On hard agar gel, there is insufficient surface hydration for bacteria to swim or swarm. Instead, growth occurs in colonies of close-packed cells, which expand purely due to repulsive interactions: individual bacteria push each other out of the way through the force of their growth. In this way, bacterial colonies represent a new type of ``active'' granular matter. In this study, we investigate the physical, biochemical, and genetic elements that determine the static and dynamic aspects of this mode of bacterial growth for E. coli. We characterize the process of colony expansion empirically, and use discrete and continuum models to examine the extent to which our observations can be explained by the growth characteristics of non-communicating cells, coupled together by physical forces, nutrients, and waste products. Our results challenge the commonly accepted modes of bacterial colony growth and provide insight into sources of growth limitation in crowded bacterial communities.
‘‘Assessing the significance of global and local correlations under spatial autocorrelation: a nonparametric approach", 2013, Julia Validomat, Rahul Mazumder, Alex McInturff, Douglas McCauley and Trevor Hastie, 2013, ,
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My research collaboration with ORC students, both doctoral and master’s, has been the most exciting part of my career at MIT. Together, we have made journeys to many sectors, including public safety (police, fire, and ambulance), sanitation, energy management, transportation, inventory management, homeland security, and many more. Along the way, we have framed and formulated new OR models, often with accompanying new methods that generalize to other domains. These new methods have involved a variety of OR sectors, including queueing, graphs, facility location, supply chains, and optimization.
Publications - University of Southern California
What does the ORC mean to me? The Operations Research Center has always been my favorite place at MIT. Why? Because among all of the various units at MIT, only the ORC has it all: charm, wit, wisdom, and the desire to showcase the very best that operations research offers the world. The charm of the ORC stems from its staff and the great students and the great student culture. I don’t know how they do it, but year after year, the students amaze us with their intellect, stamina, humanity for one another, and their delightful approach to the faculty. The wit of the ORC is seen in the decorations and the great ORC T-shirt contest. The wisdom of the ORC is really showcased when I attend a thesis defense. Not only are the students’ theses a great intellectual testament to their talents, but it is also great to see how many fellow students attend a thesis defense to support and uphold the camaraderie of the Center. But most of all, the ORC truly showcases the can-do spirit of operations research by engendering a fearless sense of “I can solve your problem” in the students and the faculty, and shows me month after month, year after year, why I keep coming back to the MIT Operations Research Center.
PhD Thesis Chapter 3 contains ..
Interactions between nanometer-sized particles or molecules suspended in a bulk fluid are well understood. However, when such particles are embedded in a membrane, the inter-particle potential is significantly modified by membrane mediated forces and gives rise to novel phase behavior. Visualizing and manipulating such inclusions in a lipid bilayer is difficult due to the nanometer length scales involved. Here, we use a model system of micron sized colloidal membranes doped with molecules shorter or longer than that of the bulk. Surprisingly, the dopant molecules form self-limited finite size clusters. These clusters further self-organize into a wide variety of higher order structures such as hexagonal and square lattice arrays, lamellar patterns and saddle shaped surfaces. Understanding the phase behavior and measuring repulsive forces between such clusters may have implications for the similar mechanisms that operate in conventional lipid bilayers.