Fixed-time Method Research Articles

Pre-specifiable fixed-time control for quadrotor aircraft with output constraints

For the controller design of quadrotor aircraft with six-DOF, a pre-specifiable fixed-time method combined with state constraints is researched in this paper. The 6-DOF aircraft model is divided into position loop and attitude loop through time scale decomposition method for the convenience of decoupling. Adaptive pre-specifiable fixed-time controllers for the position subsystem and attitude subsystem are proposed to ensure the desired trajectory and the desired attitude angle can be reached within a fixed-time which is independent of initial conditions. Meanwhile, the convergence time can be user-assignable in advance. Time-varying state constraints are considered in the controller design process in order to guarantee the safety of the system and prolong the life of actuator. The Barrier Lyapunov function is applied to ensure quadrotor aircraft’s output constraints are not violated. Finally, the effectiveness of the proposed controller is verified by the simulation experiment.

Antisaturation fixed-time backstepping fuzzy integral sliding mode control for automatic landing of fixed-wing unmanned aerial vehicles

This paper proposes a robust adaptive fixed-time control for automatic landing systems (ALS) of small-scale fixed-wing UAVs exposed to wind disturbances, parametric uncertainties, and input saturation. The control structure consists of three subsystems, i.e., the guidance system, the attitude control system, and the thrust control system. Considering the landing geometry, the guidance system computes the desired Euler angles to stabilize the dynamics of altitude deviation, lateral deviation, and lateral speed. An auxiliary system is designed to compensate for the effect of input saturation in the attitude control system. The fixed-time method, the backstepping control (BSC), the fuzzy logic control (FLC), and the integral sliding mode control (ISMC) techniques are adopted to synthesize the control law. All three functional parts of the proposed ALS are equipped with a fixed-time fuzzy sliding mode disturbance observer (FSMDO). FLC computes the gains of signum functions adaptively to attenuate the chattering. Fixed-time convergence of the system errors to an arbitrary residual set is proved by comprehensive stability analysis. Finally, the comparative simulation results verify the better dynamic response and stronger robustness under the proposed ALS.

Fixed-time trajectory tracking control of a quadrotor UAV under time-varying wind disturbances: theory and experimental validation

This paper adopts a fixed-time method to study the trajectory tracking issue of a quadrotor unmanned aerial vehicle (UAV) under time-varying wind disturbances. Firstly, in order to address the impact of time-varying wind disturbances on UAV, a fixed-time disturbance observer is constructed to accurately estimate wind disturbances. Secondly, to improve control accuracy and convergence rate, a robust fixed-time controller is designed for the position and attitude system by combining the sliding mode control theory with fixed-time techniques. Furthermore, it is rigorously analyzed that the tracking error of the observer and controller can converge to zero via Lyapunov criterion, and the convergence time is independent of the initial state. Finally, the effectiveness and robustness of the designed control strategy are verified by numerical simulations and actual flight experiments, providing an effective connection between control theory and practical applications.

Observer-based fault-tolerant fixed-time attitude tracking control for rigid spacecraft without angular velocity measurement

This paper investigates the problem of adaptive nonsingular fast terminal sliding mode fixed-time tracking control method for rigid spacecraft without angular velocity measurement. First, a novel fixed-time extended state observer is proposed to obtain accurate estimates of both unmeasurable angular velocities and integrated disturbance. Then, based on this sufficient qualification, an adaptive fast nonsingular terminal sliding mode controller is designed to make the state of the following spacecraft track a target spacecraft even when the tracking system has an actuator fault. Adaptive technology is introduced to compensate for the effect of observation error on the controller. Using the Lyapunov function and fixed-time property, it is proved that the control scheme can ensure that the attitude tracking error converges to the neighborhood of the origin in a fixed time and is independent of the initial conditions. Finally, numerical simulation examples are carried out to evaluate the effectiveness of the proposed fixed-time method.

