Improved bounds on the multicolor Ramsey numbers of paths and even cycles

We study the multicolor Ramsey numbers for paths and even cycles, $R_k(P_n)$ and $R_k(C_n)$, which are the smallest integers $N$ such that every coloring of the complete graph $K_N$ has a monochromatic copy of $P_n$ or $C_n$ respectively. For a long time, $R_k(P_n)$ has only been known to lie between $(k-1+o(1))n$ and $(k + o(1))n$. A recent breakthrough by S\'ark\"ozy and later improvement by Davies, Jenssen and Roberts give an upper bound of $(k - \frac{1}{4} + o(1))n$. We improve the upper bound to $(k - \frac{1}{2}+ o(1))n$. Our approach uses structural insights in connected graphs without a large matching. These insights may be of independent interest

Enhancing interaction in mixed reality

With continuous technological innovation, we observe mixed reality emerging from research labs into the mainstream. The arrival of capable mixed reality devices transforms how we are entertained, consume information, and interact with computing systems, with the most recent being able to present synthesized stimuli to any of the human senses and substantially blur the boundaries between the real and virtual worlds. In order to build expressive and practical mixed reality experiences, designers, developers, and stakeholders need to understand and meet its upcoming challenges. This research contributes a novel taxonomy for categorizing mixed reality experiences and guidelines for designing mixed reality experiences. We present the results of seven studies examining the challenges and opportunities of mixed reality experiences, the impact of modalities and interaction techniques on the user experience, and how to enhance the experiences. We begin with a study determining user attitudes towards mixed reality in domestic and educational environments, followed by six research probes that each investigate an aspect of reality or virtuality. In the first, a levitating steerable projector enables us to investigate how the real world can be enhanced without instrumenting the user. We show that the presentation of in-situ instructions for navigational tasks leads to a significantly higher ability to observe and recall real-world landmarks. With the second probe, we enhance the perception of reality by superimposing information usually not visible to the human eye. In amplifying the human vision, we enable users to perceive thermal radiation visually. Further, we examine the effect of substituting physical components with non-functional tangible proxies or entirely virtual representations. With the third research probe, we explore how to enhance virtuality to enable a user to input text on a physical keyboard while being immersed in the virtual world. Our prototype tracked the user’s hands and keyboard to enable generic text input. Our analysis of text entry performance showed the importance and effect of different hand representations. We then investigate how to touch virtuality by simulating generic haptic feedback for virtual reality and show how tactile feedback through quadcopters can significantly increase the sense of presence. Our final research probe investigates the usability and input space of smartphones within mixed reality environments, pairing the user’s smartphone as an input device with a secondary physical screen. Based on our learnings from these individual research probes, we developed a novel taxonomy for categorizing mixed reality experiences and guidelines for designing mixed reality experiences. The taxonomy is based on the human sensory system and human capabilities of articulation. We showcased its versatility and set our research probes into perspective by organizing them inside the taxonomic space. The design guidelines are divided into user-centered and technology-centered. It is our hope that these will contribute to the bright future of mixed reality systems while emphasizing the new underlining interaction paradigm.Mixed Reality (vermischte Realitäten) gehen aufgrund