Consistent parameter constraints for soil hydraulic functions   总被引：2，自引：0，他引：2  

Andre Peters  Wolfgang DurnerGerd Wessolek 《Advances in water resources》2011,34(10):1352-1365

Parameters of functions to describe soil hydraulic properties are derived from measurements by means of parameter estimation. Of crucial importance here is the choice of correct constraints in the parameter space. Often, the parameters are mere shape parameters without physical meaning, giving flexibility to the model. A fundamental requirement is that the hydraulic functions are monotonic: the retention function and the conductivity function can only decrease as the capillary suction increases. A stricter physical requirement for the conductivity function is that its decrease with respect to saturation is at least linear. This linear decrease would occur if all pores of a capillary bundle had an equal radius. In the first part of this contribution, we derive constraints for the so-called tortuosity parameter of the Mualem conductivity model, which allow highest possible flexibility on one hand and guarantee physical consistency on the other hand. In combination with the retention functions of Brooks and Corey, van Genuchten, or Durner, such a constraint can be expressed as a function of the pore-size distribution parameters. In the second part, we show that a common modification of retention models, which is applied to reach zero water content at finite suction, can lead to the physically unrealistic case of increasing water content with increasing suction. We propose a solution for this problem by slightly modifying these models and introducing a correct parameter constraint.  相似文献   

Geoacoustic character,sedimentology and chronology of a cross-shelf Holocene sediment deposit off Cabo Frio,Brazil (southwest Atlantic Ocean)     

Ursula Mendoza  Arthur Ayres Neto  Rodrigo C. Abuchacra  Cátia Fernandes Barbosa  Alberto G. Figueiredo Jr.  Manoela C. Gomes  Andre L. Belem  Ramsés Capilla  Ana Luiza S. Albuquerque 《Geo-Marine Letters》2014,34(4):297-314

The Cabo Frio region in the state of Rio de Janeiro, southeast coast of Brazil, is characterized by a local coastal upwelling system and converging littoral sediment transport systems that are deflected offshore at Cabo Frio, as a consequence of which a thick cross-shelf sediment deposit has developed over time. To investigate the evolution of this muddy deposit, geophysical, sedimentological and geochemical data from four sediment cores (3.8–4.1 m in length) recovered in water depths between 88 and 141 m were analyzed. The high-resolution seismic data show variable sediment thicknesses ranging from 1 to 20 m, comprising two sedimentary units separated by a high-impedance layer at a depth of about 10 m below the seafloor at the coring sites. According to the available age datings, the upper sedimentary unit is late Pleistocene to Holocene in age, whereas the lower unit (not dated) must, by implication, be entirely Pleistocene in age. The boomer-seismic reflection signal can be divided into three echo-types, namely transparent (inner shelf), stratified (middle shelf) and reflective (outer shelf), each type seemingly related to the local sediment composition. The upper 4 m of the upper sedimentary unit is dominated by silty sediment on the middle shelf, and by upward-fining sediments (silty sand to sandy silt) on the inner and outer shelf. The downcore trends of P-wave velocity, gamma-ray density and acoustic impedance are largely similar, but generally reversed to those of water and organic carbon contents. Total organic carbon contents increase with decreasing mean grain size, periodic fluctuations suggesting temporal changes in the regional hydrodynamics and primary productivity fuelled by the local upwelling system. The reconstruction of sedimentation rates in the course of the Holocene is based on 35 AMS age datings of organic material recovered from variable downcore depths. These range from a maximum of 13.3 cm/decade near the base of the inner shelf core (7.73–7.70 ka BP) to generally very low values (<0.11 cm/century) over the last thousand years in all cores. Over the last 6 ka there appear to have been three distinct sedimentation peaks, one between 6 and 5 ka BP, another between 4 and 3 ka PB, and one around 1 ka BP. Due to different time intervals between dates, not every peak is equally well resolved in all four cores. Based on the similar sedimentology of the inner and outer shelf cores, an essentially identical sedimentation model is proposed to have been active in both cases, albeit at different times. Thus, already during the last glacial maximum, alongshore sediment transport was deflected offshore by a change in shoreline orientation caused by the Cabo Frio structural high. The source of terrigenous material was probably a barrier-island complex that was subsequently displaced landward in the course of sea-level rise until it stabilized some 6.5 ka BP along the modern coast.  相似文献   

