Effect of Ca2+ and Zn2+ on UO2 dissolution rates

The dissolution of UO(2) in a continuously stirred tank reactor (CSTR) in the presence of Ca(2+) and Zn(2+) was investigated under experimental conditions relevant to contaminated groundwater systems. Complementary experiments were performed to investigate the effect of adsorption and precipitation reactions on UO(2) dissolution. The experiments were performed under anoxic and oxic conditions. Zn(2+) had a much greater inhibitory effect on UO(2) dissolution than did Ca(2+). This inhibition was most substantial under oxic conditions, where the experimental rate of UO(2) dissolution was 7 times lower in the presence of Ca(2+) and 1450 times lower in the presence of Zn(2+) than in water free of divalent cations. EXAFS and solution chemistry analyses of UO(2) solids recovered from a Ca experiment suggest that a Ca-U(VI) phase precipitated. The Zn carbonate hydrozincite [Zn(5)(CO(3))(2)(OH)(6)] or a structurally similar phase precipitated on the UO(2) solids recovered from experiments performed in the presence of Zn. These precipitated Ca and Zn phases can coat the UO(2) surface, inhibiting the oxidative dissolution of UO(2). Interactions with divalent groundwater cations have implications for the longevity of UO(2) and the mobilization of U(VI) from these solids in remediated subsurface environments, waste disposal sites, and natural uranium ores.     

Size-controlled dissolution of organic-coated silver nanoparticles

The solubility of Ag NPs can affect their toxicity and persistence in the environment. We measured the solubility of organic-coated silver nanoparticles (Ag NPs) having particle diameters ranging from 5 to 80 nm that were synthesized using various methods, and with different organic polymer coatings including poly(vinylpyrrolidone) and gum arabic. The size and morphology of Ag NPs were characterized by transmission electron microscopy (TEM). X-ray absorption fine structure (XAFS) spectroscopy and synchrotron-based total X-ray scattering and pair distribution function (PDF) analysis were used to determine the local structure around Ag and evaluate changes in crystal lattice parameters and structure as a function of NP size. Ag NP solubility dispersed in 1 mM NaHCO(3) at pH 8 was found to be well correlated with particle size based on the distribution of measured TEM sizes as predicted by the modified Kelvin equation. Solubility of Ag NPs was not affected by the synthesis method and coating as much as by their size. Based on the modified Kelvin equation, the surface tension of Ag NPs was found to be ～1 J/m(2), which is expected for bulk fcc (face centered cubic) silver. Analysis of XAFS, X-ray scattering, and PDFs confirm that the lattice parameter, a, of the fcc crystal structure of Ag NPs did not change with particle size for Ag NPs as small as 6 nm, indicating the absence of lattice strain. These results are consistent with the finding that Ag NP solubility can be estimated based on TEM-derived particle size using the modified Kelvin equation for particles in the size range of 5-40 nm in diameter.     

Nanostructures and polymorphisms in protein stabilised lipid nanoparticles,as food bioactive carriers: contribution of particle size and adsorbed materials

Eight oil-in-water emulsions were prepared using melt high-pressure homogenisation (HPH) at 300 or 1200 Bar. The emulsions produced from lipid phase (20%) were composed by palm oil alone or in mixture with α-tocopherol at 4:1 weight ratio, and an aqueous phase containing whey proteins alone or in mixture with phospholipids. The resulting nanoemulsions (fat droplet size ranging from 200-500 nm) presented different stability against aggregation and coalescence, fat crystallinity and polymorphisms in relation to different degrees of α-tocopherol encapsulation and protection against chemical degradation. Protein stabilised emulsions were monomodal, while emulsions stabilised by proteins and lecithins were slightly bimodal. Application of an isothermal treatment (4 °C for 2 hours) to these emulsions showed crystallization peaks located at longer time values in smaller particle size emulsions, while in the presence of added α-tocopherol average particle size values were higher and crystallization was not observed in 2 hours storage. Study of fat polymorphisms performed after 12 hours storage at 4 °C revealed the formation of 2L structures with coexistence of α, β’ and β forms in all of the emulsions. Increasing HPH from 300 to 1200 Bar favoured development of β structure (4.5 A^-1) in α-tocopherol added emulsions, with the presence of one extra peak β structure evolved at 3.9 A^-1 only in emulsions containing lecithins. α-tocopherol addition decreased in 2L structures (by approx. 40-50%). The formation of lipid nanoparticles with decreasing size values (increasing HPH parameters) was accompanied by increased long-term stability against aggregation and coalescence, but increased vitamin degradation (up to 15 wt% for 1200 bar). Degradation of α-tocopherol after 2 months storage at 4 °C was lower for nanoparticles stabilised by whey proteins alone (21 and 33%, respectively) than for nanoparticles stabilised by whey proteins in mixture with phospholipids and presenting higher size values (44 and 52%, respectively), where β polymorphs were more evolved.     

