Comparison of available measurements of the absolute fluorescence yield

The uncertainty in the absolute value of the fluorescence yield is still one of the main contributions to the total error in the reconstruction of the primary energy of ultra-energetic air showers using the fluorescence technique. A significant number of experimental values of the fluorescence yield have been published in the last years, however reported results are given very often in different units (photons/MeV or photons/m) and for different wavelength intervals. In this work we present a comparison of available results normalized to its value in photons/MeV for the 337 nm band at 800 hPa and 293 K. The conversion of photons/m to photons/MeV requires an accurate determination of the energy deposited by the electrons in the field of view of the experimental setup. We have calculated the energy deposition for each experiment by means of a detailed Monte Carlo simulation including when possible the geometrical details of the particular setup. Our predictions on deposited energy, as well as on some geometrical factors, have been compared with those reported by the authors of the corresponding experiments and possible corrections to the fluorescence yields are proposed.Comment: 29 pages, 5 figures Revised version submitted to Astroparticle Physic

Error Estimates on Parton Density Distributions

Error estimates on parton density distributions are presently based on the traditional method of least squares minimisation and linear error propagation in global QCD fits. We review the underlying assumptions and the various mathematical representations of the method and address some technical issues encountered in such a global analysis. Parton distribution sets which contain error information are described.Comment: Latex, 12 pages, 5 figures. Needs iopart.cls and iopart12.clo. Presented at New Trends in HERA Physics 2001, Ringberg Castle, Tegernsee, Germany, June 17-22, 200

Improved model for the analysis of air fluorescence induced by electrons

A model recently proposed for the calculation of air-fluorescence yield excited by electrons is revisited. Improved energy distributions of secondary electrons and a more realistic Monte Carlo simulation including some additional processes have allowed us to obtain more accurate results. The model is used to study in detail the relationship between fluorescence intensity and deposited energy in a wide range of primary energy (keVs - GeVs). In addition, predictions on the absolute value of the fluorescence efficiency in the absence of collisional quenching will be presented and compared with available experimental data.Comment: Contribution to the 5th Fluorescence Workshop, El Escorial, Madrid, Spain, September 2007, to appear in Nuclear Instruments and Methods A. Revised version.- More details on the comparison with experimental dat

MACiE: a database of enzyme reaction mechanisms.

SUMMARY: MACiE (mechanism, annotation and classification in enzymes) is a publicly available web-based database, held in CMLReact (an XML application), that aims to help our understanding of the evolution of enzyme catalytic mechanisms and also to create a classification system which reflects the actual chemical mechanism (catalytic steps) of an enzyme reaction, not only the overall reaction. AVAILABILITY: http://www-mitchell.ch.cam.ac.uk/macie/.EPSRC (G.L.H. and J.B.O.M.), the BBSRC (G.J.B. and J.M.T.—CASE studentship in association with Roche Products Ltd; N.M.O.B. and J.B.O.M.—grant BB/C51320X/1), the Chilean Government’s Ministerio de Planificacio´n y Cooperacio´n and Cambridge Overseas Trust (D.E.A.) for funding and Unilever for supporting the Centre for Molecular Science Informatics.application note restricted to 2 printed pages web site: http://www-mitchell.ch.cam.ac.uk/macie

On UHECR energy estimation algorithms based on the measurement of electromagnetic component parameters in EAS

Model calculations are performed of extensive air shower (EAS) component energies using a variety of hadronic interaction parameters. A conversion factor from electromagnetic component energy to the energy of ultra-high energy cosmic rays (UHECRs) and its model and primary mass dependence is studied. It is shown that model dependence of the factor minimizes under the necessary condition of the same maximum position and muon content of simulated showers.Comment: contracted version is accepted for publication in Doklady Physic

Percolation and high energy cosmic rays above 101710^{17} eV

In this work we argue that, in the interpretation of the energy dependence of the depth of the shower maximum and of the muon content in high energy cosmic ray showers ($E > 10^{17}$ eV), other variables besides the composition may play an important role, in particular those characterising the first (high energy) hadronic collisions. The role of the inelasticity, of the nature of the leading particle, and of the particle multiplicity are discussed. A consistent interpretation of existing data within a string percolation model implemented in a hybrid, one dimensional simulation method is given.Comment: 15 pages, 6 eps figure