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Larsen, Elisabeth S. "Stratified neighborhoods, stratified schools : intradistrict transfer and racial and socioeconomic stratification /." Diss., CLICK HERE for online access, 2009. http://contentdm.lib.byu.edu/ETD/image/etd2900.pdf.
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Larsen, Elisabeth Stuart. "Stratified Neighborhoods, Stratified Schools: Intradistrict Transfer and Racial and Socioeconomic Stratification." BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/1710.
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Intra-district transfer policies allow students to attend any school within a district and thus may have unique consequences for stratification within a district. If parents make choices based on common academic interests, this policy can create racial and socioeconomic integration across the schools in a district. However, socially motivated choices may lead to the creation of increasingly stratified zones. This study examines one urban school district with an intra-district transfer policy to examine if the schools in the district become more racially and economically stratified under the choice policy and if the level of stratification at family's zoned schools is correlated with participation in choice. Results show that families zoned to schools mirroring the district's diverse composition are more likely to participate in choice, suggesting that more factors than simple academically-based motivations guide choice behavior. Exploration of the levels of stratification in schools with and without the choice policy suggests that the overall trend is to maintain the level of stratification present in the residential areas. Although most changes under the choice policy are small in magnitude, the changes that do occur push the district towards increased stratification.
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Orpen, David Lisle. "Characterization of stratified L-topological spaces by convergence of stratified L-filters." Thesis, Rhodes University, 2011. http://hdl.handle.net/10962/d1005216.
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For the case where L is an ecl-premonoid, we explore various characterizations of SL-topological spaces, in particular characterization in terms of a convergence function lim: FS L(X) ! LX. We find we have to introduce a new axiom , L on the lim function in order to completely describe SL-topological spaces, which is not required in the case where L is a frame. We generalize the classical Kowalski and Fischer axioms to the lattice context and examine their relationship to the convergence axioms. We define the category of stratified L-generalized convergence spaces, as a generalization of the classical convergence spaces and investigate conditions under which it contains the category of stratified L-topological spaces as a reflective subcategory. We investigate some subcategories of the category of stratified L-generalized convergence spaces obtained by generalizing various classical convergence axioms.
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Schober, Benjamin. "Membrane Stratified Solar Ponds." Thesis, University of Gävle, Faculty of Engineering and Sustainable Development, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-7083.
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This project deals with the potential of membrane stratified solar ponds which consist of two water layers, where one is a salt solution here, and a separating translucent membrane. An experimental pond was set up to study the thermal behaviour of such collector systems. The input is mainly solar radiation, sometimes when the ambient temperatures are higher than the pond temperatures also heat from the environment is transferred into the pond.
The measured temperatures of the pond, the ambient temperature, the global radiation and wind speed were the basis data for thermal calculations which showed that the pond was working well as a solar collector and thermal storage system all in one. Heat was not extracted from the pond however, only the losses to the environment were studied.
It was found out that the pond temperatures were higher than the ambient temperature over the whole measurement period of 12 days, and insulation and pollution problems as well as future prospects and suggestions for further studies are discussed at the end of this paper.
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Lee, V. "Layered stratified shear flows." Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364874.
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Chilakamarri, Kiran Babu. "Rotating and stratified fluids /." The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487584612163036.
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Charalambides, Alexandros G. "Charge stratified HCCI engine." Thesis, Imperial College London, 2006. http://hdl.handle.net/10044/1/11511.
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Kurban, Adib Paulo Abdalla. "Stratified liquid-liquid flow." Thesis, Imperial College London, 1997. http://hdl.handle.net/10044/1/7553.
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Bourban, Sebastien E. "Stratified shallow flow modelling." Thesis, Open University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.664520.
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Environmental hydraulics covers a very wide range of applications including free surface flows in rivers. estuaries and lakes. To find engineering solutions to environmental hydraulics problems. 3D numerical modelling is nowadays widely used. However. the computation of sharp spatial gradients (such as found in stratified estuaries and lakes. around plumes near outfalls along rivers and coasts or in exchange areas of high shear). and the modelling of these processes along steep bathymetric slopes (such as found at the edge of dredged channels or of the continental shelf) remains a challenge. In addition. crude assumptions (such as the hydrostatic assumption) are often made to the primary differential equations in order to simplify the problem and enable long term prediction of environmental hydraulic changes. In this thesis. a robust adaptive mesh displacement (AMD) method is implemented and validated against the lock exchange case in particular. The AMD method aims at vertically focusing nodes within each water column to capture sharp gradients. while reducing the number of nodes or requiring prior knowledge of the flow structure. Second. a direct computation of dynamic pressure is introduced based on the equation of vertical momentum and validated against the analytical potential flow theory solution of a source-sink pair. Dynamic pressure is necessary to model destratification recirculation devices. or flow over dredge channel. or solitary waves. for instance. This direct computation method makes the hydrostatic assumption redundant. Third. a new advection scheme is implemented. whose main advantage is simplicity averaging over Riemann problems without solving them. while excessive numerical viscosity is compensated for by using high-resolution MUSCL type reconstruction. Recommendations are made in this thesis to extend the advection scheme developed herein for tracer advection to the non-linear shallow water equations. to the diffusion terms and to turbulence closure laws within the same finite element framework.
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Al-Wahaibi, Talal Khamis. "Investigations on the transition between stratified and non-stratified horizontal oil-water flows." Thesis, University College London (University of London), 2006. http://discovery.ucl.ac.uk/1348916/.
