Interstellar Scintillation and Annual Cycles in the BL Lac Source PKS 1519-273     

David L. Jauncey  Helen M. Johnston  Hayley E. Bignall  J.E.J. Lovell  Lucyna Kedziora-Chudczer  A.K. Tzioumis  Jean-Pierre Macquart 《Astrophysics and Space Science》2003,288(1-2):63-68

We have measured annual cycles in the time scales of the rapid, intra-day variability of the total and circularly polarized flux density, of the unusual BL Lac source PKS 1519–273 at 4.8 and 8.6 GHz. This data was collected at the ATCA over the last seven years, and establishes unequivocally interstellar scintillation as the principal mechanism responsible for this cm-wavelength intra-day variability.  相似文献   

STEREO/Extreme Ultraviolet Imager (EUVI) Event Catalog 2006 – 2012     

Markus J. Aschwanden  Jean-Pierre Wülser  Nariaki V. Nitta  James R. Lemen  Sam Freeland  William T. Thompson 《Solar physics》2014,289(3):919-938

We generated an event catalog with an automated detection algorithm based on the entire EUVI image database observed with the two Solar Terrestrial Relations Observatory (STEREO)-A and -B spacecraft over the first six years of the mission (2006?–?2012). The event catalog includes the heliographic positions of some 20?000 EUV events, transformed from spacecraft coordinates to Earth-based coordinates, and information on associated GOES flare events (down to the level of GOES A5-class flares). The 304 Å wavelength turns out to be the most efficient channel for flare detection (79?% of all EUVI event detections), while the 171 Å (4?%), 195 Å (10?%), and the 284 Å channel (7?%) retrieve substantially fewer flare events, partially due to the suppressing effect of EUV dimming, and partially due to the lower cadence in the later years of the mission. Due to the Sun-circling orbits of STEREO-A and -B, a large number of flares have been detected on the farside of the Sun, invisible from Earth, or seen as partially occulted events. The statistical size distributions of EUV peak fluxes (with a power-law slope of α _P =2.5±0.2) and event durations (with a power-law slope of α _T =2.4±0.3) are found to be consistent with the fractal-diffusive self-organized criticality model. The EUVI event catalog is available on-line at secchi.lmsal.com/EUVI/euvi_autodetection/euvi_events.txt and may serve as a comprehensive tool to identify stereoscopically observed flare events for 3D reconstruction and to study occulted flare events.  相似文献   

Balancing the Oceanic Calcium Carbonate Cycle: Consequences of Variable Water Column ��     

Stephen V. Smith  Jean-Pierre Gattuso 《Aquatic Geochemistry》2011,17(4-5):327-337

The paired chemical reactions, Ca²⁺ + 2HCO₃ ^? ? CaCO₃ + CO₂ + H₂O, overestimate the ratio of CO₂ flux to CaCO₃ flux during the precipitation or dissolution of CaCO₃ in seawater. This ratio, which has been termed ??, is about 0.6 in surface seawater at 25°C and at equilibrium with contemporary atmospheric CO₂ and increases towards 1.0 as seawater cools and pCO₂ increases. These conclusions are based on field observations, laboratory experiments, and equilibrium calculations for the seawater carbonate system. Yet global geochemical modeling indicates that small departures of ?? from 1.0 would cause dramatic, rapid, and unrealistic change in atmospheric CO₂. ?? can be meaningfully calculated for a water sample whether or not it is in equilibrium with the atmosphere. The analysis presented here demonstrates that the atmospheric CO₂ balance can be maintained constant with respect to seawater CaCO₃ reactions if one considers the difference between CaCO₃ precipitation and burial and differing values for ?? (both <1.0) in regions of precipitation and dissolution within the ocean.  相似文献   

Pliocene to Recent shallow-water contourite deposits on the shelf and shelf edge off south-western Mallorca, Spain   总被引：2，自引：2，他引：0  

Thomas Philippe Vandorpe  David Van Rooij  Dorrik A. V. Stow  Jean-Pierre Henriet 《Geo-Marine Letters》2011,31(5-6):391-403

