Constant Initial Concentration Research Articles

Explosion Load Characteristics of Fuel—Air Mixture in a Vented Chamber: Analysis and New Insights

The advances in research on the explosion load characteristics of the fuel–air mixture in vented chambers are reviewed herein. The vented explosion loads are classified into three typical types based on this comprehensive literature research. These models are the accumulation load model, attenuation load model, and interval jump load model. The characteristics of the three different typical vented explosion load models are analyzed using Fluidy-Ventex. The research results show that overpressure is largely determined by methane concentrations and vented pressure. The turbulent strength increased from the original 0.0001 J/kg to 1.73 J/kg, which was an increase of 17,300 times, after venting in the case of a 10.5 v/v methane concentration and 0.3 kPa vented pressure. When the vented pressure increased to 7.3 kPa, the turbulent strength increased to 62.2 J/kg, and the overpressure peak correspondingly increased from 69 kPa to 125 kPa. In the case of the interval jump load model, the explosion overpressure peak tends to ascend when the intensity of the fluid disturbance rises due to the venting pressure increasing at a constant initial gas concentration. When the venting pressure reaches tens of kPa, the pressure differential increases sharply on both sides of the relief port, and a large amount of combustible gas is released. Therefore, there is an insufficient amount of indoor combustible gas, severe combustion is difficult to maintain, and the explosion load mode becomes the attenuation load model.

Adsorption of Copper Ions from Aqueous Systems Using Moss Peat: Reaction Kinetics and Adsorption Isotherm

The removal of copper ions from aqueous systems using moss peat was investigated. Kinetic experiments were conducted at a constant temperature, pH, and initial copper concentration. The data obtained from the kinetic experiments were analysed and fitted well using the pseudo-second-order model. The data of the isotherm experiment were modelled and fitted well with the Langmuir models. This finding suggests that copper ions are chemically adsorbed on the moss peat and assume monolayer adsorption. The optimum pH for copper ion adsorption by moss peat was investigated over a range of (2-4.5), and it was found that the maximum adsorption capacity of moss peat was achieved at pH 4.5. The results of this study suggest the potential use of moss peat as an effective material for the adsorption of copper ions from aqueous solutions under a range of environmental conditions.

210Pb-based dating of recent sediments with χ-mapping versions of the CFCS, CIC, CF and TERESA models

The 210Pb-based method allows for absolute age determination in recent sediments on the centennial scale. The most common sedimentary scenarios involve ideal deposition without any further redistribution. The conventional models apply to such conditions by adding specific assumptions that allow analytical formulations: constant flux (CF), constant initial concentration (CIC), and constant flux with constant sedimentation (CFCS). The χ-mapping models are presented as a novel methodological approach. They generate a large number (105 to 106) of potential solvers, consisting of sets of n (the number of slices in the core) values of initial activity concentrations, A0, and sedimentation rates, w. Empirical data serve to attract the solver that minimizes a χ function after encountering the best sorting along the core of the A0 and w values. The specific assumptions of the above models are reformulated in terms of the statistical distributions of A0 and w. The performance of the χ-mapping versions is demonstrated with a set of cores from the literature with independent chronologies. The main advantages compared to known analytical formulations are: i) χ-mapping provides a more robust fitting method. ii) It overcomes the problem of age reversals often found in the CIC model. iii) The CF model successfully applies to cores with unsteady and/or incomplete inventories. iv) The TERESA model (time estimates from random entries of sediments and activities), without analytical counterpart, is the only model that can manage continuous trends of change in the fluxes of unsupported 210Pb. The work discusses the conditions for compensating model errors in the chronologies, and the use of the palaeorecords of fluxes, A0 and w. The methodology can be extended to other assumptions (models) and provides novel and insightful views on the 210Pb-based dating of recent sediments.

