Search Results (163)

Addressing the low efficiency associated with single-frequency serial acquisition in urban exploration using traditional electrical resistivity tomography (ERT) instruments, this study introduces a Frequency Division Multiplexing Electrical Resistivity Tomography (FDM-ERT) method and hardware system. By utilizing transmission modules that simultaneously output AC excitation signals at distinct frequencies, coupled with receiver modules that enable multi-channel parallel acquisition and data transmission, the system achieves a “one-time layout, multi-frequency synchronous measurement” workflow. Laboratory tests under controlled conditions and preliminary field tests conducted at the Xiangjiang River beach demonstrate that this method maintains relatively high consistency with traditional single-frequency measurements. The relative error of apparent resistivity across frequency points remains below 2%, with an inversion root mean square error (RMSE) of 0.4%. Furthermore, the multi-frequency synchronous mode reduces total measurement time by approximately 66.7%. While these results were obtained in relatively controlled environments, they substantiate the core feasibility of the FDM-ERT system for multi-frequency synchronous measurement, providing a certain hardware foundation for subsequent validation and optimization in complex, real-world urban settings. Full article

Coaxial cable plays a vital role in the wide application of telecommunications, network, and television broadcasting and other fields, with its transmission performance directly affecting signal quality and transmission efficiency. In practical applications, the length of the cable and the terminal load state of the connection often affect the stability of the signal. In order to solve this problem, we used STMicroelectronics STM32F407VET6 (STMicroelectronics, Geneva, Switzerland) as the master controller in this system, and deduced the length of the cable by analyzing the functional relationship between the length of the cable and the open circuit frequency. An open cable is regarded as a capacitor, and any two core wires are regarded as two plates of a flat capacitor. The linear relationship between open frequency and length is used to detect the length of the coaxial cable. The system then determines whether the terminal load is capacitance or resistance based on the detected frequency. If no frequency is detected, then the load is considered resistance. The system detects the resistance value of the resistor through series voltage division. If a frequency is detected, this indicates that the load is capacitance. At this time, the system uses an RC oscillation circuit composed of HGSEMI ICL8038 (Huagao Semiconductor Co., Ltd., Wuxi, China) for testing, and provides the phase shift required by the corresponding signal through the RC network, so as to detect the capacitance value. Finally, we successfully designed a coaxial cable length and terminal load detection system based on STM32F407VET6. Through this system, the user can accurately understand the length of the coaxial cable and the load of the connection terminal, which provides a reliable guarantee for the stability of signal transmission. Full article

Background: During aging, skeletal muscle mass constantly diminishes and myogenic potential declines. At the cellular level, a decline in mitochondrial function is a hallmark of the aging process and the deficiency of the mitochondrial network contributes to a progressive reduction in muscle mass. Autophagic clearance of mitochondria through the process of mitophagy is required to remove impaired or damaged mitochondria, while mitophagy is a key regulator of muscle maintenance. Dysfunctional degradation of mitochondria is increasingly associated with aging (mitophaging), while mechanical stimuli have been shown to ameliorate the aging-induced impaired muscle mass and function; however, less is known about the potential effects of mechanical loading on mitophaging. The aim of the present study was to investigate the effect of mechanical stretching on mitophagy in aged myoblasts, in vitro. Methods: Cell senescence was replicated using a multiple cell division model of C2C12 myoblasts. The control and aged cells were cultured on elastic membranes and underwent passive stretching using a mechanical loading protocol of 15% elongation for 12 h at a frequency of 1 Hz. Cell signaling and gene expression responses of mitophagy-associated and myogenic regulatory factors (MRFs) were assessed through immunoblotting and qRT-PCR of the cell lysates derived from stretched and non-stretched control and aged myoblasts. Results: Mitophagy factor AMP-activated protein kinase (AMPK), mitochondrial biogenesis stimulator peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1a), and mitophagy/mitochondrial biogenesis factor Parkin were downregulated in control stretched myoblasts compared to non-stretched cells, while the specific mechanical loading protocol used also reduced the phosphorylation of unc-51-like autophagy-activating kinase 1 (p-ULK1) (p < 0.05), as well as the expression of myogenic factor 5 (Myf5) and myogenic factor 4 (myogenin) (p < 0.001). Interestingly, this mechanical loading resulted in increased PGC-1a and Parkin expression (p < 0.05) and induced the previously undetected BCL2 interacting protein 3-like (BNIP3L/NIX) and AMPK expression and p-ULK1 activation in the aged myoblasts. In addition, mechanical stretching differentially affected the expression of MRFs in aged cells, upregulating the early differentiation factor, Myf5 (p < 0.01), while downregulating the late differentiation factor myogenin (p < 0.001). Conclusions: These findings suggest the beneficial effects of mechanical loading on the impaired mitophagy and early differentiation in aged myoblasts, as indicated by the mitophagy initiation and the promotion of mitochondrial biogenesis in these cells. The mechanical loading-induced downregulation of mitophagy and myogenesis in the control myoblasts might indicate their loading-specific differential responses compared to the aged cells. Full article

