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  • Polymer and Materials Science  (14)
  • Soils  (2)
  • Wiley-Blackwell  (14)
  • Springer  (2)
  • American Meteorological Society (AMS)
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  • Wiley-Blackwell  (14)
  • Springer  (2)
  • American Meteorological Society (AMS)
  • 1
    ISSN: 1573-5052
    Keywords: Mesembryanthemaceae ; Nutrients ; Organic matter ; Soils
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Zones of nutrient enrichment beneath shrubs, the so called 'fertile islands', are the result of a range of interacting physical and biotic concentrating mechanisms. These concentrating mechanisms lead to specific spatial patterns of soil properties across a landscape and it has been suggested that disruption of the normal patterns into more aggregated 'fertile islands' might be a useful index of desertification in semi-arid regions. The objective of this paper was to determine whether 'fertile islands' are as characteristic a feature of succulent deserts as they are of shrub dominated deserts. Results indicate that, even in a community dominated by succulent species fertile islands develop under extremely arid conditions and that the degree of development is dependent on plant dynamics. Long-lived species showed greater concentration effects. However, the patterns of nutrient accretion in islands are very different to shrub invaded grasslands in North America. In particular nitrogen accretion dominated the 'fertile islands' in Namaqualand, and we suggest that these islands are more ephemeral than carbon and phosphorus dominated islands reported for other systems. These more dynamic islands are a consequence of rapid community dynamics since the Namaqualand region is characterised by many short-lived perennials which turnover generations very rapidly in response to environmental conditions. Using the development of 'fertile islands' to assess desertification as applied elsewhere might be inappropriate in Namaqualand because of the different patterns of community dynamics underlying the formation and characteristics of these islands.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Plant ecology 130 (1997), S. 143-153 
    ISSN: 1573-5052
    Keywords: Community boundaries ; Fynbos ; Nitrogen ; Phosphorus ; Soils
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The relationship between changes in soil nutrient characteristics and fynbos community boundaries was investigated near Cape Agulhas, South Africa. Soil characteristics relating to total nutrient content (pH, total N and total P, organic carbon, and various cations) were assessed at sites along three transects crossing the boundaries between five plant communities. Dynamics of available N and P in soils of three communities were studied in the field over one year, using ion-exchange resins. There was a wide range in the degree of change in soil nutrient content across different community boundaries. The characteristics that varied most were pH, total N, Ca and total P. Differences in available nutrients among soils indicated that the communities in this landscape were associated with a mosaic of N and P availability. It is proposed that spatial variation in soil nutrient availability rather than total soil nutrient contents may be important in explaining landscape-level species distributions and community composition in nutrient-poor mediterranean-climate ecosystems.
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  • 3
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 2 Ill.
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  • 4
    ISSN: 0308-0501
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In order to evaluate the performance of the indices of toxicity which have been developed, thermal decomposition products of three polymers, polyvinylchloride, polychloroprene, and polycarbonate were tested for sensory irritation, physiological stress induction, and acute lethality. Each polymer has been contrasted with the same polymer containing 5% zinc ferrocyanide. The most irritating and the most stressful pyrolysis products were those from polyvinylchloride. The least irritation and stress were associated with polycarbonate decomposition products. The acute lethality for polychloroprene was higher than that of the other two polymers by a factor of 4. The addition of zinc ferrocyanide had a variable effect, depending on the polymer and the index of toxicity being evaluated. Sensory irritation was lessened by the presence of zinc ferrocyanide in polycarbonate. The sample weight required to cause death of 50% of the animals was reduced for the two hydrogen chloride-generating polymers, polyvinylchloride and polychloroprene. However, the acute lethality of polycarbonate did not change with addition of zinc ferrocyanide. By itself, zinc ferrocyanide decomposed very slowly during heating, caused almost no irritation or stress, and no deaths.
