The microstructures and crystal growth directions of permanent mould casting and directionally solidified Al-Mg alloys with different Mg contents have been investigated. The results indicate that the effect of Mg cont...The microstructures and crystal growth directions of permanent mould casting and directionally solidified Al-Mg alloys with different Mg contents have been investigated. The results indicate that the effect of Mg content on microstructure is basically same for the alloys prepared by these two methods. The primary grains change from cellular crystals to developed columnar dendrites, and then to equiaxed dendrites as the Mg content is increased. Simultaneously, both the cellular or columnar grain region and the primary trunk spacing decrease. All of these changes are mainly attributed to the constitutional supercooling resulting from Mg element. Comparatively, the cellular or columnar crystals of the directionally solidified alloys are straighter and more parallel than those of the permanent mould casting alloys. These have straight or wavy grain boundaries, one of the most important microstructure characteristics of feathery grains. However, the transverse microstructure and growth direction reveal that they do not belong to feathery grains. The Mg seemingly can affect the crystal growth direction, but does not result in the formation of feathery grains under the conditions employed in the study.展开更多
Sapphire, belonging to hexagonal crystal system, is typically anisotropic which makes it direction-sensitive. To research the effects of growth directions on properties of sapphire, c-[0001] seed(c-sapphire) and a-[...Sapphire, belonging to hexagonal crystal system, is typically anisotropic which makes it direction-sensitive. To research the effects of growth directions on properties of sapphire, c-[0001] seed(c-sapphire) and a-[11-20] seed(a-sapphire) were used to prepare sapphire by edge-defined film-fed growth(EFG) method. The samples were analyzed through lattice integrity, dislocation and corrosion performance by double-crystal XRD, OM, AFM, SEM and EDX. It was shown that the lattice integrities of two growth-direction crystals were both well due to the small FWHM values. While the average densities of dislocation in c-sapphire and a-sapphire were 9.2×103 and 3.9×103 cm-2 respectively, the energy of dislocation in c-sapphire was lower than that in a-sapphire. During Strong Phosphoric Acid(SPA) etching, the surface of c-sapphire basically kept smooth but in a-sapphire there were many point-like corrosion pits where aluminum and oxygen atoms lost by 2:1. Our work means that it will be promising for growing c-[0001] seed sapphire by EFG if aided by parameter optimization.展开更多
Investigation of selectivity of crystal growth direction in layered double hydroxides is helpful to control their particle sizes in different directions. Mg-AI layered double hydroxides (LDHs) were synthesized using a...Investigation of selectivity of crystal growth direction in layered double hydroxides is helpful to control their particle sizes in different directions. Mg-AI layered double hydroxides (LDHs) were synthesized using a coprecipitation method. The influences of aging temperature, aging time, and Mg/AI molar ratio on the crystal structure, the LDHs particle size, and the selectivity of crystal growth in different directions were investigated. The results show that the size of the crystallites in the a direction is larger than that in the c direction for all experimental conditions, indicating faster crystal growth in the a direction than in the c direction. The crystallite sizes in the a and c directions both increase with decreasing Mg/AI molar ratio but with less difference between the sizes in the two directions. Therefore, the crystal growth rate in the c direction increases more than that in the a direction as the Mg/AI molar ratio decreases. The influence of the aging time, aging temperature, and Mg/AI molar ratio on the selectivity of the crystal growth direction can be used to prepare LDHs with selected sizes in the a and c directions.展开更多
A quantitative cellular automaton model is used to study the cell-to-dendrite transition(CDT) in directional solidification. We give a detailed description of the CDT by carefully examining the influence of the phys...A quantitative cellular automaton model is used to study the cell-to-dendrite transition(CDT) in directional solidification. We give a detailed description of the CDT by carefully examining the influence of the physical parameters, including:the Gibbs–Thomson coefficient Γ, the solute diffusivity Dl, the solute partition coefficient k0, and the liquidus slope ml. It is found that most of the parameters agree with the Kurz and Fisher(KF) criterion, except for k0. The intrinsic relations among the critical velocity Vcd, the cellular primary spacing λc,max, and the critical spacing λcd are investigated.展开更多
