Maximum Dwell Time Research Articles

Imbalanced temporal states of cortical blood-oxygen-level-dependent signal variability during rest in episodic migraine

BackgroundMigraine has been associated with functional brain changes including altered connectivity and activity both during and between headache attacks. Recent studies established that the variability of the blood-oxygen-level-dependent (BOLD) signal is an important attribute of brain activity, which has so far been understudied in migraine. In this study, we investigate how time-varying measures of BOLD variability change interictally in episodic migraine patients.MethodsTwo independent resting state functional MRI datasets acquired on 3T (discovery cohort) and 1.5T MRI scanners (replication cohort) including 99 episodic migraine patients (n3T = 42, n1.5T=57) and 78 healthy controls (n3T = 46, n1.5T=32) were analyzed in this cross-sectional study. A framework using time-varying measures of BOLD variability was applied to derive BOLD variability states. Descriptors of BOLD variability states such as dwell time and fractional occupancy were calculated, then compared between migraine patients and healthy controls using Mann-Whitney U-tests. Spearman’s rank correlation was calculated to test associations with clinical parameters.ResultsResting-state activity was characterized by states of high and low BOLD signal variability. Migraine patients in the discovery cohort spent more time in the low variability state (mean dwell time: p = 0.014, median dwell time: p = 0.022, maximum dwell time: p = 0.013, fractional occupancy: p = 0.013) and less time in the high variability state (mean dwell time: p = 0.021, median dwell time: p = 0.021, maximum dwell time: p = 0.025, fractional occupancy: p = 0.013). Higher uptime of the low variability state was associated with greater disability as measured by MIDAS scores (maximum dwell time: R = 0.45, p = 0.007; fractional occupancy: R = 0.36, p = 0.035). Similar results were observed in the replication cohort.ConclusionEpisodic migraine patients spend more time in a state of low BOLD variability during rest in headache-free periods, which is associated with greater disability. BOLD variability states show potential as a replicable functional imaging marker in episodic migraine.

Microstructure and magnetic properties of Nanomet compacted by spark plasma sintering

Nanocrystalline soft magnetic materials with high saturation polarization and low losses have a high potential in motor applications. Thus, toroidal cores were compacted by spark plasma sintering of flakes of the melt-spun Nanomet alloy Fe-Si-B-P-Cu. The thermal properties of the ribbons were analyzed by DSC to determine the crystallization temperatures. The influence of the initial powder and of the compacting parameters such as maximum temperature and dwell time on the density and the magnetic properties in DC and AC were investigated. An optimum temperature range of approximately 50 K was determined for good soft magnetic properties. An effect of the dwell time was not recognized in the observed range. By compacting flakes of different sizes, the maximum permeability can be adjusted in the range of up to 7000. The microstructure was observed by means of XRD and TEM in order to confirm the amorphous and nanocrystalline state, respectively. Using the Lorenz mode of the TEM, it was possible to calculate the magnetic domain wall width for the samples and compare the resulting calculated magnetic properties with the experiments.

The Allium Ureteral Stent for the Treatment of Ureteral Complications Following Renal Transplantation-A Single-Center, Single-Surgeon Series.

Ureteral complications such as urinary leak, ureteral necrosis or ureteral stenosis are common complications after renal transplantation with major short- and long-term issues, including graft impairment and graft loss. At present, there is no agreement on the optimal management of ureteral complications. The aim of the current study was to evaluate the safety and efficacy of the self-expanding, large-caliber Allium ureteral stent in patients with ureteral complications following renal transplantation. In this retrospective study, the electronic database of Charité University Hospital was screened for patients receiving the self-expandable Allium ureteral stent in the transplant ureter after kidney transplantation between January 2016 and March 2022. Descriptive statistics were used to describe the outcomes. There were six men and four women with a median age of 61 years (interquartile range, 55 to 68 years). Nine out of 10 patients had ureteric stenosis, which was diagnosed at a median of two years (interquartile range 10 months to 9 years) following renal transplantation. The median operating time was 49 min (interquartile range, 30 to 60 min). Endoscopic Allium stent placement was successful in all patients with ureteric stenosis. The median length of stay in the hospital was four days (interquartile range 2 to 7 days). Only one patient (#5) had a postoperative grade IIIb Clavien-Dindo complication. Patients had follow-ups every 3 months with ultrasound and serum creatinine. Dislocation of the Allium stent was seen in four patients; all occurred within three months. Ultimately, three patients required ureteric re-implantation, two of which had early dislocation of the stent. Six patients are managed with a permanent Allium stent. The median dwell time was 11 months (interquartile range 3 to 20 months) and maximum dwell time was 23 months. The overall success rate was 60% (6 out of 10). According to our data, the Allium stent represents a safe and minimally invasive option with a success rate of 60%. It might, therefore, represent an alternative to DJ stents, nephrostomies or immediate re-implantation. As all dislocations occurred within three months, frequent early postoperative follow-up is required.

