Observation Interval Research Articles

Estimated Thresholds of Minimum Necessary Adherence for Effective Treatment with Direct Oral Anticoagulants - A Retrospective Cohort Study in Health Insurance Claims Data.

BackgroundAn essential contribution regarding the prevention of thromboembolic events in patients with (non-valvular) atrial fibrillation (AF) is good adherence to direct oral anticoagulants (DOACs). However, it is an open question what “good” adherence means for DOACs or below which threshold non-adherence is clinically relevant for AF patients. Ultimately, such a classification could prevent strokes and associated costs through adjusted treatment regimens or supportive measures.MethodsWe selected 10,092 AF patients from health insurance claims data between 2014 and 2018 who were issued a majority (at least half of the number) of maximum approved strength prescriptions of one of the following DOACs, namely rivaroxaban, apixaban, or dabigatran. Due to the limited sample size, the prescriptions of dabigatran had to be finally excluded for the cut-off analysis. DOAC adherence was calculated as the proportion of days covered (PDC) by dividing the days of theoretical use (days covered) of the drug by the duration in days of the observation interval. PDC cut-off values were derived from stroke risk as a function of continuous PDC values in time-to-event analyses and corresponding dose-response models. The influence of adherence-promoting interventions (targeted and untargeted) on the occurrence of strokes and related costs was then projected, considering intervention costs per patient.ResultsThe population had a mean age of 74.5 years and 50% were female. The median PDC was 0.79 ± 0.28 with a median follow-up time of 1218 days, in which 2% of all DOAC patients had a stroke. The adherence cut-offs for good adherence were identified at 0.78 for rivaroxaban and 0.8 for apixaban. Targeted interventions appeared to be far more cost-effective than untargeted interventions.ConclusionClear adherence cut-offs enable healthcare professionals to identify patients with clinically relevant non-adherence. Interventions based on these cut-offs appear to be a promising means to optimize DOAC treatment.

Improved results on state estimation for switched continuous‐time linear systems

AbstractThis paper investigates the state estimation problem for switched linear systems involving additive disturbance and measurement noise, whose modes need not to be cooperative. Under the assumption that there exist nonsingular matrices that transform the observer error system matrices into Metzler ones, by using multiple Lyapunov functions and average dwell time method, hybrid state observers, which can produce a framer covering all possible state trajectories, are designed in two cases, that is, all the subsystems are stable and some of the subsystems may be unstable. The constructed interval observer for the considered systems are hybrid dynamical systems and the initialized states of the upper and lower observers at each switching instants are coupled, since the transformation matrices for different subsystems are different. Compared with the robust observer design for switched systems with arbitrary switching sequences in the literature, the difficulty consists in proposing new observer design conditions related to the state reset at the switching instants for switched systems under average dwell time scheme. Finally, two examples are given to show the efficiency of the proposed approach.

Feedback delay control of highly nonlinear stochastic functional differential equations with discrete‐time state observations

The purpose of this paper is to give the delay control based on discrete‐time state observations to stabilize highly nonlinear hybrid stochastic functional differential equations (SFDEs). It is considered that time lag generated by the controller in each discrete observation should be different. The new controlled hybrid SFDEs are affected the variable delay caused by the controller, the distributed delay, and the superlinear coefficients of the systems itself, which makes the problem handling more complicated. Then, a series of criteria for the exponential stability of the controlled SFDEs are obtained, and an upper bound for the discrete observation interval and variable delay is given. Finally, numerical example illustrates the proposed theoretical results.