Neurotrophins play a major role in the regulation of neuronal growth such as neurite sprouting or regeneration in response to nerve injuries. The role of nerve growth factor, neurotrophin-3, and brain-derived neurotro...Neurotrophins play a major role in the regulation of neuronal growth such as neurite sprouting or regeneration in response to nerve injuries. The role of nerve growth factor, neurotrophin-3, and brain-derived neurotrophic factor in maintaining the survival of peripheral neurons remains poorly understood. In regenerative medicine, different modalities have been investigated for the delivery of growth factors to the injured neurons, in search of a suitable system for clinical applications. This study was to investigate the influence of nerve growth factor, neurotrophin-3 and brain-derived neurotrophic factor on the growth of neurites using two in vitro models of dorsal root ganglia explants and dorsal root ganglia-derived primary cell dissociated cultures. Quantitative data showed that the total neurite length and tortuosity were differently influenced by trophic factors. Nerve growth factor and, indirectly, brain-derived neurotrophic factor stimulate the tortuous growth of sensory fibers and the formation of cell clusters. Neurotrophin-3, however, enhances neurite growth in terms of length and linearity allowing for a more organized and directed axonal elongation towards a peripheral target compared to the other growth factors. These findings could be of considerable importance for any clinical application of neurotrophic factors in peripheral nerve regeneration. Ethical approval was obtained from the Regione Piemonte Animal Ethics Committee ASLTO1(file # 864/2016-PR) on September 14, 2016.展开更多
The growth of proeutectoid ferrite in Fe-0.15%C-0.8 % Mn carbon steel during continuous cooling process was observed in situ and tracked dynamically by using a high temperature confocal scanning laser microscope ( HT...The growth of proeutectoid ferrite in Fe-0.15%C-0.8 % Mn carbon steel during continuous cooling process was observed in situ and tracked dynamically by using a high temperature confocal scanning laser microscope ( HTC SLM), and the growing process was also investigated. The growth regularity of proeutectoid ferrite plates within austenite was obtained by analyzing the growth fashions and directions and quantitatively studying the growth rates. The results show that the proeutectoid ferrite plates grow in the fashion of creeping, twisting, branching off and de flection within austenite grain. The proeutectoid ferrite plates can grow up along preferential orientation but not strictly. Its growth direction fluctuates and changes in a small range. The growth rate also changes with the change in growth fashion and direction. When the proeutectoid ferrite grows in the fashion of deflection, the average growth rate of proeutectoid ferrite before its deflection is about 61.9, and 46.2 μm/s after the 15°deflection. At the begin ning of proeutectoid ferrite growing, there is a fast growing stage. As the tip of proeutectoid ferrite extends forward continuously, the growth rate will slow down. Therefore, it will induce the proeutectoid ferrite to deflect and grow along another favorable direction, then it will grow rapidly again.展开更多
Broadband optoelectronic devices intrigue enormous interests on account of their promising potential in optical communications,sensors and environmental monitoring.PbSe nanocrystals are promising candidates for the co...Broadband optoelectronic devices intrigue enormous interests on account of their promising potential in optical communications,sensors and environmental monitoring.PbSe nanocrystals are promising candidates for the construction of next-generation photodetectors due to their fascinating intrinsic properties and solution-processed compatibility with varied substrates.Here,we report the fabrication of a broadband photodetector on the basis of high-quality solution-processed PbSe nanorods in rock-salt phase grown along unconventionally anisotropic growth direction of<112>zone axis.The rock-salt PbSe nanorods are synthesized in solution phase over the catalysis of Ag2Se with relatively high-temperature body-centered cubic phase via a solution-solid-solid growth regime using oleylamine and oleic acid as solvents and stabilizer surfactants,from which the PbSe nanorods with the unconventionally anisotropic growth direction are controllably grown in size and shape in the synthetic procedure typically with about 17 nm in diameter and 58 nm in length on average.Meanwhile,the PbSe nanorods-based photodetector exhibits a broadband response from 405 to 1,064 nm with a high responsivity of 0.78 A·W^(-1)and a fast response time of 17.5μs.The response time is much faster in comparison with most of the PbSe-based photodetectors with response time in millisecond level.展开更多
