Minh Q. Phan

Thayer School of Engineering
Dartmouth College, Hanover, NH 03755
mqphan@dartmouth.edu
(603) 646-0917

http://www.dartmouth.edu/~mqphan

 

Education:

Ph.D., Mechanical Engineering, Columbia University, New York, 1989.
M.Phil., Mechanical Engineering, Columbia University, New York, 1988.
M.S., Mechanical Engineering, Columbia University, New York, 1986.
B.S., Mechanical Engineering, University of California at Berkeley, 1985.

Experience:

Associate Professor, Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, 2000-Present.

Assistant Professor, Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, 1994-2000.
Senior Engineer, Lockheed Engineering and Sciences Company, Hampton, Virginia, 1991-1994.
Post-Doctoral Research Associate, National Research Council, NASA Langley Research Center, Virginia,
1989-1991.
Research Assistant, Department of Mechanical Engineering, Columbia University, New York, 1987-1989.
Teaching Assistant, Department of Mechanical Engineering, Columbia University, New York, 1986-1987.

Awards and Honors:

NASA Tech Brief Award, April 1995
          "Learning Identification from One Set of Input-Output Data"
NASA Tech Brief Award, September 1994
          "Robust Controller Designs for Second-Order Dynamic Systems: A Virtual Passive Approach"
Technical Excellence Award, Lockheed Engineering Sciences Company, 1992
          "Theoretical Contribution to the Development of a New, Highly Efficient Method for
          Identification of Large Space Structures Using Experimental Input-Output Data"
National Research Council Fellowship, 1989-1991
          Spacecraft Dynamics Branch, NASA Langley Research Center, Virginia
NASA Graduate Student Researcher Award, 1987-1988
Recipient of the only Mechanical Engineering Fellowship, 1985-1986
          Columbia University, New York
Departmental Citation at Graduation, UC Berkeley, 1985
          "Student with the Most Outstanding Academic Record in Mechanical Engineering"
Pi-Tau-Sigma, National Honor Society in Mechanical Engineering
Tau-Beta-Pi, National Honor Society in Engineering
Sigma-Xi, Scientific Research Society

Research Areas:

Identification and Control of Aerospace Structures
Iterative Learning Control

Research supported by NASA, NSF, Lockheed-Martin Missiles and Space, NJ Space Grant Consortium, Princeton Satellite Systems, University Research Board, and the U.S. Department of Defense (Airforce)

Research Laboratory:

Developed the System Identification and Intelligent Control Laboratory. This laboratory contains:

          State-of-the-art digital data acquisition and control system
          Re-configurable flexible truss structure for research in identification and control
          Testbed for iterative learning control of flexible dynamical systems
          Agile laser scanner system (under development)

The developed identification and control algorithms are evaluated on actual hardware in this Laboratory so that the true issues of practical importance are revealed and addressed.

Professional Membership and Activities:

Member, American Institute of Aeronautics and Astronautics (AIAA)
Member, Organizing Committee, Iterative Learning Control Workshop and Roundtable, Tampa, Florida, Dec. 14-15, 1998
Organizer and Co-Chair, Invited Session on New Results in Iterative Learning Control with Model Uncertainty, the IEEE CDC, Phoenix, Arizona, Dec. 7-10, 1999

Journal Editorship:

Associate Editor, Journal of Intelligent Automation and Soft Computing, since 1998
          (Official Journal of the World Automation Congress)
Associate Editor, Journal of the Astronautical Sciences, 1999-2002
          (American Astronautical Society)
Associate Editor, Journal of Guidance, Control, and Dynamics, 2000-2003
          (American Institute of Aeronautics and Astronautics)

Short Course Lecturer and Co-Organizer:

Tutorial on Learning Control
          Given in conjunction with the 1991 IEEE Conference on Intelligent Control
          (with S. Arimoto, R.W. Longman, and J.-N. Juang)

Undergraduate and Graduate Teaching:

Dynamics and Control of Flexible Structures (MAE 435), Spring 95.
Engineering Dynamics (MAE 330), Fall 95, Fall 96, Fall 97, Fall 98.
System Identification (MAE 574), Spring 96, Spring 98.
Optimal Control and Estimation (MAE 570), Spring 97.
Learning Control and Soft Computing (MAE 578), Spring 99.
Modern Control (MAE 444), Spring 00.

