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71.
Fresneda MÁ Alibés R Font J Bayón P Figueredo M 《The Journal of organic chemistry》2012,77(11):5030-5035
The first total synthesis of (+)-gabosine J and that of the epimer at C4 of its enantiomer have been accomplished through an enantioselective approach from a common intermediate 1. These syntheses have allowed us to establish the correct relative configuration of the natural metabolite, which was originally misassigned. This work, together with our former syntheses of other gabosines and related compounds, validates enone 1 as a general synthetic precursor for this kind of carbasugars. 相似文献
72.
AlGaN-based UV photodetectors 总被引:6,自引:0,他引:6
E. Monroy F. Calle J. L. Pau E. Mu oz F. Omn s B. Beaumont P. Gibart 《Journal of Crystal Growth》2001,230(3-4):537-543
AlxGa1−xN alloys are very attractive materials for application to ultraviolet photodetection. AlGaN photoconductors, Schottky photodiodes, metal–semiconductor–metal photodiodes, p–n junction photodetectors and phototransistors have been recently developed. In this work we analyse the performance of AlGaN-based photodetectors, discussing present achievements, and comparing the characteristics of the various photodetector structures developed to date. 相似文献
73.
Several aspects of past and current studies in the area of iminium salt photochemistry are discussed. Investigations of olefin-iminium salt photoaddition and photocyclization reactions are reviewed and conclusions about electron-transfer pathways for fluorescence quenching and reaction are discussed. The results of recent studies of alcohol and ether photoaddition to 2-phenyl-1-pyrrolinium salts are presented. These C-C bond forming processes occur in moderate yields to produce β-amino alcohol or ether products. In addition, alcohols and ethers serve as efficient quenchers of pyrrolinium salt fluorescence. Rate constants for quenching appear to be dependent upon both the oxidation potential of the alcohols and ethers and the availability of C-H bond α to oxygen. This data along with deuterium isotope effects on quenching combine to suggest a common mechanism for both fluorescence quenching and photoaddition. The nature of this mechanism is tested using the comparative quenching effeciencies of the tertiary alcohols t-butyl alcohol and 1,2,2-trimethyl-1-cyclopropanol. The latter alcohol having a weak C-C bond adjacent to the hydroxyl function quenches the fluorescence of 2-phenyl-1-pyrrolium salts at a rate two orders of magnitude greater than for t-butyl alcohol. The observations made are interpreted in terms of a sequential electron-proton transfer mechanism for quenching and photoaddition. Lastly, the relationship of iminium salt photochemical studies to other investigations of electron-transfer photochemistry is discussed. 相似文献
74.
Chen KF Hara K Hazumi M Higuchi T Miyabayashi K Nakahama Y Sumisawa K Tajima O Ushiroda Y Yusa Y Abe K Abe K Adachi I Aihara H Anipko D Arinstein K Aulchenko V Aushev T Aziz T Bakich AM Balagura V Banerjee S Barberio E Barbero M Bay A Belous K Bitenc U Bizjak I Blyth S Bondar A Bozek A Bracko M Brodzicka J Browder TE Chang P Chao Y Chen A Chen WT Cheon BG Chistov R Choi SK Choi Y Choi YK Chuvikov A Cole S Dalseno J Danilov M Dash M Dragic J Drutskoy A Eidelman S Epifanov D Fratina S Garmash A 《Physical review letters》2007,98(3):031802
We present improved measurements of CP-violation parameters in B(0) --> phiK(0), eta(')K(0), KS(0)KS(0)KS(0) decays based on a sample of 535 x 10(6) BB pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB energy-asymmetric e(+)e(-) collider. We obtain sin2phi1(eff)=+0.64+/-0.10(stat)+/-0.04(syst) for B(0) --> eta(')K(0), +0.50+/-0.21(stat)+/-0.06(syst) for B(0) --> phiK(0), and +0.30+/-0.32(stat)+/-0.08(syst) for B(0) --> KS(0)KS(0)KS(0) decays. We have observed CP violation in the B(0) --> eta(')K(0) decay with a significance of 5.6 standard deviations. We also perform an improved measurement of CP asymmetries in B(0) --> J/psiK(0) decays and obtain sin2phi1=+0.642+/-0.031(stat)+/-0.017(syst). 相似文献
75.
Go A Bay A Abe K Aihara H Anipko D Aulchenko V Aushev T Bakich AM Barberio E Belous K Bitenc U Bizjak I Blyth S Bozek A Bracko M Browder TE Chang P Chao Y Chen A Chen KF Chen WT Cheon BG Chistov R Choi Y Choi YK Cole S Dalseno J Danilov M Dash M Drutskoy A Eidelman S Epifanov D Fratina S Gabyshev N Gershon T Gokhroo G Golob B Gorisek A Ha H Hastings NC Hayasaka K Hayashii H Hazumi M Heffernan D Hokuue T Hoshi Y Hou S Hou WS Iijima T Ikado K Imoto A Inami K Ishikawa A Ishino H Itoh R Iwasaki M 《Physical review letters》2007,99(13):131802
The neutral B meson pair produced at the Upsilon(4S) should exhibit a nonlocal correlation of the type discussed by Einstein, Podolsky, and Rosen. We measure this correlation using the time-dependent flavor asymmetry of semileptonic B(0) decays, which we compare with predictions from quantum mechanics and two local realistic models. The data are consistent with quantum mechanics, and inconsistent with the other models. Assuming that some B pairs disentangle to produce B(0) and B(0) with definite flavor, we find a decoherent fraction of 0.029 +/ -0.057, consistent with no decoherence. 相似文献
76.
