Lateral instability in normal viscous fingers

We study a low-amplitude, long-wavelength lateral instability of the Saffman-Taylor finger by means of a phase-field model. We observe such an instability in two situations in which small dynamic perturbations are overimposed to a constant pressure drop. We first study the case in which the perturbation consists of a single oscillatory mode and then a case in which the perturbation consists of temporal noise. In both cases the instability undergoes a process of selection

The long cross-over dynamics of capillary imbibition

Spontaneous capillary imbibition is a classical problem in interfacial fluid dynamics with a broad range of applications, from microfluidics to agriculture. Here we study the duration of the cross-over between an initial linear growth of the imbibition front to the diffusive-like growth limit of Washburn's law. We show that local-resistance sources, such as the inertial resistance and the friction caused by the advancing meniscus, always limit the motion of an imbibing front. Both effects give rise to a cross-over of the growth exponent between the linear and the diffusive-like regimes. We show how this cross-over is much longer than previously thought - even longer than the time it takes the liquid to fill the porous medium. Such slowly slowing-down dynamics is likely to cause similar long cross-over phenomena in processes governed by wetting

Outcomes from elective colorectal cancer surgery during the SARS-CoV-2 pandemic

This study aimed to describe the change in surgical practice and the impact of SARS-CoV-2 on mortality after surgical resection of colorectal cancer during the initial phases of the SARS-CoV-2 pandemic

Dynamics of driven three-dimensional thin films: from hdrophilic to superhydrophobic substrates

We study the forced displacement of a thin film of fluid in contact with vertical and inclined substrates of different wetting properties, that range from hydrophilic to hydrophobic, using the lattice-Boltzmann method. We study the stability and pattern formation of the contact line in the hydrophilic and superhydrophobic regimes, which correspond to wedge-shaped and nose-shaped fronts, respectively. We find that contact lines are considerably more stable for hydrophilic substrates and small inclination angles. The qualitative behavior of the front in the linear regime remains independent of the wetting properties of the substrate as a single dispersion relation describes the stability of both wedges and noses. Nonlinear patterns show a clear dependence on wetting properties and substrate inclination angle. The effect is quantified in terms of the pattern growth rate, which vanishes for the sawtooth pattern and is finite for the finger pattern. Sawtooth shaped patterns are observed for hydrophilic substrates and low inclination angles, while finger-shaped patterns arise for hydrophobic substrates and large inclination angles. Finger dynamics show a transient in which neighboring fingers interact, followed by a steady state where each finger grows independently

Three-dimensional aspects of fluid flows in channels. II. Effects of meniscus and thin film regimes on viscous fingers

We perform a three-dimensional study of steady state viscous fingers that develop in linear channels. By means of a three-dimensional lattice-Boltzmann scheme that mimics the full macroscopic equations of motion of the fluid momentum and order parameter, we study the effect of the thickness of the channel in two cases. First, for total displacement of the fluids in the channel thickness direction, we find that the steady state finger is effectively two-dimensional and that previous two-dimensional results can be recovered by taking into account the effect of a curved meniscus across the channel thickness as a contribution to surface stresses. Second, when a thin film develops in the channel thickness direction, the finger narrows with increasing channel aspect ratio in agreement with experimental results. The effect of the thin film renders the problem three-dimensional and results deviate from the two-dimensional prediction

Theory of Wetting-Induced Fluid Entrainment by Advancing Contact Lines on Dry Surfaces

We report on the onset of fluid entrainment when a contact line is forced to advance over a dry solid of arbitrary wettability. We show that entrainment occurs at a critical advancing speed beyond which the balance between capillary, viscous, and contact-line forces sustaining the shape of the interface is no longer satisfied. Wetting couples to the hydrodynamics by setting both the morphology of the interface at small scales and the viscous friction of the front. We find that the critical deformation that the interface can sustain is controlled by the friction at the contact line and the viscosity contrast between the displacing and displaced fluids, leading to a rich variety of wetting-entrainment regimes. We discuss the potential use of our theory to measure contact-line forces using atomic force microscopy and to study entrainment under microfluidic conditions exploiting colloid-polymer fluids of ultralow surface tension

Three-dimensional aspects of fluid flows in channels. I. Meniscus and thin film regimes

We study the forced displacement of a fluid-fluid interface in a three-dimensional channel formed by two parallel solid plates. Using a lattice-Boltzmann method, we study situations in which a slip velocity arises from diffusion effects near the contact line. The difference between the slip and channel velocities determines whether the interface advances as a meniscus or a thin film of fluid is left adhered to the plates. We find that this effect is controlled by the capillary and Péclet numbers. We estimate the crossover from a meniscus to a thin film and find good agreement with numerical results. The penetration regime is examined in the steady state. We find that the occupation fraction of the advancing finger relative to the channel thickness is controlled by the capillary number and the viscosity contrast between the fluids. For high viscosity contrast, lattice-Boltzmann results agree with previous results. For zero viscosity contrast, we observe remarkably narrow fingers. The shape of the finger is found to be universal

Lateral instability in normal viscous fingers

We study a low-amplitude, long-wavelength lateral instability of the Saffman-Taylor finger by means of a phase-field model. We observe such an instability in two situations in which small dynamic perturbations are overimposed to a constant pressure drop. We first study the case in which the perturbation consists of a single oscillatory mode and then a case in which the perturbation consists of temporal noise. In both cases the instability undergoes a process of selection