Mathematical Modelling of Diffusion Flows in Two-Phase Stratified Bodies with Randomly Disposed Layers of Stochastically Set Thickness

The work is dedicated to mathematical modelling of random diffusion flows of admixture particles in a two-phase stratified strip with stochastic disposition of phases and random thickness of inclusion-layers. The study of such models are especially important during the creation of composite layered materials, in the research of the transmission properties of filters, and in the prediction of the spread of pollutants in the environment. Within the model we consider one case of uniform distribution of coordinates of upper boundaries of the layers of which the body is made up and two more cases, i.e., of uniform and triangular distributions of the inclusion thickness. The initial-boundary value problems of diffusion are formulated for flux functions; the boundary conditions at one of the body’s surfaces are set for flux and, at the other boundary, the conditions are given for admixture concentration; the initial condition being concerned with zero and non-zero constant initial concentrations. An equivalent integro-differential equation is constructed. Its solution is found in terms of Neumann series. For the first time it was obtained calculation formulae for diffusion flux averaged over the ensemble of phase configurations and over the inclusion thickness. It allowed to investigate the dependence of averaged diffusion fluxes on the medium’s characteristics on the basis of the developed software. The simulation of averaged fluxes of admixture in multilayered Fe−Cu and αFe−Ni materials is made. Comparative analysis of solutions, depending on the stage of averaging procedure over thickness, is carried out. It is shown that for some values of parameters the stage of averaging procedure over thickness has almost no effect on the diffusion flow value.

Investigation and Modeling of Fluoride Ion Adsorption on an Azospirillum Biofertilizer

AbstractThe process of fluoride removal from water using an Azospirillum biofertilizer as adsorbent was modeled. Experiments were performed in a column with varying flow rates and bed depths, at constant initial fluoride concentration. The experimental data obtained from the column studies were correlated employing different models: Thomas, Yoon‐Nelson, Adams‐Bohart, Clark, and BDST (bed depth service time). The Thomas and Yoon‐Nelson models were found most suitable for describing the dynamic adsorption process with respect to key operating variables. Breakthrough curves were obtained from the modeled equations. The calculated and modeled breakthrough curves were in agreement with each other.

Sensitivity analysis of an aerosol-aware microphysics scheme in Weather Research and Forecasting (WRF) during case studies of fog in Namibia

Abstract. Aerosol-aware microphysics parameterisation schemes are increasingly being introduced into numerical weather prediction models, allowing for regional and case-specific parameterisation of cloud condensation nuclei (CCN) and cloud droplet interactions. In this paper, the Thompson aerosol-aware microphysics scheme, within the Weather Research and Forecasting (WRF) model, is used for two fog cases during September 2017 over Namibia. Measurements of CCN and fog microphysics were undertaken during the AErosols, RadiatiOn and CLOuds in southern Africa (AEROCLO-sA) field campaign at Henties Bay on the coast of Namibia during September 2017. A key concept of the microphysics scheme is the conversion of water-friendly aerosols to cloud droplets (hereafter referred to as CCN activation), which could be estimated from the observations. A fog monitor 100 (FM-100) provided cloud droplet size distribution, number concentration (Nt), liquid water content (LWC), and mean volumetric diameter (MVD). These measurements are used to evaluate and parameterise WRF model simulations of Nt, LWC, and MVD. A sensitivity analysis was conducted through variations to the initial CCN concentration, CCN radius, and the minimum updraft speed, which are important factors that influence droplet activation in the microphysics scheme of the model. The first model scenario made use of the default settings with a constant initial CCN number concentration of 300 cm−3 and underestimated the cloud droplet number concentration, while the LWC was in good agreement with the observations. This resulted in droplet size being larger than the observations. Another scenario used modelled data as CCN initial conditions, which were an order of magnitude higher than other scenarios. However, these provided the most realistic values of Nt, LWC, MVD, and droplet size distribution. From this, it was concluded that CCN activation of around 10 % in the simulations is too low, while the observed appears to be higher reaching between 20 % and 80 %, with a mean (median) of 0.55 (0.56) during fog events. To achieve this level of activation in the model, the minimum updraft speed for CCN activation was increased from 0.01 to 0.1 m s−1. This scenario provided Nt, LWC, MVD, and droplet size distribution in the range of the observations, with the added benefit of a realistic initial CCN concentration. These results demonstrate the benefits of a dynamic aerosol-aware scheme when parameterised with observations.

