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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Understanding the Mechanisms by which Cable Sway Produces Motion Artifact in Mobile Electroencephalography

Rojas, David 15 August 2023 (has links) (PDF)
Mobile brain/body imaging utilizes electroencephalography (EEG) to record brain activity during human walking in dynamic environments. Motion artifact from cable sway affects the quality of EEG signals collected from the scalp, masking contributions of synchronously firing neurons. Previous studies have explored cable sway-induced motion artifact, but only during vigorous exercise or controlled sinusoidal motion. Therefore, a need remains to further understand the underlying mechanisms of this artifact, as it may help with developing real-time mitigation methods, reducing reliance on offline signal processing. In this thesis, I aimed to show that controlled cable sway could produce specific motion artifact waveforms in a benchtop setup. I programmed a robotic arm to perform three different types of waveform motions - sinusoidal, square, and sawtooth - in two setups that had different levels of cable support: constrained and unconstrained. I used a novel dual-sided EEG electrode where one side of the electrode interfaces with the scalp to record traditional EEG signals while an outer-facing electrode interfaces with a conductive fabric cap to record isolated motion artifact and noise. Additionally, I placed the electrodes in a 3D-printed holder designed to position them between two layers of conductive fabric and eliminate any electrode movement, which has not been previously constrained. Lastly, I computed correlations between cable sway and bottom electrode EEG, cable sway and top electrode EEG, and top and bottom EEG. Correlations for all variable combinations were low, ranging from -0.122 +/- 0.223 to 0.058 +/- 0.238. Out of six correlation measure comparisons (three across testing setups and three across waveform motions), five did not show significant differences (p-values = 0.391 - 0.958). These results suggest that EEG motion artifact is not the result of just mechanical deformation of the cables but likely requires simultaneous movement of the electrode itself, altering the electrode-conductive surface interface dynamics.
12

THE RHEOLOGICAL IMPACT OF CELL ACTIVATION ON THE FLOW BEHAVIOR OF NEUTROPHILS

Horrall, Nolan M. 01 January 2016 (has links)
Previously, it was reported that the morphological changes (pseudopod projection) that circulating neutrophils adopt due to cell activation raises peripheral vascular resistance by disrupting microvascular rheology. Studies utilized murine muscle preparations to link neutrophil pseudopod formation to cell activation and a viscous impact on hemodynamic resistance. But because of the complexity associated with the organization of the vasculature and microvasculature in tissues, it was unclear whether the effects of neutrophil activation on hemodynamic resistance were associated with the macro-/micro- circulation. This research describes an in vitro analysis using viscometry and microvascular network mimics (microporous membranes) to assess the rheological impact of pseudopods on capillary-like flow. Suspensions of neutrophil-like HL-60 promyelocytes (dHL60’s) and human neutrophils, stimulated with 10 nM fMLP were used, with/without hematocrit. Stimulation of dHL60s or human neutrophils with fMLP altered their flow behavior, which was detected as an increase in solution viscosity. Addition of hematocrit negated the effect of neutrophil activation on suspension viscosity. Moreover, cell activation increased the resistance of microporous membranes to flow of neutrophil suspensions with addition of hematocrit exacerbating this effect. Combined, the results of this study provided evidence that activated neutrophils influence microscale flow resistance via a rheological impact.
13

Inverse Dynamic Analysis of ACL Reconstructed Knee Joint Biomechanics During Gait and Cycling Using OpenSim

Pottinger, Megan V. 01 August 2018 (has links)
ACL (anterior cruciate ligament) injuries of the knee joint alter biomechanics and may cause abnormal loading conditions that place patients at a higher risk of developing osteoarthritis (OA). There are multiple types of ACL reconstruction (ACLR), but all types aim to restore anterior tibial translation and internal tibial rotation following surgery. Analyzing knee joint contact loads provide insight into the loading conditions following ACLR that may contribute to the long-term development of OA. Ten ACLR subjects, who underwent the same reconstruction, performed gait and cycling experiments while kinematic and kinetic data were collected. Inverse dynamic analyses were performed on processed data using OpenSim to calculate reconstructed and contralateral knee joint contact loads which were then compared between gait and cycling at both moderate and high resistances. Significant differences were found between gait and cycling at either resistance for tibiofemoral (TF) compressive, anterior shear, lateral shear forces, and internal abduction and internal rotation moments for both ACLR and contralateral knees. Anterior shear force was largest for cycling at a high resistance, however, since the ACL provides a posterior restoring force and is more engaged at low flexion angles, adjusting for flexion angles when measuring AP shear forces should be considered. Overall, the calculated loading conditions suggest cycling provided better joint stability by limiting anterior tibial translation and internal tibial rotation compared to gait. The results suggest cycling is a better rehabilitation exercise to promote graft healing and limit abnormal loading conditions that increase the risk of developing OA.
14

