Increased Aggregate Size Research Articles

A nudge over the relaxation plateau: effect of pH, particle concentration, and medium viscosity on the AC induction heating efficiency of biocompatible chitosan-coated Fe3O4 nanoparticles

The effects of pH, MNP concentration, and medium viscosity on the magnetic fluid hyperthermia (MFH) properties of chitosan-coated superparamagnetic Fe3O4 nanoparticles (MNPs) are probed here. Due to the protonation of the amide groups, the MNPs are colloidally stable at lower pH (∼2), but form aggregates at higher pH (∼8). The increased aggregate size at higher pH causes the Brownian relaxation time (τ B) to increase, leading to a decrease in specific absorption rate (SAR). For colloidal conditions ensuring Brownian-dominated relaxation dynamics, an increase in MNP concentrations or medium viscosity is found to increase the τ B. SAR decreases with increasing MNP concentration, whereas it exhibits a non-monotonic variation with increasing medium viscosity. Dynamic hysteresis loop-based calculations are found to be in agreement with the experimental results. The findings provide a greater understanding of the variation of SAR with the colloidal properties and show the importance of relaxation dynamics on MFH efficiency, where variations in the frequency-relaxation time product across the relaxation plateau cause significant variations in SAR. Further, the in vitro cytotoxicity studies show good bio-compatibility of the chitosan-coated Fe3O4 MNPs. Higher SAR at acidic pH for bio-medically acceptable field parameters makes the bio-compatible chitosan-coated Fe3O4 MNPs suitable for MFH applications.

The contribution of microbial necromass carbon to soil organic carbon in soil aggregates

Microbial necromass is known to be the main component of soil organic carbon (C) sequestration. However, the contribution of microbial necromass to soil aggregates has not been comprehensively studied because of the heterogeneity of microhabitats in different soil aggregates, especially in different ecosystems on a global scale. To address this gap, we conducted a global-scale meta-analysis to investigate the contribution of microbial necromass to carbon sequestration in aggregates and identify the climatic and soil factors that influence necromass carbon in aggregates. The database of fungal and bacterial necromass carbon was based on the glucosamine and muramic acid contents in microaggregates (< 250 μm, 226 samples), medium macroaggregates (250–2000 μm,132 samples), and macroaggregates (> 2000 μm, 66 samples). On average, microbial necromass carbon in microaggregates, medium macroaggregates, and macroaggregates contributed 48.5 %, 40.9 %, and 42.5 % of aggregate carbon sequestration, respectively. The contribution of fungal necromass carbon was significantly higher than that of bacteria (average 30.9 % vs. 13.1 %, respectively). Meanwhile, the ratio of fungal to bacterial necromass carbon increased with the increasing aggregate size, from 2.68 (< 250 μm) to 3.11 (250–2000 μm) to 3.14 (> 2000 μm) for micro, medium size, and macroaggregates, respectively. In addition, the screening method for aggregates and the type of land use significantly affected the contribution of microbial necromass to aggregate carbon sequestration. Specifically, grassland and dry sieving significantly increased the contribution of microbial necromass carbon to aggregate carbon. Finally, the results from PLS-PM showed that climatic factors regulated fungal and bacterial necromass carbon through soil pH, sand, and nutrients in aggregates, thereby enhancing the contribution of microbial necromass to aggregate carbon sequestration. In addition, fungal and bacterial necromass carbon improved with increasing carbon and nitrogen content of the aggregates. Furthermore, a lower soil pH seemingly stimulates the accumulation of fungal and bacterial necromass in soil aggregates. These findings emphasize that the contribution of microbial necromass carbon to aggregate carbon sequestration, especially fungal necromass carbon, is an important method for improving carbon sequestration in soil aggregates.

