Texas, 1998. https://digital.library.unt.edu/ark:/67531/metadc278709/.
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Pulsed laser flash photolysis with both visible and infrared detection has been applied to the study of the displacement of weakly coordinating ligands (Lw) by strongly "trapping" nucleophiles (Ls) containing either an olefinic functionality (Ls = 1-hexene, 1-decene, 1-tetradecene) or nitrogen (Ls = acetonitrile, hydrocinnamonitrile) from the photogenerated 16 electron pentacarbonylchromium (0) intermediate. 5-Chloropent-l-ene (Cl-ol), a potentially bidentate ligand, has been shown to form (ol-Cl) pentacarbonylchromium (0), in which Cl-ol is bonded to Cr via a lone pair on the chlorine, and isomerize to (Cl-ol) pentacarbonylchromium (0), in which Cl-ol is bonded to the olefinic functionality
on the submillisecond time scale. This process has been studied in both the infrared and visible region employing both fluorobenzene or n-heptane as the "inert" diluent. Parallel studies employing 1-chlorobutane and 1-hexene were also evaluated and showed great similiarity with the Cl-ol system. The data supported a largely dissociative process with a possibility of a small interchange process involving the H's on the alkyl chain. Studies were also carried out for various Cr(CO)6/arene/Ls systems (arene = various alkyl or halogenated substituted benzenes). The data indicated that for both C6H5R (R=various
alkyl chains) or multi-alkyl substituted arenes (i.e. o-xylene, 1,2,3-trimethylbenzene) containing an "unhindered" ring-edge, bonding to the the Cr(CO)5 moiety occurs "edge on" via a partially delocalized center of unsaturation on the ring. The data indicated that both electronic and steric properties of the arenes influence the kinetics, and that an interchange pathway takes place at least, in part, through the alkyl chains on both the arenes and "trapping" nucleophiles. Moreover, halogenated arenes bond through the lone pair on the halogen for both CI- and Br- derivatives but "edge-on" for the fluorinated arenes. Finally, in the case of arene complexes without and "unhindered" ring-edge (i.e.,
1,2,3,4,5-pentamethylbenzene) bonding can occur either "edge-on" or through the ring center of the arene or combination of the two. Carbonyl stretching frequencies for the arenes are also indicative of the type of bonding.
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Blanche, Pierre-Alexandre, Brittany Lynn, Robert A. Norwood, and Nasser Peyghambarian. "Mechanisms for the reciprocity failure in photorefractive polymers." SPIE-INT SOC OPTICAL ENGINEERING, 2016. http://hdl.handle.net/10150/622716.
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We measured the diffraction efficiency response of two photorefractive polymer devices according to the duration of the single laser pulse used to record the hologram. The pulse duration was varied from 6 nanoseconds to 1 second, while the pulse energy density was maintained constant at 30 mJ/cm(2). This changed the peak power from 5 x 10(9) mW to 30 mW. We observed a strong reciprocity failure of the efficiency according to the pulse duration, with a reduction as large as a factor 35 between 1 second and 30 mu s pulse duration. At even lower pulse duration (< 30 mu s), the efficiency leveled out and remained constant down to the nanosecond exposure time. The same behavior was observed for samples composed of the same material but with and without buffer layers deposited on the electrodes, and different voltages applied during the holographic recording. We explained these experimental results based on the charge transport mechanism involved in the photorefractive process. The plateau is attributed to the single excitation of the charge carriers by short pulses (T-p < 30 mu s). The increase of efficiency for longer pulse duration (T-p > 30 mu s) is explained by multiple excitations of the charge carriers that allows longer distance to be traveled from the excitation sites. This longer separation distance between the carriers increases the amplitude of the space-charge field, and improves the index modulation. The understanding of the response of the diffraction efficiency according to the pulse duration is particularly important for the optimization of photorefractive materials to be used at high refresh rate such as in videorate 3D display.
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Norris, Andrea Rose. "Mechanisms regulating ecological responses to resource pulses within cavity-nesting bird communities." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/43044.
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Resource pulses may influence mechanisms that can regulate consumer populations directly through bottom-up effects on resource availability and indirectly via top-down effects of inter-specific interactions. Although these are well documented in food webs, the responses within nest webs (communities structured around nesting cavities in trees) have received little attention. Bark beetle (subfamily: Scolytinae) outbreaks represent food pulses that may lead to secondary pulses of nest cavities and increases in fecundity and competition among insectivores if excavating new nest cavities allows exploitation of novel habitats that increase reproductive output for both excavators and obligate secondary cavity nesters (SCNs), and if increased territory quality leads to greater energetic expenditures on territoriality. Using observational and experimental approaches, I examined how a large-scale outbreak of mountain pine beetle (Dendroctonus ponderosae) influenced the production of cavities, fecundity, and competition within nest webs at 30 sites in interior British Columbia, Canada, from 1995-2009. I used 1,018 nests of two species that varied in their ability to excavate cavities and specialize on bark beetles, Red-breasted nuthatch (Sitta canadensis; facultative excavator and bark beetle specialist) and Mountain chickadee (Poecile canadensis; SCN and generalist insectivore). I found that nuthatches excavated more cavities in lieu of using old cavities, maintained a constant clutch size throughout the breeding season (~6 eggs), and fledged up to 100% more young per nest, at sites and in years with increasing beetle abundance. Chickadee clutches were initiated earlier, mean clutch size increased from 5 to 7 eggs, and fledgling success doubled with a dual pulse of food and nest sites. I examined intra- and inter-specific territoriality by simulating conspecific and heterospecific territorial intrusions using 974 presentations with song playbacks, from 2004-2008. Chickadees, although typically subordinate to nuthatches when competing for food, attacked all intruders more frequently (24% of 397 responses elicited) than nuthatches (8% of 372 responses). Both species showed increasing territoriality with increasing beetle abundance. Overall, my research suggested that species compensated both reproductively and behaviourally in response to resource pulses, and that plasticity in foraging and nesting behaviours can promote the resilience of wildlife communities in highly variable forest environments.