THE EFFECTS OF IN UTERO AND POSTPARTUM EXPOSURE TO SELECTIVE SEROTONIN REUPTAKE INHIBITORS ON BONE PROPERTIES IN RATS

Badv, Maryam 23 September 2014 (has links)
<p>Selective serotonin reuptake inhibitors (SSRIs) are the most common drugs prescribed to treat depression during pregnancy. The influence of SSRI exposure during pregnancy on fetus bone properties is not clearly understood. The overall objective of this thesis project was to investigate the short and long-term effects of <em>in utero</em> and postpartum exposure to SSRIs on bone in rats through measuring bone structural and material properties.</p> <p>Two studies with two types of SSRIs were carried out. Dams in the treated groups were randomly assigned to receive sertraline (10 mg/kg/day, N=5) in the first study and fluoxetine (10 mg/kg/day, N=17) in the second study. Control animals in the studies received saline in a flavoured gelatin vehicle. Rats were exposed to sertraline only during pregnancy, but fluoxetine was administered to the dams during pregnancy and also during breastfeeding. Rat offspring were sacrificed at 3, 7 and 26 weeks of age and left femurs and L6 vertebrae were analyzed for differences in morphology and mechanical properties.</p> <p>Maternal sertraline exposure resulted in significantly shorter femurs for the offspring at 3 weeks of age. Rat femurs from the sertraline group were also weaker at 3 and 7 weeks of age compared to controls. In comparison, <em>in utero</em> and postpartum exposure to fluoxetine did not have a negative impact on bone properties. In fact, the femurs from fluoxetine exposed offspring were significantly stronger at 3 weeks of age compared to the controls</p> <p>Findings in this project suggest that<strong> </strong>the type of SSRI used by pregnant woman should be considered as an important factor. Maternal sertraline exposure has a negative effect on offspring bone properties. Considering the fact that various mechanisms are involved in the influence of SSRIs on bone, further studies should be conducted to determine the mechanisms of this influence on bone properties <em>in utero </em>and through stages of development.<strong></strong></p> / Master of Applied Science (MASc)
15

Design and Validation of a Computational Model for Study of Scapholunate Joint Kinematics

Tremols, Edward J 01 January 2014 (has links)
As computational power has increased, computational modeling has become a very promising tool to model the biomechanics of complex joint systems. Musculoskeletal computational models have become more complex when compared to original iterations which utilized a number of simplifications. This thesis utilized a three-dimensional computational model of the wrist joint structure to investigate scapholunate kinematics. The model accurately represented the bony anatomy of the wrist and hand and represented soft tissue structures such as ligaments, tendons, and other surrounding tissues. Creation of the model was done using commercially available computer-aided design and medical image processing software, and utilized the rigid body modeling methodology. It was validated for scapholunate kinematics against a cadaver study and then utilized to investigate further measures and surgical procedures. The simulations performed by the model demonstrated an accurate anatomical response of wrist function. As better understanding of the biomechanics of the wrist joint is achieved, this model could prove to be an important tool to further investigate wrist mechanics.
16

EFFECTS OF BACKPACK TYPE ON KINEMATICS OF THE LOWER BACK DURING WALKING AND JOGGING

Suri, Cazmon 01 January 2018 (has links)
Heavy backpacks have been suggested to have a pathogenic role in experience of low back pain among children. We have conducted a repeated-measure study to investigate the backpack-induced changes in lumbo-pelvic coordination of forty gender-balanced college age students when they walked and jogged on a treadmill with two different types of backpacks: normal and ergonomically modified. The backpack-induced changes in lumbo-pelvic coordination were larger when carrying an ergonomically modified vs. a normal backpack as well as when jogging versus walking. The larger changes in lumbo-pelvic coordination when carrying an ergonomically modified backpack were likely due to kinematic restraints imposed by rigidity and enhanced attachments devised in the backpack for increased comfort. Given the role of lower back biomechanics in low back pain, the effects of such larger mechanical abnormalities in the lower back when carrying an ergonomically-modified backpack on risk of low back pain among children requires further investigation.
17

Mechanical Properties of Bone Due to SOST Expression: A 3-Point Bending Assessment of Murine Femurs

Peterson, Kainoa John 01 May 2012 (has links)
Sclerostin, a protein coded for by the SOST gene, is an osteocyte-expressed negative regulator of bone formation. The absence of SOST in the genome may have an effect on bone formation both during skeletal maturation and full maturity. This study attempts to determine significant differences in the mechanical properties of bone that expresses SOST compared to bone that does not. One hundred femur samples from 6, 8, and 12 month old mice were obtained from Lawrence Livermore National Labs and loaded until failure using three-point bending. Results showed significant differences in treatment group effects for cross sectional area, yield force, and ultimate force. SOST knockout (KO) mice were found to have significantly higher values for these properties in comparison to transgenic (TG) and wildtype (WT) littermates. In addition, there was a noted effect dependent on the primary axis of loading, anterior-posterior versus medial-lateral. Lastly, data from this study support the existing hypothesis that there is no systematic side-to-side (left-right) difference in bone formation. This data may aid understanding of the role SOST has in bone formation. If the structural integrity and quality of bone resulting from the removal of the SOST gene is shown to be comparable to that of normal, healthy bone, the use of gene therapy to combat diseases/disorders such as osteoporosis may lead to important contributions to medical therapy.
18

