Atmospheric Stability Effects on Wind Fields and Scalar Mixing Within and Just Above a Subalpine Forest in Sloping Terrain   总被引：1，自引：1，他引：0  

Sean P. Burns  Jielun Sun  Donald H. Lenschow  Steven P. Oncley  Britton B. Stephens  Chuixiang Yi  Dean E. Anderson  Jia Hu  Russell K. Monson 《Boundary-Layer Meteorology》2011,138(2):231-262

Air temperature T _a , specific humidity q, CO₂ mole fraction χ _c , and three-dimensional winds were measured in mountainous terrain from five tall towers within a 1 km region encompassing a wide range of canopy densities. The measurements were sorted by a bulk Richardson number Ri _b . For stable conditions, we found vertical scalar differences developed over a “transition” region between 0.05 < Ri _b < 0.5. For strongly stable conditions (Ri _b > 1), the vertical scalar differences reached a maximum and remained fairly constant with increasing stability. The relationships q and χ _c have with Ri _b are explained by considering their sources and sinks. For winds, the strong momentum absorption in the upper canopy allows the canopy sublayer to be influenced by pressure gradient forces and terrain effects that lead to complex subcanopy flow patterns. At the dense-canopy sites, soil respiration coupled with wind-sheltering resulted in CO₂ near the ground being 5–7 μmol mol⁻¹ larger than aloft, even with strong above-canopy winds (near-neutral conditions). We found Ri _b -binning to be a useful tool for evaluating vertical scalar mixing; however, additional information (e.g., pressure gradients, detailed vegetation/topography, etc.) is needed to fully explain the subcanopy wind patterns. Implications of our results for CO₂ advection over heterogenous, complex terrain are discussed.  相似文献   

Chalcopyrite formation through the metathesis of pyrrhotite with aqueous copper   总被引：2，自引：0，他引：2  

Alexander Dean Elliot 《Geochimica et cosmochimica acta》2011,75(8):2103-2118

The heterogeneous chemical environment which develops in the heap leaching of some pyrrhotite-containing copper ores can promote covellite and chalcopyrite formation particularly in acid-depleted regions of a heap. In such circumstances, copper recovery will be delayed until the acid and oxidation fronts move through the bed of ore and these secondary copper sulfides are re-leached. The transition from pyrrhotite to chalcopyrite most probably follows the sequence, pyrrhotite to copper-pyrrhotite to unnamed mineral CuFe₃S₄ to isocubanite to chalcopyrite, with a major structural expansion occurring prior to CuFe₃S₄. The mechanism is one in which copper is incorporated into pyrrhotite, which maintains its NiAs-type structure up to a stability limit, above which the structure rearranges to a chalcopyrite-like structure followed by isomorphic substitution of copper for iron. The structural rearrangement proceeds with significant expansion in one of the hexagonal axis directions and contractions in the other directions. Depending on the orientation, this expansion induces different levels of strain in the product chalcopyrite. The level of strain subsequently impacts on the rate of chalcopyrite metathesis to covellite. The depth of chalcopyrite formation into the pyrrhotite varies with pyrrhotite orientation.  相似文献   

Determining individual mineral contributions to U(VI) adsorption in a contaminated aquifer sediment: A fluorescence spectroscopy study     

Zheming Wang  Yuanxian Xia  Tom C. Resch  Dean A. Moore  C. Liu 《Geochimica et cosmochimica acta》2011,75(10):2965-8740

