Correlated nucleation model for simulating nanocluster pattern formation on Si(111)7 × 7 surface

We study the aggregation mechanisms of metal nanoclusters on the Si(111)7 × 7 reconstructed surface using a correlated nucleation model, in which the nucleation and growth behavior of a cluster (irreversible or partially reversible growth) depend on the local environment of the cluster. The kinetic Monte Carlo simulation of the model shows that with increasing temperature, the correlated nucleation effect causes a transition of growth behavior from asymmetric adatom aggregation between faulted and unfaulted half cells with a strong preference of occupation of faulted half cells, to compact cluster aggregation with a low occupation preference at high temperatures. As a result the preference as a function of the temperature exhibits a nonmonotonous behavior, with a maximum located at the temperature at which the transition of growth behavior has been observed. Both the simulated cluster morphologies and the quantitative analysis of the cluster distribution are in good agreement with the results observed from relevant growth experiments.     

Simulation of damage accumulation kinetics with a probabilistic cellular automaton

The kinetics of damage accumulation and the evolution of damage clusters in loaded materials are simulated with a probabilistic cellular automaton controlled by three probabilities, namely, by the probabilities of free-cell occupation, cluster perimeter growth, and coalescence of clusters separated by a critical distance. The automaton algorithm is realized with Microsoft Visual Basic 6.0 as a single-document Windows application connected with Microsoft Excel, which is used as an automaton client to save and process output data. The operation of the automaton is illustrated by the example of the kinetics of damage accumulation and the evolution of a damage cluster structure compared for two simulation scenarios.     

Iron-dependent formation of reactive oxygen species and glutathione depletion after accumulation of magnetic iron oxide nanoparticles by oligodendroglial cells

Magnetic iron oxide nanoparticles (IONP) are currently used for various neurobiological applications. To investigate the consequences of a treatment of brain cells with such particles, we have applied dimercaptosuccinate (DMSA)-coated IONP that had an average hydrodynamic diameter of 60 nm to oligodendroglial OLN-93 cells. After exposure to 4 mM iron applied as DMSA–IONP, these cells increased their total specific iron content within 8 h 600-fold from 7 to 4,200 nmol/mg cellular protein. The strong iron accumulation was accompanied by a change in cell morphology, although the cell viability was not compromized. DMSA–IONP treatment caused a concentration-dependent increase in the iron-dependent formation of reactive oxygen species and a decrease in the specific content of the cellular antioxidative tripeptide glutathione. During a 16 h recovery phase in IONP-free culture medium following exposure to DMSA–IONP, OLN-93 cells maintained their high iron content and replenished their cellular glutathione content. These data demonstrate that viable OLN-93 cells have a remarkable potential to deal successfully with the consequences of an accumulation of large amounts of iron after exposure to DMSA–IONP.     

Cluster-cluster correlation during irreversible diffusion-limited aggregation

Summary In this paper, we discuss the evolution of the scattered intensityI(q) during irreversible diffusion-limited cluster-cluster aggregation. We analyse twodimensional simulations and interpret the results within the framework of a recently proposed theoretical approach. The theory describes the correlation among different clusters which develops during the irreversible aggregation process. The model is based on two coupled differential equations, controlling the growth of the average cluster mass and the time dependence of the probability of finding pairs of clusters as a function of their distance. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Cluster growth poised on the edge of break-up: Size distributions with small exponent power-laws

In many naturally occurring growth processes, cluster size distributions of power-law form n(s)∝s^−τ with small exponents 0<τ<1 are observed. We suggest here that such distributions emerge naturally from cluster growth, where size dependent aggregation is counterbalanced by size dependent break-up. The model used in the study is a simple reaction kinetic model including only monomer-cluster processes. It is shown that under such conditions power-law size distributions with small exponents are obtained. Therefore, the results suggest that the ubiquity of small exponent power-law distributions is related to the growth process, where aggregation driven cluster growth is poised on the edge of cluster break-up.     

Calculation of the cluster size distribution functions and small-angle neutron scattering data for C60/N-methylpyrrolidone

The aggregate growth in a C₆₀/N-methylpyrrolidone (NMP) solution has been considered in the framework of the approach developed earlier for describing the cluster growth kinetics in fullerene polar solutions. The final cluster size distribution functions in model solutions have been estimated for two fullerene aggregation models including the influence of complex formation on the cluster growth using extrapolations of the characteristics of the cluster state and distribution parameters. Based on the obtained results, the model curves of small-angle neutron scattering have been calculated for a C₆₀/NMP solution at various values of the model parameters.     

