Apparent Flux Research Articles

A Realistic Transport Model with Pressure-Dependent Parameters for Gas Flow in Tight Porous Media with Application to Determining Shale Rock Properties

A nonlinear transport model for single-phase gas flow in tight porous media is developed. The model incorporates many important physical processes that occur in such porous systems: continuous flow, transition flow, slip flow, Knudsen diffusion, adsorption and desorption into and out of the rock material, and a correction for high flow rates. This produces a nonlinear advection–diffusion type of partial differential equation with pressure-dependent model parameters and associated compressibility coefficients, and highly nonlinear apparent convective flux (velocity) and apparent diffusivity. A key finding is that all model parameters should be kept pressure dependent for the best results. An application is to the determination of rock properties, such as porosity and permeability, by history matching of the simulation results to data from pressure-pulse decay tests in a rock core sample (Pong et al. in ASME Fluids Eng Div 197:51–56, 1994).

Confinement effect on water transport in CNT membranes

Fluid transport through membrane has attracted broad interests in recent decades due to their close association with wide industrial applications. Whereas massive experimental and simulation studies have been reported, the molecular mechanisms of fluid transport in nanopores are still poorly understood. Herein, we report a non-equilibrium molecular dynamics (NEMD) simulation study for elaborating the confinement effect of water transport through carbon nanotube (CNT) membranes. By varying the tube flexibility, inner surface wettability and pore size distribution (PSD), the permeability of water flow characterized with the flux enhancement rate is extensively examined. In addition, the pore size effect and pore size distribution are carefully taken into account when evaluating the apparent water flux through CNT membranes. We show that these treatments allow us to predict the water flux in a satisfactory agreement with reported experimental measurements. This work provides a quantitative simulation model toward the rational design of high efficient membranes.

Fast Radio Bursts’ Recipes for the Distributions of Dispersion Measures, Flux Densities, and Fluences

Abstract We investigate how the statistical properties of dispersion measure (DM) and apparent flux density/fluence of (nonrepeating) fast radio bursts (FRBs) are determined by unknown cosmic rate density history [ρ FRB(z)] and luminosity function (LF) of the transient events. We predict the distributions of DMs, flux densities, and fluences of FRBs taking account of the variation of the receiver efficiency within its beam, using analytical models of ρ FRB(z) and LF. Comparing the predictions with the observations, we show that the cumulative distribution of apparent fluences suggests that FRBs originate at cosmological distances and ρ FRB increases with redshift resembling the cosmic star formation history (CSFH). We also show that an LF model with a bright-end cutoff at log10 L ν (erg s−1 Hz−1) ∼ 34 are favored to reproduce the observed DM distribution if ρ FRB(z) ∝ CSFH, although the statistical significance of the constraints obtained with the current size of the observed sample is not high. Finally, we find that the correlation between DM and flux density of FRBs is potentially a powerful tool to distinguish whether FRBs are at cosmological distances or in the local universe more robustly with future observations.

Searching for propeller-phase ULXs in the XMM–Newton Serendipitous Source Catalogue

We search for transient sources in a sample of ULXs from the 3XMM-DR4 release of the XMM-Newton Serendipitous Source Catalogue in order to find candidate neutron star ULXs alternating between an accreting state and the propeller regime, in which the luminosity drops dramatically. By examining their fluxes and flux upper limits, we identify five ULXs that demonstrate long-term variability of over an order of magnitude. Using Chandra and Swift data to further characterise their light curves, we find that two of these sources are detected only once and could be X-ray binaries in outburst that only briefly reach ULX luminosities. Two others are consistent with being super-Eddington accreting sources with high levels of inter-observation variability. One source, M51 ULX-4, demonstrates apparent bimodal flux behaviour that could indicate the propeller regime. It has a hard X-ray spectrum, but no significant pulsations in its timing data, although with an upper limit of 10% of the signal pulsed at ~1.5 Hz a pulsating ULX cannot be excluded, particularly if the pulsations are transient. By simulating XMM-Newton observations of a population of pulsating ULXs, we predict that there could be approximately 200 other bimodal ULXs that have not been observed sufficiently well by XMM-Newton to be identified as transient.