Infectious Risks Related to Umbilical Venous Catheter Dwell Time and Its Replacement in Newborns: A Narrative Review of Current Evidence.

The use of umbilical venous catheters (UVCs) has become the standard of care in the neonatal intensive care unit (NICU) to administer fluids, medications and parenteral nutrition. However, it is well known that UVCs can lead to some serious complications, both mechanical and infective, including CLABSI (Central Line-Associated Bloodstream Infections). Most authors recommend removing UVC within a maximum of 14 days from its placement. However, the last Infusion Therapy Standards of Practice (INS) guidelines recommends limiting the UVC dwell time to 7 to 10 days, to reduce risks of infectious and thrombotic complications. These guidelines also suggest as an infection prevention strategy to remove UVC after 4 days, followed by the insertion of a PICC if a central line is still needed. Nevertheless, the maximum UVC dwell time to reduce the risk of CLABSI is still controversial, as well as the time of its replacement with a PICC. In this study we reviewed a total of 177 articles, found by using the PubMed database with the following search strings: "UVC AND neonates", "(neonate* OR newborn*) AND (UVC OR central catheter*) AND (infection*)". We also analyze the INS guidelines to provide the reader an updated overview on this topic. The purpose of this review is to give updated information on CVCs infectious risks by examining the literature in this field. These data could help clinicians in deciding the best time to remove or to replace the UVC with a PICC, to reduce CLABSIs risk. Despite the lack of strong evidence, the risk of CLABSI seems to be minimized when UVC is removed/replaced within 7 days from insertion and this indication is emerging from more recent and larger studies.

Memory-Based Event-Triggered Output Regulation for Networked Switched Systems With Unstable Switching Dynamics.

This article studies an event-triggered asynchronous output regulation problem (EAORP) for networked switched systems (NSSs) with unstable switching dynamics (USDs) including all modes unstable and partial switching instants destabilization, which means that the Lyapunov function increases both on the activation intervals of all subsystems and at some switching instants. First, a memory-based mode-compared event-triggered mechanism for switched systems is proposed to effectively shorten asynchronous intervals, which employs historical sampled outputs and compares the mode of the current sampled instant and the adjacent sampled instant. Then, the maximum average dwell time for a novel switching signal is derived with a constraint on the ratio of total destabilizing switchings to total stabilizing switchings, which relaxes the requirement of the regular arrangement of destabilizing and stabilizing switchings. Moreover, with the help of different coordinate transformations in the EAORP, the discretized Lyapunov functions are no longer needed when synthesizing the NSSs with USDs, and the asynchronous switching situation is also discussed. Afterward, by designing a dynamic output feedback controller, sufficient conditions are given to solve the EAORP for NSSs with USDs subject to network-induced delays, packet disorders, and packet losses. Finally, the effectiveness of the proposed methods is verified via a switched RLC circuit.

