The Ultra High Voltage (UHV) converter transformer may generate serious inrush current during closing. It will cause commutation voltage distortion and easily result in commutation failure of ...converters on the same commutation bus. Due to the change of flux amplitude and phase caused by closing resistance in the Ultra High Voltage Direct Current (UHVDC) system, it is difficult to determine the closing time of the converter transformer when considering the influence of residual flux. Therefore, this paper first analyses the existing closing resistance strategy, and constructs the magnetic bias function according to the influence characteristics of closing resistance on the flux and phase. Then an inrush current suppression strategy based on magnetic bias simulation is proposed for star connection and delta connection of UHV converter transformers, which can accurately calculate the ideal closing time of mutual cancellation between the residual flux and bias flux during closing. Finally, the no-load closing model of the UHV converter transformer is established by PSCAD/EMTDC for simulation analysis of the feasibility, real-time verification is carried out using the RTDS closed-loop experimental platform. The results show that the proposed inrush current suppression strategy can effectively suppress the inrush current under different residual flux conditions.
•A coordinated control strategy of the converter based on the constant cut-off area;•Commutation area theory and the coupling mechanism of the system;•Improvement of transient characteristics of ...UHVDC system.
The Ultra High Voltage Direct Current (UHVDC) systems under hierarchical connection, while improving the voltage support and current assimilative capacity of the receiving-end system, also bring new challenges to the security and stability of the power grid. An AC short-circuit fault at the receiving-end system can easily induce commutation failures (CFs) of the high-end and low-end converter at the same time, which seriously affects the stability of the system. Therefore, it is urgent to study the coordinated control strategy for the commutation failures of UHVDC systems under hierarchical connection. This paper analyzes the coupling mechanism and CFs characteristics of the high-end and low-end converters of a UHVDC system under hierarchical connection. Based on the commutation area theory of the three-phase full-wave bridge circuit, a coordinated control strategy is proposed to suppress CFs of the non-faulty layer converter of the UHVDC system under hierarchical connection. It can reserve enough extinction area for the non-faulty layer converter after an AC system failure occurs, thus preventing the occurrence of commutation failure. Finally, based on PSCAD/EMTDC, Zhundong-Wannan ±1100 kV UHVDC was built and the effectiveness of the proposed control strategy was simulated and verified. The simulation results show that the proposed control strategy can effectively suppress the simultaneous commutation failure of inverter station converters when symmetrical faults and asymmetrical faults of different levels occur in the receiving-end grid. This has important engineering significance for improving the stability of the DC transmission system.
It is of important strategic significance to develop high‐efficiency narrowband organic electroluminescent materials that can be employed to fabricate ultrahigh‐definition displays with wide color ...gamut. This topic implies a great challenge to molecular design and synthesis, especially for the development of universality, diversity, scalability, and robustness of molecular architectonics. In this work, a synthetic methodology is demonstrated for functionalizing brominated BN‐containing multiple‐resonance (MR) frameworks with multifarious functional groups, such as donors, acceptors, and moieties without obvious push–pull electron properties. The m‐DPAcP–BNCz‐based organic light‐emitting diode (OLED) exhibits green emission with a full‐width at half‐maximum (FWHM) of 28 nm and a maximum external quantum efficiency (EQE) of 40.6%. The outstanding performance of m‐DPAcP–BNCz is attributed to the perfect integration of the inherent advantages of the MR framework and the donor–acceptor configuration, which can not only achieve bathochromic shift and narrowband emission, but also obtain high photoluminescence (PL) quantum yield (ΦPL) and horizontal emitting dipole orientation ratio (Θ//). This straightforward and efficient approach provides insightful guidance for the construction and enrichment of more high‐efficiency narrowband emitters.
A synthetic methodology is implemented for functionalizing brominated BN‐containing multiple‐resonance framework with multifarious electron groups, such as donors, acceptors, and moieties without obvious push–pull electron properties. The optimized m‐DPAcP–BNCz‐based organic light‐emitting diode (OLED) exhibits green emission with a full‐width at half‐maximum (FWHM) of 28 nm and a maximum external quantum efficiency (EQE) of 40.6%.