Kinetics of starch digestion in sorghum as affected by particle size

The mechanisms of starch digestion in cryomilled and hammer-milled sorghum grain were investigated by an in vitro procedure using 10 particle sizes (≅120–560 μm). The samples exhibited essentially monophasic digestograms, and three digestion models (Duggleby, first-order kinetic and Peleg models) were tested for describing the digestograms. Irrespective of the particle size, starch digestion followed first-order kinetics, and the modified first-order exponential model and Peleg model adequately (mean relative deviation modulus < 10%) described the digestograms. With or without an intercept, there was a significant linear relationship (r² > 0.61; p < 0.01) between the reciprocal of the digestion rate constant and the square of the particle size consistent with digestion proceeding by a diffusion-controlled mechanism. The reciprocal of the slope of the relationship 0.4–0.9 × 10⁻⁷ cm² s⁻¹ provides an estimate of the diffusion coefficient of α-amylase within the milled grains. Particle size affected digestion kinetics, water absorption index (WAI), pasting properties, and water solubility index (WSI) of the samples, as did hammer-milling. However, differential scanning calorimetry showed no significant effects of the hammer-milling on starch gelatinisation properties. Although particle size was the primary determinant of digestion properties, small but detectable changes to the grain particle structure due to the hammer-milling affected digestion kinetics, presumably because of additional frictional heat and mechanical effects. Suggestions were made on how to modulate starch digestion, for example to achieve efficient energy delivery to animals from sorghum-based feed.     

Retention and transport of silica nanoparticles in saturated porous media: effect of concentration and particle size

Investigations on factors that affect the fate and transport of nanoparticles (NPs) remain incomplete to date. In the present study, we conducted column experiments using 8 and 52 nm silica NPs to examine the effects of NPs' concentration and size on their retention and transport in saturated porous media. Results showed that higher particle number concentration led to lower relative retention and greater surface coverage. Smaller NPs resulted in higher relative retention and lower surface coverage. Meanwhile, evaluation of size effect based on mass concentration (mg/L) vs particle number concentration (particles/mL) led to different conclusions. A set of equations for surface coverage calculation was developed and applied to explain the different results related to the size effects when a given mass concentration (mg/L) and a given particle number concentration were used. In addition, we found that the retained 8 nm NPs were released upon lowered solution ionic strength, contrary to the prediction by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The study herein highlights the importance of NPs' concentration and size on their behavior in porous media. To the best of our knowledge, it is the first report of an improved equation for surface coverage calculation using column breakthrough data.     

超微粉碎技术对绿茶主要功能成分溶出特性的影响研究

为拓展超细绿茶粉的应用领域,研究超微粉碎技术对绿茶主要功能成分溶出特性的影响.结果发现,用20 ℃低温水浸提,超细绿茶粉中茶多酚、咖啡碱的浸出速度大于普通绿茶粉与原茶.用80 ℃热水浸提时,超细绿茶粉和普通绿茶粉中茶多酚、咖啡碱的浸出速度差别不显著,但高于原茶.     

Investigation into the performance and mechanism of SiO2 nanoparticles and starch composite films

Nanomaterials are often introduced to improve the properties of polymers. In this article, the effects of SiO₂ nanoparticles with lager specific areas and special microstructural characters on the properties of starch films were investigated. Firstly, the ultrasonic mixing was used to disperse the SiO₂ nanoparticles under different dispersion times, and then the dispersed SiO₂ nanoparticles with various ratios were added into starch size. The effects of the dispersion time and the SiO₂ content on the mechanical properties of the SiO₂/starch composite size were analysed. It was found that the dispersion time and the SiO₂ content had significant effects on the tensile and abrasion behaviour of the nanocomposite films. The mechanism of the enhanced mechanical properties of the composite films was examined by analysing the size of the dispersed SiO₂ nanoparticles in the dispersion, the surface characters of the films and the structures of the fractured surfaces. And the morphology of the abraded surface was analysed by atomic force microscopy, scanning electron microscope and video zoom microscope.     

