排序方式: 共有176条查询结果,搜索用时 250 毫秒
101.
Aubert B Barate R Boutigny D Couderc F Gaillard JM Hicheur A Karyotakis Y Lees JP Tisserand V Zghiche A Palano A Pompili A Chen JC Qi ND Rong G Wang P Zhu YS Eigen G Ofte I Stugu B Abrams GS Borgland AW Breon AB Brown DN Button-Shafer J Cahn RN Charles E Day CT Gill MS Gritsan AV Groysman Y Jacobsen RG Kadel RW Kadyk J Kerth LT Kolomensky YG Kukartsev G Lynch G Mir LM Oddone PJ Orimoto TJ Pripstein M Roe NA Ronan MT Shelkov VG Wenzel WA Barrett M Ford KE Harrison TJ Hart AJ Hawkes CM Morgan SE 《Physical review letters》2005,94(1):011801
A search for the decays B-->rho(770)gamma and B0-->omega(782)gamma is performed on a sample of 211 x 10(6) Upsilon(4S)-->BB events collected by the BABAR detector at the SLAC PEP-II asymmetric-energy e(+)e(-) storage ring. No evidence for the decays is seen. We set the following limits on the individual branching fractions: B(B+-->rho(+)gamma)<1.8 x 10(-6), B(B0-->rho(0)gamma)<0.4 x 10(-6), and B(B0-->omegagamma)<1.0 x 10(-6) at the 90% confidence level. We use the quark model to limit the combined branching fraction B [B-->(rho/omega)gamma]<1.2 x 10(-6), from which we determine a constraint on the ratio of Cabibbo-Kobayashi-Maskawa matrix elements |V(td)|/|V(ts)|. 相似文献
102.
Yuuichi Orimoto Satoru Shirane Yuriko Aoki 《Journal of computational chemistry》2019,40(30):2622-2635
The mechanism of isotactic polypropylene (iPP) polymerization with an (R,R)-ansa-zirconocene/borate catalyst system was analyzed using quantum chemistry (QC) calculations by focusing on the extent of structural change during monomer insertion. The activation energy for migratory insertion, Ea, was compared for four possible reaction paths with regard to monomer coordination, that is, 1,2-re, 1,2-si, 2,1-si, and 2,1-re, until the seventh monomer insertion step, explicitly including a borate anion cocatalyst. This indicated that the 1,2-re path was most favorable, except for the first step, which favored 1,2-si. As far as the first step, the product of 1,2-si is a conformational isomer to that of the 1,2-re path, and the exceptional favorability of 1,2-si does not affect the isoselectivity. These results support previous studies, except that our results address the unexplored seventh insertion step with a borate anion cocatalyst by QC calculations. The isoselectivity correlated with the extent of structural change in the whole system during the reaction. It was proved from our detail analysis that the advantage of 1,2-re with a small Ea is attributed to its smaller structural changes due to low steric repulsion in the system compared with other paths. Conversely, larger repulsion in the systems involved in other paths results in larger structural changes to minimize the structural strain. However, the relaxation appears insufficient due to structural restriction of the enforced four-membered ring transition state structure. A borate anion cocatalyst broke the C2 symmetry of the electronic structures of zirconocene, resulting in an odd–even Ea frequency for the monomer insertion. Molecular orbital analysis demonstrated that the d–π orbital overlaps can explain the approach direction of the olefin coordination and the bent structure of zirconocene, providing a different viewpoint from previous studies. The potential for catalyst control was discussed based on our results. © 2019 Wiley Periodicals, Inc. 相似文献
103.
The traditional standard stochastic system models, such as the autoregressive (AR), moving average (MA) and autoregressive moving average (ARMA) models, usually assume the Gaussian property for the fluctuation distribution, and the well-known least squares method is applied on the basis of only the linear correlation data. In the actual sound environment system, the stochastic process exhibits various non-Gaussian distributions, and there exist potentially various nonlinear correlations in addition to the linear correlation between input and output time series. Consequently, the system input and output relationship in the actual phenomenon cannot be represented by a simple model. In this study, a prediction method of output response probability for sound environment systems is derived by introducing a correction method based on the stochastic regression and fuzzy inference for simplified standard system models. The proposed method is applied to the actual data in a sound environment system, and the practical usefulness is verified. 相似文献
104.
