We have developed a new stacking technique in ambient noise tomography to obtain high-quality dispersion curves of Rayleigh waves. This technique is used to stack the vertical components of the Estimated Green Functio...We have developed a new stacking technique in ambient noise tomography to obtain high-quality dispersion curves of Rayleigh waves. This technique is used to stack the vertical components of the Estimated Green Functions (EGFs) obtained respectively from cross correlation of the ambient noise data recorded by a remote seismic station and one of the short distance seismic stations of a seismic array. It is based on a phase-matched filter and is implemented by a four-step iterative process: signal compression, stacking, signal extraction and signal decompression. The iterative process ends and gives the dispersion curve of Rayleigh wave when the predicted one and the processing result converge. We have tested the method using the vertical components of synthetic Rayleigh wave records. Results show that this new stacking method is stable and it can improve the quality of dispersion curves. In addition, we have applied this method to real data. We see that the results given by our new technique are obviously better than the ones employing the traditional method which is a three-step process: signal compression, signal extraction and signal decompression. In conclusion, the new method proposed in this paper can improve the signal to noise ratio of EGFs, and can therefore potentially improve the resolution of ambient noise tomography.展开更多
High-contrast imaging coronagraphs, used for the detection of exoplanets, have always adopted passive coronagraph optical components. It is therefore impossible to actively optimize the coronagraphs to achieve their b...High-contrast imaging coronagraphs, used for the detection of exoplanets, have always adopted passive coronagraph optical components. It is therefore impossible to actively optimize the coronagraphs to achieve their best performance. To solve this problem, we propose a novel high-contrast imaging coronagraph which combines a liquid crystal array (LCA) for active pupil apodization and a deformable mirror (DM) for phase correction. The LCA we use is an amplitude-only spatial light mod- ulator. The LCA is well calibrated and compensates for its amplitude non-uniformity and nonlinear intensity responsivity. We measured the imaging contrasts of the coron- agraph system with the LCA only and without the DM deployed. Imaging contrasts of 10-4 and 10-5 can be reached at an inner working angular distance of 2.5 and 5A/D, respectively. A simulation shows that the phase errors on the coronagraph pupil limit the contrast performance. The contrast could be further improved if a DM is deployed to correct the phase errors induced by the LCA and coronagraph optics.展开更多
A high-contrast coronagraph for direct imaging of an Earth-like exoplanet at the visible band needs a contrast of 10^-10 at a small angular separation of 4λ/D or less. Here we report our recent laboratory experiment ...A high-contrast coronagraph for direct imaging of an Earth-like exoplanet at the visible band needs a contrast of 10^-10 at a small angular separation of 4λ/D or less. Here we report our recent laboratory experiment that approaches these lim- its. Our test of a high-contrast imaging coronagraph is based on our step-transmission apodized filter. To achieve this goal, we use a liquid crystal array as a phase correc- tor to create a dark hole based on our dedicated algorithm. We have suppressed the diffraction and speckle noise near the point image of a star to a level of 1.68 × 10^-9 at 4λ/D, which can be used for direct imaging of Jupiter-like exoplanets. This demon- strates that a telescope incorporating a high-contrast coronagraph in space has the potential to detect and characterize Earth-like planets.展开更多
We investigated erosion-corrosion(E-C) and its mitigation on the internal surface of the expansion segment of N80 steel tube in a loop system using array electrode technique, weight-loss measurement, computational-flu...We investigated erosion-corrosion(E-C) and its mitigation on the internal surface of the expansion segment of N80 steel tube in a loop system using array electrode technique, weight-loss measurement, computational-fluid-dynamics simulation, and surface characterization techniques.The results show that high E-C rates can occur at locations where there is a high flow velocity and/or a strong impact from sand particles, which results in different E-C rates at various locations.Consequently, it can be expected that localized corrosion often occurs in such segments.The E-C rate at each location in the expansion segment can be significantly mitigated with an imidazoline derivative inhibitor, as the resulting inhibitor layer significantly impedes the electrochemical reaction rate.However, we found that this inhibitor layer could not effectively reduce the difference in the erosion rates at different locations on the internal surface of the expansion segment.This means that localized corrosion can still occur at the expansion segment despite the presence of the inhibitor.展开更多
