Why Is the Shape of the Web a Bowtie?

The first time in Graph Theory a graph was characterized as “Bowtie” was in the seminal paper by Broder et. al. Though no textbook had ever mentioned this type of graph before, no less an important network than the Web Graph itself is supposed to resemble this shape. In two large collections of crawled Web pages and in numerous smaller collections, researchers discovered Bowties and Bowtie-looking graphs by studying millions of web pages. But why do collections of Web pages resemble a Bowtie? The short answer is “because, given the way the Web is created, that’s the only shape it could have”. This paper shows why this is the case and presents an algorithm and software to visualize Bowtie graphs

Analysis of the Web Graph Aggregated by Host and Pay-Level Domain

In this paper the web is analyzed as a graph aggregated by host and pay-level domain (PLD). The web graph datasets, publicly available, have been released by the Common Crawl Foundation and are based on a web crawl performed during the period May-June-July 2017. The host graph has $\sim$1.3 billion nodes and $\sim$5.3 billion arcs. The PLD graph has $\sim$91 million nodes and $\sim$1.1 billion arcs. We study the distributions of degree and sizes of strongly/weakly connected components (SCC/WCC) focusing on power laws detection using statistical methods. The statistical plausibility of the power law model is compared with that of several alternative distributions. While there is no evidence of power law tails on host level, they emerge on PLD aggregation for indegree, SCC and WCC size distributions. Finally, we analyze distance-related features by studying the cumulative distributions of the shortest path lengths, and give an estimation of the diameters of the graphs

On the graph structure of the Web of Data

This article describes how the Web of Data has emerged as the realization of a machine readable web relying on the resource description framework language as a way to provide richer semantics to datasets. While the web of data is based on similar principles as the original web, being interlinked in the principal mechanism to relate information, the differences in the structure of the information is evident. Several studies have analysed the graph structure of the web, yielding important insights that were used in relevant applications. However, those findings cannot be transposed to the Web of Data, due to fundamental differences in the production, link creation and usage. This article reports on a study of the graph structure of the Web of Data using methods and techniques from similar studies for the Web. Results show that the Web of Data also complies with the theory of the bow-tie. Other characteristics are the low distance between nodes or the closeness and degree centrality are low. Regarding the datasets, the biggest one is Open Data Euskadi but the one with more connections to other datasets is Dbpedia.European Commissio

Distributed Dynamic Hierarchical Task Assignment for Human-Robot Teams

This work implements a joint task architecture for human-robot collaborative task execution using a hierarchical task planner. This architecture allowed humans and robots to work together as teammates in the same environment while following several task constraints. These constraints are 1) sequential order, 2) non-sequential, and 3) alternative execution constraints. Both the robot and the human are aware of each other's current state and allocate their next task based on the task tree. On-table tasks, such as setting up a tea table or playing a color sequence matching game, validate the task architecture. The robot will have an updated task representation of its human teammate's task. Using this knowledge, it is also able to continuously detect the human teammate's intention towards each sub-task and coordinate it with the teammate. While performing a joint task, there can be situations in which tasks overlap or do not overlap. We designed a dialogue-based conversation between humans and robots to resolve conflict in the case of overlapping tasks.Evaluating the human-robot task architecture is the next concern after validating the task architecture. Trust and trustworthiness are some of the most critical metrics to explore. A study was conducted between humans and robots to create a homophily situation. Homophily means when a person feels biased towards another person because of having similarities in social ways. We conducted this study to determine whether humans can form a homophilic relationship with robots and whether there is a connection between homophily and trust. We found a correlation between homophily and trust in human-robot interactions.Furthermore, we designed a pipeline by which the robot learns a task by observing the human teammate's hand movement while conversing. The robot then constructs the tree by itself using a GA learning framework. Thus removing the need for manual specification by a programmer each time to revise or update the task tree which makes the architecture more flexible, realistic, efficient, and dynamic. Additionally, our architecture allows the robot to comprehend the context of a situation by conversing with a human teammate and observing the surroundings. The robot can find a link between the context of the situation and the surrounding objects by using the ontology approach and can perform the desired task accordingly. Therefore, we proposed a human-robot distributed joint task management architecture that addresses design, improvement, and evaluation under multiple constraints

