High Power Research Articles

Supression of shielding effect of large area field emitter cathode in radio frequency gun environment

Abstract Utilisation of large area field emitters (LAFE) cathodes for rf gun injector hold promise for delivering compact, high power and high brightness electron beam for advanced accelerator technologies. LAFEs subjected to DC electric fields posses significant challenges due to the shielding effect which restricts emission from central emitters and decreases the overall current density. Mitigating the shielding effect of LAFE in rf gun environment is essential for meeting the desired beam quality requirement in an accelerator. The current distribution of LAFE under DC conditions depend on its various geometrical parameters such as emitter height, inter-emitter distance, aspect ratio, number of emitters. Additionally, in rf gunsetup, LAFEs are subjected to variable macroscopic electric field at different emitter position which can potentially alter the current distribution compared to DC fields. In this work, we have systematically studied the shielding effect properties of LAFE in rf gun environment under the influence of various LAFE parameters. A semi-analytical approachhas been adopted to estimate the current distribution which combines the analytically calculated field enhancement factor (γ) and numerically calculated applied rf field values. This new methodology was first validated using COMSOL simulation and then employed for field emission performance estimation of a LAFE cathode integrated in a½ cell S-band (2856 MHz) rf gun. The simulation results reveals that under favourable conditions, a Gaussian spatial distribution of beam can be obtained from LAFE thus countering the shielding effect typical in DC fields. By optimizing the LAFE parameters, the desired current and beam distribution pattern can be achieved. This study highlights the adoption of a promising approach for designing LAFE cathodes suitable for rf gun which can lead to advancement of field emission technologies for accelerator-related applications.

Introducing boron gallium nitride as carriers’ source layer for efficient near-ultraviolet microLED

Abstract This study explored the impact of boron gallium nitride (BGaN) in buffer layer and hole source layer. We employed B0.05Ga0.95N which reduced the lattice mismatch as well as the electric field. BGaN not only minimized the number of electrons leaking out of quantum wells (QWs) but also improved the hole injection. It is evident from our simulations that internal quantum efficiency (IQE) is enhanced significantly as more carriers are available for radiative recombination in multiple quantum wells (MQWs). Along with the increase in IQE, droop is also reduced in BGaN ultraviolet light-emitting diodes. Significantly high luminous power and emission intensity were observed along with slight blueshift because of minimized quantum confinement stark effect (QCSE).

Electrode materials optimize operating voltage and switching speed in micro/nano plasma ultrafast devices

Abstract The trade-off between ultrahigh speed and low operating voltage is a major challenge in the continuous improvement of modern electronics. Although micro/nano plasma devices have demonstrated the potential of picosecond switching speed and high output power, surpassing traditional electronic devices, versatile methods for optimizing the operating voltage and switching speed are highly desired. Here, an optimization scheme based on the work function of the electrode materials is reported, which reduces the operating voltage and improves the switching speed. Compared with traditional methods, such as narrowing gaps or distorting electric fields, this approach offers advantages such as reducing production costs, enhancing consistency, and improving tunability. The experimental results show that using silver as a low-work-function electrode material can reduce the operating voltage by 55% to 180 V and increase the switching speed by 58% to 7.1 V/ps compared to platinum, which is equivalent to a 71% reduction in gap size. In addition, the underlying working mechanisms and inherent advantages of the approach are demonstrated, providing new insights for the ultrahigh switching speed and low-power application of micro/nano plasma devices, such as high-speed communication and ultrafast electronics.

Within-Team Individual Power and Creativity: Moderating Effects of Democratic Team Leadership and Collectivistic Value

ABSTRACT Though prior research suggests that high individual power can increase individual creativity, relatively few studies have examined conditions when this positive relationship is more likely to hold. Drawing from a cognitive resource perspective and a perspective of socialized power motivation, in this study we theorize and test democratic team leadership and an individual’s collectivistic value as two moderating conditions on the relationship between an individual’s within-team individual power and his or her creativity. Using multi-source data from team members and team leaders from thirty-nine work teams, we predicted and found that within-team individual power is more positively related to individual creativity when democratic team leadership is higher. Moreover, the hypothesized positive moderating effect of democratic team leadership is stronger and more significant for individual team members with high collectivistic values. Our findings provide implications for managing employee creativity and for the responsible use of individual power in teams.