Long-Term Chemical and Organic Fertilization Differently Affect Soil Aggregates and Associated Carbon and Nitrogen in the Loess Plateau of China

Fertilizer sources may have variable effects on soil aggregation, aggregated-associated C and N, and wheat yield. A 34-year field experiment was performed to evaluate the influences of chemical and organic fertilization on soil aggregates and associated carbon and nitrogen under winter wheat in a Cumulic Haplustoll of the Loess Plateau, China. Treatments included unfertilized control (CK), inorganic N fertilizer (NF), inorganic P fertilizer (PF), inorganic N and P fertilizer (NP), organic manure (M), inorganic N fertilizer plus manure (NM), inorganic P fertilizer plus manure (PM), and inorganic N plus P fertilizers plus manure (NPM). Compared to CK, long-term fertilization significantly increased the proportion of soil macro-aggregates, mean weight diameter (MWD), and geometric mean diameter (GMD), but decreased the proportion of micro-aggregates and fractal dimension, especially fertilizer plus manure. Compared to CK, manure treatments (M, NM, PM, and NPM) had a better improvement on soil organic carbon (SOC), soil total nitrogen (STN), particle organic C, and microbial biomass C in all aggregates than the fertilizer alone. The SOC in different aggregates increased with the increased aggregate size, which was because the larger aggregates formed by the binding of the smaller aggregates and organic matter. PON increased in NM and NPM, and MBN was more sensitive to N fertilizer. The C/N ratio in bulk soil and aggregates decreased with fertilization, especially in fertilizer with manure and in macro-aggregates. The improved soil structure was related to the increased SOC and STN, which was proved by the positive correlations among SOC and STN with macro-aggregates and MWD. A correlation analysis also showed that the contribution rate of SOC and STN in macro-aggregates was positively associated with the macro-aggregate and stability. Therefore, the sequestration of C and N in soil was related to aggregate size and was mainly affected by larger aggregates. The results demonstrated that fertilizer with manure improved the soil structure and fertility better than fertilizer alone, thus increasing crop yield.

Soil aggregate modulates microbial ecological adaptations and community assemblies in agricultural soils

Soil aggregates provide spatially heterogeneous microenvironments for soil microbiome and ecological processes. Revealing the nuances of assembly processes in aggregates is critical for understanding the fine-scale organization of the soil microbiome and associated biogeochemistry. However, the effect of aggregate sizes on microbial assemblies remains poorly explored. In this study, we investigated the mechanism underlying the assembly processes of microbial communities within three different aggregates sizes across five long-term fertilization experimental stations throughout eastern China. Our results showed that although geographic sites explained most of the variations in microbial composition in aggregates, aggregates of the same size selected phylogenetically closely related microbial species with similar ecological preferences for specific nutrient variables. Null model analysis showed that environmental selection and dispersal limitation primarily governed the assembly of aggregate bacterial and fungal communities, respectively. The relative importance of deterministic processes on microbial communities increased with the increasing aggregate size across all sites. Multiple stepwise regression analysis indicated that nutrient variables associated with community assembly are distinct in different aggregate-size fractions. Bacterial assembly is mainly affected by total carbon and soil organic carbon in macro- and micro-aggregates, whereas it is influenced by the C/P ratio in the silt + clay fraction. For fungal community assembly, the C/N ratio was the major factor in macroaggregate and silt + clay fractions, while N/P ratio had stronger effects in the microaggregates. Furthermore, fertilization effects on the microbial community assembly processes varied across aggregate sizes. Organic fertilization led to a decrease for bacteria while an increase for fungi in the sorting/dispersal effect ratio. The magnitude of such an impact was higher for macro- and micro-aggregates. GeoChip and enzymatic results further demonstrated the regulation of ecological clusters and functions by nutrient variables across aggregates. Our findings highlight that microbial assembly and functional traits in large aggregate-size fractions are susceptible to nutrient changes, and thus can act as potential biological indicators for sustainable management of agricultural soils.

Gain-of-Function Variant p.Pro2555Arg of von Willebrand Factor Increases Aggregate Size through Altering Stem Dynamics.