Monte Carlo (MC) simulations, including multiple physical and chemical mechanisms, were performed to investigate the microstructure evolution of a conducting metal filament in a typical oxide-electrolyte-based ReRAM...Monte Carlo (MC) simulations, including multiple physical and chemical mechanisms, were performed to investigate the microstructure evolution of a conducting metal filament in a typical oxide-electrolyte-based ReRAM. It has been revealed that the growth direction and geometry of the conductive filament are controlled by the ion migration rate in the electrolyte layer during the formation procedure. When the migration rate is rela- tive high, the filament is shown to grow from cathode to anode. When the migration rate is low, the growth direction is expected to start from the anode. Simulated conductive filament (CF) geometries and I-V characteristics are also illustrated and analyzed. A good agreement between the simulation results and experiment data is obtained.展开更多
The microstructure, microsegregation, and mechanical properties of directional solidified Mg–3.0Nd–1.5Gd ternary alloys were experimentally studied. Experimental results showed that the solidification microstructure...The microstructure, microsegregation, and mechanical properties of directional solidified Mg–3.0Nd–1.5Gd ternary alloys were experimentally studied. Experimental results showed that the solidification microstructure was composed of dendrite primary a(Mg) phase and interdendritic a(Mg) · Mg12(Nd, Gd) eutectic and Mg5 Gd phase. The primary dendrite arm spacing k1 and secondary dendrite arm spacing k2 were found to be depended on the cooling rate R in the form k1= 8.0415 9 10-6R-0.279 and k2= 6.8883 9 10-6R-0.205, respectively, under the constant temperature gradient of40 K/mm and in the region of cooling rates from 0.4 to 4 K/s. The concentration profiles of Nd and Gd elements calculated by Scheil model were found to be deviated from the ones measured by EPMA to varying degrees, due to ignorance of the back diffusion of the solutes Nd and Gd within a(Mg) matrix. And microsegregation of Gd depended more on the growth rate, compared with Nd microsegregation. The directionally solidified experimental alloy exhibited higher strength than the non-directionally solidified alloy, and the tensile strength of the directionally solidified experimental alloy was improved,while the corresponding elongation decreased with the increase of growth rate.展开更多
Rod-shaped mesoporous titanosilicate composites (RMTSs) with controllable aspect ratios (ARs) were fabricated using cetyltrimethylammonium bromide (CTAB) and ammonium hydroxide (NH4OH) at a continuous stirring...Rod-shaped mesoporous titanosilicate composites (RMTSs) with controllable aspect ratios (ARs) were fabricated using cetyltrimethylammonium bromide (CTAB) and ammonium hydroxide (NH4OH) at a continuous stirring rate, resulting in ARs ranging from 1 to 5. Slowing the stirring rate or increasing the concentration of CTAB mainly impacted the length growth, whereas NH4OH affected the width growth. Photocatalytic activity studies revealed that the length of RMTSs played a more significant role than the width at lower ARs in their photocatalytic activity.展开更多
In this contribution,the microscopic fracture mechanism and extension criterion for mixed type crack in ductile material under plane mixed mode loading are investigated in details.A universal extension criterion for t...In this contribution,the microscopic fracture mechanism and extension criterion for mixed type crack in ductile material under plane mixed mode loading are investigated in details.A universal extension criterion for the mixed type crack,i.e.the crack propagates along the direction of the maximum gradient of equivalent stress,is suggested.This new criterion is used to predict the propagation direction of mixed type crack,showing a good agreement with other theories for different types of mode mixity.Moreover,the numerical verification is also carried out for the case of an edge crack with different mixed mode loadings.Finally,a potential application to three-dimensional fracture in the ductile material induced by holes is also discussed.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.51061010)the Program for New Century Excellent Talents in University of China(Grant No.NCET-10-0023)the Program for Hongliu Outstanding Talents of Lanzhou University of Technology
文摘The microstructures and crystal growth directions of permanent mould casting and directionally solidified Al-Mg alloys with different Mg contents have been investigated. The results indicate that the effect of Mg content on microstructure is basically same for the alloys prepared by these two methods. The primary grains change from cellular crystals to developed columnar dendrites, and then to equiaxed dendrites as the Mg content is increased. Simultaneously, both the cellular or columnar grain region and the primary trunk spacing decrease. All of these changes are mainly attributed to the constitutional supercooling resulting from Mg element. Comparatively, the cellular or columnar crystals of the directionally solidified alloys are straighter and more parallel than those of the permanent mould casting alloys. These have straight or wavy grain boundaries, one of the most important microstructure characteristics of feathery grains. However, the transverse microstructure and growth direction reveal that they do not belong to feathery grains. The Mg seemingly can affect the crystal growth direction, but does not result in the formation of feathery grains under the conditions employed in the study.
