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71.
72.
A protoneutron star is formed immediately after the gravitational collapse of the core of a massive star. At birth, the hot and high density matter in such a star contains a large number of neutrinos trapped during collapse. Trapped neutrinos generally inhibit the presence of exotic matter — hyperons, a kaon condensate, or quarks. However, as the neutrinos diffuse out in about 10–15 s, the threshold for the appearance of strangeness is reduced; hence, the composition and the structure of the star can change significantly. The effect of exotic, negatively-charged, strangeness-bearing components is always to soften the equation of state, and the possibility exists that the star collapses to a black hole at this time. This could explain why no neutron star has yet been seen in the remnant of supernova SN1987A, even though one certainly existed when neutrinos were detected on Feb. 23, 1987. With new generation neutrino detectors it is feasible to test different theoretical scenarios observationally. 相似文献
73.
J. Ellis G.G. Ross J. Williams 《The European Physical Journal C - Particles and Fields》1999,10(3):443-460
We suggest that the pseudo-rapidity cut dependence of diffractive deep-inelastic scattering events at HERA may provide a
sensitive test of models of diffraction. A comparison with the experimental cross section shows that the Donnachie-Landshoff
model and a simple two-gluon exchange model of the pomeron model are disfavoured. However a model with a direct coupling of
the pomeron to quarks is viable for a harder quark–pomeron form factor, as is a model based on the leading-twist operator
contribution. We also consider a direct-coupling scalar pomeron model. We comment on the implications of these results for
the determination of the partonic structure of the pomeron.
Received: 5 March 1999 / Published online: 3 August 1999 相似文献
74.
75.
Ellis AL Christian Mason J Lee HW Strekowski L Patonay G Choi H Yang JJ 《Talanta》2002,56(6):1099-1107
Intracellular calcium concentration in biological cells varies from 0.1 to 10 μM depending upon cell signaling and disease states. A direct estimate of calcium concentration in cell tissues within this range is possible with a novel calcium-selective reagent 15C5-774. The molecule of 15C5-774 consists of a near-infrared (NIR) chromophore (λmax=774 nm) and a metal complexing moiety of benzo-15-crown-5. The reagent shows a strong calcium binding affinity in a 1:1 ratio and metal selectivity in the order Ca2+>Mg2+>Sr2+≈K+≈Na+>Zn2+>Li+. The high sensitivity is achieved by conducting absorption measurements in the NIR region where background interference from the biological matrix is low. 相似文献
76.
We investigate the cross section for the production of a low-mass colour-singlet cluster ine + e ? annihilation with a large rapidity gap between the colour-singlet cluster and the other jets. It is argued that such events are the cross-channel analogue of large-rapidity-gap events in deep-inelastic scattering, and therefore could in principle be used to investigate the analytic continuation of the BFKL pomeron to the positive-t kinematic regime, where one would expect the trajectory to pass through glueball states. The cross section can be calculated in perturbative QCD, so that the infrared scale arising from non-perturbative effects, which prevents an exponential fall-off with rapidity gap in the case of deep-inelastic scattering, is absent ine + e ? annihilation. Correspondingly, the cross section for such events decreases rapidly with increasing rapidity gap. 相似文献
77.
Alan M. Kook Stanford L. Smith Ellis V. Brown 《Magnetic resonance in chemistry : MRC》1984,22(11):730-733
Hydrogen and carbon chemical shifts and H? H and C? H couplings are reported for six aminoquinolines and six aminoisoquinolines in DMSO-d6. 相似文献
78.
The mathematical approach to General Relativity insists that all coordinate systems are equal. However physicists and astrophysicists in fact almost always use preferred coordinate systems not merely to simplify the calculations but also to help define quantities of physical interest. This suggests we should reconsider and perhaps refine the dogma of General Covariance. 相似文献
79.
80.
The result of the first calculation of a self-consistent relativistic many electron correlation diagram ever done (for the system Au-I) leads to a good agreement of the spectral shape and position of the observed noncharacteristic X-rays within the quasi adiabatic model. 相似文献