Finite difference solver for simulating leaching process in bounded porous media: Development and application

This work, for the first time, developed an unconditionally stable, implicit numerical solution of a one-sided spatial fractional advection-dispersion equation (s-FADE) on a bounded domain to model contaminant transport through porous media during a leaching process. We used the zero-value Robin and Neumann conditions with a fractional-order derivative as the inlet and outlet boundaries, respectively, and a constant initial concentration of the contaminant in the whole domain as an initial condition. By conducting numerical analyses, we found that there is a good agreement between the results of the numerical solution and of its analytical counterpart, validating the accuracy of the numerical solution. In the case of the α variations meaningfully altered the heterogeneity degree of the porous medium, these variations significantly affected the results of the numerical solution, especially at intermediate times. Contrary to the α parameter, the numerical solution was insensitive to the spatial node number. The noisy observational data led to the maximum uncertainty in the estimated fractional dispersion coefficient. The application of the developed numerical solution to simulate sodium chloride (NaCl) leaching curves (LCs) at a laboratory scale revealed that the numerical solution described the leaching process in the homogeneous and heterogeneous sands better than COMSOL Multiphysics®, a commercial finite element software package. According to the fitting results of the developed numerical solution to the experimental data, the mean α values were 1.876 and 1.379 for the homogeneous and heterogeneous sands, respectively. The α values correctly represented the heterogeneity degrees of the used sands and the deviation rate of the transport process from the Fickian transport. Overall, the proposed numerical solution is a reliable numerical model to simulate the leaching process in homogeneous and heterogeneous porous media with bounded domains.

Modelling of anaerobic digester for the conversion of organic waste into hydrogen & methane

Multistage Anaerobic digestion (AD) nowadays plays a beneficial role compared to single-stage AD to achieve a high rate of waste conversion with higher energy recovery. Hence, obtaining a stable operation with optimal operating conditions is of paramount importance in the modeling study. In the current study, modeling of two stages continuous stirred anaerobic digesters was considered using mass balances over the substrates (organic waste) and biomass in the respective reactor. All the simulation work was performed using MATLAB, from which steady-state concentration values were taken for the calculation of Hydrogen flow rate (QH2) and Methane flow rate (QCH4). The operating volumes of both the reactors were computed by looking at the effect on the production rates (QH2 &QCH4) as a function of dilution rate of first (D1) and second (D2) reactors for constant initial substrate concentration (S0). At last, the effect of Initial substrate concentration on both QH2 &QCH4 was studied by considering different S0 values as 4 g/L, 8 g/L, and 12 g/L. From our modeling result, it was found out that for Maximum Hydrogen production, operating D1 (in day-1) was 0.8, 0.9 & 1 and the Methane production rate was Maximum at operating D2 (inday-1) of 0.25, for S0 values of 4 g/L, 8 g/L, and 12 g/L respectively.

Geochronology of Recent Sediments from the Upper Bonny Estuary (Niger Delta) Using Naturally Occurring Radionuclides

The research evaluated temporal trends of naturally occurring radionuclides and their vertical distributions in sediment cores collected from three sites of diverse sedimentation regimes in Bonny Estuary, and developed and implemented sediment dating with unsupported lead-210. Radium (Ra) isotopes exhibited a very similar distribution throughout all sampled cores in each month, with 228Ra, while 226Ra displayed some variability with generally lower specific activities in dry months than in wet months. The values found in the study were all less than unity ranging from 0.3 to 0.8, which suggested sediment accretion and that the study area corresponded to zones with different sedimentation regimes. Temporal distribution of total 210Pb in the sampled cores determined via its daughter 210Po by alpha spectrometry assumed that the secular equilibrium between both radionuclides was achieved. However, the activities in Station 3 were found to be lower than those in Station 1, with Station 2 having the lowest activity registered in the samples collected in December month. The specific activities of 228Ac (228Ra), 212Pb (228Th) and 40K against depth in the sampled cores were observed to be almost equal to one another at each stratigraphic interval. The average sedimentation rate throughout the core obtained from Constant Rate of Supply model (0.068 ± 0.015g.cm-2.y-1) was nearly the same as that obtained from the Constant Initial Concentration model (0.065 ± 0.004). However, the estimated ages were quite variable with depths of various stratigraphic layers. The age of the sediment core was dated approximately 80 years, which was qualitatively validated using 137CS whose activity was definitely undetected in the basal part of the core. The sedimentation rates calculated suggested low sedimentation characterized by low energy environment dominated by weak tidal currents.

