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Abstract The purpose of this study is to explore the effect of ¡§pressure¡¨ and ¡§buoyancy¡¨ misconceptions on the related problem solving ability for middle school students. The formal test was conducted upon 96 second-year middle school students in the Kaohsiung area. Both two-tier test and interview techniques were used to diagnose the students¡¦ misconceptions about pressure and buoyancy. The A-type and B-type situation questionnaires were the two tests used in this study. The test-retest reliabilities of these two tests are 0.84 and 0.82, respectively. Every student was required to complete the A-type questionnaire, and then take the B-type questionnaire a week later. After completing the tests, students were sample-selected as representatives for in-depth interviews. The interview for each student was based on his or her two-tier test. After dividing students into three levels within their own classes, two students were chosen from each level. The two tests¡¦ data were then analyzed and compared using statistical frequency distribution, descriptive analyses, t-test, and phi and Pearson product-moment correlation coefficients. The data from interview was transcribed into Word documents from the recorded interview tapes. The major results of this study are the following: 1. There was a significant correlation¡]P¡Õ.01¡^ between the two misconception tests. 2. There was a significant correlation¡]P¡Õ.05¡^between each misconception test and the students¡¦ school achievement. 3. There exist statistical significant differences on both A and B test scores between students from rural school from suburban school¡]P¡Õ.01¡^. This study also categorized the ¡§pressure¡¨ and ¡§buoyancy¡¨ misconceptions and unique misconceptions from different situations as tested by the A-type and B-type questionnaires.

An existing water channel facility at Texas A&M University is used to experimentally study a stratified, buoyant wake. A cylindrical obstruction placed at the centerline of a developing Rayleigh-Taylor mixing layer serves to disturb the equilibrium of the Rayleigh-Taylor mixing layer. The development of the near wake in the presence of unstable stratification is examined, in addition to the recovery of the buoyancy driven mixing layer. Planar laser induced fluorescence (PLIF) is used to visualize the mixing layer / wake interactions, and qualitative observations of the behavior have been made. Also, quantitative measurements of velocity fluctuations and density fluctuations in the near wake have been obtained using particle image velocimetry (PIV) and a high resolution thermocouple system. These experimental measurements were used to investigate how the wake and buoyancy driven mixing layer interact. Finally, a mathematical model has been used to describe the decay of vertical velocity fluctuations in the near wake due to the effects of buoyancy.

Data from the National Oceanic and Atmospheric Administration wind profiling radar network for the period 2002 2005 were used to investigate the effects of precipitation, topography and gravity waves on the measurements of winds by wind profilers, and to study the climatology and sources of atmospheric gravity waves. The comparison of the profiler winds to the NCAR/NCEP reanalysis and MM5 model winds revealed that monthly averaged wind profiler vertical velocities are strongly affected by precipitation in the lowest 3 km of the troposphere, both directly by hydrometeor velocity and indirectly via gravity wave activity produced by convection. We have determined that presence of downward wind velocities with magnitudes larger than 0.25 m/s is the sign of precipitation-affected data. This velocity threshold was used for identifying and correcting the contaminated data. The characteristics of the gravity waves in three period bands (6 min - 1 hour, 1 - 3 hours and 3 - 12 hours) and three orthogonal spatial components were obtained using spectral analysis of the profiler winds. The most kinetic energy was found to be associated with the low-frequency horizontal component of gravity waves. A consistent seasonal pattern and geographical distribution of kinetic gravity wave energy were observed in the troposphere, with maxima reaching ~25 J/kg in winter at 8 - 10 km altitude. A technique for quantifying the topography variance near the measurement sites was developed and applied to evaluate the effects of topography on gravity wave generation. We have determined that topography is an important source of the medium- and high-frequency waves in the middle troposphere. Correlation and regression analyses were used to study sources of the gravity waves. Convection was found to explain a significant part of the vertical component of the kinetic gravity wave energy throughout the troposphere and total kinetic energy in the lower troposphere, while vertical shear of the zonal wind was the predominant source in the upper troposphere. The results of this study are important for interpreting the wind measurements by wind profiling radars and for improving gravity wave parameterizations in global circulation models.

An existing water channel facility at Texas A&M University is used to experimentally study a stratified, buoyant wake. A cylindrical obstruction placed at the centerline of a developing Rayleigh-Taylor mixing layer serves to disturb the equilibrium of the Rayleigh-Taylor mixing layer. The development of the near wake in the presence of unstable stratification is examined, in addition to the recovery of the buoyancy driven mixing layer. Planar laser induced fluorescence (PLIF) is used to visualize the mixing layer / wake interactions, and qualitative observations of the behavior have been made. Also, quantitative measurements of velocity fluctuations and density fluctuations in the near wake have been obtained using particle image velocimetry (PIV) and a high resolution thermocouple system. These experimental measurements were used to investigate how the wake and buoyancy driven mixing layer interact. Finally, a mathematical model has been used to describe the decay of vertical velocity fluctuations in the near wake due to the effects of buoyancy.

