Suchergebnisse

The objective is to develop a new control strategy for quadrotor types of Unmanned Aerial Systems (UAVs) that assist in closing the existing research gaps between the undesired uncertainties and current control systems. This research investigates a system modeling and the effectiveness of error elimination through adaptation in the change of the plant/system's output. The UAV is controlled via Wi-Fi using MATLAB. Proportional-Integral-Derivative (PID) controller, the two degrees of freedom Proportional-Integral-Derivative (2DOF-PID) controller and the model reference Neural Network (NN) controller are used for the aircraft pitch control. External disturbances and modeling errors can lead to the instability and unpredictable behaviors of a system. Even though the disturbances cannot be avoided the effects of such disturbances can be reduced significantly by neural network-based adaptive controllers for high-performance tracking in the presence of the disturbances. The robust control systems with the adaptive control will improve navigation performance and operation for military, reconnaissance and surveillance applications. The application of a robust controller determines the performance by observing the system's behavior to identify and reduce the unpredictable effects of disturbances and achieve a better behavior of the whole system. By observing the system, the neural network is suitably used to learn from a set of training patterns. System identification uses a neural network to capture the behavior of system dynamics, which assists the neural network to train itself to act as a controller. Moreover, the system's performance of the controllers was tested using simulations to demonstrate the effectiveness in improving the speed and stability for the dynamic system. The presented work will produce a flexible, robust and effective control system model that provides additional stability and reduce the effects of disturbances.

To promote the development of military and civilian applications for marine technology, more and more scientific research around the world has begun to develop unmanned surface vehicles (USVs) technology with advanced control capabilities. This paper establishes and identifies the model of vector propulsion USV, which is widely used at present. After analyzing its actuator distribution, we consider that the more realistic vessel model should be an incomplete underactuated system. For this system, a virtual control point method is adopted and an adaptive sliding mode trajectory tracking controller with neural network minimum learning parameter (NNMLP) theory is designed. Finally, in the simulation experiment, the thruster speed and propulsion angle are used as the inputs of the controller, and the linear and circular trajectory tracking tests are carried out considering the delay effect of the actuator, system uncertainty, and external disturbance. The results show that the proposed tracking control framework is reasonable.

ABSTRACTThe paper analyses the impact of the Gulf crisis on the Indian economy as a whole, on the state of Kerala which was the origin of the majority of the Indian migrants in Kuwait and Iraq, and on the returning migrants them‐ selves. The scale of the disturbances is estimated both with respect to the labour market, as well as the flow of remittances. Alternative policy responses are discussed, especially in the context of the Kerala economy, and the problem is viewed separately from the vantage point of the returning migrants, as well as that of the State Government. The effects of the crisis become more acute as the focus shifts from the level of the macroeconomy, to the state of Kerala, to the migrants themselves.

AbstractWhat is the impact of digital technology on professional work? This paper addresses this question by developing a theory on professional jurisdictional control, which we define as a profession's power to maintain or shift from existing jurisdictional settlements in the face of external disturbances. Digital technology is a disturbance, and who ends up undertaking digital tasks depends on the nature of professional jurisdictional control. With protective jurisdictional control, the profession engages in full or subordinate jurisdiction, delegating new tasks to subordinate semiprofessionals. By contrast, with connective jurisdictional control, the profession prefers settlements by division of labor or advisory links, enabling equal-status professions to work together. Using a large and representative database of online job postings, we find evidence for this hypothesis. Empirically, we deploy three ways to gauge the nature of professional jurisdictional control: first, by comparing traditional law firms and alternative business structure firms in the UK; second, by contrasting the US (with protective jurisdictional control) and the UK; and third, by examining the legal sector (in which the legal profession dominates) and non-legal sectors. We also find that protective (connective) jurisdictional control is associated with lower (higher) pay premia for digital skills, consistent with theory. Our findings highlight the mediating role of professional jurisdictional control to inform the future of work debate.

