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  • 1
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Summary The electrothermal atomic-absorption spectrometry of copper and manganese in steels, which are comparatively difficult to atomize, has been studied with direct atomization from one grain of solid sample. The absorption intensities and evaporation rates of these elements are dependent on the atomization temperature and their diffusion rate in iron. Evaporation rates of copper and manganese from steel are dependent on the weight of sample taken, because of the slow diffusion rate and high atomization temperature. The surface area of a sample plays an important role for the evaporation of trace elements from solid samples. Optimum conditions for their atomization include repetitive atomization at about 2080° C. On the other hand, easily atomizable elements such as silver and lead are determined by a single heating step. Evaporation of these elements is also affected by the surface area of the solid sample. Detection limits are 0.1 ng for Cu, 0.04 ng for Mn and 0.008 ng for Ag.
    Notes: Zusammenfassung Zur direkten Spurenanalyse von Kupfer, Mangan, Silber und Blei in Stählen wird eine normale Graphit-Becherküvette verwendet, mit deren Hilfe kleine Proben direkt in fester Form eingebracht werden können. Die Absorptionsintensitäten und Verdampfungsgeschwindigkeiten hängen von der Temperatur und der Diffusionsgeschwindigkeit im Eisen ab. Die Oberfläche der Proben spielt eine wichtige Rolle bei der Verdampfung von Spurenelementen aus Festkörpern. Mehrfache Aufschmelzung für Kupfer und Mangan ist erforderlich bei Temperaturen von etwa 2080° C. Leicht atomisierbare Elemente (Ag, Pb) können mit einer einmaligen Heizstufe bestimmt werden. Die Verdampfung wird in diesem Fall auch von der Oberflächengröße der Probe beeinflußt. Die Nachweisgrenzen betragen 0,1 ng für Cu, 0,04 ng für Mn und 0,008 ng für Ag.
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  • 2
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Summary Traces of zinc and bismuth in small amounts of high purity tin (0.5 ∼ 25 mg) were determined by polarized Zeeman AAS with direct atomization of a solid sample in a electrothermal graphite-cup cuvette. Standard solutions of zinc and bismuth were employed for the calibration curve. Absorption intensities (peak areas of the absorption signals) for zinc and bismuth were not influenced by the residual tin in a graphite-cup cuvette, up to 25 mg for zinc and up to 10 mg for bismuth. The relative standard deviations of analytical results were 9 ∼ 43% for 0.002 ∼ 0.05 ppm of zinc and 5 ∼ 10 % for 0.06 ∼ 1.3 ppm of bismuth. Detection limits were 0.012 ng for zinc and 0.03ng for bismuth. These values correspond to 0.0005 ppm of zinc in 25 mg of tin and 0.03 ppm of bismuth in 10 mg of tin. Time (incl. weighing the sample) required for analyzing one sample was about 5 min.
    Notes: Zusammenfassung Spuren Zink (0,002 ∼ 0,05 ppm) und Bismut (0,06 ∼ 1,3 ppm) wurden in reinem Zinn mit polarisierter Zeeman-AAS bestimmt. Eine kleine Menge der Probe (0,5 ∼ 25 mg) in fester Form wurde direkt mit Hilfe einer elektrothermischen Graphit-Becherküvette atomisiert. Eichkurven von Zn und Bi wurden mit Standardlösungen aufgestellt. Sn in der Graphit-Becherküvette beeinflusst die Absorptionsintensität von Zn bis zu 25 mg und von Bi bis zu 10mg nicht. Die relative Standardabweichung betrug 9 ∼ 43% für 0,002 ∼ 0,05 ppm Zn und 5 ∼ 10% für 0,06 ∼ 1,3 ppm Bi, die Nachweisgrenzen 0,012 ng für Zn und 0,03ng für Bi. Diese Werte entsprechen 0,005 ppm Zn in 25 mg Sn und 0,03 ppm Bi in 10 mg Sn. Die Durchführung einer Analyse benötigt etwa 5 min.
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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 Dense spherical Ni particles were prepared from nitrate solution by spray pyrolysis in a H2–N2 atmosphere. Hollow NiO particles with rough surfaces were formed first at low temperature and then reduced to Ni by H2 above 300°C. Subsequent intraparticle sintering of the Ni crystallites gave rise to densification of Ni particles as the temperature was raised; most Ni particles became dense above the pyrolysis temperature of 1000°C. However, when a N2 atmosphere was used, hollow NiO particles were formed, which did not densify even at 1200°C due to the lack of sintering. The dense Ni particles obtained were of good crystallinity and good oxidation resistance, especially for those formed at higher pyrolysis temperatures and longer residence times.
