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The theory of electron cooling of ions and positrons is reviewed. Formulas describing the retarding force of ions in an electron beam with an 'oblate' velocity distribution, which is typical for electron cooling, are considered for arbitrary intensities of a magnetic field. Considered for positrons are the cases of intermediate and strong magnetic fields, which are of the greatest practical interest. The friction force and the components of the positron velocity diffusion tensor are calculated. Also discussed is the relaxation of positrons in their electron cooling in positron storage rings and their transition to the stationary distribution. The stationary velocity distribution function for positrons is shown to practically coincide in this case with that for electrons. The feasibility of lowering the transverse electron temperature is analyzed, which is required for decreasing the positron spread in momentum.

Background and Purpose:Inline ultrasound monitoring requires good image quality for accurate stone localization, as well as low shockwave shadowing and a robust transducer. In general, conventional transducers designed for another purpose, such as abdominal scanning, are employed. The distance between the transducer and the SWL focus can be varied by a mechanical drive. The drawback is reduced fragmentation at short distances and poor imaging at long distances. This paper introduces a new approach using a specially designed transducer without a mechanical drive.Materials and Methods: A transducer prototype with optimized beam focusing (B-K Medical, Herlev, Denmark) was integrated into a modified Compact Delta II therapy head (Dornier MedTech, Wessling, Germany). Image quality was tested at two clinical sites, where 40 kidney and 14 ureteral stones were treated. The shockwave was characterized by model stone tests and fiberoptic hydrophone measurements.Results: Both kidney and ureteral stone treatments could be monitored reliably. Despite the long distance to the SWL focus, the transducer could be operated with relatively high frequencies (3.5–6 MHz), so that high image resolution was obtained. Model stone tests yielded the same fragmentation as the standard Compact Delta II without a transducer.Conclusions:This study shows that the concept of an integrated transducer distant from the shockwave focus is feasible. Transducer elevation, which is accompanied by shockwave shadowing and early transducer failure, is avoided by employing a dedicated transducer design.

A series of nonlinear optical (NLO) polyimides were prepared by grafting 4−16 wt % zwitterionic pyridinium tricyanoquinonedimethane chromophore with a large negative hyperpolarizability (β0 = −590 × 10^-30 esu) onto the host polyimides through an ester bond formation. To enhance the temporal stability of the poled NLO polymers, a new thermally reactive group, i.e., 5-aminobenzocylcobutenone, was introduced into the NLO polymer systems to effect the cross-linking during the thermal poling process. The resulting NLO polyimides showed good solubility in polar aprotic solvents such as N,N-dimethylformamide and could form uniform films by casting or spin coating without any noticeable chromophore aggregation or phase separation as examined under an optical microscope. These NLO polyimides had glass transition temperatures in the range of 170−213 °C and were thermally stable up to 270 °C. The electrical resistivity of NLO polyimides was found to be on the order of 10¹⁵ Ω·cm at 80 °C and dependent on the applied voltages. As the temperature increased, the resistivity dropped monotonically to 2.4 × 10¹¹ Ω·cm at 200 °C. With a 10 wt % chromophore loading (or a number density of 15 × 10¹⁹ cm^-3) in the polymer, the electrooptic (EO) coefficient (r33 at 1550 nm) reached 45 pm/V. No substantial decrease in EO coefficients was observed after the test cell was kept in the dark at 85 °C under nitrogen after 1200 h nor when the test cell was irradiated with 1550 nm light (50 μW/~4 mm²) for 10 h at ambient temperature in air.

The use of coated 1 mm glass beads is shown to be promising for recycle gas chromatography. In the case of an SE-30 column, the glass beads generate plates faster than porous packings as fine as 48/60 mesh. Although packings coated with SE-30 produce nearly 400,000 plates, they are unable to fractionate a mixture of benzene and perdeuterobenzene. However, a much less efficient squalane column successfully fractionates that mixture after approximately 60,000 plates, confirming earlier work in which squalane was used. Coated beads appear to be especially useful when large numbers of plates are required and milligram amounts of product are needed.