Low-frequency (LF) words have higher hit rates (HRs) and lower false alarm rates (FARs) than high-frequency (HF) words in recognition memory, a phenomenon termed the mirror effect by Glanzer and Adams (1985). The primary mechanism for producing the mirror effect varies substantially across models of recognition memory, with some models localizing the effects during encoding and others during retrieval. The current experiments contrast two retrieval-stage models, the Source of Activation Confusion (SAC; Reder, Nhouyvanisvong, Schunn, Ayers, Angstadt, & Hiraki, 2000) model and the unequal variance signal detection theory (UVSDT) criterion shift model (e.g., DeCarlo, 2002). The SAC model proposes that two distinct processes underlie the HR and FAR effects, with a familiarity process driving the FAR effect and a recollective process driving the HR effect. The UVSDT criterion shift model assumes that subjects use different criteria when making recognition judgments for HF and LF words, with this single process driving both the HR and FAR effects. Experiment 1 incorporated divided attention and speeded responding manipulations designed to remove the contribution of recollection in the SAC model, thereby eliminating the LF HR advantage. Experiment 2 manipulated the salience of the frequency classes, as the UVSDT criterion shift model requires that subjects are aware of the distinct frequency classes in order to shift their criteria. Across both experiments, model simulations and direct fits of the SAC model demonstrated systematic errors in prediction. While the UVSDT model struggled in fits to Experiment 1 data, the model provided acceptable fits to Experiment 2 data and accurately predicted the general pattern of effects in all cases. Furthermore, state-trace analyses provided compelling evidence in favor of single-process rather than dual-process models of recognition memory, casting serious doubt on the validity of the dual-process SAC model. Finally, the current experiments highlight the importance of obtaining model-based estimates of sensitivity and bias across frequency classes, as the standard practice of conducting direct comparisons of HRs and FARs for HF and LF words confounds bias and sensitivity differences.

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No description available.

Les propriétés en fatigue à grand et très grand nombre de cycles des superalliages base Ni monogranulaires ont été étudiées à 1000°C sous trois fréquences (0.5, 70 et 20000 Hz) et quatre rapports de charge (-1, 0.05, 0.3, 0.8), en prenant le CMSX-4 comme alliage de référence.Dans un premier temps, le régime de fatigue à très grand nombre de cycles a été étudié à 20 kHz. A R = -1, la fissure fatale s’amorce à chaque fois depuis un pore de fonderie en interne et se propage suivant les plans cristallographiques {111}, pour des durées de vie entre 106 et 109 cycles, et ce malgré la présence d’autres défauts tels que les eutectiques ou carbures. Le procédé d’élaboration, en impactant directement la taille des pores de fonderie, contrôle la durée de vie alors que la microstructure a peu d’influence. A R = 0.8, le fluage contrôle la durée de vie en fatigue gigacyclique, et rend alors ce régime sensible à la microstructure et à la composition chimique de l’alliage. Les essais à très longues durées de vie (> 109 cycles) ont également été caractérisés et ont permis de proposer un mécanisme d’amorçage dans ce régime de fatigue.Dans un second temps, l’influence de la fréquence d’essai sur les endommagements dépendants du temps tels que l’oxydation et le fluage, et leur interaction, a été étudiée. A R ≤ 0, diminuer la fréquence d’essai revient à inhiber la criticité des défauts internes en favorisant l’endommagement en surface par oxydation. A R ≥ 0.8, le fluage est l’endommagement conduisant à la rupture des éprouvettes quelle que soit la fréquence de sollicitation ou la durée de vie. Les rapports de charge intermédiaires présentent une interaction importante entre les endommagements en oxydation, fatigue et fluage en fonction de la fréquence de sollicitation et des conditions de chargement. A partir de ces observations, un modèle d’endommagement a été proposé afin de prédire la durée de vie du CMSX-4 et présente des résultats satisfaisants par rapport aux données expérimentales. / High and very high cycle fatigue properties of Ni-based single crystal superalloys have been studied at 1000°C using three frequencies (0.5, 70, 20000 Hz), four stress ratios (-1, 0.05, 0.3, 0.8) and CMSX-4 alloy as reference.Firstly, the very high cycle fatigue regime (VHCF) has been studied at 20 kHz. At R = -1, fatal crack always initiates between 106 and 109 cycles from an internal casting pore et then propagates in a crystallographic mode, despite the presence of other metallurgical defects such as eutectics and carbides. The elaboration process controls VHCF life under these conditions as it directly affects casting pore size, whereas microstructure has no relevant influence. At R = 0.8, creep controls VHCF life and makes this regime sensitive to microstructure and alloy’s chemical composition. Long term tests (> 109 cycles) have also been characterized and have enabled to propose a crack initiation mechanism operating in the VHCF regime.Secondly, the influence of frequency on time-dependent damages such as oxidation and creep, and their interaction, has been studied. At R ≤ 0, reducing frequency inhibits the harmfulness of internal critical defects by promoting oxidation surface damage. At R ≥ 0.8, creep damage leads to specimens rupture for all frequency test and loading conditions. Intermediate stress ratios present an important interaction between oxidation, fatigue and creep damage according to the frequency and loading conditions. Based on these observations, a damage model that predicts CMSX-4 fatigue life has been proposed and presents satisfying results in comparison to experimental data.

