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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.

Control of Legged Robotic Systems: Substantiation of Gait Design, Multi-Modal Behaviors, and Dynamic Scaling Theory in Practice

Unknown Date (has links)
Through limb structure and neuromuscular control, animals have demonstrated the ability to navigate obstacles and uneven terrain using a variety of different mechanisms and behaviors. Learning from the capabilities of animals, it is possible to develop robotic platforms that can aid in the study of these motions towards the production of new technologies for military, search and rescue, and medical applications. To produce these systems, it is important to first understand the underlying dynamics and design principles existent in nature that afford creatures such dexterous and agile movements. The creation of robots with legs provide a means for studying different aspects of the dynamics of legged locomotion. This includes investigations of limb coordination for gait controller design, the role of passive compliance in dynamic running, mechanical leg design and configuration for optimal energetic output, and scalability of legged systems in both simulation and through experimentation. This thesis aims to provide insight into the design and implementation of terrestrial robotic platforms with legs. / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Summer Semester 2018. / July 13, 2018. / dynamic simulation, gait design, kinematics, legged robots / Includes bibliographical references. / Jonathan Clark, Professor Directing Thesis; William Oates, Committee Member; Carl A. Moore, Committee Member.

Evolution of the Material Properties of Mineralized Dental Tissues

Unknown Date (has links)
During their 473 million-year diversification, gnathostomes came to exploit an unprecedented variety of trophic niches. Modifications to dental form and mineralized tissue constituents (i.e. enamel, dentines and in a few taxa, cementum) facilitated their exploitation of novel prey and/or plant matter. In general, it has been assumed that the intra-tissue level biomechanics of these constituents had little bearing on whole-tooth functionality, aside from enamel in mammals showing dental occlusion. Specifically, many mammals possess teeth that self-wear to functionality and show a diversity of derived dental tissues (e.g. prismatic enamel fabrics, coronal cementum) – some which have been shown to possess unique biomechanical attributes to resist wear and fracture. Here I formally test the hypothesis that the primitive gnathostome hard tissue material properties remained static prior to the cladogenesis of Mammalia. An ancillary goal is to glean initial insights on how the material properties of these dental tissues in non-mammalian and mammalian taxa may contribute to whole-tooth form, function, performance and diets. Properties were tested and examined using two standardized material science techniques, microindentation and nanoindentation, as well as a novel technique for quantifying fracture propagation from cracks formed during microindentation. The results from this investigation suggest these material properties are highly variable among gnathostome dentitions. Aside from hardness, there is not a significant relationship between most material properties and diet aside from enamel hardness. There are also complex fracture patterns seen in the enamels of mammals and chondrichthyans, showing that gnathostome lineages independently evolved properties to control fracture and damage done to tooth enamel. Overall, this study suggests that in the case of enamel hardness, natural selection operated at the tissue level to bring about shifts in tooth functionality throughout the gnathostome radiation. More material properties (i.e. fracture toughness) need to be investigated to uncover the true functional import of material properties in dental tissues and establish how the tissue complexes contributed to whole tooth function. / A Thesis submitted to the Department of Biological Science in partial fulfillment of the requirements for the degree of Master of Science. / Summer Semester 2017. / August 1, 2017. / biomaterials, material properties, nanoindentation, teeth / Includes bibliographical references. / Gregory M. Erickson, Professor Directing Thesis; Steven Lenhert, Committee Member; William S. Oates, Committee Member; Scott J. Steppan, Committee Member.

When Push Comes to Shove| The Effects of Tunnel Width and Darkness on Predation Performance of Kingsnakes

