Steady-state Output Research Articles

Bifurcation Diagrams of Nonlinear Oscillatory Dynamical Systems: A Brief Review in 1D, 2D and 3D.

We discuss 1D, 2D and 3D bifurcation diagrams of two nonlinear dynamical systems: an electric arc system having both chaotic and periodic steady-state responses and a cytosolic calcium system with both periodic/chaotic and constant steady-state outputs. The diagrams are mostly obtained by using the 0-1 test for chaos, but other types of diagrams are also mentioned; for example, typical 1D diagrams with local maxiumum values of oscillatory responses (periodic and chaotic), the entropy method and the largest Lyapunov exponent approach. Important features and properties of each of the three classes of diagrams with one, two and three varying parameters in the 1D, 2D and 3D cases, respectively, are presented and illustrated via certain diagrams of the K values, -1≤K≤1, from the 0-1 test and the sample entropy values SaEn>0. The K values close to 0 indicate periodic and quasi-periodic responses, while those close to 1 are for chaotic ones. The sample entropy 3D diagrams for an electric arc system are also provided to illustrate the variety of possible bifurcation diagrams available. We also provide a comparative study of the diagrams obtained using different methods with the goal of obtaining diagrams that appear similar (or close to each other) for the same dynamical system. Three examples of such comparisons are provided, each in the 1D, 2D and 3D cases. Additionally, this paper serves as a brief review of the many possible types of diagrams one can employ to identify and classify time-series obtained either as numerical solutions of models of nonlinear dynamical systems or recorded in a laboratory environment when a mathematical model is unknown. In the concluding section, we present a brief overview of the advantages and disadvantages of using the 1D, 2D and 3D diagrams. Several illustrative examples are included.

Photovoltaic panel cooling with new composite of phase change materials and hierarchical nanoparticles

In this research, the use of a new type of phase change materials (PCM) and hierarchical nanoparticles is discussed to improve the electrical and thermal efficiency of PV panels. TiO2/CuO hierarchical nanoparticles are synthesized by hydrothermal method, and PCMs containing nanoparticles (2.5–10%wt) are prepared, and then experiments are performed in indoor conditions under solar simulator light. The PV panel with a maximum nominal power of 30W is used. The new PCM is made from a mixture of lauryl alcohol and beeswax (LABW). A spiral heat exchanger is placed in the PCM container, in which the flow rate of cool water is variable (m˙ = 0.002–0.01 kg s−1). Firstly, the temperature and voltage-current changes of the PV panel with time are investigated without using PCMs as a reference case, and in steady-state conditions, the temperature and output power values are 67.34 °C and 22.33W. The use of LABW compared to pure beeswax leads to a significant decrease in the PV panel temperature and as a result, an increase in its electrical and thermal efficiency. Also, adding nanoparticles to PCMs from 2.5 % to 7.5 %wt due to the improvement of their thermal conductivity and increasing the heat storage rate of the PV panel leads to an increase in its electrical and thermal efficiency. There is no significant change to decrease the temperature and increase the production capacity of PV panels by increasing the percentage of nanoparticles from 7.5 % to 10%wt. The maximum production power, electrical and thermal efficiency of the PV panel at a flow rate of 0.01 kg s−1, 10%wt of nanoparticles, and a radiation intensity of 1000 W m−2 are 28.92 W, 12.55 %, and 76.67 %, respectively.

Enhancing PEM fuel cell dynamic performance: Co-optimization of cathode catalyst layer composition and operating conditions using a novel surrogate model

Optimizing the cathode catalyst layer (CCL) composition and operating conditions to enhance the dynamic performance of proton exchange membrane fuel cells garners significant attention. Although machine learning surrogate models are efficient for fuel cell analysis and optimization, the varied voltage dynamic response patterns (e.g., loading failure, voltage undershoot, and voltage hysteresis) challenge regression surrogate models designed for steady-state performance predictions. In response, this study introduces a joint framework combining classification and regression models for dynamic performance prediction. For training, a transient, two-phase, non-isothermal fuel cell model with integrated catalyst agglomerate is developed. The dynamic voltage deviation (σV) is proposed as an index to characterize the dynamic performance of the fuel cell. This joint surrogate model achieves correlation coefficients of 0.9976 and 0.9961 for predicting σV in training and test sets, respectively. Through this model, sensitivity analyses of the CCL composition and operating conditions are conducted to quantify their impact and interactions on the fuel cell's dynamic performance. Besides, the analysis reveals a trade-off between dynamic performance and steady-state output. To balance these, a multi-objective optimization is conducted. The results indicate that, compared to the base case, dynamic and steady-state performance improved by 44 % and 8 %, respectively.

