In covert communications,joint jammer selection and power optimization are important to improve performance.However,existing schemes usually assume a warden with a known location and perfect Channel State Information(...In covert communications,joint jammer selection and power optimization are important to improve performance.However,existing schemes usually assume a warden with a known location and perfect Channel State Information(CSI),which is difficult to achieve in practice.To be more practical,it is important to investigate covert communications against a warden with uncertain locations and imperfect CSI,which makes it difficult for legitimate transceivers to estimate the detection probability of the warden.First,the uncertainty caused by the unknown warden location must be removed,and the Optimal Detection Position(OPTDP)of the warden is derived which can provide the best detection performance(i.e.,the worst case for a covert communication).Then,to further avoid the impractical assumption of perfect CSI,the covert throughput is maximized using only the channel distribution information.Given this OPTDP based worst case for covert communications,the jammer selection,the jamming power,the transmission power,and the transmission rate are jointly optimized to maximize the covert throughput(OPTDP-JP).To solve this coupling problem,a Heuristic algorithm based on Maximum Distance Ratio(H-MAXDR)is proposed to provide a sub-optimal solution.First,according to the analysis of the covert throughput,the node with the maximum distance ratio(i.e.,the ratio of the distances from the jammer to the receiver and that to the warden)is selected as the friendly jammer(MAXDR).Then,the optimal transmission and jamming power can be derived,followed by the optimal transmission rate obtained via the bisection method.In numerical and simulation results,it is shown that although the location of the warden is unknown,by assuming the OPTDP of the warden,the proposed OPTDP-JP can always satisfy the covertness constraint.In addition,with an uncertain warden and imperfect CSI,the covert throughput provided by OPTDP-JP is 80%higher than the existing schemes when the covertness constraint is 0.9,showing the effectiveness of OPTDP-JP.展开更多
Wind erosion is a geomorphic process in arid and semi-arid areas and has substantial implications for regional climate and desertification.In the Columbia Plateau of northwestern United States,the emissions from fine ...Wind erosion is a geomorphic process in arid and semi-arid areas and has substantial implications for regional climate and desertification.In the Columbia Plateau of northwestern United States,the emissions from fine particles of loessial soils often contribute to the exceedance of inhalable particulate matter(PM)with an aerodynamic diameter of 10μm or less(PM10)according to the air quality standards.However,little is known about the threshold friction velocity(TFV)for particles of different sizes that comprise these soils.In this study,soil samples of two representative soil types(Warden sandy loam and Ritzville silt loam)collected from the Columbia Plateau were sieved to seven particle size fractions,and an experiment was then conducted to determine the relationship between TFV and particle size fraction.The results revealed that soil particle size significantly affected the initiation of soil movement and TFV;TFV ranged 0.304-0.844 and 0.249-0.739 m/s for different particle size fractions of Ritzville silt loam and Warden sandy loam,respectively.PM10 and total suspended particulates(TSP)emissions from a bed of 63-90μm soil particles were markedly higher for Warden sandy loam than for Ritzville silt loam.Together with the lower TFV of Warden sandy loam,dust emissions from fine particles(<100μm in diameter)of Warden sandy loam thus may be a main contributor to dust in the region's atmosphere,since the PM10 emissions from the soil erosion surfaces and its ensuing suspension within the atmosphere constitute an essential process of soil erosion in the Columbia Plateau.Developing and implementing strategic land management practices on sandy loam soils is therefore necessary to control dust emissions in the Columbia Plateau.展开更多
Background: Superior sinus venosus atrial septal defect (SV-ASD) is an interatrial defect with partial anomalous pulmonary venous connection (PAPVC) draining into the right atrium. The principle for SV-ASD surgical re...Background: Superior sinus venosus atrial septal defect (SV-ASD) is an interatrial defect with partial anomalous pulmonary venous connection (PAPVC) draining into the right atrium. The principle for SV-ASD surgical repair involves redirecting the pulmonary venous blood back to the left atrium and closure of the atrial septal defect without compromising the adjoining structures. Methods: We reviewed English literature relating to this topic via a MEDLINE and Google scholar search using the following terms: surgery for sinus venosus atrial septal defect (SV-ASD), surgery for partial anomalous pulmonary venous connection (PAPVC) and complications of the surgery. Results: A total of 910 consecutive cohort patients with different surgical options between 1984 to 2012 were analyzed. The breakdown showed that 291(32.0%) had single-patch, 275(30.2%) had Warden’s procedure, 185(20.3%) had a double-patch and 159(17.5%) had use of autologous right atrial appendage for the anastomosis. The total follow-up was between 0.008-30 years. Sinus node dysfunction (SND) was the commonest complication occurring mostly in patients who had double-patch technique 16(8.6%) followed by 15(5.5%) patients with single-patch technique, 7(4.4%) patients in whom right atrial appendage was used and 5(1.8%) patients with Warden’s procedure. Venous obstruction occurred in 22(7.7%) patients with SP, 13(5.1%) patients with Warden’s Procedure and 5(2.7%) patients with double-patch. Conclusion: The two major complications, SND and venous obstruction, assumed a see-saw approach as surgical maneuvers avoiding venous obstruction encouraged SND and vice versa. However, adopting surgical options which avoided incision across the Cavoatrial junction attenuated all the complications.展开更多
基金supported by the CAS Project for Young Scientists in Basic Research under Grant YSBR-035Jiangsu Provincial Key Research and Development Program under Grant BE2021013-2.
