Stability Problem Research Articles

Three phase microcontroller based automatic change-over selection switch

The significance of electricity in a developed country cannot be underestimated because power instability problem affects the economy growth, productivity and infrastructure development. The issues of phase failure, losses and phase imbalance earth fault are main causes that lead to unstable and erratic power supply. Most homes and office complexes where single-phase supply is needed are supplied with three phases of power supply to allow change from one phase to another when there is fluctuation or complete outage of power supply on a particular phase. This operation is normally done manually and has caused a setback in terms of time wastage, strenuous operation, susceptibility to fire outbreak, electric shock and high maintenance frequency. When voltage supply on a phase is below 220V or above 415V, this system automatically disconnects the load from the phase and connects to another where the required condition is met. Therefore, this paper presents a Microcontroller Based Automatic Transfer Switching System which is made up of voltage sensing circuit, Hall Effect current sensor, relays, LEDs and LCD of PIC16F877A microcontroller. A system flow chart was developed, programmed with MikroC software and simulated using Proteus electrical software design. A 10KVA single phase generator was used as alternate power source. The load capacity of the design was determined by decoupling Maxwell’s Equations of 8KW and power loss using pointing vector equation as 0.25% of the peak load. The switch is tested to have function optimally within ±5% nominal voltage of 220 - 415V supply and produced approximately 20 seconds elapses during the entire process of power supply changeover. Hence this device is suitable for Industrial and Domestic use where 3-phase power supply is available with a stand-by power source.

Stability analysis of ultra-high and steep reinforced soil fills slopes based on strength reduction

The research focuses on solving the important problem of slope stability in the field of civil engineering. The study adopted an advanced strength double reduction coefficient method for slope stability analysis, which considers the different influence weights of cohesion and internal friction angle, and reduces them with different reduction coefficients to describe the stability of the slope. The simulation experiment results indicate that the attenuation degree of cohesion and internal friction angle affects slope stability. When the reduction coefficient of cohesion increases to 1.737 and the reduction coefficient of internal friction angle increases to 1.201, the slope is prone to instability and failure, and the safety factor of the calculated result is 1.493. Moreover, when the anti-slip pile is set in the middle of the slope (1/2), and the slope is in a critical state, the bending moment and shear force suffered by the anti-slip pile are both maximum, so the reinforcement effect is also the best.

Geotechnical Assessment of the Slopes of Hamamok Dam, NE of Koya, Kurdistan Region of Iraq

The Hamamok Dam is an earthfill dam with a height of 25 m and length of 125 m; constructed in 2011; located northwest of Koya town on a deep canyon-like valley that flows along the southeastern plunge of the Bana Bawi anticline; which forms Bawagi Mountain. The exposed rocks in the site belong to the Pila Spi and Gercus formations; however, rocks of the Khurmala and Kolosh formations are exposed upstream from the dam’s reservoir. The difference in the hardness of the carbonate rocks of the Pila Spi Formation which forms the uppermost parts of the cliffs surrounding the dam site and those of soft reddish brown clastics of the Gercus Formation caused steep slopes that suffer from slope instability problems. To assess a geotechnical study of slopes in the dam site, we have collected different field data to perform a Kinematic assessment method using Dip Analyst 2.0 software and draw the stereographic projection for the studied 10 stations using Stereonet v.11 software. Besides Bejerman’s method, which is based on field data only and indicates the Landslide Possibility Index (LPI). The results showed that the L.P.I. values range between 23 and 27, whereas the results of the Kinematic analysis showed that the right bank (Stations 1 – 5) suffers from plane sliding, whereas the left bank (Stations 6 – 10) suffers from toppling. In both cases, Joint 2 has the main role in the developed failures.

