9,367 research outputs found
Dynamics of a viscous vesicle in linear flows
An analytical theory is developed to describe the dynamics of a closed lipid
bilayer membrane (vesicle) freely suspended in a general linear flow.
Considering a nearly spherical shape, the solution to the creeping-flow
equations is obtained as a regular perturbation expansion in the excess area.
The analysis takes into account the membrane fluidity, incompressibility and
resistance to bending. The constraint for a fixed total area leads to a
non-linear shape evolution equation at leading order. As a result two regimes
of vesicle behavior, tank-treading and tumbling, are predicted depending on the
viscosity contrast between interior and exterior fluid. Below a critical
viscosity contrast, which depends on the excess area, the vesicle deforms into
a tank--treading ellipsoid, whose orientation angle with respect to the flow
direction is independent of the membrane bending rigidity. In the tumbling
regime, the vesicle exhibits periodic shape deformations with a frequency that
increases with the viscosity contrast. Non-Newtonian rheology such as normal
stresses is predicted for a dilute suspension of vesicles. The theory is in
good agreement with published experimental data for vesicle behavior in simple
shear flow
Young and very young stars in NGC 3372, the Carina nebula
Results are presented of a large-scale imaging photometric study of the stellar population in the northern part of NGC 3372 with a w avelength co verage from 0.33 to 2.5 µm. All observations were made at Las Campanas Observatory . The sizes of the three stellar clusters, Tr 14, Tr 15 and Tr 16, were determined b y means of star counts. Two-colour and colour-magnitude diagrams are presented and analyzed for eac h individual cluster. The three clusters were found to b e at a similar distance from the Sun, = 2 . 7 kpc, but with very large scatter in both A V and d . suggesting drastic variations in intracluster dust densit y . Dust particle size distribution variations are eviden t resulting in wide variations in extinction law. We determined ages bet ween 3 and 60 million years for Tr 15 and bet ween less than 1 and 6 million years for Tr 14 and Tr 16. The Tr 14 cluster is partially em bedded in a dense molecular cloud that extends to wards the south west reaching its highest densit y some three arcmin from the cluster nucleus. The ric h UV field created b y the Tr14 stars ionizes most of the visible HI I region in its vicinit y and most of the radio HI I region Car I. Deep J H K images of the Car I region reveal the presence of a young, em bedded stellar population that includes several O9–B0 stars and an ultracompact HI I region.Fil: Tapia, M.. Universidad Nacional Autónoma de México; MéxicoFil: Roth, M.. Las Campanas Observatory; ChileFil: Vazquez, Ruben Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica la Plata; ArgentinaFil: Persi, P.. IASFC, CNR; Itali
Speculative parallelism in Intel Cilk Plus
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 37).Certain algorithms can be effectively parallelized at the cost of performing some redundant work. One example is searching an unordered tree graph for a particular node. Each subtree can be searched in parallel by a separate thread. Once a single thread is successful, however, the work of the others is unneeded and should be ended. This type of computation is known as speculative parallelism. Typically, an abort command is provided in the programming language to provide this functionality, but some languages do not. This thesis shows how support for the abort command can be provided as a user-level library. A parallel version of the alpha beta search algorithm demonstrates its effectivenesss.by Ruben Perez.M.Eng
Fuzzy argumentation for trust
In an open Multi-Agent System, the goals of agents acting on behalf of their owners often conflict with each other. Therefore, a personal agent protecting the interest of a single user cannot always rely on them. Consequently, such a personal agent needs to be able to reason about trusting (information or services provided by) other agents. Existing algorithms that perform such reasoning mainly focus on the immediate utility of a trusting decision, but do not provide an explanation of their actions to the user. This may hinder the acceptance of agent-based technologies in sensitive applications where users need to rely on their personal agents. Against this background, we propose a new approach to trust based on argumentation that aims to expose the rationale behind such trusting decisions. Our solution features a separation of opponent modeling and decision making. It uses possibilistic logic to model behavior of opponents, and we propose an extension of the argumentation framework by Amgoud and Prade to use the fuzzy rules within these models for well-supported decisions
A one-parameter family of interpolating kernels for Smoothed Particle Hydrodynamics studies
A set of interpolating functions of the type f(v)={(sin[v pi/2])/(v pi/2)}^n
is analyzed in the context of the smoothed-particle hydrodynamics (SPH)
technique. The behaviour of these kernels for several values of the parameter n
has been studied either analytically as well as numerically in connection with
several tests carried out in two dimensions. The main advantage of this kernel
relies in its flexibility because for n=3 it is similar to the standard widely
used cubic-spline, whereas for n>3 the interpolating function becomes more
centrally condensed, being well suited to track discontinuities such as shock
fronts and thermal waves.Comment: 36 pages, 12 figures (low-resolution), published in J.C.
Texture control in a pseudospin Bose-Einstein condensate
We describe a wavefunction engineering approach to the formation of textures
in a two-component nonrotated Bose-Einstein condensate. By controlling the
phases of wavepackets that combine in a three-wave interference process, a
ballistically-expanding regular lattice-texture is generated, in which the
phases determine the component textures. A particular example is presented of a
lattice-texture composed of half-quantum vortices and spin-2 textures. We
demonstrate the lattice formation with numerical simulations of a viable
experiment, identifying the textures and relating their locations to a linear
theory of wavepacket interference.Comment: 4 pages, 5 figures, REVTeX4-
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