Effect of pulse duration and size of interelectrode interval on electric-spark spraying. I. Effect of pulse duration and size of interelectrode interval on rate of electric-spark transfer

The influence exerted by electric-spark spraying on the kinetics of mass transfer and the physicomechanical properties of coatings is investigated. It is shown that electric-spark spraying is determined by the dynamic properties of the cathode jets, which depend on the electrical parameters of the spark discharge, the size of the interelectrode interval, and the physical properties of the coatings, which vary during spraying.     

Simultaneous visualisation of biofouling, organic and inorganic particle fouling on separation membranes.

Fouling is a major problem in membrane processes of water treatment. It can be caused by the deposition of inorganic and organic particulate material, and of microbial cells which may subsequently form biofilms. In practice, usually more than one foulant participates in the formation of membrane deposits. Knowledge of the composition of fouling layers is important for the development of appropriate countermeasures. For this purpose, an experimental system was established for the generation and microscopic visualisation of mixed deposits, using fluorescently labelled model foulants: (i) drinking-water bacteria stained with nucleic acid-specific dyes (biofouling), (ii) synthetic clay mineral laponite stained with rhodamine 6G (inorganic particle fouling), and (iii) fluorescently labelled polystyrene microspheres (organic particle fouling). Polycarbonate and polyethersulfone membranes were challenged with these foulants by dead-end filtration. On the basis of different fluorescent labels, the single foulants in these mixed deposits could be visualised separately by confocal laser scanning microscopy which, in combination with image analysis, allowed the generation of three-dimensional views of the complete deposits. This method offers the possibility for the estimation of quantitative surface coverage by foulants and for the determination of the efficacy of cleaning measures with respect to the removal of different foulants.     

Effects of selenium and vitamin E on incidence of retained placenta

In a series of experiments over 3 yr, relatively low doses of selenium and vitamin E were injected intramuscularly 3 wk prepartum to pregnant Israeli-Holstein dairy cows in a high-producing herd (9000 kg milk/yr) with a history of retained placenta in 17% of the primiparous and 28% of the multiparous animals, as recorded for the 12 mo preceding the study. Selenium ranged from .035 to .109 ppm in the prepartum diet and from .160 to .200 ppm in the postpartum diet. Doses of selenium ranging from 2.3 to 23.0 mg reduced the incidence of retained placenta in 186 primiparous and in 428 multiparous to 7 and 15%, which was half of that of controls. Low doses of selenium (2.3 to 4.6 mg) tended to be more effective than higher ones. Selenium alone was at least as effective as a combination of selenium and vitamin E. Dosage, timing, mechanism, and interactions of selenium with other factors in reducing the incidence of retained placenta need clarification.     

Biochemical quality assessment of broiler production using a hydrogen bacteria biomass in the diet

The authors studied the biochemical composition of the meat of broilers, eggs, liver and muscles of laying hens of 3 generations on a 5, 10, 25, 50 and 100% (broilers), 10 and 20% (laying hens) replacement of the animal protein quota in the diet by protein obtained from the hydrogen bacteria Alcaligenes eutrophus L-1. No deterioration of the quality of the produce was found from the standpoint of the main biochemical parameters.     

The use of reflectors in venetian blinds to enhance irradiance in greenhouses

Using a venetian blind as a basis, we describe and analyse novel forms of high-gain, nonfocussed sunlight concentrators and test experimental versions. Generally, midday winter light passing mainly through the roof of an E-W single-span greenhouse is reflected downwards to the floor through the use of conventional and modified reflecting louvres in a venetian-blind assembly suspended from the greenhouse apex. Experimentally, in a 7.3-m wide compartment, a 2-m deep conventional louvre assembly produced approximately an 18% gain in the southern half of the house, but a 4% loss in the northern half. A modified louvre assembly, which directs light to both halves of the house, gave, without readjustment of the louvre angle, 16% in the southern half and in the northern half. Under diffuse light conditions the blind was shown to produce an average 2% loss across the house. As a percentage of light received by the plant, as opposed to external irradiance, an average of 20% gain over the whole house width is predicted under sunny conditions if better manufacturing techniques are employed.Reasonable agreement with theoretical calculations of irradiance is also shown, and a theoretical analysis shows that full irradiance enhancement before and after midday, when oblique sunlight is incident on the reflector, will still be generally obtained.     

Cavitation Damage of the single-crystal nickel-base superalloy SRR99 during creep at 850°C

Various heat treatments of the single-crystal nickel-base superalloy SRR99 have been carried out to produce a wide range of initial γ′ phase morphology. The cavitation damage has been studied after creep fracture at 850°C and stresses between 400MPa and 650 Mpa. The crep fracture surfaces and longitudinal sections of crept specimens have been examined by image analysing system in order to determine the size distribution and the area fraction of (001)-planes cracks on fracture surface characterise the creep crack damage level. The cracking morphology in fractured material as a function of stress and γ′-phase size has also been investigated. The results show, that crack propagation occurred anisotropically on (001) crystallographic planes perpendicular to the aplied stress along the γ/γ′ interfaces. It was found, that creep cracks dependent on the shape and size of γ′-phases developing at the temperature and stress level.     

The dominance of the K I-field for a crack under stress wave loading

The extent of the dominant singular field is investigated for a finite crack under stress wave loading. Using a boundary integral equation method the complete solution as well as the near field solution is determined. A comparison of the two fields indicates that the singular field dominates within a small domain at the crack tip. The size of the dominance region in the dynamic case may be very different from that in the static case.