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  • 11
    Digitale Medien
    Digitale Medien
    Experimental Observation of 2 – Anion and its para → ortho Conversion in Solid para hydrogen Using High–Resolution ESR Spectroscopy (1998)
    Springer
    Journal of low temperature physics 111 (1998), S. 509-514 
    Details
    ISSN: 1573-7357
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We present experimental observations and study of $${\text{H}}_{\text{2}}^ - $$ in solid parahydrogen. Since the parahydrogen molecule does not produce local magnetic fields, high–resolution ESR spectra of trapped radicals can be observed in the solid parahydrogen matrices. Using this high–resolution ESR spectroscopy, new quartet ESR signals were observed in γ–rays irradiated solid parahydrogen and assigned as $${\text{H}}_{\text{2}}^ - $$ In addition, para– $${\text{H}}_{\text{2}}^ - $$ was observed to convert into ortho– $${\text{H}}_{\text{2}}^ - $$ on the storage at 4.2 K. On the other hand, ortho–H 2 molecule converts into para– $${\text{H}}_{\text{2}}^ - $$ at cryogenic temperatures. The difference in the conversion between the H 2 molecule and the $${\text{H}}_{\text{2}}^ - $$ anion is explained by the parity conservation law of wavefunctions on exchanging the protons in homonuclear diatomic molecules such as the $${\text{H}}_{\text{2}}^ - $$ anion and H 2 molecule.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1022280913340
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  • 12
    Digitale Medien
    Digitale Medien
    Experimental and theoretical studies on phase separations in the Fe-Al-Co ordering alloy system (1994)
    Springer
    Journal of materials science 29 (1994), S. 652-659 
    Details
    ISSN: 1573-4803
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Phase separations in iron-rich Fe-Al-Co ternary alloys were investigated by means of transmission electron microscopy, differential thermal analysis and magnetization measurement. Two kinds of phase separations have been found at 923 K; A2+B2 and B2+B2*. The former occurs in a tongue-shaped composition region ranging from Fe-12 at % Al-15 at % Co to Fe-35 at % Al-45 at % Co and the latter appears in the small region bordering on the Fe-Al binary side of the A2+B2 field. These two-phase fields have theoretically been evaluated on the basis of the so-called Bragg-Williams-Gorsky model taking account of not only chemical but also magnetic interactions. The magnetic ordering accounts for the expansion of the A2+B2 coexistent region. In the measurement of magnetic properties, large increases in coercive force, H c, and residual magnetic flux density, B r, were observed in the two-phase microstructures.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00445974
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  • 13
    Digitale Medien
    Digitale Medien
    Experimental and theoretical phase diagrams of the iron-rich Fe-Si-Ge ordering system (1995)
    Springer
    Journal of materials science 30 (1995), S. 5056-5064 
    Details
    ISSN: 1573-4803
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The phase separation in iron-rich Fe-Si-Ge ternary alloys was investigated by means of transmission electron microscopy. The phase separations into A2 and D03 were recognized in several alloys in addition to the phase separation into B2 and D03 which has already been found in Fe-Si and Fe-Ge binary systems. On the basis of TEM observations, isothermal section diagrams are proposed for the iron-rich corner at 823, 873, 923 and 973 K. The A2 + D03 two-phase field exists in a band-shaped region at 823 K. With increase in temperature,the A2 + D03 field gradually shrinks and is eventually replaced at 973 Kwith the B2 + D03 field, which extends from both the Fe-Si and Fe-Ge binary sides. The phase diagrams were well reproduced by the calculations based on the so-called Bragg-Williams-Gorsky approximation, taking account of the chemical and magnetic pair interactions up to the second nearest neighbour. The effects of the magnetism on the equilibria are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00356049
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  • 14
    Digitale Medien
    Digitale Medien
    Computer simulation of A2/B2 second-order phase transition based upon the Khachaturyan diffusion equation (1997)
    Springer
    Journal of materials science 32 (1997), S. 5797-5804 
    Details
    ISSN: 1573-4803
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract A computer simulation, based on the Khachaturyan diffusion equation, is presented to develop the kinetics of the morphological evolution of the A2/B2 second-order phase transition in a binary solid solution. The evolution of the occupation probability, as a function of composition, shows a good similarity to the actual micrographs experimentally obtained based on the macroscopic composition gradient method. These results are used in parallel with the results of the evolution of the long-range order parameter as a function of the ageing time, to verify a new concept of the ordering behaviour inside the ordered phase.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1018634204712
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  • 15
    Digitale Medien
    Digitale Medien
    Effect of retained austenite on the microstructure and mechanical properties of martensitic precipitation hardening stainless steel (1999)
    Springer
    Journal of materials science 34 (1999), S. 3901-3908 
    Details
    ISSN: 1573-4803
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The effect of retained austenite (γ) on the microstructure and mechanical properties of a martensitic precipitation hardening stainless steel was experimentally investigated, whose chemical composition was Fe-1.8Cu-15.9Cr-7.3Ni-1.2Mo-0.08Nb-low C, N (mass %). The microstructures of all specimens consist of a typical lath martensite with interlath films of the retained γ, which is not reverted with aging. Cu-rich precipitates which may contribute to precipitation hardening can not clearly be observed. The tensile properties and Charpy absorbed energy are linearly approximated to the amount of retained γ as follows: 0.2% Y.S. (MPa) = 1192.3 − 13.6 × γ%, T.S. (MPa) = 1250.1 − 9.3 × γ%, El. (%) = 12.16 + 0.43 × γ%, R.A. (%) = 64.25 + 0.14 × γ%, and A.E. (J) = 72.5 + 0.8 × γ%. The introduction of retained γ is not beneficial to the fatigue limit. An excellent combinations of strength, ductility and toughness obtained in the present work is attributed to the introduction of retained γ and also to the chemical composition of the specimen used.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004626907367
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  • 16
    Digitale Medien