Les essais de fatigue peuvent être effectués dans une gamme de fréquences similaire, mais les fréquences les plus élevés sont généralement préférables afin de réduire le temps de test et d'obtenir des résultats dans une période raisonnable. La question reste à savoir si un effet de fréquence existe. Cette étude traite de l'effet de la fréquence de chargement sur la résistance à l'amorçage et à la propagation des fissures sur 3 matériaux (M800HY, CP1000 et DP1180) utilisés dans le domaine automobile. Deux rapports de charge (R=-1 et 0.1) et cinq fréquences de chargement (25 Hz, 30 Hz, 150 Hz et 20 kHz) ont été étudiés. Tout d'abord, nous avons réalisé des calculs par élément finis en dynamique pour dimensionner les éprouvettes et calculer l'étendue du facteur d'intensité de contrainte durant la propagation de la fissure de fatigue. Ensuite, nous avons réalisé des essais d'amorçage et de propagation. Indépendamment de la fréquence de chargement,l'amorçage de la fissure de fatigue est toujours surfacique à cause des concentrations de contraintes dues au processus de laminage ou de l'électro-galvanisation. L'observation des faciès de rupture sur éprouvettes testées à 30 Hz et 20 kHz montre que le mode de propagation est transgranulaire avec quelques localisations de rupture intergranulaire ou par clivage sur la nuance DP1180. Les stries de propagations sont présentes sur les faciès d'éprouvettes M800HY et absentes sur les faciès des deux autres nuances. La nuance DP1180 présente une meilleure résistance à l'amorçage et à la propagation de la fissure de fatigue. Concernant l'effet de la fréquence de chargement, globalement l'amorçage de la fissure de fatigue est dépendante de la fréquence de chargement, par contre, la propagation est indépendante de la fréquence. / Fatigue tests can be performed in a similar frequency range, but the higherfrequencies are generally preferable to reduce the test time and obtain results within areasonable time. The question remains whether a frequency effect exists. This study dealswith the effect of the loading frequency on fatigue strength and crack growth of 3 steels(M800HY, CP1000 and DP1180) used in automotive industry. Two load ratios (R = -1 and0.1) and five load frequencies (25 Hz, 30 Hz, 150 Hz and 20 kHz) were studied. First, weperformed dynamics finite element method to calculate the dimensions of the specimens(to vibrate with a resonance at 20 kHz), and, the stress intensity range as a function of the length of crack. Then, we have done some test on fatigue crack initiation and propagation. Whatever the loading frequency, the initiation of the fatigue crack is always on the surfacebecause of the stress concentrations due to the rolling process or the electro-galvanization.The observation with SEM of fracture surface of the specimens tested at 30 Hz and 20 kHzshows that the mode of propagation is transgranular with some locations of intergranularfailure or by cleavage on DP1180 grade. The fatigue striation on fracture surface arepresent on the M800HY and absent on the other two materials. The grade DP1180 has abetter resistance to the initiation and propagation of the crack. Regarding the effect ofloading frequency, overall the initiation of the fatigue crack is dependent on the loadingfrequency, however, the propagation is independent of the loading frequency.

