Complex Systems

Professor Sean Cornelius, Network Science Institute, Northeastern University

Title: The fundamental advantages of temporal networks

Abstract: It is increasingly recognized that many natural and social systems are best described as“temporal” networks, in which the underlying links exist only intermittently. For example, in metabolicnetworks the links correspond to relatively brief chemical reactions, and in social networksfriendship links are inferred from face-to-face or digital communications of finite duration.By effectively “fragmenting” a network's structure across time, temporality has been shown to have profound and usually deleterious effects on many dynamical processes, for example slowing down synchronization and the diffusion of innovative information, impeding exploration and navigation, and raising barriers to accessibility. Considering the ubiquity of temporal networks in nature, we must therefore ask: are there any advantages of temporality? In this talk, I will argue that there is at least one crucial dynamical process in which temporal networks enjoy unambiguous advantages, namely control—the ability to drive a system to (or keep it in) a desired state. Specifically, I will show that compared to their time-invariant counterparts, temporal systems can reach controllability faster, while demanding orders of magnitude less control energy and enjoying significantlymore compact control trajectories. These findings echo other recent work that has shown that nonlinear dynamics can be an asset, rather than an obstacle, to controlling real systems.

Host: Adilson Motter

Professor Jennifer Ross, University of Massachusetts Amherst

Title: Transient Crosslinkers Tune the Patterns of Microtubule Filaments

Abstract: The cell is a complex autonomous machine taking in information, performing computations, and responding to the environment. To enable agile read/write capabilities, much of the molecular biochemistry that performs these computations must be transient and weak, allowing signals to be carried as a function of the concentration of numerous and coupled interactions. Traditionally, biochemical experiments can only measure strongly interacting systems that can last for long times in dilute concentrations. We have developed microscopy measurements to enable to visualization of weak, transient interactions and the resulting emergent behaviors of coupled systems. I will present excerpts from stories where many weak, transient interactions can have strong repercussions on the overall activity and can, in fact, overpower strongly interacting systems. These studies involve the microtubule cytoskeleton and the transport motor, kinesin-1. Our results reveal a fundamentally important aspect of cellular self-organization: weak, transient interacting species can tune their interaction strength directly by tuning the local concentration to act like a rheostat. The tunability of weak, transient interactions is a fundamental activity of biological systems, and our insights will ultimately enable us to learn how to engineer these systems to create biological or biomimetic devices.

Host: Michelle Driscoll

Professor Daniel Needleman: Harvard University

Title: Biophysics of Spindle Positioning and Elongation

Abstract: The spindle is positioned asymmetrically during the first mitotic division in C. elegans. We are investigating how different forces coordinated to move the spindle, and if these forces are generated from interactions with the cytoplasm, the cortex, or a combination of both. For this purpose, we constructed a laser ablation system capable of cutting complex patterns with high spatial and temporal precision, and we are applying it to quantitatively perturb spindle movements. We are also using fluorescent nanodiamonds to track cytoplasmic fluid flow as the spindle moves. We interpret our data using a combination of theory and simulations (in collaboration with Mike Shelley, NYU/Courant/Flatironan and Ehssan Nazockdast, UNC). Our results argue that pulling forces from the cortex drive key aspects of spindle motions, including the initial centering, subsequent asymmetric positioning, transverse oscillating behaviors, and elongation. We hope to provide a quantitative, integrated understanding of spindle positioning.

Host: Michelle Driscoll


Professor Paul Chaikin: TBA

May 31, 2018, 2:00 PM - 3:30 PM

Professor Paul Chaikin, New York University

Title: TBA

Abstract: TBA

Host: Michelle Driscoll