The safety and longevity of small modular reactors are affected by reactor pressure vessels,which are complex integral components made of SA508 Gr.3 low-alloy steel.In this study,the impacts of heat accumulation on th...The safety and longevity of small modular reactors are affected by reactor pressure vessels,which are complex integral components made of SA508 Gr.3 low-alloy steel.In this study,the impacts of heat accumulation on the microstructural and mechanical characteristics(tensile properties and Charpy V-notched impact energy)of SA508 Gr.3 steel fabricated using laser powder-directed energy deposition were investigated.Rectangular samples were prepared using long raster and short raster scanning strate-gies for changing heat buildup,and the mechanical tests were conducted depending on build direction.The time-temperature profile measured at a fixed point in the long raster sample showed a lower max-imum temperature and a higher cooling rate,indicating lower heat accumulation compared to that of the short raster sample.In each build direction,the yield strength of the long raster sample was 45.8%-60.5%higher and its ductile-brittle transition temperature was 76.8-103.8℃ lower than that of the short raster sample.Additionally,compared to conventionally made samples and without requiring heat treat-ment,the long raster sample exhibited over a 45%increase in yield strength and a 22.7℃ reduction in the ductile-brittle transition temperature.The superior combination in long raster samples is induced by smaller effective grain size,smaller cementite,and a higher pre-existing dislocation density.The re-sults emphasize the importance of controlling heat accumulation throughout the additive manufacturing process and provide valuable insights into the use of additive manufacturing for manufacturing reactor pressure vessels in the nuclear industry.展开更多
Heavy metal pollution has received increasing attention in recent years mainly because of the public awareness of environmental issues. In this study we have evaluated the effect of cadmium （Cd） on enzymes activity,...Heavy metal pollution has received increasing attention in recent years mainly because of the public awareness of environmental issues. In this study we have evaluated the effect of cadmium （Cd） on enzymes activity, substrate utilization pattern and diversity of microbial communities in soil spiked with 0, 20, 40, 60, 80, and 100 mg/kg Cd, during 60 d of incubation at 25℃. Enzyme activities determined at 0, 15, 30, 45, and 60 d after heavy metal application（DAA） showed marked declines for various Cd treatments, and up to 60 DAA, 100 mg/kg Cd resulted in 50.1%, 47.4%, and 39.8% decreases in soil urease, acid phosphatase and dehydrogenase activities, respectively to control. At 60 DAA, substrate utilization pattern of soil microbial communities determined by inoculating Biolog ECO plates indicated that Cd addition had markedly inhibited the functional activity of soil microbial communities and multivariate analysis of sole carbon source utilization showed significantly different utilization patterns for 80 and 100 mg/kg Cd treatments. The structural diversity of soil microbial communities assessed by PCR-DGGE method at 60 DAA, illustrated that DGGE patterns in soil simplified with increasing Cd concentration, and clustering of DGGE profiles for various Cd treatments revealed that they had more than 50% difference with that of control.展开更多
In this study,single-phase NbTiZr and NbTiZr(MoTa)_(0.1) medium-entropy alloys(MEAs)were investigated for their use in biomedical implants.The alloys were prepared by arc melting,and were then cold-rolled,annealed,and...In this study,single-phase NbTiZr and NbTiZr(MoTa)_(0.1) medium-entropy alloys(MEAs)were investigated for their use in biomedical implants.The alloys were prepared by arc melting,and were then cold-rolled,annealed,and characterized in terms of phase analysis,mechanical properties,fractography,and wear resistance.Both alloys showed a single body-centered cubic phase with superior mechanical,and tribological properties compared to commercially available biomedical alloys.Mo and Ta-containing MEAs showed higher tensile yield strength(1060±18 MPa)and higher tensile ductility(~20%),thus overcoming the strength-ductility trade-off with no signs of transformation-induced plasticity,twinning,or precipitation.The generalized stacking fault energy(GSFE)calculations on the{112}<111>slip system by the first-principles calculations based on density functional theory showed that the addition of less than0.2 molar fraction of Mo and Ta lowers the GSFE curves.This behavior posits the increase in ductility of the alloy by facilitating slips although strength is also increased by solid solution strengthening.The wear resistance of both alloys against hardened steel surfaces was superior to that of commercial biomedical alloys.Thus,we concluded that NbTiZr(MoTa)_(0.1)MEA with good tensile ductility is a potential candidate for biomedical implants.展开更多
