Spores of the microsporidium Nosema algerae were stimulated to germinate in vitro while observed with video-enhanced contrast microscopy. Field-by-field playback of tape-recorded sequences yielded the first serial illustrations and kinematic analysis of the explosive discharge of the polar filament and the sporoplasm. The filament emerges from the anterior pole of the spore in a regularly pitched helicoidal course along a nearly straight axis, with a mean maximum instant velocity of 105 p d s . Just before elongation is completed the filament tip follows a tortuous path that often results in a curved or spiralling terminal configuration. Then elongation stops and, after a lag that may vary from less than 15 to over 500 ms, the sporoplasm pours out at the filament tip forming a globule that quickly grows up to a size larger than its original volume within the spore. Concomitantly, the helical filament becomes straightened and frequently the spore body is pulled forward. Thereafter a relaxed filament, usually 5-10% shorter than when maximally extended, remains connecting the empty spore case and the sporoplasmic droplet. Experiments with hyperosmolar media produced a considerable slowdown of filament extrusion and often precluded sporoplasm discharge. The present results are fully consistent with the hypothesis of a hydrostatic pressure-triggered mechanism of spore germination, and revealed that the process is composed of two discrete phases separated by a variable lag: 1) complete eversion of the polar filament, and 2 ) passage of the main sporoplasm mass along the tube.The data provide a preliminary basis toward the conception of a quantitative physical model of microsporidian spore germination. o 1992 Wiley-Liss, Inc.
Hydrocolloids and some of their mixtures were used to prepare spray-dried yogurt. Acetaldehyde retention and microbial viability were evaluated. Morphology was examined by scanning electron microscopy and the yield stress was evaluated, to assess the damage to the microstructure by the drying process. The yield stress displayed a significant irreversible decrease after spray drying and micrographs indicate that the microstructure of the yogurt was severely damaged by the drying process. Micrographs indicated that k-carrageenan and k-carrageenan-locust bean gum gave more protection to the casein matrix, leading to greater acetaldehyde retention (92% and 89%, respectively). Microbial viability was improved when pectin was used as the encapsulating agent.
We show the first estimations of long-term (100 years, 1900 to 2000) total gaseous mercury concentrations (TGM) in the urban area of Almadén. The estimation was carried out by comparing data on known metallic mercury production with measured TGM concentrations. The estimated diurnal background level ranges from 60 to 120 ng m(-3) and corresponds to periods when the metallurgical complex (cinnabar roasting plant) was shut down. The average TGM concentration during the period from 1900 to 2000 was about 600 ng m(-3) (with peaks above 1,200 ng m(-3)). Additionally, a 24-h-based TGM monitoring program has highlighted significant differences between the diurnal and nocturnal concentrations, particularly during the warmer months. In this regard, given that the average nocturnal to diurnal ratio is 2.12, we suggest that the average nocturnal concentrations must have exceeded 1,200 ng m(-3), and peak nocturnal concentrations could have reached levels up to 2,400 ng m(-3). Our estimations indicate that most parts of the town of Almadén were generally exposed to TGM concentrations in air that exceed the World Health Organization air quality guideline for Hg (1,000 ng m(-3)) for countryside and urban areas.
Poly ether ether ketone (PEEK) composite belongs to a group of high performance thermoplastic polymers and the addition of carbon fibers increases the resistance and rigidity of PEEK. Due to favorable mechanical and thermal properties and potential applications in various manufacturing industries, it is essential to analyze the machining performance of reinforced PEEK composites. The surface roughness is a widely used measure of product quality that could influence the performance of mechanical products and production costs. The present study establishes the relationships between the cutting conditions (cutting speed and feed rate) and three surface roughness parameters (centerline average surface roughness, maximum peak to valley height and root mean square roughness) by developing second order mathematical models based on response surface methodology (RSM). The reinforced PEEK with 30% of carbon fiber (PEEK-CF30) workpieces were machined using TiN-cutting tools. The experiments have been planned as per full factorial design of experiments (FFD). The developed surface roughness models were then employed with particle swarm optimization (PSO) to optimize the cutting conditions. PSO program gives the minimum values of surface roughness parameters and the corresponding optimal cutting conditions.
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