60 research outputs found

    Tetrakis(N-heterocyclic carbene)-diboron(0): double single-electron-transfer reactivity

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    The use of 1,3,4,5-tetramethylimidazol-2-ylidene (IMe) to coordinate with diatomic B2 species afforded a tetrakis(N-heterocyclic carbene)-diboron(0) [(IMe)2B-B(IMe)2] (2). The singly bonded B2 moiety therein possesses a valence electronic configuration 1σg21πu21πg*2 with four vacant molecular orbitals (1σu*, 2σg, 1πu', 1πg'*) coordinated with IMe. Its unprecedented electronic structure is analogous to the energetically unfavorable planar hydrazine with a D2h symmetry. The two highly reactive πg* antibonding electrons enable double single-electron-transfer (SET) reactivity in small-molecule activation. Compound 2 underwent a double SET reduction with CO2 to form two carbon dioxide radical anions CO2•-, which then reduced pyridine to yield a carboxylated pyridine reductive coupling dianion [O2CNC5(H)5-C5(H)5NCO2]2- and converted compound 2 to the tetrakis(N-heterocyclic carbene)-diborene dication [(IMe)2B═B(IMe)2]2+ (32+). This is a remarkable transition-metal-free SET reduction of CO2 without ultraviolet/visible (UV/vis) light conditions.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)This work was supported by the Ministry of Education Singapore, AcRF Tier 2 (MOE2019-T2-2-129) and A*STAR MTC Individual Research Grants (M21K2c0117) (C.-W.S.). M.-C. Yang and M.-D.S. acknowledge the Ministry of Science and Technology of Taiwan for the financial support

    Long-time asymptotic analysis for defocusing Ablowitz-Ladik system with initial value in lower regularity

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    Recently, we have given the l2l^2 bijectivity for defocusing Ablowitz-Ladik systems in the discrete Sobolev space l2,1l^{2,1} by inverse spectral method. Based on these results, the goal of this article is to investigate the long-time asymptotic property for the initial-valued problem of the defocusing Ablowitz-Ladik system with initial potential in lower regularity. The main idea is to perform proper deformations and analysis to the corespondent Riemann-Hilbert problem with the unit circle as the jump contour Σ\Sigma. As a result, we show that when n2t1<1|\frac{n}{2t}|\le 1<1, the solution admits Zakharov-Manakov type formula, and when n2t1>1|\frac{n}{2t}|\ge 1>1, the solution decays fast to zero

    Kinetic Analysis of Isothermal and Non-Isothermal Reduction of Iron Ore Fines in Hydrogen Atmosphere

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    Direct reduction of iron ore with H2 has become an alternative technology for iron production that reduces pollutant emissions. The reduction kinetics of iron ore fines in an H2 atmosphere under isothermal and non-isothermal conditions were studied by thermogravimetric analysis. X-ray diffraction and scanning electron microscopy were used to measure the mineral composition and analyse the morphology of the reduced fines, respectively. In the isothermal reduction experiment, it was found that the final reduction time was shorter, the higher the temperature, and the metallic iron particles formed a dense matrix structure. It is likely that the initial stages reduction process is the result of a combination of gaseous diffusion and interfacial chemical reaction mechanisms, and that the later stages a combination of interfacial chemical reaction and solid diffusion is the rate control mechanism. In the non-isothermal experiment, the heating rate had a significant effect on the reaction rate. The results show that the non-isothermal reduction proceeded through three stages: mixing control model, two-dimensional diffusion, and three-dimensional diffusion

    Shallow Sea Topography Detection from Multi-Source SAR Satellites: A Case Study of Dazhou Island in China

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    Accurate measurement of underwater topography in the coastal zone is essential for human marine activities, and the synthetic aperture radar (SAR) presents a completely new solution. However, underwater topography detection using a single SAR image is vulnerable to the interference of sea state and sensor noise, which reduces the detection accuracy. A new underwater topography detection method based on multi-source SAR (MSSTD) was proposed in this study to improve the detection precision. GF-3, Sentinel-1, ALOS PALSAR, and ENVISAT ASAR data were used to verify the sea area of Dazhou Island. The detection result was in good agreement with the chart data (MAE of 2.9 m and correlation coefficient of 0.93), and the detection accuracy was improved over that of a single SAR image. GF-3 image with 3 m spatial resolution performed best in bathymetry among the four SAR images. Additionally, the resolution of the SAR image had greater influence on bathymetry compared with polarization and radar band. The ability of MSSTD has been proved in our work. Collaborative multi-source satellite observation is a feasible and effective scheme in marine research, but its application potential in underwater topography detection still requires further exploration

    Incremental capacity curve health-indicator extraction based on gaussian filter and improved relevance vector machine for lithium–ion battery remaining useful life estimation.