MPPT Charge Controller using Fuzzy Logic for Battery Integrated with Solar Photovoltaic System

In comparison to other Renewable Energy (RE) resources, solar energy has become the most prominent and prospective source for generating electricity, substituting conventional sources. However, solar Photovoltaic (PV) energy production is dependent on solar irradiance and cell temperature. By implementing the Maximum Power Point Tracking (MPPT) algorithm, it is achievable to maximize the power from solar PV. In spite of this, there is still a slower convergence rate, a significant fluctuation around Maximum Power Point (MPP), and a drift issue caused by rapid irradiance variations in solar PV. In order to prevent oscillation and attain a steady state and continuous output of the PV module, a Fuzzy Logic (FL)-based MPPT has been designed in this work. With the buck converter as the DC-DC converter and the lead acid battery as the input, the Perturb & Observe (P&O) MPPT method is selected. The overall design will be developed using Matlab Simulink, and the efficiency of the FL-MPPT charge controller will be evaluated under constant and step irradiance. Additionally, the battery's State of Charge (SOC) will be monitored to prevent overcharging and discharge. In addition, the effectiveness of the controller will be evaluated with and without the MPPT method. On the basis of simulation results obtained from constant and step irradiance levels, the FL-MPPT charge controller with the P&O algorithm and the lead acid battery as the load was able to maintain maximum system efficiency while extending battery life. The FL-MPPT charge controller obtained about 96% efficiency for both irradiance profiles, whereas the system without the FL-MPPT algorithm only achieved 42% efficiency.

An NMOS output-capacitorless low-dropout regulator with dynamic-strength event-driven charge pump

In this paper, an NMOS output-capacitorless low-dropout regulator (OCL-LDO) featuring dual-loop regulation has been proposed, achieving fast transient response with low power consumption. An event-driven charge pump (CP) loop with the dynamic strength control (DSC), is proposed in this paper, which overcomes trade-offs inherent in conventional structures. The presented design addresses and resolves the large signal stability issue, which has been previously overlooked in the event-driven charge pump structure. This breakthrough allows for the full exploitation of the charge-pump structure's potential, particularly in enhancing transient recovery. Moreover, a dynamic error amplifier is utilized to attain precise regulation of the steady-state output voltage, leading to favorable static characteristics. A prototype chip has been fabricated in 65 nm CMOS technology. The measurement results show that the proposed OCL-LDO achieves a 410 nA low quiescent current (I Q) and can recover within 30 ns under 200 mA/10 ns loading change.

Photothermal conversion-enhanced thermoelectric generators combined with supercapacitors: An efficacious approach to integrated power generation and storage

Thermoelectric generators (TEGs), which harness and convert solar-thermal energy into electrical energy, possess immense potential within the field of photothermal conversion (PTC). However, the widespread adoption of conventional TEGs in PTC domain has encountered some obstacles, which represent that TEGs have poor inherent PTC performance, resulting in low solar-thermoelectric conversion efficiency, and this solar-thermal-electric conversion method lacks the capability of electrical energy storage. Hence, an urgent imperative exists to develop integrated and synergistic energy technologies that can respond to these underlying challenges. Herein, we reported a novel strategy for employing spinel-type Cu1.5Mn1.5O4 PTC coating to adorn conventional TEG to construct the solar-thermoelectric generator (STEG) which exhibited excellent solar-thermoelectric conversion capability, and then integrating the STEG in series with a supercapacitor composed of synthetic ionic liquid electrolytes and carbon electrodes to fulfill the conversion and storage of solar-thermal energy into electrical energy. The results indicated that, when compared to a conventional TEG, the STEG attained a drastically elevated internal temperature difference due to the excellent PTC capability of spinel-type coating. As a result, remarkable enhancements were observed in both the steady-state voltages (Voc) and maximum output power density (Pmax) of the STEG, exceeding a 6-fold and 40-fold increase, respectively. Furthermore, we conducted experimental validation to ascertain the viability of the solar-driven STEG to charge a supercapacitor, thereby achieving the conversion and storage of solar-thermal energy into electrical energy, and the working mechanism of this integrated system has been revealed. This study offers invaluable insights into the development of highly efficient solar-thermal energy conversion and storage methods.