Urban geophysical exploration faces significant hurdles due to strong electromagnetic interference and limited operational space, which restrict the efficiency and depth of traditional Electrical Resistivity Tomography (ERT). To overcome these limitations, this paper presents a novel ERT measurement and control system based on the Frequency Division Multiplexing (FDM) principle. Unlike conventional time-domain methods, this instrument synchronously transmits three independent AC signals at distinct frequencies. The acquisition station utilizes Fast Fourier Transform (FFT) to isolate specific frequency responses, enabling the simultaneous retrieval of apparent resistivity data for three different electrode spacings from a single transmission. The system architecture integrates low-power STM32 microcontrollers with an Android-based control terminal via Bluetooth, Wi-Fi, and NB-IoT technologies. This wireless design supports real-time current monitoring and cloud-based data synchronization. Experimental results demonstrate that the FDM operating mode significantly enhances data acquisition efficiency and anti-interference capability through frequency-domain separation. Controlled indoor and preliminary field tests indicate that FDM mode substantially improves acquisition efficiency through concurrent multi-channel measurement while effectively resolving target signals from noise. This study demonstrates the system’s technical feasibility and provides a practical foundation for future geophysical detection in time-constrained urban environments. Full article

With the evolution of smart grids, power communication networks are increasingly required to support high-bandwidth and diversified services such as high-definition video, real-time control, and positioning—services that impose dual challenges of communication capacity and spectrum constraints—under severe resource limitations. Conventional orthogonal modulation schemes exhibit significant limitations in spectral efficiency and concurrent access capabilities, particularly in supporting high-density user environments. To address this, we propose a communication system based on non-orthogonal overlapped chirp modulation, in which the intrinsic symmetry properties of chirp waveforms are utilized to enhance system design and performance. We first construct the system architecture with a multi-symbol concurrent transmission scheme and introduce continuous orthogonal phase modulation to improve symbol distinguishability and mitigate inter-symbol interference—an approach that effectively harnesses signal symmetry for interference suppression. At the receiver, a low-complexity demodulation algorithm based on correlation matrix computation is developed, further improved through oversampling techniques that exploit temporal and spectral symmetry in signal design. Monte Carlo simulations confirm that the proposed system outperforms traditional orthogonal chirp and orthogonal frequency division multiplexing systems in bit error rate performance and spectral efficiency across varying signal-to-noise ratios and modulation schemes. The proposed NOOC system achieves spectral efficiency scaling linearly with concurrency level K, reaching up to 16 bits/s/Hz for K = 16 with BPSK, compared to 1 bit/s/Hz in orthogonal systems. The study provides both a theoretical foundation and practical insights for developing symmetry-aware, efficient, and reliable air interface technologies suitable for future power-private networks. Full article

In communication-centric integrated sensing and communication (ISAC) systems, passive radars exploit existing communication signals of opportunity for sensing. To compute delay-Doppler or range–velocity maps (DDMs and RVMs, respectively), modern orthogonal frequency division multiplexing (OFDM)-based sensing systems use the channel frequency response (CFR) originally estimated in communication receivers for equalization. In OFDM-based passive radars utilizing 4G LTE or 5G NR waveforms, CFR estimation typically relies only on reference signals. However, simulation-based studies that assume a priori knowledge of user data symbols indicate potential performance gains when incorporating user data and other downlink channels. In this work, we present an experimental evaluation of an OFDM-based passive radar that jointly utilizes all commonly present components of the 5G NR downlink waveform: synchronization signals (PSS and SSS), broadcast and control channels (PBCHs and PDCCHs, respectively), data channels (PDSCHs), and reference signals (PBCH DM-RSs, PDCCH DM-RSs, PDSCH DM-RSs, and CSI-RSs). Our results show that utilizing user data from fully occupied 5G downlink signals, under the assumption of full knowledge of PDSCH locations, significantly improves both the probability of detection (POD) and the peak height, measured by the peak-to-noise-floor ratio (PNFR), compared with pilot-only sensing. Since perfect knowledge of the user data payload is not assumed, we estimate the transmission bit error rate (BER) and analyze its impact on sensing performance. Finally, we investigate more realistic scenarios in which only a subset of PDSCH resource element locations is known, as in practical 5G deployments, and evaluate how partial data location knowledge affects the POD and PNFR under different BER conditions. Full article