Generation of reverse time migration dip gathers with the stabilized Poynting vector and their application in the improvement of subsalt images

Subsalt imaging is challenging with coherent noise prevalent beneath complex salt structures. The coherent noise degrades the imaging quality, making image enhancement and interpretation difficult and potentially erroneous. The dip gathers of reverse time migration (RTM) serve as an ideal domain for separating signals from coherent noise due to their distinct distributions in the dip domain. Methods utilizing the Poynting vector offer an efficient and cost-effective means to produce dip gathers. However, the presence of zero points in the Poynting vector causes instabilities in direction or angle estimation, leading to the leakage of reflection energy into false dip angles. This issue complicates the separation of desired signals from coherent noise. We address this instability by employing a stabilized Poynting vector to produce high-quality RTM dip gathers. The stabilized Poynting vector does not contain zero points within the range of wave propagation, thus mitigating the instability problem. The dip gathers generated using the stabilized Poynting vector provide a clearer and more precise depiction of signal and noise distributions, allowing us to identify the boundaries of desired signals and mute all noise outside these boundaries. Two numerical examples with a synthetic dataset and a field dataset are used to demonstrate our method's effectiveness in reducing coherent noise and improving quality of subsalt images.

Robustness of reaction–diffusion PDEs predictor-feedback to stochastic delay perturbations

This paper studies the robustness of a PDE backstepping delay-compensated boundary controller for a reaction–diffusion partial differential equation (PDE) with respect to a nominal delay subject to stochastic error disturbance. The stabilization problem under consideration involves random perturbations modeled by a finite-state Markov process that further obstruct the actuation path at the controlled boundary of the infinite-dimension plant. This scenario is useful to describe several actuation failure modes in process control. Employing the recently introduced infinite-dimensional representation of the state of an actuator subject to stochastic input delay for ODEs (Ordinary Differential Equations), we convert the stochastic input delay into r+1 unidirectional advection PDEs, where r corresponds to the number of jump states. Our stability analysis assumes full-state measurement of the spatially distributed plant’s state and relies on a hyperbolic–parabolic PDE-PDE cascade representation of the plant plus actuator dynamics. Integrating the plant and the nominal stabilizing boundary control action, all while considering probabilistic delay disturbances, we establish the proof of mean-square exponential stability as well as the well-posedness of the closed-loop system when random phenomena weaken the nominal actuator compensating effect. Our proof is based on the Lyapunov method, the theory of infinitesimal operator for stability, and C0-semigroup theory for well-posedness. Our stability result refers to the L2-norm of the plant state and the H2-norm of the actuator state. Furthermore, our study presents a qualitative analysis of the maximum deviation of the stochastic disturbance relative to the nominal delay, which is expressed as a function of the severity of the plant instability, namely, the magnitude of the reactivity coefficientand the known upper bound of the transition rate of the underlying stochastic perturbations. Extensive simulation results illustrate the viability of the robustness study.

Study on prestress distribution and structural performance of heptagonal six-five-strut alternated cable dome with inner hole

The cable dome structure is a highly efficient prestressed space structure with reasonable force, attractive shape, and large spanning capacity. It is increasingly widely used in stadiums, exhibition halls, terminals, and other large-scale public buildings and the roof structure of various transport hub projects. To solve the problem of weak overall structural stability of the traditional cable dome structure, a new type of prestressed space structure is proposed - heptagonal six-five-strut alternated cable dome with an inner hole. The composition of the structural system was given and a theoretical study of the distribution of structural prestress was carried out; based on the symmetry and periodicity conditions, the initial prestress distribution of the structure was accurately calculated using the node balance method, and the formulae for the geometric parameters of the structural cable-strut were derived; the numerical model was established by using the finite element software ANSYS 2022 R1, and the force characteristics of the structure under full-span uniform load, half span uniform live load, wind load, and temperature were studied. The effects of structural prestress, overall shape, and support stiffness, totaling three categories and six parameters, on the structural mechanical performance of the internal force of the member, node displacement, and support reaction force were analysed in detail and the sensitivity of the parameters is assessed quantitatively, accordingly, the values of the main design parameters such as thick-span ratio are given as suggestions. The analysis results show that the new structural system has a high load-carrying capacity and deformation resistance, and its proposal provides a new scheme and new ideas for the selection and design of the cable dome.

