Browsing by Subject "microwave"
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Item Bayesian Analysis Of An Anisotropic Universe Model: Systematics And Polarization(2010-10) Groeneboom, Nicolaas E.; Ackerman, Lotty; Wehus, Ingunn K.; Eriksen, Hans Kristian; Ackerman, LottyWe revisit the anisotropic universe model previously developed by Ackerman, Carroll, and Wise (ACW), and generalize both the theoretical and computational framework to include polarization and various forms of systematic effects. We apply our new tools to simulated Wilkinson Microwave Anisotropy Probe (WMAP) data in order to understand the potential impact of asymmetric beams, noise misestimation, and potential zodiacal light emission. We find that neither has any significant impact on the results. We next show that the previously reported ACW signal is also present in the one-year WMAP temperature sky map presented by Liu & Li, where data cuts are more aggressive. Finally, we re-analyze the five-year WMAP data taking into account a previously neglected (-i)(l-l')-term in the signal covariance matrix. We still find a strong detection of a preferred direction in the temperature map. Including multipoles up to l = 400, the anisotropy amplitude for the W band is found to be g = 0.29 +/- 0.031, nonzero at 9 sigma. However, the corresponding preferred direction is also shifted very close to the ecliptic poles at (l, b) = (96, 30), in agreement with the analysis of Hanson & Lewis, indicating that the signal is aligned along the plane of the solar system. This strongly suggests that the signal is not of cosmological origin, but most likely is a product of an unknown systematic effect. Determining the nature of the systematic effect is of vital importance, as it might affect other cosmological conclusions from the WMAP experiment. Finally, we provide a forecast for the Planck experiment including polarization.Item Microwave Measurements of Nylon-12 Powder Ageing for Additive Manufacturing(University of Texas at Austin, 2017) Clark, N.; Lacan, F.; Porch, A.With repeated recycling, nylon powders used in Selective Laser Sintering are known to degrade and ultimately cause mechanical performance and surface finish deterioration in produced parts. In order to maintain consistent production and to reduce cost by minimising waste powder, it is desirable to monitor this degradation. However, any techniques used must be inexpensive, quick and simple in order to maintain industrial relevance; dielectric measurements by microwave cavity perturbation can offer these advantages. Here, samples are taken from a working SLS machine and their permittivity measured using microwave cavity perturbation operating around 2.5 GHz. A 2% reduction in effective dielectric constant and an 8% reduction in effective dielectric loss is observed between new powder and recycled feedstock. Furthermore, in-situ measurements simulating build chamber conditions show a similar trend.Item What Does Cosmology Tell Us About Particle Physics Beyond The Standard Model?(2012-03) Komatsu, E.; Komatsu, EiichiroCosmology demands particle physics beyond the Standard Model: we need to explain the nature of dark matter and dark energy, and the physics of cosmic inflation. Cosmology also provides the tightest upper bound on the sum of neutrino masses, and it seems only a matter of time before we measure the absolute mass of neutrinos, unveiling the neutrino mass hierarchy. It also provides a measurement of the number of relativistic species at the photon decoupling epoch (at which the temperature of the universe is 3000 K). Astronomy and Astrophysics Decadal Survey conducted by USA's National Academy of Sciences has identified these four topics (dark matter, dark energy, inflation and neutrinos) as the most important subjects to study in cosmology over the next decade. In this contribution, we review the current status on these topics, in light of the recent cosmological constraints.