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  • 1
    Electronic Resource
    Electronic Resource
    Characterization of all-chromium tunnel junctions and single-electron tunneling devices fabricated by direct-writing multilayer technique (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 6956-6964 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report about the fabrication and analysis of the properties of Cr/CrOx/Cr tunnel junctions and single-electron tunneling transistors, prepared by different variants of direct-writing multilayer technique. In all cases, the chromium oxide tunnel barriers were formed in air under ambient conditions. From the experiments on single junctions, values for the effective barrier height and thickness were derived. For the all-chromium single-electron tunneling transistors, we achieved minimal junction areas of 17×60 nm2 using a scanning transmission electron microscope for the e-beam exposure on Si3N4 membrane substrate. We discuss the electrical performance of the transistor samples as well as their noise behavior. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371778
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  • 2
    Electronic Resource
    Electronic Resource
    Metallic single electron devices fabricated using a multilayer technique (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 713-715 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single electron tunneling (SET) transistors were fabricated for the electrodes and for the island using two different resist masks. This technology overcomes disadvantages of the well-established shadow evaporation method usually used for the fabrication of SET devices and offers more flexibility in materials and layouts. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119838
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  • 3
    Electronic Resource
    Electronic Resource
    Significance of soil microorganisms for the mobilization of nonexchangeable ammonium (1996)
    Springer
    Biology and fertility of soils 22 (1996), S. 248-251 
    Details
    ISSN: 1432-0789
    Keywords: Key words Nonexchangeable ammonium ; Availability ; Soil microorganisms ; Temperature ; Available carbon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract To estimate the availability of nonexchangeable NH4 +-N for soil microorganisms four incubation experiments were conducted under controlled conditions. The following results were obtained: Incorporating glucose as a source of readily oxidizable organic material favored the release of nonexchangeable NH4 +-N. Mobilization of NH4 + from the interlayers of the clay minerals was decreased by the application of K+, while Ca2+, which is supposed to expand the lattice of the clay minerals, had no influence on the release of NH4 +. Soil temperature had no effect on microbiological mobilization of NH4 +. It is assumed that, generally, the influence of nitrifying bacteria on the mobilization of nonexchangeable NH4 +-N is negligible. However, in soils with abundant amounts of available carbon promoting the activity of heterotrophic soil microorganisms, the release of NH4 + from clay minerals is favored under fallow conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00382520
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  • 4
    Electronic Resource
    Electronic Resource
    Significance of soil microorganisms for the mobilization of nonexchangeable ammonium (1996)
    Springer
    Biology and fertility of soils 22 (1996), S. 248-251 
    Details
    ISSN: 1432-0789
    Keywords: Nonexchangeable ammonium ; Availability ; Soil microorganisms ; Temperature ; Available carbon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract To estimate the availability of nonexchangeable NH inf4 sup+ −N for soil microorganisms four incubation experiments were conducted under controlled conditions. The following results were obtained: Incorporating glucose as a source of readily oxidizable organic material favored the release of nonexchangeable NH inf4 sup+ −N. Mobilization of NH inf4 sup+ from the interlayers of the clay minerals was decreased by the application of K++, while Ca2+, which is supposed to expand the lattice of the clay minerals, had no influence on the release of NH inf4 sup+ . Soil temperature had no effect on microbiological mobilization of NH inf4 sup+ . It is assumed that, generally, the influence of nitrifying bacteria on the mobilization of nonexchangeable NH inf4 sup+ −N is negligible. However, in soils with abundant amounts of available carbon promoting the activity of heterotrophic soil microorganisms, the release of NH inf4 sup+ from clay minerals is favored under fallow conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00382520
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  • 5
    Electronic Resource
    Electronic Resource
    Estimating microbial biomass N in soils with and without living roots: Limitations of a pre-extraction step (1996)
    Springer
    Biology and fertility of soils 21 (1996), S. 314-318 
    Details
    ISSN: 1432-0789
