Wave-transparent ceramic matrix composites for the high temperature use should possess excellent oxidation resistance. In this work, Si3N4f/SiO2 composites with different fiber content were fabricated by filament wind...Wave-transparent ceramic matrix composites for the high temperature use should possess excellent oxidation resistance. In this work, Si3N4f/SiO2 composites with different fiber content were fabricated by filament winding and sol gel method. The oxidation resistance was investigated by tracking the response of flexural strength to the testing temperature. The results show that the flexural strength and toughness of the composites with fiber content of over 37% can reach high levels at around 175.0 MPa and 6.2 MPa m^1/2, respectively. After 1 h oxidation at 1100℃, the flexural strength drops a lot but can still reach 114.4 MPa, which is high enough to ensure the safety of structures. However, when the oxidation temperature rises to 1200–1400℃, the flexural strengths continue to fall to a relatively low level at 50.0–66.4 MPa. The degradation at high temperatures is caused by the combination of over strong interfacial bonding, the damage of fiber and the crystallization of silica matrix.展开更多
BACKGROUND Hepatocellular carcinoma(HCC) is one of the most common malignant tumors worldwide, and novel methods for early/rapid diagnosis of HCC are needed.Terahertz(THz) spectroscopy is considered to have the potent...BACKGROUND Hepatocellular carcinoma(HCC) is one of the most common malignant tumors worldwide, and novel methods for early/rapid diagnosis of HCC are needed.Terahertz(THz) spectroscopy is considered to have the potential to distinguish between normal liver tissue and HCC tissue; however, there are few reports on it.We conduct this observational study to explore the feasibility of THz imaging for the diagnosis of HCC.AIM To evaluate the feasibility of THz for discriminating between HCC and normal liver tissues using fresh tissue specimens obtained from HCC patients who had undergone surgery.METHODS Normal liver tissue and HCC tissue were cryosectioned into 50 μm-thick slicesand placed on cover glass. Two adjacent tissue sections were separated subjected to histopathological examination by hematoxylin and eosin staining or THz transmission examination, and THz images were compared with pathologically mapped images. We determined the typical tumor and normal liver tissue regions by pathological examination; the corresponding areas of adjacent sections were examined by THz transmission.RESULTS The transmission rate of HCC tissue was 0.15-0.25, and the transmission rate of typical HCC tissue was about 0.2. THz transmittance in normal liver tissue is slightly higher than 0.4, but there were many influencing factors, including the degree of liver cirrhosis, fat components, ice crystals in frozen sections, and apoptosis.CONCLUSION In conclusion, this study shows that THz imaging can detect HCC tissue. Further research will yield more detailed data of the THz transmission rates of HCC tissue with different degrees of differentiation.展开更多
We propose a simple pumping method to increase the effective population of cold atoms in the clock state and investigate the factors which affect the pumping efficiency in cold atom systems.We report the theory and de...We propose a simple pumping method to increase the effective population of cold atoms in the clock state and investigate the factors which affect the pumping efficiency in cold atom systems.We report the theory and demonstrate the corresponding experiment in an ^(87)Rb integrating sphere cold atom clock.The experimental results show that the population of cold atoms in the Zeeman sublevel|F=2,mF=0>is approximately 1.62 times that of the result using optical pumping alone.This method can also be applied to increase the effective population in any one of the target Zeeman sublevels in other cold atom systems.展开更多
The structure and propagation of the plasma in air breakdown driven by high-power microwave have attracted great interest.This paper focuses on the microwave amplitude and frequency dependence of plasma formation at a...The structure and propagation of the plasma in air breakdown driven by high-power microwave have attracted great interest.This paper focuses on the microwave amplitude and frequency dependence of plasma formation at atmospheric pressure using one two-dimensional model,which is based on Maxwell’s equations coupled with plasma fluid equations.In this model,we adopt the effective electron diffusion coefficient,which can describe well the change from free diffusion in a plasma front to ambipolar diffusion in the bulk plasma.The filamentary plasma arrays observed in experiments are well reproduced in the simulations.The density and propagation speed of the plasma from the simulations are also close to the corresponding experimental data.The size of plasma filament parallel to the electric field decreases with increasing frequency,and it increases with the electric field amplitude.The distance between adjacent plasma filaments is close to one-quarter wavelength under different frequencies and amplitudes.The plasma propagation speed shows little change with the frequency,and it increases with the amplitude.The variations of plasma structure and propagation with the amplitude and frequency are due to the change in the distribution of the electric field.展开更多
