• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 277
  • 115
  • 82
  • 33
  • 33
  • 33
  • 9
  • 5
  • 5
  • 5
  • 5
  • 5
  • 5
  • 5
  • 5
  • Tagged with
  • 710
  • 82
  • 81
  • 66
  • 60
  • 54
  • 52
  • 50
  • 48
  • 47
  • 46
  • 44
  • 42
  • 36
  • 35
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
121

Estratégias de fornecimento de ração para Araras Canindé (Ara ararauna, LINNAEUS, 1758) em cativeiro /

Peres, Narah Vieira. January 2018 (has links)
Orientador: Rosemeire da Silva Filardi / Resumo: Os estudos abordando a nutrição e alimentação de aves silvestres em cativeiro são bastante escassos. Os psitacídeos representam um grande grupo de aves que necessitam de atenção quanto aos aspectos conservacionistas devido ao tráfico e à grande perda de seu habitat natural. Devido a esses fatores atualmente o número de araras em zoológicos e centros de conservação é grande. A alimentação correta dessas aves em cativeiro representa um desafio, isso por possuírem alta sensibilidade gustativa, o que causa certa seletividade na alimentação e desperdício de ração. Objetivou-se avaliar diferentes estratégias de fornecimento de uma ração comercial associada à banana para Arara Canindé (Ara ararauna). O experimento foi realizado no Centro de Conservação da Fauna Silvestre, no município de Ilha Solteira, Estado de São Paulo. Foram utilizadas 8 Araras Canindé (Ara ararauna) alojadas individualmente em gaiolas adaptadas para coleta de excretas (0,75 x 0,75 x 1,0 m) e sobras ou desperdício de alimento. As aves foram distribuídas em um delineamento inteiramente casualizado com 4 tratamentos e medida repetida no tempo, totalizando seis repetições por tratamento (24 unidades experimentais). Os tratamentos avaliaram quatro estratégias de alimentação de araras: ração comercial; associação de 70% de ração comercial com 30% de banana; associação de 50% de ração comercial com 50% de banana e ração comercial moída aglomerada à banana (50% ração, 50% banana). As dietas que apresentaram a banana ti... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Studies addressing the nutrition and feeding of wild birds in captivity are rather scarce. Macaws represent a large group of birds that need attention to conservation issues due to trafficking and the great loss of their natural habitat. Due to these factors currently, the number of macaws in zoos and conservation centers is great. The correct feeding of these birds in captivity poses a challenge because they have a high gustatory sensitivity, which causes certain selectivity in feed and wastage of feed. The objective of this study was to evaluate different strategies for supplying a commercial ration associated with the banana for Arara Canindé (Ara ararauna). The experiment was carried out at the Wild Fauna Conservation Center, in Ilha Solteira city, State of São Paulo. Eight Araras Canindé (Ara ararauna) were housed individually in cages adapted for collection of excrement (0.75 x 0.75 x 1.0 m) and leftovers or food waste. The birds were distributed in a completely randomized design with four treatments during three periods of five days of harvest, with seven days of adaptation between harvests, totaling six replicates per treatment (24 experimental units). The treatments evaluated four strategies of macaw feeding: commercial ration; association of 70% commercial ration with 30% of banana; 50% commercial ration with 50% banana and ground commercial ration agglomerated with banana (50% ration, 50% banana). The diets that had fruit had a higher total food consumption, but wh... (Complete abstract click electronic access below) / Mestre
122

Comportamento ambiental e bioatividade sobre plantas daninhas de herbicidas residuais aplicados sobre a palha de cana-de-açúcar em diferentes condições hídricas do solo / Behaviour and environmental bioactivityon weeds of herbicides residualapplied on sugarcane residues in different soil with water conditions

