Size Reduction Mechanism Research Articles

Morphic features variation of solid particles after size reduction: sonification compared to jet mill grinding

Fourier descriptors of the contour were used to evaluate the effect of sonification and jet mill grinding on particle shape. While jet mill grinding produced particles with smoother boundary, less elongation and higher degree of roundness, sonification yielded fragments closer in shape to the original crystal. Data obtained suggest that the morphic features of daughter fragments are determined mainly by the mechanism of size reduction and material structure.

Lignosulfonate-modified calcium hydroxide for sulfur dioxide control

This article discusses the use of lignosulfonate-modified calcium hydroxide Ca(OH)/sub 2/ for sulfur dioxide (SO/sub 2/) control. The limestone injection multistage burner (LIMB) process is currently being developed at the U.S. EPA as a low cost retrofittable technology for controlling oxides of sulfur and nitrogen from coal-burning utility boilers. The most effective commercial calcium-based sorbent for this process is Ca(OH)/sub 2/, with SO/sub 2/ removals of about 50%. Additions of calcium lignosulfonate up to 1.5 mass % of the dry product, introduced with the water of hydration, increase the SO/sub 2/ capture of the resulting Ca(OH)/sub 2/ to 60%. This is achieved through particle-size reduction in the modified hydroxides. The principal mechanism of size reduction appears to be deagglomeration of the Ca(OH)/sub 2/ crystals; a secondary benefit is derived from crystal size reduction.

Is reduced cardiac performance the only mechanism for myocardial infarct size reduction during beta adrenergic blockade?

Equal reductions in heart rate (44 beats X min-1) were obtained in cats by treatment with either the beta blocking agent timolol or alinidine, an agent claimed to cause bradycardia without interfering with beta adrenoceptor function. Infarct size was measured by staining with triphenyltetrazolium-chloride after 5 h of coronary occlusion and related to the area of hypoperfused myocardium as measured by autoradiography. Regional myocardial blood flow was measured by 15 micron radiolabelled microspheres. Compared with the control cats, in whom 87.4 (SEM 2.2)% of hypoperfused myocardium developed into necrosis, timolol reduced infarct size to 65.8 (SEM 2.6)% (p less than 0.001) and alinidine to 76.2 (SEM 3.1)% (p less than 0.01) of the hypoperfused area. Timolol reduced infarct size more than did alinidine (p less than 0.01). Necrosis was more extensive in the endocardium than in the epicardium in all groups. In the subendocardium timolol and alinidine reduced infarct size to the same extent, whereas timolol reduced infarct size more than alinidine in the subepicardium. Although heart rate proved to be the dominant haemodynamic predictor of infarct size, this study indicates that mechanisms other than reduced oxygen demand associated with bradycardia and cardiodepression are operating in the ischaemic myocardium during beta adrenergic blockade.

Infarct size restriction in cats by the β-adrenergic blocker timolol

The β-adrenergic antagonist, timolol, was previously shown to exert a protective effect in cats subjected to 5 h of myocardinal ischemia. The present study was designed to determine the effect of timolol on infarct size in cats 24 h after coronary occlusion. Timolol (25 μg/kg) or vehicle (0.9% NaCl) was administered 0.5, 5, 10, 15 and 20 h after acute ligation of the left anterior descending coronary artery. There was no significant difference in arterial blood pressure or heart rate in MI cats receiving timolol or vehicle. Timolol markedly decreased S-T segment elevation at 2–12 h (P<0.05). Left ventricular weights in MI+ vehicle cats (8.5±0.7g, n=6) were similar to timolol-treated MI cats (8.9±0.4 g, n=7). However, the percent of the left ventricular myocardium infarcted, determined by nitroblue tetrazolium staining, was significantly less (P<0.001) in timolol MI cats compared to saline-treated cats, 9.8±1.2% (n=7) vs 18.9±1.8% (n=6), respectively. Hemodynamic or cytoprotective actions of timolol do not appear to explain these results. Rather, the mechanism of infarct size reduction by timolol is probably explained by antagonism of β-receptor-mediated metabolic effects.

Biochemical mechanism of infarct size reduction by pyruvate.

