| 1. |
- Wang, Hongdong, et al.
(författare)
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Superlubricity of Polyalkylene Glycol Aqueous Solutions Enabled by Ultrathin Layered Double Hydroxide Nanosheets
- 2019
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 11:22, s. 20249-20256
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Tidskriftsartikel (refereegranskat)abstract
- It was previously proved that the existence of a large amount of hydrogen ions in water-based lubricants can easily lead to a superlubric state; however, it was also shown that these hydrogen ions could cause severe corrosion. As part of a large family of attractive clays, layered double hydroxides (LDHs) possess excellent tribological properties in water-based lubrication systems. In the present work, two different kinds of LDHs are dispersed in polyalkylene glycol (PAG) aqueous solutions, in two distinct forms: ultrathin nanosheets (ULDH-NS) of ca. 60 nm wide and ca. 1 nm thick (single or double layer) and nanoparticles (LDH-NP) of ca. 19.73 nm wide and ca. 8.68 nm thick. We find that the addition of ULDH-NS greatly shortens (as much as 85%) the running-in period prior to reaching the superlubricity regime and increases the ultimate load-bearing capacity by about four times. As compared to the fluid film thickness of the lubricating PAG solution, their ultrathin longitudinal dimension will not impair or influence the fluid film coverage in the contact zone. The analysis of sliding solid surfaces and the atomic force microscope microscale friction test demonstrate that the adsorption of ULDH-NS enables the sliding solid surfaces to be polished and protected because of their relatively weak interlayer interaction and increased adhesion effect. Owing to their superior tribological properties as lubricant additives, ultrathin LDH nanosheets hold great potential for enabling liquid superlubricity in industrial applications in the future.
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| 2. |
- Wang, Hongdong, et al.
(författare)
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Catalytically Active Oil-based Lubricant Additives Enabled by Calcining Ni-Al Layered Double Hydroxides
- 2020
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 11, s. 113-120
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Tidskriftsartikel (refereegranskat)abstract
- Layered double hydroxides (LDHs) have lately been hailed as robust lubricant additives for improving tribological properties and as ideal catalysts for synthesizing carbon-based nanomaterials. In this paper, in situ analytical tools are used to track the evolution of the crystal structure and chemical composition of LDHs during calcination. Nickel oxide and elemental nickel can be produced by calcining NiAl-LDH in air (LDH-C-Air) and argon (LDH-C-Ar), respectively. For the base oil with 1 wt % LDH-C-Air, negligible wear can be detected even after a 2 h friction test under a severe contact pressure (∼637 MPa). A relatively thick tribofilm (∼60 nm) with a better mechanical property is formed, which protects the solid surface from severe wear. In addition, the possible formed carbon debris may also prevent the direct collision of asperities and effectively improve the wear resistance. This work provides a unique vision for the application of calcined LDHs with the combination of catalysis and tribology.
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| 3. |
- Yin, Xuan, et al.
(författare)
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Achieving ultralow friction under high pressure through operando formation of PbS QDs/graphene heterojunction with 0D/1D nanostructure
- 2024
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Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 218
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Tidskriftsartikel (refereegranskat)abstract
- In this work, ultralow friction (0.054) of graphene was achieved under high contact pressure (1.03 GPa) and atmosphere environment via the operando formation of PbS quantum dots (QDs)/graphene heterojunction at the frictional interface. It is found that PbS QDs are trapped in graphene nanosheets via shear-induced rearrangement for obtaining the PbS QDs/graphene heterojunctions, which provide an excellent rolling effect to lower friction. It is also found that the heterogeneous PbS QDs/graphene tribofilms have a strong Pb-enriched function and heterojunction nanorod phase. Our objective is to uncover the physical and chemical mechanisms governing the friction of 0D/1D nanostructures within PbS QDs/graphene heterostructures through our studies. This research will enhance our comprehension of nanomaterials' frictional behavior while offering valuable guidance and optimization strategies for their application in mechanical engineering and functional nanomaterials. Consequently, our efforts aim to foster the advancement of nanoscience and technology, leading to additional scientific and technological breakthroughs.
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| 4. |
- Zhang, Shuangshuang, et al.
(författare)
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Discovery of carbon-based strongest and hardest amorphous material
- 2022
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Ingår i: National Science Review. - : Oxford University Press. - 2095-5138 .- 2053-714X. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Carbon is one of the most fascinating elements due to its structurally diverse allotropic forms stemming from its bonding varieties (sp, sp2, and sp3). Exploring new forms of carbon has always been the eternal theme of scientific research. Herein, we report the amorphous (AM) carbon materials with high fraction of sp3 bonding recovered from compression of fullerene C60 under high pressure and high temperature previously unexplored. Analysis of photoluminescence and absorption spectra demonstrates that they are semiconducting with a bandgap range of 1.5–2.2 eV, comparable to that of widely used amorphous silicon. Comprehensive mechanical tests demonstrate that the synthesized AM-III carbon is the hardest and strongest amorphous material known so far, which can scratch diamond crystal and approach its strength. The produced AM carbon materials combine outstanding mechanical and electronic properties, and may potentially be used in photovoltaic applications that require ultrahigh strength and wear resistance.
