Streaming multimedia quality is impacted by two main factors: capacity constraint and packet loss. To match the capacity constraint while preserving real-time playout, media scaling can be used to discard the encoded multimedia content that has the least impact on perceived video quality. To limit the impact of lost packets, repair techniques, e.g. forward error correction (FEC), can be used to repair frames damaged by packet loss. However, adding data to facilitate repair requires further reduction of the original multimedia data, making the decision of how much repair data to use of critical importance. Assuming a limited network capacity and the availability of an estimate of the current packet loss rate along a flow path, selecting the best distribution of FEC packets for video frames with inherent interframe encoding dependencies can be cast as a constraint optimization problem that attempts to optimize the quality of the video stream. This thesis presents an Adjusting Repair and Media scaling with Operations Research (ARMOR) system. An analytical model is derived for streaming video with FEC and media scaling. Given parameters to represent network loss as well as video frame types and sizes, if the number of FEC packets per video frame type and media scaling pattern is specified, the model can estimate the video quality at the receiver side. The model is then used in an operations research algorithm to adjust the FEC strength and media scaling level to yield the best quality under the capacity constraint. Four different combinations of FEC type and media scaling method are studied: Media Independent FEC with Temporal Scaling (MITS), Media Independent FEC with Quality Scaling (MIQS), Media Independent FEC with Temporal and Quality Scaling (MITQS), and Media Dependent FEC with Quality Scaling (MDQS). The analytical experiments show: 1) adjusting FEC always achieves a higher video quality than streaming video without FEC or with a fixed amount of FEC; 2) Quality Scaling usually works better than Temporal Scaling; and 3) Media Dependent FEC (MDFEC) is typically less effective than Media Independent FEC (MIFEC). A user study is presented with results from 74 participants analysis shows that the ARMOR model can accurately estimate users¡¯perceptual quality. Well-designed simulations and a realistic system implementation suggests the ARMOR system can practically improve the quality of streaming video.

Users share private information on the web through a variety of applications, such as email, instant messaging, social media, and document sharing. Unfortunately, recent revelations have shown that not only is users' data at risk from hackers and malicious insiders, but also from government surveillance. This state of affairs motivates the need for users to be able to encrypt their online data.In this dissertation, we explore how to help users encrypt their online data, with a special focus on securing email. First, we explore the design principles that are necessary to create usable, secure email. As part of this exploration, we conduct eight usability studies of eleven different secure email tools including a total of 347 participants. Second, we develop a novel, paired-participant methodology that allows us to test whether a given secure email system can be adopted in a grassroots fashion. Third, we apply our discovered design principles to PGP-based secure email, and demonstrate that these principles are sufficient to create the first PGP-based system that is usable by novices. We have also begun applying the lessons learned from our secure email research more generally to content-based encryption on the web. As part of this effort, we develop MessageGuard, a platform for accelerating research into usable, content-based encryption. Using MessageGuard, we build and evaluate Private Facebook Chat (PFC), a secure instant messaging system that integrates with Facebook Chat. Results from our usability analysis of PFC provided initial evidence that our design principles are also important components to usable, content-based encryption on the Web.

<p>This report is a part of a diploma work, conducted as a part of a Master of Science degree. The diploma work consists of a preliminary study, two case studies, a user study, a paper and this report. It was created at the Linköping University for the department of Science and Technology, in cooperation with Unilever Research in the UK, and partly with the EC founded project, Smartdoc IST-2000-28137. </p><p>Hand-held, mobile devices like Personal Digital Assistances (PDAs) are becoming increasingly popular in today’s wireless world. While trying to pack all the possible information into a small window, a nightmarish scenario is created for the interface designer to deal with. The goal for this project was to investigate different Visual User Interfaces (VUIs)on PDAs, and how to apply desktop interaction techniques to PDAs. </p><p>A VUI model based on Zooming User Interface (ZUI) techniques, to adapt two complete different visualisation application areas; on-line brand-based shopping and flood warning system for PDAs, is presented. The on-line brand- based shopping was evaluated in a benchmark usability study comparing it to traditional PC based on-line shopping.</p>

