Set Of Robust Controllers Research Articles

A quasi-experimental study of the impact of college-run science, technology, engineering, and mathematics (STEM) career days on American students’ STEM career aspirations

ABSTRACT This quasi-experimental study examined the impact of participation in college-run STEM career days on American high school students’ STEM career aspirations. Data were collected from a nationwide retrospective cohort survey of 15,847 U.S. college students who provided information about their experiences during high school. Accounting for self-selection effects and a robust set of controls, results showed that students who participated in a college-run STEM career day during high school had 1.3 times the odds of expressing STEM career aspirations compared with a control group. We found that STEM career days were equally effective in promoting American students’ STEM career aspirations across background characteristics, levels of academic preparation, and prior STEM interest. Results suggest that policymakers and educators should seriously consider implementing STEM career days for high school students as an evidence-based strategy to effectively increase STEM career interest.

Optimization of Robust LMI-Control Systems for Unstable Vertical Plasma Position in D-Shaped Tokamak

The paper is devoted to the synthesis, comparison, and optimization of robust LMI-control systems for the vertical plasma position in a D-shaped tokamak, specifically the T-15MD tokamak (Kurchatov Institute, Moscow, Russia). The novelty of this work is to find out the possibilities of LMI robust control systems, according to the criteria of the robust stability radius and control power peak at the rejection of a minor disruption type disturbance and a reference step signal using a unique unstable first-order plasma model. The plant under control consists of the connected in series plasma model with additive disturbance containing plant uncertainties, horizontal field coil (HFC), and actuator model as a multiphase rectifier. A set of robust controllers was designed by Linear Matrix Inequalities (LMI) method with pole placement in the LMI regions, state H2/H∞ performance, and output signal performance. The LMI theorems of the paper are directed to design the robust controllers and study the systems with the aim of eliminating the gap between theory and practice. The main achievement of this work consists in the optimization of robust control systems of the unstable plant with uncertain disturbance on the set of LMI synthesis approaches. The control systems have original quality criteria, such as control power and robust stability radius. The best control system on the basis of two criteria, namely, Dα,r,ϑ control system provides stabilization of the vertical plasma position on the real-time digital control testbed.

Robust fuzzy gain scheduling power control of a generation IV nuclear reactor

Gen-IV nuclear reactors are deemed to actively participate in the load following operations in order to meet the ever increasing energy demands. Robust fuzzy gain scheduling is proposed in this work as an advanced and efficient control strategy for the power cycling of the BREST design of lead cooled fast reactors (LFR). To this end, a reasonably accurate coupled thermo-neutronic simulator is developed at first. System identification techniques are employed thereafter to extract a multi-model set at various operating levels relying on the data obtained from this simulator. Uncertainties incurred as a result of the statistically based identification schemes are moreover accounted for using a narrow band (99%) confidence level for the determined model parameters. A set of robust controllers are contrived through a mixed sensitivity analysis framework and are blended afterwards by way of a fuzzy inference mechanism to appropriately schedule this regulation practice with the reactor power level. Certain load following scenarios are finally examined wherein the closed loop system exhibits an efficient and quite feasible control attempt.

The Impact of Participating in College-Run STEM Clubs and Programs on Students’ STEM Career Aspirations

