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  • 1
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In situ boron-doped hydrogenated silicon films plasma-deposited on various conductive substrates (including transparent oxides on glass) have been anodized in hydrofluoric acid solutions and subsequently electrochemically oxidized in an aqueous electrolyte. At room temperature, the resulting layers yield visible photoluminescence and electroluminescence intensities and spectral shapes similar to those of p-type crystalline porous silicon obtained in the same way. The results demonstrate the technological feasibility of light-emitting devices by applying electrochemical processes to deposited silicon-based films.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Porous silicon/silicon structures under anodic oxidation conditions give rise to an electroluminescence phenomenon in the visible range. Using an optical multichannel analyzer the spectral distribution of the emitted light was measured−in situ−during the anodic oxidation step. Recorded spectra show a maximum which shifts continuously from red-orange at the beginning of the process towards the yellow range. The visible emission well above the band gap of bulk silicon is attributed to a quantum size effect in the very small size (5–20 A(ring)) silicon island which constitutes the porous silicon skeleton. The light emission is interrupted when the current flow stops due to the formation of a continuous oxide layer at the porous silicon/silicon interface.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1042-7147
    Keywords: Crystalline interphase ; Interfacial polymer chain orientation ; Elastic modulus of interphase ; Stress-free temperature ; Reversible energy of adhesion ; 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
    Notes: The aim of this third part is to analyze the structure and properties of the interfacial region between carbon fibers and PEEK as a function of different thermal conditioning treatments. First, it is shown by means of optical microscopy that the interfacial zone is not different from the bulk matrix when standard cooling conditions are used. On the contrary, a transcrystalline interphase is formed near the carbon fiber surface in systems that have been subjected to isothermal treatments. By comparison with previous results concerning the mechanical properties of the fiber-matrix interface, it appears that the interfacial shear strength decreases in the presence of a transcrystalline interphase or when the crystallization rate of PEEK increases. Moreover, it seems that the “constraint state” of the amorphous phase of PEEK near the fiber surface could also play a role in the interfacial shear strength. Secondly, a method is proposed in order to estimate the elastic modulus of crystalline interphases. It seems that this modulus is strongly dependent on the crystallization rate of the polymer. Finally, the determination of the stress-free temperature, defined as the temperature at which a longitudinal compressive stress just appears on the carbon fiber during the processing of the composites, is performed by recording the acoustic events corresponding to the fragmentation process in single-fiber composites. The results confirm that the crystallization rate and the “constraint state” of the amorphous phase of the matrix play an important role in the mechanical behavior of carbon fiber-PEEK interfaces.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The voltage-tunable electroluminescence (VTEL) observed on porous silicon-electrolyte system is investigated in relation with the material photoluminescence (PL). It is shown that the PL line is the envelope of all the emitted EL spectra obtained upon the bias variation. Consequently, a blueshift of the (PL) line leads to a similar shift of all the corresponding EL lines. This strongly suggests a common origin of these two phenomenon. Moreover, this study seems to indicate that the VTEL of porous silicon is related to the size and efficiency distributions of the silicon nanocrystallites associated with an electrically induced selective carrier injection. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Foundations of physics 5 (1992), S. 591-595 
    ISSN: 1572-9524
    Keywords: principle of relativity ; cosmic time ; special relativity ; Einstein ; backround radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In a recent article [1] M.A. Oliver argues there is a conflict between Einstein's Special Theory of Relativity (STR) and Cosmology. In ascertaining this conflict (see below), Oliver finds allies in Bergmann [2] and Bondi [3]. To resolve this conflict, he proposes to restore “the classical (mechanical) concepts of space and time” [1, p.666] and an absolute rest-frame. I shall devote a few words (1) to the Principle of Relativity and (2) to the notion of cosmic time in cosmology; this enables me (3) to argue that the alleged conflict between STR and Cosmology is based on a misunderstanding of the Principle of Relativity. (4) Finally I take a critical look at Oliver's allies.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1572-9575
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper assesses Miklós Rédei's [1991] proof of the proposition that algebraic relativistic quantum field theory is stochastic Einstein local. The conclusion is that either Rédei's proof is spurious, in that it does not really prove what it intends to establish, or that the proof is fallacious. The paper is self-contained in the sense that the few ingredients of algebraic quantum theory that go into Rédei's proof are first summed up. Then Hellman's definition of stochastic Einstein locality is discussed, a detailed exposition is offered of Rédei's proof, and finally the author's refutation is explicated.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A detailed analysis of the different characteristics of the electroluminescence that is observed during the anodic oxidation of porous silicon layers formed on lightly p-doped substrates is presented. It is shown that the emission presents characteristics very similar to that of the photoluminescence observed on the same porous layers, and that the same basic mechanisms are involved in the two phenomena. The emission intensity increase with the oxidation level is quantitatively explained by the passivation enhancement provided by the electrochemical oxidation. The spectral shift of the spectra during the oxidation is also discussed: It is shown to result from the decrease in the sizes of the largest emitting crystallites or/and from the significant improvement of the passivation of the smallest ones due to the oxide growth. The effect of the anodizing current density on the emission efficiency is also presented.
    Type of Medium: Electronic Resource
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