In CDMA network planning,it's important to understand the characteristics of multi-services.A novelmethod for analyzing the coverage of mixed voice and packet data traffics is presented in this paper.Based upon GI...In CDMA network planning,it's important to understand the characteristics of multi-services.A novelmethod for analyzing the coverage of mixed voice and packet data traffics is presented in this paper.Based upon GIS andMonte-Carlo simulation method,this method can provide more precise but less time-consuming analysis result than before.A practical analysis case using real geographic information and network parameters is applied to verify its performanceand find some useful solutions.Simulation results show that this coverage analysis method can provide helpful solution forthe radio networks planning.展开更多
Climate change is one of the most important factors that affect vegetation distribution in North China. Among all climatic factors, drought is considered to have the most significant effect on the environment. Based o...Climate change is one of the most important factors that affect vegetation distribution in North China. Among all climatic factors, drought is considered to have the most significant effect on the environment. Based on previous studies, the climate drought index can be used to assess the evolutionary trend of the ecological environment under various arid climatic conditions. It is necessary for us to further explore the relationship between vegetation coverage（index） and climate drought conditions. Therefore, in this study, based on MODIS-NDVI products and meteorological observation data, the Palmer Drought Severity Index（PDSI） and vegetation coverage in North China were first calculated. Then, the interannual variations of PDSI and vegetation coverage during 2001–2013 were analyzed using a Theil-Sen slope estimator. Finally, an ecoregion perspective of the correlation between them was discussed. The experimental results demonstrated that the PDSI index and vegetation coverage value varied over different ecoregions. During the period 2001–2013, vegetation coverage increased in the southern and northern mountains of North China, while it showed a decreasing trend in the Beijing-Tianjin-Tangshan City Circle area and suburban agricultural zone located in Hebei Province and Henan Province）. Over 13 years, the climate of the northeastern part of North China became more humid, while in the southern part of North China, it tended to be dry. According to the correlation analysis results, 73.37% of North China showed a positive correlation between the vegetation coverage and climate drought index. A negative correlation was observed mainly in urban and suburban areas of Beijing, Tianjin, Hebei Province, and Henan Province. In most parts of North China, drought conditions in summer and autumn had a strong influence on vegetation coverage.展开更多
In this paper, we propose a novel AIenabled space-air-ground integrated networks(SAGIN). This new integrated networks architecture consists of LEO satellites and civil aircrafts carrying aerial base stations, called &...In this paper, we propose a novel AIenabled space-air-ground integrated networks(SAGIN). This new integrated networks architecture consists of LEO satellites and civil aircrafts carrying aerial base stations, called "civil aircraft assisted SAGIN(CAA-SAGIN)". The assistance of civil aircrafts can reduce the stress of satellite networks, improve the performance of SAGIN, decrease the construction cost and save space resources. Taking the Chinese mainland as an example, this paper has analyzed the distribution of civil aircrafts, and obtained the coverage characteristics of civil aircraft assisted networks(CAAN). Taking Starlink as the benchmark, this paper has calculated the service gap of CAAN, and designed the joint coverage constellation. The simulation results prove that the number of satellites in CAASAGIN can be greatly reduced with the assistance of civil aircrafts at the same data rate.展开更多
This paper presents experimental results of a coverage analysis in a WCDMA network using the 850 MHz band;an urban electromagnetic propagation environment is considered. Obtained coverage estimation maps are based on ...This paper presents experimental results of a coverage analysis in a WCDMA network using the 850 MHz band;an urban electromagnetic propagation environment is considered. Obtained coverage estimation maps are based on Krige statistical method of interpolation. Key performance parameters used in this work are the CPICH and Ec. The results could be used to identify problems and help to optimize cell coverage and capacity in a given service area.展开更多
Published proof test coverage(PTC)estimates for emergency shutdown valves(ESDVs)show only moderate agreement and are predominantly opinion-based.A Failure Modes,Effects,and Diagnostics Analysis(FMEDA)was undertaken us...Published proof test coverage(PTC)estimates for emergency shutdown valves(ESDVs)show only moderate agreement and are predominantly opinion-based.A Failure Modes,Effects,and Diagnostics Analysis(FMEDA)was undertaken using component failure rate data to predict PTC for a full stroke test and a partial stroke test.Given the subjective and uncertain aspects of the FMEDA approach,specifically the selection of component failure rates and the determination of the probability of detecting failure modes,a Fuzzy Inference System(FIS)was proposed to manage the data,addressing the inherent uncertainties.Fuzzy inference systems have been used previously for various FMEA type assessments,but this is the first time an FIS has been employed for use with FMEDA.ESDV PTC values were generated from both the standard FMEDA and the fuzzy-FMEDA approaches using data provided by FMEDA experts.This work demonstrates that fuzzy inference systems can address the subjectivity inherent in FMEDA data,enabling reliable estimates of ESDV proof test coverage for both full and partial stroke tests.This facilitates optimized maintenance planning while ensuring safety is not compromised.展开更多