Degradation of emerging contaminant coumarin based on anodic oxidation, electro-Fenton and subcritical water oxidation processes

The degradation of emerging contaminant coumarin was separately investigated in anodic, electro-Fenton and subcritical water oxidation processes. With respect to the anodic and electro-Fenton oxidation, the influence of constant current, treatment time and initial concentration of coumarin was studied. Regarding subcritical water oxidation, the effect of the oxidant concentration, temperature, treatment time and initial coumarin concentration was investigated. In anodic and electro-Fenton oxidation processes, coumarin degradation proceeded in a similar manner, achieving 99% degradation, after 180 min at a constant current of 200 mA. In both set-ups, further increasing the applied current lowered the degradation efficiency due to the formation of by-products and the increasing occurrence of side-reactions. The highest degradation of 88% was achieved in subcritical conditions, specifically at 200 °C, using 150 mM H2O2 and after 37.5 min of treatment. Under subcritical conditions, temperature was the most prominent parameter, followed by the H2O2 concentration. Under all methodologies, increasing treatment time had a small positive effect on coumarin degradation, indicating that time is not the most influential parameter. A comparison of the three methodologies in terms of performance as well as energy consumption and simplicity of operation highlighted the advantages of subcritical water oxidation.

Comparative study of Cadmium adsorption on three contrasting soils from a highly industrialized region

Evaluation of natural soils potentiality to effectively immobilize heavy metals is a fundamental tool for a sustainable management of an industrialized region. Three soil textures from Bahía Blanca Citýs industrial zone (Argentina) were analyzed to quantify Cd adsorption and assess its applicability for industrial land use. Soils textural classes corresponded to sandy loam (M1), sand (M2) and silt loam (M3). Batch adsorption kinetics and isotherms were carried out with a 1:10 soil:solution ratio. Adsorption kinetics was conducted for 240 min at constant initial Cd concentration (250 mg l−1) and varying pH (4–8 range). Adsorption isotherm was done for twenty Cd concentrations (range 0.5 mg l−1 to 460 mg l−1) and contact time of 24 h. Kinetics showed a fast instantaneous initially adsorption. Soil-water partitioning coefficient (Kd) was calculated for each concentration supplied to soils, showing a direct relationship between pH and Kd. Adsorption isotherms plots showed a nonlinear shape for M1 and M2 and a linear shape for M3. The affinity of Cd for soils is in the order: M3 > M1 > M2. Metal retention in M3 was upper than 97.8%. Langmuir, Freundlich and Dubinin-Radushkevich (DRK) adsorption models correctly reproduced experimental data. However, M1 (R2 = 0.992) and M3 (R2 = 0.985) fitted better to Freundlich model. Otherwise, M2 (R2 = 0.981) fitted better to Langmuir adsorption model. M3 presented the highest buffer and Cd retention capacity, possibly related to its clay content. Based on desorption studies, M3 presented the strongest binding site as 95% of metal removal was attributed to specific sorption. Silt loam is the most suitable soil coverage for industrial land of all analyzed soils.

Adsorption properties of sugarcane bagasse and corn cob for the sulfamethoxazole removal in a fixed-bed column

