Terms Of System Stability Research Articles

Homobimetallic bis-NHC(Ptdvtms)2 Complexes for the Hydrosilylation of Alkenes

A series of six bimetallic bis-NHC(Ptdvtms)2 complexes 1–6 (dvtms = 1,1,3,3-tetramethyl-1,3-divinyldisiloxane) has been designed by expansion of the monometallic Markó-type system in anticipation of synergistic bimetallic cooperation. The new compounds are easily accessible using Karstedt's catalyst [Pt2(dvtms)3] as platinum(0) precursor and the respective bis-(imidazolium) salts (L1–6), deprotonated by potassium tert‑butoxide. Characterization via NMR spectroscopy (1H, 13C, 29Si, 195Pt) and SC-XRD reveals a strong similarity of this new complex class to the parent monometallic complexes. The hydrosilylation reactions of oct-1-ene or 1,1,1,3,3-pentamethyl-3-vinyldisiloxane (MMVi) with 1,1,3,5,5-heptamethyltrisiloxane (MDHM), respectively, are efficiently and selectively catalyzed with turn-over frequencies (TOF) of up to 78,000 h–1 after a significantly shortened induction period compared to their monometallic relatives. Mercury poisoning experiments demonstrate the superiority of bimetallic compared to monometallic systems in terms of stability when exposed to silanes.

Implementasi Sistem Informasi Pemerintah Daerah: Apakah Efektif Dalam Mendukung Pelaporan Keuangan OPD

This study aims to determine how effective the implementation of local government information systems (SIPD) in supporting financial reporting at OPDs in Mataram City, namely RSUD X. This research uses descriptive qualitative methods with data collection techniques in the form of observations and interviews. The research analysis refers to the UTAUT effectiveness indicators consisting of Performance Expectancy, Effort Expectancy, Social Influences and Facilitating Conditions. The results of this study indicate that the implementation of SIPD in supporting financial reporting at RSUD X when viewed in terms of indicators of performance expectancy, effort expectancy and facilitating conditions is still less effective because in its implementation SIPD still has many weakness both in terms of system stability and the availability of features needed, while for indicators of social influences SIPD can already be categorized as effective because the implementation of financial report data entry is adapted to user needs.

Unraveling the Role of Microalgae in Mitigating Antibiotics and Antibiotic Resistance Genes in Photogranules Treating Antibiotic Wastewater.

Harnessing the potential of specific antibiotic-degrading microalgal strains to optimize microalgal-bacterial granular sludge (MBGS) technology for sustainable antibiotic wastewater treatment and antibiotic resistance genes (ARGs) mitigation is currently limited. This article examined the performance of bacterial granular sludge (BGS) and MBGS (of Haematococcus pluvialis, an antibiotic-degrading microalga) systems in terms of stability, nutrient and antibiotic removal, and fate of ARGs and mobile genetic elements (MGEs) under multiclass antibiotic loads. The systems exhibited excellent performance under none and 50 μg/L mixed antibiotics and a decrease in performance at a higher concentration. The MBGS showed superior potential, higher nutrient removal, 53.9 mg/L/day higher chemical oxygen demand (COD) removal, and 5.2-8.2% improved antibiotic removal, notably for refractory antibiotics, and the system removal capacity was predicted. Metagenomic analysis revealed lower levels of ARGs and MGEs in effluent and biomass of MBGS compared to the BGS bioreactor. Particle association niche and projection pursuit regression models indicated that microalgae in MBGS may limit gene transfers among biomass and effluent, impeding ARG dissemination. Moreover, a discrepancy was found in the bacterial antibiotic-degrading biomarkers of BGS and MBGS systems due to the microalgal effect on the microcommunity. Altogether, these findings deepened our understanding of the microalgae's value in the MBGS system for antibiotic remediation and ARG propagation control.

