The evaporation behaviors are crucial for the flame location estimation in liquid rocketengines.This work,for the first time,experimentally reports the sub-millimeter droplet evaporationcharacteristics of the corrosiv...The evaporation behaviors are crucial for the flame location estimation in liquid rocketengines.This work,for the first time,experimentally reports the sub-millimeter droplet evaporationcharacteristics of the corrosive dinitrogen tetroxide(NTO,one prevailing hypergolic oxidizer)athigh ambient pressure up to 4.5 MPa.An in-house corrosion-resistant droplet generator is usedto generate isolated flying droplets of sub-millimeter size,which are then exposed in a gas environ-ment with temperatures between 1010 K and 1210 K and pressures in the range between 2.0 MPaand 4.5 MPa,provided by an optical rapid compression machine.Parallelly,a theoretical modelconsidering both the droplet ambient convection and the NTO dissociation is developed.Resultsindicate that firstly,the present theoretical model that considers the transient droplet-ambient con-vection as well as the temperature and pressure dependent rate of dissociation shows good agree-ment with the experimentally observed droplet lifetime.In addition,the flying droplets velocityregress gradually due to momentum exchange with the ambient,which is more prominent at higherpressure.The evaporation caused droplet size reduction is consistent with the classical D^(2)-law pre-diction,in the present temperature and pressure range.Finally,higher temperature and pressureaccelerate the evaporation and an empirical correlation for the temperature and pressure dependentevaporation rate constant is proposed,which shows good agreement with experiment and simula-tion results.展开更多
A rapid method for the determination of impurity elements, such as Zn, Ni, Co, Cr, Cu, Cd and Pb in manganese tetroxide was developed, using inductively coupled plasma atomic emission spectrometry （ICP-AES）. The cri...A rapid method for the determination of impurity elements, such as Zn, Ni, Co, Cr, Cu, Cd and Pb in manganese tetroxide was developed, using inductively coupled plasma atomic emission spectrometry （ICP-AES）. The critical instrumental parameters such as sample flow rate and radio frequency incident were thoroughly optimized. The effect of matrix was also examined. The sensitivity was investigated using calibration curves obtained in presence of the matrix. The obtained recoveries for Ni, Co, Cr, Cu, and Cd at the μg· g^ -1 level were satisfactory and practically independent of the matrix used for the calibration standards. The recoveries of Pb and Zn were less suffwient. The method can be applied for routine analysis and quality control purposes at μg· g^-1 level of concentration.展开更多
Microphase separation and lamellar structure of segmented polyether- and polyester-polyurethanes have been investigated by means of transmission electron microscopy with the ruthenium tetroxide staining technique. The...Microphase separation and lamellar structure of segmented polyether- and polyester-polyurethanes have been investigated by means of transmission electron microscopy with the ruthenium tetroxide staining technique. The results show that the RuO_4 staining technique is simpler and may give better image contrast than other staining methods for this polymer. Microphase separation and lamellar structure of segmented polyether-and polyester-polyurethanes were directly observed and discussed.展开更多
Self-excited longitudinal combustion instabilities were investigated in a hypergolic liquid bipropellant combustor, which applied single dual-swirl coaxial injector. Hot-fire tests were conducted for four different in...Self-excited longitudinal combustion instabilities were investigated in a hypergolic liquid bipropellant combustor, which applied single dual-swirl coaxial injector. Hot-fire tests were conducted for four different injector geometries, while extensive tests on injection conditions were carried out for each injector geometry. The synchronous measurement of the pressure and heat release rate was applied, successfully capturing the process of the pressure and heat release rate enhanced coupling and developing into in-phase oscillation. By calculating Rayleigh index at the head and middle section of the chamber, it is shown that Rayleigh index of the middle section is even higher than that of the head, indicating a long heat release zone. When the combustion instability occurs, the pressure in propellant manifolds also oscillates with the same frequency and lags behind the oscillation in the combustor. Compared to the oscillation in the outer injector manifold, the oscillation in the inner injector manifold shows a higher correlation with that in the chamber in amplitude and phase. Based on numerical simulations of the multiphase cold flow inside the injector and combustion process in the chamber, it is found that injector geometries affect longitudinal combustion instability by changing spray cone angle. The spray with small cone angle is more sensitive to the modulation of longitudinal pressure wave in combustion simulations, which is more likely to excite the longitudinal combustion instability. Meanwhile, the combustion instability may be related to the pulsating coherent structure generated by the spray fluctuation, which is determined by injection conditions. Besides, a positive feedback closed-loop system associated with the active fluctuation and passive oscillation of the spray is believed to excite and sustain the longitudinal combustion instability.展开更多
