119,226 research outputs found
A portable system for in-situ calibration of force platforms: Theoretical validation
No full textThe periodic calibration of measurement devices, such as force platforms (FPs), guarantees and optimizes the quality of the acquired data.
In this study, the theoretical validation of a portable system for the in-situ calibration of six-component FPs is presented. A least-squares
algorithm, that estimates the FP re-calibration matrix, was designed and tested using a simulation approach. The algorithm is the core of a
portable system, described in a separate paper, and represents a refinement of an algorithm previously presented by Cappello et al. [Cappello
A, Lenzi D, Chiari L. Periodical in-situ re-calibration of force platforms: a new method for the robust estimation of the calibration matrix. Med
Biol Eng Comput 2004;42:350–5]. The new algorithm assumes that the calibration inputs are known, 3-D, time-varying loads, applied to the
FP at known coordinates, and not constrained in their direction of application. Simulation results confirmed the a priori identifiability of the
re-calibration matrix and some of the algorithm features were optimized in the perspective of an actual building of the system.With the aid of
simple sinusoidal loads, applied in at least five different points, we proved that the algorithm can ensure errors less than 0.2 N and 0.4 Nm
when calculating force and moment components of an applied load
Nonlinear verification of the resistive-wall boundary modules in the specyl and pixie3d magneto-hydrodynamic codes for fusion plasmas
No full textA nonlinear verification benchmark is reported between the three-dimensional magneto-hydrodynamic (3D MHD) codes specyl [Cappello and Biskamp, Nucl. Fusion 36, 571 (1996)] and pixie3d [Chacón, Phys. Plasmas, 15, 056103 (2008)]. This work substantially extends a former successful verification study between the same two codes [Bonfiglio et al., Phys. Plasmas, 17, 082501 (2010)] and focuses on the verification of thin-shell resistive-wall boundary conditions, recently implemented in both codes. Such boundary conditions feature a thin resistive shell in contact with the plasma and an ideal wall placed at a finite distance, separated from the resistive shell by a vacuum region, along with a 3D boundary flow consistent with Ohm’s law. This setup allows the study of MHD modes that are influenced by the plasma magnetic boundary, such as external kink modes. The linear growth and nonlinear saturation of external kink modes are studied in both the tokamak and reversed-field pinch magnetic configurations, demonstrating excellent agreement between the two codes. For the tokamak, we present a comparison with analytical linear stability results for the external kink mode, demonstrating remarkable agreement between numerical and analytical growth rates
Identification of distinct characteristics of postural sway in Parkinson's disease: a feature selection procedure based on principal component analysis.
No full textWe selected descriptive measures of the centre of pressure (CoP) displacement in quiet standing, by means of a procedure based on principal component analysis, in two groups particularly different in terms of postural behaviours, such as subjects with Parkinson's disease (PD) in the levodopa off and on states. We computed 14 measures of the CoP: 5 measures of CoP trajectory over the support surface, 3 measures that estimated the area covered by the CoP, 1 measure that estimated the principal CoP sway direction, 1 measure that quantified the CoP total power, 1 measure that estimated the variability of CoP frequency content and 3 measures of characteristic CoP frequencies [L. Rocchi, L. Chiari, A. Cappello, Feature selection of stabilometric parameters based on principal component analysis, Med. Biol. Eng. Comput. 42 (2004) 71-79; L. Rocchi, L. Chiari, F.B. Horak, Effects of deep brain stimulation and levodopa on postural sway in Parkinson's disease, J. Neurol. Neurosurg. Psychiatry, 73 (2002) 267-274]. The feature selection, independently applied to the measures obtained in the two groups, resulted in different principal component (PC) subspaces of the 14-dimension original data set (4 PCs in the off and 3 PCs in the on state to account for over 90% of the original variance), but in the same 5 CoP measures (selected features) needed to describe the different postural behaviours: root mean square distance; mean velocity; principal sway direction; centroidal frequency of the power spectrum; frequency dispersion. The five selected features were found to provide insight into the postural control mechanisms and to describe changes in postural strategies in the two groups of PD subjects, off and on levodopa. Thus, the five selected features may be recommended for use in clinical practice and in research, in the direction toward the definition of a standard protocol in quantitative posturography
A portable system for in-situ re-calibration of force platforms: experimental validation
