1,510 research outputs found
Upscaling of dislocation walls in finite domains
We wish to understand the macroscopic plastic behaviour of metals by
upscaling the micro-mechanics of dislocations. We consider a highly simplified
dislocation network, which allows our microscopic model to be a one dimensional
particle system, in which the interactions between the particles (dislocation
walls) are singular and non-local.
As a first step towards treating realistic geometries, we focus on
finite-size effects rather than considering an infinite domain as typically
discussed in the literature. We derive effective equations for the dislocation
density by means of \Gamma-convergence on the space of probability measures.
Our analysis yields a classification of macroscopic models, in which the size
of the domain plays a key role
Dynamics of screw dislocations: a generalised minimising-movements scheme approach
The gradient flow structure of the model introduced in [CG99] for the
dynamics of screw dislocations is investigated by means of a generalised
minimising-movements scheme approach. The assumption of a finite number of
available glide directions, together with the "maximal dissipation criterion"
that governs the equations of motion, results into solving a differential
inclusion rather than an ODE. This paper addresses how the model in [CG99] is
connected to a time-discrete evolution scheme which explicitly confines
dislocations to move each time step along a single glide direction. It is
proved that the time-continuous model in [CG99] is the limit of these
time-discrete minimising-movement schemes when the time step converges to 0.
The study presented here is a first step towards a generalisation of the
setting in [AGS08, Chap. 2 and 3] that allows for dissipations which cannot be
described by a metric.Comment: 17 pages, 2 figures http://cvgmt.sns.it/paper/2781
Stabilizing Fluid-Fluid Displacements in Porous Media Through Wettability Alteration
We study experimentally how wettability impacts fluid-fluid-displacement patterns in granular media. We inject a low-viscosity fluid (air) into a thin bed of glass beads initially saturated with a more-viscous fluid (a water-glycerol mixture). Chemical treatment of glass surfaces allows us to control the wetting properties of the medium and modify the contact angle θ from 5° (drainage) to 120° (imbibition). We demonstrate that wettability exerts a powerful influence on the invasion morphology of unfavorable mobility displacements: increasing θ stabilizes fluid invasion into the granular pack at all capillary numbers. In particular, we report the striking observation of a stable radial displacement at low capillary numbers, whose origin lies on the cooperative nature of fluid invasion at the pore scale.Eni S.p.A. (Firm)ARCO Chair in Energy Studie
The role of charge-matching in nanoporous materials formation
Unravelling the molecular-level mechanisms that lead to the formation of mesoscale-ordered porous materials is a crucial step towards the goal of computational material design. For silica templated by alkylamine surfactants, a mechanism based on hydrogen-bond interactions between neutral amines and neutral silicates in solution has been widely accepted by the materials science community, despite the lack of conclusive evidence to support it. We demonstrate, through a combination of experimental measurements and multi-scale modelling, that the so-called “neutral templating route” does not represent a viable description of the synthesis mechanism of hexagonal mesoporous silica (HMS), the earliest example of amine-templated porous silica. Instead, the mesoscale structure of the material is defined by charge-matching of ionic interactions between amines and silicates. This has profound implications for the synthesis of a wide range of templated porous materials, and may shed new light on developing sustainable and economical routes to high value porous materials
Prediction model for knee osteoarthritis including clinical, genetic and biochemical risk factors
Ethnic Variation in Haplotype Structure of the Complete VDR Gene and Association with Fracture Risk
Ethnic Variation in Haplotype Structure of the Complete VDR Gene and Association with Fracture Risk
Rectification of thermal fluctuations in ideal gases
We calculate the systematic average speed of the adiabatic piston and a
thermal Brownian motor, introduced in [Van den Broeck, Kawai and Meurs,
\emph{Microscopic analysis of a thermal Brownian motor}, to appear in Phys.
Rev. Lett.], by an expansion of the Boltzmann equation and compare with the
exact numerical solution.Comment: 18 page
DAMPening COVID-19 Severity by Attenuating Danger Signals
COVID-19 might lead to multi-organ failure and, in some cases, to death. The COVID-19 severity is associated with a “cytokine storm.” Danger-associated molecular patterns (DAMPs) are proinflammatory molecules that can activate pattern recognition receptors, such as toll-like receptors (TLRs). DAMPs and TLRs have not received much attention in COVID-19 but can explain some of the gender-, weight- and age-dependent effects. In females and males, TLRs are differentially expressed, likely contributing to higher COVID-19 severity in males. DAMPs and cytokines associated with COVID-19 mortality are elevated in obese and elderly individuals, which might explain the higher risk for severer COVID-19 in these groups. Adenosine signaling inhibits the TLR/NF-κB pathway and, through this, decreases inflammation and DAMPs’ effects. As vaccines will not be effective in all susceptible individuals and as new vaccine-resistant SARS-CoV-2 mutants might develop, it remains mandatory to find means to dampen COVID-19 disease severity, especially in high-risk groups. We propose that the regulation of DAMPs via adenosine signaling enhancement might be an effective way to lower the severity of COVID-19 and prevent multiple organ failure in the absence of severe side effects
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