System size effect on crystal nuclei morphology in supercooled metallic melt
We present a molecular dynamics (MD) study of size effect on the crystal nuclei geometry, formation and growth in supercooled tantalum film. The process is studied in a set of MD trajectories that are obtained by ultrafast cooling from the stable liquid phase to the temperature below the glass transition temperature. We describe the nucleation process by two morphological parameters. Along with the nucleus size, we analyze the asphericity that is a measure of deviation of crystal nuclei from idealized spherical form. This method allows to demonstrate that there are two paths for crystal nucleus shape and size evolution. The first path is crystal growth through high asphericity values. We show that this is caused by coalescence of the crystals. This mechanism is not affected by the size of the system. The second path is formation of long-lived crystal clusters that do not lead to the crystallization of the whole system on the MD simulation timescale. We demonstrate that such clusters have common geometric features which strongly depend on the system size.
Computer simulations are fast growing approach for doing research in sciences. It is auxiliary to experimental and analytical research. The main goal of the conference is in the development of methods and algorithms which take into account trends in the hardware development, and which may help to intensive research. Conference should play role of the venue were senior scientists and students may have opportunity to speak each other and exchange ideas and views on the developments in the area of high-performance computing in most sciences.
The effect of tensile stress applied during cooling of binary glasses on the potential energy states and mechanical properties is investigated using molecular dynamics simulations. We study the three-dimensional binary mixture that was first annealed near the glass transition temperature and then rapidly cooled under tension into the glass phase. It is found that at larger values of the applied stress, the liquid glass former freezes under higher strain and its potential energy is enhanced. For a fixed cooling rate, the maximum tensile stress that can be applied during cooling is reduced upon increasing initial temperature above the glass transition point. We also show that the amorphous structure of rejuvenated glasses is characterized by an increase in the number of contacts between smaller type atoms. Furthermore, the results of tensile tests demonstrate that the elastic modulus and the peak value of the stress overshoot are reduced in glasses prepared at larger applied stresses and higher initial temperatures, thus indicating enhanced ductility. These findings might be useful for the development of processing and fabrication methods to improve plasticity of bulk metallic glasses.
Formation of carbon nanoparticles is an important type of complex non-equilibrium processes that require precise atomistic theoretical understanding. In this work, we consider the process of ultrafast cooling of pure carbon gas that results in nucleation of an onion-like fullerene. The model is based on molecular dynamics simulation with the interaction between carbon atoms described via a reactive ReaxFF model. We study the consecutive stages of fullerene-like nanoparticle formation and identify the corresponding temperature ranges. Analysis of hybridization and graphitization reveals the underlying microscopic mechanisms connected with rearrangements of dihedral angles and density changes.
Superplastic blow forming is a technology of shell parts production. The development of these processes requires computer simulation which cannot be realized without accurate parameters of the applied material. This characterization can be based on results of free bulging tests. Characterization techniques utilize the models of the dome growth during the bulging test. This study is devoted to the assessing of friction coefficient effect on the linear behavior of normalized thickness - normalized height relation.
A computer simulation of the depth course of the absorbed dose as a function of the electronic irradiation energy of the acting in the range of 30 – 60 keV was performed, and calculations of the dose accumulation factor under these conditions were performed for polyethylene terephthalate, polymethylmethacrylate, polystyrene and low-density polyethylene, as model polymers of microelectronic device housings. It is shown that the electron energy values corresponding to the maximum dose accumulation factor depend on the polymer density. The conducted studies allow us to determine with great accuracy the conductivity of plastic cases of microelectronic devices under conditions of electronic irradiation, which is of particular interest to exclude the physical possibility of the occurrence of electrostatic discharges that lead to failures of the onboard electronics of spacecraft.
The dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.
Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.
This volume presents new results in the study and optimization of information transmission models in telecommunication networks using different approaches, mainly based on theiries of queueing systems and queueing networks .
The paper provides a number of proposed draft operational guidelines for technology measurement and includes a number of tentative technology definitions to be used for statistical purposes, principles for identification and classification of potentially growing technology areas, suggestions on the survey strategies and indicators. These are the key components of an internationally harmonized framework for collecting and interpreting technology data that would need to be further developed through a broader consultation process. A summary of definitions of technology already available in OECD manuals and the stocktaking results are provided in the Annex section.