Coupling effects during steady-state solute diffusion through a semipermeable clay membrane

Two separate coupling effects are evaluated with respect to steady-state potassium chloride (KCl) diffusion through a bentonite-based geosynthetic clay liner (GCL) that behaves as a semipermeable membrane. Both of the coupling effects are correlated with measured chemico-osmotic efficiency coefficients, omega, that range from 0.14 to 0.63 for the GCL. The first coupling effect is an explicit (theoretical) salt-sieving effect expressed as a coupled effective salt diffusion coefficient, Domega*, that is lower than the true (uncoupled) effective salt diffusion coefficient, Ds*, because of the observed membrane behavior. However, the maximum difference between Domega* and Ds* based on measured chloride concentrations is relatively small (i.e., = 10%), and the difference decreases with decreasing omega (i.e., Domega* --> Ds* as omega --> 0). The second coupling effect is implicit (empirical) and is characterized by the measurement of concentration-dependent effective salt diffusion coefficients that results in an degrees 300% decrease in Ds* as omega increases from 0.14 to 0.63. The decrease in Ds* resulting from implicit coupling is attributed to solute exclusion described in terms of a restrictive tortuosity factor.     

Multicomponent diffusion modeling in clay systems with application to the diffusion of tritium, iodide, and sodium in Opalinus Clay

The hydrogeochemical transport model PHREEQC was extended with options to calculate multicomponent diffusion in free pores and in the diffuse double layer (DDL). Each solute species can be given its own tracer diffusion coefficient. The composition of the DDL is calculated with the Donnan approximation. With these options, solute species can be transported in coexisting charged and uncharged regions as may exist in clays and membranes. The model was developed to simulate in-situ tracer diffusion experiments in Opalinus Clay with tritium, iodide, and sodium. Tritium gives the formation's tortuosity factor, which applies in principle for all the neutral species. Half of the porosity is not accessible for iodide due to anion exclusion, and assumed equal to the amount of DDL-water. With this assumption, the tortuosity factor for iodide is 1.4 times higher than that for tritium. The sodium data can be matched by reducing the tortuosity factor 1.6 times relative to tritium, and by distributing the cation exchange capacity over the DDL and fixed sites that are spread heterogeneously over the model domain. The physical origin of the variable tortuosity for differently charged species is discussed.     

VOC sorption and diffusion behavior of building materials

In this study 25 different building materials often used in timber constructions (wood based panels, gypsum boards, vapor barriers, adhesive tapes, insulation materials and sealants) were investigated with regard to their adsorption, desorption and diffusion behaviour towards volatile organic compounds (VOC). The materials were exposed to four, respectively five selected VOCs typically found in indoor air: hexanal, butyl acetate, p-xylene, nonane and α-pinene. Adsorption and desorption properties were investigated under static conditions, whereas the diffusion behavior was examined in a 0.225 m³ emission chamber with an air exchange rate of 1 h^?1. The results of the experiments indicate that some building products have a high potential to reduce VOCs in indoor air. Apart from the vapor barriers, two insulating materials and one plasterboard, all tested materials represented an adsorption efficiency of about 50 % or higher related to the injected VOC standards. Materials with high adsorption capacity bound substances strongly and desorbed them less, whereas less adsorbing materials acted inversely. The obtained results indicate that material properties and processing play a considerable role in diffusion behavior of building materials.     

An analysis of moisture diffusion by diffusion equation considering the Coulomb friction

Following a previous paper, another type of diffusion equation accounting for the Coulomb friction is proposed in this paper. For the drying experiments Sitka spruce bars were used with dimensions L×R×T=10×2×2 cm, and the density was 0.4 g/cm³. The specimens were prepared at 20°C and 60% R.H., and were dried in the desiccator with silica gel at 20°C. After 1,200 h, the specimens were cut in half and dried in the desiccator again. The moisture contents were determined by using the oven-dry method and were also calculated from the above theories. The results considering friction are in good agreement with the experimental results.

