Mécanisme

Résumé

vignette|Mécanisme d'une crémaillère. Un mécanisme est un assemblage de pièces mécaniques dont certaines peuvent se déplacer par rapport aux autres. Cet assemblage ne constitue donc pas un solide. Chacun de ces mouvements indépendants, ou modes cinématiques, sont appelés degrés de mobilité. Par exemple, le mécanisme d'une montre désigne l'ensemble des ressorts, balancier et engrenages utilisés pour faire tourner les aiguilles. Les mécanismes sont généralement utilisés pour transformer un mouvement en un autre. Par extension, on appelle aussi mécanisme tout processus déterministe, évènements en cascade déterminés par des liens de cause à effet, comportement prévisible (par exemple, mécanisme de défense). Il est une doctrine selon laquelle le vivant ou les phénomènes vitaux peuvent être étudiés comme on étudie les machines. Constituants Liaison (mécanique) Un mécanisme est constitué de membrures reliées entre elles par des joints cinématiques, qui déterminent quels mouvem

Source officielle

https://fr.wikipedia.org/wiki/M%C3%A9canisme

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Laser micro-machining requires high dynamic laser spot trajectory and accuracy to control the laser beam scanning. A well-known technique to scan a laser beam over a specimen is to use a pair of wedge-prisms. However, it is difficult to master-slave the phase-shift between two rotating prisms at high angular-speed. We present here two drive mechanisms that decouple the phase-shift control and the angular-speed control. These mechanisms simplify the required control architecture and are suitable to achieve a high-dynamic trajectory. These concepts are based on differential timing belts and gears mechanisms that modify the phase-shift between the prisms without interrupting the rotation. This article focuses on the kinematic and mechanical design aspects of such mechanisms.

Taylor & Francis Inc2013

Chargement

Quantitative single cell dynamics of signaling and transcriptional response in mammalian cells

Onur Tidin

Cells live in ever-changing environments, thereby facing a variety of dynamic environmental signals. Environmental stimuli elicit intracellular responses through signaling pathways, which converge on transcriptional activation or repression of target genes. Despite intensive research, dissecting the complex interactions between pathway components that modulate mRNA and protein production still remains a difficult task. To this end, single-cell approaches provide unique insights into intracellular processes and cell responses to environmental stimuli, otherwise inaccessible with traditional bulk studies. Single-cell measurements have revealed that isogenic cells sharing the same environment display substantial heterogeneity in both transcript and protein level. As the initial step in gene expression, transcription is an important source of such variability in eukaryotic cells due to low number of molecules involved, transcription factor dynamics and the discrete nature of biochemical reactions. Notably, production of mRNA during transcription occurs in short periods of activity, termed as transcriptional bursts, followed by longer periods of inactivity. Despite widespread observations of transcriptional dynamics in mammals, upstream molecular mechanisms shaping the eukaryotic transcription remained elusive. In this study, we quantitatively linked upstream factors and transcriptional kinetics by developing an experimental system to temporally monitor, simultaneously, inputs (transcription factors) and outputs (target gene expression) in mammalian cells, in response to stimulus. We established two Tet-On inducible stable cell lines each expressing a fusion protein of a luminescence (Nanoluciferase) reporter to either SMAD4 or SMAD2, the two main transcrip- tion factors downstream of the TGF-Î² pathway. These cell lines that also contain a short-lived firefly luciferase reporter for the expression of the target endogenous connective tissue growth factor (ctgf ) gene allowed us to quantitatively link nuclear accumulation of SMADs upon TGF-Î² stimulation to the target gene expression in real-time single cell measurements. Time- lapse luminescence microscopy and image analysis with the custom developed CAST (Cell Automated Segmentation and Tracking platform) platform provided quantitative single-cell data to link the upstream transcription factor profile to its target gene activity. The data revealed weak single-cell correlations between translocation level and the target gene expression response which suggests a mechanism in which the translocation of SMADs initiates the transcriptional response but affects the response amplitude minimally. However, SMAD4 expression levels influenced the target gene response dynamics such that cells with high SMAD4 abundance favored to respond in a more sustained and even oscillatory manner. This suggests a mechanism consisting of a dynamic interplay between the transcriptional activators and feedback mechanisms in TGF-Î² signaling. We explored further the effect of different factors such as ligand concentration, ligand type on both signaling and target gene response. Taken together, this study proposes an experimental and quantitative framework that dissect mechanisms underlying transcriptional response to stimulus.

EPFL2018

Chargement

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This article presents a new modular robotic platform for enabling reconfigurable, actively controlled, high-degree-of-freedom (high-DoF) systems with compact form factor. The robotic modules exploit the advantages of origami-inspired construction methods and materials, and soft pneumatic actuators (SPAs) to achieve an actuator embedded, parallel kinematic mechanism with three independently controlled ‘‘waterbomb’’ base legs. The multi-material, layer-fabricated body of the modules features selectively compliant flexure hinge elements between rigid panels that define the module as a kinematic 6R spherical joint. The precision layer-fabrication technique is also used to form embedded distribution channels within the module base to connect actuators to onboard control hardware. A decentralized control architecture is applied by integrating each module with small-scale solenoid valves, communication electronics, and sensors. This design approach enables a single pneumatic supply line to be shared between modules, while still allowing independent control of each leg joint, driven by soft, inflatable pouch actuators. A passive pneumatic relay is also designed and incorporated in each module to leverage the coupled, inverted inflation, and exhaust states between antagonistic actuator pairs allowing both to be controlled by a single solenoid valve. A prototype module is presented as the first demonstration of integrated modular origami and SPA design, or pneumagami, which allows predefined kinematic structural mechanisms to locally prescribe specific motions by active effect, not just through passive compliance, to dictate task space and motion. The design strategy facilitates the composition of lightweight, high-strength robotic structures with many DoFs that will benefit various fields such as wearable robotics

2020

Chargement

Quantitative single cell dynamics of signaling and transcriptional response in mammalian cells

Onur Tidin

EPFL2018