661 research outputs found
First disk-resolved spectroscopy of (4) Vesta
Vesta, the second largest Main Belt asteroid, will be the first to be
explored in 2011 by NASA's Dawn mission. It is a dry, likely differentiated
body with spectrum suggesting that is has been resurfaced by basaltic lava
flows, not too different from the lunar maria.
Here we present the first disk-resolved spectroscopic observations of an
asteroid from the ground. We observed (4) Vesta with the ESO-VLT adaptive
optics equipped integral-field near-infrared spectrograph SINFONI, as part of
its science verification campaign. The highest spatial resolution of ~90 km on
Vesta's surface was obtained during excellent seeing conditions (0.5") in
October 2004.
We observe spectral variations across Vesta's surface that can be interpreted
as variations of either the pyroxene composition, or the effect of surface
aging. We compare Vesta's 2 micron absorption band to that of
howardite-eucrite-diogenite (HED) meteorites that are thought to originate from
Vesta, and establish particular links between specific regions and HED
subclasses. The overallcomposition is found to be mostly compatible with
howardite meteorites, although a small area around 180 deg. East longitude
could be attributed to a diogenite-rich spot. We finally focus our spectral
analysis on the characteristics of Vesta's bright and dark regions as seen from
Hubble Space Telescope's visible and Keck-II's near-infrared images.Comment: 13 pages, 11 figures, 3 table
Assessing the Ability of the DDES Turbulence Modeling Approach to Simulate the Wake of a Bluff Body
A detailed numerical investigation of the flow behind a square cylinder at a Reynolds number of 21,400 is conducted to assess the ability of the delayed detached-eddy simulation (DDES) modeling approach to accurately predict the velocity recovery in the wake of a bluff body. Three-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) and DDES simulations making use of the Spalart–Allmaras turbulence model are carried out using the open-source computational fluid dynamics (CFD) toolbox OpenFOAM-2.1.x, and are compared with available experimental velocity measurements. It is found that the DDES simulation tends to overestimate the averaged streamwise velocity component, especially in the near wake, but a better agreement with the experimental data is observed further downstream of the body. The velocity fluctuations also match reasonably well with the experimental data. Moreover, it is found that the spanwise domain length has a significant impact on the flow, especially regarding the fluctuations of the drag coefficient. Nonetheless, for both the averaged and fluctuating velocity components, the DDES approach is shown to be superior to the URANS approach. Therefore, for engineering purposes, it is found that the DDES approach is a suitable choice to simulate and characterize the velocity recovery in a wake
A new strategy for primary structure determination of proteins: Application to bovine β-casein
AbstractA new approach has been developed for sequencing proteins. A radioactive label is attached specifically to the C-terminus of the protein. The labelled molecule is subjected to varying proteolysis conditions. From the electrophoretic patterns (SDS-PAGE) of the hydrolysates, appropriate cleavage conditions are selected, giving labelled peptides of different lengths which are purified. The labelled peptides are sequenced in order of increasing size (from 1 to n), peptide (i) being sequenced until the N-terminal sequence of peptide (i-1) is encountered. This approach allows the determination of a complete protein sequence with a minimal number of Edman cycles. The method was successfully applied to bovine β-casein (209 residues) which was completely resequenced with only 239 Edman cycles
TMT Approach to Observatory Software Development Process
The purpose of the Observatory Software System (OSW) is to integrate all software and hardware components of the Thirty Meter Telescope (TMT) to enable observations and data capture; thus it is a complex software system that is defined by four principal software subsystems: Common Software (CSW), Executive Software (ESW), Data Management System (DMS) and Science Operations Support System (SOSS), all of which have interdependencies with the observatory control systems and data acquisition systems. Therefore, the software development process and plan must consider dependencies to other subsystems, manage architecture, interfaces and design, manage software scope and complexity, and standardize and optimize use of resources and tools. Additionally, the TMT Observatory Software will largely be developed in India through TMT’s workshare relationship with the India TMT Coordination Centre (ITCC) and use of Indian software industry vendors, which adds complexity and challenges to the software development process, communication and coordination of activities and priorities as well as measuring performance and managing quality and risk. The software project management challenge for the TMT OSW is thus a multi-faceted technical, managerial, communications and interpersonal relations challenge. The approach TMT is using to manage this multifaceted challenge is a combination of establishing an effective geographically distributed software team (Integrated Product Team) with strong project management and technical leadership provided by the TMT Project Office (PO) and the ITCC partner to manage plans, process, performance, risk and quality, and to facilitate effective communications; establishing an effective cross-functional software management team composed of stakeholders, OSW leadership and ITCC leadership to manage dependencies and software release plans, technical complexities and change to approved interfaces, architecture, design and tool set, and to facilitate effective communications; adopting an agile-based software development process across the observatory to enable frequent software releases to help mitigate subsystem interdependencies; defining concise scope and work packages for each of the OSW subsystems to facilitate effective outsourcing of software deliverables to the ITCC partner, and to enable performance monitoring and risk management. At this stage, the architecture and high-level design of the software system has been established and reviewed. During construction each subsystem will have a final design phase with reviews, followed by implementation and testing. The results of the TMT approach to the Observatory Software development process will only be preliminary at the time of the submittal of this paper, but it is anticipated that the early results will be a favorable indication of progress
