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  • 1
    Electronic Resource
    Electronic Resource
    Metabolic adaptation of Zostera marina (eelgrass) to diurnal periods of root anoxia (1984)
    Springer
    Marine biology 83 (1984), S. 141-147 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The temperate seagrass Zostera marina L. is common in coastal marine habitats characterized by the presence of reducing sediments. The roots of this seagrass grow in these anoxic sediments, yet eelgrass is highly productive. Through photosynthesis-dependent oxygen transport from leaves to roots, aerobic respiration is supported in eelgrass roots only during daylight; consequently, roots are subjected to diurnal periods of anoxia. Under anoxic root conditions, the amino acids alanine and γ-amino butyric acid accumulate within a few hours to account for 70% of the total amino acid pool, while glutamate and glutamine decline. Little ethanol is produced, and the pool size of the organic acid malate changes little or declines slowly. Upon the resumption of shoot photosynthesis and oxygen transport to the roots, the accumulated γ-amino butyric acid declines rapidly, glutamate and glutamine pools increase, and alanine declines over a 16-h period. These adaptive metabolic responses by eelgrass to diurnal root anoxia must contribute to the successful exploitation of shallow-water marine sediments that have excluded nearly all vascular plant groups. A metabolic scheme is presented that accounts for the observed changes in organic and amino acid pool sizes in response to anoxia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00394721
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  • 2
    Electronic Resource
    Electronic Resource
    Corrosion of nickel-base and iron-base alloys in a simulated fluidized-bed coal-combustion environment (1989)
    Springer
    Oxidation of metals 31 (1989), S. 123-143 
    Details
    ISSN: 1573-4889
    Keywords: high-temperature sulfidation ; fluidized bed combustor ; nickel-base alloys ; 300-series stainless steels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The modes of initiation and propagation of corrosion attack on a series of high-temperature alloys were studied in synthetic gas mixtures at 900°C. The gas mixtures were intended to simulate the oxygen and sulfur partial pressures experienced in reducing zones in a coal-fired fluidized-bed combustor and comprised mixtures of CO, CO2, and SO2. The alloys studied were candidates for in-bed heat exchanger tubing for an air-heater cycle operating at 843°C and 300–500 psig and so ranged from type 300-series stainless steels to nickel-base alloys. With the exception of two FeCrAlY alloys and types 304 and 347 stainless steels, it was found that sulfidation corrosion could be initiated on all the alloys within 0.25 hr; the rate of propagation of the corrosive attack depended on the flux of SO2 in the environment and on the nickel content of the alloys. The presence of iron in the alloys appeared to slow the initiation of sulfidation, by forming a continuous iron oxide layer. The effects of various alloying additions are discussed, and a schematic model for the initiation of sulfidation is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00665490
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  • 3
    Electronic Resource
    Electronic Resource
    Influence of solid-state CaS-CaO-CaSO4 deposits on corrosion of high-temperature alloys in simulated FBC environments (1989)
    Springer
    Oxidation of metals 31 (1989), S. 325-340 
    Details
    ISSN: 1573-4889
    Keywords: sulfidation ; nickel-base alloys ; iron-base alloys ; fluidized-bed combustion ; deposit-related attack
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This study addresses questions concerning the likelihood of sulfidation attack of heat-exchanger alloys beneath deposits of sulfur-sorbent material in fluidized-bed combustors. Alloy specimens were exposed at 900°C in calcium sulfate-calcium oxide and calcium sulfide-calcium oxide mixtures, in environments in which the oxygen partial pressures were fixed at values corresponding to the equilibrium values for each solids mixture, using controlled ratios of CO and CO2. The only source of sulfur in these systems was the calcium sulfate or sulfide. Sulfidation attack of nickel-base alloys occurred in both mixtures, the calcium sulfide-calcium oxide mixture being the more aggressive. Iron-base alloys were less susceptible to attack, although susceptibility increased with increasing nickel content. FeCrAlY-type alloys were resistant to attack. Comparison with corrosion behavior under conditions in which the oxygen and sulfur partial pressures were the same as those used here, but in which the sulfur source was in the gas phase, indicates that the form of the sulfidation attack is similar but that its progress is much slower under solid deposits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00846692
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  • 4
    Electronic Resource
    Electronic Resource
    Generation of voluminous silicic magmas and formation of mid-Cenozoic crust beneath north-central Mexico: evidence from ignimbrites, associated lavas, deep crustal granulites, and mantle pyroxenites (1996)
    Springer