Manganese tetroxide(Mn_(3)O_(4))nanofibers were prepared by electrospinning homogeneous viscous solution of 20 wt%,28 wt%and 36 wt%manganese acetate in poly vinyl alcohol(PVA)and calcining the nanofibers at 1000℃for ...Manganese tetroxide(Mn_(3)O_(4))nanofibers were prepared by electrospinning homogeneous viscous solution of 20 wt%,28 wt%and 36 wt%manganese acetate in poly vinyl alcohol(PVA)and calcining the nanofibers at 1000℃for 2 h.Electrospinning was carried out at 9 kV DC with tip to collector distance(TCD)of 7 cm.Thermo gravimetric analysis(TGA)of the fibers indicates the pure phase of manganese oxide above 500℃.XRD analysis of calcined(at 1000℃)nanofibers indicates the formation of phase-pure tetragonal Mn_(3)O_(4).Scanning electron microscopy(SEM)studies show the fibers cylindrical with the diameters in the range of 100-600 nm and aspect ratio>1000.In general,the average diameter of the green fibers decreases with the increase in manganese acetate concentration.The diameter of calcined nanofibers is reduced by 34%.展开更多
A novel p‐n heterostructure photocatalyst m‐Bi2O4/BiOCl was successfully synthetized through a facile ion‐etching method.Via adjusting the added volume of HCl solution,a series of different ratios of composite phot...A novel p‐n heterostructure photocatalyst m‐Bi2O4/BiOCl was successfully synthetized through a facile ion‐etching method.Via adjusting the added volume of HCl solution,a series of different ratios of composite photocatalysts were obtained.The as‐prepared samples of physical,chemical and optical characteristics were examined by X‐ray diffraction,scanning electron microscope,transmission electron microscope,energy dispersive X‐ray spectroscopy,selected‐area electron diffraction,Fourier transform infrared absorption,Raman microscope,N2 adsorption‐desorption,X‐ray photoelectron spectroscopy and UV‐vis spectrum technologies.The photocatalysts showed high degradation rate and complete mineralization ability for methyl orange and tetracycline solution under visible light.The reaction rate constant of m‐Bi2O4/BiOCl for methyl orange was 52.28 times higher than that of BiOCl.The characterization presented a good stability of materials.Furthermore,the photocurrent response test certified that the heterostructure effectively accelerated the separation and migration of photo‐generated carries.The scavenger experiments evidenced that hole(h+)and superoxide radical(?O2?)were the primary active radicals.A possible photocatalytic mechanism was proposed.This work provided an alternative photocatalyst applied to water environmental remediation.展开更多
A new chiral polymer-metal complex, wool-osmium tetroxide(wool-OsO4) complex was prepared by a very simple method. This complex was found to be able to catalyze the asymmetric dihydroxylation of allylamine to get (R)-...A new chiral polymer-metal complex, wool-osmium tetroxide(wool-OsO4) complex was prepared by a very simple method. This complex was found to be able to catalyze the asymmetric dihydroxylation of allylamine to get (R)-(+)-3-amino-l, 2-propanediol. The experimental results showed that OsO4 content in the complex, reaction time, allylamine/OsO4 molar ratio all have great effects on the chemical and optical yields of product. Additionally, wool-OsO4 complex catalyst could be reused without remarkable change in optical catalytic activity.展开更多
Objective ： To introduce a practical, economical, and time-saving method to stain （with osmic acid） the myelin sheath in normal and regenerated peripheral nerves. Methods： A total of 12 Sprague Dawley rats, weighi...Objective ： To introduce a practical, economical, and time-saving method to stain （with osmic acid） the myelin sheath in normal and regenerated peripheral nerves. Methods： A total of 12 Sprague Dawley rats, weighing 250-320 g （ mecan = 276 g ± 38 g ）, were divided into two groups： a normal nerve group （n = 6 ） and a regenerated nerve group （ n = 6 ）. In the normal nerve group, the ventral and dorsal roots of L4 to L6 and their sciatic nerves were harvested for histological analysis. While in the regenerated nerve group, the right sciatic nerves were severed and then repaired with an epineurial microsuture method. The repaired nerves were harvested 12 weeks postoperatively. All the specimens were fixed in 4 % paraformaldehyde and transferred to 2 % osmic acid for 3-5 days. Then the specimens were kept in 75% alcohol before being embedded in paraffin. The tissues were cut into sections of 3 ten in thickness with a conventional microtome. Results： Under a light microscope, myelin sheaths were clearly visible at all magnifications in both groups. They were stained in clear dark colour with a light yellow or colorless background, which provided high contrast images to allow reliable morphometric measurements. Morphological assessment was made in both normal and regenerated sciatic nerves. The ratios of the myelin area to the fibre area were 60. 28 % ± 7.66 % in the normal nerve group and 51. 67% ± 6. 85% in the regenerated nerve group, respectively （P〈0.01）. Conclusions： Osmic acid staining is easy to perform and a very clear image for morphometrical assessment is easy to obtain. Therefore, it is a reliable technique for quantitative evaluation of nerve morphology.展开更多
