Le raisonnement conditionnel, fondé sur les énoncés de la forme Si P alors Q, est celui qui a reçu le plus d'attention de la part des psychologues. Les arguments principaux du raisonnement conditionnel, comme le Modus Ponens (MP), sont constitués de trois éléments : la prémisse majeure (Si P alors Q), la prémisse mineure (P) et la conclusion (Q). Ces éléments constituent trois étapes de traitement distinctes. Cependant, la dimension temporelle du raisonnement a été en partie négligée dans la littérature. L’objectif central de cette thèse a été d’explorer cette dimension temporelle à l’aide d’une approche novatrice combinant l’utilisation de la mesure du temps de lecture des prémisses, de l’Electroencéphalographie (EEG) et de la Magnétoencéphalographie (MEG). Nous nous sommes donné trois objectifs : 1) Déterminer la séquence des étapes de traitement élémentaire de l’argument MP ; 2) Déterminer comment l’incertitude d’un conditionnel thématique est prise en compte ; 3) Mettre en évidence les différences interindividuelles de traitement d’un énoncé conditionnel, basique ou thématique, en introduisant l’étude de l’argument AC qui permet de dissocier deux populations : les individus qui acceptent la conclusion de AC et les individus qui la rejettent.L’ensemble des données révèle que tous les individus ont une tendance à se focaliser davantage sur P que sur Q lors du traitement du conditionnel, avec des degrés variables selon les individus. Lorsque la prémisse P (ou Q pour les participants qui acceptent AC) est présentée, elle est intégrée à la prémisse majeure afin de générer une conclusion Q encodée et stockée en mémoire de travail avant d’être comparée avec la conclusion présentée.Lorsque le conditionnel est incertain (conditionnel thématique), cette incertitude sur la suffisance de P pour Q (ou de Q pour P) semble être prise en compte par les sujets au niveau de la prémisse majeure et se manifeste par une attente moins prononcée de la conclusion Q une fois que la prémisse P a été présentée. / The conditional reasoning, based on statements of the form If P then Q, is one which has received the most attention from psychologists. The main arguments of conditional reasoning, as the Modus Ponens (MP), consist of three elements: the major premise (If P then Q), the minor premise (P) and conclusion (Q). These elements constitute three separate processing steps. However, the temporal dimension of reasoning has been partly neglected in the literature. The central objective of this thesis was to explore the temporal dimension by using an innovative approach combining the use of the measurement of premises reading time and of the electroencephalography (EEG) and magnetoencephalography ( MEG). We set three objectives: 1) Determine the sequence of processing steps of the basic argument MP 2) Determine how the uncertainty of a conditional theme is taken into account, 3) Highlight the interindividual differences in treatment a conditional statement, or basic theme by introducing the study of the AC argument, which allows to separate two populations: individuals who accept the conclusion of AC and individuals who reject it. The data reveals that all individuals have a tendency to focus more on P and Q in the processing of the conditional, with varying degrees in different individuals. When the premise P (or Q for participants that accept AC) is presented, it is integrated with the major premise to generate a conclusion Q encoded and stored in working memory before being compared with the conclusions presented. When the conditional is uncertain (Thematic conditional), this uncertainty about the sufficiency of P for Q (or Q for P) seems to be taken into account by the subjects at the major premise and is manifested by an less pronounced expectation of Q conclusion when the premise P has been presented.