Spiro-Carbon-Locking and Sulfur-Embedding Strategy for Constructing Deep-Red Organic Electroluminescent Emitter with High Efficiency.

The discovery of multiple resonance thermally activated delayed fluorescence (MR-TADF) materials with remarkable narrowband emission has opened a new avenue for the development of organic light-emitting diodes (OLEDs) with high color purity. However, the lack of construction strategies for purely red MR-TADF materials significantly impedes their application in full-color high-definition displays. Herein, we propose a unique and handy approach of spiro-carbon-locking and sulfur-embedding strategy to modify the parent MR-TADF framework, resulting in a red MR-TADF emitter with high color purity. The reported MR-TADF molecule (namely, FSBN) demonstrates a pure red emission with an emission maximum of 621 nm in toluene solution. The OLED with FSBN as emitter exhibits Commission Internationale de l'Éclairage (CIE) coordinates of (0.67, 0.33), which exactly matches the red standard defined by the National Television Standards Committee (NTSC). Importantly, the single-host OLED achieves a high power efficiency (PE) of up to 50.1 lm W-1, suggesting the potential for the development of low power consumption red OLEDs.

Multi‐operating characteristic analysis and loss optimization of novel large capacity high‐speed permanent magnet generator

AbstractRecently, the development trend of large capacity generator has gradually shifted from electrical excitation generator to permanent magnet generator (PMG). As a result, the large capacity high‐speed permanent magnet generator (HSPMG) with high power density and high efficiency have received widespread attention. This paper aims to analyse the loss optimization of novel large capacity HSPMG under multi‐operating conditions. In terms of the parameter requirements, a 2.5 MW and 7000 rpm HSPMG is designed. To verify the accuracy of simulation model and the rationality of generator design, the output characteristics of large capacity HSPMG which has been combined with prototype experimental data are calculated under both no‐load and load conditions. Based on the load power characteristics of large capacity HSPMG, the optimization range of the magnetization angle under multi‐operating conditions is explored. By analysing the no‐load back electromotive force (EMF) and loss characteristics of large capacity HSPMG, the optimal magnetization angle that corresponds to the minimum loss under three conditions is obtained. The correctness of the analysis and optimization method is verified by comparing the loss distribution and electromagnetic results before and after the optimization. The research results provide a reference for the multi‐operating characteristics analysis and loss optimization of large capacity HSPMG.

Spiro‐Carbon‐Locking and Sulfur‐Embedding Strategy for Constructing Deep‐Red Organic Electroluminescent Emitter with High Efficiency

The discovery of multiple resonance thermally activated delayed fluorescence (MR‐TADF) materials with remarkable narrowband emission has opened a new avenue for the development of organic light‐emitting diodes (OLEDs) with high color purity. However, the lack of construction strategies for purely red MR‐TADF materials significantly impedes their application in full‐color high‐definition displays. Herein, we propose a unique and handy approach of spiro‐carbon‐locking and sulfur‐embedding strategy to modify the parent MR‐TADF framework, resulting in a red MR‐TADF emitter with high color purity. The reported MR‐TADF molecule (namely, FSBN) demonstrates a pure red emission with an emission maximum of 621 nm in toluene solution. The OLED with FSBN as emitter exhibits Commission Internationale de l’Éclairage (CIE) coordinates of (0.67, 0.33), which exactly matches the red standard defined by the National Television Standards Committee (NTSC). Importantly, the single‐host OLED achieves a high power efficiency (PE) of up to 50.1 lm W−1, suggesting the potential for the development of low power consumption red OLEDs.