Barron, Elizabeth 12 April 2019 (has links)
<p> A predator's attempt to capture prey involves energetic costs and risks of injuries. The need to avoid potentially severe consequences is one of the reasons why predation often requires high performance. I investigated the effects of different environmental conditions on predation performance in Florida kingsnakes. When pursuing prey in tight spaces (e.g., rodent tunnels) kingsnakes cannot coil around the prey as they do for constriction in open areas. Instead, they use pinioning, which involves using bends of the body to compress prey against a hard surface. </p><p> First, I analyzed the effects of tunnel width on pinioning performance, quantified as the peak pressure exerted on the prey. I tested three tunnel widths and hypothesized that the moderate width would elicit the highest performance. However, I found that the narrow tunnel led to the highest performance. The lowest pressures were exerted in the broad tunnel. These results suggest that as body length increases, the postures may become less stable and have less effective force transmission, leading to weaker pressure exertion. </p><p> Second, I investigated how darkness affects pinioning performance. I hypothesized that pinioning performance would differ in the dark compared to the light. I found that kingsnakes have significantly higher performance in the dark. The higher performance in the dark could be a means of behaviorally compensating for the snake's inability to use vision to assess the size and activity of the prey, and hence its risk of escape or injury to the snake in self-defense. </p><p> Together, these projects demonstrated that extrinsic factors (spatial constraints and darkness) and intrinsic factors (specific body parts involved) can affect an individual's behavior and performance. Hence, studying performance under different conditions is important for developing a detailed understanding of functional mechanisms as well as a broader understanding of the biology, ecology, and evolution of organisms.</p><p>

Inferring Transcriptional and Post-Transcriptional Network Structure by Exploiting Natural Sequence Variation

Fazlollahi, Mina January 2013 (has links)
Understanding how cellular processes of an organism translate its genome into its phenotype is one of the grand challenges in biology. Linkage studies seek to identify allelic variants that manifest themselves as phenotypic variation between individuals in a population. The advent of high-throughput genotyping and gene expression profiling technologies has made it possible to use messenger RNA levels as quantitative traits in linkage studies. This has created new opportunities to study genetic variation at the level of gene regulatory networks rather than individual genes. This thesis consists of four parts, each of which outlines a different strategy for integrating genome-wide expression data and genotype data in order to identify transcriptional and post-transcriptional regulatory mechanisms. The data for these analyses comes from segregating populations of Saccharomyces cerevisiae (baker’s yeast) as well as Caenorhabditis elegans (roundworm). The first study focused on inferring the in vitro binding specificity of RNA-binding proteins (RBPs). We first analyzed a recent compendium of in vivo mRNA binding data to model the sequence specificity of 45 yeast RBPs in the form of a position- specific affinity matrix (PSAM). We were able to recover known consensus nucleotide sequences for 12 RBPs and discovered novel binding preferences for 3 of the RBPs namely, Scp160p, Sik1p and Tdh3p. The second study aimed to identify transacting chromosomal loci that regulate expression of a large number of genes. Traditionally, such loci are discovered by first mapping expression quantitative loci (eQTLs) for individual genes, and then looking for so-called “eQTLs hotspots”. Our method avoids the first step by integrating information across all genes, leading to a more elegant method that has increased statistical power. For yeast, we recovered 70% of the reported eQTL hotspots from two independent studies, and discovered a new transacting locus on chromosome V. For worm, we detected six transacting loci, only two of which were previously reported as eQTL hotspots. The third study focused on post-transcriptional regulatory networks in yeast, by mapping the regulatory activity level of RNA binding proteins (RBPs) as a quantitative trait in so-called “aQTL” analysis. We used the collection of 15 sequence motifs with the associated mRNA region combinations that we obtained in our first study together with mRNA expression data to estimate RBP activities across yeast segregants. Consistent with a previous study, we recovered the MKT1 locus on chromosome XIV as a genetic modulator of Puf3p activity. We also discovered that Puf3p activity is modulated through distinct loci depending on whether it is binding to 50 or 30 untranslated region (UTR) of its target mRNAs. Furthermore, we identified a locus on chromosome XV that includes the IRA2 gene as a putative aQTL for Puf4p; this prediction was validated using expression data for an IRA2 allele replacement strain. Our fourth study focused on the detection of loci whose allelic variation modulates the in vivo regulatory connectivity between a transcription factor and its target genes. We call these loci connectivity QTLs or “cQTLs”. We mapped the DIG2 locus on chromosome IV as a cQTL for the transcription factor Ste12p. Dig2p is indeed a known inhibitor of yeast mating response activator Ste12p. The coding region of the DIG2 gene contains a single non-synonymous mutation (T83I). We are experimentally testing the functional impact of this mutation in allele replacement strains. We also identified the TAF13 locus as a putative modulator of GCN4p connectivity.

