Interactive design of urban spaces using geometrical and behavioral modeling The main contribution of our work is in closing the loop between behavioral and geometrical modeling of cities. Editing of urban design variables is performed intuitively and visually using a graphical user interface. Any design variable can be constrained or changed. The design process uses an iterative dynamical system for reaching equilibrium: a state where the demands of behavioral modeling match those of geometrical modeling. 3D models are generated in a few seconds and conform to plausible urban behavior and urban geometry. Our framework includes an interactive agent-based behavioral modeling system as well as adaptive geometry generation algorithms. We demonstrate interactive and incremental design and editing for synthetic urban spaces spanning over 200 square kilometers. We present a framework for intuitive and interactive design of 3D geometric models of large, complex, and realistic urban spaces. An urban space is a collection of architectural structures arranged into buildings, parcels, blocks, and neighborhoods interconnected by roads. The key notion behind our approach is to close the loop between behavioral modeling and geometrical modeling of urban spaces. We model the design and editing process as a dynamical system using a set of functions that describe the change the variable values. Our system produces models resembling existing cities, and is useful for a variety of applications ranging from games and movies to urban planning and emergency management. Previous research in urban modeling can be divided into the areas of geometrical modeling and behavioral modeling: the first is purely computer graphics oriented (e.g., [Parish and Muller 2001 , Wonka et al. 2003 , Mueller et al. 2006 , Aliaga et al. 2008 , Chen et al. 2008 , and the second lies outside this research domain (e.g., [Alkheder et al. 2008 , Waddell 2002 ). The results of urban behavioral modeling are intended for decision-making regarding urban policies in current and future urban areas. In general, however, behavioral simulation models use limited and fixed 2D geometric features (e.g., grid cells or parcels) and are computationally too expensive to run at interactive rates. Some research has been performed in feeding the output of a behavioral modeling system into a geometrical modeling system producing 2D layouts or 3D models that change over time (e.g., [Honda et al. 2004 , Vanegas et al. 2009 , Weber et al. 2009 ). However, the focus is not on designing and editing a new urban model, but rather on computing changes (e.g., growth) over time to a provided model. Geometrical and behavioral modeling, when applied in isolation on the same underlying urban space, yields a functional disconnection between the two resulting models. This is because behavioral modeling is not concerned with generating the geometry of the urban space and because geometrical modeling usually does not consider behavioral properties of real-world cities. This disconnection is particularly disadvantageous during the computer graphics design and editing process of 3D geometric urban models. Real-world urban spaces exhibit relationships between variables such as terrain, road networks, building shapes, distribution of population, jobs, and transportation routes. Existing geometrical modeling systems can be used to perform the changes to the 3D model that are implied by altering these variables, but the designer would have to be aware of the subtle interdependencies between the variables. The consequences of changing one variable can vary from local to global changes. Consider the following examples: Our generalized design framework consists of urban space design variables with spatially-varying values defined over an urban area. The variables control the distribution of population and jobs, land values, road network, parcel shape, and building geometry. Editing the variables is performed intuitively and visually using a graphical user interface (GUI) combined with a paint-brush style tool. Any variable can be globally or locally increased, decreased, or constrained. The ability to constrain variables is crucial to support incremental design and editing at various scales. Moreover, the designer can constrain several distinct parts of an existing model and let the system complete the rest of the model. The dependencies between variables are articulated via differential equations. After an edit operation, the dynamical system attempts to bring the urban model back into equilibrium ( Figure 2 ). Our behavioral modeling is inspired by the urban simulation framework, UrbanSim, of Waddell [2002] in the sense of using an agent-based method and letting agents make individual choices. We reformulate their methodology with the objective of obtaining static equilibrium in the urban space. Their framework is a growthoriented forward simulation for offline use that does not refresh its use of geometry during the simulation and does not produce detailed geometry as output. Our objective is not to capture the numerous behavioral nuances and interacting agents, nor to model the evolutionary processes that shape cities over time. Rather, we aim to develop a system that provides a designer with a very efficient and parsimonious means to create plausibly realistic cityscapes that are internally consistent. For this objective, we take an approach of simplifying the behavioral aspects that are well studied in urban planning, geography, economics and civil engineering, and provide instead a fast implementation that even creates large multi-city regions fully detailed in their composition of roads, parcels, buildings, jobs and population. Our geometrical modeling engine consists of an adaptive road network generator, parcel generator, and building generator. Parcels are computed inside the blocks defined by a road network. Building envelopes are procedurally generated and their size is estimated from the population and jobs count that they are to contain. We use 3D models of intermediate complexity for interactive visual feedback during the design process, but support exporting our design variables for interfacing other software systems focused on creating photorealistic buildings and façades. We demonstrate our system by interactively creating large models of urban spaces and modifying the model. Our system has designed urban models containing up to 50,000 buildings, 3,000 km of roads, and 200 km 2 of area. The total interactive design process time, including several iterations of variable changes and modeling alterations, is just a few minutes on a standard desktop computer. We have presented an interactive system to design and edit 3D urban models. Our key inspiration is to close the loop between behavioral modeling and geometrical modeling producing a single dynamical system that assists a designer in creating urban models. After a user-specified change, the dynamical system attempts to bring the 3D urban model back into equilibrium, thus matching the demands of behavioral modeling with those of geometrical modeling. This ability enables the designer to only partially specify the design variables and have the system complete the rest. In addition, the designer can incrementally build the model and can explicitly constrain one or more design variables thus having both global and local editing control. Large and complex models can be produced in a few minutes or less. Our framework has the following limitations: i) it includes a stochastic component which implies the exhibited behaviors and geometries are not exactly repeatable from session to session; ii) our dynamical system is subject to oscillations, though we ameliorate this by constraining parameter values and not straying far from equilibrium; and iii) over-constraining the system can lead to an unfeasible urban model (e.g., Figure 5d ). We are pursuing two items for future work. First, we are interested in including additional elements of behavioral modeling, such as a more sophisticated accessibility model. Second, we are seeking methods to generate more complex geometric structures using socioeconomic data such as generating additional building details. Our work relates to research within the areas of urban modeling and urban planning and simulation. One of the first systems to generate entire virtual cities was presented by Parish and Mueller [2001] . The user provides several types of input layers for describing an underlying environment (e.g., a fixed population and terrain map) and a set of custom-written grammars based on environmentally-sensitive L-systems [Měch et al. 1996 ] are used for generating street layouts and simple buildings. Their work does not include behavioral modeling, but indicates as desirable future work the inclusion of behavioral schemes in the road creation mechanism. Further, a single direction of communication is provided between input layers and generated results (i.e., the generated 3D model does not alter the input layers) and there is no inter-dependency between the input layers. Although layers can be manually changed for simple inter-dependencies, it must be known to the designer and does not scale well to large models. Subsequent research has focused on improving particular aspects of city generation. For example, the process of generating a road