Synthesis of Needle-like CoO Nanowires Decorated with Electrospun Carbon Nanofibers for High-Performance Flexible Supercapacitors.

Needle-like CoO nanowires have been successfully synthesized by a facile hydrothermal process on an electrospun carbon nanofibers substrate. The as-prepared sample mesoporous CoO nanowires aligned vertically on the surface of carbon nanofibers and cross-linked with each other, producing loosely porous nanostructures. These hybrid composite electrodes exhibit a high specific capacitance of 1068.3 F g-1 at a scan rate of 5 mV s-1 and a good rate capability of 613.7 F g-1 at a scan rate of 60 mV s-1 in a three-electrode cell. The CoO NWs@CNF//CNT@CNF asymmetric device exhibits remarkable cycling stability and delivers a capacitance of 79.3 F/g with a capacitance retention of 92.1 % after 10,000 cycles. The asymmetric device delivers a high energy density of 37 Wh kg-1 with a power density of 0.8 kW kg-1 and a high power density of 16 kW kg-1 with an energy density of 23 Wh kg-1. This study demonstrated a promising strategy to enhance the electrochemical performance of flexible supercapacitors.

Recent Advancements and Future Prospects in Lithium‐Ion Battery Thermal Management Techniques

ABSTRACTLithium‐ion batteries (LiBs) are the leading choice for powering electric vehicles due to their advantageous characteristics, including low self‐discharge rates and high energy and power density. However, the degradation in the performance and sustainability of lithium‐ion battery packs over the long term in electric vehicles is affected due to the elevated temperatures induced by charge and discharge cycles. Moreover, the thermal runaway (TR) issues due to the heat generated during the electrochemical reactions are the most significant safety concern for LiBs, as inadequate heat dissipation can be potentially hazardous, leading to explosions and fires. Considering the safety of EVs and for better performance, understanding the mechanism of TR is of paramount importance. This review provides a comprehensive analysis of the TR phenomenon and underlying electrochemical principles governing heat accumulation during charge and discharge cycles. Furthermore, the article explores the cell modeling and thermal management techniques intended for both individual lithium‐ion battery cells and larger battery packs, with a particular emphasis on enhancing fire prevention and safety measures. The main goal of this review paper is to offer new insights to the developing battery community, assisting in the development of efficient battery thermal management systems (BTMS) using enhanced cooling methodologies. This article could also support the advancement of next‐generation electric vehicle battery packs equipped with built‐in safety features to improve the cycle life of LiBs and prevent thermal runaway accidents.

Potato disease identification using transfer learning approaches

Potato crop is one of the prominent consumed foods by human beings. When potato crops are infected by diseases it affects farmers negatively and to run in a loss. Therefore, early detection of the potato crop disease can play a vital role in minimizing the loss of the farmers. Nowadays, artificial intelligence technologies, more specifically deep learning techniques, provide solutions to many crops disease-related problems. However, training deep learning models requires a high computational power and huge amount of data as they are data hungry models. Also, designing a custom CNN models a difficult task and there are some variations to be considered. To avoid these difficulties, we adopted two pretrained models of DenseNet121 and VGG19 through transfer learning approaches. The achieved accuracy for DenseNet121 and VGG19 models are 82.6% and 98.56% respectively. DenseNet121 model obtained the average precision, sensitivity, and F1-score of 88.19%, 82.53, and 82.04%, respectively. Whereas VGG19 yields 98.39% of precision, 98.39% of sensitivity, and 97.26% of F1-score in ternary 3-class classification (early blight vs healthy vs late blight).

Optimization of Thermoelectric Performance of Ag2Te Films via a Co-Sputtering Method.

