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Magnetics, IEEE Transactions on

Issue 6  Part 1 • Date June 2013

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  • Front cover

    Publication Year: 2013 , Page(s): C1
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  • IEEE Transactions on Magnetics publication information

    Publication Year: 2013 , Page(s): C2
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  • Table of Contents

    Publication Year: 2013 , Page(s): 2425 - 2430
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  • Preface [to the special issue on the 2012 Asia-Pacific Magnetic Recording Conference (APMRC)]

    Publication Year: 2013 , Page(s): 2431
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  • Foreword

    Publication Year: 2013 , Page(s): 2432
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  • Motions of Air Bubbles Trapped in Grooved and Plane Journal Bearings of Operating Fluid Dynamic Bearings

    Publication Year: 2013 , Page(s): 2433 - 2436
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (734 KB) |  | HTML iconHTML  

    We investigated the motion of air bubbles trapped in grooved and plane journal bearings of operating fluid dynamic bearings (FDBs) by using the finite volume method and the volume of fluid method. The motion of a trapped air bubble in grooved journal bearing is mostly determined by surface tension and the pressure difference due to the wedge effect of the groove. Also, the motion of trapped air bubbles in plane journal bearing is mostly determined by surface tension and the Coutte flow. A novel design of FDBs was finally proposed to expel the air bubbles trapped in grooved journal and plane journal bearings out of operating FDBs. View full abstract»

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  • Experimental Verification of the Optimal FDBs in a HDD Spindle Motor to Minimize Power Loss

    Publication Year: 2013 , Page(s): 2437 - 2440
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (894 KB) |  | HTML iconHTML  

    This research experimentally verified the optimal design of the fluid dynamic bearings (FDBs) in a hard disk drive (HDD) spindle motor to minimize power consumption while maintaining the level of dynamic performance. HDD spindle motors with optimal FDBs were prototyped, and their power consumption and dynamic characteristics were measured and compared with those of conventional and simulated motors at various operating speeds. HDD spindle motors with optimal FDBs consume less power than conventional motors, as predicted in the proposed optimal design methodology. View full abstract»

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  • Analysis on the Characteristics of Stamped Base for 2.5 in HDD

    Publication Year: 2013 , Page(s): 2441 - 2446
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1394 KB) |  | HTML iconHTML  

    In this study, we investigate the dynamic characteristics of a cold-rolled steel-plate (SPCC) stamped base for use with a 2.5-in hard disk drive (HDD). A stamped base offers the advantages of a thinner form and lower manufacturing cost compared to die-cast bases. The feasibility of applying a stamped base to a 2.5-in HDD is investigated by considering the various required characteristics. The manufacturing processes for stamped and die-cast bases are compared, revealing several advantages of stamped bases, including room-temperature processing, minimal contamination, fewer processing steps, and faster processing times. Finite element analysis is used to examine the dynamic and magnetic characteristics of the stamped base. The thin stamped base exhibits limited vertical stiffness, shock performance and magnetic force sensitivity. We observe only a slight difference in the temperature characteristics of stamped and die-cast bases. Additionally, internal air-flow analysis indicates an overall similar air velocity distribution in the stamped base compared to the die-cast base. View full abstract»

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  • Numerical Study on the Performance Enhancement of Ultrasonic Motors Using Single Crystalline Piezo-Materials

    Publication Year: 2013 , Page(s): 2447 - 2450
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (426 KB) |  | HTML iconHTML  

    This paper examines the performance enhancement of a newly designed ultrasonic motor by using single crystalline piezo-materials Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMNPT) and Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZNPT). From numerical simulations, it is found that PMNPT and PZNPT can greatly improve the mechanical performance of the motor. View full abstract»

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  • DifferCloudStor: Differentiated Quality of Service for Cloud Storage

    Publication Year: 2013 , Page(s): 2451 - 2458
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1233 KB) |  | HTML iconHTML  

    For a large scale cloud cluster, providing data access which crosses through high performance computing servers, network and storage servers, and scheduling resources among multi-tenants are challenging jobs, especially with specific level of quality of service (QoS) requirements. Besides the criteria of current availability and reliability in service level agreement (SLA), throughput and latency are also critical QoS performance measurements to the tenants. Any QoS solution, unfortunately, cannot be achieved without introducing additional overhead. A good QoS design should always be cost effective. This paper proposes a cost-effective QoS infrastructure over a distributed storage system, providing work-conserving differentiated QoS for multi-tenants cloud storage. The proposed QoS infrastructure combines global service differentiation with adaptive share allocation to support differentiated QoS and achieves both service isolation among users from the same class and service differentiation among users from different classes. View full abstract»

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  • A File Assignment Strategy Towards Minimized Response Time for Parallel Storage Systems

