Characterization of Mediterranean Magnetotactic Bacteria     

Lefèvre Christopher 《中国海洋大学学报(英文版)》2007,6(4):355-359

Magnetotactic bacteria are a diverse group of motile prokaryotes that are ubiquitous in aquatic habitats and cosmopolitan in distribution. In this study, we collected magnetotactic bacteria from the Mediterranean Sea. A remarkable diversity of morphotypes was observed, including multicellular types that seemed to differ from those previously found in North and South America. Another interesting organism was one with magnetosomes arranged in a six-stranded bundle which occupied one third of the cell width. The magnetosome bundle was evident even under optic microscopy. These cells were connected together and swam as a linear entire unit. Magnetosomes did not always align up to form a straight linear chain. A chain composed of rectangle magnetosomes bent at a posi- tion with an oval crystal. High resolution transmission electron microscopy analysis of the crystal at the pivotal position suggested uncompleted formation of the crystal. This is the first report of Mediterranean magnetotactic bacteria, which should be useful for studies of biogeochemical cycling and geohistory of the Mediterranean Sea.  相似文献   

Cassini UVIS observations of Jupiter's auroral variability     

Wayne R. Pryor  A. Ian F. Stewart  William E. McClintock  Alain J. Jouchoux  Donald E. Shemansky  Robert A. West  Bruce T. Tsurutani  George B. Hospodarsky  Kenneth C. Hansen  Frank J. Crary  Norbert Krupp  Denis Grodent 《Icarus》2005,178(2):312-326

The Cassini spacecraft Ultraviolet Imaging Spectrograph (UVIS) obtained observations of Jupiter's auroral emissions in H₂ band systems and H Lyman-α from day 275 of 2000 (October 1), to day 81 of 2001 (March 22). Much of the globally integrated auroral variability measured with UVIS can be explained simply in terms of the rotation of Jupiter's main auroral arcs with the planet. These arcs were also imaged by the Space Telescope Imaging Spectrograph (STIS) on Hubble Space Telescope (HST). However, several brightening events were seen by UVIS in which the global auroral output increased by a factor of 2-4. These events persisted over a number of hours and in one case can clearly be tied to a large solar coronal mass ejection event. The auroral UV emissions from these bursts also correspond to hectometric radio emission (0.5-16 MHz) increases reported by the Galileo Plasma Wave Spectrometer (PWS) and Cassini Radio and Plasma Wave Spectrometer (RPWS) experiments. In general, the hectometric radio data vary differently with longitude than the UV data because of radio wave beaming effects. The 2 largest events in the UVIS data were on 2000 day 280 (October 6) and on 2000 days 325-326 (November 20-21). The global brightening events on November 20-21 are compared with corresponding data on the interplanetary magnetic field, solar wind conditions, and energetic particle environment. ACE (Advanced Composition Explorer) solar wind data was numerically propagated from the Earth to Jupiter with an MHD code and compared to the observed event. A second class of brief auroral brightening events seen in HST (and probably UVIS) data that last for ∼2 min is associated with auroral flares inside the main auroral ovals. On January 8, 2001, from 18:45-19:35 UT UVIS H₂ band emissions from the north polar region varied quasiperiodically. The varying emissions, probably due to auroral flares inside the main auroral oval, are correlated with low-frequency quasiperiodic radio bursts in the 0.6-5 kHz Galileo PWS data.  相似文献   

Aspects of a conceptual groundwater flow model of the Serra Geral basalt aquifer (Sao Paulo,Brazil) from physical and structural geology data     

Amélia J. Fernandes  Carlos H. Maldaner  Francisco Negri  Alain Rouleau  Ingo D. Wahnfried 《Hydrogeology Journal》2016,24(5):1199-1212

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The Late Cretaceous igneous rocks of Romania (Apuseni Mountains and Banat): the possible role of amphibole versus plagioclase deep fractionation in two different crustal terranes     

Jacqueline Vander Auwera  Tudor Berza  Julie Gesels  Alain Dupont 《International Journal of Earth Sciences》2016,105(3):819-847

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Effects of water and fines contents on the resilient modulus of the interlayer soil of railway substructure     

Trong Vinh Duong  Yu-Jun Cui  Anh Minh Tang  Jean-Claude Dupla  Jean Canou  Nicolas Calon  Alain Robinet 《Acta Geotechnica》2016,11(1):51-59

This paper deals with the resilient behavior of the interlayer soil which is created mainly by the interpenetration of ballast and subgrade soils. The interlayer soil studied was taken from a site in the southeast of France. Large-scale cyclic triaxial tests were carried out at three water contents (w = 4, 6 and 12 %) and three fines contents corresponding to 5, 10 % subgrade added to the natural interlayer soil and 10 % fine particles (<80 μm) removed from the natural interlayer soil. Soil specimens underwent various deviator stresses, and for each deviator stress, a large number of cycles was applied. The effects of deviator stress, number of cycles, water content and fines content on the resilient modulus (M _r) were analyzed. It appears that the effects of water content and fines content must be analyzed together because the two effects are closely linked. Under unsaturated conditions, the soil containing high fines content has higher resilient modulus due to the contribution of suction. When the soil approaches the saturated state, it loses its mechanical enhancement with a sharp decrease in resilient modulus.  相似文献   

Impacts of land use and climate variability on algal communities since ~1850 CE in an oligotrophic estuary in northeastern New Brunswick,Canada     

