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  • 1
    ISSN: 1432-0630
    Keywords: 52.25.Dg ; 79.20.Nc ; 82.65.Yh
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The elementary mechanisms are described which determine the plasma and surface processes during the plasma-enhanced chemical vapour deposition of hydrogenated carbon films from methane. Corresponding model calculations are reviewed and critically discussed in comparison to experimental results. A realistic modeling requires the simultaneous and self-consistent treatment of plasma and surface effects. Several experimental data sets on plasma parameters and the growth and the composition of the films have been reproduced successfully. However, a broader experimental data base is needed for more critical tests of the models. The reliability of the modeling, in particular of the surface effects, is still limited due to the poor availability of elementary data.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1612-1112
    Keywords: Affinity chromatography ; Affinity electrophoresis ; Bile acid transport proteins ; Bile acid derivatives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary For the purification of the bile acid transport proteins from rat hepatocytes high affinity taurocholic acid derivatives were synthesized. One type was designed for coupling to a Sepharose matrix and the other for copolymerization with acrylamide. The resulting matrices were found to be suitable for affinity chromatography and affinity electrophoresis. In both syntheses, 3α, 12α-dihydroxy-7β-amino (tauro) cholic acid derivatives were used as the starting material, since substitution in this position had previously been shown not to alter transport affinity constant.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A computer-controlled rotating polarizer ellipsometer, operating in the infrared spectral region between 3.00 and 3.75 μm, has been developed for in situ characterization of amorphous hydrocarbon (a-C:H) thin films, deposited from methane in a rf plasma-enhanced chemical vapor deposition reactor. Spectroscopic IR ellipsometry permits insight into the chemical bonding structure of a-C:H coatings by the nondestructive detection of infrared stimulated C:H stretch vibrations. It is shown that the sp2CHx/sp3 CHx ratio, the content of bonded hydrogen, the infrared linewidth, and the real refractive index of the films depend on the negative self-bias voltage, which is formed at the samples during the deposition process. A transition from a-C:H films with polymerlike properties to hard a-C:H films was attained at a self-bias voltage of approximately −75 V.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 971-973 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laser-induced fluorescence was applied at the B–X transition of the CH radical to measure absolute densities of the CH radicals in an electron cyclotron resonance methane plasma. The absolute experimental uncertainty is only about 30% due to a new calibration procedure. The CH density correlates well with optical emission from the CH A–X and B–X transitions over a wide pressure range. Experimental results are in satisfactory agreement with predictions from a model based on rate equations for the electron-induced dissociation and ionization of the parent methane gas. This model also includes the interaction of the plasma species with the surrounding walls and the particle transport due to pumping.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 3401-3403 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A plasma-enhanced chemical vapor deposition process by means of the so-called running discharge has been developed. Amorphous hydrogenated carbon (C:H) films were deposited over a length of 2.5 m on the inner wall of an assembled waveguide system. The average deposition rate from a running discharge in methane was 0.27 A(ring)/s. An increase of the average deposition rate to 2.6 A(ring)/s was achieved using acetylene as process gas, while the H/C ratio in the C:H films remains nearly constant at one. The breakdown of a discharge in the metallic waveguide has been studied in argon plasmas depending on magnetic field, microwave power, and gas pressure. A sharp transition between a magnetically enhanced localized discharge and a running discharge was observed at increasing pressure in the range of some Pascal at a microwave power of 100 W. The running velocity (∼104 m/s) of the plasma package increases with increasing microwave power and increasing gas pressure. This plasma behavior has been further investigated by means of the power balance and plasma modeling in methane.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 2068-2072 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hard amorphous films of a-C:D were deposited by a rf glow discharge in CD4. The implantation of 40-keV 3He+ ions in these films was studied as a function of the helium fluence at temperatures between 100 K and room temperature. The trapped amounts of helium and the deuterium losses in the layer were measured in situ using nuclear reaction analysis with 0.5-MeV D+ and 1-MeV 3He+ beams, respectively, and subsequent ex-situ elastic-recoil detection analysis. A transient helium retention appears in the carbonized layers, occurring only at temperatures below 200 K. Above a critical fluence which depends on temperature and ion flux, outdiffusion of He is observed which is ascribed to the formation of diffusion channels by radiation damage. The deuterium depletion induced by helium bombardment below 200 K sets on in correlation with the helium outdiffusion, but is otherwise independent of the helium trapping.
