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Avaliação da microbiota fúngica e da presença de micotoxinas em amostras de plantas medicinais irradiadas adquiridas no comércio varejista e atacadistaAQUINO, SIMONE 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:53:30Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:35Z (GMT). No. of bitstreams: 0 / O presente estudo analisou os efeitos da radiação gama na sobrevivência de fungos em plantas medicinais embaladas, adquiridas do comércio atacadista e varejista, em diferentes períodos (0 e 30 dias) após o tratamento por irradiação. Cinco tipos de plantas medicinais [Peumus boldus, Cameilia sinensis, Maytenus ilicifolia, Pauilinia cupana and Cássia angustifolia), foram coletadas de diferentes municípios do Estado de São Paulo e submetidas ao tratamento por irradiação, utilizando-se uma fonte 60Co (tipo Gammacell 220), com doses de 5,0 kGy e 10 kGy e taxa de dose de 3,0 kGy/h. Amostras não irradiadas (grupo controle) foram usadas na contagem de fungos e diluições seriadas de 10-1 a 10-6 das amostras foram semeadas em duplicata e plaqueadas usando o método de cultura em superfície, em ágar Dicloran Glicerol 18% (DG18) e contadas após cinco dias a 25°C. O grupo controle revelou a presença dos gêneros Aspergilius e Penicillium, os quais são conhecidos como fungos toxigênicos e poucas amostras do grupo controle estavam dentro dos limites seguros, estabelecidos pela Organização Mundial de Saúde (OMS, 1998) para plantas medicinais. Em resposta a resistência do tratamento por ionização, na dose de 5 kGy, foi obsen/ado que os gêneros Aspergilius, Piioma e Syncephalastrum foram radiorresistentes, após o processo (dia 0 e 30° dia). O tratamento por radiação gama foi efetivo na descontaminação de todas as amostras de plantas medicinais, após 30 dias, com a dose de 10 kGy e mantidas em condições de vedação. Não foram detectadas aflatoxinas nas amostras do grupo controle, ainda que estas amostras estivessem intensamente contaminadas com Aspergilius flavus. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Medida do buckling e da probabilidade de fuga de nêutrons do núcleo do reator IPEN/MB-01 / Determination of buckling and probability of leakage of neutron in the IPEN/MB-01 reactor in cylindrical configurationPURGATO, RAFAEL T. 19 January 2015 (has links)
Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-01-19T10:26:11Z
No. of bitstreams: 0 / Made available in DSpace on 2015-01-19T10:26:11Z (GMT). No. of bitstreams: 0 / Um dos parâmetros fundamentais da física de reatores é a curvatura do fluxo de nêutrons (Buckling) do núcleo do reator. Ele está relacionado com outros parâmetros importantes, tais como as taxas de reação, potencia de operação, queima de combustível, entre outros. Num reator crítico, o Buckling depende das características geométricas e de material do núcleo do reator. Este trabalho apresenta os resultados do Buckling experimental para o reator nuclear IPEN/MB-01 em sua configuração cilíndrica com 28 barras de combustível ao longo de seu diâmetro. O IPEN/MB-01 é um reator de potência zero projetado para operar em uma potência máxima nominal de 100 watts. É uma instalação nuclear versátil que permite a simulação de todas as características de um grande reator nuclear e ideal para este tipo de medição. Foi realizado um mapeamento do fluxo de nêutrons no interior do reator e, assim, determinado o Buckling total da configuração cilíndrica. O reator foi operado durante uma hora para cada experimento. Em seguida, a taxa de reação nuclear das varetas de combustível foram medidas por espectrometria gama em um detector de germânio hiper-puro (HPGe) que escaneou as varetas axial e radialmente. Foram analisados os fótons gama do 239Np ( 276,6 keV ), gerado a partir da captura de nêutrons epitérmicos e rápidos, e do 143Ce ( 293,3 keV ), gerado por fissão em ambos 238U e 235U, respectivamente. Foram analisadas as direções axial e radial. Outras medições foram realizadas com fios e folhas de ouro nas direções radial e axial do núcleo do reator. O Buckling total obtido a partir da média ponderada dos três métodos medidos é de 96,55 ± 7,47 m-2. Os objetivo dos valores experimentais obtidos é obter um conjunto de dados experimentais que permitam uma comparação direta com valores calculados pelos códigos de Física de Reatores CITATION e MCNP. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Determinação experimental do equilibrio solido-liquido de sistemas binarios de acidos graxos saturados : estudo detalhado da fase solida / Experimental determination of solid-Liquid equilibrium of binary systems of saturated fatty acids : detailed study of the solid phaseCosta, Mariana Conceição da, 1977- 09 September 2008 (has links)
Orientadores: Maria Alvina Krahenbuhl, Antonio Jose de Almeida Meirelles / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-11T21:21:37Z (GMT). No. of bitstreams: 1
