An N-body Integrator for Gravitating Planetary Rings, and the Outer Edge of Saturn's B Ring

A new symplectic N-body integrator is introduced, one designed to calculate the global 360 degree evolution of a self-gravitating planetary ring that is in orbit about an oblate planet. This freely-available code is called epi_int, and it is distinct from other such codes in its use of streamlines to calculate the effects of ring self-gravity. The great advantage of this approach is that the perturbing forces arise from smooth wires of ring matter rather than discreet particles, so there is very little gravitational scattering and so only a modest number of particles are needed to simulate, say, the scalloped edge of a resonantly confined ring or the propagation of spiral density waves. The code is applied to the outer edge of Saturn's B ring, and a comparison of Cassini measurements of the ring's forced response to simulations of Mimas' resonant perturbations reveals that the B ring's surface density at its outer edge is 195+-60 gm/cm^2 which, if the same everywhere across the ring would mean that the B ring's mass is about 90% of Mimas' mass. Cassini observations show that the B ring-edge has several free normal modes, which are long-lived disturbances of the ring-edge that are not driven by any known satellite resonances. Although the mechanism that excites or sustains these normal modes is unknown, we can plant such a disturbance at a simulated ring's edge, and find that these modes persist without any damping for more than ~10^5 orbits or ~100 yrs despite the simulated ring's viscosity of 100 cm^2/sec. These simulations also indicate that impulsive disturbances at a ring can excite long-lived normal modes, which suggests that an impact in the recent past by perhaps a cloud of cometary debris might have excited these disturbances which are quite common to many of Saturn's sharp-edged rings.Comment: 55 pages, 13 figures, accepted for publication in the Astrophysical Journa

A Relativistic Symmetry in Nuclei: Its origins and consequences

We review the status of quasi-degenerate doublets in nuclei, called pseudospin doublets, which were discovered about thirty years ago and the origins of which have remained a mystery, until recently. We show that pseudospin doublets originate from an SU(2) symmetry of the Dirac Hamiltonian which occurs when the sum of the scalar and vector potentials is a constant. Furthermore, we survey the evidence that pseudospin symmetry is approximately conserved in nuclear spectra and eigenfunctions and in nucleon-nucleus scattering for a Dirac Hamiltonian with realistic nuclear scalar and vector potentials.Comment: Invited Talk for "Nuclei and Nucleons", Darmstadt, Germany, Oct. 11-13,2000; International Symposium on the occasion of Achim Richter's 60th Birthda

Index to Library Trends Volume 14

published or submitted for publicatio

Managing the Faustian bargain: monetary autonomy in the pursuit of development in Eastern Europe and Latin America

International capital markets have grown to be a major force shaping today's world economy, presenting a range of opportunities and threats to developing countries. Capital market liberalization created large pools of much-needed capital that developing economies could access, but tapping these funds often came at the cost of increasing economic vulnerability, lost policy-making autonomy and a range of structural distortions that could ultimately undermine development in the long-term. As the potential threats of integrating one's country into global capital markets has become apparent, countries have devised a range of strategies to buffer themselves from the strains of global capital markets. This article considers the pursuit of monetary autonomy with reference to a typology of the strategies that policy-makers can use to open their markets to international capital, while simultaneously attempting to buffer themselves from the economic and political pressures of global financial integration. Such autonomy can be purchased in a myriad of ways, and a discussion of the choices facing Latin American and Eastern European countries is presented.capital market liberalization; monetary autonomy; financial policy; financial system stability

Critical Points in Nuclei and Interacting Boson Model Intrinsic States

We consider properties of critical points in the interacting boson model, corresponding to flat-bottomed potentials as encountered in a second-order phase transition between spherical and deformed $\gamma$-unstable nuclei. We show that intrinsic states with an effective $\beta$-deformation reproduce the dynamics of the underlying non-rigid shapes. The effective deformation can be determined from the the global minimum of the energy surface after projection onto the appropriate symmetry. States of fixed $N$ and good O(5) symmetry projected from these intrinsic states provide good analytic estimates to the exact eigenstates, energies and quadrupole transition rates at the critical point.Comment: 10 pages, 3 figures, Proc. Int. Conf. on "Symmetry in Physics", March 23-30, 2003, Erice, Ital

All-optical photochromic spatial light modulators based on photoinduced electron transfer in rigid matrices

A single material (not a multi-element structure) spatial light modulator may be written to, as well as read out from, using light. The device has tailorable rise and hold times dependent on the composition and concentration of the molecular species used as the active components. The spatial resolution of this device is limited only by light diffraction as in volume holograms. The device may function as a two-dimensional mask (transmission or reflection) or as a three-dimensional volume holographic medium. This device, based on optically-induced electron transfer, is able to perform incoherent to coherent image conversion or wavelength conversion over a wide spectral range (ultraviolet, visible, or near-infrared regions)