No description available.

The main and side effects of extinction were evaluated in a multiple baseline design across the problem behaviors of two elementary school boys. For each subject, functional analysis procedures resulted in the occurrence and assessment of only one of several problem behaviors reported by teachers. Extinction treatment based on functional analysis outcomes was then applied to the assessed topography and resulted in the emergence of other inappropriate response forms. Each successive behavior was exposed to extinction and changes in previous and subsequent response forms were observed. Both main effects and indirect effects of extinction were examined. Findings are discussed regarding the covariation of responses and implications for the treatment of behavior disorders in applied settings.

This experiment examined the effects of extinction on rate of responding and several topographical and temporal measures in adult humans. Three college students were trained to type the sequence 1•5•3 on a numeric keypad on a computer. The subjects were exposed to different fixed-ratio schedules of reinforcement (FR1, FR 5, and FR10 respectively) and extinction. Subjects displayed typical schedule performances during the maintenance phase of the experiment. During extinction the performances were disrupted, they showed a "break and run" pattern and a general decrease in responding. Also, new topographical and temporal patterns emerged. These data are consistent with those reported for non-human species and special human populations.

L’addiction aux drogues d’abus se caractérise par une prise compulsive de drogue et par des épisodes récurrents de rechute après abstinence. Ces épisodes de rechute, parfois mortels, sont généralement précédés par un désir intense et irrépressible pour la drogue, appelé aussi craving. Bien que le rôle causal du craving dans la rechute reste encore à démontrer, la prévention du craving est devenue récemment un enjeu important des recherches clinique et préclinique. Chez l’homme l’amorçage du craving s’effectue après exposition ou réexposition à la drogue elle-même, à un stress, ou à des stimuli conditionnés à la prise de drogue. Chez l’animal, cet amorçage peut être modélisé par la reprise du comportement de recherche de drogue après arrêt du renforcement. Cette reprise peut être amorcée par les mêmes facteurs amorçant le craving chez l’homme, notamment par la réexposition à la drogue elle-même, ce qui suggère qu’elle exprime un état ressemblant au craving. Selon une hypothèse récente, l’amorçage du craving par la drogue serait dû à un conditionnement intéroceptif. Ce conditionnement se formerait au cours de l’acquisition où les animaux apprendraient à associer les stimuli intéroceptifs périphériques de la drogue avec la disponibilité du renforcement. Après arrêt du renforcement, la réexposition à ces stimuli intéroceptifs conditionnés provoquerait la reprise de la recherche de drogue en signalant (faussement) aux animaux le retour du renforcement. Cette hypothèse a permis le développement et la validation récente d’une stratégie anti-craving basée sur l’extinction de ces stimuli conditionnés de la cocaïne. Dans ce contexte, mon travail de thèse a eu pour but principal d’évaluer l’efficacité potentielle de cette stratégie à prévenir la rechute proprement dite, c’est-à-dire le retour aux niveaux de prise de cocaïne avant l’extinction. Ce travail a permis de démontrer : 1) qu’il est possible d’éteindre complètement l’amorçage du craving par la cocaïne chez l’animal ; 2) que cette extinction est accompagnée par une perte des réponses neuronales à la cocaïne dans les régions du cerveau causalement impliquées dans l’amorçage du craving (i.e., cortex préfrontal prélimbique et partie « core » du noyau accumbens); 3) mais que malgré nos attentes initiales, l’extinction complète et prolongée de l’amorçage du craving par la cocaïne n’a aucun effet préventif majeur sur la rechute, suggérant une dissociation entre craving et rechute, du moins chez l’animal ; enfin, 4) que cet échec relatif est dû en grande partie à l’existence d’une forme résiduelle de recherche de cocaïne résistante à l’extinction, fréquemment rapportée dans la littérature mais généralement ignorée. Cibler cette résistance à l’extinction afin de l’éradiquer devrait représenter un enjeu majeur pour la recherche future dans le domaine. / Craving often precedes relapse into cocaine addiction. This explains why considerable research effort is being expended to try to develop anti-craving strategies for relapse prevention. Recently, we discovered using the classic reinstatement model of cocaine craving that the reinstating or priming effect of cocaine can be extinguished with repeated priming – a phenomenon dubbed extinction of cocaine priming. Such extinction has been interpreted as evidence that the priming effect of cocaine on reinstatement of cocaine seeking depends on an interoceptive drug conditioning mechanism whereby the interoceptive cues of cocaine become reliable conditioned Pavlovian predictors of the availability of cocaine reinforcement. Regardless of the underlying mechanisms, however, extinction of drug priming has been proposed as a potential cocaine exposure therapy for relapse prevention that may complement other, more traditional exteroceptive cue exposure therapies. The goal of my PhD thesis was to measure the potential beneficial effect of this novel extinction strategy on subsequent relapse (i.e., return to the pre-extinction pattern of cocaine self-administration once the drug is made again available after extinction). Overall and contrary to our initial hope, extensive and complete extinction of cocaine priming had no major impact on relapse. This lack of effect occurred despite evidence for post-extinction loss of neuronal responsiveness to cocaine priming in brain regions causally involved in cocaine-induced reinstatement (i.e., the anterior cingulate and prelimbic prefrontal cortex, and the core of the nucleus accumbens). An effect of extinction of cocaine priming on relapse was only observed when cocaine was available for self-administration under more demanding conditions. However, this effect was modest and short-lived. Finally, we were able to trace the origin of our failure to prevent relapse to an extinction-resistant form of cocaine seeking that is commonly reported, though often overlooked, in other reinstatement studies. We propose that this behavior should become a novel target for future preclinical research on anti-craving strategies for relapse prevention.

