Enhancing the smoothness of joint motion induced by functional electrical stimulation using co-activation strategies

The motor precision of today’s neuroprosthetic devices that use artificial generation of limb motion using Functional Electrical Stimulation (FES) is generally low. We investigate the adoption of natural co-activation strategies as present in antagonistic muscle pairs aiming to improve motor precision produced by FES. In a test in which artificial knee-joint movements were generated, we could improve the smoothness of FES-induced motion by 513% when applying co-activation during the phases in which torque production is switched between muscles – compared to no co-activation. We further demonstrated how the co-activation level influences the joint stiffness in a pendulum test.BMBF, 16SV7069K, Bewegungsfähigkeit und Mobilität wiedererlangen - BeMobi

Water Procurement Time and Its Implications for Household Water Demand: Insights from a Water Diary Study in Five Informal Settlements of Pune, India

Many private households spend considerable amounts of time accessing water, for instance by walking to and queuing at public access points, or by filling storage vessels at taps with low flow rates. This time has an opportunity cost, which can be substantial and may impact which water services and quantities of water households demand. In a novel form of diary study, we gathered detailed water consumption and time use data from 50 households in five informal settlements of the Indian metropolis Pune, accompanied by a household survey and in-depth interviews. With the data, we characterize water collection behaviors and assign monetary values to water procurement time. We statistically analyze the effects of time cost on consumed quantities in several two-level mixed effect models. Household members in our sample spend up to several hours each day filling storage vessels, even if a private connection to the piped network is available. Average time cost amounted to the equivalent of 4.23–13.81% of monthly household cash income. Our analyses indicate that procurement time reduces quantitative water demand in a significant way. The households incurring the highest per-unit time cost consumed water quantities below minimum levels recommended for human health. This substantiates that time costs can impede access to water and are a relevant issue for water management and policy

Eine allgemeine Theorie der Bestände

Im vorliegenden Aufsatz wird ein Begriffskonzept entwickelt, das zum besseren Verständnis des Zusammenspiels der Dynamiken von Ökosystemen und Wirtschaft dient: das Konzept des Bestandes. Der Bestandsbegriff wird allgemein mengentheoretisch formuliert. Die zentrale Eigenschaft eines Bestandes liegt in seiner zeitlichen Dauerhaftigkeit. Damit eignen sich Bestände zur Abbildung von Einflüssen, die die Vergangenheit von Systemen auf deren Gegenwart ausübt, und damit zur Analyse von zeitlichen Entwicklungen. Da Beständigkeit eine Eigenschaft in der Zeit darstellt, ist das Konzept des Bestandes nicht spezifisch auf den Gegenstandsbereich einzelner wissenschaftlicher Disziplinen beschränkt und so für die interdisziplinäre Analyse geeignet. Der Begriff wird auf ökonomische und ökologische Beispiele angewandt und dabei auf stochastische Mengen verallgemeinert. Durch die Abgrenzung der Bestandsperspektive von einer Systemsicht kann die hierarchische Struktur realer ökologisch-ökonomischer Systeme analysiert werden. Die Theorie der Bestände stellt einen Baustein für die konzeptionellen Grundlagen der Ökologischen Ökonomie dar. --Dynamik,Beständigkeit,System,Zeitskalen,Population,Persistenz

Traveling Wave Magnetic Particle Imaging for determining the iron-distribution in rock: Traveling Wave Magnetic Particle Imaging for determining the iron-distribution in rock

Determining the composition of solid materials is of high interest in areas such as material research or quality assurance. There are several modalities at disposal with which various parameters of the material can be observed, but of those only magnetic resonance imaging (MRI) or computer tomography (CT) offer anon-destructive determination of material distribution in 3D. A novel non-destructive imaging method is Magnetic Particle Imaging (MPI), which uses dynamic magnetic fields for a direct determination of the distribution of magnetic materials in 3D. With this approach, it is possible to determine and differentiate magnetic and non-magnetic behaviour. In this paper, the first proof-of-principle measurements of magnetic properties in solid environments are presented using a home-built traveling wave magnetic particle imaging scanner

