153,941 research outputs found
Residual entropy in a model for the unfolding of single polymer chains
We study the unfolding of a single polymer chain due to an external force. We
use a simplified model which allows to perform all calculations in closed form
without assuming a Boltzmann-Gibbs form for the equilibrium distribution.
Temperature is then defined by calculating the Legendre transform of the
entropy under certain constraints. The application of the model is limited to
flexible polymers. It exhibits a gradual transition from compact globule to
rod. The boundary line between these two phases shows reentrant behavior. This
behavior is explained by the presence of residual entropy.Comment: 5 pages, 4 figures, extended version of arXiv:cond-mat/061225
Is your article EV-TRACKed?
The EV-TRACK knowledgebase is developed to cope with the need for transparency and rigour to increase reproducibility and facilitate standardization of extracellular vesicle (EV) research. The knowledgebase includes a checklist for authors and editors intended to improve the transparency of methodological aspects of EV experiments, allows queries and meta-analysis of EV experiments and keeps track of the current state of the art. Widespread implementation by the EV research community is key to its success
Numerical simulation of grain-size effects on creep crack growth by means of grain elements
The effect of grain size on creep crack growth is investigated by means of a numerical technique in which the actual crack growth process is simulated in a discrete manner by grain elements and grain boundary elements. The grain elements account for the creep deformation of individual grains, while grain boundary cavitation and sliding are accounted for by grain boundary elements between the grains. This grain-element technique allows for an independent study of multiple grain size effects: a (direct) size effect related to the specimen size/grain size ratio or an (indirect) effect related to the effect of grain size on nucleation rate and creep resistance. Preliminary numerical results are presented concerning the direct effect of grain size, which predict that the crack growth rate and brittleness increase with grain size.
Microstructural modelling of creep crack growth from a blunted crack
The effect of crack tip blunting on the initial stages of creep crack growth is investigated by means of a planar microstructural model in which grains are represented discretely. The actual linking-up process of discrete microcracks with the macroscopic crack is simulated, with full account of the underlying physical mechanisms such as the nucleation, growth and coalescence of grain boundary cavities accompanied by grain boundary sliding. Results are presented for C*-controlled mode I crack growth under small-scale damage conditions. Particular attention is focused on creep constrained vs. unconstrained growth. Also the effect of grain boundary shear stresses on linking-up is investigated through shear-modified nucleation and growth models. The computations show a general trend that while an initially sharp crack tends to propagate away from the original crack plane, crack tip blunting reduces the crack growth direction. Under unconstrained conditions this can be partly rationalized by the strain rate and facet stress distribution corresponding to steady-state creep.
Unintended Detrimental Effects of Environmental Policy: The Green Paradox and Beyond
Well-intended policies aimed at reducing greenhouse gas emissions may have unintended undesirable consequences. Recently, a large literature has emerged showing under what conditions this so-called 'Green Paradox' may occur. We review this literature and identify the key mechanisms behind these paradoxical policy outcomes and highlight avenues for future research
Current-induced torques in textured Rashba ferromagnets
In systems with small spin-orbit coupling, current-induced torques on the
magnetization require inhomogeneous magnetization textures. For large
spin-orbit coupling, such torques exist even without gradients in the
magnetization direction. Here, we consider current-induced torques in
ferromagnetic metals with both Rashba spin-orbit coupling and inhomogeneous
magnetization. We first phenomenologically construct all torques that are
allowed by the symmetries of the system, to first order in
magnetization-direction gradients and electric field. Second, we use a
Boltzmann approach to calculate the spin torques that arise to second order in
the spin-orbit coupling. We apply our results to current-driven domain walls
and find that the domain-wall mobility is strongly affected by torques that
result from the interplay between spin-orbit coupling and inhomogeneity of the
magnetization texture.Comment: 9 pages, 3 figure
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