Highly stable Brillouin laser with controllable tuning based on fiber ring resonator

The design and fabrication processes of the stimulated Brillouin laser (SBL) are complex, and it is affected by many factors such as temperature and resonance shift. In this study, we have fabricated a Brillouin laser using a fiber ring resonator with Q factor = 7.1 × 108 and resonance depth (h) = 96%. The free spectral range automatic feedback control technology is proposed to realize the accurate matching of the resonant mode and the Stokes mode. The influence of temperature on the SBL frequency shift is suppressed. The fluctuation range of SBL’s frequency decreases by 5 times. The maximum steady state output of the SBL at the best matching position is realized, and the output power fluctuation range decreases by 15 times. The power stability of the SBL reaches 4.85 × 10−6, which is improved by two orders of magnitude. This simple scheme provides convenience for the application of the SBL, such as sensing and other applications.

A Hybrid Tri-Stable Piezoelectric Energy Harvester with Asymmetric Potential Wells for Rotational Motion Energy Harvesting Enhancement

This paper proposes an asymmetric hybrid tri-stable piezoelectric energy harvester for rotational motion (RHTPEH). The device features an asymmetric tri-stable piezoelectric cantilever beam positioned at the edge of a rotating disk. This beam is uniquely configured with an asymmetric arrangement of magnets. Additionally, an elastic amplifier composed of a vertical and a rotating spring connects the beam’s fixed end and the disk. This setup enhances both the rotational amplitude and vertical displacement of the beam during motion. A comprehensive dynamical model of the RHTPEH was developed using Lagrange’s equations. This model facilitated an in-depth analysis of the system’s behavior under various conditions, focusing on the influence of key parameters such as the asymmetry in the potential well, the stiffness ratio of the amplifier springs, the radius of the disk, and the disk’s rotational speed on the nonlinear dynamic response of the system. The results show that the asymmetric hybrid tri-stable piezoelectric energy harvester makes it easier to harvest the vibration energy in rotational motion and has excellent power output performance compared with the symmetric tri-stable piezoelectric energy harvester. The output power magnitude of the system at higher rotational speeds increases as the radius of rotation expands, but when the rotational speed is low, the steady-state output power magnitude of the system is not sensitive to changes in the radius of rotation. Theoretical analysis and numerical simulations validate the effectiveness of the proposed asymmetric RHTPEH for energy harvesting in low-frequency rotating environments.

Enhancing low-orbit vibration energy harvesting by a tri-stable piezoelectric energy harvester with an innovative dynamic amplifier

Piezoelectric energy harvesting faces a primary challenge in effectively capturing low-orbit vibration energy across a broad frequency range. In this paper, we present a tri-stable piezoelectric energy harvester that incorporates a dynamic amplifier (TPEH + DM), specifically designed for efficient collection of low-orbit vibration energy. The TPEH + DM comprises a piezoelectric cantilever beam connected to an innovative dynamic amplifier at its restrained end, which enhances both the rotational and lateral displacement of the piezoelectric cantilever beam simultaneously. The governing coupled differential equations of motion for the system is derived based on the Lagrange equation, and analytical expressions for its steady-state response are obtained using the multi-scale method. The influence of factors such as the mass and the stiffness ratio of the dynamic amplifier on the steady-state dynamic output characteristics of the system is investigated using the theoretical analysis and numerical simulation. The results indicate that TPEH + DM exhibits significantly improved energy harvesting performance compared to TPEH under low-orbit external excitations. The bandwidth of inter-well motion and the TPEH + DM power output may be further increased by suitably modifying the relative stiffness between the cantilever beam and the dynamic amplifier. In addition, we analyze the time-domain behavior of the system’s output voltage using the ode45 solver under various external excitation frequencies and intensities. The results demonstrate that with appropriate adjustments to the mass of the tip magnet and the stiffness ratio of the dynamic amplifier, the proposed TPEH + DM system can harvest energy efficiently across a broad frequency range, even under low-orbit excitations.

