Addendum: an analogue of Artin reciprocity for closed orbits of skew products

One of the unfulfilled aims of the authors of the preceding paper [W. Parry and M. Pollicott. An analogue of Bauer’s theorem for closed orbits of skew products. Ergod. Th. & Dynam. Sys. 28 (2008), 535–546] was to find a dynamical analogue of Artin reciprocity. In this addendum, we present one such version, suggested by work of Sunada

Applications of high thermal conductivity composites to electronics and spacecraft thermal design

Recently, high thermal conductivity continuous graphite fiber reinforced metal matrix composites (MMC's) have become available that can save much weight over present methods of heat conduction. These materials have two or three times higher thermal conductivity in the fiber direction than the pure metals when compared on a thermal conductivity to weight basis. Use of these materials for heat conduction purposes can result in weight savings of from 50 to 70 percent over structural aluminum. Another significant advantage is that these materials can be used without the plumbing and testing complexities that accompany the use of liquid heat pipes. A spinoff of this research was the development of other MMC's as electronic device heat sinks. These use particulates rather than fibers and are formulated to match the coefficient of thermal expansion of electronic substrates in order to alleviate thermally induced stresses. The development of both types of these materials as viable weight saving substitutes for traditional methods of thermal control for electronics packaging and also for spacecraft thermal control applications are the subject of this report

A new fabrication method for precision antenna reflectors for space flight and ground test

Communications satellites are using increasingly higher frequencies that require increasingly precise antenna reflectors for use in space. Traditional industry fabrication methods for space antenna reflectors employ successive modeling techniques using high- and low-temperature molds for reflector face sheets and then a final fit-up of the completed honeycomb sandwich panel antenna reflector to a master pattern. However, as new missions are planned at much higher frequencies, greater accuracies will be necessary than are achievable using these present methods. A new approach for the fabrication of ground-test solid-surface antenna reflectors is to build a rigid support structure with an easy-to-machine surface. This surface is subsequently machined to the desired reflector contour and coated with a radio-frequency-reflective surface. This method was used to fabricate a 2.7-m-diameter ground-test antenna reflector to an accuracy of better than 0.013 mm (0.0005 in.) rms. A similar reflector for use on spacecraft would be constructed in a similar manner but with space-qualified materials. The design, analysis, and fabrication of the 2.7-m-diameter precision antenna reflector for antenna ground tests and the extension of this technology to precision, space-based antenna reflectors are described

Weil–Petersson metrics, Manhattan curves and Hausdorff dimension

In this note we want to relate the Weil-Petersson metric on Teichm¨uller space to the boundary correspondence between the actions on the boundary of Fuchsian groups. Consider the space of Riemann metrics g on a compact surface V with negative Euler characteristic. This can be endowed with a number of natural Riemannian metrics. Of particular interest is the Weil-Petersson metric, whose definition was proposed by Weil in 1958 based on earlier work of Petersson, cf. [18]. There is a particularly intuitive equivalent definition of the Weil-Petersson metric using the second derivative of lengths of typical (closed) geodesics due to Thurston and Wolpert [19]

Equidistribution of holonomy in homology classes for Anosov flows

We obtain equidistribution results for the holonomies of periodic orbits of Anosov flows lying in a prescribed homology class. We apply this to frame flows

A frame signature matrix for analysing and comparing interaction design behaviour

Protocol studies are an established method to investigate design behaviour. In the context of a project to investigate novice interaction design (ID) behaviour across protocols and cultures, we found that existing design behaviour analysis frameworks did not provide reliable results. This paper describes the development of a new approach to analyse and compare ID behaviour using verbal protocols. We augment Schön’s basic design and reflection cycle with construction of a frame signature matrix and analogical categorisation coding. We demonstrate this approach by comparing two protocols of novice interaction designers in Botswana. The initial findings indicate that this approach increases consistency and accuracy of coding, and that there are different degrees of reframing for the design problem and solutions

Orbit counting in conjugacy classes for free groups acting on trees

In this paper we study the action of the fundamental group of a finite metric graph on its universal covering tree. We assume the graph is finite, connected and the degree of each vertex is at least three. Further, we assume an irrationality condition on the edge lengths. We obtain an asymptotic for the number of elements in a fixed conjugacy class for which the associated displacement of a given base vertex in the universal covering tree is at most T. Under a mild extra assumption we also obtain a polynomial error term

Amenability, critical exponents of subgroups and growth of closed geodesics

Let Γ be a (non-elementary) convex co-compact group of isometries of a pinched Hadamard manifold X. We show that a normal subgroup Γ0 has critical exponent equal to the critical exponent of Γ if and only if Γ/Γ0 is amenable. We prove a similar result for the exponential growth rate of closed geodesics on X/Γ. These statements are analogues of classical results of Kesten for random walks on groups and Brooks for the spectrum of the Laplacian on covers of Riemannian manifolds

A protocol study of novice interaction design behaviour in Botswana: solution-driven interaction design

Think aloud studies and protocol analysis are well-known in the field of HCI, but most often these studies focus on usability evaluations, or on the use of technology. Rarely are they used to investigate the behaviour of interaction designers. In this paper, we report on a protocol study with novice interaction designers in Botswana. Participants had just completed the design section of an undergraduate module on Interaction Design that actively promotes a problem-driven approach to the design of interactive products, yet the participants behaved in a way that is closer to a solution-driven approach. The module emphasizes user-centred design, prototyping methods to support design development, and evaluating design detail. Yet participants suggest solutions before exploring the context of use, use prototyping methods to capture, rather than to develop, designs, and do not produce detailed designs. In a problem-solving context, some of these behaviours are typical of novices, but in a design context they are also seen in experienced designers. The results presented here reveal the detail of the approach adopted by these students, and contribute to the wider debate concerning the internationalization of HCI education