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   

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.

  相似文献   

The High-Resolution Coronal Imager (Hi-C)     

Ken Kobayashi  Jonathan Cirtain  Amy R. Winebarger  Kelly Korreck  Leon Golub  Robert W. Walsh  Bart De Pontieu  Craig DeForest  Alan Title  Sergey Kuzin  Sabrina Savage  Dyana Beabout  Brent Beabout  William Podgorski  David Caldwell  Kenneth McCracken  Mark Ordway  Henry Bergner  Richard Gates  Sean McKillop  Peter Cheimets  Simon Platt  Nick Mitchell  David Windt 《Solar physics》2014,289(11):4393-4412

The High-Resolution Coronal Imager (Hi-C) was flown on a NASA sounding rocket on 11 July 2012. The goal of the Hi-C mission was to obtain high-resolution (≈?0.3?–?0.4′′), high-cadence (≈?5 seconds) images of a solar active region to investigate the dynamics of solar coronal structures at small spatial scales. The instrument consists of a normal-incidence telescope with the optics coated with multilayers to reflect a narrow wavelength range around 19.3 nm (including the Fe xii 19.5-nm spectral line) and a 4096×4096 camera with a plate scale of 0.1′′?pixel^?1. The target of the Hi-C rocket flight was Active Region 11520. Hi-C obtained 37 full-frame images and 86 partial-frame images during the rocket flight. Analysis of the Hi-C data indicates the corona is structured on scales smaller than currently resolved by existing satellite missions.  相似文献   

The behavior of magneto-acoustic-gravity waves near the cusp resonance in a lossless,compressible, isothermal,stratified, electrically conducting and uniformly magnetized atmosphere. II: The valve effect     

Leon P. J. Kamp 《地球物理与天体物理流体动力学》2013,107(4):257-271

Abstract

In the present paper the behavior of (internal) magneto-acoustic-gravity waves near the cusp resonance in a lossless, compressible, isothermal, stratified, electrically conducting atmosphere that is permeated by a uniform, nearly horizontal magnetic field is re-addressed (Kamp, 1989). The previously analyzed linear conversion of long acoustic-gravity waves into short magneto-acoustic waves that carry off the energy from the resonance region along the magnetic field, is re-analyzed with boundary layer techniques that are based on the smallness of the vertical component of the magnetic field. More specifically the existence of the so-called valve effect for the generated magneto-acoustic mode near the critical level is explicitly demonstrated and shown to be governed by two rivalling effects.  相似文献   

Response of the mesozooplankton community of the St Lucia estuary,South Africa,to a mouth-opening event during an extended drought     

Hendrik L. Jerling  Leon VivierDigby P. Cyrus 《Estuarine, Coastal and Shelf Science》2010

Mesozooplankton samples were collected between March 2005 and November 2008 in St Lucia, the largest estuarine lake system in South Africa. St Lucia experienced an extended period of drought before and during the present study. This drought led to natural closing of the estuary mouth as a result of flood-tide marine sediment deposition in 2002. In March 2007 the mouth was washed open by exceptionally high tidal and wave conditions. This resulted in an influx of a large volume of seawater. The mouth closed again in August 2007. Before opening of the mouth salinities in the Estuary were below 10 and large parts of North Lake dried up while South Lake retained a relatively stable waterbody with salinities between 10 and 30. When the mouth opened seawater flooded the system and salinities changed to about 35. After the mouth had closed again in August 2007 salinities increased in the lakes and decreased in the Estuary. The mesozooplankton community was dominated by copepods during all sampling sessions, especially by the estuarine calanoids Pseudodiaptomus stuhlmanni and Acartia natalensis. Mean mesozooplankton densities were significantly higher in South Lake before the mouth opened in March 2007. While zooplankton density decreased when the mouth opened species richness increased with the influx of coastal marine species, especially in the Estuary. Overall zooplankton densities declined progressively as salinity increased to hypersaline levels after mouth closure. Multivariate analyses supported significant differences between the lakes and the Estuary in terms of mesozooplankton community composition. Taxa mostly responsible for the similarities within and dissimilarity between sections of the system were the copepods P. stuhlmanni and A. natalensis with the meroplankton, crab zoeae and mollusc larvae, also contributing significantly after the mouth-opening event.  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   

The State of the Marine Environment Report for Australia (SOMER): process, findings and perspectives     

Leon P. Zann 《Ocean & Coastal Management》1996,33(1-3)

  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

  相似文献   

Getting from here to there – energy technology transformation pathways in the EMF27 scenarios     

Volker Krey  Gunnar Luderer  Leon Clarke  Elmar Kriegler 《Climatic change》2014,123(3-4):369-382

Based on a large number of energy-economic and integrated assessment models, the Energy Modeling Forum (EMF) 27 study systematically explores the implications of technology cost and availability for feasibility and macroeconomic costs of energy system transformations toward climate stabilization. At the highest level, the technology strategy articulated in all the scenarios in EMF27 includes three elements: decarbonization of energy supply, increasing the use of low-carbon energy carriers in end-use, and reduction of energy use. The way that the scenarios differ is in the degree to which these different elements of strategy are implemented, the timing of those implementations, and the associated macroeconomic costs. The study also discusses the value of individual technologies for achieving climate stabilization. A robust finding is that the unavailability of carbon capture and storage and limited availability of bioenergy have the largest impact on feasibility and macroeconomic costs for stabilizing atmospheric concentrations at low levels, mostly because of their combined ability to remove carbon from the atmosphere. Constraining options in the electric sector such as nuclear power, wind and solar energy in contrast has a much smaller impact on the cost of mitigation.  相似文献