The Yukawa Coupling in Three Dimensions

We consider several renormalizable, scale free models in three space-time dimensions which involve scalar and spinor fields. The Yukawa couplings are bilinear in both the spinor and scalar fields and the potential is of sixth order in the scalar field. In a model with a single scalar field and a complex Fermion field in three Euclidean dimensions, the couplings in the theory are both asymptotically free. This property is not retained in 2+1 dimensional Minkowski space, as we illustrate by considering a renormalizable scale-free supersymmetric model. This is on account of the different properties of the Dirac matrices in Euclidean and Minkowski space. We also examine a model in 2+1 dimensional Minkowski space in which two species of Fermions, associated with the two unitarily inequivalent representations of the $2 \times 2$ Dirac matrices, couple in two different ways to two distinct scalar fields. There are two types of Yukawa couplings in this model, and either one or the other of them can be asymptotically free (but not both simultaneously).Comment: 15 pages RevTex, uses epsfig.st

Coherent coupling between surface plasmons and excitons in semiconductor nanocrystals

We present an experimental demonstration of strong coupling between a surface plasmon propagating on a planar silver substrate, and the lowest excited state of CdSe nanocrystals. Variable-angle spectroscopic ellipsometry measurements demonstrated the formation of plasmon-exciton mixed states, characterized by a Rabi splitting of $\sim$ 82 meV at room temperature. Such a coherent interaction has the potential for the development of plasmonic non-linear devices, and furthermore, this system is akin to those studied in cavity quantum electrodynamics, thus offering the possibility to study the regime of strong light-matter coupling in semiconductor nanocrystals at easily accessible experimental conditions.Comment: 12 pages, 4 figure

Skipping orbits and enhanced resistivity in large-diameter InAs/GaSb antidot lattices

We investigated the magnetotransport properties of high-mobility InAs/GaSb antidot lattices. In addition to the usual commensurability features at low magnetic field we found a broad maximum of classical origin around 2.5 T. The latter can be ascribed to a class of rosetta type orbits encircling a single antidot. This is shown by both a simple transport calculation based on a classical Kubo formula and an analysis of the Poincare surface of section at different magnetic field values. At low temperatures we observe weak 1/B-periodic oscillations superimposed on the classical maximum.Comment: 4 pages, 4 Postscript figures, REVTeX, submitted to Phys Rev

Nanomechanical displacement detection using coherent transport in ordered and disordered graphene nanoribbon resonators

Graphene nanoribbons provide an opportunity to integrate phase-coherent transport phenomena with nanoelectromechanical systems (NEMS). Due to the strain induced by a deflection in a graphene nanoribbon resonator, coherent electron transport and mechanical deformations couple. As the electrons in graphene have a Fermi wavelength \lambda ~ a_0 = 1.4 {\AA}, this coupling can be used for sensitive displacement detection in both armchair and zigzag graphene nanoribbon NEMS. Here it is shown that for ordered as well as disordered ribbon systems of length L, a strain \epsilon ~ (w/L)^2 due to a deflection w leads to a relative change in conductance \delta G/G ~ (w^2/a_0L).Comment: 4 Pages, 4 figure

Dimpling process in cold roll metal forming by finite element modelling and experimental validation

The dimpling process is a novel cold-roll forming process that involves dimpling of a rolled flat strip prior to the roll forming operation. This is a process undertaken to enhance the material properties and subsequent products’ structural performance while maintaining a minimum strip thickness. In order to understand the complex and interrelated nonlinear changes in contact, geometry and material properties that occur in the process, it is necessary to accurately simulate the process and validate through physical tests. In this paper, 3D non-linear finite element analysis was employed to simulate the dimpling process and mechanical testing of the subsequent dimpled sheets, in which the dimple geometry and material properties data were directly transferred from the dimpling process. Physical measurements, tensile and bending tests on dimpled sheet steel were conducted to evaluate the simulation results. Simulation of the dimpling process identified the amount of non-uniform plastic strain introduced and the manner in which this was distributed through the sheet. The plastic strain resulted in strain hardening which could correlate to the increase in the strength of the dimpled steel when compared to plain steel originating from the same coil material. A parametric study revealed that the amount of plastic strain depends upon on the process parameters such as friction and overlapping gap between the two forming rolls. The results derived from simulations of the tensile and bending tests were in good agreement with the experimental ones. The validation indicates that the finite element analysis was able to successfully simulate the dimpling process and mechanical properties of the subsequent dimpled steel products