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The work presented in this thesis aims to investigate experimentally and theoretically the transition from stratified to non-stratified horizontal oil-water flows and to improve the understanding of the dual continuous pattern, where both phases retain their continuity at the top and bottom of the pipe respectively but there is dispersion of one phase into the other. Two experimental facilities were used in this study; a 38 mm ID stainless steel test section in a pilot scale flow facility and a 14 mm ID acrylic test section in a small flow facility running with water and oil (5.5 mPa s viscosity and 828kg/m3 density) as test fluids. A high speed video camera was employed to examine wave characteristics and flow development, capture mechanism of drop formation and determine the onset conditions of drop entrainment and the dual continuous pattern in both facilities. In the 38 mm ID test section, a conductivity probe was also used to investigate wave structures before and at the onset of entrainment. A high frequency impedance probe was used to find the phase distribution of the oil-water flow while the local drop velocity and chord length distributions were measured using a dual impedance probe. In the 14 mm ID test section, the influence of adding polymer in horizontal oil-water flows was also investigated. While the flow pattern map developed by Lovick and Angeli (2004a) was used for the 38 mm ID test section, a new flow pattern map was constructed for the 14 mm ID pipe. Dual continuous flow was found to occur for a smaller range of superficial velocities in the small test section compared to the large one. Visual observations from the two test sections revealed that no drops are formed when interfacial waves are absent. In addition annular flow with oil flowing at the core was observed in both pipes for low oil velocities and relatively high water velocities. The results from the high speed pictures and the conductivity probe showed that the amplitudes of the waves are increased as the superficial velocities of the two phases increase and as a result the required superficial water velocity,Usw,for the onset of entrainment decreases as the superficial oil velocity, Uso, increases. The model suggested by Trallero (1995) for the transition from stratified to non-stratified flow failed to predict the experimental results. Moreover, the high speed video images and the conductivity probe results showed that the amplitudes of the waves found at 2m from the inlet are smaller than those observed at 7 m. When drops and the onset of entrainment were observed at 7m from the inlet, these were not observed at 2m from the inlet, which means that all drops forming downstream the pipe resulted from the waves. In the large pipe, the presence of a bend after the inlet section (T junction) resulted in larger drops than when no bend was present (Y junction). The high speed images also revealed that drops formed as a result of the relative movement between the oil and water phases. The faster phase will undercut the other one until a drop is detached from the wave crest. The entrained fractions during dual continuous flow, or the fraction of one phase dispersed into the continuum of the other were calculated from the phase distribution data obtained with both inlet configurations (T junction and bend and Y -junction). The entrained fraction of water in oil (Ew/o) increased as the input water flow rates increased at constant superficial oil velocity. Similarly, the entrained fraction of oil in water (Eo/w) increased as the oil flow rates increased at a constant water superficial velocity. Moreover, the entrained fractions when the bend was used were higher than those obtained without it. From the chord length measurements in dual continuous flow, chord length and drop concentration were found to decrease with increasing distance from the interface while the number density of large drops decreased as Usw increased at each Uso. Also, oil drops were in general larger than water drops. Drop velocity measurements also revealed that water drops were faster than the velocity of the upper layer while oil drops could be either slower or faster than the velocity of the lower layer. The results showed that average chord length L32 was almost constant for the oil drops while it tended to decrease for the water drops as the respective layer velocity increased. In the 14 mm ID pipe, the addition of a polymer in the oil-water flow had a significant effect on the flow patterns and pressure drop. The transition from stratified to nonstratified patterns was clearly delayed and the pressure drop was found to decrease after adding the polymer. The wavy interface in the stratified, dual continuous and annular flows was damped when polymer was present. The interfacial and water wall shear stress were also found to decrease after the addition of the polymer. Theoretically a model was developed based on Kelvin-Helmholtz (KH) instability to predict whether waves in stratified wavy flow with certain amplitudes and lengths are stable or not. The model compared well with the Viscous KH correlation developed by Trallero (1995) and with some experimental results. The model was extended to predict the onset velocities of entrainment by including an empirical wave amplitude and length. The prediction agreed well with the experimental onset velocities from a number of studies. Based on a balance between drag force and surface tension on the crests of the waves, another equation was developed to predict the critical wave amplitude and length required for drop formation. This equation was used together with the stability equation to define three regions in a wave amplitude against length graph. These are; stable wave region; unstable wave region, where waves are unstable but drops may not form because waves need to grow more before drops can detach; drop entrainment region. The model agreed well with the experimental results. Finally, an entrainment model to predict the fraction of one phase entrained into the other during dual continuous flow, that was based on a balance between rate of drop entrainment and rate of drop deposition. The model was modified with experimental data from the current study and was then validated against data from literature. The comparison was reasonable in many cases.
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Koh, Sunny. "Stratified protocols for mobile gaming." University of Southern Queensland, Faculty of Sciences, 2006. http://eprints.usq.edu.au/archive/00003851/.
