To see the other types of publications on this topic, follow the link: Spine modeling.
Dissertations / Theses on the topic 'Spine modeling'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Spine modeling.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
VIEIRA, PEDRO SAMPAIO. "A SPINE 3D MODELING SYSTEM BASED ON X-RAY IMAGES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2009. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=14919@1.
Full textAbstract:
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO<br>Nos dias atuais, pesquisas envolvendo a computação gráfica e a área
médica, têm contribuído muito para a evolução tecnológica de exames e
diagnósticos. Uma vertente desses trabalhos está relacionada diretamente à
reconstrução 3D de estruturas anatômicas do corpo humano, em específico a
coluna vertebral. O sedentarismo e a alta dependência dos computadores vêm
aumentando e agravando os problemas posturais das pessoas. Por esse
motivo, novas técnicas de reconstrução 3D baseada em exames de tomografia
computadorizada (TC), ressonância magnética (RM) e raios-x são
desenvolvidas, tornando as avaliações clínicas cada vez mais precisas. Neste
trabalho é proposto um sistema de modelagem 3D baseado em radiografias
digitais com a finalidade de recriar a coluna vertebral em um ambiente virtual. A
recuperação das informações tridimensionais de cada vértebra ajuda a
melhorar a avaliação feita atualmente com base apenas em imagens 2D. A
técnica utilizada no desenvolvimento do método se baseia na
estereoradiografia. E a utilização de radiografias, em relação à TC, reduz
consideravelmente o tempo de exposição do paciente à radiação, além de ser
mais acessível à população pelo seu menor custo. Os resultados obtidos
apresentaram uma boa precisão do sistema. Além do mais, o método proposto
atingiu resultados bem próximos aos de pesquisas baseadas em TC e RM,
onde os dados de entrada são bem mais legíveis do que as imagens de raiosx.<br>Research involving computer graphics and laboratory exams has
contributed much to the quality of the Medical diagnose. One aspect of these
researches is directly related to 3D reconstruction of anatomical structures of
the human body, especially the spine. The sedentary lifestyle and the high
dependence of computers have increased the postural problems of the
population. Therefore, new techniques for 3D reconstruction based on
Computed tomography (CT), magnetic resonance imaging (MRI) and x-ray
images are required, in order to make the clinical evaluation increasingly
accurate. This work proposes a 3D modeling system based on x-ray images
that yields a virtual spine model. The recovery of three-dimensional information
of each vertebra helps improve the assessment currently made using only 2D
images. The technique used here is based on stereo radiographic. The use of
x-ray images instead of CT, significantly reduces the exposure time of the
patient to radiation, and is more useful to the general population due to its lower
cost. The results presented here show good accuracy despite its lower cost.
The proposed method has achieved results very close to those based on
expensive CT or MRI, where the input image is better than x-ray images.
2
Mavor, Matthew. "The Effects of Protective Footwear on Spine Control and Lifting Mechanics." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37205.
Full textAbstract:
Low back pain (LBP) is a common condition that affects all age groups and sexes. Although the development of LBP is multifactorial, the performance of lifting-based manual material handling (MMH) tasks are recognized as a primary risk factor. Many occupations that involve MMH tasks are performed in hazardous environments, where personal protective equipment (PPE) must be worn. Among the most commonly prescribed forms of PPE in Canada are CSA Grade 1 steel-toed work boots. According to the hazards present on the jobsite, workers may need to wear steel-toed work boots with/without a metatarsal guard or be able to wear steel-toed shoes (no upper). However, the amount of research on the interaction between protective footwear and human motion is limited. Therefore, the purpose of this thesis was to assess the effects of steel-toed shoes (unlaced), steel-toed boots (work boot), and steel-toed boots with a metatarsal guard (MET) on lifting mechanics. Specifically, three-dimensional kinematics of the lower limbs and trunk, sagittal net reaction moments of the low back, and local dynamic stability (LDS) of the lower limbs, lower back, and upper back were analyzed. Twelve males and 12 females were recruited to participate in this research project. Participants performed a repetitive lifting task at 10% of their maximum back strength, under three block-randomized footwear conditions. Ankle dorsiflexion was negatively affected by footwear type, where dorsiflexion was reduced the most in the MET condition compared to the unlaced condition (p < 0.01). However, there were no other main effects of footwear type on any other variable tested, and both male and female participants were able to maintain similar lifting mechanics and LDS values when moving up the kinematic chain. It is possible that participants were able to preserve their kinematics and stability through the appropriate recruitment of muscles, which may have implications for an increase in compressive and shear force on the spine and should be explored further in the future.
3
Campbell-Kyureghyan, Naira Helen. "Computational analysis of the time-dependent biomechanical behavior of the lumbar spine." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1095445065.
Full textAbstract:
Thesis (Ph. D.)--Ohio State University, 2004.<br>Title from first page of PDF file. Document formatted into pages; contains xix, 254 p.; also includes graphics. Includes bibliographical references (p. 234-254).
4
Williams, Matthew James. "Segmentation in 3D virtual spine modeling for assistance in surgical planning and guidance." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0010401.
Full text
5
Miller, Emily Michele. "Exercise-Induced Low Back Pain and Neuromuscular Control of the Spine - Experimentation and Simulation." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/37507.
Full textAbstract:
Low back pain (LBP) is associated with altered neuromuscular control of the trunk, as well as impaired performance during functional tasks highly dependent upon trunk neuromuscular control. Comparing measurements between individuals with and without LBP does not distinguish whether the LBP individual exhibits altered neuromuscular control only while experiencing LBP versus at all times. Additional insight was gained on the relationship between trunk neuromuscular control and LBP by investigating individuals who experience recurrent exercise-induced LBP (eiLBP). To differentiate the effects of LBP from individual differences, comparisons were made between episodes of pain and no pain within eiLBP individuals, and between eiLBP individuals while pain free and a group of healthy controls. Three studies were completed based on repeated measurements from both eiLBP and healthy individuals. Study 1 investigated effects of eiLBP on fundamental measures of neuromuscular control, including intrinsic trunk stiffness and the paraspinal reflex delay using a series of pseudo-random position perturbations. eiLBP individuals exhibited increased stiffness compared to healthy controls unaffected by the presence of pain, and increased reflex delays concurrent only with pain. Study 2 investigated effects of eiLBP on seated sway during a functional task involving maintaining balance. Seat and trunk kinematics were obtained while participants balanced on a wobble chair at two difficulty levels. eiLBP individuals exhibited impaired seat measures at all times, with altered trunk measures only while in pain and when the task was not challenging. Study 3 investigated effects of eiLBP on the underlying control of seated sway using a model of wobble chair balance. Quantified neuromuscular control indicated increases in proportional and noise gains for a challenging level compared to an easy level, more so for eiLBP individuals compared to controls and while experiencing pain compared to pain free. Overall, fundamental measures, seated sway measures, and identified control parameters using a model of wobble chair balance were all affected by the presence of pain within the eiLBP individuals and/or the eiLBP individuals compared to healthy controls. Therefore, this study shows that some characteristics appear to be inherent to the LBP individual, while others are only concurrent with pain.<br>Ph. D.
6
Perez, Miguel A. "Empirical Evaluation of Models Used to Predict Torso Muscle Recruitment Patterns." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/35381.
Full textAbstract:
For years, the human back has puzzled researchers with the complex behaviors it presents. Principally, the internal forces produced by back muscles have not been determined accurately. Two different approaches have historically been taken to predict muscle forces. The first relies on electromyography (EMG), while the second attempts to predict muscle responses using mathematical models. Three such predictive models are compared here. The models are Sum of Cubed Intensities, Artificial Neural Networks, and Distributed Moment Histogram. These three models were adapted to run using recently published descriptions of the lower back anatomy. To evaluate their effectiveness, the models were compared in terms of their fit to a muscle activation database including 14 different muscles. The database was collected as part of this experiment, and included 8 participants (4 male and 4 female) with similar height and weight. The participants resisted loads applied to their torso via a harness. Results showed the models performed poorly (average R2's in the 0.40's), indicating that further improvements are needed in our current low back muscle activation modeling techniques. Considerable discrepancies were found between internal moments (at L3/L4) determined empirically and measured with a force plate, indicating that the maximum muscle stress selected and/or the anatomy used were faulty. The activation pattern database collected also fills a gap in the literature by considering static loading patterns that had not been systematically varied before.<br>Master of Science
7
Nguyen, Ho Quang. "Material-driven mesh derived from medical images for biomechanical system : application on modeling of the lumbar spine." Thesis, Compiègne, 2016. http://www.theses.fr/2016COMP2313.
Full textAbstract:
La lombalgie est un problème de santé commun qui touche une grande partie de la population des pays industrialisés. Au cours des années, la modélisation numérique a été largement étudiée pour étudier la biomécanique du rachis lombaire pour aider fortement les cliniciens dans le diagnostic et les traitements de cette pathologie. Ce travail présente une méthodologie pour la modélisation éléments finis spécifique au patient prenant en compte à la fois la géométrie individualisée et les propriétés des matériaux des structures biologiques. Dans cette étude, le maillage est piloté par des connaissances des matériaux personnalisées qui sont extraites de l'imagerie médicale avancée. En outre, un logiciel convivial comprenant du traitement d'images, des maillages « material-driven » et de l'affectation des propriétés des matériaux, nommé C3M pour le «Computed Material-driven Mesh Model», a été développé pour générer efficacement des modèles FE spécifiques aux sujets à partir d'images médicales. Ce procédé est appliqué pour générer un modèle FE spécifique au patient du rachis lombaire à partir d'images issues par Résonance Magnétique (IRM) ou par tomodensitométrie 3D (CT). Cette approche ouvre une nouvelle perspective pour améliorer le processus de maillage à l'aide de connaissances du matériel dérivées d'images médicales. Le modèle proposé permet un assemblage précis et simple de vertèbres et des disques intervertébraux en tenant en compte à la fois la géométrie et les propriétés mécaniques des matériaux reflétant la spécificité du patient<br>Low back pain is a common health problem which impacts a large part of the population in industrialized countries. Over the years, numerical modeling has been widely studied to investigate the biomechanics of lumbar spine for strongly assisting clinicians in diagnosis and treatments of this spinal pathology. In recent years, there has been a growing interest in researching and developing patient specific computer modeling which has proven its ability to provide great promises for developing realistic model of individual subject. However, still the specificity of these models is not fully described or is often limited to patient geometry. In fact, few models consider appropriate material properties derived from tissue characterization obtained from medical images. Furthermore, patient specific models can be obtained with geometry and mechanical properties derived from CT, but few from MRI which is well-suited for examining soft tissues. Therefore, development of the high-fidelity, patient-specific finite element model of the lumbar spine still presents the challenge. In this context of patient-specific finite element modeling, mesh generation is a crucial issue which requires an accurate representation of the geometry with well-shaped and sized elements and a relevant distribution of materials. This work presents a methodology for patient-specific finite element modeling which takes both individualized geometry and material properties of biological structures into consideration. In this study, the mesh is driven by personalized material knowledge which is extracted from advanced medical imaging. Additionally, a user-friendly program including image processing, material-driven meshing and material properties assignment, named C3M for “Computed Material-driven Mesh Model”, has been developed to generate efficiently subject-specific FE models derived from medical images. This process is applied to generate a patient specific FE model of lumbar spine based on both MRI and CT images. This approach opens a new direction to improve the meshing process using material knowledge derived from medical images. The proposed model allows an accurate and straightforward assembly of vertebrae and IVDs considering both geometry and material properties reflecting patient-specificity
8
Toosizadeh, Nima. "Time-dependent assessment of the human lumbar spine in response to flexion exposures: in vivo measurement and modeling." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/19274.