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Okubo, H., N. Hayakawa, and A. Matsushita. "The Relationship Between Partial Discharge Current Pulse Waveforms and Physical Mechanisms." IEEE, 2002. http://hdl.handle.net/2237/6987.
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Xu, Ling An. "Pulsed ultrasound cross correlation flowmeter for two component flow measurement." Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277230.
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Jia, Jimmy Yi-Jie 1980. "The mechanism of thin film Si nanomachining using femtosecond laser pulses." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/35752.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 81-85).
Femtosecond (fs) laser ablation has been the subject of intense recent research. The pulse time ('width') is shorter than the electronic relaxation time, resulting in a decoupling of the period of laser illumination and the melting of the substrate. Since the laser does not directly heat the substrate, and there has been no directly observed heat affected zone (HAZ) nor vaporization, fs laser ablation is sometimes considered to be a direct solid-vapor phenomenon. Recent research indicates that the phenomenon is not as straightforward as assumed. Time-of-flight spectroscopy used to measure the reflectivity indicates that molten material is present for a few hundred picoseconds, well after the laser pulse. A material-modification threshold has been observed that is below the ablation threshold. This indicates that the laser can affect the substrate without ablation occurring. However, many scanning electron microscopy (SEM) studies have been performed, but material change in the substrate have not been observed. Transmission electron microscope (TEM) studies have also been done, but they have all been carried out in plane-view, so that it is difficult to separately observe bulk and surface effects. In this study, cross-sectional TEM analysis of holes drilled in single crystal silicon films in silicon-on-insulator (SOI) structures have been carried out, and have allowed direct observation of the subsurface modified material. Samples were prepared using a focused ion beam (FIB) system, and a metal mask was applied to protect the surface from the ion beam. Through transmission electron microscopy,
(cont.) electron diffraction analysis and energy dispersive x-ray (EDX) analysis, a surface layer of clearly modified material was identified as amorphous silicon (a-Si). This demonstrates that conventional heating of adjacent material occurs during femtosecond pulsed laser ablation. Furthermore, cross sectional transmission electron microscopy allows direct measurement of the extent of the heat-affected zone. Secondary effects were also observed in the SOI structures. An a-Si layer was observed below the insulator (SiO2) layer, indicating that the SiO2 is transparent to the laser beam and that the a-Si formed without ablation or recondensation. There was also undercutting of the top layer of silicon as well as the formation of bubble in the oxide layer. These observations also provide evidence for the nature and extent of heating that occurs during femtosecond pulsed laser ablation.
by Jimmy Yi-Jie Jia.
S.M.
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Intini, Marques Rodrigo. "A mechanism to accelerate the late ablation in pulsed plasma thrusters." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/67314/.
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Pulsed Plasma Thrusters (PPTs) are long standing electric propulsion thrusters that are reliable, relatively simple and low cost. One of the main issues with the PPT is its poor utilization of the propellant and low efficiency. Typically only 40-60% of the propellant contributes to the production significant impulse and the efficiency is around 8%. The cause of the PPT’s poor propellant utilization is the late time ablation (LTA), which has a major impact on the efficiency. LTA is the sublimation of propellant that takes place after the main discharge, due to the propellant, usually Polytetrafluoroethylene (Teflon®), being at a temperature above its sublimation point. The LTA produces a low speed gas and macro particles that do not contribute significantly to the thrust. This work presents a way of accelerating the late time ablation by employing an additional discharge after the main discharge, in a separate pair of electrodes. A new thruster, called the two-stage pulsed plasma thruster (TS-PPT) was built and tested. This thruster has two pair of electrodes: primary and secondary. The primary is placed in contact with the propellant surface, as in a regular PPT. The secondary is placed downstream, relatively far from the propellant. A new approach, dividing the PPT thrust generation in two phases, was envisioned. The first phase is responsible for the ablation process and takes place in the first pair of electrodes. The second phase takes place in the second pair of electrodes and is responsible for the acceleration process. The phase division allowed for propellant metering and better propellant utilization. Evidence was found that a pair of electrodes placed downstream, further from the propellant surface is able to discharge in the late ablation portion of the propellant and can impart extra energy into the exhaust and improve propellant utilization. A simple analytical model was developed to predict trends. A prototype of a TS-PPT was designed and built. A vacuum facility was modified, adapted, partially designed and built. An average mass bit consumption test was carried out. A simple time-of-flight experiment revealed that the fastest portions of the plasma from the primary electrodes discharge were travelling at around 33 km/s. Several current measurements were performed and calculations of the total electrical resistance, total inductance, electromagnetic impulse bit, specific impulse, efficiency, and other parameters were calculated based on experimental data. Experimental results indicated that significant improvements in the specific impulse and efficiency are possible by utilising a two-stage PPT. Specific impulses as high as 4000s were calculated based on experimental results, indicating a better propellant utilization.
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Kuděla, Jan. "Návrh horního nosníku dvousloupového regálového zakladače." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231178.
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This master thesis deals with a concept of two columned shelf stacker’s upper beam. The first part contains a research of storage systems used in logistics and a description of the shelf stack’s basic parts. The second part is dedicated to the draft of the pulley arrangement with a rope calculation, pulleys and shafts, in the same the draft of the pulley attachment to the rope leading to the counterweights. It is followed by the concept of the couple winch drive ensues synchronized with the electronic cardan. The final part depicts the dynamic analysis of the lifting truck’s movement in the dependence on the load size and distribution respecting the dynamic effect of the counterweight act.
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Coletta, Cecilia. "Study of growth mechanism of conducting polymers by pulse radiolysis." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS288/document.
