The Experts below are selected from a list of 7590 Experts worldwide ranked by ideXlab platform
Mengchu Zhou - One of the best experts on this subject based on the ideXlab platform.
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wafer Sojourn Time fluctuation analysis of Time constrained dual arm cluster tools with wafer revisiting and activity Time variation
IEEE Transactions on Systems Man and Cybernetics, 2018Co-Authors: Yan Qiao, Mengchu Zhou, Fajun Yang, Qinghua ZhuAbstract:A robotic cluster tool involves many activities whose Time is subject to some disturbance, thus leading to the activity Time variation. It results in wafer Sojourn Time fluctuation in a process module, which may in turn violate wafer residency Time constraints. Some wafer fabrication requires a revisiting process. With wafer revisiting, the effect of activity Time variation on wafer Sojourn Time fluctuation is so complicated that no analysis was reported to the best knowledge of the authors. It is vitally important to accurately analyze it. To do so, this paper adopts a Petri net model to describe the dynamical behavior of cluster tools. With this model, a real-Time control policy is proposed to offset the effect of the activity Time variation on wafer Sojourn Time fluctuation as much as possible. Then, the wafer Sojourn Time delay is analyzed and algorithms are developed to calculate its exact upper bound. With the proposed method, one can check if a given schedule is feasible under bounded activity Time variation. Some practical examples are given to show the application of the proposed approach.
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a novel algorithm for wafer Sojourn Time analysis of single arm cluster tools with wafer residency Time constraints and activity Time variation
Systems Man and Cybernetics, 2015Co-Authors: Chunrong Pan, Yan Qiao, Mengchu ZhouAbstract:This paper addresses the scheduling problem of single-arm cluster tools with both wafer residency Time constraints and activity Time variation in semiconductor manufacturing. Based on a Petri net model developed in our previous work, polynomial algorithms are proposed to obtain the exact upper bound of the wafer Sojourn Time delay for the first Time. With the obtained results, one can check the feasibility of a given schedule or find a feasible and optimal one if it exists. Illustrative examples are given to show the applications of the proposed method.
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Petri Net Modeling and Wafer Sojourn Time Analysis of Single-Arm Cluster Tools With Residency Time Constraints and Activity Time Variation
IEEE Transactions on Semiconductor Manufacturing, 2012Co-Authors: Yan Qiao, Naiqi Wu, Mengchu ZhouAbstract:With wafer residency Time constraints, it is crucial to schedule a cluster tool in semiconductor fabrication such that the wafer Sojourn Time in a processing module is in a given range. However, because of the activity Time variation in wafer fabrication by cluster tools, a feasible schedule obtained under the assumption of deterministic activity Times may become infeasible. To solve this problem, it is critically important to reveal the wafer Sojourn Time fluctuations with bounded activity Time variation. This paper targets at single-arm cluster tools. They are modeled by a Petri net to describe the fabrication processes. Based on the net, a real-Time control policy is proposed such that its use offsets the effect of the activity Time variation as much as possible. Then, the wafer Sojourn Time delay is analyzed and analytical expressions are given to calculate the upper bound. With the proposed method, we can check if a given schedule is feasible under bounded activity Time variation. Examples are given to show the applications of the research results.
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analysis of wafer Sojourn Time in dual arm cluster tools with residency Time constraint and activity Time variation
IEEE Transactions on Semiconductor Manufacturing, 2010Co-Authors: Mengchu ZhouAbstract:When scheduling cluster tools under wafer residency Time constraints, wafer Sojourn Time in a processing module should be carefully controlled such that it is in a permissive range. Activity Time variation often results in wafer Sojourn Time fluctuation and makes an originally feasible schedule infeasible. Thus, it is very important to know how the wafer Sojourn Time changes when activity Time varies. With bounded activity Time variation considered, this paper conducts a detailed analysis of wafer Sojourn Time variation in dual-arm cluster tools. To do so, a Petri net (PN) model and a real-Time control policy are presented. Based on the PN model, real-Time operational architecture, and real-Time control policy, this paper analyzes the effect of activity Time variation on wafer Sojourn Time delay at a process module and presents its upper bounds. The upper bounds are given in an analytical form and can be easily evaluated. With the wafer Sojourn Time analysis, it is possible to develop an effective method for schedulability analysis and optimal steady-state scheduling. An example is used to show the applications of the proposed approach.
