Excavation-induced microseismicity and rockburst occurrence in deep underground projects provide invaluable information that can be used to warn rockburst occurrence,facilitate rockburst mitigation procedures,and anal...Excavation-induced microseismicity and rockburst occurrence in deep underground projects provide invaluable information that can be used to warn rockburst occurrence,facilitate rockburst mitigation procedures,and analyze the mechanisms responsible for their occurrence.Based on the deep parallel tunnels with the maximum depth of 1890 m created as part of the Neelum–Jhelum hydropower project in Pakistan,similarities and differences on excavation-induced microseismicity and rockburst occurrence between parallel tunnels with soft and hard alternant strata are studied.Results show that a large number of microseismic(MS)events occurred in each of the parallel tunnels during excavation.Rockbursts occurred most frequently in certain local sections of the two tunnels.Significant differences are found in the excavation-induced microseismicity(spatial distribution and number of MS events,distribution of MS energy,and pattern of microseismicity variation)and rockbursts characteristics(the number and the spatial distribution)between the parallel tunnels.Attempting to predict the microseismicity and rockburst intensities likely to be encountered in subsequent tunnel based on the activity encountered when the parallel tunnel was previously excavated will not be an easy or accurate procedure in deep tunnel projects involving complex lithological conditions.展开更多
This paper studies two range-Doppler (RD) algorithms for the azimuth correlation in the squint mode airborne synthetic aperture radar (SAR). The modeling of squint mode airborne SAR spatial geometry and echo response ...This paper studies two range-Doppler (RD) algorithms for the azimuth correlation in the squint mode airborne synthetic aperture radar (SAR). The modeling of squint mode airborne SAR spatial geometry and echo response is given. The procedure for the squint mode airborne SAR processing using the two RD algorithms is outlined. The simulation demonstrates that these two RD algorithms are suitable for squint mode airborne SAR when the squint angle is not larger than 20(°).展开更多
In low earth orbit (LEO) satellite or missile communication scenarios, signals may experience extremely large Doppler shifts and have short visual time. Thus, direct sequence spread spectrum (DSSS) systems should be a...In low earth orbit (LEO) satellite or missile communication scenarios, signals may experience extremely large Doppler shifts and have short visual time. Thus, direct sequence spread spectrum (DSSS) systems should be able to achieve acquisition in a very short time in spite of large Doppler frequencies. However, the traditional methods cannot solve it well. This work describes a new method that uses a differential decoding technique for Doppler mitigation and a batch process of FFT (fast Fourier transform) and IFFT (invert FFT) for the purpose of parallel code phase search by frequency domain correlation. After the code phase is estimated, another FFT process is carried out to search the Doppler frequency. Since both code phase and Doppler frequency domains are searched in parallel, this architecture can provide acquisition fifty times faster than conventional FFT methods. The performance in terms of the probability of detection and false alarm are also analyzed and simulated, showing that a signal-to-noise ratio (SNR) loss of 3 dB is introduced by the differential decoding. The proposed method is an efficient way to shorten the acquisition time with slightly hardware increasing.展开更多
Objective:The aim of this study was to evaluate the application value of high-frequency color Doppler ultrasound in the diagnosis of intraductal papilloma (IDP). Methods:A retrospective analysis of 64 IDP cases was do...Objective:The aim of this study was to evaluate the application value of high-frequency color Doppler ultrasound in the diagnosis of intraductal papilloma (IDP). Methods:A retrospective analysis of 64 IDP cases was done, the pathology proven by surgery with 89 lesions. According to the ultrasonic performance, the lesions were divided into different types and the solid focal were evaluated according to the classification BI-RADS-US standard. Results:There were 47 patients corresponds with the 64 cases of surgical pathology, the accuracy was 73.4%, according to the ultrasonic performance could be divided into two types, named catheter type and solid type, catheter diagnostic accuracy was 22/25 (88%), compared the morphological features of the solid type, grouped according to their size (≥ 2 cm or < 2 cm lesions), discovered there was no statistically significant difference between the benign and malignant lesions by BI-RADS-US grading standard. Conclusion:Two-dimensional ultrasound and Color Doppler flow imaging (CDFI) can make a definite diagnosis and positioning for IDP, but there are still some limitations to differentiate the benign and malignant, it need to pay more attention to the clinical application of substantive IDP and improve the understanding, provide more relevant information for clinic, the focal will be earlier treated to reduce the possibility of malignant happened change.展开更多
