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  • Chemistry  (24)
  • Column liquid chromatography  (2)
  • 21.10.Pc  (1)
  • 42.75
  • 1990-1994  (27)
  • 1994  (27)
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  • 1990-1994  (27)
Year
  • 1
    ISSN: 1434-601X
    Keywords: 25.30.Fj ; 21.10.Pc ; 02.60.Ed
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A method for the separation of structure functions in (e, e′ p) experiments is proposed, which is an extension of the traditional Rosenbluth-type techniques of [1,2]. In our approach, we use a very flexible Ansatz to describe the structure functions within an extended kinematical regionG and determine its free parameters with a x2 minimization. The procedure is tested by pseudo data (12C(e, e′p)11Bg.s.) in the quasi-free region.
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  • 2
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Electrodialytic sample treatment ; Computer models ; Analyte enrichment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Basic considerations for analyte enrichment and recovery obtainable by electrodialysis as a sample treatment method are given. Equations are derived which describe the dependence of the concentration profiles of ionic compounds on the electric field strength in a set-up with stagnant donor and acceptor solutions. It is shown that analyte recovery increases when less ion-selective membranes are used in the electrodialysis cell. Computer models are used to estimate the analyte enrichment for a flowing donor (sample) and a stagnant acceptor phase. About 10-fold enrichment can be obtained in an electrodialytic sample treatment system within 20 min under maximum current conditions. A compromise has to be found between analyte recovery and the donor (sample) flow rate.
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  • 3
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Membrane-extraction disks ; On-line trace enrichment ; Polar pollutants ; Surface water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An on-line trace-enrichment system, using a bifunctional membrane extraction-disk cartridge, has been combined with a column liquid chromatography separation for the simultaneous determination of basic, neutral and acidic pollutants in surface water. The enrichment device consisted of a specially constructed holder containing both C-18 and cation-exchange disks. The holder can contain up to 25 disks of 0.5 mm thickness and 4.6 mm diameter. Before trace enrichment of 20 ml of surface water (pH 3.0), calcium ions were removed from the sample by means of an oxalic acid precipitation. Desorption of the cartridge was at elevated temperature using reversed-phase gradient elution; detection was performed with a diode-array UV absorbance detector. The detection limits for the test compounds in surface water are typically 0.5–2 μg/l; the calibration graphs are linear from the lower limit of determination up to 50 μg/l.
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  • 4
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: High temperature behaviour of materials for gas turbine blades manufactured in new technologyOn gas turbine blades for the middle and last stages of stationary gas turbines, the service-relevant material properties were examined. The specimens were taken from forged blades of alloys Nimonic 101 and Udimet 720 and from two fine grain versions of cast blades of alloy IN-792. In the range of service relevant temperatures long-term creep rupture tests, annealing tests, relaxations tests as well as low and high cycle fatigue tests were carried out.
    Notes: An in neuer Technologie gefertigten Schaufeln für die mittleren bis hinteren Laufreihen von stationären Gasturbinen wurden betriebsrelevante Werkstoffeigenschaften bestimmt. Die Untersuchungen erfolgten an den Schmiedelegierungen Nimonic 101 and Udimet 720 und an zwei Feinkornvarianten der Gußlegierung IN-792. Im Bereich der Anwendungstemperaturen wurden Langzeitstandversuche, Glühversuche, Relaxationsversuche sowie nieder- und hochfrequente zyklische Versuche durchgeführt.
    Additional Material: 13 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 17 (1994), S. 95-97 
    ISSN: 0935-6304
    Keywords: Chemical warfare agents ; Microcolumn liquid chromatography ; Enantiomeric separation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An improved interface for the on-line coupling of microcolumn liquid chromatography (micro-LC) with thermionic detection (TID) is described. Modifications have been made to enable separate adjustment of the eluent introduction and the detector flame temperature in order to improve the sensitivity and ease of use of the system.The micro-LC-TID was used for the chiral separation of the nerve agent O-ethyl S-2-diisopropylaminoethyl methylphosphonothioate (VX). Baseline separation for the enantiomers of VX was obtained on Chiralcel OD using 1% isopropanol in hexane as the eluent. The detection limit of VX using 60 nl injections is ca. 5 μg/ml (ppm range). However, when using large-volume injections (10 μl) the detection limit is ca. 25 ng/ml (ppb range).
    Additional Material: 2 Ill.
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  • 6
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Microbial deterioration of materials - simulation, case histories, and countermeasures for inorganic nonmetallic materials: Biodeterioration processes on inorganic materials and means of countermeasuresBiodeterioration processes on inorganic materials such as natural stone, concrete, or glass can be subdivided into biogeochemical and biogeophysiological mechanisms according to their damage characteristics. In connection with the partial acidification and dissolving of components, biocorrosion as a result of biogenic release of inorganic and organic acids, as well as the biogenic oxidation of mineral forming cations, a certain weakening in the structure of the respective material can occur. The formation of biofilms on the surfaces of the inorganic materials impairs not only the aesthetical appearance of an object but also causes alterations in its humidity and temperature behaviour. In addition, due to the shrinking and swelling effects of biofilms, mechanical pressure to the mineral unit can occur (bioerosion, bioabrasion). Location and environmental factors which could lead to specific, biogenically determined weathering phenomena on these materials will be presented and elucidated. For controlling biodeterioration processes, the development and selection of environmentally-friendly, yet effective, inorganic and organic biocidal additives for stoneprotection agents as well as the use of gas (e.g. ethylene oxide) in their far-reaching significance for future material research will be presented here.
