7,383 research outputs found
Abstracts of NASA-ASRDI publications relevant to aerospace safety research
Abstracts covering the following areas are presented: (1) oxygen technology; (2) fire safety; (3) accidents/incidents; (4) toxic spills; (5) aircraft safety; (6) structural failures; (7) nuclear systems; (8) fluid flow; and (9) zero gravity combustion
From Monomials to Words to graphs
Given a finite alphabet X and an ordering on the letters, the map \sigma
sends each monomial on X to the word that is the ordered product of the letter
powers in the monomial. Motivated by a question on Groebner bases, we
characterize ideals I in the free commutative monoid (in terms of a generating
set) such that the ideal generated by \sigma(I) in the free monoid
is finitely generated. Whether there exists an ordering such that
is finitely generated turns out to be NP-complete. The latter problem is
closely related to the recognition problem for comparability graphs.Comment: 27 pages, 2 postscript figures, uses gastex.st
BDDC and FETI-DP under Minimalist Assumptions
The FETI-DP, BDDC and P-FETI-DP preconditioners are derived in a particulary
simple abstract form. It is shown that their properties can be obtained from
only on a very small set of algebraic assumptions. The presentation is purely
algebraic and it does not use any particular definition of method components,
such as substructures and coarse degrees of freedom. It is then shown that
P-FETI-DP and BDDC are in fact the same. The FETI-DP and the BDDC
preconditioned operators are of the same algebraic form, and the standard
condition number bound carries over to arbitrary abstract operators of this
form. The equality of eigenvalues of BDDC and FETI-DP also holds in the
minimalist abstract setting. The abstract framework is explained on a standard
substructuring example.Comment: 11 pages, 1 figure, also available at
http://www-math.cudenver.edu/ccm/reports
A Transactional Analysis of Interaction Free Measurements
The transactional interpretation of quantum mechanics is applied to the
"interaction-free" measurement scenario of Elitzur and Vaidman and to the
Quantum Zeno Effect version of the measurement scenario by Kwiat, et al. It is
shown that the non-classical information provided by the measurement scheme is
supplied by the probing of the intervening object by incomplete offer and
confirmation waves that do not form complete transactions or lead to real
interactions.Comment: Accepted for publication in Foundations of Physics Letter
Spin Squeezing with Coherent Light via Entanglement Swapping
We analyze theoretically a scheme that produces spin squeezing via the
continuous swapping of atom-photon entanglement into atom-atom entanglement,
and propose an explicit experimental system where the necessary atom-field
coupling can be realized. This scheme is found to be robust against
perturbations due to other atom-field coupling channels.Comment: 6 pages, 10 figure
Quantum random walk of two photons in separable and entangled state
We discuss quantum random walk of two photons using linear optical elements.
We analyze the quantum random walk using photons in a variety of quantum states
including entangled states. We find that for photons initially in separable
Fock states, the final state is entangled. For polarization entangled photons
produced by type II downconverter, we calculate the joint probability of
detecting two photons at a given site. We show the remarkable dependence of the
two photon detection probability on the quantum nature of the state. In order
to understand the quantum random walk, we present exact analytical results for
small number of steps like five. We present in details numerical results for a
number of cases and supplement the numerical results with asymptotic analytical
results
The effects of water on the physical properties of silica aerogels
The research found in this report focuses on varying the amount of water used in the fabrication of silica aerogels and characterizing the effect this has on their physical properties, such as density, thermal conductivity and transmittance. So far, the aerogels made with the original recipe have produced average density of 0.09 g/cm3 and thermal conductivity of 0.04 W/mK; these properties are not significantly altered as the amount of water used is increased or decreased. However, there is an observable trend in transmittance; as more water is added to the standard recipe, the resulting monoliths become more transparent and less opaque indicating that more light is transmitted through the samples. Also included in this report is a study of aerogels as potential platforms for chemical sensors
Life prediction of materials exposed to monotonic and cyclic loading: A technology survey and bibliography
Announced survey directs attention toward low cycle fatigue and thermal fatigue experienced at elevated temperatures equivalent to those found in hot end of gas turbine engine. Majority of bibliographic references are on life prediction for materials exposed to monotonic and cyclic loading in high temperature environments
Directory of aerospace safety specialized information sources
Directory aids safety specialists in locating information sources and individual experts in engineering-related fields. Lists 170 organizations and approximately 300 individuals who can provide safety-related technical information in form of documentation, data, and consulting expertise. Information on hazard and failure cause identification, accident analysis, and materials characteristics are covered
Fracture toughness testing data: A technology survey and bibliography
Announced survey includes reports covering fracture toughness testing for various structural materials including information on plane strain and developing areas of mixed mode and plane strain test conditions. Bibliography references cite work and conclusions in fracture toughness testing and application of fracture toughness test data, and in fracture mechanics analysis
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