Costa_MarianaConceicaoda_D.pdf: 10674816 bytes, checksum: 76cfbb726dcbf23a7bdf88f2ccf727bd (MD5)
Previous issue date: 2008 / Resumo: Os ácidos graxos são importantes não só por serem os principais constituintes dos óleos e gorduras de origem vegetal, mas também por terem grande importância no funcionamento de alguns sistemas lipídicos e porque podem ser usados como matéria prima na fabricação de emulsões, plásticos e produtos de limpeza entre outros. Além da grande influência que causam nas características finais de alguns produtos da indústria alimentícia, recentemente pesquisas também os apontam como bons materiais para o armazenamento de energia (phase change materials ¿ PCMs). Nesse trabalho são apresentados diagramas T-x do Equilíbrio Sólido-Líquido de sistemas binários de ácidos graxos saturados através de uma reinterpretação das curvas térmicas obtidas pela calorimetria exploratória diferencial. Esses diagramas de fase apresentam os pontos peritético e eutético além de transições na fase sólida. Esse trabalho investiga detalhadamente a fase sólida das misturas de ácidos graxos saturados, com a intenção de compreender a existência do ponto peritético e das transições na fase sólida que aparecem nos diagramas de equilíbrio. Para esse estudo foram usadas as técnicas de difração de Raios-X, de espalhamento Raman, a microscopia óptica convencional, a microscopia óptica a altas pressões e a calorimetria exploratória diferencial, através da qual foram determinados os diagramas de fase estudados. Através desse estudo foi possível apresentar um diagrama de fases muito mais complexo do que até agora foi encontrado na literatura. Essa complexidade se deve, além da reação peritética e da reação eutética, já conhecidas desses sistemas, a uma reação metatética que ocorre logo acima da temperatura peritética. Também há a formação de solução sólida nos extremos do diagrama de fases, comprovada através do diagrama de Tamman e a uma região de completa miscibilidade, devido à formação de um composto com ponto de fusão incongruente. / Abstract: Fatty acids are important not just to be the main constituent of oils and fats but also because of the important behavior of lipids systems and that can be used as row materials in the manufacture of emulsions, plastics and products for cleaning and others. Besides of the big influenced that causes in the final characteristics of some products for food industries recent research points that they are excellent phase change materials (PCMs). This work presents T-x diagrams of solid-liquid equilibrium of binary systems of saturated fatty acids through the reinterpretation of the differential thermal curves obtained by differential scanning calorimetry. These phase diagrams presents the peritectic and eutectic points besides the transitions on the solid phase. This work studies the solid phase of saturated fatty acids mixtures looking forward to verify the occurrence of the peritectic point and the transitions on the solid phase. For this study it was used the following techniques: X-ray diffratometry, FT-Raman spectroscopy, conventional optical microscopy, optical microscopy under high pressure and differential scanning calorimetry. The phase diagrams studied were determined by differential scanning calorimetry. The results obtained through these techniques shows a phase diagram more complex than previously reported in the literature. This complexity is due to a peritectic and eutectic, and to a metatectic reaction that occurs closer to the peritectic temperature. Besides these reactions there is formation of solid solution on the extremes of the phase diagram proven by the Tamman plot and the existence of a region with complete miscibility, close to the peritectic point, due the formation of a compound with incongruently melting point. / Doutorado / Desenvolvimento de Processos Químicos / Doutor em Engenharia Química
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Experimental investigation of corner stall in a linear compressor cascade / Etude expérimentale et numérique du décollement de coin dans une grille d'aubes de compresseurMa, Wei 15 February 2012 (has links)
