Methods of regularization for computing orbits in celestial mechanics

Numerical and analytical methods for orbit computation in celestial mechanics during and beyond collision by introduction of regularized coordinate

Intrinsic Geometry of a Null Hypersurface

We apply Cartan's method of equivalence to construct invariants of a given null hypersurface in a Lorentzian space-time. This enables us to fully classify the internal geometry of such surfaces and hence solve the local equivalence problem for null hypersurface structures in 4-dimensional Lorentzian space-times

Balance strategy in hoverboard control.

This study examines how people learn to perform lower limb control in a novel task with a hoverboard requiring to maintain dynamic balance. We designed an experiment to investigate the learning of hoverboard balance and two control strategies: A hip strategy, which mainly uses hip movements to change the angle of the foot, and an ankle strategy relying more on ankle motion to control the orientation of hoverboard plates controlling the motion. Motor learning was indicated by a significant [Formula: see text]% decrease in the trial completion time (p < 0.001) and a significant 24 ± 11% decrease in total muscle activation (p < 0.001). Furthermore, the participants, who had no prior experience riding a hoverboard, learned an ankle strategy to maintain their balance and control the hoverboard. This is supported by significantly stronger cross-correlation, phase synchrony, lower dynamic time warping distance between the hoverboard plate orientation controlling hoverboard motion, and the ankle angle when compared to the hip angle. The adopted ankle strategy was found to be robust to the foot orientation despite salient changes in muscle group activation patterns. Comparison with results of an experienced hoverboard rider confirmed that the first-time riders adopted an ankle strategy

How virtual and mechanical coupling impact bimanual tracking.

Bilateral training systems look to promote the paretic hand's use in individuals with hemiplegia. Although this is normally achieved using mechanical coupling (i.e., a physical connection between the hands), a virtual reality system relying on virtual coupling (i.e., through a shared virtual object) would be simpler to use and prevent slacking. However, it is not clear whether different coupling modes differently impact task performance and effort distribution between the hands. We explored how 18 healthy right-handed participants changed their motor behaviors in response to the uninstructed addition of mechanical coupling, and virtual coupling using a shared cursor mapped to the average hands' position. In a second experiment, we then studied the impact of connection stiffness on performance, perception, and effort imbalance. The results indicated that both coupling types can induce the hands to actively contribute to the task. However, the task asymmetry introduced by using a cursor mapped to either the left or right hand only modulated the hands' contribution when not mechanically coupled. The tracking performance was similar for all coupling types, independent of the connection stiffness, although the mechanical coupling was preferred and induced the hands to move with greater correlation. These findings suggest that virtual coupling can induce the hands to actively contribute to a task in healthy participants without hindering their performance. Further investigation on the coupling types' impact on the performance and hands' effort distribution in patients with hemiplegia could allow for the design of simpler training systems that promote the affected hand's use.NEW & NOTEWORTHY We showed that the uninstructed addition of a virtual and/or a mechanical coupling can induce both hands to actively contribute in a continuous redundant bimanual tracking task without impacting performance. In addition, we showed that the task asymmetry can only alter the effort distribution when the hands are not connected, independent of the connection stiffness. Our findings suggest that virtual coupling could be used in the development of simpler VR-based training devices

The Impact of Stiffness in Bimanual Versus Dyadic Interactions Requiring Force Exchange.

During daily activities, humans routinely manipulate objects bimanually or with the help of a partner. This work explored how bimanual and dyadic coordination modes are impacted by the object's stiffness, which conditions inter-limb haptic communication. For this, we recruited twenty healthy participants who performed a virtual task inspired by object handling, where we looked at the initiation of force exchange and its continued maintenance while tracking. Our findings suggest that while individuals and dyads displayed different motor behaviours, which may stem from the dyad's need to estimate their partner's actions, they exhibited similar tracking accuracy. For both coordination modes, increased stiffness resulted in better tracking accuracy and more correlated motions, but required a larger effort through increased average torque. These results suggest that stiffness may be a key consideration in applications such as rehabilitation, where bimanual or external physical assistance is often provided

The control and training of single motor units in isometric tasks are constrained by a common input signal

Recent developments in neural interfaces enable the real-time and non-invasive tracking of motor neuron spiking activity. Such novel interfaces could provide a promising basis for human motor augmentation by extracting potentially high-dimensional control signals directly from the human nervous system. However, it is unclear how flexibly humans can control the activity of individual motor neurons to effectively increase the number of degrees of freedom available to coordinate multiple effectors simultaneously. Here, we provided human subjects (N = 7) with real-time feedback on the discharge patterns of pairs of motor units (MUs) innervating a single muscle (tibialis anterior) and encouraged them to independently control the MUs by tracking targets in a 2D space. Subjects learned control strategies to achieve the target-tracking task for various combinations of MUs. These strategies rarely corresponded to a volitional control of independent input signals to individual MUs during the onset of neural activity. Conversely, MU activation was consistent with a common input to the MU pair, while individual activation of the MUs in the pair was predominantly achieved by alterations in de-recruitment order that could be explained by history-dependent changes in motor neuron excitability. These results suggest that flexible MU recruitment based on independent synaptic inputs to single MUs is unlikely, although de-recruitment might reflect varying inputs or modulations in the neuron’s intrinsic excitability

Impact of processed earwigs and their faeces on the aroma and taste of 'Chasselas' and 'Pinot Noir' wines

The abundance of the European earwig Forficula auricularia L. (Dermaptera, Forficulidae) in European vineyards increased considerably over the last few years. Although earwigs are omnivorous predators that prey on viticultural pests such as grape moths, they are also known to erode berries and to transfer fungal spores. Moreover, they are suspected to affect the human perception of wines both directly by their processing with the grapes and indirectly by the contamination of grape clusters with their faeces. In this study we artificially contaminated grapes with F. auricularia adults and/or their faeces and determined the impact on aroma and taste of white 'Chasselas' and red 'Pinot noir' wines. Whereas the addition of five living adults/kg grapes affected the olfactory sensation of 'Chasselas' wines only marginally, 0.6 gram of earwig faeces/kg grapes had a strong effect on colour, aroma and the general appreciation of 'Chasselas' wines. Faeces-contaminated wines were less fruity and less floral, the aroma was described as faecal and they were judged to be of lower quality. The contamination of 'Pinot noir' grapes with four different densities of living earwig adults (e.g. 0, 5, 10 and 20 individuals/kg grapes) showed that only wines contaminated with more than 10 earwigs/kg grapes smelled and tasted significantly different than the uncontaminated control wine. Earwig-contaminated 'Pinot noir' wines were judged to be of lower quality. The descriptors “animal”, “reductive”, “vegetal”, “acidic”, “bitter” and “tannic” characterised their sensory perception. In conclusion, our results show that there is a real risk of wine contamination by F. auricularia. In particular, earwig faeces and earwig adults at densities above a threshold of 5 to 10 individuals/kg grapes have the potential to reduce the quality of wines. The evolution of earwig populations in vineyards should therefore be monitored carefully in order to anticipate problems during vinification.

Dr. Martin Hillenbrand to Receive University of Dayton Distinguished Alumnus Award

News release announcing the University of Dayton will Award Assistant Secretary of State for European Affairs, Dr. Martin Hillenbrand, with the Distinguished Alumnus Award