Space-based optical(SBO)space surveillance has attracted widespread interest in the last two decades due to its considerable value in space situation awareness(SSA).SBO observation strategy,which is related to the per...Space-based optical(SBO)space surveillance has attracted widespread interest in the last two decades due to its considerable value in space situation awareness(SSA).SBO observation strategy,which is related to the performance of space surveillance,is the top-level design in SSA missions reviewed.The recognized real programs about SBO SAA proposed by the institutions in the U.S.,Canada,Europe,etc.,are summarized firstly,from which an insight of the development trend of SBO SAA can be obtained.According to the aim of the SBO SSA,the missions can be divided into general surveillance and space object tracking.Thus,there are two major categories for SBO SSA strategies.Existing general surveillance strategies for observing low earth orbit(LEO)objects and beyond-LEO objects are summarized and compared in terms of coverage rate,revisit time,visibility period,and image processing.Then,the SBO space object tracking strategies,which has experienced from tracking an object with a single satellite to tracking an object with multiple satellites cooperatively,are also summarized.Finally,this paper looks into the development trend in the future and points out several problems that challenges the SBO SSA.展开更多
The advent of the laser has placed stringent requirements on the fabrication, performance and quality of optical elements employed within systems for most practical applications. Their high power performance is genera...The advent of the laser has placed stringent requirements on the fabrication, performance and quality of optical elements employed within systems for most practical applications. Their high power performance is generally governed by three distinct steps, firstly the absorption of incident optical radiation (governed primarily by various absorption mechanisms);secondly, followed by a temperature increase and response governed primarily by thermal properties and finally the elements thermo-optical and thermomechanical response, e.g., distortion, stress birefringenous fracture, etc. All of which needs to be understood in the design as efficient, compact, reliable and useful for many applications high power systems, under a variety of operating conditions, pulsed and continuous wave, rep-rated or burst mode of varying duty cycles.展开更多
A method of correlation analysis to determine the correlation between two too-short arcs is presented to monitor geosynchro- nous earth orbit objects on a space-based surveillance system. The necessary condition for a...A method of correlation analysis to determine the correlation between two too-short arcs is presented to monitor geosynchro- nous earth orbit objects on a space-based surveillance system. The necessary condition for a geosynchronous earth orbit object to be observed by a space-based visible sensor in two successive orbital periods is derived, and the principle for the selection of search fence parameters is proposed. The processing procedure of the correlation analysis for the two too-short arcs as well as two correlation judgment methods is given and the selection of the threshold value for the judgment is analyzed. Finally, a simulation is performed to demonstrate the applicability of the presented methods. Simulation results ir^dicate that a surveil- lance system can acquire two observation arcs in two successive orbital periods by selecting the suitable search fence parame- ters, and that the two correlation judgment methods and the selected threshold are valid. The initial orbit of the uncorrelated objects can be determined by two observation arcs, and the accuracy of the initial orbit meets the requirements of re-acquiring the object.展开更多
BACKGROUND Post-polypectomy surveillance intervals are currently determined based on pathology results.AIM To evaluate a polyp-based resect and discard model that assigns surveillance intervals based solely on polyp n...BACKGROUND Post-polypectomy surveillance intervals are currently determined based on pathology results.AIM To evaluate a polyp-based resect and discard model that assigns surveillance intervals based solely on polyp number and size.METHODS Patients undergoing elective colonoscopies at the Montreal University Medical Center were enrolled prospectively.The polyp-based strategy was used to assign the next surveillance interval using polyp size and number.Surveillance intervals were also assigned using optical diagnosis for small polyps(<10 mm).The primary outcome was surveillance interval agreement between the polyp-based model,optical diagnosis,and the pathology-based reference standard using the 2020 United States Multi-Society Task Force guidelines.Secondary outcomes included the proportion of reduction in required histopathology evaluations and proportion of immediate post-colonoscopy recommendations provided to patients.RESULTS Of 944 patients(mean age 62.6 years,49.3%male,933 polyps)were enrolled.The surveillance interval agreement for the polyp-based strategy was 98.0%[95%confidence interval(CI):0.97-0.99]compared with pathology-based assignment.Optical diagnosis-based intervals achieved 95.8%(95%CI:0.94-0.97)agreement with pathology.When using the polyp-based strategy and optical diagnosis,the need for pathology assessment was reduced by 87.8%and 70.6%,respectively.The polyp-based strategy provided 93.7%of patients with immediate surveillance interval recommendations vs 76.1%for optical diagnosis.CONCLUSION The polyp-based strategy achieved almost perfect surveillance interval agreement compared with pathology-based assignments,significantly reduced the number of required pathology evaluations,and provided most patients with immediate surveillance interval recommendations.展开更多
基金This work was supported by the National Natural Science Foundation of China(61690210,61690213).
