Search Results (8,140)

This paper presents a global fixed-time control framework to address the target circumnavigation tracking problem of underactuated unmanned surface vehicles (USV) under unknown velocity states, lumped uncertainties, and actuator saturation. At the core of this approach is a novel fixed-time target-enclosing line-of-sight (FTTELOS) guidance law, designed to generate the desired heading angle and surge velocity. To estimate unknown velocities, external disturbances, and unmeasured system states, a set of fixed-time observers is constructed, consisting of a velocity observer, a disturbance observer, and a high-dimensional extended state observer (HFTESO). Moreover, to enhance robustness and effectively tackle actuator saturation, the control scheme incorporates a fixed-time sliding mode controller, a dynamic auxiliary system, and a fixed-threshold event-triggered mechanism. Simulation results using SimuNPS demonstrate that the proposed method enables rapid and smooth target circumnavigation, with all system errors converging to an arbitrarily small neighborhood of the origin within a fixed time. Theoretical analysis and simulation studies confirm the effectiveness and robustness of both the FTTELOS guidance law and the integrated control strategy. Quantitatively, compared with the traditional target-enclosing line-of-sight (TELOS) method, the proposed FTTELOS reduces the convergence time of the distance error ${\delta }_e$ from 13.64 s to 10.22 s and the angular error ${\varphi }_e$ from 10.46 s to 7.52 s, demonstrating a significant improvement in convergence speed and overall control performance. Full article

Presently, numerous non-conventional power resources have been applied in power system networks. However, these resources are very effective in islanded microgrid (IMG) scenarios for addressing numerous operational challenges. Additionally, it is observed that the power output of most of these resources is environment-dependent and intermittent in nature. This intermittency causes a power imbalance between the overall generated power and the load demand, which results in an undesired frequency oscillation. In order to address this unwanted frequency fluctuation, this research work proposes power–frequency synchronisation considering an islanded microgrid scenario under numerous non-conventional power resources. The major contribution of this work includes implementing a suitable and optimised control scheme that effectively controls diverse power system disturbances and various uncertainties. A Fick’s law optimisation-based proportional–integral–derivative–acceleration controller (PIDA) is implemented under this proposed power scenario. Additionally, an extensive performance assessment is conducted considering different simulation test cases in order to verify the performance of the proposed control topology. Further, the effectiveness of the suggested power network is tested on a 33-bus radial distribution network. Finally, simulation results are shown to show the effectiveness of the proposed control scheme for the efficient operation of the microgrid in achieving the desired performance under the diverse operating conditions. Full article

Ecosystems and biodiversity around the globe face multiple threats, including climate change and invasive species. Non-native species are known for their resilience to disturbances and their ability to thrive more successfully than native species in urbanized or otherwise disturbed areas, and some of them can become invasive. It is a complex challenge to detect, manage, and control such species, which require coordinated efforts from society, government, and the academic community. In this study, the eMIAS (South American Invasive Mollusks Specialists) research group (27 experts from seven South American countries) aim to provide foundational knowledge for management of these species. We compiled and synthesized information on the mollusc species that are native to South America and that have been introduced to other regions of the world. A total of 29 species were detected, including 10 marine, 10 freshwater, and 9 terrestrial. For each species, the area of origin, date and place of introduction, and current distribution were determined. We could determine that (1) most of these introductions have occurred in connection with globalization processes, such as an increase in trade. (2) The potential source regions of those 29 species are also areas that received non-native species from elsewhere (e.g., Europe, Asia). (3) Regions where species introductions have taken place are subject to the impacts of climate change and/or urbanization. Full article

