Tesi sul tema "Expansion phase"
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1
Harmon, Connor. "Tucson Streetcar Phase Two Expansion". The University of Arizona, 2016. http://hdl.handle.net/10150/608579.
Abstract (sommario):
Sustainable Built Environments Senior Capstone ProjectIn a society growing towards alternative modes of transportation, this study explores the phase 2 streetcar expansion for the Tucson area. Using case studies and research articles, a criteria of factors were created to best judge three predetermined expansion routes. A case study was then done on these routes to determine which route would be best for the area. In this study, the factors that were looked at and used to rank the three routes included; population density and average annual income of the surrounding area of the route (400 meter buffer), accessibility and connectivity, which includes; bus stops, bike lanes, walkability, traffic counts and possible park & ride development. The last factor used in the case study was proximity to destination, specifically how many ‘big destinations’ (destinations that experience high volumes of people) each route had. The proximity to destination factor also determined how good of a balance each route had with housing, work and amenities/leisure destinations.
2
Winder, Daniel. "Investigating phase transitions using the linear delta expansion". Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246678.
3
Hwang, Moonkyu. "Numerical modeling of the expansion phase of vapor explosions". Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/16761.
4
Abou-Koura, G. H. "Studies of the expansion phase of a laser plasma". Thesis, Swansea University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.635840.
Abstract (sommario):
This thesis describes a theoretical investigation of the expansion phase of a laser-produced plasma. The flow of ions and electrons in the expansion phase was modelled as a "displaced Maxwellian velocity distribution" i.e. the particles were assumed to possess a Maxwellian distribution of velocities relative to an average velocity of mass motion along the whole of the flight path. Using this model equations have been set up to describe the decrease in the electron and ion temperatures and the average charge carried by the ions as the expansion proceeds. This set of non-linear equations describing the flow of particles has been solved numerically using a Runge-Kutta method. A major process in the plasma expansion is three-body recombination and its strong influence on the nature of the plasma flow has been confirmed in this work. Three-body recombination influences the plasma flow by (i) reducing the average charge state of the plasma ions when electrons are captured by ions and (ii) releasing the excess energy of recombination to the plasma electrons. The influence of these two effects is clearly demonstrated by the numerical results. For example, in the absence of three-body recombination from the calculations the decrease of the electron and ion temperatures with time t follow a t-2 law, whereas, in the presence of three-body recombination the electron temperature is found to follow a law that is close to t-1. The average charge state of the plasma ions has also been calculated during the expansion and was found to decrease with time at a rate which depended on the particle concentration in the initial plasma, decreasing more rapidly as the initial concentration increased. Results are presented for both carbon and gold plasmas. The calculations made also provide a means of studying the influence of three-body recombination on the form of the ion signals that would be produced at the output of a mass spectrometer type of instrument after the ions had travelled along a long flight path. These ion signals are then used to create ion velocity distributions for each type of ion present at the entrance aperture of the mass spectrometer. The use of this type of information as a diagnostic tool in studies of the initial plasma conditions is discussed.
5
Yusoff, Nazrul Hizam. "Stratifying of liquid-liquid two phase flows through sudden expansion". Thesis, University of Nottingham, 2012. http://eprints.nottingham.ac.uk/12939/.
Abstract (sommario):
The transport and separation of oil and water is an essential process to the oil and chemical industries. Although transporting the mixtures is often necessary due to few reasons, it is generally beneficial to separate out the phases in order to reduce installation and maintenance costs, at the same time, avoiding safety problems. Thus, separation of liquid-liquid flows is a necessary part of many industrial processes. Hence, knowledge of two-phase flow dynamics is important for the design optimisation of separators. Therefore, the aim of this research is to investigate the feasibility of a sudden pipe expansion to be used as phase separator because it compact in design and capable for converting dispersed flow to stratified flow. In the test section, spatial distribution of the liquid-liquid phases in a dynamics flow system was visualised for the first time for by means of capacitance Wire Mesh Sensor (CapWMS), providing instantaneous information about the interface shapes, waves and phase layer evolution of oil-water flow. Visual assessment and analysis of the WMS data showed three distinct layers: an oil layer at the pipe top; a water layer at the pipe bottom and a mixed layer between them. The interfaces that form between the separated phases (oil or water) and the mixed layer were classified as oil interface or water interface. Results showed interface shapes were initially concave or convex near to the inlet of the test section and became flat further downstream the expansion, especially for water interfaces. There were no waves observed for horizontal and downward pipe orientations at all flow conditions and axial position downstream of the expansion. As for the upward inclined pipe orientation, waves were found, and they formed at position close to the inlet at all input oil volume fraction except at 0.2 OVF. The amplitude of the waves was: ~ 0.29D for 0.8 OVF; ~ 0.22D for 0.6 OVF and ~ 0.26D for 0.4 OVF. The higher the input oil volume fraction, the larger the waves become. In conclusion, the WMS results demonstrated that spatial distributions are strongly dependent on the mixture velocity, input oil fraction and inclination angles for the far position. In this present work, droplets were found to be larger near the interface. Drops were large nearer to the interface at the near position (10D) for all pipe orientations and throughout the test section for horizontal flow. The drops size decreased when the distance from the interface increased for these pipe configurations. As for the furthest position from the expansion for upward and downward inclined pipe orientation, larger droplets could also be seen at distance away from the interface and vice versa. The gravity or buoyant force is one of the contributing factors to the settling of the droplets. These forces are acting simultaneously on the droplets i.e. if the buoyant force which tends to spread the droplets throughout the pipe cross-section, is not large enough to overcome the settling tendency of gravity settling of the droplets occurs. Hence, the droplets that are non-uniformly scattered within the continuous phase begin to coalesce as they flow further downstream the pipe, producing larger drops. In addition, as the distance from expansion increased, the mixed layer becomes narrow and more drops begin to coalescence to form large drop due to increased droplet-droplet collision. Owing to these factors, results indicate that the mechanisms of coalescence occurred faster at the bottom, for water droplets and at the top, for oil droplets than the other locations in a pipe cross-section. For a better separation design, the coalescence process should occur at the aforementioned (bottom for water and top for oil) locations within the expansion pipe. However, at higher mixture velocities the mixed layer would be responsible for the smaller droplet size for horizontal and both inclinations of pipe orientation. The mixed layer dominated almost entirely in the pipe cross-section.
6
Zhang, Yan. "Weakly first-order phase transitions : [epsilon] expansion vs. numerical simulation /". Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/9715.
7
Gagliardi, Giuseppe [Verfasser]. "The QCD Phase Diagram from Strong Coupling Expansion / Giuseppe Gagliardi". Bielefeld : Universitätsbibliothek Bielefeld, 2020. http://d-nb.info/1211474089/34.
8
Kanu, Elizabeth. "Expansion driven Unstable Two Phase Flows in Long Risers and Wells". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-14420.
Abstract (sommario):
Flow instabilities in long wells and risers under certain flow conditions, is well known. Expansion driven flow instability (EDI) which is relatively little known, refers to occurrence of flow instabilities in long wells and risers as a result of entrapment of gas upstream of the well or riser base. EDI can also occur in gas-lift systems at low pressure and low gas injection rate.This work was initiated to tackle flow instability problem related to deep water production operations where long wells and risers are extensively in use. The aim of this thesis is to investigate a type of flow instability known as “Expansion Driven Flow Instability (EDI) in Long Wells and Risers”. This involves experimental investigation as well numerical modelling of expansion driven flow instability in long wells and risers. Finally results of the experimental investigations are compared with numerical model data.An experimental flow loop was setup to verify EDI at varying pipe geometry, inlet flow pressure and gas flow rate to examine the effect of EDI in long wells and risers. The laboratory experiment was conducted using air and water at atmospheric conditions, in a flowline-riser system consisting of a 32mm diameter and 9.12m long riser. The expansion driven flow cycle was captured in video recording.Variation of inlet flow pressures was achieved by varying the height of the overflow tank. Three cases were considered, each at a different inlet pressure. Each inlet pressure of the fluid was examined against varying inclination angles of the horizontal pipe to the riser inlet. Different gas flow rates were tested at different inclination angles. It was observed that inclination angle has the greatest impact on EDI.Experimental result of one of the cases was modelled using OLGA and the results of the experimental compared against simulation results output. Discrepancies in the two sets of results were observed in some cases. These may be attributed to simplifications and assumptions made during the simulation model build.Both results of the experimental investigation and numerical simulation demonstrated that expansion driven flow instability can occur in laboratory setup and can probably occur in deep water natural-lift wells and risers as well as gas-lifted wells and risers under certain flow conditions and pipe inclinations. 
9
Gutierrez, Emmanuel David Mercado. "Thermal expansion coefficient for a trapped Bose gas during phase transition". Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-27102016-102903/.