    Publication Year: 2013 , Page(s): 2459 - 2465
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (882 KB) |  | HTML iconHTML  

    Prompt response to data access requests is the key performance concern of parallel storage systems. Sort partition (SP) is one of the most promising file allocation solutions for the static scenario due to its sorted partition and placing mechanism. The online variant of SP, hybrid partition (HP), however, does not perform well in the dynamic scenario. The recently proposed balanced allocation with sort (BAS) and its online version balanced allocation with sort for batch (BASB) try to compete with SP and HP by providing better load balancing together with sorting. BAS's performance is close to SP, and BASB greatly outperforms HP. In this paper, we proposed new file placement solutions for the parallel storage systems: Optimized Sort Partition (OSP) for the static scenario and Optimized Sort Partition Online (OSPOnline) for the dynamic scenario. By eliminating the drawbacks of SP/HP and BAS/BASB in the file assignment, OSP and OSPOnline can achieve optimized system response time. Conducted simulations show that OSP and OSPOnline steadily outperform their competitors under various conditions. View full abstract»

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  • An Investigation Into the Use of Four-Bar Linkage Mechanism as Actuator for Hard-Disk Drive

    Publication Year: 2013 , Page(s): 2466 - 2472
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2677 KB) |  | HTML iconHTML  

    The actuator of a hard disk drive (HDD) requires a high bandwidth for fast response to achieve higher recording density. The bandwidth is governed by several factors with the main one being the first in-plane natural frequency of the actuator arm. This paper investigates a new design that can achieve higher actuator bandwidth without sacrificing the out-of-plane stiffness. The design is structurally different from a conventional actuator arm (standard HDD single-stage actuator) and achieves improvement in the first in-plane natural frequency. View full abstract»

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  • Air Flow Analyses in an Ultra-Thin Hard Disk Drive

    Publication Year: 2013 , Page(s): 2473 - 2476
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (847 KB) |  | HTML iconHTML  

    Turbulent air flow analysis is carried out in an ultra-thin hard disk drive using the large eddy simulation (LES). Aerodynamic force acting on various structural components is obtained for about 40 ms and analyzed in detail. Using one set of full scale simulation data, aerodynamic force data for other different sets of operating conditions is obtained using scaling methods thus minimizing the computational time significantly. Validation of the scaling methods is discussed and concluded. View full abstract»

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  • Touchdown of Flying Recording Head Sliders on Continuous and Patterned Media

    Publication Year: 2013 , Page(s): 2477 - 2482
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1690 KB) |  | HTML iconHTML  

    We conduct three-dimensional transient finite-element analysis to study the contact behavior during touchdown detection by a thermal flying-height control (TFC) recording head on continuous and patterned elastic-plastic layered media. The heat generated during touchdown and the plastic strain of the media are calculated in the model. We investigated key factors such as the radius of curvature of the TFC protrusion, media compositions, bit-patterned media (BPM), and the effect of planarization. Our analysis shows that when subjected to the same TFC over-push, BPM is much more likely to result in plastic deformation than the continuous media. The temperature distribution of planarized BPM with {\hbox {SiO}}_{2} as filling material exhibits a complex and distinctive pattern different from the one without planarization. More importantly, the maximum plastic strain of the planarized BPM is 50% larger than the one without planarization, which means that filling with {\hbox {SiO}}_{2} deteriorates the media's robustness to the touchdown probably due to the mismatch of thermal properties between {\hbox {SiO}}_{2} and recording material. This suggests the filling material must be carefully chosen to avoid the excessive plastic strain. View full abstract»

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  • Influence of Neutral Line to the Optimal Drive Current of PMAC Motors

    Publication Year: 2013 , Page(s): 2483 - 2488
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1592 KB) |  | HTML iconHTML  

    The optimal drive current can reduce both the torque ripple and power loss in driving the permanent magnetic (PM) AC motor. This paper presents an analytical model for calculating the optimal drive current of the PMAC motor with surface mount PM rotor. Both the motors with and without the neutral line are analyzed. Theoretical analysis shows that, when the back-emf of the windings contains triple order harmonics, the neutral line of the motor can let the optimal drive current be different from the one without the neutral line, and it can also make the optimal drive current be more effective in the loss and torque ripple reduction. Two spindle motors are used in the analysis to show the influences of the optimal model presented. View full abstract»

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  • Vibration and Noise in a HDD Spindle Motor Arising from the Axial UMF Ripple

    Publication Year: 2013 , Page(s): 2489 - 2494
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1225 KB) |  | HTML iconHTML  

