Rural settlements are the main carriers of agriculture, rural areas and farmers; thus, optimizing the production and living space of rural settlements is highly significant to rural development. Taking the effective a...Rural settlements are the main carriers of agriculture, rural areas and farmers; thus, optimizing the production and living space of rural settlements is highly significant to rural development. Taking the effective allocation of resources as the starting point, a suitability evaluation system of rural settlements, based on accessibility of production and living, was proposed in this study to provide scientific basis for the optimization of production and living space. The accessibility of production and living was measured by an im- proved two-step floating catchment area method, which considered proximity and availability based on the inclination of rural residents. The suitability evaluation system consisted of traditional suitability evaluation and newly proposed limiting factor identification based on the loss score proportion of suitability. Tingzu Town of Hubei Province, China, was chosen as the case study area. Based on the re- suits of the suitability evaluation system, corresponding suggestions on rural land consolidation, industry division, as well as the layout of health care and education facilities were proposed to optimize the production and living space of rural settlements in Tingzu Town. It is found that the suitability evaluation based on accessibility of production and living is more scientific and accurate than the traditional ones which significantly overestimate production and living convenience. Moreover, the limiting factor identification can help us put forward suggestions according to local conditions and bring about the highly targeted optimization of production and living space of rural settlements.展开更多
BACKGROUND Coronavirus disease 2019(COVID-19)disrupted healthcare and led to increased telehealth use.We explored the impact of COVID-19 on liver transplant evaluation(LTE).AIM To understand the impact of telehealth o...BACKGROUND Coronavirus disease 2019(COVID-19)disrupted healthcare and led to increased telehealth use.We explored the impact of COVID-19 on liver transplant evaluation(LTE).AIM To understand the impact of telehealth on LTE during COVID-19 and to identify disparities in outcomes disaggregated by sociodemographic factors.METHODS This was a retrospective study of patients who initiated LTE at our center from 3/16/20-3/16/21(“COVID-19 era”)and the year prior(3/16/19-3/15/20,“pre-COVID-19 era”).We compared LTE duration times between eras and explored the effects of telehealth and inpatient evaluations on LTE duration,listing,and pretransplant mortality.RESULTS One hundred and seventy-eight patients were included in the pre-COVID-19 era cohort and one hundred and ninety-nine in the COVID-19 era cohort.Twentynine percent(58/199)of COVID-19 era initial LTE were telehealth,compared to 0%(0/178)pre-COVID-19.There were more inpatient evaluations during COVID-19 era(40%vs 28%,P<0.01).Among outpatient encounters,telehealth use for initial LTE during COVID-19 era did not impact likelihood of listing,pretransplant mortality,or time to LTE and listing.Median times to LTE and listing during COVID-19 were shorter than pre-COVID-19,driven by increased inpatient evaluations.Sociodemographic factors were not predictive of telehealth.CONCLUSION COVID-19 demonstrates a shift to telehealth and inpatient LTE.Telehealth does not impact LTE or listing duration,likelihood of listing,or mortality,suggesting telehealth may facilitate LTE without negative outcomes.展开更多
Currently,data security and privacy protection are becoming more and more important.Access control is a method of authorization for users through predefined policies.Token-based access control(TBAC)enhances the manage...Currently,data security and privacy protection are becoming more and more important.Access control is a method of authorization for users through predefined policies.Token-based access control(TBAC)enhances the manageability of authorization through the token.However,traditional access control policies lack the ability to dynamically adjust based on user access behavior.Incorporating user reputation evaluation into access control can provide valuable feedback to enhance system security and flexibility.As a result,this paper proposes a blockchain-empowered TBAC system and introduces a user reputation evaluation module to provide feedback on access control.The TBAC system divides the access control process into three stages:policy upload,token request,and resource request.The user reputation evaluation module evaluates the user’s token reputation and resource reputation for the token request and resource request stages of the TBAC system.The proposed system is implemented using the Hyperledger Fabric blockchain.The TBAC system is evaluated to prove that it has high processing performance.The user reputation evaluation model is proved to be more conservative and sensitive by comparative study with other methods.In addition,the security analysis shows that the TBAC system has a certain anti-attack ability and can maintain stable operation under the Distributed Denial of Service(DDoS)attack environment.展开更多