Natural adsorbents are a good alternative to remove antibiotic residues from wastewater. In this study, the adsorption capacity of sulfamethoxazole (SMX) onto sugarcane bagasse (SB) and corn cob (CC) in a continuous fixed-bed was compared. Brunauer Emmett Teller, Fourier transform infrared (FTIR), Boehm titration, and point of zero charge (pHpzc) were used to characterize both adsorbents. The adsorption capacity (qe) and the removal percentage of SMX (% R) were investigated at different different flow rates (2, 5, and 7 mL min− 1) and adsorbent masses (4 and 6.4 g), and a constant initial concentration of 5 mg L− 1. The results of the characterization showed that SB has a morphology with more dispersed particles and a specific surface higher than CC (2.6 > 1.2 m2 g− 1). Boehm titration indicates that both the surface of SB and CC have a greater amount of acid groups, which is in agreement with FTIR and pHpzc results. The continuous fixed-bed experiments showed that % R and qe of SMX are higher with SB in all the tests. The highest qe and maximum % R was 0.24 mg g− 1 and 74% with SB, and 0.15 mg g− 1 and 65% using CC. In most cases, the qe of both adsorbents decreased with the increase of flow rate and bed height. An analysis suggests that hydrogen bonds could be the main factor favoring the SMX adsorption with SB. Finally, the intraparticle diffusion was the rate-controlling step, predominating the pore-volume diffusion resistance.

Impact of Ship Traffic on the Characteristics of Shelf Sediments: An Anthropocene Prospective

Humans have been sailing across seas and oceans for thousands of years. However, the story of large ships capable of affecting coastal ecology and shelf sedimentary processes is only about 100 years old. Modern large seagoing vessels with a draft of 10–20 m can cause resuspension of seabed sediment, erosion of the channel slope and shoal, enhancement of seafloor sediment activity and thickening of the active layer, thereby having a significant impact on seabed topography and sedimentation processes. However, little is known about the effects of this anthropogenic agent on shelf sedimentation due to limited observational data. Here, two sediment cores were collected from a shipping lane used by vessels of 5,000- to 50,000-ton off the coast of China to analyze their sedimentary properties, with focus on both the grain size and elements. It was found that ship disturbance selectively modified the sedimentary record, with the fine-grained sediment becoming increasingly unstable. In addition, there was a reduction in grain size of sediment finer than 6.25 Φ, which decreased by 11% after the disturbance by ship. Biogenic elements that were closely related to the ecological environment were significantly altered, with Br/Cl, Si/Ti, and Ca/Ti ratios all becoming significantly smaller. This indicated that frequent disturbance caused by ships had reduced the productivity in the waters near the shipping lane. In terms of sensitivity to the effects of ship navigation, the sedimentation response was relatively rapid and began to emerge from the commencement of ship navigation, whereas the ecological response became evident later than the sedimentation response and only appeared after a significant growth in the maritime transportation of China. Following the comparison of the two sediment cores, we propose that the constant rate of supply (CRS- with ship disturbance)–constant initial concentration (CIC- without ship disturbance) dual dating model be used to establish a dating framework in waters frequently disturbed by ship. This type of anthropogenic sedimentary dynamic process and its sedimentary–ecological effects deserve attention on this era where there is a surge in shipping globally. Shipping lanes present an excellent area for quantitative studies on the impacts of human activity and defining the Anthropocene in the context of shipping.

Adsorption Desulfurization of Iraqi Light Naphtha Using Metals Modified Activated Carbon

The study aims to evaluate the removal of sulfur content from Iraqi light naphtha produced in Al-Dora refinery by adsorption desulfurization DS technique using modified activated carbon MAC loaded with nickel Ni and copper Cu as single binary metals. The experiments were carried in a batch unit with various operating parameters; MAC dosage, agitation speed, and a contact time of 300 min at constant initial sulfur concentration 155 ppm and temperature. The results showed higher DS% by AC/Ni-Cu (66.45)% at 500 rpm and 1 g dosage than DS (29.03)% by activated carbon AC, increasing MAC dosage, agitation speed, and contact time led to increasing DS% values. The adsorption capacity of MAC results was recorded (16, 15, and 20) mg sulfur/g MAC for AC/Ni, AC/Cu and, AC/Ni-Cu, respectively. Equilibrium isotherm study results show good fitting with Freundlich isotherm model with R2 value (0.95) for AC/Ni-Cu. The kinetic study results showed R2 value (0.974, 0.981, and 0.95) by pseudo first order and (0.96, 0.916 and, 0.909) by pseudo second order for AC/Ni, AC/Cu, and AC/Ni-Cu, respectively. The calculated qe(cal) (4.337-4.79) mg/g by first order model was the nearest to the obtained qe(exp) (5.125) mg/g by the experiments where no interparticle diffusion referring to more than one process is controlling the adsorption process of sulfur compounds by MAC.