Abstract (sommario):
Ultra cold quantum gas is a convenient system to study fundamental questions of modern physics, such as phase transitions and critical phenomena. This master thesis is devoted to experimental investigation of the thermodynamics susceptibilities, such as the isothermal compressibility and the thermal expansion coefficient of a trapped Bose-Einstein condensate (BEC) of 87Rb atoms. The critical phenomena and the critical exponents across the transition can explain the behavior of the isothermal compressibility and the thermal expansion coefficient near the critical temperature TC. By employing the developed formalism of global thermodynamics variables, we carry out a statistical treatment of Bose gas in a 3D harmonic potential. After that, comparison of obtained results reveals the most appropriate state variables describing the system, namely volume and pressure parameter V and Π respectively. The both are related with the confining frequencies and BEC density distribution. We apply this approach to define the set of new thermodynamic variables of BEC, and also to construct the isobaric phase diagram V T. Its allows us to extract the compressibility κT and the thermal expansion coefficient βΠ. The behavior of the isothermal compressibility corresponds to the second-order phase transition, while the thermal expansion coefficient around the critical point behaves as β ∼ tr-α, where tr is reduced temperature of the system and α is the critical exponent on the basic of these. Results we have obtained the critical exponent α = 0.15±0.09, which allows us to determine the system dimensionality by means of the scaling theory, relating the critical exponents with the dimensionality. As a result, we found out that the dimensionality of the system to be d ∼ 3, one is in agreement with the real dimension of the system.Amostras atômicas ultrafrias de um gás de Bose são convenientes para estudar questões fundamentais da física moderna, como as transições de fase e fenômenos críticos em condensados de Bose-Einstein (BEC). A minha dissertação dedica se à investigação das susceptibilidades termodinâmicas como a compressibilidade isotérmica e o coeficiente de expansão térmica de a traves da transição de um BEC de 87Rb. Os fenômenos críticos e os exponentes críticos a traves da transição podem explicar o comportamento da compressibilidade isotérmica e do coeficiente de expansão térmica perto da temperatura crítica TC. Ao empregar o desenvolvido formalismo das variáveis termodinâmicas globais, levamos a cabo o tratamento estatístico de um gás de Bose num potencial harmônico 3D. Depois da comparação dos resultados obtidos, revelam as mais apropriadas variáveis de estado descrevendo o sistema, chamadas parâmetro de volume e pressão, V e Π respectivamente. As duas estão relacionadas com as frequências de confinamento e a distribuição de densidade do BEC. Nós aplicamos esta abordagem para definir um conjunto de novas variáveis termodinâmicas do BEC, e também para construir o diagrama de fase isobárico V T. O anterior nós permite extrair a compressibilidade κT e o coeficiente de expansão termina βΠ. O comportamento da compressibilidade isotérmica corresponde a uma transição de fase de segunda ordem enquanto que o coeficiente de expansão térmica ao redor do ponto crítico comporta se como β ∼ tr-α, onde tr é a temperatura reduzida do sistema, e α o exponente crítico. Deste resultado nós obtemos um exponente critico, α = 0.15 ± 0.09, que permite determinar a dimensionalidade do sistema a traves da teoria de escala, relacionando os exponentes críticos com a dimensionalidade. Como resultado, encontramos que a dimensionalidade do sistema é d ∼ 3 que está de acordo como a dimensão real do sistema.
10
Dolgusheva, E. B., e V. Yu Trubitsin. "Lattice Parameters and Thermal Expansion of Zirconium Thin Films". Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35222.
Abstract (sommario):
Using the molecular-dynamics method with many-body potential of interatomic interaction we have studied the polymorphism of zirconium thin films. The conditions for stability of metastable bcc(001) and fcc Zr films are determined at constant zero pressure. The dependences of the lattice parameters and thermal expansion coefficients on the temperature and thickness of bcc, fcc and hcp Zr films are calculated. The peculiarities of their variation near structural transformations are discussed.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35222
11
Pan, Ruijun. "Energy density and volume expansion in solid-liquid phase change, for energy applications". Thesis, KTH, Kraft- och värmeteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-128949.
Abstract (sommario):
Phase change materials (PCMs) have long been studied as thermal energy storage media. However, the Swedish company, Exencotech AB, reaching beyond this usual scope of PCMs, has designed a system that uses PCMs as working medium to produce electricity from waste heat. To achieve high system energy efficiency, PCMs with low heats of fusion and large volume expansions are favored. Interestingly, this is the opposite of the desired properties of a PCM working in energy storage applications. This work has aimed to find suitable alternative PCMs for Exencotech. After an intensive literature survey, eight candidates are identified from several PCM types. They are subjected to T-history test and volume expansion test in order to map out their volume expansion density chart. After analyzing the results from the tests, four most promising candidates with different melting temperatures, A, B, C, D, are finally proposed. The results of the work show that A has the highest volume expansion density which is 0.97 cm 3/kJ. It is the most promising candidate found out of the many that were considered, that gives the highest energy efficiency for Exencotech, if they are able to find a suitable heat source and a heat sink. (In order to keep some information confidential to the general public, certain names and values are coded in this report)
12
Rose, Kyle. "Synthesis, Phase Development, and the Mechanism for Negative Thermal Expansion in Aluminum Tungstate". Thesis, University of North Texas, 2020. https://digital.library.unt.edu/ark:/67531/metadc1703275/.
Abstract (sommario):
An in-depth study of Al2W3O12 negative thermal expansion (NTE) ceramic was performed, focused on synthesis, phase mappings, and the underlying mechanisms shown to be responsible for NTE. Review of the literature has shown inconsistencies in reported values of the dilatometry measured coefficients of thermal expansion, and the temperature for the known monoclinic to orthorhombic phase transition. Two synthesis techniques are introduced: an ionic-liquid non-hydrolytic sol-gel synthesis route; and a low temperature solid state reaction synthesis for Al2W3O12. X-ray diffraction, Raman spectroscopy, and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) were used to verify the techniques. Two differential scanning calorimetry (DSC) experiments (high and low temperature) were performed on the material showing the transition between -5 and -20 °C and no other phase changes until a reported degradation above 1100 °C. Extensive dilatometry on the material led to the discovery of elastic transitions occurring in the polycrystalline sample capable of explaining the inconsistencies in reported dilatometry results. This is further developed into a proposed model defining the regions between these transitions. Each region has a different thermal expansion as well as a direct effect on the reaction of the material upon cooling. This proposed model may allow more consistent reporting of dilatometry results for NTE materials. Raman spectroscopy was performed from 25-725 °C on the material showing both a joining in the tungsten-oxygen bending modes as well as a broadening in the tungsten-oxygen stretching modes. This is consistent with Al-O-W angle changes along the same temperature range reported in literature as well as the transverse vibrational modes responsible for NTE.
13
Pueschel, Charles A. "First principles approach to understanding stability and phase transitions of metal A(II)B(IV)hexafluorides". Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54484.
14
Brown, Wayne. "Characterisation of low energy ions observed near and during the substorm expansion phase onset". Thesis, University of Warwick, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302621.
15
Joshi, Darshan Gajanan. "Magnetic quantum phase transitions: 1/d expansion, bond-operator theory, and coupled-dimer magnets". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-198634.
Abstract (sommario):
In the study of strongly interacting condensed-matter systems controlled microscopic theories hold a key position. Spin-wave theory, large-N expansion, and $epsilon$-expansion are some of the few successful cornerstones. In this doctoral thesis work, we have developed a novel large-$d$ expansion method, $d$ being the spatial dimension, to study model Hamiltonians hosting a quantum phase transition between a paramagnet and a magnetically ordered phase. A highlight of this technique is that it can consistently describe the entire phase diagram of the above mentioned models, including the quantum critical point. Note that most analytical techniques either efficiently describe only one of the phases or suffer from divergences near the critical point. The idea of large-$d$ formalism is that in this limit, non-local fluctuations become unimportant and that a suitable product state delivers exact expectation values for local observables, with corrections being suppressed in powers of $1/d$. It turns out that, due to momentum summation properties of the interaction structure factor, all diagrams are suppressed in powers of $1/d$ leading to an analytic expansion. We have demonstrated this method in two important systems namely, the coupled-dimer magnets and the transverse-field Ising model.
Coupled-dimer magnets are Heisenberg spin systems with two spins, coupled by intra-dimer antiferromagnetic interaction, per crystallographic unit cell (dimer). In turn, spins from neighboring dimers interact via some inter-dimer interaction. A quantum paramagnet is realized for a dominant intra-dimer interaction, while a magnetically ordered phase exists for a dominant (or of the same order as intra-dimer interaction) inter-dimer interaction. These two phases are connected by a quantum phase transition, which is in the Heisenberg O(3) universality class. Microscopic analytical theories to study such systems have been restricted to either only one of the phases or involve uncontrolled approximations. Using a non-linear bond-operator theory for spins with S=$1/2$, we have calculated the $1/d$ expansion of static and dynamic observables for coupled dimers on a hypercubic lattice at zero temperature. Analyticity of the $1/d$ expansion, even at the critical point, is ensured by correctly identifying suitable observables using the mean-field critical exponents. This method yields gapless excitation modes in the continuous symmetry broken phase, as required by Goldstone\'s theorem. In appropriate limits, our results match with perturbation expansion in small ratio of inter-dimer and intra-dimer coupling, performed using continuous unitary transformations, as well as the spin-wave theory for spin-$1/2$ in arbitrary dimensions. We also discuss the Brueckner approach, which relies on small quasiparticle density, and derive the same $1/d$ expansion for the dispersion relation in the disordered phase. Another success of our work is in describing the amplitude (Higgs) mode in coupled-dimer magnets. Our novel method establishes the popular bond-operator theory as a controlled approach.
