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  • 1
    Electronic Resource
    Electronic Resource
    Combined laser and atomic force microscope lithography on aluminum: Mask fabrication for nanoelectromechanical systems (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3206-3208 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A direct-write laser system and an atomic force microscope (AFM) are combined to modify thin layers of aluminum on an oxidized silicon substrate, in order to fabricate conducting and robust etch masks with submicron features. These masks are very well suited for the production of nanoelectromechanical systems (NEMS) by reactive ion etching. In particular, the laser-modified areas can be subsequently locally oxidized by AFM and the oxidized regions can be selectively removed by chemical etching. This provides a straightforward means to define the overall conducting structure of a device by laser writing, and to perform submicron modifications by AFM oxidation. The mask fabrication for a nanoscale suspended resonator bridge is used to illustrate the advantages of this combined technique for NEMS. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124106
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  • 2
    Electronic Resource
    Electronic Resource
    Uptake and Distribution of Radioactive Carbon from Labelled Substrates by Various Cellular Components of Spinaeb Leaves (1959)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 12 (1959), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1959.tb07970.x
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  • 3
    Electronic Resource
    Electronic Resource
    Amino acid uptake and respiration by marine heterotrophs (1976)
    Springer
    Marine biology 35 (1976), S. 41-47 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The concentration and turnover of dissolved free amino acids were measured in samples from 25 and 100 m on three occasions at a station 6 miles off the California (USA) coast. Individual amino acid concentrations varied from undetectable (〈0.05 μg/l) to 3 μg/l, the total amino acid concentration from 1.8 to 8.5 μg/l. The greater concentration of total amino acids was always found at 25 m. The predominant amino acids were serine, lysine, aspartate, glutamate and alanine; reliable analyses could not be made for glycine because of a high blank. For the 10 individual amino acids studied, the rate of heterotrophic turnover ranged from undetectable to 1.2 μg/l day-1; serine, aspartate, alanine and glutamate showed the highest rates. In samples from 25 m, the rates were 15 to 20 times higher than those taken from 100 m. The total calculated flux of the amino acids studied varied from 0.015 to 3.2 μg/l day-1 and amounted to 1–10% of photosynthetic carbon dioxide fixation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00386673
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  • 4
    Electronic Resource
    Electronic Resource
    Physiology and chemical composition of nitrogen-fixing phytoplankton in the central North Pacific Ocean (1977)
    Springer
    Marine biology 41 (1977), S. 213-227 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The magnitude and physiological characteristics of biological nitrogen fixation have been studied in the oligotrophic waters of the North pacific gyre. The filamentous blue-green algae Trichodesmium spp. and Richelia intracellularis were the important nitrogen-fixing phytoplankton. Most of the nitrogen fixation occurs in the upper 40 m of the water column, with detectable fixation as deep as 90 m, which corresponds to about the 1 % light depth. There was no evidence of photoinhibition of nitrogen fixation, although CO2 reduction was depressed slightly at the highest light levels. The rate of nitrogen fixation in the water column varied throughout the day, being highest in mid-morning and in late afternoon. Relatively high fixation rates were also found during periods of darkness. Elevated oxygen concentrations had a marked inhibitory effect on rates of nitrogen fixation, a pO2 of 0.4 atm causing a 75% inhibition. Data from studies of nitrogen fixation and assimilation rates of 15N-labelled nitrate, ammonium, and urea indicate that nitrogen fixation furnished about 3% of the total daily fixed nitrogen requirement for phytoplankton growth. Studies with isolated colonies of Trichodesmium spp. indicated that 100% of their nitrogen requirement was met by nitrogen fixation. Chemical composition of the Trichodesmium colonies showed that the C:N ratio was 4.1 and that their phosphorus content relative to carbon or nitrogen was much lower than that of the total particulate material in the water column. Elevated ratios of carbon: adenosine triphosphate (ATP) also suggest that phosphorus deficiency may be limiting the growth of Trichodesmium. The magnitude of nitrogen fixation in the gyre is seasonally dependent, with high rates in late summer and autumn. At these times the water column is stratified, with phosphate and nitrate barely detectable in the upper 100 m. Our data suggest that during these months of stratification, biological fixation of nitrogen amounts to about 33 μg-at N/m2/day.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00394908
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  • 5
    Electronic Resource
    Electronic Resource
    Methodology and measurement of adenylate energy charge ratios in environmental samples (1978)
    Springer
    Marine biology 48 (1978), S. 185-197 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A method for measuring ATP, ADP and AMP levels in environmental samples was devised, and applied to seawater and bacterial cell extracts. This procedure is specifically designed for measuring the extremely low concentrations of total adenine nucleotides ([AT]=[ATP]+[ADP]+[AMP]) that are apt to occur in most natural ecosystems (i.e., ≤10 ng AT ml-1 of sample extract). Although the current assay methodology can be used with purified firefly luciferase reagents, it has been suitably modified to accept crude luciferase preparations as well. ATP, ADP and AMP levels have been measured, and the corresponding energy charge (EC) ratios determined for seawater samples collected off the Southern California coast. The EC ratios ranged from 0.50 to 0.89, with peak values corresponding to the subsurface maxima in ATP and chlorophyll a concentrations, and the minimum values corresponding to the deepest water sampled (1500 m). The measurement of adenylate energy charge ratios in environmental samples can be a useful indicator of mean community metabolic activity and potential for cell growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00395018
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  • 6
    Electronic Resource
    Electronic Resource
    Improved methodology for ATP determination in marine environments (1976)
    Springer