`Introduction Open science is a set of principles and practices that aim to make scientific research accessible to everyone for the benefit of scientists and society.It includes sharing publications,data,software,and ...`Introduction Open science is a set of principles and practices that aim to make scientific research accessible to everyone for the benefit of scientists and society.It includes sharing publications,data,software,and hardware widely,and ensuring that the production of scientific knowledge is inclusive,equitable,and sustainable.展开更多
A review of the history of Chinese gardens beginning in the Shang Dynasty reveals that parks have become increasingly important to urban residents' lives; and hence, this paper proposes a methodology to evaluate t...A review of the history of Chinese gardens beginning in the Shang Dynasty reveals that parks have become increasingly important to urban residents' lives; and hence, this paper proposes a methodology to evaluate the suitability of parks. The analysis shows that suitability evaluations of urban parks should not be restricted to a park's basic functions, but should include a comprehensive evaluation of ecological value, cultural inheritance and feature construction. After describing the current literature of research on indices, categories, use conditions and landscape accessibility of domestic and foreign urban parks, the paper concludes with a framework for evaluating a park's suitability, i.e. the establishment of an integrated evaluation system, the selection of reasonable evaluation methods, and public participation as an indicator in the evaluation system, so as to ensure the validity of research results.展开更多
Performance of fixed relays in orthogonal frequency division multiple access （0FDMA） systems, especially the coverage and capacity performance at the cell edge, is evaluated in this paper. Two methods, theoretical a...Performance of fixed relays in orthogonal frequency division multiple access （0FDMA） systems, especially the coverage and capacity performance at the cell edge, is evaluated in this paper. Two methods, theoretical analysis and calculation and Monte Carlo simulation, are used for the evaluations. By theoreti- cal analysis and calculation, frequency efficiency equation of a relay is introduced and numerical results are calculated. Monte Carlo simulation results also verify that the calculation method is reasonable. The evaluation shows that a relay can increase system performance to a certain level if it is designed appropriately, otherwise it will be harmful for the system performance, even to reduce it.展开更多
This work aims to reduce queries on big data to computations on small data,and hence make querying big data possible under bounded resources.A query Q is boundedly evaluable when posed on any big dataset D,there exist...This work aims to reduce queries on big data to computations on small data,and hence make querying big data possible under bounded resources.A query Q is boundedly evaluable when posed on any big dataset D,there exists a fraction DQ of D such that Q(D)=Q(DQ),and the cost of identifying DQ is independent of the size of D.It has been shown that with an auxiliary structure known as access schema,many queries in relational algebra(RA)are boundedly evaluable under the set semantics of RA.This paper extends the theory of bounded evaluation to RAaggr,i.e.,RA extended with aggregation,under the bag semantics.(1)We extend access schema to bag access schema,to help us identify DQ for RAaggr queries Q.(2)While it is undecidable to determine whether an RAaggr query is boundedly evaluable under a bag access schema,we identify special cases that are decidable and practical.(3)In addition,we develop an effective syntax for bounded RAaggr queries,i.e.,a core subclass of boundedly evaluable RAaggr queries without sacrificing their expressive power.(4)Based on the effective syntax,we provide efficient algorithms to check the bounded evaluability of RAaggr queries and to generate query plans for bounded RAaggr queries.(5)As proof of concept,we extend PostgreSQL to support bounded evaluation.We experimentally verify that the extended system improves performance by orders of magnitude.展开更多
The objective of this study was to develop a method to assess and analyze the total allelopathic potential of crop germplasm and to test this method on four winter wheat accessions commonly planted in the Loess Platea...The objective of this study was to develop a method to assess and analyze the total allelopathic potential of crop germplasm and to test this method on four winter wheat accessions commonly planted in the Loess Plateau. A systems engineering model was developed and used to evaluate the total allelopathic potential of crop cultivars. In addition, a method for quantifying the total allelopathic potential in crop accessions was presented. Total allelopathic potential of four winter wheat accessions from the Loess Plateau was estimated and compared using a systems theory approach. The model assessed allelopathic potential in different parts of the plants from the time wheat turned green in spring until maturity. Results from these models indicated that the four wheat accessions had very weak allelopathic potential. Allelopathic potential declined in the order Xiaoyan 22 〉 Ningdong 1 〉 Fengchan 3 〉 Bima 1. This system engineering evaluation method allows for the assessment of allelopathic potential among crop varieties. It will help plant breeders to select and develop allelopathic crop accessions that combine weed suppression properties with agronomic traits related to yield and quality.展开更多
