LiBeB Production by Nuclei and Neutrinos

The production of LiBeB isotopes by nuclear and neutrino spallation are compared in the framework of galactic evolutionary models. As motivated by $\gamma$-ray observations of Orion, different possible sources of low-energy C and O nuclei are considered, such as supernovae of various masses and WC stars. We confirm that the low energy nuclei (LEN), injected in molecular clouds by stellar winds and type II supernovae originating from the most massive progenitors, can very naturally reproduce the observed Be and B evolution in the early galaxy (halo phase). Assuming the global importance of the LEN component, we compute upper and lower bounds to the neutrino process contribution corresponding to limiting cases of LEN particle spectra. A consistent solution is found with a spectrum of the kind proposed by Ramaty \etal (1995a,b), e.g. flat up to $E_c=30$ MeV/n and decreasing abruptly above. This solution fulfills the challenge of explaining at the same time the general Be and B evolution, and their solar system abundances without overproducing \li7 at very low metallicities, and the meteoritic \b11/\b10 ratio. In this case, neutrino spallation is constrained to play a limited role in the genesis of the solar system \b11. Galactic cosmic rays (GCR) become operative late in the evolution of the disk ([Fe/H]$>$-1), but their contribution to the solar abundances of \be9, \b10 and \b11 is not dominant (35\%, 30\% and 20\% respectively). Thus, with this LEN spectrum, GCR are {\it not}\ the main source of \be9 and B in the Galaxy. The most favorable case for neutrinos, (adopting the same kind of spectrum) has $E_c=20$ MeV/n. Even in this case, the neutrino yields of Woosley and Weaver (1995) must to be reduced by a factor of 5 to avoid \b11 overproduction. Furthermore, this solution leads to a high B/BeComment: 19 pages, 5 postscript figures, uses plain LaTeX, also available at http://www.nd.edu/~bfields/vcfo.htm

Quasi-periodic Oscillations in the X-ray Light Curves from Relativistic Tori

We use a relativistic ray-tracing code to analyze the X-ray emission from a pressure-supported oscillating relativistic torus around a black hole. We show that a strong correlation exists between the {\it intrinsic} frequencies of the torus normal modes and the {\it extrinsic} frequencies seen in the observed light curve power spectrum. This correlation demonstrates the feasibility of the oscillating-torus model to explain the multiple peaks seen in black hole high-frequency quasi-periodic oscillations. Using an optically thin, monochromatic emission model, we also determine how a relativistically broadened emission line and the amplitude of the X-ray modulations are dependent on the observer's inclination angle and on the torus oscillation amplitudes. Observations of these features can provide important information about the torus as well as the black hole.Comment: 4 pages, 3 figures, submitted to ApJ

A Methodology to Engineer and Validate Dynamic Multi-level Multi-agent Based Simulations

This article proposes a methodology to model and simulate complex systems, based on IRM4MLS, a generic agent-based meta-model able to deal with multi-level systems. This methodology permits the engineering of dynamic multi-level agent-based models, to represent complex systems over several scales and domains of interest. Its goal is to simulate a phenomenon using dynamically the lightest representation to save computer resources without loss of information. This methodology is based on two mechanisms: (1) the activation or deactivation of agents representing different domain parts of the same phenomenon and (2) the aggregation or disaggregation of agents representing the same phenomenon at different scales.Comment: Presented at 3th International Workshop on Multi-Agent Based Simulation, Valencia, Spain, 5th June 201

Inert states of spin-S systems

We present a simple but efficient geometrical method for determining the inert states of spin-S systems. It can be used if the system is described by a spin vector of a spin-S particle and its energy is invariant in spin rotations and phase changes. Our method is applicable to an arbitrary S and it is based on the representation of a pure spin state of a spin-S particle in terms of 2S points on the surface of a sphere. We use this method to find candidates for some of the ground states of spinor Bose-Einstein condensates.Comment: 4 pages, 2 figures, minor changes, references added, typos correcte

Electrical transport and low-temperature scanning tunneling microscopy of microsoldered graphene

Using the recently developed technique of microsoldering, we perform a systematic transport study of the influence of PMMA on graphene flakes revealing a doping effect of up to 3.8x10^12 1/cm^2, but a negligible influence on mobility and gate voltage induced hysteresis. Moreover, we show that the microsoldered graphene is free of contamination and exhibits a very similar intrinsic rippling as has been found for lithographically contacted flakes. Finally, we demonstrate a current induced closing of the previously found phonon gap appearing in scanning tunneling spectroscopy experiments, strongly non-linear features at higher bias probably caused by vibrations of the flake and a B-field induced double peak attributed to the 0.Landau level of graphene.Comment: 8 pages, 3 figure