基金Funded by the Special Fund of Jiangsu Province for the Transformation of Scientific and Technological Achievements(No.BA2012049)the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Sapphire, belonging to hexagonal crystal system, is typically anisotropic which makes it direction-sensitive. To research the effects of growth directions on properties of sapphire, c-[0001] seed(c-sapphire) and a-[11-20] seed(a-sapphire) were used to prepare sapphire by edge-defined film-fed growth(EFG) method. The samples were analyzed through lattice integrity, dislocation and corrosion performance by double-crystal XRD, OM, AFM, SEM and EDX. It was shown that the lattice integrities of two growth-direction crystals were both well due to the small FWHM values. While the average densities of dislocation in c-sapphire and a-sapphire were 9.2×103 and 3.9×103 cm-2 respectively, the energy of dislocation in c-sapphire was lower than that in a-sapphire. During Strong Phosphoric Acid(SPA) etching, the surface of c-sapphire basically kept smooth but in a-sapphire there were many point-like corrosion pits where aluminum and oxygen atoms lost by 2:1. Our work means that it will be promising for growing c-[0001] seed sapphire by EFG if aided by parameter optimization.
文摘Investigation of selectivity of crystal growth direction in layered double hydroxides is helpful to control their particle sizes in different directions. Mg-AI layered double hydroxides (LDHs) were synthesized using a coprecipitation method. The influences of aging temperature, aging time, and Mg/AI molar ratio on the crystal structure, the LDHs particle size, and the selectivity of crystal growth in different directions were investigated. The results show that the size of the crystallites in the a direction is larger than that in the c direction for all experimental conditions, indicating faster crystal growth in the a direction than in the c direction. The crystallite sizes in the a and c directions both increase with decreasing Mg/AI molar ratio but with less difference between the sizes in the two directions. Therefore, the crystal growth rate in the c direction increases more than that in the a direction as the Mg/AI molar ratio decreases. The influence of the aging time, aging temperature, and Mg/AI molar ratio on the selectivity of the crystal growth direction can be used to prepare LDHs with selected sizes in the a and c directions.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51271213 and 51323008)the National Basic Research Program of China(Grant No.2011CB610402)+2 种基金the National High Technology Research and Development Program of China(Grant No.2013AA031103)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20116102110016)the China Postdoctoral Science Foundation(Grant No.2013M540771)
文摘A quantitative cellular automaton model is used to study the cell-to-dendrite transition(CDT) in directional solidification. We give a detailed description of the CDT by carefully examining the influence of the physical parameters, including:the Gibbs–Thomson coefficient Γ, the solute diffusivity Dl, the solute partition coefficient k0, and the liquidus slope ml. It is found that most of the parameters agree with the Kurz and Fisher(KF) criterion, except for k0. The intrinsic relations among the critical velocity Vcd, the cellular primary spacing λc,max, and the critical spacing λcd are investigated.