Characterization of the microstructural properties that are predictive of regain in strength in phosphate-deficient mice

Simmons, Erin 20 June 2016 (has links)
Fracture healing occurs in a discrete set of steps, which recapitulates embryonic endochondral bone formation. Pathophysiologies of the fracture healing that prolong the fracture repair or result in non-union may be associated with either environmental or congenital deficiencies. Phosphate deficiency resulting from either dietary or genetic perturbations can impede proper fracture healing and if prolonged can result in delayed union. The clinical assessment of regain of mechanical function is determined by measuring weight-bearing ability, palpation and various radiological approaches. These methods in general only provide qualitative evidence but are lacking in quantitative evidence of the regain in mechanical strength. The aim of this study was to characterize the microstructural properties obtained by micro-computed tomography of fracture calluses at various stages of healing and develop correlations between these structural parameters and mechanical properties that define regain of function. Transverse, mid-diaphyseal fractures were produced on the right leg in three different murine genetic strains—A/J (AJ), C57BL/6J (B6), and C3H/HeJ (C3). Each mouse was either fed a control or phosphate deficient diet that produces a hypophosphatemic state and generates an environmental state that impairs fracture healing. Those on a phosphate deficient diet were kept on this diet for 14 days post-fracture. Fractured limbs were studied at four different post-operative time points—14, 21, 35, and 42. These four time points were based on callus stability and various phases in callus development. Contralateral limbs served as a control, representing full regain of strength. Day 0 contralateral limbs were used for the control group. Contralateral limbs were imaged and torsion tested for each strain on both control and phosphate-deficient diets. The data reveals that in regards to bone volume fraction, bone mineral density, and tissue mineral density all three strains show a progressive return to non-fractured, control values but even by post-operative day 42 do not show a 100% regain in microstructural properties. While there are interactions between specific post-operative time points and the dietary restriction, by post-operative day 42 microstructural properties showed no significant differences between the two groups, suggesting that the effects of phosphate deficiency are reversible upon a return to normal dietary conditions. The AJ and B6 strains show significant interaction between post-operative time point and dietary restrictions earlier in the fracture repair process (post-operative days 14 and 21), whereas the C3 mice show these interactions at later time points, at post-operative 35 and 42 days. Phosphate deficiency induces an overshoot in mechanical properties at post-operative day 21 for AJ and B6 strains and at post-operative day 35 for the C3 strain that appears to be part of a process in which maximum torque and work to failure undergo a compensatory phase in which these two mechanical properties are significantly higher than in non-fractured, control limbs. The overshoot in maximum torque and work to failure is part of an adaptive process in which the callus first overshoots and subsequently returns to non-fractured control values. These results suggest that while microstructural properties and mechanical properties are often affected by diet, this is a reversible phenomenon, which holds implications for those with phosphate deficiency due to either a metabolic or dietary disorder. If normal phosphate intake and absorption are achieved by the period at which couple remodeling in initiated (14 post-fracture) the effects on microstructural and weight bearing levels are reversible. The slower healing seen in C3 mice evidenced by the later regain in microstructural and mechanical integrity may provide a model for patients whose fractures show delayed healing in the clinic. The microstructural properties discussed have the potential to play a role in the clinic to assess fracture healing. With the advent of greater resolution CT imaging assessing these microstructural properties can be useful in determining the progression of healing.

Evaluation of the Effects of an Elastic Hamstring Assistance Device During Downhill Running