Recognition of leak CO 2 with wavelet analysis based on correlation monitoring between CO 2 and O 2 in atmosphere

Abstract It is necessary to monitor and identify CO2 leakage from geosequestration project. Some experiments were designed to test the feasibility of characterization and recognition method for CO2 leakage based on correlation analysis between atmospheric CO2 and O2. The monitoring results showed that atmospheric CO2 had a good linear relationship with O2, especially in the day time. The variations of CO2 and O2 were influenced by the weather condition. The results of emission experiments proved the capability of coupling monitoring atmospheric CO2 and O2 to recognize the abnormal CO2 signal due to leakage. Moreover, two parameters, ALF (apparent leakage flux) and ALFs (apparent leakage flux based on surplus variable) were used to distinguish CO2 leakage in real time. The monitoring results verified that it was feasible to identify CO2 leakage with these two parameters. Compared with the results after median filter, the abrupt leakage signal can be more easily recognized with that after wavelet filter. ALFs can be applied to estimate the elevated concentration due to leakage, which can also be predicted by interpolating with related variation of atmospheric O2. ALF reflects the relative leakage rate. Therefore, it is practicable to identify leakage event in real time with the method proposed in this paper.

High-resolution characterization of labile phosphorus, iron, and manganese in sediments of different trophic waters in Lake Taihu, China.

High-resolution combined ZrO-Chelex diffusive gradients in thin film (DGT) probes were arranged to synchronously monitor the characteristics of labile phosphorus (P), iron (Fe), and manganese (Mn) in sediments from regions of varying trophic levels in Lake Taihu, China. Results showed that P release was closely related to the lake region's trophic level. Labile P in sediments and the apparent diffusion flux (Fd) of P were higher in hyper-eutrophic algae-dominated regions than those in macrophyte-algae-dominated and macrophyte-dominated regions, indicating that P released from sediments may be facilitated in eutrophic environments. A positive correlation observed between DGT-labile P and Fe or Mn, which had similar regional spatial distributions to P, showed that reductive dissolution of Fe-Mn (oxyhydr)oxides (FeOOH-MnOOH) in sediments was responsible for internal P release, which was strengthened in eutrophic environments. Ratios of labile Fe or Mn/labile P (LFe/LP and LMn/LP) in sediments in algae-dominated regions showed lower values than those in macrophyte-algae-dominated and macrophyte-dominated regions, further confirming that FeOOH-MnOOH in algae-dominated regions were less able to fix P, which brought higher pollution risks for the overlying water. LFe/LP or LMn/LP also had a significantly positive correlation with Fd, further testament that labile Fe or Mn was much more relevant to the sediment P cycle.

Determination of Desert Soil Apparent Thermal Diffusivity Using a Conduction‐Convection Algorithm

AbstractSurface soil temperatures impact land‐atmosphere interactions in desert environments. Soil apparent thermal diffusivity (k) is a crucial physical parameter affecting soil temperature. Previous studies using the conduction‐convection algorithm reported k values of desert soils for only a few days. The main objective of this study is to determine the daily and monthly variations of desert k for a range of water contents over a 10 month period. The k values were estimated with a conduction‐convection algorithm using soil temperature measured at the 0.00 m and 0.20 m depths from 1 January to 11 October 2011 at the Tazhong station in the Taklimakan desert of China. Generally, the daily values of k ranged from 1.46 × 10−7m2 s−1 to 5.88 × 10−7m2 s−1, and the 10 month average k value was 2.5(±0.8) × 10−7m2 s−1 for the 0.00 m to 0.20 m soil layer. The k values varied significantly with soil water content. The apparent convection parameter (W), which is the sum of the vertical gradient of k and apparent water flux density, was also determined. Comparison of the magnitudes of W and k gradients indicated that little water movement occurred during the dry months, some water infiltrated downward during the wet months, and some water moved upwards in response to evaporation following the wet months. These findings confirmed that the conduction‐convection algorithm described the general pattern of soil water movement. The presented daily and monthly values of k can be used as soil parameters when modeling land‐atmosphere interactions in the Taklimakan desert.

