Shapes in vector fields : methods for continuous deformations and surface-based flow visualizations

Magdeburg, Univ., Fak. für Informatik, Diss., 2013

Perception-guided evaluation of 3D medical visualizations

Magdeburg, Univ., Fak. für Informatik, Diss., 2015

Promoting Programming Learning. Engagement, Automatic Assessment with Immediate Feedback in Visualizations

The skill of programming is a key asset for every computer science student. Many studies have shown that this is a hard skill to learn and the outcomes of programming courses have often been substandard. Thus, a range of methods and tools have been developed to assist students’ learning processes. One of the biggest fields in computer science education is the use of visualizations as a learning aid and many visualization based tools have been developed to aid the learning process during last few decades. Studies conducted in this thesis focus on two different visualizationbased tools TRAKLA2 and ViLLE. This thesis includes results from multiple empirical studies about what kind of effects the introduction and usage of these tools have on students’ opinions and performance, and what kind of implications there are from a teacher’s point of view. The results from studies in this thesis show that students preferred to do web-based exercises, and felt that those exercises contributed to their learning. The usage of the tool motivated students to work harder during their course, which was shown in overall course performance and drop-out statistics. We have also shown that visualization-based tools can be used to enhance the learning process, and one of the key factors is the higher and active level of engagement (see. Engagement Taxonomy by Naps et al., 2002). The automatic grading accompanied with immediate feedback helps students to overcome obstacles during the learning process, and to grasp the key element in the learning task. These kinds of tools can help us to cope with the fact that many programming courses are overcrowded with limited teaching resources. These tools allows us to tackle this problem by utilizing automatic assessment in exercises that are most suitable to be done in the web (like tracing and simulation) since its supports students’ independent learning regardless of time and place. In summary, we can use our course’s resources more efficiently to increase the quality of the learning experience of the students and the teaching experience of the teacher, and even increase performance of the students. There are also methodological results from this thesis which contribute to developing insight into the conduct of empirical evaluations of new tools or techniques. When we evaluate a new tool, especially one accompanied with visualization, we need to give a proper introduction to it and to the graphical notation used by tool. The standard procedure should also include capturing the screen with audio to confirm that the participants of the experiment are doing what they are supposed to do. By taken such measures in the study of the learning impact of visualization support for learning, we can avoid drawing false conclusion from our experiments. As computer science educators, we face two important challenges. Firstly, we need to start to deliver the message in our own institution and all over the world about the new – scientifically proven – innovations in teaching like TRAKLA2 and ViLLE. Secondly, we have the relevant experience of conducting teaching related experiment, and thus we can support our colleagues to learn essential know-how of the research based improvement of their teaching. This change can transform academic teaching into publications and by utilizing this approach we can significantly increase the adoption of the new tools and techniques, and overall increase the knowledge of best-practices. In future, we need to combine our forces and tackle these universal and common problems together by creating multi-national and multiinstitutional research projects. We need to create a community and a platform in which we can share these best practices and at the same time conduct multi-national research projects easily.

The role of visualizations in urban forestry. Conclusions from managers’ perspectives

