1,720,963 research outputs found
The Effect of the Loading Rate on the Full-Field Strain Distribution on Intervertebral Discs
Full text linkContrasting results are reported when the spine is tested at different strain rates. Tissue specimens from the ligaments or the intervertebral discs (IVD, including annulus fibrosus and nucleus pulposus) exhibit higher stiffness and lower dissipation at high strain rates. Counterintuitively, when spine segments are tested at high rates, the hysteresis area and loop width increase. It is unclear how the load is shared between the different structures at different loading rates. The hypotheses of this study were: (i) As the IVD stiffens at higher loading rates, the strain distribution around the disc would be depend on the loading rate; (ii) Pre-conditioning attenuates the strain-rate dependency of the IVD, thus making differences in strain distribution smaller at the different rates. Six segments of three vertebrae (L4-L6) were extracted from porcine spines and tested in presso-flexion at different loading rates (reaching full load in 0.67s, 6.7s and 67s). The full-field strain maps were measured using digital image correlation on the surface of the IVDs from lateral. The posterior-to-anterior trends of the strain were computed in detail for each IVD, for each loading rate. The values and the direction of principal strain on the surface of the IVDs, vertebrae, and endplates remained unchanged at different rates. In the transition zone between IVD and vertebra, only slight differences due to the loading rate appeared but with no statistical significance. These findings will allow better understanding of the rate-dependent behaviour and failure of the IVD
In vitro experimental studies and numerical modeling to investigate the biomechanical effects of surgical interventions on the spine
No full textThis paper offers a comprehensive systematic review of biomechanical research on the spine and on in vitro and numerical methods of investigation. This review focuses on interventions on the ligaments, on the facets, and on the lamina (facetectomies, laminectomies, and laminoplasties). Surgical interventions on the facets and lamina in some cases yield dissatisfactory clinical follow-up. Patient outcome is strongly related to the effects that such interventions have on the biomechanical functionality of the spine. The papers examined include those addressing the untreated spine (range of motion and stiffness), but the focus is on experimental and numerical investigations studying the role of the ligaments and of the posterior structures (including their role in granting spine stability and the biomechanical behavior of each ligament). The papers were classified based on the different investigation approaches. In vitro experiments exploit dedicated biomechanical spine testers to measure the mechanical properties of physical specimens. Numerical modeling (multibody dynamics, finite-element analysis) allows predicting the effect of different conditions. All the papers indicate that interventions on the ligaments, facets, and lamina increase range of motion and decrease stability. The quantitative results show great variability across studies. This review shows how it is possible to use in vitro and numerical methods to investigate the biomechanical effects of surgical interventions
Full-field in vitro investigation of hard and soft tissue strain in the spine by means of Digital Image Correlation
No full textThe spine deserves careful biomechanical investigation, because of the different types of degeneration deriving from daily stress, trauma, and hard and soft tissue pathologies. Many biomechanical studies evaluated the range of motion, structural stiffness of spine segments under different loading conditions, without addressing the strain distribution. Strain gauges have been used to measure strain in the vertebral body, in a pointwise way.What is currently missing is a method to measure the distribution of strain in the soft tissues (intervertebral discs and ligaments), and an integration between measurements in the hard and soft tissues. Digital Image Correlation (DIC) is a recently developed optical technique, which allows measuring the distribution of displacements and deformation in a contact-less way. It can provide a full-field view of the examined surface under load. DIC can therefore give a more complete knowledge of the biomechanics of the spine
In vitro full-field strain distribution on human thoracolumbar spine segment subjected to flexion
No full textThe aim of this work was measuring in vitro full-field strain maps on a human spine segment subjected to physiological flexion
Development and application of methods for the biomechanical characterization of spine ligaments and intervertebral discs
Full text linkThe spine is one of the major organs subject to trauma or genetic problems. Today 30% of people suffer from back pain and every day a large number of surgical interventions on the spine are performed to treat those patients with severe spinal deformities (i.e. scoliosis or kyphosis). From a statistical analysis, the percentage of failures for this type of interventions is around 25-30%. The aim of my PhD thesis was the improvement of the knowledge of the strain distribution on biological tissues, in particular on ligaments and intervertebral discs of the human spine. The first part of this thesis aimed at improvement of the methodologies used to measure the strain distribution, simultaneously on hard (vertebrae) and soft tissues (ligaments and intervertebral discs), using Digital Image Correlation. The second part of my research studied the biomechanical behaviour of the intervertebral discs and of the different ligaments. The disc acts as a shock absorber for the spine, reducing shocks and impacts. The anterior longitudinal ligament (ALL), supraspinous and interspinous ligaments were studied analysing how they were deformed under different loading conditions. These ligaments limit the movement of the spine during flexion reducing the overload on the intervertebral disc. The ALL does not offer great mechanical strength during lateral bending and axial torsion. Summarizing, the study underlines the necessity of having a full-field strain analysis tool to enhance the knowledge of the biomechanics of the spine and the interaction between different types of tissue. Furthermore, the results reported in this thesis could be useful also to build better multibody spine models and to include more realistic properties in finite element models. These results could be a starting point for future works in which the effect of different surgical procedures and the use of new surgical devices could be investigated
Studio biomeccanico del movimento di entrata alle parallele asimmetriche: kippe
Full text linkStudio di un esercizio dell'entrata alle parallele asimmetriche in ginnastica artistica effettuato mediante le tecniche della biomeccanica, in particolare la rilevazione per mezzo della stereo-fotogrammetria e l'analisi dei dati attraverso SMART Tracker e SMART Analyzer allo scopo di introdurre un nuovo movimento di entrata alle parallele di maggiore difficoltà
Studio della cinematica del nuoto a stile libero attraverso sensori inerziali
Full text linkAnalisi cinematica delle fasi del nuoto, velocità in vasca e body roll attraverso l'uso di sensori inerziali.
Implementazione di innovativi algoritmi di calcolo con l'utilizzo del filtro di Kalman 3D, matrici di rotazione e quaternioni per la determinazione dei parametri fondamentali del nuoto e della posizione del polso nel sistema di riferimento di torace.
Confronto dei risultati ottenuti mediante i diversi algoritmi e loro validazione con quelli ottenuti con l'uso della stereofotogrammetria.
Gli algoritmi possono essere generalizzati ad altri gesti motori
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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