• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 307
  • 83
  • 76
  • 32
  • 10
  • 8
  • 7
  • 7
  • 6
  • 5
  • 4
  • 3
  • 3
  • 2
  • 2
  • Tagged with
  • 639
  • 71
  • 68
  • 49
  • 48
  • 43
  • 43
  • 38
  • 37
  • 36
  • 36
  • 35
  • 32
  • 32
  • 27
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
181

EFFECTS OF ACUTE THC ADMINISTRATION ON EXTINCTION OF CONDITIONED FEAR RESPONSES IN HUMANS: A FUNCTIONAL ANALYSIS OF HIGH DENSITY EEG

Diggs, Herman Augustus 01 December 2014 (has links)
High density electroencephalographic (EEG) measures were used to assess the effects of acute delta 9-tetrahyrdrocannabidol (THC) administration on extinction of conditioned fear responses. Fear conditioning was initiated using a differential classical conditioning paradigm that paired an aversive unconditioned stimulus (shock) with a signaling stimulus (CS+), whereas another stimulus served as a safety signal (CS-). Evoked potentials, induced event-related spectral perturbations (ERSP), and associated intertrial coherence (ITC) measures were used to quantify the acquisition and extinction of conditioned fear responses. Participants (N = 10 males) exhibited conditioning to the CS+ across fear acquisition training, as reflected by greater late positive (posterior sites) and late negative (anterior sites) potential amplitude to the CS+ relative to the CS-. Acute administration of THC facilitated extinction of the conditioned response to the CS+ relative to placebo, as reflected by greater LPP and LNP amplitude to the CS+ relative to the CS- in the placebo, but not THC condition. ERSP analyses suggest the lack of difference between CS+ and CS- ERP amplitude may be partially explained by a shifting of attention from external stimuli to internal processing in the THC condition. However, relative to placebo, THC administration also increased the amplitude of some measures of the conditioned response (LNP) to the CS-, suggesting a generalization of fear or lack of discrimination in this condition.
182

Extinction-Induced Behavioral Variability in Older Adults with Dementia

Mattingly, Jenna 01 December 2010 (has links)
The present study attempted to investigate the effects of extinction on the behavior of older adults with moderate to severe dementia. A touch screen computer displaying four large colored buttons was employed. Participants were exposed to three conditions: baseline, intervention, and a reversal. The target response (pressing green after yellow) resulted in a video stimulus in the intervention condition, and then the videos were withheld during the reversal condition. Data on button-pressing and vocal-verbal statements were visually analyzed to determine the effect of the videos on responding; however none of the participants acquired the task. Therefore, a discussion of extinction responding was not possible. Interesting findings in terms of reinforcement and implications for the treatment of problem behaviors in older adults with dementia are discussed.
183

Estudo clínico–morfométrico, hematológico, bioquímico e imunocitoquímico em alouatta belzebul (Primates, Platyrrhini) / Clinical-Morphometric, Hematological, Biochemical and Immunocytochemical Study in Alouatta belzebul (Primates: Platyrrhini)

