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Neal, Peter. "Epidemics with two levels of mixing." Thesis, University of Nottingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394751.
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Raimondo, Gianluca. "Particle mixing, two level systems and gauge theory." Doctoral thesis, Universita degli studi di Salerno, 2012. http://hdl.handle.net/10556/1304.
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2010 - 2011In this thesis I will discuss the theory of two level systems and the theory of the oscillating particles in quantum eld theory. In the rst chapter I will consider the time evolution of a two level system, a qubit, to show that it has inside a local in time gauge invariant evolution equation. I construct the covariant derivative operator and show that it is related to the free energy. The gauge invariance of the time evolution of the two level system is analogous to the phenomenon of birefringence.I also show that the two level systems present a Berry-like and an Anandan-Aharonov phase. Finally, I discuss entropy environment e ects and the distance in projective Hilbert space between two level states to show that the last one is properly related to the Aharonov - Anandan phase. In the second chapter I review the result obtained in QFT for particle mix- ing, analyzing the theoretical construction and the oscillation formula in the fermion case.I will emphasize the di erences between the quantum mechan- ics formulas and the QFT formulas.The unitary inequivalence between the avor and the mass eigenstates is also shown and the structure of the current for charged elds is nally discussed. I found a non - perturbative vacuum structure for the mixing particles that, among the other things, will lead to a non zero contribution to the value of the cosmological constant (chapter 3). Several links between rst and second chapter will arise from this thesis and will shed the light on the fact that it is possible to construct a generic two level quantum eld theory, that is an extension of the quantum mechanics bit theory in a quantum eld theory framework. [edited by author]
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An, Sunghyuck. "Theory of multiwave mixing in two- and three-level media." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184560.
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This dissertation presents theories of multiwave mixing in two- and three-level media. The first part of the dissertation treats the semiclassical theories in two-level media. Chapter 2 gives the simple semiclassical theory of four-wave mixing when the two pump frequences differ by more than the reciprocal of the population-difference lifetime. This difference washes out the pump spatial holes as well as one of the two reflection gratings. We compare the results to the degenerate treatment of Abrams and Lind and find significant differences in the reflection coefficient spectra. Chapter 3 presents the semiclassical theory of multiwave in a squeezed vacuum characterized by unequal in-phase and in-quadrature dipole decay times. For a highly squeezed vacuum, we find sharp resonances in both probe absorption and reflection coefficients, which provide sensitive ways to measure the amount of squeezing in the vacuum. The second part of the dissertation treats the quantum theories in two- and three-level media. Chapter 4 develops the fourth-order quantum theory of multiwave mixing to describe the effects of sidemode saturation in two-level media. We derive explicit formulas for the fourth-order quantum coefficients and show that the fourth-order quantum theory reproduces the third-order semiclassical coefficient obtained by truncating a continued fraction. We apply the results to cavity problems and find significant differences in the sideband spectra given by the second- and fourth-order treatments, particularly as the sidemode approaches the laser threshold. The final chapter presents a quantum theory of multiwave mixing in three-level cascades with a two-photon pump. The explicit formulas for the resonance fluorescence spectrum and the quantum combination-tone source term are derived. The theory is applied to the generation of squeezed states of light. We find almost perfect squeezing for some strong pump intensities and good broad-band squeezing for low pump intensities.
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Bruno, Angelo. "Dissipation, mixing and two level system in quantum field theory." Doctoral thesis, Universita degli studi di Salerno, 2012. http://hdl.handle.net/10556/290.
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2010 - 2011In this dissertation we discuss several aspects of a two level system (qubit) in the context of quantum mechanics and quantum field theory. The presence of geometrical phases in the evolution of a qubit state is shown. We study geometric structures, which are correlated to an unitary time evolution and its interesting gauge structure. They can be very useful in quantum computational processes. We illustrate the quantum field theoretical formulation of boson mixed fields, and oscillation formulas for neutral and charged fields are found. We show that the space for the mixed fields is unitary inequivalent to the state space where the unmixed field are defined, and we also derive the structure of the currents and charges for the charged mixed fields. Phenomenological aspects of meson mixing in the presence of the decay are discussed. In particular, we show that the effective Hamiltonian is non-Hermitian and non-normal in the Wigner-Weisskopf approximation and we use the biorthonormal basis formalism to diagonalize such an Hamiltonian. Finally, the presence of CP and CPT violations in meson mixing is shown. [edited by author]
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Patel, Meena. "Numerical study of non-linear spectroscopy and four-wave-mixing in two and multi-level atoms." Thesis, Cape Peninsula University of Technology, 2017. http://hdl.handle.net/20.500.11838/2623.
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Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2018.In this research, we undertake a numerical study of the interaction between laser beams and two as well as multi-level atoms. The main aim of this research is to obtain a deeper understanding of laser-atom interactions and non-linear processes such as optical four-wave mixing. This work will supplement experiments to be conducted by other members of the group, who are involved in generating entangled photons via four-wave mixing in cold rubidium atoms. We begin by performing a basic study of the interaction between laser beams and two-level atoms as an aid to gain knowledge of numerical techniques, as well as an understanding of the physics behind light-atom interactions. We make use of a semi-classical approach to describe the system where the atoms are treated quantum mechanically and the laser beams are treated classically. We study the interaction between atoms and laser beams using the density matrix operator and Maxwell's equations respectively. By solving the optical Bloch equations for two-level atoms we examine the atomic populations and coherences and present plots of the density matrix elements as a function of time. The e ects of various parameters such as laser intensity, detuning and laser modulation have been tested. The behaviour of the laser beam as it propagates through the atomic sample is also studied. This is determined by Maxwell's equation where the atomic polarization is estimated from the coherence terms of the density matrix elements.
French South African Institute of Technology National Research Foundation
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Kubasch, Madeleine. "Approximation of stochastic models for epidemics on large multi-level graphs." Electronic Thesis or Diss., Institut polytechnique de Paris, 2024. https://theses.hal.science/tel-04717689.
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Nous étudions un modèle SIR à deux niveaux de mélange, à savoir un niveau global uniformément mélangeant, et un niveau local divisé en deux couches de contacts au sein des foyers et lieux de travail, respectivement. Nous cherchons à développer des modèles réduits qui approchent bien cette dynamique épidémique, tout en étant plus maniables pour l’analyse numérique et/ou théorique.D'abord, nous analysons l’impact épidémique de la distribution des tailles des lieux de travail. Notre étude par simulations montre que, si la moyenne de la distribution des tailles de lieux de travail est fixée, sa variance est un bon indicateur de son influence sur des caractéristiques clés de l’épidémie. Cela nous permet de proposer des stratégies de télétravail efficaces. Ensuite, nous montrons qu’un modèle SIR déterministe, uniformément mélangeant, calibré sur le taux de croissance épidémique fournit une approximation parcimonieuse de l'épidémie.Néanmoins, la précision de ce modèle réduit décroît au cours du temps et n'a pas de garanties théoriques. Nous étudions donc la limite grande population du modèle stochastique à foyers et lieux de travail, que nous formalisons comme un processus à valeur mesure dont l’espace de types est continu. Nous établissons sa convergence vers l’unique solution déterministe d’une équation à valeur mesure. Dans le cas où les périodes infectieuses sont exponentiellement distribuées, une réduction plus forte vers un système dynamique fini-dimensionnel est obtenue.De plus, une étude de sensibilité nous permet de comprendre l’impact des paramètres du modèle sur la performance de ces deux modèles réduits. Nous montrons que la limite grande population du modèle foyer-travail permet de bien approcher l’épidémie, même si certaines hypothèses sur le réseau de contact sont relâchées. De même, nous quantifions l’impact des paramètres épidémiques sur la capacité du modèle réduit uniformément mélangeant à prédire des caractéristiques clés de l’épidémie.Enfin, nous considérons plus généralement des processus de population densité-dépendants. Nous établissons une formule tous-pour-un qui réduit la lignée typique d’un individu échantillonné à un processus spinal inhomogène en temps. Par ailleurs, nous quantifions par couplage la convergence en grande population d'une construction spinaleWe study an SIR model with two levels of mixing, namely a uniformly mixing global level, and a local level with two layers of household and workplace contacts, respectively. More precisely, we aim at proposing reduced models which approximate well the epidemic dynamics at hand, while being more prone to mathematical analysis and/or numerical exploration.We investigate the epidemic impact of the workplace size distribution. Our simulation study shows that if the average workplace size is kept fixed, the variance of the workplace size distribution is a good indicator of its influence on key epidemic outcomes. In addition, this allows to design an efficient teleworking strategy. Next, we demonstrate that a deterministic, uniformly mixing SIR model calibrated using the epidemic growth rate yields a parsimonious approximation of the household-workplace model.However, the accuracy of this reduced model deteriorates over time and lacks theoretical guarantees. Hence, we study the large population limit of the stochastic household-workplace model, which we formalize as a measure-valued process with continuous state space. In a general setting, we establish convergence to the unique deterministic solution of a measure-valued equation. In the case of exponentially distributed infectious periods, a stronger reduction to a finite dimensional dynamical system is obtained.Further, in order to gain a finer insight on the impact of the model parameters on the performance of both reduced models, we perform a sensitivity study. We show that the large population limit of the household-workplace model can approximate well the epidemic even if some assumptions on the contact network are relaxed. Similarly, we quantify the impact of epidemic parameters on the capacity of the uniformly mixing reduced model to predict key epidemic outcomes.Finally, we consider density-dependent population processes in general. We establish a many-to-one formula which reduces the typical lineage of a sampled individual to a time-inhomogeneous spinal process. In addition, we use a coupling argument to quantify the large population convergence of a spinal process
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Ward, Duncan Estcourt. "The two-phase plane turbulent mixing layer /." Title page, contents and abstract only, 1986. http://web4.library.adelaide.edu.au/theses/09PH/09phw257.pdf.
