The Experts below are selected from a list of 153003 Experts worldwide ranked by ideXlab platform
Tomohiro Takaki - One of the best experts on this subject based on the ideXlab platform.
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uniquely selected primary dendrite arm spacing during Competitive Growth of columnar grains in al cu alloy
Journal of Crystal Growth, 2021Co-Authors: Jaehoon Lee, Yasushi Shibuta, Munekazu Ohno, Tomohiro TakakiAbstract:Abstract The steady-state value of primary dendrite arm spacing (PDAS) in the columnar dendrites growing between the converging and diverging grain boundaries is investigated by means of quantitative phase-field simulations. The simulations show that there is a unique value of PDAS under a given solidification condition in the system with grain boundaries. This is in contrast to existence of allowable range of PDAS under a given solidification in a system without the grain boundaries, i.e., an infinitely large columnar grain investigated in many early works. Such a unique value of PDAS depends on the pulling speed and inclination angle of the crystal, but not on the initial condition; that is, it is independent of the history of solidification condition. The dependences of the unique value on the pulling speed and inclination angle qualitatively agree with the theoretical models.
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Competitive Growth during directional solidification of a binary alloy with natural convection two dimensional phase field study
Modelling and Simulation in Materials Science and Engineering, 2019Co-Authors: Tomohiro Takaki, Shinji Sakane, Munekazu Ohno, Yasushi ShibutaAbstract:Due to the recent acceleration of phase-field simulations using a graphics processing unit (GPU), the mechanism of Competitive Growth among columnar grains has been better understood. In this study, the effects of natural convection, caused by the gravity driven buoyancy force, on the Competitive Growth of columnar grains during directional solidification of bi-crystal and polycrystal binary alloys are investigated by performing two-dimensional large-scale phase-field simulations using a GPU supercomputer. As a result, the downward flow accelerates and the upward flow decelerates the selection speed in Competitive Growth. It is also confirmed that these phenomena are caused by a characteristic liquid flow pattern at the converging and diverging grain boundaries.
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two dimensional phase field simulations of dendrite Competitive Growth during the directional solidification of a binary alloy bicrystal
Acta Materialia, 2014Co-Authors: Tomohiro Takaki, Munekazu Ohno, Takashi Shimokawabe, Takayuki AokiAbstract:Abstract We investigated the Competitive Growth of dendrites at the converging grain boundaries (GBs) of bicrystals during the directional solidification of an Al–Cu alloy by means of two-dimensional phase-field simulations. In particular, the focus was on the recently observed phenomenon of unusual overGrowth during the directional solidification of a Ni-based superalloy, where the favorably oriented (FO) dendrites are overgrown by the unfavorably oriented (UO) ones. The phase-field simulations were accelerated by parallel computations on graphics processing units. The simulation results showed that unusual overGrowth occurs in Al–Cu alloys, indicating that this phenomenon is a common one in metallic materials. It was also concluded that the differences in the diffusion layers in front of the FO and UO dendrites had a dominant effect on the Competitive Growth of dendrites at the converging GB as well as on the unusual overGrowth. In addition, unusual overGrowth was observed in all the FO dendrites with a spacing that allowed the dendrite array to grow stably without necessitating a change in the number of dendrites. The FO dendrite at the GB is overgrown by the UO dendrite when the spacing between the FO dendrite at the GB and the next FO dendrite is approximately equal to the critical minimum spacing. However, the unusual overGrowth was not observed for UO dendrites with a large inclination angle. In this case, all the UO dendrites are blocked by the FO dendrite at the GB, and the FO dendrites migrate toward the UO dendrites.
Jianhua Yang - One of the best experts on this subject based on the ideXlab platform.
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a Competitive lattice model monte carlo method for simulation of Competitive Growth of different polytypes in sic single crystal
Materials Science Forum, 2016Co-Authors: Wei Huang, Huijun Guo, Xi Liu, Xuechao Liu, Yanqing Zheng, Jianhua Yang, Erwei ShiAbstract:A Competitive lattice model was developed for the Kinetic Monte Carlo (KMC) simulation of the competition of 4H and 6H polytypes in SiC crystal Growth based on the on-lattice model. In the Competitive lattice model, site positions are fixed at the perfect crystal lattice positions without any adjustment of the site positions. The effect of surface steps was investigated, and behavior similar to step-controlled homoepitaxy was observed in KMC simulation of PVT grown SiC. Maintaining the step Growth mode is an important factor to maintain a stable single polytype during SiC Growth.
