Studies of multiple stellar systems – IV. The triple-lined spectroscopic system Gliese 644     

Tsevi Mazeh  David W. Latham  Elad Goldberg  Guillermo Torres  Robert P. Stefanik  Todd J. Henry †  Shay Zucker  Orly Gnat  Eran O. Ofek 《Monthly notices of the Royal Astronomical Society》2001,325(1):343-357

We present a radial velocity study of the triple-lined system Gliese 644 and derive spectroscopic elements for the inner and outer orbits with periods of 2.965 5 and 627 d. We also utilize old visual data, as well as modern speckle and adaptive optics observations, to derive a new astrometric solution for the outer orbit. These two orbits together allow us to derive masses for each of the three components in the system: M _A=0.410±0.028 (6.9 per cent), M _Ba=0.336±0.016 (4.7 per cent), and M _Bb=0.304±0.014 (4.7 per cent) M_⊙. We suggest that the relative inclination of the two orbits is very small. Our individual masses and spectroscopic light ratios for the three M stars in the Gliese 644 system provide three points for the mass–luminosity relation near the bottom of the main sequence, where the relation is poorly determined. These three points agree well with theoretical models for solar metallicity and an age of 5 Gyr. Our radial velocities for Gliese 643 and vB 8, two common proper motion companions of Gliese 644, support the interpretation that all five M stars are moving together in a physically bound group. We discuss possible scenarios for the formation and evolution of this configuration, such as the formation of all five stars in a sequence of fragmentation events leading directly to the hierarchical configuration now observed, versus formation in a small N cluster with subsequent dynamical evolution into the present hierarchical configuration.  相似文献   

Sub-electron readout noise in a Skipper CCD fabricated on high resistivity silicon     

Guillermo Fernández Moroni  Juan Estrada  Gustavo Cancelo  Stephen E. Holland  Eduardo E. Paolini  H. Thomas Diehl 《Experimental Astronomy》2012,34(1):43-64

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Coral Ba/Ca molar ratios as a proxy of precipitation in the northern Yucatan Peninsula,Mexico     

Guillermo Horta-Puga  José D. Carriquiry 《Applied Geochemistry》2012

The Yucatan Peninsula consists of a karstic terrain that allows the aquifer to directly recharge from rainfall. Due to the various dissolution/precipitation reactions occurring during groundwater flow, the groundwater discharge in the coastal zone becomes a source of trace elements including Ba. The aim of this study was to use the coralline Ba/Ca record as a proxy of precipitation under the consideration that rainfall rates vary at inter-annual time scales. Annual Ba/Ca ratios, both the total content (Ba/Ca_TC) and the Ca-substitutive fraction (Ba/Ca_CaF), were quantified in a 52-a old coral colony of Montastraea annularis from the Punta Nizuc Reef, Mexican Caribbean. Average Ba/Ca_TC (5.90 ± 0.56 μmol/mol) was ∼20% higher than Ba/Ca_CaF (4.85 ± 0.33 μmol/mol) indicating that Ba is also incorporated in other fractions. Correlation between annual precipitation and Ba/Ca_TC time-series is significant (r = 0.77, p < 0.05), allowing the use of the Ba/Ca_TC ratio as a proxy of precipitation, and hence, enabling the reconstruction of precipitation patterns through time. Likewise, the Ba/Ca_CaF ratio can be used for the reconstruction of dissolved Ba in coastal seawater.  相似文献   

Chaotic and regular motion around generalized Kalnajs discs     

Javier Ramos-Caro  Framsol López-Suspes  Guillermo A. González 《Monthly notices of the Royal Astronomical Society》2008,386(1):440-446

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Verification of a Synthesized Method for the Calculation of Low-Level Climatological Wind Fields Using a Mesoscale Boundary-Layer Model     

Guillermo J. Berri  Jorgelina S. Galli Nuin  Laura Sraibman  German Bertossa 《Boundary-Layer Meteorology》2012,142(2):329-337

Low-level climatological wind fields over the La Plata River region of South America are synthesized with a dry, hydrostatic mesoscale boundary-layer numerical model. The model is forced at the upper boundary with the 1200 UTC local radiosonde observations and at the lower boundary with a land-river differential heating function defined from the daily meteorological observations of the region. The climatological wind field is defined as the mean value of a series of individual daily forecasts, employing two methods. The simplified method considers a 192-member ensemble (16 wind directions and 12 wind-speed classes at the upper boundary). Each member has a probability of occurrence that is determined from the 1959–1984 observations; the daily method uses a total of 3,248 days with available data during the same period. In both methods each realization is a daily forecast from which the mean wind distributions at 0300, 0900, 1500 and 2100 local standard time are calculated and compared to the observations of five meteorological stations in the region. The validation of the climatological wind fields for both methods is evaluated by means of the root-mean-square error of the wind-direction frequency distribution and mean wind speed by wind sector. The results obtained with the two methods are similar, and the errors in wind speed are always smaller than those in wind direction. The combined errors of wind direction and wind speed show that the ensemble method is outperformed by the daily method, on average by meteorological station in only one out of five of them, and on average by the time of the day in only one out of 4 h. The conclusion of the study is that the ensemble method is an appropriate methodology for determining high resolution, low-level climatological wind fields, with the boundary-layer model applied to a region with a strong diurnal cycle of surface thermal contrast. The proposed methodology is of particular utility for synthesizing wind fields over regions with limited meteorological observations, since the 192-member matrix can be easily defined with few observing points, as well as in the case of relatively incomplete records.  相似文献   

Effect of the soil–pile–structure interaction in seismic analysis: case of liquefiable soils     

