The focus of this thesis is on systems that employ both flash and magnetic disks as storage media. Considering the widely disparate I/O costs of flash disks currently on the market, our approach is a cost-aware one: we explore techniques that exploit the I/O costs of the underlying storage devices to improve I/O performance. We also study the asymmetric I/O properties of magnetic and flash disks and propose algorithms that take advantage of this asymmetry. Our work is geared towards database systems; however, most of the ideas presented in this thesis can be generalised to any data-intensive application. For the case of low-end, inexpensive flash devices with large capacities, we propose using them at the same level of the memory hierarchy as magnetic disks. In such setups, we study the problem of data placement, that is, on which type of storage medium each data page should be stored. We present a family of online algorithms that can be used to dynamically decide the optimal placement of each page. Our algorithms adapt to changing workloads for maximum I/O efficiency. We found that substantial performance benefits can be gained with such a design, especially for queries touching large sets of pages with read-intensive workloads. Moving one level higher in the storage hierarchy, we study the problem of buffer allocation in databases that store data across multiple storage devices. We present our novel approach to per-device memory allocation, under which both the I/O costs of the storage devices and the cache behaviour of the data stored on each medium determine the size of the main memory buffers that will be allocated to each device. Towards informed decisions, we found that the ability to predict the cache behaviour of devices under various cache sizes is of paramount importance. In light of this, we study the problem of efficiently tracking the hit ratio curve for each device and introduce a lowoverhead technique that provides high accuracy. The price and performance characteristics of high-end flash disks make them perfectly suitable for use as caches between the main memory and the magnetic disk(s) of a storage system. In this context, we primarily focus on the problem of deciding which data should be placed in the flash cache of a system: how the data flows from one level of the memory hierarchy to the others is crucial for the performance of such a system. Considering such decisions, we found that the I/O costs of the flash cache play a major role. We also study several implementation issues such as the optimal size of flash pages and the properties of the page directory of a flash cache. Finally, we explore sorting in external memory using external merge-sort, as the latter employs access patterns that can take full advantage of the I/O characteristics of flash memory. We study the problem of sorting hierarchical data, as such is necessary for a wide variety of applications including archiving scientific data and dealing with large XML datasets. The proposed algorithm efficiently exploits the hierarchical structure in order to minimize the number of disk accesses and optimise the utilization of available memory. Our proposals are not specific to sorting over flash memory: the presented techniques are highly efficient over magnetic disks as well.

Kryžiažodis - žaidimas, kuriame spėjami žodžiai ir įrašomi į tam tikru būdu piešiamus langelius. Dažniausiai žodžiai susikerta. Kryžiažodžiai yra laikomi populiariaisiais ir labiausiai pasaulyje paplitusiais galvosūkiais. Magistro darbo teorinėje dalyje aprašomi kryžiažodžių tipai, analizuojamos esamos kryžiažodžių kūrimo programos, šablono sąvoka. Praktinėje dalyje aprašoma sukurta programa, jos veikimo principai, problemos, su kuriomis buvo susidurta programos kūrimo metu. Šis darbas demonstruoja ActionScript 3 technologijos galimybę, efektyvumą. Darbo metu susipažinta su nauja Adobe AIR technologija. / Crossword is a game in which you write words which are the answers to questions in a pattern of specially drawn squares. Mostly words intersect. Crosswords are thought to be the most popular and the most widely spread puzzles. In the theoretical part of master paper types of crosswords are described, existing crossword making programmes are analyzed. The created programme, its working principles, problems faced while creating it are described in the practical part. This paper demonstrates possibility and efficiency of ActionScript 3 technology. In the process of work new Adobe AIR technology faced.

Baigiamajame magistro darbe nagrinėjamos vartotojo sąsajos, naudojančios vektorinę grafiką, integracijos su ekspertinėmis sistemomis galimybės. Apžvelgti esami integracijos sprendimai, ekspertinių sistemų kūrimo metodai. Nagrinėjama JESS sistemos architektūra. Aprašomos vektorinės grafikos kūrimo sistemos. Praktinėje baigiamojo magistro darbo dalyje pateikiamas integracijos prototipas. Išnagrinėjus teorinius ir praktinius aspektus, pateikiamos baigiamojo darbo išvados ir pasiūlymai. Darbą sudaro 5 dalys: įvadas, analitinė dalis, tiriamoji dalis, išvados ir siūlymai, literatūros sąrašas. / The MA thesis examined the possibilities of user interface, which uses vector graphics, integration of expert systems, reviewed the existing integrated solutions, expert systems development methods. MA thesis examines JESS system architecture, describes the creation of vectorgraphics systems. The practical part provides a prototipe of integration. Afterwards the conclusions and recommendations are given. The work consists of five parts: introduction, analytical part, research, conclusions and suggestions, references.

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This research explores a higher order of fast tracking, called Flash Tracking, in response to increasing calls for faster, more reliable project deliveries. Flash Tracking is defined as a time-driven project, which by necessity requires a heightened degree of concurrency between engineering, procurement, and construction. In contrast to fast tracking, which entails a level of concurrency between engineering, procurement, and construction that has become a staple of the construction industry, Flash Tracking extends the envelope by requiring a series of innovative practices across the project delivery spectrum. The specific research questions pursued include: 1) identifying which innovative improvements in project delivery methodology could be made to compress project durations, while maintaining safety, quality, and risk tolerance, and 2) addressing how project teams can best overcome barriers to delivering shorter project durations. A multi-method research project was undertaken to address these questions, which entailed an extensive review of the literature, structured case study interviews, and multiple group decision-making exercises. The literature review focused on the construction industry, as well as manufacturing, shipbuilding, and software development, to identify practices and techniques potentially relevant to Flash Tracking that could be extended to the construction industry. Group decision-making exercises included a modified Delphi method study, an Analytic Hierarchy Process, and a series of research charrettes or focus groups. These studies produced a prioritized, two-tiered listing of 47 essential Flash Track practices, providing practitioners with both a measure to assess their readiness for undertaking a Flash Track project and strategies for increasing their readiness. A subsequent study--a semantic network analysis--refined and buttressed the research team’s earlier findings. This two-year study, conducted in concert with industry experts, led to a re-engineered engineering, procurement, and construction (EPC) model which embraces relational contract strategies, improved communications, and the early engagement of key stakeholders.

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In this MS thesis, a redundant flash analog-to-digital converter (ADC) using a ``Split-ADC' calibration structure and lookup-table-based correction is presented. ADC input capacitance is minimized through use of small, power efficient comparators; redundancy is used to tolerate the resulting large offset voltages. Correction of errors and estimation of calibration parameters are performed continuously in the background in the digital domain. The proposed flash ADC has an effective-number-of-bits (ENOB) of 6-bits and is designed for a target sampling rate of 1Gs/s in 180nm CMOS. The calibration algorithm described has been simulated in MATLAB and an FPGA implementation has been investigated.

Thesis (Ed.M.)--Boston University