The composition of ultra-high-energy cosmic rays is measured with the High Resolution Fly's Eye cosmic-ray observatory data using the X max technique. Data were collected in stereo between 1999 November and 2001 September. The data are reconstructed with well-determined geometry. Measurements of the atmospheric transmission are incorporated in the reconstruction. The detector resolution is found to be 30 g cm À2 in X max and 13% in energy. The X max elongation rate between 10 18.0 and 10 19.4 eV is measured to be 54:5 AE 6:5 stat ð Þ AE 4:5 sys ð Þg cm À2 per decade. This is compared with predictions using the QGSJet01 and SIBYLL 2.1 hadronic interaction models for both protons and iron nuclei. CORSIKA-generated extensive air showers are incorporated directly into a detailed detector Monte Carlo program. The elongation rate and the X max distribution widths are consistent with a constant or slowly changing and predominantly light composition. A simple model containing only protons and iron nuclei is compared with QGSJet and SIBYLL. The best agreement between the model and the data is for 80% protons for QGSJet and 60% protons for SIBYLL. Subject headingg s: acceleration of particles -cosmic rays -large-scale structure of universe

Diffusion in face-centered cubic (fcc) opals synthesized from 250 nm-diameter silica spheres was investigated by electrochemical methods and finite-element simulations. Opal modified electrodes (OME) ((111) opal surface orientation) were prepared by thermal evaporation of Au onto ∼1 mm-thick opals. Linear sweep voltammetry of Au OMEs in aqueous solutions containing an electroactive molecule and a supporting electrolyte (0.1 M Na 2 SO 4 ) was used to determine molecular diffusion coefficients, D fcc , within the opal. D fcc is related to the diffusion coefficient of the molecule in free solution, D sol , by the relationship D fcc , ) (E/τ)D sol , where E is the interstitial volume fraction of a fcc opal (E ) 0.260 for an infinitely thick opal) and τ is the tortuosity; the tortuosity reflects the increased distance traversed by molecules as they diffuse through the curved interstitial spaces of the opal lattice, and is a function of both the direction of transport relative to the lattice and the number of layers of spheres in the opal lattice. Finite-element simulations are used to compute τ for transport orthogonal to the (111), (110), and (100) surface orientations for 1−7 layers of spheres. Values of τ ) 1.9 ± 0.7 and 3.1 ± 1.2 were obtained from experiment for transport of Ru(NH) 6 3+ and Fe(CN) 6 4-normal to the (111) surface, respectively, in reasonable agreement with a value of ∼3.0 obtained from the simulation.Introduction. The recent interest in opals comprising a closepacked face center cubic (fcc) lattice of spheres (typically SiO 2 or polystyrene of submicrometer radius) is due, in part, to their application in the synthesis of photonic crystals, 1-10 energy storage media, 11-14 novel magnetic materials, 15-17 and sensors. 18 These materials are typically prepared by infusion or diffusional transport of precursor species through the opal lattice, followed by removal of the spheres to create an inverted opal structure. 1,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] Molecular transport occurs within the tortuous interstitial spaces of the opal, Figure 1. Based on geometric factors alone, the effective diffusivity of molecules within the fcc lattice of spheres, D fcc , can be related to the diffusivitiy of molecules in free space, D sol , by eq 1:

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We have searched for correlations between the pointing directions of ultrahigh energy cosmic rays observed by the High Resolution Fly's Eye experiment and Active Galactic Nuclei (AGN) visible from its northern hemisphere location. No correlations, other than random correlations, have been found. We report our results using search parameters prescribed by the Pierre Auger collaboration. Using these parameters, the Auger collaboration concludes that a positive correlation exists for sources visible to their southern hemisphere location. We also describe results using two methods for determining the chance probability of correlations: one in which a hypothesis is formed from scanning one half of the data and tested on the second half, and another which involves a scan over the entire data set. The most significant correlation found occurred with a chance probability of 24%.

Data taken in stereo mode by the High Resolution Fly's Eye (HiRes) air fluorescence experiment are analyzed to search for correlations between the arrival directions of ultrahigh-energy cosmic rays with the positions of BL Lacertae objects. Several previous claims of significant correlations between BL Lac objects and cosmic rays observed by other experiments are tested. These claims are not supported by the HiRes data. However, we verify a recent analysis of correlations between HiRes events and a subset of confirmed BL Lac objects from the 10th Veron Catalog, and we study this correlation in detail. Due to the a posteriori nature of the search, the significance level cannot be reliably estimated and the correlation must be tested independently before any claim can be made. We identify the precise hypotheses that will be tested with statistically independent data.