The rapid acceleration of global warming and intensifying human activities have exacerbated the fragility and climate sensitivity of ecosystems worldwide,particularly in arid regions.Vegetation,a key component of ecos...The rapid acceleration of global warming and intensifying human activities have exacerbated the fragility and climate sensitivity of ecosystems worldwide,particularly in arid regions.Vegetation,a key component of ecosystems,is critical in enhancing the ecological environment.The Ertix River Basin(ERB)is a transboundary watershed that spans multiple countries,mostly in arid regions.However,research on the fractional vegetation coverage(FVC)and its driving factors in the ERB remains limited.Investigating the spatiotemporal changes in the FVC and its relationship with various factors in the ERB can offer scientific support for optimizing regional vegetation restoration policies and promoting the coordinated development of human-environment interactions.The Moderate-resolution Imaging Spectroradiometer(MODIS)MYD13Q1 V6 data were obtained via the Google Earth Engine platform,and methods including the pixel dichotomy method,Theil-Sen median trend analysis,and Mann‒Kendall test were employed to examine the spatiotemporal dynamics of the FVC in the ERB from 2003 to 2023,with future trend forecast using the Hurst index.The impacts of natural and socioeconomic factors on the FVC were evaluated through the partial least squares-structural equation model(PLS-SEM).The results indicated that the FVC in the ERB showed a slight degradation trend with an average annual decrease of 0.046%during 2003-2023,with significant changes occurring in 2004,2010,and 2019.Spatially,53.380%of the study area was degraded,and the change in the FVC increased gradually from southeast to northwest.The FVC in 63.000%of the study area was highly stable and displayed long-term persistence;and the direct impact of natural factors(path coefficient of 0.617)on the FVC was significantly higher than that of socioeconomic factors(0.167).Among the natural factors,precipitation(0.999)was the most significant.This study reveals the significant impacts of natural and socioeconomic factors on vegetation dynamics in arid regions,and provides a scientific basis for transnational ecological conservation.展开更多
Coverage analysis serves as the foundation for designing the communication or remote sensing satellite constellations.The classical numerical method,grid-point approach(GPA),is widely utilized in constellation coverag...Coverage analysis serves as the foundation for designing the communication or remote sensing satellite constellations.The classical numerical method,grid-point approach(GPA),is widely utilized in constellation coverage analysis,yet it encounters challenges such as uneven grid distribution and substantial computational demands.In this paper,we introduce a random Fibonacci sampling method(RFSM)to achieve a more balanced distribution of sampling points,alongside a k-means region division method(KRDM)to enhance computational efficiency.In the RFSM,discrete sampling points replace grids for evaluating coverage performance.By incorporating randomness into the Fibonacci lattices method,we ensure that the sampling points exhibit a random uniform distribution.This allows for the amalgamation of coverage data from different sets of sampling points and the dynamic adjustment of the number of sampling points during computation.In the KRDM,we divide the whole target region into several sub-regions using the k-means algorithm,followed by calculating their respective visible windows.Numerical simulations demonstrate that the proposed method significantly enhances computational efficiency without compromising accuracy,achieving speed improvements of one or two orders of magnitude compared to the classical GPA.These findings suggest that the proposed method holds considerable promise for expediting constellation coverage performance calculations on a broader scale.展开更多
This paper deals with the coverage analysis problem of elliptical orbits. An algorithm based on ergodic theory, for long-term coverage of elliptical orbits, is proposed. The differential form of the invariant measure ...This paper deals with the coverage analysis problem of elliptical orbits. An algorithm based on ergodic theory, for long-term coverage of elliptical orbits, is proposed. The differential form of the invariant measure is constructed via the perturbation on mean orbital elements resulted from the J2 term of non-spherical shape of the earth. A rigorous proof for this is then given. Different from the case of circular orbits, here the flow and its space of the dynamical system are defined on a physical space, and the real-value function is defined as the characteristic function on station mask. Therefore, the long-term coverage is reduced to a double integral via Birkhoff-Khinchin theorem. The numerical implementation indicates that the ergodic algorithm developed is available for a wide range of eccentricities.展开更多