Background: The United States continues to invest considerable resources into developing the next generation of science, technology, engineering, and mathematics (STEM) talent. Efforts to shore up interest in pursuing STEM careers span decades and have increasingly focused on boosting interest among diverse student populations. Policymakers have called for engaging students in a greater STEM ecology of support that extends beyond the traditional classroom environment to increase student STEM career interest. Yet, few robust studies exist exploring the efficacy of many programmatic efforts and initiatives outside the regular curriculum intended to foster STEM interest. To maximize STEM education investments, promote wise policies, and help achieve the aim of creating STEM learning ecosystems that benefit diverse student populations and meet the nation’s STEM goals, it is crucial to examine the effectiveness of these kinds of STEM education initiatives in promoting STEM career aspirations. Purpose: The purpose of this quasi-experimental study was to examine the impact of one popular, yet understudied, STEM education initiative on students’ STEM career aspirations: participation in a university- or college-run STEM club or program activity (CPA) during high school. Specifically, we studied whether participation in a college-run STEM CPA at a postsecondary institution during high school was related to college-going students’ STEM career aspirations, and we examined whether that relationship differed depending on student characteristics and prior STEM interests. Research Design: We conducted a quasi-experimental investigation to explore the impact of participation in university- or college-run STEM CPAs on college-going students’ STEM career aspirations. We administered a retrospective cohort survey to students at 27 colleges and universities nationwide resulting in a sample of 15,847 respondents. An inverse probability of treatment weighted logistic regression model with a robust set of controls was computed to estimate the odds of expressing STEM career aspirations among those who participated in college-run STEM CPAs compared with the odds expressed among students who did not participate. Our weighting accounted for self-selection effects. Results: Quasi-experimental modeling results indicated that participation in university- or college-run STEM CPAs had a significant impact on the odds that college-going students would express STEM career aspirations relative to students who did not participate. The odds of expressing interest in a STEM career among participants in STEM CPAs were 1.49 times those of the control group. Robustness checks confirmed our results. The result held true for students whether or not they expressed interest in STEM careers prior to participation in STEM CPAs, and it held true across a diverse range of student characteristics (e.g., race, parental education, gender, standardized test scores, and family/school encouragement). Conclusions: Results suggest that university- and college-run STEM CPAs play an important role in the STEM education ecology, serving the national goal of expanding the pool of college-going students who aspire to STEM careers. Moreover, results showed that participation in university- and college-run STEM CPAs during high school is equally effective across diverse student characteristics. Policymakers, educators, and those charged with making investment decisions in STEM education should seriously consider university- and college-run STEM CPAs as a promising vehicle to promote diverse students’ STEM career aspirations in the broader STEM learning ecosystem and as an important complement to other STEM learning environments.

Challenges to the economic integration of Afghan refugees in the U.S.

ABSTRACT Informed by a modified segmented assimilation theory, we use 5% Census and American Community Survey data to examine the economic integration of Afghan refugees resettled in the U.S. First-wave Afghan refugees have made significant gains in income and employment, while their poverty rates and reliance on government assistance decreased dramatically. However, the most recent wave of Afghan refugees is not doing as well as the first at comparable points in time. Analysis of ACS data from 2006–2015 finds that, with controls, Afghan refugees’ earned incomes are the lowest of seven refugee/immigrant comparison groups. Given the robust set of controls, we hypothesise that anti-Muslim discrimination is an important unmeasured explanatory factor and suggest where to focus future research on this topic. Afghans’ lower incomes are substantially explained by lower employment levels, especially among less educated Afghan women and highly educated Afghan women and men. Evidence suggests that these patterns are influenced by distance between Afghan and U.S. gender orders, greater physical and mental disability from exposure to traumas, and the limited internal social capital of this small refugee group from a poor country.

Don’t Shoot! The Impact of Historical African American Protest on Police Killings of Civilians

There is a long-standing history of protests in response to police killings of African American citizens. However, it remains a largely unanswered question as to whether these protest events have had any impact on subsequent police killings of African American civilians. To answer this question, we turn to the over 700 racial uprisings that occurred in the 1960s and early 1970s that were largely triggered by negative and often violent interactions between the African American community and police. To determine the impact of racial uprisings on police killings of civilians, we conduct an event-study analysis with a robust set of controls. We employ data on civilian deaths by legal intervention by race, county-level uprising occurrence, and county demographic characteristics. We take advantage of variation in the location and timing of a county’s first uprising to determine the impact of uprisings on police killings of civilians. Our identification strategy relies on pre-existing trends in deaths by legal intervention being uncorrelated with the date of the first uprising in a county. The results show that counties saw a marked increase in both non-white and white deaths due to legal intervention in the years immediately following an uprising. This initial increase is substantially larger for non-whites relative to white civilians. Deaths due to legal intervention for non-white and white civilians diverge over the medium-to-long run. Non-white deaths resulting from legal intervention remain elevated after nearly a decade while deaths of whites revert to their pre-existing trend after a handful of years. Additional analysis regarding the impact of uprisings on policing shows that total crime and police employment do not change in a significant manner over the long run, however, officers are more likely to be killed or injured on duty. The results clearly show that historical protest resulted in an increase in civilian deaths by legal intervention regardless of race in the short-run and a seemingly permanent increase in killings of non-white over the medium-to-long run. These results paint a depressing picture in which uprisings represent a structural change in police-civilian relations, adversely affecting white civilians in the short-run and non-white civilians in the short and long-run.

