75 research outputs found
Validation Test Cases for Multi-Physic Problems: Application to Magneto-Hydrodynamic Numerical Simulations
In the present paper, some elementary test cases in laminar flow with
magnetic forcing terms are analyzed (Hartmann flow, Couette flow, Rayleigh
flow); equations of the coupled problem are exposed and analytical solutions
are derived in each case, highlighting the relevant non-dimensional number
which drives the physics of the problem. Several analytical calculations are
then proposed and discussed, in particular in the context of MHD propulsion by
a nozzle.Comment: 10
Visualisation de la répartition d'intensité des rayons X dans un cristal déformé
National audienceNous nous proposons de présenter le résultat d'études théoriques sur la propagation des rayons X dans un cristal contenant une dislocation
Wafer-scale integration of piezoelectric actuation capabilities in nanoelectromechanical systems resonators
In this work, we demonstrate the integration of piezoelectric actuation means on arrays of nanocantilevers at the wafer scale. We use lead titanate zirconate (PZT) as piezoelectric material mainly because of its excellent actuation properties even when geometrically constrained at extreme scal
Wafer-scale integration of piezoelectric actuation capabilities in nanoelectromechanical systems resonators
In this work, we demonstrate the integration of piezoelectric actuation means on arrays of nanocantilevers at the wafer scale. We use lead titanate zirconate (PZT) as piezoelectric material mainly because of its excellent actuation properties even when geometrically constrained at extreme scal
Images Of Serial Sectioning In Electron Microscopy : 3D Visualisation Of Objects Of Biological Interest
International audienceIn the case of serial sections observed by the means of an electron microscope, it is possible to rebuild an image of an object, using the local intelligence of an image workstation without the need of a powerful computer. We will explain the basic principles of a program that we have written and explain its further developments
Enzyme sequestration as a tuning point in controlling response dynamics of signalling networks
Signalling networks result from combinatorial interactions among many enzymes and scaffolding proteins. These complex systems generate response dynamics that are often essential for correct decision-making in cells. Uncovering biochemical design principles that underpin such response dynamics is a prerequisite to understand evolved signalling networks and to design synthetic ones. Here, we use in silico evolution to explore the possible biochemical design space for signalling networks displaying ultrasensitive and adaptive response dynamics. By running evolutionary simulations mimicking different biochemical scenarios, we find that enzyme sequestration emerges as a key mechanism for enabling such dynamics. Inspired by these findings, and to test the role of sequestration, we design a generic, minimalist model of a signalling cycle, featuring two enzymes and a single scaffolding protein. We show that this simple system is capable of displaying both ultrasensitive and adaptive response dynamics. Furthermore, we find that tuning the concentration or kinetics of the sequestering protein can shift system dynamics between these two response types. These empirical results suggest that enzyme sequestration through scaffolding proteins is exploited by evolution to generate diverse response dynamics in signalling networks and could provide an engineering point in synthetic biology applications
In silico evolution of signaling networks using rule-based models: bistable response dynamics
One of the ultimate goals in biology is to understand the design principles
of biological systems. Such principles, if they exist, can help us better
understand complex, natural biological systems and guide the engineering of de
novo ones. Towards deciphering design principles, in silico evolution of
biological systems with proper abstraction is a promising approach. Here, we
demonstrate the application of in silico evolution combined with rule-based
modelling for exploring design principles of cellular signaling networks. This
application is based on a computational platform, called BioJazz, which allows
in silico evolution of signaling networks with unbounded complexity. We provide
a detailed introduction to BioJazz architecture and implementation and describe
how it can be used to evolve and/or design signaling networks with defined
dynamics. For the latter, we evolve signaling networks with switch-like
response dynamics and demonstrate how BioJazz can result in new biological
insights on network structures that can endow bistable response dynamics. This
example also demonstrated both the power of BioJazz in evolving and designing
signaling networks and its limitations at the current stage of development.Comment: 24 pages, 7 figure
Multilocus Sequence Typing as a Replacement for Serotyping in Salmonella enterica
Salmonella enterica subspecies enterica is traditionally subdivided into serovars by serological and nutritional characteristics. We used Multilocus Sequence Typing (MLST) to assign 4,257 isolates from 554 serovars to 1092 sequence types (STs). The majority of the isolates and many STs were grouped into 138 genetically closely related clusters called eBurstGroups (eBGs). Many eBGs correspond to a serovar, for example most Typhimurium are in eBG1 and most Enteritidis are in eBG4, but many eBGs contained more than one serovar. Furthermore, most serovars were polyphyletic and are distributed across multiple unrelated eBGs. Thus, serovar designations confounded genetically unrelated isolates and failed to recognize natural evolutionary groupings. An inability of serotyping to correctly group isolates was most apparent for Paratyphi B and its variant Java. Most Paratyphi B were included within a sub-cluster of STs belonging to eBG5, which also encompasses a separate sub-cluster of Java STs. However, diphasic Java variants were also found in two other eBGs and monophasic Java variants were in four other eBGs or STs, one of which is in subspecies salamae and a second of which includes isolates assigned to Enteritidis, Dublin and monophasic Paratyphi B. Similarly, Choleraesuis was found in eBG6 and is closely related to Paratyphi C, which is in eBG20. However, Choleraesuis var. Decatur consists of isolates from seven other, unrelated eBGs or STs. The serological assignment of these Decatur isolates to Choleraesuis likely reflects lateral gene transfer of flagellar genes between unrelated bacteria plus purifying selection. By confounding multiple evolutionary groups, serotyping can be misleading about the disease potential of S. enterica. Unlike serotyping, MLST recognizes evolutionary groupings and we recommend that Salmonella classification by serotyping should be replaced by MLST or its equivalents
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