Increasing Stirring Speed Research Articles

Platelet adherence to collagen: A simple, reproducible, quantitative method for its measurement

A simple, reproducible method for quantitating platelet adherence to collagen is described. Platelet rich plasma is stirred with a stable collagen suspension, non-adherent platelets counted by Coulter counter, and percent adherence calculated. Platelet aggregation is prevented by EDTA. Platelet adherence was found to reach a maximum value within 5 minutes and also reached a maximum value with increasing stirring speed and collagen concentration. It fell exponentially with increasing platelet count although the number of adherent platelets increased to an apparent maximum suggesting saturation of collagen binding sites. Percent platelet adherence fell linearly when pH was increased. At physiologic pH a non-adherent platelet population of approximately 25% was present. Platelets of different sizes adhered to a similar extent suggesting that platelet age may not influence adherence. A relatively narrow range for normal percent adherence was established and serial determinations in a single individual showed only limited variability with time. By changing either the platelet count or collagen concentration adherence can be varied from < 20% to 70%. The technique is sufficiently versatile that it should be useful for studying many aspects of the platelet/collagen adhesion reaction.

Monomer Leakage from Polymerizing Acrylic Bone Cement An In Vitro Study on the Influence of Speed and Duration of Mixing, Cement Volume and Surface Area

An in vitro study was dthesigned to measure the effects of variable cement volumes and modified mixing techniques on the monomer leakage after simulated implantation. The cement volume as such was found to be an irrelevant parameter for calculations of the monomer loss from bone cement. The leakage was directly related to the surface area of the cement. Variations in the thickness of the cement mantle from 1 to 5 mm did not affect the leakage. Late cement insertion should reduce the total monomer leakage into the tissues. It is doubtful whether an increased stirring speed during mixing reduces the monomer leakage after implantation.

THE TEXTURE OF POLYETHYLENE PRODUCED BY γ-RAY IRRADIATION POLYMERIZATION WITH STIRRING

The effect of stirring on the polymerization of ethylene induced by γ-irradiation in a gaseous phase was studied with regard to the morphological features and the physical properties of resultant polymer. The melting temperature, the heat of fusion, the density and the content of CH3 groups of the polymers formed were independent of the stirring speed, but the specific surface area of the material showed a minimum in the range of 200-500 rpm. Similarly, the viscosity-average molecular weight showed a minimum at a speed of ca. 200 rpm. GPC molecular weight distributions showed double peaks which is characteristic of low-temperature polymerization product. The higher molecular weight species increased with increased stirring speed. The fibrillar morphologies observed under a scanning type electron microscope increased drastically with increased stirring speed. Close inspection of these fibrils revealed that many nodese fibers were produced by a partial unfolding of molecules in the lamellar crystals. It is likely that the increase of fiber-like structures leads to the increase in the specific surface area of the resultant polymers, so that the number of contact of long-lived radicals in the resultant polymeric solid with monomers increases, giving rise to the chain growth and the grafting, which produces long chain branches, and consequently the polymerization rate is accelerated.

Influence of Carbon Transport Kinetics on Solution Growth of β‐Silicon Carbide Crystals

Twinned β‐silicon carbide platelets with a (111) habit were grown from the walls of graphite crucibles in liquid silicon solutions with carbon concentrations below 0.1 a/o (atomic per cent). The observed crystal growth effects resulting from increasing the carbon solute transport rate by stirring the solution are described and correlated with boundary layer theory. Both forward growth of platelets into the solution and lateral growth of platelets were accelerated by stirring. However, crystal growth in the forward direction was eventually limited by a boundary layer region, beyond which the solution was no longer supersaturated. Because of the decrease in boundary layer thickness with increasing stirring speed, the terminal lengths of silicon carbide platelets decrease with increasing stirring speed.

Mechanism of emulsion polymerization of vinylidene chloride. III. Effects of stirring rate on kinetics

The effect of stirring speed on the rate of the persulfate-catalyzed polymerization of vinylidene chloride has been determined. It was found that the first-stage rate decreases with increasing stirring speed, that the second-stage rate increases with increasing stirring speed, and that the rate of the third stage is independent of stirring speed. These results, as well as those of an earlier paper, may be explained in the following manner. The second stage slow-down results from monomer starvation, caused by slow diffusion from coalesced droplets. Recovery is caused by transfer of monomer at the time of collision between a polymer particle and a monomer droplet. These collisions are allowed when the repulsive forces between monomer droplet and polymer particle are reduced because of surfactant deficiency.