Studies of commutation failures in Hybrid LCC/MMC HVDC systems

A hybrid of line commutated converters(LCCs) and modular multi-level converters(MMCs) can provide the advantages of both the technologies. However, the commutation failure still exists if the LCC operates as an inverter in a hybrid LCC/MMC system. In this paper, the system behavior during a commutation failure is investigated. Both halfbridge and full-bridge MMCs are considered. Control strategies are examined through simulations conducted in PSCAD/EMTDC

Feasibility and reliability analysis of LCC DC grids and LCC/VSC hybrid DC grids

Power system interconnections using high-voltage direct-current (HVDC) technologies between different areas can be an effective solution to enhance system efficiency and reliability. Particularly, the multi-terminal DC grids, that could balance and ensure resource adequacy, increase asset utilization and reduce costs. In this paper, the technical feasibility of building DC grids using the line commutated converter based (LCC) and voltage source converter based (VSC) HVDC technologies are discussed. Apart from presenting the technical challenges of building LCC DC grids and LCC/VSC hybrid DC grids, the reliability modeling and analysis of these DC grids are also presented. First, the detailed reliability model of the modular multi-level converters (MMCs) with series connected high-voltage and low-voltage bridges are developed. The active mode redundancy design is considered for the reliability model. To this end, a comprehensive whole system reliability model of the studied systems is developed. The reliability model of each subsystem is modeled in detail. Various reliability indices are calculated using this whole system reliability model. The impacts of the redundancy design of the MMCs on these indices are presented. The studies of this paper provide useful guidance for DC grid design and reliability analysis

Control strategies of full-voltage to half-voltage operation for LCC and hybrid LCC/MMC based UHVDC systems

With the increasing demand of transmitting bulk-power over long-distance, the ultra high-voltage direct-current (UHVDC) transmission systems become an attractive option. Nowadays, not only the line commutated converter (LCC) based systems, but also the modular multilevel converter (MMC) based systems have reached UHVDC levels. The converter stations of UHVDC systems normally utilize two series-connected valve-groups to reduce the difficulties of device manufacturing and transportation. This high-voltage and low-voltage valve-group configuration allows the UHVDC systems to achieve a full-voltage to half-voltage operation which increases the flexibility of the systems. However, the existing research only focuses on the full-voltage to half-voltage control of LCC-UHVDC systems. The control strategies for hybrid LCC/MMC UHVDC systems are underresearched. Moreover, the approaches to reduce the load-shedding caused by the full-voltage to half-voltage control for both LCC and hybrid LCC/MMC based UHVDC systems have not been investigated. In this paper, full-voltage to half-voltage control strategies for both LCC and hybrid LCC/MMC based UHVDC systems have been proposed. Moreover, to avoid load-shedding caused by the half-voltage operation, a power rescheduling method that re-sets the power references of the half-voltage operating and full-voltage operating poles has been proposed. The proposed full-voltage to half-voltage control strategies and power rescheduling method can achieve a stable and fast control process with a minimum power loss. The proposed methods have been verified through the time-domain simulations conducted in PSCAD/EMTDC

What Differs on the Enzymatic Acetylation Mechanisms for Arylamines and Arylhydrazines Substrates? A Theoretical Study

The acetylation mechanisms of several selected typical substrates from experiments, including arylamines and arylhydrazines, are investigated with the density functional theory in this paper. The results indicate that all the transition states are characterized by a four-membered ring structure, and hydralazine (HDZ) is the most potent substrate. The bioactivity for all the compounds is increased in a sequence of PABA ≈ 4-AS < 4-MA < 5-AS ≈ INH < HDZ. The conjunction effect and the delocalization of the lone pairs of N atom play a key role in the reaction. All the results are consistent with the experimental data

Efficient Characterizations of Multiphoton States with Ultra-thin Integrated Photonics