Assessing the Ability of the DDES Turbulence Modeling Approach to Simulate the Wake of a Bluff Body
A detailed numerical investigation of the flow behind a square cylinder at a Reynolds number of 21,400 is conducted to assess the ability of the delayed detached-eddy simulation (DDES) modeling approach to accurately predict the velocity recovery in the wake of a bluff body. Three-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) and DDES simulations making use of the Spalart–Allmaras turbulence model are carried out using the open-source computational fluid dynamics (CFD) toolbox OpenFOAM-2.1.x, and are compared with available experimental velocity measurements. It is found that the DDES simulation tends to overestimate the averaged streamwise velocity component, especially in the near wake, but a better agreement with the experimental data is observed further downstream of the body. The velocity fluctuations also match reasonably well with the experimental data. Moreover, it is found that the spanwise domain length has a significant impact on the flow, especially regarding the fluctuations of the drag coefficient. Nonetheless, for both the averaged and fluctuating velocity components, the DDES approach is shown to be superior to the URANS approach. Therefore, for engineering purposes, it is found that the DDES approach is a suitable choice to simulate and characterize the velocity recovery in a wake
Challenges and Innovative Technologies On Fuel Handling Systems for Future Sodium-Cooled Fast Reactors
International audienceThe reactor refuelling system provides the means of transporting, storing, and handling reactor core subassemblies. The system consists of the facilities and equipment needed to accomplish the scheduled refuelling operations. The choice of a FHS impacts directly on the general design of the reactor vessel (primary vessel, storage, and final cooling before going to reprocessing), its construction cost, and its availability factor. Fuel handling design must take into account various items and in particular operating strategies such as core design and management and core configuration. Moreover, the FHS will have to cope with safety assessments: a permanent cooling strategy to prevent fuel clad rupture, plus provisions to handle short-cooled fuel and criteria to ensure safety during handling. In addition, the handling and elimination of residual sodium must be investigated; it implies specific cleaning treatment to prevent chemical risks such as corrosion or excess hydrogen production. The objective of this study is to identify the challenges of a SFR fuel handling system. It will then present the range of technical options incorporating innovative technologies under development to answer the GENERATION IV SFR requirements
WOODS: Benchmarks for Out-of-Distribution Generalization in Time Series
Machine learning models often fail to generalize well under distributional
shifts. Understanding and overcoming these failures have led to a research
field of Out-of-Distribution (OOD) generalization. Despite being extensively
studied for static computer vision tasks, OOD generalization has been
underexplored for time series tasks. To shine light on this gap, we present
WOODS: eight challenging open-source time series benchmarks covering a diverse
range of data modalities, such as videos, brain recordings, and sensor signals.
We revise the existing OOD generalization algorithms for time series tasks and
evaluate them using our systematic framework. Our experiments show a large room
for improvement for empirical risk minimization and OOD generalization
algorithms on our datasets, thus underscoring the new challenges posed by time
series tasks. Code and documentation are available at
https://woods-benchmarks.github.io .Comment: 47 pages, 21 figure
Heinrich event 1: an example of dynamical ice-sheet reaction to oceanic changes
Heinrich events, identified as enhanced ice-rafted
detritus (IRD) in North Atlantic deep sea sediments (Heinrich,
1988; Hemming, 2004) have classically been attributed
to Laurentide ice-sheet (LIS) instabilities (MacAyeal, 1993;
Calov et al., 2002; Hulbe et al., 2004) and assumed to lead to
important disruptions of the Atlantic meridional overturning
circulation (AMOC) and North Atlantic deep water (NADW)
formation. However, recent paleoclimate data have revealed
that most of these events probably occurred after the AMOC
had already slowed down or/and NADW largely collapsed,
within about a thousand years (Hall et al., 2006; Hemming,
2004; Jonkers et al., 2010; Roche et al., 2004), implying that
the initial AMOC reduction could not have been caused by
the Heinrich events themselves.
Here we propose an alternative driving mechanism, specifically
for Heinrich event 1 (H1; 18 to 15 ka BP), by which
North Atlantic ocean circulation changes are found to have
strong impacts on LIS dynamics. By combining simulations
with a coupled climate model and a three-dimensional
ice sheet model, our study illustrates how reduced NADW
and AMOC weakening lead to a subsurface warming in the
Nordic and Labrador Seas resulting in rapid melting of the
Hudson Strait and Labrador ice shelves. Lack of buttressing
by the ice shelves implies a substantial ice-stream acceleration,
enhanced ice-discharge and sea level rise, with peak values 500–1500 yr after the initial AMOC reduction. Our
scenario modifies the previous paradigm of H1 by solving
the paradox of its occurrence during a cold surface period,
and highlights the importance of taking into account the effects
of oceanic circulation on ice-sheets dynamics in order
to elucidate the triggering mechanism of Heinrich events.Peer reviewe
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