Rat pups and random robots generate similar self‐organized and intentional behavior

Biorobotic research continually demonstrates that behavior and cognition can be the emergent products of (1) embodied agents that are (2) dynamically embedded within an environment and (3) equipped with simple sensorimotor rules. Thigmotaxis is an orientation response to contact manifested in infant rats by wall following, corner burrowing, and group aggregation. Orientation responses have been long thought to be mediated only by sensory or central processes. Here we show that a random control architecture in a morphologically similar robot embedded in a scaled environment can reproduce thigmotaxic behaviors seen in infant rats. We conclude that (1) and (2) may play a larger role than previously thought in the generation of complex behaviors. © 2006 Wiley Periodicals, Inc. Complexity 12: 53–66, 2006     

A lower bound for the number of Reidemeister moves of type III

We study the number of Reidemeister type III moves using Fox n-colorings of knot diagrams.     

Chemical morphology: The chemistry of our shape, <Emphasis Type="Italic">in vivo</Emphasis> and <Emphasis Type="Italic">in vitro</Emphasis>

Our shape is defined and maintained by the connective tissues (skin, tendons, cartilages, blood vessels, etc.) or more precisely by their extracellular matrices. These highly ordered supramolecular organisations are modules of protein fibrils held together by elastic carbohydrate strings. I called these the ‘shape modules.’ The ‘laws.’ which underpin this tissue jigsaw, the changes which come with age and the insight that the concepts give in economically important disorders such as osteoarthrosis begin to provide a new and coherent picture stretching across the animal world and its evolution. This structure/function picture is built on biochemical analyses, which developed into histochemical microscopy and thence into electron histochemistry, and from nuclear magnetic resonance (NMR), molecular modelling and computer simulations on the physicochemical and biomechanical side. As usual, originality bred dissent.     

High-order compact finite-difference methods on general overset grids

This work investigates the coupling of a very high-order finite-difference algorithm for the solution of conservation laws on general curvilinear meshes with overset-grid techniques originally developed to address complex geometric configurations. The solver portion of the algorithm is based on Padé-type compact finite-differences of up to sixth-order, with up to 10th-order filters employed to remove spurious waves generated by grid non-uniformities, boundary conditions and flow non-linearities. The overset-grid approach is utilized as both a domain-decomposition paradigm for implementation of the algorithm on massively parallel machines and as a means for handling geometric complexity in the computational domain. Two key features have been implemented in the current work; the ability of the high-order algorithm to accommodate holes cut in grids by the overset-grid approach, and the use of high-order interpolation at non-coincident grid overlaps. Several high-order/high-accuracy interpolation methods were considered, and a high-order, explicit, non-optimized Lagrangian method was found to be the most accurate and robust for this application. Several two-dimensional benchmark problems were examined to validate the interpolation methods and the overall algorithm. These included grid-to-grid interpolation of analytic test functions, the inviscid convection of a vortex, laminar flow over single- and double-cylinder configurations, and the scattering of acoustic waves from one- and three-cylinder configurations. The employment of the overset-grid techniques, coupled with high-order interpolation at overset boundaries, was found to be an effective way of employing the high-order algorithm for more complex geometries than was previously possible.     

Designing Conferences to Improve Resource Utilization and Participant Satisfaction

We look at a conference scheduling problem with the objective of maximizing the ability of participants to attend sessions of interest. This problem was addressed in an article by Eglese and Rand; conference scheduling has otherwise received little attention in management science literature. Related problems of class- and exam-scheduling have been extensively studied and published, yet few cases consider participant (e.g. student) preferences. Our formulation, which a variation of that used by Eglese and Rand, includes prioritized preferences for conference sessions, as well as schedule resource constraints. The purpose of this paper is to extend the previous work by exploring the impact of various scheduling decisions on participant satisfaction (measured by enrollment in desired sessions). We use a previously published algorithm to look at issues such as conference length and make general observations that may aid the conference-scheduling decision maker.     

