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  • 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).
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  • 2
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The mean squared slowing-down distance, 〈r 2〉, and the age to themal capture (Migration Area),M 2, are direct measures of the slowing-down, and the spreading out, processes of neutrons in a medium. They also enter directly into reactor calculations. These parameters have been determined experimentally for Am-Be neutrons (mean energy 4.46 Me V), in a block of perpex, using the activities induced in thin indium foils from the115In(n,γ)116In reactions.
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  • 3
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Instrumental neutron activation analysis (INAA) technique has been employed viak 0 approximation method to determine elemental composition of five shaving powders commonly marketed in Nigeria. Fe displayed the highest concentrations in the range 1000–2000 μg·g−1. Na and Zn concentrations were established in the range 200–400 μg·g−1. Heavy elements like Ga, La, Cr, Co, Ag, Ce and Nd concentrations were noted in the lower range of 1–10 μg·g−1 Br, As, Sb, Sm, Eu, W, Cs, Tb, Yb, Hf, Ta, Th and U concentrations were established in even lower traces in the 〈1 μg·g−1 range. Results obtained for a certified reference material, CANMET BL-1 and CERT (in house) Kaolin standard compared favourably with the literature values thus establishing the results presented for the shaving powders.
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  • 4
    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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  • 5
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Batch experiments have been performed to study the sorption and transport properties of Cs+, Sr2+ and Eu3+ on different clay minerals already established to be predominantly kaolinite and montmorillonite. The uptake of these radionuclides increases in the order Cs〈Sr〈Eu. This trend agrees perfectly with the overall sequence in ion-exchange equilibria.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Natural hazards 8 (1993), S. 171-188 
    ISSN: 1573-0840
    Keywords: Drought ; drought frequency ; drought severity ; northern Nigeria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A long-period instrumental data set (1916–1987) of monthly growing season (April–October) rainfall totals for 34 stations in northern Nigeria is used to quantify drought following the method of H. N. Bhalme and D. A. Mooley. It is established that there are remarkable seasonal changes in the patterns of wetness and dryness over the region with no consistent recurrent spatial patterns in the moisture anomalies. In general, large-scale droughts only rarely cover the region as a whole, and there are distinct spatial differences dominating the wet and dry years. The length and severity of drought varies from sub-area to sub-area with very low interannual persistence. Although discrete areas do catch the brunt of drought on a year-by-year basis, drought occurrence in the region is largely sporadic in its spatial distribution. The rather noisy spatial characteristics of drought in northern Nigeria suggests that the seasonal shift in the Intertropical Discontinuity (ITD) is not likely the most important causal mechanism of drought in the region.
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  • 7
    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.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Natural hazards 8 (1993), S. 235-261 
    ISSN: 1573-0840
    Keywords: Drought ; desertification ; northern Nigeria ; drought and desertification planning policy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Drought has been a recurring feature of the arid and semi-arid areas of Nigeria. This paper reviews the extent, severity, and consequences of drought and desertification in Nigeria with particular emphasis on the northern part of the country. The haphazard manner in which these environmental hazards have been tackled is examined and a systematic approach for the formulation of a national policy is proposed. It is recommended that a detailed formulation and implementation of the proposed policy plan is imperative to mitigate the often devastating impacts of drought and desertification in the very prone areas of Nigeria. Until such is done, some areas of Nigeria will always be vulnerable to the whims of an inevitable climatic hazard of drought and associated land degradation in the form of desertification.
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  • 9
    ISSN: 1434-4483
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary The interannual variability of seasonal Bhalme-and-Mooley-type drought indices over the savanna belt of Nigeria is examined and a 57-year (1931–1987) drought area series has been derived using 34 stations. The area under drought conditions is obtained by considering areas which have drought indices of less than — 1.0. The interannual variability of the drought areas is large, demonstrating large variations in the seasonal rainfall over the region. Statistical tests suggest a significant long-term increasing trend in the areal extent of drought. In particular, there is a major shift towards an increase in the mean areal extent of drought between the two periods 1931–1960 and 1961–1987.
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  • 10
    ISSN: 1434-4483
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary A simple water balance method is used to compute the dates of the onset and termination and length of the growing season from long-term rainfall series in northern Nigeria. For most of the stations, the time series of onset and termination dates and growing season length are homogeneous and random, and can be taken as normally distributed. There is a progressive decrease in the length of the growing season from a mean of about 200 days in the south to less than 155 days in the extreme northern part. While there is no statistically significant trend in the onset dates, there is some evidence for statistically significant decreasing trend in the termination dates and the length of the growing season over the region. The results indicate that recent trends in the length of the growing season are more sensitive.to large interannual fluctuations in the start of the rains than to variations in the cessation dates.
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