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Morlock, Merlin B. "Nonlinear mixing of two collinear Rayleigh waves." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50280.
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Nonlinear mixing of two collinear, initially monochromatic, Rayleigh waves propagating in the same direction in an isotropic, nonlinear elastic solid is investigated: analytically, by finite element method simulations and experimentally. In the analytical part, it is shown that only collinear mixing in the same direction
fulfills the phase matching condition based on Jones and Kobett 1963 for the resonant generation of the second harmonics, as well as the sum and difference frequency components
caused by the interaction of the two fundamental waves. Next, a coupled
system of ordinary differential equations is derived based on the Lagrange equations of the second kind for the varying amplitudes of the higher harmonic and combination
frequency components of the fundamentals waves. Numerical results of the evolution of the amplitudes of these frequency components over the propagation distance are provided for different ratios of the fundamental wave frequencies. It is shown that the energy transfer is larger for higher frequencies, and that the oscillation of the energy between the different frequency components depends on the amplitudes and frequencies of the fundamental waves. Furthermore, it is illustrated that the horizontal velocity component forms a shock wave while the vertical velocity component
forms a pulse in the case of low attenuation. This behavior is independent of the two fundamental frequencies and amplitudes that are mixed. The analytical model is then extended by implementing diffraction effects in the parabolic approximation.
To be able to quantify the acoustic nonlinearity parameter, β, general relations based on the plane wave assumption are derived. With these relations a β is expressed, that is analog to the β for longitudinal waves, in terms of the second harmonics and the sum and the difference frequencies. As a next step, frequency and amplitude ratios of the fundamental frequencies are identified, which provide a maximum amplitude of one of the second harmonics as well as the sum or difference frequency components
to enhance experimental results.
Subsequently, the results of the analytical model are compared to those of finite element method simulations. Two dimensional simulations for small propagation distances gave similar results for analytical and finite element simulations. Consquently.
this shows the validity of the analytical model for this setup. In order to demonstrate the feasibility of the mixing technique and of the models, experiments were conducted using a wedge transducer to excite mixed Rayleigh waves and an air-coupled transducer to detect the fundamentals, second harmonics and the sum frequency. Thus, these experiments yield more physical information compared to the case of using a single fundamental wave. Further experiments were conducted
that confirm the modeled dependence on the amplitudes of the generated waves. In conclusion, the results of this research show that it is possible to measure the acoustic nonlinearity parameter β to quantify material damage by mixing Rayleigh
waves on up to four ways.
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CAPRON, BARBARA ANNE. "TWO-PHOTON MULTIWAVE MIXING (DOPPLER-FREE SPECTROSCOPY)." Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/183854.
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This dissertation examines aspects of the interaction of multiple coherent light fields for the two-photon two-level model. In this model the interacting energy levels are not connected by an atomic dipole and a two-photon transition between them is necessary. We employ the density matrix formalism allowing easy comparison between the one- and two-photon two-level models. Significant differences are found due to dynamic Stark shifts and conjugate scattering off the pump-induced two-photon coherence. Averages over Doppler broadening are performed and the new upper-level relaxation mechanisms of decay to an intermediate nonresonant level and ionization from the upper state are included. The new relaxation mechanisms, introduced to the theory to better model experiments, are similar except that ionization is intensity dependent. They cause the resulting probe absorption spectra to become more complex and in general asymmetric. Doppler broadening is also important in experiments using gases. We analytically average over a Lorentzian velocity distribution for both co- and counterpropagating pump and probe beams. For copropagating fields the results are similar to those for the one-photon case averaged over inhomogeneous broadening, whereas counterpropagating pump and probe fields yield the so-called Doppler-free configuration that is normally only modelled to third order in the pump amplitude. We consider the pump field amplitude to all orders and find that as long as the width of the Doppler velocity distribution is significantly larger than the two-photon Rabi frequency the results are Doppler-free. The final part of the dissertation treats the question of two-photon squeezed states. This requires quantized sidemodes. Squeezed states are minimum uncertainty states with unequal variances in the two quadratures of the electromagnetic field amplitude. One way to generate these states is via multiwave mixing and we present here the first calculation for nondegenerate two-photon multiwave mixing as it applies to squeezed states. We find that in general two-photon squeezed states require lower intensities and detuning than those predicted by the one-photon model.
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Costa-Patry, Etienne. "Mixing of two scalars in turbulent channel flow." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=83859.
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The interaction of two scalars (both temperature) emitted from concentrated line sources is studied in fully-developed, high-aspect-ratio, turbulent channel flow. The thermal fields are measured using cold-wire thermometry in a flow with a Reynolds number (Uh/nu) of 10200.The transverse, total RMS temperature profiles are a function of the separation distance between the line sources (d/h), their average wall-normal position (ys_av/h), and the downstream location (x/h) (relative to the line sources). The non-dimensional form of the scalar covariance, the correlation coefficient (rho), is a function of the same parameters and quantifies the mixing of the two scalars.
In all cases, the transverse profiles of the correlation coefficient flatten and tend towards 1 as x/h increases. The minimum value of the correlation coefficient for a given transverse profile (rhomin) drifts towards the wall for line source combinations that are not symmetric about the channel centreline. (For profiles that are symmetric about the centreline, the minimum correlation coefficient always occurs at the centreline.) The initial downstream evolution of rhomin (and rhoys_av/h - the value of the correlation coefficient measured at the average wall-normal source location) depend mostly on d/h. Therefore, to an extent, the measured evolutions are similar to those in homogeneous turbulence. However, the dependence on Ys_av/h is never entirely negligible. At a certain downstream position, the (inhomogeneous) high turbulence intensity (found near the wall) serves to accelerate the scalar mixing.
For line source combinations that are not influenced by the above-mentioned, near-wall, high turbulence intensities, spectral analysis indicates that the degree of mixing across scales is relatively constant for the range of parameters studied herein. In the case of near-wall mixing, the large scales were found to evolve more rapidly. This presumably derives from the large-scale nature of turbulence production, which is strong in the nearwall region.
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Grunnet-Jepsen, Anders. "Two-wave mixing and subharmonic instability in photorefractive materials." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260761.
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Peereboom, Nick C. (Nicolaas Christopher) Carleton University Dissertation Engineering Electrical. "Optical two-wave mixing in iron-doped indium phosphide." Ottawa, 1992.
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Abadie, Thomas. "Hydrodynamics of gas-liquid Taylor flow in microchannels." Phd thesis, Toulouse, INPT, 2013. http://oatao.univ-toulouse.fr/11986/1/abadie.pdf.
