74 research outputs found
Complete 0 hbar omega calculations of Gamow-Teller strengths for nuclei in the iron region
Gamow-Teller strengths for selected nuclei in the iron region (A~56) have
been investigated via shell-model Monte Carlo calculations with realistic
interactions in the complete fp basis. Results for all cases show significant
quenching relative to single-particle estimates, in quantitative agreement with
(n,p) data. The J=1,T=0 residual interaction and the f_{7/2}-f_{5/2} spin-orbit
splitting are shown to play major roles in the quenching mechanism. Calculated
B(E2, 2^+_1 -> 0^+_1) values are in fair agreement with experiment using
effective charges of e_p=1.1e and e_n=0.1e.Comment: 13 pages + 1 postscript file, Caltech preprint MAP-16
Gamow-Teller strength in 54Fe and 56Fe
Through a sequence of large scale shell model calculations, total
Gamow-Teller strengths ( and ) in Fe and Fe are
obtained. They reproduce the experimental values once the operator
is quenched by the standard factor of . Comparisons are made with recent
Shell Model Monte Carlo calculations. Results are shown to depend critically on
the interaction. From an analysis of the GT+ and GT strength functions it is
concluded that experimental evidence is consistent with the sum rule.Comment: 6 pages, RevTeX 3.0 using psfig, 7 Postscript figures included using
uufile
The nucleon-nucleon interaction
We review the major progress of the past decade concerning our understanding
of the nucleon-nucleon interaction. The focus is on the low-energy region
(below pion production threshold), but a brief outlook towards higher energies
is also given. The items discussed include charge-dependence, the precise value
of the coupling constant, phase shift analysis and high-precision NN
data and potentials. We also address the issue of a proper theory of nuclear
forces. Finally, we summarize the essential open questions that future research
should be devoted to.Comment: 42 pages, 12 figures, iopart.cls style; Topical Review prepared for
J. Phys. G: Nucl. Part. Phy
Dopamine acting at D1-like, D2-like and α1-adrenergic receptors differentially modulates theta and gamma oscillatory activity in primary motor cortex
The loss of dopamine (DA) in Parkinson’s is accompanied by the emergence of exaggerated theta and beta frequency neuronal oscillatory activity in the primary motor cortex (M1) and basal ganglia. DA replacement therapy or deep brain stimulation reduces the power of these oscillations and this is coincident with an improvement in motor performance implying a causal relationship. Here we provide in vitro evidence for the differential modulation of theta and gamma activity in M1 by DA acting at receptors exhibiting conventional and non-conventional DA pharmacology. Recording local field potentials in deep layer V of rat M1, co-application of carbachol (CCh, 5 μM) and kainic acid (KA, 150 nM) elicited simultaneous oscillations at a frequency of 6.49 ± 0.18 Hz (theta, n = 84) and 34.97 ± 0.39 Hz (gamma, n = 84). Bath application of DA resulted in a decrease in gamma power with no change in theta power. However, application of either the D1-like receptor agonist SKF38393 or the D2-like agonist quinpirole increased the power of both theta and gamma suggesting that the DA-mediated inhibition of oscillatory power is by action at other sites other than classical DA receptors. Application of amphetamine, which promotes endogenous amine neurotransmitter release, or the adrenergic α1-selective agonist phenylephrine mimicked the action of DA and reduced gamma power, a result unaffected by prior co-application of D1 and D2 receptor antagonists SCH23390 and sulpiride. Finally, application of the α1-adrenergic receptor antagonist prazosin blocked the action of DA on gamma power suggestive of interaction between α1 and DA receptors. These results show that DA mediates complex actions acting at dopamine D1-like and D2-like receptors, α1 adrenergic receptors and possibly DA/α1 heteromultimeric receptors to differentially modulate theta and gamma activity in M1
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