The piscine bioconcentration characteristics of cyclic and linear oligomeric permethylsiloxanes

Using a conventional "resaturation" method whereby aquarium water was continuously passed through a column containing sand or fine glass beads coated with cyclic and linear permethylsiloxanes, their uptake levels by rainbow trout and fathead minnows have been compared. Because of the uncertainty associated with defining the actual aqueous concentrations of such poorly soluble substances, this study was focused on defining the "attainable uptake" levels from saturated solutions rather than precise definition of actual bioconcentration factor values. Although cyclic Me2SiO-oligomers accumulated to a greater extent in fish than did comparable linear oligomers, uptake decreased sharply with increasing molecular weight. Thus, in the cyclic series (Dx), order of magnitude decreases were observed for each incremental molecular weight increase; i.e., for the compounds D4, D5, and D6 uptake levels of approximately 200, 20 and 2 ppm, respectively, were observed. Uptake of D8 was below our detection limit of 300 ppb. In the linear series, uptake of the tetramer MD2M was an order of magnitude less than observed for D4 and little or no uptake (i.e., less than 0.5 ppm) was observed for MD3M, MD4M and MD7M. The branched oligomer M3T exhibited levels comparable to its unbranched isomer MD2M, while M4Q was more comparable to the D6 uptake of 1-2 ppm. Very similar uptake levels of D5 resulted with and without a surfactant, even though the surfactant afforded a 20-fold increase in the D5 content of the water. This suggests that bio-availability is defined by the amount present in true solution as individual molecules and is not affected by the presence of aggregates or micelles. The highly inverse relationship observed in this study between uptake and molecular weight is strongly supportive of earlier estimates of a limiting molecular weight of about 600. These findings also strongly contradict a recent Japanese study, which concluded that bioconcentration not only occurred but actually increased with molecular weight in a series of commercial polydimethylsiloxane fluids. Also contrary to a recently published inference of biotransformation in fish, no evidence for such phenomena was observed in this study.     

Quantitative real-time imaging of myocardium based on ultrasonic integrated backscatter

The integrated backscatter calculation over the full, two-dimensional echocardiographic sector is implemented to produce images from closed-chest dogs. This new real-time integrated backscatter measurement system allows a continuous determination of integrated backscatter from all myocardial regions in the ultrasonic view. By replacing the conventional video processor in a commercial two-dimensional echocardiographic imager with this new real-time backscatter measurement system, it is possible to produce real-time two-dimensional images based on integrated backscatter.     

Measurements and analysis of transmitted spectra from LOTUS fission-suppressed hybrid blanket driven by D-T neutrons

The neutron spectra transmitted across a fission-suppressed hybrid blanket and its components, driven by a low intensity 14 MeV Haefely neutron generator, were measured with a 2×2 NE213 detector at LOTUS facility. These experiments have been analyzed with 2D and 3D codes DOT3.5 and MCNP, respectively. The spectral integrals between 15 to 1 MeV show good agreement among the 2D, the 3D, and the NE213 for 15 cm lead, 18 cm beryllium, and 25 cm graphite slabs. However, there are large discrepancies for 6.2 cm stainless steel and 15 cm lithium carbonate slabs. The assemblies involving two or more of these slabs reflect these tendencies. We observe also considerable disagreement over pointwise spectra for a number of assemblies.Work done while on visiting assignment to Institut de Génie Atomique, E.P.F.L.     

Distribution of the number of jobs in a GI/GI/1/∞ queue with a constant flow time constraint

We derive the Laplace transform of the joint distribution density of the number of jobs and of the vector of their flow time in a GI/GI/1/ queue with a constant constraint on job flow time.Translated from Kibernetika, No. 1, pp. 78–81, January–February, 1889.