| 1. |
- Shi, Feng, et al.
(författare)
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A multi-proxy reconstruction of spatial and temporal variations in Asian summer temperatures over the last millennium
- 2015
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Ingår i: Climatic Change. - : Springer Science and Business Media LLC. - 0165-0009 .- 1573-1480. ; 131:4, s. 663-674
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Tidskriftsartikel (refereegranskat)abstract
- To investigate climate variability in Asia during the last millennium, the spatial and temporal evolution of summer (June–July–August; JJA) temperature in eastern and south-central Asia is reconstructed using multi-proxy records and the regularized expectation maximization (RegEM) algorithm with truncated total least squares (TTLS), under a point-by-point regression (PPR) framework. The temperature index reconstructions show that the late 20th century was the warmest period in Asia over the past millennium. The temperature field reconstructions illustrate that temperatures in central, eastern, and southern China during the 11th and 13th centuries, and in western Asia during the 12th century, were significantly higher than those in other regions, and comparable to levels in the 20th century. Except for the most recent warming, all identified warm events showed distinct regional expressions and none were uniform over the entire reconstruction area. The main finding of the study is that spatial temperature patterns have, on centennial time-scales, varied greatly over the last millennium. Moreover, seven climate model simulations, from the Coupled Model Intercomparison Project Phase 5 (CMIP5), over the same region of Asia, are all consistent with the temperature index reconstruction at the 99 % confidence level. Only spatial temperature patterns extracted as the first empirical orthogonal function (EOF) from the GISS-E2-R and MPI-ESM-P model simulations are significant and consistent with the temperature field reconstruction over the past millennium in Asia at the 90 % confidence level. This indicates that both the reconstruction and the simulations depict the temporal climate variability well over the past millennium. However, the spatial simulation or reconstruction capability of climate variability over the past millennium could be still limited. For reconstruction, some grid points do not pass validation tests and reveal the need for more proxies with high temporal resolution, accurate dating, and sensitive temperature signals, especially in central Asia and before AD 1400.
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| 2. |
- Shi, Feng, et al.
(författare)
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Multi-proxy reconstruction of Arctic summer temperatures over the past 1400 years
- 2012
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Ingår i: Climate Research (CR). - : Inter-Research Science Center. - 0936-577X .- 1616-1572. ; 54:2, s. 113-128
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Tidskriftsartikel (refereegranskat)abstract
- A new multi-proxy summer (June–August) temperature reconstruction for the Arctic region (60°N–90°N) with annual resolution over the past 1400 years is presented. The reconstruction is performed using a novel ensemble method, Ensemble-LOC, designed to preserve low-frequency variability and minimize the influence of the “spurious correlation” between the proxy and instrumental data. The reconstruction is based on a set of 22 proxy records with annual resolution. We find clear evidences for a cold anomaly c. AD 630–770 related to the Dark Age Cold Period, a warm anomaly c. 950–1050 related to the Medieval Climate Anomaly, and a cold anomaly c. AD 1200–1900 related to the Little Ice Age. The strong 20th century warming is also evident. There are three different and distinct warm periods occurring during the Little Ice Age: AD 1470–1510, AD 1550–1570, and AD 1750–1770. However, about half of the total input proxies are not used in the large majority of the reconstructions. We still need additional proxy records from the Arctic region with annual resolution and a strong response to local temperature to further verify the results of this study and in order to investigate possible spatial patterns of past Arctic temperature variability.
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| 3. |
- Sendeku, Marshet Getaye, et al.
(författare)
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Frontiers in Photoelectrochemical Catalysis: A Focus on Valuable Product Synthesis
- 2024
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Ingår i: Advanced Materials. - : John Wiley & Sons. - 0935-9648 .- 1521-4095. ; 36:21
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Forskningsöversikt (refereegranskat)abstract
- Photoelectrochemical (PEC) catalysis provides the most promising avenue for producing value-added chemicals and consumables from renewable precursors. Over the last decades, PEC catalysis, including reduction of renewable feedstock, oxidation of organics, and activation and functionalization of C─C and C─H bonds, are extensively investigated, opening new opportunities for employing the technology in upgrading readily available resources. However, several challenges still remain unsolved, hindering the commercialization of the process. This review offers an overview of PEC catalysis targeted at the synthesis of high-value chemicals from sustainable precursors. First, the fundamentals of evaluating PEC reactions in the context of value-added product synthesis at both anode and cathode are recalled. Then, the common photoelectrode fabrication methods that have been employed to produce thin-film photoelectrodes are highlighted. Next, the advancements are systematically reviewed and discussed in the PEC conversion of various feedstocks to produce highly valued chemicals. Finally, the challenges and prospects in the field are presented. This review aims at facilitating further development of PEC technology for upgrading several renewable precursors to value-added products and other pharmaceuticals.
