A reach‐scale biogeochemical model for temporary rivers     

Ourania Tzoraki  Nikolaos P. Nikolaidis  Anna Rosa Trancoso  Frank Braunschweig  Ramiro Neves 《水文研究》2009,23(2):272-283

The RS‐tempQ Model ( r each– s cale t emporary flow biogeochemical model) is a conceptual model that can describe the hydrologic, sediment transport and biogeochemical processes of temporary rivers at the reach scale. The model takes into account the expansion–contraction of the inundated area of the river. It simulates the sediment transport and the nutrient fluxes that are transferred to the coastal area due to the first flash flood and during extreme rain events. The RS‐tempQ Model simulates the in‐stream processes during the wet and dry cycles as the river corridor expands and contracts. The model was used to assess and quantify the hydrologic and geochemical processes occurring in a temporary river reach (Krathis River) in Greece. Since the conventional gauging techniques cannot measure the flow in rivers that are split into small braided streams, discharge measurements could not be obtained in order to calibrate and verify the model. Other field measurements such as infiltration losses and sediment accumulation were used for model calibration. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

High-resolution record of tectonic and sedimentary processes in growth strata     

Stphane Pochat  Sbastien Castelltort  Gaël Choblet  Jean Van Den Driessche 《Marine and Petroleum Geology》2009,26(8):1350-1364

Growth strata are used to determine the kinematics of synsedimentary structures such as faults. Classical methods of analysis such as thickness versus throw plot consider that the available space created by fault slip in the hanging wall of faults is instantaneously filled up by sediments. This has lead many previous works to identify a cyclic activity for growth faults. Here we perform a careful analysis of the variation of strata thicknesses on each side of a very well documented normal growth fault in the Niger delta. We show that these thickness variations are induced by the alternation of sedimentary processes during continuous fault slip. Suspended-load processes induce either uniform or slightly variable thickness of a large majority of mudstone layers. Bedload processes result in a preferential thickening of sand layers in the hanging wall. These high quality data thus provide strong grounds for doubting the polycyclic growth diagnosed for some faults at the scale of sedimentary cycles and supports the notion that fault displacement rates can be very well behaved. Our study emphasizes the important conclusion that stable fault growth, and related displacement rates, can appear to be punctuated when viewed at the scale of sedimentary cycles. It follows that care should be taken when attempting to derive displacement rates on temporal scales equivalent to those of alternating sedimentological cycles.  相似文献   

Quantum peculiarities of the primordial hydrogen recombination     

V. K. Dubrovich 《Astronomy Letters》2007,33(10):645-648

Some problems of the two-photon decay of highly excited atomic hydrogen and helium levels are considered. The necessary accuracy of calculating the transition probabilities is shown to require abandoning the purely dipole approximation in the theory of atomic hydrogen radiation. The range of applicability of the perturbation theory to this process is discussed. We suggest a new mechanism of the Lyman photon redistribution due to very close locations of the 20P and 19P levels in the hydrogen and deuterium atoms, respectively (hydrogen-deuterium resonance).  相似文献   

A mass‐balance approach to estimate in‐stream processes in a large river     

Samuel Teissier  Sabine Sauvage  Philippe Vervier  Frédéric Garabétian  José‐Miguel Sánchez‐Pérez 《水文研究》2008,22(3):420-428

A mass‐balance approach was used to estimate in‐stream processes related to inorganic nitrogen species (NH₄⁺, NO₂^? and NO₃^?) in a large river characterized by highly variable hydrological conditions, the Garonne River (south‐west France). Studies were conducted in two consecutive reaches of 30 km located downstream of the Toulouse agglomeration (population 760 000, seventh order), impacted by modification of discharge regime and high nitrogen concentrations. The mass‐balance was calculated by two methods: the first is based on a variable residence time (VRT) simulated by a one‐dimensional (1‐D) hydraulic model; the second is a based on a calculation using constant residence time (CRT) evaluated according to hydrographic peaks. In the context of the study, removal of dissolved inorganic nitrogen (DIN) for a reach of 30 km is underestimated by 11% with the CRT method. In sub‐reaches, the discrepancy between the two methods led to a 50% overestimation of DIN removal in the upper reach (13 km) and a 43% underestimation in the lower reach (17 km) using the CRT method. The study highlights the importance of residence time determination when using modelling approaches in the assessment of whole stream processes in short‐duration mass‐balance for a large river under variable hydrological conditions. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