Objectives: The goal of this project was to evaluate the quality of the accessibility of the adult population to services in Primary Health Care, with a view to contribute to the development of measures that will prop...Objectives: The goal of this project was to evaluate the quality of the accessibility of the adult population to services in Primary Health Care, with a view to contribute to the development of measures that will propose improvement in the offered assistance. Methods: This is a quantitative and evaluative study made in the municipality of Santa Cruz, State of Rio Grande do Norte, Brazil, with a sample of 180 people. The study was approved by the Ethics and Research Committee of the Federal University of Rio Grande do Norte under Opinion number 152/2012. Results: It was found that the adult population classified the quality of care from regular to good, showing an association with the waiting time, time spent from the unit to one’s house and the reception. Conclusions: It could be concluded that this study contributes to the development of strategies able to provide a full and equitable care to the adult population in the primary health care network, since this is the gateway to other levels of care, because it aims to promote adult health and prevent diseases.展开更多
BACKGROUND Indications to refer patients with cirrhosis for liver transplant evaluation(LTE)include hepatic decompensation or a model for end stage liver disease(MELDNa)score≥15.Few studies have evaluated how delayin...BACKGROUND Indications to refer patients with cirrhosis for liver transplant evaluation(LTE)include hepatic decompensation or a model for end stage liver disease(MELDNa)score≥15.Few studies have evaluated how delaying referral beyond these criteria affects patient outcomes.AIM To evaluate clinical characteristics of patients undergoing inpatient LTE and to assess the effects of delayed LTE on patient outcomes(death,transplantation).METHODS This is a single center retrospective cohort study assessing all patients undergoing inpatient LTE(n=159)at a large quaternary care and liver transplant center between 10/23/2017-7/31/2021.Delayed referral was defined as having prior indication(decompensation,MELD-Na≥15)for LTE without referral.Early referral was defined as referrals made within 3 mo of having an indication based on practice guidelines.Logistic regression and Cox Hazard Regression were used to evaluate the relationship between delayed referral and patient outcomes.RESULTS Many patients who require expedited inpatient LTE had delayed referrals.Misconceptions regarding transplant candidacy were a leading cause of delayed referral.Ultimately,delayed referrals negatively affected overall patient outcome and an independent predictor of both death and not receiving a transplant.Delayed referral was associated with a 2.5 hazard risk of death.CONCLUSION Beyond initial access to an liver transplant(LT)center,delaying LTE increases risk of death and reduces risk of LT in patients with chronic liver disease.There is substantial opportunity to increase the percentage of patients undergoing LTE when first clinically indicated.It is crucial for providers to remain informed about the latest guidelines on liver transplant candidacy and the transplant referral process.展开更多
When evaluating the accessibility of a large website, we rely on sampling methods to reduce the cost of evaluation. This may lead to a biased evaluation when the distribution of checkpoint violations in a website is s...When evaluating the accessibility of a large website, we rely on sampling methods to reduce the cost of evaluation. This may lead to a biased evaluation when the distribution of checkpoint violations in a website is skewed and the selected samples do not provide a good representation of the entire website. To improve sampling quality, stratified sampling methods first cluster web pages in a site and then draw samples from each cluster. In existing stratified sampling methods, however, all the pages in a website need to be analyzed for clustering, causing huge I/O and computation costs. To address this issue, we propose a novel page sampling method based on URL clustering for web accessibility evaluation, namely URLSamp. Using only the URL information for stratified page sampling, URLSamp can efficiently scale to large websites. Meanwhile, by exploiting similarities in URL patterns, URLSamp cluster pages by their generating scripts and can thus effectively detect accessibility problems from web page templates. We use a data set of 45 web sites to validate our method. Experimental results show that our URLSamp method is both effective and efficient for web accessibility evaluation.展开更多