network through the interactive manipulation of tensor fields was recently addressed by Chen et al. [2008] . In our previous work [Aliaga et al. 2008] , we used an example-based approach to produce a layout of roads and to complete it with imagery synthesized from aerial photographs. While these methods can produce a variety of road configurations, the ad hoc design processes do not consider both the distribution of population and jobs and the accessibility between different parts of the model. Such consideration requires manual editing (for [Chen at al. 2008 ]) or many well-chosen example inputs (for [Aliaga et al. 2008] ). Various authors have focused on detailed modeling of either individual buildings or their parts (e.g., [Lipp et al. 2008 , Merrell and Manocha 2008 , Mueller et al. 2006 , Mueller et al. 2007 , Wonka et al. 2003 ). CityEngine [Procedural 2009 ] implements some of the previous algorithms in a commercial software system. Urban planning and simulation focuses on behavioral modeling (e.g., [Alkheder et al. 2008 , Leonard et al. 1998 , Portugali 2000 , Waddell 2002 ). As opposed to shorter term simulations of traffic flow and crowds in 3D environments, our use of the term behavioral simulation refers to modeling long term behaviors of an urban space based on socio-economic factors. The dominant methods for urban simulations are cellular automata [Leonard et al. 1998 ], agent-based models [Portugali 2000] , and aggregate equilibrium models [Putman 2000 ]. In addition, micro-simulation models attempt to simulate decision-theoretic individual agents responding to both localized and broader environments [Waddell 2002 ] and leverage the Random Utility Maximization framework to provide the behavioral and statistical theory consistent with decision-theoretic agents [McFadden 1973 , Train 2003 ]. In general, these simulation systems model an urban environment as a set of interconnected processes and are computationally expensive. Micro-simulation discrete choice models, such as UrbanSim [Waddell 2002 ], contain agents that make decisions to locate and move within the urban environment. This method works with very small cells or parcels, but it differs from others by integrating discrete choice models, an explicit representation of real estate markets, and statistical methods to estimate model parameters and to calibrate uncertainty in the model system. Our work leverages off UrbanSim (Section 3.2). Some recent works model the change of an urban space over time.. In Vanegas et al. [2009] , we used the output of an offline behavioral simulation to make changes to current aerial imagery and produce tentative 2D aerial views of the urban space in the future -no feedback to the urban simulation is performed. Lechner et al. [2007] describe an offline agent-based temporal simulation to generate realistic 2D land-use maps based on a user-sketched global behavior, but their system does not provide tools for editing and designing 3D geometric models of urban spaces. Weber et al.. [2009] presented a geometric simulation of a city over time (e.g., 25 years). Their interactive simulator focused on urban growth. However, their simulation is a forward computation without feedback. For instance, the alteration of building heights by the user does not modify the distribution of population and jobs, large changes to the road network based on designer input for altering agent behavior are not shown, and completion of urban models from a set of constrained design variables is not implemented. Furthermore, their typical total design and simulation time is between one hour and one day. In contrast, our system focuses on providing tools to design urban models from scratch and to yield complete models within minutes.

B O O B I O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O B O O O O B O O B I O O O O O O O O O O O O B O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O B I O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Cognitive heuristics in design: Instructional strategies to increase creativity in idea generation This paper explores the use of heuristics as cognitive strategies invoked during the process of design. Heuristics are reasoning processes that do not guarantee the best solution, but often lead to potential solutions by providing a simple cognitive "shortcut." We propose that designers use specific design heuristics to explore the problem space of potential designs, leading to the generation of creative solutions. We test whether design heuristics can be taught to novices, and suggest their use will facilitate the design process at multiple levels of instruction. In the present empirical study, we evaluate a set of six instructional heuristics and validate their effectiveness with product concepts generated by novice designers. Six hundred seventy-three drawings were created by 120 first-year college students under four instructional conditions. Drawings were coded according to their content, use of heuristics, creativity, and practicality. The most creative concepts emerged from the experimental conditions where heuristics were introduced. Heuristics appeared to help the participants "jump" to a new problem space, resulting in more varied designs, and a greater frequency of designs judged as more creative. Our findings suggest that simple demonstration of design heuristics may, at times, be sufficient to stimulate divergent thinking, perhaps because these heuristics are readily grasped and contextual application is not required. Based on these findings, a conceptual model for design education emphasizing the importance of using a variety of heuristics is proposed. This model suggests that learning can be enhanced through exposure to a variety of design heuristics, and can supplement formal education and foster personal development in design learning. One of the key design education issues in engineering design is the enhancement of creative abilities. The typical paradigm underlying design education is the experiential learning approach (Tynjala, 1998) . The curriculum of experiential learning activities usually takes the form of complex projects consisting of generally structured, guided experiential activities (Tynjala, 1998) . Project-based learning has also been adopted as the key teaching-learning strategy in most design schools, but questions about the effectiveness of this approach remain unanswered. It assumes that students will have their curiosity aroused with an increased motivation to learn, and that when in a novel design situation, students will transfer the meaningful insights they learned in school into other design tasks (Pietersen, 2002) . However, in these later activities, students are often faced with unstructured, ambiguous design problems, for which they may not have acquired strategies to assist them in developing new solutions. With a critique-based evaluation of student projects, the set of design knowledge and strategies acquired may not be apparent even to the successful student.. Our broad research agenda is to develop a theory of design education based on the cognitive processes involved in successful design, and to identify instructional methods that may help novice designers gain knowledge and experience in creative design. Which cognitive strategies enhance innovation in design? How can strategies used by successful designers be communicated through explicit instruction? Although the importance of design strategies is well recognized (Finke et al., 1992) , little is known about how designers apply them, and how they affect the quality or creativity of the resulting design. Pedagogy for enhancing design creativity is essential because most engineering problems demand innovative approaches in the design of products, equipment, and systems. This demand can come from the market, new technologies, new legislation, or additional criteria such as sustainability concerns. The result of engineering design activity is often expected to be original, adding value to the base of existing designs by solving technical problems in new ways. This paper presents an empirical approach to the study of cognitive processes in design, and the utility of explicit instruction on strategy use in design. We begin by reviewing previous research on cognitive processes in engineering design, leading to our research questions and experimental approach described in the following sections. Then, we present an empirical study examining the use of heuristics in conceptual design, and finally, the implications of this work for design pedagogy. Students learn to generalize and abstract rules from their practice of design as they develop an understanding of why their cognitive processes result in more or less successful paths to design. Our approach, demonstrated in the empirical study presented here, is to make explicit the types of design heuristics used by expert designers in ideation; then, to prepare a design pedagogy that presents these heuristics to students as part of their own generation practice. Over time, these design heuristics may become internalized and applicable in design problems where the need to be creative is a driving concern.. This research reports the beginning of a larger empirical program of research on design heuristics, including examining heuristics in expert design, testing training programs for novice designers, and