Дисертації з теми "Right/left symmetry"

Dissertação para obtenção do Grau de Mestre em Genética Molecular e Biomedicina
We tend to view the vertebrate body as bilaterally symmetric, but in fact, this only happens from the outside. Internally, most of the organs from heart to liver are asymmetrically positioned. Skeleton and its associated muscles, symmetric structures of the vertebrate body, have its origins in the transient symmetric blocks of mesoderm called somites whereas the asymmetric morphogenesis of the internal organs is due to asymmetric gene expression in the lateral plate mesoderm (LPM). Previous studies using Morpholino (MO) technology have shown that dmrt2a is involved in these two processes in zebrafish. When Dmrt2a levels are reduced, asymmetric gene expression in the LPM becomes randomized and symmetric gene expression in the presomitic mesoderm (PSM) is disrupted. The paralogous of dmrt2a, the fish specific dmrt2b has been shown to be involved in regulating asymmetric gene expression in the LPM as well. Here we used the recent Transcription activator-like effector nucleases (TALENs) technology to generate dmrt2a and dmrt2b mutant alleles that will allow us in the future to uncover the downstream effectors of these transcription factors using high-throughput experiments. In addition, we overexpressed dmrt2a at the one-cell stage to characterize asymmetry versus symmetry phenotypes. The results show clearly the ability of TALEN technology to generate mutant alleles in zebrafish. Nevertheless, dmrt2a and dmrt2b homozygous mutants developed so far fail to recapitulate their previously described MO phenotypes which raise the question on what molecular mechanism(s) allow(s) zebrafish to cope with frameshift mutations. The overexpression of dmrt2a shows that a time window of opportunity during which symmetric embryonic territories are able to respond to asymmetric signals does exist during embryonic development.

La coordination des membres est un élément essentiel pour la marche terrestre chez les mammifères. Les mécanismes neuronaux et biomécaniques s'ajustent pour assurer le maintien d'un équilibre dynamique dans un environnement changeant. Lorsque le système est confronté à une perturbation persistante, la coordination des membres s'adapte. L'adaptation est définie comme un recalibrage du mouvement en réponse à une perturbation persistante ainsi que la présence d'après-effets une fois la perturbation disparue, ce qui indique que le nouveau patron a été entreposé dans le système nerveux central. Chez l'homme, le patron locomoteur s'adapte à une marche prolongée sur un tapis roulant partitionné, où l’une des jambes marche à une vitesse supérieure à l'autre, en rétablissant progressivement la symétrie des variables inter-jambes: périodes de double support et des longueurs des pas, ainsi qu’en réduisant l'amplitude de l'activité musculaire (EMG, électromyographie). L’objectif de notre étude était de déterminer si des chats intacts et des chats ayant subis une lésion complète de la moelle épinière (chat spinalisé) s’adaptent à la marche partitionnée prolongée. Pour caractériser l’adaptation locomotrice chez le chat intact et spinalisé, une prise de données cinématiques et électromyographiques des membres postérieurs a été effectuée chats intacts et les chats spinalisés, les longueurs de pas et les périodes de doubles supports étaient, en moyenne, symétriques, pendant la locomotion sur tapis roulant non-partitionné, et sont devenus asymétriques lors de la locomotion sur tapis roulant partitionné. Ces mesures inter-jambes sont demeurées asymétriques tout au long de la période de marche sur tapis roulant partitionné. Au retour à la marche sur tapis roulant non-partitionné, la symétrie a été immédiatement restaurée sans la présence d’après-effets. Chez les chats intacts, l'amplitude EMG moyenne des extenseurs a augmenté pendant la locomotion sur tapis roulant partitionné et elle est restée augmentée tout au long de cette période, alors que chez les chats spinalisés, l'amplitude EMG des membres postérieurs n'a pas changé. Ces résultats indiquent qu’il n’y a pas d’adaptation locomotrice chez le chat intact et spinalisé, ce qui suggère une importante différence physiologique dans le contrôle de la locomotion entre les chats et les humains lors d’une marche asymétrique prolongée. Par conséquent, nous proposons que la symétrie gauchedroite ne s’avère pas importante pour maintenir un équilibre dynamique pendant la locomotion asymétrique prolongée chez le chat, un quadrupède, comparé à l’humain adulte, un bipède.
Abstract : Coordination of the limbs is an essential component of terrestrial locomotion in mammals. When the system is confronted with persistent perturbations from the environment, the interlimb pattern learns to adapt. Adaptation is defined as a recalibration of the movement in response to a persistent perturbation as well as the presence of after-effects upon removal of the perturbation, indicating storage of the new pattern within the central nervous system. In humans, the pattern adapts to prolonged locomotion on a split-belt treadmill, where one leg steps faster than the other, by gradually restoring the symmetry of interlimb variables (double support periods, step lengths) and by reducing the amplitude of muscle activity (EMG, electromyography). The adaptation is also characterized by a reversal of the asymmetry of interlimb kinematic variables initially observed during the early split-belt period when returning to tied-belt locomotion (i.e. an after-effect). To assess the presence of locomotor adaptation, we measured intralimb (stance durations) and interlimb (double support periods, step lengths) variables bilaterally as well as EMG in the hindlimbs of intact and spinal-transected cats before, during and after 10 mins of split-belt locomotion. In both intact and spinal cats, step lengths and double support periods were, on average, symmetric, during tied-belt locomotion, and became asymmetric during split-belt locomotion. These interlimb variables remained asymmetrical throughout the split-belt period and upon returning to the tied-belt condition, left-right symmetry was immediately restored. In intact cats, the mean EMG amplitude of extensors increased during split-belt locomotion and remained increased throughout the split-belt period, while in spinal cats, hindlimb EMG amplitude did not change. The results indicate a lack of adaptation during prolonged split-belt locomotion in intact and spinal cats, suggesting an important physiological difference in the control of locomotion between cats and humans during prolonged asymmetric stepping. We propose that restoring left-right symmetry is not important to maintain dynamic balance during prolonged asymmetrical locomotion in the cat, a quadruped, as opposed to the adult human, a biped.