Doppler centroid frequency is an essential parameter in the imaging processing of the Scanning mode Synthetic Aperture Radar (ScanSAR). Inaccurate Doppler centroid frequency will result in ghost images in imaging resu...Doppler centroid frequency is an essential parameter in the imaging processing of the Scanning mode Synthetic Aperture Radar (ScanSAR). Inaccurate Doppler centroid frequency will result in ghost images in imaging result. In this letter, the principle and algorithms of Doppler centroid frequency estimation are introduced. Then the echo data of ScanSAR system is analyzed. Based on the algorithms of energy balancing and correlation Doppler estimator in the estimation of Doppler centroid frequency in strip mode SAR, an improved method for Doppler centroid frequency estimation in ScanSAR is proposed. The method has improved the accuracy of Doppler centroid frequency estimation in ScanSAR by zero padding between burst data. Finally, the proposed method is validated with the processing of ENVIronment SATellite Advanced Synthetic Aperture Radar (ENVISAT ASAR) wide swath raw data.展开更多
AIM: To estimate the characteristics of Color Doppler findings and the results of hepatic radionuclide angiography (HRA) in secondary Hodgkin's hepatic lymphoma. METHODS: The research included patients with a dia...AIM: To estimate the characteristics of Color Doppler findings and the results of hepatic radionuclide angiography (HRA) in secondary Hodgkin's hepatic lymphoma. METHODS: The research included patients with a diagnosis of Hodgkin's lymphoma with metastatic focal lesions in the liver and controls. Morphologic characteristics of focal liver lesions and hemodynamic parameters were examined by pulsed and Color Doppler in the portal, hepatic and splenic veins were examined. Hepatic perfusion index (HPI) estimated by HRA was calculated. was observed. Lesions were mostly hypoechoic and mixed, solitary or multiple. Some of the patients presented with dilated splenic veins and hepatofugal blood flow. A pulse wave was registered in the centre and at the margins of lymphoma. The average velocity of the pulse wave was higher at the margins (P 〉 0.05). A continuous venous wave was found only at the margins of lymphoma. There was no linear correlation between lymphoma size and velocity of pulse and continuous wave (r = 390, P 〈 0.01). HPI was significantly lower in patients with lymphomas than in controls (P 〈 0.05), pointing out increased arterial perfusion in comparison to portal perfusion. CONCLUSION: Color Doppler ultrasonography is a sensitive method for the detection of neovascularization in Hodgkin's hepatic lymphoma and estimation of its intensity. Hepatic radionuclide angiography can additionally help in the assesment of vascularisation of liver lesions.展开更多
A comparative spectral analysis of high-latitude magnetic and Doppler radar measurements is presented. The analysis takes into account the Doppler effect that is inherent in magnetic observations. The frequency shifts...A comparative spectral analysis of high-latitude magnetic and Doppler radar measurements is presented. The analysis takes into account the Doppler effect that is inherent in magnetic observations. The frequency shifts between the magnetic and radar data are estimated (removed) indirectly by formulating the spectral analysis of magnetic data as the Schuster problem of hidden periodicities. There is a satisfactory agreement between the basic frequencies of equidistant spectra found in the magnetic data and frequencies found in the corresponding Doppler radar data. Some conclusions relevant to these findings are discussed.展开更多
Abstract A few important integrals involving the product of two universal associated Legendre polynomials Pl'm', (x),Pk'n'(x)and x2a(1-x2)-p-1,xb(1± x)-p-1and xc(1-x2)-p-1(1 ± x)axe evaluated...Abstract A few important integrals involving the product of two universal associated Legendre polynomials Pl'm', (x),Pk'n'(x)and x2a(1-x2)-p-1,xb(1± x)-p-1and xc(1-x2)-p-1(1 ± x)axe evaluated using the operator form of Taylor's theorem and an integral over a single universal associated Legendre polynomial. These integrals are more general since the quantum numbers are unequal, i.e.l' ≠ k' and m'≠ n' .Their selection rules are a/so given. We also verify the correctness of those integral formulas numerically.展开更多
The propagation of a weak probe field in a four-level N-type quantum system in the presence of spontaneously generated coherence(SGC) is theoretically investigated. The optical properties of the system are studied and...The propagation of a weak probe field in a four-level N-type quantum system in the presence of spontaneously generated coherence(SGC) is theoretically investigated. The optical properties of the system are studied and it is shown that the group velocity of light pulse can be controlled by relative phase of applied fields. By changing the relative phase of applied fields, the group velocity of light pulse changes from transparent subluminal to the transparent superluminal light propagation. Thus, the phase-controlled absorption-free superluminal light propagation is obtained without applying an incoherent laser fields to the system. The propagation of a weak probe light pulse is studied by solving the Maxwell's wave equation on numerical grid in space and time. Moreover, we study the third order self- and cross-Kerr susceptibility of probe field and calculate the nonlinear cross-phase shift for different values of intensity of applied fields. In addition, we take into account the effect of Doppler broadening on the light pulse propagation and it is found that a suitable choice of laser propagation directions allows us to preserve our results even in the presence of Doppler effect. It is demonstrated that by increasing the Doppler width of distribution to the room temperature,the dispersion changes from transparent subluminal to transparent superluminal light propagation which is our major motivation for this work.展开更多
