The structure of the all-d-metal alloy Ni_(50-x)Co_(x)Mn_(25)V_(25)(x=0–50)is investigated by using theoretical and experimental methods.The first-principles calculations indicate that the most stable structure of th...The structure of the all-d-metal alloy Ni_(50-x)Co_(x)Mn_(25)V_(25)(x=0–50)is investigated by using theoretical and experimental methods.The first-principles calculations indicate that the most stable structure of the Ni_2MnV alloy is face-centered cubic (fcc)type structure with ferrimagnetic state and the equilibrium lattice constant is 3.60A,which is in agreement with the experimental result.It is remarkable that replacing partial Ni with Co can turn the alloy from the fcc structure to the B2-type Heusler structure as Co content x>37 by using the melting spinning method,implying that the d–d hybridization between Co/Mn elements and low-valent elements V stabilizes the Heusler structure.The Curie temperature T_(C) of all-dmetal Heuser alloy Ni_(50-x)Co_(x)Mn_(25)V_(25)(x>37)increases almost linearly with the increase of Co due to that the interaction of Co–Mn is stronger than that of Ni–Mn.A magnetic transition from ferromagnetic state to weak magnetic state accompanying with grinding stress induced transformation from B2 to the dual-phase of B2 and fcc has been observed in these all-d-metal Heusler alloys.This phase transformation and magnetic change provide a guide to overcome the brittleness and make the all-d-metal Heusler alloy interesting in stress and magnetic driving structural transition.展开更多
A novel hair sample pre-treatment method based on high-speed grinding and solid-phase microextraction(SPME)had been applied for the determination of amphetamines,ketamine and their metabolites in hair samples by liqui...A novel hair sample pre-treatment method based on high-speed grinding and solid-phase microextraction(SPME)had been applied for the determination of amphetamines,ketamine and their metabolites in hair samples by liquid chromatography mass spectrometry(LC-MS).A 20mg sample of hair was ground with 2 mL of saturated sodium carbonate solution using a high-efficiency hair grinder with 70 Hz osillation for 2min at 4℃.After centrifuging,1.5mL of the supernatant was transferred and treated with SPME by direct immersion(DI-SPME).The target analytes extracted by fibre were desorbed and analysed using LC-MS.Under the optimum conditions,a recovery of 90.2%-95.8%was obtained for all analytes.The analytical method was linear for all analytes in the range from 0.2 to 10 ng/mg with the correlation coefficient ranging from 0.9985 to 0.9993.The detection limits for all analytes were estimated to be 0.067 ng/mg.The accuracy(mean relative error)was within±6.9%and the precision(relative standard error)was less than 6.8%.The combination of high-speed grinding of hair and SPME had the advantages of being easy to perform,environment-friendly and high in detection sensitivity.The proposed method offered an altermative ana lytical approach for the sensitive detection of drugs in hair samples for forensic purposes.展开更多
Monocrystalline beta-phase gallium oxide (β-Ga_(2)O_(3)) is a promising ultrawide bandgap semiconductor material. However, the deformation mechanism in ultraprecision machining has not yet been revealed. The aim of t...Monocrystalline beta-phase gallium oxide (β-Ga_(2)O_(3)) is a promising ultrawide bandgap semiconductor material. However, the deformation mechanism in ultraprecision machining has not yet been revealed. The aim of this study is to investigate the damage pattern and formation mechanism of monocrystalline β-Ga_(2)O_(3)in different grinding processes. Transmission electron microscopy was used to observe the subsurface damage in rough, fine, and ultrafine grinding processes. Nanocrystals and stacking faults existed in all three processes, dislocations and twins were observed in the rough and fine grinding processes, cracks were also observed in the rough grinding process, and amorphous phase were only present in the ultrafine grinding process. The subsurface damage thickness of the samples decreased with the reduction in the grit radius and the grit depth of cut. Subsurface damage models for grinding process were established on the basis of the grinding principle, revealing the mechanism of the mechanical effect of grits on the damage pattern. The formation of nanocrystals and amorphous phase was related to the grinding conditions and material characteristics. It is important to investigate the ultraprecision grinding process of monocrystalline β-Ga_(2)O_(3). The results in this work are supposed to provide guidance for the damage control of monocrystalline β-Ga_(2)O_(3)grinding process.展开更多
