1,536 research outputs found
Hydrodynamic friction of fakir-like super-hydrophobic surfaces
A fluid droplet located on a super-hydrophobic surface makes contact with the
surface only at small isolated regions, and is mostly in contact with the
surrounding air. As a result, a fluid in motion near such a surface experiences
very low friction, and super-hydrophobic surfaces display strong drag-reduction
in the laminar regime. Here we consider theoretically a super-hydrophobic
surface composed of circular posts (so called fakir geometry) located on a
planar rectangular lattice. Using a superposition of point forces with suitably
spatially-dependent strength, we derive the effective surface slip length for a
planar shear flow on such a fakir surface as the solution to an infinite series
of linear equations. In the asymptotic limit of small surface coverage by the
posts, the series can be interpreted as Riemann sums, and the slip length can
be obtained analytically. For posts on a square lattice, our analytical results
are in excellent quantitative agreement with previous numerical computations
Which canonical algebras are derived equivalent to incidence algebras of posets?
We give a full description of all the canonical algebras over an
algebraically closed field that are derived equivalent to incidence algebras of
finite posets. These are the canonical algebras whose number of weights is
either 2 or 3.Comment: 8 pages; slight revision; to appear in Comm. Algebr
Finite-size effects in intracellular microrheology
We propose a model to explain finite-size effects in intracellular
microrheology observed in experiments. The constrained dynamics of the
particles in the intracellular medium, treated as a viscoelastic medium, is
described by means of a diffusion equation in which interactions of the
particles with the cytoskeleton are modelled by a harmonic force. The model
reproduces the observed power-law behavior of the mean-square displacement in
which the exponent depends on the ratio between
particle-to-cytoskeleton-network sizes.Comment: 6 pages 2 figures. To appear in the Journal of Chemical Physic
Singular point characterization in microscopic flows
We suggest an approach to microrheology based on optical traps in order to
measure fluid fluxes around singular points of fluid flows. We experimentally
demonstrate this technique, applying it to the characterization of controlled
flows produced by a set of birefringent spheres spinning due to the transfer of
light angular momentum. Unlike the previous techniques, this method is able to
distinguish between a singular point in a complex flow and the absence of flow
at all; furthermore it permits us to characterize the stability of the singular
point.Comment: 4 pages and 4 figure
Hydrodynamics of flagellated microswimmers near free-slip interfaces
The hydrodynamics of a flagellated microorganism is investigated when
swimming close to a planar free-slip surface by means of numerical solu- tions
of the Stokes equations obtained via a Boundary Element Method. Depending on
the initial condition, the swimmer can either escape from the free-slip surface
or collide with the boundary. Interestingly, the mi- croorganism does not
exhibit a stable orbit. Independently of escape or attraction to the interface,
close to a free-slip surface, the swimmer fol- lows a counter-clockwise
trajectory, in agreement with experimental find- ings, [15]. The hydrodynamics
is indeed modified by the free-surface. In fact, when the same swimmer moves
close to a no-slip wall, a set of initial conditions exists which result in
stable orbits. Moreover when moving close to a free-slip or a no-slip boundary
the swimmer assumes a different orientation with respect to its trajectory.
Taken together, these results contribute to shed light on the hydrodynamical
behaviour of microorgan- isms close to liquid-air interfaces which are relevant
for the formation of interfacial biofilms of aerobic bacteria
Critical Teaching Behaviors: What Does Good Teaching Look Like?
How can faculty and administrators identify and document evidence of “good” teaching? Defining “good” teaching as the implementation of evidence-based practices proven to foster success, we developed a Critical Teaching Behaviors framework consisting of six categories of observable behaviors: alignment, assessment, inclusive learning environment, student engagement, educational technology, and reflective practice. We will present an overview of the meta-analysis conducted to construct the framework, participants will then use the framework to reflect on their teaching practice before providing feedback on its design and usefulness in documenting effective teaching behaviors at their institutions
Partial synchronisation of stochastic oscillators through hydrodynamic coupling
Holographic optical tweezers are used to construct a static bistable optical
potential energy landscape where a Brownian particle experiences restoring
forces from two nearby optical traps and undergoes thermally activated
transitions between the two energy minima. Hydrodynamic coupling between two
such systems results in their partial synchronisation. This is interpreted as
an emergence of higher mobility pathways, along which it is easier to overcome
barriers to structural rearrangement.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
Tilted algebras and short chains of modules
We provide an affirmative answer for the question raised almost twenty years
ago concerning the characterization of tilted artin algebras by the existence
of a sincere finitely generated module which is not the middle of a short
chain
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