The adsorption and speciation of U(VI) was investigated on contaminated, fine grained sediment materials from the Hanford 300 area (SPP1 GWF) in simulated groundwater using cryogenic laser-induced U(VI) fluorescence spectroscopy combined with chemometric analysis. A series of reference minerals (montmorillonite, illite, Michigan chlorite, North Carolina chlorite, California clinochlore, quartz and synthetic 6-line ferrihydrite) was used for comparison that represents the mineralogical constituents of SPP1 GWF. Surface area-normalized K_d values were measured at U(VI) concentrations of 5 × 10⁻⁷ and 5 × 10⁻⁶ mol L⁻¹ that displayed the following affinity series: 6-line-ferrihydrite > North Carolina chlorite ≈ California clinochlore > quartz ≈ Michigan chlorite > illite > montmorillonite. Both time-resolved spectra and asynchronous two-dimensional (2D) correlation analysis of SPP1 GWF at different delay times indicated that two major adsorbed U(VI) species were present in the sediment that resembled U(VI) adsorbed on quartz and phyllosilicates. Simulations of the normalized fluorescence spectra confirmed that the speciation of SPP1 GWF was best represented by a linear combination of U(VI) adsorbed on quartz (90%) and phyllosilicates (10%). However, the fluorescence quantum yield for U(VI) adsorbed on phyllosilicates was lower than quartz and, consequently, its fractional contribution to speciation may be underestimated. Spectral comparison with literature data suggested that U(VI) exist primarily as inner-sphere complexes with surface silanol groups on quartz and as surface U(VI) tricarbonate complexes on phyllosilicates.  相似文献   

Evaluation of mineral substrates for in situ iron removal from groundwater     

Yu Wang  Saraya Sikora  Hwidong Kim  Jean-Claude Bonzongo  Dean Rhue  Timothy G. Townsend 《Environmental Earth Sciences》2013,69(7):2247-2255

Calcium carbonate-based materials (CCBM) have been found to remove Fe(II) and other divalent metal cations from aqueous solution and thus have the potential for incorporation into remediation systems to remove Fe(II) from groundwater at landfills. Research was conducted to examine the ability of a range of CCBM to remove Fe(II) and assess the mechanism of removal. Different CCBM (limestone, concrete, dolomite, marble), as well as gypsum, witherite, and quartz sand, were tested for their ability to remove Fe(II) from water using batch tests conducted under anaerobic conditions. Limestone (specific surface area of approximately 0.46 m²/g) was found to have the best removal effectiveness, and the final Fe(II) concentration was reduced from 50 to <0.01 mg/L. Kinetics experiments conducted over a 72 h period indicated that the removal process of Fe(II) by CCBM was a two-step process. The first step is rapid sorption of Fe(II) onto the CCBM surfaces within the first hour, and the second step is relatively slow co-precipitation of iron-containing solids formed through various chemical reactions. The two best performing CCBM (limestone and concrete) were evaluated for their removal ability based on media particle size (diameters of 3–5, 7–10, 15–25, and 40–50 mm) and revealed statistically significant (p < 0.01) increases in Fe(II) removal for each particle size class examined. SEM analysis of reacted materials revealed visible precipitates on the reactive material surface; XRD analysis was not able to detect crystalline Fe minerals on limestone surface.  相似文献   

Visualizing robust geographically weighted parameter estimates     

Robert G. Cromley  Dean M. Hanink 《制图学和地理信息科学》2013,40(1):100-110

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Recent advances in global lake coring hold promise for global change research in paleolimnology     

Walter E. Dean 《Journal of Paleolimnology》2010,44(2):741-743

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Estimation and propagation of volcanic source parameter uncertainty in an ash transport and dispersal model: application to the Eyjafjallajokull plume of 14–16 April 2010     

Marcus Bursik  Matthew Jones  Simon Carn  Ken Dean  Abani Patra  Michael Pavolonis  E. Bruce Pitman  Tarunraj Singh  Puneet Singla  Peter Webley  Halldor Bjornsson  Maurizio Ripepe 《Bulletin of Volcanology》2012,74(10):2321-2338

