Vestibular hair cells are mechanotransducing sensory receptors in the vertebrate inner ear that detect movement and orientation of the head with respect to gravity. The morphologies of their ciliary bundles vary greatly for different species, endorgans, and within the same endorgan. Bundle morphology in the turtle utricle, like other species, demonstrates highly organized regional variations. These structural differences in bundles impact their mechanical behavior and the process of mechanotransduction. To further understanding of the mechanical behavior of hair bundles, this work experimentally measured the stiffness of bundles with differing morphology, the stiffness contribution of interciliary links and the mechanical properties of the kinocilium in the turtle utricle. The stiffness of hair bundles of varying structure and location along a medial to lateral transect of the utricle was examined. Bundle stiffness was greatest in the striola and demonstrated a systematic decline with location from the line of polarity reversal. The average stiffness of bundles in the striola and extrastriola were 82 ± 46 (n=48) and 9 ± 5 (n=25) µN/m, respectively. The stiff and weak bundles demonstrated characteristic morphologies. The stiffest bundles have short kinocilium, tall stereocilia, and ratios of kinocilium to tallest stereocilia height (KS) close to 1. In contrast, the compliant bundles have tall kinocilium, short stereocilia, and KS ratios ranging from 1.6 – 8. The stiffer bundles also tend to have longer array lengths and steeper slopes. Measurements of bundle stiffness in the turtle utricle are lower than those previously reported which may be attributed to morphological differences between species. The stiffness contributions of the interciliary links were also examined through their selective removal with exposure to the Ca²⁺ chelator BAPTA and the protease subtilisin. BAPTA treatment reportedly breaks tip, kinocilial and ankle links while subtilisin breaks the shaft and ankle links. Following BAPTA and subtilisin treatments, bundle stiffness reduced by 65 ± 10% and 63 ± 11%, respectively. The mechanical properties of the kinocilium were measured with novel techniques. Flexural rigidity (EI) was measure while the kinocilium was fixed at the height of the tallest stereocilia using a glass supporting probe. Through both force deflection and a high speed video technique, measured values of EI ranged from 1460 – 6150 pN·µm2. The rotational stiffness of the kinocilium about its apical insertion was also measured. Bundles were treated with BAPTA to break the kinocilial links and separate the kinocilium from neighboring stereocilia. Using a force deflection technique, the rotational stiffness of the kinocilium was measured as 120 ± 17 pN·µm/rad. / Ph. D.

Cardiovascular disease (CVD) is the leading cause of death in the United States. Recently, the gut microbiota has been implicated in the pathophysiology and progression of CVD. Experimental evidence suggests that high fat feeding alters the functional composition of the gut microbiota (dysbiosis); leading to increased translocation of the pro-inflammatory, endotoxin, and increased production of the pro-atherogenic, trimethylamine-N-oxide (TMAO). Together, these changes are hypothesized to accelerate CVD progression. Conversely, administration of gut microbiota modulating agents, such as antibiotics and probiotics, attenuate high fat feeding induced CVD in rodent models. In humans, the capacity to produce TMAO following L-carnitine or phosphatidylcholine challenges is abolished after receiving broad spectrum antibiotics for a period of one week. However, whether gut modulation over a longer period of time decreases fasting serum endotoxin, fasting plasma TMAO, and CVD risk in response to high fat feeding has been unexplored in humans. To address these issues we conducted a randomized, placebo controlled, parallel group designed, controlled feeding study in healthy, non-obese males receiving the multi-strain probiotic, VSL #3 (or placebo), while a consuming a high fat diet for 4-weeks. First, we tested the hypothesis that VSL #3 would attenuate the rise in serum endotoxin and consequent arterial stiffening following high fat feeding in healthy, non-obese males. Second, we tested the hypothesis that VSL #3 would attenuate the rise in plasma TMAO concentrations following high fat feeding in healthy, non-obese males. In contrast to our first hypotheses, serum endotoxin concentrations and arterial stiffness did not change in response to high fat feeding or with VSL#3 treatment. Interestingly, VSL #3 significantly attenuated the increase in body mass (+ 1.4±0.4 vs. +2.3±0.3 kg; P < 0.05) and fat mass (+0.7±0.1 vs. + 1.4±0.3 kg; P < 0.05) following high fat feeding compared to the placebo. In contrast to our second hypothesis, probiotic supplementation did not attenuate the rise in plasma TMAO following high fat feeding. Future studies are necessary to elucidate the mechanisms responsible for the prevention of body mass and fat mass gain with VSL#3 supplementation following high fat feeding. In addition, studies are needed to determine whether higher doses of VSL #3, other single or multispecies probiotics, prebiotics, or synbiotics attenuate the production of the proatherogenic, TMAO. / Ph. D.

