| 1. |
- Hashemi, Hossein, et al.
(author)
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Using Floodwater for Artificial Recharge and Spate Irrigation
- 2017
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In: Sustainable Water Resources Management. - Reston, VA : American Society of Civil Engineers. - 9780784414767 - 9780784480908 ; , s. 697-736
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Book chapter (peer-reviewed)abstract
- Floodwater harvesting (FWH) for artificial recharge of groundwater (ARG) and spate irrigation (SI) is the most widely practiced large catchment water harvesting technique. It has recently received renewed attention for research, improvement, and implementation. This chapter first introduces an innovative, locally adaptive, and improved FWH technique—floodwater spreading systems (FWS)—to guide policymakers and practitioners in the management of groundwater (GW) resources and efficient rain-fed agriculture in water scarce countries. This is done by evaluating the effects of a large-scale FWH system on a local aquifer. The chapter assesses the contribution of FWH to GW recharge and improved agricultural yield by introducing SI technique through FWH. In line with the GW modeling and recharge estimation, a three-year field study to investigate improved rain-fed agricultural yield in a FWS system using the SI technique is explained. Barley was tested as an indicator plant for crop yield.
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| 2. |
- Howard, Ian A., et al.
(author)
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Charge Recombination and Exciton Annihilation Reactions in Conjugated Polymer Blends
- 2010
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In: Journal of the American Chemical Society. - 0002-7863. ; 132:1, s. 328-335
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Journal article (peer-reviewed)abstract
- Bimolecular interactions between excitations in conjugated polymer thin films are important because they influence the efficiency of many optoelectronic devices that require high excitation densities. Using time-resolved optical spectroscopy, we measure the bimolecular interactions of charges, singlet excitons, and triplet excitons in intimately mixed polyfluorene blends with band-edge offsets optimized for photoinduced electron transfer. Bimolecular charge recombination and triplet−triplet annihilation are negligible, but exciton−charge interactions are efficient. The annihilation of singlet excitons by charges occurs on picosecond time-scales and reaches a rate equivalent to that of charge transfer. Triplet exciton annihilation by charges occurs on nanosecond time-scales. The surprising absence of nongeminate charge recombination is shown to be due to the limited mobility of charge carriers at the heterojunction. Therefore, extremely high densities of charge pairs can be maintained in the blend. The absence of triplet−triplet annihilation is a consequence of restricted triplet diffusion in the blend morphology. We suggest that the rate and nature of bimolecular interactions are determined by the stochastic excitation distribution in the polymer blend and the limited connectivity between the polymer domains. A model based on these assumptions quantitatively explains the effects. Our findings provide a comprehensive framework for understanding bimolecular recombination and annihilation processes in nanostructured materials.
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| 3. |
- Jarfors, Anders E. W., et al.
(author)
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Tool wear and life span variations in cold forming operations and their implications in microforming
- 2017
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In: Technologies. - : MDPI. - 2227-7080. ; 5:1
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Research review (peer-reviewed)abstract
- The current paper aims to review tooling life span, failure modes and models in cold microforming processes. As there is nearly no information available on tool-life for microforming the starting point was conventional cold forming. In cold forming common failures are (1) over stressing of the tool; (2) abrasive wear; (3) galling or adhesive wear, and (4) fatigue failure. The large variation in tool life observed in production and how to predict this was reviewed as this is important to the viability of microforming based on that the tooling cost takes a higher portion of the part cost. Anisotropic properties of the tool materials affect tool life span and depend on both the as-received and in-service conditions. It was concluded that preconditioning of the tool surface, and coating are important to control wear and fatigue. Properly managed, the detrimental effects from surface particles can be reduced. Under high stress low-cycle fatigue conditions, fatigue failure form internal microstructures and inclusions are common. To improve abrasive wear resistance larger carbides are commonly the solution which will have a negative impact on tooling life as these tend to be the root cause of fatigue failures. This has significant impact on cold microforming.
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| 4. |
- Wang, Xinping, et al.
