Accelerated switching function model of hybrid MMCs for HVDC system simulation

An accelerated switching function model (SFM) of the hybrid modular multilevel converter comprising both full-bridge (FB) and half-bridge (HB) submodules (SMs) in each arm is presented for HVDC system simulation, where auxiliary circuits are adopted to represent all possible current paths during normal and fault conditions. The proposed SFM can represent the negative voltage generating capability of the FB SMs and the equivalent switching functions in the blocking states of the FB and HB SMs are also introduced in the proposed model to accurately replicate the potential charging of the SM capacitors, yielding improved simulation accuracy compared to other alternatives. In addition to the faster simulation speed, the proposed model accurately reproduces the converter behaviour during various operating conditions, including normal operation, AC fault, and DC fault, etc. The proposed SFMs are assessed in MATLAB/Simulink environment using both down- and full-scale HVDC links and the simulation results confirm the validity of the proposed model in terms of model accuracy and improved simulation speed

Specific Targeting MRI of Chitosan Oligosaccharide Modified Fe3O4 Nanoprobe on Macrophage and the Inhibition of Macrophage Foaming Induced by ox-LDL

Atherosclerosis (AS) is a primary cause of morbidity and mortality all over the world. Molecular imaging techniques can enable early localization and diagnosis of atherosclerosis plaques. Recent newly developed chitooligosaccharides (CSO) is considered to be capable of target mannose receptors on the surface of macrophages and to inhibit foam cell formation. Here we present a targeting magnetic resonance imaging (MRI) nanoprobe, which was successfully constructed with polyacrylic acid (PAA) modified nanometer iron oxide (Fe3O4) as the core, and coating with CSO molecules, possessing the abilities of targeted MRI and specifically inhibition of the formation of foamy macrophages in the atherosclerotic process. The experimental results showed that the distributions of PAA-Fe3O4 and CSO-PAA-Fe3O4 were uniform and the corresponding sizes were about 5.93 nm and 8.15 nm, respectively. The Fourier transform infrared spectra (FTIR) testified the CSO was coupled with PAA-Fe3O4 successfully. After coupled with CSO, the r1 of PAA-Fe3O4 was increased from 5.317 mM s-1 to 6.147 mM s-1, indicating their potential as MRI contrast agent. Oil Red O staining and total cholesterols (TC) determination showed that CSO-PAA-Fe3O4 could significantly inhibit the foaming process of RAW264.7 cells induced by oxidatively modified low density lipoprotein (ox-LDL). In vitro cellular MRI displayed that, compared with PAA-Fe3O4,CSO-PAA-Fe3O4 could lower the T1 relaxation time of RAW264.7 cells better. In summary, construction of CSO-PAA-Fe3O4 nanoprobe in this study could realize the targeted MRI of macrophages and inhibition of ox-LDL induced macrophage foaming process. This will provide a new avenue in the diagnosis and treatment of AS

Site-specific selection reveals selective constraints and functionality of tumor somatic mtDNA mutations.

BACKGROUND: Previous studies have indicated that tumor mitochondrial DNA (mtDNA) mutations are primarily shaped by relaxed negative selection, which is contradictory to the critical roles of mtDNA mutations in tumorigenesis. Therefore, we hypothesized that site-specific selection may influence tumor mtDNA mutations. METHODS: To test our hypothesis, we developed the largest collection of tumor mtDNA mutations to date and evaluated how natural selection shaped mtDNA mutation patterns. RESULTS: Our data demonstrated that both positive and negative selections acted on specific positions or functional units of tumor mtDNAs, although the landscape of these mutations was consistent with the relaxation of negative selection. In particular, mutation rate (mutation number in a region/region bp length) in complex V and tRNA coding regions, especially in ATP8 within complex V and in loop and variable regions within tRNA, were significantly lower than those in other regions. While the mutation rate of most codons and amino acids were consistent with the expectation under neutrality, several codons and amino acids had significantly different rates. Moreover, the mutations under selection were enriched for changes that are predicted to be deleterious, further supporting the evolutionary constraints on these regions. CONCLUSION: These results indicate the existence of site-specific selection and imply the important role of the mtDNA mutations at some specific sites in tumor development