Ekram Hossain - One of the best experts on this subject based on the ideXlab platform.
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stochastic geometry analysis of Sojourn Time in multi tier cellular networks
IEEE Transactions on Wireless Communications, 2021Co-Authors: Mohammad Salehi, Ekram HossainAbstract:Impact of mobility will be increasingly important in future generation wireless services and the related challenges will need to be addressed. Sojourn Time, the Time duration that a mobile user stays within a cell, is a mobility-aware parameter that can significantly impact the performance of mobile users and it can also be exploited to improve resource allocation and mobility management methods in the network. In this paper, we derive the distribution and mean of the Sojourn Time in multi-tier cellular networks, where spatial distribution of base stations (BSs) in each tier follows an independent homogeneous Poisson point process (PPP). To obtain the Sojourn Time distribution in multi-tier cellular networks with maximum biased averaged received power association, as the first step, we derive the area of contact, based on which we then derive the linear contact distribution function and chord length distribution of each tier. We also study the relation between mean Sojourn Time and other mobility-related performance metrics. We show that the mean Sojourn Time is inversely proportional to the handoff rate, and the complementary cumulative distribution function (CCDF) of Sojourn Time is bounded from above by the complement of the handoff probability. Moreover, we study the impact of user velocity and network parameters on the Sojourn Time.
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handover rate and Sojourn Time analysis in mobile drone assisted cellular networks
IEEE Wireless Communications Letters, 2021Co-Authors: Mohammad Salehi, Ekram HossainAbstract:To improve capacity and overcome some of the limitations of traditional terrestrial cellular wireless networks, drones with aerial base stations can be deployed (e.g., to improve coverage, alleviate congestion, support overflow traffic). The mobility of drones allows flexible network reconfiguration to adapt to dynamic traffic and channel conditions. However, this is achieved at the expense of more handovers since even a static user may experience a handover when the drones are mobile. In this letter, we provide an exact analysis of the handover rate and Sojourn Time (Time between two subsequent handovers) for a network of drone base stations. We also show that among different speed distributions with the same mean, the handover rate is minimum when all drone base stations move with the same speed.
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handover rate and Sojourn Time analysis in mobile drone assisted cellular networks
arXiv: Networking and Internet Architecture, 2020Co-Authors: Mohammad Salehi, Ekram HossainAbstract:To improve capacity and overcome some of the limitations of cellular wireless networks, drones with aerial base stations can be deployed to assist the terrestrial cellular wireless networks. The mobility of drones allows flexible network reconfiguration to adapt to dynamic traffic and channel conditions. However, this is achieved at the expense of more handovers since even a static user may experience a handover when the drones are mobile. In this letter, we provide an exact analysis of the handover rate and Sojourn Time (Time between two subsequent handovers) for a network of drone base stations. We also show that among different speed distributions with the same mean, the handover rate is minimum when all drone base stations move with same speed.
Yan Qiao - One of the best experts on this subject based on the ideXlab platform.
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wafer Sojourn Time fluctuation analysis of Time constrained dual arm cluster tools with wafer revisiting and activity Time variation
IEEE Transactions on Systems Man and Cybernetics, 2018Co-Authors: Yan Qiao, Mengchu Zhou, Fajun Yang, Qinghua ZhuAbstract:A robotic cluster tool involves many activities whose Time is subject to some disturbance, thus leading to the activity Time variation. It results in wafer Sojourn Time fluctuation in a process module, which may in turn violate wafer residency Time constraints. Some wafer fabrication requires a revisiting process. With wafer revisiting, the effect of activity Time variation on wafer Sojourn Time fluctuation is so complicated that no analysis was reported to the best knowledge of the authors. It is vitally important to accurately analyze it. To do so, this paper adopts a Petri net model to describe the dynamical behavior of cluster tools. With this model, a real-Time control policy is proposed to offset the effect of the activity Time variation on wafer Sojourn Time fluctuation as much as possible. Then, the wafer Sojourn Time delay is analyzed and algorithms are developed to calculate its exact upper bound. With the proposed method, one can check if a given schedule is feasible under bounded activity Time variation. Some practical examples are given to show the application of the proposed approach.
