Astronomical catalogs derived from wide-field imaging surveys are an important tool for understanding the Universe. We construct an astronomical catalog from 55 TB of imaging data using Celeste, a Bayesian variational inference code written entirely in the high-productivity programming language Julia. Using over 1.3 million threads on 650,000 Intel Xeon Phi cores of the Cori Phase II supercomputer, Celeste achieves a peak rate of 1.54 DP PFLOP/s. Celeste is able to jointly optimize parameters for 188M stars and galaxies, loading and processing 178 TB across 8192 nodes in 14.6 minutes. To achieve this, Celeste exploits parallelism at multiple levels (cluster, node, and thread) and accelerates I/O through Cori's Burst Buffer. Julia's native performance enables Celeste to employ high-level constructs without resorting to hand-written or generated low-level code (C/C++/Fortran), and yet achieve petascale performance.

Videogames are often played socially with both co-players and audiences. Audience members' experiences are not well understood, nor are the factors of videogaming sessions that influence their experience. We conducted a study to examine the effects of game physicality and turn anticipation on audience members' experiences in social videogaming sessions. Pairs of participants played games under three conditions of physicality (controller-based, Wii, and Kinect) and their expectation of turn-taking was manipulated. Their enjoyment, game engagement, social engagement and sense of participation were measured. We found that the introduction of turn-taking into the session had positive effects for audience members -- both anticipated and residual play effects -- and that Kinect gameplay resulted in a more enjoyable experience for audience members. We argue that audience members' experience changes as they become more active within a session, and suggest there are design opportunities between purely active 'players' and passive 'audience members'.

Reunion is one of the most important facets in the lives of periodically transitioning families - families who experience repeated transitions between being together and apart due to work-related or personal reasons. Even though the role of technology in mediating essential family interactions has been a longstanding focus within HCI and CSCW, the experience of periodic family reunion and its relationship with technology use while apart is little explored. To address this gap, we conducted a field study with nine families from two different professional backgrounds - defence and academic. Through a comparison between the two cohorts, our findings generate a qualitative understanding of the experience of reunion and describe specific aspects of this experience that are influenced by technology-use while apart. We discuss the complexity of this relationship and reflect on the role of technology in shaping the experience of periodic family reunion.

Photography is now a highly automated activity where people enjoy phototaking by pointing and pressing a button. While this liberates people from having to interact with the processes of photography, e.g., controlling the parameters of the camera or printing images in the darkroom, we argue that an engagement with such processes can in fact enrich people's experience of phototaking. Drawing from fieldwork with members of a film-based photography club, we found that people who engage deeply with the various processes of phototaking experienced photography richly and meaningfully. Being able to participate fully in the entire process gave them a sense of achievement over the final result. Having the opportunity to engage with the process also allowed them to learn and hone their photographic skills. Through this understanding, we can imagine future technologies that enrich experiences of photography through providing the means to interact with photographic processes in new ways.

Social interaction can be a powerful strategy for persuasive technology interventions, yet many users are reluctant to engage with others online because they fear pressure, failure and shame. We introduce the 'ambivalent socialiser', a person who is simultaneously keen but also reluctant to engage with others via social media. Our contribution is to identify four approaches to introducing sociality to ambivalent socialisers: structured socialising, incidental socialising, eavesdropping and trace sensing. We discuss the rationale for these approaches and show how they address recent critiques of persuasive technology. Furthermore, we provide actionable insights for designers of persuasive technology by showing how these approaches can be implemented in a social media application.

People have reported encountering coincidences when using particular technologies to interact with personal digital content. However, to date, there is a paucity of research to understand these experiences. This article applies McCarthy and Wright's [2004; 2005] experiential framework to analyze these kinds of technology-mediated coincidences. By focusing upon encounters of coincidence during people's digital music listening, we identified the elements at play, elucidated the properties of the individual elements, their inter-relationships, and an understanding of how coincidences can arise. We also reveal how, under particular conditions, such elements provide people with opportunities to encounter coincidence. This understanding of coincidence demonstrates how McCarthy and Wright's [2004; 2005] framework can be usefully applied to an empirical investigation of user experience.

