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The development of an indium gallium arsenide junction field effect transistor for use in optical receiversWake, D. January 1987 (has links)
The objective of this work was to design and develop a high performance field effect transistor to be suitable for monolithic integration with a photodetector for use in long wavelength optical communication systems. It was decided that the most promising type of device for this application was a junction field effect transistor (JFET), fabricated using the alloy In.53Ga.47As grown epitaxially onto an InP substrate. The requirements for such a device were that it should have high transconductance, low input capacitance, and low gate leakage current (for high receiver sensitivity), and that it should have a structure which would be easily integrated monolithically with the desired type of photodetector - an In.53Ga.47As PIN-photodiode. Although this alloy semiconductor has favourable electron transport properties, at the start of this work, high performance field effect transistors had not been realised in this material. In particular, the In.53Ga.47AS FETs that had been made at that time were characterised by low transconductance. Using a device design that incorporated many novel and efficacious features, the JFET described in this work gave results which greatly surpassed all previous (and current) published results of similar devices. This device not only showed high performance, but the novel design features also enabled a simple fabrication scheme. Having developed this very high performance discrete device, the feasibility of monolithic integration with a In.53Ga.47As PIN-photodiode was demonstrated. Although the physical size and material requirements of these two devices were very different, novel design features enabled the construction of a monolithic PIN-FET combination, in which the performance of the JFET was not compromised.
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Fundamental Measurements in Standing-Wave and Traveling-Wave ThermoacousticsPetculescu, Gabriela 02 August 2002 (has links)
No description available.
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Evaluation and calibration of the CroBas-PipeQual model for Jack Pine (Pinus banksiana Lamb.) using Bayesian melding : hybridization of a process-based forest growth model with empirical yield curvesEwen, Stephanie 19 April 2018 (has links)
CroBas-PipeQual a été élaboré pour étudier les effets de croissance des arbres sur la qualité du bois. Ainsi, il s’agit d’un modèle d’intérêt pour maximiser la valeur des produits extraits des forêts. Nous avons évalué qualitativement une version de CroBas-PipeQual calibrée pour le pin gris (Pinus banksiana Lamb.) de façon à vérifier l’intérêt de l’utiliser comme outil de planification forestière. Par la suite, nous avons fait une analyse de sensibilité et une calibration bayesienne à partir d’une table de production utilisée au Québec. Les principales conclusions sont: 1. Les prédictions de hauteur sont les plus sensibles aux intrants et aux paramètres liés à la photosynthèse; 2. La performance de CroBas est améliorée en tenant compte de la relation observée entre deux paramètres utilisés pour estimer la productivité nette et l'indice de qualité de station; et 3. CroBas requiert d’autres améliorations avant de pouvoir être utilisé comme outil de planification. / CroBas-PipeQual is a process-based forest growth model designed to study foliage development and how growth processes relate to changes in wood quality. As such, CroBas-PipeQual is of interest as a component model in a forest level decision support model for value assessment. In this thesis, the version of CroBas-PipeQual calibrated for jack pine (Pinus banksiana Lamb.) in Québec, Canada was qualitatively evaluated for use in forest management decision-making. Then, sensitivity analyses and Bayesian melding were used to create and calibrate a stand-level version of CroBas-PipeQual to local empirical height yield models in a hybrid-modelling approach. Key findings included: 1. Height predictions were most sensitive to input values and to parameters related to net photosynthesis; 2. Model performance was improved by varying two net-productivity parameters with site quality; and 3. Model performance needs further improvement before CroBas-PipeQual can be used as a component of a forest-management decision tool.
