Thomas L. Harman

Applications of Kalman filtering to real-time trace gas concentration measurements

A Kalman filtering technique is applied to the simultaneous detection of NH3 and CO2 with a diode-laser-based sensor operating at 1.53 micrometers. This technique is developed for improving the sensitivity and precision of trace gas concentration levels based on direct overtone laser absorption spectroscopy in the presence of various sensor noise sources. Filter performance is demonstrated to be adaptive to real-time noise and data statistics. Additionally, filter operation is successfully performed with dynamic ranges differing by three orders of magnitude. Details of Kalman filter theory applied to the acquired spectroscopic data are discussed. The effectiveness of this technique is evaluated by performing NH3 and CO2 concentration measurements and utilizing it to monitor varying ammonia and carbon dioxide levels in a bioreactor for water reprocessing, located at the NASA-Johnson Space Center. Results indicate a sensitivity enhancement of six times, in terms of improved minimum detectable absorption by the gas sensor.

Atmospheric Formaldehyde Monitoring in the Greater Houston Area in 2002

A laser spectrometer based on difference frequency generation (DFG) was deployed for real-time long-term monitoring of HCHO concentrations at an environmental monitoring site located at Deer Park, Texas, in the Greater Houston area. Three HCHO concentration measurements were made during the periods of July 20–31 (period I), August 2–14 (period II), and August 24–September 25 (period III), 2002. In periods I and II, differences in HCHO concentrations are apparent between day and night measurements, with elevated concentrations during daylight hours. Most of the HCHO peak values are less than 20 ppbV except for two intense peaks on August 02 (∼25 ppbV) and August 04 (∼30 ppbV). The formaldehyde concentration levels in ambient air at the measurement site are produced mainly by the photochemical oxidation of volatile organic compounds (VOCs) caused by intense sunlight during periods I and II. This observation was made based on a comparison with the ozone concentration, solar radiation, temperature, relative humidity, and wind speed data obtained from the Texas Commission on Environmental Quality (TCEQ). During period III, data collected by a time-integrating wet-chemical technique are compared to the data collected by the spectroscopic instrument.

Volume-conductor fields of the isolated axon

Abstract A solution of Laplaces equation relating the transmembrane potential distribution of an active fiber in a volume conductor to its extracellular field distribution utilizing a Fourier-transform method [4] has been reformulated as a one-dimensional linear filtering problem. Formulation of the solution in this manner allows the application of well-known techniques in linear system theory and optimal linear filtering, thereby facilitating the solution for both the forward (from transmembrane to field potential distribution) and inverse (from field to transmembrane potential distribution) problems. The forward problem is shown to be a simple two-stage filtering process composed of a membrane and medium filter. In the inverse case, the field potential distribution is considered in the presence of additive measurement noise, and the best estimate in the least-mean-square sense is obtained for the transmembrane potential distribution. Discrete Fourier-transform techniques are applied to this reformulated Fourier-transform method, resulting in a fast, efficient algorithm for solution of the forward and inverse field problems.

A Comparison of Two Methods for Determining the Extracellular Potential Field of an Isolated Purkinje Strand in a Volume Conductor

The models considered in this study are those of Spach et al., [1], and Clark and Plonsey [6], [7]. Both assume circular cylindrical geometry for the isolated Purkinje strand and input information to the models consists mainly of the recorded transmembrane action potential, the ratio of conductivities of the intra- and extracellular media, the conduction velocity of the action potential, and the radius of the strand. In general the extracellular potentials computed using both methods agree with measured potential data and with each other. However, the Clark-Plonsey method provides a more accurate prediction of both the peak-to-peak magnitude and the separation between peaks of the bipolar extracellular potential waveform, particularly at field points close to the strand.