(author)
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Canopy storage capacity of xerophytic shrubs in northwestern China
- 2012
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In: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 454-455, s. 152-159
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Journal article (peer-reviewed)abstract
- Abstract in UndeterminedThe capacity of shrub canopy water storage is a key factor in controlling the rainfall interception. Thus, it affects a variety of hydrological processes in water-limited arid desert ecosystems. Vast areas of revegetated desert ecosystems in Northwestern China are occupied by shrub and dwarf shrub communities. Yet, data are still scarce regarding their rainwater storage capacity. In this study, simulated rainfall tests were conducted in controlled conditions for three dominant xerophytic shrub types in the arid Tengger Desert. Eight rainfall intensities varying from 1.15 to 11.53 mm h−1 were used to determine the canopy water storage capacity. The simulated rainfall intensities were selected according to the long-term rainfall records in the study area. The results indicate that canopy storage capacity (expressed in water storage per leaf area, canopy projection area, biomass, and volume of shrub respectively) increased exponentially with increase in rainfall intensity for the selected shrubs. Linear relationships were found between canopy storage capacity and leaf area (LA) or leaf area index (LAI), although there was a striking difference in correlation between storage capacity and LA or LAI of Artemisia ordosica compared to Caragana korshinskii and Hedysarum scoparium. This is a result of differences in biometric characteristics, especially canopy morphology between the shrub species. Pearson correlation coefficient indicated that LA and dry biomass are better predictors as compared to canopy projection area and volume of samples for precise estimation of canopy water storage capacity. In terms of unit leaf area, mean storage capacity was 0.39 mm (range of 0.24–0.53 mm), 0.43 mm (range of 0.28–0.60 mm), and 0.61 mm (range of 0.29–0.89 mm) for C. korshinskii, H. scoparium, and A. ordosica, respectively. Correspondingly, divided per unit dry biomass, mean storage capacity was 0.51 g g−1 (range of 0.30–0.70 g g−1), 0.41 g g−1 (range of 0.26–0.57 g g−1), and 0.73 g g−1 (range of 0.38–1.05 g g−1) for C. korshinskii, H. scoparium, and A. ordosica, respectively, when the rainfall intensities ranged from 1.15, 2.31, 3.46, 4.61, 6.92, 9.23 to 11.53 mm h−1. The needle-leaved species A. ordosica had a higher canopy water storage capacity than the ovate-leaved species C. korshinskii and H. scoparium at the same magnitude of rainfall intensity, except for C. korshinskii when it was expressed in unit of canopy projection area. Consequently, A. ordosica will generate higher interception losses as compared to C. korshinskii and H. scoparium. This is especially the case as it often forms dense dwarf shrub communities despite its small size.
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| 5. |
- Wang, Xinping, et al.
(author)
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Desert shrub stemflow and its significance in soil moisture replenishment
- 2011
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In: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1607-7938. ; 15:2, s. 561-567
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Journal article (peer-reviewed)abstract
- Stemflow of xerophytic shrubs represents a significant component of water replenishment to the soil-root system influencing water utilization of plant roots at the stand scale, especially in water scarce desert ecosystems. In this study, stemflow of Caragana korshinskii was quantified by an aluminum foil collar collection method on re-vegetated sand dunes of the Shapotou restored desert ecosystem in northwestern China. Time domain reflectometry probes were inserted horizontally at 20 different soil profile depths under the C. korshinskii shrub to monitor soil moisture variation at hourly intervals. Results indicated that 2.2 mm precipitation was necessary for the generation of stemflow for C. korshinskii. Stemflow averaged 8% of the gross precipitation and the average funnelling ratio was as high as 90. The soil moisture in the uppermost soil profile was strongly correlated with individual rainfall and the stemflow strengthened this relationship. Therefore, it is favourable for the infiltrated water redistribution in the deeper soil profile of the root zone. Consequently, stemflow contributes significantly to a positive soil moisture balance in the root zone and the replenishment of soil moisture at deeper soil layers. This plays an important role in plant survival and the general ecology of arid desert environments.
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| 6. |
- Xu, Weidong, et al.