Leakage of stored bulk phase CO₂ is of particular risk to sequestration in deep saline aquifers due to the fact that when injected into typical saline aquifers, the CO₂ rich gas phase has lesser density than the aqueous phase resulting in buoyancy driven flow of the fluids. As the CO₂ migrates upward, the security of its storage depends upon the trapping mechanisms that counteract the migration. While there are a variety of trapping mechanisms the mechanism serving as motivation for this research is local capillary trapping. Local capillary trapping occurs during buoyancy-driven migration of bulk phase CO₂ within a saline aquifer (Saadatpoor, 2009). When the rising CO₂ plume encounters a region where capillary entry pressure is locally larger than average, CO₂ accumulates beneath the region. While research is continued by means of numerical simulation, research at the bench scale is needed to validate the conclusions made from simulation work. Presented is the development of a bench scale experiment whose objective is to assess local capillary trapping. The initial step in accomplishing this objective is to understand the fluid dynamics of CO₂ and brine in a saline aquifer which is categorized as two phase immiscible buoyancy driven displacement. Parameters influencing this displacement include density, viscosity, wettability and heterogeneity. A bench scale environment created to be analogous to CO₂ and brine in a saline aquifer is created in a quasi-two dimensional experimental apparatus, which allows for observation of plume migration at ambient conditions. A fluid pair analogous to supercritical CO₂ and brine is developed to mimic the density and viscosity relationship found at pressure and temperature typical of storage aquifers. The influences of viscosity ratio, density differences, porous medium wettability and heterogeneity are observed in series of experimental sequences. Three different fluid pairs with different viscosity ratios and density differences are used to assess density and viscosity influences. Porous media of varying grain size and wettability are used to assess the influence of heterogeneity and wettability. Results are qualitatively consistent with theoretical results and those from previous works. / text

Hurricanes rapidly destroy large expanses land in coastal Louisiana marsh. Research shows that freshwater marsh with organic soils experience increased destruction during hurricanes compared to other marsh. A relevant question surfaces, do some restoration projects create marsh similar to marshes that are more susceptible to hurricane damage. This study analyzes soil, bulk density, plant composition, and buoyancy of restoration projects and sites adjacent to those that experienced land loss during Hurricanes Katrina and Rita. Results indicate that high organic matter percentages in marsh soil increases hurricane susceptibility attributed to decreased bulk density and increased buoyancy. Buoyancy is episodic and is highest during late summer months when soil temperature and decomposition are highest. Late summer is typically when most intense hurricanes occur. If marsh is less dense, decomposing, and buoyant when strongest hurricanes hit, then potential for destruction during a hurricane increases. Samples were collected from August 2009 to October 2009.