The method of spectral analysis of the determination of random digital signals

The methods of spectral analysis based on the use of any model to describe the signal are considered in the article, while using them some assumptions about the behavior of the signal outside the observation interval are made. The task of spectral analysis or evaluation, in this case, is to find the parameters of the model used, which is selected based on the available a priori information about the studied process. A new spectral analysis method is proposed, which uses the partially classical Prony method, and this method has been improved by replacing the damping sine wave with the use of damped sine wave. Replacing damped sine wave with the use of non-damped sine wave, allows you to very accurately isolate the signal and determine its characteristics against the background of very rich in interference with air space, against the background of radio devices that work legally. For the first time, a fast conversion algorithm was applied to solve the normal equations for finding variables to sequentially determine the parameters of random short-term signals such as amplitude, frequency, and phase. It is suggested to determine not only static parameters but also the rate of change of these parameters. Speed of change of parameters allows determining more carefully the signal of the means of silent receiving of information. Modeling of processes of determination of random short-term pulses simulating digital signals of the means of silent receiving of information is carried out, on the basis of the proposed method of spectral analysis, the simulation results are presented in the form of three-dimensional graphs. The main difference is the use not only of the analysis of the amplitude, frequency, phase, and spectrum of the signal but the main analysis of the spectral density of the signal. Analyzes of the simulation result fully confirm the advantages of the proposed method for the determination of random short-term pulses.

Deployment the Spoke of a Large-Sized Transformable Refl ector Using a Sequential Optimization Algorithm

The use of large-sized opening reflectors close-packed in spacecraft is associated with spreading the spokes at a given angle, extending the fragments of the spokes and adjusting the shape of the radio-reflecting mesh. The problem of optimizing these processes with automatic output of the reflector to the deployed working state is urgent. The optimal control problem of spreading spokes of a large-sized space-based reflector with respect to bending vibrations is investigated in the article. The optimization process is complicated by ensuring convergence of iterative procedure for control finding. The bending vibrations of the spokes complicate the task of spreading. That makes it difficult to fix spokes when reaching the stops. In this paper the mathematical model of spoke dynamics is improved with respect to spoke’s bend change in length and in time, the model takes into account the presence of stop and retainer devices and an actuator. It is proposed to consider a hierarchy of two target composed functions and develop an algorithm for sequential optimization for a smooth exit to the stops. It is suggested to include the terminal condition for the angular spreading rate in the first criterion. A study was carried out using mathematical simulation for the process of turning the spoke by a given angle at small values of the angular velocity at the final moment of time taking into account bending vibrations. The exact values of the weight coefficients included in the target composed functions are found. Weight coefficients influence on transient processes is investigated. The performance of the algorithm was checked when the value of the optimization interval was changed. The comparison of the results of simulation modeling with control options using the PID controller, application of an algorithm with a predictive model and an algorithm with optimal correction of the control structure, revealed by means of the maximum principle, was carried out. The results of simulation modeling foe spokes spreading process using the sequential optimization algorithm demonstrate the achievement of the required accuracy with permissible tolerance residual vibrations. The developed algorithm of sequential optimization forms control in a real time and it is recommended to use it in more complex solutions under random disturbances using measurement process and optimization of observation intervals.

Multi-decadal shoreline morphodynamics of a shelf-edge reef island, Great Barrier Reef: Implications for future island persistence

Future climatic change and sea-level rise threaten the persistence of reef islands potentially making them uninhabitable over the next century. Improved understanding of island morphodynamics at multiple time scales is required for resolving major drivers of shoreline change and predicting future island resilience. Utilising 45 individually mapped shorelines, the morphodynamic change of a shelf-edge reef island (Raine Island, Great Barrier Reef) has been quantified over a 57-year time scale in the context of environmental change and anthropogenic impacts. Results show that between 1963 and 2020, there has been an average net shoreline movement (NSM) of −4.71 m and an average rate of retreat of −0.11 m/yr. However, only 23% of the shoreline has exhibited statistically significant erosion while the remaining 77% has remained stable. Importantly, data reveal a remarkable level of long-term shoreline stability despite large seasonal fluctuations in wind and wave climate, episodic storm events, and a regional sea level rise currently outpacing the global mean. Direct human impact, through modifications of the beach profile since 2014, have resulted in localised increases in rates of shoreline change but have only slightly decreased the proportion of stable shoreline (91% since modifications commenced versus 96% prior to modifications). Interestingly, there is a significant decreasing trend in island planform area over the 57-year period and especially over the last decade. However, the length of the observation interval between sampled shorelines has a strong effect on the change in planform area recorded over the interval, suggesting increased sampling frequency, rather than sea level rise, is a more likely cause of the decreasing trend. The findings of this study have direct implications for more accurate assessments of past, present and future shoreline change on reef islands. They also support the concept of 21st century island persistence in the face of climate change although the relative resilience of a given island to change (e.g., sea level, human modifications) will depend on a continuous adequate supply of sediment from organisms living on the surrounding reef, which may or may not be threatened in the future.

