| 1. |
- Bian, Guodong, et al.
(författare)
-
Detection and attribution of flood responses to precipitation change and urbanization : A case study in Qinhuai River Basin, Southeast China
- 2020
-
Ingår i: Hydrology Research. - : IWA Publishing. - 1998-9563 .- 0029-1277 .- 2224-7955. ; 51:2, s. 351-365
-
Tidskriftsartikel (refereegranskat)abstract
- Both flood magnitude and frequency might change under the changing environment. In this study, a procedure combining statistical methods, flood frequency analysis and attribution analysis was proposed to investigate the response of floods to urbanization and precipitation change in the Qinhuai River Basin, an urbanized basin located in Southeast China, over the period from 1986 to 2013. The Mann–Kendall test was employed to detect the gradual trend of the annual maximum streamflow and the peaks over threshold series. The frequency analysis was applied to estimate the changes in the magnitude and frequency of floods between the baseline period (1986–2001) and urbanization period (2002–2013). An attribution analysis was proposed to separate the effects of precipitation change and urbanization on flood sizes between the two periods. Results showed that: (1) there are significant increasing trends in medium and small flood series according to the Mann–Kendall test; (2) the mean and threshold values of flood series in the urbanization period were larger than those in the baseline period, while the standard deviation, coefficient of variation and coefficient of skewness of flood series were both higher during the baseline period than those during the urbanization period; (3) the flood magnitude was higher during the urbanization period than that during the baseline period at the same return period. The relative changes in magnitude were larger for small floods than for big floods from the baseline period to the urbanization period; (4) the contributions of urbanization on floods appeared to amplify with the decreasing return period, while the effects of precipitation diminish. The procedure presented in this study could be useful to detect the changes of floods in the changing environment and conduct the attribution analysis of flood series. The findings of this study are beneficial to further understanding interactions between flood behavior and the drivers, thereby improving flood management in urbanized basins.
|
|
| 2. |
- Chen, Mingming, et al.
(författare)
-
Ceria-carbonate composite for low temperature solid oxide fuel cell : Sintering aid and composite effect
- 2014
-
Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 39:23, s. 12309-12316
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the effect of carbonate content on microstructure, relative density, ionic conductivity and fuel cell performance of Ce0.8Sm0.2O1.9-(Li/Na)(2)CO3 (SDC-carbonate, abbr. SCC) composites is systematically investigated. With the addition of carbonate, the nanoparticles of ceria are well preserved after heat-treatment. The relative densities of SCC pellets increase as the carbonate content increases or sintering temperature rises. Especially, the relative density of SCC2 sintered at 900 degrees C is higher than that of pure SDC sintered at 1350 degrees C. Both the AC conductivity and DC oxygen ionic conductivity are visibly improved compared with the single phase SDC electrolyte. Among the composites, SDC-20 wt% (Li/Na)(2)CO3 (SCC20) presents high dispersion, relative small particle size, and the dense microstructure. The optimized microstructure brings the best ionic conductivity and fuel cell performance. It is hoped that the results can contribute the understanding of the role of carbonate in the composite materials and highlight their prospective application.
|
|
| 3. |
- Chi, Mingming, et al.
(författare)
-
Excellent rate capability and cycle life of Li metal batteries with ZrO2/POSS multilayer-assembled PE separators
- 2016
-
Ingår i: NANO ENERGY. - : Elsevier BV. - 2211-2855. ; 28, s. 1-11
-
Tidskriftsartikel (refereegranskat)abstract
- Today there are new interests in using metallic lithium as anode materials in lithium batteries because of its extremely large theoretical specific capacity. However, the low cycle efficiency and the lithium dendrite formation during repeated charge/discharge cycles hinder the practical application of metallic lithium anodes. Herein, we report a distinctive ZrO2/POSS multilayer deposited on PE separators by a simple layer-by-layer (LbL) self-assembly process to enable excellent rate capability and cycle life of lithium metal batteries. The ZrO2/POSS multilayer on PE separators weakens the solvation effect of lithium ions and significantly enhances the electrolyte uptake of separators, which is responsible for the enhanced ionic conductivity and Li+ transference number, as well as the improved Li/electrolyte interfacial stability. These advantageous characteristics of the resulting PE separators effectively decrease the electrode polarization and protect lithium metal anodes against lithium dendrites formation during repeated charge/discharge cycles, endowing LiCoO2/Li unit cells with both excellent electrochemical performance and high safety. The fundamental understanding on the effects of the micro/nano structures and properties of separators on the important electrochemistry processes at electrode/electrolyte interface of battery systems may lead to new approaches to tackle the intrinsic problems of Li metal anodes for energy storage applications.
|
|
| 4. |
- Fan, Liangdong, et al.
