228 research outputs found
Droplet actuation induced by coalescence: experimental evidences and phenomenological modeling
This paper considers the interaction between two droplets placed on a
substrate in immediate vicinity. We show here that when the two droplets are of
different fluids and especially when one of the droplet is highly volatile, a
wealth of fascinating phenomena can be observed. In particular, the interaction
may result in the actuation of the droplet system, i.e. its displacement over a
finite length. In order to control this displacement, we consider droplets
confined on a hydrophilic stripe created by plasma-treating a PDMS substrate.
This controlled actuation opens up unexplored opportunities in the field of
microfluidics. In order to explain the observed actuation phenomenon, we
propose a simple phenomenological model based on Newton's second law and a
simple balance between the driving force arising from surface energy gradients
and the viscous resistive force. This simple model is able to reproduce
qualitatively and quantitatively the observed droplet dynamics
Bouncing or sticky droplets: impalement transitions on superhydrophobic micropatterned surfaces
When a liquid drops impinges a hydrophobic rough surface it can either bounce
off the surface (fakir droplets) or be impaled and strongly stuck on it (Wenzel
droplets). The analysis of drop impact and quasi static ''loading'' experiments
on model microfabricated surfaces allows to clearly identify the forces
hindering the impalement transitions. A simple semi-quantitative model is
proposed to account for the observed relation between the surface topography
and the robustness of fakir non-wetting states. Motivated by potential
applications in microfluidics and in the fabrication of self cleaning surfaces,
we finally propose some guidelines to design robust superhydrophobic surfaces.Comment: 7 pages, 5 figure
Nocardial Endocarditis after Mitral Valve Replacement: Case Report and Review of the Literature
A Nocardia é responsável por diversos tipos de infecção quer em receptores imunocompetentes, quer imunocomprometidos e pode afectar qualquer órgão. A endocardite a Nocardia spp é muito rara e tem mau prognóstico. Segundo o nosso conhecimento e após revisão da literatura, foram reportados apenas 12 casos de endocardite a Nocardia, a maioria tratada com substituição valvular. Reportamos o primeiro caso descrito em Portugal de endocardite protésica a Nocardia, tratado com sucesso apenas com terapêutica antimicrobiana (trimetoprimsulfametoxazol), sem necessidade de substituição valvular
Modelling the evaporation of nanoparticle suspensions from heterogeneous surfaces
We present a Monte Carlo (MC) grid-based model for the drying of drops of a
nanoparticle suspension upon a heterogeneous surface. The model consists of a
generalised lattice-gas in which the interaction parameters in the Hamiltonian
can be varied to model different properties of the materials involved. We show
how to choose correctly the interactions, to minimise the effects of the
underlying grid so that hemispherical droplets form. We also include the
effects of surface roughness to examine the effects of contact-line pinning on
the dynamics. When there is a `lid' above the system, which prevents
evaporation, equilibrium drops form on the surface, which we use to determine
the contact angle and how it varies as the parameters of the model are changed.
This enables us to relate the interaction parameters to the materials used in
applications. The model has also been applied to drying on heterogeneous
surfaces, in particular to the case where the suspension is deposited on a
surface consisting of a pair of hydrophilic conducting metal surfaces that are
either side of a band of hydrophobic insulating polymer. This situation occurs
when using inkjet printing to manufacture electrical connections between the
metallic parts of the surface. The process is not always without problems,
since the liquid can dewet from the hydrophobic part of the surface, breaking
the bridge before the drying process is complete. The MC model reproduces the
observed dewetting, allowing the parameters to be varied so that the conditions
for the best connection can be established. We show that if the hydrophobic
portion of the surface is located at a step below the height of the
neighbouring metal, the chance of dewetting of the liquid during the drying
process is significantly reduced.Comment: 14 pages, 14 figure
Interfacial motion in flexo- and order-electric switching between nematic filled states
We consider a nematic liquid crystal, in coexistence with its isotropic
phase, in contact with a substrate patterned with rectangular grooves. In such
a system, the nematic phase may fill the grooves without the occurrence of
complete wetting. There may exist multiple (meta)stable filled states, each
characterised by the type of distortion (bend or splay) in each corner of the
groove and by the shape of the nematic-isotropic interface, and additionally
the plateaux that separate the grooves may be either dry or wet with a thin
layer of nematic. Using numerical simulations, we analyse the dynamical
response of the system to an externally- applied electric field, with the aim
of identifying switching transitions between these filled states. We find that
order-electric coupling between the fluid and the field provides a means of
switching between states where the plateaux between grooves are dry and states
where they are wet by a nematic layer, without affecting the configuration of
the nematic within the groove. We find that flexoelectric coupling may change
the nematic texture in the groove, provided that the flexoelectric coupling
differentiates between the types of distortion at the corners of the substrate.