Deep Learning Algorithm for Optimization of Wait Time at a Traffic Signal Controlled Intersection for Smart Traffic Management

Abstract: The urban landscape is constantly shifting and adapting as a result of factors such as population increase, immigration, and changes in the economy, politics, and culture. Concerns like growing road obstruction, transit delays, pollution levels, consumption of gasoline, etc. have resulted from higher traffic volumes in metropolitan areas. Life expectancy, road safety, environmental quality, and commute times are all impacted by traffic congestion. At junctions, traffic lights play a crucial role in regulating vehicular flow. The traditional pre-timed traffic systems have been ineffective due to the dramatic growth in lights become insufficient in managing traffic clearance which leads to heavy traffic congestion at intersection. Another major issue is that the Emergency vehicles like ambulance, police van, fire brigade experience prolonged waiting time to cross the intersection. For these reasons, development of smart intersections with the aid of technologies such as fuzzy logic, neural networks, artificial intelligence, multiprocessor systems etc. can help to provide the solution and improve the urban traffic management problems. Smart cities are increasingly adopting solutions by using adaptive and intelligent approach to develop smart traffic lights to improve the traffic flow at intersections. The current study on smart traffic light system makes contribution in developing intelligent and adaptive systems to resolve traffic congestion problems at single and connected intersections with an objective to improve traffic clearance and prioritize passage of Emergency vehicle at an isolated intersection. Another problem is the one generally faced by pedestrians as they have to wait for a prolonged interval of time for getting way to cross the lane of major intersection specially at peak traffic hours. This problem has also been considered in the study. System performance has been tested for a twenty-four-hour traffic pattern at an isolated intersection. The outcomes of the simulations showed that the suggested design outperformed the standard fixed-time method in terms of automotive clearing, rescue vehicles passing, and pedestrians wait time.

Kinetic study of the hydrolysis of ester with mineral acid by spectrophotometer at different temperature

To determine the kinetic parameters and activation energy of the hydrolysis of ethyl acetate with hydrochloric acid monitored by spectrophotometry. The first order fits were automatically drawn and the values of the first order rate constants (k) were calculated using standard equations as part of the program. Acidic hydrolysis of ethyl acetate is essentially an irreversible and first order reaction whereas alkaline hydrolysis is an irreversible and second order reaction. Rate of reaction is the change in the number of molecules of reacting species per unit volume per unit time. In this hydrolysis of ethyl acetate with hydrochloric acid to accelerate the reaction mixture. A simple and sensitive kinetic spectrophotometric method presented for the determination of rate constant, order of reaction and activation energy. This method based on a kinetic investigation of ethyl acetate and hydrochloric acid at 35°C and 45°C temperature. The reaction followed spectrophotometrically by measuring the absorbance at 500 nm as a function of time. The initial rate and fixed time methods utilized for construction of calibration graphs successfully for the determination of rate constant, order of reaction and activation energy. The rate constant after calculation from the graphs was approximately k1 ≈ 0.00260 Sec-1 k2 ≈ 0.00322 Sec-1 by titration and spectrophotometric method respectively, order of reaction found to be first order and the activation energy for this reaction is 17.44 kJ/mol. One factor that influences the absorbance of a sample is the concentration (c). As the concentration increases, more radiation is absorbed and the absorbance increase. Therefore, the absorbance is directly proportional to the concentration.

Analysis of immortal-time effect in post-infarction ventricular septal defect.

Time-fixed analyses have traditionally been utilized to examine outcomes in post-infarction ventricular septal defect (VSD). The aims of this study were to: (1) analyze the relationship between VSD closure/non-closure and mortality; (2) assess the presence of immortal-time bias. In this retrospective cohort study, patients with ST-elevation myocardial infarction (STEMI) complicated by VSD. Time-fixed and time-dependent Cox regression methodologies were employed. The study included 80 patients: surgical closure (n = 26), transcatheter closure (n = 20), or conservative management alone (n = 34). At presentation, patients without VSD closure exhibited high-risk clinical characteristics, had the shortest median time intervals from STEMI onset to VSD development (4.0, 4.0, and 2.0 days, respectively; P = 0.03) and from STEMI symptom onset to hospital arrival (6.0, 5.0, and 0.8 days, respectively; P < 0.0001). The median time from STEMI onset to closure was 22.0 days (P = 0.14). In-hospital mortality rate was higher among patients who did not undergo defect closure (50%, 35%, and 88.2%, respectively; P < 0.0001). Closure of the defect using a fixed-time method was associated with lower in-hospital mortality (HR = 0.13, 95% CI 0.05-0.31, P < 0.0001, and HR 0.13, 95% CI 0.04-0.36, P < 0.0001, for surgery and transcatheter closure, respectively). However, when employing a time-varying method, this association was not observed (HR = 0.95, 95% CI 0.45-1.98, P = 0.90, and HR 0.88, 95% CI 0.41-1.87, P = 0.74, for surgery and transcatheter closure, respectively). These findings suggest the presence of an immortal-time bias. This study highlights that using a fixed-time analytic approach in post-infarction VSD can result in immortal-time bias. Researchers should consider employing time-dependent methodologies.