The nonlinearity has significant effect on the ultrasonic therapy using phased ar- rays. A numerical approach is developed to calculate the nonlinear sound field generated from a phased array based on the Gaussian sup...The nonlinearity has significant effect on the ultrasonic therapy using phased ar- rays. A numerical approach is developed to calculate the nonlinear sound field generated from a phased array based on the Gaussian superposition technique. The parameters of the phased array elements are first estimated from the focal parameters using the inverse matrix algorithm; Then the elements are expressed as a set of Gaussian functions; Finally, the nonlinear sound field can be calculated using the Gaussian superposition technique. In the numerical simulation, a 64~ 1 phased array is used as the transmitter. In the linear case, the difference between the results of the Gaussian superposition technique and the Fresnel integral is less than 0.5%, which verifies the feasibility of the approach. In the nonlinear case, the nonlinear fields of single-focus modes and double-focus modes are calculated. The results reveal that the nonlinear effects can improve the focusing performance, and the nonlinear effects are related with the source pressures and the excitation frequencies.展开更多
From the point of view of system design, a configuration of fiber-optic interferomet- ric hydrophone array and its modulation and demodulation approach using frequncy division multiplexing technique based on Phase Gen...From the point of view of system design, a configuration of fiber-optic interferomet- ric hydrophone array and its modulation and demodulation approach using frequncy division multiplexing technique based on Phase Generated Carrier (PGC) is introduced. And the em- phasis on demonstrating the relationship among the number of units N, the detectable signal amplitude D and the detectable frequency ws through analyzing the frequency spectrum of the output signal of the J × K array and the key factor which restricts N, D, Ws for increasing are presented. The maximum phare shift and the law of its variation according to frequency are specially analyzed. The results induced from some relative theory were verified by experiments.展开更多
There are many possible bias errors in the measurement of structural intensity and some of them have been theoretically examined. Attempting to analyse all the bias errors at the same time results in a very complicate...There are many possible bias errors in the measurement of structural intensity and some of them have been theoretically examined. Attempting to analyse all the bias errors at the same time results in a very complicated analysis and makes it difficult to draw clear conclusions.The bias errors are usually analysed individually. In this paper a theoretical study of three bias errors in the measurement of structural intensity is presented by using the twor-accelerometer array technique. It is assumed that the physical and material properties of the test structure are known. The analysis will be restricted to one-dimensional beams, but it can be extended to two-dimensional plates.展开更多
基金supported by theNational Natural Science Foundation of China with grant No.90814002 and 40821062Institute of Crustal Dynamics with grant No.ZDJ2008-18
文摘We have developed a new stacking technique in ambient noise tomography to obtain high-quality dispersion curves of Rayleigh waves. This technique is used to stack the vertical components of the Estimated Green Functions (EGFs) obtained respectively from cross correlation of the ambient noise data recorded by a remote seismic station and one of the short distance seismic stations of a seismic array. It is based on a phase-matched filter and is implemented by a four-step iterative process: signal compression, stacking, signal extraction and signal decompression. The iterative process ends and gives the dispersion curve of Rayleigh wave when the predicted one and the processing result converge. We have tested the method using the vertical components of synthetic Rayleigh wave records. Results show that this new stacking method is stable and it can improve the quality of dispersion curves. In addition, we have applied this method to real data. We see that the results given by our new technique are obviously better than the ones employing the traditional method which is a three-step process: signal compression, signal extraction and signal decompression. In conclusion, the new method proposed in this paper can improve the signal to noise ratio of EGFs, and can therefore potentially improve the resolution of ambient noise tomography.
基金supported by the "Strategic Priority Research Program" of the Chinese Academy of Sciences(Grant No.XDA04070600)the National Natural Science Foundation of China(Grant Nos.11003031 and 10873024)+1 种基金as well as the National Astronomical Observatories' Special Fund for Astronomy-2009Part of the work described in this paper was carried out at California State University Northridge,with support from the National Science Foundation under Grant ATM-0841440
文摘High-contrast imaging coronagraphs, used for the detection of exoplanets, have always adopted passive coronagraph optical components. It is therefore impossible to actively optimize the coronagraphs to achieve their best performance. To solve this problem, we propose a novel high-contrast imaging coronagraph which combines a liquid crystal array (LCA) for active pupil apodization and a deformable mirror (DM) for phase correction. The LCA we use is an amplitude-only spatial light mod- ulator. The LCA is well calibrated and compensates for its amplitude non-uniformity and nonlinear intensity responsivity. We measured the imaging contrasts of the coron- agraph system with the LCA only and without the DM deployed. Imaging contrasts of 10-4 and 10-5 can be reached at an inner working angular distance of 2.5 and 5A/D, respectively. A simulation shows that the phase errors on the coronagraph pupil limit the contrast performance. The contrast could be further improved if a DM is deployed to correct the phase errors induced by the LCA and coronagraph optics.
