Translational diffusion coefficients of volatile compounds in various aqueous solutions at low and subzero temperatures

Translational diffusion coefficients (D(12)) of volatile compounds were measured in model media with the profile concentration method. The influence of sample temperature (from 25 to -10 degrees C) was studied on translational diffusion in sucrose or maltodextrin solutions at various concentrations. Results show that diffusivity of volatile compounds in sucrose solutions is controlled by temperature, molecule size, and the viscosity of the liquid phase as expected with the Stokes-Einstein equation; moreover, physicochemical interactions between volatile compounds and the medium are determinant for diffusion estimation. At negative temperature, the winding path induced by an ice crystal content of >70% lowered volatile compound diffusion. On the contrary, no influence on translational diffusion coefficients was observed for lower ice content.     

Evolution of fat crystal network microstructure followed by NMR

Model systems composed of tristearin in solid state and tricaprin in liquid state with different solid-fat content (SFC) and storage time have been investigated by relaxation NMR and NMR diffusometry. The T(2) relaxation of the tricaprin in the melt exhibited a bimodal distribution as previously observed. The SFC had a major effect on the T(2) relaxation. This effect was explained according to the fast diffusive exchange model in porous media. According to this model the changes in T(2) relaxation as a function of the SFC and storage time were explained by the decrease of the surface-to-volume ratio of the crystal induced by Ostwald ripening. The diffusion coefficient D of the tricaprin in the melt decreased for higher SFC. Since no significant variation of D was observed for different diffusion time, D reflected the long-range connectivity and the tortuosity was calculated. During storage the diffusion coefficient remained constant.     

Rotational and translational mobility of small molecules in sucrose plus polysaccharide solutions

The effect of different polysaccharides on the rotational (D(rot)) and translational diffusion (D(trans)) coefficients of small molecules in concentrated systems (sucrose solutions) was investigated. Dextran (1 or 10% w/w) with different molecular masses (from 10(4) to 2 x 10(6) Da), gum arabic, or pullulan was added to solutions of sucrose (57.5% w/w). Viscosity measurements of the diffusion medium studied (sucrose and sucrose plus polysaccharide) were made using a Rheometric Scientific viscometer in a temperature range from 20 to -10 degrees C. The rotational mobility of nitroxide radicals (Tempol) dispersed in the concentrated systems was measured by electron spin resonance. The translational diffusion coefficient of fluorescein was determined by the fluorescence recovery after photobleaching method. The studied temperature range for the latter two techniques was from 20 to -16 degrees C. For these conditions of concentration and temperature, there was no ice formation in the samples. No effect of the molecular mass of dextran on D(rot) and D(trans) was observed when solutions with the same dry matter content were compared. Only pullulan and gum arabic, at 10%, had a significant effect on D(trans)( )()of fluorescein. Temperature and total dry matter content were observed to be the most important factors controlling D(rot) and D(trans) in these concentrated systems.     

Losses of dissolved CO2 through the cork stopper during Champagne aging: toward a multiparameter modeling

Measurements of dissolved CO(2) concentrations from Champagne bottles initially holding the same CO(2) level after having been elaborated (close to 11.5 g L(-1)), but having experienced different periods of aging after having been corked with natural cork stoppers, were done. Losses of dissolved CO(2) close to 3.5 g L(-1) experienced by the oldest Champagne samples aged for about 75 months were reported. This very significant loss of dissolved CO(2) was logically interpreted as a consequence of the continuous diffusion of gaseous CO(2) through the pores of the cork stopper. By combining the diffusion principle through a porous medium with Henry's law (which links the solubility of a gas species in a liquid medium with its partial pressure in the vapor phase), a multiparameter model was built that provides the dissolved CO(2) content found in Champagne during its whole aging period. Both Champagne temperature and bottle volume were found to be key parameters with regard to the kinetics of CO(2) losses through the cork.     