Model-Based Torque Control of Piezoelectric Ultrasonic Motors

Traveling wave piezoelectric ultrasonic motors (PUMs) are ideal actuators for a variety of important applications including medical and space robotics, haptic interfaces, and positioning devices. Consisting of a single moving part, the motors are much simpler mechanically than other drive systems that require transmissions and brakes. Many potential PUM applications require accurate real-time control of output torque, which is difficult due to the highly nonlinear PUM dynamics. This paper presents an algorithm that adjusts PUM drive signal frequency to achieve output torque control throughout the speed range of a typical commercial PUM.Copyright

Dynamic Response Modeling of Piezoelectric Ultrasonic Motors

Piezoelectric ultrasonic motors (PUMs) fill a unique niche in mechatronic actuators. The motors are lightweight, simple, and reliable, containing a single moving part that provides the function of motor, transmission, and brake. They are ideal for a variety of robotic applications as well as commercial and medical applications. In order to exploit PUMs fully, computationally efficient models of dynamic response, capturing all important dynamics, are needed. This paper describes the experimental characterization of the dynamic response of a typical commercial PUM (Shinsei USR-30) using an inertial load and evaluation of three classes of dynamic models: second-order predictive (physics-based) models, algebraic (curve fitting) descriptive models, and neural network approximation.Copyright

Rightsizing electrical power systems in large commercial facilities

For decades, application of National Electrical Code (NEC) rules for sizing services, feeders and branch circuits has resulted in unused capacity in almost all occupancy classes. US Department of Energy data compiled in 1999 indicates average load on building transformers between 10 and 25 percent. More recent data gathered by the educational facilities industry has verified this claim. Recognizing that aggressive energy codes are driving energy consumption lower, and that larger than necessary transformers create larger than necessary flash hazard, the 2014 NEC will provide an exception in Section 220.12 that will permit designers to reduce transformer kVA ratings and all related components of the power delivery system. This is a conservative, incremental step in the direction of reduced load density that is limited to lighting systems. More study of feeder and branch circuit loading is necessary to inform discussion about circuit design methods in future revisions of the NEC.

Rightsizing Commercial Electrical Power Systems: Review of a New Exception in NEC Section 220.12

For decades, the application of National Electrical Code (NEC) rules for sizing services, feeders, and branch circuits has resulted in unused capacity in almost all occupancy classes. U.S. Department of Energy (DOE) data compiled in 1999 indicate the average load on building transformers to be between 10% and 25%. More recent data gathered by the educational facilities industry have verified this claim. Recognizing that aggressive energy codes are driving energy consumption lower and that larger-thannecessary transformers create a larger-than-necessary flash hazard, the 2014 NEC provided an exception in Section 220.12 that permitted designers to reduce transformer kilovoltampere ratings and all related components of the power delivery system. This was a conservative, incremental step in the direction of reduced load density that is limited to lighting systems. Further study of feeder and branch circuit loading is necessary to inform discussions about circuit design methods in future revisions of the NEC.

Stable Torque Regulation of Piezoelectric Ultrasonic Motors

Traveling wave piezoelectric ultrasonic motors (PUMs) are ideal actuators for a variety of important applications including medical and space robotics, haptic interfaces, and positioning devices. Consisting of a single moving part, the motors are much simpler mechanically than other drive systems that require transmissions and brakes. Many potential PUM applications require accurate real-time control of output torque, which is difficult due to the highly nonlinear PUM dynamics. This paper reviews the development of a model-based PUM torque regulation algorithm and applications of the algorithm. The paper then examines the stability of the torque control and demonstrates it experimentally.

Robot control from sequential image planes of a 3D object

Movement of a robot head between desired points in a 3D volume from (x1,y1,z1) to (x2,y2,z2) is crucial for high accuracy. When the knowledge of a 3D volume is only partial, obtained as a data set of cross-sectional image planes, control parameters for movement of the robot head are critical for best accuracy. In the present approach an attempt is being made to develop an interface for transforming control parameters of a robot system for desired movements of the robot head in the 3D volume from a sequence of cross-sectional image planes. Coordinates of a desired location from image data are obtained, and their corresponding locations on the object are estimated. These coordinates are transformed through matrix transformation into control parameters for the desired movements of the robot system. Most diagnostic medical imaging modalities obtain cross-sectional image planes of vital human organs. Treatment procedures often require 3D volume considerations. In the present approach a hypothetical radiation treatment procedure for a prostate cancer tumor in a 3D volume from given 2D cross-sectional sequential image planes is presented. Diagnostic ultrasound images of the prostate are obtained as sequential cross-sectional image planes at 2 mm apart from base to apex of the gland. An approach for robot coordinate movements for a simple robotic system with five degrees of freedom (Eshed Robotics, ER VII) is presented.