understanding our judgments of successful, creative designs. The purpose of the larger study is to empirically explore and identify heuristic use in engineering students' designs and to develop a model for representing these activities in terms of how these behaviors contribute to analysis, synthesis, and evaluation skills; how differences in these behaviors are related to expertise; and how these behaviors may influence performance as a function of process efficiency and the verall quality of the final solution.. Seda Yilmaz is a PhD candidate in the Design Science Program at the University of Michigan. She received her BID from Middle East Technical University (Ankara, Turkey) and her MFA in industrial design from the University of Michigan. Her research combines her background in product design with methods in cognitive psychology in order to understand the connections among the design process, the design outcome, design heuristics, and the information processed by the designers while generating concepts.. Colleen Seifert is a Professor of psychology at the University of Michigan in Ann Arbor. She received her PhD in psychology from Yale University in 1988. Her research interests lie in the cognitive science of higher level thought processes, including medical and legal decision making, planning, problem solving, creativity, and learning and instruction.. Richard Gonzalez is a Professor of psychology, marketing, and statistics at the University of Michigan. He received his PhD in psychology from Stanford University. His research areas include consumer decision making, social psychology, creativity, and statistics.. Cognitive heuristics in design 355 This empirical study suggests the potential effectiveness of instruction on design heuristics. Even for novice designers, a few minutes of text and illustration on six specific heuristics led to designs reliably judged as more creative. Through use of heuristics, the designs appeared more engaged with visual form, more varied, and more successful than those in the control condition. Our results suggest that the ideation phase Merge 71 76 37 26 210 Configuration 70 77 36 16 199 Substitute 23 18 10 31 82 Nest 21 34 15 4 74 Repeat 23 18 16 10 67 Scale 35 21 8 3 67 Total designs in selected set 77 89 43 57 266 of design can be assisted by explicit instruction on design heuristics. In total, 667 separate designs were generated by the 120 subjects, averaging more than 5 per subject. The majority of the participants (98%) in the three heuristics conditions generated 5 or more concepts, with an average of 5.6 (standard deviation ¼ 1.7, range ¼ 3-8). Only 2 of these 90 participants generated more than 6 concepts; however, 9 of the 30 participants in the control condition generated more than 6 concepts. This difference may have arisen because subjects in the control condition saw no heuristic instructional materials and thus had more time during the session for generating designs.

O O O O O O O O B O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O B I O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O B I O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Co-occurrence Network of Reuters News Networks describe various complex natural systems including social systems. We investigate the social network of co-occurrence in Reuters-21578 corpus, which consists of news articles that appeared in the Reuters newswire in 1987. People are represented as vertices and two persons are connected if they co-occur in the same article. The network has small-world features with powerlaw degree distribution. The network is disconnected and the component size distribution has power law characteristics. Community detection on a degree-reduced network provides meaningful communities. An edge-reduced network, which contains only the strong ties has a star topology."Importance" of persons are investigated. The network is the situation in 1987. After 20 years, a better judgment on the importance of the people can be done. A number of ranking algorithms, including Citation count, PageRank, are used to assign ranks to vertices. The ranks given by the algorithms are compared against how well a person is represented in Wikipedia. We find up to medium level Spearman's rank correlations. A noteworthy finding is that PageRank consistently performed worse than the other algorithms. We analyze this further and find reasons. Networks describe various complex real world systems such as neural network of a worm (Caenorhabditis elegans), power grid of the Western United States, phone call networks, networks of linguistics, protein-folding, the World Wide Web and social systems [1] . Social networks describe human societies whose nodes are individual people and links represent a social interaction among these people. Although obtaining data about social networks is difficult, many interesting social networks such as social network of scientific collaboration [2] , movie actors' collaboration [3] , sexual contacts [4] , email lists [5] , and terrorist network of September 11, 2001 [6] have been studied in the literature. Recent studies have shown that these networks possess some common properties such as being small-world and scale-free.. Reuters-21578 corpus is a standard data set used extensively in research in automatic document categorization, information retrieval, machine learning and other corpus-based research [7] . It consists of 21, 578 news articles, mostly about economics, that appeared in the Reuters newswire in 1987. In a previous study, 3, 000 of these news articles are randomly selected and person names are manually identified by reading [8] . An undirected, un-weighted network where nodes are people and there is a link if two people have appeared in the same news article is constructed. Then, the scale-free and small world properties of the network is studied.. In this study we extend the network to cover all the 21, 578 news articles. We investigate component structure, community structure, co-occurence in time, and the "importance" of people. A social network of co-occurrence based on Reuters-21578 corpus is constructed. Complex Network techniques are used to analyze the network. It is found to be a small-world network with power-law degree distribution. The distribution of the component size is governed by a power law.. We reduce the network by taking vertices with minimum degree of 10, where the selection of 10 is arbitrary and obtained a network with 49 strongly connected persons. This reduction enables us to interpret the results of a community detection algorithm for a large network with unknown community structure. The algorithm produced 4 communities that we can give a meaningful interpretation.. When the network is reduced by removing the edges whose weight is less than 10, where the selection of 10 is also arbitrary, the network become disconnected. Interestingly, it becomes almost a star-connected network where Ronald Reagan is in the center as a sign of his dominance. Removal of him would break the already disconnected reduced network and transform to a network where only a few vertices are connected.. The articles have time information. Using this, we have obtained time dependency of co-occurrence. Some people such as Ronald Reagan have activity, consistently. On the other hand, some people have limited time presence due to some particular events.. We try to estimate the importance of the people based on the co-occurrence network of 1987 and compare it with another importance metric of 2007 based on representation in the English Wikipedia, giving 20 years of time difference in between. The time past can make a reliable judgment of who was not already important in 1987. We present a comparative performance analysis for five common centrality measures for our network; article count, degree, PageRank, betweennes and closeness. We found low to medium normalized Spearman correlations between the two metrics. These were in our expected range and in this sense an important contribution of this paper is in providing a means of comparing the relative performances of the algorithms. We found PageRank to be the worst of the five, while closeness was the best performing algorithm. We have discovered an anomaly with PageRank which to some extent can explain why it was performing badly. We believe this may be important as it points out to a pitfall using PageRank in such a network. It is possible to use and combine results from Wikipedias of different languages, as well as different reference sources which we see as a future work.