Characteristics of geomagnetic cascading of ultra-high energy photons at the southern and northern sites of the Pierre Auger Observatory

Cosmic-ray photons above 10^19 eV can convert in the geomagnetic field and initiate a preshower, i.e. a particle cascade before entering the atmosphere. We compare the preshower characteristics at the southern and northern sites of the Pierre Auger Observatory. In addition to a shift of the preshower patterns on the sky due to the different pointing of the local magnetic field vectors, the fact that the northern Auger site is closer to the geomagnetic pole results in a different energy dependence of the preshower effect: photon conversion can start at smaller energies, but large conversion probabilitites (>90%) are reached for the whole sky at higher energies compared to the southern Auger site. We show how the complementary preshower features at the two sites can be used to search for ultra-high energy photons among cosmic rays. In particular, the different preshower characteristics at the northern Auger site may provide an elegant and unambiguous confirmation if a photon signal is detected at the southern site.Comment: 25 pages, 14 figures, minor changes, conclusions unchanged, Appendix A replaced, accepted by Astroparticle Physic

The nature of the highest energy cosmic rays

Ultra high energy gamma rays produce electron--positron pairs in interactions on the geomagnetic field. The pair electrons suffer magnetic bremsstrahlung and the energy of the primary gamma ray is shared by a bunch of lower energy secondaries. These processes reflect the structure of the geomagnetic field and cause experimentally observable effects. The study of these effects with future giant air shower arrays can identify the nature of the highest energy cosmic rays as either gamma-rays or nuclei.Comment: 15 pages of RevTeX plus 6 postscript figures, tarred, gzipped and uuencoded. Subm. to Physical Review

Resistive Plate Chambers with Gd-coated electrodes as thermal neutron detectors

Abstract Resistive Plate Chambers (RPCs) are wide spread, cheap, easy-to-build and large size detectors, used mainly to reveal ionising particles in high-energy physics experiments. Here a technique, consisting in coating the inner surface of the bakelite electrodes with a mixture of linseed oil and Gd 2 O 3 is reported. This allows to make RPCs sensitive also to thermal neutrons, making them suitable to be employed for industrial, medical or de-mining applications. Thermal neutron-sensitive RPCs can be operated at atmospheric pressure, are lightweighted, have low γ -ray sensitivity and are easy to handle even when large areas have to be covered. This paper reports the results of the first test of this detector, performed at the Geel Linear Accelerator (GELINA) in Belgium

e+e−e^+e^- Pair Production from 10 GeV to 10 ZeV

At very high energies, pair production ($\gamma\to e^+e^-$) exhibits many interesting features. The momentum transfer from the target is very small, so the reaction probes the macroscopic properties of the target, rather than individual nuclei. Interference between interactions with different atoms reduces the pair production cross section considerably below the Bethe-Heitler values. At very high energies, photonuclear interactions may outnumber pair production. In contrast, in crystals, the interaction amplitudes may add coherently, greatly increasing the cross sections. Pair production in matter-free magnetic fields is also possible. The highest energy pair production occurs at high energy particle colliders. This article will compare pair production in these very different regimes.Comment: 37 pages with 9 figures. Invited Review for "Radiation Physics and Chemistry" Version for publication, incorporating comments by the referee, and by Gerhard Baur and Roman Le

Microbial community diversity in anaerobic reactors digesting turkey, chicken, and swine wastes

© 2014 by The Korean Society for Microbiology and Biotechnology. The microbial community structures of two continuous stirred tank reactors digesting turkey manure with pine wood shavings as well as chicken and swine manure were investigated. The reactor fed with chicken/swine wastes displayed the highest organic acids concentration (up to 15.2 g/l) and ammonia concentration (up to 3.7 g/l ammonium nitrogen) and generated a higher biogas yield (up to 366 ml/gVS) compared with the reactor supplied with turkey wastes (1.5– 1.8 g/l of organic acids and 1.6–1.7 g/l of ammonium levels; biogas yield was up to 195 ml/gVS). The microbial community diversity was assessed using both sequencing and profiling terminal restriction fragment length polymorphisms of 16S rRNA genes. Additionally, methanogens were analyzed using methyl coenzyme M reductase alpha subunit (mcrA) genes. The bacterial community was dominated by members of unclassified Clostridiales with the prevalence of specific clostridial phylotypes in each reactor, indicating the effect of the substrate type on the community structure. Of the methanogenic archaea, methanogens of the genus Methanosarcina were found in high proportions in both reactors with specific methanosarcinas in each reactor, whereas the strict hydrogenotrophic methanogens of Methanoculleus sp. were found at significant levels only in the reactor fed with chicken/swine manure (based on the analyses of 16S rRNA gene). This suggests that among methanogenic archaea, Methanosarcina species which have different metabolic capabilities, including aceticlastic and hydrogenotrophic methanogenesis, were mainly involved in anaerobic digestion of turkey wastes

Comparative Analysis of Bacterial Communities Associated with Healthy and Inflamed Peri-implant Tissues

© 2016, Springer Science+Business Media New York.Dental implants are used to restore dentition defects. However, despite the high efficiency of the method of placing dental implants, their integration can be accompanied by peri-implant diseases (peri-implant mucositis and peri-implantitis), which are inflammatory reactions induced by the bacterial activity. In the present pilot study, we described and compared the bacterial communities associated with healthy and inflamed peri-implant mucosal tissues using 16S rRNA gene amplicon pyrosequencing approach. It was revealed that various representatives of the phyla Firmicutes, Bacteroidetes, Fusobacteria, and Proteobacteria were found at significant levels in healthy and peri-implant mucositis sites but in different proportions. Furthermore, it was shown that the genus Fusobacterium was the only group present in higher proportions on inflamed tissues than on healthy tissues surrounding dental implants of all patients. In addition, unclassified Methylobacteriaceae and the genus Veillonella as well as some other phylotypes were present at higher levels in peri-implant mucositis sites of some patients. This study indicates that several microbial agents may play important roles during the development of oral peri-implant diseases

Lorentz invariance violation in top-down scenarios of ultrahigh energy cosmic ray creation

The violation of Lorentz invariance (LI) has been invoked in a number of ways to explain issues dealing with ultrahigh energy cosmic ray (UHECR) production and propagation. These treatments, however, have mostly been limited to examples in the proton-neutron system and photon-electron system. In this paper we show how a broader violation of Lorentz invariance would allow for a series of previously forbidden decays to occur, and how that could lead to UHECR primaries being heavy baryonic states or Higgs bosons.Comment: Replaced with heavily revised (see new Abstract) version accepted by Phys. Rev. D. 6 page

Threshold analyses and Lorentz violation

In the context of threshold investigations of Lorentz violation, we discuss the fundamental principle of coordinate invariance, the role of an effective dynamical framework, and the conditions of positivity and causality. Our analysis excludes a variety of previously considered Lorentz-breaking parameters and opens an avenue for viable dispersion-relation investigations of Lorentz violation.Comment: 9 page

First bounds on the very high energy gamma-ray emission from Arp 220

Using the Major Atmospheric Gamma Imaging Cherenkov Telescope (MAGIC), we have observed the nearest ultra-luminous infrared galaxy Arp 220 for about 15 hours. No significant signal was detected within the dedicated amount of observation time. The first upper limits to the very high energy $\gamma$-ray flux of Arp 220 are herein reported and compared with theoretical expectations.Comment: Accepted for publication in Ap