Medical B-mode scanners operating under conditions typically encountered during clinical work produce ultrasonic wave fields that undergo nonlinear distortion. In general, the resulting harmonic beams are narrower and have lower sidelobe levels than the fundamental beam, making them ideal for imaging purposes. This work demonstrates the feasibility of nonlinear harmonic imaging in medical scanners using a simple broadband imaging arrangement in water. The ultrasonic system comprises a 2.25-MHz circular transducer with a diameter of 38 mm, a membrane hydrophone, also with a diameter of 38 mm, and a polymer lens with a focal length of 262 mm. These components are arranged coaxially giving an imaging geometry similar to that used in many commercial B-scanners, but with a receiver bandwidth sufficient to record the first four harmonics. A series of continuous wave and pulse-echo measurements are performed on a wire phantom to give 1-D transverse pressure profiles and 2-D B-mode images, respectively. The reflected beamwidths wn decrease as wn/W1 = 1/n0.78, where n is the harmonic number, and the reflected sidelobe levels fall off quickly with increasing n. In imaging terms, these effects correspond to a large improvement in lateral resolution and signal-to-clutter ratio for the higher harmonics.

Casein phosphopeptide amorphous calcium phosphate nano-complexes (CPP-ACP) in chewing gum, lozenges and mouthrinses have been shown to re-mineralize enamel subsurface lesions in human in situ experiments. The aim of this double-blind, randomized clinical study was to investigate the capacity of CPP-ACP added to bovine milk to re-mineralize enamel subsurface lesions in situ. Ten subjects drank milk containing either 2.0 or 5.0 g CPP-ACP/l or a control milk whilst wearing removable appliances with enamel slabs containing subsurface demineralized lesions. Each 200 ml milk sample was consumed once a day for each weekday over three consecutive weeks. After each treatment and one weeks rest the subjects crossed over to the other treatments. At the completion of the treatments the enamel slabs were removed and remineralization determined using microradiography and microdensitometry. The results demonstrated that all three milk samples re-mineralized enamel subsurface lesions. However, the milk samples containing CPP-ACP produced significantly greater remineralization than the control milk. The re-mineralizing effect of CPP-ACP in milk was dose-dependent with 2.0 and 5.0 g CPP-ACP/l producing an increase in mineral content of 70 and 148%, respectively, relative to the control milk. The differences in remineralization following exposure to the three milk samples were all statistically significant (P<0.001). In conclusion, this study shows that the addition of 2.0-5.0 g CPP-ACP/l to milk substantially increases its ability to re-mineralize enamel subsurface lesions.

The rate constants at 25°for the gas-phase reactions of hydrogen atoms with benzene and toluene have been determined by the technique of pulsed radiolysis and are, in units of M~x sec-1, 0.37 X 108 and 1.0 X 10s, respectively. The activation energy in the case of benzene is about 3 kcal/mole. In aqueous solution, the corresponding rate constants have been determined to be 1.1 X 109 and 2.6 X 109, respectively. The limits of error on these rate constants are ca. ±20%. The rate constants were measured by following, as a function of time, the formation of the optical absorption due to radicals produced when hydrogen atoms, produced by an electron pulse, react with the aromatic compound.Benzene and toluene yield the cyclohexadienyl radical and the methylcyclohexadienyl radical, respectively, with absorption maxima at 302 and 307 mg, respectively, in the gas phase. The half-widths of the absorption peaks are about 30 mg. In aqueous solution, the absorption maxima are 311, (e311 (5.4 ± 0.5) X 103 M~l cm-1) and 315 mg, respectively, with half-widths similar to those in the gas phase. The combination of two cyclohexadienyl radicals proceeds at least as fast as once every ten collisions in the gas phase at 25°, indicating a "loose" activated complex. In the liquid phase, the combination is diffusion controlled.(1) Based on work performed under the auspices of the U. S. Atomic Energy Commission.

No abstract

The effects of addition of EDTA on the dissociation of caseins and foaming properties of milks (100 g solids/l) reconstituted from skim milk powders given a low-heat (72°C for 30 s) or high-heat (85°C for 30 min) treatment during powder manufacture were determined. The EDTA-induced dissociation of caseins was independent of heat treatment but in high-heat milk was accompanied by release of denatured whey proteins. EDTA changed the proportions of individual caseins in the supernatant. EDTA addition improved both foam overrun and foam stability of low- and high-heat milks. The increase in serum protein on addition of EDTA contributed to the improvement in foaming properties of milks by increasing the availability of the proteins for formation of the air–water interface.