Feedback control of arm movements using Neuro-Muscular Electrical Stimulation (NMES) combined with a lockable, passive exoskeleton for gravity compensation

Within the European project MUNDUS, an assistive framework was developed for the support of arm and hand functions during daily life activities in severely impaired people. This contribution aims at designing a feedback control system for Neuro-Muscular Electrical Stimulation (NMES) to enable reaching functions in people with no residual voluntary control of the arm and shoulder due to high level spinal cord injury. NMES is applied to the deltoids and the biceps muscles and integrated with a three degrees of freedom (DoFs) passive exoskeleton, which partially compensates gravitational forces and allows to lock each DOF. The user is able to choose the target hand position and to trigger actions using an eyetracker system. The target position is selected by using the eyetracker and determined by a marker-based tracking system using Microsoft Kinect. A central controller, i.e., a finite state machine, issues a sequence of basic movement commands to the real-time arm controller. The NMES control algorithm sequentially controls each joint angle while locking the other DoFs. Daily activities, such as drinking, brushing hair, pushing an alarm button, etc., can be supported by the system. The robust and easily tunable control approach was evaluated with five healthy subjects during a drinking task. Subjects were asked to remain passive and to allow NMES to induce the movements. In all of them, the controller was able to perform the task, and a mean hand positioning error of less than five centimeters was achieved. The average total time duration for moving the hand from a rest position to a drinking cup, for moving the cup to the mouth and back, and for finally returning the arm to the rest position was 71 s.EC/FP7/248326/EU/MUltimodal Neuroprostesis for Daily Upper limb Support/MUNDU

MUNDUS project : MUltimodal neuroprosthesis for daily upper limb support

Background: MUNDUS is an assistive framework for recovering direct interaction capability of severely motor impaired people based on arm reaching and hand functions. It aims at achieving personalization, modularity and maximization of the user’s direct involvement in assistive systems. To this, MUNDUS exploits any residual control of the end-user and can be adapted to the level of severity or to the progression of the disease allowing the user to voluntarily interact with the environment. MUNDUS target pathologies are high-level spinal cord injury (SCI) and neurodegenerative and genetic neuromuscular diseases, such as amyotrophic lateral sclerosis, Friedreich ataxia, and multiple sclerosis (MS). The system can be alternatively driven by residual voluntary muscular activation, head/eye motion, and brain signals. MUNDUS modularly combines an antigravity lightweight and non-cumbersome exoskeleton, closed-loop controlled Neuromuscular Electrical Stimulation for arm and hand motion, and potentially a motorized hand orthosis, for grasping interactive objects. Methods: The definition of the requirements and of the interaction tasks were designed by a focus group with experts and a questionnaire with 36 potential end-users. Five end-users (3 SCI and 2 MS) tested the system in the configuration suitable to their specific level of impairment. They performed two exemplary tasks: reaching different points in the working volume and drinking. Three experts evaluated over a 3-level score (from 0, unsuccessful, to 2, completely functional) the execution of each assisted sub-action. Results: The functionality of all modules has been successfully demonstrated. User’s intention was detected with a 100% success. Averaging all subjects and tasks, the minimum evaluation score obtained was 1.13 ± 0.99 for the release of the handle during the drinking task, whilst all the other sub-actions achieved a mean value above 1.6. All users, but one, subjectively perceived the usefulness of the assistance and could easily control the system. Donning time ranged from 6 to 65 minutes, scaled on the configuration complexity. Conclusions: The MUNDUS platform provides functional assistance to daily life activities; the modules integration depends on the user’s need, the functionality of the system have been demonstrated for all the possible configurations, and preliminary assessment of usability and acceptance is promising

The Epistemic Status of Processing Fluency as Source for Judgments of Truth

This article combines findings from cognitive psychology on the role of processing fluency in truth judgments with epistemological theory on justification of belief. We first review evidence that repeated exposure to a statement increases the subjective ease with which that statement is processed. This increased processing fluency, in turn, increases the probability that the statement is judged to be true. The basic question discussed here is whether the use of processing fluency as a cue to truth is epistemically justified. In the present analysis, based on Bayes’ Theorem, we adopt the reliable-process account of justification presented by Goldman (1986) and show that fluency is a reliable cue to truth, under the assumption that the majority of statements one has been exposed to are true. In the final section, we broaden the scope of this analysis and discuss how processing fluency as a potentially universal cue to judged truth may contribute to cultural differences in commonsense beliefs

