Binding Energies in Benzene Dimers: Nonlocal Density Functional Calculations

The interaction energy and minimum energy structure for different geometries of the benzene dimer has been calculated using the recently developed nonlocal correlation energy functional for calculating dispersion interactions. The comparison of this straightforward and relatively quick density functional based method with recent calculations can elucidate how the former, quicker method might be exploited in larger more complicated biological, organic, aromatic, and even infinite systems such as molecules physisorbed on surfaces, and van der Waals crystals.Comment: 17 pages, 6 figure

Développement de méthodes de calcul de coefficients de sensibilité des sections efficaces multigroupes autoprotégées et de sensibilité implicite du Keff aux densités isotopiques

Les codes de calculs déterministes utilisant un schéma de calcul multigroupe, il est nécessaire de procéder à des calculs d’autoprotection des résonances avant de procéder aux calculs de transport neutronique. Ces calculs donnent des sections efficaces multigroupes pour lesquelles les dépressions dans le flux aux énergies des résonances ont été adéquatement prises en compte. Pour chaque système pour lequel on veut faite un calcul de transport, on doit faire un calcul d’autoprotection préalable. Les sections efficaces multigroupes, pour les réactions résonantes, dépendent donc du système à analyser. Cela implique donc qu’une variation sur un paramètre du système, par exemple sur une densité isotopique, a un impact sur les sections multigroupes résonantes. Il devient alors pertinent de distinguer entre deux types d’effets résultant d’une variation d’un tel paramètre. Le paramètre en question peut apparaître explicitement dans l’équation de transport (par exemple, une densité entre dans cette équation à travers la section macroscopique du mélange correspondant) et ainsi causer une perturbation sur le keff (ou toute autre quantité obtenue en résolvant l’équation de transport). Il s’agit alors d’un effet explicite. Mais cette variation d’un paramètre peut aussi affecter les calculs d’autoprotection et perturber les sections efficaces résonantes multigroupes, qui à leur tour peuvent causer une perturbation sur le keff. C’est ce qu’on appelle un effet implicite. Ces effets implicites vont en général, pour diverses raisons, dans le sens contraire des effets explicites, c’est-à-dire qu’ils contribuent à une variation sur le keff ayant le signe opposé à celui de la contribution explicite. Quand une variation sur un paramètre entraîne une perturbation sur un autre paramètre, suite à un calcul de transport par exemple, on peut établir des coefficients de sensibilité entre les deux paramètres. Dans cette thèse, il sera question des sensibilités des sections efficaces autoprotégées et du keff aux différentes densités isotopiques. Plus précisément, on développe ici des méthodes permettant de calculer les coefficients de sensibilité des sections autoprotégées pour deux modèles d’autoprotection, un par dilution équivalente et un par sous-groupes. Une fois ces coefficients obtenus, on peut les combiner avec les coefficients de sensibilité du keff aux sections efficaces multigroupes pour obtenir des coefficients de sensibilité implicite du keff . Les méthodes de calcul de sensibilité de sections efficaces développées ici se basent sur un calcul des dérivées des probabilités de collision.----------Abstract Since deterministic codes use a multigroup scheme, self-shielding calculations are required before one can carry out neutron transport calculations. These calculations are used to obtain multigroup cross sections where flux depressions at resonance energies are properly taken into account. For each system where a transport solution is required, self-shielding calculations must be carried out beforehand. Multigroup cross sections in the resonant energy range are therefore system-dependent quantities. This means that a variation on a reactor parameter, an isotopic density for example, will have an impact on the resonant self-shielded cross sections. It is therefore relevant to distinguish between two types of effects resulting from a variation on a given parameter. This parameter can explicitly appear in the transport equation (for example, an isotopic density explicitly appears through the macroscopic cross sections of the corresponding mixture) and perturb the multiplication factor keff (or any other quantity obtained from solving the transport equation). This is called an explicit effect. This parameter variation can also affect self-shielding calculations and perturb resonant multigroup cross sections, which can themselves cause a variation of keff . This is what we refer to as an implicit effect. In general, the keff perturbations resulting from the implicit effect have the opposite sign of those resulting from the explicit effect. When a variation on a parameter leads to a perturbation on another parameter, following a transport calculation for instance, we can compute sensitivity coefficients between those two parameters. In this thesis, we consider the self-shielded cross sections and keff sensitivity coefficients to isotopic densities. More precisely, we develop methods to compute the selfshielded cross sections sensitivity to densities arising from two different self-shielding models, an equivalent dilution model and a subgroup model. Once these coefficients are known, they can be combined with the keff sensitivity coefficients to the multigroup cross sections to obtain the keff implicit sensitivity coefficients to the isotopic densities. The self-shielded cross sections sensitivity computation methods developed here are based on the computation of the derivatives of the collision probabilities. Both self-shielding models considered here are based on the computation of the collision probabilities. These probabilities are then used to solve the slowing-down equation for the flux to be used for the evaluation of the self-shielded cross sections. For both self-shielding models, we develop a sensitivity analysis method by analytically differentiating all the relevant equations and then solve for the derivatives of the self-shielded cross sections with respect to the isotopic densities

