The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform

Radu Purice - One of the best experts on this subject based on the ideXlab platform.

  • Low lying spectral gaps induced by slowly varying Magnetic fields
    Journal of Functional Analysis, 2017
    Co-Authors: Horia Cornean, Bernard Helffer, Radu Purice
    Abstract:

    Consider a periodic Schrödinger operator in two dimensions, perturbed by a weak Magnetic field whose intensity slowly varies around a positive mean. We show in great generality that the bottom of the spectrum of the corresponding Magnetic Schrödinger operator develops spectral islands separated by gaps, reminding of a Landau-level structure. First, we construct an effective Magnetic Matrix which accurately describes the low lying spectrum of the full operator. The construction of this effective Magnetic Matrix does not require a gap in the spectrum of the non-Magnetic operator, only that the first and the second Bloch eigenvalues never cross. The crossing case is more difficult and it will be considered elsewhere. Secondly, we perform a detailed spectral analysis of the effective Matrix using a gauge-covariant Magnetic pseudo-differential calculus adapted for slowly varying Magnetic fields.

  • Low lying spectral gaps induced by slowly varying Magnetic fields
    Journal of Functional Analysis, 2017
    Co-Authors: Horia Cornean, Bernard Helffer, Radu Purice
    Abstract:

    Abstract We consider a periodic Schrodinger operator in two dimensions perturbed by a weak Magnetic field whose intensity slowly varies around a positive mean. We show in great generality that the bottom of the spectrum of the corresponding Magnetic Schrodinger operator develops spectral islands separated by gaps, reminding of a Landau-level structure. First, we construct an effective Hofstadter-like Magnetic Matrix which accurately describes the low lying spectrum of the full operator. The construction of this effective Magnetic Matrix does not require a gap in the spectrum of the non-Magnetic operator, only that the first and the second Bloch eigenvalues do not cross but their ranges might overlap. The crossing case is more difficult and will be considered elsewhere. Second, we perform a detailed spectral analysis of the effective Matrix using a gauge-covariant Magnetic pseudo-differential calculus adapted to slowly varying Magnetic fields. As an application, we prove in the overlapping case the appearance of spectral islands separated by gaps.

  • Peierls substitution and Magnetic pseudo-differential calculus
    arXiv: Mathematical Physics, 2015
    Co-Authors: Horia Cornean, Viorel Iftimie, Radu Purice
    Abstract:

    We revisit the celebrated Peierls-Onsager substitution employing the Magnetic pseudodifferential calculus for weak Magnetic fields with no spatial decay conditions, when the nonMagnetic symbols have a certain spatial periodicity. We show in great generality that the symbol of the Magnetic band Hamiltonian admits a convergent expansion. Moreover, if the non-Magnetic band Hamiltonian admits a localized composite Wannier basis, we show that the Magnetic band Hamiltonian is unitarily equivalent to a Hofstadter-like Magnetic Matrix. In addition, if the Magnetic field perturbation is slowly variable, then the spectrum of this Matrix is close to the spectrum of a Weyl quantized, minimally coupled symbol.

Andreas Michels - One of the best experts on this subject based on the ideXlab platform.

  • MicroMagnetic modeling and small-angle neutron scattering characterization of Magnetic nanocomposites
    Physical Review B, 2012
    Co-Authors: Sergey Erokhin, Dmitry Berkov, N. L. Gorn, Andreas Michels
    Abstract:

    A new methodology for microMagnetic simulations of Magnetic nanocomposites is presented. The methodology is especially suitable for simulations of two-phase composites consisting of Magnetically hard inclusions in a soft Magnetic Matrix phase. The proposed technique allows us to avoid unnecessary discretization of the ``hard'' inclusions (these are normally in a single-domain state) but enables arbitrary fine discretization of the ``soft'' phase. The method is applied to the determination of the equilibrium magnetization state of an iron-based nanocomposite from the Nanoperm (FeZrBCu) family of alloys and to the calculation of the corresponding small-angle neutron scattering (SANS) cross-section. The results of our simulations exhibit a remarkable agreement with nontrivial ``clover-leaf'' SANS cross-sections observed experimentally.

