Iterative detection and decoding for the four-rectangular-grain TDMR model

The performance of a rate-4/5 modulation code is evaluated in two-dimensional magnetic recording (TDMR) channels, where a magnetic medium is described by a discrete Voronoi model, and the two-dimensional sensitivity function of the reader is adopted to generate the TDMR readback signal. Since the read-head sensitivity function covers many tracks, it causes intertrack interference (ITI) that can deteriorate the system performance. Therefore, this letter proposes an ITI subtraction scheme in conjunction with the rate-4/5 modulation code in a coded TDMR channel to mitigate the ITI effect embedded in the readback signals before performing an iterative decoding process. We also investigate the data-dependent readback amplitude distributions and evaluate the TDMR system performance via computer simulation. Results show that the proposed scheme helps improve the TDMR system performance, especially when the areal density is high.

In this paper, we propose a method for estimating the Symmetric Information Rate (SIR) for Two Dimensional Magnetic Recording (TDMR) channel by using the Generalized Belief Propagation (GBP) algorithm. We consider the Voronoi model as the channel model of a TDMR system. The dominant component of noise in TDMR caused by the imperfections of the medium is called “media noise”. The nature of the media noise is data-dependent, however, the media noise can be closely approximated by additive white Gaussian noise (AWGN) with variance and mean dependent on channel bits written on the magnetic medium. Lower and upper bounds on the SIR are obtained by using the GBP algorithm. In addition, it is shown that the accuracy of the SIR estimation can be adjusted for sufficient size of the magnetic medium. Finally, the bit aspect ratio of a TDMR system is optimized by maximizing the SIR per unit area.

New magnetic recording technologies such as bit-patterned media recording (BPMR), heat (or microwave) assisted magnetic recording (HAMR) and shingled writing (SW)/two-dimensional magnetic recording (TDMR) have been proposed to push the storage density of future hard disks beyond 1Tb/in2. However, at such high recording density, many new challenges from the magnetic recording medium, read/write head as well as writing and reading channels arise. These challenges hinder the realization of Tb/in2 hard disks and should be addressed. In this paper, we review these major challenges from a communication theory perspective, and propose ways to mitigate the channel impairments by using low-complexity two-dimensional (2D) channel detection, new low-density parity-check (LDPC) code design paradigm, as well as re-synchronizable coding schemes.

The effects of grain size, dendritic structure and crystallographic orientation on fatigue crack propagation in IN713C nickel-based superalloy

Data detection in magnetic recording (MR) channels can be viewed as an image processing problem, proceeding from the 2-D image of readback bits, to higher level abstractions of features using convolutional layers that finally allow classification of individual bits. In this work, convolutional neural networks (ConvNets) are employed in place of the typical partial response equalizer and maximum-likelihood detector with noise prediction to directly process the un-equalized readback signals and output soft estimates. Several variations of ConvNets are compared in terms of network complexity and performance. The best performing ConvNet detector with two convolutional layers provides a data storage density of up to 3.7489 Terabits/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> on a low track pitch two-dimensional MR channel simulated with a grain-flipping-probability (GFP) model. An alternate ConvNet architecture reduces the network complexity by about 74%, yet results in only a 2.09% decrease in density compared to the best performing detector.

Because it is widely supported by commercial-off-the-shelf (COTS) technology, the DVB-S2 waveform standard has become an attractive solution for military communication links. The waveform uses a combination of amplitude-phase-shift keying (APSK) modulation and low-density parity-check (LDPC) codes. Typical DVB-S2 implementations select signals from the APSK signal set with uniform probability. However, information-theoretic results suggest that performance may be improved by selecting lower-energy signals more frequently than higher-energy signals. In this paper, we propose and analyze a DVB-S2-compatible system that shapes the APSK constellation by selecting signals with a nonuniform probability. The receiver iterates between the APSK demapper, the shaping decoder, and the LDPC decoder. Using 32-APSK and a rate of 3 data bits per symbol, the system described in this paper achieves a gain of over 1 dB relative to a standard DVB-S2 system (i.e. one that does not use shaping or iterative demodulation) in additive white Gaussian noise (AWGN) at a bit-error rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> . About 0.7 dB of the gain can be attributed to shaping, and rest of the gain can be attributed to iterative demodulation and decoding. Lesser gains can be achieved over Rayleigh fading channels.

