An active control concept for the TALC space telescope

Cet article présente un modèle dynamique simplifié du télescope de TALC. Malgré sa simplicité, il est représentatif d?une partie de la dynamique du système, qui ont permis l'élaboration de stratégies de contrôle préliminaires pour amortir les résonances du système. En utilisant des câbles actifs, il a été montré que les résonances peuvent être amorties de façon significative, et que l'autorité du contrôle augmente avec le nombre de câbles actifs. En outre, il a été montré que, même avec une faible valeur du gain de commande, la valeur efficace d'une grandeur représentative du chemin optique peut être réduite par un facteur trois

Merkel Cells as Putative Regulatory Cells in Skin Disorders: An In Vitro Study

Merkel cells (MCs) are involved in mechanoreception, but several lines of evidence suggest that they may also participate in skin disorders through the release of neuropeptides and hormones. In addition, MC hyperplasias have been reported in inflammatory skin diseases. However, neither proliferation nor reactions to the epidermal environment have been demonstrated. We established a culture model enriched in swine MCs to analyze their proliferative capability and to discover MC survival factors and modulators of MC neuroendocrine properties. In culture, MCs reacted to bFGF by extending outgrowths. Conversely, neurotrophins failed to induce cell spreading, suggesting that they do not act as a growth factor for MCs. For the first time, we provide evidence of proliferation in culture through Ki-67 immunoreactivity. We also found that MCs reacted to histamine or activation of the proton gated/osmoreceptor TRPV4 by releasing vasoactive intestinal peptide (VIP). Since VIP is involved in many pathophysiological processes, its release suggests a putative regulatory role for MCs in skin disorders. Moreover, in contrast to mechanotransduction, neuropeptide exocytosis was Ca2+-independent, as inhibition of Ca2+ channels or culture in the absence of Ca2+ failed to decrease the amount of VIP released. We conclude that neuropeptide release and neurotransmitter exocytosis may be two distinct pathways that are differentially regulated

Uncoupled Embryonic and Extra-Embryonic Tissues Compromise Blastocyst Development after Somatic Cell Nuclear Transfer

Somatic cell nuclear transfer (SCNT) is the most efficient cell reprogramming technique available, especially when working with bovine species. Although SCNT blastocysts performed equally well or better than controls in the weeks following embryo transfer at Day 7, elongation and gastrulation defects were observed prior to implantation. To understand the developmental implications of embryonic/extra-embryonic interactions, the morphological and molecular features of elongating and gastrulating tissues were analysed. At Day 18, 30 SCNT conceptuses were compared to 20 controls (AI and IVP: 10 conceptuses each); one-half of the SCNT conceptuses appeared normal while the other half showed signs of atypical elongation and gastrulation. SCNT was also associated with a high incidence of discordance in embryonic and extra-embryonic patterns, as evidenced by morphological and molecular “uncoupling”. Elongation appeared to be secondarily affected; only 3 of 30 conceptuses had abnormally elongated shapes and there were very few differences in gene expression when they were compared to the controls. However, some of these differences could be linked to defects in microvilli formation or extracellular matrix composition and could thus impact extra-embryonic functions. In contrast to elongation, gastrulation stages included embryonic defects that likely affected the hypoblast, the epiblast, or the early stages of their differentiation. When taking into account SCNT conceptus somatic origin, i.e. the reprogramming efficiency of each bovine ear fibroblast (Low: 0029, Med: 7711, High: 5538), we found that embryonic abnormalities or severe embryonic/extra-embryonic uncoupling were more tightly correlated to embryo loss at implantation than were elongation defects. Alternatively, extra-embryonic differences between SCNT and control conceptuses at Day 18 were related to molecular plasticity (high efficiency/high plasticity) and subsequent pregnancy loss. Finally, because it alters re-differentiation processes in vivo, SCNT reprogramming highlights temporally and spatially restricted interactions among cells and tissues in a unique way

Absorbeurs de vibrations hybrides hyperstables

info:eu-repo/semantics/publishe

A simple hybridization of active and passive mass dampers

peer reviewe

A simple hybridization of active and passive mass dampers

peer reviewe

Absorbeurs de vibrations hybrides hyperstables

peer reviewe

Experimental validation of Fail-safe Hybrid Mass Damper

A simple control law, dedicated to improving the performance and stability of hybrid mass dampers, is investigated. The resulting hybrid device is based on decentralized velocity feedback techniques. Two poles and two zeros are added to the initial control law, in order to interact with the dynamics of the structure and the actuator. The interest of these interactions is to change the poles of the closed loop system so as to make the controlled system hyperstable. The margins of gain and phase are therefore infinite. Consequently, the proposed hybrid system controller is fail-safe but also unconditionally stable in theory. Experimentation, using a tuned voice coil actuator, illustrates the performance and robustness of this hybrid control device.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Robust hybrid mass damper

In this paper, the design of a hybrid mass damper (HMD) is proposed for the reduction of the resonant vibration amplitude of a multiple degree-of-freedom structure. HMD includes both passive and active elements. Combining these elements the system is fail-safe and its performances are comparable to usual purely active systems. The control law is a revisited direct velocity feedback. Two zeros are added to the controller to interact with the poles of the plant. The developed control law presents the particularity to be simple and hyperstable. The proposed HMD is compared to other classical control approaches for similar purpose in term of vibration attenuation, power consumption and stroke.SCOPUS: ar.jSCOPUS: ar.jinfo:eu-repo/semantics/inPres