The existence of a significant electron drift instability(EDI) in the Hall thruster is considered as one of the possible causes of the abnormal increase in axial electron mobility near the outlet of the channel. In re...The existence of a significant electron drift instability(EDI) in the Hall thruster is considered as one of the possible causes of the abnormal increase in axial electron mobility near the outlet of the channel. In recent years, extensive simulation research on the characteristics of EDI has been conducted, but the excitation mechanism and growth mechanism of EDI in linear stage and nonlinear stage remain unclear. In this work, a one-dimensional PIC model in the azimuthal direction of the thruster near-exit region is established to gain further insights into the mechanism of the EDI in detail, and the effects of different types of propellants on EDI characteristics are discussed. The changes in axial electron transport caused by EDI under different types of propellants and electromagnetic field strengths are also examined. The results indicate that EDI undergoes a short linear growth phase before transitioning to the nonlinear phase and finally reaching saturation through the ion Landau damping. The EDI drives a significant ion heating in the azimuthal direction through electron–ion friction before entering the quasi-steady state, which increases the axial mobility of the electrons. Using lighter atomic weight propellant can effectively suppress the oscillation amplitude of EDI, but it will increase the linear growth rate, frequency, and phase velocity of EDI. Compared with the classical mobility, the axial electron mobility under the EDI increases by three orders of magnitude, which is consistent with experimental phenomena. The change of propellant type is insufficient to significantly change the axial electron mobility. It is also found that the collisions between electrons and neutral gasescan significantly affect the axial electron mobility under the influence of EDI, and lead the strength of the electric field to increase and the strength of the magnetic field to decrease, thereby both effectively suppressing the axial transport of electrons.展开更多
In the plasma sheath, there is a significant gradient in ion velocity, resulting in strong stress on ions treated as a fluid. This aspect has often been neglected in previous sheath studies. This study is based on the...In the plasma sheath, there is a significant gradient in ion velocity, resulting in strong stress on ions treated as a fluid. This aspect has often been neglected in previous sheath studies. This study is based on the Braginskii plasma transport theory and establishes a 1D3V sheath fluid model that takes into account the ion stress effect. Under the assumption that ions undergo both electric and diamagnetic drift in the presheath region, self-consistent boundary conditions,including the ion Bohm velocity, are derived based on the property of the Sagdeev pseudopotential.Furthermore, assuming that the electron velocity at the wall follows a truncated Maxwell distribution, the wall floating potential is calculated, leading to a more accurate sheath thickness estimation. The results show that ion stress significantly reduces the sheath thickness, enhances ion Bohm velocity, wall floating potential, and ion flux at the wall. It hinders the acceleration of ions within the sheath, leading to notable alterations in the particle density profiles within the sheath. Further research indicates that in ion stress, bulk viscous stress has the greatest impact on sheath properties.展开更多
Montmorillonite and clinoptilolite zeolite were used as representative materials to prepare calcined clay-cement binary cementitious materials in order to study the effect of calcination treatment on the activation of...Montmorillonite and clinoptilolite zeolite were used as representative materials to prepare calcined clay-cement binary cementitious materials in order to study the effect of calcination treatment on the activation of clay minerals and the activity difference between layered and framed clays in this research.The influence of different calcined clay content(2%,4%,6%,8%,10%)on the fluidity,compressive strength,microstructure,phase change,and hydration heat of cement-based materials were analyzed.The calcined clay improves the fluidity of cement-based materials as compared with the uncalcined group.The addition of calcined montmorillonite(CMT)improves the development of mechanical strength,and the optimal compressive strength reaches 85 MPa at 28 days with 8%CMT.However,the activity of calcined clinoptilolite zeolite(CZL)is weak with few reaction sites,which slightly reduced the mechanical strength as compared to the blank sample.The addition of CMT changes the microscopic morphology of hydration products such as C-S-H and C-A-H,leading to the formation and transformation of ettringite in the early stage.It promotes the gradual polymerization of Si-O bonds into Si-O-Si bonds simultaneously,which accelerates the early hydration process.However,CZL acts mainly as a filling function in the cementitious system.In brief,CMT as an admixture can improve the mechanical properties of cement,but CZL has little effect.This work provides a guideline for the applications of calcined clay in cement,considering the influence of clay type on workability and mechanical strength.展开更多
