Historical population assessment of Barents Sea harp seals (Pagophilus groenlandicus)     

Skaug  Hans J.; Frimannslund  Lennart; Oien  Nils I. 《ICES Journal of Marine Science》2007,64(7):1356-1365

  相似文献   

Fluid–Rock Interactions in Geothermal Reservoirs,Germany: Thermal Autoclave Experiments Using Sandstones and Natural Hydrothermal Brines     

Schäffer  Rafael  Götz  Emilia  Schlatter  Nils  Schubert  Gabriela  Weinert  Sebastian  Schmidt  Stefanie  Kolb  Ute  Sass  Ingo 《Aquatic Geochemistry》2022,28(2):63-110

As renewable energy, geothermal can contribute substantially to the energy transition. To generate electricity or to harvest heat, high-saline fluids are tapped by wells of a few kilometres and extracted from hydrothermal reservoirs. After the heat exchanger units have been passed by, these fluids are reinjected into the reservoir. Due to the pressure and temperature differences between the subsurface and the surface, as well as the cooling of the fluids in the power plant, unwanted chemical reactions can occur within the reservoir, in the borehole, and within the power plant itself. This can reduce the permeability of the reservoir as well as the output of the geothermal power plant. This study aims to simulate real subsurface reactions using batch and leaching experiments with sandstone or sandstone powder as solid phase, and deionised water or natural brine as liquid phase. It is demonstrated that fluid composition changes after only a few days. In particular, calcite, aragonite, clay minerals, and zinc phases precipitate from the natural brine. In contrast, in particular minerals containing potassium, arsenic, barium, and silica are dissolved. Due to the experimental set-up, these mineral reactions mainly took place on the surface of the samples, which is why no substantial changes in petrophysical properties could be observed. However, it is assumed that the observed reactions on the reservoir scale have a relevant influence on parameters such as permeability.

  相似文献   

Phase-scanning approach to correct time-shift inaccuracies in the surface-wave walk-away method   总被引：1，自引：0，他引：1  

Edwin A. Obando  Choon B. Park  Nils Ryden  Peter Ulriksen 《Soil Dynamics and Earthquake Engineering》2010

In order to maintain lateral resolution while maximizing investigation depth in a multichannel surface wave method, it is beneficial to implement the walk-away approach by using a relatively short receiver spread. Combined walk-away records, however, normally suffer from time-shift inaccuracies that adversely influence the subsequent dispersion imaging process. Time-shift inaccuracies produce phase discontinuities which can generate false apparent higher modes in the dispersion images misleading the correct interpretation of the dispersion curve. To minimize these adverse effects, we present a phase-scanning approach that searches for an optimum phase shift to correct the phase shift generated by the walk-away method. Results obtained from synthetic and real-world field data show that for the specific case of a single dominating mode the proposed approach reduces the distortions in the dispersion image caused by the walk-away approach. The proposed method is especially efficient in the presence of ambient random noise.  相似文献   

A Triggered Depth‐Dependent Sampling System to Overcome the Carry‐Over Effects of the Membrane Interface Probe          下载免费PDF全文

Jan Bumberger  Kilian Peisker  Nils Reiche  Dirk Radny  Peter Dietrich 《Ground Water Monitoring & Remediation》2016,36(3):54-61

The membrane interface probe (MIP) is widely used for the in situ characterization of volatile organic compounds (VOCs) in the subsurface. A main problem using the MIP system is the carry‐over effect of VOCs during the transport from the point of measurement to the detector using a conventional transfer line. This effect results in compound specific retention times, which is shown in disproportionately high measuring signals after the actual penetration of contaminated zones. In consequence, the lower extent of contamination is not clearly identifiable and may be overestimated. The presented field study presents an evaluation of different methods to overcome the carry‐over effect, especially with regard to the required measurement times that are needed to wait for a complete disappearance of the detector signals before forwarding the probe. This was accomplished by comparing data collected with a MIP system with (1) unheated transfer line and (2) a system including a heated transfer line to data collected with a system using (3) a depth‐dependent triggered sampling behind the membrane including two transfer lines. A comparison with analytical results from soil samples gave a good correlation for all three methods. Furthermore, it could be shown that the use of a heated transfer line has a time improvement of 30% compared to an unheated transfer line while the depth dependent triggered sampling using two separate transfer lines yielded a time improvement of over 90%. These results confirm the benefit of the latter method, particularly for the use in highly contaminated sediments.  相似文献   

