USABILITY ENHANCEMENT FOR 3D CAPTCHA MODEL : SUBJECTIVE EVALUATION OF DESIGN PARAMETERS ON KLM EXECUTION TIME

Captcha tests have been widely used to deter the misuse of services on the Internet. The most commonly used Captcha schemes are text-based. However, many Captcha schemes suffer from inadequacies in terms of aspects of security and usability, and indeed the balance between them. That is, many text-based Captcha schemes have been broken, which has motivated Captcha developers to use increasingly complex approaches to enhance the security of their new designs. However, this difficulty has reflected negatively on the usability of the Captcha scheme, as it was also hard for humans to solve the challenges. Consequently, such Captcha tests have become a key source of user frustration and abandonment of the use of the services that contain them. In addition, text-based Captcha tests, in their current forms, are unsuitable for use with touch screen devices. Although various alternatives have been recently proposed, they have either been broken, have not been widely deployed, or have not been well-examined in terms of security aspects. Accordingly, this thesis is mainly dedicated to balancing the security and usability of Captcha across different devices. For this, we first examined Captcha security from the perspective of security APIs, which to date has not been investigated. Interesting findings were obtained from this investigation, as well as a robust architecture being delineated for the design of a new Captcha Web service. An extensive analysis of Chinese Captcha schemes was also conducted to investigate the unproven hardness assumption with respect to the security provided by the recognition task of a large character set. Our findings showed that computers can recognize a distorted Chinese character perfectly well, which means that most existing Chinese Captcha schemes are insecure, and concluded also that the segmentation resistance principle is applicable to Chinese Captcha schemes, as in their Roman counterparts. This motivated us to build a new, more secure and usable Captcha technology that can be more practical and universally applicable across different devices. The new scheme is based on a new underlying AI-hard problem that greatly exacerbates the segmentation problem, resulting in improved security and robustness. Our usability studies show that the proposed scheme is easy for an average human to solve, as well as properly fitting the input and output capabilities of both ordinary computers and mobile devices. A RESTful Web service has been developed and deployed for the proposed approach.

Revealing unawareness in usability related decision-making

CAPTCHAs are employed on web systems for strengthen web security to protect from internet bots, fraudulent registration, spammers. So CAPTCHA is designed in such a way the patterns display on CAPTCHA feature that human can easily pass but hardship for automated approaches. Usability and security are two rudimental issues for CAPTCHA design and implementation. In Math calculus CAPTCHA test that be inherent with trigonometric and differential functions. Due to complexity of equations, user cannot easily solve expressions that possess poor usability of CAPTCHA. In this paper, a novel CAPTCHA design approach using Boolean algebra is presented, to improve usability and security as contrast to Math calculus CAPTCHA. In this approach, we use a logic gates. Each gate executes a Boolean expression as represented by a shape indicating operation. The shapes related to the logic gates like conjunction, disjunction and complement. To prove human, user has to identify shape of given logic gates and choose correct option to pass CAPTCHA test. From security issue, Boolean algebra CAPTCHA is non OCR based that provide no development in advance technologies like AI and automated software.

CAPTCHA is an acronym of Completely Automated Turing Test to Tell Computers and Humans Apart which is also referred to as HIP (Human Interaction Proof). It is a computer program that generates challenges or tests that only humans can solve and the machines or automated software cannot solve. CAPTCHAs are used in various Web Applications to restrict bots from doing unwanted activities in areas of protected content and unwanted submissions of web forms. In this paper a Model for Multilingual CAPTCHA challenges which can be more accessible and easy to use for non-English users is proposed. Rendering CAPTCHA tests in regional languages can improve usability and accessibility for non-native speakers of English language. The suggested model can be implemented in all major web programming languages such as PHP, .NET, J2EE, Perl, Ruby etc. I. INTRODUCTION The websites and web applications using CAPTCHA may be usually targeted for a large audience nationally or globally and not limited to a particular location or city. The websites and web applications are therefore used by people with knowledge of different languages and scripts including but not limited to English. Modern websites and web applications and designed in a way that the users can use them in their own languages. In India, there are 22 officially recognized languages and 12 different scripts. Majority of people in India have knowledge of and use their regional languages are not well versed in English. More and more websites and web applications for India are providing content and user interface in the regional languages of India. Many of these websites and web applications contain resources and areas protected by CAPTCHAs. The Government of India has also issued several guidelines for using Hindi and other regional languages in the websites of Government Departments. More and more Govt. Departmental websites are providing content in regional languages. The CAPTCHAs used in these Websites and web applications are English only even if the users choose to use them in a non-English regional language. This leads to very poor accessibility and usability of these websites.