The control of the variable reluctance machine raises a certain number of constraints, among which we can cite: the effect of the external disturbances, the nature of the nonlinearities, the ripple of its torque, and the modeling errors. The different ordering approaches proposed in this article dealt with all these constraints. The classical-control algorithms, for example, of derived full proportional action may prove sufficient if the requirements on the accuracy and performance of systems are flexible. In the opposite case, particularly when the controlled part is submitted to strong nonlinearity and temporal variations, control techniques must be designed to ensure the process's robustness concerning the uncertainties on the parameters and their variations. These techniques include artificial intelligence-based techniques constituted of neural networks and fuzzy logic. This technique can replace PID regulators with nonlinear ones using the human brain's reasoning and functioning and is simulated using MATLAB/Simulink software. Finally, by using obtained waveforms, these results will be compared.

This paper proposes the fractional-order modeling for sliding mode control of a complex four-dimensional energy-saving and emission-reduction system (ESERS). In the proposed methodology, the fractional calculus techniques are employed to accurately model the dynamics of the ESERS, and the fractional-order model of the energy-saving and emission-reduction system (FOESERS) is formulated. With the proposed FOESERS, all of the equilibrium points and the corresponding eigenvalues are obtained, and the instability region and the state trajectories of FOESERS are also given. The FOESERS can represent complex dynamic behaviours with chaotic and unstable states on the energy conservation, carbon emissions, economic growth, and renewable energy development, and have a great impact on the formulation of government energy policies. Furthermore, based on the fractional Lyapunov stability and robust control theory, a sliding-mode controller is designed to control the FOESERS with model uncertainties and external disturbances to the equilibrium point in the finite time. Finally, simulation results confirm the effectiveness and robustness of the proposed scheme.

This paper examines the dynamism and robustness of two irrigation systems of the Kok River system within the Mekong River basin in northern Thailand in the context of changing governance mechanisms and evolution of technological and market forces. It analyzes both temporal and spatial dynamism of the irrigation systems. The temporal dynamism was analyzed over three phases: before intervention, initial operation, and long-term. The before intervention phase analysis examined the effect of various attributes of users on starting an irrigation system, whereas the initial operation phase inquiry included the process of development of rules and level of autonomy in developing the users' own rules over time. The long-term phase analysis focused on external factors affecting the sustainment of these irrigation systems. Spatial dynamism was examined across upstream and downstream systems and within different locations of the system. The analysis was centered on linkages and relationships between five entities: resource, resource users, public infrastructure, public infrastructure providers, and external disturbances. Both systems were still robust, owing to the sustainment of local customs and the role of local leaders still vital, albeit in different forms. The group efforts, their self-governing capabilities, and local institutions, including the changed role of leaders in dealing with external forces, have played an important role in maintaining the robustness of these systems.

COVID-19 is a very dangerous respiratory disease that can spread quickly through the air. Doctors, nurses, and medical personnel need protective clothing and are very careful in treating COVID-19 patients to avoid getting infected with the COVID-19 virus. Hence, a medical telepresence robot, which resembles a humanoid robot, is necessary to treat COVID-19 patients. The proposed self-balancing COVID-19 medical telepresence robot is a medical robot that handles COVID-19 patients, which resembles a stand-alone humanoid soccer robot with two wheels that can maneuver freely in hospital hallways. The proposed robot design has some control problems; it requires steady body positioning and is subjected to disturbance. A control method that functions to find the stability value such that the system response can reach the set-point is required to control the robot's stability and repel disturbances; this is known as disturbance rejection control. This study aimed to control the robot using a combination of Proportional-Integral-Derivative (PID) control and a Kalman filter. Mathematical equations were required to obtain a model of the robot's characteristics. The state-space model was derived from the self-balancing robot's mathematical equation. Since a PID control technique was used to keep the robot balanced, this state-space model was converted into a transfer function model. The second Ziegler-Nichols's rule oscillation method was used to tune the PID parameters. The values of the amplifier constants obtained were Kp=31.002, Ki=5.167, and Kd=125.992128. The robot was designed to be able to maintain its balance for more than one hour by using constant tuning, even when an external disturbance is applied to it. Doi: 10.28991/esj-2021-SP1-016 Full Text: PDF