  • Neutron scattering and modeling of dipole-field-induced spin disorder in Nanoperm
    Applied Physics Letters, 2005
    Co-Authors: C. Vecchini, O. Moze, Kiyonori Suzuki, P K Pranzas, Jörg Weissmüller, Andreas Michels
    Abstract:

    We present Magnetic-field-dependent small-angle neutron scattering data for the ferroMagnetic nanocomposite Nanoperm (Fe89Zr7B3Cu1). The spin-misalignment scattering in the approach-to-saturation regime unexpectedly reveals pronounced lobes of high intensity at angles ±30−40° relative to the Magnetic-field axis. Based on numerical calculations, the four-fold angular symmetry of the scattering pattern can be explained in terms of local spin misalignment, which originates from dipolar stray fields due to the mismatch of the saturation-magnetization values between the bcc Fe particles and the amorphous Magnetic Matrix.

Horia Cornean - One of the best experts on this subject based on the ideXlab platform.

  • Low lying spectral gaps induced by slowly varying Magnetic fields
    Journal of Functional Analysis, 2017
    Co-Authors: Horia Cornean, Bernard Helffer, Radu Purice
    Abstract:

    Consider a periodic Schrödinger operator in two dimensions, perturbed by a weak Magnetic field whose intensity slowly varies around a positive mean. We show in great generality that the bottom of the spectrum of the corresponding Magnetic Schrödinger operator develops spectral islands separated by gaps, reminding of a Landau-level structure. First, we construct an effective Magnetic Matrix which accurately describes the low lying spectrum of the full operator. The construction of this effective Magnetic Matrix does not require a gap in the spectrum of the non-Magnetic operator, only that the first and the second Bloch eigenvalues never cross. The crossing case is more difficult and it will be considered elsewhere. Secondly, we perform a detailed spectral analysis of the effective Matrix using a gauge-covariant Magnetic pseudo-differential calculus adapted for slowly varying Magnetic fields.

  • Low lying spectral gaps induced by slowly varying Magnetic fields
    Journal of Functional Analysis, 2017
    Co-Authors: Horia Cornean, Bernard Helffer, Radu Purice
    Abstract:

    Abstract We consider a periodic Schrodinger operator in two dimensions perturbed by a weak Magnetic field whose intensity slowly varies around a positive mean. We show in great generality that the bottom of the spectrum of the corresponding Magnetic Schrodinger operator develops spectral islands separated by gaps, reminding of a Landau-level structure. First, we construct an effective Hofstadter-like Magnetic Matrix which accurately describes the low lying spectrum of the full operator. The construction of this effective Magnetic Matrix does not require a gap in the spectrum of the non-Magnetic operator, only that the first and the second Bloch eigenvalues do not cross but their ranges might overlap. The crossing case is more difficult and will be considered elsewhere. Second, we perform a detailed spectral analysis of the effective Matrix using a gauge-covariant Magnetic pseudo-differential calculus adapted to slowly varying Magnetic fields. As an application, we prove in the overlapping case the appearance of spectral islands separated by gaps.

  • Peierls substitution and Magnetic pseudo-differential calculus
    arXiv: Mathematical Physics, 2015
    Co-Authors: Horia Cornean, Viorel Iftimie, Radu Purice
    Abstract:

    We revisit the celebrated Peierls-Onsager substitution employing the Magnetic pseudodifferential calculus for weak Magnetic fields with no spatial decay conditions, when the nonMagnetic symbols have a certain spatial periodicity. We show in great generality that the symbol of the Magnetic band Hamiltonian admits a convergent expansion. Moreover, if the non-Magnetic band Hamiltonian admits a localized composite Wannier basis, we show that the Magnetic band Hamiltonian is unitarily equivalent to a Hofstadter-like Magnetic Matrix. In addition, if the Magnetic field perturbation is slowly variable, then the spectrum of this Matrix is close to the spectrum of a Weyl quantized, minimally coupled symbol.