Differences in ebullitive methane release from small, shallow ponds present challenges for scaling

Small, shallow waterbodies are potentially important sites of greenhouse gas release to the atmosphere. The role of ebullition may be enhanced here relative to larger and deeper systems, due to their shallow water, but these features remain relatively infrequently studied in comparison to larger systems. Herein, we quantify ebullitive release of methane (CH4) in small shallow ponds in three regions of North America and investigate the role of potential drivers. Shallow ponds exhibited open-water season ebullitive CH4 release rates as high as 40 mmol m–2 d–1, higher than previously reported for similar systems. Ebullitive release of CH4 varied by four orders of magnitude across our 15 study sites, with differences in flux rates both within and between regions. What is less clear are the drivers responsible for these differences. There were few relationships between open water–season ebullitive flux and physicochemical characteristics, including organic matter, temperature, and sulphate. Temperature was only weakly related to ebullitive CH4 release across the study when considering all observation intervals. Only four individual sites exhibited significant relationships between temperature and ebullitive CH4 release. Other sites were unresponsive to temperature, and region-specific factors may play a role. There is some evidence that where surface water sulphate concentrations are high, CH4 production and release may be suppressed. Missouri sites (n = 5) had characteristically low ebullitive CH4 release; here bioturbation could be important. While this work greatly expands the number of open-water season ebullition rates for small and shallow ponds, more research is needed to disentangle the role of different drivers. Further investigation of the potential thresholding behaviour of sulphate as a control on ebullitive CH4 release in lentic systems is one such opportunity. What is clear, however, is that efforts to scale emissions (e.g., as a function of temperature) must be undertaken with caution.

Interval State Estimator Design for Linear Parameter Varying (LPV) Systems

This brief proposes a new method to develop interval state estimator for a class of LPV systems subject to external disturbances and uncertainties. Usually, the design of such estimators is based on the system cooperativity. The proposed technique uses the previous input-output values and the observability matrix to develop an interval state estimator that can provide extra degree of freedom. The main advantage of the technique compared to the standard interval observer design method for cooperative and positive systems is that it does not require the cooperativity of the system dynamics. It is shown that the convergence time of the interval width is finite and hence proved that estimation errors are bounded. The interval state observation error bounds are calculated a-priori for the given bounded disturbances. A numerical example illustrates the high potential of the proposed technique.

Observational and Theoretical Studies of 27 δ Scuti Stars with Investigation of the Period–Luminosity Relation

The multi-color CCD photometric study of 27 δ Scuti stars is presented. By using approximately three years of photometric observations, we obtained the times of maxima and magnitude changes during the observation time interval for each star. The ephemerides of our δ Scuti stars were calculated based on the Markov Chain Monte Carlo (MCMC) method using the observed times of maxima and the period of the stars’ oscillations. We used the Gaia EDR3 parallaxes to calculate the luminosities and also the absolute magnitudes of these δ Scuti stars. The fundamental physical parameters of all the stars in our sample such as masses and radii were estimated. We determined the pulsation modes of the stars based on the pulsation constants. Moreover, the period–luminosity (P–L) relation of δ Scuti stars was investigated and discussed. Then, by using a machine learning classification, new P–L relations for fundamental and overtone modes are presented.