Dans le domaine de la recherche appliquée, les turbomachinistes sont confrontés à un manque de compréhension de la physique du décollement de coin. Ce décollement tridimensionnel (3D) à la jonction de l’extrados des aubages et du moyeu limite l’efficacité et la stabilité des compresseurs. Les simulations numériques utilisant les deux types de modélisations, « Reynolds-Averaged-Navier-Stokes » (RANS) et « Large Eddy Simulation » (LES), doivent encore être étalonnées pour des applications turbomachines. Dans la recherche fondamentale concernant la couche limite turbulente (TBL), il existe beaucoup d’études sur les effets de courbure et de gradients de pression qui jouent également un rôle important dans la physique du décollement de coin. Le but de cette thèse est de réaliser une expérience dans une grille d’aubes de compresseur pour acquérir une base de données qui pourrait être utilisée non seulement pour calibrer à la fois les approches RANS et LES, mais aussi pour donner quelques explications fondamentales sur le décollement de coin. Cette expérience permet aussi une étude de la TBL se développant sur l’extrados à mi-envergure des aubages, qui est plus complexe que les TBL rencontrées dans des configurations plus fondamentales, mais plus simples que celles existant d’un turboréacteur. Une expérience précise et détaillée de l’écoulement 3D au passage d’une grille d’aubes de compresseur a été mis en place. Les mesures ont été réalisées pour un nombre de Reynolds basé sur les conditions d’entrée et la corde de l’aubage de 3,82×105. Des mesures ont été réalisées par anémométrie à fil chaud, par des prises de pression sur la paroi latérale et sur l’aubage, par une sonde de pression à cinq trous, par de la visualisation d’huile, par la Vélocimétrie par Images de Particules (PIV) 2D, ainsi que par Anémométrie Laser Doppler (LDA) à deux composants. Une base de données originale et complète a ainsi été obtenue. Concernant l’étude de la TBL sur l’extrados à mi-envergure , le gradient négatif de pression normal à la paroi retarde le décollement, ce qui est paradoxal avec son influence sur le décollement de coin tel que présentée dans la littérature. Le gradient de pression adverse dans la direction de l’écoulement est responsable de l’accroissement des tensions de Reynolds. Un phénomène remarquable proche du bord de fuite de l’aubage est qu’il existe un point d’inflexion dans le profil de la vitesse moyenne de l’écoulement. A ce point d’inflexion, les grandeurs des tensions de Reynolds atteignent leurs valeurs maximales et la direction de diffusion de l’énergie est inversée. Le champ de vitesse dans le décollement de coin a été présenté. L’expérience met en évidence l’existence d’histogrammes bimodaux de vitesse. Les points de mesures faisant apparaitre ce caractère bimodal sont essentiellement localisés dans la région de l’interface du décollement de l’écoulement moyenné en temps. Deux modes ont été proposés pour interpréter la physique du comportement bimodal. Pour un point bimodal, les deux composantes de vitesse sont localement non-indépendantes, en raison de l’interaction apériodique de ces deux modes. / In applied research, a lack of understanding of corner stall, i.e. the three-dimensional (3D) separation in the juncture of the endwall and blade corner region, which has limited the efficiency and the stability of compressors. Both Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) still need to be calibrated for turbomachinery applications. In the fundamental research of the turbulent boundary layer (TBL), there are a lot of findings of the effects of curvature and pressure gradients, which also play an important role in physics of corner stall. The purpose of this thesis is (i) to carry out an experiment in a cascade, (ii) to gain a database that could be used to calibrate both RANS and LES, and (iii) to give some basic explanations of corner stall through investigating the TBL on the suction side at the mid-span which is more complex than those in the basic investigations but simpler than those in a real engine. A detailed and accurate experiment of 3D flow field through a linear compressor cascade has been set up. Experimental data were acquired for a Reynolds number of 3.82×10 ^5 based on blade chord and inlet flow conditions. Measurements have been achieved by hot-wire anemometry, pressure taps on blade and endwall, five-hole pressure probe, oil visualization, 2D particle image velocimetry (PIV),and two-component laser Doppler anemometry (LDA). An original and complete database was thus obtained. The TBL on the suction side at mid-span was investigated. The wall-normal negative pressure gradient restrains the separation, on the contrary to its influence in the corner stall. The streamwise adverse pressure gradient can be responsible for the development of Reynolds stresses. The remarkable phenomenon at measurement stations near the trailing edge of blade is that an inflection point occurs in each profile of the mean streamwise velocity. At this inflection point, the magnitudes of the Reynolds stresses reach their maximum values, and the direction of energy diffusion also changes. The velocity field in the corner stall was presented. Bimodal histograms of velocity exist in the experiment. The bimodal points mainly appear in the region around the mean interface of separated flow and non-separated flow. At a bimodal point the local two velocity components are non-independent from each other, due to the aperiodic interplay of two basic modes in the flow field. Two modes were proposed to interpret the physics of bimodal behaviour.
