Detection and extraction of signals from the epoch of reionization using higher-order one-point statistics     

Geraint J. A. Harker  Saleem Zaroubi  Rajat M. Thomas  Vibor Jeli&#;  Panagiotis Labropoulos  Garrelt Mellema  Ilian T. Iliev  Gianni Bernardi  Michiel A. Brentjens  A. G. de Bruyn  Benedetta Ciardi  Leon V. E. Koopmans  V. N. Pandey  reas H. Pawlik  Joop Schaye  Sarod Yatawatta 《Monthly notices of the Royal Astronomical Society》2009,393(4):1449-1458

Detecting redshifted 21-cm emission from neutral hydrogen in the early Universe promises to give direct constraints on the epoch of reionization (EoR). It will, though, be very challenging to extract the cosmological signal (CS) from foregrounds and noise which are orders of magnitude larger. Fortunately, the signal has some characteristics which differentiate it from the foregrounds and noise, and we suggest that using the correct statistics may tease out signatures of reionization. We generate mock data cubes simulating the output of the Low Frequency Array (LOFAR) EoR experiment. These cubes combine realistic models for Galactic and extragalactic foregrounds and the noise with three different simulations of the CS. We fit out the foregrounds, which are smooth in the frequency direction, to produce residual images in each frequency band. We denoise these images and study the skewness of the one-point distribution in the images as a function of frequency. We find that, under sufficiently optimistic assumptions, we can recover the main features of the redshift evolution of the skewness in the 21-cm signal. We argue that some of these features – such as a dip at the onset of reionization, followed by a rise towards its later stages – may be generic, and give us a promising route to a statistical detection of reionization.  相似文献   

The Huygens scientific data archive: Technical overview     

Olivier Witasse  Lyle Huber  Jean-Pierre Lebreton  David Heather  John Zarnecki  Roland Trautner  Piero Leon Stoppato  Chuck See  Cyril Pennanech  Lisa McFarlane  Bobby Kazeminejad  Brijen Hathi  John Haberman  Francesca Ferri  Lyn Doose  Giacomo Colombatti  Michael Bird  Alessio Aboudan 《Planetary and Space Science》2008,56(5):770-777

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Microbially induced calcite precipitation along a circular flow channel under a constant flow condition     

Wu  Chuangzhou  Chu  Jian  Wu  Shifan  Cheng  Liang  van Paassen  Leon A. 《Acta Geotechnica》2019,14(3):673-683

Biogrouting is a new ground improvement method that has been studied in recent years. This method involves mainly the use of a microbially induced calcite precipitation process to bind soil particles to increase the strength or to fill in the pores of soil or joints of rock for seepage control. There are two major challenges in the use of biogrout for seepage control through rock joints. The first is how to inject the biogrout solutions, and the second is to understand the mechanisms for the formation of calcite under seepage flow. In this paper, a study on the injection of biogrout solution and the formation of precipitates along a circular 1D flow channel is presented. To minimize the influence of flow, a new one-phase injection method to inject bacterial solution and cementation agents simultaneously was adopted in this study. Factors affecting the formation and distribution of precipitates along the flow channel such as flow velocity, flow rate, and aperture of flow channel were investigated. The experimental results indicated that less calcite was precipitated at locations further away from the injection point due to depletion of the reactants’ concentrations along the flow path. Using the one-phase injection method, the bacterial activity had a major effect on the accumulation of the calcite on the inner surface of the flow channel. The total calcite precipitated on the surface of the flow channel increased slightly with increasing bacterial activity or flow rate. An equation to predict the distance travelled by the biosolution has been derived based on the testing results.

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Analysis of one-dimensional models for exchange flows under strong stratification     

Kaptein  Steven J.  van de Wal  Koen J.  Kamp  Leon P. J.  Armenio  Vincenzo  Clercx  Herman J. H.  Duran-Matute  Matias 《Ocean Dynamics》2020,70(1):41-56

Ocean Dynamics - One-dimensional models of exchange flows driven by horizontal density gradients are well known for performing poorly in situations with weak turbulent mixing. The main issue with...  相似文献   

“Dead Zone” dynamics in Lake Erie: the importance of weather and sampling intensity for calculated hypolimnetic oxygen depletion rates     

Joseph D. Conroy  Leon Boegman  Hongyan Zhang  William J. Edwards  David A. Culver 《Aquatic Sciences - Research Across Boundaries》2011,73(2):289-304

