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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 paper explains chronologically the implementation of thek 0-standardization and other parametric methods in Cuba. Fundamental and applied results in the determination of the most important parameters are obtained, using the IBR-2 at Dubna and Triga Mark III at Mexico reactor facilities. Some modifications in the Stoughton-Halpering convention, and its comparison with the modified Westcott and Høgdahl method are presented. The application of the described methods at the CS-ISCTN low flux facility, using the big samples techniques, is presented.
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  • 2
    ISSN: 1871-4528
    Keywords: α-chaconine ; α-solanine ; potato
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A new, efficient and economic method employing Medium Pressure Liquid Chromatography (MPLC) for the isolation of the two majorSolanum tuberosum L. glycoalkaloids (α-solanine and α-chaconine) is described. Potato peelings are homogenised with 5% acetic acid, the glycoalkaloids purified by filtration through an XAD-2 column and then by precipitation from the aqueous solution. The resulting glycoalkaloid fraction was purified by MPLC using a Silica Gel column and a CHCl3:MeOH:2% NH4OH mixture (70∶30∶5) as mobile phase to yield pure α-chaconine and a-solanine. This methodology can be used to obtain glycoalkaloids for enthomology and toxicological research where large amounts of these compounds are required.
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  • 3
    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 The chemical reactivity of boron carbide (B4C) with metallic aluminium (Al) was studied at temperatures ranging from 900 to 1273 K (627–1000°C). Al–B4C powder mixtures were cold pressed, heated for 1–450 h under 105 Pa of purified argon and characterized by X-ray diffraction (XRD) optical metallography (OM), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Whatever the temperature in the investigated range, B4C has been observed to react with solid or liquid Al. As long as the temperature is lower than 933 K (660°C), i.e. as long as Al is in the solid state, interaction proceeds very slowly, giving rise to the formation of ternary carbide (Al3BC) and to diboride (AlB2). At temperatures higher or equal to 933 K, Al is in the liquid state and the reaction rate increases sharply. Up to 1141±4 K (868±4°C), the reaction products are Al3BC and AlB2: at temperatures higher than 1141 K, Al3 BC is still formed while Al3B48C2 (β-AlB12) replaces AlB2. In the three cases, interaction proceeds via the same mechanism including, successively, an incubation period, saturation of aluminium in B and C, nucleation and growth by dissolution–precipitation of Al3BC and a C-poor boride and, finally, the passivation of B4C by Al3BC. These results are discussed in terms of solid–liquid phase equilibria in the Al–B–C ternary system, with reference to the binary invariant transformation: α-AlB12+L⇔AlB2, which has been found to occur at 1165±5 K (892±5°C).
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  • 4
    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 New interesting results in the crystal structure of the perovskite βLa0.33NbO3 were revealed using selected area electron diffraction, powder X-ray diffraction techniques and Rietveld refinement method. Although the superstructure of βLa0.33NbO3 could not be seen by conventional X-ray powder diffraction technique, the electron diffraction patterns revealed weak spots resulting in a superstructure array for the atoms of βLa0.33NbO3. The crystal symmetry is compatible with an orthorhombic cell, space group Cmmm. From Rietveld refinement, the resulting lattice parameters are: a = 7.82(1) Å, b = 7.83(9) Å, c = 7.90(9) Å and goodness of fit R = 0.1107, Rwp = 0.15. The superstructure is built from distorted octahedra NbO6 along the [001] axis. Results suggest that this distortion may be produced by occupation of La atoms in (2a) and (4l) sites.
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  • 5
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Styrene-co-4-methylstyrene (S-4-MeS) colloids were obtained by cocondensation at 77 K of the monomers with several metals such as: Pd, Au, Ag, Cu, Zn, Ga, Ge, In, Sn, Sb and Bi. Au, Ga and Ge colloids are stable for months at room temperature. The colloids of these comonomers were polymerized with different amounts of initiator benzoyl peroxide (BPO) at 65°C for 3 h, and a wide range of viscosity average molecular weights ( $$\bar Mv$$ 103–105) were obtained depending upon the metal used. Transmission electron microscopy showed clusters of spherical shapes in the comonomer dispersions. The particle size of these clusters displaced in the polymer is around 100 Å. The metal comonomer colloid concentration and stability at room temperature are reported. The thermal stability and metal incorporation are also described. The polymers are stable over 350°C with decomposition temperatures around 400°C. The metal content in the polymers is ranging form 0.05 to 0.77%. The color of the polymers depends upon the metal used, e.g. In-(S-4-MeS) is black and Au-(S-4-Me) is purple.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Polymer bulletin 37 (1996), S. 175-182 
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Styrene-co-butyl methacrylate colloids were obtained by codeposition at 77 K of the monomers with several metals such as Pd, Au, Ag, Cu, Zn, Cd, Ga, In, Ge, Sn, Sb and Bi. The colloids were copolymerized with different amounts of initiator (BPO) at 65°C for 3.0 h and a wide range of viscosity average molecular weights (Mv, 104–105 g/mol) were obtained depending upon the metal used. The metal colloid concentration and stability are reported. A medium particle size of 60-244 Å comonomer colloids was found. The thermal stability and metal composition are also described. The copolymers are stable even at 380°C, Ga- poly(styrene-co-butyl methacrylate) being the most stable with 418°C. The metal content is ranging between 0.10 and 2.26% w/w for the highest MW fraction and between 0.20 and 2.41% w/w for the lowest MW fraction. Copolymers with different colors were obtained depending on the metal used.
