Virtual control with hard constraints Al‐Hajjar, Ali M. H.; Swei, Sean Shan‐Min; Zhu, Guoming
Asian journal of control,
January 2021, 2021-01-00, 20210101, Volume:
23, Issue:
1
Journal Article
Peer reviewed
Open access
Practical control problems are always subject to plant state and/or input constraints, which make designing an effective controller a challenging task. This paper introduces a novel virtual control ...approach to handling the presence of hard constraints in control systems by utilizing virtual mechanisms in the form of nonlinear springs and dampers. The augmented virtual mechanisms are to assist in better shaping the closed‐loop responses, especially when operating near the constrained boundary. A linear quadratic regulator based model predictive control method is utilized to develop stabilizing controllers that not only achieve desired system performance, but also meet the imposed hard constraints. The basic idea is to dramatically increase control penalty by way of tuning the spring and damper effect when the constrained state/input response is close to its hard constraint. The proposed method is applied to a balancing ball problem to demonstrate its applicability and effectiveness, and the simulation results validate the proposed concept.
Adjuvant paclitaxel and trastuzumab has been shown to be an effective regimen with low risk of cancer recurrence and treatment-related toxicities in early-stage node-negative, HER2-positive breast ...cancer. We investigated the cost-effectiveness of this regimen.
A Markov-based microsimulation model with six health states is used to simulate four adjuvant therapy options for women with early-stage node-negative, HER2-positive breast cancer at different age groups. The four treatment arms are 1) adjuvant paclitaxel and trastuzumab (TH), 2) doxorubicin, cyclophosphamide, paclitaxel and trastuzumab (ACTH), 3) docetaxel, carboplatin and trastuzumab (TCH), and 4) no adjuvant trastuzumab (NT). Data from randomized trials were used to estimate treatment efficacy. Societal perspective was used in this cost-effectiveness analysis. Costs were measured in 2016 US dollars (US$) and quality-adjusted life-years (QALYs) was used for health outcomes. Sensitivity analyses were performed to evaluate the impact of uncertainty in parameter estimation.
We found that 40-year-old women undergoing TH treatment would have an average of 16.17 QALYs for the cost of $178,650 when lifetime horizon is used. Compared to NT, TH has incremental cost-effectiveness ratios ranged from $10,584 (ages 40-49) to $84,981 (age 80+) per additional QALYs. The sensitivity analysis showed that TH is cheaper and leads to higher QALYs compared to both ACTH and TCH for all age groups and time horizons.
TH is cost-effective for all age groups in the base case scenario and in the sensitivity analysis. In order to reduce the parameter uncertainty, clinical trials with longer follow-up times are needed.
Hard constrained control problems are popular in practical applications due to physical and power limitations. For instance, the displacement of a linear actuator is finite. A lot of studies have ...been conducted in this area to deal with certain hard constrained control problems and some are computationally expensive. This paper introduces a novel LPV (linear parameter-varying) virtual control scheme to deal with a class of hard constrained control problems with an application to flutter suppression of a smart airfoil, leading to a state-feedback LPV gain scheduling controller with the guaranteed
ℋ
∞
performance. The basic idea of LPV virtual control is to add virtual components (such as variable stiffness springs and dampers) near to the hard constraints to prevent actuators from reaching their limits. The LPV virtual controller will be designed based on the model with virtual components and in the implementation stage, these virtual dynamics becomes part of the gain-scheduling controller. The concept is validated by a smart airfoil example. In the smart airfoil example, the virtual varying springs and dampers are placed at both ends of groove to constrain the mass movement. Comparisons studies with conventional LPV hard constrained control, nonlinear control, and regular LPV control without considering hard constraints are conducted to assess the performance of the proposed method and showed advantage over the existing methods. For instance, the control mass
ℒ
2
norm is reduced by 77.5% over the nonlinear control and 35% over the conventional LPV control.
