2,247 research outputs found

    Purcell magneto-elastic swimmer controlled by an external magnetic field

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    International audienceThis paper focuses on the mechanism of propulsion of a Purcell swimmer whose segments are magnetized and react to an external magnetic field applied into the fluid. By an asymptotic analysis, we prove that it is possible to steer the swimmer along a chosen direction when the control functions are prescribed as an oscillating field. Moreover, we discuss what are the main obstructions to overcome in order to get classical controllability result for this system

    Laccase-Carrying Polylactic Acid Electrospun Fibers, Advantages and Limitations in Bio-Oxidation of Amines and Alcohols

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    Laccases are oxidative enzymes that could be good candidates for the functionalization of biopolymers with several applications as biosensors for the determination of bioactive amine and alcohols, for bioremediation of industrial wastewater, and for greener catalysts in oxidation reactions in organic synthesis, especially used for non-phenolic compounds in combination with redox mediators in the so-called Laccase Mediator System (LMS). In this work, we describe the immobilization of Laccase from Trametes versicolor (LTv) in poly-L-lactic acid (PLLA) nanofibers and its application in LMS oxidation reactions. The PLLA-LTv catalysts were successfully produced by electrospinning of a water-in-oil emulsion with an optimized method. Different enzyme loadings (1.6, 3.2, and 5.1% (w)/(w)) were explored, and the obtained mats were thoroughly characterized. The actual amount of the enzyme in the fibers and the eventual enzyme leaching in different solvents were evaluated. Finally, the PLLA-LTv mats were successfully applied as such in the oxidation reaction of catechol, and in the LMS method with TEMPO as mediator in the oxidation of amines with the advantage of easier work-up procedures by the immobilized enzyme. However, the PLLA-LTv failed the oxidation of alcohols with respect to the free enzyme. A tentative explanation was provided

    Modeling and steering magneto-elastic micro-swimmers inspired by the motility of sperm cells

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    Controlling artificial devices that mimic the motion of real microorganisms, is attracting increasing interest, both from the mathematical point of view and applications. A model for a magnetically driven slender micro-swimmer, mimicking a sperm cell is presented, supported by two examples showing how to steer it. Using the Resistive Force Theory (RTF) approach [J. Gray and J. Hancock, J. Exp. Biol. 32, 802 (1955)] to describe the hydrodynamic forces, the micro-swimmer can be described by a driftless affine control system where the control is an external magnetic field. Moreover we discuss through at first an asymptotic analysis and then by numerical simulations how to realize different kinds of paths

    Ice nucleating properties of the sea ice diatom <i>Fragilariopsis cylindrus</i> and its exudates

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    In this study, we investigated the ice nucleation activity of the Antarctic sea ice diatom Fragilariopsis cylindrus. Diatoms are the main primary producers of organic carbon in the Southern Ocean, and the Antarctic sea ice diatom F. cylindrus is one of the predominant species. This psychrophilic diatom is abundant in open waters and within sea ice. It has developed several mechanisms to cope with the extreme conditions of its environment, for example, the production of ice-binding proteins (IBPs) and extracellular polymeric substances known to alter the structure of ice. Here, we investigated the ice nucleation activity of F. cylindrus using a microfluidic device containing individual sub-nanolitre (∼90 µm) droplet samples. The experimental method and a newly implemented Poisson-statistics-based data evaluation procedure applicable to samples with low ice nucleating particle concentrations were validated by comparative ice nucleation experiments with well-investigated bacterial samples from Pseudomonas syringae (Snomax®). The experiments reveal an increase of up to 7.2 ∘C in the ice nucleation temperatures for seawater containing F. cylindrus diatoms when compared to pure seawater. Moreover, F. cylindrus fragments also show ice nucleation activity, while experiments with the F. cylindrus ice-binding protein (fcIBP) show no significant ice nucleation activity. A comparison with experimental results from other diatoms suggests a universal behaviour of polar sea ice diatoms, and we provide a diatom-mass-based parameterization of their ice nucleation activity for use in models.</p

    Ubiquitin-Specific Protease 8 Mutant Corticotrope Adenomas Present Unique Secretory and Molecular Features and Shed Light on the Role of Ubiquitylation on ACTH Processing

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    Background: Somatic mutations in the ubiquitin-specific protease 8 (USP8) gene have recently been shown to occur in ACTH-secreting pituitary adenomas, thus calling attention to the ubiquitin system in corticotrope adenomas. Objectives: Assess the consequences of USP8 mutations and establish the role of ubiquitin on ACTH turnover in human ACTH-secreting pituitary adenomas. Methods: USP8 mutation status was established in 126 ACTH-secreting adenomas. Differences in ACTH secretion and POMC expression from adenoma primary cultures and in microarray gene expression profiles from archival specimens were sought according to USP8 sequence. Ubiquitin/ACTH coimmunoprecipitation and incubation with MG132, a proteasome inhibitor, were performed in order to establish whether ubiquitin plays a role in POMC/ACTH degradation in corticotrope adenomas. Results: USP8 mutations were identified in 29 adenomas (23%). Adenomas presenting USP8 mutations secreted greater amounts of ACTH and expressed POMC at higher levels compared to USP wild-type specimens. USP8 mutant adenomas were also more sensitive to modulation by CRH and dexamethasone in vitro. At microarray analysis, genes associated with endosomal protein degradation and membrane components were downregulated in USP8 mutant adenomas as were AVPR1B, IL11RA, and PITX2. Inhibition of the ubiquitin-proteasome pathway increased ACTH secretion and POMC itself proved a target of ubiquitylation, independently of USP8 sequence status. Conclusions: Our study has shown that USP8 mutant ACTH-secreting adenomas present a more "typical" corticotrope phenotype and reduced expression of several genes associated with protein degradation. Further, ubiquitylation is directly involved in intracellular ACTH turnover, suggesting that the ubiquitin-proteasome system may represent a target for treatment of human ACTH-secreting adenomas
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