Decrease In Aggregate Size Research Articles

Study of the precipitation trend of asphaltenes and waxes in crude oil using computational chemistry and statistical thermodynamics methods

Asphaltenes aggregation and waxes in petroleum were simulated considering five molecular structures containing functional groups: asphaltenes, resins, and non-polar hydrocarbons in a heavy oil crude. The properties of molecules were calculated using the density functional theory. The van der Waals constants associated with the pairwise interactions and the Hamaker constants for the dispersed phase (formed by asphaltenes and waxes) and the dispersion medium (created by non-polar hydrocarbons) were estimated. Sparse pass size as a function of its composition is calculated using Qyle groups and the Young–Laplace equation. We also assessed the potential colloidal pair corresponding to the interactions between the asphaltene and resin aggregates for different dispersion media, the attractive energies between the asphaltene molecules (−60 10–20 J ≈ ) are more than twice as high as the attractive energies concerning the rest of the molecules present ( × -30–10] 10–20 ≈ × J). It is predicted that attraction energy between the aggregates decreases with the increase of the presence of resin in the dispersed phase, This is explained by the fact that the increase in the concentration n of resin can lead to a decrease in the relative size d of the aggregates by up to 90 % (for n = 0.1, d = 0.1 and for n = 0.9, d = 0.1). This decrease in aggregate size is manifested in a theoretically calculated effective viscosity reduction of up to 50 %.

Study on mesostructure and stress–strain characteristics of pervious concrete with different aggregate sizes

This work aimed to study the mesostructure and compressive behavior of pervious concrete (PC) with different aggregate sizes, and to explore the mechanism responsible for the resulted performance. The mesostructure of PC was quantitatively evaluated, including the distribution of internal voids, the distribution of aggregates and the thickness of cement paste using image processing technology. In addition, the full stress–strain curve of PC was obtained by the uniaxial compressive strength test, in which the uniaxial stress–strain characteristics and the whole process of compressive failure was assessed. The results show that the larger the particle size of the aggregate, the fewer the number of voids, and the larger the average diameter of voids. The aggregate distribution in PC with different aggregate sizes is different, but is approximately uniformly distributed. The cement paste thickness of the PC studied in this paper ranges from 0.4 to 0.7 mm. With the same cement content and different aggregate composition, the thickness of cement paste gradually decreases with the decrease of aggregate size. It is found that the stress–strain curve of PC has the same change trend as that of ordinary concrete, and it is a biased unimodal curve. Furthermore, the failure of the PC is proved to be a shear failure. During the destruction of PC, the aggregate is also destroyed which is different from the damage of ordinary concrete.

Influence of Mesoscopic Structural Characteristics of Asphalt Mixture on Damage Behavior of Asphalt Pavement

Mechanical responses and damage behaviors of asphalt pavement are closely associated with the mesostructure characteristics of the asphalt mixture. The aim of this research was to investigate the effect of the different mesostructure characteristics of asphalt mixtures on pavement damage behavior through a multiscale finite-element (FE) analysis method. A two-dimensional (2D) random aggregate generation algorithm was used to construct the mesostructures of asphalt mixtures with different characteristics, including aggregate distribution uniformity, shape, volume fraction, and size range. Bilinear cohesive elements were used to model damage initiation within asphalt pavement. Also, the nonuniformity coefficient (NUC) was applied to evaluate the uniformity of aggregate distribution within asphalt pavement. The results indicated that the NUC could well characterize the uniformity of coarse aggregate distribution in pavement, and the damage initiation zone became larger as the NUC increased. Compared with regular aggregates, irregular shape aggregates led to more damage initiation in asphalt pavement. For regular shape aggregates, the damage initiation zone became smaller as the aggregate shape approached the circle. In addition, the decrease of aggregate size and volume fraction could increase the possibility of “top-down” cracking of pavement.

