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Quadrotor technology offers numerous potential applications, ranging from surveillance and power line inspection to medical delivery and more. However, achieving precise tracking control for these aircraft poses multiple challenges, including random wind disturbances, modeling uncertainties and other aerodynamic factors. To address these challenges, a new robust cooperative control scheme that combines the merits of backstepping control (BC) and non-singular fast terminal sliding mode control (NFTSMC) is developed. The super-twisting algorithm is also used to strengthen the system’s robustness and ensure the reachability of the sliding surfaces in a short time. The closed-loop stability of the proposed flight controller is demonstrated via the Lyapunov criteria. The suggested control scheme can drive the vehicle's attitude and altitude to the targeted trajectories in a short time while compensating for the influence of complex disturbances and modeling inaccuracies. The accuracy of the recommended control scheme was examined using a quadrotor aircraft exposed to random external disturbances and modeling uncertainties. Computer simulation as well as processor-in-the-loop (PIL) tests on a commercial autopilot board are executed to verify the effectiveness of the proposed strategy. Finally, multiple comparisons with recent nonlinear controllers are also realized to show the merit of the developed method.

This paper presents an imaging system based on ultrawideband microwave radars for the detection of bleeding regions and strokes inside the human head. The proposed system is portable and focuses on revealing bleeding areas with unpredictable shapes using polarimetric data acquisition. A custom-designed dual-polarized bowtie patch antenna capable of pumping the UWB pulses inside the patient’s head is designed and presented as the biomedical sensor for the system. The antenna dimensions are 25×25 mm2. It mitigates the mismatch between the air and skin needles of any coupling liquid, resulting in safe SAR levels below 0.5 W/kg and wideband operating bandwidth that covers 1.2-4.5 GHz with unidirectional radiations. To collect the raw polarimetric data, an elliptical array of the proposed antenna is formed around the patient’s head model that includes 16 elements in direct contact with the phantom. The performance of the proposed method is validated through an imaging scenario with two nonuniform bleeding areas inside the patient head model. The whole structure is simulated with a Gaussian pulse as the excitation using CST Microwave Studio tools. To produce 2D images of the voxel model, the time-domain elliptical synthetic aperture radar (ESAR) imaging algorithm is applied. Accurately detecting the presence and shape of anomalies in reconstructed images using the proposed method demonstrates the efficiency of the proposed system and determines its advantages over single-polarization systems.

The recent progress in the fields of sensor miniaturization, light materials, automatic control, and battery management systems has opened up new opportunities for low‐cost unmanned aerial vehicles (UAVs), such as quadrotors. In fact, quadrotors have transitioned from a primarily military application to being widely used almost everywhere. Evidently, controlling such robots requires a deep understanding of their dynamic behavior and the use of robust strategies to accomplish the flight missions without compromising users’ safety. This study presents a comprehensive survey of control strategies for unmanned quadrotors. In our examination, the performance assessment of widely used control algorithms is discussed. Furthermore, the concept of model‐based design is presented as a solution for bridging the gap between simulation and experimental validation of control systems. It is anticipated that the present study will provide the reader with a clear vision of quadrotor UAV control theory.

In this paper, a robust flight control system is proposed for an autonomous quadrotor to quickly and accurately achieve the targeted trajectories. A novel supertwisting nonsingular terminal sliding mode control (STNTSMC) has been developed to ensure that the tracking errors vanish in a short finite-time. A nonlinear disturbance observer (DO) is incorporated into the control system to estimate the unknown external perturbations and to strengthen the system’s robustness. The Lyapunov theory is used to verify the closed-loop stability of the synthesized controller. Moreover, processor-in-the-loop (PIL) implementations are performed to validate the efficacy of the suggested method. The merit of the proposed DO-STNTSMC is evaluated under multiple flight scenarios. The obtained results demonstrate that the proposed controller has a highly reduced tracking error and strong robustness against random parameter changes and external disturbances, compared to conventional nonsingular terminal sliding mode control. Finally, experimental tests are conducted to validate the performance of the suggested method.

Quadrotor unmanned aerial vehicles are increasingly explored due to their potential applications in many daily activities, including surveillance, cinematography, product delivery, and so on. Designing a flight control system for such a vehicle is very challenging because of its nonlinear dynamics and its sensitivity to the influence of disturbances. To meet part of this challenge, here a robust backstepping supertwisting sliding mode control (BSTSMC) has been developed to achieve a good tracking of the targeted trajectories. The proposed flight control system can drive the quadrotor's attitude to their reference values rapidly and, at the same time, reduce the impact of external perturbations and model inaccuracies. Experimental tests on an X450 quadrotor were performed to prove the practicality and disturbance rejection capability of the suggested control scheme.

