Residence time distribution of gas flows in microreactors: Measurement and model comparison

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.The optimization of microreactor designs for applications in chemical process engineering usually requires knowledge of the residence time distribution (RTD). The applicability of established models to microstructured reactors is currently under debate (Bošković et al. 2008, Günther et al. 2004, Stief et al. 2008). This work provides new experimental data on the residence time distributions of gas flows through different types of microstructured reactors and analyses the data with established RTD models. By this, the dispersion model was found to describe the RTD behavior of gas flow for a majority of the microstructured devices tested. The model could therefore be used to predict the RTD of those reactors.German Federal Ministry of Economics and Technology (IGF Project 15495

The importance of postural cues for determining eye height in immersive virtual reality

In human perception, the ability to determine eye height is essential, because eye height is used to scale heights of objects, velocities, affordances and distances, all of which allow for successful environmental interaction. It is well understood that eye height is fundamental to determine many of these percepts. Yet, how eye height itself is provided is still largely unknown. While the information potentially specifying eye height in the real world is naturally coincident in an environment with a regular ground surface, these sources of information can be easily divergent in similar and common virtual reality scenarios. Thus, we conducted virtual reality experiments where we manipulated the virtual eye height in a distance perception task to investigate how eye height might be determined in such a scenario. We found that humans rely more on their postural cues for determining their eye height if there is a conflict between visual and postural information and little opportunity for perceptual-motor calibration is provided. This is demonstrated by the predictable variations in their distance estimates. Our results suggest that the eye height in such circumstances is informed by postural cues when estimating egocentric distances in virtual reality and consequently, does not depend on an internalized value for eye height

Recognizing your own motions on virtual avatars: is it me or not?

Most of the time point-light figures are used for motion-recognition, which present motions by only displaying the moving joints of the actor. In this study we were interested in whether self-recognition of motion changes with different representations. First, we captured participants' motions and remapped them on a point-light figure and a male and female virtual avatar. In the second part the same participants were asked to recognize their own motions on all three representations. We found that the recognition rate for own motions is high across all representations and different actions. The recognition rate was better on the point-light figure, despite being perceived as most difficult from the participants. The gender of the visual avatar did not matter in self-recognition

The influence of eye height and avatars on egocentric distance estimates in immersive virtual environments

It is well known that eye height is an important visual cue in the perception of apparent sizes and affordances in virtual environments. However, the influence of visual eye height on egocentric distances in virtual environments has received less attention. To explore this influence, we conducted an experiment where we manipulated the virtual eye height of the user in a head-mounted display virtual environment. As a measurement we asked the participants to verbally judge egocentric distances and to give verbal estimates of the dimensions of the virtual room. In addition, we provided the participants a self-animated avatar to investigate if this virtual self-representation has an impact on the accuracy of verbal distance judgments, as recently evidenced for distance judgments accessed with an action-based measure. When controlled for ownership, the avatar had a significant influence on the verbal estimates of egocentric distances as found in previous research. Interestingly, we found that the manipulation of eye height has a significant influence on the verbal estimates of both egocentric distances and the dimensions of the room. We discuss the implications which these research results have on those interested in space perception in both immersive virtual environments and the real world

The influence of a scaled third-person animated avatar on perception and action in virtual environments

Newer technology is allowing for virtual environments to become more realistic by providing visual image quality that is very similar to that in the real world. Regardless, egocentric distances estimates in virtual reality have been shown to be underestimated (Thompson et al., 2004). Interestingly, this underestimation decreases after individuals view self-representing avatars in the virtual environment; especially when the avatars are self-animated (Mohler et al., 2010). These finding support perspectives on embodied perception which assert that the body and its action capabilities can act as a “perceptual ruler” that the perceiver uses to scale the world. To test this perspective, we immersed participants into a full-cue, virtual environment where they viewed a self-animated avatar from behind at a distance of 3.5 m away at the same eye-height as the avatar. We manipulated the relationship between the size of the avatar and the size of the virtual room (which included familiar objects) to see if participants would attribute these changes either to the size of the world or to the size of their body. Participants made verbal estimates about the size of self and the world and performed a walking-in-place task. We found that participants verbally attributed the apparent size difference to the virtual world and not to the self which suggests that space perception is grounded in the physical body. Further, we found an influence of condition on the post/pre walking-in-place drift suggesting that the participants felt embodied in the third person animated avatar. Further research needs to be conducted in order to fully understand the relative importance of visual cues about self, such as motion coupling, eye-height and distance of avatar from observer, on perception and action in virtual worlds