Guimarães, Victor Yunes [UNESP] 27 September 2016 (has links)
Submitted by VICTOR YUNES GUIMARAES null (medvetyunes@gmail.com) on 2016-11-24T16:11:35Z No. of bitstreams: 1 Estudo Clínico-Morfométrico, Hematológico, Bioquímico e Imunocitoquímico em Alouatta belzebul (Primates, Platyrrhini).pdf: 3544285 bytes, checksum: 357385404a2724e105deca393460efbe (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-11-25T17:16:02Z (GMT) No. of bitstreams: 1 guimaraes_vy_me_bot.pdf: 3544285 bytes, checksum: 357385404a2724e105deca393460efbe (MD5) / Made available in DSpace on 2016-11-25T17:16:02Z (GMT). No. of bitstreams: 1 guimaraes_vy_me_bot.pdf: 3544285 bytes, checksum: 357385404a2724e105deca393460efbe (MD5) Previous issue date: 2016-09-27 / Os guaribas-de-mãos-ruivas (Alouatta belzebul) são endêmicos do Brasil, atualmente classificados em nível global e nacional como “Vulnerável” e podem ser encontrados principalmente na Amazônia Oriental. Este estudo se propôs a realizar a avaliação clínica e laboratorial de primatas do complexo Alouatta belzebul no bioma amazônico, a fim de caracterizar parâmetros de higidez para uma população residente às margens do Baixo rio Xingu. 27 primatas foram capturados nas áreas de influência da UHE Belo Monte, estado do Pará, Brasil. As variáveis biométricas avaliadas reforçaram as inferências para o gênero, em relação ao dimorfismo sexual pelo tamanho corpóreo, além da constatação de polimorfismos no padrão de coloração da pelagem. Entretanto, as variações talvez possam ser atribuídas a características geográficas, não suficientes para separar as populações em nível taxonômico. A estratificação etária também revelou diferenças significativas nas contagens de eritrócitos, nas concentrações de hemoglobina, hematócrito, na atividade sérica de fosfatase alcalina e GGT para os indivíduos jovens. Enzimas como AST, CK e LDH registraram atividade sérica significantemente superior, quando comparadas aos estudos em cativeiro. Os percentuais de linfócitos T e B circulantes foram 51 e 31% respectivamente, caracterizando o predomínio de linfócitos com o imunofenótipo T. Diante dos desafios imunológicos a que estes animais estão submetidos constantemente, presume-se que o perfil imunológico encontrado corresponde ao status “ótimo” de sobrevivência. / The red-handed howler monkey (Alouatta belzebul) are endemic in Brazil, currently ranked in global and local scale as "Vulnerable" and occurs mainly in the Eastern Amazon. This study aimed to carry out the clinical and laboratory evaluation of red-handed howler “complex” of primates in the Amazon biome, in order to characterize healthiness parameters for a population living on the banks of the Lower Xingu River. 27 primates were captured under the areas of influence of UHE Belo Monte, Pará State, Brazil. The biometric parameters evaluated reinforced inferences for Gender, sexual dimorphism regarding to the body size, in addition to finding polymorphisms in the coat color pattern. However, variations can perhaps be attributed to geographical features, not enough to separate populations taxonomic level. The age stratification also revealed significant differences in erythrocyte counts, the hemoglobin concentration, hematocrit, serum activity of alkaline phosphatase and GGT for young individuals. Enzymes such as AST, CK and LDH recorded significantly higher serum activity compared to captive studies. The percentages of T and B lymphocytes were 51 and 31% respectively, characterizing the predominance of lymphocytes with immunophenotype T. In the face of immune challenges that these animals are constantly subjected, it is reasonable that this immunological profile corresponds to the status "great" survivability
184

Conception d'une unité mobile pour le post-traitement d'eau utilisée pendant des opérations d'extinction d'incendie / Design of a mobile post-treatment unit for the water used during fire extinguishment

