A computer simulation of unbiased sine wave recording

A computer simulation is described which uses the approximation that the output voltage derives from longitudinal tape magnetization acquired solely from the longitudinal head field. Using a simple noninteractingM_{r}-Hmodel, the remanent state of 200 points per half-wavelength of tape is calculated by following each point's field history as it passes the record head. We discuss the amplitude and phase angle of the magnetization sinusoids obtained by harmonic analysis. At short wavelengths (wavelength less than coating thickness) we find, for regular γ-Fe2O3tape, that although the peak output is limited by record head field gradient effects, the over-recording phenomenon is attributable to the field shape. The process of "optimizing" the record current is thus shown to be explicable in terms of the record head field geometry. These conclusions hold equally for "partial penetration" recording of high density digital waveforms.     

Optimum media thickness for digital recording

Thinner media yield narrower output pulses, and in many low density digital recorders this leads to better performance. In high density applications, however, the signal-to-noise ratio (SNR) is of greater importance than pulsewidth. The SNR depends on both the write process and the origin of the dominant noises. Several types of media noise, reproduce head, and electronic noises are discussed. A method of determining the media thickness yielding the highest SNR is outlined. The results are dependent upon the noise sources and we conclude that a generally valid rule cannot be given. In some cases a thicker medium may be preferable to a thinner one and vice versa.     

Off-Track and Azimuth Angle Effects in Perpendicular Replay

We investigated the effects of transition curvature on T₅₀ and V_p-p for a shielded giant magnetoresistive (GMR) element reading a single, isolated transition recorded on a perpendicular medium in the presence of a soft magnetic underlayer. We considered displacement and rotation of the read head relative to the recorded track and a range of read head geometries. The curvature of the transition adversely affects T₅₀, which also increases with azimuth angle. Both T₅₀ and V_p-p decrease as either the GMR element or the element-side shield spacing is reduced     

Housing for Health: The Role of Owner Occupation

Housing is widely regarded as playing an important role in the mediation and management of health inequalities. British policy-makers are increasingly looking to the research community to specify what it is about housing environments that impact on health, and to identify what housing interventions constitute healthy public policies. To feed into this debate, this paper begins by reviewing the state of the art of research on housing and health. It shows that the majority of work continues to focus on how housing affects health, while the limited attention to how health status affects housing outcomes has concentrated on medical priority for rehousing in the public sector. It is argued, however, that the market sector now merits closer scrutiny among those concerned with the health selectivity of the housing system. Drawing on a series of qualitative interviews, questions are raised about: how readily people with health problems and mobility difficulties gain access to owner occupation; how easily they sustain a position in that tenure sector; and how effective they are in maintaining their homes as healthy enabling living environments.     

Effects of HZSM-5 crystallite size on stability and alkyl-aromatics product distribution from conversion of propanal

The conversion of propanal on large (2–5 µm) and small (0.2–0.5 µm) crystallite HZSM-5 at 400 °C and atmospheric pressure has been studied. Improved catalyst stability was observed on small crystallites due to faster removal of products with the shorter diffusion path length, reducing the formation of coke precursors. As previously shown, C₉ aromatics are the initial aromatics produced from propanal via aldol condensation followed by cyclization and these have less opportunity to crack to lighter aromatics on the small crystallites. Thus, a higher ratio of C₉/(C₈+ C₇) aromatics was observed on the small crystallites. The main isomer of the C₈ aromatic products observed on small crystallites was the initial cracking product of the C₉ aromatics, and thermodynamically preferred, meta-xylene, while the shape-selective preferred para-xylene was the predominant product on large crystallites. The higher internal diffusion rate of the para isomer results in greater shape selectivity with the longer path of the large crystallite zeolite. It is concluded that the use of smaller crystallite HZSM-5 improves results for production of alkyl aromatics from light oxygenates at mild conditions that may prove useful for bio-oil upgrading.     

Achievements in rotary head magnetic recording

The principal achievements since 1980 in rotary head recording on magnetic tape are outlined. These developments are related to fundamental improvements in recording media, heads, the design of tape transports, and signal processing. The D-1 and D-2 video tape recorders (VTRs), the Hi-Band 8-mm video cassette recorder (VCR), and the rotary digital audio tape (R-DAT) recorders are discussed. The future of rotary head recorders for consumer digital VCRs, professional high-definition TV (HDTV) VTRs, and consumer HDTV VCRs is assessed     

The next decade in magnetic recording

Experimental data are given on the recording performance of several modern magnetic recording materials. On the basis that the signal to reproduce head noise will prove to be the eventual limit, estimates of the attainable recording densities are made. Areal densities of several hundred megabits per square inch are forecast.