In $d=2$, the results from our calculations are in qualitative agreement with the quantum Monte Carlo study of the square-lattice bilayer Heisenberg AF spin-$1/2$ model. In particular, our results are useful to identify the amplitude (Higgs) mode in the QMC data.
The ideas of large-$d$ are also successfully applied to the transverse-field Ising model on a hypercubic lattice. Similar to bond operators, we have introduced auxiliary Bosonsic operators to set up our method in this case.
We have also discussed briefly the bilayer Kitaev model, constructed by antiferromagnetically coupling two layers of the Kitaev model on a honeycomb lattice. In this case, we investigate the dimer quantum paramagnetic phase, realized in the strong inter-layer coupling limit. Using bond-operator theory, we calculate the mode dispersion in this phase, within the harmonic approximation. We also conjecture a zero-temperature phase diagram for this model.
16
Shaw, Leah Belinda. "Monte Carlo and Series Expansion Studies of the Anisotropic Driven Ising Lattice Gas Phase Diagram". Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/31851.
Abstract (sommario):
While the statistical mechanics of systems in thermal equilibrium is a well established discipline, nonequilibrium systems are fundamentally much less well understood, even though most natural phenomena fall into the
latter category. In particular, there is as yet no nonequilibrium analog
for the systematic formalism of Gibbs ensembles. Rather than deal with the
difficult problem of general nonequilibrium systems, this study is
restricted to the steady states of a simple model whose equilibrium
properties are well known.
The Ising lattice gas displays a number of surprising phenomena when driven into nonequilibrium steady states. This study extends previous work to a more general model with anisotropic interparticle interactions. Using Monte Carlo simulations, we obtain the phase diagram for the model, controlled by the driving field, temperature, and anisotropy parameter a. Under saturation drive, the shift in the transition temperature between ordered and disordered states can be either positive or negative, depending on a. The possible existence at large a of an additional phase ordered in only one direction is discussed. For finite drives, both first and second order transitions are observed. A novel technique for locating the first order transition line is presented.
Some aspects of the phase diagram can be predicted by investigating the
two-point correlation function to first order in a high temperature series
expansion. However, the series expansion fails to predict even
qualitatively the a-dependence of the critical temperature.
Master of Science
17
Liu, Zhi. "Transition Metal Nitrides and Their Solid Solutions: A First-Principles Approach with Cluster Expansion Computational Predictive Models". University of Toledo / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1492525178190092.
18
Youssef, Walid Mohamed Khalil Abdalla. "Experimental and computational study of indirect expansion solar assisted heat pump system with latent heat storage for domestic hot water production". Thesis, Brunel University, 2017. http://bura.brunel.ac.uk/handle/2438/15263.
Abstract (sommario):
Solar assisted heat pump (SAHP) systems have been widely applied in domestic hot water (DHW) production due to their sustainability and stability in operations. However, their performance efficiency requires further improvement using advanced technologies such as energy storage with phase change materials (PCM) and optimal system controls. Undoubtedly, employing PCMs for latent heat storage (LHS) application has a great potential to improve a solar thermal application performance. Despite this fact, the use of PCM in this area is quite limited due to the poor thermal conductivity of available PCMs. Therefore, heat transfer enhancement is one of the essential strategies that can overcome this obstacle. Accordingly, a test rig of a new indirect expansion solar assisted heat pump (IDX-SAHP) system has been designed, built and instrumented. The system can handle heating capacity up to 9 kW. The IDX-SAHP system consists of three operational loops: solar thermal, solar-air assisted heat pump and load profile. A 2 kW PCM heat exchanger (HX) was purposely designed and installed in the system solar thermal loop to store solar energy, when applicable, and release heat when required by the heat pump. The PCM HX is employed with a novel heat transfer enhancement method. The maximum coefficient of performance (COP) of the IDX-SHAP system reached 4.99 during the sunny day with the PCM (HX) integration. However, the maximum energy saving was achieved during the cloudy day with the PCM HX integration. Moreover, the proposed heat transfer enhancement method has been modelled through CFD package and validated with the experimental results. This allows a clear understanding of the reasons for the longer discharging process compared with the charging process. Furthermore, the inlet flow rate and temperature variation of the PCM HX was simulated during charging and discharging processes. The optimum inlet flow rate for this application was found at 0.1 kg/s while the optimum inlet temperature was found at 40°C. Meanwhile, the whole system was modelled by the coupling of TRNSYS, EES and CFD to investigate the potential and advantages of using the system in locations with rich solar intensity such as Cairo and Madrid. The simulation shows that the solar thermal operation loop was called more frequently in these locations. This had a significant impact on the system energy consumption, especially during winter. The maximum COP and solar performance factor (SPF) of the modelled system were 5.3 and 0.83 respectively.
19
Hartig, Maximilian [Verfasser], e T. [Akademischer Betreuer] Schulenberg. "Numerical Simulation of Fluid-Structure Interaction during the Expansion Phase in Sodium Cooled Fast Reactors / Maximilian Hartig ; Betreuer: T. Schulenberg". Karlsruhe : KIT-Bibliothek, 2019. http://d-nb.info/120047130X/34.
20
Cronin, Joseph M. "Exploring Capabilities of Electrical Capacitance Tomography Sensor & Velocity Analysis of Two-Phase R-134a Flow Through a Sudden Expansion". University of Dayton / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1495541577975687.
21
Quinteros, Milton I. "Trellis Coded Modulation Schemes Using A New Expanded 16-Dimensional Constant Envelope Quadrature-Quadrature Phase Shift Keying Constellation". ScholarWorks@UNO, 2009. http://scholarworks.uno.edu/td/924.
Abstract (sommario):
In this thesis, the author presents and analyzes two 4-dimensional Constant Envelope Quadrature-Quadrature Phase Shift Keying constellations. Optimal demodulators for the two constellations are presented, and one of them was designed and implemented by the author. In addition, a novel expanded 16-dimensional CEQ2PSK constellation that doubles the number of points without decreasing the distance between points or increasing the peak energy is generated by concatenating the aforementioned constellations with a particular method and restrictions. This original 16-dimensional set of symbols is set-partitioned and used in a multidimensional Trellis-Coded Modulation scheme along with a convolutional encoder of rate 2/3. Effective gain of 2.67 dB over uncoded CEQ2PSK constellation with low complexity is achieved theoretically. A coding gain of 2.4 dB with 8 dB SNR is obtained by using Monte Carlo simulations. The TCM systems and demodulators were tested under an Additive White Gaussian Noise channel by using Matlab's Simulink block diagrams.
22
Berg, Adrianus J. J. van den [Verfasser], e Heinrich [Akademischer Betreuer] Leonhardt. "Influence of cell-cycle phase in hematopoietic stem cell lineage production and expansion / Adrianus J. J. van den Berg ; Betreuer: Heinrich Leonhardt". München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2014. http://d-nb.info/1120923603/34.
23
Baptista, Gualter Barbas. "Bridging environmental conflicts with social metabolism : forestry expansion and socioeconomic change". Doctoral thesis, FCT - UNL, 2010. http://hdl.handle.net/10362/5891.
Abstract (sommario):
Dissertação apresentada para obtenção do Grau de Doutor em Ciências do Ambiente, pela Universidade Nova de Lisboa, Faculdade de Ciências e TecnologiaEnvironmental conflicts have traditionally been approached from several scientific fields. However, the different theoretical and empirical developments have proceeded in parallel, with often competing descriptive languages. Furthermore, they tend to focus on resolution, while neglecting the role of conflicts as an expression of groups facing social and ecological injustices perpetrated by the hegemony. This research attempted to build a politically useful understanding of why and how environmental conflicts appear, through interdisciplinary bridging and the avoidance of the post-political hegemony. By focusing on an ex-post historical analysis of the conflicts against eucalyptus plantations in Portugal in the late 1980s, it attempted to identify patterns and dynamics that relate to conflicts. Theories were anchored along the concepts of social metabolism and, more particularly, the framework of multiple scale integrated assessment of societal and ecological metabolism (MuSIASEM). An adaptation of MuSIASEM for conflict analysis was iteratively developed with the empirical analysis of the political ecology of the case study. During the pre-analytical phase, an open information space is developed, comprising environmental conflicts literature, as well as the environmental history and institutional analysis of the case study. The information space is subjected to successive compressions before reaching a relevant structure of the problem. A storyteller is defined according to the relative power imbalances of the conflict situation. Theoretical pathways are created to serve as auxiliaries for the formalization process and for structuring the analysis. The analysis process navigates through the formalizations within each theoretical pathway. Impredicative loop analysis (ILA) is used to expose tensions and constraints generated by emerging hypercycles or clashing metabolic profiles. Finally, the results are subjected to a dialectical discussion, allowing the communication between different pathways. Dialectical discussion along the pathways is particularly useful for promoting interdisciplinary dialogue. The political ecology analysis of the case study has revealed that the higher intensity of conflicts in the late 1980s was due to a series of factors. The immediate cause was resource xii scarcity, which led to a speculative race for lands that included land grabbing strategies. The growing environmental movement in Portugal has provided the rural and peasant identities (the storytellers), with new languages that empowered their struggles. Institutional changes contributed to conflicts attenuation in the 1990s. However, a growing global consumption of paper continues to push the frontiers of industrial forestry around the world. Latin America and Eastern Europe have increased their peripheral position in the world-system of the paper industry, as suppliers of cheap pulp and land for fast-growth tree plantations. Packaging, as a main end-use of paper, can be used to hide from the consumer the impacts of production. This end-use of paper might intensify unequal ecological exchange in different areas and commodities, while being reinforced by it. In this context, conflicts might lead to a relocation of impacts, leaving the hegemony untouched.
