We present a physically-based analytical model of the daytime sky. Based on the results of a first-principles brute force simulation of radiative transfer in the atmosphere, we use the same general approach of fitting basis function coefficients to radiance data as the Perez and Preetham models do. However, we make several modifications to this process, which together significantly improve the rendition of sunsets and high atmospheric turbidity setups -- known weak points of the Preetham model. Additionally, our model accounts for ground albedo, and handles each spectral component independently. The latter property makes it easily extensible to the near ultraviolet range of the spectrum, so that the daylight appearance of surfaces that include optical brighteners can be properly predicted. Due to its similar mathematical properties, the new model can be used as a drop-in replacement of the Preetham model.

This paper aims to contribute to recent innovations in social scientific methodology that aspire to address the complex, iterative, and performative dimensions of method. In particular, we focus on the becoming-with character of social events, and propose a speculative method for engaging with the notas-yet. This work, being part of a larger project that uses speculative design and ethnographic methods to explore energy-demand reduction, specifically considers the ways in which energy-demand reduction features in the Twitter-sphere. Developing and deploying three automated Bots whose function and communications are at best obscure, and not uncommonly nonsensical, we trace some of ways in which they intervene and provoke. Heuristically, we draw on the 'conceptual characters' of idiot, parasite and diplomat in order to grasp how the Bots act within Twitter to evoke the instability and emergent eventuations of energy-demand reduction, community, and related practices. We conclude by drawing out some of the wider implications of this particular enactment of speculative method.

Fig. 1. A still life photograph of our optimized printouts. The thickness of all the pictured samples is 1 cm.Color texture reproduction in 3D printing commonly ignores volumetric light transport (cross-talk) between surface points on a 3D print. Such light di usion leads to signi cant blur of details and color bleeding, and is particularly severe for highly translucent resin-based print materials. Given their widely varying scattering properties, this cross-talk between surface points strongly depends on the internal structure of the volume surrounding each surface point. Existing scattering-aware methods use simpli ed models for light di usion, and often accept the visual blur as an immutable property of the print medium. In contrast, our work counteracts heterogeneous scattering to obtain the impression of a crisp albedo texture on top of the 3D print, by optimizing for a fully volumetric material distribution that preserves the target appearance. Our method employs an e cient numerical optimizer on top of a general Monte-Carlo simulation of heterogeneous scattering, supported by a practical calibration procedure to obtain scattering parameters from a given set of printer materials. Despite the inherent translucency of the medium, we reproduce detailed surface textures on 3D prints. We evaluate our system using a commercial, ve-tone 3D print process and compare against the printer's native color texturing mode, demonstrating *Oskar Elek and Denis Sumin share the rst authorship of this work. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for pro t or commercial advantage and that copies bear this notice and the full citation on the rst page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior speci c permission and/or a fee. Request permissions from permissions@acm.org. © 2017 ACM. 0730-0301/2017/11-ART241 $15.00 DOI: 10.1145/3130800.3130890 that our method preserves high-frequency features well without having to compromise on color gamut.

is critically limited to color reproduction on planar surfaces, to arbitrary 3D shapes. Our method enables high-fidelity color texture reproduction on 3D prints by effectively compensating for internal light scattering within arbitrarily shaped objects. In addition, we propose a content-aware gamut mapping that significantly improves color reproduction for the pathological case of thin geometric features. Using a wide range of sample objects with complex textures and geometries, we demonstrate color reproduction whose fidelity is superior to state-of-the-art drivers for color 3D printers. CCS Concepts: • Computing methodologies → Reflectance modeling; Volumetric models; • Applied computing → Computer-aided manufacturing.