Powder hot isostatic pressing(HIP) is an effective method to achieve near-net-shape manufacturing of high-quality complex thinwalled titanium alloy parts, and it has received extensive attention in recent years. Howev...Powder hot isostatic pressing(HIP) is an effective method to achieve near-net-shape manufacturing of high-quality complex thinwalled titanium alloy parts, and it has received extensive attention in recent years. However, there are few reports about the microstructure characteristics on the strengthening and toughening mechanisms of powder hot isostatic pressed(HIPed) titanium alloys. Therefore, TA15powder was prepared into alloy by HIP approach, which was used to explore the microstructure characteristics at different HIP temperatures and the corresponding tensile properties and fracture toughness. Results show that the fabricated alloy has a “basket-like structure” when the HIP temperature is below 950℃, consisting of lath clusters and surrounding small equiaxed grains belts. When the HIP temperature is higher than 950℃, the microstructure gradually transforms into the Widmanstatten structure, accompanied by a significant increase in grain size. The tensile strength and elongation are reduced from 948 MPa and 17.3% for the 910℃ specimen to 861 MPa and 10% for the 970℃ specimen.The corresponding tensile fracture mode changes from transcrystalline plastic fracture to mixed fracture including intercrystalline cleavage.The fracture toughness of the specimens increases from 82.64 MPa·m^(1/2)for the 910℃ specimen to 140.18 MPa·m^(1/2)for the 970℃ specimen.Specimens below 950℃ tend to form holes due to the prior particle boundaries(PPBs), which is not conducive to toughening. Specimens above 950℃ have high fracture toughness due to the crack deflection, crack branching, and shear plastic deformation of the Widmanstatten structure. This study provides a valid reference for the development of powder HIPed titanium alloy.展开更多
The first Mars exploration mission of China(Tianwen-1)is scheduled to be launched in 2020;a charged particle telescope,the Mars Energetic Particle Analyzer(MEPA),is carried as one of the payloads on the orbiter.The ME...The first Mars exploration mission of China(Tianwen-1)is scheduled to be launched in 2020;a charged particle telescope,the Mars Energetic Particle Analyzer(MEPA),is carried as one of the payloads on the orbiter.The MEPA is designed to measure solar energetic particles(SEPs)and galactic cosmic rays(GCRs)in the near-Mars space and in the transfer orbit from Earth to Mars.Before the launch,the MEPA was calibrated in ground experiments with radioactive sources,electronic pulses,and accelerator beams.The calibration parameters,such as energy conversion constants,threshold values for the triggers,and particle identification criteria,were determined and have been stored for onboard use.The validity of the calibration parameters has been verified with radioactive sources and beams.The calibration results indicate that the MEPA can measure charged particles reliably,as designed,and that it can satisfy the requirements of the Tianwen-1 mission.展开更多
[Objectives] To investigate the characteristics of arsenic content of Ophiocordyceps sinensis in Sichuan Province. [Methods]Using ICP-MS( Inductively Coupled Plasma-Mass Spectrometry),we studied the 30 samples of O. s...[Objectives] To investigate the characteristics of arsenic content of Ophiocordyceps sinensis in Sichuan Province. [Methods]Using ICP-MS( Inductively Coupled Plasma-Mass Spectrometry),we studied the 30 samples of O. sinensis from 25 places of production in Sichuan Province as well as the arsenic content in the habitat soil. [Results] The arsenic content of O. sinensis in Sichuan Province was0. 62-9. 16 mg/kg; the arsenic content in habitat soil was 3. 93-59. 90 mg/kg. [Conclusions]90% of O. sinensis products from Sichuan Province exceeded the arsenic content limit of 1 mg/kg in the health food,and as a comparison,the arsenic content of samples from Qinghai,Tibet,Gansu was over the limit.展开更多
In this study, a cellulose-degrading bacterium was isolated from paddy soils in Chengdu City. After 2 d of culture, the average diameter of hydrolytic circles on CMC-Congo red medium was 26 -30 mm. Single colonies on ...In this study, a cellulose-degrading bacterium was isolated from paddy soils in Chengdu City. After 2 d of culture, the average diameter of hydrolytic circles on CMC-Congo red medium was 26 -30 mm. Single colonies on LB plates were white and wrinkled. The isolated strain was identified as a Gram-negative bacterium by Gram staining, which could produce short red-like spores. Colony PCR was performed using the bacterial 16S rDNA universal primers. A 1 429 kb DNA fragment was amplified. Based on sequence homology analysis and comprehensive analysis, the isolated strain was identified as Bacillus velezensi, which was named CDBV62 according to the origin.展开更多
