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

Mobility of an axisymmetric particle near an elastic interface

Using a fully analytical theory, we compute the leading-order corrections to the translational, rotational and translation–rotation coupling mobilities of an arbitrary axisymmetric particle immersed in a Newtonian fluid moving near an elastic cell membrane that exhibits resistance towards stretching and bending. The frequency-dependent mobility corrections are expressed as general relations involving separately the particle’s shape-dependent bulk mobility and the shape-independent parameters such as the membrane–particle distance, the particle orientation and the characteristic frequencies associated with shearing and bending of the membrane. This makes the equations applicable to an arbitrary-shaped axisymmetric particle provided that its bulk mobilities are known, either analytically or numerically. For a spheroidal particle, these general relations reduce to simple expressions in terms of the particle’s eccentricity. We find that the corrections to the translation–rotation coupling mobility are primarily determined by bending, whereas shearing manifests itself in a more pronounced way in the rotational mobility. We demonstrate the validity of the analytical approximations by a detailed comparison with boundary integral simulations of a truly extended spheroidal particle. They are found to be in a good agreement over the whole range of applied frequencies.A.D.-M.-I. and S.G. thank the Volkswagen Foundation for financial support and acknowledge the Gauss Center for Supercomputing e.V. for providing computing time on the GCS Supercomputer SuperMUC at Leibniz Supercomputing Center. This work has been supported by the Ministry of Science and Higher Education of Poland via the Mobility Plus Fellowship awarded to M.L. This article is based upon work from COST Action MP1305, supported by COST (European Cooperation in Science and Technology)

Hydrodynamic coupling and rotational mobilities near planar elastic membranes

We study theoretically and numerically the coupling and rotational hydrodynamic interactions between spherical particles near a planar elastic membrane that exhibits resistance towards shear and bending. Using a combination of the multipole expansion and Faxen's theorems, we express the frequency-dependent hydrodynamic mobility functions as a power series of the ratio of the particle radius to the distance from the membrane for the self mobilities, and as a power series of the ratio of the radius to the interparticle distance for the pair mobilities. In the quasi-steady limit of zero frequency, we find that the shear- and bending-related contributions to the particle mobilities may have additive or suppressive effects depending on the membrane properties in addition to the geometric configuration of the interacting particles relative to the confining membrane. To elucidate the effect and role of the change of sign observed in the particle self and pair mobilities, we consider an example involving a torque-free doublet of counterrotating particles near an elastic membrane. We find that the induced rotation rate of the doublet around its center of mass may differ in magnitude and direction depending on the membrane shear and bending properties. Near a membrane of only energetic resistance toward shear deformation, such as that of a certain type of elastic capsules, the doublet undergoes rotation of the same sense as observed near a no-slip wall. Near a membrane of only energetic resistance toward bending, such as that of a fluid vesicle, we find a reversed sense of rotation. Our analytical predictions are supplemented and compared with fully resolved boundary integral simulations where a very good agreement is obtained over the whole range of applied frequencies.Comment: 14 pages, 7 figures. Revised manuscript resubmitted to J. Chem. Phy

Structural insights into crista junction formation by the Mic60-Mic19 complex

Mitochondrial cristae membranes are the oxidative phosphorylation sites in cells. Crista junctions (CJs) form the highly curved neck regions of cristae and are thought to function as selective entry gates into the cristae space. Little is known about how CJs are generated and maintained. We show that the central coiled-coil (CC) domain of the mitochondrial contact site and cristae organizing system subunit Mic60 forms an elongated, bow tie–shaped tetrameric assembly. Mic19 promotes Mic60 tetramerization via a conserved interface between the Mic60 mitofilin and Mic19 CHCH (CC-helix-CC-helix) domains. Dimerization of mitofilin domains exposes a crescent-shaped membrane-binding site with convex curvature tailored to interact with the curved CJ neck. Our study suggests that the Mic60-Mic19 subcomplex traverses CJs as a molecular strut, thereby controlling CJ architecture and function

