Robust hovering controller for uncertain multirotor micro aerial vehicles (MAVS) in gps-denied environments: IMAGE-BASED

This paper proposes an image-based robust hovering controller for multirotor micro aerial vehicles (MAVs) in GPS-denied environments. The proposed controller is robust against the effects of multiple uncertainties in angular dynamics of vehicle which contain external disturbances, nonlinear dynamics, coupling, and parametric uncertainties. Based on visual features extracted from the image, the proposed controller is capable of controlling the pose (position and orientation) of the multirotor relative to the fixed-target. The proposed controller scheme consists of two parts: a spherical image-based visual servoing (IBVS) and a robust flight controller for velocity and attitude control loops. A robust compensator based on a second order robust filter is utilized in the robust flight control design to improve the robustness of the multirotor when subject to multiple uncertainties. Compared to other methods, the proposed method is robust against multiple uncertainties and does not need to keep the features in the field of view. The simulation results prove the effectiveness and robustness of the proposed controller

Optimización de la cristalización con metanol para una separación altamente eficiente del ácido palmítico en mezclas de ácidos grasos de palma usando metodología de superficie de respuesta

The objective of the current study was to develop parameters for the separation of palmitic acid (PA) from a crude palm oil saturated fatty acid (SFAs) mixture by using the methanol crystallization method. The conditions of methanol crystallization were optimized by the response surface methodology (RSM) with the D-optimal design. The procedure of developing the solvent crystallization method was based on various different parameters. The fatty acid composition was carried out using a gas chromatography flame ionization detector (GC-FID) as fatty acid methyl esters. The highest percentage of SFAs was more than 96% with the percentage yield of 87.5% under the optimal conditions of fatty acids-to-methanol ratio of 1: 20 (w/v), the crystallization temperature of -15 °C, and the crystallization time of 24 hours, respectively. The composition of separated SFAs in the solid fraction contains 96.7% of palmitic acid (C16:0) as a dominant component and 3.3% of stearic acid (C18:0). The results showed that utilizing methanol as a crystallization solvent is recommended because of its high efficiency, low cost, stability, availability, comparative ease of recovery and its ability to form needle-like crystals which have good filtering and washing characteristics.El objetivo del presente estudio fue desarrollar parámetros para la separación de ácido palmítico (PA) en mezclas de ácidos grasos saturados (SFAs) de aceites de palma crudo mediante el método de cristalización con metanol. Las condiciones de cristalización con metanol se optimizaron utilizando la metodología de superficie de respuesta (RSM) con el diseño D-Optimal. El procedimiento de desarrollo del método de cristalización con disolvente se basó en diversos parámetros diferentes. La composición de ácidos grasos se llevó a cabo por cromatografía de gases (GC-FID) como ésteres metílicos de ácidos grasos usando un detector de ionización de llama. El porcentaje más alto de SFAs fue mayor del 96% con un rendimiento porcentual de 87,5% bajo las condiciones óptimas de relación de ácidos grasos:metanol de 1:20 (p/v), una temperatura de cristalización de -15ºC y un tiempo de cristalización de 24 horas. La composición de la fracción de SFAs separada en fracción sólida contiene 96,7% de ácido palmítico (C16:0) como principal componente y 3,3% de ácido esteárico (C18:0). Los resultados mostraron recomendar metanol como disolvente de cristalización debido a su alta eficiencia, bajo coste, estabilidad, disponibilidad, facilidad comparativa de recuperación y su capacidad para formar cristales de aguja que tienen buenas características de filtración y lavado

Continuous and transparent multimodal authentication: reviewing the state of the art

Individuals, businesses and governments undertake an ever-growing range of activities online and via various Internet-enabled digital devices. Unfortunately, these activities, services, information and devices are the targets of cybercrimes. Verifying the user legitimacy to use/access a digital device or service has become of the utmost importance. Authentication is the frontline countermeasure of ensuring only the authorized user is granted access; however, it has historically suffered from a range of issues related to the security and usability of the approaches. They are also still mostly functioning at the point of entry and those performing sort of re-authentication executing it in an intrusive manner. Thus, it is apparent that a more innovative, convenient and secure user authentication solution is vital. This paper reviews the authentication methods along with the current use of authentication technologies, aiming at developing a current state-of-the-art and identifying the open problems to be tackled and available solutions to be adopted. It also investigates whether these authentication technologies have the capability to fill the gap between high security and user satisfaction. This is followed by a literature review of the existing research on continuous and transparent multimodal authentication. It concludes that providing users with adequate protection and convenience requires innovative robust authentication mechanisms to be utilized in a universal level. Ultimately, a potential federated biometric authentication solution is presented; however it needs to be developed and extensively evaluated, thus operating in a transparent, continuous and user-friendly manner

