Under drought conditions, the xylem of trees that conducts ascending sap produces ultrasonic emissions whose exact origin is not clear. We introduce a new method to record simultaneously both ...acoustic events and optical observation of the xylem conduits within slices of wood that were embedded in a transparent material setting a hydric stress. In this article, we resolved the rapid development of all cavitation bubbles and demonstrated that each ultrasound emission was linked to the nucleation of one single bubble, whose acoustic energy is an increasing function of the size of the conduit where nucleation occurred and also of the hydric stress. We modelled these observations by the fact that water columns in conduits store elastic energy and release it into acoustic waves when they are broken by cavitation bubbles. Water columns are thus elastic, and not rigid, ‘wires of water’ set under tension by hydric stresses. Cavitation bubbles are at the origin of an embolism, whose development was followed in our experiments. Such an embolism of sap circulation can result in a fatal condition for living trees. These findings provide new insights for the non-destructive monitoring of embolisms within trees, and suggest a new approach to study porous media under hydric stress.
Identifying, tracking and understanding changes in dynamic networks are complex and cognitively demanding tasks. We present GraphDiaries, a visual interface designed to improve support for these ...tasks in any node-link based graph visualization system. GraphDiaries relies on animated transitions that highlight changes in the network between time steps, thus helping users identify and understand those changes. To better understand the tasks related to the exploration of dynamic networks, we first introduce a task taxonomy, that informs the design of GraphDiaries, presented afterwards. We then report on a user study, based on representative tasks identified through the taxonomy, and that compares GraphDiaries to existing techniques for temporal navigation in dynamic networks, showing that it outperforms them in terms of both task time and errors for several of these tasks.
Identifying, tracking and understanding changes in dynamic networks are complex and cognitively demanding tasks. We present GraphDiaries, a visual interface designed to improve support for these ...tasks in any node-link based graph visualization system. GraphDiaries relies on animated transitions that highlight changes in the network between time steps, thus helping users identify and understand those changes. To better understand the tasks related to the exploration of dynamic networks, we first introduce a task taxonomy, that informs the design of GraphDiaries, presented afterwards. We then report on a user study, based on representative tasks identified through the taxonomy, and that compares GraphDiaries to existing techniques for temporal navigation in dynamic networks, showing that it outperforms them in terms of both task time and errors for several of these tasks.
Spreadsheet programs for interactive surfaces have limited manipulations capabilities and are often frustrating to use. One key reason is that the spreadsheet grid creates a layer that intercepts ...most user input events, making it difficult to reach the cell values that lie underneath. We conduct an analysis of commercial spreadsheet programs and an elicitation study to understand what users can do and what they would like to do with spreadsheets on interactive surfaces. Informed by these, we design interaction techniques that leverage the precision of the pen to mitigate friction between the different layers. These enable more operations by direct manipulation on and through the grid, targeting not only cells and groups of cells, but values and substrings within and across cells as well. We prototype these interaction techniques and conduct a qualitative study with information workers who perform a variety of spreadsheet operations on their own data.
Expressive Authoring of Node-Link Diagrams With Graphies Romat, Hugo; Appert, Caroline; Pietriga, Emmanuel
IEEE transactions on visualization and computer graphics,
2021-April-1, 2021-Apr, 2021-4-1, 20210401, 2021-04-01, Letnik:
27, Številka:
4
Journal Article
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Expressive design environments enable visualization designers not only to specify chart types and visual mappings, but also to customize individual graphical marks, as they would in a vector graphics ...drawing tool. Prior work has mainly investigated how to support the expressive design of a wide range of charts generated from tabular data: bar charts, scatterplots, maps, etc. We focus here on an expressive design environment for node-link diagrams generated from multivariate networks. Such data structures raise specific challenges and opportunities in terms of visual design and interactive authoring. We discuss those specificities and describe the user-centered design process that led to Graphies, a prototype environment for expressive node-link diagram authoring. We then report on a study in which participants successfully reproduced several expressive designs, and created their own designs as well.
Visual representations of time-series are useful for tasks such as identifying trends, patterns and anomalies in the data. Many techniques have been devised to make these visual representations more ...scalable, enabling the simultaneous display of multiple variables, as well as the multi-scale display of time-series of very high resolution or that span long time periods. There has been comparatively little research on how to support the more elaborate tasks associated with the exploratory visual analysis of timeseries, e.g., visualizing derived values, identifying correlations, or discovering anomalies beyond obvious outliers. Such tasks typically require deriving new time-series from the original data, trying different functions and parameters in an iterative manner. We introduce a novel visualization technique called ChronoLenses, aimed at supporting users in such exploratory tasks. ChronoLenses perform on-the-fly transformation of the data points in their focus area, tightly integrating visual analysis with user actions, and enabling the progressive construction of advanced visual analysis pipelines.
Ultra-high resolution wall-sized displays (“ultra-walls”) are effective for presenting large datasets, but their size and resolution make traditional pointing techniques inadequate for precision ...pointing. We study mid-air pointing techniques that can be combined with other, domain-specific interactions. We first explore the limits of existing single-mode remote pointing techniques and demonstrate theoretically that they do not support high-precision pointing on ultra-walls. We then explore solutions to improve mid-air pointing efficiency: a tunable acceleration function and a framework for dual-precision (DP) techniques, both with precise tuning guidelines. We designed novel pointing techniques following these guidelines, several of which outperform existing techniques in controlled experiments that involve pointing difficulties never tested prior to this work. We discuss the strengths and weaknesses of our techniques to help interaction designers choose the best technique according to the task and equipment at hand. Finally, we discuss the cognitive mechanisms that affect pointing performance with these techniques.
Observing the relationship between two or more variables over space and time is essential in many domains. For instance, looking, for different countries, at the evolution of both the life expectancy ...at birth and the fertility rate will give an overview of their demographics. The choice of visual representation for such multivariate data is key to enabling analysts to extract patterns and trends. Prior work has compared geo-temporal visualization techniques for a single thematic variable that evolves over space and time, or for two variables at a specific point in time. But how effective visualization techniques are at communicating correlation between two variables that evolve over space and time remains to be investigated. We report on a study comparing three techniques that are representative of different strategies to visualize geo-temporal multivariate data: either juxtaposing all locations for a given time step, or juxtaposing all time steps for a given location; and encoding thematic attributes either using symbols overlaid on top of map features, or using visual channels of the map features themselves. Participants performed a series of tasks that required them to identify if two variables were correlated over time and if there was a pattern in their evolution. Tasks varied in granularity for both dimensions: time (all time steps, a subrange of steps, one step only) and space (all locations, locations in a subregion, one location only). Our results show that a visualization's effectiveness depends strongly on the task to be carried out. Based on these findings we present a set of design guidelines about geo-temporal visualization techniques for communicating correlation.
We present the design and evaluation of HyperStorylines, a technique that generalizes Storylines to visualize the evolution of relationships involving multiple types of entities such as, for example, ...people, locations, and companies. Datasets which describe such multi-entity relationships are often modeled as hypergraphs, that can be difficult to visualize, especially when these relationships evolve over time. HyperStorylines builds upon Storylines, enabling the aggregation and nesting of these dynamic, multi-entity relationships. We report on the design process of HyperStorylines, which was informed by discussions and workshops with data journalists; and on the results of a comparative study in which participants had to answer questions inspired by the tasks that journalists typically perform with such data. We observe that although HyperStorylines takes some practice to master, it performs better for identifying and characterizing relationships than the selected baseline visualization (PAOHVis) and was preferred overall.
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