Calculated hypolimnetic oxygen depletion (HOD) rates depend not only on environmental factors but also logistical ones. In particular, lack of understanding of the effects of weather in addition to how sampling effort determines calculated HOD rates complicates ecological understanding and environmental management of lake ecosystems. To better determine the roles of weather and sampling effort, we combined (1) weekly measurements of temperature and dissolved oxygen (DO) concentrations from seven stations in the Sandusky subbasin of Lake Erie’s central basin during 2005, (2) contemporaneous measures of storm activity and tributary discharge, and (3) a two-dimensional coupled hydrodynamic, chemical, and biological model of Lake Erie to investigate (1) how increased storm activity and tributary discharge affected short- (daily) and long-term (seasonal) dynamics of hypolimnetic hypoxia, and (2) how spatial (number of sites sampled) and temporal (sampling frequency) sampling effort affected calculated HOD rates. Our model closely replicated field-observed DO dynamics. When comparing baseline modeled dynamics to those in a second simulation with twice the number of days with high winds, however, we found that with more storm activity (1) periods of entrainment became more frequent, (2) the hypolimnion was warmer, (3) thermal stratification occurred 1 month later, whereas autumnal turnover occurred at least 1 week earlier shortening the duration of stratification by 1–2 months, and (4) HOD rates increased 12%. Further, spatial and temporal sampling intensity also affected calculated HOD rates. Consequently, adequately quantifying actual HOD rates requires sufficient sampling effort and the particular role of weather should be assessed with rigorous field and simulation studies, especially if HOD rates are used to indicate management success.  相似文献   

Geological and thermochronological studies of the Dashui gold deposit, West Qinling Orogen, Central China   总被引：3，自引：0，他引：3  

Qingtao Zeng  Noreen J. Evans  Brent I. A. McInnes  Geoffrey E. Batt  Campbell T. McCuaig  Leon Bagas  Eric Tohver 《Mineralium Deposita》2013,48(3):397-412

The Dashui gold deposit is a structurally controlled, Carlin-type gold deposit hosted by recrystallised limestone in the West Qinling Orogen of Central China. The major, structurally late east-trending Dashui Fault forms the hanging wall to the gold mineralisation at the Dashui mine and defines the contact between Middle Triassic limestone and a steeply dipping overlying succession of Middle Triassic argillaceous limestone, dolomite, and sandstone. Multiple carbonate veins and large-scale supergene enrichment, represented by hematite, goethite, limonite and jarosite, characterise the deposit. Detailed geochronological investigation using zircon SHRIMP U-Pb dating reveals that volcanic rocks closely associated with the Dashui gold deposit were synchronous with the Ge’erkuohe Granite and pre-date mineralisation. The igneous dyke sample from the hanging wall has the same U-Pb zircon age as the footwall, ca. 213 Ma. (U-Th)/He thermochronology on dykes in the hanging wall and footwall of the Dashui Fault yields identical (U-Th)/He zircon ages of ca. 210 Ma but distinct (U-Th)/He apatite ages of ca. 136 and 211 Ma, respectively. Therefore, the hanging wall and footwall are interpreted as having distinct post-mineralisation exhumation histories. Reverse fault movement exhumed the hanging wall ~2 to 4 km since the Late Triassic with the main component of faulting taking place between the Late Triassic and Early Cretaceous. These relationships suggest a Late Triassic to Early Cretaceous age for the primary gold mineralisation at the Dashui gold deposit, with the corollary that any ‘missing portion’ of the deposit, previously hypothesised to exist in the hanging wall of the Dashui Fault, has been eroded away. The mineralisation in the footwall may have been supergene enriched soon after the primary mineralisation was emplaced, because it has been located at shallow depth since the Late Triassic. Semi-quantitative results obtained in this study also constrain the maximum depth of formation of the Dashui gold at no more than 2 km.  相似文献   

The reliability of emplacement temperature estimates using palaeomagnetic methods: a case study from Santorini, Greece   总被引：1，自引：0，他引：1  

Leon Bardot  Elizabeth McClelland 《Geophysical Journal International》2000,143(1):39-51

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Archean (about 2500 Ma) anatexis in eastern North China Block     

Si-hong Jiang  Leon Bagas  Yi-fei Liu  Li-li Zhang 《China Geology》2021,4(2):215-229