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a novel algorithm for wafer Sojourn Time analysis of single arm cluster tools with wafer residency Time constraints and activity Time variation
Systems Man and Cybernetics, 2015Co-Authors: Chunrong Pan, Yan Qiao, Mengchu ZhouAbstract:This paper addresses the scheduling problem of single-arm cluster tools with both wafer residency Time constraints and activity Time variation in semiconductor manufacturing. Based on a Petri net model developed in our previous work, polynomial algorithms are proposed to obtain the exact upper bound of the wafer Sojourn Time delay for the first Time. With the obtained results, one can check the feasibility of a given schedule or find a feasible and optimal one if it exists. Illustrative examples are given to show the applications of the proposed method.
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Petri Net Modeling and Wafer Sojourn Time Analysis of Single-Arm Cluster Tools With Residency Time Constraints and Activity Time Variation
IEEE Transactions on Semiconductor Manufacturing, 2012Co-Authors: Yan Qiao, Naiqi Wu, Mengchu ZhouAbstract:With wafer residency Time constraints, it is crucial to schedule a cluster tool in semiconductor fabrication such that the wafer Sojourn Time in a processing module is in a given range. However, because of the activity Time variation in wafer fabrication by cluster tools, a feasible schedule obtained under the assumption of deterministic activity Times may become infeasible. To solve this problem, it is critically important to reveal the wafer Sojourn Time fluctuations with bounded activity Time variation. This paper targets at single-arm cluster tools. They are modeled by a Petri net to describe the fabrication processes. Based on the net, a real-Time control policy is proposed such that its use offsets the effect of the activity Time variation as much as possible. Then, the wafer Sojourn Time delay is analyzed and analytical expressions are given to calculate the upper bound. With the proposed method, we can check if a given schedule is feasible under bounded activity Time variation. Examples are given to show the applications of the research results.
Mohammad Salehi - One of the best experts on this subject based on the ideXlab platform.
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stochastic geometry analysis of Sojourn Time in multi tier cellular networks
IEEE Transactions on Wireless Communications, 2021Co-Authors: Mohammad Salehi, Ekram HossainAbstract:Impact of mobility will be increasingly important in future generation wireless services and the related challenges will need to be addressed. Sojourn Time, the Time duration that a mobile user stays within a cell, is a mobility-aware parameter that can significantly impact the performance of mobile users and it can also be exploited to improve resource allocation and mobility management methods in the network. In this paper, we derive the distribution and mean of the Sojourn Time in multi-tier cellular networks, where spatial distribution of base stations (BSs) in each tier follows an independent homogeneous Poisson point process (PPP). To obtain the Sojourn Time distribution in multi-tier cellular networks with maximum biased averaged received power association, as the first step, we derive the area of contact, based on which we then derive the linear contact distribution function and chord length distribution of each tier. We also study the relation between mean Sojourn Time and other mobility-related performance metrics. We show that the mean Sojourn Time is inversely proportional to the handoff rate, and the complementary cumulative distribution function (CCDF) of Sojourn Time is bounded from above by the complement of the handoff probability. Moreover, we study the impact of user velocity and network parameters on the Sojourn Time.
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handover rate and Sojourn Time analysis in mobile drone assisted cellular networks
IEEE Wireless Communications Letters, 2021Co-Authors: Mohammad Salehi, Ekram HossainAbstract:To improve capacity and overcome some of the limitations of traditional terrestrial cellular wireless networks, drones with aerial base stations can be deployed (e.g., to improve coverage, alleviate congestion, support overflow traffic). The mobility of drones allows flexible network reconfiguration to adapt to dynamic traffic and channel conditions. However, this is achieved at the expense of more handovers since even a static user may experience a handover when the drones are mobile. In this letter, we provide an exact analysis of the handover rate and Sojourn Time (Time between two subsequent handovers) for a network of drone base stations. We also show that among different speed distributions with the same mean, the handover rate is minimum when all drone base stations move with the same speed.