    We investigated numerically the characteristics of axial unbalanced magnetic force (UMF) due to axial magnetic design in the spindle motor of a hard disk drive (HDD). The HDD spindle motor has a magnet-overhang and a pulling plate to generate the axial magnetic force, which is applied to the fluid dynamic bearings (FDBs) as a preload in order to increase the axial stiffness of the HDD spindle system. However, the axial UMF ripple with the least common multiple (LCM) harmonics of pole and slot is generated by the pulling plate and magnet-overhang in the HDD spindle motor. We also investigated the characteristics of the axial magnetic forces generated in the pulling plate and the stator core, separately. We found that the axial magnetic forces generated in the pulling plate and the stator core have opposite phases. Furthermore, we proposed an optimal position of permanent magnet with respect to the stator core. We experimentally verified that the LCM harmonics of pole and slot in the vibration and acoustic noise mostly originate from axial UMF ripple and that the proposed design can effectively minimize the LCM harmonics in the vibration and acoustic noise of HDD systems. View full abstract»

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  • Off-Track Capability Simulation of Shingled Magnetic Recording Under Mechanical Track Misregistration

    Publication Year: 2013 , Page(s): 2495 - 2499
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1125 KB) |  | HTML iconHTML  

    Shingled magnetic recording (SMR) is suitable for higher density recording due to its writing ability. We calculate the SMR's offset error rate with a probabilistic approach by using a linear geometric model. The results show the SMR's offset error rate as being a little better than conventional recording. We also quantify the error rate degradation of multiple adjacent track erasures in conventional recording, which is the largest merit of shingled recording. View full abstract»

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  • Application and Optimization of Factor Graph-Based Detector on 1D ISI Magnetic Recording Channel

    Publication Year: 2013 , Page(s): 2500 - 2503
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (993 KB) |  | HTML iconHTML  

    This paper introduces the application of a factor graph (FG)-based detector on a one-dimensional (1D) intersymbol interference (ISI) magnetic recording channel. The conventional Bahl-Cocke-Jelinek-Raviv (BCJR) detection algorithm operates on a trellis, which defines an equivalence between a bit sequence and a path through the trellis, as well as all possible time evolutions of states of the channel. The BCJR algorithm outputs soft information which corresponds to the a-posteriori channel bit probabilities. Unlike the BCJR, the FG-based detector employs the use of the sum product algorithm (SPA) on a FG with the objective of calculating the same a-posteriori probabilities. Employing the binary SPA to this FG detector gives rise to a suboptimal performance due to the presence of short cycles within the channel factor graph. A nonbinary implementation of the same algorithm mitigates the effect of these cycles and thereby results in an improved performance as compared to the binary implementation. In this paper we also propose an alternative method that can be used to reduce the number of these cycles for performance enhancement. This method involves using an equalizer with a generalized partial response (GPR) target. View full abstract»

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  • A Method for Eliminating Metadata Cache Deallocation Latency in Enterprise File Servers

    Publication Year: 2013 , Page(s): 2504 - 2509
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (990 KB) |  | HTML iconHTML  

    This paper presents an analysis of a performance bottleneck in enterprise file servers using Linux and proposes a modification to this operation system for avoiding the bottleneck. The analysis shows that metadata cache deallocation of current Linux causes large latency in file-request processing when the operational throughput of a file server becomes large. To eliminate the latency caused by metadata cache deallocation, a new method, called “split reclaim,” which divides metadata cache deallocation from conventional cache deallocation, is proposed. It is experimentally shown that the split-reclaim method reduces the worst response time by more than 95% and achieves three times higher throughput under a metadata-intensive workload. The split-reclaim method also reduces latency caused by cache deallocation under a general file-server workload by more than 99%. These results indicate that the split-reclaim method can eliminate metadata cache deallocation latency and make possible the use of commodity servers as enterprise file servers. View full abstract»

    Open Access
  • Investigation of Heat-Assisted Magnetic Recording Media Films in Four Dimensions

    Publication Year: 2013 , Page(s): 2510 - 2513
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (438 KB) |  | HTML iconHTML  

    Heat-assisted magnetic recording is one of the most promising approaches to achieve extremely high density magnetic recording. A laser is used to temporarily heat the recording media film to render its switching field to become lower than the magnetic field of the writing head. After writing, the film material is cooled down to room temperature for data storage. In this dynamic writing process, the challenge is to tailor and optimize the time resolved structural/thermal/magnetic properties of the media films and their correlations during/after the laser heating. In this paper, the four dimensions of current progress in HAMR media research, i.e., structure, magnetic properties, thermal properties and time, are briefly overviewed and discussed. Their correlations are also emphasized. View full abstract»

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  • DRAW: A New Data-gRouping-AWare Data Placement Scheme for Data Intensive Applications With Interest Locality

    Publication Year: 2013 , Page(s): 2514 - 2520
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1231 KB) |  | HTML iconHTML  