24
Nilsson, Linnéa, Peter Enhörning e Christoffer Lindgren. "Thoughts and reasoning in family businesses : Founders thoughts and reasoning behind decisionsduring the expansion phase in a first generation family business with few owners". Thesis, Linnéuniversitetet, Ekonomihögskolan, ELNU, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-20364.
Abstract (sommario):
This thesis focuses on the decision making in the most common business form: family businesses. A well-established theoretical model within the family business field is The three circle-model, which is based on three different dimensions: family, ownership and business. Most of the family businesses stay small but the ones expanding face the dilemma of balancing the best development of the dimensions. However, these three dimensions can contradict each other and as a result the founders are forced to choose which of the dimensions to prioritize when taking decisions.The purpose of this thesis is to create an understanding of how the family, the ownership and the business dimensions affect founders thoughts and reasoning behind decisions in the expansion phase in first generation family firms with few owners.We have reached the conclusions with a qualitative approach using case studies. We have gathered the empirical data by using Life story and Critical incident to define expansion decisions in two companies. Furthermore we used semi-structured interviews with the aim of creating an understanding of the founders thoughts and reasoning behind the taken decisions.Our conclusion shows that business opportunities and the objective to remain in control of the family business highly influence the decision making during the expansion phase. Another conclusion is that the family has been affected far more by the decisions than it has had an impact on the decisions. The thesis gives insight about an area within the family business field, which previously has been neglected by researchers.
25
Perchet, Guillaume. "Analyse des erreurs de phase introduites par l'électronique de réception d'un télémètre laser par déphasage : expansion du déphasage permettant la mesure à haute résolution". Toulouse, INPT, 1997. http://www.theses.fr/1997INPT074H.
Abstract (sommario):
Cette these prend en compte les conditions de realisations d'une electronique de reception d'un telemetre laser par mesure du dephasage a haute resolution et a grande dynamique. La premiere partie porte sur la modelisation des sources d'erreur du dephasage en fonction de l'amplitude du signal photoelectrique et de la stabilite en frequence des oscillateurs. On modelise le circuit differentiel a emetteurs couples en haute frequence et a forts niveaux avec degenerescence sur les emetteurs. L'analyse est appliquee aux circuits ecreteurs, aux amplificateurs a gain controle, puis aux circuits melangeurs. On definit les conditions pour que l'erreur du dephasage soit inferieure a 0. 1 a la frequence de 16. 66mhz. En particulier, on propose une compensation harmonique permettant de recuperer en sortie du circuit melangeur, toutes les composantes du signal ecrete a une frequence beaucoup plus basse, alors que la technique heterodyne classique ne conserve que le fondamental du signal d'entree. Afin d'eviter des erreurs de phase liees aux derives en frequence des oscillateurs, un circuit stabilisateur est propose, a base d'une boucle a verrouillage de phase et d'un asservissement thermique des oscillateurs a quartz. Enfin, on demontre ici la faisabilite d'un circuit expanseur de phase, permettant de multiplier la difference de phase entre le signal photoelectrique et la reference par un entier connu. Ce circuit, derive des synthetiseurs de frequence permet d'obtenir de tres hautes resolutions dans la mesure de distance. Des ecarts temporels de l'ordre de la pico seconde deviennent alors mesurables a la frequence de 16. 66mhz. Les sources d'erreurs sont qualifiees et des techniques permettant l'amelioration de la resolution sont proposees. L'ensemble de l'etude aboutit a la conception globale d'une electronique de reception du telemetre, permettant la mesure sur une grande plage de distance et avec une grande resolution.
26
Yamada, Ryo. "Application of Steepest-Entropy-Ascent Quantum Thermodynamics to Solid-State Phenomena". Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/85866.
Abstract (sommario):
Steepest-entropy-ascent quantum thermodynamics (SEAQT) is a mathematical and theoretical framework for intrinsic quantum thermodynamics (IQT), a unified theory of quantum mechanics and thermodynamics. In the theoretical framework, entropy is viewed as a measure of energy load sharing among available energy eigenlevels, and a unique relaxation path of a system from an initial non-equilibrium state to a stable equilibrium is determined from the greatest entropy generation viewpoint. The SEAQT modeling has seen a great development recently. However, the applications have mainly focused on gas phases, where a simple energy eigenstructure (a set of energy eigenlevels) can be constructed from appropriate quantum models by assuming that gas-particles behave independently. The focus of this research is to extend the applicability to solid phases, where interactions between constituent particles play a definitive role in their properties so that an energy eigenstructure becomes quite complicated and intractable from quantum models. To cope with the problem, a highly simplified energy eigenstructure (so-called ``pseudo-eigenstructure") of a condensed matter is constructed using a reduced-order method, where quantum models are replaced by typical solid-state models. The details of the approach are given and the method is applied to make kinetic predictions in various solid-state phenomena: the thermal expansion of silver, the magnetization of iron, and the continuous/discontinuous phase separation and ordering in binary alloys where a pseudo-eigenstructure is constructed using atomic/spin coupled oscillators or a mean-field approximation. In each application, the reliability of the approach is confirmed and the time-evolution processes are tracked from different initial states under varying conditions (including interactions with a heat reservoir and external magnetic field) using the SEAQT equation of motion derived for each specific application. Specifically, the SEAQT framework with a pseudo-eigenstructure successfully predicts: (i) lattice relaxations in any temperature range while accounting explicitly for anharmonic effects, (ii) low-temperature spin relaxations with fundamental descriptions of non-equilibrium temperature and magnetic field strength, and (iii) continuous and discontinuous mechanisms as well as concurrent ordering and phase separation mechanisms during the decomposition of solid-solutions.Ph. D.
Many engineering materials have physical and chemical properties that change with time. The tendency of materials to change is quantified by the field of thermodynamics. The first and second laws of thermodynamics establish conditions under which a material has no tendency to change; these conditions are called equilibrium states. When a material is not in an equilibrium state, it is able to change spontaneously. Classical thermodynamics reliably identifies whether a material is susceptible to change, but it is incapable of predicting how change will take place or how fast it will occur. These are kinetic questions that fall outside the purview of thermodynamics. A relatively new theoretical treatment developed by Hatsopoulos, Gyftopoulos, Beretta and others over the past forty years extends classical thermodynamics into the kinetic realm. This framework, called steepest-entropy-ascent quantum thermodynamics (SEAQT), combines the tools of thermodynamics with quantum mechanics through a postulated equation of motion. Solving the equation of motion provides a kinetic description of the path a material will take as it changes from a non-equilibrium state to stable equilibrium. To date, the SEAQT framework has been applied primarily to systems of gases. In this dissertation, solid-state models are employed to extend the SEAQT approach to solid materials. The SEAQT framework is used to predict the thermal expansion of silver, the magnetization of iron, and the kinetics of atomic clustering and ordering in binary solid-solutions as a function of time or temperature. The model makes it possible to predict a unique kinetic path from any arbitrary, non-equilibrium, initial state to a stable equilibrium state. In each application, the approach is tested against experimental data. In addition to reproducing the qualitative kinetic trends in the cases considered, the SEAQT framework shows promise for modeling the behavior of materials far from equilibrium.
27
Joshi, Darshan Gajanan [Verfasser], Matthias [Akademischer Betreuer] Vojta e Fabian [Akademischer Betreuer] Essler. "Magnetic quantum phase transitions: 1/d expansion, bond-operator theory, and coupled-dimer magnets / Darshan Gajanan Joshi. Betreuer: Matthias Vojta. Gutachter: Matthias Vojta ; Fabian Essler". Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://d-nb.info/1088185932/34.
28
Joshi, Darshan Gajanan [Verfasser], Matthias [Akademischer Betreuer] Vojta e Fabian H. L. [Akademischer Betreuer] Essler. "Magnetic quantum phase transitions: 1/d expansion, bond-operator theory, and coupled-dimer magnets / Darshan Gajanan Joshi. Betreuer: Matthias Vojta. Gutachter: Matthias Vojta ; Fabian Essler". Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-198634.
29
Roman, Abdeel J. "Studies of Horizontal Two-Phase Flow Using Electrical Capacitance Tomography and R-134a". University of Dayton / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1510840347116138.
30
Davis, Andrew Scott. "Temperature Induced Deflection of Yttria Stabilized Zirconia Membranes". The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1338369600.