OpenDA-NEMO framework for ocean data assimilation     

Nils van Velzen  Muhammad Umer Altaf  Martin Verlaan 《Ocean Dynamics》2016,66(5):691-702

Data assimilation methods provide a means to handle the modeling errors and uncertainties in sophisticated ocean models. In this study, we have created an OpenDA-NEMO framework unlocking the data assimilation tools available in OpenDA for use with NEMO models. This includes data assimilation methods, automatic parallelization, and a recently implemented automatic localization algorithm that removes spurious correlations in the model based on uncertainties in the computed Kalman gain matrix. We have set up a twin experiment where we assimilate sea surface height (SSH) satellite measurements. From the experiments, we can conclude that the OpenDA-NEMO framework performs as expected and that the automatic localization significantly improves the performance of the data assimilation algorithm by successfully removing spurious correlations. Based on these results, it looks promising to extend the framework with new kinds of observations and work on improving the computational speed of the automatic localization technique such that it becomes feasible to include large number of observations.  相似文献   

Evaluation of reanalysis and satellite-based precipitation datasets in driving hydrological models in a humid region of Southern China     

Hongliang Xu  Chong-Yu Xu  Nils Roar Sælthun  Bin Zhou  Youpeng Xu 《Stochastic Environmental Research and Risk Assessment (SERRA)》2015,29(8):2003-2020

  相似文献   

Morphological evolution of a macrotidal back-barrier environment: The Amazon Coast     

Robin L. McLachlan  Andrea S. Ogston  Nils E. Asp  Aaron T. Fricke  Charles A. Nittrouer  Carlos A. F. Schettini 《Sedimentology》2020,67(7):3492-3512

Coastal barriers provide sheltered, low-energy settings for fine-grained sediment deposition and retention, although the process of back-barrier infilling and how tidal-channel connectivity impacts this process is not well-understood. Understanding how back-barrier environments infill and evolve is necessary to predict how they will respond to future changes in sea-level and sediment supply. With this motivation, in situ observations and sedimentary signatures from an Amazonian tidal-channel system are interpreted to create a conceptual model of morphological evolution in a macrotidal back-barrier environment that is rich in fine-grained sediment, vegetated by mangroves and incised by tidal channels with multiple outlets. Results indicate that within a high-connectivity back-barrier channel, tidal processes dominate sedimentation and morphological development. Sediment cores (<60 cm) exhibited millimetre-scale tidalites composed of sand and mud. High-connectivity channels allow tidal propagation from multiple inlets, and in this case, the converging flood waves promote delivery of sediment fluxing through the system to the mangrove flats in the convergence zone. Sediment preferentially deposits in regions with adequate accommodation space and dense vegetation, and in these zones, sediment grain size is slightly finer than that transiting through the system. The greatest sediment-accumulation rates (3 to 4 cm yr⁻¹), calculated from steady-state ²¹⁰Pb profiles, were found in the convergence zone near the mangrove-channel edge. As tidal flats aggrade vertically and prograde into the channels, accommodation space diminishes. In effect, the channel’s narrowest stretch is expected to migrate along the path of net-sediment flux towards regions with more accommodation space until it reaches the tidal-convergence zone. The location of recent preferential infilling is evidenced by relatively rapid sediment-accumulation rates, finer sediment and significant clustering of small secondary tidal channels. These findings shed light on how sediment transported through vegetated back-barrier environments is ultimately preserved and how evidence preserved in surface morphology and the geological record can be interpreted.  相似文献   