The objective of this research was to investigate the effect of applied compressive strain in various environments, on the strength and stiffness of compressed wood samples. It is believed that transverse compression of wood at specific conditions of temperature and moisture will result in improved mechanical properties, which can be attributed to increased density and perhaps other physical or chemical changes. Specimens of both mature and juvenile southern pine (Pinus taeda) and yellow-poplar (Liriodendron tulipifera) were compressed radially at three different temperature, and moisture content conditions relevant to the glass transition of wood. Ultimate tensile stress and longitudinal modulus of elasticity were obtained by testing compressed, uncompressed and control samples in tension parallel-to-grain. Strain measurements were performed using laboratory-built clip-on strain gauge transducers. Results of the tensile tests have shown an increase in the ultimate tensile stress and modulus of elasticity after all densification treatments. Scanning electron microscopy was employed for observing changes in cellular structure of densified wood. Existence of the cell wall fractures was evaluated using image processing and analysis software. Changes in cellular structure were correlated with the results of the tensile test. Chemical composition of wood samples before and after desorption experiments was determined by acid hydrolysis followed by high performance liquid chromatography (HPLC). The results of the chemical analysis of the wood specimens did not reveal significant changes in chemical composition of wood when subjected to 160 °C, pure steam for up to 8 hours. The results of this research will provide information about modifications that occur during wood compression and will result in better understanding of material behavior during the manufacture of wood-based composites. In the long run, modification of wood with inadequate mechanical properties can have a significant effect on the wood products industry. Low density and juvenile wood can be used in new high-performance wood-based composite materials instead of old-growth timber. / Master of Science

In recent decades science has become an increasingly multidisciplinary field in which the lines that used to divide starkly different fields have blurred or disappeared completely. This work is a compendium of different angles focused at exploring disease progression of cancer biology through the perspective of mechanical engineering. We explore cancer through a holistic approach considering mechanistic, physical, genetic biology, biochemical, and immune cells to explore how the interplay with fiber networks can expand our understanding. We explored the physical interplay with biological processes of fibroblastic cells and show how these are critically regulated by forces that alter their ability to coil depends on fiber curvature and adhesion strength; thus, showing how cellular processes are driven by the balances of mechanical forces. Conversely, not all cell types are driven by the same factors, where we report that the structural features of migratory DCs enable them to be less influenced by the differences in fiber diameters, contrasting drastically what we previously reported on the other cell lines. Finally developing a novel composite nanofiber platform, we reported how some cancer cells are mechanistically influenced by the architecture of a substrate and thus resulting in completely different migratory responses that we have associated with key regulatory genes and responding completely differently when in the presence of clinically relevant molecular therapies. Overall, we investigated cancer biology through stiffness gradients, geometric influence through biophysics on myoblasts, and immune cell migration forces as a strong indicator of cell behavior. / Master of Science / Biology has historically been studied through chemistry and genetics, an approach that has produced incredible scientific discoveries such as vaccines and various therapies. Similarly, mechanical engineering has taken us to corners of the world that we never thought possible through the creation of machines, vehicles and the creation of new metal alloys. This research work is part of an emergent field of collaborative science which is paving the way to new ideas and the development of compound fields such as mechanobiology. Here we investigate how cells migrate through small rope-like environments that imitate the same fibers our cells can encounter in the body. We control the thickness, the arrangement, the orientation and the strength of these ropes to investigate how cells react to these environments, thus reporting on the new behaviors cells adopts in these conditions as well as their potential medical implications. Overall, we have developed new methods of studying cancer and other types of cells by tackling new questions using a mechanical perspective.

