| 1. |
- Hu, Zengyun, et al.
(författare)
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CCHZ-DISO: A Timely New Assessment System for Data Quality or Model Performance From Da Dao Zhi Jian
- 2022
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 49:23
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Tidskriftsartikel (refereegranskat)abstract
- With the rapid development of big data, assessment of data quality or model performance has become a hot scientific question. However, most existing lots of metrics focus on specific aspects of the assessment, and comprehensive assessment is rare. Therefore, it is very necessary to develop new assessment system. To address this problem, a new assessment system is constructed which is named after Chen, Chen, Hu, and Zhou (CCHZ)-distance between indices of simulation and observation (DISO) according to the contributions of Xi Chen, Deliang Chen, Zengyun Hu, and Qiming Zhou. CCHZ-DISO system builds on the Euclidean Distance and flexible determination of statistical metrics and their numbers. Due to its simplicity and flexibility, CCHZ-DISO can be readily and widely applied to any subject of science. Therefore, it follows the principle of the Chinese philosopher Lao Zi's Da Dao Zhi Jian which means that the most basic truth is very simple.
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| 2. |
- Hu, Zengyun, et al.
(författare)
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DISO: A rethink of Taylor diagram
- 2019
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418 .- 1097-0088. ; 39:5, s. 2825-2832
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Tidskriftsartikel (refereegranskat)abstract
- Climate models use quantitative methods to simulate the interactions of the important drivers of climate system, to reveal the corresponding physical mechanisms, and to project the future climate dynamics among atmosphere, oceans, land surface and ice, such as regional climate models and global climate models. A comprehensive assessment of these climate models is important to identify their different overall performances, such as the accuracy of the simulated temperature and precipitation against the observed field. However, until now, the comprehensive performances of these models have not been quantified by a comprehensive index except the existed single statistical index, such as correlation coefficient (r), absolute error (AE), and the root‐mean‐square error (RMSE). To address this issue, therefore, in this study, a new comprehensive index Distance between Indices of Simulation and Observation (DISO) is developed to describe the overall performances of different models against the observed field quantitatively. This new index DISO is a merge of different statistical metrics including r, AE, and RMSE according to the distance between the simulated model and observed field in a three‐dimension space coordinate system. From the relationship between AE, RMSE, and RMS difference (RMSD) (i.e., standard deviation [SD] of bias time series), the new index also has the information of RMSD which is the statistical index in Taylor diagram. An example is applied objectively to display the applications of DISO and Taylor diagram in identifying the overall performances of different simulated models. Overall, with the strong physical characteristic of the distance in three dimensional space and the strict mathematical proof, the new comprehensive index DISO can convey the performances among different models. It can be applied in the comparison between different model data and in tracking changes in their performances.
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| 3. |
- Hu, Zengyun, et al.
(författare)
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“Dry gets drier, wet gets wetter”: A case study over the arid regions of central Asia
- 2019
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418 .- 1097-0088. ; 39:2, s. 1072-1091
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Tidskriftsartikel (refereegranskat)abstract
- © 2018 Royal Meteorological Society The “dry gets drier, wet gets wetter” (DGDWGW) paradigm well describes the pattern of precipitation changes over the oceans. However, it has also been usually considered as a simplified pattern of regional changes in wet/dry under global warming, although GCMs mostly do not agree this pattern over land. To examine the validity of this paradigm over land and evaluate how usage of drought indices estimated from different hydrological variables affects detection of regional wet/dry trends, we take the arid regions of central Asia as a case study area and estimate the drying and wetting trends during the period of 1950–2015 based on multiple drought indices. These indices include the standardized precipitation index (SPI), the standardized precipitation evapotranspiration index (SPEI), the Palmer drought severity index (PDSI) and self-calibrating PDSI (sc_PDSI) with both the Thornthwaite (th) and Penman–Monteith (pm) equations in PDSI calculation (namely, PDSI_th, PDSI_pm, sc_PDSI_th and sc_PDSI_pm). The results show that there is an overall agreement among the indices in terms of inter-annual variation, especially for the PDSIs. All drought indices except SPI show a drying trend over the five states of central Asia (CAS5: including Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan). The four PDSIs and SPEI reveal a wetting tendency over the northwestern China (NW; including Xinjiang Uygur Autonomous Region and Hexi Corridor). The contrasting trends between CAS5 and NW can also be revealed in soil moisture (SM) variations. The nonlinear wet and dry variations are dominated by the 3–7 years oscillations for the indices. Relationships between the six indices and climate variables show the major drought drivers have regional features: with mean temperature (TMP), precipitation total (PRE) and potential evapotranspiration (PET) for CAS5, and PRE and PET for NW. Finally, our analyses indicate that the dry and wet variations are strongly correlated with the El Niño/Southern Oscillation (ENSO).
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| 4. |
- Li, Fusheng, 1985-, et al.
