Search Results (2,211)

The water consumption processes of vegetation play an important role in water resource management in semiarid regions, while the difference in water consumption between native and exotic species is unclear. In this study, the exotic Pinus sylvestris L. var. mongholica Litv. (Pinus) and the native Salix psammophila (Salix) in Mu Us Sandy Land were selected as the research objects, and their water consumption characteristics were studied via in situ experiment and stable isotopes (δ²H and δ¹⁸O). Results revealed that vegetation water consumption caused spatial variation in soil moisture, allowing the soil profile to be divided into active, stable, capillary support and saturated zones. Pinus primarily used water from the active and stable zones, whereas Salix relied more on the capillary support and saturated zones. Water consumption patterns also varied seasonally, for example, at the beginning of growth (May–June), Salix and Pinus mainly use shallow soil water and begin to use deep soil water and groundwater with growth. During July–September, they absorb soil water mainly in the active zone and stable zone. Both Salix and Pinus can freely switch water sources between deep and shallow layers according to water demand. The seasonal fluctuations in precipitation and groundwater level were the main factors driving the seasonal changes in the water consumption of the two vegetation types. Pinus has better strategies to adapt to droughts than Salix, but its water consumption is higher than that of Salix. Therefore, proper management is needed to control the reasonable density of Pinus plantation to balance the water consumption of vegetation and groundwater recharge. The results can provide a scientific basis for the reasonable vegetation reconstruction in the Mu Us Sandy Land. Full article

In this paper, based on Generalized Autoregressive Conditional Heteroskedasticity (GARCH) model, five financial serials are dynamically weighted, and then China’s Financial Conditions Index is synthesized to measure China’s financial cycle. After that, using the monthly data of 2000–2023 as sample space, this paper utilizes the Markov Switching (MS) model to analyze the characteristics of China’s financial cycle and to investigate the four-zone system. Then, the Vector Autoregression (VAR) model focuses on investigating the macroeconomic effects of China’s financial cycle. The findings are as follows: Firstly, the dynamic weighting approach based on GARCH model is more suitable for valuating China’s financial cycle. Secondly, China’s financial cycle has a strong inertia at the state of transition and the imbalance of China’s overall financial situation is very common. Additionally, China’s financial cycle is distinctly characterized by the double asymmetry of fewer contractions and more expansions, shorter expansions, and longer expansions. Thirdly, China’s financial expansion offers a nine-month short-term stimulus to output and exerts lasting upward pressure on prices. Full article

Background: Uniportal video-thoracoscopic lobectomy has improved postoperative outcomes in lung cancer patients. Thus, thoracic surgeons are increasingly required to learn this new approach. Methods: We evaluate the path of a single surgeon switching from triportal video-thoracoscopic lobectomy to the uniportal, using the cumulative sum (CUSUM) analysis, in a single center to assess the learning curve, enrolling 107 uniportal video-thoracoscopic lobectomies consecutively performed. CUSUM analysis detected how many uniportal video-thoracoscopies occur to obtain changes in mean operation time, among all procedures consecutively performed. CUSUM analysis identified the cut-off at the 67th procedure; this value was used to divide all patients into two groups: group A (first 67 patients, early phase) and group B (40 patients, experienced phase). Then, we analyze the perioperative outcomes between the two groups. Results: Gender characteristics of the two groups were statistically similar. Median operative time decreased significantly after the early phase [188 min (IQR: 151–236) vs. 170.5 (IQR: 134–202) (p-value = 0.02)], respectively. Similarly, during the second phase, the conversions rate decreased: [10 (15%) (group A) vs. 1 (2%) (group B) (p-value = 0.04)], as did the postoperative complications [28 cases (42%) vs. 9 cases (22%) (p-value = 0.04)] and the length of stay [6 days (IQR 5–9.5) vs. 5 days (IQR 4–8) (p-value = 0.04)], giving evidence of skills acquired in the second phase. Conclusions: CUSUM analysis identified 67 uniportal lobectomies, after which operative time, conversion rate, and perioperative complications significantly decreased; the moving average analysis further supports a progressive reduction in operative time. Despite prior multiportal video-thoracoscopic experience, switching to uniportal video-thoracoscopy requires a distinct learning process. Full article