Geochemical Assessment of a Subtropical Reservoir: A Case Study in Curitiba,Southern Brazil     

Ricardo Henrique Moreton Godoi  Patricia Y. Hirata  Andre V. L. Bitterncourt  Ana F. L. Godoi  Miguel Jafelicci Jr  Francisco J. dos Santos  Rafael Bini  Liuz F. Zara  Cynara L. N. Cunha  Ana P. K Soares  Eduardo F. Gobbi  Sanja Potgieter‐Vermaak  José E. F. C. Gardolinski  José M. Reis Neto  Giuliana Gatto Rotondo  Rene van Grieken 《洁净——土壤、空气、水》2012,40(4):364-372

Suspended particles and dissolved substances in water provide reactive surfaces, influence metabolic activity and contribute to the net sediment deposition. It therefore plays an important part in the ecology and quality of the water mass. The water quality in reservoirs is crucial and it is naturally maintained by flushing and sedimentation, which continuously remove phosphorus from the water. In some reservoirs, however, these removal processes are countered by recycling of ions which could play a key role to start and/or maintain the eutrophic state. The combination of macro‐, trace‐ and microanalysis techniques can be useful to trace pollution sources through a chemical fingerprint, whether be during an acute environmental disaster or a long‐term release of pollutants. The water quality and total metal content of reservoir sediments were assessed in a reservoir, situated in the capital of the Paraná State, in the South‐Eastern part of Brazil. The goal of this paper was to determine the metal presence in the sediment and metal and ionic speciation in the Green River reservoir water. Water and bed sediment samples, collected from various sites during 2008 and 2009, were investigated using XRF, ICP‐OES, ICP‐MS, XRD and zeta potential measurements. Based on the results, the heavy metal concentration and chemical composition of the suspended matter in the water samples, as well as the sediment's chemical composition will be discussed.  相似文献   

Marine biogeochemical cycles and ecosystems and their interactions with climate     

Dierk Hebbeln  Andre Paul 《International Journal of Earth Sciences》2009,98(2):247-249

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A strategy for frequency spectra of quaternary climate records     

Andre Berger  JL Melice  L Hinnov 《Climate Dynamics》1991,5(4):227-240

The paleoclimatic variability at frequencies ranging from 10^–4 cycle per year (cpy) to 10^–5 cpy is investigated using a set of four deep-sea cores from the Atlantic, Pacific and Indian Oceans. Dominant features are the presence of orbital frequencies corresponding to mean periods of 117.7, 43.6, 24.9 and 19.3 kyr. These are statistically significant according to such advanced spectral tools as Blackman-Tukey, maximum entropy and the highly efficient Thomson technique. However, the main purpose of this paper is methodological, describing the statistical analyses of time series with modern methods in order to stress their relative power, advantages and disadvantages. The more advanced statistical methods confirm the coincidence of the dominant periods in the deep sea cores and those in the astronomical elements, including combination tones. Three frequency bands of high paleoclimatic variability centred at 15.4, 13 and 10.8 kyr are indeed also detected. These two last periods are very close to those predicted by the climatic non-linear model of Ghil and Le Treut and found by Pestiaux et al. and Yiou et al.  相似文献   

Scattered PKKP: Further evidence for scattering at a rough core-mantle boundary     

Andre C. Chang  John R. Cleary 《Physics of the Earth and Planetary Interiors》1981,24(1):15-29

