Event | Date | Summary |
In proximity to novel physics: Topological Insulators coupled to Superconductors – Nadya Mason | Thu. December 5th, 2013 4:15 pm-5:15 pm |
Topological insulators (TI’s) are materials that are insulators in their interiors, but have unique conducting states on their surfaces. They have attracted significant interest as fundamentally new electronic phases having potential applications from dissipationless interconnects to quantum computing. In particular, coupling the surface state of a TI to an s-wave superconductor is predicted to produce the long-sought Majorana quasiparticle excitations, which could play a role in solid-state implementations of a quantum computer. A requisite step in the search for Majorana fermions is to understand the nature and origin of the supercurrent generated between superconducting contacts and a TI. In this talk, |
Fukushima: Implications for the Understanding of Severe Accidents and the Future of Nuclear Energy – M.V. Ramana | Thu. November 21st, 2013 4:15 pm-5:15 pm |
Like the earlier nuclear accidents at Three Mile Island (1979) and Chernobyl (1986), the multiple accidents at the Fukushima Daiichi nuclear plant will have an impact on both our understanding of severe accidents and on the likely future deployment of nuclear power. This talk will examine what happened at Fukushima from the viewpoint of multiple perspectives on nuclear safety. This will be followed by an examination of how governments in different countries have responded to the accident, and how this could affect plans for constructing nuclear reactors around the world over the coming decades. |
Magnetism Without Magnetic Atoms: The Physics of the Vacancy Center in Graphene – Sashi Satpathy | Thu. November 14th, 2013 4:15 pm-5:15 pm |
Graphene is a material of considerable current interest owing to its linear band structure and excitations that behave as massless Dirac fermions. In this talk, I will focus on the physics of a vacancy in graphene and show that it forms a magnetic center and, quite interestingly, it is also a Jahn-Teller center due to the coupling between the vacancy electronic states and the local lattice modes. However, the energetics are such that there is only a small potential barrier between the Jahn-Teller minima, leading to the quantum mechanical tunneling of the nuclei between the three minima, resulting in the dynamical Jahn-Teller effect. |
To Superconduct or Not to Superconduct; That is the Question – Michelson Postdoctoral Prizewinner Wei-Cheng Lee | Thu. November 7th, 2013 4:15 pm-5:15 pm |
Superconductor, a material losing resistivity below a critical temperature Tc, remains one of the grand challenges in physics. This field began in 1911 with the discovery of superconductivity in mercury at 4.2 K. After the birth of a complete microscopic theory of superconductivity proposed by Bardeen, Cooper, and Schrieffer in 1957, known as BCS theory, it was believed that no materials could have Tc higher than 30 K. The discovery of new classes of superconductors, cuprates in 1986 (which shatter the 30 K barrier) and iron pnictides in 2008, launched an international wave of research to find new materials with higher Tc. |
Graphene at the Boundaries – Paul McEuen | Thu. October 31st, 2013 4:15 pm-5:15 pm |
With its remarkable structural, thermal, mechanical, optical, and electronic properties, graphene is a true interdisciplinary material. In this talk we will discuss experiments where graphene shows its many sides. For example, we will discuss atomic-scale imaging experiments of bilayer graphene that reveal the presence of 1D strain solitons between the layers. These strain solitons have recently been predicted to give rise to topologically protected 1D electronic edge states. We will also present measurements of the bending stiffness of graphene on micron scales. We find that graphene is thousands of times stiffer than predicted by atomic theories, but in good agreement with calculations that take into account the effects of thermal fluctuations on the bending stiffness. |
The Cosmic Gravitational Wave Background – Tom Giblin | Thu. October 24th, 2013 4:15 pm-5:15 pm |
As we prepare for news from the Laser-Interferometer Gravitational Wave Observatory (LIGO) theoretical and computational physics are crawling over each other to identify cosmological sources of gravitational radiation in the LIGO sensitivity region. As one of those theorists, I will outline some of the progress we have made toward making precision predictions for gravitational radiation from cosmological sources. To the same end, I will discuss the limitations of observing cosmological sources at LIGO and why precision estimates are so important at this time. I will also present a “rule of thumb” that can be used to quickly evaluate to-good-to-be-true predictions. Continue reading… The Cosmic Gravitational Wave Background – Tom Giblin |
Dark Materials: the Topology of Insulators – Harsh Mathur | Thu. October 17th, 2013 4:15 pm-5:15 pm |
Topological insulators are insulating materials with conducting surfaces. In this talk I will introduce topology by its application to the analysis of tie knots. I will then describe the remarkable electrostatics of topological insulators that mimics the behavior of axion domain walls studied in particle physics. Possible experiments to observe this physics will be discussed. Finally I will give a pedagogical introduction to the Su-Schrieffer model, a simple one dimensional analog of a topological insulator. My collaborators and I have proposed a photonic realization of this model that has now been observed experimentally. Continue reading… Dark Materials: the Topology of Insulators – Harsh Mathur |
Isostatic Lattice: From Jamming to Topological Surface Phonons – Tom Lubensky | Thu. October 10th, 2013 4:15 pm-5:15 pm |
