Dirac cones for graph models of multilayer AA-stacked graphene sheets

We propose an extension, of a quantum graph model for a single sheet of graphene, to multilayer AA-stacked graphene and also to a model of the bulk graphite. Spectra and Dirac cones are explicitly characterized for bilayer and trilayer graphene, as well as for graphite. For weak layer interaction (as proposed in the text), simple perturbation arguments also cover any number of layers and it mathematically recovers basic cone existences from the theoretical and experimental physics literature; its main strength is its simplicity.

Singular Quasilinear Elliptic Systems with (super-) Homogeneous Condition

In this paper we establish existence, nonexistence and regularity of positive solutions for a class of singular quasilinear elliptic systems subject to (super-) homogeneous condition. The approach is based on sub-supersolution methods for systems of quasilinear singular equations combined with perturbation arguments involving singular terms

Couple stresses and the fracture of rock

An assessment is made here of the role played by the micropolar continuum theory on the cracked Brazilian disc test used for determining rock fracture toughness. By analytically solving the corresponding mixed boundary-value problems and employing singular-perturbation arguments, we provide closed-form expressions for the energy release rate and the corresponding stress-intensity factors for both mode I and mode II loading. These theoretical results are augmented by a set of fracture toughness experiments on both sandstone and marble rocks. It is further shown that the morphology of the fracturing process in our centrally pre-cracked circular samples correlates very well with discrete element simulations.

Existence of Positive Solutions for Some Superlinear Fourth-Order Boundary Value Problems

We are concerned with the following superlinear fourth-order equationu4t+utφt,−ut=0, t∈0, 1;−u0=u1=0, −u′0=a, −u′1=-b, wherea,−bare nonnegative constants such thata+b>0andφt,−sis a nonnegative continuous function that is required to satisfy some appropriate conditions related to a classKsatisfying suitable integrability condition. Our purpose is to prove the existence, uniqueness, and global behavior of a classical positive solution to the above problem by using a method based on estimates on the Green function and perturbation arguments.

On singular quasi-monotone (p, q)-Laplacian systems

We combine the sub- and supersolution method and perturbation arguments to obtain positive solutions of singular quasi-monotone (p, q)-Laplacian systems.

The implicit function theorem and multi-bump solutions of periodic partial differential equations

A modification of the implicit function theorem is advanced for cases where the continuity of the derivative fails. It is applied to a superposition principle for periodicpartial differential equations. The assumption of the principle, that there should exist a non-degenerate solution, is studied and instances of it realized using perturbation arguments and scaling. The positivity of solutions is considered.