The Role of Sacral Slope in the Progression of a Bilateral Spondylolytic Defect at L5 to Spondylolisthesis: A Biomechanical Investigation Using Finite Element Analysis

© The Author(s) 2017. Study Design: A biomechanical study using finite element analysis. Objectives: The main objective of this study was to investigate the role of sacral slope in the progression of a L5 bilateral spondylolytic defect to spondylolisthesis. Methods: A 3-dimensional model of lumbosacral spine was built using computed tomography (CT) data procured from an anonymized healthy male subject. The segmented CT data was manipulated to generate 3 more models representing L5 bilateral spondylolytic defect with normal sacral slope (SS), sacral slope increased by 10° (SS+10), and sacral slope decreased by 10° (SS-10). The 3D models were imported into finite element modelling software Strand7 for preprocessing, running nonlinear static solves, and postprocessing of the results. Results: Directional biomechanical instabilities were induced in the lumbosacral spine as a result of changes in the L5-S1 disc shape secondary to the changes in sacral slope. Compared with the normal L5 lytic model, wedging of the L5-S1 disc (SS+10) resulted in a significantly greater range of motion in flexion (18% ↑) but extension motion characteristics were similar. Conversely, flattening of the L5-S1 disc (SS-10) resulted in a significantly greater range of motion in extension (16% ↑) but flexion motion characteristics were similar to that of the normal L5 lytic model. Conclusions: Variations in sacral slope while preserving the L5-S1 mid-disc height and orientation of the L5 vertebra resulted in variations in the L5-S1 disc shape. The results suggest that for such extremities in the L5-S1 disc shape different pathomechanisms exist for the progression of the L5 lytic defect to spondylolisthesis

Mild (not severe) disc degeneration is implicated in the progression of bilateral L5 spondylolysis to spondylolisthesis

© 2018 The Author(s). Background: Spondylolytic (or lytic) spondylolisthesis is often associated with disc degeneration at the index-level; however, it is not clear if disc degeneration is the cause or the consequence of lytic spondylolisthesis. The main objective of this computed tomography based finite element modelling study was to examine the role of different grades of disc degeneration in the progression of a bilateral L5-lytic defect to spondylolisthesis. Methods: High-resolution computed tomography data of the lumbosacral spine from an anonymised healthy male subject (26 years old) were segmented to build a 3D-computational model of an INTACT L1-S1 spine. The INTACT model was manipulated to generate four more models representing a bilateral L5-lytic defect and the following states of the L5-S1 disc: nil degeneration (NOR LYTIC), mild degeneration (M-DEG LYTIC), mild degeneration with 50% disc height collapse (M-DEG-COL LYTIC), and severe degeneration with 50% disc height collapse(S-COL LYTIC). The models were imported into a finite element modelling software for pre-processing, running nonlinear-static solves, and post-processing of the results. Results: Compared with the baseline INTACT model, M-DEG LYTIC model experienced the greatest increase in kinematics (Fx range of motion: 73% ↑, Fx intervertebral translation: 53%↑), shear stresses in the annulus (Fx anteroposterior: 163%↑, Fx posteroanterior: 31%↑), and strain in the iliolumbar ligament (Fx: 90%↑). The S-COL LYTIC model experienced a decrease in mobility (Fx range of motion: 48%↓, Fx intervertebral translation: 69%↓) and an increase in normal stresses in the annulus (Fx Tensile: 170%↑; Fx Compressive: 397%↑). No significant difference in results was noted between M-DEG-COL LYTIC and S-COL LYTIC models. Conclusions: In the presence of a bilateral L5 spondylolytic defect, a mildly degenerate index-level disc experienced greater intervertebral motions and shear stresses compared with a severely degenerate index-level disc in flexion and extension bending motions. Disc height collapse, with or without degenerative changes in the stiffness properties of the disc, is one of the plausible re-stabilisation mechanisms available to the L5-S1 motion segment to mitigate increased intervertebral motions and shear stresses due to a bilateral L5 lytic defect

Feedup, feedback, and feedforward in curve mid-air 3D gestures

Issuing a mid-air gesture in a three-dimensional space intrinsically suffers for the lack of explicit direct representation of the gesture with which guidance and feedback can be offered. To address this challenge, we decompose the feedback problem into three components: feedup to constantly represent the goal of the gestural task, feedback to respond to what the end user already did related to the initial goal, and feedforward to modify the representation towards the ultimate goal before terminating the gesture production. We exemplify these three components with case studies representing three levels of complexity of Curve Mid-Air 3D Gestures produced in three environments

A comprehensive sensitivity analisys of the WRF model for air quality applications over the Iberian Peninsula