(författare)
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Electroless Plating of NiFeP Alloy on the Surface of Silicon Photoanode for Efficient Photoelectrochemical Water Oxidation
- 2020
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 12:10, s. 11479-11488
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Tidskriftsartikel (refereegranskat)abstract
- N- type silicon is a kind of semiconductor with a narrow band gap that has been reported as an outstanding light-harvesting material for photoelectrochemical (PEC) reactions. Decorating a thin catalyst layer on the n-type silicon surface can provide a direct and effective route toward PEC water oxidation. However, most of catalyst immobilization methods for reported n-type silicon photoanodes have been based on energetically demanding, time-consuming, and high-cost processes. Herein, a high-performance NiFeP alloy (NiFeP)-decorated n-type micro-pyramid silicon array (n-Si) photoanode (NiFeP/n-Si) was prepared by a fast and low-cost electroless deposition method for light-driven water oxidation reaction. The saturated photocurrent density of NiFeP/n-Si can reach up to similar to 40 mA cm(-2) and a photocurrent density of 15.5 mA cm(-2) can be achieved at 1.23 V-RHE under light illumination (100 mW cm(-2), AM1.5 filter), which is one of the most promising silicon-based photoanodes to date. The kinetic studies showed that the NiFeP on the silicon photoanodes could significantly decrease the interfacial charge recombination between the n-type silicon surface and electrolyte.
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| 5. |
- Liu, Huizeng, et al.
(författare)
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Estimating ultraviolet reflectance from visible bands in ocean colour remote sensing
- 2021
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Ingår i: Remote Sensing of Environment. - : Elsevier BV. - 0034-4257 .- 1879-0704. ; 258
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, ultraviolet (UV) bands have received increasing attention from the ocean colour remote sensing community, as they may contribute to improving atmospheric correction and inherent optical properties (IOPs) retrieval. However, most ocean colour satellite sensors do not have UV bands, and the accurate retrieval of UV remote sensing reflectance (Rrs) from UV satellite data is still a challenge. In order to address this problem, this study proposes a hybrid approach for estimating UV Rrs from the visible bands. The approach was implemented with two popular ocean colour satellite sensors, i.e. GCOM-C SGLI and Sentinel-3 OLCI. In situ Rrs collected globally and simulated Rrs spectra were used to develop UV Rrs retrieval models, and UV Rrs values at 360, 380 and 400 nm were estimated from visible Rrs spectra. The performances of the established models were evaluated using in situ Rrs and satellite data, and applied to a semi-analytical algorithm for IOPs retrieval. The results showed that: (i) UV Rrs retrieval models had low uncertainties with mean absolute percentage differences (MAPD) less than 5%; (ii) the model assessment with in situ Rrs showed high accuracy (r = 0.92–1.00 and MAPD = 1.11%–10.95%) in both clear open ocean and optically complex waters; (iii) the model assessment with satellite data indicated that model-estimated UV Rrs were more consistent with in situ values than satellite-derived UV Rrs; and (iv) model-estimated UV Rrs may improve the decomposition accuracy of absorption coefficients in semi-analytical IOPs algorithm. Thus, the proposed method has great potentials for reconstructing UV Rrs data and improving IOPs retrieval for historical satellite sensors, and might also be useful for UV-based atmospheric correction algorithms.
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| 6. |
- Liu, Huizeng, et al.
(författare)
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Evaluation of Ocean Color Atmospheric Correction Methods for Sentinel-3 OLCI Using Global Automatic In Situ Observations
- 2022
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Ingår i: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 60
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Tidskriftsartikel (refereegranskat)abstract
- The Ocean and Land Color Instrument (OLCI) on Sentinel-3 is one of the most advanced ocean color satellite sensors for aquatic environment monitoring. However, limited studies have been focused on a comprehensive assessment of atmospheric correction (AC) methods for OLCI. In an attempt to fill the gap, this study evaluated seven different AC methods for OLCI using global automatic in situ observations from Aerosol Robotic Network-Ocean Color (AERONET-OC). Results showed that the POLYnomial-based algorithm applied to MERIS (POLYMER) had the best performance for bands with wavelength ≤ 443 nm, and the SeaDAS method based on 779 and 865 nm was the best for longer spectral bands; however, SeaDAS (SeaWiFS Data Analysis System) processing algorithm based on 779 and 1020 nm, as well as 865 and 1020 nm, obtained degraded AC performance; Case 2 Regional CoastColor (C2RCC) also produced large uncertainties; Baseline AC (BAC) method might be better than SeaDAS method; and simple subtraction method was the worst except for turbid waters. POLYMER and C2RCC underestimated high remote sensing reflectance (Rrs) at red and green bands; SeaDAS method based on 779 and 865 nm held an advantage for clear waters over the other two band combinations, while their difference turned small for turbid waters. AC uncertainties generally impacted the performance of chlorophyll retrievals. POLYMER outperformed other methods for chlorophyll retrieval. This study provides a good reference for selecting a suitable AC method for aquatic environment monitoring with Sentinel-3 OLCI.
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| 7. |
- Ma, Shengyu, et al.
