Dipole-dipole dispersion interactions between neutrons

We investigate the long-range interactions between two neutrons utilizing recent data on the neutron static and dynamic electric and magnetic dipole polarizabilities. The resulting long-range potentials are used to make quantitative comparisons between the collisions of a neutron with a neutron and a neutron with a proton. We also assess the importance of the first pion production threshold and first excited state of the nucleon, the $\Delta$-resonance ($J^{\pi}$ = + 3/2, I = 3/2). We found both dynamical effects to be quite relevant for distances r between ~ 50 fm up to ~$10^3$ fm in the nn system, the neutron-wall system and in the wall-neutron-wall system, reaching the expected asymptotic limit beyond that. Relevance of our findings to the confinement of ultra cold neutrons inside bottles is discussed.Comment: 11 pages, 12 figures, Version to be published in the European Physical Journal A (2017

A Semiclassical Approach to Fusion Reactions

The semiclassical method of Alder and Winther is generalized to study fusion reactions. As an illustration, we evaluate the fusion cross section in a schematic two-channel calculation. The results are shown to be in good agreement with those obtained with a quantal Coupled-Channels calculation. We suggest that in the case of coupling to continuum states this approach may provide a simpler alternative to the Continuum Discretized Coupled-Channels method.Comment: 6 pages, 1 figure, invited talk at the International Symposium "A new era of Nuclear Structure Physics", Niigata, Japan, Nov. 19-22 200

A consistent four-body CDCC model of low-energy reactions: Application to 9Be + 208Pb

We investigate the $^9$Be + $^{208}$Pb elastic scattering, breakup and fusion at energies around the Coulomb barrier. The three processes are described simultaneously, with identical conditions of calculations. The $^{9}$Be nucleus is defined in an $\alpha + \alpha$ + n three-body model, using the hyperspherical coordinate method. We first analyze spectroscopic properties of $^9$Be, and show that the model provides a fairly good description of the low-lying states. The scattering with $^{208}$Pb is then studied with the Continuum Discretized Coupled Channel (CDCC) method, where the $\alpha+\alpha$ + n continuum is approximated by a discrete number of pseudostates. Optical potentials for the $\alpha$+ $^{208}$Pb and n+ $^{208}$Pb systems are taken from the literature. We present elastic-scattering and fusion cross sections at different energies.Comment: 8 pages, 3 figures, Proceedings of the International Conference on Nucleus-Nucleus Collisions, NN 2015, Catania-Italy. arXiv admin note: substantial text overlap with arXiv:1410.641

Transverse Isotropy in Identical Particle Scattering

It is pointed out that the cross section for the scattering of identical charged bosons is isotropic over a broad angular range around 90 degrees when the Sommerfeld parameter has a critical value, which depends exclusively on the spin of the particle. A discussion of systems where this phenomenon can be observed is presented.Comment: 8 pages, RevTeX format, 2 figures (.eps format

Improved WKB approximation for quantum tunneling: Application to heavy ion fusion

In this paper we revisit the one-dimensional tunneling problem. We consider Kemble's approximation for the transmission coefficient. We show how this approximation can be extended to above-barrier energies by performing the analytical continuation of the radial coordinate to the complex plane. We investigate the validity of this approximation by comparing their predictions for the cross section and for the barrier distribution with the corresponding quantum mechanical results. We find that the extended Kemble's approximation reproduces the results of quantum mechanics with great accuracy.Comment: 8 pages, 6 figures, in press, in European. Phys. Journal A (2017

Bone mechanical properties in healthy and diseased states

The mechanical properties of bone are fundamental to the ability of our skeletons to support movement and to provide protection to our vital organs. As such, deterioration in mechanical behavior with aging and/or diseases such as osteoporosis and diabetes can have profound consequences for individuals’ quality of life. This article reviews current knowledge of the basic mechanical behavior of bone at length scales ranging from hundreds of nanometers to tens of centimeters. We present the basic tenets of bone mechanics and connect them to some of the arcs of research that have brought the field to recent advances. We also discuss cortical bone, trabecular bone, and whole bones, as well as multiple aspects of material behavior, including elasticity, yield, fracture, fatigue, and damage. We describe the roles of bone quantity (e.g., density, porosity) and bone quality (e.g., cross-linking, protein composition), along with several avenues of future research.Author manuscrip

Approximate transmission coefficients in heavy ion fusion

In this paper we revisit the one-dimensional tunnelling problem. We consider different approximations for the transmission through the Coulomb barrier in heavy ion collisions at near-barrier energies. First, we discuss approximations of the barrier shape by functional forms where the transmission coefficient is known analytically. Then, we consider Kemble's approximation for the transmission coefficient. We show how this approximation can be extended to above-barrier energies by performing the analytical continuation of the radial coordinate to the complex plane. We investigate the validity of the different approximations considered in this paper by comparing their predictions for transmission coefficients and cross sections of three heavy ion systems with the corresponding quantum mechanical results.Comment: 12 pages, 6 figure