Preparation and Testing of Cordierite Monolithic Catalysts for Oxidation of Aromatic Volatile Organic Compounds

This work reports the results of catalytic oxidation of aromatic volatile organic compounds (VOCs). A gaseous mixture of benzene, toluene, ethylbenzene, and o-xylene (BTEX) in nitrogen was used as representative of VOCs. Reactions were carried out in a monolithic reactor at different temperatures, with a constant initial concentration of reactants and a constant ratio of BTEX and oxidant (synthetic air). Analysis of the oxidation products was carried out on-line before and after reaction using gas chromatography. The work involves the preparation of catalysts and their application on an inert cordierite monolithic carrier, using different combinations of mixed manganese oxides (manganese with copper, iron, and nickel) and palladium as a representative of noble metals. The prepared cordierite monolithic catalysts showed great mechanical stability and high performance regarding oxidation of the mixture of aromatic compounds. High conversion values (90 %) of all components of the mixture were achieved at temperatures below 200 °C, depending on the chemical composition of the catalytic layer. A comparison with the activity of a commercial monolithic catalyst (Purelyst PH-304), which contains Pt and Pd as catalytically active components, using toluene as a model component. A comparison of the prepared manganese oxides showed that MnFeOx and MnCuOx had the best catalytic activity. When Pd was used in combination with MnFeOx in a form of a single monolith, where Pd was applied to ¼ of the overall monolith length and MnFeOx to ¾ of overall length, achieved 90 % conversions (T90) were up to 20 °C lower when compared with the same MnFeOx monolithic catalysts without Pd. Based on the comparison of the prepared ceramic monolithic catalysts with a commercial catalyst and because the comparison was made only based on toluene conversion, it was concluded that the prepared catalysts can be considered as alternatives to commercial monolithic catalysts by introducing a low concentration of Pd.

Reconstruction of metal(loid)s pollution history in sediments of Wami Estuary, Indian Ocean Coast of Tanzania

Results of metal(loid)s pollution history, their enrichment and contamination factors in sediments of Wami River Estuary, Tanzania are presented. Two sediment cores (WE1 and WE2) were retrieved from the Estuary using hand-driven PVC coring tubes. Levels of metal(loid)s in sediment samples were determined using EDXRF spectrometer coupled with X-lab ProTM software. Metal(loid)s enrichment factors (EF) were determined using metal(loid)s baseline values established during this study. Contamination factors were determined by dividing measured metal(lod)s concentrations in the samples by their respective baseline concentrations. Sediment physical chemical parameters were determined in order to establish their relationship with metal(loid)s concentrations. Sediment chronologies were established using the Constant Initial Concentration (CIC) lead-210 sediment-dating model in order to convert sediment depth profile into timescales. The lowest concentrations of As in sediments was measured in sediments deposited during 1960s, followed by increase reaching the highest concentrations in sediments deposited between ca. 2015 and 2017. Lowest and highest concentrations of Cd were measured in 1960’s and ca. 2000, respectively. Cu and Zn had their maximum concentrations in ca. 1971 and their significant positive correlation (r = 0.94, p = 0.01) suggest common origin of these metals. Average metals enrichment factors in the core were established and are in the order As = Cd = Cu = Pb = Zn = 0.1. This EF value suggests that all metals in sediments of Wami originate from natural sources (EF < 1). Metal(loid)s contamination factors (CF) were low to moderate for As, Cu and Zn; moderate for Pb; and low to considerable for Cd. CIC model revealed that the sediment at the bottom of cores WE1 and WE2 date back about 33 and 55 years, respectively. Sediments of Wami Estuary is characterized by mixing as evidenced in the established chronologies. Therefore, reported radiometric dates should be considered as a preliminary chronological estimate and further research is needed focused on terrestrial records of anthropogenic activities.

Volcanic Rock Materials for Defluoridation of Water in Fixed-Bed Column Systems.

