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991.
992.
Summary The present paper obtains necessary and sufficient conditions for factorial orthogonality in the presence of covariates. In
particular, when interactions are absent, combinatorial characterizations of the conditions, as natural generalizations of
the well-known equal and proportional frequency criteria, have been derived. 相似文献
993.
ESR and optical absorption studies have been carried out on Cu2+-doped lithium hydrazinium sulphate single crystals at 303 K. The spin-Hamiltonian parameters evaluated indicate a N2O2 square planar environment for Cu2+ ion in this lattice. The correlation ofESR and crystal structure data leads us to conclude that Cu2+ ion enters the lattice interstitially. Charge compensation is achieved by the release of protons. Using the optical absorption
andESR data, bonding parameters and orbital reduction factors are also evaluated. 相似文献
994.
995.
《Magnetic resonance in chemistry : MRC》2002,40(5):337-345
The temperature and pressure dependences of 35Cl nuclear quadrupole resonance (NQR) frequency and spin–lattice relaxation time (T1) were investigated for 1‐chloro‐2,4‐dinitrobenzene and 1,2‐dichloro‐3‐nitrobenzene. T1 was measured in the temperature range 77–300 K. Furthermore, the NQR frequency (ν) and T1 for these compounds were measured as a function of pressure up to 5.1 kbar at 300 K. Relaxation was found to be due to the torsional motion of the molecule and the reorientation motion of the nitro group. By analysing the temperature dependence of T1, the activation energy for the reorientation motion of the nitro group was obtained. The temperature dependence of the average torsional lifetimes of the molecules and the transition probabilities W1 and W2 for the Δm = ±1 and Δm = ±2 transitions, were also obtained. Both compounds showed a non‐linear variation of NQR frequency with pressure. The pressure coefficients were observed to be positive. A thermodynamic analysis of the data was carried out to determine the constant‐volume temperature coefficients of the NQR frequency. The spin–lattice relaxation time T1 for both the compounds was found to be weakly dependent on pressure, showing that the relaxation is mainly due to the torsional motions. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
996.
In this paper some new eighth algebraic order symmetric eight-step methods are introduced. For these methods a direct formula for the computation of the phase-lag is given. Based on this formula, the calculation of free parameters is done in order the phase-lag to be minimal. The new methods have better stability properties than the classical one. Numerical illustrations on the radial Schrödinger equation indicate that the new method is more efficient than older ones. 相似文献
997.
Summary A new high-powered ultraviolet laser system is proposed. The system doubles the infrared light from a Nd-Yag laser mode-locked
at 100 MHz, injects this light into a storage-ring cavity to accumulate a high power in the visible and then doubles this
into the ultraviolet at 2600 ?. The power levels anticipated at this wavelength are much larger than those of commercially
available c.w. lasers. The new system can have a far-reaching impact in basic research and, even more so, in a great many
industrial applications. 相似文献
998.
Thomas A. Spraggins 《Magnetic resonance imaging》1990,8(6):675-681
A new “wireless” method of cardiac imaging is introduced, which, unlike ECG triggering, allows imaging the heart at end-diastole, and greatly reduces smearing artifacts in the phase-encoding direction. It is an improvement over ECG-driven retrospective gating, in that patients with poor ECGs can be imaged. This method extends the applicability of cardiac imaging, and since it requires no physiological monitoring hardware, can be implemented easily on any MR imager. The images produced by this method are superior to those from ECG triggering, especially when viewed in a “cine” loop. The technique described herein is, furthermore, extendable to any area where periodic or quasi-periodic motion is a problem. 相似文献
999.
Richard E. Wendt III Wolfgang Nitz Joel D. Morrisett Thomas D. Hedrick 《Magnetic resonance imaging》1990,8(6):723-728
A two-dimensional, flow-enhanced gradient echo pulse sequence for nuclear magnetic resonance angiography is described. It employs interleaved, presaturated slices to acquire data efficiently on imagers which favor interleaved acquisition over sequential acquisition for multislice imaging. It is useful on any imager when the effective TR is extended to enhance the sensitivity to slow flow. The technique was applied to the region from aortic bifurcation to the iliac bifurcations of three normal volunteers. The right and left common iliac arteries and veins, the separation of the external and internal iliac arteries, and secondary branches were clearly depicted. 相似文献
1000.
The cerebral involvement of a 13-yr-old boy with Wilson's disease was serially evaluated during the first 18 mo of D-penicillamine treatment. An ultra-low-field magnetic resonance imaging (ULF MRI) system, operating at 0.02 T, with computerized image processing was used. The half-yr period prior to the clinical diagnosis was set, the patient had showed poor school performance, emotional lability, deteriorating handwriting, progressively slow, gross, and fine motor functions, and a fixed rigid smile. No overt signs of liver disease were found. With D-penicillamine treatment (1–1.5 g/d) a continuous improvement was seen. The pretreatment MRI investigation showed pronounced pathological transformation in the basal ganglia. However, changes were seen also in most other parts of the brain indicating diffuse involvement. During treatment the computerized MR images became gradually more normal. The current magnetic resonance imaging system with computerized image processing is a sensitive and simple method for evaluation of subtle parenchymal changes of the brain. 相似文献