Frantz Dorcel Ady  Alain Patoine 《Journal of Paleolimnology》2016,55(2):151-165

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Application of a novel cascade-routing and reinfiltration concept with a Voronoi unstructured grid in MODFLOW 6, for an assessment of surface-water/groundwater interactions in a hard-rock catchment (Sardon,Spain)     

Daoud  Mostafa Gomaa  Lubczynski  Maciek W.  Vekerdy  Zoltan  Franc&#;s  Alain Pascal 《Hydrogeology Journal》2022,30(3):899-925

Hydrogeology Journal - Integrated hydrological modelling (IHM) can reliably characterize surface-water/groundwater interactions in complex hydrological systems such as hard-rock systems (HRS),...  相似文献   

The usefulness of outcrop analogue air permeameter measurements for analyzing aquifer heterogeneity: quantifying outcrop hydraulic conductivity and its spatial variability          下载免费PDF全文

Bart Rogiers  Koen Beerten  Tuur Smeekens  Dirk Mallants  Matej Gedeon  Marijke Huysmans  Okke Batelaan  Alain Dassargues 《水文研究》2014,28(20):5176-5188

Saturated hydraulic conductivity (K) is one of the most important parameters determining groundwater flow and contaminant transport in both unsaturated and saturated porous media. Although several well‐established laboratory methods exist for determining K, in situ measurements of this parameter remain very complex and scale dependent. Often, the limited accessibility of subsurface sediments for sampling means an additional impediment to our ability to quantify subsurface K heterogeneity. One potential solution is the use of outcrops as analogues for subsurface sediments. This paper investigates the use of air permeameter measurements on outcrops of unconsolidated sediments to quantify K and its spatial heterogeneity on a broad range of sediment types. The Neogene aquifer in northern Belgium is used as a case study for this purpose. To characterize the variability in K, 511 small‐scale air permeability measurements were performed on outcrop sediments representative over five of the aquifer's lithostratigraphic units. From these measurements, outcrop‐scale equivalent K tensors were calculated using numerical upscaling techniques. Validation of the air permeameter‐based K values by comparison with laboratory constant head K measurements reveals a correlation of 0.93. Overall, the results indicate that hand‐held air permeameters are very efficient and accurate tools to characterize saturated K, as well as its small‐scale variability and anisotropy on a broad range of unconsolidated sediments. The studied outcrops further provided a qualitative understanding of aquifer hydrostratigraphy and quantitative estimates about K variability at the centimetre‐scale to metre‐scale. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Implementation of an automatic calibration procedure for HYDROTEL based on prior OAT sensitivity and complementary identifiability analysis          下载免费PDF全文

Médard Bouda  Alain N. Rousseau  Silvio J. Gumiere  Patrick Gagnon  Brou Konan  Roger Moussa 《水文研究》2014,28(12):3947-3961

Efficiency of hydrological models mostly depends on the quality of the calibration performed prior to use. In this paper, an automatic calibration framework for the distributed hydrological model HYDROTEL is proposed. The calibration procedure was performed for three watersheds characterized with different hydroclimatological conditions: the Sassandra located in Ivory Coast, Africa, and the Montmorency and Beaurivage watersheds located in Quebec (Canada). Results of one‐a‐time (OAT) sensitivity analysis showed that the order of the most sensitive parameters differs for each watershed. Thus, the sensitivity depends on the hydroclimatic and physiographic characteristics of the watersheds. Co‐linearity indices showed that all model parameters were identifiable, that is, none of the studied parameters could be explained by a combination of the other parameters. Following these findings, an automatic calibration was run. Results indicated there was good agreement between simulated and measured streamflows at the outlet of each watershed; Nash–Sutcliffe efficiency (NSE) ranging between 0.77 and 0.92 and R² ranging from 0.87 to 0.97. When comparing NSE and R² values obtained using a process‐oriented, multiple‐objective, manual calibration strategy, a slight increase in model efficiency was reached with the automatic calibration procedure (4.15% for NSE and 2.95% for R²) improving predictions of peak flows for the Montmorency and Beaurivage watersheds (temperate climate conditions) and flows beyond the rainfall season in the Sassandra watershed. The proposed automatic calibration procedure introduced in this paper may be applied to other distributed hydrological model. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

The linear steady response of a stratified baroclinic atmosphere to elevated diabatic forcing     

Alain Robichaud  Charles A. Lin 《大气与海洋》2013,51(4):619-635

Abstract

A parameter study is presented of the linear steady response to an elevated diabatic forcing in a Boussinesq baroclinic atmosphere. The model is two‐dimensional on the vertical plane; the basic wind is perpendicular to this plane with horizontal and vertical shear. The intensity of the circulation is sensitive to the strength of the baroclinic zone only for weak static stability. A scale analysis supports this conclusion: the importance of baroclinic effects depends on the ratio of the aspect ratio of the circulation to the aspect ratio of the baroclinic basic state. Baroclinicity also leads to a tilt of the circulation due to enhanced horizontal temperature advection, and the corresponding vertical flux of horizontal momentum. The magnitude of the latter can be large when the Richardson number approaches its critical value from above, i.e. for slightly symmetrically stable basic flows; this is true even with viscosity. The resonant limit where the Richardson number approaches the critical value for symmetric instability is also examined. For non‐zero dissipation, the critical value is smaller than that of the inviscid limit.  相似文献