Eight-year impacts of conservation agriculture on soil quality, carbon storage, and carbon emission footprint

The conventional method of intensive tillage alters the soil environment, destroys soil aggregates, depletes soil organic carbon (SOC), emits more carbon, requires higher energy, alters microbial activities and ultimately degrades the soil health. These ill-effects of conventional tillage can be severe in rainfed soils with poor workability such as Vertisols of Central India. To minimize these negative effects of conventional tillage (CT), conservation agricultural (CA) practices such as reduced tillage (RT) and no-till (NT) with crop residue retentions are advocated as sustainable practices that can improve the soil health. Four cropping systems [soybean+pigeonpea (CS1); soybean–wheat (CS2); maize–chickpea (CS3); maize+pigeonpea (CS4)] were established as sub-plots under CT, RT and NT management. Soil samples were collected at 0–10 cm, 10–20 cm and 20–30 cm depths. The effects of 8 years of continuous use of CA were evaluated on soil physical, chemical and biological properties in Vertisol of Central India. After that, 20 key soil properties were subjected to calculating soil quality indices (SQI) in each tillage systems. Results indicated that mean weight diameter (MWD) and water-stable aggregates (WSA) were significantly higher (P < 0.05) in NT (1.57 mm and 79.4%) and RT (1.05 mm and 76.2%) than CT (0.71 mm and 63.8%) at 0–10 cm depth, respectively. The soil under NT had the highest SOC concentration (1.12%) followed by that under RT (1.02%), and the least was found in CT (0.91%) at 0–10 cm depth. The proportion of large macro-aggregates (LM) was the highest under NT than CT (P < 0.05) whereas that of micro-aggregates was highest under CT. The aggregate associated organic C (AOC) tended to decrease with the decrease of aggregate size. Soil dehydrogenase activity, fluorescein diacetate hydrolysis activity, β-glucosidase activity and easily extractable glomalin content were significantly higher under NT than CT (P < 0.05). The soil quality index was significantly highest in NT, followed by RT and CT at all soil depths. CA based practices favoured carbon storage, lowered carbon emission, foot print and soil quality compared to conventional farming. Therefore, under Vertisols, 8 years of CA practices likely to improve several soil quality indicators, allowing a positive trend for soil preservation.

Effects of nitrogen fertilizer on soil microbial residues and their contribution to soil organic carbon and total nitrogen in a rice-wheat system

Soil microbial residues have an impact on the stability of the soil organic carbon (SOC) pool, since they are crucial and stable sources of SOC. However, it is not clear how soil microbial residues in aggregates affect the SOC and total nitrogen (TN) at different gradients of N fertilization. Therefore, we investigated the effect of N fertilizer on microbial residues and their contribution to SOC and TN in soil aggregates under a rice-wheat (Oryza sativa-Triticum aestivum) system with four rates of N fertilizer. The results indicated that the addition of N fertilizer clearly increased the phospholipid fatty acids of bacteria and enhanced the activities of soil enzymes (β-1,4-glucosidase, β-N-acetyl-glucosaminidase and phenol oxidase) in the macroaggregates. The content of bacterial residual carbon increased noticeably when N fertilizer was added, while the content of fungal residual carbon did not appear to change. The addition of N fertilizer increased the contribution of bacterial residual carbon to SOC and TN. There was no significant difference in the contribution of bacterial residues on SOC and TN at different N fertilizer rates. Nevertheless, their contribution gradually decreased with the decrease in aggregate size. Structural equation modeling showed that the contribution of soil microbial residue to TN was influenced by activities of soil enzymes, suggesting that N is an important factor that affects soil ecology and limits the availability of nitrogenous organic matter in agroecological systems. This finding is crucial to understanding how N fertilizer influences soil C and N cycle in rice-wheat systems.

Interaction forces and suspension characteristics in an oscillatory membrane photocatalytic reactor

The effects of the interaction between the hydrodynamic and colloidal forces on the suspension and performance characteristics of a slurry photocatalytic reactor equipped with oscillatory membrane and lateral turbulence promoters are investigated. Aggregation of catalyst particles is influenced by the magnitude of colloidal forces between the particles in relation to the hydrodynamic stresses acting on the aggregate. The interaction of the axial oscillatory shear with the transverse motion of the turbulence promoters (TP) results in generation of vortices and eddies that extended further away from the membrane surface leading to reducing particle aggregation. For the range of oscillatory conditions investigated, the aggregate size remained in the viscous subrange and decreased with increasing the oscillation intensity where an almost three folds decrease in aggregate size was achieved at high oscillation intensities. This resulted in reducing particles settling and deposition on the membrane surface which increased the catalyst specific area and volume fraction in suspension and enhanced both membrane flux and reaction rates. Improvement of the latter is also achieved by the microscale eddies attenuation of the concentration boundary layer surrounding the catalyst particles which results in better mass transfer. Using methylene blue dye (MB) degradation with ZnO photocatalyst under UV illumination as a model photocatalytic reaction, the investigation showed that increasing the oscillation intensity resulted in higher membrane flux and reaction rates that asymptotically approached maximum corresponding to near maximum catalyst suspension. This was estimated based on the magnitude of the eddy forces in the suspension in relation to the sedimentation and permeate drag forces acting on the catalyst particles. Comparison between the results of the present investigation and data from the literature showed satisfactory agreement.