Interval observer‐based fault tolerant control strategy with fault estimation and compensation

AbstractIn this paper, a new strategy of fault tolerant control (FTC) is proposed for linear system with unknown inputs and actuator faults. First, a reduced‐order observer which can estimate asymptotically the system states is designed. Secondly, an interval observer which is robust to the unknown inputs but sensitive to the actuator faults in a sense of interval estimations of the states is developed for the output variables. So the interval observer is then used as actuator detector. Third, another interval observer which is different from the first one in that it is robust to not only the unknown inputs but also the actuator faults is constructed. Moreover, based on the interval observer, an asymptotical unknown input reconstruction method is proposed. Third, an observer‐based state feedback controller with a fault compensation controller is designed based on H∞ index performance. In our control strategy, the fault detector and robust H∞ state feedback controller are always in active, while the fault estimator and the fault compensation controller is activated only when the fault detector issues an alarm. Finally, a simulation example is given to illustrate the effectiveness of this new control strategy.

Estimation of solid-state sintering and material parameters using phase-field modeling and ensemble four-dimensional variational method

Sintering is a fundamental technology for powder metallurgy, the ceramics industry, and additive manufacturing processes such as three-dimensional printing. Improvement of the properties of sintered materials requires prediction of their microstructure using numerical simulations. However, the physical values and material parameters used for such predictions are generally unknown. Data assimilation (DA) enables the estimation of unobserved states and unknown material parameters by integrating simulation results and observational data. In this paper, we develop a new model that couples an ensemble-based four-dimensional variational (En4DVar) DA with a phase-field model of solid-state sintering (En4DVar-PF model) to estimate the state of the sintered material and multiple unknown material parameters. The developed En4DVar-PF model is validated by numerical experiments called twin experiments, in which a priori assumed-true initial state and multiple material parameters are estimated. The results of the twin experiments demonstrate that, using only three-dimensional morphological data of the sintered microstructure, our developed En4DVar-PF model can simultaneously and accurately estimate the particle shape, distribution of grain boundaries, and material parameters, including diffusion coefficients and mobilities related to grain boundary migration. Furthermore, our work identifies criteria for determining appropriate DA conditions such as the observational time interval required to accurately estimate the material parameters using our developed model. The developed En4DVar-PF model provides a promising framework to obtain unobservable states and difficult-to-measure material parameters in sintering, which is crucial for the accurate prediction of sintering processes and for the development of superior materials.

Stability of Retained Inferior Vena Cava Filter Fragments after Filter Removal

PurposeTo assess the stability and outcome of fractured inferior vena cava (IVC) filter fragments that are retained in patients after IVC filter removal. Materials and MethodsA retrospective analysis was conducted on all patients at a single tertiary referral center between May 2005 and June 2020 with fractured IVC filters where fragment(s) were retained after removal of the main filter body. IVC filter fragment stability was assessed by a clinician review of computed tomography images, chosen from available radiologic studies, to best visualize the fragments. Data collected included filter type, fragment location, duration of fragment follow-up, fragment stability in location, and further fragment fracture or clinical sequelae. ResultsSeventy-seven patients with retained IVC filter fragment(s) after complex filter removal were identified. Of this, 37 patients (14 men, 23 women) were deemed to have adequate imaging follow-up to assess positional stability of the retained fragments, whereas the remainder were excluded from further analysis. Excluding fractured foot processes, 51 separate filter fragments were retrospectively identified and followed for a median duration of 726 days (interquartile range, 843 days; range, 28–3353 days). Filter designs producing the studied fragments included Celect, G2, Recovery, Günther, OptEase, Meridian, and G2X/Eclipse. In all, 50 of 51 (98%) fragments were found to be unchanged in position during their respective intervals of observation. One fragment displayed a rotational change without migrating from its original location. No further fragment fractures or clinical sequelae were observed among the group. ConclusionsWhen asymptomatic, retained IVC filter fragments are predominantly stable and can be safely followed on an intermediate-term basis.

