Superalgebras, constraints and partition functions

We consider Borcherds superalgebras obtained from semisimple finite-dimensional Lie algebras by adding an odd null root to the simple roots. The additional Serre relations can be expressed in a covariant way. The spectrum of generators at positive levels are associated to partition functions for a certain set of constrained bosonic variables, the constraints on which are complementary to the Serre relations in the symmetric product. We give some examples, focusing on superalgebras related to pure spinors, exceptional geometry and tensor hierarchies, of how construction of the content of the algebra at arbitrary levels is simplified.Comment: 27 pages. v2: Explanations and references added. Published versio

The octic E8 invariant

We give an explicit expression for the primitive E8-invariant tensor with eight symmetric indices. The result is presented in a manifestly Spin(16)/Z2-covariant notation.Comment: 10 pp, plain te

Exploring Experience Curves for the Building Envelope: An Investigation for Switzerland for 1970–2020

Energy efficiency potentials slumbering in the envelopes of existing and newly constructed buildings are significant and still largely untapped. Increasing concerns of policy-makers about non-sustainable energy use and its implications especially on climate change currently spur a growing interest in research in this area. The aim of this paper is to fill part of the existing knowledge gap by focusing on experience curve aspects of energy efficiency measures that concern state-of-the-art insulation methods, materials, and windows, and by studying the usefulness of such experience curves for the building envelope for energy policy design and evaluation. The analysis draws on a recent investigation of the situation in Switzerland (Jakob et al. 2002), but also contains a wider perspective especially regarding some more global technological trends and the market diffusion of innovative energy conservation technologies for the building envelope, policy designs, and policy programmes. The results derived from historical data analysis point to significant techno-economic progress over the last 30 years, and demonstrate the basic applicability, merits and limitations of the experience curve concept for energy policy design and impact analyses concerning the building envelope. We conclude from our analysis that building standards and labels can be important drivers for technoeconomic progress, apart from the energy conservation potentials offered, and that experience curves can be a useful tool for targeted and effective policy measures and for the promotion of labels and standards.Experience curve, building envelope, energy efficiency, policy design, energy paradox

Beyond representations: towards an action-centric perspective on tangible interaction

In the light of theoretical as well as concrete technical development, we discuss a conceptual shift from an information-centric to an action-centric perspective on tangible interactive technology. We explicitly emphasise the qualities of shareable use, and the importance of designing tangibles that allow for meaningful manipulation and control of the digital material. This involves a broadened focus from studying properties of the interface, to instead aim for qualities of the activity of using a system, a general tendency towards designing for social and sharable use settings and an increased openness towards multiple and subjective interpretations. An effect of this is that tangibles are not designed as representations of data, but as resources for action. We discuss four ways that tangible artefacts work as resources for action: (1) for physical manipulation; (2) for referential, social and contextually oriented action; (3) for perception and sensory experience; (4) for digitally mediated action

Generators and relations for (generalised) Cartan type superalgebras

In Kac's classification of finite-dimensional Lie superalgebras, the contragredient ones can be constructed from Dynkin diagrams similar to those of the simple finite-dimensional Lie algebras, but with additional types of nodes. For example, $A(n-1,0) = \mathfrak{sl}(1|n)$ can be constructed by adding a "gray" node to the Dynkin diagram of $A_{n-1} = \mathfrak{sl}(n)$, corresponding to an odd null root. The Cartan superalgebras constitute a different class, where the simplest example is $W(n)$, the derivation algebra of the Grassmann algebra on $n$ generators. Here we present a novel construction of $W(n)$, from the same Dynkin diagram as $A(n-1,0)$, but with additional generators and relations.Comment: 6 pages, talk presented at Group32, Prague, July 2018. v2: Minor change

Generators and relations for Lie superalgebras of Cartan type

We give an analog of a Chevalley-Serre presentation for the Lie superalgebras W(n) and S(n) of Cartan type. These are part of a wider class of Lie superalgebras, the so-called tensor hierarchy algebras, denoted W(g) and S(g), where g denotes the Kac-Moody algebra A_r, D_r or E_r. Then W(A_{n-1}) and S(A_{n-1}) are the Lie superalgebras W(n) and S(n). The algebras W(g) and S(g) are constructed from the Dynkin diagram of the Borcherds-Kac-Moody superalgebras B(g) obtained by adding a single grey node (representing an odd null root) to the Dynkin diagram of g. We redefine the algebras W(A_r) and S(A_r) in terms of Chevalley generators and defining relations. We prove that all relations follow from the defining ones at level -2 and higher. The analogous definitions of the algebras in the D- and E-series are given. In the latter case the full set of defining relations is conjectured.Comment: 42 pages. v2: Minor changes. Version accepted for publication in J. Phys.

Setting the stage – embodied and spatial dimensions in emerging programming practices.

In the design of interactive systems, developers sometimes need to engage in various ways of physical performance in order to communicate ideas and to test out properties of the system to be realised. External resources such as sketches, as well as bodily action, often play important parts in such processes, and several methods and tools that explicitly address such aspects of interaction design have recently been developed. This combined with the growing range of pervasive, ubiquitous, and tangible technologies add up to a complex web of physicality within the practice of designing interactive systems. We illustrate this dimension of systems development through three cases which in different ways address the design of systems where embodied performance is important. The first case shows how building a physical sport simulator emphasises a shift in activity between programming and debugging. The second case shows a build-once run-once scenario, where the fine-tuning and control of the run-time activity gets turned into an act of in situ performance by the programmers. The third example illustrates the explorative and experiential nature of programming and debugging systems for specialised and autonomous interaction devices. This multitude in approaches in existing programming settings reveals an expanded perspective of what practices of interaction design consist of, emphasising the interlinking between design, programming, and performance with the system that is being developed

Global detection and analysis of coastline associated rainfall using an objective pattern recognition technique

Coastally associated rainfall is a common feature especially in tropical and subtropical regions. However, it has been difficult to quantify the contribution of coastal rainfall features to the overall local rainfall. We develop a novel technique to objectively identify precipitation associated with land-sea interaction and apply it to satellite based rainfall estimates. The Maritime Continent, the Bight of Panama, Madagascar and the Mediterranean are found to be regions where land-sea interactions plays a crucial role in the formation of precipitation. In these regions $\approx$ 40% to 60% of the total rainfall can be related to coastline effects. Due to its importance for the climate system, the Maritime Continent is a particular region of interest with high overall amounts of rainfall and large fractions resulting from land-sea interactions throughout the year. To demonstrate the utility of our identification method we investigate the influence of several modes of variability, such as the Madden-Julian-Oscillation and the El Ni\~no Southern Oscillation, on coastal rainfall behavior. The results suggest that during large scale suppressed convective conditions coastal effects tend modulate the rainfall over the Maritime Continent leading to enhanced rainfall over land regions compared to the surrounding oceans. We propose that the novel objective dataset of coastally influenced precipitation can be used in a variety of ways, such as to inform cumulus parametrization or as an additional tool for evaluating the simulation of coastal precipitation within weather and climate models