Residual force depression is not related to positive muscle fascicle work during submaximal voluntary dorsiflexion contractions in humans.

Residual force depression (rFD) following active muscle shortening is assumed to correlate most strongly with muscle work, but this has not been tested during voluntary contractions in humans. Using dynamometry, we compared steady-state ankle joint torques (N=16) following tibialis anterior (TA) muscle-tendon unit (MTU) lengthening and shortening to the time-matched torque during submaximal voluntary fixed-end dorsiflexion reference contractions (REF) at a matched MTU length and EMG amplitude. Ultrasound revealed significantly reduced (P<0.001) TA fascicle shortening amplitudes during MTU lengthening without a preload over small and medium amplitudes, respectively, relative to REF. MTU lengthening with a preload over a large amplitude significantly (P<0.001) increased fascicle shortening relative to REF, as well as stretch amplitudes relative to MTU lengthening without a preload (P=0.001). Significant (P=0.028) steady-state fascicle force enhancement relative to REF was observed following MTU lengthening, and was similar among MTU lengthening-hold conditions (3-5%). MTU shortening with and without a preload over small and large amplitudes significantly (P<0.001) increased positive fascicle and MTU work relative to REF, but significant (P=0.006) rFD was observed following MTU shortening with a preload (7-10%) only. rFD was linearly related to positive MTU work [rrm (47)=0.48, P<0.001], but not positive fascicle work [rrm (47)=0.16, P=0.277]. Our findings indicate that MTU lengthening without substantial fascicle stretch enhances steady-state force output, which might arise from less shortening-induced rFD. Our findings also indicate similar rFD following different amounts of positive fascicle/MTU work, which cautions against using work to predict rFD during submaximal voluntary contractions. KEY POINTS: Accurately predicting muscle force is challenging because active muscle shortening depresses force output. The residual force depression (rFD) that exists following active muscle shortening is commonly assumed to correlate strongly and positively with muscle work. We found that tibialis anterior muscle fascicle work and muscle-tendon unit work did not accurately predict rFD during submaximal voluntary dorsiflexion contractions. Fascicle shortening during fixed-end reference contractions also potentially induced rFD of 3-5%, which was similar to the rFD following muscle-tendon unit shortening without a preload. A higher number of active muscle fibres during shortening probably increased rFD, which suggests that motor unit recruitment during shortening might predict rFD.

High-Performance Light Emitting Diode Lighting Circuits and Their Interior Design Applications

This study explores the application of the half-bridge Inductor-Inductor-Capacitor (LLC) resonant converter in Light Emitting Diode (LED) lighting driver power supplies, with a specific focus on improving efficiency and dimming capabilities. The investigation begins with an analysis of the sliding mode control (SMC) method, utilizing a constant-current design with a fixed switching frequency (FWF). A novel fuzzy frequency-selective SMC dimming strategy is proposed to recognize the challenge of significant output voltage ripple during dimming under a FSF. To address the ripple issue during dimming, an electromagnetic filtering circuit is designed, and a zero-voltage turn-on Metal—Oxide—Semiconductor (MOS) tube is introduced, incorporating a synchronous rectification scheme to mitigate losses in the secondary-side rectification diode. The study comprehensively considers a current-mode self-driven method, specifically tailored to the LLC circuit’s different operating modes. The LLC resonant circuit, along with the subsequent synchronous rectification circuit, is meticulously designed for a 252 W LED driver power supply prototype. A closed-loop simulation circuit model is developed using PSIM software in experimental validation. The feasibility of SMC based on a FSF is affirmed through a comparative analysis of SMC signal waveforms, steady-state output current (OC) models, and resonant tank current waveforms. The investigation into the OC under various SMC conditions demonstrates the half-bridge LLC resonant converter’s ability to achieve stable output with minimal ripple. The designed LED lighting circuit is applied to indoor design, providing adjustable LED brightness and switch status at different power levels. Although obstacles slightly impact the communication quality of the circuit, it remains suitable for the majority of users’ needs.

How to Stabilize the Current of Efficient Inverted Flexible Perovskite Solar Cells at the Maximum Power Point.