The multimeric plasma glycoprotein (GP) von Willebrand factor (VWF) is best known for recruiting platelets to sites of injury during primary hemostasis. Generally, mutations in the VWF gene lead to loss of hemostatic activity and thus the bleeding disorder von Willebrand disease. By employing cone and platelet aggregometry and microfluidic assays, we uncovered a platelet GPIIb/IIIa-dependent prothrombotic gain of function (GOF) for variant p.Pro2555Arg, located in the C4 domain, leading to an increase in platelet aggregate size. We performed complementary biophysical and structural investigations using circular dichroism spectra, small-angle X-ray scattering, nuclear magnetic resonance spectroscopy, molecular dynamics simulations on the single C4 domain, and dimeric wild-type and p.Pro2555Arg constructs. C4-p.Pro2555Arg retained the overall structural conformation with minor populations of alternative conformations exhibiting increased hinge flexibility and slow conformational exchange. The dimeric protein becomes disordered and more flexible. Our data suggest that the GOF does not affect the binding affinity of the C4 domain for GPIIb/IIIa. Instead, the increased VWF dimer flexibility enhances temporal accessibility of platelet-binding sites. Using an interdisciplinary approach, we revealed that p.Pro2555Arg is the first VWF variant, which increases platelet aggregate size and shows a shear-dependent function of the VWF stem region, which can become hyperactive through mutations. Prothrombotic GOF variants of VWF are a novel concept of a VWF-associated pathomechanism of thromboembolic events, which is of general interest to vascular health but not yet considered in diagnostics. Thus, awareness should be raised for the risk they pose. Furthermore, our data implicate the C4 domain as a novel antithrombotic drug target.

Particle size analysis and characterization of nanodiamond dispersions in water and dimethylformamide by various scattering and diffraction methods

Over the past few decades, detonation nanodiamonds (NDs) have gained increased attention due to their unique physicochemical properties. Various methods for preparation of ND suspensions have been introduced. This paper presents thermally annealed nanodiamonds dispersed via sonication and separated by centrifugation in deionized water and dimethylformamide in five weight concentrations ranging from 0.05 to 1 wt%. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were applied to study the thermal behavior of NDs. Crystallographic properties of air-annealed and dispersed NDs were examined by means of X-ray diffraction (XRD). Nanodiamond dispersions were analyzed by static light scattering (SLS), dynamic light scattering (DLS), ultra-small- and small-angle X-ray scattering (USAXS/SAXS), and high-resolution transmission electron microscopy (HRTEM). SLS and DLS give similar results of ND− aggregates mean size between ~ 61 and 73 nm, regardless of solvent type and nanoparticle concentration. For dispersions with increasing concentrations of NDs, neither increased aggregate size nor different kinetics of separation during sonication and centrifugation were observed. USAXS/SAXS provided the aggregates size (2Rg) in the range from 57 to 65 nm and size of primary particles from 5.4 to 5.8 nm. HRTEM also showed presence of larger aggregates with tens of nanometers in size in both water and DMF dispersions, and size of primary particles ranging from 5.5 to 6 nm in very good agreement with SAXS.

Long-term manure application increases soil organic matter and aggregation, and alters microbial community structure and keystone taxa

Microbes play pivotal roles in soil organic matter (SOM) turnover: formation and decomposition. Organic fertilizers play crucial role for SOM accumulation, aggregate formation and influence microbial community composition and co-occurrence networks in microhabitats. Here, we investigated prokaryotic and fungal communities and their co-occurrence networks in four aggregate size classes in upland Ultisol following 27 years of mineral and/or organic fertilizer (rice straw, peanut straw, radish, or pig manure) application. Organic fertilizers and aggregate size classes have main and interactive effects on SOM content in aggregates (p < 0.001). Aggregate size classes accounted for most of the variance (43%) of SOM content, with more SOM accumulated in macroaggregates (>250 μm) than microaggregates (<250 μm). Increased aggregate size affected prokaryotic and fungal community structure by increasing Rhizobiales and decreasing Eurotiales. Solibacterales and Mortierellales were particularly abundant in small microaggregates (<53 μm) due to substrate preferences. Organic fertilizers regulate microbial community structure more than aggregate size, accounting for 41% and 29% of variance in prokaryotic and fungal communities, respectively. Pig manure exerted the strongest effect on SOM content and aggregation, and influenced microbial community structure more strongly than plant residues, primarily by increasing Bacillales, Gaiellales and Pezizales, and decreasing Thermogemmatisporales. This effect of pig manure was related with efficient increase of SOM content and pH. Co-occurrence network analysis revealed more positive or negative linear relationships among microbial groups in microaggregates than in macroaggregates, indicating stronger synergistic and antagonistic microbial interactions in microaggregates with fewer favorable niches (higher recalcitrant SOM and less labile SOM). Thermogemmatisporales was identified as the most influential keystone taxon (relative abundance ∼4.9%) in soil, and its abundance rapidly diminished with increasing SOM content in macro- and microaggregates. Thus, microbial community structure is dependent on aggregate size, and this should be considered during sampling. Overall, long-term pig manure amendment increased the SOM content and aggregation, altering prokaryotic and fungal community structure and keystone taxa.