Symbiotic nitrogen fixation occurs in plants harboring nitrogen-fixing bacteria within the plant tissue. The most widely studied association is between the legumes and rhizobia. In this relationship the plant (legumes) provides the bacteria (rhizobia) with reduced carbon derived from photosynthesis in exchange for reduced atmospheric nitrogen. This allows the plant to survive in soil, which is low in available of nitrogen. Rhizobia infect and enter plant root and reside in organs known as nodules. In the nodules the bacteria fix atmospheric nitrogen. The association between the legume, Medicago truncatula and the bacteria Sinorhizobium meliloti, has been studied in detail. Medicago mutants that have defects in nodulation help us understand the process of nitrogen fixation better. One such mutant is the Mtnip-1. Mtnip-1 plants respond to S. meliloti by producing abnormal nodules in which numerous aberrant infection threads are produced, with very rare rhizobial release into host plant cells. The mutant plant Mtnip-1 has an abnormal defense-like response in root nodules as well as defects in lateral root development. Three alleles of the Mtnip/latd mutants, Mtnip-1, Mtlatd and Mtnip-3 show different degrees of severity in their phenotype. Phylogenetic analysis showed that MtNIP/LATD encodes a protein belonging to the NRT1(PTR) family of nitrate, peptide, dicarboxylate and phytohprmone transporters. Experiments with Mtnip/latd mutants demonstrats a defective nitrate response associated with low (250 μM) external nitrate concentration rather than high (5 mM) nitrate concentration. This suggests that the mutants have defective nitrate transport. To test if MtNIP/LATD was a nitrate transporter, Xenopus laevis oocytes and Arabidopsis thaliana mutant plants Atchl1-5, defective in a major nitrate transporter AtNRT1.1(CHL1), were used as surrogate expression systems. Heterologous expression of MtNIP/LATD in X. laevis oocytes and Atchl1-5 mutant plants conferred on them the ability to take up nitrate from external media with high affinity, thus demonstrating that MtNIP/LATD was a high affinity nitrate transporter. Km for MtNIP/LATD was determined to be approximately160 μM in the X. laevis system and 113 μM in the Arabidopsis Atchl1-5 mutant lines thus supporting the previous observation of MtNIP/LATD being a high affinity nitrate transporter. X. laevis expressing the mutant Mtnip-1 and Mtlatd, were unable to transport nitrate. However X. laevis oocytes, expressing the less severe mutant allele Mtnip-3 were able to transport nitrate suggesting another role of the Mtnip/latd besides high affinity nitrate transport. Experimental evidence suggested that MtNIP/LATD might transport another substrate beside nitrate. MtNIP/LATD levels are regulated by phytohormones. Experiments performed with ABA (abscisic acid), IAA (indole acetic acid) and histidine as substrates in X. laevis system show that the MtNIP/LATD mRNA injected oocytes efflux IAA but do not transport histidine or ABA. When wild type A17 and mutant Mtnip-1 and Mtnip-3 plants, grown in the presence of different sources of nitrogen were screened in herbicide chlorate, a structural analog of nitrate, the A17 and Mtnip-3 mutant showed levels of susceptibility that was different from mutant Mtnip-1 lines. Evidence suggested that the amount of chlorate transported into the plants were regulated by the C:N status of the A17 and Mtnip-3 plants. This regulation was missing in the Mtnip-1 lines thus suggesting a sensor function of MtNIP/LATD gene.

L'activation et la fonctionnalisation du diazote atmosphérique sont l'un des enjeux les plus importants de la chimie moderne. Celles-ci mènent à la formation industrielle d'ammoniac par le procédé Haber-Bosch, indispensable à l'agriculture actuelle. La forte demande énergétique de cette transformation a donc motivé la recherche académique pour découvrir de nouveaux catalyseurs capables de travailler dans des conditions plus douces, en s'inspirant des enzymes nitrogénases. Le but principal de ce travail doctoral a donc été la synthèse et l'étude de complexes de fer à bas degré d'oxydation portant un ligand triphosphine pouvant catalyser la formation d'ammoniac ou de silylamines à partir du diazote. Ce travail expérimental a été appuyé par des calculs théoriques grâce à l'utilisation de la DFT afin de pouvoir rationaliser les résultats obtenus. La première partie de ce manuscrit présente la synthèse des précurseurs métalliques utilisés ainsi que les premiers essais de réduction en utilisant des réactifs de Grignard. Au cours de celle-ci la formation d'un complexe de Fe0 bis-diazote a été prouvée. Sa synthèse de manière efficace et sa réactivité furent étudiées dans une deuxième partie. Ce complexe est l'un des rares catalyseurs au fer de la formation d'ammoniac en phase homogène, ainsi que l'un des plus actifs pour la formation de la silylamine N(TMS)3. En plus de cela, ce Fe0 est capable de déshydrogéner une partie de son ligand alcane ainsi que d'activer une autre molécule d'intérêt, le phosphore blanc. Cette nouvelle transformation entraîne la formation du premier complexe de fer cyclo-P4 terminal jamais rapporté et est abordée dans une troisième partie. Enfin, différents complexes portant à la fois un ligand diazote et des hydrures ont été étudiés au vu de leur pertinence par rapport à la nitrogénase. Cette partie a également permis d'utiliser un nouveau système basé sur un ligand de type PCP, dont la formation de la forme carbénique est possible par une double activation C-H grâce à un intermédiaire de Fe0. / Molecular nitrogen activation and functionalization are one of the most challenging topic in modern chemistry. The industrial formation of ammonia by the Haber-Bosch process, essential for current agriculture, is the starting point of this field. Indeed, the strong energetic need of this transformation has motivated academic research to find catalyst that can work in milder conditions as observed with nitrogenase enzymes. The principal goal of this Ph.D. work was the synthesis and the study of low oxidation states iron complexes bearing triphosphine ligand for the catalytic formation of ammonia and silylamines. This experimental work was supported by theoretical calculation using DFT in order to rationalize and understand the different results. The first part of this manuscript presents the metallic precursors synthesis and the first reduction attempts using Grignard reagents. During this part, the formation of an interesting Fe0 bis-dinitrogen complex was observed. Its efficient synthesis and reactivity was studied in a second part. This complex is one of the few homogeneous iron catalysts able to perform the formation of ammonia and one of the most active for N(TMS)3 formation. Furthermore, this Fe0 center is able to dehydrogenate an alkane part of its ligand and activate another small molecule of interest, white phosphorus. This new reaction leads to the firs example of the formation of an end-deck iron cyclo-P4 complex and is the subject of the third part. Finally, several iron complexes bearing dinitrogen and hydride ligand were studied in relevance with the nitrogenase enzyme. This part was an opportunity for a change toward a PCP-type ligand. The carbenic form of this ligand was reachable by double C-H activation at an intermediate Fe0 center.