Baudequin, Clément 28 October 2011 (has links)
L’extinction de feux de liquides inflammables sur des installations industrielles telles que les dépôts de carburant ou les raffineries entraîne l'utilisation de milliers de mètres cubes d'eau, composé majeur des mousses anti-incendie. Ces dernières contiennent généralement des tensioactifs hydrocarbonés ainsi que des tensioactifs fluorés qui se retrouvent dans les eaux d'extinction, ainsi que les suies et les restes de solvants. Les tensioactifs fluorés jouent un rôle clé dans l'efficacité des mousses anti-incendie en raison de leur nature chimique particulière. En raison de la présence des tensioactifs fluorés, le traitement actuel de l'eau d'extinction d'incendie est l'incinération dans des incinérateurs haute température et résistant aux halogènes. Les tensioactifs sont des composés amphiphiles qui ont comme propriétés d'abaisser la tension superficielle de l'eau et de former des agrégats en solution : les micelles. Les tensioactifs peuvent également s'adsorber aux interfaces ainsi qu'aux surfaces solides, et éventuellement y former des agrégats de surface, analogues aux micelles en solution. L’objectif industriel de la présente thèse est de proposer une unité mobile de traitement de ces eaux afin de concentrer les composés fluorés et limiter les volumes à incinérer. Les critères de sélection des procédés que nous avons retenus sont les suivants : compacité, peu ou pas de produits chimiques ou solides nécessaires. L’objectif scientifique de ce travail est de mieux comprendre le comportement de ces composés au cours des procédés d’électrocoagulation/filtration et d’osmose inverse. Des essais préliminaires ont été réalisés et ont permis de choisir les procédés suivant : l'électrocoagulation couplée à la filtration comme prétraitement pour séparer les particules en suspension et les traces d’émulsions éventuelles de la phase aqueuse et l'osmose inverse comme traitement pour concentrer les tensioactifs fluorés. A l'échelle du laboratoire, l'électrocoagulation, permettant le retrait de la matière en suspension, a été optimisée pour des eaux d'extinction d'incendie pilotes et un mécanisme a été proposé. L'efficacité de ce procédé a ensuite été vérifiée sur un pilote industriel. L'osmose inverse d'eaux d'extinction d'incendie pilotes pré-traitées par électrocoagulation/filtration a montré de forts taux de rétention du tensioactif fluoré. Une comparaison de différents matériaux membranaires a été réalisée sur un module d’osmose inverse plan avec des solutions modèles. Des essais de filtration de longue durée, à l’échelle pilote, ont permis de suivre l’évolution de la rétention des tensioactifs et du flux de perméat. Ces données ont été utilisées pour réaliser le dimensionnement d’une unité mobile de post traitement d’eau d’extinction d’incendie. Les perspectives de ce travail sont les suivantes : La prise en charge de la réalisation d’une unité mobile devrait être menée par un partenaire de DuPont de Nemours qu’il reste à identifier. L’étude sur la modification de l’état de surface des membranes est poursuivie dans le cadre d’une nouvelle thèse et permettra à terme de mieux choisir les conditions opératoires de filtration et de nettoyage au cours des procédés membranaires et ainsi d’améliorer les performances du procédé. / Extinguishment of large solvent fire leads to the production of fire fighting water, which are collected thanks to the design of industrial infrastructures. Depending on the nature of the firefighting foam used, the resulting water may require the removal of fluorinated surfactants potentially present. After decantation of the organic phase, fire fighting waters essentially contain surfactants. Surfactants are amphiphilic chemicals having the ability to lower both interfacial and surface tensions by adsorbing in an oriented fashion at interface. Surfactant can form micellar aggregates in solution and on interfaces under certain conditions, and have a pronounced influence on interfacial phenomena. Hence, before considering any water treatment process, interfacial science and surfactant were introduced. This work has a dual purpose. The industrial purpose is to provide an economically viable alternative to water incineration. The foreseen unit will have to be mobile and able to extract fluorinated surfactants from water at a rate of 1-4.5 m3h-1 (20,000 m3 in 4-6 months). The scientific purpose of this work is the study of the behavior of surfactants in the context of water treatment processes. The state of the art of relevant water treatment processes and an experimental screening with real firefighting water permitted to identify two steps as likely to fit the constraints of a mobile unit: electrocoagulationfiltration coupled with reverse osmosis. The electrocoagulation process followed by filtration was applied to pilot, model and industrial firefighting waters. This process was found to remove efficiently the unwanted turbidity from pilot firefighting waters. Current knowledge about the separation mechanisms of small organic molecules in reverse osmosis has been reviewed, and rejection as well as flux decline were related to membrane, solution, and solute properties. Polyamide and cellulose acetate membrane materials were screened in a flat sheet cell. The stabilities of rejection and flux decline were confirmed during longer tests (several days) on an industrial pilot with the most appropriate membrane. A final design study confirmed the possibility to combine electrocoagulation-filtration and reverse osmosis to treat firefighting waters.
185

Transformismo e extinção: de Lamarck a Darwin / Transformation and extinction: from Lamarck to Darwin