    Recent years have seen an increasing number of scientists employ data parallel computing frameworks such as MapReduce and Hadoop to run data intensive applications and conduct analysis. In these co-located compute and storage frameworks, a wise data placement scheme can significantly improve the performance. Existing data parallel frameworks, e.g., Hadoop, or Hadoop-based clouds, distribute the data using a random placement method for simplicity and load balance. However, we observe that many data intensive applications exhibit interest locality which only sweep part of a big data set. The data often accessed together result from their grouping semantics. Without taking data grouping into consideration, the random placement does not perform well and is way below the efficiency of optimal data distribution. In this paper, we develop a new Data-gRouping-AWare (DRAW) data placement scheme to address the above-mentioned problem. DRAW dynamically scrutinizes data access from system log files. It extracts optimal data groupings and re-organizes data layouts to achieve the maximum parallelism per group subjective to load balance. By experimenting two real-world MapReduce applications with different data placement schemes on a 40-node test bed, we conclude that DRAW increases the total number of local map tasks executed up to 59.8%, reduces the completion latency of the map phase up to 41.7%, and improves the overall performance by 36.4%, in comparison with Hadoop's default random placement. View full abstract»

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  • Characteristics of Axial and Radial Surface Tension Sealing Structures for HDD FDB Spindles

    Publication Year: 2013 , Page(s): 2521 - 2525
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1252 KB) |  | HTML iconHTML  

    This paper presents the characteristics of the axial and radial surface tension sealing structures. Based on the 6-DOF rotor-bearing coupled dynamic analysis, the movement of the shaft relative to the sleeve during and immediately after a shock is calculated. By use of the finite volume method, volume of fluid, K-e turbulence model and dynamic mesh technique, the anti-shock capacity and anti-centrifugal force capacity of the two structures are investigated. The results are significant for optimal design of the sealing structure in hard disk drive fluid dynamic bearings spindles. View full abstract»

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  • Saturation Control for an MTA-Based Dual-Stage Actuation System

    Publication Year: 2013 , Page(s): 2526 - 2529
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1098 KB) |  | HTML iconHTML  

    The dual-stage actuation system based on a newly developed slider-level thermal microactuator has been demonstrated to be able to achieve 6 kHz control bandwidth with 60 kHz sampling rate. This paper reports the saturation control for the thermal microactuator. The aim is to release the thermal microactuator from saturation as soon as possible once the saturation occurs, and to maintain the system to be stable when the microactuator saturates. Typically, the antiwindup compensation scheme is used, due to its benefits of easy design and implementation as well as effectiveness for the thermal microactuator. Simulation and experimental testing shows the performance of this saturation control, when the dual-stage system undertakes a seeking task, especially a long distance seeking such as 40 and 80 nm seekings. View full abstract»

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  • Novel Methods for Real-Time Observation of Molecularly Thin Lubricant Films by Ellipsometric Microscopy: Application to Dewetting Observation

    Publication Year: 2013 , Page(s): 2530 - 2534
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2071 KB) |  | HTML iconHTML  

    Methods based on ellipsometric microscopy were discussed for real-time observation of molecularly thin lubricant on magnetic disks and vertical-objective ellipsometric microscopy was applied to the observation of dewetting of the lubricant. The observation revealed that the dewetting patterns in the early stage are strongly correlated with the signs of disjoining pressure and its derivative with respect to the film thickness. Conversely, our findings suggest that the tendency of the disjoining pressure can be estimated by analyzing the dewetting patterns in the early stage. View full abstract»

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  • Embedded Marker Code for Channels Corrupted by Insertions, Deletions, and AWGN

    Publication Year: 2013 , Page(s): 2535 - 2538
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (772 KB) |  | HTML iconHTML  

    In this paper, we present a new error-correction scheme, referred to as embedded marker code scheme (EMCS), for channels corrupted by insertions, deletions and additive white Gaussian noise (AWGN). The EMCS uses the pinning bits, which have the potential to lower the error floors of the outer low-density parity-check (LDPC) codes, for both resynchronization and improving error-correction performance. Furthermore, the soft-input synchronization for the inner decoder and the joint iterative decoding between the inner decoder and the outer decoder is employed to further improve the overall performance of the new scheme. Simulations show that the proposed EMCS reduces the code rate loss as compared with the conventional marker code scheme and achieves a better tradeoff between the error performance and the decoding complexity. Therefore, the new scheme can reduce code rate loss and improve storage efficiency when it is used in bit-patterned media recording (BPMR) systems. View full abstract»

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Aims & Scope

IEEE Transactions on Magnetics publishes research in science and technology related to the basic physics and engineering of magnetism, magnetic materials, applied magnetics, magnetic devices, and magnetic data storage.

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Meet Our Editors

Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology