A promising energy range to look for angular correlations between cosmic rays of extragalactic origin and their sources is at the highest energies, above a few tens of EeV (1 EeV ≡ 1018 eV). Despite the flux of these particles being extremely low, the area of ∼3000 km2 covered at the Pierre Auger Observatory, and the 17 yr data-taking period of the Phase 1 of its operations, have enabled us to measure the arrival directions of more than 2600 ultra-high-energy cosmic rays above 32 EeV. We publish this data set, the largest available at such energies from an integrated exposure of 122,000 km2 sr yr, and search it for anisotropies over the 3.4π steradians covered with the Observatory. Evidence for a deviation in excess of isotropy at intermediate angular scales, with ∼15° Gaussian spread or ∼25° top-hat radius, is obtained at the 4σ significance level for cosmic-ray energies above ∼40 EeV.

Some industries usually reduce the concentration of protons in acidic wastewater by conducting neutralization reactions and/or adding seawater to industrial effluents. This work proposes a novel electrochemical system that can harvest energy originating from entropic changes due to alteration in the concentration of sodium ions along wastewater treatment. Preparation of a self-assembled material from nickel Prussian blue analogue (NPBA) was the first step to obtain such electrochemical system. Investigation into the electrochemical properties of this material helped to evaluate its potential use in neutralization and mixing entropy batteries. Assessment of parameters such as the potentiodynamic profile of the current density as a function of the concentration of protons and sodium ions, charge capacity, and cyclability as well as the reversibility of the sodium ion electroinsertion process aided estimation of the energy storage efficiency of the system. Frequency-domain measurements and models and the proposed charge compensation mechanism provided the rate constants at different dc potentials. After each charge/discharge cycle, the NPBA electrode harvested 12.4 kJ per mol of intercalated sodium ion in aqueous solutions of NaCl at concentrations of 20 mM and 3.0 M. The full electrochemical cell consisted of an NPBA positive electrode and a negative electrode of silver particles dispersed in a polypyrrole electrode. This cell extracted 16.8 kJ per mol of intercalated ion after each charge/discharge cycle. On the basis of these results, the developed electrochemical system should encourage wastewater treatment and help to achieve sustainable growth.

Detailed simulations of the arrival directions of ultra-high-energy cosmic rays are performed under the assumption of strong and structured extragalactic magnetic field (EGMF) models. Particles leaving Centaurus A, Virgo A, and Fornax A are propagated to Earth, and the simulated anisotropic signal is compared to the dipole and hotspots published by the Pierre Auger and Telescope Array Collaborations. The dominance of the EGMF structure in the arrival directions of events generated in local sources is shown. The absence of events from the Virgo A direction is related to the strong deviation caused by the EGMF. Evidence that these three sources contribute to an excess of events in the direction of the three detected hotspots is presented. Under the EGMF considered here, M82 is shown to have no contribution to the hotspot measured by the Telescope Array Observatory.

Ultra-high-energy photons with energies exceeding 1017 eV offer a wealth of connections to different aspects of cosmic-ray astrophysics as well as to gamma-ray and neutrino astronomy. The recent observations of photons with energies in the 1015 eV range further motivate searches for even higher-energy photons. In this paper, we present a search for photons with energies exceeding 2 × 1017 eV using about 5.5 yr of hybrid data from the low-energy extensions of the Pierre Auger Observatory. The upper limits on the integral photon flux derived here are the most stringent ones to date in the energy region between 1017 and 1018 eV.