Near-wall diffusion tensor of an axisymmetric colloidal particle

Hydrodynamic interactions with confining boundaries often lead to drastic changes in the diffusive behaviour of microparticles in suspensions. For axially symmetric particles, earlier numerical studies have suggested a simple form of the near-wall diffusion matrix which depends on the distance and orientation of the particle with respect to the wall, which is usually calculated numerically. In this work, we derive explicit analytical formulae for the dominant correction to the bulk diffusion tensor of an axially symmetric colloidal particle due to the presence of a nearby no-slip wall. The relative correction scales as powers of inverse wall-particle distance and its angular structure is represented by simple functions in sines and cosines of the particle’s inclination angle to the wall. We analyse the correction for translational and rotational motion, as well as the translation-rotation coupling. Our findings provide a simple approximation to the anisotropic diffusion tensor near a wall, which completes and corrects relations known from earlier numerical and theoretical findings.M.L. acknowledges support from the National Center of Science Grant No. 2012/07/N/ST3/03120. Part of the research has been conducted under a David Crighton Fellowship awarded to M.L. at the University of Cambridge, and within the Mobility Plus Fellowship awarded to M.L. by the Polish Ministry of Science and Higher Education.This is the author accepted manuscript. The final version is available from AIP Publishing via http://dx.doi.org/10.1063/1.495872

Sedimentary palaeoenvironment of intermoraine deposits from Sucha Wieś (Ełk Lakeland) and Czarnucha (Augustów Plain), northeastern Poland

Praca została wykonana na podstawie badań chemicznych i badań litologicznych osadów z profili Sucha Wieś i Czarnucha. Oba profile są bardzo zbliżone do siebie pod względem litologii i zmian środowiska depozycji osadów. Cykl zmian sedymentacji jest zapisany od osadów klimatu borealnego do osadów jeziornych klimatu ciepłego oraz ponownie do osadów rzecznych i jeziornych klimatu borealnego.The work deals with chemical analyses and lithological studies of deposits from the Sucha Wieś and Czarnucha sections. Both these sections show much similarity in terms of lithologies and changes in sedimentary environments. The sedimentary record reveals a cycle of changes from a boreal climate to a temperate climate represented by lacustrine sediments and again towards a boreal climate with fluvial and lacustrine deposition

Lower Pleistocene stratigraphy of northeastern Poland on the basis of studies of lake deposits from the Sucha Wieś (Ełk Lakeland) and Czarnucha (Augustów Plain) sections with reference to the areas of Russia, Lithuania and Belarus

W odwierconych w latach 1988-1989 profilach otworów badawczych Sucha Wieś i Czarnucha, napotkano na organiczne i mineralne oraz rzeczne osady interglacjalne. Badania palinologiczne i litologiczno-petrograficzne tych osadów oraz datowania paleomagnetyczne określiły ich wiek na interglacjał augustowski (Augustovian), korelowany z Cromerianem I (Waardenburg). Przedstawiono stratygrafię i wiek osadów dolnego plejstocenu występujących w profilach Sucha Wieś i Czarnucha w nawiązaniu do innych profili położonych w obrębie Równiny Augustowskiej, Pojezierza Suwalskiego, Pojezierza Ełckiego oraz obszarów Rosji, Litwy i Białorusi.In the Sucha Wieś and Czarnucha boreholes drilled in 1988-1989, interglacial lacustrine and fluvial organic organic and mineral deposits were encountered. Palynological and lithologic-petrographical analyses and palaeomagnetic datings indicate that these deposits are of Augustovian Interglacial age, compared to Cromerian I (Waardenburg). This report shows the stratigraphy and age of the Lower Pleistocene deposits from the Sucha Wieś and Czarnucha sections with a correlation to other sections located in the Augustów Plain, Suwałki Lakeland, Ełk Lakeland and Russia, Lithuania and Belarus

SecuSpot: Toward cloud-assisted secure multi-tenant WiFi hotspot infrastructures

Despite the increasing popularity ofWiFi networks and the trend toward automated offloading of cellular traffic to WiFi (e.g., HotSpot 2.0), today's WiFi networks still provide a very poor actual coverage: a WiFi equipped device can typically connect to the Internet only through a very small fraction of the "available" access points. Accordingly, there is an enormous potential for multi-tenant WiFi hotspot architectures, which however also introduce more stringent requirements in terms of scalability and security. The latter is particularly critical, as HotSpots are often deployed in untrusted environments, e.g., physically accessible Access Points deployed in the user's premises (e.g., FON) or cafes. This paper proposes a Cloud-assisted multi-tenant and secure WiFi HotSpot infrastructure, called SecuSpot. SecuSpot is based on a modular access point and features interesting deployment flexibilities. These flexibilities can be exploited, e.g., to move security critical f unctions to the Cloud, and hence prevent eavesdropping even when deployed across untrusted Access Points. At the heart of SecuSpot lies a novel programmable wireless switch, the wSwitch. The wSwitch allows to (de-)multiplex the different tenants already on the HotSpot and to decouple essential security functions (association, authentication, and cryptography)