Interaction energy flow paths analysis of PMSG-based wind power integrated systems during LVRT and its parameter adjustment strategy

To solve the problem of oscillation instability in permanent magnetic synchronous generator (PMSG)-based wind power connected systems during low-voltage ride through (LVRT) process, a parameter adjustment strategy based on interaction energy path optimization is proposed in this paper. Firstly, a modular state-space model of PMSG under fault transient conditions is constructed, and the system is divided into five subsystems. Then, the dynamic energy function of subsystems reflecting the oscillation stability of the system is derived. Based on that, the dynamic energy flow path is described considering the introduction of LVRT control. On this basis, the interaction energy between LVRT control links and subsystems is analyzed, and the coupling mechanism of voltage support and damping characteristics in the LVRT process is explained. Further, aiming at the optimal change rate of the total interaction energy in the LVRT process, the adjustment strategy of LVRT control parameters is constructed to meet voltage and damping requirements. Finally, a PMSG-connected system model is built on the MATLAB/Simulink platform to verify the effectiveness of the adjustment strategy. The results show that the proposed method can effectively improve the damping level under the fault transient condition, as well as supporting system voltage.

Проблеми адаптації внутрішньо переміщених осіб в умовах воєнного часу

Adaptation of internally displaced persons (IDPs) in wartime conditions is a complex problem that requires attention and a comprehensive approach from governments, civil society organizations and international humanitarian organizations. This abstract offers an overview of the main aspects of the problem of adaptation of IDPs during hostilities, namely socio-economic instability, psychological and psychosocial problems, access to education and medical care, and the need for social adaptation. The authors substantiated the relevance of the study of the concept "internally a displaced person" in the conditions of modern realities of Ukrainian society. The article explains the need to determine the status of so-called forced migrants – population category, new for the history of independent Ukraine. Analyzed two socio-cultural and resource. Analysis of these problems will help to develop effective strategies and support programs for IDPs in wartime conditions aimed at improving their well-being and integration into society. The article, based on available research, analyzes the psychological problems faced by Ukrainians who were forcibly displaced as a result of Russian aggression, and which hinder their viability. An integrative model of psychological support for persons who were forcibly displaced due to Russian aggression is proposed. This model is based on the possibilities of different psychological approaches, such as psychodynamic, behavioral, cognitive, humanistic and existential. Its goal is to mobilize the internal resources of the individual, achieve existential self-expression, as well as to master health-preserving psychotechniques and build resistance to the destructive influences of the surrounding environment.

Improved results for T-S fuzzy systems with two additive time-varying delays via an extended binary quadratic function negative-determination lemma

This paper is concerned with the stability and stabilization problems for T-S fuzzy systems with two additive time-varying delays. Firstly, a novel Lyapounov-Krasovskii functional (LKF) is constructed by delay-product-type functional method together with the state vector augmentation. In order to handle time-delay square terms introduced into the derivative of LKF, an extended binary quadratic function negative-determination lemma is proposed. A less conservative delay-dependent stability condition is developed since not only some new bounding technologies are employed to deal with integral terms, but also the proposed lemma is employed to dispose nonlinear time-delay terms in derivative of constructed function. Then, the corresponding controller design method for closed-loop delayed fuzzy system is derived based on parallel distributed compensation scheme. Finally, four numerical examples are given to illustrate the superiority and effectiveness of the proposed criteria.