M. Döbeli M. Doser L. van Elmbt M. Schaad P. Truöl A. Bay J. P. Perroud J. Imazato 《Czechoslovak Journal of Physics》1986,36(3):386-389
Experimental results for the radiative muon capture branching ratio in several nuclei and the photon-muon spin asymmetry in40Ca are reported. For the measurements a two arm Nalspectrometer was used. Apart from26O and40Ca, where we confirm previous results of our group, new data on12C,26Fe,165Ho and209Bi are presented. No available theoretical models explain all the data consistently. The preliminary results for the asymmetry measurements, obtained using a stroboscopic method are in agreement with previous measurements and with theoretical calculations.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985. 相似文献
77.
Adachi I Aihara H Asner DM Aulchenko V Aushev T Aziz T Bakich AM Bay A Bhardwaj V Bhuyan B Bischofberger M Bondar A Bozek A Bračko M Browder TE Chen P Cheon BG Chilikin K Chistov R Cho K Choi SK Choi Y Dalseno J Danilov M Doležal Z Drásal Z Eidelman S Epifanov D Fast JE Gaur V Gabyshev N Garmash A Goh YM Golob B Haba J Hara K Hara T Hayasaka K Hayashii H Higuchi T Horii Y Hoshi Y Hou WS Hsiung YB Hyun HJ Iijima T Ishikawa A Itoh R Iwabuchi M Iwasaki Y Iwashita T Julius T Kapusta P Katayama N 《Physical review letters》2012,108(17):171802
We present a precise measurement of the CP violation parameter sin2φ1 and the direct CP violation parameter A(f) using the final data sample of 772×10(6) BB[over ˉ] pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. One neutral B meson is reconstructed in a J/ψK(S)(0), ψ(2S)K(S)(0), χ(c1)K(S)(0), or J/ψK(L)(0) CP eigenstate and its flavor is identified from the decay products of the accompanying B meson. From the distribution of proper-time intervals between the two B decays, we obtain the following CP violation parameters: sin2φ1=0.667±0.023(stat)±0.012(syst) and A(f)=0.006±0.016(stat)±0.012(syst). 相似文献
78.
Anna V. Bay Keegan P. Fitzpatrick Rick C. Betori Prof. Karl A. Scheidt 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(23):9228-9233
As a key element in the construction of complex organic scaffolds, the formation of C−C bonds remains a challenge in the field of synthetic organic chemistry. Recent advancements in single-electron chemistry have enabled new methods for the formation of various C−C bonds. Disclosed herein is the development of a novel single-electron reduction of acyl azoliums for the formation of ketones from carboxylic acids. Facile construction of the acyl azolium in situ followed by a radical–radical coupling was made possible merging N-heterocyclic carbene (NHC) and photoredox catalysis. The utility of this protocol in synthesis was showcased in the late-stage functionalization of a variety of pharmaceutical compounds. Preliminary investigations using chiral NHCs demonstrate that enantioselectivity can be achieved, showcasing the advantages of this protocol over alternative methodologies. 相似文献
79.
J.L. Pau C. Rivera J. Pereiro E. Muoz E. Calleja U. Schühle E. Frayssinet B. Beaumont J.P. Faurie P. Gibart 《Superlattices and Microstructures》2004,36(4-6):807
The performance of nitride-based photodetectors is investigated beyond the usual near-UV (400–300 nm) and mid-UV (300–200 nm) operation ranges. The responses of metal–semiconductor–metal (MSM) photodiodes were analyzed in the vacuum–UV and soft X-ray regions. To interpret the results, the absorption properties and the attributes of each of the photons with energies for producing multiple electron–hole pairs were considered. The soft X-ray characterization showed that in-plane MSMs worked efficiently up to photon energies of 600 eV. Above this value, the absorption decrease makes the diffusion length and layer thickness become critical parameters for the detector behavior. To perform detection in the violet and near-UV, InGaN-based photoconductors were fabricated and spectrally characterized. The devices presented abrupt wavelength cut-offs, demonstrating that the InGaN compositional fluctuations were tolerable up to In contents of 10% for fabricating selective photodetectors. Back-face illumination allowed us to obtain bandpass detectors for these spectral ranges. 相似文献
80.
Aihara H Alston-Garnjost M Avery RE Barker AR Bauer DA Bay A Belcinski R Bingham HH Bloom ED Buchanan CD Caldwell DO Chao HY Chun SB Clark AR Cowan GD Crane DA Dahl OI Daoudi M Derby KA Eastman JJ Eberhard PH Edberg TK Eisner AM Erné FC Fairfield KH Fridman A Godfrey G Hauptman JM Ho C Hofmann W Kamae T Kenney RW Khacheryan S Kofler RR Lambert DJ Langeveld WG Layter JG Lin WT Linde FL Loken SC Lu A Lynch GR Lys JE Madaras RJ Magnuson BD Marsiske H Masek GE Mathis LG Maxfield SJ Miller ES 《Physical review D: Particles and fields》1991,43(1):29-33