An associative, or content-addressable, memory, one in which data may he retrieved "by its value rather than by real address, has always been an attractive idea. Although such a memory has not yet proven practical for files of respectable size, much interesting work has been done on the subject, for example, Minsky (1972), Slotnick (1970) and Parker (1970, 1971). This thesis is concerned with the device proposed by Slotnick and Parker, called 'Logic Per Track Device'. After briefly reviewing the design and capabilities of their device, the thesis proceeds to propose some modifications to the design which not only lead to greatly enhanced performance, but also establish its practical application for files of respectable size. In the device of Slotnick and Parker, there is a fairly sophisticated logic chip attached directly to each non-movable read-write head. This allows all logic heads to search simultaneously for information matching a given key, so that any desired record could be located within one revolution. However, reading and writing will require a second revolution because part of the record will have passed the head before the match is recognized. Moreover, if more than one record matches the search key, the extra bookkeeping will be needed if matching records on different tracks should partially overlap. These problems have been ignored in the retrieval system developed by Parker (1970, 1971). The following four additional features of the device have been proposed: 1. Two logic heads on each track has been introduced. The leading head will continue to have the primary responsibility for simultaneous searching. The additional second head, trailing a fixed distance behind will do the actual reading and writing of records. 2. A delay register whose length is the distance between logic heads on the same track, has been added to the read-write head. The function of the delay bit is to tell the read-write head partner where to start reading (or writing) a record whenever a match is recognized so that retrieving (or writing) a single record can always be performed in the same revolution. 3. Another major design change will give the new device the ability to keep track of all records which may be retrieved within a single revolution by parallel search. To this end, the monitor, which synchronizes the activities of all logic head couples, will be provided with a record counter, and a mark entity will be prefixed to every record on the disk itself. A file identification mechanism has been established for the associative memory. Functions of such a mechanism are (a) to manage file names, and (b) to manipulate data on the storage device. Next step is to explore the use of such a modified device for file-oriented problems. 'Hierarchical search' for records possessing a specified combination of keys can be performed directly on the key part of records without the intermediate step of transmitting records into the main computer memory. In an application requiring chain processing, the chain pointer can he a key of the record because each record in the associative memory is accessed by content rather than by real address. The chain key can be generated from the key if the record it points to by a simple and reversible procedure. Such a chain technique has a number of advantages: (a) any chain is in fact a two-way chain, (b) each record in the chain can be retrieved by following the chain key, or directly by the key of the record if it is known, and (c) the tangle of actual physical addresses in the chain processing can be avoided. The storage organization for more complex data structure such as tree structures presents another unique feature of the modified memory. In a tree structure, indexes to the subordinate records may be kept with each parent record, or each subordiante recoEdsnjaays^tDreaaniaindsx to its parent record. Both data structures take the same amount of storage space. Comparison <3f its performance to the convent tional counterpart shows that significant improvements in access times can be achived. / Science, Faculty of / Computer Science, Department of / Graduate

M.Ing. / Ice storage systems are used to store thermal energy in the form of ice build-up inside storage tanks. During off peak hours, the chiller is used to charge up the storage tank until it is full. During on peak hours, the storage is discharged to meet a certain fraction of the building cooling load. The control strategy employed determines the extent to which the storage compensates the chiller and visa versa. Given the way in which electricity rates are structured, ice storage systems become an effective energy management strategy. The objective of the study is to compare energy savings derived by using conventional control strategies versus optimal control. Conventional control strategies can be classified as chiller priority control, constant proportion control and storage priority control. In chiller priority control, the chiller meets the cooling load subject to a pre-set limit not being exceeded. Should the limit be exceeded, the remaining cooling load (at each time horizon) is compensated for by the storage. In constant proportion control, both the storage and chiller meets a constant proportion of the cooling load. Storage priority control attempts to discharge as much of the storage as possible, such that at the end of the planning horizon, the ice build up in the storage tank is just depleted. Optimal control employs dynamic programming to ensure that the integrated cost of energy, during the entire planning horizon, is minimal. A steady state ice storage plant model for analysing the performance of the control strategies is presented. The model computes the inlet and outlet temperatures into the various components of the air-conditioning plant, being the air-handling units, heat exchanger, ice storage tanks and chiller. The maximal possible discharge and charging rate at each time period (for the different control strategies) is determined using the model. Given the state of charge of the ice storage tank at each time period, it is then possible to calculate chiller power consumption. The power consumed by fans, fan coil units and pumps (in the air-conditioning plant) has not been calculated in the present analysis, however, the model can easily be extended to include such calculations. The ice storage plant model, enabled simulations of the different control strategies to be carried out over building cooling load profiles for summer and winter. Based on a 24-hour planning horizon, optimal control is found to be optimal and the only consistently performing strategy for all seasons. For the 5000 kWh ice storage plant investigated, optimal control yielded 25% energy savings in June and 12% in January, amounting to a potential of R 11 000 per month. Chiller priority control was near optimal in January but consumed 25% more energy than the base case (without storage) in June. Constant proportion control was optimal in January but poorer in June. Storage priority control is found to be optimal in June but the lowest performer in January. The drawback of optimal control and storage priority control, however, is that they require prediction of future cooling loads. The variance when using auto-regressive neural network to predict the load is expected to be in the region of 2% and thus considered acceptable. Chiller priority control and constant proportion control are instantaneous and simple to implement hence their popularity.