The properties of an atmospheric-pressure collisional plasma sheath with nonextensively distributed electrons and hypothetical ionization source terms are studied in this work. The Bohm criterion for the magnetized pl...The properties of an atmospheric-pressure collisional plasma sheath with nonextensively distributed electrons and hypothetical ionization source terms are studied in this work. The Bohm criterion for the magnetized plasma is extended in the presence of an ion–neutral collisional force and ionization source. The effects of electron nonextensive distribution, ionization frequency, ion–neutral collision, magnetic field angle and ion temperature on the Bohm criterion of the plasma sheath are numerically analyzed. The fluid equations are solved numerically in the plasma–wall transition region using a modified Bohm criterion as the boundary condition. The plasma sheath properties such as charged particle density, floating sheath potential and thickness are thoroughly investigated under different kinds of ion source terms, contributions of collisions, and magnetic fields. The results show that the effect of the ion source term on the properties of atmosphericpressure collisional plasma sheath is significant. As the ionization frequency increases, the Mach number of the Bohm criterion decreases and the range of possible values narrows. When the ion source is considered, the space charge density increases, the sheath potential drops more rapidly,and the sheath thickness becomes narrower. In addition, ion–neutral collision, magnetic field angle and ion temperature also significantly affect the sheath potential profile and sheath thickness.展开更多
Objective: To observe the effect of slow-released morphine tablets by rectum in treating the patients of moderate to severe cancer pain with server nausea and vomiting or dysphagia. Methods: 54 cases of cancer patient...Objective: To observe the effect of slow-released morphine tablets by rectum in treating the patients of moderate to severe cancer pain with server nausea and vomiting or dysphagia. Methods: 54 cases of cancer patients with server nau- sea and vomiting symptoms or dysphagia were treated with slow-released morphine tablets by rectum, 30-90 mg/time, once every 12 hours. The drug dose was titrated by degree of pain, and the effects and adverse effects were observed. Results: The total effective rate was 81.48%, complete response rate was 51.85% (28/54), and the partial response rate was 29.63% (16/54); there were no obvious toxicities, and the common adverse symptoms included nausea (16.7%) and vomiting (9.3%). Conclusion: The treatment of slow-released morphine tablet by rectum could effectively control cancer pain, the adverse effects were slight than that by mouth. It is safe and effective to be worthy of the adhibition in clinic.展开更多
The secondary electron emission(SEE) and inclined magnetic field are typical features at the channel wall of the Hall thruster acceleration region(AR), and the characteristics of the magnetized sheath have a significa...The secondary electron emission(SEE) and inclined magnetic field are typical features at the channel wall of the Hall thruster acceleration region(AR), and the characteristics of the magnetized sheath have a significant effect on the radial potential distribution, ion radial acceleration and wall erosion. In this work, the magnetohydrodynamics model is used to study the characteristics of the magnetized sheath with SEE in the AR of Hall thruster. The electrons are assumed to obey non-extensive distribution, the ions and secondary electrons are magnetized.Based on the Sagdeev potential, the modified Bohm criterion is derived, and the influences of the non-extensive parameter and magnetic field on the AR sheath structure and parameters are discussed. Results show that, with the decrease of the parameter q, the high-energy electron leads to an increase of the potential drop in the sheath, and the sheath thickness expands accordingly,the kinetic energy rises when ions reach the wall, which can aggravate the wall erosion.Increasing the magnetic field inclination angle in the AR of the Hall thruster, the Lorenz force along the x direction acting as a resistance decelerating ions becomes larger which can reduce the wall erosion, while the strength of magnetic field in the AR has little effect on Bohm criterion and wall potential. The propellant type also has a certain effect on the values of wall potential,secondary electron number density and sheath thickness.展开更多
In this study,the workability and reaction mechanism of metakaolin(MK)based geopolymer blended with rice husk ash(RHA)and silica fume(SF)was investigated.The prepared samples were subjected to tests including compress...In this study,the workability and reaction mechanism of metakaolin(MK)based geopolymer blended with rice husk ash(RHA)and silica fume(SF)was investigated.The prepared samples were subjected to tests including compressive strength and fluidity tests.X-ray diffraction(XRD)and Scanning electron microscope(SEM)were employed to explore the phase composition and microstructure of geopolymers.The molecular bonding information of geopolymer was provided by Fourier transform infrared spectroscopy(FTIR).Meanwhile,the porosity of geopolymer was obtained by Mercury intrusion porosimeter(MIP)analysis.The high-activity RHA obtained after calcination at 600℃ was used as a supplementary cementitious material to prepare geopolymer.The properties of preventing morphology cracking and compressive strength are improved.The addition of RHA and SF changes the working performance of MK based geopolymer and provided a theoretical basis for future practical applications.Meanwhile,the high chemical activity of SF and RHA contributes to the healing of microcracks.展开更多