Automated Turing Tests (ATTs), also known as human-in-the-loop techniques, were recently employed in a login protocol by Pinkas and Sander (2002) to protect against online password-guessing attacks. We present modifications providing a new history-based login protocol with ATTs, which uses failed-login counts. Analysis indicates that the new protocol offers opportunities for improved security and user friendliness (fewer ATTs to legitimate users) and greater flexibility (e.g., allowing protocol parameter customization for particular situations and users). We also note that the Pinkas--Sander and other protocols involving ATTs are susceptible to minor variations of well-known middle-person attacks. We discuss complementary techniques to address such attacks, and to augment the security of the original protocol.

In the era of the fast development of the internet, e-learning has become one of the most important trends. Because of the development of the internet, a revolution of the ways to learn has been happened. Learners can do distance learning through the internet, learning in school is no longer the only way for the learners. Learners can do learning without the limit of the time and place. With e-learning becomes more popular, lots of web-based instruction platforms have been developed. In this study, the researcher designed two methods to do usability testing for the Web 2.0 instruction platform. These usability testing methods are based on the users of web-based instruction platforms. These methods are using for doing web-based instruction platforms usability test, and we can find the problems out of the platforms through the test. This is a Design-based research. The researcher constructed the methodology of usability testing for Web 2.0 instruction platform through the process includes Analysis, Design, Development, Implementation, and Evaluation. The researcher did a usability testing with Moodle web-based instruction platform of a University in Taipei, and got lots of feedback and suggestions from the users of the platform. These feedback and suggestions will be the ways of modifying Moodle web-based instruction platform, and to make platform more fit for the users. At last, the researcher modified the methods which are constructed for doing the usability testing of Web 2.0 instruction platforms with the feedback of the testers, and developed a handbook for users who’s planning to do instruction platform usability testing. The result of this study: 1.The researcher constructed two methods for doing instruction platform usability testing include usability interview and usability questionnaire survey. These two methods are constructed based on the feedback and suggestion with the experts of usability testing, instruction platform, educational technology and interface design. The result of the usability testing with Moodle web-based instruction platform shows that with these two methods, users can do instruction platform usability testing effectively and rapidly. 2.The handbook which developed in this study is designed based on a specific laboratory. The usability testing process divides into five stages which are: prepare, plan, execution, analysis and present. The handbook may help users who want to do instruction platform usability testing know the whole usability testing process and details. Suggestions to the future research: The instruction platform usability testing methods which constructed by the researcher in this study have only been used once with a Moodle web-based instruction platform. In the future, if the users are going to use these methods to do usability testing with other platform, you will be necessary to do some modification to make these methods fit with the characteristic of the platform.

Human-Interaction Proof (HIP) systems are widely used to prevent malicious acts of abusers. Legitimate users, however, are not satisfied with their ease of use. The response of Google to the complaints of difficulty in solving audio reCAPTCHAs was to introduce a much simpler version. But now we are back at the position where we have an accessible and usable but insecure solution. In this work, we propose a pure-text HIP system as an attempt to satisfy accessibility, security, usability requirements altogether. We conduct a user study involving 31 blind or partially sighted users which compares the usability of our pure-text HIP system (SMARTCHA) against Google's new audio reCAPTCHA. The results of the user study show that visually impaired users enjoy solving SMARTCHA more and prefer it against audio reCAPTCHA.

Research within the field of human-computer interaction (HCI) and website design aims at improving the users’ overall experience on websites. Knowing users’ expectations has turned out to be one of the important factors to design satisfying and successful websites. These expectations are often translated into design recommendations and summarized in usability guidelines. The aim of the present cumulative dissertation is to contribute with empirical studies to the knowledge on how to improve the overall user experience by exploring users’ expectations and analyzing their behavior on websites. The first set of manuscripts outlines a research project assessing users’ mental representations of different website types. We were interested to see which interface elements users currently expect to be on an online shop, an online newspaper and a company website and where they expect these elements to be located. Results indicate that these mental representations are dynamic and to a certain extent reflect changed in website design. In a second study, we examine which characteristics of a website determine whether an experience is judged as trustful or distrustful. In this exploratory study, we analyzed users’ reports of a previous visit to a website and identified characteristics enhancing trust or causing distrust. Our data suggests, that complex overall designs and aspects of structural design such as usability issues are related to distrust whereas content design aspects such as the display of security signs and personal and social proof are important in enhancing trust. Within the last set of studies, we explore the impact of usability guidelines for web forms. A set of 20 guidelines was applied to web forms, and these forms compared to the original ones. On all three improved registration forms, users were able to perform their task faster, experienced fewer problems when submitting the form and were more satisfied. The open comments further suggested a clear layout and structure of the web form to be important to users. All studies conducted within the present thesis contribute to the existing research in several ways. We collected data on (1) which interface elements users expect to be found on different types of websites and how these elements need to be arranged to meet their expectations, we further (2) investigated which characteristics of websites enhance trust or cause distrust and we (3) determined the impact of guidelines applied to web forms on users’ experience. In a final section of this thesis I discuss the results of the studies, draw conclusions and suggest how our findings can be beneficial to the design of websites and improve the overall user experience.