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| 4. |
- Yang, Fengmei, et al.
(författare)
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Li2FePO4F and its metal-doping for Li-ion batteries : an ab initio study
- 2014
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:91, s. 50195-50201
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Tidskriftsartikel (refereegranskat)abstract
- The electrochemical properties of three isotopic Li2FePO4F compounds, as cathode materials under different space groups Pbcn, P (1) over bar and Pnma were investigated using first principle calculations. Their structures and average open circuit voltages for step delithiation reactions were explored, and the results are in good agreement with the reported experimental data. We estimate the substitution effect of Fe by Co in Pnma-Li2FePO4F. The substitution of Fe by Co in Li2Fe1-xCoxPO4F may enhance the discharge potential of the materials, and the rate of its volume change during the redox process is between 0.6% and 2.1%. Furthermore, from the projected density of states for Li2Fe0.5Co0.5PO4F, we found strong hybridization for Fe-3d and Co-3d bands near the Fermi level, which implies that the Co-doped Li2Fe1-xCoxPO4F may possess better electronic conductivity than the pure phase.
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| 5. |
- Yang, Fengmei, et al.
(författare)
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Multi-Proxy Temperature Reconstruction from the West Qinling Mountains, China, for the Past 500 Years
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:2, s. e57638-
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Tidskriftsartikel (refereegranskat)abstract
- A total of 290 tree-ring samples, collected from six sites in the West Qinling Mountains of China, were used to develop six new standard tree-ring chronologies. In addition, 73 proxy records were assembled in collaboration with Chinese and international scholars, from 27 publically available proxy records and 40 tree-ring chronologies that are not available in public datasets. These records were used to reconstruct annual mean temperature variability in the West Qinling Mountains over the past 500 years (AD 1500–1995), using a modified point-by-point regression (hybrid PPR) method. The results demonstrate that the hybrid PPR method successfully integrates the temperature signals from different types of proxies, and that the method preserves a high degree of low-frequency variability. The reconstruction shows greater temperature variability in the West Qinling Mountains than has been found in previous studies. Our temperature reconstruction for this region shows: 1) five distinct cold periods, at approximately AD 1520–1535, AD 1560–1575, AD 1610–1620, AD 1850–1875 and AD 1965–1985, and four warm periods, at approximately AD 1645–1660, AD 1705–1725, AD 1785–1795 and AD 1920–1945; 2) that in this region, the 20th century was not the warmest period of the past 500 years; and 3) that a dominant and persistent oscillation of ca. 64 years is significantly identified in the 1640–1790 period.
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| 6. |
- Yang, Fengmei, et al.
(författare)
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The spatial distribution of precipitation over the West Qinling region, China, AD 1470–2000
- 2016
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 443, s. 278-285
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Tidskriftsartikel (refereegranskat)abstract
- The West Qinling Mountains form part of the climatic barrier that separates southern and northern China, and are located at the edge of the region dominated by the Asian summer monsoon. To investigate the spatial distribution of regional hydroclimatic variability in the West Qinling region, the annually resolved spatial field of rainy season (May–June–July–August–September, MJJAS) precipitation anomalies from AD 1470 to 2000 was reconstructed using 39 tree-ring chronologies, as well as 28 dryness/wetness indices derived from historical documentary data. The results indicate that the El Niño–Southern Oscillation (ENSO) and the Tropospheric Biennial Oscillation (TBO) may jointly affect the spatial pattern of precipitation over the West Qinling Mountains at inter-annual timescales. The drought in the 1990s was found to exceed the amplitude and duration of all other periods of drought that have occurred since AD 1470 in this region. The new precipitation field reconstruction assesses the spatial pattern of historical hydroclimatic variability in the West Qinling region and provides an opportunity to test the performance of climate models in simulating regional precipitation variability and change.
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