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Caractérisation fonctionnelle d'une carboxylestérase impliquée dans la libération d'une phéromone d'agrégation de Dendroctonus ponderosaeBernier, Kathia 28 September 2023 (has links)
Titre de l'écran-titre (visionné le 25 septembre 2023) / Dendroctonus ponderosae, appelé le dendroctone du pin ponderosa (DPP), est l'un des insectes ravageurs les plus destructeurs de l'ouest de l'Amérique du Nord. Les champignons qu'il transporte causent de la mortalité chez plusieurs espèces du genre Pinus. L'infestation d'un pin commence par la libération d'une phéromone d'agrégation, le trans-verbénol, par un DPP femelle adulte, initiant ainsi une attaque de masse. En grand nombre, le DPP réussit à surmonter les défenses du pin incluant la production d'oléorésine contenant des composés toxiques comme l'α-pinène. La phéromone est initialement produite par l'insecte au stade larvaire par hydroxylation de l'α-pinène dans un processus de détoxification. Le trans-verbénol ainsi produit est ensuite lié à un acide gras afin d'être entreposé sous forme d'esters. Quand l'adulte colonise un nouveau pin, une carboxylestérase prédite causerait la libération de la phéromone séquestrée. L'hypothèse émise est que cette réaction est catalysée par l'estérase du clone DPO062_I20 du DPP. La production recombinante de l'enzyme a été faite dans Escherichia coli, mais celle-ci formait des corps d'inclusion. Les corps d'inclusion ont été solubilisés et la protéine solubilisée a été repliée, mais aucune activité enzymatique n'a été mesurée lors des essais préliminaires avec les esters de trans-verbénol identifiés dans le DPP. Une analyse des homologues de l'estérase a révélé qu'un organisme eucaryote pourrait être mieux adapté pour l'expression d'une enzyme active. L'estérase a donc été produite dans la levure Pichia pastoris dans laquelle elle a été retrouvée sous forme glycosylée. Cependant, aucune activité enzymatique n'a été mesurée dans les conditions testées. Différentes conditions d'expression et d'essais enzymatiques devront être étudiées afin d'obtenir une conclusion fiable quant à la caractérisation enzymatique de l'estérase. Finalement, un arbre phylogénétique des carboxylestérases du DPP a révélé que la carboxylestérase d'intérêt pourrait être spécifique à l'ordre Coleoptera ou à la sous-famille Scolytinae. / Dendroctonus ponderosae, known as the mountain pine beetle (MPB), is one of the most destructive insect pests in western North America. The fungi carried by MPB cause mortality in several Pinus species. Pine colonization is started by an adult female MPB releasing an aggregation pheromone called trans-verbenol, thus initiating a mass attack. In large numbers, MPB can overcome the host's defenses, which includes the production of oleoresin which contains toxic molecules such as α-pinene. The pheromone is initially produced at the larval stage through hydroxylation of α-pinene as a detoxification process. The resulting trans-verbenol is then conjugated with a fatty acid in order to be stored in the form of esters. When an adult MPB colonizes a new host, a predicted carboxylesterase causes the release of the sequestered pheromone. It is hypothesized that the esterase from the MPB clone DPO062_I20 catalyzes this reaction. The enzyme was recombinantly produced in Escherichia coli but formed inclusion bodies. These inclusion bodies were solubilized and the proteins were refolded, but no enzyme activity was detected in preliminary assays using trans-verbenol esters identified in MPB. Analysis of the esterase's homologs suggested that a eukaryotic organism could be more suitable for the expression of an active enzyme. The esterase was thus produced in the yeast Pichia pastoris, in which it was found to be glycosylated. However, no enzyme activity was measured under the tested conditions. Further exploration of different expression and assay conditions will be necessary to obtain a reliable conclusion regarding the enzymatic characterization of the carboxylesterase. Lastly, a phylogenetic tree of MPB carboxylesterases revealed that the carboxylesterase of interest may be specific to the Coleoptera order or to the Scolytinae subfamily (bark beetles).