L’expression de sortie de contrat renvoie naturellement aux mécanismes légaux permettant la sortie, aux hypothèses de résolution judiciaire et aux cas de révocation par mutuus dissensus. Pourtant, il existe une autre voie possible, sans doute moins spontanément envisagée : celle offerte par les clauses de sortie de contrat. Cette discrétion s’explique sans doute par le fait que la systématisation de ces mécanismes contractuels a fait l’objet de peu d’écrits. En effet, si l’existence de chaque clause de sortie de contrat prise isolément est aujourd’hui incontestable, l’ordonnancement de ces solutions éparses au sein d’un ensemble cohérent semble toujours faire défaut. La présente étude se propose donc d’aborder la question des clauses de sortie de contrat dans sa diversité, en partant du constat que les parties ont bien la capacité d’organiser dès l’origine, c’est-à-dire dès la conclusion, la sortie éventuelle du contrat qu’elles ont pourtant souhaité conclure. Cette anticipation se traduit ainsi par l’insertion d’un mécanisme de libération, lequel pourra produire effet du fait de la seule volonté du contractant bénéficiaire et sans recours préalable au juge.Plus encore, les contractants qui souhaiteraient anticiper la sortie en prévoyant ce mécanisme de libération sont confrontés à une myriade de choix. Il n’y a pas une mais des clauses de sortie de contrat. L’intérêt de l’étude de ces clauses est alors double : d’une part, si l’existence de ces mécanismes est aujourd’hui incontestable, le constat est celui du foisonnement et de ce qui s’impose a priori comme une irréductible diversité. Or la démonstration de l’existence des clauses de sortie de contrat permet d’ordonner cette diversité en contemplation de l’objet et donc de proposer une grille de lecture nouvelle des différentes clauses ayant pour fonction de permettre la sortie. D’autre part, une fois ces clauses identifiées et classifiées, l’exposé du fonctionnement de celles-ci permet de mettre en lumière l’existence d’un socle commun de règles mais aussi de règles propres à certaines clauses. L’analyse permet à cet égard également de revenir sur le rôle du juge, de facto écarté par l’insertion même de la clause, et qui pourtant conserve une place certes plus réduite que dans d’autres hypothèses, mais néanmoins réelle et parfois déterminante. / The term of “exit of contract” naturally refers to legal mechanisms enabling to exit, judicial resolution and revocation by mutuus dissensus. Yet there is another possible way, maybe less spontaneously considered: the one offered by the contract exit clauses. This discretion can be explained by the fact that very few studies have been made on this topic. While the existence of each exit clause taken separately is now indisputable, the ordering of solutions in a consistent set still seems to be lacking. The aim of this study is to look at this question of the exit clauses in the broadest way, based on the observation that the parties to a contract have the ability to organize from the beginning – that is to say when concluding – the eventual exit of the contract they nevertheless wished to conclude. This anticipation is thus reflected by the insertion of a release mechanism, which can product the intended effect because of the only will of the contracting party beneficiary, without prior recourse to the courts.Moreover, the parties who would wish to anticipate the exit by providing this freedom mechanism are faced with multiple choices. There is no one but many contract exit clauses. The purpose of the present study is therefore twofold: firstly, the existence of these mechanisms is now indisputable, but this observation leads to a proliferation and an irreducible diversity. In this regard, the demonstration of the existence of the contract exit clauses allows to organize this diversity in contemplation of the object and thus to propose a new reading grid of the various clauses that anticipate the exit. Secondly, once these clauses identified and classified, the presentation of their working allows to highlight the existence of a common set of rules, simultaneously with rules which are specific to certain clauses. From that point of view, the analysis also allows to reconsider the judge’s place, who is de facto removed by the insertion of the clause in the contract, but yet retains a real and sometimes decisive part, even if his place is more reduced than in other assumptions.