This dissertation consists of a review of the N2 component of the ERP and five experiments investigating the role of complex visual object categorization in modulating the N2 and two other ERP components: the P300, and a late prefrontal positivity. In the review, we focus on paradigms that elicit N2 components with an anterior scalp distribution, namely cognitive control, novelty, and sequential matching, arguing that the anterior N2 should be divided into separate control- and mismatch-related subcomponents. The experiments manipulated categorical typicality and the presence of conflicting information as participants categorized multi-featured artificial animals. In Experiments 1 and 2, rule-irrelevant features were correlated with particular categories during training. During transfer, participants applied a one- dimensional rule to stimuli with category-congruent, category-incongruent, or novel rule-irrelevant features. Category-incongruent and novel features delayed RT and P300 latency, but had no effect on the N2. Experiment 3 used a two-dimensional rule to create conflict between rule-relevant features. Conflict resulted in prolonged RTs, P300 latency, and larger amplitudes of a prefrontal positive component, but had no impact on the N2. Novel features did enhance the N2 relative to frequent features. In Experiments 4 and 5, participants categorized stimuli using a more complex three dimensional rule. Conflicting stimuli shared two features with one prototype and one feature with a second prototype while prototypes contained no conflicting information. A third category contained stimuli with either common or novel features. Again, perceptual novelty, but not conflict, increased the amplitude of the N2. Compared to prototypes, stimuli with conflicting information slowed reaction times but had no effect on P300 latency, instead enhancing a late prefrontal positive component. These results suggest limitations on the generality of the N2's sensitivity to conflicting information, while confirming its sensitivity to attended visual novelty. We suggest that, while P300 latency tracks stimulus evaluation time, application of a complex categorization rule requires a later stage of evaluation involving prefrontal cortex. In very complex rules, computations indexed by the P3 may be terminated early in favor of computations in PFC.

Discrepant findings on whether children with autism display response inhibition deficits may be partially due to the wide variety of behavioral tasks used to assess inhibition. A more useful way of understanding early cognitive/attentional processes that influence response inhibition may be to look at neurophysiological measures. Specifically, the event related potential N2, a measurement of cognitive control or the effortful decision to inhibit a prepotent behavioral response, may be useful in understanding the discrepancy in response inhibition. In the current study we measured the N2 as high-functioning autistic children and age, IQ-matched control children performed a modified Flanker task. We further examined the associations between N2 amplitude and latency and variations in social communication within the HFA sample. Behavioral and electrophysiological data from a modified Flanker task were collected from 27 HFA (1 female) and 24 typically developing controls (1 female) ranging in age from 8- to 16-years. Symptom severity was measured using the ASSQ, ADI, and SCQ. Regarding behavioral performance, HFA children committed more errors than control children when controlling for age and verbal IQ. Electrophysiological performance indicated marginal group differences in N2 amplitude when controlling for age. Typical age-related decline in N2 amplitude was observed in the control group but not in the HFA group. There were no significant group differences found for N2 latency. In addition, greater N2 amplitude was correlated with lower scores on the SCQ for the HFA children. Behavioral performance does not conclude that the HFA children show deficits in inhibition, but deficits regarding impulsivity. Electrophysiological data suggest developmental change in N2 amplitude differentiates the HFA and control groups. Finally, the relationship between larger N2 amplitude and lower scores on the SCQ, within the HFA children, indicate that social communication deficits are less when greater cognitive effort is utilized.

