Recording Density Research Articles

A gap in the woods: Wood density knowledge as impediment to develop sustainable use in Atlantic Forest

To achieve sustainable forest management, forests scientists and managers require ecological data such as tree size, growth rate, wood density, species abundance and forest structure. Lack of specific knowledge on these features may compromise the sustainable use of natural resources. Considering tree species, wood density may be considered as the most integrative trait, usually associated with two major growth syndromes, setting apart pioneer and climax species, and driving potential uses of wood. Therefore, we chose this trait as an indicator for the scientific knowledge level about Atlantic Forest tree species, under the assumption that it is an impediment for their management and conservation. We use Logistic Regression models to test if wood density is less known (i) due to species restricted distribution, (ii) due to species abundance, and/or (iii) species unknown use value. As an alternative to fill this gap we test if it is possible to predict wood density from related species using a null model. We could not find any wood density record for 73.4% of the studied species. We also detected a consistent spatial bias with collection data closer to research centers than expected by chance. Also, larger distribution area and more recognized use value of a given species is associated with a higher chance of having wood density records in the literature. It was possible to use available knowledge about wood density of related species in a genus for 15 of the 57 studied genera. Our results show that, besides the lack of information on wood density, there is uncertainty about the capability of the existent data to express trait variability for Atlantic Forest trees. Therefore, to ensure adequate wood supply and species conservation it is imperative to fill knowledge gaps on wood density in the Atlantic Forest.

Analysis of Temperature Modes of Hologram Recording on Photothermoplastic Materials

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Overview of manufacturing technologies under development in Russia for ITER plasma facing components

Manufacturing of the plasma-facing components (PFC) for the ITER is under qualification now (Merola et al., 2014) [1]. To start production of 179 first wall (FW) panels and 58 divertor domes (DD), for which the RF DA is responsible, it is necessary to manufacture their full-scale prototypes. In preparation for their manufacturing a wide range of technologies has been developed, which are continuously progressing (Mazul et al., 2011, 2012, 2016) [2–4]. Considering that changes were made in the DD design in view of the change-over to an all-tungsten divertor, as well as on the basis of the obtained results of manufacturing of the FW panel semi- prototype, the necessity arose to optimize some technological manufacturing stages. Thus, for the DD the composition of structural materials has been changed, the new assembly structure has been developed and analyzed; some technological operations have been optimized. The technological operations for FW panel have been also optimized, namely, the brazing temperature of the beryllium armor has been decreased, preparation works are under way on replacement of explosion welding by diffusion bonding for the steel-bronze joint. Most of the technological stages should be accompanied by non- destructive testing (ultrasonic, X-ray), the methods of which have been developed as well. The RF DA is also responsible for thermal testing of divertor elements. Due to application of the X-ray matrix the methods have been improved for recording of density of the applied heat flux produced by the electron beam. The ways for and the results of optimization of the technological and testing procedures are also presented below.

Numerical analysis of microwaviness-excited vibrations of a flying head slider at touchdown

The dynamics and stability of a flying head slider at proximity to and touchdown on a magnetic recording disk are attracting considerable research attention, because it is necessary to reduce the head clearance from the lubricant film to ~ 0.5 nm to achieve a higher recording density. As a succeeding study continuing the theoretical investigation of slider dynamics at touchdown, this study theoretically analyzes further details of the different behaviors of a practically applied head slider. The experimental touchdown behaviors at inner, middle, and outer radius positions in a commercially available hard disk drive are introduced. From the improved theoretical analyses, it is determined that different behaviors result from differences in air-bearing stiffness at the inner, middle, and outer radius positions. Moreover, it is found that the first half of the period for which a loss-of-contact signal is obtained corresponds to a light asperity contact state between the head and disk surfaces, whereas the latter half of this period corresponds to a flying state. It is thought that the former light asperity contact state can be well lubricated even at a high bond ratio, and that the light contact state can be used for future contact recording.

Heat-assisted magnetic recording media materials

Abstract

Statistically Reconstructed Multiplexing for Very Dense, High-Channel-Count Acquisition Systems.