Impact of vegetation restoration on soil organic carbon stocks and aggregates in a karst rocky desertification area in Southwest China

The objectives of the study were as follows: (a) to determine the response of soil organic carbon (SOC) fractions to vegetation restoration; (b) to examine the contributions of aggregate-associated OC to total soil OC accumulation along vegetation restoration, (c) to identify the factors that affect SOC accumulation along natural vegetation restoration in a karst region in Southwest China. Four vegetation restoration stages, namely, grassland, shrubland, shrub-arbor mixed forestland, and arbor forestland, were compared with cropland (CL). Soil samples were collected at depths of 0–10 cm and separated into five aggregate size fractions. SOC, light fraction OC (LFOC), easily oxidizable OC (EOC), and aggregate-associated OCs were determined for different aggregate sizes and total soil. Natural vegetation restoration increased macroaggregate amount but decreased the fractions of meso- and microaggregates. Vegetation restoration significantly increased total SOC, EOC, and LFOC concentrations and stocks and soil aggregate-associated OC concentrations. The responses of EOC and LFOC in total soil and soil aggregates were more sensitive than those of SOC along with vegetation restoration. Aggregate-associated OC concentrations generally increased with a decrease in aggregate size. Macro- and microaggregate-associated OC stocks increased, but mesoaggregate-associated OC stocks decreased following the conversion of CL to a natural vegetation ecosystem. The increase in SOC stocks was primarily attributed to the macroaggregate-associated OC stocks and their changes. OC concentrations and stocks in total soil and the soil aggregates were significantly positively related to exchangeable calcium content. Vegetation restoration considerably affects the amount of soil aggregates, OC concentrations, and stocks in total soil and soil aggregates. Changes in OC concentrations and stocks can be more pronounced in the liable carbon fraction than in total SOC. The increase in SOC was mostly attributed to OC accumulation in macroaggregates. Exchangeable calcium also affected soil OC accumulation in total soil and soil aggregates.

Gel properties of salty liquid whole egg as affected by preheat treatment.

Heat treatment is an indispensable processing step of seasoned liquid egg. The effects of preheat treatment (60-75°C) on gel properties of liquid whole egg (LWE) at different NaCl concentrations (0-3%, w/w) were investigated to provide guidance for the production of salty LWE. Results showed that LWE exhibited higher particle size after heating, with coincidental increases in surface hydrophobicity and decreases in protein solubility. While LWE with NaCl added exhibited increase in protein solubility and decrease in particle size of aggregates. Electrophoresis and optical microscopy showed that NaCl would induce the transformation of egg granules from insoluble form to soluble form, inhibiting the aggregation of LWE proteins during preheat treatment, reflected by the reduced particle size. The analysis of gel aggregated force and texture indicated that NaCl addition and preheat treatment can improve gelling properties of LWE synergistically by strengthening the hydrophobic interaction and hydrogen bonds.