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This thesis focuses on the hydrodynamics of gas-liquid Taylor flow (or slug flow) in microchannels. These flows, which are generally dominated by surface tension forces, have been investigated in rectangular channels of various cross-sectional aspect ratios by means of both experimental visualizations and numerical simulations. The first experimental part aims at characterizing the bubble generation process (bubble length and frequency of break-up) depending on the operating conditions, the fluid properties, as well as the junction where both fluids merge. Numerical simulations of fully developed Taylor flow have been carried out with the JADIM code. The computation of such surface tension dominated flows requires an accurate calculation of the surface tension force. Some limitations of the Volume of Fluid method have been highlighted and a Level Set method has been developed in order to improve the calculation of capillary effects. Both methods have been compared in detail in terms of spurious currents. 3D numerical simulations have been performed and the influence of the capillary number, as well as the effects of geometry have been highlighted. Inertial effects have been taken into account and their influence on the pressure drop has been shown to be non-negligible. Mixing in the liquid slug has also been studied.
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Seyed, Mahmoudi Seyed Mohammad. "Velocity and mixing characteristics of stirred vessels with two impellers." Thesis, King's College London (University of London), 1993. https://kclpure.kcl.ac.uk/portal/en/theses/velocity-and-mixing-characteristics-of-stirred-vessels-with-two-impellers(b0de9b2e-70e2-4133-9d3e-3955562edfb0).html.
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Dimou, Konstantina. "Simulation of estuary mixing using a two-dimensional random walk model." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/14351.
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Lee, Wei-Koon. "Chaotic mixing in wavy-type channels and two-layer shallow flows." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:f5fcbe34-babb-4fae-9204-28de8774eb98.
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This thesis examines chaotic mixing in wavy-type channels and two-layer shallow water flow. For wavy-type channels, the equations of motion for vortices and fluid particles are derived assuming two-dimensional irrotational, incompressible flow. Instantaneous positions of the vortices and particles are determined using Lagrangian tracking, and are conformally mapped to the physical domain. Unsteady vortex motion is analysed, and vortex-induced chaotic mixing in the channels studied. The dynamics of mixing associated with the evolution of the separation bubble, and the invariant manifolds are examined. Mixing efficiencies of the different channel configurations are compared statistically. Fractal enhancement of productivity is identified in the study of auto-catalytic reaction in the wavy channel. For the two-layer shallow water model, an entropy-correction free Roe type two-layer shallow water solver is developed for a hyperbolic system with non-conservative products and source terms. The scheme is well balanced and satisfies the C-property such that smooth steady solutions are second order accurate. Numerical treatment of the wet-dry front of both layers and the loss of hyperbolicity are incorporated. The solver is tested rigorously on a number of 1D and 2D benchmark test cases. For 2D implementation, a dynamically adaptive quadtree grid generation system is adopted, giving results which are in excellent agreement with those on regular grids at a much lower cost. It is also shown that algebraic balancing cannot be applied directly to a two-layer shallow water flow due to the lack of simultaneous referencing for the still water position for both layers. The adaptive two-layer shallow water solver is applied successfully to flow in an idealised tidal channel and to tidal-driven flow in Tampa Bay, Florida. Finally, chaotic advection and particle mixing is studied for wind-induced recirculation in two-layer shallow water basins, as well as Tampa Bay, Florida.
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Daneshvar, Ahrash. "Interaction and mixing effects in two and one dimensional hole systems." Thesis, University of Cambridge, 2008. https://www.repository.cam.ac.uk/handle/1810/198364.
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This thesis describes electrical measurements performed on low dimensional p-type devices, fabricated from GaAs/AlGaAs heterostructures. The Coulomb interaction between holes is similar to that between electrons. However, the kinetic energy is suppressed, which makes interaction effects particularly important. Holes may also be used to study band structure effects which arise from spin-orbit coupling in the valence band. The effects of Coulomb interactions in low dimensional electron systems are currently being studied extensively. Experiments presented in this thesis indicate the possible importance of Coulomb exchange interactions in both one and two dimensional hole systems (1DHSs,2DHSs). Tilted magnetic field studies of 2DHSs in the quantum Hall regime indicate that Landau levels at even filling factors will not cross. For high filling factor, this is attributed to a spin-orbit mixing effect which arises from the low symmetry ofthe system. At lower filling factor, activation-energy measurements verify that the energy gaps decrease and then increase as the field is tilted. However, the energy gap versus field dependences do not exhibit the curvature that might be expected from a perturbative anticrossing. It is speculated that the origin of this effect is a phase transition driven by the exchange interaction. Balanced arguments contrasting the relative strengths of the mixing and interactions theories are provided. The second part of this thesis describes a new method for the fabrication ofballistic 1DHSs, which exhibit clear conductance quantization. The quantization changes from even to odd multiples of e2/h as a function of the magnetic field in the plane of the heterostructure, as 'spin splitting' causes the 1D subbands to cross. Measurements of the 1D subband energy spacings are used together with the magnetic fields at which the crossings occur to calculate the in-plane g factors of the 1D subbands. These are found to increase as the number of occupied 1D subbands decreases. This enhancement of the g factor is attributed to exchange interactions; possible mixing explanations are also discussed. At higher magnetic fields, the pattern of quantization features shows that the subbands have crossed many times, and that the 1DHS can be strongly magnetized.
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Gartside, James Nicholas Burgess. "Nonlinear interaction of two oblique modes in a supersonic mixing layer." Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187386.
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We study the spatial instability of a pair of symmetric oblique modes in the long-wave limit using multiple time scales and matched asymptotic expansions. The base flow is a supersonic mixing layer that satisfies Miles' condition, namely that the Mach number is chosen so that the corresponding vortex sheet is marginally stable. We introduce the small disturbance far upstream where nonlinear terms are small and study the growth of the disturbance as it convects downstream. Even though we are using a long wavelength, the growth rate is small enough so that the disturbance is essentially periodic from one wavelength to the next. We use linear analysis to solve the problem initially, and then determine a distinguished scaling between the small characteristic frequency and the small characteristic amplitude in order to do the nonlinear analysis. The nonlinear analysis results in a nonlinear integro-differential equation for the amplitude of the disturbance that must be solved numerically. When the angle of obliqueness is than π /4, the growth of the disturbance is much larger than the growth predicted by linear theory, and the growth becomes unbounded at a singularity located at a finite distance downstream. The result is similar to the findings of other analyses done near the neutral point by other authors. When the angle of obliqueness is larger than π /4, the amplitude of the disturbance experiences a series of modulations in the downstream direction; however, the the overall growth of the amplitude is again much larger than the growth predicted by linear theory, but is not as large as the growth experienced for angles less than π/4. The modulations in the amplitude are caused by the nonlinear term in the integro-differential equation; when the angle of obliqueness is less than π /4, the nonlinear term enhances growth, but when the the angle is larger than π/ 4, the nonlinear term alternately enhances and dampens growth as the disturbance convects downstream. So, in either case, the nonlinear interaction between two oblique modes causes the disturbance to grow much more quickly than the growth predicted by linear theory alone.
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Oliver, Eric C. J. "Spinning and mixing: Two studies of microfluidic problems using molecular dynamics simulations." Thesis, University of Ottawa (Canada), 2006. http://hdl.handle.net/10393/27400.
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Advances in microfluidics have led to the development of devices which can perform simple operations on fluids with the aim of developing a fully integrated "lab-on-a-chip". Of prime importance to this procedure is the efficient operation of each individual component. Using theoretical prediction sand two-dimensional Molecular Dynamics (MD) simulations, we have explored the operation of two such devices: one which forces a cavity of fluid into rotational motion and one to mix two different fluid species. For the rotational operation, we have referred to experimental results for a circular cavity coupled to a microfluidic channel in which a laminar flow is induced. This flow causes the fluid in the cavity to rotate which we model with MD simulations. We examine the role of wall-fluid interactions and its effect on enhancing the amount of angular momentum generated in the cavity. The reduction in wall-fluid interaction allows the fluid to slip along the wall and acquire a greater level of spin. We hope this technique can be applied experimentally to enhance the rotation in these devices. For the mixing operation, we examined a previously studied theoretical system where the authors claim obstacles in microchannels increase mixing efficiency for a fluid composed of two species. We make theoretical predictions to the contrary and demonstrate, using MD simulations, that our predictions are correct. Our results show that obstacles have two effects. First, obstacles increase the amount of contact between fluid species which only has a negligible effect on increasing the mixing efficiency. Second, the obstacles flatten the normally Poiseuille (quadratic) flow profile over a finite channel length which decreases the distance required for partial but not complete mixing. We demonstrate that all channels of at least a certain length, defined by the diffusive properties of the channel, will reach full mixing at the same point. Both projects illustrate the utility of MD simulations in predicting fluid behaviour in microfluidic systems. Our aim is that these studies can be integrated into the greater body of knowledge pertaining to microfluidics.
