Simulating wide-field quasar surveys from the optical to near-infrared     

Natasha Maddox  Paul C. Hewett 《Monthly notices of the Royal Astronomical Society》2006,367(2):717-731

A number of deep, wide-field, near-infrared (NIR) surveys employing new infrared cameras on 4-m class telescopes are about to commence. These surveys have the potential to determine the fraction of luminous dust-obscured quasars that may have eluded surveys undertaken at optical wavelengths. In order to understand the new observations it is essential to make accurate predictions of surface densities and number–redshift relations for unobscured quasars in the NIR based on information from surveys at shorter wavelengths. The accuracy of the predictions depends critically on a number of key components. The commonly used single power-law representation for quasar spectral energy distributions (SEDs) is inadequate and the use of an SED incorporating the upturn in continuum flux at  λ∼ 12 000 Å  is essential. The presence of quasar host galaxies is particularly important over the rest-frame wavelength interval  8000 < λ < 16 000 Å  and we provide an empirical determination of the magnitude distribution of host galaxies using a low-redshift sample of quasars from the Sloan Digital Sky Survey Data Release 3 quasar catalogue. A range of models for the dependence of host galaxy luminosity on quasar luminosity is investigated, along with the implications for the NIR surveys. Even adopting a conservative model for the behaviour of host galaxy luminosity the number counts for shallow surveys in the K band increase by a factor of 2. The degree of morphological selection applied to define candidate quasar samples in the NIR is found to be an important factor in determining the fraction of the quasar population included in such samples.  相似文献   

Hydroxyl in mantle olivine xenocrysts from the Udachnaya kimberlite pipe   总被引：6，自引：1，他引：5  

Monika Koch-Müller  Stanislav S. Matsyuk  Dieter Rhede  Richard Wirth  Natasha Khisina 《Physics and Chemistry of Minerals》2006,33(4):276-287

The incorporation of hydrogen in mantle olivine xenocrysts from the Udachnaya kimberlite pipe was investigated by Fourier-transform infrared spectroscopy and secondary ion mass spectrometry (SIMS). IR spectra were collected in the OH stretching region on oriented single crystals using a conventional IR source at ambient conditions and in situ at temperatures down to −180°C as well as with IR synchrotron radiation. The IR spectra of the samples are complex containing more than 20 strongly polarized OH bands in the range 3,730–3,330 cm⁻¹. Bands at high energies (3,730–3,670 cm⁻¹) were assigned to inclusions of serpentine, talc and the 10 Å phase. All other bands are believed to be intrinsic to olivine. The corresponding point defects are (a) associated with vacant Si sites (3,607 cm⁻¹ E || a, 3,597 E || a, 3,571 cm⁻¹ E || c, 3,567 E || c, and 3,556 E || b), and (b) with vacant M1 sites (most of the bands polarized parallel to a). From the pleochroic behavior and position of the OH bands associated with the vacant M1 sites, we propose two types of hydrogen—one bonded to O1 and another to O2, so that both OH vectors are strongly aligned parallel to a. The O2–H groups may be responsible for the OH bands at higher wavenumbers than those for the O1–H groups. The multiplicity of the corresponding OH bands in the spectra can be explained by different chemical environments and by slightly different distortions of the M1 sites in these high-pressure olivines. Four samples were investigated by SIMS. The calculated integral molar absorption coefficient using the IR and SIMS results of 37,500±5,000 L mol H₂O cm⁻² is within the uncertainties slightly higher than the value determined by Bell et al. (J Geophys Res 108(B2):2105–2113, 2003) (28,450±1,830 L mol H₂O cm⁻²). The reason for the difference is the different distributions of the absorption intensity of the spectra of both studies (mean wavenumber 3,548 vs. 3,570 cm⁻¹). Olivine samples with a mean wavenumber of about 3,548 cm⁻¹ should be quantified with the absorption coefficient as determined in this study; those containing more bands at higher wavenumber (mean wavenumber 3,570 cm⁻¹) should be quantified using the value determined by Bell et al. (J Geophys Res 108(B2):2105–2113, 2003).

Monika Koch-MüllerEmail: Phone: +49-331-2881492

  相似文献   

Environmental Change and Terrestrial Resource Use by the Thule and Inuit of Labrador,Canada     

Natasha Roy  Najat Bhiry  James Woollett 《Geoarchaeology》2012,27(1):18-33

The object of this study is to document how the Inuit on the northern coast of Labrador, Canada used terrestrial resources such as peat and wood during the Little Ice Age (LIA; A.D. 1500–1870). Paleoecological investigations consisting of pollen and macrofossil analyses were undertaken in conjunction with archaeological excavations at the Inuit winter settlement sites of Oakes Bay 1, located in the Nain region of north‐central Labrador. Our data indicate that the major changes in terrestrial ecosystems of this coastal region were triggered by climate change. From ca. 5700 to 3000 cal. yr B.P., climatic conditions were relatively warm and moist. At ca. 3000 cal. yr B.P. conditions became significantly drier and colder, which corresponds to broader climatic trends during the Neoglacial period. At ca. 1000 cal. yr B.P., the reappearance of hygrophilic species and the establishment of Larix laricina provide evidence of a return to more humid conditions that in turn triggered the onset of the paludification of sandy terraces in the Dog Island region. Peat accumulation persisted after ca. 580 cal. yr B.P. likely due to the elevation of the frost table during the LIA. Elevated frost tables contributed to water saturation of the surface during the spring, creating conditions that were conducive to the preservation of organic material. Natural resources such as trees and peat were therefore readily available and more abundant during the LIA and extensively used by the Inuit for house construction and heating in the Dog Island region.  相似文献   