In this study,the application of medium-and high-entropy(Mo Ta)_(x)Nb Ti Zr alloys in biomedical implants was systematically analyzed.The alloy with the best combination of mechanical properties was selected and chara...In this study,the application of medium-and high-entropy(Mo Ta)_(x)Nb Ti Zr alloys in biomedical implants was systematically analyzed.The alloy with the best combination of mechanical properties was selected and characterized for in vitro and in vivo response for the first time to examine its biomedical properties.A logarithmic increase in the hardness and the yield strength was observed as a function of the Mo and Ta content.Alloys with up to 0.4 mol fraction of Mo and Ta showed a plastic strain of more than 30%under compression.The nanoindentation results showed that the addition of Mo and Ta increased the elastic modulus of the system linearly.It was surmised that the addition of Ta and Mo above a critical concentration(mole fraction=0.4)was unfavorable from a biomedical perspective as it increased the brittleness and elastic modulus and decreased the ductility of the system.Therefore,the(Mo Ta)_(0.2)Nb Ti Zr alloy is a potential structural material for biomedical implants because of its excellent strength and ductility.The developed alloy was investigated for its corrosion properties and compared with commercial biomedical alloys.Furthermore,the biocompatibility of the alloy was examined using an in vivo examination.The alloy was implanted in the skeletal muscles of mice for four weeks and the histology of the surrounding tissue was studied.The alloy exhibited strong passive behavior in a phosphate buffer solution and non-toxic soft tissue response.展开更多
Forest soils have high carbon densities compared to other land-uses.Soil carbon sequestration is important to reduce CO 2 concentrations in the atmosphere.An eff ective climate change mitigation strategy involves limi...Forest soils have high carbon densities compared to other land-uses.Soil carbon sequestration is important to reduce CO 2 concentrations in the atmosphere.An eff ective climate change mitigation strategy involves limiting the emissions of greenhouse gases from soils.Khyber Pakhtunkhwa is the most forested province of Pakistan,hosting about one-third of the country’s 4.5×106 ha forest area.Soil organic carbon in the province’s forests was estimated through a fi eld-based study carried out during 2014–17 covering the whole province.Data was collected from 373 sample plots laid out in diff erent forest types using a stratifi ed cluster sampling technique.The total quantity of soil organic carbon was estimated at 59.4×106 t with an average of 52.4±5.3 t/ha.About 69%of the total soil carbon is present in temperate forests.Subtropical broad-leaved and subtropical pine forests constitute 11.4%and 8.8%of the soil carbon stock respectively.Similarly,subalpine and oak forests have respective shares of 5.1%and 5.7%in the soil carbon pool.The lowest carbon stock(0.1%)was found in dry-tropical thorn forests.The highest soil carbon density was found in subalpine forests(69.5±7.2 t/ha)followed by moist temperate forests(68.5±6.7 t/ha)and dry temperate forests(60.7±6.5 t/ha).Oak forests have carbon density of 43.4±7.1 t/ha.Subtropical pine,subtropical broad-leaved and dry tropical thorn forests have soil carbon densities of 36.3±3.7,32.8±6.2 and 31.5±3.5 t/ha,respectively.The forests of the Khyber Pakhtunkhwa province have substantial amounts of soil carbon which must be conserved for climate change mitigation and maintenance of sound forest health.展开更多
基金supported by the National Research Foundation of the Ministry of Science and ICT(MSIT)of the Republic of Korea(grant No.2022M3H4A1A02076759)also supported financially by the Korea Atomic Energy Research Institute R&D program(Con-tract No.524590-24).