Air pollution has altered the Earth’s radiation balance, disturbed the ecosystem, and increased human morbidity and mortality. Accordingly, a full-coverage high-resolution air pollutant data set with ...timely updates and historical long-term records is essential to support both research and environmental management. Here, for the first time, we develop a near real-time air pollutant database known as Tracking Air Pollution in China (TAP, http://tapdata.org.cn/) that combines information from multiple data sources, including ground observations, satellite aerosol optical depth (AOD), operational chemical transport model simulations, and other ancillary data such as meteorological fields, land use data, population, and elevation. Daily full-coverage PM2.5 data at a spatial resolution of 10 km is our first near real-time product. The TAP PM2.5 is estimated based on a two-stage machine learning model coupled with the synthetic minority oversampling technique and a tree-based gap-filling method. Our model has an averaged out-of-bag cross-validation R 2 of 0.83 for different years, which is comparable to those of other studies, but improves its performance at high pollution levels and fills the gaps in missing AOD on daily scale. The full coverage and near real-time updates of the daily PM2.5 data allow us to track the day-to-day variations in PM2.5 concentrations over China in a timely manner. The long-term records of PM2.5 data since 2000 will also support policy assessments and health impact studies. The TAP PM2.5 data are publicly available through our website for sharing with the research and policy communities.
Since 2013, clean-air actions in China have reduced ambient concentrations of PM2.5. However, recent studies suggest that ground surface O3 concentrations increased over the same period. To ...understand the shift in air pollutants and to comprehensively evaluate their impacts on health, a spatiotemporal model for O3 is required for exposure assessment. This study presents a data-fusion algorithm for O3 estimation that combines in situ observations, satellite remote sensing measurements, and model results from the community multiscale air quality model. Performance of the algorithm for O3 estimation was evaluated by five-fold cross-validation. The estimates are highly correlated with the in situ observations of the maximum daily 8 h averaged O3 (R 2 = 0.70). The mean modeling error (measured using the root-mean-squared error) is 26 μg/m3, which accounts for 29% of the mean level. We also found that satellite O3 played a key role to improve model performance, particularly during warm months. The estimates were further used to illustrate spatiotemporal variation in O3 during 2013–2017 for the whole country. In contrast to the reduced trend of PM2.5, we found that the population-weighted O3 mean increased from 86 μg/m3 in 2013 to 95 μg/m3 in 2017, with a rate of 2.07 (95% CI: 1.65, 2.48) μg/m3 per year at the national level. This increased trend in O3 suggests that it is becoming an important contributor to the burden of diseases attributable to air pollutants in China. The developed method and the results generated from this study can be used to support future health-related studies in China.
By integrating a free-standing cadmium sulfide (CdS) nanowire onto a silicon nitride (SiN) photonic chip, we demonstrate a highly compact on-chip single-mode CdS nanowire laser. The mode selection is ...realized using a Mach-Zehnder interferometer (MZI) structure. When the pumping intensity exceeds the lasing threshold of 4.9 kW/cm
, on-chip single-mode lasing at ~518.9 nm is achieved with a linewidth of 0.1 nm and a side-mode suppression ratio of up to a factor of 20 (13 dB). The output of the nanowire laser is channelled into an on-chip SiN waveguide with high efficiency (up to 58%) by evanescent coupling, and the directional coupling ratio between the two output ports can be varied from 90 to 10% by predesigning the coupling length of the SiN waveguide. Our results open new opportunities for both nanowire photonic devices and on-chip light sources and may pave the way towards a new category of hybrid nanolasers for chip-integrated applications.
China promulgated the Air Pollution Prevention and Control Action Plan (the Action Plan) in 2013 and developed stringent control measures to mitigate fine particulate matter (PM
2.5
) pollution. ...Here, we investigated the PM
2.5
chemical composition changes over eastern China associated with the Action Plan during 2013–2017 using satellite-based PM
2.5
chemical composition data derived using CMAQ simulations and satellite inputs. The PM
2.5
concentrations decreased considerably during this time as a result of the reductions in all chemical species in PM
2.5
. The population-weighted mean concentrations over eastern China decreased from 11.1 to 6.7 μg m
-3
for
S
O
4
2
−
, 13.8–13.1 μg m
-3
for
N
O
3
−
, 7.4–5.8 μg m
-3
for
N
H
4
+
, 9.9–8.4 μg m
-3
for OM, 4.6–3.8 μg m
-3
for BC and 12.9–9.6 μg m
-3
for other species in PM
2.5
.
