Flounder health status in the Seine Bay. A multibiomarker study.     

C Minier  F Levy  D Rabel  G Bocquené  D Godefroy  T Burgeot  F Leboulenger 《Marine environmental research》2000,50(1-5):373-377

The Seine Bay is used as a pilot area to assess the usefulness of monitoring programmes using a suite of biological measurements. These biomarkers included ethoxyresorfin-O-deethylase (EROD) and acetylcholinesterase (AChE) activities, multixenobiotic resistance (MXR) protein expression level assessment and gonad histopathology. Samples of European flounder collected in three sites close to the Seine Estuary in late September 1998 showed that 8% of the males were intersex, i.e. had gonads with both male and female tissues. Another 10% of individuals, identified as male by morphological observation during sampling, showed only female tissues on histological sections. These dramatic changes were associated with different patterns of EROD activity, MXR expression or AChE activity inhibition that might reflect shorter time effects of xenobiotics and constitute a starting point to integrate biological responses for the assessment of the health status of flounder in the Seine Bay.  相似文献   

The activity of chromite in multicomponent spinels: Implications for T‐fO2 conditions of equilibrated H chondrites     

Ronit Kessel  John R. Beckett  Gary R. Huss  Edward M. Stolper 《Meteoritics & planetary science》2004,39(8):1287-1305

Abstract— Activities of chromite in multicomponent spinels with compositions similar to those of H chondrites were experimentally determined by equilibrating Pt‐alloys with spinel at known temperature and fO₂. Our results are consistent with predictions based on the spinel solid solution model incorporated into the MELTS program. Therefore, we combined literature formulations for the activities of components in spinel, the ferromagnesian silicates, and alloys with measured and literature (bulk alloy) compositions of the meteoritic phases to constrain T‐fO₂ conditions for the H‐group chondrites Avanhandava (H4), Allegan (H5), and Guareña (H6). Log₁₀fO₂ values based on the assemblage of olivine + orthopyroxene + metal are 2.19–2.56 log units below the iron‐wüstite (IW) buffer for any equilibration temperature between 740 and 990 °C, regardless of petrographic type. Only lower limits on fO₂ could be determined from spinel + metal equilibria because of the extremely low concentrations of Cr in the alloys of equilibrated H chondrites (≤3 ppb). Log₁₀fO₂ values required by spinel + metal equilibria are inconsistent with those for olivine + orthopyroxene + metal if equilibration temperatures were at or above those inferred from olivine‐spinel thermometry. This probably indicates that the closure for spinel + metal equilibria occurred under retrograde conditions at temperatures below ～625 °C for Allegan and Guareña and below ～660 °C for Avanhandava.  相似文献   

Estimation of Aquifer Diffusivity from Analysis of Constant-Head Pumping Test Data   总被引：1，自引：0，他引：1  

Christian K. Hiller  Benjamin S. Levy 《Ground water》1994,32(1):47-52

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Seasonal controls on sediment transport and deposition in Lake Ohau,South Island,New Zealand: Implications for a high‐resolution Holocene palaeoclimate reconstruction          下载免费PDF全文

Heidi A. Roop  Gavin B. Dunbar  Richard Levy  Marcus J. Vandergoes  Alexander L. Forrest  Sharon L. Walker  Jennifer Purdie  Phaedra Upton  James Whinney 《Sedimentology》2015,62(3):826-844

Laminated sediments in Lake Ohau, Mackenzie Basin, New Zealand, offer a potential high‐resolution climate record for the past 17 kyr. Such records are particularly important due to the relative paucity of detailed palaeoclimate data from the Southern Hemisphere mid‐latitudes. This paper presents outcomes of a study of the sedimentation processes of this temperate lake setting. Hydrometeorological, limnological and sedimentological data were collected over a 14 month period between 2011 and 2013. These data indicate that seasonality in the hydrometeorological system in combination with internal lake dynamics drives a distinct seasonal pattern of sediment dispersal and deposition on a basin‐wide scale. Sedimentary layers that accumulate proximal to the lake inflow at the northern end of the lake form in response to discrete inflow events throughout the year and display an event stratigraphy. In contrast, seasonal change in the lake system controls accumulation of light (winter) and dark (summer) laminations at the distal end of the lake, resulting in the preservation of varves. This study documents the key processes influencing sediment deposition throughout Lake Ohau and provides fundamental data for generating a high‐resolution palaeoclimate record from this temperate lake.  相似文献   

