Annealing Kinetics of Single Displacement Cascades in Ni: An Atomic Scale Computer Simulation

1998 ◽  
Vol 540 ◽  
Author(s):  
A. Almazouzi ◽  
M. J. Caturla ◽  
T. Diaz de la Rubia ◽  
M. Victoria
Keyword(s):  
Interatomic Potential ◽  
Kinetic Monte Carlo ◽  
Scale Up ◽  
Md Simulations ◽  
Atomic Scale ◽  
Displacement Cascade ◽  
Atomistic Study ◽  
Kinetics Of

AbstractIn order to describe the long term evolution of the defects produced by a displacement cascade, Molecular dynamics (MD) and Kinetic Monte Carlo (KMC) methods are employed. Using an empirical Ni interatomic potential in MD, the damage resulting from primary knock-on atom (PKA) energies up to 30 keV has been simulated. The annealing kinetics and the fraction of freely migrating defects (FMD) are determined for each single displacement cascade, by a KMC code which is based on a set of parameters extracted mainly from MD simulations. It allows an atomistic study of the evolution of the initial damage over a time scale up to lOOs and the determination of the fraction of the defects that escape the KMC box, compared to those obtained by MD, as function of temperature and PKA energy. It has been found that this fraction depends strongly on the temperature but reaches a saturation value above stage V.

Computer Simulation of Irradiation Growth in Zirconium

2008 ◽  
Vol 33-37 ◽  
pp. 889-894
Author(s):  
Akiyuki Takahashi ◽  
Masahiro Arita ◽  
Masanori Kikuchi
Keyword(s):  
Computer Simulation ◽  
Md Simulation ◽  
Kinetic Monte Carlo ◽  
Md Simulations ◽  
Defect Cluster ◽  
Simulation Code ◽  
Displacement Cascade ◽  
Irradiation Growth ◽  
Simple Models

This paper describes the computer simulation of irradiation growths induced by neutron irradiations in zirconium using a combination of Molecular Dynamics (MD) and Kinetic Monte Carlo (KMC) methods. First, we performed the MD simulation of the displacement cascade on a defect cluster to study the interaction between the defect cluster and the displacement cascade. The MD simulations provide a lot of information on the amount of the defect production and the subsequent morphological change in the defect cluster. The results are used to make simple models that describe the nature of the displacement cascade overlap on the defect clusters. The models are then implemented into the KMC simulation code to extend the length- and time-scale of the simulation, which allows us to evaluate directly the defect cluster accumulations during a long-term irradiation. The irradiation growth strain resulting from the defect cluster accumulations is simply evaluated, and compared to an available experimental data. The comparison suggests that the displacement cascade overlap plays an important role on the irradiation growth, and, consequently, the KMC method with the simple models must be appropriate for the simulations of the irradiation growth.

Kinetics of Precipitation: Comparison between Monte Carlo Simulations, Cluster Dynamics and the Classical Laws

2005 ◽  
Vol 237-240 ◽  
pp. 671-676 ◽  
Author(s):  
Philippe Maugis ◽  
Frédéric Soisson ◽  
Ludovic Lae
Keyword(s):  
Monte Carlo ◽  
Kinetic Monte Carlo ◽  
Diffusion Mechanism ◽  
Interface Energy ◽  
Atomic Scale ◽  
Atomistic Simulations ◽  
Model Based ◽  
Kinetics Of Precipitation ◽  
Kinetics Of ◽  
Nucleation Growth

We test the main approximations of the classical laws for nucleation, growth and coarsening by comparison with atomistic simulations of the kinetics of precipitation. We investigate the kinetics of phase separation in dilute A-B solid solutions by precipitation of B atoms in the Arich matrix. Classically, the kinetics is represented by the time evolution of the total number of particles and their mean radius. In this work, the kinetics is predicted by three types of models: (a) an Atomic-scale Kinetic Monte Carlo (AKMC) model based on a vacancy diffusion mechanism, (b) a Cluster Dynamics model, and (c) the MultiPreci model, based on the coupling of the classical laws of nucleation, growth and coarsening. Cluster Dynamics and the Multipreci model have been parameterized such that the thermodynamic and kinetic parameters (solubility, diffusion coefficient, interface energy) be identical to that of the AKMC. Under these conditions we find that the classical laws are in good agreement with the atomistic simulations as long as the thermodynamics of the solid solution remains strictly regular. As expected, Cluster Dynamics compares better with the atomistic simulations, especially if a precise description of the energetics of the smallest clusters is applied.

Atomistic study of chemical effect on local structure in Mg-based metallic glasses

RSC Advances ◽  
2015 ◽  
Vol 5 (58) ◽  
pp. 46861-46868
Author(s):  
Q. Wang ◽  
J. H. Li ◽  
J. B. Liu ◽  
B. X. Liu
Keyword(s):  
Molecular Dynamics ◽  
Metallic Glasses ◽  
Local Structure ◽  
Interatomic Potential ◽  
Md Simulations ◽  
Chemical Effect ◽  
Chemical Effects ◽  
Atomistic Study

By applying a recently constructed interatomic potential, molecular dynamics (MD) simulations were performed to investigate the structural origin of chemical effects in Mg–Cu–Ni ternary metallic glasses.