Assessing potential release tendency of As, Mo and W in the tributary sediments of the Three Gorges Reservoir, China

As the largest man-made reservoir in China, the Three Gorges Reservoir (TGR) has significant influence on national drinking water safety. The geochemical behavior of trace elements at the sediment-water interface (SWI) is still unknown. The mobilization characteristics of trace elements (As, Mo and W)-determined by diffusive gradients in thin films (DGT)-were studied to quantitatively calculate the release trends in the SWI in three typical tributaries and the mainstream of the TGR in the summer. The results showed that concentrations of DGT-labile As, Mo and W in the overlying water and sediment cores showed significant variations in the ranges of 0.05–50.90, 0.30–1.63 and 0.01–0.42μgL−1, respectively. The apparent net diffusive fluxes were significantly positive in most sampling sites (77.8% for As, 88.8% for Mo and 66.6% for W), suggesting that the sediment was the source of these three elements. It was noteworthy that the maximum net diffusive fluxes of As and W were found in the upstream of Meixi tributary, which may be attributed to anthropogenic activities. In addition, As, Mo and W may be incorporated in Fe and Mn oxyhydroxides and these three elements simultaneously remobilized with Fe and Mn.

Plume propagation direction determination with SO<sub>2</sub> cameras

Abstract. SO2 cameras are becoming an established tool for measuring sulfur dioxide (SO2) fluxes in volcanic plumes with good precision and high temporal resolution. The primary result of SO2 camera measurements are time series of two-dimensional SO2 column density distributions (i.e. SO2 column density images). However, it is frequently overlooked that, in order to determine the correct SO2 fluxes, not only the SO2 column density, but also the distance between the camera and the volcanic plume, has to be precisely known. This is because cameras only measure angular extents of objects while flux measurements require knowledge of the spatial plume extent. The distance to the plume may vary within the image array (i.e. the field of view of the SO2 camera) since the plume propagation direction (i.e. the wind direction) might not be parallel to the image plane of the SO2 camera. If the wind direction and thus the camera–plume distance are not well known, this error propagates into the determined SO2 fluxes and can cause errors exceeding 50 %. This is a source of error which is independent of the frequently quoted (approximate) compensation of apparently higher SO2 column densities and apparently lower plume propagation velocities at non-perpendicular plume observation angles.Here, we propose a new method to estimate the propagation direction of the volcanic plume directly from SO2 camera image time series by analysing apparent flux gradients along the image plane. From the plume propagation direction and the known location of the SO2 source (i.e. volcanic vent) and camera position, the camera–plume distance can be determined. Besides being able to determine the plume propagation direction and thus the wind direction in the plume region directly from SO2 camera images, we additionally found that it is possible to detect changes of the propagation direction at a time resolution of the order of minutes. In addition to theoretical studies we applied our method to SO2 flux measurements at Mt Etna and demonstrate that we obtain considerably more precise (up to a factor of 2 error reduction) SO2 fluxes. We conclude that studies on SO2 flux variability become more reliable by excluding the possible influences of propagation direction variations.

