Reactive transport in stratified flow fields with idealized heterogeneity     

James N. Carleton  Hubert J. Montas 《Advances in water resources》2009

A two-dimensional equation governing the steady state spatial concentration distribution of a reactive constituent within a heterogeneous advective–dispersive flow field is solved analytically. The solution which is developed for the case of a single point source can be generalized to represent analogous situations with any number of separate point sources. A limiting case of special interest has a line source of constant concentration spanning the domain’s upstream boundary. The work has relevance for improving understanding of reactive transport within various kinds of advection-dominated natural or engineered environments including rivers and streams, and bioreactors such as treatment wetlands. Simulations are used to examine quantitatively the impact that transverse dispersion (deviations from purely stochastic-convective flow) can have on mean concentration decline in the direction of flow. Results support the contention that transverse mixing serves to enhance the overall rate of reaction in such systems.  相似文献   

Factors Influencing the Stream‐Aquifer Flow Exchange Coefficient     

Hubert J. Morel‐Seytoux  Steffen Mehl  Kyle Morgado 《Ground water》2014,52(5):775-781

Knowledge of river gain from or loss to a hydraulically connected water table aquifer is crucial in issues of water rights and also when attempting to optimize conjunctive use of surface and ground waters. Typically in groundwater models this exchange flow is related to a difference in head between the river and some point in the aquifer, through a “coefficient.” This coefficient has been defined differently as well as the location for the head in the aquifer. This paper proposes a new coefficient, analytically derived, and a specific location for the point where the aquifer head is used in the difference. The dimensionless part of the coefficient is referred to as the SAFE (stream‐aquifer flow exchange) dimensionless conductance. The paper investigates the factors that influence the value of this new conductance. Among these factors are (1) the wetted perimeter of the cross‐section, (2) the degree of penetration of the cross‐section, and (3) the shape of the cross‐section. The study shows that these factors just listed are indeed ordered in their respective level of importance. In addition the study verifies that the analytical correct value of the coefficient is matched by finite difference simulation only if the grid system is sufficiently fine. Thus the use of the analytical value of the coefficient is an accurate and efficient alternative to ad hoc estimates for the coefficient typically used in finite difference and finite element methods.  相似文献   

Comment la Terre a-t-elle pu vieillir de plus de quatre milliards d’années en quatre siècles ?     

Hubert Krivine 《Comptes Rendus Geoscience》2017,349(3):91-95

The history of the determination of the Earth's age is interesting in two ways. First, it is a great school for understanding the genesis of a scientific theory. It stands at the crossroads of almost all scientific disciplines, and also philosophy or even theology. This history shows how what one may well call a “scientific truth” was established through polemics. Second, that age of 4.567 billion years is not just another figure in the series of ages that would be of concern only to astrophysicists; this scale is the only one that makes it possible to understand the genesis of the marvelous order of the solar system (that Newton attributed to God) and the fantastic complexity of Life on Earth.  相似文献   

Fluid flow and sediment entrainment in the Garonne River bore and tidal bore collision          下载免费PDF全文

Claire E. Keevil  Hubert Chanson  David Reungoat 《地球表面变化过程与地形》2015,40(12):1574-1586

A detailed field study was carried out on a tidal bore to document the turbulent processes and sediment entrainment which occurred. The measured bore, within the Arcins Channel of the Garonne River (France), was undular in nature and was followed by well‐defined secondary wave motion. Due to the local river geometry a collision between the Arcins channel tidal bore and the bore which formed within the main Garonne River channel was observed about 800 m upstream of the sampling site. This bore collision generated a transient standing wave with a black water mixing zone. Following this collision the bore from the main Garonne River channel propagated ‘backward’ to the downstream end of the Arcins channel. Velocity measurements with a fine temporal resolution were complemented by measurements of the sediment concentration and river level. The instantaneous velocity data indicated large and rapid fluctuations of all velocity components during the tidal bore. Large Reynolds shear stresses were observed during and after the tidal bore passage, including during the 'backward' bore propagation. Large suspended sediment concentration estimates were recorded and the suspended sediment flux data showed some substantial sediment motion, consistent with the murky appearance of the flood tide waters. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Constraints on the average magnetic field strength of relic radio sources 0917+75 and 1401−33 from XMM–Newton observations     

C. M. Hubert Chen  D. E. Harris  Fiona A. Harrison  Peter H. Mao † 《Monthly notices of the Royal Astronomical Society》2008,383(3):1259-1268

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Meeting review: The nice symposium on the origin of the solar system     

Hubert Reeves 《Icarus》1973,19(4):604-606

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Excursion to Cardiff: March 31st to April 8th. Easter, 1920     

A. Hubert Cox  T. Franklin Sibly  A.E. Trueman 《Proceedings of the Geologists' Association. Geologists' Association》1920,31(4):200-IN5

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Quality assurance of hydroacoustic surveys: the repeatability of fish-abundance and biomass estimates in lakes within and between hydroacoustic systems   总被引：1，自引：1，他引：1  

Wanzenbock  Josef; Mehner  Thomas; Schulz  Michael; Gassner  Hubert; Winfield  Ian J 《ICES Journal of Marine Science》2003,60(3):486-492

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Resilience,Adaptability, and Regime Shifts Thinking: A Perspective of Dryland Socio-ecology System     

PENG Yu  ZHANG Qiuying  CHEN Yuanzhan  XU Ning  QIAO Yunfeng  TIAN Chao  Hubert HIRWA  Salif DIOP  Aliou GUISSE  LI Fadong 《资源与生态学报(英文版)》2021,12(3):376-383

Arid areas are widespread globally and support a third of the world’s population’s livelihoods. The increasing population, urbanization, land-use changes, and the climate significantly affect coupled natural and human systems and threaten environments and socio-ecological land systems. The degradation of drylands poses a severe and widespread threat to the lives of millions of people, especially in developing countries and in the global environment. This review assesses published literature on dryland socio-ecological systems to reveal current research trends and changes in research themes over time and introduces basic theories and advances in dryland socio-ecological system frameworks, resilience measurement, and regime shifts. Developing a more general but adaptable framework and a more practical strategy for long-term coordination and partnership and attaining specific insights into ecological services should receive more attention and be strengthened in future studies on drylands sustainability.  相似文献   

Measurements of the helium 584 Å airglow during the Cassini flyby of Venus     

J.-C. Gérard  J. Gustin  B. Hubert  G.R. Gladstone  L.W. Esposito 《Planetary and Space Science》2011,59(13):1524-1528

The helium resonance line at 584 Å has been observed with the UltraViolet Imaging Spectrograph (UVIS) Extreme Ultraviolet channel during the flyby of Venus by Cassini at a period of high solar activity. The brightness was measured along the disk from the morning terminator up to the bright limb near local noon. The mean disk intensity was ∼320 R, reaching ∼700 R at the bright limb. These values are slightly higher than those determined from previous observations. The sensitivity of the 584 Å intensity to the helium abundance is analyzed using recent cross-sections and solar irradiance measurements at 584 Å. The intensity distribution along the UVIS footprint on the disk is best reproduced using the EUVAC solar flux model and the helium density distribution from the VTS3 empirical model. It corresponds to a helium density of 8×10⁶ cm⁻³ at the level of where the CO₂ is 2×10¹⁰ cm⁻³.  相似文献