We identify intermediate stages of the transitions, and the role played by the
motion of the nematic-isotropic interface. We determine quantitatively the
field magnitudes and orientations required to effect each type of transition.Comment: 14 pages, 12 fig
Dynamics of the spontaneous breakdown of superhydrophobicity
Drops deposited on rough and hydrophobic surfaces can stay suspended with gas
pockets underneath the liquid, then showing very low hydrodynamic resistance.
When this superhydrophobic state breaks down, the subsequent wetting process
can show different dynamical properties. A suitable choice of the geometry can
make the wetting front propagate in a stepwise manner leading to {\it
square-shaped} wetted area: the front propagation is slow and the patterned
surface fills by rows through a {\it zipping} mechanism. The multiple time
scale scenario of this wetting process is experimentally characterized and
compared to numerical simulations.Comment: 7 pages, 5 figure
Geometry dominated fluid adsorption on sculptured substrates
Experimental methods allow the shape and chemical composition of solid
surfaces to be controlled at a mesoscopic level. Exposing such structured
substrates to a gas close to coexistence with its liquid can produce quite
distinct adsorption characteristics compared to that occuring for planar
systems, which may well play an important role in developing technologies such
as super-repellent surfaces or micro-fluidics. Recent studies have concentrated
on adsorption of liquids at rough and heterogeneous substrates and the
characterisation of nanoscopic liquid films. However, the fundamental effect of
geometry has hardly been addressed. Here we show that varying the shape of the
substrate can exert a profound influence on the adsorption isotherms allowing
us to smoothly connect wetting and capillary condensation through a number of
novel and distinct examples of fluid interfacial phenomena. This opens the
possibility of tailoring the adsorption properties of solid substrates by
sculpturing their surface shape.Comment: 6 pages, 4 figure
Hydrokinetic simulations of nanoscopic precursor films in rough channels
We report on simulations of capillary filling of high-wetting fluids in
nano-channels with and without obstacles. We use atomistic (molecular dynamics)
and hydrokinetic (lattice-Boltzmann) approaches which point out clear evidence
of the formation of thin precursor films, moving ahead of the main capillary
front. The dynamics of the precursor films is found to obey a square-root law
as the main capillary front, z^2(t) ~ t, although with a larger prefactor,
which we find to take the same value for the different geometries (2D-3D) under
inspection. The two methods show a quantitative agreement which indicates that
the formation and propagation of thin precursors can be handled at a
mesoscopic/hydrokinetic level. This can be considered as a validation of the
Lattice-Boltzmann (LB) method and opens the possibility of using hydrokinetic
methods to explore space-time scales and complex geometries of direct
experimental relevance. Then, LB approach is used to study the fluid behaviour
in a nano-channel when the precursor film encounters a square obstacle. A
complete parametric analysis is performed which suggests that thin-film
precursors may have an important influence on the efficiency of
nanochannel-coating strategies.Comment: 16 pages, 8 figures; To be published on JSTAT: Journal of statistical
mechanics: Theory and experiment
Triagem de Manchester nas Síndromes Coronárias Agudas
INTRODUCTION:
A growing number of hospitals have implemented the Manchester Triage System (MTS) in their Emergency Department (ED), so as to better prioritize the evaluation of those attending these departments.
OBJECTIVES:
To assess whether the MTS was used effectively in patients admitted to the hospital with a diagnosis of acute coronary syndrome (ACS).
METHODS:
We evaluated 114 consecutive patients admitted to the Cardiology Department with a diagnosis of ACS. We recorded the color assigned in the MTS, mean time from arrival in the ED to MTS, mean time from MTS to first medical assessment (1-MA) and mean time from 1-MA to admission. We also analyzed the correlation between the type of ACS and clinical presentation and its relation with MTS.
RESULTS:
Of the 114 patients, one was coded red (0.9%), 71 orange (62.3%), 12 green (11%), and two were not assigned a color code according to MTS because they were admitted via a Medical Emergency and Resuscitation Vehicle. Mean time from arrival in the ED to MTS was 5.2 +/- 0.6 min and from MTS to MA was 20 +/- 2.5 min. In patients triaged as orange the time from MTS to MA was 15.1 +/- 1.5 min, as yellow 36.2 +/- 7 min, and as green 35.2 +/- 20.6 min (p = 0.003). Mean time from 1-MA to admission was 144.4 +/- 17 min, with no differences according to triage code or ACS type. Clinical presentation influenced triage and the speed of 1-MA and admission, patients with typical presentation being evaluated and admitted more quickly.
CONCLUSIONS:
Most patients admitted for ACS are initially triaged as orange or yellow, an indication for prompt assessment in the ED; this has a positive effect on time to first medical assessment, but has no effect on time to hospital admission
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