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

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

The objective of this thesis is to study methods for the flexible and secure storage of sensitive data in an unaltered cloud. While current cloud storage providers make guarantees on the availability and security of data once it enters their domain, clients are not given any options for customization. All availability and security measures, along with any resulting performance hits, are applied to all requests, regardless of the data's sensitivity or client's wishes. In addition, once a client's data enters the cloud, it becomes vulnerable to different types of attacks. Other cloud users may access or disrupt the availability of their peers' data, and cloud providers cannot protect from themselves in the event of a malicious administrator or government directive. Current solutions use combinations of known encoding schemes and encryption techniques to provide confidentiality from peers and sometimes the cloud service provider, but its an all-or-nothing model. A client either uses the security methods of their system, or does not, regardless of whether the client's data needs more or less protection and availability. Our approach, referred to as the Data Storage Facilitating Service (DSFS), involves providing a basic set of proven protection schemes with configurable parameters that encode input data into a number of fragments and intelligently scatters them across the target cloud. A client may choose the encoding scheme most appropriate for the sensitivity of their data. If none of the supported schemes are sufficient for the client's needs or the client has their own custom encoding, DSFS can accept already encoded fragments and perform secure placement. Evaluation of our prototype service demonstrates clear trade-offs in performance between the different levels of security encoding provides, allowing clients to choose how much the importance of their data is worth. This amount of flexibility is unique to DSFS and turns it into more of a secure storage facilitator that can help clients as much or as little as required. We also see a significant effect on overhead from the service's location relative to its cloud when we compare performances of our own setup with a commercial cloud service.

Thesis (M.Phil.)--University of Hong Kong, 2003. / Includes bibliographical references. Also available in print.

Computer data storage is growing at an astonishing rate. With cloud computing and the growth of the Internet enterprise storage has been predicted to grow at rates as high as 300\% per year. To fulfill this need technologies such as Redundant Array of Independent Disks or RAID are being used in industry today. Not only does RAID increase I/O performance but also provides redundancy measures to protect against hardware failure. Even though RAID has existed for some time now and is well understood, proprietary optimizations such as command scheduling and cache strategies that are employed by current RAID controllers are not well known. This thesis presents a model for RAID 5 that incorporates these features and describes the overall function of hardware RAID controllers. Also a python implementation of this model, Accurate Hardware RAID Simulator (AHRS) is presented and validated against a current hardware RAID controller. It is shown that AHRS can reproduce the behavior of a hardware RAID system with an accuracy of 97.92\% on average compared to a LSI hardware RAID controller.