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  • 4
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 2483-2485 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This letter shows theoretically and experimentally that Fresnel end reflection of the waveguide under test degrades the sensitivity of low coherence optical time domain reflectometry (OTDR). Optical mixing of end reflection and reference light in the OTDR produces the phase noise in proportion to end reflectivity. With the balanced detection technique, the excess photon noise is subdued and the phase noise becomes the dominant source of sensitivity degradation. At 3.2% end reflection and 300 μA mean photocurrent, the noise floor due to the phase noise is −138 dB/Hz. By reducing the fiber end reflection with matching oil, a shot-noise limited sensitivity of −140 dB at a 3 Hz bandwidth has been demonstrated at submillimeter resolution.
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  • 6
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The long-term (1- and 2-year) adverse tissue responses including tumor formation by subcutaneous implanation of polyurethanes (PUS) and silicone (Sil) films intorats were compared. The weight-averaged molecular weights (Mw) of the PUS prepared from 4,4′-diphenylmethanediisocyanate, poly (tetramethyleneglycol) of M, = 1000 and 1,4-butanediol are 220,000 (U-4), 124,000 (U-6), and 55,600 (U-8). The 50:50 mixed film of U-6 and silicone (U-b/sil) was prepared by rollmixing of the noncured silicone and the U-6 solution followed by evaporation of the solvent and heat-curing at 70°C. The tissue responses around implants were classified into four groups as follows: (A) tumor, (B) atypical cell proliferation accompanied by preneoplastic changes, (C) cell proliferation without preneoplastic changes, (D) no obvious responses. In both implantation periods, the PUS gave higher incidents of the adverse responses including tumor formation in comparison to Sil. No significant molecular weightdependent trend was found in a 1-year study using U-4, 6, and 8. Significant PU-dose-dependent trends were found in a 2-year study: the total active incidence (A + B + C), U-6(22/29) 〉 U-6/si1(11/29) 〉 sil(7/28); tumor incidence (A), U-6(11/29) 〉 U-6/si1(2/29) = si1(2/28). No detectable amounts of 4,4′-methylenedianiline (MDA) were found in the PUS. The methanol extracts from the PUS were negative in the mutagenicity tests. These indicate no relationship between the tumor formation by the PU films and the mutagenicities of the chemicals (mainly oligomers) leached from the PUs.
    Additional Material: 4 Ill.
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  • 7
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: HCN evolution from linear polyurethane has been studied over a range of temperatures from 261 to 480°C as function of exposure time, oxygen pressure, film thickness, and chain length. Infrared spectra have also been measured as function of exposure time. In addition, gas evolution during thermal degradation in vacuo has been investigated in a quartz spoon reaction vessel. Rate constants and energies of activation have been evaluated for all reactions. Gas evolution and adsorption are diffusion-controlled during thermal and thermal-oxidative degradation up to at least 330°C. Thermal degradation consists essentially of a reversal of the polycondensation process. The thermal-oxidative degradation is a complicated reaction involving chain scission, crosslinking, carbonization, and gas evolution. HCN evolution, although appreciable, is only a minor side reaction of the total oxidation process. A tentative mechanism for HCN evolution has been proposed.
    Additional Material: 14 Ill.
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  • 8
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal oxidative degradation of two aromatic and one segmented polyurethane has been studied, with special emphasis on HCN evolution over a range of temperatures and oxygen concentrations. A tentative mechanism for HCN formation has been presented. Other gaseous products were ascertained by chromatography. Infrared spectra during degradation were measured, and the extent of crosslinking was also determined. It is shown that HCN evolution can be inhibited by copper or its oxide.
    Additional Material: 26 Ill.
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  • 9
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Trace amounts of gold and silver in high-purity iron or steel were preconcentrated by reductive coprecipitation with palladium using ascorbic acid, and determined by electrothermal atomic absorption spectrometry (ET-AAS). Both gold and silver could be simultaneously separated and sensitively determined in 10 metals (aluminum, cobalt, chromium, copper, iron, manganese, molybdenum, nickel, vanadium and zinc). Comparable values were obtained for gold and silver in reference materials (low alloy steel) by the proposed method and a non-separation method; good agreement was found between the analytical values by both methods and the certified values. The proposed method is easy, simple and not dependent on sample composition and content. Moreover, gold and silver in metal samples could be simultaneously separated together with selenium and tellurium. The detection limits for gold and silver (3 σ) are 0.003 μg g–1 and 0.002 μg g–1, respectively.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Shock waves 6 (1996), S. 167-175 
    ISSN: 1432-2153
    Keywords: Key words:Supersonic free shear layer, Instability, Coherent structure, Acoustic interaction, Shock-avoiding mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract. Although the suppressed instability of supersonic free shear layer flow has been documented by many investigators, the underlying physics are still ambiguous. In the present study, numerical simulations were performed to cast physical insight into the two-dimensional large-scale structure which is organized in a supersonic free shear layer. It is found that an acoustic interaction of the disturbed shear layer with a flow channel wall or another shear layer is indispensable to generate the organized structure. The undisturbed vorticity layer is deformed into a traveling wavy one. As the flow Mach number increases, its degree of deformation decreases so that the formation of shock waves embedded in the structure is avoided.
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