Multiplexing is an important strategy in multichannel acquisition systems. The per-channel antialiasing filters needed in the traditional multiplexing architecture limit its scalability for applications requiring high channel density, high channel count, and low noise. A particularly challenging example is multielectrode arrays for recording from neural systems. We show that conventional approaches must tradeoff recording density and noise performance, at a scale far from the ideal goal of one-to-one mapping between neurons and sensors. We present a multiplexing architecture without per-channel antialiasing filters. The sparsely sampled data are recovered through a compressed sensing strategy, involving statistical reconstruction and removal of the undersampled thermal noise. In doing so, we replace large analog components with digital signal processing blocks, which are much more amenable to scaled CMOS implementation. The resulting statistically reconstructed multiplexing architecture recovers input signals at significantly improved signal-to-noise ratios when compared to conventional multiplexing with antialiasing filters at the same per-channel area. We implement the new architecture in a 65536-channel neural recording system and show that it is able to recover signals with performance comparable to conventional high-performance, single-channel systems, despite a more than four-orders-of-magnitude increase in channel density.

Read sensor technology for ultrahigh density magnetic recording

Abstract

Size, growth, and density data for shallow-water sea urchins from Mexico to the Aleutian Islands, Alaska, 1956-2016.

Size, growth, and density have been studied for North American Pacific coast sea urchins Strongylocentrotus purpuratus, S.droebachiensis, S.polyacanthus, Mesocentrotus (Strongylocentrotus) franciscanus, Lytechinus pictus, Centrostephanus coronatus, and Arbacia stellata by various workers at diverse sites and for varying lengths of time from 1956 to present. Numerous peer-reviewed publications have used some of these data but some data have appeared only in graduate theses or the gray literature. There also are data that have never appeared outside original data sheets. Motivation for studies has included fisheries management and environmental monitoring of sewer and power plant outfalls as well as changes associated with disease epidemics. Studies also have focused on kelp restoration, community effects of sea otters, basic sea urchin biology, and monitoring. The data sets presented here are a historical record of size, density, and growth for a common group of marine invertebrates in intertidal and nearshore environments that can be used to test hypotheses concerning future changes associated with fisheries practices, shifts of predator distributions, climate and ecosystem changes, and ocean acidification along the Pacific Coast of North America and islands of the north Pacific. No copyright restrictions apply. Please credit this paper when using the data.

Performance of the hybrid MLPNN based VE (hMLPNN-VE) for the nonlinear PMR channels

This paper proposes a hybrid of multilayer perceptron neural network (MLPNN) and Volterra equalizer (VE) denoted hMLPNN-VE in nonlinear perpendicular magnetic recording (PMR) channels. The proposed detector integrates the nonlinear product terms of the delayed readback signals generated from the VE into the nonlinear processing of the MLPNN. The detection performance comparison is evaluated in terms of the tradeoff between the bit error rate (BER), complexity and reliability for a nonlinear Volterra channel at high normalized recording density. The proposed hMLPNN-VE outperforms MLPNN based equalizer (MLPNNE), VE and the conventional partial response maximum likelihood (PRML) detector.

気体軸受圧力による磁気ディスク媒体及びスライダの表面変形

The slider/disk spacing of magnetic disk drives has been reduced in order to increase the recording density. Especially, the thermal flying-height control technology, where the electromagnetic transducer is protruded into the slider/disk spacing by heating the slider partially, contributes to make the flying height less than 2nm. Because of the narrower gas bearing clearance, the bearing pressure rises up to several tens times of atmospheric pressure. This pressure rise causes the deformation of slider and disk surface. The slider and disk surface deformation causes the change of gas bearing clearance and consequently the change of air bearing pressure. The pressure change causes the flying attitude. The flying characteristics also may be different from that of expected at the design, where the effect of deformation is not included. It is important to estimate correct flying characteristics affected by the deformation to realize stable flying and accurate recording. We introduced iterative method for searching the flying attitude affected by the slider/disk deformation. We obtained the air bearing pressure by solving the molecular gas lubrication equation numerically. And the simple numerical method, which utilizes the elastic half-space assumption, was employed for calculating the deformation of pressurized disk surface. The finite element method was applied to analyze the slider deformation. And the effect of deformation on the slider attitude is evaluated.

