Wavelike Structures in the Turbulent Layer During the Morning Development of Convection at Dome C,Antarctica     

Igor Petenko  Stefania Argentini  Giampietro Casasanta  Margarita Kallistratova  Roberto Sozzi  Angelo Viola 《Boundary-Layer Meteorology》2016,161(2):289-307

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Solid phases controlling the mobility of potentially toxic elements and the generation of acid drainage in abandoned mine gold wastes from San Antonio–El Triunfo mining district,Baja California Sur,México     

Ernesto Hernández-Mendiola  Francisco Martín Romero  Margarita Gutiérrez-Ruiz  Carlos Alberto Magdaleno Rico 《Environmental Earth Sciences》2016,75(11):969

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Low-Level Jets in the Moscow Region in Summer and Winter Observed with a Sodar Network     

Margarita A. Kallistratova  Rostislav D. Kouznetsov 《Boundary-Layer Meteorology》2012,143(1):159-175

We evaluate the statistical properties of low-level jets (LLJs) observed by means of a network of Doppler sodars in the Moscow region, Russia. Continuous long-term measurements of the echo-signal intensity and wind-velocity profiles were carried out in July 2005 and in 2008–2010 synchronously in the centre of Moscow and at a rural site. The summertime nocturnal LLJs have a very clear diurnal cycle and exhibit features predicted by the Blackadar mechanism. In contrast, the long-lasting wintertime jets do not have any clear diurnal variability. The urban environment strongly influences LLJs in both seasons: above the city LLJs are higher, weaker and observed more rarely than at the rural site. In very cold periods (air temperature below −8°C) no LLJs were observed over the city, instead convection emerged in the urban boundary layer. The results are based on observations made in July 2005, January and December 2009, and January 2011.  相似文献   

The fresnel interferometric imager     

Laurent Koechlin  Denis Serre  Paul Deba  Roser Pelló  Christelle Peillon  Paul Duchon  Ana Ines Gomez de Castro  Margarita Karovska  Jean-Michel Désert  David Ehrenreich  Guillaume Hebrard  Alain Lecavelier des Etangs  Roger Ferlet  David Sing  Alfred Vidal-Madjar 《Experimental Astronomy》2009,23(1):379-402

The Fresnel Interferometric Imager has been proposed to the European Space Agency (ESA) Cosmic Vision plan as a class L mission. This mission addresses several themes of the CV Plan: Exoplanet study, Matter in extreme conditions, and The Universe taking shape. This paper is an abridged version of the original ESA proposal. We have removed most of the technical and financial issues, to concentrate on the instrumental design and astrophysical missions. The instrument proposed is an ultra-lightweight telescope, featuring a novel optical concept based on diffraction focussing. It yields high dynamic range images, while releasing constraints on positioning and manufacturing of the main optical elements. This concept should open the way to very large apertures in space. In this two spacecraft formation-flying instrument, one spacecraft holds the focussing element: the Fresnel interferometric array; the other spacecraft holds the field optics, focal instrumentation, and detectors. The Fresnel array proposed here is a 3.6 ×3.6 m square opaque foil punched with 10⁵ to 10⁶ void “subapertures”. Focusing is achieved with no other optical element: the shape and positioning of the subapertures (holes in the foil) is responsible for beam combining by diffraction, and 5% to 10% of the total incident light ends up into a sharp focus. The consequence of this high number of subapertures is high dynamic range images. In addition, as it uses only a combination of vacuum and opaque material, this focussing method is potentially efficient over a very broad wavelength domain. The focal length of such diffractive focussing devices is wavelength dependent. However, this can be corrected. We have tested optically the efficiency of the chromatism correction on artificial sources (500 < λ < 750 nm): the images are diffraction limited, and the dynamic range measured on an artificial double source reaches 6.2 10^− 6. We have also validated numerical simulation algorithms for larger Fresnel interferometric arrays. These simulations yield a dynamic range (rejection factor) close to 10^− 8 for arrays such as the 3.6 m one we propose. A dynamic range of 10^− 8 allows detection of objects at contrasts as high as than 10^− 9 in most of the field. The astrophysical applications cover many objects in the IR, visible an UV domains. Examples are presented, taking advantage of the high angular resolution and dynamic range capabilities of this concept.  相似文献   

Geochemistry of the Kola River, northwestern Russia     

Larisa Pekka  Johan Ingri  Anders Widerlund  Olga Mokrotovarova  Margarita Riabtseva  Bjrn hlander 《Applied Geochemistry》2004,19(12):62

The Kola River in the northern part of the Kola Peninsula, northwestern Russia, flows into the Barents Sea via the Kola Bay. The river is a unique place for reproduction of salmon and an important source of drinking water for more than 500,000 people in Murmansk and the surrounding municipalities. To evaluate the environmental status of the Kola River water, sampling of the dissolved (<0.22 μm) and suspended (>0.22 μm) phases was performed at 12 sites along the Kola River and its tributaries during 2001 and 2002. Major (Ca, K, Mg, Na, S, Si, HCO₃ and Cl) and trace (Al, As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sr, Ti, and Zn) elements, total and particulate organic C (TOC and POC), N and P were analysed. Comparison with the boreal pristine Kalix River, Northern Sweden, shows that, except for Na, Cl, Al, Cu and Ni, which exceed the concentrations in the Kalix River by as much as 2–3 times, the levels of other major and trace elements are close to or even below the levels in the Kalix River. However, the results also demonstrate that pollutants from the three major sources: (1) the Cu–Ni smelter in Monchegorsk, (2) the open-pit Fe mine and ore concentration plant in Olenegorsk, and (3) the Varlamov, the Medveziy and the Zemlanoy creeks, draining the area of the large agricultural enterprises in the lower part of the watershed, have a major influence on the water quality of the Kola River.  相似文献   