A Framework for the Semantics-aware Modelling of Objects

The evolution of 3D visual content calls for innovative methods for modelling shapes based on their intended usage, function and role in a complex scenario. Even if different attempts have been done in this direction, shape modelling still mainly focuses on geometry. However, 3D models have a structure, given by the arrangement of salient parts, and shape and structure are deeply related to semantics and functionality. Changing geometry without semantic clues may invalidate such functionalities or the meaning of objects or their parts. We approach the problem by considering semantics as the formalised knowledge related to a category of objects; the geometry can vary provided that the semantics is preserved. We represent the semantics and the variable geometry of a class of shapes through the parametric template: an annotated 3D model whose geometry can be deformed provided that some semantic constraints remain satisfied. In this work, we design and develop a framework for the semantics-aware modelling of shapes, offering the user a single application environment where the whole workflow of defining the parametric template and applying semantics-aware deformations can take place. In particular, the system provides tools for the selection and annotation of geometry based on a formalised contextual knowledge; shape analysis methods to derive new knowledge implicitly encoded in the geometry, and possibly enrich the given semantics; a set of constraints that the user can apply to salient parts and a deformation operation that takes into account the semantic constraints and provides an optimal solution. The framework is modular so that new tools can be continuously added. While producing some innovative results in specific areas, the goal of this work is the development of a comprehensive framework combining state of the art techniques and new algorithms, thus enabling the user to conceptualise her/his knowledge and model geometric shapes. The original contributions regard the formalisation of the concept of annotation, with attached properties, and of the relations between significant parts of objects; a new technique for guaranteeing the persistence of annotations after significant changes in shape's resolution; the exploitation of shape descriptors for the extraction of quantitative information and the assessment of shape variability within a class; and the extension of the popular cage-based deformation techniques to include constraints on the allowed displacement of vertices. In this thesis, we report the design and development of the framework as well as results in two application scenarios, namely product design and archaeological reconstruction

A Stochastic Grammar of Images

This exploratory paper quests for a stochastic and context sensitive grammar of images. The grammar should achieve the following four objectives and thus serves as a unified framework of representation, learning, and recognition for a large number of object categories. (i) The grammar represents both the hierarchical decompositions from scenes, to objects, parts, primitives and pixels by terminal and non-terminal nodes and the contexts for spatial and functional relations by horizontal links between the nodes. It formulates each object category as the set of all possible valid configurations produced by the grammar. (ii) The grammar is embodied in a simple And-Or graph representation where each Or-node points to alternative sub-configurations and an And-node is decomposed into a number of components. This representation supports recursive top-down/bottom-up procedures for image parsing under the Bayesian framework and make it convenient to scale up in complexity. Given an input image, the image parsing task constructs a most probable parse graph on-the-fly as the output interpretation and this parse graph is a subgraph of the And-Or graph after making choice on the Or-nodes. (iii) A probabilistic model is defined on this And-Or graph representation to account for the natural occurrence frequency of objects and parts as well as their relations. This model is learned from a relatively small training set per category and then sampled to synthesize a large number of configurations to cover novel object instances in the test set. This generalization capability is mostly missing in discriminative machine learning methods and can largely improve recognition performance in experiments. (iv) To fill the well-known semantic gap between symbols and raw signals, the grammar includes a series of visual dictionaries and organizes them through graph composition. At the bottom-level the dictionary is a set of image primitives each having a number of anchor points with open bonds to link with other primitives. These primitives can be combined to form larger and larger graph structures for parts and objects. The ambiguities in inferring local primitives shall be resolved through top-down computation using larger structures. Finally these primitives forms a primal sketch representation which will generate the input image with every pixels explained. The proposal grammar integrates three prominent representations in the literature: stochastic grammars for composition, Markov (or graphical) models for contexts, and sparse coding with primitives (wavelets). It also combines the structure-based and appearance based methods in the vision literature. Finally the paper presents three case studies to illustrate the proposed grammar.Mathematic