Full textAbstract:
Among several work-related injuries, low back disorders (LBDs) are the leading cause of lost workdays, and with annual treatment costs in excess of $10 billion in the US. Epidemiological evidence has indicated that prolonged and/or repetitive non-neutral postures, such as trunk flexion, are commonly associated with an increased risk of LBDs. Trunk flexion can result in viscoelastic deformations of soft tissues and subsequent mechanical and neuromuscular alterations of the trunk, and may thereby increase LBD risk. While viscoelastic behaviors of isolated spinal motion segments and muscles have been extensively investigated, in vivo viscoelastic responses of the trunk have not, particularly in response to flexion exposures. Further, most biomechanical efforts at understanding occupational LBDS have not considered the influence of flexion exposures on spine loads.
Four studies were completed to characterize viscoelastic deformation of the trunk in response several flexion exposures and to develop and evaluate a computational model of the human trunk that accounts for time-dependent characteristics of soft tissues. Participants were exposed to prolonged flexion at different trunk angles and external moments, and repetitive trunk flexion with different external moments and flexion rates. Viscoelastic properties were quantified using laboratory experiments and viscoelastic models. A multi-segment model of the upper body was developed and evaluated, and then used to estimate muscle forces and spine loads during simulated lifting tasks before and after prolonged trunk flexion at a constant angle and constant external moment. Material properties from the earlier experiments were used to evaluate/calibrate the model.
Experimental results indicated important effects of flexion angle, external moment, and flexion rate on trunk viscoelastic behaviors. Material properties from fitted Kelvin-solid models differed with flexion angle and external moment. Nonlinear viscoelastic behavior of the trunk tissues was evident, and predictive performance was enhanced using Kelvin-solid models with ≥2 iii retardation/relaxation time constants. Predictions using the multi-segment model suggested increases in spine loads following prolonged flexion exposures, primarily as a consequence of additional muscle activity. As a whole, these results help to characterize the effects of trunk flexion exposures on trunk biomechanics, contribute to more effective estimates of load distribution among passive and active components, enhance our understanding of LBD etiology, and may facilitate future controls/interventions.<br>Ph. D.
9
Carlson, Robin. "Clinical Significance of Response Shift in a Spine Interventional Clinical Trial." ScholarWorks, 2015. https://scholarworks.waldenu.edu/dissertations/231.
Full textAbstract:
The effectiveness of treatments for degenerative spine conditions, where the primary symptom is back pain, is typically determined using patient-reported quality of life (QoL) measures. However, patients may adjust their internal standards when scoring QoL based on factors other than their health. This response shift phenomenon could confound the interpretation of study data and impact effectiveness conclusions. In the current study, response shift was examined using structural equation modeling (SEM) and previously collected clinical trial data comparing 2 minimally invasive medical devices in lumbar spinal stenosis patients through 1 year postintervention. In subject QoL results, reprioritization shift between 3 months and 12 months that could confound standard analysis was identified. Treatment group did not influence response shift identified at 12 months. SEM provided an effective and practical tool for clinical investigators to assess response shift in available clinical study data. As response shift could lead to invalid conclusions when QoL measures are analyzed, clinical investigators should include response shift assessment in the design of clinical trials. This research into how response shift phenomenon can impact clinical trial results improves the ability of clinical investigators to interpret clinical trial data, potentially preventing erroneous conclusions. This research may also assist researchers and government regulators in the identification and reimbursement of beneficial, cost-effective medical treatments for patients worldwide. For clinical research designers, this study demonstrates a practical application of response shift assessment.
10
López, Picazo Mirella. "3D subject-specific shape and density modeling of the lumbar spine from 2D DXA images for osteoporosis assessment." Doctoral thesis, Universitat Pompeu Fabra, 2019. http://hdl.handle.net/10803/666513.
Full textAbstract:
Osteoporosis is the most common bone disease, with a significant morbidity and mortality caused by the increase of bone fragility and susceptibility to fracture. Dual Energy X-ray Absorptiometry (DXA) is the gold standard technique for osteoporosis and fracture risk evaluation at the spine. However, the standard analysis of DXA images only provides 2D measurements and does not differentiate between bone compartments; neither specifically assess bone density in the vertebral body, which is where most of the osteoporotic fractures occur. Quantitative Computed Tomography (QCT) is an alternative technique that overcomes limitations of DXA-based diagnosis. However, due to the high cost and radiation dose, QCT is not used for osteoporosis management. In this thesis, a method providing a 3D subject-specific shape and density estimation of the lumbar spine from a single anteroposterior DXA image is proposed. The method is based on a 3D statistical shape and density model built from a training set of QCT scans. The 3D subject-specific shape and density estimation is obtained by registering and fitting the statistical model onto the DXA image. Cortical and trabecular bone compartments are segmented using a model-based algorithm. 3D measurements are performed at different vertebral regions and bone compartments. The accuracy of the proposed methods is evaluated by comparing DXA-derived to QCT-derived 3D measurements. Two case-control studies are also performed: a retrospective study evaluating the ability of DXA-derived 3D measurements at lumbar spine to discriminate between osteoporosis-related vertebral fractures and control groups; and a study evaluating the association between DXA-derived 3D measurements at lumbar spine and osteoporosis-related hip fractures. In both studies, stronger associations are found between osteoporosis-related fractures and DXA-derived 3D measurements compared to standard 2D measurements. The technology developed within this thesis offers an insightful 3D analysis of the lumbar spine, which could potentially improve osteoporosis and fracture risk assessment in patients who had a standard DXA scan of the lumbar spine without any additional examination.<br>La osteoporosis es la enfermedad ósea más común, con una morbilidad y mortalidad significativas causadas por el aumento de la fragilidad ósea y la susceptibilidad a las fracturas. La absorciometría de rayos X de energía dual (DXA, por sus siglas en inglés) es la técnica de referencia para la evaluación de la osteoporosis y del riesgo de fracturas en la columna vertebral. Sin embargo, el análisis estándar de las imágenes DXA solo proporciona mediciones 2D y no diferencia entre los compartimentos óseos; tampoco evalúa la densidad ósea en el cuerpo vertebral, que es donde se producen la mayoría de las fracturas osteoporóticas. La tomografía computarizada cuantitativa (QCT, por sus siglas en inglés) es una técnica alternativa que supera las limitaciones del diagnóstico basado en DXA. Sin embargo, debido al alto costo y la dosis de radiación, la QCT no se usa para el diagnóstico de la osteoporosis. En esta tesis, se propone un método que proporciona una estimación personalizada de la forma 3D y la densidad de la columna vertebral en la zona lumbar a partir de una única imagen DXA anteroposterior. El método se basa en un modelo estadístico 3D de forma y densidad creado a partir de un conjunto de entrenamiento de exploraciones QCT. La estimación 3D personalizada de forma y densidad se obtiene al registrar y ajustar el modelo estadístico con la imagen DXA. Se segmentan los compartimentos óseos corticales y trabeculares utilizando un algoritmo basado en modelos. Se realizan mediciones 3D en diferentes regiones vertebrales y compartimentos óseos. La precisión de los métodos propuestos se evalúa comparando las mediciones 3D derivadas de DXA con las derivadas de QCT. También se realizan dos estudios de casos y controles: un estudio retrospectivo que evalúa la capacidad de las mediciones 3D derivadas de DXA en la columna lumbar para discriminar entre sujetos con fracturas vertebrales relacionadas con la osteoporosis y sujetos control; y un estudio que evalúa la asociación entre las mediciones 3D derivadas de DXA en la columna lumbar y las fracturas de cadera relacionadas con la osteoporosis. En ambos estudios, se encuentran asociaciones más fuertes entre las fracturas relacionadas con la osteoporosis y las mediciones 3D derivadas de DXA en comparación con las mediciones estándar 2D. La tecnología desarrollada dentro de esta tesis ofrece un análisis en 3D de la columna lumbar, que podría mejorar la evaluación de la osteoporosis y el riesgo de fractura en pacientes que se sometieron a una exploración DXA estándar de la columna lumbar sin ningún examen adicional.
11
Seeliger, Christine. "Spatial and stochastic modeling of TrkB mediated signaling pathways involved in long term potentation in the dendritic spine." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708013.
Full text
12
Vestgaarden, Tov I. "Experimental and analytical modeling of the in vivo and in vitro biomechanical behavior of the human lumbar spine." [Tampa, Fla] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0002277.
Full text
13
Denoziere, Guilhem. "Numerical Modeling of a Ligamentous Lumbar Motion Segment." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4998.
Full textAbstract:
Eight out of ten people in the United States will have problems with low back pain at some point in their life. The most significant surgical treatments for low back pain can be distributed into two main groups of solutions: arthrodesis and arthroplasty. Spinal arthrodesis consists of the fusion of a degenerated functional spine unit (FSU) to alleviate pain and prevent mechanical instability. Spinal arthroplasty consists of the implantation of an artificial disc to restore the functionality of the degenerated FSU. The objective of this study is to analyze and compare the alteration of the biomechanics of the lumbar spine treated either by arthrodesis or arthroplasty.
A three-dimensional finite element model of a ligamentous lumbar motion segment, constituted of two FSUs, was built and simulated through a static analysis with the finite element software ABAQUS.
It was shown that the mobility of the segment treated by arthrodesis was reduced in all rotational degrees of freedom by an average of approximately 44%, relative to the healthy model. Conversely, the mobility of the segment treated by arthroplasty was increased in all rotational degrees of freedom by an average of approximately 52%. The FSU implanted with the artificial disc showed a high risk of instability and further degeneration. The mobility and the stresses in the healthy FSU, adjacent to the restored FSU in the segment treated by arthroplasty, were also increased.
In conclusion, the simulation of the arthroplasty model showed more risks of instability and further degeneration, on the treated level as well as on the adjacent levels, than in the arthrodesis model.
14
Karadogan, Ernur. "A Cable-Actuated Robotic Lumbar Spine as the Haptic Interface for Palpatory Training of Medical Students." Ohio University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1320958588.
Full text
15
Andersson, Evelina. "The 2-dimensional biomechanical modeling of the loads on the spine (L5-L1) during a “Back Walkover” maneuver in gymnastics." Thesis, Högskolan i Halmstad, Bio- och miljösystemforskning (BLESS), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-27203.