The use of herbicides in cropping systems is routine in western Canada as is the practice of rotating crops between cereals, oilseeds and pulse crops. Often, herbicides that are appropriate one year in the crop rotation are not compatible with the following crop. Additionally, certain herbicides are designed to target certain enzyme pathways that can interfere with amino acid synthesis. These pathways also exist in the microbial community, including Rhizobium species. Rhizobia have a unique symbiotic relationship with legumes. In return for a carbon source, rhizobia not only fix atmospheric dinitrogen (N2) for the plant, but also can increase soil N reserves for the following year. With herbicides targeting amino acid synthesis in both plants and microbes, there is a possibility that N2 fixation may be inhibited by the application of certain herbicides.<p> This project was designed to examine possible negative effects of herbicide application on N2 fixation in field pea (Pisum sativum L.) and chickpea (Cicer arietinum L.). The study included field, growth chamber and laboratory experiments in which the effects of pre- and post-emergent herbicides, as well as herbicide residues in soil were examined.<p> In the field experiments, some early season measurements suggested that herbicide application had a negative impact on various growth and N2 fixation parameters. However, as the season progressed, plants recovered from early herbicide damage and N2 fixation ultimately was relatively unaffected. Growth chamber experiments similarly revealed that N2 fixation was largely unaffected by herbicide application when the application rates were relatively low (i.e., at rates intended to simulate partial herbicide breakdown, and thus lower than the recommended field rate). Although, N2 fixation was suppressed where high rates of herbicide (i.e., greater than recommended field rate) were applied, the efficiency of the rhizobia to fix N2, (i.e., the amount of N2 fixed per unit nodule mass), was unaffected. This along with a laboratory experiment which monitored growth of rhizobia in vitro, confirmed that rhizobia were not directly affected by the herbicides used in this study and that overall N2 fixation was not inhibited directly by the application of these herbicides. It was concluded that any negative impact on N2 fixation caused by herbicides used in this study, was related to the impact of the herbicide on crop growth, and was not due to any direct effects of the herbicide on the rhizobia.

The use of herbicides in cropping systems is routine in western Canada as is the practice of rotating crops between cereals, oilseeds and pulse crops. Often, herbicides that are appropriate one year in the crop rotation are not compatible with the following crop. Additionally, certain herbicides are designed to target certain enzyme pathways that can interfere with amino acid synthesis. These pathways also exist in the microbial community, including Rhizobium species. Rhizobia have a unique symbiotic relationship with legumes. In return for a carbon source, rhizobia not only fix atmospheric dinitrogen (N2) for the plant, but also can increase soil N reserves for the following year. With herbicides targeting amino acid synthesis in both plants and microbes, there is a possibility that N2 fixation may be inhibited by the application of certain herbicides.<p> This project was designed to examine possible negative effects of herbicide application on N2 fixation in field pea (Pisum sativum L.) and chickpea (Cicer arietinum L.). The study included field, growth chamber and laboratory experiments in which the effects of pre- and post-emergent herbicides, as well as herbicide residues in soil were examined.<p> In the field experiments, some early season measurements suggested that herbicide application had a negative impact on various growth and N2 fixation parameters. However, as the season progressed, plants recovered from early herbicide damage and N2 fixation ultimately was relatively unaffected. Growth chamber experiments similarly revealed that N2 fixation was largely unaffected by herbicide application when the application rates were relatively low (i.e., at rates intended to simulate partial herbicide breakdown, and thus lower than the recommended field rate). Although, N2 fixation was suppressed where high rates of herbicide (i.e., greater than recommended field rate) were applied, the efficiency of the rhizobia to fix N2, (i.e., the amount of N2 fixed per unit nodule mass), was unaffected. This along with a laboratory experiment which monitored growth of rhizobia in vitro, confirmed that rhizobia were not directly affected by the herbicides used in this study and that overall N2 fixation was not inhibited directly by the application of these herbicides. It was concluded that any negative impact on N2 fixation caused by herbicides used in this study, was related to the impact of the herbicide on crop growth, and was not due to any direct effects of the herbicide on the rhizobia.