Copper(II) binding by free and kaolinite-sorbed humic substances

Humic preparations isolated from different sources—soils (a soddy-podzolic soil and a typical chernozem), high-moor peat, and brown coal—have been used. To analyze the binding of copper ions by humic substances (HSs), the preparations were obtained in two forms: solutions and humic-clay complexes (HSs irreversibly sorbed on kaolinite). With this approach, the binding of copper(II) ions by HSs has been studied in different systems: (1) Cu(II)-HSs irreversibly sorbed on kaolinite, (2) Cu(II)-dissolved HSs, and (3) Cu(II)-dissolved HSs-HSs irreversibly sorbed on kaolinite. In the systems containing both dissolved HSs and humic-clay complexes, HSs of similar structure isolated from the same source were used. The quantitative estimation of the copper binding was based on the constant of sorption (K) for HSs in humic-kaolinite complexes and the stability constant (β) of complexes for free (dissolved) substances. Both parameters were expressed in similar units: L/kg. The values of logK = 3.31—3.33 are independent of the quantity and quality of the HSs in the sorption complexes but reliably exceed the K value for pure kaolinite (2.92). The value of β is not affected by the presence of insoluble HSs together with their soluble forms, but it depends on the source of HSs. The value of logβ varies in the range from 5.62 to 6.93, which significantly exceeds K and indicates a significantly higher affinity of dissolved HSs for copper ions than that of irreversibly sorbed HSs. The revealed regularities have shown that the content of HSs in the soil solution can significantly affect the mobility of a heavy metal bound to the soil organic matter.     

大气CO2浓度升高对谷子生长发育及玉米螟发生的影响

人类活动导致全球大气CO_2浓度持续升高,研究大气CO_2浓度升高对C4作物谷子(Setaria italica)生长发育及虫害发生的影响,可以为谷子等C4作物制订应对气候变化栽培措施提供理论依据。本研究利用OTC(Open Top Chamber)系统,设两个CO_2浓度梯度(正常大气CO_2浓度、正常CO_2浓度+200μmol·mol-1)模拟CO_2浓度升高对谷子生长发育的影响。结果表明:大气CO_2浓度升高后,谷子净光合速率(Pn)、气孔导度(gs)、叶片蒸腾速率(Tr)和水分利用率(WUE)分别增加38.73%、27.53%、6.93%和40.56%;谷子叶片光系统Ⅱ最大光化学量子产量(Fv/Fm)和非光化学淬灭系数(NPQ)显著下降,光系统Ⅱ实际光化学量子产量(ΦPSII)和表观电子传递效率(ETR)显著增加,而对光化学淬灭系数(q P)无显著影响;此外,谷子株高、茎粗和小穗数分别增加3.41%、13.28%和13.11%;而叶重、茎重、千粒重、单株粒数和产量无显著变化,穗重和地上部分生物量分别显著下降12.8%和7.44%;大气CO_2浓度升高后,谷子灌浆期和收获期玉米螟(Ostrinia furnacalis)发生数量显著增加。大气CO_2浓度升高将有利于谷子的生长发育,但会增加玉米螟危害。     

Isolation of tetra-acyl sucrose esters from turkish tobacco using supercritical fluid CO2 and comparison with conventional solvent extraction

Pure supercritical CO2 at various pressures and temperatures was used to effect the fractionation of tetra-acyl sucrose esters (SE) from dried, ground Turkish tobacco without any further pretreatment of the matrix. It was determined that SE cannot be extracted using low density CO2 (150 atm, 60 degrees C, and 0.62 gm/mL or 200 atm, 100 degrees C, and 0.49 gm/mL), whereas other analytes, which strongly interfere with the conventional solvent extraction of SE, can be easily removed under the same conditions. At the higher temperature (100 degrees C), these same analytes that interfere with the conventional solvent extraction of SE are even more readily removed, while the very poor extractability of SE is not affected. It was demonstrated, however, that SE can be removed from the pre-extracted tobacco with supercritical CO2 if the density is greater than (or equal to) 0.73 gm/mL. The supercritical fluid extraction method has been compared with other previous extraction methods that employ conventional solvents. This study provides one of the clearest examples of how the variable density property of a supercritical fluid can be utilized to effect the fractionation of a complex mixture.     

