A test object for assessing image quality in mammography

The problems inherent in the design and manufacture of mammographic test objects are discussed and a test object is described which may be used for assessing image quality. Some typical results from both good and bad mammographic machine/film combinations are presented.     

Characterisation of thin surface films on germanium in various solvents by ellipsometry

Ellipsometric techniques were used to investigate the thin films that formed on cleaved germanium samples in air, deionised water, and 30% hydrogen peroxide. In all three cases the films were less than 100 Å in thickness. The films formed in air and water had a refractive index of 1.63±0.02 which is close to that of glassy GeO₂. An increase of refractive index to about 1.74 was observed when the samples were immersed in a solution of 30% H₂O₂. The thickness of this film (18Å) remained relatively constant in a period of 5 min to 6 h. The film is attributed to a layer of Ge(OH)₂ ²⁺ surface complexes, and a thick reaction envelope of metagermanic acid (H₂GeO₃). After rinsing surfaces covered with glassy GeO₂ with a 48% HF solution, the original oxide was removed; however, within 5 min a 50Å thick film of glassy GeO₂ had formed.Also affiliated with the Department of Physics.Also affiliated with the Department of Geochemistry and Mineralogy.     

Composites formed by interstitial polymerization of vinyl monomers in polyurethane elastomers: 2. Morphology and relaxation processes in methyl methacrylate based composites

The morphology and loss properties of polymeric composites of poly(methyl methacrylate) (PMMA) and polyurethane (PU) prepared according to an interstitial method have been studied. To a first approximation the structure is shown to consist of PMMA domains embedded in a PU matrix. A second approximation shows that there is some molecular interaction between the polymeric species, probably at the domain boundaries. Variations in the domain size and molecular motions are studied as a function of composition and experimental variables. Attempts are made to correlate these results with the mechanical properties of the composites.     

Immediate and long term effects of instrumental dilation of the sphincter of Oddi

Large dilators passed through the sphincter of Oddi do not prevent retained or recurrent common bile duct stones. Large dilators are more likely to cause postoperative pancreatitis than are small ones. Pancreatitis resulting from maximal dilation is more likely to be severe, and the patients are more likely to die from it.     

Motion of continuous surfaces through stagnant viscous non-Newtonian fluids

An analysis is given of the hydrodynamics and drag of a rigid sheet moving through a stagnant non-Newtonian fluid. The methods of boundary layer theory are applied and it is shown that a ‘similarity’ transformation is sometimes possible. The effect of the apparent viscosity on the velocity field and drag is discussed and detailed solutions for different non-Newtonian viscosities are obtained by integral momentum methods. The problem of drawing a cylinder through a non-Newtonian fluid is also discussed.     

Evaluating curriculum fit with class ability.

To evaluate curriculum fit with class ability, the magnitude of individual differences in size and number of instructional subunits read were examined, as well as number of repetitions (days) of a unit required to achieve a criterion level of performance. Two groups of 5th graders—a high IQ group (40 Ss) and an average IQ group (28 Ss)—read units of social science material from textbooks used in their own schools and in the other group's school. Empirical ratios (for the time to achieve criterion level and for the number of subunits to criterion level) of 3:1 and 5:1 were obtained for the average IQ group and the high IQ group, respectively, on their own curricula. The time to criterion and the number of subunits mastered in 8 days were correlated with IQ and reading achievement for both groups. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Degradation of ammonium carbonate based uranium leach solutions by sulphide minerals and possible methods of control

One problem in the use of ammonium carbonate solutions in conventional metallurgy is reagent loss following the oxidation of sulphide minerals in the ore. This problem could be of importance in solution mining. Degradation of a stock feed solution of 1 g/l (NH₄)₂CO₃ and H₂O₂ as an oxidant by a variety of sulphide minerals was studied. The minerals including pyrite, sphalerite, chalcopyrite and bornite were each loaded into a column of sand and the degradation was studied by analysing the effluent obtained when a leach solution was allowed to percolate through the column. Pyrite was the only mineral studied that showed degradation of carbonate above 10%. This however, was reduced c considerably by treatment with lead nitrate or sodium silicate. The indications are that losses in the order of 0.1 gram (NH₄)₂CO₃ per gram of pyrite might be expected in solution mining.     

Specific heat of halocarbon 25-5s grease (polychlorotrifluoroethylene in silica gel) below 4.5K

The specific heat for halocarbon 25-5s grease is reported for the temperature range 1.8 to 4.5 K. The grease is a commercially prepared mixture of polychlorotrifluorethylene in silica gel (PCTFE-SG). It can be used to protect samples which are reactive to the atmosphere. Its suitability for such use when making specific heat measurements was investigated. The specific heat at low temperatures was well described by the expression, C = 0.283 T³ mJ gm^?1 K^?4. It was found to be suitable for samples with relatively large low temperature specific heats.