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[en] RADIO SIGNAL PREDICTIONS FOR INDOOR LOCATIONS WITH TRANSMITTER IN MICROCELLULAR ENVIRONMENT / [pt] PREDIÇÃO DE COBERTURA PARA O INTERIOR DAS EDIFICAÇÕES COM TRANSMISSORES EM AMBIENTES MICROCELULARESJASON PAULO TAVARES FARIA JUNIOR 22 July 2003 (has links)
[pt] Neste trabalho, um - software - foi desenvolvido para
prover predições do sinal em ambientes exteriores e
interiores. O programa inclui dois diferentes modelos de
propagação. Para situações urbanas com antenas baixas
(Microcélulas) e para situações urbanas onde o receptor
pode ser posicionado numa área - indoor - e o transmissor
numa área urbana ( - outdoor -). O procedimento
automatizado combina técnicas de várias diferentes
disciplinas, incluindo computação gráfica e teoria
eletromagnética assintótica, para reduzir o tempo de
computação sem comprometer a precisão. Usando técnicas de
computação gráfica, o tempo necessário para o lançamento de
raios através da geometria urbana é grandemente reduzido.
Os dados teóricos foram testados e validados por comparação
com dados experimentais. Para modelar os diferentes
mecanismos de propagação, a aproximação eletromagnética
usada foi a OG/UTD. / [en] In this work, a software tool has been developed that
provides accurate, sitespecific radio signal predictions
for outdoor to indoor/outdoor locations. The program
includes two different propagation models. For urban
calculations with low antennas (Microcells) and for urban
situations where receiver can be located at indoor
area and transmitter antennas can be located at Urban area
(outdoor). The software combines techniques from several
different disciplines, including computer graphics
and asymptotic electromagnetic theory, to reduce the
calculation time without compromising accuracy. Using
computer graphics techniques, the time necessary for
shooting the rays through the urban geometry is greatly
reduced. The calculation engine used has been tested and
validated by comparison with measured data. In order to
model the diferent propagation mechanisms, the
eletromagnetic approach considered has been the GO/UTD
combination.