文摘In covert communications,joint jammer selection and power optimization are important to improve performance.However,existing schemes usually assume a warden with a known location and perfect Channel State Information(CSI),which is difficult to achieve in practice.To be more practical,it is important to investigate covert communications against a warden with uncertain locations and imperfect CSI,which makes it difficult for legitimate transceivers to estimate the detection probability of the warden.First,the uncertainty caused by the unknown warden location must be removed,and the Optimal Detection Position(OPTDP)of the warden is derived which can provide the best detection performance(i.e.,the worst case for a covert communication).Then,to further avoid the impractical assumption of perfect CSI,the covert throughput is maximized using only the channel distribution information.Given this OPTDP based worst case for covert communications,the jammer selection,the jamming power,the transmission power,and the transmission rate are jointly optimized to maximize the covert throughput(OPTDP-JP).To solve this coupling problem,a Heuristic algorithm based on Maximum Distance Ratio(H-MAXDR)is proposed to provide a sub-optimal solution.First,according to the analysis of the covert throughput,the node with the maximum distance ratio(i.e.,the ratio of the distances from the jammer to the receiver and that to the warden)is selected as the friendly jammer(MAXDR).Then,the optimal transmission and jamming power can be derived,followed by the optimal transmission rate obtained via the bisection method.In numerical and simulation results,it is shown that although the location of the warden is unknown,by assuming the OPTDP of the warden,the proposed OPTDP-JP can always satisfy the covertness constraint.In addition,with an uncertain warden and imperfect CSI,the covert throughput provided by OPTDP-JP is 80%higher than the existing schemes when the covertness constraint is 0.9,showing the effectiveness of OPTDP-JP.
基金Basic Research Funds for Colleges and Universities directly under the Inner Mongolia Autonomous Region:Desert Ecosystem Protection and Restoration Innovation Team(BR 22-13-03).
文摘Wind erosion is a geomorphic process in arid and semi-arid areas and has substantial implications for regional climate and desertification.In the Columbia Plateau of northwestern United States,the emissions from fine particles of loessial soils often contribute to the exceedance of inhalable particulate matter(PM)with an aerodynamic diameter of 10μm or less(PM10)according to the air quality standards.However,little is known about the threshold friction velocity(TFV)for particles of different sizes that comprise these soils.In this study,soil samples of two representative soil types(Warden sandy loam and Ritzville silt loam)collected from the Columbia Plateau were sieved to seven particle size fractions,and an experiment was then conducted to determine the relationship between TFV and particle size fraction.The results revealed that soil particle size significantly affected the initiation of soil movement and TFV;TFV ranged 0.304-0.844 and 0.249-0.739 m/s for different particle size fractions of Ritzville silt loam and Warden sandy loam,respectively.PM10 and total suspended particulates(TSP)emissions from a bed of 63-90μm soil particles were markedly higher for Warden sandy loam than for Ritzville silt loam.Together with the lower TFV of Warden sandy loam,dust emissions from fine particles(<100μm in diameter)of Warden sandy loam thus may be a main contributor to dust in the region's atmosphere,since the PM10 emissions from the soil erosion surfaces and its ensuing suspension within the atmosphere constitute an essential process of soil erosion in the Columbia Plateau.Developing and implementing strategic land management practices on sandy loam soils is therefore necessary to control dust emissions in the Columbia Plateau.
文摘Background: Superior sinus venosus atrial septal defect (SV-ASD) is an interatrial defect with partial anomalous pulmonary venous connection (PAPVC) draining into the right atrium. The principle for SV-ASD surgical repair involves redirecting the pulmonary venous blood back to the left atrium and closure of the atrial septal defect without compromising the adjoining structures. Methods: We reviewed English literature relating to this topic via a MEDLINE and Google scholar search using the following terms: surgery for sinus venosus atrial septal defect (SV-ASD), surgery for partial anomalous pulmonary venous connection (PAPVC) and complications of the surgery. Results: A total of 910 consecutive cohort patients with different surgical options between 1984 to 2012 were analyzed. The breakdown showed that 291(32.0%) had single-patch, 275(30.2%) had Warden’s procedure, 185(20.3%) had a double-patch and 159(17.5%) had use of autologous right atrial appendage for the anastomosis. The total follow-up was between 0.008-30 years. Sinus node dysfunction (SND) was the commonest complication occurring mostly in patients who had double-patch technique 16(8.6%) followed by 15(5.5%) patients with single-patch technique, 7(4.4%) patients in whom right atrial appendage was used and 5(1.8%) patients with Warden’s procedure. Venous obstruction occurred in 22(7.7%) patients with SP, 13(5.1%) patients with Warden’s Procedure and 5(2.7%) patients with double-patch. Conclusion: The two major complications, SND and venous obstruction, assumed a see-saw approach as surgical maneuvers avoiding venous obstruction encouraged SND and vice versa. However, adopting surgical options which avoided incision across the Cavoatrial junction attenuated all the complications.
