Random gap model for graphene and graphene bilayers

The effect of a randomly fluctuating gap, created by a random staggered potential, is studied in a monolayer and a bilayer of graphene. The density of states, the one-particle scattering rate and transport properties (diffusion coefficient and conductivity) are calculated at the neutrality point. All these quantities vanish at a critical value of the average staggered potential, signaling a continuous transition to an insulating behavior. The calculations are based on the self-consistent Born approximation for the one-particle scattering rate and a massless mode of the two-particle Green's function which is created by spontaneous symmetry breaking. Transport quantities are directly linked to the one-particle scattering rate. Moreover, the effect of disorder is very weak in the case of a monolayer but much stronger in bilayer graphene.Comment: 5 pages, 1 figur

Geodynamo alpha-effect derived from box simulations of rotating magnetoconvection

The equations for fully compressible rotating magnetoconvection are numerically solved in a Cartesian box assuming conditions roughly suitable for the geodynamo. The mean electromotive force describing the generation of mean magnetic flux by convective turbulence in the rotating fluid is directly calculated from the simulations, and the corresponding alpha-coefficients are derived. Due to the very weak density stratification the alpha-effect changes its sign in the middle of the box. It is positive at the top and negative at the bottom of the convection zone. For strong magnetic fields we also find a clear downward advection of the mean magnetic field. Both of the simulated effects have been predicted by quasi-linear computations (Soward, 1979; Kitchatinov and Ruediger, 1992). Finally, the possible connection of the obtained profiles of the EMF with mean-field models of oscillating alpha^2-dynamos is discussed.Comment: 17 pages, 9 figures, submitted to Phys. Earth Planet. Inte

Investigation of exit-velocity stratification effects on jets in a crossflow (STRJET)

Program determines flow field about jets with velocity stratification exhausting into crossflow. Jets with three different types of exit-velocity stratification have been considered: (a) jets with relatively high-velocity core, (b) jets with relatively low-velocity core, and (c) jets originating from vaned nozzle

Perceiving Orientation: Defining Sexuality After Obergefell

In the aftermath of the Supreme Court’s recent decision in Obergefell v. Hodges, constitutional jurisprudence will have to more clearly define sexual orientation itself. The Obergefell majority describes sexuality as binary and suggests that any sexual orientation is immutable, normal, and constitutive of individual identity. Other scholars have shown how the kind of binary created by Obergefell excludes those with more fluid sexual identities and experiences from legal protection. This Article illuminates new problems with Obergefell’s approach to sexuality by putting that definition in historical context. While describing sexuality as a matter of orientation may now seem inevitable, this Article shows that nothing could be further from the truth. In the 1970s, leading GLBTQ activists considered and rejected the language of sexual orientation. Instead, movement members battled for civil-rights laws banning discrimination on the basis of sexual or affectional preference. The rhetoric of preference gained support for reasons that remain relevant to sexualorientation jurisprudence today. Drawing on the history of debates about sexual orientation, this Article proposes a definition that protects individuals on the basis of actual or perceived sexual orientation. A perceived-orientation approach addresses problems mentioned in leading studies as well as those spotlighted by activists in over time. First, this strategy will make it harder for discriminators to separate conduct and status. This approach also protects those who do not fit within established heterosexual or homosexual categories, but does not depend for its success on the rejection of those entrenched binaries. Perhaps most importantly, a perceived-orientation approach promises relief to all victims of orientation-based stereotyping, not only to those who can prove their “true” status

Circular edge states in photonic crystals with a Dirac node

Edge states are studied for the two-dimensional Dirac equation in a circular geometry. The properties of the two-component electromagnetic field are discussed in terms of the three-component polarization field, which can form a vortex structure near the Dirac node with a vorticity changing with the sign of the Dirac mass. The Berry curvature of the polarization field is related to the Berry curvature of the Dirac spinor state. This quantity is sensitive to a change of boundary conditions. In particular, it vanishes for a geometry with a single boundary but not for a geometry with two boundaries. This effect is robust against the creation of a step-like edge inside the sample.Comment: 8 pages, 5 figure