A recent history of science cases for optical interferometry     

Denis Defrère  Conny Aerts  Makoto Kishimoto  Pierre Léna 《Experimental Astronomy》2018,46(3):389-399

Optical long-baseline interferometry is a unique and powerful technique for astronomical research. Since the 1980’s (with I2T, GI2T, Mark I to III, SUSI, ...), optical interferometers have produced an increasing number of scientific papers covering various fields of astrophysics. As current interferometric facilities are reaching their maturity, we take the opportunity in this paper to summarize the conclusions of a few key meetings, workshops, and conferences dedicated to interferometry. We present the most persistent recommendations related to science cases and discuss some key technological developments required to address them. In the era of extremely large telescopes, optical long-baseline interferometers will remain crucial to probe the smallest spatial scales and make breakthrough discoveries.  相似文献   

Methane-derived authigenic carbonates from active hydrocarbon seeps of the St. Lawrence Estuary,Canada     

Denis Lavoie  Nicolas Pinet  Mathieu Duchesne  Andrée Bolduc  Richard Larocque 《Marine and Petroleum Geology》2010

Nearly 2000 pockmarks with diameters ranging from a few tens of meters up to 700 m are present on the seafloor of the St. Lawrence Estuary in eastern Canada. Coring of some pockmarks resulted in the recovery of various-sized and shaped carbonate concretions in a predominantly silty mud matrix. Petrographic and geochemical data on four authigenic carbonate concretions are reported as well as data from shell material in the unconsolidated sediment. Video observations and echo-sounder images indicate that the sampled pockmarks are actively gas venting. The video images show significant look-alike microbial mats in areas where gas is venting. The carbonate concretions are primarily made up of carbonate cements with varying percentage of shell fragments, micrite particles and fine-grained clastics. Orthorhombic crystal morphology and diagenetic fabrics including isopachous layers and botryoids characterize the aragonite cement. Oxygen isotopes ratios for the cement crusts do not record any thermal anomaly at the site of precipitation with δ¹⁸O_VPDB ratios (+3‰) in equilibrium with cold (5 °C) deep marine waters, whereas significant negative δ¹³C_VPDB ratios (−9.9 to −33.5‰) for cement and shell material within concretions indicate that the carbonates largely derive from the microbial oxidation of methane. The δ¹³C_VPDB ratios of aragonite shells (−2.7 to −5.6‰) taken from unconsolidated sediments at some distance from the concretions/vents show variable dilution of HCO₃⁻ with negative δ¹³C_VPDB ratios derived from microbial oxidation of methane with isotopically normal (0‰) marine bicarbonate. These results are in agreement with other lines of evidence suggesting that pockmarks formed through the recent and still active release of gas from a reservoir within the Paleozoic sedimentary succession.  相似文献   

Benthic nutrient fluxes along the Laurentian Channel: Impacts on the N budget of the St. Lawrence marine system     

Benoît Thibodeau  Moritz F. Lehmann  Jacqueline Kowarzyk  Alfonso Mucci  Yves Gélinas  Denis Gilbert  Roxane Maranger  Mohammad Alkhatib 《Estuarine, Coastal and Shelf Science》2010

Water column concentrations and benthic fluxes of dissolved inorganic nitrogen (DIN) and oxygen (DO) were measured in the Gulf of St. Lawrence and the Upper and Lower St. Lawrence Estuary (USLE and LSLE, respectively) to assess the nitrogen (N) budget in the St. Lawrence (SL) system, as well as to elucidate the impact of bottom water hypoxia on fixed-N removal in the LSLE. A severe nitrate deficit, with respect to ambient phosphate concentrations (N*∼−10 μmol L⁻¹), was observed within and in the vicinity of the hypoxic bottom water of the LSLE. Given that DO concentrations in the water column have remained above 50 μmol L⁻¹, nitrate reduction in suboxic sediments, rather than in the water column, is most likely responsible for the removal of fixed N from the SL system. Net nitrate fluxes into the sediments, derived from pore water nitrate concentration gradients, ranged from 190 μmol m⁻² d⁻¹ in the hypoxic western LSLE to 100 μmol m⁻² d⁻¹ in the Gulf. The average total benthic nitrate reduction rate for the Laurentian Channel (LC) is on the order of 690 μmol m⁻² d⁻¹, with coupled nitrification-nitrate reduction accounting for more than 70%. Using average nitrate reduction rates derived from the observed water column nitrate deficit, the annual fixed-N elimination within the three main channels of the Gulf of St. Lawrence and LSLE was estimated at 411 × 10⁶ t N, yielding an almost balanced N budget for the SL marine system.  相似文献   