S
O
4
2
−
had the largest reduction of 40%, while
N
O
3
−
had the lowest reduction of 5%, resulting in a greater fraction of
N
O
3
−
and a smaller fraction of
S
O
4
2
−
in PM
2.5
. Among the three key regions, Beijing-Tianjin-Hebei had the largest reduction in PM
2.5
and its chemical compositions. The decrease in SO4 2 concentrations was in line with the reduction of SO
2
emissions, and the major driver of the SO
2
emission reductions was the industrial sector. The decrease in
N
O
3
−
concentrations was limited because the decrease in SO
2
emissions and the stable NH
3
emissions facilitated the formation of
N
O
3
−
from HNO
3
, which partially offset the reduction in NO
x
emissions driven by the power sector. To mitigate PM
2.5
pollution more effectively, future efforts are needed to reduce NH
3
emissions.
The efficient use of regenerative braking energy between trains can significantly reduce the net traction energy consumption in urban rail transit systems, and has attracted considerable attention in ...recent years. An effective way of using regenerative braking energy is to adjust the train's coasting or cruising phase to an acceleration phase to match the braking phase of a nearby train within the same substation. This paper formulates the train driving phase adjustment problem as a cooperative optimal control problem, where a novel energy constraint is introduced to ensure efficient use of regenerative braking energy during the adjusted phase with optimal traction effort. By applying the control parameterisation method and elaborate handling of the energy constraint and the non-smooth control bound constraint, we transform the formulated problem into a nonlinear programming problem. We then use the sequential quadratic programming algorithm to solve the resulting problem, with the gradients of the cost and constraint functions computed using the sensitivity method. Numerical examples based on real-world data for a subway line show the effectiveness of the proposed method and its advantages over a genetic algorithm in terms of energy savings and computational efficiency.
•A novel energy constraint is proposed to sufficiently utilize the regenerative energy.•The control parameterisation method is employed to solve the cooperative optimal train operation problem.•The non-smooth control bound constraint is transformed equivalently into point constraints.•Performance of the proposed approach is demonstrated using data for a real subway line.
Acquired chemoresistance represents a major obstacle in cancer treatment, the underlying mechanism of which is complex and not well understood. MiR‐425‐5p has been reported to be implicated ...tumorigenesis in a few cancer types. However, its role in regulating chemoresistance has not been investigated in colorectal cancer (CRC) cells. Microarray analysis was performed in isogenic chemosensitive and chemoresistant HCT116 cell lines to identify differentially expressed miRNAs. miRNA quantitative real‐time PCR was used to detect miR‐425‐5p expression levels between drug resistant and parental cancer cells. MiR‐425‐5p mimic and inhibitor were transfected, followed by CellTiter‐Glo® assay to examine drug sensitivity in these two cell lines. Western Blot and luciferase assay were performed to investigate the direct target of miR‐425‐5p. Xenograft mouse models were used to examine in vivo function of miR‐425‐5p. Our data showed that expression of miR‐425‐5p was significantly up‐regulated in HCT116‐R compared with parental HCT116 cells. Inhibition of miR‐425‐5p reversed chemoresistance in HCT116‐R cells. Programmed cell death 10 (PDCD10) is the direct target of miR‐425‐5p which is required for the regulatory role of miR‐425‐5p in chemoresistance. MiR‐425‐5p inhibitor sensitized HCT116‐R xenografts to chemo drugs in vivo. Our study demonstrated that miR‐425‐5p regulates chemoresistance of CRC cells by modulating PDCD10 expression level both in vitro and in vivo. MiR‐425‐5p may represent a new therapeutic target for the intervention of CRC.
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