Estimating the Relationship Between Preschool Attendance and Kindergarten Science Achievement: Implications for Early Science Achievement Gaps

Recent evidence demonstrates that disparities by race/ethnicity and socioeconomic status in science achievement are present in the earliest grades of school. Preschool represents one potential policy solution; however, little research has explored the relationship between preschool attendance and science outcomes. This study examines whether preschool participation may improve science outcomes overall and reduce science achievement gaps by race/ethnicity, gender, and socioeconomic status. Using data from the Early Childhood Longitudinal Study of 2011, this study uses school and classroom fixed effects models with a robust set of controls to estimate the relationship between preschool attendance and early science outcomes. Results suggest that attending preschool is predictive of higher teacher-rated science ability in the fall of kindergarten but that preschool is not predictive of higher science achievement in the spring of kindergarten. The relationship is not found to consistently differ by student race, socioeconomic status, or gender, though descriptive results demonstrate that subgroups have different patterns of preschool attendance. Implications for policy and practice are discussed.

How Financial Literacy, Federal Aid Knowledge, and Credit Market Experience Predict Loan Aversion for Education

Many students are averse to taking out loans to pay for education—a phenomenon that is commonly discussed but rarely systematically analyzed. This study explores the relationship between student loan aversion and individual financial characteristics. In this analysis, we rely on a unique dataset of survey responses from more than 5,000 high school seniors, community college students who did and did not borrow for higher education, and adults without a college degree. Regression analyses, using a robust set of controls and institutional fixed effects, show that higher financial literacy and higher knowledge of federal student loans are related to lower loan aversion for education. The magnitude of these effects is large, as much as a 30 to 50 percent reduction in loan aversion in some samples. There is also evidence that prior experience with payday lending is related to increased loan aversion for community college students who did not borrow for college.

"Opt Out" and Access to Anesthesia Care for Elective and Urgent Surgeries among U.S. Medicare Beneficiaries.

In 2001, the Centers for Medicare and Medicaid Services issued a rule allowing U.S. states to "opt out" of the regulations requiring physician supervision of nurse anesthetists in an effort to increase access to anesthesia care. Whether "opt out" has successfully achieved this goal remains unknown. Using Medicare administrative claims data, we examined whether "opt out" reduced the distance traveled by patients, a common measure of access, for patients undergoing total knee arthroplasty, total hip arthroplasty, cataract surgery, colonoscopy/sigmoidoscopy, esophagogastroduodenoscopy, appendectomy, or hip fracture repair. In addition, we examined whether "opt out" was associated with an increase in the use of anesthesia care for cataract surgery, colonoscopy/sigmoidoscopy, or esophagogastroduodenoscopy. Our analysis used a difference-in-differences approach with a robust set of controls to minimize confounding. "Opt out" did not reduce the percentage of patients who traveled outside of their home zip code except in the case of total hip arthroplasty (2.2% point reduction; P = 0.007). For patients travelling outside of their zip code, "opt out" had no significant effect on the distance traveled among any of the procedures we examined, with point estimates ranging from a 7.9-km decrease for appendectomy (95% CI, -19 to 3.4; P = 0.173) to a 1.6-km increase (95% CI, -5.1 to 8.2; P = 0.641) for total hip arthroplasty. There was also no significant effect on the use of anesthesia for esophagogastroduodenoscopy, appendectomy, or cataract surgery. "Opt out" was associated with little or no increased access to anesthesia care for several common procedures.