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Les polymères conducteurs (PC) sont des matériaux organiques semi-conducteurs très utilisés dans diverses applications technologiques. Les propriétés optiques et conductrices de ces matériaux organiques conjugués résultent de la délocalisation électronique le long des chaînes polymères et dépendent, de ce fait, de la longueur de conjugaison. Les différentes méthodologies de synthèse des PC ont toujours pour finalité la fabrication de nouvelles structures polymères stables dans différents environnements, et dont les propriétés optiques et conductrices seraient ajustables. Néanmoins, les PC qui sont actuellement fabriqués présentent encore un certain nombre de défauts, du fait d’un manque de compréhension et de contrôle du processus de polymérisation.Parmi tous les polymères conducteurs, le poly (3, 4-éthylènedioxythiophène) (PEDOT, un dérivé de polythiophène) et le polypyrrole (PPy) sont déjà utilisés dans plusieurs applications pour leurs propriétés chimiques et physiques. Les PC, comme le PEDOT et le PPy, sont habituellement synthétisés par voie chimique ou électrochimique, la polymérisation étant systématiquement initiée par une étape d’oxydation des monomères. D'autre part, les propriétés complexes des polymères ne peuvent être contrôlées que si une bonne connaissance du procédé de polymérisation est acquise. Dans ce cas, il est possible d’orienter le processus lors de la synthèse (fonctionnalisation, caractère hydrophile, longueur de la chaîne, niveau de dopage) afin d’améliorer les propriétés conductrices des polymères synthétisés.La radiolyse de l'eau représente une méthode simple et efficace qui permet la polymérisation dans des conditions douces (température et pression ambiantes), sans aucun dopant externe, mais qui à notre connaissance n’avait jamais été utilisée seule pour la synthèse de PC. Au sein de notre laboratoire, une méthodologie alternative basée sur l’interaction rayonnement-matière a récemment été utilisée avec succès pour la synthèse de PC nanostructurés en solution aqueuse. Le présent travail est plus spécifiquement consacré à la synthèse de PEDOT et PPy en solution aqueuse et à l'étude de leur mécanisme de croissance par radiolyse pulsée.Grace à l'accélérateur d'électrons ELYSE, l'utilisation de la radiolyse pulsée couplée à la spectroscopie d'absorption résolue dans le temps a permis d'étudier la cinétique des réactions à l’échelle de la nanoseconde et de la milliseconde. Les spectres d’absorption des espèces transitoires impliquées dans le mécanisme réactionnel ont été identifiés grâce à des calculs de chimie quantique. Tout d'abord, la réaction du radical hydroxyle avec les monomères EDOT et Py a été étudiée, ainsi que la polymérisation induite par le rayonnement. Ensuite, l'étude a été transposée à d'autres radicaux oxydants tels que CO3.-, N3. et SO4.- à différents pH. Cette approche a permis de mettre en évidence l'influence des espèces oxydantes sur les premières étapes transitoires lors de l’oxydation des monomères (radical cation, produit d'addition ou radical neutre). Enfin, le faisceau d'électrons a été utilisé comme source de rayonnement ionisant (accumulation de pulses) afin de synthétiser in situ les polymères conducteurs PEDOT et PPy. Ces résultats démontrent que le mécanisme de croissance des PC n'est pas un mécanisme en chaine, mais un mécanisme par stadesToday conductive polymers have many applications in several devices. For these reasons they have received much attention in recent years. Despite intensive research, the mechanism of conducting polymers growth is still poorly understood and the methods of polymerization are limited to two principal ways: chemical and electrochemical synthesis. On the other hand, the complex properties of polymers can be controlled only if a good knowledge of polymerization process is acquired. In this case, it is possible to control the process during the synthesis (functionalization, hydrophilicity, chain length, doping level), and consequently to improve the conductive properties of the synthesized polymers. Water radiolysis represents an easy and efficient method of synthesis comparing to chemical and electrochemical polymerization routes. It enables the polymerization under soft conditions: ambient temperature and pressure, without any external dopant.Among all conductive polymers, poly(3, 4-ethylenedioxythiophene) (PEDOT, a derivate of polythiophene) and polyPyrrole (PPy) have gained some large scale applications for their chemical and physical proprieties. The aim of the present work was the synthesis of PEDOT and PPy in aqueous solution and the study of their growth mechanism by pulsed radiolysis. Thanks to the electron accelerator ELYSE, the use of pulsed radiolysis coupled with time-resolved absorption spectroscopy allowed to study the kinetics of polymerization. The first transient species involved in the mechanism were identified by time resolved spectroscopy and the rate constants were determined.First, the reaction of hydroxyl radicals onto EDOT and Py monomers was studied, as well as the corresponding radiation induced polymerization. Then, the study was transposed to others oxidizing radicals such as CO3.-, N3. and SO4.- at different pHs. This approach allowed to check and to highlight the influence of oxidizing species onto the first transient species produced by monomers oxidation (radical cation, adduct or neutral radical) and onto the resulting morphology and properties of the radiosynthesized polymers. Finally, the electron beam was originally used as a simple electron irradiator in order to in situ synthesize PEDOT and PPy
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Puts, Regina [Verfasser]. "Physico-Biological Mechanisms of Focused Low-Intensity Pulsed Ultrasound in Musculoskeletal Regeneration / Regina Puts." Berlin : Freie Universität Berlin, 2017. http://d-nb.info/112917445X/34.
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Phillips, Monifa Louise. "Spectroscopic investigation of resistive switching mechanisms in pulsed laser deposited metal-oxide thin films." Thesis, University of Glasgow, 2018. http://theses.gla.ac.uk/38989/.