Throughput-Aware Dynamic Task Offloading Under Resource Constant for MEC With Energy Harvesting Devices

With the explosive increase of Internet of Things (IoT) devices, an increasing number of computation-intensive applications are emerging in IoT system. However, most IoT devices are limited by size and location, equipped with low-performance CPUs and low-capacity batteries, which cannot go well with computation-intensive applications. Mobile edge computing (MEC) is considered as a promising solution to provide computation-intensive and latency-sensitive services in IoT system, but it is still challenging to improve the throughput and extend the battery life of IoT devices under communication constraints. This paper focuses on the task offloading problem for an MEC system with multiple energy harvesting (EH) devices. To accommodate the system dynamics and ensure the system stability in terms of task queue and battery level, we apply Lyapunov optimization theory, and design a computation tasks maximum offloading algorithm to maximize the system throughput. The algorithm can determine the offloading decision in real-time without knowing any statistical information about the system. We first give a series of mathematical analysis to verify the system stability and discuss the performance of the algorithm. In addition, a number of simulation experiments are conducted to present the efficiency of the algorithm.

Dynamical Analysis of a Local Lengley-Epstein System Coupled with Fractional Delayed Differential Equations

We consider a system of fractional delayed differential equations. The ordinary differential version of the system without delay is introduced in the Lengyel-Epstein reaction-diffusion system. We evaluate the system with and without delay and explore the stability of the unique positive equilibrium. We also prove the existence of Hopf bifurcation for both cases. Furthermore, the impacts of Caputo fractional order parameter and time delay parameter on the dynamics of the system are investigated with numerical simulations. It is also concluded that for different values of time delay parameter, the decreament of the Caputo fractional order parameter has opposite effects on the system in terms of stability.

Networked fault detection for fuzzy systems using a quantizer with event-triggered strategy

This paper concerns with the problem of fault detection for networked fuzzy systems. Considering the digital communication channel, quantization is adopted to make the data transmission feasible and the induced data distortion is converted into a bounded uncertain term. For the purpose of saving network resources, a new quantizer with an event-triggered strategy is designed to reduce the length and the number of the transmitted data packets, simultaneously. In the process of stability analysis, the T-S fuzzy model approach is employed to approximate the nonlinear networked system, and a more flexible fuzzy design method is presented to get the fault detection filter which can detect the sensor fault in the presence of external disturbance. And sufficient conditions are constructed to guarantee the stability of the filter error system in terms of linear matrix inequalities. Finally, the simulation example is given to verify the feasibility of the method.

Power System Stability With a High Penetration of Inverter-Based Resources

Inverter-based resources (IBRs) possess dynamics that are significantly different from those of synchronous-generator-based sources and as IBR penetrations grow the dynamics of power systems are changing. This article discusses the characteristics of the new dynamics and examines how they can be accommodated into the long-standing categorizations of power system stability in terms of angle, frequency, and voltage stability. It is argued that inverters are causing the frequency range over which angle, frequency, and voltage dynamics act to extend such that the previously partitioned categories are now coupled and further coupled to new electromagnetic modes. While grid-forming (GFM) inverters share many characteristics with generators, grid-following (GFL) inverters are different. This is explored in terms of similarities and differences in synchronization, inertia, and voltage control. The concept of duality is used to unify the synchronization principles of GFM and GFL inverters and, thus, established the generalized angle dynamics. This enables the analytical study of GFM-GFL interaction, which is particularly important to guide the placement of GFM apparatuses and is even more important if GFM inverters are allowed to fall back to the GFL mode during faults to avoid oversizing to support short-term overload. Both GFL and GFM inverters contribute to voltage strength but with marked differences, which implies new features of voltage stability. Several directions for further research are identified, including: 1) extensions of nonlinear stability analysis to accommodate new inverter behaviors with cross-coupled time frames; 2) establishment of spatial–temporal indices of system strength and stability margin to guide the provision of new stability services; and 3) data-driven approaches to combat increased system complexity and confidentiality of inverter models.

