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  • 1
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    A single iron site confined in a graphene matrix for the catalytic oxidation of benzene at room temperature (2015)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2015-12-06
    Description: Coordinatively unsaturated (CUS) iron sites are highly active in catalytic oxidation reactions; however, maintaining the CUS structure of iron during heterogeneous catalytic reactions is a great challenge. Here, we report a strategy to stabilize single-atom CUS iron sites by embedding highly dispersed FeN 4 centers in the graphene matrix. The atomic structure of FeN 4 centers in graphene was revealed for the first time by combining high-resolution transmission electron microscopy/high-angle annular dark-field scanning transmission electron microscopy with low-temperature scanning tunneling microscopy. These confined single-atom iron sites exhibit high performance in the direct catalytic oxidation of benzene to phenol at room temperature, with a conversion of 23.4% and a yield of 18.7%, and can even proceed efficiently at 0°C with a phenol yield of 8.3% after 24 hours. Both experimental measurements and density functional theory calculations indicate that the formation of the FeO intermediate structure is a key step to promoting the conversion of benzene to phenol. These findings could pave the way toward highly efficient nonprecious catalysts for low-temperature oxidation reactions in heterogeneous catalysis and electrocatalysis.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    Improving Physical Absorption of Carbon Dioxide by Ionic Liquid Dispersion (2013)
    Wiley
    Details
    Publication Date: 2013-07-05
    Description: An ionic liquid (IL), 1-butylimidazole hexafluoride phosphate [bmim]PF 4 , was dispersed in surfactant solution to form an IL-in-water emulsion. Physical absorption of CO 2 was carried out in this emulsion system. Absorption rates of CO 2 under different operating conditions were obtained by experimental measurements. CO 2 concentrations in the bulk of absorbent and the local volumetric mass transfer coefficients of the liquid phase were calculated by model calculation. Experimental results indicate that the dispersed IL droplets in aqueous solution can significantly enhance CO 2 mass transfer at the gas-liquid interface. This phenomenon can be ascribed to the increase of mass transfer driving force and local volumetric mass transfer coefficient. The shuttle effect and hydrodynamic effect proved to play important roles for CO 2 absorption improved by dispersed IL. The ionic liquid 1-butylimidazole hexafluoride phosphate [bmim]PF 4 is dispersed into water to create an ionic liquid-in-water emulsion which is applied to absorb CO 2 . The presence of dispersed ionic liquid droplets significantly enhances the CO 2 mass transfer rate at a gas-liquid interface due to both the shuttle effect and hydrodynamic effect.
    Print ISSN: 0930-7516
    Electronic ISSN: 1521-4125
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Published by Wiley
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  • 3
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    Subsurface catalysis-mediated selectivity of dehydrogenation reaction (2018)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2018-08-11
    Description: Progress in heterogeneous catalysis is often hampered by the difficulties of constructing active architectures and understanding reaction mechanisms at the molecular level due to the structural complexity of practical catalysts, in particular for multicomponent catalysts. Although surface science experiments and theoretical simulations help understand the detailed reaction mechanisms over model systems, the direct study of the nature of nanoparticle catalysts remains a grand challenge. This paper describes a facile construction of well-defined Pt-skin catalysts modified by different 3d transition metal (3dTM) atoms in subsurface regions. However, on the catalyst containing both surface and subsurface 3dTMs, the selectivity of propane dehydrogenation decreases in the sequences of Pt ~ PtFe 〉 PtCo 〉 PtNi due to the easier C–C cracking on exposed Co and Ni sites. After the exposed 3dTMs were removed completely, the C 3 H 6 selectivity was found to increase markedly in the row Pt 〈 PtNi@Pt 〈 PtCo@Pt 〈 PtFe@Pt, which is in line with the calculated trend of d-band center shifting. The established relationship between reactivity and d-band center shifting illustrates the role of subsurface catalysis in dehydrogenation reaction.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Pattern recognition applied to the prediction of three seismic elements (1988)
    In:  Earthq. Res. in China, Taipei, Ges. f. Geowissenschaften e.V., vol. 2, no. 6, pp. 485-494, pp. 1307, (ISSN 0343-5164)
    Details
    Publication Date: 1988
    Keywords: Earthquake precursor: prediction research ; Earthquake precursor: statistical anal. of seismicity ; Pattern recognition
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    BIBLIOGRAPHY SEISMOLOGY
