Alternative mechanisms of increased eggshell hardness of avian brood parasites relative to host species

Obligate brood parasitic birds lay their eggs in nests of other species and parasite eggs typically have evolved greater structural strength relative to host eggs. Increased mechanical strength of the parasite eggshell is an adaptation that can interfere with puncture ejection behaviours of discriminating hosts. We investigated whether hardness of eggshells is related to differences between physical and chemical traits from three different races of the parasitic common cuckoo Cuculus canorus, and their respective hosts. Using tools developed for materials science, we discovered a novel correlate of increased strength of parasite eggs: the common cuckoo''s egg exhibits a greater microhardness, especially in the inner region of the shell matrix, relative to its host and sympatric non-host species. We then tested predictions of four potential mechanisms of shell strength: (i) increased relative thickness overall, (ii) greater proportion of the structurally harder shell layers, (iii) higher concentration of inorganic components in the shell matrix, and (iv) elevated deposition of a high density compound, MgCO₃, in the shell matrix. We confirmed support only for hypothesis (i). Eggshell characteristics did not differ between parasite eggs sampled from different host nests in distant geographical sites, suggesting an evolutionarily shared microstructural mechanism of stronger parasite eggshells across diverse host-races of brood parasitic cuckoos.     

Input selection and shrinkage in multiresponse linear regression

The regression problem of modeling several response variables using the same set of input variables is considered. The model is linearly parameterized and the parameters are estimated by minimizing the error sum of squares subject to a sparsity constraint. The constraint has the effect of eliminating useless inputs and constraining the parameters of the remaining inputs in the model. Two algorithms for solving the resulting convex cone programming problem are proposed. The first algorithm gives a pointwise solution, while the second one computes the entire path of solutions as a function of the constraint parameter. Based on experiments with real data sets, the proposed method has a similar performance to existing methods. In simulation experiments, the proposed method is competitive both in terms of prediction accuracy and correctness of input selection. The advantages become more apparent when many correlated inputs are available for model construction.     

A density based segmentation method to determine the coordination number of a particulate system

The coordination number is an important parameter for understanding the particulate systems, especially when agglomerated particles are present. However, experimental determination of the coordination number is not trivial. In this study, we describe a 3D classification method, which is based on the revised DBSCAN (Density-Based Spatial Clustering of Applications with Noise) and its application to X-ray micro-tomographic (XMT) images to determine the coordination number distribution. Pellets of micro-crystalline cellulose were used as model particles. The validity of the segmentation was checked by comparing the particle size distribution (PSD) obtained by XMT-DBSCAN with PSD obtained by optical microscopy. The results were found to be in good agreement, demonstrating the suitability of the DBSCAN method. The means and standard deviations of coordination numbers were (8.2±1.7, n=994 particles), (8.1±1.5, n=904) and (6.2±1.2, n=159) for pellets with length based mean sizes of 157, 307 and 437 μm, respectively. The coordination number distribution was in line with previous finding in mono-sized acrylic beads.     

On the power of L-systems in image generation

Image generation with DOL-systems is discussed. It is shown that, if either the vector or the turtle geometry interpretation is used, DOL-systems can produce step-by-step all images that can be generated by regular languages (or by equivalent Iterative Matrix Homomorphisms of Shallit and Stolfi). An extension of turtle geometry interpretation is introduced that enables L-systems to generate gray-tone images. It is shown that with our extension every Weighted Finite Automaton can be simulated step-by-step by a DOL-system.An abbreviated version of this paper was presented at the conference Developments in Formal Languages, Turku, July 1993.Research supported by the NSF Grant No. CCR-9202396This article was processed by the author using the LATEX style file pljourl from Springer-Verlag.     

Using 2- and 2 -dimensional seed filling in view lattice to accelerate volumetric rendering

In this paper we propose new methods for calculating the projection of an opaque 3-dimensional 6-connected volumetric object into a two-dimensional view using 2- and 2 -dimensional seed-filling in the view space. When a 3-dimensional volumetric data set is sampled by parallel rays at a resolution exceeding the Nyquist ratio, the 6-connectivity of objects is maintained from volume lattice to view lattice. Given a seed point for each 6-connected object in the volumetric data set, a seed-filling algorithm may access all sample points in view lattice, while simultaneously composing the rendered view. The algorithms presented in this paper minimize the number of voxels that need to be processed. We implemented these methods on a general purpose computer architecture and tested them with several artificial and real-life medical volumetric data sets. It is shown that the algorithms may be used to speed up the parallel ray casting of opaque medical objects. The actual frame rate achieved by the combined method allows interactive (10 frames/sec) rotation of the object on a common single-processor personal computer without specialized hardware.     

On time-symmetry in cellular automata

The notion of reversibility has been intensively studied in the field of cellular automata (CA), for several reasons. However, a related notion found in physical theories has been so far neglected, not only in CA, but generally in discrete dynamical systems. This is the notion of time-symmetry, which refers to the inability of distinguishing between backward and forward time directions. Here we formalize it in the context of CA, and study some of its basic properties. We also show how some well-known CA fit into the class of time-symmetric CA, and provide a number of results on the relation between this and other classes of CA. The existence of an intrinsically universal time-symmetric CA within the class of reversible CA is proved. Finally, we show the undecidability of time-symmetry for CA of dimension 2 or higher, even within the class of reversible CA. The case of dimension 1 is one of several open questions discussed in the conclusions.