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991.
O'Connell R Den Hartog DJ Forest CB Anderson JK Biewer TM Chapman BE Craig D Fiksel G Prager SC Sarff JS Terry SD Harvey RW 《Physical review letters》2003,91(4):045002
Confinement of runaway electrons has been observed for the first time in a reversed field pinch during improved-confinement plasmas in the Madison Symmetric Torus. Energy-resolved hard-x-ray flux measurements have been used to determine the velocity dependence of the electron diffusion coefficient, utilizing computational solutions of the Fokker-Planck transport equation. With improved-confinement, the fast electron diffusivity drops by 2 orders of magnitude and is independent of velocity. This suggests a change in the transport mechanism away from stochastic magnetic field diffusion. 相似文献
992.
We present a new method for laser direct writing in self-assembled hydrogel microparticle colloidal crystals via photothermal excitation of co-assembled colloidal Au particles. Close-packed colloidal crystals are assembled from approximately 224 nm diameter, thermoresponsive, poly-N-isopropylacrylamide hydrogel microparticles (microgels); these crystals display sharp Bragg diffraction peaks in the mid-visible region of the spectrum due to the periodic dielectric function of the assembly. Raising the temperature of the crystal above the characteristic volume phase transition temperature of the microgel particles results in a reversible melting of the crystalline material due to the particle-based deswelling event. This transition can be used either to anneal defects from the crystalline material or to controllably and reversibly convert the assembly from the colored, crystalline state to a nondiffracting glassy material. Crystal-to-glass transitions are similarly accomplished via photothermal excitation when 16 nm diameter colloidal Au particles are co-assembled with the responsive microgels. Excitation of the colloidal Au plasmon absorption with a frequency doubled Nd:YAG laser (lambda = 532 nm) results in optically directed conversion of either glasses to crystals or crystals to glasses, depending on the initial state of the assembly and the illumination time. These results represent a fundamentally new method for the patterning of self-assembled photonic materials. 相似文献
993.
Anderson S Frolov VV Kubota Y Lee SJ Mahapatra R O'Neill JJ Poling R Riehle T Smith A Stepaniak CJ Urheim J Ahmed S Alam MS Athar SB Jian L Ling L Saleem M Timm S Wappler F Anastassov A Duboscq JE Eckhart E Gan KK Gwon C Hart T Honscheid K Hufnagel D Kagan H Kass R Pedlar TK Schwarthoff H Thayer JB von Toerne E Zoeller MM Richichi SJ Severini H Skubic P Undrus A Chen S Fast J Hinson JW Lee J Miller DH Shibata EI Shipsey IP Pavlunin V Cronin-Hennessy D Lyon AL Thorndike EH Jessop CP Marsiske H 《Physical review letters》2001,86(13):2732-2736
We report the first observation of exclusive decays of the type B-->D(*)N_NX, where N is a nucleon. Using a sample of 9.7x10(6)B_B pairs collected with the CLEO detector operating at the Cornell Electron Storage Ring, we measure the branching fractions B(B0-->D(*-)p_p pi(+)) = (6.5(+1.3)(-1.2)+/-1.0)x10(-4) and B(B0-->D(*-)p_n) = (14.5(+3.4)(-3.0)+/-2.7)x10(-4). Antineutrons are identified by their annihilation in the CsI electromagnetic calorimeter. 相似文献
994.
995.
996.
W. S. Lyon 《Journal of Radioanalytical and Nuclear Chemistry》1996,213(5):311-316
997.
998.
W. S. Lyon 《Journal of Radioanalytical and Nuclear Chemistry》1987,119(6):419-423
999.
1000.
Edwin M. Kaiser William R. Thomas Terry E. Synos James R. McClure Tarek S. Mansour Joseph R. Garlich James E. Chastain 《Journal of organometallic chemistry》1981,213(2):405-417
Metalation of 2,4-dimethylpyridine and -quinolines by strong basic reagents in ethyl ether in the absence of HMPA affords 2-lithiomethyl derivatives regardless of the reaction length. The use of THF in such metalations promotes the formation of the 2-lithiomethyl reagents which isomerize to the more thermodynamically stable 4-lithiomethyl derivatives after relatively long reaction periods or in the presence of amines or an excess of the parent heterocycle. The latter derivatives appear to be formed directly from the heterocycles in ammonia or in the presence of HMPA. The results are discussed in terms of “coordination-only” versus “acid-base” limiting mechanisms for metalations as a function of ion pairing. NMR spectra for certain of the carbanions in ethyl ether and THF are described which support the above concepts. Related metalations of 2,4-dimethylquinoline-N-oxide give only the 2-lithiomethyl derivative. Similar reactions of 7-hydroxy-2,4-dimethyl-1,8-naphthyridine lead in synthetically useful yields to derivatization of the 2- and 4-methyl groups via dianions by using n-butyllithium in ethyl ether and sodium amide in liquid ammonia, respectively, followed by the addition of appropriate electrophiles. 相似文献