Optimization of Copper Removal from Aqueous Solutions Using Emulsion Liquid Membranes with Benzoylacetone as a Carrier

The presence of heavy metals in aqueous solutions above certain limits represents a serious threat to the environment due to their toxicity and non-degradability. Thus, the removal of these metals from contaminated waters has received increasing attention during recent decades. This paper describes the removal of Cu(II) from aqueous solutions by emulsion liquid membranes, through a carrier-facilitated counter-transport mechanism, using benzoylacetone as the carrier and HCl as the stripping agent (protons as counter-ions). To optimize the Cu(II) removal process, the effect of the following operating parameters on the on the stability of the emulsion liquid membrane and on the Cu(II) removal efficiency was studied: feed pH, HCl concentration in the permeate phase, carrier and emulsifier concentration in the membrane phase, feed phase/emulsion phase and permeate phase/membrane phase volume ratios, emulsification time and speed in the primary emulsion preparation and stirring speed in the whole feed phase/emulsion phase system. Typical membrane transport parameters, such as flux and permeability, were also determined. Optimal Cu(II) removal conditions were: 5.5 feed pH, 10 kg/m3 benzoylacetone concentration in the membrane phase, 18.250 kg/m3 HCl concentration in the permeate phase, 50 kg/m3 Span 80 concentration in the membrane phase, 200 rpm stirring rate, 5 min emulsification time, 2700 rpm emulsification rate, 2:1 feed:emulsion volume ratio and 1:1 permeate:membrane volume ratio. In these optimal conditions, 80.3% of Cu(II) was removed in 15 min with an apparent initial flux and permeability of 0.3384 kg·m−3·min−1 and 0.3208 min−1, respectively.

皆伐火烧对亚热带森林不同深度土壤CO2通量的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 皆伐火烧对亚热带森林不同深度土壤CO2通量的影响 DOI: 10.5846/stxb201606241245 作者: 作者单位: 福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地,福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地,福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地,福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地,福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地,福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金重点项目（31130013）；国家重点研发计划（2016YFD0600304） The impact of clear-cutting and slash burning on soil CO2 flux at different soil depths in a subtropical forest Author: Affiliation: College of Geograthy Science, Fujian Normal University;State Key Laboratory of Subtropical Mountain Ecology(Funded by Ministry of Science and Technology and Fujian Province),College of Geograthy Science, Fujian Normal University;State Key Laboratory of Subtropical Mountain Ecology(Funded by Ministry of Science and Technology and Fujian Province),College of Geograthy Science, Fujian Normal University;State Key Laboratory of Subtropical Mountain Ecology(Funded by Ministry of Science and Technology and Fujian Province),College of Geograthy Science, Fujian Normal University;State Key Laboratory of Subtropical Mountain Ecology(Funded by Ministry of Science and Technology and Fujian Province),College of Geograthy Science, Fujian Normal University;State Key Laboratory of Subtropical Mountain Ecology(Funded by Ministry of Science and Technology and Fujian Province),College of Geograthy Science, Fujian Normal University;State Key Laboratory of Subtropical Mountain Ecology(Funded by Ministry of Science and Technology and Fujian Province) Fund Project: Key Projects of National Natural Science Foundation of China (31130013) and National Key Research and Development Program of China （2016YFD0600304） 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:评估不同深度土壤的CO2通量是研究土壤碳动态的重要手段。目前有关皆伐火烧对森林土壤碳排放的影响研究仅局限于表层土壤，而对不同深度土壤碳排放影响鲜见报道。以米槠（Castanopsis carlesii）次生林（对照）及其皆伐火烧后林地为研究对象，利用非红外散射CO2探头测定土壤CO2浓度，并结合Fick第一扩散法则估算不同深度（0-80 cm）土壤CO2通量。结果表明：（1）皆伐火烧改变土壤向大气排放的表观CO2通量，在皆伐火烧后的2个月内土壤表观CO2通量显著高于对照68%；2个月后，土壤表观CO2通量低于对照37%。（2）皆伐火烧后，除10-20 cm的CO2通量提高外，其余各深度（0-10、20-40、40-60 cm和60-80 cm）的CO2通量均降低。同时，皆伐火烧改变不同土层对土壤呼吸的贡献率，降低0-10 cm土层的贡献率，提高10-20 cm土层的贡献率。（3）对照样地仅0-10 cm土壤CO2通量与温度呈显著指数相关，10-40 cm深度CO2通量则与土壤含水率呈显著线性相关。皆伐火烧后0-10 cm和10-20 cm处土壤的CO2通量均与温度呈指数相关。说明皆伐火烧改变了不同深度土壤CO2通量对于环境因子的响应。因此为准确评估和预测皆伐火烧对土壤与大气间碳交换的影响，应考虑皆伐火烧后不同时期土壤CO2通量的变化，以及不同深度土壤CO2通量对皆伐火烧的响应。 Abstract:Soil CO2 flux at different depths is an important means of researching the soil carbon dynamics. At present, the impacts of clear-cutting and slash burning on forest soil carbon emissions focus on surface soil, while their impacts on soil carbon emissions at different depths are not well known. In this study, CO2 flux along a soil profile (0-80 cm) was measured in an uncut secondary Castanopsis carlesii forest (CT) and a clear-cut, slash burnt (SB) stand of Castanopsis carlesii located in Sanming, Fujian. A scattered infrared CO2 detector was used to measure soil CO2 concentration, combined with Fick's laws of diffusion to estimate soil CO2 flux at different depths. Results showed that, (1) SB changed the apparent CO2 flux significantly. Within two months after SB, the soil surface CO2 flux increased by 68%. However, the soil surface CO2 flux decreased by 37% two months later. (2) After SB, soil CO2 fluxes at depths of 0-10, 20-40, 40-60 cm and 60-80 cm decreased with the exception of an increase at a depth of 10-20 cm. In the meantime, SB decreased the contribution rate of CO2 flux in the 0-10 cm soil layer, and increased the contribution rate of CO2 flux in the 10-20 cm soil layer. (3) There was an exponential relationship between soil CO2 flux at 0-10 cm and temperature, and the soil CO2 fluxes at other soil depths were linearly correlated with soil moisture in the control plot. After SB, soil CO2 fluxes at depths of 0-10 cm and 10-20 cm were exponentially correlated with soil temperature, which illustrated that SB changed the soil CO2 flux response at different depths due to environmental factors. Thus, in order to estimate and predict the impact of clear-cutting and SB on carbon exchange between soil and the atmosphere accurately, it is necessary to consider the changes in soil CO2 flux during different periods after SB and the response of soil CO2 flux to SB at different depths. 参考文献 相似文献 引证文献