The current trend in Human-Computer Interaction aims at bridging the gap between the digital and the real world, exploring novel ways to engage users with computational devices. Computers take new forms that are better integrated into our environment and can be embedded in buildings, furniture or clothes. Novel forms of interfaces take advantage of people's intuitive knowledge of everyday objects to offer more direct and natural interactions. Tangible User Interfaces (TUIs) allow users to interact with digital objects through tangible artifacts, building on their rich physical affordances. Paper User Interfaces (PUIs) add digital capabilities to paper documents, synchronizing for instance their content with their digital counterpart. Unique properties of paper are also used to create engaging and intuitive interfaces to computer applications. This dissertation is interested in the complementarity of tangible and paper interfaces in tabletop environments. We introduce the concept of Tangible and Paper Environments (TaPEs) where Interactive Paper Forms (IPFs), a particular type of PUIs based on the paper form metaphor, are used as a complementary interface to a TUI. We evaluate the potential of IPFs to overcome two main shortcomings of TUIs, in terms of scalability and pedagogy. The scalability issue comes from the limited expressiveness of task-specific physical artifacts, which offer rich physical affordances but limit the complexity of applications that can be controlled by a TUI. The pedagogy issue is raised by the lack of consistent evidence regarding the use of physical manipulatives in educational settings, which is one of the main application domain of TUIs. IPFs overcome the scalability issue by offering a set of generic interaction elements that allow TaPEs to cope with applications of any complexity. In a pedagogical setting, IPFs present learners with abstract representation which facilitate understanding by the embodied and concrete representations offered by tangible artifacts. A TaPE, the Tinker Environment, has been developed with two logistics teachers in the context of the Swiss vocational training system. It consists of a warehouse physical small-scale model (TUI) and TinkerSheets, our implementation of IPFs. It aims at helping apprentices understand theoretical concepts presented at schools. We followed a Design-based Research (DBR) approach: ten studies were conducted during the development of the Tinker Environment in authentic classroom settings. Controlled experiments were conducted to address specific questions. v The general research questions concern the respective affordances of paper and tangible components of TaPEs. The analysis is not limited to usability aspects but also considers their impact on group problem-solving activities and their potential in terms of integration of the system in its context of use. A descriptive model is proposed, built around three interaction circles: individual (usability), group (collaboration) and context (integration). Results identify design guidelines that limit the impact of the less direct interaction modality offered by IPFs, allowing TaPEs to overcome the scalability issue while supporting rich interactions. At the group level, observations of groups of apprentices solving problems around the Tinker Environment show that the consistent physical interaction modality offered by TaPEs naturally supports collaborative interactions. Apprentices tend to take implicit roles based on their location around the system. Regarding the context circle, we observed that carefully designed IPFs play the role of bridges between offline and online activities and contribute to a tight integration of the system in a its context (i.e. a classroom). The specific research questions address the potential of the Tinker Environment in this pedagogical context and its appropriation by teachers. The observations conducted with the Tinker Environment show that the warehouse small-scale model reduces the complexity of problems and allows apprentices to engage in meaningful problem-solving activities. Controlled experiments comparing a TUI to a mulitouch interface demonstrate that tangible artifacts lead to a higher learning gain and an increased performance in a problem-solving activity. Collaboration quality and perceived playfulness are also improved. The teacher plays a central role in the use of the environment, guiding apprentices through activities and encouraging reflections during debriefing sessions. The design of IPFs, emphasizing either their interface or document nature, has a strong influence on their ability to support teachers. We finally discuss the two-way adaptation process that took place between teachers and the system during the development of the Tinker Environment.

