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  • Books
  • Articles  (13)
  • Springer  (13)
  • American Association for the Advancement of Science
  • 1990-1994  (13)
  • Physics  (13)
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  • Books
  • Articles  (13)
Year
  • 1
    Publication Date: 1994-12-01
    Print ISSN: 0170-9739
    Electronic ISSN: 1431-5858
    Topics: Physics
    Published by Springer
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  • 2
    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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  • 3
    ISSN: 1572-9605
    Keywords: Y1Ba2Cu3O7−δ ; electrophoretic films ; grain aligned
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract In order to apply highT c superconductivity to general microwave cavities and to shielding devices for quasistationary magnetic fields, we have developed an electrophoretic coating technique. This work reports about the continuation of our experiments. More than 60 samples of electrophoretic layers deposited on silver substrates were fabricated by systematically varying the processing parameters. The r.f. surface resistance measured at 21.5 GHz and 77 K at low excitation fields is found to be a sensitive measure of the quality of the samples and falls rapidly with increasing average grain size. Textured electrophoretic layers of large grain size show the smallest sensitivity ofR s against the r.f. surface magnetic fieldH s. The magnetic sensitivitydR s /dH s is found to be in direct proportion toR s (77 K). After optimizing the sintering procedure the electrodes of the prototype cavity for a compact hydrogen maser were coated. The cavity was successfully operated at 1.42 GHz, and a surface resistance of 1 mΩ was achieved at 77 K. This compares to 4 mΩ for copper at the same temperature.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1572-9605
    Keywords: High-temperature superconductivity ; microwave cavities ; sample surface impedance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We used a dielectric resonator technique for highly sensitive measurements of the temperature dependence of the microwave surface resistanceR s of 1×1 cm2 superconducting films at 18.7 GHz. It consists of a sapphire disc positioned on the film under investigation within a copper cavity which is acting as a radiation shield. In the TE01δ oscillation mode the highly reproducible quality factor of about 105 results in a sensitivity of ±50μΩ forR s measurements. The temperature dependence ofR s can be measured up to values as high as 1 Ω. We have investigated several YBa2Cu3O7 thin films prepared by high oxygen pressure d.c. sputtering on LaAlO3 and NdGaO3. Our best films exhibit a pronounced nonlinear behavior of the d.c. resistivityρ(T) withρ(300K)/ρ(100K) values of about 3.7. Those films show, besides the initial fall-off just belowT c , a further strong decrease ofR s at low temperatures. This was observed both at 18.7 GHz and 87 GHz, as measured by a conventional cavity end plate replacement technique. ForT≪Tc/2 these films exhibit an exp (−αT c/T) dependence ofR s withα-values around 0.4. These observations may be explained by a superconducting energy gap with 2Δ/kT c≈0.8 for charge carriers localized in the CuO chains for YBa2Cu3O7.
    Type of Medium: Electronic Resource
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  • 5
    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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  • 6
    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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  • 7
    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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  • 8
    ISSN: 1573-6881
    Keywords: Mammalian endoplasmic reticulum ; prepromelittin ; prepropeptide GLa ; preprocecropin A ; M13 procoat protein ; protein transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract There are at least two different mechanisms for the transport of secretory proteins into the mammalian endoplasmic reticulum. Both mechanisms depend on the presence of a signal peptide on the respective precursor protein and involve a signal peptide receptor on the cis-side and signal peptidase on the trans-side of the membrane. Furthermore, both mechanisms involve a membrane component with a cytoplasmically exposed sulfhydryl. The decisive feature of the precursor protein with respect to which of the two mechanisms is used is the chain length of the polypeptide. The critical size seems to be around 70 amino acid residues (including the signal peptide). The one mechanism is used by precursor proteins larger than about 70 amino acid residues and involves two cytosolic ribonucleoparticles and their receptors on the microsomal surface. The other one is used by small precursor proteins and relies on the mature part within the precursor molecule and a cytosolic ATPase.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 80 (1990), S. 25-38 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this paper we present reflection experiments with thermal phonon pulses at bare crystal surfaces of a-cut sapphire, [111]-cut silicon,X-cut quartz andZ-cut quartz. The observed bolometer signals are compared with an adequate rigorous model calculation. The parameters for the phonon-detection properties of the used superconducting bolometer are taken from a preceding paper which is devoted to the phonon transmission in the same crystal, measured with the same experimental setup. An attempt is made to investigate also for the first time quantitatively the strong background signal which is mainly due to scattering from isotopes and other crystal defects but contains also contributions from phonon-phonon scattering as is shown by a detailed investigation.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 80 (1990), S. 15-23 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using pulse-heated constantan films as a thermal phonon radiator and superconducting tin bolometer as a phonon detector, we present for the first time a full quantitative comparison between observed bolometer signals and adequate rigorous model calculations for transmission experiments ina-cut sapphire, [111]-cut silicon, as well asX-cut quartz andZ-cut quartz. Details of the observed phonon signals are explained and understood. From these experiments, we are also able to extract information about the phonon absorption coefficient in the normal state of the polycrystalline tin bolometer for longitudinal and transverse polarized phonons in quantitative agreement with an earlier experiment ina-cut sapphire which was performed with a superconducting tunnel junction as a detector. The observed transmission signals can be explained for sapphire and silicon by ballistic propagation with additional small angle scattering, but for quartz strong frequency downconversion occurs for phonons with frequencies above half a Terahertz. In a succeding paper (Part II) the parameter deduced from the transmission experiment are applied to the analysis of the observed phonon signals in reflection experiments in the same crystals under the same conditions.
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