This concept poem ekphrastically manifests Ornette Coleman’s landmark album Free Jazz: A Collective Improvisation. Separated into two columns, the piece features the work of two quartets of poets, reflecting Coleman’s own separation of his double quartet ensemble into left and right recording channels. The poets Bob Kaufman, Jayne Cortez, Cecil Taylor and Lawrence Ferlinghetti are the quartet in the left column; Amiri Baraka, Langston Hughes, M. NourbeSe Philip and Boris Vian are the quartet in the right. The work of these poets has been scrambled and interwoven in the first and third-from-last stanzas, mimicking the two polymelodic interludes found in Coleman’s album. The remaining stanzas either combine lines from a quartet of poets or are entirely from the work of a single poet, who ‘solos’ against the quartet in the adjacent column (again, mimicking the general structure of Coleman’s album).

The long-term bit error rate (BER) performance of partial response maximum likelihood (PRML) system in a perpendicular magnetic recording (PMR) channel with thermal decay is studied. A thermal decay model based on the experimental data for three CoPtCr-SiO2 PMR media with different thermal stability is obtained. Then, the performance of PR1ML channel for the 16/17(0,6/6) and 128/130(0,16/8) codes as a run-length-limited (RLL) code is evaluated by computer simulation using the model. Moreover, the relationships between the elapsed time and the BER are obtained for the combinations of two RLL codes and three PMR media and their performances are compared. The results show that for the combination of the 128/130(0,16/8) code and the medium with the poorest thermal stability, the degradation with the elapsed time is noticeable compared with the other combinations

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, we provide a survey of the novel read channel technologies that found their implementation in products over the past decade, and we outline possible technology directions for the future of read channels. Recently, magnetic recording read channels have undergone several changes. In addition to switching from longitudinal to perpendicular recording channels, detectors tuned to media noise sources are now readily implemented in read channel chips. Powerful numerical techniques have emerged to evaluate the capacity of the magnetic recording channel. Further, improved coding/decoding methods have surfaced both for the incumbent Reed–Solomon codes and the promising low-density parity-check codes. The paper is a tutorial-like survey of these emerging technologies with the aim to propel the reader to the forefront of research and development in the areas of signal processing and coding for magnetic recording channels. </para>

Although foams have been recognized for improving in oil recovery process, detailed descriptions of the relative importance of viscous and capillary effects are still lacking. Previous work has largely been concerned with the measurement of effective viscosities or dispersed phase permeabilities which masks both viscous and capillary effects. A first step in separating such effects requires the measurement of capillary pressure for foam systems in porous media. To date, only isolated data of this type have been reported. In this work, a capillary pressure cell has been designed to investigate capillary behavior of foams in bead packs. This experimental setup has several unique and versatile features such as: (1) Hydrophobic and hydrophilic membranes placed at the entrance and exit ends of the bead pack to selectively restrict the flow of gas and liquid to and from the cell and hence insure correct capillary pressure (PC = PG-PL) measurement; (2) a compression spring imposed on the top of the bead pack to insure a stable bead pack and good capillary contact between the bead pack and the membranes; and (3) back pressure control to allow high pressure testing and to minimize in situ bubble size changes (compressibility effects) during testing. With the above system, sequential drainage and imbibition cycles can be repeatedly traversed without interruption. Multicycle drainage and imbibition experiments were performed under conditions where the foam was generated in situ, and the static capillary effects were obtained for both non-dispersed phase (gas-water system with no film stabilizing surface active agents) and dispersed phase (surface active agent present) systems. While only two drainage-imbibition cycles are necessary for non-dispersed phase systems to achieve invariant capillary pressure curves, 4 to 6 cycles are required for dispersed phase systems. In all cases, the irreducible and residual wetting phase saturations at the end of drainage and imbibition are lower than for those of non-dispersed phase systems. Studies of pore structure effects provide direct evidence that dispersed phase systems effectively reduce the degree of heterogeneous behavior in a bed. Studies of wetting effects show that both the irreducible and residual saturations at the end of drainage and imbibition are significantly decreased as the degree of oil wettability is increased. Finally, from tests at different surfactant concentrations, the largest changes in gas trapping occur as the concentration is increased below the CMC (critical micelle concentration); at higher concentrations additional trapping takes place but the effect is less dramatic.