Inverted flexible perovskite cells (fPSCs) have attracted much attention for their high efficiency and power per weight. Still, the steady-state output is one of the critical factors for their commercialization. In this paper, it is found that the steady-state current of inverted fPSCs based on nickel oxide nanoparticles (n-NiOx) continuously decreases under light illumination. Conversely, those based on magnetron-sputtered NiOx (sp-NiOx) exhibit the opposite result. Based on visualization of ion migration in the photoluminescence (PL) imaging microscopy tests, the discrepancies in the buried surfaces lead to the differences in ion migration in perovskite films, which triggers the temporary instability of the output current of devices during operation. The DFT theoretical calculation and experimental results reveal that NiOx films with different contents of Ni vacancies can modulate the crystallization of the perovskite films on the NiOx surfaces. Tuning the crystallization of the perovskite films is essential to stabilize the output current of fPSCs at a steady state. To demonstrate that, capsaicin is doped into the perovskite solutions to improve the quality of the perovskite buried interface. Finally, the corresponding fPSCs exhibit outstanding efficiency and stability during operation. These results provide valuable scientific guidance for fabricating fPSCs with stable operation under illumination conditions.

Sudden change of the photon output field marks phase transitions in the quantum Rabi model

The experimental observation of quantum phase transitions predicted by the quantum Rabi model in quantum critical systems is usually challenging due to the lack of signature experimental observables associated with them. Here, we describe a method to identify the dynamical critical phenomenon in the quantum Rabi model consisting of a three-level atom and a cavity at the quantum phase transition. Such a critical phenomenon manifests itself as a sudden change of steady-state output photons in the system driven by two classical fields, when both the atom and the cavity are initially unexcited. The process occurs as the high-frequency pump field is converted into the low-frequency Stokes field and multiple cavity photons in the normal phase, while this conversion cannot occur in the superradiant phase. The sudden change of steady-state output photons is an experimentally accessible measure to probe quantum phase transitions, as it does not require preparing the equilibrium state.

Output Stream from the AQM Queue with BMAP Arrivals

We analyse the output stream from a packet buffer governed by the policy that incoming packets are dropped with a probability related to the buffer occupancy. The results include formulas for the number of packets departing the buffer in a specific time, for the time-dependent output rate and for the steady-state output rate. The latter is the key performance measure of the buffering mechanism, as it reflects its ability to process a specific number of packets in a time unit. To ensure broad applicability of the results in various networks and traffic types, a powerful and versatile model of the input stream is used, i.e., a BMAP. Numeric examples are provided, with several parameterisations of the BMAP, dropping probabilities and loads of the system.

Revisiting the effects of labour, capital and scale-augmenting technological progress on steady-state output

The effects of technical change may not exclusively be labour-augmenting, if it is assumed that linear homogeneity or balanced growth is not applicable. This study identified these effects on the steady-state output growth from labour, capital and scale-augmenting technological progress. The findings imply that a drop in investment-goods prices accelerates output growth but to a lesser extent than capital growth, and increasing (decreasing) returns to scale (IRS/DRS) will lead to faster (slower) per-capita output growth, but the effect is free from constant returns to scale (CRS). It was also found that a higher output elasticity of capital can be beneficial to output growth and that a substantial labour supply is conducive to higher income per capita under IRS but will reduce it if DRS are present, but again, CRS does not occur. Differentiating between labour and capital augmentations in empirical research is challenging, as a direct estimation of the impacts of technical change on output growth is impossible. Thus, an indirect estimation was conducted to measure these impacts as a Solow residual.

Development of wind and solar systems for power charging: An application of an electric vehicle to grid systems

&lt;abstract&gt; &lt;p&gt;In response to escalating environmental concerns driven by greenhouse gas emissions, Pakistan, amid accelerated climate change and deteriorating air quality, struggles with power crisis. Our purpose of this research was to develop a pivotal strategy to address the power crisis and provide clean transportation facilities by involving power transitioning from fossil fuel vehicles to electric vehicles (EVs). We aimed to establish EV charging stations powered by renewable sources like solar and wind energy using grid to vehicle (V2G) mechanism. Utilizing MATLAB Simulink, an optimal electric vehicle charging system with a Level 2 fast charging mechanism was designed, aiming to significantly reduce greenhouse gas emissions from both the transportation and energy sectors. This framework aligned with global trends in climate change mitigation, providing developing countries like Pakistan with a practical solution. The results indicated a 10-kW, AC power output at 240 V coupled with an ideal 50 kWh EV battery rating, which was achieved for EV charging. The output parameters, including current voltage and power output of solar PV, micro wind, and battery levels, were used before and after the incorporation of a boost converter. Consequently, the application of a boost converter and proportional integral (PI) controller resulted in low overshoot and steady state output parameters of the proposed system. Also, the battery backup helped to optimize the power output for load driven EVs.&lt;/p&gt; &lt;/abstract&gt;