Background: Anterior cruciate ligament (ACL) injuries have become commonplace among female athletes in today’s society. With more than 70% of injuries resulting from noncontact mechanisms such as jump landing, the relationship between fatigue and altered movements patterns has become an important topic of research. Purpose: The main purpose of this study was to investigate the influence of residual fatigue on lower extremity kinematics and vertical leg stiffness at landing as experienced by female athletes. Method: The participants in this study were 12 NCAA female intercollegiate soccer players. Participants completed five single-leg drop jumps on their dominant leg every day for 4 days. The first day was completed without intervention to obtain pre-fatigue data and drop jumps on days two through four were completed after a fatigue protocol. Results: A repeated measures MANOVA did not reveal significant differences in post-fatigue peak knee flexion angle, vertical ground reaction forces, or vertical leg stiffness. Despite lack of statistical significance, vertical leg stiffness was increased during post-fatigue testing when compared to pre-fatigue values. Implications: The increased vertical leg stiffness may indicate altered landing techniques in post-fatigue states. If fatigue results in compromised movement patterns, it may explain the increased number of ACL injuries during the end of soccer matches. Suggestions for Future Research: Future research with a larger sample size should include post-fatigue dominant and nondominant leg comparison due to previous conflicting findings regarding which limb is most often injured. Future researchers should also quantify the magnitude of fatigue induced by the fatiguing protocol to document the strength of the independent variable. / text

The objective of this research is to determine the three-dimensional stiffness matrix of a rectangular cross-section helical coil compression spring. The stiffnesses of the spring are derived using strain energy methods and Castigliano's second theorem. A theoretical model is developed and presented in order to describe the various steps undertaken to calculate the spring's stiffnesses. The resulting stiffnesses take into account the bending moments, the twisting moments, and the transverse shear forces. In addition, the spring's geometric form which includes the effects of pitch, curvature of wire and distortion due to normal and transverse forces are taken into consideration. Similar methods utilizing Castigliano's second theorem and strain energy expressions were also used to derive equations for a circular cross-section spring. Their results are compared to the existing solutions and used to validate the equations derived for the rectangular cross-section helical coil compression spring. A finite element model was generated using IDEAS (Integrated Design Engineering Analysis Software) and the stiffness matrix evaluated by applying a unit load along the spring's axis, then calculating the corresponding changes in deformation. The linear stiffness matrix is then obtained by solving the linear system of equations in changes of load and deformation. This stiffness matrix is a six by six matrix relating the load (three forces and three moments) to the deformations (three translations and three rotations). The natural frequencies and mode shapes of a mechanical system consisting of an Additional mass and the spring are also determined. Finally, a comparison of the stiffnesses derived using the analytical methods and those obtained from the finite element analysis was made and the results presented. / Master of Science

Researchers have offered a variety of solutions for overcoming the old and challenging problem of undesired vibrations. The optimum vibration-control solution that can be a passive, semi-active or active solution, is chosen based on the desired level of vibration-control, the budget and the nature of the vibration source. Mechanical vibration-control systems, which work based on variable stiffness control, are categorized as semi-active solutions. They are advantageous for applications with multiple excitation frequencies, such as seismic applications. The available mechanical variable stiffness systems that are used for vibration-control, however, are slow and usually big, and their slowness and size have limited their application. A new semi-active variable stiffness solution is introduced and developed in this thesis to address these challenges by providing a faster vibration-control system with a feasible size. The new solution proposed in this thesis is a semi-active variable stiffness mount/isolator called the antagonistic Variable Stiffness Mount (VSM), which uses a variable stiffness spring called the Antagonistic Variable stiffness Spring (AVS). The AVS is a kinematically singular prestressable mechanism. Its stiffness can be changed by controlling the prestress of the mechanisms links. The AVS provides additional stiffness for a VSM when such stiffness is needed and remains inactive when it is not needed. The damping of the VSM is constant and an additional constant stiffness in the VSM supports the deadweight. Two cable-mechanisms - kinematically singular cable-driven mechanisms and Prism Tensegrities - are developed as AVSs in this thesis. Their optimal configurations are identified and a general formulation for their prestress stiffness is provided by using the notion of infinitesimal mechanism. The feasibility and practicality of the AVS and VSM are demonstrated through a case study of a typical engine mount by simulation of the mathematical models and by extensive experimental analysis. A VSM with an adjustable design, a piezo-actuation mechanism and a simple on-off controller is fabricated and tested for performance evaluation. The performance is measured based on four criteria: (1) how much the VSM controls the displacement near the resonance, (2) how well the VSM isolates the vibration at high frequencies, (3) how well the VSM controls the motion caused by shock, and (4) how fast the VSM reacts to control the vibration. For this evaluation, first the stiffness of the VSM was characterized through static and dynamic tests. Then performance of the VSM was evaluated and compared with an equivalent passive mount in two main areas of transmissibility and shock absorption. The response time of the VSM is also measured in a realistic scenario.