BACKGROUND Glomus tumors are rare neoplasms,usually found on the fingers or toes.Glomus tumours that occur in the lower leg are even rarer and is likely to be misdiagnosed or underdiagnosed.This article will document ...BACKGROUND Glomus tumors are rare neoplasms,usually found on the fingers or toes.Glomus tumours that occur in the lower leg are even rarer and is likely to be misdiagnosed or underdiagnosed.This article will document the diagnosis,treatment,and follow-up of a rare glomus tumor of the lower leg,which had been misdiagnosed for up to 15 years.CASE SUMMARY The patient was a A 36-year-old woman who had suffered from localized pain in her left lower leg for 15 years.After a complete physical examination,a glomus tumor on her lower leg was considered and removed surgically.The specimen was pathologically diagnosed as a glomus tumor.There was no relapse at a 4-year follow-up.CONCLUSION Correct diagnosis and complete removal of the glomus tumor is important.展开更多
Folding of molecules is an essential process in nature,and various molecular machines achieve their chemical and mechanical function via controlled folding of molecular conformations.The electric field offers a unique...Folding of molecules is an essential process in nature,and various molecular machines achieve their chemical and mechanical function via controlled folding of molecular conformations.The electric field offers a unique strategy to drive the folding of molecular conformation and to control charge transport through single molecules but remains unexplored.The single-molecule break junction technique provides access to detect the conformational changes via the monitoring of single-molecule conductance,and the electric field between two metal electrodes with nanoscale spacing can provide an extremely strong to achieve in-situ control and detection of molecular folding at the single-molecule level.Here,we use the electric field to control the single-molecule folding using the scanning tunneling microscope break junction(STM-BJ)technique.The electric fields induced folding could lead to a∼1400%conductance change of the single-molecule junctions,and the folding/unfolding process can be in-situ switched at the scale of milliseconds.DFT calculations suggest the conformational control originates from the electric fieldinduced charge injection,and the formation of homoconjugated conformation with the overlapped orbitals.This work provides the first demonstration of electric field-driven molecular folding,which is essential for the understanding of molecular machines in nature and for the design of artificial molecular machines.展开更多
Seeking the strategies of designing highly conductive molecular structures is one of the core researches in molecular electronics.As asymmetric structure has manifested feasible properties in comprehensive fields, we ...Seeking the strategies of designing highly conductive molecular structures is one of the core researches in molecular electronics.As asymmetric structure has manifested feasible properties in comprehensive fields, we introduce the structures of asymmetric platinum(Ⅱ) complexes into the charge transport study at single-molecule scale for the first time. The single-molecule conductance measurement results reveal that, in platinum(Ⅱ)-aryloligoynyl structures, the conductance of asymmetrically coordinated complexes is obviously higher than that of the symmetric isomers with the same molecular length, while the conductance is almost identical in symmetric and asymmetric platinum(Ⅱ)-oligoynyl complexes. Theoretical study uncovers that, upon connecting to the oligoynyl structure, the aromatic group effectively extends the π-system of the whole conductive backbone and gathers the HOMO population mainly on the longer oligoynyl ligand, which reduces the energy barrier in electron transport and enhances the conductance through HOMO energy lifting. This result provides feasible strategy for achieving high conductive molecular devices.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos.11975062 and 11605021)the Fundamental Research Funds for the Central Universities (Grant No.3132023192)。
文摘The existence of a significant electron drift instability(EDI) in the Hall thruster is considered as one of the possible causes of the abnormal increase in axial electron mobility near the outlet of the channel. In recent years, extensive simulation research on the characteristics of EDI has been conducted, but the excitation mechanism and growth mechanism of EDI in linear stage and nonlinear stage remain unclear. In this work, a one-dimensional PIC model in the azimuthal direction of the thruster near-exit region is established to gain further insights into the mechanism of the EDI in detail, and the effects of different types of propellants on EDI characteristics are discussed. The changes in axial electron transport caused by EDI under different types of propellants and electromagnetic field strengths are also examined. The results indicate that EDI undergoes a short linear growth phase before transitioning to the nonlinear phase and finally reaching saturation through the ion Landau damping. The EDI drives a significant ion heating in the azimuthal direction through electron–ion friction before entering the quasi-steady state, which increases the axial mobility of the electrons. Using lighter atomic weight propellant can effectively suppress the oscillation amplitude of EDI, but it will increase the linear growth rate, frequency, and phase velocity of EDI. Compared with the classical mobility, the axial electron mobility under the EDI increases by three orders of magnitude, which is consistent with experimental phenomena. The change of propellant type is insufficient to significantly change the axial electron mobility. It is also found that the collisions between electrons and neutral gasescan significantly affect the axial electron mobility under the influence of EDI, and lead the strength of the electric field to increase and the strength of the magnetic field to decrease, thereby both effectively suppressing the axial transport of electrons.
