64,206 research outputs found
A note on the breathing mode of an elastic sphere in Newtonian and complex fluids
Experiments on the acoustic vibrations of elastic nanostructures in fluid
media have been used to study the mechanical properties of materials, as well
as for mechanical and biological sensing. The medium surrounding the
nanostructure is typically modeled as a Newtonian fluid. A recent experiment
however suggested that high-frequency longitudinal vibration of bipyramidal
nanoparticles could trigger a viscoelastic response in water-glycerol mixtures
[M. Pelton et al., "Viscoelastic flows in simple liquids generated by vibrating
nanostructures," Phys. Rev. Lett. 111, 244502 (2013)]. Motivated by these
experimental studies, we first revisit a classical continuum mechanics problem
of the purely radial vibration of an elastic sphere, also called the breathing
mode, in a compressible viscous fluid, and then extend our analysis to a
viscoelastic medium using the Maxwell fluid model. The effects of fluid
compressibility and viscoelasticity are discussed. Although in the case of
longitudinal vibration of bipyramidal nanoparticles, the effects of fluid
compressibility were shown to be negligible, we demonstrate that it plays a
significant role in the breathing mode of an elastic sphere. On the other hand,
despite the different vibration modes, the breathing mode of a sphere triggers
a viscoelastic response in water-glycerol mixtures similar to that triggered by
the longitudinal vibration of bipyramidal nanoparticles. We also comment on the
effect of fluid viscoelasticity on the idea of destroying virus particles by
acoustic resonance
Simon Grant, Monti, Martin Osherson, Daniel
The classical theory of preference among monetary bets represents people as expected utility maximizers with nondecreasing concave utility functions. Critics of this account often rely on assumptions about preferences over wide ranges of total wealth. We derive a prediction of the theory that bears on bets at any fixed level of wealth, and test the prediction behaviorally. Our results are discrepant with the classical account. Competing theories are also examined in light of our data.
Design and use of a hackable digital instrument
This paper introduces the D-Box, a new digital musical instrument specifically designed to elicit unexpected creative uses and to support modification by the performer. Rather than taking a modular approach, the D-Box is a hackable instrument which allows for the discovery of novel working configurations through circuit bending techniques. Starting from the concept of appropriation, this paper describes the design, development and evaluation process lasting more than one year and made in collaboration with musicians and hackers.This work was funded by the UK Engineering and Physical Sciences Research Council under grant EP/K032046/1 (2013-14)
Learning mixtures of structured distributions over discrete domains
Let be a class of probability distributions over the discrete
domain We show that if satisfies a rather
general condition -- essentially, that each distribution in can
be well-approximated by a variable-width histogram with few bins -- then there
is a highly efficient (both in terms of running time and sample complexity)
algorithm that can learn any mixture of unknown distributions from
We analyze several natural types of distributions over , including
log-concave, monotone hazard rate and unimodal distributions, and show that
they have the required structural property of being well-approximated by a
histogram with few bins. Applying our general algorithm, we obtain
near-optimally efficient algorithms for all these mixture learning problems.Comment: preliminary full version of soda'13 pape
The Stable Manifold Theorem for Stochastic Differential Equations
We formulate and prove a {\it Local Stable Manifold Theorem\/} for stochastic
differential equations (sde's) that are driven by spatial Kunita-type
semimartingales with stationary ergodic increments. Both Stratonovich and
It\^o-type equations are treated. Starting with the existence of a stochastic
flow for a sde, we introduce the notion of a hyperbolic stationary trajectory.
We prove the existence of invariant random stable and unstable manifolds in the
neighborhood of the hyperbolic stationary solution. For Stratonovich sde's, the
stable and unstable manifolds are dynamically characterized using forward and
backward solutions of the anticipating sde. The proof of the stable manifold
theorem is based on Ruelle-Oseledec multiplicative ergodic theory
Quantum MHV diagrams
Over the past two years, the use of on-shell techniques has deepened our understanding of the S-matrix of gauge theories and led to the calculation of many new scattering amplitudes. In these notes we review a particular on-shell method developed recently, the quantum MHV diagrams, and discuss applications to one-loop amplitudes. Furthermore, we briefly discuss the application of D-dimensional generalised unitarity to the calculation of scattering amplitudes in non-supersymmetric Yang-Mills
Comparative evaluation of predicted and measured performance of a 68-cubic meter truncated reverberant noise chamber
The performance of a medium size, truncated reverberation chamber is evaluated in detail. Chamber performance parameters are predicted, using classical acoustic theory, and are compared to results from actual chamber measurements. Discrepancies are discussed in relation to several available empirical corrections developed by other researchers. Of more practical interest is the confirmation of a recent theory stating that the present guide for the ratio of specimen volume to test chamber volume, approximately 10 percent, is overly conservative, and can be increased by a factor of at least 2 and possibly 3. Results and theoretical justification of these findings are presented
Recommended from our members
Do you want to bet? The prevalence of problem gambling amongst athletes in the UK
This presentation was given as part of the 2011 London Workshop on Problem Gambling: Theory and (Best) Practice by Dr Daniel Rhind from the Sports Sciences subject area at Brunel University. The workshop was organised by Professor Fernand Gobet and Dr Marvin Schiller and hosted by Brunel University on the 13th September 2011
- …