POTENTIOMETRY IN DETERMINING THE CONDITIONS FOR THE FORMATION OF TETRAFLUORBORATE AS AN ANALYTICAL FORM OF BORON

The present paper deals with the research on the optimal conditions for the formation of fluoroborate as an analytical form of boron. Despite numerous scientific publications related to the determination of boron using various methods involving [BF4]ˉ ions as an analytical form, the conditions for obtaining the latter differ significantly. This difference is likely due to the complexity of the H3BO3-F--H3O+ system, where polymolecular forms of hydrofluoric acid can exist. Factors such as the inability to measure pH using a glass electrode, the velocity of the complexation process, and the requirement for specialized labware and equipment resistant to aggressive environments contribute to this complexity. In this study, potentiometry with PVC plasticized [BF4]ˉ - sensors, known for their metrological and operational characteristics, was used as a convenient tool to investigate such systems. The [BF4]ˉ - selective electrode based on the electroactive substance ion pair 2-(N-ethylcarbazole-3)-ethenyl-1,3,3-trimethyl-3H-indole tetrafluoroborate, which retains its metrological characteristics in acidic and strongly acidic environments and exhibits selectivity up to F-(= -4. 0), was employed as a sensor.&#x0D; The sensor allowed for the study of [BF4]ˉ - complex formation under different reaction conditions by recording kinetic curves in EMF-time coordinates. The yield of the analytical form was estimated at different concentrations of acid, fluoride ions, and temperature. The obtained data were used to construct the yield surface of tetrafluoroborate, revealing that the optimal conditions for the formation and stability of tetrafluoroborate at room temperature are a medium of 1 M sulfuric acid and 0. 25 M NH4F. Under these conditions, the yield of [BF4]ˉ reaches 99% within 10 minutes. Although the use of phosphoric acid does not allow for the attainment of an appropriate yield of the analytical form under equilibrium conditions, its low process velocity makes it suitable for kinetic - potentiometric determination of boron. This characteristic was utilized to develop a method for the determination of boron in phosphoric acid using the fixed-time method.&#x0D; Keywords: tetrafluoroborate ion; potentiometric sensor; kinetic determination of boron.

Kinetic Potentiometry as a Method for Studying the Interactions of Antioxidants with Peroxyl Radicals.

This work presents a new method using kinetic potentiometry to study the thermodynamic and kinetic parameters of the reactions of antioxidants with peroxyl radicals. The rate constants of the reaction of antioxidants with radicals have been determined, and the groups of "fast" and "slow" antioxidants have been conventionally distinguished. Fast antioxidants include ascorbic, uric, gallic, chlorogenic, caffeic acids, glutathione, L-cysteine, and catechol with constant values from (1.05-9.25) × 103 M·s-1; "slow" antioxidants are α-tocopherol (in aqueous media), ionol, 2,6-ditretbutylphenol, and compounds of the azoloazine series, modified with polyphenolic fragments, with constant values from (4.00-8.50) × 102 M·s-1. It is shown that the value of the rate constant is directly related to the type of kinetic dependence of the potential recorded when an antioxidant is introduced into the solution of the radical initiator. It is shown that the method with the determination of the induction period is difficult in the study of "slow" antioxidants. It has been established that the area above the curve of the kinetic dependence Exp(∆E) is directly related to the amount of inhibited peroxyl radicals and can be used to assess the inhibitory properties of an antioxidant from a thermodynamic point of view. "Fixed time method" and "Initial rate method" were used. Positive correlations between the described method have been established. The utility of the parameter of the area above the curve of the kinetic dependence Exp(∆E) in the study of objects of complex composition is shown.