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| 5. |
- Zhao, Jun, et al.
(författare)
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The Tribological Performance of Metal-/Resin-Impregnated Graphite under Harsh Condition
- 2021
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Ingår i: Lubricants. - : MDPI. - 2075-4442. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Graphite-based composites are well recognized as ideal functional materials in mechanical seals, bearings of canned pumps, and electrical contact systems because of their outstanding self-lubricating ability, thermostability, and chemical stability. Working in harsh conditions is a huge challenge for the graphite materials, and their tribological properties and wear mechanisms are not well studied. In this study, the tribological performance of metal-impregnated graphite, resin-impregnated graphite, and non-metal-impregnated graphite under high temperature and high load are studied using a ball-on-disc tribometer. The results show that the metal-impregnated graphite (Metal-IG) has a stable friction regime and exhibits better anti-friction and anti-wear properties than that of resin-impregnated graphite (Resin-IG) and non-impregnated graphite (Non-IG) under extreme pressure (200~350 MPa) and high temperature (100–350 °C). The Metal-IG and Resin-IG can reduce the wear depth by 60% and 80%, respectively, when compared with Non-IG substrate. The impregnated materials (metal or resin) can enhance the strength of the graphite matrix and improve the formation of graphite tribofilm on the counterpart surfaces. Friction-induced structural ordering of graphite and slight oxidation of metal in the formed mechanically mixed layer is also beneficial for friction and wear reduction. This study demonstrates the tribological characteristics of impregnated graphite under harsh conditions and provides the experimental basis for the advanced usage of high-reliability and self-lubrication graphite composites.
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| 6. |
- Fan, Kuan, et al.
(författare)
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Dredas : Decentralized, reliable and efficient remote outsourced data auditing scheme with blockchain smart contract for industrial IoT
- 2020
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Ingår i: Future Generation Computer Systems. - : Elsevier. - 0167-739X .- 1872-7115. ; 110, s. 665-674
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Tidskriftsartikel (refereegranskat)abstract
- The development of cloud computing and the Internet of things (IOT) attracts more and more enterprises to outsource the data from their Industrial Internet of things (IIOT) to cloud servers in order to save operating costs and improve efficiency. However, in this environment, protecting the security and privacy of data storage is an important challenge for IIOT and cloud server provider (CSP). Data auditing could allow data owner discover malicious behaviors of CSP which destroy their outsourced data. The public auditing authorizes the trusted third part auditor (TPA) to audit the owner’s outsourced data and frees owner from regular tasks. However, the public auditing using TPA is considered a centralized auditing, and the TPA is assumed totally honest, but it is difficult to find a reliable auditing organization. In this paper, a novel decentralized auditing smart contract in Ethereum is proposed. By replacing the TPA with a designed smart contract, a decentralized auditing scheme (Dredas) is proposed, where anyone can obtain the auditing result from Ethereum without worrying about semi-honest TPA. Compared with traditional auditing, apart from being able to perform traditional auditing functions, Dredas has three important benefits over previous work. First, the random values of challenge are more secure. Dredas chooses the current blockchain nonce as a random seed to prevent any party forging random values. Secondly, in order to achieve a safe, regular, proactive auditing, the protocol writes the auditing rules into the blockchain, and uses the number blocks on the Ethereum as the security timestamp. Finally, data owner, user and CSP must pay some ether for smart contract as deposit. This way not only inhibits the malicious behavior of these three parties, but also makes it more reasonable in real life. We implement Dredas to show that the computation costs are reasonable and efficient.
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| 7. |
- Liu, Dongyun, et al.
(författare)
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Mechanical and durability properties of concrete subjected to early-age freeze–thaw cycles
- 2021
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Ingår i: Materials and Structures. - : Springer. - 1359-5997 .- 1871-6873. ; 54:6
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Tidskriftsartikel (refereegranskat)abstract
- Early-age frost damage to concrete used in winter construction or in cold environments negatively affects the development of the hydration process and the performance of the concrete, thereby reducing the service life of the building structure. Experimental research was carried out to investigate the compressive strength, resistance to chloride penetration and resistance to freeze–thaw of concrete specimens subjected to early-age freeze–thaw cycles (E-FTCs). The effects that different pre-curing times of concrete and mineral admixtures have on the properties of early-age frost-affected concrete were also analyzed. Results show that the earlier the freeze–thaw cycles (FTCs), the poorer the later-age performance. Later-age water-curing cannot completely restore the damage that E-FTCs do to concrete. In the same conditions used in this study, the effects of E-FTCs on later-age mechanical and durability properties of ordinary Portland cement concrete (OPC) are small. The incorporation of fly ash significantly reduces the resistance to freeze–thaw of concrete during early-age and later-age. The presence of silica fumes has an adverse effect on the later-age resistance to freeze–thaw. In general, the recovery percentage of later-age durability indexes of concrete subjected to E-FTCs is lower than that of compressive strength. For concrete subjected to E-FTCs, it is more important to ensure the recovery of later-age durability.