不同CO2浓度下鸡蛋呼吸仿真分析及验证

贮存环境中CO_2浓度对鸡蛋呼吸作用及新鲜度变化具有重要影响,为了进一步考察在不同CO_2浓度下鸡蛋呼吸释放CO_2的扩散及新鲜度变化情况,该研究测定贮存在温度为25℃、相对湿度为65%、CO_2体积分数分别为1.5%、3.0%、4.5%及空气(对照组)环境下鸡蛋呼吸和新鲜度,利用FLUENT软件完成不同CO_2浓度下鸡蛋第1天呼吸释放CO_2的扩散过程仿真。结果表明,利用Fluent软件计算所得气体速度值和试验值基本一致,模拟值与实测值相对误差在4%～9%。不同CO_2浓度下鸡蛋释放CO_2的扩散过程符合重气扩散的特点,其扩散方向受到CO_2浓度的影响,且随着贮存环境中CO_2浓度的增加,鸡蛋呼吸释放CO_2的扩散量和扩散速度逐渐变小,呼吸得到抑制。再通过分析贮存过程中不同CO_2体积分数下鸡蛋呼吸强度和新鲜度变化得出,对照组1.5%CO_2与3.0%CO_2下的鸡蛋呼吸强度和新鲜度具有显著差异(P0.05),当贮存环境中CO_2体积分数达到3.0%时,对鸡蛋呼吸强度的抑制效果不再明显,且新鲜度变化保持不变。3.0%CO_2和4.5%CO_2体积分数下贮存鸡蛋20 d,其新鲜度等级仍在AA级以上,综合经济因素,3.0%CO_2保鲜鸡蛋效果较优。该研究可为鸡蛋呼吸和气调保鲜技术提供理论及数据基础。     

Diffusion of oxygen in cork

This work reports measurements of effective oxygen diffusion coefficient in raw cork. Kinetics of oxygen transfer through cork is studied at 298 K thanks to a homemade manometric device composed of two gas compartments separated by a cork wafer sample. The first compartment contains oxygen, whereas the second one is kept under dynamic vacuum. The pressure decrease in the first compartment is recorded as a function of time. The effective diffusion coefficient D(eff) is obtained by applying Fick's law to transient state using a numerical method based on finite differences. An analytical model derived from Fick's law applied to steady state is also proposed. Results given by these two methods are in close agreement with each other. The harmonic average of the effective diffusion coefficients obtained from the distribution of 15 cork wafers of 3 mm thickness is 1.1 × 10(-9) m(2) s(-1) with a large distribution over four decades. The statistical analysis of the Gaussian distribution obtained on a 3 mm cork wafer is extrapolated to a 48 mm cork wafer, which length corresponds to a full cork stopper. In this case, the probability density distribution gives a mean value of D(eff) equal to 1.6 × 10(-9) m(2) s(-1). This result shows that it is possible to obtain the effective diffusion coefficient of oxygen through cork from short time (few days) measurements performed on a thin cork wafer, whereas months are required to obtain the diffusion coefficient for a full cork stopper. Permeability and oxygen transfer rate are also calculated for comparison with data from other studies.     