Adaptive fractional tracking control of robotic manipulator using fixed-time method

This paper proposes an adaptive fractional-order sliding mode controller to control and stabilize a nonlinear uncertain disturbed robotic manipulator in fixed-time. Fractional calculus is used to construct a fractional-order sliding mode controller (FtNTSM) that suppresses chattering to help the robotic manipulator converge to equilibrium in a fixed-settling time based on fixed-time stability theory. Then, adaptive control is introduced and combined with FtNTSM to overcome the unknown system dynamics. The convergence time of the proposed fixed-time fractional-order sliding mode controller (AFtNTSM) is independent of beginning circumstances and can be precisely assessed, unlike the finite-time control approach. Finally, numerical simulations show that the adaptive fractional-order sliding mode controller outperforms finite-time sliding mode controller.

Determination and Speciation of Selenium in Pharmaceutical Samples, Spiked Veterinary Drug Samples with a Kinetic Catalytic Method

In the present study a new kinetic catalytic method was developed for the sensitive determination of selenium in pharmaceutical formulations. The reaction between basic blue 3 (BB3) and sulphide catalysed by Se (IV) in the presence of acetic-phosphoric-boric acid buffer system. The decrease in the absorbance at 654 nm indicated the reduction of BB3. The presence of selenium (IV) accelerated the reaction rate. The method based on the linear correlation between amount of Se(IV) and reaction rate. Under optimum conditions, the linear calibration range was found as 0.1-2.0 µg ml-1 by the fixed time method for the 0.5-5 min. The tolerance limits of various species was also studied. The interfering effect of some cations such as Cr3+, Fe3+, and Hg2+ was reduced with using cation exchange resin. The proposed method was successfully applied to spiked nasal spray and veterinary drug samples. Besides, total selenium, Se (IV) and Se (VI) speciation also conducted with reducing Se (VI) to Se (IV) with HCl in the synthetic mixtures.

KINETIC SPECTROPHOTOMETRIC DETERMINATION OF TAPENTADOL

A simple, inexpensive, accurate and sensitive spectrophotometric method and kinetic assay have been established to determine tapentadol in pure form, tablets and urine samples. The method is based on the reaction of tapentadol with ferric ions in an acidic solution in the presence of ferricyanide to give water-soluble Prussian blue dye with a maximum absorption wavelength of 735 nm, with a maximum reaction time of 40 minutes. Several experimental factors affect the colour intensity and stability time approaches. The reaction was identified as a first-order pseudo-reaction by calculating the initial rate, and the results of the fixedtime method (at 30 min) are more suitable for quantification and used to construct the calibration curves. The correlation between concentration and absorbance was linear. Moreover, varies from 2 to 12 μg/mL and has a detection limit of 0.1737 μg/mL and a quantification limit of 0.5264 μg/mL. The molar absorption coefficient and Sandel sensitivity were 1.5484 x 10 4 L.mol-1.cm-1 and 0.01430 μg.cm-2, respectively. A comparison of spectrophotometric data with a well-established fixed time kinetic demonstrated that the fixed time technique offers good accuracy, precision, low detection and quantification limitations, and is time efficient. These procedures were effectively used to analyze tapentadol in its pure form, tablet form, and urine sample, which were not observed in literature before

Ultimately Bounded TSK Fuzzy Management in Urban Traffic Stream Mechanism: Multi-Agent Modeling Approach

In this paper, a novel control approach based on the selection of the type of traffic light and the period of the green phase to accomplish an optimum balance at intersections is proposed. This balance should be flexible to the static behavior of time, and randomness in a traffic situation, which the goal of the proposed method is to reduce traffic volume in transportation, the average delay for each vehicle, and control over the crash of cars. The proposed method was specifically investigated at the intersection through an appropriate timing of traffic lights by sampling a multi-agent system. It consists of a large numbers of intersections, each of which is considered as an independent agent that exchanges information with each other, and the stability of each agent is provided separately. The robustness against uncertainties, scalability, and stability of the closed-loop overall system are the main merits of the proposed methodology. The simulation results show that the fuzzy intelligent controller in this multi-factor system which is a TS fuzzy is more useful than scheduling in the fixed-time method and it reduces the lengths of vehicles queuing.