OSS (Outer Solar System): a fundamental and planetary physics mission to Neptune, Triton and the Kuiper Belt     

B. Christophe  L. J. Spilker  J. D. Anderson  N. André  S. W. Asmar  J. Aurnou  D. Banfield  A. Barucci  O. Bertolami  R. Bingham  P. Brown  B. Cecconi  J. -M. Courty  H. Dittus  L. N. Fletcher  B. Foulon  F. Francisco  P. J. S. Gil  K. H. Glassmeier  W. Grundy  C. Hansen  J. Helbert  R. Helled  H. Hussmann  B. Lamine  C. L?mmerzahl  L. Lamy  R. Lehoucq  B. Lenoir  A. Levy  G. Orton  J. Páramos  J. Poncy  F. Postberg  S. V. Progrebenko  K. R. Reh  S. Reynaud  C. Robert  E. Samain  J. Saur  K. M. Sayanagi  N. Schmitz  H. Selig  F. Sohl  T. R. Spilker  R. Srama  K. Stephan  P. Touboul  P. Wolf 《Experimental Astronomy》2012,34(2):203-242

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Moveout approximation for horizontal transversely isotropic and vertical transversely isotropic layered medium. Part II: effective model‡     

Zvi Koren  Igor Ravve  Ronit Levy 《Geophysical Prospecting》2010,58(4):599-617

We use residual moveouts measured along continuous full azimuth reflection angle gathers, in order to obtain effective horizontal transversely isotropic model parameters. The angle gathers are generated through a special angle domain imaging system, for a wide range of reflection angles and full range of phase velocity azimuths. The estimation of the effective model parameters is performed in two stages. First, the background horizontal transversely isotropic (HTI)/vertical transversely isotropic (VTI) layered model is used, along with the values of reflection angles, for converting the measured residual moveouts (or traveltime errors) into azimuthally dependent normal moveout (NMO) velocities. Then we apply a digital Fourier transform to convert the NMO velocities into azimuthal wavenumber domain, in order to obtain the effective HTI model parameters: vertical time, vertical compression velocity, Thomsen parameter delta and the azimuth of the medium axis of symmetry. The method also provides a reliability criterion of the HTI assumption. The criterion shows whether the medium possesses the HTI type of symmetry, or whether the azimuthal dependence of the residual traveltime indicates to a more complex azimuthal anisotropy. The effective model used in this approach is defined for a 1D structure with a set of HTI, VTI and isotropic layers (with at least one HTI layer). We describe and analyse the reduction of a multi‐layer structure into an equivalent effective HTI model. The equivalent model yields the same NMO velocity and the same offset azimuth on the Earth's surface as the original layered structure, for any azimuth of the phase velocity. The effective model approximates the kinematics of an HTI/VTI layered structure using only a few parameters. Under the hyperbolic approximation, the proposed effective model is exact.  相似文献   

Long‐term variability of proglacial groundwater‐fed hydrological systems in an area of glacier retreat,Skeiðarársandur,Iceland          下载免费PDF全文

Amir Levy  Zoe Robinson  Stefan Krause  Richard Waller  John Weatherill 《地球表面变化过程与地形》2015,40(7):981-994