31
Agarwal, Akhil. "Heat Transfer and Pressure Drop During Condensation of Refrigerants in Microchannels". Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/14129.
Abstract (sommario):
Two-phase flow, boiling, and condensation in microchannels have received considerable
attention in the recent past due to the growing interest in the high heat
fluxes made possible by these channels. This dissertation presents a study on
the condensation of refrigerant R134a in small hydraulic diameter (100 < Dh
< 160 mm) channels. A novel technique is used for the measurement
of local condensation heat transfer coefficients in small quality increments,
which has typically been found to be difficult due to the low heat transfer
rates at the small flow rates in these microchannels. This method is used to
accurately determine pressure drop and heat transfer coefficients for mass
fluxes between 300 and 800 kg/m2-s and quality 0 < x <
1 at four different saturation temperatures between 30 and 60oC. The
results obtained from this study capture the effect of variations in mass flux,
quality, saturation temperature, hydraulic diameter, and channel aspect ratio
on the observed pressure drop and heat transfer coefficients. Based on the available
flow regime maps, it was assumed that either the intermittent or annular flow
regimes prevail in these channels for the flow conditions under consideration.
Internally consistent pressure drop and heat transfer models are proposed
taking into account the effect of mass flux, quality, saturation temperature, hydraulic
diameter, and channel aspect ratio. The proposed models predict 95% and 94% of
the pressure drop and heat transfer data within ±25%, respectively. Both
pressure drop and heat transfer coefficient increase with a decrease in
hydraulic diameter, increase in channel aspect ratio and decrease in saturation
temperature. A new non-dimensional parameter termed Annular Flow Factor is also
introduced to quantify the predominance of intermittent or annular flow in the
channels as the geometric parameters and operating conditions change. This
study leads to a comprehensive understanding of condensation in microchannels
for use in high-flux heat transfer applications.
32
Chalfi, Toufik Yacine. "Pressure loss associated with flow area change in micro-channels". Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/24725.
33
He, Mi. "Caractérisation du comportement à rupture des alliages de zirconium de la gaine du crayon combustible des centrales nucléaires dans la phase post-trempe d'un APRP (Accident de Perte de Réfrigérant Primaire)". Phd thesis, Ecole Nationale Supérieure des Mines de Paris, 2012. http://pastel.archives-ouvertes.fr/pastel-00819279.
Abstract (sommario):
Dans le cadre des études visant à garantir l'intégrité de la gaine du crayon combustible, EDF est amené à caractériser la ductilité de la gaine après un Accident de Perte de Réfrigérant Primaire (APRP). La thèse porte sur la caractérisation du comportement à rupture des gaines en Zircaloy-4 détendu pour lesquels les conditions d'APRP ont été simulées en laboratoire par une oxydation à haute température suivie d'un refroidissement. L'oxydation est effectuée à 1100°C et à 1200°C pour différentes durées ce qui conduit à des niveaux d'oxydation de 3% à 30% d'ECR (Equivalent Cladding Reacted). Deux types de refroidissement sont mis en oeuvre : la trempe à l'eau et le refroidissement à l'air. Les gaines oxydées comportent deux couches fragiles, la couche de zircone externe ZrO2 et la couche α(O), et une couche présentant une ductilité résiduelle, la couche ex-β.Les gaines oxydées ont fait l'objet de caractérisations en microscope optique, par analyse à la microsonde et par nano-indentation. Une corrélation entre la teneur en oxygène et la nano-dureté et le module d'Young a été proposée.L'essai Expansion due à la Compression (EDC) a été développé avec une instrumentation par stéréo-corrélation d'images puis a été utilisé pour caractériser le comportement mécanique des gaines oxydées. Le comportement des gaines oxydées a été étudié à partir de l'analyse des courbes macroscopiques de l'essai EDC et à partir des observations des échantillons rompus ou pré-déformés.Un scénario de rupture des gaines oxydées a été proposé. Ce scénario a été validé d'une part par la réalisation d'essais sur gaines sablées ne comportant que la couche ex-β et d'autre part par la modélisation de l'essai par la méthode des éléments finis. Un critère de rupture des gaines oxydées a par ailleurs été établi. La modélisation du comportement et le critère de rupture proposés ont été validés par la modélisation des essais de compression d'anneau.
34
Guo, Longkai. "Numerical investigation of Taylor bubble and development of phase change model". Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI095.
Abstract (sommario):
Le mouvement d'une bulle d'azote de Taylor dans des solutions mixtes glycérol-eau s'élevant à travers différents types d'expansions et de contractions est étudié par une approche numérique. La procédure CFD est basée sur un solveur open-source Basilisk, qui adopte la méthode du volume de fluide (VOF) pour capturer l'interface gaz-liquide. Les résultats des expansions/contractions soudaines sont comparés aux résultats expérimentaux. Les résultats montrent que les simulations sont en bon accord avec les expériences. La vitesse de la bulle augmente dans les expansions soudaines et diminue dans les contractions soudaines. Le modèle de rupture des bulles est observé dans les expansions soudaines avec de grands taux d'expansion, et un modèle de blocage des bulles est observé dans les contractions soudaines avec de petits rapports de contraction. De plus, la contrainte de cisaillement de la paroi, l'épaisseur du film liquide et la pression dans les simulations sont étudiées pour comprendre l'hydrodynamique de la bulle de Taylor montant par expansions/contractions. Le processus transitoire de la bulle de Taylor passant par une expansion/contraction soudaine est ensuite analysé pour trois singularités différentes: graduelle, parabolique convexe et parabolique concave. Une caractéristique unique de la contraction concave parabolique est que la bulle de Taylor passe par la contraction même pour de petits rapports de contraction. De plus, un modèle de changement de phase est développé dans le solveur Basilisk. Afin d'utiliser la méthode VOF géométrique existante dans Basilisk, une méthode VOF géométrique générale en deux étapes est implémentée. Le flux de masse n'est pas calculé dans les cellules interfaciales mais transféré aux cellules voisines autour de l'interface. La condition aux limites de température saturée est imposée à l'interface par une méthode de cellule fantôme. Le modèle de changement de phase est validé par évaporation de gouttelettes avec un taux de transfert de masse constant, le problème de Stefan unidimensionnel, le problème d'aspiration de l'interface et un cas d'ébullition à film plan. Les résultats montrent un bon accord avec les solutions analytiques ou les corrélationsThe motion of a nitrogen Taylor bubble in glycerol-water mixed solutions rising through different types of expansions and contractions is investigated by a numerical approach. The CFD procedure is based on an open-source solver Basilisk, which adopts the volume-of-fluid (VOF) method to capture the gas-liquid interface. The results of sudden expansions/contractions are compared with experimental results. The results show that the simulations are in good agreement with experiments. The bubble velocity increases in sudden expansions and decreases in sudden contractions. The bubble break-up pattern is observed in sudden expansions with large expansion ratios, and a bubble blocking pattern is found in sudden contractions with small contraction ratios. In addition, the wall shear stress, the liquid film thickness, and pressure in the simulations are studied to understand the hydrodynamics of the Taylor bubble rising through expansions/contractions. The transient process of the Taylor bubble passing through sudden expansion/contraction is further analyzed for three different singularities: gradual, parabolic convex and parabolic concave. A unique feature in parabolic concave contraction is that the Taylor bubble passes through the contraction even for small contraction ratios. Moreover, a phase change model is developed in the Basilisk solver. In order to use the existed geometric VOF method in Basilisk, a general two-step geometric VOF method is implemented. Mass flux is calculated not in the interfacial cells but transferred to the neighboring cells around the interface. The saturated temperature boundary condition is imposed at the interface by a ghost cell method. The phase change model is validated by droplet evaporation with a constant mass transfer rate, the one-dimensional Stefan problem, the sucking interface problem, and a planar film boiling case. The results show good agreement with analytical solutions or correlations
35
Aulbach, Maximilian Wolfgang [Verfasser]. "Magnetic order and magnetic phase transitions in triangular or depleted periodic Anderson lattices: Studies within the framework of dynamical mean-field theory powered by hybridization expansion continuous-time quantum Monte Carlo / Maximilian Wolfgang Aulbach". Hamburg : Staats- und Universitätsbibliothek Hamburg Carl von Ossietzky, 2021. http://d-nb.info/1236695046/34.
36
Young, Lindsay Kay. "Synthesis and Characterization of A2Mo3O12 Materials". University of Toledo / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1431517117.
37
Latham, Tina Joy. "Structure and properties of MTiOXOâ†4 crystals". Thesis, University of Warwick, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364604.
38
Belmkaddem, Kawtar. "Contrôle du rayonnement des antennes miniatures". Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAT031.