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Today, CMOS-compatible Flash memory technology dominates the non-volatile memory storage market due to high density and low fabrication costs. However, with CMOS approaching fundamental scaling limits, research into novel emerging non-volatile memory storage technologies that exploit materials properties including resistance, spin and polarisation, has significantly progressed. The ideal non-volatile memory technology would compete with Flash, offering high-density memory storage at low costs, however it would outperform Flash due to its faster operating speeds, lower energy requirements, greater endurance and greater potential for scaling. Of all the emerging technologies, resistive RAM (RRAM) elements, in which reproducible (switchable) and distinct high and low resistance states are the basis of memory storage, are considered most advantageous due to their superior potential for scaling, fastest exhibited operating speeds and extremely low energy requirements. Despite progress in the field of RRAM research, the underlying mechanisms that allow a device to switch between high and low resistance states remains unclear in many materials systems and is the key motivation behind this work. Here, Pulsed Laser Deposited (PLD) RRAM devices that incorporate resistive switching transition metal oxide thin films were studied using Electron Energy Loss Spectroscopy (EELS). Basic metal/oxide/metal RRAM heterostructures that incorporated strongly oxidising titanium electrodes and polycrystalline ZnO and manganese-doped ZnO were investigated in Chapter 3. These devices were designed for direct comparison to a device in presented the literature which displayed the simultaneous co-switching of resistance and magnetisation states. In the devices fabricated here, EELS analysis revealed Mn-phase segregation both at grain boundaries both above and below the top and bottom electrodes, which supported the proposed co-switching mechanism. In Chapter 4, epitaxial single crystal perovskite oxide Pr0.48Ca0.52MnO3 was incorporated into a novel metal/oxide/tunnel-oxide/metal RRAM structure, where the thickness of the interfacial Yttria-stabilised Zirconia tunnel oxide varied the output current density. In both the ZnO and Pr0.48Ca0.52MnO3 devices, EELS analysis revealed that the observed resistive switching was mediated by the field-induced exchange of oxygen vacancies between the bulk oxide and an interfacial oxide. Despite this similarity, the overall device resistance was governed by different effects: for the polycrystalline ZnO-based devices, this was the oxygen-vacancy induced formation and dissolution of a highly resistive TiO2 interfacial layer; in contrast, for the epitaxial Pr0.48Ca0.52MnO3 device, this was the oxygen-vacancy induced charge accumulation and dissipation in the tunnel oxide, which modulated the tunnel barrier height.
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Mandich, Nenad V. "Mechanisms of chromium deposition and dissolution under direct and pulse reverse plating conditions." Thesis, Aston University, 1996. http://publications.aston.ac.uk/15349/.
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Baths containing sulphuric acid as catalyst and others with selected secondary catalysts (methane sulphonic acid - MSA, SeO2, a KBrO3/KIO3 mixture, indium, uranium and commercial high speed catalysts (HEEF-25 and HEEF-405)) were studied. The secondary catalysts influenced CCE, brightness and cracking. Chromium deposition mechanisms were studied in Part II using potentiostatic and potentiodynamic electroanalytical techniques under stationary and hydrodynamic conditions. Sulphuric acid as a primary catalyst and MSA, HEEF-25, HEEF-405 and sulphosalycilic acid as co-catalysts were explored for different rotation, speeds and scan rates. Maximum current was resolved into diffusion and kinetically limited components, and a contribution towards understanding the electrochemical mechanism is proposed. Reaction kinetics were further studied for H2SO4, MSA and methane disulphonic acid catalysed systems and their influence on reaction mechanisms elaborated. Charge transfer coefficient and electrochemical reaction rate orders for the first stage of the electrodeposition process were determined. A contribution was made toward understanding of H2SO4 and MSA influence on the evolution rate of hydrogen. Anodic dissolution of chromium in the chromic acid solution was studied with a number of techniques. An electrochemical dissolution mechanism is proposed, based on the results of rotating gold ring disc experiments and scanning electron microscopy. Finally, significant increases in chromium electrodeposition rates under non-stationary conditions (PRC mode) were studied and a deposition mechanisms is elaborated based on experimental data and theoretical considerations.
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Rathbun, David. "Pulse modulation control for flexible systems under the influence of nonlinear friction /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/6097.
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Strutton, Paul Henry. "An investigation into mechanisms underlying the suppression of luteinizing hormone pulses in the female rat." Thesis, King's College London (University of London), 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265254.
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Noll, Scott Allen. "Residual stress fields due to laser-pulse-generated shock waves." The Ohio State University, 1999. http://rave.ohiolink.edu/etdc/view?acc_num=osu1407411599.
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Wang, Hai. "Enhancement mechanisms of hot electron effects in NMOS transistors during gate pulse transient time /." The Ohio State University, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487676261010004.
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VIDAL, JOSE T. "Desenvolvimento de um sistema opto-mecanico para micro usinagem com laser de fentossegundos." reponame:Repositório Institucional do IPEN, 2010. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9563.
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Richard, Marc J. P. "Modulation of the cardiac voltage-sensitive release mechanism by conditioning pulse voltage." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ49432.pdf.
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Hayakawa, N., Y. Sugimori, and H. Okubo. "Partial discharge current pulse waveform analysis (PD-CPWA) based on PD mechanisms in solid and gas media." IEEE, 2005. http://hdl.handle.net/2237/6827.
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Myers, Charles B. "Initiation mechanisms of low-loss swept-ramp obstacles for deflagration to detonation transition in pulse detonation combustors." Thesis, Monterey, California : Naval Postgraduate School, 2009. http://edocs.nps.edu/npspubs/scholarly/theses/2009/Dec/09Dec%5FMyers.pdf.
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Thesis (M.S. in Astronautical Engineering)--Naval Postgraduate School, December 2009.Thesis Advisor(s): Brophy, Christopher M. Second Reader: Hobson, Garth V. "December 2009." Description based on title screen as viewed on January 28, 2010. Author(s) subject terms: Pulse Detonation Combustors, PDC, Pulse Detonation Engines, PDE, PDE ignition, PDE initiation, low-loss obstacles, ramp, swept ramp, DDT, DDT initiation. Includes bibliographical references (p. 89-90). Also available in print.
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Balsamy, Kamaraj Abishek. "Study of Pulse Electrochemical Micromachining using Cryogenically Treated Tungsten Microtools." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1352484381.
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Zhu, Shuangye, and 朱霜叶. "Numerical investigations into root vertical pull-out behavior." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/197554.
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Plant roots provide important soil reinforcement and improve the stability of slopes. From an engineering view, roots mechanically increase soil shear strength by transforming shear stress from soil into tensile forces of roots themselves via interface friction thus acting like soil nails. However, due to the complex spatial geometries and mechanical heterogeneities of natural root systems, more specific considerations are needed when analyzing the root reinforcement issues.