基金Supported by the National Natural Science Foundation of China
文摘A high-contrast coronagraph for direct imaging of an Earth-like exoplanet at the visible band needs a contrast of 10^-10 at a small angular separation of 4λ/D or less. Here we report our recent laboratory experiment that approaches these lim- its. Our test of a high-contrast imaging coronagraph is based on our step-transmission apodized filter. To achieve this goal, we use a liquid crystal array as a phase correc- tor to create a dark hole based on our dedicated algorithm. We have suppressed the diffraction and speckle noise near the point image of a star to a level of 1.68 × 10^-9 at 4λ/D, which can be used for direct imaging of Jupiter-like exoplanets. This demon- strates that a telescope incorporating a high-contrast coronagraph in space has the potential to detect and characterize Earth-like planets.
基金financially supported by the 111 Project (No.D18016)the Application and Fundamental Research of Sichuan Province, China (No.2017JY0171)the Scientific and Technological Innovation Team for the Safety of Petroleum Tubular Goods in Southwest Petroleum University (No.2018CXTD01)。
文摘We investigated erosion-corrosion(E-C) and its mitigation on the internal surface of the expansion segment of N80 steel tube in a loop system using array electrode technique, weight-loss measurement, computational-fluid-dynamics simulation, and surface characterization techniques.The results show that high E-C rates can occur at locations where there is a high flow velocity and/or a strong impact from sand particles, which results in different E-C rates at various locations.Consequently, it can be expected that localized corrosion often occurs in such segments.The E-C rate at each location in the expansion segment can be significantly mitigated with an imidazoline derivative inhibitor, as the resulting inhibitor layer significantly impedes the electrochemical reaction rate.However, we found that this inhibitor layer could not effectively reduce the difference in the erosion rates at different locations on the internal surface of the expansion segment.This means that localized corrosion can still occur at the expansion segment despite the presence of the inhibitor.
基金supported by the National Basic Research Program 973(2011CB707900)National Natural Science Foundation of China(81127901,81227004,11174141,11274170 and 11161120324)+2 种基金the Natural Science Foundation of Jiangsu Province of China(BK2011543 and BE2011110)the National High Technology Research and Development Program 863(2012AA022700)the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘The nonlinearity has significant effect on the ultrasonic therapy using phased ar- rays. A numerical approach is developed to calculate the nonlinear sound field generated from a phased array based on the Gaussian superposition technique. The parameters of the phased array elements are first estimated from the focal parameters using the inverse matrix algorithm; Then the elements are expressed as a set of Gaussian functions; Finally, the nonlinear sound field can be calculated using the Gaussian superposition technique. In the numerical simulation, a 64~ 1 phased array is used as the transmitter. In the linear case, the difference between the results of the Gaussian superposition technique and the Fresnel integral is less than 0.5%, which verifies the feasibility of the approach. In the nonlinear case, the nonlinear fields of single-focus modes and double-focus modes are calculated. The results reveal that the nonlinear effects can improve the focusing performance, and the nonlinear effects are related with the source pressures and the excitation frequencies.
文摘From the point of view of system design, a configuration of fiber-optic interferomet- ric hydrophone array and its modulation and demodulation approach using frequncy division multiplexing technique based on Phase Generated Carrier (PGC) is introduced. And the em- phasis on demonstrating the relationship among the number of units N, the detectable signal amplitude D and the detectable frequency ws through analyzing the frequency spectrum of the output signal of the J × K array and the key factor which restricts N, D, Ws for increasing are presented. The maximum phare shift and the law of its variation according to frequency are specially analyzed. The results induced from some relative theory were verified by experiments.
文摘There are many possible bias errors in the measurement of structural intensity and some of them have been theoretically examined. Attempting to analyse all the bias errors at the same time results in a very complicated analysis and makes it difficult to draw clear conclusions.The bias errors are usually analysed individually. In this paper a theoretical study of three bias errors in the measurement of structural intensity is presented by using the twor-accelerometer array technique. It is assumed that the physical and material properties of the test structure are known. The analysis will be restricted to one-dimensional beams, but it can be extended to two-dimensional plates.