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991.
A straightforward derivation of the Dirac-Schwinger covariance condition is given within the framework of classical field
theory. The crucial role of the energy continuity equation in the derivation is pointed out. The origin of higher order derivatives
of delta function is traced to the presence of higher order derivatives of canonical coordinates and momenta in the energy
density functional. 相似文献
992.
993.
Letq be an odd prime power not divisible by 3. In Part I of this series, it was shown that the number of points in a rank-n combinatorial geometry (or simple matroid) representable over GF(3) and GF(q) is at mostn
2. In this paper, we show that, with the exception ofn = 3, a rank-n geometry that is representable over GF(3) and GF(q) and contains exactlyn
2 points is isomorphic to the rank-n Dowling geometry based on the multiplicative group of GF(3).This research was partially supported by the National Science Foundation under Grants DMS-8521826 and DMS-8500494. 相似文献
994.
Methods of sensitivity analysis are extended to find the parametric dependencies of systems of ordinary differential equations which exhibit limit cycle oscillations. The quantitative relations between the system parameters and the observable period, amplitude, phase and cycle shape are developed. These formulae, presented for both the first and second order, are applicable to systems of arbitrary size and complexity. The techniques are used here to develop correlations for period and amplitude in a non-isothermal oscillating stirred-tank chemical reactor, and to find and optimize a beneficial periodic operating strategy for a lumped-parameter catalytic reacting system. 相似文献
995.
Ralph Weissleder David D. Stark Guillermo Elizondo Peter F. Hahn Carolyn Compton Sanjay Saini Jack Wittenberg Joseph T. Ferrucci 《Magnetic resonance imaging》1988,6(6):675-681
Thirteen patients with biopsy proven hepatic lymphoma (2 Hodgkin, 11 Non-Hodgkin) and a control group of 15 patients with hepatic metastases were analyzed quantitatively and qualitatively by MRI. Focal hepatic lymphoma was most reliably detected (eight of eight patients) and appeared hypointense relative to liver on T1 weighted (CNR − 7.4 ± 2.3) and hyperintense on T2 weighted (CNR + 8.4 ± 2.9) images. The mean T1 and T2 relaxation times of focal hepatic lymphoma (T1 = 832 ± 234 msec, T2 = 84 ± 16 ms) differed significantly from adjacent non-tumorous liver (T1 = 420 ± 121 ms, T2 = 51 ± 9 ms; p < 0.05), however CNR values and relaxation times were similar to those of hepatic metastases. Diffuse hepatic lymphoma (microscopic periportal infiltration) was undetectable by MRI in three patients by either morphologic features or quantitative criteria. A mixed pattern of hepatic lymphoma (focal lesions and diffuse infiltration) showed focal areas of slightly decreased signal intensity on T1 weighted images (CNR = −1.7 ± 0.4) while T2 weighted images revealed multiple regions of focal hyperintensity (CNR = +13.3 ± 8.4) superimposed on a diffusely hyperintense liver. Our experience demonstrates that either T1 or T2 weighted techniques are useful in detecting focal and that T2 weighted techniques are useful in detecting mixed hepatic lymphoma. Conventional image derived relaxation time measurements and quantitative parameters were of no additional diagnostic value. 相似文献
996.
Joseph B. Schlenoff Joseph M. Machado P. J. Glatkowski Frank E. Karasz 《Journal of Polymer Science.Polymer Physics》1988,26(11):2247-2256
Blends of poly(p-phenylene vinylene) (PPV), with other polymers were made by film-casting from an aqueous mixture of the water-soluble sulfonium salt precursor to PPV and the second polymer. The rates of chemical doping, using As F5, and of electrochemical doping, using perchlorate counter ion, of the PPV component are strongly influenced by the nature of the added macromolecule. In all cases studied the blends appear to be phase separated under all conditions. The most versatile blend was with poly(ethylene oxide) (PEO), which could be heated to 225°C without degradation and which yielded the highest electrical conductivity when doped. The utility of blends was demonstrated using free-standing PPV/PEO blend samples as rechargeable battery electrodes. 相似文献
997.
Joseph J. Brophy Chang-Ming Sun Berhane Tecle Robert F. Toia 《Journal of mass spectrometry : JMS》1989,24(8):609-614
The detailed mass spectral fragmentation pathways of a series of both naturally occurring and synthetic 5-methyl-3-alkyl-2-aIkenylpyrazines have been elucidated with the aid of deuterium labels placed specifically in the alkenyl side-chain. The influence on the fragmentation pattern of the stereochemistry of the alkenyl group as well as the relative placement of the groups on the pyrazine nucleus have also been evaluated. This provides information of some diagnostic value in the assignment of structures by mass spectrometry to new compounds within this class. 相似文献
998.
Joseph J. Hlavka Panayota Bitha Yang-I Lin Timothy Strohmeyer 《Journal of heterocyclic chemistry》1984,21(5):1537-1541
A series of new 2,3-diamino-4-pyrimidinones and 3-amino-2-hydrazino-4-pyrimidinones were synthesized by the reactions of β-ketoesters with amino or diaminoguanidines. 相似文献
999.
1000.
The alkaloids (±)-hygrine, (±)-dehydrodarlinine, (±)-dehydrodarlingianine, and (±)-N-methylruspolinone have been synthesised by selective reduction of vinylogous amides formed by sulphide contraction of the salts prepared by reaction of N-methyl-2-thiopyrrolidone with the appropriate bromomethyl ketones. 相似文献