PHP72 - DOWNSTREAM MEDICAL COST OFFSETS IN MEDICARE FROM PRESCRIPTION DRUG USE IN EMPLOYER-SPONSORED INSURANCE

To estimate the impact of prescription drug utilization during pre-Medicare coverage years under employer-sponsored insurance on later medical spending in Medicare. Individuals found in both the Commercial and Medicare Supplemental Marketscan® files were selected. Study subjects were required to be 64 years old or younger at baseline and continuously eligible throughout the entire 5-year study period 2008-2012. The resulting panel dataset was comprised of 133,412 individuals who aged into Medicare, each with 5 annual observations. Conducted was an econometric analysis of the impact of aggregate prescription drug utilization on total, inpatient, and outpatient medical costs. Individual fixed effects Poisson models of these cost measures were estimated as a function of 1-, 2-, and 3-year lagged values of prescription drug utilization—measured as the number of days’ supply-adjusted fills. All models also included a robust set of controls. Among individuals covered by Medicare (ages 65-68), a 1 percent increase in prescription drug utilization 1 year prior was associated with a 0.363 percent decrease in total medical costs. Notably, medication use 2 years prior prompted a 0.123 percent decrease in total medical costs, and these offsets still persisted after 3 years (0.059 percent decrease). Effects were more pronounced for inpatient relative to outpatient costs. The pattern of declining, yet persistent, medical cost offsets for at least 3 years emerged for all three measures of medical costs. Pharmaceutical use is expected to lower spending on other medical services. The duration of these offsets may span multiple payers. Retirees entering Medicare who are healthier due to prior medication use are less costly. Indeed, the Medicare program is exposed to the consequences of prescription drug use 3 years prior to coverage. The evaluation of policies that could alter medication use among the near retired (such as the “Cadillac Tax”) should consider this important finding.

Design of a switched robust control scheme for drug delivery in blood pressure regulation

A control algorithm based on switching robust controllers is presented for a Linear Parameter Varying (LPV) time-delay system modeling automatic infusion of vasodilator drug to regulate postsurgical hypertension. The system is scheduled along a measurable signal trajectory. The prospective controllers are robustly designed at various operating points forming a finite set of robust controllers and then a hysteresis switching is performed between neighboring robust controllers for a larger operating range of the LPV system. The stability of the switching LPV system for the entire operating range is ensured by providing a sufficient condition in terms of bound on the scheduling signal variation using the concept of dwell time. Simulation results are provided to verify the performance of the designed control scheme.

Switching robust controllers for automatic regulation of postoperative hypertension using vasodilator drug infusion rate

This paper proposes a new switching robust control algorithm, employing a stable hysteresis switching between neighboring controllers within a set of robust controllers designed for five different operating ranges of the system, for regulating the mean arterial blood pressure (MAP) in postsurgical scenario using infusion of vasodilator drug-Sodium Nitroprusside (SNP). Postoperative hypertension is very critical in patients with cardiac disorder and if it is left untreated, it may lead to adverse consequences. Since the sensitivity to the drug, injection delay and drug fraction recirculating vary among individuals, a robust control algorithm becomes an attractive candidate for regulating MAP in the presence of such parameter uncertainties. In addition, the sensitivity to the drug may even vary with time within the same patient, therefore, it is also treated in the model as time-varying value of the parameter. A stable hysteresis switching between neighboring robust controllers is proposed for larger operating range of the system due to considerably large uncertainty range of the patients’ sensitivity to the drug.

Is Bus Versus Rail Investment a Zero-Sum Game?