文摘The safety and longevity of small modular reactors are affected by reactor pressure vessels,which are complex integral components made of SA508 Gr.3 low-alloy steel.In this study,the impacts of heat accumulation on the microstructural and mechanical characteristics(tensile properties and Charpy V-notched impact energy)of SA508 Gr.3 steel fabricated using laser powder-directed energy deposition were investigated.Rectangular samples were prepared using long raster and short raster scanning strate-gies for changing heat buildup,and the mechanical tests were conducted depending on build direction.The time-temperature profile measured at a fixed point in the long raster sample showed a lower max-imum temperature and a higher cooling rate,indicating lower heat accumulation compared to that of the short raster sample.In each build direction,the yield strength of the long raster sample was 45.8%-60.5%higher and its ductile-brittle transition temperature was 76.8-103.8℃ lower than that of the short raster sample.Additionally,compared to conventionally made samples and without requiring heat treat-ment,the long raster sample exhibited over a 45%increase in yield strength and a 22.7℃ reduction in the ductile-brittle transition temperature.The superior combination in long raster samples is induced by smaller effective grain size,smaller cementite,and a higher pre-existing dislocation density.The re-sults emphasize the importance of controlling heat accumulation throughout the additive manufacturing process and provide valuable insights into the use of additive manufacturing for manufacturing reactor pressure vessels in the nuclear industry.
基金The National Basic Research Programof China(2005CB121104) the National Key Project for Science and Technology of China(No.2001BA804A25andthe Natural Science Foundation of Zhejiang Province(Y504128)
文摘Heavy metal pollution has received increasing attention in recent years mainly because of the public awareness of environmental issues. In this study we have evaluated the effect of cadmium （Cd） on enzymes activity, substrate utilization pattern and diversity of microbial communities in soil spiked with 0, 20, 40, 60, 80, and 100 mg/kg Cd, during 60 d of incubation at 25℃. Enzyme activities determined at 0, 15, 30, 45, and 60 d after heavy metal application（DAA） showed marked declines for various Cd treatments, and up to 60 DAA, 100 mg/kg Cd resulted in 50.1%, 47.4%, and 39.8% decreases in soil urease, acid phosphatase and dehydrogenase activities, respectively to control. At 60 DAA, substrate utilization pattern of soil microbial communities determined by inoculating Biolog ECO plates indicated that Cd addition had markedly inhibited the functional activity of soil microbial communities and multivariate analysis of sole carbon source utilization showed significantly different utilization patterns for 80 and 100 mg/kg Cd treatments. The structural diversity of soil microbial communities assessed by PCR-DGGE method at 60 DAA, illustrated that DGGE patterns in soil simplified with increasing Cd concentration, and clustering of DGGE profiles for various Cd treatments revealed that they had more than 50% difference with that of control.
基金supported by the National Research Foundation of Korea(NRF-2020R1A5A6017701,NRF-2121R1A2C2014025)。
文摘In this study,single-phase NbTiZr and NbTiZr(MoTa)_(0.1) medium-entropy alloys(MEAs)were investigated for their use in biomedical implants.The alloys were prepared by arc melting,and were then cold-rolled,annealed,and characterized in terms of phase analysis,mechanical properties,fractography,and wear resistance.Both alloys showed a single body-centered cubic phase with superior mechanical,and tribological properties compared to commercially available biomedical alloys.Mo and Ta-containing MEAs showed higher tensile yield strength(1060±18 MPa)and higher tensile ductility(~20%),thus overcoming the strength-ductility trade-off with no signs of transformation-induced plasticity,twinning,or precipitation.The generalized stacking fault energy(GSFE)calculations on the{112}<111>slip system by the first-principles calculations based on density functional theory showed that the addition of less than0.2 molar fraction of Mo and Ta lowers the GSFE curves.This behavior posits the increase in ductility of the alloy by facilitating slips although strength is also increased by solid solution strengthening.The wear resistance of both alloys against hardened steel surfaces was superior to that of commercial biomedical alloys.Thus,we concluded that NbTiZr(MoTa)_(0.1)MEA with good tensile ductility is a potential candidate for biomedical implants.