(författare)
-
Electrochemical study of lithiated transition metal oxide composite as symmetrical electrode for low temperature ceramic fuel cells
- 2013
-
Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 38:26, s. 11398-11405
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, Lithiated NiCuZnOx (LNCZO) composite is synthesized and evaluated as a potential symmetrical electrode for ceria-carbonate composite electrolyte based low temperature ceramic fuel cells. Its crystal structures, the hydrogen oxidation/oxygen reduction electrochemical activities and fuel cell performances are systematically examined on the symmetrical cell configuration. Nano crystallite particles in the form of composite are observed for these oxides. The LNCZO shows relatively high catalytic activities for hydrogen oxidation and oxygen reduction reaction according to the electrochemical impedance spectroscopy measurements. A remarkable low oxygen reduction activation energy of 42 kJ mol(-1) is obtained on the LNCZO/ceria-carbonate composite, demonstrating excellent electro-catalytic activity. Especially, the catalytic activity can be further improved in the presence of water in the cathode chamber. The results show that the lithiated transition metal oxide composite is a promising symmetrical electrode for ceria-carbonate electrolyte and composite approach might a probable solution to develop super-performance electrodes for reduced temperature ceramic fuel cells.
|
|
| 5. |
- Fan, Liangdong, et al.
(författare)
-
Proton and Oxygen Ionic Conductivity of Doped Ceria-Carbonate Composite by Modified Wagner Polarization
- 2012
-
Ingår i: International Journal of Electrochemical Science. - 1452-3981. ; 7:9, s. 8420-8435
-
Tidskriftsartikel (refereegranskat)abstract
- The impressive ionic conductivity and tunable conduction behaviors have made the ceria-carbonate composite an attractive electrolyte for low temperature ceramic fuel cells. However, the conduction mechanism is not yet well studied. In the present study, both proton and oxygen ion conductivity as well as the transport properties of samaria-doped ceria/ sodium-lithium-carbonate (denoted as SDCLN) composite are investigated by the fuel cell study and the modified Hebb-Wagner polarization measurements. The multi-ionic polarization behaviors and the transfer processes in composite electrolyte under external electrical field are analyzed. A maximum power density of 780 mW cm(-2) and a calculated total ion (proton and oxygen ion) conductivity of 0.153 S cm(-1) are obtained under H-2/air condition at 550 degrees C. The Wagner DC polarization measurements show that the proton conduction dominates the total ionic conductivity. A synergistic effect exists between the charge carriers in the doped ceria-carbonate composite system. An ideal interfacial conduction model is also proposed based on the obtained results.
|
|
| 6. |
- Gao, Mingming, et al.
(författare)
-
Engineered 2D MXene-based materials for advanced supercapacitors and micro-supercapacitors
- 2024
-
Ingår i: Materials Today. - 1369-7021 .- 1873-4103. ; 72, s. 318-358
-
Forskningsöversikt (refereegranskat)abstract
- The class of two-dimensional transition metal carbides/nitrides/oxycarbides (known as MXenes) has shown great potential in energy storage applications due to their intrinsic layered structure, outstanding electrical conductivity, tunable surface chemistry, and unique physicochemical properties. This review summarizes the latest progresses of MXene-based materials for supercapacitors and micro-supercapacitors. First, state-of-the-art structural engineering strategies for the construction of novel MXene-based electrodes are highlighted, as the electrochemical performance of MXenes is influenced by their structure, such as interlayer spacing and surface functional group density. Furthermore, the charge storage mechanisms of MXene-based electrodes in different electrolytes are discussed to stimulate further design and development of tailored materials for high-performance devices. Moreover, different device fabrication technologies are summarized and the achievements of specific device geometries (e.g., fiber-shape, planar-type, and three-dimensional devices) containing MXene-based materials are critically reviewed. Finally, perspectives and outlook for the development of high-performance MXene-based electrodes in terms of material engineering, performance improvement and device innovation are provided, clearly indicating research directions for next-generation advanced energy storage devices.
|
|
| 7. |
- Sun, Tianrui, et al.