General efficiency relation for dissipative molecular machines

Living systems use chemical fuel to process information, assemble structures and maintain fluxes. Many of these processes are dissipative: energy is consumed purely to maintain non-equilibrium steady-state outputs. How efficiently the input energy is transduced toward the output dissipation as opposed to being lost during intermediate steps, and whether the efficiency is constrained by general principles or specific fine-tuning, are open questions. Here, applying a recent mapping from non-equilibrium systems to battery-resistor circuits, an analytic expression for the efficiency of any dissipative molecular machine driven by a chemical potential difference is derived. This expression disentangles the chemical potential from the machine’s details, whose effect on the efficiency is fully specified by a constant called the load resistance. The efficiency passes through an inflection point separating totally inefficient machines from efficient machines if the balance between chemical potential difference and load resistance exceeds thermal noise. This explains all-or-none dynein stepping with increasing ATP concentration observed in single-molecule experiments. These results indicate that energy transduction in living systems is efficient not because of idiosyncratic optimization of biomolecules, but rather because the concentration of chemical fuel is kept above a threshold level.

Spectrally resolved ultrafast transient dynamics of a femtosecond fiber-feedback optical parametric oscillator.

We report on spectrotemporal transient dynamics in a femtosecond fiber-feedback optical parametric oscillator (FFOPO) system. Burst modulation of the pump beam in combination with dispersive Fourier transformation sampling allows to record single-pulse signal spectra at 41 MHz sampling rate. Therefore, each individual pulse of the signal transients can be spectrally resolved. We characterize the signal output behavior for anomalous as well as for normal intra-cavity dispersion. Amongst steady state output we observed period-doubling cycles and other attractors, which occured at higher intra-cavity nonlinearity levels. The experimental findings are supported by numerical simulations, in order to identify the linear and nonlinear effects, which govern the wavelength tuning behavior of this FFOPO system. We find that steady state operation is preferred and that the wavelength tuning stability of the FFOPO dramatically increases when using a normal dispersion feedback fiber.

Resonant behaviors of two coupled fluctuating-frequency oscillators with tempered Mittag-Leffler memory kernel

The dynamics of coupled oscillators and their collective behaviors are of great significance in various fields. This paper explores the resonant behaviors in the system composed of two coupled fluctuating-frequency oscillators with tempered Mittag-Leffler (M-L) memory kernel. The study begins by demonstrating that the two particles synchronize in the long-time limit, indicating that the mean-field behavior aligns with that of each individual particle. Accordingly, we derive an exact analytical expression for the steady-state output amplitude gain (OAG) of the mean field using the stochastic average method. Furthermore, the research investigates the diverse phenomena of generalized stochastic resonance (GSR) and examines how various system parameters influence GSR. To validate the theoretical analysis, numerical simulations are conducted to support and verify our findings.

Towards low-carbon papermaking wastewater treatment process based on Kriging surrogate predictive model

Papermaking wastewater contains a diverse range of organic carbon, nitrogen and other pollutants, which could lead to the emission of greenhouse gases (GHG) during biochemical treatment process. Despite the importance of decarbonizing the papermaking wastewater treatment process, the mechanisms underlying the generation of greenhouse gases remain elusive and no models currently exist to describe the process. To address this issue, this study employed benchmark simulation model No. 1 (BSM1) to simulate, the papermaking wastewater treatment process, and applied the steady-state output value of simulation to calculate the GHG emissions. Kriging surrogate model was applied to establish the emission model for GHG in the papermaking wastewater treatment process. The model provides a reference for the control and optimization of GHG emission reduction and a high accuracy was achieved with determination coefficient (R2) of above 96%. Further analysis of the parameter impact of process control on GHG emissions and the optimization effects of controllable variables contributes to the goal of reducing GHG emissions in the papermaking wastewater treatment process.