379,674 research outputs found

    Two-neutron transfer reactions and shape phase transitions in the microscopically-formulated interacting boson model

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    Two-neutron transfer reactions are studied within the interacting boson model based on the nuclear energy density functional theory. Constrained self-consistent mean-field calculations with the Skyrme energy density functional are performed to provide microscopic input to completely determine the Hamiltonian of the IBM. Spectroscopic properties are calculated only from the nucleonic degrees of freedom. This method is applied to study the (t,p)(t,p) and (p,t)(p,t) transfer reactions in the assorted set of rare-earth nuclei 146158^{146-158}Sm, 148160^{148-160}Gd, and 150162^{150-162}Dy, where spherical-to-axially-deformed shape phase transition is suggested to occur at the neutron number N90N\approx 90. The results are compared with those from the purely phenomenological IBM calculations, as well as with the available experimental data. The calculated (t,p)(t,p) and (p,t)(p,t) transfer reaction intensities, from both the microscopic and phenomenological IBM frameworks, signal the rapid nuclear structural change at particular nucleon numbers.Comment: 12 pages, 12 figures, 2 table

    Scale disparities and magnetohydrodynamics in the Earth’s core

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    Fluid motions driven by convection in the Earth’s fluid core sustain geomagnetic ­ fields by magnetohydrodynamic dynamo processes. The dynamics of the core is critically influenced by the combined effects of rotation and magnetic ­ fields. This paper attempts to illustrate the scale-related difficulties in modelling a convection-driven geodynamo by studying both linear and nonlinear convection in the presence of imposed toroidal and poloidal ­ fields. We show that there exist three extremely large disparities, as a direct consequence of small viscosity and rapid rotation of the Earth’s fluid core, in the spatial, temporal and amplitude scales of a convection-driven geodynamo. We also show that the structure and strength of convective motions, and, hence, the relevant dynamo action, are extremely sensitive to the intricate dynamical balance between the viscous, Coriolis and Lorentz forces; similarly, the structure and strength of the magnetic field generated by the dynamo process can depend very sensitively on the fluid flow. We suggest, therefore, that the zero Ekman number limit is strongly singular and that a stable convection-driven strong-­field geodynamo satisfying Taylor’s constraint may not exist. Instead, the geodynamo may vacillate between a strong ­field state, as at present, and a weak ­ field state, which is also unstable because it fails to convect sufficient heat

    Toward parton equilibration with improved parton interaction matrix elements

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    The Quark-Gluon Plasma can be produced in high energy heavy ion collisions and how it equilibrates is important for the extraction of the properties of strongly interacting matter. A radiative transport model can be used to reveal interesting characteristics of Quark-Gluon Plasma thermalization. For example, screened parton interactions always lead to partial pressure isotropization. Systems with different initial pressure anisotropies evolve toward the same asymptotic evolution. In particular, radiative processes are crucial for the chemical equilibration of the system. Matrix elements under the soft and collinear approximation for these processes, as first derived by Gunion and Bertsch, are widely used. A different approach is to start with the exact matrix elements for the two to three and its inverse processes. General features of this approach will be reviewed and the results will be compared with the Gunion-Bertsch results. We will comment on the possible implications of the exact matrix element approach on Quark-Gluon Plasma thermalization.Comment: Presented at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, 27 May-1 June 201

    Gamma-ray and X-ray luminosities from spin-powered pulsars in the full polar cap cascade model

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    We modify the conventional curvature radiation (inverse Compton scattering) + synchrotron radiation polar cap cascade model by including the inverse Compton scattering of the higher generation pairs. Within the framework of the space-charge-limited-flow acceleration model with frame-dragging proposed by Harding & Muslimov (1998), such a full polar cap cascade scenario can well reproduce the Lγ(Lsd)1/2L_\gamma \propto (L_{\rm sd})^{1/2} and the Lx103LsdL_x \sim 10^{-3} L_{\rm sd} dependences observed from the known spin-powered pulsars. According to this model, the ``pulsed'' soft ROSAT-band X-rays from most of the millisecond pulsars might be of thermal origin, if there are no strong multipole magnetic components near their surfaces.Comment: To appear in Proc. 5th Compton Symposium, Portsmouth, New Hampshire, concise version of the ApJ pape