Data on source conditions for the 14 April 2010 paroxysmal phase of the Eyjafjallaj?kull eruption, Iceland, have been used as inputs to a trajectory-based eruption column model, bent. This model has in turn been adapted to generate output suitable as input to the volcanic ash transport and dispersal model, puff, which was used to propagate the paroxysmal ash cloud toward and over Europe over the following days. Some of the source parameters, specifically vent radius, vent source velocity, mean grain size of ejecta, and standard deviation of ejecta grain size have been assigned probability distributions based on our lack of knowledge of exact conditions at the source. These probability distributions for the input variables have been sampled in a Monte Carlo fashion using a technique that yields what we herein call the polynomial chaos quadrature weighted estimate (PCQWE) of output parameters from the ash transport and dispersal model. The advantage of PCQWE over Monte Carlo is that since it intelligently samples the input parameter space, fewer model runs are needed to yield estimates of moments and probabilities for the output variables. At each of these sample points for the input variables, a model run is performed. Output moments and probabilities are then computed by properly summing the weighted values of the output parameters of interest. Use of a computational eruption column model coupled with known weather conditions as given by radiosonde data gathered near the vent allows us to estimate that initial mass eruption rate on 14 April 2010 may have been as high as 10⁸?kg/s and was almost certainly above 10⁷?kg/s. This estimate is consistent with the probabilistic envelope computed by PCQWE for the downwind plume. The results furthermore show that statistical moments and probabilities can be computed in a reasonable time by using 9⁴?=?6,561 PCQWE model runs as opposed to millions of model runs that might be required by standard Monte Carlo techniques. The output mean ash cloud height plus three standard deviations??encompassing c. 99.7?% of the probability mass??compares well with four-dimensional ash cloud position as retrieved from Meteosat-9 SEVIRI data for 16 April 2010 as the ash cloud drifted over north-central Europe. Finally, the ability to compute statistical moments and probabilities may allow for the better separation of science and decision-making, by making it possible for scientists to better focus on error reduction and decision makers to focus on ??drawing the line?? for risk assessment.  相似文献   

Exposing local adaptation: synergistic stressors elicit population-specific lactate dehydrogenase-B (<Emphasis Type="Italic">ldh</Emphasis>-<Emphasis Type="Italic">b</Emphasis>) expression profiles in Australian barramundi, <Emphasis Type="Italic">Lates calcarifer</Emphasis>     

Richard?C.?EdmundsEmail author  Carolyn?Smith-Keune  Lynne?van Herwerden  Christopher?J.?Fulton  Dean?R.?Jerry 《Aquatic Sciences - Research Across Boundaries》2012,74(1):171-178

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Positron annihilation radiation from Seyfert nuclei and the cosmic diffuse γ-ray background     

L. Bassani  A. J. Dean 《Astrophysics and Space Science》1983,93(1):135-140

Observational features in the low energy γ-ray spectra of Seyfert galaxies are interpreted in terms of broad and blueshifted annihilation radiation. The possibility that this ‘line’ emission is the underlying source of the bump in the cosmic diffuse γ-ray background is investigated. The observational data available in the literature are then used to estimate the maximum temperature of the electron positron plasma and the average positron annihilation rate for Seyfert galaxies. The assumption that other active nuclei, namely radio galaxies and quasars, are powered by the same annihilation mechanism is used to set limits on their contribution to the cosmic diffuse γ-ray background.  相似文献   

Plasma radiation diagnostics of the primary energy release region in solar flares     

Dean F. Smith  Daniel S. Spicer 《Solar physics》1979,62(2):359-373

The possibility is investigated that the plasma turbulence used in many recent models of the primary energy release and acceleration in solar flares should be detectable by radiation near the fundamental and second harmonic of the plasma frequency. Formulae are derived for fundamental emission due to the combination of ion-acoustic and Langmuir plasma turbulence and for second harmonic emission due to the combination of two Langmuir waves. These results are applied to recent primary energy release and acceleration models which shows that either such radiation should be detectable and possibly distinguishable with suitable microwave interferometers or that its absence places fairly stringent constraints on the possible level of Langmuir or Langmuir and ion-acoustic waves in these models.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献