Graduate Students:

Neil E. Goodzeit, Ph.D. 1998
          System and Disturbance Identification for Adaptive Disturbance-Rejection Control

Ryoung K. Lim, Ph.D. 1998
          System Identification, Observer Identification, and Data-Based Controller Design

James A. Frueh, Ph.D. 1999
          Iterative Learning Control with Basis Functions

Nilesh V. Kulkarni
          Optimal Control Synthesis by Neural Networks

Thomas J. Weaver
          Non-Linear System Identification

Undergraduate Work Advised:

Christopher Griffith, 1995-1996
          Fuzzy Control for Target Acquisition in the Presence of Obstacles
          Winner of the 1996 Donald J. Dike Award for Excellence in Undergraduate Research
          Department of Mechanical and Aerospace Engineering, Princeton University

Dennis Crouch and Kotaro Akita, 1997-1998
          Artificial Learning Strategy (1-year Independent Work Project)

KaiFai Kork, 1999
          A Numerical Approach to Detection of Changes in Structural Parameters

Christopher Johnson, NASA-NJSGC Summer Fellow, 1999
          Design and Construction of an Agile Laser Scanner
          Work performed in my Laboratory to design a laser scanning system.
          Results presented at the 1999 Summer Fellowship Student Conference,
          
Stevens Institute of Technology, August 4, 1999.

Book:

Juang, J.-N. and Phan, M.Q., Identification and Control of Mechanical Systems, to be published by Cambridge University Press.

Software:

Phan, M.Q., Observer/Kalman Filter Identification (OKID): Step-by-Step Guide and References, A Matlab-based system identification software package, Department of Mechanical and Aerospace Engineering, Princeton University, 1997.

Chapters in Books:

Phan, M.Q. and Frueh, J.A., "System Identification and Learning Control," Chapter 15, Iterative Learning Control: Analysis, Design, Integration, and Applications, Z. Bien and J. Xu, Editors, Kluwer Academic Publishing, Norwell, MA, 1998, pp. 285-306.

Phan, M.Q., Juang, J.-N., and Longman, R.W., "Markov Parameters in System Identification: Old and New Concepts," Chapter 16, Structronic Systems: Smart Structures, Devices, and Systems, Vol. 2, H.S. Tzou and A. Guran, Editors, World Scientific, Singapore, 1997, pp. 263-293.

Phan, M.Q., Juang, J.-N., and Hyland, D.C., "On Neural Networks in Identification and Control of Dynamic Systems," Chapter 7, Wave Motion, Intelligent Structures, and Nonlinear Mechanics, A. Guran and D. Inman, Editors., World Scientific, 1995, pp. 194-225.

Refereed Journal Articles:

Goodzeit, N.E. and Phan, M.Q., "An Intelligent Adaptive System for Flexible Spacecraft Identification and Disturbance Rejection," Journal of Vibration and Control, in press.

Goodzeit, N.E. and Phan, M.Q., "System and Disturbance Identification for Feedforward-Feedback Control Applications," Journal of Guidance, Control, and Dynamics, in press.

Goodzeit, N.E. and Phan, M.Q., "System Identification in the Presence of Completely Unknown Periodic Disturbances," Journal of Guidance, Control, and Dynamics, in press.

Lee, S.C., Longman, R.W., and Phan, M.Q., "Direct Model Reference Learning and Repetitive Control," International Journal of Intelligent Automation and Soft Computing, in press.
Phan, M.Q. and Rabitz, H., "A Self-Guided Algorithm for Learning Control of Quantum-Mechanical Systems," Journal of Chemical Physics, Vol. 110, No. 1, 1999, pp. 34-41.

Phan, M.Q. and Juang, J.-N., "Predictive Controllers for Feedback Stabilization," Journal of Guidance, Control, and Dynamics, Vol. 21, No. 5, 1998, pp. 747-753.

Juang, J.-N., and Phan, M.Q., "Deadbeat Predictive Controllers," Journal of the Chinese Society of Mechanical Engineers, Vol. 19, No. 1, 1998, pp. 25-37.

Juang, J.-N., and Phan, M.Q., "Recursive Deadbeat Controller Design," Journal of Guidance, Control, and Dynamics, Vol. 21, No. 4, 1998, pp. 624-631.