The measurement performance of the atom interferometry absolute gravimeter is strongly affected by the ground vibration noise.We propose a vibration noise evaluation scheme using a Michelson laser interferometer const...The measurement performance of the atom interferometry absolute gravimeter is strongly affected by the ground vibration noise.We propose a vibration noise evaluation scheme using a Michelson laser interferometer constructed by the intrinsic Raman laser of the atomic gravimeter.Theoretical analysis shows that the vibration phase measurement accuracy is better than 4 mrad,which corresponds to about 10-^10 g accuracy for a single shot gravity measurement.Compared with the commercial seismometer or accelerometer,this method is a simple,low cost,direct,and fully synchronized measurement of the vibration phase which should benefit the development of the atomic gravimeter.On the other side,limited by equivalence principle,the result of the laser interferometer is not absolute but relative vibration measurement.Triangular cap method could be used to evaluation the noise contribution of vibration,which is a different method from others and should benefit the development of the atomic gravimeter.展开更多
The outer-product decomposition algorithm(OPDA)performs well at blindly identifying system function.However,the direct use of the OPDA in systems using bandpass source will lead to errors.This study proposes an approa...The outer-product decomposition algorithm(OPDA)performs well at blindly identifying system function.However,the direct use of the OPDA in systems using bandpass source will lead to errors.This study proposes an approach to enhance the channel estimation quality of a bandpass source that uses OPDA.This approach performs frequency domain transformation on the received signal and obtains the optimal transformation parameter by minimizing the p-norm of an error matrix.Moreover,the proposed approach extends the application of OPDA from a white source to a bandpass white source or chirp signal.Theoretical formulas and simulation results show that the proposed approach not only reduces the estimation error but also accelerates the algorithm in a bandpass system,thus being highly feasible in practical blind system identification applications.展开更多
High-precision piezoresistive pressure sensors play a significant role in aerospace,automotive,and other fields.Nonlinear error is the key factor that restricts the improvement of the sensor precision.A mathematical m...High-precision piezoresistive pressure sensors play a significant role in aerospace,automotive,and other fields.Nonlinear error is the key factor that restricts the improvement of the sensor precision.A mathematical model for evaluating the sensor’s nonlinear error is established,based on which a piezoresistor sensitivity matching method is proposed to suppress the nonlinear error.By adjusting the piezoresistors'structure and position on the sensing membrane,four piezoresistors with equal sensitivity are obtained,and theoretical quasi-zero nonlinear error is achieved.To verify the design,sensor prototypes are fabricated utilizing the MEMS technology.After sensor packaging,a cylindrical absolute pressure sensor featuring a 4 mm diameter with a range from 0 to 100 kPa is acquired.The experimental results demonstrate the excellent performance of the proposed sensor,which indicates a nonlinear error as low as±0.004%FS.Besides,the proposed sensor has a sensitivity of 1.6810 mV/kPa,a hysteresis of 0.025%,a repeatability of 0.015%,a zero drift of 0.03%FS,and a 3 dB frequency from 0 to 121.82 kHz.Moreover,the prototype is tested in the Mach 4 wind tunnel,and the measurement error between the proposed sensor and the true pressure is±0.98%.This paper provides key sensing technology for high-precision surface pressure analysis of aircraft.展开更多
The conventional method of deep-sea acoustic source localization usually uses the multi-path arrival information of the acoustic source signals received by hydrophone arrays to match with the simulation results to ach...The conventional method of deep-sea acoustic source localization usually uses the multi-path arrival information of the acoustic source signals received by hydrophone arrays to match with the simulation results to achieve localization.Aiming at the problem that it is difficult to extract the similar multi-path arrival angle directly by the conventional method,a deconvolution positioning method for deep-sea vertical array underwater target is proposed.By using this method,not only the adaptive iterative frequency-domain Richardson-Lucy algorithm is used to directly estimate the multipath angle of arrival of deep-sea acoustic targets,but also the ranging and depth fixing are realized by matching the sound field angle of arrival feature template.Simulation and experimental results show that this positioning method has higher localization accuracy and applicability than the conventional method,and has high computational efficiency.展开更多
基金the financial support from the National Natural Science Foundation of China (Grant No. 51702361)the Natural Science Foundation of Hunan Province (Grant No. 2017JJ3353)
文摘Wave-transparent ceramic matrix composites for the high temperature use should possess excellent oxidation resistance. In this work, Si3N4f/SiO2 composites with different fiber content were fabricated by filament winding and sol gel method. The oxidation resistance was investigated by tracking the response of flexural strength to the testing temperature. The results show that the flexural strength and toughness of the composites with fiber content of over 37% can reach high levels at around 175.0 MPa and 6.2 MPa m^1/2, respectively. After 1 h oxidation at 1100℃, the flexural strength drops a lot but can still reach 114.4 MPa, which is high enough to ensure the safety of structures. However, when the oxidation temperature rises to 1200–1400℃, the flexural strengths continue to fall to a relatively low level at 50.0–66.4 MPa. The degradation at high temperatures is caused by the combination of over strong interfacial bonding, the damage of fiber and the crystallization of silica matrix.