Interface p-n à base de cuprates supraconducteurs

Cette thèse porte sur l'exploration des propriétés de l'interface entre les deux cuprates supraconducteurs La1.85Sr0.15CuO4 et Pr1.85Ce0.15CuO4 réunis selon l'axe c sous la forme d'une bicouche. En particulier, on y démontre l'existence d'un phénomène de transfert de charge entre ces deux matériaux qui génère, à l'interface, une région isolante que nous surnommons le "plateau de Mott". Cette thèse couvre de nombreux sujets que l'on peut diviser en deux axes principaux. D'abord les aspects liés à la croissance et à la structure de la bicouche et ensuite les propriétés de transport de l'interface isolante. Dans un premier temps, une interface directe et franche entre ces deux cuprates de dopages opposés est réalisée via une optimisation de la croissance épitaxiale de ces matériaux en bicouche par ablation laser pulsé. La qualité cristalline des meilleurs échantillons obtenus est exceptionnelle, et ce, malgré l'important désaccord de maille entre les deux structures. La structure cristalline est ensuite principalement caractérisée par la diffraction des rayons X. Cette mesure permet d'obtenir des informations pertinentes sur la composition, l'homogénéité et les dimensions caractéristiques des couches minces. Le champ de déformation causé principalement par le désaccord de maille et la présence de dislocations à l'interface est également étudié. À cet effet, le formalisme de séparation des effets de taille et des déformations structurelles de Warren et Averbach est adapté au cas particulier des couches minces. L'accord frappant avec laquelle ce formalisme s'applique à nos résultats témoigne de la qualité des mesures expérimentales et de la netteté de ces structures. Afin d'expliquer la forme du champ de déformation mesuré, un modèle analytique basé sur la présence de dislocations d'interface est développé. Celui-ci nous permet, entre autres, d'extraire les paramètres caractéristiques du champ de déformation. Ces nouveaux outils d'analyse permettront sans doute de tirer davantage d'informations pertinentes de la diffraction des rayons X dans des projets futurs. La mise en évidence de l'existence du plateau de Mott et la caractérisation des propriétés sont menées via des mesures de résistance électrique. Plusieurs obstacles liés à la microfabrication des échantillons doivent d'abord être considérés. Le présent travail permet d'identifier un certain nombre de procédés qui provoquent une dégradation, parfois fatale, des propriétés des bicouches de cuprates. Dans certains cas, des solutions sont fournies ou suggérées. Les causes de ces dégradations sont généralement en lien avec la mobilité des atomes d'oxygène dans ces structures. Le savoir-faire développé ici pourra donc s'appliquer à l'étude des systèmes à base d'oxydes en général. Finalement, des mesures de transport électrique doublées du modèle analytique de la barrière ohmique permettent d'observer l'apparition d'une zone isolante à l'interface entre les cuprates supraconducteurs La1.85Sr0.15CuO4 et Pr1.85Ce0.15CuO4. Les propriétés de transport non linéaires et asymétriques en tension de cette interface indiquent qu'elle conduit principalement par effet tunnel. L'existence de cette barrière isolante est causée par un transfert de charge entre les deux matériaux à la manière d'une jonction p-n semi-conductrice. Par contre, dans ce cas-ci, la barrière isolante est le résultat d'une transition de Mott dans la zone d'appauvrissement ce qui lui vaut l'appellation de plateau de Mott