López Jiménez  Guillermo A.  Dias  Daniel  Jenck  Orianne 《Acta Geotechnica》2019,14(5):1509-1525

The design of earthquake-resistant structures depends greatly on the soil–foundation–structure interaction. This interaction is more complex in the presence of liquefiable soils. Pile and rigid inclusion systems represent a useful practice to support structures in the presence of liquefiable soils in seismic zones. Both systems increase the bearing capacity of soil and allow reducing the settlements in the structure. Numerical models with a 3-storey reinforced concrete frame founded on inclusions systems (soil–inclusion–platform–structure) and pile systems (soil–pile–structure) were analyzed. Finite difference numerical models were developed using Flac 3D. Two different soil profiles were considered. A simple constitutive model for liquefaction analysis that relates the volumetric strain increment to the cyclic shear strain amplitude was utilized to represent the behavior of the sand, and the linear elastic perfectly plastic constitutive model with a Mohr–Coulomb failure criterion was used to represent the behavior of the earth platform. Two earthquakes were used to study the influence of the different frequency of excitation in the systems. The results were presented in terms of maximum shear forces distribution in the superstructure and spectrum response of each system. The efforts and displacements in the rigid elements (piles or rigid inclusions) were compared for the different systems. The bending and buckling failure modes of the pile were examined. The results show that the pile system, the soil profile and the frequency of excitation have a great influence on the magnitude and location of efforts and displacements in the rigid elements.

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The Ba/Ca record of corals from the Southern Gulf of Mexico: Contributions from land-use changes, fluvial discharge and oil-drilling muds     

José D. Carriquiry  Guillermo Horta-Puga 《Marine pollution bulletin》2010,60(9):1625-187

The Ba/Ca in the growth bands of Montastraea faveolata from the Veracruz Reef System was used to reconstruct the long-term environmental change associated to anthropogenic activity in the Southern Gulf of Mexico (SGM). The 168-yr coral record shows two periods of distinct Ba concentrations: a pre-industrial period (1835-1965: 7.54 μmol/mol) followed by an industrial one (1966-2000: 8.57 μmol/mol). As human population quadrupoled during the latter, sediment load in the fluvial discharge also increased due to changes in land-use, yielding a 14% increase in the Ba-levels. A remarkable finding is that the periods at which the coral Ba/Ca ratio losses its correlation with fluvial discharge coincide exactly with peak periods of high barite consumption (used for oil drilling) in the Northern Gulf of Mexico, and the onset of oil drilling in the SGM. This finding suggests that barite may be one of the dominant sources for dissolved-Ba in the SGM.  相似文献   

Applications of 2D-NMR maps and geometric pore scale modeling for petrophysical evaluation of a gas well     

Pedro Romero  Mikhail Gladkikh  Guillermo Azpiroz 《Computational Geosciences》2009,13(2):171-180

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Precision abundance analysis of bright H ii galaxies     

Guillermo F. Hägele †  Ángeles I. Díaz ‡  Elena Terlevich §  Roberto Terlevich ‡  Enrique Pérez-Montero ¶  Mónica V. Cardaci 《Monthly notices of the Royal Astronomical Society》2008,383(1):209-229

We present high signal-to-noise ratio spectrophotometric observations of seven luminous H  ii galaxies. The observations have been made with the use of a double-arm spectrograph which provides spectra with a wide wavelength coverage, from 3400 to 10 400 Å free of second-order effects, of exactly the same region as that of a given galaxy. These observations are analysed applying a methodology designed to obtain accurate elemental abundances of oxygen, sulphur, nitrogen, neon, argon and iron in the ionized gas. Four electron temperatures and one electron density are derived from the observed forbidden line ratios using the five-level atom approximation. For our best objects, errors of 1 per cent in t _e([O  iii ]), 3 per cent in t _e([O  ii ]) and 5 per cent in t _e([S  iii ]) are achieved with a resulting accuracy of 7 per cent in total oxygen abundances, O/H.
The ionization structure of the nebulae can be mapped by the theoretical oxygen and sulphur ionic ratios, on the one side, and the corresponding observed emission line ratios, on the other – the η and η' plots. The combination of both is shown to provide a means to test photoionization model sequences presently applied to derive elemental abundances in H  ii galaxies.  相似文献   

Occurrence and distribution of polycyclic aromatic hydrocarbons in surface sediments of San Diego Bay marinas     

Carlos Neira  Jennifer Cossaboon  Guillermo Mendoza  Eunha Hoh  Lisa A. Levin 《Marine pollution bulletin》2017,114(1):466-479

Polycyclic aromatic hydrocarbons (PAHs) have garnered much attention due to their bioaccumulation, carcinogenic properties, and persistence in the environment. Investigation of the spatial distribution, composition, and sources of PAHs in sediments of three recreational marinas in San Diego Bay, California revealed significant differences among marinas, with concentrations in one site exceeding 16,000 ng g^? 1. ‘Hotspots’ of PAH concentration suggest an association with stormwater outfalls draining into the basins. High-molecular weight PAHs (4–6 rings) were dominant (> 86%); the average percentage of potentially carcinogenic PAHs was high in all sites (61.4–70%) but ecotoxicological risks varied among marinas. Highly toxic benzo(a)pyrene (BaP) was the main contributor (> 90%) to the total toxic equivalent quantity (TEQ) in marinas. PAHs in San Diego Bay marina sediments appear to be derived largely from pyrogenic sources, potentially from combustion products that reach the basins by aerial deposition and stormwater drainage from nearby streets and parking lots.  相似文献