Search

A novel centimeter-wave (CMW) and millimeter-wave (MMW) ultra-wideband (UWB) signal generator based on optical up-conversion technique is presented. A dual-parallel Mach–Zehnder modulator is employed to modulate the electrical baseband UWB signal to an optical carrier and eliminate the local oscillator component. Meanwhile, a Mach–Zehnder modulator and an optical bandpass filter produce a carrier-suppressed single sideband (CS-SSB) signal. Then, the UWB modulated optical signal is combined with the CS-SSB signal for photonic frequency up-conversion. Subsequently, the combined optical signal is injected into a balanced photodetector that is used for both heterodyne detection and low-frequency components suppression. A theoretical simulation and a proof-of-concept experiment are carried out to verify the feasibility of the proposed scheme. Eventually, a CMW-UWB signal is generated having a spectral power efficiency (SPE) of 54.25% and a 10-dB bandwidth of 5.89 GHz. An MMW-UWB signal is generated having an SPE of 54.12% and a 10-dB bandwidth of 5.67 GHz. Compared with other methods, the proposed generator can generate high-order CMW-UWB signal in a simpler structure since the up-conversion technique is employed. And the SSB up-conversion technique used in this generator overcomes the instability problem existing in the uncorrelated heterodyne method. The generated UWB signals both fulfil the requirements specified by the Federal Communications Commission. [ABSTRACT FROM AUTHOR]

Background & Aims Methods Results Conclusions Many systematic reviews explore the association of non‐alcoholic fatty liver disease (NAFLD) with mortality, but none of them explores sex‐based differences in detail. We aimed to assess whether NAFLD is associated with cause‐specific mortality, all‐cause mortality, and cancer incidence in both men and women.The PubMed, Embase, and Medline databases were searched from inception through April 2023 for eligible studies. We separately pooled relative risks (RRs) for men and women using a random effects model. Subsequently, the RRs and 95% CIs (confidence intervals) in each study were used to calculate the women‐to‐men ratio of RRs (RRR). Furthermore, subgroup analyses were performed to explore the robustness of outcomes. The random‐effects model was employed to conduct sensitivity analyses to determine the impact of specific studies on the overall findings.The meta‐analysis included nine cohort studies comprising 557 614 patients with NAFLD were chosen. Women were 44% more likely than men to get cancer among those with NAFLD (RRR: 1.44; 95% CI: 1.02–2.04; p = .039). However, no sex‐related differences were observed between NAFLD and all‐cause mortality (RRR: 1.06; 95% CI: 0.56–2.01; p = .861), liver‐related mortality (RRR: 1.06; 95% CI: 0.02–69.82; p = .977), cardiovascular mortality (RRR: 1; 95% CI: 0.65–1.53; p = .987) and liver cancer (RRR: 0.76; 95% CI: 0.43–1.36; p = .36).There may be sex variations between NAFLD and the risk of cancer, with the connection being stronger in females than in males. [ABSTRACT FROM AUTHOR]

Multiphase machines are famous for their fault-tolerant capability. Conventional fault-tolerant model predictive current control (FT-CMPC) of multiphase machines suffers from high computational burden, low switching frequency, and relatively high current harmonics. This paper proposes a fault-tolerant PWM predictive control (FT-PWMPC) to enhance the performance of fault-tolerant predictive control strategy without using complex enumeration method. The reference phase voltages are generated by a postfault mathematical model in stationary reference frame and transformed to duty cycles with a properly set common-mode voltage. Then, a comparative study of fault-tolerant predictive control strategies is presented, including FT-CMPC, FT-two-vector-based-predictive control, and the proposed FT-PWMPC. The control strategies are implemented with the same sampling frequency or switching frequency on a six-phase permanent magnet synchronous machine test bench. Experimental results of dynamic response, steady-state currents, vibration, and parameter sensitivities are given to identify the advantages and limitations of each control strategy. [ABSTRACT FROM AUTHOR]