Consumption of drinking water with a high concentration of fluoride (>1.5 mg/L) causes detrimental health problems and is a challenging issue in various regions around the globe. In this study, a continuous fixed-bed column adsorption system was employed for defluoridation of water using volcanic rocks, virgin pumice (VPum) and virgin scoria (VSco), as adsorbents. The XRD, SEM, FTIR, BET, XRF, ICP-OES, and pH Point of Zero Charges (pHPZC) analysis were performed for both adsorbents to elucidate the adsorption mechanisms and the suitability for fluoride removal. The effects of particle size of adsorbents, solution pH, and flow rate on the adsorption performance of the column were assessed at room temperature, constant initial concentration, and bed depth. The maximum removal capacity of 110 mg/kg for VPum and 22 mg/kg for VSco were achieved at particle sizes of 0.075–0.425 mm and <0.075 mm, respectively, at a low solution pH (2.00) and flow rate (1.25 mL/min). The fluoride breakthrough occurred late and the treated water volume was higher at a low pH and flow rate for both adsorbents. The Thomas and Adams–Bohart models were utilized and fitted well with the experimental kinetic data and the entire breakthrough curves for both adsorbents. Overall, the results revealed that the developed column is effective in handling water containing excess fluoride. Additional testing of the adsorbents including regeneration options is, however, required to confirm that the defluoridation of groundwater employing volcanic rocks is a safe and sustainable method.

Largest marsh in New England near a precipice

The Great Marsh in northern Massachusetts and southern New Hampshire is the largest salt marsh in New England and includes the marsh surrounding Plum Island Sound, one of the most studied coastal wetlands in the United States. A primary goal in marsh research today is predicting their resilience in a regime of sea-level rise, which has become increasingly based on modeling studies with sparse or site-specific field data input. Here, we present the results of a vertical accretion study using 210Pb and 137Cs geochronology developed from 50-cm long auger cores taken at 15 locations throughout the PIS marsh. Two significant outliers were omitted from the final analyses due to their unusual depositional settings. The 137Cs spike produced the shortest-term record and lowest average accretion rate (2.5 mm/yr). Of the various 210Pb accretion models (Constant Flux-Constant Sedimentation: CF-CS, Constant Rate of Supply: CRS, Constant Initial Concentration: CIC), we chose the CF-CS model accretion rate for comparison to other environmental parameters and future marsh projections due to the robust R2 linear regression values and its wide use. The 13 stations exhibited an average accretion rate of 3.13 mm/yr, which is 0.6 mm/yr greater than the average rate reported elsewhere in New England. Individual accretion rates show no correlation with geography, elevation, bulk density, loss on ignition, distance to tidal channels, or peat thickness, indicating the complexity of the interacting factors that control marsh growth. Using moderate sea-level rise predictions, we show that large portions of the high marsh are likely to be converted to low marsh by 2050, and that the entire marsh high platform will become low marsh prior to 2070. This is the first time that wide spread field data are used to project a major transformation of the Plum Island Sound platform marsh that undoubtedly will lead to dramatic changes to marsh drainage, backbarrier hypsometry, tidal current dominance, and redistribution of sediment reservoirs, that will include the fronting barrier islands.

Application and problems of &lt;sup&gt;210&lt;/sup&gt;Pb and &lt;sup&gt;137&lt;/sup&gt;Cs dating techniques in lake sediments

