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  • 1
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 2299-2310 
    ISSN: 0887-624X
    Keywords: plasma ; x-ray photoelectron spectroscopy surface modification ; O3P ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas phase downstream products of an air glow discharge have been measured, using absorption and emission spectroscopies, as a function of plasma power, air flow rate, and distance from the plasma. In addition, the reaction of these products with a linear low density polyethylene (LLDPE) polymer surface has been followed using x-ray photoelectron spectroscopy (XPS). At higher air flow rates (〉300 sccm), the primary reactive species is confirmed to be O(3P) atomic oxygen. Some O(3P) is generated in the plasma itself, but more appears to be formed in the downstream region, because of dissociation of molecules in their excited states. At low flow rates, the concentration of O(3P) is strongly depleted at the sample position, but other atomic oxygen states become more prominent. O(5S) and O(3S) are two states which are identified. XPS studies of the polyethylene surface reacted at high flow rates shows oxygen functionalities that are likely the result of an initiation by hydrogen abstraction. At low flow rates, the products suggest initiation by oxygen insertion. Thus, changes in flow rate can result in major changes to the polymer surface chemistry. © 1996 John Wiley & Sons, Inc.
    Additional Material: 13 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 60 (1996), S. 1015-1023 
    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: Bales of antioxidant-stabilized guayule rubber underwent significant losses in bulk viscosity when stored under ambient conditions at an Arizona processing facility. Previous work implicated the unsaturated fatty acid esters present in entrained resin as promoters of such degradation. Aging studies as functions of storage temperature and unsaturated acid ester content were carried out on both bulk rubber and rubber-resin solution (miscella) for cultivar AZ-101. The rate of thermooxidative degradation, determined as a function of Mooney viscosity, was increased by the addition of unsaturated ester. Anaerobic degradation was not affected in this way. The activation energy of chain thermolysis was found to be 116 ± 6 kJ/mol (28 ± 1 kcal/mol). At temperatures above 60°C, chain recombination successfully competed with chain scission in lower viscosity rubber. The rate of thermoox-idative degradation was substantially higher in a typical process miscella. A hindered amine antioxidant significantly reduces chain scission under these conditions. © 1996 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Transgenic research 5 (1996), S. 257-262 
    ISSN: 1573-9368
    Keywords: antisense RNA ; peroxidase ; ribozyme ; tobacco
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Five short hammerhead ribozymes (Rzs) were constructed and tested, using a range ofin vitro reaction conditions, for catalytic activity against the mRNA encoding the lignin-forming peroxidase (TPX) of tobacco. Although all 5 Rzs were shown to be able to cleave the RNA substrate, percentage cleavage varied with pre-denaturation of Rz and substrate, incubation temperature, length of incubation and ribozyme (Rz)-to-substrate ratio. One Rz with two catalytic units and 60 nucleotides of complementary sequence in 3 regions was shown to most efficiently cleave the substrate under allin vitro conditions tested. This ribozyme cleaved better than the two single ribozymes from which it was made. The superior cleaving ability of this Rz was shown to be due to the accessibility of the chosen target site and to the increased length of the hybridizing arms spanning this accessible region of the RNA.
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  • 4
    ISSN: 1573-9368
    Keywords: antisense RNA ; lignin ; peroxidase ; ribozyme ; tobacco
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Several strategies involving the use of antisense and ribozyme constructs in different expression vectors were investigated as methods of suppressing gene expressionin planta. We had previously identified an efficiently cleaving ribozyme (Rz), with two catalytic units and 60 nucleotide (nt) of complementary sequence, to the ligninforming peroxidase of tobacco (TPX). This Rz was cloned behind the 35S CaMV (35S) and nopaline synthase (NOS) promoters, and into a vector utilising the tobacco tyrosine tRNA for expression. For comparison with more traditional antisense strategies, full-length TPX antisense (AS) constructs were also constructed behind the NOS and 35S promoters. Populations of transgenic tobacco containing these constructs were produced and compared to control plants transformed with the vector only. Significant suppression of peroxidase expression in the range of 40–80% was seen in the T0 and T1 populations carrying 35S-AS, 35S-Rz and tRNA-Rz constructs. Co-segregation of the suppressed peroxidase phenotype and the tRNA-Rz transgenes was demonstrated. Northern blot analysis indicated that levels of TPX mRNA were lower in the Rz plants. No evidence of mRNA cleavage was observed and thus it was unclear if the Rz constructs were acting as Rzsin vivo. Transgenic plants containing the tRNA-Rz construct had significantly lower levels of peroxidase than the other transgenic plants. There was no significant difference in levels of suppression of TPX between the short Rz in the 35S vector and the full-length AS constructs. Although peroxidase levels were significantly reduced in transgenic plants carrying 35S-AS, 35S-Rz and tRNA-Rz constructs, no significant difference in lignin levels was observed.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 23 (1995), S. 873-878 
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A mass-separated low-energy ion beam system was used to deliver pure OH+ and NH+ to 15nm thick polystyrene films on silicon in ultrahigh vacuum. This was done in an effort to produce specific surface chemical functional groups. X-ray photoelectron spectroscopy showed that when the bombardment energy of OH+ exceeded 10 eV, or the dose was higher than 1 × 1016 ions cm-2, a mixture of C—OH, C—C=O and C—COOH groups was produced, along with severe damage to the aromatic rings. However, for bombardment at 10 eV with a dose of 1 × 1016 ions cm-2, only C—OH (or COR) groups were found. Similarly, bombardment with NH+ at 10 eV and a dose 1 × 1016 ions cm-2 induced incorporation of a single nitrogen-containing functionality. The C 1s data indicated that the major chemical functionality on such surfaces in a C—NH2 (or C—NHR) group with a minor component of C—(NH2)2. Hence, surface functionality can indeed be controlled by altering the molecular nature, energy and dose of the bombarding species.