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    Accurate prediction of the remaining useful life (RUL) of lithium–ion batteries is the focus of lithium–ion battery health management. To achieve high–precision RUL estimation of lithium–ion batteries, a novel RUL prediction model is proposed by combining the extraction of health indicators based on incremental capacity curve (IC) and the method of improved adaptive relevance vector machine (RVM). First, the IC curve is extracted based on the charging current and voltage data. To attenuate the noise effects on the IC curve, Gaussian filtering is used and the optimal filtering window is determined to remove the noise interference. Based on this, the peak characteristics of the IC curve are analyzed and four groups of health indicators are extracted, and the strong correlation between health indicators and capacity degradation is determined using Pearson correlation analysis. Then, to optimize the traditional fixed kernel parameter RVM model, an RVM regression model whose kernel parameters are optimized by the Bayesian algorithm is established. Finally, four sets of datasets under CS2 battery in the public dataset of the University of Maryland are carried out for experimental validation. The validation results show that the improved RVM model has better short–term prediction performance and long–term prediction stability, the RUL prediction error is less than 20 cycles, and the mean absolute error is less than 0.02. The performance of the improved RVM model is better than that of the traditional RVM model

    Phenothiazine-benzimidazole architecture as an efficient interfacial charge transport layer for perovskite blue light emitting diodes

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    Solution-processed metal halide perovskite light-emitting diodes (Pe-LEDs) show great promise in a range of optoelectronic applications. However, these devices can be limited by poor interfaces to the perovskite films due to poor crystallization control during film processing caused by de-wetting from the bottom layer. The deep (Highest Occupied Molecular Orbital) HOMO levels of the emitters also lead to large charge injection barriers for standard electrodes. To improve this, we develop and report on a small molecule, BPS2, based on phenothiazine-benzimidazole with Lewis base sites. This promising interfacial material is then applied to blue PeLEDs where the energy band alignment of BPS2 to the blue perovskite emitter helps to reduce the hole-injection barrier while blocking electrons. BPS2 can be solution-processed with non-chlorinated organic solvents and provides improved wettability towards perovskite precursor solutions compared to conventional PEDOT:PSS hole transport films. A thin interlayer of BPS2 introduced between PEDOT:PSS and a perovskite emission layer is shown to improve both the device external quantum efficiency and luminance in comparison to the reference device without the interlayer

    A Retrospective Study on Risk Factors for Urinary Tract Infection in Patients with Intracranial Cerebral Hemorrhage

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    Objective. This study aimed to explore the risk factors of urinary tract infection (UTI) in patients with intracranial cerebral hemorrhage (ICH). Design. This is a retrospective study, and a total of 77 patients with ICH consecutively admitted to the First Affiliated Hospital of USTC (Anhui Provincial Hospital, Hefei, China) during the period of August 2015 to August 2017 were included. The patients were divided into an UTI group (24 cases) and a non-UTI group (53 cases); patients with UTI were diagnosed according to clinical manifestations, recent urinary routines, and urine culture results. The following information in these two groups was recorded: age, sex, course of disease, side of paralysis, location and type of cerebral hemorrhage, disturbance of consciousness or not, the Brunnstrom stage of paralysed lower limbs, number of basic diseases, whether there were complications (tracheotomy, retention catheterization, pulmonary infection, pressure sore, deep venous thrombosis, etc.), whether rehabilitation interventions were conducted, blood routine, biochemistry index, DIC complete set, urine routine, and urine culture data. Univariate analysis and multivariate logistic regression analysis were used to examine the risk factors of UTI in patients with ICH. Results. Univariate analysis showed that age, side of paralysis, disturbance of consciousness, the Brunnstrom stage of lower limbs, tracheotomies, retention catheterization, pulmonary infection, leukocyte count, neutrophil proportion, sodium, uric acid, D-dimer, and fibrinogen may be related to UTI in patients with ICH (P<0.05). Regression analysis showed that age (OR (95% CI) = 1.207 (1.022–1.424), P=0.026), right-sided paralysis (OR (95% CI) = 0.20 (0.001–0.650), P=0.028), and D-dimer (OR (95% CI) = 1.403 (1.003–1.961), P=0.048) were associated with UTI in ICH patients. Conclusions. Increased age and high D-dimer are independent risk factors for UTI in patients with ICH, while right-sided paralysis is a protective factor for UTI in patients with ICH

    A systematic strategy for estimating hERG block potency and its implications in a new cardiac safety paradigm

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    © 2020 Introduction: hERG block potency is widely used to calculate a drug's safety margin against its torsadogenic potential. Previous studies are confounded by use of different patch clamp electrophysiology protocols and a lack of statistical quantification of experimental variability. Since the new cardiac safety paradigm being discussed by the International Council for Harmonisation promotes a tighter integration of nonclinical and clinical data for torsadogenic risk assessment, a more systematic approach to estimate the hERG block potency and safety margin is needed. Methods: A cross-industry study was performed to collect hERG data on 28 drugs with known torsadogenic risk using a standardized experimental protocol. A Bayesian hierarchical modeling (BHM) approach was used to assess the hERG block potency of these drugs by quantifying both the inter-site and intra-site variability. A modeling and simulation study was also done to evaluate protocol-dependent changes in hERG potency estimates. Results: A systematic approach to estimate hERG block potency is established. The impact of choosing a safety margin threshold on torsadogenic risk evaluation is explored based on the posterior distributions of hERG potency estimated by this method. The modeling and simulation results suggest any potency estimate is specific to the protocol used. Discussion: This methodology can estimate hERG block potency specific to a given voltage protocol. The relationship between safety margin thresholds and torsadogenic risk predictivity suggests the threshold should be tailored to each specific context of use, and safety margin evaluation may need to be integrated with other information to form a more comprehensive risk assessment