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Integrovaný e-learning v oblasti kvantové fyziky a optiky / Integrated e-learning in quantum physics and opticsBrom, Pavel January 2018 (has links)
This doctoral thesis concerns the designs, creation, and a pilot survey of real remotely controlled laboratories that can be used for the introduction to modern physics within the integrated e-learning strategy. With grant support four new remote laboratory experiments could be created, featuring some innovations like the possibility to modify experimental setup, and the design allowing to make a mistake and to obtain nonsensical experimental data in order to test students' critical thinking. The new remote experiment topics are: laws of radioactivity, polarisation state of light, photoelectric effect, and the origin of spectral lines. The emphasis is put on easy experimental data acquision (measurement, record, and download) for further scientific statistical or advanced graphical data proces- sing. The pilot survey aims to select adequate research designs, tools, and data sources and it describes the results and experience from the observation at several Czech secondary schools. The most interesting findings were revealed by action log file analysis and interviews with teachers and students. Finally, real usability of remote laboratory experiments in lessons and physics education is discussed. 1
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Thermodynamische Untersuchungen von Phasengleichgewichten in komplexen Systemen mit assoziierenden KomponentenGrenner, Andreas 19 June 2006 (has links)
The knowledge of phase equilibrium is essential for the planning and realisation of separation processes in chemical engineering. In this work an equipment for measurement of precise isothermal vapour–liquid equilibria (VLE) using the dynamic method was developed. The pool of experimental data for cyclohexylamine was extended significantly. Isothermal VLE were measured in 3 binary and 4 ternary systems, liquid-liquid equilibria (LLE) were measured in 4 ternary systems and in one quarternary system, in each case for two temperatures, whereas in 2 ternary systems and in the quarternary system even liquid-liquid-liquid equilibria (LLLE) occur. Furthermore, activity coefficients at infinite dilution in 4 binary systems and excess molar volumes in 7 binary systems have been estimated. Binary VLE and LLE data of the components water, octane, cyclohexylamine and aniline of this work and data from literature were fitted with the activity coefficient models NRTL and UNIQUAC, as well as with the equations of state Elliott-Suresh-Donohue (ESD) and Perturbed-Chain-Statistical Associating Fluid Theory (PC-SAFT) which contain both a term to consider explicit hydrogen bonds. In addition, the predictive capabilities of the equations of state (EoS) were investigated. With parameters obtained by simultaneous fitting of VLE and, if available, LLE data similar results with the models NRTL and UNIQUAC could be obtained. Each time the deviations for the vapour pressure were lower than 3 % and lower than 2 % in vapour phase composition. The deviations, in three out of the six systems for vapour pressure and vapour phase composition, were larger with the ESD-EoS than with the activity coefficient models. NRTL, UNIQUAC and ESD delivered similar results with the simultaneously fitted parameters for the LLE, whereas the deviations were lower than 5 %. Comparable results were delivered by the ESD-EoS and PC-SAFT for the fitting and the prediction in the investigated binary systems. Also a fitting for NRTL, UNIQUAC and ESD was carried out, but only to one data set. The intention was to show the effect of parameterization on prediction in ternary systems. Predictions were made for VLE and LLE in ternary systems of the above mentioned components, solely with interaction parameters fitted to binary data. For the models NRTL, UNIQUAC und ESD predictions of simultaneously and separately fitted parameters are presented. It is shown that with parameters simultaneously fitted to several data sets significantly better results could be obtained compared to the parameters separately fitted to a single data set. Additionally, for the equations of state ESD and PC-SAFT predictions for the LL(L)E in ternary systems are compared, but here only with separately fitted parameters. For three out of the four investigated ternary systems a too large miscibility gap is calculated with the models NRTL, UNIQUAC and ESD. In the system water+octane+aniline good results could be obtained for the prediction of the LLLE. In summary the equations of state deliver similar results. In the systems water+octane+CHA and octane+CHA+aniline also too large two phase regions were delivered. Better predictions could be obtained in the systems water+octane+aniline and water+CHA+aniline. The forecasts of the VLE in the ternary systems are good with the simultaneously fitted parameters. The deviations for the vapour phase compositions are as for the vapour pressures under 6 %. Larger deviations occur for the system water+octane+aniline only. As evaluation result for the thermodynamic models can be mentioned that the activity coefficient models NRTL and UNIQUAC deliver somewhat better results for the fitting of the binary data than the equations of state ESD and PC-SAFT however, with a larger number of adjustable parameters. The prediction of the VLE is satisfactorily in the ternary systems and with similar quality of all considered models. Larger deviations occur for the prediction of the LL(L)E in the ternary systems. The results of the ESD-EoS were, with one exception, each time better than those of the activity coefficient models. There is no significant difference between the prediction of the ternary systems for the ESD-EoS and the PC-SAFT.
