117 research outputs found
Charge Transfer and Charge Broadening of GEM Structures in High Magnetic Fields
We report on measurements of charge transfer in GEM structures in high
magnetic fields. These were performed in the framework of the R&D work for a
Time Projection Chamber at a future Linear Collider. A small test chamber has
been installed into the aperture of a superconducting magnet with the GEM
structures mounted perpendicular to the B field direction. The charge transfer
is derived from the electrical currents monitored during irradiation with an
Fe source. No severe loss of primary ionisation charge is observed,
but an improved ion feedback suppression is achieved for high magnetic fields.
Additionally, the width of the charge cloud released by individual Fe
photons is measured using a finely segmented strip readout after the triple GEM
structure. Charge widths between 0.3 and 0.5 mm RMS are observed, which
originate from the charge broadening inside the GEM readout. This charge
broadening is only partly suppressed at high magnetic fields.Comment: 11 pages, 9 figure
Factors controlling coccolithophore biogeography in the Southern Ocean
The biogeography of Southern Ocean phytoplankton controls the local
biogeochemistry and the export of macronutrients to lower latitudes and
depth. Of particular relevance is the competitive interaction between
coccolithophores and diatoms, with the former being prevalent along the
Great Calcite Belt (40–60° S), while diatoms tend to dominate
the regions south of 60° S. To address the factors controlling
coccolithophore distribution and the competition between them and diatoms, we
use a regional high-resolution model (ROMS–BEC) for the Southern Ocean
(24–78° S) that has been extended to include an explicit
representation of coccolithophores. We assess the relative importance of
bottom-up (temperature, nutrients, light) and top-down (grazing by
zooplankton) factors in controlling Southern Ocean coccolithophore
biogeography over the course of the growing season. In our simulations,
coccolithophores are an important member of the Southern Ocean phytoplankton
community, contributing 17 % to annually integrated net primary
productivity south of 30° S. Coccolithophore biomass is highest
north of 50° S in late austral summer, when light levels are high
and diatoms become limited by silicic acid. Furthermore, we find top-down
factors to be a major control on the relative abundance of diatoms and
coccolithophores in the Southern Ocean. Consequently, when assessing
potential future changes in Southern Ocean coccolithophore abundance, both
abiotic (temperature, light, and nutrients) and biotic factors (interaction
with diatoms and zooplankton) need to be considered.</p
Integrated Detector Control and Calibration Processing at the European XFEL
The European X-ray Free Electron Laser is a high-intensity X-ray light source
currently being constructed in the area of Hamburg, that will provide spatially
coherent X-rays in the energy range between and
. The machine will deliver ,
consisting of up to , with a
repetition rate. The LPD, DSSC and AGIPD detectors are being developed to
provide high dynamic-range Mpixel imaging capabilities at the mentioned
repetition rates. A consequence of these detector characteristics is that they
generate raw data volumes of up to . In addition the
detector's on-sensor memory-cell and multi-/non-linear gain architectures pose
unique challenges in data correction and calibration, requiring online access
to operating conditions and control settings. We present how these challenges
are addressed within XFEL's control and analysis framework Karabo, which
integrates access to hardware conditions, acquisition settings (also using
macros) and distributed computing. Implementation of control and calibration
software is mainly in Python, using self-optimizing (py) CUDA code, numpy and
iPython parallels to achieve near-real time performance for calibration
application.Comment: Proceeding ICALEPS 201
Emissions from mechanically-biologically treated waste landfills at field scale
Modern waste management tends towards greater sustainability in landfilling, with the implementation of strategies such as the pretreatment of solid waste. This work assesses the behaviour of rejects from a refining stage of mechanically-biologically treated municipal solid waste at the landfill. The main results of 18 months' monitoring of an experimental pilot cell with waste from a full-scale plant are presented. This first stages are expected to be the most problematic period for this type of waste. The evolution of the temperature and the composition of leachate and gas at various points within the cell are included. During the first weeks, pollutant concentrations in the leachate exceeded the reference ranges in the literature, coinciding with a rapid onset of methanogenic conditions. However, there was a quick wash, reducing concentrations to below one third of the initial values before the first year. pH values influenced concentrations of some pollutants such as copper. These results indicate that, right from the beginning of disposal, such facilities should be prepared to treat a high pollution load in the leachate and install the gas emissions control elements due to the rapid onset of methanogenesis.This work is funded by the Spanish Ministry of Economics and Competitiveness through the CTM2012-35055 project. The project is financed jointly by the European Regional Development Fund, FEDER (operational period 2007-2013). The authors wish to thank the Government of Cantabria, through the public company MARE, and TirCantabria, the landfill operator company, for their collaboration