A global wave parameter database for geophysical applications. Part 1: Wave-current–turbulence interaction parameters for the open ocean based on traditional parameterizations     

Nicolas Rascle  Fabrice Ardhuin  Pierre Queffeulou  Denis Croiz-Fillon 《Ocean Modelling》2008,25(3-4):154-171

Ocean surface mixing and drift are influenced by the mixed layer depth, buoyancy fluxes and currents below the mixed layer. Drift and mixing are also functions of the surface Stokes drift U_ss, volume Stokes transport T_S, a wave breaking height scale H_swg, and the flux of energy from waves to ocean turbulence Φ_oc. Here we describe a global database of these parameters, estimated from a well-validated numerical wave model, that uses traditional forms of the wave generation and dissipation parameterizations, and covers the years 2003–2007. Compared to previous studies, the present work has the advantage of being consistent with the known physical processes that regulate the wave field and the air–sea fluxes, and also consistent with a very large number of in situ and satellite observations of wave parameters. Consequently, some of our estimates differ significantly from previous estimates. In particular, we find that the mean global integral of Φ_oc is 68 TW, and the yearly mean value of T_S is typically 10–30% of the Ekman transport, except in well-defined regions where it can reach 60%. We also have refined our previous estimates of U_ss by using a better treatment of the high frequency part of the wave spectrum. In the open ocean, U_ss  0.013U₁₀, where U₁₀ is the wind speed at 10 m height.  相似文献   

The relationship between the radio core-dominance parameter and spectral index in different classes of extragalactic radio sources(Ⅱ)     

Zhi-Yuan Pei  Jun-Hui Fan  Denis Bastieri  Utane Sawangwit  Jiang-He Yang 《天文和天体物理学研究(英文版)》2019,(5):75-90

Active galactic nuclei(AGNs) can be divided into two major classes, namely radio-loud and radio-quiet AGNs. A small subset of the radio-loud AGNs is called blazars, which are believed to be unified with Fanaroff-Riley type Ⅰ/Ⅱ(FRI/Ⅱ) radio galaxies. Following our previous work(Fan et al.), we present a sample of 2400 sources with measured radio flux densities of the core and extended components. The sample contains 250 BL Lacs, 520 quasars, 175 Seyferts, 1178 galaxies, 153 FRI or FRⅡ galaxies and 104 unidentified sources. We then calculate the radio core-dominance parameters and spectral indices, and study their relationship. Our analysis shows that the core-dominance parameters and spectral indices are quite different for different types of sources. We also confirm that the correlation between core-dominance parameter and spectral index exists for a large sample presented in this work.  相似文献   

Estimating masses of selected stars in the Pulkovo program by means of astrometry methods     

Natalia A.Shakht  Denis L.Gorshanov  Olga O.Vasilkova 《天文和天体物理学研究(英文版)》2018,(8)

Stars in the Pulkovo Observatory program are observed with a 65-cm refractor during many years to study their positions and movements. We present examples of two visual binary stars, for which orbits and masses of components were determined, and two astrometric stars, for which masses of their unseen companions were estimated. The first two stars are ADS 14636(61 Cygni) and ADS 7251,and the others are Gliese 623 and ADS 8035(Alpha UMa). Direct astrometric methods are used for estimation of mass-ratio and masses.  相似文献   

