2,292 research outputs found
The effect of amino acid deprivation on the transfer of iron through Caco-2 cell monolayers
Funding Source Rural and Environmental Scientific and Analytical Services, the Scottish Government Acknowledgments We thank Dr Helen Hayes for her technical support during this project. We also thank Dr Christine Kennedy for her involvement at the beginning of this project. This study was funded by Rural and Environmental Scientific and Advisory Service of Scottish Government.Peer reviewedPostprin
Nanorheology : an Investigation of the Boundary Condition at Hydrophobic and Hydrophilic Interfaces
t has been shown that the flow of a simple liquid over a solid surface can
violate the so-called no-slip boundary condition. We investigate the flow of
polar liquids, water and glycerol, on a hydrophilic Pyrex surface and a
hydrophobic surface made of a Self-Assembled Monolayer of OTS
(octadecyltrichlorosilane) on Pyrex. We use a Dynamic Surface Force Apparatus
(DSFA) which allows one to study the flow of a liquid film confined between two
surfaces with a nanometer resolution. No-slip boundary conditions are found for
both fluids on hydrophilic surfaces only. Significant slip is found on the
hydrophobic surfaces, with a typical length of one hundred nanometers.Comment: 8 pages, 7 figures, 2 tables. Accepted for European Physical Journal
E - Sofr Mate
Slippage of water past superhydrophobic carbon nanotube forests in microchannels
We present in this letter an experimental characterization of liquid flow
slippage over superhydrophobic surfaces made of carbon nanotube forests,
incorporated in microchannels. We make use of a micro-PIV (Particule Image
Velocimetry) technique to achieve the submicrometric resolution on the flow
profile necessary for accurate measurement of the surface hydrodynamic
properties. We demonstrate boundary slippage on the Cassie superhydrophobic
state, associated with slip lengths of a few microns, while a vanishing slip
length is found in the Wenzel state, when the liquid impregnates the surface.
Varying the lateral roughness scale L of our carbon nanotube forest-based
superhydrophobic surfaces, we demonstrate that the slip length varies linearly
with L in line with theoretical predictions for slippage on patterned surfaces.Comment: under revie
Colloidal motility and pattern formation under rectified diffusiophoresis
In this letter, we characterize experimentally the diffusiophoretic motion of
colloids and lambda- DNA toward higher concentration of solutes, using
microfluidic technology to build spatially- and temporally-controlled
concentration gradients. We then demonstrate that segregation and spatial
patterning of the particles can be achieved from temporal variations of the
solute concentration profile. This segregation takes the form of a strong
trapping potential, stemming from an osmotically induced rectification
mechanism of the solute time-dependent variations. Depending on the spatial and
temporal symmetry of the solute signal, localization patterns with various
shapes can be achieved. These results highlight the role of solute contrasts in
out-of-equilibrium processes occuring in soft matter
Effect of Patterned Slip on Micro and Nanofluidic Flows
We consider the flow of a Newtonian fluid in a nano or microchannel with
walls that have patterned variations in slip length. We formulate a set of
equations to describe the effects on an incompressible Newtonian flow of small
variations in slip, and solve these equations for slow flows. We test these
equations using molecular dynamics simulations of flow between two walls which
have patterned variations in wettability. Good qualitative agreement and a
reasonable degree of quantitative agreement is found between the theory and the
molecular dynamics simulations. The results of both analyses show that
patterned wettability can be used to induce complex variations in flow. Finally
we discuss the implications of our results for the design of microfluidic
mixers using slip.Comment: 13 pages, 12 figures, final version for publicatio
Dynamic clustering in active colloidal suspensions with chemical signaling
In this paper, we explore experimentally the phase behavior of a dense active
suspension of self- propelled colloids. In addition to a solid-like and a
gas-like phase observed for high and low densities, a novel cluster phase is
reported at intermediate densities. This takes the form of a stationary
assembly of dense aggregates, with an average size which grows with activity as
a linear function of the self-propelling velocity. While different possible
scenarii can be considered to account for these observations - such as a
generic velocity weakening instability recently put forward -, we show that the
experimental results are reproduced by a chemotactic aggregation mechanism,
originally introduced to account for bacterial aggregation, and accounting here
for diffusiophoretic chemical interaction between colloidal swimmers.Comment: supplementary video :http://
www-lpmcn.univ-lyon1.fr/~lbocquet/Movie-Theurkauff-SI.av
Sedimentation of active colloidal suspensions
In this paper, we investigate experimentally the non-equilibrium steady state
of an active colloidal suspension under gravity field. The active particles are
made of chemically powered colloids, showing self propulsion in the presence of
an added fuel, here hydrogen peroxide. The active suspension is studied in a
dedicated microfluidic device, made of permeable gel microstructures. Both the
microdynamics of individual colloids and the global stationary state of the
suspension under gravity - density profiles, number fluctuations - are measured
with optical microscopy. This allows to connect the sedimentation length to the
individual self-propelled dynamics, suggesting that in the present dilute
regime the active colloids behave as 'hot' particles. Our work is a first step
in the experimental exploration of the out-of-equilibrium properties of
artificial active systems.Comment: 4 pages, 4 figure
Rate effects on layering of a confined linear alkane
We perform drainage experiments of a linear alkane fluid (n-hexadecane) down
to molecular thicknesses, and focus on the role played by the confinement rate.
We show that molecular layering is strongly influenced by the velocity at which
the confining walls are approached: under high enough shear rates, the confined
medium behaves as a structureless liquid of enhanced viscosity for film
thickness below 10 nm. Our results also lead us to conclude that a
rapidly confined film can be quenched in a metastable disordered state, which
might be related with recent intriguing results on the shear properties of
confined films produced at different rates [Zhu and Granick, Phys. Rev. Lett.
{\bf 93}, 096101 (2004)]
The effect of maternal iron deficiency on zinc and copper levels and on genes of zinc and copper metabolism during pregnancy in the rat
Fe deficiency is relatively common in pregnancy and has both short- and long-term consequences. However, little is known about the effect on the metabolism of other micronutrients. A total of fifty-four female rats were fed control (50 mg Fe/kg) or Fe-deficient diets (7·5 mg/kg) before and during pregnancy. Maternal liver, placenta and fetal liver were collected at day 21 of pregnancy for Cu and Zn analysis and to measure expression of the major genes of Cu and Zn metabolism. Cu levels increased in the maternal liver (P=0·002) and placenta (P=0·018) of Fe-deficient rats. Zn increased (P<0·0001) and Cu decreased (P=0·006) in the fetal liver. Hepatic expression of the Cu chaperones antioxidant 1 Cu chaperone (P=0·042) and cytochrome c oxidase Cu chaperone (COX17, P=0·020) decreased in the Fe-deficient dams, while the expression of the genes of Zn metabolism was unaltered. In the placenta, Fe deficiency reduced the expression of the chaperone for superoxide dismutase 1, Cu chaperone for superoxide dismutase (P=0·030), ceruloplasmin (P=0·042) and Zn transport genes, ZRT/IRT-like protein 4 (ZIP4, P=0·047) and Zn transporter 1 (ZnT1, P=0·012). In fetal liver, Fe deficiency increased COX17 (P=0·020), ZRT/IRT-like protein 14 (P=0·036) and ZnT1 (P=0·0003) and decreased ZIP4 (P=0·004). The results demonstrate that Fe deficiency during pregnancy has opposite effects on Cu and Zn levels in the fetal liver. This may, in turn, alter metabolism of these nutrients, with consequences for development in the fetus and the neonate.</p
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