| 641. |
- Li, Xueying, et al.
(författare)
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Triple collocation-based merging of multi-source gridded evapotranspiration data in the Nordic Region
- 2023
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Ingår i: Agricultural and Forest Meteorology. - 1873-2240. ; 335
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Tidskriftsartikel (refereegranskat)abstract
- Accurate evapotranspiration (ET) data are required for many hydro-meteorological applications. Compared with the traditional evaluation that requires in-situ measurements, the triple collocation (TC) technique estimates geophysical product errors without the need for ground truth, which is especially suitable over large areas lacking a dense in-situ network. However, violations of the zero-error cross-correlation (ECC) assumption are found to be the dominant sources of impairing the TC robustness. This study presents the first application of a TC-based merging framework that optimally considers ECC to merge multi-source gridded ET products in the Nordic Region during 2003–2018. The ECC estimates of each ET dataset pair calculated by the quadruple collocation approach are used to select the qualified triplets from four products, including FLUXCOM, Global Land Surface Satellite (GLASS), Global Land Evaporation and Amsterdam Model (GLEAM), and Penman-Monteith-Leuning Version 2 (PML-V2). Then the ET merged datasets are generated by weighting TC-based rescaled error variances of the parent datasets through least square merging. Finally, the accuracy of both the parent and the merged datasets are assessed with the Integrated Carbon Observation System (ICOS) flux data in the Nordic Region based on multiple statistical metrics. Results demonstrate that the ECC values provide intuitive evidence for filtering unqualified TC triplets. Both the absolute and relative error variances (signal-to-noise ratio) are considered for ET dataset evaluation. Overall PML-V2 has the best performance among the evaluated four products. Two merged ET datasets with the reference climatology of FLUXCOM outperform all parent products with the lowest errors by using ICOS data as reference among all sites – indicating the feasibility of TC technique for improving ET accuracy in the Nordic Region. This study also analyses the impacts of reference climatology selection on the TC merged results.
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| 642. |
- Li, Yuling, et al.
(författare)
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Composite Adaptive Control for Bilateral Teleoperation Systems without Persistency of Excitation
- 2020
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Ingår i: Journal of the Franklin Institute. - : Elsevier BV. - 0016-0032. ; 357:2, s. 773-795
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Tidskriftsartikel (refereegranskat)abstract
- Composite adaptive control schemes, which use both the system tracking error and the prediction error to drive the updating law, have become widespread in achieving an improvement of system performance. However, a strong persistent-excitation (PE) condition is required to guarantee the convergence of the parameter estimation errors. This paper proposes a novel composite adaptive control for nonlinear teleoperation systems with dynamic uncertainties and time-varying communication delays, by which the parameter convergence is achieved without the PE condition. The novelty lies in the construction of the prediction errors by designing lower-bounded gain matrices of the prediction errors. The stability criteria of the closed-loop teleoperation system are given in terms of linear matrix inequalities. Simulation studies are given to show the effectiveness of the proposed method.
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| 643. |
- Li, Y. J., et al.
(författare)
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Growth decline of Pinus Massoniana in response to warming induced drought and increasing intrinsic water use efficiency in humid subtropical China
- 2019
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Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865. ; 57:October
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Tidskriftsartikel (refereegranskat)abstract
- Pinus Massoniana is the most widely distributed coniferous species in southern China and one of the most distributed species for plantation in China. It is not uncertain about the responses of tree growth to the combined effects of regional drying and the increase in the intrinsic water-use efficiency (iWUE) due to increased atmospheric CO2. This study addressed this issue by comparing the tree growth patterns as represented by three tree-ring width chronologies with climate variables and three iWUE series derived from three tree-ring stable carbon isotope discrimination chronologies (Delta C-13) from Pinus Massoniana in Daiyun Mountain, central Fujian province of China. Among these chronologies, we reported the first tree-ring carbon isotope discrimination chronologies (Delta C-13) from Fuzhou area spanning last 210 years. It was found that tree radial growth is mainly limited by dry condition from May to October. Growth limitation by cold condition was only found in one high altitude site (780m) in early spring and late autumn. The tree-ring carbon discrimination was enhanced under conditions with low relative humidity and sufficient sunshine in late summer and autumn. In general, the iWUE showed a significantly increasing trend since the 1850s for all the sites in response to the increase in atmospheric CO2. However, the growth promotion of the increased iWUE on tree growth could not compensate the growth limitation caused by drought. Especially since the 1960s, a growth decline was found at two drought stressed sites at low altitudes. On the other hand, the increase in temperature of spring and autumn and iWUE has most likely enhanced tree growth at the high altitude site.