Public transportation(PT)often fails to provide door-to-door service.Passengers often have to walk a distance to reach their destination after getting off the public transportation station.Therefore,the walking access...Public transportation(PT)often fails to provide door-to-door service.Passengers often have to walk a distance to reach their destination after getting off the public transportation station.Therefore,the walking accessibility of the station area directly affects the attractiveness of the PT.For walking,accurate calculation or prediction of accessibility should consider not only the objective distance,but also the environment and psychological perception factors of pedestrians.This paper aims to map the pedestrian perceived cost to the transportation environment to evaluate the walking accessibility of the public transportation station area accurately.From the perspective of psychological perception of walking environment,four key impedance factors are selected and a pedestrian perceived impedance model is established.Then an evaluation model of station area accessibility is set employing POIs(Point of Interests)based on the accumulative opportunity method.Finally,the case is given to show the application of the model.The results show that the number of crosswalks with signal lights,mixed use of sidewalk and non-motorized lane,the obstacle quantity and the vehicle entrance quantity on sidewalks can increase perceived impedance significantly.For example,pedestrians are willing to spend 4.21 extra minutes to adopt routes with one fewer obstacle per 100 meters.Within 10 minutes of walking time,walking perception has a greater impact on station area accessibility.The perceived walking time thresholds for evaluating bus and rail transit station area accessibility are recommended to be 15 minutes and 20 minutes,respectively.The evaluation results can provide a reliable basis for improving the walking network around public transportation station.展开更多
A novel distributed cognitive radio multichannel medium access protocol without common control channel was proposed.The protocol divided a transmission interval into two parts for exchanging control information and da...A novel distributed cognitive radio multichannel medium access protocol without common control channel was proposed.The protocol divided a transmission interval into two parts for exchanging control information and data,respectively.In addition to evaluating system saturation throughput of the proposed protocol,a three-dimensional multi channel Markov chain model to describe the sate of the cognitive users (CUs) in dynamic spectrum access was presented.The proposed analysis was applied to the packet transmission schemes employed by the basic,RTS/CTS access mechanism adopted in the normal IEEE 802.11.Analyzing the advantage of the two methods,a hybrid access mechanism was proposed to improve the system throughput.The simulation results show that the experiment results are close to the value computed by the model (less than 5%),and the proposed protocol significantly improves the performance of the system throughput by borrowing the licensed spectrum.By analyzing the dependence of throughput on system parameters,hybrid mechanism dynamically selecting access mechanism can maintain high throughput.展开更多
基金Under the auspices of National Scientific and Technical Supporting Programs During 12th Five-year Plan(No.2012BAJ22B02)
文摘Rural settlements are the main carriers of agriculture, rural areas and farmers; thus, optimizing the production and living space of rural settlements is highly significant to rural development. Taking the effective allocation of resources as the starting point, a suitability evaluation system of rural settlements, based on accessibility of production and living, was proposed in this study to provide scientific basis for the optimization of production and living space. The accessibility of production and living was measured by an im- proved two-step floating catchment area method, which considered proximity and availability based on the inclination of rural residents. The suitability evaluation system consisted of traditional suitability evaluation and newly proposed limiting factor identification based on the loss score proportion of suitability. Tingzu Town of Hubei Province, China, was chosen as the case study area. Based on the re- suits of the suitability evaluation system, corresponding suggestions on rural land consolidation, industry division, as well as the layout of health care and education facilities were proposed to optimize the production and living space of rural settlements in Tingzu Town. It is found that the suitability evaluation based on accessibility of production and living is more scientific and accurate than the traditional ones which significantly overestimate production and living convenience. Moreover, the limiting factor identification can help us put forward suggestions according to local conditions and bring about the highly targeted optimization of production and living space of rural settlements.