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a Competitive lattice model monte carlo method for simulation Competitive Growth of different polytypes in close packed crystals 4h and 6h silicon carbide
Computational Materials Science, 2015Co-Authors: Huijun Guo, Wei Huang, Xi Liu, Pan Gao, Shiyi Zhuo, Jun Xin, Chengfeng Yan, Xuechao Liu, Yanqing Zheng, Jianhua YangAbstract:Abstract A Competitive lattice model Kinetic Monte Carlo method has been developed and implemented to simulate the SiC crystals Growth by physical vapor transport method. The model is an advancement with respect to standard Monte Carlo algorithms, allowing to simulate polytypes Competitive Growth and defective evolution. The model can simulate the formation and evolution of threading screw dislocations in SiC as well. Kinetics processes with surface energy and bond energy, including deposition, evaporation and diffusion processes are considered in physical criterion in our model. Periodic boundary conditions and non-periodic boundary conditions are carried out. The Competitive Growth between 4H- and 6H-SiC polytypes suggests that retaining the step Growth mode is an important factor to maintain a stable single 4H polytype during SiC Growth. The threading screw dislocations simulation indicates that screw dislocations drive the Growth of SiC. The evolution of surface morphologies demonstrates that fast surface diffusion rate and low Growth rate may be one way to grow high quality, low-roughness 4H-SiC crystals.
Rowena E Martin - One of the best experts on this subject based on the ideXlab platform.
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functional profiling of a plasmodium genome reveals an abundance of essential genes
Cell, 2017Co-Authors: Ellen Bushell, Ana Rita Gomes, Theo Sanderson, Burcu Anar, Gareth Girling, Colin Herd, Tom Metcalf, Katarzyna Modrzynska, Frank Schwach, Rowena E MartinAbstract:The genomes of malaria parasites contain many genes of unknown function. To assist drug development through the identification of essential genes and pathways, we have measured Competitive Growth rates in mice of 2,578 barcoded Plasmodium berghei knockout mutants, representing >50% of the genome, and created a phenotype database. At a single stage of its complex life cycle, P. berghei requires two-thirds of genes for optimal Growth, the highest proportion reported from any organism and a probable consequence of functional optimization necessitated by genomic reductions during the evolution of parasitism. In contrast, extreme functional redundancy has evolved among expanded gene families operating at the parasite-host interface. The level of genetic redundancy in a single-celled organism may thus reflect the degree of environmental variation it experiences. In the case of Plasmodium parasites, this helps rationalize both the relative successes of drugs and the greater difficulty of making an effective vaccine.
Munekazu Ohno - One of the best experts on this subject based on the ideXlab platform.
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uniquely selected primary dendrite arm spacing during Competitive Growth of columnar grains in al cu alloy
Journal of Crystal Growth, 2021Co-Authors: Jaehoon Lee, Yasushi Shibuta, Munekazu Ohno, Tomohiro TakakiAbstract:Abstract The steady-state value of primary dendrite arm spacing (PDAS) in the columnar dendrites growing between the converging and diverging grain boundaries is investigated by means of quantitative phase-field simulations. The simulations show that there is a unique value of PDAS under a given solidification condition in the system with grain boundaries. This is in contrast to existence of allowable range of PDAS under a given solidification in a system without the grain boundaries, i.e., an infinitely large columnar grain investigated in many early works. Such a unique value of PDAS depends on the pulling speed and inclination angle of the crystal, but not on the initial condition; that is, it is independent of the history of solidification condition. The dependences of the unique value on the pulling speed and inclination angle qualitatively agree with the theoretical models.
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Competitive Growth during directional solidification of a binary alloy with natural convection two dimensional phase field study
Modelling and Simulation in Materials Science and Engineering, 2019Co-Authors: Tomohiro Takaki, Shinji Sakane, Munekazu Ohno, Yasushi ShibutaAbstract:Due to the recent acceleration of phase-field simulations using a graphics processing unit (GPU), the mechanism of Competitive Growth among columnar grains has been better understood. In this study, the effects of natural convection, caused by the gravity driven buoyancy force, on the Competitive Growth of columnar grains during directional solidification of bi-crystal and polycrystal binary alloys are investigated by performing two-dimensional large-scale phase-field simulations using a GPU supercomputer. As a result, the downward flow accelerates and the upward flow decelerates the selection speed in Competitive Growth. It is also confirmed that these phenomena are caused by a characteristic liquid flow pattern at the converging and diverging grain boundaries.