Multiphase machines and drives are attractive to researchers due to the capability of fault tolerance. Finite‐control‐set model predictive control (FCS‐MPC) has been introduced to the post‐fault operation of multiphase drives and is superior with rapid dynamic response. However, conventional FCS‐MPC is always troubled with low switching frequency and the consequent current ripples. This study proposes a fault‐tolerant two‐vector predictive control (FT‐TVPC) that utilises a zero voltage vector to modulate with the active vector in each sampling period. The post‐fault model of the machine and the drive is obtained in original phase frame with the purpose of achieving various control modes with different reference currents. A group of experiments are carried out and proves the effectiveness of the proposed control technique on improving the current quality. The average switching frequency of the inverter increases in exchange. The results also demonstrate that different control modes have little influence but working conditions have a great impact on the improvement of performance. [ABSTRACT FROM AUTHOR]

This paper investigates the postfault operation of a novel six-phase double-stator axial-flux permanent-magnet machine with detached winding connection. In previous research, this configuration was found to be superior to existing winding connection except that its unbalanced magnetic force in the postfault operation cannot be ignored. In this paper, an axial magnetic force balancing method (AMFBM) is proposed to reduce unbalanced magnetic force by deducing a set of special winding current. By comparing electromagnetic torque and axial magnetic force of the traditional winding current and the proposed method in postfault operations through a finite-element analysis, it is verified that AMFBM can reduce most of the unbalanced axial magnetic force as well as keeping torque ripple at a low level. In order to realize the AMFBM, finite control set model predictive control is adopted. A postfault model of dual-three-phase permanent-magnet machines with modified vector space decomposition method is first brought forward to predict the future behavior of the controlled variables with various voltage inputs. After that, a cost function is designed to track the desired winding current by evaluating all the predictions to decide the next step of the inverter. Experimental results show that the control scheme performs well in both dynamic and steady-state situations. [ABSTRACT FROM PUBLISHER]

Across development, people tend to demonstrate a preference for contexts in which they have the opportunity to make choices. However, it is not clear how children, adolescents, and adults learn to calibrate this preference based on the costs and benefits of agentic choice. Here, in both a primary, in-person, reinforcement-learning experiment (N = 92; age range = 10–25 years) and a preregistered online replication study (N = 150; age range = 8–25 years), we found that participants overvalued agentic choice but also calibrated their agency decisions to the reward structure of the environment, increasingly selecting agentic choice when choice had greater instrumental value. Regression analyses and computational modeling of participant choices revealed that participants’ bias toward agentic choice—reflecting its intrinsic value—remained consistent across age, whereas sensitivity to the instrumental value of agentic choice increased from childhood to early adulthood. [ABSTRACT FROM AUTHOR]

This paper proposes a novel detached winding configuration for asymmetric six-phase double-stator axial flux permanent magnet machines aiming at fault-tolerant applications. Due to the machine unique double-stator structure, the six-phase winding can be separated into two three-phase windings with 30 electrical degree angle shift and arranged in different stators, which is the basic idea of the detached winding. In this paper, the connection of detached six-phase winding is first given, followed by a comprehensive comparison of the conventional six-phase winding and the detached winding in aspect such as the winding factor, electromotive force, inductances, rotor eddy current loss, and torque in normal condition. Performance under fault-tolerant operation is investigated by the copper loss minimization control strategy. The results show that by applying the detached winding instead of the conventional winding, rotor eddy current losses could be reduced by 25% and 70% under normal and fault-tolerant operation, respectively, without sacrificing torque output. This implies that under fault operation, the excess heating in rotor could be reduced and the machine durability can be enhanced. A prototype machine is built to validate the performance of the detached winding design. The experimental results match well with simulation analysis. [ABSTRACT FROM AUTHOR]

This paper presents a detailed analysis of the electromagnetic force and vibration behavior of an axial flux permanent magnet synchronous machine (AFPMSM). First, the AFPMSM configuration and two types of dual three-phase winding are introduced. Subsequently, the electromagnetic force of the double-stator inner-rotor AFPMSM is investigated. Its spatial and temporal characteristics are derived analytically and validated through two-dimensional Fourier decomposition. A multiphysics model is established to calculate the vibration of the AFPMSM, which includes control, electromagnetic, structural, and vibration model. The accuracy of this multiphysics model is verified by the modal and vibration test. Furthermore, the vibration of the AFPMSM with three winding types considering current harmonics are calculated based on the multiphysics model. The vibration performance of the AFPMSM with three different winding types are compared and the mechanism of vibration is discussed. It was concluded that the novel detached winding could mitigate the vibration of dual three-phase AFPMSMs. Finally, the vibration test is carried out to validate the theoretical analysis and the experimental results agree well-with the simulation results. This paper provides an effective method for double-stator permanent magnet synchronous machine (PMSMs) to reduce vibration. [ABSTRACT FROM AUTHOR]