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Assessing the Effectiveness of a Fingerprint Biometric and a Biometric Personal Identification Number (BIO-PIN™) when used as a Multi-Factor Authentication MechanismBatie, Robert B. 01 January 2016 (has links)
The issue of traditional user authentication methods, such as username/passwords, when accessing information systems, the Internet, and Web-based applications still pose significant vulnerabilities. The problem of user authentication including physical and logical access appears to have limited, if any, coverage in research from the perspective of biometric as ‘something the user knows.’ Previous methods of establishing ones’ identity by using a password, or presenting a token or identification (ID) card are vulnerable to circumvention by misplacement or unauthorized sharing. The need for reliable user authentication techniques has increased in the wake of heightened concerns about information security and rapid advancements in networking, communication, and mobility. The main goal of this research study was to examine the role of the authentication method (BIO-PIN™ or username/password) and time, on the effectiveness of authentication, as well as the users’ ability to remember the BIO-PIN™ versus username/password (UN/PW). Moreover, this study compared the BIO-PIN™ with a traditional multi-factor biometric authentication using multiple fingerprints (without sequence) and a numerical PIN sequence (noted as "BIO+PIN"). Additionally, this research study examined the authentication methods when controlled for age, gender, user’s computer experience, and number of accounts. This study used a quasi-experimental multiple baseline design method to evaluate the effectiveness of the BIO-PIN™ authentication method. The independent, dependent, and control variables were addressed using descriptive statistics and Multivariate Analysis of Variance (MANOVA) statistical analysis to compare the BIO-PIN™, the BIO+PIN, and UN/PW authentication methods for research questions (RQs) 1 and 2. Additionally, the Multivariate Analysis of Covariance (MANCOVA) was used to address RQ 3 and RQ4, which seeks to test any differences when controlled by age, gender, user experience, and number of accounts. This research study was conducted over a 10-week period with participant engagement occurring over time including a registration week and in intervals of 2 weeks, 3 weeks, and 5 weeks. This study advances the current research in multi-factor biometric authentication and increases the body of knowledge regarding users’ ability to remember industry standard UN/PWs, the BIO-PIN™ sequence, and traditional BIO+PIN.
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Imaginando a mulher: Pin-up, da chérette à playmate / Imagining the female: pin-up, of the chérette to playmateSaggese, Antonio José 23 September 2008 (has links)
Análise da produção da imagem da mulher enquanto mercadoria na era moderna. O imaginário erótico na sociedade de consumo, na mídia gráfica do Século XIX ao Século XX. A imagem técnica e suas relações com a pintura acadêmica na representação da figura feminina e do nu, pela fotografia, cinema, ilustração e cartum. A pin-up sua origem e suas variações. / Analysis of the production of the female image as a commodity in modern age. The erotic imagery in the consumer society, in the graphic media from XIX to XX century. The technical image and its relation with the academic painting in the representation of the womens figure and the nude in the photography, cinema, illustration and cartoon. The pin-up, its origins and variations.
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Transfer Layer Formation And Friction In Extrusion Of Aluminum : An Experimental Study Using A High Temperature Vacuum Based Pin-On-Disc MachineRanganatha, S 04 1900 (has links)
Hot extrusion of aluminum is widely practiced in industries for economic production of structural components. The surface finish and tolerance of the extruded components, both from design and aesthetic requirement, are important parameters. Hot extrusion involves forcing of aluminum in the form of a billet at a predetermined temperature through a shaped opening called die. Attempts, over time, are made to evolve the die profile to produce quality components. The main geometric feature of the die enables it in imparting plastic deformation and subsequent surface generation of the extrudate. The surface of extrudate is generated on the portion of the die called bearing channel or die land. Aluminum metal which moves relative to bearing channel experiences a different state-of-stress as it passes through the bearing channel. At the entry side of the bearing channel, the stress is compressive which is large in magnitude and this magnitude of compressive stress gets diminished as metal moves towards exit side and eventually becomes zero at the exit. Temperature gradients and its distribution along the bearing channel, similar to stress gradient, are reported. Literature reports formation of the transfer layer on the bearing channel. The transfer layer is of two distinctive types, the one near entry side which virtually leads to contact between aluminum and die steel and the other nearer to exit side which isolates aluminum from die steel. The understanding of the mechanism of formation of transfer layer is most important since it is instrumental in determining the surface finish of the extruded component.
