AliFreeFoldMulti : une méthode sans alignement pour prédire les structures secondaires d'ARN homologues

Prédire la structure d'un ARN est crucial pour la compréhension du mécanisme d'action de l'ARN. Les approches comparatives pour la prédiction de structures d'ARN peuvent être classées en quatre stratégies. Les trois premières, «aligner-et-replier», «aligner-puis-replier» et «replier-puis-aligner», exploitent des alignements multiples de séquences et/ou de structures pour améliorer la précision de la prédiction de la structure d'ARN conservée. Les méthodes «aligner-et-replier» performent généralement mieux, mais sont aussi typiquement plus lentes que les deux autres approches. La quatrième stratégie «sans-alignement», consiste à la prédiction de la structure de l'ARN conservée sans s'appuyer sur l'alignement de séquences ou de structures. Cette stratégie a l'avantage d'être plus rapide, tout en prédisant des structures précises grâce à l'utilisation de représentations latentes des structures candidates pour chaque séquence. Cet article présente aliFreeFoldMulti, une extension de l'algorithme d'aliFreeFold. Ce dernier prédit une structure secondaire représentative de plusieurs ARN homologues en utilisant une représentation vectorielle de leurs structures sous-optimales. aliFreeFoldMulti améliore aliFreeFold en calculant en plus la structure conservée pour chaque séquence. aliFreeFoldMulti est évaluée en comparant ses performances de prédiction et son efficacité de temps avec un ensemble de méthodes de prédiction de la structure d'ARN. aliFreeFoldMulti a les temps de calcul les plus bas et les scores de précision maximum les plus élevés. Il atteint une précision de prédiction de structures moyenne comparable à celle d'autres méthodes, à l'exception de TurboFoldII qui est la meilleure en termes de précision moyenne mais avec les temps de calcul les plus élevés. Nous présentons aliFreeFoldMulti comme une illustration du potentiel des approches «sans-alignement» pour fournir des méthodes rapides et précises de prédiction de la structure d'ARN.Le sujet de ce mémoire est la prédiction de structures secondaires de familles d’ARN homologues. La structure secondaire d’une séquence d’ARN non-codant définit généralement la fonction de cet ARN au sein de la cellule. Dans cette maîtrise, nous avons développé un nouvel algorithme sans alignement pour prédire la structure secondaire de chacune des séquences d’ARN d’une famille d’ARN non-codants. Cet outil, aliFreeFoldMulti, est une extension d’un outil qui a été précédemment développé au sein du laboratoire CoBIUS, soit aliFreeFold. Initialement, aliFreeFold permet de prédire une seule structure secondaire représentative pour une famille de séquences d’ARN homologues. Avec les algorithmes développés dans cette maîtrise, aliFreeFoldMulti a la capacité de retourner une structure secondaire prédite pour chacune des séquences d’ARN qui composent une famille. Quatre stratégies ont été développées afin d’explorer de nouvelles approches pour prédire des structures secondaires à partir d’aliFreeFold. En comparant l’outil aliFreeFoldMulti avec les différents outils existants permettant de faire de la prédiction de structures secondaires de plusieurs séquences d’ARN homologues, aliFreeFoldMulti est le plus rapide et retourne des scores du même ordre de grandeur que les autres méthodes et les scores maximaux les plus élevés. Une analyse approfondie des résultats d’aliFreeFoldMulti permet de mettre en évidence le potentiel des méthodes sans alignement pour la prédiction de structures secondaires d’ARN

Achieving Media Responsibilities in Multicultural Societies

This resource pack of information material and advocacy briefs consists of 5 leaflets. The first three leaflets deal respectively with the international legal standards, with a regional cross section of the issues concerned as well as effective practices of interaction between media, media structures and citizen's organisations. The last two leaflets provide recommendations addressed to media, media regulatory bodies, national and international institutions and non-governmental organisations and set out principles for journalists and editors for ethical and professional coverage of ethnic issues

Triplet-pair states in exciton fission and fusion

In this thesis, we present our investigations into the intermediate triplet-pair states that mediate the twin photophysical processes of singlet fission and triplet fusion. Unique to certain conjugated organic materials, singlet fission and triplet fusion refer to the splitting of bright, spin-0 singlet excitons into pairs of dark, spin-1 triplet excitons, and vice versa. First invoked more than 50 years ago, the triplet-pair states that mediate these processes have recently enjoyed a resurgence of interest, largely due to the realisation that exciton fission and fusion could be harnessed in photovoltaic devices to exceed the theoretical power conversion efficiency limit. Despite great progress in our understanding of these intriguing states, many aspects of their nature and behaviour remain unclear. We begin by probing the photoluminescence signatures of the strongly exchange-coupled spin-0 triplet-pair state, 1(TT), in polycrystalline films of diF-TES-ADT and single crystals of pentacene, demonstrating that it is a real, observable intermediate state. We then present brief investigations of 1(TT) photoluminescence, or lack thereof, and 1(TT) formation in rubrene single crystals. Our results here cast doubt on the vibronic coherent mechanism of singlet fission and highlight the role of defect sites and disorder. Next, we turn to the spin statistical factor governing the probability of obtaining a spin-0 state from the annihilation of two spin-1 triplets and explain why it has been incorrectly described in much of the recent literature. Using rubrene as a model system, we investigate the key parameters affecting this important quantity and uncover previously overlooked strategies for engineering materials with favourable spin statistics. Finally, we investigate the photophysics of rubrene nanoparticles for photon upconversion. We show that the addition of a singlet energy collector, used to improve the upconversion quantum yield, does not suppress singlet fission as previously assumed but instead competes with triplet-pair separation

