Tidal dissipation in rotating low-mass stars and implications for the orbital evolution of close-in planets I. From the PMS to the RGB at solar metallicity

Star-planet interactions must be taken into account in stellar models to understand the dynamical evolution of close-in planets. The dependence of the tidal interactions on the structural and rotational evolution of the star is of peculiar importance and should be correctly treated. We quantify how tidal dissipation in the convective envelope of rotating low-mass stars evolves from the pre-main sequence up to the red-giant branch depending on the initial stellar mass. We investigate the consequences of this evolution on planetary orbital evolution. We couple the tidal dissipation formalism described in Mathis (2015) to the stellar evolution code STAREVOL and apply it to rotating stars with masses between 0.3 and 1.4 M$_\odot$. In addition, we generalize the work of Bolmont & Mathis (2016) by following the orbital evolution of close-in planets using the new tidal dissipation predictions for advanced phases of stellar evolution. On the PMS the evolution of tidal dissipation is controlled by the evolution of the internal structure of the contracting star. On the MS it is strongly driven by the variation of surface rotation that is impacted by magnetized stellar winds braking. The main effect of taking into account the rotational evolution of the stars is to lower the tidal dissipation strength by about four orders of magnitude on the main-sequence, compared to a normalized dissipation rate that only takes into account structural changes. The evolution of the dissipation strongly depends on the evolution of the internal structure and rotation of the star. From the pre-main sequence up to the tip of the red-giant branch, it varies by several orders of magnitude, with strong consequences for the orbital evolution of close-in massive planets. These effects are the strongest during the pre-main sequence, implying that the planets are mainly sensitive to the star's early history.Comment: 13 pages, 7 figures, accepted for publication in A&

Moving usable security research out of the lab: evaluating the use of VR studies for real-world authentication research

Empirical evaluations of real-world research artefacts that derive results from observations and experiments are a core aspect of usable security research. Expert interviews as part of this thesis revealed that the costs associated with developing and maintaining physical research artefacts often amplify human-centred usability and security research challenges. On top of that, ethical and legal barriers often make usability and security research in the field infeasible. Researchers have begun simulating real-life conditions in the lab to contribute to ecological validity. However, studies of this type are still restricted to what can be replicated in physical laboratory settings. Furthermore, historically, user study subjects were mainly recruited from local areas only when evaluating hardware prototypes. The human-centred research communities have recognised and partially addressed these challenges using online studies such as surveys that allow for the recruitment of large and diverse samples as well as learning about user behaviour. However, human-centred security research involving hardware prototypes is often concerned with human factors and their impact on the prototypes’ usability and security, which cannot be studied using traditional online surveys. To work towards addressing the current challenges and facilitating research in this space, this thesis explores if – and how – virtual reality (VR) studies can be used for real-world usability and security research. It first validates the feasibility and then demonstrates the use of VR studies for human-centred usability and security research through six empirical studies, including remote and lab VR studies as well as video prototypes as part of online surveys. It was found that VR-based usability and security evaluations of authentication prototypes, where users provide touch, mid-air, and eye-gaze input, greatly match the findings from the original real-world evaluations. This thesis further investigated the effectiveness of VR studies by exploring three core topics in the authentication domain: First, the challenges around in-the-wild shoulder surfing studies were addressed. Two novel VR shoulder surfing methods were implemented to contribute towards realistic shoulder surfing research and explore the use of VR studies for security evaluations. This was found to allow researchers to provide a bridge over the methodological gap between lab and field studies. Second, the ethical and legal barriers when conducting in situ usability research on authentication systems were addressed. It was found that VR studies can represent plausible authentication environments and that a prototype’s in situ usability evaluation results deviate from traditional lab evaluations. Finally, this thesis contributes a novel evaluation method to remotely study interactive VR replicas of real-world prototypes, allowing researchers to move experiments that involve hardware prototypes out of physical laboratories and potentially increase a sample’s diversity and size. The thesis concludes by discussing the implications of using VR studies for prototype usability and security evaluations. It lays the foundation for establishing VR studies as a powerful, well-evaluated research method and unfolds its methodological advantages and disadvantages

