12,218 research outputs found
Effects of carbon fibers on consumer products
The potential effects of carbon fibers on consumer products such as dishwashers, microwave ovens, and smoke detectors were investigated. The investigation was divided into two categories to determine the potential faults and hazards that could occur if fibers should enter the electrical circuits of the selected appliances. The categories were a fault analysis and a hazard analysis. Hazards considered were fire, flood, physical harm, explosion, and electrical shock. Electrical shock was found to be a possible occurrence related to carbon fibers. Faults were considered to be any effect on the performance of an appliance which would result in complaint or require service action
Finiteness properties of cubulated groups
We give a generalized and self-contained account of Haglund-Paulin's
wallspaces and Sageev's construction of the CAT(0) cube complex dual to a
wallspace. We examine criteria on a wallspace leading to finiteness properties
of its dual cube complex. Our discussion is aimed at readers wishing to apply
these methods to produce actions of groups on cube complexes and understand
their nature. We develop the wallspace ideas in a level of generality that
facilitates their application.
Our main result describes the structure of dual cube complexes arising from
relatively hyperbolic groups. Let H_1,...,H_s be relatively quasiconvex
codimension-1 subgroups of a group G that is hyperbolic relative to
P_1,...,P_r. We prove that G acts relatively cocompactly on the associated dual
CAT(0) cube complex C. This generalizes Sageev's result that C is cocompact
when G is hyperbolic. When P_1,...,P_r are abelian, we show that the dual
CAT(0) cube complex C has a G-cocompact CAT(0) truncation.Comment: 58 pages, 12 figures. Version 3: Revisions and slightly improved
results in Sections 7 and 8. Several theorem numbers have changed from the
previous versio
Exotic Statistics for Strings in 4d BF Theory
After a review of exotic statistics for point particles in 3d BF theory, and
especially 3d quantum gravity, we show that string-like defects in 4d BF theory
obey exotic statistics governed by the 'loop braid group'. This group has a set
of generators that switch two strings just as one would normally switch point
particles, but also a set of generators that switch two strings by passing one
through the other. The first set generates a copy of the symmetric group, while
the second generates a copy of the braid group. Thanks to recent work of
Xiao-Song Lin, we can give a presentation of the whole loop braid group, which
turns out to be isomorphic to the 'braid permutation group' of Fenn, Rimanyi
and Rourke. In the context 4d BF theory this group naturally acts on the moduli
space of flat G-bundles on the complement of a collection of unlinked unknotted
circles in R^3. When G is unimodular, this gives a unitary representation of
the loop braid group. We also discuss 'quandle field theory', in which the
gauge group G is replaced by a quandle.Comment: 41 pages, many figures. New version has minor corrections and
clarifications, and some added reference
Production of superconductor/carbon bicomponent fibers
Certain materials are unable to be drawn or spun into fiber form due to their improper melting characteristics or brittleness. However, fibrous samples of such materials are often necessary for the fabrication of intricate shapes and composites. In response to this problem, a unique process, referred to as the piggyback process, was developed to prepare fibrous samples of a variety of nonspinnable ceramics. In this technique, specially produced C shaped carbon fibers serve as micromolds to hold the desired materials prior to sintering. Depending on the sintering atmosphere used, bicomponent or single component fibers result. While much has been shown worldwide concerning the YBa2Cu3O(7-x) superconductor, fabrication into unique forms has proven quite difficult. However, a variety of intricate shapes are necessary for rapid commercialization of the superconducting materials. The potential for producing fibrous samples of the YBa2Cu3O(7-x) compound by the piggyback process is being studied. Various organic and acrylic materials were studied to determine suspending ability, reactivity with the YBa2Cu3O(7-x) compound during long term storage, and burn out characteristics. While many questions were answered with respect to the interfacial reactions between YBa2Cu3O(7-x) and carbon, much work is still necessary to improve the quality of the sintered material if the fibers produced are to be incorporated into useful composite or cables
Renormalization of the Vector Current in QED
It is commonly asserted that the electromagnetic current is conserved and
therefore is not renormalized. Within QED we show (a) that this statement is
false, (b) how to obtain the renormalization of the current to all orders of
perturbation theory, and (c) how to correctly define an electron number
operator. The current mixes with the four-divergence of the electromagnetic
field-strength tensor. The true electron number operator is the integral of the
time component of the electron number density, but only when the current
differs from the MSbar-renormalized current by a definite finite
renormalization. This happens in such a way that Gauss's law holds: the charge
operator is the surface integral of the electric field at infinity. The theorem
extends naturally to any gauge theory.Comment: 9 pages. Corresponds to published version (Phys. Rev. D), including
appendix about Weeks's parado
Investigation of atomic oxygen-surface interactions related to measurements with dual air density explorer satellites
For a number of candidate materials of construction for the dual air density explorer satellites the rate of oxygen atom loss by adsorption, surface reaction, and recombination was determined as a function of surface and temperature. Plain aluminum and anodized aluminum surfaces exhibit a collisional atom loss probability alpha .01 in the temperature range 140 - 360 K, and an initial sticking probability. For SiO coated aluminum in the same temperature range, alpha .001 and So .001. Atom-loss on gold is relatively rapid alpha .01. The So for gold varies between 0.25 and unity in the temperature range 360 - 140 K
Heavy meson chiral perturbation theory in finite volume
We present the first step towards the estimation of finite volume effects in
heavy-light meson systems using heavy meson chiral perturbation theory. We
demonstrate that these effects can be amplified in both light-quark and
heavy-quark mass extrapolations (interpolations) in lattice calculations. As an
explicit example, we perform a one-loop calculation for the neutral B meson
mixing system and show that finite volume effects, which can be comparable with
currently quoted errors, are not negligible in both quenched and partially
quenched QCD.Comment: Talk presented at Lattice2004(heavy), Fermilab, June 21st-26th, 2004.
Three pages, two figure
Production of superconductor/carbon bicomponent fibers
Certain materials are unable to be drawn or spun into fiber form due to their improper melting characteristics or brittleness. However, fibrous samples of such materials are often necessary for the fabrication of intricate shapes and composites. In response to this problem, a unique process, referred to as the piggyback process, was developed to prepare fibrous samples of a variety of nonspinnable ceramics. In this technique, specially produced C-shaped carbon fibers serve as micromolds to hold the desired materials prior to sintering. Depending on the sintering atmosphere used, bicomponent or single component fibers result. While much has been demonstrated worldwide concerning the YBa2Cu3O(7-x) superconductor, fabrication into unique forms has proven quite difficult. However, a variety of intricate shapes are necessary for rapid commercialization of the superconducting materials. The potential for producing fibrous samples of the YBa2Cu3O(7-x) compound by the piggyback process is being investigated. Various organic and acrylic materials were investigated to determine suspending ability, reactivity with the YBa2Cu3O(7-x) compound during long term storage, and burn out characteristics. While many questions were answered with respect to the interfacial reactions between YBa2Cu3O(7-x) and carbon, much work is still necessary to improve the quality of the sintered material if the fibers produced are to be incorporated into useful composites or cables. Additional research is necessary to evaluate quality of the barrier layer during long soakings at the peak temperature; adjust the firing schedule to avoid microcracking and improve densification; and increase the solids loading in the superconductive suspension to decrease porosity
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