Effect of aggregate size on bond behaviour between basalt fibre reinforced polymer sheets and concrete

The effect of aggregate size on the interfacial bond behaviour between BFRP sheets and concrete is investigated in this study by conducting single-lap shear tests. The effect of aggregate sizes (i.e. 5–10 mm, 10–15 mm, and 15–20 mm) on the debonding load, maximum bond stress, effective bond length, local slip at peak shear stress, as well as the bond-slip relationship between the BFRP sheets and concrete are presented and discussed. The experimental results have shown a significant effect of the aggregate size on the interfacial bond-slip behaviour. The interfacial shear stress decreased when the aggregate size increased due to the decreased tensile strength of concrete. The relative slip between BFRP and concrete at the peak bond stress increased with the increasing aggregate size also because of the reduced tensile strength of concrete. Existing models regarding the bond strength and interfacial bond-slip are adopted and recalibrated against the experimental results in which the size effect of aggregates is incorporated.

Preparation of ultra-stable ZIF-8 dispersions in water and ethanol

In the fabrication of zeolitic imidazolate frameworks (ZIFs) thin films and membranes, the preparation of stable ZIFs dispersions is crucial. Herein, ultra-stable ZIF-8 aqueous dispersions were obtained successfully for the first time. It was found that, after the synthesis of ZIF-8, with the increased washing times, the positive surface potentials of ZIF-8 particles decrease, resulting in increased aggregate size. The ZIF-8 dispersions washed for zero times are very stable in water, and there is no settlement even after centrifuging at 8000 rpm for 6 min. The aggregate size of ZIF-8 dispersions in ethanol aqueous solutions decreases with increased ethanol content, and there is no apparent settlement in absolute ethanol even after 13 days. The ultra-stable ZIF-8 dispersions display great potentials in fabrication of thin films and membranes.

Salinity-dependent toxicities of zinc oxide nanoparticles to the marine diatom Thalassiosira pseudonana

This study comprehensively investigated the influences of salinity, exposure concentration and time on the aggregate size, surface charge and dissolution of zinc oxide nanoparticles (ZnO–NPs; 20nm) in seawater, and examined the interacting effect of salinity and waterborne exposure of ZnO–NPs on the marine diatom Thalassiosira pseudonana for 96h. We found that aggregate sizes of ZnO–NPs significantly increased with increasing salinity, but generally decreased with increasing exposure concentration. Ion release decreased with increasing salinity, whereas the surface charge of the particles was not affected by salinity. The increased aggregate size and decreased ion release with increasing salinity, and consequently lower concentration of bioavailable zinc ions, resulted in decreased toxicity of ZnO–NPs at higher salinity in general in terms of growth inhibition (IC50) and chlorophyll fluorescence (EC50 – ФPo and EC50 – Ф2). However, IC50s and EC50s of ZnO–NPs were smaller than those of Zn2+ (from ZnO–NPs ultrafiltrate and ZnCl2), indicating that dissolved Zn2+ can only partially explain the toxicity of ZnO–NPs. SEM images showed that ZnO–NPs attached on the diatom frustule surface, suggesting that the interaction between the nanoparticles and the cell surface may acerbate the toxicity of ZnO–NPs. Our results linked the physicochemical characteristics of ZnO–NPs in seawater with their toxicities to the marine diatom and highlighted the importance of salinity as an influential environmental factor governing the aggregation, dissolution and the toxicity of ZnO–NPs.