Visual markers are graphic symbols designed to be easily recognised by machines. They are traditionally used to track goods, but there is increasing interest in their application to mobile human-computer interaction (HCI). By scanning a visual marker through a camera phone, users can retrieve localised information and access mobile services. In particular the dissertation examines the application of visual markers to physical tagging: practices of association of digital information with physical items. One missed opportunity in current visual marker systems is that the markers themselves cannot be visually designed; they are not expressive to humans, and thus fail to convey information before being scanned. To address this limitation, this dissertation introduces the idea of designable markers, visual markers that are both machine-readable and visually communicative to humans, and presents an investigation of the ways in which they can support mobile human-computer interaction. The application of designable visual markers to the creation of mobile interfaces is explored through a variety of methods: through formal usability experiments, through the creation and analysis of example designs, as well as through the qualitative analysis of two field trials. All three approaches were enabled by the engineering and development of d-touch, an actual recognition system that supports designable visual markers and by its integration in a variety of applications and experimental probes. D-touch is based on image topology, and its markers are defined in terms of constraints on the nesting of dark and light regions. The constraints imposed by d-touch are flexible enough to allow novice users to create markers which are visually expressive and at the same time machine readable. A user study demonstrates how such system enables people to design their own functional visual markers, determining their aesthetic qualities and what they visually communicate to others. A desktop application to support users in the creation of valid markers, the d-touch analyser, is presented and its usefulness is demonstrated through the same study. A formal usability experiment comparing five variations of marker-based interfaces on keypad and touch-screen phones shows that all of them allow users to reliably select targets within, on average, less than 4 seconds. Participants of the experiment reported a strong preference for interfaces that involve only marker scanning, compared to those that require a combination of marker scanning and key-presses or touch selections. Example designs of mobile interface generated by the author as well as others are presented to expose how the d-touch recognition system can be integrated in mobile applications. The examples illustrate a variety of ways in which markers can be used to augment printed materials such as cards, books and product packages, adding to them interactive capabilities. The examples show also different approaches to marker design, ranging from simple and recognisable iconic design, to symbols that integrate cues about the interactive functionality, to making them invisible by hiding them in existing graphics. Finally, the dissertation reports and analyses two field trials conducted to study what practices of physical tagging can emerge from, and be supported by, the use of markers. The trials were centred around the use of uWiki, a functional prototype based on d-touch, that allows users to associate digital content to markers printed on physical tags that can be affixed to objects or buildings. Observations show that a variety of practices emerge around the use of this technology, indicating that they provide a rich medium that has potential to attract the interest of real users. Though the results of this work are preliminary, they serve to demonstrate the range of potential for the future of such systems.

Despite the growing attention given to Web usability, little is understood as to what Web design features contribute to Web users' attitude, a major component of the usability of a Web site. This research investigates the effects of interactivity level on Web user's attitude towards commercial Web sites. It extends existing Web interface design and usability literature by empirically examining the critical roles of interactivity. Three Web sites with different levels of interactivity were compared in a controlled laboratory experiment. Three eighteen-person groups completed each treatment. The independent variable is the incremental levels of interactivity. The dependent variables are satisfaction, effectiveness, efficiency, value, and attitude towards the Web site. Results suggest that increased level of interactivity on a Web site have positive effects on user's perceived satisfaction, effectiveness, efficiency, value, and overall attitude towards a Web site. Implications for Web site designers and researchers are discussed.

Usability testing is an important part of health information technology HIT design. However, usability issues will vary by the contexts where a system is used. To date there are few studies that have described contextual factors of usability testing. This paper uses a case study of a surgical information system to develop a model of four contextual categories that impact usability testing. We discuss each of the contexts in detail and then suggest how they can be used to develop a general framework to enable better understanding of the role of context in usability testing and evaluation of HIT.