Silva, Paulo Vinícius da 30 May 2018 (has links)
Herbicidas aplicados nos sistemas de cana-de-açúcar, diretamente no solo ou sobre palha, ficam disponíveis a fenômenos de transporte, retenção e transformação. Nesse contexto, o objetivo desse trabalho foiavaliar a lixiviação e sorção de herbicidas residuais em solos com diferentes características físicoquímicas e em palha de cana-de-açúcar. Para tal, foram realizados quatro experimentos. O primeiro relativo à lixiviação, através da metodologia de bioensaios, seguindo o esquema fatorial 8 x 2 x 2, em delineamento inteiramente casualizado, com quatro repetições, sendo oito profundidades do perfil do solo, dois períodos de seca (0 e 30 dias após a aplicação dos tratamentos - DAT) e duas quantidades de palha, esse fatorial foi adotado de forma individual para os herbicidas amicarbazone (1225 g i.a. ha-1 ); imazapic (147 g i.a ha- 1 ), sulfentrazone (800 g i.a ha-1 ) e tebuthiuron (900 g i.a ha-1 ). Os herbicidas foram aplicados no topo de colunas de solo montadas em tubos de PVC com 0 e 10 t ha-1 de palha, esses tratamentos foram submetidos aos três diferentes períodos de seca (0 e 30 DATs), ao final dessas épocas foi realizada uma simulação de chuva de 30 mm e realizada a semeadura de Cucumis sativus (planta bioindicadora), as avaliações de fitoxicidade foram efetuadas aos 7, 10 e 15 dias após a emergencia - DAE, aos 15 DAE foramrealizadas as avaliações de massa seca e altura da parte aérea das plantas. O segundo experimento consistiu na determinação de coeficientes de adsorção e dessorção (Kd e Koc) em 15 solos com diferentes características físico-químicas, para os herbicidas indaziflam, imazapic e amicarbazone. Foi utilizada a metodologia de herbicidas rádio marcados com C14, aplicou-se cinco diferentes concentrações dos herbicidas frios (0,125, 0,25, 0,50, 0,75 e 1,00 ppm), associados aos diferentes solos e herbicidas rádio marcados nas concentrações de 0,24 KBq de indaziflam, 0,26 KBq de imazapic ou 0,20 KBq de amicarbazone, de forma individual em cada unidade experimental. A concentração dos herbicidas rádio marcados presentes no sobrenadante foi determinada por espectroscopia de cintilação líquida (LSS) e por diferença entre a quantidade inicialmente aplicada e a presente na solução do solo, determinando-se adsorção. Através do mesmo processo também foi avaliada a dessorção dos herbicidas em quatro dias de análise. O terceiro experimento avaliou a adsorção de indaziflam, imazapic e amicarbazone em palha de cana-de-açúcar. Um estudo típico e equilíbrio em lotes foi conduzido para determinar adsorção e dessorção em diferentes concentrações dos herbicidas. A palha de cana-de-açúcar (0,27 g) foi combinada com três concentrações dos herbicidas (0,125, 0,5 e 1 ppm) mais os herbicidas radiomarcados nas seguintes quantidades: 0,24 KBq de indaziflam, 0,26 KBq imazapic e 0,20 KBq de amicarbazone. Após o estabelecimento do equilíbrio que foi de 24 horas para os três herbicidas, foi determinada a quantidade de herbicida adsorvida na palha de cana-de-açucar. Após a analise da adsorção, a solução presente nas unidades experimentais foi descartada e reposta por uma solução de cloreto de cálcio, e a dessorção foi então analisada após 24 horas, durante o período de um dia para amicarbazone, cinco dias para indaziflam, e não foi realizada analise de dessorção para o herbicida imazapic.Um quarto experimento, abordou a intercepção de herbicidas pela palha de cana-de-açúcar mediante a simulação de chuvas em diferentes precipitações (3, 6, 12 e 24 mm). Os herbicidas foram aplicados em duas quantidades de palha de cana-de-açúcar, as quais foram espalhadas de forma uniforme sobre uma tela de aço inoxidável (5 t ha-1 e 10 t ha-1), em seguida, essa tela foi colocada sobre um recipiente de vidro. As simulações de chuva ocorreram aos 0 horas, 24 horas e sete dias após a aplicação dos tratamentos. Para o