8 research outputs found
EFFECTS OF COLD-ROLLING AND POST-DEFORMATION ANNEALING ON THE MARTENSITIC TRANSFORMATION OF A TiNi SHAPE MEMORY ALLOY
No full textThe thermoelastic transformation of shape-memory titanium -nickel alloys is highly influenced by the microstructural state of the alloy and particularly by the plastic deformation of the metal. In this study, the influence of cold-work and annealing on martensitic and austenitic transformations is performed with "in situ" thermoelectric power measurements during thermal cycling. In the recrystallized state the transformations are very well defined, and the thermal hysteresis is generally less than 30 degrees. After work hardening the transformation becomes "diffuse" and is no longer observed if the deformation is greater than a critical value of approximately 25%. The effects of post-deformation heat treatments were also characterized using a heavily cold- worked metal within a temperature range of 300-600°C. Thermoelectric power measurements applied to the characterization of shape-memory alloy transformation proves to be a high performance tool displaying a great sensitivity to martensitic transformation
COMPOSITION GRADIENTS THROUGH RIBBON THICKNESS OF THE MELT SPUN AMORPHOUS Al70Fe13Si17 ALLOY
No full textLa recherche d'inhomogénéités à travers l'épaisseur d'un ruban amorphe Al70Fe13Si17 élaboré par "melt spinning" a permis de mettre en évidence des gradients de composition chimique localisés au niveau de concavités "coté roue", vraisemblablement issues du piégeage de bulles de gaz pendant la fabrication du ruban. Ces gradients de composition ont été caractérisés par analyse "XEDS" en microscopie électronique analytique à balayage "STEM" sur des sections de ruban (ca.100nm) préparées par ultramicrotomie.The investigation of inhomogeneities through the ribbon thickness of an Al70Fe13Si17 glass obtained by melt spinning has allowed to evidence the existence of composition gradients localized on the "wheel contact side" concavities, probably due to gas bubble trapping effects. The composition gradients were analyzed by XEDS in a scanning transmission electron microscope STEM on ultrathin ribbon sections prepared by ultramicrotomy
Sea ice meltwater and Circumpolar Deep Water drive contrasting productivity in three Antarctic polynyas
No full textAuthor Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124(5), (2019): 2943-2968, doi:10.1029/2019JC015071.In the Southern Ocean, polynyas exhibit enhanced rates of primary productivity and represent large seasonal sinks for atmospheric CO2. Three contrasting east Antarctic polynyas were visited in late December to early January 2017: the Dalton, Mertz, and Ninnis polynyas. In the Mertz and Ninnis polynyas, phytoplankton biomass (average of 322 and 354 mg chlorophyll a (Chl a)/m2, respectively) and net community production (5.3 and 4.6 mol C/m2, respectively) were approximately 3 times those measured in the Dalton polynya (average of 122 mg Chl a/m2 and 1.8 mol C/m2). Phytoplankton communities also differed between the polynyas. Diatoms were thriving in the Mertz and Ninnis polynyas but not in the Dalton polynya, where Phaeocystis antarctica dominated. These strong regional differences were explored using physiological, biological, and physical parameters. The most likely drivers of the observed higher productivity in the Mertz and Ninnis were the relatively shallow inflow of iron‐rich modified Circumpolar Deep Water onto the shelf as well as a very large sea ice meltwater contribution. The productivity contrast between the three polynyas could not be explained by (1) the input of glacial meltwater, (2) the presence of Ice Shelf Water, or (3) stratification of the mixed layer. Our results show that physical drivers regulate the productivity of polynyas, suggesting that the response of biological productivity and carbon export to future change will vary among polynyas.This work was cofunded by the Australian Antarctic Division research projects AAS 4131 and 4291. This project was also supported by the Australian Government Cooperative Research Centres Programme through the Antarctic Climate & Ecosystems (ACE CRC). S. Moreau and C. Genovese were supported by the Australian Research Council's Special Research Initiative for Antarctic Gateway Partnership (project ID SR140300001). V. Puigcorbé and M. Roca‐Martí are grateful for the support from Pere Masque and Edith Cowan University. M.C. Arroyo was supported by the Dickhut Fellowship, administered by the Virginia Institute of Marine Science. The authors would like to thank the officers and crew of the R/V Aurora Australis for their logistic support, the CSIRO hydrochemists for their analyses of nutrient concentrations, and E. J. Yang for her microscope analysis of phytoplankton species. We also want to thank two anonymous reviewers for their very good comments on this study. The data presented in this paper are available on the Australian Antarctic Division (AAD) Data Centre at https://data.aad.gov.au/aadc/metadata/metadata_by_parameter.cfm.2019-09-2
Totten Glacier Ice Shelf cavity bathymetry
No full textProgress Code: completedThis is a derived product containing two products blended together that describes the elevation of the seafloor beneath and out to approximately seaward of the Totten Glacier Ice Shelf cavity as well as the elevation of the ice bottom beneath the ice sheet immediately sounding the ice shelf cavity. The seafloor was inferred by inverting airborne gravity observations; the terrain beneath grounded ice was observed with airborne ice sounding radar measurements. The two products were blended along the grounding line observed with satellite observations [Rignot, E., Mouginot, J. and Scheuchl, B. Antarctic grounding line mapping from differential satellite radar interferometry. Geophys. Res. Lett. 38, L10504 (2011)]. <br/><br/>We have provided a text file that contains three columns that may be used to produce a gridded bathymetry of the Totten Glacier Ice Shelf and surrounding area with a cell size of 1-km. The first two columns contain grid coordinates using the Polar Stereographic projection based on WGS84 with true scale at 71 degrees S. The third column contains the vertical coordinate representing the seafloor beneath and the ice-bottom elevation around the Totten Glacier Ice Shelf cavity. The center of the region is located near 115E and 67S and spans an area about 217 km by 131 km.<br/><br/>The data are described in detail in the publication and supplementary materials that can be found by following this link:<br/>http://www.nature.com/ngeo/journal/v8/n4/abs/ngeo2388.html#supplementary-informatio
