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排序方式: 共有118条查询结果,搜索用时 15 毫秒
61.
J. Dyck S. Zavorine A. Capretta J. Britten 《Journal of organometallic chemistry》2005,690(10):2548-2552
High chemical yields and high levels of stereochemical inversion are demonstrated in the phosphorane-mediated esterification reaction of chiral alcohols with non-hindered carboxylic acids through the incorporation of sterically non-hindered alkyl groups of phosphorus. 相似文献
62.
63.
It is known that every torsion free C n -module of finite degree is completely reducible. In this article, we provide a formula for the decomposition of the tensor product of a simple torsion free C n -module of finite degree with a simple finite dimensional C n -module. As a byproduct we obtain a recursion formula for the decomposition of the tensor product of any two simple finite dimensional C n -modules. 相似文献
64.
Rushford MC Molander WA Nissen JD Jovanovic I Britten JA Barty CP 《Optics letters》2006,31(2):155-157
Future energy scaling of high-energy chirped-pulse amplification systems will benefit from the capability to coherently tile diffraction gratings into larger apertures. Design and operation of a novel, accurate alignment diagnostic for coherently tiled diffraction gratings is required for successful implementation of this technique. An invariant diffraction direction and phase for special moves of a diffraction grating is discussed, allowing simplification in the design of the coherently tiled grating diagnostic. An analytical proof of the existence of a unique diffraction grating eigenvector for translational and rotational motion that conserves the diffraction direction and diffracted wave phase is presented. 相似文献
65.
Rushford MC Britten JA Barty CP Jitsuno T Kondo K Miyanaga N Tanaka KA Kodama R Xu G 《Optics letters》2008,33(16):1902-1904
We introduce a four-pass laser pulse compressor design based on two grating apertures with two gratings per aperture that is tolerant to some alignment errors and, importantly, to grating-to-grating period variations. Each half-beam samples each grating in a diamond-shaped compressor that is symmetric about a central bisecting plane. For any given grating, the two half-beams impinge on opposite sides of its surface normal. It is shown that the two split beams have no pointing difference from paired gratings with different periods. Furthermore, no phase shift between half-beams is incurred as long as the planes containing a grating line and the surface normal for each grating of the pair are parallel. For grating pairs satisfying this condition, gratings surfaces need not be on the same plane, as changes in the gap between the two can compensate to bring the beams back in phase. 相似文献
66.
The attempted Diels-Alder reaction between 9-phenylethynylfluorene and tetracyclone yields instead three products resulting from the dimerization of the isomeric allene. The major product is 8,16-diphenyl-diindeno[1,2,3-de:1',2',3'-mn]naphthacene, in which each terminal ring is derived from a fluorenyl unit; aerial oxidation then yields a peroxide. A dihydronaphthacene bearing fluorenyl moieties spiro-bonded at the C(5) and C(11) positions was also identified. The structures of the naphthacenes were elucidated by X-ray crystallography, and a mechanistic rationale is offered. [reaction: see text] 相似文献
67.
Petawatt laser pulses 总被引:17,自引:0,他引:17
Perry MD Pennington D Stuart BC Tietbohl G Britten JA Brown C Herman S Golick B Kartz M Miller J Powell HT Vergino M Yanovsky V 《Optics letters》1999,24(3):160-162
We have developed a hybrid Ti:sapphire-Nd:glass laser system that produces more than 1500 TW (1.5 PW) of peak power. The system produces 660 J of power in a compressed 440+/-20 fs pulse by use of 94-cm master diffraction gratings. Focusing to an irradiance of >7x10(20) W/cm (2) is achieved by use of a Cassegrainian focusing system employing a plasma mirror. 相似文献
68.
Toyoda H Trischuk W de Troconiz JF Truitt S Tseng J Turini N Ukegawa F Valls J Vejcik S Velev G Vidal R Vilar R Vologouev I Vucinic D Wagner RG Wagner RL Wahl J Wallace NB Walsh AM Wang C Wang CH Wang MJ Watanabe T Waters D Watts T Webb R 《Physical review letters》2000,84(10):2094-2099
We have reconstructed the radiative decays chi(b)(1P)-->Upsilon(1S)gamma and chi(b)(2P)-->Upsilon(1S)gamma in p&pmacr; collisions at sqrt[s] = 1.8 TeV, and measured the fraction of Upsilon(1S) mesons that originate from these decays. For Upsilon(1S) mesons with p(Upsilon)(T)>8.0 GeV/c, the fractions that come from chi(b)(1P) and chi(b)(2P) decays are [27.1+/-6.9(stat)+/-4. 4(syst)]% and [10.5+/-4.4(stat)+/-1.4(syst)]%, respectively. We have derived the fraction of directly produced Upsilon(1S) mesons to be [50.9+/-8.2(stat)+/-9.0(syst)]%. 相似文献
69.
Poolman HR Boersma DJ Harvey M Higinbotham DW Passchier I Six E Alarcon R van Amersfoort PW Bauer TS Boer Rookhuizen H van Den Brand JF van Buuren LD Bulten HJ Ent R Ferro-Luzzi M Geurts DG Heimberg P de Jager CW Klimin P Koop I Kroes F van Der Laan J Luijckx G Lysenko A Militsyn B Nesterenko I 《Physical review letters》2000,84(17):3855-3858
We report on first measurements with polarized electrons stored in a medium-energy ring and with a polarized internal target. Polarized electrons were injected at 442 MeV (653 MeV), and a partial (full) Siberian snake was employed to preserve the polarization. Longitudinal polarization at the interaction point and polarization lifetime of the stored electrons were determined with laser backscattering. Spin observables were measured for electrodisintegration of polarized 3He, with simultaneous detection of scattered electrons, protons, neutrons, deuterons, and 3He nuclei, over a large phase space. 相似文献
70.
Leitch AA Reed RW Robertson CM Britten JF Yu X Secco RA Oakley RT 《Journal of the American Chemical Society》2007,129(25):7903-7914
A general synthetic route to the resonance-stabilized pyrazine-bridged bisdithiazolyl framework, involving the reductive deprotection of 2,6-diaminopyrazine-bisthiocyanate and cyclization with thionyl chloride, has been developed. An N-methyl bisdithiazolyl radical, 4-methyl-4H-bis[1,2,3]dithiazolo[4,5-b:5',4'-e]pyrazin-3-yl, has been prepared and characterized in solution by electron paramagnetic resonance spectroscopy and cyclic voltammetry. Its crystal structure has been determined at several temperatures. At 295 K, the structure belongs to the space group Cmca and consists of evenly spaced radicals pi-stacked in an alternating ABABAB fashion along the x-direction. At 123 K, the space group symmetry is lowered by loss of C-centering to Pccn, so that the radicals are no longer evenly spaced along the pi-stack. At 88 K, a further lowering of space group symmetry to P21/c is observed. Extended Hückel Theory band structure calculations indicate a progressive opening of a band gap at the Fermi level in the low-temperature structures. Magnetic susceptibility measurements over the range 4-300 K reveal essentially diamagnetic behavior below 120 K. Variable-temperature single-crystal conductivity (sigma) measurements indicate that the conductivity is activated, even at room temperature, with a room-temperature value sigma RT=0.001 S cm-1 and a thermal activation energy Eact=0.19 eV. Under an applied pressure of 5 GPa, sigma RT is increased by 3 orders of magnitude, but the conductivity remains activated, with Eact being lowered to 0.11 eV at 5.5 GPa. 相似文献