Luminous K-band selected quasars from UKIDSS     

Natasha Maddox  Paul C. Hewett  S. J. Warren  S. M. Croom 《Monthly notices of the Royal Astronomical Society》2008,386(3):1605-1624

  相似文献   

Geophysical fingerprints of hyper-extended,exhumed and embryonic oceanic domains: the example from the Iberia–Newfoundland rifted margins     

Natasha Stanton  Gianreto Manatschal  Julia Autin  Daniel Sauter  Marcia Maia  Adriano Viana 《Marine Geophysical Researches》2016,37(3):185-205

This study investigates the magnetic and gravity signatures and associated seismic character of hyper-extended, exhumed and embryonic oceanic domains along the conjugate Iberia–Newfoundland rifted margins. As these margins have been drilled down to basement along their distal parts, it is possible to explore and test different geophysical techniques and interpretations. The aims of this work are twofold: (1) to investigate the location and nature of the two main marginal boundaries—the necking zone and the J Anomaly, which define the limits of major domains; and (2) to map the lateral variations of gravity and magnetic signatures and their detailed correlation with seismic data, from the proximal margin until the first unequivocal oceanic magnetic anomaly (e.g. C34 Anomaly). The results point out that the J Anomaly corresponds to a first-order tectono-magmatic boundary, with a basement formed by polyphase magmatism. It marks the boundary between the exhumed mantle domain, with little magmatic additions, from a domain oceanwards that reveals comparable trends, frequencies and a general magnetic pattern at both sides of the Atlantic, suggesting a coeval evolution. We propose that the domain between the J and the C34 Anomalies was formed by an embryonic spreading system, with intermittent budgets of magma, similar to those observed at very slow spreading systems. The J Anomaly may thus correspond to the location of lithospheric breakup though its origin and the nature of the domain oceanwards remains to be constrained.  相似文献   

Gas/solid carbon branching ratios in surface‐mediated reactions and the incorporation of carbonaceous material into planetesimals          下载免费PDF全文

Joseph A. Nuth  Natasha M. Johnson  Frank T. Ferguson  Alicia Carayon 《Meteoritics & planetary science》2016,51(7):1310-1322

We report the ratio of the initial carbon available as CO that forms gas‐phase compounds compared to the fraction that deposits as a carbonaceous solid (the gas/solid branching ratio) as a function of time and temperature for iron, magnetite, and amorphous iron silicate smoke catalysts during surface‐mediated reactions in an excess of hydrogen and in the presence of N₂. This fraction varies from more than 99% for an amorphous iron silicate smoke at 673 K to less than 40% for a magnetite catalyst at 873 K. The CO not converted into solids primarily forms methane, ethane, water, and CO₂, as well as a very wide range of organic molecules at very low concentration. Carbon deposits do not form continuous coatings on the catalytic surfaces, but instead form extremely high surface area per unit volume “filamentous” structures. While these structures will likely form more slowly but over much longer times in protostellar nebulae than in our experiments due to the much lower partial pressure of CO, such fluffy coatings on the surfaces of chondrules or calcium aluminum inclusions could promote grain–grain sticking during low‐velocity collisions.  相似文献   

Overcoming cross-scale challenges to climate change adaptation for local government: a focus on Australia     

Pierre Mukheibir  Natasha Kuruppu  Anna Gero  Jade Herriman 《Climatic change》2013,121(2):271-283

This paper aims to identify key cross-scale challenges to planned adaptation within the context of local government in Australia, and suggest enabling actions to overcome such challenges. Many of the impacts of climate change and variability have or will be experienced at the local level. Local governments are embedded in a larger governance context that has the potential to limit the effectiveness of planned adaptation initiatives on the ground. This study argues that research on constraints and barriers to adaptation must place greater attention to understanding the broader multi-governance system and cross-scale constraints that shape adaptation at the local government scale. The study identified seven key enabling actions for overcoming cross-scale challenges faced by local governments in Australia when undertaking climate change adaptation planning and implementation. A central conclusion of this study is that a cooperative and collaborative approach is needed where joint recognition of the scale of the issue and its inherent cross-scale complexities are realised. Many of the barriers or constraints to adaptation planning are interlinked, requiring a whole government approach to adaptation planning. The research suggests a stronger role at the state and national level is required for adaptation to be facilitated and supported at the local level.  相似文献   

