Region Of Attraction Research Articles

МОЛЕКУЛЯРНО-ДИНАМИЧЕСКОЕ МОДЕЛИРОВАНИЕ СТРУКТУРЫ И СВОЙСТВ СТЕКЛООБРАЗНОЙ ПОДЛОЖКИ SiO2 В ШИРОКОМ ДИАПАЗОНЕ ТЕМПЕРАТУР

F.V. Grigoriev's paper “Force Fields for Molecular-Dynamic Modeling of Sputter Deposition Process on Silicon Dioxide Film”, proposes a simple DESIL inter-ion potential for modeling amorphous SiO2 substrates widely used for thin film sputter deposition. This potential provides an important advantage when compared with popular potential of BKS due to the absence of a non-physical attraction region at short distances between particles. This is important when simulating SiO2 substrate sputtering where collisions between particles result in short-range proximity. In this case an artifact of particle inter-capture may be observed which distorts the simulation results. The purpose of this work is to demonstrate the potential for predicting the structural and thermodynamic characteristics of amorphous silicate glasses over a broad temperature range.

Comparison of methods of nonlinear control systems design

The issue of designing nonlinear control systems is a complex problem. A lot of methods are known that allow us to find a suitable control for a given nonlinear object that provides asymptotic stability of the nonlinear system equilibrium and an acceptable quality of the transient process. Many of these methods are difficult to apply in practice. Thus, comparing some of the methods in terms of simplicity of use is of great interest. Two analytical methods for the synthesis of nonlinear control systems are considered. They are the algebraic polynomial-matrix method that uses a quasilinear model, and the feedback linearization method that uses the Brunovsky model in combination with special feedbacks. A comparative analysis of the algebraic polynomial-matrix method and the feedback linearization method is carried out. It is found out that the algebraic polynomial-matrix method (APM) is much simpler than the feedback linearization method (FLM). A numerical example of designing a system that is synthesized by these methods is considered. It is found out that the system synthesized by the APM method has a region of attraction of the equilibrium position twice as large as the region of attraction of the system synthesized by the FLM method. It is reasonable to use the algebraic polynomial-matrix method with the quasilinear models in case of synthesis of control systems of objects with differentiable nonlinearities.

ТЕНДЕНЦІЇ ТА СУЧАСНІ ЗРУШЕННЯ В ІНВЕСТИЦІЙНОМУ СЕРЕДОВИЩІ НА РИНКУ ЖИТЛОВОЇ НЕРУХОМОСТІ

The article analyzes the development trends of the primary and secondary residential real estate market in Ukraine for 2020-2021 and identifies the main changes in the investment environment in this market. The economic essence of the concept of "investment attractiveness" and related concepts "investment process", "investment activity" and "investment climate" are clarified. A comparative analysis of the investment attractiveness of residential real estate in different regions of Ukraine revealed that in 2020 the secondary housing market was more attractive for investment, but in 2021 the investment attractiveness of the primary and secondary residential real estate market generally deteriorated. It was found that the main reason for the decline in the investment attractiveness of the national housing stock is that in 2020-2021 apartment prices in the most attractive regions of Ukraine continued to grow, although their pace slowed down. It is substantiated that in order to intensify investment activity in the real estate market in Ukraine it is necessary to create a favorable investment climate for all business entities on a civilized basis and in accordance with the principles of transparency and social conditions. To improve the investment climate and improve the investment attractiveness of the residential real estate market, the Ukrainian government is recommended to develop effective measures aimed at significantly reducing mortgage interest rates to a level where mortgages will be available to most citizens.