Bien qu'ayant beaucoup de succès pour décrire la grande variété de phénomènes de la physique des particules, le Modèle Standard (MS) laisse certaines propriétés de la nature sans explication. Ici, nous allons mettre l'accent sur le traitement différent des chiralités de type gauche et droite dans le cadre du MS. Une façon naturelle d'expliquer cela est de plonger le MS dans un modèle plus fondamental, capable de traiter les chiralités d'une manière symétrique. Cette classe de modèles, connue sous le nom de "modèles à symétrie droite-gauche" (LR models, en anglais), introduit une nouvelle interaction qui couple préférentiellement aux champs "droitiers". Puis, à une haute échelle d'énergie, la symétrie reliant droite et gauche est brisée spontanément donnant naissance au MS et aux phénomènes de violation de symétrie de parité. La manière spécifique par laquelle le mécanisme Brout-Englert-Higgs (BEH) se produit dans les modèles LR peut être sondée par des observables électrofaibles de précision, ce qui sert de premier test de l'extension du MS dans le secteur électrofaible. Comme conséquence du mécanisme BEH dans les modèles LR, de nouveaux bosons de jauge sont présents. Ce sont W’ et Z’, censés être beaucoup plus lourds que les bosons de jauge W et Z afin d'expliquer pourquoi ils n'ont jamais été vus jusqu'à présent. Ces nouvelles particules sont accompagnées d'une riche phénoménologie, comme de nouvelles sources de violation de CP au-delà de celle du MS. En outre, un nouveau secteur scalaire neutre introduit des courants qui changent la saveur (FCNC, en anglais) au niveau des arbres, un processus fortement restreint dans le MS, où il arrive seulement à l'ordre des boucles. L'existence de FCNCs fournit des contraintes extrêmement puissantes sur les modèles LR, et mérite donc une attention spéciale, en particulier lors du calcul des corrections venant de la QCD. Nous calculons donc les corrections au Next-to-Leading Order des effets à de courtes distances venant de la QCD aux contributions du modèle LR aux observables liées au mélange de mésons neutres et sensibles donc aux FCNC.Ensuite, nous considérons l'étude phénoménologique des modèles LR afin de tester leur viabilité et leur structure. Plus particulièrement, nous considérons le cas où des doublets scalaires sont responsables de la brisure du groupe de jauge des modèles LR. A cet effet, nous menons une étude combinée des observables de précision électrofaible, des bornes directes sur la masse des nouveaux bosons de jauge et des observables qui dérivent de l'oscillation des mésons neutres, dans le cas plus simple où la matrice de mixing dans le secteur droit est égal à la matrice CKM. Ces observables sont combinées dans le cadre du paquet CKMfitter d'analyse statistique. La combinaison de différentes classes d'observables doit prendre en compte la particularité des incertitudes théoriques, qui ne sont pas de nature statistique comme d'autres sources d'incertitude. A ce propos, nous considérons aussi la comparaison de différentes modèles d'incertitude théorique, afin de trouver des méthodes bien adaptées à la situation actuelle de notre connaissance des incertitudes théoriques impliquées dans un fit global en physique de la saveur
Though very successful in explaining a wide variety of particle physics phenomena, the Standard Model (SM) leaves unexplained some properties of nature. Here we focus on the different behaviours of left- and right-handed chiralities, or in other words the violation of parity symmetry. A possible and somewhat natural avenue to explain this feature is to embed the SM into a more symmetric framework, which treats the chiralities on equal footing. This class of models, the Left-Right (LR) Models, introduces new gauge interactions that couple preferentially to right-handed fields. Then, at an energy scale high enough, LR symmetry is spontaneously broken through the Brout-Englert-Higgs (BEH) mechanism, thus giving origin to the SM and to parity violating phenomena. The specific way in which the BEH mechanism operates in LR Models can be probed by EW Precision Observables, consisting of quantities that have been very accurately measured, serving as a first test of consistency for extensions of the SM in the EW sector. We revisit a simple realization of LR Models containing doublet scalars, and consider the phenomenological study of this doublet scenario in order to test the viability and structure of the LR Models. In particular, there is a rich phenomenology associated to the new gauge bosons W’ et Z’ introduced by LR Models, such as new sources of CP violation beyond the one of the SM. Moreover, the extended neutral scalar sector introduces Flavour Changing Neutral Couplings (FCNC) at tree level, which are strongly suppressed in the SM where they arrive first at one loop. FCNCs typically lead to extremely powerful constraints since they contribute to meson-mixing processes, and therefore deserve close attention. For this reason, we consider the calculation of short-distance QCD effects correcting the LR Model contributions to meson-mixing observables up to the Next-to-Leading Order (NLO), a precision required to set solid lower bounds on the LR Model scales. Finally, we combine in a global fit electroweak precision observables, direct searches for the new gauge bosons and meson oscillation observables in the simple case where the right-handed analogous of the CKM mixing-matrix is equal to the CKM matrix itself (a scenario called CKMfitter symmetry). The full set of the observables is combined by using the CKMfitter statistical framework, based on a frequentist analysis and a particular scheme for modeling theoretical uncertainties. We also discuss other possible modelings of theoretical uncertainties in a prospective study for future global flavour fits made by the CKMfitter Collaboration