According to a literature review, most studies on slope stability consider root reinforcement as an apparent cohesion by upscaling the behaviour of static individual roots. However, recent studies have shown that better predictions can be made if the progressive failure of roots is considered, thus highlighting the importance of load-displacement relations of soil-root interaction. Therefore, numerical pull-out tests considering the progressive friction interface relationship were carried out in this study to investigate the mechanism and the influences of various factors on plant root pull-out behaviour, which is of great importance to evaluating the stabilization effect of roots.
In this study, the classic Coulomb friction model was adopted to simulate the interaction along the root-soil interface with the surface to surface modelling technique available in ABAQUS. The numerical investigations could be mainly divided into three parts: study of single straight root pull-out behaviour, study of the branched root segments with only first-order lateral branches (herringbone system), and study of the root segments with second-order branches (dichotomous system).
Conclusions regarding the mechanism of the root pull-out process, the influence of geometry-related factors and the influence of the intrinsic factors related to mechanical properties and root-soil interaction were drawn based on the observations of the numerical pull-out tests. Progressive stick-to-slip behaviours along the root-soil interface were observed in the numerical models. Generally, the pullout resistance of roots increased with the branch depth and branch length. It was also observed that the pullout resistance had strong regression with the weight of the soil potentially lifted by the root system. The most efficient branch angle for providing pull-out resistance for the herringbone system was between 60 and 90 degrees and the most efficient branch angle for the dichotomous root system was shown to be around 45. The central symmetrical branch arrangement pattern was observed to be the most efficient in providing pull-out resistance compared with the plate symmetrical and asymmetrical patterns.published_or_final_version
Civil Engineering
Master
Master of Philosophy
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Reiners, Peter W., Huiping Zhang, Michael E. Oskin, Jing Liu-Zeng, Peizhen Zhang, and Ping Xiao. "Pulsed exhumation of interior eastern Tibet: Implications for relief generation mechanisms and the origin of high-elevation planation surfaces." ELSEVIER SCIENCE BV, 2016. http://hdl.handle.net/10150/621300.
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River incision into a widespread, upland low-relief landscape, and related patterns of exhumation recorded by low-temperature thermochronology, together underpin geodynamic interpretations for crustal thickening and uplift of the eastern Tibetan Plateau. We report results from a suite of 11 (U-Th-Sm)/He cooling-age samples. Eight samples comprise a 1.2 km relief section collected from elevations up to 4800 m in the Jiulong Shan, an elevated, rugged region located in the hinterland of the Yalong-Longmen Shan Thrust Belt, and surrounded on three sides by upland low-relief landscape surfaces. Zircon and apatite cooling ages record two episodes of rapid exhumation in the early Oligocene and late Miocene, that were separated by a period of stability from similar to 30 to 15 Ma. The first episode is consistent with a similar pulse evident from the Longmen Shan. The second episode is ongoing, and when integrated with adjacent cooling-age data sets, shows that doming of the Jiulong Shan has resulted in 2 to 4 km of differential exhumation of the plateau interior. We show from a compilation of glacial landform-mapping that the elevation of the plateau surface closely tracks global last glacial maximum equilibrium line altitude. We hypothesize that smoothing of highlands by efficient glacial and periglacial erosion, coupled with potential river captures and conveyance of sediments via external drainage, can yield an apparently continuous low-relief plateau landscape formed diachronously at high elevation. (C) 2016 Elsevier B.V. All rights reserved.
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Jeong, Hae-won. "Study of the heat transfer mechanism from a submerged pulse combustor to a fluidized bed." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/12458.
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Abdallah, Sadoon Mushrif. "Bonding mechanisms and strength of hooked-end steel fibre reinforced cementitious composites." Thesis, Brunel University, 2017. http://bura.brunel.ac.uk/handle/2438/15827.
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Concrete is a strong material as to its compressive strength. However, it is a material with a low tensile and shear strength, and brittleness at failure. Concrete has to be reinforced with appropriate materials. Steel fibre is one of the most common materials currently being used to develop reinforced concrete, which may replace partially or completely conventional steel reinforcement. Successful reinforcement of concrete composite is closely related to the bond characteristics between the reinforcing fibre and matrix. The effective utilisation of steel fibre reinforced concrete (SFRC) requires in-depth and detailed understanding of bonding mechanisms governing the tensile behaviour. In response to this demand, this study embraced two main areas: understanding the reinforcing mechanisms of fibres in SFRC and material's post-cracking behaviour. Comprehensive experimental and theoretical programmes have therefore been developed: the experimental work is subdivided into three parts. The first part was to investigate the effect of various physical parameters, such as fibre characteristics (i.e. geometry, inclination angle, embedded length, diameter and tensile strength) and matrix strength which controls the pull-out behaviour of steel fibres. The second part is concerned with the assessment of the bond mechanisms of straight and hooked end fibres after exposure to elevated temperatures and varying matrix strength. The third part is devoted to gain further insight on the bond mechanisms governing the post-cracking behaviour through uniaxial and bending tests. It was found that the varying hook geometry and matrix strength each had a major influence on the pull-out response of hooked end fibres. As the number of the hook's bends increased, the mechanical anchorage provided by fibre resulted in significant improvement of mechanical properties of SFRC. The reduction in bond strength at elevated temperatures is found to be strongly related to the degradation in properties of the constituent materials, i.e. the fibre and concrete. The most effective combination of matrix strength and fibre geometry was found to be as follows: 3DH (single bend) fibre with normal-medium strength matrix, 4DH (double bend) fibre with high strength matrix and 5DH (triple bend) fibre with ultra-high performance matrix. Two analytical models to predict the pull-out behaviour of hooked end fibres were developed. Both models were able to predict the pull-out response of SFRC made from a variety of fibre and matrix characteristics at ambient temperature. This work has established a comprehensive database to illustrate the bonding mechanisms of SFRC and anchorage strengthening of various hooked end fibres, and this should contribute towards an increasing interest and growing number of structural applications of SFRC in construction.