Full textAbstract:
Injuries in the female gymnast are common and it is important to understand the biomechanical factors responsible for injury. The Back Walkover maneuver requires one of the greatest amounts of lumbar hyperextension compared to other common gymnastic maneuvers. During the Back Walkover large lateral and vertical impact forces follows on the spine. The spine and muscles around the spine have to absorb generally large forces; therefore the loads on the back and certainly on the lower back are of significant interest. Additionally, it takes a lot of strength and a vast range of motion to perform gymnastic maneuvers such as The Back Walkover. It is of interest to study mechanical loads on a female gymnast since they show higher occurrences of stress-related pathologies of the lumbar spine. Therefore the purpose of this project was to examine the loads on the spine during the gymnastic maneuver Back Walkover. Tests on a single female gymnast were made at the sports engineering lab at the University of Adelaide in Australia. Using the 3D-camera system; Optitrack Motion Capture System and Kistler Force Plate, positional data for two dimensions, X-direction (anterior-posterior) and Z-direction (vertical), and ground force were received. Data received were progressed into a graph, diagrams and biomechanical calculations where forces for the vertebrae L1 were calculated in vertical and horizontal direction. The received forces were compared to vertical and horizontal forces in L1 during standing position. Together with developed videos this assisted to model the loads of the spine (L1) during the gymnastic maneuver the “Back Walkover”. The study has led to a deeper knowledge for the community about the risks for female gymnasts and has widened the experience of the project participant, as the project aimed.
16
Groth, Kevin M. "Nonlinear Lumped-Parameter Model of the Lumbar Intervertebral Disc: A Study on Viscoelastic Deformation and Three-Dimensional Modeling of the Spine." Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/34313.
Full textAbstract:
Due to the mathematical complexity of current musculoskeletal spine models, there is a need for computationally-efficient models of the intervertebral disc (IVD). The aim of this study is to develop a mathematical model that will adequately describe the motion of the IVD under axial cyclic loading and three-dimensional quasi-static loading as well as maintain computational efficiency for use in future musculoskeletal spine models.
<p> A viscoelastic standard nonlinear solid (SNS) model is introduced within this study. It was developed to predict the axial response of the human lumbar IVD subjected to low-frequency vibration. Nonlinear axial behavior of the SNS model was simulated by a strain-dependent elastic modulus on the standard linear solid (SLS) model.
<p>
The SNS model was able to predict the dynamic modulus of the IVD for frequencies of 0.01, 0.1, and 1 Hz. Furthermore, the model was able to quantitatively predict the load relaxation at a frequency of 0.01 Hz. However, model performance was unsatisfactory when predicting load relaxation and hysteresis at higher frequencies (0.1 Hz and 1 Hz). Results suggest that the standard solid model may require strain-dependent elastic and viscous behavior to represent the dynamic response to compressive strain.
<p>
The SNS model was expanded to a three-dimensional elastic model by adding a matrix of spring elements in parallel with the SNS model. The geometry and orientation of the added elements represent the regional variations in stiffness and physiologic fiber angle. Results suggest that lordotic posture may be advantageous when modeling the intervertebral joint (IVJ) behavior.<br>Master of Science
17
Stoner, Kirsten Elizabeth. "Surgical treatment for cervical myelopathy: the effect on spinal cord strain using magnetic resonance imaging and finite element modeling." Diss., University of Iowa, 2017. https://ir.uiowa.edu/etd/5646.
Full textAbstract:
Cervical myelopathy is the most common form of spinal cord injury in North America with roughly 19,000 new cases in the US every year. It results from chronic compression of the spinal cord by osteophytes, intervertebral disc herniation, and ossified ligaments. It commonly affects adults over the age of 50 years and causes upper extremity numbness, loss of hand dexterity, gait disturbances, and decreased proprioception. Recent studies imaging studies have shown this injury is highly dependent on the dynamic motion of the spine, often worsening in extreme flexion and extension. Surgical intervention is the accepted mode of treatment with the aim of decompressing the spinal canal and stabilizing the spine. However, 25% of patients have reoccurrence of symptoms indicating that surgical treatments may not be adequately addressing the injury. A main reason for this is little data has been reported on the spinal cord mechanics during cervical spinal motion in either healthy or cervical myelopathy subjects. To address this, we utilized MR imaging and finite element modeling to investigate spinal cord mechanics. As far as we know, we are the first group to obtain in vivo 3 dimensional spinal cord displacement and strain data from human subjects and the first to develop a C2 to T1 FE model of the healthy and cervical myelopathic spine and spinal cord.
Utilizing high resolution 3T MR imaging in neutral, flexion, and extension positions we were able to obtain spinal cord displacement and strain fields from both healthy subjects and cervical myelopathy subjects before and after surgical intervention. In healthy subjects, flexion motion of the spine causes the spinal cord to move superiorly and in extension the spinal cord moves inferiorly. During extension, localizations of high principal strain can be seen in healthy subjects at areas of bony impingement and dural buckling. In both flexion and extension, cervical myelopathy subjects exhibited very little spinal cord displacement due to spinal cord compression. Principal strains during flexion and extension were greater in cervical myelopathy patients than healthy patients, specifically at the C4-6 vertebral levels. Surgical treatments for cervical myelopathy did restore spinal cord motion however, not in the same pattern or direction as healthy subjects. Additionally principal strains of the spinal cord were not reduced after surgical intervention. This indicates that surgical interventions are not adequately addressing the altered mechanics of the spinal cord during cervical myelopathy.
To determine the how common surgical techniques for cervical myelopathy affect spinal cord mechanics, a FE model of the cervical spine and spinal cord was developed. The spinal cord motion was validated against MR imaging data obtained from normal subjects. Once validated, the model was used to develop a FE model of cervical myelopathy and surgical interventions. The native FE model predicted spinal cord motion well and replicated bony spinal cord impingement and dural buckling seen in healthy subjects. The FE model of cervical myelopathy also replicated spinal cord motion well as compared to MR imaging data of cervical myelopathy. Principal strains obtained from the healthy and cervical myelopathy FE models were similar in flexion however in extension, principal strains were higher at the C3, C6 and C7 levels. This is different than the patterns exhibited in the MR imaging and is most likely due to the percent of spinal cord compression induced in the FE model.
Three, C4 to C7 surgical interventions were introduced to the model: anterior discectomy and fusion, anterior discectomy and fusion with laminectomy, and double door laminoplasty. In flexion, all surgical treatments doubled spinal cord principal strains at the C3 level and minimally reduced tensile strain at C4. The majority of strain reduction occurred at C5-7. In extension, all surgical techniques increased principal strains at the C3 and C4 levels. Little or no reduction in principal strains was seen at the C5 and C7 levels. All surgical techniques reduced principal strains at the C6 level. Of the surgical techniques, ACDF tended to reduce spinal cord principal strains the least in both flexion and extension and tended to induce the highest von Mises stresses.
Combining the data obtained from MR imaging and FE modeling we can see that cervical myelopathy alters spinal cord mechanics by limiting spinal cord motion and increasing spinal cord strain. Additionally, current surgical techniques are not addressing the change in spinal cord mechanics effectively. Specifically after surgery, and especially with ACDF, spinal cord displacements and strains are being increased and transferred to different sections of the spinal cord. This indicates not only the need and importance of further research in spinal cord mechanics but also the need to improve treatments for cervical myelopathy which adequately restore the spinal cord mechanics.
18
Mahato, Niladri Kumar. "Development of Novel Imaging and Image Modeling Techniques for the Assessment andQuantification of Inter-Vertebral Motion Using MRI." Ohio University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1470841487.
Full text
19
Van, Den Abbeele Maxim. "Modélisation Musculo-Squelettique Personnalisée du Rachis Cervical." Thesis, Paris, ENSAM, 2018. http://www.theses.fr/2018ENAM0037.
Full textAbstract:
Dans le cadre du programme scientifique de chaire BiomecAM, la modélisation musculo-squelettique du rachis cervical répond à différents besoins: comprendre les mécanismes d’endommagement de cette structure fonctionnelle essentielle, améliorer la prévention des pathologies, aider à la conception de nouveaux dispositifs (orthèses ou implants) et planification de traitements orthopédiques et chirurgicaux. De grandes avancées ont été faites ces dernières années pour progresser vers la modélisation personnalisée: des approches innovantes pour générer des maillages en éléments finis efficaces, des moyens d’analyse quantitative in vivo pour personnaliser les propriétés mécaniques du disque intervertébral et du système musculaire, des premières modélisations pertinentes de la commande neuro-motrice d’activation musculaire.L’objectif de cette thèse est de s’appuyer sur ces avancées pour proposer une modélisation musculo squelettique personnalisée du rachis cervical intact, lésé et restauré chirurgicalement, dans le but de mieux comprendre les mécanismes de dégénération du rachis cervical et d’évoluer vers un outil de planification de traitements orthopédiques et chirurgicaux s’appuyant sur cette modélisation personnalisée<br>Within the context of the scientific program chaired by BiomecAM, the musculoskeletal modelling of the cervical spine responds to various needs: understanding the damage mechanisms to this functional and essential structure, augmenting the efficiency level of pathology prevention, contributing to the design of new medical devices (orthoses or implants) and enabling orthopaedic and surgical treatment planning. Strong advancements have been made during the recent past years to evolve towards personalised modelling: innovative finite element mesh generation methods, in vivo quantitative analysis techniques to personalise the assignment of material properties to the intervertebral disc and the muscular system and preliminary models incorporating muscle activation have been developed.The aim of this PhD project is to exploit these scientific advancements to evolve towards a personalised musculoskeletal model of the intact, degenerated and instrumented cervical spine, thus contributing to the understanding of the degeneration mechanisms of the cervical spine and offering a means of orthopaedic and surgical treatment planning
20
Ceran, Murat. "Parametric human spine modelling." Thesis, Loughborough University, 2006. https://dspace.lboro.ac.uk/2134/7958.
Full textAbstract:
3-D computational modelling of the human spine provides a sophisticated and cost-effective medium for bioengineers, researchers, and ergonomics designers in order to study the biomechanical behaviour of the human spine under different loading conditions. Developing a generic parametric computational human spine model to be employed in biomechanical modelling introduces a considerable potential to reduce the complexity of implementing and amending the intricate spinal geometry. The main objective of this research is to develop a 3-D parametric human spine model generation framework based on a command file system, by which the parameters of each vertebra are read from the database system, and then modelled within commercial 3-D CAD software. A novel data acquisition and generation system was developed as a part of the framework for determining the unknown vertebral dimensions, depending on the correlations between the parameters estimated from existing anthropometrical studies in the literature. The data acquisition system embodies a predictive methodology that comprehends the relations between the features of the vertebrae by employing statistical and geometrical techniques. Relations amongst vertebral parameters such as golden ratio were investigated and successfully implemented into the algorithms. The validation of the framework was carried out by comparing the developed 3-D computational human spine models against various real life human spine data, where good agreements were achieved. The constructed versatile framework possesses the capability to be utilised as a basis for quickly and effectively developing biomechanical models of the human spine such as finite element models.
21
Mihcin, Senay. "Spine modelling for lifting." Thesis, Loughborough University, 2007. https://dspace.lboro.ac.uk/2134/8065.
