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End date: 2019 × Start date: 2016 × End date: 2009 × Start date: 2000 × DDC: 620 × Type: article ×

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Now showing 1 - 5 of 5
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    Simulation of microwave circuits and laser structures including PML by means of FIT
    (München : European Geopyhsical Union, 2004) Hebermehl, G.; Schefter, J.; Schlundt, R.; Tischler, Th.; Zscheile, H.; Heinrich, W.
    Field-oriented methods which describe the physical properties of microwave circuits and optical structures are an indispensable tool to avoid costly and time-consuming redesign cycles. Commonly the electromagnetic characteristics of the structures are described by the scattering matrix which is extracted from the orthogonal decomposition of the electric field. The electric field is the solution of an eigenvalue and a boundary value problem for Maxwell’s equations in the frequency domain. We discretize the equations with staggered orthogonal grids using the Finite Integration Technique (FIT). Maxwellian grid equations are formulated for staggered nonequidistant rectangular grids and for tetrahedral nets with corresponding dual Voronoi cells. The interesting modes of smallest attenuation are found solving a sequence of eigenvalue problems of modified matrices. To reduce the execution time for high-dimensional problems a coarse and a fine grid is used. The calculations are carried out, using two levels of parallelization. The discretized boundary value problem, a large-scale system of linear algebraic equations with different right-hand sides, is solved by a block Krylov subspace method with various preconditioning techniques. Special attention is paid to the Perfectly Matched Layer boundary condition (PML) which causes non physical modes and a significantly increased number of iterations in the iterative methods.
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    Electronic structure and aspects of unconventional superconductivity in NaxCoO2.yH2O
    (São Carlos : Universidade Federal de São Carlos, 2003) Rosner, H.; Drechsler, S.-L.; Fuchs, G.; Handstein, A.; Wälte, A.; Müller, K.-H.
    We examine the electronic structure of NaxCoO2.yH2O within the local density approximation. The parametrization of the band which forms the largest hole-Fermi surface centered at G shows significant deviations from what is frequently assumed in recent sophisticated theoretical studies. In particular, the commonly used nearest neighbor approaches in the framework of single band pictures are found to be unrealistic. The special role of H2O in screening the disorder in the charge reservoir is briefly discussed and compared with the case of Y1–xCaxCu3O6+d.
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    Magnetic field effects of double-walled carbon nanotubes
    (São Carlos : Universidade Federal de São Carlos, 2006) Latgé, A.; Grimm, D.; Ferreira, M.S.
    A theoretical discussion of electronic and transport properties of a particular family of double-wall carbon nanotubes, named commensurate structures of the armchair type (n,n)@(2n,2n) is addressed. A single p-band tight binding hamiltonian is considered and the magnetic field is theoretically described by following the Peierls approximation into the hopping energies. Our emphasis is put on investigating the main effects of the geometrical aspects and relative positions of the tubes on the local density of states and on the conductance of the system. By considering intershell interactions between a set of neighboring atoms on the walls of the inner and outer tubes, we study the possibility of founding Aharonov-Bohm effects in the DWCNs when a magnetic field is applied along the axial direction.
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    An X-Band low-power and low-phase-noise VCO using bondwire inductor
    (München : European Geopyhsical Union, 2009) Hu, K.; Herzel, F.; Scheytt, J.C.
    In this paper a low-power low-phase-noise voltage-controlled-oscillator (VCO) has been designed and, fabricated in 0.25 μm SiGe BiCMOS process. The resonator of the VCO is implemented with on-chip MIM capacitors and a single aluminum bondwire. A tail current filter is realized to suppress flicker noise up-conversion. The measured phase noise is −126.6 dBc/Hz at 1 MHz offset from a 7.8 GHz carrier. The figure of merit (FOM) of the VCO is −192.5 dBc/Hz and the VCO core consumes 4 mA from a 3.3 V power supply. To the best of our knowledge, this is the best FOM and the lowest phase noise for bondwire VCOs in the X-band. This VCO will be used for satellite communications.
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    The scale-up of material microstructuring: a perspective
    (Saarbrücken : Leibniz-Institut für Neue Materialien, 2009) Kraus, Tobias
    [no abstract available]