Browsing by Subject "dynamics"
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Item A Case Study of NGO-Government Collaboration in Vietnam: Partnership Dynamics Explained through Contexts, Incentives, and Barriers(2012-10-19) Nguyen, Anh ThucCollaboration between international NGOs (INGOs) and governmental organizations (GOs) have contributed significantly to the goals of poverty alleviation and agricultural development in developing countries. Much of the literatures on NGO-GO partnerships have explored theoretically or empirically what motivate and hinder cross-sector collaboration. But not many have studied cross-sector collaboration from both analytical and descriptive perspectives. This study filled in this gap by drawing from previous studies a conceptual framework through which contexts, incentives, and barriers that influence INGO-GO partnerships were described and explained. The researcher adopted a qualitative case-study method with emergent design. Personal interviews were conducted with 20 key informants, including eight Vietnamese staff from one INGO and 12 government officials from six GOs who partnered with the INGO. All participating organizations were institutions serving agricultural and rural development in the south of Vietnam. The data were collected in 2010 and analyzed using the software package ATLAS.ti. The results showed four categories that interact to form a framework of a dynamic continuum of partnership development. The four categories included conditioning factors, incentives, barriers, and feedback loop. The categories held the following themes: 1) socio-political contexts and organizational natures for conditioning factors, 2) shared missions, resource mobilization, capacity building, and networking for incentives, 3) ideological conflicts, structural constraints, and operational hurdles for barriers, and 4) reflections and recommendations for feedback loop. The study contributed a theoretical- and empirical-based perspective on INGO-GO partnerships in post-reform countries. It provided a framework that comprehensively describes and explains partnership dynamics. The study also shared knowledge of the intricacies of INGO-GO partnerships in rural Vietnam. For institutions serving agricultural and rural development, the study could assist in strategic management to minimize constraints and maximize opportunities in collaborative environments.Item A visual simulation playground for engineering dynamics(Texas A&M University, 2008-10-10) Fong, Donald BrianPast educational studies reveal that students have difficulty making the connection between the mathematical and analytical models used to describe building behavior and the behavior itself. This thesis examines the development and use of visual simulation software as a tool to help students create connections between abstract mathematical models and the real world. A framework for the software was designed and implemented, enabling students to interactively construct, analyze, and evaluate models within a single environment. The software was tested by students in an undergraduate dynamics course to assess its effectiveness as a learning tool. Results are presented through scenarios that demonstrate the extensibility and flexibility of the framework and an analysis of student responses from the Student Assessment of Learning Gains instrument.Item Full vehicle dynamics model of a formula SAE racecar using ADAMS/Car(Texas A&M University, 2005-11-01) Mueller, Russell LeeThe Texas A&M University Formula SAE program currently has no rigorous method for analyzing or predicting the overall dynamic behavior of the student-designed racecars. The objective of this study is to fulfill this need by creating a full vehicle ADAMS/Car model incorporating an empirical tire-road force model and validating the longitudinal performance of the model by using vehicle responses recorded at the track. Creating the model requires measuring mass and inertia properties for each part, measuring the locations of all the kinematic joints, testing the Risse Racing Jupiter-5 shocks to characterize damping and stiffness, measuring engine torque, and modeling the tire behavior. Measuring the vehicle performance requires installation of the Pi Research DataBuddy data acquisition system and appropriate sensors. The 2002 Texas A&M University Formula SAE racecar, the subject vehicle, was selected because it already included some accommodations for sensors and is almost identical in layout to the available ADAMS/Car model Formula SAE templates. The tire-road interface is described by the Pacejka ??94 handling force model within ADAMS/Car that is based on a set of Goodyear coefficients. The majority of the error in the model originated from the Goodyear tire model and the 2004 engine torque map. The testing used Hoosier tires and the 2002 engine intake and exhaust configuration. The deliverable is a full vehicle model of the 2002 racecar with a 2004 engine torque map and a tire model correlated to longitudinal performance recorded at the track using the installed data acquisition system. The results of the correlation process, confirmed by driver impressions and