    Keywords: Key words Microbial biomass N ; Fumigation-extraction ; Pre-extraction ; Rhizosphere ; Roots ; Net-closed soil containers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Special net-closed soil containers were used in a pot experiment with low and high plant densities to give soil samples with and without roots. Soils from the containers were analysed either by the fumigation-extraction method or by a modified procedure starting with a pre-extraction and sieving step to remove plant roots from the samples. In the extracts NO-N, NH-N, organic N, and total N were measured. Microbial biomass N was calculated from the differences in total N in fumigated and unfumigated soils. Different plant densities had almost no influence on the values of the N compounds using either method. In soils with roots, significantly more organic N (and total N) was found by the fumigation-extraction method compared to soils without roots while no differences were obtained using pre-extractions and sieving. Though the organic N content in pre-extracts from soils with roots was significantly higher than from soils without roots, the NO-N and NH-N content was lower. Significant differences in biomass N in soils with and without roots were found only with the fumigation-extraction method. Biomass N levels calculated using the results after pre-extraction and sieving were about 50% lower than levels detected using fumigation-extraction alone. With the use of special net-closed soil containers, not only were soil samples produced with and without roots, but it was also possible to induce a rhizophere in the soils. A comparison of the two methods using these soils clearly demonstrated that the method used has profound influence on the final biomass N results. While higher ”biomass“ levels were found by fumigation-extraction in soils with roots, because root N becomes extractable after fumigation, the use of a pre-extraction and a sieving step may underestimate the total biomass N content due to the pre-extraction of microbial N (especially from rhizosphere microorganisms) from the sample. Nevertheless, pre-extraction and sieving followed by fumigation-extraction does seem to be the preferable method for biomass N measurement in comparative studies, because in most cases only minor errors will occur.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00334909
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  • 6
    Electronic Resource
    Electronic Resource
    Highly Sensitive Electrometers Based on Single Cooper Pair Tunneling (1999)
    Springer
    Journal of superconductivity 12 (1999), S. 747-755 
    Details
    ISSN: 1572-9605
    Keywords: Coulomb and Josephson effects ; thermal and quantum fluctuations ; ultrasmall tunnel junctions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A superconducting transistor structure comprising two Josephson tunnel junctions connected in series and a small island in between, which is capacitively coupled to a gate, is considered. When self-capacitances of the junctions are sufficiently small that the corresponding charging energy E c is of the order of magnitude of the Josephson coupling strength E J (and both are ≫k B T), the interplay of the charging and Josephson effects in the circuit becomes essential. This leads to a characteristic IV curve which can be effectively modulated by the gate in two limit cases of external electrodynamic impedance Z s (ω): (a) Z s = R s ≫ R Q ≈ 6.5 kΩ and (b) R s ≪ R Q . Both circuits can serve as electrometers which are competitive with traditional single-electron devices. Preliminary experimental results are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007780925567
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  • 7
    Electronic Resource
    Electronic Resource
    Ammonium fixation by clay minerals in different layers of two paddy soils after flooding (1999)
    Springer
    Biology and fertility of soils 29 (1999), S. 152-156 
    Details
    ISSN: 1432-0789
    Keywords: Key words Non-exchangeable ammonium ; Paddy soils ; Redox potential ; Organic substance ; Nitrogen immobilization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  The influence of flooding and cellulose addition on the fixation of NH4 + in different soil layers of two paddy soils from China (an entisol and an ultisol) was investigated. In both soils the content of total reducing substances (TRS) sharply increased during the first days after flooding and was highest in the anoxic layers. This increase, which was more pronounced in the entisol with the higher total C content, was accompanied by an increase in the concentration of non-exchangeable NH4 + in both soils. The increase in mineralization after flooding, resulting in higher concentrations of exchangeable NH4 +, favoured the fixation of NH4 +. Although the application of cellulose resulted in higher TRS contents, the fixation of NH4 + ions decreased, which may have been the result of microbiological N immobilization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050538
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  • 8
    Electronic Resource
    Electronic Resource