We have explored the biochemical mechanism of the infarct size reduction found after intracoronary pyruvate infusion. Using the double infarct model, we simultaneously produced in nine dogs a control- and a therapy-infarct and compared the infarct sizes in each dog after 90 min of occlusion and 90 min of reflow. Intracoronary pyruvate reached the therapy infarct only by way of collaterals but had no access to the control infarct. Tissue levels of reduced nicotinamide dinucleotide (NADH) were measured in control-normal-, therapy-normal-, control-ischaemic-and pyruvate-treated ischaemic areas. In all nine dogs we found a significant reduction in infarct size and NADH levels in the pyruvate-treated areas. Therapy-normal NADH levels fell to 30+/-10% (mean+/-SD) of control-normal levels and therapy-ischaemic NADH levels to 26+/-17% of control-ischaemic levels. We assumed that the infused pyruvate was converted to lactate and at the same time NAD was generated from NADH. Thereby the blockage of glyceraldehyde-3-phosphate-dehydrogenase (GAPDH) by high NADH/NAD-ratios in ischaemic myocardium should be moderated, and ATP production by anaerobic glycolysis stimulated. These small amounts of ATP may be sufficient to guarantee membrane integrity over 90 min of ischaemia and so diminish its harmful effects on the myocardium.

Deformation of biotite and muscovite: Tem microstructure and deformation model

Growth and deformation defects have been observed in 1M and 2M1 biotites and 2M1 muscovites using transmission electron microscope (TEM) techniques. These have been related to optical observations. In deformed biotite, the dislocation density increases as the strain increases. The density of stacking faults also increases with strain. The spatial ordering of stacking faults decreases as the strain increases. In muscovites selected from the same areas as the biotites, stacking fault and dislocation densities show little or no variation with deformation. The different responses of biotite and muscovite to deformation are explained, in part, by the physical and chemical differences between 1M biotite and 2M1 muscovite. There is strong evidence, in both the biotites and muscovites, that stacking faults may be result of deformation as well as a crystal growth process. The grain size of the deformed mica aggregates is reduced by the nucleation of new micas. There is also evidence for a grain size reduction mechanism (segmentation) in biotites. This mechanism appears to achieve the same result as recovery-recrystallization mechanisms, but not by the same method. Segmentation may be a mechanism which is favoured in strongly anisotropic minerals with a limited number of slip-systems. A model is proposed that attempts to correlate response of the biotite to deformation. The deformation is synchronous with, and post-dates, the nucleation of the new metamorphic micas.

In vitro studies on the mechanism of herpesvirus plaque growth inhibition by sensitized lymphocytes

Inhibition of herpesvirus plaque growth was observed when herpes simplex virus (HSV)-sensitized rabbit lymphocytes were placed in contact with an HSV-infected human foreskin monolayer. This inhibition was obtained as early as 3 h when a ratio of 6 viable lymphocytes to target cells was used, and the supernatants of these cultures also demonstrated plaque size reduction when put onto newly infected cell monolayers. Interferon, which is present in this system, had no effect on HSV when tested on human foreskin monolayers, indicating that interferon was not the mechanism for plaque size reduction. Plaque growth inhibition was attributed to the T lymphocyte, because purified T cells reduced plaque growth and anti-rabbit thymocyte serum eliminated the effect of T cells. The specificity of this assay was determined by the facts that nonsensitized lymphocytes did not reduce the size of a plaque and the recognition of an infected cell by the sensitized lymphocyte was necessary for the release of a soluble mediator into the supernatant fluid. This cytotoxic lymphocyte was detected in the peripheral blood of rabbits as early as 4 days after initial corneal infection, with a maximum response at 7 to 10 days.

Abrasion in Place: A Mechanism for Rounding and Size Reduction of Coarse Sediments in Rivers

Rounding and reduction in size and weight of coarse particles occur over a significantly shorter distance in a stream as compared to the “distance” of travel required to produce a similar result in a tumbling barrel or flume. This suggests that either the known processes of wear are more effective in streams than in the laboratory or that other processes are at work. Investigations of riprap failure by hydraulic engineers provide data on the forces acting on coarse particles and particle behavior prior to downstream movement. The experiments demonstrate that lift forces acting on a submerged cobble are large and vary significantly with time. When this effect of lift is combined with drag forces, a particle vibrates in place without downstream movement. With increased velocity, the particle lifts off the stream bed and saltates downstream to a new position of temporary stability. During high-velocity flow, abrasion of cobbles in place and the chipping and fracturing during saltation can be significant factors causing rounding and size reduction of coarse sediments in rivers.

Closed circuit grinding of agricultural products

Preliminary studies intended to determine the feasibility of the closed-circuit system of grinding for agricultural grains were conducted. A small quantity of grain was ground in a mill adjusted for coarse grinding. The ground material was sorted, the fine material put aside and the coarse material returned to the mill for additional grinding. This process was repeated a number of times. A single grinding with a mill adjusted for finer grinding was used as a standard comparison. The multiple ground material was more uniform in size and required less energy per unit of newly created surface area. The basic mechanisms of size reduction were reviewed and analytical procedures were developed for the closed circuit procedure. The results indicate that this procedure should be studied in greater detail because it appears to have significant potential to improve grinding processes.