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O B I O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Empirical Evidence of Priming, Transfer, Reinforcement, and Learning in the Real and Virtual Trillium Trails Abstract-Over the past 20 years, there has been a debate on the effectiveness of virtual reality used for learning with young children, producing many ideas but little empirical proof. This empirical study compared learning activity in situ of a real environment (Real) and a desktop virtual reality (Virtual) environment, built with video game technology, for discovery-based learning. The experiences were in the form of two field trips featuring statistically identical wildflower reserves. While the results support that the Real is superior for learning activity, they also show that the Virtual is useful for priming and reinforcing in-curriculum material, or for situations when the real environment is inaccessible. Offering the Virtual first primes for learning activity in the Real; if used second, it reinforces the Real experience, as supporting evidence shows significant transfer effects. Thus, the Virtual may serve educational goals, if used appropriately, and can come close to the Real. As informal learning environments, such as field trips and video games, are accepted as motivational, an attitudinal survey was conducted postexperiences to capture motivational factors at play, to aid in comparison and contrast, and to provide context to the empirical results on learning activity in situ; however, more work is needed. I N May 2007, amid the springtime bloom of wild trillium at a long-term NSF deer exclosure study site, a group of elementary school students from a suburban Pittsburgh school district went on a field trip-with a twist. In this study of the Virtual Trillium Trail (VTT), students took both real and virtual field trips to the protected site, with the real trip functioning as the control.. A driving question behind the VTT was: Could a desktop virtual environment (Virtual) draw on elements of simulations, games, and educational software to enhance perceptual, cognitive, and emotional experiences?. The best way to approach this design problem was to frame it within the context of a proven, successful realworld model: the field trip. The real-environment field trip (Real) is such a baseline model that, at its best, embodies discovery-based learning experiences beyond the confines of the classroom.. In comparing a real field trip to a virtual one through empirical evaluation of in situ discovery-based learning activity and postexperience attitudes, the study held to the assumption that Real is preferable to Virtual; this common sense "given" is too often ignored in studies centered on the effectiveness of virtual environments, perhaps due to the theoretical idealism of designers. In contrast, the study underscored this primary assumption, thereby allowing for empirical, statistical measurements that provide instructional designers with tangible ways to implement highly realistic virtual reality (VR) applications and reality-based simulations (see Fig. 1 ), as an extension of the classroom, as educational simulations.. The central software design focus was on the child and the child's needs. Personalization is used to advantage in intelligent tutoring systems [1] , where extreme personalization is the goal, and where each student can have a personally unique and meaningful experience. As is advocated in user-centered design (UCD) [2] and humancomputer interaction (HCI) [3] , the child, as the main user, drives the software requirements and assessment (see Fig. 2 ).. While formal statistical hypotheses were stated to structure the work of the study, the study itself was driven by the desire to explore, generate insights, and frame future research in this area. The results inform design and development of virtual environments for independent and intrinsic learning. The empirical analyses reported here are unique and have not been reported elsewhere; however, they are part of a larger body of work, and the ethnographic and nonparametric results have been reported and published elsewhere [4] . This submission to the IEEE TLT is an empirical analysis using parametric statistics to show differences in learning activity between Real and Virtual discovery-based learning activity, transfer effects, and attitudes, where the paper published in [4] is an ethnographic report and a nonparametric analysis of the experiences. The two papers complement and support each other, while allowing detailed analysis from either a qualitative or a quantitative approach. Significantly higher Total learning activity, combined with higher attitudinal ranks for Learning in the Real, gives supporting evidence to the claim that more Total learning activity occurs in the Real. However, Plant-Only learning activity is identical in Real and Virtual, which gives supporting evidence to the claim that the Virtual may be used for in-curriculum material. Thus, the Real is the superior learning environment overall, but the Virtual shows value for carefully targeted learning objectives of in-curriculum material, especially when the real environment is not available.. This result does not imply that schools should substitute "expensive" real-world field trips with "inexpensive" virtual reality field trips, but it does suggest the value of virtual environments for learning, if used properly. The empirical data show order and transfer effects. Therefore, for schools to maximize the learning impact of real-world field trips, they should prime the students before, and reinforce afterward, with follow-up virtual reality field trips. If only one experience is possible, use the Real. If the Real is impossible, carefully use the Virtual.. Great scientific exploration and discovery can only logically come from real and true environmental awareness, curiosity, a sense of wonder, and the ability to inquire when we recognize that we do not know. We must remember to "know that we do not know," and therefore, cannot program artifacts, such as virtual environments, that are as authentic as the real world. These new tools require sensitive understanding to maximize their potential while respecting their limitations. We can design and build virtual environments for ecology education to support particular goals of factual, conceptual, and contextual awareness; strategically use features of free navigation and information annotation; and respect the interaction of form and function. At the same time, we should not use these powerful emotional and intellectual tools to mislead, frame, sell, or advance a biased or destructive agenda. In final conclusion, virtual environments present opportunities for research of the child-computer-environment interface. However, much future research is required to understand the complex interactions of learning in virtual worlds and to responsibly harness this powerful new technology as it approaches the truth. The real field trip was to the real Trillium Trail, a wildflower reserve located outside of Pittsburgh, Pennsylvania, and the virtual field trip utilized the Virtual Trillium Trail, a high-fidelity virtual environment simulation of the real-world location installed in a PC-lab classroom in the School of Information Sciences at the University of Pittsburgh. Each experience lasted 1.5 hours, and the study with this sample was conducted over the first two weekends in May 2007. The field trip activities were carefully controlled to be the same, except that the Real was in the real outdoor location and the Virtual occurred through the VTT software run in a computer lab at the University of Pittsburgh. In the Real, the students followed the naturalist guide on the trail and were presented with information, or the guide responded to the spontaneous inquiries of the students. In the Virtual, each student sat at a PC station, used an earphone on one ear, and independently selected when to listen to the naturalist guide and when to explore independently. At times, students would find something of interest and share with the guide and the class, while at other times, they would share information with the closest student in the room. Frequently, the students did not listen to verbal narration but instead were off exploring the software on their own. The students positioned the mouse to select a direction, tapped on the arrow keys to navigate, and used the space bar to select an object's fact card for more information on an onscreen object. At other times, the students navigated to an audio Sprite and listened to the concept, story, or lesson. The Sprites made it easy for the younger children to listen to and hear the entire concept, whereas the fact cards allowed students to read and flip through, read several times, or leave once some basic information was reviewed. When students found objects of interest, they would mark them on the paper maps distributed at the beginning of the session.. The obvious difference was that the Real was fully multimodal in that a student could smell, taste, and touch plants as well as perceive the temperature and feel the wind in the context of the environment. The students had to stay on the footpath, as it was a nature reserve that restricted human activity, and thus, the wayfinding and navigation were restricted to, essentially, a linear route. Additionally, there were surprises, conveniently provided by nature: a doe and her fawn, a mother turkey hen on her nest, a salamander in the stream, the cry of a red-tailed hawk, or a woodpecker pounding. The Virtual only had plants, so there was no opportunity for interaction with insects, amphibians, reptiles, or mammals.. However, the Virtual did allow for the students to fly, travel off-trail, and freely explore the entire space independently. The simulation allowed for the student and the teacher to interact in dynamic, real-time, synchronous, and asynchronous ways. It also allowed the teacher to present alternative views, such as a fly-through in the forest canopy, not possible in the Real. A more detailed account of the activity is published in Harrington [4] .