herbicida amicarbazone aos 0 DAT sem palha, a lixiviação do herbicida amicarbazone foi notada ate os 25 cm, sendo os efeitos fitotoxicos mais expressivos observados nos primeiros 15 cm, já nas aplicações de 30 DAT, nos tratamentos com palha e sem palha a lixiviação foi notada até os 10 cm, com maior fitotoxicidade nos primeiros 5 cm. Na lixiviação tebuthiuron e imazapic e sulfentrazone a permanência do produto sobre a palha de cana-de-açúcar durante 30 DAT tornou a lixiviação desses herbicidas menor. Para o herbicida sulfentrazone a presença de palha imapctou de maneira mais expressiva na lixiviação desse herbicida que o perido de seca. Para imazapic e amicarbazone, os valores de Kd foram baixos devido à sua alta solubilidade em água; no entanto, a adsorção de imazapic foi fortemente influenciada pelo pH do solo, e para amicarbazone a adsorção e dessorção foi influenciada pela matéria orgânica e pH dos solos. Para indaziflam, Kd foi correlacionado negativamente com o teor de argila, mas foi positivamente correlacionado com a matéria orgânica. A adsorção de indaziflam foi superior a 80% em todas as concentrações, enquanto que a adsorção imazapic foi inferior a 7% em todas as concentrações. A adsorção de amicarbazone foi inferior a 20% em todas as concentrações. A dessorção de indaziflam foi de 30%, 28,5% e 27,5% a 0,125, 0,5 e 1 ppm, respectivamente, após 5 dias. A dessorção máxima para amicarbazone foi observada a 1 ppm com 11%. Para o indaziflam, após um período de sete dias após a aplicação dos herbicidas sobre a palha de cana-de-açúcar simulou-se uma precipitação de 24 mm resultando na remoção de apenas 25% do herbicida interceptado. Para o herbicida imazapic a palha de cana-de-açúcar não apresentou uma barreira de expressiva para interceptação desse produto. Dessa forma, as características dos herbicidas, como a solubilidade em água e Kow, podem ser utilizadas para determinar a sua dinâmica em sistemas de produção de cana-de-açúcar, sendo que os atributos lixiviação, sorção em palha e em solo, podem direcionar a uma predileção do comportamento agronômico e destino ambiental de herbicidas residuais. Dessa forma, pode-se concluir que a presença de palha na superfície do solo atrelada aos diferentes períodos de seca pode afetar a mobilidade desses herbicidas no ambiente. Conclui-se que as cracteristicas físico-quimicas dos herbicidas associadas com os atributos do solo podem direcionar a dinâmica de adsorção e dessorção dos herbicidas. As características dos herbicidas, como a solubilidade em água e Kow, podem ser utilizadas para determinar a dificuldade de remoção dos herbicidas em palha de cana-de-açucar. / Herbicides applied to sugar cane systems, directly on the soils our by residues, are available to transport, retention and transformation phenomenon. In this context, the objective of this work was to evaluate the leaching and sorption of residual herbicides in soils with different physicochemical characteristics and in sugarcane residues. Four experiments were carried out. The first, was based on the bioassay methodology, followed the 8 x 2 x 2 factorial scheme, in a completely randomized design, with four replications, eight depths of the soil profile, two dry periods (0 and 30 days after application of the treatments (DAT) and two quantities of residues, this factorial was adopted individually for the herbicides amicarbazone (1225 g ia ha-1); imazapic (147 g i.a ha-1), sulfentrazone (800 g i.a ha-1) and tebuthiuron (900 g i.a ha-1). The herbicides were applied to the top of soil columns mounted in PVC tubes with 0 and 10 t ha-1 of straw, these treatments were submitted to the three different periods of dry (0 and 30 DATs), at the end of those times a 30 mm rainfall simulation and Cucumis sativus sowing (bioindicator plant), phytotoxicity (7, 10 and 15 DAE), dry mass and shoot height were evaluated. It was noted that the greatest