La presente tesis examina el uso potencial y actual de las técnicas de simulación visual aplicadas al campo de la gestión y la planificación del arbolado urbano. El estudio incluye las aplicaciones potenciales de las visualizaciones por ordenador, así como los beneficios que esto acarrearía. También se analizan las posibles barreras que surgirían de la implementación de esta nueva herramienta y se ofrece una lista de recomendaciones para superarlas. La investigación tiene un carácter exploratorio que utiliza una combinación de técnicas de investigación cuantitativas y cualitativas, dónde se emplean cuestionarios y entrevistas personales semi-estructuradas para estudiar y analizar las opiniones y reacciones de los gestores de arbolado urbano de los distritos de la ciudad de Londres (Reino Unido), denominados Tree Officers (LTOs). Para el desarrollo de la tesis se recopilaron y analizaron las respuestas al cuestionario del 41 por ciento de los LTOs pertenecientes al 88 por ciento de los distritos de Londres y se realizaron un total de 17 entrevistas personales. Los resultados del análisis estadístico de las respuestas del cuestionario y los análisis cruzados de las distintas variables se complementaron con las conclusiones obtenidas del análisis temático de los datos cualitativos recopilados durante las entrevistas. Los usos potenciales de las técnicas de simulación visual aplicadas a la gestión y planificación del arbolado urbano sugeridos fueron obtenidos combinado las conclusiones de, primero, la comparación de las cuestiones que los LTOs consideraron que más tiempo y recursos necesitaban y que actualmente no era posible resolverlas satisfactoriamente con las herramientas y los procesos disponibles, con la información acerca de cómo se habían empleado las visualizaciones en situaciones similares en otros campos tales como planificación urbano, el paisajismo o la gestión forestal. Segundo, se analizaron las reacciones y opiniones de los LTOs ante un conjunto de visualizaciones presentadas durante las entrevistas, desarrolladas ad hoc para mostrar un abanico representativo de ejemplos de utilización de las técnicas de simulación visual, que, a su vez se complementaron con los usos adicionales que los propios LTOs sugirieron tras ver las visualizaciones presentadas. Los resultados muestran que el uso actual de simulaciones visuales por parte de los LTOs es muy limitado pero si que reciben un gran número de visualizaciones de otros departamentos y como parte de la documentación presentada en las solicitudes de permisos para edificación o desarrollo urbanístico. Los resultados indican que las visualizaciones que son presentadas a los LTOs no son objetivas ni precisas por lo que se argumenta que esta situación es un factor importante que impide una toma de decisiones adecuada y una correcta transmisión de infracción al público y al resto de partes implicadas. Se sugiere la creación de un código que regule el uso de visualizaciones en el campo de la gestión y planificación del arbolado urbano. ABSTRACT This thesis examined the use of computer visualizations in urban forestry management and planning. Potential roles of visualizations were determined the benefits that its use would provide. Additionally, the possible barriers in the implementation of visualizations in urban forestry management and planning were also studied and recommendations on how to overcome them were provided The research conducted was an exploratory study using survey research methods and personal semi-structured interviews. The perspectives and reactions of London (UK) boroughs’ tree officers (LTOs) were analysed combining quantitative and qualitative research methods. The study surveyed 41 percent of all Tree Officers in London, obtaining responses from 88 percent of the boroughs and performed 17 personal interviews. Statistical analysis of the data and cross-variables analysis provided rich information that was then complemented with the conclusions from thematic analysis of the qualitative data from the interviews. Potential roles of visualizations were determined first by understanding the challenges that LTOs are facing today and comparing them with how visualizations have helped in similar situations in urban forestry and other related fields like landscape architecture, urban planning and forestry; second, the reactions of LTOs to a set of examples of proposed uses of visualizations were also complemented with the additional uses proposed by LTOs after seeing the visualizations. The visualizations were created ad hoc to show a variety of representative examples of the sue of visualization in urban forestry management and planning and were presented during the interviews to LTOS. Results show that the current production of visualizations is very reduced among tree officers but that they are frequent receptors of visualizations coming from other departments and as part of the documentation of planning applications. Findings show that the current visualizations that get to Tree Officers are biased and inaccurate and therefore it is argued the the current use of visualizations is a threat to legitimate informed decision making and public information. The development of a code for the use of visualizations in urban forestry management and planning is suggested.

Pervasive Software Visualizations

A picture tells a thousand words. We all know that. Then why are our development tools showing mainly text with so much obstinacy? Even when visualizations do make it into our tools, they typically do not make it past the periphery. Something is deeply wrong. We argue that visualizations must become pervasive in software development, and to accommodate this goal, the integrated development environments must change significantly.