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


The Wandering Token: Congestion Avoidance of a Shared Resource In a distributed system where scalability is an issue, like in a GRID [4] , the problem of enforcing mutual exclusion often arises in a soft form: the infrequent failure of the mutual exclusion predicate is tolerated, without compromising the consistent operation of the overall system. For instance this occurs when the operation subject to mutual exclusion requires massive use of a shared resource.We introduce a scalable soft mutual exclusion algorithm, based on token passing: one distinguished feature of our algorithm is that instead of introducing an overlay topology we adopt a random walk approach.The consistency of our proposal is evaluated by simulation, and we exemplify its use in the coordination of large data transfers in a backbone based network. In an ideal distributed system there are no centralized resources, all of them being equivalently able to play any role. However, in practical applications, it is often the case that the introduction of a centralized resource may be appropriate, in order to reduce the cost, or to improve the performance. The loss of scalability and fault tolerance, which is inherent to the introduction of a centralized resource, is accepted as a tradeoff.. For instance, consider the communication infrastructure of a network: be it geographical, or located inside a building, it will probably be based on a backbone. Although this may be replicated for fault tolerance, nonetheless it will break the symmetry of the system. A system that uses certification based on public/private yields another example, since it exhibits a centralized resource located at the certification authority site. Although public keys may be cached locally, the presence of a certification authority breaks the symmetry.. Components of a large distributed system may need to regularly perform operations that require a relevant share of such centralized resources: for instance, peripheral components may want to update local caches of data from a database, or upgrade local software by downloading new revisions from remote mirrors, or simply renew their credentials. In a system that wants to scale, the performance of such operations should not be tightly bound: occasional congestion of the centralized resource should be tolerated with a tolerable degradation the high level service running at the edge.. In order to keep congestion an occasional event, applications must be equipped with a congestion avoidance mechanism. Such mechanism should coordinate the access to the centralized resource so that congestion is avoided as long as the overall load is nominal. When requests overtake the capacity of the resource, it should reproduce at the edge the effect of a congestion, but without stress for the centralized resource.. One key requirement for a congestion avoidance mechanism is that it must not impact system operation: this excludes the adoption centralized algorithms, that are not scalable, as well as distributed algorithms based on deterministic consensus, that have an heavy footprint.. Summarizing, unlike traditional mutual exclusion, modeled by a concurrent write on a shared register, our problem statement includes the occasional occurrence of simultaneous instances of the protected operation. This is due to the nature of the controlled operation whose performance may degrade when many are executed simultaneously, but without damage for the consistency of the system. This is formally translated in the following definition:. Requirement 1 A soft mutual exclusion algorithm for the protected operational A ensures that at any time, with high probability, there is just one component enabled to perform A. The probability that more than one component is enabled falls exponentially in the number of enabled components.. We propose a simple distributed algorithm that implements soft mutual exclusion. The algorithm falls into the peer to peer family, since there is no centralized agent, and all participants run the same code. The result is the circulation of a token, ensuring that, with high probability, exactly one token is present in the system. We do not assume a fixed topology or a preliminary overlay design phase (as in [9] , aimed at multicast). The token is circulated according with a random walk concept, that can be tailored to run on any topology. We evaluate its performance in a full mash that represents the transport (not network) level of the Internet. Formal results (see [8] ) justify the claim that our algorithm may be of interest also in networks with an average degree comparable with log N , where N is the number of components in the system.. The algorithm relies on the knowledge of the membership of components that may execute the protected operation. Without impact on scalability, this can be maintained on a centralized server, which can be replicated for fault tolerance. Indeed, the algorithm we propose can be used in order to manage a membership, with an approach which is an alternative to gossiping (see [5] ).. The relationships with Dijkstra's (deterministic) self-stabilization [3] are evident: however, instead of using the knowledge of neighbor's state, we enforce mutual exclusion using time constraints computed locally. We share with some randomized self-stabilizing algorithms the basic idea of performing random moves in order to compensate lack of information. Our approach may be regarded as an evolution of [6] : with respect to that work, we introduce a probabilistic definition of closure, since the token management scheme may itself induce divergence from stable operation. Such event occurs with low probability, and is promptly compensated. As for the token elimination rule, the probability of collision is augmented by widening the collision window so that recovery is substantially improved with respect to [6] .. Although many topics discussed in this paper have been extensively treated in formal papers, here we prefer a simulation approach: this is motivated by the fact that the solution we introduce uses technical details that would make difficult a formal evaluation. Whenever appropriate, we will make reference to formal works that motivate the framework of our approach. The wandering token algorithm is proposed as a solution for those architecture where moderating the concurrent access to a shared resource can improve the performance. Its cost, in terms of communication and computation, is negligible.. The algorithm is fully scalable: when the scale (i.e., the number of components in the system) overtakes the capacity of the shared resource, the wandering token algorithm gradually reduces the resource share granted to each component, thus shielding the shared resource from the consequences of the overload.. While token duplication is avoided by a 3-way token passing protocol, the loss of the token cannot be excluded. When such event occurs, the operation We introduce a case study that justifies the system constants used in the simulation described in section 6.. We consider a network where large amount of data must be processed by specialized processing units. The shared resource in a 10GBps network backbone. Although this is not a bottleneck during normal operation, when a user requires the processing of remote data, the application will try to exploit as much as possible the capability of the backbone. Other best effort traffic will not suffer for this, but concurrence of other similar operations would require the intervention of traffic shaping, which would degrade the performance of the network. A centralized database records the identity of the applications that want to use the backbone, after checking their credentials.. We configure our system to support nominally N = 150 data transfer applications. Applications are enabled to use the backbone for ∆ op = 4 seconds, which corresponds to a data transfer of 40GB. Each application should be enabled to use the network typically once every ∆ min = 10 minutes, in order to feed its computational activity with data, or to upload the results. This is consistent with the fact the each of the 150 unit should periodically enjoy the availability of the unit for 4 seconds: 150 * 4 = 600. So the input for our problem is the nominal number of units, and the duration of each operation.. Based on the above parameters, we can figure out the behavior of the system: as long as one token is wandering in the system and the number of units is nominal or less, 80% of the times the applications have access to the backbone within 2 * ∆ min . Occasionally (less than one percent of the time) two or more applications are allowed to use the backbone: which should be hardly noticeable, since such overlap is produced for a few seconds.. When the system grows up to two times the nominal size, the chance of concurrent execution increases, but the event that more than 3 data transfers are occurring simultaneously is rare, and should be manageable by the application and by the network with a noticeable but sporadic degradation of the performance. The period between successive data transfers is 90% of the times lower than 3 * ∆ min : this reflects the increased number of users of the shared resource, and should slow down the application of approximately 30%.. The transient after a token loss event may be quite long, taking several hours to terminate: during that time a system of nominal size performs, for the sake of simplicity, like an overloaded one. This may be admissible in our case study, since the user application will simply experience a slightly degraded level of network performance. When the system is seriously overloaded, the congestion avoidance mechanisms of the underlying network may undertake traffic shaping.