    Contributions to mineralogy and petrology 123 (1996), S. 375-389 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Isotopic and trace element data from mantle and granulite xenoliths are used to estimate the relative contributions of mantle and crustal components to a large ignimbrite, referred to as the upper ignimbrite, that is representative of the voluminous mid-Cenozoic rhyolites of northwestern Mexico. The study also uses data from the volcanic rocks to identify deep crustal xenoliths that are samples of new crust created by the Tertiary magmatism. The isotopic composition of the mantle component is defined by mantle-derived pyroxenites that are interpreted to have precipitated from mid-Cenozoic basaltic magmas. This component has ɛNd≈+1.5, 87Sr/86Sr≈0.7043 and 206Pb/204Pb≈18.6. Within the upper ignimbrite and associated andesitic and dacitic lavas, initial 87Sr/86Sr is positively correlated with SiO2, reaching 0.7164 in the ignimbrite. Initial 206Pb/204Pb ratios also show a positive correlation with silica, whereas ɛNd values have a crude negative correlation, reaching values as low as −2. Of the four isotopically distinct crustal components identified from studies of granulite xenoliths, only the sedimentary protolith of the paragneiss xenoliths can be responsible for the high initial 87Sr/86Sr of the upper ignimbrite. The Nd, Sr, and Pb isotopic compositions of the upper ignimbrite can be modeled with relatively modest assimilation (≤20%) of the sedimentary component ± Proterozoic granulite. Gabbroic composition granulite xenoliths have distinctive Nd, Sr, and Pb isotope ratios that cluster closely within the range of compositions found in the andesitic and dacitic lavas. These mafic granulites are cumulates, and their protoliths are interpreted to have precipitated from the intermediate to silicic magmas at 32–31 Ma. These mafic cumulate rocks are probably representative of much of the deep crust that formed during mid-Cenozoic magmatism in Mexico. Worldwide xenolith studies suggest that the relatively great depth (≤20 km) at which assimilation-fractional crystallization took place in the intermediate to silicic magma systems of the La Olivina region is the rule rather than the exception. Oligocene ignimbrites of the southwestern United States (SWUS) have substantially lower ɛNd values (e.g. 〈−6) than the upper ignimbrite and other rhyolites from Mexico. This difference appears to reflect a greater crustal contribution to ignimbrites of the SWUS, perhaps due to a higher temperature of the lower crust prior to the emplacement of the Oligocene basaltic magmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004100050163
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of anaerobiosis on root metabolism of Zostera marina (eelgrass): implications for survival in reducing sediments (1988)
    Springer
    Marine biology 98 (1988), S. 131-141 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The temperate seagrass Zostera marina L. typically grows in highly reducing sediments. Photosynthesis-mediated O2 supplied to below-ground tissues sustains aerobic respiration during photosynthetic periods. Roots, however, experience daily periods of anoxia and/or hypoxia at night and under conditions that reduce photosynthesis. Rhizosphere cores of Z. marina were collected in August 1984 from Great Harbor, Massachusetts, USA. We examined short-term anaerobic metabolism of [U-14C]sucrose in excised roots and roots of intact plants. Under anaerobic conditions roots showed appreciable labeling of CO2, ethanol and lactate, and slight labeling of alanine and other metabolites. Over 95% of the 14C-ethanol was recovered in the root exudate. Release of other metabolites from the roots was minimal. Ethanol was also released from hypoxic/anoxic roots of intact plants and none of this ethanol was transported to the shoot under any experimental conditions. Loss of ethanol from roots prevented tissue levels of this phytotoxin from increasing during anaerobiosis despite increased synthesis of ethanol. Anaerobic metabolism of [U-14C]glutamate in excised roots led to appreciable labelling of γ-aminobutyrate, which was known to accumulate in eelgrass roots. Roots recovered to fully aerobic metabolism within 4 h after re-establishment of aerobic conditions. The contributions of these root metabolic responses to the ability of Z. marina to grow in reducing marine sediments are related to light-regulated interactions of shoots and roots that likely dictate depth penetration, distribution and ecological success of eelgrass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392668
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  • 6
    Electronic Resource
    Electronic Resource
    Protein-phosphatase inhibitors block root hair growth and alter cortical cell shape ofArabidopsis roots (1994)
    Springer
    Planta 194 (1994), S. 516-524 
    Details
    ISSN: 1432-2048
    Keywords: Arabidopsis ; Calyculin-A ; Okadaic acid ; Protein phosphatase ; Root development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Emerging evidence suggests that protein phosphatases play an important role in the growth and development of higher plants. We report here on the effects of okadaic acid and calyculin-A, two specific and potent inhibitors of the type-1 and type-2A families of serine/ threonine protein phosphatases, on the growth and development ofArabidopsis thaliana L. roots. Application of these drugs in nanomolar ranges arrested root hair growth, severely affected the shape of cells within the zone of elongation and inhibited root growth rates. Root hair elongation was inhibited by concentrations of okadaic acid and calyculin-A as low as 3 nM. The pleiotropic effects of okadaic acid and calyculin-A point to multiple functions for type-1 and -2A protein phosphatases in controlling root growth and development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00714465