Gelling properties of surimi as affected by the particle size of fish bone

The effects of adding fish bone with two different particle sizes (micro and nano) on Alaska pollock surimi gels prepared by two heating procedures were investigated. Heating procedures (with or without setting) resulted in significantly different gel texture values. The addition of nano-scaled fish bone (NFB) (up to 1 g/100 g) effectively increased gel breaking force and penetration distance while micro-scaled fish bone (MFB) did not. Endogenous transglutaminase (TGase) activity of surimi paste increased obviously as the concentration of NFB increased, indicating calcium ions readily released from NFB and assisting gel formation through TGase-induced covalent bonds. With MFB, TGase activity increased slightly, but not significantly. Scanning electron microscopy (SEM) results revealed NFB was capable of being imbedded in the gel matrices without disrupting the myofibrillar gel network. Surimi with MFB formed a discontinuous and porous network with pores near the size of MFB. Lightness (L*) and whiteness (L*-3b*) of NFB gels were higher than those of MFB.     

Restructured beef with different proportions of walnut as affected by meat particle size

Microstructure, texture, colour and sensory properties of precooked restructured beef made with different proportions of walnut (0, 5, 10, 15%) were studied in relation to meat particle size (grinder plate hole: 0.6 and 1.4 cm). In general, increasing amounts of walnut were matched by decreasing Kramer shear force (KSF), bind strength and elongation values. When walnut (5 and 15%) was added, products made with coarsely ground meat presented higher KSF values than those made with finely ground meat. Walnut decreased lightness and increased redness and yellowness. Morphology characteristics suggest that walnut interferes with the formation of a gel protein network. Sensory properties were judged acceptable with 5 and 10% of walnut; however, the products scored highest with 10% walnut in finely ground products and 5% walnut in coarsely ground products.     

Effect of particle size on droplet infiltration into hydrophobic porous media as a model of water repellent soil

The wettability of soil is of great importance for plants and soil biota, and in determining the risk for preferential flow, surface runoff, flooding,and soil erosion. The molarity of ethanol droplet (MED) test is widely used for quantifying the severity of water repellency in soils that show reduced wettability and is assumed to be independent of soil particle size. The minimum ethanol concentration at which droplet penetration occurs within a short time (≤ 10 s) provides an estimate of the initial advancing contact angle at which spontaneous wetting is expected. In this study, we test the assumption of particle size independence using a simple model of soil, represented by layers of small (~0.2-2 mm) diameter beads that predict the effect of changing bead radius in the top layer on capillary driven imbibition. Experimental results using a three-layer bead system show broad agreement with the model and demonstrate a dependence of the MED test on particle size. The results show that the critical initial advancing contact angle for penetration can be considerably less than 90° and varies with particle size, demonstrating that a key assumption currently used in the MED testing of soil is not necessarily valid.     

Robust size control of bovine serum albumin (BSA) nanoparticles by intermittent addition of a desolvating agent and the particle formation mechanism

In polymeric nanoparticle preparation, despite similar conditions, large fluctuations in particle size distributions are usually observed. Herein, we demonstrate that the intermittent addition of a desolvating agent can improve reproducibility in the preparation of polymeric bovine serum albumin (BSA) nanoparticles. Using this modification, BSA nanoparticles of controlled size can be manufactured with narrow particle size distributions. In our study, ethanol as a desolvating agent was added intermittently to 1% BSA solutions at different pHs with stirring at 700 rpm. The effect of the preparation parameters on size and optical density of the fabricated nanoparticles were studied. The average particles sizes of BSA nanoparticles prepared at pH values of 6, 7 and 9 were approximately 100, 200 and 300 nm, respectively. As ethanol addition increased, desolvation of BSA molecules resulted in formation of loose-structured particles with pH-dependent size. Beyond that, only particle density increased, but size remained unchanged with further addition of ethanol. Consistently uniform particle size distribution was achieved by adding ethanol intermittently.     

Aggregation and dissolution of silver nanoparticles in natural surface water

This study investigated aggregation and silver release of silver nanoparticles suspended in natural water in the absence and presence of artificial sun light. The influence of the capping layer was investigated using uncoated particles and particles coated with citrate or Tween 80. The experiments were conducted over 15 days in batch mode using a river water matrix. Silver release was monitored over this time while the aggregation state and morphological changes of the silver nanoparticles were tracked using dynamic light scattering and transmission electron microscopy. Results indicate sterically dispersed particles coated with Tween released silver quicker than did bare- and citrate-coated particles, which rapidly aggregated. A dissolved silver concentration of 40 μg/L was reached after just 6 h in the Tween-coated particle systems, accounting for ca. 3% of the total silver. Similar levels of dissolved silver were reached in the uncoated and citrate-coated systems at the end of the 15 days. Silver release was not significantly impacted by the artificial sun light; however, the light (and citrate) imparted significant morphological changes to the particles. Their impact was masked by aggregation, which seemed to be the controlling process in this study.     

