A new postural stability-indicator to predict the level of fear of falling in Parkinson's disease patients

Background: Fear of falling (FoF) is defined as a lasting concern about falling that causes a person to limit or even stop the daily activities that he/she is capable of. Seventy percent of Parkinson's disease (PD) patients report activity limitations due to FoF. Timely identification of FoF is critical to prevent its additional adverse effects on the quality of life. Self-report questionnaires are commonly used to evaluate the FoF, which may be prone to human error. Objectives: In this study, we attempted to identify a new postural stability-indicator to objectively predict the intensity of FoF and its related behavior(s) in PD patients. Methods: Thirty-eight PD patients participated in the study (mean age, 61.2 years), among whom 10 (26.32) were identified with low FoF and the rest (73.68) with high FoF, based on Falls Efficacy Scale-International (FES-I). We used a limit of stability task calibrated to each individual and investigated the postural strategies to predict the intensity of FoF. New parameters (FTR i s; functional time ratio) were extracted based on the center of pressure presence pattern in different rectangular areas (i = 1, 2, and 3). The task was performed on two heights to investigate FoF-related behavior(s). Results: FTR 1/2 (the ratio between FTR 1 and FTR 2) was strongly correlated with the FES-I (r =-0.63, p < 0.001), Pull test (r =-0.65, p < 0.001), Timed Up and Go test (r =-0.57, p < 0.001), and Berg Balance Scale (r = 0.62, p < 0.001). The model of FTR 1/2 was identified as a best-fitting model to predicting the intensity of FoF in PD participants (sensitivity = 96.43, specificity = 80), using a threshold level of � 2.83. Conclusions: Using the proposed assessment technique, we can accurately predict the intensity of FoF in PD patients. Also, the FTR 1/2 index can be potentially considered as a mechanical biomarker to sense the FoF-related postural instability in PD patients. © 2020 The Author(s)

A New Cryogenic Apparatus to Search for the Neutron Electric Dipole Moment

A cryogenic apparatus is described that enables a new experiment, nEDM@SNS, with a major improvement in sensitivity compared to the existing limit in the search for a neutron Electric Dipole Moment (EDM). It uses superfluid $^4$He to produce a high density of Ultra-Cold Neutrons (UCN) which are contained in a suitably coated pair of measurement cells. The experiment, to be operated at the Spallation Neutron Source at Oak Ridge National Laboratory, uses polarized $^3$He from an Atomic Beam Source injected into the superfluid $^4$He and transported to the measurement cells as a co-magnetometer. The superfluid $^4$He is also used as an insulating medium allowing significantly higher electric fields, compared to previous experiments, to be maintained across the measurement cells. These features provide an ultimate statistical uncertainty for the EDM of $2-3\times 10^{-28}$ e-cm, with anticipated systematic uncertainties below this level

A planar neuro-musculoskeletal arm model in post-stroke patients

Mathematical modeling of the neuro-musculoskeletal system in healthy subjects has been pursued extensively. In post-stroke patients, however, such models are very primitive. Besides improving our general understanding of how stroke affects the limb motions, they can be used to evaluate rehabilitation strategies by computer simulations before clinical evaluations. A planar neuro-musculoskeletal arm model for post-stroke patients is developed. The main idea is to use a set of new coefficients, Muscle Significance Factors (MSF), to incorporate the effects of stroke in the muscle control performance. The model uses the optimal control theory to mimic the performance of the CNS and a two-link skeletal model with six muscles for the biomechanical part. The model was developed and evaluated using experimental data from six post-stroke patients with Brunnstrom levels of 4�6. The results show that MSFs are relatively distinct and independent from the arm motion which is used to determine their values. Its variation is in the range of 0�2.58 and decreases in higher Brunnstrom levels. The mean error of the model in predicting the path of motion varies from 0.9 in level 6 to 5.58 in level 4 subjects which can be considered a promising level of accuracy. Using the proposed model and the MSF to customize the model for each individual stroke patient seems a promising approach. It shows a reasonable level of robustness, i.e., independence from the type of motions and correlated with the severity of stroke, and accuracy in predicting the shape of the motion path. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature