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two dimensional phase field simulations of dendrite Competitive Growth during the directional solidification of a binary alloy bicrystal
Acta Materialia, 2014Co-Authors: Tomohiro Takaki, Munekazu Ohno, Takashi Shimokawabe, Takayuki AokiAbstract:Abstract We investigated the Competitive Growth of dendrites at the converging grain boundaries (GBs) of bicrystals during the directional solidification of an Al–Cu alloy by means of two-dimensional phase-field simulations. In particular, the focus was on the recently observed phenomenon of unusual overGrowth during the directional solidification of a Ni-based superalloy, where the favorably oriented (FO) dendrites are overgrown by the unfavorably oriented (UO) ones. The phase-field simulations were accelerated by parallel computations on graphics processing units. The simulation results showed that unusual overGrowth occurs in Al–Cu alloys, indicating that this phenomenon is a common one in metallic materials. It was also concluded that the differences in the diffusion layers in front of the FO and UO dendrites had a dominant effect on the Competitive Growth of dendrites at the converging GB as well as on the unusual overGrowth. In addition, unusual overGrowth was observed in all the FO dendrites with a spacing that allowed the dendrite array to grow stably without necessitating a change in the number of dendrites. The FO dendrite at the GB is overgrown by the UO dendrite when the spacing between the FO dendrite at the GB and the next FO dendrite is approximately equal to the critical minimum spacing. However, the unusual overGrowth was not observed for UO dendrites with a large inclination angle. In this case, all the UO dendrites are blocked by the FO dendrite at the GB, and the FO dendrites migrate toward the UO dendrites.
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theoretical investigation of coarsening process of l10 ordered domain based on phase field method and cluster variation method
Materials Transactions, 2002Co-Authors: Munekazu Ohno, Tetsuo MohriAbstract:A hybridized calculation of Phase Field Method and Cluster Variation Method is applied to investigate the relaxation process of Long-Range-Order parameter (LRO) originating from Competitive Growth of ordered domains. It is shown that the coarsening process proceeds by both the curvature-driven Growth and coalescence among in-phase ordered domains. In the early annealing period, an average radius of ordered domains increases proportional to t 1/2 as predicted by the curvature-driven Growth. In the later period, however, a deviation from this relation is manifested by coalescence process. The LRO relaxation kinetics largely depends on the frequency of coalescence event.
Yasushi Shibuta - One of the best experts on this subject based on the ideXlab platform.
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uniquely selected primary dendrite arm spacing during Competitive Growth of columnar grains in al cu alloy
Journal of Crystal Growth, 2021Co-Authors: Jaehoon Lee, Yasushi Shibuta, Munekazu Ohno, Tomohiro TakakiAbstract:Abstract The steady-state value of primary dendrite arm spacing (PDAS) in the columnar dendrites growing between the converging and diverging grain boundaries is investigated by means of quantitative phase-field simulations. The simulations show that there is a unique value of PDAS under a given solidification condition in the system with grain boundaries. This is in contrast to existence of allowable range of PDAS under a given solidification in a system without the grain boundaries, i.e., an infinitely large columnar grain investigated in many early works. Such a unique value of PDAS depends on the pulling speed and inclination angle of the crystal, but not on the initial condition; that is, it is independent of the history of solidification condition. The dependences of the unique value on the pulling speed and inclination angle qualitatively agree with the theoretical models.
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Competitive Growth during directional solidification of a binary alloy with natural convection two dimensional phase field study
Modelling and Simulation in Materials Science and Engineering, 2019Co-Authors: Tomohiro Takaki, Shinji Sakane, Munekazu Ohno, Yasushi ShibutaAbstract:Due to the recent acceleration of phase-field simulations using a graphics processing unit (GPU), the mechanism of Competitive Growth among columnar grains has been better understood. In this study, the effects of natural convection, caused by the gravity driven buoyancy force, on the Competitive Growth of columnar grains during directional solidification of bi-crystal and polycrystal binary alloys are investigated by performing two-dimensional large-scale phase-field simulations using a GPU supercomputer. As a result, the downward flow accelerates and the upward flow decelerates the selection speed in Competitive Growth. It is also confirmed that these phenomena are caused by a characteristic liquid flow pattern at the converging and diverging grain boundaries.