Lim, R.K. and Phan, M.Q., "Identification of a Multistep-Ahead Observer and Its Application to Predictive Control," Journal of Guidance, Control, and Dynamics, Vol. 20, No. 6, 1997, pp. 1200-1206.

Phan, M.Q. and Rabitz, H., "Learning Control of Quantum-Mechanical Systems by Identification of Effective Input-Output Maps," Chemical Physics, Vol. 217, No. 2&3, 1997, pp. 389-400.

Phan, M.Q. and Juang, J.-N., "Designs of Learning Controllers Based on an Auto-Regressive Representation of a Linear System," Journal of Guidance, Control, and Dynamics, Vol. 19, No. 2, 1996, pp. 355-362.

Phan, M.Q., Horta, L.G., Juang, J.-N., and Longman, R.W., "Improvement of Observer/Kalman Filter Identification (OKID) by Residual Whitening," Journal of Vibrations and Acoustics, Vol. 117, 1995, pp. 232-238.

Phan, M.Q., Juang, J.-N., Horta, L.G., and Longman, R.W., "System Identification from Closed-Loop Data with Known Output Feedback Dynamics," Journal of Guidance, Control, and Dynamics, Vol. 17, No. 4, 1994, pp. 661-669.

Juang, J.-N. and Phan, M.Q., "Linear System Identification Via A Backward-Time Observer," Journal of Guidance, Control, and Dynamics, Vol. 17, No. 3, 1994, pp. 505-512.

Juang, J.-N. and Phan, M.Q., "Identification of System, Observer, and Controller from Closed-loop Experimental Data," Journal of Guidance, Control, and Dynamics, Vol. 17, No. 1, 1994, pp. 91-96.

Phan, M.Q., Horta, L.G., Juang, J.N., and Longman, R.W., "Linear System Identification Via An Asymptotically Stable Observer," Journal of Optimization Theory and Applications, Vol. 79, No. 1, 1993, pp. 59-86.

Juang, J.-N., Wu, S.-C., Phan, M.Q., and Longman, R.W., "Passive Dynamic Controllers for Non-Linear Mechanical Systems," Journal of Guidance, Control, and Dynamics, Vol. 16, No. 5, 1993, pp. 845-851.

Chen, C.-W., Juang, J.-N., and Phan, M.Q., "Estimation of Kalman Filter Gain from Output Residuals," Journal of Guidance, Control, and Dynamics, Vol. 16, No. 5, 1993, pp. 903-908.

Horta, L.G., Phan, M.Q., Juang, J.-N., Longman, R.W., and Sulla, J.L., "Frequency Weighted System Identification and Linear Quadratic Controller Design," Journal of Guidance, Control, and Dynamics, Vol. 16, No. 2, 1993, pp. 330-336.

Juang, J.-N., Phan, M.Q., Horta, L.G., and Longman, R.W., "Identification of Observer/Kalman Filter Markov Parameters: Theory and Experiments," Journal of Guidance, Control, and Dynamics, Vol. 16, No. 2, 1993, pp. 320-329.

Juang, J.-N. and Phan, M.Q., "Robust Controller Designs for Second-Order Dynamic Systems: A Virtual Passive Approach," Journal of Guidance, Control, and Dynamics, Vol. 15, No. 5, 1992, pp. 1192-1198.

Phan, M.Q., Juang, J.-N., and Longman, R.W., "Identification of Linear Multivariable Systems by Identification of Observers with Assigned Real Eigenvalues," Journal of the Astronautical Sciences, Vol. 40, No. 2, 1992, pp. 261-279.

Chen, C.-W., Huang, J.-K., Phan, M.Q., and Juang, J.-N., "Integrated System Identification and Modal State Estimation for Control of Large Flexible Space Structures," Journal of Guidance, Control, and Dynamics, Vol. 15, No. 1, 1992, pp. 88-95.

Refereed Journal Articles Submitted:

Frueh, J.A. and Phan, M.Q., "Linear Quadratic Optimal Learning Control (LQL)." Previously presented at the 1998 IEEE Conference on Decision and Control, Tampa, Florida.