No description available.

Šio baigiamojo darbo tikslas yra išnagrinėti pagrindo standumo įvertinimo įtaką skaičiuojant konstrukcijas. Taigi nagrinėjamas pagrindo standumas, norint išanalizuoti, kokią įtaką parinktas pagrindo standumo įvertinimo metodas turi projektuojant statinio konstrukcijas. Darbą sudaro pagrindo standumo įvertinimo metodų, konstrukcijos mazgų standumo vertinimo ir pastato skaičiavimo ant deformuojamojo pagrindo dalys. Pirmoje dalyje yra aptariamos klasikinės pagrindo standumo įvertinimo teorijos, analizuojami pagrindo standumo įvertinimo metodai ir atliekamas grunto standumo vertinimas pagal kompresinį aparatą. Antroje dalyje yra pateikiamas konstrukcijos mazgų standumo vertinimo principas ir konstrukcijos mazgų standumo skaičiavimas kompiuterinėmis programomis. Paskutinėje darbo dalyje yra atliekami skaičiavimai pagal skirtingus pagrindo standumo įvertinimo metodus. Nagrinėjamas UAB ,,Philip Morris Lietuva‘‘ tabako paruošimo cecho pastatas. Modeliuojamas pastatas ant deformuojamojo pagrindo (STAAD.Pro 2005) kompiuterine programa, įvertinant pagrindo standumą pagal apskaičiuotus metodus. Pagrindas skaičiuojamas kaip tam tikro standumo spyruoklės (Vinklerio modelis). Gauti analizės rezultatai lyginami tarpusavyje ir pagal konstrukcijos skaičiavimus neįvertinant pagrindo standumo. Gautos priklausomybės tarp nagrinėjamųjų parametrų yra išreiškiamos grafikais ir lentelių forma, formuluojamos išvados. Darbo apimtis – 108 p. teksto be priedų, 73 iliustr., 32 lent., 33 bibliografiniai... [toliau žr. visą tekstą] / The purpose of this final work is to research influence evaluation of the ground stiffness calculating bearing structures. The research is of ground stiffness purpose influence to selected stiffness method for bearing structures. The work consist of influence evaluation of the ground stiffness methods, the influence evaluation of structure‘s joints stiffness and analysis of structures‘s on elastic ground parts. The first part is about classical ground stiffness theories, influence of the ground stiffness methods and evaluation of the ground stiffness with compression device. The second part of this work is about the influence evaluation of structure‘s joints stiffness and calculations with computer programs of it. In the last part of this work there are analysis and calculation by evaluated stiffness methods. It is analysing UAB ,,Philip Morris Lietuva‘‘ tobacco preparative building. The structure is modeling on the distort ground with computer program (STAAD.Pro 2005). The ground is calculating like particular rigidy spring (Vinclar model). The results of this work analysis between pending parameters are in comparing diagrams and tables. Work size – 108 p. of text, 73 iliustr., 32 tables, 33 source of litr. Appendixes included.

Finite element models were created in Abaqus 6.14 to characterize the rotational stiffness of shallowly embedded column-foundation connections. Scripts were programmed to automate the model generation process and allow study of multiple independent variables, including embedment length, column size, baseplate geometry, concrete modulus, column orientation, cantilever height, and applied axial load. Three different connection types were investigated: a tied or one part model; a contact-based model; and a cohesive-zone based model. Cohesive-zone modeling was found to give the most accurate results. Agreement with previous experimental data was obtained to within 27%. Baseplate geometry was found to affect connection stiffness significantly, especially at lower embedment depths. The connection rotational stiffness was found to vary only slightly with cantilever height for typical column heights. Results from varying other parameters are also discussed.