Every year 9000 children are estimated to die in traffic accidents in China. Fast motorization of the country in combination with low usage of child restraint system’s (CRS’s), are the two contributing factors to this alarming number. The vision of this thesis is to increase the usage of CRS’s in China, by understanding why the users are using the CRS and why the non-users are not using. The behavioural methodology Switch was used to investigate what positive behaviours could be copied and implemented in a larger scale to increase the usage. Interviews were performed with 30 users and 30 non-users in tier 1, tier 2, and tier 3 cities on the east coast of China. The main findings from the interviews showed that the reasons for not using was that the parents found the CRS complicated to install and to use, that it took too much space, that they did not know the benefits with a CRS and found it unnecessary and that they could not convince their children to sit in the CRS. Surprisingly most non-users already owned a CRS, but stopped using it. The users were using because they had experienced the CRS from abroad or got knowledge from other sources such as media or friends. Some parents were using because of a practicality issues such as the trouble to hold a heavy 3-year old child during a long trip. The behaviours chosen to represent the users for further work were learning from others, selection support, how to install, how to persist, and how to pay the knowledge of the CRS forward. The behaviour of the users was copied and implemented in a strategy consisting of the five parts above. The strategy is an interactive webpage with a close linkage to social networks to encourage sharing, and with a supporting poster- and bumper sticker campaign for spreading. The final product of the thesis work is a campaign including a fully working prototype of the webpage, which will be handed over to Volvo Cars for verification internally to make sure that the concept supports the different parts in a suitable and correct way before a public implementation. Material for poster and bumper stickers is also a part of the final delivery.

En relativamente poco tiempo el mundo lexicográfico ha experimentado cambios radicales respecto a la producción, a la disponibilidad y al uso de los distintos recursos lexicográficos. Han surgido nuevos medios que, aunque no ti enen la búsqueda lexicográfica como primera función, bien pueden servir pa ra este objetivo: buscadores de internet, corpus de textos paralelos, foros electrónicos, medios social es, traductores automáticos, etc. En este contexto se plantean preguntas como qué papel desempeñan los distintos recursos lexicográficos en una búsqueda lexicográfica concreta, cuál es la combinación de ellos y cuál su cronología de uso. Este artículo profun diza en estas preguntas a base de un análisis del comportamiento lexicográfico en cinco leng uas extranjeras diferentes de 62 estudiantes de Administración de Empresas y, de esta manera, determina distintas estrategias de búsqueda.

This report is a part of a diploma work, conducted as a part of a Master of Science degree. The diploma work consists of a preliminary study, two case studies, a user study, a paper and this report. It was created at the Linköping University for the department of Science and Technology, in cooperation with Unilever Research in the UK, and partly with the EC founded project, Smartdoc IST-2000-28137. Hand-held, mobile devices like Personal Digital Assistances (PDAs) are becoming increasingly popular in today’s wireless world. While trying to pack all the possible information into a small window, a nightmarish scenario is created for the interface designer to deal with. The goal for this project was to investigate different Visual User Interfaces (VUIs)on PDAs, and how to apply desktop interaction techniques to PDAs. A VUI model based on Zooming User Interface (ZUI) techniques, to adapt two complete different visualisation application areas; on-line brand-based shopping and flood warning system for PDAs, is presented. The on-line brand- based shopping was evaluated in a benchmark usability study comparing it to traditional PC based on-line shopping.

Participants from recent secure email user studies have expressed a need to use secure email tools only a few times a year. At the same time, Internet users are expressing concerns over the permanence of personal information on the Internet. Support for short-lived keys has the potential to address both of these problems. However, the short-lived keys usability and security space is underdeveloped and unexplored. In this thesis, we present an exploration of the short-lived keys usability and security design space. We implement both a short-lived keys and a long-term keys secure email prototype. With these two prototypes, we conduct a within-subjects user study. Results from our study show that participants believe the short-lived keys prototype is more secure and more trusted. Participants also provide feedback on what they want in a system supporting short-lived keys. They also discuss how concerned they are about the permanence of their information on the Internet and on their devices.

Sentiment visualization techniques are information visualization approaches that focus on representing the results of sentiment analysis and opinion mining methods. Sentiment visualization techniques have been becoming more and more popular in the past few years, as demonstrated by recent surveys. Many techniques exist, and a lot of researchers and practitioners design their own. But the question of usability of these various techniques still remains generally unsolved, as the existing research typically addresses individual design alternatives for a particular technique implementation only. Multiple surveys and evaluations exist that argue for the importance of investigating the usability of such techniques further. This work focuses on evaluating the effectiveness, and efficiency of common visual representations for low-level visualization tasks in the context of sentiment visualization. It shows what previous work has already been done by other researchers and discusses the current state of the art. It further describes a task-based user study for various tasks, carried out as an online survey and taking the task completion time and error rate into account for most questions. This study is used for evaluating sentiment visualization techniques on their usability with regard to several sentiment and emotion datasets. This study shows that each visual representation and visual variable has its own weaknesses and strengths with respect to different tasks, which can be used as guidelines for future work in this area.

