A Major Role for the Plasmodium falciparum ApiAP2 Protein PfSIP2 in Chromosome End Biology

The heterochromatic environment and physical clustering of chromosome ends at the nuclear periphery provide a functional and structural framework for antigenic variation and evolution of subtelomeric virulence gene families in the malaria parasite Plasmodium falciparum. While recent studies assigned important roles for reversible histone modifications, silent information regulator 2 and heterochromatin protein 1 (PfHP1) in epigenetic control of variegated expression, factors involved in the recruitment and organization of subtelomeric heterochromatin remain unknown. Here, we describe the purification and characterization of PfSIP2, a member of the ApiAP2 family of putative transcription factors, as the unknown nuclear factor interacting specifically with cis-acting SPE2 motif arrays in subtelomeric domains. Interestingly, SPE2 is not bound by the full-length protein but rather by a 60kDa N-terminal domain, PfSIP2-N, which is released during schizogony. Our experimental re-definition of the SPE2/PfSIP2-N interaction highlights the strict requirement of both adjacent AP2 domains and a conserved bipartite SPE2 consensus motif for high-affinity binding. Genome-wide in silico mapping identified 777 putative binding sites, 94% of which cluster in heterochromatic domains upstream of subtelomeric var genes and in telomere-associated repeat elements. Immunofluorescence and chromatin immunoprecipitation (ChIP) assays revealed co-localization of PfSIP2-N with PfHP1 at chromosome ends. Genome-wide ChIP demonstrated the exclusive binding of PfSIP2-N to subtelomeric SPE2 landmarks in vivo but not to single chromosome-internal sites. Consistent with this specialized distribution pattern, PfSIP2-N over-expression has no effect on global gene transcription. Hence, contrary to the previously proposed role for this factor in gene activation, our results provide strong evidence for the first time for the involvement of an ApiAP2 factor in heterochromatin formation and genome integrity. These findings are highly relevant for our understanding of chromosome end biology and variegated expression in P. falciparum and other eukaryotes, and for the future analysis of the role of ApiAP2-DNA interactions in parasite biology

Non-linear acoustic echo cancellation with loudspeaker modelling and pre-processing

Cette thèse présente des solutions pour l annulation d écho acoustique non-linéaire utilisant un prétraitement du haut-parleur. D abord, nous avons effectué une étude expérimentale et théorique des effets de non-linéarité sur les annuleurs d écho linéaire. Celle-ci montre clairement une dégradation des performances des annuleurs d écho linéaire. D où la nécessité de développer des solutions non-linéaires. A cette fin, nous avons effectué des mesures avec un téléphone portable. Ces mesures ont montré que le haut-parleur est la principale source de non-linéarités. Celles-ci ont ensuite permis de modéliser les non-linéarités au niveau du haut-parleur. Puis, le modèle de haut-parleur a été utilisé pour développer deux types de structures d annuleur d écho non-linéaire. Ces structures utilisent un prétraitement du haut-parleur et un annuleur d écho linéaire. La première structure utilise un prétraitement du signal d entrée de l annuleur d écho linéaire. Ce prétraitement consiste en l émulation du haut-parleur pour tenir compte des non-linéarités. Après, nous avons améliorer les performances de ce système en y ajoutant un modèle de saturation au prétraitement et un filtre blanchisseur à l annuleur d écho linéaire pour augmenter sa vitesse de convergence et sa capacité de poursuivre les variations du canal acoustique. La seconde structure utilise un prétraitement du signal d entrée du haut-parleur. Ceci a pour objectif de linéariser la sortie du haut-parleur afin d améliorer les performances des annuleurs d échos linéaires. Enfin, une analyse comparative a été menée pour vérifier l efficacité des différentes approches d annulation d écho acoustique non-linéaires.This thesis presents new solutions to non-linear echo cancellation using loud-speaker pre-processing. A theoretical and experimental analysis of linear echo cancellation behavior in non-linear environments is first introduced and shows that performance is typically degraded in the presence of non-linearities. This supports the need for dedicated non-linear solutions. Two new approaches to non-linear acoustic echo cancellation are proposed. They involve a common approach to loud-speaker modeling which is based on measurements from a real mobile phone and simulations. Results are used to characterize and model the loud-speaker which is proven to be the dominant cause of non-linarites. The loud-speaker model is used in one of two different pre-processing structures both with the aim of improving acoustic echo cancellation performance in non-linear environments. The pre-processor is placed either before the linear acoustic echo cancellation module or before the loud-speaker in an otherwise conventional approach to acoustic echo cancellation. The first arrangement aims to emulate loud-speaker behavior so that non-linearities are taken into account by the linear acoustic echo cancellation module. Performance remains affected by clipping and subject to increased computational burden. An improved approach, combining clipping compensation in the pre-processor and decorrelation filtering in the linear acoustic echo cancellation module is subsequently introduced and demonstrates improved convergence and tracking capability compared to the existing state of the art. When placed before the loud-speaker the pre-processor aims to linearise the loud-speaker output in a form of pre-compensation. This approach naturally improves the performance of otherwise standard approaches to linear acoustic echo cancellation. Compared to current state-of-the-art solutions, where the pre-processor is static, the new algorithm can dynamically adapt to the changes in loud-speaker characteristics over time. However, the pre-processor adaptation can be paused without significant losses in performance so that re-initialization of parameters is not required for each new call. Finally, we report a comparative analysis of the different non-linear acoustic echo cancellers which shows that the classical approach using loud-speaker emulation has a good reactivity to echo path changes, however convergence can be slow in highly non-linear conditions. Hence, by incorporating clipping compensation and decorrelation filtering, the system is more robust to clipping distortion, has better pre-compensate the loud-speaker, the robustness of linear acoustic echo cancellation to echo path changes and echo reduction performance are both improved. The analysis demonstrate that the combination of clipping compensation and decorrelation filtering represent a good practical solution to non-linear acoustic echo cancellation for mobile communication systems. The new algorithms are shown to outperform existing, well-known solutions with real signals.NICE-BU Sciences (060882101) / SudocSudocFranceF

SMASIS08-605 ENERGY HARVESTING BY PYROELECTRIC EFFECT USING PZT

ABSTRACT This paper considers energy harvesting using pyroelectric materials such as INTRODUCTION Due to recent advances in low-power portable electronics and the fact that batteries in general provide a finite amount of power, attention has been given to explore methods for energy harvesting and scavenging. Energy can be recovered from mechanical vibration [1], light, and spatial and temporal temperature variations Thermal energy in the environment is a potential source of energy for low-power electronics. For example, a recent commercial product, a wristwatch, uses thermoelectric modules to generate enough power to run the clock's mechanical component