Problem, research strategy, and findings: Bus and rail transit are often assumed to compete for the same pot of transit dollars, with one, therefore, substituting for another. Advocates for each mode lobby accordingly. However, this article presents evidence that spending on the two transit services may be unrelated or even complementary, based on a multivariate analysis of transit spending in the 55 largest U.S. metropolitan statistical areas from 1992 through 2006. In all the estimated models, using a robust set of controls and statistical strategies, bus spending is positively associated with rail spending; that is, spending on the two modes rise or fall together. This supports the argument that, over the long term, rail investment does not come at the expense of bus investment; the existence of a tradeoff between the modes in investment spending is not supported. Takeaway for practice: Many conventional transportation policy debates presume bus and rail spending is a zero-sum game, with investment in rail transit, therefore, coming at the cost of lower bus investment. By contrast, this analysis suggests an alternative scenario: Spending on one transit mode is, in general, positively associated with spending on other modes. This may occur because of needed interaction between the modes, as with feeder bus service, through the fostering of transit-supportive land uses or through broadening of transit coalitions into more affluent sectors of society. Assertions that rail investment inherently requires cutbacks in buses stems from a rhetorical misuse of the opportunity-cost concept. Research support: Environmental Protection Agency project RD-83334901-0.

Agricultural policy, migration, and malaria in the United States in the 1930s

The Agricultural Adjustment Act (AAA) was associated with a population shift in the United States in the 1930s. Evaluating the relationship between the AAA and the incidence of malaria can therefore offer important lessons regarding the broader consequences of demographic changes. Using a quasi-first difference model and a robust set of controls, we find a negative association between AAA expenditures and malaria death rates at the county level. Further, we find that the AAA was associated with increased out-migration of low-income groups from counties with high-risk malaria ecologies. These results suggest that the AAA-induced migration played an important role in the reduction of malaria.

GA-optimized fuzzy logic control of a large-scale building for seismic loads

Validation of fuzzy logic controllers that are optimized by a genetic algorithm is pursued in this study. Fuzzy logic controllers are designed to manage two 20 kN magnetorheological dampers for mitigation of seismic loads applied to a 9 m tall, three-story steel frame benchmark building. In order to develop a set of robust controllers that are sensitive to a variety of excitations, a genetic algorithm that considers multiple objectives concurrently is proposed. Four optimization objectives have been selected which necessitates employment of a controlled elitist genetic algorithm. Optimal controllers are identified and validated through numerical simulation and full-scale experimental shake table tests for a variety of seismic excitations. Furthermore, a modified version of the same genetic algorithm is used to identify a state-space representation of the benchmark structure. Results show that optimized fuzzy logic controllers are robust and effective in reduction of both displacement and acceleration responses for both near- and far-field seismic events.

Robust Synergetic Design of Structural Dynamic Engine Out Controllers in Parameter Space

Engineoutisadesigncriterionforalargetransportaircraftfromtheviewpointofe ightsafety,handlingqualities, and structural dynamics. A structural dynamic engine out controller covers these aspects, especially the reduction of the loads level at the vertical tail. It is designed by a new robust synergetic design method, using Ackermann’ s parameter space method (Ackermann, J., Robust Control , Springer-Verlag, Berlin, 1993, Chap. 11, pp. 307 ‐353). It allows the combination of different controller structures, each of which satise es specie c requirements. This combination of controllers robustly satise es all of the multidisciplinary requirements. Here, three controllers are combined: a standard lateral controller and a proportional ‐integral controller for safety and handling qualities and a structural dynamiccontroller, which robustly decouplestheshear force atthevertical tail from the yaw rate. This unilateral decoupling controller achieves an early efe cient yawing moment compensation before the pilot. The controller consists of a feedback of the yaw rate to the rudder. Thereby, critical e ight and load conditions due to a delayed overreaction of the pilot are prevented. The three controllers are characterized by eigenvalue regions for the closed-loop system. These C regions offer compromises between the cone icts in design goals. Using the parameter space method, this approach yields a set of robust controllers. A controller is selected and simulated on a nonlinear model.

Characterization of robust controllers

This paper presents a procedure for designing a robust controller which is able to stabilize a multivariable system with interval uncertainties in the system parameters. The uncertain parameters are assumed to lie within known intervals. The fundamental idea behind the procedure is to characterize the set of robust controllers as a convex set by the new matrix inequalities result. A suitable controller can then be chosen by means of an optimization algorithm. The controller thus chosen will be able to ensure that the closed-loop matrix lies within “desired” intervals for all the prescribed interval uncertainties in the system parameters.