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  • 1
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    Storm-time evolution of ELF/VLF waves observed by DEMETER satellite (2014)
    Wiley-Blackwell
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    Publication Date: 2014-03-21
    Description: In this paper, using the data of sunsynchronous satellite DEMETER, we investigated the storm-time variations of ELF/VLF waves during the intense CME-driven storms from 2005 to 2009. The results show that there is a good correlation between the enhancement of ELF/VLF waves and the CME events. Immidately following the enhanced wave activity driven by CMEs during the initial phase, the wave intensity decreases temporarily at the beginning of storm main phase. The strongest waves predominantly occur from the late main phase to early recovery phase. The ELF waves below 3 kHz are significantly intensified during the whole storm time, while the high-frequency waves above 3 kHz seem strengthened only during the late main and early recovery phase. The ELF waves below 3 kHz can exist in a wide L-shell range, with the intensity peaking at L ~ 3-4. High-frequency waves at f  〉 9 kHz exist mostly outside the plasmapause. The stronger ELF/VLF waves on the dayside can last longer time than those on the nightside.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 2
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    Increased precipitation and weathering across the Paleocene-Eocene thermal maximum in central China (2016)
    Wiley-Blackwell
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    Publication Date: 2016-05-22
    Description: Global warming during the Paleocene-Eocene Thermal Maximum (PETM) ∼55.5 million years ago (Ma) was associated with a massive release of carbon to the ocean-atmosphere system, as evidenced by a prominent negative carbon isotope excursion (CIE) and widespread dissolution of marine carbonates. The paleohydrologic response to the PETM warming has been studied worldwide; however, relevant records of environmental perturbation in Asia are lacking so far. Here we extend the record of this event in central China, a subtropical paleosetting, through geochemical and mineralogical analyses of lacustrine sediments. Geochemical indicators of authigenic carbonates – including molar Mg/Ca and Sr/Ca ratios – suggest an overall increased precipitation across the PETM, compatible with the disappearance of authigenic dolomite and the appearance of kaolinite in the strata. The relatively humid conditions persisted long after the carbon-cycle perturbation had stopped, implying that the transient hyper-greenhouse warming might have forced the regional climate system into a new climate state that was not easily reversed. Additionally, a gradual increase in chemical index of alteration (CIA) and the appearance of kaolinite are associated with the PETM, indicating an intensified silicate weathering and pedogenesis in the watershed in response to warmer and more humid climate. Our results corroborate the theory that an accelerated continental chemical weathering served as a negative feedback to sequester carbon and lower the atmospheric greenhouse-gas levels during the PETM. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 3
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    Influence of fracture extension on in-situ stress in tight reservoir (2018)
    Institute of Physics (IOP)
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    Publication Date: 2018-01-31
    Description: Currently, hydraulic fracturing is an important way to develop low permeability reservoirs. The fractures produced during the fracturing process are the main influencing factors of changing in-situ stress. In this paper, the influence of fracture extension on in-situ stress is studied by establishing a mathematical model to describe the relationship between fracture length and in-situ stress. The results show that the growth rate gradually decreases after the fracture reaches a certain length with the increase of fracturing time; the continuous extension of the fracture is the main factor to change the in-situ stress. In order to reduce the impact on the subsequent fracture extension due to the changing of in-situ stress, controlling fracturing time and fracture length without affecting the stimulated reservoir effect is an important way. The results presented in this study can effectively reduce the impact of changing of in-situ stress on subsequent fracturing construction.
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
    Published by Institute of Physics (IOP)
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  • 4
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    Suppression Methods for Low Frequency Oscillation of Wind Farm Considering SVG Minimum Output Dead Zone (2018)
    Institute of Physics (IOP)
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    Publication Date: 2018-11-06
    Description: At present, the research of Static Var Generator (SVG) mainly focuses on the main circuit topology, the optimization of control strategy, the method of selection, and lack of research on the low frequency oscillation of the wind farm caused by SVG minimum reactive output dead zone in practical engineering applications. For this reason, this paper first studies the mechanism of the low frequency oscillation of the wind electric field induced by the SVG minimum output dead zone of the wind farm, and discusses the conditions of this type of oscillation. On this basis, the automatic voltage control system (AVC) optimization model of wind farm is established with the minimum reactive variation of SVG output near the zero point as the optimization goal, and an optimization control strategy of wind farm with SVG minimum output reactive dead zone is proposed. Finally, the correctness of the result is verified by simulation. The results show that, due to the existence of the minimum outp...