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| 644. |
- Li, Yong Qiang, et al.
(författare)
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Carbonation of the synthetic calcium silicate hydrate (C-S-H) under different concentrations of CO2: Chemical phases analysis and kinetics
- 2020
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Ingår i: Journal of CO2 Utilization. - : Elsevier BV. - 2212-9820. ; 35, s. 303-313
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the chemical phases analysis and the kinetics of synthetic calcium silicate hydrate (C-S-H) under differentCO2concentrations (natural (0.03%), 3%, 10%, 20%, 50%, 100%) were investigated. For this aim, the scanning electron microscope (SEM) and transmission electron microscope (TEM) were employed for microstructure characterisation. The 29Si magic angle spinning nuclear magnetic resonance (29Si MAS NMR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) coupled with mass spectrometer (MS) were used for characterising the chemical phases before and after carbonation. From the NMR results, it was found that C-S-H would be partly decalcified under the natural condition but completely under the accelerated conditions. Two equations related to the carbonation kinetics under natural and accelerated conditions were proposed respectively. The compositions in decalcified C-S-H were not affected by the CO2 concentration. The XRD analysis showed that vaterite, aragonite and calcite were coexistent after carbonation, which would be transformed to aragonite and calcite with further carbonation. The preferential formation of the allotropic calcium carbonate was not impacted by the concentration of CO2 either. Based on the TGA-MS test, the stoichiometric formula of synthetic C-S-H was determined with CaOâ'™SiO2â'™0.87H2O or Câ Sâ H0.87. In addition, a carbonation kinetics model was proposed to learn the carbonation kinetics of C-S-H carbonated in different CO2 concentrations. The experimental data fitted well with the model. The carbonation kinetics between 3% and 20% CO2 are similar, but different from that under 50% and 100% CO2
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| 645. |
- Li, Zuxing, et al.
(författare)
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A Game Theoretic Analysis of LQG Control under Adversarial Attack
- 2020
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Ingår i: 2020 59th IEEE Conference on Decision and Control (CDC). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 1632-1639
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Konferensbidrag (refereegranskat)abstract
- Motivated by recent works addressing adversarial attacks on deep reinforcement learning, a deception attack on linear quadratic Gaussian control is studied in this paper. In the considered attack model, the adversary can manipulate the observation of the agent subject to a mutual information constraint. The adversarial problem is formulated as a novel dynamic cheap talk game to capture the strategic interaction between the adversary and the agent, the asymmetry of information availability, and the system dynamics. Necessary and sufficient conditions are provided for subgame perfect equilibria to exist in pure strategies and in behavioral strategies; and characteristics of the equilibria and the resulting control rewards are given. The results show that pure strategy equilibria are informative, while only babbling equilibria exist in behavioral strategies. Numerical results are shown to illustrate the impact of strategic adversarial interaction.
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| 646. |
- Li, Zhenzhen, et al.
(författare)
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Endogenous Sulfur Dioxide Inhibits Vascular Calcification in Association with the TGF-beta/Smad Signaling Pathway
- 2016
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Ingår i: International Journal of Molecular Sciences. - : MDPI AG. - 1661-6596 .- 1422-0067. ; 17:3
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Tidskriftsartikel (refereegranskat)abstract
- The study was designed to investigate whether endogenous sulfur dioxide (SO2) plays a role in vascular calcification (VC) in rats and its possible mechanisms. In vivo medial vascular calcification was induced in rats by vitamin D3 and nicotine for four weeks. In vitro calcification of cultured A7r5 vascular smooth muscle cells (VSMCs) was induced by calcifying media containing 5 mmol/L CaCl2. Aortic smooth muscle (SM) alpha-actin, runt-related transcription factor 2 (Runx2), transforming growth factor-beta (TGF-beta) and Smad expression was measured. VC rats showed dispersed calcified nodules among the elastic fibers in calcified aorta with increased aortic calcium content and alkaline phosphatase (ALP) activity. SM alpha-actin was markedly decreased, but the osteochondrogenic marker Runx2 concomitantly increased and TGF-beta/Smad signaling was activated, in association with the downregulated SO2/aspartate aminotransferase (AAT) pathway. However, SO2 supplementation successfully ameliorated vascular calcification, and increased SM alpha-actin expression, but inhibited Runx2 and TGF-beta/Smad expression. In calcified A7r5 VSMCs, the endogenous SO2/AAT pathway was significantly downregulated. SO2 treatment reduced the calcium deposits, calcium content, ALP activity and Runx2 expression and downregulated the TGF-beta/Smad pathway in A7r5 cells but increased SM alpha-actin expression. In brief, SO2 significantly ameliorated vascular calcification in association with downregulation of the TGF-beta/Smad pathway.