Metasurface enables the generation and manipulation of multiphoton entanglement with flat optics, providing a more efficient platform for large-scale photonic quantum information processing. Here, we show that a single metasurface optical chip would allow more efficient characterizations of multiphoton entangled states, such as shadow tomography, which generally requires fast and complicated control of optical setups to perform projective measurements in different bases, a demanding task using conventional optics. The compact and stable device here allows implementations of general positive observable value measures with a reduced sample complexity and significantly alleviates the experimental complexity to implement shadow tomography. Integrating self-learning and calibration algorithms, we observe notable advantages in the reconstruction of multiphoton entanglement, including using fewer measurements, having higher accuracy, and being robust against optical loss. Our work unveils the feasibility of metasurface as a favorable integrated optical device for efficient characterization of multiphoton entanglement, and sheds light on scalable photonic quantum technologies with ultra-thin integrated optics.Comment: 15 pages, 9 figure

Does Economic Agglomeration Lead to Efficient Rural to Urban Land Conversion? An Examination of China’s Metropolitan Area Development Strategy

Urbanization involves expansion of the amount of land covered by urban uses. Rural to urban land conversion (RULC) can satisfy demand for the additional space that growing cities require. However, there can be negative consequences, such as the loss of productive agricultural land and/or the destruction of natural habitats. Considerable interest therefore exists among policy makers and researchers regarding how the efficiency of RULC can be maximized. We used the Gini index and a data envelopment analysis to quantify the relationship between RULC and economic development for 17 metropolitan areas in China. We did this from two perspectives: (i) coordination; and (ii) efficiency. We found that economic agglomeration fosters the coordination of the amount of rural land that is allocated to be converted to urban uses. Similarly, economic agglomeration increases the efficiency of RULC in terms of the processes of socio-economic production. Through production technology innovation and readjustment in the scale of input factors, the productive efficiency of RULC can be promoted. Our findings suggest a need to strictly limit the amount of RULC, design differential land management policies according to location and development level, and adjust RULC allocation between different cities. Further, in harnessing the potential of intensive urban land use and restructuring, production factors, including land, can be enhanced through technological innovation. Research presented in this paper provides insights for areas of the world which are yet to undergo the rapid urbanization that China has experienced, but where it is projected to occur over the coming decades

Suspected adverse reactions reported for blood, blood components, and blood products in VigiBase

INTRODUCTION: Since being designated as medicines by World Health Organization (WHO), blood components are subject to pharmacovigilance reporting. Using VigiBase, the WHO global database of individual case safety reports (ICSRs), we characterized reports of adverse reactions for all blood products. STUDY DESIGN AND METHODS: ICSRs involving blood products as the suspected medicine in VigiBase between 1968 and 2021 were extracted. MedDRA preferred terms and the International Society of Blood Transfusion haemovigilance definitions were used to stratify adverse reactions. Descriptive statistics were used to characterize ICSR demographics. RESULTS: A total of 111,033 ICSRs containing 577,577 suspected adverse reactions with 6152 MedDRA preferred terms were reported for 34 blood products. There were 12,153 (10.9%) reports for blood components, 98,135 (88.4%) reports for plasma-derived medicines, and 745 (0.7%) reports for recombinant products. The majority of reports (21.0% and 19.7%, respectively) were from patients aged 45-64 and over 65 years. The Americas contributed the most ICSRs (49.7%). Top reported suspected adverse reactions were for the following MedDRA preferred terms: headache (3.5%), pyrexia (2.8%), chills (2.8%), dyspnoea (1.8%), and nausea (1.8%). CONCLUSION: VigiBase already has a large number of reports on blood products. When compared to other existing haemovigilance databases, our study found reports from a broader range of countries and reporters. This may provide us with new perspectives, but for VigiBase to reach its full potential in haemovigilance some alterations in what is captured in reports are required

Apolipoprotein A1 suppresses the hypoxia-induced angiogenesis of human retinal endothelial cells by targeting PlGF

