Scale size of magnetic turbulence in tokamaks probed with 30-MeV electrons

Measurements of synchrotron radiation emitted by 30-MeV runaway electrons in the TEXTOR-94 tokamak show that the runaway population decays after switching on neutral beam injection (NBI). The decay starts only with a significant delay, which decreases with increasing NBI heating power. This delay provides direct evidence of the energy dependence of runaway confinement, which is expected if magnetic modes govern the loss of runaways. Application of the theory by Mynick and Strachan [Phys. Fluids 24, 695 (1981)] yields estimates for the "mode width" (delta) of magnetic perturbations: delta<0.5 cm in Ohmic discharges, increasing to delta = 4.4 cm for 0. 6 MW NBI.     

Mechanistic Studies on the SCS‐Pincer Palladium(II)‐Catalyzed Tandem Stannylation/Electrophilic Allylic Substitution of Allyl Chlorides with Hexamethylditin and Benzaldehydes

This paper describes a mechanistic study of the SCS‐pincer Pd^II‐catalyzed auto‐tandem reaction consisting of the stannylation of cinnamyl chloride with hexamethylditin, followed by an electrophilic allylic substitution of the primary tandem‐reaction product with 4‐nitrobenzaldehyde to yield homoallylic alcohols as the secondary tandem products. As it turned out, the anticipated stannylation product, cinnamyl trimethylstannane, is not a substrate for the second part of the tandem reaction. These studies have provided insight in the catalytic behavior of SCS‐pincer Pd^II complexes in the auto‐tandem reaction and on the formation and possible involvement of Pd⁰ species during prolonged reaction times. This has led to optimized reaction conditions in which the overall tandem reaction proceeds through SCS‐pincer Pd^II‐mediated catalysis, that is, true auto‐tandem catalysis. Accordingly, this study has provided the appropriate reaction conditions that allow the pincer catalysts to be recycled and reused.     

Rapid catalytic oxidation of CO to CO(2) - On the development of a new approach to on-line oxygen isotope analysis of organic matter

A new approach to on-line oxygen isotope analysis has been developed which utilises existing elemental analyser and mass spectrometry technology to produce a sample of carbon dioxide gas for oxygen isotople analysis. The method relies on on-line high temperature pyrolysis of the sample over a carbon source followed by a rapid, non-contributive partial catalytic oxidation over nickel powder at between 550 and 600 degrees C. Initial results demonstrate both good precision (better than 0.2 per thousand) and accuracy for both cellulose and silver nitrate samples. Copyright 1999 John Wiley & Sons, Ltd.     

Editorial for Focus Issue on Enabling Science and Technology for High-Speed Optical Communications

<正>Fiber optics underpins the communications infrastructure for the information society today. Cables consisting of hair-like fibers speed data around the globe in the form of rapid pulses of light. Modern telecom     

Nonlinear polarization effects and mitigation in polarization-division-multiplexed coherent transmission systems

Using numerical simulations, the nonlinear transmission performance of polarization-division-multiplexed quadrature-phase-shift-keying （PDM-QPSK） coherent systems is studied. It is found that inter-channel cross-polarization modulation （XPolM） induced nonlinear polarization scattering can significantly degrade the transmission performance of PDM-QPSK coherent systems and change the perspective of dispersion management in optical coherent transmission systems. Some techniques to mitigate nonlinear polarization scattering in dispersion-managed PDM coherent transmission systems are discussed, including the use of time-interleaved return-to-zero （RZ） PDM formats, the use of periodic-group-delay PGD dispersion compensators, and the judicious addition of some polarization-mode-dispersion （PMD） in the transmission link. It is shown that if nonlinear polarization scattering can be well mitigated, a polarization multiplexed optical coherent transmission system with dispersion management could perform better than that without it.     

Heat convection and transport barriers in low-magnetic-shear rijnhuizen tokamak project plasmas

Layers of reduced electron heat transport ("transport barriers") have been observed in the Rijnhuizen Tokamak Project when the plasma is dominantly heated by electron cyclotron heating (ECH). Experiments into the properties of the transport barriers are reported. Modulation of the ECH power was used to probe electron heat transport in the barriers by means of propagating electron temperature perturbations. The observed propagation shows that transport inside the barriers is dominated by heat convection. This convection is inward, i.e., up the temperature gradient.