Radial velocities in the open cluster IC 2391     

Hugo Levato  Beatriz García  Carlos Loustó  Nidia Morrell 《Astrophysics and Space Science》1988,146(2):361-373

We have determined radial velocities for 31 stars in the field of the open cluster IC 2391, and derived the percentage of probable radial-velocity variables. We improved the orbit of one previously known spectroscopic binary, and confirmed the existence of two double-line binaries. We discussed with such data the membership to the cluster, the average cluster radial velocity and compared the incidence of short-period binaries among the Main-Sequence members of IC 2391 with the incidence for other clusters with similar average axial rotation of its members.Member of the Carrera del Investigador Científico del Consejo Nacional de Investigaciones Científicas y Técnicas de la República ArgentinaVisiting Astronomer, Cerro Tololo Inter-American Observatory, operated by AURA, Inc. under contract with the National Science Foundation.  相似文献   

Rb-Sr dating of alteration events in granitoids     

Frans E. Wickman  Göran Åberg  Beatriz Levi 《Contributions to Mineralogy and Petrology》1983,83(3-4):358-362

Veins and other effects of low-grade metamorphism are often found in igneous rocks. A method for dating such veins is proposed. It is based on the presence of Ca-bearing, Rb-free minerals in the veins and their aureoles. The method is applicable if five conditions are satisfied. The effects of low-grade metamorphism on Rb-Sr dating of the emplacement (extrusion) age are also studied. Veins and their aureoles in granitoid rocks from Central Sweden are used as a working example. Two groups of vein ages were found, 1600-1500 Ma and 1250-1100 Ma, which coincide with the two known periods of tensional movements in the region. The ratio ⁸⁷Sr/⁸⁶Sr in the aureoles and their neighbourhood at the time of vein formation (Sr(a)) shows several different patterns. One with constant Sr(a), independent of the distance to the vein, indicates complete homogenization at the time of alteration. Another shows an increase in Sr(a) close to the vein, indicating that it was rejuvenated. Furthermore, the Sr ratio might determine whether an alteration effect could be of deuteric origin or not: deuteric effects should be characterized by a Sr(a) value equal to the initial Sr-isotope ratio.  相似文献   

Volcanic emissions and atmospheric pollution:A study of nanoparticles     

Erika M.Trejos  Luis F.O.Silva  James C.Hower  Eriko M.M.Flores  Carlos Mario González  Jorge E.Pachón  Beatriz H.Aristizábal 《地学前缘(英文版)》2021,12(2):746-755

The influence of emissions of an active volcano on the composition of nanoparticles and ultrafine road dust was identified in an urban area of the Andes.Although many cities are close to active volcanoes,few studies have evaluated their influence in road dust composition.Air quality in urban areas is significantly affected by nonexhaust emissions(e.g.road dust,brake wear,tire wear),however,natural sources such as volcanoes also impact the chemical composition of the particles.In this study,elements from volcanic emissions such as Si>Al>Fe>Ca>K>Mg,and Si-Al with K were identified as complex hydrates.Similarly,As,Hg,Cd,Pb,As,H,Cd,Pb,V,and salammoniac were observed in nanoparticles and ultrafine material.Mineral composition was detected in the order of quartz>mullite>calcite>kaolinite>illite>goethite>magnetite>zircon>monazite,in addition to salammoniac,a tracer of volcanic sources.The foregoing analysis reflects the importance of carrying out more studies relating the influence of volcanic emissions in road dust in order to protect human health.The road dust load(RD₁₀)ranged between 0.8 and 26.8 mg m^?2in the city.  相似文献   

Mapping climate change adaptive capacity and vulnerability of smallholder agricultural livelihoods in Central America: ranking and descriptive approaches to support adaptation strategies   总被引：1，自引：0，他引：1  

Claudia Bouroncle  Pablo Imbach  Beatriz Rodríguez-Sánchez  Claudia Medellín  Armando Martinez-Valle  Peter Läderach 《Climatic change》2017,141(1):123-137

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Unexpected High Levels of Ozone Measured in Córdoba, Argentina     

Luis E. Olcese  Beatriz M. Toselli 《Journal of Atmospheric Chemistry》1998,31(3):269-279

Results of field measurements carried out from June 15 to December 31, 1995, in Córdoba city (Argentina) are presented. During this field campaign, surface ozone mixing ratios were generally around 30–35 ppb (afternoon peak). However, during the first week of September, days with excessive ozone values close to 100 ppb were found. These elevated ozone concentrations appeared together with high values of NOx, CO, PM10, and an unusual meteorological situation for this time of the year. These results made this episode an interesting one to be studied in more detail. In this work, we used chemical and meteorological data to trace the region from where the assumed precursors were emitted and we identified possible source characteristics.  相似文献   

Groundwater capture processes under a seasonal variation in natural recharge and discharge   总被引：1，自引：1，他引：0  

Thomas Maddock III.  Leticia Beatriz Vionnet 《Hydrogeology Journal》1998,6(1):24-32

