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A. M. de S. Bueno C. A. de B. Pereira M. N. Rabello-Gay J. M. Stern 《Stochastic Environmental Research and Risk Assessment (SERRA)》2002,16(4):267-278
The data analyzed in this paper are part of the results described in Bueno et al. (2000). Three cytogenetics endpoints were
analyzed in three populations of a species of wild rodent – Akodon montensis – living in an industrial, an agricultural, and
a preservation area at the Itajaí Valley, State of Santa Catarina, Brazil. The polychromatic/normochromatic ratio, the mitotic
index, and the frequency of micronucleated polychromatic erythrocites were used in an attempt to establish a genotoxic profile
of each area. It was assumed that the three populations were in the same conditions with respect to the influence of confounding
factors such as animal age, health, nutrition status, presence of pathogens, and intra- and inter-populational genetic variability.
Therefore, any differences found in the endpoints analyzed could be attributed to the external agents present in each area.
The statistical models used in this paper are mixtures of negative-binomials and Poisson variables. The Poisson variables
are used as approximations of binomials for rare events. The mixing distributions are beta densities. The statistical analyzes
are under the bayesian perspective, as opposed to the frequentist ones often considered in the literature, as for instance
in Bueno et al. (2000). 相似文献
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Emmanuel Fritsch Etienne Balan Nadia Régina Do Nascimento Thierry Allard Marion Bardy Guilherme Bueno Sylvie Derenne Adolpho José Melfi Georges Calas 《Comptes Rendus Geoscience》2011,343(2-3):188-198
This article reports major results from collaborative research between France and Brazil on soil and water systems, carried out in the Upper Amazon Basin. It reveals the weathering processes acting in the partly inundated, low elevation plateaus of the Basin, mostly covered by evergreen forest. Our findings are based on geochemical data and mineral spectroscopy that probe the crystal chemistry of Fe and Al in mineral phases (mainly kaolinite, Al- and Fe-(hydr)oxides) of tropical soils (laterites). These techniques reveal crystal alterations in mineral populations of different ages and changes of metal speciation associated with mineral or organic phases. These results provide an integrated model of soil formation and changes (from laterites to podzols) in distinct hydrological compartments of the Amazon landscapes and under altered water regimes. 相似文献
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The development of effective iterative methods capable of accurately solving NLTE Stokes transfer problems is of considerable importance for the investigation of solar and stellar magnetic fields. After briefly indicating the iterative approach which is being presently pursued for the exact solution of such problems, the particular regime where polarization signals can only be due to the Zeeman effect is considered in some detail. By means of NLTE Stokes transfer calculations for a two-level atomic model it is first shown that the currently-used field-free approximation (Rees, 1969) cannot be safely applied in the presence of magnetic field gradients. Such gradients lead to changes in the shape and width of the line profiles and they can produce non-negligible effects on the atomic level populations and line source functions. A new approximate method is then proposed, which does not require the actual solution of the Stokes vector transfer equation and is practically as fast as the field-free one. This polarization-free approximation provides a fairly good account of the effects of homogeneous and inhomogeneous magnetic fields on the statistical equilibrium and is very easy to implement in any existing non-magnetic, multi-level transfer code.On leave from the Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Largo E. Fermi 5, I-50125 Firenze, Italia 相似文献
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N. G. Shchukina J. Trujillo Bueno I. E. Vasilyeva K. V. Frantseva 《Kinematics and Physics of Celestial Bodies》2017,33(4):166-179
The limb darkening and center-to-limb variation of the continuum polarization is calculated for a grid of one-dimensional stellar model atmospheres and for a wavelength range between 300 and 950 nm. Model parameters match those of the transiting stars taken from the NASA exoplanet archive. The limb darkening of the continuum radiation for these stars is shown to decrease with the rise in their effective temperature. For the λ = 370 nm wavelength, which corresponds to the maximum of the Johnson–Cousins UX filter, the limb darkening values of the planet transiting stars lie in a range between 0.03 and 0.3. The continuum linear polarization depends not only on the effective temperature of the star but also on its gravity and metallicity. Its value decreases for increasing values of these parameters. In the UX band, the