Electrical and Electrochemical Tests of Performance of Polographs: I. Needs and Methods; II. Diagnostic Criteria for Establishing the Degree to Which Recorded Polarograms Are Adversely Affected by Circuit Performance†

SUMMARY

Both electrical and electrochemical tests are required to define, describe, and specify the performance of a polarograph when a polarograph or a cell or an electrode is newly constructed or placed in service, when work is to be started that is of special importance, or when poor results are obtained with a combination that has been in use. In the last case, the first question is whether the malfunction originates in the polarograph itself or in the cell-electrode assembly or is due to electrochemical problems specific to the sample just introduced. The polarograph is tested by means of electrical tests. If it is performing according to specifications, the overall system (and thus the cell and electrodes) is checked out by means of obtaining polarograms with reactions of well-known characteristics. Satisfactory electrical and electrochemical test methods which have evolved at Oak Ridge National Laboratory (ORNL) are set forth in this paper. For any specific polarograph, each of these tests is generally applicable, provided, of course, that the polarograph includes the feature or mode of operation for which the test is designed. Also, diagnostic criteria are given for establishing the degree to which the forms of recorded regular, first derivative, and second derivative dc polarograms (for simple, polarographically reversible test reactions) are adversely affected by circuit performance.     

New methods for competitive coevolution

We consider "competitive coevolution," in which fitness is based on direct competition among individuals selected from two independently evolving populations of "hosts" and "parasites." Competitive coevolution can lead to an "arms race," in which the two populations reciprocally drive one another to increasing levels of performance and complexity. We use the games of Nim and 3-D Tic-Tac-Toe as test problems to explore three new techniques in competitive coevolution. "Competitive fitness sharing" changes the way fitness is measured; "shared sampling" provides a method for selecting a strong, diverse set of parasites; and the "hall of fame" encourages arms races by saving good individuals from prior generations. We provide several different motivations for these methods and mathematical insights into their use. Experimental comparisons are done, and a detailed analysis of these experiments is presented in terms of testing issues, diversity, extinction, arms race progress measurements, and drift.     

Adaptive Retrieval Agents: Internalizing Local Context and Scaling up to the Web

This paper discusses a novel distributed adaptive algorithm and representation used to construct populations of adaptive Web agents. These InfoSpiders browse networked information environments on-line in search of pages relevant to the user, by traversing hyperlinks in an autonomous and intelligent fashion. Each agent adapts to the spatial and temporal regularities of its local context thanks to a combination of machine learning techniques inspired by ecological models: evolutionary adaptation with local selection, reinforcement learning and selective query expansion by internalization of environmental signals, and optional relevance feedback. We evaluate the feasibility and performance of these methods in three domains: a general class of artificial graph environments, a controlled subset of the Web, and (preliminarly) the full Web. Our results suggest that InfoSpiders could take advantage of the starting points provided by search engines, based on global word statistics, and then use linkage topology to guide their search on-line. We show how this approach can complement the current state of the art, especially with respect to the scalability challenge.     

A Controlled-Potential and Derivative DC Polarograph for Regular and First and Second Derivative DC Polarography: Circuits,Theory, and Performance Characteristics. Advantages of Rapid and Derivative DC Polarography†

SUMMARY

The circuits, theory, and performance characteristics are described of a controlled-potential dc polarograph (ORNL Model Q-1988-FES) which is designed to take advantage of the inherent high sensitivity and resolution of derivative dc polarography. Several circuit modifications for specific applications are described. Cell and electrode design considerations are given. The advantages of potentiostatic electrolysis in polarography, the advantages of the use of current-averaging and analog derivative circuits in improving the measurement and the interpretation of recorded dc polarograms, the attainment of ultimate high resolution through the recording of first derivative dc polarograms of good waveform, the achievement of high sensitivity by means of rapid derivative dc polarography, the practical advantages of first derivative over regular dc polarography, the relative advantages of first and second derivative dc polarography, and the practical advantages of rapid dc polarography are discussed. Conclusions are illustrated and substantiated by data.     

Coevolutionary analysis of resistance-evading peptidomimetic inhibitors of HIV-1 protease

We have developed a coevolutionary method for the computational design of HIV-1 protease inhibitors selected for their ability to retain efficacy in the face of protease mutation. For HIV-1 protease, typical drug design techniques are shown to be ineffective for the design of resistance-evading inhibitors: An inhibitor that is a direct analogue of one of the natural substrates will be susceptible to resistance mutation, as will inhibitors designed to fill the active site of the wild-type or a mutant enzyme. Two design principles are demonstrated: (i) For enzymes with broad substrate specificity, such as HIV-1 protease, resistance-evading inhibitors are best designed against the immutable properties of the active site-the properties that must be conserved in any mutant protease to retain the ability to bind and cleave all of the native substrates. (ii) Robust resistance-evading inhibitors can be designed by optimizing activity simultaneously against a large set of mutant enzymes, incorporating as much of the mutational space as possible.     

Dynamic Parameter Encoding for Genetic Algorithms

The common use of static binary place-value codes for real-valued parameters of the phenotype in Holland's genetic algorithm (GA) forces either the sacrifice of representational precision for efficiency of search or vice versa. Dynamic Parameter Encoding (DPE) is a mechanism that avoids this dilemma by using convergence statistics derived from the GA population to adaptively control the mapping from fixed-length binary genes to real values. DPE is shown to be empirically effective and amenable to analysis; we explore the problem of premature convergence in GAs through two convergence models.     

Learning and Programming in Classifier Systems

Both symbolic and subsymbolic models contribute important insights to our understanding of intelligent systems. Classifier systems are low-level learning systems that are also capable of supporting representations at the symbolic level. In this paper, we explore in detail the issues surrounding the integration of programmed and learned knowledge in classifier-system representations, including comprehensibility, ease of expression, explanation, predictability, robustness, redundancy, stability, and the use of analogical representations. We also examine how these issues speak to the debate between symbolic and subsymbolic paradigms. We discuss several dimensions for examining the tradeoffs between programmed and learned representations, and we propose an optimization model for constructing hybrid systems that combine positive aspects of each paradigm.     

A Cell Design for Minimizing iR Error in Controlled-Potential Polarography of High Specific Resistance Solutions

SUMMARY

A design is presented for a polarographic cell that minimizes the iR error in controlled-potential polarography of solutions possessing a high specific resistance. A sharpened Smoler 90° vertical orifice DME is used. With this electrode, the mercury drop grows principally in the downward direction. This and the fact that the end of the capillary is sharpened to a point allows the positioning of a micro reference electrode probe directly above the mercury drop and to within 0.1 of the maximum radius of the mercury drop from the mercury surface during the entire drop life time. With this apparatus it is also possible to observe the iR error as a function of the distance between the reference electrode tip and the mercury drop surface. The effect of reference electrode position on iR error introduced is illustrated by a series of uranium and cadmium polarograms in high specific resistance media. Controlled-potential polarograms with little distortion attributable to iR error can be obtained with this cell design in solutions with specific resistances up to at least 22,000 Ω-cm.     

Evolving robot morphology and control

Most robotic approaches beging with a fixed robot hardware design and then experiment with control structures. We take a different approach that considers both the robot hardware and the control structure as variables in the evolution process. This paper reports the results of experiments which explore the placement of sensors and effectors around the perimeter of a simulated agent's body, and the neural network (NNet) that controls them. This work was presented in part at the Fourth International Symposium on Artificial Life and Robotics, Oita, Japan, January 19–22, 1999