phytotoxicity of the herbicide amicarbazone was in the 0-5 cm layer. And that periods of drought and straw decreased the mobility of this herbicide in the columns. In leaching tebuthiuron, imazapic and sulfentrazone the permanence of the product on the sugarcane straw during 30 DAT made the leaching of this herbicide minor. Thus, it can be concluded that the presence of straw on the soil surface coupled to the different periods of drought can affect the mobility of these herbicides in the environment. The second experiment consisted in the determination of coeficivity of adosorption and desorption (Kd and Koc) in 16 soils with different physicochemical characteristics, for the herbicides indaziflam, imazapic and amicarbazone. The C14- labeled radio-herbicide methodology was used to apply five different concentrations of the cold herbicides (0.125, 0.25, 0.50, 0.75 and 1.00 ppm), associated with the different soils and herbicides radio -marked at the concentrations of 0.24 KBq of indaziflam, 0.26 KBq of imazapic or 0.20 KBq of amicarbazone, individually in each experimental unit. The concentration of radiolabelled herbicides present in the supernatant was determined by liquid scintillation spectroscopy (LSS) and by difference between the amount initially applied and the present in the soil solution, determining adsorption. Through the same process the herbicide desorption was also evaluated in four days of analysis For imazapic and amicarbazone, Kd values were low due to their high solubility in water; however, the adsorption of imazapic was strongly influenced by the pH of the soil, and for amicarbazone the adsorption and desorption was influenced by the organic matter and pH of the soils. For indaziflam, Kd was negatively correlated with clay content but was positively correlated with organic matter. The third experiment evaluated the adsorption of indaziflam, imazapic and amicarbazone in sugarcane straw. A typical study and batch equilibrium was conducted to determine adsorption and desorption at different concentrations of the herbicides. Sugarcane residues (0.27 g) was combined with three concentrations of the herbicides (0.125, 0.5 and 1 ppm) plus 0.24 KBq of indaziflam, 0.26 KBq imazapic or 0.20 KBq of labeled amicarbazone radio. The adsorption of indaziflam, imazapic and amicarbazone was evaluated 24, 48 and 120 hours, respectively, after the contact of sugarcane residues. Indaziflam adsorption was greater than 80% at all concentrations, while imazapic adsorption was below 7% at all concentrations. The adsorption of amicarbazone was less than 20% at all concentrations. Indaziflam desorption was 30%, 28.5% and 27.5% at 0.125, 0.5 and 1 ppm, respectively, after 5 days. Maximum desorption for amicarbazone was observed at 1 ppm with 11%. The desorption for imazapic was not determined due to the low initial adsorption. A fourth experiment, addressed the interception of herbicides by sugarcane straw through simulated rainfall in various amounts of precipitation (3, 6, 12 and 24 mm). Two amounts of sugarcane straw were uniformly spread over a stainless steel screen (5 t ha-1 and 10 t ha-1), then the screen was placed on a Pyrex® pan. The rain simulations occurred at 0 hr, 24 hrs and seven days after the treatments were applied. For indaziflam, a period of seven days after application of the herbicides on the sugarcane straw was simulated a precipitation of 24 mm resulting in the removal of only 25% of the adsorbed herbicide. For the herbicide imazapic the sugarcane straw did not present an expressive barrier to interception of this product. Thus, the characteristics of the herbicides, such as water solubility and Kow, can be used to determine their dynamics in sugarcane production systems, and the leaching, straw sorption and soil attributes can a predilection for agronomic behavior and environmental fate of residual herbicides.
123