Soil Apparent Thermal Diffusivity Estimated by Conduction and by Conduction–Convection Heat Transfer Models

Abstract Soil heat transfer is complex, and conduction-alone models may not always perform well in estimating soil apparent thermal diffusivity. Soil apparent thermal diffusivity is related to soil temperature change propagation rates. Soil temperature data collected at the Tazhong station in China were used to examine the characteristics of soil apparent thermal diffusivity determined by three different algorithms and the sum of vertical gradient of soil apparent thermal diffusivity and apparent water flux density . The results showed that 1) soil apparent thermal diffusivity obtained with a conduction–convection algorithm had a better agreement with soil apparent thermal diffusivity obtained with a phase algorithm than with soil apparent thermal diffusivity obtained with an amplitude algorithm except for the case of = 0; 2) when > 0, , and when < 0, ; 3) for a given soil temperature phase shift, increased (decreased) with increasing logarithmic amplitude attenuation when the phase shift was larger (smaller) than the logarithmic amplitude attenuation, reached a maximum value when the phase shift equaled the logarithmic amplitude attenuation, and increased with increasing logarithmic amplitude attenuation; and 4) for a given logarithmic amplitude attenuation, decreased with increasing phase shift and increased (decreased) with increasing phase shift when the phase shift was larger (smaller) than times the logarithmic amplitude attenuation. These mathematical conclusions were also confirmed with field data.

