Instabilities of the AA-stacked graphene bilayer

Tight-binding calculations predict that the AA-stacked graphene bilayer has one electron and one hole conducting bands, and that the Fermi surfaces of these bands coincide. We demonstrate that as a result of this degeneracy, the bilayer becomes unstable with respect to a set of spontaneous symmetry violations. Which of the symmetries is broken depends on the microscopic details of the system. We find that antiferromagnetism is the more stable order parameter. This order is stabilized by the strong on-site Coulomb repulsion. For an on-site repulsion energy typical for graphene systems, the antiferromagnetic gap can exist up to room temperatures.Comment: 4 pages, 2 eps figure, submitted to Phys. Rev. Let

Evaluating the effectiveness of innovative psychological intervention tools in optimizing health outcomes: A multimethod approach

The main aim of this thesis is to examine the effectiveness of innovative psychological interventions on health optimization by (1) evaluating the effectiveness of innovative psychological tools, i.e., serious gaming, verbal suggestions, and internet-based interventions, to optimize various health behaviors and psychophysiological outcomes; (2) providing a concise overview of the currently existing evidence of psychological interventions in optimizing immune function in response to in vitro or in vivo immunological as well as psychophysiological challenges; and (3) incorporating various self-reporting, behavioral and psychophysiological outcome measures, but also physical and psychophysiological challenges, including psychophysiological, physical and/or cognitive stressors, to evaluate the effectiveness of psychological interventions on health outcomes. Health and self-regulatio

Audio-visual speech in noise perception in dyslexia

Individuals with developmental dyslexia (DD) may experience, besides reading problems, other speech-related processing deficits. Here, we examined the influence of visual articulatory information (lip-read speech) at various levels of background noise on auditory word recognition in children and adults with DD. We found that children with a documented history of DD have deficits in their ability to gain benefit from lip-read information that disambiguates noise-masked speech. We show with another group of adult individuals with DD that these deficits persist into adulthood. These deficits could not be attributed to impairments in unisensory auditory word recognition. Rather, the results indicate a specific deficit in audio-visual speech processing and suggest that impaired multisensory integration might be an important aspect of DD

Induced quantum numbers in the (2+1)-dimensional electron gas

A gas of electrons confined to a plane is examined in both the relativistic and nonrelativistic case. Using a (0+1)-dimensional effective theory, a remarkably simple method is proposed to calculate the spin density induced by an uniform magnetic background field. The physical properties of possible fluxon excitations are determined. It is found that while in the relativistic case they can be considered as half-fermions (semions) in that they carry half a fermion charge and half the spin of a fermion, in the nonrelativistic case they should be thought of as fermions, having the charge and spin of a fermion.Comment: 19 pages, REVTE

Collective Excitations, Nambu-Goldstone Modes and Instability of Inhomogeneous Polariton Condensates

We study non-equilibrium microcavity-polariton condensates (MPCs) in a harmonic potential trap theoretically. We calculate and analyze the steady state, collective-excitation modes and instability of MPCs. Within excitation modes, there exist Nambu-Goldstone modes that can reveal the pattern of the spontaneous symmetry breaking of MPCs. Bifurcation of the stable and unstable modes is identified in terms of the pumping power and spot size. The unstable mechanism associated with the inward supercurrent flow is characterized by the existence of a supersonic region within the condensate.Comment: 16 pages, 3 figure