Effect of Inhomogeneities on the Apparent Location and Magnitude of a Cardiac Current Dipole Source

A mathematical model was used to investigate the effects of electrical inhomogeneities introduced by the intracavitary blood mass and the lungs on the apparent location and magnitude of a current dipole source representing local activity in the myocardium. Radial and tangential current source moments were considered, and lung conductivity was taken as a variable parameter. Both the blood mass and the lungs cause a current source to appear closer to the heart center than it actually is. The effect increases as the source moves away from the endocardial surface, and maximum displacement is estimated to be of the order of 1 cm. The net effect of the inhomogeneities is to increase the magnitude of the radial component of a source dipole while diminishing its tangential component. These effects depend on source location.     

Softening and melting mechanisms of polyamides interfering with sliding stability under adhesive conditions

The thermal stability of polymers is a main issue when used as friction elements under dry sliding. Cast polyamide grades processed with either natrium or magnesium catalysors are slid on a small-scale and a large-scale test configuration to reveal the effect of softening or degradation on the sliding stability and to investigate possibilities for extrapolation of friction and wear rates between both testing scales. The combination of softening and afterwards transition into the glassy state is detrimental for the sliding stability of natrium catalysed polyamides, characterised by heavy noise during sliding. A transfer film formed under continuous softening also provides high friction. Melting during initial sliding is necessary for stabilisation in both friction and wear, and eventual softening of a molten film near the end of the test then not deteriorates the sliding stability. Softening of magnesium catalysed polyamides is favourable for the formation of a coherent transfer film resulting in more stable sliding than natrium catalysed polyamides. The differences in softening mechanisms of both polyamide grades is correlated to structural changes investigated by thermal analysis and Raman spectroscopy: the γ crystalline structure prevails in magnesium catalysed samples and the α crystalline structure is predominant in natrium catalysed samples. For internal oil lubricated polyamides, a time dependent degradation of the polyamide bulk deteriorates the supply of internal oil lubricant to the sliding interface, resulting in high friction and wear under overload conditions. As the degradation mechanisms during sliding are strongly correlated to the test set-up, extrapolation is only possible for friction in a limited application range, while wear rates cannot be extrapolated.     

Chemical modification of hemp,sisal, jute,and kapok fibers by alkalization

Plant fibers are rich in cellulose and they are a cheap, easily renewable source of fibers with the potential for polymer reinforcement. The presence of surface impurities and the large amount of hydroxyl groups make plant fibers less attractive for reinforcement of polymeric materials. Hemp, sisal, jute, and kapok fibers were subjected to alkalization by using sodium hydroxide. The thermal characteristics, crystallinity index, reactivity, and surface morphology of untreated and chemically modified fibers have been studied using differential scanning calorimetry (DSC), X‐ray diffraction (WAXRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), respectively. Following alkalization the DSC showed a rapid degradation of the cellulose between 0.8 and 8% NaOH, beyond which degradation was found to be marginal. There was a marginal drop in the crystallinity index of hemp fiber while sisal, jute, and kapok fibers showed a slight increase in crystallinity at caustic soda concentration of 0.8–30%. FTIR showed that kapok fiber was found to be the most reactive followed by jute, sisal, and then hemp fiber. SEM showed a relatively smooth surface for all the untreated fibers; however, after alkalization, all the fibers showed uneven surfaces. These results show that alkalization modifies plant fibers promoting the development of fiber–resin adhesion, which then will result in increased interfacial energy and, hence, improvement in the mechanical and thermal stability of the composites. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2222–2234, 2002     

The nutritive value of refined rapeseed oils: A review

Recent findings on the nutritive value of rapeseed oil (RSO) with high erucic acid content have been compared to those of canbra oil (CO), an oil extracted from newly bred Canadian rapeseed with no erucic acid. Erucic acid in diets retards animal growth even if food consumption is not altered. Growth performances of CO are as good as olive or peanut oil. The unbalanced ratio of palmitic acid to monoethylenic acids of CO does not affect rat growth rate. Because of its glyceride structure and high content of erucic acid, RSO has a lower digestibility (81%) than CO (96%) in the rat. Unabsorbed erucic acid is not preferentially excreted as calcium soaps. Interesterification of RSO which converts 31.7% of the erucic chains to the 2 position improves digestibility of erucic acid. 2-Monoerucin is more efficiently absorbed than the free acid. In vivo metabolic conversion of erucic to oleic acid has been proved in the rat. β-oxidation of injected 14-¹⁴C labeled erucic acid proceeded at the same rate as oleic acid but the over-all yield of the reaction was lower. Fatty acid composition of tissues in animals fed RSO or CO is influenced on one hand by erucic and gadoleic (C_20∶1) acids of RSO, and on the other hand by the unbalanced ratio of palmitic-monoethylenic acids and the linolenic acid content of both oils. Nonnegligible amounts of erucic acid are deposited in the body fats of rats, chickens, turkeys, lambs and found in the milk of female rats fed RSO. Almost no erucic acid is incorporated in liver and testicles in the rat and it is not recovered in chicken egg yolk. The effect of RSO on rat reproduction has been re-examined. Dietary lipid and vitamin levels are of great importance in the results obtained. RSO induces myocarditis in several animal species. Similar lesions, although less frequent and severe, have been observed also with CO in the rat. Some authors have reported that erucic acid of RSO was responsible for the effect on heart muscle. Common fatty acid patterns to both RSO and CO have to be further investigated to explain the persisting effect of CO. One of 9 papers presented at the Symposium, “Cruciferous Oil-seeds,” ISF-AOCS World Congress, Chicago, September 1970.     