Role of hydration in phosphatidylcholine reverse micelle structure and gelation in cyclohexane: a molecular dynamics study.

In this work, we employ all-atom molecular dynamics simulations to examine the hydration response of phospholipid reverse micelles in cyclohexane. This ternary phospholipid-water-cyclohexane system is an important organogel forming system and the focus of this study is on gaining insight on the factors governing the gelation transition. We map the contributions rising from specific lipid-lipid and lipid-water interactions, and their response to increasing aggregate size and changes in water-to-lipid ratio. We find that, opposed to phospholipid-heptane organogels, in cyclohexane, lipid bridging and hydrogen bond driven stabilization of the lipid head group packing is at minor role in dictating the reverse micelle structural transitions corresponding to the organosol-organogel phase transition in this system. Instead, increasing the lipid head hydration changes the lipid packing factor directly which leads to gelation through the formation of long, wormlike micelles. Furthermore, the confined environment in the reverse micellar cores slows down the water dynamics significantly in comparison to fully hydrated phospholipid bilayers and at low water-to-lipid ratios this slow-down is even more significant. The findings map the role of hydration at microscopic level in these systems and could enable tailoring reverse micellar systems for applications relying on the structure and dynamics of the reverse micelles. Examples include such as drug transport, nanotemplating, or confined chemistry in the reverse micelle core water space, e.g., in catalysis.

PH-Responsive Assembly of Gold Nanoparticles and “Spatiotemporally Concerted” Drug Release for Synergistic Cancer Therapy

A challenge in using plasmonic nanostructure-drug conjugates for thermo-chemo combination cancer therapy lies in the huge size discrepancy; the size difference can critically differentiate their biodistributions and hamper the synergistic effect. Properly tuning the plasmonic wavelength for photothermal therapy typically results in the nanostructure size reaching ∼100 nm. We report a new combination cancer therapy platform that consists of relatively small 10 nm pH-responsive spherical gold nanoparticles and conjugated doxorubicins. They are designed to form aggregates in mild acidic environment such as in a tumor. The aggregates serve as a photothermal agent that can selectively exploit external light by their collective plasmon modes. Simultaneously, the conjugated doxorubicins are released. The spatiotemporal concertion is confirmed at the subcellular, cellular, and organ levels. Both agents colocalize in the cell nuclei. The conjugates accumulate in cancer cells by the rapid phagocytic actions and effective blockage of exocytosis by the increased aggregate size. They also effectively accumulate in tumors up to 17 times over the control because of the enhanced permeation and retention. The conjugates exhibit a synergistic effect enhanced by nearly an order of magnitude in cellular level. The synergistic effect is demonstrated by the remarkable reductions in both the therapeutically effective drug dosage and the photothermal laser threshold. Using an animal model, effective tumor growth suppression is demonstrated. The conjugates induce apoptosis to tumors without any noticeable damage to other organs. The synergistic effect in vivo is confirmed by qRT-PCR analysis over the thermal stress and drug-induced growth arrest.

Dielectric Properties of Asphaltene Solutions: Solvency Effect on Conductivity

Electrical demulsification is considered an elegant method to enhance the separation of water-in-crude-oil emulsions. Understanding the mechanisms involved during this process remains a challenge for the further development of this separation method. The aim of this study is to elucidate the influence of the aggregation state of the asphaltenes on their conductivity, to determine the mechanisms governing conductivity in crude oils. Dielectric properties of two different asphaltenes extracted from crude oils (labeled CrA and CrB) and their solutions diluted in toluene or heptane were measured by frequency domain spectroscopy. When the heptane volume fraction increases, conductivity decreases. It also appears that the conductivity decreases with an increasing aggregate size. Conversely, decreasing the aggregate size increases the mobility of the charge carriers in the system and, consequently, increases the conductivity. On the basis of these observations, we propose here that the conductivity of asphaltene...