This thesis proposes a new genre of outdoor games for children, namely Head Up Games. The concept was inspired by the observation that existing pervasive outdoor games for children were mostly played head down, as the predominantly screen-based interaction of existing games required constant attention of the children. First, the vision of Head Up Games is described and illustrated with several design cases (Chapter 2). In contrast to the head down games, Head Up Games aim to encourage and support rich social interaction and physical activity, play behaviors that are similar to play behaviors seen in traditional outdoor games (such as tag and hide-and-seek). The design process of Head Up Games poses several challenges. In User Centered Design it is commonly accepted to start the development of a new product using low-fi mock-ups, e.g., paper prototypes, and evaluate these with end-users. In the case of Head Up Games this proved to be difficult, as the emerging game experience is significantly altered when using paper prototypes. Therefore, a study was carried out that used high-fi prototypes, i.e. working, interactive, prototypes, from a very early stage in the design process (Chapter 3). This way, the effect of interactions on the game experience can be addressed earlier and better in the design process. Furthemore, having access to technology early in the design process, allows designers to better explore the design space. However, designers often do not possess adequate skills to quickly prototype interactive products, particularly products that need to be evaluated in an outdoor context. Such a development is often costly and time-consuming. Therefore, the RaPIDO platform was developed (Chapter 4). The platform not only includes the appropriate hardware for creating outdoor games, but is also bundled with software libraries, to allow designers not specifically trained in software engineering to adopt the platform easily. RaPIDO was evaluated using a case study methodology with two Industrial Design master students. The evaluation not only focused on the usability of the platform, but, more importantly, how the use of the platform affected the design process. The main conclusion of the study was that the designers indeed were able to rapidly create mobile games, and that the hardware offered was suitable for creating outdoor games. Furthermore, issues were identified with regard to writing the game software, e.g., managing the complexity of the software. Finally, for evaluating Head Up Games with children two methods were applied: the Outdoor Play Observation Scheme (OPOS) was used to quantify the intended play behavior. Furthermore, GroupSorter was developed to provide a framework to interview a group of children simultaneously, resulting in qualitative comments. Both OPOS and GroupSorter were applied for evaluating three Head Up Games, which are described in Chapter 5.