文摘Space-based optical(SBO)space surveillance has attracted widespread interest in the last two decades due to its considerable value in space situation awareness(SSA).SBO observation strategy,which is related to the performance of space surveillance,is the top-level design in SSA missions reviewed.The recognized real programs about SBO SAA proposed by the institutions in the U.S.,Canada,Europe,etc.,are summarized firstly,from which an insight of the development trend of SBO SAA can be obtained.According to the aim of the SBO SSA,the missions can be divided into general surveillance and space object tracking.Thus,there are two major categories for SBO SSA strategies.Existing general surveillance strategies for observing low earth orbit(LEO)objects and beyond-LEO objects are summarized and compared in terms of coverage rate,revisit time,visibility period,and image processing.Then,the SBO space object tracking strategies,which has experienced from tracking an object with a single satellite to tracking an object with multiple satellites cooperatively,are also summarized.Finally,this paper looks into the development trend in the future and points out several problems that challenges the SBO SSA.
文摘The advent of the laser has placed stringent requirements on the fabrication, performance and quality of optical elements employed within systems for most practical applications. Their high power performance is generally governed by three distinct steps, firstly the absorption of incident optical radiation (governed primarily by various absorption mechanisms);secondly, followed by a temperature increase and response governed primarily by thermal properties and finally the elements thermo-optical and thermomechanical response, e.g., distortion, stress birefringenous fracture, etc. All of which needs to be understood in the design as efficient, compact, reliable and useful for many applications high power systems, under a variety of operating conditions, pulsed and continuous wave, rep-rated or burst mode of varying duty cycles.
文摘A method of correlation analysis to determine the correlation between two too-short arcs is presented to monitor geosynchro- nous earth orbit objects on a space-based surveillance system. The necessary condition for a geosynchronous earth orbit object to be observed by a space-based visible sensor in two successive orbital periods is derived, and the principle for the selection of search fence parameters is proposed. The processing procedure of the correlation analysis for the two too-short arcs as well as two correlation judgment methods is given and the selection of the threshold value for the judgment is analyzed. Finally, a simulation is performed to demonstrate the applicability of the presented methods. Simulation results ir^dicate that a surveil- lance system can acquire two observation arcs in two successive orbital periods by selecting the suitable search fence parame- ters, and that the two correlation judgment methods and the selected threshold are valid. The initial orbit of the uncorrelated objects can be determined by two observation arcs, and the accuracy of the initial orbit meets the requirements of re-acquiring the object.
基金The study protocol and data collection were approved by the local institutional research board as an amendment to the two prospective clinical studies(17.135 and 16.367,respectively).
文摘BACKGROUND Post-polypectomy surveillance intervals are currently determined based on pathology results.AIM To evaluate a polyp-based resect and discard model that assigns surveillance intervals based solely on polyp number and size.METHODS Patients undergoing elective colonoscopies at the Montreal University Medical Center were enrolled prospectively.The polyp-based strategy was used to assign the next surveillance interval using polyp size and number.Surveillance intervals were also assigned using optical diagnosis for small polyps(<10 mm).The primary outcome was surveillance interval agreement between the polyp-based model,optical diagnosis,and the pathology-based reference standard using the 2020 United States Multi-Society Task Force guidelines.Secondary outcomes included the proportion of reduction in required histopathology evaluations and proportion of immediate post-colonoscopy recommendations provided to patients.RESULTS Of 944 patients(mean age 62.6 years,49.3%male,933 polyps)were enrolled.The surveillance interval agreement for the polyp-based strategy was 98.0%[95%confidence interval(CI):0.97-0.99]compared with pathology-based assignment.Optical diagnosis-based intervals achieved 95.8%(95%CI:0.94-0.97)agreement with pathology.When using the polyp-based strategy and optical diagnosis,the need for pathology assessment was reduced by 87.8%and 70.6%,respectively.The polyp-based strategy provided 93.7%of patients with immediate surveillance interval recommendations vs 76.1%for optical diagnosis.CONCLUSION The polyp-based strategy achieved almost perfect surveillance interval agreement compared with pathology-based assignments,significantly reduced the number of required pathology evaluations,and provided most patients with immediate surveillance interval recommendations.