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Analyse der Feuchtediffusion mittels der Diffusionsgleichung unter Berücksichtigung der Coulomb-Reibung

Zusammenfassung In Fortführung eines früheren Artikels wird hier eine neue Diffusionsgleichung mit Berücksichtigung der Coulomb-Reibung vorgestellt. Für die Trocknungsexperimente wurden Fichtenproben der Abmessungen L×R×T=10×2×2 cm und 0,4 g/cm³ Dichte verwendet. Die Proben wurden bei 20°C und 60% rel. Feuchte konditioniert und über Silikagel getrocknet. Nach 1.200 Stunden wurden die Proben halbiert und weiter getrocknet. Die Feuchte wurde durch Ofentrocknung und nach den Modellgleichungen bestimmt. Die Ergebnisse zeigen bei Berücksichtigung der Reibung eine gute Übereinstimmung der experimentellen und berechneten Werte.

     

Determination of interstitial water chemistry and porosity in consolidated aquifer materials by diffusion equilibrium-exchange

Diffusion equilibrium exchange (DEE) is presented as a novel, practical alternative to centrifugation for the recovery and chemical analysis of interstitial water in contaminated core samples from consolidated rocks and aquifers. The methodology is suitable for sampling organic and inorganic compounds, including redox sensitive species such as SO4(2-), NO3-, NO2-, Mn(II), Fe(II), and sulfide (HS-). DEE also permits analyte extraction from kilogram quantities of core, which avoids extended centrifugation or sample amalgamation and provides analyte masses appropriate for stable isotope analysis. The procedure involves simple and rapid on-site sectioning of representative core samples, which are preserved in the field by storage in airtight bottles filled with deoxygenated deionized water containing a conservative tracer (Br-). Equilibration times for individual solutes can be estimated in advance to reduce the need for time-series analysis; for an effective diffusion coefficient of 2.5 x 10(-10) m2 s(-1) (Br- in chalk rock) equilibration was >90% completed after 30 h, consistent with the predicted equilibration time. The DEE method presented minimizes sampling errors from temperature changes, oxidation of reduced chemical species, and loss of volatile compounds, which can occur with other interstitial water sampling techniques. It also gives superior resolution of in situ solute distributions and geochemical processes in consolidated sediments than centrifugation and can provide estimates of aquifer porosity in core samples. Laboratory experiments using chalk rock core and simulated extraction procedures confirm the superior performance of the DEE method over centrifugation for a range of solutes. The method has been used to generate detailed interstitial water profiles of electron acceptor and contaminant concentrations along the flow path of a petroleum hydrocarbon plume in the U.K. Upper Chalk aquifer as part of a natural attenuation assessment.     

一类带有扩散项的捕食-食饵模型的分歧解

本文研究了一类在齐次Dirichlet边界条件下带有传染病的捕食-食饵模型.利用上下解方法得到了正解的先验估计;借助分歧理论,以扩散系数d为分歧参数,构造了发自半平凡解(槇d;θr,0)处的平衡解分支,从而给出了模型平衡态正解的存在性.     

An experimentally simple method for measuring diffusion in food gels

A simple method for measuring the diffusion coefficients of small molecules in food gels is described. The method is based on diffusion in a gel column and requires only the availability of a tube of constant cross section for the experiment. Determination of the concentration gradient in the column is made by sectioning, followed by analysis using any suitable technique. Both mutual and self-diffusion measurements may be made. The method is used to study the diffusion of K₂CrO₄ in agar and agarose gels and amaranth dye in agar.     

Intermolecular interactions in phytochemical model systems studied by NMR diffusion measurements

Novel functional foods, such as tomato juice with soy, represent a new strategy to increase consumption of health promoting ingredients and phytochemicals. Interactions between soy protein, isoflavones, and tomato carotenoids could impact the bioaccessibility and bioavailability of individual phytochemicals. The primary objective of this study was to assess possible interactions between daidzein and daidzin, soy protein and carotenoids using proton one-dimensional and two-dimensional pulsed field gradient nuclear magnetic resonance spectroscopy experiments.     