Full textAbstract:
Mathematical modelling is widely used in the field of biomechanics. The traditional approach to investigate spine related injuries is to check the strength of the components of the spine. Spinal stability approach focuses on the force polygons formed by the body weight, muscle forces, ligament forces and external load. This force polygon is expected to stay within the boundaries of the spine to ensure stability. Proving the possibility of one force polygon within the spine boundaries proves the stability of the spine. This study focuses on the full curvature of the spine for spinal stability investigations in a lifting activity. An experiment has been designed to investigate the postural differences in males and females by measuring the full spinal curvature with a skin surface device. Distributed body weight force, with increased detail of muscle and ligament forces acting on the spine have been modelled by writing a code in Visual Basic, while lifting a load from the boot of a car in the sagittal plane. This model is flexible enough to reflect changes in body weight parameter. Results show that there is a difference between male and female postures during the full span of lifting activities. Application of individual muscle forces provides greater control of stability at each vertebral level. By considering the elongation of the ligaments and the force requirements of the muscle groups, it is possible to diagnose soft tissue failure. The differences in posture result in different moment arms for muscles and ligaments causing different loading on the spine. Most critical postures have been identified as the fully flexed postures with external load acting on the spine. Conceptual design ideas have been proposed to assist lifting a load from the boot of a car to eliminate the excessive flexion and loading on the spine.
22
Wagnac, Eric. "Expérimentation et modélisation détaillée de la colonne vertébrale pour étudier le rôle des facteurs anatomiques et biomécaniques sur les traumatismes rachidiens." Thesis, Aix-Marseille 2, 2011. http://www.theses.fr/2011AIX22140.
Full textAbstract:
L’objectif de la thèse était d’étudier l’influence de facteurs anatomiques et biomécaniques tels que la présence d’ostéophytes vertébraux, le taux de chargement et le profil sagittal rachidien (défini par l’orientation et la forme de la colonne vertébrale dans le plan sagittal) sur les traumatismes de la colonne vertébrale thoracique et lombaire. Pour ce faire, des essais expérimentaux sur spécimens cadavériques rachidiens ont été réalisés et un modèle biomécanique détaillé du rachis T1-sacrum a été raffiné, validé expérimentalement et exploité. Les résultats ont démontré que les segments ostéophytiques présentaient des fractures de moindre sévérité localisées au niveau de la vertèbre proximale, contrairement aux segments sans ostéophytes, qui présentaient des fractures sévères (souvent comminutives) au niveau de la vertèbre médiane. Ils ont également confirmé que le taux de déformation jouait un rôle-clé dans l’initiation du traumatisme et que le profil sagittal avait une influence significative sur les caractéristiques des fractures osseuses lors d’accidents impliquant un mécanisme principalement en compression. En revanche, le profil sagittal n’exercerait qu’une influence limitée sur la nature des traumatismes lors d’un accident impliquant un mécanisme de flexion-distraction<br>The objective of this thesis was to study the influence of anatomical and biomechanical factors such as the presence of vertebral osteophytes, the loading rate and the sagittal profile of the spine (defined by the orientation and shape of the spine in the sagittal plane) on spinal injuries at the thoracic and lumbar levels. To fulfill this objective, experiments on human cadaveric spines were performed and a detailed biomechanical model of the spine was refined, validated against experimental data, and exploited. Results showed that the presence of large osteophytes significantly influenced the location, pattern and type of fracture, and provided to the underlying vertebra a protective mechanism against severe compression fractures (e.g. burst fractures). They also showed that the loading rate played a key-role on the onset of spinal trauma and that the sagittal profile of the spine had a significant influence on the bone fracture in accidents that involve compression mechanisms. On the other hand, the sagittal profile of the spine had a limited influence on the nature of spinal injuries in accidents that involved flexion-distraction mechanisms
23
Stein, Félix. "SPICE Modeling of TeraHertz Heterojunction bipolar transistors." Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0281/document.
Full textAbstract:
Les études qui seront présentées dans le cadre de cette thèse portent sur le développement et l’optimisation des techniques pour la modélisation compacte des transistors bipolaires à hétérojonction (TBH). Ce type de modélisation est à la base du développement des bibliothèques de composants qu’utilisent les concepteurs lors de la phase de simulation des circuits intégrés. Le but d’une technologie BiCMOS est de pouvoir combiner deux procédés technologiques différents sur une seule et même puce. En plus de limiter le nombre de composants externes, cela permet également une meilleure gestion de la consommation dans les différents blocs digitaux, analogiques et RF. Les applications dites rapides peuvent ainsi profiter du meilleur des composants bipolaires et des transistors CMOS. Le défi est d’autant plus critique dans le cas des applications analogiques/RF puisqu’il est nécessaire de diminuer la puissance consommée tout en maintenant des fréquences de fonctionnement des transistors très élevées. Disposer de modèles compacts précis des transistors utilisés est donc primordial lors de la conception des circuits utilisés pour les applications analogiques et mixtes. Cette précision implique une étude sur un large domaine de tensions d’utilisation et de températures de fonctionnement. De plus, en allant vers des nœuds technologiques de plus en plus avancés, des nouveaux effets physiques se manifestent et doivent être pris en compte dans les équations du modèle. Les règles d’échelle des technologies plus matures doivent ainsi être réexaminées en se basant sur la physique du dispositif. Cette thèse a pour but d’évaluer la faisabilité d’une offre de modèle compact dédiée à la technologie avancée SiGe TBH de chez ST Microelectronics. Le modèle du transistor bipolaire SiGe TBH est présenté en se basant sur le modèle compact récent HICUMversion L2.3x. Grâce aux lois d’échelle introduites et basées sur le dessin même des dimensions du transistor, une simulation précise du comportement électrique et thermique a pu être démontrée.Ceci a été rendu possible grâce à l’utilisation et à l’amélioration des routines et méthodes d’extraction des paramètres du modèle. C’est particulièrement le cas pour la détermination des éléments parasites extrinsèques (résistances et capacités) ainsi que celle du transistor intrinsèque. Finalement, les différentes étapes d’extraction et les méthodes sont présentées, et ont été vérifiées par l’extraction de bibliothèques SPICE sur le TBH NPN Haute-Vitesse de la technologie BiCMOS avancée du noeud 55nm, avec des fréquences de fonctionnement atteignant 320/370GHz de fT = fmax<br>The aim of BiCMOS technology is to combine two different process technologies intoa single chip, reducing the number of external components and optimizing power consumptionfor RF, analog and digital parts in one single package. Given the respectivestrengths of HBT and CMOS devices, especially high speed applications benefit fromadvanced BiCMOS processes, that integrate two different technologies.For analog mixed-signal RF and microwave circuitry, the push towards lower powerand higher speed imposes requirements and presents challenges not faced by digitalcircuit designs. Accurate compact device models, predicting device behaviour undera variety of bias as well as ambient temperatures, are crucial for the development oflarge scale circuits and create advanced designs with first-pass success.As technology advances, these models have to cover an increasing number of physicaleffects and model equations have to be continuously re-evaluated and adapted. Likewiseprocess scaling has to be verified and reflected by scaling laws, which are closelyrelated to device physics.This thesis examines the suitability of the model formulation for applicability to production-ready SiGe HBT processes. A derivation of the most recent model formulationimplemented in HICUM version L2.3x, is followed by simulation studies, whichconfirm their agreement with electrical characteristics of high-speed devices. Thefundamental geometry scaling laws, as implemented in the custom-developed modellibrary, are described in detail with a strong link to the specific device architecture.In order to correctly determine the respective model parameters, newly developed andexisting extraction routines have been exercised with recent HBT technology generationsand benchmarked by means of numerical device simulation, where applicable.Especially the extraction of extrinsic elements such as series resistances and parasiticcapacitances were improved along with the substrate network.The extraction steps and methods required to obtain a fully scalable model library wereexercised and presented using measured data from a recent industry-leading 55nmSiGe BiCMOS process, reaching switching speeds in excess of 300GHz. Finally theextracted model card was verified for the respective technology
24
Waernlund, Angelica. "Modelling the Nordic Hydro Power System with Spine Toolbox." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-293977.
Full textAbstract:
In the Nordic power system, the largest balancing resource is hydro power. For future developments of the Nordic power system with more renewable and varying energy, such as wind power, the hydro power and its limitations must thus be taken into account. To be able to study this, a model with these limitations is needed. In earlier projects at KTH, a model of the Swedish hydro power system was built, but with the interconnected Nordic power system and the large amount of hydro power in Norway, the Norwegian hydro power system also needs to be considered. In this project, a model of both the Swedish and Norwegian hydro power system is built. Most of the data of the Swedish hydro power system is reused from the earlier projects, while new data of the Norwegian hydro power system is collected. Also data of transmission capacities and power generation and consumption for all areas, both in Sweden and Norway, were needed. Most of the data could be found, or calculated from, the Norwegian Water Resources and Energy Directorate, Nord Pool and Svenska Kraftnät. The new model built in this project includes 363 Norwegian and 256 Swedish hydro power plants, divided into four Swedish and five Norwegian electricity areas. The model is built in Spine Toolbox and is an expanded and remade model based on an earlier, smaller model of the Skellefte river, which maximised the profits of sold electricity. In this project the model is changed to instead minimise the spillage and explore the flexibility of the hydro power system. That is, its possibility to adjust its power generation to both variable levels of demand and other sources of power generation without being forced to spill water. The results from the simulations were hourly values of water flow between hydro power plants, discharged water and spilled water, electricity flow from each hydro power plant and between electricity areas, and reservoir volumes in each reservoir. From this, the simulated production in Sweden, Norway and all their electricity areas could be compared to real data of energy production. This comparison showed that the total simulated production was very similar to real data when factoring out import and export. The spillage and reservoir volumes were also discussed. Further work could improve the models performance, for example adding import and export, implementing minimum reservoir volumes, and base local inflow of water on real data, but overall the model provided promising results. This project has shown that is it possible to build large models in Spine, and adjust them to investigate different cases.<br>I det nordiska kraftsystemet är vattenkraft den största resursen för att balansera variationer i elproduktion. För framtida ändringar och utbyggnader i kraftsystemet med mer förnybara och varierade energikällor, som vindkraft, måste vattenkraften och dess begränsningar tas hänsyn till. För att kunna studera det nordiska kraftsystemet behövs en modell som tar häsyn till dessa begränsningar. I tidigare projekt på KTH togs en modell av det svenska vattenkraftsystemet fram, men med det sammankopplade nordiska kraftsystemet och den stora mängden vattenkraft i Norge, måste även Norges vattenkraftsystem beaktas. I detta projekt skapas en modell över det svenska och norska vattenkraftsystemet. Majoriteten av data för det svenska vattenkraftsystemet återanvänds från tidigare projekt, medan ny data för det norska vattenkraftsystemet samlas in. Även data över överföringskapaciteter och elproduktion och konsumtion för alla områden, både i Sverige och Norge, behövdes. Den nya modellen som byggs i detta projekt inkluderar 363 norska och 256 svenska vattenkraftverk, uppdelade i fyra elområden i Sverige, och fem i Norge. Modellen byggs i Spine Toolbox, och är en ombyggd och expanderad modell, baserad på en tidigare, mindre modell av Skellefteälven som maximerade inkomst från såld energi. I detta projekt ändras modellen till att istället minimera spillet och undersöka flexibiliteten i vattenkraftsystemet. Det vill säga, dess möjlighet att anpassa kraftproduktionen till både varierande efterfrågan och annan elproduktion, utan att tvingas spilla vatten. Resultaten från simuleringarna bestod av timvärden för vattenflöde mellan vattenkraftverk, tappat och spillt vatten, flöde av el från varje kraftverk och mellan elområden, och magasinvolymer. Den simulerade elproduktionen i Sverige, Norge och i alla elområden kunde sedan jämföras med verklig data. Denna jämförelse visade att den totala simulerade produktionen var mycket lik den verkliga vattenkraftproduktionen med import och export exkluderat. Även spill och magasinvolymer diskuterades. Ytterligare arbete kan ge en ännu bättre modell, exempelvis kan framtida arbete vara att lägga till export och import, implementera minimala magasinvolymer, och lägga in verklig data för lokalt inflöde av vatten, men överlag gav dock modellen lovande resultat. Detta projekt har visat att det är möjligt att skapa stora modeller över energisystem i Spine, och anpassa dem för att undersöka olika scenarion och se hur framtida förändringar i kraftsystemet kan påverka, och påverkas av, vattenkraftsystemet.
