Increased attention has been paid in recent years to the means in which the body maintains stability and the subtleties of the neurocontroller. Variability of kinematic data has been used as a measure of stability but these analyses are not appropriate for quantifying stability of dynamic systems. Response of biological control systems depend on both temporal and spatial inputs, so means of quantifying stability should account for both. These studies utilized tools developed for the analysis of deterministic chaos to quantify local dynamic stability of musculoskeletal systems. The initial study aimed to answer the oft assumed conjecture that reduced gait speeds in people with neuromuscular impairments lead to improved stability. Healthy subjects walked on a motorized treadmill at an array of speeds ranging from slow to fast while kinematic joint angle data were recorded. Significant (p < 0.001) trends showed that stability monotonically decreased with increasing walking speeds. A second study was performed to investigate dynamic stability of the trunk. Healthy subjects went through a variety of motions exhibiting either symmetric flexion in the sagittal plane or asymmetric flexion including twisting at both low and high cycle frequencies. Faster cycle frequencies led to significantly (p<0.001) greater instability than slower frequencies. Motions that were hybrids of flexion and rotation were significantly (p<0.001) more stable than motions of pure rotation or flexion. Finding means of increasing dynamic stability may provide great understanding of the neurocontroller as well as decrease instances of injury related to repetitive tasks. Future studies should look in greater detail at the relationships between dynamic instability and injury and between local dynamic stability and global dynamic stability. / Master of Science

The goal of this thesis is to develop a dynamic stability and control module that can be used in the concept exploration phase of design. The purpose of the module is to determine the hydrodynamic coefficients/derivatives and stability characteristics of a given design. Two tools, GEORGE and CEBAXI and LA_57, were used to model a submarine, calculate its hydrodynamic coefficients, and determine its stability in the horizontal and vertical plane. GEORGE was developed and used heavily at Naval Coastal Systems Laboratory (NSWCPC) in Panama City, FL and the CEBAXI and LA_57 program was developed partially at University of California State at Long Beach and at the Carderock Division of the Naval Surface Warfare Center (NSWCCD) and is in use at NSWCCD in Bethesda, MD. Both programs require the hull offsets and geometry of the control surfaces as input. The hull offsets were determined by assuming an idealistic teardrop shape and a method for sizing control surfaces was developed by using previous designs to determine sizing trends. ModelCenter software was used to integrate the methods to determine the offsets and control surface geometry with the stability programs. A design of experiments was performed to determine the influence of various input variables on the stability indices and response surface models were created. The response surfaces were implemented into a Total Ship Systems Engineering optimization process used in the senior ship design course at Virginia Tech. / Master of Science

On Monday, 29 August 2005, Hurricane Katrina struck the U.S. gulf coast. The storm caused damage to 169 miles of the 284 miles that compose the Hurricane Protection System (HPS) of the area. The system suffered 46 breaches due to water levels overtopping and another four caused by instability due to soil foundation failure. The Interagency Performance Evaluation Task Force (IPET) conducted a study to analyze what happened on the I-wall breach of the various New Orleans flood control structures and looked for solutions to improve the design of these floodwalls. The purpose of the investigation, describe in this document, is to evaluate different methods to improve the analysis model created by IPET, select the best possible analysis techniques, and apply them to a current cross-section that did not fail during Hurrican Katrina. The use of Finite Element (FE) analysis to obtain the vertical total stress distribution in the vicinity of the I-wall and to calculate pore pressures proved to be an effective enhancement. The influence of overconsolidation on the shear strength distribution of the foundation soils was examined as well. / Master of Science

Automotive turbochargers experience self-excited instabilities through the majority of their operating speed range. The results of these instabilities can cause damage to the bearings, shafts, and housing walls. Preventing this damage while maintaining or increasing performance characteristics is a huge concern to industry due to the time and money needed to replace vital components. The aim of this research is to determine which characteristics of the bearings have the greatest influence on the damped natural frequencies. It was believed that axial groove bearings could offer an acceptable alternative to the floating ring bearings currently found in automotive turbochargers. DyRoBeS rotor dynamics software was used to determine analytically damped natural frequencies for floating ring bearings, and also for six, eight, and ten axial groove fixed geometry bearings, under different speed and loading conditions. The resulting data were compared to experimental test results from an on-engine turbocharger test stand and presented in this report. / Master of Science