High-voltage and high-power IGBT chips have a noticeable carrier storage effect,which is related to the load current.However,the research on the carrier storage effect of existing IGBT behavior models is insufficient....High-voltage and high-power IGBT chips have a noticeable carrier storage effect,which is related to the load current.However,the research on the carrier storage effect of existing IGBT behavior models is insufficient.In this paper,An improved behavioral model for high-voltage and high-power insulated gate bipolar transistor(IGBT)chips is proposed,which could be used under different load conditions.The problems for applying the traditional behavioral model to more load conditions are discussed.Carrier behavior,in the wide base region,is analyzed,and the analytical expression of the carrierstorage-effect equivalent capacitance and the initial value of the tail current are provided to establish an improved IGBT behavioral model.A corresponding parameter extraction method is proposed.In order to verify the improved behavioral model,an experimental platform is built for resistive load and inductive load,and the results show that the accuracy of the improved behavioral model is much better than that of the traditional model.In addition,the errors of the improved model are within 12.5%under different current and load types.Considering that the maximum error of other models,which could be applied in a variety of load conditions,is more than 25%,the accuracy of the model proposed in this paper is excellent.展开更多
Parkinson's disease(PD)is one of the most common neu-rodegenerative diseases with progressive motor dysfunction and pathologically characterized by the degeneration of dopaminergic neurons in the substantia nigra ...Parkinson's disease(PD)is one of the most common neu-rodegenerative diseases with progressive motor dysfunction and pathologically characterized by the degeneration of dopaminergic neurons in the substantia nigra of the midbrain and the development of neuronal Lewy bodies.Autosomal recessive mutations in the gene PINK1 leads to inherited idiopathic PD.PINK1 is known to regulate PARKIN translocation upon mitochondrial damage which drives their removal via selective autophagy,a process known as mito-phagy(Pickrell and Youle 2015;Cummins and Gotz 2018).While mitochondrial defects had been noted in postmortem studies of patient brain samples with PD,there is a continuing debate as how mutations in PINK1 may lead to selective neuronal death in the substantia nigra.展开更多
基金financially supported by the National Natural Science Foundation of China (Nos. 51874037 and 51922004)the Beijing Natural Science Foundation (No. 2212035)+1 种基金the Fundamental Research Funds for the Central Universities (No. FRF-TP-19005C1Z)the National Defense Basic Research Project (No. JCKY2017213004)。
文摘Powder hot isostatic pressing(HIP) is an effective method to achieve near-net-shape manufacturing of high-quality complex thinwalled titanium alloy parts, and it has received extensive attention in recent years. However, there are few reports about the microstructure characteristics on the strengthening and toughening mechanisms of powder hot isostatic pressed(HIPed) titanium alloys. Therefore, TA15powder was prepared into alloy by HIP approach, which was used to explore the microstructure characteristics at different HIP temperatures and the corresponding tensile properties and fracture toughness. Results show that the fabricated alloy has a “basket-like structure” when the HIP temperature is below 950℃, consisting of lath clusters and surrounding small equiaxed grains belts. When the HIP temperature is higher than 950℃, the microstructure gradually transforms into the Widmanstatten structure, accompanied by a significant increase in grain size. The tensile strength and elongation are reduced from 948 MPa and 17.3% for the 910℃ specimen to 861 MPa and 10% for the 970℃ specimen.The corresponding tensile fracture mode changes from transcrystalline plastic fracture to mixed fracture including intercrystalline cleavage.The fracture toughness of the specimens increases from 82.64 MPa·m^(1/2)for the 910℃ specimen to 140.18 MPa·m^(1/2)for the 970℃ specimen.Specimens below 950℃ tend to form holes due to the prior particle boundaries(PPBs), which is not conducive to toughening. Specimens above 950℃ have high fracture toughness due to the crack deflection, crack branching, and shear plastic deformation of the Widmanstatten structure. This study provides a valid reference for the development of powder HIPed titanium alloy.