No description available.

Three applications of Smith's model of magneto-optical effects in stratified magnetic media are presented. Each application involves the incident-angle dependence of magneto-optical effects which Smith's model treats explicitly. In addition. the three applications address current issues in magnetic and magneto-optical recording. The first problem considered is that of nonmagnetic surface layers which form on magnetic recording heads. The second is a theoretical treatment of effects which arise in magneto-optical recording when high numerical-aperture optical systems are combined with media exhibiting interference-enhanced optical properties. The final application is a novel technique for determining the entire dielectric tensor of materials used for magneto-optical recording. The incident-angle dependence of the longitudinal Kerr effect is employed to study nonmagnetic surface layers which form on ferrite recording heads. Calculations based on the Smith model show a correlation between the inert-layer thickness and the incident-angle dependence of the longitudinal Kerr effect. Experimental results confirm the shift in the angular position of the signal peak. in agreement with the theory for finite inert-layer thickness. An unambiguous determination of the inert-layer thickness for ferrite materials is prevented because of a periodic dependence of the peak angle on the inert-layer thickness. Jones-matrix algebra is used with the Smith model to quantitatively determine the effects of obliquely-incident rays on the reflectance and magneto-optical readout signals for various magneto-optical media structures. The most antireflective structure is found to be very sensitive to incident-angle effects. Structures with moderate reflectance (>10%). however. are not significantly affected by incident-angle effects. Finally. a technique for the determination of the optical and magneto-optical constants from multiple incident-angle measurements of reflectance and Kerr rotation is presented. The experimental system employs a Helium-Neon laser and a rotating differential detection system. The technique is used to investigate the optical properties of a series of Cu/Co multilayers and a comparison with a model based on the bulk optical. constants of Cu and Co is made. Anomalous behavior is observed for multilayers with very thin periods.

Light can be coupled out of a waveguide to a focused point by a focusing grating coupler and has possible applications in optical data storage. The grating can be fabricated with either e-beam techniques or holographic techniques. Two design methods are demonstrated that model the focusing grating coupler with holographic optical elements. Both methods take a geometrical optics approach to designing the holographic optical elements and both methods make use of commercially available ray trace programs. The first method uses complicated non-rotationally symmetric construction optics and requires either a modified ray trace program or special user defined surfaces. The second method involves a much simpler approach which did not require any changes to an existing ray trace program and requires only rotationally symmetric elements to correct the aberrations.

This study develops the foundation of a digitally implemented control system for the radial positioning of the read/write heads of an optical disk drive system. Topics addressed are: sample rate selection, state reconstruction, closed-loop system response, disk track-following filters, and measurement noise filters. Consideration is given to the unmodeled dynamic's influence on system performance, system sensitivity to parameter variations, and a one sample computational delay. What has been concluded from this work is that the system must be further desensitized to parameter variations, and, at this stage of the development of the control scheme, neither a computational delay nor the unmodeled dynamics degrade system performance significantly.

Digitized by Kansas Correctional Industries

Digitized by Kansas Correctional Industries

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2006. / Title from title screen (site viewed on Feb. 6, 2007). PDF text: vii, 138 p. : ill. (some col.). UMI publication number: AAT 3216420. Includes bibliographical references. Also available in microfilm and microfiche format.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: XML; path expression; axis; order; indexing; inlined; compression; XPath; lossless. Includes bibliographical references (p. 45-46).