performance of the 2004 racecar, show that the 2004 engine torque map predicts higher performance than the measured response with the 2002 engine. The Hoosier tire on the Texas A&M University Riverside Campus track surface produces 75??3% of peak longitudinal tire performance predicted by the Goodyear tire model combined with a road surface friction coefficient of 1.0. The ADAMS/Car model can now support the design process as an analysis tool for full vehicle dynamics and with continued refinement, will be able to accurately predict behavior throughout a complete autocross course.Item Identification of powered parafoil-vehicle dynamics from modelling and flight test data(Texas A&M University, 2006-08-16) Hur, Gi-BongDuring the final approach and landing phase of the X-38/Crew Return Vehicle, a steerable parafoil is used to maneuver and land at a targeted ground base under autonomous control. To simulate and verify performance of the onboard Parafoil Guidance, Navigation and Control system (PGNC), a commercial powered parafoil- vehicle, called the Buckeye consisting of a parafoil and vehicle two-body system like the X-38/CRV was modified to accommodate the avionics and scale-downed parafoil for aerodynamic similarity and a series of flight tests were conducted. Dynamic modelling and system identification results for the Buckeye are de- scribed in this dissertation. The vehicle dynamics are modelled as all 8 degrees-of- freedom system comprising 6 states for the parafoil and 2 states for the relative pitch and yaw motion of the vehicle with respect to the parafoil. Modal analysis for the linearized model from the nonlinear model shows the number and order of dynamic modes as well as the system is controllable and observable. For system identifica- tion, the overparameterized Observer/Kalman Filter Identification (OKID) method is applied to identify a linear model of the Buckeye two-body system from the flight data assuming that disturbances at a calm day are represented as periodic distur- bances. The identification results show that the overparameterized OKID works well for powered parafoil-vehicle two-body system identification under calm day condi- tions using flight data. For the data with possible discrete gusts the OKID shows limitation to identify a linearized model properly. Several sensor packages including airdata and Inertial Measurement Unit are designed and installed for the parameters for identification. The sensor packages successfully supply data of the parameters for identification and suggest a feasible, low cost method for the parafoil-vehicle two-body dynamic parameters.Item Illuminating the Heterotropic Communication of the Pair-wise Interactions in Phosphofructokinase from Bacillus stearothermophilus(2012-10-17) Perez, StephanieThe number of allosteric sites and active sites in phosphofructokinase from Bacillus stearothermophilus create an intricate network of communication within the enzyme. With thermodynamic linkage analysis, the overall allosteric communication can be quantified. This value, however, represents an average contribution for all the interactions involved. The recent development of a hybrid strategy has allowed for the quantification of single interactions, both heterotropic and homotropic. Focusing on the heterotropic interactions whose inhibition is entropy-driven, residues and regions within the enzyme can now be identified to further characterize each specific interaction using the hybrid strategy. Among the many components of entropy, the hybrid strategy has now allowed for the strategic placement of a reporter of side chain dynamics to identify conformational differences between the four ligand bound enzyme species of a single heterotropic interaction. In this study, a combination of these approaches was used in the methodology including constructing hybrids to isolate a single heterotropic interaction along with single tryptophan reporter. Site directed mutagenesis combined with the hybrid strategy was also implemented to directly assess the role of a single residue in the communication path of a single interaction. The region surrounding the allosteric site with the nearest active site has been implicated to be significant in transmitting the allosteric signal. In addition two single residues, T158 and D59, within this region have been identified to potentially contribute to the inhibition of this same interaction. An additional residue, G184, located outside this local region has also been identified as possibly having a significant role in the transmission of the inhibitory signal of a unique heterotropic interaction. The implications of this study have led to the initial identification of residues involved in the 22A route of allosteric communication of a single active site and allosteric site. This allosteric communication occurs to allow the enzyme to compensate for the binding of both ligands. With the location of these residues implicated to be involved in the communication of this isolated interaction, this compensation is not contained within a confined region but is however felt throughout the single subunit.Item Kinetics and dynamics study on the allosteric