The large-scale adoption of renewable energy sources, while environmentally beneficial, introduces significant frequency fluctuations due to the inherent variability of wind and solar output. Electric vehicle (EV) integration with substantial battery storage and bidirectional charging capabilities offers potential mitigation for these fluctuations. This study addresses load frequency regulation in multi-area interconnected power systems incorporating diverse generation resources: renewables (solar/wind), conventional plants (thermal/gas/hydro), and EV units. A hybrid controller combining the proportional–integral–derivative with second derivative (PIDD²) and tilted derivative (TD) structures is proposed, with parameters tuned using an innovative optimization method called the Tianji’s Horse Racing Optimization (THRO) technique. The THRO-optimized PIDD²-TD controller is evaluated under realistic conditions including system nonlinearities (generation rate constraints and governor deadband). Performance is benchmarked against various combination structures discussed in earlier research, such as PID-TID and PIDD²-PD. THRO’s superiority in optimization has also been proven against several recently published optimization approaches, such as the Dhole Optimization Algorithm (DOA) and Water Uptake and Transport in Plants (WUTPs). The simulation results show that the proposed controller delivers markedly better dynamic performance across load disturbances, system uncertainties, operational constraints, and high-renewable-penetration scenarios. The THRO-based PIDD²-TD controller achieves optimal overshoot, undershoot, and settling time metrics, reducing overshoot by 76%, undershoot by 34%, and settling time by 26% relative to other controllers, highlighting its robustness and effectiveness for modern hybrid grids. Full article

Background: Fibromyalgia (FM) is a chronic pain syndrome characterized by widespread musculoskeletal pain, fatigue, unrefreshed sleep, and cognitive disturbances. Despite extensive research, its pathophysiology remains incompletely understood, and there are no validated biomarkers for diagnosis. Videocapillaroscopy is a non-invasive imaging technique that enables detailed visualization of microvascular structures and may provide insights into microcirculatory alterations associated with FM. Methods: Thirty patients with FM and 30 healthy controls underwent oral videocapillaroscopy at four sites: right and left buccal mucosa and upper and lower labial mucosa. Quantitative parameters, including capillary caliber, density, and length, were extracted using a validated neural-network-based software, while qualitative parameters, including visibility, orientation, and the presence of microhemorrhages, were assessed by the operator. Results: Capillary length was significantly reduced in fibromyalgia patients (297.49 ± 26.82 µm) compared to healthy controls (324.43 ± 37.59 µm; p = 0.002), and capillary orientation differed significantly between groups (p < 0.05). Capillary caliber, density, and visibility did not show statistically significant differences. Conclusions: These findings indicate subtle microvascular alterations in the oral mucosa of patients with fibromyalgia. Although the observed changes are not sufficient for diagnostic purposes or early detection, they provide preliminary evidence that videocapillaroscopy can detect microvascular features associated with FM in the oral mucosa. Further studies with larger cohorts and longitudinal designs are warranted to clarify the clinical relevance of these observations and to explore their potential association with symptom severity or disease progression. Full article

This paper proposes a novel fixed-time super-twisting sliding mode control (ST-SMC) strategy for uncertain robotic arm systems, aiming to address the issues of control chattering and the uncontrollable upper bound of convergence time in traditional sliding mode control algorithms. The proposed approach enhances system robustness, suppresses chattering, and ensures that the convergence time of the robotic arm can be explicitly bounded. First, a sliding surface with fixed-time convergence characteristics is constructed to guarantee that the tracking errors on this surface converge to the origin within a prescribed time. Then, an immersion and invariance (I&I) disturbance observer with exponential convergence properties is designed to estimate large, time-varying disturbances in real time, thereby compensating for system uncertainties. Based on this observer, a new super-twisting sliding mode controller is developed to drive the trajectory tracking errors toward the sliding surface within fixed time, achieving global fixed-time convergence of the tracking errors. Simulation results demonstrate that, regardless of the initial conditions, the proposed controller ensures fixed-time convergence of the tracking errors, effectively eliminates control torque chattering, and achieves a tracking error accuracy as low as 2 × 10⁻⁹. These results validate the proposed method’s applicability and robustness for high-precision robotic systems. Full article