Pre-stressed dry grinding can result in a hardened layer on the part surface while the surface residual stress is controlled.Considering the factors of the thermal field,pre-stress,and microstructural transformation,a...Pre-stressed dry grinding can result in a hardened layer on the part surface while the surface residual stress is controlled.Considering the factors of the thermal field,pre-stress,and microstructural transformation,a proximate model of surface residual stress for pre-stressed dry grinding is established using the ANSYS finite element simulation method and verified through experiment.The variation laws and mechanisms of the residual stress along with the grinding parameters are revealed.Under the comprehensive effect of pre-stress and phase transformation,the residual stress of pre-stressed dry grinding is revealed mainly as compressive stress.This increases as the pre・stress and grinding depth increase.Under the coupling effect,pre-stress has larger influence on the residual stress than the grinding depth.The model can analyze and predict the residual stress of pre-stressed dry grinding in general.展开更多
The precursor of Bi Pb Sr Ca Cu O superconductor was prepared by spray drying nitrate solution with nominal composition of Bi∶Pb∶Sr∶Ca∶Cu=1.84∶0.34∶1.91∶2.03∶3.06. Instrumentation of XRD、 DTA、 DTA TG...The precursor of Bi Pb Sr Ca Cu O superconductor was prepared by spray drying nitrate solution with nominal composition of Bi∶Pb∶Sr∶Ca∶Cu=1.84∶0.34∶1.91∶2.03∶3.06. Instrumentation of XRD、 DTA、 DTA TG、 FT IR and SEM was used for the evaluation of the influences of calcination and fine grinding on the synthesis of sperconducting materials with “high T c phase”. The experimental results indicated that the fine grinding with organic additives influenced the formation and the transition of the superconducting phase. The phase transition of the superconductor can be reduced greatly by means of high temperature grinding.展开更多
Time-frequency methods are effective tools in identifying the frequency content of a signal and revealing its timevariant features.This paper presents the use of instantaneous features(i.e.,instantaneous energy and si...Time-frequency methods are effective tools in identifying the frequency content of a signal and revealing its timevariant features.This paper presents the use of instantaneous features(i.e.,instantaneous energy and signal phase)of acoustic emission(AE)in the detection of thermal damage to the workpiece in grinding.The low-order frequency moments of a scalogram are used to obtain both the instantaneous energy and the mean frequency at which the signal phase is recovered.The grinding process is monitored using AE for a variety of operating conditions,including regular grinding,grinding at higher cutting speed and larger feed,and small dressing depth of cut.The instantaneous features extracted by the scalogram are compared with the results obtained by the empirical mode decomposition.It has been found that both the instantaneous energy and phase deviation indicate the presence of burn damage and serve as robust and reliable indicators,providing a basis for detecting the grinding burn.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51671024 and 52088101)State Key Lab of Advanced Metals and Materials(Grant No.2019Z12)the Fundamental Research Funds for the Central Universities(Grant No.FRF-BD-20-12A)。
文摘The structure of the all-d-metal alloy Ni_(50-x)Co_(x)Mn_(25)V_(25)(x=0–50)is investigated by using theoretical and experimental methods.The first-principles calculations indicate that the most stable structure of the Ni_2MnV alloy is face-centered cubic (fcc)type structure with ferrimagnetic state and the equilibrium lattice constant is 3.60A,which is in agreement with the experimental result.It is remarkable that replacing partial Ni with Co can turn the alloy from the fcc structure to the B2-type Heusler structure as Co content x>37 by using the melting spinning method,implying that the d–d hybridization between Co/Mn elements and low-valent elements V stabilizes the Heusler structure.The Curie temperature T_(C) of all-dmetal Heuser alloy Ni_(50-x)Co_(x)Mn_(25)V_(25)(x>37)increases almost linearly with the increase of Co due to that the interaction of Co–Mn is stronger than that of Ni–Mn.A magnetic transition from ferromagnetic state to weak magnetic state accompanying with grinding stress induced transformation from B2 to the dual-phase of B2 and fcc has been observed in these all-d-metal Heusler alloys.This phase transformation and magnetic change provide a guide to overcome the brittleness and make the all-d-metal Heusler alloy interesting in stress and magnetic driving structural transition.
基金Financial supports from Major Project of Sichuan Provincial Public Security Department[grant number 201901]Support Program of Outstanding Talents in the New Century in Universities of Fujian,China,Young Scientific Natural Science Foundation of Universities in Fujian,China and Funding for High-Level Talent of Luzhou Municipal People's Government-Southwest Medical University are gratefully acknowledged.