SE-CNN based emergency control coordination strategy against voltage instability in multi-infeed hybrid AC/DC systems

For receiving-end power systems with multi-infeed HVDCs and large-scale renewable energy generation, the challenges of weak reactive power support and limited anti-interference capacity pose a threat to the power system voltage stability. To enhance the voltage stability under large disturbances, this paper proposes a data-driven method for coordinated emergency control strategy against voltage instability in multi-infeed hybrid AC/DC systems based on the squeeze and excitation (SE) module and convolutional neural network (CNN). Firstly, the SE module and CNN are integrated to intuitively capture correlations among various feature channels and extract key features related to voltage stability levels. Secondly, a voltage stability evaluation method is proposed based on the SE-CNN model, utilizing a dual channel structure to unveil the quantitative relationship between key response characteristics and voltage stability margin. Finally, regarding the control measures containing load shedding and DC modulation, the emergency control sensitivity index is proposed to assess the stability margin improvement effect of various control objects, and the optimal emergency control strategy is formulated to coordinate multiple voltage stability emergency control measures. Case studies were conducted on a typical China local region receiving-end power grid test system with voltage instability problems, and the simulation results verified the effectiveness of the proposed method. © 2017 Elsevier Inc. All rights reserved.

Stabilization effect and interaction mechanism of mannoprotein on anthocyanins in mulberry juice

This study aimed to investigate the problem of color instability in mulberry juice, examine the effect of mannoprotein (MP) dosage on improving the stability of anthocyanins in mulberry juice, and explore the molecular binding mechanism between them. As the mass ratio of anthocyanins to MP of 1.07 × 10−3: 1–1.65 × 10−3: 1, the retention rates of anthocyanins in mulberry juice and simulated system were significantly improved in the photostability experiment, with the highest increase of 128.89 % and 24.11 %, respectively. In the thermal stability experiment, it increased by 7.96 % and 18.49 %, respectively. The synergistic effect of combining MP with anthocyanins has been demonstrated to greatly enhance their antioxidant capacity, as measured by ABTS, FRAP, and potassium ferricyanide reduction method. Furthermore, MP stabilized more anthocyanins to reach the intestine in simulated in vitro digestion. MP and cyanidin-3-glucoside (C3G) interacted with each other through hydrogen bonding and hydrophobic interactions. Specific amino acid residues involved of MP in binding process were identified as threonine (THR), isoleucine (ILE) and arginine (ARG). The identification of the effective mass concentration ratio range and binding sites of MP and anthocyanins provided valuable insights for the application of MP in mulberry juice.

Hybrid data clustering algorithm and interactive experience in E-learning electronic course simulation of legal education

With the development of multimedia technology, interactive entertainment experience is an important feature of online teaching mode. Students can engage in interactive learning through various mobile apps and online tools. E-learning provides an innovative way of learning that enables distance learning through electronic course simulation. The objective of this research is to design and develop an improved E-learning course simulation for law teaching by applying hybrid data clustering algorithms and enhancing interactive experiences to improve student engagement and learning outcomes. This article analyzes the simulation of legal education E-learning electronic courses based on mixed data clustering algorithms and interactive experiences. On the basis of the mixed data clustering model of the k-means algorithm, we propose a probability based mixed clustering model that can effectively handle the clustering problem of mixed data. Based on this algorithm, we have established a legal teaching network system platform based on artificial intelligence. The hybrid data clustering algorithm solves the instability problem of the k-means algorithm in the construction of the legal teaching network course platform, providing a reliable solution for the development of artificial intelligence network courses. Based on teaching concepts and combined with various technological characteristics such as network technology and multimedia technology in the information age, users who pass through this teaching system can fully utilize the teaching resources and various functions in the system. The hybrid data clustering algorithm proposed in this article has good clustering performance.