Experimental characterization of wingtip vortices using smoke flow visualizations

In order to predict the axial development of the wingtip vortices strength an accurate theoretical model is required. Several experimental techniques have been used to that end, e.g. PIV or hotwire anemometry, but they imply a significant cost and effort. For this reason, we have carried out experiments using the smoke-wire technique to visualize smoke streaks in six planes perpendicular to the main stream flow direction. Using this visualization technique, we obtained quantitative information regarding the vortex velocity field by means of Batchelor's model~\cite{batchelor}, which only depends on two free parameters, i.e. the vortex strength, $S$, and the virtual origin, $z_0$. Results for two chord based Reynolds numbers have been compared with those provided by del Pino et at. (2011), finding good agreement.

Visibility of the mandibular canal on CBCT crosssectional images

The identification of the mandibular canal (MC) is an important prerequisite for surgical procedures involving the posterior mandible. Cone beam computed tomography (CBCT) represents an advance in imaging technology, but distinguishing the MC from surrounding structures may remain a delicate task. OBJECTIVES: The aim of this study was to assess the visibility of the MC in different regions on CBCT cross-sectional images. MATERIAL AND METHODS: CBCT cross-sectional images of 58 patients (116 hemi-mandibles) were analyzed, and the visibility of the MC in different regions was assessed. RESULTS: The MC was clearly visible in 53% of the hemi-mandibles. Difficult and very difficult visualizations were registered in 25% and 22% of the hemi-mandibles, respectively. The visibility of the MC on distal regions was superior when compared to regions closer to the mental foramen. No differences were found between edentulous and tooth-bearing areas. CONCLUSIONS: The MC presents an overall satisfactory visibility on CBCT cross-sectional images in most cases. However, the discrimination of the canal from its surrounds becomes less obvious towards the mental foramen region when cross-sectional images are individually analyzed.

Integration and visualization of systems biology data in context of the genome

Background: High-density tiling arrays and new sequencing technologies are generating rapidly increasing volumes of transcriptome and protein-DNA interaction data. Visualization and exploration of this data is critical to understanding the regulatory logic encoded in the genome by which the cell dynamically affects its physiology and interacts with its environment. Results: The Gaggle Genome Browser is a cross-platform desktop program for interactively visualizing high-throughput data in the context of the genome. Important features include dynamic panning and zooming, keyword search and open interoperability through the Gaggle framework. Users may bookmark locations on the genome with descriptive annotations and share these bookmarks with other users. The program handles large sets of user-generated data using an in-process database and leverages the facilities of SQL and the R environment for importing and manipulating data. A key aspect of the Gaggle Genome Browser is interoperability. By connecting to the Gaggle framework, the genome browser joins a suite of interconnected bioinformatics tools for analysis and visualization with connectivity to major public repositories of sequences, interactions and pathways. To this flexible environment for exploring and combining data, the Gaggle Genome Browser adds the ability to visualize diverse types of data in relation to its coordinates on the genome. Conclusions: Genomic coordinates function as a common key by which disparate biological data types can be related to one another. In the Gaggle Genome Browser, heterogeneous data are joined by their location on the genome to create information-rich visualizations yielding insight into genome organization, transcription and its regulation and, ultimately, a better understanding of the mechanisms that enable the cell to dynamically respond to its environment.

Evaluation of flow patterns and elongated bubble characteristics during the flow boiling of halocarbon refrigerants in a micro-scale channel