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Que, Fucheng. "Dynamic simulation of gas-liquid mixing in a two-dimensional bubble column." Thesis, University of Manchester, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.281982.
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McGinnis, Daniel Frank. "Two-Dimensional Lake and Reservoir Modeling: Natural and Plume-Induced Mixing Mechanisms." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/29395.
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Lakes and reservoirs exhibit a number of mixing and transport mechanisms. Understanding the transport is crucial to understanding and predicting constituent and density structures. Transport in waterbodies can be natural, such as seiche-induced boundary mixing or advectively-driven inflows. Hypolimnetic oxygenation using bubble-plumes also leads to enhanced mixing. Whether natural or plume-induced, increased mixing will alter the waterbody properties. Conversely, the density structure affects the behavior of plumes as well as inflowing and outflowing water. For example, stratification resulting from impounding a river can result in nutrient and suspended solids retention. Similarly, operation of plumes can induce mixing in the hypolimnion, resulting in warming, increased nutrient transport, and resuspension of settled particles.
Modeling is extremely useful in determining the effects of dams on water quality constituents, enhanced transport, and the performance of mitigation techniques, such as hypolimnetic oxygenation. In this work, a variety of modeling techniques are used to evaluate natural and man-made mixing mechanisms. These include simple temperature and mass budgets, a two-dimensional lake model, and a two-phase plume model.
A bubble-plume and plume-enhanced mixing was studied in Lake Hallwil. It was found that the plume-lake interaction was much more complex then previously expected, and knowledge of the seiche- and plume-enhanced near-field was necessary to accurately model the plume performance. A two-dimensional lake model was then coupled with a linear-plume model to accurately predict not only the plume performance, but also the plume-enhanced mixing in Spring Hollow Reservoir. The same two-dimensional lake model, used in conjunction with data analysis, demonstrated that the Iron Gate I Reservoir was not a significant sink for suspended solids, with only the large, adjacent side bay (Orsova Bay) thought to be the permanent sink. Furthermore, significant stratification did not develop, preventing substantial primary productivity. While the impoundment did change the water quality characteristics, the extent is much less than previously expected. The modeling methods presented here and the coupled plume-reservoir model should be useful tools for the design, modeling and greater understanding of bubble-plumes and other transport-related phenomena in lakes and reservoirs.Ph. D.
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Landel, Julien Rémy Dominique Gérard. "Dynamics of quasi-two-dimensional turbulent jets." Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/244569.
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The study of quasi-two-dimensional turbulent jets is relevant to chemical reactors, the coking process in oil refinement, as well as rivers flowing into lakes or oceans. In the event of a spillage of pollutants into a river, it is critical to understand how these agents disperse with the flow in order to assess damage to the environment. For such flows, characteristic streamwise and cross-stream dimensions can be much larger than the fluid-layer thickness, and so the flow develops in a confined environment. When the distance away from the discharge location is larger than ten times the fluid-layer thickness, the flow is referred to as a quasi-two-dimensional jet. From experimental observations using dyed jets and particle image velocimetry, we find that the structure of a quasi-two-dimensional jet consists of a high-speed meandering core with large counter-rotating eddies developing on alternate sides of the core. The core and eddy structure is self-similar with distance from the discharge location. The Gaussianity of the cross-stream distribution of the time-averaged velocity is due, in part, to the sinuous instability of the core. To understand the transport and dispersion properties of quasi-two-dimensional jets we use a time-dependent advection--diffusion equation, with a mixing length hypothesis accounting for the turbulent eddy diffusivity. The model is supported by experimental releases of dye in jets or numerical releases of virtual passive tracers in experimentally-measured jet velocity fields. We consider the statistical properties of this flow by releasing and then tracking large clusters of virtual particles in the jet velocity field. The probability distributions of two-point properties (such as the distance between two particles) reveal large streamwise dispersion. Owing to this streamwise dispersive effect, a significant amount of tracers can be transported faster than the speed predicted by a simple advection model. Using potential theory, we determine the flow induced by a quasi-two-dimensional jet confined in a rectangular domain. The streamlines of the induced flow predicted by the theory agree with experimental measurements away from the jet boundary. Finally, we investigate the case of a quasi-two-dimensional particle-laden jet. Depending on the bulk concentration of dense particles, we identify different flow regimes. At low concentrations, the jet features the same core and eddy structure observed without the particles, and thus quasi-two-dimensional jet theory can apply to some extent. At larger concentrations, we observe an oscillating instability of the particle-laden jet.
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Lemus, Jorge Ernesto 1961. "Phonology at two levels: A new model of lexical phonology." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/289144.
Full textAbstract:
This dissertation proposes a new model of Lexical Phonology: the Two-Level Theory (TLT). The TLT consists of dividing phonological rules into two different sets. One set is active at the Lexical Level, and the other set is active at the Postlexical Level. Lexical rules are active at the Lexical Level and, possibly, at the Postlexical Level, too (the choice being language specific). This new model is a simplification of previous models that hold that rules found at the Lexical Level can be further subdivided into other strata, producing multilevel representations. This new model of Lexical Phonology is tested with regard to a number of phonological problems in Pipil (Chapter 2), in Spanish (Chapter 3), and in Malayalam (Chapter 4). These analyses within the TLT demonstrate that the multiple levels of previous analyses of comparable phenomena within these languages are unnecessary.
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Donaldson, Paul Murray. "Two dimenstional infrared four wave mixing spectroscopy of simple molecules, peptides and proteins." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/1245.
Full textAbstract:
In this thesis, measurements of electron-vibration-vibration two dimensional infrared (EVV 2DIR) spectra are demonstrated for the first time from aliphatic, aromatic and amide containing compounds. Bioanalytical applications of EVV 2DIR spectroscopy are explored and the first EVV 2DIR measurements on proteins reported. Operational protocols for collecting EVV 2DIR spectra are described and it is shown for the case of benzene Fermi resonances how excitation pulse ordering can be used to isolate different EVV coherence pathways, giving signals that report on several aspects of a molecule’s electrical and mechanical anharmonicity. Experimental spectra are compared with first principles simulations and in general found to be in good agreement with one another. It is shown that inter-pulse delays can substantially clean up frequency domain spectra and for the range of compounds studied, the 2DIR spectra are significantly decongested compared with their 1D infrared and Raman counterparts. EVV 2DIR coherence lifetime measurements are reported and applied to a range of simple organic compounds. Measurements of exponential dephasing, nonexponential dephasing and quantum beating are demonstrated, with the exponential decays used to accurately measure vibrational linewidths and the quantum beats to measure line splittings.
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Berube, D. Steven. "Assessing differences in data and information makeup at two different organizational levels using two managerial jobs." Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-03032009-040410/.
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Hazelton, William Donald. "Configuration mixing of quark states in nucleons and other baryons in the MIT bag model /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/9770.
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Akhtar, Kareem. "Numerical Investigation using RANS Equations of Two-dimensional Turbulent Jets and Bubbly Mixing layers." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/34512.
Full textAbstract:
This thesis presents numerical investigations of two-dimensional
single-phase turbulent jets and bubbly mixing layers using
Reynolds-Averaged Navier-Stokes (RANS) equations.