Abiotic contribution to total soil CO2 flux across a broad range of land-cover types in a desert region

As an important component of ecosystem carbon (C) budgets, soil carbon dioxide (CO2) flux is determined by a combination of a series of biotic and abiotic processes. Although there is evidence showing that the abiotic component can be important in total soil CO2 flux (Rtotal), its relative importance has never been systematically assessed. In this study, after comparative measurements of CO2 fluxes on sterilized and natural soils, the Rtotal was partitioned into biotic flux (Rbiotic) and abiotic flux (Rabiotic) across a broad range of land-cover types (including eight sampling sites: cotton field, hops field, halophyte garden, alkaline land, reservoir edge, native saline desert, dune crest and interdune lowland) in Gurbantunggut Desert, Xinjiang, China. The relative contribution of Rabiotic to Rtotal, as well as the temperature dependency and predominant factors for Rtotal, Rbiotic and Rabiotic, were analyzed. Results showed that Rabiotic always contributed to Rtotal for all of the eight sampling sites, but the degree or magnitude of contribution varied greatly. Specifically, the ratio of Rabiotic to Rtotal was very low in cotton field and hops field and very high in alkaline land and dune crest. Statistically, the ratio of Rabiotic to Rtotal logarithmically increased with decreasing Rbiotic, suggesting that Rabiotic strongly affected Rtotal when Rbiotic was low. This pattern confirms that soil CO2 flux is predominated by biotic processes in most soils, but abiotic processes can also be dominant when biotic processes are weak. On a diurnal basis, Rabiotic cannot result in net gain or net loss of CO2, but its effect on transient CO2 flux was significant. Temperature dependency of Rtotal varied among the eight sampling sites and was determined by the predominant processes (abiotic or biotic) of CO2 flux. Specifically, Rbiotic was driven by soil temperature while Rabiotic was regulated by the change in soil temperature (ΔT). Namely, declining temperature (ΔT 0) resulted in positive Rabiotic (i.e., CO2 released from soil). Without recognition of Rabiotic, Rbiotic would be overestimated for the daytime and underestimated for the nighttime. Although Rabiotic may not change the sum or the net value of daily soil CO2 exchange and may not directly constitute a C sink, it can significantly alter the transient apparent soil CO2 flux, either in magnitude or in temperature dependency. Thus, recognizing the fact that abiotic component in Rtotal exists widely in soils has widespread consequences for the understanding of C cycling.

Performance Evaluation of an Integrated Open-Path Eddy Covariance System in a Cold Desert Environment

AbstractPerformance evaluation of an integrated eddy covariance (EC) instrument called the IRGASON, with a separated EC for reference, was conducted in a desert riparian Populus euphratica stand in the lower Tarim River basin in northwestern China. The separated EC consisted of an open-path gas analyzer and a sonic anemometer separated by 20 cm. The IRGASON integrates an open-path gas analyzer and a sonic anemometer into the same sensing volume, thus eliminating sensor separation in comparison to the traditional open-path EC setup. Integrating the infrared gas analyzer’s sensing head into the sensing volume of the sonic anemometer had negligible effects on wind speed and friction velocity observations of the IRGASON. Physiologically unreasonable daytime CO2 uptake was observed by both systems during the cold winter season (mean air temperature of −6.7°C), when the trees were dormant without any photosynthetic activities. The mean midday CO2 flux was −1.65 and −1.61 μmol m−2 s−1 for the IRGASON and the separated EC setup, respectively. No evidence was found for sensor self-heating as the cause of the apparent uptake CO2 flux. Instead, the uptake CO2 flux appeared to be an artifact of the spectroscopic effect of the IRGASON’s gas analyzer. After adjusting for this spectroscopic effect using a relationship with the sensible heat flux, the wintertime IRGASON CO2 flux became physiologically reasonable (mean value of −0.04 μmol m−2 s−1).