Canard-induced mixed mode oscillations as a mechanism for the Bonhoeffer-van der Pol circuit under parametric perturbation

PurposeThis paper aims to investigate the singular Hopf bifurcation and mixed mode oscillations (MMOs) in the perturbed Bonhoeffer-van der Pol (BVP) circuit. There is a singular periodic orbit constructed by the switching between the stable focus and large amplitude relaxation cycles. Using a generalized fast/slow analysis, the authors show the generation mechanism of two distinct kinds of MMOs.Design/methodology/approachThe parametric modulation can be used to generate complicated dynamics. The BVP circuit is constructed as an example for second-order differential equation with periodic perturbation. Then the authors draw the bifurcation parameter diagram in terms of a containing two attractive regions, i.e. the stable relaxation cycle and the stable focus. The transition mechanism and characteristic features are investigated intensively by one-fast/two-slow analysis combined with bifurcation theory.FindingsPeriodic perturbation can suppress nonlinear circuit dynamic to a singular periodic orbit. The combination of these small oscillations with the large amplitude oscillations that occur due to canard cycles yields such MMOs. The results connect the theory of the singular Hopf bifurcation enabling easier calculations of where the oscillations occur.Originality/valueBy treating the perturbation as the second slow variable, the authors obtain that the MMOs are due to the canards in a supercritical case or in a subcritical case. This study can reveal the transition mechanism for multi-time scale characteristics in perturbed circuit. The information gained from such results can be extended to periodically perturbed circuits.

Substantiation of analytical dependences for hydraulic calculation of high-viscosity oil transportation

One of the development priorities in oil and gas industry is to maintain gas and oil pipeline networks and develop pipeline-connected gas and oil fields of the Arctic zone of the Russian Federation, a promising region the resource potential of which will not only meet a significant portion of internal and external demand for various types of raw materials and primary energy carriers, but will also bring great economic benefits to subsoil users and the state. The mineral and raw material centers of the Nadym-Purskiy and Pur-Tazovskskiy oil and gas bearing areas are among the most attractive regions of the Arctic zone. It is necessary to develop a scientifically substantiated approach to improve the methods of oil transportation from the field to the existing pipelines. As it is known, the task of increasing the efficiency of pipeline transportation of high-viscosity oil is inseparably connected with solving problems in the field of thermal and hydraulic calculation of pipeline system. The article presents the substantiation of dependencies for hydraulic calculation of pipelines transporting high-viscosity oil exhibiting complex rheological properties. Based on the laws of hydraulics for non-Newtonian fluids, the formulas for calculating head losses for fluids obeying Ostwald's law are proposed, their relationship to the classical equations of hydraulics is shown. The theoretical substantiation of looping installation for increasing the efficiency of pipeline transportation of high-viscosity oil taking into account the received dependences for power fluid is considered.

Analysis of an Extremum Seeking Controller Under Bounded Disturbance.

One of the applications of Extremum Seeking (ES) is to localize the source of a scalar field by using a mobile agent that can measure this field at its current location. While the scientific literature has presented many approaches to this problem, a formal analysis of the behavior of ES controllers for source seeking in the presence of disturbances is still lacking. This paper aims to fill this gap by analyzing a specific version of an ES control algorithm in the presence of source movement and measurement disturbances. We define an approximate version of this controller that captures the main features but allows for a simplified analysis and then formally characterize the convergence properties of this approximation. Through simulations and physical experiments, we compare the theoretically-predicted regions of attraction of the simplified system with the behavior of the full system and show that the simplified version is a good predictor of the behavior of the initial ES controller.

Security Analysis of Linearization for Nonlinear Networked Control Systems Under DoS

We explore a security analysis of nonlinear networked control systems under denial-of-service (DoS) attacks. In particular, we focus on the vulnerability of a linearization approach in a stabilization problem. When linearization-based control is used, DoS attacks can make the state leave the region of attraction. This situation can occur when the initial state lies outside a certain region around the equilibrium, the size of which depends on the strength of the attacks on the network. In this article, we first derive a sufficient condition for local stability of a nonlinear system under averagely constrained DoS attacks. Then, we investigate the region of attraction and derive an explicit relation between the initial states and the DoS parameters to guarantee convergence of the state trajectories. Furthermore, we investigate a destabilization problem from the perspective of malicious attackers and present an instability condition. By a numerical example, we demonstrate a new insight foattackers to induce undesired behaviors of the control system.

