| 15611. |
- Liu, H., et al.
(författare)
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Precipitation during high temperature aging of Al−Cu alloys : A multiscale analysis based on first principles calculations
- 2019
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Ingår i: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 167, s. 121-135
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Tidskriftsartikel (refereegranskat)abstract
- Precipitation during high temperature aging of Al−Cu alloys is analysed by means of the integration of classical nucleation theory and phase-field simulations into a multiscale modelling approach based on well-established thermodynamics principles. In particular, thermal stability of θ'', θ′ and θ precipitates was assessed from first principles calculations of the Helmholtz free energy while homogeneous and heterogeneous nucleation of θ'' and θ′ was analysed using classical nucleation theory. Precipitate growth was finally computed by means of a mesoscopic phase-field model. The model parameters that determine quantitatively the driving forces for each transformation were obtained by means of first principles calculations and computational thermodynamics. The predictions of the models were in good agreement with experimental results and provided a comprehensive understanding of the precipitation pathway in Al−Cu alloys. It is envisaged that the strategy presented in this investigation can be used in the future to design optimum microstructures based on the information of the different energy contributions obtained from first principles calculations. © 2019 Acta Materialia Inc.
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| 15612. |
- Liu, Hong, et al.
(författare)
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Three-dimensional shape and stress field of a deformation twin in magnesium
- 2023
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Ingår i: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 250
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Tidskriftsartikel (refereegranskat)abstract
- While the three-dimensional (3D) shape and stress field of a twin in hexagonal close-packed (HCP) metals have attracted considerable interest in recent years due to their substantial impact on internal stress and mechanical properties, a detailed understanding of their variation with twin size is still lacking. An analytical model that is not restricted by spatial scale is developed in this work by considering the effects of anisotropic twin boundary energy, elastic strain energy and plastic relaxation to predict the 3D shape with the minimum energy, and the stress field, of an isolated ellipsoidal twin of different sizes. The model is applied to Mg with a focus on the {101¯2} twin type. The analytical calculation results show that the nucleation of the nano-sized twin embryos is facilitated by the stress field near structural defects such as dislocations. During the expansion of this nano-sized twin embryo, the interplay between the elastic strain energy and interfacial energy changes the length of the twin along the twin shear (forward) direction from being shorter to longer than that along the lateral direction. In contrast to the current understandings, the maximum shear stress on the twin plane along the twin shear direction occurs at the lateral, rather than the forward, side of the twin. At the forward side, the maximum shear stress occurs at a distance ahead of the twin tip and this distance increases with increasing twin thickness.
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| 15613. |
- Liu, Hong, et al.
(författare)
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Variant selection of primary–secondary extension twin pairs in magnesium : An analytical calculation study
- 2021
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 219, s. 1-19
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Tidskriftsartikel (refereegranskat)abstract
- Twining is an important deformation mode in magnesium. In a deformed magnesium sample, an extension twin crystal, i.e., {101¯2} twin, can form inside a {101¯2} primary twin, which is named {101¯2}–{101¯2} secondary twin. These secondary twins often appear at the intersection of two primary twins, and form primary–secondary twin pairs. Experimental observations show that the most frequently observed primary–secondary twin pairs have a unique misorientation, i.e., twin variant selection exists. Such variant selection of the primary–secondary twin pairs is studied in this work. The crystallographic analysis reveals that the twin planes of the primary and secondary twins that form a twin pair have coincident intersection lines with the boundary where the twin pair adjoins. An analytical calculation method based on Eshelby's inclusion theory is developed, and the calculation results show that only for this unique misorientation, the stress fields concentrated at the rims of the primary and the secondary twins are mutually favoured. The analysis is further extended to the incoming–outgoing twin pairs across ordinary grain boundaries, and compared with the commonly used geometrical compatibility factor m′. It is found that m′ only gives good prediction for twin transmission when the shear stress component on the twin plane along the twin shear direction of the incoming twin is the major contributor to the resolved shear stress of the outgoing twin. When other stress components play a dominant role, m′ becomes ineffective in prediction, which is the case for the primary–secondary twin pairs.
