Stabilization of localized structures by inhomogeneous injection in Kerr resonators

We consider the formation of temporal localized structures or Kerr comb generation in a microresonator with inhomogeneities. We show that the introduction of even a small inhomogeneity in the injected beam widens the stability region of localized solutions. The homoclinic snaking bifurcation associated with the formation of localized structures and clusters of them with decaying oscillatory tails is constructed. Furthermore, the inhomogeneity allows not only to control the position of localized solutions, but strongly affects their stability domains. In particular, a new stability domain of a single peak localized structure appears outside of the region of multistability between multiple peaks of localized states. We identify a regime of larger detuning, where localized structures do not exhibit a snaking behavior. In this regime, the effect of inhomogeneities on localized solutions is far more complex: they can act either attracting or repelling. We identify the pitchfork bifurcation responsible for this transition. Finally, we use a potential well approach to determine the force exerted by the inhomogeneity and summarize with a full analysis of the parameter regime where localized structures and therefore Kerr comb generation exist and analyze how this regime changes in the presence of an inhomogeneity

Motor Learning in Virtual Reality: From Motion to Augmented Feedback

Hülsmann F. Motor Learning in Virtual Reality: From Motion to Augmented Feedback. Bielefeld: Universität Bielefeld; 2019.Sports and fitness exercises are an important factor in health improvement. The acquisition of new movements - motor learning - and the improvement of techniques for already learned ones are a vital part of sports training. Ideally, this part is supervised and supported by coaches. They know how to correctly perform specific exercises and how to prevent typical movement errors. However, coaches are not always available or do not have enough time to fully supervise training sessions. Virtual reality (VR) is an ideal medium to support motor learning in the absence of coaches. VR systems could supervise performed movements, visualize movement patterns, and identify errors that are performed by a trainee. Further, feedback could be provided that even extends the possibilities of coaching in the real world. Still, core concepts that form the basis of effective coaching applications in VR are not yet fully developed. In order to diminish this gap, we focus on the processing of kinematic data as one of the core components for motor learning. Based on the processing of kinematic data in real-time, a coaching system can supervise a trainee and provide varieties of multi-modal feedback strategies. For motor learning, this thesis explores the development of core concepts based on the usage of kinematic data in three areas. First, the movement that is performed by a trainee must be observed and visualized in real-time. The observation can be achieved by state-of-the-art motion capture techniques. Concerning the visualization, in the real world, trainees can observe their own performance in mirrors. We use a virtual mirror as a paradigm to allow trainees to observe their own movement in a natural way. A well established feedback strategy from real-world coaching, namely improvement via observation of a target performance, is transfered into the virtual mirror paradigm. Second, a system that focuses on motor learning should be able to assess the performance that it observes. For instance, typical errors in a trainee's performance must be detected as soon as possible in order to react in an effective way. Third, the motor learning environment should be able to provide suitable feedback strategies based on detected errors. In this thesis, real-time feedback based on error detection is integrated inside a coaching cycle that is inspired from real-world coaching. In a final evaluation, all the concepts are brought together in a VR coaching system. We demonstrate that this system is able to help trainees in improving their motor performance with respect to specific error patterns. Finally, based on the results throughout the thesis, helpful guidelines in order to develop effective environments for motor learning in VR are proposed

Wind and warmth in virtual reality: implementation and evaluation

Hülsmann F, Fröhlich J, Mattar N, Wachsmuth I. Wind and warmth in virtual reality: implementation and evaluation. In: VRIC '14: Proceedings of the Virtual Reality International Conference: Laval Virtual. ACM; 2014.One possibility to make virtual worlds more immersive is to address as many human senses as possible. This paper presents the development of a system for creating wind and warmth simulations in Virtual Reality (VR). Therefore, suitable hardware and an implemented software model are described. Technical evaluations of the hardware and of the software components demonstrate the usability of the system in VR Applications. Furthermore, a user study underlines users’ acceptance and indicates a positive influence of wind and warmth stimuli on perceived presence

Stationary localized structures and the effect of the delayed feedback in the Brusselator model

The Brusselator reaction-diffusion model is a paradigm for the understanding of dissipative structures in systems out of equilibrium. In the first part of this paper, we investigate the formation of stationary localized structures in the Brusselator model. By using numerical continuation methods in two spatial dimensions, we establish a bifurcation diagram showing the emergence of localized spots. We characterize the transition from a single spot to an extended pattern in the form of squares. In the second part, we incorporate delayed feedback control and show that delayed feedback can induce a spontaneous motion of both localized and periodic dissipative structures. We characterize this motion by estimating the threshold and the velocity of the moving dissipative structures.Comment: 18 pages, 11 figure

Simulating wind and warmth in virtual reality: conception, realization and evaluation for a CAVE environment

Hülsmann F, Mattar N, Fröhlich J, Wachsmuth I. Simulating wind and warmth in virtual reality: conception, realization and evaluation for a CAVE environment. JVRB - Journal of Virtual Reality and Broadcasting. 2014;11(10).Wind and warmth sensations proved to be able to enhance users' state of presence in Virtual Reality applications. Still, only few projects deal with their detailed effect on the user and general ways of implementing such stimuli. This work tries to fill this gap: After analyzing requirements for hardware and software concerning wind and warmth simulations, a hardware and also a software setup for the application in a CAVE environment is proposed. The setup is evaluated with regard to technical details and requirements, but also - in the form of a pilot study - in view of user experience and presence. Our setup proved to comply with the requirements and leads to satisfactory results. To our knowledge, the low cost simulation system (approx. 2200 Euro) presented here is one of the most extensive, most flexible and best evaluated systems for creating wind and warmth stimuli in CAVE-based VR applications

Accurate online alignment of human motor performances

Hülsmann F, Richter A, Kopp S, Botsch M. Accurate online alignment of human motor performances. In: Proceedings of ACM Motion in Games. Barcelona: ACM; 2017: pp. 7:1-7:6

Realizing a Low-latency Virtual Reality Environment for Motor Learning

Waltemate T, Hülsmann F, Pfeiffer T, Kopp S, Botsch M. Realizing a Low-latency Virtual Reality Environment for Motor Learning. In: Proceedings of the 21st ACM Symposium on Virtual Reality Software and Technology. VRST '15. New York, NY, USA: ACM; 2015: 139-147.Virtual Reality (VR) has the potential to support motor learning in ways exceeding beyond the possibilities provided by real world environments. New feedback mechanisms can be implemented that support motor learning during the performance of the trainee and afterwards as a performance review. As a consequence, VR environments excel in controlled evaluations, which has been proven in many other application scenarios. However, in the context of motor learning of complex tasks, including full-body movements, questions regarding the main technical parameters of such a system, in particular that of the required maximum latency, have not been addressed in depth. To fill this gap, we propose a set of requirements towards VR systems for motor learning, with a special focus on motion capturing and rendering. We then assess and evaluate state-of-the-art techniques and technologies for motion capturing and rendering, in order to provide data on latencies for different setups. We focus on the end-to-end latency of the overall system, and present an evaluation of an exemplary system that has been developed to meet these requirements

A Multimodal System for Real-Time Action Instruction in Motor Skill Learning

de Kok I, Hough J, Hülsmann F, Botsch M, Schlangen D, Kopp S. A Multimodal System for Real-Time Action Instruction in Motor Skill Learning. In: Proceedings of ACM ICMI 17th ACM International Conference on Multimodal Interaction. 2015: 355-362