The topic of this thesis deals with the spiral structure in disk galaxies with a specific aim of probing the influence of the dark matter halo and the interstellar gas on the origin and longevity of the spiral arms in late-type galaxies through theoretical modeling and numerical calculations. The basic theoretical model of the galactic disk used involves gravitationally-coupled two-component system (stars and gas) embedded in a rigid and non-responsive dark matter halo, i.e., the static potential of the dark matter is used in the calculations. However, at places, depending on the nature of the problem addressed, the disk is treated as consisting of only stellar component or only gas component followed by proper justifications for the assumptions. The disk is rotationally-supported in the plane and pressure-supported perpendicular to the plane of the disk. The first part of the thesis involves searching for the dynamical effect of dark matter halo on small-scale spiral structure in dwarf low surface brightness (LSB) galaxies and also some dwarf ir-regular galaxies which host an extended H I disk. In both cases, the rotation curves are found to be dominated by the contribution of the dark matter halo over a large radial distance, starting from the inner regions of the galaxies. The next part of the thesis deals with the investigation of the possible effect of the interstellar gas on the persistence is-sue and the pattern speeds of the spiral structure in the disk galaxies. The last part of the thesis involves in studying the dynamical effect of dark matter halo on large-scale spiral structure. Following is the layout of the thesis. Chapter 1 gives a general introduction to the topic of spiral structure of late-type disk galaxies, followed by a broad overview of the theoretical development of the topic and the present status of the topic. Then the thesis starts with studying the small-scale spiral features and evolves to studying the large-scale spiral features seen in disk galaxies in the following way: Chapters 2 & 3 deal with the effect of dark matter halo on small- scale spiral structure. Chapters 4 & 5 focus on the dynamical effect of the interstellar gas on the spiral structure using the local dispersion relation. Chapters 6 & 7 discuss the possible effect of dark matter halo on large-scale spiral structure in disk galaxies. Chapter 8 contains the summary of results and future plans. Effect of dark matter halo on small-scale spiral structure The spiral arms in the disks of galaxies are often broken into several smaller parts or patches that create a messy visual impression when viewed from a ‘face-on’ configura-tion. They are generally termed as ‘small-scale’ or flocculent spiral arms. Several stud-ies showed that the small-scale spiral arms are basically material arm, i.e., they can be thought of as ‘tubes’ filled with stars and gas. Spiral arms are known to participate in the secular evolution of the disk galaxies. Since disk galaxies are believed to reside within a halo of dark matter, therefore a detailed understanding of possible effects of dark matter halo on the spiral arms is necessary. In Chapter 2, we investigate the effect of dark matter halo on small-scale spiral fea-tures in the disks of LSB galaxies. Modeling the mass distribution within a galaxy from the rotation curve of a typical small LSB galaxy reveals the generic fact that for most of the radii, dark matter halo dominates over the stellar disk. This trend is found to be true from the very inner regions of an LSB disk which in turn makes the LSBs a suitable laboratory for probing the effect of dark matter halo on the dynamics of disk galaxies. Following a semi-analytic approach, and using the observationally measured input pa-rameters for a typical superthin LSB galaxy, UGC 7321, we showed that the dominant dark matter halo suppresses the small-scale spiral structure in the disk of UGC 7321. Since UGC 7321 possesses features typical of a LSB galaxy, we argued that this finding will also hold true for other typical LSBs. The result is at par with the observational evi-dences for the lack of prominent, strong small-scale spiral structure in LSB galaxies. In Chapter 3, we employed the similar techniques for probing the effect of dark matter halo on small-scale spiral structure, except this time we took five dwarf irregular galaxies with an extended H I disk as the sample for our investigation. The main im-portant difference between these dwarf irregular galaxies with the earlier LSB galaxies is that for these dwarf irregular galaxies with extended H I disk, the largest baryonic con-tribution comes from the interstellar gas (mainly H I ), and not from the stars (as seen in LSBs). The extended H I disks of these galaxies allow one measure the rotation curve, and hence modeling the dark matter halo parameters for a large radial range from the galactic center. Here also the rotation curves are found to be dominated by dark matter halo over most of the disk, thus providing yet another ‘laboratory’ for testing the dynam-ical effect of dark matter halo on the dynamics of the disks. Using the observed input parameters for five such dwarf irregular galaxies, we showed that the dense and com-pact dark matter halo is responsible for preventing strong small-scale spiral structure in these galaxies, which is in fair agreement with the observations. Dynamical effect of interstellar gas on longevity of spiral arms Any late-type disk galaxy contains a finite amount of interstellar gas along with the stel-lar component. The atomic hydrogen (H I ) constitutes the bulk of the interstellar gas along with the molecular hydrogen (H2), ionized hydrogen (H I I ), and a trace amount of heavy elements like helium. The mass fraction present in the interstellar gas in disk galaxies is found to vary with the Hubble sequence, with the amount of interstellar gas increasing from Sa type to Scd type of galaxies. Due to the lower value of velocity disper-sion as compared to that of stars, gas is known to have a larger destabilizing effect in the disk. Therefore, the natural question arises about what possible role the interstellar gas could play in the origin and the persistence issue of spiral arms. In Chapter 4, we explored how the interstellar gas could influence the longevity of the spiral arms in late-type disk galaxies by treating the spiral structure as density waves in the disk. The disk is modeled as a gravitationally coupled stars plus gas (two-component) system, where the stars are modeled as a collisionless system and the gas treated as a fluid system. Using the appropriate local dispersion relation for the above mentioned model for the disk of galaxy, we calculated the group velocity of a wavepacket of density wave and then studied the variation of the group velocity with increasing amount of interstellar gas in the system. We showed that the group velocity of a wavepacket in a Milky Way-like disk galaxy decreases steadily with the inclusion of gas, implying that the spiral pattern will survive for a longer time-scale in a more gas-rich galaxy by a factor of few. In Chapter 5, we investigated the role of interstellar gas in obtaining a stable den-sity wave corresponding to the observed pattern speed for the spiral arms. The under-lying local dispersion relation remains same as that is in Chapter 4. Using the observa-tionally measured pattern speed and the rotation curves for three late-type disk galaxies we showed that the presence of interstellar gas in necessary in order to maintain a stable density wave corresponding to the observed values for pattern speeds. Also we proposed a method to determine a range of pattern speed values at any particular radius, corre- sponding to which the density wave can be stable. We applied this method to the same three late-type galaxies which we used in the earlier part of this chapter. We found that, for these three galaxies, the observed pattern speed values indeed fall in the predicted range. Imprint of dark matter halo on large-scale spiral structure Along with the small-scale spiral arms, there also exists another type of spiral arms – the large-scale spiral structure, like what we see M 51 or in NGC 2997, which occupy almost the entire outer optical disk in the galaxy. These spiral arms are termed as ‘grand-design’ spiral structure. One of the competing theories, namely, Density wave theory proposes that the large-scale structure is basically a density wave in the disk and the pattern ex-hibits a rigid-body rotation with a definite constant pattern speed. In the earlier part this thesis (Chapters 2 & 3), it was shown that the small-scale spiral structure gets damped by the dominant dark matter halo. Therefore, a natural question arises whether dominant dark matter plays any role on these large-scale spiral structure; and if yes, to what extent it affects the large-scale spiral structure. In Chapters 6 & 7, we investigated how the large-scale structure in disk galaxies gets affected when the disk galaxy hosts a dark matter halo that dominates over most of the disk regions. We again chose the LSB galaxies as laboratory for this study. In Chapter 6, we modeled the stellar component as a fluid system and in Chapter 7, we treated the stellar system as more realistic collisionless system. In both cases, global spiral modes are identified from the appropriate dispersion relations via a novel quantization rule, and they are used as a ‘proxy’ for the large-scale spiral structure. Using the input pa-rameters for UGC 7321, in Chapter 6 we showed that the fluid representation of stellar system failed to make an impression in suppression of the global spiral modes. However, when stellar component is treated as a more realistic collisionless system, we found that the dark matter halo suppresses the large-scale spiral features as well in the disks of LSB galaxies, in fair agreement with the observations. Finally, in Chapter 8, the thesis concludes with a summary of main results and a brief discussion of the scope for future work.