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[Abstract]: Mobile Games are becoming very popular. Players play games under various conditions and so we need protocols which can adapt. However, unlike the desktop, there are many issues with that of mobile communication. This dissertation proposes a stratified protocol to be implemented in order to solve these communication problems more effectively. The protocol itself dynamically adapts to the changing bandwidth capacity of the network. The term stratified means that the payload in the protocol packets is subdivided into different categories, or strata, of data which are handled differently dependingon network conditions. Such a protocol needs to be responsible as it must make decisions which do notworsen the problem of network congestion when it arises.An experiment was conducted with a view to determining whether it is important to address difficulties with technical quality of communication. This experiment showedthat gaming satisfaction of players does depend on technical quality of communication and that the way in which this dependence on technical quality is exhibited depends upon the particular gaming genre. This dependence on genre and the fact that different games make use of communication services differently suggests that stratification of communication protocols could be useful.
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Grover, B. "Waves in locally stratified media." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599757.
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The main objective is to provide a wide range of approaches that yield useful understanding for the different scenarios of waves in locally stratified media. A classification system is constructed, where the physical problems are put into categories with common mathematical models and problems. This provides a convenient tool for identifying which methods and approaches to employ for a particular physical problem. The bulk of the analysis is centred around two methods or theories - multiple scale homogenisation and generalised ray theory. Multiple scale homogenisation is relevant for long-wave propagation and finding the effective medium of the layered structure. The Backus average for finely layered media is derived in a new way, where multiple scale techniques and the propagator matrix formulation are combined to form a general framework for most linear waves in locally stratified media. With this framework, one can easily derive known formulae for effective media, including the anisotropic effective mass density for acoustic waves. Since the original Backus average was derived for systems close to the static limit, and the anisotropic mass density is a low frequency dynamic effect, acoustic waves are analysed in more detail. The technique is also applied to more complicated media, and it is shown how effective stiffness tensor can be found for piezoelectric media. However, the key feature of this framework is that higher order terms are easily calculated. Nevertheless, the higher order terms are sensitive to the distance propagated, and the effective medium solution is only valid for short distances of propagation. This is in agreement with previous simulations. The validity of Backus averaging or accuracy of effective medium theory is investigated for the one dimensional case. Using Magnus series and manipulation of exponential operators, a new relationship between the effective medium and exact solutions are derived. Based on this relation, the same observations are made as in previous numerical work. Bounds for the factor between the effective and exact solutions are also calculated.
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Miller, David. "Homotopy theory for stratified spaces." Thesis, University of Aberdeen, 2010. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=158352.
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There are many different notions of stratified spaces. This thesis concerns homotopically stratified spaces. These were defined by Frank Quinn in his paper Homotopically Stratified Sets ([16]). His definition of stratified space is very general and relates strata by “homotopy rather than geometric conditions”. This makes homotopically stratified spaces the ideal class of stratified spaces on which to define and study stratified homotopy theory. In the study of stratified spaces it is useful to examine spaces of popaths (paths which travel from lower strata to higher strata) and holinks (those spaces of popaths which immediately leave a lower stratum for their final stratum destination). It is not immediately clear that for adjacent strata these two path spaces are homotopically equivalent and even less clear that this equivalence can be constructed in a useful way. The first aim of this thesis is to prove such an equivalence exists for homotopically stratified spaces. We will define stratified analogues of the usual definitions of maps, homotopies and homotopy equivalences. Then we will provide an elementary criterion for deciding when a strongly stratified map is a stratified homotopy equivalence. This criterion states that a strongly stratified map is a stratified homotopy equivalence if and only if the induced maps on strata and holink spaces are homotopy equivalences. Using this criterion we will prove that any homotopically stratified space is stratified homotopy equivalent to a homotopically stratified space where neighborhoods of strata are mapping cylinders. Finally we will develop categorical descriptions of the class of homotopically stratified spaces up to stratified homotopy. The first of these categorical descriptions will involve categories with a topology on their object and morphism sets. The second categorical description will involve only categories with discrete object spaces.
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Rea, Suzanne. "Stratified flow at T-junctions." Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287195.
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Cowan, Ian Robert. "Density-stratified turbulent boundary layers." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321001.
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Blanchette, François Alain 1978. "Sedimentation in a stratified ambient." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/29986.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 2003.Includes bibliographical references (p. 147-156).
We study the interaction between settling particles and a stratified ambient in a variety of contexts. We first study the generation of large scale fluid motions by the localised release of a finite mass of particles in the form of plumes or gravity currents. We present the results of a combined theoretical and experimental study describing the evolution of particle clouds formed by the release of heavy particles. In the early stages of motion, particle clouds behave as turbulent fluid thermals; however, their radial expansion eventually stops and particles settle from the base of the cloud at their individual settling speed. We focus on deducing a criterion for the various modes of particle deposition from particle clouds in a stratified ambient. We proceed to study the deposition patterns resulting from particle-laden gravity currents that spread horizontally when released in a particle-free ambient. Using a box-model, we focus on bidisperse gravity currents and examine the resulting particle distribution and maximal deposit length. We then turn to suspensions where particles are initially present throughout the fluid. The simultaneous presence of particles and of a stratified ambient may lead to behaviour analogous to double-diffusive systems, with particles playing the role of a diffusing component. We examine the linear stability of the settling of a particle concentration gradient in a stratified fluid. Numerical simulations allow us to determine the stability of the system for a broad range of particle settling speeds and diffusion coefficients. We then report on layering arising from sedimentation in a density stratified ambient beneath an inclined wall.