Influence of extrinsic induced tensile stress on the self-propagating high-temperature synthesis of nanosized Al/Ni multilayers

Reactive multilayer systems consisting of alternating nanoscale Al and Ni layers are applicable in joining, various pyrotechnic applications and thermal batteries. Since diffusion based high-temperature synthesis occurs without the presence of air, efforts have focused on investigating the understanding of the fundamental reaction processes and characteristics. The aim of this study is to expose the reactive multilayers to extrinsic induced tensile stress so that the self-propagating synthesis can proceed under these conditions. Further, the properties during and after the reaction will be investigated. Multilayers deposited by sputtering on Kapton® substrates with different bilayer– and total thicknesses as well as commercial Nanofoils® with thicknesses of 40 µm and 60 µm were used as samples. The investigations focused on the propagation velocity measured with a high-speed camera, the temperature regime determined with a high-speed pyrometer, and the formed phases after the synthesis examined via X-ray diffraction. The gained results of this study reveal important insights for the application of the reactive Al/Ni multilayer system in terms of stability or reliability related to propagation front velocity, maximum temperature and formed phases under induced external tensile stresses.Graphical abstract

Special issue on “Optimal design and operation of energy systems”

Special issue on “Optimal design and operation of energy systems”

BANKING SYSTEM FRAGILITY IN NIGERIA: HANGING ON THE PRECIPICE?

The health of a country’s banking system is a key determinant to the development of the country. A fragile banking system portends danger not only to the financial system but the entire economy. This study investigates the state of the Nigerian banking system in terms of stability or fragility from 1981 to 2020. We used the banking system fragility index (BSFI) proposed by Kibritçioğlu (2003) to analyze Nigerian banking industry aggregate data from three risk areas: credit, market and liquidity. We estimated that out of the 40 years examined, the banking system was fragile for 23 years given their BSFI less than 0 while it was not fragile for 17 years with BSFI = 0 or greater. We found that most of the years when the Nigerian banking system was fragile were periods of relaxed monetary policies, deregulation and credit expansion. Secondly, the years of banking system stability were when the county’s banking system was subjected to stiff regulation and consolidation. Given the number of years that the system was fragile, we observed that sustained economic growth and development requires that the banking system remain strong as long as possible, and that the Nigerian situation could not promote this important objective. We recommend that the financial regulatory authorities put in place more stringent policies as banks are more fragile during the deregulation of the banking industry.

Аналіз підходів до оцінки стійкості банківської системи України

Ensuring the sustainability of the banking system is one of the key tasks of economic policy of countries, regardless of their level of economic development. The purpose of the article is to define and analyze existing approaches to assessing the financial sustainability of the banking system of Ukraine. When considering the essence of the terms «stability» and «sustainability», it is determined that they are closely related, but have certain nuances that need to be taken into account in the context of the financial condition of the banking system. The scientific literature uses different terms to describe the state of the system, its structure and processes, which differ from the approach to defining these terms in the context of the financial sector. A study of the factors affecting the financial sustainability of the banking system has shown that they can be divided into the external and internal factors. The external factors include economic, legal, political, competitive trends, technology, and automation. The internal factors include economic, organizational and technological aspects, as well as the quality of management. It is noted that various factors are interrelated and have a multidirectional impact on the indicators of financial sustainability of the banking system. It is defined that currently there are many methods for assessing the banking system and individual banks, which differ in various parameters and indicators. The author identifies several main approaches to assessing the sustainability of banking systems in the world countries, including stress testing of the banking sector, analysis of indicators of financial sustainability of banks, assessment of the system of regulation and supervision, assessment of the level of financial stability of banks, and risks. These approaches can be used to analyze and monitor the financial sustainability of the banking system both separately and in complex combination. There are also various complex indicators and indices, such as the Financial Condition Index (FCI) and the Financial Stress Index (FSI), which are used to reflect the financial stability of countries of the world. The Financial Stress Index (FSI), developed by the National Bank of Ukraine in 2017, which consists of four sub-indices and sets the weight of each sub-index according to the volume of each market, is also examined. The author proposes general directions for improving the financial stability of the Ukrainian banking system in terms of wartime, including strengthening regulatory policy, improving financial literacy of citizens, and developing digital payment infrastructure. The carried out study contributes to the understanding of the factors that affect the financial sustainability of the banking system of Ukraine and should be taken into account when developing strategies to ensure such stability in the future.

