Current commutator anomalies in finite-element quantum electrodynamics

Four-dimensional quantum electrodynamics has been formulated on a hypercubic Minkowski finite-element lattice. The equations of motion have been derived so as to preserve lattice gauge invariance and have been shown to be unitary. In addition, species doubling is avoided due to the nonlocality of the interactions. The model is used to investigate the lattice current algebra. Regularization of the current is shown to arise in a natural and nonarbitrary way. The commutators of the lattice current are calculated and shown to have the expected qualitative behavior. These lattice results are compared to various continuum calculations. (Five figures available from author.)Comment: 15, OKHEP-93-1

A Methodology for the Robust Procedure Development of Fillet Welds

Though Gas Metal Arc Welding has been a basic component of fabrication in manufacturing over the last half-century, a standard methodology for optimizing welding procedures is lacking. A new procedure development method which minimizes trial runs, while maximizing accuracy has been recently developed by T.T. Allen, et al, in 2002. The use of the method is presently restricted to lap joint type welds. This work looked to extend this methodology to the application of fillet welds, test its effectiveness with different response variables, and study the effect of increasing the number of response variables. The development of a robust weld procedure that produces a consistent root penetration was used as the application for the developed methodology. The significance of this application lies in the fact that typical codes and standards currently give no consideration to root penetration when calculating joint strength from a lack of confidence in consistency and robustness. The benefits of incorporating penetration in strength calculations are numerous and consequential for industry. An increase in strength would result allowing welds to be made smaller, thus, resulting in decreases in weld time, filler wire used, and heat input, reducing distortion. Showing the capability of robust penetration through this statistical process procedure is the first step towards inclusion of penetration as a variable in joint strength calculations and the reaping of its benefits. Fillet welds were made on 12 mm thick A572 Grade 50 steel and cross-sectioned to allow for the critical response variables of penetration, undercut, convexity, maximum and minimum leg length, to be measured. Regression models were created along with contour plots displaying penetration and quality ratings on a plot of WFS/TS ratio versus travel speed. The optimization of travel speed against penetration and quality restrictions was also performed revealing a set of nominal procedural variables which produce sound welds for a range of noise variables. The optimized welding procedure included a travel speed of 11.3 in/min, a 1/16” arc length, a WFS/TS ratio of 28.4, and a contact-tip-to-work distance of 22 mm. The low travel speed resulted primarily from a need to maintain a minimum leg length in specification. It was also, observed from the contour plots that the robustness of the process was low from both the minimum leg length and convexity quality response factors. While the application conclusions show low robustness results, the significance of the developments with the process procedure were significant. The combination of optimization and the contour plots provides the engineer with a tool for determining the nominal input welding variables along with gaining an understanding of the robustness of the certain procedure, according to each significant quality issue. Also, the development of a rating scale based on code adds authenticity to the procedure, while at the same time increasing the ease at which the common scale is developed.John Deere Dubuque Work

Exact solutions of Dirac equation on a 2D gravitational background

We obtain classes of two dimensional static Lorentzian manifolds, which through the supersymmetric formalism of quantum mechanics admit the exact solvability of Dirac equation on these curved backgrounds. Specially in the case of a modified supersymmetric harmonic oscillator the wave function and energy spectrum of Dirac equation is given explicitly.Comment: 10 pages, title changed, content reduced, some references removed, To be published in PL

Electrodynamics in accelerated frames revisited

Maxwell's equations are formulated in arbitrary moving frames by means of tetrad fields, which are interpreted as reference frames adapted to observers in space-time. We assume the existence of a general distribution of charges and currents in an inertial frame. Tetrad fields are used to project the electromagnetic fields and sources on accelerated frames. The purpose is to study several configurations of fields and observers that in the literature are understood as paradoxes. For instance, are the two situations, (i) an accelerated charge in an inertial frame, and (ii) a charge at rest in an inertial frame described from the perspective of an accelerated frame, physically equivalent? Is the electromagnetic radiation the same in both frames? Normally in the analysis of these paradoxes the electromagnetic fields are transformed to (uniformly) accelerated frames by means of a coordinate transformation of the Faraday tensor. In the present approach coordinate and frame transformations are disentangled, and the electromagnetic field in the accelerated frame is obtained through a frame (local Lorentz) transformation. Consequently the fields in the inertial and accelerated frames are described in the same coordinate system. This feature allows the investigation of paradoxes such as the one mentioned above.Comment: 17 pages, no figure

The Role of Color-Magnetic Monopoles in a Gluonic Plasma

The role of color-magnetic monopoles in a pure gauge plasma at high temperature $T>2T_c$ is considered. In this temperature regime, monopoles can be considered heavy, rare objects embedded into matter consisting mostly of the usual "electric" quasiparticles, quarks and gluons. The gluon-monopole scattering is found to hardly influence thermodynamic quantities, yet it produces a large transport cross section, significantly exceeding that for pQCD gluon-gluon scattering up to quite high $T$. This mechanism keeps viscosity small enough for hydrodynamics to work at LHC.Comment: 4 pages, 4 figures, Talk presented at the Quark Matter 2009 Conference, Knoxville, T

Gravity from self-interaction redux

I correct some recent misunderstandings about, and amplify some details of, an old explicit non-geometrical derivation of GR.Comment: Final, amplified, published version; GRG (2009

Gauss-Bonnet Gravity with Scalar Field in Four Dimensions

We give all exact solutions of the Einstein-Gauss-Bonnet Field Equations coupled with a scalar field in four dimensions under certain assumptions.Comment: Latex file, 7 page

Exact solutions of Dirac equation on (1+1)-dimensional spacetime coupled to a static scalar field

We use a generalized scheme of supersymmetric quantum mechanics to obtain the energy spectrum and wave function for Dirac equation in (1+1)-dimensional spacetime coupled to a static scalar field.Comment: 7 pages, Late

Some Interesting Properties of Field theories with an Infinite Number of Fields

We give an indication that gravity coupled to an infinite number of fields might be a renormalizable theory. A toy model with an infinite number of interacting fermions in four-dimentional space-time is analyzed. The model is finite at any order in perturbation theory. However, perturbation theory is valid only for external momenta smaller than $\lambda ^{-\frac{1}{2}}$ , where $\lambda$ is the coupling constant.Comment: 12 pages, LaTe

On the inflationary solutions in higher-derivative gravity with dilaton field

We discuss the existence of de Sitter inflationary solutions for the string-inspired fourth-derivative gravity theories with dilaton field. We consider a space-time of arbitrary dimension D and an arbitrary parametrization of the target space metric. The specific features of the theory in dimension D=4 and those of the special ghost-free parametrization of the metric are found. We also consider similar string-inspired theories with torsion and construct an inflationary solution with torsion and dilaton for D=4. The stability of the inflationary solutions is also investigated.Comment: 13 pages, LaTeX, no figure