(cont.) From our experimental study, we describe the series of horizontal intrusions formed by particle-free fluid intruding at its level of neutral buoyancy. We present numerical models describing the time evolution of the concentration of particles and the layer formation. Finally, we present an experimental and theoretical study of the combined influence of hindered settling and settling speed variations due to an ambient stratification. We develop a criterion for the stability of a suspension settling in a stratified ambient and experimental observations allow us to qualify the main features of this instability.
by François Alain Blanchette.
Ph.D.
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Hargreaves, James. "Wave Propagation in Stratified Plasmas." Thesis, University of Sheffield, 2008. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.489650.
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In this Thesis the theoretical aspects of MHD wave propagation in stratified magnetic flux tubes are studied. In particular the focus is directed firstly to the study of wave propagation in flux tubes with the presence of a background flow and secondly to wave propagation in non-ideal, i.e. viscous, media. Recent observational evidence from the Hinode satellite shows clearly that plasma flows are ubiquitous in the solar atmosphere. Longitudinal and transverse tube waves in flux tubes with a background flow are studied, with the governing equations being derived and solved for a number of footpoint drivers. Applications to the Sun are made and some interesting and important effects on wave propagation are found. The solar atmosphere is widely recognised as a dissipative medium, although most previous studies of wave propagation in stratified atmospheres have assumed an ideal medium. In the second half of the Thesis the effect of viscosity on wave propagation is investigated for both longitudinal and transverse tube waves in a stratified flux tube. The governing equations are derived and solved for both temporal and spatial boundary conditions.
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Platts, Alexander. "Functional quantization-based stratified sampling." Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/27105.
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Functional quantization-based stratified sampling is a method for variance reduction proposed by Corlay and Pagès (2015). This method requires the ability to both create functional quantizers and to sample Brownian paths from the strata defined by the quantizers. We show that product quantizers are a suitable approximation of an optimal quantizer for the formation of functional quantizers. The notion of functional stratification is then extended to options written on multiple stocks and American options priced using the Longstaff-Schwartz method. To illustrate the gains in performance we focus on geometric brownian motion (GBM), constant elasticity of variance (CEV) and constant elasticity of variance with stochastic volatility (CEV-SV) models. The pricing algorithm is used to price knock-in, knockout, autocall, call on the max and path dependent call on the max options.
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Yong, Florence Hiu-Ling. "Quantitative Methods for Stratified Medicine." Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:17463130.
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Stratified medicine has tremendous potential to deliver more effective therapeutic intervention to improve public health. For practical implementation, reliable prediction models and clinically meaningful categorization of some comprehensible summary measures of individual treatment effect are vital elements to aid the decision-making process and bring stratified medicine to fruitful realization. We tackle the quantitative issues involved from three fronts : 1) prediction model building and selection; 2) reproducibility assessment; and 3) stratification.
First, we propose a systematic model development strategy that integrates cross-validation and predictive accuracy measures in the prediction model building and selection process. Valid inference is made possible via internal holdout sample or external data evaluation to enhance generalizability of the selected prediction model. Second, we employ parametric or semi-parametric modeling to derive individual treatment effect scoring systems. We introduce a stratification algorithm with constrained optimization by utilizing dynamic programming and supervised-learning techniques to group patients into different actionable categories. We integrate the stratification and newly proposed prediction performance metric into the model development process. The methodologies are first presented in single treatment case, and then extended to two treatment cases. Finally, adapting the concept of uplift modeling, we provide a framework to identify the subgroup(s) with the most beneficial prospect; wasteful, harmful, and futile subgroups to save resources and reduce unnecessary exposure to treatment adverse effects. The proposals are illustrated by AIDS clinical study data and cardiology studies for non-censored and censored outcomes.
The contribution of this dissertation is to provide an operational framework to bridge predictive modeling and decision making for more practical applications in stratified medicine.Biostatistics
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Lukiyanov, Vladimir. "Cohomology for multicontrolled stratified spaces." Thesis, Loughborough University, 2016. https://dspace.lboro.ac.uk/2134/20707.
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In this thesis an extension of the classical intersection cohomology of Goresky and MacPherson, which we call multiperverse cohomology, is defined for a certain class of depth 1 controlled stratified spaces, which we call multicontrolled stratified spaces. These spaces are spaces with singularities -- this being their controlled structure -- with additional multicontrol data. Multiperverse cohomology is constructed using a cochain complex of tau-multiperverse forms, defined for each case tau of a parameter called a multiperversity. For the spaces that we consider these multiperversities, forming a lattice M, extend the general perversities of intersection cohomology. Multicontrolled stratified spaces generalise the structure of (the compactifications of) Q-rank 1 locally symmetric spaces. In this setting multiperverse cohomology generalises some of the aspects of the weighted cohomology of Harder, Goresky and MacPherson. We define two special cases of multicontrolled stratified spaces: the product-type case, and the flat-type case. In these cases we can calculate the multiperverse cohomology directly for cones and cylinders, this yielding the local calculation at a singular stratum of a multicontrolled space. Further, we obtain extensions of the usual Mayer-Vietoris sequences, as well as a partial Kunneth Theorem. Using the concept a dual multiperversity we are able to obtain a version of Poincare duality for multiperverse cohomology for both the flat-type and the product-type case. For this Poincare duality there exist self-dual multiperversities in certain cases, such as for non-Witt spaces, where there are no self-dual perversities. For certain cusps, called double-product cusps, which are naturally compactified to multicontrolled spaces, the multiperverse cohomology of the compactification of the double-product cusp for a certain multiperversity is equal to the L2-cohomology, analytically defined, for certain doubly-warped metrics.