Two Neoarchean alkaline feldspar-rich granites sourced from partially melted granulite-facies granodioritic orthogneiss have been here recognised in the eastern part of the North China Block (NCB). These poorly foliated granites have previously been assumed to be Mesozoic in age and never dated, and so their significance has not been recognised until now. The first granite (AG1) is a porphyritic syenogranite with megacrystic K-feldspar, and the second (AG2) is a quartz syenite with perthitic megacryst. Zircons from the granites yield LA-ICP-MS U-Pb ages of 2499 ± 10 Ma (AG1), and 2492 ± 28 Ma (AG2), which are slightly younger than the granodioritic orthogneiss that they intrude with a crystallisation U-Pb age of 2537 ± 34 Ma. The younger granites have higher assays for SiO₂ (71.91% for AG1 and 73.22% for AG2) and K₂O (7.52% for AG1 and 8.37% for AG2), and much lower assays for their other major element than the granodioritic orthogneiss. All of the granodioritic orthogneiss and granite samples have similar trace element patterns, with depletion in Th, U, Nb, and Ti and enrichment in Rb, Ba, K, La, Ce, and P. This indicates that the granites are derived from the orthogneiss as partial melts. Although they exhibit a similar REE pattern, the granites have much lower total REE contents (30.97×10⁻⁶ for AG1, and 25.93×10⁻⁶ for AG2), but pronounced positive Eu anomalies (Eu/Eu* = 8.57 for AG1 and 27.04 for AG2). The granodioritic orthogneiss has an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.70144, εNd(t) value of 3.5, and εHf(t) values ranging from −3.2 to +2.9. The orthogneiss is a product of fractional crystallisation from a dioritic magma, which was derived from a mantle source contaminated by melts derived from a felsic slab. By contrast, the AG1 sample has an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.6926 that is considered too low in value, εNd(t) value of 0.3, and εHf(t) values between +0.57 and +3.82; whereas the AG2 sample has an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.70152, εNd(t) value of 1.3, and εHf(t) values between +0.5 and +14.08. These assays indicate that a Sr-Nd-Hf isotopic disequilibrium exists between the granite and granodioritic orthogneiss. The elevated εHf(t) values of the granites can be explained by the involvement of Hf-bearing minerals, such as orthopyroxene, amphibole, and biotite, in anatectic reactions in the granodioritic orthogneiss. Based on the transitional relationship between the granites and granodioritic orthogneiss and the geochemical characteristics mentioned above, it is concluded that the granites are the product of rapid partial-melting of the granodioritic orthogneiss after granulite-facies metamorphism, and their crystallisation age of about 2500 Ma provides the minimum age of the metamorphism. This about 2500 Ma tectonic-metamorphic event in NCB is similar to the other cratons in India, Antarctica, northern and southern Australia, indicating a possible connection between these cratons during the Neoarchean.  相似文献   

海相沉积物中的氧化作用和有机质保存:来自富有机碳古沉积物的直接实验证据     

Leon Moodley  徐明芝 《海洋地质前沿》2006,22(2):20-22

什么变量控制着海相沉积物中的有机质(OM)保存是当今生物地球化学研究中的一个最复杂和有争议的问题(Hedges等,1999),使均变论的应用复杂化,即不能简单地用现在的现象去解释过去。具体说,氧化作用在形成富有机碳古沉积物(如地中海腐泥)中扮演一个什么角色一直是人们争论的问题。实验室试验研究了氧对现代沉积物OM降解的影响,研究中主要使用了富碳的海岸沉积物,揭示了除最具反应性的部分之外,在缺氧情况下OM降解过程明显缓慢。然而,在氧化性好、有机质缺乏的深海沉积物中可能有不同的趋势,现在我们仍需要弄清在地质年代中是否缺氧条件增强…  相似文献   

Spectral-type simulation of spatially correlated fracture set properties     

Stanley M. Miller  Leon E. Borgman 《Mathematical Geology》1985,17(1):41-52

Fracture set properties such as orientation, spacing, trace length, and waviness tend to be spatially correlated. These properties can be efficiently simulated by spectral analysis procedures that take advantage of the computational speed of the fast Fourier transform. The covariance function of each property to be simulated is obtained from the variogram function estimated from mapped fracture set data and is typically referenced to the mean vector of the set. Simulation procedures for normally and exponentially distributed data involve generating uncorrelated Fourier coefficients that are assigned proper variance according to the spectral density, which is the Fourier transform of the covariance function. These coefficients are then reverse Fourier transformed to produce simulated set properties that have the desired variance and variogram function.  相似文献