13,714 research outputs found
Period fissioning and other instabilities of stressed elastic membranes
We study the shapes of elastic membranes under the simultaneous exertion of
tensile and compressive forces when the translational symmetry along the
tension direction is broken. We predict a multitude of novel morphological
phases in various regimes of a 2-dimensional parameter space
that defines the relevant mechanical and geometrical conditions. Theses
parameters are, respectively, the ratio between compression and tension, and
the wavelength contrast along the tension direction. In particular, our theory
associates the repetitive increase of pattern periodicity, recently observed on
wrinkled membranes floating on liquid and subject to capillary forces, to the
morphology in the regime () where tension is dominant
and the wavelength contrast is large.Comment: 4 pages, 4 figures. submitted to Phys. Rev. Let
Ramsey numbers and the size of graphs
For two graph H and G, the Ramsey number r(H, G) is the smallest positive
integer n such that every red-blue edge coloring of the complete graph K_n on n
vertices contains either a red copy of H or a blue copy of G. Motivated by
questions of Erdos and Harary, in this note we study how the Ramsey number
r(K_s, G) depends on the size of the graph G. For s \geq 3, we prove that for
every G with m edges, r(K_s,G) \geq c (m/\log m)^{\frac{s+1}{s+3}} for some
positive constant c depending only on s. This lower bound improves an earlier
result of Erdos, Faudree, Rousseau, and Schelp, and is tight up to a
polylogarithmic factor when s=3. We also study the maximum value of r(K_s,G) as
a function of m
Supporting shop floor workers with a multimedia task-oriented information system
This paper reports the work carried out as part of an industrial research
project sponsored by a major telecommunication industry based in the UK. The
main aim of the research was to investigate the extent to which a multimedia-
based information system, developed for shop floor workers, has contributed to
the increased efficiency and productivity Of manufacturing operations. To
achieve this, the work has focused on the design and execution of the evaluation
of the system. Due to the fact that the direct impact of the implementation of
the information system developed was difficult to demonstrate, it was decided to
adopt the system usage as a surrogate of the system's Success and the User
acceptance of the system was evaluated using both the Technology Acceptance
Model and the Task-Technology Fit model. (C) 2009 Elsevier B.V. All rights
reserved
Quick connect coupling
A coupling device has a transversely arranged, open-end groove in a flange attached to a pipe end. The groove in the flange receives a circumferentially arranged locking flange element on the other coupling member and permits alignment of the bores of the coupling members when the locking flange element is in the open end groove. Upon alignment of the bores of the coupling members, a trigger member is activated to automatically release a spring biased tubular member in one of the coupling members. The tubular member has a conical end which is displaced into the other coupling member to lock the coupling members to one another. A tensioning nut is threadedly movable on a coupling member so as to be moved into tightening engagement with the other coupling member
Global attraction of ODE-based mean field models with hyperexponential job sizes
Mean field modeling is a popular approach to assess the performance of large
scale computer systems. The evolution of many mean field models is
characterized by a set of ordinary differential equations that have a unique
fixed point. In order to prove that this unique fixed point corresponds to the
limit of the stationary measures of the finite systems, the unique fixed point
must be a global attractor. While global attraction was established for various
systems in case of exponential job sizes, it is often unclear whether these
proof techniques can be generalized to non-exponential job sizes. In this paper
we show how simple monotonicity arguments can be used to prove global
attraction for a broad class of ordinary differential equations that capture
the evolution of mean field models with hyperexponential job sizes. This class
includes both existing as well as previously unstudied load balancing schemes
and can be used for systems with either finite or infinite buffers. The main
novelty of the approach exists in using a Coxian representation for the
hyperexponential job sizes and a partial order that is stronger than the
componentwise partial order used in the exponential case.Comment: This paper was accepted at ACM Sigmetrics 201
Free Energy Approximations for CSMA networks
In this paper we study how to estimate the back-off rates in an idealized
CSMA network consisting of links to achieve a given throughput vector using
free energy approximations. More specifically, we introduce the class of
region-based free energy approximations with clique belief and present a closed
form expression for the back-off rates based on the zero gradient points of the
free energy approximation (in terms of the conflict graph, target throughput
vector and counting numbers). Next we introduce the size clique free
energy approximation as a special case and derive an explicit expression for
the counting numbers, as well as a recursion to compute the back-off rates. We
subsequently show that the size clique approximation coincides with a
Kikuchi free energy approximation and prove that it is exact on chordal
conflict graphs when . As a by-product these results provide us
with an explicit expression of a fixed point of the inverse generalized belief
propagation algorithm for CSMA networks. Using numerical experiments we compare
the accuracy of the novel approximation method with existing methods
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