Frames consisting of nodes connected pairwise by rigid rods or central-force springs, possibly with preferred relative angles controlled by bending forces, are useful models for systems as diverse as architectural structures, crystalline and amorphous solids, sphere packings and granular matter, networks of semi-flexible polymers, and protein structure. The rigidity of these networks depends on the average coordination number z of the nodes: If z is small enough, the frames have internal zero-frequency modes, and they are “floppy”; if z is large enough, they have no internal zero modes and they are rigid. The critical point separating these two regimes occurs at a rigidity threshold, Continue reading… Isostatic Lattice: From Jamming to Topological Surface Phonons – Tom Lubensky |
Modeling and simulating cellular processes in the brain: a mathematical challenge – Daniela Calvetti | Thu. October 3rd, 2013 4:15 pm-5:15 pm |
Abstract: Understanding human brain is one of the greatest challenges of science, not the least because, almost by definition, it is too complex to be understood by a human brain. The brain accounts for about 2% of our body weight, yet it consumes about 20% of the oxygen we intake, showing how central the energy metabolism must be for signalling. What we know about the functioning of the brain is based on indirect information: brain imaging, cell cultures and animal models. Therefore, to quantitatively integrate the information into a comprehensive picture requires an across-the-scales mathematical model that, at the microscopic end of the scale, |
Michelson and Morley –the men, the experiment, and the 1987 Centennial Celebration – Various + P. Taylor | Thu. September 26th, 2013 4:15 pm-5:15 pm |
The Michelson-Morley experiment is arguably the most important measurement ever performed in the history of science. If its result had been different, then our whole conception of space and time would be very far from the picture that Einstein gave us in his special theory of relativity. The collaboration between these two great men was literally born in fire, and was ended by an arrest. After a brief discussion of the history and importance of the experiment, and a description of the remarkably dissimilar personalities of Cleveland’s two most famous scientists, we will see some excerpts from the 1987 Celebration at which all but one of America’s living Physics Nobelists spoke. |
Green commercial buildings: are they saving energy or are they just making us feel good? – John Scofield | Thu. September 19th, 2013 4:15 pm-5:15 pm |
US buildings consume roughly 40% of the nation’s primary energy and are responsible for a similar fraction of our greenhouse gas emission. There is tremendous documented potential for lowering both of these figures through cost-effective energy efficiency improvements in buildings. Green building rating systems such as ENERGY STAR and LEED represent national efforts to realize these savings. But what do the data tell us about their success in reducing building energy consumption and greenhouse gas emission. Because building energy data are the property of building owners energy performance data are limited. What little data we have shows us that 1) there is a huge performance gap between a building’s predicted energy consumption and its measured consumption. |
To wet or not to wet? That is the Question – Milton Cole | Thu. September 12th, 2013 4:15 pm-5:15 pm |
If one looks at a leaf of a plant after a rainfall, one sees water droplets of varying sizes. What determines this “wetting” behavior? The answer, known in principle for two centuries, involves the surface tension of the water itself, as well as the two surface tensions at the water-leaf interface (liquid-leaf and vapor-leaf). At the microscopic level, the wetting behavior depends on the relationship between two interactions: the cohesive interaction between two water molecules and the adhesive interaction between a water molecule and the leaf. In this talk, I will report the first wetting phase transition for water ever to be seen. Continue reading… To wet or not to wet? That is the Question – Milton Cole |
Light or Dark? Mass and Gravity in the Universe – Stacy McGaugh | Thu. September 5th, 2013 4:15 pm-5:15 pm |
We now have a well developed cosmological paradigm, LCDM, in which most of the mass-energy is composed of unknown dark components. This picture provides a satisfactory description of large scale structure but has serious failings on the small scales of individual galaxies. Simultaneously, we have some unlikely successes of an alternative theory of gravity, MOND, in predicting the dynamical behavior of galaxies while offering little in the way of a cosmology. Neither theory obviously subsumes the other, posing a dilemma with profound implications. Continue reading… Light or Dark? Mass and Gravity in the Universe – Stacy McGaugh |
“Look to the Stars” – an episode starring Case’s first Physics Professor – Albert A. Michelson | Thu. August 29th, 2013 4:15 pm-5:15 pm |
The semester’s first colloquium will be somewhat out of the ordinary – a screening of an old TV episode. The highly popular and long-running series Bonanza was a staple of American television from the late 1950s until the early 1970s, and continues in syndication. The series often tackled difficult and highly charged cultural themes. Here, a 1962 episode centers on high school-aged and Case-physics-professor-to-be Albert Michelson’s dealings with science, education, and bigotry in the Old West. The show’s science and history may be somewhat dubious, but it provides an interesting and amusing insight into late 19th century frontier culture and a connection with our own department. |