Collective dissolution of microbubbles

© 2018 American Physical Society. A microscopic bubble of soluble gas always dissolves in finite time in an undersaturated fluid. This diffusive process is driven by the difference between the gas concentration near the bubble, whose value is governed by the internal pressure through Henry's law, and the concentration in the far field. The presence of neighboring bubbles can significantly slow down this process by increasing the effective background concentration and reducing the diffusing flux of dissolved gas experienced by each bubble. We develop theoretical modeling of such diffusive shielding process in the case of small microbubbles whose internal pressure is dominated by Laplace pressure. We first use an exact semianalytical solution to capture the case of two bubbles and analyze in detail the shielding effect as a function of the distance between the bubbles and their size ratio. While we also solve exactly for the Stokes flow around the bubble, we show that hydrodynamic effects are mostly negligible except in the case of almost-touching bubbles. In order to tackle the case of multiple bubbles, we then derive and validate two analytical approximate yet generic frameworks, first using the method of reflections and then by proposing a self-consistent continuum description. Using both modeling frameworks, we examine the dissolution of regular one-, two-, and three-dimensional bubble lattices. Bubbles located at the edge of the lattices dissolve first, while innermost bubbles benefit from the diffusive shielding effect, leading to the inward propagation of a dissolution front within the lattice. We show that diffusive shielding leads to severalfold increases in the dissolution time, which grows logarithmically with the number of bubbles in one-dimensional lattices and algebraically in two and three dimensions, scaling respectively as its square root and 2/3 power. We further illustrate the sensitivity of the dissolution patterns to initial fluctuations in bubble size or arrangement in the case of large and dense lattices, as well as nonintuitive oscillatory effects

Viscous growth and rebound of a bubble near a rigid surface

Motivated by the dynamics of microbubbles near catalytic surfaces in bubble-powered microrockets, we consider theoretically the growth of a free spherical bubble near a flat no-slip surface in a Stokes flow. The flow at the bubble surface is characterised by a constant slip length allowing us to tune the hydrodynamic mobility of its surface and tackle in one formulation both clean and contaminated bubbles as well as rigid shells. Starting with a bubble of infinitesimal size, the fluid flow and hydrodynamic forces on the growing bubble are obtained analytically. We demonstrate that, depending on the value of the bubble slip length relative to the initial distance to the wall, the bubble will either monotonically drain the fluid separating it from the wall, which will exponentially thin, or it will bounce off the surface once before eventually draining the thin film. Clean bubbles are shown to be a singular limit which always monotonically get repelled from the surface. The bouncing events for bubbles with finite slip lengths are further analysed in detail in the lubrication limit. In particular, we identify the origin of the reversal of the hydrodynamic force direction as due to the change in the flow pattern in the film between the bubble and the surface and to the associated lubrication pressure. Last, the final drainage dynamics of the film is observed to follow a universal algebraic scaling for all finite slip lengths.ER

Geometric tuning of self-propulsion for Janus catalytic particles

Catalytic swimmers have attracted much attention as alternatives to biological systems for examining collective microscopic dynamics and the response to physico-chemical signals. Yet, understanding and predicting even the most fundamental characteristics of their individual propulsion still raises important challenges. While chemical asymmetry is widely recognized as the cornerstone of catalytic propulsion, different experimental studies have reported that particles with identical chemical properties may propel in opposite directions. Here, we show that, beyond its chemical properties, the detailed shape of a catalytic swimmer plays an essential role in determining its direction of motion, demonstrating the compatibility of the classical theoretical framework with experimental observations.This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme under grant agreements 714027 (S.M.) and 682754 (E.L.)

Phoretic flow induced by asymmetric confinement

Internal phoretic flows due to the interactions of solid boundaries with local chemical gradients may be created using chemical patterning. Alternatively, we demonstrate here that internal flows might also be induced by geometric asymmetries of chemically homogeneous surfaces. We characterise the circulatory flow created in a cavity enclosed between two eccentric cylindrical walls of uniform chemical activity. Local gradients of the diffusing solute induce a slip flow along the surface of the cylinders, leading to a circulatory bulk flow pattern which can be solved analytically in the diffusive limit. The flow strength can be controlled by adjusting the relative positions of the cylinders, and an optimal configuration is identified. These results provide a model system for tunable phoretic pumps.This work was funded in part by a David Crighton Fellowship at the University of Cambridge (ML), a Mobility Plus Fellowship from the Polish Ministry of Science and Higher Education (ML), the EU through a Marie-Curie CIG grant (EL) and the French Ministry of Defense DGA (SM).This is the author accepted manuscript. The final version is available from Cambridge University Press via http://dx.doi.org/10.1017/jfm.2016.40