Although there is no obvious communication between the left and right limb buds they develop to form bilaterally symmetrical structures of equal size (Summerbell & Wolpert, 1973). The underlying mechanisms that ensure symmetrical limb formation are unknown. Holt-Oram Syndrome (HOS) [OMIM 142900] is a congenital syndrome associated with mutations in TBX5 that lead to heart and upper limb defects. Strikingly, over 70% of HOS patients have left-biased upper limb defects. Using two separate strategies, I show that hypomorphic levels of Tbx5 in both the left and right forelimb buds produces forelimb defects that are consistently more severe in the left limb than the right. Using the INV/INV mutant background, in which the left-right axis is reversed, I show that the laterality of these defects is reversed in Tbx5 hypomorphic mutants with situs inversus. Additionally, I also show that transgenic expression of equal levels of Fgf10 in the forelimb buds of these Tbx5 hypomorphs can partially rescue outgrowth defects but not the left-bias asymmetry of their presentation. Together, this data suggests that Tbx5 has a role in ensuring symmetrical forelimb formation and that this is independent of its transcriptional regulation of Fgf10. Tbx4, the paralogue of Tbx5, is expressed in the hindlimb. I have used a conditional deletion approach to delete Tbx4 expression from the hindlimb area thus avoiding early embryonic lethality. I show that deletion of Tbx4 leads to a loss of proximal hindlimb skeletal elements as well as mispatterning of the distal hindlimb. I also show that Pitx1 partially contributes towards the establishment of the FGF signalling positive feedback loop during initiation of hindlimb bud outgrowth.

