The Convergence of Particle-in-Cell Schemes for Cosmological Dark Matter Simulations

Particle methods are a ubiquitous tool for solving the Vlasov-Poisson equation in comoving coordinates, which is used to model the gravitational evolution of dark matter in an expanding universe. However, these methods are known to produce poor results on idealized test problems, particularly at late times, after the particle trajectories have crossed. To investigate this, we have performed a series of one- and two-dimensional "Zel'dovich Pancake" calculations using the popular Particle-in-Cell (PIC) method. We find that PIC can indeed converge on these problems provided the following modifications are made. The first modification is to regularize the singular initial distribution function by introducing a small but finite artificial velocity dispersion. This process is analogous to artificial viscosity in compressible gas dynamics, and, as with artificial viscosity, the amount of regularization can be tailored so that its effect outside of a well-defined region - in this case, the high-density caustics - is small. The second modification is the introduction of a particle remapping procedure that periodically re-expresses the dark matter distribution function using a new set of particles. We describe a remapping algorithm that is third-order accurate and adaptive in phase space. This procedure prevents the accumulation of numerical errors in integrating the particle trajectories from growing large enough to significantly degrade the solution. Once both of these changes are made, PIC converges at second order on the Zel'dovich Pancake problem, even at late times, after many caustics have formed. Furthermore, the resulting scheme does not suffer from the unphysical, small-scale "clumping" phenomenon known to occur on the Pancake problem when the perturbation wave vector is not aligned with one of the Cartesian coordinate axes.Comment: 29 pages, 29 figures. Accepted for publication in ApJ. The revised version includes a discussion of energy conservation in the remapping procedure, as well as some interpretive differences in the Conclusions made in response to the referee report. Results themselves are unchange

A 4th-Order Particle-in-Cell Method with Phase-Space Remapping for the Vlasov-Poisson Equation

Numerical solutions to the Vlasov-Poisson system of equations have important applications to both plasma physics and cosmology. In this paper, we present a new Particle-in-Cell (PIC) method for solving this system that is 4th-order accurate in both space and time. Our method is a high-order extension of one presented previously [B. Wang, G. Miller, and P. Colella, SIAM J. Sci. Comput., 33 (2011), pp. 3509--3537]. It treats all of the stages of the standard PIC update - charge deposition, force interpolation, the field solve, and the particle push - with 4th-order accuracy, and includes a 6th-order accurate phase-space remapping step for controlling particle noise. We demonstrate the convergence of our method on a series of one- and two- dimensional electrostatic plasma test problems, comparing its accuracy to that of a 2nd-order method. As expected, the 4th-order method can achieve comparable accuracy to the 2nd-order method with many fewer resolution elements.Comment: 18 pages, 10 figures, submitted to SIS

Gaming For Life: Gaming Practices, Self-Care, and Thriving Under Neoliberalism

This dissertation frames gaming practices in relationship to thriving, an area of inquiry that has received little attention within the fields of video game studies and cultural studies. It argues that video games can be used by audiences as a tool for thriving, provided we define thriving outside of the framework of success and failure established by a neoliberal political rationality. Using survey data from 70 video game audience members, textual analysis, and ethnographic and auto-ethnographic methodologies, this dissertation first describes how video game audience members define thriving by distinguishing it from a related term, self-care. It then moves to a discussion of how the participants view the relationship between thriving, self-care, and gaming, arguing that their perspectives are informed by a neoliberal political rationality that cultivates a disposition structured by self-surveillance, self-government, and productivity. From there, it moves to a discussion of a representative example of a video game used for the purposes of self-care and thriving, Final Fantasy XIV, to examine the affordances and limitations to thriving a video game can provide

Friends With Benefits: Plausible Optimism and the Practice of Teabagging in Video Games

Recent scholarship in gaming studies has challenged the field to investigate and critique the hard core gaming audience (stereotypically seen as straight, White, cis-gendered male gamers) in a way that does not reinforce either the perceived marginalization of gamers or broader social hierarchies of gender, sexuality, and class. This article demonstrates a way to acknowledge the complexity of this audience without dismissing its most virulent tendencies via practice theory and weak theory. Using data drawn from a qualitative survey of 393 self-identified first-person shooter video game players, this article looks at the specific practice of “teabagging” in online competitive gaming contexts. Ultimately, this article argues that drawing attention to the gaps and fissures that local gaming practices can produce in broader structures of gaming, sexuality, and class can help critical gaming scholars encourage and cultivate such practices as well as construct new, reparative alliances between different fields and communities

An Improved Measurement of the Hubble Constant from the Sunyaev-Zeldovich Effect

We present a determination of the Hubble constant from measurements of the Sunyaev-Zeldovich Effect (SZE) in an orientation-unbiased sample of 7 z < 0.1 galaxy clusters. With improved X-ray models and a more accurate 32-GHz calibration, we obtain H_O = 64+14-11 +/- 14_sys km/s/Mpc. for a standard CDM cosmology, or 66+14-11 +/- 15_sys km/s/Mpc for a flat LambdaCDM cosmology. In combination with X-ray cluster measurements and the BBN value for Omega_B, we find Omega_M = 0.32 +/- 0.05.Comment: 5 pp., Accepted for publication in ApJ

Making the Grade: What\u27s Motivating China\u27s Educational Outreach in LAC?

This paper considers the multiple motivations for China’s educational outreach in the region, drawing from Chinese policy and analysis and many dozens of examples of academic linkages forged between China and Latin America and the Caribbean in recent years. Whether initiated by Chinese or LAC institutions, these programs are an increasingly central feature of China-LAC relations, a part of the extension of China’s BRI to LAC, and a useful measure of China’s varied and evolving interests throughout the region.https://digitalcommons.fiu.edu/jgi_research/1049/thumbnail.jp

Effect of Physical Educators’ Appearance and Sex on Middle School Students’ Learning Outcomes and Perceptions of Teacher Effectiveness

Physical Education (PE) teachers can have a great impact on the future physical activity levels of their students, and later, as adults. Professional appearance of teachers has been shown through previous research to have influence on student learning outcomes and perceptions of teacher effectiveness. This research aimed to build on prior studies to investigate the interaction between formal and informal appearance and gender of physical education teachers with middle school student learning outcomes and teacher perspectives. Four 20-minute videos were produced on the non-traditional invasion sport Tchoukball. The four videos consisted of female informal appearance, female formal appearance, male informal appearance, and male formal appearance. The videos were randomly shown to 433 middle school students located in southeastern United States followed by a post-video content examination and a teacher perception survey. Factoral ANOVAs were performed to identify any significant main effects or interactions on overall content exam, two content areas (skill technique and game strategy), and three teacher perspectives (likability, competence, and teacher as a role model). There was no significant main effect for teacher appearance and student learning outcomes. When considering sex of the teacher, there was a significant main effect for overall examination (F(1, 428) = 9.45, p &lt; .001, η2 = .022, 1-β = .866) and for strategies ((F(1, 428) = 17.22, p &lt; .001, η2 = .039, 1-β = .985), while nothing was found for technique-related questions. On the three teacher perspectives, no significance was found between likability and competence, however there was a main effect on the survey questions about teachers as a role model when taking teacher appearance into consideration ((F(1, 424) = 5.01, p &lt; .001, η2 = .025, 1-β = .612)