1,747 research outputs found
Roughness induced boundary slip in microchannel flows
Surface roughness becomes relevant if typical length scales of the system are
comparable to the scale of the variations as it is the case in microfluidic
setups. Here, an apparent boundary slip is often detected which can have its
origin in the assumption of perfectly smooth boundaries. We investigate the
problem by means of lattice Boltzmann (LB) simulations and introduce an
``effective no-slip plane'' at an intermediate position between peaks and
valleys of the surface. Our simulations show good agreement with analytical
results for sinusoidal boundaries, but can be extended to arbitrary geometries
and experimentally obtained surface data. We find that the detected apparent
slip is independent of the detailed boundary shape, but only given by the
distribution of surface heights. Further, we show that the slip diverges as the
amplitude of the roughness increases.Comment: 4 pages, 6 figure
Random-roughness hydrodynamic boundary conditions
We report results of lattice Boltzmann simulations of a high-speed drainage
of liquid films squeezed between a smooth sphere and a randomly rough plane. A
significant decrease in the hydrodynamic resistance force as compared with that
predicted for two smooth surfaces is observed. However, this force reduction
does not represent slippage. The computed force is exactly the same as that
between equivalent smooth surfaces obeying no-slip boundary conditions, but
located at an intermediate position between peaks and valleys of asperities.
The shift in hydrodynamic thickness is shown to depend on the height and
density of roughness elements. Our results do not support some previous
experimental conclusions on very large and shear-dependent boundary slip for
similar systems.Comment: 4 pages, 4 figure
Entrainment to an auditory signal: Is attention involved?
Many natural auditory signals, including music and language, change periodically. The effect of such auditory rhythms on the brain is unclear however. One widely held view, dynamic attending theory, proposes that the attentional system entrains to the rhythm and increases attention at moments of rhythmic salience. In support, 2 experiments reported here show reduced response times to visual letter strings shown at auditory rhythm peaks, compared with rhythm troughs. However, we argue that an account invoking the entrainment of general attention should further predict rhythm entrainment to also influence memory for visual stimuli. In 2 pseudoword memory experiments we find evidence against this prediction. Whether a pseudoword is shown during an auditory rhythm peak or not is irrelevant for its later recognition memory in silence. Other attention manipulations, dividing attention and focusing attention, did result in a memory effect. This raises doubts about the suggested attentional nature of rhythm entrainment. We interpret our findings as support for auditory rhythm perception being based on auditory-motor entrainment, not general attention entrainment
Simulation of fluid flow in hydrophobic rough microchannels
Surface effects become important in microfluidic setups because the surface
to volume ratio becomes large. In such setups the surface roughness is not any
longer small compared to the length scale of the system and the wetting
properties of the wall have an important influence on the flow. However, the
knowledge about the interplay of surface roughness and hydrophobic
fluid-surface interaction is still very limited because these properties cannot
be decoupled easily in experiments.
We investigate the problem by means of lattice Boltzmann (LB) simulations of
rough microchannels with a tunable fluid-wall interaction. We introduce an
``effective no-slip plane'' at an intermediate position between peaks and
valleys of the surface and observe how the position of the wall may change due
to surface roughness and hydrophobic interactions.
We find that the position of the effective wall, in the case of a Gaussian
distributed roughness depends linearly on the width of the distribution.
Further we are able to show that roughness creates a non-linear effect on the
slip length for hydrophobic boundaries.Comment: 10 pages, 5 figure
Autoantibodies to granulocytes in chronic inflammatory bowel disease are not correlated with antibodies to intestinal goblet cells in ulcerative colitis and to pancreatic juice in Crohn`s disease
Anti-idiotypic antibody Ab2/3H6 mimicking gp41: a potential HIV-1 vaccine?
Meeting abstract from 22nd European Society for Animal Cell Technology(ESACT) Meeting on Cell Based Technologies Vienna, Austria. 15-18 May 2011(VLID)90658
Aspectos hormonais, bioquĂmicos e hematolĂłgicos de prĂŠ e pĂłs-parto de suĂnos.
bitstream/item/84751/1/DCOT-045.pd
RSFQ devices with selective dissipation for quantum information processing
We study the possibility to use frequency dependent damping in RSFQ circuits
as means to reduce dissipation and consequent decoherence in RSFQ/qubit
circuits. We show that stable RSFQ operation can be achieved by shunting the
Josephson junctions with an circuit instead of a plain resistor. We derive
criteria for the stability of such an arrangement, and discuss the effect on
decoherence and the optimisation issues. We also design a simple flux generator
aimed at manipulating flux qubits
Realization of a classical counterpart of a scalable design for adiabatic quantum computation
We implement a classical counterpart of a scalable design for adiabatic
quantum computation. The key element of this design is a coupler providing
controllable coupling between two bistable elements (in our case
superconducting rings with a single Josephson junction playing the role of a
classical counterpart of superconducting flux qubits) The coupler is also a
superconducting ring with a single Josephson junction that operates in the
non-hysteretic mode. The flux coupling between two bistable rings can be
controlled by changing the magnetic flux through the coupler. Thereby, the
coupling can be tuned from ferromagnetic trough zero to to anti-ferromagnetic.Comment: 3 pages, 3 figures v2: extended discussion experimental result
Simulations of slip flow on nanobubble-laden surfaces
On microstructured hydrophobic surfaces, geometrical patterns may lead to the
appearance of a superhydrophobic state, where gas bubbles at the surface can
have a strong impact on the fluid flow along such surfaces. In particular, they
can strongly influence a detected slip at the surface. We present two-phase
lattice Boltzmann simulations of a flow over structured surfaces with attached
gas bubbles and demonstrate how the detected slip depends on the pattern
geometry, the bulk pressure, or the shear rate. Since a large slip leads to
reduced friction, our results allow to assist in the optimization of
microchannel flows for large throughput.Comment: 22 pages, 12 figure
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