A Computational Assessment of Lisfranc Injuries and their Surgical Repairs

Perez, Michael 01 January 2019 (has links)
While Lisfranc injuries in the mid foot are less common than other ankle and mid foot injuries, they pose challenges in both properly identifying them and treating them. When Lisfranc injuries are ligamentous and do not include obvious fractures, they are very challenging for clinicians to identify unless weight bearing radiographs are used. The result is that 20%-40% of Lisfranc injuries are missed in the initial evaluation. Even when injuries are correctly identified the outcomes of surgical procedures remain poor. Existing literature has compared the different surgical procedures but has not had a standard approach or procedures across studies. This study uses a computational biomechanical model validated on a cadaveric study to evaluate factors that impact injury presentation and to compare the different procedures ability to stabilize the Lisfranc joint after an injury. Using SolidWorks® a rigid body kinematic model of a healthy human foot was created whereby the 3D bony anatomy, articular contacts, and soft tissue restraints guided biomechanical function under the action of external perturbations and muscle forces. The model was validated on a cadaveric study to ensure it matched the behavior of a healthy Lisfranc joint and one with a ligamentous injury. The validated model was then extended to incorporate muscle forces and different foot orientations when simulating a weight bearing radiograph. The last section of work was to compare the stability of four different surgical repairs for Lisfranc injuries. These procedures were three open reduction and internal fixation (ORIF) procedures with different hardware (screws, screws and dorsal plates, and endobuttons) and primary arthrodesis with screws. They required use of finite element analysis which was performed in Ansys Workbench. For the presentation of injuries, both muscle forces and standing with inversion or eversion could reduce the diastasis (separation) observed for weight bearing radiographs and thus confuse the diagnosis. When comparing the different surgical procedures, the ORIF with screws and primary arthrodesis with screws showed the most stable post-operative Lisfranc joint. However, the use of cannulated screws for fixation showed regions of high stress that may be susceptible to breakage. A challenge in the literature has been the use of different experimental designs and metrics when comparing two of the possible procedures for a Lisfranc injury head to head. This study has been able to benchmark four procedures using the same model and set of metrics. Since none of the existing procedures showed consistently good to excellent patient outcomes, more procedures could be proposed in the future. If this were to occur, this study offers a standard procedure for benchmarking the new procedure’s post-operative mechanical stability versus those procedures currently in use.
19

Effects of Static Stretching on Foot Velocity During the Instep Soccer Kick

Workman, Craig D. 01 May 2010 (has links)
The purpose of this study was to assess the acute effects of static stretching on foot velocity at impact with a soccer ball. Eighteen Division I female soccer athletes underwent two test conditions separated by 48 hr. Each condition was randomly assigned and began by placing four retro-reflective markers on bony landmarks of the ankle (total of eight markers, four on each ankle). One condition was the no-stretch condition, in which each participant performed a self-paced jog for 5 min as a warm-up, and then sat quietly for 6 min before performing three maximal instep kicks into a net. The second condition was the stretch condition, which was identical to the no-stretch condition, except the participants performed a series of six randomly ordered stretches instead of sitting quietly for 6 min. Three-dimensional motion analysis was used to quantify the resultant velocity of the head of the 5th metatarsal immediately prior to foot impact with a soccer ball. The results of a dependent t test indicated that there was no significant difference between the no-stretch (18.34 ± 1.29 m/s) and stretch conditions (17.96 ± 1.55 m/s; p = .102, d = .3) Based on these findings, acute stretching performed one time for 30 s before maximal instep soccer kicking has no effect on the resultant foot velocity of Division 1A university female soccer players. Pre-event stretching performed in a like manner may best be prescribed at the discretion of the athlete.
20

Mechanical Simulation of Articular Cartilage Based on Experimental Results

Stewart, Kevin Matthew 01 June 2009 (has links) (PDF)
Recently, a constituent based cartilage growth finite element model (CGFEM) was developed in order to predict articular cartilage (AC) biomechanical properties before and after growth. Previous research has noted limitations in the CGFEM such as model convergence with growth periods greater than 12 days. The main aims of this work were to address these limitations through (1) implementation of an exact material Jacobian matrix definition using the Jaumann-Kirchhoff (J-K) method and (2) quantification of elastic material parameters based upon research findings of the Cal Poly Cartilage Biomechanics Group (CPGBG). The J-K method was successfully implemented into the CGFEM and exceeded the maximum convergence strains for both the “pushed forward, then differentiated” (PFD) and “differentiated, then pushed forward” (DPF) methods, while maintaining correct material stress responses. Elastic parameters were optimized for confined compression (CC), unconfined compression (UCC), and uniaxial tension (UT) protocols. This work increases the robustness of the CGFEM through the J-K method, as well as defines an accurate starting point for AC growth based on the optimized material parameters.

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