PO-718-06 MAXIMUM OUTPUT PACING: IMPROVING POSTERIOR LEFT ATRIAL EPICARDIAL ISOLATION

Benefits of posterior wall isolation for persistent AF are unclear. Epicardial posterior wall connection may persist despite achieving standardized endocardial isolation ablation goals. To determine how often epicardial posterior wall connection remains when traditionally defined endocardial isolation is present, where and how does epicardial connection persist and should posterior wall isolation be redefined. Ablation was performed in 34 AF patients with THERMOCOOL SMARTTOUCH SF catheters at 50W, ablation index goal of 350 on the posterior wall, 7 second maximum dwell time. To avoid heat stacking, consecutive lesions were separated by >/=1.5cm. Three horizontal lines at roof, carinal and inferior vein levels were created with confirmed lack of pace capture 10ma/2ms on the lines. Pacing was then performed at 10ma/2ms within the posterior wall and exit maps created with ablation at the earliest exit. If posterior wall capture remained after ablation at the earliest exit, the posterior wall was ablated until no capture remained. This was repeated at 20ma/4ms, then 20ma/10ms. 14/34 patients (41%) had residual pace capture within the posterior wall at 10ma/2ms. After ablation achieved lack of 10ma/2ms capture, 27/34 (79.41%) had recurrent capture at 20ma/4ms. After ablation to lack of capture at 20ma/4ms, 28/34 (82.4%) had residual 20ma/10ms capture. Mean number of additional lesions to achieve posterior wall isolation beyond lack of 10ma/2ms capture was 14.5, 33% greater than the number of lesions to achieve traditional isolation. Compared to 10ma/2ms, areas of residual capture were significantly more frequent in all (p<.05) but one quadrant with 20ma/10ms (figure).Despite using exit mapping with ablation at the earliest exit, connection persisted in 1/14 10ma/2ms pace maps (7.14%), 23/27 20ma/4ms pace maps (85.2%) and 24/28 20ma/10ms pace maps (85.7%) (p<0.01). Traditional endocardial ablation techniques fail to identify epicardial posterior wall connection. Higher output pacing reveals residual epicardial connection at multiple locations in a given patient. Higher output pacing (20ma/10ms) can guide endocardial posterior wall ablation to improve transmural posterior wall isolation.

Influence of Electrolyte Concentration on Single-Molecule Sensing of Perfluorocarboxylic Acids.

Perfluorocarboxylic acids (PFCAs) are an emerging class of persistent organic pollutants. During the fabrication process, it is unavoidable to form PFCA homologs or isomers which exhibit distinct occurrence, bioaccumulation, and toxicity. The precision measurement of PFCAs is therefore of significant importance. However, the existing characterization techniques, such as LC-MS/MS, cannot fully meet the requirement of isomer-specific analysis, largely due to the lack of authentic standards. Single-molecule sensors (SMSs) based on nanopore electrochemistry may be a feasible solution for PFCAs determination, thanks to their ultra-high spatiotemporal resolutions. Hence, as a first step, this work was to elucidate the influence of electrolyte concentration on the four most critical indicators of nanopore measurements, and furthermore, performance of nanopore SMSs. More specifically, three of the most representative short-chain PFCAs, perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA) and perfluoroheptanoic acid (PFHpA), were adopted as the target analytes, aerolysin nanopore was employed as the sensing interface, and 2, 3 and 4 M KCl solutions were used as electrolytes. It was found that, when the concentration of KCl solution increased from 2 to 4 M, the conductance of aerolysin nanopore increased almost linearly at a rate of 0.5 nS per molar KCl within the whole voltage range, the current blockade of PFPeA at −50 mV increased from 61.74 to 66.57% owing to the enhanced steric exclusion effect, the maximum dwell time was more than doubled from 14.5 to 31.5 ms, and the barrier limited capture rate increased by 8.3 times from 0.46 to 3.85 Hz. As a result, when using 4 M KCl as the electrolyte, over 90% of the PFPeA, PFHxA and PFHpA were accurately identified from a mixed sample, and the calculated limit of detection of PFPeA reached 320 nM, more than 24 times lower than in 2 M KCl. It was thus clear that tuning the electrolyte concentration was a simple but very effective approach to improve the performance of nanopore SMSs for PFCAs determination.

Novel prestressing applications in civil engineering structures enabled by Fe[sbnd]Mn[sbnd]Al[sbnd]Ni shape memory alloys

The present study reports on the feasibility of using Fe-Mn-Al-Ni shape memory alloys as prestressing elements in civil engineering. Polycrystalline Fe-Mn-Al-Ni specimens were prestrained and subsequently heated up under constant strain in order to evaluate the prestressing potential of the material. Due to the formation of precipitates as a function of both, maximum heating temperature and dwell time, the prestress level of the material can be tailored. Moreover, in oligocrystalline specimens prestress losses, e.g., due to shrinkage and creep of concrete, can be impeded by changing the functional properties from shape memory effect to superelasticity. Based on the results presented it can be concluded that the Fe-Mn-Al-Ni system is a promising alternative to conventional shape memory alloys used for prestressing applications eventually enabling novel and innovative applications in numerous civil engineering structures by utilizing the well-defined evolution of precipitates during activation.

