Perforated structures are commonly used to reduce sloshing in many fields, owing to their anti-sloshing and mass reduction advantage. This structure shows greater potential for slosh damping of heavy liquid metal as the fluids have complex properties. As the most promising nuclear technology of the next generation, the lead-cooled fast reactor (LFR) is facing the problem that liquid heavy metal sloshing is challenging the component and system safety, which is the top priority of reactor design. Therefore, the sloshing-damping effect of perforated structures is of great significance in this area, especially when harsh conditions. Although some researchers have paid attention to the sloshing behavior of liquid heavy metal, the influence of perforated structures has not been mentioned. For this study, models of heavy-liquid metal containers with perforated structures were built, and simulations were carried out to fill the gap. The sloshing effect was compared under 3 cases of seismic excitations with different accelerations. In simulation results, the sloshing behavior of water agrees well with LBE and perforated structures have effectively restrained the sloshing. The liquid elevation is reduced to 40.5%. It indicates that perforated structures cannot be ignored in experiments. Water can only be used as a potential substitution if perforated structures are considered. Three models with different ratios of holes and clearance (RHC) values are established to investigate the influence of holes distributions. The Newmark-beta algorithm is employed to calculate the deformation of components. Signals of component deformation show that lower RHC has good reliability, and the maximum reduction of deformation is nearly 25.8%. The deformation will increase with increasing sloshing acceleration, and the amplification is nearly 13.5%. This work enriches the sloshing-damping study of heavy liquid metal. It guides the design and sloshing experiments of the advanced LFR. 

Sloshing damping assessment and structural dynamic analysis of perforated structures for heavy liquid metal under seismic excitation

Due to environmental friendliness, small size, long lifetime, and adjustable light-emitting wavelength, AlGaN-based deep ultraviolet light-emitting diodes (DUV-LEDs) have great development potential in the fields of biochemical detection, sterilization and disinfection, and non-line-of-sight communication. After decades of research, AlGaN-based DUV-LEDs have significantly improved in the direction of luminous efficiency. However, the luminous efficiency of the present AlGaN-based DUV-LEDs is still at a low level compared with that of the fully commercialised nitride blue LEDs, making it difficult to meet the market demand. This paper first introduces the present development status of AlGaN-based DUV-LEDs and the reasons for the low luminous efficiency. Then from the preparation of AlGaN-based, AlGaN doping and the design of AlGaN-based DUV-LEDs structure to elaborate the research progress in recent years in the direction of improving the luminous efficiency of AlGaN-based DUV-LEDs. Finally discusses the challenges that the AlGaN-based DUV-LEDs are presently faced with, and their future opportunities for development. 

A Review of Recent Research Advances on AlGaN-Based Deep Ultraviolet Light-Emitting Diodes

In this paper, a near-ultraviolet LED structure was fabricated on a sapphire substrate by using metal–organic chemical vapor deposition with an undoped AlGaN insertion layer introduced between multiple quantum wells and electron blocking layers, and the effect of layer thickness on light-electric performance was investigated. Results of epitaxial structure characterization show that the introduction of an undoped AlGaN insertion layer almost does not affect the crystal quality and surface morphology of the LED epitaxial structure. Electroluminescence testing results indicate that as the insertion layer thickness increases, the device performance initially increases and then decreases. Furthermore, simulation analysis suggests that increasing the insertion layer thickness reduces the injection efficiency of carriers, lowers the radiative recombination rate and light emission performance of the active region's carriers. Additionally, the AlGaN insertion layer can effectively suppress the diffusion of Mg impurities, reduce the non-radiative recombination rate in the multiple quantum well active region, and thus improve the LED's light emission performance. Overall, under the competing effects of these two mechanisms, the optimal light emission performance for the near-ultraviolet LED is achieved when the insertion layer thickness is 1 nm. 

