The temporal sequence of radiofrequency (RF) pulses and magnetic field gradients forms the equivalent of a “musical score” in nuclear magnetic resonance experiments. Like the notes in music, the number, duration, and shapes of RF pulses in the pulse sequence can be altered to create different effects. In MRI, for example, the pulse sequence can be “tuned” to maximize contrast for detecting different microscopic and macroscopic properties of tissue. In this way, MR images can be generated to display not only anatomy, but molecular signatures, physiology, and function. Advances in pulse sequence design are leading to improved data quality, as well as greater sensitivity and specificity to differentiate between normal tissues and pathology with MRI.
Traditionally, only the amplitude, and not the frequency of the RF pulse is modulated when it is transmitted in a pulse sequence. Exceptions to this include the class of frequency-modulated (FM) pulses that function “adiabatically” (for review, see (1)). Currently, adiabatic pulses are exploited mostly to avoid deleterious effects from experimental imperfections, such as RF field non-uniformity. However, recently we have demonstrated that FM pulses operating sub-adiabatically can be used to manipulate nuclear spins in new ways and to create unique images with contrast based on spin relaxation never observed previously. Examples include MRI signals that decay too rapidly to be detected by conventional methods.
In this presentation, I will describe methodologies and applications for this fundamentally different approach to MRI. The main technique to be discussed is known as SWIFT (SWeep Imaging with Fourier Transformation) (2). This and other new FM techniques promise to expand the role of MRI in areas such as materials science, neuroscience, molecular imaging, and clinical medicine.

1. Garwood M, DelaBarre L. The return of the frequency sweep: Designing adiabatic pulses for contemporary NMR. J Magn Reson 2001;153:155-177.
2. Idiyatullin D, Corum C, Park J-Y, Garwood M. Fast and quiet MRI using a swept radiofrequency. J Magn Reson 2006;181:342-349.

The University of Minnesota operates the only deep underground, multi-experiment physics laboratory currently existing in the United States at Soudan MN. Soudan is the target for one of three long baseline neutrino beams in the world. The lab at Soudan provides opportunities for physics research on multiple topics.

Research in the Thomas lab focuses on protein structure and dynamics in skeletal and cardiac muscle, to determine the molecular mechanisms of muscle function and malfunction. Principal tools: optical and magnetic resonance spectroscopy, enzyme kinetics, and computational molecular modeling. A rotation project or thesis project, tailored to the student’s interests, can involve any of four muscle proteins (myosin, actin, calcium pump, phospholamban) and five spectroscopic techniques (fluorescence, phosphorescence, luminescence, EPR, NMR), and can focus on fundamental mechanisms, spectrosocopic techniques or theory.
Example 1 (see figure at left above): Express single-Cys mutants of myosin in cell culture, label them with fluorescent dyes, measure function at the single molecule level, use laser spectroscopy to measure myosin structural dynamics during ATP hydrolysis, use data to construct a new computer model of muscle contraction.
Recent Reference: Nesmelov, Y. E., R. V. Agafonov, A. Burr, R. T. Weber, and D. D. Thomas. 2008. Structure and dynamics of the force generating domain of myosin probed by multifrequency electron paramagnetic resonance. Biophys J, 95: 247-256.
Link to web site: http://ddt.biochem.umn.edu/Papers/S1WX.pdf
Example 2 (see figure at right above): Express functional mutants of phospholamban, related to heart disease, and use spectroscopy to determine effects of these mutations on protein structural dynamics.
Recent Reference: Winters, D. L., J. M. Autry, B. Svensson, and D. D. Thomas. 2008. Interdomain FRET in SERCA Probed by Cyan Fluorescent Protein Fused to the Actuator Domain. Biochemistry, 47: 4246–4256.
Link to web site: http://ddt.biochem.umn.edu/Papers/CFPFITC.pdf

