Micron-sized particles moving through a solution in response to self-generated chemical gradients serve as model systems for studying active matter. Their far-reaching potential applications will ...require the particles to sense and respond to their local environment in a robust manner. The self-generated hydrodynamic and chemical fields, which induce particle motion, probe and are modified by that very environment, including confining boundaries. Focusing on a catalytically active Janus particle as a paradigmatic example, we predict that near a hard planar wall such a particle exhibits several scenarios of motion: reflection from the wall, motion at a steady-state orientation and height above the wall, or motionless, steady "hovering." Concerning the steady states, the height and the orientation are determined both by the proportion of catalyst coverage and the interactions of the solutes with the different "faces" of the particle. Accordingly, we propose that a desired behavior can be selected by tuning these parameters via a judicious design of the particle surface chemistry.
Introduction La vitamine D (VD) joue un rôle majeur dans l’homéostasie phosphocalcique mais est aussi indispensable au bon fonctionnement de nombreuses cellules. Le récepteur de la VD est exprimé au ...niveau des cellules gonadiques et des travaux chez l’homme ont révélé une association entre le déficit en VD et l’hypogonadisme. Objectif Déterminer si le statut en VD module le profil de l’hypogonadisme chez le sujet diabétique. Matériel/patients Inclusion prospective de sujets diabétiques de type 2 pendant 5 mois. Enregistrement des paramètres cliniques, biologiques, du statut en VD déterminé par le dosage sérique de la 25(OH)D. Dosages sériques de la testostérone totale (TT). Hypogonadisme défini par une concentration de TT < 9 nmol/L, déficit en VD par une concentration de 25(OH)D < 50 nmol/L. Tous les patients ont donné leur accord oral. Résultats Cinquante-six hommes inclus (57 ± 8 ans) avec une moyenne de VD de 75 ± 5 nmol/L, de TT 12,54 ± 0,93 nmol/L. Fréquence de l’hypogonadisme : 31,3 %. Un déficit en VD était noté chez 16,7 % des sujets avec hypogonadisme. Les sujets avec hypogonadisme et déficit en VD étaient plus âgés que les non déficitaires, avec une durée de diabète plus longue. Il n’y avait pas d’autres différences entre les 2 groupes. Discussion Le déficit en VD chez les sujets diabétiques avec hypogonadisme est moins fréquent qu’attendu. Le statut en VD ne semble pas déterminer de profil différent de l’hypogonadisme chez le diabétique. La faible taille de l’échantillon étudié explique sans doute les résultats.
Introduction La résistance à l’insuline (IR) de type B (IRB) est une maladie auto-immune rare avec positivité des auto-anticorps dirigés contre le récepteur de l’insuline (IRA), avec hyperglycémie ...associée et IR marquée. Le mycophénolate de mofétil (MMF) est un immunosuppresseur utilisé dans le lupus érythémateux disséminé (SLE). Le sulfate d’hydroxychloroquine (HS) est un médicament antipaludique utilisé pour réduire l’inflammation dans le SLE. Observation Une femme âgée de 51 ans d’origine Afro-Caribéen a été hospitalisée pour découverte de diabète avec acidocétose métabolique. Un traitement par insuline IV sera introduit avec des besoins en insuline très élevés (jusqu’à 10 unités/kg/jour pour un IMC à 18,5 kg/m2 ) dépassant 500 unités d’insuline par jour. L’examen clinique montre un acanthosis nigricans du visage et des adénopathies diffuses. Le bilan biologique retrouve : CPK : 880 UI/L, hypergammaglobulinémie polyclonale de 38 g/L, avec IgG 4 : 3,19 g/L. Les anticorps anti-décarboxylase de l’acide glutamique, anti-insuline et anticorps anti-protéine tyrosine phosphatase IA-2 sont négatifs. Positivités des IRA, du facteur antinucléaire à 1/2560 d’aspect moucheté, des anti-SNR et RNP. CD4 : 113/mm3 . CH50 et fractions C3, C4 du complément abaissé. Une pathologie lymphomateuse est éliminée. Un diagnostic de SLE avec IRB est posé. Un traitement par HS et MMF permettra un contrôle progressif du diabète avec réduction des besoins en insuline à moins de 30 unités par jour, amélioration des marqueurs d’activation lymphocytaire et négativation des IRA. Discussion L’utilisation de MMF et HS sans corticoïdes est une alternative à considérer dans le traitement de l’IRB associée au SLE.
For active particles the interplay between the self-generated hydrodynamic flow and an external shear flow, especially near bounding surfaces, can result in a rich behavior of the particles not ...easily foreseen from the consideration of the active and external driving mechanisms in isolation. For instance, under certain conditions, the particles exhibit "rheotaxis",
i.e.
, they align their direction of motion with the plane of shear spanned by the direction of the flow and the normal of the bounding surface and move with or against the flow. To date, studies of rheotaxis have focused on elongated particles (
e.g.
, spermatozoa), for which rheotaxis can be understood intuitively in terms of a "weather vane" mechanism. Here we investigate the possibility that spherical active particles, for which the "weather vane" mechanism is excluded due to the symmetry of the shape, may nevertheless exhibit rheotaxis. Combining analytical and numerical calculations, we show that, for a broad class of spherical active particles, rheotactic behavior may emerge
via
a mechanism which involves "self-trapping" near a hard wall owing to the active propulsion of the particles, combined with their rotation, alignment, and "locking" of the direction of motion into the shear plane. In this state, the particles move solely up- or downstream at a steady height and orientation.