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| 15614. |
- Liu, Yipeng, et al.
(författare)
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Brand management in mergers and acquisitions : Emerging market multinationals venturing into advanced economies
- 2018
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Ingår i: International Marketing Review. - : Emerald Group Publishing Limited. - 0265-1335 .- 1758-6763. ; 35:5, s. 710-732
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Tidskriftsartikel (refereegranskat)abstract
- Purpose – The purpose of this paper is to focus on emerging market companies that internationalize into advanced economies by means of acquisitions and to investigate brand management during post-acquisition integration from a multi-level perspective and to identify how a brand management strategy can be constructed. It takes into account the influences of country-of-origin image, corporate brand and brand portfolio to obtain a granular view of post-acquisition brand management.Design/methodology/approach – A multiple case study approach was adopted. By using case studies and storytelling qualitative research methods, the empirical setting was related to the acquisitions undertaken by Chinese companies in Germany.Findings – The authors identified three mechanisms for brand management in the post-acquisition integration of emerging market companies – namely, transferring, dynamically redeploying and categorizing – that underpin the interconnection and combined influence of country-of-origin image at the national level, corporate brand at the organizational level and brand portfolio at the product level.Practical implications – Brand has been viewed as a strategic asset in Chinese cross-border mergers and acquisitions (M&As). Brand management is a dynamic process that involves learning and interaction between the acquirer and target. The research offers a practical guideline for both acquirers and targets in managing brand in the context of acquisitions undertaken by emerging market companies in advanced economies.Originality/value – The findings provide important insights into the brand management strategies adopted in Chinese cross-border M&As in particular, and emerging market companies venturing into advanced economies in general. The interlinking of country, company and product levels introduces new ideas to the brand literature related to acquisitions, and the setting of Chinese companies acquiring German ones constitutes an important contribution to the understanding of the different ways in which companies from emerging economies may pursue branding strategies in the context of cross-border M&As.
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| 15615. |
- Liu, Yanfeng, et al.
(författare)
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In Situ Optical Spectroscopy Demonstrates the Effect of Solvent Additive in the Formation of All-Polymer Solar Cells
- 2022
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 13:50, s. 11696-11702
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Tidskriftsartikel (refereegranskat)abstract
- 1-Chloronaphthalene (CN) has been a common solvent additive in both fullerene- A nd nonfullerene-based organic solar cells. In spite of this, its working mechanism is seldom investigated, in particular, during the drying process of bulk heterojunctions composed of a donor:acceptor mixture. In this work, the role of CN in all-polymer solar cells is investigated by in situ spectroscopies and ex situ characterization of blade-coated PBDB-T:PF5-Y5 blends. Our results suggest that the added CN promotes self-aggregation of polymer donor PBDB-T during the drying process of the blend film, resulting in enhanced crystallinity and hole mobility, which contribute to the increased fill factor and improved performance of PBDB-T:PF5-Y5 solar cells. Besides, the nonradiative energy loss of the corresponding device is also reduced by the addition of CN, corresponding to a slightly increased open-circuit voltage. Overall, our observations deepen our understanding of the drying dynamics, which may guide further development of all-polymer solar cells.
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| 15616. |
- Liu, Yanfeng, et al.
(författare)
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In Situ Optical Studies on Morphology Formation in Organic Photovoltaic Blends
- 2021
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Ingår i: Small Methods. - : John Wiley & Sons. - 2366-9608. ; 5:10, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- The efficiency of bulk heterojunction (BHJ) based organic solar cells is highly dependent on the morphology of the blend film, which is a result of a fine interplay between donor, acceptor, and solvent during the film drying. In this work, a versatile set-up of in situ spectroscopies is used to follow the morphology evolution during blade coating of three iconic BHJ systems, including polymer:fullerene, polymer:nonfullerene small molecule, and polymer:polymer. the drying and photoluminescence quenching dynamics are systematically study during the film formation of both pristine and BHJ films, which indicate that the component with higher molecular weight dominates the blend film formation and the final morphology. Furthermore, Time-resolved photoluminescence, which is employed for the first time as an in situ method for such drying studies, allows to quantitatively determine the extent of dynamic and static quenching, as well as the relative change of quantum yield during film formation. This work contributes to a fundamental understanding of microstructure formation during the processing of different blend films. The presented setup is considered to be an important tool for the future development of blend inks for solution-cast organic or hybrid electronics.