The behavior of a turbulent jet confined in a channel depends
on the Reynolds number and geometry of the channel which
is given by the expansion ratio (channel width to jet thickness)
and offset ratio (eccentricity of the jet entrance). Steady
solutions to the RANS equations for a two-dimensional turbulent
jet injected in the middle of a channel have been obtained. When
no entrainment from the channel base is allowed, the flow is
asymmetric for a wide range of expansion ratio at high Reynolds
number. The jet attaches to one of the channel side walls. The
attachment length increases linearly with the channel
width for fixed value of Reynolds number. The attachment length is
also found to be independent of the (turbulent) jet Reynolds
number for fixed expansion ratio. By simulating half of the
channel and imposing symmetry, we can construct a steady symmetric
solution to the RANS equations. This implies that there are
possibly two solutions to the steady RANS equations, one is
symmetric but unstable, and the other solution is asymmetric (the
jet attaches to one of the side walls) but stable. A symmetric
solution is also obtained if entrainment from jet exit plane is
permitted. Fearn et al. (Journal of Fluid Mechanics, vol. 121,
1990) studied the laminar problem, and showed that the flow
asymmetry of a symmetric expansion arises at a symmetry-breaking
bifurcation as the jet Reynolds number is increased from zero. In
the present study the Reynolds number is high and the jet is
turbulent. Therefore, a symmetry-breaking bifurcation parameter
might be the level of entrainment or expansion ratio.
The two-dimensional turbulent bubbly mixing layer, which is a
multiphase problem, is investigated using RANS based models.
Available experimental data show that the spreading rate of
turbulent bubbly mixing layers is greater than that of the
corresponding single phase flow. The presence of bubbles also
increases the turbulence level. The global structure of the flow
proved to be sensitive to the void fraction. The present
RANS simulations predict this behavior, but different turbulence
models give different spreading rates. There is a significant
difference in turbulence kinetic energy between numerical
predictions and experimental data. The models tested include
k-ε, shear-stress transport (SST), and Reynolds stress
transport (SSG) models. All tested turbulence models under predict
the spreading rate of the bubbly mixing layer, even though they
accurately predict the spreading rate for single phase flow. The
best predictions are obtained by using SST model.Master of Science
28
Hellenthal, Alexander Johannes. "A tale of two levels : there is an "I" in team /." Ridderkerk : Labyrinth Publications, 2004. http://www.gbv.de/dms/sub-hamburg/393558754.pdf.
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Davila, Yvonne A. "QSEN Competency Confidence Levels in Two Groups of New Registered Nurses." ScholarWorks, 2019. https://scholarworks.waldenu.edu/dissertations/6549.
Full textAbstract:
Healthcare agencies and stakeholders expect registered nurses to be competent at all times. When nurses are not confident in competencies, negative patient outcomes can occur. The purpose of this quantitative quasiexperimental with posttest only study was to investigate Quality and Safety Education for Nurses (QSEN) competency confidence levels of 2 groups of new nurses who had 5-6 months of clinical experience. Framed by the Duchscher theory and the QSEN framework, the research question was developed to examine the differences between QSEN competency confidence levels of new nurses who participated in a prelicensure program plus a residency program and nurses who only attended the residency program. Sixty-eight new nurses from 1 health facility answered the Nursing Quality and Safety Self-Inventory (NQSSI). An independent t test was used to compare each knowledge, skills, and attitudes (KSA) QSEN competency confidence levels for two groups. The results of this study demonstrated a difference between QSEN competency confidence levels between the 2 groups, but not all 18 NQSSI items reached a statistically significant difference. The 7 items that reached a statistically significant difference included the QSEN competency confidence level in knowledge and skills in evidence-based practice, quality improvement, and informatics. A statistically significant difference was also noted in the QSEN competency confidence level for patient-centered care skills. A 3-day professional development (PD) workshop was developed based on the results. Participating in the PD workshop could further increase the new nurses' QSEN competency confidence levels which can enhance patient outcomes resulting in positive social change.
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Threlfall, James W. "Wave propagation, phase mixing and dissipation in Hall MHD." Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/3182.
Full textAbstract:
In this thesis the effect of the Hall term in the generalised Ohm's law on Alfvén (shear) and fast wave propagation and dissipation in the ion cyclotron frequency range is investigated. The damping of an initially Gaussian field perturbation in a uniform Hall MHD plasma is treated analytically. Subsequently a 2D Lagrangian remap code (Lare2d) is used to study the damping and phase mixing of initially Gaussian field perturbations and a harmonic series of boundary-driven perturbations in a uniform field (in the presence of a transverse equilibrium density gradient). The same code is then used to study a range of initially shear and fast-wave perturbations in the vicinity of a magnetic X-type null point. The magnetic energy associated with an initially Gaussian field perturbation in a uniform resistive plasma is shown to decay algebraically at a rate that is unaffected by the Hall term to leading order in kδ where k is wavenumber and δ is ion skin depth. A similar decay law applies to whistler perturbations in the limit kδ>>>1. We demonstrate that in both geometries considered, the inclusion of the Hall term reduces the effectiveness of phase-mixing in plasma heating. The reduction in the damping rate in the uniform field (non-uniform density) cases, arising from dispersive effects, tends to zero in both the weak and strong phase mixing limits. In the Hall MHD X-point case, minimal reductions are seen for initially shear wave pulses, suggesting that little or no phase-mixing takes place. Nonlinear fast wave pulses which interact with the initial X-point destabilise the local field sufficiently to generate multiple null pairs; subsequent oscillatory current sheet behaviour appears unaffected by earlier differences between the MHD and Hall MHD cases.
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Salegio, Julius. "Agroforestry participation, a comparison of organizational levels in two Salvadoran rural communities." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ60492.pdf.
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Akers, Stephen Andrew. "Two-Dimensional Finite Element Analysis of Porous Geomaterials at Multikilobar Stress Levels." Diss., Virginia Tech, 2001. http://hdl.handle.net/10919/30070.
Full textAbstract:
A technique was developed for analyzing and developing mechanical properties for porous geomaterials subjected to the high pressures encountered in penetration and blast-type loadings. A finite element (FE) code was developed to verify laboratory test results or to predict unavailable laboratory test data for porous media loaded to multikilobar stress levels. This FE program eliminates a deficiency in the process of analyzing and developing mechanical properties for porous geomaterials by furnishing an advanced analysis tool to the engineer providing properties to material modelers or ground shock calculators. The FE code simulates quasi-static, axisymmetric, laboratory mechanical property tests, i.e., the laboratory tests are analyzed as boundary value problems. The code calculates strains, total and effective stresses, and pore fluid pressures for fully- and partially-saturated porous media. The time dependent flow of the pore fluid is also calculated. An elastic-plastic strain-hardening cap model calculates the time-independent skeletal responses of the porous solids. This enables the code to model nonlinear irreversible stress-strain behavior and shear-induced volume changes. Fluid and solid compressibilities were incorporated into the code, and partially-saturated materials were simulated with a "homogenized" compressible pore fluid. Solutions for several verification problems are given as proof that the program works correctly, and numerical simulations of limestone behavior under drained and undrained boundary conditions are also presented.Ph. D.
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Naußed, David, and Ruta Sapokaite. "Evaluation of Procedural Content Generators for Two-Dimensional Top-Down Dungeon Levels." Thesis, Uppsala universitet, Institutionen för speldesign, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-446471.
Full textAbstract:
This research evaluates two-dimensional top-down dungeon generated levels regarding fundamental and micro dungeon design patterns. Additionally, it investigates the meaningfulness of the evaluation results in terms of accessibility to level designers and similar. The research method concentrates on two dungeon-generation techniques – Cellular Automata and Drunkard Walk. Each generated level gets evaluated based on three evaluation stages that build on top of each other: the passability of each tile; categorization of each collection of tiles with the same attributes; and player-centric gameplay data. The results show key differences between Cellular Automata and Drunkard Walk as the risk of using Cellular Automata to generate up to 90% unreachable space, while drunkard walk always has a playable relative space size of 100%. The evaluation also shows results that depend on the requirements of a game or constraints of a level designer. Cellular Automata generates more rooms, while Drunkard Walk provides more decisions per room. In conclusion, the evaluation results show differences between the two algorithms, presented using a vocabulary that is familiar to a level designer.
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Pendyam, Sandeep Nair Satish S. "Computational neural modeling at the cellular and network levels two case studies /." Diss., Columbia, Mo. : University of Missouri--Columbia, 2007. http://hdl.handle.net/10355/4899.
Full textAbstract:
The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on September 15, 2009). Thesis advisor: Satish S. Nair. Includes bibliographical references.
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Livingston, M., D. T. Ray, and D. J. Jr Garrot. "Evaluation of Two Levels of Irrigation in Relation to Calsweet Watermelon Yield." College of Agriculture, University of Arizona (Tucson, AZ), 1987. http://hdl.handle.net/10150/221259.