Environmental Monitoring Using Electrical Resistivity Tomography (ERT) in the Subsoil of Three Former Petrol Stations in SE of Spain

Electrical resistivity tomography (2D ERT) is a powerful tool for the diagnosis of the subsoil state and to pursue an environmental monitoring in time to detect and follow a temporal evolution of plumes in hydrocarbon-contaminated soils. In situ, 2D ERT was conducted to investigate the electrical properties of the subsoil in three petrol stations in Murcia semiarid Region (SE Spain), which have been active for many years, in order to look for anomalous areas that could be related to the presence of a non-aqueous phase liquid (NAPL) contaminant plume in the subsoil. A total of 18 ERT profiles in wet and dry season were conducted to study the seasonal effects in the resistivity values of the subsoil. Dipole?Cdipole array was set up to make the soil diagnosis, achieving a good vertical and lateral resistivity distributions for the sites investigated. Interpretations obtained from ERT pseudo-sections, after a processing and inversion data process with PROSYS II and RES2DINV software, show delimited highly resistive regions above 2,000 ??·m at 2?m deep related to the underground storage tanks (USTs) position and the filling ports and anomalous resistivity areas where boreholes and further GC?CFID determination in soil samples have been done. No significant differences have been found between results obtained in dry and wet seasons. Thus, the geo-electrical non-destructive technique ERT is presented as a tool to delineate the USTs positions and to point out anomaly in the subsoil that could contain NAPL, helping to design sampling strategies, saving cost and time.     

Self-diffusion coefficient of water in tofu determined by pulsed field gradient nuclear magnetic resonance

The self-diffusion coefficient of water in soybean protein dispersion and tofu was measured by pulsed field gradient (PFG) NMR. A soy protein isolate (SPI) dispersion (6 and 12%, w/w) in water, calcium cross-linked precipitate, and tofu were used for comparison. The self-diffusion coefficient of water (D) in the SPI dispersion, 2.23 x 10(-9) m2/s, was estimated lower than that of free water, 2.6 x 10(-9) m2/s at 25 degrees C, and decreased as the SPI concentration increased. It further decreased by the addition of calcium chloride, reflecting the obstruction effect induced by the precipitates in addition to the hydration and hydrodynamic interaction in the protein dispersion. The two water regions in tofu were interpreted by the two-site K?rger model: D1 and D2 of soft tofu were 2.26 (+/-0.11) x 10(-9) and 6.84 (+/-0.34) x 10(-11) m2/s, respectively. The relative amount of proton (water) was p1 = 0.98 and p2 = 0.02 at 100 ms of diffusion time. The self-diffusion coefficients of water decreased in pressed tofu, and their relative amounts of water changed to p1 = 0.93 and p2 = 0.07. It was suggested that D1 corresponded to obstructed water in the network structure and D2 corresponded to hydrated water on the surface layer of pores formed in the protein network of tofu. The pore sizes estimated from the diffusion length of obstructed water were 21.3 microm in soft tofu and 20.8 microm in pressed tofu. The removal of fat from pressed tofu led to a decrease in D2 from 6.26 (+/-0.31) x 10(-11) to 3.53 (+/-0.18) x 10(-11) m2/s, and the relative amount of hydrated water increased from 0.07 to 0.14, which indicated hydrophobic hydration.     

Determination of vitamin D3 in liquid multivitamin preparation, using reverse phase, solid phase extraction liquid chromatography

A method is described for the determination of vitamin D3 in a liquid multivitamin preparation by liquid chromatography. Samples are purified on a disposable reverse phase extraction (SPE) column with a mobile phase of methanol-2-propanol (97 + 3) and are analyzed on a Zorbax ODS (5 micron) column with an acetonitrile-2-propanol-water (90 + 8 + 2) solvent system. Vitamin D3 is completely resolved from other interfering compounds within approximately 21 min and is detected with a UV detector at 254 nm. A mean of 98.5% of theory with a coefficient of variation of 3.8% was found for determination of vitamin D3 in a commercial preparation.     