Proglacial groundwater‐fed features, such as seeps, substantially impact proglacial geomorphology, hydrology, and ecology. However, there is a paucity of research on the impacts of climate change and glacier retreat on the extent of these important features. This paper aims to investigate the impact of glacier retreat on proglacial groundwater levels and on the extent of groundwater‐fed seeps. Research has taken place in western Skeiðarársandur, the large proglacial outwash plain of Skeiðarárjökull, a retreating temperate glacier in southeast Iceland. Changes in the extent of proglacial groundwater seeps were mapped using historical aerial photographs from 1986, 1997, and 2012. Proglacial groundwater levels were monitored in shallow boreholes between 2000 and 2012. The western margin of Skeiðarárjökull has retreated approximately 1 km beyond its position in 1986. However, this retreat was punctuated by short periods of readvance. The geomorphology and groundwater systems at the site were substantially impacted by the November 1996 jökulhlaup, whose deposits altered approximately 18% of the area of groundwater seeps. The surface areas of groundwater seeps and lakes in the study area have declined by ~97% between 1986 and 2012. Most of the decline took place after 1997, when the mean annual rate of retreat increased three‐fold. Groundwater levels also declined substantially between 2000 and 2012, although this trend varies spatially. The paper provides a conceptual model of the controls on proglacial shallow groundwater systems. Direct impacts of glacier retreat are suggested as the main cause for the declines in proglacial groundwater levels and in the extent of groundwater seeps. These declines are expected to adversely impact sandur ecology. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

The circumstellar imager: Direct detection of extra-solar planetary systems     

Christ Ftaclas  Andreas L. Nonnenmacher  Richard J. Terrile  Steven H. Pravdo  George D. Gatewood  Eugene H. Levy 《Astrophysics and Space Science》1994,212(1-2):441-452

The Astrometric Imaging Telescope (AIT) is designed to probe the circumstellar environment by both direct imaging and indirect astrometric measurements. The Circumstellar Imager (CI) is a coronagraphic camera and is the direct imaging component of the AIT. The CI is designed to obtain high-sensitivity images of the circumstellar region. It provides crucial non-inferential information relating to the frequency, origin, and evolution of planetary systems and all forms of circumstellar matter. Such imaging is usually limited by the scattered and diffracted light halos of the star itself, which are greatly suppressed in the CI by mating a novel high-efficiency coronagraph with a phasecompensated optical system. For faint point sources in the circumstellar region, the CI will have a sensitivity in excess of 5 magnitudes fainter than the as-designed Hubble Space Telescope (HST). Laboratory data are shown for the coronagraph, which, in a diffraction-limited environment, is capable of suppressing the stellar diffraction sidelobes by several orders of magnitude without significant sacrifice of field of view. In order to realize the high rejection levels inherent in the coronagraph design, it is necessary to limit scatter in the optical systems, imposing a mid-spatial frequency figure error requirement an order of magnitude smaller than that of the HST. Experimental data directed toward meeting this requirement are also shown.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.  相似文献   

The mean coronal magnetic field determined from HELIOS Faraday rotation measurements     

M. Pätzold  M. K. Bird  H. Volland  G. S. Levy  B. L. Seidel  C. T. Stelzried 《Solar physics》1987,109(1):91-105

Coronal Faraday rotation of the linearly polarized carrier signals of the HELIOS spacecraft was recorded during the regularly occurring solar occultations over almost a complete solar cycle from 1975 to 1984. These measurements are used to determine the average strength and radial variation of the coronal magnetic field at solar minimum at solar distances from 3–10 solar radii, i.e., the range over which the complex fields at the coronal base are transformed into the interplanetary spiral. The mean coronal magnetic field in 1975–1976 was found to decrease with radial distance according to r ^?α, where α = 2.7 ± 0.2. The mean field magnitude was 1.0 ± 0.5 × 10 ^?5 tesla at a nominal solar distance of 5 solar radii. Possibly higher magnetic field strengths were indicated at solar maximum, but a lack of data prevented a statistical determination of the mean coronal field during this epoch.  相似文献   

A magnetic dynamo in the moon?     

Eugene H. Levy 《Earth, Moon, and Planets》1974,9(1-2):49-56

The existence of fossil lunar magnetism has caused speculation that the Moon had, at one time, an internally produced dynamo magnetic field. Quantitative analysis of this idea, constrained by the largest iron lunar core compatible with observations, implies that the Moon would have had to rotate faster than its breakup angular velocity in order to support a dynamo magnetic field.A paper presented at the Lunar Science Institute Conference on Geophysical and Geochemical Exploration of the Moon and Planets, January 10–12, 1973.  相似文献