Robust Optimal Attitude Controller for MIMO Uncertain Hexarotor MAVs: Disturbance Observer-Based

This paper proposes a robust optimal attitude control design for multiple-input, multiple-output (MIMO) uncertain hexarotor micro aerial vehicles (MAVs) in the presence of parametric uncertainties, external time-varying disturbances, nonlinear dynamics, and coupling. The parametric uncertainties, external time-varying disturbances, nonlinear dynamics, and coupling are treated as the total disturbance in the proposed design. The proposed controller is achieved in two simple steps. First, an optimal linear-quadratic regulator (LQR) controller is designed to guarantee that the nominal closed-loop system is asymptotically stable without considering the total disturbance. After that, a disturbance observer is integrated into the closed-loop system to estimate the total disturbance acting on the system. The total disturbance is compensated by a compensation input based on the estimated total disturbance. Robust properties analysis is given to prove that the state is ultimately bounded in specified boundaries. Simulation results illustrate the robustness of the disturbance observer-based optimal attitude control design for hovering and aggressive flight missions in the presence of the total disturbance

Robust attitude control design for a low-cost hexarotor micro aerial vehicle

This article proposes a new practical robust attitude state feedback controller of a low-cost hexarotor micro aerial vehicle under the effects of noise in angular velocity measurements and multiple uncertainties (called the equivalent disturbance), which consist of external time-varying wind disturbance, nonlinear dynamics, coupling and parametric uncertainties. The proposed method is designed in two simple steps. Firstly, a nominal cascade controller is designed to reduce noise in angular velocity measurements and to achieve good attitude tracking performance in nominal conditions. Then, a second-order robust compensator is integrated into the closed-loop system to reduce the effects of the equivalent disturbance. The proposed control design is a linear time-invariant controller which is easily implemented in practical applications. Compared to other advanced attitude controllers, the proposed controller incurs lower computational costs and can easily be implemented in a low-cost embedded microcontroller system. In addition, a practical computational design procedure and an intuitive online tuning method for the proposed controller are presented in this article in order to provide a complete reference to micro aerial vehicle developers. The simulation and experimental results are presented to demonstrate the robustness of the proposed controller in operation in outdoor environments, to show good steady-state and dynamic tracking performance of the closed-loop system and to prove that the tracking errors are ultimately bounded within desired limits

Mesoporous NiO/Al-SBA-15 catalysts for solvent-free deoxygenation of palm fatty acid distillate

A series of 5 wt% NiO/Al-SBA-15 catalysts were prepared by wet impregnation of ordered, mesoporous Al-SBA-15 supports (Si/Al molar ratios spanning 5-75) synthesised by a true liquid crystal templating (TLCT) method. The catalytic activity of the resulting catalysts was studied in the solvent-less, hydrogen-free deoxygenation (DO) of palm fatty acid distillate (PFAD), using a semi-batch reactor at 350 °C. 27Al and 29Si MAS-NMR was used to quantify the speciation of framework and extra-framework Al as a function of Si:Al ratio, before and after NiO functionalisation; TEM and XRD confirmed the formation of 9-10 nm NiO nanoparticles in all cases. NiO/Al-SBA-15 catalysts exhibited excellent catalytic activity for PFAD deoxygenation, with hydrocarbon yields reaching 86% and a selectivity to the diesel fraction (C11-C17) of 91%

Robust attitude tracking control of hexarotor MAVs using plug-in gain scheduling robust compensator technique

This paper proposes a robust attitude tracking control scheme for hexarotor micro aerial vehicles (MAVs) under the effects of uncertainties (equivalent disturbances) which consist of external disturbances, nonlinear dynamics, coupling, and parametric uncertainties. The proposed scheme is easy to be implemented compared to other robust controller techniques since it consists of a nominal controller and a plug-in gain scheduling robust compensator only for pitch, roll, and yaw subsystems. The nominal controller is based on cascade PID (P, I, D denote for proportional, integral, and derivative term, respectively) control approach. A plug-in gain scheduling robust compensator is added in order to improve the attitude tracking performance due to the presence of uncertainties. The simulation results prove the attitude tracking errors are bounded in specified boundaries and demonstrate the robustness of the proposed controller and thus suitable for outdoor flight condition