Browsing by Subject "stratification"
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Item Diel Temperature and Dissolved Oxygen Patterns in Sites with and without Planktonic Life Stage of Thompsodinium intermedium in Comal Springs, TX(2012-07-16) Gilpin, CherylBetween July 2009 and October 2011, a new habitat was found for a rarely reported freshwater dinoflagellate species, Thompsodinium intermedium - Comal Springs (Comal County), Texas. In 2011, diel in-situ monitoring in monospecific blooms of this species revealed previously undetected negative impacts on endangered species habitat availability associated with conditions of low flow levels, recorded at the U.S. Geological Survey gage # 08169000 on Texas Commission on Environmental Quality river segment 1811 station 12655. During a period of low springflow in the summer of 2011, late afternoon and early morning measurements of dissolved oxygen and temperature and presence of dinoflagellate blooms were monitored at six sites. Significant differences in diel fluctuations were found in all of these parameters among sites with and without the planktonic blooms. These fluctuations increased risk of hypoxia and hyperthermia conditions at sites of planktonic bloom events. Arrays of in-situ continuous monitoring temperature/light probes were used inside and outside of blooms. Wildlife and human health implications are that hypoxia and hyperthermia are known to promote conditions favorable to harmful microbes which may be transported from springs to coastal bays. In-situ data demonstrated that T. intermedium blooms, hypoxia, and hyperthermia occurred in the upper Comal headwaters. These natural environmental stressors may be avoidable if adequate springflows are maintained to buffer against these impacts.Item Entrainment and mixing properties of multiphase plumes: Experimental studies on turbulence and scalar structure of a bubble plume(2009-05-15) Seol, Dong GuanThis dissertation presents a series of laboratory experiments to study flow and mixing properties of multiphase plumes. The particle image velocimetry (PIV) and laserinduced fluorescence (LIF) techniques are developed to measure two-dimensional velocity and concentration fields of multiphase plumes. The developed measurement techniques are applied to bubble plumes in different ambient conditions. The problems and errors in the two-phase PIV application to a bubble plume case are addressed through a comparative study between the optical separation method using fluorescent particles and a new phase separation method using vector postprocessing. The study shows that the new algorithm predicts well the instantaneous and time-averaged velocity profiles and has errors comparable to those for image masking techniques. The phase separation method developed in the previous section is applied to study the mean flow characteristics of a bubble plume in quiescent and unstratified condition. The entrainment coefficients representing the mixing properties of a bubble plume are calculated to lie between 0.08 near the plume source and 0.05 in the upper region, and to depend on the non-dimensional quantity us/(B/z)1/3, where us is the bubble slip velocity, B is the initial buoyancy flux, and z is the height from the diffuser. Further, the LIF technique is investigated to measure the scalar concentration field around a bubble plume in quiescent, unstratified condition. This new application to bubble plumes accounts for light scattering by bubbles using an attenuation coef- ficient that is proportional to the local void fraction. Measured scalar concentration fields show similar trend in concentration fluctuation to turbulent plume cases. Finally, the velocity and concentration field measurements using the developed two-phase PIV and LIF methods are applied for a bubble plume in a density-stratified ambient. The turbulent flow characteristics induced by a bubble plume in a stratified ambient water are studied. The plume fluctuation frequency is measured as about 0.1 Hz and compares well to plume wandering frequency measured in unstratified plume cases.Item Ethnic niches, pathway to economic incorporation or exploitation? Labor market experiences of Latina/os(Texas A&M University, 2006-04-12) Morales, Maria CristinaThis dissertation investigates the ethnic labor market activities of the Latina/os. This study is important since regardless of their historical and increasing presence in the U.S., Latinos continue to find themselves disproportionately at the bottom of the social hierarchy (Saenz, Morales, and Ayala 2004). Furthermore, due to their lack of access, a significant amount of the members of this group are turning to employment in an ethnic niche. While there is no consensus as to what exactly constitutes an ethnic niche, a distinct characteristic is the co-ethnic nature of the work environments. Special focus is placed on how immigration status/nativity, gender, nativity, and skin color influences job search activities and wage differentials in the ethnic niche. While these factors have been found to impact the mainstream labor market, our knowledge of how these factors operate in a work environment with a dominant presence of co-ethnics is ambiguous. Utilizing data from the Multi-City Study of Urban Inequality (MCSUI), results show that Latina/os workers in co-ethnic niches receive fewer economic rewards than their ethnic counterparts in the general labor market. Furthermore, within the Latina/o population dark-skinned