971 research outputs found

    Optimization of Semiautomated Calibration Algorithm of Multichannel Electrotactile Feedback for Myoelectric Hand Prosthesis

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    The main drawback of the commercially available myoelectric hand prostheses is the absence of somatosensory feedback. We recently developed a feedback interface for multiple degrees of freedom myoelectric prosthesis that allows proprioceptive and sensory information (i.e., grasping force) to be transmitted to the wearer instantaneously. High information bandwidth is achieved through intelligent control of spatiotemporal distribution of electrical pulses over a custom-designed electrode array. As electrotactile sensations are location-dependent and the developed interface requires that electrical stimuli are perceived to be of the same intensity on all locations, a calibration procedure is of high importance. The aim of this study was to gain more insight into the calibration procedure and optimize this process by leveraging a priori knowledge. For this purpose, we conducted a study with 9 able-bodied subjects performing 10 sessions of the array electrode calibration. Based on the collected data, we optimized and simplified the calibration procedure by adapting the initial (baseline) amplitude values in the calibration algorithm. The results suggest there is an individual pattern of stimulation amplitudes across 16 electrode pads for each subject, which is not affected by the initial amplitudes. Moreover, the number of user actions performed and the time needed for the calibration procedure are significantly reduced by the proposed methodology.The research was supported by Tecnalia Research & Innovation, Spain, and the Ministry of Education, Science and Technological Development of Republic of Serbia (Project no. 175016). The authors would like to thank all the volunteers who participated in this study

    Matrix Product State applications for the ALPS project

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    The density-matrix renormalization group method has become a standard computational approach to the low-energy physics as well as dynamics of low-dimensional quantum systems. In this paper, we present a new set of applications, available as part of the ALPS package, that provide an efficient and flexible implementation of these methods based on a matrix-product state (MPS) representation. Our applications implement, within the same framework, algorithms to variationally find the ground state and low-lying excited states as well as simulate the time evolution of arbitrary one-dimensional and two-dimensional models. Implementing the conservation of quantum numbers for generic Abelian symmetries, we achieve performance competitive with the best codes in the community. Example results are provided for (i) a model of itinerant fermions in one dimension and (ii) a model of quantum magnetism.Comment: 11+5 pages, 8 figures, 2 example

    A model for transcutaneous current stimulation: simulations and experiments

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    Complex nerve models have been developed for describing the generation of action potentials in humans. Such nerve models have primarily been used to model implantable electrical stimulation systems, where the stimulation electrodes are close to the nerve (near-field). To address if these nerve models can also be used to model transcutaneous electrical stimulation (TES) (far-field), we have developed a TES model that comprises a volume conductor and different previously published non-linear nerve models. The volume conductor models the resistive and capacitive properties of electrodes, electrode-skin interface, skin, fat, muscle, and bone. The non-linear nerve models were used to conclude from the potential field within the volume conductor on nerve activation. A comparison of simulated and experimentally measured chronaxie values (a measure for the excitability of nerves) and muscle twitch forces on human volunteers allowed us to conclude that some of the published nerve models can be used in TES models. The presented TES model provides a first step to more extensive model implementations for TES in which e.g., multi-array electrode configurations can be teste

    Pressure effects on the magnetic structure in La0.5Ca0.5-xSrxMnO3 (0.1 -< x -< 0.4) manganites

