Gary T. Anderson

A Bayesian method on adaptive preventive maintenance problem

Abstract In this paper we consider a Bayesian theoretic approach to determine an optimal adaptive preventive maintenance policy with minimal repair. By incorporating minimal repair, major repair, planned replacement, unplanned replacement and periodic scheduled maintenance in the model, the mathematical formulas of the expected cost per unit time are obtained. When the failure density is Weibull with uncertain parameters, a Bayesian approach is established to formally express and update the uncertain parameters for determining an optimal adaptive preventive maintenance policy. Furthermore, various special cases of our model are discussed in detail.

Self-heated thermistor measurements of perfusion

A microcomputer-based control system applies a combination of steady-state and sinusoidal power to a thermistor probe which is inserted into the tissue of interest. The steady-state temperature response is an indication of the effective thermal conductivity (k/sub eff/), which includes a component due to intrinsic conduction plus a convective component due to the tissue blood flow near the probe. By careful choice of the excitation frequency, the sinusoidal temperature response can be used to measure intrinsic thermal conductivity (k/sub m/) in the presence of blood flow. Optimal sinusoidal heating frequency depends on the thermistor size. Experimental results show that perfusion is linearly related to the difference k/sub eff/ minus k/sub m/. The instrument can measure tissue thermal conductivity with an accuracy of 2% and resolve changes in perfusion of 10 mL/100g-min. The maximum error in measured perfusion is about 30%. When tissue trauma due to probe insertion is minimized, the self-heated thermistor method gives a reliable indication of local tissue blood flow.<<ETX>>

Coupled Oscillator Control of Autonomous Mobile Robots

This paper introduces a nonlinear oscillator scheme to control autonomous mobile robots. The method is based on observations of a successful control mechanism used in nature, the Central Pattern Generator. Simulations were used to assess the performance of oscillator controller when used to implement several behaviors in an autonomous robot operating in a closed arena. A sequence of basic behaviors (random wandering, obstacle avoidance and light following) was coordinated in the robot to produce the higher behavior of foraging for light. The controller is explored in simulations and tests on physical robots. It is shown that the oscillator—based controller outperforms a reactive controller in the tasks of exploring an arena with irregular walls and in searching for light.

Analysis of the Weinbaum-Jiji Model of Blood Flow in the Canine Kidney Cortex for Self-Heated Thermistors

The Weinbaum-Jiji equation can be applied to situations where: 1) the vascular anatomy is know; 2) the blood velocities are known; 3) the effective modeling volume includes many vessels; and 4) the vessel equilibration length is small compared to the actual length of the vessel. These criteria are satisfied in the situation where steady-state heated thermistors are placed in the kidney cortex. In this paper, the Weinbaum-Jiji bioheat equation is used to analyze the steady state response of four different sized self-heated thermistors in the canine kidney. This heat transfer model is developed based on actual physical measurements of the vasculature of the canine kidney cortex. In this model, parallel-structured interlobular arterioles and venules with a 60 microns diameter play the dominant role in the heat transfer due to blood flow. Continuous power is applied to the thermistor, and the instrument measures the resulting steady state temperature rise. If an accurate thermal model is available, perfusion can be calculated from these steady-state measurements. The finite element simulations correlate well in shape and amplitude with experimental results in the canine kidney. In addition, this paper shows that the Weinbaum-Jiji equation can not be used to model the transient response of the thermistor because the modeling volume does not include enough vessels and the vessel equilibration length is not small compared to the actual length of the vessel.

A comparison of search patterns for cooperative robots operating in remote environment

In this paper, two scanning paradigms are presented and compared that may be used for robotic scanning of a harsh environment such as a celestial body or earth poles. The first paradigm, tight scanning, includes three algorithms, which may be used to find small objects or gasses confined to small regions such as the methane gas given off by bacteria in buried hot springs in the Canadian arctic. The second paradigm, relaxed scanning, includes four algorithms which may be used to find large objects such as large ice deposits that may be buried just below the surface of Mars. The algorithms are compared against their peer algorithms by their quality of performance. Such performance quality is determined by the ratio of scanned area to the traveled distance by the two robots.

Agent-based robot control design for multi-robot cooperation

This paper presents an agent-based robot control (ARC) architecture. ARC features a flexible real-time control system, which is suitable for multi-robot cooperative tasks. It also provides an efficient platform for building up a multi-robot system consisting of heterogeneous robots. In this paper, an experimental study of this architecture is investigated. A cooperative exploration using two mobile robots will be demonstrated. In this experiment, one robot explores the environment by looking for a color-coded target and the other is responsible for task execution at the target position. While exploring in an unknown environment, the first robot, which is equipped with ultrasonic sensors for exploration, records its position as it sees deployed checkpoints. In a later phase, the second robot plans a path to the target directly using information passed from the first robot and get to the target position in an efficient way.

A Small Artery Heat Transfer Model for Self-Heated Thermistor Measurements of Perfusion in the Kidney Cortex

A small artery model (SAM) for self-heated thermistor measurements of perfusion in the canine kidney is developed based on the anatomy of the cortex vasculature. In this model interlobular arteries and veins play a dominant role in the heat transfer due to blood flow. Effective thermal conductivity, kss, is calculated from steady state thermistor measurements of heat transfer in the kidney cortex. This small artery and vein model of perfusion correctly indicates the shape of the measured kss versus perfusion curve. It also correctly predicts that the sinusoidal response of the thermistor can be used to measure intrinsic tissue conductivity, km, in perfused tissue. Although this model is specific for the canine kidney cortex, the modeling approach is applicable for a wide variety of biologic tissues.

A RFID Landmark Navigation Auxiliary System

This paper proposes the development of an RFID system to aid in the navigation of autonomous mobile robots. The use of the system to enable a mobile robot to estimate its pose is described. The paper presents a method to obtain fine orientation readings, a task neglected by former works. We also analyze one uncertainty source of this approach. Experimental and simulation results are presented in the paper to demonstrate the effect of the method. Finally, we present a possible alternative method to adapt to non-constant speed movement.

Robot System to Search for Signs of Life on Mars

This describes a robot system that can be used to look for the tell-tale signs of life on Mars. Currently, NASA has satellites in orbit that can identify broad regions to explore in its search for life. NASA also has instruments that can examine samples of Martian soil to see if they contain any indications of biological activity. This leaves the problem of deciding specifically where to look for suitable samples in the large area around a landing site. This also describes a robot system that can rapidly search thousands of square meters around the landing position to find sources of biogenic gas samples that may harbor important clues in the search for extra-terrestrial life.

A Mobile Robot System for Remote Measurements of Ammonia Vapor in the Atmosphere

In recent years there has been growing evidence that Mars once had a warm, wet environment that was capable of supporting life. This leads to questions as to whether life ever arose on the planet. Space agencies are actively supporting projects to answer this question. As part of that effort, this paper proposes a robotic system to rapidly scan large areas of the Martian surface for specific biogenic gases in the atmosphere. The long-term goal of the project is to develop a system that can locate local emissions of water vapor and biogases on Mars. The paper presents preliminary proof of concept experiments for a practical robotic measurement system to search for biogenic gases on Mars. In this work, an open path spectrometer to measure the biogenic gas ammonia was developed and deployed on a rover. Initial tests in an outdoor setting indicate that the system is effective in measuring ammonia. Difficulties in taking measurements outdoors include compensating for wind gusts and changes in ambient lighting. The paper proposes improvements in the current system that will compensate for current limitations and allow measurements to be taken over longer distances.