276 research outputs found
Derivation of a line-tension model for dislocations from a nonlinear three-dimensional energy: The case of quadratic growth
No full textIn this paper we derive a line tension model for dislocations in 3D starting from a geometrically nonlinear elastic energy with quadratic growth. In the asymptotic analysis, as the amplitude of the Burgers vectors (proportional to the lattice spacing) tends to zero, we show that the elastic energy linearizes and the line tension energy density, up to an overall constant rotation, is identi_ed by the linearized cell problem formula given in [S. Conti, A. Garroni, and M. Ortiz, Arch. Ration. Mech. Anal., 218 (2015), pp. 699{755]
Concentration phenomena for the volume functional in unbounded domains: identification of concentration points
No full textWe study the variational problem [GRAPHICS] in possibly unbounded domains Qsubset ofR(n), where n greater than or equal to 3, 2* = (2n)/(n-2) and F satisfies 0less than or equal toF(t)less than or equal toalphat(2)* and is upper semicontinuous. Extending earlier results for bounded domains, we show that (almost) maximizers of S-epsilon(F) (Omega) concentrate at a harmonic center, i.e. a minimum point of the Robin function tau(Omega) (the regular part of the Green function restricted to the diagonal). Moreover, we obtain the asymptotic expansion [GRAPHICS] where S-F and winfinity depend only on F but not on Omega and can be computed from radial maximizers of the corresponding problem in R-n. The crucial point is to find a suitable definition Of tau(Omega)(infinity). Interestingly the correct definition may be different from the lower semicontinuous extension of tau(Omega)(Omega{infinity}) to infinity, at least for n greater than or equal to 5. (C) 2003 Published by Elsevier Science (USA)
Sharp rigidity estimates for incompatible fields as a consequence of the Bourgain Brezis div-curl result
No full textIn this note we show that a sharp rigidity estimate and a sharp Korn s inequality for matrixvalued fields whose incompatibility is a bounded measure can be obtained as a consequence of a Hodge decomposition with critical integrability due to Bourgain and Brezis
Gamma-limit of a phase-field model of dislocations
No full textWe study, by means of ?-convergence, the asymptotic behavior of a variational problem modeling a dislocation ensemble moving on a slip plane through a discrete array of obstacles. The variational problem is a two-dimensional phase transition-type energy given by a nonlocal term and a nonlinear potential which penalizes noninteger values. In this paper we consider a regime corresponding to a diluted distribution of obstacles. In this case the leading term of the energy can be described by means of a cell problem formula defining an appropriate notion of capacity (that we call dislocation capacity)
A multi-phase transition model for dislocations with interfacial microstructure
No full textWe study, by means Gamma-convergence, the asymptotic behavior of a variational model for dislocations moving on a slip plane. The variational functional is a two-dimensional multi-phase transition-type energy given by a nonlocal term and a nonlinear potential which penalizes noninteger values for the components of the phase. In the limit we obtain an anisotropic sharp interfaces model. The relevant feature of this problem is that optimal sequences in general are not given by a one-dimensional profile, but they can create microstructure
Introduzione, commento, traduzione e note a Sul culto degli dei feticci. Parallelo tra la Religione egiziana e la Religione attuale della Nigrizia
No full textMesostructural refinement in the early stages of mechanical alloying
No full textThis study focuses on the early stages of the mechanical alloying of 22 different binary mixtures. In each case, the number of alloyed particles increases linearly with the number of collisions, and the volume of powder effectively processed during a single collision is ∼9.0 × 10−3 mm3. The alloyed particles exhibit a heterogeneous mesostructure with characteristic lengths decreasing exponentially with the number of collisions. The rate of mesostructural refinement is inversely proportional to the difference between the hardnesses of the individual metals
Reduction of grain size in metals and metal mixtures processed by ball milling
No full textThis study focuses on the microstructural refinement induced by ball milling in individual metals and Cu-based metal mixtures. A
phenomenological model is developed to rationalize the kinetics of grain size reduction. A discontinuous change of the average grain
size is predicted to occur in very small powder volumes during each collision. The final average grain size and the rate of grain size
reduction are shown to vary with the composition depending on the difference in hardness between the metals
New amide-chloride phases in the Li-Al-N-H-Cl system: Formation and hydrogen storage behaviour
No full textNew amide-chloride phases were successfully synthesized by mechanical milling of the LiNH2-AlCl3 mixture at a molar ratio of 1:0.11 and further heating at 150 °C under argon (0.1 MPa) or under hydrogen pressure (0.7 MPa). Powder X-ray diffraction measurements as a function of milling time increase revealed that the milling of the LiNH2-0.11AlCl3 mixture results in the formation of a FCC solid solution with an excess of LiNH2. Subsequent heating of the LiNH2-0.11AlCl3 sample ball milled for 5 hours at 150 °C under argon or under hydrogen induces the appearance of an amide-chloride phase isostructural with cubic Li4(NH2)3Cl. This Li-Al-N-H-Cl phase transforms progressively into the trigonal phase after prolonged heating at 300 °C under hydrogen pressure. The thermal behaviour of the amide-chloride without and with LiH addition displays dissimilar decomposition pathways. The decomposition of amide-chloride alone involves the formation of ammonia and hydrogen from 120 to 300 °C. Conversely, the amide-chloride material in the presence of LiH only releases hydrogen avoiding the emission of ammonia. The resultant material is able to be rehydrogenated under moderate conditions (300 °C, 0.7 MPa H2), providing a new reversible hydrogen storage system.Fil: Fernández Albanesi, Luisa Francisca. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Universidad Nacional de Cuyo; ArgentinaFil: Garroni, S.. University of Sassari; ItaliaFil: Enzo, S.. University of Sassari; ItaliaFil: Gennari, Fabiana Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Universidad Nacional de Cuyo; Argentin
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