9,500 research outputs found

    Influence of pairing correlations on the radius of neutron-rich nuclei

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    The influence of pairing correlations on the neutron root mean square (rms) radius of nuclei is investigated in the framework of self-consistent Skyrme Hartree-Fock-Bogoliubov calculations. The continuum is treated appropriately by the Green's function techniques. As an example the nucleus 124^{124}Zr is treated for a varying strength of pairing correlations. We find that, as the pairing strength increases, the neutron rms radius first shrinks, reaches a minimum and beyond this point it expands again. The shrinkage is due to the the so-called `pairing anti-halo effect', i. e. due to the decreasing of the asymptotic density distribution with increasing pairing. However, in some cases, increasing pairing correlations can also lead to an expansion of the nucleus due to a growing occupation of so-called `halo' orbits, i.e. weakly bound states and resonances in the continuum with low-â„“\ell values. In this case, the neutron radii are extended just by the influence of pairing correlations, since these `halo' orbits cannot be occupied without pairing. The term `anti-halo effect' is not justified in such cases. For a full understanding of this complicated interplay self-consistent calculations are necessary.Comment: 18 pages, 5 figure

    Analysis and evaluation of the entropy indices of a static network structure

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    Although degree distribution entropy (DDE), SD structure entropy (SDSE), Wu structure entropy (WSE) and FB structure entropy (FBSE) are four static network structure entropy indices widely used to quantify the heterogeneity of a complex network, previous studies have paid little attention to their differing abilities to describe network structure. We calculate these four structure entropies for four benchmark networks and compare the results by measuring the ability of each index to characterize network heterogeneity. We find that SDSE and FBSE more accurately characterize network heterogeneity than WSE and DDE. We also find that existing benchmark networks fail to distinguish SDSE and FBSE because they cannot discriminate local and global network heterogeneity. We solve this problem by proposing an evolving caveman network that reveals the differences between structure entropy indices by comparing the sensitivities during the network evolutionary process. Mathematical analysis and computational simulation both indicate that FBSE describes the global topology variation in the evolutionary process of a caveman network, and that the other three structure entropy indices reflect only local network heterogeneity. Our study offers an expansive view of the structural complexity of networks and expands our understanding of complex network behavior.The authors would like to thank the financial support of the National Natural Science Foundation of China (71501153), Natural Science Foundation of Shaanxi Province of China (2016JQ6072), and the Foundation of China Scholarship Council (201506965039, 201606965057). (71501153 - National Natural Science Foundation of China; 2016JQ6072 - Natural Science Foundation of Shaanxi Province of China; 201506965039 - Foundation of China Scholarship Council; 201606965057 - Foundation of China Scholarship Council)Published versio

    The Extended Wronskian Determinant Approach and the Iterative Solutions of One-Dimensional Dirac Equation

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    An approximation method, namely, the Extended Wronskian Determinant Approach, is suggested to study the one-dimensional Dirac equation. An integral equation which can be solved by iterative procedure to find the wave functions is established. We employ this approach to study the one-dimensional Dirac equation with one-well potential, and give the energy levels and wave functions up to the first order iterative approximation. For double-well potential, the energy levels up to the first order approximation are given.Comment: 3 figures, 21 page

    Lions grazing on the dragon’s land: South African firms’ business strategies in the Chinese market: navigating institutions

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    This research project is one of the first studies to focus on South African foreign direct investment (FDI) in Mainland China. Specifically, the research aims to identify and specify the key institutional factors that have contributed to the effectiveness or otherwise of South African firms entering and operating within the Chinese market, as well as to investigate the characteristics and processes that have effectively shaped South African firms’ business strategies to negotiate the current Chinese institutional environment. The research adopts an institutional perspective, fusing two separate disciplinary study frameworks, international business (IB) and international political economy (IPE), to draw out the key institutional factors that South African firms entering and operating within the Chinese market have encountered. The principal contributions of the thesis are conceptual and empirical: the latter presenting case studies of a cross-section of South African business actors who have sought to penetrate the Chinese market; the former centring of a model which emphasises the importance of both formal and informal business processes and practices in influencing business success and failure in context
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