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  • 1
    ISSN: 1434-6036
    Keywords: PACS. 81.05.Ys Nanophase materials - 78.40.Fy Semiconductors - 78.40.Ha Other nonmetallic inorganics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: A modification of the polyol process has enabled the direct synthesis of nm-sized Ag particles with narrow size distribution and controlled average dimension embedded in a polymeric matrix. Dispersion of colloidal silver was obtained by reduction of silver nitrate in ethylene-glycol in the presence of a polymeric protective agent (i.e., poly(N-vinylpyrrolidone)) and ultrasounds. The final particle size was controlled by removing the colloid from the reactive mixture by addition of acetone. The very strong plasmon resonance peak at 410 nm and a feature at 350 nm in the UV-visible spectra are a clear consequence of the nano-size of dilute Ag particles. The proposed process offers the possibility to effectively use these synthesised materials for the production of colour filters for advanced optical devices.
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  • 2
    ISSN: 1434-6036
    Keywords: PACS. 78.67.Bf Nanocrystals and nanoparticles – 36.40.Gk Plasma and collective effects in clusters – 82.30.Nr Association, addition, insertion, cluster formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: A simple and high-reproducible method for the synthesis of polymer-protected silver cluster of controlled size is described. UV-visible spectroscopy has been used for investigating the influence of the aging of the protective poly(vinylpyrrolidone) layer on the cluster growth rate at different reaction temperatures and poly(vinylpyrrolidone)/ethylene glycol weight ratios. The obtained results show that the aging time of the polymeric stabilizer solution plays a fundamental role in the reproducibility of the cluster growth process. A model for the metal cluster formation-grow process is also proposed.
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  • 3
    ISSN: 1434-6036
    Keywords: PACS. 72.80.-r Conductivity of specific materials – 72.80.Le Polymers; organic compounds (including organic semiconductors) – 81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: A composite material of a polyethylene matrix filled by a fine silver powder was prepared with different Ag contents and physical behaviours ranging from insulator to conductor. Ac differential magnetic susceptibility χ measurements show the samples are paramagnetic up to an Ag concentration of ∼65%. At low temperatures the composite is spin-glass type, whereas the transition from insulator to conductor corresponds to an abatement of χ at zero magnetizing field. Magneto-conductivity effects have been observed in resistivity measurements at low temperatures. They can be explained in terms of an effective exchange electronic scattering mechanism between the conduction electrons and the diluted magnetic moments arising from unpaired electron spins of boundary silver particles. Moreover, the presence of a broad minimum in the resistivity curve at T = ∼ 20 K, observed in samples with an Ag concentration just above the percolation threshold, addresses to possible interference effects similar to those reported in disordered materials.
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  • 4
    ISSN: 1434-6036
    Keywords: PACS. 68.43.-h Chemisorption/physisorption: adsorbates on surfaces – 81.07.Pr Organic-inorganic hybrid nanostructures – 81.16.Be Chemical synthesis methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Nano-sized cobalt clusters passivated by alkane-thiol molecules were obtained by the action of concentrated thiol solutions on micrometric cobalt particles. Thiol molecules caused an erosive process on the metal grains with the consequent formation of nano-sized metal debris and cobalt thiolate as by-product. The final material microstructure was composed by cobalt clusters embedded into a continuum cobalt thiolate matrix. Depending on the thiol molecule length, the material texture ranged from rubbery to waxy. These new types of nanocomposite materials were found to be crystalline, thermally stable up to ca. 300 °C, intensely red colored, and high hydrophobic. In addition, they generated polymeric structures when dissolved in non-polar solvents.
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  • 5
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Experimental results concerning the synthesis of gold nanoparticles prepared by alcoholic reduction of Au(III) ions in presence of a polymeric stabilizer, and UV-visible spectroscopic characterization is presented. Optical spectroscopic data have been correlated to off-line size measurements obtained analysing transmission electron micrographs. The gold cluster size, coming from both TEM micrographs and absorbance cubic root, behaved linearly with time above a threshold temperature (70 $^\circ$ C) according to a deposition-controlled growth mechanism. The plasmon peak halfwidth behaved linearly with inverse particle radius (obtained by TEM), thus proving the hypothesized mechanism growth. The spectroscopic approach allows an on-line gold cluster measurement with possibility to fine control particle size also in the case of a fast process.
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  • 6
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The clinical use of glass ionomers is well established in the odontological field. In particular; (i) high biocompatibility (unincreased macrophages activity), and consquently no inflammation in post-operative course; (ii) total non-toxicity of components; (iii) absence of mutagenic consequence on osteoblasts; (iv) dimensional stability and absence of macroscopic changes after very long implantation times; (v) stability to water and biological compounds, make these materials attractive for further clinical applications. The high adhesion both to metallic or ceramic surfaces and bone tissue makes this materials excellently usable for the adjustment of bone defects. This goal necessitates suitable knowledge of the mechanical, chemical, physical and biological properties of commercial materials so that the most suitable product can be identified. The characterization of representative products of each of the principal classes of glass ionomers material is reported.
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 2 (1983), S. 201-203 
    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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  • 9
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Carbon fiber posts (CFP) are widely used in the restoration of endodontically treated teeth to enhance the mechanical behavior in spite of metallic posts and to prevent vertical fractures of the tooth under chewing loads. The post is cemented inside the canal lumen using polymer resins with Young's modulus lower than Dentine. In this conditions the stress concentration is located at the post-cement interface and in the cement bulk itself, preserving radicular Dentine from dangerous stress accumulation. The mechanical resistance of CFP posts cemented in human Dentine was evaluated by the means of mechanical pull-out tests assisted by the finite element analysis. The average bond strength and the critical stress values of the CHP-cement interface were 25 MPa and 50 MPa respectively. ©2000 Kluwer Academic Publishers
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  • 10
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Some important eye pathologies, such as diabetic proliferative retinopathy and retinal detachment, are strictly connected to different gel vitreus alterations. Therefore there is a strong need in ophthalmology for vitreal substitutes. Until now many synthetic and natural polymers have been tested as vitreal substitutes, but no one has proved to be an ideal vitreal substitute. An ideal vitreal substitute, apart from other characteristics, such as transparency, permanency, biocompatibility, etc. must have a rheological behaviour compatible with the surrounding tissues. The viscoelastic behaviour of different animals' gel vitreus, evaluated by means of steady shear viscosity and small-amplitude oscillatory measurements, is typical of solid-like rubbery gels with dynamic elastic modulus G′ higher than the dynamic viscous modulus G″ in the typical frequency range investigated (0.05–10 Hz). On the other hand the rheological behaviour of current or candidate vitreal substitutes (silicone oil, HPMC, high molecular weight hyaluronic acid and chemically-crosslinked hyaluronic acid), analysed with the same technique, is generally different from that of natural vitreus.
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