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Rachimov, Rustam Ch, and Peter John. "Mechanismus zur Erzeugung von Infrarotimpulsen mit funktionellen Keramiken." Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2014. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-135637.
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Es wird aufgezeigt, wie mit funktionellen Keramiken hochenergetische elektromagnetische Impulse bis zu 320 W/cm² und kurze Zeiten, beispielsweise innerhalb von 10 Mikrosekunden, erzeugt und nachgewiesen werden können.
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Ichino, Yusuke, Kimihiko Sudoh, Koji Miyachi, Yutaka Yoshida, Yoshiaki Takai, 祐亮 一野, and 隆. 吉田. "Orientation mechanism of REBa/sub 2/Cu/sub 3/O/sub y/ (RE = Nd, Sm, Gd, Y, Yb) thin films prepared by pulsed laser deposition." IEEE, 2003. http://hdl.handle.net/2237/6741.
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Cates, Philippa Susan. "Elucidating the neural mechanisms underlying stress-induced suppression of the gonadotrophin releasing hormone pulse generator in the female rat." Thesis, King's College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392328.
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Donovan, Molly Hope. "Unsteady Effects of a Pulsed Blowing System on an Endwall Vortex." Wright State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=wright1559398697459176.
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DiFrancia, Célene. "The single fiber pull-out test : a study of fiber/matrix interactions /." This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-07282008-134341/.
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Sudoh, K., Y. Ichino, Y. Yoshida, Y. Takai, I. Hirabayashi, 祐亮 一野, and 隆. 吉田. "Magnetic field dependence of critical current density in Sm/sub 1+x/Ba/sub 2-x/Cu/sub 3/O/sub 6+/spl delta// films prepared by pulsed laser deposition." IEEE, 2003. http://hdl.handle.net/2237/6742.
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Vion, Jérémy. "Study of the Mechanisms Underlying Neurostimulation Induced by Low- Energy Pulsed Ultrasound : Towards Approaches for the Management of Cancer-Related Chronic Pain." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1045.
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Les applications thérapeutiques de la neurostimulation ultrasonore représentent un terrain de recherche très prometteur, auquel il fait défaut un modèle valide décrivant les biomécanismes sous-jacents. Le premier objectif de ce travail de thèse était de proposer un modèle nerveux propice à une étude mécanistique du phénomène de neurostimulation ultrasonore. L’objectif suivant était de prouver l’intérêt d’exploiter ce modèle pour recueillir des informations concernant les interactions biophysiques ayant lieu entre les ultrasons (US) focalisés et le système nerveux. La majorité des études réalisées a porté sur le système nerveux du ver de terre commun, Lumbricus terrestris. Elles ont consisté d’une part à comparer entre elles les caractéristiques temporelles des réponses nerveuses associées à différentes modalités de stimulation, et d’autre part à évaluer l’influence de chacun des paramètres acoustiques du stimulus ultrasonore sur le taux de succès de neurostimulation (NSR). Dans les deux cas, la méthodologie suivie reposait sur l’administration de différents stimuli aléatoirement alternés. Complémentairement, le rôle joué par la cavitation acoustique a été étudié. La faisabilité de la stimulation du système nerveux du ver de terre, au moyen d’US et dans des conditions in vivo, a été prouvée. Les aires sensorielles et la dynamique de réponses associées aux trois modalités de stimulation ont été caractérisées. Il a été conclu que, dans ce modèle nerveux invertébré, pendant le phénomène de neurostimulation ultrasonore, les structures nerveuses interagissant fonctionnellement avec les US sont les nerfs afférents segmentaux. Les résultats des études paramétriques ont indiqué que le NSR augmente avec l’intensité acoustique, la durée de pulse et la fréquence de répétition des pulses. Il a été proposé que la structure nerveuse visée est sensible à la « force de radiation moyenne » transportée par le stimulus US, indépendamment des paramètres menant à cette valeurUltrasound neurostimulation applied to therapy is a promising field of research but still lacks of a validated model explaining the biomechanisms underlying the phenomenon. The first objective of this PhD thesis was to propose a nervous model suited for a mechanistic study of the phenomenon of ultrasound neurostimulation. In a second time, it was intended to practically prove the interest of this model by using it to gain knowledge regarding the biophysical interactions between focused ultrasound and the nervous system. Studies were performed on the nervous system of the anesthetized earthworm, Lumbricus terrestris. They consisted in either comparing the timings of the nervous responses associated with different modalities of stimulation, or evaluating the influence of each acoustic parameter on the neurostimulation success rate (NSR). In both cases, the methodology followed was to administer randomly mixed sequences of different stimuli. The feasibility of the in vivo activation of the anesthetized earthworm’s nervous system was proven. The sensory fields and response dynamics associated with the three modalities of stimulation were characterized. The parametric studies indicated that the NSR increases with pulse amplitude, pulse duration, pulse repetition frequency, but is more weakly influenced by the harmonic content and number of pulses. By applying a causal approach to interpret the results, we concluded that, in this nervous model, during the phenomenon of ultrasound neurostimulation, the structures functionally responding to the ultrasound stimulus are the segmental afferent nerves. We hypothesize that the main interaction with the axonal regions is mediated by ultrasound radiation force, without excluding the involvement of other biomechanisms
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Sörensen, Nicolai. "Kinetics and Mechanism of Cu-Catalyzed Atom Transfer Radical Polymerization." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2015. http://hdl.handle.net/11858/00-1735-0000-0023-9662-7.
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Wickersham, Paul Brian. "Jet Mixing Enhancement by High Amplitude Pulse Fluidic Actuation." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19718.
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Turbulent mixing enhancement has received a great deal of attention in the fluid mechanics community in the last few decades. Generally speaking, mixing enhancement involves the increased dispersion of the fluid that makes up a flow. The current work focuses on mixing enhancement of an axisymmetric jet via high amplitude fluidic pulses applied at the nozzle exit with high aspect ratio actuator nozzles. The work consists of small scale clean jet experiments, small scale micro-turbine engine experiments, and full scale laboratory simulated core exhaust experiments using actuators designed to fit within the engine nacelle of a full scale aircraft.