Fault reconstruction and fault tolerant control design for a network of dynamical systems

This paper investigates the problems of the fault reconstruction and fault compensation controller design for a network of dynamic systems in which subsystems are interconnected through each subsystem’s outputs. First, under some assumptions, we prove that the minimum phase system condition, the observer matching condition and the controllability can be kept for the overall system. Second, an augmented descriptor system is constructed and we further prove that the minimum phase system condition, the observer matching condition are kept, and then a reduced-order observer is designed for the augmented system to obtain the estimates of the overall system states and the sensor faults simultaneously. Third, an interval observer is designed for the measured output, and based on the interval observer, an asymptotical actuator fault reconstruction method is developed. Finally, an observer-based H infinite and fault compensation scheme is designed and the stability of the closed-loop system is analyzed. We point out that the closed-loop system satisfies the so-called separation property. In the end, a simulation example is given to demonstrate the effectiveness of the proposed methods.

Improved Unmanned Aerial Vehicle Noise Direction Finding System

The work is devoted to the development of the acoustic direction of creation of means of detection of unmanned aerial vehicles (UAVs). The work of these tools is based on the principles of noise direction finding with the use of such variable characteristics of the acoustic field as: sound intensity, frequency spectrum and spatial spectrum. The architecture of UAV detection devices on the acoustic field corresponds to the algorithms of reproduction in separate paths of the device of ideology of registration and control of dynamics of change of characteristic of an acoustic field which defines the specified change as the fact of detection. The technical implementation of the above detection devices is to create a path of parallel octave, ½ octave and ⅓ octave filters, a path of narrowband filtering and a path of detection by power (intensity). 
 The ideology of construction of detection devices is based on variability and physical manifestations of changes in such characteristics of acoustic noise as: sound intensity in the space - time interval of observation, broadband filtering, narrowband filtering, correlation characteristics.
 To ensure the detection of acoustic power (or intensity) with subsequent measurement of the level, the counter-inclusion (by switching or using operational amplifiers) of the elements of the cross-shaped group is used. An important and new feature is that one of the linear discrete acoustic antennas with an enlarged base additionally has two more pressure receivers symmetrically relative to the phase center.
 For broadband filtration, a comb of ⅓ octave band and semi-octave filters is used. In turn, the path of the narrowband spectrum is an octave band filter and a unit for calculating the fast Fourier transform.
 The path of the correlation direction-finding method implements the determination of changes in the autocorrelation coefficient and the corresponding electrical parameter (say the current through the display circuit) in the processing path in situations of fixing the direction to the target.
 Therefore, the proposed system for detecting useful noise signals should contain four paths, the physical implementation of detection in which is performed by software implementation of detection algorithms and, threshold processing and indication of results
 In order to improve and increase the reliability of detection, the direction finder is supplemented by the path of detection on the mutual spectrum and the path of the correlation method of direction finding.
 The processing of input acoustic information of the type of specific noise-like signal is carried out by using the instrumental laboratory software package Lab View and Math Lab. We will add that the article contains theoretical and practical results of measurements of noise loading and range of action of a noise direction finder. Experimental studies in terms of detection and measurement of the main characteristics of the device were conducted in laboratory and field conditions.
 At the same time, the present demonstrates the rapid development of the UAV fleet, which determines the urgency of the work and the development of the device as a means of counteracting small aircraft of various recognitions is its goal.

Robust free‐time‐stable fault tolerant control for rigid satellite attitude system with output constraint

ABSTRACTThis article investigates the robust fault tolerant control strategy for a rigid satellite attitude system with external disturbance and actuator fault while the predesigned output constraint is taken into consideration. Based on the interval observer technique, an identical faulty signal reconstruction is first realized by utilizing pure mathematical calculation. Then, to guarantee the desired output constraint, the proposed prescribed performance fault tolerant control framework is constructed with a novel error interval representation which not only reduces the computation burden but also simplifies the output constrained controller design. In addition, by comparing with the existing finite/fixed time control method, the setting time for this control strategy can be assigned freely. The stability of the whole method is guaranteed by Lyapunov method. Finally, simulation results including comparisons with existing work show the effectiveness and advantages of the proposed approach.

