Discrete Disk Research Articles

Robust Dynamic Balancing of Dual Rotor-Active Magnetic Bearing System Through Virtual Trial Unbalances as Low and High Frequency Magnetic Excitation

Abstract This work focuses on in situ residual unbalance estimation of the dual rotor system with the implementation of active magnetic bearing (AMB) as a controller and exciter. The excessive vibration generated due to the presence of residual unbalances limits the operating speed of the system. The compact structure of the dual rotor system provides constraints to the conventional balancing procedure that requires manual addition of the trial unbalances for balancing. In order to overcome the difficulty in balancing of the dual rotor system, an identification algorithm based on the modified influence coefficient method (MICM) is developed for the simultaneous estimation of residual unbalances in both inner and outer rotors with the generation of virtual trial unbalances as magnetic excitation through AMB. The controlling action of AMB attenuates the vibrational response of the system within the required limit and allows the safe operation of the system in the presence of rotor faults and additional excitations. The vibrational responses of the system at the limited locations and the magnitude and phase of the virtual trial unbalances are only required in the MICM for the estimation of unbalances. To numerically illustrate the present methodology, the displacement response is obtained from the developed finite element model of the dual rotor system with discrete disk unbalances and randomly distributed shaft. The robustness of the algorithm in the estimation of residual unbalances is verified with the addition of a different percentage of measurement noises. After balancing, the dual rotor system is found to traverse its critical speed with a less vibrational response.

Wireless Fading Paradigm for Antenna Array Receiver for a Disk-Type Cluster of Scatterers

This correspondence presents a signal processing based alternate approach for simulating the flat fading narrowband wireless channels for the antenna array receivers under the time-varying environment, in which the discrete disk of scatterers is incorporated around the mobile wireless transmitter to model the spreading of azimuth. The disk-type cluster of scatterers continuously changes due to the movement of the mobile wireless transmitter. Under this time-varying environment, each scatterer, at the successive stages of the disk, is correlated with the scatterers at the preceding stages of the disk using the second-order autoregressive process AR(2). At the receiver, one signal waveform is associated with each element of the antenna array taking into account the spread in azimuth of the received signal. The correlation of the fading waveforms generated by using the presented paradigm is compared with the expected analytical correlation results, which clearly manifests that the simulation results are consistent with the findings based on Jakes’ model. Moreover, the presented discrete disk-type cluster of scatterers fading model may be used to generate/simulate the variable diameter ring-type cluster of scatterers fading paradigm. The proposed channel model may play a significant role in the emerging field of wireless signal processing for the latest mobile communication systems.

Convexity properties of coverings of 1-convex surfaces

We prove that there exists a 1-convex surface whose universal covering does not satisfy the discrete disk property.

Size-topology correlations in disk packings: terminal bidispersity in order–disorder transitions

In random packings or tilings, the size distribution of individual elements (domains) and the statistics of numbers of neighbours of those domains are strongly correlated. In the case of circular disks forming a random packing in the plane, it has long been known empirically that a certain critical amount of bidispersity avoids crystallization of the packing. We demonstrate how the formalism of a simplified granocentric model allows for an analytical computation of the size-topology correlation as a function of both size ratio and frequency of small disks. The results, obtained without free parameters, are in excellent agreement with the empirical findings of packing simulations concerning critical (terminal) bidispersity. It is also shown that, at equal size variance, the discrete (bidisperse) disk size distributions induce stronger disorder than continuously polydisperse disks.

Polar Zernike moments and rotational invariance

Zernike moments (ZM) have potentials in pattern recognition, image analysis/processing, and in computer vision. Their invariance and orthogonality are attractive in many applications. Unfortunately, direct computation of factorials in them is time consuming and discouraging. Also, people have shown poor invariance for Cartesian ZM in the discrete case. Need of a faster computing algorithm with better rotational invariance is already felt in various research communities. To find a solution, we have examined a completely new approach which comprises a unique mapping of a gray-level image on a discrete circular disk to compute Cartesian as well as polar ZM through a new recursive relation. Such a map does not require any special sampling. The proposed new recursion is based on the computational structure of the radial polynomial embedded in the ZM. Fast computation of ZM, in our case, uses the developed new recursion and the properties of discrete circles, e.g., symmetry, uniqueness, and hole-free generation of discrete disk. This discrete circular map helps not only the fast computation of ZM but also lends its support to provide better rotational invariance for polar ZM over that of Cartesian ZM. The invariance is useful in recognition.

The disk property of coverings of 1-convex surfaces

Let X X be a 1-convex surface and p : X ~ → X p:\tilde X\to X an (unbranched) covering map. We prove that if X ~ \tilde X does not contain an infinite Nori string of rational curves, then X ~ \tilde X satisfies the discrete disk property.

