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  • Wiley-Blackwell  (49)
  • Oxford University Press  (23)
  • American Chemical Society (ACS)
  • 1990-1994  (72)
Collection
Year
  • 11
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 142 (1990), S. 425-433 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Normal human diploid fibroblasts exhibit a limited lifespan in vitro and are used as a model to study in vivo aging. Monoclonal antibodies were generated against partially purified surface membranes from human diploid fibroblasts at the end of their lifespan (senescent). Three hybridomas were isolated that secreted antibodies reacting to cellular determinants expressed specifically on senescent human fibroblasts of different origin, including neonatal foreskin, embryonic lung, and adult skin punch biopsy, but not expressed on matched young cells. The antibodies did not bind to immortal human cells and normal young cells made reversibly nondividing, indicating the antigens are not expressed in cells that are not senescent. The antibodies identified senescent cells in a mixed cell population and expression of the senescent cell antigens correlated strongly with the cells inability to synthesize DNA at the onset of senescence. The antigens appeared to be cell surface or extracellular matrix associated, and the epitopes were destroyed by mild trypsin treatment. Western analysis indicated all three antibodies reacted with fibronectin. Though the antigenic determinants on the fibronectir molecule were not accessible in the intact young cell, the epitopes were present in fibronectin extracted from both senescent and young cells, as well as purified human plasma fibronectin. These antibodies and the senescent specific expression of the antigens provide powerful tools to investigate the mechanisms leading to in vitro senescence. This may enable us to investigate directly the relationship between cellular aging and aging of the individual.
    Additional Material: 6 Ill.
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  • 12
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 21 (1994), S. 814-817 
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The structure of electropolymerized thin films of polyaniline has been studied using the techniques of contact and non-contact scanning probe microscopy (SPM). Films exposed to Ir+ cations in solution, as well as unexposed films, were examined. Contact-mode SPM images of these films reveal only a diffuse, amorphous surface structure in both types of film, while non-contact SPM images indicate an intricate, nanometer-scale domain structure. Film growth is in a layer-by-layer mode, with each layer consisting of small polymer bundles of average dimension 1000 ± 75 Å. The Ir+ incorporation in these films does not involve a restructuring of the film morphology. The relevance of the microscopic domain structure to models describing conduction mechanisms in these films is also discussed.
    Additional Material: 4 Ill.
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  • 13
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 12 (1991), S. 393-402 
    ISSN: 0192-253X
    Keywords: Clonal variation ; gene expression ; DNAase I hypersensitive sites ; matrix-associated regions ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The chinchilla-mottled (cm) mutation at the mouse tyrosinase-encoding locus leads to a transversely striped pattern of dark- and light-grey coat colors in homozygotes. The same basic pattern occurs in various other genotypes and has previously been found to represent the clonal developmental history of melanocytes. In a homozygote such as cm/cm, cis-acting mechanisms would be expected to account for the color differences. To search for these mechanisms, the genomic structure of the mutation was examined and compared with the wild-type, and its function was compared in cultured melanocyte clones of the respective colors. Evidence from restriction mapping indicated that the coding region of the mutant gene resembles that of the fully and uniformly pigmented wild-type. However, the upstream sequences are rearranged in the mutation. The rearrangement begins 5 kb 5′ of the transcription initiation site and is estimated to encompass at least 30 kb of distal upstream sequence. At least two stable functional states of the cm gene were detectable: Light-cell clones have low levels of tyrosinase-specific transcription, reduced DNAase I sensitivity of tyrosinase chromatin, and no detectable hypersensitive sites near the gene; dark-cell clones have higher (but subnormal) levels of transcription, greater sensitivity of chromatin to DNAase I, and a hypersensitive site in the promoter region. The changed relation between the structural gene and its upstream region may separate it from cis-acting control elements, resulting in reduced and variable ability to achieve the appropriate chromatin configuration near the time of melanocyte determination; differences in expression among clonal initiator cells are then mitotically perpetuated. © 1992 Wiley-Liss, Inc.
    Additional Material: 10 Ill.
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  • 14
    Electronic Resource
    Electronic Resource
    Basel : Wiley-Blackwell
    Die Makromolekulare Chemie, Theory and Simulations 1 (1992), S. 119-128 
    ISSN: 1018-5054
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The tube diameter in the reptation model is the distance between a given chain segment and its nearest segment in adjacent chains. This dimention is thus related to the cross-sectional area of polymer chains and the nearest approach among chains, without effects of thermal fluctuation and steric repulsion. Prior calculated tube diameters are much larger, about 5 times, than the actual chain cross-sectional areas. This is ascribed to the local freedom required for mutual rearrangement among neighboring chain segments. This tube diameter concept seems to us to infer a relationship to the corresponding entanglement spacing. Indeed, we report here that the critical molecular weight, Mc, for the onset of entanglements is found to be Mc = 28 A/(〈R2〉0/M), where A is the chain cross-sectional area and 〈R2〉0 the mean-square end-to-end distance of a freely jointed chain of molecular weight M. The new, computed relationship between the critical number of backbone atoms for entanglement and the chain cross-sectional area of polymers, Nc = A0,44, is concordant with the cross-sectional area of polymer chains being the parameter controlling the critical entanglement number of backbone atoms of flexible polymers.