Relationship of peroxide value and thiobarbituric acid value to development of undesirable flavor characteristics in fats

The peroxide value and thiobarbituric acid value were compared with the flavor score for a series of different types of fats, with and without added monoglyceride and with and without different stabilizers. The data indicated that the flavor score cannot be estimated for any given fat from either the peroxide value or the thiobarbituric acid value. Either can be used to follow the development of off flavors in a given product or formulation but the relative level may vary from product to product. Presented at the AOCS Meeting in Minneapolis, 1963.     

Tensile strength of polyurethane exposed to nitrogen dioxide

Polyurethane prepared from tetramethylene glycol and diisocyanate was exposed in the form of films to small pressures of NO₂ and to NO₂ plus air. Tensile strength was measured as a function of exposure time and temperature with an apparatus especially constructed for the purpose of measuring mechanical properties in different environmental “atmospheres.”     

Experimental research and prediction of the effect of chemical and biogenic sulfuric acid on different types of commercially produced concrete sewer pipes

New equipment and procedures for chemical and microbiological tests, simulating biogenic sulfuric acid corrosion in sewerage systems, are presented. Subsequent steps of immersion and drying, combined with mechanical abrasion, were applied to simulate events occurring in sewer systems. Both chemical and microbiological tests showed that the aggregate type had the largest effect on degradation. Concrete with limestone aggregates showed a smaller degradation depth than did the concrete with inert aggregates. The limestone aggregates locally created a buffering environment, protecting the cement paste. This was confirmed by microscopic analysis of the eroded surfaces. The production method of concrete pipes influenced durability through its effect on W/C ratio and water absorption values. In the microbiological tests, HSR Portland cement concrete performed slightly better than did the slag cement concrete. A possible explanation can be a more rapid colonisation by microorganisms of the surface of slag cement samples. A new method for degradation prediction was suggested based on the parameters alkalinity and water absorption (as a measure for concrete porosity).     

The use of direct osmosis tests as complementary experiments to determine the water and salt permeabilities of reinforced cellulose acetate membranes

In this article the use of the direct osmosis test as a complementary experiment to the reverse osmosis test is described. The membranes investigated are cellulose acetate membranes reinforced with mineral fillers. In both tests the same influence of the type of fillers on the water permeability coefficients is found. The salt permeability coefficients indicate the presence of pressure sensitive defects in the reinforced membranes. The direct osmosis test is found to be a suitable test to confirm and predict the membrane properties under reverse osmosis conditions.     

Characterisation of the neutral oil from a low-temperature coal tar

Tar resulting from fluidised-bed, low-temperature carbonisation of coal was treated to yield a neutral oil from which a series of six other samples was extracted. These were examined by proton magnetic resonance (p.m.r.) spectroscopy, low-ionising-voltage (11 eV) mass spectroscopy (m.s.), gel chromatography followed by fluorescent indicator analysis, and cryoscopy. Aliphatic fractions separated chromatographically were also examined by infra-red spectroscopy. Distributions of hydrogen between chemical types were found for the several fractions from 60 MHz p.m.r. spectra and presented in terms of average structural parameters. M.s. analysis indicated negligible cracking of paraffin components, and the average molecular weight of 197 agreed well with cryoscopic determinations. For the carbon ratio, f_a, between aromatic and total, agreement between m.s. and p.m.r. depends on the p.m.r. structural analysis scheme adopted. P.m.r. and m.s. structural analyses of the aromatics emphasise the predominance of di- and tri-nuclears, with about 40% of available sites substituted, and the importance of acenes in lowtemperature carbonisation material. Gas and gel chromatography showed urea-adductable paraffins to be largely straight-chain C₁₀-C₂₆, much as for tars from carbonisation at higher temperature.