Search Results (10,325)

This paper presents a cost-efficient estimation method, the filtering observer (FOBS), which provides a smooth estimation through prior estimation, enhancing the field-oriented control (FOC) performance of motion control systems by estimating the angular rotor position, angular rotor velocity, and disturbance torque of permanent magnet synchronous motors (PMSMs). The cost-effective FOBS demonstrates characteristics akin to optimal estimating methods and employs arbitrary pole placement, facilitating more straightforward adjustment of the FOBS gain. The non-linear characteristics of low-resolution and low-cost encoders, the computation of angular rotor velocity using traditional techniques, and disturbances over broad frequency ranges in the servo drive system impair the efficacy of the motion control system. As a cost-effective solution, the FOBS minimizes the deficiencies of the low-cost encoder, reduces oscillations and measurement delays in the speed feedback signal, and provides smooth estimation of disturbance torque. Based on the results from experiments, the FOBS was compared against traditional approaches and the performance of the motion control system was examined. Also, the performance of the motion control system was investigated. The results indicate that these enhancements were achieved with low processing power and an easily implementable estimate technique suitable for low-cost industrial systems. Full article

This study reconstructed the annual lake surface area (LSA) and absolute lake water storage (LWS) changes of Lake Sarez, the world’s largest high-altitude landslide-dammed lake, from 1992 to 2023 using multi-source remote sensing data. All available Landsat images were used to extract the LSA using an improved multi-index threshold method, which incorporates a slope mask and threshold adjustment to enhance the boundary delineation accuracy (Kappa coefficient = 0.94). By combining the LSA with high-resolution DEM and the GLOBathy bathymetry dataset, the absolute LWS was reconstructed, fluctuating between 12.3 × 10⁹ and 12.8 × 10⁹ m³. A water balance analysis revealed that inflow runoff (IRO) was the primary driver of LWS changes, contributing 54.57%. The cross-wavelet transform and wavelet coherence analyses showed that the precipitation (PRE) and snow water equivalent (SWE) were key climatic factors that directly influenced the variability of IRO, impacting the interannual water availability in the lake, with PRE having a more sustained impact. Temperature indirectly regulated IRO by affecting SWE and potential evapotranspiration. Furthermore, IRO exhibited different resonance periods and time lags with various atmospheric circulation factors, with the Pacific Decadal Oscillation and North Atlantic Oscillation having the most significant influence on its interannual variations. These findings provide crucial insights into the hydrological behavior of Lake Sarez under climate change and offer a novel approach for studying water storage dynamics in high-altitude landslide-dammed lakes, thereby supporting regional water resource management and ecological conservation. Full article

An all-optical single-longitudinal-mode (SLM) forward Brillouin microwave oscillator (FB-MO) with an unbalanced Fiber Mach–Zehnder interferometer (UF-MZI) for microwave photonics (MWP) generation is proposed and experimentally investigated. UF-MZI consists of an optical coupler (OC), a polarization controller (PC), and two asymmetric length arms with 5 km and 500 m single-mode fibers (SMFs), which implements two unbalanced length feedback rings that are connected to one another. One long-length ring with a forward Brillouin gain cooperates with the other short-length ring to maintain a spectral Vernier effect and improve the effective free spectral range (FSR). By contrast with traditional optoelectronic oscillators (OEOs), this design does not require any photoelectric conversion devices and additional modulation, avoids external electromagnetic interference, and side-mode suppression and linewidth are favorable. Experimental results reveal that the 3-dB linewidth of the all-optical SLM FB-MO with UF-MZI is about 140 Hz. The acoustic-mode and side-mode suppression ratios are 26 dB and 31 dB. Within 60 min of the stability experiment, the power and frequency stability fluctuation were ±1 dB and ±100 Hz. Thanks to its long main ring cavity length, our all-optical SLM FB-MO with UF-MZI maintains good phase-noise performance. The measurement shows that a phase noise as low as −120 dBc/Hz at an offset frequency of 100 kHz is achieved. This SLM MWP generation technology holds great potential for applications in radar monitoring and wireless communication systems. Full article

