Eric Sembrat's Test Bonanza

Microbial ecosystems in the top decimeters of sediment play an important role in determining the chemistry of the atmosphere and help support multicellular life. The metabolic rates of these microbes are strongly limited by the time it takes nutrients to diffuse from the surface. Here we combine experiments, mathematical models, and field work to understand how two microbes, the bacteria Thiovulum majus and the eukaryote Uronemella, respond collectively to overcome diffusion limitation. These microbes have independently evolved the ability attach to surfaces by means of a mucus tether. Once tethered, cells use their flagella or cilia to pump nutrient-rich water. Microbes also attach to members of their own species to form a centimeter-scale community called a ``veil''. In a veil, cells generate a macroscopic flow that mixes its environment 40 times more efficiently than do individuals. We show how this collective behavior arises from the individual behavior of cells. In the second part of the talk, we describe a new form of collective dynamics displayed by T. majus. Untethered bacteria self organize on a surface into rotating two-dimensional crystals of quickly spinning cells. These crystals show a number of rich phenomena including the formation of fixed points, limit cycles, and surface melting. Proceeding from a force balance on each cell, we show how this visually-striking behavior arises from the flow of water being created by each cell. These results provide mathematically tractable examples of how the large-scale behavior of microbial communities in the environment arises from the response of individual cells to nutrient limitation.

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Exoplanet surveys have revealed an amazing diversity of planets orbiting other stars in the last two decades. Studying the atmospheres of representative exoplanets is the key next step in leveraging these detections to further transform our understanding of planet formation and planetary physics. Additionally, atmospheric studies are critical for determining if any of the small habitable zone exoplanets that are now being detected are truly habitable, and even inhabited. In this talk I will describe recent results from exoplanet atmosphere observations with an emphasis on results from major programs using the Hubble Space Telescope. Although atmospheric studies of potentially habitable planets are currently out of reach, I will discuss how future facilities may open up this possibility in the near future.

Galaxy clusters are the most massive virialized objects in the universe, and have the potential to be highly accurate probes of cosmological parameters. A fundamental challenge for cluster cosmology is to estimate the masses of these objects using observational proxies such as X-ray luminosity and temperature, which are complicated by the merger history of clusters and the microphysical properties of the intracluster medium. These effects, while frustrating to cosmologists, provide a rich laboratory for exploring the plasma physical processes that are occurring in these massive objects. In this talk I will present recent efforts to understand the effects that several plasma processes - including conduction and AGN feedback - have on the observable properties of galaxy clusters.

Take a break from studying and come listen to Prof. Yoshida describe the history of the universe over 13 billion years since the Big Bang. He will use the visual results from recent state-of-the-art computer simulations that aid our understanding on how astronomical objects such as stars, galaxies, and black holes form in an expanding universe. He will explore prospects for future high-performance computing using exascale computers.

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Dehydration and lack of fresh water are key problems for vertebrates that have secondarily invaded marine environments. However, recent investigations of 9 species representing the principal clades of sea snakes indicate these reptiles do not drink seawater but will drink fresh water at variable thresholds of dehydration, which these snakes tolerate well. Marine reptiles were previously thought to remain in water balance without consuming fresh water owing to the ability of extrarenal salt glands to excrete excess salts obtained either from prey or from drinking sea water directly. Thus, species of marine snakes which dehydrate at sea and are dependent on environmental sources of fresh water represent a shift of paradigm from previous “textbook” literature. Recent studies also demonstrate that the abundance and diversity of sea snakes correlate with access to fresh water, and that global distributions and evolutionary origins are related to low and variable ocean salinity. Currently available data indicate that sea snakes have relatively high levels of total body water (around 80% of body mass), are comparatively resistant to dehydration, and have diverse thresholds for thirst.

The Ebola epidemic in West Africa has spurred an international response. This response has been strongly influenced by epidemiological models that predicted a devastating rise in cases without large-scale changes in behavior and intervention. In this talk, I introduce the mathematical principles underlying predictions of the rate and scope of a disease epidemic. I then explain how such principles have been applied to forecasting Ebola virus disease (EVD) dynamics and identifying the type and scale of necessary control. One control mechanism involves influencing behavior and social norms to limit post-death transmission, e.g., during burial ceremonies of individuals who died from EVD. Post-death transmission for EVD has been recognized for over 10 years, yet its relative importance in the current epidemic remains uncertain. I conclude my talk with an analysis of ongoing challenges in estimating the relative importance of post-death transmission from early-stage epidemic data. I show why such estimation is hard and yet, nonetheless, why controlling post-death transmission is likely to have a substantial effect on short- and long-term epidemic outcomes.