Preparation And elemental analysis of ancient fibers

1987 ◽  
Vol 45 ◽  
pp. 410-411
Author(s):  
Allen Angel ◽  
Kathryn A. Jakes
Keyword(s):  
Cross Sections ◽  
Physical Structure ◽  
Energy Dispersive ◽  
Archaeological Sites ◽  
X Ray ◽  
Long Term Storage ◽  
Backscattered Electron ◽  
Electron Imaging

Fabrics recovered from archaeological sites often are so badly degraded that fiber identification based on physical morphology is difficult. Although diagenetic changes may be viewed as destructive to factors necessary for the discernment of fiber information, changes occurring during any stage of a fiber's lifetime leave a record within the fiber's chemical and physical structure. These alterations may offer valuable clues to understanding the conditions of the fiber's growth, fiber preparation and fabric processing technology and conditions of burial or long term storage (1).Energy dispersive spectrometry has been reported to be suitable for determination of mordant treatment on historic fibers (2,3) and has been used to characterize metal wrapping of combination yarns (4,5). In this study, a technique is developed which provides fractured cross sections of fibers for x-ray analysis and elemental mapping. In addition, backscattered electron imaging (BSI) and energy dispersive x-ray microanalysis (EDS) are utilized to correlate elements to their distribution in fibers.

Comparative Labelling and Biokinetic Studies of 99mTc-EDTA(Sn) and 99mTc-DTPA(Sn)

1977 ◽  
Vol 16 (01) ◽  
pp. 30-35 ◽  
Author(s):  
N. Agha ◽  
R. B. R. Persson
Keyword(s):  
Complex Formation ◽  
Significant Influence ◽  
Room Temperature ◽  
Ph Value ◽  
Maximum Activity ◽  
Reduction Step ◽  
Labelling Yield ◽  
Different Temperatures ◽  
Kinetics Of

SummaryGelchromatography column scanning has been used to study the fractions of 99mTc-pertechnetate, 99mTcchelate and reduced hydrolyzed 99mTc in preparations of 99mTc-EDTA(Sn) and 99mTc-DTPA(Sn). The labelling yield of 99mTc-EDTA(Sn) chelate was as high as 90—95% when 100 μmol EDTA · H4 and 0.5 (Amol SnCl2 was incubated with 10 ml 99mTceluate for 30—60 min at room temperature. The study of the influence of the pH-value on the fraction of 99mTc-EDTA shows that pH 2.8—2.9 gave the best labelling yield. In a comparative study of the labelling kinetics of 99mTc-EDTA(Sn) and 99mTc- DTPA(Sn) at different temperatures (7, 22 and 37°C), no significant influence on the reduction step was found. The rate constant for complex formation, however, increased more rapidly with increased temperature for 99mTc-DTPA(Sn). At room temperature only a few minutes was required to achieve a high labelling yield with 99mTc-DTPA(Sn) whereas about 60 min was required for 99mTc-EDTA(Sn). Comparative biokinetic studies in rabbits showed that the maximum activity in kidneys is achieved after 12 min with 99mTc-EDTA(Sn) but already after 6 min with 99mTc-DTPA(Sn). The long-term disappearance of 99mTc-DTPA(Sn) from the kidneys is about five times faster than that for 99mTc-EDTA(Sn).

Improvement Of Curvilinear Diagrams Of Concrete Deformation

2019 ◽  
pp. 99-104
Keyword(s):  
Reinforced Concrete ◽  
Peak Load ◽  
Experimental Studies ◽  
Concrete Structures ◽  
Deformation Model ◽  
Reinforced Concrete Structures ◽  
Significant Difference ◽  
Deformation Diagrams

Problems when calculating reinforced concrete structures based on the concrete deformation under compression diagram, which is presented both in Russian and foreign regulatory documents on the design of concrete and reinforced concrete structures are considered. The correctness of their compliance for all classes of concrete remains very approximate, especially a significant difference occurs when using Euronorm due to the different shape and sizes of the samples. At present, there are no methodical recommendations for determining the ultimate relative deformations of concrete under axial compression and the construction of curvilinear deformation diagrams, which leads to limited experimental data and, as a result, does not make it possible to enter more detailed ultimate strain values into domestic standards. The results of experimental studies to determine the ultimate relative deformations of concrete under compression for different classes of concrete, which allowed to make analytical dependences for the evaluation of the ultimate relative deformations and description of curvilinear deformation diagrams, are presented. The article discusses various options for using the deformation model to assess the stress-strain state of the structure, it is concluded that it is necessary to use not only the finite values of the ultimate deformations, but also their intermediate values. This requires reliable diagrams "s–e” for all classes of concrete. The difficulties of measuring deformations in concrete subjected to peak load, corresponding to the prismatic strength, as well as main cracks that appeared under conditions of long-term step loading are highlighted. Variants of more accurate measurements are proposed. Development and implementation of the new standard GOST "Concretes. Methods for determination of complete diagrams" on the basis of the developed method for obtaining complete diagrams of concrete deformation under compression for the evaluation of ultimate deformability of concrete under compression are necessary.

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