25
Bacorisen, Dnyansingh. "Modelling radiation damage in spinel oxides." Thesis, Loughborough University, 2006. https://dspace.lboro.ac.uk/2134/34089.
Full textAbstract:
In this thesis, defect formation by a radiation event in the normal MgAl2O4 was investigated using molecular dynamics (MD) simulations. The mechanisms and activation barriers for point defects to diffuse were determined using temperature accelerated dynamics (TAD). The role of cation inversion on defect formation and defect diffusion in spinel-structured oxides was analysed by performing the simulations in three spinels: the normal MgAl2O4, the half-inverse MgGa2O4 and the fully inverse MgIn2O4. The methodology employed in this thesis can be utilised for simulations in other ionic materials.
26
Bonhomme, Phillip. "Circuit modeling of spintronic devices: a SPICE implementation." Thesis, Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51818.
Full textAbstract:
Every engineer that has worked on designing an integrated circuit has to leverage an under- standing of device physics. Understanding device physics is essential when optimizing a design for speed, power, etc. These characteristics affect the bottom line when considering an integrated circuit used in a particular application. In order for there to be an under- standing of device physics, there must be a device model that is developed for a device of interest. The development of a device model often involves utilizing fundamental physical equations in a manner that is solvable by either analytical or numerical means.
This typically begins by simplifying fundamental physical equations, possibly spanning multiple domains, and considering the physical quantities of interest. In order to make simplifications, assumptions about the underlying physics must be made. It is the process of transitioning from known physics laws to simplified mathematical models that a device modeler spans.
This thesis will cover the device modeling aspects of a new classification of computing devices, spintronics. It will begin by stating the physical assumptions necessary for the operation of spintronic devices. Then it will go the process of deriving the underlying physical equations and stating them in a tractable form with the appropriate boundary conditions. Then these equations will be manipulated and mapped into an equivalent circuit. The equivalent circuits will them be validated against analytical solutions provided from other works. It will then finish by providing example devices that can be simulated with the develop device models, and some optimization results are proposed based off a simplified circuit model.
27
Johansson, Jonny. "SPICE modeling of ultrasound systems : improvements and verifications." Licentiate thesis, Luleå tekniska universitet, EISLAB, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-18643.
Full textAbstract:
The success of modern electronics is built on the possibility to accurately predict system behavior by the use of simulation tools. This paradigm can be extended to components such as sensors attached to the electronics. The ability to simulate both sensors (mechanical components) and electronics together renders possible effective optimizations at system level, i.e. minimizing size, cost and power consumption. In this thesis the simulation of a combined electronics and ultrasound sensor system is explored. The environment used is compatible with the electronic simulation tool SPICE. Improvements and verifications of existing SPICE models for ultrasound equipment is described, and applied in the design of integrated analog electronics for an ultrasound measurement system. Emphasis is put on the interdependence between acoustic performance and electronics design. The goal is to improve precision in the simulations to a level where real systems can be implemented from simulation results alone. The thesis is divided into introduction and three attached papers. In the introduction, an overview of ultrasound devices, measurement technology and simulation is given. Tools and design flow for analog integrated circuits are discussed. The first paper shows that system simulations can be used to minimize the size of the transistors used to excite an ultrasound transducer, while keeping maximum output ultrasound energy. A design of an ASIC (Application Specific Integrated Circuit) driver stage for piezoelectric crystals is made and performance of the system is predicted using system simulations. Measurements and simulations are compared, showing that the optimum transistor size can be chosen from simulation data with very good precision. The goal with paper number two is to achieve absolute amplitude correctness in PSpice simulations of ultrasonic systems. Previously published models of the ultrasound propagation medium include viscoelastic loss but disregard loss due to diffraction, i.e. beam spreading. This paper presents a method to include diffraction loss in the models. Measurements and simulations have been performed using a pulse echo system in water. Results show that the simulated amplitude of the returned echo differs less than 10% from measured values in both near and far fields. In paper number three, the influence of parasitic electrical components on measurements and simulations is investigated. It is shown that simulation of excitation pulses can be done with very high accuracy if parasitics are taken into account. The coaxial cable which connects the electronics and the transducer represents one of the major parasitic components in the system. As the cable length is varied, pulse echo amplitudes and time delays shift. It is shown that simulations can be used to predict these effects with good accuracy.<br>Godkänd; 2001; 20070313 (ysko)
28
Gatton, Michelle L. "Mathematical modelling of muscle recruitment and function in the lumbar spine." Thesis, Queensland University of Technology, 2000. https://eprints.qut.edu.au/31211/1/Michelle_Gatton_Thesis.pdf.
Full textAbstract:
Low back pain is an increasing problem in industrialised countries and although it is a major socio-economic problem in terms of medical costs and lost productivity, relatively little is known about the processes underlying the development of the condition. This is in part due to the complex interactions between bone, muscle, nerves and other soft tissues of the spine, and the fact that direct observation and/or measurement of the human spine is not possible using non-invasive techniques. Biomechanical models have been used extensively to estimate the forces and moments experienced by the spine. These models provide a means of estimating the internal parameters which can not be measured directly. However, application of most of the models currently available is restricted to tasks resembling those for which the model was designed due to the simplified representation of the anatomy. The aim of this research was to develop a biomechanical model to investigate the changes in forces and moments which are induced by muscle injury. In order to accurately simulate muscle injuries a detailed quasi-static three dimensional model representing the anatomy of the lumbar spine was developed. This model includes the nine major force generating muscles of the region (erector spinae, comprising the longissimus thoracis and iliocostalis lumborum; multifidus; quadratus lumborum; latissimus dorsi; transverse abdominis; internal oblique and external oblique), as well as the thoracolumbar fascia through which the transverse abdominis and parts of the internal oblique and latissimus dorsi muscles attach to the spine. The muscles included in the model have been represented using 170 muscle fascicles each having their own force generating characteristics and lines of action. Particular attention has been paid to ensuring the muscle lines of action are anatomically realistic, particularly for muscles which have broad attachments (e.g. internal and external obliques), muscles which attach to the spine via the thoracolumbar fascia (e.g. transverse abdominis), and muscles whose paths are altered by bony constraints such as the rib cage (e.g. iliocostalis lumborum pars thoracis and parts of the longissimus thoracis pars thoracis). In this endeavour, a separate sub-model which accounts for the shape of the torso by modelling it as a series of ellipses has been developed to model the lines of action of the oblique muscles. Likewise, a separate sub-model of the thoracolumbar fascia has also been developed which accounts for the middle and posterior layers of the fascia, and ensures that the line of action of the posterior layer is related to the size and shape of the erector spinae muscle. Published muscle activation data are used to enable the model to predict the maximum forces and moments that may be generated by the muscles. These predictions are validated against published experimental studies reporting maximum isometric moments for a variety of exertions. The model performs well for fiexion, extension and lateral bend exertions, but underpredicts the axial twist moments that may be developed. This discrepancy is most likely the result of differences between the experimental methodology and the modelled task. The application of the model is illustrated using examples of muscle injuries created by surgical procedures. The three examples used represent a posterior surgical approach to the spine, an anterior approach to the spine and uni-lateral total hip replacement surgery. Although the three examples simulate different muscle injuries, all demonstrate the production of significant asymmetrical moments and/or reduced joint compression following surgical intervention. This result has implications for patient rehabilitation and the potential for further injury to the spine. The development and application of the model has highlighted a number of areas where current knowledge is deficient. These include muscle activation levels for tasks in postures other than upright standing, changes in spinal kinematics following surgical procedures such as spinal fusion or fixation, and a general lack of understanding of how the body adjusts to muscle injuries with respect to muscle activation patterns and levels, rate of recovery from temporary injuries and compensatory actions by other muscles. Thus the comprehensive and innovative anatomical model which has been developed not only provides a tool to predict the forces and moments experienced by the intervertebral joints of the spine, but also highlights areas where further clinical research is required.
29
Panzer, Matthew. "Numerical Modelling of the Human Cervical Spine in Frontal Impact." Thesis, University of Waterloo, 2006. http://hdl.handle.net/10012/2865.
Full textAbstract:
Motor vehicle accidents continue to be a leading cause of cervical spine injury despite a conscientious effort to improve occupant safety. Accurately predicting occupant head and neck response in numerical crash simulations is an essential part of the process for developing better safety solutions. <br /><br /> A biofidelic model of the human cervical spine was developed with a focus on accurate representation of the cervical spine at the local tissue level. These tissues were assembled to create a single segment model that was representative of <em>in vitro</em> spine in quasi-static loading. Finally, the single segment models were assembled to create a full cervical spine model that was simulated in dynamic loading and compared to human volunteer response. <br /><br /> Models of each segment were constructed from the basic building blocks of the cervical spine: the intervertebral disc, the vertebrae, the ligaments, and the facet joints. Each model was simulated in all modes of loading and at different levels of load. The results of the study indicate that the cervical spine segments performed very well in flexion, compression, and tension. Segment response to lateral bending and axial rotation was also good, while response in extension often proved too compliant compared to the experimental data. Furthermore, the single segment models did not fully agree with the experimental shear response, again being more compliant. <br /><br/> The full cervical spine model was assembled from the single segment models incorporating neck musculature. The model was simulated dynamically using a 15 G frontal impact test. Active muscles were used to simulate the response of the human volunteers used in the study. The response of the model was in reasonable agreement with the experimental data, and compared better than current finite element cervical spine models. Higher frequency oscillation caused most of the disagreement between the model and the experimental data, which was attributed to a lack of appropriate dynamic material properties of the soft tissues of the spine. In addition, a study into the active properties of muscle indicated that muscle response has a significant influence on the response of the head. <br /><br /> A number of recommendations were proposed that would improve the biofidelity of the model. Furthermore, it was recommended that the future goal of this model would be to implement injury-predicting capabilities through the development of advance material models.
30
Castro, Mateos Isaac. "Statistical anatomical modelling for efficient and personalised spine biomechanical models." Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/13802/.