The regularity of rainfall seasonality is very important for vegetation growth, the livelihood of the population, agricultural production, and ecosystem sustainability. Changes in precipitation and its extremes have been widely reported; however, the spatial and temporal variations in rainfall seasonality and their underlying mechanisms are less understood. Here, we analyzed the changes in rainfall seasonality and possible teleconnection mechanisms in the eastern China monsoon region during 1981–2022, with a special focus on the El Niño-Southern Oscillation (ENSO), El Niño Modoki (ENSO_M), and Indian Ocean Dipole (IOD). Our results show that due to the changes in rainfall concentration, rainfall magnitude, or both, rainfall seasonality has developed in the northern China (NC, 0.15 × 10⁻³ yr⁻¹) and central China (CC, 0.07 × 10⁻³ yr⁻¹) monsoon regions, and weakened in the northeastern China (NEC, −0.08 × 10⁻³ yr⁻¹) and southern China (SC, −0.15 × 10⁻³ yr⁻¹) monsoon regions during the recent decades. The large-scale circulation and SST anomalies induced by cold or warm phases of the IOD, ENSO_M, and (or) ENSO can explain the enhanced seasonality in the NC and CC monsoon regions and weakened seasonality in the NEC and SC monsoon regions. The wavelet coherence analysis further shows that the dominated climatic factors for rainfall seasonality changes are different in the CC, NC, SC, and NEC monsoon regions, and that rainfall seasonality is also affected by the coupling of the IOD, ENSO_M, and ENSO. Our results highlight that the IOD, ENSO_M, and ENSO are important climatic causes for rainfall seasonality changes in the eastern China monsoon region. Full article

We analyze the anisotropic Bianchi models, and in particular the Bianchi Type IX known as the Mixmaster universe, where the Misner anisotropic variables obey Deformed Commutation Relations inspired by Quantum Gravity theories. We consider three different deformations, two of which have been able to remove the initial singularity similarly to Loop Quantum Cosmology when implemented in the single-volume variable. Here, the two-dimensional algebras naturally implement a form of Non-Commutativity between the space variables that affects the dynamics of the anisotropies. In particular, we implement the modifications in their classical limit, where the Deformed Commutators become Deformed Poisson Brackets. We derive the modified Belinskii–Khalatnikov–Lifshitz map in all the three cases, and we study the fate of the chaotic behavior that the model classically presents. Depending on the sign of the deformation, the dynamics will either settle into oscillations between two almost-constant angles, or stop reflecting after a finite number of iterations and reach the singularity as one last simple Kasner solution. In either case, chaos is removed. Full article

A novel time delay Lotka–Volterra (TDLV) model was developed by extending the concept of time delay from integer order to fractional order. The TDLV model was constructed to simulate the dynamics of aboveground biomass per individual of three dominant herbaceous plant species (Leymus chinensis, Agropyron cristatum, and Stipa grandis) in the typical grasslands of Inner Mongolia. Comparative analysis indicated that the TDLV model outperforms candidate models, such as Logistic, GM(1,1), GM(1,N), DGM(2,1), and Lotka–Volterra model, in terms of all fitting criteria. The results demonstrate that interspecies competition exhibits clear feedback and suppression effects, with Leymus chinensis playing a central role in regulating community dynamics. The system is locally stable and eventually converges to an equilibrium point, though Stipa grandis maintains relatively low biomass, requiring further monitoring. Time delays are prevalent in the system, influencing dynamic processes and causing damping oscillations as populations approach equilibrium. Full article

Eutrophication in Canadian lakes degrades water quality, disrupts ecosystems, and poses health risks due to potential development of harmful algal blooms. It also economically impacts the general public, industries like recreational and commercial fishing, and tourism. Analysis of a 140-year core record from Utikuma Lake, northern Alberta, revealed the processes behind the lake’s current hypereutrophic conditions. End-member modeling analysis (EMMA) of the sediment grain size data identified catchment runoff linked to specific sedimentological processes. ITRAX X-ray fluorescence (XRF) elements/ratios were analyzed to assess changes in precipitation, weathering, and catchment runoff and to document changes in lake productivity over time. Five end members (EMs) were identified and linked to five distinct erosional and sedimentary processes, including moderate and severe precipitation events, warm and cool spring freshet, and anthropogenic catchment disturbances. Cluster analysis of EMMA and XRF data identified five distinct depositional periods from the late 19th century to the present, distinguished by characteristic rates of productivity, rainfall, weathering, and runoff linked to natural and anthropogenic drivers. The most significant transition in the record occurred in 1996, marked by an abrupt increase in both biological productivity and catchment runoff, leading to the hypereutrophic conditions that persist to the present. This limnological shift was primarily triggered by a sudden discharge from a decommissioned sewage treatment lagoon into the lake. Spectral and wavelet analysis confirmed the influence of the Arctic Oscillation, El Niño Southern Oscillation, North Atlantic Oscillation, and Pacific Decadal Oscillation on runoff processes in Utikuma Lake’s catchment. Full article

