12,008 research outputs found
Extraction of nuclear matter properties from nuclear masses by a model of equation of state
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 and the nuclear incompressibility depend
essentially on , whereas the symmetry energy
and the density symmetry coefficient as well as symmetry incompressibility
depend essentially on , where
, and are the
neutron and proton chemical potentials respectively, the nuclear energy,
and the Coulomb energy. The obtained symmetry energy is ,
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
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
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
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
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 .
In the extrapolation toward states far away from the standard one, it is shown
that the asymmetry dependence of the critical point ()
depends on the model used. However, when the equations of state are fitted to
the same standard state, the value of is almost the same in Skyrme
and in Myers-Swiatecki interactions, while is much lower in Tondeur
interaction. Furthermore, does not depend sensitively on the choice
of the parameter in Skyrme interaction.Comment: 15 pages, 9 figure
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Modified Green's Functions for Shallow Water Acoustic Wave Propagation
This article presents an assessment of alternative forms of the Greenâs function for boundary element simulations of acoustic wave propagation in shallow water. It is assumed that the problem is two-dimensional, the source of acoustic disturbance is time-harmonic, the velocity of sound is constant and the medium in the absence of perturbations is quiescent.
Efficient implementations of the boundary element method for underwater acoustics should employ Green's functions which directly satisfy the boundary conditions on the free surface and the horizontal parts of the bottom boundary. In the present work, these Green's functions are constructed by using different techniques, namely the method of images, eigenfunction expansions and the Ewaldâs method
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