    Notes: Biodeteriorationsprozesse an anorganischen Werkstoffen wie Naturstein, Beton oder Glas können in ihren Schädigungsweisen nach biogeochemischen und biogeophysikalischen Mechanismen unterteilt werden. Im Zusammenhang mit der partiellen Ätzung und Lösung von Bestandteilen, hervorgerufen durch die biogene Freisetzung anorganischer bzw. organischer Säuren (Biokorrosion) sowie der biogenen Oxidation mineralbildender Kationen (Biooxidation), kommt es zur Schwächung, des Gefüges im jeweiligen Werkstoff. Durch den Aufwuchs von Biofilmen auf den Oberflächen anorganischer Materialien kommt es neben ästhetischen Beeinträchtigungen auch zu Veränderungen im Feuchte- und Temperaturverhalten des Werkstoffes sowie aufgrund von Schrumpfungs- und Quellungsprozessen von Biofilmen zu mechanischer Druckbelastung auf den Mineralverband (Bioerosion, Bioabrasion). Standort- und Umweltfaktoren, die zu entsprechend biogenen Verwitterungsphänomenen an anorganischen Werkstoffen führen, werden vorgestellt und erläutert. für die Bekämpfung der Biodeteriorationsprozesse werden die Entwicklung und Auswahl umweltgerechter, aber dennoch wirksamer anorganischer bzw. organischer biozider Zuschlagstoffe für Gesteinsschutzstoffe sowie Begasungen (z. B. Ethylenoxid) in ihrer weitreichenden Bedeutung für die zukünftige Materialforschung vorgestellt.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 51 (1994), S. 407-413 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Isothermal DSC investigations on pure as well as glass, carbon, and aramid fibre-reinforced poly(phenylene sulfide) (PPS) were carried out in order to obtain informations on the crystallization kinetics, that is, the Avrami exponent, constant, half-time of crystallization, and (final) degree of crystallinity. PPS is a typical representative of semicrystalline polymers with a maximum degree of crystallinity of about 60%. The Avrami exponent reaches values from n = 2.1-2.7 depending on fibre type but independent of crystallization temperature. The system aramid fibre/PPS has a much shorter half-time of crystallization than the other three systems that could be attributed to the high nucleation effect of the aramid fibre surface to PPS. As a consequence of the high nuclei density a transcrystalline zone is built up around the aramid fibre. The relatively low value of the Avrami constant was discussed and a computer simulation attempt was made to understand the measured value quantitatively. © 1994 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 53 (1994), S. 1011-1023 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The formation of nodular structures in the top layer of ultrafiltration membranes is considered. A critical review of mechanisms described in the literature is given. Flat-sheet poly(ether sulfone) membranes and hollow-fiber poly(ether sulfone)/polyvinylpyrrolidone membranes were made by coagulation of a polymer solution in a nonsolvent medium under different circumstances. From these experiments, a number of empirical rules are found to describe the resulting morphology of the top layer. A new mechanism for the formation of a nodular structure is proposed. It is based on the small diffusion coefficient of the polymer molecules compared to the diffusion coefficient of solvent and nonsolvent combined with a high degree of entanglement of the polymer network. For unstable compositions, phase separation will proceed by growth in amplitude of concentration fluctuations. The rapid diffusional exchange of solvent for nonsolvent in the top layer leads to vitrification of the maxima of the concentration fluctuations that form the nodules. Complete disentanglement of the polymer chains between the nodules is not reached, which explains the small pores and the low porosity of ultrafiltration membranes. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 53 (1994), S. 1497-1512 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The mechanism of foaming a glassy polymer using sorbed carbon dioxide is studied in detail. A glassy polymer supersaturated with nitrogen forms a microcellular foam, if the polymer is quickly heated above its glass transition temperature. A glassy polymer supersaturated with CO2 forms this foam-like structure at much lower temperatures which indicates the Tg-depressing effect of CO2. Having this interpretation in mind, the overall sample morphology, i.e., a porous foam enclosed by dense outer skins, can be completely explained. The dense skins, however, are not homogeneous but show a nodular structure when analyzed by SEM and AFM. Foaming experiments with samples having a different thermal history suggest that the nucleation mechanism underlying the foaming process is heterogeneous in nature. © 1994 John Wiley & Sons, Inc.
    Additional Material: 13 Ill.
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  • 10
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is described for the determination of the antitumour drug cyclophosphamide and six stable metabolites in plasma of cancer patients, namely dechloroethyl-cyclophosphamide, 4-keto-cyclophosphamide, carboxy-phosphamide, alcophosphamide, nor-nitrogen mustard and the N-chloroethyl-1,3-oxazolidine-2-one, as methyl and/or trifluoroacetyl derivatives by single ion monitoring gas chromatography/mass spectrometry, mostly in the electron capture chemical ionization mode. The isolation of most metabolites was performed by solid-phase C-18 extraction in weakly acidic medium. The phosphoramide mustard isolated under these conditions decomposes readily to the nor-nitrogen mustard during derivatization. The original nor-nitrogen mustard and the chloroethyl-1,3-oxazolidine-2-one were isolated by liquid extraction with ethyl acetate in alkaline medium. Recoveries of 75-99% were measured using spiked blank plasma samples. Quantitation of metabolites in patient plasma samples was performed using two sets of calibration curves for the concentration ranges of 1-100 ng and 0.1-10 μg of metabolite per millilitre of original plasma.
    Additional Material: 9 Ill.
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