41 research outputs found
On the hysteresis and the recording process in magnetic media
No full textThe information densities in magnetic recording systems have been in- creased considerably over the last few decades. Much af the gain in the in- formation density can be ascribed ta the improvement af the magnetic prop- erties af the recording media. However, recording on a magnetic medium is a camplex process which, despite extensive research in the past, is only partly understood. The purpose af the research described in this thesis is ta contribute towards a better understanding af the recording process. The approach that has been followed is a combination af experiment al study with numerical modelling. The thesis consists af four parts, two on the magnetic hysteresis and two on the recording process. 1: Experimental study of the hysteresis The technique af magnetic recording is possible only thanks ta the magnetic hysteresis. (Hysteresis is the property af magnetic media ta remain magne- tized af ter a temporary exposure ta a magnetic field. ) Two new methods for studying the hysteresis af recording media have been developed. The first methad is based upon a generalization af the Wohlfarth re- lation. With this methad, the interactions between the magnetic units in the medium can be studied. In the original methad, the effects af these interactions could be compared for only two initial states af the material, the bulk-erased and the entirely-magnetized state. The generalization en- ables a comparison ta be made between any two initial remanent states. Application af this new methad on a particulate tape sample has revealed the complexity af the interactions. The second methad cap be used ta study the intrinsic magnetic proper- ties af recording media, irrespective af their easy magnetization direction. The demagnetizing fields that may arise from components af the magne- tization perpendicular ta a sample are compensated in this methad. The methad has been applied ta a sputtered Co-Cr medium and a Metal Evap- orated Go-Ni-O medium. The results show that there is a remarkablë re- semblance between these two media in respect of the angular dependence of their coercivity. 2: Modelling the hysteresis For an accurate simulation of the magnetic hysteresis process, the well- known moving-Preisach and Stoner-Wohlfarth hysteresis models have been combined. With a simple modification, a fast numerical implementation of the combined hysteresis model has been obtained. The magnetic interac- tions, incorporated in a fashion similar to that used in the moving-Preisach model, can account for many of the details of the minor loops, including the anhysteretic susceptibility. The vector properties of the new hystere- sis model are the same as those of the Stoner- Wohlfarth model. With the combination of the two models, the hysteresis 100ps of different recording media, including the Metal Evaporated Go-Ni-O medium, can be repro- duced very accurately. Only the very fine details of the hysteresis process, involving the interactions between the magnetic units, are not simulated correctly. This has been demonstrated with the new method for studying these interactions. 3: Experimental study of the recording process Much about the recording process itself can be learned from specific record- ing experiments. The recording process on thick particulate media has been investigated by applying a new analysis method. This method is based upon a scaling argument. The length of a magnetic transition is assumed to be proportion al to the magnetic potential over the gap of the recording head. With this scaling-based analysis, the spacing 1088 can be estimated from a series of frequency responses measured at selected yalues-of the recording current. The method yields a reasonably accurate indication of the head- to-tape spacing. However, the indicated value is somewhat sensitive to the range of recording currents usesl in the experiments. Application of the method to different particulate recording media shows that the Hi8 MP tape has the best intrinsic frequency response, whereas un-oriented barium ferrite media have a relatively high optimal recording depth. Entirely different phenomena are encountered when thin Go-Gr me- dia with a perpendicular easy axis orientation are rec?rded with a ring head. Additional minima appear in the frequency response of these media. The occurrence of these minima can be described with a double-transition model, in which the transition recorded at the leading edge of the recording head is only partially erased at the trailing edge. 4: Modelling the recording process The basic principles of the recording process can be understood from simple recording models. For a more detailed simulation of the recording process, the combined hysteresis model has been implemented in a numerical record- ing model. A modified Newton iteration scheme reduces the computation time considerably. The scaling-based analysis has been evaluated with this recording model. The assumptions on which the analysis was based proved not to be justified. However, owing to a cancellation of errors, the value of the head-to-tape spacing that results from the analysis is still within 25% of the actual value. The recording model is still under development. Simulations with the current version show that the basic recording characteristics of very differ- ent tapes can be reproduced within 2 dB. However, similar results can be obtained with simpIer models. Future research will have to show that this new recording model is better suited for also reproducing more complex phenomena such as overwrite and bias recording
De rol van ontwerp volgens publieke en private opdrachtgevers
No full textDe kracht van het (stedenbouwkundig) ontwerp staat weer op de agenda. Waar in de eerste sLIM Masterclass het begrip complexiteit werd ontrafeld, stond in de tweede sessie op 20 mei het publieke en private perspectief centraal. Na een introductielezing van initiator Agnes Franzen kwamen Ton Schaap van de gemeente Amsterdam en Hans-Hugo Smit van gebiedsontwikkelaar BPD aan het woord, gevolgd door scherpe reacties van referenten
Active learning in redesigning mathematics courses for engineering students
No full text“Prepare, Participate, Practice”: active learning in designing basic maths courses for engineering students at TU Delft works! The PRoject Innovation Mathematics Education (PRIME) at Delft University of Technology (TU Delft) is all about redesigning mathematics courses for engineers. This paper describes the process of developing, implementing, evaluating and implementing again of three basic courses at TU Delft using a blended learning approach developed by a growing team of teachers from the mathematics department. Our findings suggest that the approach taken enhances students’ learning performance in maths education. The main results show that students have a more active learning experience compared to the traditional setup of these courses, leading to more engagement, more interaction and better results. An important role is played by meaningful examples taken from the engineering faculty where the students are studying, showing students from that faculty what role the mathematics play in their field of interest. This is also used to develop their skills in mathematical modelling.StatisticsTeaching & Learning Service
FORECASTING SPOT ELECTRICITY PRICES WITH TIME SERIES MODELS