A new marine climate metric, marine season, is introduced for Foxe Basin, Nunavut, Canada capturing the time of the year that the Basin is influenced by open water. The metric is developed with a day-to-day temperature variability framework using the Hall Beach (Sanirajak) climate record (1957–2023). Day-to-day minimum temperature variability provides a clear signal of the marine season. The new metric is compared to the more traditional breakup and freeze-up dates of sea ice that uses a 5/10th sea-ice spatial coverage threshold. While the two metrics are in general agreement, some important differences occur related to the time required for the breakup (full ice coverage to 5/10th sea-ice coverage). The timing from onset of the marine season to 5/10th ice coverage has shortened in time in a statistically significant fashion, indicating a more rapid breakup in recent years. In contrast, the freeze-up period, 5/10th to full sea-ice coverage has increased. The longer ice-free season, as determined by sea-ice data, arises primarily from open water changes in the breakup (shorter) and freeze-up (longer) period timing. These are novel insights that suggest that the basic sea-ice regime, oscillating from a full sea-ice platform and ice-free conditions has not changed, but rather the observed changes are in the nature of the transitions between these two states, breakup and freeze-up. Full article

This study evaluates the performance of the IMERSPEC methodology combined with the Spalart–Allmaras turbulence model for simulating fully developed turbulent flows in a plane channel. Turbulent flows, known for their complexity, require numerical methods that balance computational efficiency with accuracy. The IMERSPEC approach, recognized for its spectral accuracy and efficiency, was applied alongside the Spalart–Allmaras model, valued for its simplicity and robustness in representing turbulence, particularly in scenarios where flow over solid surfaces is critical. Simulations were conducted at Reynolds numbers (Reτ) of 180, 550, and 1000, with results validated against direct numerical simulation (DNS) data. The study investigated various grid resolutions, revealing that finer meshes substantially enhance accuracy by mitigating velocity profile oscillations and reducing the L2 error norm. Key findings highlight the method’s ability to accurately replicate turbulent flow characteristics, including velocity distributions and shear stress profiles, while maintaining a favorable computational cost-to-accuracy ratio. This work provides valuable insights into turbulence modeling, demonstrating the potential of the IMERSPEC methodology for practical engineering applications. Full article

With advancements in mobile robot technology, wheel-legged robots have emerged as promising next-generation mobile solutions, reducing design costs and enhancing adaptability in unstructured environments. As underactuated systems, their balance control has become a prominent research focus. Despite there being numerous control approaches, challenges remain. Balance control methods for wheel-legged robots are influenced by hardware characteristics, such as motor friction, which can induce oscillations and hinder dynamic convergence. This paper presents a friction feedforward Linear Quadratic Regulator (LQR) balance control method. Specifically, a basic LQR controller is developed based on the dynamics model of the wheel-legged robot, and a Stribeck friction model is established to characterize motor friction. A constant-speed excitation trajectory is designed to gather data for friction identification, and the Particle Swarm Optimization (PSO) algorithm is applied to determine the optimal friction parameters. The identified friction model is subsequently incorporated as feedforward compensation for the LQR controller’s torque output, resulting in the proposed friction feedforward LQR balance control algorithm. The minimum standard deviation for friction identification is approximately 0.30, and the computed friction model values closely match the actual values, indicating effective and accurate identification results. Balance experiments demonstrate that under diverse conditions—such as flat ground, single-sided bridges, and disturbance scenarios—the convergence performance of the friction feedforward LQR algorithm markedly surpasses that of the baseline LQR, effectively reducing oscillations, accelerating convergence, and improving the robot’s stability and robustness. Full article

Two-flavor neutrino oscillation is analyzed using the consistent histories approach. We identify the properties of neutrinos and the oscillation conditions, such as the presence of matter or the impact of measurement, that ensure the consistency of three-time neutrino histories. The connection between the consistency of these histories and the well-known CP violation explored in this study serves as a specific example. Full article