文摘BACKGROUND Coronavirus disease 2019(COVID-19)disrupted healthcare and led to increased telehealth use.We explored the impact of COVID-19 on liver transplant evaluation(LTE).AIM To understand the impact of telehealth on LTE during COVID-19 and to identify disparities in outcomes disaggregated by sociodemographic factors.METHODS This was a retrospective study of patients who initiated LTE at our center from 3/16/20-3/16/21(“COVID-19 era”)and the year prior(3/16/19-3/15/20,“pre-COVID-19 era”).We compared LTE duration times between eras and explored the effects of telehealth and inpatient evaluations on LTE duration,listing,and pretransplant mortality.RESULTS One hundred and seventy-eight patients were included in the pre-COVID-19 era cohort and one hundred and ninety-nine in the COVID-19 era cohort.Twentynine percent(58/199)of COVID-19 era initial LTE were telehealth,compared to 0%(0/178)pre-COVID-19.There were more inpatient evaluations during COVID-19 era(40%vs 28%,P<0.01).Among outpatient encounters,telehealth use for initial LTE during COVID-19 era did not impact likelihood of listing,pretransplant mortality,or time to LTE and listing.Median times to LTE and listing during COVID-19 were shorter than pre-COVID-19,driven by increased inpatient evaluations.Sociodemographic factors were not predictive of telehealth.CONCLUSION COVID-19 demonstrates a shift to telehealth and inpatient LTE.Telehealth does not impact LTE or listing duration,likelihood of listing,or mortality,suggesting telehealth may facilitate LTE without negative outcomes.
基金supported by NSFC under Grant No.62341102National Key R&D Program of China under Grant No.2018YFA0701604.
文摘Currently,data security and privacy protection are becoming more and more important.Access control is a method of authorization for users through predefined policies.Token-based access control(TBAC)enhances the manageability of authorization through the token.However,traditional access control policies lack the ability to dynamically adjust based on user access behavior.Incorporating user reputation evaluation into access control can provide valuable feedback to enhance system security and flexibility.As a result,this paper proposes a blockchain-empowered TBAC system and introduces a user reputation evaluation module to provide feedback on access control.The TBAC system divides the access control process into three stages:policy upload,token request,and resource request.The user reputation evaluation module evaluates the user’s token reputation and resource reputation for the token request and resource request stages of the TBAC system.The proposed system is implemented using the Hyperledger Fabric blockchain.The TBAC system is evaluated to prove that it has high processing performance.The user reputation evaluation model is proved to be more conservative and sensitive by comparative study with other methods.In addition,the security analysis shows that the TBAC system has a certain anti-attack ability and can maintain stable operation under the Distributed Denial of Service(DDoS)attack environment.
文摘`Introduction Open science is a set of principles and practices that aim to make scientific research accessible to everyone for the benefit of scientists and society.It includes sharing publications,data,software,and hardware widely,and ensuring that the production of scientific knowledge is inclusive,equitable,and sustainable.
基金Supported by Natural Science Fund Project of Tianjin City(08JCYBJC05100)Social Science Fund Project of Tianjin City(E10030)~~
文摘A review of the history of Chinese gardens beginning in the Shang Dynasty reveals that parks have become increasingly important to urban residents' lives; and hence, this paper proposes a methodology to evaluate the suitability of parks. The analysis shows that suitability evaluations of urban parks should not be restricted to a park's basic functions, but should include a comprehensive evaluation of ecological value, cultural inheritance and feature construction. After describing the current literature of research on indices, categories, use conditions and landscape accessibility of domestic and foreign urban parks, the paper concludes with a framework for evaluating a park's suitability, i.e. the establishment of an integrated evaluation system, the selection of reasonable evaluation methods, and public participation as an indicator in the evaluation system, so as to ensure the validity of research results.
文摘Performance of fixed relays in orthogonal frequency division multiple access （0FDMA） systems, especially the coverage and capacity performance at the cell edge, is evaluated in this paper. Two methods, theoretical analysis and calculation and Monte Carlo simulation, are used for the evaluations. By theoreti- cal analysis and calculation, frequency efficiency equation of a relay is introduced and numerical results are calculated. Monte Carlo simulation results also verify that the calculation method is reasonable. The evaluation shows that a relay can increase system performance to a certain level if it is designed appropriately, otherwise it will be harmful for the system performance, even to reduce it.
