College of Arts and Sciences

Measurements of the electron magnetic moment (the “g-value”) probe the electron’s interaction with the fluctuating vacuum. With a quantum electrodynamics calculation, they provide the most accurate determination of the fine structure constant. Comparisons with independent determinations of the fine structure constant are the most precise tests of quantum electrodynamics and probe extensions to the Standard Model of particle physics. I will present two new measurements of the electron magnetic moment. The second, at a relative uncertainty of 0.28 parts-per-trillion, yields a value of the fine structure constant with a relative accuracy of 0.37 parts-per-billion, over 10-times smaller uncertainty than the next-best methods.

Continue reading… Cavity Control in a Single-Electron Quantum Cyclotron: An Improved Measurement of the Electron Magnetic Moment – David Hanneke

In 1781, William Herschel became the first person in human history to discover a new planet. This feat was enough to make his reputation and enable him to give up his day job to concentrate on the heavens full-time. But he believed–correctly, in retrospect–that it wasn’t nearly as important as his real astronomical work. Working alongside his sister Caroline, William Herschel was the first astronomer to think about the universe in the same way astrophysicists do today.

Continue reading… William Herschel and the Invention of Modern Astronomy – Michael D. Lemonick

We discuss the progress and successes obtained in recent years in predicting fundamental properties of systems in condensed phases and at the nanoscale, using ab-initio, quantum simulations. Our examples will focus on nanostructured materials for opto-electronic, photovoltaic and thermoelectric applications, and on solvation processes in simple aqueous solutions. We will also discuss open issues related to the validation of the approximate, first principles theories used in large scale simulations, and the resulting complex interplay between computation and experiment.

Continue reading… Understanding and predicting material properties: insight from quantum simulations – Giulia Galli

Organic semiconductors have been used as active layer in devices such as organic light-emitting diodes (OLEDs), photovoltaic cells, field-effect transistors, and lasers. Recently there has been a growing interest in spin and magnetic field effects in these materials. This include optically detected magnetic resonance where long spin coherence time was demonstrated; OLEDs where substantive magneto-electroluminescence and magneto-conductance were obtained; and organic spin valves (OSV) where spin injection from ferromagnetic (FM) electrodes was obtained. The interest in organic semiconductors has been motivated by the weak spin-orbit interaction that is caused by the light building block elements such as carbon and hydrogen,

Continue reading… Organic Spintronics – Valy Vardeny

Although the Moon was widely thought to be anhydrous, OH and H2O absorptions were detected on the lunar surface by infrared spectrometers on three different spacecraft. Complimentary data from Moon Mineralogy Mapper (M-cubed; M3) on Chandrayaan-1, the IR spectrometer on Deep Impact, and VIMS on Cassini have mapped widespread hydration at the 0.1 wt% level. The 140 m scale M3 data reveal differences with composition and maturity, while temporal variations in Deep Impact data show the entire surface to be hydrated during some portions of the day. In particular, comparisons between data collected one week (a quarter lunar day) apart show a dynamic process with diurnal changes in hydration,

Continue reading… Water on the Surface of the Moon – Jessica Sunshine (jointly with Astronomy)

Continue reading… Deterministic Isoeffective Dose – Proposal for a New Unit – The Barendsen (Bd) – Barry Wessels,

Even talented students struggle with fundamental concepts in mathematics and physics. They cannot reason with graphs and have no feel for physical magnitudes. Their instincts are Aristotelian; in their gut they believe that force is proportional to velocity. With such handicaps in mathematical and physical reasoning, they can learn only by rote. I’ll discuss these difficulties and how the art of approximation can improve our teaching and students’ learning. Students then cannot conceal misconceptions behind mathematical agility, and can enjoy estimating the size of raindrops, the pitches of xylophone slats, or the distance that birds (and 747’s) can fly without refueling.

Continue reading… 2=1: The Gentle Art of Lying

Over a century ago, Boltzmann and others provided a microscopic understanding for the tendency of entropy to increase. But this understanding relies ultimately on an empirical fact about cosmology: the early universe had a very low entropy. Why was it like that? Cosmologists aspire to provide a dynamical explanation for the observed state of the universe, but have had very little to say about the dramatic asymmetry between early times and late times. I will argue that the observed breakdown of time-reversal symmetry in statistical mechanics provides good evidence that we live in a multiverse.