基金supported by the research start-up and the MWU’s intramural grant(to MF)the Italian MURST-MIUR foundation(to SG and IP)
文摘Neurotrophins play a major role in the regulation of neuronal growth such as neurite sprouting or regeneration in response to nerve injuries. The role of nerve growth factor, neurotrophin-3, and brain-derived neurotrophic factor in maintaining the survival of peripheral neurons remains poorly understood. In regenerative medicine, different modalities have been investigated for the delivery of growth factors to the injured neurons, in search of a suitable system for clinical applications. This study was to investigate the influence of nerve growth factor, neurotrophin-3 and brain-derived neurotrophic factor on the growth of neurites using two in vitro models of dorsal root ganglia explants and dorsal root ganglia-derived primary cell dissociated cultures. Quantitative data showed that the total neurite length and tortuosity were differently influenced by trophic factors. Nerve growth factor and, indirectly, brain-derived neurotrophic factor stimulate the tortuous growth of sensory fibers and the formation of cell clusters. Neurotrophin-3, however, enhances neurite growth in terms of length and linearity allowing for a more organized and directed axonal elongation towards a peripheral target compared to the other growth factors. These findings could be of considerable importance for any clinical application of neurotrophic factors in peripheral nerve regeneration. Ethical approval was obtained from the Regione Piemonte Animal Ethics Committee ASLTO1(file # 864/2016-PR) on September 14, 2016.
基金Item Sponsored by Scientific Director Fund of National Natural Science Foundation of China(51141010)
文摘The growth of proeutectoid ferrite in Fe-0.15%C-0.8 % Mn carbon steel during continuous cooling process was observed in situ and tracked dynamically by using a high temperature confocal scanning laser microscope ( HTC SLM), and the growing process was also investigated. The growth regularity of proeutectoid ferrite plates within austenite was obtained by analyzing the growth fashions and directions and quantitatively studying the growth rates. The results show that the proeutectoid ferrite plates grow in the fashion of creeping, twisting, branching off and de flection within austenite grain. The proeutectoid ferrite plates can grow up along preferential orientation but not strictly. Its growth direction fluctuates and changes in a small range. The growth rate also changes with the change in growth fashion and direction. When the proeutectoid ferrite grows in the fashion of deflection, the average growth rate of proeutectoid ferrite before its deflection is about 61.9, and 46.2 μm/s after the 15°deflection. At the begin ning of proeutectoid ferrite growing, there is a fast growing stage. As the tip of proeutectoid ferrite extends forward continuously, the growth rate will slow down. Therefore, it will induce the proeutectoid ferrite to deflect and grow along another favorable direction, then it will grow rapidly again.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.U1932150 and 21571166)Anhui Provincial Natural Science Foundation(No.1908085QB72).
文摘Broadband optoelectronic devices intrigue enormous interests on account of their promising potential in optical communications,sensors and environmental monitoring.PbSe nanocrystals are promising candidates for the construction of next-generation photodetectors due to their fascinating intrinsic properties and solution-processed compatibility with varied substrates.Here,we report the fabrication of a broadband photodetector on the basis of high-quality solution-processed PbSe nanorods in rock-salt phase grown along unconventionally anisotropic growth direction of<112>zone axis.The rock-salt PbSe nanorods are synthesized in solution phase over the catalysis of Ag2Se with relatively high-temperature body-centered cubic phase via a solution-solid-solid growth regime using oleylamine and oleic acid as solvents and stabilizer surfactants,from which the PbSe nanorods with the unconventionally anisotropic growth direction are controllably grown in size and shape in the synthetic procedure typically with about 17 nm in diameter and 58 nm in length on average.Meanwhile,the PbSe nanorods-based photodetector exhibits a broadband response from 405 to 1,064 nm with a high responsivity of 0.78 A·W^(-1)and a fast response time of 17.5μs.The response time is much faster in comparison with most of the PbSe-based photodetectors with response time in millisecond level.