While most investigators focus on their signal, and seek to eliminate any noise, studies of fluctuation phenomena can reveal important information concerning defect kinetics and conduction mechanisms not easily available through conventional transport measurement techniques. In this talk I will describe studies of current noise in thin film hydrogenated amorphous silicon (a-Si:H) that displays a spectral density that varies as the inverse of the frequency (termed 1/f noise). The conductance noise in a-Si:H is non-Gaussian, where the magnitude and spectral slope of the noise power varying in time. Fourier analysis of the noise power fluctuations yields a “second spectrum” which itself has an 1/f frequency dependence. That is, in amorphous silicon, the 1/f noise has 1/f noise! We observe striking random telegraph switching noise in these materials that is interpreted as indicating the presence of inhomogeneous current filaments whose connectivity and conductivity vary with time. These studies have been extended to other complex systems whereby current microchannels fluctuate in time. We have studied voltage fluctuations recorded from awake, behaving rats and applied the noise analysis techniques developed to investigate non-Gaussian phenomena in amorphous semiconductors. We have developed a simple yet powerful technique for identifying coherent oscillations in neurological signals that we have then been able to correlate for particular actions taken by the animal. The implications of these studies for our understanding of Parkinson’s disease will be discussed.

There has been a renaissance in magnetism in the last decade or so. In the area of micromagnetics (although in the modern context it should be nanomagnetics), major breakthroughs have resulted from the development of new magnetic imaging techniques 1. A powerful magnetic microscope is the magnetic force microscope (MFM), a variant of the atomic force microscope. One of the frontiers in magnetism being pushed back is to understand the domain structure and the magnetization reversal in nanometer sized particles. We have utilized the high resolution MFM (30 nm) we developed 2 to increase our fundamental understanding of magnetism on this length scale. First I will present a very elementary introduction to micromagnetics research and a description of MFM with a hands on demonstration of the basic principle. First we will present a very elementary introduction to micromagnetics research and a description of MFM with a hands on demonstration of the basic principle. We will next discuss, in some detail, one of the magnetic materials we study, 50nm magnetite crystals (a magnetosome) grown in magnetotactic bacteria (this includes a video of the bacteria trying to find food at the end of the magnetic rainbow). At the end of the talk we will discuss the magnetic states and the magnetization reversal process in magnetosome chains and lithographically prepared stadia of the soft magnetic material, permalloy.

1. E. Dan Dahlberg and Jian-Gian Zhu, Physics Today 48, 34 April 1995.

Supported by ONR and the University of Minnesota MRSEC.

Very clean two-dimensional electron systems can be realized on the interface of two semiconductors, such as GaAs and AlGaAs, by molecular beam epitaxy. The most remarkable phenomena discovered in such systems, when it is subject to high magnetic field and low temperature, are integral (Nobel Prize, 1985 - http://nobelprize.org/nobel_prizes/physics/laureates/1985/press.html) and fractional (Nobel Prize, 1998 - http://nobelprize.org/nobel_prizes/physics/laureates/1998/illpres/) quantized Hall effects. Over the past few years it was realized that various classes of magnetoresistance oscillations (other than Shubnikov-de Haas oscillations) can appear in these systems when subject to microwaves, dc electric fields, elevated temperatures, or their combinations. This seminar will survey recent experimental and theoretical developments in this growing field of non-equilibrium quantum transport. Interested students are encouraged to visit our group website: http://groups.physics.umn.edu/zudovlab/

A cell-free expression system is used to reconstruct genetic circuits in vitro. Reactions are carried out in batch mode to study quantitatively the properties of synthetic genetic circuits. The extract can be also encapsulated in synthetic phospholipids vesicles. This system is used as a model of protocell. Perspectives and limitations of this approach will be discussed.

This lecture presents a perspective of modern ideas regarding large extra dimensions which, possibly, exist in our world. I base my presentation on general physics, quantum mechanics, basics of field theory and some commonly known facts from high-energy physics, leaving aside technicalities.