Comparison between fertilizers and untreated sewage effluent as sources for nutrient recovery by wheat (Triticum aestivum)-soybean (Glycine max) cropping system

Recovery and recycling of plant nutrients from municipal sewage effluent (SE) can reduce consumption of costly chemical fertilizers, besides reducing eutrophication of water bodies. Field experiment was conducted on Vertisol of central India for six years with the objective of quantifying recovery of major plant nutrients by aboveground biomass of wheat-soybean cropping system from untreated SE. Wheat crop was grown with irrigation (groundwater and sewage effluent) and fertilizer treatments; while soybean was grown without any treatments. Recoveries of nitrogen (N), phosphorus P) and potassium (K) by the aboveground biomass were considerably more from SE than from fertilizers and manures. Recovery of nutrients from SE was the highest by wheat grain for N and by soybean straw for P and K. Straw biomass of both the crops recovered about 31% N, 22% P and 69% K from SE, which can be recycled back into agricultural land of groundwater (GW) irrigated as well as rainfed area.     

Comparative Study on the Kinetic Equations of Potassium Release from Soils

Elovich,two-constant,parabolic diffusion,exponential,second-order,first-order and zero-order equations were used to describe the kinetic characteristics of potassium desorption from six paddy soils of Zhejiang Province in a constant electric field (44.4V/cm) of EUF.Results showed that the second-order and Elovich equations could describe the potassium desorption kinetics best,as evidenced by the highest correlation coefficients (r) and the lowest standard errors (SE).The first-order,two-constant and parabolic diffusion equations also described the K desorption kinetics well,as showed by the relatively high correlation coefficients and relatively low standard errors.The zero-order equation did not describe the K desorption satisfactorily with a relatively low correlation coefficient and relatively high standard error.However,the exponential equation could not be used to describe the K desorption kinetics,due to the lowest correlation coefficient and the highest standarderror.     

Flavor authenticity studies by (2)h/(1)h ratio determination using on-line gas chromatography pyrolysis isotope ratio mass spectrometry

Based on (2)H/(1)H ratio measurements of commercial synthetic and "natural" references, the recently developed on-line gas chromatography pyrolysis isotope ratio mass spectrometry (HRGC-P-IRMS) technique was used to determine the delta(2)H(SMOW) values of the flavor compounds decanal, linalool, and linalyl acetate, as well as those of E-2-hexenal and E-2-hexenol in foods and essential oils. In preceding model studies, the influence of sample preparation steps (simultaneous distillation extraction, SDE; solvent extraction, SE; liquid liquid extraction, LLE) on the delta(2)H values was found to be negligible. For decanal, the typical (2)H abundance, with higher content of (2)H for synthetic material (delta(2)H(SMOW) from -90 to -156 per thousand) and lower (2)H content for natural references (delta(2)H(SMOW) from -138 to -262 per thousand) was observed. Although the delta(2)H data recorded for linalool did not allow one to distinguish between synthetic (delta(2)H(SMOW) from -207 to -301 per thousand) and natural (delta(2)H(SMOW) from -234 to -333 per thousand) materials, the situation was somewhat more encouraging for linalyl acetate; delta(2)H(SMOW) values from -199 to -239 per thousand and from -213 to -333 per thousand were found for synthetic and natural samples, respectively. E-2-Hexenal and E-2-hexenol showed clear-cut origin-dependent differences in their (2)H/(1)H ratios; that is, delta(2)H(SMOW) values from -14 to -109 per thousand and from -263 to -415 per thousand as well as from -41 to -131 per thousand and from -238 to -348 per thousand were recorded for products from synthetic and natural origins, respectively.     

Effects of Soil pH, Texture, Moisture, Organic Matter and Cadmium Content on Cadmium Diffusion Coefficient

The supply of cadmium from soil to plant roots mainly depends on the diffusion prooess.This work was conducted to study the effects of some soil properties on cadmium diffusion coefficient (D) in soil. Measurements were made using the Shofield and Graham-Bryce‘s isotopic labelling method.Cadmium diffusion coefficients varied from 10^-7to 10^-9 cms^2-1.Higher values were observed in acid sandy soils and lower values in calcareous clay soils.Liming an acid soil resulted in a substantial decrease of D.Addition of cadmium as nitrate salt generally increased D,while addition of sewage sludge and organic matter resulted in a significant decrease of cadmium diffusion.The rhizospheric activity also induced a moderate reduction in D.The relationships between D(10^-9cms^2-1)on the on hand and soil pH.moisture(Mc,g kg^-1) ,organic matter(OM,g kg^-1),clay(Cy,gkg^-1)and cadmium content(Cd,mgkg^-1) on the other were obtained by the multiple regression:D=182.1-29.91pH 0.210Mc-0.303OM 0.011Cy 1.64Cd(R^2=0.859,n=22).     