  • 5
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    Suzaku observation of supernova remnant G332.5-5.6 (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-06
    Description: We analyse the Suzaku X-ray Imaging Spectrometer data of the central region of supernova remnant G332.5-5.6. The X-ray data are well described by a single non-equilibrium ionization thermal model, vnei , with an absorbing hydrogen column density of 1.4 $^{+0.4}_{-0.1}$   x  10 21  cm –2 . The plasma is characterized by an electron temperature of 0.49 $^{+0.08}_{-0.06}$ keV with subsolar abundances for O (0.58 $^{+0.06}_{-0.05}$ solar value) and Fe (0.72 $^{+0.06}_{-0.05}$ solar value) and slightly overabundance for Mg (1.23 $^{+0.14}_{-0.14}$ solar value). It seems that the central X-ray emission originates from a projection effect or evaporation of residual clouds inside G332.5-5.6. We estimate a distance of 3.0 ± 0.8 kpc for G332.5-5.6 based on the extinction–distance relation. G332.5-5.6 has an age of 7–9 kyr.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Privacy-Preserving Data Publication with Features of Independent {ell}-Diversity (2015)
    Oxford University Press
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    Publication Date: 2015-03-27
    Description: Datasets containing individuals’ information (stored in back-end databases) are often published and shared in social networks. The disclosure of sensitive individuals’ information in social networks is potentially a serious problem. When an attacker studies a published table in a social network, the attacker could infer valuable information of individuals if the attacker learnt some sensitive information of other related individuals from other sources which are different from the published table. This type of attack is referred to as corruption attack . Existing privacy-preserving data publication ( PPDP ) approaches have been developed against corruption attacks, however, they could cause severe information loss, and reduce the usefulness of the published data. In addition, PPDP models based on -diversity and its variants may lead to individual sensitive information disclosure. Motivated by providing a solution to overcome these drawbacks, an independent -diversity principle is proposed in this study. Based on this principle a PPDP model is presented. The model could prevent attacks from attackers who have known data publishing algorithms and have the corruption abilities. A new data utility measurement global loss penalty is also proposed in this study. Related algorithms to our approach have been developed and implemented. Extensive experiments have been performed and comparisons with other related methods have been made. The results have shown the effectiveness of our approaches. It has been noted that when compared with -diversity model and its variant models, our model could resist corruption attacks more effectively; furthermore, when compared with other solutions against corruption attacks, our method would result in less information loss.
    Print ISSN: 0010-4620
    Electronic ISSN: 1460-2067
    Topics: Computer Science
    Published by Oxford University Press
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  • 7
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    Activating mutations in MEK1 enhance homodimerization and promote tumorigenesis (2018)
    The American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2018
    Description: 〈p〉RAS-RAF-MEK-ERK signaling has a well-defined role in cancer biology. Although aberrant pathway activation occurs mostly upstream of the kinase MEK, mutations in MEK are prevalent in some cancer subsets. Here, we found that cancer-related, activating mutations in MEK can be classified into two groups: those that relieve inhibitory interactions with the helix A region and those that are in-frame deletions of the β3-αC loop, which enhance MEK1 homodimerization. The former, helix A–associated mutants, are inhibited by traditional MEK inhibitors. However, we found that the increased homodimerization associated with the loop-deletion mutants promoted intradimer cross-phosphorylation of the activation loop and conferred differential resistance to MEK inhibitors both in vitro and in vivo. MEK1 dimerization was required both for its activation by the kinase RAF and for its catalytic activity toward the kinase ERK. Our findings not only identify a previously unknown group of MEK mutants and provide insight into some key steps in RAF-MEK-ERK activation but also have implications for the design of therapies targeting RAS-ERK signaling in cancers.〈/p〉
    Print ISSN: 1945-0877
    Electronic ISSN: 1937-9145
    Topics: Biology , Medicine
    Published by The American Association for the Advancement of Science (AAAS)
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  • 8
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    Two-dimensional correlation functions for density and magnetic field fluctuations in magnetosheath turbulence measured by the Cluster spacecraft (2011)
    Wiley
    Details
    Publication Date: 2011-06-09