EFFECT OF AGGREGATE SIZE AND GRADING ON THE FAILURE BEHAVIOR OF LIQUID RUBBER-BASED CONCRETE UNDER STATIC TENSION

The effect of the aggregate size and grading on the tensile strength and fracture behavior of Liquid rubber-based concrete (LRBC) are analyzed by a numerical approach. A 2D FE model was constructed in which the aggregates are represented by random distributed polygon and the interfaces are the areas surrounding each aggregate. The mechanical parameters of the rubber matrix and the bonding properties between the rubber matrix and aggregate were experimentally determined. Compressive testing of the LRBC specimens was first carried out to provide experimental benchmark for calibration of the proposed numerical model. Numerical simulations on static tension were then carried out using 39 generated specimens and the tensile stress–strain curves were obtained. It was found that with the increasing aggregate size, the tensile strength of LRBC increased steadily while the failure strain decreased. The LRBC samples with multi-grading of aggregate exhibit better mechanical properties with the higher tensile strength and larger failure strain. Based on the numerical analysis, the optimized grading design of the LRBC was recommended.

Sphagnum re-introduction in degraded peatlands: The effects of aggregation, species identity and water table

In European peatlands which have been drained and cut-over in the past, re-vegetation often stagnates after the return of a species-poor Sphagnum community. Re-introduction of currently absent species may be a useful tool to restore a typical, and more diverse, Sphagnum vegetation and may ultimately improve the functioning of peatland ecosystems, regarding atmospheric carbon sequestration. Yet, the factors controlling the success of re-introduction are unclear. In Ireland and Estonia, we transplanted small and large aggregates of three Sphagnum species into existing vegetation. We recorded changes in cover over a 3-year period, at two water levels (?5 and ?20 cm). Performance of transplanted aggregates of Sphagnum was highly species specific. Hummock species profited at low water tables, whereas hollow species profited at high water tables. But our results indicate that performance and establishment of species was also promoted by increased aggregate size. This mechanism (positive self-association) has earlier been seen in other ecosystems, but our results are the first to show this mechanism in peatlands. Our results do not agree with present management, which is aimed at retaining water on the surface of peat remnants in order to restore a functional and diverse Sphagnum community. More than the water table, aggregate size of the reintroduced species is crucial for species performance, and ultimately for successful peatland restoration.

The influence of dispersing and stabilizing of indium tin oxide nanoparticles upon the characteristic properties of thin films

Stable suspensions of indium tin oxide nanoparticles were prepared by dispersing for 1 h in ethanol and stabilizing with 2-[2-(2-Methoxyethoxy)ethoxy]acetic acid. Particle size, morphology, and structure were characterized by a combination of dynamic light scattering, high resolution transmission electron microscopy, and X-ray diffraction. Spin coating of the stable suspensions resulted in densely packed films with a high transparency. Dispersing times exceeding 1 h led to a significant “overdispersing” effect, i.e. an increasing aggregate size of the suspensions was observed. Zeta-potential, pH, and X-ray photoelectron spectroscopy measurements were conducted to achieve a detailed understanding of the effect of “overdispersing”. With an increasing time of dispersion, i.e. with a decreasing stability of the suspensions, the thin films fabricated by spin coating displayed an increasing pore size distribution and surface roughness. In addition a strong decrease in transmittance and in conductivity was observed.

Aggregate Effects on Pervious Portland Cement Concrete Static Modulus of Elasticity

The effects of aggregate gradation, amount, and size on pervious portland cement concrete (PCC) static modulus of elasticity were compared using four different mixtures. A standard mix and three variable mixes using a uniform gradation, increased aggregate amount, and increased aggregate size were used. The effective air void content was determined for each mixture. The compressive strengths and static elastic moduli were determined and compared at equal void contents. For a uniform gradation, the compressive strengths and static elastic moduli appeared to be higher within an optimal range of voids; however, there was no statistically significant difference between the results from the different gradations. An increased aggregate amount resulted in a statistically significant decrease in both compressive strength and static elastic moduli due to the subsequent decrease in paste amount. While the compressive strengths were higher for mixtures containing smaller aggregate sizes, there was no significant difference between the static elastic moduli when different aggregate sizes were used. Further research is needed to understand the effects of aggregate size on the static modulus of elasticity of pervious PCC.

