1,720,995 research outputs found
Rinnovare la tutela. Modelli matematici e grafici per la ridefinizione delle prospettive
No full text
Asymptotic analysis of Lennard-Jones systems beyond the nearest-neighbour setting: A one-dimensional prototypical case
No full textWe consider a one-dimensional system of Lennard-Jones nearest- and next-to-nearest-neighbour interactions. It is known that if a monotone parameterization is assumed then the limit of such a system can be interpreted as a Griffith fracture energy with an increasing condition on the jumps. In view of possible applications to a higher-dimensional setting, where an analogous parameterization does not always seem reasonable, we remove the monotonicity assumption and describe the limit as a Griffith fracture energy where the increasing condition on the jumps is removed and is substituted by an energy that accounts for changes in orientation (creases'). In addition, fracture may be generated by macroscopic' or microscopic' cracks
Discrete double-porosity models for spin systems
No full textWe consider spin systems between a finite number N of "species" or "phases" partitioning a cubic lattice Zd. We suppose that interactions between points of the same phase are coercive while those between points of different phases (or possibly between points of an additional "weak phase") are of lower order. Following a discrete-to-continuum approach, we characterize the limit as a continuum energy defined on N-tuples of sets (corresponding to the N strong phases) composed of a surface part, taking into account homogenization at the interface of each strong phase, and a bulk part that describes the combined effect of lowerorder terms, weak interactions between phases, and possible oscillations in the weak phase
Interfacial energies on Penrose lattices
No full textIn this paper we prove a homogenization theorem for interfacial discrete energies defined on an a-periodic Penrose tiling in two dimensions. A general result on the homogenization of surface energies cannot be directly adapted to this case; the existence of the limit interfacial energy is therefore proved by showing some refined "quasi-periodic" properties of the tilings
A derivation of linear elastic energies from pair-interaction atomistic systems
No full textPair-interaction atomistic energies may give rise, in the framework of the passage from discrete systems to continuous variational problems, to nonlinear energies with genuinely quasiconvex integrands. This phenomenon takes place even for simple harmonic interactions as shown by an example by Friesecke and Theil [19]. On the other hand, a rigorous derivation of linearly elastic energies from energies with quasiconvex integrands can be obtained by Gamma-convergence following the method by Dal Maso, Negri and Percivale [14]. We show that the derivation of linear theories by Gamma-convergence can be obtained directly from lattice interactions in the regime of small deformations. Our proof relies on a lower bound by comparison with the continuous result, and on a direct Taylor expansion for the upper bound. The computation is carried over for a family of lattice energies comprising interactions on the triangular lattice in dimension two
Motion of Discrete Interfaces Through Mushy Layers
No full textWe study the geometric motion of sets in the plane derived from the homogenization of discrete ferromagnetic energies with weak inclusions. We show that the discrete sets are composed by a 'bulky' part and an external 'mushy region' composed only of weak inclusions. The relevant motion is that of the bulky part, which asymptotically obeys to a motion by crystalline mean curvature with a forcing term, due to the energetic contribution of the mushy layers, and pinning effects, due to discreteness. From an analytical standpoint, it is interesting to note that the presence of the mushy layers implies only a weak and not strong convergence of the discrete motions, so that the convergence of the energies does not commute with the evolution. From a mechanical standpoint it is interesting to note the geometrical similarity of some phenomena in the cooling of binary melts
Interfacial energies on quasicrystals
No full textWe consider nearest-neighbour ferromagnetic energies defined on a quasicrystal modeled following the so-called cut-and-project approach as a portion of a regular lattice contained in a possibly irrational stripe defined as a neighborhood of a k-dimensional subspace in an n-dimensional space. The overall properties of this system are described by an effective surface energy on a k-dimensional space obtained as Gamma-limit of the scaled discrete energies
Rinnovare la tutela. Modelli matematici e grafici per la ridefinizione delle prospettive.
No full textBeyond the Classical Cauchy–Born Rule
Full text linkPhysically motivated variational problems involving non-convex energies are often formulated in a discrete setting and contain boundary conditions. The long-range interactions in such problems, combined with constraints imposed by lattice discreteness, can give rise to the phenomenon of geometric frustration even in a one-dimensional setting. While non-convexity entails the formation of microstructures, incompatibility between interactions operating at different scales can produce nontrivial mixing effects which are exacerbated in the case of incommensurability between the optimal microstructures and the scale of the underlying lattice. Unraveling the intricacies of the underlying interplay between non-convexity, non-locality and discreteness represents the main goal of this study. While in general one cannot expect that ground states in such problems possess global properties, such as periodicity, in some cases the appropriately defined ‘global’ solutions exist, and are sufficient to describe the corresponding continuum (homogenized) limits. We interpret those cases as complying with a Generalized Cauchy–Born (GCB) rule, and present a new class of problems with geometrical frustration which comply with GCB rule in one range of (loading) parameters while being strictly outside this class in a complimentary range. A general approach to problems with such ‘mixed’ behavior is developed
- …