    Description: Knowledge of multidimensional correlation functions is crucial for understanding the anisotropy of turbulence. The two-dimensional (2-D) spatial correlation functions (SCFs) obtained in previous studies of space plasma turbulence were restricted to large-length scales and covered a limited angular domain of the two-point separation vector with respect to the mean magnetic field. Here we aim to derive 2-D SCFs with smaller-length scale and nearly full angular distribution for the fluctuations of the number density and magnetic field in magnetosheath turbulence. We use the Cluster four-spacecraft measurements of the fluctuations with respect to a temporally and spatially varying background magnetic field to construct the 2-D SCFs. We find that the correlation function of the density fluctuations shows a pattern similar to that of the magnetic field fluctuations, both of which appear to be composed of two populations, whereby the major population extends along the coordinate parallel to mean magnetic field (S$\parallel$) and the minor one deviates toward the perpendicular coordinate (S$\perp$). This pattern of 2-D SCFs implies that the energy of magnetosheath turbulence seems to cascade, in the inertial range close to the ion scale, mostly transverse to the background magnetic field and meanwhile partly along the field (i.e., k$\perp$ $\gg$ k$\parallel$).
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Changes of soil prokaryotic communities after clear-cutting in a karst forest: evidences for cutting-based disturbance promoting deterministic processes (2016)
    Oxford University Press
    Details
    Publication Date: 2016-03-02
    Description: To understand the temporal responses of soil prokaryotic communities to clear-cutting disturbance, we examined the changes in soil bacterial and archaeal community composition, structure and diversity along a chronosequence of forest successional restoration using high-throughput 16S rRNA gene sequencing. Our results demonstrated that clear-cutting significantly altered soil bacterial community structure, while no significant shifts of soil archaeal communities were observed. The hypothesis that soil bacterial communities would become similar to those of surrounding intact primary forest with natural regeneration was supported by the shifts in the bacterial community composition and structure. Bacterial community diversity patterns induced by clear-cutting were consistent with the intermediate disturbance hypothesis. Dynamics of bacterial communities was mostly driven by soil properties, which collectively explained more than 70% of the variation in bacterial community composition. Community assembly data revealed that clear-cutting promoted the importance of the deterministic processes in shaping bacterial communities, coinciding with the resultant low resource environments. But assembly processes in the secondary forest returned a similar level compared to the intact primary forest. These findings suggest that bacterial community dynamics may be predictable during the natural recovery process.
    Print ISSN: 0168-6496
    Electronic ISSN: 1574-6941
    Topics: Biology
    Published by Oxford University Press
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  • 10
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    Genetic basis of field-evolved Bt resistance [Agricultural Sciences] (2012)
    National Academy of Sciences
    Details
    Publication Date: 2012-06-27
    Description: Evolution of pest resistance reduces the efficacy of insecticidal proteins from Bacillus thuringiensis (Bt) used in sprays or in transgenic crops. Although several pests have evolved resistance to Bt crops in the field, information about the genetic basis of field-evolved resistance to Bt crops has been limited. In particular, laboratory-selected resistance to Bt toxin Cry1Ac based on recessive mutations in a gene encoding a toxin-binding cadherin protein has been identified in three major cotton pests, but previous work has not determined if such mutations are associated with field-selected resistance to Bt cotton. Here we show that the most common resistance alleles in field populations of cotton bollworm, Helicoverpa armigera, selected with Bt cotton in northern China, had recessive cadherin mutations, including the deletion mutation identified via laboratory selection. However, unlike all previously studied cadherin resistance alleles, one field-selected cadherin resistance allele conferred nonrecessive resistance. We also detected nonrecessive resistance that was not genetically linked with the cadherin locus. In field-selected populations, recessive cadherin alleles accounted for 75–84% of resistance alleles detected. However, most resistance alleles occurred in heterozygotes and 59–94% of resistant individuals carried at least one nonrecessive resistance allele. The results suggest that resistance management strategies must account for diverse resistance alleles in field-selected populations, including nonrecessive alleles.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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