No full textA system for the in-situ re-calibration of six-component force platforms is presented. The system consists of a device, a data-acquisition procedure and an algorithm. The device, simple and lightweight, is composed of a high-precision, 3-D load cell, loaded through a triangular stage, and precisely positioned on the force platform under re-calibration by means of a template. The data-acquisition procedure lasts about 1h and requires up to 13 measurements consisting of manual positioning the load cell on the force platform, and then having the operator exerting loads on both load cell and force platform by his/her body movement. As a result, the procedure makes use of loads in the same range of posture and gait tests. The algorithm estimates the local or global six-by-six re-calibration matrix of the force platform through a least-squares optimization, and is presented in detail in a separate paper [Cedraro A, Cappello A, Chiari L., A portable system for in-situ re-calibration of force platforms: Theoretical validation. Gait Posture 2008;28:488-94]. The system was validated on four commercial force platforms (Amti OR6, Bertec 4060-08, Bertec 4080-10, and Kistler 9286A). The average accuracy in the measurement of the center of pressure were 2.3+/-1.4mm, 2.6+/-1.5mm, 11.8+/-4.3mm, 14.0+/-2.5mm before re-calibration, 1.1+/-0.6mm, 1.8+/-1.1mm, 1.0+/-0.6mm, 3.2+/-1.1mm after global re-calibration, and 0.7+/-0.4mm, 0.8+/-0.5mm, 0.5+/-0.3mm, 2.0+/-1.2mm after local re-calibration (results presented in random order). The force platform re-calibration influenced the value, sign, and timing of net joint moments, estimated during a gait task through an inverse dynamics approach
Spectral Composition of the Scattered Field from a Large Metallic Cloaked Cylinder
No full textAn analysis of the spectral content of the scattered field by metallic cylinders covered by homogeneous mantle cloak is performed. In particular, a theoretical approach based on Mie Theory is considered for the computation of the scattered field, which is examined in terms of radar cross-section and scattering coefficients. The values of surface impedance that lead to the minimum of the radar cross section are determined as a function of the cylinder radius normalized with respect to the frequency of operation and of the dielectric material characteristics. Furthermore, the spectral composition of the scattered field for this optimal condition is evaluated and compared with that of the bare cylinder case
Synovial sarcoma and malignant mesothelioma of the pleura: Review, differential diagnosis and possible role of apoptosis
No full textSynovial sarcoma of the pleural cavity is exceptionally rare and may be confused, both clinically and histologically, with malignant mesothelioma, with subsequent inappropriate therapy. To address this dilemma, four biphasic synovial sarcomas (BSSs) and four biphasic malignant mesotheliomas (BMMs) were studied with a panel of mucin and immunohistochemical stains to determine if they would allow one to distinguish between the two. The BMMs were all pleural-based. The BSSs were extrapleural. The mucin and immunohistochemical stains were all performed on formalin-fixed, paraffin-embedded tissue using standard techniques, with appropriate positive and negative controls. Mucin present in BSS is, in general, mucicarmine-positive and resistant to both hyaluronidase and diastase. Of the immune markers evaluated, only calretinin, Ber-Ep4 and bcl-2 were of limited discriminatory value. Subsets of cytokeratins, CEA and CD 34 were not helpful. With the exception of bcl-2, the apoptotic markers p53, bax and cpp32 (caspase) also were not useful. However, when the apoptotic stains were viewed collectively, variations in expression between the two tumours raised the possibility that alterations in apoptotic activity might be responsible for their pathogenesis and behavior. The diagnosis of BSS or BMM of the pleural should be made only after total consideration of clinical, radiological, histochemical and immunohistochemical findings. Although mucin stains are useful in differential diagnosis, reliance solely on immunohistochemical markers, with the possible exception of calretinin, Ber-Ep4 and bcl-2, is not dependable. The role of apoptosis in the pathogenesis of these tumours needs to be explored with a much larger series
Harmonic analysis and reduction of the scattered field from electrically large cloaked metallic cylinders
No full textIn this paper, an analysis of the spectral composition of the scattered field from coated metallic cylinders is performed, focusing particularly on the cloaking of electrically large structures. An expression of the scattering coefficients is derived, considering both a dielectric and a metasurface coating. Modeling the metasurface as a surface impedance boundary condition, the surface impedance, which annuls one harmonic of the scattered field, is formulated in a closed and compact form. Moreover, in the case of cylinders with radius comparable with the wavelength of interest, it is demonstrated that a reduction of the scattering is possible by using a homogeneous metasurface coating, which presents a positive surface reactance. In particular, a reduction of the scattering width of 4 dB is achieved for a cylinder radius of a = 0.917λ0
Control implementation of compliant composite material actuators for wearable robotic exoskeleton
No full textIn previous work [1], [2], a novel actuator is presented that merges traditional electromechanical motors and multistable composite structures. It has been shown that these structures are able to arrange themselves in multi-stable configurations corresponding to local minima of their strain enery. When this composite structure is connected with the electromechanical motor as proposed, the resulting actuator shows significant benefits in terms of safety, energy saving and control implementation using the compliant property of the overall structure, the particular shape of the strain energy landscape, and the accurately predictable non-linear behavior. Hence the proposed actuator is well-suited for many robotic applications requiring continuous assistance and robust stability. In this paper, the structure's multistability property is exploited for energy saving purpose. In order to do that, a supervised learning method named Extreme Learning Machine is introduced to approximate the elastic force applied by the structure and Gradient Descent algorithm is used to compute the local minimum points equivalent to local minima of structure's strain energy
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