Trajectory Tracking Control of Euler–Lagrange Systems Using a Fractional Fixed-Time Method

The results of this research provide fixed-time fractional-order control for Euler–Lagrange systems that are subject to external disturbances. The first step in the process of developing a new system involves the introduction of a method known as fractional-order fixed-time non-singular terminal sliding mode control (FoFtNTSM). The advantages of fractional-order calculus and NTSM are brought together in this system, which result in rapid convergence, fixed-time stability, and smooth control inputs. Lyapunov analysis reveals whether the closed-loop system is stable over the duration of the time period specified. The performance of the suggested method when applied to the dynamics of the Euler–Lagrange system is evaluated and demonstrated with the help of computer simulations.

A simple uric acid assay by using 3‐hydroxytyramine as a chromogenic colorimetric sensor in human serum samples: Density functional theory supported mechanistic approach

A simple, fast, sensitive, convenient, and economical accurate enzymatic colorimetric sensor is developed for the quantification of the clinically important biomarker uric acid (UA) in human serum samples. The method is based on the quantification of UA using 3-hydroxytyramine (3-HT) as a chromogenic substrate by using peroxidase (POD) and uricase (UOx). UOx catalyzes the oxidation of UA where H2O2 is generated in-situ to produce allantoin and CO2. The POD in oxidative coupling of peroxide in presence of 3-HT, forms an intense orange-colored product with λmax = 500 nm. The reaction was carried out in a citric acid-tripotassium-citrate buffer (12.5 mM) of pH = 6.8 at room temperature. Computational calculations were done by Gaussian-16 employing the B3LYP functional basis set. The standard curve for UA was found to be linear between 12.3–297.3 and 3.07–396.5 μM by rate and fixed time method, respectively. The LOD and LOQ for UA were 1.5 and 2.9 μM, respectively. Within-day and day-to-day precision was 1.50–3.07 and 3.10–4.16% (n = 7), respectively. The accuracy ranges for UA concentrations of 24.7, 198 and 297.3 μM were 87%–101.50%, 90%–105%, and 89%–107%, respectively. The UA recovery range by the proposed method was 98.00%–100.47% with a mean recovery of 99.5% and has A good correlation coefficient of 0.981 with the standard method.

Fixed-time observer-based control of DFIG-based wind energy conversion systems for maximum power extraction

To extract maximum power from the available wind energy, it is necessary that the doubly-fed induction generator (DFIG) based wind energy conversion system (WECS) outputs that maximum power at each instant of time for different wind speeds. This can be achieved by controlling the rotor voltage of the DFIG. To make it possible, a novel maximum power point tracking (MPPT) controller in combination with state and disturbance observers and fixed-time stability notion is proposed in this paper. The sliding mode control (SMC) method is used to design the observer-based controller and ensure the robustness. The sliding mode state observer is designed while only the measurement of the stator reactive power and rotor speed is required. The modelling uncertainties and external disturbances are estimated by the sliding mode disturbance observer without information about their upper bounds in advance. Then, the combinatorial effect of uncertainties and disturbances are fully compensated by the designed controller. The fixed-time convergence issue is addressed where the bound on the settling time is user-defined using design parameters regardless of initial conditions. The elimination of chattering issue is considered in the design of the SMC laws. The stability analysis of the closed-loop system is obtained via the Lyapunov stability theory. The validity and robustness of the proposed method is tested in Simulink/MATLAB for a DFIG under two different scenarios of wind speed modelling. The proposed fixed-time method is also compared with a classical finite-time method. Comparing the results demonstrate that the proposed method outperforms the other method.

Spectrophotometric determination of glucose in human serum samples using para‐phenylenediamine and alpha‐naphthol as a chromogenic reagent