The accurate acquisition and real-time calculation of the attitude angle of precision firefighting extinguishing projectiles are essential for ensuring stable flight and precise extinguishing agent release. However, measuring the roll attitude angle in such projectiles is challenging due to their highly dynamic nature and environmental disturbances such as fire smoke, high temperature, and electromagnetic interference. Traditional methods for measuring attitude angles rely on multi-sensor fusion schemes, which suffer from complex structure and high cost. This paper proposes a single-gyro attitude calculation method based on micro-electromechanical inertial measurement units (MIMUs). This method integrates Fourier transform time-frequency analysis with a second-order Infinite Impulse Response (IIR) bandpass filtering algorithm optimized by dynamic coefficients. Unlike conventional fixed-coefficient filters, the proposed algorithm adaptively updates filter parameters according to instantaneous roll angular velocity, thereby maintaining tracking capability under time-varying conditions. This theoretical contribution provides a general framework for adaptive frequency-tracking filtering, beyond the specific engineering case of firefighting projectiles. Through joint time-frequency domain processing, it achieves high-precision dynamic decoupling of the roll angle, eliminating the dependency on external sensors (e.g., radar/GPS) inherent in conventional systems. This approach drastically reduces system complexity and provides key technical support for low-cost and high-reliability firefighting projectile attitude control. The research contributes to enhancing the effectiveness of urban firefighting, forest fire suppression, and public safety emergency response. Full article

Background: The Kingdom of Saudi Arabia is adjacent to two vital marine ecosystems; the semi-enclosed Arabian Gulf and the largely landlocked Red Sea. Dinoflagellates are repeatedly found in these bodies of marine water, which serve as significant routes for cargo ships. Through these ships and ballast water, invasive dinoflagellate species and their cysts are introduced. They compete with indigenous species for nutrients and space, cause massive fish kill-off and disturb the ecological balance and biodiversity. To address these threats, the International Convention for the Control and Management of Ships’ Ballast Water and Sediments (BWM Convention) set forth guidelines intended to curtail the dissemination of such detrimental organisms. The Kingdom of Saudi Arabia was one of the co-signatory countries to this Convention. Methods of detection and monitoring include microscopy, molecular characterization and remote sensing, which are employed for the detection and monitoring of these harmful algae, in order to avert disasters such as fish die-offs. The results of several reports confirmed the presence of number of dinoflagellates in both the Arabian Gulf and the Red Sea, some of which are toxin producers, with certain species being highlighted as invasive species whose presence requires a high level of alert. Discussion: The monitoring, the change in engineering of cargo ships and the introduction of advanced surveillance methods, together with the proper treatments of ballast water, are all important security elements that ensure the safe disposal of ballast water without introducing harmful species. Full article

Background: Antibodies to glutamic acid decarboxylase (anti-GAD) can give rise to stiff person syndrome (SPS), an infrequent autoimmune condition of the central nervous system marked by fluctuating muscular rigidity and stimulus-evoked spasms. Disturbances in eye-movement control are rarely identified yet may provide insight into underlying neural involvement. Methods: Two individuals with anti-GAD-related SPS showing distinctive ocular-motor abnormalities were examined with quantitative videonystagmography, supplemented by representative video documentation. Results: Recordings demonstrated varied patterns of ocular-motor disturbance, including reduced smooth-pursuit accuracy, delayed saccadic initiation, dysmetria, intrusive saccades, and several nystagmus types. Partial improvement occurred after immunomodulatory therapy. Conclusions: These findings extend current understanding of the anti-GAD SPS phenotype and indicate that quantitative analysis of eye movements may offer a sensitive, non-invasive marker of disease activity. Larger, prospective studies are needed to clarify prevalence and responsiveness to treatment. Full article

Traditional heat diffusion systems are typically regulated using Proportional–Integral–Derivative (PID) controllers. PID controllers still remain the backbone of numerous industrial control applications due to their simplicity, robustness, and efficiency. However, traditional tuning methods—such as Ziegler–Nichols or Cohen–Coon—often exhibit limitations when applied to systems with nonlinear dynamics, time-varying behaviors, or parametric uncertainties. To address these challenges, Fuzzy Logic Controllers (FLC) have emerged as a promising hybrid strategy, by translating quantitative and imprecise linguistic inputs into quantitative control actions, thereby enabling more adaptive and precise regulation. This is achieved through the integration of fuzzy inference mechanisms that dynamically adjust PID gains in response to changing system conditions. This study proposes a fuzzy logic control strategy for a heat diffusion system and conducts a comparative analysis against conventional PID control. The methodology encompasses system modeling, design of the fuzzy inference system, and simulation studies. To improve transient response and address time delays, additional features such as Anti-Windup compensation and a Smith Predictor are integrated into the control scheme. The final validation step involves the introduction of simulated environmental disturbances, including abrupt temperature drops, to evaluate the controller’s robustness. Simulation results demonstrate that the proposed FLC provides superior dynamic performance compared to the conventional PID controller, achieving approximately 5–7% faster rise time and 8–10% lower settling time. The incorporation of an anti-windup mechanism did not yield significant benefits in this application. In contrast, the integration of a Smith Predictor further reduced oscillatory behavior and substantially improved disturbance rejection, tracking accuracy, and adaptability under simulated thermal variations. These results underscore the effectiveness of the FLC in handling systems with time delays and nonlinearities, reinforcing its role as a robust and adaptable control strategy for thermal processes with complex dynamics. Full article