kontinuierlicher technologischer Innovationen langsam von der reinen Forschung in den Massenmarkt über. Mit der Einführung von leistungsfähigen Mixed-Reality-Geräten verändert sich die Art und Weise, wie wir Unterhaltungsmedien und Informationen konsumieren und wie wir mit Computersystemen interagieren. Verschiedene existierende Geräte sind in der Lage, jeden der menschlichen Sinne mit synthetischen Reizen zu stimulieren. Hierdurch verschwimmt zunehmend die Grenze zwischen der realen und der virtuellen Welt. Um eindrucksstarke und praktische Mixed-Reality-Erfahrungen zu kreieren, müssen Designer und Entwicklerinnen die künftigen Herausforderungen und neuen Möglichkeiten verstehen. In dieser Dissertation präsentieren wir eine neue Taxonomie zur Kategorisierung von Mixed-Reality-Erfahrungen sowie Richtlinien für die Gestaltung von solchen. Wir stellen die Ergebnisse von sieben Studien vor, in denen die Herausforderungen und Chancen von Mixed-Reality-Erfahrungen, die Auswirkungen von Modalitäten und Interaktionstechniken auf die Benutzererfahrung und die Möglichkeiten zur Verbesserung dieser Erfahrungen untersucht werden. Wir beginnen mit einer Studie, in der die Haltung der nutzenden Person gegenüber Mixed Reality in häuslichen und Bildungsumgebungen analysiert wird. In sechs weiteren Fallstudien wird jeweils ein Aspekt der Realität oder Virtualität untersucht. In der ersten Fallstudie wird mithilfe eines schwebenden und steuerbaren Projektors untersucht, wie die Wahrnehmung der realen Welt erweitert werden kann, ohne dabei die Person mit Technologie auszustatten. Wir zeigen, dass die Darstellung von in-situ-Anweisungen für Navigationsaufgaben zu einer deutlich höheren Fähigkeit führt, Sehenswürdigkeiten der realen Welt zu beobachten und wiederzufinden. In der zweiten Fallstudie erweitern wir die Wahrnehmung der Realität durch Überlagerung von Echtzeitinformationen, die für das menschliche Auge normalerweise unsichtbar sind. Durch die Erweiterung des menschlichen Sehvermögens ermöglichen wir den Anwender:innen, Wärmestrahlung visuell wahrzunehmen. Darüber hinaus untersuchen wir, wie sich das Ersetzen von physischen Komponenten durch nicht funktionale, aber greifbare Replikate oder durch die vollständig virtuelle Darstellung auswirkt. In der dritten Fallstudie untersuchen wir, wie virtuelle Realitäten verbessert werden können, damit eine Person, die in der virtuellen Welt verweilt, Text auf einer physischen Tastatur eingeben kann. Unser Versuchsdemonstrator detektiert die Hände und die Tastatur, zeigt diese in der vermischen Realität an und ermöglicht somit die verbesserte Texteingaben. Unsere Analyse der Texteingabequalität zeigte die Wichtigkeit und Wirkung verschiedener Handdarstellungen. Anschließend untersuchen wir, wie man Virtualität berühren kann, indem wir generisches haptisches Feedback für virtuelle Realitäten simulieren. Wir zeigen, wie Quadrokopter taktiles Feedback ermöglichen und dadurch das Präsenzgefühl deutlich steigern können. Unsere letzte Fallstudie untersucht die Benutzerfreundlichkeit und den Eingaberaum von Smartphones in Mixed-Reality-Umgebungen. Hierbei wird das Smartphone der Person als Eingabegerät mit einem sekundären physischen Bildschirm verbunden, um die Ein- und Ausgabemodalitäten zu erweitern. Basierend auf unseren Erkenntnissen aus den einzelnen Fallstudien haben wir eine neuartige Taxonomie zur Kategorisierung von Mixed-Reality-Erfahrungen sowie Richtlinien für die Gestaltung von solchen entwickelt. Die Taxonomie basiert auf dem menschlichen Sinnessystem und den Artikulationsfähigkeiten. Wir stellen die vielseitige Verwendbarkeit vor und setzen unsere Fallstudien in Kontext, indem wir sie innerhalb des taxonomischen Raums einordnen. Die Gestaltungsrichtlinien sind in nutzerzentrierte und technologiezentrierte Richtlinien unterteilt. Es ist unsere Anliegen, dass diese Gestaltungsrichtlinien zu einer erfolgreichen Zukunft von Mixed-Reality-Systemen beitragen und gleichzeitig die neuen Interaktionsparadigmen hervorheben

