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91.
Peter A. Jacobi Lisa M. Armacost Joseph I. Kravitz Michael J. Martinelli 《Tetrahedron letters》1988,29(52):6869-6872
The electrocyclizaton of enynones to methylenecyclopentenones is markedly accelerated by phenols and catechols having a low oxidation potential. 相似文献
92.
Fukaya A Fudamoto Y Gat IM Ito T Larkin MI Savici AT Uemura YJ Kyriakou PP Luke GM Rovers MT Kojima KM Keren A Hanawa M Hiroi Z 《Physical review letters》2003,91(20):207603
Muon spin relaxation and magnetic susceptibility measurements have been performed on the pure and diluted spin 1/2 kagomé system (CuxZn(1-x))3V2O7(OH)2 2H2O. In the pure x=1 system we found a slowing down of Cu spin fluctuations with decreasing temperature towards T approximately 1 K, followed by slow and nearly temperature-independent spin fluctuations persisting down to T=50 mK, indicative of quantum fluctuations. No indication of static spin freezing was detected in either of the pure (x=1.0) or diluted samples. The observed magnitude of fluctuating fields indicates that the slow spin fluctuations represent an intrinsic property of kagomé network rather than impurity spins. 相似文献
93.
Chakhalian JA Kiefl RF Miller R Brewer J Dunsiger SR Morris G MacFarlane WA Sonier JE Eggert S Affleck I Keren A Verdaguer M 《Physical review letters》2003,91(2):027202
We report muon spin rotation measurements of the local magnetic susceptibility around a positive muon in the paramagnetic state of the quasi-one-dimensional spin 1/2 antiferromagnet dichlorobis (pyridine) copper (II). Signals from three distinct sites are resolved and have a temperature dependent frequency shift which is significantly different than the magnetic susceptibility. This difference is attributed to a muon induced perturbation of the spin 1/2 chain. The obtained frequency shifts are compared with transfer matrix density-matrix renormalization-group numerical simulations. 相似文献
94.
We demonstrate a three-dimensional (3-D) distributed refractometer that measures refractive index in a small volume. The sensor is based on an evanescent-wave fiber Bragg grating that is interrogated by low-coherence spectral interferometry. The measurement can be performed on a short time scale without the need for a mechanical scan. The new sensor was used to simultaneously measure glucose concentration in several droplets along a single sensor and to interrogate the time-dependent evaporation process of a water droplet. The new measurement technique might enable novel 3-D distributed sensors to be developed and multiple discrete measurements to be made in a small volume. 相似文献
95.
H. Keren J. L. Hirshfield 《International Journal of Infrared and Millimeter Waves》1981,2(6):1097-1112
The influence of space charge forces on the performance of a single cacity gyrotron oscillator which uses a solid electron beam was investigated. It was found that space charge effects cause a large efficiency degradation as the beam current is increased, if the other experimental parameters are unchanged. A small increase in the magnetic field, however, can restore the efficiency to higher values.This research was supported by the U.S. Office of Naval Research. 相似文献
96.
Investigations of the spin dynamics of the geometrically frustrated pyrochlore (Tb(p)Y(1-p))2Ti2O7, using muon spin relaxation and neutron spin echo, as a function of magnetic coverage p, have been carried out. Our major finding is that paramagnetic fluctuations prevail as T-->0 for all values of p, and that they are sensitive to dilution, indicating a cooperative spin motion. However, the percolation threshold pc is not a critical point for the fluctuations. We also find that the low temperature spectral density has a 1/f behavior, and that dilution slows down the spin fluctuations. 相似文献
97.
We present an angle dependent nuclear quadrupole resonance (ADNQR) method to determine the electric field gradient asymmetry parameter eta in systems where the resonance line is so broad that the radio frequency field can excite only a portion of the nuclear spins. In this situation, the recently developed spectroscopic methods are not applicable. ADNQR is useful for single crystals and oriented powders, and, for small eta determines eta4. Therefore, it can be used to evaluate fluctuations in eta due to inhomogeneities. We demonstrate the application of ADNQR experimentally to oriented superconducting YBa2Cu3O7 powder. 相似文献
98.
Wu Chaojun He Juan Chen Ningning Li Yuanyuan Yuan Linlin Zhao Dongxin He Lijun Gu Keren Zhang Shusheng 《Analytical and bioanalytical chemistry》2018,410(26):6943-6954
Analytical and Bioanalytical Chemistry - In this work, cobalt magnetic nanoporous carbon (Co-MNPC) is employed as an alternative to intensively used Fe3O4 cores for the preparation of magnetic... 相似文献
99.
A relation between the spin-lattice relaxation rate (1/T
1) of positive muons and the scattering functionS
T
(q,) is derived for the antiferromagnet MnF2. We find good agreement between previousSR measurements of 1/T
1 and our calculation using neutron scattering measurements ofS
T
(q,). 相似文献
100.