An extremely energetic cosmic ray observed by a surface detector array.

Cosmic rays are energetic charged particles from extraterrestrial sources, with the highest-energy events thought to come from extragalactic sources. Their arrival is infrequent, so detection requires instruments with large collecting areas. In this work, we report the detection of an extremely energetic particle recorded by the surface detector array of the Telescope Array experiment. We calculate the particle's energy as [Formula: see text] (~40 joules). Its arrival direction points back to a void in the large-scale structure of the Universe. Possible explanations include a large deflection by the foreground magnetic field, an unidentified source in the local extragalactic neighborhood, or an incomplete knowledge of particle physics.

Indications of proton-dominated cosmic-ray composition above 1.6 EeV.

We report studies of ultrahigh-energy cosmic-ray composition via analysis of depth of air shower maximum (X(max)), for air shower events collected by the High-Resolution Fly's Eye (HiRes) observatory. The HiRes data are consistent with a constant elongation rate d/d[log(E)] of 47.9+/-6.0(stat)+/-3.2(syst) g/cm2/decade for energies between 1.6 and 63 EeV, and are consistent with a predominantly protonic composition of cosmic rays when interpreted via the QGSJET01 and QGSJET-II high-energy hadronic interaction models. These measurements constrain models in which the galactic-to-extragalactic transition is the cause of the energy spectrum ankle at 4x10(18) eV.

First observation of the Greisen-Zatsepin-Kuzmin suppression.

The High Resolution Fly's Eye (HiRes) experiment has observed the Greisen-Zatsepin-Kuzmin suppression (called the GZK cutoff) with a statistical significance of five standard deviations. HiRes' measurement of the flux of ultrahigh energy cosmic rays shows a sharp suppression at an energy of 6 x 10(19) eV, consistent with the expected cutoff energy. We observe the ankle of the cosmic-ray energy spectrum as well, at an energy of 4 x 10(18) eV. We describe the experiment, data collection, and analysis and estimate the systematic uncertainties. The results are presented and the calculation of the statistical significance of our observation is described.

Evaluation of X-ray beam angulation for successful twin canal identification in mandibular incisors.

This study was undertaken to determine the most effective horizontal beam angulation for the diagnosis of twin canals in mandibular incisors. Two hundred extracted mandibular incisor teeth, in groups of four, were aligned in the form of a lower dental arch and radiographed using a beam alignment device at 10 degrees intervals between 0 degree and 50 degrees from both right and left sides. Five observers with varying degrees of experience were asked to assess the number of canals in each of the four teeth from these radiographs. A further radiograph of each individual tooth was taken at 90 degrees through the mesio-distal plane to identify the number of twin canals present. A random sample of 10% of the radiographs were viewed for a second time 3 months later to assess intra-observer variation. The 20 degrees right and 30 degrees left horizontal beam angulations showed significantly more accurate diagnosis of twin canals than the ortho-radial view (0 degree) by all five observers. Analysis of the inter-observer results suggests that the experienced viewers were no better but more consistent at identifying twin canals in mandibular incisors.