Particle Swarm Optimization for Optimal Frequency Response with High Penetration of Photovoltaic and Wind Generation

As the installation of solar-photovoltaic and wind-generation systems continue to grow, the location must be strategically selected to maintain a reliable grid. However, such strategies are commonly subject to system adequacy constraints, while system security constraints (e.g., frequency stability, voltage limits) are vaguely explored. This may lead to inaccuracies in the optimal placement of the renewables, and thus maximum benefits may not be achieved. In this context, this paper proposes an optimization-based mathematical framework to design a robust distributed generation system, able to keep system stability in a desired range under system perturbance. The optimum placement of wind and solar renewable energies that minimizes the impact on system stability in terms of the standard frequency deviation is obtained through particle swarm optimization, which is developed in Python and executed in PowerFactory-DIgSILENT. The results reveal that the proposed approach has the potential to reduce the influence of disturbances, enhancing critical clearance time before frequency collapse and supporting secure power system operation.

Development of Liquid Crystal Cream Containing Germinated Brown Rice

Herbal cosmetics are gaining popularity over chemicals for beauty products. However, natural products are often prone to deterioration. Therefore, stability and compatibility testing are the main examinations of the safety and reliability of herbal cosmetics. Liquid crystal structures provide better application performances than conventional emulsion systems in terms of stability, controlled release, and moisturizing. Rice is the most profitable crop in Thailand, and the skin healing benefits of rice have been reported. Thus, the current study aimed to develop a liquid crystal cream containing germinated brown rice extract (GBR) or biological cosmetic active ingredients, to study its efficacy on hydration effects and moisturizer, to identify the active ingredient content, such as gamma-aminobutyric acid (GABA), phenolic content, and to evaluate the physical properties and stability of the product. Results revealed that GBR contained GABA and a total phenolic content of 273.28 mg GABA/100 g of rice and 2.58 mg GAE/100 g of rice, respectively. The GBR-liquid crystal cream had good stability and moisturizing effect. The developed products were statistically significantly in hydrating more than a counter brand product. The product that increased moisture the most was the GBR-liquid crystal cream. The GBR-liquid crystal cream provided a high-efficiency moisturizing effect and reliability enabling it to be a premium commercial product shortly.

Free-will arbitrary time stabilisation problem for a class of nonlinear strict-feedback systems based on the backstepping method

In this paper, the problem of free-will arbitrary time stabilisation for a class of nonlinear systems is investigated. In an effort to extend the idea of fixed-time theory to a broader class of systems, a prescribed-time controller has been developed by the examination of a general form of the strict-feedback systems. By means of the designed control scheme, the arbitrary convergence of the system states is guaranteed. Furthermore, the implementation of this approach is independent of any initial values and system design parameters. In real-world applications, this approach can be used to achieve system stability in terms of efficient time management. For many well-known systems, the proposed control can be used to solve the pre-defined convergence problem of asymptotic and finite-time controllers. Based on the backstepping control strategy, the stability of the proposed method for a strict-feedback system is demonstrated in the design section. Ultimately, the simulation results verify the accuracy and effectiveness of the proposed method.

User-Adaptive Variable Damping Control Using Bayesian Optimization to Enhance Physical Human-Robot Interaction

This letter presents a user-adaptive variable damping controller that enhances the overall performance of coupled human-robot systems in terms of stability, agility, user effort, and energy expenditure during physical human-robot interaction. The controller accounts for impedance properties of the human limbs and adaptively changes robotic damping from negative to positive values based on user's intent of motion while minimizing energy of the coupled human-robot system. Bayesian optimization is used to evaluate an unknown objective function and optimize noisy performance, which builds on a Gaussian process to account for the uncertainty of human behaviors and noisy observations. To validate the effectiveness of the presented approach and evaluate its potential applications in real-world scenarios, we performed human experiments using a common robotic arm manipulator. Experimental results from five pilot subjects demonstrated that the controller does not require a long parameter tuning process. Compared to variable damping control without user-adaptive parameter changes, the presented adaptive control strategy could reduce ∼45% energy expenditure and achieve average performance improvement of ∼20% when several performance metrics of stability, agility, and user effort are considered together.