Abstract
This paper identifies and characterizes vulnerability to climatic change in the Ngöbe-Buglé Indigenous community of Playitas, Panama, using a "trajectories of change" approach. Playitas is a community composed of swidden forest farmers that is undergoing rapid rates of change as a result of demographic shifts, regional development, and climate change. Working in collaboration with a community organization, various methods were used to identify and characterize livelihoods, social-ecological dynamics, environmental change, and behavioral responses to change, with the aim of informing future planning in the community. Qualitative methods included semistructured interviews (n = 26), community workshops, and participant observation. Causal-loop diagrams based on field data and the perceptions of community members were created to model trajectories of change. The research reveals that change is driven by both internal and external factors and that the responses of community members create both reinforcing and balancing feedback loops that overall generate increased stress in agricultural systems, social structures, and environmental components. Although community members historically relied on social relationships, Indigenous knowledge, and remoteness as sources of resilience to external disturbances, climate change is acting as a "multiplier" of their existing vulnerabilities and is undermining their capacity to adapt to current and future climatic changes.

This is the author accepted manuscript. The final version is available from American Physical Society via the DOI in this record ; The version of this paper which was originally published at arXiv.org is in ORE: http://hdl.handle.net/10871/25921 ; Meandering spiral waves are often observed in excitable media such as the Belousov-Zhabotinsky reaction and cardiac tissue. We derive a theory for drift dynamics of meandering rotors in general reaction-diffusion systems and apply it to two types of external disturbances: an external field and curvature-induced drift in three dimensions. We find two distinct regimes: with small filament curvature, meandering scroll waves exhibit filament tension, whose sign determines the stability and drift direction. In the regimes of strong external fields or meandering motion close to resonance, however, phase locking of the meander pattern is predicted and observed. ; H. D. was funded by FWO-Flanders during part of this work. The computational resources (Stevin Supercomputer Infrastructure) and services used in this work were provided by the VSC (Flemish Supercomputer Center), funded by Ghent University, FWO and the Flemish Government–department EWI. I. V. B. and V. N. B. gratefully acknowledge EPSRC (UK) support via Grant No. EP/D074789/1. I. V. B. acknowledges EPSRC (UK) support via Grant No. EP/P008690/1. V. N. B. acknowledges EPSRC (UK) current support via Grant No. EP/N014391/1 (UK).

International audience Call combinations allow animals to expand the communicative power of small repertoires with acoustically inflexible elements. In Campbell's monkeys, Cercopithecus campbelli, males possess a small repertoire of calls that can be merged to an acoustically invariable suffix and which are concatenated into various sequences, mainly in response to external disturbances. The vocal repertoire of adult females has been less well studied although it is much richer, containing both alarm and various social calls. In particular, females possess a low-pitched contact call, produced either alone or merged with a high-pitched, arched unit. Combined contact calls are identity-richer and easier to detect than simple calls. Here, we investigated the socioecological factors that determined the production of single and combined utterances and found that combined utterances were more common when identity was relevant such as in mixed-species associations and during socially important vocal exchanges. In contrast, single calls were used mainly when predation risk was high, as part of this species' generally cryptic antipredator strategy. We discuss these finding in the light of current theories regarding the evolution of combinatorial signalling.

Though Zambia is well endowed with natural resources, its agricultural sector is extremely underdeveloped, and almost half of the small-scale farmers do not even achieve food security. While internal political problems are a major cause for this, external disturbances such as climate change and economic shocks are additional threats to the sector. This study explores the main challenges and presents suggestions for resolutions based on empirical research. The e-voucher system, crop diversification and conservation agriculture belong to the bundle of suggested measures, which – when implemented together – could lead to pro-poor agricultural development. They would not only buffer climate and economic shocks but also increase income in a pro poor manner and show spill-over effects. Accompanied by suitable "software" measures at all levels in order to increase knowledge as well as adaptive and organisational capacity, farmers' resilience can be comprehensively strengthened. However, political will and more commitment from all stakeholders, including the engagement of the private sector and the self initiative of farmers, are needed to really make things happen.

