20,399 research outputs found
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
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
Recommended from our members
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
Orbital Debris-Debris Collision Avoidance
We focus on preventing collisions between debris and debris, for which there
is no current, effective mitigation strategy. We investigate the feasibility of
using a medium-powered (5 kW) ground-based laser combined with a ground-based
telescope to prevent collisions between debris objects in low-Earth orbit
(LEO). The scheme utilizes photon pressure alone as a means to perturb the
orbit of a debris object. Applied over multiple engagements, this alters the
debris orbit sufficiently to reduce the risk of an upcoming conjunction. We
employ standard assumptions for atmospheric conditions and the resulting beam
propagation. Using case studies designed to represent the properties (e.g. area
and mass) of the current debris population, we show that one could
significantly reduce the risk of nearly half of all catastrophic collisions
involving debris using only one such laser/telescope facility. We speculate on
whether this could mitigate the debris fragmentation rate such that it falls
below the natural debris re-entry rate due to atmospheric drag, and thus
whether continuous long-term operation could entirely mitigate the Kessler
syndrome in LEO, without need for relatively expensive active debris removal.Comment: 13 pages, 8 figures. Accepted for publication in Advances in Space
Researc
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
Modeling of the Metal Powder Flow with Carrier Gas in Coaxial Nozzle for Direct Laser Deposition Process
In direct laser deposition process, metal powder is directly fed with carrier gas
through the coaxial nozzle into the melt pool created by the laser to form the solid parts.
Many operational parameters of the process depend on the characteristic of the powder
stream structure below the exit of the coaxial nozzle. In this paper, a computational
approach is developed for the simulation of the gas-particle flow in the coaxial nozzle.
By taking into account the nozzle geometry and operating parameters, such as width and
inclination angle of powder passage and carrier gas velocity, the developed
computational code allows the simulation, optimization and control of the delivery of the
metal powders.Mechanical Engineerin
- …