Dear SCPE Reader, We present a selection of papers which are extensions of papers presented at the 7-th International Symposium on Parallel and Distributed Computing, 1–5 July 2008, in Krakow, Poland. The motivation for publishing the selection in the SCPE Journal was, on the one hand, to present the flavour of the research reported at the conference and on the other hand to present some of the most relevant topics currently focused on the research on parallel and distributed computing in general. The selection contains only 6 papers out of about 60 presented at the conference, and thus, is far from covering all relevant topics represented at the ISPDC 2008. This is because not all of the invited authors were patient enough to accept a fairly long paper publishing process. Nevertheless, we hope that the presented papers will bring you closer to the research covered by the ISPDC conferences and will encourage you to participate in future ISPDC editions. The first paper ``The Impact of Workload Variability on Load Balancing Algorithms'' is by Marta Beltran and Antonio Guzman from King Juan Carlos University in Spain. It concerns an important topic of load balancing in cluster systems, namely adaptativity of the load balancing algorithms to changes of the workload in the system. Adequate accounting for additional load in the hosting system is of great relevance for correct optimization effects. The paper presents a thorough formal analysis of the workload variability metrics and their influence on the quality of load balancing algorithms. Four basic activities appearing in load balancing algorithms are identified, and based on them some algorithmic solutions are proposed to correctly deal with workload variability in system load balancing. The problem of dynamic load balancing algorithms robustness has been discussed. Two different robustness metrics sensitive to the applied type of opimization: local task-oriented or a global one enable selecting task remote execution or migration as load balancing operations. The proposed approach is illustrated with experiments. The second paper ``Model-Driven Engineering and Formal Validation of High-Performance Embedded Systems'' is by Abdoulaye Gamatie, Eric Rutten, Huafeng Yu, Pierre Boulet, Jean-Luc Dekeyser, from University of Lille and INRIA in France. The paper is concerned with a very advanced methodology of designing correct parallel embedded systems for intensive data-parallel computing. In their previous research, the authors of the paper designed the GASPARD embedded system design framework. It is based on the hardware/software co-design approach through model-driven engineering. The framework is based on an UML-like model specification language in which hardware and software elements are modelled using a component approach with special mechanisms for repetitive structures. This paper tries to combine the modelling framework of GASPARD with the mechanisms of synchronous languages to achieve design verifiability provided for such languages. The paper shows how GASPARD models can be translated into synchronous models based on data flow equations in order to formally check their correctness. The proposed approach is illustrated with an example of a video processing system. The third paper ``Relations Between Several Parallel Computational Models'' is by Stephan Bruda and Yuanqiao Zhang from Bishop’s University in Canada. The paper is concerned with theoretical aspects of shared memory systems described by the parallel random access machine PRAM model and aims in studying performance properties of different types of PRAM systems. The attention is focussed on analysing the computational power of two more sophisticated PRAM models (Combining CRCW and Broadcast Selective Reduction), which include data reduction in case of concurrent writes. The paper shows that these two models have equivalent computational power, which is a new result comparing the existing literature. The performance of both models applied to reconfigurable multiple bus machines was studied as a possible architectural solution for current VLSI processor implementations. It was shown that in such systems under reasonable assumptions concurrent-write does not enhance performance comparing the exclusive-write model. Another result important for the VLSI technology is that the Combining CRCW PRAM model (in which data of concurrent writes are arthmetically or logically combined before write) and the exclusive-write on directed reconfigurable busses perform in equivalent way under strong real-time requirements. The fourth paper ``Experiences with Mesh-Like Computations Using Prediction Binary Trees'' is by Gennaro Cordasco, Biagio Cosenza, Rosario de Chiara, Ugo Erra and Vittorio Scarano from the University ``degli Studi'' of Salerno and the University ``degli Studi della Biasilicata'' of Potenza in Italy. The paper concerns optimization methods for mesh-like computations in clusters of processors. The computations are perfomed assuming a phase-like program execution control using a tiling approach which reduces inter-processor communication. A temporal coherence is also assumed, which means that task sizes provide similar execution times in consecutive phases. Temporary coherent computations are structured in a Prediction Binary Tree, in which leaves represent computing tiles to be mapped to processors. A phase-by-phase semi-static load balancing is introduced to the scheduling algorithm. The scheduling algorithm is equipped with a predictor, which estimates the computation time of next phase tiles based on previous execution times and modifies the tiles to achieve balanced execution in phases. For this, two heuristics are used to leverage on data locality in processors. The proposed approach is illustrated by the example of interactive rendering with Parallel Ray Tracing algorithm. The fifth paper ``The Influence of the IBM pSeries Servers Virtualization Mechanism on Dynamic Resource Allocation in AIX 5L'' is by Maciej Mlynski from ASpartner Limited in Poland. The paper concerns a very up-to-date problem of system virtualization and presents the results of research carried on IBM pSeries servers. IBM is strongly developing the virtualization technique especially on IBM pSeries servers enabling an improved and flexible sharing of system resources between applications. The paper investigates novel facilities for dynamic resource management such as micro-partitioning and partition load manager. They enable dynamic creation of workload logical partitions of system resources and their dynamic mangement. It includes run-time resource re-alocation between logical partitions including setting of sharing specifications as well as run-time adding/removing/setting parameters of resources in the system. It remains an open question how to properly tune parameters of the operating system using the provided virtualization facilities to obtain the best efficiency for a given application program. The paper presents the results of experiments which study the effects of tuning the disk subsystem parameters under the IBM AIX 5L operating system with the use of the provided virtualization facilities on the resulting application execution performance. The results show that even small deterioration in the resource pool status requires an immediate adaptation of the operating system parameters to maintain the required performance. The sixth paper ``HeteroPBLAS: A Set of Parallel Basic Linear Algebra Subprograms Optimized for Heterogeneous Computational Clusters'' is by Ravi Reddy, Alexey Lastovetsky and Pedro Alonso from University College Dublin in Ireland and Polytechnic University of Valencia in Spain. The paper concerns the methodology for parallelization of linear algebra computations for execution in heterogeneous cluster environments. The design of the HeteroPBLAS library (Parallel Basic Linear Algebra Subprograms) for heterogeneous computational clusters is presented. The main contribution of the paper is the automation of the parallelization and optimization of the PBLAS, which is done by means of a special user interface and the underlying set of functions. An important element is here a performance model that is based on program code instrumentation, which determines parameters of the application and the executive heterogeneous platform relevant for execution performance of parallel code. The parameter values specified for or returned by execution of the performance model functions are next used for generation and optimal mapping of the parallel code of the library subroutines. The proposed approach is illustrated by experimental results of execution of optimized HeteroPBLAS programs on homogeneous and heterogeneous computing clusters. Marek Tudruj

information refers to information that a user can't directly obtain just by visualizing the spatial information of objects in a 3D virtual environment (3DVE). This thesis first reviews the state of the art on interactive 3DVEs development, abstract information visualization techniques and the evaluation of interactive 3DVEs. Then, this thesis presents a conceptual model, reusable toolkit and usability evaluation methodology for comparing the usability of different abstract information visualization techniques. In order to control the navigation skill variable, the design of a constrained navigation approach for teleporting the user from one user context to another is proposed. Finally, this thesis presents case studies for validating the proposed conceptual model, toolkit and usability evaluation methodology by performing usability testing experiments. The contributions of this thesis are a conceptual model, reusable toolkit and usability evaluation methodology for measuring and comparing the usability of abstract information visualization techniques in interactive 3DVEs.