Structure transforming for constructing constraint force field in musculoskeletal robot

PurposeHuman-like musculoskeletal robots can fulfill flexible movement and manipulation with the help of multi joints and actuators. However, in general, sophisticated structures, accurate sensors and well-designed control are all necessary for a musculoskeletal robot to achieve high-precision movement. How to realize the reliable and accurate movement of the robot under the condition of limited sensing and control accuracy is still a bottleneck problem. This paper aims to improve the movement performance of musculoskeletal system by bio-inspired method.Design/methodology/approachInspired by two kinds of natural constraints, the convergent force field found in neuroscience and attractive region in the environment found in information science, the authors proposed a structure transforming optimization algorithm for constructing constraint force field in musculoskeletal robots. Due to the characteristics of rigid-flexible coupling and variable structures, a constraint force field can be constructed in the task space of the musculoskeletal robot by optimizing the arrangement of muscles.FindingsWith the help of the constraint force field, the robot can complete precise and robust movement with constant control signals, which brings in the possibility to reduce the requirement of sensing feedback during the motion control of the robot. Experiments are conducted on a musculoskeletal model to evaluate the performance of the proposed method in movement accuracy, noise robustness and structure sensitivity.Originality/valueA novel concept, constraint force field, is proposed to realize high-precision movements of musculoskeletal robots. It provides a new theoretical basis for improving the performance of robotic manipulation such as assembly and grasping under the condition that the accuracy of control and sensory are limited.

Quality as strategy, the evolution of co-production in the Region Jönköping health system, Sweden: a descriptive qualitative study

BackgroundPursuing the vision ‘for a good life in an attractive region,’ the Region Jönköping County (RJC) in Sweden oversees public health and health-care services for its 360 000 residents. For more than three decades, RJC has applied ‘quality as strategy,’ which has included increasing involvement of patients, family and friends and citizens. This practice has evolved, coinciding with the growing recognition of co-production as a fundamental feature in health-care services. This study views co-production as an umbrella term including different methods, initiatives and organizational levels. When learning about co-production in health-care services, it can be helpful to approach it as a dynamic and reflective process.ObjectiveThis study aims to describe the examples of key developmental steps toward co-production as a system property and to highlight ‘lessons learned’ from a Swedish health system’s journey.MethodThis qualitative descriptive study draws on interviews with key stakeholders and on documents, such as local policy documents, project reports, meeting protocols and presentations. Co-production initiatives were defined as strategies, projects, quality improvement (QI) programs or other efforts, which included persons with patient experience and/or their next of kin (PPE). We used directed manifest content analysis to identify initiatives, timelines and methods and inductive conventional content analysis to capture lessons learned over time.ResultsThe directed content analyses identified 22 co-production initiatives from 1997 until today. Methods and approaches to facilitate co-production included development of personas, storytelling, person-centered care approaches, various co-design methods, QI interventions, harnessing of PPEs in different staff roles, and PPE-driven improvement and networks. The lessons learned included the following aspects of co-production: relations and structure; micro-, meso- and macro-level approaches; attitudes and roles; drivers for development; diversity; facilitating change; new perspectives on current work; consequences; uncertainties; theories and outcomes; and regulations and frames.ConclusionsCo-production evolved as an increasingly significant aspect of services in the RJC health system. The initiatives examined in this study provide a broad overview and understanding of some of the RJC co-production journey, illustrating a health system’s approach to co-production within a context of long-standing application of QI and microsystem theories. The main lessons include the constancy of direction, the strategy for improvement, engaged leaders, continuous learning and development from practical experience, and the importance of relationships with national and international experts in the pursuit of system-wide health-care co-production.