Yuuichi Orimoto Feng Long Gu Jacek Korchowiec Akira Imamura Yuriko Aoki 《Theoretical chemistry accounts》2010,125(3-6):493-501
The elongation method has been applied to elucidate the spin-dependent behavior of the pyrrole-based spin-polarized molecular wire containing 1-pyrrolylphenyl nitronyl nitroxide with oligothiophene units under the influence of an applied electric field. It was found that the donor pyrrole ring causes the delocalization of electrons over the molecular wire regardless of the spin-orientation. In addition, nitronyl nitroxide as a radical unit shows two important features. First, it changes the spin-distribution of the delocalized electrons from same ratio of α- and β-spins to dominant β-spin. Second, it shifts the distribution of electrons in the same direction as that of the applied electric field. 相似文献
105.
106.
We approached the solvatochromic transition observed in polysilane derivatives (poly[bis(4‐propoxybutyl)silylene] (PPBS)) from the standpoint of various quantum chemical treatments. It was found from conventional geometry optimizations at the levels of semiempirical and ab initio molecular orbital methods that a protonation to polysilane oligomers with side chain R = ? OCH3 results in the conformational change of Si‐backbone to a trans‐zigzag structure. Using the Elongation method, which was developed for efficient calculations of huge systems, it was demonstrated that a protonation could change the conformation of Si‐backbone to a trans‐zigzag structure over 10–14 Si atoms. In addition, ab initio calculations showed that the positive charge of a proton can delocalize into the Si‐backbone through a long side chain in PPBS. Positively charged polysilane oligomers provide a rotational barrier that prefers a trans‐zigzag structure, whereas neutral oligomers have a barrier that results to a random structure. This unique behavior of the charged polysilane oligomers should not be disregarded in understanding the mechanism of the solvatochromic transition in PPBS. In ab initio configuration interaction/Mφller‐Plesset through‐space/bond interaction analysis, it was found that such a unique behavior of the rotational barrier in polysilane oligomers could be explained by the effect of orbital delocalization through σ‐conjugation on the Si‐backbone. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 119–133, 2006 相似文献
107.
Aubert B Barate R Bona M Boutigny D Couderc F Karyotakis Y Lees JP Poireau V Tisserand V Zghiche A Grauges E Palano A Pappagallo M Chen JC Qi ND Rong G Wang P Zhu YS Eigen G Ofte I Stugu B Abrams GS Battaglia M Brown DN Button-Shafer J Cahn RN Charles E Day CT Gill MS Groysman Y Jacobsen RG Kadyk JA Kerth LT Kolomensky YG Kukartsev G Lynch G Mir LM Oddone PJ Orimoto TJ Pripstein M Roe NA Ronan MT Wenzel WA Barrett M Ford KE Harrison TJ Hart AJ Hawkes CM Morgan SE Watson AT Goetzen K Held T 《Physical review letters》2006,96(25):251802
We report the results of a search for T, CP, CPT, and violation in B0-B0 mixing using an inclusive dilepton sample collected by the BABAR experiment at the PEP-II factory. Using a sample of 232 x 10(6) BB pairs, we measure the T and CP violation parameter |q/p| - 1 = (-0.8 +/- 2.7(stat) +/- 1.9(syst) x 10(-3), and the CPT and CP parameters Imz = (13.9 +/- 7.3(stat) +/- 3.2(syst)) x 10(-3) and Delta Gamma x Rez = (7.1 +/- 3.9(stat) +/- 2.0(stat)) x 10(-3) ps(-1). The statistical correlation between the measurements of Imz and Delta Gamma x Rez is 76%. 相似文献
108.