Deforestation effects on soil aggregate stability quantified by the high energy moisture characteristic method

Soil aggregate size distribution and structure stability are important soil physical quality indices. The objective of this study was to quantify soil structure stability as a result of land-use conversion from forest to tea farm within Guilan Province of northern Iran over the past 50 years. Soil aggregate or structure stability metrics, along with more common soil chemical and physical properties, were determined on triplicate soil samples (0–30 cm depth), randomly collected from six sites. Dexter's S-index (slope of soil water retention curve at its inflection point), tensile strength (TS), aggregate mean weight diameter (MWD), and water stable aggregate (WSA) were also used to assess stability. Lastly, the high energy moisture characteristic (HEMC) method measured the destructive force used to break the aggregates through controlled wetting. Structure stability using HEMC method and S-index was determined based on the soil water retention curve but using different ranges of matric potentials. The results showed that despite an insignificant decrease in TS, WSA and MWD between land use types there was significant correlation (P < 0.05) between tensile strength with HEMC method's, stability ratio (SR) and Dexter's S-index. The volume of drainable pores after fast wetting of aggregates (fast-VDP) in HEMC method reflected a significant (P < 0.01) decrease in aggregate size between forest and tea farms with means of 0.347 and 0.297 g g−1, respectively. In only one of six locations, the soil water retention curves and the aggregate stability indexes (SI and SR) of HEMC method decreased significantly after land use change. Our results indicated that macro aggregates and structure stability in HEMC method could distinguish differences between two land uses and better than previous methods like MWD, WSA, and TS. The results of S-index and stability ratio of HEMC method were different. This difference can be related to: 1) the soil initial aggregate size that is between 0.5 and 1 mm in HEMC method and about 4 mm in Dexter's S-index and 2) the range of matric potential in each method that is 0 to 50 and 0 to 15,000 hPa in HEMC and S-index, respectively. Although both methods are based on soil water retention curve to estimate soil structure stability and physical quality, but HEMC results show macrostructure stability (macro aggregates) whereas S-index is inflection point of soil water retention curve between textural and structural porosity and estimate microstructure stability.

Hemicellulosic Polysaccharides Mimics: Synthesis of Tailored Bottlebrush-Like Xyloglucan Oligosaccharide Glycopolymers as Binders of Nanocrystalline Cellulose.

We report in this contribution that while low molecular weight hemicellulosic building blocks are known not to interact with cellulosic materials, their multivalent presentation on a polymeric scaffold significantly enhanced the binding interactions that are remarkably in the same range as those usually observed for lectin-carbohydrate interactions. We developed a poly(propargyl methacrylate) scaffold on which we conjugated, by "post-click" reaction, a variety of azide reducing-end functionalized xyloglucan oligosaccharides with controlled enzymatic-mediated rate of degalactosylation. Bottlebrush-like xyloglucan oligosaccharide glycopolymers (poly(XGOn)) were obtained and their self-assemblies in aqueous solution were investigated using dynamic light scattering (DLS). We demonstrated that increasing the extent of degalactosylation promoted self-association of poly(XGOn), which we attribute to the appearance of hydrophobic domains. A sharp thermoresponsiveness, which corresponds to a decrease in aggregate size with increasing temperature, was observed when the extent of degalactosylation was 30% or greater. Importantly, isothermal titration calorimetry (ITC) and polarized/depolarized DLS revealed that poly(XGOn) exhibit a significant capacity to interact with nanocrystalline cellulose (NCC) surfaces particularly for the nondegalactosylated form, emphasizing the important role of galactosyl residues in the binding mechanism and in the 3-dimensional structures of glycopolymers.

Effects of Nominal Maximum Aggregate Size on the Performance of Stone Matrix Asphalt

It is well known that the performance of hot mix asphalt (HMA) in service life is closely related to a proper aggregate gradation. A laboratory study was conducted to investigate the effects of nominal maximum aggregate size (NMAS) on the performance of stone matrix asphalt (SMA). The volumetric characteristics and performance properties obtained from wheel tracking tests, permeability test, beam bending test, contabro test are compared for SMA mixes with different NMAS. The results indicated that voids in mineral aggregate (VMA) and voids filled with asphalt (VFA) of SMA mixtures increased with a decrease of aggregate size in aggregate gradation. SMA30 had the lowest optimum asphalt content among all the mixtures. Increase of NMAS contributed to improvement of the rutting resistance of SMA mixtures. However, a decrease of NMAS showed better cracking and raveling resistance. Permeability rate of SMA was primarily affected by the air voids (AV) and break point sieve, but was also sensitive to aggregate gradation to some extent, with reduced NMAS corresponding to less permeability rate. Based on the test results, SMA5 and SMA13 are suggested to be used as a water-proof layer in bridge deck pavement, and SMA20 and SMA30 are suggested to be used as binder course in asphalt pavement, which needs to possess superior rutting resistance at high temperature.