In this project I have studied the left-right symmetric model (LRSM) as a candidate beyond standard model theory of particle physics. The most common version of the theory, called the minimal LRSM, has been studied and tested extensively for several decades. I have therefore modied this minimal LRSM by adapting the scalar sector and computing the mass of the charged right-handed gauge bosons WR for this particular scalar sector. I carried out a study of the theory and implemented it into FeynRules, in order to simulate LHC events using MadGraph. This allowed computation of the cross-section for the decay WR to a top and a bottom quark as a function of the mass of WR , which was compared with CMS data for the same decay, with proton-proton collisions at a centre of mass energy of 13 TeV. The final result was a constraint on the mass of WR , with a lower bound of 3 TeV.

Nous nous sommes intéressés à la restauration de la symétrie de réflexion droite-gauche brisée dans certains calculs effectués en utilisant l'approche HTDA (Higher Tamm-Dancoff Approximation). Cette approche a été proposée par le groupe de Bordeaux pour traiter de façon microscopique les corrélations en conservant explicitement les nombres de nucléons. La projection sur la parité par la méthode PAV (projection après variation) utilisant une généralisation du théorème de Wick de type Löwdin s'est avérée être très bien adaptée dans le cadre d'un modèle simplifié pour ce type de calcul et a permis de tourner certaines difficultés propres aux calculs qui utilisent la théorie de la fonctionnelle de la densité déduite par exemple de l'interaction de Skyrme. Les résultats obtenus pour des noyaux lourds manifestant une déformation octupôlaire ou à tout le moins une grande déformabilité pour ce mode, sont en gros tout à fait cohérents avec les calculs antérieurs effectués dans une approche HFB ou HF+BCS. D'autre part nos résultats montrent qu'on peut abaisser par projection sur la parité positive la hauteur de la seconde barrière de fission par une quantité de l'ordre de 1 MeV
This thesis has been concerned with the restoration of the left-right symmetry broken in some instances. This has been achieved in the framework of the Higher Tamm-Dancoff Approximation (HTDA) proposed by the Bordeaux group to treat correlations in an explicitly particle-number conserving microscopic approach. The parity-projected calculations performed within a PAV (projection after variation) method using a generalized Wick's theorem due to Löwdin has appeared to be a very well-suited frame. It has been implemented within a simple model approach. This has been proposed to clear out some difficulties appearing when one uses an Energy Density Functional approach with an energy density functional issued from an underlying Skyrme interaction. As a result we obtain a fairly good global agreement of our results with previous ones issuing from an HFB approach or its HF+BCS limit, for some heavy nuclei exhibiting a stable octupole deformation or at least a remarkable smoothness for this collective mode. As another result, we have shown that the projection on a positive parity solution is able to reduce the second fission barrier height by about 1 MeV

Tout visage est structuré selon un ordre symétrique. La thèse explore les conséquences de cette spécificité formelle du visage sur la construction du portrait dans le contexte spécifique de la Renaissance. Elle débute par une remise en cause de l’approche neuropsychologique qui fait de la dissymétrie et de la partition du visage dans le portrait la simple expression d’un donné physionomique. À travers une réflexion autour de la symétrie et de la dissymétrie dans l’ordre de la représentation, notre recherche rend compte de l’intérêt de ces catégories esthétiques pour la compréhension des enjeux formels et philosophiques propres à la construction du portrait. Elle révèle également la richesse et la complexité des significations allouées à la symétrie et à la dissymétrie dans le cosmos culturel de la Renaissance, celles-ci allant parfois à contre-courant de nos représentations contemporaines. Une dernière partie de cette recherche est consacrée au symbolisme théologique séculaire distinguant entre le côté droit et le côté gauche du visage, un côté tourné vers le céleste, l’autre vers le terrestre, et à son influence sur l’art du portrait. La démonstration est rythmée par diverses études de cas, parmi lesquelles des analyses approfondies de portrait peints par Jan Van Eyck, Giovanni Bellini, Raphaël et Albrecht Dürer
Every face is structured in a symmetrical order. This research paper explores the consequences of this formal specificity on the construction of the portrait in the particular context of the European Renaissance. It starts with a critique of the neuropsychological approach that makes the asymmetry and the distinction between the two sides of the face in the portrait the mere expression of a particular physiognomy. Through a reflection on the aesthetic categories of symmetry and asymmetry in the order of representation, the research demonstrates the interest of these concepts for the understanding of the formal and philosophical issues specific to the construction of portraits. It also reveals the richness and complexity of meanings assigned to symmetry and asymmetry in the cultural cosmos of the Renaissance, these ones sometimes going against the grain of contemporary representations. The final section is devoted to the secular theological symbolism distinguishing between the right side and the left side of the face, one side turned to the heavenly, the other to the earthly, and the resulting influence on the art of portraiture. The demonstration is punctuated by various case studies, including an in-depth analysis of portraits painted by Jan Van Eyck, Giovanni Bellini, Raphael and Albrecht Dürer