(författare)
-
Influence of the Tip Clearance on the Aeroelastic Characteristics of a Last Stage Steam Turbine
- 2019
-
Ingår i: Applied Sciences. - : MDPI. - 2076-3417. ; 9:6
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, the tip clearance effects on the aeroelastic stability of a last-stage steam turbine model are investigated. Most of the unsteady aerodynamic work contributing to flutter of the long blades of the last-stage of a steam turbine is done near the tip of the blade. The flow in this region is transonic and sensitive to geometric parameters such as the tip clearance height. The KTH Steam Turbine Flutter Test Case was chosen as the test case, which is an open geometry with similar parameters to modern free-standing last-stage steam turbines. The energy method based on 3D URANS simulation was applied to investigate the flutter characteristics of the rotor blade with five tip gap height varying from 0-5% of the chord length. The numerical results show that the global aerodynamic damping for the least stable inter-blade phase angle (IBPA) increases with the tip gap height. Three physical mechanisms are found to cause this phenomenon. The primary cause of the variation in total aerodynamic damping is the interaction between tip clearance vortex and the trailing edge shock from the adjacent blade. Another mechanism is the acceleration of the flow near the aft side of the suction surface in the tip region due to the well-developed tip leakage vortex when the tip clearance height is greater than 2.5% of chord. This causes a stabilizing effect at the least stable IBPA. The third mechanism is the oscillation of the tip leakage vortex due to the blade vibration. This has a negative influence on the aeroelastic stability.
|
|
| 8. |
- Wang, Ling-Zhi, et al.
(författare)
-
Sphagnumspore banks in two montane peatlands at different elevations
- 2020
-
Ingår i: Wetlands Ecology and Management. - : SPRINGER. - 0923-4861 .- 1572-9834. ; 28:5, s. 825-835
-
Tidskriftsartikel (refereegranskat)abstract
- Spore production of bryophytes is common in subalpine ecosystems, but how spore banks of bryophytes vary with elevations is unknown. We used peat cores from twoSphagnumdominated peatlands, a low- (780 m a.s.l.) and a high-elevation (1480 m a.s.l.) site to test the hypotheses that spore concentration, accumulation rate, germinability and longevity are lower at a high-elevation peatland than those at lower elevation due to the assumed climatic limitations at high elevation. Along the cores,Sphagnumspores were extracted, burial time of spores was dated and spore germinability was tested layer by layer.Sphagnumspore concentration, accumulation rate and germinability were greater at the high-elevation peatland than at the low-elevation site. Both peatlands had long-term persistentSphagnumspore banks with a predicted longevity (the burial time when 1% spores are viable) ofc. 390 and 140 years for the low- and high-elevation sites, respectively. Our study suggests thatSphagnum, the ecological engineer of peatlands, by regulating spore production and longevity can maintain relatively constant spore banks which may be of great importance in population regeneration and persistence in a changing world.
|
|
| 9. |
- Yusup, Shuayib, et al.
(författare)
-
Smoke promotes germination of peatland bryophyte spores
- 2023
-
Ingår i: Journal of Experimental Botany. - : Oxford University Press. - 0022-0957 .- 1460-2431. ; 74:1, s. 251-264
-
Tidskriftsartikel (refereegranskat)abstract
- Northern peatlands are globally important carbon stores. With increasing fire frequency, the re-establishment of bryophytes becomes crucial for their carbon sequestration. Smoke-responsive germination is a common trait of seeds in fire-prone ecosystems but has not been demonstrated in bryophytes. To investigate the potential role of smoke in post-fire peatland recovery, we tested the germination of spores of 15 bryophyte species after treatment with smoke-water. The smoke responsiveness of spores with different laboratory storage times and burial depths/age (3-200 years) was subsequently tested. Smoke increased the germination percentage for 10 of the species and the germination speed for four of these. Smoke responsiveness increased along the fire frequency gradient from open expanse to forest margin, consistent with the theory that this selects for the maintenance of fire-adapted traits. Smoke enhanced the germinability of 1-year but not 4-year laboratory-stored spores, and considerably increased the germinability of spores naturally buried in peat for up to similar to 200 years. The effect of fire may be overlooked in non-fire-prone ecosystems, such as those in which wetland bryophytes dominate. Our study reveals a mechanism by which an increase in fire frequency may lead to shifts in species dominance, which may affect long-term carbon sequestration in peatlands.
|
|