All of the previous studies were conducted either in an actual extrusion press or using an instrumented extrusion press in the laboratory. The variables during these experiments could be the temperature of billet, extrusion ratio and speed of ram. Conducting these experiments using extrusion press is expensive and time consuming. To do experiments where the condition in a bearing channel can be simulated would be useful in conducting a more comprehensive study. To simulate the condition in the bearing channel a high temperature vacuum based pin-on-disc machine is designed and built. The fact that in a bearing channel there is virtually metal to metal contact with minimal or no chance of any intervening oxide layer, necessitated studies to be conducted under vacuum. A pin-on-disc test conducted under vacuum and high temperature would almost simulate condition on a bearing channel. Using this specially designed and built experimental setup the parameters influencing the transfer layer formation, temperature, sliding speed, load on the specimen, vacuum level and surface characteristics of the die are studied. Another feature of the test rig is that the configuration of pin and disc setup is vertical, which is different from regular pin on disc tribo-system, where pin and disc are held in horizontal configuration. The advantage of holding in vertical configuration is to eliminate the possibility of trapping the debris which alters the existing friction force and conditions.
The test rig is constructed using a cylindrical shell and a matching dome shell. The test rig, to facilitate the isolation of the instrumentations used to measure the forces and wear from the heat source is partitioned into two portions. The cylindrical bottom compartment called test chamber and dome shaped top compartment called sensor chambers are separated by a plate. On the plate in the sensor chamber, a load-cell to pickup friction force, a linear variable differential transformer (LVDT) to measure linear wear and loading lever mechanisms for imparting normal load and measuring friction force are fitted. The lever mechanism, in particular the one which magnifies the normal load is designed to conserve the space in the vacuum chamber. Housing the instrumentation inside the vacuum chamber thereby reducing the number of ports required to sense mechanical signals, increases the efficiency of the pumping system. The cylindrical shell of the testing chamber is a double walled structure and water cooled in order to prevent the exposer of sensors to higher testing temperature. Rubber ‘O’ rings are used, wherever it is required to seal the vacuum.
The necessary temperature required at the contact interface in the testing chamber is obtained by an electric resistance furnace, which is configured in such a way in the chamber that the heat generated is completely directed to the area where pin and disc are positioned. The interface temperature is monitored using a chromal-alumal thermocouple which is fixed very close to sliding interface on the pin holder. The power input to the furnace is controlled using PID (proportional integral derivative).
The required sliding speed is achieved with the help of direct current (DC) servomotor. The shaft on which the disc or ring is fixed is connected to a timer-pulley. The timer-pulley in turn is connected to servomotor through a timer-belt. The diameter ratio of the driving pulley and driven -timer-pulley is selected in such a way that the rpm of driven-pulley is reduced by four times and the torque increased by four times resulting in a more stable mechanical input to the sliding pair. The necessary high vacuum level in the test chamber is created by using rotary pump and diffusion pump combination.
Following tests are carried out.
1. Compression test: The strain rate response of aluminum (6060) under compressive state of loading is studied at strain rates 10-3s-1, 10-2s-1, 10-1s-1, 1s-1, 10s-1 and 102sand temperature ranging from 573 to 823K. The compression specimen is machined out of homogenized aluminum alloy (6060) cast ingots. True stress and true strain are estimated from load-displacement data of compression test. The true stress and true strain data are made use of in predicting the friction coefficient and sliding mode during sliding of aluminum relative to die steel at various temperature and other independent variables in vacuum.
2. The tensile test: A series of tensile tests at different temperatures and 10-1s-1 strain rate are conducted. The temperatures employed are from 423K to 723K. True stress, true strain, ultimate tensile strength and total percentage of elongation are estimated using load displacement data. The estimated ultimate tensile strength and total percentage of elongation are used for qualitatively explaining the morphology of transfer layer formed in the sliding experiments under different independent variables like temperature, speed, normal load, and surface texture of steel surface.
3. Adhesion test: The interaction at different temperature between the die steel (H11) and aluminum (6060) pair under static load is studied by conducting test in vacuum. The pin is made of homogenized aluminum and disc is made of die steel whose surface is generated by polishing on diamond paste until the average surface roughness (Sa) is of the order of 0.1 microns. The test temperatures are varied from 423 to 723K. The result is used in qualitatively explaining the morphology of transfer layer formed during sliding of aluminum and die steel pair in vacuum at various temperature, speeds and, normal load.
