A centrifugo-magnetically actuated gas micropump

This paper describes a novel gas micropump on a centrifugal microfluidic platform. The pump is integrated on a passive and microstructured polymer disk which is sealed with an elastomer lid featuring paramagnetic inlays. The rotational motion of this hybrid disk over a stationary magnet induces a designated sequence of volume displacements of the elastic lid, leading to a net transport of gas. The pumping pressure scales linearly with the frequency, with a maximum observable pressure of 4.1 kPa. The first application of this rotary device is the production of gas-liquid flows by pumping ambient air into a continuous centrifugal flow of liquid. The injected gas volume segments the liquid stream into a series of liquid compartments. Apart from such multi-phase flows, the new pumping technique supplements a generic air-to-liquid sampling method to centrifugal microfluidic platforms

Alginate micro-bead fabrication on a centrifugal microfluidics platform

We present a novel method for the direct, centrifugally induced fabrication of small alginate beads displaying adjustable diameters between 180 mum and 800 mum by polymer-tube micronozzles. The size distribution features a CV of 7 - 16 % for the main peak. Up to 600 beads per second and channel are issued from the micronozzle through an air gap towards a standard lab tube ("Eppi") attached to the rotor spinning and containing a curing agent. At spinning frequencies between 5 Hz and 28 Hz, the tubes align horizontally under rotation and return to a vertical position as soon as the rotor is at rest. The hardened beads are collected within the tube for further processing or characterization. This method is considered as a low cost technology for micro encapsulation technologies

Resonant Diffraction Radiation and Smith-Purcell Effect

An approach has been developed where the Smith-Purcell radiation (SPR), i.e. emission of electrons moving close to a periodic structure, is treated as the resonant diffraction radiation. Simple formulas have been designed for the SPR intensity for a grating having perfectly conducting strips spaced by a vacuum gap. The results have been compared with those obtained via other techniques. It has been shown that the intensity of radiation for the said gratings for a relativistic case sufficiently exceeds the SPR intensity for the grating made up by a periodically deformed continuous surface.Comment: 9 pages, LATEX, 3 Postscript figures, uses epsf.sty, submitted to Phys.Letters

Enhanced granular medium-based tube press hardening

Active and passive control strategies of internal pressure for hot forming of tubes and profiles with granular media are described. Force transmission and plastic deformation of granular medium is experimentally investigated. Friction between tube, granular medium and die as also the external stress field are shown to be essential for the process understanding. Wrinkling, thinning and insufficient forming of the tube establishes the process window for the active pressure process. By improving the punch geometry and controlling tribological conditions, the process limits are extended. Examples for the passive pressure process reveal new opportunities for hot forming of tubes and profiles.Comment: 4 pages, 11 figure

A Model for the Coregulation of Smooth Muscle Actomyosin by Caldesmon, Calponin, Tropomyosin and Myosin Light Chain Phosphorylation

The purpose of these studies was to evaluate the effects of the actin-binding proteins tropomyosin. caldesmon, and calponin on the activation of smooth muscle actomyosin by phosphorylation of the regulatory light chain of myosin (LC20), and to interpret these findings in the context of a two-state kinetic model for the cross-bridge cycle. An in vitro motility assay was used to broadly classify each regulatory protein according to whether it modulates the apparent on-rate for cross bridges (fapp) or the apparent off-rate (garp). In addition to measuring actin-filament velocity, a method was developed to measure relative changes in the force exerted on actin filaments under isometric conditions. Based primarily on the results of these motility studies, a qualitative model is proposed in which LC20 phosphorylation, tropomyosin, and caldesmon all regulate fapp and calponin regulates gapp- The model predicts that the sensitivity of activation by LC20 phosphorylation is determined by tropomyosin. caldesmon, and calponin, whereas unloaded shortening velocity is regulated primarily by calponin

Aliquoting structure for centrifugal microfluidics based on a new pneumatic valve

We present a new microvalve that can be monolithically integrated in centrifugally driven lab-on-a-chip systems. In contrast to existing operation principles that use hydrophobic patches, geometrically defined capillary stops or siphons, here we present a pneumatic principle. It needs neither additional local coatings nor expensive micro sized geometries. The valve is controlled by the spinning frequency and can be switched to be open when the centrifugal pressure overcomes the pneumatic pressure inside an unvented reaction cavity. We designed and characterized valves ranging in centrifugal burst pressure from 6700 Pa to 2100 Pa. Based on this valving principle we present a new structure for aliquoting of liquids. We experimentally demonstrated this by splitting 105 muL volumes into 16 aliquots with a volume CV of 3 %

Resonant Diffraction Radiation from an Ultrarelativistic Particle Moving Close to a Tilted Grating

A simple model for calculating the diffraction radiation characteristics from an ultrarelativistic charged particle moving close to a tilted ideally conducting strip is developed. Resonant diffraction radiation (RDR) is treated as a superposition of the radiation fields for periodically spaced strips. The RDR characteristics have been calculated as a function of the number of grating elements, tilted angle, and initial particle energy. An analogy with both the resonant transition radiation in absorbing medium and the parametric X-ray radiation is noted.Comment: 17 pages, 12 figures, RevTe

Electron iduced light emission in photonic crystals

The interaction of a fast electron with a photonic crystal is studied by solving the Maxwell equations exactly for the external field provided by the electron in the presence of the crystal. The polarization currents and charges produced by the passage of the electron give rise to the emission of the so-called Smith-Purcell radiation. The emitted light probability is obtained by integrating the Poynting vector over planes parallel to the crystal at a large distance from the latter. Both reflected and transmitted light components are analyzed and related to the photonic band structure of the crystal. Emission spectra are compared with the energy loss probability and also with the reflectance and transmittance of the crystal.Comment: 9 pages, 3 figures, nano-7/ecoss-21 proceedings, submitted to Surface Scienc