Analytical extension of lunar libration tables     

Natasha Petrova 《Earth, Moon, and Planets》1996,73(1):71-99

Tables of lunar physical libration defining the analytical dependence upon the parameters of the lunar gravitational field are presented. The tables are obtained on the framework of the main problem in lunar libration by integration of the Hamilton equations reduced to the harmonic oscillator equations.The variables of physical libration have been obtained in the form of Poisson series. The distinguishing feature of the tables is that these series are the analytical extension of semianalytical solution computed for a number of dynamical parameters LURE2.A comparison with the Eckhardt's solution is briefly presented. The previously revealed disagreement of the mean inclination of lunar equator to ecliptic with that in Eckhardt's solution 500 has been maintained.  相似文献   

Soil and water conservation measures improve soil carbon sequestration and soil quality under cashews   总被引：2，自引：1，他引：1  

Gopal Ramdas Mahajan  Bappa Das  Sandrasekaran Manivannan  Begur Lakshminarasimha Manjunath  Ram Ratan Verma  Sujeet Desai  Rahul Mukund Kulkarni  Ashish Marotrao Latare  Reshma Sale  Dayesh Murgaonkar  Kiran Puna Patel  Shaiesh Morajkar  Ashwini Desai  Natasha Barnes  Heena Mulla 《国际泥沙研究》2021,36(2):190-206

Land degradation is becoming a serious problem in the west coast region of India where one of the world's eight biodiversity hotspots,the‘Western Ghats’,is present.Poor land management practices and high rainfall have led to increasing problems associated with land degradation.A long-term(13-year)experiment was done to evaluate the impact of soil and water conservation measures on soil carbon sequestration and soil quality at three different depths under cashew nut cultivation on a 19%slope.Five soil and water conservation measures-continuous contour trenches,staggered contour trenches,halfmoon terraces,semi-elliptical trenches,and graded trenches all with vegetative barriers of Stylosanthes scabra and Vetiveria zizanoides and control were evaluated for their influence on soil properties,carbon sequestration,and soil quality under cashews.The soil and water conservation measures improved significantly the soil organic carbon,soil organic carbon stock,carbon sequestration rate and microbial activity compared to the control condition(without any measures).Among the measures tested,continuous contour trenches with vegetative barriers outperformed the others with respect to soil organic carbon stock,sequestration rate,and microbial activity.The lower metabolic quotient with the measures compared to the control indicated alleviation of environmental stress on microbes.Using principal component analysis and a correlation matrix,a minimum dataset was identified as the soil available nitrogen,bulk density,basal soil respiration,soil pH,acid phosphatase activity,and soil available boron and these were the most important soil properties controlling the soil quality.Four soil quality indices using two summation methods(additive and weighted)and two scoring methods(linear and non-linear)were developed using the minimum dataset.A linear weighted soil quality index was able to statistically differentiate the effect of soil and water conservation measures from that of the control.The highest value of the soil quality index of 0.98 was achieved with continuous contour trenches with a vegetative barrier.The results of the study indicate that soil and water conservation measures for cashews are a potential strategy to improve the soil carbon sequestration and soil quality along with improving crop productivity and reducing the erosion losses.  相似文献   

Extended time series measurements of submarine groundwater discharge tracers (222Rn and CH4) at a coastal site in Florida     

Isaac R. Santos  Natasha Dimova  Richard N. Peterson  Benjamin Mwashote  Jeffrey Chanton  William C. Burnett 《Marine Chemistry》2009,113(1-2):137-147

We report the results of an experiment in which we measured ²²²Rn (15,000 observations), CH₄ (40,000 observations), and associated variables in seawater nearly continuously at a coastal site in the Gulf of Mexico for almost two years. Significant correlations between ²²²Rn and CH₄ imply that they are derived from a common source, most likely groundwater. However, we were unable to explain the overall tracer variability as a single function of groundwater table height, temperature, tidal range, and wind speed, indicating multiple, overlapping controls on SGD dynamics at this site. Methane and radon concentrations may vary 2-fold in a given well in the subterranean estuary over tidal time scales, demonstrating the complexity of determining SGD endmember concentrations and suggesting that unaccounted for temporal changes in groundwater may explain some of the patterns observed in seawater. Surprisingly, the variability of ²²²Rn and CH₄ in seawater over short (e.g., hourly) time scales was generally comparable to or even more pronounced than fluctuations over much longer (e.g., monthly) scales. While high tracer concentrations usually occurred during low tide and low tracer concentrations during high tide, this pattern was occasionally inverted or absent indicating that no single model can be used to describe the entire data set. We also describe a sequence of events in which SGD tracers were depleted in coastal waters during storms and regenerated afterwards. We found no increase in radon activities immediately after the largest storm (75 mm rainfall) perhaps because of the short residence times of groundwater in contrast to the ingrowth time of radon. Marine controls appeared to be the most important SGD drivers with only minor influence relating to the shallow and deep aquifers. This implies that seasonal investigations of SGD tracers in the coastal ocean may be masked by short-term variability.  相似文献