    N2 fixation and growth of legumes as affected by sulphur fertilization (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 449-453 
    Details
    ISSN: 1432-0789
    Keywords: Sulphur ; Legumes ; N2 fixation ; Rhizobia Nitrogenase ; Nodulation ; Acetylene reduction assay 15N dilution technique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The influence of three sulphur application rates in combination with two nitrogen application rates on N2 fixation and growth of different legumes was investigated. N was applied as N-labelled 15NH4 15NO3. The 15N isotope dilution technique was used to estimate N2 fixation. At both N increments dry matter yield was highest with high S supply. Independently of the N supply, the high S application rate resulted in a significantly higher N accumulation, which was mainly caused by a higher N2 fixation rate. With the grain legumes the weight of nodules was increased by the high S application rate. The higher number of nodules per pot with optimum S supply was the result of a better root growth. Rates of acetylene reduction correlated significantly with S supply.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00335921
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    Estimating microbial biomass N in soils with and without living roots: Limitations of a pre-extraction step (1996)
    Springer
    Biology and fertility of soils 21 (1996), S. 314-318 
    Details
    ISSN: 1432-0789
    Keywords: Microbial biomass N ; Fumigation-extraction ; Pre-extraction ; Rhizosphere ; Roots ; Net-closed soil containers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Special net-closed soil containers were used in a pot experiment with low and high plant densities to give soil samples with and without roots. Soils from the containers were analysed either by the fumigation-extraction method or by a modified procedure starting with a pre-extraction and sieving step to remove plant roots from the samples. In the extracts NO 3 - -N, NH 4 + -N, organic N, and total N were measured. Microbial biomass N was calculated from the differences in total N in fumigated and unfumigated soils. Different plant densities had almost no influence on the values of the N compounds using either method. In soils with roots, significantly more organic N (and total N) was found by the fumigation-extraction method compared to soils without roots while no differences were obtained using pre-extractions and sieving. Though the organic N content in pre-extracts from soils with roots was significantly higher than from soils without roots, the NO 3 - -N and NH 4 + -N content was lower. Significant differences in biomass N in soils with and without roots were found only with the fumigation-extraction method. Biomass N levels calculated using the results after pre-extraction and sieving were about 50% lower than levels detected using fumigation-extraction alone. With the use of special net-closed soil containers, not only were soil samples produced with and without roots, but it was also possible to induce a rhizophere in the soils. A comparison of the two methods using these soils clearly demonstrated that the method used has profound influence on the final biomass N results. While higher “biomass” levels were found by fumigation-extraction in soils with roots, because root N becomes extractable after fumigation, the use of a pre-extraction and a sieving step may underestimate the total biomass N content due to the pre-extraction of microbial N (especially from rhizosphere microorganisms) from the sample. Nevertheless, pre-extraction and sieving followed by fumigation-extraction does seem to be the preferable method for biomass N measurement in comparative studies, because in most cases only minor errors will occur.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00334909
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    N2 fixation and growth of legumes as affected by sulphur fertilization (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 449-453 
    Details
    ISSN: 1432-0789
    Keywords: Key words Sulphur ; Legumes ; N2 fixation ; Rhizobia ; Nitrogenase ; Nodulation ; Acetylene reduction assay ; 15N dilution technique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The influence of three sulphur application rates in combination with two nitrogen application rates on N2 fixation and growth of different legumes was investigated. N was applied as N-labelled 15NH4 15NO3. The 15N isotope dilution technique was used to estimate N2 fixation. At both N increments dry matter yield was highest with high S supply. Independently of the N supply, the high S application rate resulted in a significantly higher N accumulation, which was mainly caused by a higher N2 fixation rate. With the grain legumes the weight of nodules was increased by the high S application rate. The higher number of nodules per pot with optimum S supply was the result of a better root growth. Rates of acetylene reduction correlated significantly with S supply.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00335921
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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