    Additional Material: 7 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 25 (1997), S. 788-789 
    ISSN: 0142-2421
    Keywords: SIMS ; topography ; AFM ; imaging ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: In order to provide an accurate rendition of a three-dimensional (3D) volume obtained by SIMS, it is necessary to take account of the topography of the original surface and the relative sputter rates of the different structures within the volume. We describe a method that corrects both distortions to 3D SIMS images. An atomic force microscope is used to produce a topographic images of the area analysed by SIMS, both before and after the depth profile. This information is convoluted with the 3D SIMS image to produce a correct 3D image of the changes in composition within the volume of the material. © 1997 by John Wiley & Sons, Ltd.
    Additional Material: 5 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 23 (1995), S. 573-580 
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Factor analysis (FA), the multivariate statistical technique, has been used to extract chemical bonding information from SIMS secondary ion energy distributions. The method is outlined in detail and shown to be capable of constructing quantitative profiles for the chemical states of zirconium present in ZrO2/Zr and ZrNx/Zr structures. In addition, a truncated data collection procedure wherein secondary ion intensity values are collected at a fixed number of emission energy values during the depth profile is outlined. This method, which enables data to be collected in a shorter time and from a smaller sample volume, is subsequently shown to yield reliable results, as confirmed by FA of Auger depth profiles on similar specimens.
    Additional Material: 8 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 23 (1995), S. 163-170 
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: This report illustrates, in a stepwise fashion, the application of a new method for quantifying SIMS results (termed the infinite velocity method) to the depth profile analysis of multilayered samples. The two samples analysed comprised a silicon substrate implanted with cobalt and a silicon substrate bearing an oxide layer implanted with boron. Concentrations were extracted by: sampling the secondary ion emissions over several kinetic energies during the depth profile; correcting the resulting intensities for instrument transmission and sputter yield effects, so that these may be poltted against the inverse of the velocity; and referencing the point at which the resulting curves intersect with the intensity axis (intensity at infinite velocity) to an element whose concentration is known, or to the sum of all major element intercept data. Characteristic velocity data obtained from each cycle of the depth profiles were also used to illustrate a new method for defining the position of the interface. To illustrate the validity of these results, peak concentrations were compared with those calculated via the integration method as well as Auger depth profile analysis.
    Additional Material: 7 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 24 (1996), S. 529-530 
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: No Abstract
    Additional Material: 2 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 24 (1996), S. 591-596 
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A number of binary oxides, sulphide compounds and complex minerals have been analysed by x-ray photoelectron spectroscopy to give the relative intensities of major photoelectron lines. Where possible, compound surfaces were prepared by fracturingin vacuoor in inert gas to avoid contamination. Alternatively, some of these compounds have undergone a mild thermal treatmentin vacuoto remove much of the surface contamination which normally affects such intensity measurements. The experimental line intensity ratios were corrected only by their particular photoelectron cross-section and inelastic mean free paths. For most oxides and complex minerals studied, good agreement is obtained with the expected stoichiometry, particularly when using photoelectron lines of higher kinetic energy. This tends to support the use of a simple background approximation when measuring specifically with those oxides involving non-transition elements. The sulphides studied mostly involved transition metals; agreement between calculated and actual stoichiometry was only modest. Some differences in measured surface stoichiometry occurred as a result of the ambient conditions within which the fracture was made; fracturein vacuoproduced a different S/M ratio than did fracture in an inert gas environment.
    Additional Material: 3 Ill.
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