Full textAbstract:
Calsweet watermelons were irrigated at two levels, utilizing a drip irrigation system for accurate rate measurements. Number and weight of harvested melons were recorded for four harvest dates. There were no significant differences in weight per melon, number of melons and total mean weight for the water treatments within the four harvest dates. For the entire season, number and total weight of melons were higher in the wet treatment; the weight per melon was higher in the dry treatment.
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Elgort, andrew Charles. "Reducing teachers' levels of stress: A comparison of two counseling treatment models." W&M ScholarWorks, 1992. https://scholarworks.wm.edu/etd/1539618684.
Full textAbstract:
Teachers are experiencing heightened levels of stress throughout the school day the impact of which may be seen in increased absenteeism, turnover, poor performance and waste. This study taught classroom teachers cognitive-behavioral methods to reduce and manage their professional stress comparing a Group Counseling (GC) approach with a Cooperative Professional Development (CPD) approach.;Participating classroom teachers were randomly selected for each treatment condition. The participants in the GC approach met for ten 2-hour consecutive weekly sessions. The CPD treatment initially met as a group for a {dollar}6{lcub}1\over2{rcub}{dollar} hour inservice. at the end of the inservice, the participants formed dyads which met for nine 90 minute consecutive weekly sessions. Both treatment conditions received the same information, strategies, and activities. A follow-up session was held for each treatment condition one month after the conclusion of the program.;All participants, including those in the Waiting-List Control Group, completed two self-report inventories (Teacher Stress Index and State-Trait Anxiety Inventory) three times during the course of the study (pretest, post-test, and one-month follow-up). Additionally, a demographical questionnaire was completed at the beginning of the study and a Course Evaluation Form was completed at the end of the study.;It was predicted that both treatment groups would demonstrate significantly less of an increase in their measured stress and anxiety levels compared to the control group. It was also predicted that there would be no significant difference between the three conditions in their measured levels of "Trait" anxiety.;A MANOVA design was employed to analyze whether significant differences existed for each dependent variable. When analyzed, none of the hypotheses were supported. However, the data were suggestive of a number of trends.;This study re-affirmed the efficacy of delivering stress management techniques to teachers through a "traditional" counseling group method. The efficacy of the Cooperative Professional Development model was also demonstrated. This study also found that teachers valued the flexibility, independence and enhanced feelings of professionalism the latter model offered, suggesting that staff development programs capitalizing on these components may have a greater positive impact on participants and may present a cost-effective way to increase a participant's level of motivation and willingness to implement new techniques.
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Harrell, Greg S. "Testing and modeling of a two-phase ejector." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/39122.
Full textAbstract:
The ejector expansion refrigeration cycle is a modified vapor compression cycle in which a two phase ejector is used to recover a portion of the work otherwise lost in the expansion valve. The ejector improves cycle performance by increasing compressor inlet pressure and by lowering the quality of the fluid entering the evaporator. Theoretically, a cooling COP improvement of approximately 21 % is achievable for a typical refrigerating cycle and an ideal ejector. If the ejector performed as well as typical single-phase ejectors, an improvement of 12% could be achieved. Previous tests have demonstrated a smaller 3.7% improvement; the difference is in the poor performance of the two-phase ejector.
The purpose of this research is to understand the operating characteristics of the two phase ejector and to improve design. A two-phase ejector test rig has been constructed and tested. Preliminary data show performance superior to previously tested two-phase ejectors, but still inferior to single phase ejectors. Ejector performance corresponds to refrigeration cycle COP improvements ranging from 3.9010 to 7.6%. This performance was obtained with an ejector designed from single-phase ejector and wet steam ejector design methods. The poor performance indicates the design methods must be improved for two-phase ejectors. This research has begun the development of design methods for the two-phase ejectors and this research has developed models to describe the fluid dynamics and thermodynamics of the ejector.Ph. D.
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Suberg, Lavinia A. "Investigations of the variability of tidal mixing fronts and their importance for shelf-sea ecosystems across multiple trophic levels." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/400389/.
Full textAbstract:
Tidal mixing fronts establish during the summer months over shelf-seas, and separate tidally-mixed from stratified water masses. They play an important part in shelf-sea bio-physical processes, including volume transport and facilitation of primary productivity. Frontal hydrodynamics provide the physical necessities for prey aggregations to develop, holding the potential for biodiversity hotspots. However, there is limited knowledge on long-term variability of tidal mixing fronts and its effect on associated ecosystems, due to a lack of adequate datasets. Such information would greatly benefit spatial conservation efforts and improve our understanding of ecosystem dynamics on the continental shelf. Satellite-derived frontal maps and extensive biological datasets (from 1990-2010) are employed here to investigate spatio-temporal variability of tidal mixing fronts and their significance for shelf-sea biology from zooplankton tomegavertebrates in the Celtic Sea. In addition, this study assesses the suitability and limitations of satellite-derived frontal metrics for quantitative analyses and employs innovative technology (submarine gliders) to fill data gaps in species-environment interactions. This research provides guidance on the use of frontal metrics in quantitative analysis, such as the need to account for data variability over the years and the careful consideration of the employed frontal metric. This thesis furthermore, represents the first description of long-term temporal variability of tidal mixing fronts on the European shelf and highlights a potential sensitivity to climate change due to positive correlations with rising temperatures. Consequences could include extension of the frontal season and intensification of the frontal density gradient with knock-on effects on associated biota. The density gradient of tidal mixing fronts was shown to act as a direct distribution boundary for plankton between different shelf-sea domains. Climate-change-driven shifts in the seasonality of these fronts may have a direct impact on dispersal of passive floating organisms, habitat connectivity and adult populations of species with planktonic larvae, including commercially important fish and the benthos. Apart from a barrier function, fronts were also found to be important foraging areas for specialist megavertebrates, which were strongly associated with persistent frontal areas, whereas generalist feeders were not. Tidal mixing fronts represent suitable conservation areas for sensitive species in shelf-seas. The underlying mechanisms leading to bio-aggregations at these sites require more research. High-resolution data, simultaneously collected across multiple trophic levels can be obtained by autonomous robotic fleets in the near future.
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Sadek, Nabel. "Comparison of Two Vortex-in-cell Schemes Implemented to a Three-dimensional Temporal Mixing Layer." Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/23198.
Full textAbstract:
Numerical simulations are presented for three dimensional viscous incompressible free shear flows. The numerical method is based on solving the vorticity equation using Vortex-In-Cell method. In this method, the vorticity field is discretized into a finite set of Lagrangian elements (particles) and the computational domain is covered by Eulerian mesh. Velocity field is computed on the mesh by solving Poisson equation. The solution proceeds in time by advecting the particles with the flow. Second order Adam-Bashford method is used for time integration. Exchange of information between Lagrangian particles and Eulerian grid is carried out using the M’4 interpolation scheme. The classical inviscid scheme is enhanced to account for stretching and viscous effects. For that matter, two schemes are used. The first one used periodic remeshing of the vortex particles along with fourth order finite difference approximation for the partial derivatives of the stretching and viscous terms. In the second scheme, derivatives are approximated by least squares polynomial. The novelty of this work is signified by using the moving least squares technique within the framework of the Vortex-in-Cell method and implementing it to a three dimensional temporal mixing layer. Comparisons of the mean flow and velocity statistics are made with experimental studies. The results confirm the validity of the present schemes. Both schemes also demonstrate capability to qualitatively capture significant flow scales, and allow gaining physical insight as to the development of instabilities and the formation of three dimensional vortex structures. The two schemes show acceptable low numerical diffusion as well.
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Mitchell, Radford. "Transition to turbulence and mixing in a quasi-two-dimensional Lorentz force-driven Kolmogorov flow." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49045.
Full textAbstract:
The research in this thesis was motivated by a desire to understand the mixing properties of quasi-two-dimensional flows whose time-dependence arises naturally as a result of fluid-dynamic instabilities. Additionally, we wished to study how flows such as these transition from the laminar into the turbulent regime. This thesis presents a numerical and theoretical investigation of a particular fluid dynamical system introduced by Kolmogorov. It consists of a thin layer of electrolytic fluid that is driven by the interaction of a steady current with a magnetic field produced by an array of bar magnets.