Ce travail vise à améliorer notre compréhension du comportement en fatigue à grand et très grand nombre de cycles d’un acier ferrito-martensitique dual phase, notamment les effets de la température et de la vitesse de déformation résultant de chargements cycliques à haute fréquence. L'effet de la fréquence sur la réponse en fatigue de l'acier DP600 a été étudié en effectuant des essais de fatigue sur une machine ultrasonique travaillant à 20 kHz et sur une machine conventionnelle travaillant à des fréquences inférieures à 100 Hz. Des études de fractographie et des observations microscopiques à la surface des échantillons ont été effectuées pour étudier les mécanismes de déformation et de rupture. De plus, la thermographie infrarouge in situ a été utilisée pour étudier la réponse thermique et les mécanismes dissipatifs du matériau lors des essais de fatigue. Les courbes S-N ont été déterminées à partir de chargements de fatigue ultrasoniques à 20 kHz et d’essais conventionnels à 30 Hz. La durée de vie pour une amplitude de contrainte donnée est plus élevée dans le cas de la fatigue ultrasonique bien que la limite de fatigue soit identique dans les deux cas. L’augmentation inévitable de la température en fatigue ultrasonique à fortes amplitudes de contraintes, ainsi que le comportement dépendant de la vitesse de déformation de la ferrite, en tant que structure CC, ont été trouvés comme les paramètres clés expliquant le comportement observé en fatigue, et la réponse thermique sous les fréquences faibles et ultrasoniques. Les écarts observés entre l’essai de fatigue conventionnel et celui ultrasonique ont été évalués à travers les mécanismes de mobilité des dislocations vis dans la phase ferritique de structure cubique centrée (CC). La durée de vie plus élevée et l’amorçage de la fissure principale sur une inclusion observés en fatigue ultrasonique ont été attribués au vieillissement dynamique résultant du fort auto-échauffement du matériau aux fortes amplitudes de contraintes. L'existence d'une transition du régime thermiquement activé au régime athermique avec l’augmentation de l'amplitude de contrainte a été mise en évidence. Au-dessous de la limite de fatigue, la déformation a lieu dans un régime thermiquement activé alors qu'elle est dans un régime athermique au-dessus de la limite de fatigue. En fatigue conventionnelle, la déformation est athermique pour toutes les amplitudes de contrainte. Une carte de transition a été produite en utilisant les résultats expérimentaux pour l'acier DP600 ainsi que les données disponibles dans la littérature pour d'autres aciers à base de ferrite, montrant ainsi la corrélation entre le mouvement des dislocations vis thermiquement activé et l'absence de rupture en fatigue à très grand nombre de cycle. / This work is an attempt towards a better understanding of the high cycle and very high cycle fatigue behaviors of a ferritic-martensitic dual-phase steel, with a regard to temperature and strain rate effects, resulting from accelerated fatigue loading frequencies. The influence of frequency on fatigue response of DP600 steel was investigated by conducting ultrasonic and conventional low frequency fatigue tests. Fractography studies and microscopic observations on the surface of specimens were carried out to study the deformation and fracture mechanisms under low and ultrasonic frequencies. Moreover, in situ infrared thermography was carried out to investigate the thermal response and dissipative mechanisms of the material under fatigue tests. The S-N curves were determined from ultrasonic 20-kHz fatigue loadings and conventional tests at 30 Hz. Fatigue life for a given stress amplitude was found to be higher in the case of ultrasonic fatigue whereas the fatigue limit was the same for both cases. Moreover, crack initiation was always inclusion-induced under ultrasonic loading while under conventional tests it occurred at slip bands or defects on the surface. The inevitable temperature increase under ultrasonic fatigue at high stress amplitudes along with the rate dependent deformation behavior of ferrite, as a body centered cubic (BCC) structure, were found as the key parameters explaining the observed fatigue behavior and thermal response under low and ultrasonic frequencies. The discrepancies observed between conventional and ultrasonic fatigue tests were assessed through the mechanisms of screw dislocation mobility in the ferrite phase as a BCC structure. The higher fatigue life and inclusion-induced crack initiations in the case of ultrasonic loading were attributed to the dynamic strain aging, which resulted from the high temperature increases at high stress amplitudes. The existence of a transition in deformation regime from thermally-activated to athermal regime under ultrasonic fatigue loading by increasing the stress amplitude was confirmed. Below the fatigue limit, deformation occurred in thermally-activated regime while it was in athermal regime above the fatigue limit. Under conventional loading deformation occurred in athermal regime for all stress amplitudes. From the analysis of the experimental data gathered in this work, guidelines were given regarding the comparison and interpretation of S-N curves obtained from conventional and ultrasonic fatigue testing. A transition map was produced using the experimental results for DP600 steel as well as data available in the literature for other ferrite based steels, showing the correlation between thermally-activated screw dislocation movement and the absence of failure in very high cycle fatigue.

