| 1. |
- Li, Zheng, et al.
(author)
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A Review of Spatter in Laser Powder Bed Fusion Additive Manufacturing: In Situ Detection, Generation, Effects, and Countermeasures
- 2022
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In: Micromachines. - : MDPI AG. - 2072-666X. ; 13:8
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Research review (peer-reviewed)abstract
- Spatter is an inherent, unpreventable, and undesired phenomenon in laser powder bed fusion (L-PBF) additive manufacturing. Spatter behavior has an intrinsic correlation with the forming quality in L-PBF because it leads to metallurgical defects and the degradation of mechanical properties. This impact becomes more severe in the fabrication of large-sized parts during the multi-laser L-PBF process. Therefore, investigations of spatter generation and countermeasures have become more urgent. Although much research has provided insights into the melt pool, microstructure, and mechanical property, reviews of spatter in L-PBF are still limited. This work reviews the literature on the in situ detection, generation, effects, and countermeasures of spatter in L-PBF. It is expected to pave the way towards a novel generation of highly efficient and intelligent L-PBF systems.
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| 2. |
- Pecunia, Vincenzo, et al.
(author)
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Roadmap on energy harvesting materials
- 2023
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In: Journal of Physics. - : IOP Publishing. - 2515-7639. ; 6:4
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Journal article (peer-reviewed)abstract
- Ambient energy harvesting has great potential to contribute to sustainable development and address growing environmental challenges. Converting waste energy from energy-intensive processes and systems (e.g. combustion engines and furnaces) is crucial to reducing their environmental impact and achieving net-zero emissions. Compact energy harvesters will also be key to powering the exponentially growing smart devices ecosystem that is part of the Internet of Things, thus enabling futuristic applications that can improve our quality of life (e.g. smart homes, smart cities, smart manufacturing, and smart healthcare). To achieve these goals, innovative materials are needed to efficiently convert ambient energy into electricity through various physical mechanisms, such as the photovoltaic effect, thermoelectricity, piezoelectricity, triboelectricity, and radiofrequency wireless power transfer. By bringing together the perspectives of experts in various types of energy harvesting materials, this Roadmap provides extensive insights into recent advances and present challenges in the field. Additionally, the Roadmap analyses the key performance metrics of these technologies in relation to their ultimate energy conversion limits. Building on these insights, the Roadmap outlines promising directions for future research to fully harness the potential of energy harvesting materials for green energy anytime, anywhere.
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| 3. |
- Li, Houpei, et al.
(author)
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Matching characteristics and AC performance of the photovoltaic-driven air conditioning system
- 2023
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In: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 264
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Journal article (peer-reviewed)abstract
- Photovoltaic-driven Air Conditioning systems (PVAC) use local electricity generated by distributed Photovoltaic (PV) to drive Air Conditioners (AC). Both the AC cooling load and the PV electricity generation are affected by solar radiation. The PV generation cannot dynamically supply the AC power consumption during the operation. In this study, the matching characteristics of a PVAC were investigated using a case in a 207.34 m2 office room. A coupled simulation model was built, which integrated with a building model, a PV calculation model, an AC model, and a control strategy. More specifically, the AC was modeled with two heat exchangers, a compressor, and a throttling device. Both the building and the PV were simulated in EnergyPlus. The AC compressor speed was controlled so the AC power consumption could match the PV generation when the indoor temperature was within the temperature control zone. The daily matching characteristics of PVAC were strongly affected by the PV capacity. The results showed that the PV factor (PVF) should be set to 1 in order to match the AC and PV power and maximize the AC efficiency. A battery factor of at least 0.7 could ensure the grid flexibility. Finally, the optimized design of PV, battery, and AC capacities was suggested.
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| 4. |
- You, Xiaohu, et al.
(author)
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Towards 6G wireless communication networks: vision, enabling technologies, and new paradigm shifts
- 2021
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In: Science China Information Sciences. - : Science Press. - 1674-733X .- 1869-1919. ; 64:1
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Research review (peer-reviewed)abstract
- The fifth generation (5G) wireless communication networks are being deployed worldwide from 2020 and more capabilities are in the process of being standardized, such as mass connectivity, ultra-reliability, and guaranteed low latency. However, 5G will not meet all requirements of the future in 2030 and beyond, and sixth generation (6G) wireless communication networks are expected to provide global coverage, enhanced spectral/energy/cost efficiency, better intelligence level and security, etc. To meet these requirements, 6G networks will rely on new enabling technologies, i.e., air interface and transmission technologies and novel network architecture, such as waveform design, multiple access, channel coding schemes, multi-antenna technologies, network slicing, cell-free architecture, and cloud/fog/edge computing. Our vision on 6G is that it will have four new paradigm shifts. First, to satisfy the requirement of global coverage, 6G will not be limited to terrestrial communication networks, which will need to be complemented with non-terrestrial networks such as satellite and unmanned aerial vehicle (UAV) communication networks, thus achieving a space-air-ground-sea integrated communication network. Second, all spectra will be fully explored to further increase data rates and connection density, including the sub-6 GHz, millimeter wave (mmWave), terahertz (THz), and optical frequency bands. Third, facing the big datasets generated by the use of extremely heterogeneous networks, diverse communication scenarios, large numbers of antennas, wide bandwidths, and new service requirements, 6G networks will enable a new range of smart applications with the aid of artificial intelligence (AI) and big data technologies. Fourth, network security will have to be strengthened when developing 6G networks. This article provides a comprehensive survey of recent advances and future trends in these four aspects. Clearly, 6G with additional technical requirements beyond those of 5G will enable faster and further communications to the extent that the boundary between physical and cyber worlds disappears.