Minimising the travel time on congested urban rail lines with a dynamic bi-modelling of trains and users

User assignment models in transit networks are relevant for the planning of new lines but less relevant for management. Other types of models are used for management, which is very efficient for the simulation of supply but less efficient for the simulation of users, who nevertheless influence train traffic on urban railway lines. This paper proposes to use a combined train and passenger simulation model on a railway line to propose line management solutions in order to minimise the passenger travel time. An application of this method on line 13 of the Paris subway network, shows how the relationship between frequency and dwell-time impact the railway traffic. Precisely, the current frequency of the line associated with a maximum dwell time of the 40s minimise the travel time. These optimal time conditions correspond to significant congestion in the line’s train traffic.

Stability Analysis of Multi-Agent Tracking Systems with Quasi-Cyclic Switching Topologies

In this paper, the stability problem of a class of multi-agent tracking systems with quasi-cyclic switching topologies is investigated. The existing results of systems with switching topologies are usually achieved based on the assumption that the piecewise constant communication topologies are connected and the switchings are cyclic. The communication topologies are possible to be unconnected and it is difficult to guarantee the topologies switch circularly. The piecewise unconnected topology makes the interactive multi-agent tracking system to be an unstable subsystem over this time interval. In order to relax the assumption constraint, a quasi-cyclic method is proposed, which allows the topologies of multi-agent systems to switch in a less conservative way. Moreover, the stability of the tracking system with the existence of unstable subsystems is analyzed based on switched control theory. It is obtained that the convergence rate is affected by the maximum dwell time of unstable subsystems. Finally, a numerical example is provided to demonstrate the effectiveness of the theoretical results.

State of the Art of Lead-Free Solder Joint Reliability

AbstractThe state of the art of lead-free solder joint reliability is investigated in this study. Emphasis is placed on the design for reliability (DFR) and reliability testing and data analysis. For DFR: (a) the Norton power creep constitutive equations and examples for Au20Sn, Sn58Bi, Sn3.8Ag0.7Cu, and Sn3.8Ag0.7Cu0.03Ce, (b) the Wises two power creep constitutive equations and examples for Sn3.5Ag and Sn4Ag0.5Cu, (c) the Garofalo hyperbolic sine creep constitutive equations and examples for Sn3.5Ag, Sn3Ag0.5Cu, Sn3.9Ag0.6Cu, Sn3.8Ag0.7Cu, Sn3.5Ag0.5Cu, and Sn3.5Ag0.75Cu, Sn4Ag0.5Cu, Sn(3.5-3.9)Ag(0.5-0.8)Cu, 100In, Sn52In, Sn3.8Ag0.7Cu0.03Ce, and Au20Sn, and (d) the Anand viscoplasticity constitutive equations and examples for Sn3.5Ag, Sn3Ag0.5Cu, Sn3.8Ag0.7Cu, Sn3.8Ag0.7CuCe, Sn3.8Ag0.7CuAl, Au20Sn, Sn3.5Ag with temperature and strain rate-dependent parameters, and Sn1Ag0.5Cu, Sn2Ag0.5Cu, Sn3Ag0.5Cu, and Sn4Ag0.5Cu after extreme aging will be discussed. For reliability testing and data analysis: (a) the Weibull and lognormal life distributions for lead-free solder joints under thermal-cycling and drop tests, (b) the true Weibull slope, true characteristic life, and true mean life, and (c) the linear acceleration factors for various lead-free solder alloys based on: (i) frequency and maximum temperature, (ii) dwell time and maximum temperature, and (iii) frequency and mean temperature will be presented. Some recommendations will also be provided.

Study on the Overload and Dwell-Fatigue Property of Titanium Alloy in Manned Deep Submersible

With the rapid development of ocean technology, the deep-sea manned submersible is regarded as a high-tech equipment for the exploration and exploitation of ocean resources. The safety of manned cabin has a decisive effect on the whole system. Ti-6Al-4V with the superior strength-to-weight ratio and corrosion resistance has been used for the manned cabin. The manned cabin experiences loading spectrum with different maximum stresses and different dwell time during their service life. The load sequence effects on dwell fatigue crack growth behavior of Ti-6Al-4V under different dwell time are investigated experimentally in this paper. The experimental results show that the crack tip plastic zone is enlarged by the dwell time and the overload retardation zone increases with dwell time under the same overload rate. A dwell fatigue crack growth model is proposed by modifying the crack tip plastic zone under the loading history with combinations of the single overload and dwell time factors are included in the modified model. Based on the experimental data, the overload retardation zone and the crack growth rates of Ti-6Al-4V are predicted by the modified model. A reasonable model for the load sequence effect on the dwell fatigue crack growth rates of Ti-6Al-4V is verified.

