70,027 research outputs found

    Revelation of double magicity in N=Z nuclei in the rp-process region

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    In rapid-proton capture (rp-process), N=Z nuclei above Ni are understood to act as waiting-point nuclei. The N=Z nuclei 68Se, 72Kr, 76Sr and 80Zr among others are known to give rise to a large-energy x-ray flux and peaks in abundances of these nuclei synthesized in the astrophysical rp-process. Investigating the experimental isotope shifts in Kr isotopes near the proton drip-line within the framework of the deformed Relativistic Hartree-Bogoliubov theory, we have discovered that N=Z rp-process nuclei 68Se, 72Kr, 76Sr and 80Zr exhibit large shell gap both at the proton and neutron numbers in the deformed space with the consequence that pairing correlations for protons and neutrons vanish. This lends a doubly magic character to these nuclei. A significant number of nuclei in this region are also shown to exhibit neutron magicity at N=34, 36, 38, and 40 in the deformed space. A unique case of concomitance of the double magicity and the shape-coexistence is found for 68Se.Comment: 10 pages, 4 figures; Invited contribution presented at the International Symposium on Exotic Nuclei, EXON 2009, Sochi, Russia, Sept. 28-Oct. 2, 200

    Firm corruption in the presence of an auditor

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    This paper develops a framework to explore firm corruption taking account of interaction with an auditor. The basic idea is that an auditor can provide auditing and other (consultancy) services. The extent of the other services depends on firm profitability. Hence auditor profitability can increase with firm corruption that may provide an incentive to collude in corrupt practices. This basic idea is developed using a game theoretic framework. It is shown that a multiplicity of equilibria exist from stable corruption, through auditor controlled corruption, via multiple equilibria to honesty on behalf of both actors. Following the development of the model various policy options are highlighted that show the difficulty of completely removing corrupt practices

    Isospin Dependence of the Spin-Orbit Force and Effective Nuclear Potentials,

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    The isospin dependence of the spin-orbit potential is investigated for an effective Skyrme-like energy functional suitable for density dependent Hartree-Fock calculations. The magnitude of the isospin dependence is obtained from a fit to experimental data on finite spherical nuclei. It is found to be close to that of relativistic Hartree models. Consequently, the anomalous kink in the isotope shifts of Pb nuclei is well reproduced.Comment: Revised, 11 pages (Revtex) and 2 figures available upon request, Preprint MPA-833, Physical Review Letters (in press)

    The microscopic origin of thermodynamic entropy in isolated systems

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    A microscopic understanding of the thermodynamic entropy in quantum systems has been a mystery ever since the invention of quantum mechanics. In classical physics, this entropy is believed to be the logarithm of the volume of phase space accessible to an isolated system [1]. There is no quantum mechanical analog to this. Instead, Von Neumann's hypothesis for the entropy [2] is most widely used. However this gives zero for systems with a known wave function, that is a pure state. This is because it measures the lack of information about the system rather than the flow of heat as obtained from thermodynamic experiments. Many arguments attempt to sidestep these issues by considering the system of interest coupled to a large external one, unlike the classical case where Boltzmann's approach for isolated systems is far more satisfactory. With new experimental techniques, probing the quantum nature of thermalization is now possible [3, 4]. Here, using recent advances in our understanding of quantum thermalization [5-10] we show how to obtain the entropy as is measured from thermodynamic experiments, solely from the self-entanglement of the wavefunction, and find strong numerical evidence that the two are in agreement for non-integrable systems. It is striking that this entropy, which is closely related to the concept of heat, and generally thought of as microscopic chaotic motion, can be determined for systems in energy eigenstates which are stationary in time and therefore not chaotic, but instead have a very complex spatial dependence.Comment: Manuscript is 5 pages, 2 figures, plus supplementary materials of 8 pages and 5 figure

    On the design of optimal compliant walls for turbulence control

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    This paper employs the theoretical framework developed by Luhar et al. (J. Fluid Mech., 768, 415-441) to consider the design of compliant walls for turbulent skin friction reduction. Specifically, the effects of simple spring-damper walls are contrasted with the effects of more complex walls incorporating tension, stiffness and anisotropy. In addition, varying mass ratios are tested to provide insight into differences between aerodynamic and hydrodynamic applications. Despite the differing physical responses, all the walls tested exhibit some important common features. First, the effect of the walls (positive or negative) is greatest at conditions close to resonance, with sharp transitions in performance across the resonant frequency or phase speed. Second, compliant walls are predicted to have a more pronounced effect on slower-moving structures because such structures generally have larger wall-pressure signatures. Third, two-dimensional (spanwise constant) structures are particularly susceptible to further amplification. These features are consistent with many previous experiments and simulations, suggesting that mitigating the rise of such two-dimensional structures is essential to designing performance-improving walls. For instance, it is shown that further amplification of such large-scale two-dimensional structures explains why the optimal anisotropic walls identified by Fukagata et al. via DNS (J. Turb., 9, 1-17) only led to drag reduction in very small domains. The above observations are used to develop design and methodology guidelines for future research on compliant walls
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