Big Bang Nucleosynthesis (BBN), together with the analyses of the Cosmic Microwave Background (CMB) anisotropies, confirm what our day to day experience of life attests :antimatter is far less present than matter in the Universe. In addition, these observables also permit to evaluate that there exists about one proton for every 10^{10} photons present in the Universe. This is in contradiction with expectations coming from the standard hot big bang, where no distinction between matter and antimatter is made, and where subsequent annihilations would lead to equal matter and antimatter contents, at a level 10^{−10} smaller than the observed one. The Standard Model of fundamental interactions fails to explain this result, leading us to search for ‘Beyond the Standard Model’ physics.

Among the possible mechanism which could be responsible for the creation of such a matter asymmetry, leptogenesis is particularly attractive because it only relies on the same ingredients previously introduced to generate neutrino masses. Unfortunatelly, this elegant proposal suffers from a major difficulty :it resists to any tentative of being probed by our low energy observables. In this thesis, we tackle the problem the other way around and propose a way to falsify this mechanism. Considering the type-I leptogenesis mechanism, i.e. a mechanism based on the asymmetric decay of right-handed neutrinos, in a left-right symmetric framework, we show that the observation of a right-handed gauge boson W_R at future colliders would rule out any possibility for such mechanism to be responsible of the matter asymmetry present in our Universe.

Another intriguing question that analyses of the anisotropies of the CMB confirmed is the presence of a non-baryonic component of matter in our Universe, i.e. the dark matter. As hinted by observations of galactic rotation curves, it should copiously be present in our galactic halo, but is notoriously difficult to detect directly. We can take advantage on the fact that antimatter almost disappeared from our surroundings to detect the contamination of cosmic rays from standard sources the annihilation products of dark matter would produce.

The second subject tackled in this work is the study of the imprints the Inert Doublet Modem (IDM) could leave in (charged) cosmic rays, namely positrons, antprotons and antideuterons. This model, first proposed to allow the Bout-Englert-Higgs particle to evade the Electroweak Precision Test (EWPT) measurements, introduces an additional scalar doublet which is inert in the sense that it does not couple directly to fermions. This latter property brings an additional virtue to this additional doublet :since it interacts weakly with particles, it can play the role of dark matter. This study will be done in the light of the data recently released by the PAMELA, ATIC and Fermi-GLAST collaborations, which reported e^± excesses in two different energy ranges.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

In this thesis we study the production and decays of $W_R$ gauge bosons in several left-right symmetric models. We first use experimental constraints on the branching ratios of $b \to s \gamma$, $b \to c e {\bar \nu}_e$, and $B_{d,s}^0-\bar{B}^0_{d,s}$ mixing to restrict the parameter space of the model. We then analyze the branching ratios of $W_R$ and look for signals in $pp \to W_R\ t \to t ~(dijet)$ and show that the LHC could find a significant resonance for new gauge bosons. Finally, we analyze the top pair production and forward-backward asymmetry, and show that while the cross section at the Tevatron and the LHC are in agreement with the predictions of the model, the asymmetry observed at the Tevatron is inconsistent with LR model predictions, while the small asymmetry observed at the LHC is compatible with the model.