pathway of phosphofructokinase from Escherichia coli(Texas A&M University, 2008-10-10) Tie, CuijuanPhosphofructokinase from Escherichia coli (EcPFK) is allosterically regulated by MgADP and phosphoenolpyruvate (PEP), which act to activate or inhibit, respectively, by changing the substrate (Fru-6-P) affinity of the enzyme. Both ligands bind to the same allosteric site in EcPFK. Therefore, the questions we want to address are how these two molecules regulate EcPFK and how the allosteric signal is propagated throughout the enzyme. EcPFK has 28 potential site-site interactions. These interactions in turn derive from multiple copies of 6 potentially unique homotropic interactions and 4 potentially unique heterotropic interactions. Making hybrid tetramer of EcPFK is used to isolate a single heterotropic interaction. To improve the yield of the 1:3 hybrid, the in vivo hybrid formation method was developed. Four heterotropic interactions were isolated by this manner and re-evaluated. The same kinetics characteristics were obtained for each 1:3 hybrid from both the in vivo and in vitro method. To address the question of how the allosteric signal is transmitted throughout EcPFK, we identified residues (G184, Asp59 and S157) that are important for the allosteric regulation for both PEP inhibition and MgADP activation. The impact of each mutation on individual interaction is unique and also suggests that the structural basis for PEP inhibition is different from that for MgADP activation. Most importantly, since the sum of each heterotropic interaction with a modification in only one subunit is equal to the total heterotropic interaction with a modification in all four subunits, this result indicates that the heterotropic allosteric signal transmission is realized in a single subunit. The 23? heterotropic interaction, which contributes the most to the PEP inhibition, was chosen to study the dynamic properties. Fluorescence was used to study the dynamic perturbations of the 23? interaction upon ligand binding. Taking advantage of the hybrid formation strategy and the tryptophan-shift mutagenesis method, a tryptophan residue can be placed at different individual locations throughout the native subunit containing the 23? heterotropic interaction. The steady-state anisotropy and lifetime measurement at each tryptophan position indicate that the 23? allosteric interaction involves the perturbation of side-chain dynamics both near and quite far away from the respective ligand binding sites.Item Modeling plankton dynamics during a Prymnesium parvum bloom: The importance of inflows and allelopathic relationships on bloom dynamics(2012-07-16) Hewitt, Natalie CaseHarmful algal blooms' global amplification has driven research on growth characteristics and instigating mechanisms. These blooms prosper under diverse environmental conditions, creating challenges identifying bloom initiation. The haptophyte, Prymnesium parvum, plagues the southwestern United States with massive system disruptions and huge fish kills caused by its toxin. Despite many abiotic factors' association with P. parvum blooms, low nutrient levels stress the alga increasing toxin production, eliminating nutrient competition, and alleviating grazing pressures. This model examines the relationship between nutrient availability and P. parvum toxin production against another phytoplankton and a single grazing zooplankton, using a Monod function relating population growth rate with limiting nutrient concentrations. Sensitivity analyses emphasize plankton biological parameters most influential in accumulating biomass. The impact of toxin production on zooplankton grazing rates underscores P. parvum's need for top-down control suppression. The toxin production equation increases production when P. parvum experiences low specific growth rates from nutrient availability and low biomass. This equation is analyzed against previously published allelopathic relationships, comparing plankton reactions and bloom endurance. The model's toxin production equation proves more ecologically feasible, incorporating competing phytoplankton species' mortality and variables easily verified through laboratory experiments. Though not intended for management strategy development, the model explores and supports the proposed strategy of incorporating hydraulic flushing, pulsed and continuous inflows, to eliminate biomass accumulation. Inflows relieve stressful nutrient-limiting conditions, introducing resources affecting bloom stability and plankton community dynamics. The faster-growing competing phytoplankton gains survival advantages when inflow rates fall lower than its maximum specific growth rate, but greater than P. Parvum's, emphasizing the accurate measuring of competitors' maximum specific growth rates and identifying a dilution rate range where P. parvum loses at nutrient intake. Inflows with various nutrient levels representing different source waters from freshwater lakes were tested for impacts on plankton dynamics. Adding any hydrological effect reduced P. parvum biomass. Disruptions create disturbance, removing P. parvum's system-dominating position, allowing the phytoplankton to