316 research outputs found
Ionic contrast terahertz time resolved imaging of frog auricular heart muscle electrical activity
International audienceThe authors demonstrate the direct, noninvasive and time resolved imaging of functional frog auricular fibers by ionic contrast terahertz (ICT) near field microscopy. This technique provides quantitative, time-dependent measurement of ionic flow during auricular muscle electrical activity, and opens the way of direct noninvasive imaging of cardiac activity under stimulation. ICT microscopy technique was associated with full three-dimensional simulation enabling to measure precisely the fiber sizes. This technique coupled to waveguide technology should provide the grounds to development of advanced in vivo ion flux measurement in mammalian hearts, allowing the prediction of heart attack from change in K+ fluxes. Cop. 2006 American Institute of Physics
A time-step-robust algorithm to compute particle trajectories in 3-D unstructured meshes for Lagrangian stochastic methods
The purpose of this paper is to propose a time-step-robust cell-to-cell
integration of particle trajectories in 3-D unstructured meshes in
particle/mesh Lagrangian stochastic methods. The main idea is to dynamically
update the mean fields used in the time integration by splitting, for each
particle, the time step into sub-steps such that each of these sub-steps
corresponds to particle cell residence times. This reduces the spatial
discretization error. Given the stochastic nature of the models, a key aspect
is to derive estimations of the residence times that do not anticipate the
future of the Wiener process. To that effect, the new algorithm relies on a
virtual particle, attached to each stochastic one, whose mean conditional
behavior provides free-of-statistical-bias predictions of residence times.
After consistency checks, this new algorithm is validated on two representative
test cases: particle dispersion in a statistically uniform flow and particle
dynamics in a non-uniform flow
Atomic-scale grain boundary engineering to overcome hot-cracking in additively-manufactured superalloys
There are still debates regarding the mechanisms that lead to hot cracking in
parts build by additive manufacturing (AM) of non-weldable Ni-based
superalloys. This lack of in-depth understanding of the root causes of hot
cracking is an impediment to designing engineering parts for safety-critical
applications. Here, we deploy a near-atomic-scale approach to investigate the
details of the compositional decoration of grain boundaries in the
coarse-grained, columnar microstructure in parts built from a non-weldable
Ni-based superalloy by selective electron-beam melting. The progressive
enrichment in Cr, Mo and B at grain boundaries over the course of the
AM-typical successive solidification and remelting events, accompanied by
solid-state diffusion, causes grain boundary segregation induced liquation.
This observation is consistent with thermodynamic calculations. We demonstrate
that by adjusting build parameters to obtain a fine-grained equiaxed or a
columnar microstructure with grain width smaller than 100 m enables to
avoid cracking, despite strong grain boundary segregation. We find that the
spread of critical solutes to a higher total interfacial area, combined with
lower thermal stresses, helps to suppress interfacial liquation.Comment: Accepted version at Acta Materiali
Nouvelle approche par l’archéozoologie dans les nécropoles antiques d’Egiin Gol et de Gol Mod (Mongolie)
Présupposés sur la civilisation xiongnu La connaissance de la civilisation xiongnu (iiie siècle avant notre ère - iiie de notre ère) de Mongolie s’est longtemps fondée sur les informations textuelles émanant de leurs voisins chinois, chroniqueurs de la dynastie des Han (206 avant notre ère-220 de notre ère) et des suivantes. Les annales historiques de l’Empire constituent en effet des sources primordiales, mais l’objectivité de certains auteurs antiques demeure aléatoire, de même que la fiabi..
Therapeutic administration of Tregitope-Human Albumin Fusion with Insulin Peptides to promote Antigen-Specific Adaptive Tolerance Induction.
Type 1 Diabetes (T1D) is an autoimmune disease that is associated with effector T cell (Teff) destruction of insulin-producing pancreatic beta-islet cells. Among the therapies being evaluated for T1D is the restoration of regulatory T cell (Treg) activity, specifically directed toward down-modulation of beta-islet antigen-specific T effector cells. This is also known as antigen-specific adaptive tolerance induction for T1D (T1D ASATI). Tregitopes (T regulatory cell epitopes) are natural T cell epitopes derived from immunoglobulin G (IgG) that were identified in 2008 and have been evaluated in several autoimmune disease models. In the T1D ASATI studies presented here, Tregitope peptides were administered to non-obese diabetic (NOD) mice at the onset of diabetes within two clinically-relevant delivery systems (liposomes and in human serum albumin [HSA]-fusion products) in combination with preproinsulin (PPI) target antigen peptides. The combination of Tregitope-albumin fusions and PPI peptides reduced the incidence of severe diabetes and reversed mild diabetes, over 49 days of treatment and observation. Combining HSA-Tregitope fusions with PPI peptides is a promising ASATI approach for therapy of T1D
Approximation schemes for the dynamics of diluted spin models: the Ising ferromagnet on a Bethe lattice
We discuss analytical approximation schemes for the dynamics of diluted spin
models. The original dynamics of the complete set of degrees of freedom is
replaced by a hierarchy of equations including an increasing number of global
observables, which can be closed approximately at different levels of the
hierarchy. We illustrate this method on the simple example of the Ising
ferromagnet on a Bethe lattice, investigating the first three possible
closures, which are all exact in the long time limit, and which yield more and
more accurate predictions for the finite-time behavior. We also investigate the
critical region around the phase transition, and the behavior of two-time
correlation functions. We finally underline the close relationship between this
approach and the dynamical replica theory under the assumption of replica
symmetry.Comment: 21 pages, 5 figure
Relaxation and Metastability in the RandomWalkSAT search procedure
An analysis of the average properties of a local search resolution procedure
for the satisfaction of random Boolean constraints is presented. Depending on
the ratio alpha of constraints per variable, resolution takes a time T_res
growing linearly (T_res \sim tau(alpha) N, alpha < alpha_d) or exponentially
(T_res \sim exp(N zeta(alpha)), alpha > alpha_d) with the size N of the
instance. The relaxation time tau(alpha) in the linear phase is calculated
through a systematic expansion scheme based on a quantum formulation of the
evolution operator. For alpha > alpha_d, the system is trapped in some
metastable state, and resolution occurs from escape from this state through
crossing of a large barrier. An annealed calculation of the height zeta(alpha)
of this barrier is proposed. The polynomial/exponentiel cross-over alpha_d is
not related to the onset of clustering among solutions.Comment: 23 pages, 11 figures. A mistake in sec. IV.B has been correcte
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