Water level dynamics of Amazon wetlands at the watershed scale by satellite altimetry
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J., 1986, P IGARSS 86 S ZUR SE, P1339 Zelli C, 1999, ACTA ASTRONAUT, V44, P323, DOI 10.1016/S0094-5765(99)00063-6 Da Silva, Joecila Santos Seyler, Frederique Calmant, Stephane Rotunno Filho, Otto Correa Roux, Emmanuel Magalhaes Araujo, Afonso Augusto Guyot, Jean Loup ROUX, Emmanuel/G-9814-2011; SEYLER, Frederique/D-5518-2011; SILVA, Joecila/B-1478-2014 Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq), Brazil; Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES) Brazil [516/05]; French Centre National d'Etudes Spatiale through the TOSCA We thank the reviewers who greatly helped in rewriting the preliminary version of the manuscript. We are grateful for the financial support provided to the first author by Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq), Brazil and by Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES) Brazil (ref. CAPES/COFECUB no. 516/05), and to the French contributors funded by the French Centre National d'Etudes Spatiale through the TOSCA programme, project Hydrologie Spatiale. Acquisition of JERS-1 imagery was made possible by NASDA's Global Rain Forest Mapping Project. We thank the Instituto Brasileiro de Geografia e Estatistica (IBGE) for the maps of the region, the Agencia Nacional de Aguas (ANA), Brazil for the gauge data and the CTOH (Centre de Topographie des Oceans et de l'Hydrosphere, LEGOS, France) for access to ERS-2 and ENVISAT GDRs and additional tropospheric corrections through their online database system, and the European Space Agency (ESA) for granting the use of the data. We are also grateful to Gerard Cochonneau for his work on the treatment of the altimetric data. 3 TAYLOR & FRANCIS LTD ABINGDON INT J REMOTE SENSIn this study we used satellite altimetry to characterize the time and space variations in water stored in or circulating through rivers, floodplains, wetlands and lakes in the major sub-basins of the Amazon basin. Using a specific methodology to rigorously select original three-dimensional (3D) data from an Environmental Satellite (ENVISAT) mission, water level time series were calculated at the crossing path of the satellite tracks with the water bodies. We took advantage of the continuous sampling of the water level along the satellite track segments that cross the watershed to analyse both spatial and temporal relationships between: (i) the river and its floodplain and (ii) different basins. This work evidences in particular the existence of water leaking between the Negro and Solimoes basins at the high water stage. It highlights that the phenomenon of a secondary flood peak occurring in the water level series in the Solimoes basin at rising water, known as repiquete, is caused by the rain equatorial regime of the northern upstream tributaries of the Solimoes River, but is disconnected from the same phenomenon occurring within the Rio Negro basin
Global sea-level budget 1993-present
No full textInternational audienceGlobal mean sea level is an integral of changes occurring in the climate system in response to un-forced climate variability as well as natural and anthropogenic forcing factors. Its temporal evolution allows changes (e.g., acceleration) to be detected in one or more components. Study of the sea-level budget provides constraints on missing or poorly known contributions, such as the unsurveyed deep ocean or the still uncertain land water component. In the context of the World Climate Research Programme Grand Challenge entitled "Re-gional Sea Level and Coastal Impacts", an international effort involving the sea-level community worldwide has been recently initiated with the objective of assessing the various datasets used to estimate components of the sea-level budget during the altimetry era (1993 to present). These datasets are based on the combination of a broad range of space-based and in situ observations, model estimates, and algorithms. Evaluating their quality, quantifying uncertainties and identifying sources of discrepancies between component estimates is extremely useful for various applications in climate research. This effort involves several tens of scientists from about 50 research teams/institutions worldwide (www.wcrp-climate.org/grand-challenges/gc-sea-level, last access: 22 August 2018). The results presented in this paper are a synthesis of the first assessment performed during 2017-2018. We present estimates of the altimetry-based global mean sea level (average rate of 3.1 ± 0.3 mm yr −1 and acceleration of 0.1 mm yr −2 over 1993-present), as well as of the different components of the sea-level budget (http://doi.org/10.17882/54854, last access: 22 August 2018). We further examine closure of the sea-level budget, comparing the observed global mean sea level with the sum of components. Ocean thermal expansion, glaciers, Greenland and Antarctica contribute 42 %, 21 %, 15 % and 8 % to the global mean sea level over the 1993-present period. We also study the sea-level budget over 2005-present, using GRACE-based ocean mass estimates instead of the sum of individual mass components. Our results demonstrate that the global mean sea level can be closed to within 0.3 mm yr −1 (1σ). Substantial uncertainty remains for the land water storage component, as shown when examining individual mass contributions to sea level
Altimetry for the future: Building on 25 years of progress
No full textIn 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology.
The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the “Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion
