This work is a simulation modelling with the LAMMPS calculation code of an electrode based on alkali metals (lithium, sodium and potassium) using the MEAM potential. For different multiplicities, two models were studi...This work is a simulation modelling with the LAMMPS calculation code of an electrode based on alkali metals (lithium, sodium and potassium) using the MEAM potential. For different multiplicities, two models were studied;with and without gap. In this work, we present the structural, physical and chemical properties of the lithium, sodium and potassium electrodes. For the structural properties, the cohesive energy and the mesh parameters were calculated, revealing that, whatever the chemical element selected, the compact hexagonal hcp structure is the most stable, followed by the face-centred cubic CFC structure, and finally the BCC structure. The most stable structure is lithium, with a cohesion energy of -6570 eV, and the lowest bcc-hcp transition energy of -0.553 eV/atom, followed by sodium. For physical properties, kinetic and potential energies were calculated for each of the sectioned chemical elements, with lithium achieving the highest value. Finally, for the chemical properties, we studied the diffusion coefficient and the activation energy. Only potassium followed an opposite order to the other two, with the quantities with lacunae being greater than those without lacunae, whatever the multiplicity. The order of magnitude of the diffusion coefficients is given by the relationship D<sub>Li</sub> > D<sub>Na</sub> > D<sub>k</sub> for the multiplicity 6*6*6, while for the activation energy the order is reversed.展开更多
In this work we present the results of our study on the physical and mechanical properties of titanium in volume. The work consisted in determining its physical and mechanical properties under different crystallograph...In this work we present the results of our study on the physical and mechanical properties of titanium in volume. The work consisted in determining its physical and mechanical properties under different crystallographic structures (HCP, FCC, BCC and SC) using the Modified Embedded Atom Method (MEAM) and the MEAM potential of titanium. We used the LAMMPS calculation code, based on classical molecular dynamics, to determine the most stable structure of titanium, which is the hexagonal compact structure (HCP) with crystal parameters a = 2.952 Å and c = 4.821 Å and a cohesion energy of -4.87 eV. This structure is seconded by the cubic centred structure (BCC) with a lattice parameter a = 3.274 Å and a cohesive energy of -4.84 eV. It was shown that titanium can crystallise into a third structure which is the face-centred cubic (FCC) structure with a lattice parameter a = 4.143 Å and a cohesive energy of -4.82 eV. The results obtained in this study were compared with the theoretical results and showed considerable agreement.展开更多
In this work, we have studied the vacancy formation energy of TiN alloy of structure B2 of size 10 × 10 × 10 for nitrogen percentages of 45%, 50% and 55% under the influence of temperature at 1320 K, 1420 K ...In this work, we have studied the vacancy formation energy of TiN alloy of structure B2 of size 10 × 10 × 10 for nitrogen percentages of 45%, 50% and 55% under the influence of temperature at 1320 K, 1420 K and 1520 K using the Modified Embedded Atom Method MEAM under the calculation code LAMMPS version 2020. This study has enabled us to understand the behavior of the TiN alloy under different nitrogen percentages in terms of total energy, vacancy formation energy, crystalline parameter, occupancy rate and order parameter. For total energy, we have shown that as temperature increases, total energy decreases, making it easier to obtain TiN at higher temperatures;reaching the value of -7344.9169 eV for the 55% nitrogen structure for the temperature of 1420 K. For the energy of formation, we have shown that the compounds obtained at 1320 K and 1520 K have a more considerable energy of formation than that obtained at 1420 K. The study of fractions and the order parameter showed us that the structure of TiN with 55% nitrogen is less likely, as the composition obtained is at most 53.35%.展开更多
Al,Ca,and Zn are representative commercial alloying elements for Mg alloys.To investigate the effects of these elements on the deformation and recrystallization behaviors of Mg alloys,we develop interatomic potentials...Al,Ca,and Zn are representative commercial alloying elements for Mg alloys.To investigate the effects of these elements on the deformation and recrystallization behaviors of Mg alloys,we develop interatomic potentials for the Al-Ca,Al-Zn,Mg-Al-Ca and Mg-Al-Zn systems based on the second nearest-neighbor modified embedded-atom method formalism.The developed potentials describe structural,elastic,and thermodynamic properties of compounds and solutions of associated alloy systems in reasonable agreement with experimental data and higher-level calculations.The applicability of these potentials to the present investigation is confirmed by calculating the generalized stacking fault energy for various slip systems and the segregation energy on twin boundaries of the Mg-Al-Ca and Mg-Al-Zn alloys,accompanied with the thermal expansion coefficient and crystal structure maintenance of stable compounds in those alloys.展开更多
Bemisia tabaci-transmitted geminiviruses are one of the major threats on cassava and vegetable crops in Africa. However, to date, few studies are available on the diversity orB. tabaci and their associated endosymbion...Bemisia tabaci-transmitted geminiviruses are one of the major threats on cassava and vegetable crops in Africa. However, to date, few studies are available on the diversity orB. tabaci and their associated endosymbionts in Africa. More than 28 species have been described in the complex ofB. tabaci cryptic species; among them, 2 are invasive pests worldwide： MED and MEAM1. In order to assess the species diversity orB. tabaci in vegetable crops in Senegal, several samplings in different localities, hosts and seasons were collected and analyzed with nuclear （microsatellite） and mitochondrial （COI） markers. The bacterial endosymbiont community was also studied for each sample. Two species were detected： MED Q1 and MEAM1 B. Patterns of MED Q1 （dominance on most of the samples and sites, highest nuclear and mitochondrial diversity and broader secondary endosymbiont community： Hamiltonella, Cardinium, Wolbachia and Rickettsia）, point toward a predominant resident begomovirus vector group for MED Q 1 on market gardening crops. Furthermore, the lower prevalence of the second species MEAM1 B, its lower nuclear and mitochondrial diversity and a narrower secondary endosymbiont community （Hamiltonella/Rickettsia）, indicate that this genetic group is exotic and results from a recent invasion in this area.展开更多
A density functional theory (DFT)-calculation scheme for constructing the modified embedded atom method (MEAM) potentials for face-centered cubic (fcc) metals is presented. The input quantities are carefully selected ...A density functional theory (DFT)-calculation scheme for constructing the modified embedded atom method (MEAM) potentials for face-centered cubic (fcc) metals is presented. The input quantities are carefully selected and a more reliable DFT approach for surface energy determination is introduced in the parameterization scheme, enabling MEAM to precisely predict the surface and nanoscale properties of metallic materials. Molecular dynamics simulations on Pt and Au crystals show that the parameterization employed leads to significantly improved accuracy of MEAM in calculating the surface and nanoscale properties, with the results agreeing well with both DFT calculations and experimental observations. The present study implies that rational DFT parameterization of MEAM may lead to a theoretical tool to bridge the gap between nanoscale theoretical simulations and DFT calculations.展开更多
文摘This work is a simulation modelling with the LAMMPS calculation code of an electrode based on alkali metals (lithium, sodium and potassium) using the MEAM potential. For different multiplicities, two models were studied;with and without gap. In this work, we present the structural, physical and chemical properties of the lithium, sodium and potassium electrodes. For the structural properties, the cohesive energy and the mesh parameters were calculated, revealing that, whatever the chemical element selected, the compact hexagonal hcp structure is the most stable, followed by the face-centred cubic CFC structure, and finally the BCC structure. The most stable structure is lithium, with a cohesion energy of -6570 eV, and the lowest bcc-hcp transition energy of -0.553 eV/atom, followed by sodium. For physical properties, kinetic and potential energies were calculated for each of the sectioned chemical elements, with lithium achieving the highest value. Finally, for the chemical properties, we studied the diffusion coefficient and the activation energy. Only potassium followed an opposite order to the other two, with the quantities with lacunae being greater than those without lacunae, whatever the multiplicity. The order of magnitude of the diffusion coefficients is given by the relationship D<sub>Li</sub> > D<sub>Na</sub> > D<sub>k</sub> for the multiplicity 6*6*6, while for the activation energy the order is reversed.
文摘In this work we present the results of our study on the physical and mechanical properties of titanium in volume. The work consisted in determining its physical and mechanical properties under different crystallographic structures (HCP, FCC, BCC and SC) using the Modified Embedded Atom Method (MEAM) and the MEAM potential of titanium. We used the LAMMPS calculation code, based on classical molecular dynamics, to determine the most stable structure of titanium, which is the hexagonal compact structure (HCP) with crystal parameters a = 2.952 Å and c = 4.821 Å and a cohesion energy of -4.87 eV. This structure is seconded by the cubic centred structure (BCC) with a lattice parameter a = 3.274 Å and a cohesive energy of -4.84 eV. It was shown that titanium can crystallise into a third structure which is the face-centred cubic (FCC) structure with a lattice parameter a = 4.143 Å and a cohesive energy of -4.82 eV. The results obtained in this study were compared with the theoretical results and showed considerable agreement.
文摘In this work, we have studied the vacancy formation energy of TiN alloy of structure B2 of size 10 × 10 × 10 for nitrogen percentages of 45%, 50% and 55% under the influence of temperature at 1320 K, 1420 K and 1520 K using the Modified Embedded Atom Method MEAM under the calculation code LAMMPS version 2020. This study has enabled us to understand the behavior of the TiN alloy under different nitrogen percentages in terms of total energy, vacancy formation energy, crystalline parameter, occupancy rate and order parameter. For total energy, we have shown that as temperature increases, total energy decreases, making it easier to obtain TiN at higher temperatures;reaching the value of -7344.9169 eV for the 55% nitrogen structure for the temperature of 1420 K. For the energy of formation, we have shown that the compounds obtained at 1320 K and 1520 K have a more considerable energy of formation than that obtained at 1420 K. The study of fractions and the order parameter showed us that the structure of TiN with 55% nitrogen is less likely, as the composition obtained is at most 53.35%.
文摘Al,Ca,and Zn are representative commercial alloying elements for Mg alloys.To investigate the effects of these elements on the deformation and recrystallization behaviors of Mg alloys,we develop interatomic potentials for the Al-Ca,Al-Zn,Mg-Al-Ca and Mg-Al-Zn systems based on the second nearest-neighbor modified embedded-atom method formalism.The developed potentials describe structural,elastic,and thermodynamic properties of compounds and solutions of associated alloy systems in reasonable agreement with experimental data and higher-level calculations.The applicability of these potentials to the present investigation is confirmed by calculating the generalized stacking fault energy for various slip systems and the segregation energy on twin boundaries of the Mg-Al-Ca and Mg-Al-Zn alloys,accompanied with the thermal expansion coefficient and crystal structure maintenance of stable compounds in those alloys.
文摘Bemisia tabaci-transmitted geminiviruses are one of the major threats on cassava and vegetable crops in Africa. However, to date, few studies are available on the diversity orB. tabaci and their associated endosymbionts in Africa. More than 28 species have been described in the complex ofB. tabaci cryptic species; among them, 2 are invasive pests worldwide： MED and MEAM1. In order to assess the species diversity orB. tabaci in vegetable crops in Senegal, several samplings in different localities, hosts and seasons were collected and analyzed with nuclear （microsatellite） and mitochondrial （COI） markers. The bacterial endosymbiont community was also studied for each sample. Two species were detected： MED Q1 and MEAM1 B. Patterns of MED Q1 （dominance on most of the samples and sites, highest nuclear and mitochondrial diversity and broader secondary endosymbiont community： Hamiltonella, Cardinium, Wolbachia and Rickettsia）, point toward a predominant resident begomovirus vector group for MED Q 1 on market gardening crops. Furthermore, the lower prevalence of the second species MEAM1 B, its lower nuclear and mitochondrial diversity and a narrower secondary endosymbiont community （Hamiltonella/Rickettsia）, indicate that this genetic group is exotic and results from a recent invasion in this area.
基金supported by the National Natural Science Foundation of China (Grant Nos. 20973131, 50632050)the Education Ministry of China under the program for New Century Excellent Talents in Universi-ties of China (NCET-06-0612)
文摘A density functional theory (DFT)-calculation scheme for constructing the modified embedded atom method (MEAM) potentials for face-centered cubic (fcc) metals is presented. The input quantities are carefully selected and a more reliable DFT approach for surface energy determination is introduced in the parameterization scheme, enabling MEAM to precisely predict the surface and nanoscale properties of metallic materials. Molecular dynamics simulations on Pt and Au crystals show that the parameterization employed leads to significantly improved accuracy of MEAM in calculating the surface and nanoscale properties, with the results agreeing well with both DFT calculations and experimental observations. The present study implies that rational DFT parameterization of MEAM may lead to a theoretical tool to bridge the gap between nanoscale theoretical simulations and DFT calculations.
文摘目的研究杭州地区男性素食者平均血小板体积(meam platelet volume,MPV)与血浆磷脂脂肪酸构成、血清维生素B12(vitamin B12,VB12)及同型半胱氨酸(homocysteine,Hcy)等指标的相关性。方法采用气相色谱法测定89例男性素食者和103例对照组的血浆磷脂脂肪酸的构成,采用常规方法测定MPV和血清生化指标。结果与对照组相比,素食组血浆多不饱和脂肪酸(n-3 PUFA)水平降低,而n-6 PUFA水平升高;素食组血清VB12水平显著降低(160.7±64.3 vs 373.9±160.9,P<0.01),Hcy水平显著增高,约为对照组的1.74倍(23.74±12.66 vs 13.62±9.17,P<0.01);素食组MPV高于对照组(9.14±1.04 vs 8.82±1.00,P<0.05)。相关性分析显示,MPV与22:5n-6(DPA n-6)呈正相关,与血清VB12水平呈负相关。结论杭州地区男性素食者MPV增高,血清Hcy升高,VB12与n-3 PUFA摄入不足,补充VB12与n-3 PUFA可能对降低素食者的MPV和Hcy有益。