Assessment of mobilization of labile phosphorus and iron across sediment-water interface in a shallow lake (Hongze) based on in situ high-resolution measurement

The internal loading of P is reported to be the main factor initiating algal blooms. However, there are only a few reports on the dynamic variation of labile P in the sediment and overlying water during the decomposition of algal. In addition, the widely perceived relationship between labile P and Fe was not supported by in situ obtained values in freshwater. Consequently, the in situ simultaneous measurement of diffusion gradients in thin-film techniques (DGT) was applied on a large scale to detect the mechanisms of labile P and Fe in a typical shallow lake (Lake Hongze). The newly developed ZrO-DGT and ZrO-Chelex DGT were combined to obtain the concentration of labile P and Fe. Results showed that decomposition of algal might be the main contributor for the concentration dots and peaks of labile P in sediment profiles, as well as for the high values on the horizontal heterogeneity index of labile P at the depth of 0–30 mm of the sediment. Moreover, there existed significant difference between the apparent diffusion fluxes of labile P and Fe across the sediment–water interface which obtained from June sampling and October sampling. The results of apparent diffusion flux in two periods indicated the sediments changed from “sink” to “source” for labile P, especially at Sites 4–8, 10, 13–14, and 18. However, the role of the labile Fe has no significantly variation in the values of the diffusion flux. This phenomenon also contributed to the poor relationship between labile P and Fe in the sediment which obtained from the October sampling. Accordingly, we conclude that algal decomposition might be essential for internal loading of P in this aquatic ecosystem, and that also be the reason for vicious circle of algal occurrence in the following year in the center of Lake Hongze.

Characteristics of cadmium remobilization in tributary sediments in Three Gorges Reservoir using chemical sequential extraction and DGT technology

The Three Gorges Reservoir (TGR) is the largest reservoir in China. Cadmium (Cd) is a primary pollutant in the TGR, and its speciation and bioavailability have attracted extensive attention since TGR submergence. In this study, Chelex-100 DGT (diffusive gradient in thin films) and the sequential extraction method were used to investigate the bioavailable Cd in sediments obtained from a typical tributary (Meixi) and mainstream (Yangtze) in the TGR. The total Cd concentrations in sediments of the four stations were also determined. In comparison to the concentrations of labile Cd measured by DGT (CDGT-Cd) in four profiles, CJ and MX-upstream/downstream were at potential risk for Cd release from surface sediments using the apparent diffusion flux across the interface numerical model. The order of CDGT-Cd in surface sediments was as follows: CJ > MX-downstream > MX-upstream > MX-midstream. Additionally, a positive correlation was demonstrated between CDGT-Cd and Cd in the exchangeable fraction (F1) in the surface sediments, indicating that Cd in the exchangeable fraction was readily captured by DGT. A negative correlation was observed between CDGT-Cd and CDGT-Fe, CDGT-Mn in the sediment-water-interface (SWI), suggesting that Fe/Mn oxides did not control the release of labile-Cd from sediments. Furthermore, a positive correlation existed between the CDGT-Cd in the surface sediments and Cd in the oxidizable fraction (F3), illustrating that Cd sorbed or bound with organic matter or sulfide was labile and released into the water phase from the surface sediments. A dark area was found in the AgI gel, which further demonstrated that Cd simultaneously was released with sulfide in this area.

Thermoresponsive cationic copolymer microgels as high performance draw agents in forward osmosis desalination

Thermoresponsive cationic copolymer microgels with aliphatic and aromatic cationic comonomers are synthesized and applied as the draw agents in forward osmosis (FO) desalination for the first time. The results show the FO desalination performance depends on the chemical structures and the dissociation constants (pKa) of the cationic comonomers. Cationic copolymer microgel containing 2-(diethylamino) ethyl methacrylate has the best overall performance with an initial water flux of 45.6 LMH and water recovery of 44.8%. This microgel also shows the shortest equilibrium swelling time which in turn reveals significant improvement in apparent flux of 5.5 LMH compared to other cationic and anionic copolymer microgels. Furthermore, Hansen solubility parameters are used to correlate the solvation behavior of these cationic microgels and their performance in forward osmosis desalination. Our results show Hansen solubility parameters and the dissociation constants of cationic comonomers can be used to estimate the performance of microgels in microgel-driven FO desalination systems.