Numerical modelling of downstream migrating antidunes          下载免费PDF全文

Nils Reidar B. Olsen 《地球表面变化过程与地形》2017,42(14):2393-2401

A numerical model is presented that compute the geometrical dimensions and movement of downstream migrating antidunes. The model solves the Navier–Stokes equations together with the k‐epsilon turbulence model to find the water flow field over the bedforms. A two‐dimensional width‐averaged grid is used. The bed elevation changes are computed by solving the convection–diffusion equation for suspended sediments and bedload, together with the Engelund–Hansen sediment transport formula. The free surface is computed with an algorithm based on water continuity in the surface cells. Non‐orthogonal adaptive grids were used, moving vertically with the computed location of the bed and the free water surface. The numerical model was tested on data from a physical model study where regular downstream migrating antidunes had been observed. The numerical model started out with a flat bed and the trains of antidunes formed over time. Many of the physical processes observed in earlier studies were replicated by the numerical model. Four dune parameters were computed in the current tests: The antidune wavelength, height and celerity, together with the average water depth. The antidune wavelengths were best predicted with an accuracy of 3 to 8% compared with the measurements. The antidune heights were computed with a deviation of 11 to 25% compared with an empirical formula. The water depths over the antidunes were predicted with an accuracy of 3 to 9% related to the measured values. The average antidune celerity was the parameter with largest deviation: For the coarsest grid it was overpredicted with 37%. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Black hole dynamics: A survey of black hole physics from the point of view of perturbation theory     

Nils Andersson 《Journal of Astrophysics and Astronomy》1999,20(3-4):269-280

This article is a brief survey of the contribution of perturbative studies to our understanding of black hole physics. For natural reasons, I will not be able to discuss all details required for an exhaustive understanding of a field that has been active for the last forty years. Neither will — I be able to cover all problem areas where perturbation theory has been applied. My aim is simply to provide the interested reader with a few pointers that can serve as useful starting points for an odyssey through the literature.  相似文献   

Seasonal,tidal, and geomorphic controls on sediment export to Amazon River tidal floodplains     

Daniel J. Nowacki  Andrea S. Ogston  Charles A. Nittrouer  Aaron T. Fricke  Nils E. Asp  Pedro Walfir M. Souza Filho 《地球表面变化过程与地形》2019,44(9):1846-1859

Mainstem–floodplain material exchange in the tidal freshwater reach of major rivers may lead to significant sequestration of riverine sediment, but this zone remains understudied compared to adjacent fluvial and marine environments. This knowledge gap prompts investigation of floodplain-incising tidal channels found along the banks of tidal rivers and their role in facilitating water and suspended-sediment fluxes between mainstem and floodplain. To evaluate this role, and how it evolves along the tidal river and with time, we measured water level, flow velocity, temperature, and suspended-sediment concentration (SSC) in four tidal channels along the tidal Amazon River, Brazil. Eleven deployments were made during low, rising, high, and falling seasonal Amazon discharge. Generally, channels export high-SSC water from the mainstem to the tidal floodplain on flood tides and transfer low-SSC water back to the mainstem on ebbs. Along the length of the tidal river, the interaction between tidal and seasonal water-level variations and channel–floodplain morphology is a primary control on tidal-channel sediment dynamics. Close to the river mouth, where tides are large, this interaction produces transient flow features and current-induced sediment resuspension, but the importance of these processes decreases with distance upstream. Although the magnitude of the exchange of water and sediment between mainstem and floodplain via tidal channels is a small percentage of the total mainstem discharge in this large tidal-river system, tidal channels are important conduits for material flux between these two environments. This flux is critical to resisting floodplain submergence during times of rising sea level. © 2019 John Wiley & Sons, Ltd.  相似文献