Abstract (sommario):
Dans le contexte actuel où l’évolution des systèmes sans-fil est jugée importante, il estnécessaire de pouvoir réduire les pollutions électromagnétiques qui limitent l’acceptabilité descommunications et la cohabitation des systèmes. D’une façon générale, les besoins de contrôle durayonnement des antennes miniatures répondent donc à une demande croissante pour améliorer lesportées mais aussi pour limiter les interférences dans les systèmes sans-fil. Ces dernières années,malgré le développement connu dans les domaines des antennes, la question du contrôle durayonnement des antennes miniatures connait plusieurs barrières empêchant leur déploiementtechnologique. L’approche retenue dans le cadre de cette thèse est le développement de nouveauxconcepts de contrôle du rayonnement des antennes miniatures par la mise en oeuvre de différentestechniques. Cette étude a pour objectif de soulever quelques questions concernant un sujet d’étude peuexploréIn the current context where the evolution of communicating objects is important indifferent growing fields such as: localization, wireless multimedia systems, etc., controlling theradiation pattern of antennas is one of the most important issues for future radio communicationsystems. In recent years, despite the growth experienced in the areas of antennas, the issue of smallantennas radiation control knows several barriers preventing their deployment. This thesis focuses onthe analysis of the problem of controlling the radiation pattern of small antennas and aims to raisesome questions about a little-explored subject of study. This work gives an approach using differenttechniques to develop new concepts of controlling the radiation pattern of antennas
39
Mouly, Aude. "Modélisation de la formation et de la détente rapide d'une bulle polyphasique pour l'évaluation des conséquences d'un accident grave de RNR_Na". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0362.
Abstract (sommario):
Une nouvelle génération de réacteurs est aujourd'hui développée pour répondre aux enjeux économiques, environnementaux et sociétaux du 21e siècle. Parmi les différents concepts retenus pour créer cette quatrième génération, les réacteurs à neutrons rapides à caloporteur sodium (RNR-Na) sont étudiés dans le cadre de cette thèse. Ce sont les seuls réacteurs de quatrième génération présentant déjà un retour d'expérience considérable en France. Afin de répondre aux objectifs de sûreté de cette nouvelle génération, la démarche d'étude de sûreté doit être adaptée dès les phases de préconception et de conception afin d'y intégrer les accidents graves et ainsi identifier puis définir les moyens de limitation de leurs conséquences. Ces travaux de thèse se positionnent dans la dynamique des travaux effectués au CEA contribuant au développement de cette démarche de sûreté par l'étude et la modélisation de la phase d'expansion d'un accident grave en RNR-Na. L'objectif de la thèse est de réaliser un outil de calcul traitant des phénomènes physiques pertinents lorsqu'un bain fondu de matériaux est surchauffé par une excursion de puissance dans le cœur entraînant la formation et la détente rapide d'une bulle de vapeur de sodium et de matériaux surchauffés. Suite à l'étude détaillée de l'état de l'art des différentes phénoménologies présentes au cours de la phase d'expansion, des analyses dimensionnelles des processus physiques impliqués sont effectuées afin d'identifier ceux qui sont prépondérants. Sur la base de ces analyses, une modélisation est ensuite développée puis intégrée dans un outil de calcul, dont l'objet est de déterminer et de hiérarchiser l'ensemble des contributions aux chargements mécaniques de la cuve d'un RNR-Na en fonction des configurations accidentelles simulées. Une étape de validation de l'outil est réalisée au travers de tests à effets séparés, de tests globaux à l'aide de résultats d'expériences et de résultats de calculs issus d'autres codes de calcul validés. Enfin, des études de conception paramétriques sont menées afin de quantifier la variabilité des résultats par rapport aux choix de modélisation et aux incertitudes des scénarios et des données physiquesA new generation of nuclear reactor is nowadays developed in order to take into account the economic, environmental and societal stakes of the 21th century. Among the different concepts taking part of the fourth generation, the sodium fast reactors (SFR) are studied in this PhD thesis. These reactors are the only ones of the fourth generation already having a considerable operating feedback in France.To achieve the safety objective of this new generation, the safety approach has to be adapted as soon as the reactor preconceptual and conceptual phases in order to integrate severe accidents, identify and define limitation ways as well as their consequences. This work, dedicated to the study and to the modelling of the expansion phase of a severe accident in SFR, is positioned in the CEA's work dynamic by contributing to the development of the safety approach. The goal of this PhD is to create a tool modelling the important physical phenomena induced by a power excursion in a molten material pool. This involves the formation of a vaporized sodium and molten material bubble and its subsequent expansion.After conducting detailed state of art of the different phenomena involved in the expansion phase, dimensional analysis of the physical processes is performed in order to identify the important ones. Based on this analysis, a model is developed and integrated into a tool, aiming at determining and prioritising the total phenomenon contributions to mechanical loadings on SFR vessel depending on the studied severe accident scenario. A validation step of the tool is then realised in two parts; Separate effect tests and global tests, using experimental results and calculation results obtained with other validated tools. Finally, preconceptual parametrical studies are performed to quantify the results variability due to modelling, scenarios and physical data uncertainties
40
Bouzar, Khalida. "Approche thermodynamique de l'organisation moléculaire de la phase liquide du toluène sous pression : détermination des expansivités et compressibilités sivities". Paris 6, 1986. http://www.theses.fr/1986PA066312.
Abstract (sommario):
Mesures, par la méthode piezothermique, du coefficient de dilatation thermique et du coefficient de compressibilité isotherme, dans l'intervalle 200-450 k, sous des pressions atteignant 4000 bars; ajustement des résultats, établissement d'une équation phénoménologique du coefficient de dilatation comme fonction de la pression et de la température, permettant la détermination des propriétés thermodynamiques. Discussion de l'organisation moléculaire à la lumière des résultats obtenus et de données spectroscopiques (RMN, diffusion de la lumière).
41
Yang, Limin. "Liquid-liquid two-phase flows at T-junctions and through expansions". Thesis, University of Nottingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404047.
42
Sloan, Jennifer Marina. "Controlling leaf growth by phased induction of expansin". Thesis, University of Sheffield, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.522368.
43
Gana, Inès. "Caractérisation physique et chimique des substances à activité thérapeutique : application aux études de profil de stabilité et de préformulation". Thesis, Sorbonne Paris Cité, 2015. http://www.theses.fr/2015USPCB164/document.
Abstract (sommario):
Le développement d’un médicament pour une cible thérapeutique donnée passe par plusieurs étapes qui se résument en une étape de criblage, une phase préclinique et plusieurs phases cliniques. Ces étapes permettent de sélectionner une substance active et de démontrer son efficacité thérapeutique et sa sécurité toxicologique. Ces deux critères définissent la qualité du médicament qui, une fois démontrée, doit être garantie pendant toute sa durée de validité. La qualité est évaluée au moyen d’études de stabilité qui sont réalisées d’abord sur la matière première de la substance active au cours de la phase de pré-développement du médicament, ensuite sur le produit fini. La stabilité intrinsèque de la substance active concerne à la fois ses propriétés chimiques et ses propriétés physiques qui sont liées à la nature de la substance. L’étude de stabilité repose d’abord sur la caractérisation de ces propriétés, et ensuite sur l’étude de la sensibilité de la substance à l’égard des facteurs environnementaux pouvant modifier les propriétés intrinsèques de la substance. L’approche adoptée dans ce travail repose d’une part sur l’évaluation de la stabilité chimique c’est à dire de la réactivité chimique des substances à usage pharmaceutique au travers des études de pureté chimique et des études de dégradation forcée de ces substances en solution, et d’autre part, sur l’évaluation de la stabilité physique. Dans ce cadre, l’étude du polymorphisme cristallin revêt une grande importance, tout comme l’aptitude à la formation d’hydrates ou de solvates. Cette étude, basée sur la thermodynamique, consiste pour l’essentiel à construire un diagramme de phases pression-température permettant de définir les domaines de stabilité relative des différentes formes cristallines. Cinq substances actives, existant à l’état solide et entrant dans la composition de médicaments administrés par voie orale, ont été étudiées dans le cadre de ce travail. L’analyse chimique du tienoxolol, présentant un effet anti-hypertenseur, a montré qu’il est très sensible à l’hydrolyse et à l’oxydation. Sept produits de dégradation ont été identifiés pour ce produit dont un schéma probable de fragmentation a été établi. Des diagrammes de phases pression-température ont été construits pour le bicalutamide et le finastéride, médicaments du cancer de prostate, en utilisant une approche topologique basée simplement sur les données disponibles dans la littérature. Cette étude a montré que la relation thermodynamique (énantiotropie ou monotropie) entre les formes cristallines sous conditions ordinaires peut être modifiée en fonction de la température et de la pression. Ce résultat est important pour la production des médicaments car il montre comment une telle information peut être obtenue par des mesures simples et accessibles aux laboratoires de recherche industrielle, sans que ces derniers soient contraints d’expérimenter sous pression. La méthode topologique de construction de diagramme de phases a été validée ensuite en la comparant à une méthode expérimentale consistant à suivre, par analyse thermique, des transitions de phases en fonction de la pression. La méthode expérimentale a été appliquée à deux composés, la benzocaine, anesthésique local, et le chlorhydrate de cystéamine, médicament utilisé pour les cystinoses. Les deux formes étudiées