Federated identity management systems synthesise complex and fragmented user information into a single entity. Literature from the provider's perspective notes this integration extends many benefits to the end user and the privileges provided by digital identity authentication schemes have been well documented from this perspective. Less explored are the perceptions of federation from the user's perspective. This study reports an empirical user study that examines the relationship between identity and technology using contextual interviews, focus groups and cultural probes. It emerges that while current federated systems satisfy user needs by allowing the construction of multiple digital data sets that are moored to a central identifier, they fail to provide the user with control over the capability to act in the ‘hatch’, ‘match’ and ‘dispatch’ phases of the digital identity lifecycle. Ultimately, this reduces the user's trust in providers and results in reluctance to disclose personal details.

As urban environments become increasingly hybridized, mixing the social, built, and digital in interesting ways, designing for computing in the city presents new challenges—how do we understand such hybridization, and then respond to it as designers? Here we synthesize earlier work in human-computer interaction, sociology and architecture in order to deliberately influence the design of digital systems with an understanding of their built and social context of use. We propose, illustrate, and evaluate a multidisciplinary approach combining rapid ethnography, architectural analysis, design sketching, and paper prototyping. Following the approach we are able to provide empirically grounded representations of the socio-physical context of use, in this case people socializing in urban spaces. We then use this understanding to influence the design of a context aware system to be used while out on the town. We believe that the approach is of value more generally, particularly when achieving powerfully situated interactions is the design ambition.

Many people today have access to enormous libraries of digital content. Increasingly these libraries contain personal content, consumed in support of people's non-instrumental needs. If current trends persist, these repositories will only increase. Having to choose from so much could be unpleasant especially in the absence of strong preferences. This raises some concerns for user experience (UX) design. Approaches for such interactions should not only be optimized for UX but must also support users' non-instrumental needs. People face this predicament during digital music listening and yet report positive experiences when listening in shuffle. Through an empirical study of digital music listening and close examination of people's listening practices and experiences, we argue that a shuffle-based approach--whereby people can abdicate choice to a random process while being able to modulate the randomness--not only mitigates the unpleasantness of choosing but also supports their non-instrumental needs while fostering desirable experiential outcomes.

Research on social network sites has examined how people integrate offline and online life, but with a particular emphasis on their use by friendship groups. We extend earlier work by examining a case in which offline ties are non-existent, but online ties strong. Our case is a study of bodybuilders, who explore their passion with like-minded offline 'strangers' in tightly integrated online communities. We show that the integration of offline and online life supports passion-centric activities, such as bodybuilding.

AC coupling in a transmission link is preferred and often required for the functioning of high speed transceivers. But at data rate of 1OGbps and beyond, both the external AC coupling and the conventional on-chip AC coupling approaches bring in heavy burden that pushes to the fundamental limits and are difficult to afford. This paper examines the AC-coupling methods for multi-Gb/s transceivers, and points out the impairments in the existing implementations. A hybrid structure offering both the signal-bump and the AC-capacitor functions under the stringent return-loss requirements of a 1OGb/s+ I/O is proposed and implemented in 65nm standard CMOS. A sizeable 5.1pF AC capacitor is measured with ultra low parasitic expense ratio of less than 120fF.

Randomness is being harnessed in the design of some interactive systems. This is observed in random blogs, random web searching, and in particular Apple's iPod Shuffle. Yet the role of randomness in design of interactive systems in not well understood. This paper reports on an empirical study examining the influence of randomness on the user experience of music listening. 113 instances of self-reporting were collected and analysed according to four themes: listening mode, content organisation, activities during listening, and affective outcomes. The analysis provides insights into how randomness is used to engender certain affective responses (such as feeling refreshed) by using various constraining techniques (such as playlists) whilst engaging in everyday activities (such as driving a car). The paper argues that randomness can be used as an innovative design resource for supporting rich and novel user experiences.

