Writing essays by pictures : redrawing the textbook

This opinion piece considers the textbook as an academic genre and wonders whether, as it could be seen to have been developed based on now outmoded concepts and technologies, the textbook is outmoded itself. It is argued that learning resources need to be designed with the different types of knowledge to be learnt in mind. This is demonstrated with the example of Writing Essays by Pictures, a recently published stand-alone resource that aims to facilitate the researching and writing of a basic research based essay for first year undergraduate students

A note on non-reduced reflection factorizations of Coxeter elements

We extend a result of Lewis and Reiner from finite Coxeter groups to all Coxeter groups by showing that two reflection factorizations of a Coxeter element lie in the same Hurwitz orbit if and only if they share the same multiset of conjugacy classes.Comment: Comments welcom

Competitive Boolean Function Evaluation: Beyond Monotonicity, and the Symmetric Case

We study the extremal competitive ratio of Boolean function evaluation. We provide the first non-trivial lower and upper bounds for classes of Boolean functions which are not included in the class of monotone Boolean functions. For the particular case of symmetric functions our bounds are matching and we exactly characterize the best possible competitiveness achievable by a deterministic algorithm. Our upper bound is obtained by a simple polynomial time algorithm.Comment: 15 pages, 1 figure, to appear in Discrete Applied Mathematic

Photorealistic ray tracing of free-space invisibility cloaks made of uniaxial dielectrics

The design rules of transformation optics generally lead to spatially inhomogeneous and anisotropic impedance-matched magneto-dielectric material distributions for, e.g., free-space invisibility cloaks. Recently, simplified anisotropic non-magnetic free-space cloaks made of a locally uniaxial dielectric material (calcite) have been realized experimentally. In a two-dimensional setting and for in-plane polarized light propagating in this plane, the cloaking performance can still be perfect for light rays. However, for general views in three dimensions, various imperfections are expected. In this paper, we study two different purely dielectric uniaxial cylindrical free-space cloaks. For one, the optic axis is along the radial direction, for the other one it is along the azimuthal direction. The azimuthal uniaxial cloak has not been suggested previously to the best of our knowledge. We visualize the cloaking performance of both by calculating photorealistic images rendered by ray tracing. Following and complementing our previous ray-tracing work, we use an equation of motion directly derived from Fermats principle. The rendered images generally exhibit significant imperfections. This includes the obvious fact that cloaking does not work at all for horizontal or for ordinary linear polarization of light. Moreover, more subtle effects occur such as viewing-angle-dependent aberrations. However, we still find amazingly good cloaking performance for the purely dielectric azimuthal uniaxial cloak.Comment: 12 pages, 3 figures, journal pape

Study of experiments on condensation of nitrogen by homogeneous nucleation at states modelling those on the national transonic facility

A cryogenic wind tunnel is based on the twofold idea of lowering drive power and increasing Reynolds number by operating with nitrogen near its boiling point. There are two possible types of condensation problems involved in this mode of wind tunnel operation. They concern the expansion from the nozzle supply to the test section at relatively low cooling rates, and secondly the expansion around models in the test section. This secondary expansion involves higher cooling rates and shorter time scales. In addition to these two condensation problems it is not certain what purity of nitrogen can be achieved in a large facility. Therefore, one cannot rule out condensation processes other than those of homogeneous nucleation

Regional aspects of decision-making support for rural development in Poland

Measures for rural development should be adapted to the specific regional conditions and national programs should allow for different regional priorities. However, decision-making for policy measures often takes place under special conditions with many concerned actors, unstructured decision problems and time pressure. These conditions, decision-makers in administrations and institutions are faced with, make the formation of policy-measures for rural development a complex matter. Thus, there is the question arising how decision-makers can be supported in setting priorities for allocating budgets for policy measures among regions. Recently, multi criteria decision-making approaches are discussed to tackle these kinds of decision problems. We show exemplarily for the Polish program of rural development, how decision-making could be supported using a multi-objective programming approach. Different preferences of actors can be considered explicitly by visualizing “trade-offs” and an interactive use of the approach. For example, a political "equity" objective is implemented as a constraint in the programming approach, restricting the budget differences between regions to a defined level. By a parameterization of the bound for budget differences, the "trade-off" between three objectives is displayed and evaluated. Using the exemplary programming approach, it is shown that the objective values of the two main objectives of the PROW decline, when the budget differences between regions are restricted for pursuing a political "equity" objective.Regional Budgeting, Interactive Decision-making support, Multi-objective Programming (MOP), Community/Rural/Urban Development,