Professional expectations of medical university graduates in solving the issues of health care system staffing

Introduction. At present, in most regions of the Russian Federation there is a shortage of medical personnel in the public health system. The issue is particularly acute in medical organizations providing primary health care, as well as in municipal districts remote from the regional center. The purpose of the paper is to examine the professional expectations and intentions of medical university students. Materials and methods. The method of questioning was applied in the study. Questionnaires were taken by 296 students of the fifth year of the specialties «Medicine» and «Pediatrics», studying on the budget and commercial forms of education.Results. Only 22% of respondents considered primary care as a place of work. Large cities are chosen for work by 90% of respondents, and 42% of them would like to leave their home region and find a job in economically more attractive regions. Only 6% of respondents are ready to go to the countryside, and 4% of respondents are interested in ambulance service. Approximately evenly distributed were opinions on work in public and private health care system, respectively, 54% and 56% of respondents. At the stage of graduation, 16.6% of the students were disappointed in their chosen profession, another 22.3% found it difficult to answer, and 5.7% do not plan to stay in healthcare after graduation. Discussion. The main reasons for this situation are salaries that do not meet the needs of graduates, especially at the start of their professional career, the social unsettlement of young doctors, mainly in small towns and rural areas, and insufficient practical training. Conclusion. The solution to the problem lies in the sphere of socio-economic provision of living conditions and stimulation of quality training of specialists, taking into account professional orientation.

Natural tourist resources in Rhodope tourist region

Abstract Rhodope Tourist Region is one of the most attractive tourist regions in Bulgaria and one of the few that stand out with almost uniform year-round development of tourist activities. The outlines of the tourist area largely coincide with the outlines of the mountain of the same name. This fact predetermines the exceptional richness and diversity of natural tourist resources. Here are the largest coniferous forests in the country, some of the largest dams, the largest number of caves used for tourist purposes, many mineral springs, bizarre rock formations, etc. The relatively well-preserved natural environment is a prerequisite for the presence of extremely high biodiversity, as well as a large number of protected areas. The region is specialized in mountain tourism, incl. ski tourism and hiking. In connection with the available natural tourist resources, the tourism product is increasingly enriched with various specialized types of tourism, incl. balneotherapy tourism, ecotourism, rural tourism, etc. In connection with the increasingly intensive tourist load, the problem of protecting the natural tourist resources from the growing anthropogenic pressure, as well as the prospects for sustainable development of the tourist industry in the region are becoming especially relevant. The aim of the present paper is to valorize the natural tourist resources of the Rhodope tourist region and to give guidelines for their sustainable use.

Lyapunov-based continuous-time nonlinear control using deep neural network applied to underactuated systems

Several learning-based control with computational intelligence strategies handle challenges related to the difficulty of modeling complex systems or the need for control strategies with provably safe. In recent years, learning-based control using machine learning has been successfully demonstrated in robotics applications and applied to deal with nonlinearities. These control methods may lead to better solutions to nonlinear problems, such as the safety-critical industry, which requires strong guarantees about the controller behavior. Learning-based neural network control can comprehend and learn about plants, disturbances, the environment, and operating conditions. In this paper, we presented a Lyapunov-based nonlinear control determined from a deep neural network, which uses the Lyapunov theory to compute a control law for a nonlinear system. For advance stability analysis, an estimation of the region of attraction is presented. A numerical example and experimental simulations using the rotational inverted pendulum system are performed and compared with a conventional control technique. The proposed method calculated a control law that provided the stabilizability of the system and produced better solutions considering different tracking and process disturbance.

Swarm fixed-time reference tracking: a discrete model

This paper proposes a discrete-time kinematic model for a swarm/flock of multidimensional agents combining two problems that are usually addressed separately: trajectory tracking and shape control. Relying only on local information, for the first time in the discrete-time domain, the model provides a time control on the evolution of the swarm/flock, that is: in fixed-time, the swarm centroid tracks a given reference trajectory; in finite-time, the connections graph becomes complete and the agents reach an aggregation inside a region of attraction centred on the moving centroid. The shape of such a region can vary among polytopes, oriented ellipsoids/spheres and straight lines by only changing the eigenvalues of a coordinates-coupling matrix. Compared to classic shape control methods where agents inter-distances must be provided, this model is more suitable for large swarms. Finally, numerical simulations and a laboratory experiment are proposed to highlight the described model properties.