de benzocaine présentent une relation énantiotrope qui se transforme en relation monotrope à haute pression. Une nouvelle forme cristalline (forme III) du chlorhydrate de cystéamine a été découverte au cours de ce travail. La relation thermodynamique entre cette forme III et la forme I est énantiotrope dans tout le domaine de température et de pression. De plus, le chlorhydrate de cystéamine, classé hygroscopique, a fait l’objet d’une étude quantitative de sa sensibilité à l’eau, montrant qu’il devient déliquescent sans formation préalable d’hydrate (...)The development of a drug for a given therapeutic target requires several steps, which can be summarized by drug screening, a preclinical phase and a number of clinical phases. These steps allow the selection of an active substance and a verification of its therapeutic efficacy and toxicological safety. The latter two criteria define the quality of the drug, which once demonstrated, must be guaranteed throughout its shelf life. Quality is assessed through stability studies that are carried out with the raw material of the active substance (preformulation phase) and with the final product. The intrinsic stability of the active substance depends on its chemical and physical properties and their characterization is the core of the stability studies, which in addition consists of sensitivity studies of the active pharmaceutical ingredient (API) for environmental factors that can modify the intrinsic properties of the substance. The approach presented in this work is based on the one hand on the assessment of the chemical stability, i.e. the reactivity of APIs through chemical purity studies and forced degradation in solution, and on the other hand on the assessment of the physical stability. For the latter, crystalline polymorphism is of great importance, as is the ability of the API to form hydrates or solvates. The study of crystalline polymorphism is based on the construction of pressure-temperature phase diagrams in accordance with thermodynamic requirements leading to the stability condition domains of the different crystalline forms. The stability behavior of five APIs used or meant for oral applications has been studied as part of this work. The chemical analysis of tienoxolol, an antihypertensive drug, has demonstrated its sensitivity for hydrolysis and oxidation. Seven degradation products were identified and patterns of fragmentation have been established. Pressure-temperature phase diagrams have been constructed for bicalutamide and finasteride, drugs against prostate cancer, using a topological approach based on data available in the literature. The study demonstrates that the thermodynamic relationship (enantiotropy or monotropy) between crystalline forms under ordinary conditions can change depending on the pressure. This is important for drug development as it demonstrates how stability information can be obtained by standard laboratory measurements accessible to industrial research laboratories without the necessity to carry out experiments under pressure. The topological approach for the construction of phase diagrams has subsequently been validated by measuring transition temperatures as a function of pressure. Experiments have been carried out with benzocaine, a local anesthetic, and with cysteamine hydrochloride, a drug used against cystinosis. Two crystalline forms were observed in the case of benzocaine. They exhibit an enantiotropic relationship that becomes monotropic at high pressure. For cysteamine hydrochloride, a new crystalline form (form III) was discovered. The thermodynamic relationship between the new form III and the known form I is enantiotropic for the entire temperature and pressure range. Cysteamine hydrochloride’s sensitivity to water has been studied, as it is hygroscopic. It has been demonstrated that it becomes deliquescent in the presence of water and no trace of a hydrate has been found. Finally, a study combining thermal and chromatographic methods showed that, under the effect of temperature, cysteamine hydrochloride turns into cystamine in the solid as well as in the liquid state, The latter is known to be an important impurity of cysteamine hydrochloride. In conclusion, the approach developed in this work allowed to characterize the stability properties of a number of APIs and to determine the factors that may change these properties and influence the intrinsic stability (...)
44
Lavrentovich, Maxim Olegovich. "Diffusion, Absorbing States, and Nonequilibrium Phase Transitions in Range Expansions and Evolution". Thesis, Harvard University, 2014. http://nrs.harvard.edu/urn-3:HUL.InstRepos:13070032.
Abstract (sommario):
The spatial organization of a population plays a key role in its evolutionary dynamics and growth. In this thesis, we study the dynamics of range expansions, in which populations expand into new territory. Focussing on microbes, we first consider how nutrients diffuse and are absorbed in a population, allowing it to grow. These nutrients may be absorbed before reaching the population interior, and this "nutrient shielding" can confine the growth to a thin region on the population periphery. A thin population front implies a small local effective population size and enhanced number fluctuations (or genetic drift). We then study evolutionary dynamics under these growth conditions. In particular, we calculate the survival probability of mutations with a selective advantage occurring at the population front for two-dimensional expansions (e.g., along the surface of an agar plate), and three-dimensional expansions (e.g., an avascular tumor). We also consider the effects of irreversible, deleterious mutations which can lead to the loss of the advantageous mutation in the population via a "mutational meltdown," or non-equilibrium phase transition. We examine the effects of an inflating population frontier on the phase transition. Finally, we discuss how spatial dimension and frontier roughness influence range expansions of mutualistic, cross-feeding variants. We find here universal features of the phase diagram describing the onset of a mutualistic phase in which the variants remain mixed at long times.Physics
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Pérez, Mellor Ariel. "Effets d’environnement sur la reconnaissance chirale : une étude spectroscopique". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS466.
Abstract (sommario):
Ce travail est consacré à l’étude des effets de chiralité dans des dipeptides cycliques construits sur un cycle dikétopiperazine (DKP) et comportant deux résidus de chiralités identiques ou opposées, LL et LD. Les mêmes systèmes sont étudiés dans différents environnements par spectroscopie optique couplée à des calculs de chimie quantique. Les molécules neutres sont isolées et refroidies en jet supersonique et caractérisées par spectroscopie laser UV et IR sélective en conformère. La structure des systèmes protonés, isolés dans un spectromètre de masse ICR, est déterminée par spectroscopie de dissociation induite par absorption de multiples photons IR. Enfin, le dichroïsme circulaire vibrationnel (VCD) est appliqué aux échantillons en phase solide. Les systèmes étudiés comportent un résidu aromatique tyrosine (cyclo Tyr-Pro) ou phénylalanine (cyclo Phe-Phe et Phe-His). Le diastéréomère LD est en général moins stable et plus flexible que LL, et ils ne diffèrent structurellement que par des interactions faibles de type NH…π ou CH…π. Le conformère le plus stable correspond en général à une structure où le chromophore aromatique est replié sur le cycle peptidique, l’autre partie étant étendue. Un effet très important de la chiralité est observé dans certains dimères protonés. Enfin, les expériences de VCD en phase condensée montrent que la phase cristalline de cyclo LPhe-DPhe formée par déshydratation du dipeptide linéaire en phase solide est chirale à cause de la synchronisation des chiralités transitoires des monomèresThis work focuses on the study of chirality effects on the structure of cyclic dipeptides built on a diketopiperazine (DKP) ring with residues of identical (LL) or opposite (LD) chirality. The same systems are studied in different environments by means of optical spectroscopy coupled to quantum chemical calculations. The neutral molecules are isolated and cooled down to a few K in a supersonic expansion and characterized by UV and conformer-specific IR laser spectroscopy. The structure of the protonated systems, isolated in an ICR mass spectrometer, is determined by infrared multiple photon dissociation spectroscopy. Last, vibrational circular dichroism (VCD) is applied to the solid-state samples.The studied systems possess an aromatic residue, either tyrosine (cyclo Tyr-Pro) or phenylalanine (cyclo Phe-Phe and Phe-His). The LD diastereomer is in most of the cases less stable and more flexible than LL. LL and LD differ from each other by weak interactions like NH…π or CH…π interactions. The most stable conformer usually corresponds to a structure with the aromatic chromophore folded over the DKP ring, the other part being extended. A dramatic effect of chirality is observed for some of the protonated dimers. Last, VCD experiments in the condensed phase show that the crystal phase of LPhe-DPhe formed by solid-state dehydration of the linear dipeptide is chiral due to synchronization of the transient chirality of the monomers
46
Han, Jingyi. "Phrase table expansion for statistical machine translation with reduced parallel corpora: the Chinese-Spanish case". Doctoral thesis, Universitat Pompeu Fabra, 2017. http://hdl.handle.net/10803/458530.
Abstract (sommario):
Parallel data scarcity problem is a major challenge faced by Statistical Machine Translation (SMT). The aim of this thesis is to enrich a SMT system by adding more morphological variants and new translation lexicon automatically generated out of monolingual data. To induce bilingual lexicon, instead of taking advantages of comparable corpora or parallel data, we proposed a supervised classifier trained using monolingual features (e.g. word embedding vectors, plus Brown clustering or word frequency information) of only a small amount of translation equivalent word pairs. The classifier is able to predict whether a new word pair is under a translation relation or not.
Our experiments of SMT phrase table expansion were conducted on Chinese and Spanish, since we realised that although they are two of the most widely spoken languages of the world, this language pair is suffering from a data scarcity situation. In addition to the problems caused by the words that are not included in the training corpus, the inflection differences between this language pair make the translation even more challenging when only limited parallel data are available.