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 1771-1773 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We compare reported compositions of a-C:H films in a ternary phase diagram. It is assumed that the films comprised three phases: sp3 hybridized carbon, sp2 hybridized carbon and hydrogen. The data are found to split into two well-separated groups. This separation depends on the method used to measure the sp3/sp2 ratio. We conclude from the comparison of NMR and infrared data that infrared analysis does not provide a quantitative measure of the sp3/sp2 ratio.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 937-939 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An electron cyclotron resonance plasma was used to prepare C:H layers from methane. The temperature dependence of the deposition rate was investigated at substrate temperatures ranging from room temperature to 700 K, at a gas pressure of 1.6 Pa. Despite low ion energies corresponding to the plasma potential, transparent hard coatings were obtained at elevated temperature with a density up to 2 g cm−3. A deposition model is proposed which describes the growth from an adsorbed layer, including surface reactions with radicals and atomic hydrogen as well as the direct incorporation of ions. Two different deposition processes can be identified, yielding polymerlike films in the temperature range up to 450 K and dense hydrocarbons above this temperature. The observed temperature dependence of the film properties such as H/C ratio, index of refraction, and density is consistent with the predictions of the model.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-1432
    Keywords: Transfer RNA ; Acceptor helix stem ; Primordial code ; Statistics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The specificity of interaction of amino acids with triplets in the acceptor helix stem of tRNA was investigated by means of a statistical analysis of 1400 tRNA sequences. The imprint of a prototypic genetic code at position 3–5 of the acceptor helix was detected, but only for those major amino acids, glycine, alanine, aspartic acid, and valine, that are formed by spark discharges of simple gases in the laboratory. Although remnants of the code at position 3–5 are typical for tRNAs of archaebacteria, eubacteria, and chloroplasts, eukaryotes do not seem to contain this code, and mitochondria take up an intermediary position. A duplication mechanism for the transposition of the original 3–5 code toward its present position in the anticodon stern of tRNA is proposed. From this viewpoint, the mode of evolution of mRNA and functional ribosomes becomes more understandable.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-0878
    Keywords: Pineal organ ; Organ culture ; Pinealocytes ; Differentiation ; Melatonin ; Radioimmunoassay ; Chick embryo
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The development of sensory structures in the pineal organ of the chick was examined by means of scanning electron microscopy from embryonic day 10 through day 12 post-hatching. At embryonic day 10, the wall of the tubules within the pineal primordium is composed of cells with unspecialized luminal surface. Differentiation of sensory structures starts at embryonic day 12 when pinealocytes and supporting cells can be distinguished. Pinealocytes are recognized by virtue of an inner segment only rarely endowed with a cilium, whereas supporting cells exhibit numerous short microvilli. Further differentiation of the sensory apparatus is achieved by development of an oval-shaped, biconcave swelling at the tip of the cilium, 1×2 μm in size, and a collar of long microvilli at the base of the inner segment. Membrane specializations of sensory cilia, however, were not detected. Since during embryonic life new tubules and follicles are continuously formed, all stages of differentiation of sensory structures are found in the chick pineal organ during the second half of the incubation period and the first two weeks after hatching. In 200-μm-thick Vibratome sections of chick-embryo pineal organs cultured in medium BM 86 Wissler for periods up to 13 days the cytodifferentiation parallels the development in vivo. Using an organ-culture system the 24-h release of melatonin into the culture medium was measured by means of radioimmunoassay after solid-phase extraction. At embryonic day 10, the 24-h secretion of melatonin was at the lower range of detection of the RIA (5 pg). The rapid increase in 24-h secretion in melatonin until hatching (∼50 μg) is approximated by an exponential curve.
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