Field Trials of Chaotic Advection to Enhance Reagent Delivery     

Michelle S. Cho  Felipe Solano  Neil R. Thomson  Michael G. Trefry  Daniel R. Lester  Guy Metcalfe 《Ground Water Monitoring & Remediation》2019,39(3):23-39

Chaotic advection is a novel approach that has the potential to enhance contact between an injected reagent and target contaminants, and thereby improve the effectiveness of in situ treatment technologies. One configuration that is capable of generating chaotic advection is termed the rotated potential mixing (RPM) flow. A conventional RPM flow system involves periodically reoriented dipole flow driven by transient switching of pressures at a series of radial wells. To determine whether chaotic advection can be engineered using such an RPM flow system, and to assess the consequent impact on the spatial distribution of a conservative tracer, a series of field-scale experiments were conducted. These experiments involved the injection of a tracer in the center of a circular array of wells followed by either mixing using an engineered RPM flow system to invoke chaotic advection, or by natural processes (advection and diffusion) as the control. Pressure fluctuations from the mixing tests using the RPM flow system showed consistent peak amplitudes during injection and extraction at a frequency corresponding to the switching time, suggesting that the target hydraulic behavior was achieved with the time-dependent flow field. The tracer breakthrough responses showed oscillatory behavior at all monitoring locations during the mixing tests which indicated that the desired RPM flow was generated. The presence of chaotic advection was supported by comparisons to observations from a previous laboratory experiment using RPM flow, and the Fourier spectrum of the temporal tracer data. Results from several quantitative metrics adopted to demonstrate field-scale evidence of chaotic advection showed that mixing led to improved lateral tracer spreading and approximately uniform concentrations across the monitoring network. The multiple lines of evidence assembled in this proof-of-concept study conclusively demonstrated that chaotic advection can be engineered at the field scale. This investigation is a critical step in the development of chaotic advection as a viable and efficient approach to enhance reagent delivery.  相似文献   

The prehistoric and preindustrial deforestation of Europe   总被引：1，自引：0，他引：1  

Jed O. Kaplan  Kristen M. Krumhardt  Niklaus Zimmermann 《Quaternary Science Reviews》2009,28(27-28):3016-3034

Humans have transformed Europe's landscapes since the establishment of the first agricultural societies in the mid-Holocene. The most important anthropogenic alteration of the natural environment was the clearing of forests to establish cropland and pasture, and the exploitation of forests for fuel wood and construction materials. While the archaeological and paleoecological record documents the time history of anthropogenic deforestation at numerous individual sites, to study the effect that prehistoric and preindustrial deforestation had on continental-scale carbon and water cycles we require spatially explicit maps of changing forest cover through time. Previous attempts to map preindustrial anthropogenic land use and land cover change addressed only the recent past, or relied on simplistic extrapolations of present day land use patterns to past conditions. In this study we created a very high resolution, annually resolved time series of anthropogenic deforestation in Europe over the past three millennia by 1) digitizing and synthesizing a database of population history for Europe and surrounding areas, 2) developing a model to simulate anthropogenic deforestation based on population density that handles technological progress, and 3) applying the database and model to a gridded dataset of land suitability for agriculture and pasture to simulate spatial and temporal trends in anthropogenic deforestation. Our model results provide reasonable estimations of deforestation in Europe when compared to historical accounts. We simulate extensive European deforestation at 1000 BC, implying that past attempts to quantify anthropogenic perturbation of the Holocene carbon cycle may have greatly underestimated early human impact on the climate system.  相似文献   

RAT0455+1305: another pulsating hybrid sdB star     

Andrzej Baran  Lester Fox-Machado 《Astrophysics and Space Science》2010,329(1-2):193-197

RAT0455+1305 was discovered during the Rapid Temporal Survey which aims in finding any variability on timescales of a few minutes to several hours. The star was found to be another sdBV star with one high amplitude mode and relatively long period. These features along with estimation of T _eff and log?g makes this star very similar to Balloon?090100001. Encouraged by prominent results obtained for the latter star we have decided to perform white light photometry on RAT0455+1305. In 2009 we used the 1.5 m telescope located in San Pedro Martir Observatory in Mexico. Fourier analysis confirmed the dominant mode found in the discovery data, uncovered another peak close to the dominant one, and three peaks in the low frequency region. This shows that RAT0455+1305 is another hybrid sdBV star pulsating in both p- and g-modes.  相似文献   

Geologic controls on gas hydrate occurrence in the Mount Elbert prospect, Alaska North Slope   总被引：1，自引：0，他引：1  