Full textAbstract:
Personalised medicine is redefining the present and future of healthcare by increasing treatment efficacy and predicting diseases before they actually manifest. This innovative approach takes into consideration patient’s unique genes, environment, and lifestyle. An essential component is physics-based simulations, which allows the outcome of a treatment or a disease to be replicated and visualised using a computer. The main requirement to perform this type of simulation is to build patient-specific models. These models require the extraction of realistic object geometries from images, as well as the detection of diseases or deformities to improve the estimation of the material properties of the studied object. The aim of this thesis was the design of a general framework for creating patient- specific models for biomechanical simulations using a framework based on statistical shape models. The proposed methodology was tested on the construction of spine models, including vertebrae and intervertebral discs (IVD). The proposed framework is divided into three well-defined components: The paramount and first step is the extraction of the organ or anatomical structure from medical images. In the case of the spine, IVDs and vertebrae were extracted from Magnetic Resonance images (MRI) and Computed Tomography (CT), respectively. The second step is the classification of objects according to different factors, for instance, bones by its type and grade of fracture or IVDs by its degree of degeneration. This process is essential to properly model material properties, which depends on the possible pathologies of the tissue. The last component of the framework is the creation of the patient-specific model itself by combining the information from previous steps. The behaviour of the developed algorithms was tested using different datasets of spine images from both computed tomography (CT) and Magnetic resonance (MR) images from different institutions, type of population and image resolution.
31
Esat, Volkan. "Biomechanical modelling of the whole human spine for dynamic analysis." Thesis, Loughborough University, 2006. https://dspace.lboro.ac.uk/2134/7839.
Full textAbstract:
Developing computational models of the human spine has been a hot topic in biornechanical research for a couple of decades in order to have an understanding of the behaviour of the whole spine and the individual spinal parts under various loading conditions. The objectives of this thesis are to develop a biofidefic multi-body model of the whole human spine especially for dynamic analysis of impact situations, such as frontal impact in a car crash, and to generate finite element (FE) models of the specific spinal parts to investigate causes of injury of the spinal components. As a proposed approach, the predictions of the multi-body model under dynamic impact loading conditions, such as reaction forces at lumbar motion segments, were utilised not only to have a better understanding of the gross kinetics and kinematics of the human spine, but also to constitute the boundary conditions for the finite element models of the selected spinal components. This novel approach provides a versatile, cost effective and powerful tool to analyse the behaviour of the spine under various loading conditions which in turn helps to develop a better understanding of injury mechanisms.
32
Flanagin, Maik. "The Hydraulic Spline: Comparisons of Existing Surface Modeling Techniques and Development of a Spline-Based Approach for Hydrographic and Topographic Surface Modeling." ScholarWorks@UNO, 2007. http://scholarworks.uno.edu/td/613.
Full textAbstract:
Creation of accurate and coherent surface models is vital to the effective planning and construction of flood control and hurricane protection projects. Typically, topographic surface models are synthesized from Delaunay triangulations or interpolated raster grids. Although these techniques are adequate in most general situations, they do not effectively address the specific case where topographic data is available only as cross-section and profile centerline data, such as the elevation sampling produced by traditional hydrographic surveys. The hydraulic spline algorithm was developed to generate irregular two-dimensional channel grids from hydrographic cross-sections at any desired resolution. Hydraulic spline output grids can be easily merged with datasets of higher resolution, such as LIDAR data, to build a complete model of channel geometry and overbank topography. In testing, the hydraulic spline algorithm faithfully reproduces elevations of known input cross-section points where they exist, while generating a smooth transition between known cross-sections. The algorithm performs particularly well compared to traditional techniques with respect to aesthetics and accuracy when input data is sparse. These qualities make the hydraulic spline an ideal choice for practical applications where available data may be limited due to historic or budgetary reasons.
33
Bourdet, Léo. "Modeling of electrical manipulation in silicon spin qubits." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY058/document.
Full textAbstract:
Dans la course à l’ordinateur quantique, le silicium est devenu ces dernières années un matériau de choix pour l'implémentation des qubits de spin. De tels dispositifs sont fabriqués au CEA en utilisant les technologies CMOS, afin de faciliter leur intégration à grande échelle. Cette thèse porte sur la modélisation de ces qubits, et en particulier sur la manipulation de l’état de spin par un champ électrique. Pour cela nous utilisons un ensemble de techniques numériques avancées pour calculer le potentiel et la structure électronique des qubits (notamment les méthodes de liaisons fortes et k.p), afin d’être le plus proche possible des dispositifs expérimentaux. Ces simulations nous ont permis d’étudier deux résultats expérimentaux d’importance : l’observation de la manipulation par champ électrique du spin d’un électron d’une part, et la caractérisation de l’anisotropie de la fréquence de Rabi d’un qubit de trou d’autre part. Le premier résultat était plutôt inattendu, étant donné; le très faible couplage spin-orbite dans la bande de conduction du silicium. Nous développons un modèle, validé par les simulations et certains résultats expérimentaux, qui met en évidence le rôle essentiel du couplage spin-orbite inter-vallée, exacerbé par la faible symétrie du système. Nous utilisons ces résultats pour proposer et tester numériquement un schéma de manipulation électrique consistant à passer réversiblement d’un qubit de spin à un qubit de vallée. Concernant les qubits de trous, le couplage spin-orbite relativement élevé autorise la manipulation du spin par champ électrique, toutefois les mesures expérimentales d’anisotropie donnent à voir une physique complexe, insuffisamment bien décrite par les modèles actuels. Nous développons donc un formalisme permettant de caractériser simplement la fréquence de Rabi en fonction du champ magnétique, et qui peut s’appliquer à d’autre type de qubit spin-orbite. Les simulations permettent de reproduire les résultats expérimentaux, et de souligner le rôle important de la contrainte<br>In the race for quantum computing, these last years silicon has become a material of choice for the implementation of spin qubits. Such devices are fabricated in CEA using CMOS technologies, in order to facilitate their large-scale integration. This thesis covers the modeling of these qubits andin particular the manipulation of the spin state with an electric field. To that end, we use a set numerical tools to compute the potential and electronic structure in the qubits (in particular tightbinding and k.p methods), in order to be as close as possible to the experimental devices. These simulations allowed us to study two important experimental results: on one hand the observation of the electrical manipulation of an electron spin, and on the other hand the characterization of the anisotropy of the Rabi frequency of a hole spin qubit. The first one was rather unexpected, since the spin-orbit coupling is very low in the silicon conduction band. We develop a model, confirmed by thesimulations and some experimental results, that highlights the essential role of the intervalley spinorbit coupling, enhanced by the low symmetry of the system. We use these results to propose and test numerically a scheme for electrical manipulation which consists in switching reversibly betweena spin qubit and a valley qubit. Concerning the hole qubits, the relatively large spin-orbit coupling allows for electrical spin manipulation. However the experimental measurements of Rabi frequency anisotropy show a complex physics, insufficiently described by the usual models. Therefore we developa formalism which allows to characterize simply the Rabi frequency as a function of the magnetic field, and that can be applied to other types of spin-orbit qubits. The simulations reproduce the experimental features, underline the important role of strain
34
Leung, Hong Man. "SPICE simulation and modeling of DC-DC flyback converter." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/36643.
Full text
35
Monk, Scott. "Neural response modelling and spike rate estimation techniques." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=123255.
Full textAbstract:
Using point processes to model neural spike sequences allows the application of classical estimation techniques in their analysis. Estimation of the time varying rate at which spikes occur is often conducted to draw inference on the stimulus which triggered the response. Such estimation schemes are often founded on the assumption that spiking follows Poisson statistics, however, the observed firing rate is a product of both the stimulus and bio-physical properties of the neuron. A point process model for neural data must then incorporate dependency both on stimulus and intrinsic characteristics of the cell. To achieve this we modify the Poisson model such that it includes the refractory phenomenon observed in spiking behaviour. This results in a modified firing rate which is free from distortion caused by refractory effects. A Maximum Likelihood (ML) estimation technique for this adjusted firing rate which better represents some relation to the stimulus is presented. We propose and justify a parametric model to represent a broad class of arbitrary firing rates. The corresponding likelihood equation for the firing rate parameters given an observed spike sequence is derived, however, several numerical methods are required to findthe ML estimate. These techniques are presented in detail and include model order selection and non-convex optimization. An empirical study is conducted to determine which model selection rule, from several approaches found in the literature, is most accurate. Global maximization of the non-convex likelihood equation is carried out using a transformation method known as a filled function. Computer simulations show that our proposed estimator can potentially lead to more accurate estimates of firing rates, as opposed to a Poisson scheme, when the data is affected by a refractory period. Results demonstrate that the error is relatively constant across datasets influenced by a range of refractory periods, indicating the estimator is robust. Rate estimates on real neural data taken from various cortices also show improved goodness of fit when contrasted with results from the Poisson estimator. A brief performance comparison with other popular estimation schemes suggests superior estimates are produced by our proposed scheme.<br>Un processus de point pour modeler des séquences de piques neuraux permet l'application des techniques d'estimation classiques dans leur analyse. L'estimation du taux variable de temps auquel les piques ont lieu est souvent faite afin de trouver l'inférence sur le stimulus qui déclenche la réaction. Ces schémas d'estimation sont souvent basés sur la suppositionque la fréquence de piques élevés suit les statistiques Poisson. Cependant, le taux depiques est un produit du stimulus et des propriétés biophysiques du neurone. Un modèle de processus de point pour les données neuraux doit intégrer la dépendance du stimulus etdes propriétés intrinsèques de la cellule. À cet effet, on modifie le modèle Poisson pour qu'il inclue le phénomène réfractaire observé dans le comportement piquant. Selon ce modèle ajusté, on présente la technique d'estimation Maximum de Vraisemblance (MV) pour letaux de tir qui provoque la réaction piquante. On propose et justifie un modèle paramétrique pour représenter des taux de tir arbitraireset extensifs. L'équation de vraisemblance correspondante pour les paramètres detaux de tir se produit quand une séquence piquante est dérivée. Néanmoins, plusieurs méthodes numériques sont requises pour trouver l'estimation du MV. Ces techniques sont présentées en détail et incluent la sélection d'ordre modèle et l'optimisation non convexe. Une étude empirique, menée afin de déterminer quelle règle de sélection de modèle etinspirée de plusieurs approches trouvées dans la littérature, est la plus exacte. La maximisation globale de l'équation de vraisemblance non convexe est menée en se servant d'une méthode de transformation qui est connue comme une fonction de remplissage. Des simulations informatiques montrent que notre estimateur proposé livre des estimations de taux de tir plus exactes qu'un schéma semblable de Poisson quand les données sont affectées par une période réfractaire. Les résultats démontrent que l'erreur est relativement constante à travers les ensembles de données influencés par plusieurs périodes réfractaires,ce qui indique un estimateur robuste. Les estimations de taux de tir sur des réelles données prises de plusieurs cortex montrent aussi une bonté de convenance (goodness of fit)lorsqu'elles sont contrastées avec les résultats de l'estimateur Poisson. Une comparaison de performance avec d'autres schémas d'estimation populaires suggère que des estimations supérieures sont produites par notre schéma proposé.
36
Hamadeh, Mohamad Ali. "Une approche unifiée pour la segmentation et la mise en correspondance 3D/2D d'images multimodales : application à l'étude cinématique 3D de la colonne vertébrale." Grenoble INPG, 1997. http://www.theses.fr/1997INPG0035.