The dispersion and dissipation properties of a numerical scheme are critical in simulating flow fields involving a wide range of length scales. In this study, we highlight the common oversight of focusing merely on controlling dispersion error without considering the importance of appropriate dispersion and scalability in computational efficiency. This study demonstrates that adjusting dispersion to match the local flow field near discontinuities is more effective in suppressing oscillations than simply minimizing dispersion. This proposed high-order finite difference scheme with adaptive dispersion minimized dissipation (ADMD) achieves adaptive controllable dispersion near flow field discontinuities, known as the ADMD scheme. This scheme, derived as a fourth-order finite difference scheme with seven points based on Taylor expansion, comprises a basic central component, additional dissipation component, and dispersion component. By exploring the effect of dispersion on numerical oscillations and the importance of adjusting dispersion according to the local flow field, a discontinuity detection function was established to enable the dispersion properties to adapt to the local flow field. Drawing inspiration from flow field smoothing in the weighted essentially non-oscillatory (WENO) scheme, efforts were made to minimize scheme dissipation. The main benefits of the ADMD scheme over several WENO-type schemes are robustness and efficiency, as the ADMD scheme saves at least 40–90% CPU time compared to the same-order WENO-type schemes for some numerical examples. Additionally, the numerical scheme proves advantageous in terms of simulating the decaying isotropic turbulence problem of three-dimensional compressible turbulence. Full article

Over the past 70 years since the founding of the People’s Republic of China, urban development has achieved remarkable progress but also encountered severe atmospheric pollution, which has become a significant obstacle to high-quality urban development. Understanding the interaction mechanisms between urban development and atmospheric pollution is thus crucial for promoting sustainable urban construction. This paper explores these mechanisms by analyzing the interplay between urban population, industry, space, social development, and pollution through a theoretical framework. Using a simultaneous equations model and the Three-Stage Least Squares (3SLS) method, it examines these relationships and further investigates threshold effects. The findings reveal a nonlinear relationship with significant thresholds: (1) High levels of PM_2.5, population size, and industrial agglomeration can shift from exacerbating pollution to enabling governance, though excessive thresholds reverse this trend. (2) PM_2.5 mediates the impact of spatial sprawl, environmental regulation, and population dynamics, oscillating between governance and pollution effects. (3) Industrial agglomeration and spatial sprawl show variable impacts on pollution mitigation depending on pollution intensity and urban thresholds. These findings provide critical insights into the intricate dynamics between urban development and atmospheric pollution, emphasizing the importance of adopting differentiated strategies based on specific urban thresholds. Ultimately, this research contributes to the broader goal of harmonizing economic growth, social development, and environmental sustainability in urban areas, serving as a valuable reference for cities worldwide facing similar challenges. Full article

The increasing complexity of modern power systems (MPSs), driven by the integration of renewable energy sources and multi-area configurations, demands robust and adaptive load frequency control (LFC) strategies. This paper proposes a novel approach to the LFC of the MPS by integrating a proportional–integral–derivative (PID) controller optimized using the gray wolf optimizer (GWO) algorithm. The effectiveness of the GWO-PID method is evaluated on multi-area power systems, including systems integrated with wind energy. The GWO-PID controller shows superior frequency stability, achieving deviations of 49.67 Hz, 49.68 Hz, 49.87 Hz, 49.87 Hz and 49.88 Hz for area 1 and area 2 of the two-area multisource MPS, as well as for area 1, area 2 and area 3 in the three-area multisource MPS. The results demonstrate significant improvements in frequency stabilization, reduced oscillations and enhanced steady-state accuracy compared to traditional optimization techniques. This study emphasizes the scalability and adaptability of the proposed method to changing load conditions and complexity of the MPSs, providing a potential solution to ensure stability and reliability for the MPSs. Full article

As one of the most precise timekeeping instruments ever developed, the optical clock will be used as the measuring equipment for the next generation of second definition. The demand for the miniaturization of optical clocks is progressively urgent. In this paper, a multi-channel radio frequency (RF) module with a 20% volume of the commercial module is designed and implemented for the transportable ⁴⁰Ca⁺ ion optical clock. Based on the double-crystal oscillator interlocking technique, a 1 GHz low-phase noise reference source is developed for direct digital synthesis. Through the simulation and optimization of the signal link design, the frequency range of the low phase-noise RF signal can reach 0–400 MHz with a 4 μHz resolution. Through two-stage power amplifying with different kinds of filters, it can achieve an output power of up to +33 dBm (2 W) at 100 MHz with a 25 dB phase noise lower than the commercial module at 1 Hz, and its third harmonic suppression ratio has been reduced by more than 20 dB at the frequency point of 300 MHz. This multi-channel RF module is used for the power stability and timing control test of a 729 nm clock laser to meet the requirements of the transportable ⁴⁰Ca⁺ optical clock. Additionally, this module can also be applied to other quantum systems such as the quantum absolute gravimeter, quantum gyroscopes, and quantum computers. Full article