He Conductivity in Cool White Dwarf Atmospheres     

S. Mazevet  M. Challacombe  P. M. Kowalski  D. Saumon 《Astrophysics and Space Science》2007,307(1-3):273-277

We investigate the conductivity of warm dense helium under conditions found in the atmospheres of cool white dwarfs using ab initio simulations. The calculations performed consist of quantum molecular dynamics simulations where the electronic wavefunction at each time step is obtained using density functional theory, while the ion trajectories are calculated using the resulting quantum mechanical forces. We use both conventional DFT (PW91) and hybrid (PBE0) functionals to calculate the conductivities that provide an estimate of the ionization fraction. While the calculations are in good agreement with the measurements for the equation of state, a significant discrepancy exists with the recently measured conductivity.  相似文献   

低部主序恒星锂和铍的衰减     

熊大闰  邓李才 《天文学报》2007,48(2):165-180

根据化学非均匀恒星的非局部对流理论,计算了质量为0．7-1．15M(?)恒星主序演化模型锂和铍的衰减,并将理论和不同年龄疏散星团锂丰度的观测进行了比较．结果表明,贯穿对流混合能重现温度低于6400 K的晚型主序星锂丰度观测的一般性质．贯穿对流混合可能是晚型矮星锂衰减的一种重要机制．  相似文献   

Electron-impact rotational and hyperfine excitation of HCN, HNC, DCN and DNC     

Alexandre Faure  Hemal N. Varambhia  Thierry Stoecklin  Jonathan Tennyson 《Monthly notices of the Royal Astronomical Society》2007,382(2):840-848

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OPserver: interactive online computations of opacities and radiative accelerations     

C. Mendoza  M. J. Seaton  P. Buerger  A. Bellorín  M. Meléndez †  J. González  L. S. Rodríguez  F. Delahaye  E. Palacios  A. K. Pradhan  C. J. Zeippen 《Monthly notices of the Royal Astronomical Society》2007,378(3):1031-1035

Codes to compute mean opacities and radiative accelerations for arbitrary chemical mixtures using the Opacity Project recently revised data have been restructured in a client–server architecture and transcribed as a subroutine library. This implementation increases efficiency in stellar modelling where element stratification due to diffusion processes is depth dependent, and thus requires repeated fast opacity re-estimates. Three user modes are provided to fit different computing environments, namely, a web browser, a local workstation and a distributed grid.  相似文献   

Experimental and theoretical transition probabilities in singly ionized gold     

É. Biémont  K. Blagoev  V. Fivet  G. Malcheva  R. Mayo  M. Ortiz  P. Quinet 《Monthly notices of the Royal Astronomical Society》2007,380(4):1581-1588

Absolute transition probabilities have been measured for lines originating from the 5d⁹6d and 5d⁹7s electronic configurations in the spectrum of singly ionized gold (Au  ii ). The laser-induced breakdown spectroscopy has been applied to free gold atoms and ions produced by laser ablation. Absolute transition probabilities have been determined using the branching fraction and the Boltzmann plot methods. Theoretical branching fractions as well as radiative lifetime values have also been obtained by a relativistic Hartree–Fock method taking core polarization and configuration interaction effects into account. The new results are compared with previous results when available.  相似文献   

High-temperature behaviour of the helium-like KαG ratio: the effect of improved recombination rate coefficients for calcium, iron and nickel     

J. Oelgoetz  C. J. Fontes  H. L. Zhang  M. Montenegro  S. N. Nahar  A. K. Pradhan 《Monthly notices of the Royal Astronomical Society》2007,382(2):761-769

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