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Date:  Fri, April 21, 2017
Time:  11:30am
Location:  Holmes 287
Speaker:  Dr. June Zhang, EE Dept. Dr. Sangwoo Shin, ME Dept.

Synthesis and Analysis of Graph Signals: Combining Network Processes and Signal Processing

Dr. June Zhang:

Complex systems of interdependent agents are of interest in many research areas. Examples of such systems are social networks or contact networks, through which rumors or viruses can spread from individual to individual, engineered networked systems such as the power grid, through which cascading failures can lead to large blackouts. These kinds of systems give rise to a new type of signal: graph signals, which exist not only in time but also in space (in the graph sense). First, we will discuss network processes, random processes over networks from which graph signals can arise. Network processes have been used to model the spread of infection in a population or cascading failures in the power grid. We will see the challenges in analysis due to the inclusion of graph structure. Under special conditions, we can analyze the equilibrium distribution of a network process in closed-form. Second, we will show how we can analyze graph signals in the spectral domain by extending classical Fourier transform to include a network structure. We relate how looking at graph signals in the spectral domain can give insights into the behavior of network processes.

Membraneless Water Filtration Using CO2

Dr. Sangwoo Shin

Water purification technologies such as microfiltration/ultrafiltration and reverse osmosis utilize porous membranes to remove suspended particles and solutes. These membranes, however, cause man drawbacks such as a high pumping cost and a need for periodic replacement due to fouling. In this talk, I will introduce an alternative membraneless method for separating suspended particles, which is enabled by exposing the colloidal suspension to CO2. Dissolution of CO2 into the suspension creates solute gradients that drive phoretic motion of particles. Using such a directed motion, we demonstrate a scalable, continuous flow, membraneless particle filtration process that exhibits low energy consumption, three orders of magnitude lower than conventional microfiltration/ultrafiltration processes, and is essentially free from fouling.

Please RSVP by noon on Thursday April 20, to Carrie Matsuzaki at x62286 or email: carrie@eng.hawaii.edu