Increased operations of aircraft, both commercial and military, in hostile desert environments have increased risks of micro-sized particle ingestion into engines. The probability of increased sand and dust ingestion results in increased life cycle costs, in addition to increased potential for performance loss. Thus, abilities to accurately characterize inlet sand would be useful for engine diagnostics and prognostic evaluation. Previous characterization studies were based on particle measurements performed a posteriori. Thus, there exists a need for in situ quantification of ingested particles. The work presented in this thesis describes initial developments of a line-of-sight optical technique to characterize ingested particles at concentrations similar to those experienced by aircraft in brownout conditions using light extinction with the end goal of producing an onboard aircraft diagnostic sensor. By measuring the extinct light intensity in presence of particles over range of concentrations, a relationship between diameters, concentration and light extinction was used for characterization. The particle size distribution was assumed log-normal and size range of interest 1-10 μm. To validate the technique, particle characterization in both static and flow based tests were performed on polystyrene latex spheres of sizes 1.32 μm, 3.9 μm, 5.1 μm, and 7 μm in mono-disperse and poly-disperse mixtures. Results from the static experiments were obtained with a maximum relative error of 11%. Concentrations from the static experiments were obtained with a maximum relative error of 18%. Mono-dispersed and poly-dispersed particle samples were sized in a flow setup, with a maximum relative error of 12% and 10% respectively across all diameter samples tested. Uncertainty in measurements were quantified, with results indicating a maximum error of 17% in diameters due to sources of variability and showed that shorter wavelength lasers provide lower errors in concentration measurements, compared to longer wavelengths. For real time, on-board measurements, where path lengths traveled by light are much larger than distances traveled in initial proof of concept experimental setups, requirements would be to install sensitive detectors and powerful lasers to prevent operation near noise floors of detectors. Vibration effects from the engine can be mitigated by using larger area collection optics to ensure that the transmitted light falls on active detector areas. Results shown in this thesis point towards validity of the light extinction technique to provide real time characterization of ingested particles, and will serve as an impetus to carry out further research using this technique to characterize particles entering aircraft engine inlets. / Master of Science

No description available.