High-resolution imaging of labile phosphorus and its relationship with iron redox state in lake sediments

A thorough understanding of the labile status and dynamics of phosphorus (P) and iron (Fe) across the sediment-water interface (SWI) is essential for managing internal P release in eutrophic lakes. Fe-coupled inactivation of P in sediments is an important factor which affects internal P release in freshwater lakes. In this study, two in-situ high-resolution diffusive gradients in thin films (DGT) techniques, Zr-Oxide DGT and ZrO-Chelex DGT, were used to investigate the release characteristics of P from sediments in a large freshwater lake (Dongting Lake, China; area of 2691 km2) experiencing a regional summer algal bloom. Two-dimensional distributions of labile P in sediments were imaged with the Zr-Oxide DGT without destruction of the original structure of the sediment layer at four sites of the lake. The concentration of DGT-labile P in the sediments, ranging from 0.007 to 0.206 mg L−1, was highly heterogeneous across the profiles. The values of apparent diffusion flux (Fd) and release flux (Fr) of P varied between −0.027–0.197 mg m−2 d−1 and 0.037–0.332 mg m−2 d−1, respectively. Labile P showed a high and positive correlation (p < 0.01) with labile Fe(II) in the profiles, providing high-resolution evidence for the key role of Fe-redox cycling in labile P variation in sediments.

Ellc: A fast, flexible light curve model for detached eclipsing binary stars and transiting exoplanets

Very high quality light curves are now available for thousands of detached eclipsing binary stars and transiting exoplanet systems as a result of surveys for transiting exoplanets and other large-scale photometric surveys. I have developed a binary star model (ELLC) that can be used to analyse the light curves of detached eclipsing binary stars and transiting exoplanet systems that is fast and accurate, and that can include the effects of star spots, Doppler boosting and light-travel time within binaries with eccentric orbits. The model represents the stars as triaxial ellipsoids. The apparent flux from the binary is calculated using Gauss-Legendre integration over the ellipses that are the projection of these ellipsoids on the sky. The model can also be used to calculate the flux-weighted radial velocity of the stars during an eclipse (Rossiter-McLaughlin effect). The main features of the model have been tested by comparison to observed data and other light curve models. The model is found to be accurate enough to analyse the very high quality photometry that is now available from space-spaced instruments, flexible enough to model a wide range of eclipsing binary stars and extrasolar planetary systems, and fast enough to enable the use of modern Monte Carlo methods for data analysis and model testing.

Method for improving line flux and redshift measurements with narrowband filters

High redshift star-forming galaxies are discovered routinely through a flux excess in narrowband filters (NB) caused by an emission line. In most cases, the width of such filters is broad compared to typical line widths, and the throughput of the filters varies substantially within the bandpass. This leads to substantial uncertainties in redshifts and fluxes that are derived from the observations with one specific NB. In this work we demonstrate that the uncertainty in measured line parameters can be sharply reduced by using repeated observations of the same target field with filters that have slightly different transmittance curves. Such data are routinely collected with some large field imaging cameras that use multiple detectors and a separate filter for each of the detectors. An example is the NB118 data from ESO's VISTA InfraRed CAMera (VIRCAM). We carefully developed and characterized this method to determine more accurate redshift and line flux estimates from the ratio of apparent fluxes measured from observations in different narrowband filters and several matching broadband filters. Then, we tested the obtainable quality of parameter estimation both on simulated and actual observations for the example of Ha in the VIRCAM NB118 filters combined with broadband data in Y, J, H. We find that by using this method, the errors in the measured lines fluxes can be reduced up to almost an order of magnitude and that an accuracy in wavelength of better than 1nm can be achieved with the ~13nm wide NB118 filters.