In the subtribe Maydeae, Tripsacum and Zea are closely related genera. Tripsacum is a horticultural crop widely used as pasture forage. Previous studies suggested that Tripsacum might play an important role in maize o...In the subtribe Maydeae, Tripsacum and Zea are closely related genera. Tripsacum is a horticultural crop widely used as pasture forage. Previous studies suggested that Tripsacum might play an important role in maize origin and evolution. However, our understanding of the genomics and the evolution of Tripsacum remains limited. In this study, two diploids,T. dactyloides var. meridionale(2n = 36, MR) and T. dactyloides(2n = 36, DD), and one tetraploid,T. dactyloides(2n = 72, DL) were sequenced by low-coverage genome sequencing followed by graph-based cluster analysis. The results showed that 63.23%, 59.20%, and 61.57% of the respective genome of MR, DD, and DL were repetitive DNA sequence. The proportions of different repetitive sequences varied greatly among the three species. Fluorescence in situ hybridization(FISH) analysis of mitotic metaphase chromosomes with satellite repeats as the probes showed that the FISH signal patterns of DL were more similar to that of DD than to that of MR. Comparative analysis of the repeats also showed that DL shared more common repeat families with DD than with MR. Phylogenetic analysis of internal transcribed spacer region sequences further supported the evolutionary relationship among the three species. Repetitive sequences comparison showed that Tripsacum shared more repeat families with Zea than with Coix and Sorghum. Our study sheds new light on the genomics of Tripsacum and differential speciation in the Poaceae family.展开更多
With the rapid development of emerging 5G and beyond(B5G),Unmanned Aerial Vehicles(UAVs)are increasingly important to improve the performance of dense cellular networks.As a conventional metric,coverage probability ha...With the rapid development of emerging 5G and beyond(B5G),Unmanned Aerial Vehicles(UAVs)are increasingly important to improve the performance of dense cellular networks.As a conventional metric,coverage probability has been widely studied in communication systems due to the increasing density of users and complexity of the heterogeneous environment.In recent years,stochastic geometry has attracted more attention as a mathematical tool for modeling mobile network systems.In this paper,an analytical approach to the coverage probability analysis of UAV-assisted cellular networks with imperfect beam alignment has been proposed.An assumption was considered that all users are distributed according to Poisson Cluster Process(PCP)around base stations,in particular,Thomas Cluster Process(TCP).Using thismodel,the impact of beam alignment errors on the coverage probabilitywas investigated.Initially,the ProbabilityDensity Function(PDF)of directional antenna gain between the user and its serving base station was obtained.Then,association probability with each tier was achieved.A tractable expression was derived for coverage probability in both Line-of-Sight(LoS)andNon-Line-of-Sight(NLoS)condition links.Numerical results demonstrated that at low UAVs altitude,beam alignment errors significantly degrade coverage performance.Moreover,for a small cluster size,alignment errors do not necessarily affect the coverage performance.展开更多
Bus stop accessibility is a vital component of a successful transportation system. This study aimed at spatially analyzing bus stops to determine their physical accessibility considering the connecting roads surroundi...Bus stop accessibility is a vital component of a successful transportation system. This study aimed at spatially analyzing bus stops to determine their physical accessibility considering the connecting roads surrounding the bus stops. This research used satellite imagery, Global Navigation Satellite System and Kaduna State Traffic and Environment Law Enforcement Authority documents. The spatial analysis covered bus stop accessibility and obtained data of transport routes, bus stop coordinates, bus stop spacing and physical characteristics of bus stops. GIS buffer, network and area analysis was used in measuring bus stop accessibility considering the road network surrounding it. The ratio of ideal access coverage to the actual access coverage of a stop was calculated. Paired sample statistics were used to compare ideal and actual access coverage;the finding revealed a significant difference between the ideal and actual access coverage. A range of 0 - 1.0 was used in the analysis where, a bus stop is less accessible the closer the value is to 0, and more accessible the closer the value is to 1.0. Linear regression statistics was used to determine if the level of accessibility of a bus stop is dependent on the length of roads within the buffer. This revealed that at R = 0.694, a strong degree of correlation exists between the level of accessibility and road length within the buffer. The study concluded that before siting bus stops, surrounding road networks need to be considered in order to make them accessible.展开更多