The two atom switching reactions referred to in the title were originally studied at temperatures greater than 2000°K in shock tubes by other investigators. For each reaction they proposed a direct four-center exchange mechanism in which one of the reactant molecules must be vibrationally excited, (the vibrational excitation mechanism or VEM). One of the predictions of the VEM is that molecules which are vibrationally hot but translationally cold should react through the four center transition state that leads to exchange. Using a mercury photosensitization technique, it is shown in the present work that excitation of CO to high vibrational levels is not sufficient to cause the CO self-exchange reaction. Similar attempts were also made to verify the VEM for the N2 reaction, but no exchange was observed. Kinetic modeling studies show that an atomic chain mechanism triggered by traces of oxygen impurity is responsible for all or much of the CO exchange observed in the shock tubes. Modeling studies show that many of the observed features of the N2 reaction are also correctly predicted by an atomic chain mechanism; however, the critical step in the mechanism, the N + N2 exchange reaction, has never been observed. Potential surface calculations show that at the restricted Hartree-Fock level of approximation the N3 potential surface has an energy barrier for exchange of over 80 kcal/mole, which is much too high if the atomic mechanism is to operate in the shock tubes. By comparison with similar calculations on N2o+, it is argued that the RHF calculations probably overestimate the true barrier height by about 80 kcal/mole, so the barrier to exchange on the N3 potential surface is probably no more than a few kcal/mole, and the N + N2 reaction is probably fast at high temperatures. Potential surface calculations on N4 show that the barrier to exchange through the four-center transition state is almost certainly much too high to account for the exchange observed in the shock tubes. Certain limitations on the rate law and energy barrier to exchange are derived for the VEM. It is concluded that both exchange reactions can be explained by atomic chain mechanisms and there is no need to invoke the VEM for either reaction.

Upwelling, atmospheric nitrogen (N2) fixation by cyanobacteria, and freshwater inputs from the Mississippi River system have been shown to stimulate new production by alleviating nitrogen (N) limitation in the northern Gulf of Mexico (GoM). Stable carbon (delta13C) and nitrogen (delta15N) isotopes were used to investigate whether these sources are utilized differentially by coastal and marine pelagic food webs. Particulate organic matter (POM), Trichodesmium, and zooplankton were collected from the Mississippi River plume and Loop Current (LC) which were detected using remote sensing data. Stable isotope values were used to separate coastal and marine water masses and environmental data (salinity, nutrient and pigment concentrations) allowed me to relate variability to the degree of freshwater influence. Published food web data from these two environments were then assessed to establish whether isotopic baseline shifts observed in our data occur at an ecosystem level. Isotope values of the POM and zooplankton were found to be significantly different between coastal and marine water masses. This was not the case for Trichodesmium whose isotope values were not significantly different between the two water masses. We found that marine water masses (sal > 35) exhibited silicate concentrations, cyanobacterial pigments and DIN: P that suggest an increased abundance of diazotrophs. In contrast, coastal water masses (sal < 35) exhibited increased diatom pigments and molar C:N indicating terrestrial sources fuel phytoplankton production. When published food web data were compared, we found producer and consumer delta15N values were enriched in the coastal compared to the marine environments. This work suggests that differences in delta15N values within my data set and published data reflect a shift in the use of biologically available N where higher trophic levels are sustained by diazotrophic activity in marine environments versus those supported by terrestrial sources in coastal ones. Food webs that have been constructed without considering Trichodesmium as a significant source of organic matter in the GoM should be reconsidered. By re-evaluating published data, this research gives insight into the early life ecology of larval fishes and works to help answer questions about the structure and function of pelagic food webs.

Adults and young children have been found to distinguish between moral and social conventional acts, which are considered to entail distinct domains of reasoning (e.g., Turiel 1983). Recently, research has begun to examine the neural basis of moral judgments (e.g., Greene et al., 2001), but these studies did not examine the development of neurocognitive processing of judgments in these two domains. The present study focused on detection of cognitive conflict as a neurocognitive process that distinguished judgments of moral and conventional violations. The N2 component of the ERP was examined in order to determine whether the two types of violation are associated with different neurophysiological correlates and whether they change with development. In a series of five experiments, reaction times and ERPs were recorded from 12- to 14-year-old children and undergraduates who read scenarios that had one of three possible endings: (1) moral violations, (2) conventional violations, (3) no violation (neutral acts). Participants judged whether the act was acceptable or unacceptable when a rule was assumed or removed. Results indicate that reaction times were faster for moral than conventional violations when a rule was assumed for both undergraduates and children, as well as when a rule was removed for children but not for undergraduates. ERP data indicated that adults’, but not children’s, N2 amplitudes were larger (i.e., more negative) for conventional than iii moral violations when a rule was assumed. Furthermore, source analysis indicated generators for the N2 in dorsomedial and ventromedial prefrontal cortices. The results suggest that judgments of conventional violations involve increased conflict detection as compared to moral violations, and these two domains are processed differently across development. The findings were explained by the idea that judgments of conventional violations are more explicitly dependant on rules, whereas judgments of moral violations are based more directly on the intrinsic negative consequences of the act.