To improve the dynamic response and steady-state frequency quality of a wind–storage coordinated system during primary frequency regulation, and to address the secondary frequency dip caused by rotor kinetic energy recovery when a doubly fed induction generator (DFIG)-based wind turbine (DFIG-WT) participates in frequency support, this paper proposes a coordinated wind–storage primary frequency regulation strategy. This strategy synergistically controls the wind turbine’s rotor kinetic energy recovery and exploits the advantages of hybrid energy storage system (HESS). During the DFIG-WT control stage, an adaptive weighted model is developed for the inertial and droop power contributions of the DFIG-WT based on the available rotor kinetic energy, enabling a rational distribution of primary frequency regulation power. In the control segment of HESS, an adaptive complementary filtering frequency division strategy is proposed. This approach integrates an adaptive adjustment method based on state of charge (SOC) to control both the battery energy storage system (BESS) and supercapacitor (SC). Additionally, the BESS assists in completing the rotor kinetic energy recovery process. Through simulation experiments, the results demonstrate that under operating conditions of 9 m/s wind speed and a 30 MW step disturbance, the proposed adaptive weight integrated inertia control elevates the frequency nadir to 49.84 Hz and reduces the secondary frequency dip to 0.0035 Hz. Under the control strategy where wind and storage coordinated participate in frequency regulation and BESS assist in rotor kinetic energy recovery, secondary frequency dips were eliminated, with steady-state frequency rising to 49.941 Hz. The applicability of this strategy was further validated under higher wind speeds and larger disturbance conditions. Full article

Enhancing the flexibility of hydropower units is essential for adapting to future power systems dominated by intermittent renewable energy sources such as wind and solar, which introduce significant frequency stability challenges due to their inherent variability. To improve the primary frequency regulation capability of the hydropower unit, this study incorporates a flywheel energy storage system—known for its fast response and high short-term power output. Using fuzzy control theory, a frequency regulation command decomposition method with a variable filtering time constant is proposed. In this fuzzy control design, the frequency change rate and the state of charge of the flywheel energy storage are used as inputs to dynamically adjust the filtering time constant, which serves as the output. Additionally, a logistic function is introduced to constrain the output power of the flywheel energy storage under different states of charge, ensuring operational safety and durability. Based on these techniques, a fuzzy frequency division control strategy is designed for flywheel-assisted hydropower primary frequency regulation. Simulation results show that the integration of flywheel energy storage significantly improves the primary frequency regulation performance of the hydropower unit. Compared to the system without energy storage, the proposed strategy reduces the maximum frequency deviation by 53.49% and the steady-state frequency deviation by 39.06%, while also markedly decreasing fluctuations in hydropower output. This study offers both a theoretical basis and practical guidance for enhancing the operational flexibility of hydropower systems. Full article