<div style="text-align:justify;"> <span style="font-family:Verdana;">Software systems have become complex and challenging to develop and maintain because of the large size of test cases...<div style="text-align:justify;"> <span style="font-family:Verdana;">Software systems have become complex and challenging to develop and maintain because of the large size of test cases with increased scalability issues. Test case prioritization methods have been successfully utilized in test case management. However, the prohibitively exorbitant cost of large test cases is now the mainstream in the software industry. The growth of agile test-driven development has increased the expectations for software quality. Yet, our knowledge of when to use various path testing criteria for cost-effectiveness is inadequate due to the inherent complexity in software testing. Existing researches attempted to address the issue without effectively tackling the scalability of large test suites to reduce time in regression testing. In order to provide a more accurate way of fault detection in software projects, we introduced novel coverage criteria, called Incremental Cluster-based test case Prioritization (ICP), and investigated its potentials by making a comparative evaluation with three un-clustered traditional coverage-based criteria: Prime-Path Coverage (PPC), Edge-Pair Coverage (EPC) and Edge Coverage (EC) based on mutation analysis. By clustering test suites, based on their dynamic run-time behavior, the number of pair-wise comparisons is reduced significantly. To compare, we analyzed 20 functions from 25 C programs, instrumented faults into the programs, and used the Mull mutation tool to generate mutants and perform a statistical analysis of the results. The experimental results show that ICP can lead to cost-effective improvements in fault detection.</span> </div>展开更多
A Monte Carlo Analysis of nodes deployment for large-scale and non-homogeneous wireless sensor networks, has been done. Through simulations of random deployments of nodes over a square area using different densities, ...A Monte Carlo Analysis of nodes deployment for large-scale and non-homogeneous wireless sensor networks, has been done. Through simulations of random deployments of nodes over a square area using different densities, assuming that our network is composed by Anchor nodes （special sensors with known position） and simple Sensor nodes, the latter are supposed to estimate their own position after being placed within the coverage area with the minimum Anchor nodes needed to ＇feed＇ them with the necessary information. The goal is then to assist decision-makers in selecting among different alternatives to deploy the networks, according to resources features and availability, hence this method provides an estimate value of how many Anchor nodes should be deployed in a given area to trigger the location algorithm in the greatest possible number of Sensor nodes in the network.展开更多
In this paper,we study an SS_(v)EIQR model with nonlinear contact rate,isolation rate and vaccination rate driven by media coverage.First,the basic reproduction number R_(0)is derived.Then,the threshold dynamics of th...In this paper,we study an SS_(v)EIQR model with nonlinear contact rate,isolation rate and vaccination rate driven by media coverage.First,the basic reproduction number R_(0)is derived.Then,the threshold dynamics of the disease are obtained in terms of R_(0):when R_(0)≤1,the global stability of the disease-free equilibrium is obtained by constructing an appropriate Lyapunov function;when R_(0)>1,the sufficient conditions to prove the globally stability of endemic equilibrium are obtained by applying the geometric method into the four-dimensional system,which needs to estimate the Lozinskii measure of a 6×6 matrix.Further,we conduct some numerical simulations to validate our theoretical results,and analyze the impact of media coverage on disease transmission,the results show that media coverage could effectively suppress the spread of the disease and reduce the number of infected individuals.Finally,through the sensitivity analysis of R_(0),we obtain some measures to control the spread of the disease,such as reducing contact,strengthening isolation and vaccination.展开更多
数据库管理系统(database management system,DBMS)作为数据管理与存储的关键软件,其可靠性直接影响数据密集型系统的安全稳定运行。近年来,模糊测试因其具备人工成本低、测试效率高等特点,成为DBMS测试方法之一。然而现有的DBMS模糊测...数据库管理系统(database management system,DBMS)作为数据管理与存储的关键软件,其可靠性直接影响数据密集型系统的安全稳定运行。近年来,模糊测试因其具备人工成本低、测试效率高等特点,成为DBMS测试方法之一。然而现有的DBMS模糊测试方法面临测试用例覆盖能力不足与多DBMS适配性差两大问题,限制了测试的效果和泛用性。为此,CLCC(curated LLM case construct)是一种基于大语言模型(large language model,LLM)的DBMS模糊测试方法。该方法在模糊测试前,利用LLM对初始种子进行构建,并在模糊测试过程中,根据边覆盖情况筛选种子,引导LLM生成测试用例。与SQUIRREL、SQLRight和ParserFuzz进行的对比实验表明,CLCC测试SQLite、MySQL、MariaDB、DuckDB和PostgreSQL的边覆盖数量比SQUIRREL增加了14.96%~49.31%;测试SQLite、MySQL和PostgreSQL的边覆盖数量比SQLRight增加了6.09%~17.10%;测试SQLite、MySQL和MariaDB的边覆盖数量比ParserFuzz增加了17.95%~41.20%。展开更多
文摘In CDMA network planning,it's important to understand the characteristics of multi-services.A novelmethod for analyzing the coverage of mixed voice and packet data traffics is presented in this paper.Based upon GIS andMonte-Carlo simulation method,this method can provide more precise but less time-consuming analysis result than before.A practical analysis case using real geographic information and network parameters is applied to verify its performanceand find some useful solutions.Simulation results show that this coverage analysis method can provide helpful solution forthe radio networks planning.