In the present study, quasi-diabatic two-phase flow pattern visualizations and measurements of elongated bubble velocity, frequency and length were performed. The tests were run for R134a and R245fa evaporating in a stainless steel tube with diameter of 2.32 mm, mass velocities ranging from 50 to 600 kg/m(2) s and saturation temperatures of 22 degrees C, 31 degrees C and 41 degrees C. The tube was heated by applying a direct DC current to its surface. Images from a high-speed video-camera (8000 frames/s) obtained through a transparent tube just downstream the heated sections were used to identify the following flow patterns: bubbly, elongated bubbles, churn and annular flows. The visualized flow patterns were compared against the predictions provided by Barnea et al. (1983) [1], Felcar et al. (2007) [10], Revellin and Thome (2007) [3] and Ong and Thome (2009) [11]. From this comparison, it was found that the methods proposed by Felcar et al. (2007) [10] and Ong and Thome (2009) [1] predicted relatively well the present database. Additionally, elongated bubble velocities, frequencies and lengths were determined based on the analysis of high-speed videos. Results suggested that the elongated bubble velocity depends on mass velocity, vapor quality and saturation temperature. The bubble velocity increases with increasing mass velocity and vapor quality and decreases with increasing saturation temperature. Additionally, bubble velocity was correlated as linear functions of the two-phase superficial velocity. (C) 2010 Elsevier Inc. All rights reserved.

Investigation of Normal Force and Moment Coefficients for an AUV at Nonlinear Angle of Attack and Sideslip Range

This paper presents a comparative study of computational fluid dynamics (CFD) and analytical and semiempirical (ASE) methods applied to the prediction of the normal force and moment coefficients of an autonomous underwater vehicle (AUV). Both methods are applied to the. bare hull of the vehicle and to the body-hydroplane combination. The results are validated through experiments in a towing tank. It is shown that the CFD approach allows for a good prediction of the coefficients over the range of angles of attack considered. In contrast with the traditional ASE formulations used in naval and aircraft fields, an improved methodology is introduced that takes advantage of the qualitative information obtained from CFD flow visualizations.

Using multidimensional projection techniques for reaching a high distinguishing ability in biosensing

Recent advances in the control of molecular engineering architectures have allowed unprecedented ability of molecular recognition in biosensing, with a promising impact for clinical diagnosis and environment control. The availability of large amounts of data from electrical, optical, or electrochemical measurements requires, however, sophisticated data treatment in order to optimize sensing performance. In this study, we show how an information visualization system based on projections, referred to as Projection Explorer (PEx), can be used to achieve high performance for biosensors made with nanostructured films containing immobilized antigens. As a proof of concept, various visualizations were obtained with impedance spectroscopy data from an array of sensors whose electrical response could be specific toward a given antibody (analyte) owing to molecular recognition processes. In addition to discussing the distinct methods for projection and normalization of the data, we demonstrate that an excellent distinction can be made between real samples tested positive for Chagas disease and Leishmaniasis, which could not be achieved with conventional statistical methods. Such high performance probably arose from the possibility of treating the data in the whole frequency range. Through a systematic analysis, it was inferred that Sammon`s mapping with standardization to normalize the data gives the best results, where distinction could be made of blood serum samples containing 10(-7) mg/mL of the antibody. The method inherent in PEx and the procedures for analyzing the impedance data are entirely generic and can be extended to optimize any type of sensor or biosensor.

Multi-dimensional scaling applied to histogram-based DNA analysis

This paper aims to study the relationships between chromosomal DNA sequences of twenty species. We propose a methodology combining DNA-based word frequency histograms, correlation methods, and an MDS technique to visualize structural information underlying chromosomes (CRs) and species. Four statistical measures are tested (Minkowski, Cosine, Pearson product-moment, and Kendall τ rank correlations) to analyze the information content of 421 nuclear CRs from twenty species. The proposed methodology is built on mathematical tools and allows the analysis and visualization of very large amounts of stream data, like DNA sequences, with almost no assumptions other than the predefined DNA “word length.” This methodology is able to produce comprehensible three-dimensional visualizations of CR clustering and related spatial and structural patterns. The results of the four test correlation scenarios show that the high-level information clusterings produced by the MDS tool are qualitatively similar, with small variations due to each correlation method characteristics, and that the clusterings are a consequence of the input data and not method’s artifacts.