Fractal Structure of Random Matrices

A multifractal analysis is performed on the universality classes of random matrices and the transition ones.Our results indicate that the eigenvector probability distribution is a linear sum of two chi-squared distribution throughout the transition between the universality ensembles of random matrix theory and Poisson

Decay theory of double giant resonances

The decay theory of double giant resonances incorporating fluctuation contributions of the Brink-Axel type is developed. The gamma and neutron emission decay of Double Giant Dipole Resonances (DGDR) in 208Pb is discussed in connection with a recent measurement.Comment: 5 pages, Late

A Coupled-Channels Study of 11Be^{11}Be Coulomb Excitation

We study the effects of channel coupling in the excitation of $^{11}Be$ projectiles incident on heavy targets. The contribution to the excitation from the Coulomb and the nuclear fields in peripheral collisions are considered. Our results are compared with recent data on the excitation of the \halfm state in $^{11}Be$ projectiles. We show that the experimental results cannot be explained, unless very unusual parameters are used.Comment: 8 pages, 2 Postscript figures available upon request, corrected misprints in eqs. 2 and

Influence of the halo upon angular distributions for elastic scattering and breakup

The angular distributions for elastic scattering and breakup of halo nuclei are analysed using a near-side/far-side decomposition within the framework of the dynamical eikonal approximation. This analysis is performed for 11Be impinging on Pb at 69 MeV/nucleon. These distributions exhibit very similar features. In particular they are both near-side dominated, as expected from Coulomb-dominated reactions. The general shape of these distributions is sensitive mostly to the projectile-target interactions, but is also affected by the extension of the halo. This suggests the elastic scattering not to be affected by a loss of flux towards the breakup channel.Comment: 11 pages, 3 figures, accepted for publication in Phys. Lett.

Small Effects in Astrophysical Fusion Reactions

We study the combined effects of vacuum polarization, relativity, Bremsstrahlung, and atomic polarization in nuclear reactions of astrophysical interest. It is shown that these effects do not solve the longstanding differences between the experimental data of astrophysical nuclear reactions at very low energies and the theoretical calculations which aim to include electron screening.Comment: 13 pages, 1 figur

Approximations in Fusion and Breakup reactions induced by Radioactive Beams

Some commonly used approximations for complete fusion and breakup transmission coefficients in collisions of weakly bound projectiles at near barrier energies are assessed. We show that they strongly depend on the adopted classical trajectory and can be significantly improved with proper treatment of the incident and emergent currents in the WKB approximation.Comment: 15 pages, 7 figure

Identification of a multi-dimensional space-dependent heat source from boundary data

We investigate the linear but ill-posed inverse problem of determining a multi-dimensional space-dependent heat source in the parabolic heat equation from Cauchy boundary data. This model is important in practical applications where the distribution of internal sources is to be monitored and controlled with care and accuracy from non-invasive and non-intrusive boundary measurements only. The mathematical formulation ensures that a solution of the inverse problem is unique but the existence and stability are still issues to be dealt with. Even if a solution exists it is not stable with respect to small noise in the measured boundary data hence the inverse problem is still ill-posed. The Landweber method is developed in order to restore stability through iterative regularization. Furthermore, the conjugate gradient method is also developed in order to speed up the convergence. An alternating direction explicit finite-difference method is employed for discretising the well-posed problems resulting from these iterative procedures. Numerical results in two-dimensions are illustrated and discussed

Blurred femtoscopy in two-proton decay

We study the effects of final state interactions in two-proton emission by nuclei. Our approach is based on the solution the time-dependent Schr\"odinger equation. We show that the final relative energy between the protons is substantially influenced by the final state interactions. We also show that alternative correlation functions can be constructed showing large sensitivity to the spin of the diproton system.Comment: 5 pages. 4 figures, accepted for publication in Phys. Lett.

Multiphonon and ``hot''-phonon Isovector Electric-Dipole Excitations

We argue that a substantial increase in the cross section for Coulomb excitation in the region of the Double Giant Dipole Resonance should be expected from Coulomb excitation of excited states involved in the spreading of the one-phonon resonance, in a manifestation of the Brink-Axel phenomenon. This generates an additional fluctuating amplitude and a corresponding new term to be added incoherently to the usual cross-section. The appropriate extension of an applicable reaction calculation is considered in order to estimate this effect.Comment: 6 pages, Latex, 1 figure available on reques

SU(2,1) Dynamics of Multiple Giant Dipole Resonance Coulomb Excitation

We construct a three-dimensional analytically soluble model of the nonlinear effects in Coulomb excitation of multiphonon Giant Dipole Resonances (GDR) based on the SU(2,1) algebra. The full 3-dimensional model predicts further enhancement of the Double GDR (DGDR) cross sections at high bombarding energies. Enhancement factors for DGDR measured in thirteen different processes with various projectiles and targets at different bombarding energies are well reproduced with the same value of the nonlinearity parameter with the exception of the anomalous case of $^{136}$Xe which requires a larger value.Comment: 10 pages, 3 Postscript figures, late