Air-Cooled Heat Exchangers (ACHE) have gained importance through their extensive use in the oil and gas industry. Many researchers studied ACHE extensively and proposed analysis methods. Most of them ...investigate part of the ACHE in their modeling. Others consider only pressure drop in their calculations in simulating the porous media (fins and surrounding air). These assumptions lead to unprecise modeling results. In contrast to existing literature, by incorporating computational fluid dynamics (CFD) with real geometry design, this paper includes a study of a full-size ACHE with precise geometric measurements, commencing at the hot water's input and going all the way to the ACHE's exit through a U-path tube. By incorporating the complete geometry dimensions of the U-path tube length from the hot water inlet to the outlet, this methodology has the potential to produce more accurate predictions of temperature distribution, heat flow rate, logarithmic mean temperature difference (LMTD), and fin efficiency for each tube along the entire length of the ACHE. Further, unlike other works of literature, the porous media in this research includes calculations for pressure drops and heat transmission in place of real geometry design which gives more sensible and accurate modeling results. Moreover, a novel verification method is proposed by presenting an iterative process for verification of entire geometry design calculations by comparison with the Real Geometric Design. The incorporation of Real Geometry Design and Computational Fluid Dynamics (CFD) Code programs can lead to more precise and efficient methodologies for modeling air-cooled exchangers, offering valuable insights that can ultimately enhance their design and performance. In this work, the convergence with the actual geometrical design is less than 1%, demonstrating the superiority of the suggested strategy.
•Modeling the full-size geometric ACHE accuracy results.•Introducing the tortuosity factor leads to predict real parameters of ACHE.•Porous media plays a vital role in enhancing the CFD results.
Most of the multi-agent formation and obstacle avoidance algorithms in the literature are computationally expensive and/or presents an ad hoc method for a specific type of systems. A general ...inexpensive, in term of computational complexity, multi-agent formation and obstacle avoidance algorithm is modeled and designed in this paper. The method builds on the leader-follower strategy for the simplicity and applicability for a wide range of the engineering systems. A novel artificial potential function (APF) is proposed. The proposed function has unique attributes which differentiate it superior to what is reported in the literature. The proposed algorithm can be applied for first order systems, second order systems, and non-holonomic systems. Also, the proposed method is free of local minima problem and oscillations. In addition, a novel multi-agent system formation control design is proposed in this work. The proposed design allows to embed any formation in the system paradigm and reduces complexity. Moreover, the stability of the proposed method is investigated in terms of Riccati equation and Lyapunov method. Furthermore, to show the effectiveness of the proposed method it applied and simulated for a second order leader and one follower system with specific formation. Then, a five second order agents with leader in a circular formation avoiding simple and complex obstacles are also introduced with different scenarios. Finally, twenty agents with square formation with two obstacles are simulated and investigated.
•An algorithm for multi-agent system obstacle avoidance and formation control that can be used for first, second order, and non-holonomic systems.•A multi-agent system formation control design is proposed. The design allows to embed any formation in the system paradigm and reduces complexity.•Novel general potential function is constructed which has many unique properties.•The stability of the proposed method is investigated and presented in terms of the Riccati equation and Lyapunov method.•The proposed method is simulated in many scenarios with formation and obstacle avoidance.
Background
Diabetes mellitus has been associated with increased breast cancer (BC) risk; however, the magnitude of this effect is uncertain. This study focused on BC risk for women with type 2 ...diabetes mellitus (T2DM).
Methods
Two separate meta‐analyses were conducted (1) to estimate the relative risk (RR) of BC for women with T2DM and (2) to evaluate the risk of BC for women with T2DM associated with the use of metformin, a common diabetes treatment. In addition, subgroup analyses adjusting for obesity as measured by body mass index (BMI) and menopausal status were also performed. Studies were identified via PubMed/Scopus database and manual search through April 2021.