基金supported by National Natural Science Foundation of China (Nos.11975062 and 11605021)the Fundamental Research Funds for the Central Universities (No.3132023192)。
文摘In the plasma sheath, there is a significant gradient in ion velocity, resulting in strong stress on ions treated as a fluid. This aspect has often been neglected in previous sheath studies. This study is based on the Braginskii plasma transport theory and establishes a 1D3V sheath fluid model that takes into account the ion stress effect. Under the assumption that ions undergo both electric and diamagnetic drift in the presheath region, self-consistent boundary conditions,including the ion Bohm velocity, are derived based on the property of the Sagdeev pseudopotential.Furthermore, assuming that the electron velocity at the wall follows a truncated Maxwell distribution, the wall floating potential is calculated, leading to a more accurate sheath thickness estimation. The results show that ion stress significantly reduces the sheath thickness, enhances ion Bohm velocity, wall floating potential, and ion flux at the wall. It hinders the acceleration of ions within the sheath, leading to notable alterations in the particle density profiles within the sheath. Further research indicates that in ion stress, bulk viscous stress has the greatest impact on sheath properties.
基金The research presented in this paper was supported by National Natural Science Foundation of China(Grant No.52272031)the Fundamental Research Funds for the Central Universities,China University of Geosciences(Wuhan),and the Opening Fund of Guangxi Key Laboratory of New Energy and Building Energy Saving(Grant No.19-J-22-2)+3 种基金Key Research and Development Program of Hubei Province(Grant No.2020BAB065)Key Research and Development Program of Jiangxi Province(Grant No.20201BBG71011)Fundamental Research Funds for the Central Universities,CHD(Grant No.300102211506)Opening Fund of Key Laboratory of Advanced Building Materials of Anhui Province(Grant No.JZCL001KF).
文摘Montmorillonite and clinoptilolite zeolite were used as representative materials to prepare calcined clay-cement binary cementitious materials in order to study the effect of calcination treatment on the activation of clay minerals and the activity difference between layered and framed clays in this research.The influence of different calcined clay content(2%,4%,6%,8%,10%)on the fluidity,compressive strength,microstructure,phase change,and hydration heat of cement-based materials were analyzed.The calcined clay improves the fluidity of cement-based materials as compared with the uncalcined group.The addition of calcined montmorillonite(CMT)improves the development of mechanical strength,and the optimal compressive strength reaches 85 MPa at 28 days with 8%CMT.However,the activity of calcined clinoptilolite zeolite(CZL)is weak with few reaction sites,which slightly reduced the mechanical strength as compared to the blank sample.The addition of CMT changes the microscopic morphology of hydration products such as C-S-H and C-A-H,leading to the formation and transformation of ettringite in the early stage.It promotes the gradual polymerization of Si-O bonds into Si-O-Si bonds simultaneously,which accelerates the early hydration process.However,CZL acts mainly as a filling function in the cementitious system.In brief,CMT as an admixture can improve the mechanical properties of cement,but CZL has little effect.This work provides a guideline for the applications of calcined clay in cement,considering the influence of clay type on workability and mechanical strength.