The work deals with the design of a USB floppy drive driver. It describes the theory needed to design your own floppy drive driver and the output of individual components. The following is a schematic of the floppy drive driver design. The functions for controlling the floppy drive are described, as well as the pitfalls of the ATSAMD21J18A-AU processor used.

The work deals with flash technology, the history of its development, current application of this technology and discusses the advantages and disadvantages of flash memories. It describes the integration of flash technology into mass storage devices and commonly used mechanisms that suppress the flash shortcomings for such application. The next part of the work focuses on analysis of commonly used buses for flash storage devices. Based on these theoretical foundations, text presents way to develop own flash based disk. The work focuses mainly on finding the most accessible platform for connecting the disk to personal computers - USB, on PCB design for storage module in Eagle CAD and implementation of necessary firmware for MCU and VHDL design for FPGA, that provide the disk functionality. At the end the work summarizes the results and outlines the way of further development.

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Friction continues to be one of the main causes of energy loss in mechanical systems despite the advances in technology. As a result, this not only involves energy overuse but also maintains high levels of CO2 emissions that cannot be assumed if society wishes to shift towards a more sustainable industry. In this regard, textured surfaces have proven to be a useful feature to decrease or increase friction between two surfaces in contact. Through several pin-on-disk tribotests, this thesis aims to study the influence of three different textures on the friction coefficient: crosspatched, circumferential smooth, and circumferential rough. Height and functional parameters were extracted from the surfaces by measuring them with an optical profiler to study their influence on the tribological properties of the disks. The wear volume and film parameter were also calculated from the measured data. The crosspatched texture yielded the lowest coefficient of friction, followed by circumferential smooth and circumferential rough. The highest values of the film parameter and lowest values of wear volume were achieved by the circumferential smooth texture. Three significant correlations were found: The Sdr parameter and the Svk/Spk ratio are statistically related to the film parameter. The interaction between Sdr and Sk is correlated with the friction coefficient, although their relation does not have a practical use. Future possibilities for research can be centred around studying the validity of these correlations and the phenomena behind them, as well as expanding the study of crosspatched textures to further optimize friction. / Friktion fortsätter att vara en av de främsta orsakerna till energiförluster i mekaniska system trots teknikens framsteg. Som ett resultat av detta, innebär det inte bara överanvändning av energi utan även höga nivåer av CO2-utsläpp upprätthålls vilket inte kan antas om samhället vill ställa om mot en mer hållbar industri. I detta avseende har texturerade ytor visat sig vara en användbar egenskap för att minska eller öka friktionen mellan två ytor i kontakt. Genom flera pin-on-disk-tribotester, syftar denna avhandling till att studera inverkan av tre olika texturer på friktionskoefficienten: korspatchad, periferiell slät, och periferiell grov. Höjd- och funktionsparametrar extraherades från ytorna genom att mäta dem med en optisk profilerare för att studera deras inverkan på skivornas tribologiska egenskaper. Slitvolymen och filmparametern beräknades också från den uppmätta data. Den korspatchade texturen gav den lägsta friktionskoefficienten, följt av periferiell slät och periferiell grov. De högsta värdena för filmparametern och de lägsta värdena för slitagevolymen uppnåddes genom den periferiella släta texturen. Tre signifikanta korrelationer hittades: Sdr-parametern och Svk/Spk förhållandet är statistiskt relaterade till filmparametern. Interaktionen mellan Sdr och Sk är korrelerad med friktionskoefficienten, även om deras relation inte har någon praktisk användning. Framtida möjligheter för forskning kan centreras kring att studera giltigheten av dessa korrelationer och fenomenen bakom dem, samt att utöka studiet av korspatchade texturer för att ytterligare optimera friktionen.

Using a forensic imager to produce a copy of the storage is a common practice. Due to the large volumes of the modern disks, the imaging may impose severe time overhead which ultimately delays the investigation process. We proposed automated disk analysis techniques that precisely identify regions on the disk that contain data. We also developed a high performance imager that produces AFFv3 images at rates exceeding 300MB/s. Using multiple disk analysis strategies we can analyze a disk within a few minutes and yet reduce the imaging time of by many hours. Partial AFFv3 images produced by our imager can be analyzed by existing digital forensics tools, which makes our approach to be easily incorporated into the workflow of practicing forensics investigators. The proposed approach renders feasible in the forensic environments where the time is critical constraint, as it provides significant performance boost, which facilitates faster investigation turnaround times and reduces case backlogs.