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  • 7
    Electronic Resource
    Electronic Resource
    The link between physics and chemistry in track modelling (1999)
    Springer
    Radiation and environmental biophysics 38 (1999), S. 221-228 
    Details
    ISSN: 1432-2099
    Keywords: Key words Track structure ; Radiation tracks ; Stochastic simulations ; Molecular dynamics ; Spin effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract  The physical structure of a radiation track provides the initial conditions for the modelling of radiation chemistry. These initial conditions are not perfectly understood, because there are important gaps between what is provided by a typical track structure model and what is required to start the chemical model. This paper addresses the links between the physics and chemistry of tracks, with the intention of identifying those problems that need to be solved in order to obtain an accurate picture of the initial conditions for the purposes of modelling chemistry. These problems include the reasons for the increased yield of ionisation relative to homolytic bond breaking in comparison with the gas phase. A second area of great importance is the physical behaviour of low-energy electrons in condensed matter (including thermolisation and solvation). Many of these processes are not well understood, but they can have profound effects on the transient chemistry in the track. Several phenomena are discussed, including the short distance between adjacent energy loss events, the molecular nature of the underlying medium, dissociative attachment resonances and the ability of low-energy electrons to excite optically forbidden molecular states. Each of these phenomena has the potential to modify the transient chemistry substantially and must therefore be properly characterised before the physical model of the track can be considered to be complete.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050162
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  • 8
    Electronic Resource
    Electronic Resource
    β-Methyl carboline, a benzodiazepine inverse agonist, attenuates the effect of triazolam on the circadian rhythm of locomotor activity (1989)
    Springer
    Cellular and molecular life sciences 45 (1989), S. 334-337 
    Details
    ISSN: 1420-9071
    Keywords: Benzodiazepine ; circadian rhythm ; gamma-aminobutyric acid ; inverse agonist ; suprachiasmatic nucleus ; triazolam
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The benzodiazepine triazolam, the benzodiazepine inverse agonist, β-methyl carboline (β-CCM) or both, were administered to adult male hamsters under conditions of constant light. When given alone, triazolam induced phase advances in the circadian activity rhythm of about 90 min, while β-CCM when given alone, had no effect on phase of the activity rhythm. However, when triazolam and β-CCM were given at the same time, the magnitude of the phase advances induced by triazolam were attenuated to about 30 min. These data, in conjunction with previous results, provide pharmacological evidence for a GABAergic system involved in the regulation of a central circadian pacemaker.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01957468
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  • 9
    Electronic Resource
    Electronic Resource
    Glas (1933)
    Springer
    Fresenius' Zeitschrift für analytische Chemie 93 (1933), S. 227-229 
    Details
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01392883
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  • 10
    Electronic Resource
    Electronic Resource
    Application of capillary supercritical fluid chromatography to the analysis of a middle distillate fuel (1984)
    Springer
    Chromatographia 18 (1984), S. 542-545 
    Details
    ISSN: 1612-1112
    Keywords: Supercritical fluid chromatography ; Alumina ; Fused silica capillary columns ; Middle distillate fuel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The application of capillary supercritical fluid chromatography (SFC) to the analysis of a middle distillate fuel is described. Small diameter (50μm i.d.) fused-silica capillary columns coated with crosslinked 50% phenyl polymethylphenyl siloxane provided high separation efficiency and good compatibility with flame ionization detection. High resolution separations of the chemical class fractions obtained by adsorption chromatography on alumina were obtained using carbon dioxide as the supercritical mobile phase and simple pressure programming techniques. In addition to the less polar fuel components, supercritical carbon dioxide allowed chromatography of the nitrogen-containing polycyclic aromatic hydrocarbon fraction and the hydroxylated polycyclic aromatic materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02265691
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