exceed P. parvum's density. The model highlights the importance of P. parvum's toxin's presence to maintain dominance and emphasizes flushing agitation as potential and feasible management schemes to deter bloom continuation and increase species diversity.Item Novel Isotope Effects and Organic Reaction Mechanisms(2010-07-14) Kelly, Kelmara K.A variety of organic reactions provide experimental observations that are not explained by current models of reactivity and selectivity. This dissertation describes a combination of experimental and theoretical studies of such reactions. In the ene reaction of singlet oxygen with tetramethylene, it is found that standard statistical rate theories fail to account for the observed kinetic isotope effects, particularly with regard to their broad temperature independence. Dynamics trajectories are found to account for the observed isotope effects. In the dimerization of cyclopentadiene, novel "dynamic" isotope effects are observed on the 13C distribution in the product, and a method for the prediction of these isotope effects is developed here. In the cycloaddition of diazomethane with dimethylfulvene, it is found that the current model of the mechanism as a [6 + 4] cycloaddition is incorrect, and a new mechanism is proposed. Isotope effects have been measured for the recently reported unusual "on water" quadricyclane cycloadditions, and the implications of these observations toward the mechanism are discussed.Item Rock-Around Orbits(2010-07-14) Bourgeois, Scott K.The ability to observe resident space objects (RSOs) is a necessary requirement for space situational awareness. While objects in a Low-Earth Orbit are easily ob- servable by ground-based sensors, diffculties arise when trying to monitor objects with larger orbits far above the Earth's surface, e.g. a Geostationary Orbit. Camera systems mounted on satellites can provide an eff ective way to observe these objects. Using a satellite with a speci c orbit relative to the RSO's orbit, one can passively observe all the objects that share the RSO's orbit over a given time without active maneuvering. An orbit can be defi ned by ve parameters: semi-major axis, eccentricity, right ascension of ascending node, inclination, and argument of perigee (a; e; ; i; !). Using these parameters, one can create an orbit that will surround the target orbit allowing the satellite in the Rock-Around Orbit (RAO) orbit to have a 360 degree view of RSOs in the target orbit. The RAO orbit can be applied to any circular or elliptical target orbit; and for any target orbit, there are many possible RAO orbits. Therefore, diff erent methods are required to narrow down the selection of RAO orbits. These methods use distance limitations, time requirements, orbit perturbations, and other factors to limit the orbit selections. The first step is to determine the range of RAO semi-major axes for any given target orbit by ensuring the RAO orbit does not exceed a prescribed maximum al- lowable distance, dmax from the target orbit. It is then necessary to determine the eccentricity range for each possible RAO semi-major axis. This is done by ensuring the RAO still does not exceed dmax but also ensuring that the RAO orbit travels inside and outside of the target orbit. This comprises one half of the rock-around motion. The final step is to determine the inclination of the RAO orbit. Only a small inclination different from that of the target orbit is required to complete the rock-around motion while the maximum inclination is found by making sure the RAO orbit does not exceed dmax. It is then important to consider orbit perturbations, since they can destroy the synchronization between the RAO and target orbit. By examining the e ffects of the linear J2 perturbations on the right ascension of ascending node and argument of perigee, the correct semi-major axis, eccentricity, and inclination can be chosen to minimize the amount of fuel required for station keeping. The optimal values can be found by finding the Delta v needed for di fferent combinations of the variables and then choosing the values that provide the minimum Delta v. For any target orbit, there are multiple RAO orbit possibilities that can provide 360 degree coverage of a target orbit. Even after eliminating some of them based on the methods already described, there are still many possibilities. The rest of the elimination process would then be based on the mission requirements which could be the range of an on-board sensor, the thruster or reaction wheel controls, or any other number of possibilities.Item Systematic examination of dynamically driven organic reactions via kinetic isotope effects(Texas A&M University, 2007-04-25) Ussing, Bryson RichardOrganic reactions are systematically examined experimentally and theoretically to determine the role dynamics plays in the outcome of the reaction. It is shown that trajectory studies are of vital importance in understanding reactions influenced by dynamical motion. This dissertation discusses how a combination of kinetic isotope effects, theoretical calculations, and quasiclassical dynamics trajectories aid in the understanding of the solvolysis of