Continue reading… The Origin of the Universe and the Arrow of Time – Sean Carroll

The physical processes that govern planet formation, migration, and evolution are imprinted on the orbital element and mass distributions of exoplanets. Theories of planet formation and evolution have matured to the point where specific predictions for these distributions have been made, yet there are relatively few robust comparisons of these predictions with observations. I will discuss the progress and prospects for measuring the demographics of exoplanets using a variety of techniques, emphasizing the importance of homogeneous statistical analyses and proper accounting of selection effects, and highlighting the ability of various techniques to probe complementary regions of parameter space. In particular,

Continue reading… The Demographics of Exoplanets – Scott Gaudi

Molecular self-assembly mediated by noncovalent bonds is becoming increasingly popular as a “bottom up” approach in forming nano- and meso-scale soft materials. One of the most attractive aspects of this approach is the prospect of assembling structures with molecular precision under experimentally straightforward and inexpensive conditions. This talk will focus on self-assembled chiral lipid tubes, which are promising candidates for drug delivery vehicles. Three issues will be addressed in this talk. First, I will describe the interactions and mechanisms underling chiral lipid assembly based on the structural characterization of lipid tubes. Second, I will discuss the elasticity and buckling instability of lipid tubes under local radial indentation,

Continue reading… From the Bottom Up: Self-Assembled One-Dimension Soft Materials – Jiyu Fang

It is well known that one cannot image directly through a nonlinear medium, as intensity-dependent phase changes distort signals as they propagate. For this reason, nearly all nonlinear imaging techniques are point-by-point methods that rely on the frequency dependence of multi-photon effects, such as two-photon fluorescence and harmonic generation. Here, we focus on spatial effects by taking advantage of spatially dependent changes in the index of refraction. In particular, we apply wave mixing to (lensless) imaging by extending digital holography to the nonlinear domain. The method relies on propagation and provides a new means of super-resolution, e.g. by coupling low and high spatial frequencies.

Continue reading… Dynamical Imaging using Spatial Nonlinearity – Jason W. Fleischer

Colloidal dispersions consist of small particles that are immersed in a molecular fluid. The particles move by diffusion, driven by the thermal motion of the molecules surrounding them. However, as the particle concentration increases, the diffusion of the particles becomes increasingly hindered due the presence of their neighbors; consequently, the structural relaxation time, describing the time-scale over which the system reconfigures, increases. This structural relaxation time appears to diverge at a critical concentration that defines the colloidal glass transition, where solid-like behavior sets in. We use new dynamic light scattering methods to probe structural relaxation processes of systems composed of deformable spheres extending the range of volume fraction investigated to deeply quenched systems,

Continue reading… Structural relaxations beyond the colloidal glass transition – Veronique Trappe

The presentation will outline the physics of photonic crystals and photonic nanowires employing silicon and organic materials. Dispersion properties and slow light effects will be discussed as well as nonlinear optical phenomena in such structures. Application perspectives in computer industry will be illustrated.

Continue reading… Photonics with Organic-Inorganic Nanostructures – Manfred Eich

Soft Condensed Matter (SCM) is a broad area of science, which includes studying liquids, colloids, gels, polymers, foams, biomaterials, etc. The common feature shared by all SCM materials is the energy associated with their behavior, which is comparable with the ambient thermal energy. With the development of new instrumental and modeling base, SCM faces discoveries of new phenomena, and consequently, new challenges of their understanding. In this talk, I will describe several of such challenges, and focus on two of them, the challenges we came across recently. The first challenge is the understanding of abnormally slow diffusion in silica nanochannels (nanotubes).

Continue reading… On a Few Challenges in Soft Condensed Matter Physics – Igor Sokolov

I will address the problem of DNA packing in the bacteriophage capsid. I will show that it can be formulated in the framewrok of a liquid crystalline nematic nanodrop model. The elastic equilibrium condition can be written as a first intergral of the EL equations and gives the elastic stresses in the system. Solving the first integral for the DNA density field leads to the encapsidation equation of state that compares well with osmotic stress experiments and predicts the ejection characteristics in the presence of polyvalent counterions. I will also discuss the effects of osmotic stress on empty viral capsids and show that there exists a critcal value of the osmotic stress that destabilizes the capsid.

Continue reading… Effects of osmotic stress on DNA packing and capsid stability in simple viruses – Rudi Podgornik

Come hear about the Nobel prizes in Chemistry, Medicine or Physiology, and Physics from local experts.