基金supported in part by Royal Society YVolfson Research Merit Award WRM/R1/180014,ERC 652976,EPSRC EP/M025268/1,Shenzhen Institute of Computing Sciences,and Beijing Advanced Innovation Center for Big Data and Brain Computing.
文摘This work aims to reduce queries on big data to computations on small data,and hence make querying big data possible under bounded resources.A query Q is boundedly evaluable when posed on any big dataset D,there exists a fraction DQ of D such that Q(D)=Q(DQ),and the cost of identifying DQ is independent of the size of D.It has been shown that with an auxiliary structure known as access schema,many queries in relational algebra(RA)are boundedly evaluable under the set semantics of RA.This paper extends the theory of bounded evaluation to RAaggr,i.e.,RA extended with aggregation,under the bag semantics.(1)We extend access schema to bag access schema,to help us identify DQ for RAaggr queries Q.(2)While it is undecidable to determine whether an RAaggr query is boundedly evaluable under a bag access schema,we identify special cases that are decidable and practical.(3)In addition,we develop an effective syntax for bounded RAaggr queries,i.e.,a core subclass of boundedly evaluable RAaggr queries without sacrificing their expressive power.(4)Based on the effective syntax,we provide efficient algorithms to check the bounded evaluability of RAaggr queries and to generate query plans for bounded RAaggr queries.(5)As proof of concept,we extend PostgreSQL to support bounded evaluation.We experimentally verify that the extended system improves performance by orders of magnitude.
文摘The objective of this study was to develop a method to assess and analyze the total allelopathic potential of crop germplasm and to test this method on four winter wheat accessions commonly planted in the Loess Plateau. A systems engineering model was developed and used to evaluate the total allelopathic potential of crop cultivars. In addition, a method for quantifying the total allelopathic potential in crop accessions was presented. Total allelopathic potential of four winter wheat accessions from the Loess Plateau was estimated and compared using a systems theory approach. The model assessed allelopathic potential in different parts of the plants from the time wheat turned green in spring until maturity. Results from these models indicated that the four wheat accessions had very weak allelopathic potential. Allelopathic potential declined in the order Xiaoyan 22 〉 Ningdong 1 〉 Fengchan 3 〉 Bima 1. This system engineering evaluation method allows for the assessment of allelopathic potential among crop varieties. It will help plant breeders to select and develop allelopathic crop accessions that combine weed suppression properties with agronomic traits related to yield and quality.
文摘Objectives: The goal of this project was to evaluate the quality of the accessibility of the adult population to services in Primary Health Care, with a view to contribute to the development of measures that will propose improvement in the offered assistance. Methods: This is a quantitative and evaluative study made in the municipality of Santa Cruz, State of Rio Grande do Norte, Brazil, with a sample of 180 people. The study was approved by the Ethics and Research Committee of the Federal University of Rio Grande do Norte under Opinion number 152/2012. Results: It was found that the adult population classified the quality of care from regular to good, showing an association with the waiting time, time spent from the unit to one’s house and the reception. Conclusions: It could be concluded that this study contributes to the development of strategies able to provide a full and equitable care to the adult population in the primary health care network, since this is the gateway to other levels of care, because it aims to promote adult health and prevent diseases.
文摘BACKGROUND Indications to refer patients with cirrhosis for liver transplant evaluation(LTE)include hepatic decompensation or a model for end stage liver disease(MELDNa)score≥15.Few studies have evaluated how delaying referral beyond these criteria affects patient outcomes.AIM To evaluate clinical characteristics of patients undergoing inpatient LTE and to assess the effects of delayed LTE on patient outcomes(death,transplantation).METHODS This is a single center retrospective cohort study assessing all patients undergoing inpatient LTE(n=159)at a large quaternary care and liver transplant center between 10/23/2017-7/31/2021.Delayed referral was defined as having prior indication(decompensation,MELD-Na≥15)for LTE without referral.Early referral was defined as referrals made within 3 mo of having an indication based on practice guidelines.Logistic regression and Cox Hazard Regression were used to evaluate the relationship between delayed referral and patient outcomes.RESULTS Many patients who require expedited inpatient LTE had delayed referrals.Misconceptions regarding transplant candidacy were a leading cause of delayed referral.Ultimately,delayed referrals negatively affected overall patient outcome and an independent predictor of both death and not receiving a transplant.Delayed referral was associated with a 2.5 hazard risk of death.CONCLUSION Beyond initial access to an liver transplant(LT)center,delaying LTE increases risk of death and reduces risk of LT in patients with chronic liver disease.There is substantial opportunity to increase the percentage of patients undergoing LTE when first clinically indicated.It is crucial for providers to remain informed about the latest guidelines on liver transplant candidacy and the transplant referral process.
