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  • 1985-1989  (7)
  • 1
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract This work has been motivated by the need to establish reference materials from locally available sources. Neutron Activation Analysis (NAA) with Ge(Li) detector has been used to determine 26 elements in seven homogeneous clay samples with a wide range of composition. Short half-life nuclides (10s-10 m) were used to assay Na, Mg, K, Tl, Al, V, Mn, Ba, Dy, Ca and U by a fast rabbit transfer system. The long-lived nuclides were used to assay Sc, Sm, Cr, Eu, Ce, Cs, La, Fe, Lu, Hf, Co, Rb, Ta, Sb, and Pa(Th) after decay of24Na. The approach was purely instrumental. The accuracy of the resutls was tested by atomic absorption spectrometriy (AAS).
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-0840
    Keywords: Drought ; maximum entropy spectral analysis ; quasi-periodicities
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The maximum entropy spectral technique is used to search for periodicities in drought indices over the Great Plains of North America, covering a period of at least 70 years. The results show that in general, quasi-biennial, quasi-triennial and quasi-five-year cycles dominate the spectra of drought indices of many stations in the region. These significant periodicities in the 2–6 year waveband are, however, sporadic in their spatial distribution; they can be evident at one station while being absent at another a few hundred kilometres away. From the results of the spectral analysis, it is concluded that significant peaks obtained in the drought indices are only short-lived time variabilities in drought as recorded by individual stations and do not represent any persistent drought characteristics over a broad geographical region. In general, the drought series display only what appears to be a random variation, with the possible exception of a systematic quasi-biennial oscillation.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-4483
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Description / Table of Contents: Zusammenfassung Drei unabhängige Techniken werden in Spektralanalysen von Zeitreihen verwendet: Die konventionelle Periodogramm-Methode, die Maximalentropie-Spektralanalyse und die Non-Integer-Methode werden auf Zeitserien des Trockenheits-Index angewandt und die Resultate verglichen. Diese Resultate zeigen, daß die drei Verfahren grundsätzlich zu vergleichbaren Ergebnissen führen, v.a. im Hochfrequenz-Bereich. Der wesentliche Nachteil der Periodogramm-Methode ist ihre Frequenzungenauigkeit, besonders im Fall kurzer Aufzeichnungszeiträume. Daraus folgt, daß die im Periodogramm ausgewiesenen Positionen der Sinuskurven-Frequenzen genau zu stimmen scheinen, die Spitzen aber ungenau bleiben, v. a. auf Grund begrenzter Datenerhebungen. Die Maximalentropie-Spektralanalyse wiederum weist höhere Frequenzgenauigkeit als die beiden anderen Methoden auf, reagiert jedoch äußerst sensibel auf die Anzahl der Filterterme wodurch die Qualität der Spektren stark beeinflußt wird. Die Non-Integer-Spektren sind den Maximalentropie-Spektren höherer Ordnung vergleichbar. Da jedoch die niedrigste Frequenz, die auf den Non-Integer-Spektren gemessen werden kann, reziprok zur Aufzeichnungsdauer ist, sind diese Spektren (bei kurzer Aufzeichnungsdauer) im Niederfrequenzbereich nicht so zuverlässig wie jene der Maximalentropie-Spektralanalysen. Daraus ergibt sich, daß bei Vorliegen kurzer klimatologischer Zeitserien der Maximalentropie-Spektralanalyse der Vorzug vor den beiden anderen Methoden zu geben ist. Ein Vergleich der Ergebnisse der Maximalentropie mit jenen der Non-Integer-Methode scheint empfehlenswert, da dies verstärkt Rückschlüsse auf die Art der Periodiziät in den untersuchten klimatologischen Zeitreihen erlaubt.
    Notes: Summary Three independent techniques used in spectral analysis of time series, the conventional periodogram, the maximum entropy spectral analysis and the non-integer method, are applied to a drought index time series and the results are compared. The results reveal that in general the three approaches give similar estimates, especially in the high frequency domain. The main drawback of the periodogram method is its poor frequency resolution, especially in case of short records. Consequently, while the position of the sinewave frequencies computed by the periodogram seems accurate, the peaks are broad mainly because of the limited length of the data sample. The maximum entropy spectral analysis on the other hand, gives better frequency resolution than either the periodogram or the non-integer method. This method is, however, sensitive to the number of terms of the filter and this has a great influence on the quality of the spectrum. The non-integer spectra are comparable to higher order maximum entropy spectra. However, because the lowest frequency at which the non-integer spectra can be estimated is the inverse of the length of record, their spectra (for short records) may not be as reliable as those resolved by the maximum entropy spectral analysis in the low frequency domain. Overall, it is suggested that the maximum entropy spectral analysis is preferable to either the periodogram or the noninteger method when one deals with short climatological time series. A good practice will be to compare the results of the maximum entropy with those of the non-integer method in order to strengthen inferences about the nature of periodicity in the analysed climatological time series.
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  • 4
    ISSN: 1520-5118
    Source: ACS Legacy Archives
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 1989-01-01
    Print ISSN: 0921-030X
    Electronic ISSN: 1573-0840
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Published by Springer
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  • 6
    Publication Date: 1988-01-01
    Print ISSN: 0177-798X
    Electronic ISSN: 1434-4483
    Topics: Geosciences , Physics
    Published by Springer
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  • 7
    Publication Date: 1985-10-01
    Print ISSN: 0043-1656
    Electronic ISSN: 1477-8696
    Topics: Geosciences
    Published by Wiley
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