排序方式: 共有33条查询结果,搜索用时 31 毫秒
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Grossman RB Hattori K Parkin S Patrick BO Varner MA 《Journal of the American Chemical Society》2002,124(46):13686-13687
A cage-shaped N,N'-diacylaminal crystallizes from some aromatic solvents as "supramolecular chair cyclohexanes", squat cylindrical hexamers with approximate D3d symmetry containing two arene molecules, and from other aromatic and nonaromatic solvents as infinite tapes. A homologous diacylaminal crystallizes only as an infinite tape. The hexamers represent the first examples of cyclic hexamers held together by %@mt;sys@%%@bold@%R%@rsf@%%@sx@%2%@be@%2%@sxx@%%@fn;(;vis;full;auto@%8%@fnx;);vis;full@%-type%@mx@% hydrogen bonds in which the hydrogen-bonded atoms are not coplanar. The diacylaminal represents a new supramolecular synthon, one perhaps more suited to the design of three-dimensional architectures. 相似文献
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Liang JF Shapira D Gross CJ Beene JR Bierman JD Galindo-Uribarri A Gomez del Campo J Hausladen PA Larochelle Y Loveland W Mueller PE Peterson D Radford DC Stracener DW Varner RL 《Physical review letters》2003,91(15):152701
Evaporation residue cross sections have been measured with neutron-rich radioactive 132Sn beams on 64Ni in the vicinity of the Coulomb barrier. The average beam intensity was 2 x 10(4) particles per second and the smallest cross section measured was less than 5 mb. Large sub-barrier fusion enhancement was observed. Coupled-channel calculations taking into account inelastic excitation significantly underpredict the measured cross sections below the barrier. The presence of several neutron transfer channels with large positive Q values suggests that multinucleon transfer may play an important role in enhancing the fusion of 132Sn and 64Ni. 相似文献
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Tong GL Varner GS Wang F Wang LS Wang LZ Wang M Wang P Wang PL Wang SM Wang TJ Wang YY Wei CL Wu N Wu YG Xi DM Xia XM Xie PP Xie Y Xie YH Xu GF Xue ST Yan J Yan WG Yang CM Yang CY Yang HX 《Physical review letters》2000,84(4):594-597
Using the upgraded Beijing Spectrometer, we have measured the total cross section for e(+)e(-) annihilation into hadronic final states at center-of-mass energies of 2.6, 3.2, 3.4, 3.55, 4.6, and 5.0 GeV. Values of R, sigma(e(+)e(-)-->hadrons)/sigma(e(+)e(-)-->&mgr;(+)&mgr;(-)), are determined. 相似文献
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Kohley Z Liang JF Shapira D Varner RL Gross CJ Allmond JM Caraley AL Coello EA Favela F Lagergren K Mueller PE 《Physical review letters》2011,107(20):202701
The fusion excitation functions for radioactive (132)Sn + (58)Ni and stable (130)Te + (58,64)Ni were measured at energies near the Coulomb barrier. The coupling of transfer channels in heavy-ion fusion was examined through a comparison of Sn + Ni and Te + Ni systems, which have large variations in the number of positive Q-value nucleon transfer channels. In contrast with previous experimental comparisons, where increased sub-barrier fusion cross sections were observed in systems with positive Q-value neutron transfer channels, the reduced excitation functions were equivalent for the different Sn + Ni and Te + Ni systems. The present results suggest a dramatically different influence of positive Q-value transfer channels on the fusion process for the Sn + Ni and Te + Ni systems. 相似文献
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R. P. Schmitt T. Botting G. G. Chubarian K. L. Wolf B. J. Hurst H. Jabs M. Hamelin A. Bacak Yu. Ts. Oganessian M. G. Itkis E. M. Kozulin N. A. Kondratiev V. S. Salamatin I. V. Pokrovsky F. Hanappe E. de Goès Brennand A. Huck L. Stuttgé E. Liatard J. Beene R. Varner M. Halbert N. Gan 《Physics of Atomic Nuclei》2003,66(6):1163-1167