Results
A total of 30 and 15 studies were included in the first and second meta‐analyses, respectively. The summary RR of BC for women with T2DM was 1.15 (95% confidence interval CI, 1.09–1.21). The subgroup analyses adjusting BMI and adjusting BMI and menopause resulted in a summary RR of 1.22 (95% CI, 1.15–1.30) and 1.20 (95% CI, 1.05–1.36), respectively. For women with T2DM, the summary RR of BC was 0.82 (95% CI, 0.60–1.12) for metformin users compared with nonmetformin users.
Conclusions
Women with T2DM were more likely to be diagnosed with BC and this association was strengthened by adjusting for BMI and menopausal status. No statistically significant reduction of BC risk was observed among metformin users.
Impact
These two meta‐analyses can inform decision‐making for women with type 2 diabetes regarding their use of metformin and the use of screening mammography for early detection of breast cancer.
Relative risk of breast cancer among women with type 2 diabetes (CI, confidence interval; IV, inverse variance; SE, standard error).
Guidelines recommend biannual surveillance for hepatocellular carcinoma (HCC) in hepatitis C individuals with cirrhosis if the HCC incidence rate is above 1.5 per 100 person-years (PY). However, the ...incidence threshold for surveillance in individuals who achieve a virologic cure is unknown. We estimated the HCC incidence rate above which routine HCC surveillance is cost-effective in this growing population of virologically cured hepatitis C individuals with cirrhosis or advanced fibrosis.
We developed a Markov-based microsimulation model of the natural history of HCC in individuals with hepatitis C who achieved virologic cure with oral direct-acting antivirals. We used published data on the natural history of hepatitis C, competing risk post virologic cure, HCC tumor progression, real-world HCC surveillance adherence, contemporary HCC treatment options and associated costs, and utilities of different health states. We estimated the HCC incidence above which biannual HCC surveillance using ultrasound and alpha-fetoprotein would be cost-effective.
In virologically cured hepatitis C individuals with cirrhosis or advanced fibrosis, HCC surveillance is cost-effective if HCC incidence exceeds 0.7 per 100 PY using $100,000 per quality-adjusted life year willingness-to-pay. At this HCC incidence, routine HCC surveillance would result in 2650 and 5700 additional life years per 100,000 cirrhosis and advanced fibrosis persons, respectively, compared with no surveillance. At $150,000 willingness-to-pay, surveillance is cost-effective if HCC incidence exceeds 0.4 per 100 PY. Sensitivity analysis showed that the threshold mostly remained below 1.5 per 100 PY.
The contemporary HCC incidence threshold is much lower than the previous 1.5% incidence value used to guide HCC surveillance decisions. Updating clinical guidelines could improve the early diagnosis of HCC.
Successful treatment of chronic hepatitis C with oral direct-acting antivirals (DAAs) leads to virological cure, however, the subsequent risk of hepatocellular carcinoma (HCC) persists. Our objective ...was to evaluate the cost-effectiveness of biannual surveillance for HCC in patients cured of hepatitis C and the optimal age to stop surveillance.
We developed a microsimulation model of the natural history of HCC in individuals with hepatitis C and advanced fibrosis or cirrhosis who achieved virological cure with oral DAAs. We used published data on HCC incidence, tumor progression, real-world HCC surveillance adherence, and costs and utilities of different health states. We compared biannual HCC surveillance using ultrasound and alpha-fetoprotein for varying durations of surveillance (from 5 years to lifetime) vs. no surveillance.
In virologically cured patients with cirrhosis, the incremental cost-effectiveness ratio (ICER) of biannual surveillance remained below $150,000 per additional quality-adjusted life year (QALY) (range: $79,500-$94,800) when surveillance was stopped at age 70, irrespective of the starting age (40-65). Compared with no surveillance, surveillance detected 130 additional HCCs in ‘very early’/early stage and yielded 51 additional QALYs per 1,000 patients with cirrhosis. In virologically cured patients with advanced fibrosis, the ICER of biannual surveillance remained below $150,000/QALY (range: $124,600-$129,800) when surveillance was stopped at age 60, irrespective of the starting age (40-50). Compared with no surveillance, surveillance detected 24 additional HCCs in ‘very early’/early stage and yielded 12 additional QALYs per 1,000 patients with advanced fibrosis.
