RESEARCH INTERESTS

     Dr. Hull has been involved in a variety of research projects during her years at TSU. Early in her career, she worked in the area of solar energy and holds a patent on a solar engine. During the last ten years, however, much of her research has been in characterizing microscopic materials using polarized light scattering. The focus of that work is threefold: 

  to develop a practical model of polarized light scattering from non-spherical particles, 

  to build a data-base of experimental measurements of the Mueller matrix elements for 
                    light scattering from a variety of microscopic particles, and 

  to design artificial neural networks that are capable of extracting size distribution, 
                    optical properties and shape information from light scattering data. 
 
 

The Scanning Polarization-modulated Nephelometer

     Dr. Hull's research in polarized light scattering began in 1990 when she received a grant from  the Office of Naval Research to evaluate analytical models for light scattering from cylindrically- shaped microscopic objects. Over the next four years, the analytical work was broadened to include modeling light scattering from particles of all shapes. To date, she has instrumental in developing numerical models for describing polarized light scattering from a number of particle shapes such as coated spheres, ellipsoids, helices, cylinders, and fractals. 

     In 1994, an experimental component was added to the research effort in polarized light  scattering. A Laser Optics Laboratory was opened using an equipment grant from the Department 
of Defense Infra-structure Support Program for HBCU/MI's, through the Office of Naval  Research. The computerized light scattering instrument was operational in January of 1995 and  numerous experimental measurements of the Mueller matrix elements have been made for polarized light scattering from particles both in aerosols and in liquid suspension. 

     The third component of research in polarized light scattering funded by ONR, the design and  testing of artificial neural networks for interpreting light scattering data, was added in 1996.  Dr. Hull has designed neural networks that have been successful in extracting particle size  distributions, effective relative index of refraction, and absorption coefficient, from polarized light scattering data. Both analytical and experimental data are used to train and test the artificial neural  networks. The results of the work in neural networks was presented at Ocean Optics Conferences 
in 1996 and 1998.  The last annual report may be viewed by clicking the underlined words, ONR Annual Report 1999. 
 

The primary work in light scattering is funded by the Office of Naval Research. The objective of 
that modeling and experimental work is to understand and quantify polarized light scattering  from ensembles of marine micro-organisms,marine detritus and inorganic particles and to assess
the effect of this scattering on the propagation of light through sea water. In a cooperative effort 
with Mary Quinby-Hunt and Arlon Hunt at Lawrence Berkeley National Laboratory, we have written computer code that takes advantage of the computing power of LBNL's parallel  processing computer facilities to model the light scattering in the marine environment from collections of organisms of different shapes, sizes and optical properties. 

Measurement and Modeling of Polarized Light Scattering from Diesel Soot Particles

A second project with Hunt and Quinby-Hunt is the measurement and modeling of the polarized light scattering from diesel soot particles. The soot particles are modeled by generating shapes  with a computer program using a random walk technique. The light scattering from the particle is then calculated using a  coupled-dipole approximation. Experimental measurements of the lightscattering are compared to that predicted from computer calculations to determine size  distribution of the soot particles. The goal of this project is to develop an instrument for analyzing the soot particle size distribution as the particles exit the exhaust pipe. (New EPA requirements necessitate improved methods for measuring the sizes of exhaust particles.) Due to
the hazardous nature of diesel exhaust, all measurements involving diesel exhaust are made in a  specially constructed laboratory at the University of California. The data from those measurements provide input for the neural network design and testing at TSU. 

Determination of Fiber Orientation in Paper Using Polarized Light Scattering

A third project with Hunt and Quinby-Hunt involves both modeling and experimental measurement of polarized light scattering from microscopic fibers in paper. The goal of this  project is to develop an instrument for measuring the alignment of the fibers in paper as the paper is being made. Adjustments can be made in the production process to correct the fiber alignment when the light scattering instrument indicates particular adjustments are needed. Alignment of the fibers an important factor in determining the strength and quality of the paper. 

Student Involvement

Undergraduate students have been involved in the light scattering research at TSU since 1991 and at least one TSU student has participated in LBNL's Summer Student Program every summer  since 1992. In this program, they were required to write a paper, prepare a poster and present the results of their research work at the fall meeting of theTennessee Academy of Science. Table 1 below lists the students who have participated in research funded by ONR since 1992. 
 

Acknowledgement 

The work at TSU in the mathematical modeling of light scattering from marine micro-organisms
was supported by the Office of Naval Research, Grant Number N00014-96-1-0307, "Experimental Measurements of the Mueller Scattering Matrix for Marine Micro-organisms." The basic instrument used for the experimental measurements and the components for its modification were purchased with an equipment grant from the Department of Defense  Infra-structure Support Program for HBCU/MI's, through the Office of Naval Research, Grant Number N00014-93-I-1267.