Providing self-powered energy for wearable electronic devices is currently an important research direction in the field of thermoelectric (TE) thin films. In this study, a simple dual-source magnetron sputtering method was used to prepare Ag2Te thin films, which exhibit good TE properties at room temperature, and the growth temperature and subsequent annealing process were optimized to obtain high-quality films. The experimental results show that films grown at a substrate temperature of 280 °C exhibit a high power factor (PF) of ~3.95 μW/cm·K2 at room temperature, which is further improved to 4.79 μW/cm·K2 after optimal annealing treatment, and a highest PF of ~7.85 μW/cm·K2 was observed at 200 °C. Appropriate annealing temperature effectively increases the carrier mobility of the Ag2Te films and adjusts the Ag/Te ratio to make the composition closer to the stoichiometric ratio, thus promoting the enhancement of electrical transport properties. A TE device with five legs was assembled using as-fabricated Ag2Te thin films. With a temperature difference of 40 K, the device was able to generate an output voltage of approximately 14.43 mV and a corresponding power of about 50.52 nW. This work not only prepared a high-performance Ag2Te film but also demonstrated its application prospects in the field of self-powered electronic devices.

Research on High Power Density Flyback Converter With a New Passive Lossless Snubber

ABSTRACTThis paper proposes a flyback converter with a new passive lossless snubber. It eliminates the power dissipation of the traditional RCD snubber, while providing protection against MOS breakdown from energy stored in the power‐transformer leakage. This energy is used to power the power chip, which simplifies the design of the transformer. Meanwhile, an optimal design method for high power density planar transformers is presented. Applying the principle of flux cancellation, a matrix transformer that originally needed an independent magnetic core was integrated into a single magnetic core to reduce the volume of the core. This method effectively reduces the printed circuit board (PCB) layer number of the planar transformer and increases the possibility of the application of the planar transformer in the flyback converter. The detailed operation principle and design considerations are presented. Finally, a multi‐output flyback converter with a frequency of 100 kHz is designed to verify the practical performance of the structure.

Comparison of Bi-Directional Topologies for On-Board Charger: A 10.9 kW High-Efficiency High Power Density of DC-DC Stage

In recent years, the trend in power electronics has been toward high-efficiency and high-power-density converters. Additionally, this trend has allowed electric vehicles to accommodate larger batteries, which necessitate bi-directional capabilities not only for driving but also for vehicle to grid (V2G), etc. This article proposes a comparative analysis of GaN-based bi-directional topologies, namely the dual active bridge (DAB) converter and the CLLC converter. To ensure a fair analysis of the proposed topologies, prototypes with the same target of efficiency above 97.5% and a power density of 5.5 kW/L have been constructed. This research can support the adoption of 10.9 kW bi-directional topologies in GaN-based on-board chargers (OBCs) for EVs.

Validation of the adult asthma epidemiological score: a secondary analysis of the EPI-ASTHMA population-based study.

The A2 score is an eight-question patient-reported outcome measure that has been validated for ruling in (score ≥4) and ruling out (score 0-1) asthma. However, this screening tool has been validated in a cohort similar to the derivation cohort used. This study aims to validate the predictive accuracy of the A2 score in a primary care population against general practitioner (GP) clinical assessment and to determine whether the proposed cut-offs are the most appropriate. This accuracy study is a secondary analysis of the EPI-ASTHMA population-based study. Primary care centres in Portugal. Random adult participants answered the A2 score by phone interview. Those with an A2 score ≥1 (plus 5% with an A2 score of 0) were invited to a diagnostic visit carried out by a GP to confirm or not a diagnosis of asthma. Diagnostic accuracy was assessed using receiver operating characteristic (ROC) curves. A total of 1283 participants (median 54 (p25-p75 43-66) years; 60% women) were analysed. The A2 score showed high discriminatory power in identifying asthma, with an area under the ROC curve of 82.9% (95% CI 80.4% to 85.4%). The proposed cut-off ≥4 was the most appropriate to rule in asthma (specificity 83.1%, positive predictive value 62.4%, accuracy 78%). Similarly, the proposed cut-off<2 was the most suitable for excluding asthma (sensitivity 92.7%, negative predictive value 93.7%, accuracy 60.5%). The A2 score is a useful tool to identify patients with asthma in a primary care population. NCT0516961.