<p>U doktorskoj disertaciji razmatra se unapređenje konstrukcije magnetoreolo&scaron;ke disk kočnice sa ciljem povećanja vrednosti ukupnog kočnog momenta. Radi potpunog razumevanja međusobnog odnosa materijala i magnetskog polja na prvom mestu je izvr&scaron;eno utvrđivanje magnetskih svojstava materijala. Unapređenje konstrukcije je izvr&scaron;eno kroz vi&scaron;e iteracija i prototipova. Merenje vrednosti ukupnog kočnog momenta je podeljeno na merenje vi&scaron;e njegovih komponenti pri različitim vrednostima broja obrtaja i upravljačke struje namotaja.</p> / <p>In this thesis magnetorheological disk brake construction improvement is considered, with the goal to increase the overall braking torque value. For purposes of better understanding of material to magnetic field relationship, series of magnetic field testing were conducted. Construction improvement has been carried out through several iterations and different prototypes. Overall braking torque value measurements have been divided into several component measurements, utilizing different rotational speeds and coil control currents.</p>

Modern disk-storage systems have to accomplish the requirements of a variety of application classes. Applications that process continuous-media data such as video and audio streams require the storage system to guarantee sustained bandwidths. Interactive applications demand the storage system to ensure bounded response times, posing timing constraints on the execution of individual disk requests. Traditional timesharing applications may require both high throughput or overall short response times. With the described applications being more and more used together in todays computing systems, the disk-storage subsystems have to efficiently combine the different requirements of this application mix. In this thesis, I develop the design of a storage system that comprehensively addresses the various challenges posed by including the support for quality-of-service guarantees in disk-storage systems. The presented storage system provides three main properties. First, the admission control includes the support for statistical guarantees to increase the share of the disk bandwidth that can be utilized by the admission control. Second, the disk-request scheduling clearly separates the enforcement of real-time guarantees from the task to establish the optimal execution order of the requests, and it provides a flexible mechanism to combine the execution of requests with different quality-of-service requirements. Finally, the file system addresses both the needs of the former two elements of the storage system and of the various file types used by the applications by providing a flexible block-allocation policy and customized client interfaces. I show the implementation of the presented designs with the DROPS Disk-Storage System and I provide a detailed evaluation based on this implementation.

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Made available in DSpace on 2014-06-11T19:29:42Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-07-07Bitstream added on 2014-06-13T20:39:09Z : No. of bitstreams: 1 oi_wm_me_ilha.pdf: 664612 bytes, checksum: 2e783e9660ca16d379613389e5f3a9cc (MD5) / O trabalho foi conduzido no ano agrícola de 2005/06, no município de Selvíria, Estado do Mato Grosso do Sul e teve como objetivo avaliar o comportamento do arroz de terras altas irrigado por aspersão em função do manejo do solo e da adubação nitrogenada em cobertura. O delineamento experimental utilizado foi o de blocos ao acaso disposto em um esquema fatorial 3 x 2 x 7, totalizando 42 tratamentos constituídos pela combinação de três modalidades de preparo do solo (grade pesada + grade niveladora, escarificador + grade niveladora e plantio direto), duas fontes de adubos nitrogenados, na dose de 90 kg ha-1 (Uréia e um sulfonitrato de amônio com inibidor de nitrificação = Entec) e da aplicação de nitrogênio em diferentes épocas de desenvolvimento da cultura do arroz de terras altas, com quatro repetições. Os manejos do solo utilizados influenciaram a altura de plantas, grau de acamamento, total de grãos por panícula, grãos cheios e chochos por panícula e produtividade de grãos, onde o manejo com grade pesada apresentou melhores resultados. O manejo da adubação influenciou apenas a produtividade de grãos. O uso do Entec proporcionou um maior número de grãos cheios e menor número de grãos chochos em relação à uréia / The research was conducted in 2005/06, in Selvíria, Mato Grosso do Sul State, and had the objective of evaluating the development of upland rice irrigated by aspersion considering the management of soil and top-dress nitrogenous fertilization as to grain productivity and quality. The experimental design was a randomized in a factorial scheme of 3 x 2 x 7, totalizing 42 treatments as a result of a combination of three types of soil management (heavy disk + leveling disk; disk plow + leveling disk; no-till), two nitrogenous seasoning sources, urea and sulfatenitrate ammonium with inhibitor of nitrification (Entec) and 90 kg ha-1, of applied at different growth stages on upland rice crop under sprinkler irrigation, with four repetitions. The soil management influenced the height of plants, degree of lodging rate, total of full and empty grainsser panicle and productivity of grains. The soil management with disk + leveling disk presented better resulted. Handling of the fertilization influenced only the productivity of grains. The use of Entec provided a bigger number of full grains and less empty grains in relation to use of urea