湖泊沉积记录研究对了解流域侵蚀、揭示区域气候环境变化及人类活动影响、建立外生地球化学循环模式等均具有重要意义.放射性同位素²¹⁰Pb和¹³⁷Cs组合定年法是百年尺度湖泊沉积记录研究的首选方法，在过去几十年中得到了广泛应用，大力推动了湖泊沉积记录的高分辨率气候环境变化研究的开展.然而，如何理解和选择适用的计算模式来尽可能地提高定年准确度目前仍存在争议，这在一定程度上限制了该方法的应用.鉴于上述问题，本文基于本实验室近年来从青藏高原获取的若干支代表性湖芯的定年结果，从样品前处理、仪器及测试、数据分析及计算等全过程对²¹⁰Pb、¹³⁷Cs定年原理和方法进行了较为系统的阐述；在此基础上，提出了²¹⁰Pb定年样品封装原则，探讨了高纯锗γ谱仪在放射性活度测量中的影响因素，并建立了准确有效的比活度校正方法；明确指出了恒定初始浓度模式（constant initial concentration，CIC）可用于计算沉积物每层的年龄，而不是部分研究中认为的平均沉积速率，这对于深刻理解该定年模式并提供准确的定年结果具有重要的参考意义.同时，通过对比两种放射性核素的分布特征发现，相对于²¹⁰Pb而言，¹³⁷Cs更容易发生垂向迁移进而影响其时标准确性，这需引起研究者的充分重视，因此，当二者定年结果出现明显差异时，建议以²¹⁰Pb定年结果为准.;The study of lacustrine sedimentary records is of great significance for understanding basin erosion, revealing regional climatic and environmental changes and the influence of human activities, and establishing exogenous geochemical cycle patterns. The combined dating method of ²¹⁰Pb and ¹³⁷Cs is the preferred method for the study of centennial-scale lake sedimentary records. It has been widely used in the past decades, which greatly promotes the study of high-resolution climate and environmental changes in lake sedimentary records. However, it is still controversial how to understand and select the applicable calculation model to improve the accuracy of the dating as much as possible, which limits the application of this method to a certain extent. Because of the above problems, based on the dating results of several representative lake cores obtained from the Tibetan Plateau by our laboratory in recent years, the principles and methods of dating with ²¹⁰Pb and ¹³⁷Cs were systematically expounded from the whole process of sample pretreatment, instrument and sample measurement, data analysis and calculation. On this basis, the packing principle of ²¹⁰Pb dating samples was proposed, the influencing factors of High-purity germanium Gamma-Ray Spectrometer in radioactive activity measurement were discussed, and an accurate and effective specific activity correction method was established. It was pointed out that constant initial concentration (CIC) model could be used to calculate the age of each layer of sediments, rather than the average deposition rate in some studies, which is of great significance for understanding the model and providing accurate dating results. Meanwhile, by comparing the distribution characteristics of the two radioisotopes, it was found that ¹³⁷Cs was more likely to have vertical migration compared with ²¹⁰Pb, and thus affected the dating accuracy, which should be paid more attention to by researchers. Therefore, in case of the obvious difference between the two results, it was suggested that ²¹⁰Pb results should prevail.

Effects of Initial Temperature on the Deflagration Characteristics and Flame Propagation Behaviors of CH4 and Its Blends with C2H6, C2H4, CO, and H2

An experimental study was performed on pressure evolution and flame propagation for CH4 and its blends with C2H6, C2H4, CO, and H2 over its entire flammable range for systems with various concentrations (0.4–2.0 %) and initial temperatures (298–373 K) of closed-vessel deflagration. The peak explosion pressure (Pmax) and the maximum pressure rise rate (dp/dt)max were observed and analyzed. In the outwardly spherically propagating flame method, the unstretched laminar burning velocity (Ul) was obtained from the flame radius with time. Within the range of the experiments, the results show that Pmax decreases linearly and that (dp/dt)max first increases and then decreases with increasing initial temperature at a constant initial concentration. When a gas mixture is added to a 9.5 % CH4–air mixture, Pmax and (dp/dt)max exhibit decreasing trends at a constant initial temperature. A nonlinear regression formula was obtained, and this formula can be used to predict Pmax at different temperatures and concentrations. The kinetic model using two detailed mechanisms (GRI-Mech 3.0, FFCM-1) is compared with the experimental results using linear and nonlinear models of stretch extrapolation. The laminar burning velocities (LBVs) measured by FFCM-1 are closer to the experimental value than those measured by GRI-Mech 3.0. The Ul values of CH4 and its blends with C2H6, C2H4, CO, and H2 increase with an increase in the initial temperature. Based on the analysis of experimental values, the temperature exponent (α) is derived to predict the LBVs of the mixture at an elevated temperature under atmospheric pressure.