Degeneracy of Ground State in Two-dimensional Electron-Lattice System

We discuss the ground state of a two dimensional electron-lattice system described by a Su-Schrieffer-Heeger type Hamiltonian with a half-filled electronic band, for which it has been pointed out in the previous paper [J. Phys. Soc. Jpn. 69 (2000) 1769-1776] that the ground state distortion pattern is not unique in spite of a unique electronic energy spectrum and the same total energy. The necessary and sufficient conditions to be satisfied by the distortion patterns in the ground state are derived numerically. As a result the degrees of degeneracy in the ground state is estimated to be about $N^{N/4}$ for $N \gg 1$ with $N$ the linear dimension of the system.Comment: 2pages, 2figure

Flight-measured X-24A lifting body control surface hinge moments and correlation with wind tunnel predictions

Control-surface hinge-moment measurements obtained in the X-24A lifting body flight-test program are compared with results from wind-tunnel tests. The effects of variations in angle of attack, angle of sideslip, rudder bias, rudder deflection, upper-flap deflection, lower-flap deflection, Mach number, and rocket-engine operation on the control-surface hinge moments are presented. In-flight motion pictures of tufts attached to the inboard side of the right fin and the rudder and upper-flap surfaces are discussed

All-electrical control of single ion spins in a semiconductor

We propose a method for all-electrical initialization, control and readout of the spin of single ions substituted into a semiconductor. Mn ions in GaAs form a natural example. In the ion's ground state the Mn core spin magnetic moment locks antiparallel to the spin and orbital magnetic moment of a bound valence hole from the GaAs host. Direct electrical manipulation of the ion spin is possible because electric fields manipulate the orbital wave function of the hole, and through the spin-orbit coupling the spin is reoriented as well. Coupling two or more ion spins can be achieved using electrical gates to control the size of the valence hole wave function near the semiconductor surface. This proposal for coherent manipulation of individual ionic spins and controlled coupling of ionic spins via electrical gates alone may find applications in extremely high density information storage and in scalable coherent or quantum information processing.Comment: 5 pages, 3 figure

Magnetic circular dichroism from the impurity band in III-V diluted magnetic semiconductors

The magnetic circular dichroism of III-V diluted magnetic semiconductors, calculated within a theoretical framework suitable for highly disordered materials, is shown to be dominated by optical transitions between the bulk bands and an impurity band formed from magnetic dopant states. The theoretical framework incorporates real-space Green's functions to properly incorporate spatial correlations in the disordered conduction band and valence band electronic structure, and includes extended and localized electronic states on an equal basis. Our findings reconcile unusual trends in the experimental magnetic circular dichroism in III-V DMSs with the antiferromagnetic p-d exchange interaction between a magnetic dopant spin and its host.Comment: 5 pages, 4 figure

Spin-orientation-dependent spatial structure of a magnetic acceptor state in a zincblende semiconductor

The spin orientation of a magnetic dopant in a zincblende semiconductor strongly influences the spatial structure of an acceptor state bound to the dopant. The acceptor state has a roughly oblate shape with the short axis aligned with the dopant's core spin. For a Mn dopant in GaAs the local density of states at a site 8 angstrom away from the dopant can change by as much by 90% when the Mn spin orientation changes. These changes in the local density of states could be probed by scanning tunneling microscopy to infer the magnetic dopant's spin orientation.Comment: 5 pages, 4 figure

Novel Precursors for Boron Nanotubes: The Competition of Two-Center and Three-Center Bonding in Boron Sheets

We present a new class of boron sheets, composed of triangular and hexagonal motifs, that are more stable than structures considered to date and thus are likely to be the precursors of boron nanotubes. We describe a simple and clear picture of electronic bonding in boron sheets and highlight the importance of three-center bonding and its competition with two-center bonding, which can also explain the stability of recently discovered boron fullerenes. Our findings call for reconsideration of the literature on boron sheets, nanotubes, and clusters.Comment: 4 pages, 4 figures, 1 tabl

Dynamic communicability predicts infectiousness

Using real, time-dependent social interaction data, we look at correlations between some recently proposed dynamic centrality measures and summaries from large-scale epidemic simulations. The evolving network arises from email exchanges. The centrality measures, which are relatively inexpensive to compute, assign rankings to individual nodes based on their ability to broadcast information over the dynamic topology. We compare these with node rankings based on infectiousness that arise when a full stochastic SI simulation is performed over the dynamic network. More precisely, we look at the proportion of the network that a node is able to infect over a fixed time period, and the length of time that it takes for a node to infect half the network.We find that the dynamic centrality measures are an excellent, and inexpensive, proxy for the full simulation-based measures

The Chromo-Dielectric Soliton Model: Quark Self Energy and Hadron Bags

The chromo-dielectric soliton model (CDM) is Lorentz- and chirally-invariant. It has been demonstrated to exhibit dynamical chiral symmetry breaking and spatial confinement in the locally uniform approximation. We here study the full nonlocal quark self energy in a color-dielectric medium modeled by a two parameter Fermi function. Here color confinement is manifest. The self energy thus obtained is used to calculate quark wave functions in the medium which, in turn, are used to calculate the nucleon and pion masses in the one gluon exchange approximation. The nucleon mass is fixed to its empirical value using scaling arguments; the pion mass (for massless current quarks) turns out to be small but non-zero, depending on the model parameters.Comment: 24 pages, figures available from the author

Photomechanical Investigation of Structural Behavior of Gyroscope Components. Task IV - Analysis of Initial Redesign of AB5-K8 GYROSCOPE

Photomechanics of structure and materials in redesigned AB5-K8 gyroscope component

Interaction driven metal-insulator transition in strained graphene

The question of whether electron-electron interactions can drive a metal to insulator transition in graphene under realistic experimental conditions is addressed. Using three representative methods to calculate the effective long-range Coulomb interaction between $\pi$-electrons in graphene and solving for the ground state using quantum Monte Carlo methods, we argue that without strain, graphene remains metallic and changing the substrate from SiO$_2$ to suspended samples hardly makes any difference. In contrast, applying a rather large -- but experimentally realistic -- uniform and isotropic strain of about $15\%$ seems to be a promising route to making graphene an antiferromagnetic Mott insulator.Comment: Updated version: 6 pages, 3 figure