Ray Boswell  Kelly RoseTimothy S. Collett  Myung LeeWilliam Winters  Kristen A. LewisWarren Agena 《Marine and Petroleum Geology》2011,28(2):589-607

Data acquired at the BPXA-DOE-USGS Mount Elbert Gas Hydrate Stratigraphic Test Well, drilled in the Milne Point area of the Alaska North Slope in February, 2007, indicates two zones of high gas hydrate saturation within the Eocene Sagavanirktok Formation. Gas hydrate is observed in two separate sand reservoirs (the D and C units), in the stratigraphically highest portions of those sands, and is not detected in non-sand lithologies. In the younger D unit, gas hydrate appears to fill much of the available reservoir space at the top of the unit. The degree of vertical fill with the D unit is closely related to the unit reservoir quality. A thick, low-permeability clay-dominated unit serves as an upper seal, whereas a subtle transition to more clay-rich, and interbedded sand, silt, and clay units is associated with the base of gas hydrate occurrence. In the underlying C unit, the reservoir is similarly capped by a clay-dominated section, with gas hydrate filling the relatively lower-quality sands at the top of the unit leaving an underlying thick section of high-reservoir quality sands devoid of gas hydrate. Evaluation of well log, core, and seismic data indicate that the gas hydrate occurs within complex combination stratigraphic/structural traps. Structural trapping is provided by a four-way fold closure augmented by a large western bounding fault. Lithologic variation is also a likely strong control on lateral extent of the reservoirs, particularly in the D unit accumulation, where gas hydrate appears to extend beyond the limits of the structural closure. Porous and permeable zones within the C unit sand are only partially charged due most likely to limited structural trapping in the reservoir lithofacies during the period of primary charging. The occurrence of the gas hydrate within the sands in the upper portions of both the C and D units and along the crest of the fold is consistent with an interpretation that these deposits are converted free gas accumulations formed prior to the imposition of gas hydrate stability conditions.  相似文献   

Geological Applications of Laser‐Induced Breakdown Spectroscopy     

Nancy J. McMillan  Shannon Rees  Kristen Kochelek  Catherine McManus 《Geostandards and Geoanalytical Research》2014,38(3):329-343

Laser‐induced breakdown spectroscopy (LIBS) records light emitted from the decay of electrons to lower‐energy orbitals during cooling of laser‐induced ablation plasmas; the resultant spectra can be used in a variety of geoanalytical applications. Four aspects of LIBS analysis distinguish LIBS from traditional laboratory‐based analytical techniques: (i) the lack of necessary sample preparation, allowing rapid analysis of many samples, (ii) the ability to analyse both 20 to 100 μm‐diameter spots and whole rocks, (iii) the detailed chemical signature contained in a LIBS spectrum and (iv) the ability to take LIBS into the field in backpack portable instrumentation. Three case studies illustrate potential applications of LIBS in the geosciences. First, analysis of the Carrizozo basalt flow in New Mexico, USA, illustrated that LIBS spectra could discriminate between samples of similar composition within uncertainties typical of whole‐rock analysis by X‐ray fluorescence spectrometry. Second, spectra from four sets of rubies from Madagascar and Tanzania illustrate the use of LIBS and multivariate analysis to determine provenance with success rates of > 95%. This technique can also be applied to correlation of units. Finally, a chemical map of a copper ore from Butte, MT, USA, illustrates the use of spatially defined LIBS spectra to understand chemical variations within textural context.  相似文献   

Flow and sediment regimes at tributary junctions on a regulated river: impact on sediment residence time and benthic macroinvertebrate communities     

Kristen M. Svendsen  Carl E. Renshaw  Francis J. Magilligan  Keith H. Nislow  James M. Kaste 《水文研究》2009,23(2):284-296

Tributaries may either ameliorate or exacerbate the geomorphic and ecologic impacts of flow regulation by altering the flux of water and sediment into the flow‐regulated mainstem. To capture the effects of tributary influences on a flow regulated river, long‐term discharge and cross‐sectional data are used to assess the geomorphic and hydrologic impacts of impoundment. In addition, the use of the short‐lived cosmogenic radioisotope ⁷Be (half‐life 53·4 days) to link sediment transport dynamics to benthic macroinvertebrate community structure is evaluated. It is found that the ⁷Be activity of transitional bed load sediment is highly seasonal and reflects both variations in activity of sediment sources and limited sediment residence time within the junction. Benthic communities also exhibit a strong seasonal variability. In the spring, neither the ⁷Be activity of the sediment, nor benthic communities exhibit clear relationships with sample site location. In contrast, during the late summer the ratio of Ephemeroptera (mayflies)/Trichoptera (caddisflies) decreased significantly below tributary junctions. This decrease in benthic community ratio was driven by increases in caddisfly abundance and was strongly correlated with the presence of recently ⁷Be tagged transitional bedload sediment. These observations are probably associated with the presence of coarse, stable, and unembedded substrate downstream of tributaries and the rapid turnover of sediment that may also be associated with a rapid flux in nutrients or seston. The results show that tributaries are impacting the flow‐regulated mainstem and that these impacts are reflected in the benthic community structure and in the ⁷Be activity of transitional bed load sediment. Moreover, the observed reduction in competence and capacity of the mainstem following flood control suggests that these spatial discontinuities may be a consequence of impoundment. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