First, we derive a theoretical model for the system by depth-averaging the Navier-Stokes equation, reducing it to a two-dimensional scalar evolution equation for the vertical component of vorticity. A code was then developed in order to both numerically simulate the fluid flow as well as to compute invariant solutions. As the strength of the driving force is increased, we find a number of steady, time-periodic, quasiperiodic, and chaotic flows as the fluid transitions into the turbulent regime.
Through long-time advection of a large number of passive tracers, the mixing properties of the various flows that we found were studied. Specifically, the mixing was quantified by computing the relative size of the mixed region as well as the mixing rate. We found the mixing efficiency of the flow to be a non-monotonic function of the driving current and that significant changes in the flow did not always lead to comparable changes in its transport properties. However, some very subtle changes in the flow dramatically altered the degree of mixing. Using the theory of chaos as it applies to Hamiltonian systems, we were able to explain many of our results.
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Barriquand, Tamara. "The Impact of Environmental Conditions on Internal Waves and Mixing in Two Distinct Ocean Basins." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066682/document.
Full textAbstract:
Les ondes internes sont omniprésentes dans les océans. Cette thèse analyse le cycle de vie des ondes internes et l'impact du déferlement de ces ondes sur le mélange turbulent dans deux bassins océaniques, aux caractéristiques contrastées, l'Arctique et l'Indien. Ces deux régions sont en effet aux antipodes de la circulation thermohaline avec l'océan Arctique lieu de formations d'eaux denses et l'Océan Indien région d'upwelling d'eaux denses. L'analyse de données de mouillage recueillies dans le Sud-Ouest de l'Océan Indien au niveau d'une dorsale océanique révèle la présence d'une forte marée interne. Cette marée interne montre une focalisation de l'énergie sous forme de 'rayons' dont la propagation est fortement influencée par les structures de méso-échelle. Malgré ce fort signal de marée interne, nous mettons en évidence la contribution majeure des ondes internes de fréquence proche-inertielle au mélange turbulent. Aux hautes latitudes l'analyse des séries temporelles recueillies au cours de trois printemps consécutifs dans le Storfjord, un fjord Arctique dans l'archipel Svalbard, montre la forte variabilité des ondes en fonction de la stratification et par conséquent un impact variable de ces ondes en terme de mélange turbulent. Les flux de chaleur diffusifs induits par le déferlement de ces ondes sont enfin estimés dans ces deux régions, permettant ainsi de replacer ces résultats dans le contexte global de la circulation thermohalineInternal waves are ubiquitous in the ocean, and play a key role in the global overturning circulation. This thesis analyzes the life cycle of internal waves in two distinct ocean basins: the Arctic and Indian Oceans. Hydrographic and velocity data are used to study the generation, propagation, and dissipation of internal waves in these two ocean basins. In the Indian Ocean, an area of mixing-driven upwelling, mooring data reveal the presence of a strong internal tide propagating as tidal beams above the Southwest Indian Ridge in the Indian Ocean basin. These tidal beams show a strong vertical structure, and their path of propagation is highly dependent on the mesoscale activity in the region. Despite this strong internal tide signal, however, mixing in the region is dominated by inertial internal waves. On the other side of the globe, in a region of deep water formation, shipboard data from four short time series from three consecutive springs in Storfjorden, an Arctic fjord in the Svalbard Archipelago, reveal a link between the vertical structure of the stratification profile and mixing in the Arctic. These environmental conditions, the changing mesoscale in the Indian Ocean, and the changing stratification in the Arctic Ocean, greatly impact the generation, propagation, and dissipation of internal waves, and subsequent turbulent mixing in theses two ocean basins
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Barriquand, Tamara. "The Impact of Environmental Conditions on Internal Waves and Mixing in Two Distinct Ocean Basins." Electronic Thesis or Diss., Paris 6, 2014. http://www.theses.fr/2014PA066682.
Full textAbstract:
Les ondes internes sont omniprésentes dans les océans. Cette thèse analyse le cycle de vie des ondes internes et l'impact du déferlement de ces ondes sur le mélange turbulent dans deux bassins océaniques, aux caractéristiques contrastées, l'Arctique et l'Indien. Ces deux régions sont en effet aux antipodes de la circulation thermohaline avec l'océan Arctique lieu de formations d'eaux denses et l'Océan Indien région d'upwelling d'eaux denses. L'analyse de données de mouillage recueillies dans le Sud-Ouest de l'Océan Indien au niveau d'une dorsale océanique révèle la présence d'une forte marée interne. Cette marée interne montre une focalisation de l'énergie sous forme de 'rayons' dont la propagation est fortement influencée par les structures de méso-échelle. Malgré ce fort signal de marée interne, nous mettons en évidence la contribution majeure des ondes internes de fréquence proche-inertielle au mélange turbulent. Aux hautes latitudes l'analyse des séries temporelles recueillies au cours de trois printemps consécutifs dans le Storfjord, un fjord Arctique dans l'archipel Svalbard, montre la forte variabilité des ondes en fonction de la stratification et par conséquent un impact variable de ces ondes en terme de mélange turbulent. Les flux de chaleur diffusifs induits par le déferlement de ces ondes sont enfin estimés dans ces deux régions, permettant ainsi de replacer ces résultats dans le contexte global de la circulation thermohalineInternal waves are ubiquitous in the ocean, and play a key role in the global overturning circulation. This thesis analyzes the life cycle of internal waves in two distinct ocean basins: the Arctic and Indian Oceans. Hydrographic and velocity data are used to study the generation, propagation, and dissipation of internal waves in these two ocean basins. In the Indian Ocean, an area of mixing-driven upwelling, mooring data reveal the presence of a strong internal tide propagating as tidal beams above the Southwest Indian Ridge in the Indian Ocean basin. These tidal beams show a strong vertical structure, and their path of propagation is highly dependent on the mesoscale activity in the region. Despite this strong internal tide signal, however, mixing in the region is dominated by inertial internal waves. On the other side of the globe, in a region of deep water formation, shipboard data from four short time series from three consecutive springs in Storfjorden, an Arctic fjord in the Svalbard Archipelago, reveal a link between the vertical structure of the stratification profile and mixing in the Arctic. These environmental conditions, the changing mesoscale in the Indian Ocean, and the changing stratification in the Arctic Ocean, greatly impact the generation, propagation, and dissipation of internal waves, and subsequent turbulent mixing in theses two ocean basins
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Franche, Renée-Louise. "The interpersonal response to depression as a function of two levels of intimacy." Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/26814.
Full textAbstract:
Coyne's interactional formulation of depression (Coyne, 1976) states that the demands for support of the depressed individual are initially met with understanding but that over time, depressed persons engender increasingly negative reactions from others. The rejection of the depressed person is said to be mediated by a depressed mood induction in the other person. Coyne's model is primarily concerned with interactions involving family and friends of the depressed person, but in the past it has consistently been tested in laboratory situations examining interactions between strangers.
The present study attempted to examine subjects' reactions to interaction with a depressed person, within the context of simulated relationships between friends or between strangers. It distinguished between compliance and initiation as expressions of rejection, and investigated the controversial issue of whether or not rejection is mediated by a depressed mood induction. An exploratory aspect of the study involved an inquiry into the potential role of interpersonal needs in the response to depressed individuals.
The study was twofold: in the first part, the stimulus consisted of a videotaped interaction between two trained actresses portraying a depressed woman and a non-depressed woman in the experimental condition, and two non-depressed women in the control condition. In the second part, the same interactions were described in written scenarios. Subjects were instructed to imagine themselves as the non-depressed person interacting with the target person, as either strangers or best friends. Thus, the study consisted of two parallel 2X2 designs.
Subjects completed the Multiple Affect Adjective Checklist, the Wessman-Ricks Depression-Elation Scale, and the Mehrabian-Russell Semantic Differential at pretest and posttest to measure mood induction. Need for nurturance and need for autonomy were measured at pretest with the Interpersonal Adjective Scale, the Jackson Personality Research Form and the Campbell Need Scale. Posttest acceptance-rejection measures included a modified version of the Opinion Scale and the Impact Message Inventory.
