44,761 research outputs found
Development program to produce mullite fiber insulation
Processing methods were utilized to form a mullite fiber-Kaowool felt. The formation of a blended felt using the Rotoformer wet-laying method was successful. Felt products were evaluated for tensile strength, thermal stability, thermal conductivity and structural integrity at 1259 C and 1371 C. Textile processing methods failed in an attempt to form a yarn from staple and multifilament mullite fiber due to fiber damage through mechanical handling. The refractoriness of pure Kaowool ceramic fiber is improved with additions of 30% or greater mullite fiber
Single and Many Particle Correlation Functions and Uniform Phase Bases for Strongly Correlated Systems
The need for suitable many or infinite fermion correlation functions to
describe some low dimensional strongly correlated systems is discussed. This is
linked to the need for a correlated basis, in which the ground state may be
postive definite, and in which single particle correlations may suffice. A
particular trial basis is proposed, and applied to a certain quasi-1D model.
The model is a strip of the 2D square lattice wrapped around a cylinder, and is
related to the ladder geometries, but with periodic instead of open boundary
conditions along the edges. Analysis involves a novel mean-field approach and
exact diagonalisation. The model has a paramagnetic region and a Nagaoka
ferromagnetic region. The proposed basis is well suited to the model, and
single particle correlations in it have power law decay for the paramagnet,
where the charge motion is qualitatively hard core bosonic. The mean field also
leads to a BCS-type model with single particle long range order.Comment: 23 pages, in plain tex, 12 Postscript figures included. Accepted for
publication in J.Physics : Condensed Matte
Development of fine diameter mullite fiber
Results are presented of a program to develop and evaluate mullite fiber with a mean diameter under two microns. The two micron fiber is produced by a blowing process at room temperature from a low viscosity (10-25 poise) solution. The blown fiber was evaluated for dimensional stability in thermal cycling to 1371 C, and was equivalent to the 5 micron spun B and W mullite fiber. An additive study was conducted to evaluate substitutes for the boron. Three levels of chromium, lithium fluoride, and magnesium were added to the standard composition in place of boron and the fiber produced was evaluated for chemical and dimensional stability in thermal cycling to 1371 C. The magnesium was the most chemically stable, but the chrome additive imparted the best dimensional stability
Should Optimal Designers Worry About Consideration?
Consideration set formation using non-compensatory screening rules is a vital
component of real purchasing decisions with decades of experimental validation.
Marketers have recently developed statistical methods that can estimate
quantitative choice models that include consideration set formation via
non-compensatory screening rules. But is capturing consideration within models
of choice important for design? This paper reports on a simulation study of a
vehicle portfolio design when households screen over vehicle body style built
to explore the importance of capturing consideration rules for optimal
designers. We generate synthetic market share data, fit a variety of discrete
choice models to the data, and then optimize design decisions using the
estimated models. Model predictive power, design "error", and profitability
relative to ideal profits are compared as the amount of market data available
increases. We find that even when estimated compensatory models provide
relatively good predictive accuracy, they can lead to sub-optimal design
decisions when the population uses consideration behavior; convergence of
compensatory models to non-compensatory behavior is likely to require
unrealistic amounts of data; and modeling heterogeneity in non-compensatory
screening is more valuable than heterogeneity in compensatory trade-offs. This
supports the claim that designers should carefully identify consideration
behaviors before optimizing product portfolios. We also find that higher model
predictive power does not necessarily imply better design decisions; that is,
different model forms can provide "descriptive" rather than "predictive"
information that is useful for design.Comment: 5 figures, 26 pages. In Press at ASME Journal of Mechanical Design
(as of 3/17/15
Technique for extending the frequency range of digital dividers
A technique for extending the frequency range of a presettable digital divider is described. The conventional digital divider consists of several counter stages with the count of each stage compared to a preselected number. When the counts for all stages are equal to the preselected numbers, an output pulse is generated and all stages are reset. For high input frequencies, the least significant stage of the divider has to be reset in a very short time. This limits the frequency that can be handled by the conventional digital divider. This invention provides a technique in which the second least significant and higher stages are reset and the least significant stage is permitted to free-run. Hence, the time in which the reset operation can be performed is increased thereby extending the frequency range of the divider
Spin density wave in oxypnictide superconductors in a three-band model
The spin density wave and its temperature dependence in oxypnictide are
studied in a three-band model. The spin susceptibilities with various
interactions are calculated in the random phase approximation(PPA). It is found
that the spin susceptibility peaks around the M point show a spin density
wave(SDW) with momentum (0, ) and a clear stripe-like spin configuration.
The intra-band Coulomb repulsion enhances remarkably the SDW but the Hund's
coupling weakens it. It is shown that a new resonance appears at higher
temperatures at the point indicating the formation of a paramagnetic
phase. There is a clear transition from the SDW phase to the paramagnetic
phase.Comment: 4 pages,8 figure
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