基金Supported by the National Natural Science Foundation of China,No.11622542 and No.51677145
文摘BACKGROUND Hepatocellular carcinoma(HCC) is one of the most common malignant tumors worldwide, and novel methods for early/rapid diagnosis of HCC are needed.Terahertz(THz) spectroscopy is considered to have the potential to distinguish between normal liver tissue and HCC tissue; however, there are few reports on it.We conduct this observational study to explore the feasibility of THz imaging for the diagnosis of HCC.AIM To evaluate the feasibility of THz for discriminating between HCC and normal liver tissues using fresh tissue specimens obtained from HCC patients who had undergone surgery.METHODS Normal liver tissue and HCC tissue were cryosectioned into 50 μm-thick slicesand placed on cover glass. Two adjacent tissue sections were separated subjected to histopathological examination by hematoxylin and eosin staining or THz transmission examination, and THz images were compared with pathologically mapped images. We determined the typical tumor and normal liver tissue regions by pathological examination; the corresponding areas of adjacent sections were examined by THz transmission.RESULTS The transmission rate of HCC tissue was 0.15-0.25, and the transmission rate of typical HCC tissue was about 0.2. THz transmittance in normal liver tissue is slightly higher than 0.4, but there were many influencing factors, including the degree of liver cirrhosis, fat components, ice crystals in frozen sections, and apoptosis.CONCLUSION In conclusion, this study shows that THz imaging can detect HCC tissue. Further research will yield more detailed data of the THz transmission rates of HCC tissue with different degrees of differentiation.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61727821,61875215,and 11904408).
文摘We propose a simple pumping method to increase the effective population of cold atoms in the clock state and investigate the factors which affect the pumping efficiency in cold atom systems.We report the theory and demonstrate the corresponding experiment in an ^(87)Rb integrating sphere cold atom clock.The experimental results show that the population of cold atoms in the Zeeman sublevel|F=2,mF=0>is approximately 1.62 times that of the result using optical pumping alone.This method can also be applied to increase the effective population in any one of the target Zeeman sublevels in other cold atom systems.
基金supported by China National Natural Science Foundation of Shaanxi Province(No.2020JQ-643)China Postdoctoral Science Foundation funded project(No.2019M653545)the Fundamental Research Funds for the Central Universities,China(No.JB210510)。
文摘The structure and propagation of the plasma in air breakdown driven by high-power microwave have attracted great interest.This paper focuses on the microwave amplitude and frequency dependence of plasma formation at atmospheric pressure using one two-dimensional model,which is based on Maxwell’s equations coupled with plasma fluid equations.In this model,we adopt the effective electron diffusion coefficient,which can describe well the change from free diffusion in a plasma front to ambipolar diffusion in the bulk plasma.The filamentary plasma arrays observed in experiments are well reproduced in the simulations.The density and propagation speed of the plasma from the simulations are also close to the corresponding experimental data.The size of plasma filament parallel to the electric field decreases with increasing frequency,and it increases with the electric field amplitude.The distance between adjacent plasma filaments is close to one-quarter wavelength under different frequencies and amplitudes.The plasma propagation speed shows little change with the frequency,and it increases with the amplitude.The variations of plasma structure and propagation with the amplitude and frequency are due to the change in the distribution of the electric field.
