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  • 61.40  (3)
  • Laser angioplasty  (1)
  • SPACE VEHICLES
  • SPACE SCIENCES
  • STRUCTURAL MECHANICS
  • 1990-1994  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Lasers in medical science 6 (1991), S. 241-254 
    ISSN: 1435-604X
    Keywords: Laser angioplasty ; Photoablation ; Photohydraulic effect ; Fast thermal explosion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Besides the coagulation, where the body digests the necrotic tissue and direct evaporation of tissue, the photoablation effect turns out to be very important in tissue removal. In the case of high tissue absorption the process channels in photoablation can either be photochemical (bond breaking) or fast thermal. In the case of transparent media, a plasma formation due to high irradiances and an optical breakdown is necessary for ablation or photodisruption. All the process channels lead to a fast microscale explosion and to Shockwaves. For soft tissue the main process channel is the fast thermal explosion. Assuming that tissue will be disintegrated, if the energy deposited within a single laser pulse is larger than a material specific threshold, the thresholds for the radiant exposure and ablation rates respectively can be calculated. There is a large difference, whether the laser radiation is applied to the tissue surface in noncontact or through a fibre in contact. In contact the ‘fast thermal explosion’ happens in a closed chamber and hence the photohydraulic effect will support the photoablation. The thermally damaged zone in the surrounding tissue depends on the optical penetration depth mainly in cases that the pulse duration is shorter than a critical time given by the heat conductivity. Pulsed lasers can be used ‘non-thermally’ only if the average power is less than a tenth of a watt. With a higher amount of average power a pulsed laser will act comparable to a cw laser.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 54 (1992), S. 40-46 
    ISSN: 1432-0630
    Keywords: 61.40 ; 71.55 ; 82.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Amorphous (a-) semiconductors like a-Si:H and the chalcogenide glasses possess a general tendency to establish an overall equilibrium between the electronic system and the lattice with its dopant and defect sites. In the present paper the chemical interactions which establish these equilibria within the bulk of the a-semiconductor lattices are compared to chemical interactions in liquid electrolytes, particularly to those in H2O. These considerations reveal close similarities between autocompensation doping in a-semiconductors and acid/base reactions in H2O. The effects of light and field-effect induced defect formation, on the other hand, are shown to be related to the phenomenon of electrolysis in H2O. The consideration of these analogies further emphasizes the roles of charge-carrier localization and that of H-diffusion in promoting dopant and defect equilibration reactions in a-semiconductors.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 52 (1991), S. 335-338 
    ISSN: 1432-0630
    Keywords: 61.40 ; 61.80 ; 72.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract n-type a-Si:H films have been irradiated with light, electrons, protons and heavy ion beams. It is shown that the non-thermal creation of dangling-bond defects activates significant densities of previously inactive phosphorus dopants. The relevance of these results is discussed with respect to equilibration phenomena in doped material and with respect to degradation phenomena in a-Si:H solar cells.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 53 (1991), S. 235-240 
    ISSN: 1432-0630
    Keywords: 61.40 ; 61.80 ; 72.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Hydrogenated amorphous silicon (a-Si:H) films have been irradiated with H+, B+, P+, and Ar+ ion beams. The accumulation and the annealing of irradiation-induced defects has been investigated through a series of electronic transport and PDS measurements. We find that for all projectiles damage accumulation is dominated by atomic displacement collisions with the damage saturating for energy transfers in excess of about 10 eV/target atom. Annealing at elevated temperatures causes the conductivity of doped and irradiated a-Si:H films to increase according to stretched exponential decay curves. All annealing parameters derivable from such fits scale with the energy originally dissipated into atomic displacement collisions. For energy transfers up to 10 eV/target atom the activation energy for annealing increases up to a saturation value and, at the same time, an increasing fraction of the irradiation-induced defects becomes stable against annealing at moderate temperatures (T a〈250° C). We discuss these results with respect to damage accumulation data in crystalline silicon (c-Si) and with regard to the annealing of metastable defects in a-Si:H.
    Type of Medium: Electronic Resource
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