26,209 research outputs found
Time-Dependent Current Partition in Mesoscopic Conductors
The currents at the terminals of a mesoscopic conductor are evaluated in the
presence of slowly oscillating potentials applied to the contacts of the
sample. The need to find a charge and current conserving solution to this
dynamic current partition problem is emphasized. We present results for the
electro-chemical admittance describing the long range Coulomb interaction in a
Hartree approach. For multiply connected samples we discuss the symmetry of the
admittance under reversal of an Aharonov-Bohm flux.Comment: 22 pages, 3 figures upon request, IBM RC 1971
MoM-SO: a Complete Method for Computing the Impedance of Cable Systems Including Skin, Proximity, and Ground Return Effects
The availability of accurate and broadband models for underground and
submarine cable systems is of paramount importance for the correct prediction
of electromagnetic transients in power grids. Recently, we proposed the MoM-SO
method for extracting the series impedance of power cables while accounting for
skin and proximity effect in the conductors. In this paper, we extend the
method to include ground return effects and to handle cables placed inside a
tunnel. Numerical tests show that the proposed method is more accurate than
widely-used analytic formulas, and is much faster than existing proximity-aware
approaches like finite elements. For a three-phase cable system in a tunnel,
the proposed method requires only 0.3 seconds of CPU time per frequency point,
against the 8.3 minutes taken by finite elements, for a speed up beyond 1000 X.Comment: This paper has now been published in the IEEE Trans. on Power
Delivery in Oct. 2015, vol. 30, no. 5, pp. 2110-2118. DOI:
10.1109/TPWRD.2014.237859
Analysis of resonant responses of split ring resonators using conformal mapping techniques
We report a novel method for modeling the resonant frequency response of infra-red light, in the range of 2 to 10 microns, reflected from metallic spilt ring resonators (SRRs) fabricated on a silicon substrate. The calculated positions of the TM and TE peaks are determined from the plasma frequency associated with the filling fraction of the metal array and the equivalent LC circuit defined by the SRR elements. The capacitance of the equivalent circuit is calculated using conformal mapping techniques to determine the co-planar capacitance associated with both the individual and the neighbouring elements. The inductance of the equivalent circuit is based on the self-inductance of the individual elements and the mutual inductance of the neighboring elements. The results obtained from the method are in good agreement with experimental results and simulation results obtained from a commercial FDTD simulation software package. The method allows the frequency response of a SRR to be readily calculated without complex computational methods and enables new designs to be optimised for a particular frequency response by tuning the LC circuit
Numerical investigation of novel microwave applicators based on zero-order mode resonance for hyperthermia treatment of cancer
This paper characterizes three novel microwave applicators based on zero-order mode resonators for use in hyperthermia treatment of cancer. The radiation patterns are studied with numerical simulations in muscle tissue-equivalent model at 434 MHz. The relative performance of the applicators is compared in terms of reflection coefficient, current distribution, power deposition (SAR) pattern, effective field size in 2D and 3D tissue volumes, and penetration depth. One particular configuration generated the most uniform SAR pattern, with 25% SAR covering 84 % of the treatment volume extending to 1 cm depth under the aperture, while remaining above 58% coverage as deep as 3 cm under the aperture. Recommendations are made to further optimize this structure
Spin transport in Heisenberg antiferromagnets
We analyze spin transport in insulating antiferromagnets described by the XXZ
Heisenberg model in two and three dimensions. Spin currents can be generated by
a magnetic-field gradient or, in systems with spin-orbit coupling,
perpendicular to a time-dependent electric field. The Kubo formula for the
longitudinal spin conductivity is derived analogously to the Kubo formula for
the optical conductivity of electronic systems. The spin conductivity is
calculated within interacting spin-wave theory. In the Ising regime, the XXZ
magnet is a spin insulator. For the isotropic Heisenberg model, the
dimensionality of the system plays a crucial role: In d=3 the regular part of
the spin conductivity vanishes linearly in the zero frequency limit, whereas in
d=2 it approaches a finite zero frequency value.Comment: 9 pages, 5 figure
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