The design of a new X-band circularly or linearly polarized transmitarray antenna capable of beam scanning via the guided-wave approach is proposed. To achieve beam scanning, a new design of a 3-bit loaded line phase shifter employing PIN diodes is used. The transmitarray antenna consists of 8 × 8 unit cells fed by a linearly polarized rectangular pyramidal horn antenna. The unit cell consists of a receiving antenna, the 3-bit phase shifter and the transmitting antenna, all in one dielectric substrate, which makes the overall fabrication process very simple. The transmitarray antenna uses the proposed phase shifters to produce the plane wave required as well as to steer the beam in space. The output is a linearly polarized wave. To produce circular polarization, a three-layer quarter-wave polarizer compatible with the transmitarray antenna is used. Each 8 × 1 sub-array of unit cells are fabricated on a single Rogers RO4003 board, and the overall transmitarray antenna producing either linear or circular polarization is tested. The antenna has a beam scan range of 30° × 30° over a bandwidth of 6%. The structure is simulated via HFSS (High-Frequency Structure Simulator) and ADS (Advanced Distributed Simulation), and good agreement between simulation and measurement results is also observed. Furthermore, a new improved antenna design is presented and simulated via HFSS in which its beam scan range is upgraded to 45° × 45°.

Exposure to mercury (Hg) as a heavy metal can cause health effects. The objective of this study was to assess occupational exposure to Hg in a chlor-alkali petrochemical industry in Iran by determining of Hg concentrations in air, blood and urine samples. The study was performed on 50 exposed subjects and 50 unexposed controls. Air samples were collected in the breathing zone of exposed subjects, using hopcalite sorbents. Analysis was performed using a cold vapor atomic absorption spectrophotometer (CV-AAS) according to NIOSH analytical method 6009. For all participants, blood and urine samples were collected and then transferred into sterile glass tubes. After micro-extraction with ionic liquid and back extraction with nitric acid, Hg concentrations in blood and urine samples were determined by CV-AAS. The mean concentration of air Hg was 0.042± 0.003 mg/m(3). The mean concentrations of Hg in blood and urine samples of exposed subjects were significantly higher than unexposed controls (22.41± 12.58 versus 1.19± 0.95 μg/l and 30.61± 10.86 versus 1.99± 1.34 μg/g creatinine, respectively). Correlation of air Hg with blood Hg, urine Hg and blood Hg-urine Hg ratio were significant statistically (P< 0.05). The values of Hg in blood and urine samples of chlor-alkali workers were considerably high. Correlation coefficients showed that blood Hg and blood Hg-urine Hg ratio are better indicators than urine Hg for assessing occupationally exposed workers in terms of current exposure assessment.

This paper presents a novel approach to design a circularly polarized transmitarray antenna using a non-resonant frequency selective surface (FSS) unitcell (sub-wavelength in size). The antenna design aims to convert a linearly polarized (LP) wave into a circularly polarized (CP). The proposed unitcell utilizes a single substrate with a patch and metal grid on each side, simplifying the fabrication process. The key advantage of the proposed design is its wideband polarization conversion capability. An equivalent circuit of the transmitarray antenna is presented from which, the initial dimension of the unitcell for starting the optimization process through the full-wave simulation is given. The transmitarray antenna consists of 16*16 elements operating over X band frequency. The proposed unitcell 360° phase shift is achieved through rotation of the lower layer elements. The array achieves a gain of around 24 dBi, a 3 dB gain bandwidth of 27%, and a high axial ratio bandwidth exceeding 30%. To validate the design, the antenna is fabricated, and the experimental results show good agreement with the simulation results. This confirms the reliability and accuracy of the proposed approach.

PurposeThe purpose of this research is to provide a framework in which new data quality dimensions are defined. The new dimensions provide new metrics for the assessment of lecture video indexing. As lecture video indexing involves various steps, the proposed framework containing new dimensions, introduces new integrated approach for evaluating an indexing method or algorithm from the beginning to the end.Design/methodology/approachThe emphasis in this study is on the fifth step of design science research methodology (DSRM), known as evaluation. That is, the methods that are developed in the field of lecture video indexing as an artifact, should be evaluated from different aspects. In this research, nine dimensions of data quality including accuracy, value-added, relevancy, completeness, appropriate amount of data, concise, consistency, interpretability and accessibility have been redefined based on previous studies and nominal group technique (NGT).FindingsThe proposed dimensions are implemented as new metrics to evaluate a newly developed lecture video indexing algorithm, LVTIA and numerical values have been obtained based on the proposed definitions for each dimension. In addition, the new dimensions are compared with each other in terms of various aspects. The comparison shows that each dimension that is used for assessing lecture video indexing, is able to reflect a different weakness or strength of an indexing method or algorithm.Originality/valueDespite development of different methods for indexing lecture videos, the issue of data quality and its various dimensions have not been studied. Since data with low quality can affect the process of scientific lecture video indexing, the issue of data quality in this process requires special attention.

Among different type of transition metal oxides, tungsten trioxide (WO 3 ) is a suitable candidate for electronic device fabrication due to its n-type property and wide band gap. Herein, one-dimensional tungsten trioxide (WO 3 ) nanorods were achieved from an aqueous solution of sodium tungstate dihydrate (Na 2 WO 4 ·2H 2 O) and sodium chloride (NaCl) in an acidic media by a time-optimized hydrothermal synthesis in autoclave at 180°C or different synthesis durations. For studying morphology and size of obtained powder, X-ray diffraction (XRD), scanning electron microscope (SEM), and high resolution transmission electron microscope (HRTEM) were applied. Finally, WO 3 nanorods of about 2–3 μm in length and 100–200 nm in diameter were obtained during 3 h hydrothermal process.