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  • 1
    Electronic Resource
    Electronic Resource
    An Updated and Comprehensive rRNA Phylogeny of (Crown) Eukaryotes Based on Rate-Calibrated Evolutionary Distances (2000)
    Springer
    Journal of molecular evolution 51 (2000), S. 565-576 
    Details
    ISSN: 1432-1432
    Keywords: Key words: SSU rRNA database — Among-site rate variation — Eukaryotic diversity — Crown eukaryotes — Distance trees — Rate variation among lineages
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Recent experience with molecular phylogeny has shown that all molecular markers have strengths and weaknesses. Nonetheless, despite several notable discrepancies with phylogenies obtained from protein data, the merits of the small subunit ribosomal RNA (SSU rRNA) as a molecular phylogenetic marker remain indisputable. Over the last 10 to 15 years a massive SSU rRNA database has been gathered, including more then 3000 complete sequences from eukaryotes. This creates a huge computational challenge, which is exacerbated by phenomena such as extensive rate variation among sites in the molecule. A few years ago, a fast phylogenetic method was developed that takes into account among-site rate variation in the estimation of evolutionary distances. This ``substitution rate calibration'' (SRC) method not only corrects for a major source of artifacts in phylogeny reconstruction but, because it is based on a distance approach, allows comprehensive trees including thousands of sequences to be constructed in a reasonable amount of time. In this study, a nucleotide variability map and a phylogenetic tree were constructed, using the SRC method, based on all available (January 2000) complete SSU rRNA sequences (2551) for species belonging to the so-called eukaryotic crown. The resulting phylogeny constitutes the most complete description of overall eukaryote diversity and relationships to date. Furthermore, branch lengths estimated with the SRC method better reflect the huge differences in evolutionary rates among and within eukaryotic lineages. The ribosomal RNA tree is compared with a recent protein phylogeny obtained from concatenated actin, α-tubulin, β-tubulin, and elongation factor 1-α amino acid sequences. A consensus phylogeny of the eukaryotic crown based on currently available molecular data is discussed, as well as specific problems encountered in analyzing sequences when large differences in substitution rate are present, either between different sequences (rate variation among lineages) or between different positions within the same sequence (among-site rate variation).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002390010120
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  • 2
    Electronic Resource
    Electronic Resource
    High yield synthesis of propanal from methane and air (1992)
    Springer
    Catalysis letters 13 (1992), S. 341-347 
    Details
    ISSN: 1572-879X
    Keywords: Methane ; oxidation ; oxidative coupling ; hydroformylation ; propanal ; catalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract High yield synthesis of propanal from methane and air can be obtained in a single pass at atmospheric pressure. Three catalytic processes are combined to give 13% yield of propanal based on total methane input. Ethene is made from the oxidative coupling reaction and carbon monoxide and hydrogen is generated from partial oxygenation of methane. These gases are combined and passed to a hydroformylation catalyst to give liquid propanal. The unreacted methane is inert in the hydroformylation stage, while oxygen deactivates the catalyst readily. The results imply that propanal can be obtained, in good yield, from methane and air provided that total oxygen conversion is achieved. The yield of propanal from the three combined processes can be substantially higher than that of ethene from the oxidative coupling reaction. Thus, higher yields of a condensible and oxygenated product are obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00765036
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  • 3
    Electronic Resource
    Electronic Resource
    Redox properties of molten salts for methane activation (1993)
    Springer
    Catalysis letters 21 (1993), S. 123-131 
    Details
    ISSN: 1572-879X
    Keywords: Molten salts ; redox mode ; oxidative coupling of methane ; transition metal halides/sodium metavanadate mixtures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Molten salt mixtures have been tested in a redox mode as catalysts for the activation of methane at 750 °C. It is found that after pre-treatment with dioxygen a transition metal halide/ sodium vanadate melt can convert methane selectively to C2+ products in the absence of molecular oxygen. The melt can be reactivated by passing dioxygen. Electron paramagnetic resonance studies of the quenched samples showed that the transition metal ions are reduced by methane and can be reoxidised by dioxygen. It is also found that higher C2+ selectivity, C2+ yield and C2H4/C2H6 ratio are promoted by added transition metal chlorides and, surprisingly, also by the corresponding metal bromides. It supports the suggestion that surface modification by halogen is more important than gas radical reactions. Comparison of the molten mixtures under redox and cofeed conditions showed that the former gave a higher C2+ selectivity, but no oxygenated products whereas formaldehyde was only detected in the cofeed conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00767377
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  • 4
    Electronic Resource
    Electronic Resource
    A study of carbon deposition on catalysts during the partial oxidation of methane to synthesis gas (1993)
    Springer
    Catalysis letters 22 (1993), S. 299-305 
    Details
    ISSN: 1572-879X
    Keywords: Methane partial oxidation ; carbon deposition ; kinetic barrier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The deposition of carbon on catalysts during the partial oxidation of methane to synthesis gas has been investigated and it has been found that the relative rate of carbon deposition follows the order Ni〉Pd〉Rh〉Ir. Methane decomposition was found to be the principal route for carbon formation over a supported nickel catalyst, and electron micrographs showed that both “whisker” and “encapsulate” forms of carbon are present on the catalyst. Negligible carbon deposition occurred on iridium catalysts, even after 200 h.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00807237
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  • 5