基金Projects(41972295,U1965205)supported by the National Natural Science Foundation of ChinaProject(2019ZDK034)supported by the Guangxi Key Laboratory of Disaster Prevention and Engineering Safety,China。
文摘Excavation-induced microseismicity and rockburst occurrence in deep underground projects provide invaluable information that can be used to warn rockburst occurrence,facilitate rockburst mitigation procedures,and analyze the mechanisms responsible for their occurrence.Based on the deep parallel tunnels with the maximum depth of 1890 m created as part of the Neelum–Jhelum hydropower project in Pakistan,similarities and differences on excavation-induced microseismicity and rockburst occurrence between parallel tunnels with soft and hard alternant strata are studied.Results show that a large number of microseismic(MS)events occurred in each of the parallel tunnels during excavation.Rockbursts occurred most frequently in certain local sections of the two tunnels.Significant differences are found in the excavation-induced microseismicity(spatial distribution and number of MS events,distribution of MS energy,and pattern of microseismicity variation)and rockbursts characteristics(the number and the spatial distribution)between the parallel tunnels.Attempting to predict the microseismicity and rockburst intensities likely to be encountered in subsequent tunnel based on the activity encountered when the parallel tunnel was previously excavated will not be an easy or accurate procedure in deep tunnel projects involving complex lithological conditions.
文摘This paper studies two range-Doppler (RD) algorithms for the azimuth correlation in the squint mode airborne synthetic aperture radar (SAR). The modeling of squint mode airborne SAR spatial geometry and echo response is given. The procedure for the squint mode airborne SAR processing using the two RD algorithms is outlined. The simulation demonstrates that these two RD algorithms are suitable for squint mode airborne SAR when the squint angle is not larger than 20(°).
基金Project(60904090) supported by the National Natural Science Foundation of China
文摘In low earth orbit (LEO) satellite or missile communication scenarios, signals may experience extremely large Doppler shifts and have short visual time. Thus, direct sequence spread spectrum (DSSS) systems should be able to achieve acquisition in a very short time in spite of large Doppler frequencies. However, the traditional methods cannot solve it well. This work describes a new method that uses a differential decoding technique for Doppler mitigation and a batch process of FFT (fast Fourier transform) and IFFT (invert FFT) for the purpose of parallel code phase search by frequency domain correlation. After the code phase is estimated, another FFT process is carried out to search the Doppler frequency. Since both code phase and Doppler frequency domains are searched in parallel, this architecture can provide acquisition fifty times faster than conventional FFT methods. The performance in terms of the probability of detection and false alarm are also analyzed and simulated, showing that a signal-to-noise ratio (SNR) loss of 3 dB is introduced by the differential decoding. The proposed method is an efficient way to shorten the acquisition time with slightly hardware increasing.
文摘Objective:The aim of this study was to evaluate the application value of high-frequency color Doppler ultrasound in the diagnosis of intraductal papilloma (IDP). Methods:A retrospective analysis of 64 IDP cases was done, the pathology proven by surgery with 89 lesions. According to the ultrasonic performance, the lesions were divided into different types and the solid focal were evaluated according to the classification BI-RADS-US standard. Results:There were 47 patients corresponds with the 64 cases of surgical pathology, the accuracy was 73.4%, according to the ultrasonic performance could be divided into two types, named catheter type and solid type, catheter diagnostic accuracy was 22/25 (88%), compared the morphological features of the solid type, grouped according to their size (≥ 2 cm or < 2 cm lesions), discovered there was no statistically significant difference between the benign and malignant lesions by BI-RADS-US grading standard. Conclusion:Two-dimensional ultrasound and Color Doppler flow imaging (CDFI) can make a definite diagnosis and positioning for IDP, but there are still some limitations to differentiate the benign and malignant, it need to pay more attention to the clinical application of substantive IDP and improve the understanding, provide more relevant information for clinic, the focal will be earlier treated to reduce the possibility of malignant happened change.