The small scale clean jet experiments show that mixing enhancement compared to the unforced case is likely due to a combination of mechanisms. The first mechanism is the growth of shear layer instabilities, similar to that which occurs with an acoustically excited jet except that, in this case, the forcing is highly nonlinear. The result of the instability is a frequency bucket with an optimal forcing frequency. The second mechanism is the generation of counter rotating vortex pairs similar to those generated by mechanical tabs. The penetration depth determines the extent to which this mechanism acts. The importance of this mechanism is therefore a function of the pulsing amplitude. The key mixing parameters were found to be the actuator to jet momentum ratio (amplitude) and the pulsing frequency, where the optimal frequency depends on the amplitude. The importance of phase, offset, duty cycle, and geometric configuration were also explored.
The experiments on the jet engine and full scale simulated core nozzle demonstrated that pulse fluidic mixing enhancement was effective on realistic flows. The same parameters that were important for the cleaner small scale experiments were found to be important for the more realistic cases as well. This suggests that the same mixing mechanisms are at work. Additional work was done to optimize, in real time, mixing on the small jet engine using an evolution strategy.
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Zhou, Y. "The production and properties of TCO coatings prepared by pulsed magnetron sputtering from powder targets." Thesis, University of Salford, 2005. http://usir.salford.ac.uk/2167/.
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Mith their unique transparent and conductive properties, TCO (transparent conductive oxide) coatings are becoming increasingly studied These commercially important coatings have a promising future due to their various applications as components in optoelectronic devices, photovoltaic solar cells, flat panel displays, electroluminescent devices, etc. Their high transmittance and low resistivity are generally achieved through the use of specific dopant materials, whilst adjustments are made to the deposition processes to improve the structure of the coatings. TCO coatings are commonly deposited by the magnetron sputtering process. Sputtering normally takes place from a solid plate, known as the target, of the material to be deposited. Clearly, each solid target can only be of a single composition. Thus, to change the compositions ofthe coatings, the whole target has to be replaced Furthermore, alloy, or doped targets can be very expensive and the choice ofavailable compositions is likely to be limited. In this project, instead of using solid targets, metal or ceramic powder blends were used as the targets. The powder blends were spread across the surface of a magnetron and lightly tamped down to produce a smooth surface. The benefits of this approach are that any material that is available in powderform can be considered as a target material and alloy or multi-component compositions can be readily blended The basic aim of this project, therefore, was to produce novel TCO coatings by magnetron sputteringfrom powder targets. The coatings were deposited in a specially designed rig with a number of important features, including a pulsed DC power supply and a closed magnetic field. The project concentrated on the production of commercially useful zinc oxide-based TCO coatings. Coatings were produced with different dopant materials and concentrations, and their optical and electrical properties were measured. After the coatings were annealed at 500 *Cfor 2 hours in vacuo, aluminum and gallium doped zinc oxide coatings showed their low resistivity, which were no larger than 5.19xI0-3S2cm, and the lowest resistivity was obtained from 3at% A 1-doped ZnO coating; 1.95 xI 00cm. The average transmittance in the visible range of the ZnO coatings was 90%. From this, optimal compositions were identified For comparison purposes, coatings were also produced of the TCO material most commonly used at present; namely ITO (Indium tin oxide). The results showed that ITO coatings generally had lower resistivity and visible transmittance, (4-6xlO-492cm and 80-8216), than doped ZnO coatings. Also, the electrical and optical properties of ITO coatings were very sensitive to the content of oxygen in the deposition atmosphere. Finally, theflexibility offered by this approach was exploited through the use of multi-component target compositions to produce TCO coatings with tailored optical and electrical properties.
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Ghasemi, Esfahani Ata. "Physics and Control of Flow Over a Thin Airfoil using Nanosecond Pulse DBD Actuators." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1503204430451055.
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DiFrancia, Célene. "The single fiber pull-out test: a study of fiber/matrix interactions." Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/38866.
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Quessab, Yassine. "Mechanism and size effects of helicity-dependent all-optical magnetization switching in ferromagnetic thin films." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0116/document.
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Pour des applications technologiques d’enregistrement magnétique de l’information à haute densité et vitesse d’écriture et de lecture ultra-rapide, les chercheurs se sont penchés vers des méthodes de manipulation de l’aimantation sans application de champ magnétique externe. Il a été découvert qu’il était possible de renverser de manière déterministe l’aimantation de plusieurs matériaux ferri- et ferro-magnétiques à l’aide uniquement d’impulsions laser ultracourtes polarisées circulairement. Ce retournement tout-optique s’est avéré être un processus cumulatif nécessitant plusieurs impulsions ultracourtes dans les matériaux ferromagnétiques. Notamment dans les multicouches (Co/Pt), le retournement tout-optique se fait en deux étapes : une désaimantation indépendamment de l’hélicité suivie d’une ré-aimantation dans une direction ou l’autre selon l’hélicité. Pour autant, le mécanisme à l’origine du rétablissement de l’ordre magnétique n’a pas été étudié jusqu’à présent. Dans cette thèse, nous avons étudié le mécanisme de renversement de l’aimantation dans les couches ferromagnétiques résultant de l’excitation par impulsions laser ultracourtes polarisées circulairement. Pour cela, nous étions intéressé par la réponse d’une paroi de domaine dans les couches minces de Pt/Co/Pt à la suite d’une excitation laser et en fonction de la polarisation de la lumière. Nous avons démontré la possibilité d’induire un déplacement tout-optique et déterministe d’une paroi de domaine. Nous montrons que la propagation de la paroi résulte de la compétition entre trois contributions : le gradient de température dû aux effets de chauffage par le laser, l’effet de l’hélicité de la lumière et les effets de piégeages de la paroi. Par ailleurs, par mesures expérimentales du dichroïsme circulaire, nous excluons un mécanisme purement thermique du