Geregelte funktionelle Elektrostimulation zur Wiederherstellung motorischer Fähigkeiten der oberen Extremität : Regelung der muskulären Rekrutierung und automatische Anpassung für die Vereinfachung des klinischen Einsatzes von neuartigen Neuroprothesen

This thesis considers Neuro-prosthetic systems using Functional Electrical Stimulation (FES) to restore or support motor functions in neurologically impaired patients. An often encountered difficulty is the precise control of limb motion by adjusting the stimulation intensity. The musculoskeletal systems involving muscle mechanics, limb motion dynamics, and muscle recruitment due to FES and possibly volitional activity are highly complex and non-linear. Hence, the stimulation effect is hard to model and predict. An intensive effort during a calibration phase would be required to adapt models describing such systems to the full extent, which is unfeasible in clinical environments or at home. Further, many parameters vary under the rapid progression of muscle fatigue with FES. Hence, most practically relevant devices focus on simple open-loop strategies that trigger pre-defined stimulation patterns on different events caused by the user. This thesis presents new methods to improve the applicability and movement precision of closed-loop FES systems and applies them to practically relevant applications to support or to restore functional arm reaching movements in entirely or partially paralyzed patients. The compensation of muscle fatigue and the linearization of the highly non-linear process of muscle recruitment is addressed in this thesis. Electromyography (EMG)-measurements can give insight into the muscular recruitment process. Therefore, a feedback of the stimulation-evoked EMG (eEMG) enforcing the desired recruitment level is presented. Because of this enforcement, a more predictable behavior is obtained such that muscles are much easier to model and control using this method as an underlying feedback loop. The positive effects on the predictability are shown in a study involving five healthy subjects. Further, the applicability of this approach was successfully tested in two stroke patients. In partially paralyzed patients it is often beneficial to take account the residual volitional activity to, e.g., realize a user-control of the neuroprosthesis. Devices exist that control FES based on a measurement the volitional EMG (vEMG). The low signal to noise ratio, however, typically leads to many restrictions in control performance. Hence, a different approach based on angular measurements is presented: An arm weight relief is realized by a FES-activation proportional to the elevation angle. This FES-activation reduces the required volitional effort significantly as demonstrated in five healthy subjects. In two acute stroke patients, arm function could be partially and fully restored, respectively, as long as the controller was active. For patients who have a complete paralysis of the upper extremity, the functional restoration of movements is difficult due to the numerous degrees of freedom (DoF). Hence, a system using a combination of a passive, light-weight exoskeleton with FES is proposed, wherein each DoF can be locked by brakes to reduce muscle fatigue during holding-postures and to guide movements. FES is feedback controlled, and the movement precision was evaluated in five healthy subjects showing a sufficient performance for performing simple reaching tasks. Further considered aspects include the improvement of motor precision by artificially introducing co-activations in antagonistic muscle pairs and the potential reduction of muscle fatigue by varying the stimulation frequency as desired for the contrary objectives "motor precision" and "muscle fatigue." For the former aspect, a non-linear system inversion based approach is developed to realize desired joint torques and co-activation levels and, further, applied to joint angle control yielding good results in a healthy subject. For the latter, a time-discretization method for linear time-invariant systems is presented that also considers variable sampling