Detailed quantitative comparison of half-bridge modular multilevel converter modelling methods

This paper presents a detailed comparison of different modelling methods of the half-bridge modular multilevel converter (HB-MMC), namely, switching function, Thevenin equivalent and averaged, considering both MMC implementations (large and reduced number of cells). The theoretical basis that underpins each modelling method are discussed. Offline PSCAD simulations are used to validate user-defined switching function and averaged MMC models against the Thevenin equivalent model provided in PSCAD library for accuracy, considering steady-state and dc fault conditions. Furthermore, the RTDS based real-time simulation results of the user-defined HB-MMC switching function model are validated against the above mentioned offline models, considering steady-state and dc short circuit fault operations. Simulation speed and efficiency of different offline HB-MMC models being studied in this paper are compared. From comprehensive corroboration of different HB-MMC models presented in this paper, it has been found that the averaged, switching function and Thevenin equivalent models produce practically identical results during steady-state and dc faults. In detailed offline and real-time simulation studies where fundamental and harmonic dynamics are of interest, switching function model is found to be faster and computational efficient compared to the Thevenin equivalent model

Design and direct assembly of synthesized uracil-containing non-clonal DNA fragments into vectors by USER^TM cloning

This protocol describes how to order and directly assemble uracil-containing non-clonal DNA fragments by uracil excision based cloning (USER cloning). The protocol was generated with the goal of making synthesized non-clonal DNA fragments directly compatible with USER(TM) cloning. The protocol is highly efficient and would be compatible with uracil-containing non-clonal DNA fragments obtained from any synthesizing company. The protocol drastically reduces time and handling between receiving the synthesized DNA fragments and transforming with vector and DNA fragment(s)

Identification of genes involved in shea butter biosynthesis from Vitellaria paradoxa fruits through transcriptomics and functional heterologous expression

Shea tree (Vitellaria paradoxa) is one economically important plant species that mainly distributes in West Africa. Shea butter extracted from shea fruit kernels can be used as valuable products in the food and cosmetic industries. The most valuable composition in shea butter was one kind of triacylglycerol (TAG), 1,3-distearoyl-2-oleoyl-glycerol (SOS, C18:0-C18:1-C18:0). However, shea butter production is limited and little is known about the genetic information of shea tree. In this study, we tried to reveal genetic information of shea tree and identified shea TAG biosynthetic genes for future shea butter production in yeast cell factories. First, we measured lipid content, lipid composition, and TAG composition of seven shea fruits at different ripe stages. Then, we performed transcriptome analysis on two shea fruits containing obviously different levels of SOS and revealed a list of TAG biosynthetic genes potentially involved in TAG biosynthesis. In total, 4 glycerol-3-phosphate acyltransferase (GPAT) genes, 8 lysophospholipid acyltransferase (LPAT) genes, and 11 diacylglycerol acyltransferase (DGAT) genes in TAG biosynthetic pathway were predicted from the assembled transcriptome and 14 of them were cloned from shea fruit cDNA. Furthermore, the heterologous expression of these 14 potential GPAT, LPAT, and DGAT genes in Saccharomyces cerevisiae changed yeast fatty acid and lipid profiles, suggesting that they functioned in S. cerevisiae. Moreover, two shea DGAT genes, VpDGAT1 and VpDGAT7, were identified as functional DGATs in shea tree, showing they might be useful for shea butter (SOS) production in yeast cell factories

Interoperability of different voltage source converter topologies in HVDC grids

This paper presents a detailed study of DC grid operation using a range of user-defined offline and real-time HVDC converter models which were rigorously validated against offline and real-time benchmarks. Provided that these models are destined for use in real-time hardware in the loop simulation and a wide range of offline system studies, this paper assesses their suitability for studying complex DC grids that consist of multiple voltage source converters which differ in their control range and fault ride-through capabilities. Detailed quantitative studies show that the offline and real-time DC grid models produce well matched results and provide efficient approaches to investigate DC grid operation during normal condition and AC and DC faults