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Sodium (Na) vanadium (V) fluorophosphate Na x V2(PO4)2F3 (NVPF) is a highly attractive intercalation electrode material due to its high operation voltage, large capacity, and long cycle life. However, several practical issues limit the full utilization of NVPF’s energy density: (1) the high voltage plateau associated with extracting the “third” Na ion in the reaction N1VPF → VPF (∼4.9 V vs Na/Na+) appears above the electrochemical stability window (ESW) of most practical electrolytes (∼4.5 V vs Na/Na+); and (2) a sudden drop in Na-ion diffusivity is observed near composition Na1V2(PO4)2F3. Therefore, it is important to investigate the potential substitution of V by other transition metals (TMs) in NVPF derivatives, which can practically access the extraction of the third Na-ion. In this work, we investigate the partial substitution of V with molybdenum (Mo), niobium (Nb), or tungsten (W) in NVPF to improve its energy density. Using first-principles calculations, we examine the structural and electrochemical behaviors of Na x V2–y Mo y (PO4)2F3, Na x V2–y Nb y (PO4)2F3, and Na x W2(PO4)2F3 across the whole Na composition region of 0 ≤ x ≤ 4, and at various transition metal (TM) substitution levels, namely, y = 0.5, 1.0, 1.5, and 2.0 for Mo, and y = 1.0 and 2.0 for Nb. We found that partial substitution of 50% V by Mo in NVPF reduces the voltage plateau for extracting the third Na ion by 0.6 volts, which enables further Na extraction from Na1VMo­(PO4)2F3 and increases the theoretical gravimetric capacity from ∼128 to ∼174 mAh/g. Analysis of the migration barriers for Na-ions in Na x VMo­(PO4)2F3 unveils improved kinetic properties over NVPF. The proposed Na x VMo­(PO4)2F3 material provides an optimal gravimetric energy density of ∼577.3 Wh/kg vs ∼507 Wh/kg for the pristine NVPF, which amounts to an increase of ∼13.9%.

X (inactive)-specific transcript (XIST) has been known as long noncoding RNA, which regulates X-chromosome inactivation in female mammals to provide dosage equivalence between male and females. Its important roles in early embryo and stem cells development have been suggested in humans and mice. However, its coding region has been unclear in pigs. To determine the coding region of XIST in pigs, we examined candidate XIST coding region using BLAST, PCR, and sequencing techniques. By comparing pig whole genome sequence (Sus scrofa 10.2) with human, murine, and bovine XIST transcript sequence using BLAST, we selected candidate coding regions of XIST in pig. The result showed that XIST is coded on the minus strand of NW_003612825 contig, and its length was nearly 32 kb, which was similar to the length of human and bovine XIST genes. In order to identify the coding region of XIST in this candidate sequence, we designed 24 primer pairs and RT-PCR was performed using porcine embryonic fibroblast cells (PEF) established from porcine male and female lines.The XIST transcripts were expressed in female PEF but not in male PEF. Thus, by designing candidate intron-spanning primers, we confirmed the existence of introns between the first and last exons. The amplicon sequence was analysed and 5 short exons (<400 bp) that have similarity to the XIST coding region of other characterised species were identified. Moreover, to examine the XIST coding strand in pig genome, we conducted strand-specific reverse transcription. With BLAST homology searches, we confirmed that XIST was coded on the negative strand of the contig on the X chromosome. To analyse stage and origin of XIST transcript in the pig, we subsequently performed real-time PCR using cDNA template synthesised from sperm, oocyte, 1, 2, 4, 8, morular, and blastocyst of fertilized embryo and parthenotes, and intron-spanning primer sets were used. The results revealed that XIST was expressed after maternal to zygote transition (4- to 8-cell stage in pig) and not expressed in mature germ cells (sperm and oocyte). Moreover, parthenotes showed a higher expression level compared with fertilized embryos after the 8-cell stage. These results verify the existence of XIST in pig early embryos and may contribute to the comparative analysis of XIST mechanisms in different species. Further study using FISH and methylation analysis may reveal its mechanisms of action. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST; No. 2012006276) and the Biogreen 21 program (PJ0081382011) of the Rural Development Administration, Republic of Korea.