Shower development of particles with momenta from 15 GeV to 150 GeV in the CALICE scintillator-tungsten hadronic calorimeter
We present a study of showers initiated by electrons, pions, kaons, and
protons with momenta from 15 GeV to 150 GeV in the highly granular CALICE
scintillator-tungsten analogue hadronic calorimeter. The data were recorded at
the CERN Super Proton Synchrotron in 2011. The analysis includes measurements
of the calorimeter response to each particle type as well as measurements of
the energy resolution and studies of the longitudinal and radial shower
development for selected particles. The results are compared to Geant4
simulations (version 9.6.p02). In the study of the energy resolution we include
previously published data with beam momenta from 1 GeV to 10 GeV recorded at
the CERN Proton Synchrotron in 2010.Comment: 35 pages, 21 figures, 8 table
Low-frequency variability of the Indian monsoon-ENSO relationship and the tropical Atlantic : the "Weakening" of the 1980s and 1990s
Author Posting. © American Meteorological Society, 2007. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 20 (2007): 4255-4266, doi:10.1175/JCLI4254.1The Indian monsoon–El Niño–Southern Oscillation (ENSO) relationship, according to which a drier than normal monsoon season precedes peak El Niño conditions, weakened significantly during the last two decades of the twentieth century. In this work an ensemble of integrations of an atmospheric general circulation model (AGCM) coupled to an ocean model in the Indian Basin and forced with observed sea surface temperatures (SSTs) elsewhere is used to investigate the causes of such a weakening.
The observed interdecadal variability of the ENSO–monsoon relationship during the period 1950–99 is realistically simulated by the model and a dominant portion of the variability is associated with changes in the tropical Atlantic SSTs in boreal summer.
In correspondence to ENSO, the tropical Atlantic SSTs display negative anomalies south of the equator in the last quarter of the twentieth century and weakly positive anomalies in the previous period. Those anomalies in turn produce heating anomalies, which excite a Rossby wave response in the Indian Ocean in both the model and the reanalysis data, impacting the time-mean monsoon circulation.
The proposed mechanism of remote response of the Indian rainfall to tropical Atlantic sea surface temperatures is further tested forcing the AGCM coupled to the ocean model in the Indian Basin with climatological SSTs in the Atlantic Ocean and observed anomalies elsewhere. In this second ensemble the ENSO–monsoon relationship is characterized by a stable and strong anticorrelation through the whole second half of the twentieth century.The experiments in this paper
were performed as a contribution to the ENSEMBLES
project funded by the European Commission’s 6th
Framework Programme, Contract GOCE-CT-2003-50553
The Time Structure of Hadronic Showers in highly granular Calorimeters with Tungsten and Steel Absorbers
The intrinsic time structure of hadronic showers influences the timing
capability and the required integration time of hadronic calorimeters in
particle physics experiments, and depends on the active medium and on the
absorber of the calorimeter. With the CALICE T3B experiment, a setup of 15
small plastic scintillator tiles read out with Silicon Photomultipliers, the
time structure of showers is measured on a statistical basis with high spatial
and temporal resolution in sampling calorimeters with tungsten and steel
absorbers. The results are compared to GEANT4 (version 9.4 patch 03)
simulations with different hadronic physics models. These comparisons
demonstrate the importance of using high precision treatment of low-energy
neutrons for tungsten absorbers, while an overall good agreement between data
and simulations for all considered models is observed for steel.Comment: 24 pages including author list, 9 figures, published in JINS
Megahertz pulse trains enable multi-hit serial femtosecond crystallography experiments at X-ray free electron lasers
The European X-ray Free Electron Laser (XFEL) and Linac Coherent Light Source (LCLS) II are extremely intense sources of X-rays capable of generating Serial Femtosecond Crystallography (SFX) data at megahertz (MHz) repetition rates. Previous work has shown that it is possible to use consecutive X-ray pulses to collect diffraction patterns from individual crystals. Here, we exploit the MHz pulse structure of the European XFEL to obtain two complete datasets from the same lysozyme crystal, first hit and the second hit, before it exits the beam. The two datasets, separated by <1 µs, yield up to 2.1 Å resolution structures. Comparisons between the two structures reveal no indications of radiation damage or significant changes within the active site, consistent with the calculated dose estimates. This demonstrates MHz SFX can be used as a tool for tracking sub-microsecond structural changes in individual single crystals, a technique we refer to as multi-hit SFX
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