THE MEASUREMENT AND MECHANISM OF ION DIFFUSION IN SOIL

If an exchangeable ion in soil diffuses along a liquid and solid pathway, its diffusion coefficient may be expressed as where D, v, f, C are diffusion coefficient, volume fraction, impedance factor, and concentration terms and the suffixes _l,_S refer to liquid and solid. The self-diffusion coefficient of the ion is then where D′, D′_t, and D′_s, are self-diffusion coefficients. D and D′ will vary with concentration. In diffusion out of the soil to a zero sink, the appropriate average diffusion coefficient is, approximately, the self-diffusion coefficient in the undisturbed soil. Diffusion of one ion species is influenced by other ions diffusing in the system through the diffusion potential set up. When ions are diffusing to plant roots, the diffusion potential is likely to be small. A more likely, though more complicated, expression for D than the first equation above is derived by assuming the ion to follow solid and liquid pathways in series as well as in parallel.     

施用秸秆和接种蚯蚓对土壤温室气体排放的影响

通过施用秸秆并接种蚯蚓于微系统实验研究发现,在 21 天的培养期内,蚯蚓活动显著增加土壤C02和N20的排放速率,与对照处理相比,单接种蚯蚓处理与单施加秸秆的处理导致CO2排放量分别增加了60%和1.35倍,相应的N2O .排放量增加了1.06倍和3.94倍.另一方面,与单施加秸秆的处理相比,接种蚯蚓配合施加秸秆的处理导致C02和N20排放分别增加了41%和45%.施用秸秆显著提高了土壤微生物生物量C含量,而单接种蚯蚓处理的土壤相比对照处理反而降低.接种蚯蚓显著提高了土壤N03--N和NH4 -N含量,秸秆处理土壤并不显著增加土壤中的NH4 -N含量.     

Anthocyanins from maize (Zea mays) and reed canarygrass (Phalaris arundinacea)

Flowers of maize, Zea mays, and reed canarygrass, Phalaris arundinacea, contain the same anthocyanins: cyanidin 3-glucoside, cyanidin 3-(6' '-malonylglucoside), cyanidin 3-(3' ',6' '-dimalonylglucoside), peonidin 3-glucoside, peonidin 3-(6' '-malonylglucoside), and peonidin 3-(dimalonylglucoside). The latter pigment has previously not been reported to occur in plants. Structure elucidations were primarily based on homo- and heteronuclear two-dimensional NMR and electrospray MS. During the isolation procedure using various mixtures of H(2)O, CF(3)CO(2)H, and CH(3)OH, and during storage in NMR solvent (CF(3)CO(2)D/CD(3)OD; 1:19, v/v) methyl esterification of the free acid function of the malonyl units of the pigments occurs. The acylated anthocyanins constitute more than 80% and 40% of the anthocyanins in P. arundinacea and Z. mays, respectively. Flowers and leaves of maize, Zea mays, contain the same anthocyanins in nearly equal relative proportions.     

Control factors in bubble aeration

Based on molecular motion and turbulent diffusion, a mathematical model is presented to determine the relationships between the diffusion coefficient and different variables in a bubble aeration process. The different variables affecting the diffusion coefficient are rate of air flow, pressure, absolute temperature, and size of bubbles. Because of the turbulent nature of the rising bubble, Oz, and H2O molecules at the gas-liquid interface are ripped away instantaneously. Molecular diffusion plays an insignificant role in the process.