In this paper, we demonstrate the existence of a bidirectional causal relationship between smartphone application use and user emotions. In a two-week long in-the-wild study with 30 participants we captured 502,851 instances of smartphone application use in tandem with corresponding emotional data from facial expressions. Our analysis shows that while in most cases application use drives user emotions, multiple application categories exist for which the causal effect is in the opposite direction. Our findings shed light on the relationship between smartphone use and emotional states. We furthermore discuss the opportunities for research and practice that arise from our findings and their potential to support emotional well-being.

Near-Infrared Spectroscopy (NIRS) is a non-invasive sensing technique which can be used to acquire information on an object's chemical composition. Although NIRS is conventionally used in dedicated laboratories, the recent introduction of miniaturized NIRS scanners has greatly expanded the use cases of this technology. Previous work from the UbiComp community shows that miniaturized NIRS can be successfully adapted to identify medical pills and alcohol concentration. In this paper, we further extend this technology to identify sugar (sucrose) contents in everyday drinks. We developed a standalone mobile device which includes inter alia a NIRS scanner and a 3D printed clamp. The clamp can be attached to a straw-like tube to sense a liquid's sucrose content. Through a series of studies, we show that our technique can accurately measure sucrose levels in both lab-made samples and commercially available drinks, as well as classify commercial drinks. Furthermore, we show that our method is robust to variations in the ambient temperature and lighting conditions. Overall, our system can estimate the concentration of sugar with ±0.29 g/100ml error in lab-made samples and < 2.0 g/100ml error in 18 commercial drinks, and can identify everyday drinks with > 99% accuracy. Furthermore, in our analysis, we are able to discern three characteristic wavelengths in the near-infrared region (1055 nm, 1235 nm and 1545 nm) with acute responses to sugar (sucrose). Our proposed protocol contributes to the development of everyday "food scanners" consumers.

Inspired by the increasing prevalence of digital voice assistants, we demonstrate the feasibility of using voice interfaces to deploy and complete crowd tasks. We have developed Crowd Tasker, a novel system that delivers crowd tasks through a digital voice assistant. In a lab study, we validate our proof-ofconcept and show that crowd task performance through a voice assistant is comparable to that of a web interface for voicecompatible and voice-based crowd tasks for native English speakers. We also report on a field study where participants used our system in their homes. We find that crowdsourcing through voice can provide greater flexibility to crowd workers by allowing them to work in brief sessions, enabling multitasking, and reducing the time and effort required to initiate tasks. We conclude by proposing a set of design guidelines for the creation of crowd tasks for voice and the development of future voice-based crowdsourcing systems.

Our work investigates the use of a Near InfraRed Spectroscopy scanner for the identification of liquids. While previous work has shown promising results for the identification of solid objects, identifying liquids poses additional challenges.These challenges include light scattering and low reflectance caused by the transparency of liquids, which interfere with the infrared measurement. We develop a prototype solution consisting of a 3D printed clamp that attaches to a tube, such that it blocks ambient light from interfering. Our preliminary results indicate that our prototype works, and we demonstrate this by measuring sugar levels in a liquid solution.

We propose a context-free semantic localisation approach to visualise and analyse indoor movements. We focus on settings where indoor location or rooms have strongly associated semantics, such as hospitals. We describe an approach that can work with different localisation systems, with little knowledge of the physical space properties, and with minimal bootstrapping required. We propose a movement representation that consists of time-encoded strings, and discuss how our approach can be used for analysing and visualising longitudinal indoor localisation data. CCS CONCEPTS • Human-centered computing → Empirical studies in HCI; • Human-centered computing → Ubiquitous and mobile computing; • Human-centered computing → Smartphones.