The effect of different AlGaN insertion layer thicknesses on the photoelectric properties of InGaN/AlGaN near UV light emitting diodes

Boosting external quantum efficiency of AlGaN-based deep-ultraviolet LEDs enabled by heuristic optimization-based inverse design

In this paper, a deep ultraviolet light-emitting diodes (DUV LEDs) at ∼275 nm with an interval-graded barrier superlattice (IBSL) Electron Blocking Layer (EBL) has been proposed and numerically investigated. The IBSL EBL structure has greatly increased the carrier concentration within the active region. It has been shown that DUV LEDs with IBSL EBL structure exhibits transcendent electron blocking and hole injection capabilities compared to conventional DUV LEDs, which is attributed to the increased lattice matching and decreased polarization effects brought about by the smaller Al content difference between the superlattice barriers and wells. Consequently, compared to the conventional DUV LEDs at a 60 mA injection current, the internal quantum efficiency and the light output power of DUV LEDs with IBSL EBL have been enhanced by 34% and 30%, respectively. 

Enhanced Characteristics in AlGaN-Based Deep Ultraviolet Light-Emitting Diodes with Interval-graded Barrier Superlattice Electron Blocking Layers

The liquid metal fast reactor (LMFR), the most promising nuclear energy technology, has been experiencing accelerating development in recent years. Given the higher thermal conductivity of its coolant and smaller size with better portability, the current prior task of LMFR is to address its safety issue under harsh natural conditions. The sloshing behavior inside liquid metal containers under seismic excitation needs comprehensive research because of its importance to the safety and development of this technology. Lead‐bismuth‐eutectic (LBE) is well recognized as the coolant for LMFR for its chemical stability and self‐circulation advantages. Since the direct experimental research of LBE is not practical for its opacity, high melting point, and corrosivity, alternatives have been screened to assist the research. This paper focuses on the two‐phase flow behavior caused by the sloshing effect of LBE and its potential experimental alternatives, including water and mercury. A numerical study was carried out to verify the case of the “Multi‐purpose Hybrid Research Reactor for High‐tech Applications” (MYRRHA) and build the model of its upper plenum liquid lead‐bismuth container with internal components. The Volume of Fluid (VOF) method is employed based on OpenFoam. The sloshing effect of three alternative coolants was compared under the resonance excitation, operation‐based‐earthquake (OBE) excitation, and design‐based‐earthquake (DBE) excitation. Results demonstrate that the sloshing behavior of three coolants is generally in good agreement, and the complex sloshing behavior of LBE can be well predicted by water in the container. However, quantification studies of liquid levels inside the container show different relative magnitudes of three coolant alternatives under different excitation conditions. Finally, the safety of internal components has been evaluated, which shows that LBE can be well predicted by water under resonance and OBE excitation. However, the force load is underestimated during the sloshing of water under DBE excitation. Overall, water is a valid option to predict the sloshing effect of LBE unless the sloshing is violent enough. This work provides a design reference of liquid metal containers and a predictive method for coolant sloshing assessment which is critical to the safety and efficiency of the LMFR system.

Coolant's sloshing behavior and components' safety assessment of lead‐bismuth‐cooled reactors under seismic excitation

The serious electron leakage and poor transport of hole injection layers in deep‐ultraviolet (DUV) light‐emitting diodes (LEDs) lead to an imbalance between the hole and electron currents, which reduces the device's performance. Herein, a new DUV LED structure is designed. The aluminum composition of the p‐type electron‐blocking layer (p‐EBL) gradually decreases from 0.95 to 0.75 along the growth direction, replacing the traditional bulk p‐EBL. When the injection current is 100 mA, the optical power of this structure is about 32% higher than that of the traditional structure. In addition, when the p‐EBL adopts the opposite gradient (the Al composition gradually increases from 0.75 to 0.95), the device performance suddenly drops dramatically. The related devices are simulated by Silvaco TCAD software. The results show that the performance outputs of the two opposite aluminum gradient growth modes are completely opposite. The proposed p‐EBL with a gradual step‐down Al composition along the growth direction helps to improve the efficiency of hole injection into multiple quantum wells (MQWs) and reduce the level of electron leakage. This work provides an effective solution for increasing the light output power of high‐performance DUV LEDs.

Efficient Carrier Confinement in AlGaN‐Based Deep‐Ultraviolet Light‐Emitting Diodes with a Composition‐Graded Electron‐Blocking Layer

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Coolant's sloshing behavior and components' safety assessment of lead‐bismuth‐cooled reactors under seismic excitation

Efficient Carrier Confinement in AlGaN‐Based Deep‐Ultraviolet Light‐Emitting Diodes with a Composition‐Graded Electron‐Blocking Layer