Congruences for Fourier Coefficients of Modular Functions of Levels 2 and 4

Moss, Eric Brandon 01 July 2018 (has links)
We give congruences modulo powers of 2 for the Fourier coefficients of certain level 2 modular functions with poles only at 0, answering a question posed by Andersen and Jenkins. The congruences involve a modulus that depends on the binary expansion of the modular form's order of vanishing at infinity. We also demonstrate congruences for Fourier coefficients of some level 4 modular functions.
124

Validation of software for the calculation ofaerodynamic coefficients : with a focus on the software package Tornado

Lopez Pereira, Ramon January 2010 (has links)
<p>Several programs exist today for calculating aerodynamic coefficients that with some simplificationsprovide fast approximations of the values for a real aircraft.Four different programs were analyzed for this report: Tornado, AVL, PANAIR and a handbook-typepreliminary method. In addition, ANSYS CFX was used for airfoil validation. For calculation of the zerolift drag, an approximation was computed in order to calculate the remaining values that were notcalculated by the software: drag contribution for fuselages, nacelles and some horizontal stabilizersand fins.Different types of aircraft were selected for trial: two commercial aircraft (Boeing 747-100 and 777-300), a TF-8A research airplane (with area rule application: some additions were made to the fuselageto prevent large variations in the cross-section when the contribution of the wing is added), a LockheedConstellation C-69 used as a military cargo airplane, a Boeing Stratocruiser used by the USAF withtwo configurations (basic and bomber), and an Aero Commander 680 Super, similar to a Cessna 162.Two airfoils (NACA2412, 0012) were also analyzed, to investigate the limitations of software designedfor three-dimensional calculations.The accuracy of the results showed that the validity of the software depends on the planform of theaircraft, as well as the simulation parameters Mach number and Reynolds number. The shape of thewing caused some of the methods to have serious difficulties in converging to valid results, orincreased the simulation time beyond acceptable limits.</p> / <p>Numera finns det olika program för beräkning av de aerodynamiska koefficienterna från en modellmed vissa förenklingar som ger en snabb approximation av värdena för ett verkligt flygplan.Fyra olika program har analyserats för denna rapport: Tornado, AVL, PANAIR och en handbokbaserad preliminär metod. Dessutom användes ANSYS CFX för validering av vingprofiler . Vidberäkningen av noll-lyft motståndet, en approximation användes för de återstående delarna som inteberäknas av de andra metoderna: motståndsbidraget från flygkroppar, gondoler och vissa horisontellastabilisatorer och fenor.Olika flygplaner har testats: två trafikflygplan (Boeing 747-100 och 777-300), ett TF-8Aforskningsflygplan (med area regel användning: några tillägg gjordes på flygkroppen för att tvärsnitteninte har stora variationer när bidraget från vingen läggas), ett Lockheed Constellation C-69, ett BoeingStratocruiser som används av USAF i två konfigurationer (den vanliga och bombplan), och ett AeroCommander 680 Super, som liknar ett Cessna 162. Två vingprofiler (NACA 2412, 0012) analyseradesockså, för att kontrollera begränsningarna av programmen avsedd för tredimensionella beräkningar.Riktigheten av resultaten visade att giltigheten av programmen beror på formen av flygplanernasvingar, samt de simulationernas parametrar: Mach nummer och Reynolds nummer. Formen på vingenorsakade några av de metoderna att ha stora svårigheter med konvergensen till giltiga resultat, ellerökat simulering tid över acceptabla gränser.</p>
125

An Experimental re-evaluation of Photon Mass Attenuation Coefficients

2013 February 1900 (has links)
Photon mass attenuation coefficients are indispensable input parameters for use in several disciplines. They are of value for medical diagnostics, radiation therapy, material science, etc. Currently, photon mass attenuation coefficients derived from model calculations are widely used. This project directly measured the photon mass attenuation coefficients of water and a number of water based solutions. These measurements were made using a High Purity Germanium (HPGe) detector allowing for increased resolution beyond traditional techniques. Four sources were used (\Ba, \Eu, \Cs, \Am) producing multiple photons of interest over the range of 40 keV to 1.4 MeV, allowed for simultaneous collection of data and a refining of uncertainties beyond past techniques. Direct measurements using a new liquid technique supported the validity of Bragg's additive law, allowing for the mass attenuation coefficient of a constituent element to be calculated from a set of independent measurements. This technique allows materials not easily directly measured to be determined without an overburdening increase in uncertainty. The same direct measurements showed a deviation from the currently relied upon National Institute of Standards and Technology (NIST) database - XCOM. Investigations of the deviation and surrounding references showed XCOM being at most accurate to 5 \% relative uncertainty.
126

Characterization of mixing and spreading in heterogeneous media

Zavala Sánchez, Gabriela Vanessa 02 July 2008 (has links)
No description available.
127

Validation of software for the calculation ofaerodynamic coefficients : with a focus on the software package Tornado

