Efficient 3D Pointing Selection in Cluttered Virtual Environments

Most pointing techniques for 3D selection in spatially immersive virtual environments rely on a ray originating at the user's hand and controlled by the hand orientation. However, mismatches between visible objects (those appearing unoccluded from the user's eye position) and selectable objects (those appearing unoccluded from the user's hand position) could hinder selection performance. The authors propose a new device-ray mapping, Ray Casting from the Eye (RCE), to overcome this problem. In a controlled experiment involving selection tasks with complex 3D scenes, RCE clearly outperformed ray casting in terms of speed and accuracy. This article is part of a special issue on 3D user interfaces.     

The rotation graph of k-ary trees is Hamiltonian

In this paper we show that the graph of k-ary trees, connected by rotations, contains a Hamilton cycle. Our proof is constructive and thus provides a cyclic Gray code for k-ary trees. Furthermore, we identify a basic building block of this graph as the 1-skeleton of the polytopal complex dual to the lower faces of a certain cyclic polytope.     

Point set stratification and Delaunay depth

In the study of depth functions it is important to decide whether a depth function is required to be sensitive to multimodality. An analysis of the Delaunay depth function shows that it is sensitive to multimodality. This notion of depth can be compared to other depth functions such as the convex and location depths. The stratification that Delaunay depth induces in the point set (layers) and in the whole plane (levels) is investigated. An algorithm for computing the Delaunay depth contours associated with a point set in the plane is developed. The worst case and expected complexities of the algorithm are and O(nlogn), respectively. The depth of a query point p with respect to a data set S in the plane is the depth of p in S∪{p}. The Delaunay depth can be computed in O(nlogn) time, which is proved to be optimal, when S and p are given in the input.     

Characterisation of industrial tomato by-products from infrared drying process

The thin-layer infrared drying behaviour of industrial tomato residues, peels and seeds, was experimentally investigated in the temperature range from 100 °C to 160 °C. The drying rate was found to increase with temperature, hence reducing the total drying time. In particular, as drying temperature was raised from 100 °C up to 160 °C, the time period needed to reduce the moisture content of the sample from 236.70 wt% down to 5.26 wt% (dry basis) was observed to decrease from 99.5 min to 35 min.Using a non-linear regression (Marquart's method) together with a multiple regression analysis, a mathematical model for the thin-layer infrared drying process of industrial tomato residues was proposed. The effective moisture diffusivity is dependent on moisture content; the average values for the diffusivity coefficients at each temperature were obtained using Fick's second law of diffusion, and varied from 5.179 × 10^?9 m²/s to 1.429 × 10^?8 m²/s over the temperature range. The temperature dependence of the effective diffusivity coefficient was described following an Arrhenius-type relationship. Activation energy for the moisture diffusion was determined as 22.23 kJ/mol.     

Dynamic behaviour in a nonlinear directional coupler with feedback

Abstract

A new kind of resonator based on a nonlinear directional coupler with feedback is presented. The steady states are found and the map of the system is iterated, showing the existence of bistability, period doubling and chaos. The dependence of the dynamic features is discussed in terms of the parameters of the two different schemes of feedback studied in this work. A new device based on one of these schemes of feedback suitable as a routing unit is proposed.     

Rethinking economy-wide rebound measures: An unbiased proposal

In spite of having been first introduced in the last half of the ninetieth century, the debate about the possible rebound effects from energy efficiency improvements is still an open question in the economic literature. This paper contributes to the existing research on this issue proposing an unbiased measure for economy-wide rebound effects. The novelty of this economy-wide rebound measure stems from the fact that not only actual energy savings but also potential energy savings are quantified under general equilibrium conditions. Our findings indicate that the use of engineering savings instead of general equilibrium potential savings downward biases economy-wide rebound effects and upward-biases backfire effects. The discrepancies between the traditional indicator and our proposed measure are analysed in the context of the Spanish economy.     

GAT: a Graphical Annotation Tool for semantic regions

This article presents GAT, a Graphical Annotation Tool based on a region-based hierarchical representation of images. The proposed solution uses Partition Trees to navigate through the image segments which are automatically defined at different spatial scales. Moreover, the system focuses on the navigation through ontologies for a semantic annotation of objects and of the parts that compose them. The tool has been designed under usability criteria to minimize the user interaction by trying to predict the future selection of regions and semantic classes. The implementation uses MPEG-7/XML input and output data to allow interoperability with any type of Partition Tree. This tool is publicly available and its source code can be downloaded under a free software license.     

The bipenalty method for arbitrary multipoint constraints

In finite element (FE) analysis, traditional penalty methods impose constraints by adding virtual stiffness to the FE system. In dynamics, this can decrease the critical time step of the system when conditionally stable time integration schemes are used by introducing spurious modes with high eigenfrequencies. Recent studies have shown that using mass penalties alongside traditional stiffness penalties can mitigate this effect for systems with a one single‐point constraint. In the present work, we extend this finding to include systems with an arbitrary set of multipoint constraints. By analysing the generalised eigenvalue problem, we show that the values of spurious eigenfrequencies may be controlled by the choice of stiffness and mass penalty parameters. The method is demonstrated using numerical examples, including a one‐dimensional contact–impact formulation and a two‐dimensional crack propagation analysis. The results show that constraint imposition using the bipenalty method can be employed such that the critical time step of an analysis is unaffected, whereas also displaying superiority over the mass penalty method in terms of accuracy and versatility. Copyright © 2012 John Wiley & Sons, Ltd.     

Connectivity-preserving transformations of binary images

A binary image I is B_a, W_b-connected, where a, b ∈ {4, 8}, if its foreground is a-connected and its background is b-connected. We consider a local modification of a B_a, w_b-connected image I in which a black pixel can be interchanged with an adjacent white pixel provided that this preserves the connectivity of both the foreground and the background of I. We have shown that for any (a, b) ∈ {(4, 8), (8, 4), (8, 8)}, any two B_a, w_b-connected images I and J each with n black pixels differ by a sequence of Θ(n²) interchanges. We have also shown that any two B₄, W₄-connected images I and J each with n black pixels differ by a sequence of O(n⁴) interchanges.