Utilisation du séquençage à haut débit dans l’identification des gènes prédisposant à l’épilepsie et aux syndromes neurocutanés

Epilepsy is a common neurological disorder affecting 1-3 % of the population. It is characterized by transitory neurological symptoms caused by excessive or synchronized abnormal neuronal activity—a seizure. Many factors can contribute to the etiology of epilepsy. It can be caused by genetic factors, morphological abnormalities, altered levels of biochemical molecules, excessive immune response in the brain, or by infections. Importantly, these factors are not mutually exclusive and can be caused by genetic aberrations. Thus, epilepsy associated with genetic mutations can be part of a complex symptomatology including several monogenic disorders such as progressive myoclonus epilepsies and neurocutaneous syndromes. The first objective of this thesis is to use modern sequencing methods in order to identify genetic causes of rare forms of epilepsies and neurocutaneous syndrome. Firstly, we studied Kufs disease, an adult form of neuronal ceroid lipofuscinosis, part of the progressive myoclonus epilepsies. The study of two American families and one sporadic case led us to identify two causative mutations (p.L116del, p.L115R) in the gene DNAJC5. Other families with this rare but fatal syndrome were reported with mutations in that gene, corroborating our findings. The gene DNAJC5 encodes for the cysteine string protein alpha (CSPα), a presynaptic protein involved in neurodegeneration. Secondly, using the same methods, we discovered the causative mutation for the Giroux-Barbeau syndrome, a neurocutaneous syndrome characterized by spinocerebellar ataxia and erythrokeratodermia variabilis. Thus, following the study of a large French Canadian family, we found the p.L168F mutation in the gene ELOVL4. This gene encodes an enzyme involved in the metabolism of very long chain fatty acid. These fatty acids participate in a wide variety of physiological functions, including skin barrier formation and peroxisome β-oxidation. The second objective of this work is to use whole exome sequencing in the context of molecular diagnostics. To achieve that, we studied a large family presenting skin lesions at the extremities following exposure to cold. Initially diagnosed as a primary form of cryofibrinogenemia, our work showed that these patients were affected with an atypical form of chilblain lupus. In turn, the phenotypical resemblance as well as the presence of the p.D18N mutation in the gene TREX1 led to that new diagnosis. This study shows the role of whole exome sequencing in the diagnosis of rare disease and widen the phenotypic spectrum associated with TREX1 mutations. The last objective of this research is to apply whole exome sequencing in the discovery of genetic mechanisms predisposing to genetic generalized epilepsy (GGE). For this study, we recruited 7 large families with GGE. We showed that variants found in the genes GLI2, MBD5, CELSR2, CELSR3, TNIK and CACNA1G could participate in the genetic etiology in our families. However, because of the numbers of variants identified, other factors could contribute to the epileptic phenotype in our families. Other large scale studies are necessary in order to validate the implication of those genes in epilepsy

Viscous photons in relativistic heavy ion collisions

Theoretical studies of the production of real thermal photons in relativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) are performed. The space-time evolution of the colliding system is modelled using MUSIC, a 3+1D relativistic hydrodynamic simulation, using both its ideal and viscous versions. The inclusive spectrum and its azimuthal angular anisotropy are studied separately, and the relative contributions of the different photon sources are highlighted. It is shown that the photon v2 coefficient is especially sensitive to the details of the microscopic dynamics like the equation of state, the ratio of shear viscosity over entropy density, eta/s, and to the morphology of the initial state.Comment: 15 pages, 12 figures. References updated and discussion adde

Mixed pairing symmetry in \kappa-(BEDT-TTF)_2 X organic superconductors from ultrasonic velocity measurements