Spherical active particles can achieve rheotaxis (stable upstream swimming) through the interplay between near-surface swimming activity and external shear flow.
Precursor films in wetting phenomena Popescu, M N; Oshanin, G; Dietrich, S ...
Journal of physics. Condensed matter,
06/2012, Letnik:
24, Številka:
24
Journal Article
Recenzirano
Odprti dostop
The spontaneous spreading of non-volatile liquid droplets on solid substrates poses a classic problem in the context of wetting phenomena. It is well known that the spreading of a macroscopic droplet ...is in many cases accompanied by a thin film of macroscopic lateral extent, the so-called precursor film, which emanates from the three-phase contact line region and spreads ahead of the latter with a much higher speed. Such films have been usually associated with liquid-on-solid systems, but in the last decade similar films have been reported to occur in solid-on-solid systems. While the situations in which the thickness of such films is of mesoscopic size are fairly well understood, an intriguing and yet to be fully understood aspect is the spreading of microscopic, i.e. molecularly thin, films. Here we review the available experimental observations of such films in various liquid-on-solid and solid-on-solid systems, as well as the corresponding theoretical models and studies aimed at understanding their formation and spreading dynamics. Recent developments and perspectives for future research are discussed.
We show theoretically that near a fluid-fluid interface a single active colloidal particle generating, e.g., chemicals or a temperature gradient experiences an effective force of hydrodynamic origin. ...This force is due to the fluid flow driven by Marangoni stresses induced by the activity of the particle; it decays very slowly with the distance from the interface, and can be attractive or repulsive depending on how the activity modifies the surface tension. We show that, for typical systems, this interaction can dominate the dynamics of the particle as compared to Brownian motion, dispersion forces, or self-phoretic effects. In the attractive case, the interaction promotes the self-assembly of particles into a crystal-like monolayer at the interface.
Machine learning (ML), a branch of artificial intelligence, where machines learn from big data, is at the crest of a technological wave of change sweeping society. Cardiovascular medicine is at the ...forefront of many ML applications, and there is a significant effort to bring them into mainstream clinical practice. In the field of cardiac electrophysiology, ML applications have also seen a rapid growth and popularity, particularly the use of ML in the automatic interpretation of ECGs, which has been extensively covered in the literature. Much lesser known are the other aspects of ML application in cardiac electrophysiology and arrhythmias, such as those in basic science research on arrhythmia mechanisms, both experimental and computational; in the development of better techniques for mapping of cardiac electrical function; and in translational research related to arrhythmia management. In the current review, we examine comprehensively such ML applications as they match the scope of this journal. The current review is organized in 3 parts. The first provides an overview of general ML principles and methodologies that will afford readers of the necessary information on the subject, serving as the foundation for inviting further ML applications in arrhythmia research. The basic information we provide can serve as a guide on how one might design and conduct an ML study. The second part is a review of arrhythmia and electrophysiology studies in which ML has been utilized, highlighting the broad potential of ML approaches. For each subject, we outline comprehensively the general topics, while reviewing some of the research advances utilizing ML under the subject. Finally, we discuss the main challenges and the perspectives for ML-driven cardiac electrophysiology and arrhythmia research.
Catalytically active Janus particles suspended in solution create gradients in the chemical composition of the solution along their surfaces, as well as along any nearby container walls. The former ...leads to self-phoresis, while the latter gives rise to chemiosmosis, providing an additional contribution to self-motility. Chemiosmosis strongly depends on the molecular interactions between the diffusing chemical species and the wall. We show analytically, using an approximate "point-particle" approach, that by chemically patterning a planar substrate one can direct the motion of Janus particles: the induced chemiosmotic flows can cause particles to either "dock" at the chemical step between the two materials or follow a chemical stripe. These theoretical predictions are confirmed by full numerical calculations. Generically, docking occurs for particles which tend to move away from their catalytic caps, while stripe following occurs in the opposite case. Our analysis reveals the physical mechanisms governing this behavior.
Telocytes revisited Cretoiu, Sanda M.; Popescu, Laurentiu M.
Biomolecular concepts,
10/2014, Letnik:
5, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Telocytes (TCs) are a novel interstitial (stromal) cell type described in many tissues and organs (www.telocytes.com). A TC is characterized by a small cell body (9–15 μm) and a variable number (one ...to five) of extremely long and thin telopodes (Tps), with alternating regions of podomers (∼80 nm) and podoms (250–300 nm). Tps are interconnected by homo- and heterocellular junctions and form three-dimensional networks. Moreover, Tps release three types of extracellular vesicles: exosomes, ectosomes, and multivesicular cargos, which are involved in paracrine signaling. Different techniques have been used to characterize TCs, from classical methods (light microscopy, electron microscopy) to modern ‘omics’. It is considered that electron microscopy is essential for their identification, and CD34/PDGFRα double immunohistochemistry can orientate the diagnosis. Functional evidence is accumulating that TCs may be intimately involved in the maintenance of tissue homeostasis and renewal by short- and long-distance intercellular communication. This review focuses on the most recent findings regarding TC features and locations and the principal hypotheses about their functions in normal and diseased organs. TC involvement in regenerative medicine is also considered.
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