Guide Me in Analysis: A Framework for Guidance Designers

Guidance is an emerging topic in the field of visual analytics. Guidance can support users in pursuing their analytical goals more efficiently and help in making the analysis successful. However, it is not clear how guidance approaches should be designed and what specific factors should be considered for effective support. In this paper, we approach this problem from the perspective of guidance designers. We present a framework comprising requirements and a set of specific phases designers should go through when designing guidance for visual analytics. We relate this process with a set of quality criteria we aim to support with our framework, that are necessary for obtaining a suitable and effective guidance solution. To demonstrate the practical usability of our methodology, we apply our framework to the design of guidance in three analysis scenarios and a design walk-through session. Moreover, we list the emerging challenges and report how the framework can be used to design guidance solutions that mitigate these issues

Molybdenum trioxide thin films for infrared Photonics

Alpha-phase molybdenum trioxide (-MoO3) has attracted in-creasing attention in recent years due to its exciting physical properties which offer new opportunities for realizing Photonic devices with enhanced or novel functionalities. In fact, besides its strong anisotropy related to optical phonons, which allows polarization control and rotation, MoO3 supports strong field lo-calization by the excitation of surface waves called surface phonon polaritons (SPhPs), achieved through the coupling of the electromagnetic field with lattice vibrations. In this work we report on fabrication and structural, morphological, and optical characterization of polycrystalline -MoO3 thin films synthesized by pulsed laser deposition at 400 °C. Raman spectroscopy measurements re-vealed the polycrystalline single α-phase nature of the deposited MoO3 films, while scanning electron microscope analysis showed a random grain distribu-tion, which prevents optical anisotropy at normal incidence. Moreover, optical measurements in the mid-infrared showed an enhanced polarization-tuneable reflection peak at 1005 cm−1 both in amplitude and frequency, and a polariza-tion-independent perfect absorption behaviour at 979 cm−1, when 15° angular incidence is used. These interesting spectral properties, not least having pre-served the typical strong dispersion related to the phononic response of α-MoO3 flakes, indicate that pulsed laser deposition is a valuable technique to obtain large area and good quality α-MoO3 thin films for infrared Photonic applica-tions, including mid-infrared metamaterial devices for sensing applications

Interactive Visual Labelling versus Active Learning: An Experimental Comparison

Methods from supervised machine learning allow the classification of new data automatically and are tremendously helpful for data analysis. The quality of supervised maching learning depends not only on the type of algorithm used, but also on the quality of the labelled dataset used to train the classifier. Labelling instances in a training dataset is often done manually relying on selections and annotations by expert analysts, and is often a tedious and time-consuming process. Active learning algorithms can automatically determine a subset of data instances for which labels would provide useful input to the learning process. Interactive visual labelling techniques are a promising alternative, providing effective visual overviews from which an analyst can simultaneously explore data records and select items to a label. By putting the analyst in the loop, higher accuracy can be achieved in the resulting classifier. While initial results of interactive visual labelling techniques are promising in the sense that user labelling can improve supervised learning, many aspects of these techniques are still largely unexplored. This paper presents a study conducted using the mVis tool to compare three interactive visualisations, similarity map, scatterplot matrix (SPLOM), and parallel coordinates, with each other and with active learning for the purpose of labelling a multivariate dataset. The results show that all three interactive visual labelling techniques surpass active learning algorithms in terms of classifier accuracy, and that users subjectively prefer the similarity map over SPLOM and parallel coordinates for labelling. Users also employ different labelling strategies depending on the visualisation used

ConAn: Measuring and Evaluating User Confidence in Visual Data Analysis Under Uncertainty

User confidence plays an important role in guided visual data analysis scenarios, especially when uncertainty is involved in the analytical process. However, measuring confidence in practical scenarios remains an open challenge, as previous work relies primarily on self‐reporting methods. In this work, we propose a quantitative approach to measure user confidence—as opposed to trust—in an analytical scenario. We do so by exploiting the respective user interaction provenance graph and examining the impact of guidance using a set of network metrics. We assess the usefulness of our proposed metrics through a user study that correlates results obtained from self‐reported confidence assessments and our metrics—both with and without guidance. The results suggest that our metrics improve the evaluation of user confidence compared to available approaches. In particular, we found a correlation between self‐reported confidence and some of the proposed provenance network metrics. The quantitative results, though, do not show a statistically significant impact of the guidance on user confidence. An additional descriptive analysis suggests that guidance could impact users' confidence and that the qualitative analysis of the provenance network topology can provide a comprehensive view of changes in user confidence. Our results indicate that our proposed metrics and the provenance network graph representation support the evaluation of user confidence and, subsequently, the effective development of guidance in VA.Computer Graphics ForumOriginal Article44

Tuning of the Berreman mode of GaN/AlxGa1-xN heterostructures on sapphire: The role of the 2D-electron gas in the mid-infrared

We investigated the mid-infrared optical properties of GaN/Al(x)Ga(1-x)N-type heterostructures on sapphire substrate grown by the Metal-Organic Chemical Vapor Deposition. We show how the polarization-dependent reflection spectrum is affected by the presence of the strain-induced 2D electron gas at the interfaces between Al(x)Ga(1-x)N and GaN layers. In particular, we show that the 2D electron gas contribution, modeled from its density and transport properties, can play a relevant role at the Berreman mode excitation condition. In this framework, our results offer an advanced approach for the optimization and design of GaN-based broadband optoelectronic and energy management devices

W-doped vanadium dioxide films by pulsed laser deposition for IR Photonics

The semiconductor-to-metal phase transition exhibited by vanadium dioxide at the critical temperature of 68 °C, enables reversible changes in its optical and electrical properties. Moreover, the possibility to modify the transition temperature by introducing dopants within the VO2 crystal, allows a temperature tunability of all these properties, making this phase change material very appealing for active, dynamic, tunable Photonic applications. In this work we report on fabrication and structural, morphological, and optical characterization of tungsten (W)-doped VO2 thin films synthesized by pulsed laser deposition, a technique which allows a unique versatility to obtain W-doped VO2 films using custom made VO2 targets with different amounts of W. Results show that appropriate W-doping leads to VO2 thin films with tunable and controllable perfect IR absorption, paving the way to the development of promising thermooptical devices including infrared filters, radiative cooling devices, and thermal emitters. Furthermore, by varying the amount of W, tailored infrared phonon and plasmon polaritonic responses at room temperature can be obtained, allowing then the realization of VO2 films with a given degree of semiconducting/metallic behaviour, exploitable for the realization of tunable midinfrared metamaterial devices operating at room temperature