Having efficient and effective transport infrastructure (e.g. bridges, roads, railways, airways and tunnels) in place is essential for supporting the economic and social well-being of an economy. External disturbances that emerge as a result of climate change, for example, are impacting its performance. Delivering, managing and maintaining transport assets that are resilient and adaptive to changing environmental conditions have become a priority for many governments worldwide. Central to ensuring that transport infrastructure functions at their optimum and is resilient to external changes is performance measurement, as it enables those processes that need to be modified and improved for enhancing the asset's adaptability throughout their lifecycle to be identified. Despite the importance of performance measurement in ensuring the resilience of transport infrastructure, it has received limited attention by governments in their policy making. Therefore, this paper provides a review of the extant literature and proposes a life-cycle resilient performance measurement framework (PMF) within transport context. The developed PMF is robust in comprehensively capturing the underlying perspectives that are significant for: (1) understanding the current state of the resilient level of transport assets; and (2) enabling a higher ability of the assets to adapt to environment-related changes in the future. The implications of the proposed framework for transport policy development are also discussed in this paper.

The Southern African Development Community (SADC) and its member countries are potentially vulnerable to external disturbances, including environmental, economic, and social shocks. Regional policy emphasizes interventions to ensure long-term growth and development in the face of potential disturbance. Current emphasis is placed on mitigating the impact of climate change, including the creation of the SADC Climate Change Strategy and Action Plan. However, the need for long-term adaptation and associated policy is evident to reduce regional vulnerabilities. Research is an important source of evidence to support policymaking, with specific importance to institutions in developing regions such as the SADC and during times of global change and disruption. SADC development policy related to resilience outcomes ought to be informed by research. This paper investigates the extent to which existing research supports regional resilience policymaking. Objectives include investigating available research on resilience in the SADC, identifying potential limitations, and delineating areas of future research to be considered by researchers that contribute to knowledge and evidence creation. A bibliometric review and selective content review of existing research were utilized. Relevant publications for the aforesaid analysis were delineated using the source concepts "resilience", "adaptation", "adaptability", and "Southern African Development Community" (or "SADC"). Using the SCOPUS database, bibliometric data of 65 publications were imported into the VOSviewer application (v.1.6.17). Keyword occurrences and network and overlay visualizations were applied to identify the research themes underlying current research. The findings, which were supported by the selective content review, indicate that existing research focuses primarily on environmental and social disturbances, while the applicable regional planning scale and development policy are considered to a limited extent. Areas of future research ought to create evidence that is thematically relevant to policy areas and applicable to policy interventions, which necessitates increased research on economic disturbances, a broadening of existing themes to the appropriate regional planning scale, and consideration of explicit regional development objectives and policy. Transdisciplinarity ought to be central to future research on the diverse disturbances facing the region, while researchers ought to leverage knowledge-creation opportunities catalyzed by SDG implementation.

As the "Third Pole", the Qinghai-Tibet Plateau is threatened by environmental changes. Ecosystem vulnerability refers to the sensitivity and resilience of ecosystems to external disturbances. However, there is a lack of relevant studies on the driving factors of ecosystem vulnerability. Therefore, based on spatial principal components analysis and geographic detectors methods, this paper evaluates the ecosystem vulnerability and its driving factors on the Qinghai-Tibet Plateau from the years 2005 to 2015. The results were as follows: (1) The ecosystem vulnerability index (EVI) of the Qinghai-Tibet Plateau is mainly heavy and extreme, showing a gradually increasing trend from southeast to northwest. (2) The spatial heterogeneity of the EVI is significant in the southeast and northwest, but not in the southwest and central parts. (3) Analysis of influencing factors shows that environmental factors have more significant effects on EVI than socioeconomic variables, facilitating the proposal of adequate policy implications. More efforts should be devoted to ecological protection and restoration to prevent grassland degradation and desertification in the high-EVI areas in northwest. The government is also urged to improve the ecological compensation mechanisms and balance ecological protection and residents' development needs in the southeast.