基金supported by National Natural Science Foundation of China(Nos.11975062,11605021 and 11975088)the China Postdoctoral Science Foundation(No.2017M621120)。
文摘The properties of an atmospheric-pressure collisional plasma sheath with nonextensively distributed electrons and hypothetical ionization source terms are studied in this work. The Bohm criterion for the magnetized plasma is extended in the presence of an ion–neutral collisional force and ionization source. The effects of electron nonextensive distribution, ionization frequency, ion–neutral collision, magnetic field angle and ion temperature on the Bohm criterion of the plasma sheath are numerically analyzed. The fluid equations are solved numerically in the plasma–wall transition region using a modified Bohm criterion as the boundary condition. The plasma sheath properties such as charged particle density, floating sheath potential and thickness are thoroughly investigated under different kinds of ion source terms, contributions of collisions, and magnetic fields. The results show that the effect of the ion source term on the properties of atmosphericpressure collisional plasma sheath is significant. As the ionization frequency increases, the Mach number of the Bohm criterion decreases and the range of possible values narrows. When the ion source is considered, the space charge density increases, the sheath potential drops more rapidly,and the sheath thickness becomes narrower. In addition, ion–neutral collision, magnetic field angle and ion temperature also significantly affect the sheath potential profile and sheath thickness.
文摘Objective: To observe the effect of slow-released morphine tablets by rectum in treating the patients of moderate to severe cancer pain with server nausea and vomiting or dysphagia. Methods: 54 cases of cancer patients with server nau- sea and vomiting symptoms or dysphagia were treated with slow-released morphine tablets by rectum, 30-90 mg/time, once every 12 hours. The drug dose was titrated by degree of pain, and the effects and adverse effects were observed. Results: The total effective rate was 81.48%, complete response rate was 51.85% (28/54), and the partial response rate was 29.63% (16/54); there were no obvious toxicities, and the common adverse symptoms included nausea (16.7%) and vomiting (9.3%). Conclusion: The treatment of slow-released morphine tablet by rectum could effectively control cancer pain, the adverse effects were slight than that by mouth. It is safe and effective to be worthy of the adhibition in clinic.
基金supported by National Natural Science Foundation of China (Nos. 11975062, 11605021, 11975088)the China Postdoctoral Science Foundation (No. 2017M621120)。
文摘The secondary electron emission(SEE) and inclined magnetic field are typical features at the channel wall of the Hall thruster acceleration region(AR), and the characteristics of the magnetized sheath have a significant effect on the radial potential distribution, ion radial acceleration and wall erosion. In this work, the magnetohydrodynamics model is used to study the characteristics of the magnetized sheath with SEE in the AR of Hall thruster. The electrons are assumed to obey non-extensive distribution, the ions and secondary electrons are magnetized.Based on the Sagdeev potential, the modified Bohm criterion is derived, and the influences of the non-extensive parameter and magnetic field on the AR sheath structure and parameters are discussed. Results show that, with the decrease of the parameter q, the high-energy electron leads to an increase of the potential drop in the sheath, and the sheath thickness expands accordingly,the kinetic energy rises when ions reach the wall, which can aggravate the wall erosion.Increasing the magnetic field inclination angle in the AR of the Hall thruster, the Lorenz force along the x direction acting as a resistance decelerating ions becomes larger which can reduce the wall erosion, while the strength of magnetic field in the AR has little effect on Bohm criterion and wall potential. The propellant type also has a certain effect on the values of wall potential,secondary electron number density and sheath thickness.
基金The research presented in this paper was supported by Natural Science Foundation of Hubei Province(No.2020CFB575)Natural Science Foundation of Zhejiang Province(No.LY19E080003)+5 种基金the Opening Fund of Key Laboratory of Geological Survey and Evaluation of Ministry of Education(Grant No.GLAB2020ZR09)the Fundamental Research Funds for the Central Universities,China University of Geosciences(Wuhan)and the Opening Fund of Guangxi Key Laboratory of New Energy and Building Energy Saving(Grant No.19-J-22-2)Key Research and Development Program of Hubei Province(Grant No.2020BAB065)Key Research and Development Program of Jiangxi Province(Grant No.20201BBG71011)Fundamental Research Funds for the Central Universities,CHD(Grant No.300102211506)Opening Fund of Key Laboratory of Advanced Building Materials of Anhui Province(Grant No.JZCL001KF).
