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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4706-4713 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The spatial distribution of backscattered electrons is studied for an Au target with a new Monte Carlo simulation including the discrete energy loss process. The new model is based on the Mott cross section for elastic scattering and the Vriens cross section for inelastic scattering. Some results are compared with the ones by the old Monte Carlo simulation which is based on the screened Rutherford cross section and the Bethe law. The new model results in a larger peak near the incident point and a more gradual decrease of the background part of the radial distribution. The incident energy dependence of the spatial distribution of backscattered electrons is shown for 0° and 45° incident angles. The calculated spatial distribution of low-loss backscattered electrons indicates the possibility of very high resolution even in the backscattered electron image. The exit angle dependence of the penetration depth of backscattered electrons is also studied with the new simulation. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    ISSN: 1520-5827
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Journal of industrial microbiology and biotechnology 23 (1999), S. 425-435 
    ISSN: 1476-5535
    Schlagwort(e): Keywords: Sphingomonas; macromolecule transport; pit; polysaccharide lyase; ABC transporter
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A bacterium isolated from soil as an alginate lyase producer shows characteristic morphological and taxonomical properties consistent with being classified in the genus Sphingomonas. The bacterium utilizes high molecular weight (HMW)-alginate for growth by depolymerization of the polymer with intracellular alginate lyases, which are generated from a common precursor protein through autoregulated post-translational modifications. Electron microscopic observations of the cell surface and of thin sections of cells grown on HMW-alginate revealed dynamic changes in both cell surface and membrane structures. The most remarkable change is recognized in the formation of mouth-like pits which open and close depending on the presence or absence of HMW-alginate. Enzymatic and genetic analyses of HMW-alginate incorporation processes confirmed the presence of a pit-dependent and macromolecule-specific ABC transporter system in cells of Sphingomonas species A1. This is the first description of a bacterium with a pit on the cell surface and a pit-dependent endocytosic uptake system for macromolecules.
    Materialart: Digitale Medien
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  • 4
    ISSN: 1572-8862
    Schlagwort(e): Gold clusters ; liquid metal ion source ; TEM ; STM
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Ions of gold monomer and clusters emitted from a liquid metal ion source were mass-selected, and deposited on cleaved HOPG (highly oriented pyrolytic graphite) surfaces and on amorphous carbon thin films at room temperature with the impinging energy E i from 0 to 500 eV. The coverage of deposited ions were 1/100 and 1/1000 monolayers on HOPG surfaces and 1/3 monolayers on carbon films. Scanning tunneling microscopy of the HOPG surfaces deposited with low impinging energy (E i〈50 eV) revealed that large clusters with diameters ranging from 2 to 5 nm and height of 1–2 layers were present instead of isolated monomers and original clusters. When E i was higher than 100 eV, HOPG surfaces were damaged and only bumpy surfaces were observed by STM. Transmission electron microscopy of Au+-deposited carbon films showed the formation of clusters with diameter 0.5–20 nm, depending on the E i and the time elapsed after deposition.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Adsorption 3 (1997), S. 197-208 
    ISSN: 1572-8757
    Schlagwort(e): micropore filling ; supercritical gas ; carbon micropore ; nitrogen monooxide ; methane ; molecular assembly
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Physik , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract The supercritical gas adsorbed in the micropore having a strong molecular field was presumed to transform into the quasi-vapor to be filled in the micropore (quasi-vaporization adsorption mechanism). The Dubinin-Radushkevitch (DR) equation for micropore filling of vapor was extended to the quasi-vaporized supercritical gas using the quasi-saturated vapor pressureP 0 q and the inherent micropore volumeW L . The reason why the concepts ofP 0q andW L were introduced was explained with the molecule-pore interaction potential theory which is based on the Lennard-Jones interaction. The extended DR equation was named the supercritical DR equation. TheW L was evaluated by the Langmuir plot of the adsorption isotherm for a supercritical gas and both ofP 0q andW L provided the single reduced adsorption isotherms of supercritical NO, N2, and CH4 on activated carbon fibers and high surface area carbons were analyzed by the supercritical DR plots. The wide applicability of the reduced adsorption isotherm to these adsorption data was explicity shown. The two phase model of the organized and confined fluids was proposed in order to improve the quasi-vaporization adsorption mechanism.