The many faces of ecosystem-based management: Making the process work today in real places     

Heather Tallis  Phillip S. Levin  Mary Ruckelshaus  Sarah E. Lester  Karen L. McLeod  David L. Fluharty  Benjamin S. Halpern 《Marine Policy》2010,34(2):340-348

Despite the widely accepted need for ecosystem-based management of coastal and marine systems, many managers struggle with how to put these principles into practice. Commonly voiced concerns include complicated and expensive implementation, prohibitive data requirements, and lack of testing with long-term applications. We address some of these perceived barriers by providing guidance on strategies and approaches that can be used for the steps of one ecosystem-based management process, the integrated ecosystem assessment framework, including scoping, defining indicators, setting thresholds, risk analysis, management strategy evaluation, monitoring and evaluation. Importantly, we demonstrate how an ecosystem-based management approach can be utilized in a variety of contexts which vary widely in data quality and availability, governance structure, and time frame. We then illustrate the suggested steps in the process by exploring two case studies that represent realistic ends of the data/governance/time frame spectrum: Puget Sound, Washington, USA and Raja Ampat, Indonesia. By providing concrete suggestions for how to move forward with key steps in an integrated management process, we show that ecosystem-based management is feasible from a range of starting points and that for any given starting point there are numerous productive paths forward.  相似文献   

Burning through organizational boundaries? Examining inter-organizational communication networks in policy-mandated collaborative bushfire planning groups     

Rachel F. Brummel  Kristen C. Nelson  Pamela J. Jakes 《Global Environmental Change》2012,22(2):516-528

Collaboration can enhance cooperation across geographic and organizational scales, effectively “burning through” those boundaries. Using structured social network analysis (SNA) and qualitative in-depth interviews, this study examined three collaborative bushfire planning groups in New South Wales, Australia and asked: How does participation in policy-mandated collaboration affect bushfire communication networks amongst organizational representatives? Inter-organizational communication networks became more active, less centralized, and more closely connected during planning than they had been prior. However, efforts to institutionalize collaboration were intrinsically biased towards placing administrative power and influence in public agencies. Further, collaborative planning groups did not maintain “during planning” levels of network activity and structure after planning was completed. In one case, the mandated planning process had a negative impact on inter-agency communication networks. Contextual aspects such as group size, history of inter-organizational conflict and fire occurrence, and process management were important in the development of inter-organizational networks. Though communication diminished after planning was completed, participation in the collaborative planning effort may serve as an important basis for the continuation of inter-organizational relationships beyond the scope of the planning process.  相似文献   

Period and chemical evolution of SC stars     

Albert A. Zijlstra  Timothy R. Bedding  rew J. Markwick  Rita Loidl-Gautschy  Vello Tabur  Kristen D. Alexander  rew P. Jacob  László L. Kiss  Aaron Price  Mikako Matsuura  Janet A. Mattei† 《Monthly notices of the Royal Astronomical Society》2004,352(1):325-337

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On the effect of line current width and relative position on the multi-spacecraft curlometer technique     

C. Forsyth  M. Lester  C.J. Owen 《Planetary and Space Science》2011,59(7):598-605

The response of the multi-spacecraft curlometer technique to variations in the size and relative position of infinitely long line currents with radially varying current density is systematically investigated for spacecraft in a regular tetrahedral formation. It is shown that, for line currents with a width less than the spacecraft separation, there is significant variation in the returned current with position of that current within the tetrahedron. For infinitely thin line currents, the curlometer tends to detect approximately 20% of the input current. For increasingly wide line currents there is less variation of the curlometer results with position of the current and the percentage of current magnitude detected increases. When the width of the current system is half the spacecraft separation, the curlometer tends to detect approximately 80% of the input current. These results are discussed in the context of multi-scale, multi-spacecraft missions.  相似文献