An experimental study has been carried out to investigate the effects of buoyancy on smoldering of polyurethane foam. The experiments are conducted with a high void fraction flexible polyurethane foam as fuel and air as oxidizer, in a geometry that approximately produces a one dimensional smolder propagation. The potential effect of buoyancy in the process is analyzed by comparing upward and downward smolder propagation through a series of normal gravity and variable gravity experiments. Both opposed and forward mixed (free and forced) flow smolder configurations are studied. In opposed smolder the oxidizer flow opposes the direction of smolder propagation, and in forward smolder both move in the same direction. Variable gravity free flow tests are also conducted in an aircraft flying a parabolic trajectories that provides low gravity periods of up to 25 sec. Measurements are performed of the smolder reaction propagation velocity and temperature as a function of the location in the sample interior, the foam and air initial temperature, the direction of propagation and the air flow velocity. This information is used in conjunction with previously developed smolder theoretical models to determine the smolder controlling mechanisms and the effect of gravity. Three zones in the fuel sample with clearly defined smolder characteristics are identified. A zone close to the igniter where smolder is affected by the external heat, a zone at the end of the sample where smolder is affected by the environment, and a zone at the end of the sample where smolder is affected by the environment, and a zone, in the middle of the foam, that is free from external effects. This last zone is the most characteristic of one dimensional, self-supported smolder, and the one that is studied in greater detail. In mixed flow convection buoyancy induced flows together with the forced flow are the primary mechanism of oxidizer transport to the reaction zone, while diffusion has a secondary importance. In natural convection, downward smoldering is of the opposed type while upward smoldering resembles more the forward type. For opposed flow smoldering, both natural and forced, the smolder propagation velocity is found to increase with the oxidizer mass flux reaching the reaction zone. This result confirms predictions from previously developed theoretical models that the smolder velocity is proportional to the oxygen mass flow. The experimental data is correlated in terms of a non-dimensional smolder velocity derived from these models, the results show very good agreement between theory and experiments for strong smolder. To implement the models, an analysis of the gas flow field is developed where the effect of significantly different permeabilities between char and foam is been Extinction is observed for very low and for very high flow rates, which shows that smolder is controlled by a sensitive competition between oxygen supply and heat losses to and from the reaction zone. Under these conditions the models do not describe the experiments well. The forward flow smolder experiments show that forward smoldering is controlled not only by the competition between oxygen supply and heat losses to and from the reaction zone but also by the competition between pyrolysis and oxidation. For low flow velocities a regime resembling the opposed flow is observed. As the air flow velocity is increased, foam pyrolysis followed by char oxidation is the controlling smolder mechanism. For both these conditions the theoretical models describe the experiments well. Increasing the flow velocity further results in a smolder propagation velocity controlled by total fuel consumption, in downward burining. For upward burning transition to flaming is observed for very high air flow velocities. This last regime is not well predicted by the theoretical models. The results from the experiments in variable gravity environment conducted in the KC-135A and Leajet airplanes confirm the normal gravity observations that the competition between heat losses and oxidizer transport is the major mechanism controlling smolder. The absence of convective flow in low gravity results in higher temperature in the unburnt fuel and char due to smaller heat losses to the surroundings. However, the oxidizer transport to the reaction zone also decreases and as a result the temperature at the reaction zone decreases indicating a weakening of the eaction, The presence of pyrolytic reactions in foward smolder and their capability to inhibit smoldering complicates the above described smolder mechanisms.

The design of passive heat removal systems is one of the main concerns for the modular Very High Temperature Gas-Cooled Reactors (VHTR) vessel cavity. The Reactor Cavity Cooling System (RCCS) is an important heat removal system in case of accidents. The design and validation of the RCCS is necessary to demonstrate that VHTRs can survive to the postulated accidents. The commercial Computational Fluid Dynamics (CFD) STAR-CCM+/ V3.06.006 code was used for three-dimensional system modeling and analysis of the RCCS. Two models were developed to analyze heat exchange in the RCCS. Both models incorporate a 180 degree section resembling the VHTR RCCS bench table test facility performed at Texas A&M University. All the key features of the experimental facility were taken into account during the numerical simulations. Two cooling fluids (i.e., water and air) were considered to test the capability of maintaining the RCCS concrete walls temperature below design limits. Mesh convergence was achieved with an intensive parametric study of the two different cooling configurations and selected boundary conditions. To test the effect of turbulence modeling on the RCCS heat exchange, predictions using several different turbulence models and near-wall treatments were evaluated and compared. The models considered included the first-moment closure one equation Spalart-Allmaras model, the first-moment closure two-equation k-e and k-w models and the second-moment closure Reynolds Stress Transport (RST) model. For the near wall treatments, the low y+ and the all y+ wall treatments were considered. The two-layer model was also used to investigate the effect of near-wall treatment. The comparison of the experimental data with the simulations showed a satisfactory agreement for the temperature distribution inside the RCCS cavity medium and at the standpipes walls. The tested turbulence models demonstrated that the Realizable k-e model with two-layer all y+ wall treatment performs better than the other k-e models for such a complicated geometry and flow conditions. Results are in satisfactory agreement with the RST simulations and experimental data available. A scaling analysis was developed to address the distortion introduced by the experimental facility and CFD model in simulating the physics inside the RCCS system with respect to the real plant configuration. The scaling analysis demonstrated that both the experimental facility and CFD model give a satisfactory reproduction of the main flow characteristics inside the RCCS cavity region, with convection and radiation heat exchange phenomena being properly scaled from the real plant to the model analyzed.

It is incumbent upon teachers to reach out to students through methods that capitalize on the students' own motivations. Because of the diversity of self-referential personal styles of learning, reaching every student with a cookie-cutter approach to teaching is nearly impossible. This report explores the application of a type of problem-based learning known as "Legacy Cycles" that apply web technology to answer challenges presented as scenarios. The scenarios give students a similar experience to scientists pursuing investigation and research. Students then search for answers to questions, learn more about the processes being taught with hands-on activities, and prepare a product to demonstrate mastery of the content. In this example of the Legacy Cycle, three challenges are used to teach concepts of density, ocean currents and plastic pollution. / text