This paper describes the involvement of teachers as facilitators in user-based evaluation of educational software. Findings from a case study that compare the behaviour of teachers and designers during the evaluation indicate that there is no strong evidence to support the current practice of teachers' tangential participation in the evaluation of educational software. Further research is needed to better understand the role teachers can play in this type of evaluation so that their knowledge and experience can positively contribute to the evaluation process and outcomes, whilst retaining the children's valuable contribution.

On the basis of a longitudinal field study of domestic communication, we report some essential constituents of the user experience of awareness of others who are distant in space or time, i.e. presence-in-absence.We discuss presence-in-absence in terms of its social (Contact) and informational (Content) facets, and the circumstances of the experience (Context).The field evaluation of a prototype, 'The Cube', designed to support presence-in-absence, threw up issues in the interrelationships between contact, content and context; issues that the designers of similar social artifacts will need to address.

Extraction plays an important role in the performance of device models especially in the high frequency regime. The present day extraction techniques mostly use a grounded source or common source (CS) device configuration. The models extracted from the grounded source devices are then used for devices in other configurations in a circuit application. This leads to discrepancies in accurate prediction of the circuit performance. This work investigates, the applicability of the models extracted using CS for other device configurations. It was shown with the help of measured data, in the frequency range of 1-20 GHz, that the models extracted from CS configuration do not predict the performance of a device in common drain (CD) configuration. Based on the above observation, a universal gate impedance model that works for both CS and CD configurations for BSIM3v3 was developed. The gate impedance model was then extended to BSIM4 for both CS and CD configurations. The models for BSIM3v3 and BSIM4 are verified using simulations and compared with the measured data.

Intimacy is a crucial element of domestic life, and many interactive technologies designed for other purposes have been appropriated for use within intimate relationships. However, there is a deficit in current understandings of how technologies are used within intimate relationships, and how to design technologies to support intimate acts. In this paper we report on work that has addressed these deficits. We used cultural probes and contextual interviews and other ethnographically informed techniques to investigate how interactive technologies are used within intimate relationships. From this empirical work we generated a thematic understanding of intimacy and the use of interactional technologies to support intimate acts. We used this understanding to inform the design of intimate technologies. A selection of our design concepts is also presented.

When designing a usability evaluation, choices must be made regarding methods and techniques for data collection and analysis. Mobile guides raise new concerns and challenges to established usability evaluation approaches. Not only are they typically closely related to objects and activities in the user's immediate surroundings, they are often used while the user is ambulating. This paper presents results from an extensive, multi-method evaluation of a mobile guide designed to support the use of public transport in Melbourne, Australia. In evaluating the guide, we applied four different techniques; field-evaluation, laboratory evaluation, heuristic walkthrough and rapid reflection. This paper describes these four approaches and their respective outcomes, and discusses their relative strengths and weaknesses for evaluating the usability of mobile guides.

This paper describes research that seeks to facilitate the capture, representation, and reasoning about, temporal information by usability engineers. The product, a method we call KAT-LITTER, is an extension of Johnson and Johnson's (1991) Knowledge Analysis of Tasks (KAT). An evaluation of KAT-LITTER showed that it influenced the design process in two significant ways: firstly, designers using KAT-LITTER spent more time reasoning about temporal issues than designers using KAT alone, and secondly these same designers considered a broader spectrum of temporal issues. Further developments of KAT-LITTER are briefly discussed.

Welcome to the Australasian special issue of Interacting with Computers. The seven papers included in this special issue (split over two numbers, four papers included in volume 7 number 2 and a further three to follow in number 3) were selected from 44 papers presented at OZCHI'94, the annual Australian HCI conference.