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| 5. |
- Zeng, Xiao, et al.
(author)
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A scoping study on remelting process of a debris bed in the lower head of reactor pressure vessel
- 2023
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In: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 189
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Journal article (peer-reviewed)abstract
- Coolability and retention of core melt (corium) in the lower head of reactor pressure vessel (RPV) has been accepted as a severe accident management strategy to maintain the reactor pressure vessel (RPV) integrity of a light water reactor. To qualify the in-vessel melt retention strategy, lots of studies have been performed to investigate the natural convection heat transfer of a melt pool in the lower head. However, little work has been attributed to the precursory phase of the melt pool, i.e., the remelting process of a debris bed which is formed in the lower head at the very beginning of corium relocation from the core the lower head. The present study is motivated to conduct an experimental study on the debris remelting process. For this purpose, a dedicated test facility named COREM (COrium REMelting) is conceived and constructed, which features internal heating of electromagnetic induction and visualization of debris remelting dynamics. The test section is a semicircular vessel representing a slice of scaled-down RPV lower head, whose front and back walls are made of transparent tempered glass which facilitate visualization and induction heating of the debris bed. Fiber probes with multiple optical temperature sensors are mounted in the semicircular wall of the test section to measure its temperature distribution. In the scoping test, n-octanol and Wood's metal are selected as the simulant materials of metallic and oxidic components of corium, respectively, and their particles ware loaded in the test section to form a debris bed. This paper presents the first two scoping tests which have been performed with the COREM facility so far, under different mixing ratios of two debris materials. The measured data include the photography of debris remelting processes and the temperatures in the debris bed and the semicircular wall. Based on the temperature distributions, heat flux profile along the semicircular vessel wall is also estimated. The scoping tests well reproduce the dynamic process of debris remelting, with two distinct stages of fusion of n-octanol and Wood's metal, i.e., melting successively from low to high melting-point debris particles. During the remelting process, the vessel wall temperatures increase with the polar angle firstly and then decrease gradually, leading to the highest temperature appearing in the middle of the lower layer of the stratified molten pool which is finally formed.
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| 6. |
- Zeng, Changfeng, et al.
(author)
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Synthesis of ZIF-8/PVA microspheres with the assistance of a microfluidic device and their controlled drug release properties
- 2024
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In: Microporous and Mesoporous Materials. - : Elsevier B.V.. - 1387-1811 .- 1873-3093. ; 376
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Journal article (peer-reviewed)abstract
- ZIF-8/PVA microspheres with an even size were synthesized with the assistance of a simple microfluidic device. The ZIF-8/PVA microdroplets were first generated in a simple co-flow microfluidic device using a PVA aqueous solution dispersed with ZIF-8 nanoparticles as the dispersed phase and fatty acid methyl ester (FAME) as the continuous phase. Subsequently, the ZIF-8/PVA microdroplets were further extracted to form ZIF-8/PVA microspheres. The influence of the type of continuous phase on the sphericity of microspheres was investigated and the effect of ZIF-8 content was studied. Further studies showed that decreasing the extraction rate and using additives of NaCl in the dispersed phase could improve the sphericity of the ZIF-8/PVA microspheres. Finally, the synthesized ZIF-8/PVA microspheres were used to study the loading and release of tetracycline. The results showed that the loading of ZIF-8/PVA microspheres was more than 5 times higher than that of pure PVA microspheres. The drug release time of ZIF-8/PVA microspheres was much longer than that of the PVA microspheres and the release rate was significantly affected by the pH of the environment.
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| 7. |
- Li, Yajie, et al.
(author)
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Side Channel Attack-Aware Resource Allocation for URLLC and eMBB Slices in 5G RAN
- 2020
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In: IEEE Access. - 2169-3536 .- 2169-3536. ; 8, s. 2090-2099
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Journal article (peer-reviewed)abstract
- Network slicing is a key enabling technology to realize the provisioning of customized services in 5G paradigm. Due to logical isolation instead of physical isolation, network slicing is facing a series of security issues. Side Channel Attack (SCA) is a typical attack for slices that share resources in the same hardware. Considering the risk of SCA among slices, this paper investigates how to effectively allocate heterogeneous resources for the slices under their different security requirements. Then, a SCA-aware Resource Allocation (SCA-RA) algorithm is proposed for Ultra-reliable and Low-latency Communications (URLLC) and Enhanced Mobile Broadband (eMBB) slices in 5G RAN. The objective is to maximize the number of slices accommodated in 5G RAN. With dynamic slice requests, simulation is conducted to evaluate the performance of the proposed algorithm in two different network scenarios. Simulation results indicate that compared with benchmark, SCA-RA algorithm can effectively reduce blocking probability of slice requests. In addition, the usage of IT and transport resources is also optimized.
