Spatial concepts and perception of physical and diagrammed scenes

The accessibility of objects in mental spatial frameworks depends on their relation to the spatial axes of the world and people's typical interactions with space. The current study investigated perception of space. Subjects viewed either a physical model of a person surrounded by objects (Exp. 1) or diagrams of scenes (Exp. 2). Subjects named objects at directions from their own external perspective. For physical scenes, subjects were faster to name objects at Above/Below locations, followed by Front/Behind locations, followed by Left/Right locations. This finding indicates that subjects used spatial frameworks to locate objects perceptually. For diagrams, response times to name objects did not conform to this pattern, perhaps because the spatial axes of a diagram do not correspond to stable spatial axes of the world.     

Space charge studies in LDPE using combined isothermal and nonisothermal current measurements

Using a recently developed procedure combining isothermal and nonisothermal current measurements space charge trapping and transport in LDPE was successfully studied. Unaged, thermally and electrically aged samples were investigated. The samples were conditioned before each measurement in order to obtain reproducible results. In the nonisothermal measurements appeared a broad peak (40/spl deg/C to 50/spl deg/C) that was possible to decompose into two or three peaks (35, 45 and 65/spl deg/C). At even higher temperature another peak was sometimes present (85/spl deg/C) depending on the prior sample conditioning. The space charge is trapped near the surface in deep traps (maximum depth of /spl ap/15 /spl mu/m). Relaxation times, mobilities and activation energies have been calculated for different charging/discharging conditions. For unaged samples the reproducibility of the results was poor while for the aged polyethylene it was quite good, meaning that aging helps conditioning. In the electrically aged LDPE there is a decrease of conductivity and the broad peak of the nonisothermal spectra shows a slight shift towards higher temperatures when compared with the data found in the thermally aged polymer.     

The fractal analysis of water trees: an estimate of the fractaldimension

Water trees result from ac electrical aging of the polymeric insulation of medium and HV power cables in a humid or wet environment. As suggested by their name, they arise from penetration of water in the polymer. Visual observation with the help of an optical microscope shows tree (bush) type structures. This suggests that water trees might be fractal objects. Calculation of the fractal dimension from experimental samples may confirm the fractal characteristics and also give information on the damage caused to the polymer. In this work images of water trees taken under the optical microscope, dyed by methylene blue and etched for scanning electron microscopy (SEM), were studied in order to estimate the fractal dimension using a box-counting algorithm. The photographs, made using an optical microscope (scale of 100 μm), of the dyed samples were obtained from laboratory-aged low-density polyethylene (LDPE) specimens using accelerated techniques. Different field amplitude and frequency and also time of aging were used and the dimension values were compared. SEM images resulting from aged cross-linked polyethylene (XLPE) cables revealed a structure at a different scale (~3 μm). Each photograph was analyzed to compare regions with and without water trees     

Three-Dimensional Representations of Contour Maps

Contour map learning may require three-dimensional representation of the area depicted by a contour map. The purpose of the study was to test the hypothesis that participants created three-dimensional mental representations of contour maps when asked to generate a cross-section profile of the map terrain from one point on the contour map to another. Gender differences in cross-section performance were also investigated, and it was hypothesized that males would perform better than females in a contour map cross-section test. Participants studied a series of contour maps or landsurface maps (three-dimensional drawings of an area), and answered two cross-section questions per map. Following the cross-section test, participants were given an incidental recognition test for the previously studied maps, either in a contour map format or a landsurface map format. Males recognized the landsurface maps corresponding to the contour map cross-section questions answered correctly better than contour map cross-section questions answered incorrectly, whereas females did not. This finding suggested that males, but not females, formed three-dimensional representations of the contour maps. There were no gender differences in performance on the contour map cross-section test, but males achieved higher recognition scores than females when the cross-section stimuli were contour maps. It was concluded that multiple spatial and verbal processing strategies can be used successfully to solve a contour map cross-section test, but that three-dimensional spatial processing may be more efficient than other forms of processing for long-term memory of contour maps. Copyright 1998 Academic Press.     

Performance optimization of nonlinear electrical networks

A program suite for the optimization of nonlinear networks is described. This suite provides an interactive automated design aid within a small-machine environment.A unified approach for time-domain design is presented. A generalized form of performance function is used and is based on the development of the adjoint-network from Tellegen's theorem. A suitable set of the adjoint-network excitations is also obtained.The constrained optimization of the performance function is transformed by a change of variables into an unconstrained problem. Powell's algorithm for unconstrained minimization is used. The optimization algorithm requires the value of the performance function and its derivatives which are obtained from analyses of the network and its adjoint.The program is implemented on a small computer with 16k words of (16-bit) core store. The overall structure of the program suite is described and results of the optimization of some simple circuits are given.