An all-aqueous redox flow battery with unprecedented energy density

A hybrid alkaline zinc–iodine redox flow battery has been designed with an unprecedented energy density record to date for an all-aqueous redox flow battery.

Effects of head field and AC field on magnetization reversal for microwave assisted magnetic recording

Microwave assisted magnetic recording (MAMR) is a promising recording method for achieving high recording densities in hard disk drives. In MAMR, the AC field from a spin-torque oscillator (STO) assists the head field with magnetization reversal in a medium. Therefore, the relationship between the head field and the AC field is very important. In this study, the effects of the head field and the AC field on magnetization reversal were analyzed using a micromagnetic simulator that takes the magnetic interactions between a single-pole type (SPT) write-head, an exchange coupled composite (ECC) medium, and the STO into account. As a result, the magnetization reversal was assisted not just by the y-component of the AC field (Hstoy) but also by the y-component of the head field (Hhy) in the medium. The Hhy over 100 kA/m with a frequency of about 15.5 GHz induced the magnetic resonance. The large Hhy was produced by the field from the STO to the SPT head.

High-Density Shingled Heat-Assisted Recording Using Bit-Patterned Media Subject to Track Misregistration

Shingled recording employing bit-patterned media when used in conjunction with heat-assisted magnetic recording can significantly enhance the recording density. This paper investigates writing of dots that are not directly under the laser pulse. Such a shifted scheme of writing allows higher densities when used with shingled recording. A further increase in the recording density can be obtained by using composite structures, comprising a superparamagnetic writing layer, and a (doped) FePt storage layer. Effect of head velocity, Curie temperature variation, track mis-registration, and dot position jitter on the standard deviation of switching distribution is studied to evaluate the designs that offer data densities as high as ~16 Tbpsi.

Superconducting magnetic energy storage and superconducting self-supplied electromagnetic launcher

Superconductors can be used to build energy storage systems called Superconducting Magnetic Energy Storage (SMES), which are promising as inductive pulse power source and suitable for powering electromagnetic launchers. The second generation of high critical temperature superconductors is called coated conductors or REBCO (Rare Earth Barium Copper Oxide) tapes. Their current carrying capability in high magnetic field and their thermal stability are expanding the SMES application field. The BOSSE (Bobine Supraconductrice pour le Stockage d’Energie) project aims to develop and to master the use of these superconducting tapes through two prototypes. The first one is a SMES with high energy density. Thanks to the performances of REBCO tapes, the volume energy and specific energy of existing SMES systems can be surpassed. A study has been undertaken to make the best use of the REBCO tapes and to determine the most adapted topology in order to reach our objective, which is to beat the world record of mass energy density for a superconducting coil. This objective is conflicting with the classical strategies of superconducting coil protection. A different protection approach is proposed. The second prototype of the BOSSE project is a small-scale demonstrator of a Superconducting Self-Supplied Electromagnetic Launcher (S3EL), in which a SMES is integrated around the launcher which benefits from the generated magnetic field to increase the thrust applied to the projectile. The S3EL principle and its design are presented.

Modeling of cross-talk phenomena in thin film ferroelectric nanocapacitor arrays by finite element method combined with Monte Carlo calculations

In the last few years, the interest in developing ferroelectric systems with high recording density close to 1Tb/in.2 has strongly increased. The ferroelectric thin films are subjected to the electric field applied by using nanocapacitors (diameters of ∼70 nm) containing a ferroelectric active material. In order to increase the memory density, the nanocapacitor dimensions and the distance between them have to be strongly decreased. However, if the lateral distance between the nanoelectrodes is reduced too much, a domain wall propagation from the nanocapacitor subjected to the voltage to the neighboring capacitors (so-called “cross talk”) is observed. This phenomenon is undesired because the memory spatial resolution is affected. In the present paper, the role of the geometrical characteristics (electrode radius, lateral distance between the electrodes and the film thickness) is investigated, by using a combined Finite Element Method with the Monte Carlo model to describe the local switching properties. The distributions of the electrical potential and local fields were computed by using the Finite Element Method. After describing the conditions for the appearance of the “cross-talk” phenomenon in ferroelectric nanocapacitor systems, some valuable solutions to avoid it are presented.