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| 647. |
- Li, Zhao, et al.
(författare)
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Non-uniform seasonal warming regulates vegetation greening and atmospheric CO2 amplification over northern lands
- 2018
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 13:12
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Tidskriftsartikel (refereegranskat)abstract
- The enhanced vegetation growth by climate warming plays a pivotal role in amplifying the seasonal cycle of atmospheric CO2 at northern lands (>50° N) since 1960s. However, the correlation between vegetation growth, temperature and seasonal amplitude of atmospheric CO2 concentration have become elusive with the slowed increasing trend of vegetation growth and weakened temperature control on CO2 uptake since late 1990s. Here, based on in situ atmospheric CO2 concentration records from the Barrow observatory site, we found a slowdown in the increasing trend of the atmospheric CO2 amplitude from 1990s to mid-2000s. This phenomenon was associated with the paused decrease in the minimum CO2 concentration ([CO2]min), which was significantly correlated with the slowdown of vegetation greening and growing-season length extension. We then showed that both the vegetation greenness and growing-season length were positively correlated with spring but not autumn temperature over the northern lands. Furthermore, such asymmetric dependences of vegetation growth upon spring and autumn temperature cannot be captured by the state-of-art terrestrial biosphere models. These findings indicate that the responses of vegetation growth to spring and autumn warming are asymmetric, and highlight the need of improving autumn phenology in the models for predicting seasonal cycle of atmospheric CO2 concentration.
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| 648. |
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| 649. |
- Lin, Y. B., et al.
(författare)
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Energy-effectively printed all-polymer solar cells exceeding 8.61% efficiency
- 2018
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Ingår i: Nano Energy. - : Elsevier BV. - 2211-2855. ; 46, s. 428-435
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Tidskriftsartikel (refereegranskat)abstract
- All-polymer solar cells (all-PSCs) have attracted tremendous attention in the past few years due to their unique advantages. However, up to now most of high-efficiency all-PSCs are processed by spin-coating with complicated post treatment processes, which is ill-suited to a large-area roll-to-roll (R2R) technique. In this work, high-efficiency all-PSCs based on PTB7-Th and PNDI-T10 are achieved by one of R2R compatible printing techniques, i.e. doctor-blading, without any annealing treatment. It was found that incorporating an additive into all polymer blends solution can prolong the drying time of all polymer nanocomposites from 120 to 1000 s to form a better bulk heterojunction morphology and a higher crystallinity, which thus reduce charge recombination and show much better electrical impedance spectroscopy parameters. Record-breaking power conversion efficiencies (PCEs) of 8.61% and high fill factors (FF) of 0.71 are achieved by doctor-blading under an extremely process-simple and energy-effective conditions. Moreover, large-area (2.03 cm 2 ) flexible ITO-free all-PSCs by doctor-blading with record-breaking PCEs of 6.65% and FF of 0.65 are realized, which are much higher than conventional fullerene-based ones under the same condition, demonstrating that all-PSCs are more suitable for the flexible device structure and have a bright future towards practical application with R2R manufacture.
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| 650. |
- Liu, Bingbing, et al.
(författare)
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Effects of silver films with different nano-particle sizes on SERS of single-walled carbon nanotubes
- 2005
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Ingår i: Chemical Journal of the Chinese Universities. - 0251-0790. ; 26:10, s. 1930-1933
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Tidskriftsartikel (refereegranskat)abstract
- Surface-enhanced Raman scattering (SERS) spectra of single-walled carbon nanotubes (SWCNTs) on silver films with different nano-particle sizes from 20 to 100 nm deposited on quartz and glass substrates were studied systematically. The characteristic Raman spectral features of SWCNT G-band and D-band were analyzed. The two bands show a similar tendency with the change of nano-particle size of silver on quartz and glass substrates. The position and the intensity of the G-band are less sensitive to the films' silver particle sizes in the studied range, indicating that hexagonal carbon rings are stable and have a weak interaction with silver films. The shape of the D-band depends on the silver size. The smaller the silver particle size, the more the contribution of high frequency vibrations to the D-band, indicating that disorder carbon has a strong interaction with the active silver films.
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