Reduced-order interval observer design for continuous-time descriptor LPV systems with uncertainties

In this paper, a reduced-order interval observer (R-IO) design technique is developed for continuous-time descriptor linear-parameter-varying systems with unknown-but-bounded uncertainties. First, by introducing an intermediate variable, the R-IO design amounts to estimating the linear functional of the system states. Then, with a parameter-dependent Luenberger-like structure, the R-IO existence condition is eventually formulated into a set of differential-algebraic equations, not involving any linear transformation process. Further, a parametric solution to such an R-IO is derived through solving the equation set, which clearly shows the design degrees of freedom. Finally, the correctness of the proposed results is verified by a numerical system and an electrical circuit system.

Set-membership state estimators based on cooperative output injections

To estimate validated bounds on the actual state vector of uncertain non-linear systems, cooperative output injections methods are proposed in this contribution. The aim of the output injections is to design set-membership state estimators that ensure the order-preserving property between the lower, actual and upper state trajectories. Based on a special sensors placement, continuous-time and event-triggered output injections are proposed to cope with the conservatism of the classical bounding system methods. Furthermore, based on some properties of monotone dynamical systems, the convergence of the proposed set-membership state estimators is shown. It is worth pointing out that the proposed set-membership state estimation method allows one: on one hand, to avoid the conservatism related to the use of similarity transformations usually required in the framework of interval observer design approaches, and on the other hand, to circumvent the pessimism accumulation related to the wrapping effect of set-valued iterative numerical schemes.

Interval observer-based finite-time control for linear parameter-varying systems

The paper is concerned with the finite-time control of linear parameter-varying systems by means of the interval observer method. An unknown input observer framework is utilized to construct the interval observer to avoid the cooperativity constraint in estimation error dynamics. The corresponding control scheme composed of upper-lower bounds of the controller is established to treat the time-varying parameter in control input channel. Sufficient conditions are formulated as LMIs to guarantee the finite-time boundedness of error systems. The effectiveness of the proposed strategy is evaluated by numerical simulations.

Event-triggered control using a positive systems approach

We provide a new event-triggered control strategy that relies on the notion of positive systems. Our results cover output feedback, and robustness with respect to uncertain dynamics. Our proofs are based on interval observers. Our examples show potential advantages of our approach over earlier event-triggered methods.

Effect of care programme based on Comfort Theory on reducing parental anxiety in the paediatric day surgery: Randomised controlled trial.

The aim of the study was to determine the effect of a care programme based on the Comfort Theory on reducing parental anxiety forming during the perioperative process of paediatric day surgery. According to the Comfort Theory, nurses provide comfort and take precautions related to comfort, and they provide care and assistance by encouraging individuals/families/society and supporting coping methods. This study is the first randomised controlled study to test the effect of a nursing care programme based on the Comfort Theory for paediatric day surgery. Randomised controlled trial. The research was completed from June-September 2019 with participation of parents whose children were undergoing paediatric day surgery at a hospital in the Mediterranean region of Turkey. A total of 120 participants were randomly assigned to two equal groups. The intervention group received care programme based on Comfort Theory. The control group received nursing care routinely provided in the clinic. Data were collected using the State-Trait Anxiety Inventory. Measures were obtained at six points, at baseline, at four interval observations after the initial point and during follow-up on the 10th postoperative day. The repeated measures ANOVA test and t-test for independent samples were used to compare the anxiety levels between the intervention and control groups. There was a statistically significant difference in favour of the group receiving the care programme based on the Comfort Theory when the anxiety levels between the intervention and control groups were compared. The care programme based on the Comfort Theory was effective in reducing parental anxiety forming in the perioperative process of paediatric day surgery. The results of this study show the applicability of the care programme for paediatric day surgery. It is recommended that this programme be introduced to nurses in paediatric day surgery.