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1.
A. F. Privalov S. V. Dvinskikh F. Fujara H. M. Vieth 《Applied magnetic resonance》1998,15(3-4):353-361
The sensitivity of the19F spin-lattice relaxation dispersion, T1,(ω), to motional disorder in crystalline superionic conductors of the type La1?xSrxF3?x (x = 0; 0.03) is shown. T1 times are measured in the frequency range from 90 kHz to 370 MHz using standard techniques in combination with field-cycling. The relaxation dispersion shows qualitative differences from the standard Bloembergen-Purcell-Pound behavior. At low frequencies a relaxation model using a distribution of correlation times for diffusing ions is found to be consistent with the experimental results. At frequencies higher than 50 MHz another process of the Debye type which is not induced by ionic hopping dominates the relaxation. 相似文献
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The analytical performance of a glow discharge quadrupole mass spectrometer is demonstrated using sintered tungsten as an example. The inherent problem of molecular interferences in glow discharge mass Spectrometry has been considerably reduced using neon as a complementing discharge gas. Particular attention has been paid to time dependences. Analytical figures of merit are presented. 相似文献
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A. Yilmaz M. Yurdakoc J. Bernarding H. -M. Vieth J. Braun A. Yurt 《Applied magnetic resonance》2002,22(1):11-22
Spin-spin relaxation timeT 2 values of serum with and without iron were measured by magnetic resonance imaging (MRI) to find the proton relaxivity of Fe(III) in serum.T 2 values in serum containing definite amounts of added iron were also measured before and after addition of ascorbic acid. The difference in the 1/T 2 of serum with and without ascorbic acid was used for recalculation of the added iron values. Recalculated iron values confirm that the difference in healthy serum is caused by iron only. In addition, in order to find the paramagnetic contribution of serum iron,T 2 values of iron-deficient, healthy and iron-overloaded serum were measured before and after addition of ascorbic acid. The difference in the 1/T 2 values was then applied to the calculation of the serum iron values. The consistency of iron values determined from the difference to those by autoanalyzer suggests that the differences in diseased serum also represent the paramagnetic contribution of serum iron. The data imply that serum iron content in healthy, iron-deficient and iron-overloaded serum may be assessed by MRI. 相似文献
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The Feynman path integral Monte Carlo approach has been coupled to the gauge including atomic orbital formalism in order to analyse the absolute magnetic shieldings of the benzene nuclei under the conditions of thermal equilibrium. The Hamiltonian employed in the derivation of ensemble averaged NMR quantities is of the Hartree-Fock type. The basis set used is of 6–31G quality. The spatial delocalization of the atoms leads to a deshielding of both types of benzene nuclei relative to the shieldings experienced at the minimum of the potential energy surface. This deshielding has to be traced back to bond length elongations in thermal equilibrium. The influence of the nuclear fluctuations on the NMR parameters of benzene is quantum driven up to temperatures of 400 K; classical fluctuations are of minor importance in this low-temperature window. 相似文献
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K. L. Ivanov K. Miesel A. V. Yurkovskaya S. E. Korchak A. S. Kiryutin H. -M. Vieth 《Applied magnetic resonance》2006,30(3-4):513-534
Coherent polarization transfer among groups of dynamically polarized spins is explored and applied to field cycling experiments where spin evolution proceeds at low magnetic field while observation is performed at high field. The case of two nonequivalent spins-1/2 with scalar spin coupling is considered theoretically in detail for the cases of sudden and adiabatic field change. The criterion for efficient polarization transfer is derived theoretically and consistently confirmed experimentally for three photochemical reactions, involving spin systems of increasing complexity that exhibit chemically induced dynamic nuclear polarization: (1) the two polarized protons of the purine base of adenosine monophosphate; (2) four coupled indole protons of tryptophan; and (3) long-range polarization transfer among the aliphatic protons of cycloundecanone. The importance of polarization transfer in other cases with non-equilibrium population of the nuclear spin levels and the possibility of its utilization in field cycling NMR studies are discussed. 相似文献
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R. Furrer P. Fujara C. Lange D. Stehlik H.M. Vieth W. Vollmann 《Chemical physics letters》1980,75(2):332-339
Transient ESR nutation signals following laser pulse excitation are analyzed for the case of the photoexcited triplet state of acridine in a molecular crystal matrix. Essential features, in particular the short rise-time (< 10?7) of the signals, can be related to the inhomogeneous nature of the ESR linewidth. Applications are discussed. 相似文献
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M. Kanowski H. Werner R. Schlögl H. -M. Vieth K. Lüders 《Applied magnetic resonance》1995,8(1):173-180
Results of13C MAS NMR measurements of the Rb x C60 system (x=2.75, 3, 4, 6) and the A6C60 compounds (A=K, Rb, Cs) are presented. Special attention was paid to sample preparation in order to suppress effects of impurities and lattice defects due to imperfect C60 starting material. The13C MAS NMR measurements of the Rb x C60 system demonstrate the usefulness of this method to reveal valuable information about its phase diagram. The existence of underdoped Rb3C60 is proved. Well resolved lines in all investigated A6C60 compounds confirm the orientational order of the C60 ions. An assignment of the signals to the three magnetically inequivalent carbon atom positions in the crystal structure is proposed. 相似文献