Description:

Utilizing complex networks with error bars

István Kovács, Assistant Professor

Network theory is a powerful tool to describe and study complex systems, and there has been tremendous progress in mapping large networks in science and art, leading to a growing library of complex network topologies. However, it is unrealistic to assume that the obtained graphs are exact. Inherent limitations of the measurement process lead to errors, biases and missing data, resulting in incomplete and biased snapshots. Hence, it would be of paramount importance to characterize and utilize the uncertainty of our maps. Yet, the uncertainty of a network structure is expected to have a complex network structure itself, posing deep open challenges. Currently, there are only a few cases where not only an observation of the graph structure is available, but also a full quantification of the error and incompleteness patterns. On the prominent example of the yeast genetic interaction network we will overview how such detailed information can help us to solve key problems, such as inferring missing data and functional annotations as well as finding efficacious drug combinations.

What sets the masses of stars (and what doesn't)?

Mike Grudić

Stars form with a wide range of masses, ranging from 0.01x to more than 100x the mass of the Sun. The empirical distribution of stellar masses over this range, the stellar initial mass function (IMF), indicates that a typical star has a mass slightly less than that of the Sun, wherever we look in the Galaxy. The physical origins of the IMF, and its characteristic mass scale, are not currently well-understood, despite their immense importance in all areas of astrophysics. I will describe various past theoretical approaches to the IMF, evaluating their successes and failures, and outline a set of criteria that any successful theory of the IMF must satisfy based on existing constraints. I will then present the results of the first ever numerical magnetohydrodynamics (MHD) simulations to simulate the formation of individual stars in conditions typical in our Galaxy. Our preliminary model is minimalist, only the physics of MHD and gravity acting in concert, and their IMF results can be boiled down to a simple power-law expression for the typical stellar mass. These results turn out to be incompatible with observations, however they allow us to consderably narrow down which additional physics are setting the masses of stars in our Galaxy.