    Electronic Resource
    Electronic Resource
    Dry reforming of methane to synthesis gas over supported molybdenum carbide catalysts (2000)
    Springer
    Catalysis letters 70 (2000), S. 117-122 
    Details
    ISSN: 1572-879X
    Keywords: supported molybdenum carbide ; methane dry reforming ; syngas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The dry reforming of methane at elevated pressure over supported molybdenum carbide catalysts, prepared from oxide precursors using ethane TPR, has been studied. The relative stability of the catalysts is Mo2C/Al2O3〉Mo2C/ZrO2〉Mo2C/SiO2〉Mo2C/TiO2, and calcination of the oxide precursor for short periods was found to be beneficial to the catalyst stability. Although the support appears to play no beneficial role in the methane dry reforming reaction, the alumina-supported material was stable for long periods of time; this may be important for the production of pelletised industrial catalysts. The evidence suggests that the differences in the stabilities may be due to interaction at the precursor stage between MoO3 and the support, while catalyst deactivation is due to oxidation of the carbide to MoO2, which is inactive for methane dry reforming.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018829116093
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  • 6
    Electronic Resource
    Electronic Resource
    Characterisation of the active phase in caesium-doped iron-vanadium-oxide catalysts for the selective oxidation of polyaromatics (1997)
    Springer
    Catalysis letters 43 (1997), S. 107-115 
    Details
    ISSN: 1572-879X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The addition of caesium sulphate to unsupported vanadium-iron-oxide materials leads to the formation of an amorphous non-stoichiometric phase, as well as the crystalline phases, FeVO4, Fe2V4O13, and Fe1-XS (pyrrhotite). Caesium was only present in the amorphous parts of the sample, and the amount of the new phase formed was found to vary depending on the vanadium:iron ratio and the amount of caesium dopant added. The new phase contains Fe3+ ions with oxide lattice vacancies in their coordination sphere, i.e. Fe3+-VO(e-) species. Catalytic testing demonstrated that the caesium-doped samples were more selective for the oxidation of fluorene to 9-fluorenone. The role of the caesium is probably to modify the surface acidity of the catalyst and act in the formation of stable oxide lattice vacancies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018926219595
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  • 7
    Electronic Resource
    Electronic Resource
    Bayesian image restoration, with two applications in spatial statistics (1991)
    Springer
    Annals of the Institute of Statistical Mathematics 43 (1991), S. 1-20 
    Details
    ISSN: 1572-9052
    Keywords: Bayesian restoration ; image analysis ; spatial statistics ; Gibbs sampler ; archeology ; epidemiology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract There has been much recent interest in Bayesian image analysis, including such topics as removal of blur and noise, detection of object boundaries, classification of textures, and reconstruction of two- or three-dimensional scenes from noisy lower-dimensional views. Perhaps the most straightforward task is that of image restoration, though it is often suggested that this is an area of relatively minor practical importance. The present paper argues the contrary, since many problems in the analysis of spatial data can be interpreted as problems of image restoration. Furthermore, the amounts of data involved allow routine use of computer intensive methods, such as the Gibbs sampler, that are not yet practicable for conventional images. Two examples are given, one in archeology, the other in epidemiology. These are preceded by a partial review of pixel-based Bayesian image analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00116466
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  • 8
    Electronic Resource
    Electronic Resource
    A note on TI-subgroups (1988)
    Springer
    Archiv der Mathematik 51 (1988), S. 97-103 
    Details
    ISSN: 1420-8938
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01206465
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  • 9
    Electronic Resource
    Electronic Resource
    Visual unpatterned input determines the occurrence of reward-contingent positive variation (1971)
    Springer
    Cellular and molecular life sciences 27 (1971), S. 51-52 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Résumé Des chats porteurs d'électrodes corticales Ag-AgCl non polarisables et de lentilles de contact translucides, ont été entraînés, dans obscurité, à presser un levier pour obtenir 0,8 ml de lait. Ils montrent des périodes d'activité lente de haut voltage, c'est-à-dire un phénomène ECoG connu comme synchronisation de post-reinforcement sur le cortex pariéto-occipital. Quand cette synchronisation associée à la variation positive de contingent est supprimée dans l'obscurité, ces phénomènes dépendent de l'influx de la lumière diffuse et non de la perception visuelle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02137736
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  • 10
    Electronic Resource
    Electronic Resource
    Oxidative dehydrogenation of ethane over La1−xSrxFeO3−δ perovskite oxides (1996)
    Springer
    Catalysis letters 38 (1996), S. 189-195 
    Details
    ISSN: 1572-879X
    Keywords: perovskite ; La1−xSrxFeO3−δ ; dehydrogenation ; oxidation ; ethane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Catalysts of the composition La1−xSrxFeO3−δ, 0⩽x ⩽1, have been tested for the oxidative dehydrogenation of ethane in the temperature range 300–800°C. The catalyst is active above 400°C, giving a maximum yield of 37% ethylene at 650°C. Above 650°C, synthesis gas was formed together with methane, suggesting that the reforming reaction and thermal cracking of ethane took place. The catalytic data are compared to conductivity measurements on the same material, and a good correlation between the activity and p-type conductivity has been found. In the phase diagram for the system LaFeO3-SrFeO3−δ, a phase separation to two types of (La, Sr)FeO3−δ perovskites was observed in the La/Sr binary composition in the temperature range below 800°C. The phase separation can elucidate the dependency of the catalytic activity on its p-type conductivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00806567
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