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Darbyshire, Oliver Richard. "Modelling of turbulent stratified flames." Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/247473.
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Due to concerns about pollutant emission combustion systems are increasingly being designed to operate in a lean premixed mode. However, the reduction in emissions offered by lean premixed combustion can be offset by its susceptibility to instabilities and ignition and extinction problems. These instabilities, caused by the coupling of unsteady heat release and pressure fluctuations can cause significant damage to combustion devices. One method of avoiding these problems whilst still operating a globally lean system is to employ a stratified premixed mode where areas of richer mixture are used to enhance the stability of the flame. In this thesis a computational modelling methodology for the simulation of stratified premixed flames is developed. Firstly, several sub-models for the dissipation rate of a reacting scalar are evaluated by the simulation of two laboratory scale flames, a turbulent stratified V-flame and a dump combustor fed by two streams of different mixture strength. This work highlights the importance of this quantity and its influence on the simulation results. Any model for stratified combustion requires at least two variables to describe the thermochemical state of the gas: one to represent the mixing field and another to capture the progress of reaction. In turbulent stratified flames the joint probability density function (pdf) of these variables can be used to recover the mean reaction rates. A new formulation for this pdf based on copula methods is presented and evaluated alongside two alternative forms. The new method gives improved results in the simulation of the two test cases above. As it is likely that practical stratified combustion devices will have some unsteadiness to the flow the final part of this work applies the modelling methodology to an unsteady test case. The influence of the unsteady velocity forcing on the pollutant emissions is investigated. Finally the methodology is used to simulate a developmental, liquid fuelled, lean burn aero-engine combustor. Here the model gives reasonable predictions of the measured pollutant emissions for a relatively small computational cost. As such it is hoped that the modelling methodology presented can be useful in the iterative industrial design process of stratified combustion systems.
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Hernandez, Barral A. "Stratified wavy oil-water flows." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1448338/.
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The structure of the oil-water interface of stratified flows in a 38 mm ID pipe is investigated in this Thesis with double-wire conductance probes. The fluids used – tap water and Exxsol™ D140 oil (ρo = 830 kgm-3; μo = 0.0055 kgm-1s-1) – are pumped into the facility and brought together in a “Y” inlet section, designed to minimize the mixing between phases (r = 0.6 – 2.4; Umix = 0.5 – 2.5 ms-1). The piping is made of acrylic and the flow was observed with the aid of high-speed imaging. The waves seen on the oil-water interface further downstream the inlet consists of small 3D fluctuations, rather than 2D structures. Conductance probes are used to investigate the oil-water interface in cases where clear wavy structures cannot be followed or analyzed. The signal of interface height in time is found to be stationary and follow a Gaussian distribution when the signal is collected at 256 Hz during 4 min. Based on these properties, a thorough methodology for analysis is presented, which allows estimating time-average parameters of the flow and the power spectrum of the interface. This analysis reveals that, in fully-developed flow conditions, oil and water phases show very little slip and tend to flow both at roughly the mixture velocity regardless of the flow conditions. The power spectrum detects a unique frequency of 19 Hz, but reveals that mechanic vibrations propagating through the facility are a major contribution to the structure of the interface. The 19 Hz frequency corresponds to clearly identifiable waves that develop at the inlet section only if the oil-to-water input ratio is different from 1. The power spectrum at the inlet tends to be dominated by this frequency. This finding is verified with the information of high-speed images. Wave characteristics and their evolution along the inlet are determined from high-speed images collected with a Phantom Miro 4 camera at 1,000 – 1,200 fps. The theoretical analysis of the stability of inlet waves suggests that their origin is a Kelvin-Helmholtz instability and characterizes the waves as dynamic in nature. The two types of oil-water interfaces seen (i.e. that at the inlet with 2D waves and that downstream the pipe with small 3D contributions) are discussed in this Thesis at length and abundant details are given.
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Janes, Nigel. "SIMPLIFIED MODELING OF STRATIFIED-CHARGE COMBUSTION IN A CONSTANT VOLUME CHAMBER." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1010419896.
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Skrynnikov, Yuri 1959. "Nonlinear coupled waves in stratified flows." Monash University, School of Mathematical Sciences, 2002. http://arrow.monash.edu.au/hdl/1959.1/7779.
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Kirby, Christopher William. "An investigation of stratified population estimates." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq23364.pdf.
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Zhong, C. X. Bob. "Empirical likelihood inference under stratified sampling." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0032/NQ26890.pdf.
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Frisk, Anders. "On Stratified Algebras and Lie Superalgebras." Doctoral thesis, Uppsala : Department of Mathematics, Uppsala university, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7781.
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Huq, Ikramul Pablo. "Turbulence and mixing in stratified fluids." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306426.
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Scase, Matthew Murray. "Vortex rings in a stratified fluid." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615911.
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Sung, Kyung-Sub. "Turbulent dispersion in strongly stratified turbulence." Thesis, Imperial College London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.582577.