    Materialart: Digitale Medien
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  • 6
    ISSN: 1572-879X
    Schlagwort(e): ethane dehydrogenation ; ethylene ; CO2 ; Cr2O3 ; sulfated silica
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The oxidative dehydrogenation of ethane into ethylene by carbon dioxide over unsupported Cr2O3, Cr2O3/SiO2 and a series of Cr2O3/SiO2 catalysts modified by sulfate was investigated. The results show that Cr2O3/SiO2 is an effective catalyst for dehydrogenation of ethane and CO2 in the feed promotes the catalytic activity. Sulfation of silica will influence the catalytic behavior of Cr2O3/SiO2 in dehydrogenation of ethane with carbon dioxide depending on the amount of sulfate. Cr2O3/6 wt% SO 4 2- –SiO2 catalysts exhibit an excellent performance for this reaction, giving an ethylene yield of 55% at 67% ethane conversion at 650°C. Characterizations indicate that addition of sulfate changes the bulk and surface properties of Cr2O3/SiO2, promoting the reduction of Cr6+ to Cr3+ and favoring the catalytic conversion.
    Materialart: Digitale Medien
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  • 7
    ISSN: 1572-879X
    Schlagwort(e): oxidative dehydrogenation ; ethane ; sulfated zirconia ; lithium chloride
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The oxidative dehydrogenation of ethane over sulfated-zirconia-supported lithium chloride catalysts has been systematically investigated. The optimal experimental parameters were obtained. It is found that sulfation of zirconia increases the catalytic activity. 2–3.5 wt% lithium chloride on sulfated zirconia catalysts exhibit high catalytic activity for oxidative dehydrogenation of ethane, with particularly high activity for ethene production. 70% selectivity to ethene at 98% ethane conversion, giving 68% ethene yield, is achieved over 3.5 wt% LiCl/SZ at 650°C.
    Materialart: Digitale Medien
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  • 8
    ISSN: 1572-879X
    Schlagwort(e): sulfated zirconia ; lithium chloride ; metal oxides ; ethane ; oxidative dehydrogenation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The effects of some transition‐ and lanthanide‐metal oxides in LiCl/sulfated‐zirconia (SZ) catalysts on catalytic behavior in the oxidative dehydrogenation of ethane were investigated. It is found that modification of LiCl/SZ by metal oxides significantly improves the catalytic activity and ethene yield. Among those additives, Ni and Nd oxides show the best promoting effect in terms of ethane conversion and ethene yield. 93% ethane conversion with 83% selectivity to ethene has been achieved over the Nd2O3–LiCl/SZ catalyst at 650°C. In addition, those oxide‐promoted LiCl/SZ catalysts are also found to exhibit a longer stability in catalytic performance. Metal‐oxide additives change the chemical structure and surface redox properties, which accounts for the enhancement of activity.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    s.l. ; Stafa-Zurich, Switzerland
    Advanced materials research Vol. 4-5 (Oct. 1997), p. 307-312 
    ISSN: 1662-8985
    Quelle: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Thema: Maschinenbau
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Archives of environmental contamination and toxicology 29 (1995), S. 135-139 
    ISSN: 1432-0703
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik , Medizin
    Notizen: Abstract The relationship between occupational exposure to methyl ethyl ketone (MEK) and its concentration in urine and blood was studied in a group of 72 workers in a printing factory. Personal exposure monitoring was carried out with passive samplers during the workshifts. The time weighted average (TWA) concentration of MEK ranged from 1.3 to 223.7 ppm, with a mean concentration of 47.6 ppm. In addition to MEK, toleuene, xylene, isopropyl alcohol, and ethyl acetate were detected as the main contaminants in all samples. At the end of the workshift, urine samples were collected to determine the urinary MEK, hippuric acid (HA), and creatinine, and blood samples were also collected at the same time for determination of MEK. The concentrations of urinary MEK ranged from 0.20 to 8.08 mg/L with a mean of 1.19 mg/L and significantly correlated with TWA concentrations of MEK in the air with a correlation coefficient of 0.889 for uncorrected urine samples. The concentration of MEK in the blood was also significantly correlated with the TWA concentration of MEK with a correlation coefficient of 0.820. From these relationships, MEK concentrations in urine and blood corresponding to the threshold limit value-TWA (200 ppm; ACGIH 1992) were calculated to be 5.1 mg/L and 3.8 mg/L as a biological exposure index (BEI), respectively. Although the BEI for urinary MEK obtained from the present study was higher than that of previous reports and ACGIH's recommendation (2.0 mg/L), the BEI agreed well with a previous study in Japan. On the other hand, the relationship between toluene exposure and urinary HA level, an index of toluene exposure, was also studied at the same time. The urinary concentration of HA corresponding to TWA at 100 ppm was 2.6 g/g creatinine as BEI. This value agreed well with both ACGIH's recommendation (2.5 g/g creatinine) and the values reported by Japanese researchers who have studied Japanese workers. Ethnic differences of MEK metabolism may affect the relationship between exposure and BEI.
    Materialart: Digitale Medien
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