In this paper, we investigate the stability of a triangularly coupled triple-loop thermosyphon system with momentum and heat exchange at the coupling point as well as the existence of disturbances. The controller consists of a single, local-state feedback. From the stability analysis, we obtain explicit bounds on the feedback gains, which depend on the Rayleigh numbers and the momentum coupling parameter, but independent of the thermal coupling parameter. The existence of the stability bounds allows us to design decentralized adaptive controllers to automatically search for the feasible gains when the system parameters are unknown. In the case of existing disturbances in the system, we approximate the disturbances via an extended-state observer for the purpose of disturbance rejection. Numerical results are given to demonstrate the performance of the proposed decentralized disturbance rejection controller design. Full article

Hemodynamics significantly impact the biology of endothelial cells (ECs) lining the blood vessels. ECs are exposed to various hemodynamic forces, particularly frictional shear stress from flowing blood. While physiological flows are critical for the normal functioning of ECs, abnormal flow dynamics, known as disturbed flows, may trigger endothelial dysfunction leading to atherosclerosis and other vascular conditions. Such flows can occur due to sudden geometrical variations and vascular abnormalities in the cardiovascular system. In the current study, a microfluidic system was used to investigate the impact of different flow conditions (i.e, normal vs. disturbed) on ECs in vitro. We particularly explored the relationship between specific flow patterns and cellular pathways linked to oxidative stress and inflammation related to atherosclerosis. Here, we utilized a 2D cell culture perfusion system featuring an immortalized human vascular endothelial cell line (EA.hy926) connected to a modified peristaltic pump system to generate either steady laminar flows, representing healthy conditions, or disturbed oscillatory flows, representing diseased conditions. EA.hy926 were exposed to an oscillatory flow shear stress of 0.5 dynes/cm² or a laminar flow shear stress of 2 dynes/cm² up to 24 h. Following flow exposure, cells were harvested from the perfusion chamber for quantitative PCR analysis of gene expression. Reactive oxygen species (ROS) generation under various shear stress conditions was also measured using DCFDA/H2DCFDA fluorescent assays. Under oscillatory shear stress flow conditions (0.5 dynes/cm²), EA.hy926 ECs showed a 3.5-fold increase in the transcription factor nuclear factor (NFκ-B) and a remarkable 28.6-fold increase in cyclooxygenase-2 (COX-2) mRNA expression, which are both proinflammatory markers, compared to static culture. Transforming growth factor-beta (TGFβ) mRNA expression was downregulated in oscillatory and laminar flow conditions compared to the static culture. Apoptosis marker transcription factor Jun (C-Jun) mRNA expression increased in both flow conditions. Apoptosis marker C/EBP homologous protein (CHOP) mRNA levels increased significantly in oscillatory flow, with no difference in laminar flow. Endothelial nitric oxide synthase (eNOS) mRNA expression was significantly decreased in cells exposed to oscillatory flow, whereas there was no change in laminar flow. Endothelin-1 (ET-1) mRNA expression levels dropped significantly by 0.5- and 0.8-fold in cells exposed to oscillatory and laminar flow, respectively. ECs subjected to oscillatory flow exhibited a significant increase in ROS at both 4 and 24 h compared to the control and laminar flow. Laminar flow-treated cells exhibited a ROS generation pattern similar to that of static culture, but at a significantly lower level. Overall, by exposing ECs to disturbed and normal flows with varying shear stresses, significant changes in gene expression related to inflammation, endothelial function, and oxidative stress were observed. In this study, we present a practical, optimized system as an in vitro model that can be employed to investigate flow-associated diseases, such as atherosclerosis and aortic aneurysm, thereby supporting the understanding of the underlying molecular mechanisms. Full article

