Building a control sample for galaxy pairs     

Josefa Perez  Patricia Tissera  Jeremy Blaizot 《Monthly notices of the Royal Astronomical Society》2009,397(2):748-756

Several observational works have attempted to isolate the effects of galaxy interactions by comparing galaxies in pairs with isolated galaxies. However, different authors have proposed different ways to build these so-called control samples (CS). By using mock galaxy catalogues of the Sloan Digital Sky Survey Data Release 4 buildup from the Millennium Simulation, we explore how the way of building a CS might introduce biases which could affect the interpretation of results. We make use of the fact that the physics of interactions are not included in the semi-analytic model, to infer that any difference between the mock control and pair samples can be ascribed to selection biases. Thus, we find that galaxies in pairs artificially tend to be older and more bulge dominated, and to have less cold gas and different metallicities than their isolated counterparts. Also because of a biased selection, galaxies in pairs tend to live in higher density environments and in haloes of larger masses. We find that imposing constraints on redshift, stellar masses and local densities diminishes the selection biases by  ≈70 per cent  . Based on these findings, we suggest observers how to build a unique and unbiased CS in order to reveal the effect of galaxy interactions.  相似文献   

Xenon in Archean barite: Weak decay of Ba, mass-dependent isotopic fractionation and implication for barite formation     

Magali Pujol  Bernard Marty  Pascal Philippot 《Geochimica et cosmochimica acta》2009,73(22):6834-306

In order to investigate radioactive decay of ¹³⁰Ba and ¹³²Ba which have half-lives on the order 10²⁰-10²¹ a, the isotopic composition of xenon has been measured in 3.5 Ga barite of the Dresser Formation, Pilbara, Western Australia. The analyzed samples were collected at about 86 m depth from a diamond drill core (Pilbara Drilling Project). The fact that the sample has been shielded from modern cosmic ray exposure reduces the number of potentially interfering production pathways, simplifying interpretation of the Xe isotope spectrum. This spectrum is clearly distinct from that of either modern or ancient atmospheric Xe. A strong excess of ¹³⁰Xe is identified, as well as other isotopic excursions which are attributed to mass-dependent isotopic fractionation and contributions from products of uranium fission. The mass-dependent fractionation, estimated at 2.1 ± 0.3% amu⁻¹, can be accounted for by mutual diffusion and Rayleigh distillation during barite formation that is consistent with geological constraints. After correction for mass-dependent fractionation, the concentrations of fissiogenic Xe isotopes demonstrate that the U-Xe isotope system has remained closed over 3.5 Ga. From the excess of ¹³⁰Xe, the two successive electron capture half life of this isotope is estimated at 6.0 ± 1.1 × 10²⁰ a, which is 3.4 times faster than previously estimated (Meshik et al., 2001). We could not find evidence of ¹³²Ba decay within our Xe isotope spectra.  相似文献   

Synthesis of In‐House Produced Calibrated Silver Phosphate with a Large Range of Oxygen Isotope Compositions     

Christophe Lcuyer  Franois Fourel  Magali Seris  Romain Amiot  Jean Goedert  Laurent Simon 《Geostandards and Geoanalytical Research》2019,43(4):681-688

The large range of stable oxygen isotope values of phosphate‐bearing minerals and dissolved phosphate of inorganic or organic origin requires the availability of in‐house produced calibrated silver phosphate of which isotopic ratios must closely bracket those of studied samples. We propose a simple protocol to synthesise Ag₃PO₄ in a wide range of oxygen isotope compositions based on the equilibrium isotopic fractionation factor and the kinetics and temperature of isotopic exchange in the phosphate–water system. Ag₃PO₄ crystals were obtained from KH₂PO₄ that was dissolved in water of known oxygen isotope composition. Isotopic exchange between dissolved phosphate and water took place at a desired and constant temperature into PYREX? tubes that were placed in a high precision oven for defined run‐times. Samples were withdrawn at desired times, quenched in cold water and precipitated as Ag₃PO₄. We provide a calculation sheet that computes the δ¹⁸O of precipitated Ag₃PO₄ as a function of time, temperature and δ¹⁸O of both reactants KH₂PO₄ and H₂O at t = 0. Predicted oxygen isotope compositions of synthesised silver phosphate range from ?7 to +31‰ VSMOW for a temperature range comprised between 110 and 130 °C and a range of water δ¹⁸O from ?20 to +15‰ VSMOW.  相似文献   