    Digitale Medien
    Electronic structure of icosahedral alloys: The case of Al65Cu20Os15 (1995)
    Springer
    The European physical journal 97 (1995), S. 439-452 
    Details
    ISSN: 1434-6036
    Schlagwort(e): 61.44.+p ; 71.20.Cf ; 72.15.-v ; 79.60.-i
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Measurements with photoemission spectroscopy in the photon-energy range 35–130 eV have been used to determine the valence band of the stable icosahedral Al65Cu20Os15. Resonant photoemission near the Os 5p → 5d and 4f → 5d transitions has been employed to show that the feature in the valence band with the maximum intensity at 1.5 (1) eV below the Fermi level is predominantly of the Os 5d character. This has been additionally verified by conducting the photoemission measurements in the constant-initial-state mode and by using the effect of the Cooper minimum in the photoionization cross section of the Os 5d orbitals. The valence band feature with the maximum intensity at 3.7 (1) eV below the Fermi level has been shown as being due mainly to the states of the Cu 3d character. The Os 5d and Cu 3d empirical partial density of states have been determined from the photoemission spectra. The decrease of intensity towards the Fermi level has been interpreted as being indicative of the presence of a theoretically predicted pseudogap around the Fermi level. It has been indicated, however, that the Fermi cut-off also contributes to the observed intensity decrease. It has been demonstrated that the energy resolution of the spectroscopic measurements performed so far on quasicrystals was not high enough to unambiguously determine the presence of such a pseudogap. No unusual features in the valence band of icosahedral Al65Cu20Os15, which could be ascribed to its quasiperiodic nature, have been observed within the resolution of the experiment. High energy-resolution spectroscopic measurements were also shown to be essential to observe the theoretically predicted spikiness of the density of states in quasicrystals. A critical review of published spectroscopic data on the electronic structure of quasicrystals has also been presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01317227
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  • 17
    Digitale Medien
    Digitale Medien
    Alternative formulation in the constrained Hamiltonian system of a rigid rotator (1990)
    Springer
    The European physical journal 48 (1990), S. 105-108 
    Details
    ISSN: 1434-6052
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract An alternative form of the constraint characterizing the motion of a rigid rotator is introduced and is shown to lead to the same constrained Hamiltonian system as the one constructed with the conventional constraintx 2=constant. In this new formulation, the canonical pairs of phase-space variables can easily be found, and the relationx 2=constant appears through an equation of motion rather than through a constraint. Application toO(N) nonlinear sigma model is also discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01565611
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  • 18
    Digitale Medien
    Digitale Medien
    Theoretical and experimental investigations on elastic interactions between γ′-precipitates in a Ni-Al alloy (1981)
    Springer
    Journal of materials science 16 (1981), S. 1197-1203 
    Details
    ISSN: 1573-4803
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Elastic interaction energies between two identical inhomogeneous plates in an anisotropic matrix were calculated with respect to particle separation distance and alignment orientation on the basis of the microscopic theory of elasticity developed by Yamauchi and de Fontaine. Four types of plate-arrangement along the cube directions; two plates whose faces were mutually parallel, two plates which were arranged on a cube plane as a raft, two plates which were perpendicularly arranged with face—edge configuration and two plates which were perpendicularly aligned with edge—edge configuration were energetically stable, while other arrangements were not stable. Compared with experimental observations on the local arrangement of γ′plates in a Ni-Al single crystal, the calculated results were confirmed to be qualitatively correct.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01033832
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  • 19
    Digitale Medien
    Digitale Medien
    Computer simulations of the phase decomposition on Cu-Co binary alloys based on the non-linear diffusion equation (1992)
    Springer
    Journal of materials science 27 (1992), S. 2444-2448 
    Details
    ISSN: 1573-4803
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Computer simulations of phase decomposition were performed for the Cu-Co alloy system on the basis of the non-linear diffusion equation. In the calculations, the modified regular solution approximation was adopted, i.e. the composition and temperature dependences of the interaction parameter, Ω, between the nearest neighbour atoms were taken into account and the mobility of atoms was defined as a function of solute composition. The phase decompositions were successfully computed for the Cu-Co alloys. The calculation method proposed here is applicable to many actual alloy systems.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01105056
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  • 20
    Digitale Medien
    Digitale Medien
    A new parameter for describing the structure bifurcation in two-phase alloys containing coherent particles (1992)
    Springer
    Journal of materials science 27 (1992), S. 6291-6298 
    Details
    ISSN: 1573-4803
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The so-called bifurcation diagrams for γ′ precipitate particles in nickel-based alloys were obtained by calculating the energy state for a pair of particles on the basis of the bifurcation theory. Based on the bifurcation diagrams, we have proposed a new parameter for describing the two-phase structure containing coherent particles. The parameter is defined as the mean particle radius at the intersection of the energy ridge and the line ofR=−0.5 orR=0.5 in the bifurcation diagram (R≡(r α−r β)/(r α+r β), wherer α andr β are the radii of α and β), and is symbolized by¯r * ±0.5. Because the energy state of the paired α and β is maximum at¯r * ±0.5 whenR=±0.5,¯r * ±0.5 is just like the watershed and hence we have termed it “structureshed”. This parameter successfully describes the effects of elastic energy as well as surface energy on the microstructural changes during coarsening of precipitate particles.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00576274
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