Two-step nested optical-electrical Monte-Carlo approach to analyze the influence of tolerances on Micro-CPV module performance

In manufacturing and product optimization, understanding the influence of tolerances, which are inevitable variations in production processes, is crucial for enhancing performance while managing costs. However, previous analytical approaches lacked the capability to quantitatively assess the cumulative effect of multiple tolerances due to their random combination and statistical independence. In this work, we introduce a novel method that overcomes these limitations by effectively modeling complex dependencies among tolerances through a two-step nested Monte-Carlo approach. We apply this model to a micro-CPV module developed at Fraunhofer ISE. First, we randomly select and combine tolerances in a cell-lens unit using ray tracing. Then, we randomly select and combine these units in a full 690-cell module using an electrical network model considering different angles of incidence. The considered tolerances include deviations in component geometries and displacements and are based on measurements. The model predicts the acceptance angle and allows to identify the optimal interconnection schemes. Further, it is capable to determine the maximum tolerances permissible for maintaining a certain module power. While tolerances lead to a distribution in current generation among the cell-lens units, we find that parallel interconnections can compensate for such variations. Further, we identify that the positions of secondary lens and micro solar cell are the most sensitive parameters for achieving high module power. These findings are crucial for refining module design cost-effectively. Moreover, the model facilitates a quantitative assessment of optimization potentials, guiding decision-making in product development and manufacturing, and a techno-economic optimization.

Self, Other, and Higher Power: A “Relational Triad” Moderates Associations Between Mystical Experience and Mental Health

ABSTRACT The present study aimed to characterize the relationship between mystical experience and psychopathology measures in a general-population sample of 763 U.S. adults. The participants were assessed across various domains including psychopathology, spirituality, personality, and life experience. The analysis revealed three distinct profiles among individuals: Transcendent Wellness, Transcendent Struggle, and Non-Transcendent Wellness. The Transcendent Wellness profile demonstrated higher scores in belongingness, mindfulness, and lived/integrated spirituality compared to the Transcendent Struggle profile. Belongingness and mindfulness were identified as mitigating factors, reducing the positive association between mystical experience and depression and anxiety symptoms. Additionally, lived/integrated spirituality attenuated this association, particularly in relation to anxiety. Conventional religiosity measures, however, did not exhibit the same moderating effects. The authors propose a framework in which relationally grounded spirituality, manifesting in the form of connection to fellow human, self, and higher power, constitutes a foundation for processing of and sense-making around mystical experience.

Development of hybrid first principles – Artificial intelligence models for transient modeling of power plant superheaters under load-following operation

This paper develops different approaches for synergistic integration of physics-based models with data-driven models for modeling of high temperature power plant superheaters. Two types of data-driven models are developed, namely all-nonlinear static-dynamic neural network models as well as models obtained using a Bayesian machine learning approach. Series, integrated, and parallel coupling of first-principles models and data-driven models are proposed. Algorithms for solving the training problems for the data-driven models and for simulation of the hybrid models are developed. The developed approach is applied to high temperature power plant superheaters that face considerable modeling and measurement challenges. Measurement challenges arise due to harsh operating conditions that not only make placement of sensors difficult, but life of the placed sensors very limited. Modeling challenges arise due to complex inhomogeneous spatial distribution of flue gas and steam flowrates, especially under load-following operation and uncertainties in heat transfer characteristics because of multiple factors such as stochastic spatio-temporal variation of ash deposits on the superheater tubes in coal-fired power plants, internal oxide scale formation in the tubes, etc. First-principles two-dimensional differential–algebraic equation models of two industrial superheaters, one from a natural gas combined cycle plant and another from a coal-fired power plant, are developed. The results from the models are compared against industrial operational data. For all cases studied in this work, it is observed that both for steady-state and dynamic data, the hybrid models have much higher accuracy than when only the respective first-principles models are used. For example, during prediction of the average outside tube wall temperature of superheater tubes at the combined cycle power plant, the root mean squared error observed for the standalone first-principles model improved from 12.3 °C to 0.5 °C post hybridization with data-driven models. Similarly, while predicting the main steam outlet temperature in the coal-fired plant, the hybrid models resulted in reduction of the root mean squared error value from 19.5 °C to around 2 °C. In addition, the hybrid models yield highly resolved spatio-temporal temperature profiles that can be helpful for developing monitoring approaches of these critical components under load-following operation.