面記録密度1Tb/in^2-2.5Tb/in^2を達成するための熱アシスト磁気記録計算機シミュレーション(媒体,一般)

面記録密度1Tb/in^2-2.5Tb/in^2を達成するための熱アシスト磁気記録計算機シミュレーション(媒体,一般)

Coupled Granular/Continuous Media – Results and Challenges

ABSTRACTWhile the most promising longitudinal recording systems cannot surpass the theoretical limit of about 200 Gb/in2 for areal recording density and the demand for higher densities is permanently increasing, the perpendicular magnetic recording constitutes the realistic issue to the longitudinal one. The perpendicular magnetic recording offers significant advantages, the most important being stronger write and read fields, and therefore the use of media of higher anisotropy, smaller grain size, higher signal-to-noise ratio, and a better thermal stability. Unfortunately, the perpendicular recording has to cope some important physical and technological difficulties. To overcome them, many ingenious solutions were proposed. In this paper the coupled granular/continuous (CGC) media, a subtle association of the continuous and, respectively, granular media, are analysed from the viewpoint of their magnetic and recording properties. The challenges and possible improvements of CGC media are discussed.

Digital image multiplexing/demultiplexing method using spatial spectral diffusion and virtual phase conjugation technique for reduction of dynamic range consumption in holographic medium

The recording density in holographic data storage (HDS) systems is determined by the dynamic range of the recording medium. If a hologram is recorded with a small exposure, the consumption amount of the dynamic range per hologram is reduced, and the recording density can be improved. In this report, we propose a digital image multiplexing/demultiplexing method using spatial spectral diffusion and a virtual phase conjugation technique to reduce the consumption amount of the dynamic range in a recording medium. In our method, multiple signals are simultaneously recorded in a medium by multiplexing those signals using a beam combiner before recording, unlike the general multiplexing method of HDS. Then, each original signal can be reproduced independently by utilizing the property of a random diffuser and a phase-conjugated light. In the simulation, we confirmed that our method can improve the recording density because the consumption of the dynamic range is reduced.

Two-photon lithography for 3D magnetic nanostructure fabrication

Ferromagnetic materials have been utilized as recording media in data storage devices for many decades. The confinement of a material to a two-dimensional plane is a significant bottleneck in achieving ultra-high recording densities, and this has led to the proposition of three-dimensional (3D) racetrack memories that utilize domain wall propagation along the nanowires. However, the fabrication of 3D magnetic nanostructures of complex geometries is highly challenging and is not easily achieved with standard lithography techniques. Here, we demonstrate a new approach to construct 3D magnetic nanostructures of complex geometries using a combination of two-photon lithography and electrochemical deposition. The magnetic properties are found to be intimately related to the 3D geometry of the structure, and magnetic imaging experiments provide evidence of domain wall pinning at the 3D nanostructured junction.

Tape transport control with suppression of time-varying tension disturbances

Disturbance suppression in the transport system of tape drives is essential for achieving high volumetric densities in tape storage, as improved tension control will enable operation with thinner tape media. In addition, tension variations lead to dimensional changes in the cross-track direction of the tape that must be accounted for in the track width budget. Hence, better tension control enables a higher track density. Furthermore, fluctuations of the tape velocity and tension around the nominal values impact the performance of the data channels, and consequently also the achievable areal recording density. In a tape transport system, disturbances are mainly induced by reel eccentricities that lead to time-varying tension disturbances. In this paper, the tension disturbances are first characterized using a strain-gauge sensor included in one of the rollers that determine the tape path. Then, a second characterization method that does not rely on a strain-gauge sensor is introduced. The new method is based on an estimate of the tension variation signal, which is derived from the difference of head lateral position measurements obtained by reading servo patterns on two adjacent servo bands. A tension feedback system is proposed, which uses time-varying controllers that adapt their frequency characteristics depending on the longitudinal tape position. The closed-loop system is designed to enhance disturbance suppression at the reel rotation frequencies. Experimental results are presented to illustrate the performance of the proposed tape transport control system.