65 research outputs found
Finite time singularities in a class of hydrodynamic models
Models of inviscid incompressible fluid are considered, with the kinetic
energy (i.e., the Lagrangian functional) taking the form in 3D Fourier representation, where
is a constant, . Unlike the case (the usual Eulerian
hydrodynamics), a finite value of results in a finite energy for a
singular, frozen-in vortex filament. This property allows us to study the
dynamics of such filaments without the necessity of a regularization procedure
for short length scales. The linear analysis of small symmetrical deviations
from a stationary solution is performed for a pair of anti-parallel vortex
filaments and an analog of the Crow instability is found at small wave-numbers.
A local approximate Hamiltonian is obtained for the nonlinear long-scale
dynamics of this system. Self-similar solutions of the corresponding equations
are found analytically. They describe the formation of a finite time
singularity, with all length scales decreasing like ,
where is the singularity time.Comment: LaTeX, 17 pages, 3 eps figures. This version is close to the journal
pape
Modeling water waves beyond perturbations
In this chapter, we illustrate the advantage of variational principles for
modeling water waves from an elementary practical viewpoint. The method is
based on a `relaxed' variational principle, i.e., on a Lagrangian involving as
many variables as possible, and imposing some suitable subordinate constraints.
This approach allows the construction of approximations without necessarily
relying on a small parameter. This is illustrated via simple examples, namely
the Serre equations in shallow water, a generalization of the Klein-Gordon
equation in deep water and how to unify these equations in arbitrary depth. The
chapter ends with a discussion and caution on how this approach should be used
in practice.Comment: 15 pages, 1 figure, 39 references. This document is a contributed
chapter to an upcoming volume to be published by Springer in Lecture Notes in
Physics Series. Other author's papers can be downloaded at
http://www.denys-dutykh.com
N-body simulations of gravitational dynamics
We describe the astrophysical and numerical basis of N-body simulations, both
of collisional stellar systems (dense star clusters and galactic centres) and
collisionless stellar dynamics (galaxies and large-scale structure). We explain
and discuss the state-of-the-art algorithms used for these quite different
regimes, attempt to give a fair critique, and point out possible directions of
future improvement and development. We briefly touch upon the history of N-body
simulations and their most important results.Comment: invited review (28 pages), to appear in European Physics Journal Plu
Gendering the careers of young professionals: some early findings from a longitudinal study. in Organizing/theorizing: developments in organization theory and practice
Wonders whether companies actually have employees best interests at heart across physical, mental and spiritual spheres. Posits that most organizations ignore their workforce – not even, in many cases, describing workers as assets! Describes many studies to back up this claim in theis work based on the 2002 Employment Research Unit Annual Conference, in Cardiff, Wales
Association of accelerated atherosclerosis and myocardial hypertrophy with systemic lupus erythematosus
Relation of Osteoclast Activating Factor Production to Extent of Bone Disease in Multiple Myeloma
Capsular serotype, toxA gene, and antimicrobial susceptibility profiles of Pasteurella multocida isolated from pigs with pneumonia in Korea
Formation of vitisin A during red wine fermentation and maturation
The definitive version is available at www.blackwell-synergy.comDuring alcoholic fermentation the formation of vitisin A occurred mainly in the period between 20% and 85% glucose utilisation, when the concentrations of the precursors, malvidin-3-glucoside and pyruvic acid were at a maximum. The maximum rate of vitisin A synthesis of 11 mg/Lh occurred when 57% of glucose had been utilised and 440 mg/L malvidin-3-glucoside, 114 mg/L pyruvic acid and 3.1 mg/L measured oxygen were present. During maturation, production of vitisin A appeared to be linked with the availability of a suitable oxidant. Synthesis of vitisin A continued for approximately 6 months of maturation in air-tight bottles while the precursors were available. In wines that underwent malolactic fermentation, the malolactic bacteria consumed pyruvic acid and thereby limited the production of vitisin A. At the end of a 12 month maturation period, the concentration of vitisin A declined in wines made without any malolactic fermentation, even though malvidin-3-glucoside and pyruvic acid were still present. This indicated that there was a shortage of a suitable oxidant required to complete the reaction.Robert E. Asenstorfer, Andrew J. Markides, Patrick G. Iland and Graham P. Jone
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