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Spiral chain O? form of dense oxygen.

ABSTRACT: Oxygen is in many ways a unique element: It is the only known diatomic molecular magnet, and it exhibits an unusual O(8) cluster in its high-pressure solid phase. Pressure-induced molecular dissociation as one of the fundamental problems in physical sciences has been reported from theoretical or experimental studies of diatomic solids H(2), N(2), F(2), Cl(2), Br(2), and I(2) but remains elusive for molecular oxygen. We report here the prediction of the dissociation of molecular oxygen into a polymeric spiral chain O(4) structure (space group I4(1)/acd, ?-O(4)) above 1.92-TPa pressure using the particle-swarm search method. The ?-O(4) phase has a similar structure as the high-pressure phase III of sulfur. The molecular bonding in the insulating ?-O(8) phase or the isostructural superconducting ?-O(8) phase remains remarkably stable over a large pressure range of 0.008-1.92 TPa. The pressure-induced softening of a transverse acoustic phonon mode at the zone boundary V point of O(8) phase might be the ultimate driving force for the formation of ?-O(4). Stabilization of ?-O(4) turns oxygen from a superconductor into an insulator by opening a wide band gap (approximately 5.9 eV) that originates from the sp(3)-like hybridized orbitals of oxygen and the localization of valence electrons.

SUBMITTER: Zhu L

PROVIDER: S-EPMC3271893 | biostudies-other | 2012 Jan

REPOSITORIES: biostudies-other

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Spiral chain O₄ form of dense oxygen.

Zhu Li L Wang Ziwei Z Wang Yanchao Y Zou Guangtian G Mao Ho-kwang HK Ma Yanming Y

Proceedings of the National Academy of Sciences of the United States of America 20120103 3

Oxygen is in many ways a unique element: It is the only known diatomic molecular magnet, and it exhibits an unusual O(8) cluster in its high-pressure solid phase. Pressure-induced molecular dissociation as one of the fundamental problems in physical sciences has been reported from theoretical or experimental studies of diatomic solids H(2), N(2), F(2), Cl(2), Br(2), and I(2) but remains elusive for molecular oxygen. We report here the prediction of the dissociation of molecular oxygen into a pol ...[more]

PMID: 22215589

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Project description:IntroductionDisplacement encoding with stimulated echoes (DENSE) is a phase contrast technique that encodes tissue displacement into phase images, which are typically processed into measures of cardiac function such as strains. For improved signal to noise ratio and spatiotemporal resolution, DENSE is often acquired with a spiral readout using an 11.1 ms readout duration. However, long spiral readout durations are prone to blurring due to common phenomena such as off-resonance and T2* decay, which may alter the resulting quantifications of strain. We hypothesized that longer readout durations would reduce image quality and underestimate cardiac strains at both 3.0 T and 1.5 T and that using short readout durations could overcome these limitations.Material and methodsComputational simulations were performed to investigate the relationship between off-resonance and T2* decay, the spiral cine DENSE readout duration, and measured radial and circumferential strain. Five healthy participants subsequently underwent 2D spiral cine DENSE at both 3.0 T and 1.5 T with several different readout durations 11.1 ms and shorter. Pearson correlations were used to assess the relationship between cardiac strains and the spiral readout duration.ResultsSimulations demonstrated that long readout durations combined with off-resonance and T2* decay yield blurred images and underestimate strains. With the typical 11.1 ms DENSE readout, blurring was present in the anterior and lateral left ventricular segments of participants and was markedly improved with shorter readout durations. Radial and circumferential strains from those segments were significantly correlated with the readout duration. Compared to the 1.9 ms readout, the 11.1 ms readout underestimated radial and circumferential strains in those segments at both field strengths by up to 19.6% and 1.5% (absolute), or 42% and 7% (relative), respectively.ConclusionsBlurring is present in spiral cine DENSE images acquired at both 3.0 T and 1.5 T using the typical 11.1 ms readout duration, which yielded substantially reduced radial strains and mildly reduced circumferential strains. Clinical studies using spiral cine DENSE should consider these limitations, while future technical advances may need to leverage accelerated techniques to improve the robustness and accuracy of the DENSE acquisition rather than focusing solely on reduced acquisition time.

Project description:Chain elongation fermentation allows for the synthesis of biobased chemicals from complex organic residue streams. To expand the product spectrum of chain elongation technology and its application range we investigated 1) how to increase selectivity towards branched chain elongation and 2) whether alternative branched carboxylates such as branched valerates can be used as electron acceptors. Elongation of isobutyrate elongation towards 4-methyl-pentanoate was achieved with a selectivity of 27% (of total products, based on carbon atoms) in a continuous system that operated under CO2 and acetate limited conditions. Increasing the CO2 load led to more in situ acetate formation that increased overall chain elongation rate but decreased the selectivity of branched chain elongation. A part of this acetate formation was related to direct ethanol oxidation that seemed to be thermodynamically coupled to hydrogenotrophic carboxylate reduction to corresponding alcohols. Several alcohols including isobutanol and n-hexanol were formed. The microbiome from the continuous reactor was also able to form small amounts of 5-methyl-hexanoate likely from 3-methyl-butanoate and ethanol as substrate in batch experiments. The highest achieved concentration of isoheptanoate was 6.4 ± 0.9 mM Carbon, or 118 ± 17 mg/L, which contributed for 7% to the total amount of products (based on carbon atoms). The formation of isoheptanoate was dependent on the isoform of branched valerate. With 3-methyl-butanoate as substrate 5-methylhexanoate was formed, whereas a racemic mixture of L/D 2-methyl-butanoate did not lead to an elongated product. When isobutyrate and isovalerate were added simultaneously as substrates there was a large preference for elongation of isobutyrate over isovalerate. Overall, this work showed that chain elongation microbiomes can be further adapted with supplement of branched-electron acceptors towards the formation of iso-caproate and iso-heptanoate as well as that longer chain alcohol formation can be stimulated.

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Spiral chain O? form of dense oxygen.

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Spiral chain O₄ form of dense oxygen.

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