Marcelo Alves Ferreira 17 September 2007 (has links)
A teoria da descendência com modificação de Darwin, que explica a origem de espécies através da seleção natural, é considerada um marco na história da ciência. A possibilidade de unificação de toda a biologia e a mudança que ela trouxe para nossos valores e para a nossa compreensão da posição da humanidade no universo ainda causam um grande impacto na sociedade e na relação entre ciência e filosofia. O objetivo do presente estudo é compreender alguns aspectos dos desenvolvimentos da ciência que antecederam essa teoria. Dois elementos foram estabelecidos como referências para essa análise: a teoria de Jean-Baptiste Lamarck, a mais importante a propor o conceito da transformação das espécies antes de Darwin e o problema científico da explicação da extinção. As várias teorias elaboradas para dar conta da diversidade de espécies na Terra, bem como para explicar o fenômeno da extinção são discutidas através das obras de Georges Cuvier, Geoffroy Saint-Hilaire e Richard Owen. Nessas teorias, as questões da adaptação e das noções teleológicas são destacadas devido à sua relação com o problema da extinção. A abordagem de Darwin para o problema da extinção é discutida em sua relação com o conceito de seleção natural e com o conceito de adaptação defendido pela teologia natural britânica. / Darwin\'s theory of descent with modification, which explains the origin of species by natural selection, is considered a milestone in the history of science. The possibility of unification of the entire field of biology and the changes that it brought to our values and to our understanding of the position of mankind in the universe are still causing great impact in society and in the relationship between science and philosophy. The aim of this study is to understand some aspects of the developments of science that preceded this theory. Two elements were established as references for this analysis: the theory of Jean-Baptiste Lamarck, the most important work proposing the concept of transformation of species before Darwin, and the scientific problem of the explanation of extinction. The several theories elaborated to account for the diversity of species on Earth as well as to explain the phenomenon of extinction are discussed through the works of Georges Cuvier, Geoffroy Saint-Hilaire and Richard Owen. Within these theories, the issues of adaptation and teleological notions are stressed because of their connection to the problem of extinction. Darwin\'s approach to the problem of extinction is discussed for its relation to the concept of natural selection and to the concept of adaptation defended by the british natural theology.
186

Redes tróficas do Pleistoceno: estrutura e fragilidade / Pleistocene trophic networks: structure and fragility