A software based mentor system

This thesis describes the architecture, implementation issues and evaluation of Mentor - an educational support system designed to mentor students in their university studies. Students can ask (by typing) natural language questions and Mentor will use several educational paradigms to present information from its Knowledge Base or from data-mined online Web sites to respond. Typically the questions focus on the student’s assignments or in their preparation for their examinations. Mentor is also pro-active in that it prompts the student with questions such as "Have you started your assignment yet?". If the student responds and enters into a dialogue with Mentor, then, based upon the student’s questions and answers, it guides them through a Directed Learning Path planned by the lecturer, specific to that assessment. The objectives of the research were to determine if such a system could be designed, developed and applied in a large-scale, real-world environment and to determine if the resulting system was beneficial to students using it. The study was significant in that it provided an analysis of the design and implementation of the system as well as a detailed evaluation of its use. This research integrated the Computer Science disciplines of network communication, natural language parsing, user interface design and software agents, together with pedagogies from the Computer Aided Instruction and Intelligent Tutoring System fields of Education. Collectively, these disciplines provide the foundation for the two main thesis research areas of Dialogue Management and Tutorial Dialogue Systems. The development and analysis of the Mentor System required the design and implementation of an easy to use text based interface as well as a hyper- and multi-media graphical user interface, a client-server system, and a dialogue management system based on an extensible kernel. The multi-user Java-based client-server system used Perl-5 Regular Expression pattern matching for Natural Language Parsing along with a state-based Dialogue Manager and a Knowledge Base marked up using the XML-based Virtual Human Markup Language. The kernel was also used in other Dialogue Management applications such as with computer generated Talking Heads. The system also enabled a user to easily program their own knowledge into the Knowledge Base as well as to program new information retrieval or management tasks so that the system could grow with the user. The overall framework to integrate and manage the above components into a usable system employed suitable educational pedagogies that helped in the student’s learning process. The thesis outlines the learning paradigms used in, and summarises the evaluation of, three course-based Case Studies of university students’ perception of the system to see how effective and useful it was, and whether students benefited from using it. This thesis will demonstrate that Mentor met its objectives and was very successful in helping students with their university studies. As one participant indicated: ‘I couldn’t have done without it.

Interactive illumination and navigation control in an image-based environment.