No full textIn this paper we study simple time series models and assess their forecasting performance. In particular we calibrate ARMA and ARMAX (where the exogenous variable is the system load) processes. Models are tested on a time series of California power market system prices and loads from the period proceeding and including the market crash.Electricity, price forecasting, ARMA model, seasonal component
Ventricular Activity Signal Removal in Atrial Electrograms of Atrial Fibrillation
No full textDiagnosis and treatment of atrial fibrillation can benefit from various signal processing approaches employed on atrial electrograms. However, the performance and interpretation of these approaches get highly degraded by far-field ventricular activities (VAs) that distort the morphology of the pure atrial activities (AAs). In this study, we aim to remove VAs from the recorded unipolar electrogram while preserving the AA components. To do so, we have developed a framework which first removes the VA-containing segments and interpolates the remaining samples. This will also partly remove the atrial components that overlap with VA signals, e.g., during atrial fibrillation. To reconstruct the AA components, we estimate them from the removed VA-containing segments based on a low-rank and sparse matrix decomposition and add them back to the electrograms. The presented framework is of rather low complexity, preserves AA components, and requires only a single EGM recording. Instrumental comparison to template matching and subtraction and independent component analysis shows that the proposed approach leads to smoother results with better similarity to the true atrial signal.Signal Processing System
The Vibe of Skating: Design and Testing of a Vibro-Tactile Feedback System
No full textProviding athletes with real-time feedback on their performance is becoming common in many sports, also in speed skating. This research-by-design project aims at finding a tool that allows the speed skater to get real-time feedback on his performance. Speed skaters often mention a so-called “good feeling” when skating behind a better skater. It is the feeling nearly every speed skater is after when skating alone; skate with less power while maintaining the same speed and feeling of ease. A longer push-off phase at a constant cadence has proven to contribute to this ideal situation but is hard for the coach alone to influence this. Therefore, a system was designed that measures the skating cadence and challenges the skater to change his skating stroke by means of vibro-tactile feedback. Four subjects have tested the feedback system. From this test, we concluded that the system provides meaningful feedback towards changing the skating cycle.Product Architecture DesignApplied Ergonomics and Desig
Investigating Recording Patterns Using Magnetic Force Microscopy
No full textThe magnetic force microscope is a valuable tool for the qualitative analysis of local phenomena in magnetic recording media. To study the possibilities for a more quantitative analysis, the MFM results have been compared with recording results. It is shown that such analysis is hampered by the nonlinear transfer characteristic and by the masking of local high-definition details due to the application of an auxiliary electrostatic field in the current instrument
Understanding Creative Partnerships: An examination of policy and practice
No full textCreative Partnerships was launched in 2002 as an arts-based education programme that aimed to transform the aspirations of young people living in socially and economically deprived areas of England. The organisation was established in response to the National Advisory Committee on Creative and Cultural Education (NACCCE, 1999), which offered an account of creativity as a means to foster individual self-reliance and social unity. This thesis explores how the NACCCE’s construction of creativity enabled New Labour to appear to endorse the value of the arts in education whilst promoting the model of the self as an autonomous economic unit, and considers how Creative Partnerships was paradoxically welcomed by supporters of the arts in education who were displeased with the instrumentalism at work in much of New Labour’s education policy. The aim of this thesis is to understand Creative Partnerships by examining the discourse that constitutes the programme, and by offering an empirical enquiry into a project that took place within a secondary school in the north of England. In so doing, this thesis critically evaluates the political motivation for the use of arts-based education as a means to develop self-reliance, and considers how successive governments have imported the free market economic model into education to promote efficiency, and the role that Creative Partnerships might be said to play in the maximisation of the total social system. Finally, this thesis considers the current limitations of Creative Partnerships, and how arts-based education might be used to develop social cohesion
Transient observations : the textualizing of St Helena through five hundred years of colonial discourse
No full textThis thesis explores the textualizing of the South Atlantic island of St Helena (a
British Overseas Territory) through an analysis of the relationship between
colonizing practices and the changing representations of the island and its
inhabitants in a range of colonial 'texts', including historiography, travel writing,
government papers, creative writing, and the fine arts.
Part I situates this thesis within a critical engagement with post-colonial
theory and colonial discourse analysis primarily, as well as with the recent
'linguistic turn' in anthropology and history. In place of post-colonialism's rather
monolithic approach to colonial experiences, I argue for a localised approach to
colonisation, which takes greater account of colonial praxis and of the continuous
re-negotiation and re-constitution of particular colonial situations.
Part II focuses on a number of literary issues by reviewing St Helena's
historiography and literature, and by investigating the range of narrative tropes
employed (largely by travellers) in the textualizing of St Helena, in particular
with respect to recurrent imaginings of the island in terms of an earthly Eden.
Part III examines the nature of colonial 'possession' by tracing the island's
gradual appropriation by the Portuguese, Dutch and English in the sixteenth and
early seventeenth century and the settlement policies pursued by the English
East India Company in the late seventeenth and early eighteenth century.
Part IV provides an account of the changing perceptions, by visitors and
colonial officials alike, of the character of the island's inhabitants (from the late
eighteenth to the early twentieth century) and assesses the influence that these
perceptions have had on the administration of the island and the political status of
its inhabitants (in the mid- to late twentieth century).
Part V, the conclusion, reviews the principal arguments of my thesis by
addressing the political implications of post-colonial theory and of my own
research, while also indicating avenues for further research.
A localised and detailed exploration of colonial discourse over a period of
nearly five hundred years, and a close analysis of a consequently wide range of
colonial 'texts', has confirmed that although colonising practices and
representations are far from monolithic, in the case of St Helena their continuities
are of as much significance as their discontinuities
