Imagine Magazine - Johns Hopkins - September/October 2011 - (Page 18)

solid. How does that work? Microscopically, milk contains many small clumps of protein. The yogurt bacteria produce acid, which changes the protein clumps so that they stick to each other. As these clumps stick, they form a network such as I described, so that the yogurt becomes a solid. The major differences between yogurt and my experiments are that my experiments aren’t edible (unfortunately), and that my particles stick together because of opposite charges and not because of acid. Once I form these networks of particles, I study their properties. With a microscope, I can see where every particle in the network is and track where they move over time. This allows me to study the properties of the system on a single-particle level; for instance, I can determine how many neighbors a typical particle is stuck to. The second tool I use is called a rheometer, which measures the flow or deformation of a material—essentially, how “squishy” it is. Combining the information from these two instruments lets me describe the macroscopic properties (the squishiness of my system) in terms of the microscopic properties (the arrangement and motion of the individual particles that make up the network). I then change the properties of the network—making it more or less squishy, even making it dissolve back into a fluid—by changing the density of the particles, by changing how strongly the particles stick together, or even by adding more of one type of particle than the other. While I do this, I study precisely how these changes to the microscopic structure affect the macroscopic properties. By understanding how this system works, I can draw analogies to more complex systems, such as yogurt, or ceramics, which are also formed of small particles that stick to each other. I can answer fundamental questions about how the interactions between charged particles can create more complex systems such as gels. In the process, I get to see lots of colorful microscope images and get my hands (or rather, gloves) dirty measuring the properties of the gels I study. emily Russell is a PhD student in physics at Harvard University. She was an undergraduate at Caltech, and also obtained a master’s degree at Cambridge University. When not in the lab, she rings bells, dances, and bakes when she can find the time. JoURneY To THe CenTeR oF THe aToM by cory schillaci Just as I arrived home for winter break in my freshman year of college, a massive windstorm swept through the Seattle area. My parents’ house was without electricity for a week, so I read quite a few books by the fireplace—including Atoms in the Family, a biography of Enrico Fermi written by his wife, Laura. Fermi’s life story struck me as a true adventure, a marvelous experience that I had never associated with physics. The next quarter, I signed up for my first physics class, and I’ve never looked back. These days I am a PhD student at the University of California, Berkeley, where I use theoretical tools to study nuclear physics with Professor Wick Haxton. At the core of every atom is a nucleus made up of protons and neutrons. These particles are made up of quarks, which bind together to form not only the familiar protons and neutrons but an entire zoo of exotic particles called hadrons. The fundamental theory that describes the interactions of quarks is called quantum chromodynamics (QCD). Unfortunately, although QCD tells us what equations to write down, nobody knows how to solve them except in very special cases. This is where nuclear physicists come in: we figure out what goes on in systems where QCD is important. At the smallest scales, we are still struggling even to understand what’s inside a proton. We know that if you look closely enough, a proton is really a roiling sea of quarks, anti-quarks (yes, there is antimatter in every proton!), and gluons (particles that hold quarks together). But we don’t know how many of each of these are in Sept/Oct 2011 18 imagine

Table of Contents for the Digital Edition of Imagine Magazine - Johns Hopkins - September/October 2011

Imagine Magazine - Johns Hopkins - September/October 2011
Contents
Big Picture
In My Own Words
Physics Is…
Making the Team
Nuclear by Nature
Physics: The Next Generation
Telescopic Views
Exploring the Mysterious Lives of Stars
Around the Universe in Three Weeks
Selected Opportunities & Resources
Book Buddies
Meeting the (Economics) Challenge
Off the Shelf
Word Wise
Exploring Career Options
One Step Ahead
Planning Ahead for College
Students Review
Creative Minds Imagine
Mark Your Calendar
Knossos Games

Imagine Magazine - Johns Hopkins - September/October 2011