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  • 7
    ISSN: 1573-5117
    Keywords: macroinfauna ; temporal variation ; community structure ; disturbance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Benthic samples were collected from 1982 to 1985 in two stations in La Coruña Bay in order to study the temporal changes of two subtidal benthic assemblages: (1) a Tellina fabula — Paradoneis armata community, and (2) a Thyasira fluxuosa facies of an Abra alba community. The Tellina station is located in an area with little human disturbance, whereas the Thyasira station is located inside the organically polluted harbour area, where dredging operations took place at the beginning of this study. Temporal changes in both communities follow quite different patterns. The sedimentary environment of the Tellina station remains fairly constant through time: sediment size ranges from 2.80 to 3.85 Φ, and organic matter content (loss by ignition) varies between 3.15 and 4.53%. In the Thyasira station these sedimentary variables cover a much wider range: 3.10 to 5.75 Φ mean diameter and 5.19 to 17.05% organic matter. Community structure is quite stable in the Tellina station. The mean similarity of every sample with the following ones is relatively high and stable, and diversity (H′) and evenness (J′) fluctuations are small. However, in the Thyasira station the community structure has changed drastically after dredging operations ended as a result of the recolonization and further stabilization of the community. At the Tellina station biomass varies between 10 and 32 g ashfree DW m−2, and it does not show a discernible temporal pattern. However, at the Thyasira station biomass increased from less than 1 g ash-free DW m−2 during the dredging period up to 16 g ash-free DW m−2 18 months after the end of dredging. In conclusion, the Tellina fabula community seems very stable through time, whereas the Thyasira flexuosa facies has wider fluctuations due to human disturbances.
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  • 8
    ISSN: 1573-0972
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Description / Table of Contents: Résumé Parmi 50 souches deBradyrhizobium japonicum, 64%, 44% et 54% sont résistantes respectivement aux agents fongicides suivants: le captan, le pentachloronitrobenzyne et le disulfate de tetraméthylthiurame, à des concentrations supérleures à celles recommandées pour le traitement des sojas. Cent pour cent et 84% des souches sont résistantes respectivement aux herbicides sulvants: le trifluraline et le métribuzine, également à des concentrations supérleures à celles recommandées pour les sojas. Aucune souche ne présente de résistance à l'alachlore au delà de 3.5 μg/ml mais 40% sont senslbles jusqu'à 2.5 μl/ml, les concentrations maximum et minimum en alachlore, recommandées pour les sojas.
    Notes: Abstract Of 50 strains ofB. japonicum, 64%, 44% and 54% were resistant to the fungicides captan, pentachloronitrobenzene and tetramethylthiuram disulphate, respectively, at concentrations above those recommended for treatment of soybeans. 100% and 84% of the strains were resistant to the herbicides trifluralin and metribuzin, respectively, also at concentrations above those recommended for soybeans. No strain was resistant to alachlor above 3.5 μg/ml but 40% were sensitive to 2.5 μg/ml, these being, respectively, the maximum and minimum concentrations recommended for soybeans.
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  • 9
    ISSN: 1573-0972
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Description / Table of Contents: Résumé La majorité de la cinquantaine de souches deBradyrhizobium japonicum s'est révélée résistante à l'ampicilline, à la kanamycine, à la streptomycine et à la tétracycline aux concentrations intérieures à 100μg/ml mais au chloramphenicol aux concentrations égales ou supérieures à 100 μg/ml. Deux souches présentalent un haut degré de résistance à l'ampicilline et à la streptomycine. Six souches étaient très sensibles à plusleurs antibiotiques.
    Notes: Abstract The majority of the 50Bradyrhizobium japonicum strains tested were resistant to ampicillin, kanamycin, streptomycin and tetracycline in concentrations below 100 μg/ml but resistant to chloramphenicol in concentrations equal to or above 100 μg/ml. Two strains had high levels of resistance to ampicillin and to streptomycin and six strains were very sensitive to several antibiotics.
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  • 10
    ISSN: 1573-2932
    Keywords: bacteria ; chromium resistance ; contamination ; hexavalent chromium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Chromium-containing industrial effluents are primarily responsible for environmental contamination by toxic and highly mobile, hexavalent chromium. The dilution plate-count method, using media amended with Cr(VI) at concentrations ranging from 0 to 1000 mg L-1, was used to compare the sizes of Cr(VI)-resistant bacterial populations from a soil contaminated with 25 100 mg kg-1 total Cr [12 400 mg kg-1 Cr(VI)] to those isolated from a slightly contaminated soil (99.6 mg kg-1 total Cr) and two other soils without any history of Cr contamination. Bacterial populations resistant to 500 mg L-1 Cr(VI) were isolated from all soils except the heavily contaminated soil. To determine whether Cr-resistant bacterial populations were indigenous to both the contaminated and the uncontaminated soils, enrichment cultures containing Cr(VI) at concentrations ranging from 0 to 1000 mg L-1 were employed. Bacterial populations, as high as 105 (colony forming units) CFU g-1 soil, tolerant of 500 mg L-1 Cr(VI) were isolated from all soils within 48 h of enrichment suggesting that the presence of aerobic Cr(VI)-resistant bacterial populations is unrelated to contamination levels or contamination history. However, identification of these resistant bacteria using fatty acid profiles was unsuccessful suggesting that these populations may have unique characteristics. Fungal colonies resistant to 1000 mg L-1 Cr(VI) were routinely isolated from both uncontaminated and contaminated soils. The results suggest that Cr-resistant microorganisms may be present in soils, even those with no history of Cr contamination.
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