No abstract

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 Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Pathogenic bacterial biofilms can be life threatening, greatly decrease patients' quality of life and are a substantial burden on the healthcare system. Current methods for evaluation of antibacterial treatments in clinics and in vitro systems used in drug development and screening either do not facilitate biofilm formation or are cumbersome to operate, need large reagent volumes and are costly, limiting their usability. To address these issues, this work presents the development of a robust in vitro cell culture platform compatible with confocal microscopy. The platform shaped as a compact disc, facilitates long-term bacterial culture without external pumps and tubing and can be operated for several days without additional liquid handling. As an example, Pseudomonas aeruginosa biofilm is grown from single cells and it is shown that: 1) the platform delivers reproducible and reliable results; 2) growth is dependent on flow rate and growth medium composition; and 3) efficacy of antibiotic treatment depends on the formed biofilm. This platform enables biofilm growth, quantification and treatment as in a conventional flow setup, while decreasing the application barrier of lab-on-chip systems. It provides an easy-to-use, affordable option for end users working with cell culturing in relation to e.g. diagnostics and drug screening.

Sine-Gordon kink propagation in a curved planar waveguide is considered. The waveguide consists of two rectangular regions joined by a bent section of constant curvature. Transverse homogeneous and inhomogeneous Neumann boundary conditions are used. The latter models an energy-providing mechanism for Josephson junctions of overlap type. A collective variable approach based on the kink position and the kink width depending on the transversal coordinate is developed. The latter allows to take into account both longitudinal and centrifugal forces which act on the nonlinear excitation moving in a region with finite curvature and to obtain a qualitatively good agreement with the numerical simulations. The region with finite curvature acts as a potential barrier whose height and width depend on the radius of curvature of the waveguide. The kink transmission, reflection, and trapping are investigated. The kink may be captured when a driving force, provided by a magnetic field, is applied to the kink.

Context. Massive stars with solar metallicity lose important amounts of rotational angular momentum through their winds. When a magnetic field is present at the surface of a star, efficient angular momentum losses can still be achieved even when the mass-loss rate is very modest, at lower metallicities, or for lower-initial-mass stars. In a close binary system, the effect of wind magnetic braking also interacts with the influence of tides, resulting in a complex evolution of rotation. Aims. We study the interactions between the process of wind magnetic braking and tides in close binary systems. Methods. We discuss the evolution of a 10 M⊙ star in a close binary system with a 7 M⊙ companion using the Geneva stellar evolution code. The initial orbital period is 1.2 days. The 10 M⊙ star has a surface magnetic field of 1 kG. Various initial rotations are considered. We use two different approaches for the internal angular momentum transport. In one of them, angular momentum is transported by shear and meridional currents. In the other, a strong internal magnetic field imposes nearly perfect solid-body rotation. The evolution of the primary is computed until the first mass-transfer episode occurs. The cases of different values for the magnetic fields and for various orbital periods and mass ratios are briefly discussed. Results. We show that, independently of the initial rotation rate of the primary and the efficiency of the internal angular momentum transport, the surface rotation of the primary will converge, in a time that is short with respect to the main-sequence lifetime, towards a slowly evolving velocity that is different from the synchronization velocity. This “equilibrium angular velocity” is always inferior to the angular orbital velocity. In a given close binary system at this equilibrium stage, the difference between the spin and the orbital angular velocities becomes larger when the mass losses and/or the surface magnetic field increase. The treatment of the internal angular momentum transport has a strong impact on the evolutionary tracks in the Hertzsprung-Russell Diagram as well as on the changes of the surface abundances resulting from rotational mixing. Our modelling suggests that the presence of an undetected close companion might explain rapidly rotating stars with strong surface magnetic fields, having ages well above the magnetic braking timescale. Our models predict that the rotation of most stars of this type increases as a function of time, except for a first initial phase in spin-down systems. The measure of their surface abundances, together, when possible, with their mass-luminosity ratio, provide interesting constraints on the transport efficiencies of angular momentum and chemical species. Conclusions. Close binaries, when studied at phases predating any mass transfer, are key objects to probe the physics of rotation and magnetic fields in stars.

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We consider radial sine-Gordon kinks in two, three, and higher dimensions. A full two-dimensional simulation showing that azimuthal perturbations remain small allows us to reduce the problem to the one-dimensional radial sine-Gordon equation. We solve this equation on an interval [r 0 ,r 1 ] and absorb all outgoing radiation. As the kink shrinks toward r 0 , before the collision, its motion is well described by a simple law derived from the conservation of energy. In two dimensions for r 0 2, the collision disintegrates the kink into a fast breather, while for r 0 4 we obtain a kink-breather metastable state where breathers are shed at each kink "return." In three and higher dimensions d, an additional kink-oscillon state appears for small r 0 . On the application side, the kink disintegration opens the way for new types of terahertz microwave generators.