Soil Quality after Six Years of Paper Mill Industrial Wastewater Application

The application of wastewater to irrigate soils may be an attractive option for paper mills, especially when the effluents can also provide nutrients to plants. Since there could be negative environmental effects, such activity must be preceded by a thorough evaluation of the consequences. The changes in soil quality of a Neossolo Fluvico Distrofico (Typic Udifluvent) were evaluated over a period of six years of irrigation with treated effluent from a wood pulp company. Although effluent application for six years did not affect soil resistance to penetration and soil hydraulic conductivity, it promoted a decrease in the mean size of aggregates and an increase in clay dispersion. Effluent application increased soil pH but did not change exchangeable Ca and Mg contents and organic carbon. After a full rotation of eucalyptus cultivation common in Brazil (six years), no negative effects in tree growth were found due to effluent irrigation. However, effluent addition caused higher values of Na adsorption ratio and intermediate electrical conductivity in the soil, which indicates a possible negative effect on soil quality if the application continues over a longer period. Therefore, a monitoring program should be carried out during subsequent crop rotations, and alternatives must be studied to obtain better effluent quality, such as adding Ca and Mg to the wastewater and using gypsum in the soil.

Heat-Induced Aggregation Properties of Whey Proteins as Affected by Storage Conditions of Whey Protein Isolate Powders

The control of storage as any other manufacturing steps of dairy powders is essential to preserve protein functional properties. This study aimed to determine the effects of different storage conditions on both protein denaturation and protein lactosylation in whey protein isolate (WPI) powder, and also on heat-induced aggregation. Two different storage temperature conditions (20 and 40 °C) were studied over 15 months. Our results showed that protein lactosylation progressively increased in WPI powders over 15 months at 20 °C, but heat-induced aggregation properties did not significantly differ from non-aged WPI. On the other hand, powders presented a high level of denaturation and aggregation at 40 °C from the first 2 weeks of storage, involving first protein lactosylation and then aggregation in the dry state. This was correlated with an increasing Browning Index from 15 days of storage. These changes occurred with a decrease in aggregate size after heat treatment at 5.8 ≤ pH ≤ 6.6 and modification of heat-induced aggregate shapes.

Aggregate densification in the thickening of flocculated suspensions in an un-networked bed

Experimental data from batch settling tests on polymer flocculated suspensions was used to determine the material properties that quantify dewatering behaviour and relate settling rate to solids concentration. These material properties were subsequently used to predict the performance of a pilot-scale gravity thickener, including the expected solids concentration profile in the thickener. Analysis of data from a novel laboratory fluidisation rig, used to simulate the hindered settling zone of a thickener, and the pilot-scale thickener, indicates that relative to simple batch settling tests, the dewatering behaviour and related material properties of flocculated aggregates change over time, even at concentrations less than the gel point of the suspension and in the absence of mechanical shear. The change is primarily attributed to the phenomenon of aggregate densification as a result of aggregate-aggregate buffeting and manifests as enhanced settling and increased thickener throughput. A fluidisation case study using calcite with no added mechanical shear (only that due to fluidisation) found that the aggregates densified to 86% of their original diameter over a period of order 4000s. This was enhanced with the addition of mechanical shear with a further decrease in aggregate size to 76% of their original diameter. Almost identical results were observed for the pilot thickener. Laboratory data typically underestimates thickener performance, even at the pilot scale, and the agreement between laboratory and pilot results represents a novel outcome for the characterisation of material dewatering properties. The observations herein are an important step towards full-scale thickener modelling incorporating aggregate densification effects due to shear.

Is truffle brûlé a case of perturbational niche construction?