Discontinuities in elastic constants are detected at the superconducting transition of layered organic conductors \kappa-(BEDT-TTF)_{2}X by longitudinal and transverse ultrasonic velocity measurements. Symmetry arguments show that discontinuities in shear elastic constants can be explained in the orthorhombic compound only if the superconducting order parameter has a mixed character that can be of two types, either A_{1g}+B_{1g} or B_{2g}+B_{3g} in the classification of irreducible representations of the orthorhombic point group D_{2h}. Consistency with other measurements suggests that the A_{1g}+B_{1g} (d_{xy}+d_{z(x+y)}) possibility is realized. Such clear symmetry-imposed signatures of mixed order parameters have not been observed in other superconducting compounds.Comment: 5 pages, LaTeX,3 figure

Mixed pairing symmetry in \kappa-(BEDT-TTF)_2 X organic superconductors from ultrasonic velocity measurements

Discontinuities in elastic constants are detected at the superconducting transition of layered organic conductors \kappa-(BEDT-TTF)_{2}X by longitudinal and transverse ultrasonic velocity measurements. Symmetry arguments show that discontinuities in shear elastic constants can be explained in the orthorhombic compound only if the superconducting order parameter has a mixed character that can be of two types, either A_{1g}+B_{1g} or B_{2g}+B_{3g} in the classification of irreducible representations of the orthorhombic point group D_{2h}. Consistency with other measurements suggests that the A_{1g}+B_{1g} (d_{xy}+d_{z(x+y)}) possibility is realized. Such clear symmetry-imposed signatures of mixed order parameters have not been observed in other superconducting compounds.Comment: 5 pages, LaTeX,3 figure

Can ‘Hebb’ Be Distracted? Testing the Susceptibility of Sequence Learning to Auditory Distraction

Sequence learning plays a key role in many daily activities such as language and skills acquisition. The present study sought to assess the nature of the Hebb repetition effect—the enhanced serial recall for a repeated sequence of items compared to random sequences—by examining the vulnerability of this classical sequence-learning phenomenon to auditory distraction. Sound can cause unwanted distraction by either interfering specifically with the processes involved in the focal task (interference-by-process), or by diverting attention away from a focal task (attentional capture). Participants were asked to perform visual serial recall, in which one to-be-remembered sequence was repeated every four trials, while ignoring irrelevant sound. Whereas both changing-state (Experiment 1) and deviant sounds (Experiment 2) disrupted recall performance compared to steady-state sounds, performance for the repeated sequence increased across repetitions at the same rate regardless of the sound condition. Such findings suggest that Hebbian sequence learning is impervious to environmental interference, which provides further evidence that the Hebb repetition effect is an analogue of word-form learning

The children’s eating attitudes test: French validation of a short version

Purpose : Disordered eating attitudes and behaviors (DEAB) in childhood have been prospectively associated with eating disorders and obesity in adolescence. Therefore, evaluating DEAB in children with a reliable, sensitive and well-adapted scale is very important. The Children’s Eating Attitudes Test (ChEAT) is one of the most popular measuring tools for DEAB in children, but no French version is available. Moreover, while completion time is an important factor to be considered when working with children, only one recent study proposed a shorter version of the ChEAT. Taking the previous works of Murphy and colleagues (2019) as a starting point, the current study aimed to provide the first French-speaking validated 14-item short version of the ChEAT. Methods : A sample of 1092 boys and girls aged between 8 and 12 years old were recruited in two urban areas in the province of Quebec, Canada. They completed the ChEAT, and their height and weight were measured at school. Factorial structure and internal consistency were assessed. Results : After the initial factorial analysis, two “vomiting (or purging)” items were yielded as problematic and were thus removed from the analysis. The remaining 12 items provided a good fit to the data and a good internal consistency. Moreover, the factorial structure was proved to be invariant across sexes. Conclusion : This study is the first to provide a French assessment of DEAB in elementary school children. The French short version of the ChEAT provided a quick and reliable assessment for DEAB with non-clinical children population and could be used as a screening tool, even though no cut-off was established yet. Level of evidence : Cross-sectional, descriptive study, Level V