maximum linear polarization of stars with transiting planets amounts to 4%, while the minimum value is approximately 0.3%. The continuum limb darkening and the linear polarization decrease rapidly with wavelength. At the R band maximum (λ = 700 nm), the linear polarization close to the limb is in fact two orders of magnitude smaller than in the UX band. The center- to-limb variation of the continuum intensity and the linear polarization of the stars with transiting planets can be approximated, respectively, by polynomials of the fourth and the sixth degree. The coefficients of the polynomials, as well as the IDL procedures for reading them, are available in electronic form. It is shown that there are two classes of stars with high linear polarization at the limb. The first one consists of cold dwarfs. Their typical representatives are HATS-6, Kepler-45, as well as all the stars with similar parameters. The second class of stars includes hotter giants and subgiants. Among them we have CoRoT-28, Kepler-91, and the group of stars with effective temperatures and gravities of approximately 5000 K and 3.5, respectively. 相似文献
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Morris RV Golden DC Bell JF rd Lauer HV Adams JB 《Geochimica et cosmochimica acta》1993,57(19):4597-4609
We have examined a Hawaiian palagonitic tephra sample (PN-9) that has spectroscopic similarities to Martian bright regions using a number of analytical techniques, including Mossbauer and reflectance spectroscopy, X-ray diffraction, instrumental neutron activation analysis, electron probe microanalysis, transmission electron microscopy, and dithionite-citrate-bicarbonate extraction. Chemically, PN-9 has a Hawaiitic composition with alkali (and presumably silica) loss resulting from leaching by meteoric water during palagonitization; no Ce anomaly is present in the REE pattern. Mineralogically, our results show that nanophase ferric oxide (np-Ox) particles (either nanophase hematite (np-Hm) or a mixture of ferrihydrite and np-Hm) are responsible for the distinctive ferric doublet and visible-wavelength ferric absorption edge observed in Mossbauer and reflectivity spectra, respectively, for this and other spectrally similar palagonitic samples. The np-Ox particles appear to be imbedded in a hydrated aluminosilicate matrix material; no evidence was found for phyllosilicates. Other iron-bearing phases observed are titanomagnetite, which accounts for the magnetic nature of the sample; olivine; pyroxene; and glass. By analogy, np-Ox is likely the primary pigmenting agent of the bright soils and dust of Mars. 相似文献
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敦煌三危山地区白垩纪OIB型基性岩墙的特征及地质意义 总被引：4，自引：3，他引：1
本文首次报道甘肃敦煌三危山地区早白垩世玄武质岩浆活动的记录。在三危山附近,基性岩墙侵入于敦煌群TTG和表壳岩大理岩和片岩中。全岩的K-Ar年龄为136.00±11.56Ma到99.11±6.35Ma,形成时代属于早白垩世。基性岩墙SiO2含量变化范围较小,集中在47.95%~50.65%之间,以富TiO2 (2.07%~2.35%,平均为2.21%)、MgO(6.03 %~6.51%,平均为6.32%)、贫K2O(<1.29%),Na2O>K2O, Mg#值中等且比较稳定(48.9~53.1,平均为51.7)为特征。基性岩相容元素含量相对较低,Ni含量变化相对较小,分布在112.7×10-6~182.7×10-6之间。而V含量变化较大,介于184×10-6~267×10-6之间,表明岩浆早期可能发生了一定的以橄榄石和单斜辉石为主的分离结晶作用。基性岩富集LREE((La/Yb)N ＝3.97~4.66)和LILE,无Eu负异常,较高的Fe/Mn比值等,具有与洋岛玄武岩(OIB)相似的特征。微量元素比值等特征表明其来源与富集地幔关系密切,玄武质岩浆的形成可能与岩石圈的减薄和软流圈的上涌有关。 相似文献
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华北地台南缘张士英岩体的锆石SHRIMP U-Pb测年、Hf同位素组成及其地质意义 总被引：6，自引：3，他引：3
张士英岩体位于华北地台南缘,岩石类型包括钾长花岗岩、似斑状花岗岩和石英斑岩脉,其中只在钾长花岗岩中发育有暗色岩石包体,在包体和寄主岩中发育反映岩浆混合作用的岩石结构。钾长花岗岩、似斑状花岗岩和石英斑岩脉的SHRIMP锆石U-Pb年龄分别为107.3±2.4Ma、106.7±2.5Ma和101±3Ma。锆石Hf同位素分析结果显示,钾长花岗岩的锆石εHf(t)为-15.96～-20.80,单阶段模式年龄(tDM1)为1396～1643Ma,两阶段模式年龄(tDM2)为1880～2018Ma;似斑状花岗岩的锆石εHf(t)为-18.97～-22.18,tDM1为1512～1640Ma,tDM2为1925～2080Ma;除了一粒年龄为2.6Ga的锆石具有εHf(t)为-0.71、tDM1为2943Ma和tDM2为3036Ma的组成,石英斑岩的锆石εHf(t)为-23.41～-27.95,tDM1为1678～1896Ma,tDM2为2144～2330Ma。这些数据暗示,除了存在少量太古宙地壳物质的贡献外,张士英岩体的物质来源可能主要为1.9～2.3Ga期间形成的新生地壳,但也不排除古老地壳与富集地幔源混合的可能。综合分析前人研究成果表明,在太平洋板块俯冲方向发生转变的过程中,先存断裂带发生拉张。张士英岩体与中国东部同期岩浆活动一起可能形成于这种受断裂带控制的伸展环境。 相似文献
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Thiago J.F. Costa Hudson T. Pinheiro João Batista Teixeira Eric F. Mazzei Leonardo Bueno Mike S.C. Hora Jean-Christophe Joyeux Alfredo Carvalho-Filho Gilberto Amado-Filho Claudio L.S. Sampaio Luiz A. Rocha 《Marine pollution bulletin》2014
Invasive coral species of the genus Tubastraea have been increasingly recorded in Southwestern Atlantic waters since the 1980s. Their invasion and infestation are mainly related to port and oil exploration activities. For the first time the presence of Tubastraea tagusensis colonies is reported in Espírito Santo State, colonizing a port shore area, and incrusting oil/gas platform structures situated in the southern Abrolhos Bank, which is part of the most important coral reef system of the South Atlantic Ocean. Tubastraea colonies exhibit fast growth and high recruitment rates, and colonized 40% of the analyzed structures in just four years. The projection of port and oil/gas industry growth for the Espírito Santo State (more than 300%) highlights an alert to the dispersal of this alien species to natural areas. 相似文献