Spatio-temporal analysis of commercial trawler data using General Additive models: patterns of Loliginid squid abundance in the north-east Atlantic   总被引：5，自引：1，他引：5  

Denis  V.; Lejeune  J.; Robin  J. P. 《ICES Journal of Marine Science》2002,59(3):633-648

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A luminescence‐based chronology for the Harletz loess sequence,Bulgaria     

Johanna Lomax  Markus Fuchs  Pierre Antoine  Denis‐Didier Rousseau  France Lagroix  Christine Hatt  Samuel N. Taylor  Jessica L. Till  Maxime Debret  Olivier Moine  Diana Jordanova 《Boreas: An International Journal of Quaternary Research》2019,48(1):179-194

The Harletz loess‐palaeosol sequence is located in northwestern Bulgaria and represents an important link between well‐studied loess sequences in eastern Romania and further sites to the west of the Carpathians (e.g. Serbia and Hungary). The aim of this study was to establish a chronostratigraphy of the deposits, using various methods of luminescence dating, together with basic stratigraphical field observations as well as magnetic properties. Luminescence dating was carried out using the quartz fine grain fraction and a SAR protocol, and the feldspar coarse grain fraction, applying the MET‐pIRIR protocol. Due to underestimation of the quartz fine grain fraction in the lower parts of the sequence, the resulting chronology is mainly based on the feldspar ages, which are derived from the stimulation temperature at 150 °C. A comparison with nearby sequences from Serbia, Hungary and Romania, and interpretations obtained through the stratigraphical and sedimentological signature of the sequence, supports the established chronology. Our data suggest that the prominent palaeosol (soil complex) in the upper quarter of the sequence was formed during MIS 5. It would follow that large parts of the Last Glacial loess overlying this palaeosol were probably eroded, and that the thick loess accumulation underlying this soil complex can be allocated to the penultimate glacial (MIS 6). A prominent MIS 6 tephra, which has been reported from other sequences in the area, is also present at Harletz.  相似文献   

Book review     

Denis Marcotte  B. D. Ripley  C. John Mann 《Mathematical Geology》1986,18(8):861-868

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Vehicle tax policies and new passenger car CO2 performance in EU member states     

Denis Dineen  Brian Ó Gallachóir 《Climate Policy》2018,18(4):396-412

This article explores the causes for differences in the average CO₂ emissions intensity of the new passenger car (NPC) fleet in member states (MS) across Europe. Although EU policies mitigating CO₂ emissions from NPCs have been in place since 1999, MS strongly diverge in the absolute amount and relative change in emissions over the last decade. The authors employ a qualitative approach to analyse the factors, in particular national vehicle taxes, contributing to this divergence and the relative contribution of national and European policies in reducing national CO₂ emissions from NPCs. The analysis shows that there has been a significant reduction in CO₂ emissions intensity of NPCs since 2007 across most MS, compared with the six years previous to that date. This would indicate that EU-wide policies, such as the CO₂ vehicles regulation, along with the economic recession in 2008, have influenced national NPC CO₂ emissions. Generally, countries with CO₂-differentiated vehicle taxes are observed as more likely to have achieved greater reductions in CO₂ emissions. However, over the same period there have been many confounding factors, such as economic instability in the EU, that also influence NPC emissions. Using more detailed case study analyses of six countries, the authors find that there is scope for well-designed national vehicle tax policies to drive NPC emissions down further than the EU average. In countries with the highest success rate, such as the Netherlands, the design of the vehicle tax, as part of a well-aligned policy package, has been very important in delivering the biggest reductions in CO₂ emissions from NPCs.

POLICY RELEVANCE

The transport sector continues to be an intractable source of CO₂ emissions. Governments around the world are seeking effective policies to deal with the increase in passenger car CO₂ emissions appropriate to their own circumstances. This article examines the experience of EU MS with CO₂-differentiated vehicle taxes in reducing CO₂ emissions in the context of other national and international contributing factors. It should therefore both be useful to policy makers and contribute to climate policy research in general.  相似文献