    Additional Material: 3 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Fire and Materials 8 (1984), S. 54-55 
    ISSN: 0308-0501
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 6
    ISSN: 0308-0501
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A decrease in respiratory rate in mice during exposure to irritating airborne chemicals has been utilized as a response parameter to characterize the degree of upper respiratory tract irritation (sensory irritation) to the thermal decomposition products of plasticized poly(vinyl chloride). The plasticized poly(vinyl chloride) was placed in a low mass vertical furnace and thermally decomposed in an air atmosphere at a programmed heating rate of 20°C min-1. The thermogravimetric study of the plasticized poly(vinyl chloride) demonstrated that two distinct weight loss fractions occurred during the decomposition process. Groups of four male swiss-webster mice were exposed to the thermal decomposition products of the first weight loss fraction in the range 0.03-0.77 mg l-1 and to the second weight loss fraction in the range 0.03-0.38 mg l-1. Dose-response curves were plotted by utilizing the maximum percent decrease in respiratory rate during each exposure as the response parameter. Comparison of these curves to a dose-response curve for hydrogen chloride showed that both the first and second weight loss fraction of plasticized poly(vinyl chloride) were more potent than hydrogen chloride in terms of sensory irritation. From these dose-response relationships qualitative and quantitative predictions of human responses to the thermal decomposition products of plasticized.
    Additional Material: 8 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 39 (1990), S. 2419-2441 
    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: Dielectric techniques have been implemented to study aqueous colloidal suspensions. A four electrode cell was used in two configurations; the first, a sweep of frequencies using a sequence of standard single frequency null-balance measurements, and the second relying on the dielectric response to a Fourier synthesized pseudo random white noise (FSPN) with measurements performed using correlation techniques in the time domain. Single frequency measurements, which take on the order of 5-10 min per spectrum, were performed on polymer latex standards of varying size, latex concentration, and electrolyte concentration and were extended from 0.02 to over 500 kHz. It was found that the central relaxation frequency fc was inversely propotional to the square of the particle size, consistent with previous experimental results. Experiments were performed at different particle concentration and ionic strengths, and the magnitude and breadth of the dielectric dispersion was analyzed in terms of current theories. The distribution of relaxation times was found to be in general qualitative agreement with those predicted by some existing theories. The results indicate that a wide range of conditions exist in terms of latex concentration and ionic environment where the rapid and accurate measurement of polymer latex particle size and size distribution is feasible. FSPN measurements, which take on the order of seconds, were shown to be accurate over a moderate frequency range for model electrical network studies but were only partially successful for aqueous suspensions of latex because of high frequency limitations in the electronics. Experimental details and difficulties concerning the application of this technique are discussed.
    Additional Material: 16 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 1 (1947), S. 60-69 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Viskosefasern mit einem Polymerisationsgrad über 1000 haben nicht die gleichen günstigen Eigenschaften wie Baumwolle vom gleichen Polymerisationsgrad. Für die guten Eigenschaften der Baumwollfaser ist also nicht nur die Länge der Fadenmoleküle von Einfluß, sondern auch ihre besondere Lagerung in der gewachsenen Faser. Dies wird durch Vergleich von nativen und regenerierten Baumwollnitratfasern nachgewiesen. Der Unterschied in der Löslichkeit von nativen und regenerierten Celluloseacetaten wird ebenfalls mit der besonderen Anordnung der Fadenmoleküle in nativen Fasern in Zusammenhang gebracht.
    Additional Material: 10 Tab.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 24 (1993), S. 125-130 
    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
    Notes: HSS-Zerspanwerkzeuge wurden mittels Magnetron-Sputtern mit TiN beschichtet unter Variation der Sputterparameter Druck, Leistung und Bias-Spannung. Untersucht wurde der Zusammenhang zwischen den grundlegenden Schichteigenschaften Eigenspannung, Härte und Morphologie und dem Verhalten gegen tribologische Beanspruchung mittels Modellverschleißversuchen und Zerspanversuchen von Mumetall. Sowohl die Schichtmorphologie als auch die Eigenspannungen wurden durch die Parameter-variation verändert, um optimale Beschichtungsbedingungen ableiten zu können. Die tribologischen Untersuchungen zeigen, daß die Beschichtungsparameter und die Schichtdicke den Verschleißwiderstand maßgeblich beeinflussen können. Dabei führen die Modellverschleiß- und Zerspanergebnisse zu qualitativ gleichen Aussagen, so daß eine aussagekräftige Simulation des Werkzeugverschleißes als Test für weitere modifizierte Schichten verwendet werden kann.