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    The effect of high pressure (0 - 8 GPa) on the magnetic structure of polycrystalline samples of La0.5Ca0.5-xSrxMnO3 (0.1 -< x -< 0.4) manganites at 5 K is investigated using neutron diffraction technique. Application of pressure is found to modify the previously reported magnetic structure, observed under ambient conditions, in these compounds [I. Dhiman et al., Phys. Rev. B 77, 094440 (2008)]. In x = 0.1 composition, at 4.6(2) GPa and beyond, A-type antiferromagnetic structure is found to coexist with CE-type antiferromagnetic phase, observed at ambient pressure, with TN ~ 150 K. For x = 0.3 sample, as a function of pressure the CE-type phase is fully suppressed at 2.3(1) GPa and A-type antiferromagnetic phase is favored. Further Sr doping at x = 0.4, the A-type antiferromagnetic phase is observed at ambient pressure and for T < TN (~ 250K). This phase is retained in the studied pressure range. However, the magnetic moment progressively reduces with increasing pressure, indicating the suppression of A-type antiferromagnetic phase. The present study brings out the fragile nature of the CE-type antiferromagnetic state in half doped manganites as a function of pressure and disorder \sigma 2. We observe that pressure required for destabilizing the CE-type antiferromagnetic state is reduced with increasing disorder \sigma 2. External pressure and changing A-site ionic radii have analogous effect on the magnetic structure.Comment: 9 pages, 6 figures, 1 table, To appear in Physical Review

    Did volcanism and climate change cause the K-T mass extinction?

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    Transcutaneous FES-induced pain maps on post-stroke upper limb

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    Functional Electrical Stimulation (FES) is a technique to artificially stimulate motor nerves in order to restore motor/sensory functions for assistive and therapeutic applications. This preliminary study attempts to detect differences in the perception of transcutaneous FES in upper limbs. Three chronic stroke survivors participated in the study. Multi-field electrodes were used to selectively activate the targeted areas over the wrist-finger flexors, wrist-finger extensors, biceps, and triceps muscles. Results showed no significant correlation between the applied current and pain ratings. Differences in the rating of pain in different fields over the four targeted areas were observed. The initial results suggest that here is a common pattern to most subjects for each area of the upper limb

    Stimulation Discomfort Comparison of Asynchronous and Synchronous Methods with Multi-Field Surface Electrodes

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    Functional Electrical Stimulation (FES) is a technique that artificially stimulates motor nerves in order to restore motor/sensory functions for assistive and therapeutic applications. Recently, multi-field surface electrodes for transcutaneous electrical stimulation have been suggested to overcome problems of single channel surface stimulation. This study compares sensation perceived by 15 healthy subjects on upper limb when two different stimulation methods are applied by means of multi-field electrodes. Asynchronous and synchronous stimulation methods are compared for four different cases: activation of two neighbor fields, three neighbor fields, two distant fields and three distant fields. Two descriptors rated from 1 to 5 are used to describe discomfort: superficial discomfort and deep discomfort. Results expressed no differences in superficial discomfort for any case, but showed significant differences in deep discomfort for distant field activations. In these cases, synchronous stimulation resulted in higher perceived deep discomfort than asynchronous stimulation and affected its efficacy

    Modelling the Component-based Architecture and Safety Contracts of ArmAssist in Papyrus for Robotics

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    Healthcare robots are increasingly being used and the way they are engineered they still have several challenges regarding reference models and validation. In this experience report we focus on the ArmAssist robotic system and how it can be modelled including safety considerations for validation in early design phases. ArmAssist is an upper-limb robotic system for stroke rehabilitation based on serious games. The open-source tool Papyrus for Robotics was used for modelling the robotic system in close collaboration with neurorehabilitation domain experts. Papyrus for Robotics includes new functionalities that we contributed for contract-based design at component and system level, allowing to make explicit and validate the safety considerations using formal languages. In our case, the assertions are expressed in OCL and Othello. We present the resulting model and a discussion from domain experts.This work has been funded by the SafeCC4Robot Integrated Technical Project which received funding from the European Union‚Äôs Horizon 2020 Research and Innovation Programme under grant agreement No. 732410, in the form of financial support to third parties of the RobMoSys Project. We would like to thank Angel Lopez, Elixabete Ostolaza, Matteo Morelli, ¬ī and Huascar Espinoza for their help during the tool design and development. The authors also would like to thank to Inigo Dorronsoro, Javier Arcas Ruiz-Ruano, Gabriel Gaminde, ňú Benat Garcia-Mendizabal, Je Hyung Jung, Cristina Rodriguez- ňú de-Pablo, Joel Perry, Aitor Belloso, David Valencia and Haritz Zabaleta for their contributions to the ArmAssist system development
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