Spatial and Chemical Dual Nano‐Confined Ultrastable Perovskite Quantum Dots Glass Manifesting Exciton Modulation

AbstractNano‐confined synthesis of perovskite quantum dots (QDs) in solid matrix is emerging as a promising route to solve their long‐standing stability problem. Utilizing sol‐gel derived nanoporous glass as matrix that has high flexibility in chemical composition and pore size, a novel spatial and chemical dual nano‐confined strategy is presented for the synthesis of ultrastable perovskite QDs with tunable composition and bandgap in glass. The findings reveal that the Pb─O bonding is formed at perovskite QDs/glass interface during a nano‐confined chemical vapor deposition (CVD) reaction. In particular, the presence of interfacial chemical bonding is discovered to be critical for passivating surface traps and stabilizing the perovskite QDs during the final densification process (related photoluminescence intensity maintained ≈100% after immersed in aqueous solution for 30 days). Series optical spectroscopy unravels the exciton modulation (80 meV) of perovskite QDs in nanoporous and densified glass related to the unique combination of dual physical and chemistry nano‐confined effect. By shedding light on the nano‐confined growth of functional nanocrystals, the research offers the key paths for fabricating high‐performance perovskite devices.

Zr4+-modified chitosan coated nZVI enhance the removal of Cr(VI) by adsorption-reduction interaction

In order to solve the problems of poor mechanical properties and stability of chitosan and easy agglomeration and oxidation of nano zero-valent iron, Zr4+ crosslinked chitosan-coated nano zero-valent iron composites (CS-Zr@nZVI) were prepared for Cr(VI) removal from wastewater. The Zr-O, Zr-N and chitosan characteristic peaks in FTIR spectrum and the nZVI characteristic peaks in XRD pattern confirmed its successful synthesis. SEM and TEM showed that nZVI was dispersed on the surface of CS-Zr@nZVI, which solved the problem of easy agglomeration of nZVI. CS-Zr@nZVI has a wide operating pH range (pH= 2.0–10.0), high pHpzc, good stability and regeneration ability. The removal of Cr(VI) by CS-Zr@nZVI accords with pseudo-second-order kinetic model and Langmuir isotherm model, and it is a spontaneous, disordered and endothermic process. The maximum adsorption capacity was 344.82 mg g−1 at 318 K and pH = 2.0. At the dosage of 1.0 g L−1, CS-Zr@nZVI can treat 134.56 mg L−1 chromium-containing wastewater (pH = 3.5) to meet the discharge standard, which proves that CS-Zr@nZVI has the application prospect of removing Cr(VI). The main mechanisms of Cr(VI) removal by CS-Zr@nZVI are electrostatic interaction, ion exchange, reduction, complexation and co-precipitation. XPS analysis showed that 84.87 % of Cr(VI) was reduced to Cr(III). The above results provide a reference for the design of efficient Cr(VI) removal materials.

Robust stabilization of uncertain switched nonlinear systems via saturated impulsive control

AbstractThis article investigates the stabilization problem of uncertain switched nonlinear systems. Uncertainty and saturated impulses are first considered together in switched nonlinear systems. It appears that the considered systems are robustly locally exponentially stable under the fast average dwell time method and the designed saturated impulsive controller even though subsystems are unstable. At the same time, our conclusions cover some previous results. A step‐by‐step strategy for optimizing multiple objectives is designed to estimate the basin of attraction of the systems as large as possible. At last, the efficacy of our conclusions is illustrated by two given examples.

Recent Progresses in Quantum‐Dot‐Sensitized Solar Cells: The Role of Counter Electrodes

Energy demand, global warming, environmental impacts, sustainability, and energy sources are some of the concerns faced by humanity. Quantum‐dot‐sensitized solar cells (QDSSC) are an alternative solution to addressing some of these issues, in addition to reducing the costs of producing electrical energy. However, QDSSCs present stability problems and low efficiency, less than 16%. In light of this challenge, this review aims to present the main strategies adopted to reduce energy losses that occur in each component of the solar cell, with a focus on one key component: the counter electrode (CE). The CE plays a crucial role in collecting electrons and regenerating the electrolyte, thus impacting the lifespan and efficiency of QDSSCs. As such, this review discusses the main advancements in CEs based on key materials such as metal sulfides, carbonaceous materials, and composites. The efforts related to the synthesis and application of different counter electrodes for QDSSCs are explored.

