Search

Neptunea cumingii is an important nutrition-rich economic species in China. Juveniles of N. cumingii suffer from high mortality at low temperatures, which has proved a limiting factor in raising seedlings in artificial habitats. Previous research has shown that N. cumingii displays aggregation behavior in response to adverse environmental changes. Therefore, we determined the effects of temperature, food, size of juvenile snails, substratum type, and density of juvenile snails on the aggregation behavior of N. cumingii. Results show that, at a low (4°C) or a high (22°C) temperature, juvenile snails adjusted to the inhospitable environment by exhibiting increased aggregation behavior. However, their aggregation behaviors differed at these two temperatures. There was no significant difference in the aggregation rate, but the typical aggregation size was larger at 4°C than at 22°C. At 10°C or 16°C, aggregation behavior of juvenile snails reduced. Aggregation increased in the satiation treatment at 10°C and 16°C. Small-sized juveniles tended to have higher aggregation rates (92.22%) and a larger typical aggregation size. More juveniles were distributed in the bottom of shaded substrata. A larger typical aggregation size or higher density significantly reduced the mortality of juvenile snails at a low temperature (4°C). These results broaden our understanding of gastropod aggregation behavior and can be used to develop and improve commercial breeding strategies and resource recovery for N. cumingii.

The aggregation of amyloid-𝛽 (A𝛽) proteins through their self-assembly into oligomers, fibrils, or senile plaques is advocated as a key process of Alzheimer's disease. Recent studies have revealed that metal ions play an essential role in modulating the aggregation rate of amyloid-𝛽 (A𝛽) into senile plaques because of high binding affinity between A𝛽 proteins and metal ions. In this paper, we proposed a mathematical model as a set of coupled kinetic equations that models the self-assembly of amyloid-𝛽 (A𝛽) proteins in the presence of metal ions. The numerical simulations capture four timescales in the A𝛽 dynamics associated with three important events which include the formation of the amyloid-metal complex, the homogeneous aggregation of the amyloid-metal complexes, and the non-homogeneous aggregation of the amyloid-metal complexes. The method of singular perturbation is used to identify these timescales in the framework of slow-fast systems.

To gain insight into the colloidal stability in the presence of proteins, we measured the electrophoretic mobility and aggregation rate constant of silica particles coated with lysozymes, and the adsorbed amount of lysozymes on the silica. We also examined model analyses, which are based on the Derjaguin, Landau, Verwey, and Overbeek theory with the effect of charge heterogeneity, to discuss the aggregation of lysozyme-coated silica. Our results show that lysozymes enhance the aggregation of silica when the lysozyme-coated silica is near the isoelectric point. When the adsorbed amount of lysozyme is low, the effect of charge-patch attractive force promotes the aggregation of silica. The effect of charge heterogeneity weakens with the increase of adsorbed amount of lysozyme. Our model which takes account of the effect of charge heterogeneity can capture the trend of the aggregation of silica in the presence of lysozyme qualitatively, but there are also large quantitative discrepancies between the theoretical prediction and experimental results. Further improvement is required to describe realistic charge heterogeneity and the effect of the surface coverage of lysozyme on the silica.

Molecular dynamics simulations are used to investigate the aggregation and behavior of two parallel graphene sheets (22.0–64.0 A in length) in dodecane. The dodecane layer formed on the graphene surface leads to an energy barrier which slows the rate of the graphene aggregation process when the two sheets are totally separated by dodecane molecules. The graphene sheets aggregate in dodecane only when portions of one graphene sheet are in contact with another sheet. The aggregation rate depends on the combined structures of the two graphene sheets. The aggregation rate for two parallel graphene sheets in half contact with one another is constant since the relative sheet geometry and spacing are nearly constant in the transition region between sheets where dodecane molecules are being displaced during aggregation. The aggregation rate for partially overlapped graphene sheets becomes progressively slower as aggregation continues since the area not overlapped decreases as the aggregation proceeds.

The kinetics of slow aggregation and disag- gregation of the plate-shaped TiO2 nanocrystals in aqueous HCl solutions at room temperature was studied using tur- bidimetry and small-angle X-ray scattering. The rate of slow aggregation of the diluted TiO2 hydrosols with 0.3 B pH B 3 was compared. The sols with pH about 1 were the most stable and the aggregation rate increased at the decrease of pH from 1 to 0.3 and at the increase of pH from 1 to 3. The reversible loose aggregates slowly formed at the low pH, while the more stable aggregates grew at higher pH.

