Papers by Keyword: Monte-Carlo

Abstract: The process of nanowhisker formation on the substrates activated by catalyst drops was investigated by Monte Carlo simulation. Influence of deposition conditions on whisker morphology was considered. Straight whiskers with uniform diameter could be grown using catalyst possessing large contact angle with whisker material. It was demonstrated that variation of growth conditions in such physicochemical system may result in nanotube formation. Atomic mechanism of hollow whisker formation was suggested. The range of model growth conditions for nanowhisker and nanotube formation were identified.

Abstract: Recently, there has been a great deal of interest in the properties of hollow nanoparticles for use in advanced technologies. The diffusion phenomenon known as the Kirkendall effect features in one of the important experimental methods of synthesis of hollow binary nanoparticles. Diffusion naturally features prominently in shrinkage mechanisms of hollow nanoparticles. In this paper, we summarize the progress made so far in understanding the formation and shrinkage by diffusion processes of hollow nanoparticles and their apparent stability.

Abstract: In this paper, we review the recent developed method based around lattice-based random walks and the Monte Carlo method. This method, which is now called the Lattice Monte Carlo method, permits complex phenomenological problems in diffusion, thermal conductivity and elasticity to be addressed. It is shown how the effective mass diffusivity, thermal diffusivity/thermal conductivity and the bulk modulus in composites can be calculated and also how concentration profiles and temperature profiles can be determined in situations where the diffusivity depends on position and concentration and the thermal conductivity depends on position and temperature respectively.

Abstract: Self-assembled amphiphile systems are utilized in a wide variety of applications including drug delivery and energy storage. Nano-scale physical and chemical interactions govern the packing of self-assembled amphiphilic molecules, resulting in thermodynamically stable phases of defined geometries. Possible phases include micellar, hexagonal, cubic, lamellar and sponge phases. The internal nano-structure of the amphiphile self-assembly materials plays an important role in the properties of these systems and their application. To date small angle x-ray scattering (SAXS) has been the most common technique used to characterise their structure. We explore positron annihilation lifetime spectroscopy (PALS) as an alternative and/or complementary technique for this purpose, using the phytantriol/water system. While PALS is a well established technique for characterising many materials, the coexistence of aqueous and hydrophobic regions in a soft self-assembled amphiphile material poses a challenge to the analysis and interpretation of the results. In order to alleviate these difficulties we developed a computer program for general-purpose PALS data analysis called PAScual. Amongst the most salient features of this new code are the possibility to perform bounded fits and the option of using advanced algorithms to provide a more robust and unbiased fit: on the one hand, it incorporates a global nonlinear optimisation routine based on the Simulated Annealing algorithm and, on the other hand it gives information on the reliability of the results by means of a Markov Chain Monte-Carlo Bayesian Inference method. In this work we present the newly developed PALS data analysis techniques as well as the results for the phytantriol/water system, comparing them with additional data obtained from complementary techniques.

Abstract: In this paper, a new analytical method is proposed to generate concrete random aggregate structure (RAS) in meso-scopic level. This method is particular useful for the progressive failure of concrete under various external loads. In the meso-mechanics level, the concrete is taken as the composite material consisting of aggregate, mortar and interface between them. As a result, it is generated a random aggregate structure in which the shape, size and distribution of the aggregate particles resemble real concrete in the statistical sense using the Monte Carlo random sampling principle in this paper, and the method proposed can generate both regular aggregate particles and irregular ones in 2-Dimmension. It is should be noted that vector concept and some controlling measures are also proposed to avoid generating aggregate particles not consistent with real ones. Numerical examples are simulated to validate the proposed method finally.

Abstract: Neutron brachytherapy show better results than conventional photon therapy for radioresistant tumors with hypoxic regions. Herein a comparative radiodosimetric analysis is presented considering 125I photon emitter seeds, often applied to brachytherapy, and a proposed Sol-Gel glass, synthesized with incorporated 252Cf neutron emitter, on a brain tumor implant. The proposition is to verify the viability of applying this bioceramic material. The methodology is based on the investigation of the specific energy deposition (dose) from 252Cf-Glass in deep brain interstitial implants through a stochastic computer code (MCNP5) and comparison with 125I seed’s energy deposition. 252Cf-Glass show dose per transition values higher than 125I seed’s set. RBE-isodose curves show a faster decrease of dose with the source distance increasing which can improve healthy tissue sparing.

Abstract: Monte Carlo simulation was used to observe the dynamic magnetic behavior of dilute Ising ultra-thin-film. The hysteresis properties were investigated as varying the non-magnetic concentration, field frequency and field amplitude where the Metropolis algorithm was used. From the results, at fixed temperature and field amplitude, the hysteresis loop increases in size with increasing frequency at low frequency region but reduces at high frequency region due to the increase of the phase-lag between magnetization and external field signals. With the inclusion of non-magnetic sites, the phase-lag shifts to higher frequency as a result of weaker magnetic interaction. In addition, the scaling relation among the hysteresis area, the field parameters and non-magnetic concentration was proposed to provide general information of how the dilution affects hysteresis properties of dilute magnetic in ultra-thin-film structure.

Abstract: With the application of explicit dynamics and probability finite element method, reliability virtual experiment of deep groove ball bearing is carried out. Based on self –adaptive mesh module of the ANSYS/LS-DYNA, true numerical simulation of the working process is presented after the three-dimensional finite element bearing model is built. Then, the contact stress and strain among balls, retainer and inner (outer) race and also the pressure law during the contact process are obtained. As the randomness of manufacture and assemblage tolerance is inevitable, Monte Carlo method is adopted when samples the bearing system. From the random sampling, a large sample data of the maximum contact stress is got and the reliability coefficient is calculated; and the contribution of each original manufacture error to the reliability sensitivity of the bearing is analyzed. Reliability virtual experiment offers a theoretical reference to fatigue strength calculation and dynamic optimum design of the bearing system, and the analysis process is easy to be program controlled.

Abstract: We propose a model for explanation the “domain-wall” type configuration states in binary lipid mixtures of cationic and neutral lipids, associated with observed relaxation effects in their aggregates. We apply the analogy with formation of Kibble-Zurek topological defects, which we suppose connected with structural dynamics of the lipid phases. In frames of the proposed model, the density of kink-type defects and the energy of the configurations are calculated.

Abstract: Laser cutting error has large influence on the beam width of intravascular stents. Minor random variation in beam width of stents may significantly impact the expansion uniformity. In this paper, the relevant factors that may affect the beam width during the manufacture are investigated. Based on the randomization model, the pattern how the factors affect expansion uniformity is explored, and the method for calculating uniformity index is proposed. A detailed computation is made on the width randomization for the two expansion elements. The results show that with the increase of the value range of beam width, probability of uniformity index decreases gradually; the strengthening factor has large effect on the expansion uniformity. The method is meaningful for studying how the processing error affects expansion uniformity.