Full textAbstract:
Dans cette these nous proposons une approche unifiee pour la mise en correspondance 3d/2d entre le modele surfacique 3d d'un objet et deux projections radiographiques 2d de cet objet. Il s'agit de trouver la transformation rigide 3d entre le modele de l'objet defini dans le referentiel r#m#o#d#e#l et les donnees radiographiques definies dans le referentiel du systeme d'imagerie radiographique r#s#e#n#s#o#r en tenant compte de la dualite entre mise en correspondance et segmentation dans un systeme de vision a base de modeles. Apres une presentation des diverses etapes de traitement necessaires pour realiser un tel systeme : calibrage du dispositif d'imagerie, segmentation des contours de l'objet, et l'elaboration d'une strategie de minimisation de distance entre modele et donnees, nous presentons un algorithme de mise en correspondance 3d/2d base sur une modelisation mecanique et qui tient compte de la specificite des images radiographiques, a savoir la presence des points du contour interne de l'objet sur les images segmentees. Une approche unifiee est ensuite proposee. Elle permet une extraction automatique des points de contour de l'objet d'interet en associant une credibilite a chaque pixel de l'image. Cette credibilite traduit la probabilite pour un pixel d'etre un element du contour de l'objet d'interet et depend des caracteristiques propres du pixel (gradient, laplacien, etiquette). Elle depend aussi de l'estimation d'une position initiale de l'objet dans le referentiel d'imagerie radiographique. Cette estimation est realisee par une mise en correspondance entre reperes anatomiques apparies sur le modele 3d et sur les radiographies 2d. Les resultats de validation de cette approche sont egalement presentees sur des donnees radiographiques reelles. Enfin une application clinique de la mise en correspondance 3d/2d pour l'etude cinematique 3d de la colonne vertebrale est presentee avec les premiers resultats obtenus sur fantome.
37
RAHIM, ARBAB ABDUR. "Numerical Modeling of Spin Waves in Magnetic Thin Films." Doctoral thesis, Politecnico di Torino, 2015. http://hdl.handle.net/11583/2595559.
Full textAbstract:
Magnonics is a newly emerging area of magnetism, wherein new classes of devices can be foreseen. Here magnetic spin waves can be utilized to store, carry and process information.
Due to particular properties of spin wave spectra, magnonic devices offer new functionalities
that are currently unavailable in electronic devices. For example, magnonic devices are easily manipulated by the applied magnetic field. As an emerging area, it opens up a number of challenges and problems that need to be addressed, such as governing the propagation
of spin waves using nano-patterned media. From a computation point of view, the
governing dynamics can be modeled by extending the mathematical formalism of Landau-
Lifshitz (LL) equation. This lead to the development of micromagnetic solvers for the
modeling of magnetization dynamics and for the interpretation of the experimental results
in complex magnetic structures. For this purpose we developed a micromagnetic solver in
MATLAB for the solution of LL equation. For a micromagnetic solver the computation
of the effective field and an efficient time-stepping scheme are of significant importance.
For this purpose we have utilized the Fast Fourier Transforms (FFT) in our solver for
the computation of the magnetostatic field that reduced the computational complexity
of the system. A novel time stepping scheme is also proposed which exploited the properties
of the mid-point rule and Runge-Kutta scheme. The proposed scheme preserves
the magnetization dynamics and provides a larger time step with fewer computations of
the effective field per time step. The solver was validated by simulating μ-mag standard
problem 4 and the results were compared to the standard micromagnetic solver OOMMF,
which were in close agreement.
38
Grove, Olya. "Heterogeneous Modeling of Medical Image Data Using B-Spline Functions." Scholar Commons, 2011. http://scholarcommons.usf.edu/etd/3130.
Full textAbstract:
Ongoing developments in the field of medical imaging modalities have pushed the frontiers of modern medicine and biomedical engineering, prompting the need for new applications to improve diagnosis, treatment and prevention of diseases.
Biomedical data visualization and modeling rely predominately on manual processing and utilization of voxel and facet based homogeneous models. Biological structures are naturally heterogeneous and in order to accurately design and biomimic biological structures, properties such as chemical composition, size and shape of biological constituents need to be incorporated in the computational biological models.
Our proposed approach involves generating a density point cloud based on the intensity variations in a medical image slice, to capture tissue density variations through point cloud densities. The density point cloud is ordered and approximated with a set of cross-sectional least-squares B-Spline curves, based on which a skinned B-Spline surface is generated. The aim of this method is to capture and accurately represent density variations within the medical image data with a lofted surface function.
The fitted B-Spline surface is sampled at uniformly distributed parameters, and our preliminary results indicate that the bio-CAD model preserves the density variations of the original image based point cloud. The resultant surface can thus be visualized by mapping the density in the parametric domain into color in pixel domain. The B-Spline function produced from each image slice can be used for medical visualization and heterogeneous tissue modeling. The process can be repeated for each slice in the medical dataset to produce heterogeneous B-Spline volumes.
The emphasis of this research is placed on accuracy and shape fidelity needed for medical operations.
39
Jenkner, Carolin [Verfasser], and Martin [Akademischer Betreuer] Schumacher. "Multivariable modeling of continuous covariates with a spike at zero." Freiburg : Universität, 2018. http://d-nb.info/1162054719/34.
Full text
40
Alexander, Julie G. "Hydrographic Surface Modeling Through A Raster Based Spline Creation Method." ScholarWorks@UNO, 2014. http://scholarworks.uno.edu/td/1842.
Full textAbstract:
The United States Army Corp of Engineers relies on accurate and detailed surface models for various construction projects and preventative measures. To aid in these efforts, it is necessary to work for advancements in surface model creation. Current methods for model creation include Delaunay triangulation, raster grid interpolation, and Hydraulic Spline grid generation. While these methods produce adequate surface models, attempts for improved methods can still be made.
A method for raster based spline creation is presented as a variation of the Hydraulic Spline algorithm. By implementing Hydraulic Splines in raster data instead of vector data, the model creation process is streamlined. This method is shown to be more efficient and less computationally expensive than previous methods of surface model creation due to the inherent advantages of raster data over vector data.
41
Naber, John F. "The optimization of SPICE modeling parameters utilizing the Taguchi methodology." Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/38542.
Full textAbstract:
A new optimization technique for SPICE modeling parameters has been developed in this dissertation to increase the accuracy of the
circuit simulation. The importance of having accurate circuit simulation models is to prevent the very costly redesign of an
Integrated Circuit (IC). This radically new optimization technique utilizes the Taguchi method to improve the fit between measured and
simulated I-V curves for GaAs MESFETs. The Taguchi method consists of developing a Signal-to-Noise Ratio (SNR) equation that will find the optimum combination of controllable signal levels in a design or process to make it robust or as insensitive to noise as
possible. In this dissertation, the control factors are considered the circuit model curve fitting parameters and the noise is
considered the variation in the simulated I-V curves from the measured I-V curves. This is the first known application of the
Taguchi method to the optimization of IC curve fitting model parameters. In addition, this method is not technology or device dependent and can be applied to silicon devices as well. Improvements in the accuracy of the simulated I-V curve fit reaching 80% has been achieved between DC test extracted parameters and the Taguchi optimized parameters. Moreover, the computer CPU execution time of the optimization process is 96% less than a commercial optimizer utilizing the Levenberg-Marquardt algorithm (optimizing 31 FETs). This technique does a least square fit on the data comparing measured currents versus simulated currents for various combinations of SPICE parameters. The mean and standard deviation of this least squares fit is incorporated in determining the SNR, providing the best combination of parameters within the evaluated range. Furthermore, the optimum values of the parameters are found without additional simulation by fitting the response curves to a quadratic equation and finding the local maximum. This technique can easily be implemented with any simulator that utilizes simulation modeling parameters extracted from measured DC test data. In addition, two methods are evaluated to obtain the worst case modeling parameters. One method lobks at the correlation coefficients between modeling parameters and the second looks at the actual device parameters that define the +/- 30 limits of the process. Lastly, an example is given that describes the applicability of the Taguchi methodology in the design of a differential amplifier, that accounts for the effect of offset voltage.<br>Ph. D.
42
Sanchez, Justin Cort. "From cortical neural spike trains to behavior modeling and analysis /." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0004289.
Full text
43
Nandihalli, Sunil S. "A B-spline geometric modeling methodology for free surface simulation." Master's thesis, Mississippi State : Mississippi State University, 2004. http://library.msstate.edu/etd/show.asp?etd=etd-04072004-185017.
Full text
44
Golinski, Waldemar Z. "Three-dimensional dynamic modelling of the human cervical spine in whiplash situations." Thesis, Nottingham Trent University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324592.
Full text
45
Sigurdsson, Ari. "Micromagnetic study of spin Hall nano-oscillator arrays and their synchronization dynamics." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-285562.
Full textAbstract:
Spintronics is the study of electron spins and their utilization in electronic devices. Within this field, spin-based oscillators have shown promise for mi- crowave signal generation as they can operate at high frequencies, are small in scale and are compatible with modern fabrication techniques. Among these oscillators are the spin Hall nano-oscillators (SHNOs). They are nanoscale thin-film structures driven by pure spin-current injection from a primary con- ductor into a ferromagnetic material. This process can be used to generate microwave signals through oscillations in the material’s magnetization. By constraining the current flow in the device to individual constrictions, an ar- ray arrangement of multiple oscillators can be realized. These oscillators can then be coupled together via their internal interactions to achieve mutual syn- chronization and improve their characteristics.In this work, a versatile micromagnetic modelling procedure for simulating constriction-based SHNOs and their synchronization dynamics in different ar- ray arrangements is presented. A case study of various 2x2 array geometries is conducted along with an exploration of higher-order networks of 4x4, 6x6 and 8x8 oscillators. A perturbative optimization algorithm is developed to improve excitation conditions and drive geometries into a synchronized regime. Lastly, a comparison to nonlinear auto-oscillator theory is presented to illustrate the dependence of generated signals on constriction sizes and the spacing between oscillators. Mutual synchronization between multiple oscillators is achieved and favourable geometry and excitation conditions are defined. The conducted simulations show good agreement with experimental results and illustrate the potential for future studies of SHNO characteristics through micromagnetic modelling.<br>Spinntronik är ett forskningsområde, som handlar om hur elektronens s.k. spinn kan användas i elektroniska komponenter. Inom detta område har spinnbaserade oscillatorer visat sig ha lovande egenskaper för generering av mikrovågssignaler, eftersom de har höga arbetsfrekvenser, liten storlek och är kompatibla med moderna tillverkningstekniker. En typ av dessa oscillatorer kallas spinn-Hall nano-oscillatorer (SHNO). De är nanometerstora tunnfilms- strukturer, vilka drivs av en ren spinnström, som injiceras från en (metallisk) ledare till en ett ferromagnetiskt material. Denna mekanism kan användas för att skapa mikrovågssignaler genom oscillationer i materialets magnetisering. Genom att begränsa strömflödet i komponenten till enskilda gap kan man skapa en matris med ett stort antal oscillatorer. Dessa oscillatorer kan sedan kopplas till varandra genom interna utbytesmekanismer och på så sätt uppnår man en ömsesidig koppling och förbättrade egenskaper.I detta arbete presenteras ett mångsidigt mikromagnetiskt modelleringsflö- de, för att simulera SHNO:er, baserade på nano-gap, och deras synkronisering i olika matriskonfigurationer. En fallstudie som inkluderar olika 2x2 matris- geometrier har genomförts tillsammans med explorativ utforskning av högre ordnings nätverk, såsom 4x4, 6x6 och 8x8 oscillatorer. En störnings-baserad optimerings-algoritm har utvecklats för att förbättra exciterings-parametrarna och för att tvinga geometrierna in i en synkroniserad regim. Som en avslutning presenteras en jämförelse med icke-linjär auto-oscillatorteori för att visa den genererade signalens beroende på gapens storlek och avståndet mellan dem. Ömsesidig synkronisering mellan flera oscillatorer kunde uppnås och en för- delaktig geometri samt lämpliga värden på exciterings-parametrarna kunde definieras. Simuleringarna i studien hade bra överensstämmelse med experi- mentella resultat och visar på potentialen för vidare studier av SHNO egen- skaper med hjälp av mikromagnetisk modellering.