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| 8. |
- Liu, Ling, et al.
(författare)
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Time-domain ICIC and optimized designs for 5G and beyond : a survey
- 2019
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Ingår i: Science China Information Sciences. - Beijing, Peoples republic of China : Zhongguo Kexue Zazhishe/Science in China Press. - 1674-733X .- 1869-1919. ; 62:2
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Tidskriftsartikel (refereegranskat)abstract
- Time-domain enhanced inter-cell interference coordination (eICIC) is an effective technique to reduce the cross-tier inter-cell interference (ICI) in long term evolution (LTE)-based heterogeneous small cell networks (HetSCNs). This paper first clarifies two main communication scenarios in HetSCNs, i.e., macrocells deployed with femtocells (macro-femto) and with picocells (macro-pico). Then, the main challenges in HetSCNs, particularly the severe cross-tier ICI in macro-femto caused by femtocells with closed subscribe group (CSG) access or in macro-pico caused by picocells with range expansion are analyzed. Based on the prominent feature of dominant interference in HetSCNs, the main idea of time-domain interference coordination and two basic schemes in the eICIC standardization, i.e., almost blank subframe (ABS) and orthogonal frequency division multiplexing symbol shift are presented, with a systematic introduction to the interactions of these techniques with other network functions. Then, given macro-femto and macro-pico HetSCNs, an overview is provided on the advanced designs of ABS-based eICIC, including self-optimized designs with regard to key parameters such as ABS muting ratio, and joint optimized designs of ABS-based eICIC and other radio resource management techniques, such as user association and power control. Finally, the open issues and future research directions are discussed.
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| 9. |
- Liu, Zhixin, et al.
(författare)
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Microclimatic measurements in tropical cities: Systematic review and proposed guidelines
- 2022
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Ingår i: Building and Environment. - : Elsevier. - 0360-1323 .- 1873-684X. ; 222
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Forskningsöversikt (refereegranskat)abstract
- To tackle urban overheating induced by the combined effect of global warming and intensive urbanization, researchers have recommended assimilating microclimate-related strategies into urban design practices. Field measurements, playing a central role in urban climatology, have been widely applied worldwide. Reviewing the last five years' field measurement studies and existing guidelines and standards from WMO (World Meteorological Organization) and ISO (International Organization for Standardization), this study identified a gap between available guidelines and researchers' practical needs to ascertain the collection of high caliber data. Therefore, dedicated guidelines are required to explain the crucial conceptual and application issues and refine systematic field measurement methods. This demand is particularly acute for microscale and urban environments. This study proposed and explained integrated and comprehensive guidelines for systematic microclimate field measurements. The suggested workflow included four main steps: formulating field measurement plan, preparing for field measurements, sustaining measurement quality, and curating data. The complex and heterogeneous environment in urban areas was carefully evaluated to hone the data acquisition campaign and ascertain data quality. Relevant concepts and practices learned from existing guidelines and standards, experiences from actual field studies, and professional recommendations were distilled and incorporated into the guidelines. The significance of a complete report with full metadata was emphasized. Detailed hints, precautions, recommendations, examples, and a metadata checklist were provided as a helpful and actionable package of research procedures.
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| 10. |
- Ouyang, Wanlu, et al.
(författare)
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Comparing different recalibrated methods for estimating mean radiant temperature in outdoor environment
- 2022
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Ingår i: Building and Environment. - : Elsevier. - 0360-1323 .- 1873-684X. ; 216
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Tidskriftsartikel (refereegranskat)abstract
- Mean radiant temperature (MRT) is a significant variable for outdoor thermal comfort studies. Two measurement-based methods can estimate MRT, one is globe thermometer – cheap, easily-applied but relatively inaccurate, another is integral radiation measurement method (also known as the six-directional method) - accurate but expensive. Due to low-cost and convenience, the globe thermometer has been widely used. Previous studies have improved its estimation accuracy by recalibrating the convection coefficients in the ISO method. Thus, it is pending to cross-compare the performance of these recalibrated methods.This study aims to investigate the transferability of the recalibrated methods for estimating MRT in outdoor environment. First, field measurement was conducted in a subtropical city, Hong Kong. MRT was obtained through two methods: globe thermometer and integral radiation method. Second, the existing recalibrated convection coefficients were summarized, and the localized convection coefficient was recalibrated. Third, all recalibrated methods were compared for their performance. The impacts of measurement locations, devices, analysis time intervals were examined.The results showed that the newly recalibrated method achieved the lowest estimation errors (RMSE = 3.84 °C). Other recalibrated methods presented higher RMSE (3.84–17.52 °C), similar as conventional ISO method (7.91 °C). Especially for open spaces, the coefficients from other cities should be cautiously applied when the accuracy requirement is less than ±2 °C. Kestrel and Grey globe are more recommended in subtropical cities. This study shed light on the application of globe thermometer for outdoor environment, and emphasized the necessity in recalibrating the convection coefficients locally.
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