文摘In this study,the workability and reaction mechanism of metakaolin(MK)based geopolymer blended with rice husk ash(RHA)and silica fume(SF)was investigated.The prepared samples were subjected to tests including compressive strength and fluidity tests.X-ray diffraction(XRD)and Scanning electron microscope(SEM)were employed to explore the phase composition and microstructure of geopolymers.The molecular bonding information of geopolymer was provided by Fourier transform infrared spectroscopy(FTIR).Meanwhile,the porosity of geopolymer was obtained by Mercury intrusion porosimeter(MIP)analysis.The high-activity RHA obtained after calcination at 600℃ was used as a supplementary cementitious material to prepare geopolymer.The properties of preventing morphology cracking and compressive strength are improved.The addition of RHA and SF changes the working performance of MK based geopolymer and provided a theoretical basis for future practical applications.Meanwhile,the high chemical activity of SF and RHA contributes to the healing of microcracks.
文摘BACKGROUND Glomus tumors are rare neoplasms,usually found on the fingers or toes.Glomus tumours that occur in the lower leg are even rarer and is likely to be misdiagnosed or underdiagnosed.This article will document the diagnosis,treatment,and follow-up of a rare glomus tumor of the lower leg,which had been misdiagnosed for up to 15 years.CASE SUMMARY The patient was a A 36-year-old woman who had suffered from localized pain in her left lower leg for 15 years.After a complete physical examination,a glomus tumor on her lower leg was considered and removed surgically.The specimen was pathologically diagnosed as a glomus tumor.There was no relapse at a 4-year follow-up.CONCLUSION Correct diagnosis and complete removal of the glomus tumor is important.
基金the National Natural Science Foundation of China(Nos.22250003 and 22205084)National Key R&D Program of China(No.2017YFA0204902).
文摘Folding of molecules is an essential process in nature,and various molecular machines achieve their chemical and mechanical function via controlled folding of molecular conformations.The electric field offers a unique strategy to drive the folding of molecular conformation and to control charge transport through single molecules but remains unexplored.The single-molecule break junction technique provides access to detect the conformational changes via the monitoring of single-molecule conductance,and the electric field between two metal electrodes with nanoscale spacing can provide an extremely strong to achieve in-situ control and detection of molecular folding at the single-molecule level.Here,we use the electric field to control the single-molecule folding using the scanning tunneling microscope break junction(STM-BJ)technique.The electric fields induced folding could lead to a∼1400%conductance change of the single-molecule junctions,and the folding/unfolding process can be in-situ switched at the scale of milliseconds.DFT calculations suggest the conformational control originates from the electric fieldinduced charge injection,and the formation of homoconjugated conformation with the overlapped orbitals.This work provides the first demonstration of electric field-driven molecular folding,which is essential for the understanding of molecular machines in nature and for the design of artificial molecular machines.
基金the National Natural Science Foundation of China(21601182,U1405252,21531008,21673195,21703188,31871877,21933012)the National Key Research and Development Program of China(2014CB845603,2017YFA0204902)+1 种基金the CAS/SAFEA International Partnership Program for Creative Research Teams,the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB20000000)China Postdoctoral Science Foundation(2017M622060).
文摘Seeking the strategies of designing highly conductive molecular structures is one of the core researches in molecular electronics.As asymmetric structure has manifested feasible properties in comprehensive fields, we introduce the structures of asymmetric platinum(Ⅱ) complexes into the charge transport study at single-molecule scale for the first time. The single-molecule conductance measurement results reveal that, in platinum(Ⅱ)-aryloligoynyl structures, the conductance of asymmetrically coordinated complexes is obviously higher than that of the symmetric isomers with the same molecular length, while the conductance is almost identical in symmetric and asymmetric platinum(Ⅱ)-oligoynyl complexes. Theoretical study uncovers that, upon connecting to the oligoynyl structure, the aromatic group effectively extends the π-system of the whole conductive backbone and gathers the HOMO population mainly on the longer oligoynyl ligand, which reduces the energy barrier in electron transport and enhances the conductance through HOMO energy lifting. This result provides feasible strategy for achieving high conductive molecular devices.