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| 8. |
- Yuan, G., et al.
(author)
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Thermally reduced graphene oxide/carbon nanotube composite films for thermal packaging applications
- 2020
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In: Materials. - : MDPI AG. - 1996-1944. ; 13:2
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Journal article (peer-reviewed)abstract
- Thermally reduced graphene oxide/carbon nanotube (rGO/CNT) composite films were successfully prepared by a high-temperature annealing process. Their microstructure, thermal conductivity and mechanical properties were systematically studied at different annealing temperatures. As the annealing temperature increased, more oxygen-containing functional groups were removed from the composite film, and the percentage of graphene continuously increased. When the annealing temperature increased from 1100 to 1400 °C, the thermal conductivity of the composite film also continuously increased from 673.9 to 1052.1 W m-1 K-1. Additionally, the Young's modulus was reduced by 63.6%, and the tensile strength was increased by 81.7%. In addition, the introduction of carbon nanotubes provided through-plane thermal conduction pathways for the composite films, which was beneficial for the improvement of their through-plane thermal conductivity. Furthermore, CNTs apparently improved the mechanical properties of rGO/CNT composite films. Compared with the rGO film, 1 wt% CNTs reduced the Young's modulus by 93.3% and increased the tensile strength of the rGO/CNT composite film by 60.3%, which could greatly improve its flexibility. Therefore, the rGO/CNT composite films show great potential for application as thermal interface materials (TIMs) due to their high in-plane thermal conductivity and good mechanical properties.
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| 9. |
- Li, Kai, et al.
(author)
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Metal thermopile infrared detector with vertical graphene
- 2023
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In: Wuli Xuebao/Acta Physica Sinica. - : Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences. - 1000-3290. ; 72:3
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Journal article (peer-reviewed)abstract
- Thermopile infrared detector is a kind of detector device mainly composed of thermocouple as the basic unit. Because of its simple principle, no need of cooling equipment, and other advantages, it has been widely used in various fields of production and life. However, the absorption rates of the materials in conventional thermopile devices are poor, and the majority of them are incompatible with microfabrication methods. In this work, a metal thermopile infrared detector with vertical graphene (VG) is designed and fabricated. The VG is grown via plasma enhanced chemical vapor deposition, and retained at the device’s thermal ends to provide the thermopile IR detector’s wideband and high response characteristics. The detector achieves a room temperature responsivity reaching a value as high as 1.53 V/W at 792 nm, which can increase the response results about 28 times and reduce the response time to 0.8 ms compared with the thermopile detector without VG. After systematically measuring the response results, it is finally found that there are three main mechanisms responsible for the response on the composite device. The first one is the response generated by the metal thermopile itself alone. The second one is the response increased eventually by the contribution of VG covered at the metal thermal junction that expands the temperature difference. The last one is the response generated by the temperature gradient existing inside the VG on the surface of the device after the absorption of heat. The portion of each partial response mechanism in the total response is also analyzed, providing a new reference direction for analyzing the response generation mechanism of thermopile detectors with other absorbing materials. The process is compatible with the microfabrication, while the device performance is enhanced and suitable for mass production. Furthermore, by utilizing the surface plasmon resonance to combine VG with metal nanoparticles, the material’ s light absorption is found to be enhanced significantly under the same conditions, and the resulting thermal voltage can be increased to 6 times. The results indicate that VG promises to possess practical applications, in many fields such as photoelectric sensing and power production devices. This technology provides a new method to manufacture high-performance thermopile infrared detectors and other sensor devices.
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| 10. |
- Li, Yajie, et al.
(author)
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End-to-end URLLC slicing based on packet duplication in 5G optical transport networks
- 2020
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In: Journal of Optical Communications and Networking. - 1943-0620 .- 1943-0639. ; 12:7, s. 192-199
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Journal article (peer-reviewed)abstract
- With the stringent requirements of high reliability and low latency, ultra-reliable low latency communications (URLLCs) are one of three typical services in the fifth generation of mobile network (5G) paradigm. The packet duplication (PD) technique has been proposed as a promising solution to satisfy the extreme requirements of URLLC services. However, the benefit of PD comes at the cost of doubling resource usage. This paper investigates how to efficiently perform end-to-end URLLC slicing based on PD in 5G optical transport networks. Two heuristic algorithms are proposed, including PD-based slicing with wavelength isolation (PDS-WI) and PD-based slicing with link isolation (PDS-LI). The target of this paper is to maximize the number of accommodated URLLC slices by optimizing the allocation of heterogenous resources. The time complexity of these two algorithms is analyzed in detail. With dynamic slice requests, simulations are performed to evaluate and compare their performance in terms of slice blocking probability and resource usage. Meanwhile, two different network scenarios are considered in simulation. Simulation results indicate that PDS-WI outperforms PDS-LI by accommodating more URLLC slices. © 2009-2012 OSA.
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