We consider ballistic aggregation equation for gases in which each particle is iden- ti?ed either by its mass and impulsion or by its sole impulsion. For the constant aggregation rate we prove existence of self-similar solutions as well as convergence to the self-similarity for generic solutions. For some classes of mass and/or impulsion dependent rates we are also able to estimate the large time decay of some moments of generic solutions or to build some new classes of self-similar solutions.

In experiments on rats of the Wistar line and on spontaneously hypertensive animals of the SHR line, a complex study was performed of rheological (deformability and aggregation properties) and hematological parameters of erythrocytes at the single (40 min) and multiple (20–30 min for 7 and 14 days) exercise load (a forced tredmill running at a rate of 14 m/min). It has been shown that rats of both lines respond to the single, sufficiently light exercise load by a manifestation of stress-reaction. After the repeated exercise load, all stress-induced changes were leveled and replaced by adaptation to this action in Wistar rats, but not in the SHR line rats. The hypertensive rats were characterized by a greater fatigue and refusal of the tredmill running; therefore, this load to them had to be shortened to 20 min. For the 1st week of running, no statistically significant differences in the studied parameters were found between rats of the Wistar and SHR lines; however, by the 14th day of training, substantial differences between these lines were noticed: the Wistar rats were easily adapted to the tredmill running, whereas the SHR animals completely refused to run. At the single running, the stress-polycythemia, an increased hematocrit, a decreased hemoglobin concentration per erythrocyte, an increased plasma corticosterone level, and changes of blood rheological characteristics were shown, the erythrocyte deformability and the spontaneous aggregation rate under the stress conditions being in the direct positive correlational dependence that was absent in control. The Wistar rat training to the exercise load for 14 days led to normalization of the parameters, which indicates a favorable effect of trainings on the animal health state.

We have systematically studied the effects of 40 single point mutations on the conversion of the denatured form of the alpha/beta protein acylphosphatase (AcP) into insoluble aggregates. All the mutations that significantly perturb the rate of aggregation are located in two regions of the protein sequence, residues 16-31 and 87-98, each of which has a relatively high hydrophobicity and propensity to form beta-sheet structure. The measured changes in aggregation rate upon mutation correlate with changes in the hydrophobicity and beta-sheet propensity of the regions of the protein in which the mutations are located. The two regions of the protein sequence that determine the aggregation rate are distinct from those parts of the sequence that determine the rate of protein folding. Dissection of the protein into six peptides corresponding to different regions of the sequence indicates that the kinetic partitioning between aggregation and folding can be attributed to the intrinsic conformational preferences of the denatured polypeptide chain.

Preliminary results of an aggregation model that takes into account both the Brownian motion as well as the gravitational drift experienced by the colloidal particles and clusters is presented. It is shown that for high strengths of the drift the system crosses over to a regime different from diffusion-limited colloid aggregation, for which there is an increase of the fractal dimension, a speeding up of the aggregation rate and a widening of the cluster size distribution, becoming algebraically decaying with an exponent τ.

THE aggregation of colloidal particles is of fundamental importance in colloid science and its applications. The recent application of scaling concepts1,2 has resulted in a much deeper understanding of the structure of colloidal aggregates and the kinetics of their formation. Two distinct, limiting regimes of irreversible colloid aggregation have been identified3. Diffusion-limited colloid aggregation occurs when there is negligible repulsive force between the colloidal particles, so that the aggregation rate is limited solely by the time taken for clusters to encounter each other by diffusion. Reaction-limited colloid aggregation occurs when there is still a substantial, but not insurmountable, repulsive force beween the particles, so that the aggregation rate is limited by the time taken for two clusters to overcome this repulsive barrier by thermal activation. These regimes correspond to the limiting cases of rapid and slow colloid aggregation that have long been recognized in colloid science4. An intriguing possibility suggested by recent work is that each of these limiting regimes of colloid aggregation is universal, independent of the chemical details of the particular colloid system. Here we investigate the aggregation of three chemically different colloidal systems under both diffusion-limited and reaction-limited aggregation conditions. A scaling analysis of light-scattering data is used to compare the behaviour and provides convincing experimental evidence that the two regimes of aggregation are indeed universal.