基金International Science & Technology Cooperation Program of China,No.2014DFA21620The China Scholarship Fund
文摘Climate change is one of the most important factors that affect vegetation distribution in North China. Among all climatic factors, drought is considered to have the most significant effect on the environment. Based on previous studies, the climate drought index can be used to assess the evolutionary trend of the ecological environment under various arid climatic conditions. It is necessary for us to further explore the relationship between vegetation coverage（index） and climate drought conditions. Therefore, in this study, based on MODIS-NDVI products and meteorological observation data, the Palmer Drought Severity Index（PDSI） and vegetation coverage in North China were first calculated. Then, the interannual variations of PDSI and vegetation coverage during 2001–2013 were analyzed using a Theil-Sen slope estimator. Finally, an ecoregion perspective of the correlation between them was discussed. The experimental results demonstrated that the PDSI index and vegetation coverage value varied over different ecoregions. During the period 2001–2013, vegetation coverage increased in the southern and northern mountains of North China, while it showed a decreasing trend in the Beijing-Tianjin-Tangshan City Circle area and suburban agricultural zone located in Hebei Province and Henan Province）. Over 13 years, the climate of the northeastern part of North China became more humid, while in the southern part of North China, it tended to be dry. According to the correlation analysis results, 73.37% of North China showed a positive correlation between the vegetation coverage and climate drought index. A negative correlation was observed mainly in urban and suburban areas of Beijing, Tianjin, Hebei Province, and Henan Province. In most parts of North China, drought conditions in summer and autumn had a strong influence on vegetation coverage.
基金supported by National Nature Science Foundation of China (No. 61871155)。
文摘In this paper, we propose a novel AIenabled space-air-ground integrated networks(SAGIN). This new integrated networks architecture consists of LEO satellites and civil aircrafts carrying aerial base stations, called "civil aircraft assisted SAGIN(CAA-SAGIN)". The assistance of civil aircrafts can reduce the stress of satellite networks, improve the performance of SAGIN, decrease the construction cost and save space resources. Taking the Chinese mainland as an example, this paper has analyzed the distribution of civil aircrafts, and obtained the coverage characteristics of civil aircraft assisted networks(CAAN). Taking Starlink as the benchmark, this paper has calculated the service gap of CAAN, and designed the joint coverage constellation. The simulation results prove that the number of satellites in CAASAGIN can be greatly reduced with the assistance of civil aircrafts at the same data rate.
文摘This paper presents experimental results of a coverage analysis in a WCDMA network using the 850 MHz band;an urban electromagnetic propagation environment is considered. Obtained coverage estimation maps are based on Krige statistical method of interpolation. Key performance parameters used in this work are the CPICH and Ec. The results could be used to identify problems and help to optimize cell coverage and capacity in a given service area.
