| 1. |
- An, Rong, et al.
(författare)
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Ionic liquids on uncharged and charged surfaces: In situ microstructures and nanofriction
- 2022
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Ingår i: Friction. - : Springer. - 2223-7690 .- 2223-7704. ; 10:11, s. 1893-1912
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Tidskriftsartikel (refereegranskat)abstract
- In situ changes in the nanofriction and microstructures of ionic liquids (ILs) on uncharged and charged surfaces have been investigated using colloid probe atomic force microscopy (AFM) and molecular dynamic (MD) simulations. Two representative ILs, [BMIM][BF4] (BB) and [BMIM][PF6] (BP), containing a common cation, were selected for this study. The torsional resonance frequency was captured simultaneously when the nanoscale friction force was measured at a specified normal load; and it was regarded as a measure of the contact stiffness, reflecting in situ changes in the IL microstructures. A higher nanoscale friction force was observed on uncharged mica and highly oriented pyrolytic graphite (HOPG) surfaces when the normal load increased; additionally, a higher torsional resonance frequency was detected, revealing a higher contact stiffness and a more ordered IL layer. The nanofriction of ILs increased at charged HOPG surfaces as the bias voltage varied from 0 to 8 V or from 0 to —8 V. The simultaneously recorded torsional resonance frequency in the ILs increased with the positive or negative bias voltage, implying a stiffer IL layer and possibly more ordered ILs under these conditions. MD simulation reveals that the [BMIM]+ imidazolium ring lies parallel to the uncharged surfaces preferentially, resulting in a compact and ordered IL layer. This parallel “sleeping” structure is more pronounced with the surface charging of either sign, indicating more ordered ILs, thereby substantiating the AFM-detected stiffer IL layering on the charged surfaces. Our in situ observations of the changes in nanofriction and microstructures near the uncharged and charged surfaces may facilitate the development of IL-based applications, such as lubrication and electrochemical energy storage devices, including supercapacitors and batteries.
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| 2. |
- Bu, Junling, et al.
(författare)
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Catalytic promiscuity of O-methyltransferases from Corydalis yanhusuo leading to the structural diversity of benzylisoquinoline alkaloids
- 2022
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Ingår i: Horticulture Research. - : Oxford University Press (OUP). - 2662-6810 .- 2052-7276. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- O-methyltransferases play essential roles in producing structural diversity and improving the biological properties of benzylisoquinoline alkaloids (BIAs) in plants. In this study, Corydalis yanhusuo, a plant used in traditional Chinese medicine due to the analgesic effects of its BIA-active compounds, was employed to analyze the catalytic characteristics of O-methyltransferases in the formation of BIA diversity. Seven genes encoding O-methyltransferases were cloned, and functionally characterized using seven potential BIA substrates. Specifically, an O-methyltransferase (CyOMT2) with highly efficient catalytic activity of both 4′- and 6-O-methylations of 1-BIAs was found. CyOMT6 was found to perform two sequential methylations at both 9- and 2-positions of the essential intermediate of tetrahydroprotoberberines, (S)-scoulerine. Two O-methyltransferases (CyOMT5 and CyOMT7) with wide substrate promiscuity were found, with the 2-position of tetrahydroprotoberberines as the preferential catalytic site for CyOMT5 (named scoulerine 2-O-methyltransferase) and the 6-position of 1-BIAs as the preferential site for CyOMT7. In addition, results of integrated phylogenetic molecular docking analysis and site-directed mutation suggested that residues at sites 172, 306, 313, and 314 in CyOMT5 are important for enzyme promiscuity related to O-methylations at the 6- and 7-positions of isoquinoline. Cys at site 253 in CyOMT2 was proved to promote the methylation activity of the 6-position and to expand substrate scopes. This work provides insight into O-methyltransferases in producing BIA diversity in C. yanhusuo and genetic elements for producing BIAs by metabolic engineering and synthetic biology.
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| 3. |
- Qiu, Xiuhua, et al.
(författare)
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Probing the nanofriction of non-halogenated phosphonium-based ionic liquid additives in glycol ether oil on titanium surface
- 2022
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Ingår i: Friction. - : Springer. - 2223-7690 .- 2223-7704. ; 10:2, s. 268-281
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Tidskriftsartikel (refereegranskat)abstract
- The nanofrictional behavior of non-halogentated phosphonium-based ionic liquids (ILs) mixed with diethylene glycol dibutyl ether in the molar ratios of 1:10 and 1:70 was investigated on the titanium (Ti) substrate using atomic force microscopy (AFM). A significant reduction is observed in the friction coefficient μ for the IL-oil mixtures with a higher IL concentration (1:10, μ ∼ 0.05), compared to that for the lower concentration 1:70 (μ ∼ 0.1). AFM approaching force-distance curves and number density profiles for IL-oil mixtures with a higher concentration revealed that the IL preferred to accumulate at the surface forming IL-rich layered structures. The ordered IL-rich layers formed on the titanium surface facilitated the reduction of the nanoscale friction by preventing direct surface-to-surface contact. However, the ordered IL layers disappeared in the case of lower concentration, resulting in an incomplete boundary layers, because the ions were displaced by molecules of the oil during sliding and revealed to be less efficient in friction reduction.
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| 4. |
- Zhang, Huan, et al.
(författare)
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East Asian warm season temperature variations over the past two millennia
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- East Asia has experienced strong warming since the 1960s accompanied by an increased frequency of heat waves and shrinking glaciers over the Tibetan Plateau and the Tien Shan. Here, we place the recent warmth in a long-term perspective by presenting a new spatially resolved warm-season (May-September) temperature reconstruction for the period 1-2000 CE using 59 multiproxy records from a wide range of East Asian regions. Our Bayesian Hierarchical Model (BHM) based reconstructions generally agree with earlier shorter regional temperature reconstructions but are more stable due to additional temperature sensitive proxies. We find a rather warm period during the first two centuries CE, followed by a multi-century long cooling period and again a warm interval covering the 900-1200 CE period (Medieval Climate Anomaly, MCA). The interval from 1450 to 1850 CE (Little Ice Age, LIA) was characterized by cooler conditions and the last 150 years are characterized by a continuous warming until recent times. Our results also suggest that the 1990s were likely the warmest decade in at least 1200 years. The comparison between an ensemble of climate model simulations and our summer reconstructions since 850 CE shows good agreement and an important role of internal variability and external forcing on multi-decadal time-scales.
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| 5. |
- Zhang, Xiuhua
(författare)
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User Participation in Object-Oriented Contexts - From Methodological and Practical Perspectives
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this study, user participation is suggested as a means, a process and role-playing between system users and developers in systems development. User participation in object-oriented contexts is observed from methodological and practical perspectives as a combined field of study. From the methodological perspective, three object-oriented methods are assessed according to NIMSAD, a method evaluation framework. The method evaluation indicates that user participation is weak in the three object-oriented methods. From the practical perspective, object-oriented systems practice is investigated in six industrial organizations in Sweden, from which two forms of user participation are found and provided. They reveal that user participation could be explored from the understanding of objects and be studied from the method application. It is argued that system users can play a role as method users in the whole development process. Such an argument is only found from the systems practice far.
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