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The first part is the derivation of one-particle vertical diffusion for stably stratified turbulence with or without rapid rotation. Nicolleau & Vassilicos (2000) have analytically calculated vertical one-particle diffusion in stably stratified turbulence without rotation. One-particle vertical diffusion for turbulence with stable stratification and with or without rapid rotation has been derived here analytically using the solutions of the linearized equations of motions. The second part is an attempt to explain the depletion of horizontal pair diffusion in strongly stratified turbulence. "Recently, Nicolleau et al. (2005) have shown that in their Kinematic Simulations (KS) of vertically stably and strongly stratified homogeneous turbulence (Froude number smaller than 1). horizontal pair diffusion is significantly depleted by comparison to unstratified isotropic and homogeneous two- and three-dimensional turbulence. We have seeked to explain this depletion of horizontal pair diffusion by vertical stratification in terms of the probability density function of the horizontal divergence of the velocity field and the statistics of stagnation points following the recent approach to Richardson pair diffusion by Davila & Vassilicos (2003), Goto & Vassilicos (2004), Goto et al. (2005) and Osborne et al. (2005). We measure the number density of stagnation points in the KS of three-dimensional strongly stratified turbulence and find that it is virtually identical to what it is in KS of three-dimensional isotropic turbulence The third part is a study of the vertical motions of small, spherical inertial particles in strongly stratified turbulence.
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Weltmer, Micah A. "Stratified fronts in well-mixed estuaries." Thesis, Monterey, California: Naval Postgraduate School, 2013. http://hdl.handle.net/10945/37742.
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Approved for public release; distribution is unlimitedThe occurrence of tidal intrusion fronts in a well-mixed estuary is demonstrated through both model simulation and field observation. Strong vertical mixing in well-mixed estuaries typically does not allow for development of stratification, which is a defining feature of tidal intrusion fronts. New methodology to compute a mutual realization surface of critical width and depth from model output is described that evaluates how the geometry of a basin releases tidal inflow from the hydraulic control of an inlet and the resulting front character. Force balance relationships of these features are evaluated in three dimensions for the first time. From this, Froude angle techniques are adapted to assess and predict how the geometry controls the behavior of the front after it is formed. Intrusion fronts observed in the field do not precisely conform to the conceptual model, but a modest field validation of Froude angle usage informs an axis rotation that results in agreement with established hydraulic theory. Frontogenetic mechanisms are proposed from the observations to describe the importance of morphological complexity and water mass segregation to the occurrence of bathymetrically induced confluent subduction in a well-mixed estuary.
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Iial-Awad, Ahmad Salmeh. "Stratified flow in the built environment." Thesis, University of Hertfordshire, 2006. http://hdl.handle.net/2299/14350.
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Stratified flow in an environmental chamber has been investigated. The chamber of dimensions (7.5m long, 5.6m wide and 3.0m) at the University of Hertfordshire has been used. Sets of experiments investigating the effect of the major flow parameters such as airflow rate, jet momentum, flow conditions and height of the air supply device have been conducted. Results have been obtained to evaluate the flow characteristics and thermal stratification mechanism. The study has demonstrated the validity of using smoke visualization to evaluate the stratified flow characteristics such as interface level height, stratified layer thickness, and degree of stratification. The effects of both hot and cold airflow rates in the ranges of (0.0 to 8.0 m3 /min) were investigated. The flow characteristics vary depending on the flow parameters and the experimental conditions. The effect of supply terminal and extract terminal at various airflow rates on the flow characteristics is experimentally investigated. It has been found that relative influence of inertia and buoyancy forces resolves the stratified flow characteristics. The stratification interface level height and the ventilation flow rates are two main factors in the design of natural ventilation system. The results can be used to obtain a good estimation of the effectiveness of a ventilation system at design stage. Experimental work was carried out using ceiling jet to supply hot and cold air to a confined space, to investigate the effect of jet momentum in breaking and mixing the stratified layer. The flow of high momentum was supplied downward from the ceiling. The magnitude of momentum needed depends on the degree of stratification, stratified layer interface level height and the stratification conditions. It can be seen that the jet momentum has significant influence on the mixing of the stratified flow characteristics. The results indicated that once the momentum was initiated a mixed flow grew in the occupied zone above the floor. The height of this zone depends on the stratified flow characteristics, and the temperature and momentum of the ceiling jet. Another area of experimentation was the inversion of input airflow supplies. In this case, the flow of high buoyancy was supplied upward, whilst the flow of high momentum was supplied downward from the ceiling. The stratified layer lost its stability and broke down due to the drag and tearing of cold air penetrated downward from higher levels. The compound effect of these two conditions will circulate the air in the whole space and disturb the stability of the stratified layer to reach fully mixed flow A comprehensive definition of the degree of stratification was formulated. Analytical solutions were developed for the stratified layer thickness and location as a function of temperature gradient and airflow ratios. These expressions were calibrated using the experimental results. The critical momentum needed to breakdown the stratified layer also evaluated. Comparisons with previous studies where also carried out. It was found that the stratified layer interface level height is dependent on the ratio of airflow rate and geometrical effects. If mixed flow is desired then the cold inflow aperture should be located higher than the hot inflow aperture, whiles the interface level height is not located at the exhaust aperture height. The critical vertical momentum necessary in order to break down a stratified layer has been found to depend on the stratified layer interface level height. A semi-empirical formula based on the present experimental results has been developed to predict the critical vertical momentum for given stratified conditions. Based on the present experimental results, the effect of momentum is greater than the effect of buoyancy and the time needed to break down the stratified layer is considerable less than the time it takes to stratify. Experimental data also demonstrate a ventilation method for increasing the occupied zone height without breaking down the stratified layer.
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LeBel, Andre. "Framed stratified sets in Morse theory." Thesis, University of Warwick, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338715.