    Additional Material: 9 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 525-536 
    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: Temperature of cutting tools by thin filmsDuring the cutting process, cutting tools are exposed to complex mechanical, thermal, dynamic and tribological loads. Especially in the case of dry machining the demands on cutting tools are very high. Dry machining becomes more and more interesting because of tightened up ecolaws and increased costs for the handling of coolants. Due to a renunciation on coolants the cutting tools need to be modified to the process of dry machining. Thereby modern plasma and ion based surface technologies can be used to deposit a thin film adopting the functions of coolants, e.g. cooling and lubricating.In this research project several coating types, e.g. titanium and chromium based coatings, where developed and characterized regarding their mechanical, tribological and thermal properties. For the research, four partners collaborated permuting all steps of surface and coatings design. Materials Science Institute (WW), Aachen University of Technology, performed the development of PVD coatings and the thermophysical characterization by thermal wave analysis. Surface modifications of uncoated and coated tools by ion beam assisted deposition were carried out at Stiftung Institut für Werkstofftechnik (IWT), Bremen. To determine the cutting properties of coated tools, practical tests were performed at Laboratory for Machine Tools and Production Engineering (WZL), Aachen University of Technology.
    Notes: Zerspanwerkzeuge sind während ihres Einsatzes einem komplexen und schwer zu erfassenden Beanspruchungskollektiv ausgesetzt. Dieses wird besonders durch die aus ökonomischen und ökologischen Gründen angestrebte Trockenzerspanung beeinflußt. Der vollständige Verzicht auf Kühlschmierstoffe bedeutet aus technologischer Sicht, daß Werkzeuge, Schneidstoffe und Zerspanoperationen auf die Bedingungen der Trockenzerspanung umgestellt werden müssen. Dabei bieten moderne ionen-und plasmagestütze Oberflächentechnologien insofern einen Lösungsansatz, daß durch Beschichtungen bzw. Oberflächenmodifikationen wichtige Aufgaben der Kühlschmiermittel durch den beschichteten Schneidstoff selbst übernommen werden können. Dies sind vor allem der Ersatz von Schmierung und Kühlung.Für den Bereich der Trockenzerspanung wurden im Rahmen eines Verbundvorhabens u.a Titanbasisschichten sowie Chrombasisschichten entwickelt und hinsichtlich der physikalischen Eigenschaften untersucht. Durch die enge Zusammenarbeit der beteiligten Forschungsstellen konnte das jeweils vorhandene Erfahrungspotential vollständig in die Schichtsystementwicklung einfließen. Diese umfaßte alle iterativen Schritte des Schichtmodifikation, begleitende Schichtanalytik bis hin zum Praxistest. So war beispielsweise das Lehr- und Forschungsgebiet Werkstoffwissenschaften der RWTH Aachen für die Schichtentwicklung sowie fü die thermophysikalische Charakterisierung der Schichten zuständig. Die Stiftung Institut für Werkstofftechnik, Bremen, führte eine Optimierung der Interfaces und der Hartstoffschichten mittels ionenstrahlgestützter Beschichtungsverfahren durch. So konnte das Substrat vor bzw. die Hartstoffschicht nach der Beschichtung an den Anwendungsfall angepaßt werden. Die Untersuchung hinsichtlich der Praxistauglichkeit der beschichteten Schneidstoffe erfolgte am Werkzeugmaschinenlabor der RWTH Aachen durch entsprechende Zerspanversuche.
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