Quantification of Soil Aggregates Treated with Bituminous Emulsion and Other Organic Amendments by Using Scanning Electron Microscope

ABSTRACT Several organic amendments have been used for recovering soil physical properties that become worse when losses in soil organic matter take place. Bituminous emulsion has proved to be quite effective for improving aggregates, but the mechanisms involved are still unknown. This research aims to extend current knowledge about bituminous emulsions by using scanning electron microscopy in the quantification of aggregates. Two different soils (clay and sandy-loamy) were amended with emulsion bituminous and other organic amendments. Total and partial numbers (different-size fractions) of aggregates after 60-days of treatment, obtained by scanning electronic microscopy (SEM), were compared to aggregates percentages obtained by analytical methods. Water-soluble and EDTA-extractable fractions of the elements most likely involved in the aggregation processes were also determined. Better results in aggregate stability were obtained in the clay soil amended, which is probably due to a greater clay-organic matter interaction in this soil. While treatments having bituminous emulsion increased aggregate size and water-stability in both soils, treatments having organic matter caused formation of small low-stable aggregates in sandy soil and formation of stable aggregates in clay soil as showed the number of large aggregates, mean diameter, and total aggregated area. Bituminous emulsion seems to exert two effects in both soils: an hydrophobic effect which increases aggregate stability, and a colligating effect, favored by the clay content, which increases aggregate size. Organic matter seems to act by forming new aggregates from silt + clay particles, which are joined together by cation bridges.

Effects of carrot growing on volcanic ash soils in the Ohakune area, New Zealand

Effects of intensive carrot production on soils derived from young volcanic ash were determined at Ohakune, New Zealand. Erosion rates (derived from caesium-137) and key soil physical and chemical properties were determined in 3 fields with differing management history (6 and 16 years cropping) or topography (sloping and flat).Caesium-137 areal activity in cropped fields ranged from 90 to 2034 Bq/m2, compared with a reference value under long-term pasture of 602 Bq/m2. Mean areal activity was lower than the reference value in 2 sloping fields, but not in a flat field. Net erosion rates were low in both sloping fields (–16 and –5 t/ha.year), but within each field there was a wide range of erosion and deposition rates (–109 to +293 t/ha.year in Field 1 and –145 to +514 t/ha.year in Field 2). These very high rates imply total soil losses up to 238 mm and deposition up to 670 mm, consistent with observed elevation differences between the cropped fields and adjacent fields in long-term pasture and with topsoil depth variation from 145 to 1165 mm. Tillage erosion and deposition rates are high (up to c. 40 t/ha.year) but water erosion is the dominant mechanism of soil redistribution.Cropping has reduced organic matter and aggregate stability, increased bulk density in the lower part of the topsoil and subsoil, and increased aggregate size. Hydraulic conductivity was higher in the topsoil and lower in the subsoil under cropping than it was under pasture. However, it would not limit soil water movement as it was higher than typical rainfall intensities. Compacted wheel tracks were the primary control on runoff and erosion as they have low infiltration rates (4 mm/h) compared with carrot beds (853 mm/h).

Cadmium Sulfide Aggregates through Reverse Micelles

CdS aggregates, composed of primary nanocrystalline particles, were synthesized in cyclohexane‐sorbitan monooleate (Span 80) reverse micelles at 80°± 1°C under mechanical agitation and sonication with varying Cd2+ concentrations in the solutions. The critical micelle concentration (CMC) of the surfactant Span 80 in cyclohexane was determined from discernible breaks in the surface tension and optical (ultraviolet) absorbance versus surfactant concentration curves. The synthesized aggregates were characterized using transmission electron microscopy, X‐ray diffractometry, particle‐size analysis, Fourier‐transform infrared spectroscopy, and thermal analyses. The generated aggregates exhibited the characteristic green emission at 520 nm. A minor decrease in emission intensity with increased aggregate size at the same wavelength was observed.