Mathias Mistretta Pires 10 March 2014 (has links)
A extinção de grandes mamíferos terrestres no final do Pleistoceno (entre 50 e 11 mil anos atrás) é um dos temas mais debatidos em ecologia. A maioria dos estudos sobre as causas das extinções do Pleistoceno tem como foco o papel de fatores externos como mudanças climáticas e a chegada do homem. Entretanto, a forma como uma comunidade ecológica responde a perturbações depende de suas propriedades, como o número e composição de espécies e a forma como essas espécies interagem. O objetivo final dos estudos reunidos nessa tese foi entender como estavam organizadas as interações ecológicas entre os mamíferos do Pleistoceno e o possível papel dessas interações no episódio de extinção da megafauna. Em primeiro lugar adaptei modelos de teias tróficas para reproduzir redes formadas por diferentes tipos de interações entre consumidores e recursos. Em seguida, utilizei esses modelos para reconstruir redes de interação entre predadores e presas da megafauna do Pleistoceno e examinei as propriedades estruturais e dinâmicas dessas redes. Por fim, investiguei uma das possíveis consequências da extinção da megafauna: a perda de serviços de dispersão de sementes. Os resultados aqui apresentados mostram que (i) diferentes tipos de redes de interação entre consumidores e recursos compartilham características estruturais e podem ser reproduzidas por modelos de teias tróficas; (ii) redes de interação entre grandes mamíferos do Pleistoceno estavam, provavelmente, estruturadas de forma similar aos sistemas atuais na África. Entretanto, as comunidades do Pleistoceno seriam especialmente vulneráveis às mudanças estruturais e na dinâmica causadas pela chegada de um predador como o homem; (iii) entre as consequências da extinção do Pleistoceno está a reorganização de outros tipos de rede de interação como as redes de dispersão de sementes. Em conjunto os resultados apresentados aqui enfatizam a importância de considerarmos o possível papel das interações ecológicas em modular os efeitos de perturbações ao estudarmos eventos de extinção / The extinction of large terrestrial mammals during the late Pleistocene (between 50 and 11 kyrs ago) is one of the most debated topics in ecology. Most studies on the causes of Pleistocene extinctions focus on the role of external factors such as climate changes and the arrival of humans. Nevertheless, the way an ecological community responds to perturbations depends on its properties, such as its number of species, species composition and the way these species interact. This thesis encloses studies with the final objective of understanding how ecological interactions between Pleistocene large mammals were organized and the potential role of such interactions in the Pleistocene extinction episode. First, I adapted food-web models to reproduce networks depicting different types of ecological interactions between consumers and resources. Then, I used these models to reconstruct predator-prey interaction networks between Pleistocene large mammals and examined the structural and dynamic properties of these systems. Finally, as an overview of the ecological impacts of Pleistocene extinctions, I discuss one of the possible consequences of the demise of Pleistocene large mammals: the loss of seed-dispersal services. The results presented here show that (i) different types of interaction networks between consumers and resources share structural properties and can be reproduced by food-web models; (ii) interactions between Pleistocene large mammals were most likely structured in a similar way to modern large-mammals assemblages in Africa, but the former were especially vulnerable to the changes in structure and dynamics caused by a newly arriving predator such as humans; (iii) among the consequences of Pleistocene extinctions is the reconfiguration of other types of interaction networks such as seed-dispersal networks. Taken together these findings emphasize how important it is to consider the role of ecological interactions in modulating the effects of perturbations when studying extinctions events
187

Chronic Stress Has Lasting Influences on Fear Extinction Cued Discrimination Early in Extinction That is Mediated by the Infralimbic Cortex

January 2020 (has links)
abstract: Post-Traumatic Stress Disorder (PTSD) is characterized by intrusive memories from a traumatic event. Current therapies rarely lead to complete remission. PTSD can be modeled in rodents using chronic stress (creating vulnerable phenotype) combined with fear conditioning (modeling a traumatic experience), resulting in attenuated extinction learning and impaired recall of extinction. Studies typically investigate cognition soon after chronic stress ends; however, as days and weeks pass (“rest” period) some cognitive functions may improve compared to soon after stress. Whether a rest period between chronic stress and fear conditioning/extinction would lead to improvements is unclear. In Chapter 2, male rats were chronically stressed by restraint (6hr/d/21d), a reliable method to produce cognitive changes, or assigned to a non-stressed control group (CON). After chronic stress ended, fear conditioning occurred within a day (STR-IMM), or after three (STR-R3) or six weeks (STR-R6). During the first three extinction trials, differences emerged in fear to the non-shock context: STR-R3/R6 showed significantly less fear to the context than did STR-IMM or CON. Differences were unlikely attributable to generalization or to second-order conditioning. Therefore, a rest period following chronic stress may lead to improved fear extinction and discrimination between the conditioned stimulus and environment. In Chapter 3, the infralimbic cortex (IL) was investigated due to the IL’s importance in fear extinction. Rats were infused with chemogenetics to target IL glutamatergic neurons and then assigned to CON, STR-IMM or STR-R3. During the rest period of STR-R3 and the restraint for STR-IMM, the IL was inhibited using CNO (1mg/kg BW, i.p., daily), which ended before behavioral testing. STR-R3 with IL inhibition failed to demonstrate a tone-shock association as spontaneous recovery was not observed. CON with IL inhibition behaved somewhat like STR-IMM; freezing to the extinction context was enhanced. Consequently, inhibiting IL function during the rest period following chronic stress was particularly disruptive for learning in STR-R3, impaired freezing to a safe context for CON, and had no effect in STR-IMM. These studies show that time since the end of chronic stress (recently ended or with a delay) can interact with IL functioning to modify fear learning and response. / Dissertation/Thesis / Doctoral Dissertation Psychology 2020
188