This paper addresses the long-standing question of understanding the origin and evolution of low-frequency unsteadiness interactions associated with shock waves impinging on a turbulent boundary layer in transonic flow (Mach: $1.1$ to $1.3$). To that end, high-speed experiments in a blowdown open-channel wind tunnel have been performed across a convergent–divergent nozzle for different expansion ratios (PR = 1.44, 1.6, and 1.81). Quantitative evaluation of the underlying spectral energy content has been obtained by processing time-resolved pressure transducer data and Schlieren images using the following spectral analysis methods: Fast Fourier Transform (FFT), Continuous Wavelet Transform (CWT), as well as coherence and time-lag evaluations. The images demonstrated the presence of increased normal shock-wave impact for PR = 1.44, whereas the latter were linked with increased oblique $\lambda$-foot impact. Hence, significant disparities associated with the overall stability, location, and amplitude of the shock waves, as well as quantitative assertions related to spectral energy segregation, have been inferred. A subsequent detailed spectral analysis revealed the presence of multiple discrete frequency peaks (magnitude and frequency of the peaks increasing with PR), with the lower peaks linked with large-scale shock-wave interactions and higher peaks associated with shear-layer instabilities and turbulence. Wavelet transform using the Morlet function illustrates the presence of varying intermittency, modulation in the temporal and frequency scales for different spectral events, and a pseudo-periodic spectral energy pulsation alternating between two frequency-specific events. Spectral analysis of the pixel densities related to different regions, called spatial FFT, highlights the increased influence of the feedback mechanism and coupled turbulence interactions for higher PR. Collation of the subsequent coherence analysis with the previous results underscores that lower PR is linked with shock-separation dynamics being tightly coupled, whereas at higher PR values, global instabilities, vortex shedding, and high-frequency shear-layer effects govern the overall interactions, redistributing the spectral energy across a wider spectral range. Complementing these experiments, time-resolved numerical simulations based on a transient 3D RANS framework were performed. The simulations successfully reproduced the main features of the shock motion, including the downstream migration of the mean position, the reduction in oscillation amplitude with increasing PR, and the division of the spectra into distinct frequency regions. This confirms that the adopted 3D RANS approach provides a suitable predictive framework for capturing the essential unsteady dynamics of shock–boundary layer interactions across both temporal and spatial scales. This novel combination of synchronized Schlieren imaging with pressure transducer data, followed by application of advanced spectral analysis techniques, FFT, CWT, spatial FFT, coherence analysis, and numerical evaluations, linked image-derived propagation and coherence results directly to wall pressure dynamics, providing critical insights into how PR variation governs the spectral energy content and shock-wave oscillation behavior for nozzles. Thus, for low PR flows dominated by normal shock structure, global instability of the separation zone governs the overall oscillations, whereas higher PR, linked with dominant $\lambda$-foot structure, demonstrates increased feedback from the shear-layer oscillations, separation region breathing, as well as global instabilities. It is envisaged that epistemic understanding related to the spectral dynamics of low-frequency oscillations at different PR values derived from this study could be useful for future nozzle design modifications aimed at achieving optimal nozzle performance. The study could further assist the implementation of appropriate flow control strategies to alleviate these instabilities and improve thrust performance. Full article

Cognitive tasks play a pivotal role in posture control among young adults. This study examined how concurrent cognitive tasks alter balance stability and sensory integration during single-leg stance by analyzing center-of-pressure trajectories and wavelet spectra to elucidate the neurobehavioral mechanisms underlying dual-task balance degradation. A cohort of 24 young adults completed both single postural control tasks and dual cognitive–postural tasks on a force plate. COP data and wavelet decomposition energy were computed and analyzed. The results revealed significant differences between the dual-task and single-task groups for Lxy, Ly, Vxy, and Vy (p < 0.05). Energy content analysis showed that the dual-task group had significantly different energy ratios across four frequency bands along the x-axis (p < 0.05). Our findings showed that dual-task conditions impair postural control in young adults, increasing anteroposterior sway and altering mediolateral energy patterns. This suggests a shift toward proprioceptive reliance during cognitive division, revealing cognitive–postural interference. These results support using dual-task assessments for fall risk evaluation and inform interventions for populations requiring cognitive–motor integration. Full article

This paper presents the design and experimental evaluation of a compact microstrip patch antenna and a 4 × 4 phased antenna array system tailored for Wi-Fi 6E applications, U-NII-5 band. A single inset-fed microstrip patch antenna was first optimized through full-wave simulations, achieving a resonant frequency of 5.96 GHz with a measured return loss of −17.5 dB and stable broadside radiation. Building on this element, a corporate-fed 4 × 4 array was implemented on an FR4 substrate, incorporating stepped-impedance transmission lines and λ/4 transformers to ensure equal power division and impedance matching across all ports. A 4-bit digital phase shifter, controlled by an ATmega328p microcontroller, was integrated to enable electronic beam steering. Simulated results demonstrated accurate beam control within ±28°, with directional gains above 13 dBi and minimal degradation compared to the broadside case. Over-the-air measurements validated these findings, showing main lobe steering at 0°, ±15°, +33° and −30° with peak gains between 7.8 and 11.5 dBi. The proposed design demonstrates a cost-effective and practical solution for Wi-Fi 6E phased array antennas, offering enhanced beamforming, improved spatial coverage, and reliable performance in next-generation wireless networks. Full article