Transport infrastructure of Spain as a factor in tourism development


 
 
 This article considers features of functioning of a modern transport network. Transport is an important area of infrastructure supply for the population and the state economy, the key function of which is the movement of people and goods. The current transport complex is subject to contradictory trends: as an infrastructure industry, transport is located in a position dependent on the production of social goods, and as a special sector of the economy, transport has an important impact on the regional location of production capacity and participates in the process of reproduction part of the system of economic relations. The importance of transport infrastructure in the economy, its development and operating conditions are difficult to overestimate. After all, it is the basis of the supporting framework of territorial social systems of any level. On the current state, level and opportunities for the development of the transport infrastructure depends not only the social and economic growth of territorial economic systems, but also their spatial development. Tourism plays a significant role in the development of transport infrastructure. Europe is one of the most attractive regions for tourists in the world. In turn, Spain is one of the most popular destinations for tourists from around the world as well as for European tourists. Spain plays an important role in tourist traffic in Europe. This is facilitated by its efficient transport and geographical location, developed production infrastructure, as well as historical aspects. Spain is a key country of transit by air and sea with the Americas. The flat terrain promotes the development of road and rail passenger transport across the centre of the country. And given the attractiveness to tourists and direction of tourist flows to the regions of the country, the study of geographical features of transport infrastructure is quite relevant. The peculiarities of the functioning and formation of the transport infrastructure of Spain are considered. The geographical features of the development of the infrastructure of railway, road and sea and air transport of Spain are analyzed. As for the terminals in the regions of Spain, their number also corresponds to the number of airports. Therefore, the largest number of terminals is in the Canary Islands – 9 (all airports have one terminal, except Lanzarote). There are 8 terminals in the airports of Andalusia, where all airports except Malaga have one terminal, in Malaga there are three. The two Madrid airports have 6 terminals, but 5 of them are located at the country's main airport – Madrid-Barajas. Catalonia's airports have 5 terminals, two of which are located in Barcelona El Prat. There are 4 terminals in Galicia – one each in Vigo and La Coruna and two in Santiago de Compostela. There are 4 terminals in Galicia – one each in Vigo and La Coruna and two in Santiago de Compostela. In all other regions, the number of terminals is proportional to the number of airports. An assessment of the level of development of transport infrastructure for tourism in the regions of Spain was conducted. On the basis of quantitative indicators of the analysis of the transport infrastructure of Spain, a point assessment of the level of development of the transport infrastructure of the country’s regions for the needs of tourism was carried out. Administrative units are divided into 5 groups: with the highest, high, sufficient, medium and low level of development of transport infrastructure for tourism. Transport infrastructure is most developed in the tourist regions of the country – Catalonia, Andalusia, Madrid, the Canary and Balearic Islands.
 
 

Acceleration of Global Optimization Algorithm by Detecting Local Extrema Based on Machine Learning.

This paper features the study of global optimization problems and numerical methods of their solution. Such problems are computationally expensive since the objective function can be multi-extremal, nondifferentiable, and, as a rule, given in the form of a “black box”. This study used a deterministic algorithm for finding the global extremum. This algorithm is based neither on the concept of multistart, nor nature-inspired algorithms. The article provides computational rules of the one-dimensional algorithm and the nested optimization scheme which could be applied for solving multidimensional problems. Please note that the solution complexity of global optimization problems essentially depends on the presence of multiple local extrema. In this paper, we apply machine learning methods to identify regions of attraction of local minima. The use of local optimization algorithms in the selected regions can significantly accelerate the convergence of global search as it could reduce the number of search trials in the vicinity of local minima. The results of computational experiments carried out on several hundred global optimization problems of different dimensionalities presented in the paper confirm the effect of accelerated convergence (in terms of the number of search trials required to solve a problem with a given accuracy).

Lyapunov Analysis of Two Imbalanced Power System Areas

The transient stability is the capability of the system to preserve synchronism while being affected by large disturbances. It is a nonlinear problem that requires a simultaneous solution for many differential equations. Therefore, a thorough analysis is needed to resolve it. In this paper, we present the transient stability for multimachine under different fault cases and to analyze using the Lyapunov function. It serves as an analytical tool to determine the necessary condition to be stable. The system is stable as long as it is contained in the region of attraction. Meanwhile, the swing equation and reduced admittance matrix are used to model the system in three conditions, pre-fault, during the fault, and post-fault. The numerical simulations are conducted to verify that the synchronism can be preserved despite under faults on the transmission lines by achieving the critical clearing time.