Continue reading… The 2009 Nobel (Sciences) Prize-fest – Kathy Kash, William Merrick, Ken Singer, and Derek Taylor

Over the past decade, observations have sparked a renaissance of planetary studies, with nearly 400 planets discovered in orbit about external stars and an ever-increasing inventory of our solar system. These planetary systems display an unexpected diversity in their observed orbits and in the types of bodies found. This wealth of new data poses a number of dynamical issues that will be discussed in this talk: How do planets migrate from one location in a solar system to another, and how does migration ultimately produce the observed distribution of orbital elements? How does turbulence, which provides stochastic forcing, affect both early migration of planetary cores and the maintenence of mean motion resonance?

Continue reading… Dynamical Processes in Extrasolar Planetary Systems – Fred Adams

Graphene, a single atomic layer of sp2-hybridized carbon atoms, has been the subject of intense scientific interest recently. Many of the most intriguing transport and optical properties of graphene relate directly to its two-dimensional (2D) electronic band structure, with its linear dispersion relation for the low-energy excitations near the K-point of the Brillion zone. Optical Spectroscopy provides a powerful tool to probe the structure of electronic excitations in graphene. In this talk I will review some of the basic properties of this novel material. I will then report several optical studies that I have been involved in the past year during my sabbatical at Columbia University.

Continue reading… Probing electrons in a flatland: optical spectroscopy of graphene – Jie Shan

While it is not quite true that one can learn physics from superhero comic books, it is the motivation for a Freshman Seminar class I teach at the University of Minnesota entitled: “Everything I Know About Science I Learned from Reading Comic Books”. This class covers everything from Isaac Newton to the transistor, but there’s not an inclined plane or pulley in sight. Rather, ALL the examples come from superhero comic books, and as much as possible, those cases where the superheroes get their physics right! For example, have you ever wondered how strong you would have to be to “leap a tall building in a single bound?”

Continue reading… The Uncanny Physics of Superhero Comic Books – James Kakalios

A follow-up experiment to the Sudbury Neutrino Observatory is being developed, called SNO+. With a liquid scintillator replacing the heavy water, SNO+ will examine neutrino phenomena at lower energies than SNO. Physics goals include: detecting the CNO solar neutrinos and using them to resolve a new puzzle related to solar chemical composition; precision measurements of the survival probability of pep solar neutrinos at the transition energy between vacuum- and matter-dominated oscillations; and measuring the flux of geo-neutrinos at a detector site where the local geology has been extensively characterized, enabling the measurement to address fundamental questions in geoscience. We also plan to add neodymium to the SNO+ liquid scintillator in order to perform a competitive next-generation 0-nu double beta decay search.

Continue reading… Neutrino Physics Beyond SNO – Mark Chen

If we deform a material and restore it precisely back to its starting point, our everyday intuition tells us that the material before and afterwards is identical. This is true classically, and was believed to be true quantum mechanically until recently. Even if all the atoms, electrons, and other ingredients are returned exactly to where they started, we now know that the restored material can differ from the undeformed material by nontrivial quantum mechanical phase factors. The importance of these so-called geometric or Berry phases has garnered increasing appreciation and attention in recent years. The quantum Berry phase can fundamentally alter the ground state of a system,

Continue reading… Close Encounters with the Quantum Berry Phase – Hari Manoharan

The Fermi Gamma-ray Space Telescope has completed its first year of observations. The two instruments on Fermi cover more than 7 decades in energy: the Large Area Telescope (LAT) is a wide field-of-view pair-conversion telescope covering the energy range from 20 MeV to more than 300 GeV; the Gamma-ray Burst Monitor complements the LAT in its observations of transient sources and is sensitive to X-rays and g-rays with energies between 8 keV and 40 MeV. During the first year in orbit, Fermi has continually surveyed the entire sky every 3 hours and observed a large number of sources that include active galaxies,

Continue reading… Fermi Gamma-ray Space Telescope: The First Year – Peter Michelson

How do we weigh the Universe? Where is the Dark Matter? I will discuss these questions and show that several independent methods, including the observed abundance of rich clusters , the baryon-fraction in clusters, the observed Mass-to-Light function from galaxies to superclusters, and other large-scale structure observations, all reveal a universe with a low mass density of ~20% of the critical density. The data suggest that the mass in the Universe, including the dark-matter, follows light on large scales, and most of the mass resides in huge dark halos around galaxies. I will review the combined observational evidence for dark-matter and for dark-energy in the universe and their cosmological implications.

