Autocorrelation analysis of particle magnetization in erased particulate media.

notes: This paper developed a complete analytical description of the origins and effects of noise in magnetic storage media. The research was part of an EPSRC project (GR/M46648/01, Noise in Advanced Magnetic Recording Tapes) with Hewlett Packard Peripherals (Bristol) to explore sources of media noise and their impact on the performance of HP's commercial (DDS-4) tape systems. The theory presented is generic, applicable to other media used in data storage, and provides guidelines for the reduction of noise and therefore errors in storage systems in general.© 2002 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.General analytical expressions for the magnetization power spectral densities of particulate media are derived by using the three-dimensional autocorrelation function. Expressions include the effects of AC demagnetized media and any DC components resulting from the presence of particle chains. The replay flux power spectral density is then obtained, assuming a linear replay transducer

Particle distributions and noise in metal particle tapes

©2002 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.The magnetization spectrum from an erased (ac demagnetized or dc saturated) particulate medium was derived analytically using the autocorrelation function of a long line of separate and contiguous particles. The derived expressions indicated a strong dependence on the percentage of chains and their length inside the magnetic medium. Using the values of these quantities as fitting parameters, good agreement to measured noise spectra from a digital tape system was obtained

Correlations and noise in magnetic recording media

publication-status: Publishedtypes: Proceedings PaperA theory is presented which predicts the role of interparticle correlations in determining the magnetisation power spectral densities within magnetic recording media in the absence of recorded signal magnetisation. Magnetic correlations are represented in terms of the probabilities of the changes of magnetisation direction between neighbouring particles and this feeds through into determining the shapes of the power spectral densities and the correlation lengths

Accuracy of expressions for the magnetic field of a ring head

©2000 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.The Fourier method used by Fan has produced a representation of the field of a semi-infinite pole head consisting of a simple analytical approximation (Karlqvist field) plus an infinite series of correction terms. A method is developed in this paper by which other approximations to head fields have their infinite series of correction terms evaluated to make them exact. Expressions with only one correction term produced by Ruigrok and Szczech et al., are studied, and enhancement of them is shown to offer accurate approximations to the exact head fields

Switching times and transition widths in digital recording theory

©2001 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.Calculations are carried out to show the effects of finite switching times of head fields and of recording media on recorded transition widths. In both cases the transition widths are increased and these effects are captured in simple analytical expressions

Hysteresis loops and transition shapes during recording

©2000 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.Hysteresis loop shapes corresponding to particular recorded transition shapes are calculated self-consistently. It is found that the closer a ramp function comes to the shape of the transition, the squarer the hysteresis loop that is needed

Recorded magnetization distributions in thin film disk media

©1998 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.The magnetization distributions in recorded transitions in thin film disk media are shown to consist of simple longitudinal magnetization transitions along with flux closure patterns. Together they give rise to the familiar sawtooth patterns but also indicate why arctangent and other approximations used in record theory have proved so successful even when sawteeth are known to be present

Angular two-photon interference and angular two-qubit states

Using angular-position-orbital-angular-momentum entangled photons, we study angular two-photon interference in a scheme in which entangled photons are made to pass through apertures in the form of double angular slits, and using this scheme, we demonstrate an entangled two-qubit state that is based on the angular-position correlations of entangled photons. The entanglement of the two-qubit state is quantified in terms of concurrence. These results provide an additional means for preparing entangled quantum states for use in quantum information protocols

Listening and learning : the reciprocal relationship between worker and client

The relationship between worker and client has for the best part of 100 years been the mainstay of probation, and yet has recently been eroded by an increased emphasis on punishment, blame and managerialism. The views of offenders are in direct contradiction to these developments within the criminal justice system and this article argues that only by taking account of the views of those at the 'coal face' will criminologists, policy makers and practitioners be able to effect real change in crime rates. The article thus focuses on the views of a sample of previously persistent offenders in Scotland about offending, desistance and how the system can help them. It explores not only their need for friendship and support in youth but also the close association between relationships and the likelihood of offending. It also demonstrates the views of offenders themselves about the importance of the working relationship with supervising officers in helping them desist from crime. The article concludes that the most effective way of reducing offending is to re-engage with the message of the Probation Act of 100 years ago, namely, to 'advise, assist and befriend' offenders rather than to 'confront, challenge and change' offending behaviour