Rare GBA1 genotype associated with severe bone disease in Gaucher disease type 1

Introduction:Gaucher disease (GD) type 1 is a lysosomal disease characterised by hepatosplenomegaly, anemia,thrombocytopenia, bone changes, and bone marrow infiltration. The disease is caused by biallelic pathogenicvariants inGBA1which codes for glucocerebrosidase, an enzyme involved in the catabolic pathway of complexlipids.Aims:To report on the case of two sisters with GD type 1 who bear a genotype never reported in the literature.Case report:Patient 1 is a 47-year-old female diagnosed at 42 years of age with chronic lumbar pain, mildsplenomegaly, slightly reduced platelets and normal hemoglobin values, severe Bone Marrow Burden (BMB)score, high chitotriosidase activity, and low glucocerebrosidase. Patient 2 is a 50-year-old female, sister of pa-tient 1, who was diagnosed after familial screening. At 45 years of age, she had osteonecrosis of the left femurand a total hysterectomy because of uncontrollable bleeding. Atfirst evaluation, she had bone pain with a highBMB score, mild splenomegaly, normal hemoglobin, normal platelets count, elevated chitotriosidase activity,and low glucocerebrosidase activity. Both patients were found to be compound heterozygotes for thep.Glu388Lys and the p.Ser405Asn variants inGBA1.Conclusions:This is thefirst family with GD and this combination of variants which causes a phenotype re-markable for severe bone disease with no or mild hematological manifestations

Lysosomal diseases : overview on current diagnosis and treatment

Lysosomal diseases (LDs), also known as lysosomal storage diseases (LSDs), are a heterogeneous group of conditions caused by defects in lysosomal function. LDs may result from deficiency of lysosomal hydrolases, membrane-associated transporters or other non-enzymatic proteins. Interest in the LD field is growing each year, as more conditions are, or will soon be treatable. In this article, we review the diagnosis of LDs, from clinical suspicion and screening tests to the identification of enzyme or protein deficiencies and molecular genetic diagnosis. We also cover the treatment approaches that are currently available or in development, including hematopoietic stem cell transplantation, enzyme replacement therapy, small molecules, and gene therapy

Spin-exchange effects in elastic electron scattering from linear triatomic radicals

In this work, we present a theoretical investigation on spin-exchange effects in elastic electron collisions by two linear triatomic free radicals namely, NCN and CNN. Spin-polarization differential and integral cross sections calculated in the (1-10) eV energy range are reported. For both targets, our study has shown that the exchange between the scattering and the unpaired target electrons is strongly influenced by the occurrence of shape resonances. As a consequence, significant spin-polarization fractions are only observed in the resonance region

The long-time dynamics of two hydrodynamically-coupled swimming cells

Swimming micro-organisms such as bacteria or spermatozoa are typically found in dense suspensions, and exhibit collective modes of locomotion qualitatively different from that displayed by isolated cells. In the dilute limit where fluid-mediated interactions can be treated rigorously, the long-time hydrodynamics of a collection of cells result from interactions with many other cells, and as such typically eludes an analytical approach. Here we consider the only case where such problem can be treated rigorously analytically, namely when the cells have spatially confined trajectories, such as the spermatozoa of some marine invertebrates. We consider two spherical cells swimming, when isolated, with arbitrary circular trajectories, and derive the long-time kinematics of their relative locomotion. We show that in the dilute limit where the cells are much further away than their size, and the size of their circular motion, a separation of time scale occurs between a fast (intrinsic) swimming time, and a slow time where hydrodynamic interactions lead to change in the relative position and orientation of the swimmers. We perform a multiple-scale analysis and derive the effective dynamical system - of dimension two - describing the long-time behavior of the pair of cells. We show that the system displays one type of equilibrium, and two types of rotational equilibrium, all of which are found to be unstable. A detailed mathematical analysis of the dynamical systems further allows us to show that only two cell-cell behaviors are possible in the limit of $t\to\infty$, either the cells are attracted to each other (possibly monotonically), or they are repelled (possibly monotonically as well), which we confirm with numerical computations

Using trendsetting chefs to design new culinary preparations with the "Penjar" tomato

New food products are normally marketed after research regarding consumers' preferences. As an alternative, we used trendsetting chefs to develop and evaluate products with the traditional, long shelf life,Postprint (published version