The experiments reported in this thesis attempted to examine the influence of thirst on the extinction of taste aversions in rats. Differences in the amount of stimulus exposure and deprivation state between groups were controlled for. The first experiment presented two novel flavours twelve times to rats when either thirsty or sated. A preference for the flavour presented when thirsty was established. The next three experiments examined whether this preference would accelerate the extinction of a taste aversion, by first pairing a novel flavour with lithium and then presenting the conditioned flavour when rats were either sated or thirsty. No evidence of accelerated extinction was found. The final two experiments examined whether the associatively-activated representation of sucrose could function to extinguish a taste-aversion to that sucrose without presenting sucrose itself. No evidence of representation-mediated extinction was found despite evidence that the context was associated with sucrose. The results indicate that the extinction of conditioned taste aversions is not influenced by counter-conditioning due to thirst relief, and extinction of such aversions appears to be due to similar processes as other forms of conditioning.

Anomodonts are a group of non-mammalian synapsids (“mammal-like reptiles”) that represents the dominant herbivores of their time. Their great taxonomic and morphological diversity, unparalleled by any other clade of Permian-Triassic terrestrial tetrapods, is well documented by a cosmopolitan fossil record. In addition, anomodonts survived the most severe extinction event in Earth’s history at the end of the Permian and experienced a second diversification in the Triassic. Thus, they are an ideal clade to investigate macroevolutionary patterns and play an important role in evaluating the impact of the end-Permian extinction on the terrestrial realm. This work combines descriptive, phylogenetic, and quantitative approaches to study evolutionary patterns of anomodonts with special focus on diversity patterns through time. A taxonomic revision of the Late Permian dicynodont genus Emydops reflects the necessity for a solid taxonomic basis for diversity studies. The description of a new species of this genus is combined with a discussion of dental variability and pathology in dicynodont anomodonts. A detailed description of the postcranial anatomy of the basal anomodont Suminia reveals new insights into the early evolution of anomodonts and therapsids in general. Several derived features, in particular in the autopodium, are unique to Suminia and together with a comparative morphometric analysis indicate grasping abilities of this taxon and the earliest evidence for arboreality in the vertebrate fossil record. The cranial anatomy of the Triassic dicynodont Kombuisia is restudied and a phylogenetic evaluation of the survivorship of anomodonts across the Permian-Triassic boundary reveals more surviving lineages than previously recognized. A review of anomodont-bearing tetrapod faunas forms the basis for a faunal similarity analysis that reveals stratigraphic as well as geographic patterns in faunal groupings. The taxonomic diversity of anomodonts reflects three diversifications and subsequent extinctions in the early Middle Permian, the Early Triassic and the mid-late Triassic.

Anomodonts are a group of non-mammalian synapsids (“mammal-like reptiles”) that represents the dominant herbivores of their time. Their great taxonomic and morphological diversity, unparalleled by any other clade of Permian-Triassic terrestrial tetrapods, is well documented by a cosmopolitan fossil record. In addition, anomodonts survived the most severe extinction event in Earth’s history at the end of the Permian and experienced a second diversification in the Triassic. Thus, they are an ideal clade to investigate macroevolutionary patterns and play an important role in evaluating the impact of the end-Permian extinction on the terrestrial realm. This work combines descriptive, phylogenetic, and quantitative approaches to study evolutionary patterns of anomodonts with special focus on diversity patterns through time. A taxonomic revision of the Late Permian dicynodont genus Emydops reflects the necessity for a solid taxonomic basis for diversity studies. The description of a new species of this genus is combined with a discussion of dental variability and pathology in dicynodont anomodonts. A detailed description of the postcranial anatomy of the basal anomodont Suminia reveals new insights into the early evolution of anomodonts and therapsids in general. Several derived features, in particular in the autopodium, are unique to Suminia and together with a comparative morphometric analysis indicate grasping abilities of this taxon and the earliest evidence for arboreality in the vertebrate fossil record. The cranial anatomy of the Triassic dicynodont Kombuisia is restudied and a phylogenetic evaluation of the survivorship of anomodonts across the Permian-Triassic boundary reveals more surviving lineages than previously recognized. A review of anomodont-bearing tetrapod faunas forms the basis for a faunal similarity analysis that reveals stratigraphic as well as geographic patterns in faunal groupings. The taxonomic diversity of anomodonts reflects three diversifications and subsequent extinctions in the early Middle Permian, the Early Triassic and the mid-late Triassic.