Results indicated that interactions with depressed individuals elicit a diffuse negative mood, more so in the context of relationships between friends, in the case of the written scenarios method. Depressed targets were also more rejected than non-depressed targets, but contrary to predictions intimacy decreased the degree of rejection.
Rejection was not differentiated into the two concepts of compliance and initiation; however, results pointed to two distinct aspects of rejection - a behavioral aspect and a perceptual one. Mood induction appeared to be related only to the perceptual aspect of rejection, and not to the more salient behavioral one. The contribution of interpersonal needs to rejection appears equivocal; if indeed needs play a role in the mediation of rejection, need for nurturance seems to be more involved than need for autonomy.
Although no Method effects were predicted, levels of intimacy were apparently not successfully reproduced in the videotaped stimuli. The two methods at times yielded different results, and further research will clarify their respective external validity.
In light of the results of the present study, Coyne's model was in part supported but appears to be in need of serious revisions concerning the mediation of rejection and the effect of intimacy on rejection.Arts, Faculty of
Psychology, Department of
Graduate
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Pokhrel, Usmita. "Role of Mixing of Two Bacteria on Compressive Strength, Water Absorption and Microstructure of Mortar Cubes." Thesis, North Dakota State University, 2019. https://hdl.handle.net/10365/31691.
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Major/minor cracks is inevitable in concrete because of its lower tensile strength and different load and non-load factors. Addition of bacteria in mortar is an emerging concept. Despite the fact that the live cells has proven to be beneficial towards enhancement of several concrete properties, the trend of increment in the compressive strength has not been significant with addition of single bacteria. This study introduces a new approach of mixing two bacteria: B Subtilus and B Megaterium, and investigating the role of the microbes on compressive strength, water absorption and SEM analysis. The results demonstrated an increment of compressive strength by 18.09 % when two bacteria’s were mixed. Also, cubes with B Megaterium absorbed 17.03% less water than normal cubes. This new method of mixing bacteria can potentially solve major/minor concrete cracking issues, could be economical in the long run, and is an environment friendly approach.
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Huth, Anne M. Kramer. "Geochemical and isotopic mixing models : two case studies in a snow-dominated and semi-arid environment." Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/191260.
Full textAbstract:
The influence of climate and antecedent moisture conditions on hydrological and biogeochemical fluxes was studied and contrasted in three nested, high-elevation, snowmelt-dominated catchments in the Sierra Nevada, California and one basin-floor, semi-arid catchment in southeastern Arizona. Investigations were completed within a different two-year period at each site, with the second year being climatically different (typically drier) than the first. Spring snowmelt, widespread winter frontal precipitation, and episodic summer rains induce surface water flow in these catchments, though the timing and magnitude of nutrient redistribution among soil and stream compartments varies in each. Surface water flow from spring snowmelt in high-elevation catchments travels through the subsurface or across the surface as direct runoff A more typical process producing surface water flow in semi-arid catchments is flooding during episodic or widespread rainfall. Hydrograph separations at Emerald Lake, Topaz Lake and Marble Fork catchments in Sequoia National Park, California, revealed that the majority of snowmelt flowed through soil before entering the stream in both average and highsnow years. The Emerald Lake watershed had a higher fraction of old water in its outflow in the average accumulation year because of the previous year's high accumulation and longer melt season. A mixing model analysis performed of the upper San Pedro River, Arizona, for wet and dry years showed that summer flood hydrographs were composed mainly of precipitation and surface runoff in both years, though a higher soil-water input occurred in the wetter year and in early season floods in the dry year. Stream and soil water nitrate concentrations were higher during floods in the dry year. Early season floods in the dry year exhibited more variability in stream water nitrate and sulfate, whereas late season flood concentrations reflected a well-mixed system and therefore less variation of these species during flood hydrographs. These data showed that periods of below average precipitation preceding major runoff periods result both in less soil water and solute export during summer floods in basin-floor catchments and less direct snowmelt in high-elevation catchments. Hydrologic and solute export in each catchment, despite their differing geographical locations, responds in similar ways to climate variability.
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Sparks, Sara A. "Two phase mixing comparison, oil contamination comparison and manufacturing accuracy effect on calibration of slotted orifice meter." Thesis, Texas A&M University, 2004. http://hdl.handle.net/1969.1/1088.
Full textAbstract:
In previous studies the slotted orifice plate has demonstrated superior performance characteristics to those of the standard orifice plate. In this study, these comparisons are investigated further. The response characteristics of the slotted orifice plate to the standard orifice plate and V-Cone for two-phase flows of water and air at various qualities, flow rates, and pressures are shown visually. The effect of oil as it flows through a slotted orifice plate and standard orifice plate are visually documented. The effect of manufacturing accuracy on the slotted orifice plates is investigated as to the effect on the coefficient of discharge, percent change in pressure, and Reynolds number. The slotted orifice plate mixes two-phase flow better than the standard orifice plate and V-Cone. There is a manufacturing effect on the slotted orifice plates; the larger the area of the slots, the larger the discharge coefficient.
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Sparks, Sara A. "Two phase mixing comparison, oil contamination comparison and manufacturing accuracy effect on calibration of slotted orifice meters." Texas A&M University, 2004. http://hdl.handle.net/1969.1/1088.
Full textAbstract:
In previous studies the slotted orifice plate has demonstrated superior performance characteristics to those of the standard orifice plate. In this study, these comparisons are investigated further. The response characteristics of the slotted orifice plate to the standard orifice plate and V-Cone for two-phase flows of water and air at various qualities, flow rates, and pressures are shown visually. The effect of oil as it flows through a slotted orifice plate and standard orifice plate are visually documented. The effect of manufacturing accuracy on the slotted orifice plates is investigated as to the effect on the coefficient of discharge, percent change in pressure, and Reynolds number. The slotted orifice plate mixes two-phase flow better than the standard orifice plate and V-Cone. There is a manufacturing effect on the slotted orifice plates; the larger the area of the slots, the larger the discharge coefficient.
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Shaw, Duncan Andrew. "The effect of suspended sediment concentration on the mixing of neutrally buoyant aqueous phase tracers in open channel flows." Thesis, University of Sheffield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340129.
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Ibrahim, Rita M. "Effect of Two Breeds and Two Dietary Concentrate Levels on Feedlot Performance, Carcass Merit, Tenderness parameters and fatty Acid Profiles." Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/196131.
Full textAbstract:
The objectives of this study were to investigate the different characteristics of the newly introduced breed, Waguli (Wagyu x Tuli) when comparing it with the Brahman breed. Twenty-four animals were used. Six steers of each breed were fed 94% concentrate diet (94C) and the other six were fed 86% concentrate diet (86C). Eight steers, two from each group, each were harvested at 128 days, 142 days, and 156 days on feed. Feedlot performance data indicated that Waguli steers were highly efficient (P < 0.05) and gained more than Brahman steers on a daily basis (P < 0.05). Carcass characteristic data showed that Waguli steers have larger ribeye area with more 12th rib fat thickness, marbling score and higher quality grade (P < 0.05). It is well known that Wagyu is a highly marbled and tender Japanese breed. It was found that the reason for the Waguli tenderness and low shear force values to be the low level of calpastatin activity (P < 0.05), the inhibitor of the postmortem proteolytic enzyme-calpain. While the toughness of the Brahman meat was due to the high level of calpastatin activity. The calpain activity did not differ between the two breeds. Shear force values agreed with the calpain and calpastatin activities data, in which the Waguli steaks showed less shear force values at day 7 and 10 postmortem than the Brahman steaks (P < 0.05). However, at day 14 postmortem there was no difference in shear force values between the two breeds (P < 0.05). Fatty acid data analysis indicated that Waguli steers had a profile with less saturated fatty acids (SFA) and more unsaturated fatty acids (UFA) content than those in Brahman steers fat. Looking at the ratio of unsaturated fatty acids (UFA) to saturated fatty acids (SFA), it is observed that Waguli steers had a greater ratio than Brahman steers. In conclusion, Waguli steers produce tender meat with good marbling ability, which likely to satisfy the consumers demand. In addition, they have a desirable average daily gain and feed efficiency with high polyunsaturated fatty acids comparatively with Brahman steers.
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Lowe, Leroy. "Improving student's intrinsic motivation levels in a two year college international business diploma program." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0019/MQ56789.pdf.
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