Finite-time stability of a class of nonlinear cascaded systems with time-varying output constraints

The finite-time stabilization problem of a class of cascaded systems with time-varying output constraints is investigated in this paper. The system consists of input-to-state stable inverse dynamics and a nonholonomic system. The technology of changing the supply rate eliminates dynamic uncertainty. A new tan-type barrier Lyapunov function is utilized to handle time-varying output constraints. Under the unified framework of constrained and unconstrained systems, combined with the addition of power integrator technology and switch control strategy, a state feedback control strategy is proposed to ensure that the state of the closed-loop system converges to zero in a finite-time and always satisfies time-varying output constraints. Finally, simulation results verify the proposed control scheme’s effectiveness.

Experimental and Numerical Investigation of Macroencapsulated Phase Change Materials for Thermal Energy Storage.

Among the different types of phase change materials, paraffin is known to be the most widely used type due to its advantages. However, paraffin's low thermal conductivity, its limited operating temperature range, and leakage and stabilization problems are the main barriers to its use in applications. In this research, a thermal energy storage unit (TESU) was designed using a cylindrical macroencapsulation technique to minimize these problems. Experimental and numerical analyses of the storage unit using a tubular heat exchanger were carried out. The Ansys 18.2-Fluent software was used for the numerical analysis. Two types of paraffins with different thermophysical properties were used in the TESU, including both encapsulated and non-encapsulated forms, and their thermal energy storage performances were compared. The influence of the heat transfer fluid (HTF) inlet conditions on the charging performance (melting) was investigated. The findings demonstrated that the heat transfer rate is highly influenced by the HTF intake temperature. When the effect of paraffin encapsulation on heat transfer was examined, a significant decrease in the total melting time was observed as the heat transfer surface and thermal conductivity increased. Therefore, the energy stored simultaneously increased by 60.5% with the encapsulation of paraffin-1 (melting temperature range of 52.9-60.4 °C) and by 50.7% with the encapsulation of paraffin-2 (melting temperature range of 32.2-46.1 °C), thus increasing the charging rate.

A fibrous Ir-doped NiFeOx on two-dimensional materials for high efficiency oxygen evolution reaction (OER)

As a clean and renewable energy, hydrogen gas can be generated from water electrolysis which also involves the sluggish oxygen evolution reaction (OER). The main commercial catalysts for OER are Ir and Ru based but have the problems of high cost and poor cycling stability. Herein, we designed a new electrocatalyst based on Ni, Fe and Ir compounds loaded on a unique two-dimensional carbon material, which can efficiently catalyze OER with high stability in alkaline solution. The composite was prepared by physical vapor deposition, showing a fibrous microscopic morphology with uniform particle size distribution. The fibrous structure ensured the exposure of active sites, which further improved OER activity. The loading of metallic iridium in the material is only 0.0858 mg cm−2. The catalytic activity of OER was maintained for 54 h under alkaline conditions at a current density of 50 mA cm−2 without significant changes in current density. Characterization showed that the excellent activity and stability of the catalysts originated from the Ir insertion into the NiFe2O4 lattice.

Macrocyclic thiol ligand additive engineering for stable and efficient perovskite solar cells

Perovskite solar cells have a rapid development speed and excellent prospects, but still face performance and stability problems for practical applications. Excessive Pb2+ defects often accompany the preparation of perovskite, which greatly affect the performance and stability of perovskite solar cells. Herein, a macrocyclic thiol ligand (DXPSH) is introduced as an additive for organic amine salt. It effectively reduces the defect density of perovskite, induces better crystal orientation of perovskite, and improves carrier lifetime. As a result, the optimized DXPSH-modified PSCs achieves a maximum power conversion efficiency of 24.03 % and good long-term stability in ambient air.