149 research outputs found

    Incompressibility in finite nuclei and nuclear matter

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    The incompressibility (compression modulus) K0K_{\rm 0} of infinite symmetric nuclear matter at saturation density has become one of the major constraints on mean-field models of nuclear many-body systems as well as of models of high density matter in astrophysical objects and heavy-ion collisions. We present a comprehensive re-analysis of recent data on GMR energies in even-even 112‚ąí124^{\rm 112-124}Sn and 106,100‚ąí116^{\rm 106,100-116}Cd and earlier data on 58 ‚ȧ\le A ‚ȧ\le 208 nuclei. The incompressibility of finite nuclei KAK_{\rm A} is expressed as a leptodermous expansion with volume, surface, isospin and Coulomb coefficients KvolK_{\rm vol}, KsurfK_{\rm surf}, KŌĄK_\tau and KcoulK_{\rm coul}. \textit{Assuming} that the volume coefficient KvolK_{\rm vol} is identified with K0K_{\rm 0}, the KcoulK_{\rm coul} = -(5.2 ¬Ī\pm 0.7) MeV and the contribution from the curvature term Kcurv_{\rm curv}A‚ąí2/3^{\rm -2/3} in the expansion is neglected, compelling evidence is found for K0K_{\rm 0} to be in the range 250 <K0< < K_{\rm 0} < 315 MeV, the ratio of the surface and volume coefficients c=Ksurf/Kvolc = K_{\rm surf}/K_{\rm vol} to be between -2.4 and -1.6 and KŌĄK_{\rm \tau} between -840 and -350 MeV. We show that the generally accepted value of K0K_{\rm 0} = (240 ¬Ī\pm 20) MeV can be obtained from the fits provided c‚ąľc \sim -1, as predicted by the majority of mean-field models. However, the fits are significantly improved if cc is allowed to vary, leading to a range of K0K_{\rm 0}, extended to higher values. A self-consistent simple (toy) model has been developed, which shows that the density dependence of the surface diffuseness of a vibrating nucleus plays a major role in determination of the ratio Ksurf/Kvol_{\rm surf}/K_{\rm vol} and yields predictions consistent with our findings.Comment: 26 pages, 13 figures; corrected minor typos in line with the proof in Phys. Rev.

    Short range correlations in relativistic nuclear matter models

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    Short range correlations are introduced using unitary correlation method in a relativistic approach to the equation of state of the infinite nuclear matter in the framework of the Hartree-Fock approximation. It is shown that the correlations give rise to an extra node in the ground-state wave-function in the nucleons, contrary to what happens in non-relativistic calculations with a hard core. The effect of the correlations in the ground state properties of the nuclear matter and neutron matter is studied. The nucleon effective mass and equation of state (EOS) are very sensitive to short range correlations. In particular, if the pion contact term is neglected a softening of the EOS is predicted. Correlations have also an important effect on the neutron matter EOS which presents no binding but only a very shallow minimum contrary to the Walecka model.Comment: 8pages, 4 figure

    A Complete Axiom System for Propositional Interval Temporal Logic with Infinite Time

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    Interval Temporal Logic (ITL) is an established temporal formalism for reasoning about time periods. For over 25 years, it has been applied in a number of ways and several ITL variants, axiom systems and tools have been investigated. We solve the longstanding open problem of finding a complete axiom system for basic quantifier-free propositional ITL (PITL) with infinite time for analysing nonterminating computational systems. Our completeness proof uses a reduction to completeness for PITL with finite time and conventional propositional linear-time temporal logic. Unlike completeness proofs of equally expressive logics with nonelementary computational complexity, our semantic approach does not use tableaux, subformula closures or explicit deductions involving encodings of omega automata and nontrivial techniques for complementing them. We believe that our result also provides evidence of the naturalness of interval-based reasoning

    Moments of Inertia of Nuclei in the Rare Earth Region: A Relativistic versus Non-Relativistic Investigation

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    A parameter free investigation of the moments of inertia of ground state rotational bands in well deformed rare-earth nuclei is carried out using Cranked Relativistic Hartree-Bogoliubov (CRHB) and non-relativistic Cranked Hartree-Fock-Bogoliubov (CHFB) theories. In CRHB theory, the relativistic fields are determined by the non-linear Lagrangian with the NL1 force and the pairing interaction by the central part of finite range Gogny D1S force. In CHFB theory, the properties in particle-hole and particle-particle channels are defined solely by Gogny D1S forces. Using an approximate particle number projection before variation by means of the Lipkin Nogami method improves the agreement with the experimental data, especially in CRHB theory. The effect of the particle number projection on the moments of inertia and pairing energies is larger in relativistic than in non-relativistic theory.Comment: 18 pages + 2 PostScript figure

    A timeband framework for modelling real-time systems

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    Complex real-time systems must integrate physical processes with digital control, human operation and organisational structures. New scientific foundations are required for specifying, designing and implementing these systems. One key challenge is to cope with the wide range of time scales and dynamics inherent in such systems. To exploit the unique properties of time, with the aim of producing more dependable computer-based systems, it is desirable to explicitly identify distinct time bands in which the system is situated. Such a framework enables the temporal properties and associated dynamic behaviour of existing systems to be described and the requirements for new or modified systems to be specified. A system model based on a finite set of distinct time bands is motivated and developed in this paper

    Borromean Binding of Three or Four Bosons

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    We estimate the ratio R=g3/g2R=g_{3}/g_{2} of the critical coupling constants g2g_{2} and g3g_{3} which are required to achieve binding of 2 or 3 bosons, respectively, with a short-range interaction, and examine how this ratio depends on the shape of the potential. Simple monotonous potentials give R‚ČÉ0.8R\simeq 0.8. A wide repulsive core pushes this ratio close to R=1. On the other hand, for an attractive well protected by an external repulsive barrier, the ratio approaches the rigorous lower bound R=2/3R=2/3. We also present results for N=4 bosons, sketch the extension to N>4N>4, and discuss various consequences.Comment: 12 pages, RevTeX, 5 Figures in tex include

    Improved lower bounds for the ground-state energy of many-body systems

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    New lower bounds for the binding energy of a quantum-mechanical system of interacting particles are presented. The new bounds are expressed in terms of two-particle quantities and improve the conventional bounds of the Hall-Post type. They are constructed by considering not only the energy in the two-particle system, but also the structure of the pair wave function. We apply the formal results to various numerical examples, and show that in some cases dramatic improvement over the existing bounds is reached.Comment: 29 pages, 5 figures, to be published in Phys. Rev.
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