RepliCueAuth: Validating the Use of a lab-based Virtual Reality Setup for Evaluating Authentication System

Evaluating novel authentication systems is often costly and time-consuming. In this work, we assess the suitability of using Virtual Reality (VR) to evaluate the usability and security of real-world authentication systems. To this end, we conducted a replication study and built a virtual replica of CueAuth [52], a recently introduced authentication scheme, and report on results from: (1) a lab-based in-VR usability study (N=20) evaluating user performance; (2) an online security study (N=22) evaluating system’s observation resistance through virtual avatars; and (3) a comparison between our results and those previously reported in the real-world evaluation. Our analysis indicates that VR can serve as a suitable test-bed for human-centred evaluations of real-world authentication schemes, but the used VR technology can have an impact on the evaluation. Our work is a first step towards augmenting the design and evaluation spectrum of authentication systems and offers ground work for more research to follow

Can I Borrow Your ATM? Using Virtual Reality for (Simulated) In Situ Authentication Research

In situ evaluations of novel authentication systems, where the system is evaluated in its intended usage context, are often infeasible due to ethical and legal constraints. Consequently, researchers evaluate their authentication systems in the lab, which questions the eco-logical validity. In this work, we explore how VR can overcome the shortcomings of authentication studies conducted in the lab and contribute towards more realistic authentication research. We built a highly realistic automated teller machine (ATM) and a VR replica to investigate through a user study (N=20) the impact of in situ evaluations on an authentication system‘s usability results. We evaluated and compared: Lab studies in the real world, lab studies in VR, in situ studies in the real world, and in situ studies in VR. Our findings highlight 1) VR‘s great potential to circumvent potential restrictions researchers experience when evaluating authentication schemes and 2) the impact of the context on an authentication system‘s usability evaluation results. In situ ATM authentications took longer (+24.71% in the real world, +14.17% in VR) than authentications in a traditional (VR) lab environment and elicited a higher sense of being part of an ATM authentication scenario compared to a real-world and VR-based evaluation in the lab. Our quantitative findings, along with participants‘ qualitative feedback, provide first evidence of increased authentication realism when using VR for in situ authentication research. We provide researchers with a novel research approach to conduct (simulated) in situ authentication re-search, discuss our findings in the light of prior works, and conclude with three key lessons to support researchers in deciding when to use VR for in situ authentication research

Augmenting TV Viewing using Acoustically Transparent Auditory Headsets

This paper explores how acoustically transparent auditory headsets can improve TV viewing by intermixing headset and TV audio, facilitating personal, private auditory enhancements and augmentations of TV content whilst minimizing occlusion of the sounds of reality. We evaluate the impact of synchronously mirroring select audio channels from the 5.1 mix (dialogue, environmental sounds, and the full mix), and selectively augmenting TV viewing with additional speech (e.g. Audio Description, Directors Commentary, and Alternate Language). For TV content, auditory headsets enable better spatialization and more immersive, enjoyable viewing; the intermixing of TV and headset audio creates unique listening experiences; and private augmentations offer new ways to (re)watch content with others. Finally, we reflect on how these headsets might facilitate more immersive augmented TV viewing experiences within reach of consumers

Virtual Reality Observations: Using Virtual Reality to Augment Lab-Based Shoulder Surfing Research

Given the difficulties of studying the shoulder surfing resistance of authentication systems in a live setting, researchers often ask study participants to shoulder surf authentications by watching two-dimensional (2D) video recordings of a user authenticating. How-ever, these video recordings do not provide participants with a realistic shoulder surfing experience, creating uncertainty in the value and validity of lab-based shoulder surfing experiments. In this work, we exploit the unique characteristics of virtual reality (VR) and study the use of non-immersive/immersive VR recordings for shoulder surfing research. We conducted a user study (N=18) to explore the strengths and weaknesses of such a VR-based shoulder surfing research approach. Our results suggest that immersive VR observations result in a more realistic shoulder surfing experience, in a significantly higher sense of being part of the authentication environment, in a greater feeling of spatial presence, and in a higher level of involvement than 2D video observations without impacting participants’ observation performance. This suggests that studying shoulder surfing in VR is advantageous in many ways compared to currently used approaches, e.g., participants can freely choose their observation angle rather than being limited to a fixed observation angle as done in current methods. We discuss the strengths and weaknesses of using VR for shoulder surfing research and conclude with four recommendations to help researchers decide when (and when not) to employ VR for shoulder surfing research in the authentication research domain