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Kunskap, motivation och stöd : En studie om kompetensutveckling inom statistisk analys av experimentella stöd / Knowledge, Motivation and Support : A study about competence development in statistical analysis of experimental dataPettersson, Jennifer January 2014 (has links)
Testing and analysis of measurement data is a major part of the workday for development engineers within the section Fluid and Emission Treatment to assure the quality of products developed by Scania CV. The ineluctable variation and therefore uncertainty of results can be quantified and discussed with the use of statistical methods. The overall objective of this study is to examine how the competence of development engineers can be improved within the area of statistics. This has been done by relating the concept of competence with the use of statistical methods to analyse experimental data and by investigating which factors that influence the competence of the engineers. Observations of the daily operations, interviews and a focus group with development engineers and a workshop with management personnel, has been used as research methods in this study. The results show that the desired competence, from the perspective of the individual, consists of knowledge, motivation and support. It is important that none of these parts are neglected when the competence of engineers is to be strengthened. The demand of statistical analysis by management and decision makers is a factor that has been shown to have great influence on the competence of development engineers. The competence of development engineers is also influenced by which tools and other types of support the organisation offers. The conclusion is that competence development is more comprehensive than a one-time-effort, as for example a short course, since the competence needs to be maintained and develop as the business evolves. A continuous support from the organisation would probably contribute to a more active development of competence. Knowledge sharing between colleagues on internal digital platforms has great potential and could be a component of a continuous support for the development engineers. / Provtagningar och analys av mätdata är en stor del av utvecklingsingenjörernas arbetsvardag inom sektionen Fluid and Emission Treatment för att säkerställa kvalitén på de produkter som Scania CV AB utvecklar. Den ofrånkomliga variationen och därmed osäkerheten i resultat kan kvantifieras och diskuteras med statistiska metoder. Syftet med denna studie är att undersöka hur utvecklingsingenjörernas kompetens inom statistikämnet kan förstärkas. Detta har gjorts genom att relatera kompetensbegreppet till användningen av statistiska metoder för att analysera experimentella data samt utreda vilka faktorer som påverkar ingenjörens kompetens. Observationer av verksamheten, intervjuer och en fokusgrupp med utvecklingsingenjörer samt en workshop med personer i ledande befattning har använts som forskningsmetod i studien. Resultatet visar att den önskade kompetensen, ur individens perspektiv, består av tre delar, kunskap, motivation och stöd. Det är viktigt att ingen av dessa delar bortses ifrån när ingenjörernas kompetens ska utvecklas. Efterfrågan av statistiska analyser från chefer och beslutsfattare är en faktor som har visat sig ha stor påverkan på utvecklingsingenjörernas kompetens. Vilka hjälpmedel och övriga stöd som erbjuds från organisationen har även stor inverkan på kompetensen. Slutsatsen är att kompetensutvecklingen är mer omfattande än en punktinsats, som exempelvis en kort kurs, eftersom kompetensen måste underhållas samt utvecklas vartefter verksamheten utvecklas. Ett kontinuerligt stöd från organisationen bidrar sannolikt till en mer aktiv kompetensutveckling. Kunskapsdelning mellan kollegor via interna digitala plattformar har stor potential och skulle kunna utgöra en del av ett kontinuerligt stöd för utvecklingsingenjörerna.