Cette thèse présente le travail effectué sur la conception d’un oscillateur à quartz miniature (volume visé de 1 cm3) con-trôlé en température. Les équipements de télémétrie, poursuite et contrôle tels que ceux utilisés dans les microsatellites (comme Myriades) sont d'un volume très important (8 litres). Des équipements avec un volume 8 fois moindre (1 litre) sont envisagés sur les pico et nano satellites. Une réduction drastique du volume et de la consommation est donc nécessaire, à performances égales. Elle nécessite une remise en question de l'ensemble des éléments composant l'équipement dont le micro-oscillateur, tant au niveau volume qu'au niveau consommation d’énergie. Les études préliminaires ont servi à définir le résonateur adapté pour satisfaire les spécifications de stabilité demandées. La simulation thermique d'un modèle d’oscillateur OCXO (Oven Controlled Xtal Oscillator) a permis d'obtenir une bonne compréhension des transferts de chaleur dans le dispositif. La réduction des pertes thermiques et l'augmentation de la stabilité thermique du résonateur étaient les principaux défis. La dilatation thermique du résonateur entraine des contraintes mécaniques au niveau de ses fixations et décale la fréquence de résonance. Un MEMS en silicium a été conçu pour supporter le résonateur à l’aide de simulations thermomécaniques. Ce support est compatible avec les contraintes de faible con-sommation et de sensibilité thermique tout en gardant une bonne résistance aux chocs. En ce qui concerne l’électronique, une puce ASIC utilisée depuis plusieurs années a été caractérisée pour établir un modèle numérique. Cette étude a dévoilé les facteurs limitants des performances de l’ensemble et permis d’envisager des solutions correctives. En intégrant dans la démarche les coûts de fabrication, l’utilisation d’un ASIC a été écartée (au moins provisoirement) au profit d’une solution exploitant des composants électroniques du commerce. Enfin, un démonstrateur de module physique miniature a été monté et caractérisé. Les résultats de mesures montrent que la consommation du démonstrateur reste inférieure à la spécification demandée (50 mW à une température extérieure de 25°C et à 100 mW pour -40°C). L’importance de la participation du rayonnement dans les échanges thermiques a aussi été validée expérimentalement. / This thesis presents the work on designing a miniature temperature controlled crystal oscillator (required volume is 1 cm3). TTC (Telemetry, Tracking and Control) equipment which is used in microsatellites (as Myriades) has a very important volume (8 liters). 8 times lower volume equipment (1 liter) is planned for pico and nano satellites. Therefore, a significant reduction of volume and consumption for equal performance is necessary. Redesign is required for all components of equipment items including micro-oscillator, as in volume as at the level of energy consumption. Preliminary studies have served to define the resonator adapted to satisfy the request stability specifications. Thermal simulation of an OCXO oscillator model (Oven Con-trolled Xtal Oscillator) has permitted to achieve a good understanding of heat transfer into the device. Reducing heat loss and increases the thermal stability of resonator were major challenges. Thermal expansion of the resonator causes mechanical stresses in its mountings and shifts the resonance frequency. A silicon MEMS has designed for supporting the resonator by using thermo-mechanical simulations. This support is compatible with the constraints of low consumption and heat sensitivity retaining good impact resistance. As regards electronics, an ASIC chip which is used during many years has characterized with the purpose to obtain the digital model. This study has revealed the limiting factors of the oscillator performance. Also it has allowed to provide remedial solutions. The ASIC using was rejected in favor of the solution operating with commercial electronic components (at least temporarily). Finally, a miniature demonstrator of physical module was assembled and characterized. The measuring results show that demonstrator consumption remains below the required specification (50 mW at outside temperature 25°C and 100 mW at -40 ° C). The importance of the participation of radiation within the thermal exchanges has also validated experimentally.

Orientador: Sérgio Kurokawa / Resumo: Sabe-se que existe um modelo de linha bifásica a parâmetros discretos e constantes, desenvolvido diretamente no domínio do tempo. Porém, o fato de considerar os parâmetros longitudinais para uma frequência fixa, faz com que as respostas de corrente e de tensão apresentem um comportamento aproximado. Para melhorar a qualidade das formas de onda, deve-se levar em consideração o efeito da frequência sobre os parâmetros longitudinais. Nesta dissertação foi densenvolvido um modelo de linha de transmissão bifásica a parâmetros discretos, diretamente no domínio do tempo, que leva em consideração o efeito da frequência. A sintetização do mesmo, tanto para as fases quanto para o acoplamento magnético, é representada por meio de uma associação série e paralela de resistores e indutores, onde a quantidade de blocos RL deve ser a necessária para obter o melhor ajuste da resposta em frequência dos parâmetros longitudinais próprios e mútuos. No modelo proposto, as quedas de tensão nas fases produzidas pelo acoplamento magnético, foram calculadas por meio de uma extensão do modelo de Schulze. As equações de corrente e de tensão ao longo da cascata de circuitos π da linha bifásica foram escritas na forma de equação de estado. Tal equação é resolvida utilizando o método de Heun. No processo de validação do modelo proposto, o modelo clássico modal foi utilizado como modelo de referência, tanto para linhas bifásicas que possuem plano de simetria vertical quanto para linhas bifásicas que não pos... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: It is know that exist a lumped and constant parameters two-phase line model, desenveloped directly in time domain. However, the fact to considerer the longitudinal parameters for a fixed frequency, it does what current and voltage responses present an approximated behavior. To improve the quality of the waveforms must be taked into consideration the frequency effect on the longitudinal parameters. In this dissertation was desenveloped a lumped parameters two-phase transmission line model, directly in time domain, that takes into consideration the frequency effect. The synthesis of the same, both for the phases and for the magnetic coupling, is represented by a series and parallel association of resistors and inductors, where the quantity of RL-blocks must be the necessary to obtain the best adjustment of the frequency response of the own and mutual longitudinal parameters. In the proposed model, the voltage drops in the phases produced by the magnetic coupling, were calculated by an extension of Schulze’s Model. Current and voltage equations along the cascade of π-circuits of the two-phase line were written in the form of state equation. Such equation is solutioned using Heun’s Method. In the validation process of the proposed model, the classical modal model was used as reference model, both for two-phase lines that possess vertical symmetry plane and for two-phase lines that do not possess vertical symmetry plane. / Mestre

Submitted by MIGUEL ANGEL ESPINOZA CRUZ null (maecuni2006i@gmail.com) on 2018-02-25T13:46:23Z No. of bitstreams: 1 Dissertação.pdf: 5516624 bytes, checksum: a926e8b18f63107cea2ad701b1023b13 (MD5) / Approved for entry into archive by Cristina Alexandra de Godoy null (cristina@adm.feis.unesp.br) on 2018-02-26T13:14:09Z (GMT) No. of bitstreams: 1 espinozacruz_ma_me_ilha.pdf: 5516624 bytes, checksum: a926e8b18f63107cea2ad701b1023b13 (MD5) / Made available in DSpace on 2018-02-26T13:14:09Z (GMT). No. of bitstreams: 1 espinozacruz_ma_me_ilha.pdf: 5516624 bytes, checksum: a926e8b18f63107cea2ad701b1023b13 (MD5) Previous issue date: 2018-02-02 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Sabe-se que existe um modelo de linha bifásica a parâmetros discretos e constantes, desenvolvido diretamente no domínio do tempo. Porém, o fato de considerar os parâmetros longitudinais para uma frequência fixa, faz com que as respostas de corrente e de tensão apresentem um comportamento aproximado. Para melhorar a qualidade das formas de onda, deve-se levar em consideração o efeito da frequência sobre os parâmetros longitudinais. Nesta dissertação foi densenvolvido um modelo de linha de transmissão bifásica a parâmetros discretos, diretamente no domínio do tempo, que leva em consideração o efeito da frequência. A sintetização do mesmo, tanto para as fases quanto para o acoplamento magnético, é representada por meio de uma associação série e paralela de resistores e indutores, onde a quantidade de blocos RL deve ser a necessária para obter o melhor ajuste da resposta em frequência dos parâmetros longitudinais próprios e mútuos. No modelo proposto, as quedas de tensão nas fases produzidas pelo acoplamento magnético, foram calculadas por meio de uma extensão do modelo de Schulze. As equações de corrente e de tensão ao longo da cascata de circuitos π da linha bifásica foram escritas na forma de equação de estado. Tal equação é resolvida utilizando o método de Heun. No processo de validação do modelo proposto, o modelo clássico modal foi utilizado como modelo de referência, tanto para linhas bifásicas que possuem plano de simetria vertical quanto para linhas bifásicas que não possuem plano de simetria vertical. / It is know that exist a lumped and constant parameters two-phase line model, desenveloped directly in time domain. However, the fact to considerer the longitudinal parameters for a fixed frequency, it does what current and voltage responses present an approximated behavior. To improve the quality of the waveforms must be taked into consideration the frequency effect on the longitudinal parameters. In this dissertation was desenveloped a lumped parameters two-phase transmission line model, directly in time domain, that takes into consideration the frequency effect. The synthesis of the same, both for the phases and for the magnetic coupling, is represented by a series and parallel association of resistors and inductors, where the quantity of RL-blocks must be the necessary to obtain the best adjustment of the frequency response of the own and mutual longitudinal parameters. In the proposed model, the voltage drops in the phases produced by the magnetic coupling, were calculated by an extension of Schulze’s Model. Current and voltage equations along the cascade of π-circuits of the two-phase line were written in the form of state equation. Such equation is solutioned using Heun’s Method. In the validation process of the proposed model, the classical modal model was used as reference model, both for two-phase lines that possess vertical symmetry plane and for two-phase lines that do not possess vertical symmetry plane.