A Search for Photons with Energies Above 2X10(17) eV Using Hybrid Data from the Low-Energy Extensions of the Pierre Auger Observatory

Ultra-high-energy photons with energies exceeding 10(17) 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 10(15) eV range further motivate searches for even higher-energy photons. In this paper, we present a search for photons with energies exceeding 2 x 10(17) 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 10(17) and 10(18) eV

Middle East - North Africa and the millennium development goals : implications for German development cooperation

          Closed-loop controlled combustion is a promising technique to improve the overall performance of internal combustion engines and Diesel engines in particular. In order for this technique to be implemented some form of feedback from the combustion process is required. The feedback signal is processed and from it combustionrelated parameters are computed. These parameters are then fed to a control process which drives a series of outputs (e.g. injection timing in Diesel engines) to control their values. This paper’s focus lies on the processing and computation that is needed on the feedback signal before this is ready to be fed to the control process as well as on the electronics necessary to support it. A number of feedback alternatives are briefly discussed and for one of them, the in-cylinder pressure sensor, the CA50 (crank angle in which the integrated heat release curve reaches its 50% value) and the IMEP (Indicated Mean Effective Pressure) are identified as two potential control variables. The hardware architecture of a system capable of calculating both of them on-line is proposed and necessary feasibility size and speed considerations are made by implementing critical blocks in VHDL targeting a flash-based Actel ProASIC3 automotive-grade FPGA

On the Mechanisms of Hydrogen Spillover in MoO3

Hydrogen spillover on the MoO3 (010) surface in the presence of a platinum catalyst was modeled using periodic density functional theory (DFT). The migration of H from a saturated Pt6 cluster to the MoO3(010)surface was found to undergo a transition from repulsive electrostatic to attractive proton-oxygen interactions. The hydrogen is able to move nearly freely on the surface and diffuse into the bulk lattice at ambient temperatures, leading to the formation of hydrogen molybdenum bronze. We show that the high proton mobility is largely attributed to the massive H-bonding network in the MoO3 lattice.Hydrogen spillover on the MoO3 (010) surface in the presence of a platinum catalyst was modeled using periodic density functional theory (DFT). The migration of H from a saturated Pt6 cluster to the MoO3(010)surface was found to undergo a transition from repulsive electrostatic to attractive proton-oxygen interactions. The hydrogen is able to move nearly freely on the surface and diffuse into the bulk lattice at ambient temperatures, leading to the formation of hydrogen molybdenum bronze. We show that the high proton mobility is largely attributed to the massive H-bonding network in the MoO3 lattice

Hydrogen Absorption and Diffusion in Bulk α-MoO3

The absorption, diffusion, and desorption of atomic hydrogen in layered orthorhombic molybdenum trioxide (α-MoO3) was investigated using density functional theory. Hydrogen atoms are absorbed in bulkα-MoO3 to form the hydrogen molybdenum bronze HxMoO3 (x=0.25, 0.5, 0.75, 1, 1.25, and 1.5). The semiconductor band gap of bulkα-MoO3 shifts to metallic upon hydrogen bronze formation at the H atom loadings selected in the present study. The hydrogen atoms become protonic when coordinated to oxygen, which gives rise to a charge reduction on the Mo atoms adjacent to the absorption sites. Hydrogen migration along a prescribed diffusion pathway in the lattice was found to be facile due to small energy barriers for H atom transfer between O atoms, facilitated by a hydrogen bonding network. The sequential hydrogen desorption from the bronze and the mechanisms of hydrogen spillover in α-MoO3 are also discussed