O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O


Web composition with WCAG in mind Accessibility should be a part of the Web design process instead of being a post-design repair process. Thus, it should be more integrated within the internal authoring tools' mechanism of generating new accessible Web contents. Web pages are usually composed of small pieces of HTML code which, dynamically nested and combined, generate full Web pages. This Web composition, specially when creating Web pages from data extracted from heterogeneous or external sources, should have accessibility into account in order to guarantee that the final page being constructed is accessible. This paper presents the set of rules that, in a Web composition process, a design tool must follow in order to create accessible Web pages. These rules are formalized with W3C standards like XPath and XQuery expressions. We also present WSLS as an accessibility enabled authoring tool that makes this task feasible, and focus in how this tool incorporates accessibility into the process of generating new Web contents. Web browsers have evolved since their inception at the beginning of the Web. We can find plenty of them in very different and heterogeneous devices. Wireless devices like PDA, palm-tops or mobile phones can be connected to Internet, as well as other new devices like digital TV's, or vehicle's assistants. However, many difficulties (namely barriers) arise when these devices are used for surfing legacy Web sites, i.e., Web sites without accessibility features in their designer's mind.. Disabled people also experiment similar problems when using specific platforms adapted to their special needs, like Braille displays, voice browsers or screen magnifiers to Web sites having these accessibility barriers. As a result, ac-cessibility has become a very important feature, and W3C defined WCAG [1, 2] as a set of guidelines that Web pages should follow in order to be considered accessible. The ability for a Web site to be surfed by any device has become a major target for Web designers.. However, most authoring tools still lack from features for generating accessible and device-independent markup. At this point, accessibility is usually treated as a post-design repair process, most of the times guided by an accessibility evaluator tool, like Bobby [9] , Tawdis [10] or Torquemada [11] that spots accessibility barriers that specialized persons have to supervise with no little effort.. Removing accessibility barriers for already made Web sites involves a huge amount of human effort because a lot of human supervision is required for these evaluation tools. This post-design repair process is much less effective than having accessibility features in mind during the design process. Since authoring tools should produce high quality markup for new Web contents, we believe that most of accessibility benefits can be achieved if authoring tools implement accessible-aware creation process mechanisms that guarantee that their generated Web content will be accessible.. Web composition [12] has emerged as a consistent, flexible and dynamic way of generating Web contents by combining reusable pieces of HTML code into other reusable pieces that, guided by a composition process, will be used to create whole Web pages and whole Web sites. This is the approach of several authoring tools like WSLS [14] , that extracts dynamic contents from heterogeneous sources and automatically generates new updated Web contents without the need of a person to guide the process in running time. For these tools, it would be highly desirable to guarantee that final Web contents will be accessible, provided that smaller pieces of reusable HTML code to be used in Web composition are already accessible. In other words, provided that a Web Composition based authoring tool manages small pieces of accessible HTML code (both static templates or dynamically generated) we want to guarantee that the Web composition process will always yield an accessible Web page (or site). So, we must make sure that no kind of new accessibility barriers can be introduced by the Web composition process itself. This paper is focused on formalizing the conditions to be met so that accessible chunks of Web pages can be safely compounded into a page that also results accessible from a WCAG point of view. As we will see, non accessible results can be obtained from accessible pieces, unless some rules are followed. This paper provides a formalized set of such rules. 2. Given wailevel($S) = {No|A|AA|AAA} (an ordered set, so that No < A < AA < AAA). 3. Provided that snippets $S1 and $S2 are WCAG compliant, i.e., wailevel($S1) ∈ {A|AA|AAA} ∧ wailevel($S2) ∈ {A|AA|AAA}. 4. Provided that snippet $S2 will be nested inside snippet $S1 and that pos($S1,$position) is the insertion point for $S2 inside $S1, as depicted in figure 1 . 5. Assuming bottom-up document construction, i.e., $S2 has no position where other HTML reusable pieces might be inserted. 6. Provided that comp($S1,$S2,$position) is the composition of $S2 inserted into pos($S1,$position), i.e., $S2 nested somewhere in $S1. This article has presented conditions formalized with W3C standards that guarantee that the Web Composition [12] approach will always yield accessible contents if accessible ingredients are provided. As expressed, there are some accessibility conditions that will be inherited from smaller pieces and Web Composition guarantees by process (section 4), but other accessibility features require extra conditions in order to be kept. We have formalized the conditions that will avoid that accessibility barriers might be introduced by the Web Composition process itself. We introduced WSLS, a supporting system that affords compliance to these rules by process and by architecture. The realization of selected rules in WSLS yielded already to promising results. For the future we plan to adopt architectural issues as well as augmented processes that guide the design, implementation and evolution of sites and applications towards the vision of the compliant and accessible Web.