Investigation of potential extreme load reduction for a two-bladed upwind turbine with partial pitch

This paper presents a wind turbine concept with an innovative design combining partial pitch with a two-bladed (PP-2B) turbine configuration. Special emphasis is on extreme load reduction during storm situations at standstill, but operational loads are also investigated. In order to compare the loads and dynamics of the PP-2B turbine, a partial pitch three-bladed (PP-3B) turbine and a normal pitch regulated three-bladed (3B) turbine are introduced on the basis of solidity similarity scaling. From the dynamic comparisons between two- and three-bladed turbines, it has been observed that the blade vibrations are transferred differently from the rotor to the tower. For a three-bladed turbine, blade vibrations seen in a fixed frame of reference are split with ±1P only. A two-bladed turbine has a similar split of ±1P but also includes contributions on higher harmonics (±2P, ±3P, ... etc.). Further on, frequency split is also seen for the tower vibrations, where an additional ±2P contribution has been observed for the two-bladed turbine. Regarding load comparisons, the PP-2B turbine produces larger tower load variations because of 2P excitation during the operational cases. However, extreme loads are reduced by approximately 20% for the PP-2B and 18% for the PP-3B compared with the 3B turbine for the parked condition in a storm situation. Moreover, a huge potential of 60% is observed for the reduction of the extreme tower bottom bending moment for the PP-2B turbine, when the wind direction is from ±90° to the turbine, but this also requires that the turbine is parked in a T-configuration

Analysis and design of Coleman transform-based individual pitch controllers for wind-turbine load reduction

As the size of wind turbines increases, the effects of dynamic loading on the turbine structures become increasingly significant. There is therefore a growing demand for turbine control systems to alleviate these unsteady structural loads in addition to maintaining basic requirements such as power and speed regulation. This has motivated the development of blade individual pitch control (IPC) methodologies, many of which employ the Coleman transformation to simplify the controller design process. However, and as is shown in this paper, the Coleman transformation significantly alters the rotational system dynamics when these are referred to the non-rotating frame of reference, introducing tilt-yaw coupling in the process. Unless this transformation is explicitly included in the model employed for IPC design, then the resulting controllers can yield poor performance. Therefore, in this paper, we show how to model the Coleman transformation in a form that is amenable to IPC analysis and synthesis. This enables us to explain why traditional design parameters of gain and phase margin are poor indicators of robust stability and hence motivate the need for a multivariable design approach. The robust multivariable IPC approach advocated in this paper is based upon H∞ loop shaping and has numerous desirable properties, including reliable stability margins, improved tilt-yaw decoupling and simultaneous rejection of disturbance loads over a range of frequencies. The design of a robust multivariable IPC is discussed, and simulation results are presented that demonstrate the efficacy of this controller, in terms of load reduction on both rotating and non-rotating turbine parts

Supplementing wind turbine pitch control with a trailing edge flap smart rotor

Placement of additional control devices along the span of the wind turbine blades is being considered for multi-MW wind turbines to actively alter the local aerodynamic characteristics of the blades. This smart rotor approach can reduce loads on the rotor due to wind field non-uniformity, but also, as presented in this paper, can supplement the pitch control system. Rotor speed and tower vibration damping are actively controlled using pitch. By supplementing the speed control using smart rotor control, pitch actuator travel is reduced by 15 pitch rates by 23 and pitch accelerations by 42 This is achieved through filtering the pitch demand such that high frequency signals are dealt with by the smart rotor devices while the low frequency signal is dealt with by pitching the blades. It is also shown that this may be achieved while also using the smart rotor control for load reduction, though with reduced effectiveness. This shows that smart rotor control can be used to trade pitch actuator requirements as well as load reductions with the cost of installing and maintaining the distributed devices

Un Intrus dans l’édition : l’artiste comme créateur de livres

Récemment publié, Esthétique du Livre d’Artiste 1960-1980, est un véritable tour de force. Il s’agit en effet de la première étude en profondeur de l’utilisation, depuis ses origines, de techniques d’imprimerie peu coûteuses, dont notamment la lithographie offset, par des plasticiens, pour créer des livres d’artiste – à savoir des œuvres d’art sous forme de livres – diffusés à bas prix. Cet ouvrage retrace également le développement rapide de publications à travers lesquelles des artistes ont..

Fault-tolerant individual pitch control using adaptive sliding mode observer

Due to the increasing size of wind turbines, the unbalanced loads caused by the uneven spatial distribution of wind speed and turbulence are becoming larger and larger. As has been proved, individual pitch control (IPC) can mitigate the blade asymmetric loads greatly in region 3. On the other hand, the pitch actuator faults can affect the pitching performance with slow dynamics, resulting in generator power instability and even deteriorating the unbalanced loads of blades. However, the effects of unbalanced blade loads deterioration caused by pitch actuator faults have not been taken into account by the traditional IPC design. In the present paper, a fault-tolerant control (FTC) strategy using adaptive sliding mode estimation is combined with a traditional IPC system based on two different control methods (Proportional-Integral and H∞ loop-shaping). It maintains the nominal pitch performance and removes the negative effects of pitch actuator faults on generator power and unbalanced blade loads perfectly. The effectiveness of the proposed strategy is verified on the 5MW NREL wind turbine system