The obtained results demonstrate that, on the one hand, with the method of morphology expansion, the SMT system achieves an improvement of up to + 0.61 BLEU compared to the results of a low resource Chinese-Spanish phrase-based SMT baseline. On the other hand, our supervised classifier reaches a 0.94 F1-score and the SMT experiment results show an improvement of up to +0.70 BLEU with the resulting bilingual lexicon, demonstrating that the errors of the classifier are ultimately controlled by the SMT system.La escasez de datos paralelos es un problema importante para la Traducción Automática Estadística (TAE). El objetivo de esta tesis es enriquecer un sistema de TAE añadiendo más variantes morfológicas y un nuevo léxico de traducción generado automáticamente desde datos monolingües. Para inducir el léxico bilingüe, en lugar de depender de corpus comparables o de datos paralelos, proponemos un clasificador supervisado entrenado con representaciones monolingües (por ejemplo, vectores distribuidos, agrupaciones de Brown e información de la frecuencia de palabras) de sólo una pequeña cantidad de traducciones. El clasificador es capaz de predecir si un nuevo par de palabras es una traducción la una de la otra, o no. Realizamos los experimentos para enriquecer el sistema de TAE con chino y español, porque a pesar de que estas lenguas son dos de las más habladas del mundo, este par de idiomas sufre de escasez de datos paralelos. Además de los problemas causados por las palabras que no están incluidas en el corpus de entrenamiento, las diferencias de flexión morfológica entre este par de idiomas hace que la traducción sea de peor calidad cuando se dispone de pocos recursos paralelos. Los resultados obtenidos demuestran que, por un lado, con el método de expansión morfológica, el sistema de TAE logra una mejora de hasta + 0,61 BLEU en comparación con los resultados obtenidos con un sistema básico chino-español con poco corpus. Por otro lado, nuestro clasificador supervisado, que alcanza una F1 de 0,94, proporciona nuevos pares de traducción que resultan en una mejora de hasta +0,70 BLEU con respecto al sistema básico, demostrando que los errores del clasificador son, en último término, controlados por el sistema de TAE.
47
Li, Guanshu. "Etude du phénomène de l'expansion sulfatique dans les bétons : comportement des enrobés de déchets radioactifs sulfatés". Phd thesis, Ecole Nationale des Ponts et Chaussées, 1994. http://tel.archives-ouvertes.fr/tel-00523043.
Abstract (sommario):
Le problème d'attaque des bétons par sulfates demeure d'actualité dans le domaine du stockage des déchets radioactifs, parce que certains déchets contiennent des sulfates. Le présent rapport contribue à l'étude des mécanismes de dégradation des enrobés de déchets radioactifs par sulfate. Les systèmes expansifs CaO-Al2O3-SO3-H2O sans et avec alcalins ont été étudiés. Dans le système sans alcalins, c'est la formation de l'ettringite secondaire par apport d'eau externe qui conduit à l'expansion importante par effet stérique. Dans le système avec alcalins, les comportements d'expansion sont complètement différents. Un nouveau minéral baptisé "phase U", de type AFm incorporant du sodium, a été mis en évidence. Il semble être le responsable de l'expansion observée. Les conditions de formation, le produit de solubilité, les méthodes de synthèse et les distances interréticulaires de la phase U ont été discutés. Les différentes configurations des enrobés réels ont été ensuite étudiées, le comportement étant lié notamment à la phase U, très peu étudiée jusqu'à présent en milieu de ciment. Nous avons retenu comme mécanismes expansifs possibles soit la formation de la phase U secondaire, soit la transformation de la phase U en ettringite, soit la transformation de la thénardite en mirabilite. La première hypothèse a été validée sur un système simplifié, la modélisation de toutes les configurations des enrobés par les bilans massique et volumique nous permet de déterminer théoriquement la répartition massique des hydrates et d'estimer l'expansion par formation de la phase U secondaire. La deuxième hypothèse a été aussi parfaitement vérifiée : l'observation de l'expansion et l'analyse minéralogique des échantillons contenant la phase U et subissant la lixiviation dans différentes solutions nous permettent de supposer que l'expansion est provoquée par la répulsion électrique interparticulaire d'ettringite colloïdale, issue de la transformation de la phase U initiale et formée en présence de chaux. La cinétique de transformation de la phase U en ettringite a été suivie expérimentalement et analysée avec la théorie de la diffusion. La troisième hypothèse n'a pas été validée. En conclusion, la phase U peut provoquer une expansion par deux principaux mécanismes se manifestant individuellement ou simultanément : la formation de la phase U secondaire et la transformation de îa phase U en ettringite colloïdale en présence de chaux. Le présent travail constitue une première étape importante et nécessaire pour prédire la durabilité d'une structure du stockage de déchets radioactifs sulfatés.
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Shafeie, Samrand. "Structure and Properties Investigations of the La2Co1+z(Ti1-xMgx)1-zO6 Perovskite System". Licentiate thesis, Stockholms universitet, Institutionen för material- och miljökemi (MMK), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-55418.
Abstract (sommario):
Perovskite based materials have great potentials for various energy applications and the search for new materials for uses in SOFCs has largely been concentrated to this class of compounds. In this search, we have studied perovskite phases in the system La2Co1+z(Ti1-xMgx)1-zO6, with 0 x 0.9 and z = 0.0, 0.2, 0.4, 0.6. Crystal structures were characterized by XRD and, for selected compositions, also by NPD and SAED. They exhibit with increasing x, as well as increasing z, a progressive increase in symmetry from monoclinic to orthorhombic to rhombohedral. The main focus in this work has been on the investigation of structure-property relations for compositions with 0.0 x 0.5 and z = 0. The nominal oxidation state of Co increases for these with increasing x, from Co2+ for x = 0 to Co3+ for x = 0.5. Magnetic measurements and XANES studies showed that the average spin state of Co changes linearly with increasing x, up to x = 0.5, in accordance with varying proportions of Co with two fixed oxidation states, i.e. Co2+ and Co3+. The data suggests that the Co3+ ions have an IS spin state or a mixture of LS and HS spin states for all compositions with nominally only Co2+ and Co3+ ions, possibly with the exception of the composition with x = 0.1, 0.2 and z = 0, for which the data indicate that the spin state might be HS. The XANES data indicate furthermore that for the perovskite phases with z = 0 and x > 0.5, which in the absence of O atom vacancies contain formally Co4+, the highest oxidation state of Co is Co3+, implying that the substitution of Ti4+ by Mg2+ for x ³ 0.5 effects an oxidation of O2- ions rather than an oxidation of Co3+ ions. The thermal expansion was found to increase nearly linearly with increasing oxidation state of Co. This agrees well with findings in previous studies and is attributable to an increase in the ionic radius of Co3+ ions with increasing temperature, due to a thermal excitation from a LS to IS or LS/HS spin states. High temperature electronic conductivity measurements indicate that the electronic conductivity increases with an increase of both relative and absolute amount of Co3+. The latter can be attributed to an increase in the number of Co-O-Co connections. Additional high temperature magnetic measurements for selected samples, whose susceptibilities did not follow a Curie law behaviour up to room temperature, showed effective magnetic moments that did approach plateaus even at high temperatures (900 K). Interpretations of these data are, however, hindered by the samples losing oxygen during the applied heating-cooling cycle. The present study has shown that the investigated system is suitable for further studies, of more fundamental character, which could provide further insight of the structure-property relationships that depend on the oxidation state of Co.Studies of cobalt based perovskites for cathode materials in solid oxide fuel cells.
49
Canivenc, Romain. "Assemblage de bagues par expansion : définition de modèles et d’outils d’assistance utiles aux phases de prédimensionnement". Toulouse, INSA, 2009. http://www.theses.fr/2009ISAT0007.
Abstract (sommario):
La simplicité, l’efficacité et les nombreux domaines d’applicabilité du procédé d’assemblage par expansion à froid le rendent particulièrement attrayant. La prédiction de l’état résiduel est rendue complexe par la non linéarité du comportement des matériaux écrouissables et les multiples combinaisons de caractéristiques géométriques et matérielles qui sont à l’origine de situations de non-assemblage. . . .The bushing assembly by a coldworking process is particularly attractive thanks to its simplicity and its relevant efficiency in numerous design cases. The non linear behaviour of hardening materials and the miscellaneous combinations of geometrical and material characteristics leading to non assembly, make the residual state prediction complex. . . .
50
Belletti, Jaqueline da Silva. "Arqueologia do Lago Tefé e a expansão polícroma". Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/71/71131/tde-13102015-153201/.
Abstract (sommario):
Este trabalho procura entender as relações entre a diversidade da Tradição Polícroma em escala local e seus significados em termos de escala regional. Desta forma partimos dos contextos de dois sítios arqueológicos no Lago Tefé (Médio Solimões, AM) para adentrarmos as discussões sobre a Tradição Polícroma da Amazônia e os modelos de expansão criados para explicar sua ampla dispersão geográfica. Para isso apresentamos três etapas, a descrição de contextos arqueológicos com material Polícromo no Lago Tefé; uma revisão geral dos dados existentes sobre a Tradição Polícroma; e uma discussão reflexiva sobre os modelos existentes para explicar essa tradição.This paper seeks to understand the relationship between diversity of Polychrome Tradition at the local level and its significance in terms of the regional scale. From two archaeological site contexts at Lake Tefé (Middle Solimões, AM), we enter the discussions over the Amazon Polychrome Tradition and expansion models created to explain its wide geographical spread. For this, we present the debate in three parts: the description of the archaeological contexts with Polychrome material in the Lake Tefé; a general review of the existing data on the Polychrome Tradition; and a reflective discussion about the existing models to explain this tradition.