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31.
Avalos M Babiano R Cintas P Clemente FR Gordillo R Hursthouse MB Jiménez JL Light ME Palacios JC 《The Journal of organic chemistry》2002,67(7):2378-2381
The present contribution discloses a simple and unexpected acid-catalyzed cleavage of tetrahydrotetrazines leading to 1,2-bis(hydrazones). Incorporation of a chiral fragment derived from carbohydrates enables the rapid preparation of glycosazones, a family of compounds employed by Emil Fischer to elucidate the configuration of sugars. In addition, a mechanistic proposal accounts for experimental observations. 相似文献
32.
Link JM Reyes M Yager PM Anjos JC Bediaga I Göbel C Magnin J Massafferi A de Miranda JM Pepe IM dos Reis AC Carrillo S Casimiro E Cuautle E Sánchez-Hernández A Uribe C Vazquez F Agostino L Cinquini L Cumalat JP O'Reilly B Ramirez JE Segoni I Butler JN Cheung HW Gaines I Garbincius PH Garren LA Gottschalk E Kasper PH Kreymer AE Kutschke R Bianco S Fabbri FL Zallo A Cawlfield C Kim DY Rahimi A Wiss J Gardner R Kryemadhi A Chung YS Kang JS Ko BR Kwak JW Lee KB Park H Alimonti G Boschini M 《Physical review letters》2002,88(16):161801
A high statistics measurement of the Lambda(+)(c) lifetime from the Fermilab fixed-target FOCUS photoproduction experiment is presented. We describe the analysis technique with particular attention to the determination of the systematic uncertainty. The measured value of 204.6 +/- 3.4 (stat) +/- 2.5 (syst) fs from 8034 +/- 122 Lambda(+)(c)-->pK(-)pi(+) decays represents a significant improvement over the present world average. 相似文献
33.
We report the spin Knight shift (K(s)) and the nuclear spin-lattice relaxation rate (1/T1) in the vortex state as a function of magnetic field (H) up to 28 T in the high-Tc superconductor TlSr2CaCu2O6.8 (Tc = 68 K). At low temperatures well below Tc, both K(s) and 1/T1 measured around the middle point between the two nearest vortices (saddle point) increase substantially with increasing field, which indicate that the quasiparticle states with an ungapped spectrum are extended outside the vortex cores in a d-wave superconductor. The density of states (DOS) around the saddle point is found to be kappaN(0)square root[H/H(c2)], with kappa = 0.5-0.7 and N0 being the normal-state DOS. 相似文献
34.
F. J. L zaro M. C. Mor n J. Reyes J. Garí n F. Palacio 《Solid State Communications》1991,80(12):969-973
Within the search for magnetic ordering in organic and metal-organic compounds, the polymeric material of formula {[Fe(C13H17N3)2]SO4·6H2O}n has been extensively studied by magnetic measurements. Our results show a basic agreement with the previous ones. Nevertheless, our study, including more data, leads to an interpretation in terms of superparamagnetism rather than metamagnetism as was previously reported. 相似文献
35.
36.
We apply strong magnetic fields of H=28.5 to 43 T to suppress superconductivity (SC) in the cuprates Bi2Sr2-xLaxCuO6+delta (x=0.65, 0.40, 0.25, 0.15, and 0), and investigate the low temperature (T) normal state by 63Cu nuclear spin-lattice relaxation rate (1/T1) measurements. We find that the pseudogap (PG) phase persists deep inside the overdoped region but terminates at x approximately 0.05, which corresponds to the hole doping concentration of approximately 0.21. Beyond this critical point, the normal state is a Fermi liquid that persists as the ground state when superconductivity is removed by the magnetic field. A comparison of the superconducting state with the H-induced normal state in the x=0.40 (Tc=32 K) sample indicates that there remains substantial part of the Fermi surface even in the fully developed PG state, which suggests that the PG and SC are coexisting matters. 相似文献
37.
Christian DC Felix J Gottschalk EE Gutierrez G Hartouni EP Knapp BC Kreisler MN Moreno G Reyes MA Sosa M Wang MH Wehmann A 《Physical review letters》2005,95(15):152001
We report the results of a high-statistics, sensitive search for narrow baryon resonances decaying to Xi-pi-, Xi-pi+, Xi+pi-, and Xi+pi+. The only resonances observed are the well known Xi0(1530) and Xi0(1530). No evidence is found for the states near 1862 MeV, previously reported by NA49 [Phys. Rev. Lett. 92, 042003 (2003)]. At the 95% confidence level, we find the upper limit for the production of a Gaussian enhancement with sigma=7.6 MeV in the Xi-pi- effective mass spectrum to be 0.3% of the number of observed Xi0(1530)-->Xi-pi+. We find similarly restrictive upper limits for an enhancement at 1862 MeV in the Xi-pi+, Xi+pi-, and Xi+pi+ mass spectra. 相似文献
38.
39.
Wang MH Berisso MC Christian DC Félix J Gara A Gottschalk E Gutiérrez G Hartouni EP Knapp BC Kreisler MN Lee S Markianos K Moreno G Reyes MA Sosa M Wehmann A Wesson D 《Physical review letters》2001,87(8):082002
We report the first observation of diffractively produced open charm in 800-GeV/c pp collisions of the type pp-->pD*X. We measure cross sections of sigma(diff)(D*+) = (0.185+/-0.044+/-0.054) (mu)b and sigma(diff)(D(*-)) = (0.174+/-0.034+/-0.029) (mu)b. Our measurements are based on 4.3x10(9) events recorded by FNAL E690 in the fixed-target run of 1991. We compare our results with previous fixed-target charm experiments. 相似文献
40.
Sigmund EE Calder ES Thomas GW Mitrović VF Bachman HN Halperin WP Kuhns PL Reyes AP 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,148(2):309-313
We have studied the temporal instability of a high field resistive Bitter magnet through nuclear magnetic resonance (NMR). This instability leads to transverse spin decoherence in repeated and accumulated NMR experiments as is normally performed during signal averaging. We demonstrate this effect via Hahn echo and Carr--Purcell--Meiboom--Gill (CPMG) transverse relaxation experiments in a 23-T resistive magnet. Quantitative analysis was found to be consistent with separate measurements of the magnetic field frequency fluctuation spectrum, as well as with independent NMR experiments performed in a magnetic field with a controlled instability. Finally, the CPMG sequence with short pulse delays is shown to be successful in recovering the intrinsic spin--spin relaxation even in the presence of magnetic field temporal instability. 相似文献