Phan, M.Q., Goodzeit, N.E., and Juang, J.N., "Identification of Model and Periodic Disturbances from Disturbance-Corrupted Structural Acoustic Data." Previously presented at the 1997 ASME Design Engineering Technical Conferences, Sacramento, California.

Phan, M.Q., Lim, R.K., and Longman, R.W., "Unifying Input-Output and State-Space Perspectives of Predictive Control," available as Department of Mechanical and Aerospace Engineering Technical Report No. 3044, Princeton University, Sept. 1998.

Lim, R.K., Phan, M.Q., and Longman, R.W., "State Space System Identification with Identified Hankel Matrix," available as Department of Mechanical and Aerospace Engineering Technical Report No. 3045, Princeton University, Sept. 1998.

Lim, R.K., Phan, M.Q., and Longman, R.W., "State Estimation with ARMarkov Models," available as Department of Mechanical and Aerospace Engineering Technical Report No. 3046, Princeton University, Oct. 1998.

Referreed Journal Articles Under Preparation:

Goodzeit, N.E., Frueh, J.A., and Phan, M.Q., "Experiments in Clear-Box Identification and Disturbance Rejection on a Flexible T-Truss Structure." Also, Chapter 7, System and Disturbance Identification for Adaptive Disturbance-Rejection Control, Ph.D. Dissertation (N.E. Goodzeit), Department of Mechanical and Aerospace Engineering, Princeton University, 1998.

Frueh, J.A. and Phan, M.Q., "System Identification, Inverse Control, and Learning Control with Basis Functions." Also, Chapter 2, Iterative Learning Control with Basis Functions, Ph.D. Dissertation (J.A. Frueh), Department of Mechanical and Aerospace Engineering, Princeton University, 1999.

Publications in Conference Proceedings:

Frueh, J.A. and Phan, M.Q., "Model Reference Learning Control with Basis Functions," Proceedings of the 38th IEEE Conference on Decision and Control, Phoenix, AZ, December 1999 (in press).

Phan, M.Q., Juang, J.N., and Eure, K., "Design of Predictive Controllers for Simultaneous Feedback Stabilization and Disturbance Rejection from Disturbance-Corrupted Data," Proceedings of the 137th ASA Meeting and the 2nd EAA Convention, Berlin, Germany, March 1999.

Frueh, J.A. and Phan, M.Q., "Linear Quadratic Optimal Learning Control (LQL)," Proceedings of the 37th IEEE Conference on Decision and Control, Tampa, Florida, December 1998, pp. 678-683.

Wen, H.P, Phan, M.Q., and Longman, R.W., "Bridging Learning and Repetitive Control Using Basis Functions," Advances in the Astronautical Sciences, Vol. 99, Part 1, 1998, pp. 335-354.

Frueh, J.A. and Phan, M.Q., "System Identification and Inverse Control Using Input-Output Data from Multiple Trials," Proceedings of the 2nd Asian Control Conference, Vol. 2, Seoul, Korea, July 1997, pp. 251-254.

Goodzeit, N.E. and Phan, M.Q., "System and Periodic Disturbance Identification for Feedforward-Feedback Control of Flexible Spacecraft," Proceedings of the Nonlinear Dynamical Systems Symposium. The 35th AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada, January 1997, pp. 386-400.

Lim, R.K. and Phan, M.Q., "Identification of a Multistep-Ahead Observer and Its Application to Predictive Control," Proceedings of the Nonlinear Dynamical Systems Symposium. The 35th AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada, January 1997, pp. 401-411.

Juang, J.-N. and Phan, M.Q., "Deadbeat Predictive Control," AIAA Paper Number 97-0455, The 35th AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada, January 1997.

Phan, M.Q., Goodzeit, N.E., and Juang, J.-N., "Identification of Systems and Periodic Disturbances," Paper DETC97/VIB-4256, Proceedings of the ASME Design Engineering Technical Conferences, Sacramento, CA, September 1997.

Oh, S.J., Phan, M.Q., and Longman, R.W., "Use of Decoupling Basis Functions in Learning Control for Local Learning and Improved Transients," Advances in the Astronautical Sciences, Vol. 95, Part 2, 1997, pp. 651-670.

Phan, M.Q. and Frueh, J.A., "Learning Control for Trajectory Tracking Using Basis Functions," Proceedings of the IEEE Conference on Decision and Control, Kobe, Japan, 1996, pp. 2490-2492.

