Showing 3051 - 3060 of 5708 Items
Acoustic measurements of the stripe and the bubble quantum Hall phase
Date: 2015-04-01
Creator: M. E. Msall, W. Dietsche
Access: Open access
- We launch surface acousticwaves (SAW) along both the and the directions of aHall bar and measure the anisotropic conductivity in a high purity GaAs two-dimensional electron system in the quantum Hall regime of the stripe and the bubble phases. In the anisotropic stripe phase,SAW propagating along the 'easy' direction sense a compressible behavior (finite resistance)which is seen in standard transportmeasurement only if current flows along the 'hard' direction. In the isotropic bubble phase, the SAW data show compressible behavior in both directions, in marked contrast to the incompressible quantum Hall behavior seen in transport measurements. These results challenge models that assume that both the stripe and the bubble phase consist of incompressible domains and raise important questions about the role of domain boundaries in SAW propagation.
Improving Energy Efficiency through Compiler Optimizations
Date: 2021-01-01
Creator: Jack Beckitt-Marshall
Access: Open access
- Abstract--- Energy efficiency is becoming increasingly important for computation, especially in the context of the current climate crisis. The aim of this experiment was to see if the compiler could reduce energy usage without rewriting programs themselves. The experimental setup consisted of compiling programs using the Clang compiler using a set of compiler flags, and then measuring energy usage and execution time on an AMD Ryzen processor. Three experiments were performed: a random exploration of compiler flags, utilization of SIMD, as well as benchmarking real world applications. It was found that the compiler was able to reduce execution time, especially when optimizing for the specific architecture, to a degree that depends on the program being compiled. Faster execution time tended to correlate with reduced energy usage as well, further suggesting that optimizing programs for speed and architecture is the most effective way of decreasing their overall energy usage.
Collapse of a magnetized star to a black hole
Date: 2003-01-01
Creator: T.W. Baumgarte, S.L. Shapiro
Access: Open access
Can Small Donations Have Big Consequences? Candidate Ideology, Small Donations, and Election Results in the 2016 and 2018 Congressional Cycles
Date: 2021-01-01
Creator: Michael Borecki
Access: Open access
- Small donors have provided an increased share of total campaign contributions in the 2016, 2018, and 2020 U.S. federal election cycles, including about $3 billion of the $14.4 billion raised in 2020. Campaign funding is still dominated by an influential set of large donors, but small donations may be the basis for an effective response to the disproportionate amount of “big money” in politics. This study investigates whether candidates who are more extreme perform better with small donors, and then examines the impact of small donations and overall funding on election results. These analyses were performed using linear sum-of-squares regression models. The results in Chapter 2 show that candidates who are more politically-extreme receive more of their funding from small donations, but perform worse in general elections when fundraising is equal. Chapter 3 shows that small donations do not have an impact on candidate performance in general elections more generally, but candidates who outraise their opponent also outperform relative to the district’s partisan lean. However, that effect disappears when looking only at elections decided by less than 10 percent of the vote. These results suggest that small donors are more likely to support candidates who are more politically polarized, but the effects of small donors on the makeup of Congress is marginal at best, at least as far as general election outcomes are concerned. The project concludes by considering reform proposals that seek to broaden the pool of Americans who donate small sums to political candidates.