Thesis (Ph. D.)--Drexel University, 2006. / Includes abstract and vita. Includes bibliographical references (leaves 170-193).

Electrical energy is an essential resource for the modern world. Unfortunately, its price has almost doubled in the last decade. Furthermore, energy production is also currently one of the primary sources of pollution. These concerns are becoming more important in data-centers. As more computational power is required to serve hundreds of millions of users, bigger data-centers are becoming necessary. This results in higher electrical energy consumption. Of all the energy used in data- centers, including power distribution units, lights, and cooling, computer hardware consumes as much as 80%. Consequently, there is opportunity to make data-centers more energy efficient by designing systems with lower energy footprint. Consuming less energy is critical not only in data-centers. It is also important in mobile devices where battery-based energy is a scarce resource. Reducing the energy consumption of these devices will allow them to last longer and re-charge less frequently. Saving energy in computer systems is a challenging problem. Improving a sys- tem’s energy efficiency usually comes at the cost of compromises in other areas such as performance or reliability. In the case of secondary storage, for example, spinning-down the disks to save energy can incur high latencies if they are accessed while in this state. The challenge is to be able to increase the energy efficiency while keeping the system as reliable and responsive as before. This thesis tackles the problem of improving energy efficiency in existing systems while reducing the impact on performance. First, we propose a new technique to achieve fine grained energy proportionality in multi-disk systems; Second, we design and implement an energy-efficient cache system using flash memory that increases disk idleness to save energy; Finally, we identify and explore solutions for the page fetch-before-update problem in caching systems that can: (a) control better I/O traffic to secondary storage and (b) provide critical performance improvement for energy efficient systems.

We use the APOSTLE simulation suite to study the formation of galactic disks, in order to better understand the origin of their vertical structure. We select a disk-dominated Milky Way analogue galaxy from the simulation which experiences a minimum of external interaction with its environment as a generalizable test case. The simulated stellar disk is found to form upside-down from a gradually thinning, flared gaseous disk, where the rate of thinning is regulated by feedback from in-situ star formation. No significant sources of vertical heating are present in the disk, allowing the vertical structure of newly-formed stellar populations to be preserved over time. As a result, the properties of the stellar disk as a function of age accurately trace the properties of the gaseous disk as a function of time. This allows us to derive a physical model, in which the disk is isothermal, in quasi-hydrostatic equilibrium, and vertically supported by bulk motions rather than thermal pressure, which relates the present-day vertical age-velocity dispersion relation (AVR) at a given radius to the local star formation history as a simple power-law relation, with a best fit power law index $n=1.82$. This relation is then applied to the observed AVRs in the Milky Way from the recent literature, providing a predicted local star formation history for the Milky Way as a function of radius. We then compare this predicted history to others from the literature, in order to test whether our upside-down model from the simulation is consistent with the observed Galaxy. We also examine the observed ratio of vertical to radial velocity dispersions for consistency with our model. While our predicted history is broadly consistent with other predictions, the range of possible histories in the literature makes a more definitive conclusion difficult. / Graduate

This thesis describes the experimental test results and computer simulation investigations which were conducted to verify the existing theory of skewed disk forced response predictions. The experimental tests were conducted on a horizontal flexible shaft rotor system supported in two hydrodynamic journal bearings. The computer simulations were conducted with a program that uses a matrix transfer method to get the desired solution. The agreement between experiment and simulation is very good for most skewed disk response characteristics. The influence of measurement errors and operation condition uncertainties are discussed.In the first part of this study, the dynamic behavior of experimental investigations focused on two different skewed disk designs which were mounted at midspan, 1/3 span and 2/3 span of the shaft. The two skewed disks were designed to allow a fine angle adjustment of the desired skew angle. The two designs are (a) the angle tiltable disk and (b) the couple unbalanced mass disk. The experimental results are shown to be close to the theoretical predictions of other authors.In the second part of this study, an existing computer program was used to simulate the experimental test rotor. The results give excellent qualitative agreement although there are some differences in quantitative analysis comparisons. The forced response characteristics of the computer simulation match the experimental results. It has been shown that by using the approximate linear skewed disk model, it is possible to get similar results to the experimental tests for similar disk skew conditions. / Master of Science

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Hardy space scalar theory on the disk is now classical. Some extensions have been done, one of them is the approach done by Donald Sarason using Laurent series. We present the more complicated function theory, without the use of either power series or Laurent series, for finitely-connected planar domains. / Master of Science

京都大学 / 新制・課程博士 / 博士(理学) / 甲第25119号 / 理博第5026号 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 野上 大作, 教授 上田 佳宏, 教授 前田 啓一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Call number: LD2668 .T4 1985 W33 / Master of Science

We present optical and near-infrared high-contrast images of the transitional disk HD 100546 taken with the Magellan Adaptive Optics system (MagAO) and the Gemini Planet Imager (GPI). GPI data include both polarized intensity and total intensity imagery, and MagAO data are taken in Simultaneous Differential Imaging mode at Ha. The new GPI H-band total intensity data represent a significant enhancement in sensitivity and field rotation compared to previous data sets and enable a detailed exploration of substructure in the disk. The data are processed with a variety of differential imaging techniques (polarized, angular, reference, and simultaneous differential imaging) in an attempt to identify the disk structures that are most consistent across wavelengths, processing techniques, and algorithmic parameters. The inner disk cavity at 15 au is clearly resolved in multiple data sets, as are a variety of spiral features. While the cavity and spiral structures are identified at levels significantly distinct from the neighboring regions of the disk under several algorithms and with a range of algorithmic parameters, emission at the location of HD 100546 "c" varies from point-like under aggressive algorithmic parameters to a smooth continuous structure with conservative parameters, and is consistent with disk emission. Features identified in the HD 100546 disk bear qualitative similarity to computational models of a moderately inclined two-armed spiral disk, where projection effects and wrapping of the spiral arms around the star result in a number of truncated spiral features in forward-modeled images.