The complex interplay between tidal inertial waves and zonal flows in differentially rotating stellar and planetary convective regions:I. Free waves

Quantifying tidal interactions in close-in two-body systems is of prime interest since they have a crucial impact on the architecture and on the rotational history of the bodies. Various studies have shown that the dissipation of tides in either body is very sensitive to its structure and to its dynamics, like differential rotation which exists in the outer convective enveloppe of solar-like stars and giant gaseous planets. In particular, tidal waves may strongly interact with zonal flows at the so-called corotation resonances, where the wave's Doppler-shifted frequency cancels out. We aim to provide a deep physical understanding of the dynamics of tidal inertial waves at corotation resonances, in the presence of differential rotation profiles typical of low-mass stars and giant planets. By developping an inclined shearing box, we investigate the propagation and the transmission of free inertial waves at corotation, and more generally at critical levels, which are singularities in the governing wave differential equation. Through the construction of an invariant called the wave action flux, we identify different regimes of wave transmission at critical levels, which are confirmed with a one-dimensional three-layer numerical model. We find that inertial waves can be either fully transmitted, strongly damped, or even amplified after crossing a critical level. The occurrence of these regimes depends on the assumed profile of differential rotation, on the nature as well as the latitude of the critical level, and on wave parameters such as the inertial frequency and the longitudinal and vertical wavenumbers. Waves can thus either deposit their action flux to the fluid when damped at critical levels, or they can extract action flux to the fluid when amplified at critical levels. Both situations could lead to significant angular momentum exchange between the tidally interacting bodies.Comment: 25 pages, 12 figures, 4 tables, accepted for publication in Astronomy & Astrophysic

Can Privacy-Aware Lifelogs Alter Our Memories?

The abundance of automatically-triggered lifelogging cameras is a privacy threat to bystanders. Countering this by deleting photos limits relevant memory cues and the informative content of lifelogs. An alternative is to obfuscate bystanders, but it is not clear how this impacts the lifelogger's recall of memories. We report on a study in which we compare viewing 1) unaltered photos, 2) photos with blurred people, and 3) a subset of the photos after deleting private ones, on memory recall. Findings show that obfuscated content helps users recall a lot of content, but it also results in recalling less accurate details, which can sometimes mislead the user. Our work informs the design of privacy-aware lifelogging systems that maximizes recall and steers discussion about ubiquitous technologies that could alter human memories

GazeWheels: Comparing Dwell-time Feedback and Methods for Gaze Input

We present an evaluation and comparison of GazeWheels: techniques for dwell time gaze input and feedback. In GazeWheel, visual feedback is shown to the user in the form of a wheel that is filled. When completely filled, a selection is made where the user is gazing. We compare three methods for responding to the user when gazing away from the target: Resetting GazeWheel, Pause-and-Resume GazeWheel, and Infinite GazeWheel. We also compare the position of the GazeWheel; Co-located Feedback: shown on the target being gazed at, and Remote Feedback: shown at the top of the interface. To this end, we report on results of a user study (N=19) that investigates the benefits and drawbacks of each method at different dwell times: 500ms, 800ms, and 1000ms. Results show that Infinite GazeWheel and Pause-and-Resume GazeWheel are more error prone but significantly faster than Resetting GazeWheel when using 800-1000 ms dwell time, even when including the time for correcting errors

GazeWheels: recommendations for using wheel widgets for feedback during dwell-time gaze input

We present GazeWheels: a series of visual feedback methods for dwell-based gaze input in the form of a wheel that is filled gradually until target selection. We evaluate three variations: Resetting, Pause & Resume and Infinite GazeWheel, and study how dwell duration and visual feedback position (co-located vs remote) impact performance. Findings from a user study (N = 19) show that Infinite and Pause & Resume GazeWheels are error prone but significantly faster than Resetting GazeWheel even when including error correction time. We conclude with five design recommendations