This paper presents dual-layer frequency selective surfaces (FSSs) with frequency division control function through an integrated tunable transmission window at a lower frequency and an absorption performance at a higher frequency. The bottom frequency selective surface (FSS) layer, configured as a bandpass structure, incorporates a gradient gap square-ring element loaded with varactor diodes. This configuration enables dynamic tuning of the L-band transmission window from 1.26 GHz to 1.9 GHz via varactor capacitance modulation. Simultaneously, the top FSS layer utilizes a square-ring-cross-slot topology. Leveraging the strong reflection characteristic of the bottom FSS at higher frequencies in conjunction with dielectric loss mechanisms, the structure achieves absorption performance within the 5.56 GHz to 5.72 GHz band. Measurement results indicate insertion loss at operational frequencies within the transmission window remains below 1.41 dB, while the absorption peak reaches approximately −30 dB. Close agreement between simulated and measured results validates the proposed design. Full article

The uplink of 5G networks allows selecting the transmit waveform between cyclic prefix orthogonal frequency division multiplexing (CP-OFDM) and discrete Fourier transform spread OFDM (DFT-S-OFDM) to cope with the diverse operational conditions of the power amplifiers (PAs) in different user equipment (UEs). CP-OFDM leads to higher throughput when the PAs are operating in their linear region, which is mostly the case for cell-interior users, whereas DFT-S-OFDM is more appealing when PAs are exhibiting non-linear behavior, which is associated with cell-edge users. Therefore, existing waveform selection solutions rely on predefined signal-to-noise ratio (SNR) thresholds that are computed offline. However, the varying user and channel dynamics, as well as their interactions with power control, require an adaptable threshold selection mechanism. In this paper, we propose an intelligent waveform-switching mechanism based on deep reinforcement learning (DRL) that learns optimal switching thresholds for the current operational conditions. In this proposal, a learning agent aims at maximizing a function built using available throughput percentiles in real networks. Said percentiles are weighted so as to improve the cell-edge users’ service without dramatically reducing the cell average. Aggregated measurements of signal-to-noise ratio (SNR) and timing advance (TA), available in real networks, are used in the procedure. In addition, the solution accounts for the switching cost, which is related to the interruption of the communication after every switch due to implementation issues, which has not been considered in existing solutions. Results show that our proposed scheme achieves remarkable gains in terms of throughput for cell-edge users without degrading the average throughput. Full article

The phase detection of abnormal gait and the prediction of lower-limb angles are key challenges in controlling lower-limb exoskeletons. This study simulated three types of abnormal gaits: scissor gait, foot-drop gait, and staggering gait. To enhance the recognition capability for abnormal gait phases, a four-discrete-phase division for a single leg is proposed: pre-swing, swing, swing termination, and stance phases. The four phases of both legs further constitute four stages of walking. Using the Euler angles of the ankle joints as inputs, the capabilities of a Convolutional Neural Network and a Support Vector Machine in recognizing discrete gait phases are verified. Based on these discrete gait phases, a continuous phase estimation is further performed using an adaptive frequency oscillator. For predicting the lower-limb motion angle, this study innovatively proposes an input scheme that integrates three-axis ankle joint angles and continuous gait phases. Comparative experiments confirmed that this information fusion scheme improved the limb angle prediction accuracy, with the Convolutional Neural Network–Long Short-Term Memory network yielding the best prediction results. Full article

Capacitive-coupling non-contact voltage sensors face a key challenge: their probe-conductor coupling capacitance varies, making it hard to accurately determine the division ratio. This capacitance is influenced by factors like the conductor’s insulation material, radius, and relative position. To address this challenge, this paper proposes a sensor gain self-calibration method based on switching capacitors. This method obtains multiple sets of real-time measurement outputs by connecting and switching different standard capacitors in parallel with the sensor’s structural capacitance, and then simultaneously solves for the coupling capacitance and the voltage under test, thereby achieving on-site autonomous calibration of the sensor gain. To effectively suppress interference from stray electric fields in the surrounding space, a shielded coaxial probe structure and corresponding back-end processing circuitry were designed, significantly enhancing the system’s anti-interference capability. Finally, an experimental platform incorporating insulated conductors of various diameters was built to validate the method’s effectiveness. Within the 100–300 V power-frequency range, the reconstructed voltage amplitude shows a maximum relative error of 1.06% and a maximum phase error of 0.76°, and harmonics are measurable up to the 50th order. Under inter-phase electric field interference, the maximum relative error of the reconstructed voltage amplitude is 1.34%, demonstrating significant shielding effectiveness. For conductors with diameters ranging from 6 mm² to 35 mm², the measurement error is controlled within 1.57%. These results confirm the method’s strong environmental adaptability and broad applicability across different conductor diameters. Full article