(author)
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Iodomethane-Mediated Organometal Halide Perovskite with Record Photoluminescence Lifetime
- 2016
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In: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 8:35, s. 23181-23189
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Journal article (peer-reviewed)abstract
- Organometallic lead halide perovskites are excellent light harvesters for high-efficiency photovoltaic devices. However, as the key component in these devices, a perovskite thin film with good morphology and minimal trap states is still difficult to obtain. Herein we show that by incorporating a low boiling point alkyl halide such as iodomethane (CH3I) into the precursor solution, a perovskite (CH3NH3PbI3-xClx) film with improved grain size and orientation can be easily achieved. More importantly, these films exhibit a significantly reduced amount of trap states. Record photoluminescence lifetimes of more than 4 mu s are achieved; these lifetimes are significantly longer than that of pristine CH3NH3PbI3-xClx films. Planar heterojunction solar cells incorporating these CH3I-mediated perovskites have demonstrated a dramatically increased power conversion efficiency compared to the ones using pristine CH3NH3PbI3-xClx. Photoluminescence, transient absorption, and microwave detected photoconductivity measurements all provide consistent evidence that CH3I addition increases the number of excitons generated and their diffusion length, both of which assist efficient carrier transport in the photovoltaic device. The simple incorporation of alkyl halide to enhance perovskite surface passivation introduces an important direction for future progress on high efficiency perovskite optoelectronic devices.
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| 7. |
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| 8. |
- Yuan, Feifei, et al.
(författare)
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Hydro Climatic Trend and Periodicity for the Source Region of the Yellow River
- 2015
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Ingår i: Journal of Hydrologic Engineering. - 1084-0699. ; 20:10
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Tidskriftsartikel (refereegranskat)abstract
- The hydrology of the Yellow River source region is expected to be affected by coming climate change. This will have repercussions for the 110million basin inhabitants. Consequently, precipitation, temperature, and streamflow trends and periodicities during the last 50years were investigated to identify significant changes in time and space over the study area. Results showed that mean annual temperature increased for all stations and it had an accelerated increasing trend during the last decade. Mean annual precipitation trends varied depending on the station; however, they were generally slightly decreasing. Annual streamflow decreased markedly, especially from the 1990s, but showed recovery during recent years. Statistically significant changes in trend occurred for temperature in 1998 and for streamflow in 1990. Based on the streamflow change point, seasonal analysis results showed that precipitation mainly decreased during the summer monsoon period (July-September) and temperature increased throughout the year. Corresponding to the weakened monsoon period the average runoff depth is decreasing by 0.74mm/year over the whole area. Statistically significant 2- to 4-year periodicities for mean areal precipitation and temperature occurred over the area. For streamflow, an even stronger 8-year periodicity was revealed from the end of the 1960s to the beginning of the 1990s. Frequency analysis investigated the magnitudes of mean annual precipitation and discharge corresponding to a given frequency. Hydroclimatic trends and linkages at each subbasin were investigated to further improve the understanding of observed streamflow changes. The investigated results have important implications for future water availability in the Yellow River source region.
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| 9. |
- Yuan, Feifei, et al.
(författare)
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Regional sea-surface temperatures explain spatial and temporal variation of summer precipitation in the source region of the Yellow River
- 2016
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Ingår i: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435. ; 61:8, s. 1383-1394
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Tidskriftsartikel (refereegranskat)abstract
- The summer precipitation (June–September) in the source region of the Yellow River accounts for about 70% of the annual total, playing an important role in water availability. This study divided the source region of the Yellow River into homogeneous zones based on precipitation variability using cluster analysis. Summer precipitation trends and teleconnections with global sea-surface temperatures (SST) and the Southern Oscillation Index (SOI) from 1961 to 2010 were investigated by Mann-Kendall test and Pearson product-moment correlation analysis. The results show that the northwest part (Zone 1) had a non-significantly increasing trend, and the middle and southeast parts (zones 2 and 3) that receive the most precipitation displayed a statistically significant decreasing trend for summer precipitation. The summer precipitation in the whole region showed statistically significant negative correlations with the central Pacific SST for 0–4 month lag and with the Southern Indian and Atlantic oceans SST for 5–8 month lag. Analyses of sub-regions reveal intricate and complex correlations with different SST areas that further explain the summer precipitation variability. The SOI had significant positive correlations, mainly for 0–2 months lag, with summer precipitation in the source region of the Yellow River. It is seen that El Niño Southern Oscillation (ENSO) events have an influence on summer precipitation, and the predominant negative correlations indicate that higher SST in equatorial Pacific areas corresponding to El Niño coincides with less summer precipitation in the source region of the Yellow River. Editor Z.W. Kundzewicz; Associate editor D. Gerten
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