A Lyapunov function for the combined system-optimizer dynamics in inexact model predictive control

In this paper, an asymptotic stability proof for a class of methods for inexact nonlinear model predictive control is presented. General Q-linearly convergent online optimization methods are considered and an asymptotic stability result is derived for the setting where a limited number of iterations of the optimizer are carried out per sampling time. Under the assumption of Lipschitz continuity of the solution, we explicitly construct a Lyapunov function for the combined system-optimizer dynamics, which shows that asymptotic stability can be obtained if the sampling time is sufficiently short. The results constitute an extension to existing attractivity results which hold in the simplified setting where inequality constraints are either not present or inactive in the region of attraction considered. Moreover, with respect to the established results on robust asymptotic stability of suboptimal model predictive control, we develop a framework that takes into account the optimizer’s dynamics and does not require decrease of the objective function across iterates. By extending these results, the gap between theory and practice of the standard real-time iteration strategy is bridged and asymptotic stability for a broader class of methods is guaranteed.

Robust tube-based MPC with enlarging the region of attraction for tracking of switched systems

This paper addresses a robust tube based model predictive control (RTBMPC) strategy for tracking problem of piecewise affine (PWA) linear systems. The core idea of the RTBMPC strategy is to robustly control an uncertain system through its nominal system and an additional feedback term which rejects a bounded additive disturbance. In tracking problem, RTBMPC strategy should be capable to steer the uncertain system to a given setpoint fulfilling the constraints. But if the setpoint changes, the controller may not success due to the loss of feasibility of the optimization problem. This paper employs several novel features to deal with tracking problem. First, the tracking problem is converted into the regulation problem by introducing an extra system called regulation nominal system that its constraints are translated from tracking into regulation. It leads to a reduction in complexity of the objective function. Then, the feasibility region is enlarged for given setpoint without increasing the prediction horizon by changing the terminal constraint set at different steps of RTBMPC problem solving. Simulation examples, including two different case studies, are presented to illustrate the effectiveness of the proposed RTBMPC.

Stabilization of time delay systems with saturations via PDE predictor boundary control design

This paper addresses the stabilization issue of linear time delay system with input saturation and distinct input delays via predictor feedback boundary control algorithm by employing transport partial differential equations (PDEs). First, the addressed ordinary differential equation (ODE) system with input delay is equivalently represented as a cascade of an ODE and transport PDEs. Second, by employing the backstepping Volterra integral transformation technique, the equivalent cascade system is transformed into a stable target system, whose kernels are solved by the constraints satisfying transport PDEs. Third, based on the boundary conditions of the obtained invertible transformation, the proposed feedback control law can be formulated. Fourth, by applying semigroup operator theory, the well-posedness of the resulting system is proved and consequently, novel exponential stability conditions of the addressed system are established. Then, the domain of attraction region under the given actuator saturation constraints is estimated with the help of the solution of obtained stability conditions. Finally, a demonstrative simulation example is offered to verify the feasibility and usefulness of the results.

Bifurcation analysis of a class of generalized Hénon maps with hidden dynamics

Although continuous systems such as the Chua circuit are known as systems with hidden attractors, hidden attractors also exist in classical discrete maps, such as a generalized Hénon map. A hidden attractor is an attractor that does not overlap with its own attracting region in its vicinity, which makes it difficult to visualize. In this paper, a local bifurcation analysis method for discrete maps is described, and the bifurcation analysis of the generalized Hénon map is performed using the method. The bifurcation structure, as the parameters are changed, shows a certain law, and the interesting Neimark–Sacker bifurcation and period‐doubling bifurcation are confirmed to occur simultaneously. It was also found that the hidden attractors exist in the rectangular characteristic chaotic regions, and they appear relatively frequently near the window of chaos. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.