31,052 research outputs found
National Educators' Workshop: Update 1988. Standard Experiments in Engineering Materials Science and Technology
Presented here is a collection of experiments presented and demonstrated at the National Educators' Workshop: Update 88, held May 10 to 12, 1988 at the National Institute of Standards and Technology (NIST), Gaithersberg, Maryland. The experiments related to the nature and properties of engineering materials and provided information to assist in teaching about materials in the education community
National Educators' Workshop: Update 1989 Standard Experiments in Engineering Materials Science and Technology
Presented here is a collection of experiments presented and demonstrated at the National Educators' Workshop: Update 89, held October 17 to 19, 1989 at the National Aeronautics and Space Administration, Hampton, Virginia. The experiments related to the nature and properties of engineering materials and provided information to assist in teaching about materials in the education community
Shock enhancement and control of hypersonic mixing and combustion
The possibility that shock enhanced mixing can
substantially increase the rate of mixing between
coflowing streams of hydrogen and air has been
studied in experimental and computational investigations.
Early numerical computations indicated that
the steady interaction between a weak shock in air
with a coflowing hydrogen jet can be well approximated
by the two-dimensional time-dependent interaction
between a weak shock and an initially circular
region filled with hydrogen imbedded in air. An experimental
investigation of the latter process has been
carned out in the Caltech 17 Inch Shock Tube in experiments
in which the laser induced fluorescence of
byacetyl dye is used as a tracer for the motion of the
helium gas after shock waves have passed across the
helium cylinder. The flow field has also been studied
using an Euler code computation of the flow field.
Both investigations show that the shock impinging
process causes the light gas cylinder to split into two
parts. One of these mixes rapidly with air and the
other forms a stably stratified vortex pair which mixes
more slowly; about 60% of the light gas mixes rapidly
with the ambient fluid. The geometry of the flow field
and the mixing process and scaling parameters are
discussed here. The success of this program encouraged
the exploration of a low drag injection system in
which the basic concept of shock generated streamwise
vorticity could be incorporated in an injector for
a Scramjet combustor at Mach numbers between 5
and 8. The results of a substantial computational
program and a description of the wind tunnel model and preliminary experimental results obtained in the
High Reynolds Number Mach 6 Tunnel at NASA Langley
Research Center are given here
Healthiness from Duality
Healthiness is a good old question in program logics that dates back to
Dijkstra. It asks for an intrinsic characterization of those predicate
transformers which arise as the (backward) interpretation of a certain class of
programs. There are several results known for healthiness conditions: for
deterministic programs, nondeterministic ones, probabilistic ones, etc.
Building upon our previous works on so-called state-and-effect triangles, we
contribute a unified categorical framework for investigating healthiness
conditions. We find the framework to be centered around a dual adjunction
induced by a dualizing object, together with our notion of relative
Eilenberg-Moore algebra playing fundamental roles too. The latter notion seems
interesting in its own right in the context of monads, Lawvere theories and
enriched categories.Comment: 13 pages, Extended version with appendices of a paper accepted to
LICS 201
Approximate theoretical performance evaluation for a diverging rocket
A simplified combustion model, which is motivated by available performance studies on the diverging rocket reactor, has been used as basis for an engine performance
evaluation. Comparison with conventional rocket configurations shows that an upper performance limit for the diverging reactor is comparable with performance
estimates for engines using an adiabatic work cycle. Development of the diverging reactor for engine applications may, however, offer some advantages for very hot, high-energy, propellant systems
National Educators' Workshop: Update 1991. Standard Experiments in Engineering Materials Science and Technology
Given here is a collection of experiments presented and demonstrated at the National Educators' Workshop: Update 91, held at the Oak Ridge National Laboratory on November 12-14, 1991. The experiments related to the nature and properties of engineering materials and provided information to assist in teaching about materials in the education community
Magnetic structures of RbCuCl_3 in a transverse field
A recent high-field magnetization experiment found a phase transition of
unknown character in the layered, frustrated antiferromagnet RbCuCl_3, in a
transverse field (in the layers). Motivated by these results, we have examined
the magnetic structures predicted by a model of RbCuCl_3, using the classical
approximation. At small fields, we obtain the structure already known to be
optimal, an incommensurate (IC) spiral with wave vector q in the layers. At
higher fields, we find a staircase of long-period commensurate (C) phases
(separated initially by the low-field IC phase), then two narrow IC phases,
then a fourth IC phase (also with intermediate C phases), and finally the
ferromagnetically aligned phase at the saturation field H_S. The
three-sublattice C states familiar from the theory of the triangular
antiferromagnet are never optimal. The C phases and the two intermediate IC
phases were previously unknown in this context. The magnetization is
discontinuous at a field \approx 0.4H_S, in qualitative agreement with
experiment, though we find much fine structure not reported.Comment: 9 pages, 8 figure
A simple formula for pooling knowledge about a quantum system
When various observers obtain information in an independent fashion about a
classical system, there is a simple rule which allows them to pool their
knowledge, and this requires only the states-of-knowledge of the respective
observers. Here we derive an equivalent quantum formula. While its realm of
applicability is necessarily more limited, it does apply to a large class of
measurements, and we show explicitly for a single qubit that it satisfies the
intuitive notions of what it means to pool knowledge about a quantum system.
This analysis also provides a physical interpretation for the trace of the
product of two density matrices.Comment: 5 pages, Revtex
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