142 research outputs found
A new theory for tropical instability waves
Large-scale westward propagating waves, so-called "Legeckis" or "Tropical Instabil- ity Waves", are a prominent feature of sea surface temperature images of the equatorial Pacific. Our analyses of satellite altimetry data and long-term moorings reveals that the Legeckis waves can be interpreted as a superposition of two distinct wave modes, a first equatorial Rossby wave and a Rossby-gravity wave. We present evidence that the energy sources for both waves are the mean currents. Our results imply that Legeckis waves can be explained within the framework of linear equatorial waves
Financing a portfolio of projects
This paper shows that investors financing a portfolio of projects may use the depth of their financial pockets to overcome entrepreneurial incentive problems. Competition for scarce informed capital at the refinancing stage strengthens investors’ bargaining positions. And yet, entrepreneurs’ incentives may be improved, because projects funded by investors with “shallow pockets” must have not only a positive net present value at the refinancing stage, but one that is higher than that of competing portfolio projects. Our paper may help to understand provisions used in venture capital finance that limit a fund’s initial capital and make it difficult to add more capital once the initial venture capital fund is raised
Performance of Particle Flow Calorimetry at CLIC
The particle flow approach to calorimetry can provide unprecedented jet
energy resolution at a future high energy collider, such as the International
Linear Collider (ILC). However, the use of particle flow calorimetry at the
proposed multi-TeV Compact Linear Collider (CLIC) poses a number of significant
new challenges. At higher jet energies, detector occupancies increase, and it
becomes increasingly difficult to resolve energy deposits from individual
particles. The experimental conditions at CLIC are also significantly more
challenging than those at previous electron-positron colliders, with increased
levels of beam-induced backgrounds combined with a bunch spacing of only 0.5
ns. This paper describes the modifications made to the PandoraPFA particle flow
algorithm to improve the jet energy reconstruction for jet energies above 250
GeV. It then introduces a combination of timing and p_T cuts that can be
applied to reconstructed particles in order to significantly reduce the
background. A systematic study is performed to understand the dependence of the
jet energy resolution on the jet energy and angle, and the physics performance
is assessed via a study of the energy and mass resolution of W and Z particles
in the presence of background at CLIC. Finally, the missing transverse momentum
resolution is presented, and the fake missing momentum is quantified. The
results presented in this paper demonstrate that high granularity particle flow
calorimetry leads to a robust and high resolution reconstruction of jet
energies and di-jet masses at CLIC.Comment: 14 pages, 11 figure
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
Mesoscale contribution to the long-range offshore transport of organic carbon from the Canary Upwelling System to the open North Atlantic
Several studies in upwelling regions have suggested that mesoscale
structures, such as eddies and filaments, contribute substantially to the
long-range transport of the organic carbon from the nearshore region of
production to the offshore region of remineralization. Yet a comprehensive
analysis of this mesoscale flux and of its impact across the Canary Upwelling
System (CanUS) has not been provided. Here, we fill this gap using
simulations with the Regional Oceanic Modeling System (ROMS) coupled to a
Nutrient, Phytoplankton, Zooplankton and Detritus (NPZD) ecosystem model. We
run climatological simulations on an Atlantic telescopic grid with an
eddy-resolving resolution in the CanUS. Using both a Reynolds flux
decomposition and structure-identification algorithms, we quantify and
characterize the organic carbon fluxes driven by filaments and eddies within
the upper 100 m and put them in relationship to the total offshore transport.
Our analysis reveals that both coastal filaments and eddies enhance the
offshore flux of organic carbon, but that their contribution is very
different. Upwelling filaments, with their high speeds and high
concentrations, transport the organic carbon offshore in a very intense, but
coastally confined manner, contributing nearly 80 % to the total flux of
organic carbon at 100 km offshore. The filament contribution tapers off
quickly to near zero values at 1000 km off the coast, leading to a strong
offshore flux divergence that is the main lateral source of organic carbon in
the coastal waters up to 1000 km offshore. Some of this divergence is also
due to the filaments inducing a substantial vertical subduction of the
organic carbon below 100 m. Owing to the temporal persistence and spatial
recurrence of filaments, the filament transport largely constitutes a
time-mean flux, while the time-varying component, i.e., the turbulent flux,
is comparatively small. At distances beyond 500 km from the coast, eddies
dominate the mesoscale offshore transport. Although their contribution
represents only 20 % of the total offshore flux and its divergence, eddies,
especially cyclones, transport organic carbon offshore to distances as great
as 2000 km from the coast. The eddy transport largely represents a turbulent
flux, but striations in this transport highlight the existence of typical
formation spots and recurrent offshore propagation pathways. While they
propagate slowly, eddies are an important organic carbon reservoir for the
open waters, as they contain, on average, a third of the organic carbon in
this region, two thirds of which is found in cyclones. Our analysis confirms
the importance of mesoscale processes for the offshore organic carbon
transport and the fueling of the heterotrophic activity in the eastern
subtropical North Atlantic, and highlights the need to consider the mesoscale
flux in order to fully resolve the three-dimensionality of the marine organic
carbon cycle.</p
Southern Ocean eddy phenomenology
Mesoscale eddies are ubiquitous features in the Southern Ocean, yet their phenomenology is not well quantified. To tackle this task, we use satellite observations of sea level anomalies and sea surface temperature (SST) as well as in situ temperature and salinity measurements from profiling floats. Over the period 1997–2010, we identified over a million mesoscale eddy instances and were able to track about 105 of them over 1 month or more. The Antarctic Circumpolar Current (ACC), the boundary current systems, and the regions where they interact are hot spots of eddy presence, representing also the birth places and graveyards of most eddies. These hot spots contrast strongly to areas shallower than about 2000 m, where mesoscale eddies are essentially absent, likely due to topographical steering. Anticyclones tend to dominate the southern subtropical gyres, and cyclones the northern flank of the ACC. Major causes of regional polarity dominance are larger formation numbers and lifespans, with a contribution of differential propagation pathways of long-lived eddies. Areas of dominance of one polarity are generally congruent with the same polarity being longer-lived, bigger, of larger amplitude, and more intense. Eddies extend down to at least 2000 m. In the ACC, eddies show near surface temperature and salinity maxima, whereas eddies in the subtropical areas generally have deeper anomaly maxima, presumably inherited from their origin in the boundary currents. The temperature and salinity signatures of the average eddy suggest that their tracer anomalies are a result of both trapping in the eddy core and stirring
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
Alleviating the Last Mile of Encoding: The mei-friend Package for the Atom Text Editor
MEC 2021 BEST PAPER AWARD. Though MEI is widely used in music informatics and digital musicology research, the relative lack of authoring software and the specialised nature of its community have limited the availability of high-quality MEI encodings. Translating to MEI from other encoding formats, or generating MEI via optical music recognition processes, is thus a typical component of many MEI-project workflows. However, automated translations rarely achieve results of sufficient quality, a problem well-known in the community and documented in the literature. Final correction and validation by hand is therefore a common requirement. In this paper, we present meifriend, an extension to the Atom text editor, which aims to relieve the degree of manual labour required in this process. The tool facilitates most common MEI editing tasks including the insertion and manipulation of MEI elements, makes the encoded score visible and interactively accessible to the user, and provides quality-of-life conveniences including keyboard shortcuts for editing functions as well as intelligent navigation of the MEI hierarchy. We detail the tool’s implementation, describe its functionalities, and evaluate its responsiveness during the editing process, even when editing very large MEI files
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