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Near Wall Investigation of Three Dimensional Turbulent Boundary LayersKuhl, David Derieg 22 August 2001 (has links)
This report documents the experimental study for four different three-dimensional turbulent flows. The investigation focuses on near wall measurements in these flows. Several experimental techniques are used in the studies; however, the bulk of the investigation focuses on a three-orthogonal-velocity-component fiber-optic laser Doppler anemometer (3D-LDA) system. The control volume of the 3D-LDA is on the order of 50 micro-meter in size, or a y<sup>+</sup> distance of around 2.3 units (using average values of U<sub>τ</sub> and ν from the experiment). An auxiliary small boundary layer wind tunnel (auxiliary tunnel) and a low speed linear compressor cascade wind tunnel (cascade tunnel) are utilized in this study. One of four flow experiments is done in the auxiliary tunnel the other three are in the cascade tunnel. The first three-dimensional turbulent flow is a vortical flow created by two half-delta wing vortex generators. Near wall secondary flow features are found. The second flow is an investigation of the first quarter chord tip gap flow in the cascade tunnel. Strong three-dimensional phenomena are found. The third flow investigated is the inflow to the compressor cascade with the moving wall. The experiment records shear layer interaction between the upstream flow and moving wall. Finally the fourth flow investigated is the inflow to the compressor cascade with the moving wall with half-delta wing vortex generators attached. Phase-averaged data reveal asymmetrical vortex structures just downstream of the vortex generators. This is the first time any near wall data has been taken on any of these flows. / Master of Science
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Contributions to Data Reduction and Statistical Model of Data with Complex StructuresWei, Yanran 30 August 2022 (has links)
With advanced technology and information explosion, the data of interest often have complex structures, with the large size and dimensions in the form of continuous or discrete features. There is an emerging need for data reduction, efficient modeling, and model inference. For example, data can contain millions of observations with thousands of features. Traditional methods, such as linear regression or LASSO regression, cannot effectively deal with such a large dataset directly. This dissertation aims to develop several techniques to effectively analyze large datasets with complex structures in the observational, experimental and time series data.
In Chapter 2, I focus on the data reduction for model estimation of sparse regression. The commonly-used subdata selection method often considers sampling or feature screening. Un- der the case of data with both large number of observation and predictors, we proposed a filtering approach for model estimation (FAME) to reduce both the size of data points and features. The proposed algorithm can be easily extended for data with discrete response or discrete predictors. Through simulations and case studies, the proposed method provides a good performance for parameter estimation with efficient computation.
In Chapter 3, I focus on modeling the experimental data with quantitative-sequence (QS) factor. Here the QS factor concerns both quantities and sequence orders of several compo- nents in the experiment. Existing methods usually can only focus on the sequence orders or quantities of the multiple components. To fill this gap, we propose a QS transformation to transform the QS factor to a generalized permutation matrix, and consequently develop a simple Gaussian process approach to model the experimental data with QS factors.
In Chapter 4, I focus on forecasting multivariate time series data by leveraging the au- toregression and clustering. Existing time series forecasting method treat each series data independently and ignore their inherent correlation. To fill this gap, I proposed a clustering based on autoregression and control the sparsity of the transition matrix estimation by adap- tive lasso and clustering coefficient. The clustering-based cross prediction can outperforms the conventional time series forecasting methods. Moreover, the the clustering result can also enhance the forecasting accuracy of other forecasting methods. The proposed method can be applied on practical data, such as stock forecasting, topic trend detection. / Doctor of Philosophy / This dissertation focuses on three projects that are related to data reduction and statistical modeling of data with complex structures. In chapter 2, we propose a filtering approach of data for parameter estimation of sparse regression. Given data with thousands of ob- servations and predictors or even more, large storage and computation spaces is need to handle these data. It is challenging to computational power and takes long time in terms of computational cost. So we come up with an algorithm (FAME) that can reduce both the number of observations and predictors. After data reduction, this subdata selected by FAME keeps most information of the original dataset in terms of parameter estimation. Compare with existing methods, the dimension of the subdata generated by the proposed algorithm is smaller while the computational time does not increase.
In chapter 3, we use quantitative-sequence (QS) factor to describe experimental data. One simple example of experimental data is milk tea. Adding 1 cup of milk first or adding 2 cup of tea first will influence the flavor. And this case can be extended to cases when there are thousands of ingredients need to be input into the experiment. Then the order and amount of ingredients will generate different experimental results. We use QS factor to describe this kind of order and amount. Then by transforming the QS factor to a matrix containing continuous value and set this matrix as input, we model the experimental results with a simple Gaussian process.
In chapter 4, we propose an autoregression-based clustering and forecasting method of multi- variate time series data. Existing research works often treat each time series independently. Our approach incorporates the inherent correlation of data and cluster related series into one group. The forecasting is built based on each cluster and data within one cluster can cross predict each other. One application of this method is on topic trending detection. With thousands of topics, it is unfeasible to apply one model for forecasting all time series. Considering the similarity of trends among related topics, the proposed method can cluster topics based on their similarity, and then perform forecasting in autoregression model based on historical data within each cluster.
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