Towards Universal Interaction for Extended Reality

Extended Reality (XR) is a rapidly growing field offering unique immersive experiences, social networking, learning, and collaboration opportunities. The continuous advancements in XR technology and industry efforts are gradually moving this technology toward end consumers. However, a universal one-size-fits-all solution for seamless XR interaction still needs to be discovered. Currently, we face a diverse landscape of interaction modalities that depend on the environment, user preferences, task, and device capabilities. Commercially available input methods like handheld controllers, hand gestures, voice commands, and combinations of those need universal flexibility and expressiveness. Additionally, hybrid user interfaces, such as smartwatches and smartphones as ubiquitous input and output devices, expand this interaction design space. In this position paper, we discuss the idea of a universal interaction concept for XR. We present challenges and opportunities for implementing hybrid user interfaces, emphasizing Environment, Task, and User. We explore the potential to enhance user experiences, interaction capabilities, and the development of seamless and efficient XR interaction methods. We examine challenges and aim to stimulate a discussion on the design of generic, universal interfaces for XR

Drone-based Privacy Interfaces: Opportunities and Challenges

ABSTRACT Providing users with awareness and control about privacysensitive information flows is a major challenge in Internet of Things scenarios, because of constrained input and output capabilities of the involved sensors and devices. We propose the use of autonomous personal drones, specifically nanocopters, as device-independent drone-based privacy interfaces. Nanocopters have the potential to indicate privacy risks, visualize information flows, and provide tangible privacy controls within a smart environment without being tethered to specific IoT devices. We provide an overview of recent advancements in human-drone interaction and describe our vision of leveraging personal drones as privacy indicators and controls, including a discussion of opportunities and associated challenges

Mid-Air gestures for window management on large displays

We can observe a continuous trend for using larger screens with higher resolutions and greater pixel density. With advances in hard- and software technology, wall-sized displays for daily office work are already on the horizon. We assume that there will be no hard paradigm change in interaction techniques in the near future. Therefore, new concepts for wall-sized displays will be included in existing products. Designing interaction concepts for wall-sized displays in an office environment is a challenging task. Most crucial is designing appropriate input techniques. Moving the mouse pointer from one corner to another over a longer distance is cumbersome. However, pointing with a mouse is precise and common-place. We propose using mid-air gestures to support input with mouse and keyboard on large displays. In particular, we designed a gesture set for manipulating regular windows

Understanding Shoulder Surfer Behavior and Attack Patterns Using Virtual Reality

In this work, we explore attacker behavior during shoulder surfing. As such behavior is often opportunistic and difficult to observe in real world settings, we leverage the capabilities of virtual reality (VR). We recruited 24 participants and observed their behavior in two virtual waiting scenarios: at a bus stop and in an open office space. In both scenarios, participants shoulder surfed private screens displaying different types of content. From the results we derive an understanding of factors influencing shoulder surfing behavior, reveal common attack patterns, and sketch a behavioral shoulder surfing model. Our work suggests directions for future research on shoulder surfing and can serve as a basis for creating novel approaches to mitigate shoulder surfing

Kr-factors in graphs with low independence number

A classical result by Hajnal and Szemerédi from 1970 determines the minimal degree conditions necessary to guarantee for a graph to contain a Kr-factor. Namely, any graph on n vertices, with minimum degree δ(G) ≥ (1 − 1/r) n and r dividing n has a Kr-factor. This result is tight but the extremal examples are unique in that they all have a large independent set which is the bottleneck. Nenadov and Pehova showed that by requiring a sub-linear independence number the minimum degree condition in the Hajnal-Szemerédi theorem can be improved. We show that, with the same minimum degree and sub-linear independence number, we can find a clique-factor with double the clique size. More formally, we show for every r ∈ N and constant μ > 0 there is a positive constant γ such that every graph G on n vertices with δ(G) ≥ (1 − 2/r + μ) n and α(G) < γn has a Kr-factor. We also give examples showing the minimum degree condition is asymptotically best possible. © 2020 Elsevier Inc.ISSN:0095-895