| 1. |
- Cheng, Jie, et al.
(författare)
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Guanidimidazole-quanternized and cross-linked alkaline polymer electrolyte membrane for fuel cell application
- 2016
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 501, s. 100-108
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Tidskriftsartikel (refereegranskat)abstract
- A modified imidazole, namely guanidimidazole (GIm) was designed and synthesized as a novel quaternizing- and cross-linking agent for alkaline polymer electrolyte membrane fabrication. The resulting membrane was more alkali tolerant and swelling resistant than that quaternized purely by 1-methylimidazole owing to the enhanced resonance and cross-linking ability of GIm, the former confirmed by a LUMO (lowest unoccupied molecular orbital) energy calculation. The membrane also showed good ionic conductivity, mechanical strength and thermal stability. A H2/O2 fuel cell using the synthesized membrane showed a peak power density of 39 mW cm−2 at 50 °C. This work preliminarily demonstrates the beneficial effect of imidazole modification by both experimental and computational investigation; it provides a new cation design strategy that may potentially achieve simultaneous improvement of alkali-stability and swelling resistance of alkaline electrolyte membranes.
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| 2. |
- De Luca, Alberto, et al.
(författare)
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On the generalizability of diffusion MRI signal representations across acquisition parameters, sequences and tissue types : Chronicles of the MEMENTO challenge
- 2021
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Ingår i: NeuroImage. - : Elsevier BV. - 1053-8119 .- 1095-9572. ; 240
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion MRI (dMRI) has become an invaluable tool to assess the microstructural organization of brain tissue. Depending on the specific acquisition settings, the dMRI signal encodes specific properties of the underlying diffusion process. In the last two decades, several signal representations have been proposed to fit the dMRI signal and decode such properties. Most methods, however, are tested and developed on a limited amount of data, and their applicability to other acquisition schemes remains unknown. With this work, we aimed to shed light on the generalizability of existing dMRI signal representations to different diffusion encoding parameters and brain tissue types. To this end, we organized a community challenge - named MEMENTO, making available the same datasets for fair comparisons across algorithms and techniques. We considered two state-of-the-art diffusion datasets, including single-diffusion-encoding (SDE) spin-echo data from a human brain with over 3820 unique diffusion weightings (the MASSIVE dataset), and double (oscillating) diffusion encoding data (DDE/DODE) of a mouse brain including over 2520 unique data points. A subset of the data sampled in 5 different voxels was openly distributed, and the challenge participants were asked to predict the remaining part of the data. After one year, eight participant teams submitted a total of 80 signal fits. For each submission, we evaluated the mean squared error, the variance of the prediction error and the Bayesian information criteria. The received submissions predicted either multi-shell SDE data (37%) or DODE data (22%), followed by cartesian SDE data (19%) and DDE (18%). Most submissions predicted the signals measured with SDE remarkably well, with the exception of low and very strong diffusion weightings. The prediction of DDE and DODE data seemed more challenging, likely because none of the submissions explicitly accounted for diffusion time and frequency. Next to the choice of the model, decisions on fit procedure and hyperparameters play a major role in the prediction performance, highlighting the importance of optimizing and reporting such choices. This work is a community effort to highlight strength and limitations of the field at representing dMRI acquired with trending encoding schemes, gaining insights into how different models generalize to different tissue types and fiber configurations over a large range of diffusion encodings.
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| 3. |
- Jensen, D. Juul, et al.
(författare)
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Importance of local structural variations on recrystallization
- 2013
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Ingår i: Material Science Forum. - : Trans Tech Publications Inc.. - 9783037856888 ; , s. 37-41
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Konferensbidrag (refereegranskat)abstract
- Effects of local variations in the deformation microstructure on subsequent recrystallization are discussed and illustrated by three examples. The three examples consider local variations on different length scales and are: 1. Effects of local variations in the deformation microstructure on the formation of protrusions on migrating boundaries. 2. Effects of an inhomogeneous spatial distribution of second phase particles on growth. 3. Effects of stored energy and orientation variations on recrystallization kinetics.
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| 4. |
- Chen, Fengxiang, et al.
(författare)
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Adaptive chaos synchronization based on LMI technique
- 2007
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 75:3, s. 285-288
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Tidskriftsartikel (refereegranskat)abstract
- The paper investigates the robust synchronization for two identical uncertain chaotic systems with different parameters perturbation and external disturbances. Based on Lyapunov stability theory, linear matrix inequality (LMI) techniques and adaptive techniques, a novel controller is proposed. With the resulting controller, global asymptotical synchronization between two identical uncertain chaotic systems is achieved. Finally, a Lorenz system is given as an example to verify the effectiveness of the proposed controller.
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| 5. |
- Chen, Fengxiang, et al.
(författare)
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Robust control of chaos in the Lorenz system with the variable structure control approach
- 2008
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Ingår i: Physica scripta. T. - : IOP Publishing. - 0281-1847 .- 0031-8949 .- 1402-4896. ; 77:2
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- This paper is concerned with the robust control for a class of the uncertain Lorenz system subject to sector nonlinear input. Based on rigorous mathematical analysis, the proposed variable structure controller can drive the system state exactly to a class of a specific point or in the predictable neighborhood of an arbitrary desired point in the state space even with mismatch uncertainties. Moreover, the controller ensures that one of the error components can approach zero as time approaches infinity. Finally, numerical simulation results show the effectiveness of our work.