individuals are more likely to be employed in ethnic niches while the lighter-skinned are more likely to be employed in the general labor market. When examining the stratification factors of immigration/nativity status, gender, and skin color, in addition to social networks, findings show that these stratification factors operate in a similar fashion in ethnic niches as they do in more mainstream labor markets. Thus these findings question the presumably protective work environment of ethnic niches.Item Sociospatial Inequality: A Multilevel and Geo-Spatial Analysis of Latino Poverty(2012-02-14) Siordia, CarlosSociology at its core has always been interested in understanding how society works. Previous studies on social stratification have sought to outline who gets what, when, and why. This project introduces the where element to advance our understanding of how resource distribution affects life chances. The research question is: Does the percent of Latinos in the area of residence have an influence on Latino?s individual poverty over and above the influence on poverty of the person characteristics? The study ascertains how micro-level inequality is influenced by macro-level attributes and explores how spatial non-stationarity plays a role in these mechanics. This sociospatial inequality investigation will delineate how individual-level stratifying mechanisms are influenced by context-level structural attributes and how sociospatial non-stationary processes play a role in these mechanics. The dissertation is conceptually driven by Hubert M. Blalock's 1970 theory on minority relationships. Blalock posited the testable hypothesis that discrimination against oppressed groups increases when their population rises. Using theoretical propositions inspired by Blalock leads to the testing of the following two formal hypothesis: the multilevel hypothesis (H1) focuses on macro-level effects, I hypothesize that as the percent of Latinos/as in the area of residence increases, the odds of being in poverty will increase for Latinas/os; on the spatial hypothesis (H2), I hypothesize that the statistical association between percent Latina/o and percent poverty is spatially nonstationary. I find that H1 cannot be falsified. The models reveal, as Blalock predicted, that as the percent of Latinos/as in the area of residence increases, the odds of being in poverty increase for Latinas/os (even after controlling for various level-1, level-2, and GWR-level-2 factors). I also find that H2 could not be falsified. I find that the statistical association between percent Latina/o and percent poverty is spatially nonstationary. My multilevel and spatial modeling investigation was unable to falsify Blalock's minority group threat theory. Hierarchical models indicate that as the percent of Latino/a increases, the likelihood of being in poverty for Latinas/os increases. This statically significant relationship holds constant even after spatial nonstationarity level-2 control factors are introduced.Item Stratification Prediction and Bottom Boundary Layer Dynamics over the Texas-Louisiana Continental Shelf(2015-03-02) Zhang, WenxiaThe bottom boundary layer is an unstratified thin layer above the sea floor, separated from the more strongly stratified interior. Formation of a thin bottom boundary layer in the presence of stratification and a sloping bottom is common, and well characterized by theory. This thin layer is an important source of mixing over the continental shelf, and it plays a fundamental role in several continental shelf physical and biogeochemical processes, such as buoyancy advection, bottom material transport and hypoxia formation. In this research, Both observations and numerical models are used to study models' ability of reproducing observed stratification and bottom boundary layer dynamics over the Texas-Louisiana shelf. Simulated vertical stratification, which is also representing the vertical density structure, was first evaluated since it directly controls the bottom boundary layer structure itself and is important for other bottom boundary layer dynamics. A new metric, the histogram of vertical stratification, is introduced in this research to evaluate the models' ability of reproducing observed stratification in a bulk sense. The improvement in model performance is attributed to the finer horizontal and temporal resolutions of a model, while factors like open boundary conditions and vertical resolutions are modified without any improvement in the ability of the model to simulate observed stratification. Towed, undulating CTD profiles collected during Mechanisms Controlling Hypoxia (MCH) program also detected mid-water oxygen minima in many transects. These intrusions are connected with the bottom boundary layer and follows the pycnocline seaward as a mid-water column tongue of low oxygen. We calculate convergence within the bottom boundary layer relative to density surfaces using the simulated results; there is a convergence in the bottom boundary layer at the location where the pycnocline intercepts the bottom, creating an injection of bottom boundary layer water into the pycnocline. Convergent flow at the bottom, relative to isopycnal surfaces, is strongest in the density classes associated with the oxygen minimum layer. We believe these mid-water oxygen minima are actually intrusions of low oxygen protruding from the bottom boundary layer via buoyancy advection driven convergence, following the main pycnocline.