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
    Published by Institute of Physics (IOP)
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  • 5
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    Geosciences, Vol. 8, Pages 222: Potential Indicator Value of Subfossil Gastropods in Assessing the Ecological Health of the Middle and Lower Reaches of the Yangtze River Floodplain System (China) (2018)
    MDPI Publishing
    Details
    Publication Date: 2018-06-18
    Description: Geosciences, Vol. 8, Pages 222: Potential Indicator Value of Subfossil Gastropods in Assessing the Ecological Health of the Middle and Lower Reaches of the Yangtze River Floodplain System (China) Geosciences doi: 10.3390/geosciences8060222 Authors: Giri Kattel Yongjiu Cai Xiangdong Yang Ke Zhang Xu Hao Rong Wang Xuhui Dong The lakes across China’s middle and lower reaches of the Yangtze River system have a long history of sustaining human pressures. These aquatic resources have been exploited for fisheries and irrigation over millennia at a magnitude of scales, with the result that many lakes have lost their ecological integrity. The consequences of these changes in the ecosystem health of lakes are not fully understood; therefore, a long-term investigation is urgently needed. Gastropods (aquatic snails) are powerful bio-indicators that link primary producers, herbivores, and detritivores associated with macrophytes and grazers of periphyton and higher-level consumers. They are sensitive to abrupt environmental change such as eutrophication, dehydration, flooding, and proliferation of toxicity in floodplain lake systems. The use of the remains of gastropod shells (subfossils) preserved in the sedimentary archives of the floodplain lakes of the middle and lower reaches of the Yangtze River system holds high significance, as their potential in environmental change has not been studied in detail in the past. Here, we aim to test the hypothesis that modern and sub-fossil gastropods in the sediments of the middle and lower reaches of the Yangtze River floodplains systems have significant value as bioindicators, as they have the ability to reveal health-gradients of lake-ecosystem change in the region.
    Electronic ISSN: 2076-3263
    Topics: Geosciences
    Published by MDPI Publishing
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  • 6
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    Whistler-mode wave generation at the edges of a magnetic dip structure (2015)
    Wiley-Blackwell
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    Publication Date: 2015-03-04
    Description: On 18 May 2011, the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite observed whistler-mode waves associated with a magnetic dip behind a dipolarization front (DF) structure in the bursty bulk flow (BBF) braking region. For the first time, we find that whistler-mode waves are generated at the edges of magnetic dip, rather than at the center (also known as “minimum- B -pocket”). Detailed wave analysis indicates that the waves are likely lower and upper band whistler-mode chorus. We examine electron pitch angle distributions at the edges of dip, and compare them with those at the center and far outside the magnetic dip. Results confirm that the positive temperature anisotropy and pancake distributions at the edges of magnetic dip provide free energy source for growth of the whistler-mode waves. We also interpret the whole physical process of how whistler-mode waves generate in this event.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 7
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    Crystallographic studies of SarV, a global regulator from Staphylococcus aureus (2015)
    Wiley-Blackwell
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    Publication Date: 2015-08-08
    Description: SarV, a member of the SarA protein family, is a global transcriptional regulator which has been reported to be involved in the regulation of autolysis in Staphylococcus aureus . In this study, SarV from S. aureus was successfully cloned, expressed, purified and crystallized. X-ray diffraction data were collected to 2.10 Å resolution. The crystals of SarV belonged to the monoclinic space group P 2 1 , with unit-cell parameters a = 36.40, b = 119.64, c = 66.80 Å, α = γ = 90, β = 98.75°. The Matthews coefficient and the solvent content were estimated to be 2.57 Å 3  Da −1 and 52%, respectively, suggesting the presence of four molecules in the asymmetric unit. The results of size-exclusion chromatography (SEC) indicated that S. aureus SarV exists as a homodimer in solution. Unfortunately, the structure cannot be solved by molecular replacement because of the low sequence identity of S. aureus SarV to known structures. Further phase determination by selenomethionine single-wavelength anomalous dispersion (SAD) and the heavy-atom method is in progress.
    Electronic ISSN: 1744-3091
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley-Blackwell on behalf of International Union of Crystallography (IUCr).
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  • 8
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    The Unit Commitment Model and Analysis for Promoting Clean Energy Consumption with Considering of Tie Line Plan Adjustment (2018)
    Institute of Physics (IOP)
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    Publication Date: 2018-11-06
    Description: In recent years, China’s clean energy has developed rapidly. The development level of clean energy does not match the local power consumption, resulting in a large number of abandoned winds and abandoned light. With the gradual completion of the UHV network, the transmission capacity between regions has been rapidly enhanced, providing a broad space for optimizing the allocation of resources across a wide range of areas and improving the level of clean energy consumption. In order to cope with the problem of difficult local consumption in clean energy delivery areas and current cross-regional power delivery methods, this paper considers the factors of the adjustment of the tie line plan and increases the consumption of new energy through more reasonable tie line planning based on the traditional unit commitment algorithm. A case study shows that the model proposed in this paper can promote cross-regional consumption of clean energy and improve the economics of the interconnected...
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
    Published by Institute of Physics (IOP)
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