This paper first studies the electromagnetic force and vibration characteristics of the permanent-magnet-assisted synchronous reluctance machines (PM-SynRMs). First, an analytical method to calculate the radial force is proposed based on the Maxwell stress tensor method. The temporal and spatial orders of radial force are obtained by two-dimensional fast Fourier transform, then the combination of stator slots and rotor virtual slots of PM-SynRMs is proposed to give a guideline for the initial design of PM-SynRM to achieve low noise and vibration. A PM-SynRM is designed and a multiphysics model for electromagnetic vibration is established. The radial and tangential force under no-load and load conditions are calculated by finite element method, and then compared with the analysis results. Modal analysis is implemented to capture the structural parameters of the stator. Based on the proposed multiphysics model, the vibration responses under both no-load and load conditions are calculated through modal superposition method. Finally, a PM-SynRM is built and vibration test is performed to investigate its vibration characteristics. [ABSTRACT FROM AUTHOR]

Recently, stator dc current excited vernier reluctance machines (dc-VRMs) which have concentrated field and armature windings in stator, are gaining more and more research interest due to their features of robustness rotor structure, low cost, and easy heat dissipation. This paper proposes a novel field winding connection for dc-VRMs. Taking the stator/rotor slots of 12/10 machine as an example, the electromagnetic performance including back electromotive force (EMF), pulsating torque, and capability are analyzed using the theoretical and finite element analysis. The results show that compared with the previous machine having the same stator/rotor slots, machine with the proposed field winding connections exhibits a doubling back EMF, and 60% higher torque density. [ABSTRACT FROM AUTHOR]

Stator dc field winding excited vernier reluctance machines are increasingly attracting research interest recently due to their low cost and highly reliable rotor structure. In this paper, the design of these machines is studied systematically using both theoretical equations and finite element analysis (FEA). First, the general structures of these machines and their operation principles are discussed. Second, based on the operation principle, the back electromotive force, torque, and power factor expressions are deduced in terms of the geometrical variables. Several key design parameters are defined, including stator/rotor slot/pole combinations, air gap, split ratio, field/armature coil turn ratio, and stator/rotor tooth arc combination. Third, the deduced theoretical expressions are verified by the FEA. Finally, a prototype is designed and tested to verify the analysis results. [ABSTRACT FROM PUBLISHER]

• Radical concentrations of co-pyrolysis are lower than calculated values. • Mass loss of co-pyrolysis is lower than the calculated values at ~ 380–600 °C. • Combination of S· and V· is the main interaction and mainly occur at ~ 380–600 °C. • Yields of coke, tar, and gas increase while water decreases for co-pyrolysis. • Secondary reaction of volatiles increased for co-pyrolysis. In this study, interactions between free radicals during co-pyrolysis of lignite and biomass were explored. Changes in free radical concentrations were investigated using electron spin resonance (ESR). Additionally, the interactions between free radicals during co-pyrolysis were analyzed based on free radical concentration, thermogravimetric (TG) behavior, and changes in yields and properties of pyrolysis products in a fixed-bed reactor. The results of ESR and TG analyses indicate that, during co-pyrolysis, the combination of radicals, especially that of stable and volatile free radicals, leads to a decrease in both radical concentration and mass loss. The main temperature range for the interaction of free radicals was ~ 380–600 °C. The co-pyrolysis results from the fixed-bed reactor show that the yields of products such as gas, tar, and char are higher than their calculated values, except for water, which confirms the existence of synergy between the coal and biomass. As the resistance of the volatile free radicals escaping from the bed increases, the secondary reactions of volatiles increase during co-pyrolysis, which leads to changes in the composition and properties of gas and tar. [ABSTRACT FROM AUTHOR]