Commissioning of the ATLAS Level-1 Trigger with Cosmic Rays

The ATLAS detector at CERN's Large Hadron Collider will be exposed to proton-proton collisions from beams crossing at 40 MHz. A three-level trigger system was designed to select potentially interesting events and reduce the incoming rate to 100-200 Hz. The first trigger level (LVL1) is implemented in custom-built electronics, the second and third trigger levels are realized in software. Based on calorimeter information and hits in dedicated muon-trigger detectors, the LVL1 decision is made by the central-trigger processor yielding an output rate of less than 100 kHz. The allowed latency for the trigger decision at this stage is less than 2.5 microseconds. Installation of the final LVL1 trigger system at the ATLAS site is in full swing, to be completed later this year. We present a status report of the main components of the first-level trigger and the in-situ commissioning of the full trigger chain with cosmic-ray muons.Comment: On behalf of the ATLAS TDAQ Level-1 Trigger Group. Proceedings for 2007 Europhysics Conference on High Energy Physics, Manchester, July 200

Modeling CO, CO2_2 and H2_2O ice abundances in the envelopes of young stellar objects in the Magellanic Clouds

Massive young stellar objects in the Magellanic Clouds show infrared absorption features corresponding to significant abundances of CO, CO$_2$ and H$_2$O ice along the line of sight, with the relative abundances of these ices differing between the Magellanic Clouds and the Milky Way. CO ice is not detected towards sources in the Small Magellanic Cloud, and upper limits put its relative abundance well below sources in the Large Magellanic Cloud and the Milky Way. We use our gas-grain chemical code MAGICKAL, with multiple grain sizes and grain temperatures, and further expand it with a treatment for increased interstellar radiation field intensity to model the elevated dust temperatures observed in the MCs. We also adjust the elemental abundances used in the chemical models, guided by observations of HII regions in these metal-poor satellite galaxies. With a grid of models, we are able to reproduce the relative ice fractions observed in MC massive young stellar objects (MYSOs), indicating that metal depletion and elevated grain temperature are important drivers of the MYSO envelope ice composition. Magellanic Cloud elemental abundances have a sub-galactic C/O ratio, increasing H$_2$O ice abundances relative to the other ices; elevated grain temperatures favor CO$_2$ production over H$_2$O and CO. The observed shortfall in CO in the Small Magellanic Cloud can be explained by a combination of reduced carbon abundance and increased grain temperatures. The models indicate that a large variation in radiation field strength is required to match the range of observed LMC abundances. CH$_3$OH abundance is found to be enhanced in low-metallicity models, providing seed material for complex organic molecule formation in the Magellanic Clouds.Comment: Accepted in ApJ 20 pages, 8 figures, 6 table

On the Formation of CO2 and Other Interstellar Ices

We investigate the formation and evolution of interstellar dust-grain ices under dark-cloud conditions, with a particular emphasis on CO2. We use a three-phase model (gas/surface/mantle) to simulate the coupled gas--grain chemistry, allowing the distinction of the chemically-active surface from the ice layers preserved in the mantle beneath. The model includes a treatment of the competition between barrier-mediated surface reactions and thermal-hopping processes. The results show excellent agreement with the observed behavior of CO2, CO and water ice in the interstellar medium. The reaction of the OH radical with CO is found to be efficient enough to account for CO2 ice production in dark clouds. At low visual extinctions, with dust temperatures ~12 K, CO2 is formed by direct diffusion and reaction of CO with OH; we associate the resultant CO2-rich ice with the observational polar CO2 signature. CH4 ice is well correlated with this component. At higher extinctions, with lower dust temperatures, CO is relatively immobile and thus abundant; however, the reaction of H and O atop a CO molecule allows OH and CO to meet rapidly enough to produce a CO:CO2 ratio in the range ~2--4, which we associate with apolar signatures. We suggest that the observational apolar CO2/CO ice signatures in dark clouds result from a strongly segregated CO:H2O ice, in which CO2 resides almost exclusively within the CO component. Observed visual-extinction thresholds for CO2, CO and H2O are well reproduced by depth-dependent models. Methanol formation is found to be strongly sensitive to dynamical timescales and dust temperatures.Comment: 22 pages, 12 figure

Growth, mortality and recruitment of commercially important fishes and penaeid shrimps in Indonesian waters

Population dynamics, Stock assessment, Commercial species, Shrimp fisheries, Arafura Sea, Indonesia, Penaeus merguiensis

The Flash Pattern of Photosynthetic Oxygen Evolution after Treatment with Low Concentrations of Hydroxylamine as a Function of the Previous S1/S0-Ratio Further Evidence that NH2OH Reduces the Water Oxidizing Complex in the Dark

Flash induced oxygen evolution patterns of isolated PS II complexes from the cyanobacterium Synechococcus were measured with a Joliot-type electrode. By suitable preflash and dark adaptation procedures, samples were prepared in the state S1 (100%), as well as enriched in S0 (60% S0, 40% S,). After treatment with low concentrations of NH2OH (≤ 100 μм), the two flash patterns were identical. This is further evidence for a reduction of the water oxidizing complex by hydroxylamine in the dark. Two reduced states (S-1 and S-2) below S0 are formed by this reduction

First measurements of the index of refraction of gases for lithium atomic waves

We report here the first measurements of the index of refraction of gases for lithium waves. Using an atom interferometer, we have measured the real and imaginary part of the index of refraction $n$ for argon, krypton and xenon, as a function of the gas density for several velocities of the lithium beam. The linear dependence of $(n-1)$ with the gas density is well verified. The total collision cross-section deduced from the imaginary part is in very good agreement with traditional measurements of this quantity. Finally, as predicted by theory, the real and imaginary parts of $(n-1)$ and their ratio $\rho$ exhibit glory oscillations