14 research outputs found
Finite size effects in a model for plasticity of amorphous composites
We discuss the plastic behavior of an amorphous matrix reinforced by hard
particles. A mesoscopic depinning-like model accounting for Eshelby elastic
interactions is implemented. Only the effect of a plastic disorder is
considered. Numerical results show a complex size-dependence of the effective
flow stress of the amorphous composite. In particular the departure from the
mixing law shows opposite trends associated to the competing effects of the
matrix and the reinforcing particles respectively. The reinforcing mechanisms
and their effects on localization are discussed. Plastic strain is shown to
gradually concentrate on the weakest band of the system. This correlation of
the plastic behavior with the material structure is used to design a simple
analytical model. The latter nicely captures reinforcement size effects in
observed numerically. Predictions of the effective flow
stress accounting for further logarithmic corrections show a very good
agreement with numerical results.Comment: 18 pages, 19 figure
Cooee bitumen. II. Stability of linear asphaltene nanoaggregates
Asphaltene and smaller aromatic molecules tend to form linear nanoaggregates
in bitumen.Over the years bitumen undergoes chemical aging and during this
process, the size of the nanoaggregate increases. This increase is associated
with an increase in viscosity and brittleness of the bitumen, eventually
leading to road deterioration. This paper focuses on understanding the
mechanisms behind nanoaggregate size and stability. We used molecular dynamics
simulations to quantify the probability of having a nanoaggregate of a given
size in the stationary regime. To model this complicated behavior, we chose
first to consider the simple case where only asphaltene molecules are counted
in a nanoaggregate. We used a master equation approach and a related
statistical mechanics model. The linear asphaltene nanoaggregates behave as a
rigid linear chain. The most complicated case where all aromatic molecules are
counted in a nanoaggregate is then discussed. The linear aggregates where all
aromatic molecules are counted seem to behave as a flexible linear chain.Comment: 31 pages, 9 figure
Non-Newtonian behavior and molecular structure of Cooee bitumen under shear flow:A non-equilibrium molecular dynamics study
The rheology and molecular structure of a model bitumen (Cooee bitumen) under shear are investigated in the non-Newtonian regime using non-equilibrium molecular dynamics simulations. The shear viscosity, normal stress differences, and pressure of the bitumen mixture are computed at different shear rates and different temperatures. The model bitumen is shown to be a shear-thinning fluid at all temperatures. In addition, the Cooee model is able to reproduce experimental results showing the formation of nanoaggregates composed of stacks of flat aromatic molecules in bitumen. These nanoaggregates are immersed in a solvent of saturated hydrocarbon molecules. At a fixed temperature, the shear-shinning behavior is related not only to the inter- and intramolecular alignments of the solvent molecules but also to the decrease of the average size of the nanoaggregates at high shear rates. The variation of the viscosity with temperature at different shear rates is also related to the size and relative composition of the nanoaggregates. The slight anisotropy of the whole sample due to the nanoaggregates is considered and quantified. Finally, the position of bitumen mixtures in the broad literature of complex systems such as colloidal suspensions, polymer solutions, and associating polymer networks is discussed
Dynamics and Structure of Bitumen-Water Mixtures
Systems of Cooee bitumen and water up to 4% mass are studied by molecular dynamics simulations. The cohesive energy density of the system is shown to decrease with an increasing water content. This decrease is due mainly to an increase in the interaction energy which is not high enough to counterbalance the increase in volume due to the addition of water. It is not due to a decrease of interaction energy between the slightly polar asphaltene molecules. The water molecules tend to form a droplet in bitumen. The size and the distribution of sizes of the droplets are quantified, with multiple droplets being more stable at the highest temperature simulated. The droplet is mainly located close to the saturates molecules in bitumen. Finally, it is shown that the water dynamics is much slower in bitumen than in pure water because it is governed by the diffusion of the droplet and not of the single molecules
Intramyocardial Delivery of Mesenchymal Stem Cell-Seeded Hydrogel Preserves Cardiac Function and Attenuates Ventricular Remodeling after Myocardial Infarction
Recognition As Integration: Indigenous Rights and National Citizenship in the Philippines
Genome-wide physical activity interactions in adiposity:a meta-analysis of 200,452 adults
Abstract
Physical activity (PA) may modify the genetic effects that give rise to increased risk of obesity. To identify adiposity loci whose effects are modified by PA, we performed genome-wide interaction meta-analyses of BMI and BMI-adjusted waist circumference and waist-hip ratio from up to 200,452 adults of European (n = 180,423) or other ancestry (n = 20,029). We standardized PA by categorizing it into a dichotomous variable where, on average, 23% of participants were categorized as inactive and 77% as physically active. While we replicate the interaction with PA for the strongest known obesity-risk locus in the FTO gene, of which the effect is attenuated by ~30% in physically active individuals compared to inactive individuals, we do not identify additional loci that are sensitive to PA. In additional genome-wide meta-analyses adjusting for PA and interaction with PA, we identify 11 novel adiposity loci, suggesting that accounting for PA or other environmental factors that contribute to variation in adiposity may facilitate gene discovery