文摘Published proof test coverage(PTC)estimates for emergency shutdown valves(ESDVs)show only moderate agreement and are predominantly opinion-based.A Failure Modes,Effects,and Diagnostics Analysis(FMEDA)was undertaken using component failure rate data to predict PTC for a full stroke test and a partial stroke test.Given the subjective and uncertain aspects of the FMEDA approach,specifically the selection of component failure rates and the determination of the probability of detecting failure modes,a Fuzzy Inference System(FIS)was proposed to manage the data,addressing the inherent uncertainties.Fuzzy inference systems have been used previously for various FMEA type assessments,but this is the first time an FIS has been employed for use with FMEDA.ESDV PTC values were generated from both the standard FMEDA and the fuzzy-FMEDA approaches using data provided by FMEDA experts.This work demonstrates that fuzzy inference systems can address the subjectivity inherent in FMEDA data,enabling reliable estimates of ESDV proof test coverage for both full and partial stroke tests.This facilitates optimized maintenance planning while ensuring safety is not compromised.
基金funded by the Third Xinjiang Comprehensive Scientific Investigation Project,China(2022xjkk0702)the Western Young Scholars Project of the Chinese Academy of Sciences(2022-XBQNXZ-001)the Tianshan Talent Development Program,China(2022TSYCCX0006).
文摘The rapid acceleration of global warming and intensifying human activities have exacerbated the fragility and climate sensitivity of ecosystems worldwide,particularly in arid regions.Vegetation,a key component of ecosystems,is critical in enhancing the ecological environment.The Ertix River Basin(ERB)is a transboundary watershed that spans multiple countries,mostly in arid regions.However,research on the fractional vegetation coverage(FVC)and its driving factors in the ERB remains limited.Investigating the spatiotemporal changes in the FVC and its relationship with various factors in the ERB can offer scientific support for optimizing regional vegetation restoration policies and promoting the coordinated development of human-environment interactions.The Moderate-resolution Imaging Spectroradiometer(MODIS)MYD13Q1 V6 data were obtained via the Google Earth Engine platform,and methods including the pixel dichotomy method,Theil-Sen median trend analysis,and Mann‒Kendall test were employed to examine the spatiotemporal dynamics of the FVC in the ERB from 2003 to 2023,with future trend forecast using the Hurst index.The impacts of natural and socioeconomic factors on the FVC were evaluated through the partial least squares-structural equation model(PLS-SEM).The results indicated that the FVC in the ERB showed a slight degradation trend with an average annual decrease of 0.046%during 2003-2023,with significant changes occurring in 2004,2010,and 2019.Spatially,53.380%of the study area was degraded,and the change in the FVC increased gradually from southeast to northwest.The FVC in 63.000%of the study area was highly stable and displayed long-term persistence;and the direct impact of natural factors(path coefficient of 0.617)on the FVC was significantly higher than that of socioeconomic factors(0.167).Among the natural factors,precipitation(0.999)was the most significant.This study reveals the significant impacts of natural and socioeconomic factors on vegetation dynamics in arid regions,and provides a scientific basis for transnational ecological conservation.
文摘Coverage analysis serves as the foundation for designing the communication or remote sensing satellite constellations.The classical numerical method,grid-point approach(GPA),is widely utilized in constellation coverage analysis,yet it encounters challenges such as uneven grid distribution and substantial computational demands.In this paper,we introduce a random Fibonacci sampling method(RFSM)to achieve a more balanced distribution of sampling points,alongside a k-means region division method(KRDM)to enhance computational efficiency.In the RFSM,discrete sampling points replace grids for evaluating coverage performance.By incorporating randomness into the Fibonacci lattices method,we ensure that the sampling points exhibit a random uniform distribution.This allows for the amalgamation of coverage data from different sets of sampling points and the dynamic adjustment of the number of sampling points during computation.In the KRDM,we divide the whole target region into several sub-regions using the k-means algorithm,followed by calculating their respective visible windows.Numerical simulations demonstrate that the proposed method significantly enhances computational efficiency without compromising accuracy,achieving speed improvements of one or two orders of magnitude compared to the classical GPA.These findings suggest that the proposed method holds considerable promise for expediting constellation coverage performance calculations on a broader scale.
基金Project supported by the Innovation Foundation of BUAA (Beijing University of Aeronautics and Astronautics) for PhD Graduatesthe National Natural Science Foundation of China (Grant No 60535010)
文摘This paper deals with the coverage analysis problem of elliptical orbits. An algorithm based on ergodic theory, for long-term coverage of elliptical orbits, is proposed. The differential form of the invariant measure is constructed via the perturbation on mean orbital elements resulted from the J2 term of non-spherical shape of the earth. A rigorous proof for this is then given. Different from the case of circular orbits, here the flow and its space of the dynamical system are defined on a physical space, and the real-value function is defined as the characteristic function on station mask. Therefore, the long-term coverage is reduced to a double integral via Birkhoff-Khinchin theorem. The numerical implementation indicates that the ergodic algorithm developed is available for a wide range of eccentricities.