Over the past decade, two-dimensional materials have become a research hotspot in chemistry, physics, materials science, and electrical and optical engineering due to their excellent properties. Graphene is one of the earliest discovered 2D materials. The absence of a bandgap in pure graphene limits its application in digital electronics where switching behavior is essential. In the present study, researchers have proposed a variety of methods for tuning the graphene bandgap. Machine learning methodologies have demonstrated the capability to enhance the efficiency of materials research by automating the recording of characteristic parameters from the discovery and preparation of 2D materials, property calculations, and simulations, as well as by facilitating the extraction and summarization of governing principles. In this work, we use first principle calculations to build a dataset of graphene band gaps under various conditions, including the application of a perpendicular external electric field, nitrogen doping, and hydrogen atom adsorption. Support Vector Machine (SVM), Random Forest (RF), and Multi-Layer Perceptron (MLP) Regression were utilized to successfully predict the graphene bandgap, and the accuracy of the models was verified using first principles. Finally, the advantages and limitations of the three models were compared. Full article

A radiation-hardened RCC (Ring Choke Converter) isolated power supply design is proposed, which provides an innovative solution to the challenge of providing stable power to the PWM controller in DC-DC converters under nuclear radiation environments. By optimizing circuit architecture and component selection, and incorporating transformer isolation and dynamic parameter compensation technology, the RCC maintains an 8.9 V output voltage after exposure to neutron irradiation of 3 × 10¹³ n/cm², significantly outperforming conventional designs with a failure threshold of 1 × 10¹³ n/cm². For the first time, the degradation mechanisms of VDMOS devices under neutron irradiation during switching operations are systematically revealed: a 32–36% reduction in threshold voltage (with the main power transistor dropping from 5 V to 3.4 V) and an increase in on-resistance. Based on these findings, a selection criterion for power transistors is established, enabling the power supply to achieve a 2 W output in extreme environments such as nuclear power plant monitoring and satellite systems. The results provide a comprehensive solution for radiation-hardened power electronics systems, covering device characteristic analysis to circuit optimization, with significant engineering application value. Full article

This research explores a phase-shift-based discontinuous PWM method used for 24 V battery-powered onboard micro inverters, which are critical for thermally limited applications like micromachines, where efficient heat dissipation and compact size are paramount. Discontinuous pulse width modulation (DPWM) reduces switching losses by clamping the phase voltage to the DC bus in order to improve inverter efficiency. Due to the change in power factor at different operating points from motors or the inductor load, the use of only one DPWM method cannot achieve the optimal efficiency of a three-phase voltage source inverter (3ph-VSI). This paper proposes a generalized DPWM method with a continuously adjustable phase shift angle, which extends the six traditional DPWM methods to any type. According to different power factors, the proposed DPWM method is divided into five power factor angle intervals, namely [−90°, −60°], [−60°, −30°], [−30°, 30°], [30°, 60°], and [60°, 90°], and automatically adjusts the phase shift angle to the optimal-efficiency DPWM mode. The power factor is calculated by means of the Synchronous Reference Frame Phase-Locked Loop (SRF-PLL) method. The switching losses and harmonic characteristics of the proposed DPWM are analyzed, and finally, a 24 V onboard 3ph-VSI experimental platform is built. The experimental results show that the efficiency of DPWM methods can be improved by 3–6% and the switching loss can be reduced by 40–50% under different power factors. At the same time, the dynamic performance of the proposed algorithm with a transition state is verified. This method is particularly suitable for miniaturized inverters where efficiency and thermal management are critical. Full article

This study investigates the 3RPUR (3-Revolute–Prismatic–Universal–Revolute) variable parallel mechanism, employing screw theory and linear geometry to analyze the geometric relationships and constraint characteristics of the RPUR (Revolute–Prismatic–Universal–Revolute) limb kinematic pairs. The findings reveal that the constraint moment in the always remains perpendicular to the two axes of the U pair, forming an equivalent plane. Through the locking/unlocking mechanism of universal joints (U pair), the mechanism achieves dynamic degree-of-freedom reconstruction, enabling seamless switching between three translational (3T) and three translational-one-rotation (3T1R) motion modes. The continuity between motion and degrees of freedom during the variable cell process is demonstrated. This research reveals a strict 1:1 linear coupling between the rotational angle of the moving platform around the Z-axis and the U pair’s rotation angle under 3T1R mode. Simulation experiments validate the feasibility and coupling characteristics of both motion modes, providing theoretical and technical support for this mechanism’s adaptation to complex working conditions in mobile robotics applications, particularly where reconfigurable parallel mechanisms are required for multi-task flexibility. Full article