Políticas públicas

Amputación de extremidades superiores: caracterización epidemiológicaAnálisis comparado de las políticas de promoción de la salud entre Chile y CataluñaAnálisis de los Avisa para la toma de decisiones en políticas de saludAntecedentes de colelitiasis en pacientes que presentaron colecistitis aguda. ¿Se puede prevenir la urgencia?Asociación entre alcoholemia y traumatismos en Copiapó, 2009Automedicación en la población asistente al Cesfam de Puerto NatalesAutotoma vaginal para detección de VPH para la prevención de cáncer cervicouterino, ChileCalidad de atención programa Auge- cáncer cervicouterino: la perspectiva de los profesionalesCaracterización de los casos de traumatismo encéfalo craneano en la comuna de Til-TilConocimiento de conductores universitarios sobre la alcoholemia permitida para conducir y su equivalencia en bebidas alcohólicasDescripción de la consulta dermatológica pediátrica en el Hospital Roberto del Río (2007-2008)Elementos para un abordaje metodológico de la salud intercultural en la Región Metropolitana de SantiagoEstudio descriptivo de consultas Sapu Cesfam Angachilla, visión tras dos años de registro clínico-electrónicoEstudio descriptivo de ingresos a Conin Valdivia, una revisión de 10 años (1998-2008)Estudio descriptivo de pacientes hospitalizados por absceso y celulitis peritonsilar en el hospital de PurranqueEvaluación de la aceptabilidad y consumo de alimentos del Pacam inscritos en el Cesfam Dr. V.M.FEvaluación de la interacción de medicinas alternativas o complementarias (MAC) en dos centros APSExposición a humo de tabaco ambiental. Signos y síntomas respiratorios bajos: estudio de prevalenciaFactores relacionados con la rotación laboral de médicos en consultorios del Gran SantiagoFibrosis quística como patología GES: una mirada críticaHipersensibilidad dentinaria: comparación de diferentes alternativas terapéuticasImpacto del GES en cáncer mamario: seguimiento a 5 años en un hospital del SSMSImplementación de la política nacional de medicamentos: percepción del profesional químico farmacéuticoLa implementación de políticas públicas cambió mortalidad de los pacientes gran quemado en Chile¿La infertilidad debería ser considerada un problema de salud pública en el Perú?Modelo de monitoreo de una política de protección a la infanciaMortalidad materna en el Hospital Dr. Alfredo van Grieken Coro, Estado Falcón, Venezuela 2005-2009Objetivos de desarrollo del milenio. Modelación de la mortalidad infantil Nicaragua - Costa Rica 1978-2008Percepción de riesgo y beneficio respecto del cigarrillo y su relación con el tabaquismo adolescentePolíticas públicas y salud intercultural: la experiencia de la organización indígena Taiñ adkimnPrevalencia de atipias celulares del cuello uterino en mujeres entre 18 y 24 añosProceso de ser histerectomizada: relatos de experiencias de mujeres en un hospital público de SantiagoProceso de ser histerectomizada: relatos de experiencias de mujeres en un hospital público de SantiagoPrograma Auge y cáncer cervicouterino: calidad de atención percibida por las usuarias del programaResolución quirúrgica por patología adenoamigdalina: ¿Es la población mapuche un grupo de riesgo?Resultados de alcoholemias tanatológicas del Servicio Médico Legal de Copiapó 1999-2009Resultados de la evaluación de los objetivos sanitarios de la década 2000-2010Una mirada a los servicios de salud para adolescentes en Puente Alt

Elliptic anisotropy measurement of the f0_0(980) hadron in proton-lead collisions and evidence for its quark-antiquark composition

International audienceDespite the f$_0$(980) hadron having been discovered half a century ago, the question about its quark content has not been settled: it might be an ordinary quark-antiquark ($\mathrm{q\bar{q}}$) meson, a tetraquark ($\mathrm{q\bar{q}q\bar{q}}$) exotic state, a kaon-antikaon ($\mathrm{K\bar{K}}$) molecule, or a quark-antiquark-gluon ($\mathrm{q\bar{q}g}$) hybrid. This paper reports strong evidence that the f$_0$(980) state is an ordinary $\mathrm{q\bar{q}}$ meson, inferred from the scaling of elliptic anisotropies ($v_2$) with the number of constituent quarks ($n_\mathrm{q}$), as empirically established using conventional hadrons in relativistic heavy ion collisions. The f$_0$(980) state is reconstructed via its dominant decay channel f$_0$(980) $\to$$\pi^+\pi^-$, in proton-lead collisions recorded by the CMS experiment at the LHC, and its $v_2$ is measured as a function of transverse momentum ($p_\mathrm{T}$). It is found that the $n_q$ = 2 ($\mathrm{q\bar{q}}$ state) hypothesis is favored over $n_q$ = 4 ($\mathrm{q\bar{q}q\bar{q}}$ or $\mathrm{K\bar{K}}$ states) by 7.7, 6.3, or 3.1 standard deviations in the $p_\mathrm{T}$$\lt$ 10, 8, or 6 GeV/$c$ ranges, respectively, and over $n_\mathrm{q}$ = 3 ($\mathrm{q\bar{q}g}$ hybrid state) by 3.5 standard deviations in the $p_\mathrm{T}$$\lt$ 8 GeV/$c$ range. This result represents the first determination of the quark content of the f$_0$(980) state, made possible by using a novel approach, and paves the way for similar studies of other exotic hadron candidates