Colloquium Schedule

Fall 2016

Singing Stars, Eclipsing Stars, and Other Worlds: Imminent Advances from the TESS and Gaia Missions

Keivan Stassun, Vanderbilt University and Fisk University
Wed., Sep. 21, 2016, 4:30 PM in Science Center 199

The upcoming Gaia mission will measure the trigonometric parallaxes to some 1 billion stars with an accuracy of 20 micro-arcseconds. Such precision distance measurements promise to revolutionize our understanding of many areas of stellar astrophysics. However, it is imperative that these distances be benchmarked against independent, accurate distance measurements, which eclipsing binary stars are uniquely poised to provide. The upcoming TESS mission will discover dozens of Earth-link planets around nearby Sun-like stars. However, to determine the physical properties of these "Earth 2.0" with precision requires accurate knowledge of the physical properties of the stars they orbit. The "singing" of stars induced by gas motions at their surfaces provide a powerful way of determining these properties. These exciting, upcoming discoveries represent superb examples of the application of basic physics in astronomical contexts.


Sentiment Analysis of Student and Instructor Feedback: Gender Bias and Affective Patterns

Scott Franklin, Rochester Institute of Technology
Fri., Sep. 30, 2016, 12:30 PM in Science Center 199

Sentiment analysis is a computational linguistics tool that characterizes affective meaning, such as positive-negative tone, expressed in language data. In this talk I present two projects that use sentiment analysis to reveal subtle patterns in student and faculty feedback. First, I present a study of more than 5,500 student comments spanning over eight years of biology, chemistry, physics, and math courses and explore differences in sentiment pertaining to instructor competence, organization/presentation, personality/helpfulness, and overall satisfaction. Of particular interest are differences in perception conveyed toward male and female faculty, and between faculty of different disciplines. We also compare automatically extracted sentiment scores with quantitative Likert ratings that students enter alongside their comments, and report on the extent to which the quantitative and qualitative evaluations correlate. The second project analyzes instructor feedback to student Guided Reflection Forms, weekly online reflections about challenges and setbacks students experience. Sentiment analysis supports the development of a stable basis set (rubric) to describe responses that is robust across both introductory and advanced classes. The analysis also reveals the instructor’s subconscious use of the “praise sandwich,” instinctively embedding critiques and suggestions between specific and general encouragements. In both studies, validated, automated, sentiment analysis becomes a useful method by which to analyze large corpuses of written text.


Physical Guidance of Cell Migration

Wolfgang Losert, University of Maryland
Fri., Oct. 28, 2016, 12:30 PM in Science Center 199

Cells migrate as individuals or groups, to perform critical functions in life from organ development to wound healing and the immune response.  While directed migration of cells is often mediated by chemical or physical gradients,  our recent work has demonstrated that the physical properties of the microenvironment can also control and guide migration.  I will describe how an underlying wave-like process of the actin scaffolding drives persistent migration, and how such actin waves are nucleated and guided by the texture of the microenvironment.  Based on this observation we design textures capable of guiding cells in a single preferred direction using local asymmetries in nano/microtopography on subcellular scales.  This phenomenon is observed both for the pseudopod-dominated migration of Dictyostelium cells and for the lamellipod-driven migration of human neutrophils.  The conservation of this mechanism across cell types suggests that actin-wave-based guidance is important in biology and physiology.


The Radiation-Driven Winds and X-ray Emission of Massive Stars

David Cohen, Swarthmore College
Fri., Nov. 4, 2016, 12:30 PM in Science Center 199

The most massive, hot, and luminous stars in the Galaxy drive powerful outflows via the force of their own starlight. These radiation-driven winds return heavy-element-enriched material to the interstellar medium, sculpt beautiful nebulae, and strongly affect the evolutionary paths and end-states of massive stars. In this talk I will describe my research group's work on two categories of massive stars and their winds, focusing on the stellar X-ray emission and what we can learn from it. Both magnetic and non-magnetic massive stars generate copious X-ray emission by converting some of their wind kinetic energy to heat in via dissipation in shocks. The majority of massive stars - the non-magnetic ones - do it via an instability intrinsic to radiation-driving, while the magnetic massive stars channel their winds into a confined magnetosphere where head-on collisions of wind flows from opposite hemispheres cause strong shocks. In both cases, X-ray spectroscopy can be used to diagnose the shock physics and spatial structure of the stellar winds and provide insights about the fundamental physical processes that characterize the most massive stars in the Galaxy. 


Life as a Matter of Chance

Jané Kondev, Brandeis University
Fri., Nov. 11, 2016, 12:30 PM in Science Center 199

The living cell is bustling with nanometer sized protein machines. These machines perform a variety of functions such as the reading of genetic information, the transport of molecules from one side of the cell to the other, the building of the tracks required for this transport, and so forth. Protein machines in cells are very different from man made ones as Brownian motion, the constant agitation of proteins by water and other small molecules, plays a critical role. Brownian motion makes protein machines behave randomly and unpredictably. In this talk I will discuss recent experiments and theory that reveal how this randomness at the molecular scale produces variability in cellular behavior. I will also comment on how these discoveries, which are being made by biologists and physicists working together, has the potential of transforming cell biology and medicine.