文摘Doppler centroid frequency is an essential parameter in the imaging processing of the Scanning mode Synthetic Aperture Radar (ScanSAR). Inaccurate Doppler centroid frequency will result in ghost images in imaging result. In this letter, the principle and algorithms of Doppler centroid frequency estimation are introduced. Then the echo data of ScanSAR system is analyzed. Based on the algorithms of energy balancing and correlation Doppler estimator in the estimation of Doppler centroid frequency in strip mode SAR, an improved method for Doppler centroid frequency estimation in ScanSAR is proposed. The method has improved the accuracy of Doppler centroid frequency estimation in ScanSAR by zero padding between burst data. Finally, the proposed method is validated with the processing of ENVIronment SATellite Advanced Synthetic Aperture Radar (ENVISAT ASAR) wide swath raw data.
基金Supported by The grant of the Republic of Science of Serbia (M145033,Chief investigatior:Professor Vladimir Obradovic)
文摘AIM: To estimate the characteristics of Color Doppler findings and the results of hepatic radionuclide angiography (HRA) in secondary Hodgkin's hepatic lymphoma. METHODS: The research included patients with a diagnosis of Hodgkin's lymphoma with metastatic focal lesions in the liver and controls. Morphologic characteristics of focal liver lesions and hemodynamic parameters were examined by pulsed and Color Doppler in the portal, hepatic and splenic veins were examined. Hepatic perfusion index (HPI) estimated by HRA was calculated. was observed. Lesions were mostly hypoechoic and mixed, solitary or multiple. Some of the patients presented with dilated splenic veins and hepatofugal blood flow. A pulse wave was registered in the centre and at the margins of lymphoma. The average velocity of the pulse wave was higher at the margins (P 〉 0.05). A continuous venous wave was found only at the margins of lymphoma. There was no linear correlation between lymphoma size and velocity of pulse and continuous wave (r = 390, P 〈 0.01). HPI was significantly lower in patients with lymphomas than in controls (P 〈 0.05), pointing out increased arterial perfusion in comparison to portal perfusion. CONCLUSION: Color Doppler ultrasonography is a sensitive method for the detection of neovascularization in Hodgkin's hepatic lymphoma and estimation of its intensity. Hepatic radionuclide angiography can additionally help in the assesment of vascularisation of liver lesions.
文摘A comparative spectral analysis of high-latitude magnetic and Doppler radar measurements is presented. The analysis takes into account the Doppler effect that is inherent in magnetic observations. The frequency shifts between the magnetic and radar data are estimated (removed) indirectly by formulating the spectral analysis of magnetic data as the Schuster problem of hidden periodicities. There is a satisfactory agreement between the basic frequencies of equidistant spectra found in the magnetic data and frequencies found in the corresponding Doppler radar data. Some conclusions relevant to these findings are discussed.
文摘Abstract A few important integrals involving the product of two universal associated Legendre polynomials Pl'm', (x),Pk'n'(x)and x2a(1-x2)-p-1,xb(1± x)-p-1and xc(1-x2)-p-1(1 ± x)axe evaluated using the operator form of Taylor's theorem and an integral over a single universal associated Legendre polynomial. These integrals are more general since the quantum numbers are unequal, i.e.l' ≠ k' and m'≠ n' .Their selection rules are a/so given. We also verify the correctness of those integral formulas numerically.
文摘The propagation of a weak probe field in a four-level N-type quantum system in the presence of spontaneously generated coherence(SGC) is theoretically investigated. The optical properties of the system are studied and it is shown that the group velocity of light pulse can be controlled by relative phase of applied fields. By changing the relative phase of applied fields, the group velocity of light pulse changes from transparent subluminal to the transparent superluminal light propagation. Thus, the phase-controlled absorption-free superluminal light propagation is obtained without applying an incoherent laser fields to the system. The propagation of a weak probe light pulse is studied by solving the Maxwell's wave equation on numerical grid in space and time. Moreover, we study the third order self- and cross-Kerr susceptibility of probe field and calculate the nonlinear cross-phase shift for different values of intensity of applied fields. In addition, we take into account the effect of Doppler broadening on the light pulse propagation and it is found that a suitable choice of laser propagation directions allows us to preserve our results even in the presence of Doppler effect. It is demonstrated that by increasing the Doppler width of distribution to the room temperature,the dispersion changes from transparent subluminal to transparent superluminal light propagation which is our major motivation for this work.