187,643 research outputs found
On the genesis of directional friction through bristle-like mediating elements
No full textWe propose an explanation of the genesis of directional dry friction, as emergent property of the oscillations produced in a bristle-like mediating element by the interaction with microscale fluctuations on the surface. Mathematically, we extend a convergence result by Mielke, for Prandtl–Tomlinson-like systems, considering also non-homothetic scalings of a wiggly potential. This allows us to apply the result to some simple mechanical models, that exemplify the interaction of a bristle with a surface having small fluctuations. We find that the resulting friction is the product of two factors: a geometric one, depending on the bristle angle and on the fluctuation profile, and a energetic one, proportional to the normal force exchanged between the bristle-like element and the surface. Finally, we apply our result to discuss the with the nap/against the nap asymmetry
Lavoro ripartito, sub artt. 41-45
No full textPresentazione (Giorgio Ghezzi). - I: Disposizioni generali (F. Borgogelli, T. Groppi, P. Lambertucci, L. Marinucci). - II: Organizzazione e disciplina del mercato del lavoro (E. Gragnoli, A. Lassandari, G. Fontana, C. La Macchia, G. Zilio Grandi, R. Altavilla, M. Garattoni, F. Bano, M. Mantovani). - III: Somministrazione di lavoro, appalto di servizi, distacco (V. Speziale, F. Bano, A. Lassandari, F. Scarpelli). - IV: Disposizioni in materia di gruppi di impresa e trasferimento d'azienda (N. Rondinone, P. Lambertucci). - V: Tipologie contrattuali a orario ridotto, modulato o flessibile (D. Gottardi, G. De Simone, S. Scarponi). - VI: Apprendistato e contratto di inserimento (D. Garofalo, E. Balletti). - VII: Tipologie contrattuali a progetto e occasionali (A. Perulli, G. Zilio Grandi, A. Bellavista, A. Lo Faro). - VIII: Procedure di certificazione (P. Tullini, E. Gragnoli). - IX: Disposizioni transitorie e finali. - Appendice. - Indice degli Autori citati. - Qualifiche degli Autori
Optimal control of slender microswimmers
No full textWe discuss a reduced model to compute the motion of slender swimmers which propel themselves by changing the curvature of their body. Our approach is based on the use of Resistive Force Theory for the evaluation of the viscous forces and torques exerted by the surrounding fluid, and on discretizing the kinematics of the swimmer by representing its body through an articulated chain of N rigid links capable of planar deformations. The resulting system of ODEs, governing the motion of the swimmer, is easy to assemble and to solve, making our reduced model a valuable tool in the design and optimization of bio-inspired artificial microdevices. We prove that the swimmer is controllable in the whole plane, for N ≥ 3 and for almost every set of stick lengths. As a direct result, there exists an optimal swimming strategy to reach a desired configuration in minimum time. Numerical experiments for N = 3 (Purcell swimmer) suggest that the optimal strategy is periodic, namely a sequence of identical strokes. Our results indicate that this candidate for an optimal stroke, indeed gives a better displacement speed than the classical Purcell stroke
Energetics and switching of quasi-uniform states in small ferromagnetic particles
No full textWe present a numerical algorithm to solve the micromagnetic equations based on tangential-plane minimization for the magnetization update and a homothethic-layer decomposition of outer space for the computation of the demagnetization field. As a first application, detailed results on the flower-vortex transition in the cube of Micromagnetic Standard Problem number 3 are obtained, which confirm, with a different method, those already present in the literature, and validate our method and code. We then turn to switching of small cubic or almost-cubic particles, in the single-domain limit. Our data show systematic deviations from the Stoner-Wohlfarth model due to the non-ellipsoidal shape of the particle, and in particular a non-monotone dependence on the particle size
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Strain-order coupling in nematic elastomers: equilibrium configurations
No full textWe consider models that describe liquid crystal elastomers either in a biaxial or in a uniaxial phase and in the framework of Frank's director theory. We prove the existence of static equilibrium solutions in the presence of frustrations due to electro-mechanical boundary conditions and to applied loads and fields. We find explicit solutions arising in connection with special boundary conditions and the corresponding phase diagrams, leading to significant implications on possible experimental observations
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