B I O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Towards procedural level generation for rehabilitation This paper introduces the concept of procedural content generation for physical rehabilitation. In this initial study a ski-slalom game is developed on the Wii platform that procedurally places the gates of the game according to player performance. A preliminary game evaluation study is conducted on patients with injured legs and showcases the efficiency of the procedural gate generation mechanism tailoring the game difficulty to match rehabilitation goals. The study also validates certain usability aspects of the patients. The Nintendo Wii game console is the best-selling console available today [3] utilizing physical interaction via controllers such as the Wii Remote and the Wii Balance Board. The Wii Balance Board allows game interaction through foot pressure and body weight balancing on the board. These features push video game design to incorporate body movement as a key control modality. In particular, Wii Sports (2006) constitutes of different sport games such as boxing, bowling, golf, and tennis in which the player's avatar can be controlled via a physical motion, e.g. bowling using the Wii Remote. In We Ski (2008), the player is skiing by controlling the pressure on the Wii Balance Board. On that basis, Wii technology gives players new motivations to immerse Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. themselves both mentally and physically. This has inspired many hospitals and rehabilitation centers in the USA [14] to use existing Wii physical games for rehabilitation purposes. The use of Wii technology for physical rehabilitation is also known as Wiihabilitation.. Existing commercial Wii games, however, are not designed for rehabilitation which, in turn, may over-challenge people with partly disabled extremities. Moreover, different patients have different rehabilitation goals to reach and a fixed Wii game does not tailor the gameplay for the patient to meet specific rehabilitation milestones. A solution to those usability problems would be the development of an adaptive Wii physical game that can adjust game parameters to match the patient's physical ability level.. The main aim of this initial study is the development and evaluation of an adaptive Wii game for rehabilitation, which can procedurally generate content in real-time and, furthermore, provide effective training to each patient given the level of her physical ability. For this purpose, an adaptive ski-slalom game played with the Wii Balance Board is developed and tested on patients of a rehabilitation center. The game procedurally generates the placement of the slalom gates based on heuristics of player performance. The preliminary user study presented here reveals that the game adjusts the ski-slalom track effectively to match patient skills. This paper is novel in that it introduces the concept of procedural content generation (PCG) and player modeling for physical rehabilitation utilizing the Wii Balance Board. This is an initial study investigating the interplay between procedural level generation and player profiling on physical Wii games developed for physical rehabilitation. The adaptive mechanism proposed adjusts elements of a skiing game (ReSkii) for the purpose of personalizing the rehabilitation process via PCG. For the gameplay experience to be personalized, patient characteristics are captured during play and guide PCG. Results indicate that it is possible to build simple, yet successful, computational models of physical interaction of patients with partial leg disabilities and proce- To increase the effectiveness of the training, patients' physiological responses such as heart rate and skin conductance may be measured and embedded as additional inputs to the level generation mechanism. Moreover, to keep the levels interesting and the game immersive for the player over extended periods of rehabilitation, more elements can be added or procedurally generated in the game such as narrative, level geometry, jumps and multiple-track choices. More sophisticated algorithms for modeling playing behavior (e.g. via patient preference learning [12] ) as well as richer PCG mechanisms (e.g. via ski track evolution [15] ) will be investigated in future studies and integrated in the ReSkii game. Such patient models could identify more types of physical disability a patient might have, measure the patient's performance based on multiple gameplay characteristics and thereby evaluate better the "goodness" of content that is procedurally generated within the game level. Research in physical rehabilitation [1, 5] has shown that exercises for patients recovering from physical disabilities and injuries are more effective when the exercises are integrated within a game. Patients get more engaged and motivated through a game environment and they tend to forget the pain caused by and the dull repetitive nature of rehabilitation exercises. Physical interactivity, portability, low-cost and commercial availability make the Wii Remote and Wii Balance Board the ideal controllers for developing physical rehabilitation games [8] .. With the popularization of physical interactive game platforms considerable research has been conducted for capturing player immersion [11] , engagement [2] and player affective states [7, 16] in physical interactive games. On the other hand, very few studies investigate the design of adaptive mechanisms for maximizing player experience in such augmented-reality game platforms [16] .. PCG in games has been used for a wide variety of purposes including terrain [6, 10] and space [9] generation, environmental modeling [13] , and race track [15] generation. However, to the best of the authors' knowledge there has been no study investigating procedurally generated content for Wii games and its impact to the rehabilitation process.

O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


The dynamics of two entangled qubits exposed to classical noise: role of spatial and temporal noise correlations We investigate the decay of two-qubit entanglement caused by the influence of classical noise. We consider the whole spectrum of cases ranging from independent to fully correlated noise affecting each qubit. We take into account different spatial symmetries of noises, and the regimes of noise autocorrelation time. The latter can be either much shorter than the characteristic qubit decoherence time (Markovian decoherence), or much longer (approaching the quasi-static bath limit). We express the entanglement of two-qubit states in terms of expectation values of spherical tensor operators which allows for transparent insight into the role of the symmetry of both the two-qubit state and the noise for entanglement dynamics. Quantum entanglement is an information resource [1, 2] . Unfortunately, contact with the environment adversely affects quantum systems, and entanglement is known to be extremely fragile when exposed to environmental fluctuations [3] . While, in principle, the disentanglement occurs due to unitary dynamics of the total system consisting of the initially entangled subsystem of interest and its environment, such an approach requires full knowledge of the environmental Hamiltonian and of the Hamiltonian describing the subsystem-environment coupling. This knowledge is often lacking. Furthermore, even if the full Hamiltonian is known, the exact solution of the problem of the joint unitary dynamics might be simply too hard to obtain. It is thus often assumed that the influence of the environment on the quantum subsystem can be mapped onto the interaction of the subsystem of interest with a noise source.. In what follows we consider environmental noise experienced by two initially entangled qubits (the subsystem of interest here). The noise dominating the decoherence of the qubits can be effectively classical or quantum, depending on the relation between the bath temperature and the relevant energy scale of the subsystem. When considering the process of relaxation (i.e., energy exchange between the qubits and the bath) the energy scale of the subsystem is the qubit energy splitting, Ω, and in order for the noise to be classical, one needs Ω < k B T , where T is the temperature of the bath [4] . However, for dephasing of the qubits, the low-frequency fluctuations of the environment have dominant influence, and the corresponding energy scale of interest is ≪ k B T for many types of qubits, including superconducting circuits [5] , many kinds of spin qubits in semiconductors [6, 7] , and ion trap qubits [8, 9] . Quantum noise is most often modeled using a bosonic environment [4, 10, 11] for which the pure dephasing problem (with the coupling only to the σ z operator of the qubit) can easily be solved [12] , but the case of general coupling to an environment which causes decoherence is a challenging problem for environments with nonzero correlation time [10, 13] . In this paper we assume that the environmental noise is classical, and focus on the influence of its spatial and temporal correlations on the entanglement decay of two qubits.. Much work has been reported on the