A mini-array for large air showers

A mini-array that utilizes the Linsley effect is proposed for the measurement of large air showers. An estimate of the detectable shower rates for various shower sizes is made. Details of the detection and data collection systems are also described

Radiation Damage Studies of Silicon Photomultipliers

We report on the measurement of the radiation hardness of silicon photomultipliers (SiPMs) manufactured by Fondazione Bruno Kessler in Italy (1 mm$^2$ and 6.2 mm$^2$), Center of Perspective Technology and Apparatus in Russia (1 mm$^2$ and 4.4 mm$^2$), and Hamamatsu Corporation in Japan (1 mm$^2$). The SiPMs were irradiated using a beam of 212 MeV protons at Massachusetts General Hospital, receiving fluences of up to $3 \times 10^{10}$ protons per cm$^2$ with the SiPMs at operating voltage. Leakage currents were read continuously during the irradiation. The delivery of the protons was paused periodically to record scope traces in response to calibrated light pulses to monitor the gains, photon detection efficiencies, and dark counts of the SiPMs. The leakage current and dark noise are found to increase with fluence. Te leakage current is found to be proportional to the mean square deviation of the noise distribution, indicating the dark counts are due to increased random individual pixel activation, while SiPMs remain fully functional as photon detectors. The SiPMs are found to anneal at room temperature with a reduction in the leakage current by a factor of 2 in about 100 days.Comment: 35 pages, 25 figure

Suite of simple metrics reveals common movement syndromes across vertebrate taxa

ecause empirical studies of animal movement are most-often site- and species-specific, we lack understanding of the level of consistency in movement patterns across diverse taxa, as well as a framework for quantitatively classifying movement patterns. We aim to address this gap by determining the extent to which statistical signatures of animal movement patterns recur across ecological systems. We assessed a suite of movement metrics derived from GPS trajectories of thirteen marine and terrestrial vertebrate species spanning three taxonomic classes, orders of magnitude in body size, and modes of movement (swimming, flying, walking). Using these metrics, we performed a principal components analysis and cluster analysis to determine if individuals organized into statistically distinct clusters. Finally, to identify and interpret commonalities within clusters, we compared them to computer-simulated idealized movement syndromes representing suites of correlated movement traits observed across taxa (migration, nomadism, territoriality, and central place foraging)

Post-spinel transformations and equation of state in ZnGa2O4: Determination at high-pressure by in situ x-ray diffraction

Room temperature angle-dispersive x-ray diffraction measurements on spinel ZnGa2O4 up to 56 GPa show evidence of two structural phase transformations. At 31.2 GPa, ZnGa2O4 undergoes a transition from the cubic spinel structure to a tetragonal spinel structure similar to that of ZnMn2O4. At 55 GPa, a second transition to the orthorhombic marokite structure (CaMn2O4-type) takes place. The equation of state of cubic spinel ZnGa2O4 is determined: V0 = 580.1(9) A3, B0 = 233(8) GPa, B0'= 8.3(4), and B0''= -0.1145 GPa-1 (implied value); showing that ZnGa2O4 is one of the less compressible spinels studied to date. For the tetragonal structure an equation of state is also determined: V0 = 257.8(9) A3, B0 = 257(11) GPa, B0'= 7.5(6), and B0''= -0.0764 GPa-1 (implied value). The reported structural sequence coincides with that found in NiMn2O4 and MgMn2O4.Comment: 20 pages, 4 figures, 2 Table

Measurement of the local density spectrum

Since there is still disagreement among the results of various groups, a measurement of the local density spectrum with a close-packed array of four scintillators, each of area 0.14 sq cm was made. Data are taken with conventional electronics, supervised by an on-line microcomputer. The data are stored on audio cassettes and analyzed with the aid of another microcomputer. Since four independent samples for each shower are available, uncertainties inherent in results from many earlier experiments can be minimized

Inhomogeneities on the surface of 21 Lutetia, the asteroid target of the Rosetta mission

CONTEXT: In July 2010 the ESA spacecraft Rosetta will fly-by the main belt asteroid 21 Lutetia. Several observations of this asteroid have been so far performed, but its surface composition and nature are still a matter of debate. For long time Lutetia was supposed to have a metallic nature due to its high IRAS albedo. Later on it has been suggested to have a surface composition similar to primitive carbonaceous chondrite meteorites, while further observations proposed a possible genetic link with more evolved enstatite chondrite meteorites. AIMS: In order to give an important contribution in solving the conundrum of the nature of Lutetia, in November 2008 we performed visible spectroscopic observations of this asteroid at the Telescopio Nazionale Galileo (TNG, La Palma, Spain). METHODS: Thirteen visible spectra have been acquired at different rotational phases. RESULTS: We confirm the presence of a narrow spectral feature at about 0.47-0.48 micron already found by Lazzarin et al. (2009) on the spectra of Lutetia. We also find a spectral feature at about 0.6 micron, detected by Lazzarin et al. (2004) on one of their Lutetia's spectra. More importantly, our spectra exhibit different spectral slopes between 0.6 and 0.75 micron and, in particular, we found that up to 20% of the Lutetia surface could have flatter spectra. CONCLUSIONS: We detected a variation of the spectral slopes at different rotational phases that could be interpreted as possibly due to differences in the chemical/mineralogical composition, as well as to inhomogeneities of the structure of the Lutetia's surface (e.g., the presence of craters or albedo spots) in the southern hemisphere.Comment: 3 pages, 2 figures. Accepted for publication in Astronomy and Astrophysics. Updated on 25 March 2010

Study of a mini-array for the Linsley effect in cosmic-ray air showers

The arrival-time distribution of shower particles far from the core has been measured as a function of shower axis distance at the Akeno Observatory by a cluster of 64 scintillators (total area 16 m2) located near the centre of the 1 km2 array. More than 3500 1 km2 array events and about 300 20 km2 array events have been analysed. The authors compare parameters tau (exponential fit to arrival times), sigma (conventional dispersion) and tr (rise time) for the specification of the spread in arrival times. From a measurement of time spread, the shower axis distance can be determined with an uncertainty of 25 to 30% with this detector system. The resulting uncertainty in shower size, including a 60% uncertainty in particle density measurement, is 120 to 140%. The resultant smearing of changes in slope of the frequency spectrum of incident showers is calculated. The smearing masks all but the gross changes in slope. The method may be useful for anisotropy studies, when a system for finding direction is included.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49016/2/jgv15i1p113.pd