Aim of study: in the context of niche construction theory, the investigation was aimed at assessing if truffle brûlé is a case of niche construction by testing if the disappearance of grasses in the brûlé induces a non-arbitrary perturbation in the soil physical environment and, in that case, which are the physical processes involved.Area of study: a natural truffle bed located in the Italian Apennines inside an experimental truffle-producing area of the University of Perugia.Material and methods: Three aggregate size classes in the soil of a brûlé and of the neighbouring grass-covered area were determined with the wet-sieving technique in accordance with international standards. In the first part of the investigation, the area was sampled according to a systematic sampling design and the spatial patterns of aggregate size classes in the brûlé and in the neighbouring grass-covered area were compared by means of geostatistics. In the second part, the suppression of grasses in the brûlé was mimicked in the laboratory by removing roots from a sample collected in the grass-covered area and the effect of freeze-thaw cycles was tested by comparing a control treatment to other four treatments consisting in sub-samples equilibrated at a water tension of -2.5, -5, -10 and -20 kPa. Samples were submitted to a number of freeze-thaw cycles equal to those recorded in the area, analysed for aggregate size distribution and compared with univariate ANOVA.Main results: The aggregate size classes larger than 0.25mm displayed a spatial pattern comparable to that of the brûlé, with sharp changes along the boundaries of the brûlé itself. The laboratory experiment showed that such changes are attributable to freeze-thaw cycles that in one winter season may produce a significant decrease in aggregate size compared to the grass-covered area. Both results indicate that the disappearance of grasses in the brûlé fulfils the requirement of perturbational niche construction.Research highlights: the observed change of soil aggregation in the brûlé can be useful in delineating soils suitable for truffle farming and in creating suitable soil physical conditions for truffle production by exploiting freeze-thaw cycles after irrigation in winter.Keywords: aggregates; brûlé; niche construction; Tuber, soil structure.

Experimental Study on the Air-Cooling of Concrete Aggregate

The temperature distribution and the flow resistance of air-cooled concrete aggregate are investigated in order to provide engineering guidance for the energy economization and design optimization. First, an aggregate bin is down-scaled and installed on an indoor experiment table, then tests are performed for different aggregate sizes and different inlet air velocity, with or without upper air duct. The results show that with the decrease of aggregate size, the temperature distribution turns more uniform, but the flow resistance increases; with the increase of wind velocity, the cooling rate is enhanced, but meanwhile the flow resistance is increased. So for different size of aggregates, an optimal wind velocity exists. Having an upper air duct not only enhances the cooling rate but also increases the cooling uniformity.

Characterization of Soil Organic Matter in Aggregates and Size-Density Fractions by Solid State 13C CPMAS NMR Spectroscopy

Understanding the changes in soil organic matter (SOM) composition during aggregate formation is crucial to explain the stabilization of SOM in aggregates. The objectives of this study were to investigate (i) the composition of SOM associated with different aggregates and size-density fractions and (ii) the role of selective preservation in determining the composition of organic matter in aggregate and size-density fractions. Surface soil samples were collected from an Alfisol on the Northern Tablelands of NSW, Australia, with contrasting land uses of native pasture, crop–pasture rotation and woodland. Solid-state 13C cross-polarization and magic angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectroscopy was used to determine the SOM composition in macroaggregates (250–2000 μm), microaggregates (53–250 μm), and <53-μm fraction. The chemical composition of light fraction (LF), coarse particulate organic matter (cPOM), fine particulate organic matter (fPOM), and mineral-associated soil organic matter (mSOM) were also determined. The major constituent of SOM of aggregate size fractions was O-alkyl carbon, which represented 44–57% of the total signal acquired, whereas alkyl carbon contributed 16–27%. There was a progressive increase in alkyl carbon content with decrease in aggregate size. Results suggest that SOM associated with the <53-μm fraction was at a more advanced stage of decomposition than that of macroaggregates and microaggregates. The LF and cPOM were dominated by O-alkyl carbon while alkyl carbon content was high in fPOM and mSOM. Interestingly, the relative change in O-alkyl, alkyl, and aromatic carbon between aggregates and SOM fractions revealed that microbial synthesis and decomposition of organic matter along with selective preservation of alkyl and aromatic carbon play significant roles in determining the composition of organic matter in aggregates.

Surfactant Self-Assembly in Cylindrical Pores: Insights from Mesoscale Simulations

Motivated by the inconclusive results of three small-angle neutron scattering experiments on nonionic surfactants adsorbed in nanoporous silica, we determine the structure of the surfactant aggregates by computer simulations and provide a deeper understanding of the self-assembly mechanism. The experiments showed that surfactants adsorbed into the nanometer-sized cylindrical pores of SBA-15 self-assemble into aggregates that are far smaller than bulk aggregates. Their morphology has been assumed to depend on the hydrophilicity of the pores. Because of the limited resolution of the scattering experiments, a detailed analysis of the morphological changes was not feasible. Here we show that our mesoscale simulations reproduce the experimental findings and also allow us to study the subtle interplay between aggregation and adsorption. We find that increased adsorption in more hydrophilic pores leads to an increase in the effective area required by the surfactant head groups and consequently to a decrease in aggregate size.

