9,006 research outputs found
Physics of beer tapping
The popular bar prank known in colloquial English as beer tapping consists in
hitting the top of a beer bottle with a solid object, usually another bottle,
to trigger the foaming over of the former within a few seconds. Despite the
trick being known for long time, to the best of our knowledge, the phenomenon
still lacks scientific explanation. Although it seems natural to think that
shock-induced cavitation enhances the diffusion of CO from the
supersaturated bulk liquid into the bubbles by breaking them up, the subtle
mechanism by which this happens remains unknown. Here we show that the overall
foaming-over process can be divided into three stages where different physical
phenomena take place in different time-scales, namely: bubble-collapse (or
cavitation) stage, diffusion-driven stage and buoyancy-driven stage. In the
bubble-collapse stage, the impact generates a train of expansion-compression
waves in the liquid that leads to the fragmentation of pre-existing gas
cavities. Upon bubble fragmentation, the sudden increase of the
interface-area-to-volume ratio enhances mass transfer significantly, which
makes the bubble volume grow by a large factor until CO is locally
depleted. At that point buoyancy takes over, making the bubble clouds rise and
eventually form buoyant vortex rings whose volume grows fast due to the
feedback between the buoyancy-induced rising speed and the advection-enhanced
CO transport from the bulk liquid to the bubble. The physics behind this
explosive process might also be connected to some geological phenomena.Comment: 7 pages, 4 figures, 4 movies Accepted in Physical Review Letter
Bubbles dynamics in microchannels: inertial and capillary migration forces
This work focuses on the dynamics of a train of unconfined bubbles flowing in
microchan- nels. We investigate the transverse position of a train of bubbles,
its velocity and the associated pressure drop when flowing in a microchannel
depending on the internal forces due to viscosity, inertia and capillarity.
Despite the small scales of the system, inertia, referred to as inertial
migration force, play a crucial role in determining the transverse equilibrium
position of the bubbles. Beside inertia and viscosity, other effects may also
affect the transverse migration of bubbles such as the Marangoni surface
stresses and the surface deformability. We look at the influence of surfactants
in the limit of infinite Marangoni effect which yields rigid bubble interface.
The resulting migration force may balance external body forces if present such
as buoyancy, Dean or magnetic ones. This balance not only determines the
transverse position of the bubbles but, consequently, the surrounding flow
structure, which can be determinant for any mass/heat transfer process
involved. Finally, we look at the influence of the bubble deformation on the
equilibrium position and compare it to the inertial migration force at the
centred position, explaining the stable or unstable character of this position
accordingly. A systematic study of the influence of the parameters - such as
the bubble size, uniform body force, Reynolds and capillary numbers - has been
carried out using numerical simulations based on the Finite Element Method,
solving the full steady Navier-Stokes equations and its asymptotic counterpart
for the limits of small Reynolds and/or capillary numbers.Comment: Submitted to JF
Molecular dynamics simulations of Ibuprofen release from pH-gated silica nanochannels
The iboprufen delivery process from cylindrical silica pores of diameter 3~nm, with polyamine chains anchored at the pore outlets,was investigated by means of massive molecular dynamics simulations. Effects from pH were introduced by considering polyamine chains with different degree of protonation. High, low and intermediate pH environments were investigated. The increment of the acidity of the environment leads to a significant decrease of the pore aperture, yielding an effective diameter, for the lowest pH case, that is 3.5~times smaller than the one associated to the highest pH one. Using a biased sampling procedure, Gibbs free energy profiles for the ibuprofen delivery process were obtained. The joint analysis of the corresponding profiles, time evolution of the ibuprofen position within the channel, orientation of the molecule and instantaneous effective diameter of the gate, suggests a 3-steps mechanism for ibuprofen delivery. A complementary analysis of the translational mobility of ibuprofen along the axial direction of the channel revealed a sub-diffusive dynamics in the low and intermediate pH cases.Deviations from Brownian diffusive dynamics are discussed and compared with direct experimental results. Fil: Rodriguez, Javier. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Núcleo de Investigación en Educacion Ciencia y Tecnologia; ArgentinaFil: Elola, Maria Dolores. Comisión Nacional de Energía Atómica; Argentin
On the von Neumann and Frank-Wolfe Algorithms with Away Steps
The von Neumann algorithm is a simple coordinate-descent algorithm to
determine whether the origin belongs to a polytope generated by a finite set of
points. When the origin is in the of the polytope, the algorithm generates a
sequence of points in the polytope that converges linearly to zero. The
algorithm's rate of convergence depends on the radius of the largest ball
around the origin contained in the polytope.
We show that under the weaker condition that the origin is in the polytope,
possibly on its boundary, a variant of the von Neumann algorithm that includes
generates a sequence of points in the polytope that converges linearly to zero.
The new algorithm's rate of convergence depends on a certain geometric
parameter of the polytope that extends the above radius but is always positive.
Our linear convergence result and geometric insights also extend to a variant
of the Frank-Wolfe algorithm with away steps for minimizing a strongly convex
function over a polytope
Project based learning on industrial informatics: applying IoT to urban garden
Copyright (c) 2018 IEEEThe fast evolution of technologies forces teachers to
trade content off for self-learning. PBL is one of the best ways
to promote self-learning and simultaneously boost motivation. In
this paper, we present our experience introducing project-based
learning in the last year subject. New Internet of Things (IoT) topic
allows us to carry out complete projects, integrating different
technologies and tools. Moreover, the selection of open-source and
standard free technologies makes easy and cheap the access to
hardware and software platforms used. We carefully have picked
communication, data management, and programming tools that
we think would be attractive to our students. They can start
making fast prototyping with little initial skills and, at the same
time, these are serious and popular tools widely used in the
industry. In this paper, we report on the design of a project-based
learning for our course and the impact this has on the
student satisfaction and motivation. Surveys taught us that tuning
the courses towards developing real projects on the field, has a
large impact on acceptance, learning objectives achievements and
motivation towards the course content.”I Plan Propio Integral de Docencia de la Universidad de Málaga” y Proyecto de Innovación Educativa PIE17/085, de la Universidad de Málaga. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
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