 "Capture" is the increase in recharge and the decrease in discharge that occurs when pumping is imposed on an aquifer system that was in a previous state of approximate dynamic equilibrium. Regional groundwater models are usually used to calculate capture in a two-step procedure. A steady-state solution provides an initial-head configuration, a set of flows through the boundaries for the modeled region, and the initial basis for the capture calculation. The transient solutions provide the total change in flows through the boundaries. A difference between the transient and steady-state solutions renders the capture calculation. When seasonality is a modeling issue, the use of a single initial hydraulic head and a single set of boundary flows leads to miscalculations of capture. Instead, an initial condition for each season should be used. This approach may be accomplished by determining steady oscillatory solutions, which vary through the seasons but repeat from year to year. A regional groundwater model previously developed for a portion of the San Pedro River basin, Arizona, USA, is modified to illustrate the effect that different initial conditions have on transient solutions and on capture calculations. Received, September 1996 · Revised, October 1997 · Accepted, October 1997  相似文献   

A Drowned Lagunar Channel in the Southern Brazilian Coast in Response to the 8.2-ka Event: Diatom and Seismic Stratigraphy     

Cristiane Bahi dos Santos-Fischer  Jair Weschenfelder  Iran Carlos Stalliviere Corrêa  Jeffery Robert Stone  Beatriz Appel Dehnhardt  Eduardo Calixto Bortolin 《Estuaries and Coasts》2018,41(6):1601-1625

Drowning of the coast was initiated by a marine inundation after the Last Glacial Maximum (marine isotope stage (MIS) 2) and has continued during the mid-Holocene and highstand (MIS 1). Detailed analyses of two previously examined core stratigraphy and seismic profiles combined with new grain-size and detailed diatom analyses are used to study the history of the Barra Falsa paleochannel over the last 11,000 years BP and to document the peculiar deposition within the channel fill. A rapid sea-level rise was responsible for flooding the coast in 11,180–10,780, 8420–7930, 8150–7870, and 7640–7430 cal years BP, infilling a low topographic back-barrier region. High deposition rates suggest a rapid filling of the channel, which coincides with an accelerated period of sea-level rise, closely linked to the global 8.2-ka event. The morphology of the channel is recognized by facies units in the underlying strata related to one episode of cut and fill during a single cycle of base-level fall and rise. An overall transgressive sequence above the regional surface is related to marine and marine-brackish sediments, which corresponds to a seaward/central basil fill of a wave-dominated estuary.  相似文献   

Spatial distribution pattern analysis of subtidal macroalgae assemblages by a non-destructive rapid assessment method     

Xabier Guinda  José Antonio JuanesAraceli Puente  Beatriz Echavarri-Erasun 《Journal of Sea Research》2012,67(1):34-43

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Late Pleistocene: Holocene record of environmental changes in Lake Zirahuen,Central Mexico     

Beatriz Ortega  Gabriel Vázquez  Margarita Caballero  Isabel Israde  Socorro Lozano-García  Peter Schaaf  Esperanza Torres 《Journal of Paleolimnology》2010,44(3):745-760

Geochemical data obtained from X-ray fluorescence, physical properties, total organic and inorganic carbon content (TOC/TIC), and diatom analysis from a 6.61-m-long sedimentary sequence near the modern northern shore of Lake Zirahuen (101° 44′ W, 19° 26′ N, 2000 m asl) provide a reconstruction of lacustrine sedimentation during the last approximately 17 cal kyr BP. A time scale is based on ten AMS ¹⁴C dates and by tephra layers from Jorullo (AD 1759-1764) and Paricutin (AD 1943-1952) volcanoes. The multiproxy analyses presented in this study reveal abrupt changes in environmental and climatic conditions. The results are compared to the paleo-record from nearby Lake Patzcuaro. Dry conditions and low lake level are inferred in the late Pleistocene until ca. 15 cal kyr BP, followed by a slight but sustained increase in lake level, as well as a higher productivity, peaking at ca. 12.1 cal kyr BP. This interpretation is consistent with several regional climatic reconstructions in central Mexico, but it is in opposition to record from Lake Patzcuaro. A sediment hiatus bracketed between 12.1 and 7.2 cal kyr BP suggests a drop in lake level in response to a dry early Holocene. A deeper, more eutrophic and turbid lake is recorded after 7.2 cal kyr BP. Lake level at the coring site during the mid Holocene is considered the highest for the past 17 cal kyr BP. The emplacement of the La Magueyera lava flows (LMLF), dated by thermoluminiscence at 6560 ± 950 year, may have reduced basin volume and contributed to the relative deepening of the lake after 7.2 cal kyr BP. The late Holocene (after 3.9 cal kyr BP) climate is characterized by high instability. Extensive erosion, lower lake levels, dry conditions and pulses of high sediment influx due to high rainfall are inferred for this time. Further decrease in lake level and increased erosion are recorded after ca. AD 1050, at the peak of Purepechas occupation (AD 1300–1521), and until the eighteenth century. Few lacustrine records extend back to the late Pleistocene—early Holocene in central Mexico; this paper contributes to the understanding of late Pleistocene-Holocene paleoclimates in this region.  相似文献   

Bioremediation of Oil‐Contaminated Beach and Restinga Sediments Using a Slow‐Release Fertilizer          下载免费PDF全文

Beatriz Rohden Becker  Eliane Soares de Souza  Rodrigo Lemes Martins  Júlia da Luz Bueno 《洁净——土壤、空气、水》2016,44(9):1154-1162

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