Meteorological inputs play a vital role on regional air quality modelling. An extensive sensitivity analysis of the Weather Research and Forecasting (WRF) model was performed, in the framework of the Integrated Assessment Modelling System for the Iberian Peninsula (SIMCA) project. Up to 23 alternative model configurations, including Planetary Boundary Layer schemes, Microphysics, Land-surface models, Radiation schemes, Sea Surface Temperature and Four-Dimensional Data Assimilation were tested in a 3 km spatial resolution domain. Model results for the most significant meteorological variables, were assessed through a series of common statistics. The physics options identified to produce better results (Yonsei University Planetary Boundary Layer, WRF Single-Moment 6-class microphysics, Noah Land-surface model, Eta Geophysical Fluid Dynamics Laboratory longwave radiation and MM5 shortwave radiation schemes) along with other relevant user settings (time-varying Sea Surface Temperature and combined grid-observational nudging) where included in a “best case” configuration. This setup was tested and found to produce more accurate estimation of temperature, wind and humidity fields at surface level than any other configuration for the two episodes simulated. Planetary Boundary Layer height predictions showed a reasonable agreement with estimations derived from routine atmospheric soundings. Although some seasonal and geographical differences were observed, the model showed an acceptable behaviour overall. Despite being useful to define the most appropriate setup of the WRF model for air quality modelling over the Iberian Peninsula, this study provides a general overview of WRF sensitivity and can constitute a reference for future mesoscale meteorological modelling exercises

Effets de l'ozone sur quelques peuplements forestiers du réseau RENECOFOR

Depuis 2001, le GIEFS et l'ONF s'associent pour repérer la présence de symptômes d'ozone sur une quarantaine de placettes forestières du réseau RENECOFOR, en France. Cet article présente les résultats des observations menées entre 2001 et 2005 sur les placettes des régions méditerranéennes. Les dégâts d'ozone ont été repérés sur l'ensemble des sites de l'étude

L'ozone et les conifères du Sud-Est de la France

Dans le Sud-Est de la France des défoliations importantes chez plusieurs espèces de conifères s'observent parallèlement à de fortes concentrations d'ozone. Des recherches récentes permettent de discriminer les symptômes spécifiques d'ozone dans des feuilles ou des aiguilles par rapport aux altérations causées par d'autres facteurs de stress. Cette étude présente les niveaux d'ozone mesurés en 2000 sur le littoral et dans l'arrière-pays niçois et les compare aux taux de décoloration et de défoliation observés sur cinq espèces de conifères. Chez le pin cembro, des aiguilles ont été prélevées pour détecter et vérifier la présence de symptômes spécifiques d'ozone. Les niveaux d'ozone mesurés étaient suffisants pour causer des symptômes visibles et, probablement, pour affecter la croissance des pins étudiés. Des symptômes macroscopiques et microscopiques typiques de l'ozone, observables dans l'arrière pays, indiquent un état de stress et une accélération de la sénescence des aiguilles symptomatiques chez les pins cembro, contribuant probablement à leur mauvais état sanitaire dans les Alpes-Maritimes

Effets de l'ozone sur la forêt et la végétation dans les Alpes franco-italiennes.

Depuis le début des années 80, dans le sud des Alpes (frontière franco-italienne), plusieurs essences ont présenté des endommagements de leur feuillage avec un déficit foliaire bien marqué. Des premières études ont montré que la pollution par l'ozone influait sur le mauvais état de santé général des peuplements concernés. A partir de 1999, il importait d'évaluer (programme européen Interreg II) l'impact spécifique de la pollution par l'ozone sur les dommages observés. Les premiers résultats ont révélé des concentrations en ozone élevées. Parallèlement, l'endommagement foliaire a été estimé sur des placettes forestières. Ont été recherchés également des symptômes spécifiques de l'ozone sur quelques essences arborées, mais aussi sur toute la végétation de proximité. Des essais de corrélation ont été réalisés entre les niveaux d'ozone et les dégâts foliaires observés et des analyses microscopiques ont permis de confirmer la spécificité des dégâts observés

Saturation of optical absorption in CdS single crystals

The absorption saturation of CdS single crystals was investigated in the Urbach region. It was shown that the threshold behaviour of the absorption coefficient is caused by recharging of the shallow acceptors, and the absorption edge has exponential character both at low and high pumping intensities. The calculation method of nonlinear transmission dependencies was proposed. Using the known formulae one can minimize the value of root mean square deviation of the measured data from the calculated ones in the whole region of the light intensities

Experimental review of the performances of protective coatings for interconnects in solid oxide fuel cells

Ferritic stainless steel interconnects are used in solid oxide fuel cells; however, coatings are required to improve their performance. Although several types of coatings have been proposed, they have been scarcely investigated under similar conditions. This study compares the characteristics of uncoated Crofer 22 APU and eight different coatings on Crofer 22 APU for up to 3000\ua0h at 800\ua0\ub0C. The coatings were deposited at various research laboratories around the world, and the experiments were performed at Chalmers University of Technology, Sweden. Cross-sections of the samples were analysed using scanning electron microscopy and energy-dispersive x-ray spectroscopy. The (Co,Mn)-based coated steels showed more than 50-fold lower chromium evaporation and at least 3 times thinner Cr2O3 scale thickness compared to uncoated steel. The coated steel samples showed lower area-specific resistance (ASR) values than the uncoated steel after 3000\ua0h of exposure, irrespective of the coating thickness, composition and deposition method