华南陡山沱期古地理环境及"雪球地球"研究新进展   总被引：4，自引：1，他引：4  

孙知明杨振宇  裴军令Jean BESSE　Melina MACOUIN　Stuart GILDER　Magali ADER 《地质通报》2004,23(8):728-731

华南地块陡山沱组的古地磁和C同位素研究揭示了其形成于赤道附近的古地理环境。对冰期后的盖帽白云岩的C同位素研究表明，δ^13C从-5‰开始有缓慢升高的趋势，与世界上Marinoan冰期其他剖面的c同位素变化相一致。陡山沱期大气中CO2含量的升高可能与kodinia超大陆的裂解及火山活动等密切相关。  相似文献   

Discussion on paper by K. Kawashima and K. Aizawa     

V. Perez  K. Kawashima  K. Aizawa 《地震工程与结构动力学》1987,15(5):653-657

  相似文献   

Coupling an equation of state and Henry's Law to model the phase equilibria of gases and brines: Examples in the N₂–H₂O–NaCl system     

Renee J. Perez  Robert A. Heidemann   《Journal of Geochemical Exploration》2006,89(1-3):331

We propose a thermodynamic model for the mixing of gases in aqueous sodium chloride solutions valid to high pressures, high temperatures, and high ionic strength solutions. Our model couples Henry's Law with any equation of state to reproduce experimental data in the aqueous-rich liquid and gas-rich vapor region. In our model, the chemical potential of the solute in the brine is related to the chemical potential of the solute in pure water through salting-out coefficients. The model reproduces all crucial phenomena of binary (gas–water) and pseudo-binary (gas–water–salt) vapor–liquid mixtures below their critical point. We applied the model to reproduce the phase behavior of nitrogen in water and NaCl brines. Results and discussions are shown.  相似文献   

A large epeiric methanogenic Bambuí sea in the core of Gondwana supercontinent?     

Sergio Caetano-Filho  Pierre Sansjofre  Magali Ader  Gustavo M.Paula-Santos  Cristian Guacaneme  Marly Babinski  Carolina Bedoya-Rueda  Matheus Kuchenbecker  Humberto L.S.Reis  Ricardo I.F.Trindade 《地学前缘(英文版)》2021,12(1):203-218

Carbon isotope compositions of both sedimentary carbonate and organic matter can be used as key proxies of the global carbon cycle and of its evolution through time,as long as they are acquired from waters where the dissolved inorganic carbon(DIC)is in isotope equilibrium with the atmospheric CO2.However,in shallow water platforms and epeiric settings,the influence of local to regional parameters on carbon cycling may lead to DIG isotope variations unrelated to the global carbon cycle.This may be especially true for the terminal Neoproterozoic,when Gondwana assembly isolated waters masses from the global ocean,and extreme positive and negative carbon isotope excursions are recorded,potentially decoupled from global signals.To improve our understanding on the type of information recorded by these excursions,we investigate the pairedδ^13Ccarb andδ^13Corg evolution for an increasingly restricted late Ediacaran-Cambrian foreland system in the West Gondwana interior:the basal Bambui Group.This succession represents a 1~(st)-order sedimentary sequence and records two majorδ^13Ccarb excursions in its two lowermost lower-rank sequences.The basal cap carbonate interval at the base of the first sequence,deposited when the basin was connected to the ocean,hosts antithetical negative and positive excursions forδ^13Ccarb andδ^13Corg,respectively,resulting inΔ^13C values lower than 25‰.From the top of the basal sequence upwards,an extremely positiveδ^13Ccarb excursion is coupled toδ^13Corg,reaching values of+14‰and-14‰,respectively.This positive excursion represents a remarkable basin-wide carbon isotope feature of the Bambui Group that occurs with only minor changes inΔ^13C values,suggesting change in the DIC isotope composition.We argue that this regional isotopic excursion is related to a disconnection between the intrabasinal and the global carbon cycles.This extreme carbon isotope excursion may have been a product of a disequilibria between the basin DIC and atmospheric CO2 induced by an active methanogenesis,favored by the basin restriction.The drawdown of sulfate reservoir by microbial sulfate reduction in a poorly ventilated and dominantly anoxic basin would have triggered methanogenesis and ultimately methane escape to the atmosphere,resulting in a^13C-enriched DIC influenced by methanogenic CO2.Isolated basins in the interior of the Gondwana supercontinent may have represented a significant source of methane inputs to the atmosphere,potentially affecting both the global carbon cycle and the climate.  相似文献   