AbstractThe global surge in chronic hyperglycemia, the autoimmune disease resulting from diabetes mellitus, has attracted worldwide scientists to develop novel methods for assaying blood glucose levels in the human body. In this work, we reported a new sensitive chromogenic reagent‐based single beam spectrophotometric assay of glucose. This method is based on the catalytic oxidation of D‐glucose to D‐gluconolactone and H2O2 by glucose oxidase (GOD), later by the oxidative coupling of quinone with imine radical to give purple‐colored quinone‐imine chromogenic species with λmax = 540 nm. The linearity of glucose lies in the range of 57.81–1850.2 and 14.45–925.1 µmol L–1 by rate and fixed time method. The Michaelis–Menten constant attained by the Lineweaver–Burk plot at the optimal concentration of the reagents was 526.31 µM with Vmax of 0.2659 EU min–1 and catalytic constant of 1.3295 min–1. Intra‐ and inter‐day precision ranged between 0.73%–1.4% and 1.76%–2.4%, respectively. The standard addition method for the recovery of glucose fluctuated between 97.78% and 104.35%, registering minimal common interference species present in the blood samples. The results showed a good accuracy level (90%–102%), and the calculated limit of detection (LOD) and limit of quantification (LOQ) were as low as 2.17 and 8.56 µM. The proposed work has a good correlation with the standard enzyme kit method. Hence, the proposed system can be convenient for the determination of glucose in biological samples.

NOVEL FAST ANALYTICAL METHODS FOR THE ANALYSIS OF FLUOXETINE IN PURE AND PHARMACEUTICAL DOSAGE FORM

Novel and accurate analytical methods were developed and validated for the characterization of Fluoxetine in its pure and pharmaceutical dosage form Prozac®. Fluoxetine was determined by IBA techniques (PIGE, PIXE and RBS). It has been also analyzed spectrophotometrically at 610 nm after oxidation with potassium permanganate in alkaline medium. In addition, Fluoxetine was kinetically determined using the initial rate method, the fixed absorbance method and the fixed time method. Moreover, a Gas chromatography - mass spectrometry technique is proposed for the investigation of Fluoxetine without a prederivatization phase. The spectrophotometric method was performed with a concentration array of 2-10 μg/mL at 610 nm and a regression coefficient (r) of 0.996. The fixed time method was the most suitable one to determine Fluoxetine with correlation coefficient value (r) of 0.9966. The Gas chromatography - mass spectrometry investigated the drug in a concentration range of 20-100 μg/mL and a regression coefficient (r) of 0.999. IBA analysis presented a precision of less than 3% and a very low limit of detection. Consequently, these proposed methods would be useful tools for determining Fluoxetine as all the assay results exposed satisfactory sensitivity, accuracy and reproducibility

Arduino Based Congestion Control System for Ambulance

Abstract: Congestion problem is a fact which contributed large impact on the transport system in the country. because many problems especially when there are emergency cases at traffic light junctions which are always busy with so many vehicles. A congestion control system is designed in order to solve all these problems. This system was designed in such a way that it should be activated when it receives a signal from an ambulance based on radio frequency (RF) transmission and uses a microcontroller to change the sequence back to the normal sequence before the emergency mode is activated. This system will lessen what often happens at the traffic light intersections because other vehicles have to gather together for giving a special route to an emergency vehicle. As a result, this project is successful and the implementation of wireless communication i.e. the radio frequency (RF) transmission in the traffic light control system for emergency vehicles like an ambulance is made possible. The main aim of this project is to design a system that is capable to identify an emergency situation in an ambulance and automatically controls the traffic at the signal. In the future, this system can be improved by controlling real traffic congestion, in fact improving the present traffic light system technology. The existing traffic control system has a lot of limitations because of its fixed time method used. The traffic signal will not alter based on the real-time traffic on road near the junction of two or more roads. Due to this, the traffic congestion cannot be controlled efficiently and the utilization of roads cannot be done to its maximum limit.

Comparative Analysis of Derivative Parameters of Chemoresistive Sensor Signals for Gas Concentration Estimation

Signals from resistive gas sensors based on zirconium dioxide and silicon–carbon films have been extensively investigated to estimate gas concentration. In this study, the change in the normalized resistance of the sensor’s response under NO2 exposure is shown and the analysis of the first and second derivatives of the response curves were carried out. A signal-processing scheme, reducing the effect of noise and signal drift, is proposed. The extreme of the second derivative of the sensor response, the initial reaction rate, and the slope of the curve of the approximating line in the coordinates of the Elovich equation are proposed as calibration dependencies. The calibration curves built from the values of the maximum second derivative turned out to be the most stable, with the lowest relative error in estimating gas concentration compared to the traditional fixed-time point method.