基金supported by the Natural Science Foundation of China(No.52236001)The support from Research Grants Council of Hong Kong,China(No.CityU 15218820)was also appreciated。
文摘The evaporation behaviors are crucial for the flame location estimation in liquid rocketengines.This work,for the first time,experimentally reports the sub-millimeter droplet evaporationcharacteristics of the corrosive dinitrogen tetroxide(NTO,one prevailing hypergolic oxidizer)athigh ambient pressure up to 4.5 MPa.An in-house corrosion-resistant droplet generator is usedto generate isolated flying droplets of sub-millimeter size,which are then exposed in a gas environ-ment with temperatures between 1010 K and 1210 K and pressures in the range between 2.0 MPaand 4.5 MPa,provided by an optical rapid compression machine.Parallelly,a theoretical modelconsidering both the droplet ambient convection and the NTO dissociation is developed.Resultsindicate that firstly,the present theoretical model that considers the transient droplet-ambient con-vection as well as the temperature and pressure dependent rate of dissociation shows good agree-ment with the experimentally observed droplet lifetime.In addition,the flying droplets velocityregress gradually due to momentum exchange with the ambient,which is more prominent at higherpressure.The evaporation caused droplet size reduction is consistent with the classical D^(2)-law pre-diction,in the present temperature and pressure range.Finally,higher temperature and pressureaccelerate the evaporation and an empirical correlation for the temperature and pressure dependentevaporation rate constant is proposed,which shows good agreement with experiment and simula-tion results.
基金Supported bythe financial support of Sino-Romanian GovernmentalInternational Science and Technology Cooperation Projeet( No.37-11)the Scientific and Technological Project of Tackle Key Problemin Science and Technology Branch of Hunan Province ( No.00GKY2020 +4 种基金01GKY2027 03GKY2022)Key Project of Hunan Pro-vincial Educational Branch(No.02A040) Key Project of RegionalUniversityin Chinese Ministry of Education(No.204103)and Fundfor Returned Overseas Scholars ,China University of Geosciences(No.XLX04901)
文摘A rapid method for the determination of impurity elements, such as Zn, Ni, Co, Cr, Cu, Cd and Pb in manganese tetroxide was developed, using inductively coupled plasma atomic emission spectrometry （ICP-AES）. The critical instrumental parameters such as sample flow rate and radio frequency incident were thoroughly optimized. The effect of matrix was also examined. The sensitivity was investigated using calibration curves obtained in presence of the matrix. The obtained recoveries for Ni, Co, Cr, Cu, and Cd at the μg· g^ -1 level were satisfactory and practically independent of the matrix used for the calibration standards. The recoveries of Pb and Zn were less suffwient. The method can be applied for routine analysis and quality control purposes at μg· g^-1 level of concentration.
文摘Microphase separation and lamellar structure of segmented polyether- and polyester-polyurethanes have been investigated by means of transmission electron microscopy with the ruthenium tetroxide staining technique. The results show that the RuO_4 staining technique is simpler and may give better image contrast than other staining methods for this polymer. Microphase separation and lamellar structure of segmented polyether-and polyester-polyurethanes were directly observed and discussed.
基金support from the National Natural Science Foundation of China(No.12002386).
文摘Self-excited longitudinal combustion instabilities were investigated in a hypergolic liquid bipropellant combustor, which applied single dual-swirl coaxial injector. Hot-fire tests were conducted for four different injector geometries, while extensive tests on injection conditions were carried out for each injector geometry. The synchronous measurement of the pressure and heat release rate was applied, successfully capturing the process of the pressure and heat release rate enhanced coupling and developing into in-phase oscillation. By calculating Rayleigh index at the head and middle section of the chamber, it is shown that Rayleigh index of the middle section is even higher than that of the head, indicating a long heat release zone. When the combustion instability occurs, the pressure in propellant manifolds also oscillates with the same frequency and lags behind the oscillation in the combustor. Compared to the oscillation in the outer injector manifold, the oscillation in the inner injector manifold shows a higher correlation with that in the chamber in amplitude and phase. Based on numerical simulations of the multiphase cold flow inside the injector and combustion process in the chamber, it is found that injector geometries affect longitudinal combustion instability by changing spray cone angle. The spray with small cone angle is more sensitive to the modulation of longitudinal pressure wave in combustion simulations, which is more likely to excite the longitudinal combustion instability. Meanwhile, the combustion instability may be related to the pulsating coherent structure generated by the spray fluctuation, which is determined by injection conditions. Besides, a positive feedback closed-loop system associated with the active fluctuation and passive oscillation of the spray is believed to excite and sustain the longitudinal combustion instability.