(författare)
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Metal–Molybdenum Sulfide Nanosheet Arrays Prepared by Anion Exchange as Catalysts for Hydrogen Evolution
- 2020
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Ingår i: Energy Technology. - : Wiley-VCH Verlag. - 2194-4288 .- 2194-4296. ; 8:10
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Tidskriftsartikel (refereegranskat)abstract
- Metal–molybdenum sulfide (MMoSx)-based catalysts exhibit good performance over a wide pH range toward hydrogen evolution with relatively low overvoltage requirements. Therefore, they are considered as suitable alternatives to Pt as catalysts for hydrogen evolution reaction. Herein, self-supported amorphous CuMoSx and NiMoSx nanosheet arrays are prepared on copper foam (CF) and nickel foam (NF), respectively, through an anion-exchange strategy. CF and NF are first converted into CuTCNQ and NiTCNQ nanowire arrays (TCNQ = tetracyanoquinodimethane), which are then in situ reacted with (NH4)2MoS4 solution to generate amorphous CuMoSx/CF and NiMoSx/NF nanosheets, respectively, as efficient electrocatalysts for H2 generation. NiMoSx/NF exhibits a superior catalytic activity to CuMoSx/CF in 0.5 m H2SO4 solution, as CuMoSx/CF requires overpotentials (η) of 213 and 275 mV to obtain current densities of 10 and 50 mA cm−2, respectively, whereas NiMoSx/NF only requires η of 174 and 248 mV to receive the same current densities, respectively. Furthermore, these electrodes exhibit considerable long-term electrochemical durability. Herein, an effective and easy-to-operate strategy for the construction of self-supported metal–molybdenum sulfide nanosheet arrays films toward a highly efficient electrochemical hydrogen generation reaction is provided.
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| 8. |
- Pilesjö, Petter, et al.
(författare)
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An integrated raster-tin surface flow algorithm
- 2008
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Ingår i: Lecture Notes in Geoinformation and Cartography. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 1863-2351 .- 1863-2246. - 9783540777991 - 9783540778004 ; :199049, s. 237-255
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Bokkapitel (refereegranskat)abstract
- In this chapter, an alternative surface flow algorithm is presented. The basic idea behind the algorithm is the use of the advantages of TIN-based algorithms within a raster based environment. A gridded raster DEM is used to create a ‘regular TIN’, over which surface flow is estimated. Since each facet in the TIN has a constant slope and slope direction, the estimations of, for example, flow velocity and diversion/convergence are less complicated compared to traditional ‘cell based’ solutions. The flow is treated as ‘water packages’, given specific (point) positions on the surface. The number of water packages per cell is initially set to eight, but this number can be increased or decreased. After each time step, the water packages have moved a certain distance (depending on slope and water depth), and new water packages have been created due to precipitation. In order to keep the number of water packages constant (to reduce memory and computer time), all water packages within a TIN facet are merged after each iteration. Parameters in time and space, e.g. precipitation, infiltration, vegetation and elevation, can all be loaded into the software.
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| 9. |
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| 10. |
- Zhou, Dinghua, et al.
(författare)
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In Situ Induced Crystalline-Amorphous Heterophase Junction by K+ to Improve Photoelectrochemical Water Oxidation of BiVO4
- 2021
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:2, s. 2723-2733
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Tidskriftsartikel (refereegranskat)abstract
- Solar water splitting is one of the most efficient technologies to produce H-2, which is a clean and renewable energy carrier. Photoanodes for water oxidation play the determining roles in solar water splitting, while its photoelectrochemical (PEC) performance is severely limited by the hole injection efficiency at the interface of semiconductor/electrolyte. To address this problem, in this research, by employing BiVO4 as the model semiconductor for photoanodes, we develop a novel, facile, and efficient method, which simply applies K cations in the preparation process of BiVO4 photoanodes, to in situ induce a crystalline-amorphous heterophase junction by the formation of an amorphous BiVO4 layer (a-BiVO4) on the surface of the crystalline BiVO4 (c-BiVO4) film for PEC water oxidation. The K cation is the key to stimulate the formation of the heterophase, but not incorporated in the final photoelectrodes. Without sacrificing the light absorption, the in situ formed a-BiVO4 layer accelerates the kinetics of the hole tranfer at the photoanode/electrolyte interface, leading to the significantly increased efficiency of the surface hole injection to water molecules. Consequently, the BiVO4 photoanode with the crystalline-amorphous heterophase junction (a-BiVO4/c-BiVO4) exhibits almost twice the photocurrent density at 1.23 V (vs reversible hydrogen electrode) for water oxidation than the bare c-BiVO4 ones. Such advantages from the crystalline-amorphous heterophase junction are still effective even when the a-BiVO4/c-BiVO4 is coated by the cocatalyst of FeOOH, reflecting its broad applications in PEC devices. We believe this study can supply an efficient and simple protocol to enhance the PEC water oxidation performance of photoanodes, and provide a new strategy for the potential large-scale application of the solar energy-conversion related devices.
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