entanglement dynamics of two qubits in the presence of classical environmental noise. The case of pure dephasing has received considerable attention [14] [15] [16] [17] [18] . Calculations for white noise (i.e., noise having negligible temporal correlations, leading to Markovian decoherence) were carried out both in the case of spatially uncorrelated [19] [20] [21] and correlated noise [20] acting on the two qubits. For fluctuations with finite correlation time (leading to non-Markovian decoherence), pure dephasing due to two mutually spatially uncorrelated [22] [23] [24] and correlated [23] [24] [25] [26] noise was considered. The case of general coupling of qubits to noise also received attention; uniaxial transverse coupling to spatially correlated white noise was considered in Ref. [27] , and the case of transverse coupling to a more general class of noise (of 1/f type, both Gaussian and non-Gaussian) was considered in Refs. [23, 26] , and in [28, 29] where the influence qubit-qubit coupling was also studied.. Here we consider the dynamics of two-qubit entanglement when the qubits having both longitudinal and transverse couplings to a classical Gaussian noise field [30] [31] [32] . We treat noise which exhibits correlations on a length scale of the inter-qubit separation, and which has either negligible or finite autocorrelation time. A possible physical realization of this picture is a system of spin qubits [6, 7, 33] interacting with fluctuating magnetic field, or an array of qubits in an ion trap [8, 9] . The fluctuations could be caused by an ensemble of param-agnetic spins located in the neighborhood of the qubits (e.g., impurity spins), or they could be generated in a nearby solid-state based magnet. The properties of the noise that we shall assume correspond to such a setting. Noise generated by many weakly correlated sources can be expected to have Gaussian statistics. Due to the longrange nature of magnetic forces, the random field has a finite correlation length, so that, depending on the relation between the inter-qubit distance and this length, the limits of fully correlated and completely uncorrelated noises can be realized. Finally, in the presence of an external magnetic field the total system (and the noise in particular) should exhibit at least cylindrical symmetry with respect to the axis distinguished by the field.. In our analysis we use the language of spherical tensor operators, which allows for transparent discussion of the role of rotational symmetry of quantum states in decoherence and disentanglement processes resulting from coupling to noise. The averaging over noise realizations is carried out by using a second-order cumulant expansion of relevant operator products [32] . The cumulant expansion approach is exact in the pure dephasing case, but in the presence of transverse noise it is exact only when the noise has a white spectrum [30, 34] . For strong coupling to slow fluctuations, the quasi-static bath limit [35, 36] is reached (i.e., the average is over random fields static on the timescale of entanglement decay) and the secondorder cumulant expansion for transverse noise fails (in fact a re-summation of all cumulants is needed in such a case [37, 38] ). We resort to numerical simulations in this limit, and to approximate analytical theory (applicable when the qubit energy splitting is much larger than the noise amplitude) in which the influence of transverse noise is treated as a second-order correction to the qubit splitting.. In the calculations we focus on the environmental noise induced dynamics of maximally entangled two-qubit Bell states, and we show that their rotational symmetry is the main source of the difference of their sensitivity to correlated noise. For example the spherically symmetric singlet state |Ψ − is immune to fully correlated noise, in contradistinction to the other three Bell states. Furthermore, the symmetries of the noise itself also lead to significant differences in the character of entanglement decay: the presence of transverse noise is necessary for the sudden death of entanglement [39] [40] [41] to occur, and lowering of noise symmetry from a full rotational one (i.e., isotropic noise) to a cylindrical one causes the decay of the entanglement of |Ψ + Bell state to be different from the decay of entanglement of |Φ ± Bell states. These results have a transparent interpretation when the formalism of spherical tensor operators is used.. The paper is organized in the following way. In Sec. II we introduce the Hamiltonian of the two-qubit system and we discuss the statistical properties of the noise field affecting it. In Sec. III we introduce the spherical tensor operators, which we use to decompose the two-qubit density matrix into parts with distinct transformation properties under spatial rotations. We also show how a measure of entanglement (the commonly used concurrence [42] ) of a Bell-diagonal mixed state of two qubits can be expressed by averages of products of appropriate spherical tensor operators and spin operators, and we introduce the cumulant expansion for the superoperator governing the evolution of the density matrix of the two qubits. Then in Sec. IV we present an exact solution for the pure dephasing case, both for white and colored noise, and consider various degrees of correlation between the two noises. In Sec. V we extend our analysis to include the transverse noise, and we consider both the isotropic noise and noise with lower symmetry, for the whole spectrum of cases: from independent to fully correlated noises affecting the two qubits. In the case of white noise we obtain an exact analytical solution, while in the case of noise with finite correlation time we present approximate solutions, using the effective pure dephasing Hamiltonian and also the cumulant expansion carried out to the second order. Finally, we compare our analytic results with numerical simulations. Section VI contains the summary and conclusions. We investigated the decay of entanglement of two qubits due to exposure to classical noise when the two-qubit state is initialized to be in one of the Bell states. The cases of longitudinal noise (pure dephasing), isotropic noise, and purely transverse noise having various degrees of cross-correlation were considered. Exact results were obtained for noise with a white spectrum (autocorrelation time much shorter than characteristic decoherence times, leading to Markovian decoherence of the qubits), and for a general Gaussian noise leading to pure dephasing. The employed language of spherical tensor operators has allowed for an easy insight into relation between the rotational symmetry of a given Bell state and its subsequent decay dynamics caused by noise with a given symmetry and degree of cross-correlation. For pure dephasing, all the states disentangle in the same way for independent noises acting on the two qubits. As the degree of the cross-correlation of the noises increases, the entanglement decay of the |Ψ ± states is suppressed while the decay of the entanglement of the |Φ ± states is being accelerated. For isotropic white noise, the |Ψ − state (i.e., a scalar in spherical tensor language) is unaffected by fully correlated noise. For partially correlated noises, its entanglement decays at a slower rate than the entanglement of the three other Bell states, which decay in the same fashion. When the noise symmetry is lowered to cylindrical symmetry, in the case of purely transverse white noise we found that for finite cross-correlation of noises, the |Ψ − state has the smallest rate of entanglement loss, and it does not decay at all for fully correlated noise; the entanglement of the |Φ ± states decay faster, and the |Ψ + state is the most fragile. Again, this result can be understood by examining the decomposition of states in basis spherical tensors. Finally, we have discussed the case of transverse noise with finite autocorrelation time. The limit of strong dephasing due to slow noise (the quasi-static bath limit) was investigated for qubit energy splitting much larger than the noise amplitude using an effective Hamiltonian approach. In this case one obtains asymptotic power-law decay of entanglement and interestingly, the nonzero correlations between the noises suppresses the entanglement of |Φ ± states at short times, while enhancing it (with respect to the independent noise case) at long times.. 1m1 ⊗T (2) 1m2 L(T . where blank spaces are zero. The matrix has a block-diagonal form and each block can be diagonalized analytically. In particular, spherical tensor prod-ucts T 11 } form one of the blocks. Because the X corr -states (including the Bell states) are spanned by these five operators, it follows that any state which belongs to this class remains in it for all time when it is evolved with U tr .. Below we list the eigenoperators and the corresponding eigenvalues of L: . 10 ⊗T. 10 ,. −1 + 4γ + 3η : T. 11 ⊗T. 1−1 + T. 1−1 ⊗T. 11 + + 1 + 3η 2γ T. 10 ⊗T. 10 ,. 6γ : T. 10 ⊗T. 1±1 + T. 1±1 ⊗T. 10 ,. 2γ : T. 10 ⊗T. 1±1 − T. 1±1 ⊗T. 10 ,. where η = 1 3. 1 + 8γ 2 .

O O O O O O O O B I O O O O O O O O O O O O B I O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O