4. Sliding experiment: Steel pin and aluminum disc Pin on disc experiments are conducted at different temperatures in vacuum of the order of 4X10-4Pa. The experiments are conducted employing factorial design. The temperature, speed and load are the experimental parameters. The pin and disc are respectively made out of die steel and aluminum. Experiments are carried out with normal loads 20N, 40N, 63N, 80N, and 100N and speeds 0.1ms-1, 0.3ms-1, 0.5ms-1, 1.0ms-1, and 1.5ms-1 and with temperature over a range from 423 to 773K. The sliding distance covered is 500 meters. The friction force during sliding is monitored and used for estimating friction coefficient. Scanning electron microscopic study is carried out on surface, subsurface, wear track. The results, specifically, the friction coefficient and morphology of transfer layer are used to evaluate the influence of independent parameters on transfer mechanisms. The data generated from subsurface study and compression tests are used for estimating friction coefficient using Rigney’s plastic deformation model at 0.1ms-1.
5. Sliding experiment: aluminum pin and Steel disc The experiments reported in the previous paragraph where aluminum disc is slid against die steel pin had developed only the stresses of the order 16MPa. The estimated magnitude of stress level on bearing surface of extrusion die by various methods including numerical analysis is found to be more than 16MPa. In order to achieve a higher magnitude of stress and preserve the transfer layer mechanism, sliding an aluminum pin over the part of the textured surface of die steel ring is carried out. The changed boundary condition resulted in a nominal stress of 28 MPa which is comparatively more at 723K. The experiments are conducted employing factorial design. The other advantage of doing these experiments is that the effect of texture on the die surface can be studied by sliding aluminum pin over various surfaces. Thus temperature and surface texture are the experimental parameters for the present test. Different textured die steel surface is generated by machining process like, milling, electro discharge machining (EDM), wire electro discharge machining, silicon carbide slurry polishing, silicon carbide wheel grinding, CNC-milling and diamond paste polishing. Thus surfaces are basically of two types 1) with a lay on the surface and 2) a random surface. The tests are conducted at ambient temperature, 423, 573, 673, and 723K with a normal load of 56N and speed of 0.129ms-1. The morphology of transfer layer on the die steel ring is studied in scanning electron microscope. The friction coefficient is estimated from monitored friction force. The average surface roughness (Sa), results of compression test, and transfer layer are made use of to identify the sliding mode. The sliding of aluminum pin on diamond polished surface showed interesting results. Hence, another series of experiments using only diamond polished surface are conducted. The surface roughness of the steel surface achieved is 0.05 micro-meters. The load is 47N and speed is 0.043ms-1. The morphology of transfer layer and pin surface is studied using a Scanning Electron Microscope.
Results of compression and tensile test:
The flow stress is found to decrease with increase in compression test temperature. The SEM micrograph indicates large amount of fragmentation of harder phase with increase in strain rate at all temperature except for 423K. The fractured surface under tensile loading shows both intergranular and transgranular failure.
Results of adhesion test:
The area covered by the material transfer is found to increase with increase in temperature. The test can be used, to study the adhesive tendency between two pair of contacting surfaces. The area covered by the material transfer is found to be maximum at 723K.
Results of sliding of die-steel pin on aluminum disc in vacuum:
1. The ANOVA (analysis of variance) results indicate the existence of transition speed of about 0.5ms-1, more than which the friction coefficient was found constant. The extrusion speeds employed in industries are in the range of 0.1ms-1 to 1.7ms-1 and the transition speed found in the present study is within this range.
2. The magnitude of friction, with a few exceptions, is found to be independent of temperature and sliding speed when the sliding speed is 0.5ms-1and above. The invariance of friction coefficient with temperature and sliding speed beyond 0.5ms-1 is beneficial in that it will not lead to any instability like stick-slip or squeal.
3. Though both ambient temperature and speed influence the morphology of transfer layer and friction coefficient, speed is found to be dominant according to statistical analysis.