L. Lanotte - One of the best experts on this subject based on the ideXlab platform.

  • Mechanical vibration sensor based on elastoMagnetic composite
    Sensors and Actuators A: Physical, 2006
    Co-Authors: Giovanni Ausanio, A. C. Barone, C. Hison, Vincenzo Iannotti, Carlo Luponio, L. Lanotte
    Abstract:

    A mechanical vibration sensor based on a novel elastoMagnetic composite made of Magnetic microparticles uniformly dispersed in an elastic non-Magnetic Matrix is presented. A theoretical model predicting a linear behaviour of the sensor response with the vibration frequency and amplitude is reported. The obtained experimental results are in agreement with the model predictions for Magnetic particle volume content lower than 15%. The ability of this kind of sensor to work at low frequencies, where other devices present a lack of reliability, is a very interesting characteristic of this elastoMagnetic sensor. © 2006.

  • Mechanical vibration sensor based on elastoMagnetic composite
    Sensors and Actuators A: Physical, 2006
    Co-Authors: Giovanni Ausanio, A. C. Barone, C. Hison, Vincenzo Iannotti, Carlo Luponio, L. Lanotte
    Abstract:

    A mechanical vibration sensor based on a novel elastoMagnetic composite made of Magnetic microparticles uniformly dispersed in an elastic non-Magnetic Matrix is presented. A theoretical model predicting a linear behaviour of the sensor response with the vibration frequency and amplitude is reported. The obtained experimental results are in agreement with the model predictions for Magnetic particle volume content lower than 15%. The ability of this kind of sensor to work at low frequencies, where other devices present a lack of reliability, is a very interesting characteristic of this elastoMagnetic sensor. (c) 2006 Published by Elsevier B.V

Bernard Helffer - One of the best experts on this subject based on the ideXlab platform.

  • Low lying spectral gaps induced by slowly varying Magnetic fields
    Journal of Functional Analysis, 2017
    Co-Authors: Horia Cornean, Bernard Helffer, Radu Purice
    Abstract:

    Consider a periodic Schrödinger operator in two dimensions, perturbed by a weak Magnetic field whose intensity slowly varies around a positive mean. We show in great generality that the bottom of the spectrum of the corresponding Magnetic Schrödinger operator develops spectral islands separated by gaps, reminding of a Landau-level structure. First, we construct an effective Magnetic Matrix which accurately describes the low lying spectrum of the full operator. The construction of this effective Magnetic Matrix does not require a gap in the spectrum of the non-Magnetic operator, only that the first and the second Bloch eigenvalues never cross. The crossing case is more difficult and it will be considered elsewhere. Secondly, we perform a detailed spectral analysis of the effective Matrix using a gauge-covariant Magnetic pseudo-differential calculus adapted for slowly varying Magnetic fields.

  • Low lying spectral gaps induced by slowly varying Magnetic fields
    Journal of Functional Analysis, 2017
    Co-Authors: Horia Cornean, Bernard Helffer, Radu Purice
    Abstract:

    Abstract We consider a periodic Schrodinger operator in two dimensions perturbed by a weak Magnetic field whose intensity slowly varies around a positive mean. We show in great generality that the bottom of the spectrum of the corresponding Magnetic Schrodinger operator develops spectral islands separated by gaps, reminding of a Landau-level structure. First, we construct an effective Hofstadter-like Magnetic Matrix which accurately describes the low lying spectrum of the full operator. The construction of this effective Magnetic Matrix does not require a gap in the spectrum of the non-Magnetic operator, only that the first and the second Bloch eigenvalues do not cross but their ranges might overlap. The crossing case is more difficult and will be considered elsewhere. Second, we perform a detailed spectral analysis of the effective Matrix using a gauge-covariant Magnetic pseudo-differential calculus adapted to slowly varying Magnetic fields. As an application, we prove in the overlapping case the appearance of spectral islands separated by gaps.