Shear wave splitting beneath South Kamchatka during the 3-year period associated with the 1997 Kronotsky Earthquake     

Margarita N. Luneva  Jung Mo Lee   《Tectonophysics》2003,374(3-4):135-161

Shear wave splitting measurements in South Kamchatka during the 3-year period (1996–1998) in which the Kronotsky Earthquake (M=7.7, December 5, 1997) occurred are used to determine anisotropic parameters of the subduction zone and shear wave splitting variations with time. The local small seismic events recorded at the Petropavlovskaya IRIS station (PET) were analyzed. The dominant azimuths of the fast shear wave polarizations for the 3-year period are defined within N95±15°E, which are consistent with the general Pacific Plate motion direction. Modeling of fast shear wave polarizations shows that HTI model with the symmetry axis oriented along N15°E±10° fit well the observed data for events the focal depths of which are less than 80 km. For the greater depths, the orthorhombic symmetry of medium is not excluded. The anisotropy coefficient increases generally with depth from 1–2% in the crust to 4–7.5% in the subducting plate. Variations in time delays show a general increase up to 10–15 ms/km during 1996–1997 before the large crustal earthquake series (M≈5.5–7) in the Avacha Bay and before the Kronotsky Earthquake. Analysis of fast S-wave azimuths of mantle events reveals a temporal cyclic variation. The most regular variations are observed for fast azimuths of deep events with a period of about 172 days over the 3-year period. The fast polarizations of crustal events behave comparatively stable. It is assumed that the major instabilities in stress state are localized in the descending slab and influenced the upper mantle and comparatively stable crust.  相似文献   

Evolutionary calculations of carbon dredge-up in helium envelope white dwarfs     

James MacDonald  Margarita Hernanz  & Jordi José 《Monthly notices of the Royal Astronomical Society》1998,296(3):523-530

We investigate the evolution of cooling helium atmosphere white dwarfs using a full evolutionary code, specifically developed to follow the effects of element diffusion and gravitational settling on white dwarf cooling. The major difference between this work and previous work is that we use more recent opacity data from the OPAL project. Since, in general, these opacities are higher than those available 10 years ago, at a given effective temperature, convection zones go deeper than in models with older opacity data. Thus convective dredge-up of observationally detectable carbon in helium atmosphere white dwarfs can occur for thicker helium layers than found by Pelletier et al. We find that the range of observed C to He ratios in different DQ white dwarfs of similar effective temperature is well explained by a range of initial helium layer mass between 10⁻³ and 10⁻² M⊙, in good agreement with stellar evolution theory, assuming a typical white dwarf mass of 0.6 M⊙. We also predict that oxygen will be present in DQ white dwarf atmospheres in detectable amounts if the helium layer mass is near the lower limit compatible with stellar evolution theory. Determination of the oxygen abundance has the potential of providing information on the profile of oxygen in the core and hence on the important ¹²C(α,γ)¹⁶O reaction rate.  相似文献   

A water balance model to estimate climate change impact on groundwater recharge in Yucatan Peninsula,Mexico     

Edgar Rodríguez-Huerta  Martí Rosas-Casals  Laura Margarita Hernández-Terrones 《水文科学杂志》2020,65(3):470-486

ABSTRACT

The aim of this paper is to estimate the effect that climate change will have on groundwater recharge at the Yucatan Peninsula, Mexico. The groundwater recharge is calculated from a monthly water balance model considering eight methods of potential and actual evapotranspiration. Historical data from 1961–2000 and climate model outputs from five downscaled general circulation models in the near horizon (2015–2039), with representative concentration pathway (RCP) 4.5 and 8.5 are used. The results estimate a recharge of 118 ± 33 mm·year^–1 (around 10% of precipitation) in the historical period. Considering the uncertainty from GCMs under different RCP and evapotranspiration scenarios, our monthly water balance model estimates a groundwater recharge of 92 ± 40 mm·year^–1 (RCP4.5) and 94 ± 38 mm·year^–1 (RCP8.5) which represent a reduction of 23% and 20%, respectively, a result that threatens the socio-ecological balance of the region.  相似文献   

Prospects for observations of transient UV Events with the TAUVEX UV observatory     

Margarita Safonova  C. Sivaram  Jayant Murthy 《Astrophysics and Space Science》2008,318(1-2):1-12

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Responses to a warming trend and “El Niño” events in a tropical lake in western Mexico     

Margarita Caballero  Gabriela Vázquez  Beatriz Ortega  Mario E. Favila  Socorro Lozano-García 《Aquatic Sciences - Research Across Boundaries》2016,78(3):591-604

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