Aubert B Barate R Boutigny D Couderc F Karyotakis Y Lees JP Poireau V Tisserand V Zghiche A Grauges E Palano A Pappagallo M Pompili A Chen JC Qi ND Rong G Wang P Zhu YS Eigen G Ofte I Stugu B Abrams GS Battaglia M Breon AB Brown DN Button-Shafer J Cahn RN Charles E Day CT Gill MS Gritsan AV Groysman Y Jacobsen RG Kadel RW Kadyk J Kerth LT Kolomensky YG Kukartsev G Lynch G Mir LM Oddone PJ Orimoto TJ Pripstein M Roe NA Ronan MT Wenzel WA Barrett M Ford KE Harrison TJ Hart AJ Hawkes CM Morgan SE 《Physical review letters》2006,96(5):052002
We study the two-body decays of B+/- mesons to K+/- and a charmonium state X(cc) in a sample of 210.5 fb(-1) of data from the BABAR experiment. We perform measurements of absolute branching fractions beta(B+/- --> K+/-X(cc)) using a missing mass technique, and report several new or improved results. In particular, the upper limit beta(B+/- --> K+/- X(3872)) < 3.2 x 10(-4) at 90% C.L. and the inferred lower limit beta(X(3872)J/psipi+ pi-) > 4.2% will help in understanding the nature of the recently discovered X(3872). 相似文献
109.
Aubert B Bona M Karyotakis Y Lees JP Poireau V Prudent X Tisserand V Zghiche A Garra Tico J Grauges E Lopez L Palano A Pappagallo M Eigen G Stugu B Sun L Abrams GS Battaglia M Brown DN Button-Shafer J Cahn RN Jacobsen RG Kadyk JA Kerth LT Kolomensky YG Kukartsev G Lopes Pegna D Lynch G Orimoto TJ Osipenkov IL Ronan MT Tackmann K Tanabe T Wenzel WA Del Amo Sanchez P Hawkes CM Soni N Watson AT Koch H Schroeder T Walker D Asgeirsson DJ Cuhadar-Donszelmann T Fulsom BG Hearty C Mattison TS 《Physical review letters》2008,100(7):071802
A search for lepton flavor violating decays of a tau to a lighter-mass charged lepton and an omega vector meson is performed using 384.1 fb(-1) of e(+)e(-) annihilation data collected with the BABAR detector at the Stanford Linear Accelerator Center PEP-II storage ring. No signal is found, and the upper limits on the branching ratios are determined to be B(tau(+/-)-->e;{+/-}omega)<1.1 x10 (-7) and B(tau(+/-)-->micro(+/-)omega)<1.0 x 10(-7) at 90% confidence level. 相似文献
110.
Aubert B Bona M Boutigny D Karyotakis Y Lees JP Poireau V Prudent X Tisserand V Zghiche A Garra Tico J Grauges E Lopez L Palano A Pappagallo M Eigen G Stugu B Sun L Abrams GS Battaglia M Brown DN Button-Shafer J Cahn RN Groysman Y Jacobsen RG Kadyk JA Kerth LT Kolomensky YG Kukartsev G Lopes Pegna D Lynch G Mir LM Orimoto TJ Osipenkov IL Ronan MT Tackmann K Tanabe T Wenzel WA Del Amo Sanchez P Hawkes CM Watson AT Koch H Schroeder T Walker D Asgeirsson DJ Cuhadar-Donszelmann T Fulsom BG Hearty C 《Physical review letters》2008,100(5):051803
We present branching fraction measurements of the decays B(+)-->a(1)(+)(1260)K(0) and B(0)-->a(1)(-)(1260)K(+) with a(1)(+/-)(1260)-->pi(-/+)pi(+/-)pi(+/-). The data sample corresponds to 383 x 10(6) BB pairs produced in e(+)e(-) annihilation through the Upsilon(4S) resonance. We measure the products of the branching fractions B(B(+)-->a(1)(+)(1260)K(0)B(a(1)(+)(1260)-->pi(-)pi(+)pi(+))=(17.4+/-2.5+/-2.2) x 10(-6) and B(B(0)-->a(1)(-)(1260)K(+)B(a(1)(-)(1260)-->pi(+)pi(-)pi(-)) = (8.2+/-1.5+/-1.2) x 10(-6). We also measure the charge asymmetries A(ch)(B(+)-->a(1)(+)(1260)K(0) = 0.12+/-0.11+/-0.02 and A(ch)(B(0)-->a(1)(-)(1260)K+) = -0.16+/-0.12+/-0.01. The first uncertainty quoted is statistical and the second is systematic. 相似文献