文摘Manganese tetroxide(Mn_(3)O_(4))nanofibers were prepared by electrospinning homogeneous viscous solution of 20 wt%,28 wt%and 36 wt%manganese acetate in poly vinyl alcohol(PVA)and calcining the nanofibers at 1000℃for 2 h.Electrospinning was carried out at 9 kV DC with tip to collector distance(TCD)of 7 cm.Thermo gravimetric analysis(TGA)of the fibers indicates the pure phase of manganese oxide above 500℃.XRD analysis of calcined(at 1000℃)nanofibers indicates the formation of phase-pure tetragonal Mn_(3)O_(4).Scanning electron microscopy(SEM)studies show the fibers cylindrical with the diameters in the range of 100-600 nm and aspect ratio>1000.In general,the average diameter of the green fibers decreases with the increase in manganese acetate concentration.The diameter of calcined nanofibers is reduced by 34%.
基金supported by the National Natural Science Foundation of China(51578354)Suzhou Science and Technology Bureau(SS201667)+1 种基金Six Talent Peaks Program(2016-JNHB-067)Qing Lan Project of Jiangsu Province~~
文摘A novel p‐n heterostructure photocatalyst m‐Bi2O4/BiOCl was successfully synthetized through a facile ion‐etching method.Via adjusting the added volume of HCl solution,a series of different ratios of composite photocatalysts were obtained.The as‐prepared samples of physical,chemical and optical characteristics were examined by X‐ray diffraction,scanning electron microscope,transmission electron microscope,energy dispersive X‐ray spectroscopy,selected‐area electron diffraction,Fourier transform infrared absorption,Raman microscope,N2 adsorption‐desorption,X‐ray photoelectron spectroscopy and UV‐vis spectrum technologies.The photocatalysts showed high degradation rate and complete mineralization ability for methyl orange and tetracycline solution under visible light.The reaction rate constant of m‐Bi2O4/BiOCl for methyl orange was 52.28 times higher than that of BiOCl.The characterization presented a good stability of materials.Furthermore,the photocurrent response test certified that the heterostructure effectively accelerated the separation and migration of photo‐generated carries.The scavenger experiments evidenced that hole(h+)and superoxide radical(?O2?)were the primary active radicals.A possible photocatalytic mechanism was proposed.This work provided an alternative photocatalyst applied to water environmental remediation.
文摘A new chiral polymer-metal complex, wool-osmium tetroxide(wool-OsO4) complex was prepared by a very simple method. This complex was found to be able to catalyze the asymmetric dihydroxylation of allylamine to get (R)-(+)-3-amino-l, 2-propanediol. The experimental results showed that OsO4 content in the complex, reaction time, allylamine/OsO4 molar ratio all have great effects on the chemical and optical yields of product. Additionally, wool-OsO4 complex catalyst could be reused without remarkable change in optical catalytic activity.
基金This study was supported by the National Natural Science Foundation of China （ No. 39700141 ） and Foshan Science and Technology Committee （ No. 03080051 ）.
文摘Objective ： To introduce a practical, economical, and time-saving method to stain （with osmic acid） the myelin sheath in normal and regenerated peripheral nerves. Methods： A total of 12 Sprague Dawley rats, weighing 250-320 g （ mecan = 276 g ± 38 g ）, were divided into two groups： a normal nerve group （n = 6 ） and a regenerated nerve group （ n = 6 ）. In the normal nerve group, the ventral and dorsal roots of L4 to L6 and their sciatic nerves were harvested for histological analysis. While in the regenerated nerve group, the right sciatic nerves were severed and then repaired with an epineurial microsuture method. The repaired nerves were harvested 12 weeks postoperatively. All the specimens were fixed in 4 % paraformaldehyde and transferred to 2 % osmic acid for 3-5 days. Then the specimens were kept in 75% alcohol before being embedded in paraffin. The tissues were cut into sections of 3 ten in thickness with a conventional microtome. Results： Under a light microscope, myelin sheaths were clearly visible at all magnifications in both groups. They were stained in clear dark colour with a light yellow or colorless background, which provided high contrast images to allow reliable morphometric measurements. Morphological assessment was made in both normal and regenerated sciatic nerves. The ratios of the myelin area to the fibre area were 60. 28 % ± 7.66 % in the normal nerve group and 51. 67% ± 6. 85% in the regenerated nerve group, respectively （P〈0.01）. Conclusions： Osmic acid staining is easy to perform and a very clear image for morphometrical assessment is easy to obtain. Therefore, it is a reliable technique for quantitative evaluation of nerve morphology.