déplacement de paroi. Ainsi nous confirmons que le retournement tout-optique des couches ferromagnétiques se fait par une nucléation suivie d’une ré-aimantation par propagation déterministe des parois de domaines selon l’hélicité. De plus, nous avons exploré la possibilité d’utiliser le retournement tout-optique dans des dispositifs spintroniques pour l’enregistrement de l’information à haute densité. Pour se faire, il est nécessaire d’étudier les effets de tailles du retournement lorsque le matériau est structuré en îlots à l’échelle du micro- ou nanomètre. Nous avons montré qu’un plus grand nombre d’impulsions laser est nécessaire afin de renverser l’aimantation de micro-disques comparés à la couche continue ferromagnétique. Il en résulte que le champ dipolaire aide le renversement de l’aimantation dans les couches continues rendant ainsi le retournement tout-optique énergétiquement plus favorableOver the past decade, the demand for an even higher capacity to store data has been gradually increasing. To achieve ultrafast and ultrahigh density magnetic data storage, low-power methods to manipulate the magnetization without applying an external magnetic field has attracted growing attention. The possibility to deterministically reverse the magnetization with only circularly polarized light was evidenced in multiple ferri- and ferro-magnetic materials. This phenomenon was called helicity-dependent all-optical switching (HD-AOS). In ferromagnets, it was demonstrated that HD-AOS was a cumulative and multishot process with a helicity-independent demagnetization followed by a helicity-dependent magnetization recovery. Yet, the microscopic mechanism of this helicity-dependent remagnetization remained highly debated. In this thesis, we investigated the magnetization reversal mechanism of all-optical switching in ferromagnetic materials. To explore a potential switching process through domain nucleation and domain wall (DW) propagation, we studied the response of a DW upon femto- or pico-second laser irradiation in Co/Pt thin films that exhibit HD-AOS. We reported helicity-dependent all-optical domain wall motion. We demonstrated that it results from the balance of three contributions: the temperature gradient due to the laser heating, the helicity effect and the pinning effects. By measuring the magnetic circular dichroism, a purely thermal mechanism of the laser-induced DW motion appears to be excluded. Furthermore, we examined the size effects in AOS in Co/Pt films patterned into microdots with a diameter between 10 and 3 μm. This allowed us to explore the role of the dipolar field in the switching mechanism. We discovered that a larger number of laser pulses was required to reverse the magnetization of a microdot compared to the continuous film. This indicated that the dipolar field actually eases the magnetization reversal in the full film. Thus, AOS is less energy-efficient in patterned films, hence making Pt/Co/Pt multilayers not an ideal candidate for integrating AOS in spintronic devices
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Bleu, Yannick. "Graphene and doped graphene elaborated by pulsed laser deposition." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSES033.
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Le graphène est, par définition, un matériau bidimensionnel, cristallin, constitué d’un réseau d’atomes de carbone en nid d’abeilles répartis sur une monocouche atomique. Le graphène a suscité un grand intérêt dans les communautés scientifiques au cours des 15 dernières années, en raison de propriétés remarquables, en particulier la conductivité électrique, la transparence optique, la résistance et la conductivité thermique, avec de nombreuses applications technologiques potentielles, comme les électrodes transparentes, l’émission de champs, les biocapteurs, les futures générations de batteries, les matériaux composites, etc. L’un des plus grands défis avec le graphène, demeure le contrôle et la reproductibilité de la synthèse sur de grandes surfaces, ainsi que l'étude analytique, à l’échelle nanométrique, de films si particuliers à une échelle très réduite, films constitués de l’élément carbone formant une ou plusieurs couches déposées sur des substrats adéquats en fonction des applications visées. Dans cette thèse, nous avons proposé une méthode de synthèse alternative basée sur un procédé physique (et non chimique), combinant le dépôt par laser pulsé (PLD) avec un recuit thermique rapide (Rapid Thermal Annealing). Cette approche particulière permet en particulier le dopage des couches de graphène par des atomes choisis, de manière contrôlée et reproductible. Nos travaux ont contribué à élargir les champs d'études de la PLD dans le domaine de la synthèse des couches minces. Aussi, Ils contribuent à une avancée des connaissances fondamentales sur la synthèse du graphène et du graphène dopé au bore, au cœur des efforts actuels de la recherche pour intégrer ces matériaux dans des applications technologiques exigeants des performances toujours plus élevéesGraphene is, by definition, a one-atom-thick pure carbon crystal with a honeycomb-like structure. Graphene has become of great interest in both scientific and engineering communities from the past 15 years, owing to its range of unique properties including high conductivity, transparency, strength, and thermal conductivity, with many potential applications in research and industry, as transparent electrodes, field emitters, biosensors, batteries, composites, and so on. One of the greatest challenges with graphene remains the control and reproducibility of the synthesis on large surfaces, as well as the analytical study, at the nanometric scale. In this thesis, we have proposed an alternative synthesis method based on a physical (and not chemical) process, combining pulsed laser deposition (PLD) with rapid thermal annealing (Rapid Thermal Annealing). This particular approach allows in particular the doping of the graphene layers with selected atoms, in a controlled and reproducible manner. Our work has contributed to broadening the fields of study of PLD in the field of thin-film synthesis. It also contribute to an advance in fundamental knowledge on the synthesis of graphene and boron-doped graphene, at the heart of current research efforts to integrate these materials into technological applications requiring ever-higher performance
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Barth, Katja [Verfasser], Thomas F. [Gutachter] Prisner, Benesh [Gutachter] Joseph, Clemens [Gutachter] Glaubitz, and Inga [Gutachter] Hänelt. "Transport mechanism of a multidrug resistance protein investigated by pulsed EPR spectroscopy / Katja Barth ; Gutachter: Thomas F. Prisner, Benesh Joseph, Clemens Glaubitz, Inga Hänelt." Frankfurt am Main : Universitätsbibliothek Johann Christian Senckenberg, 2019. http://d-nb.info/1201131502/34.
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Atmaoui, Nassima. "Development of pull apart basins and associated structures by the Riedel shear mechanism insight from scaled clay analogue models /." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980651336.
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