4. The observed dependency of friction coefficient and morphology of transfer layer on test temperature and normal load is attributed to decrease in flow stress and increase in friction factor ‘m’, a ratio of interfacial shear stress to shear yield stress of the softer material. Though ANOVA shows the significance of speed and not that of temperature, the observed dependence of friction coefficient on temperature is attributed to the enhanced effect of adhesion at elevated temperature observed in the adhesion test.
5. The state of stress at the contacting surface is found to control the morphology of transfer layer. When the normal load exceeded 40N, it gave rise to higher magnitude of stress state at the contacting surface, resulting in formation of continuous transfer layer and hence the higher magnitude of friction coefficient.
6. Plastic deformation model based on Rigney’s approach for estimating friction coefficient can be used. The estimated friction coefficient is on the higher side. Hence, any design of equipments based on the Rigney’s plastic deformation model is a conservative design.
7. There appears to be a close relation between the morphology of wear track and quantity of wear-loss. The formation of debris and rough track, primarily for low temperature sliding indicate larger magnitude of wear-loss. The parameters, which bring about increased ductility of aluminum as observed in the case of higher temperature of sliding, results in reduced wear-loss due to large scale smearing and back transfer of material.
The results of sliding of aluminum pin on die-steel ring in vacuum:
1. The mode of sliding changes from adhesive to abrasive mode depending on depth of penetration, tan(θ) where θ is the base angle of the conical asperity and average roughness parameter Sa ,all of them in turn depend on morphology of die steel surface and test temperature.
2. The friction coefficient and morphology of transfer layer are found to depend on the mode of sliding. The sub-surface plastic deformation, which characterizes the friction coefficient and morphology of transfer layer, is dependent on temperature of sliding.
3. The sliding experiment is capable of simulating the stress state on the bearing channel of the die; elucidating evolution of transfer layer, with change in operating parameters.
4. The ANOVA has clearly indicated the significance in friction coefficient at different temperatures and surface textures. In addition, the complex comparison below and above homogenization temperature (573K) has indicated significance in friction coefficient and thereby recognizing the importance of extrusion of aluminum at a temperature where it is in a single phase. Also, ANOVA indicates the dependency of both friction coefficient and transfer layer on the texture, i.e. either a lay or random.
The results of sliding aluminum pin on diamond polished die steel ring:
1. Shearing of the cold welded junction is a probable mechanism involved in the formation of transfer layer up to 423K.
2. The transgranular and intergranular mode of fracture are identified to be the two possible modes of fracture of the asperity at temperatures greater than 573K. The large ductility of the aluminum alloy facilitated smearing resulting in a continuous transfer layer at temperatures greater than 573K.
3. The formation of a continuous transfer layer at temperatures greater than 573K is responsible for the observed high friction coefficient at these temperatures. Scanning electron microscopy observations of the fracture surfaces of the tensile test specimen revealed fracture to be a combination of both transgranular and intergranular modes.
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Organische Leuchtdioden mit PolymeranodenFehse, Karsten 28 February 2008 (has links) (PDF)
In organischen Leuchtdioden (OLEDs) werden üblicherweise anorganische Materialien wie Indium-Zinn-Oxid (ITO) als transparente leitfähige Anoden verwendet. ITO besitzt allerdings eine geringe Austrittsarbeit und kann deshalb Löcher nicht effizient in organische Materialien injizieren. Weiterhin ist ITO eine Quelle von Indium- und Sauerstoff-Ionen, die in die organischen Materialien diffundieren und dort mit der Organik reagieren bzw. als effiziente Exzitonenvernichter agieren. Eine mögliche Alternative zu ITO sind hoch leitfähige Polymere wie PEDOT:PSS und Polyaniline. Diese Studie untersucht die physikalischen Aspekte von OLEDs mit elektrisch dotierten Ladungstransportschichten auf Polymeranoden. Hierbei werden pin-OLEDs auf ITO mit OLEDs auf Polymeranoden direkt verglichen und mit dem derzeitigen Stand der Technik diskutiert. Die Untersuchungen zeigen, daß OLEDs auf PEDOT:PSS Anoden eine höhere Effizienz erreichen als OLEDs auf ITO Anoden. Um die physikalischen Unterschiede von pin-OLEDs auf ITO und PEDOT:PSS Anoden zu untersuchen, werden optische Simulationen sowie Ultraviolett-Photoemissions-Spektroskopie (UPS) und Lebensdauermessungen durchgeführt. Die optischen Simulationen zeigen, daß die Polymeranoden durch ihren geringen Brechungsindex eine höhere Lichtauskopplungseffizienz besitzen als OLEDs mit einer ITO-Anode. Außerdem finden UPS-Messungen eine geringere Löcherinjektionsbarriere von PEDOT:PSS zu dotierten und undotierten Lochtransportschichten. Aus diesem Grund ist die Ladungsträgerinjektion an der Anoden-Organik-Grenzfläche effizienter, wenn eine PEDOT:PSS-Anode verwendet wird. Lebensdauermessungen von pin-OLEDs auf PEDOT:PSS-Anoden zeigen eine vergleichbare Lebensdauer zu OLEDs auf ITO-Anoden. Die Ergebnisse dieser Untersuchungen zeigen eindeutig, daß Polymeranoden das Potential besitzen, ITO als Anode zu ersetzen und zusätzlich die OLED-Effizienz zu erhöhen.
