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  • Electronic Resource  (4)
  • Polymer and Materials Science  (3)
  • Light stress  (1)
  • 1
    ISSN: 1432-1939
    Keywords: Carotenoids ; Chlorophyll fluorescence ; Lichens ; Light stress ; Phycosymbiodeme
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The effect of high light levels on the two partners of a Pseudocyphellaria phycosymbiodeme (Pseudocyphellaria rufovirescens, with a green phycobiont, and P. murrayi with a blue-green phycobiont), which naturally occurs in deep shade, was examined and found to differ between the partners. Green algae can rapidly accumulate zeaxanthin, which we suggest is involved in photoprotection, through the xanthophyll cycle. Blue-green algae lack this cycle, and P. murrayi did not contain or form any zeaxanthin under our experimental conditions. Upon illumination, the thallus lobes with green algae exhibited strong nonphotochemical fluorescence quenching indicative of the radiationless dissipation of excess excitation energy, whereas thallus lobes with blue-green algae did not possess this capacity. The reduction state of photosystem II was higher by approximately 30% at each PFD beyond the light-limiting range in the blue-green algal partner compared with the green algal partner. Furthermore, a 2-h exposure to high light levels resulted in large reductions in the efficiency of photosynthetic energy conversion which were rapidly reversible in the lichen with green algae, but were long-lasting in the lichen with blue-green algae. Changes in fluorescence characteristics indicated that the cause of the depression in photosynthetic energy conversion was a reversible increase in radiationless dissipation in the green algal partner and “photoinhibitory damage” in the blue-green algal partner. These findings represent further evidence that zeaxanthin is involved in the photoprotective dissipation of excessive excitation energy in photosynthetic membranes. The difference in the capacity for rapid zeaxanthin formation between the two partners of the Pseudocyphellaria phycosymbiodeme may be important in the habitat selection of the two species when living separate from one another.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 1 (1992), S. 293-297 
    ISSN: 1057-9257
    Keywords: Liquid crystals ; Spiropyran ; Holographic grating ; Optical data storage ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The application of liquid crystalline siloxanes consisting of pentamethylhydrocyclosiloxane cores with attached cholesteryl-, biphenyl- and photochromic spiropyran-based mesogens as reversible optical data storage materials is demonstrated by grating formation with an argon ion laser beam operating in the UV and visible regions. Erasure of the gratings with heat or visible radiation was possible.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 61 (1996), S. 1163-1171 
    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: An investigation was made of the optical and waveguiding properties of thin films fabricated from solutions of chitosan-acetic acid (chitosan/HAc) and chitosan/HAc doped with rare-earth metal ions (Er+++ or Nd+++). For all three films, the refractive indices were approximately 1.5 and there was nearly no absorption in the range of 300 to 2700 nm. The optical loss in a waveguides was less than 0.5 dB/cm. Morphological observations disclosed that all the films possessed a dense and homogeneous amorphous structure with smooth surfaces. Extrinsic scattering, especially the scattering caused by surface impurities, was the dominating factor affecting the optical loss value. It is also interesting to note that for all the films, doped with rare-earth metal ions or not, the morphological characteristics were alike and the optical properties were similar. Doping rare-earth metal ions into chitosan thin films did not seriously influence optical waveguiding. This paper reports, we believe, the first study of chitosan films for optical applications. The experimental results demonstrate that chitosan and its derivatives are potential candidates for optical materials. © 1996 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 1975-1982 
    ISSN: 0887-6266
    Keywords: poly(p-phenylene) oligomer ; p-sexiphenyl ; molecular dynamics ; thermal expansion ; rigid-rod polymers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We have studied the conformation and coefficient of thermal expansion in the poly(p-phenylene) oligomer p-sexiphenyl (C36H26) by molecular dynamics simulations. Studies of the backbone phenyl-phenyl torsion angle in a simulated p-sexiphenyl crystal at room temperature indicate the presence of torsional librations of approximately ±20°. Further analysis of the phenyl-phenyl backbone torsion angle in less closely packed regions of the simulated crystal (crystal ends) indicate the presence of 180° phenyl ring flips, in agreement with solid-state deuterium NMR data on poly(p-phenylene oligomers). The linear coefficient of thermal expansion was also calculated and found to be negative, in qualitative agreement with experimental data on rigid-rod compounds. © 1993 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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