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

Tame Decompositions and Collisions

A univariate polynomial f over a field is decomposable if f = g o h = g(h) for nonlinear polynomials g and h. It is intuitively clear that the decomposable polynomials form a small minority among all polynomials over a finite field. The tame case, where the characteristic p of Fq does not divide n = deg f, is fairly well-understood, and we have reasonable bounds on the number of decomposables of degree n. Nevertheless, no exact formula is known if $n$ has more than two prime factors. In order to count the decomposables, one wants to know, under a suitable normalization, the number of collisions, where essentially different (g, h) yield the same f. In the tame case, Ritt's Second Theorem classifies all 2-collisions. We introduce a normal form for multi-collisions of decompositions of arbitrary length with exact description of the (non)uniqueness of the parameters. We obtain an efficiently computable formula for the exact number of such collisions at degree n over a finite field of characteristic coprime to p. This leads to an algorithm for the exact number of decomposable polynomials at degree n over a finite field Fq in the tame case

Controlling dynamical entanglement in a Josephson tunneling junction

We analyze the evolution of an entangled many-body state in a Josephson tunneling junction. A N00N state, which is a superposition of two complementary Fock states, appears in the evolution with sufficient probability only for a moderate many-body interaction on an intermediate time scale. This time scale is inversely proportional to the tunneling rate. Interaction between particles supports entanglement: The probability for creating an entangled state decays exponentially with the number of non-interacting particles, whereas it decays only like the inverse square root of the number of interacting particles.Comment: 9 pages, 5 figure