基金supported by the National Natural Science Foundation of China (Nos. 31471499, 91535206)
文摘In the subtribe Maydeae, Tripsacum and Zea are closely related genera. Tripsacum is a horticultural crop widely used as pasture forage. Previous studies suggested that Tripsacum might play an important role in maize origin and evolution. However, our understanding of the genomics and the evolution of Tripsacum remains limited. In this study, two diploids,T. dactyloides var. meridionale(2n = 36, MR) and T. dactyloides(2n = 36, DD), and one tetraploid,T. dactyloides(2n = 72, DL) were sequenced by low-coverage genome sequencing followed by graph-based cluster analysis. The results showed that 63.23%, 59.20%, and 61.57% of the respective genome of MR, DD, and DL were repetitive DNA sequence. The proportions of different repetitive sequences varied greatly among the three species. Fluorescence in situ hybridization(FISH) analysis of mitotic metaphase chromosomes with satellite repeats as the probes showed that the FISH signal patterns of DL were more similar to that of DD than to that of MR. Comparative analysis of the repeats also showed that DL shared more common repeat families with DD than with MR. Phylogenetic analysis of internal transcribed spacer region sequences further supported the evolutionary relationship among the three species. Repetitive sequences comparison showed that Tripsacum shared more repeat families with Zea than with Coix and Sorghum. Our study sheds new light on the genomics of Tripsacum and differential speciation in the Poaceae family.
基金supported by Princess Nourah bint Abdulrahman University Researchers Supporting Project number(PNURSP2022R323)Princess Nourah bint Abdulrahman University,Riyadh,Saudi Arabia,and Taif University Researchers Supporting Project Number TURSP-2020/34,Taif,Saudi Arabia.
文摘With the rapid development of emerging 5G and beyond(B5G),Unmanned Aerial Vehicles(UAVs)are increasingly important to improve the performance of dense cellular networks.As a conventional metric,coverage probability has been widely studied in communication systems due to the increasing density of users and complexity of the heterogeneous environment.In recent years,stochastic geometry has attracted more attention as a mathematical tool for modeling mobile network systems.In this paper,an analytical approach to the coverage probability analysis of UAV-assisted cellular networks with imperfect beam alignment has been proposed.An assumption was considered that all users are distributed according to Poisson Cluster Process(PCP)around base stations,in particular,Thomas Cluster Process(TCP).Using thismodel,the impact of beam alignment errors on the coverage probabilitywas investigated.Initially,the ProbabilityDensity Function(PDF)of directional antenna gain between the user and its serving base station was obtained.Then,association probability with each tier was achieved.A tractable expression was derived for coverage probability in both Line-of-Sight(LoS)andNon-Line-of-Sight(NLoS)condition links.Numerical results demonstrated that at low UAVs altitude,beam alignment errors significantly degrade coverage performance.Moreover,for a small cluster size,alignment errors do not necessarily affect the coverage performance.
文摘Bus stop accessibility is a vital component of a successful transportation system. This study aimed at spatially analyzing bus stops to determine their physical accessibility considering the connecting roads surrounding the bus stops. This research used satellite imagery, Global Navigation Satellite System and Kaduna State Traffic and Environment Law Enforcement Authority documents. The spatial analysis covered bus stop accessibility and obtained data of transport routes, bus stop coordinates, bus stop spacing and physical characteristics of bus stops. GIS buffer, network and area analysis was used in measuring bus stop accessibility considering the road network surrounding it. The ratio of ideal access coverage to the actual access coverage of a stop was calculated. Paired sample statistics were used to compare ideal and actual access coverage;the finding revealed a significant difference between the ideal and actual access coverage. A range of 0 - 1.0 was used in the analysis where, a bus stop is less accessible the closer the value is to 0, and more accessible the closer the value is to 1.0. Linear regression statistics was used to determine if the level of accessibility of a bus stop is dependent on the length of roads within the buffer. This revealed that at R = 0.694, a strong degree of correlation exists between the level of accessibility and road length within the buffer. The study concluded that before siting bus stops, surrounding road networks need to be considered in order to make them accessible.
