The University of Utah
Department of Physics & Astronomy at the University of Utah

Annular Eclipse Party at South Physics

Annular Solar Eclipse party

South Physics Observatory (map)

Sunday, May 20, 2012


Priti Shah Thesis Defense 05/10/12

Thesis Defense

Priti Shah

Thursday, May 10, 2012
3:00pm (206 JFB)

Title: Monocular Measurement of the Ultra High Energy Cosmic Ray Spectrum while Relaxing the Profile Constraint


Cosmic rays are charged particles of galactic and extragalactic origin. In the ultra high energy regime, due to their extremely low flux, cosmic rays can only be observed indirectly via an extensive air shower induced when they interact in the Earth's atmosphere. The Telescope Array (TA) experiment, the largest experiment in operation in the northern hemisphere, observes the longitudinal profile of the fluorescence light from these extensive air showers via telescopes. The Middle Drum fluorescence telescope station utilizes the same equipment as the HiRes-I site of the High Resolution Fly's Eye (predecessor to Telescope Array) experiment. The equipment has simply been reconfigured. As HiRes-I, the telescopes viewed 3-17o in elevation and nearly 360o in azimuth. As a result of this, the track length in the cameras tended to be short. In the Telescope Array configuration, the telescopes view 3-31o in elevation, but only about 120o in azimuth, however, the resulting track lengths are significantly longer. With the short track lengths, one needed to make an assumption about the shape of the profile; that it had a Gaisser-Hillas shape. The longer track lengths make this unnecessary. I have analyzed the data using a Time vs Angle geometry method. The results show an ultra high energy cosmic ray energy spectrum that is consistent with the previous results of the HiRes experiment as well as that measured by the TA surface detectors.


Su Liu Thesis Defense 05/09/12

Thesis Defense

Su Liu

Wednesday, May 9, 2012
9:30am (334 JFB)

Title: Manipulation of Exciton Dynamics in Macrocycle Molecules and Inorganic Semiconductor Nanocrystals


The temporal dynamics of excitons and the evolution of excited states of a material system reflect both the excitation conditions and the final destination of the excitation energy. Precise control of material structure through modern nanofabrication provides nanostructures with well-defined relaxation paths of excitons, which can be manipulated and probed using external stimulation. In particular, electrostatic manipulation of exciton dynamics with external electric fields can be used to study electronic properties of novel material systems such as semiconductor nanocrystals and pi-conjugated molecules, which may be well suited for future applications in optoelectronic devices.

In this work, electric field induced quenching of photoluminescence through generation of indirect excitons is performed on colloidal tetrapod heterostructure nanocrystals and a multichromophoric model molecular system. The dependence of quenching on optical excitation density, which shows opposite trends in these two material systems, reflects the specific origin of quenching in each system. The large reduction in decay lifetime of indirect excitons in the tetrapods also enables storage of optical information with external electric field, which can be observed using time-resolved spectroscopy. As a model light-harvesting system with efficient energy funneling from the arm to the core, the tetrapod is an ideal system to study the impact of electric field on multiexciton states in the core and the “hot” excitons in the arm, thus providing insight into the effects of an electric field on intraparticle energy transfer. While energy transfer in the heterostructure tetrapods is through direct charge carrier thermalization, it is coherent and incoherent dipolar energy transfer that couple chromophores in the multichromophoric molecules which mimic the intermolecular interactions in organic electronics. Both single molecule spectroscopy and time-resolved spectroscopy were employed to probe the structurally dependent coherent and incoherent energy transfer.


Fanxiang Jiao Thesis Defense 05/08/12

Thesis Defense

Fanxiang Jiao

Tuesday, May 8, 2012
10:00am (3780 WEB)

Title: Uncertainty Analysis and Visualization of Diffusion Tensor Images


Diffusion magnetic resonance imaging (dMRI) has become a popular technique to detect brain white matter structure. However, imaging noise, imaging artifacts, and modeling techniques, etc., create many uncertainties, which may generate misleading information for further analysis or applications, such as surgical planning. Therefore, how to analyze, effectively visualize, and reduce these uncertainties become very important research questions. In this dissertation, we present both rank-k decomposition and direct decomposition approaches based on spherical deconvolution to decompose the fiber directions more accurately for high angular resolution diffusion imaging (HARDI) data, which will reduce the uncertainties of the fiber directions. By applying volume rendering techniques to an ensemble of 3D orientation distribution function (ODF) glyphs, which we call SIP functions of diffusion shapes, one can elucidates the complex heteroscedastic structural variation in these local diffusion shapes. Furthermore, we quantify the extent of this variation by measuring the fraction of the volume of these shapes, which is consistent across all noise levels, the certain volume ratio. To better understand the uncertainties in white matter fiber tracks, we propose three metrics to quantify the differences between the results of diffusion tensor magnetic resonance imaging (DT-MRI) fiber tracking algorithms: the area between corresponding fibers of each bundle, the Earth Mover's Distance (EMD) between two fiber bundle volumes, and the current distance between two fiber bundle volumes. Based on these metrics, we discuss an interactive fiber track comparison visualization toolkit we have developed to visualize these uncertainties more efficiently. Physical phantoms, with high repeatability and reproducibility, are also designed with the hope of validating the dMRI techniques. In summary, this dissertation provides a better understanding about uncertainties in diffusion magnetic resonance imaging: where and how much are the uncertainties? How to reduce these uncertainties? How to possibly validate our algorithms?


Follow Us

Support Us

Make A Difference

Outreach: The Department of Physics & Astronomy at the U

Community Outreach

Scholarships: The Department of Physics & Astronomy at the U

Academic Scholarships

General_Development: The Department of Physics & Astronomy at the U

Other Areas
of Support


Our Newest Program:

Crimson Laureate Society


Click to download full size.

The Department of Physics & Astronomy at the U


Science, it makes us all go


Even Our English Majors Study Physics


The Formula For The Perfect Pass


  • Dept of Physics & Astronomy • 201 James Fletcher Bldg. 115 S. 1400 E., Salt Lake City, UT 84112-0830
  • PHONE 801-581-6901
  • Fax 801-581-4801
  • ©2018 The University of Utah