基金supported by the Engineering and Technological Research Project on Civil Aerospace Technologies of the CNSA.
文摘The first Mars exploration mission of China(Tianwen-1)is scheduled to be launched in 2020;a charged particle telescope,the Mars Energetic Particle Analyzer(MEPA),is carried as one of the payloads on the orbiter.The MEPA is designed to measure solar energetic particles(SEPs)and galactic cosmic rays(GCRs)in the near-Mars space and in the transfer orbit from Earth to Mars.Before the launch,the MEPA was calibrated in ground experiments with radioactive sources,electronic pulses,and accelerator beams.The calibration parameters,such as energy conversion constants,threshold values for the triggers,and particle identification criteria,were determined and have been stored for onboard use.The validity of the calibration parameters has been verified with radioactive sources and beams.The calibration results indicate that the MEPA can measure charged particles reliably,as designed,and that it can satisfy the requirements of the Tianwen-1 mission.
基金Supported by Special Fiscal Funds in Sichuan Province(ZL2017-06)
文摘[Objectives] To investigate the characteristics of arsenic content of Ophiocordyceps sinensis in Sichuan Province. [Methods]Using ICP-MS( Inductively Coupled Plasma-Mass Spectrometry),we studied the 30 samples of O. sinensis from 25 places of production in Sichuan Province as well as the arsenic content in the habitat soil. [Results] The arsenic content of O. sinensis in Sichuan Province was0. 62-9. 16 mg/kg; the arsenic content in habitat soil was 3. 93-59. 90 mg/kg. [Conclusions]90% of O. sinensis products from Sichuan Province exceeded the arsenic content limit of 1 mg/kg in the health food,and as a comparison,the arsenic content of samples from Qinghai,Tibet,Gansu was over the limit.
文摘In this study, a cellulose-degrading bacterium was isolated from paddy soils in Chengdu City. After 2 d of culture, the average diameter of hydrolytic circles on CMC-Congo red medium was 26 -30 mm. Single colonies on LB plates were white and wrinkled. The isolated strain was identified as a Gram-negative bacterium by Gram staining, which could produce short red-like spores. Colony PCR was performed using the bacterial 16S rDNA universal primers. A 1 429 kb DNA fragment was amplified. Based on sequence homology analysis and comprehensive analysis, the isolated strain was identified as Bacillus velezensi, which was named CDBV62 according to the origin.
基金This work was supported by the National Natural Science Foundation of China-State Grid Corporation Joint Fund for Smart Grid(No.U1766219).
文摘High-voltage and high-power IGBT chips have a noticeable carrier storage effect,which is related to the load current.However,the research on the carrier storage effect of existing IGBT behavior models is insufficient.In this paper,An improved behavioral model for high-voltage and high-power insulated gate bipolar transistor(IGBT)chips is proposed,which could be used under different load conditions.The problems for applying the traditional behavioral model to more load conditions are discussed.Carrier behavior,in the wide base region,is analyzed,and the analytical expression of the carrierstorage-effect equivalent capacitance and the initial value of the tail current are provided to establish an improved IGBT behavioral model.A corresponding parameter extraction method is proposed.In order to verify the improved behavioral model,an experimental platform is built for resistive load and inductive load,and the results show that the accuracy of the improved behavioral model is much better than that of the traditional model.In addition,the errors of the improved model are within 12.5%under different current and load types.Considering that the maximum error of other models,which could be applied in a variety of load conditions,is more than 25%,the accuracy of the model proposed in this paper is excellent.
文摘Parkinson's disease(PD)is one of the most common neu-rodegenerative diseases with progressive motor dysfunction and pathologically characterized by the degeneration of dopaminergic neurons in the substantia nigra of the midbrain and the development of neuronal Lewy bodies.Autosomal recessive mutations in the gene PINK1 leads to inherited idiopathic PD.PINK1 is known to regulate PARKIN translocation upon mitochondrial damage which drives their removal via selective autophagy,a process known as mito-phagy(Pickrell and Youle 2015;Cummins and Gotz 2018).While mitochondrial defects had been noted in postmortem studies of patient brain samples with PD,there is a continuing debate as how mutations in PINK1 may lead to selective neuronal death in the substantia nigra.