The bridge arms and DC voltage of China’s Four-Terminal Flexible DC Transmission Project exhibit persistent high-frequency harmonics over the medium to long term, causing issues such as overheating losses and electromagnetic interference within the converter stations. To address this issue, this paper first introduces the structure of the Four-Terminal Flexible DC Grid and the high-frequency harmonic characteristics on the DC side, clarifying the impact of control cycles on the harmonic distribution at converter stations. Through analysis of the modulating wave, it is demonstrated that the sideband harmonics originate from the coupling effect between the control cycle and the modulating wave, inducing high-frequency sideband harmonics on the bridge arm. A discrete switching equation for bridge arm voltage was established. Based on double Fourier decomposition, a mathematical model for sideband harmonics was derived, and the flow direction of these harmonics was analyzed. A four-terminal flexible DC system was constructed using PSCAD electromagnetic transient simulation, yielding harmonic distributions in the arm and DC-side sidebands. This validated the accuracy of theoretical analysis and ultimately identified the factors influencing sideband harmonics. Full article

Ship noise not only has an impact on crew comfort, but also causes damage to the marine environment. Longitudinal vibration of propulsion shaft system is one of the most important causes of ship noise, so in order to indirect control the vibration noise, the development of a propulsion shaft system vibration controller is an effective method. In this paper, a Kdamper with a magnetorheological damper (Kdamper-MRD) is proposed to control the longitudinal vibrations transmitted along the propulsion shaft system. The vibration characteristics of the propulsion shaft system are analyzed using the transfer matrix method and the optimal Kdamper-MRD design parameters for controlling the target modes are given. Specific structural design parameters are given as well as material selection. The magnetic field distribution and the magnitude of the output damping force of the MRD are obtained by the simulation method, and the negative stiffness characteristics of the disk spring are also discussed. An on–off current switching control strategy is proposed to further improve the vibration damping performance of the Kdamper-MRD. A comparison with the traditional DVA under simple harmonic excitation and random excitation proves that the Kdamper-MRD has better low-frequency vibration damping performance and is able to attenuate longitudinal vibration of the axle system in the whole frequency domain. Full article

For power electronic transformer (PET) based Modular Multilevel DC-Link Based T-type Converters (MMDTC) with Double Active Bridges (DABs) (namely DABs-based MMDTC-PET), the sub-module capacitor voltages exhibit relatively large ripples. To reduce the voltage ripple of sub-module capacitors, this paper proposes a novel MMDTC-PET structure that utilizes the Three-Port Active Bridges (TABs) to replace the DABs as the isolation stage (TABs-based MMDTC-PET). When the two full bridges of the TAB on the primary side adopt identical phase-shift modulation, the two sub-module capacitors within the upper and lower arms form a parallel connection. This configuration endows the sub-module capacitors with switched-capacitor characteristics, suppressing voltage ripple in the sub-module capacitors and enabling power ripple flow to the secondary side. Meanwhile, by leveraging the characteristic that the AC power components of the upper and lower arm sub-modules have equal amplitudes but opposite phases, these AC power components are mutually canceled on the secondary side of the TAB. Simulation and experimental results verify the effectiveness of the proposed scheme. Full article

In complex electromagnetic environments, traditional static absorbers struggle to meet dynamic control requirements. Tunable absorbers based on metasurfaces have emerged as a research hotspot due to their ability to flexibly control electromagnetic wave properties. This paper provides a systematic review of research progress in tunable absorbers across the microwave, terahertz, and infrared bands, with a focus on analyzing the physical mechanisms, material systems, and performance characteristics of five dynamic control methods: electrical control, magnetic control, optical control, temperature control, and mechanical control. Electrical control achieves rapid response through materials such as graphene and varactor diodes; magnetic control utilizes ferrites and other materials for stable tuning; optical control relies on photosensitive materials for ultrafast switching; temperature control employs phase-change materials for large-range reversible regulation; and mechanical control expands tuning freedom through structural deformation. Research indicates that multi-band compatibility faces challenges due to differences in structural scale and physical mechanisms, necessitating the integration of emerging materials and synergistic control strategies. This paper summarizes the core performance metrics and typical applications of absorbers across various bands and outlines future development directions such as multi-field synergistic control and low-power design, providing theoretical references and technical pathways for the development of intelligent tunable absorber devices. Full article

