Storytime with an iPad

Storytime using iPads?? How is this possible? Let Ramsey County Library show you how you can use the technology of the iPad along with pre-selected apps to explore early literacy with your preschool-aged patrons and their caregivers. The library\u27s eTot Storytime was introduced to patrons in the fall and has given families the opportunity to try out the iPad with their young children, focusing on literacy and reading through librarian-led and guided storytimes

Onset and stabilization of delay-induced instabilities in piezoelectric digital vibration absorbers

The stability of a piezoelectric structure controlled by a digital vibration absorber emulating a shunt circuit is investigated in this work. The formalism of feedback control theory is used to demonstrate that systems with a low electromechanical coupling are prone to delay-induced instabilities entailed by the sampling procedure of the digital unit. An explicit relation is derived between the effective electromechanical coupling factor and the maximum sampling period guaranteeing a stable controlled system. Since this sampling period may be impractically small, a simple modification procedure of the emulated admittance of the shunt circuit is proposed in order to counteract the effect of delays by anticipation. The theoretical developments are experimentally validated on a clamped-free piezoelectric beam

RAD54 family translocases counter genotoxic effects of RAD51 in human tumor cells.

The RAD54 family DNA translocases have several biochemical activities. One activity, demonstrated previously for the budding yeast translocases, is ATPase-dependent disruption of RAD51-dsDNA binding. This activity is thought to promote dissociation of RAD51 from heteroduplex DNA following strand exchange during homologous recombination. In addition, previous experiments in budding yeast have shown that the same activity of Rad54 removes Rad51 from undamaged sites on chromosomes; mutants lacking Rad54 accumulate nonrepair-associated complexes that can block growth and lead to chromosome loss. Here, we show that human RAD54 also promotes the dissociation of RAD51 from dsDNA and not ssDNA. We also show that translocase depletion in tumor cell lines leads to the accumulation of RAD51 on chromosomes, forming complexes that are not associated with markers of DNA damage. We further show that combined depletion of RAD54L and RAD54B and/or artificial induction of RAD51 overexpression blocks replication and promotes chromosome segregation defects. These results support a model in which RAD54L and RAD54B counteract genome-destabilizing effects of direct binding of RAD51 to dsDNA in human tumor cells. Thus, in addition to having genome-stabilizing DNA repair activity, human RAD51 has genome-destabilizing activity when expressed at high levels, as is the case in many human tumors

Piezoelectric digital vibration absorbers for vibration mitigation of bladed structures

Climate change and resource scarcity pose increasingly difficult challenges for the aviation industry requiring a reduction in fossil fuel consumption. To address these problems and increase the efficiency of aircraft engines, some of their parts are now manufactured in one piece. For example, a rotor of the compressor stage of an airplane engine consist of a drum with a large number of blades and is called BluM. These structures are lightweight and feature low structural damping and high modal density. Their particular dynamic characteristics require sophisticated solutions for vibration mitigation of these structures. This is precisely the starting point of this thesis. Based on a digital realization of piezoelectric shunt circuits, we provide a damping concept that is able to tackle the complex dynamics of bladed structures and to mitigate their vibrations. To this end, multiple digital vibration absorbers (DVAs) are used simultaneously. Two new strategies to tune these DVAs are proposed in the thesis, namely the isolated mode and mean shunt strategies. These strategies not only take advantage of the fact that multiple absorbers act simultaneously on the structure, but they also address the problem of closely-spaced modes. In order to target multiple families of BluM modes, these strategies are incorporated in a multi-stage shunt circuit. The concepts are demonstrated experimentally using two bladed structures with increasing complexity, namely a bladed rail and a BluM. Both methods exhibit excellent damping performances on multiple groups of modes. In addition, they prove robust to changes in the host structure which could, e.g., be due to mistuning. Thanks to their digital realization, DVAs are also easily adjustable. Finally, this thesis reveals the parallel that exists between resonant piezoelectric shunts with a negative capacitance and active positive position feedback (PPF) controllers. Based on this comparison, a new H∞ norm-based tuning rule is found for a PPF controller. It is demonstrated using both numerical and experimental cantilever beams. To this end, a method that accounts for the influence of modes higher in frequency than the targeted one is developed.Le changement climatique et la raréfaction des ressources posent des défis de plus en plus complexes à relever pour l'industrie aéronautique. Un de ces défis est la réduction de la consommation en énergies fossiles. Pour accroître l'efficacité des moteurs d'avion, certains de leurs composants sont désormais fabriqués en une seule pièce. Dans le cas des compresseurs, ces pièces monoblocs sont appelées BluMs et sont constituées d’un tambour avec un grand nombre d'aubes. Ce type de structures bénéficie d'un allègement significatif, ce qui conduit à un faible amortissement structurel. De plus, ces pièces monoblocs présentent une densité modale élevée en raison du nombre important de diamètres nodaux. Ces caractéristiques dynamiques particulières nécessitent des solutions d'amortissement sophistiquées. Cette thèse de doctorat aborde cette problématique. En exploitant le concept d'absorbeur de vibration digital (DVA), nous proposons une nouvelle technique d'amortissement des structures aubagées. Deux nouvelles stratégies d'accordage de ces DVA sont développées dans cette thèse, à savoir la stratégie du mode isolé et la stratégie du shunt moyen. Ces méthodes tirent non seulement parti du fait que plusieurs absorbeurs agissent simultanément sur la structure, mais elles s'attaquent aussi au problème des modes proches en fréquence. Afin de cibler plusieurs familles de modes, ces stratégies ont été incorporées dans un circuit de shunt à plusieurs étages. Les concepts sont testés expérimentalement sur deux structures aubagées de complexité croissante, à savoir un rail à aubes et un BluM comme application finale. Ces méthodes permettent d'obtenir d'excellentes performances d'amortissement sur plusieurs groupes de modes. Elles s'avèrent également robustes face à des variations de la structure, dues par exemple à un désaccordage de celle-ci. Il est à noter que, grâce à leur caractère digital, ces méthodes sont facilement adaptables. Finalement, nous révélons le parallèle qui existe entre les shunts piézoélectriques résonants avec une capacitance négative et le contrôleur actif à rétroaction positive de position (PPF). Sur base de cette comparaison, de nouvelles règles d'accordage basées sur la norme H∞ sont développées pour le contrôleur PPF. Leur efficacité est démontrée à la fois numériquement et expérimentalement sur une poutre encastrée-libre. Dans ce but, une méthode prenant en compte l'influence des modes dont la fréquence est supérieure au mode ciblé a été mise sur pied au moyen de facteurs de correction

Tuning and performance comparison of multiresonant piezoelectric shunts

peer reviewedThis work presents tuning rules for piezoelectric shunts aiming to mitigate multiple structural resonances. Starting from a specification procedure of the shunt characteristics, the electrical parameters are derived for shunt topologies proposed in the literature, namely Hollkamp’s shunt, the current flowing shunt, the series parallel impedance structure and the current blocking shunt. Effective vibration mitigation of multiple structural modes is demonstrated numerically and experimentally on a piezoelectric beam. Performance in terms of vibration reduction obtained with the different shunts is shown to be comparable if similar shunt characteristics are considered