arXiv subjects

Zhimin Yang

Publications and source records attributed to Zhimin Yang.

7 recordsLinked to original sources

arXiv2025

Performance optimization of Nernst-based thermionic engines

In this paper, we examine the power and efficiency of the thermionic device utilizing the Nernst effect, with a specific focus on its potential application as an engine. The device operates by utilizing the vertical heat current to generate a horizontal particle current against the chemical potential. By considering the influence of a strong magnetic field, we derive analytical expressions for the current and heat flux. These expressions are dependent on the temperature and chemical potential of heat reservoirs, providing valuable insights into the device performance. The impact of driving temperatures on the performance of the thermionic engine has been assessed through numerical analysis. The research findings will guide the experimental design of Nernst-based thermionic engines.

cond-mat.stat-mech↗

arXiv2025

Optimal neutralization of negative space charges in photon-enhanced thermionic emission devices under bidirectional discharge

In this study, we innovatively modeled photon-enhanced thermionic emission (PETE) devices, incorporating positive ion injection and bidirectional discharge's effects on the space charge barrier simultaneously. Compared to previous models, our model allows the positive ion distribution function to be compatible with scenarios in which the anode motive is either higher or lower than the cathode motive, and also adapts to significant anode discharge. Through numerical simulations and parametric analyses, we found that: (1) As the ratio of the positive ion increases, the capability for space charge neutralization becomes stronger. (2) The lower the electron affinity is, the smaller the ratio of positive ions are required. (3) When the anode temperature is higher or the anode work function is lower, the impact of reverse discharge on the net current density is more pronounced. Conversely, when the anode temperature is higher or the anode work function is greater, the ratio of positive ions required to achieve complete space charge neutralization increases. This study further elucidates the mechanisms and characteristics of space charge neutralization effects in PETE devices, providing a theoretical foundation for optimizing their design. Additionally, the accompanying theory and algorithm possess the potential to spark innovative research across diverse fields.

physics.acc-ph↗

arXiv2024

Hot-carrier photocatalysts with energy-selective contacts based on quantum wells and dots

In this paper, we simulate the function of hot-carrier photocatalysts (HCPCs) with quantum well and quantum dot energy-selective contacts (ESCs) in the water-splitting reaction. The transport equations for these ESCs are derived by using ballistic transport theory. The results indicate that thermalization loss from non-ideal ESCs is a primary factor diminishing the efficiency of HCPCs. The performance of HCPCs can be enhanced by optimizing the position of ESCs and the width of the extraction energy. Notably, HCPCs with quantum dot ESCs demonstrate superior performance compared to those with quantum well ESCs.

physics.app-ph↗

arXiv2024

The effect of space charge on photon-enhanced thermionic emission in the presence of the bidirectional discharge

The bidirectional space charge effects in photon-enhanced thermionic emission (PETE) devices are investigated systematically. First, we precisely determine the carrier concentrations and cathode temperatures by taking into account the electron recycling effect, energy balance constraints, and space charge effects arising from the concurrent discharge of the cathode and anode. Next, we analyze the impact of critical parameters, including anode properties and operating conditions, on the space charge barrier distribution and the overall performance of the device. The results demonstrate that the impact of reverse discharge on the net current becomes more pronounced when the PETE device operates at high anode temperatures, low anode work functions, and with a moderate solar concentration ratio and gap width. This discovery not only deepens our understanding of the bidirectional space charge effect, but also provides valuable guidance for the future optimization of PETE device performance.

physics.acc-ph↗

arXiv2023

PNet -- A Deep Learning Based Photometry and Astrometry Bayesian Framework

Time domain astronomy has emerged as a vibrant research field in recent years, focusing on celestial objects that exhibit variable magnitudes or positions. Given the urgency of conducting follow-up observations for such objects, the development of an algorithm capable of detecting them and determining their magnitudes and positions has become imperative. Leveraging the advancements in deep neural networks, we present the PNet, an end-to-end framework designed not only to detect celestial objects and extract their magnitudes and positions but also to estimate photometry uncertainty. The PNet comprises two essential steps. Firstly, it detects stars and retrieves their positions, magnitudes, and calibrated magnitudes. Subsequently, in the second phase, the PNet estimates the uncertainty associated with the photometry results, serving as a valuable reference for the light curve classification algorithm. Our algorithm has been tested using both simulated and real observation data, demonstrating the PNet's ability to deliver consistent and reliable outcomes. Integration of the PNet into data processing pipelines for time-domain astronomy holds significant potential for enhancing response speed and improving the detection capabilities for celestial objects with variable positions and magnitudes.

astro-ph.IM↗

arXiv2023

Sequential Condition Evolved Interaction Knowledge Graph for Traditional Chinese Medicine Recommendation

Traditional Chinese Medicine (TCM) has a rich history of utilizing natural herbs to treat a diversity of illnesses. In practice, TCM diagnosis and treatment are highly personalized and organically holistic, requiring comprehensive consideration of the patient's state and symptoms over time. However, existing TCM recommendation approaches overlook the changes in patient status and only explore potential patterns between symptoms and prescriptions. In this paper, we propose a novel Sequential Condition Evolved Interaction Knowledge Graph (SCEIKG), a framework that treats the model as a sequential prescription-making problem by considering the dynamics of the patient's condition across multiple visits. In addition, we incorporate an interaction knowledge graph to enhance the accuracy of recommendations by considering the interactions between different herbs and the patient's condition. Experimental results on a real-world dataset demonstrate that our approach outperforms existing TCM recommendation methods, achieving state-of-the-art performance.

cs.AI↗

arXiv2017

Coulomb-coupled quantum-dot thermal transistors

A quantum-dot thermal transistor consisting of three Coulomb-coupled quantum dots coupled to respective electronic reservoirs by tunnel contacts is established. The heat flows through the collector and emitter can be controlled by the temperature of the base. It is found that a small change in the base heat flow can induce a large heat flow change in the collector and emitter. The huge amplification factor can be obtained by optimizing the Coulomb interaction between the collector and the emitter or by decreasing the energy-dependent tunneling rate at the base. The proposed quantum-dot thermal transistor may open up potential applications in low-temperature solid-state thermal circuits at the nanoscale.

physics.app-ph↗