Phan, M.Q. and Juang, J.-N., "Predictive Feedback Controllers for Stabilization of Linear Multivariable Systems," Proceedings of the AIAA Conference on Guidance, Navigation, and Control, San Diego, CA, July 1996.

Phan, M.Q. and Maghami, P., "Estimation of Vibration Levels in Flexible Structures Under Periodic Disturbances in the Presence of Modeling Uncertainties," Proceedings of the AIAA Conference on Guidance, Navigation, and Control, San Diego, CA, July 1996.

Phan, M.Q. and Chew, M., "Synthesis of Four-Bar Function Generators by an Iterative Learning Control Procedure," Proceedings of the ASME Mechanism Conference, Irvine, CA, August 1996.

Phan, M.Q. and Longman, R.W., "Relationship Between State-Space and Input-Output Models via Observer Markov Parameters," Proceedings of the International Conference on Dynamics of Flexible Structures in Space, London, England, June 1996.

Elci, H., Longman, R.W., Phan, M.Q., Juang, J.-N., and Ugoletti, R., "Discrete Frequency-Based Learning Control for Precision Motion Control," Proceedings of the 1994 IEEE International Conference on Systems, Man and Cybernetics, San Antonio, Texas, October 1994, pp. 2767-2773.

Elci H., Longman, R. W., Phan, M.Q., Juang, J.-N., and Ugoletti, R., "Automated Learning Control Through Model Updating For Precision Motion Control," Adaptive Structures and Composite Materials: Analysis and Applications, AD-Vol. 45/MD-Vol. 54, ASME, Nov. 1994, pp. 299-314.

Phan, M.Q. and Chew, M., "Application of Learning Control Theory to Mechanisms, Part I: Inverse Kinematics and Parametric Error Compensation," Proceedings of the 23rd ASME Mechanisms Conference, Minneapolis, MN, September 1994.

Phan, M.Q. and Chew, M., "Application of Learning Control Theory to Mechanisms, Part II: Reduction of Residual Vibrations in Electromechanical Bonding Machines," Proceedings of the 23rd ASME Mechanisms Conference, Minneapolis, MN, September 1994.

Bialasiewicz, J.T., Horta, L.G., and Phan, M.Q., "Identified Predictive Control," Proceedings of the 1994 American Control Conference, Baltimore, Maryland, June 1994.

Elci H., Phan, M.Q., Longman, R. W., Juang, J.-N., and Ugoletti, R., "Experiments in The Use of Learning Control for Maximum Precision Robot Trajectory Tracking," Proceedings of the 1994 Conference on Information Sciences and Systems, Princeton University, Princeton, NJ, March 1994, pp. 951-958.

Lee, S.C., Longman, R.W., and Phan, M.Q., "Direct Model Reference Learning and Repetitive Control," Advances in the Astronautical Sciences, Vol. 85, Part 3, March 1994, pp. 2047-2066.

Phan, M.Q., "Concepts in Adaptive Neural Networks for Identification and Control of Dynamics Systems," Proceedings of the Industry/Government Forum of Adaptive Neural Control for Aerospace Structural Systems, Melbourne, Florida, August 1993.

Phan, M.Q., Juang, J.-N., and Hyland, D.C., "On Neural Networks in Identification and Control of Dynamic Systems," 1992 Workshop on Adaptive/Intelligent/Smart Materials and Systems, Langley Research Center, October 26-27, 1992. Also, NASA Technical Memorandum TM-107702, Langley Research Center, June 1993.

Longman, R.W., Phan, M.Q., and Juang, J.-N., "An Overview of a Sequence of Research Developments in Learning and Repetitive Control," Proceedings of the First International Conference on Motion and Vibration Control (MOVIC), Yokohama, Japan, Japan Society of Mechanical Engineers Publisher, September 1992, pp. 952-957.

Longman, R.W., Chang, C.-K., and Phan, M.Q., "Discrete-Time Learning Control in Non-Linear Systems," Proceedings of the AAS/AIAA Astrodynamics Conference, Hilton Head, South Carolina, August 1992, pp. 501-511.