Trahan, Brittany A. 27 August 2015 (has links)
<p>Trahan, Brittany A. Bachelor of Science, University of Louisiana at Lafayette, Spring 2011; Master of Science, University of Louisiana at Lafayette, Spring 2015 Major: Kinesiology Title of Thesis: Evaluation of the Effects of an Elastic Hamstring Assistance Device During Downhill Running Thesis Director: Dr. Randy Aldret Pages in Thesis: 72; Words in Abstract: 207 ABSTRACT This investigation determined the benefits of the Hamstrong device after downhill running. Sixteen healthy college-aged males volunteered to participate in the repeated measures experimental study. They were assigned to either run with or without the device. They ran for forty minutes at 75% of their calculated VO2 Max speed. The effects of the device or absence of the device were examined as well as the PROM and isometric hamstring strength. The subjects had to repeat the protocol (minus the running) at three different time periods following the exercise. Repeated measures ANOVA did not reveal a significant (F=0.119, p=0.705) effect for the left leg PROM, nor a significant (F=0.016, p=0.977) effect for the right leg PROM. Repeated measures ANOVA did not reveal a significant effect (F=0.578, p=0.128) for the right leg at 90 degrees of extension during isometric strength testing, but there was a significant effect (F=1.027, p=0.032) for the left leg at the same angle. Repeated measures ANOVA did not reveal a significant effect (F=0.797, p=0.063) for the right leg at 135 degrees of extension during isometric strength testing, nor a significant effect (F=0.227, p=0.467) for the left leg at the same angle. There were no other changes regarding the effects of the device regarding myoglobin concentration.

Kinetic And Kinematic Adaptations To Use Of A Personal Lift Assist Device

Agnew, Michael 02 October 2008 (has links)
The purpose of this work was to quantify the effect of the personal lift assist device (PLAD) on kinetic and kinematic variables commonly indentified as risk factors for low back pain (LBP). As such, three investigations were undertaken to document adaptations that occur as a consequence of wearing the PLAD. The first study involved an investigation of the effects of the PLAD on intervertebral compression and shear, using an EMG-assisted biomechanical model across a range of trunk flexion. Muscle activation (EMG), trunk posture, and PLAD support data were input into a biomechanical model that estimated L4/L5 joint loads. Use of the PLAD significantly reduced joint compression across the range of trunk flexion. Significant changes in shear were also found, although this was varied across conditions. The second study was conducted to quantify differences in lifting posture, lifting kinematics, and co-ordination attributable to use of the PLAD. Over two testing sessions, subjects completed a repetitive lifting task with and without use of the PLAD. Kinematic data describing lumbar spine, hip and knee motion were used to quantify lifting posture, lifting velocities, and co-ordination. The results of the study suggest that the PLAD causes users to lift with significantly less lumbar flexion and greater hip flexion. Significant changes in co-ordination were also observed, reflective of motor adaptation to the assistance provided by the PLAD. The final study was conducted to investigate the effect of the PLAD on active trunk stiffness. Subjects were required to assume a series of static, symmetrical flexed postures. Muscle activation (EMG), trunk posture, and PLAD stiffness data were input into a stability model that estimated active trunk stiffness. Up to 15 degrees of flexion, the PLAD increased the overall stiffness of the trunk. However, use of the PLAD significantly reduced the active stiffness of the trunk as flexion increased. This effect was consistent across PLAD conditions. Further research is needed to confirm these findings and evaluate a potential redesign. In general, the results of these studies illustrate the potential for the PLAD to be used as an ergonomic intervention for industrial tasks requiring lifting and/or flexed static postures. / Thesis (Ph.D, Kinesiology & Health Studies) -- Queen's University, 2008-10-02 15:07:22.11

A biomechanical comparison of the long snap to punter between high school and university level football players

Chizewski, Michael George 06 November 2009 (has links)
The study compared the kinematics used to perform fast and accurate long snaps in high school (HS) and university level (UNI) athletes. The study also determined the kinematic variables related to greater release velocity and which variables are significant predictors of release velocity or total snap time* (TST) for HS, UNI, and both groups combined*. Ten HS and ten UNI subjects were recruited. The athletes were filmed with eighty-three variables measured using Dartfish TeamPro 4.5.2 software. UNI athletes had significantly greater release velocity (15.15m/s) and left elbow extension velocity (752 deg/sec) than the HS group (13.21m/s and 498 deg/sec). TST had the strongest correlation to release velocity in HS (r=-0.915) and UNI snappers (r=-0.918). HS long snappers may benefit from less elbow flexion and more knee flexion in the set position. UNI long snappers may benefit from increased left elbow extension ROM and decreased shoulder flexion at release.

The mechanical properties of the human cornea

Shin, Thomas Jungwoog 08 1900 (has links)
No description available.

The mechanical properties of normal and pathological bone

Dickenson, R. P. January 1978 (has links)
No description available.

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