Indwelling ureteric stents: Patterns of use and nomenclature

ABSTRACT Objectives: To evaluate ureteric stenting practice patterns amongst a range of academic and community urologists, and to examine the nomenclature used to identify an indwelling ureteric stent from both our questionnaire and from a review of the literature. Subjects and methods: A 16-question, peer-reviewed online survey was distributed to members of the Mid-Atlantic American Urological Association. Responses were collected over a 1-month period. Questions included demographics, ureteric stenting practice patterns, and utilization of stenting nomenclature. Inappropriate use of nomenclature was defined as a mismatch between the visually depicted stents and the written description amongst urologists. Trends in ureteric stenting and nomenclature usage were tabulated and analyzed. Results: Of 863 members, 105 (12.2%) responded to the survey. There was a wide variety of practice settings, with the single-specialty group (44.2%) and academic/university (27.9%) being the two most common. Most providers used both cystoscopy and fluoroscopy to place stents (87.5%) as compared to fluoroscopy alone (12.5%). Most urologists (63.5%) removed stents with cystoscopy as compared to using a stent string (36.5%). While about half (51.0%) of the respondents left stents in situ for ≤3 months, many respondents (43.3%) felt comfortable with maximum dwell times of up to 6 months. The most commonly placed stent was the double pigtail stent (80.8%). However, most respondents inappropriately described this stent design as a Double J stent (72.1%). In the recent literature, 80% of articles clearly defined as using double pigtail stents, incorrectly identified their stent as a ‘Double J’. Conclusions: Variations in ureteric stenting practice patterns exist amongst community and academic urologists. Although most urologists utilize double pigtail ureteric stents, the majority inaccurately identified this stent design as a Double J. We propose use of the term ‘indwelling ureteric stent’ (IUS) unless describing any specific stent design.

Analysis of the Container Dwell Time at Container Terminal by Using Simulation Modelling

One of the parameters that affecting efficiency of container terminal is dwell time (DT). The more least the DT the more efficient a container terminal would be. As the government regulations of the Ministry of Transportation that stated in Number PM 25 in 2017 in Article 2 Paragraph 1 explains that the maximum dwell time must not exceed than 3 days. The purpose of this study is to identify the major factor of prolonged DT in a container terminal. The authors used discrete event simulation to model the system inside the container terminal operation by using Arena Simulation software. The Root Cause Analysis (RCA) is being used for the data analysis and finding the root cause. The container handling inside the container terminal data is collected, then the effect container of handling the equipment on dwelling time was testified by creating a model then analyzed. The result of the simulation is that there is a small impact from container handling equipment towards DT. From the Problem Tree framework that created based on the operational data and interviews. It shows that the most DT is contributed by the prolonged time of container stay at container yard .

Robust matrix commutator conditions for stability of switched linear systems under restricted switching

This article treats global uniform exponential stability (GUES) of discrete-time switched linear systems under restricted switching. Given admissible minimum and maximum dwell times, we provide sufficient conditions on the subsystems under which they admit a set of switching signals that obeys the given restrictions on dwell times and preserves stability of the resulting switched system. Our analysis relies on combinatorial arguments applied to matrix commutators. The proposed set of stabilizing switching signals is characterized in terms of duration of activation of Schur stable subsystems and non-consecutive activation of distinct unstable subsystems.

Path Following with Stable and Unstable Modes Subject to Time-Varying Dwell-Time Conditions

Systems are often tasked with operating in modes where state feedback is available intermittently. The analysis of such systems involves analyzing the behavior of individual subsystems and the time that each subsystem is active, i.e., dwell-time conditions. Often, these dwell-time conditions are conservative, potentially limiting the performance of the overall system. In an effort to reduce conservativeness of the dwell-time condition, an adaptive data-driven extremum seeking (ESC) method is used to develop a time-varying dwell-time condition. Specifically, the ESC drives the evolution of the dwell-time condition to a less conservative dwell-time condition while simultaneously ensuring stability of the overall system. Simulations demonstrate a nearly threefold increase in a maximum dwell-time that results in significant changes to the behavior of an agent tasked with following a path outside a feedback region.

