Feedback tuning of bifurcations

The present paper studies a feedback regulation problem that arises in at least two different biological applications. The feedback regulation problem under consideration may be interpreted as an adaptive control problem for tuning bifurcation parameters, and it has not been studied in the control literature. The goal of the paper is to formulate this problem and to present some preliminary results.     

New substrates of papain, based on the conserved sequence of natural inhibitors of the cystatin family

A discontinuous borate/formate buffer system is presented for horizontal polyacrylamide gel electrophoresis of DNA fragments. The resolution potential of the system could be altered by changing the total monomer concentration (5-9%T), the concentration of the crosslinker piperazine diacrylamide (2-5%CPDA), as well as the concentration of formate in the gel (40-120 mM), the leading ion of the buffer system. The separation of DNA fragments would be improved by increasing the migration distance from 22 to 28 cm. This discontinuous polyacrylamide gel electrophoresis system proved highly reproducible.     

Effect of a DC corona electrical discharge on the airflow along a flat plate

Ability of a DC electrical discharge to control low-velocity airflow along a flat plate is analyzed. Specifically, the electrodes are flush mounted on the insulating surface of the plate creating a tangential corona discharge at close vicinity of the wall. In this paper, visualizations of the low-velocity airflow (up to 1.4 m/s corresponding to Re=16 000) along the flat plate are presented. They show that the ionic wind induced by the corona discharge modifies the original airflow considerably, resulting in the airflow reattachment to the wall and reduction of the wake size. Velocity measurements by particle imaging velocimetry and by Pitot tube are conducted in a wind-tunnel loop for higher airflow velocities (up to 11 m/s corresponding to Re=117 800). Results show that the corona discharge at such high airflow velocities does affect significantly the velocity profile within the viscous boundary layer.     

Surface designing of polypropylene by critical monitoring of the grafting conditions

The grafting of acrylic acid onto electron beam‐irradiated polypropylene was carried out using preirradiation method. The stability of peroxy radicals was investigated by electron spin resonance. It was found that the decay of peroxy radicals is much faster at 70°C than at 40°C and ambient temperature. The grafting has been observed to be strongly dependent on the monomer dilution in the reaction medium. The grafting was ascertained by attenuated total reflectance (ATR). The distribution of grafts across the samples was monitored by infrared microscopy. It was found that the graft management is considerably influenced by composition of the grafting medium. The grafting involving pure monomer leads to the surface enrichment with the polyacrylic acid chains. The samples grafted in pure monomer led to much lower contact angles as compared to the diluted monomer solution. The swelling of the grafted samples also showed a trend that was governed by the graft management. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 546–553, 2006     

Internal Reduction of Chromium-Doped α-Alumina

(Al,Cr)₂O₃ single crystals and polycrystals were internally reduced at 1873 K in an Al/Al₂O₃ buffer for periods of time ranging from 1 to 100 h. The growth kinetics of the reduction scale were measured. The microstructure of the reduction scale was investigated by SEM and TEM. As a result of the reduction, two types of discrete chromium precipitates developed inside the alumina matrix (inside the single crystal or the polycrystalline grains), each one being characterized by a particular morphology (needle or spheroid) and a low-energy orientation relationship with respect to the alumina matrix. In addition, larger precipitates without special orientation relationship developed along the grain boundaries and at the triple junctions of the polycrystais. In the first part of this paper, the precipitate morphology and size are described in terms of the crystallography of the interface between the two crystal structures in relation to the reduction mechanism. In the second part, the global reduction scale growth is analyzed in terms of point defect fluxes across the reduction scale.     

Photographing impact of molten molybdenum particles in a plasma spray

Plasma-sprayed molten molybdenum particles (∼40 μm in diameter) were photographed impinging at high velocity (∼140 m/s) on a glass substrate at room temperature. An optical sensor detected thermal radiation emitted by a droplet as it approached the substrate and activated a time delay unit. After a selected time interval, an Nd:YAG laser was triggered, emitting a 5 ns pulse that provided illumination for a charge-coupled device (CCD) camera to photograph the impacting droplet through a long-range microscope. By varying the delay before pulsing the laser, different stages of droplet deformation were recorded. Impacting droplets spread into a thin circular film that ruptured and broke into small fragments. An optical detector recording thermal radiation from the impacting droplet gave a signal that increased as the droplet spread out, reached a maximum when the liquid film began to rupture, and decreased as portions of the droplet recoiled because of surface tension and then flew out of view of the photodetector.