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81.
82.
Gawronski J Gawronska K Grajewski J Kacprzak K Rychlewska U 《Chemical communications (Cambridge, England)》2002,(6):582-583
Chiral oligomeric diimides prepared from pyromellitic dianhydride, (R,R)-1,2-diaminocyclohexane and phthalic anhydride fold into M or P helical conformers; trimer 1 folds into the P conformer in the crystal but the M conformer dominates in solution; longer chain oligomers 2 and 3 form preferentially P conformers in solution, as a result of intermolecular interactions. 相似文献
83.
Ján Jakubík 《Czechoslovak Mathematical Journal》2002,52(4):881-888
In this paper we prove a theorem of Cantor-Bernstein type for orthogonally -complete lattice ordered groups. 相似文献
84.
Ján Jakubík 《Czechoslovak Mathematical Journal》2002,52(2):275-294
In this paper we introduce and investigate the notion of half cyclically ordered group generalizing the notion of half partially ordered group whose study was begun by Giraudet and Lucas. 相似文献
85.
Baril N Lewa CJ de Certaines JD Canioni P Franconi JM Thiaudière E 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,154(1):22-27
A new method for NMR characterization of mechanical waves, based upon radiofrequency field gradient for motion encoding, is proposed. A binomial B1 gradient excitation scheme was used to visualize the mobile spins undergoing a periodic transverse mechanical excitation. A simple model was designed to simulate the NMR signal as a function of the wave frequency excitation and the periodicity of the NMR pulse sequence. The preliminary results were obtained on a gel phantom at low vibration frequencies (0-200 Hz) by using a ladder-shaped coil generating a nearly constant RF field gradient along a specific known direction. For very small displacements and/or B1 gradients, the NMR signal measured on a gel phantom was proportional to the vibration amplitude and the pulse sequence was shown to be selective with respect to the vibration frequency. A good estimation of the direction of vibrations was obtained by varying the angle between the motion direction and the B1 gradient. The method and its use in parallel to more conventional MR elastography techniques are discussed. The presented approach might be of interest for noninvasive investigation of elastic properties of soft tissues and other materials. 相似文献
86.
Kowalewski J Effemey M Jokisaari J 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,157(2):171-177
Multiple-field (4.7, 9.4, 14.1 T) carbon-13 relaxation data are reported for hexamethylenetetramine (HMTA) in the cryosolvent D(2)O/DMSO at 243 K. Under these conditions, the reorientational motion of HMTA is outside of the extreme narrowing range and the relaxation data can be subjected to a quantitative interpretation. Because of the high symmetry of the HMTA molecule, the reorientation must be isotropic. Treating the reorientation as a small-step rotational diffusion of a rigid body, we obtain a rotational correlation time of 1.0 ns and a carbon-proton dipole-dipole coupling constant corresponding to an effective internuclear distance of 114. 2 pm. The harmonic vibrational correction to the dipole-dipole coupling constant, based on a known force field, yields an NMR estimate of the r(alpha) distance of 110.8 +/- 0.3 pm. 相似文献
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We report lifetime measurements of the 1s 2 3d 2 D, 1s 24d 2 D, and 1s 22p 2 P states of lithium. The results τ=14.5±0.7 ns, τ=31.0±1.0 ns, and τ=27.9±1.0 ns respectively were obtained by time resolved detection of the resonance fluorescence following pulsed laser excitation. 相似文献