Call number: LD2668 .T4 1946 M6 / Master of Science

Call number: LD2668 .T4 1953 M8 / Master of Science

This investigation was concerned with the reduction of waste in raw vegetables and fruits between the times of harvest and consumption. Reduction of spoilage in produce was attempted by means of chemical and. physical agents as well as a combination of both. The first phase of the work consisted of an evaluation of a number of chemical compounds with respect to their effectiveness in reducing post-harvest spoilage. The second part dealt with an evaluation of several transparent films applied to raw produce as wrappers and their effect on the keeping quality of the plant material until consumed. Finally combinations of surface disinfection and overwrapping were evaluated for effectiveness against raw produce spoilage. 1. Disinfection Approximately 26 compounds were tested as aqueous dips using 3 concentrations of each on 7 major vegetables and 2 fruits. The following types of compounds were studied. 1. Quaternary ammonium compounds (chlorides, bromides and pyridinium derivatives) 2. Chlorine liberators (organic and inorganic) 3. Phenols (simple and poly-phenols) 4. Quinones and hydroquinones 5. Salts of fatty acids 6. SO₂ liberators 7. Benzoates The chemical treatments were evaluated for each produce by comparison with untreated controls using duplicate tests with triplicate samples for each chemical and concentration. Promising treatments were found for all but one produce (strawberries). The treatments showing promise for each of Pascal celery and Emperor grapes were further tested on a larger scale uaing commercial size units of produce as test samples and long term cold storage. Three chemical treatments for each product were judged satisfactory enough to warrant further testing by means of field trials. The chemicals found most promising for celery were Onyxide, Cetab and Decco while Roccal, Dowicide C and Phygon were selected for grapes. A field test of the three above mentioned treatments for Pascal celery was completed. One thousand bunches per chemical were tested under commercial conditions of dipping and storing. An equal number of untreated bunches was also tested. Half-lots of each treatment were evaluated on each bunch for 11 subjective characteristics and standard mold and bacterial counts of each crate of celery were made after 8 and 14 weeks of storage. On the basis of a statistical analysis of the results, 0.1% Decco of pH=5 can be recommended for the reduction of general rot development in cold storage Pascal celery. Onyxide and Cetab significantly reduce the development of mold but commercial application cannot be recommended because the amount of visible stalk injury was significantly increased over that shown by corresponding untreated or Decco treated celery. 2. Prepackaging The following films were compared for their merit in prolonging the salable life of raw produce. Pliofilm 75FF, Pliofilm 75N2, Pliofilm 75P6A, Cellophane 300LSAT, Cellophane 300MSAT-86, Lumarith P-912, Dupont Acetate 100CA48, Polythene and Kodapak II-130. Wrapping techniques were also evaluated using the followng variations; Complete seals, tent-flap closures, single hole punctures, multiple punctures and windo bags. The following products were studied: celery, tomatoes, carrots, lettuce, cauliflower, chopped salad mix, spinach, strawberries, raspberries, blackberries, and boysenberries. Harvested produce was packaged both before and after the removal of field heat. Behavior of the pre-packaged products in both 33°F storage and subsequent 8O°F storage was studied. Cold storage was extended as long as 120 days while subsequent holding at room temperature varied widely from produce to produce. Observations were made at regular intervals for each product. Several hundred uniform samples were evaluated for most products using duplicates of each treatment for every observation period. Evaluation of most samples included weightloss, C0₂ (and sometimes O₂) of the container atmosphere, mold and decay development, flavor, color, odor, wilting and shriveling. The following conclusions were drawn: All films and wrapping methods affect produce quality. For each produce, treatments could be singled out which were superior to unwrapped controls. However any particular film and type of seal found to be superior for one produce was often not acceptable for another fruit or vegetable. Among the factors found to be critical for the proper choice of treatment were type of produce, produce temperature when packed, length of storage, and temperature of storage. A. Cold Storage For most products, the partially sealed, low permeability MSAT containers and the completely sealed Polythene wraps scored highst for overall product quality. These treatments prevented the accumulation of undesirable CO₂ while at the same time protecting the produce against weightloss and consequent wilting. For some produce, especially berries, wilting was not apparent even in high permeability films such as acetates. B. Warm Storage For produce with high respiration rates (spinach, and berries) only acetate films were acceptable as wraps. The partially sealed low permeability films maintained good quality in warm storage but the high humidity within the package was conducive to micro-organism activity. Thus, in many cases samples disinfected prior to packaging in those films improved the warm storage quality. Disinfection also improved the quality of tomatoes and chopped salad mix in acetate wraps. Of the high permeability films, no significant difference was found among the Dupont acetate, Lumarith and Kodapak II. The type of seal also did not affect the characteristics of these wraps. The low permeability films differed principally in the amount of CO₂, retained by the container during storage. The Pliofilms retained the highest C0₂, levels followed by LSAT and then MSAT Cellophane. The sealed polyethylene, the single puncture and tent flap MSAT wraps exhibited similarity, especially with respect to C0₂ accumulation. The multiple puncture low permeability wraps showed characteristics between acetates and the last mentioned group. Correlation between CO₂ accumulation and off-flavor formation could be determined for most products. Higher CO₂ levels were tolerated at short storage intervals without off- flavor formation by most products but the rate of change in CO₂ tolerance varied from produce to produce. Correlation between % weightioss and degree of wilting could also be expressed as a function of the pre-packaging treatments used. Storage infection was eliminated by all films independent of the type of seal used. It should be emphasized that only a study of the resuits and relationships discussed under each product can serve as a basis for future work and commercial application of the methods presented in this work. / Graduation date: 1950

Call number: LD2668 .T4 1986 E86 / Master of Science / Grain Science and Industry

"Large amounts of renewable energy generation are being introduced into modern power systems to decrease the environmental impact of power generation. Despite benefits, increased renewable energy penetration will likely create additional system instability and unpredictability. Increasing line capacity via redundancy of transmission networks and utilizing energy storage are two methods that can be used to increase transmission power system stability. This thesis investigates the economic effects of energy storage and line capacity in isolated test systems. Utilizing Powerworld Simulator, test systems based off two common industry test bed standards (WECC 9-bis, IEEE 14-bus) were built using scaled real-world generation and load data. Multiple Optimal Power Flow studies performed on the test systems with and without the addition of energy storage model revealed the incremental change in overall system cost of adding energy storage and highlighted the impact energy storage has on isolated systems with renewable energy."