Numerical Solution of the Boltzmann Based Lubrication Equation for the Air-Bearing Interface Between a Skewed Slider and a Disk With Discrete Data Tracks

Discrete track recording (DTR) is a method for increasing the recording density of a data storage disk by use of a pattern arrangement of discrete tracks. The DTR track structure consists of a pattern of very narrow concentric raised areas and recessed areas underneath a magnetic recording layer. In order to design the air-bearing slider platform that houses the magnetic transducer for DTR application at very low fly heights, the influence of the disk surface topography as a surface roughness effect must be taken into account. This paper is focused on the numerical solution of the roughness averaged lubrication equation reported recently in the work of White (2010, “A Gas Lubrication Equation for High Knudsen Number Flows and Striated Rough Surfaces,” ASME J. Tribol., 132, p. 021701) and is specialized for the influence of discrete disk data tracks on the recording head slider-disk air-bearing interface subject to a nonzero skew angle formed between the slider longitudinal axis and the direction of disk motion. The generalized lubrication equation for a smooth surface bearing and appropriate for high Knudsen number analysis is quite nonlinear. And including the averaging process required for treatment of a nonsmooth disk surface, as well as the rotational transformation required to allow for a nonzero skew angle, increases further the nonlinearity and general complexity of the lubrication equation. Emphasis is placed on development of a numerical algorithm that is fast, accurate, and robust for air-bearing analysis of complex slider surfaces. The numerical solution procedure developed utilizes a time integration of the lubrication equation for both steady-state and dynamic analyses. The factored-implicit scheme, a form of the more general alternating-direction-implicit numerical approach, was chosen to deal with the two-dimensional and highly nonlinear aspects of the problem. Factoring produces tightly banded coefficient matrices and results in an algorithm that is second-order accurate in time while requiring only the solution of tridiagonal systems of linear equations in advancing the computation from one time level to the next. Numerical solutions are presented that demonstrate the performance of the computational scheme and illustrate the influence of some discrete track parameters on skewed air-bearing performance as compared with a flat surface data storage disk.

A Gas Lubrication Equation for High Knudsen Number Flows and Striated Rough Surfaces

This paper describes the derivation and numerical solution of a lubrication equation appropriate for high Knudsen number flows and certain types of striated rough surfaces. The derivation begins with the compressible form of the lubrication equation together with the nonlinear series form of the Poiseuille flow reported by Fukui and Kaneko (1990, “A Database for Interpolation of Poiseuille Flow Rates for High Knudsen Number Lubrication Problems,” ASME J. Tribol., 112, pp. 78–83.). A multiple-scale analysis is performed on the lubrication equation for a finite-width time-dependent bearing and is limited to either stationary-transverse or longitudinal striated surface roughness of very short length scale. The rough surface averaging that takes place within the multiple-scale analysis includes a fully coupled treatment of the Poiseuille flow. What results is an especially nonlinear lubrication equation with averaged surface roughness effects that is appropriate for high Knudsen number analysis. A rotational transformation is also introduced to provide the roughness averaged lubrication equation in a form that allows analysis of the skewed orientation of a recording head slider with roughness defined relative to the direction of disk motion but with the lubrication equation conveniently expressed in the coordinate system of the slider. A factored-implicit numerical algorithm is described that provides the solution of the roughness averaged lubrication equation. Even though the lubrication equation is highly nonlinear, the numerical scheme is crafted to be fully second-order, time-accurate, and noniterative for tracking the solution in time either to an asymptotic steady-state or in response to a dynamic event. Numerical solutions of several simple geometry bearings are presented that utilize parameters that are typical of the slider-disk interface of current hard disk drives. It is anticipated that the primary benefit of this work may be the ability to accurately and efficiently include the influence of discrete disk data tracks in the air bearing design of very low clearance recording head sliders.

1102 300μmの変位量を有する圧電素子型アクチュエータの高速高精度制御(要旨講演,一般セッション:情報機器コンピュータメカニクス)

A piggyback actuator indispensables for a spin-stand system that evaluates high density magnetic recording, because magnetic recording head must follow a very narrow track precisely on a high speed rotating disk for a read-back signal evaluation. The authors had designed the Nano-Motion Actuator of 10nm spec, which was applied for the spin-stand. However, the actuator can not apply for a pre-write servo disk and a discrete disk, because when these types of disks are clamped on an air-spindle, eccentricity between the disk center and the center axis of the air-spindle occurs. Since the error of the eccentricity reaches to one handled micron meter, a new Nano-Motion Actuator of large work distance is required.