Biannual surveillance for HCC in patients cured of hepatitis C is cost-effective until the age of 70 for patients with cirrhosis, and until the age of 60 for patients with stable advanced fibrosis.
Individuals who are cured of hepatitis C using oral antiviral drugs remain at risk of developing liver cancer. The value of lifelong screening for liver cancer in these individuals is not known. By simulating the life course of hepatitis C cured individuals, we found that ultrasound-based biannual screening for liver cancer is cost-effective up to age 70 in those with cirrhosis and up to age 60 in those with stable advanced fibrosis.
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•The value of lifelong surveillance for HCC in individuals after SVR is not known.•Ultrasound-based bi-annual surveillance for HCC appears to be cost-effective up to age 75 in those with cirrhosis.•This surveillance strategy was cost effective up to age 60 in those with stable advanced fibrosis.•Compared with no surveillance, surveillance detected 86 additional HCCs in ‘very early’/early stage per 1,000 patients with cirrhosis.
Depending on personal and hereditary factors, each woman has a different risk of developing breast cancer, one of the leading causes of death for women. For women with a high-risk of breast cancer, ...their risk can be reduced by two main therapeutic approaches: 1) preventive treatments such as hormonal therapies (i.e., tamoxifen, raloxifene, exemestane); or 2) a risk reduction surgery (i.e., mastectomy). Existing national clinical guidelines either fail to incorporate or have limited use of the personal risk of developing breast cancer in their proposed risk reduction strategies. As a result, they do not provide enough resolution on the benefit-risk trade-off of an intervention policy as personal risk changes. In addressing this problem, we develop a discrete-time, finite-horizon Markov decision process (MDP) model with the objective of maximizing the patient’s total expected quality-adjusted life years. We find several useful insights some of which contradict the existing national breast cancer risk reduction recommendations. For example, we find that mastectomy is the optimal choice for the border-line high-risk women who are between ages 22 and 38. Additionally, in contrast to the National Comprehensive Cancer Network recommendations, we find that exemestane is a plausible, in fact, the best, option for high-risk postmenopausal women.
ABSTRACT
Background
Women with Down syndrome have a lower breast cancer risk and significantly lower life expectancies than women without Down syndrome. Therefore, it is not clear whether mammography ...screening strategies used for women without Down syndrome would benefit women with Down syndrome in the same way.
Objective
To determine the benefits and harms of various mammography screening strategies for women with Down syndrome using collaborative simulation modeling.
Design
Two established Cancer Intervention and Surveillance Modeling Network (CISNET) simulation models estimated the benefits and harms of various screening strategies for women with Down syndrome over a lifetime horizon.
Participants
We modeled a hypothetical cohort of US women with Down syndrome who were born in 1970.
Interventions
Annual, biennial, triennial, and one-time digital mammography screenings during the ages 40–74.
Main Measures
The models estimated numbers of mammograms, false-positives, benign biopsies, breast cancer deaths prevented, and life-years gained per 1000 screened women when compared with no screening.
Key Results
In average-risk women 50–74, biennial screening incurred 122 mammograms, 10 false-positive mammograms, and 1.4 benign biopsies per one life-year gained compared with no screening. In women with Down syndrome, the same screening strategy incurred 2752 mammograms, 242 false-positive mammograms, and 34 benign biopsies per one life-year gained compared with no screening. The harm/benefit ratio varied for other screening strategies, and was most favorable for one-time screening at age 50, which incurred 1629 mammograms, 144 false-positive mammograms, and 20 benign biopsies per one life-year gained compared with no screening.
Conclusions
The harm/benefit ratios for various mammography screening strategies in women with Down syndrome are not as favorable as those for average-risk women. The benefit of screening mammography for women with Down syndrome is less pronounced due to lower breast cancer risk and shorter life expectancy.
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