École Polytechnique de Montréal

About: École Polytechnique de Montréal is a education organization based out in Montreal, Quebec, Canada. It is known for research contribution in the topics: Finite element method & Computer science. The organization has 8015 authors who have published 18390 publications receiving 494372 citations.

Muscle activity, internal loads, and stability of the human spine in standing postures: combined model and in vivo studies.

Abstract: Study design The load in active and passive spinal components as well as the stability margin in standing postures +/- load in hands are studied using both computational model and in vivo studies. Objective To investigate muscle activity, spinal loads, and system stability in standing postures. Summary of background data Study of the human trunk yields a redundant system, the satisfactory solution of which remains yet to be done. Existing biomechanical models are often oversimplified or attempt to solve the problem by equilibrium of loads at only one cross section along the spine. Methods In vivo measurements are performed to obtain kinematics (by skin markers) as input data into model and EMG activity (by surface electrodes) for validation of predictions. A thoracolumbar model, while accounting for nonlinear ligamentous properties and trunk musculature, solved the redundant active-passive system by a novel kinematics-based approach that used both the posture and gravity/external loads as input data. In both studies, neutral standing posture was considered with weights up to 380 N held in hands with arms extended close to the body either in front or on sides. Results Predicted muscle forces were in satisfactory agreement with measured EMG activities. The activity in extensor muscles significantly increased with the load magnitude when held in front, a trend that disappeared as loads were held on sides. Abdominal muscles remained relatively silent. Large compression forces of approximately 2000 N were computed in lower lumbar levels when 380 N was held in front. Coactivity in abdominal muscles markedly increased internal loads and stability margin. Conclusion A tradeoff exists between lower loads in passive tissues (i.e., tissue risk of failure) and higher stability margins as both increase with greater muscle coactivation. Greater muscle activity observed under load held in front did not necessarily yield larger stability margin as the position of load appeared to play an important role as well. The strength of the proposed model is in realistic consideration of both passive-active structures under postures and gravity/external loads, yielding results that satisfy kinematics, equilibrium, and stability requirements in all directions along the spine.

Function points analysis: an empirical study of its measurement processes

Abstract: Function point analysis (FPA) was initially designed on the basis of expert judgments, without explicit reference to any theoretical foundation. From the point of view of the measurement scales used in its measurement process, FPA constitutes a potpourri of scales not admissible without the transformations imbedded in the implicit models of expert judgments. The results of this empirical study demonstrate that in a homogeneous environment not burdened with major differences in productivity factors there is a clear relationship between FPA's primary components and work-effort. This empirical study also indicates that there is such a relationship for each step of the FPA measurement process prior to the mixing of scales and the assignments of weights. Comparisons with FPA productivity models based on weights confirm, on the one hand, that the weights do not add information and, on the other, that the weights are fairly robust and can be used when little historical data is available. The full data set is provided for future studies.

Design and Experimental Verification of Compact Frequency-Selective Surface With Quasi-Elliptic Bandpass Response

Abstract: A compact frequency-selective surface (FSS) having a quasi-elliptic bandpass response is presented in this paper. This was realized by vertically cascading substrate integrated waveguide (SIW) cavities. A single SIW cavity FSS has been fully studied and approximate analytical formulas are introduced to calculate its resonant frequencies. Two different resonances can be excited by a plane wave in the single SIW cavity FSS. According to theories of the cascading cavity filter and dual-mode filter, cross coupling can be realized in cascading SIW cavity FSSs, thus a compact FSS with a quasi-elliptic bandpass response is implemented. A Ka-band sample was fabricated by a printed circuit board (PCB) process. Experiments were carried out to validate this design method. Measured results are in agreement with predicted ones. The proposed quasi-elliptic FSS presents a number of advantages, namely, high selectivity, stable performance, and much reduced volume.