Complexity Bounds for Ordinal-Based Termination

`What more than its truth do we know if we have a proof of a theorem in a given formal system?' We examine Kreisel's question in the particular context of program termination proofs, with an eye to deriving complexity bounds on program running times. Our main tool for this are length function theorems, which provide complexity bounds on the use of well quasi orders. We illustrate how to prove such theorems in the simple yet until now untreated case of ordinals. We show how to apply this new theorem to derive complexity bounds on programs when they are proven to terminate thanks to a ranking function into some ordinal.Comment: Invited talk at the 8th International Workshop on Reachability Problems (RP 2014, 22-24 September 2014, Oxford

Elastic scattering with weakly bound projectiles

Possible effects of the break-up channel on the elastic scattering threshold anomaly has been investigated. We used the weakly bound 6,7Li nuclei, which is known to undergo break-up, as projectiles in order to study the elastic scattering on a 27Al target. In this contribution we present preliminary results of these experiments, which were analyzed in terms of the Optical Model and compared with other elastic scattering data using weakly bound nuclei as projectile. © 2007 American Institute of Physics.Fil:Figueira, J.M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Fernández Niello, J.O. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Arazi, A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Capurro, O.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Martí, G.V. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Pacheco, A.J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

9^9Be+120^{120}Sn scattering at near-barrier energies within a four body model

Cross sections for elastic and inelastic scattering of the weakly-bound $^9$Be nucleus on a $^{120}$Sn target have been measured at seven bombarding energies around and above the Coulomb barrier. The elastic angular distributions are analyzed with a four-body continuum-discretized coupled-channels (CDCC) calculation, which considers $^9$Be as a three-body projectile ($\alpha$ + $\alpha$ + n). An optical model analysis using the S\~ao Paulo potential is also shown for comparison. The CDCC analysis shows that the coupling to the continuum part of the spectrum is important for the agreement with experimental data even at energies around the Coulomb barrier, suggesting that breakup is an important process at low energies. At the highest incident energies, two inelastic peaks are observed at 1.19(5) and 2.41(5) MeV. Coupled-channels (CC) calculations using a rotational model confirm that the first inelastic peak corresponds to the excitation of the 2$_1^+$ state in $^{120}$Sn, while the second one likely corresponds to the excitation of the 3$_1^-$ state.Comment: 11 pages, 9 figures. Accepted as PR

Experimental Search for Solar Axions via Coherent Primakoff Conversion in a Germanium Spectrometer

Results are reported of an experimental search for the unique, rapidly varying temporal pattern of solar axions coherently converting into photons via the Primakoff effect in a single crystal germanium detector. This conversion is predicted when axions are incident at a Bragg angle with a crystalline plane. The analysis of approximately 1.94 kg.yr of data from the 1 kg DEMOS detector in Sierra Grande, Argentina, yields a new laboratory bound on axion-photon coupling of $g_{a\gamma \gamma} < 2.7\cdot 10^{-9}$ GeV$^{-1}$, independent of axion mass up to ~ 1 keV.Comment: RevTeX, 11 pages, figures can be obtained by fax from [email protected]. Submitted to Phys. Lett.

A Decommissioned LHC Model Magnet as an Axion Telescope

The 8.4 Tesla, 10 m long transverse magnetic field of a twin aperture LHC bending magnet can be utilized as a macroscopic coherent solar axion-to-photon converter. Numerical calculations show that the integrated time of alignment with the Sun would be 33 days per year with the magnet on a tracking table capable of $\pm 5^o$ in the vertical direction and $\pm 40^o$ in the horizontal direction. The existing lower bound on the axion-to-photon coupling constant can be improved by a factor between 50 and 100 in 3 years, i.e., $g_{a\gamma\gamma} \lesssim 9\cdot 10^{-11} GeV^{-1}$ for axion masses $\lesssim$ 1 eV. This value falls within the existing open axion mass window. The same set-up can simultaneously search for low- and high-energy celestial axions, or axion-like particles, scanning the sky as the Earth rotates and orbits the Sun.Comment: Final version, accepted for publication in Nucl. Instr. Meth. A. More information can be found at http://wwwinfo.cern.ch/~collar/SATAN/alvaro.htm

Effect of carbon starvation on toluene degradation activity by toluene monooxygenase-expressing bacteria

Subsurface bacteria commonly exist in a starvation state with only periodic exposure to utilizable sources of carbon and energy. In this study, the effect of carbon starvation on aerobic toluene degradation was quantitatively evaluated with a selection of bacteria representing all the known toluene oxygenase enzyme pathways. For all the investigated strains, the rate of toluene biodegradation decreased exponentially with starvation time. First-order deactivation rate constants for TMO-expressing bacteria were approximately an order of magnitude greater than those for other oxygenase-expressing bacteria. When growth conditions (the type of growth substrate and the type and concentration of toluene oxygenase inducer) were varied in the cultures prior to the deactivation experiments, the rate of deactivation was not significantly affected, suggesting that the rate of deactivation is independent of previous substrate/inducer conditions. Because TMO-expressing bacteria are known to efficiently detoxify TCE in subsurface environments, these findings have significant implications for in situ TCE bioremediation, specifically for environments experiencing variable growth-substrate exposure conditions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45353/1/10532_2005_Article_9014.pd

Development of a Reference Database for Ion Beam Analysis: Report of a Coordinated Research Project on Reference Database for Ion Beam Analysis

Ion beam analysis (IBA) includes modern analytical techniques involving the use of energetic ion beams to probe the composition of the surface layers of solids. Major areas of application include microelectronics, cultural heritage, forensics, biology and materials sciences. The underlying science for IBA is the physics of the interactions between the ions in the beam and the atoms in the solid. Emission products from the interaction of charged particles with matter are measured, and specialized simulation and data analysis software provide information on the material composition. Although the basic physical processes are well understood, the reliability of data interpretation is limited by the knowledge of the physical data. The primary quantities required are the stopping powers describing the slowing of the ion in the material and the cross-sections of the interactions involved. The need for reliable data on stopping powers is adequately catered for by Stopping and Range of Ions in Matter (SRIM) computer code. The situation, however, is quite different for cross-sections for nuclear reactions and non- Rutherford elastic scattering. Although there is a considerable body of published data in nuclear physics literature, examination of the unevaluated experimental data has revealed numerous discrepancies beyond the error limits reported by the authors. The lack of reliable cross-sections has been recognized by the IBA community and has been discussed at several workshops and IAEA meetings, resulting in various recommendations including the organization of a coordinated research project (CRP) on a reference database for IBA. The main objective of the CRP was to develop a reference database for IBA that contains reliable and usable data that will be made freely available to the user community. Starting from the existing collection of data in the IAEA Ion Beam Analysis Nuclear Data Library (IBANDL), the CRP focused exclusively on the relevant nuclear cross-sections (nuclear reactions and non-Rutherford elastic scattering). During the course of the CRP, however, it was soon realized that there was also a growing demand for compilation and evaluation of nuclear reactions with gamma rays in the exit channel, which are used in the particle induced gamma ray emission technique. The recommendations led to a second CRP on the development of a reference database for particle induced gamma ray emission spectroscopy. The output of which will be published in a forthcoming IAEA publication. The IAEA wishes to thank all the participants of the CRP for their contributions to IBANDL and to this publication. The IAEA officers responsible for this publication were D. Abriola and P. Dimitriou of the Division of Physical and Chemical Sciences.</p