4,842 research outputs found
Understanding crack versus cavitation in pressure-sensitive adhesives: the role of kinetics
We perform traction experiments on viscous liquids highly confined between
parallel plates, a geometry known as the probe-tack test in the adhesion
community. Direct observation during the experiment coupled to force
measurement shows the existence of several mechanisms for releasing the stress.
Bubble nucleation and instantaneous growth had been observed in a previous
work. Upon increasing further the traction velocity or the viscosity, the
bubble growth is progressively delayed. At high velocities, cracks at the
interface between the plate and the liquid appear before the bubbles have grown
to their full size. Bubbles and cracks are thus observed concomitantly. At even
higher velocities, cracks develop fully so early that the bubbles are not even
visible. We present a theoretical model that describes these regimes, using a
Maxwell fluid as a model for the actual fluid, a highly viscous silicon oil. We
present the resulting phase diagramme for the different force peak regimes. The
predictions are compatible with the data. Our results show that in addition to
cavitation, interfacial cracks are encountered in a probe-tack traction test
with viscoelastic, \emph{liquid} materials and not solely with viscoelastic
solids like adhesives.Comment: 44 page
Prediction of microgeometrical influences on micropitting fatigue damage on 32CrMoV13 steel
Dr Fabre's sabbatical period at the Cardiff School of Engineering allowed the research to be conducted. Thanks are due to the M2P department of Arts et Métiers ParisTech, to Arts et Métiers ParisTech—Aix en Provence, and to the MécaSurf laboratory for supporting the visit financially, and to Cardiff University for provision of research facilities. Dr Sharif's contribution to the research was supported financially by UK Engineering & Physical Sciences Research Council (EPSRC) with Grant no. EP/G06024X/1.Micropitting is a form of surface fatigue damage that occurs in the gear teeth. It is due to the effect of variation in the mechanical loading in the contact zone between the two teeth, induced especially by flank roughness. In this study, generic roughness profiles were built with geometrical parameters to simulate the contact between two rough surfaces. Using elastohydrodynamic lubrication code and Crossland’s fatigue criteria, the influence on fatigue lifetime was analysed for changes in each parameter. The relevant parameters were determined that influence(i) the conventional pitting,(ii) the extent to which the von Mises equivalent stress exceeds the material yield stress in the zone where micropitting occurs, and(iii) the fatigue lifetime for steel teeth. With nitriding benefits, the same trends were shown with weaker effects
Direct Production of Tripartite Pump-Signal-Idler Entanglement in the Above-Threshold Optical Parametric Oscillator
We calculate the quantum correlations existing among the three output fields
(pump, signal, and idler) of a triply resonant non-degenerate Optical
Parametric Oscillator operating above threshold. By applying the standard
criteria [P. van Loock and A. Furusawa, Phys. Rev. A 67, 052315 (2003)], we
show that strong tripartite continuous-variable entanglement is present in this
well-known and simple system. Furthermore, since the entanglement is generated
directly from a nonlinear process, the three entangled fields can have very
different frequencies, opening the way for multicolored quantum information
networks.Comment: 4 pages, 3 figure
A CFD technique for estimating the flow distortion effects on LiDAR measurements when made in complex flow fields
The effect of flow distortion on the measurements produced by a LiDAR or SoDAR in close proximity to either complex terrain or a structure creating localised flow distortion is difficult to determine by analytical means. Also, as LiDARs and SoDARs are not point measurement devices, the techniques they employ for velocity measurements leads to complexities in the estimation of the effect of flow distortion on the accuracy of the measurements they make. This paper presents a method by which the effect of flow distortion on measurements made by a LiDAR in a distorted flow field may be determined using computational fluid dynamics. The results show that the error created by the flow distortion will cause the vector measured by a LiDAR to differ significantly from an equivalent point measurement. However, the results of the simulation show that, if the LiDAR is being used to measure the undisturbed flow field above a structure which creates highly localised flow distortion, the LiDAR results are less affected by the distortion of the local flow field than data acquired by a point measurement technique such as a cup anemometer
Three-Nucleon Continuum by means of the Hyperspherical Adiabatic Method
This paper investigates the possible use of the Hyperspherical Adiabatic
basis in the description of scattering states of a three-body system. In
particular, we analyze a 1+2 collision process below the three-body breakup.
The convergence patterns for the observables of interest are analyzed by
comparison to a unitary equivalent Hyperspherical Harmonic expansion.
Furthermore, we compare and discuss two different possible choices for
describing the asymptotic configurations of the system, related to the use of
Jacobi or hyperspherical coordinates. In order to illustrate the difficulties
and advantages of the approach two simple numerical applications are shown in
the case of neutron-deuteron scattering at low energies using s-wave
interactions. We found that the optimization driven by the Hyperspherical
Adiabatic basis is not as efficient for scattering states as in bound state
applications.Comment: 29 pages, 5 figures, accepted for publication in Few-Body Systems (in
press
Effect of Changing the Vocal Tract Shape on the Sound Production of the Recorder: An Experimental and Theoretical Study
Changing the vocal tract shape is one of the techniques which can be used by
the players of wind instruments to modify the quality of the sound. It has been
intensely studied in the case of reed instruments but has received only little
attention in the case of air-jet instruments. This paper presents a first study
focused on changes in the vocal tract shape in recorder playing techniques.
Measurements carried out with recorder players allow to identify techniques
involving changes of the mouth shape as well as consequences on the sound. A
second experiment performed in laboratory mimics the coupling with the vocal
tract on an artificial mouth. The phase of the transfer function between the
instrument and the mouth of the player is identified to be the relevant
parameter of the coupling. It is shown to have consequences on the spectral
content in terms of energy distribution among the even and odd harmonics, as
well as on the stability of the first two oscillating regimes. The results
gathered from the two experiments allow to develop a simplified model of sound
production including the effect of changing the vocal tract shape. It is based
on the modification of the jet instabilities due to the pulsating emerging jet.
Two kinds of instabilities, symmetric and anti-symmetric, with respect to the
stream axis, are controlled by the coupling with the vocal tract and the
acoustic oscillation within the pipe, respectively. The symmetry properties of
the flow are mapped on the temporal formulation of the source term, predicting
a change in the even / odd harmonics energy distribution. The predictions are
in qualitative agreement with the experimental observations
A quantum study of multi-bit phase coding for optical storage
We propose a scheme which encodes information in both the longitudinal and
spatial transverse phases of a continuous-wave optical beam. A split
detector-based interferometric scheme is then introduced to optimally detect
both encoded phase signals. In contrast to present-day optical storage devices,
our phase coding scheme has an information storage capacity which scales with
the power of the read-out optical beam. We analyse the maximum number of
encoding possibilities at the shot noise limit. In addition, we show that using
squeezed light, the shot noise limit can be overcome and the number of encoding
possibilities increased. We discuss a possible application of our phase coding
scheme for increasing the capacities of optical storage devices.Comment: 8 pages, 7 figures (Please email author for a PDF file if the
manuscript does not turn out properly
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