Fu Chi-wing.Thesis (M.Phil.)--Chinese University of Hong Kong, 1999.Includes bibliographical references (leaves 141-149).Abstract --- p.iAcknowledgments --- p.iiiChapter 1 --- Introduction --- p.1Chapter 1.1 --- Introduction to Image-based Rendering --- p.1Chapter 1.2 --- Scene Complexity Independent Property --- p.2Chapter 1.3 --- Application of this Research Work --- p.3Chapter 1.4 --- Organization of this Thesis --- p.4Chapter 2 --- Illumination Control --- p.7Chapter 2.1 --- Introduction --- p.7Chapter 2.2 --- Apparent BRDF of Pixel --- p.8Chapter 2.3 --- Sampling Illumination Information --- p.11Chapter 2.4 --- Re-rendering --- p.13Chapter 2.4.1 --- Light Direction --- p.15Chapter 2.4.2 --- Light Intensity --- p.15Chapter 2.4.3 --- Multiple Light Sources --- p.15Chapter 2.4.4 --- Type of Light Sources --- p.18Chapter 2.5 --- Data Compression --- p.22Chapter 2.5.1 --- Intra-pixel coherence --- p.22Chapter 2.5.2 --- Inter-pixel coherence --- p.22Chapter 2.6 --- Implementation and Result --- p.22Chapter 2.6.1 --- An Interactive Viewer --- p.22Chapter 2.6.2 --- Lazy Re-rendering --- p.24Chapter 2.7 --- Conclusion --- p.24Chapter 3 --- Navigation Control - Triangle-based Warping Rule --- p.29Chapter 3.1 --- Introduction to Navigation Control --- p.29Chapter 3.2 --- Related Works --- p.30Chapter 3.3 --- Epipolar Geometry (Perspective Projection Manifold) --- p.31Chapter 3.4 --- Drawing Order for Pixel-Sized Entities --- p.35Chapter 3.5 --- Triangle-based Image Warping --- p.36Chapter 3.5.1 --- Image-based Triangulation --- p.36Chapter 3.5.2 --- Image-based Visibility Sorting --- p.40Chapter 3.5.3 --- Topological Sorting --- p.44Chapter 3.6 --- Results --- p.46Chapter 3.7 --- Conclusion --- p.48Chapter 4 --- Panoramic Projection Manifold --- p.52Chapter 4.1 --- Epipolar Geometry (Spherical Projection Manifold) --- p.53Chapter 4.2 --- Image Triangulation --- p.56Chapter 4.2.1 --- Optical Flow --- p.56Chapter 4.2.2 --- Image Gradient and Potential Function --- p.57Chapter 4.2.3 --- Triangulation --- p.58Chapter 4.3 --- Image-based Visibility Sorting --- p.58Chapter 4.3.1 --- Mapping Criteria --- p.58Chapter 4.3.2 --- Ordering of Two Triangles --- p.59Chapter 4.3.3 --- Graph Construction and Topological Sort --- p.63Chapter 4.4 --- Results --- p.63Chapter 4.5 --- Conclusion --- p.65Chapter 5 --- Panoramic-based Navigation using Real Photos --- p.69Chapter 5.1 --- Introduction --- p.69Chapter 5.2 --- System Overview --- p.71Chapter 5.3 --- Correspondence Matching --- p.72Chapter 5.3.1 --- Basic Model of Epipolar Geometry --- p.72Chapter 5.3.2 --- Epipolar Geometry between two Neighbor Panoramic Nodes --- p.73Chapter 5.3.3 --- Line and Patch Correspondence Matching --- p.74Chapter 5.4 --- Triangle-based Warping --- p.75Chapter 5.4.1 --- Why Warp Triangle --- p.75Chapter 5.4.2 --- Patch and Layer Construction --- p.76Chapter 5.4.3 --- Triangulation and Mesh Subdivision --- p.76Chapter 5.4.4 --- Layered Triangle-based Warping --- p.77Chapter 5.5 --- Implementation --- p.78Chapter 5.5.1 --- Image Sampler and Panoramic Stitcher --- p.78Chapter 5.5.2 --- Interactive Correspondence Matcher and Triangulation --- p.79Chapter 5.5.3 --- Basic Panoramic Viewer --- p.79Chapter 5.5.4 --- Formulating Drag Vector and vn --- p.80Chapter 5.5.5 --- Controlling Walkthrough Parameter --- p.82Chapter 5.5.6 --- Interactive Web-based Panoramic Viewer --- p.83Chapter 5.6 --- Results --- p.84Chapter 5.7 --- Conclusion and Possible Enhancements --- p.84Chapter 6 --- Compositing Warped Images for Object-based Viewing --- p.89Chapter 6.1 --- Modeling Object-based Viewing --- p.89Chapter 6.2 --- Triangulation and Convex Hull Criteria --- p.92Chapter 6.3 --- Warping Multiple Views --- p.94Chapter 6.3.1 --- Method I --- p.95Chapter 6.3.2 --- Method II --- p.95Chapter 6.3.3 --- Method III --- p.95Chapter 6.4 --- Results --- p.97Chapter 6.5 --- Conclusion --- p.100Chapter 7 --- Complete Rendering Pipeline --- p.107Chapter 7.1 --- Reviews on Illumination and Navigation --- p.107Chapter 7.1.1 --- Illumination Rendering Pipeline --- p.107Chapter 7.1.2 --- Navigation Rendering Pipeline --- p.108Chapter 7.2 --- Analysis of the Two Rendering Pipelines --- p.109Chapter 7.2.1 --- Combination on the Architectural Level --- p.109Chapter 7.2.2 --- Ensuring Physical Correctness --- p.111Chapter 7.3 --- Generalizing Apparent BRDF --- p.112Chapter 7.3.1 --- Difficulties to Encode BRDF with Spherical Harmonics --- p.112Chapter 7.3.2 --- Generalize Apparent BRDF --- p.112Chapter 7.3.3 --- Related works for Encoding the generalized apparent BRDF --- p.113Chapter 7.4 --- Conclusion --- p.116Chapter 8 --- Conclusion --- p.117Chapter A --- Spherical Harmonics --- p.120Chapter B --- It is Rare for Cycles to Exist in the Drawing Order Graph --- p.123Chapter B.1 --- Theorem 3 --- p.123Chapter B.2 --- Inside and Outside-directed Triangles in a Triangular Cycle --- p.125Chapter B.2.1 --- Assumption --- p.126Chapter B.2.2 --- Inside-directed and Outside-directed triangles --- p.126Chapter B.3 --- Four Possible Cases to Form a Cycle --- p.127Chapter B.3.1 --- Case(l) Triangular Fan --- p.128Chapter B.3.2 --- Case(2) Two Outside-directed Triangles --- p.129Chapter B.3.3 --- Case(3) Three Outside-directed Triangles --- p.130Chapter B.3.4 --- Case(4) More than Three Outside-directed Triangles --- p.131Chapter B.4 --- Experiment --- p.132Chapter C --- Deriving the Epipolar Line Formula on Cylindrical Projection Manifold --- p.133Chapter C.1 --- Notations --- p.133Chapter C.2 --- General Formula --- p.134Chapter C.3 --- Simplify the General Formula to a Sine Curve --- p.137Chapter C.4 --- Show that the Epipolar Line is a Sine Curve Segment --- p.139Chapter D --- Publications Related to this Research Work --- p.141Bibliography --- p.14