Symmetry analysis for uniaxial compression of a hypoplastic granular material

A variety of modelling approaches currently exist to describe and predict the diverse behaviours of granular materials. One of the more sophisticated theories is hypoplasticity, which is a stress-rate theory of rational continuum mechanics with a constitutive law expressed in a single tensorial equation. In this paper, a particular version of hypoplasticity, due to Wu [2], is employed to describe a class of one-dimensional granular deformations. By combining the constitutive law with the conservation laws of continuum mechanics, a system of four nonlinear partial differential equations is derived for the axial and lateral stress, the velocity and the void ratio. Under certain restrictions, three of the governing equations may be combined to yield ordinary differential equations, whose solutions can be calculated exactly. Several new analytical results are obtained which are applicable to oedometer testing. In general this approach is not possible, and analytic progress is sought via Lie symmetry analysis. A complete set or “optimal system” of group-invariant solutions is identified using the Olver method, which involves the adjoint representation of the symmetry group on its Lie algebra. Each element in the optimal system is governed by a system of nonlinear ordinary differential equations which in general must be solved numerically. Solutions previously considered in the literature are noted, and their relation to our optimal system identified. Two illustrative examples are examined and the variation of various functions occuring in the physical variables is shown graphically.     

Analytical characteristics of a continuum-source tungsten coil atomic absorption spectrometer.

A continuum-source tungsten coil electrothermal atomic absorption spectrometer has been assembled, evaluated, and employed in four different applications. The instrument consists of a xenon arc lamp light source, a tungsten coil atomizer, a Czerny-Turner high resolution monochromator, and a linear photodiode array detector. This instrument provides simultaneous multi-element analyses across a 4 nm spectral window with a resolution of 0.024 nm. Such a device might be useful in many different types of analyses. To demonstrate this broad appeal, four very different applications have been evaluated. First of all, the temperature of the gas phase was measured during the atomization cycle of the tungsten coil, using tin as a thermometric element. Secondly, a summation approach for two absorption lines for aluminum falling within the same spectral window (305.5-309.5 nm) was evaluated. This approach improves the sensitivity without requiring any additional preconcentration steps. The third application describes a background subtraction technique, as it is applied to the analysis of an oil emulsion sample. Finally, interference effects caused by Na on the atomization of Pb were studied. The simultaneous measurements of Pb and Na suggests that negative interference arises at least partially from competition between Pb and Na atoms for H2 in the gas phase.     

The effect of cryogenic sample cooling on X-ray absorption spectra

It is common for samples to be cooled to near liquid He temperature (4 K) during measurement of their X-ray absorption spectra (XAS). This procedure is believed to improve spectrum quality either by minimizing radiation damage, or by decreasing thermal motions of atoms. The actual benefits realized by cooling are rarely assessed, since that would require duplicate measurements at multiple temperatures, followed by duplicate data analyses. With a cryostat installed, it is difficult to measure room temperature or hotter spectra, which often requires removing the cryostat from the beam path.Here we investigate the effect of cooling and show that it is not globally useful in X-ray absorption spectroscopy. Photolysis does not occur, or its consequences are not controlled by cooling. Secondary photochemical damage is delayed and is remote from the absorption site. Thermal motions do not usually contribute significantly to disorder and consequent damping of EXAFS, either because vibrational amplitudes are small, or because static disorder and structural complexity affect EXAFS in the same way but more profoundly.The low probability of photochemical effects on XAS is in contrast to the situation with crystallography of biological specimens, where photochemical damage anywhere in the sample degrades the data set regardless of proximity to atoms of one specific element. Thermal disorder becomes important in certain types of samples and when the Debye-Waller factor is itself used as a tool. In most cases, it is more efficient to first measure room temperature spectra, and then repeat measurement using a cryostat of only those spectra where the objectives of the analysis justify an attempt to gain more information.