文摘<div style="text-align:justify;"> <span style="font-family:Verdana;">Software systems have become complex and challenging to develop and maintain because of the large size of test cases with increased scalability issues. Test case prioritization methods have been successfully utilized in test case management. However, the prohibitively exorbitant cost of large test cases is now the mainstream in the software industry. The growth of agile test-driven development has increased the expectations for software quality. Yet, our knowledge of when to use various path testing criteria for cost-effectiveness is inadequate due to the inherent complexity in software testing. Existing researches attempted to address the issue without effectively tackling the scalability of large test suites to reduce time in regression testing. In order to provide a more accurate way of fault detection in software projects, we introduced novel coverage criteria, called Incremental Cluster-based test case Prioritization (ICP), and investigated its potentials by making a comparative evaluation with three un-clustered traditional coverage-based criteria: Prime-Path Coverage (PPC), Edge-Pair Coverage (EPC) and Edge Coverage (EC) based on mutation analysis. By clustering test suites, based on their dynamic run-time behavior, the number of pair-wise comparisons is reduced significantly. To compare, we analyzed 20 functions from 25 C programs, instrumented faults into the programs, and used the Mull mutation tool to generate mutants and perform a statistical analysis of the results. The experimental results show that ICP can lead to cost-effective improvements in fault detection.</span> </div>
文摘A Monte Carlo Analysis of nodes deployment for large-scale and non-homogeneous wireless sensor networks, has been done. Through simulations of random deployments of nodes over a square area using different densities, assuming that our network is composed by Anchor nodes （special sensors with known position） and simple Sensor nodes, the latter are supposed to estimate their own position after being placed within the coverage area with the minimum Anchor nodes needed to ＇feed＇ them with the necessary information. The goal is then to assist decision-makers in selecting among different alternatives to deploy the networks, according to resources features and availability, hence this method provides an estimate value of how many Anchor nodes should be deployed in a given area to trigger the location algorithm in the greatest possible number of Sensor nodes in the network.
基金supported by the Natural Science Foundation of Xinjiang Uygur Autonomous Region(2022D01C64,2022D01C699)Natural Science Foundation of China(12201540)the Doctoral Foundation of Xinjiang University(620320024).
文摘In this paper,we study an SS_(v)EIQR model with nonlinear contact rate,isolation rate and vaccination rate driven by media coverage.First,the basic reproduction number R_(0)is derived.Then,the threshold dynamics of the disease are obtained in terms of R_(0):when R_(0)≤1,the global stability of the disease-free equilibrium is obtained by constructing an appropriate Lyapunov function;when R_(0)>1,the sufficient conditions to prove the globally stability of endemic equilibrium are obtained by applying the geometric method into the four-dimensional system,which needs to estimate the Lozinskii measure of a 6×6 matrix.Further,we conduct some numerical simulations to validate our theoretical results,and analyze the impact of media coverage on disease transmission,the results show that media coverage could effectively suppress the spread of the disease and reduce the number of infected individuals.Finally,through the sensitivity analysis of R_(0),we obtain some measures to control the spread of the disease,such as reducing contact,strengthening isolation and vaccination.
文摘数据库管理系统(database management system,DBMS)作为数据管理与存储的关键软件,其可靠性直接影响数据密集型系统的安全稳定运行。近年来,模糊测试因其具备人工成本低、测试效率高等特点,成为DBMS测试方法之一。然而现有的DBMS模糊测试方法面临测试用例覆盖能力不足与多DBMS适配性差两大问题,限制了测试的效果和泛用性。为此,CLCC(curated LLM case construct)是一种基于大语言模型(large language model,LLM)的DBMS模糊测试方法。该方法在模糊测试前,利用LLM对初始种子进行构建,并在模糊测试过程中,根据边覆盖情况筛选种子,引导LLM生成测试用例。与SQUIRREL、SQLRight和ParserFuzz进行的对比实验表明,CLCC测试SQLite、MySQL、MariaDB、DuckDB和PostgreSQL的边覆盖数量比SQUIRREL增加了14.96%~49.31%;测试SQLite、MySQL和PostgreSQL的边覆盖数量比SQLRight增加了6.09%~17.10%;测试SQLite、MySQL和MariaDB的边覆盖数量比ParserFuzz增加了17.95%~41.20%。
