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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 34 (1993), S. 5493-5508 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: It is known that the symmetry of two-mode squeezed states is governed by the group Sp(4) which is locally isomorphic to the O(3,2) de Sitter group. It is shown that this complicated ten-parameter group can be regarded as a product of two three-parameter Sp(2) groups. It is shown also that two coupled harmonic oscillators serve as a physical basis for the symmetry decomposition. It is shown further that the concept of entropy is needed when one of the two modes is not observed. The entropy is zero when the system is uncoupled. The system reaches thermal equilibrium when the entropy becomes maximal.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 27 (1986), S. 2228-2235 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A set of rotations and Lorentz boosts is presented for studying the three-parameter little groups of the Poincaré group. This set constitutes a Lorentz generalization of the Euler angles for the description of classical rigid bodies. The concept of Lorentz-generalized Euler rotations is then extended to the parametrization of the E(2)-like little group and the O(2,1)-like little group for massless and imaginary-mass particles, respectively. It is shown that the E(2)-like little group for massless particles is a limiting case of the O(3)-like or O(2,1)-like little group. A detailed analysis is carried out for the two-component SL(2,c) spinors. It is shown that the gauge degrees of freedom associated with the translationlike transformation of the E(2)-like little group can be traced to the SL(2,c) spins that fail to align themselves to their respective momenta in the limit of large momentum and/or vanishing mass.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 28 (1987), S. 2373-2378 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: It is shown that every Lorentz transformation can be decomposed into a helicity-preserving transformation that changes the momentum of a free particle and a helicity-changing transformation that leaves the momentum invariant. Since momentum-preserving transformations constitute a subgroup of the Lorentz group, helicity-preserving transformations form a coset space. It is shown further that, for massive particles, every Lorentz transformation can be decomposed into the Wigner rotation and helicity-preserving transformations. For massless particles, every Lorentz transformation can be decomposed into the gauge transformation and helicity-preserving transformation. The gauge transformation in this case is a Lorentz-boosted Wigner rotation.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 1146-1150 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We measured the angular dependence of coercivity Hc and remnant coercivity Hr of oriented, Co-Ti substituted, plate-like barium ferrite particulate samples. The experimental results were compared to those modelled by a chain of two oblate ellipsoids. By including the effects of the uniaxial magnetocrystalline anisotropy, the shape anisotropy, and the interaction anisotropy of the ellipsoids, the model of a chain of oblate ellipsoids can explain the magnetization reversal mechanism of the barium ferrite samples. In an individual particle, the magnetic moment tends to reverse coherently because of it large uniaxial magnetocrystalline anisotropy, while in the oriented particulate samples the magnetization reversal of the stacked assembly occurs by symmetrical fanning, consistent with the larger uniaxial magnetocrystalline anisotropy and stronger interaction anisotropy. © 1995 American Institute of Physics.
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of P doping on the coercivity and magnetic-thermal stability of Co-substituted iron oxides have been investigated by means of magnetic measurements, torque curves, and Mössbauer spectra. It is found that the P doping of cobalt-substituted acicular oxides promotes the coercivity and the stability with temperature of the coercivity. Then effects may be attributed to the increase of the cubic magnetocrystalline anisotropy constant K1 and the activation energy E, respectively. The Mössbauer results suggest that P ions are located in the neighborhood of the B-site Fe ions. © 1995 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5845-5848 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mn- and Co-doped acicular γ-Fe2O3 particles with a coercivity of 923 Oe and Co content of 3.5 wt % have been prepared by a special process. This involves high-temperature ion diffusion, then step annealing. These particles exhibit a high magnetic thermal stability and low-temperature coefficient of coercivity. The latter demonstrates a striking contrast to the ordinary cobalt-body-doped γ-Fe2O3 particles. The induced uniaxial anisotropy constant Ku and the magnetocrystalline anisotropy constant K1 of the particles were determined by torque measurements. The novel properties of these particles are mainly due to the high uniaxial anisotropy, resulting from the anisotropic arrangements of cobalt ions. With the above characteristics and low Co content, these acicular particles can be one of the promising candidates for particulate high-density magnetic recording materials.
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The causes of the coercivity enhancement and the coercivity instability of acicular cobalt ferrite particles containing 0–9.2 wt % Fe2+ ions under the influence of magnetic field and temperature were investigated by means of transverse magnetic field annealing, torque, and Mössbauer experiments. The coercivity enhancement and the instability of Co modified iron oxide particles are closely related to the uniaxial magnetic anisotropy. A Fe2+-CO2+ pair model was proposed to explain the uniaxial magnetic anisotropy of Co modified iron particles. To verify the nature of the Fe2+-Co2+ pair, the probability of one or more Co ions appearing in the neighborhood of a B site Fe2+ ion was calculated using the chemical composition, the Mössbauer parameters, Pi(Fe+2) and Pi(Fe+3) and discussed conditions for forming the pair between the nearest-neighbor Co2+ and Fe2+ ion.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 8355-8364 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A Fourier transform infrared study has resulted in the first observation of a vibrational spectrum of the nonplanar H2SiCCH radical produced by trapping the products of the vacuum ultraviolet photolysis of a mixture of SiH4 silane, and C2H2 acetylene, in an Ar matrix at ∼10 K. Two vibrational fundamentals have been observed, the ν3(a′), silicon–carbon stretching mode at 2055.6 cm−1 and the ν4(a′), hydrogen–silicon bending mode at 926.8 cm−1. The vibrational frequencies, relative intensities, and extensive measurements of D and 13C isotopic shifts are all in good agreement with the values predicted by new density functional theory calculations. © 1998 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 3504-3508 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A Fourier transform infrared (FTIR) study of the products of the vacuum ultraviolet (VUV) photolysis of a mixture of silane (SiH4) and methane (CH4) trapped in solid Ar at ∼10 K has resulted in the first detection of the linear SiCH radical by means of its silicon–carbon stretching mode ν1(σ), which has been observed at 1010.4 cm−1. The results of extensive measurements of D and 13C isotopic shifts are in good agreement with the predictions of new ab initio calculations performed at the CCSD(T)/6-31G** (coupled cluster with single, double and partial inclusion of triple excitations) level, and confirm the identification of the linear SiCH radical. © 1998 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 36 (1995), S. 3940-3954 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: In classical mechanics, the system of two coupled harmonic oscillators is shown to possess the symmetry of the Lorentz group O(3,3) or SL(4,r) in the four-dimensional phase space. In quantum mechanics, the symmetry is reduced to that of O(3,2) or Sp(4), which is a subgroup of O(3,3) or SL(4,r), respectively. It is shown that among the six Sp(4)-like subgroups, only one possesses the symmetry which can be translated into the group of unitary transformations in quantum mechanics. © 1995 American Institute of Physics.
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