The spatial correlations of acoustic field have important implications for underwater target detection and other ap- plications in deep water. In this paper, the spatial correlations of the high intensity zone in the ...The spatial correlations of acoustic field have important implications for underwater target detection and other ap- plications in deep water. In this paper, the spatial correlations of the high intensity zone in the deep-water acoustic field are investigated by using the experimental data obtained in the South China Sea. The experimental results show that the structures of the spatial correlation coefficient at different ranges and depths are similar to the transmission loss structure in deep water. The main reason for this phenomenon is analyzed by combining the normal mode theory with the ray theory. It is shown that the received signals in the high intensity zone mainly include one or two main pulses which are contributed by the interference of a group of waterbome modes with similar phases. The horizontal-longitudinal correlations at the same receiver depth but in different high intensity zones are analyzed. At some positions, more pulses are received in the arrival structure of the signal due to bottom reflection and the horizontal-longitudinal correlation coefficient decreases accordingly. The multi-path arrival structure of receiving signal becomes more complex with increasing receiver depth.展开更多
Background Discography is a gold standard for the diagnosis of the low back pain （LBP）, but it has potential dangers for the development of discitis, cerebral spinal fluid leakage, retroperitoneal bleeding, acute ne...Background Discography is a gold standard for the diagnosis of the low back pain （LBP）, but it has potential dangers for the development of discitis, cerebral spinal fluid leakage, retroperitoneal bleeding, acute new back pain and the tremendous radiation exposure to the patient. Using ＂evidence-based radiology＂ methods, the comparative roles of high intensity zone （HIZ） in diagnosing discogenic LBP were evaluated. Methods A focused clinical question was designed and a Pubmed and manual search were performed to identify the role of HIZ on MRI T2WI compared with discography. The studies retrieved were assessed for validity and strength. Sensitivity, specificity, likelihood ratios （LRs） and graphs of conditional probability were evaluated from the best current study by evidence-based radiology. Results Best evidence was retrieved in ten articles from 1992 to 2007. The best evidence level was lb and the strength of the evidence included： sensitivity 0.63 （0.51,0.76）, specificity 0.97 （0.92, 1.00）, positive predictive value 0.95, negative predictive value 0.72, positive LRs 18.37 and negative LRs 0.38. The gold standard of discogenic LBP is the provocative discography. Conclusions For suspected discogenic LBP, HIZ is limited for the diagnosis if HIZ is positive, which suggests further discography. In contrast HIZ is a good test for diagnosis if HIZ is negative, which indicates the disease can be excluded.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11434012 and 41561144006)
文摘The spatial correlations of acoustic field have important implications for underwater target detection and other ap- plications in deep water. In this paper, the spatial correlations of the high intensity zone in the deep-water acoustic field are investigated by using the experimental data obtained in the South China Sea. The experimental results show that the structures of the spatial correlation coefficient at different ranges and depths are similar to the transmission loss structure in deep water. The main reason for this phenomenon is analyzed by combining the normal mode theory with the ray theory. It is shown that the received signals in the high intensity zone mainly include one or two main pulses which are contributed by the interference of a group of waterbome modes with similar phases. The horizontal-longitudinal correlations at the same receiver depth but in different high intensity zones are analyzed. At some positions, more pulses are received in the arrival structure of the signal due to bottom reflection and the horizontal-longitudinal correlation coefficient decreases accordingly. The multi-path arrival structure of receiving signal becomes more complex with increasing receiver depth.
文摘Background Discography is a gold standard for the diagnosis of the low back pain （LBP）, but it has potential dangers for the development of discitis, cerebral spinal fluid leakage, retroperitoneal bleeding, acute new back pain and the tremendous radiation exposure to the patient. Using ＂evidence-based radiology＂ methods, the comparative roles of high intensity zone （HIZ） in diagnosing discogenic LBP were evaluated. Methods A focused clinical question was designed and a Pubmed and manual search were performed to identify the role of HIZ on MRI T2WI compared with discography. The studies retrieved were assessed for validity and strength. Sensitivity, specificity, likelihood ratios （LRs） and graphs of conditional probability were evaluated from the best current study by evidence-based radiology. Results Best evidence was retrieved in ten articles from 1992 to 2007. The best evidence level was lb and the strength of the evidence included： sensitivity 0.63 （0.51,0.76）, specificity 0.97 （0.92, 1.00）, positive predictive value 0.95, negative predictive value 0.72, positive LRs 18.37 and negative LRs 0.38. The gold standard of discogenic LBP is the provocative discography. Conclusions For suspected discogenic LBP, HIZ is limited for the diagnosis if HIZ is positive, which suggests further discography. In contrast HIZ is a good test for diagnosis if HIZ is negative, which indicates the disease can be excluded.