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handover rate and Sojourn Time analysis in mobile drone assisted cellular networks
arXiv: Networking and Internet Architecture, 2020Co-Authors: Mohammad Salehi, Ekram HossainAbstract:To improve capacity and overcome some of the limitations of cellular wireless networks, drones with aerial base stations can be deployed to assist the terrestrial cellular wireless networks. The mobility of drones allows flexible network reconfiguration to adapt to dynamic traffic and channel conditions. However, this is achieved at the expense of more handovers since even a static user may experience a handover when the drones are mobile. In this letter, we provide an exact analysis of the handover rate and Sojourn Time (Time between two subsequent handovers) for a network of drone base stations. We also show that among different speed distributions with the same mean, the handover rate is minimum when all drone base stations move with same speed.
Helen M Colhoun - One of the best experts on this subject based on the ideXlab platform.
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use of personalised risk based screening schedules to optimise workload and Sojourn Time in screening programmes for diabetic retinopathy a retrospective cohort study
PLOS Medicine, 2019Co-Authors: Andreas Ochs, Stuart J Mcgurnaghan, Mike W Black, Graham P Leese, Sam Philip, Naveed Sattar, Caroline Styles, Sarah H Wild, Paul M Mckeigue, Helen M ColhounAbstract:Background National guidelines in most countries set screening intervals for diabetic retinopathy (DR) that are insufficiently informed by contemporary incidence rates. This has unspecified implications for interval disease risks (IDs) of referable DR, disparities in ID between groups or individuals, Time spent in referable state before screening (Sojourn Time), and workload. We explored the effect of various screening schedules on these outcomes and developed an open-access interactive policy tool informed by contemporary DR incidence rates. Methods and findings Scottish Diabetic Retinopathy Screening Programme data from 1 January 2007 to 31 December 2016 were linked to diabetes registry data. This yielded 128,606 screening examinations in people with type 1 diabetes (T1D) and 1,384,360 examinations in people with type 2 diabetes (T2D). Among those with T1D, 47% of those without and 44% of those with referable DR were female, mean diabetes duration was 21 and 23 years, respectively, and mean age was 26 and 24 years, respectively. Among those with T2D, 44% of those without and 42% of those with referable DR were female, mean diabetes duration was 9 and 14 years, respectively, and mean age was 58 and 52 years, respectively. Individual probability of developing referable DR was estimated using a generalised linear model and was used to calculate the intervals needed to achieve various IDs across prior grade strata, or at the individual level, and the resultant workload and Sojourn Time. The current policy in Scotland—screening people with no or mild disease annually and moderate disease every 6 months—yielded large differences in ID by prior grade (13.2%, 3.6%, and 0.6% annually for moderate, mild, and no prior DR strata, respectively, in T1D) and diabetes type (2.4% in T1D and 0.6% in T2D overall). Maintaining these overall risks but equalising risk across prior grade strata would require extremely short intervals in those with moderate DR (1–2 months) and very long intervals in those with no prior DR (35–47 months), with little change in workload or average Sojourn Time. Changing to intervals of 12, 9, and 3 months in T1D and to 24, 9, and 3 months in T2D for no, mild, and moderate DR strata, respectively, would substantially reduce disparity in ID across strata and between diabetes types whilst reducing workload by 26% and increasing Sojourn Time by 2.3 months. Including clinical risk factor data gave a small but significant increment in prediction of referable DR beyond grade (increase in C-statistic of 0.013 in T1D and 0.016 in T2D, both p < 0.001). However, using this model to derive personalised intervals did not have substantial workload or Sojourn Time benefits over stratum-specific intervals. The main limitation is that the results are pertinent only to countries that share broadly similar rates of retinal disease and risk factor distributions to Scotland. Conclusions Changing current policies could reduce disparities in ID and achieve substantial reductions in workload within the range of IDs likely to be deemed acceptable. Our tool should facilitate more rational policy setting for screening.