基金Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB 21030200)the National Natural Science Foundation of China(Grant No.11904408).
文摘The measurement performance of the atom interferometry absolute gravimeter is strongly affected by the ground vibration noise.We propose a vibration noise evaluation scheme using a Michelson laser interferometer constructed by the intrinsic Raman laser of the atomic gravimeter.Theoretical analysis shows that the vibration phase measurement accuracy is better than 4 mrad,which corresponds to about 10-^10 g accuracy for a single shot gravity measurement.Compared with the commercial seismometer or accelerometer,this method is a simple,low cost,direct,and fully synchronized measurement of the vibration phase which should benefit the development of the atomic gravimeter.On the other side,limited by equivalence principle,the result of the laser interferometer is not absolute but relative vibration measurement.Triangular cap method could be used to evaluation the noise contribution of vibration,which is a different method from others and should benefit the development of the atomic gravimeter.
基金This study is supported by the Natural Science Foundation of China(NSFC)under Grant Nos.11774073 and 51279033.
文摘The outer-product decomposition algorithm(OPDA)performs well at blindly identifying system function.However,the direct use of the OPDA in systems using bandpass source will lead to errors.This study proposes an approach to enhance the channel estimation quality of a bandpass source that uses OPDA.This approach performs frequency domain transformation on the received signal and obtains the optimal transformation parameter by minimizing the p-norm of an error matrix.Moreover,the proposed approach extends the application of OPDA from a white source to a bandpass white source or chirp signal.Theoretical formulas and simulation results show that the proposed approach not only reduces the estimation error but also accelerates the algorithm in a bandpass system,thus being highly feasible in practical blind system identification applications.
基金supported in part by the National Natural Science Foundation of China(Grant No.52205602,No.52075455 and 62204264)the Fundamental Research Funds for the Central Universities(Grant No.D5000240226).
文摘High-precision piezoresistive pressure sensors play a significant role in aerospace,automotive,and other fields.Nonlinear error is the key factor that restricts the improvement of the sensor precision.A mathematical model for evaluating the sensor’s nonlinear error is established,based on which a piezoresistor sensitivity matching method is proposed to suppress the nonlinear error.By adjusting the piezoresistors'structure and position on the sensing membrane,four piezoresistors with equal sensitivity are obtained,and theoretical quasi-zero nonlinear error is achieved.To verify the design,sensor prototypes are fabricated utilizing the MEMS technology.After sensor packaging,a cylindrical absolute pressure sensor featuring a 4 mm diameter with a range from 0 to 100 kPa is acquired.The experimental results demonstrate the excellent performance of the proposed sensor,which indicates a nonlinear error as low as±0.004%FS.Besides,the proposed sensor has a sensitivity of 1.6810 mV/kPa,a hysteresis of 0.025%,a repeatability of 0.015%,a zero drift of 0.03%FS,and a 3 dB frequency from 0 to 121.82 kHz.Moreover,the prototype is tested in the Mach 4 wind tunnel,and the measurement error between the proposed sensor and the true pressure is±0.98%.This paper provides key sensing technology for high-precision surface pressure analysis of aircraft.
基金supported by the National Natural Science Foundation of China(41906169).
文摘The conventional method of deep-sea acoustic source localization usually uses the multi-path arrival information of the acoustic source signals received by hydrophone arrays to match with the simulation results to achieve localization.Aiming at the problem that it is difficult to extract the similar multi-path arrival angle directly by the conventional method,a deconvolution positioning method for deep-sea vertical array underwater target is proposed.By using this method,not only the adaptive iterative frequency-domain Richardson-Lucy algorithm is used to directly estimate the multipath angle of arrival of deep-sea acoustic targets,but also the ranging and depth fixing are realized by matching the sound field angle of arrival feature template.Simulation and experimental results show that this positioning method has higher localization accuracy and applicability than the conventional method,and has high computational efficiency.