Investigation on interface morphology and joint configuration of dissimilar sheet thickness FSSW of marine grade Al alloy

Aim of this study is to investigate the interface morphology and joint configuration of dissimilar thickness aluminium alloy 5052-H32 sheets during friction stir spot welding. The investigation begins with the optimization of two important process parameters, viz. tool rpm and dwell time, from welding of similar thickness sheets. Further, different combinations of sheet thicknesses were welded using the optimized parameters. Effect of altering sheet thickness on the mechanical and structural properties were compared with welds of similar sheet thickness. For similar thickness welds, maximum failure load of 4020 N was noted at minimum tool rotational speed of 450 rpm and maximum dwell time of 8 s. The obtained weld zones revealed the presence of hook which was found to vary in its pattern and location for different combinations of sheet thicknesses. Minimum hardness of 63 HV was obtained in the periphery of the thermo-mechanically affected zone and heat-affected zone. In addition, welds with thinner top sheets showed higher load-bearing capacity and wider bonded area as compared to thicker and equal thickness top sheet welds. The maximum failure load of 7160 N was obtained for 1.5 and 2.5-mm-thick top and bottom sheets, respectively. Moreover, three fracture modes were observed in tensile/shear tests, namely interfacial, circumferential and nugget pullout fracture mode. Samples which failed in circumferential and nugget pullout fracture mode showed better joint strength.

Exercise-based correlates to calcaneal osteogenesis produced by a chronic training intervention.

Thirty workouts on a gravity-independent device (Impulse Training Systems, Newnan GA) evoked significant calcaneal bone mineral content (BMC, +29%) and density (BMD, +33%) gains. High speeds and impact loads were produced per repetition. We examined exercise performance variables from the 30-workout intervention to identify correlates to delta (∆) calcaneal BMC and BMD variance. Workouts included hip extension and seated calf press exercises done with subject's left legs. ∆ values were obtained from the first and 12th workouts for the hip extension movement, and for the first and 24th workouts for the seated calf press exercise. Per exercise the following variables were quantified: peak force (∆PF), peak acceleration (∆PA), impulse (∆I), and dwell times (∆DT). Dwell times are the elapsed time between the end of the eccentric phase, and the start of the next repetition's concentric phase. Pearson Coefficients assessed correlations between performance and criterion variables. With hip extension ∆DT calculated with data from the first and 12th workouts, there were significant correlations with calcaneal ∆BMC (r = -0.64) and ∆BMD (r = -0.63). With seated calf press ∆DT derived as the difference from the first and 24th workouts, there was a significant correlation with calcaneal ∆BMC (r = -0.48), but only a trend (r = -0.45) with ∆BMD as the criterion. No other variables correlated with significant amounts of calcaneal ∆BMC and ∆BMD variance. Negative correlations infer shorter dwell times evoked greater gains. The gravity-independent device warrants continued inquiry to treat and abate calcaneal losses.

Evaluation of the chemical risk of the miners of the transfer station ET2 Zámbiza by heavy metals in the breathable particulate material

Introduction.The chemical risk was determined by heavy metals in the respirable air of the Handmade Environmental Managers, in the Zámbiza urban waste transfer station. Total PTS suspended particles were determined in the working atmosphere of the Managers. ObjectiveTo determine the quality of the breathable air in the work environment of the miners, fixing its objective in the concentration of Nickel, Cadmium, Zinc, Chromium, Barium, Lead. Materials and methodswill be used a high volume sampled, in order to perform a first sweep of metals: Nickel, Cadmium, Zinc, Chromium, Barium, Lead in the work environment. Resultswith respect to the VLA of suspended total particles that is 3 mg / m3, it can be seen that in none of the samplings this value is exceeded. DiscussionIt is important to minimize the duration and intensity of exposures to these metals, establish maximum dwell times at the same place of classification. ConclusionsEPIS individual protection equipment should be the last means to be used for the protection of workers.

A Switched Systems Approach to Path Following With Intermittent State Feedback

Autonomous agents are often tasked with operating in an area where feedback is unavailable. Inspired by such applications, this paper develops a novel switched system-based control method for uncertain nonlinear systems with temporary loss-of-state feedback. To compensate for intermittent feedback, an observer is used while state feedback is available to reduce the estimation error, and a predictor is utilized to propagate the estimates while state feedback is unavailable. Based on the resulting subsystems, maximum and minimum dwell time conditions are developed via a Lyapunov-based switched systems analysis to relax the constraint of maintaining constant feedback. Using the dwell time conditions, a switching trajectory is developed to enter and exit the feedback denied region in a manner that ensures that the overall switched system remains stable. A scheme for designing a switching trajectory with a smooth transition function is provided. Simulation and experimental results are presented to demonstrate the performance of control design.