More Like this

1. Assessment of Task and Joint-Based Exoskeleton Designs for Elbow Joint Rehabilitation

   https://doi.org/10.1115/DMD2022-1034  

   Delgado, Pablo; Jaradat, Lieth; Yihun, Yimesker (April 2022, Frontiers in Biomedical Devices)

   Exoskeletons and robots have been used as a common practice to assist and automate rehabilitation exercises. Exoskeleton fitting and alignments are important factors and challenges that need to be addressed for smooth and safe operations and better outcomes. Such challenges often dictate the exoskeleton design approaches. Some focus on simplifying and mimicking human joints (joint-based) while others have a focus on a specific task (task-based), which does not need to align with the corresponding limb joint/s to generate the desired anatomical motion. In this study, the two design approaches are assessed in an elbow flexion-extension task. The muscle responses have been collected and compared with and without the exoskeletons. Based on 6 with no disability participants, the normalized Electromyography (EMG) RMS values are plotted. The plot profiles and magnitudes are used as a base to assess the exoskeleton alignment. For this specific task, the task-based exoskeleton has shown a profile closer to the one without exoskeleton with a relatively identical support as the joint-based one; the latter is evidenced through most subjects’ muscle response magnitudes. This preliminary data has shown a good methodology and insight towards the assessment of exoskeletons, but more human subject data is needed with different task combinations to further strengthen the findings. 

   more » « less
2. Joint localization of directed polymers

   https://doi.org/10.1214/23-EJP1000  

   Bakhtin, Yuri; Dow, Douglas (January 2023, Electronic Journal of Probability)

   We consider (1 + 1)-dimensional directed polymers in a random potential and provide sufficient conditions guaranteeing joint localization. Joint localization means that for typical realizations of the environment, and for polymers started at different starting points, all the associated endpoint distributions localize in a common random region that does not grow with the length of the polymer. In particular, we prove that joint localization holds when the reference random walk of the polymer model is either a simple symmetric lattice walk or a Gaussian random walk. We also prove that the very strong disorder property holds for a large class of space-continuous polymer models, implying the usual single polymer localization. 

   more » « less
3. Joint inversion of compact operators

   https://doi.org/10.1515/jiip-2019-0068  

   Mead, Jodi L.; Ford, James F. (February 2020, Journal of Inverse and Ill-posed Problems)

   Abstract Joint inversion of multiple data types was studied as early as 1975 in [K. Vozoff and D. L. Jupp,Joint inversion of geophysical data,Geophys. J. Internat. 42 1975, 3, 977–991],where the authors used the singular value decomposition to determine the degree of ill-conditioning of joint inverse problems. The authors demonstrated in several examples that combining two physical models in a joint inversion, and by effectively stacking discrete linear models, improved the conditioning as compared to individual inversions. This work extends the notion of using the singular value decomposition to determine the conditioning of discrete joint inversion to using the singular value expansion to determine the well-posedness of joint operators. We provide a convergent technique for approximating the singular values of continuous joint operators. In the case of self-adjoint operators, we give an algebraic expression for the joint singular values in terms of the singular values of the individual operators. This expression allows us to show that while rare, there are situations where ill-posedness may be not improved through joint inversion and in fact can degrade the conditioning of an individual inversion. The expression also quantifies the benefits of including repeated measurements in an inversion. We give an example of joint inversion with two moderately ill-posed Green’s function solutions, and quantify the improvement over individual inversions. This work provides a framework in which to identify data types that are advantageous to combine in a joint inversion. 

   more » « less
4. The Joint Simon task is not joint for capuchin monkeys

   https://doi.org/10.1038/s41598-024-55885-x  

   Martínez, Mayte; Babb, Matthew H.; Range, Friederike; Brosnan, Sarah F. (March 2024, Scientific Reports)

   Abstract Human cooperation can be facilitated by the ability to create a mental representation of one’s own actions, as well as the actions of a partner, known as action co-representation. Even though other species also cooperate extensively, it is still unclear whether they have similar capacities. The Joint Simon task is a two-player task developed to investigate this action co-representation. We tested brown capuchin monkeys (Sapajus [Cebus] apella), a highly cooperative species, on a computerized Joint Simon task and found that, in line with previous research, the capuchins' performance was compatible with co-representation. However, a deeper exploration of the monkeys’ responses showed that they, and potentially monkeys in previous studies, did not understand the control conditions, which precludes the interpretation of the results as a social phenomenon. Indeed, further testing to investigate alternative explanations demonstrated that our results were due to low-level cues, rather than action co-representation. This suggests that the Joint Simon task, at least in its current form, cannot determine whether non-human species co-represent their partner’s role in joint tasks. 

   more » « less
5. Joint realizability of monotone Boolean functions

   https://doi.org/10.1016/j.tcs.2022.04.045  

   Crawford-Kahrl, Peter; Cummins, Bree; Gedeon, Tomáš (June 2022, Theoretical Computer Science)