A liquid diffusion model for thin-layer drying of rough rice

In this study, the drying behavior of single-layer rough rice with a moisture content of between 22 and 24% on the dry basis was simulated by means of a liquid diffusion model, based on a prolate spheroid geometry. For this purpose, the solution of liquid diffusion equation was fitted to the experimental moisture ratios for drying air temperatures between 40 and 60 °C and velocity 1.5 m s⁻¹. In order to make a comparison, the predictions of liquid diffusion equations for a spherical and finite cylindrical geometry were also fitted to the experimental results. Modeling was performed by selecting the diffusion coefficients in diffusion equations in such a manner as to minimize the sum of the squared differences between the experimental results and the theoretical predictions. It was found that the liquid diffusion model, based on a prolate spheroid geometry, explains single-layer drying behavior of rough rice well. It was also found that the model, based on a prolate spheroid geometry, has better agreement with the experimental results than the other geometries.     

混纺纱截面图像分析中的光斑扩散模型

针对传统的轮廓跟踪算法只能应用在二值图像上,无法处理目标间相互溶结的现象,提出基于人眼视觉原理的光斑扩散模型,并从逼近、贴近、径长突变和命中率4个方面阐述了其控制参数。该模型直接运行在灰度图像上,能够自动分离相互溶结的目标。在光斑扩散模型的基础上,构建了面积系数、异形度和波动强度3个新的特征指标,分别用于描述目标形状的尺寸大小、与圆形偏离的程度以及边缘的粗糙程度。结果表明,新的模型可以准确地提取纤维截面的轮廓,在此基础上构建的特征指标能够有效地反映目标形状特征。     

纤维质多孔材料中纤维间接触点数量的理论模型

为深入研究纤维质多孔材料的微观结构,通过建立纤维间接触点数量的理论模型,分别研究纤维在空间中三维和二维分布情况下,纤维间接触点数量的理论值。根据泊松分布的特点,结合Sampson等的研究结论,建立纤维间接触点数量、纤维直径和孔隙率的函数关系。使用Geo-Dict软件模拟纤维结构,同时计算纤维间接触点数量,再分别将纤维不同取向的理论预测值和前人研究结果相比较。结果表明:当纤维长径比不变时,纤维数量与纤维间接触点数量呈线性正比关系;当孔隙率不变时,纤维直径与纤维间接触点数量呈反比关系;当纤维直径固定时,纤维间接触点数量随孔隙率增加而减少;当纤维直径大于40 μm时,接触点数量不随孔隙率的变化而改变。     

A study of diffusion of dyes in model foods using a visual method

Many food processing operations involve mass transfer. The application of electric fields can influence the mass transfer properties of foods. A major limitation of infusion studies is the lack of successful measurement techniques to quantify the depth of penetration and localisation of infused material. Diffusion of two dyes (rhodamine 6G and methylene blue) in agar and alginate gels was visualised insitu for 10 min. The experiments were performed at three temperatures (30, 50, and 70 °C) and four voltage gradients (167, 333, 500, 667 V m⁻¹) plus a control (0 V m⁻¹). The effect of hydrocolloid concentration and electrical conductivity on diffusion and response to the electric field were tested. The limitations of Fickian analysis led to a new method of data analysis, the penetration model. The effect of the type of gel and the diffusing molecule charge and mass on the combined diffusion and electric field process is discussed.     

Apparent diffusion model assessment in extraction processes by means of a Luenberger observer

In this work a clear methodology is proposed that allows the estimation of diffusion-concentration functional relationship in extraction processes, which are modelled by Fick’s second law. A criterion is proposed for deciding when the diffusivity should be considered a constant value (comparable to those obtained by the standard regression technique) and when a function depending on concentration. The methodology is based in a Luenberger observer. The diffusion-concentration relationship is refined by an optimization procedure making use of a numerical solution of the diffusion equation. The robustness of the methodology is assessed by a noise propagation analysis. The methodology is illustrated for oil extraction from tung seeds with experimental data taken from the literature.     

