UNDERSTANDING ACTIVE MATTER UNLOCKS NEW MATERIAL PROPERTIES

Fakhreddine Joins CEE as Assistant Professor

Sarah Fakhreddine recently joined CEE as an Assistant Professor, bringing to the department a background in both engineering and earth sciences.

Fakhreddine’s area of expertise is focused on developing approaches to improve the resilience of freshwater supplies to climate change and population growth. She will officially start in the department January 2023.

Her teaching style emphasizes explaining topics in ways that prioritize an active, adaptive learning environment. Her priority is to keep students engaged—by dividing up lectures with exercises like demos, group activities, and interactive example problems.

She seeks to foster a supportive learning and research environment that enables students to achieve their academic and career goals. “In an environmental engineering context, my goals are to provide students the broader context of the environmental challenges we face and the technical skills and training to address those challenges.”

A graduate of Stanford University, Fakhreddine completed her post doc research at the University of Texas at Austin. “I studied strategies to store excess water underground in depleted groundwater aquifers as a way to balance disconnects between water supply and demand,” she says. Fakhreddine explains that during wet periods, floodwater could be stored in aquifers and recovered during times of drought to offset variability in water availability. One of her current research topics focuses on understanding the fundamental geochemical process that controls water quality in order to design aquifer storage strategies that prevent contamination of water supplies and protects human and ecosystem health.

Now that she is relocated to Pittsburgh, Fakhreddine is excited to explore the region’s parks and museums. She is also a theater fan and is ready to experience the active theater community within CMU.

Remembering Tung Au

Dr. Tung Au, emeritus professor in the Carnegie Mellon Civil and Environmental Engineering and Engineering and Public Policy Departments, passed away on May 31, 2022 at 98 years old. Au served on the faculty with great distinction from 1957 until retiring in 1992.

In his 35 years with CEE, Dr. Au touched the lives of many CEE students, staff members, and fellow instructors. The CEE Tung Au Lab in Porter Hall, a flexible educational facility and the central meeting space for CEE events, was dedicated in honor of Dr. Au in October 1988.

Au was an internationally recognized researcher and engineering educator. As a CEE faculty member, Au taught and conducted research across a spectrum of topics in civil engineering, with deep expertise in applied mechanics, structural engineering, systems analysis and design, and construction project management. Au was the author or co-author of seven books and received numerous honors throughout his career.

Au received his BS degree in Civil Engineering from St. John’s University in China in 1943. Following graduation he was involved with designing a new airfield in China for the American Air Force Group, better known as the "Flying Tigers." After World War II, Au immigrated to the U.S. and earned his MS and PhD degrees in Civil Engineering from the University of Illinois in 1948 and 1951. He worked as a structural engineer in consulting firms in Detroit, Michigan for several years before joining the Civil Engineering faculty at the Carnegie Institute of Technology (now Carnegie Mellon) in 1957.

The CEE Department extends its condolences to the friends and family of Dr. Au. We fondly remember his time with Carnegie Mellon and know that he will be missed by many.

Understanding Active Matter Unlocks New Material Properties

CEE Assistant Professor

Jerry Wang

and Mechanical Engineering PhD student Arman Ghaffarizadeh recently published new insights into modeling and understanding the inner workings of active-matter systems. Though ubiquitous throughout natural (and, in some cases, synthetic) systems, “active matter” is a relatively new categorization of matter that describes particles with the ability to convert stored or ambient energy into motion. When introduced to a system, active matter harvests energy and begins to move.

The term refers to systems that can be either biological or artificial, ranging from the self-organizing components of a living cell to synthetic colloids that react to light with movement. When added to an ordinary material, active particles can change the properties and behavior of that material.

“Any time you have an active fluid, you have a dial that you can use to change its transport properties,” said Wang. “What’s exciting about active particles is that you can change the transport properties of an existing fluid simply by adding an active component and adjusting its level of activity.”

This offers the versatility in design to fine-tune the properties of existing fluids, ultimately increasing their performance and range of applications. However, researchers must first be able to define the properties of active fluids and predict their behavior as energy is added or removed, ideally without exhaustive testing in a lab setup.

Wang and Ghaffarizadeh set out to define predictive and theoretically grounded techniques for describing transport in these active-matter systems. They performed a series of simulations of a model active-matter system, studying its properties as the number of active particles and their level of activity were changed. The relations hip they observed between fluid structure and transport in their active-matter system closely resembled a similar relationship for inactive matter, called excess entropy scaling.

What’s exciting about active particles is that you can change the transport properties of an existing fluid simply by adding an active component and adjusting its level of activity.

Excess entropy is a measure of the difference between the entropy of a system and its maximum possible entropy, in the state of an ideal gas. Excess entropy scaling describes an exponential relationship between the excess entropy of a system and the system’s diffusivity, a critical quantity for fluids engineering that measures how quickly particles wander within a system through small random movements. With Wang and Ghaffarizadeh’s model, researchers would only need to know some basic thermodynamic details about a system and its constituent makeup to determine its transport properties.

This research could save researchers significant time and effort as they explore applications for active matter. For example, heat transfer fluids move heat from one area of a system to another, and include substances like coolants and a variety of oils. The addition of active matter could alter properties like viscosity or thermal diffusion within these common compounds, allowing for improved performance and versatility.