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Hughes, Graham Owen. "Aspects of mixing in stratified flows." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324969.
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Lai, Hung-Liang. "Seismic modeling of complex stratified reservoirs." [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1322.
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Zhong, Bob Chongxin Carleton University Dissertation Mathematics and Statistics. "Empirical likelihood inference under stratified sampling." Ottawa, 1997.
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Kirk, Joshua Robert. "Dynamics of stratified regions in Saturn." Thesis, University of Leeds, 2018. http://etheses.whiterose.ac.uk/22193/.
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Saturn has a rather peculiar magnetic field in that it is highly spin axisymmetric. Evidence for the decay time of a magnetic field on the scale of Saturn would suggest that a dynamo operates deep within its interior. As a consequence, the observed field would be in violation of Cowling’s theorem. It is believed that a stably stratified layer under the influence of a thermal shear is the reason for the observed axisymmetric field. This stable layer is believed to be formed from helium sedimentation deep within Saturn, with the thermal shear driven by pole-equator temperature differences. The combined effects of shearing and the stable layer attenuate the non-axisymmetric field components leaving only the axisymmetric field at the surface. Motivated by the influence of this stable stratification, we follow on from initial work by Stevenson (1982b) by first considering the linear problem with variable conductivity and looking at the consequences of increasing the parameter that controls the strength of the thermal wind as mentioned in his paper. In subsequent chapters the analysis concentrates on the nonlinear contributions by including the momentum equation into our calculations. We present asymptotic analysis of such a system and show that the geostrophic flow, found by satisfying Taylor’s constraint, is singular for an inviscid interior solution in the limit of small Rm, where Rm, the magnetic Reynolds number, controls the strength of the shearing effect within the layer. Numerical treatment of the system of equations for a viscous system are also considered. The results of exploring the parameter space for Rm and Ha, the Hartmann number, lead to further asymptotic analysis in which viscosity is considered. A boundary layer solution is found, which is validated by the numerical solution. The latter part of the thesis looks at the numerical solution with the inclusion of a horizontal field, the motivation for which will become apparent in the analysis of the inviscid regime.
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Persson, Westin Elin. "Homological properties of some stratified algebras." Licentiate thesis, Uppsala universitet, Algebra och geometri, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-426125.
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Willacy, Sarah. "Homogeneous and stratified vented gas explosions." Thesis, University of Leeds, 2008. http://etheses.whiterose.ac.uk/1584/.
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Explosion tests were carried out in four medium-scale test-vessels incorporating closed, vented, duct vented and interconnected vessels. A systematic investigation into the influence of homogeneous and stratified mixtures was undertaken by varying mixture reactivity, ignition position, injection position and mixture composition. A feature of this work has been the similarities in explosion phenomena between stratified and homogeneous explosions and between partially filled and fully filled geometries to the conclusion that the explosion severity recorded in stratified mixtures towards the lean flammability limit was in many cases much higher than the fuel concentration would normally suggest. Stratified mixtures with global equivalence ratio around stoichiometric produced significantly lower pressures than their homogeneous equivalents. However, stratified (globally) near-limit mixtures produced overpressures that were several hundred mbar higher than those of the equivalent homogeneous mixtures. Even beyond the flammable range (globally) the stratified mixtures produced significant overpressures. The phenomena discussed in this thesis illustrate the difficulty in designing adequate protection for such vented, duct vented and interconnected geometries, since even relatively small pocket of weak fuel-air mixtures produced relatively severe explosions. This can have implications for the safety design of inter-connected installations which are not intended to be subject to flammable mixtures. While it is an important conclusion from the work presented in this chapter that close to the flammability limits the stratified explosion severity was greater than its global concentration would normally indicate, it should be stressed that homogeneous stoichiometric tests still constitute the worst case tests. Therefore, it is not the suggestion of this work that the design of vented vessels should be modified to represent the maxima obtained in stratified work. However, the value of this research in the field of post-explosion investigation is clear.
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Ng, Tzuu Shing. "Interfacial structure of stratified pipe flow." Thesis, Imperial College London, 2002. http://hdl.handle.net/10044/1/11274.
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Shaha, Jonathan. "Phase interactions in transient stratified flow." Thesis, Imperial College London, 2000. http://hdl.handle.net/10044/1/8653.
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Marsden, Antonia. "Causal modelling in stratified and personalised health : developing methodology for analysis of primary care databases in stratified medicine." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/causal-modelling-in-stratified-and-personalised-health-developing-methodology-for-analysis-of-primary-care-databases-in-stratified-medicine(99ffb1e0-aed8-4185-b939-d29e12873dd0).html.