Enhancing stress management techniques using virtual reality

Chronic stress is one of the major problems in our current fast paced society. The body reacts to environmental stress with physiological changes (e.g. accelerated heart rate), increasing the activity of the sympathetic nervous system. Normally the parasympathetic nervous system should bring us back to a more balanced state after the stressful event is over. However, nowadays we are often under constant pressure, with a multitude of stressful events per day, which can result in us constantly being out of balance. This highlights the importance of effective stress management techniques that are readily accessible to a wide audience. In this paper we present an exploratory study investigating the potential use of immersive virtual reality for relaxation with the purpose of guiding further design decisions, especially about the visual content as well as the interactivity of virtual content. Specifically, we developed an underwater world for head-mounted display virtual reality. We performed an experiment to evaluate the effectiveness of the underwater world environment for relaxation, as well as to evaluate if the underwater world in combination with breathing techniques for relaxation was preferred to standard breathing techniques for stress management. The underwater world was rated as more fun and more likely to be used at home than a traditional breathing technique, while providing a similar degree of relaxation

Evoking and Assessing Vastness in Virtual Environments

Many have experienced vastness, the feeling when the visual space seems to extend without limits away from you, making you feel like a small element within the space. For over 200 years, people have been writing about this experience, for example stating that vastness is important to the experience of awe [Mikulak 2015]. Yet vastness has received little attention in empirical research. Specifically, it is unknown which aspects of the visual stimulus contribute to perceived vastness. This may be due to the inherent difficulties in presenting a variety of vast stimuli while varying only specific visual cues. Using virtual reality addresses these difficulties, as this technology provides precise control over the presented visual stimuli. Here we investigate whether the feeling of vastness can be evoked using virtual reality and explore potential objective measures to assess vastness. We used three different measures during this experiment: 1) An avatar height adjustment task where participants had to adjust an avatar to be equivalent to their own height as viewed from a distance, 2) a distance estimation task and 3) a subjective vastness rating task. These tasks were performed in four environments: a plain (used in all subsequent environments for the ground and sky surfaces), a forest, a mountain and the mountain and forest environments combined. Our results indicate that the feeling of vastness can indeed be experienced to various degrees in virtual environments, demonstrating the potential of VR as a tool for exploring the perception of vastness. Yet the results combined suggest that the percept of vastness is a rather complex construct

Turbulent Motions Cannot Shake VR

The International Air Transport Association forecasts that there will be at least a 30 increase in passenger demand for flights over the next five years. In these circumstances the aircraft industry is looking for new ways to keep passengers occupied, entertained and healthy, and one of the methods under consideration is immersive virtual reality. It is therefore becoming important to understand how motion sickness and presence in virtual reality are influenced by physical motion. We were specifically interested in the use of head-mounted displays (HMD) while experiencing in-flight motions such as turbulence. 50 people were tested in different virtual environments varying in their context (virtual airplane versus magic carpet ride over tropical islands) and the way the physical motion was incorporated into the virtual world (matching visual and auditory stimuli versus no incorporation). Participants were subjected to three brief periods of turbulent motions realized with a motion simulator. Physiological signals (postural stability, heart rate and skin conductance) as well as subjective experiences (sickness and presence questionnaires) were measured. None of our participants experienced severe motion sickness during the experiment and although there were only small differences between conditions we found indications that it is beneficial for both wellbeing and presence to choose a virtual environment in which turbulent motions could be plausible and perceived as part of the scenario. Therefore we can conclude that brief exposure to turbulent motions does not get participants sick