Abstract: CASS All-Hands Meet & Greet this Friday, October 4, from 12:00 to 1:00 pm in SERF 383. This meeting will be an opportunity for new members of CASS to introduce themselves and present a quick overview of their research. It will also give established members of CASS a chance to summarize their recent work. New graduate students are especially encouraged to attend. Pizza and soda will be provided. Journal Club is an informal environment in which graduate students can give short talks on any subject of interest to them, be it a recent paper, their own research, or any other topic. Talks will resume next week. All are welcome to attend.

 Abstract: Clusters of Galaxies are the largest gravitationally-bound objects in the Universe. They form via mergers with energetics that are only rivaled by the Big Bang. The study of these objects and collisions can reveal the complex processes that govern the interactions. Observations at 90 GHz with the Mustang instrument on the GBT provide high (9”) resolution of the Sunyaev-Zel’dovich effect inside the clusters. Observations with the MUSTANG instrument have unlocked a new view of these massive objects. I will also show exciting data from objects much closer to home.

 Abstract: (in lieu of Journal Club)

Pizza & soda provided!

Helen Kaiser from the Office for the Prevention of Harassment & Discrimination (OPHD) will be the featured speaker. Everyone is encouraged to attend.

 Abstract: The recent tension between early- and late-Universe measurements of the Hubble constant highlights the necessity for independent and precise probes such as the time-delay cosmography. The measured time-delays between the lensed images of a background quasar depend on the absolute physical scales in the lens configuration. Thus, the time-delays allow measurements of these scales to infer the Hubble constant, H_0. Due to a number of great advancements over the past decade in both the data quality and modeling techniques, the measurement of H_0 from the time-delays has fulfilled its promise to be competitive with other traditional methods such as the cosmic distance ladder. This is evident from the recent 2.4% blind measurement of H_0 from only six lenses (Wong et al. 2019). Simulation shows that a sample of nine lenses shrinks the uncertainty on this measurement to 2% (Shajib et al. 2018). I will present the Hubble constant measured from a newly analyzed lens system taking the sample size to seven. In addition, I will present the future roadmap of time-delay cosmography to independently reach 1% precision within a few years.

Dr. Patwardhan's Abstract: Abstract: We investigate the importance of going beyond the mean-field approximation in the dynamics of collective neutrino oscillations. To expand our understanding of the coherent neutrino oscillation problem, we apply concepts from many-body physics and quantum information theory. Specifically, we use measures of nontrivial correlations (otherwise known as “entanglement”) between the constituent neutrinos of the many-body system, such as the entanglement entropy and the Bloch vector of the reduced density matrix. The relevance of going beyond the mean field is demonstrated by comparisons between the evolution of the neutrino state in the many-body picture vs the mean-field limit, for different initial conditions.

 Abstract: Over the past decade, an increasing number of studies have shown the benefits of Active Learning vs. Traditional Lecturing. In this Journal Club talk I review the results of a meta-study which compiled results of 225 individual studies in Science, Engineering and Mathematics to compare the impact of active learning vs. traditional lecturing. The results indicate an improvement of exam scores and a reduction of failure rates or withdrawals in classes that used active learning techniques.
Article Reference: https://www.pnas.org/content/early/2014/05/08/1319030111

 Abstract: BICEP3 is a small aperture refracting telescope at the South Pole to measure the polarization of the cosmic microwave background (CMB). The main goal is to measure the primordial B-mode polarization at the degree angular scales, which holds a key to probe inflation theory. During the austral summer of 2018-19, we tested the feasibility of using BICEP3 to observe the CMB at low elevation. A particularly interesting feature in the extended field is the anomalous CMB Cold Spot. This talk will discuss the possibility of testing polarization anomaly deviating from the standard Gaussian fluctuation around the Cold Spot and present the progress of BICEP3 observation.

 Abstract: The theory of potential vorticity (PV) mixing in a disordered (tangled) magnetic field is presented. The analysis is in the context of β-plane MHD, with a special focus on the physics of momentum transport in the stably stratified, quasi-2D solar tachocline. A physical picture of mean PV evolution by vorticity advection and tilting of magnetic fields is proposed. In the case of weak field perturbations, quasilinear theory predicts that the Reynolds and magnetic stresses balance as turbulence Alfvénizes for the larger mean magnetic field. The jet formation is explored quantitatively in the mean field-resistivity parameter space. However, since even modest mean magnetic field leads to large magnetic perturbations for large magnetic Reynolds number, the physically relevant case is that of a strong but disordered field. We show that numerical calculations indicate that the Reynolds stress is modified well before Alfvénization — i.e. the balance of fluid and magnetic energies. To understand these trends, a double average model of PV mixing in a stochastic magnetic field is developed. Calculations indicate that mean square fields strongly modify Reynolds stress phase coherence and also induce a magnetic drag on zonal flows. The physics of transport reduction by tangled fields is elucidated and linked to the related quench of turbulent resistivity. A physical picture of the system as a resisto-elastic medium threaded by a tangled magnetic network is proposed. Applications of the theory to momentum transport in the tachocline and other systems are discussed in detail.