This paper presents evidence for the presence of shallow-water contourite drifts on the south-western shelf and shelf edge off Mallorca in water depths between 150 and 275?m. These are called the Mallorca contourite depositional system (CDS). The elongate-mounded shallow-water CDS in this area is ascribed to an offshoot of the Balearic Current, which flows north to south through the Mallorca Channel as part of the overall thermohaline circulation in the Mediterranean Sea. Drift geometry suggests that the north?Csouth current is deflected into an east?Cwest flow pattern by interaction with a marked seafloor bathymetry, associated with major fault displacement. Four seismic units separated by three prominent discontinuities can be identified. The three internal discontinuities are correlated to large-scale basin-wide events: the lower Pliocene revolution (4.2?Ma), the upper Pliocene revolution (2.4?Ma) and the mid-Pleistocene revolution (0.9?Ma). The Plio-Quaternary succession has been deposited on top of a Miocene reef, which serves as an acoustic basement and is affected by a large fault, offsetting the basement on average by 150?m. Marked erosional features throughout and further incision of the Sant Jordi Channel along the basement fault in the Pleistocene deposits indicate stronger currents in this period. The Pleistocene deposits also show a pronounced cyclicity, which is tentatively ascribed to climatic variations and the effects of eustatic sea-level fluctuation over the south-western Mallorca shelf at that time.  相似文献   

Biological productivity enhancement over a continental shelf break (Bay of Biscay, NE Atlantic) evidenced by mesozooplankton aspartate transcarbamylase activity     

Jean-Pierre Bergeron  Noussith?? Koueta 《Journal of Oceanography》2011,67(2):249-252

  相似文献   

Paul Pellas (1924–1997)     

Brigitte Zanda  Roger H. Hewins  Jean-Pierre Bibring 《Meteoritics & planetary science》1997,32(6):983-984

  相似文献   

Comprehensive study of the biophysical parameters of agricultural crops based on assessing Landsat 8 OLI and Landsat 7 ETM+ vegetation indices     

Nima Ahmadian  Sahar Ghasemi  Jean-Pierre Wigneron  Reinhard Zölitz 《地理信息系统科学与遥感》2016,53(3):337-359

For three agricultural crop types, winter wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and canola (Brassica napus L.), we estimated biophysical parameters including fresh and dry biomass, leaf area index (LAI), and vegetation water content, for which we found the equivalent water thickness (EWT), fuel moisture content per fresh weight (FMC_FW), and fuel moisture content per dry weight (FMC_DW). We performed these estimations using data from the newly launched Landsat 8 Operational Land Imager (OLI) sensor, as well as its predecessor the Landsat 7 Enhanced Thematic Mapper Plus (ETM+). Progress in the design of the new sensor (i.e., Landsat 8), including narrower near-infrared (NIR) wavebands, higher signal-to-noise ratio (SNR), and greater radiometric resolution highlights the necessity to investigate the biophysical parameters of agricultural crops, especially compared to data from its predecessor. This study aims to evaluate vegetation indices (VIs) derived from the Landsat 8 OLI and the Landsat 7 ETM+. Both the Landsat 8 OLI and Landsat 7 ETM+ VIs agreed well with in-situ data measurements. However, the Landsat 8 OLI-derived VIs were generally more consistent with in situ data than the Landsat 7 ETM+ VIs. We also note that the Landsat 8 OLI is better able to capture the small variability of the VIs because of its higher SNR and wider radiometric range; in addition, the saturation phenomenon occurred earlier for the Landsat 7 ETM+ than for the Landsat 8 OLI. This indicates that the new sensor is better able to estimate the biophysical parameters of crops.  相似文献   

Boron isotopes as pH proxy: A new look at boron speciation in deep-sea corals using B MAS NMR and EELS     

Claire Rollion-Bard  Dominique Blamart  Grégory Tricot  Jean-Pierre Cuif 《Geochimica et cosmochimica acta》2011,75(4):1003-1012

Dissolved boron in modern seawater occurs in the form of two species, trigonal boric acid B(OH)₃ and tetrahedral borate ion . One of the key assumption in the use of boron isotopic compositions of carbonates as pH proxy is that only borate ions, , are incorporated into the carbonate. Here, we investigate the speciation of boron in deep-sea coral microstructures (Lophelia pertusa specimen) by using high field magic angle spinning nuclear magnetic resonance (¹¹B MAS NMR) and electron energy-loss spectroscopy (EELS). We observe both boron coordination species, but in different proportions depending on the coral microstructure, i.e. centres of calcification versus fibres. These results suggest that careful sampling is necessary before performing boron isotopic measurements in deep-sea corals. By combining the proportions of B(OH)₃ and determined by NMR and our previous ion microprobe boron isotope measurements, we propose a new equation for the relation between seawater pH and boron isotopic composition in deep-sea corals.  相似文献   

Drowning discontinuities and stratigraphic correlation in platform carbonates. The late Barremian–early Aptian record of southeast France     

Jean-Pierre Masse  Mukerrem Fenerci-Masse 《Cretaceous Research》2011,32(6):659-684

In Provence and Languedoc, four drowning events were identified in platform carbonates of late Barremian–Bedoulian age. Their recognition is based on sedimentological and stratigraphical evidence, and their timing, referred to ammonite zones or subzones, is as follows:

• (1) 

  Late Barremian, at the G. sartousiana–Imerites giraudi transition, or merely the lowermost part of the I. giraudi zone,

• (2) 

  Middle Bedoulian, at the Deshayesitesweissi–Deshayesites deshayesi transition,

• (3) 

  Mid late Bedoulian in correspondence with the “Roloboceras hambrovi subzone”,

• (4) 

  Late Bedoulian at the Deshayesites grandis–Deshayesites furcata transition.