In this paper, the new rate tangent–fast Fourier transform-based elasto-viscoplastic crystal plasticity (CP) constitutive framework (RTCP-FFT) developed by Nagra et al (2017 Int. J. Plast. 98 65–82) is implemented in the so-called Marciniak–Kuczynski (M–K) (Marciniak and Kuczyński 1967 Int. J. Mech. Sci. 9 609–20) framework to predict the forming limit diagrams (FLDs) of face-centered cubic polycrystals. The RTCP-FFT approach that accounts for 3D grain morphologies and grain interactions is used to compute the FLDs for aluminum alloys (AAs). The model employs two statistically representative volume elements with identical initial microstructures, one inside the imperfection band region (required for M–K analysis) and other outside the imperfection band region of the sheet metal. The proposed RTCP-FFT-based M–K model is a full-field, mesh-free and efficient CP formulation that enables a comprehensive investigation of the effects of 3D microstructural features on the FLDs with extremely small computational times. The new model is validated by comparing the predicted FLDs for AA5754 and AA3003 AAs with experimental measurements. Furthermore, the predicted FLDs are compared with the well-known Taylor-type homogenization scheme-based M–K model (MK–Taylor) predictions. Furthermore, the effects of different grain shapes as well as local grain interactions on the FLD predictions are studied. The study reveals that among the various microstructural features, the grain morphology has the strongest effect on the predicted FLDs and the FLD predictions can be significantly improved if the actual grain structure of the material is properly accounted for in the numerical models.

The stress–strain and stress path characteristics of sands are influenced by their grain size, shape, and packing. Morphological characteristics and size of particles play important role on the undrained shear strength of sands. Often, effects of these parameters are complex and cannot be easily distinguished. This study advances the knowledge of the role of particle size and shape on the undrained shear strength of sands. To eliminate the consequence of morphological characteristics, two sands with different particle sizes but similar angularity, and another sand with different roundness were selected for the study. These morphological characteristics for all three sands were determined from the analysis of scanning electron microscope images. F131 sand with higher median grain size and lower shape factors (rr and rs) had highest undrained peak shear strength and phase transformation value. Undrained strength (qpt) and effective principal stress (P′pt) in phase transformation point had direct relationship with grain median grain size (D50) and inversely effect of shape factor (rr and rs). F131 and F161 sands represented highest peak and ultimate steady-state strengths, respectively. Flow potential appeared to be directly proportional with (rr and rs) and inversely with D50. The peak index decreased with increasing shape factors (rr and rs).

Effect of grain size and intergranular stresses on the cyclic behaviour of a ferritic steel

Equations-of-motion approach to a quantum theory of large-amplitude collective motion

A soft-decision Reed-Solomon decoding algorithm has been recently proposed by Koetter and Vardy, which provides significant coding gains by fully utilizing channel output reliability information. The algorithm converts this reliability information into a set of interpolation points and their multiplicities, and consists of three day steps: multiplicity matrix calculation, soft interpolation, and polynomial factorization. Large coding gains have been observed only for low-rate codes in additive white Gaussian noise channels, and with very high decoding complexity. Here we present a new suboptimal algorithm for computing the multiplicity matrix, discuss architectures for soft-decision decoders and evaluate the performance of the soft-decision algorithm on magnetic recording channels in the presence of erasures.