A study was performed on the performance of soft reed-solomon (RS) decoding for magnetic recording channels with erasures. The results were compared with a similar system using a low-density parity-check (LDPC) code w...
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A study was performed on the performance of soft reed-solomon (RS) decoding for magnetic recording channels with erasures. The results were compared with a similar system using a low-density parity-check (LDPC) code when the length of a continuous erasure exceeded a certain threshold. The results showed that LDPC codes performed better than RS codes in the presence of random noise.
A new finite-element mesh regeneration method is presented for three-dimensional shape optimization of elec.romagnetic devices. The method has its theoretical basis in the structural deformation of an elastic body und...
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A new finite-element mesh regeneration method is presented for three-dimensional shape optimization of elec.romagnetic devices. The method has its theoretical basis in the structural deformation of an elastic body under stress. When the design surface changes in the optimization process, the method maps the surface displacement onto the nodal points of the finite-element mesh without a change in mesh topology. Numerical examples with design sensitivity analysis show the method guarantees a smooth shape with proper mesh quality and keeps the initial mesh topology.
The performance of nested error-correction codes for perpendicular magnetic recording channels is evaluated in the presence of burst noise using Reed-Solomon codes as well as low-density parity-check codes as componen...
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The performance of nested error-correction codes for perpendicular magnetic recording channels is evaluated in the presence of burst noise using Reed-Solomon codes as well as low-density parity-check codes as component codes. Erasure detection and iterative decoding algorithms for nested codes are considered, and their performance is evaluated using computer simulations. The results illustrate the advantages of the nested sch.mes over noninterleaved architectures in terms of sector error rate and complexity for both current and future native block sizes.
The effects of precoding on the detection of erasures based on violations of run-length-limited (RLL) constraints for low-density parity-check (LDPC) coded magnetic recording channels are investigated and an improved ...
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The effects of precoding on the detection of erasures based on violations of run-length-limited (RLL) constraints for low-density parity-check (LDPC) coded magnetic recording channels are investigated and an improved erasure detection algorithm is proposed. Its performance on an ME2PR4 channel is evaluated using computer simulations.
Measurements in phantoms are used to predict temperature changes that would occur in vivo for medical implants due to the radio frequency (RF) field in magnetic resonance imaging (MRI). In this study, the impact of co...
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Measurements in phantoms are used to predict temperature changes that would occur in vivo for medical implants due to the radio frequency (RF) field in magnetic resonance imaging (MRI). In this study, the impact of concentration of the gelling agent in a saline-based phantom on the RF-induced temperature rise was measured using an apparatus that accurately reproduces the RF environment present in a 1.5-T whole-body MR system. The temperature was measured using fluoroptic thermometry at the elec.rode and other sites for a deep brain neurostimulation system. The average power deposition in the 30-kg phantom was about 1.5 W/kg. Four phantom formulations were evaluated, using different concentrations of polyacrylic acid (PAA) added to saline solution, with NaCl concentration adjusted to maintain an elec.rical conductivity near 0.24 S/m. The greatest temperature rises occurred at the elec.rode, ranging from 16.2 °C for greatest concentration of PAA to 2.9 °C for only saline solution. The temperature rise attained the maximal value for sufficient concentration of PAA. Similar behavior was observed in the temperature versus time relationship near a current-carrying resistor, immersed in gel and saline, which was used to model a localized heat source. The temperature rise for insufficient PAA concentration is reduced due to convection of phantom material. In conclusion, an appropriate gelling agent is required to accurately simulate the thermal properties of body tissues for measurements of RF-induced heating with medical implants.
This paper presents a new technique for characterizing a magnetic source using truncated singular value decomposition (TSVD). It shows how the smallest singular value of the matrix of signature magnetic fields relates...
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This paper presents a new technique for characterizing a magnetic source using truncated singular value decomposition (TSVD). It shows how the smallest singular value of the matrix of signature magnetic fields relates to the sensitivity of the restored multipoles to noises. The crosstalk and altercation due to the truncation of singular values are introduced as the parameters to determine an acceptable truncation limit. Numerical simulations with standard sources are tested using a rectangular array of magnetic field sensors. The results show that TSVD can greatly improve the accuracy of the field restoration.
This paper considers a decision-feedback-equalizer (DFE)-based soft decision detector as an alternative for the Bahl-Cocke-Jelinek-Raviv (BCJR) front-end for a coded magnetic recording channel. In previous work, a bid...
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This paper considers a decision-feedback-equalizer (DFE)-based soft decision detector as an alternative for the Bahl-Cocke-Jelinek-Raviv (BCJR) front-end for a coded magnetic recording channel. In previous work, a bidirectional-arbitrated DFE (BAD) was shown to perform in between a BCJR detector and a minimum mean-square error DFE. We propose a soft-output BAD (S-BAD) which takes advantage of the original structure and is suitable for iterative decoding when used with outer codes. We show that with a convolutional code as an outer code. S-BAD performs close to higher complexity detectors.
A multidipole searching technique using a moving dipole concept is proposed for magnetoencephalography (MEG) source localization. The proposed method can be a promising method to resolve a critical disadvantage of con...
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A multidipole searching technique using a moving dipole concept is proposed for magnetoencephalography (MEG) source localization. The proposed method can be a promising method to resolve a critical disadvantage of conventional equivalent current dipole (ECD) method - the number of current dipoles should be given a priori. From several simulation results, the accuracy and effectiveness of the method will be verified.
The surface-wave diffraction at the edge of a finite-size substrate with a high dielec.ric constant is the dominant mechanism affecting the radiation pattern of a patch antenna fabricated on this material. A soft-and-...
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The surface-wave diffraction at the edge of a finite-size substrate with a high dielec.ric constant is the dominant mechanism affecting the radiation pattern of a patch antenna fabricated on this material. A soft-and-hard surface (SHS) can be used to block the surface waves from propagating outward along the dielec.ric substrate, thus reducing the unwanted diffraction. Patch antennas surrounded by the SHS are analyzed using the finite-difference time-domain (FDTD) technique that implements the SHS boundary conditions using a simple modified subcell model. A square stacked-patch antenna and a circularly polarized (CP) patch antenna on a thick LTCC multilayer substrate are investigated. It is shown that the radiation pattern of the square patch on a big-size substrate can be significantly improved using SHS while the backward radiation level of the CP antenna with SHS on a small-size substrate is considerably reduced.
We briefly outline the use of spheroidal functions in extrapolation of the external field of magnetic sources. The extrapolation is carried out by means of spatial harmonic analysis, in which the expansion functions a...
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We briefly outline the use of spheroidal functions in extrapolation of the external field of magnetic sources. The extrapolation is carried out by means of spatial harmonic analysis, in which the expansion functions are the spheroidal harmonics. An efficient method for computing external spheroidal harmonic functions of magnetostatic problems has been developed. The method can be utilized to the spatial harmonic characterization of magnetic sources in the prolate and oblate spheroidal coordinates. The new approach minimizes numerical imprecision in a wide range of parameters by using the Wronski determinant as a recurrence basis.
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