rates. Further, a system linearization approach is suggested allowing to apply standard discrete-time controllers for variable sampling rate systems.Diese Dissertation beschäftigt sich mit der Erforschung von Algorithmen zur Regelung von Neuroprothesen, die Funktionelle Elektrostimulation (FES) verwenden, um motorische Funktionen in neurologisch beeinträchtigten Patienten wiederherzustellen oder zu unterstützen. Die Generierung von feinmotorischen Bewegungen mittels einer Regelung der Stimulationsintensität ist oftmals schwierig. Da die involvierten biomechanischen Systeme sehr komplex und nichtlinear sind, ist der Effekt der Stimulation nur schwierig durch Modelle beschreibbar. Es wäre ein sehr hoher Zeitaufwand notwendig, um die Parameter eines solchen Modells für die jeweiligen Patienten anzupassen. Mit der schnell fortschreitenden Muskelermüdung bei Anwendung von FES ändern sich diese Parameter typischerweise im Laufe der Zeit so stark, dass nach kurzer Zeit eine neue Anpassung vorgenommen werden muss. Die meisten praktisch relevanten Ansätze konzentrieren sich deshalb auf einfache aber robuste Steuerstrategien ohne die Rückführung von Messgrößen und die Verwendung von komplexen Modellen. Hierbei werden oftmals fest einprogrammierte Stimulationsverläufe verwendet, die durch den Benutzter initiiert werden. Ein wichtiger Teil der Dissertation beschreibt eine neue Methode, mit der sich der Bedarf eines komplexen Modells bei der FES-Regelung zum großen Teil erübrigt. Eine Reduzierung der Komplexität wird hierbei durch eine unterlagerte Regelung der Muskelrekrutierung erreicht, welche durch eine Messung des FES-evozierten Elektromyogramms (EMG) bestimmt wird. Damit verbessert sich die Anwendbarkeit und die Feinmotorik mittels geregelter FES. In einer Studie mit fünf gesunden Probanden wurde gezeigt, dass dadurch z.B. der Einfluss muskulärer Ermüdung kompensiert wird und das nichtlineare muskuläre Ansprechverhalten teilweise linear wird. Dieser neue Ansatz der Rekrutierungsregelung wurde in praktisch relevanten Systemen zur Unterstützung/Wiederherstellung von Armbewegungen bei teilweise/komplett Gelähmten im Rahmen meiner Dissertation angewandt. Bei teilweise gelähmten Patienten ist es sinnvoll, die noch vorhandene Restaktivität des Patienten zur Steuerung der Neuroprothese zu verwenden. Hierzu gibt es bereits Geräte, die die FES anhand einer Willkür-EMG-Messung steuern. Allerdings beschränkt das schwache Signal zu Rauschverhältnis des Willkür-EMG die erzielbare Feinmotorik der Bewegungen. In der Dissertation wurde deshalb ein anderer Ansatz zur Unterstützung der Armhebung vorgestellt, welcher mittels einer Messung des Gelenkwinkels die Willküraktivität indirekt einbezieht. Hierbei wird eine Armgewichtsunterstützung durch Generierung einer mit dem Winkel proportional ansteigenden Muskelrekrutierung erzielt. Bei fünf gesunden Probanden konnte gezeigt werden, dass dies die willkürliche Armhebungen erleichtert. Bei zwei Schlaganfallpatienten konnte der Bewegungsumfang im einen Fall teilweise und im anderen Fall vollständig wiederhergestellt werden. Bei Patienten mit einer kompletten Lähmung der oberen Extremität ist die Wiederherstellung von Armfunktionen mittels FES durch die hohe Anzahl an Freiheitsgraden in der Bewegung sehr schwierig. Um dieses Problem zu lösen, wird eine Kombination aus geregelter FES mit einem leichten passiven Exoskelett zur Führung der Bewegungen und zur partiellen Gewichtsentlastung vorgeschlagen. Die einzelnen Freiheitsgrade können dafür mit Bremsen blockiert werden, was auch stabile Armhaltungen bei abgeschalteter FES ermöglicht. Die Positioniergenauigkeit der Hand mit dem System wurde bei fünf Probanden untersucht und ist ausreichend genug, um funktionelle Bewegungen des täglichen Lebens durchzuführen. Eine weitere Untersuchung der Dissertation beinhaltet die Verbesserung der Feinmotorik durch eine künstliche Koaktivierung in antagonistischen Muskelpaaren. Hierzu wird ein Regelungsansatz vorgestellt, der gewünschte Momente und Koaktivierung einstellt. Dieser wurde in einer Gelenkwinkelregelung an einem gesunden Probanden erfolgreich erprobt