2,038 research outputs found
Pair creation, motion, and annihilation of topological defects in 2D nematics
We present a novel framework for the study of disclinations in
two-dimensional active nematic liquid crystals, and topological defects in
general. The order tensor formalism is used to calculate exact multi-particle
solutions of the linearized static equations inside a uniformly aligned state.
Topological charge conservation requires a fixed difference between the number
of half charges. Starting from a set of hydrodynamic equations, we derive a
low-dimensional dynamical system for the parameters of the static solutions,
which describes the motion of a half-disclination pair, or of several pairs.
Within this formalism, we model defect production and annihilation, as observed
in experiments. Our dynamics also provide an estimate for the critical density
at which production and annihilation rates are balanced
Multiplicity dependence of correlation functions in \bar{p}p reactions at sqrt(s) = 630 GeV
Discussions about Bose-Einstein correlations between decay products of
coproduced W-bosons again raise the question about the behaviour of
correlations if several strings are produced. This is studied by the
multiplicity dependence of correlation functions of particle pairs with
like-sign and opposite-sign charge in \bar{p}p reactions at sqrt{s} = 630 GeV.Comment: 11 pages latex, 4 figs, includes elsart.cls, submitted to Phys Lett
Determining source cumulants in femtoscopy with Gram-Charlier and Edgeworth series
Lowest-order cumulants provide important information on the shape of the
emission source in femtoscopy. For the simple case of noninteracting identical
particles, we show how the fourth-order source cumulant can be determined from
measured cumulants in momentum space. The textbook Gram-Charlier series is
found to be highly inaccurate, while the related Edgeworth series provides
increasingly accurate estimates. Ordering of terms compatible with the Central
Limit Theorem appears to play a crucial role even for nongaussian
distributions.Comment: 11 pages, 2 figure
Combustion of hydrogen in a two-dimensional duct with step fuel injectors
An investigation of the combustion of hydrogen perpendicularly injected from step fuel injectors into a Mach 2.72, 2100 K vitiated test gas was conducted. The model simulated the flow between the center and side struts of an integrated scramjet module at Mach 7 flight and an altitude of 29 km. Parametric variation included equivalence ratio, fuel dynamic pressure ratio, and area distribution of the model. The overall area ratio of the model was held constant at 2.87. The data analysis indicated that no measurable improvement in mixing or combustion efficiency was obtained by varying the fuel dynamic pressure ratio from 0.79 to 2.45. Computations indicated approximately 80 percent of the fuel was mixed so that it could react; however, only approximately 50 percent of the mixed fuel actually reacted in two test configurations, and 74 percent in later tests where less area expansion of the flow occurred
One-Dimensional Approximation of Viscous Flows
Attention has been paid to the similarity and duality between the
Gregory-Laflamme instability of black strings and the Rayleigh-Plateau
instability of extended fluids. In this paper, we derive a set of simple
(1+1)-dimensional equations from the Navier-Stokes equations describing thin
flows of (non-relativistic and incompressible) viscous fluids. This
formulation, a generalization of the theory of drop formation by Eggers and his
collaborators, would make it possible to examine the final fate of
Rayleigh-Plateau instability, its dimensional dependence, and possible
self-similar behaviors before and after the drop formation, in the context of
fluid/gravity correspondence.Comment: 17 pages, 3 figures; v2: refs & comments adde
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