Comment on ``Validity of certain soft-photon amplitudes''

The criteria suggested by Welsh and Fearing (nucl-th/9606040) to judge the validity of certain soft-photon amplitudes are examined. We comment on aspects of their analysis which lead to incorrect conclusions about published amplitudes and point out important criteria which were omitted from their analysis.Comment: 6 pages plus 1 postscript figure, Revte

Reply to the comment on 'Validity of certain soft photon amplitudes'

We respond to the accompanying Comment on our paper, 'Validity of certain soft photon amplitudes'. While we hope the discussion here clarifies the issues, we have found nothing which leads to a change in the original conclusions of our paper.Comment: 6 pages, Latex, uses ReVTeX, now publishe

Migration of Interplanetary Dust

We numerically investigate the migration of dust particles with initial orbits close to those of the numbered asteroids, observed trans-Neptunian objects, and Comet Encke. The fraction of silicate asteroidal particles that collided with the Earth during their lifetime varied from 1.1% for 100 micron particles to 0.008% for 1 micron particles. Almost all asteroidal particles with diameter d>4 microns collided with the Sun. The peaks in the migrating asteroidal dust particles' semi-major axis distribution at the n:(n+1) resonances with Earth and Venus and the gaps associated with the 1:1 resonances with these planets are more pronounced for larger particles. The probability of collisions of cometary particles with the Earth is smaller than for asteroidal particles, and this difference is greater for larger particles.Comment: Annals of the New York Academy of Sciences, 15 pages, 8 Figures, submitte

An efficient method for solving the steady Euler equations

An efficient numerical procedure for solving a set of nonlinear partial differential equations is given, specifically for the steady Euler equations. Solutions of the equations were obtained by Newton's linearization procedure, commonly used to solve the roots of nonlinear algebraic equations. In application of the same procedure for solving a set of differential equations we give a theorem showing that a quadratic convergence rate can be achieved. While the domain of quadratic convergence depends on the problems studied and is unknown a priori, we show that firstand second-order derivatives of flux vectors determine whether the condition for quadratic convergence is satisfied. The first derivatives enter as an implicit operator for yielding new iterates and the second derivatives indicates smoothness of the flows considered. Consequently flows involving shocks are expected to require larger number of iterations. First-order upwind discretization in conjunction with the Steger-Warming flux-vector splitting is employed on the implicit operator and a diagonal dominant matrix results. However the explicit operator is represented by first- and seond-order upwind differencings, using both Steger-Warming's and van Leer's splittings. We discuss treatment of boundary conditions and solution procedures for solving the resulting block matrix system. With a set of test problems for one- and two-dimensional flows, we show detailed study as to the efficiency, accuracy, and convergence of the present method

Sensitivity Analysis of Process Parameters in Laser Deposition

In laser cladding with powder injection process, process output parameters, including melt pool temperature and melt pool dimensions, are critical for part quality. This paper uses simulation and experiments to investigate the effect of the process input parameters: laser power, powder mass flow rate, and scanning speed on the output parameters. Numerical simulations and experiments are conducted using a factorial design. The results are statistically analyzed to determine the significant factors and their interactions. The simulation results are compared to experimental results. The quantitative agreement/disagreement is discussed and further research is outlined.Mechanical Engineerin

Disrupting the Ideology of Settled Expectations: Forging New Social Movements to Dismantle the Educational Racial Contract

This paper draws on the concepts of settled expectations and the educational racial contract to provide an analysis of the current social movements calling for the improvement of teacher salaries and work conditions in K-12 schools. This paper argues that some teacher unions’ lack of centering race in their advocacy to ameliorate educational inequities will not radically transform how teachers are treated in the profession, unless there is an increase in motivation to fully recognize the humanity and educational needs of Students of Color in American society. The author calls for teacher activists to reject the false consciousness of their own settled expectations and work on equal footing with Communities of Color to co-author an emancipatory educational contract on the basis of relational equity, respect, and sympathetic touch

Color-neutral heavy particle production in nucleus-nucleus collisions in the quasi-classical approximation

We use a diagrammatic approach to study color-neutral heavy particle production in nucleus-nucleus collisions in a quasi-classical approximation without small-$x$ evolution. In order to treat the two nuclei symmetrically, we use the Coulomb gauge which gives the appropriate light cone gauge for each nucleus. The resulting cross section is factorized into a product of two Weizs\"{a}cker-Williams gluon distributions of the two nuclei when the transverse momentum of the produced scalar particle is around the saturation momentum. We confirm our results in covariant gauge where the transverse momentum broadening of hard gluons can be described as a diffusion process. The transverse momentum factorization manifests itself in light cone gauge but not so clearly in covariant gauge.Comment: 25 pages, 29 figures, v2: extended and improved discussion, a new appendix and references adde

Workpiece Alignment for Hybrid Laser Aided Part Repair Process

Work piece alignment is a key issue for hybrid laser aided part repair, a process utilizing both machining and laser deposition. Proper alignment can greatly improve the accuracy of the repair process. This paper introduces a method for aligning a physical work piece and a CAD model using a Renishaw touch probe and software tools. Also discussed is a model for computing 5-axis CNC positions based on a desired work piece orientation.Mechanical Engineerin