46
Griffith, Thomas John Owen. "Spatiotemporal modelling of Ca²⁺ and calmodulin in dentritic spines." Thesis, University of Bristol, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.715806.
Full text
47
Janson, Oleg. "DFT-based microscopic magnetic modeling for low-dimensional spin systems." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-91976.
Full textAbstract:
In the vast realm of inorganic materials, the Cu2+-containing cuprates form one of the richest classes. Due to the combined effect of crystal-field, covalency and strong correlations, all undoped cuprates are magnetic insulators with well-localized spins S=1/2, whereas the charge and orbital degrees of freedom are frozen out. The combination of the spin-only nature of their magnetism with the unique structural diversity renders cuprates as excellent model systems. The experimental studies, boosted by the discovery of high-temperature superconductivity in doped La2CuO4, revealed a fascinating variety of magnetic behaviors observed in cuprates. A digest of prominent examples should include the spin-Peierls transition in CuGeO3, the Bose-Einstein condensation of magnons in BaCuSi2O6, and the quantum critical behavior of Li2ZrCuO4. The magnetism of cuprates originates from short-range (typically, well below 1 nm) exchange interactions between pairs of spins Si and Sj, localized on Cu atoms i and j. Especially in low-dimensional compounds, these interactions are strongly anisotropic: even for similar interatomic distances |Rij|, the respective magnetic couplings Jij can vary by several orders of magnitude. On the other hand, there is an empirical evidence for the isotropic nature of this interaction in the spin space: different components of Si are coupled equally strong. Thus, the magnetism of cuprates is mostly described by a Heisenberg model, comprised of Jij(Si*Sj) terms. Although the applicability of this approach to cuprates is settled, the model parameters Jij are specific to a certain material, or more precisely, to a particular arrangement of the constituent atoms, i.e. the crystal structure. Typically, among the infinite number of Jij terms, only several are physically relevant. These leading exchange couplings constitute the (minimal) microscopic magnetic model. Already at the early stages of real material studies, it became gradually evident that the assignment of model parameters is a highly nontrivial task. In general, the problem can be solved experimentally, using elaborate measurements, such as inelastic neutron scattering on large single crystals, yielding the magnetic excitation spectrum. The measured dispersion is fitted using theoretical models, and in this way, the model parameters are refined.
Despite excellent accuracy of this method, the measurements require high-quality samples and can be carried out only at special large-scale facilities. Therefore, less demanding (especially, regarding the sample requirements), yet reliable and accurate procedures are desirable. An alternative way to conjecture a magnetic model is the empirical approach, which typically relies on the Goodenough-Kanamori rules. This approach links the magnetic exchange couplings to the relevant structural parameters, such as bond angles. Despite the unbeatable performance of this approach, it is not universally applicable. Moreover, in certain cases the resulting tentative models are erroneous. The recent developments of computational facilities and techniques, especially for strongly correlated systems, turned density-functional theory (DFT) band structure calculations into an appealing alternative, complementary to the experiment. At present, the state-of-the-art computational methods yield accurate numerical estimates for the leading microscopic exchange couplings Jij (error bars typically do not exceed 10-15%).
Although this computational approach is often regarded as ab initio, the actual procedure is not parameter-free. Moreover, the numerical results are dependent on the parameterization of the exchange and correlation potential, the type of the double-counting correction, the Hubbard repulsion U etc., thus an accurate choice of these crucial parameters is a prerequisite. In this work, the optimal parameters for cuprates are carefully evaluated based on extensive band structure calculations and subsequent model simulations.
Considering the diversity of crystal structures, and consequently, magnetic behaviors, the evaluation of a microscopic model should be carried out in a systematic way. To this end, a multi-step computational approach is developed. The starting point of this procedure is a consideration of the experimental structural data, used as an input for DFT calculations. Next, a minimal DFT-based microscopic magnetic model is evaluated. This part of the study comprises band structure calculations, the analysis of the relevant bands, supercell calculations, and finally, the evaluation of a microscopic magnetic model. The ground state and the magnetic excitation spectrum of the evaluated model are analyzed using various simulation techniques, such as quantum Monte Carlo, exact diagonalization and density-matrix renormalization groups, while the choice of a particular technique is governed by the dimensionality of the model, and the presence or absence of magnetic frustration.
To illustrate the performance of the approach and tune the free parameters, the computational scheme is applied to cuprates featuring rather simple, yet diverse magnetic behaviors: spin chains in CuSe2O5, [NO]Cu(NO3)3, and CaCu2(SeO3)2Cl2; quasi-two-dimensional lattices with dimer-like couplings in alpha-Cu2P2O7 and CdCu2(BO3)2, as well as the 3D magnetic model with pronounced 1D correlations in Cu6Si6O18*6H2O. Finally, the approach is applied to spin liquid candidates --- intricate materials featuring kagome-lattice arrangement of the constituent spins. Based on the DFT calculations, microscopic magnetic models are evaluated for herbertsmithite Cu3(Zn0.85Cu0.15)(OH)6Cl2, kapellasite Cu3Zn(OH)6Cl2 and haydeeite Cu3Mg(OH)6Cl2, as well as for volborthite Cu3[V2O7](OH)2*2H2O. The results of the DFT calculations and model simulations are compared to and challenged with the available experimental data.
The advantages of the developed approach should be briefly discussed. First, it allows to distinguish between different microscopic models that yield similar macroscopic behavior. One of the most remarkable example is volborthite Cu3[V2O7](OH)2*2H2O, initially described as an anisotropic kagome lattice. The DFT calculations reveal that this compound features strongly coupled frustrated spin chains, thus a completely different type of magnetic frustration is realized.
Second, the developed approach is capable of providing accurate estimates for the leading magnetic couplings, and consequently, reliably parameterize the microscopic Hamiltonian. Dioptase Cu6Si6O18*6H2O is an instructive example showing that the microscopic theoretical approach eliminates possible ambiguity and reliably yields the correct parameterization.
Third, DFT calculations yield even better accuracy for the ratios of magnetic exchange couplings. This holds also for small interchain or interplane couplings that can be substantially smaller than the leading exchange. Hence, band structure calculations provide a unique possibility to address the interchain or interplane coupling regime, essential for the magnetic ground state, but hardly perceptible in the experiment due to the different energy scales.
Finally, an important advantage specific to magnetically frustrated systems should be mentioned. Numerous theoretical and numerical studies evidence that low-dimensionality and frustration effects are typically entwined, and their disentanglement in the experiment is at best challenging. In contrast, the computational procedure allows to distinguish between these two effects, as demonstrated by studying the long-range magnetic ordering transition in quasi-1D spin chain systems.
The computational approach presented in the thesis is a powerful tool that can be directly applied to numerous S=1/2 Heisenberg materials. Moreover, with minor modifications, it can be largely extended to other metallates with higher value of spin. Besides the excellent performance of the computational approach, its relevance should be underscored: for all the systems investigated in this work, the DFT-based studies not only reproduced the experimental data, but instead delivered new valuable information on the magnetic properties for each particular compound.
Beyond any doubt, further computational studies will yield new surprising results for known as well as for new, yet unexplored compounds. Such "surprising" outcomes can involve the ferromagnetic nature of the couplings that were previously considered antiferromagnetic, unexpected long-range couplings, or the subtle balance of antiferromagnetic and ferromagnetic contributions that "switches off" the respective magnetic exchange. In this way, dozens of potentially interesting systems can acquire quantitative microscopic magnetic models.
The results of this work evidence that elaborate experimental methods and the DFT-based modeling are of comparable reliability and complement each other. In this way, the advantageous combination of theory and experiment can largely advance the research in the field of low-dimensional quantum magnetism. For practical applications, the excellent predictive power of the computational approach can largely alleviate designing materials with specific properties.
48
Chen, Tingsu. "Spin Torque Oscillator Modeling, CMOS Design and STO-CMOS Integration." Doctoral thesis, KTH, Integrerade komponenter och kretsar, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-176890.
Full textAbstract:
Spin torque oscillators (STOs) are microwave oscillators with an attractive blend of features, including a more-than-octave tunability, GHz operating frequencies, nanoscale size, nanosecond switching speed and full compatibility with CMOS technology. Over the past decade, STOs' physical phenomena have been explored to a greater extent, their performance has been further improved, and STOs have already shown great potential for a wide range of applications, from microwave sources and detectors to neuromorphic computing. This thesis is devoted to promoting the STO technology towards its applications, by means of implementing the STO's electrical model, dedicated CMOS integrated circuits (ICs), and STO-CMOS IC integration. An electrical model, which can capture magnetic tunnel junction (MTJ) STO's characteristics, while enabling system- and circuit-level designs and performance evaluations, is of great importance for the development of MTJ STO-based applications. A comprehensive and compact analytical model, which is based on macrospin approximations and can fulfill the aforementioned requirements, is proposed. This model is fully implemented in Verilog-A, and can be used for efficient simulations of various MTJ STOs. Moreover, an accurate phase noise generation approach, which ensures a reliable model, is proposed and successfully used in the Verilog-A model implementation. The model is experimentally validated by three different MTJ STOs under different bias conditions. CMOS circuits, which can enhance the limited output power of MTJ STOs to levels that are required in different applications, are proposed, implemented and tested. A novel balun-low noise amplifier (LNA), which can offer sufficient gain, bandwidth and linearity for MTJ STO-based magnetic field sensing applications, is proposed. Additionally, a wideband amplifier, which can be connected to an MTJ STO to form a highly-tunable microwave oscillator in a phase-locked loop (PLL), is also proposed. The measurement results demonstrate that the proposed circuits can be used to develop MTJ STO-based magnetic field sensing and microwave source applications. The investigation of possible STO-CMOS IC integration approaches demonstrates that the wire-bonding-based integration is the most suitable approach. Therefore, a giant magnetoresistance (GMR) STO is integrated with its dedicated CMOS IC, which provides the necessary functions, using the wire-bonding-based approach. The RF characterization of the integrated GMR STO-CMOS IC system under different magnetic fields and DC currents shows that such an integration can eliminate wave reflections. These findings open the possibility of using GMR STOs in magnetic field sensing and microwave source applications.<br><p>QC 20151112</p>
49
Radloff, Robert W. Jr. "Modeling Polarization Sensitivity of Qweak Apparatus for Transverse Beam Spin." Ohio University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1542130841901331.
Full text
50
Xu, Jing. "Modeling and simulation of spin transport and precession in silicon." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 69 p, 2008. http://proquest.umi.com/pqdweb?did=1601517971&sid=9&Fmt=2&clientId=8331&RQT=309&VName=PQD.
Full text