基金Project supported by the National Natural Science Foundation of China （Nos. 61173185 and 61173186） and the Natural Science Foun- dation of Zhejiang Province, China （No. LZ13F020001）
文摘When evaluating the accessibility of a large website, we rely on sampling methods to reduce the cost of evaluation. This may lead to a biased evaluation when the distribution of checkpoint violations in a website is skewed and the selected samples do not provide a good representation of the entire website. To improve sampling quality, stratified sampling methods first cluster web pages in a site and then draw samples from each cluster. In existing stratified sampling methods, however, all the pages in a website need to be analyzed for clustering, causing huge I/O and computation costs. To address this issue, we propose a novel page sampling method based on URL clustering for web accessibility evaluation, namely URLSamp. Using only the URL information for stratified page sampling, URLSamp can efficiently scale to large websites. Meanwhile, by exploiting similarities in URL patterns, URLSamp cluster pages by their generating scripts and can thus effectively detect accessibility problems from web page templates. We use a data set of 45 web sites to validate our method. Experimental results show that our URLSamp method is both effective and efficient for web accessibility evaluation.
基金supported the National Social Science Found of China(No.20BGL291).
文摘Public transportation(PT)often fails to provide door-to-door service.Passengers often have to walk a distance to reach their destination after getting off the public transportation station.Therefore,the walking accessibility of the station area directly affects the attractiveness of the PT.For walking,accurate calculation or prediction of accessibility should consider not only the objective distance,but also the environment and psychological perception factors of pedestrians.This paper aims to map the pedestrian perceived cost to the transportation environment to evaluate the walking accessibility of the public transportation station area accurately.From the perspective of psychological perception of walking environment,four key impedance factors are selected and a pedestrian perceived impedance model is established.Then an evaluation model of station area accessibility is set employing POIs(Point of Interests)based on the accumulative opportunity method.Finally,the case is given to show the application of the model.The results show that the number of crosswalks with signal lights,mixed use of sidewalk and non-motorized lane,the obstacle quantity and the vehicle entrance quantity on sidewalks can increase perceived impedance significantly.For example,pedestrians are willing to spend 4.21 extra minutes to adopt routes with one fewer obstacle per 100 meters.Within 10 minutes of walking time,walking perception has a greater impact on station area accessibility.The perceived walking time thresholds for evaluating bus and rail transit station area accessibility are recommended to be 15 minutes and 20 minutes,respectively.The evaluation results can provide a reliable basis for improving the walking network around public transportation station.
基金Project(61071104) supported by the National Natural Science Foundation of China
文摘A novel distributed cognitive radio multichannel medium access protocol without common control channel was proposed.The protocol divided a transmission interval into two parts for exchanging control information and data,respectively.In addition to evaluating system saturation throughput of the proposed protocol,a three-dimensional multi channel Markov chain model to describe the sate of the cognitive users (CUs) in dynamic spectrum access was presented.The proposed analysis was applied to the packet transmission schemes employed by the basic,RTS/CTS access mechanism adopted in the normal IEEE 802.11.Analyzing the advantage of the two methods,a hybrid access mechanism was proposed to improve the system throughput.The simulation results show that the experiment results are close to the value computed by the model (less than 5%),and the proposed protocol significantly improves the performance of the system throughput by borrowing the licensed spectrum.By analyzing the dependence of throughput on system parameters,hybrid mechanism dynamically selecting access mechanism can maintain high throughput.
