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Cryogenic microwave oscillators offer the highest short term stability of any frequency sources.

The gas bubbles in liquid are the strong scatters of the sound propagation in such liquid. A liquid containing microbubbles is used as an effective ultrasound contrast agent in medical diagnosis to improve the contrast of the ultrasonic image. However, the existence of bubbles in liquid may enhance its nonlinearity parameter. In our previous paper, the preliminary results of some ultrasound contrast agents were reported and their large values of the nonlinearity parameter were obtained. This paper is devoted to an experimental demonstration of the influence of microbubbles on the nonlinearity parameter B/A values. These include measuring the dependence of B/A values of Echovist 300 on time. Results show that B/A values decrease with time (from 2678 to 16 over 45 min). B/A values of human blood with a different portion of Echovist were also studied. Larger B/A values are obtained with more Echovist. B/A values of a kind aqua, such as 76% Injectio Meglumini Diatrizoatis Composita (MDC), were studied before and after sonication with different bubble contents. Results indicate that the values of nonlinearity parameter depend on the presence of microbubbles obviously. Some explanation of this effect is discussed. [Work supported by NSF of China.]

On admission to the hospital, a splenectomized man was found to have 85% of his erythrocytes parasitized by Babesia microti. His extensive parasitemia allowed for direct study of the morphology and ultrastructure of this organism as it appears in human infection; the need for animal inoculation and rescue techniques was thus eliminated. Positive characteristics (other than the tetrad form) that are diagnostic for babesiosis were identified. By transmission and scanning electron microscopy, parasite-induced changes in the erythrocyte membrane were observed; these alterations may explain the hemolysis seen in babesiosis. Factors that may have allowed the patient to sustain such high-level parasitemia are considered. The experience with this patient confirms that exchange transfusion is a reliable, rapid method for reduction of the parasite load in serious infection with B microti.

This final report summarizes the research activities under the 'Systematic Study of Light Scattering by Irregularly Shaped Particles.' The beginning one and one-half years were devoted to the analysis of existing experimental data and the related theoretical light-scattering studies, in parallel with the reconstruction, renovation and calibration of the microwave analog scattering facility then relocated from the Albany, N.Y. area. The following one and one-half year period was devoted to actual measurement tasks and analysis of data in our original proposal; e.g., the investigations of scattering by interacting spheres and by particles with rough surfaces. Simultaneous with these measurements a number of 2:1 finite cylinders were also measured on their extinction properties when they were either preferentially or randomly oriented in space.

With the corrections and developments on the theory of light scattering by spheroidal particles, we have computed the scattering parameters of both prolate and oblate spheroids with high aspect ratio 7:1 in dielectric and metallic cases. The theoretical results come out to be satisfactory if compared with our microwave measurements in P-Q plot form.

Microwave analog measurements of θ=0° scattering by particles of various shape and refractive indexes are presented. The scattering targets are non-isotropic spheres, aggregates of 2n (n=1,2,3) identical spheres, and stacked 7-cylinder rough particles. Both the orientation and the physical properties of the target produce signatures in the extinction and polarization curves. Theoretical explanations are presented wherever possible.

Although fish have been used repeatedly in bioassays of toxicity of petroleum oils, little information is available for marine species (Nelson-Smith 1970, 1972). Anderson and colleagues ( 1974) studied the effects of crude and fuel oil on survival of estuarine species. Using a marine catfish readily available, the effects of a fuel oil on survival, feeding behavior and heart rate are examined. The latter has frequently been used as a sensitive test for environmental stress.

Some results of experimental studies on microwave scattering by artificially constructed axially symmetric spheres with anisotropic refractive indices are presented. An approximation using Mie theory for spheres with appropriate orientation dependent indices of refraction is shown to provide a good explanation of the observed dependence of the complex forward-scattering amplitudes on target orientation.

A method for obtaining detailed dependence of extinction cross sections on the orientation of nonspherical particles is described. The results of experimental scattering studies of several different particles are presented.