Effect of injection strategy on spray and combustion processes in 2-stroke rod-less opposed piston engine (2S-ROPE)

The 2-stroke Rod-less Opposed Piston Engine (2S-ROPE) is a novel engine design that has garnered attention owing to its high power and low fuel consumption. This study investigated the effects of different fuel injection strategies on the in-cylinder working process of a 2S-ROPE engine, which features a smaller combustion space and lateral injection than conventional diesel engines. A high-precision three-dimensional simulation model was developed to examine the fuel atomization and in-cylinder combustion processes under four distinct injection strategies (S1, S2, S3, and S4). The results demonstrated that the injection strategy significantly influenced the number of oil droplets, particularly for small particles. The number of small droplets in S4 was approximately 6 times that in S1. The double-layer injection strategies (S3 and S4) exhibited a better atomization breakup and oil-air mixing, leading to a faster combustion rate and higher lift power than the single-layer injection strategies (S1 and S2). These findings suggest that the double-layer injection strategy is more suitable for a 2S-ROPE engine, increasing the lift power by up to 23 %. The results can guide the improvement of combustion parameters in most opposed piston engines.

Ultrasound treatment on commercial pea protein isolates systems: Effect on structure, rheology and gelling properties

Pea protein has attracted great attention due to its capability to meet the growing requirements from consumers for desired nutrition and texture from plant protein. Hence, the current study aimed to investigate the effects of different ultrasonic treatment parameters (power and duration) on the gelling characteristics of commercial pea protein isolates (PPIc). The findings demonstrated that by manipulating the ultrasonic power and treatment duration, great enhancement of the solubility, adhesiveness and formation strength of PPIc gel can be realized. The reduction in particle size was positively correlated with higher power and longer treatment durations. Interestingly, no direct correlation between average particle size, solubility, turbidity, and ζ-potential was observed. Additionally, the ultrasound-modified PPIc in this study exhibited comparable characteristics to laboratory-prepared pea protein isolates, in terms of solubility, water-holding capacity, and gel strength. Overall, manipulating ultrasonic parameters presents a feasible method to customize the texture of pea-protein-based substitute.

Heterointerfacial engineering of N,P-doped carbon nanosheets supported Co/Co2P nanoparticles for boosting oxygen reduction and oxygen evolution reactions towards rechargeable Zn-air battery

Transition metal phosphides (TMPs) with high electrocatalytic activity for the oxygen evolution reaction (OER) are reckoned as a substitution of precious group metals catalysts in rechargeable Zn-air battery. In this work, Co/Co2P heterojunction nanoparticles supported N,P-doped carbon nanosheets (Co/Co2P@NPCNS) were designed and prepared via a facile one-step molten salt-assisted pyrolysis process. Density function theory calculations reveal that the heterogeneous interactions of Co/Co2P effectively enhance the bifunctional electrocatalytic activity for oxygen reduction reaction (ORR) and OER. The synergistic interaction between the Co/Co2P heterojunction nanoparticles with highly exposed active sites and excellent catalytic activity and the two-dimensional doped carbon nanosheets with high conductivity contributes to Co/Co2P@NPCNS exhibiting preeminent bifunctional ORR/OER activity and stability with a high half-wave potential for ORR (0.87 V), a low overpotential for OER (302 mV at 10 mA cm−2) and a low potential gap (0.66 V). The homemade rechargeable Zn-air battery performs high peak power density (187 mW cm−2) and exceptional endurance. This heterogeneous interface tactic of integrating TMPs with heteroatom-doped carbon materials may shed light on the research and development of non-precious metal electrocatalysts.