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| 6. |
- Chen, Fengxiang, et al.
(författare)
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Stabilization of parameters perturbation chaotic system via adaptive backstepping technique
- 2008
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Ingår i: Applied Mathematics and Computation. - : Elsevier BV. - 0096-3003 .- 1873-5649. ; 200:1, s. 101-109
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Tidskriftsartikel (refereegranskat)abstract
- The work of Yassen [M.T. Yassen, Chaos control of chaotic dynamical systems using backstepping design, Chaos Soliton Fract. 27 (2006) 537-548] which mainly investigated the stabilization problem for a class of chaotic systems without the parameters perturbation. This paper is concerned with stabilization problem for a class of parameters perturbation chaotic systems via both backstepping design method and adaptive technique. The proposed controllers can guarantee that the parameters perturbation systems will be stabilized at a fixed bounded point. Furthermore, the paper also proposes controllers to stabilize the uncertain chaotic system at equilibrium point with only backstepping design method. Finally, numerical simulations are given to illustrate the effectiveness of the proposed controllers
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| 7. |
- Lin, Fengxiang, et al.
(författare)
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Effects of structural heterogeneity of nanostructured copper on the evolution of the sizes of recrystallized grains during annealing
- 2015
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Ingår i: IOP Conference Series. - : Institute of Physics (IOP).
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Konferensbidrag (refereegranskat)abstract
- Recrystallization in copper deformed by dynamic plastic deformation was investigated using electron backscatter diffraction. The recrystallized grains show a broad size distribution. The kinetics of grains of different sizes is observed to be different: In the beginning of recrystallization, the area fraction of small recrystallized grains increases rapidly. At later stages of recrystallization, the area fraction of small recrystallized grains is stable, while the area fractions of medium and large recrystallized grains increase. Correlation between the broad grain size distribution (and its evolution) and the heterogeneous deformed microstructure is discussed. © Published under licence by IOP Publishing Ltd.
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| 8. |
- Lin, Fengxiang, et al.
(författare)
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Importance of Non-uniform Boundary Migration for Recrystallization Kinetics
- 2018
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 49:11, s. 5246-5258
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Tidskriftsartikel (refereegranskat)abstract
- Recrystallization kinetics is studied by three characterization methods: post-mortem electron microscopy, in situ three-dimensional X-ray diffraction (3DXRD), and ex situ electron microscopy. Cold-rolled copper is used as a model material. The post-mortem analysis shows that the average migration velocity of unimpinged recrystallizing boundaries decreases strongly with annealing time, leading to a low Avrami exponent. For individual grains, the in situ 3DXRD measurement reveals that the growth rates decrease significantly shortly after nucleation. This is explained by the ex situ characterizations, which show that different segments of the recrystallizing boundaries migrate with significantly different velocities, and some boundaries, although unimpinged, remain stationary. This non-uniform migration of recrystallizing boundaries leads to an amoeba-like growth, and is proposed to be responsible for the decrease of the average boundary migration velocity, because the fraction of slowly moving/stationary boundaries increases during the recrystallization. Reasons for stationary boundaries are discussed based on a quantitative analysis of the local deformed microstructure. It is concluded that non-uniform boundary migration has a significant influence on recrystallization kinetics and needs to be included in recrystallization models. © 2018, The Minerals, Metals & Materials Society and ASM International.
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| 9. |
- Lin, Fengxiang, et al.
(författare)
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Local strain distributions in partially recrystallized copper determined by in situ tensile investigation
- 2015
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Ingår i: IOP Conference Series. - : Institute of Physics Publishing (IOPP).
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Konferensbidrag (refereegranskat)abstract
- A partially recrystallized copper sample produced by cold-rolling and annealing was deformed in situ by uniaxial tension in a scanning electron microscope, and electron backscatter diffraction data were collected before and after deformation to certain strains. The local strain distributions are quantified using digital image correlation. Distributions of the normal strain along the tensile direction (εxx) are shown in this paper. The recrystallized grains are found to deform more than the remaining unrecrystallized matrix. When εxx is averaged along lines perpendicular to the tensile direction, significant variation are observed, which may be related to the local recrystallized volume fraction. © Published under licence by IOP Publishing Ltd.
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| 10. |
- Lin, Fengxiang, et al.
(författare)
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Supercube grains leading to a strong cube texture and a broad grain size distribution after recrystallization
- 2015
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Ingår i: Philosophical Magazine. - : Taylor & Francis. - 1478-6435 .- 1478-6443. ; 95:22, s. 2427-2449
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Tidskriftsartikel (refereegranskat)abstract
- This work revisits the classical subject of recrystallization of cold-rolled copper. Two characterization techniques are combined: three-dimensional X-ray diffraction using synchrotron X-rays, which is used to measure the growth kinetics of individual grains in situ, and electron backscatter diffraction, which is used for statistical analysis of the microstructural evolution. As the most striking result, the strong cube texture after recrystallization is found to be related to a few super large cube grains, which were named supercube grains. These few supercube grains become large due to higher growth rates. However, most other cube grains do not grow preferentially. Because of the few supercube grains, the grain size distribution after recrystallization is broad. Reasons for the higher growth rates of supercube grains are discussed, and are related to the local deformed microstructure. © 2015 Taylor & Francis.
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