No / The predicted stability differences of the conformational polymorphs of oxalyl dihydrazide and ortho-acetamidobenzamide are unrealistically large when the modeling of intermolecular energies is solely based on the isolated-molecule charge density, neglecting charge density polarization. Ab initio calculated crystal electron densities showed qualitative differences depending on the spatial arrangement of molecules in the lattice with the greatest variations observed for polymorphs that differ in the extent of inter- and intramolecular hydrogen bonding. We show that accounting for induction dramatically alters the calculated stability order of the polymorphs and reduces their predicted stability differences to be in better agreement with experiment. Given the challenges in modeling conformational polymorphs with marked differences in hydrogen bonding geometries, we performed an extensive periodic density functional study with a range of exchange-correlation functionals using both atomic and plane wave basis sets. Although such electronic structure methods model the electrostatic and polarization contributions well, the underestimation of dispersion interactions by current exchange-correlation functionals limits their applicability. The use of an empirical dispersion-corrected density functional method consistently reduces the structural deviations between the experimental and energy minimized crystal structures and achieves plausible stability differences. Thus, we have established which types of models may give worthwhile relative energies for crystal structures and other condensed phases of flexible molecules with intra- and intermolecular hydrogen bonding capabilities, advancing the possibility of simulation studies on polymorphic pharmaceuticals.

Equilibrium relations between garnet and orthopyroxene have been investigated by reversal experiments in the range of 20-45Kb and 975-1400°C in the FeO-MgO-Al₂O₃-SiO₂(FMAS) system. The Fe-Mg exchange reaction seems to have little or no compositional dependence at these conditions. The experimental results can be fitted adequately by the linear relation: ln K(D) = 2243/T°K - 0.9522 at 25Kb where K(D) = (X(Fe)/X(Mg))ᴳᵗ/(X(Fe)/X(Mg))ᴼᵖˣ. Combination of the available data for the mixing properties of garnet and V° for the Fe-Mg exchange reaction with the above experimental results yields the following geothermometric expression for the common natural assemblages that can be represented essentially within the system CaO-MnO-FeO-MgO-Al₂O₃-SiO₂. T°K = (1968 + 11P(Kb) + 1510(X(Ca)+X(Mn))ᴳᵗ)/(ln K(D) + 0.9522). The stability field of pyrope+quartz, defined by the reaction pryope+quartz=opx+sill, has been calculated as a function of P,T,X(Fe)ᴳᵗ in the FMAS system using the reversal experimental data of Perkins (1983) in the MAS system, and the present data on K(D)(Fe-Mg) between garnet and orthopyroxene. This reaction is very sensitive to pressure and compositional effects. Combination of P,T conditions for the garnet stability and that defined by (K(D)(Fe-Mg))ᴳᵗ⁻ᴼᵖˣ yields a simultaneous solution for both P and T of equilibration of garnet and orthopyroxene in the presence of Al₂SiO₅ and SiO₂. The effect of FeO on Al₂O₃ solubility in orthopyroxene in equilibrium with garnet has been determined experimentally at several pressures at 975 and 1200°C. These data have been modeled to develop a thermodynamic method for the calculation of Al₂O₃ in orthopyroxene as a function of P,T and composition. The Al₂O₃ isopleths have moderate P-T slopes, and provide virtually the only means of determining the pressure of mantle derived rocks.

The present study is an effort to examine and understand the relationship between modernization and political instability. The following chapters focus on the effects of modernization on political instability. Data on twenty-four African nations are analyzed to test empirically the validity of the hypothesis. Chapter IV concludes the thesis by offering a general summary and conclusions.