A complete hydro-climate model chain to investigate the influence of sea surface temperature on recent hydroclimatic variability in subtropical South America (Laguna Mar Chiquita,Argentina)     

Magali Troin  Mathieu Vrac  Myriam Khodri  Daniel Caya  Christine Vallet-Coulomb  Eduardo Piovano  Florence Sylvestre 《Climate Dynamics》2016,46(5-6):1783-1798

  相似文献   

Derivation of Cloud Index from Geostationary Satellites and Application to the Production of Solar Irradiance and Daylight Illuminance Data     

P. Ineichen  R. Perez 《Theoretical and Applied Climatology》1999,64(1-2):119-130

Summary  We investigate in the present paper the relationship between satellite count, global irradiance and other solar and illumination resource components, bringing a particular attention to low solar elevation situations (below 20 °) which are very important in northern latitudes. Our investigation is based on data from two geostationary satellites, METEOSAT and GOES, backed by ground measurements in Switzerland and the northeastern USA. The study of different clear sky normalizations lead to the conclusion that a linear correlation between the global clearness index and the irradiance (like the heliosat method) would be inaccurate for low solar elevations, and therefore for high latitude regions. We developed a model that directly relates an elevation dependent clearness index to the could index. This methodology presents a definite advantage because it can be generalized to address the clearness index of other solar radiation components, besides global irradiance, such as direct irradiance, diffuse illuminance, etc. The correlations described in this paper were developed on the data from Geneva (in the frame of the EC program “Satellight”) and evaluated on two other independent data sets (Albany, USA and Lausanne, Switzerland). Their precisions, on a hourly basis, are respectively 30%, 40% and 60% for the global, diffuse and beam components) (90,55 and 95 W/m²). The use of independent data for thederivation and the validation of the models shows thatthose can be used in a wide range of locations, even if the applicability has to be assessed for very different climates. Received June 27, 1998 Revised February 26, 1999  相似文献   

When Fields Revert to Forest: Development and Spontaneous Reforestation in Post‐War Puerto Rico     

Thomas K. Rudel  Marla Perez‐Lugo  Heather Zichal 《The Professional geographer》2000,52(3):386-397

During the past 50 years forests have recolonized extensive areas of Puerto Rico. Between 1950 and 1990 forest cover increased from 9% to 37% of the island's land area. In proportional terms more land has reverted to forest in Puerto Rico than anywhere else on earth during the second half of the twentieth century. This paper explores the geography of this process by matching changes in land cover with the characteristics of the land and communities in Puerto Rico. The reversion of agricultural lands to forest occurred most frequently in humid, upland, coffee‐growing regions characterized by heavy out‐migration and populations of smallholders who earned some of their income from off‐farm sources. These findings suggest that changes in non‐farm labor markets, as well as changes in the political economy of agriculture, have important impacts on the prospects for converting agricultural lands into forests.  相似文献