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  • 15
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 41 (1990), S. 1355-1356 
    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
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  • 16
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 43 (1991), S. 1559-1564 
    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: Ultrahigh molecular weight polyethylene (UHMWPE) reactor powders have been found to be processable in the solid state by the techniques of rolling and roll-drawing. Plates of compacted UHMWPE reactor powder were prepared below their melting points. These plates were then rolled at 124°C. The maximum uniaxial draw ratio (DR) obtained by multiple rolling was about 10. In additional experiments, rolled plates of a DR of 6 were further drawn by tensile stretching at a temperature of 135°C. The specimens prepared by rolling and by the two-stage draw were characterized by tensile measurements, differential scanning calorimetry (DSC), and X-ray diffraction. Results show that, on rolling alone, the tensile modulus and tensile strength achieved were 3 GPa and 42 MPa, respectively, at a DR of 9.6. The rolled plates were effectively drawn further to a total DR of 86. Such highly drawn films exhibited tensile moduli and tensile strength up to 81 and 1.3 GPa, respectively. A high crystallinity and high crystal orientation were also obtained by the two-stage draw.
    Additional Material: 6 Ill.
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  • 17
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 41 (1990), S. 455-465 
    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: it-Polypropylene films were coextruded by using dies of varying extrusion draw ratio (EDR) from 2-10. Among the resulting films, the film coextruded at EDR 9 possesses the most attractive superstructure and the highest modulus. The dynamic modulus at room temperature was 7 GPa and an αc dispersion peak occurred at 100°C in E″-temperature curves, which is higher by about 20°C than that of the multistep zone-drawn and zone-annealed fibers previously reported. Further, to prepare films with higher draw ratio and higher modulus, repetition of the coextrusion was attempted. Consequently, the draw ratio and the E′ at room temperature reached 12 and 13 GPa, respectively. The present paper discusses changes in molecular orientation, crystallinity, uniformity of the superstructure, and dynamic viscoelasticity, with increasing of the used EDR and repeating the coextrusion with some combinations of EDR.
    Additional Material: 8 Ill.
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  • 18
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 39 (1990), S. 1873-1885 
    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: A polycarbonate (PC)/carbon fiber (CF) composite system has been examined with regard to interfacial adsorption and crystallization by altering times and temperatures of annealing. Times up to 180 min and temperatures of 245, 275, and 300°C have been investigated. Tranverse tensile, tranverse toughness, and scanning electron microscopy results on unidirectional, continuous-fiber composites indicate improved fiber/matrix adhesion at longer times and higher temperatures of annealing. Improvements in transverse toughness and transverse tensile strength of a factor of two is achieved. The data indicate that primarily adsorption rather than secondary interfacial crystallization is the likely mechanism for increased adhension. Isothermal transverse toughness values have been found to fit well to a Langmuir-type expression. The temperature dependence of adsorption as measured by transverse toughness is described well by an Arrhenius equation. The dependence of transverse toughness on PC molecular weights from Mw = 26,600 to 39,800 was found to be large, with higher molecular weights adsorbing more effectively.
    Additional Material: 8 Ill.
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  • 19
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 43 (1991), S. 429-435 
    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: In order to improve the mechanical properties of polypropylene film, a new processing combining extrusion and zone-annealing has been applied. It was found that there are suitable conditions for each step in the combined processing. When the coextrusion draw ratio was low, the total draw ratio and modulus could be increased by the zone-annealing subsequently done. The highest modulus was obtained when the film was coextruded at extrusion draw ratio 4 and then zone-annealed at 120°C under 7 kg/mm2. The value was 12 GPa in Young's modulus or 17 GPa in dynamic modulus. The peak temperature of αc dynamic dispersion for the combinedly processed film was 109°C, which is higher by 10°C than that for the as-coextruded film. Four drawing methods were compared in dynamic viscoelasticity. These methods are the coextrusion, zone-drawing/zone-annealing, two-step coextrusion, and the combined processing by coextrusion and zone-annealing. The highest dynamic modulus for each method was arranged in the above order. The combined processing indicated the most effective improvement in mechanical properties, because it is believed that lamellae in the original film were broken by cooperating interaction of shear stress, compression, and tension on coextrusion and then the superstructure with a high crystallinity and a high molecular orientation was formed on zone-annealing.
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  • 20
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 44 (1992), S. 1679-1683 
    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: The performance of PET [poly(ethylene terephthalate)] and a copolymer of PET has been tested as an adhesive for chromium-coated steel. Crystallinity in the polyesters is found to limit adhesion, probably by restricting chain mobility. Lamination temperatures above the melting point of each polyester give the best adhesion. Degradation of the polyesters at yet higher temperature resulted in both reduced polymer cohesion and adhesion.Optimum bonding to steel was obtained at lamination temperatures between 230 and 275°C for the copolyester and between 280 and 300°C for PET. The standard laminate compression time was 15 min at 50 kg/cm2. Adhesion was evaluated by the ASTM T-peel test. Assessments were made by both the peel energy and the peak load for peel.
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