基金the National Research Foundation of Korea(NRF-2020R1A5A6017701,NRF2015R1A2A2A01002436)。
文摘In this study,the application of medium-and high-entropy(Mo Ta)_(x)Nb Ti Zr alloys in biomedical implants was systematically analyzed.The alloy with the best combination of mechanical properties was selected and characterized for in vitro and in vivo response for the first time to examine its biomedical properties.A logarithmic increase in the hardness and the yield strength was observed as a function of the Mo and Ta content.Alloys with up to 0.4 mol fraction of Mo and Ta showed a plastic strain of more than 30%under compression.The nanoindentation results showed that the addition of Mo and Ta increased the elastic modulus of the system linearly.It was surmised that the addition of Ta and Mo above a critical concentration(mole fraction=0.4)was unfavorable from a biomedical perspective as it increased the brittleness and elastic modulus and decreased the ductility of the system.Therefore,the(Mo Ta)_(0.2)Nb Ti Zr alloy is a potential structural material for biomedical implants because of its excellent strength and ductility.The developed alloy was investigated for its corrosion properties and compared with commercial biomedical alloys.Furthermore,the biocompatibility of the alloy was examined using an in vivo examination.The alloy was implanted in the skeletal muscles of mice for four weeks and the histology of the surrounding tissue was studied.The alloy exhibited strong passive behavior in a phosphate buffer solution and non-toxic soft tissue response.
基金This research is part of the doctoral dissertation of the fi rst author at PMAS Arid Agriculture University,Rawalpindi,Pakistan(AAUR).The authors are extremely grateful to Prof.Dr.Sarwat N.Mirza,former Vice-Chancellor of PMAS Arid Agriculture University,Rawalpindi,for his valuable inputs and support during the study period.Thanks are also extended to the staff of Forest Mensuration Branch,Pakistan Forest Institute,Peshawar for their help in data collection in the fi eld.
文摘Forest soils have high carbon densities compared to other land-uses.Soil carbon sequestration is important to reduce CO 2 concentrations in the atmosphere.An eff ective climate change mitigation strategy involves limiting the emissions of greenhouse gases from soils.Khyber Pakhtunkhwa is the most forested province of Pakistan,hosting about one-third of the country’s 4.5×106 ha forest area.Soil organic carbon in the province’s forests was estimated through a fi eld-based study carried out during 2014–17 covering the whole province.Data was collected from 373 sample plots laid out in diff erent forest types using a stratifi ed cluster sampling technique.The total quantity of soil organic carbon was estimated at 59.4×106 t with an average of 52.4±5.3 t/ha.About 69%of the total soil carbon is present in temperate forests.Subtropical broad-leaved and subtropical pine forests constitute 11.4%and 8.8%of the soil carbon stock respectively.Similarly,subalpine and oak forests have respective shares of 5.1%and 5.7%in the soil carbon pool.The lowest carbon stock(0.1%)was found in dry-tropical thorn forests.The highest soil carbon density was found in subalpine forests(69.5±7.2 t/ha)followed by moist temperate forests(68.5±6.7 t/ha)and dry temperate forests(60.7±6.5 t/ha).Oak forests have carbon density of 43.4±7.1 t/ha.Subtropical pine,subtropical broad-leaved and dry tropical thorn forests have soil carbon densities of 36.3±3.7,32.8±6.2 and 31.5±3.5 t/ha,respectively.The forests of the Khyber Pakhtunkhwa province have substantial amounts of soil carbon which must be conserved for climate change mitigation and maintenance of sound forest health.