基金Project supported by the Ministry of Science and Technology of China(Nos.2010CB934200,2011CBA00602,2009CB930803,2011CB921804,2011AA010401,2011AA010402,XDA06020102)the National Natural Science Foundation of China(Nos.61221004,61274091,60825403,61106119,61106082,61306117)
文摘Monte Carlo (MC) simulations, including multiple physical and chemical mechanisms, were performed to investigate the microstructure evolution of a conducting metal filament in a typical oxide-electrolyte-based ReRAM. It has been revealed that the growth direction and geometry of the conductive filament are controlled by the ion migration rate in the electrolyte layer during the formation procedure. When the migration rate is rela- tive high, the filament is shown to grow from cathode to anode. When the migration rate is low, the growth direction is expected to start from the anode. Simulated conductive filament (CF) geometries and I-V characteristics are also illustrated and analyzed. A good agreement between the simulation results and experiment data is obtained.
基金supported by the National Basic Research Program(973 Program) of China under Grant No.2010CB631200(2010CB631206)the National Natural Science Foundation of China(NSFC) under Grant No.50801061,No.50931004,No.51071165the fund of the State Key Laboratory of Solidification Processing in NWPU under Grant No.SKLSP201112
基金financially supported by the National Natural Science Foundation of China (No. 51071129)the Special Funds of the National Natural Science Foundation of China (No. 51227001)
文摘The microstructure, microsegregation, and mechanical properties of directional solidified Mg–3.0Nd–1.5Gd ternary alloys were experimentally studied. Experimental results showed that the solidification microstructure was composed of dendrite primary a(Mg) phase and interdendritic a(Mg) · Mg12(Nd, Gd) eutectic and Mg5 Gd phase. The primary dendrite arm spacing k1 and secondary dendrite arm spacing k2 were found to be depended on the cooling rate R in the form k1= 8.0415 9 10-6R-0.279 and k2= 6.8883 9 10-6R-0.205, respectively, under the constant temperature gradient of40 K/mm and in the region of cooling rates from 0.4 to 4 K/s. The concentration profiles of Nd and Gd elements calculated by Scheil model were found to be deviated from the ones measured by EPMA to varying degrees, due to ignorance of the back diffusion of the solutes Nd and Gd within a(Mg) matrix. And microsegregation of Gd depended more on the growth rate, compared with Nd microsegregation. The directionally solidified experimental alloy exhibited higher strength than the non-directionally solidified alloy, and the tensile strength of the directionally solidified experimental alloy was improved,while the corresponding elongation decreased with the increase of growth rate.
基金supported by the National Natural Science Foundation of China(Nos.20976100,51372124)the Natural Science Foundation of Shandong Province(Nos.ZR2010BM013, ZR2011BQ009)+1 种基金the Program for Scientific Research Innovation Team in Colleges and Universities of Shandong Province(No. 201207)Key Laboratory of Colloid and Surface Chemistry, Ministry of Education(Shandong University,No.201205)
文摘Rod-shaped mesoporous titanosilicate composites (RMTSs) with controllable aspect ratios (ARs) were fabricated using cetyltrimethylammonium bromide (CTAB) and ammonium hydroxide (NH4OH) at a continuous stirring rate, resulting in ARs ranging from 1 to 5. Slowing the stirring rate or increasing the concentration of CTAB mainly impacted the length growth, whereas NH4OH affected the width growth. Photocatalytic activity studies revealed that the length of RMTSs played a more significant role than the width at lower ARs in their photocatalytic activity.
基金supported by the Natural Science Foundation of Shannxi (No. 2005A19)the Open Foundation of Engineering Key Laboratory of Disaster Prevention and Structural Safety,Guangxi Univ.(No. 2008TMKF004)the National Natural Science Foundation (Nos. 10932007 and 11172228)
文摘In this contribution,the microscopic fracture mechanism and extension criterion for mixed type crack in ductile material under plane mixed mode loading are investigated in details.A universal extension criterion for the mixed type crack,i.e.the crack propagates along the direction of the maximum gradient of equivalent stress,is suggested.This new criterion is used to predict the propagation direction of mixed type crack,showing a good agreement with other theories for different types of mode mixity.Moreover,the numerical verification is also carried out for the case of an edge crack with different mixed mode loadings.Finally,a potential application to three-dimensional fracture in the ductile material induced by holes is also discussed.