Chang, C.-K., Longman, R.W., and Phan, M.Q., "Techniques for Improving Transients in Learning Control Systems," Advances in the Astronautical Sciences, Vol. 76, Part 3, 1992, pp. 2035-2052.

Lee, S.C., Longman, R.W., and Phan, M.Q., "Linear Decentralized Learning Control," Advances in the Astronautical Sciences, Vol. 76, Part 3, 1992, pp. 2023-2034.

Longman, R.W., Lee, S.C., and Phan, M.Q., "Indirect Decentralized Learning Control," Advances in the Astronautical Science, Vol. 79, Part 1, 1992, pp. 371-386.

Juang, J.-N. and Phan, M.Q., "Identification of System, Observer, and Controller from Closed-loop Experimental Data," Proceedings of the AIAA Guidance, Navigation, and Control Conference, Hilton Head, South Carolina, August 1992, pp. 1482-1490.

Phan, M.Q., Longman, R.W., and Juang, J.-N., "Input-Output Matrices in Modal Identification," Proceedings of the 9th International Modal Analysis Conference, Florence, Italy, April 1991.

Phan, M.Q., Juang, J.-N., and Longman, R.W., "Recent Developments in Learning Control and System Identification for Robots and Structures," Dynamics of Flexible Structures in Space, C.L. Kirk and J.L. Junkins, Editors, Computational Mechanics Publications, Southhampton, Boston and Springer-Verlag, New York, co-publishers, May 1990, pp. 321-334.

Juang, J.-N., Phan, M.Q., Horta, L.G., Longman, R.W., "Learning System Identification for Flexible Structures," Proceedings of the 2nd USAF/NASA Workshop on System Identification and Health Monitoring of Precision Space Structures, California Institute of Technology, Pasadena, California, March 1990.

Phan, M.Q., Longman, R.W., and Juang, J.-N., "Indirect Repetitive Control for Linear Discrete Multivariable Systems," Proceedings of the 27th Annual Allerton Conference on Communication, Control, and Computing, University of Illinois, Urbana-Champaign, Illinois, September 1989, pp. 867-876.

Phan, M.Q., Wei, Y., Horta, L.G., Juang, J.-N., and Longman, R.W., "Learning Control for Slewing of a Flexible Panel," Dynamics and Control of Large Structures, L. Meirovitch, Editor, May 1989, pp. 39-52.

Phan, M.Q. and Longman, R.W., "A Model Reference Adaptive Control Method for a Class of Linear Discrete Multivariable Systems," Modeling and Simulation, Instrument Society of America, Vol. 20, Part 5, 1989, pp. 1865-1869.

Phan, M.Q. and Longman, R.W., "Learning System Identification," Modeling and Simulation, Instrument Society of America, Vol. 20, Part 5, 1989, pp. 1857-1864.

Phan, M.Q. and Longman, R.W., "Indirect Learning Control with Guaranteed Stability," Proceedings of the 1989 Johns Hopkins Conference on Information Sciences and Systems, Baltimore, Maryland, March 1989, pp. 125-131.

Phan, M.Q. and Longman, R.W., "Liapunov-Based Model Reference Learning Control," Proceedings of the 26th Annual Allerton Conference on Communication, Control, and Computing, Coordinated Sciences Laboratory, University of Illinois, Urbana-Champaign, Illinois, September 1988, pp. 927-936.

Phan, M.Q. and Longman, R.W., "A Mathematical Theory of Learning Control for Linear Discrete Multivariable Systems," Proceedings of the AIAA/AAS Astrodynamics Conference, AIAA Publishers, Minneapolis, Minnesota, August 1988, pp. 740-746.

Technical Reports:

Phan, M.Q., Horta, L.G., Juang, J.-N., and Longman, R.W., "Identification of Linear Systems Via An Asymptotically Stable Observer," NASA Technical Paper TP-3164, Langley Research Center, Hampton, VA, June 1992.

Juang, J.-N., Horta, L.G., and Phan, M.Q., "User's Guide for System/Observer/Controller Identification Toolbox," NASA Technical Memorandum TM-107566, Langley Research Center, Hampton, VA, February 1992.

Phan, M.Q., Juang, J.-N., and Longman, R.W., "On Markov Parameters in System Identification," NASA Technical Memorandum 104156, Langley Research Center, Hampton, VA, October 1991.