The time scales for nuclear fission have been explored using both pre-and postfission neutrons and GDR gamma rays. Four systems were investigated: 133-MeV 16O + 176Yb and 208Pb and 104-MeV 4He + 188Os and 209Bi. Fission fragments were measured in coincidence with PPACs. The neutrons were detected using eight detectors from the DEMON array, while gamma rays were measured using the US BaF2 array. The pre-and postfission gamma rays were determined using moving source fits parallel and perpendicular to the fission fragment emission directions. The time scales for fission for the neutrons were determined using the neutron clock technique. The gamma-ray data were fitted using a statistical model calculation based on the code CASCADE. The results of the fits from both data types were used to extract nuclear friction coefficients, γ, and fission time scales. The γ values ranged from 7 to 20, while the fission times were (31–105)×10?21 s. 相似文献
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MO Xiao-Hu E.V.Abakumova M.N.Achasov V.E.Blinov CHU Yuan-Ping DONG Hai-Yi FU Cheng-Dong F.A.Harris V.V.Kaminskiy A.A.Krasnov LI Xiao-Nan LIU Qian N.Yu.Muchnoi I.B.Nikolaev E.E.Pyata QU Hua-Min QIN Qing A.G.Shamov SHEN Cheng-Ping G.S.Varner WANG Yi-Fang XU Jin-Qiang ZHANG Jian-Yong ZHANG Qing-Jiang ZHANG Yin-Hong ZHANG Tian-Bao V.N.Zhilich ZHAO Zhuo A.A.Zhukov 《中国物理C(英文版)》2010,34(6)
The beam energy measurement system at BEPCII is composed of there parts: laser source and optics system,laser-electron interaction system and High Purity Germanium(HPGe)detector system.The special components and construction of each part are introduced,especially about radiation background mea-surement in the storage ring,which is of great importance for the safe commissioning of HPGe detector. 相似文献
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J.P. Seitz B.B. Back M.P. Carpenter I. Diszegi K. Eisenman P. Heckman D.J. Hofman M.P. Kelly T.L. Khoo S. Mitsuoka V. Nanal T. Pennington R.H. Siemssen M. Thoennessen R.L. Varner 《Nuclear Physics A》2005,750(2-4):245-255
The giant dipole resonance built on excited states was observed in very fissile nuclei in coincidence with evaporation residues. The reaction 48Ca + 176Yb populated evaporation residues of mass A=213–220 with a cross section of 200 μb at 259 MeV. The extracted giant dipole resonance parameters are in agreement with theoretical predictions for this mass region. 相似文献
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The structure of 81Kr has been investigated via the 80Kr(d?, p)81Kr reaction using an 11.0 MeV vector-polarized deuteron beam. Differential cross sections σ and vector analyzing powers Ay have been measured from 20° to 90° for 17 excited states below 3.0 MeV excitation energy. Comparisons of these distributions to DWBA calculations and empirical shapes were made to extract spectroscopic factors and values of spin and parity for these states. The significance of these measurements to the design of a bromine solar neutrino detector is discussed. 相似文献
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M. B. Chadwick M. Hussein E. Ramakrishnan T. Baumann A. Azhari R. A. Kryger R. Pfaff M. Thoennessen S. Yokoyama J. R. Beene M. L. Halbert P. E. Mueller D. W. Stracener R. L. Varner G. van Buren R. J. Charity P-F. Hua D. G. Sarantites L. G. Sobotka 《Acta Physica Hungarica A》1995,2(3-4):347-353
New experimental data has been obtained for the208Pb(α, α′) reaction induced by 160 MeV alpha particles, for inelastic scattering to forward angles. We use these data to investigate the applicability of the multistep scattering theory of Feshbach, Kerman, and Koonin for describing this reaction. The mechanism we study, following the work of Gadioli et al. [1], is of the incident alpha particle remaining intact throughout the scattering process, exciting nucleon particle-hole pairs through multistep process. We conclude that this mechanism, combined with compound nucleus decay at low emission energies, can account for much of the observed data. However, there are indications that other processes also contribute at energies above the compound nucleus emission regime, and we outline future theoretical analyses that are needed. 相似文献