AIM: To investigate the anti-angiogenic effect of apolipoprotein A1 (apoA1) on primary human retinal vascular endothelial cells (HRECs) and explore the possible mechanism. METHODS: The primary HRECs were transfected with apoA1-GFP recombinant lentiviral and were compared with cells undergoing transfection with empty lentiviral vectors. Hypoxia chambers were used to simulate the anoxic environment of cells under pathological condition. The concentrations of secreted vascular endothelial growth factor (VEGF) and placental growth factor (PlGF) were measured by enzyme-linked immunosorbent assay (ELISA). Cell migration ability was detected by wound healing assay. The sprouting of HRECs was determined by tube formation assay. The protein levels of extracellular signal regulated kinase 1/2 (ERK1/2) and phosphorylated ERK1/2 (p-ERK1/2) were measured by Western blot. RESULTS: Overexpressed apoA1 in hypoxia-induced HRECs significantly suppressed PlGF (0.67±0.10 folds, P=0.007). Overexpressed apoA1 also attenuated hypoxia-induced cell migration (0.32±0.11 folds, P<0.0001), tube formation (0.66±0.01 folds, P<0.0001) and the phosphorylation levels of ERK (0.6±0.11 folds, P=0.025). Pretreatment of mitogen-activated protein kinase kinase (MEK) inhibitor (U0126) further reduced the PlGF and angiogenesis in hypoxia-induced HRECs. CONCLUSION: ApoA1 inhibits the angiogenesis at least in part by inactivating ERK1/2 in hypoxia-induced HRECs. Moreover, apoA1 suppresses the PlGF expression, which selectively associated with pathological angiogenesis

A 9 bp cis-element in the promoters of class I small heat shock protein genes on chromosome 3 in rice mediates L-azetidine-2-carboxylic acid and heat shock responses

In rice, the class I small heat shock protein (sHSP-CI) genes were found to be selectively induced by L-azetidine-2-carboxylic acid (AZC) on chromosome 3 but not chromosome 1. Here it is shown that a novel cis-responsive element contributed to the differential regulation. By serial deletion and computational analysis, a 9 bp putative AZC-responsive element (AZRE), GTCCTGGAC, located between nucleotides –186 and –178 relative to the transcription initiation site of Oshsp17.3 was revealed. Deletion of this putative AZRE from the promoter abolished its ability to be induced by AZC. Moreover, electrophoretic mobility shift assay (EMSA) revealed that the AZRE interacted specifically with nuclear proteins from AZC-treated rice seedlings. Two AZRE–protein complexes were detected by EMSA, one of which could be competed out by a canonical heat shock element (HSE). Deletion of the AZRE also affected the HS response. Furthermore, transient co-expression of the heat shock factor OsHsfA4b with the AZRE in the promoter of Oshsp17.3 was effective. The requirement for the putative AZRE for AZC and HS responses in transgenic Arabidopsis was also shown. Thus, AZRE represents an alternative form of heat HSE, and its interaction with canonical HSEs through heat shock factors may be required to respond to HS and AZC

Power reversal strategies for hybrid LCC/MMC HVDC systems

Power reversal control strategies for different types of hybrid line-commutated-converter (LCC)/modular multi-level converter (MMC) based high-voltage direct-current (HVDC) systems have been proposed with the consideration of system configurations and MMC's topologies. The studies show that the full-bridge (FB) MMC gives better performance than halfbridge (HB) MMCs in terms of power reversal in hybrid LCC/MMC systems. The modulation method employed in this paper can achieve a smooth online polarity reversal for hybrid LCC/FB-MMC HVDC systems. Additional DC switches and/or discharging resistors may be needed to reverse the DC polarity of LCC/HB-MMC HVDC systems. Based on the proposed strategies, the power reversal processes of the studied systems can be accomplished within several seconds. The speed can be changed according to system operation requirements. The effectiveness of the proposed control strategies has been verified through simulations conducted in PSCAD/EMTDC