PKKP signals from Novaya Zemlya recorded at LASA at distances around 60° show consistent anomalies in both slowness and azimuth. The observed anomaly suggests that the signal is a BC branch arrival, although the arrival time corresponds to the DF branch. The BC branch, however, does not extend back to this distance. The azimuth of approach is in the range 229–245°, instead of the expected 186°. These anomalies are associated only with PKKP; analysis of the core phases PKiKP and P′P′ (BC) from the same events show that they arrived at LASA with the appropriate slownesses and azimuths.The PKKP signals can be interpreted as “scattered” PKKP; the scattering occurs on underside reflection at the core-mantle boundary and is probably caused by topographic irregularities on the boundary itself. The calculated scattering region has a surface projection at about 60°S, 134°E, which is outside the diametral plane through source and receiver, and about 21° from the expected PKKP reflection point at 76°S, 95°E.Both the “direct” and “scattered” arms of the PKKP signal have a PK path close to that of the “C” end of the BC branch. The unexpectedly large amplitude of the arrival suggests that there may be a focusing of energy at C, which would indicate a change in velocity gradient just above the inner core boundary. The observations nevertheless require, on the scattering interpretation, lateral variations in the topography of the core-mantle boundary and a region of relatively large topography responsible for the anomalous PKKP observations.  相似文献   

Similarity studies of entrainment in convective mixed layers     

Marie-Agnes Artaz  Jean-Claude Andre 《Boundary-Layer Meteorology》1980,19(1):51-66

A similarity study of entrainment at the top of convectively driven mixed layer is presented. The similarity framework is used for a comparison between various parameterized models of mixed-layer growth rate and between closely related models for the ratio of heat fluxes at ground and inversion levels. These various models are also tested, in dimensionless form, against data from laboratory, field experiments and numerical higher-order-modeling of the convective layer. It is concluded that a rather accurate prediction of mixed-layer growth can be achieved with the simple constant flux ratio model, but that more refined studies of entrainment are required to account for the decrease of the heat flux ratio with increasing convective intensity.List of acronyms CRPE Centre de Recherches en Physique de l'Environnement, Issy-les-Moulineaux, France - EERM Etablissement d'Etudes et de Recherches Météorologiques, Boulogne, France - INRA Institut National de la Recherche Agronomique, Versailles, France - LAMP Laboratoire Associé de Météorologie Physique, Clermont-Ferrand, France - NCAR National Center for Atmospheric Research, Boulder, U.S.A. - NOAA National Oceanic and Atmospheric Administration, Environmental Research Laboratories, Boulder, U.S.A.  相似文献   

Filter-Based Classification of Training Image Patterns for Spatial Simulation   总被引：16，自引：0，他引：16  

Tuanfeng Zhang  Paul Switzer  Andre Journel 《Mathematical Geology》2006,38(1):63-80

Multiple-point simulation, as opposed to simulation one point at a time, operates at the pattern level using a priori structural information. To reduce the dimensionality of the space of patterns we propose a multi-point filtersim algorithm that classifies structural patterns using selected filter statistics. The pattern filter statistics are specific linear combinations of pattern pixel values that represent directional mean, gradient, and curvature properties. Simulation proceeds by sampling from pattern classes selected by conditioning data.  相似文献   

The Necessity of a Multiple-Point Prior Model   总被引：9，自引：0，他引：9  

Andre Journel  Tuanfeng Zhang 《Mathematical Geology》2006,38(5):591-610

Any interpolation, any hand contouring or digital drawing of a map or a numerical model necessarily calls for a prior model of the multiple-point statistics that link together the data to the unsampled nodes, then these unsampled nodes together. That prior model can be implicit, poorly defined as in hand contouring; it can be explicit through an algorithm as in digital mapping. The multiple-point statistics involved go well beyond single-point histogram and two-point covariance models; the challenge is to define algorithms that can control more of such statistics, particularly those that impact most the utilization of the resulting maps beyond their visual appearance. The newly introduced multiple-point simulation (mps) algorithms borrow the high order statistics from a visually and statistically explicit model, a training image. It is shown that mps can simulate realizations with high entropy character as well as traditional Gaussian-based algorithms, while offering the flexibility of considering alternative training images with various levels of low entropy (organized) structures. The impact on flow performance (spatial connectivity) of choosing a wrong training image among many sharing the same histogram and variogram is demonstrated.  相似文献   

Association Announcement     

Andre G. Journel NAE  Donald  Donald. M Steel 《Mathematical Geosciences》2006,38(3):391-392

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