91 research outputs found
Pattern formation in directional solidification under shear flow. I: Linear stability analysis and basic patterns
An asymptotic interface equation for directional solidification near the
absolute stabiliy limit is extended by a nonlocal term describing a shear flow
parallel to the interface. In the long-wave limit considered, the flow acts
destabilizing on a planar interface. Moreover, linear stability analysis
suggests that the morphology diagram is modified by the flow near the onset of
the Mullins-Sekerka instability. Via numerical analysis, the bifurcation
structure of the system is shown to change. Besides the known hexagonal cells,
structures consisting of stripes arise. Due to its symmetry-breaking
properties, the flow term induces a lateral drift of the whole pattern, once
the instability has become active. The drift velocity is measured numerically
and described analytically in the framework of a linear analysis. At large flow
strength, the linear description breaks down, which is accompanied by a
transition to flow-dominated morphologies, described in a companion paper.
Small and intermediate flows lead to increased order in the lattice structure
of the pattern, facilitating the elimination of defects. Locally oscillating
structures appear closer to the instability threshold with flow than without.Comment: 20 pages, Latex, accepted for Physical Review
The combination of Index of NASH score and liver stiffness improves the noninvasive diagnostic accuracy for severe liver fibrosis in patients with NonAlcoholic Fatty Liver Disease.
Laparoendoscopic single site surgery in pediatric urology: does it require specialized tools?
Root polytopes and abelian ideals
We study the root polytope of a finite irreducible
crystallographic root system using its relation with the abelian ideals
of a Borel subalgebra of a simple Lie algebra with root system . We
determine the hyperplane arrangement corresponding to the faces of codimension
2 of and analyze its relation with the facets of . For of type or , we show that the orbits of some
special subsets of abelian ideals under the action of the Weyl group
parametrize a triangulation of . We show that this
triangulation restricts to a triangulation of the positive root polytope
.Comment: 41 pages, revised version, accepted for publication in Journal of
Algebraic Combinatoric
AU COMMENCEMENT ÉTAIT LA MÉTAPHORE: UNE INTUITION PRÉCOCE DE NIETZSCHE SUR LA PRIMAUTÉ DE LA MÉTAPHORE COMME MATRICE COGNITIVE
Design and realization of a low-noise front end for a RDSS mobile terminal
low-cost high-gain front-end amplifier has been developed at 2.5-GHz frequency for use in RDSS (radio determination satellite services) mobile terminals. The RDSS system allows an accurate positioning with the possibility of serving a large user population using the spread-spectrum modulation. Such an amplifier, built on 0.8-mm PTFE board, provides a low noise figure, a 31-dB gain and good input and output matching on the 16-MHz bandwidth allocation. All the results have been obtained using low-cost commercially available devices. (C) 1993 John Wiley & Sons, Inc
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