The Power of One Reinforcer

Hunter, Mary E. 08 1900 (has links)
Animal trainers use shaping to teach many behaviors. However, during shaping, the organism may engage in behaviors other than the target behavior or approximations to the target behavior. If the animal is engaged in other behaviors, the rate of reinforcement may decrease and the trainer may resort to what is sometimes referred to as a “desperation click.” That is, the trainer delivers one reinforcer for a behavior that is not a successive approximation to the target response. Anecdotal reports from trainers suggest that sometimes the animal continues to repeat this other behavior that received only one reinforcer, even in the absence of further reinforcement for that behavior. This study compared whether, during a one minute extinction period, participants spent more time engaged in a behavior that had been reinforced only once after a brief period of no reinforcement or in a behavior that had been reinforced multiple times. Participants, who were university students, played a tabletop game that involved touching and manipulating small objects. Five conditions were repeated twice for each participant: reinforcement for interacting with a training object alone, reinforcement for interacting with a training object with other objects present, reinforcement for interacting with a target object, one reinforcer for interacting with a third object immediately following a brief period of no reinforcement, and reinforcement for interacting with any object. Results from this study show that a desperation click situation can be reliably produced in a controlled setting. When participants received one reinforcer for interacting with a new object following a period of no reinforcement, they interacted with the new object for a longer or equal amount of time as compared to an object that had a history of reinforcement.
189

Enhanced mental reinstatement of exposure treatment to improve the generalization of learning in claustrophobia

Carpenter, Joseph K. 19 February 2021 (has links)
Exposure therapy is the gold standard treatment for anxiety disorders, but reductions in fear following exposure often do not generalize well outside the context in which they took place. This study tested a strategy for increasing generalization that involved revisiting the memory of a prior exposure experience in order to enhance the retrieval of the learning that occurred. Forty-five participants (29 females, 16 males) with claustrophobia received exposure training consisting of repeated 5-minute trials lying inside a narrow cabinet laid on its back. One week later, they were randomly assigned to either enhanced mental reinstatement (EMR) or control procedures. Results of the exposure training showed significant decreases in subjective fear, heart rate and avoidance in the training context, as well as reduced claustrophobia symptoms. As expected, fear levels in the mock MRI scanner one week later increased relative to the exposure training context post-treatment. Compared to the control condition, the EMR intervention led to significantly reduced heart rate reactivity in the mock MRI scanner, but not to reduced self-reported fear or avoidance of the mock scanner, nor to differences in claustrophobia symptoms at one-month follow-up. Expectancy violations about coping self-efficacy, measured via participants’ surprise about their ability to effectively cope during exposure, predicted lower fear in the mock MRI regardless of condition. Fear-related expectancy violations, reflecting greater discrepancy in expected vs. actual fear levels during exposure, predicted greater fear in the mock MRI. Results highlight the potential for mental reinstatement of exposure to improve generalization of learning in claustrophobia, though effects may be limited. The impact of expectancy violations on exposure outcomes may depend on the type of expectancy that is violated.
190

Translational Evaluation of History Effects on Resurgence

Talhelm, Paige L. 06 March 2019 (has links)
Resurgence is the reappearance of an extinguished operant response when an alternative behavior is subsequently treated with extinction (Podlesnik & Shahan, 2009). A potential solution to this problem is training serial alternative responses. During the present study, undergraduate students were trained to engage in an arbitrary response analogous to problem behavior and two alternative responses. Each response was reinforced for a distinct duration to establish different reinforcement histories and then tested under conditions of resurgence. The purpose of the present study was to evaluate the effects of duration of reinforcement on behavior subsequently exposed to resurgence contingencies. Three subjects engaged in the target response most often, five subjects engaged in alternative responses most often, and one subject engaged in all response equally during resurgence.

Page generated in 0.0999 seconds