A new variable stiffness spring using a prestressed mechanism

A novel design of a semi-active variable stiffness element is proposed, with possible applications in vibration isolation. Semi-active vibration isolators usually use variable dampers. However, it is known from the fundamental vibration theory that a variable spring can be far more effective in shifting the frequencies of the system and providing isolation. Geometry change is a common technique for building variable springs, but has disadvantages due to the complexity of the required mechanism, and slow response due to the inertia of moving parts. In the variable spring introduced here (VS), the stiffness is changed by force control in the links which corresponds to infinitesimal movements of the links, and does not need a change of geometry to provide a change of stiffness. This facilitates a fast response. The proposed VS is a simple prestressed cable mechanism with an infinitesimal mechanism. Theoretically the level of the prestress in the cables can be used to control the stiffness from zero to a maximum value that is only limited by the strength of the links. In this work, the statics, kinematics and stability of the VS are studied, the stiffness is formulated, and possible configurations of the VS are found. © 2010 by ASME

A patient specific finite element simulation of intramedullary nailing to predict the displacement of the distal locking hole

Distal locking is a challenging subtask of intramedullary nailing fracture fixation due to the nail deformation that makes the proximally mounted targeting systems ineffective. A patient specific finite element model was developed, based on the QCT data of a cadaveric femur, to predict the position of the distal hole of the nail postoperatively. The mechanical interactions of femur and nail (of two sizes) during nail insertion was simulated using ABAQUS in two steps of dynamic pushing and static equilibrium, for the intact and distally fractured bone. Experiments were also performed on the same specimen to validate the simulation results. A good agreement was found between the model predictions and the experimental observations. There was a three-point contact pattern between the nail and medullary canal, only on the proximal fragment of the fractured bone. The nail deflection was much larger in the sagittal plane and increased for the larger diameter nail, as well as for more distally fractured or intact femur. The altered position of the distal hole was predicted by the model with an acceptable error (mean: 0.95; max: 1.5 mm, in different tests) to be used as the compensatory information for fine tuning of proximally mounted targeting systems. © 2018 IPE

Stiffness Matrix of 6-DOF Cable-Driven Parallel Robots and Its Homogenization

International audienceIn this paper, several issues of the stiffness matrix of a general 6-DOF Cable-Driven Parallel Robot (CDPR) are addressed. First, the stiffness matrix of a CDPR with hefty cable is derived analytically. Then, a homogenization of this stiffness matrix is introduced. The discussion on this procedure gives an intuitive meaning of the stiffness matrix of the CDPR and its homogeneous form. This analysis can be used to solve a set of CDPR design problems

Investigating the relationship between job stress, workload and oxidative stress in nurses

Objectives. Occupational stress and workload are common risk factors among nurses that increase absenteeism, reduce the quality and quantity of patient care, increase care costs and increase the patient safety risk. The relation between these risk factors and oxidative stress levels has not been clearly defined. Methods. This study was conducted with 258 participants (126 nurses as the case group and 132 healthy adults as the control group). Information was collected using a demographic questionnaire, the nurses� occupational stress scale and the NASA task load index workload questionnaire. Blood samples were taken from the participants and then the levels of malondialdehyde (MDA), superoxide dismutase (SOD), catalase and total antioxidant capacity (TAC) were measured in the serum samples. Independent t tests and one-way analysis of variance were used for statistical analysis. Results. SOD and TAC were significantly higher and MDA was significantly lower among the case group compared to the control group. TAC levels significantly decreased with increased stress. MDA levels showed negative associations with stress and workload. Nurses experience high levels of occupational stress and workload. Conclusion. Biomarkers such as SOD, TAC and MDA are the most important predictors of work stress and overwork in this study. © 2021 Central Institute for Labour Protection�National Research Institute (CIOP-PIB)

Stiffness Oriented Tension Distribution Algorithm for Cable-Driven Parallel Robots

International audienceA novel criterion is introduced in this paper to determine the set of cable tensions for Cable-Driven Parallel Robots (CDPRs) with the aim of maximizing the robot stiffness along a specific direction. Based on the feasible polygon of the CDPR and its stiffness matrix, an algorithm selects the set of admissible cable tensions leading to the smallest moving-platform displacement, the moving-platform being subject to an external wrench. The proposed tension distribution is implemented in a control scheme and experimented on a fully-constrained CDPR for a window cleaning application