Nutritive value of fresh and brackish water catfish as a function of size and processing methods

Catfish (Clarias gariepinus) of different sizes (small, 30.33–30.83 cm and 191.67–195.00 g; medium, 36.67–37.50 cm and 275.00–303.33 g; large, 41.33–49.67 cm and 536.67–726.00 g) collected from brackish (Igbokoda) and fresh water (Ogbese) bodies was subjected to different treatments (fried, boiled with/without salt solution and roasted). The proximate (ash, fat and protein) and mineral (Ca, Zn, Fe, Mg, P and I) compositions of all the treatments were determined. The highest protein concentrations (on a dry weight basis percent) (Ogbese, 73.25; Igbokoda, 72.52) of fish samples were recorded by boiling with water, while the ones roasted recorded the lowest values of 57.51 and 58.33%, respectively. The iodine level (grams of I per 100 g) in the flesh of fish varied with size, treatment and location; it increased with size, was reduced by some treatments (boiling with either water or NaCl solution), while frying and roasting had the highest level compared with boiling. The lowest iodine concentrations were 93.45 (Ogbese fish boiled with NaCl solution) and 160.94 (Igbokoda fish boiled with either water or NaCl solution). On the whole, Igbokoda brackish water fish (160.94–314.08) had a higher iodine content than Ogbese fresh water fish (93.45–205.06) with the highest concentration in fried and roasted fish samples (205.06, 314.08) in Ogbese and Igbokoda water bodies, respectively. Higher mineral compositions were also found in the brackish water fish (for flesh and serum), and also increased with size and were reduced by some treatments (boiling and frying) in the flesh of fish samples. The fish (catfish) from the brackish water body appeared to be more nutritious than that from the fresh water body. The highest protein values were recorded by boiling with water, while frying and roasting gave the highest iodine value. Moreover, the study revealed that size is a factor to be considered by the population dependent on fish as a source of protein, iodine and other vital elements.     

PMF analysis of wide-range particle size spectra collected on a major highway

Particle number concentration data have been collected on a very busy road in central London (Marylebone Road). Continuous size distributions from 15 nm to 10 μm diameter, collected over 21 days, were analyzed using positive matrix factorization which identified 10 factors, five of which were observed to make major contributions (greater than 8%) to either the total number or volume of particulate matter. The sources associated with each factor were identified from the size distribution, directional association, diurnal variation and their relationship to meteorological pollution and traffic volume variables. The factors related to the emissions on Marylebone Road accounted for 40.5% of particle volume and 71.9% of particle number. These comprised nucleation mode exhaust particles (3.6% of total volume and 27.4% of total number), solid mode exhaust particles (18.8% of total volume and 38.0% of total number), brake dust (13.7% of total volume and 1.7% of total number and resuspension (4.4% of total volume and 4.8% of total number). Another six factors were associated with the urban background accounting for 59.5% of total volume and 28.2% of total particle number count. The method is extremely successful at separating the components of on-road emissions including brake wear and resuspension.     

The determination of particle size distribution in soil. A collaborative study

A collaborative trial on the determination of particle size distribution in soil is described. The analytical method used was that of Avery and Bascombe. Twelve laboratories participated, all of which had considerable experience of the method. Eight soils were collected, divided and distributed by one of the laboratories. The variation in the results is due to errors arising both from the sampling technique and from the analytical method. Estimates of the within and between laboratories variation for the values found in each particle size class for the eight soils are given. Those analyses with high loss are found to give, on average, almost the same particle size distribution as those with low loss.     

Evaluation of thermal stability of confectionary sunflower protein isolate and its effect on nanoparticulation and particle size of the produced nanoparticles

In this study, the effect of different defatting conditions on heat stability of confectionary sunflower protein isolate (SnPI) and the particle size of the produced nanoparticles was investigated. The evaluated factors included temperatures of defatting (40, 50, and 60 °C), time of defatting (2, 6, and 10 h), and the amount of activated carbon (0, 25, and 50% of sample weight). The results of the central composite design showed a significant effect (P < 0.05) among the studied factors, where denaturation temperature and particle size of SnPI nanoparticles were found to be in the ranges of 75.05–89.12 °C and 268–1594 nm, respectively. Moreover, the interaction of activated carbon with temperature and time of defatting proved to be influential factors for the heat stability of confectionary SnPI.     