Programming resistive switching memory by a charged capacitor

The performances of bulk-heterojunction (BHJ) solar cells are investigated for time-dependent thermal annealing with different morphology evolution scales, having special consideration for the diffusion and aggregation of fullerene derivative molecules based on blends of poly(3-hexylthiophene):[6,6]-phenyl-C₆₁-butyric acid methyl ester (P3HT:PCBM). Meaningfully, rapid formation of dot-like and needle-like crystalline PCBM structures of a few micrometers up to 60 μm in size is obtained with thermal annealing treatment from 2 to 15 min, which dynamically reflects a fast process of PCBM molecule and cluster aggregation. Upon ultrasonic-assisted processing and annealing treatment, the scale of P3HT crystals is drastically increased in view of X-ray diffraction (XRD) patterns, leading to a high hole mobility. And, the P3HT domains can be gradually converted into larger P3HT crystals approved by the decreased full width at half-maximum in the XRD patterns. Corresponding current–voltage curves are measured in quantity and we propose a model to explain the effect of the crystalline degree of P3HT domains and aggregation of PCBM molecules and clusters on the phase segregation, expressing a viewpoint towards high performance of BHJ solar cells.     

CSF from Parkinson disease Patients Differentially Affects Cultured Microglia and Astrocytes

Background  

Excessive and abnormal accumulation of alpha-synuclein (α-synuclein) is a factor contributing to pathogenic cell death in Parkinson's disease. The purpose of this study, based on earlier observations of Parkinson's disease cerebrospinal fluid (PD-CSF) initiated cell death, was to determine the effects of CSF from PD patients on the functionally different microglia and astrocyte glial cell lines. Microglia cells from human glioblastoma and astrocytes from fetal brain tissue were cultured, grown to confluence, treated with fixed concentrations of PD-CSF, non-PD disease control CSF, or control no-CSF medium, then photographed and fluorescently probed for α-synuclein content by deconvolution fluorescence microscopy. Outcome measures included manually counted cell growth patterns from day 1-8; α-synuclein density and distribution by antibody tagged 3D model stacked deconvoluted fluorescent imaging.     

A qualitative model for the growth mechanism of silver clusters in polymer solution

A simple and high-reproducible method for the synthesis of polymer-protected silver cluster of controlled size is described. UV-visible spectroscopy has been used for investigating the influence of the aging of the protective poly(vinylpyrrolidone) layer on the cluster growth rate at different reaction temperatures and poly(vinylpyrrolidone)/ethylene glycol weight ratios. The obtained results show that the aging time of the polymeric stabilizer solution plays a fundamental role in the reproducibility of the cluster growth process. A model for the metal cluster formation-grow process is also proposed. Received 18 July 2001 and Received in final form 3 October 2001     

A study of the effect of JB particles on Saccharomyces cerevisiae (yeast) cells by Raman spectroscopy

The mechanism of interaction of particulate matter with living system is not completely understood. Evaluation of the effect of particulate Indian traditional medicine JB(JB) on Saccharomyces cerevisiae (yeast) cells is the major focus of the present study. In India, JB is considered as a rejuvenating medicine and used for the treatment of diseases such as diabetes and age‐related eye diseases, as well as a health promoting tonic by the traditional practitioners. In presence of JB, higher growth has been observed at the late stationary growth phase of yeast. Ultra‐structure analysis using transmission electron microscopy (TEM) has shown that JB‐treated yeast cells have better morphology over control in the late stationary growth phase. In this investigation, cellular response from yeast cells after interaction with JB particles was measured using Raman spectroscopy. Raman spectroscopy—a noninvasive tool to distinguish between particle‐treated and untreated cells—revealed that treatment with JB is able to slow the degradation of cellular components (e.g. DNA, proteins and lipids) with the aging of yeast cells. Copyright © 2008 John Wiley & Sons, Ltd.     