Morphological plasticity (MP) is an essential strategy for plants in nutrient acquisition, disturbance alleviation, and community coexistence during environmental and climatic changes. However, to date, there has been little research concerning the MP for alpine–subalpine forests on the Qinghai–Tibet plateau. These forests are representative of the ectomycorrhizal (ECM) type, and morphological traits of these ECM roots, such as root tip lengths, diameters, and their adherent hyphal lengths and exploration types, have rarely been studied in the context of nutrient and environmental gradients. In this study, we examined the morphological traits of ECM roots for faxon fir (Abies fargesii var. faxoniana), which dominated in subalpine forests across nine elevations on the Eastern Qinghai–Tibet plateau. By quantifying ca. 90,000 root tips, the hyphal lengths of ectomycorrhizal extraradical mycelium (EEM, i.e., short- and long-distance exploration types) reached up to 1.1 × 10⁶ cm/m³ in soil, which decreased significantly due to gradually increasing altitude. In contrast, the variability of ECM root traits (diameter, length, and superficial area) was highly conserved along the altitudinal gradients, yet the root tip lengths were positively associated with soil protease enzyme activity. The increase in diameter and length of ECM root tips was climate-independent yet significantly associated with increasing root N concentration. In the studied forests, a long-distance exploration type of ECM hyphae was controlled by precipitation (p < 0.05), whereas the short-distance one was controlled by precipitation and temperature simultaneously. The EEM lengths of short- and long-distance exploration types were associated with high C concentration and low N concentration in host tree root tissues. Our findings demonstrated that MP expression in nutrient-foraging strategies for the dominant coniferous trees facilitates the adaptation to changing environments by specialized hyphal structures. In conclusion, ECM root tips and hyphal structures are two dimensions of functional traits linked to root N concentration in opposite ways, and their MP collectively ensures the temporal stability and resistance of subalpine forests on the Qinghai–Tibet plateau. These results provide new insights into ECM morphological traits and their adaptation in changing environments, which is valuable for understanding responses of subalpine forests to climate change. Full article

Virtual synchronous generator (VSG) simulates the dynamic characteristics of synchronous generator, offering significant advantages in flexibly adjusting virtual inertia and damping parameters. However, their dynamic stability is susceptible to constraints such as control parameter design, grid disturbances, and the intermittent nature of distributed power sources. This study addresses the degradation of transient performance in traditional sliding mode control for VSG, caused by insufficient multi-parameter cooperative adaptation. It proposes an adaptive sliding mode control strategy based on radial basis function (RBF) neural networks. Through theoretical analysis of the influence mechanism of virtual inertia and damping coefficient perturbations on system stability, the RBF neural network achieves dynamic parameter decoupling and nonlinear mapping. Combined with an integral-type sliding surface to design a weight-adaptive convergence law, it effectively avoids local optima and ensures global stability. This strategy not only enables multi-parameter cooperative adaptive regulation of frequency fluctuations but also significantly enhances the system’s robustness under parameter perturbations. Simulation results demonstrate that compared to traditional control methods, the proposed strategy exhibits significant advantages in dynamic response speed and overshoot suppression. Full article

Micro and nano-plastics pose a significant threat to the global environment, affecting agricultural systems, food security, and human health. Some studies indicate that microplastics can induce physiological damage in plants, including oxidative stress, reduced germination, stunted biomass growth, and impaired photosynthesis. The extent of the damage varies depending on the type of microplastics, their size, and concentration. Moreover, micro- and nano-plastics can disturb the delicate balance of the soil microbiome. Microbial communities play a significant role in the health and functioning of ecosystems by facilitating nutrient turnover, breaking down organic matter, preserving soil integrity, and controlling diseases caused by soil-dwelling pathogens. This review highlights the role of omics technologies in elucidating the molecular mechanisms underlying plant responses to micro- and nanoplastics. The findings can enhance our comprehension of how micro- and nanoplastics affect agricultural systems when they contaminate soil. Full article