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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Electrical engineering 79 (1996), S. 303-310 
    ISSN: 1432-0487
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Contents This paper describes the implementation of a new control approach for the Unified Poer Flow Controller (UPFC), which provides active filtering capabilities to this equipment, besides the functions of power flow control and voltage control, as originally proposed by L. Gyugyi [1,2]. The power circuit is made up from two PWM converters which share a common dc link without the need of dc power supplies. An integrated controller attends to both series and shunt converters of the UPFC. It is based on the theory of instantaneous active and reactive power defined in the α-β-0 reference frame [3,4]. A complete model of the new UPFC has been implemented in a digital simulator. Simulation results have confirmed that the new approach has higher performance than those UPFCs which use traditional definitions of powers in the controller.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Double-differential cross sections for the interaction of Na(3 2S) and Na(3 2P) with SF6 have been measured in crossed beam experiments for center of mass collision energies between 0.25 and 1.75 eV. In comparison with recently reported experiments the reaction with vibrationally excited SF6 is found to be more effective than the one with electronically excited Na. Results from an ab initio CASSCF calculation with Na in the ground state and the 3P state are presented. The experimental findings and the results from the calculation lead us to two different models for the reaction in the ground state and the excited state: While the well known harpooning model is verified for the ground state the reactive collisions with excited Na are mediated by nonadiabatic (nonreactive) transitions to the ground state surface. For these transitions the vibrational motion of SF6 is much more efficient than the relative motion in the collision. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The importance of test kits is increasing due to economical reasons. The different types of test kits allow qualitative, semiquantitative or quantitative results depending on the requirements. For applications where rapidity and mobility are absolutely necessary, they have advantages compared to laboratory methods. This is demonstrated by two typical examples. Besides the advantages, the limits of test kits are also mentioned. Test kits look very simple and are really easy to handle; nevertheless, not only the producers but also the users have to fulfil some basic demands.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A technique for precise boron isotope ratio measurements with a high detection power has been developed by negative thermal ionization mass spectrometry (NTIMS). Relative standard deviations in the range of 0.03–0.3% have been obtained for the determination of the 11B/10B isotope ratio using nanogram amounts of boron. Ba(OH)2 has been applied as ionization promoter for the formation of negative thermal ions. By adding MgCl2 better reproducibilities of the measurement have been achieved. A possible interference of BO- 2 ions at mass number 42 by CNO- could be excluded by the sample preparation technique used. Contrary to other NTI techniques no dependence of the measured isotope ratio on the boron amount used has been observed. Anthropogenic and natural saline influences in ground water have been successfully identified by boron isotope ratio determinations with this NTIMS method, due to the different isotopic composition of boron in natural and anthropogenic substances. In sewage, the boron isotope ratio is substantially influenced by washing powder, which contains low 11B/10B ratios (expressed in δ11B values normalized to the standard reference material NIST SRM 951). In contaminated ground water, low δ11B values are normally correlated with high boron and high chloride concentrations. On the other hand, δ11B shifts to higher values in less contaminated samples. For ground water with saline influences, only the δ11B determination, and not the boron or chloride content, allowed the correct identification of this natural source of contamination.
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 1996-07-05
    Description: When the Mg2+ ion in the catalytic center of Escherichia coli RNA polymerase (RNAP) is replaced with Fe2+, hydroxyl radicals are generated. In the promoter complex, such radicals cleave template DNA near the transcription start site, whereas the beta' subunit is cleaved at a conserved motif NADFDGD (Asn-Ala-Asp-Phe-Asp-Gly-Asp). Substitution of the three aspartate residues with alanine creates a dominant lethal mutation. The mutant RNAP is catalytically inactive but can bind promoters and form an open complex. The mutant fails to support Fe2+-induced cleavage of DNA or protein. Thus, the NAD-FDGD motif is involved in chelation of the active center Mg2+.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zaychikov, E -- Martin, E -- Denissova, L -- Kozlov, M -- Markovtsov, V -- Kashlev, M -- Heumann, H -- Nikiforov, V -- Goldfarb, A -- Mustaev, A -- New York, N.Y. -- Science. 1996 Jul 5;273(5271):107-9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Limnological Institute, Russian Academy of Sciences, Irkutsk, Russia.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/8658176" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Aspartic Acid/metabolism ; Binding Sites ; DNA/metabolism ; DNA-Directed RNA Polymerases/*chemistry/genetics/*metabolism ; Dithiothreitol/pharmacology ; Electrophoresis, Polyacrylamide Gel ; Escherichia coli/*enzymology ; Ferrous Compounds/metabolism ; Hydroxyl Radical ; Magnesium/metabolism ; Molecular Sequence Data ; Mutagenesis ; Promoter Regions, Genetic
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 6
    Publication Date: 1996-03-01
    Description: The distribution of dimethylsulphide (DMS), together with the precursor dimethylsulphonio-propionate (DMSP) and the oxidation product dimethylsulphoxide (DMSO), was measured in melt waters on the McMurdo Ice Shelf in the immediate vicinity of Bratina Island. Conductivity in these sulphate dominated ponds was extremely variable, ranging from 0.106–52.3 mS cm−1. Similarly, chlorophyll a concentrations in the pond waters (1–150 μg 1−1) and mats (1.4–33 μg cm−2) differed considerably. The biomass was dominated by benthic felts of phototrophic cyanobacteria, which might act as a source of biogenic sulphur compounds in the ponds. The mean (and ranges) of concentrations of dissolved sulphur compounds (nmol 1−1) were: CS2 0.16 (
    Print ISSN: 0954-1020
    Electronic ISSN: 1365-2079
    Topics: Biology , Geography , Geosciences
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  • 7
    Publication Date: 1996-03-01
    Description: During January 1994 seven meltwater ponds on the McMurdo Ice Shelf were investigated for their content of biogenic iodinated and brominated volatile hydrocarbons. An efficient purge and trap system in combination with a powerful gas chromatographic separation and an electron capture detector achieved detection limits of 0.02–0.4 ng 1−1, depending on the different substances. The following compounds could be identified and quantified: CH3I, CH2I2, CH2C1I, CHBr3, CH2Br2, BrCH2CH2Br, CHBr2Cl, and CHBrCl2. This is the first time that 1,2–dibromoethane has been detected as a biogenic substance in the environment. In contrast to many other aquatic systems, where CH3I is found to be the most volatile iodine compound, CH2I2 showed the highest concentration in all ponds falling in the range of 5–20 ng 1−1. In three of seven ponds investigated, CH2CII was the second abundant iodinated substance. CHBr3 usually exhibited concentrations in the range of 2.5–8.6 ng 1−1. BrCH2CH2Br, previously not observed as a biogenic compound, was found to have concentrations similar to those of bromoform and even exceeded the bromoform content in two ponds and the CH2Br2 content in all ponds. Whether cyanobacteria, the dominant organisms in the ponds, are responsible for this distribution pattern must be clarified by further investigations.
    Print ISSN: 0954-1020
    Electronic ISSN: 1365-2079
    Topics: Biology , Geography , Geosciences
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