530 research outputs found
An electron backscatter diffraction study of geesops: a broader view of trilobite vision?
The calcite eyes of trilobites have been studied for over 100 years using methods including light microscopy (e.g. Clarke 1889; Campbell 1975; Towe 1973; Clarkson 1979 and Bruton and Haas 2003) and more recently cathodoluminescence (CL) imaging coupled with scanning electron microscopy (SEM) of samples etched in EDTA (Miller and Clarkson 1980). This work has provided a great deal of information on the mechanisms by which lenses collected light, drawing attention to the importance of the crystallographic orientation of lens calcite for focusing, and leading to sophisticated models of trilobite vision (Clarkson and Levi-Setti, 1975; Gál et al., 2000). The morphology and mode of life of phacopids, in particular Geesops, are well understood (Bruton and Haas, 2003a; 2003b) but observations on the internal structure of their lenses contradict the generally accepted models for image formation by schizochroal eyes. Recent technological advances have given new impetus to the analysis of crystalline materials and especially important has been electron backscatter diffraction (EBSD). This is a SEM-based technique that can be used to accurately ‘map’ variations in the crystallographic orientation of a sample down to the sub-micrometre scale by recording on a sensitive camera Kikuchi patterns that are formed by diffraction of an electron beam when focused on a polished sample tilted at 70°. Although this technique has been understood for over 50 years (Alam et al., 1954) and has been extensively used in disciplines such as metallography (Humphreys, 2001), until recently its Earth Science applications were limited to studies of structural geology and petrology (Nuchter and Stockhert, 2007). Recent applications of EBSD to biomineralisation research (Dalbeck and Cusack, 2006; Griesshaber et al., 2007) have mapped the crystal orientation and microstructure of calcite shells and in 2006 Lee et al. were able to apply this technique to investigating the microstructure of lenses in the schizochroal eye of Dalmanites. This paper describes results of an EBSD study of eyes of Geesops schlotheimi (Bronn, 1825) combined with more traditional microscopy techniques to reveal new aspects of trilobite lens structure
Absence of kinetic effects in reaction-diffusion processes in scale-free networks
We show that the chemical reactions of the model systems of A+A->0 and A+B->0
when performed on scale-free networks exhibit drastically different behavior as
compared to the same reactions in normal spaces. The exponents characterizing
the density evolution as a function of time are considerably higher than 1,
implying that both reactions occur at a much faster rate. This is due to the
fact that the discerning effects of the generation of a depletion zone (A+A)
and the segregation of the reactants (A+B) do not occur at all as in normal
spaces. Instead we observe the formation of clusters of A (A+A reaction) and of
mixed A and B (A+B reaction) around the hubs of the network. Only at the limit
of very sparse networks is the usual behavior recovered.Comment: 4 pages, 4 figures, to be published in Physical Review Letter
Framework for the Integration of Service and Technology Strategies
Organised by: Cranfield UniversityAfter sales service is a highly profitable business for manufacturers of technology-driven products. Due to
this fact competitors want to share in high profit margins. At the same time after sales business has to deal
with an increasing range of variants of products and technologies, shorter life cycles and changing
customer demands. In spite of these manifold challenges, often neither after sales departments are
involved in the early product development stage nor are customer demands and technical parameters
considered in the service development processes entirely. Therefore an integration of service and
technology strategies is necessary. This paper presents a framework for this integration that visualises the
complex interdependencies and interfaces between service as well as product and motor vehicle workshop
technologies.Mori Seiki – The Machine Tool Compan
Subwords in reverse-complement order
We examine finite words over an alphabet of pairs of letters, where each word is identical with its {it reverse complement} (where ). We seek the smallest such that every word of length composed from , is uniquely determined by the set of its subwords of length up to . Our almost sharp result () is an analogue of a classical result for ``normal\u27\u27 words.
This classical problem originally was posed by M.P. Sch"utzenberger and I. Simon, and gained a considerable interest for several researchers, foremost by Vladimir Levenshtein.
Our problem has its roots in bioinformatics
Characteristics of reaction-diffusion on scale-free networks
We examine some characteristic properties of reaction-diffusion processes of
the A+A->0 type on scale-free networks. Due to the inhomogeneity of the
structure of the substrate, as compared to usual lattices, we focus on the
characteristics of the nodes where the annihilations occur. We show that at
early times the majority of these events take place on low-connectivity nodes,
while as time advances the process moves towards the high-connectivity nodes,
the so-called hubs. This pattern remarkably accelerates the annihilation of the
particles, and it is in agreement with earlier predictions that the rates of
reaction-diffusion processes on scale-free networks are much faster than the
equivalent ones on lattice systems
A finite word poset : In honor of Aviezri Fraenkel on the occasion of his 70th birthday
Our word posets have �nite words of bounded length as their elements, with
the words composed from a �nite alphabet. Their partial ordering follows from the
inclusion of a word as a subsequence of another word. The elemental combinatorial
properties of such posets are established. Their automorphism groups are determined
(along with similar result for the word poset studied by Burosch, Frank and
R¨ohl [4]) and a BLYM inequality is veri�ed (via the normalized matching property)
From single steps to mass migration: the problem of scale in the movement ecology of the Serengeti wildebeest
A central question in ecology is how to link processes that occur over
different scales. The daily interactions of individual organisms ultimately
determine community dynamics, population fluctuations and the functioning
of entire ecosystems. Observations of these multiscale ecological
processes are constrained by various technological, biological or logistical
issues, and there are often vast discrepancies between the scale at which
observation is possible and the scale of the question of interest. Animal
movement is characterized by processes that act over multiple spatial and
temporal scales. Second-by-second decisions accumulate to produce
annual movement patterns. Individuals influence, and are influenced by,
collective movement decisions, which then govern the spatial distribution
of populations and the connectivity of meta-populations. While the
field of movement ecology is experiencing unprecedented growth in the
availability of movement data, there remain challenges in integrating
observations with questions of ecological interest. In this article, we present
the major challenges of addressing these issues within the context of the
Serengeti wildebeest migration, a keystone ecological phenomena that
crosses multiple scales of space, time and biological complexity.
This article is part of the theme issue ’Collective movement ecology’
High-predation habitats affect the social dynamics of collective exploration in a shoaling fish
Collective decisions play a major role in the benefits that animals gain from living in groups. Although the mechanisms of how groups collectively make decisions have been extensively researched, the response of within-group dynamics to ecological conditions is virtually unknown, despite adaptation to the environment being a cornerstone in biology. We investigate how within-group interactions during exploration of a novel environment are shaped by predation, a major influence on the behavior of prey species. We tested guppies (Poecilia reticulata) from rivers varying in predation risk under controlled laboratory conditions and find the first evidence of differences in group interactions between animals adapted to different levels of predation. Fish from high-predation habitats showed the strongest negative relationship between initiating movements and following others, which resulted in less variability in the total number of movements made between individuals. This relationship between initiating movements and following others was associated with differentiation into initiators and followers, which was only observed in fish from high-predation rivers. The differentiation occurred rapidly, as trials lasted 5 min, and was related to shoal cohesion, where more diverse groups from high-predation habitats were more cohesive. Our results show that even within a single species over a small geographical range, decision-making in a social context can vary with local ecological factors
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