A viscoelastic model for the compaction of fibrous materials

Fibrous materials experience compression in many important industrial and technical applications. They are known to undergo a viscoelastic response in such circumstances, exhibiting phenomena such as dependence on compaction velocity, stress relaxation and stress–strain hysteresis. In this paper, a model has been developed for the stress in compacting fibrous materials. The model is based on the multiplicative decomposition of the stress into a function of the strain and a second function of the strain‐rate. The model is applicable to that class of materials whose stress–strain responses at different compaction velocities can be collapsed onto a single master curve when the stress is normalised appropriately. The model parameters can be determined using a least‐squares fitting to a select number of test data. The model has been tested for two materials of different architectures over a range of compaction speeds and maximum volume fractions; the match to experimental data is excellent.     

离子色谱-直接紫外检测法测定食品接触材料中的六价铬迁移量

目的建立一种离子色谱-直接紫外检测法测定食品接触材料中六价铬迁移量的新方法。方法样品经碱性食品模拟物(碳酸钠-盐酸,pH=8.5)浸泡后,使用氯化铵-氨水溶液为淋洗液,IonPacA S7(4 mm×250 mm)阴离子分析柱分离,以紫外检测器在350 nm波长直接检测。结果本方法在0.001～0.5 mg/L范围内线性关系良好,线性方程为y=10.8554x+0.00472,r=0.999 9,检出限为0.000 3 mg/L,定量限为0.001 mg/L,样品加标回收率为88%～113%,相对标准偏差(n=6)为1.9%～9.0%。结论本方法具有灵敏度高、准确性好、检出限低、操作简便易行等特点,适用于日常样品检测。     

黑莓渗糖过程中水分和溶质扩散的数学模型

以黑莓-白糖固液体系为研究对象,研究了黑莓在不同条件糖溶液中的渗透脱水规律,得出了渗糖过程中水分和溶质扩散的数学模型。渗透液的质量分数选取40%、50%、60%,溶液的温度选取30、40、50℃,糖溶液和黑莓的质量比为10∶1,渗透脱水时间为0~5 h。利用AZUARA等提出的双组分系统数学模型得到了每种实验条件下黑莓样品最终渗透平衡状态时的失水率和固形物增加率,结果表明,在一定实验条件范围内,黑莓脱水率和固形物增加率均随渗透液浓度、渗透时间和溶液温度的增大而增大;同时使用菲克第二定律估算了每种试验条件下水分和糖的有效扩散系数,上述渗透条件下水分和糖的有效扩散系数分别在1.77×10~(-9)~2.10×10~(-9)m~2/s和1.36×10~(-9)~1.60×10~(-9)m~2/s范围内。     

Temperature prediction in air drying of food materials: a simple model

The problem of one-dimensional heat and mass transfer in infinite slabs during drying of porous solids is considered. Assuming a known distribution of moisture and temperature, it is possible to estimate effective thermal and mass diffusion coefficients in solids. In this paper it is demonstrated that from these coefficients the equations describing heat and mass transfer processes in the system are easily integrated to obtain average sample temperature and moisture during drying. These theoretical results may be used to evaluate the effects of the degradation reactions during food drying, which depend on the foodstuff moisture content and temperature.     

Dietary plant materials reduce acrylamide formation in cookie and starch-based model systems

BACKGROUND: Dietary plant materials have attracted much attention because of their health benefits to humans. Acrylamide is found in various heated carbohydrate‐rich foods. Our previous results showed that crude aqueous extracts from diverse dietary plants and some phenolic compounds could mitigate acrylamide formation in an asparagine–glucose model system. Based on our previous study, several plant materials were selected to further investigate their inhibitory effects on acrylamide formation in cookies and starch‐based model systems. RESULTS: Addition of raw powders from selected dietary plants and their crude aqueous extracts could considerably reduce acrylamide formation in both cookie and potato starch‐based models. Aqueous extracts of clove at 4% caused the largest reduction (50.9%) of acrylamide in cookies, whereas addition of 2% proanthocyanidins from grape seeds gave the greatest acrylamide reduction (62.2%) in a starch‐based model system. CONCLUSION: It may be feasible to use some of the tested dietary plant materials to reduce acrylamide formation in cookies and other starchy foods. Copyright © 2011 Society of Chemical Industry