文摘A novel hair sample pre-treatment method based on high-speed grinding and solid-phase microextraction(SPME)had been applied for the determination of amphetamines,ketamine and their metabolites in hair samples by liquid chromatography mass spectrometry(LC-MS).A 20mg sample of hair was ground with 2 mL of saturated sodium carbonate solution using a high-efficiency hair grinder with 70 Hz osillation for 2min at 4℃.After centrifuging,1.5mL of the supernatant was transferred and treated with SPME by direct immersion(DI-SPME).The target analytes extracted by fibre were desorbed and analysed using LC-MS.Under the optimum conditions,a recovery of 90.2%-95.8%was obtained for all analytes.The analytical method was linear for all analytes in the range from 0.2 to 10 ng/mg with the correlation coefficient ranging from 0.9985 to 0.9993.The detection limits for all analytes were estimated to be 0.067 ng/mg.The accuracy(mean relative error)was within±6.9%and the precision(relative standard error)was less than 6.8%.The combination of high-speed grinding of hair and SPME had the advantages of being easy to perform,environment-friendly and high in detection sensitivity.The proposed method offered an altermative ana lytical approach for the sensitive detection of drugs in hair samples for forensic purposes.
基金the National Natural Science Foundation of China(Grant Nos.51975091,51991372,and 51735004)the National Key R&D Program of China(Grant No.2018YFB1201804-1)+1 种基金the Lab of Space Optoelectronic Measurement&Perception(LabSOMP-2019-05)Jiangsu Key Laboratory of Precision and Micro-Manufacturing Technology.
文摘Monocrystalline beta-phase gallium oxide (β-Ga_(2)O_(3)) is a promising ultrawide bandgap semiconductor material. However, the deformation mechanism in ultraprecision machining has not yet been revealed. The aim of this study is to investigate the damage pattern and formation mechanism of monocrystalline β-Ga_(2)O_(3)in different grinding processes. Transmission electron microscopy was used to observe the subsurface damage in rough, fine, and ultrafine grinding processes. Nanocrystals and stacking faults existed in all three processes, dislocations and twins were observed in the rough and fine grinding processes, cracks were also observed in the rough grinding process, and amorphous phase were only present in the ultrafine grinding process. The subsurface damage thickness of the samples decreased with the reduction in the grit radius and the grit depth of cut. Subsurface damage models for grinding process were established on the basis of the grinding principle, revealing the mechanism of the mechanical effect of grits on the damage pattern. The formation of nanocrystals and amorphous phase was related to the grinding conditions and material characteristics. It is important to investigate the ultraprecision grinding process of monocrystalline β-Ga_(2)O_(3). The results in this work are supposed to provide guidance for the damage control of monocrystalline β-Ga_(2)O_(3)grinding process.
基金This paper is supported by the Fundamental Research Funds for the Central Universities of China(Grant No.N170303012)the National Natural Science Foundation of China(Grant No.51775101).
文摘Pre-stressed dry grinding can result in a hardened layer on the part surface while the surface residual stress is controlled.Considering the factors of the thermal field,pre-stress,and microstructural transformation,a proximate model of surface residual stress for pre-stressed dry grinding is established using the ANSYS finite element simulation method and verified through experiment.The variation laws and mechanisms of the residual stress along with the grinding parameters are revealed.Under the comprehensive effect of pre-stress and phase transformation,the residual stress of pre-stressed dry grinding is revealed mainly as compressive stress.This increases as the pre・stress and grinding depth increase.Under the coupling effect,pre-stress has larger influence on the residual stress than the grinding depth.The model can analyze and predict the residual stress of pre-stressed dry grinding in general.
文摘The precursor of Bi Pb Sr Ca Cu O superconductor was prepared by spray drying nitrate solution with nominal composition of Bi∶Pb∶Sr∶Ca∶Cu=1.84∶0.34∶1.91∶2.03∶3.06. Instrumentation of XRD、 DTA、 DTA TG、 FT IR and SEM was used for the evaluation of the influences of calcination and fine grinding on the synthesis of sperconducting materials with “high T c phase”. The experimental results indicated that the fine grinding with organic additives influenced the formation and the transition of the superconducting phase. The phase transition of the superconductor can be reduced greatly by means of high temperature grinding.
文摘Time-frequency methods are effective tools in identifying the frequency content of a signal and revealing its timevariant features.This paper presents the use of instantaneous features(i.e.,instantaneous energy and signal phase)of acoustic emission(AE)in the detection of thermal damage to the workpiece in grinding.The low-order frequency moments of a scalogram are used to obtain both the instantaneous energy and the mean frequency at which the signal phase is recovered.The grinding process is monitored using AE for a variety of operating conditions,including regular grinding,grinding at higher cutting speed and larger feed,and small dressing depth of cut.The instantaneous features extracted by the scalogram are compared with the results obtained by the empirical mode decomposition.It has been found that both the instantaneous energy and phase deviation indicate the presence of burn damage and serve as robust and reliable indicators,providing a basis for detecting the grinding burn.