The reliability of the generator circuit breaker (GCB) switching coil affects the safe and stable operation of the power system, in which the faults of abnormal voltage, poor contact, and mechanical jamming of the switching coil can easily lead to the refusal of the circuit breaker, which threatens the safety of the power grid. In order to study the fault characteristics of the GCB switching coil, this paper combines multi-physical field simulation and experimental testing, establishes the electromagnetic field simulation model of the switching coil, and analyzes the characteristics of current waveforms under typical faults such as voltage abnormality, poor contact, and core jamming. Through simulation and testing to verify the mechanism of current waveform distortion under different fault states, demonstrated the change rule of characteristic parameters when the fault occurs, and provided a basis for the diagnosis of the operation status of the switching coil based on current waveform. Full article

Due to their high carrier mobility, thermal conductivity, and exceptional foldability, transition metal dichalcogenides (TMDs) present promising prospects in the realm of flexible semiconductor devices. Concurrently, tunneling field-effect transistors (TFETs) have garnered significant attention owing to their low energy consumption. This study investigates a TMD van der Waals heterojunction (VdWH) TFET, specifically by fabricating MoS₂ field-effect transistors (FETs), WSe₂ FETs, and MoS₂/WSe₂ VdWH TFETs. The N-type characteristics of the MoS₂ and P-type characteristics of WSe₂ are established through an analysis of the electrical characteristics of the respective FETs. Finally, we analyze the energy band and electrical characteristics of the MoS₂/WSe₂ VdWH TFET, which exhibits a drain current switching ratio of 10⁵. This study provides valuable insights for the development of novel low-power devices. Full article

This paper develops multiple control strategies for a precision long-travel stage, which comprises motor and piezoelectric transducer (PZT) stages. First, the PZT stage is equipped with control switching and model estimation mechanisms to achieve nm-level precision within 100 μm distances. The control switching mechanism selects the optimal control sequences by predicting system responses, while the model estimation algorithm updates the system model to improve the prediction accuracy. Second, the motor stage is equipped with gain-scheduling and feedforward control mechanisms to achieve a maximum displacement of 100 mm with a resolution of 0.1 μm. The gain scheduling control modifies the control gain in accordance with tracking errors, while the feedforward control can mitigate phase lags. We integrate the stages to achieve nm-level precision over long travels and conduct simulations and experiments to show the advantages of the control mechanisms. Finally, we apply the long-travel precision stage to fabricate micro-lenses using two-photon polymerization and evaluate the fabricated micro-lenses’ optical characteristics to illustrate the merits of the control strategies. Full article

Linear motor electromagnetic energy regenerative suspension (LMEERS), integrating dual functionalities of energy regeneration and active control, possesses the potential to overcome the performance limitations inherent in existing suspension architectures. Research on key technologies for LMEERS aligns with the contemporary automotive development theme of “enhanced comfort, improved safety, and optimized energy efficiency”. This paper reviews the research progress of the configuration design, performance optimization, functionality switching criterion identification, and top-layer control strategies of LMEERS. Regarding configuration design, a systematic summary is provided for the design schemes of fundamental configuration and the technical features of three composite configurations. In the aspect of performance optimization, the specific approaches and their effectiveness in enhancing LMEERS comprehensive characteristics are analyzed. Concerning functionality switching criterion identification, the operating principles and performance differences among various estimation methods in identifying road surface information are discussed. For top-layer control strategies, the characteristics and applicability of various control methods in exploiting the dual functionalities of LMEERS are summarized. Future developments in LMEERS are anticipated to trend towards integration, lightweighting, standardization, intellectualization, and multi-mode operation. This review provides a theoretical reference for the design optimization and technological innovation of LMEERS, contributing to the advancement of automotive chassis systems in terms of electrification, intellectualization, and energy conservation. Full article