Long-Term Phosphorus Application Impacts on Aggregate-Associated Carbon and Nitrogen Sequestration in a Vertisol in the Mediterranean Turkey

Fertilizers are among major contributors to the production of aboveground and belowground biomass. Soil organic carbon (SOC) concentration is an important factor affecting crop productivity in semiarid clayey soils of low fertility. A long-term experiment was established in 1998 on a Vertisol in the Mediterranean coast of Turkey, to assess the effects of four rates of application of inorganic phosphorus (P) fertilizers (0, 50, 100, and 200 kg P2O5 ha−1) on soil bulk density (ρb), carbon (C) and nitrogen (N) concentrations, SOC and N pools, C and N sequestration rate, aggregate fractions, water-stable aggregates, and the mean weight diameter (MWD). Thus, disturbed and undisturbed soil samples were collected from the 0- to 15-cm depth after wheat (Triticum aestivum L.) harvest in June 2010 to analyze soil properties. Increase in the rate of application of P fertilizers significantly increased ρb and reduced porosity (%). The SOC concentration was significantly more in the treatment receiving 200 kg P2O5 ha−1 than in the control. The carbon-nitrogen ratio was less than 10 in control and greater than 10 in high P fertilizer treatments. Total amount and rate of C and N sequestration increased with increase in the rate of application of P fertilizers. The mean rate (kg C ha−1 y−1) of C sequestration was −110.9 for control and 556.9 for the highest rate of P fertilizer. Increase in fertilizer rate also significantly increased the rate (kg N ha−1 y−1) of N sequestration, which was −0.21 for control and 28.9 for the highest rate of P fertilizer treatment. The SOC concentrations differed among aggregate-size fractions, which were greater in 0.5- to 2.0-mm aggregate size than those in the fraction of less than 0.25 mm. Greater SOC concentrations were observed in 1- to 2-mm and 0.5- to 1-mm size fractions than in fractions of less than 0.25 mm. Concentrations of C and N decreased significantly with decrease in aggregate size of less than 0.25 mm. There was a general trend of increase in water-stable aggregates and MWD with increase in application of P fertilizer. The highest MWD (1.81 mm) was observed in the high P rate and lowest (1.36 mm) in the control. Macroaggregates were more enriched in C and N than microaggregates. The mean rate of SOC sequestration with 200 kg P2O5 ha−1 treatment is ∼560 kg C ha−1 y−1. The effects of long-term P fertilizer application on C and N sequestration finding(s) of from this study have not been previously observed.

Amelogenin–enamelin association in phosphate‐buffered saline

The structures and interactions among macromolecules in the enamel extracellular matrix play vital roles in regulating hydroxyapatite crystal nucleation, growth, and maturation. We used dynamic light scattering (DLS), circular dichroism (CD), fluorescence spectroscopy, and transmission electron microscopy (TEM) to investigate the association of amelogenin and the 32-kDa enamelin, at physiological pH 7.4, in phosphate-buffered saline (PBS). The self-assembly behavior of amelogenin (rP148) was altered following addition of the 32-kDa enamelin. Dynamic light scattering revealed a trend for a decrease in aggregate size in the solution following the addition of enamelin to amelogenin. A blue-shift and intensity increase of the ellipticity minima of rP148 in the CD spectra upon the addition of the 32-kDa enamelin, suggest a direct interaction between the two proteins. In the fluorescence spectra, the maximum emission of rP148 was red-shifted from 335 to 341 nm with a marked intensity increase in the presence of enamelin as a result of complexation of the two proteins. In agreement with DLS data, TEM imaging showed that the 32-kDa enamelin dispersed the amelogenin aggregates into oligomeric particles and stabilized them. Our study provides novel insights into understanding the possible cooperation between enamelin and amelogenin in macromolecular co-assembly and in controlling enamel mineral formation.