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| 15617. |
- Liu, Yang, 1960-
(författare)
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Syllogistic Analysis and Cunning of Reason in Mathematics Education
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This essay explores the issue of organizing mathematics education by means of syllogism. Two aspects turn out to be particularly significant. One is the syllogistic analysis while the other is the cunning of reason. Thus the exploration is directed towards gathering evidence of their existence and showing by examples their usefulness within mathematics education.The syllogistic analysis and the cunning of reason shed also new light on Chevallard's theory of didactic transposition. According to the latter, each piece of mathematical knowledge used inside school is a didactic transposition of some other knowledge produced outside school, but the theory itself does not indicate any way of transposing, and this empty space can be filled with the former.A weak prototype of syllogism considered here is Freudenthal's change of perspective. Some of the major difficulties in mathematics learning are connected with the inability of performing change of perspective. Consequently, to ease the difficulties becomes a significant issue in mathematics teaching. The syllogistic analysis and the cunning of reason developed in this essay are the contributions to the said issue.
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| 15618. |
- Liu, Zonghao, et al.
(författare)
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Gas-solid reaction based over one-micrometer thick stable perovskite films for efficient solar cells and modules
- 2018
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Besides high efficiency, the stability and reproducibility of perovskite solar cells (PSCs) are also key for their commercialization. Herein, we report a simple perovskite formation method to fabricate perovskite films with thickness over 1 mu m in ambient condition on the basis of the fast gas-solid reaction of chlorine-incorporated hydrogen lead triiodide and methylamine gas. The resultant thick and smooth chlorine-incorporated perovskite films exhibit full coverage, improved crystallinity, low surface roughness and low thickness variation. The resultant PSCs achieve an average power conversion efficiency of 19.1 +/- 0.4% with good reproducibility. Meanwhile, this method enables an active area efficiency of 15.3% for 5 cmx 5 cm solar modules. The un-encapsulated PSCs exhibit an excellent T-80 lifetime exceeding 1600 h under continuous operation conditions in dry nitrogen environment.
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| 15619. |
- Liu, Zihao, et al.
(författare)
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ICT support supporting healting healthcare for chinese elderl thcare for chinese elderly at home: perspectives of informal caregivers and professionalsICT suppor t supporting heal ting healthcare for chinese elderl thcare for chinese elderly at home: perspectives of informal caregivers and professionals
- 2019
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Ingår i: <em>MCIS 2019 Proceedings</em>. 37.
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Konferensbidrag (refereegranskat)abstract
- Informal caregivers are a significant resource when elderly people need assistance and support to remain living at home. Today, state-of-the-art technology provides the possibilities of applying ways to ease the workload and make it possible to stay at home instead of living in an institutional care setting, such as hospitals or special sheltered accommodations. The current study analysed how information and communication technology (ICT) could support healthcare in Chinese homes from the perspectives of informal caregivers and healthcare professionals. The study focused on elderly people who benefit from caregiving or need personal assistance to help them live at home. A mapping study was conducted to identify existing ICT solutions, and qualitative semi-structured interviews were performed to obtain the perspectives of informal caregivers and professionals. The contributions were identified as objectives of using ICT solutions, relatives’ feedback on ICT solutions, opinions about popular ICT solutions and thoughts about future ICT solutions. The empirical study revealed that alarming, communication, monitoring, positioning and assistance are the most important reasons to acquire and apply ICT-based support for elderly people living at home.
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| 15620. |
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