THE REALISM OF ALGORITHMIC HUMAN FIGURES A Study of Selected Examples 1964 to 2001

It is more than forty years since the first wireframe images of the Boeing Man revealed a stylized hu-man pilot in a simulated pilot's cabin. Since then, it has almost become standard to include scenes in Hollywood movies which incorporate virtual human actors. A trait particularly recognizable in the games industry world-wide is the eagerness to render athletic muscular young men, and young women with hour-glass body-shapes, to traverse dangerous cyberworlds as invincible heroic figures. Tremendous efforts in algorithmic modeling, animation and rendering are spent to produce a realistic and believable appearance of these algorithmic humans. This thesis develops two main strands of research by the interpreting a selection of examples. Firstly, in the computer graphics context, over the forty years, it documents the development of the creation of the naturalistic appearance of images (usually called photorealism ). In particular, it de-scribes and reviews the impact of key algorithms in the course of the journey of the algorithmic human figures towards realism . Secondly, taking a historical perspective, this work provides an analysis of computer graphics in relation to the concept of realism. A comparison of realistic images of human figures throughout history with their algorithmically-generated counterparts allows us to see that computer graphics has both learned from previous and contemporary art movements such as photorealism but also taken out-of-context elements, symbols and properties from these art movements with a questionable naivety. Therefore, this work also offers a critique of the justification of the use of their typical conceptualization in computer graphics. Although the astounding technical achievements in the field of algorithmically-generated human figures are paralleled by an equally astounding disregard for the history of visual culture, from the beginning 1964 till the breakthrough 2001, in the period of the digital information processing machine, a new approach has emerged to meet the apparently incessant desire of humans to create artificial counterparts of themselves. Conversely, the theories of traditional realism have to be extended to include new problems that those active algorithmic human figures present