Asymptotic Trajectory Tracking of Underactuated Non-minimum Phase Marine Vessels

This paper presents a trajectory tracking scheme for a class of underactuated non-minimum phase marine vessels. Through proper coordinates transformations, the vessels tracking model can be transformed into two-input-two-output strict-feedback form for which general backstepping method can be applicable to solve the control problem. To avoid possible singularity problem in the recursive control design, an AMO (asymptotic modification of orientation) concept is applied. In this case, the vessels are forced to track this modified trajectory instead of directly tracking the predefined reference trajectory. Since the vessels’ tracking model is transformed into two-input-two-output strict-feedback form with invertible control gain matrix, the non-minimum phase problem can be easily handled by the proposed method. Proposed tracking method can guarantee the asymptotic stability of closed-loop system in terms of polar coordinates. Simulation studies are also carried out to demonstrate the effectiveness of presented tracking scheme.

LMI-Based Anti-Windup Control Design for Discrete-Time Switched Systems With Actuator Saturation

In this paper, the stabilization problem for discrete-time switched systems with actuator saturation is investigated. Using switched Lyapunov functions and L2-gain analysis, a one-step method is proposed to design the controller and the anti-windup compensator. Some sufficient conditions are derived to guarantee the local asymptotic stability of the closed-loop system in terms of linear matrix inequalities (LMI). To illustrate to effectiveness of the proposed technique, a speed tracking controller of a freight train is designed for the automatic train operation (ATO). This system is modeled as a switched system since it is equipped with an electric traction system and a pneumatic brake system which different dynamics and saturation bounds.

Tuning the Parameters of Power System Stabilizer Using Runge Kutta Algorithm

Low-frequency oscillations due to unpredictable disturbances in an interconnected power grid are a serious threat to the stability of the power system. Reliable operation of a modern power system, when exposed to sudden disturbances, is crucial, and the safe operation of the system is directly related to success in damping oscillations. Power System Stabilizer (PSS) devices have been used to reduce fluctuations caused by short-time disturbances in power systems. These devices provide additional damping torque components to the generators as an auxiliary control device of the excitation system. Due to the non-linearity of electrical power systems, it is significant to design multi-machine power systems with optimum PSS parameters under critical conditions. In this paper, the PSS design problem was solved using the Runge Kutta Algorithm (RUN). The PSS design problem was considered an optimization problem in which an eigenvalue-based objective function has developed, and the proposed RUN method was tested in a WSCC 3-machine 9-bus test system using the linearized Heffron-Phillips model. In the linearized model, system stability has been enhanced by shifting the eigenvalues to the stability regions. When the results obtained from the test system are examined, it has seen that the proposed RUN is the most effective method in terms of system stability.

Editorial for the special issue on operation and control of power electronics dominated power systems

With the ever increasing penetration of renewable energy and power electronics, the current energy network is being transformed to power electronics dominated power system (PEDPS). Different from conventional power grid, PEDPS has its own characteristics such as much lower inertia, lower short circuit capacity, multi-timescale dynamic behavior, etc. These features bring tremendous challenges to the analysis, design, modeling and control of the modern power grid systems. Significant efforts have been made by researches to address these challenges, and also promote technological advancements for the entire modern power systems in terms of stability, reliability, flexibility, and efficiency.

Investigations on Practical Issues in Solid Immersion Lens Based Sub-Wavelength Terahertz Imaging Technique: System Stability Verification and Interference Pattern Removal.

Terahertz (THz) imaging techniques are attractive for a wide range of applications, such as non-destructive testing, biological sensing, and security imaging. We investigate practical issues in THz imaging systems based on a solid immersion lens (SIL). The system stability in terms of longitudinal misalignment of the SIL is experimentally verified by showing that the diffraction-limited sub-wavelength beam size (0.7 λ) is maintained as long as the SIL is axially located within the depth-of-focus (~13 λ) of the objective lens. The origin of the fringe patterns, which are undesirable but inevitable in THz imaging systems that use continuous waves, is analytically studied, and a method for minimizing the interference patterns is proposed. By combining two THz images obtained at different axial positions of the object and separated by λ/4, the interference patterns are significantly reduced, and the information hidden under the interference patterns is unveiled. The broad applicability of the proposed method is demonstrated by imaging objects with different surface profiles. Our work proves that the resolution of conventional THz imaging systems can easily be enhanced by simply inserting a SIL in front of the object with high tolerance in the longitudinal misalignment and provides a method enabling THz imaging for objects with different surface profiles.