Corresponding events are also well expressed in basinal settings where they are marked by significant facies and faunal changes.These four successive drowning events distinguish four successive steps in platform development and demise. Step 1 was coeval with the onset of the Bedoulian palaeogeography and started after drowning event (1) with a drastic reduction of shallow platform settings with rudists, usually replaced by Palorbitolina facies. The ensuing recovery of rudist facies and, following drowning event (2), subsequent step 2 marked the developmental phase of the platform system, whereas steps 3 and 4, each prefaced by a drowning event, were associated with its demise. Step 1 represents the major spreading phase of the Urgonian type facies spectrum including bioclastics, coral and rudist facies groups. In Provence, step 1 was characterized by a bipolar (N-S) progradation, and aggradation was coeval with a maximum of subsidence. The termination of step 1 was marked by the emergence of the antecedent platform margin. Step 2, which followed the disappearance of rudist facies and the extreme spatial reduction of both coral and bioclastic facies, started with the flooding of the antecedent platform and the development of Palorbitolina and cherty limestones. Shallow water bioclastics and/or coral facies recovered rapidly on top of the pre-existing emerged areas and developed locally as bioclastic shoals. Step 2 documents a regional reorganisation of subsidence patterns.The infralittoral (high illuminated environments) “Urgonian facies” are therefore essentially present in the Lower Bedoulian, and circalittoral (relatively deep low illuminated environments) deposits dominate in the Upper Bedoulian. This pattern, typical for SE France and wide parts of the Helvetic shelf, departs from that of adjacent regions (e.g. SW France, Spain) where late Bedoulian platform carbonates have a significant record. The record thus shows that the demise of the Urgonian platform was a step-wise phenomenon which cannot be ascribed to a single event, i.e. the Goguel/Selli OAE1a main event.  相似文献   

Ductile crust exhumation and extensional detachments in the central Aegean (Cyclades and Evvia Islands).     

Pierre Gautier  Jean-Pierre Brun 《Geodinamica Acta》2013,26(2):57-85

Abstract

The Aegean continental domain is known to be the site of widespread “back-arc” extension since at least 13 Ma, on the basis of seismotectonic, stratigraphic and fault analysis studies. This extension is documented to overprint structures related to the Mesozoic-Cenozoic Hellenic orogeny. Features attributed to early thrusting include the overall ductile deformation within two broad belts that have suffered HP/LT metamorphism across the Aegean. This study presents a structural analysis of the central Aegean area (Cyclades and Evvia Islands), examining in particular the relationship between ductile and brittle deformation, both in the field and on a regional scale. Extension appears to be responsible for most of the ductile deformation within HP rock units that have experienced penetrative greenschist facies and higher grade metamorphic over-printing. On each studied island, progressive extensional deformation has occurred through the development of a major normal-sense detachment zone down to depths of about 18-25 km. Large displacement along the detachment zone accounts for rapid cooling and exhumation of ductile lower crust to form a local metamorphic dome or core complex. Structural and stratigraphic features support a progressive migration of normal faulting away from the dome axis, and a rotation of previously active faults toward low dips, as in kinematic models recently suggested for the development of extensional detachment systems. All the studied domes, except that seen on los Island, show a dominant top-to-the north or north-east sense of shear, while on the southern flank of many of them, an opposite sense of shear is observed, displaying the same progressive evolution from ductile to brittle rock behaviour. This opposite sense of shear is thought not to result from shearing along a major conjugate detachment zone, as in some recent models, but from the accommodation in the ductile crust of upward bending of the brittle upper crust in the footwall of the north-dipping detachment. Available radiometric and stratigraphie data indicate an early minimum age (22-19 Ma) for the onset of extension. The relationship between early metamorphic domes and shallow-dipping detachments, on one hand, and Messinian-Quaternary steep normal faults and grabens, on the other hand, is best explained with the progressive and continuous development of new normal faults away from the domes axes, rather than with a two-stage evolutionary model (core-complex stage, then Basin-and-Range stage) of the type invoked for the North American Cordillera.  相似文献