Performance of Two-Disk Failure-Tolerant Disk Arrays

RAID5 disk arrays use the rebuild process to reconstruct the contents of a failed disk on a spare disk, but this process is unsuccessful if latent sector failures are encountered or a second disk failure occurs. The high cost of data loss has led to two-disk failure-tolerant (2DFT) arrays: RAID6, EVENODD, row-diagonal parity (RDP), and RM2. RAID6 uses Reed-Solomon (RS) codes, whereas the latter three use parity encoding. This paper is concerned with the performance from the viewpoint of disk accesses, which, with an appropriate choice of symbol sizes, is the same for RAID6, EVENODD, and RDP, rather than the computational cost (number of XOR operations). We compare the performance of 2DFTs with each other, as well as RAIDO and RAID5 in normal and degraded operating modes. We derive cost functions for processing discrete disk accesses. The mean response time can be obtained analytically with Poisson arrivals and first-come, first-served (FCFS) scheduling. A simulation is used for validation, calibrating the approximate fork-join response analysis, and shortest-access-time-first (SATF) scheduling. The response time for read requests in RAID6 and RM2 is higher than RAID5 and RAIDO and increases with the fraction of write requests. When there is a single disk failure, RM2 outperforms RAID6 since it has a smaller parity group size than RAID6, but RAID6 outperforms RM2 with two disk failures because of its costlier recovery process. Disk loads in RM2 and RAID6 in degraded mode are unbalanced, and a solution based on pseudorandom permutations is proposed for this purpose

High-finesse disk microcavity based on a circular Bragg reflector

We made disk-shaped microcavities of approximately 10 μm2 in area in a GaAs/AlGaAs waveguide structure by etching deep vertical concentric trenches. The trenches form a circular Bragg-like reflector that confines light in the remaining two lateral dimensions. We demonstrate from photoluminescence excited in the waveguide the confinement of discrete disk modes whose wave vector is mainly radial, in contrast with whispering gallery modes. Their quality factors up to Q=650 indicate in-plane reflectivities approaching 90%. In the near infrared, this represents a demonstration of wavelength-scale light confinement based on photonic crystal effects in two dimensions.

Maintaining a minimassive database of microdrinking measures

For longitudinal studies of rats’ consumption of ethanol, water, and food, we require manual entry of directly observed measurements, consolidation with computer-collected measurements, quick computation of derived statistics, and the export of selected data for further analysis and graphing. As in a spreadsheet, our solution propagates changes in data values through all computations dependent on them but, as in a relational database, maintains data in discrete disk records indexed by day and cage, in which the format of these records is also described by records stored in the same database. During manual data updates, each day’s data are presented in a spreadsheet-like format but with more control over data entry validity than a spreadsheet typically affords. Experimental integrity is further enhanced by producing printed worksheets for data entry, assignment of rats to treatments, and printed injection instructions directly from such customized data files.

Differential population synthesis of SO galaxies. I - The data

view Abstract Citations (31) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Differential Population Synthesis of S0 Galaxies. I. The Data Gregg, Michael D. Abstract Spectrophotometric observations of elliptical galaxy nuclei, S0 nuclei, and S0 disks obtained with the Kitt Peak National Observatory intensified image dissector scanner are presented. The 12 normal eliipticals observed span 7 mag in luminosity and sample a wide range of line strengths in early-type systems. The S0 disk spectra are of discrete disk locations and are not disk-plus-bulge integrated light spectra. In a companion paper these spectra are used to investigate the stellar populations and star formation histories of S0 galaxies by a differential method of population synthesis in which the S0 galaxies are compared with normal ellipticals. Here, the spectrophotometry and supplementary broad-band photometry are described. The second half of the paper describes the effect of the recently reported nonlinearity of the IIDS on the flux calibrations and the procedures adopted to deal with it, correcting the spectra to the AB79 system of Oke and Gunn. The results of a principal component analysis of the normal ellipticals show this sample to be a one parameter family in line strength and color. Publication: The Astrophysical Journal Supplement Series Pub Date: February 1989 DOI: 10.1086/191311 Bibcode: 1989ApJS...69..217G Keywords: Astronomical Spectroscopy; Elliptical Galaxies; Galactic Evolution; Star Distribution; Abundance; Magnesium; Metallicity; Principal Components Analysis; Stellar Spectrophotometry; Astrophysics; GALAXIES: EVOLUTION; GALAXIES: PHOTOMETRY; GALAXIES: STELLAR CONTENT; SPECTROPHOTOMETRY full text sources ADS | data products SIMBAD (32) NED (29) Related Materials (1) Part 2: 1989ApJ...337...45G

Conic Sections in Digital Grid

This paper examines some properties and generation techniques of conics and quadrics in digital grid. In the generation of discrete ring and disk, the scheme does not produce any hole during their successive generations. Methods for finding an approximate radius of curvature of a digital circular arc are also discussed. The properties and generation techniques of discrete conics and quadrics are useful in digital geometry and computer art design.

Prebunched beam traveling-wave tube studies

A traveling-wave tube with a prebunched beam is found to have a considerably higher efficiency than the same tube without prebunching. For the particular tube tested the efficiency is increased from 20 to over 35 per cent at a gain of 8. Computer calculations using a discrete disk model give similar results. The beam is bunched tightly in energy at the position of highest efficiency, indicating that very high efficiency could be obtained with a depressed collector. Both current and velocity modulation are required for prebunching, and are obtained by means of a current grid followed by an inductively tuned velocity modulation cavity. The requirements of the current grid are not great so that operation should be possible at frequencies well above the normal operating region of a microwave triode. The operation of the tube is sensitive to the output match, and it appears to be difficult to obtain a good match with the beam on.