It has been observed that thermophilic enzymes are often more sluggish at lower temperatures but comparable active as their mesophilic homologues at their corresponding living temperatures. Although these thermophilic enzymes exhibit high structural stability, the increased stability leads to a decreased flexibility of the thermophilic enzymes in return. To yield further advances in analysis of the interrelationships between flexibility and activity of enzymes, also the molecular basis of enzyme adaptation, we used a pair of thermo-meso acylphosphatase homologues with high level of similarity isolated from hyperthermophilic archeaon Pyrococcus horikoshii (PhAcP) and human (HuAcP) as model to study this issue. Despite the fact that their active-site residues are highly conserved, activity (kcat) of PhAcP is remarkably reduced compared with HuAcP at low temperatures. Based on crystal structure comparison, an extra salt bridge was formed between active site residue and C-terminus of PhAcP. To examine the role of salt bridge plays in catalytic reaction of AcPs, we designed a mutant PhG91A to disrupt the salt bridge in thermophilic PhAcP. In parallel, a salt bridge was re-engineered into mesophilic HuAcP to create HuA99K. Interestingly, the thermophilic variant PhG91A exhibited a more mesophilic-like manner in terms of activity and thermodynamic parameters. On the contrary, mesophilic HuA99K displayed a more thermophilic-like character. This is supplemented by detailed molecular dynamics (MD) simulations, revealing good qualitative agreement with experimental findings. Both theory and experiment results had provided evidences that the presence of a specific salt bridge is directly associated with the temperature adaptation of AcPs by reducing the catalytic site flexibility. / Lam, Yan. / Adviser: K. B. Wong. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3364. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 120-127). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Objective: To explore currently accepted return-to-play tests and a jumps protocol in a single subject design following anterior cruciate ligament reconstruction. Background: The subject sustained 2 ruptures of the ACL in the left knee in a 12-month period. Both events were noncontact injuries occurring on the landing phase of a jump. A physical exam and magnetic resonance imaging were performed for both injuries by multiple orthopedic surgeons in the United States (1st rupture) and in Brazil (1st & 2nd rupture) to diagnose the injury. Treatment: Following the initial injury the subject attended 2 rehabilitation sessions per week for 16 weeks with an outpatient physical therapy clinic in the US. After the second surgery the athlete returned to the US and received treatment 6 days per week for 8 months with the University sports medicine staff. Return-to-play testing: Along with the hop test and an isokinetic knee flexion/extension test as a general protocol to determine the return-to-play, a jumps protocol to assess bilateral asymmetry and performance was also used. The symmetry index score (SI) was used to evaluate the magnitude of asymmetry. Conclusions: Following ACL reconstruction, objective data from the Hop Test, Isokinetic Test and Jumps Protocol can assist the healthcare provider in determining return-to-play status.

In this study, we have considered the modal and non-modal stability of fluids with shear-dependent viscosity flowing in a rigid straight pipe. A second order finite-difference code is used for the simulation of pipe flow in the cylindrical coordinate system. The Carreau-Yasuda model where the rheological parameters vary in the range of 0.3 &lt; n &lt; 1.5 and 0.1 &lt; λ &lt; 100 is represents the viscosity of shear- thinning and shear thickening fluids. Variation of the periodic pulsatile forcing is obtained via the ratio Kω/Kο and set between 0.2 and 20. Zero and non-zero streamwise wavenumber have been considered separately in this study. For the axially invariant mode, energy growth maxima occur for unity azimuthal wave number, whereas for the axially non-invariant mode, maximum energy growth can be observed for azimuthal wave number of two for both Newtonian and non-Newtonian fluids. Modal and non-modal analysis for both Newtonian and non-Newtonian fluids show that the flow is asymptotically stable for any configuration and the pulsatile flow is slightly more stable than steady flow. Increasing the maximum velocity for shear-thinning fluids caused by reducing power-low index n is more evident than shear-thickening fluids. Moreover, rheological parameters of Carreau-Yasuda model have ignored the effect on the peak velocity of the oscillatory components. Increasing Reynolds number will enhance the maximum energy growth while a revers behavior is observed by increasing Womersley number.