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An analytical appraisal of copper alloy pin production: 400-1600 AD : the development of the copper alloy, pin industry in Britain during the post-Roman period, based on analytical, metallographic and typological examination with consideration of historical and archaeological archivesCaple, Christopher January 1986 (has links)
No description available.
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Simulation numérique d’un assemblage métal / composite thermoplastique par CMT pins / Numerical simulation of a metal / thermoplastic assembly by CMT pinsParoissien, Simon 14 November 2016 (has links)
Une méthode est proposée pour la modélisation d’unassemblage multimatériaux innovant visant des applicationsdans l’allègement structurel des véhicules. Dans cetassemblage une partie composite thermoplastique, est fixée àune plaque acier texturée par la technologie CMT pins.L’interface est particulièrement complexe et non linéaire : unereprésentation fine du comportement local serait extrêmementpénalisante en temps de calcul. Dans cette optique il a étéchoisi d’orienter la méthodologie vers une modélisation la plussimple possible tout en conservant de bons résultats globaux.Pour ce faire, en s’inspirant de l’état de l’art existant sur lesmultimatériaux, une campagne expérimentale a été menée surdes éprouvettes longitudinales à double recouvrement afin decaractériser cette interface. Une fois les mécanismes locauxinvestigués, deux modèles sont proposés. Le premiernumérique basé sur la méthode des éléments finis etl’introduction d’éléments cohésifs nous permet de valider leshypothèses de modélisation tout en quantifiant la répartitiondes efforts entre les picots. Le deuxième se base sur le calcullocal d’un Volume Élémentaire Représentatif pour établiranalytiquement la loi de comportement de l’interface. Cette loiest ensuite introduite sous la forme d’un ressort non linéaire ausein d’un modèle numérique simplifié de l’éprouvette. Pourfinir ces approches sont appliquées au cas d’étude industriel etles résultats sont validés par une deuxième campagneexpérimentale. / A method is proposed to simulate an innovative multimaterialassembly which has applications in structural lightweight forvehicles. In this assembly, a thermoplastic composite part isfixed on a steel plate, textured by the CMT pins technology.This is an especially complex and nonlinear interface: a finerepresentation of local behaviour would be extremely costlyfor calculation. So, it has been chosen to investigate a model assimple as possible which still demonstrates accurate globalresults.An experimental campaign on double lap shear specimen,inspired by existing state of the art on multimaterial has beenset up to characterize this interface. Once local mechanismshave been understood, two models are proposed and compared.The first is numerical and based on finite elements method andcohesive elements. It allows us to validate the modelhypotheses while describing the effort repartition between thepins. The second one is based on a Representative VolumeElement. It establishes analytically the behaviour law of theinterface. This law is then inserted inside a simplifiednumerical model of the specimen by means of a nonlinearspring. To conclude, these approaches are applied to theindustrial case of study and the result have been validated by asecond experimental campaign.
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