1,720,997 research outputs found
Driving-induced crossover: from classical criticality to self-organized criticality
No full textWe propose a spin model with quenched disorder which exhibits in slow driving two drastically different types of critical nonequilibrium steady states. One of them corresponds to classical criticality requiring fine-tuning of the disorder. The other is a self-organized criticality which is insensitive to disorder. The crossover between the two types of criticality is determined by the mode of driving. As one moves from “soft” to “hard” driving the universality class of the critical point changes from a classical order-disorder to a quenched Edwards-Wilkinson universality class. The model is viewed as prototypical for a broad class of physical phenomena ranging from magnetism to earthquakes
Training-induced criticality in martensites.
No full textWe propose an explanation for the self-organization towards criticality observed in martensites during the cyclic process known as “training.” The scale-free behavior originates from the interplay between the reversible phase transformation and the concurrent activity of lattice defects. The basis of the model is a continuous dynamical system on a rugged energy landscape, which in the quasistatic limit reduces to a sandpile automaton. We reproduce all the principal observations in thermally driven martensites, including power-law statistics, hysteresis shakedown, asymmetric signal shapes, and correlated disorder
Martensitic transformations: from continuum mechanics, to spin models and automata.
No full textWe present a new procedure for the systematic reduction of a continuum theory of martensitic transformations to a spin system whose dynamics can be described by an automaton. Our prototypical model reproduces most of the experimental observations in martensites associated with criticality and power-law acoustic emission. In particular, it explains in a natural way why cyclic training is necessary to reach scale-free behavior
A mechanical model of muscle mechanics
No full textThe thesis describes the skeletal muscle contraction from a purely (micro)mechanical point of view. The fast time scale processes related to the power stroke event is firstly described as diffusion in a non-convex energy which leads to an overcoming of some drawbacks of the classical Huxley and Simmons model. The new model allows the description of the power stroke in the same framework of the Brownian ratchet theory, already used to describe the slower process of the attachment detachment of the myosin head from the actin sites. A global model is finally presented, able to reproduce not only the main features of the muscle contraction, but also to interpret the main phases of the whole cross bridge cycle. The efforts to maintain the modeling in the purely mechanical framework represent a first step to the possible construction of artificial machines based on skeletal muscle mechanics, more than a limitation on the physical interpretation of the chemical events
Inertial Effects in the Dynamics of Martensitic Phase Boundaries
No full textAbstractLocalized phase transitions, as well as shock waves, can be modeled by material discontinuities satisfying appropriate jump conditions. One can show that the classical system of Rankine-Hugoniot jump conditions is incomplete in the case of subsonic phase boundaries. The supplementary condition which generalizes the condition of phase equilibrium, can be obtained from the traveling wave solution of the truly dynamic system of equations describing the interface structure.</jats:p
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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