Ergonomie ist seit Jahren ein wichtiges Thema in allen Bereichen des Lebens. Unter anderem beinhaltet dies auch die Anpassung der Arbeit an den Arbeiter, um so kurz- und langfristige gesundheitliche Probleme zu minimieren. Ergonomen begutachten in diesem Kontext zum Beispiel den Arbeitsplatz eines Werkers. Sie beobachten ihn bei seiner Tätigkeit, führen Messungen durch und untersuchen die erlangten Daten. Nach der Analyse präsentieren sie ihre Erkenntnisse Dritten (bspw. im Rahmen eines Workshops), dem Management und den Werkern. Insbesondere wenn es um die Auswertung über einen längeren Zeitraum geht (eine ganze Schicht oder mehrere Arbeitszyklen) sind gute Visualisierungen Mangelware und beschränken sich häufig nur auf einfache Linien- oder Balkendiagramme. Um den Ergonomen ihre Tätigkeit zu erleichtern, wurde ein Programm entwickelt, dass die ergonomischen Probleme in einer einfachen Weise als Gesamtüberblick dargestellt. Es ist hierbei möglich von der groben Übersicht aller kritischen Situationen bis hin zu einer detaillierten Ansicht eines Einzelfalls zu navigieren. Ungünstige Posen werden als Piktogramme in Form digitaler Menschmodelle repräsentiert und ermöglichen somit eine intuitive Darstellung. Die Visualisierung berücksichtigt mehrere Methoden aus dem Umfeld der Ergonomie. Eine Methode ist zum Beispiel RULA (Rapid Upper Limb Assessment). Hier wird eine statische Pose des Werkers betrachtet, sozusagen eine Momentaufnahme bei der Ausübung seiner Arbeit. Es basiert auf der Betrachtung der Gelenkwinkel und berücksichtigt zusätzlich Gewichte und Kräfte, die der Werker zu tragen hat beziehungsweise die er aufbringen muss. Darüber hinaus werden auch Anzeichen grenzwertiger Arbeitsumweltfaktoren dargestellt. Die finale interaktive Visualisierung wurde während des gesamten Entwicklungsprozesses in unterschiedlichen Studien evaluiert. Dies beinhaltet unter anderem die Erfassung der Benutzeranforderungen durch Expertenbefragungen, iteratives Prototyping und einer abschließenden Benutzbarkeitsstudie. / Ergonomics deals with the analysis and design of work processes. To identify ergonomically critical situations, appropriate evaluation options have to be developed to enable an efficient analysis process. Nowadays, such analyses are typically carried out with the help of digital models of the surrounding area and virtual humans. These produce a multitude of geo-referenced and time-oriented data. A design study was conducted on how to visualize this data to support the ergonomically analysis process optimally. We propose a novel interactive visualization which provides the user an overview of ergonomically critical situations and their causes. Simultaneously, the user obtains the main stress factors in a compressed form by a glyph-based visual design. During the implementation of the prototype, usability and ergonomics experts were consulted and their suggestions were included in the development of the system. Final expert interviews and a usability study depict the utility of the proposed visualization tool.

The threat of government and corporate surveillance around the world, as well as the publicity surrounding major cybersecurity attacks, have increased interest in secure and private end-to-end communications. In response to this demand, numerous secure messaging applications have been developed in recent years. These applications have been welcomed and publically used not just by political activists and journalists but by everyday users as well. Most of these popular secure messaging applications are usable because they hide many of the details of how encryption is provided. The strength of the security properties of these applications relies on the authentication ceremony, wherein users validate the keys being used for encryption that is exchanged through the service providers. The validation process typically involves verifying the fingerprints of encryption keys to protect the communication from being intercepted.In this dissertation, we explore how to help users enhance the privacy of their communica- tions, with a particular focus on secure messaging applications. First, we explore whether secure messaging applications are meeting the security and privacy needs of their users, especially in countries that practice censorship and restrict civil liberties, including blocking access to social media and communication applications. Second, we studied existing popular secure messaging applications to explore how users interact with these applications and how well they are using the authentication ceremony during lab studies. Third, we applied design principles to improve the interfaces for the authentication ceremony, and also to help users find and perform the authentication ceremony faster. Forth, we applied the lessons from our interviews with participants in our user studies to help users comprehend the importance of authentication. As part of the effort, we developed an authentication ceremony using social media accounts to map key fingerprints to social features, pushing the ceremony to a more natural domain for users. We modified the Signal secure messaging application to include this social authentication ceremony and used a user study to compare this method to other common methods. We found that social authentication has some promising features, but that social media companies are too distrusted by users. Based on our results, we make several recommendations to improve the use of security and privacy features in secure messaging applications and outline areas for future work.