12,008 research outputs found

    Extraction of nuclear matter properties from nuclear masses by a model of equation of state

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    The extraction of nuclear matter properties from measured nuclear masses is investigated in the energy density functional formalism of nuclei. It is shown that the volume energy a1a_1 and the nuclear incompressibility K0K_0 depend essentially on μnN+μˉpZ−2EN\mu_n N+\bar{\mu}_p Z-2E_N, whereas the symmetry energy JJ and the density symmetry coefficient LL as well as symmetry incompressibility KsK_s depend essentially on μn−μˉp\mu_n-\bar{\mu}_p, where μˉp=μp−∂EC/∂Z\bar{\mu}_p=\mu_p-\partial E_C/\partial Z, μn\mu_n and μp\mu_p are the neutron and proton chemical potentials respectively, ENE_N the nuclear energy, and ECE_C the Coulomb energy. The obtained symmetry energy is J=28.5MeVJ=28.5MeV, while other coefficients are uncertain within ranges depending on the model of nuclear equation of state.Comment: 12 pages and 7 figure

    Education choices in Mexico: using a structural model and a randomised experiment to evaluate PROGRESA

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    In this paper we evaluate the effect of a large welfare program in rural Mexico. For such a purpose we use an evaluation sample that includes a number of villages where the program was not implemented for evaluation purposes. We estimate a structural model of education choices and argue that without such a framework it is impossible to evaluate the effect of the program and, especially, possible changes to its structure. We also argue that the randomized component of the data allows us to identify a more flexible model that is better suited to evaluate the program. We find that the program has a positive effect on the enrollment of children, especially after primary school. We also find that an approximately revenue neutral change in the program that would increase the grant for secondary school children while eliminating for the primary school children would have a substantially larger effect on enrollment of the latter, while having minor effects on the former

    Recursion relations for multi-gluon off-shell amplitudes on the light-front and Wilson lines

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    We analyze the off-shell scattering amplitudes in the framework of the light-front perturbation theory. It is shown that the previously derived recursion relation between tree level off-shell amplitudes in this formalism actually resums whole classes of graphs into a Wilson line. More precisely, we establish a correspondence between the light-front methods for the computation of the off-shell amplitudes and the approach which makes use of the matrix elements of straight infinite Wilson lines, which are manifestly gauge invariant objects. Furthermore, since it is needed to explicitly verify the gauge invariance of light-front amplitudes, it is demonstrated that the Ward identities in this framework need additional instantaneous terms in the light-front graphs.Comment: 26 pages, a few figure

    Monopole ordered phases in dipolar and nearest-neighbours Ising pyrochlore: from spin ice to the "all-in--all-out" antiferromagnet

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    We study Ising pyrochlores by means of Monte Carlo simulations. We cover a set of exchange constants ranging from the frustrated ferromagnetic case (spin-ice) to the fully-ordered "all-in--all-out" antiferromagnet in the dipolar model, reinterpreting the results --as in an ionic system-- in terms of a temperature vs. magnetic charge density phase diagram. In spite of its spin nature and the presence of both double and single non-conserved magnetic charges, the dipolar model gives place to a phase diagram which is quite comparable with those previously obtained for on-lattice systems of electric charges, and on spin ice models with conserved number of single magnetic charges. The contrast between these systems, to which we add results from the nearest-neighbours model, put forward other features of our phase diagram --notably, a monopole fluid with charge order at high monopole densities that persists up to arbitrarily high temperatures-- that can only be explained taking into account construction constraints forced by the underlying spin degrees of freedom.Comment: 9 pages, 10 figure

    Effective nucleon-nucleon interactions and nuclear matter equation of state

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    Nuclear matter equations of state based on Skyrme, Myers-Swiatecki and Tondeur interactions are written as polynomials of the cubic root of density, with coefficients that are functions of the relative neutron excess δ\delta. In the extrapolation toward states far away from the standard one, it is shown that the asymmetry dependence of the critical point (ρc,δc\rho_c, \delta_c) depends on the model used. However, when the equations of state are fitted to the same standard state, the value of δc\delta_c is almost the same in Skyrme and in Myers-Swiatecki interactions, while is much lower in Tondeur interaction. Furthermore, δc\delta_c does not depend sensitively on the choice of the parameter γ\gamma in Skyrme interaction.Comment: 15 pages, 9 figure
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