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Personalised medicine describes the practice of tailoring medical care to the individual characteristics of each patient. Fundamental to this practice is the identification of markers associated with differential treatment response. Such markers can be identified through the assessment of treatment effect modification using statistical methods. Randomised controlled trials provide the optimal setting for evaluating differential response to treatment. Due to restrictions regarding sample size, study length and ethics, observational studies are more appropriate in many circumstances, particularly for the identification of markers associated with adverse side-effects and long term response to treatments. However, the analysis of observational data raises some additional challenges. The overall aim of this thesis was to develop statistical methodology for the analysis of observational data, specifically primary care databases, to identify and evaluate markers associated with differential treatment response. Three aspects of the assessment of treatment effect modification in an observational setting were addressed. The first aspect related to the assessment of treatment effect modification on the additive measurement scale which corresponds to a comparison of absolute treatment effects across patient subgroups. Various ways in which this can be assessed in an observational setting were reviewed and a novel measure, the ratio of absolute effects, which can be calculated from certain multiplicative regression models, was proposed. The second aspect regarded the confounding adjustment and it was investigated how the presence of interactions between the moderator and confounders on both treatment receipt and outcome can bias estimates of treatment effect modification if unaccounted for using Monte Carlo simulations. It was determined that the presence of bias differed across different confounding adjustment methods and, in the majority of settings, the bias was reduced when the interactions between the moderator and confounders were accounted for in the confounding adjustment model. Thirdly, it has been proposed that patient data in observational studies be organised into and analysed as series of nested nonrandomised trials. This thesis extended this study design to evaluate predictive markers of differential treatment response and explored the benefits of this methodology for this purpose. It was suggested how absolute treatment effect estimates can be estimated and compared across patient subgroups in this setting. A dataset comprising primary care medical records of adults with rheumatoid arthritis was used throughout this thesis. Interest lay in the identification of characteristics predictive of the onset of type II diabetes associated with steroid (glucocorticoid) therapy. The analysis in this thesis suggested older age may be associated with a higher risk of steroid-associated type II diabetes, but this warrants further investigation. Overall, this thesis demonstrates how observational studies can be analysed such that accurate and meaningful conclusions are made within personalised medicine research.
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Sit, Ming-fai. "Computation of stratified flow past three dimensional surface mounted obstacles /." [Hong Kong] : University of Hong Kong, 1988. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12431060.
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Men’shov, Igor, and Yoshiaki Nakamura. "Instability of isolated compressible entropy-stratified vortices." American Institute of Physics, 2005. http://hdl.handle.net/2237/7085.
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Biesheuvel, Egbertus Hendrikus Evert. "Many-to-one comparisons in stratified designs." [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=968545149.
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Kraft, Wayne Neal. "Experimental investigation of a stratified buoyant wake." Thesis, Texas A&M University, 2004. http://hdl.handle.net/1969.1/1086.
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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.
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Yeates, Peter Stafford. "Deep mixing in stratified lakes and reservoirs." University of Western Australia. Centre for Water Research, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0046.
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The onset of summer stratification in temperate lakes and reservoirs forces a decoupling of the hypolimnion from the epilimnion that is sustained by strong density gradients in the metalimnion. These strong gradients act as a barrier to the vertical transport of mass and scalars leading to bottom anoxia and subsequent nutrient release from the sediments. The stratification is intermittently overcome by turbulent mixing events that redistribute mass, heat, dissolved parameters and particulates in the vertical. The redistribution of ecological parameters then exerts some control over the ecological response of the lake. This dissertation is focused on the physics of deep vertical mixing that occurs beneath the well-mixed surface layer in stratified lakes and reservoirs. The overall aim is to improve the ability of numerical models to reproduce deep vertical mixing, thus providing better tools for water quality prediction and management. In the first part of this research the framework of a one-dimensional mixed-layer hydrodynamic model was used to construct a pseudo two-dimensional model that computes vertical fluxes generated by deep mixing processes. The parameterisations developed for the model were based on the relationship found between lake-wide vertical buoyancy flux and the first-order internal wave response of the lake to surface wind forcing. The ability of the model to reproduce the observed thermal structure in a range of lakes and reservoirs was greatly improved by incorporating an explicit turbulent benthic boundary layer routine. Although laterally-integrated models reproduce the net effect of turbulent mixing in a vertical sense, they fail to resolve the transient distribution of turbulent mixing events triggered by local flow properties defined at far smaller scales. Importantly, the distribution of events may promote tertiary motions and ecological niches. In the second part of the study a large body of microstructure data collected in Lake Kinneret, Israel, was used to show that the nature of turbulent mixing events varied considerably between the epilimnion, metalimnion, hypolimnion and benthic boundary layer, yet the turbulent scales of the events and the buoyancy flux they produced collapsed into functions of the local gradient Richardson number. It was found that the most intense events in the metalimnion were triggered by high-frequency waves generated near the surface that grew and imparted a strain on the metalimnion density field, which led to secondary instabilities with low gradient Richardson numbers. The microstructure observations suggest that the local gradient Richardson number could be used to parameterise vertical mixing in coarse-grid numerical models of lakes and reservoirs. However, any effort to incorporate such parameterisations becomes meaningless without measures to reduce numerical diffusion, which often dominates over parameterised physical mixing. As a third part of the research, an explicit filtering tool was developed to negate numerical diffusion in a threedimensional hydrodynamic model. The adaptive filter ensured that temperature gradients in the metalimnion remained within bounds of the measured values and so the computation preserved the spectrum of internal wave motions that trigger diapycnal mixing events in the deeper reaches of a lake. The results showed that the ratio of physical to numerical diffusion is dictated by the character of the dominant internal wave motions.
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Schofield, Samuel Phillip. "Dynamics of Laminar Jets in Stratified Fluids." Diss., Tucson, Arizona : University of Arizona, 2006. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1474%5F1%5Fm.pdf&type=application/pdf.
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Frisk, Anders. "On the structure of standardly stratified algebras /." Uppsala, 2004. http://www.math.uu.se/research/pub/Frisk5lic.pdf.
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Li, Ming. "Models for gravity currents in stratified fluids." Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291279.
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