The kinetics and mechanism of caffeine infusion from coffee: The effect of particle size

Measurements have been made of the rate of infusion of caffeine into distilled water from medium roast Kenyan Arabica coffee beans and from eight sieved fractions of the ground beans at 25.8°C. The first-order rate constants increased dramatically as the particle size decreased. For one of the size fractions the rate constants were then measured at various temperatures up to 84.1°C and were found to rise eight-fold over this temperature interval. The partition coefficients of caffeine between ground beans and water were also determined. These results, interpreted by a new steady-state theory of extraction, show that the rate-determining step in the infusion is diffusion of caffeine through the swollen coffee particles. The low magnitude of the diffusion coefficient and its high activation energy demonstrate that caffeine diffusion within the bean particles is a hindered process.     

The effect of reducing alfalfa haylage particle size on cows in early lactation

The objective of this experiment was to evaluate effects of reducing forage particle size on cows in early lactation based on measurements of the Penn State Particle Separator (PSPS). Eight cannulated, multiparous cows averaging 19 +/- 4 d in milk and 642 +/- 45 kg BW were assigned to one of two 4 x 4 Latin Squares. During each of the 23-d periods, animals were offered one of four diets, which were chemically identical but included alfalfa haylage of different particle size; short (SH), mostly short (MSH), mostly long (MLG), and long (LG). Physically effective neutral detergent fiber (peNDF) was determined by measuring the amount of neutral detergent fiber retained on a 1.18 mm screen and was similar across diets (25.7, 26.2, 26.4, 26.7%) but the amount of particles >19.0 mm significantly decreased with decreasing particle size. Reducing haylage particle size increased dry matter intake linearly (23.3, 22.0, 20.9, 20.8 kg for SH, MSH, MLG, LG, respectively). Milk production and percentage fat did not differ across treatments averaging 35.5 +/- 0.68 kg milk and 3.32 +/- 0.67% fat, while a quadratic effect was observed for percent milk protein, with lowest values being observed for LG. A quadratic effect was observed for mean rumen pH (6.04, 6.15, 6.13, 6.09), while A:P ratio decreased linearly (2.75, 2.86, 2.88, 2.92) with decreasing particle size. Total time ruminating increased quadratically (467, 498, 486, 468 min/d), while time eating decreased linearly (262, 253, 298, 287 min/d) with decreasing particle size. Both eating and ruminating per unit of neutral detergent fiber intake decreased with reducing particle size (35.8, 36.7, 44.9, 45.6 min/kg; 19.9, 23.6, 23.5, 23.5 min/kg). Although chewing activity was closely related to forage particle size, effects on rumen pH were small, indicating factors other than particle size are critical in regulating pH when ration neutral detergent fiber met recommended levels. Feeding alfalfa haylage based rations of reduced particle size resulted in animals consuming more feed but did not affect milk production.     

Effect of varying total mixed ration particle size on rumen digesta and fecal particle size and digestibility in lactating dairy cows

The objective of this experiment was to evaluate the effects of feeding rations of different particle sizes on rumen digesta and fecal matter particle size. Four rumen-cannulated, multiparous, Holstein cows (104 ± 15 d in milk) were randomly assigned to treatments in a 4 × 4 Latin square design. The diets consisted of 29.4% corn silage, 22.9% ground corn, 17.6% alfalfa haylage, and 11.8% dry grass hay [20% of forage dry matter (DM)] on a DM basis. Dry grass hay was chopped to 4 different lengths to vary the total mixed ration (TMR) particle size. Geometric mean particle sizes of the rations were 4.46, 5.10, 5.32, and 5.84 mm for short, medium, long, and extra long diets, respectively. The ration affected rumen digesta particle size for particles ≥3.35 mm, and had no effect on distribution of particles <3.35 mm. All rumen digesta particle size fractions varied by time after feeding, with soluble particle fractions increasing immediately after feeding and 0.15, 0.6, and 1.18-mm particle size fractions decreasing slightly after feeding. Particle fractions >1.18 mm had ration by time interactions. Fecal neutral detergent fiber (NDF) and indigestible NDF concentrations decreased with increasing TMR particle size. Fecal particle size expressed as total geometric mean particle length followed this same tendency. Fecal particle size, expressed as retained geometric mean particle length, averaged 1.13 mm with more than 36% of particles being larger than 1.18 mm. All fecal nutrient concentrations measured were significantly affected by time after feeding, with NDF and indigestible NDF increasing after feeding and peaking at about 12 h later and then decreasing to preprandial levels. Starch concentrations were determined to have the opposite effect. Additionally, apparent digestibility of diet nutrients was analyzed and DM digestibility tended to decrease with increasing TMR particle size, whereas other nutrient digestibilities were not different among rations. These results show that the critical size for increased resistance to rumen escape is larger than 1.18 mm and this critical size is constant throughout the day. This study also concludes that, when using average quality grass hay to provide the range of particle sizes fed, DM digestibility tends to decrease with increasing ration particle size.