p-tolyldiazonium cation in water, the cycloadditions of cyclopentadiene with diphenylketene and dichloroketene, and the cycloaddition of 2- methyl-2-butene with dichloroketene. In the solvolysis of p-tolyldiazonium cation, significant 13C kinetic isotope effects are qualitatively consistent with a transition state leading to formation of an aryl cation, but on a quantitative basis, the isotope effects are not adequately accounted for by simple SN1 heterolysis to the aryl cation. The best predictions of the 13C isotope effects for the heterolytic process arise from transition structures solvated by clusters of water molecules. Dynamic trajectories starting from these transition structures afford products very slowly. The nucleophilic displacement process for aryldiazonium ions in water is determined to be at the boundary of the SN2Ar and SN1 mechanisms. The reaction of cyclopentadiene with diphenylketene affords both [4 + 2] and [2 + 2] cycloadducts directly. This is surprising. There is only one low-energy transition structure for adduct formation. Investigation of this reaction indicates that quasiclassical trajectories started from a single transition structure afford both [4 + 2] and [2 + 2] products. Overall, an understanding of the products, rates, selectivities, isotope effects, and mechanism in these reactions requires the explicit consideration of dynamic trajectories.Item The Dynamics and Predictability of Tropical Cyclones(2010-01-15) Sippel, Jason A.Through methodology unique for tropical cyclones in peer-reviewed literature, this study explores how the dynamics of moist convection affects the predictability of tropical cyclogenesis. Mesoscale models are used to perform short-range ensemble forecasts of a non-developing disturbance in 2004 and Hurricane Humberto in 2007; both of these cases were highly unpredictable. Taking advantage of discrepancies between ensemble members in short-range ensemble forecasts, statistical correlation is used to pinpoint sources of error in forecasts of tropical cyclone formation and intensification. Despite significant differences in methodology, storm environment and development, it is found in both situations that high convective instability (CAPE) and mid-level moisture are two of the most important factors for genesis. In the gulf low, differences in CAPE are related to variance in quasi-geostrophic lift, and in Humberto the differences are related to the degree of interaction between the cyclone and a nearby front. Regardless of the source of CAPE variance, higher CAPE and mid-level moisture combine to yield more active initial convection and more numerous and strong vortical hot towers (VHTs), which incrementally contribute to a stronger vortex. In both cases, strength differences between ensemble members are further amplified by differences in convection that are related to oceanic heat fluxes. Eventually the WISHE mechanism results in even larger ensemble spread, and in the case of Humberto, uncertainty related to the time of landfall drives spread even higher. It is also shown that initial condition differences much smaller than current analysis error can ultimately control whether or not a tropical cyclone forms. Furthermore, even smaller differences govern how the initial vortex is built. Differences in maximum winds and/or vorticity vary nonlinearly with initial condition differences and depend on the timing and intensity of small mesoscale features such as VHTs and cold pools. Finally, the strong sensitivity to initial condition differences in both cases exemplifies the inherent uncertainties in hurricane intensity prediction. This study illustrates the need for implementing advanced data analysis schemes and ensemble prediction systems to provide more accurate and event-dependent probabilistic forecasts.Item The nonlinear dynamics of the sea breeze(Texas A&M University, 2004-11-15) Walter, Kevin RobertThe response of the land and sea breeze circulation to two highly simplified dynamical models is presented. The first dynamical model is the explicit specification of an oscillating interior heat source analogous to that from Rotunno (1983). Emphasis is placed on the variation of the response with heating amplitude and latitude. In addition, a weakly nonlinear analysis focuses on the dynamic forcing of nonlinear features such as a semi-diurnal gravity wave, fronts, and asymmetry in the magnitude of onshore and offshore flow. One surprising result is the identification of a cycle-mean surface divergence pattern at both 0? and 45?. At 45?, this divergence pattern is accompanied by a cycle mean shore-parallel response due to the Earth's rotation. The second dynamical model is the explicit specification of an oscillating surface heat flux. Again, comparison is made between simulations at different heating amplitudes, and between simulations at different latitudes. To address changes in the solution due to the heating method itself, comparison is made between solutions from the surface heating method and solutions from the interior heating method. Finally, solutions across the planetary continuum are explored for critical latitude dependence in high-amplitude simulations.