Control of island morphology by dynamic coalescence of soft-landed clusters

The deposition of preformed clusters on surfaces has been established as a new way for growing nano-suctures on surfaces. It has been shown that supported island morphology relies on the dynamics of clusters, during the growth, giving rise to shapes from compact to ramified types. This paper identifies and discusses, in the case of antimony cluster deposits, several processes responsible for the non-equilibrium island shapes: limited kinetic cluster aggregation, size dependent coalescence, “wetting-like behavior” of antimony clusters on antimony islands. Using successive predetermined cluster sizes during the deposition process to synthesize polymorphic structure involves the interplay of those mechanisms. Received 1st December 2000     

Two-spin-majority cellular automaton as a model of 2D cluster and interface growth

A new probabilistic cellular automaton model is introduced to simulate cluster and interface growth in two dimensions. The dynamics of this model is an extension to higher dimensions of the compact directed percolation studied by Essam. Numerical results indicate that the two-dimensional cluster coarsening and growth can be described only approximately by the conventional cluster size scaling due to a crossover in the growth mode. The spreading of the initially flat interface follows a purely diffusional,t ^1/2, law.     

Ion-induced sputtering of a metal in the form of large clusters

A model is proposed for the ion-induced sputtering of a metal in the form of large clusters with a number of atoms N⩾5. The model is based on simple physical assumptions and is consistent with experiment. As an example, calculations are made of the relative cluster yield as a function of the number of atoms in the cluster as a result of the bombardment of various metals by singly charged 5 keV argon ions. A comparison is made with experimental data. Zh. Tekh. Fiz. 69, 64–68 (March 1999)     

有限步扩散反应置限分形聚集

综合考虑扩散粒子浓度n、粒子扩散限制范围Δ、扩散粒子与种粒子或团簇相遇时，反应概率P及粒子扩散步数W的影响，提出了有限步扩散反应置限聚集的分形生长模型，模拟得到一系列典型的聚集生长图形，计算了相应的分形维数.结果表明，在粒子浓度n较小时，呈离散团簇状生长；而在粒子浓度较大时，则随反应概率P或粒子扩散步数W的增大，从离散团簇状生长转变为连续枝叉状生长. 关键词：     

Curcumin reduces α-synuclein induced cytotoxicity in Parkinson's disease cell model

Background  

Overexpression and abnormal accumulation of aggregated α-synuclein (αS) have been linked to Parkinson's disease (PD) and other synucleinopathies. αS can misfold and adopt a variety of morphologies but recent studies implicate oligomeric forms as the most cytotoxic species. Both genetic mutations and chronic exposure to neurotoxins increase αS aggregation and intracellular reactive oxygen species (ROS), leading to mitochondrial dysfunction and oxidative damage in PD cell models.     

Correlation and anticorrelation of fractal aggregates. A model for «spinodal-type» aggregation

Summary We present a simple phenomenological model, based on mass conservation arguments, in order to describe aggregation in dense solutions. It has been previously shown that fordiffusion-limited processes scattered intensity distributions exhibit a peak atq≠0 which grows in time and moves to smaller and smallerq vectors. According to the model, each aggregate is surrounded by a depletion region whose size depends on the aggregation kinetics. The form factor for such a cluster should satisfy local mass conservation and hence exhibit a pronounced depression atq=0. the initial stages of aggregation, when the clusters are far apart, are accounted on the basis of a form factor alone. The model shows good agreement with the data and also explains the experimental evidence that the peak does not appear inreaction-limited conditions. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Kinetic Simulation of Fractal Aggregation on Liquid Surfaces

A modified fractal growth model based on the deposition, diffusion, and aggregation (DDA) with cluster rotation is presented to simulate two-dimensional fractal aggregation on liquid surfaces. The mobility (including diffusion and rotation) of clusters is related to its mass, which is given by D_m=D₀ s^-γ_D and θ_m=θ₀s^-γ_θ, respectively. We concentrate on revealing the details of the influence of deposition flux F, cluster diffusion factor γ_D and cluster rotation factor γ_θ on the dynamics of fractal aggregation on liquid surfaces. It is shown that the morphologies of clusters and values of cluster density and fractal dimension depend dramatically on the deposition flux and migration factors of clusters.     

In-situ characterization of metal clusters supported on a birefringent substrate using reflectance difference spectroscopy

Reflectance difference spectroscopy has been applied for the in-situ characterization of the growth of Ag cluster films on insulating birefringent Al₂O₃ (10[`1]0)(10\overline{1}0) substrates in the spectral range of 1.5–5 eV. Information on the individual cluster, cluster film morphology and growth are derived from the anisotropy of the in-plane plasmon resonances in comparison with scanning electron microscopy images. In particular, the evolution of the dipolar resonance has been attributed to two distinct stages of coarsening involving particle aggregation and ripening, and to the development of anisotropic particle shapes for higher Ag coverages. The effect of the formation of anisotropic electrostatic images in the birefringent substrate is used to explain the spectra even in the absence of structural anisotropies.