    Marine biology 34 (1976), S. 143-149 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A simple technique is described for de-salting and concentrating adenosine triphosphate (ATP) extracted from seawater or marine sediment samples prior to assays with the standard luciferin-luciferase procedure. The technique involves chromatography of H2SO4 extracts on columns of activated carbon. The efficiency of ATP recovery from marine sediments using this pre-treatment was superior to that attained with either boiling “Tris” extraction or with H2SO4 extraction without subsequent purification. All ions which interfere with the luciferase reaction or precipitate ATP upon neutralization of acid extracts are removed with this procedure, thus eliminating the 50- to 100-fold dilutions required with other acid-extraction procedures. In addition, the purified ATP extracts may be concentrated up to 100-fold, thus greatly improving the sensitivity of ATP measurement in samples containing very low biomass. This procedure has been applied to ATP determination in marine sediments in the upwelling area off northwest Africa. The average ATP concentrations in the upper 6 cm of sediment from 1000 and 200 m were 195 and 545 ng per ml wet sediment, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00390756
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  • 7
    Electronic Resource
    Electronic Resource
    High-affinity uptake of an ammonium analogue by two marine microflagellates from the oligotrophic Pacific (1983)
    Springer
    Marine biology 74 (1983), S. 161-168 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two marine microflagellates, isolated from the North Pacific Central Gyre, and tentatively identified as Platymonas sp. and Mantoniella sp., were examined for uptake of 14C-methylamine, a non-metabolizable analogue of ammonium. Half-saturation constants (K m) for ammonium transport, estimated from competitive inhibition of methylamine transport by ammonium, were 50 nM for Platymonas sp. and 2.9 nM for Mantoniella sp. These values are the lowest so far reported, indicating that the transport systems are well adapted to extremely low ammonium environments. The ratio of the K m for methylamine to the K m for ammonium was 17 for Platymonas sp. and 41 for Mantoniella sp. The observed ratios fell within the relatively narrow range reported for various organisms, including bacteria, fungi and phytoplankton (25.0±15.5, $$\bar x$$ ± SD, n=9), although the reported K mvalues for both ammonium and methylamine vary over a thousand-fold range. The use of 14C-methylamine may therefore be a promising technique for studying the kinetics of ammonium transport by marine microorganisms, particularly those in oligotrophic environments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00413919
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of temperature on rate of photosynthesis in Antarctic phytoplankton (1982)
    Springer
    Polar biology 1 (1982), S. 33-38 
    Details
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The rate of photosynthesis of marine antarctic phytoplankton (western Scotia Sea and Bransfield Strait) was determined as a function of temperature, from ambient (-0.8°C to 1.0°C) to 28°C. Photosynthetic rates, based on radiocarbon incorporation during half-day incubations, were increased by as much as 2x with temperatures up to 7°C; at higher temperatures the rates decreased rapidly, so that at 28°C the rates were only 3% of that at ambient temperatures. In antarctic surface waters during the austral summer the rate of photosynthesis by phytoplankton thus is limited by thermodynamic effects on metabolic reactions, in spite of high nutrient concentrations and saturating light levels. The observed rates were in agreement with thermodynamic models of the dependence of phytoplankton growth rate on temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00568752
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  • 9
    Electronic Resource
    Electronic Resource
    Nitrogen assimilation by phytoplankton in the Scotia Sea (1983)
    Springer
    Polar biology 2 (1983), S. 137-147 
    Details
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary This study of nitrogen metabolism of phytoplankton was one component of a large multidisciplinary program designed to examine the biological productivity of the eastern Scotia Sea, Antarctica, with regard to the importance of the zone of mixing of the northern outflow of the Weddell Sea with Drake Passage waters. The total integrated N-uptake for the euphotic zone in the southwest part of the Scotia Sea was estimated to be in the range of 9.7–14.1 mmol N·m-2·d-1, while for the eastern part of the Scotia Sea it was less than half of this, being 2.1 to 4.7 mmol N·m-2·d-1. The rate of primary production could not be correlated with the front between the two major water masses. Assimilation rates of 15N-enriched substrates indicate that phytoplankton production in the Scotia Sea during austral summer subsists predominantly on ammonia (85%), with lower incorporation rates for nitrate (14%) and nitrite (1%). Nitrate assimilation was much more light-dependent than the uptake of ammonia. These data indicate that there is a rapid and extensive mineralization of organic matter in the surface waters, resulting in a recycling of nitrogen approximately eight times before it is lost from the euphotic zone. This has important implications with regard to the dynamics of the microbial food web in antarctic waters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00448963
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  • 10
    Electronic Resource
    Electronic Resource
    Microbial uptake of dissolved organic matter in Mcmurdo Sound, Antarctica (1981)
    Springer
    Marine biology 61 (1981), S. 89-94 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The distribution and activity of bacterioplankton, and the turnover of dissolved organic matter (DOM) were examined in McMurdo Sound, Antarctica. On the eastern side of the Sound, bacteria averaged 6.5×108 l-1, and turnover rates of dissolved adenosine triphosphate, D-glucose and l-leucine averaged 16, 116 and 124 h, respecitvely. These molecules as well as thymidine were taken up maximally from 0° to 5°C and near-maximally from -1.5° to 0°C, indicating bacterial adaptation to rapid turnover of dissolved organic matter at the ambient temperature. On the west side of the Sound, bacteria averaged only 0.65×108 l-1, and turnover times for adenosine triphosphate, D-glucose and lleucine averaged 59, 20454, and 3070 h, respectively. Total microbial adenosine triphosphate (an indicator of total microbial biomass) and chlorophyll a were also much lower at the western than at the eastern side stations. Moreover, no primary production could be detected at one western side station (New Harbor). Thus, in McMurdo Sound, the western side is highly oligotrophic, but the eastern side has an abundant active bacterioplankton, comparable to that of temperate coastal waters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00386648
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