Continue reading… Weighing the Universe – Neta Bahcall

Virtually all aspects of RNA metabolism involve RNA helicases, enzymes that remodel RNA and RNA-protein complexes in an ATP-dependent fashion. How RNA helicases catalyze such reactions is a key question in RNA metabolism, with implications ranging from understanding the regulation of gene expression to delineating the cellular response to viral infections. In this seminar, I will present recent results that illuminate how different RNA helicases couple ATP binding and hydrolysis to RNA duplex unwinding. Our data reveal a remarkable diversity of unwinding mechanisms among these enzymes.

Continue reading… How RNA helicases unwind – Eckhard Jankowsky

The potential of emerging technologies such as fuel cells (FCs) and photovoltaics for environmentally-benign power generation and conversion has sparked intense interest in the development of new materials for high density energy storage. For applications in the transportation sector, the demands placed upon energy storage media are especially stringent, as a potential replacement for internal combustion engines — the PEM FC — requires hydrogen as a fuel. Although hydrogen has about three times the energy density of gasoline by weight, its volumetric energy density (even at 700 bar) is roughly a factor of six smaller. Consequently, the safe and efficient storage of hydrogen has been identified as one of the key challenges to realizing a transition to FC vehicles.

Continue reading… Combining computation and experiment to accelerate the discovery of new hydrogen storage materials – Donald J. Siegel

In this colloquium I will discuss my recent work in electronic-structure theory, which allows us to more accurately study water from first-principles. First, I will address a shortcoming of standard density functional theory, which gives poor results for systems with van der Waals interactions such as bulk water. To remedy the situation, I will introduce a new exchange-correlation functional that includes van der Waals interactions in a seamless manner. The main advantage of our approach is the much more favorable scaling of the computational expense compared to standard quantum-chemistry approaches. Second, I will present a Wannier-function approach to derive a fully quantum-mechanical theory for the orbital magnetization in periodic crystals,

Continue reading… A van der Waals DFT Approach to Modeling Water – Timo Thonhauser

I will provide an introduction to quantum dots, a problem where disorder, interactions and finite size combine to make a perfect storm. Yet it is just this combination that makes an exact solution possible. I will describe that solution and give an introduction to the tools used: renormalization group and random Matrix Theory.

Continue reading… Dots for Dummies – Ramamurti Shankar

This talk examines how American foreign relations and national security between 1840 and 1920 were shaped by developments in geology, steam engineering, and the science of logistics. At the same time, technical experts trained their research on the combustion and distribution of coal, the design of steam engines, and the rational management of resources to address new challenges faced by the United States’ growing power in world affairs. This history examines how a new energy technology answered old problems while creating new ones.

Continue reading… When Coal was an Alternative Energy: Engineering, Efficiency, and American Foreign Relations in the Age of Steam – Peter Shulman

The Cosmic Microwave Background Radiation is our most important source of information about the early universe. Many of its features are in good agreement with the predictions of the so-called standard model of cosmology — the Lambda Cold Dark Matter Inflationary Big Bang. However, the large-angle correlations of the microwave background exhibit several closely related statistically significant departures from the standard model. The lowest multipoles seem to be correlated with each other, rather than statistically independent as inflationary theory demands. Indeed, they also seem to be correlated with the geometry of the solar system, suggesting that they are not cosmologically produced.

Continue reading… How the CMB challenges cosmology’s standard model – Glenn Starkman

Overwhelming cosmological and astrophysical evidence suggests that the dominant mass in the universe is in the form of as-yet-unidentified dark matter. The most favored candidate for dark matter is weakly interacting particles (WIMPs), which are also a generic prediction in supersymmetry. WIMPs in our galaxy can be measured by their interactions in detectors operated deep underground with backgrounds from radioactive and cosmic-rays suppressed by some 10 orders of magnitude from ambient levels. Recent advances in detectors based on liquified noble elements promise a radical increase in the sensitivity of these experiments, and will allow a nearly complete test of supersymmetric dark matter in the next decade.

Continue reading… LUX, LZ, and the Limits of our Ability to Directly Detect Dark Matter – Tom Shutt