Fitness functions in evolutionary robotics: A survey and analysis

This paper surveys fitness functions used in the field of evolutionary robotics (ER). Evolutionary robotics is a field of research that applies artificial evolution to generate control systems for autonomous robots. During evolution, robots attempt to perform a given task in a given environment. The controllers in the better performing robots are selected, altered and propagated to perform the task again in an iterative process that mimics some aspects of natural evolution. A key component of this process–one might argue, the key component–is the measurement of fitness in the evolving controllers. ER is one of a host of machine learning methods that rely on interaction with, and feedback from, a complex dynamic environment to drive synthesis of controllers for autonomous agents. These methods have the potential to lead to the development of robots that can adapt to uncharacterized environments and which may be able to perform tasks that human designers do not completely understand. In order to achieve this, issues regarding fitness evaluation must be addressed. In this paper we survey current ER research and focus on work that involved real robots. The surveyed research is organized according to the degree of a priori knowledge used to formulate the various fitness functions employed during evolution. The underlying motivation for this is to identify methods that allow the development of the greatest degree of novel control, while requiring the minimum amount of a priori task knowledge from the designer.     

The effects of multifocal refractive lenses on occipital extension and forward head posture during a visual task

The purpose of this study was to determine if a change in forward head posture and occipital extension occurred in participants who wore multifocal lenses vs. those persons with non-multifocal lenses while performing an 8-min visual reading task on a visual display unit (VDU). Forty-two healthy human participants were recruited for this study. Thirty-three participants completed the study. Fourteen participants wore multifocal lenses and 19 wore frames with non-multifocal lenses. To evaluate the degree of change of forward head posture and occipital extension digital photographs of cervical posture were taken at four different time intervals: prior to performing the reading task and at 3, 5 and 8 min during the reading task. The digital photographs were analysed utilizing a computer program. Two one-way ANOVA were utilized to determine the degree of change of forward head posture and occipital extension between groups. A significant difference was identified between groups for changes in degrees of forward head posture while performing a visual reading task on a VDU. However, no significant difference between groups was found for occipital extension while performing the same task. Multifocal wearers exhibit greater degrees of change in forward head posture and occipital extension than non-multifocal wearers. These postural changes may place them at a greater risk for musculoskeletal disorders and headaches.     

Symbolic computation with finite biquandles

A method of computing a basis for the second Yang–Baxter cohomology of a finite biquandle with coefficients in Q$\mathbb{Q}$ and _Zp${\mathbb{Z}}_p$ from a matrix presentation of the finite biquandle is described. We also describe a method for computing the Yang–Baxter cocycle invariants of an oriented knot or link represented as a signed Gauss code. We provide a URL for our Maple implementations of these algorithms.     

Temporal alignment of tissue and arterial data and selection of integration start times for the H(2)(15)O autoradiographic CBF model in PET

A technique has been developed and tested that provides an automated method of temporally aligning the PET tissue activity curve with the arterial activity curve for quantification of cerebral blood flow using the H(2)(15)O autoradiographic model. This technique not only determines the relative time delay between the two curves, but also provides the start time of integration. Variability in computing global cerebral blood flow using this technique is shown to be less than that obtained by trained observers manually selecting parameters and at least as good as that obtained by using another automated alignment technique.     

Identification of two distinct properties of class II major histocompatibility complex-associated peptides

We have examined the interactions of various peptides with the mouse class II major histocompatibility complex molecule I-Ak. The peptides were derived from the model protein hen egg white lysozyme (HEL). The immunodominant peptide of HEL is a 10-mer, residues 52-61. Our previous work established that this sequence contains the key residues for binding and presentation to T cells. Now we show that the binding of this 10-mer sequence resulted in complexes of I-Ak and peptide that, in SDS/PAGE (without boiling the protein), rapidly dissociated from the component alpha and beta chains. The binding interactions were studied in vitro, by incubating purified I-Ak and radiolabeled peptide, or ex vivo, by using antigen-presenting cells incubated with peptides. Peptides with additional residues at either the amino or carboxyl terminus behaved dramatically differently. Complexes of I-Ak with the longer peptides were stable to SDS/PAGE. Very few amino acid additions result in the change from unstable to stable complexes. The important issue here is that when cultured with HEL, antigen-presenting cells selected the HEL peptides containing the 52-61 sequences that favored stability [Nelson, C. A., Roof, R. W., McCourt, D. W. & Unanue, E. R. (1992) Proc. Natl., Acad. Sci. USA 89, 7380-7383]. Also, from other studies, such sequences correlate with a high immunogenicity of the peptide. We conclude that there are structural features of peptides that change the stability of the class II molecule and that are independent of the "core" peptide seen by the T cells.     

Resistive transition in superconducting films

The consequences of a vortex unbinding picture of two-dimensional superconductivity are worked out. Although there is no true finite-temperature phase transition, dirty superconducting films should display anomalous behavior below the BCS transition temperature and above an effective Kosterlitz-Thouless vortex unbinding temperature. In particular, both the conductivity and fluctuation diamagnetism behave like ₊ ² in this regime, where ₊ is the correlation length calculated by Kosterlitz, _{+ c} exp (B/T – T _c)^1/2. We estimate _c, B, and the vortex unbinding temperature, and determine the nonlinear resistivity below T _c. A recent theory of vortex dynamics, together with a time-dependent Ginzburg-Landau theory, lead to a determination of the frequency-dependent conductivity.This work was supported by the National Science Foundation under Grant No. DMR 77-10210.     

Grounding power systems above 600 V

The multigrounded neutral system for power systems above 600 V is a reasonable and safe design. The multigrounded neutral system provides 1) safety, 2) low zero sequence impedance than the single-point grounded neutral system, 3) lightning-arrester sizes can be optimized, 4) freezing and arctic conditions have an adverse impact on the zero sequence impedance, 5) cost of equipment for the multigrounded system is lower.