Lamellar lubrication in vivo and vitro: friction testing of hexagonal boron nitride.

Phospholipid molecules (PLs) in vivo and graphite, molybdenum disulfide, tungsten disulfide and hexagonal boron nitride (h-BN) in vitro are good examples of frictionless lubricants. PLs and solid materials have the ability to form multi-bilayer or layered structures similar to lamellate solid. It has been confirmed experimentally that PLs as lamellar lubricants protect the surface of joints against wear while acting as frictionless lubricant. An experimental study has been conducted on the friction properties of h-boron nitride on porous non-full journal bearings. The porous non-full journal bearings were a mixture of 97.5 wt.% Fe and 2.5 wt.% Cu powder, and compressed to a density of 5.9 g/cm(3). The porosity of non-full journal bearings were 15.5 and 27.8 wt.% and were impregnated with vaseline and vaseline+5 wt.% h-BN. Additionally, the two additives SFR NLGI #2 (or SFR 2522) grease and graphite grease were used for comparison to h-BN. The tribological tests were performed on a four-ball machine under load of 49 daN, and a friction tribotester. The above experiment strongly suggested that h-BN has the ability to lubricate under load with very low friction coefficient comparable to phospholipids. Relatively low surface energy and low adhesion between the crystallites are giving the additives low friction coefficient. The results of the experimental studies showed that h-BN as an additive in vaseline possesses friction reducing properties, and excellent anti-wear properties.

Study of arsenic content in mine groundwater commonly used for human consumption in Utah.

Of the various sources of arsenic released in to the environment, the presence of arsenic in water probably poses the greatest threat to human health. Arsenic is released in to the environment through water by dissolution of minerals and ores. Natural release is slow, but in some areas the concentration of arsenic in groundwater (commonly referred to as Acid Mine Drainage (or AMD)) is accelerated by mining activity. In fact the presence of arsenic may last a long time even after the mining activity has ceased. Hence it is imperative to study the quality of water (especially for those areas in the vicinity of mines) used for different purposes to identify an appropriate remediation technique for effective pollution control. In this paper, contents of arsenic and other metals in the water were quantified from three different sources: (1) groundwater from the mining tunnel (Judge tunnel), (2) drinking water, and (3) water used in the hydrant-flushed distribution system (Park City) in Utah (USA). The results showed the content of arsenic from the mining tunnel, after chlorination, and in tap water were below 10 microgl(-1). However, significant amounts of arsenic, lead, zinc, iron, manganese and antimony have been found in water samples taken from the distribution systems. In the consideration of the further use of mine groundwater for drinking purposes and the distribution system, Park City should regularly be maintained by a flushing program in the distribution system.

Modification of iodometric determination of total and reactive sulfide in environmental samples.

In iodometric determination of sulfide two reactions are taking place when alkaline solution is added to HCl acid-iodine. The main oxidation reaction (1), H(2)S+I(2)=2HI+S; and side reaction of sulfide (2), S(-2)+4I(2)+8OH(-)=SO(4)(2-)+8I(-)+4H(2)O. Preference of reaction (2) over (1) is dependent on pH increasing to >7. When sulfide solution of pH 9 was mixed with HCl acid-iodine, the recovery exceeded 120%, but the recovery of a solution with a pH of 13 exceeded 200%. To eliminate the side reaction in iodometric titration, the sulfide solution must be acidic when it is mixed with HCl-iodine. To avoid the side reaction (2), the pH of sulfide solutions were adjusted with acetic acid to pH 5.5, mixed with HCl-iodine solution and then titrated with standard thiosulfate with precision and accuracy <+/-3%.

[Factors contributing to recurrence of intracranial meningiomas and indications to postoperative radiotherapy]. / Czynniki sprzyjajace odrostowi oponiaków wewnatrzczaskowych i wskazania do pooperacyjnej radioterapii.

The incidence of various histological subtypes of intracranial meningiomas and recurrences was examined in 565 patients with surgically treated meningiomas in the Department of Neurosurgery in Poznan, between 1960-1992. Approximately 60% of the tumours were located on the convexity (39.5%) and parasagitally (23%). Histological diagnosis in 88% of the patients was endotheliomatous (61%), fibroblastic (17%) and angiomatous (10%) meningiomas. The incidence of recurrence after complete removal of the meningioma was 7% for all sites, but much higher after partial removal. Among the recurrences, there was a higher degree of malignant and angiomatous subtypes. Surgery is the accepted form of treatment for meningiomas but it may prove insufficient as the only method of therapy in certain situations. Implications for the potential role of postoperative radiation therapy are discussed.

The assay and resolution of the beta-blocker atenolol from its related impurities in a tablet pharmaceutical dosage form.

For the complete resolution and determination of the beta-blocker atenolol and its manufacturing impurities a high-performance liquid chromatographic method is developed using structured optimization techniques. The method utilizes a 300 x 3.9 mm i.d. stainless steel column packed with mu Bondapak C18 and a mobile phase containing methanol-25 mM potassium dihydrogen orthophosphate containing 0.06% (v/v) dibutylamine (20:80, v/v) (pH 3.0). The flow rate of 1.0 ml min-1 is used and a detection wavelength of 226 nm. The linearity and repeatability are good for the present compound over the range 1.5-510.0 micrograms ml-1 (r greater than 0.99 and RSD 0.27%, n = 10). Application of the method to 50 and 100 mg tablets gave recoveries of 99% (w/w) and reproducibilities of (RSD) 1.1 and 0.52%, respectively (n = 5). The manufacturing impurities are found to be greater than 0.5% (w/w) of the atenolol peak.

[Development of antigens ABH and Ii in children between 0 to 16 years old]. / Développement des antigènes ABH et Ii chez les enfants de 0 à 16 ans.

The ABH and I, i erythrocyte antigens of 926 children from birth to sixteen years were tested in a semi-quantitative assay in order to follow their development. Results show that total activities of A, B and H erythrocyte antigens are reached within 13 and 24 months, the main modifications being observed within the first three months of life. However, these activities depend on the agglutinins used in the test; notably the results with anti-H lectins from Ulex europaeus and Laburnum alpinum are not totally identical. The decrease of i reactivity and the increase of I reactivity are simultaneous, but at birth the I reactivity of cord red cells is widely distributed, while that of i is more homogeneous. The increase in H activity tested with Laburnum alpinum is directly related to the decrease of foetal hemoglobin in the children's red cells.