Lopez Pereira, Ramon January 2010 (has links)
Several programs exist today for calculating aerodynamic coefficients that with some simplificationsprovide fast approximations of the values for a real aircraft.Four different programs were analyzed for this report: Tornado, AVL, PANAIR and a handbook-typepreliminary method. In addition, ANSYS CFX was used for airfoil validation. For calculation of the zerolift drag, an approximation was computed in order to calculate the remaining values that were notcalculated by the software: drag contribution for fuselages, nacelles and some horizontal stabilizersand fins.Different types of aircraft were selected for trial: two commercial aircraft (Boeing 747-100 and 777-300), a TF-8A research airplane (with area rule application: some additions were made to the fuselageto prevent large variations in the cross-section when the contribution of the wing is added), a LockheedConstellation C-69 used as a military cargo airplane, a Boeing Stratocruiser used by the USAF withtwo configurations (basic and bomber), and an Aero Commander 680 Super, similar to a Cessna 162.Two airfoils (NACA2412, 0012) were also analyzed, to investigate the limitations of software designedfor three-dimensional calculations.The accuracy of the results showed that the validity of the software depends on the planform of theaircraft, as well as the simulation parameters Mach number and Reynolds number. The shape of thewing caused some of the methods to have serious difficulties in converging to valid results, orincreased the simulation time beyond acceptable limits. / Numera finns det olika program för beräkning av de aerodynamiska koefficienterna från en modellmed vissa förenklingar som ger en snabb approximation av värdena för ett verkligt flygplan.Fyra olika program har analyserats för denna rapport: Tornado, AVL, PANAIR och en handbokbaserad preliminär metod. Dessutom användes ANSYS CFX för validering av vingprofiler . Vidberäkningen av noll-lyft motståndet, en approximation användes för de återstående delarna som inteberäknas av de andra metoderna: motståndsbidraget från flygkroppar, gondoler och vissa horisontellastabilisatorer och fenor.Olika flygplaner har testats: två trafikflygplan (Boeing 747-100 och 777-300), ett TF-8Aforskningsflygplan (med area regel användning: några tillägg gjordes på flygkroppen för att tvärsnitteninte har stora variationer när bidraget från vingen läggas), ett Lockheed Constellation C-69, ett BoeingStratocruiser som används av USAF i två konfigurationer (den vanliga och bombplan), och ett AeroCommander 680 Super, som liknar ett Cessna 162. Två vingprofiler (NACA 2412, 0012) analyseradesockså, för att kontrollera begränsningarna av programmen avsedd för tredimensionella beräkningar.Riktigheten av resultaten visade att giltigheten av programmen beror på formen av flygplanernasvingar, samt de simulationernas parametrar: Mach nummer och Reynolds nummer. Formen på vingenorsakade några av de metoderna att ha stora svårigheter med konvergensen till giltiga resultat, ellerökat simulering tid över acceptabla gränser.
128

Essays on Dynamic Demand Estimation

Wang, Yucai Emily January 2011 (has links)
<p>This dissertation consists of three chapters relating to dynamic demand models of storable goods and their application to taxes that are imposed on soft drinks. Broadly speaking, the first chapter builds the estimation strategy for dynamic demand models of storable goods that allows for unobservable heterogeneous preferences in household's tastes. The second chapter uses the estimation strategy developed in the first chapter to study the policy implications of taxes that are imposed on sugary soft drinks. The last chapter explores and provides an explanation for the level of pass-through for soda taxes. </p><p>To be more specific, the first chapter develops techniques for incorporating systematic brand preferences in dynamic demand models of storable goods. Dynamic demand models are important for correctly measuring price elasticities of products that can be stockpiled. However, most of the literature excludes systematic preferences over consumers' brand tastes. This chapter resolves this issue by incorporating random coefficient Logit models into a dynamic demand framework and hence allows for realistic demand substitution patterns. It builds on Hendel and Nevo's 2006 Econometrica paper, where the authors introduce a model of dynamic demand that flexibly incorporates observable heterogeneity and estimates it via a three-step procedure that separates brand and volume choices. While a powerful tool, this method is tricky to execute. Therefore, this chapter also discusses the difficulties that may face implementers.</p><p>The second chapter predicts the effects of taxes on sugar sweetened soft drinks (sugar taxes) on both total consumption and the welfare of different types of consumers. It specifies and estimates a structural dynamic demand model of storable goods with rational and forward-looking households. It flexibly incorporates persistent heterogeneous consumer preferences and develops a computationally attractive method for estimating its parameters. Sugar taxes have been proposed at both the national and state-level, and passed in three states, as a means of slowing or reversing the growth in obesity and diabetes. To accurately analyze the effects of these policies, this chapter takes two specific aspects of soft drinks into account: storability and differentiation. It compares the results from this model to two benchmark studies: a static model with consumer heterogeneity and a dynamic model without households' persistent heterogeneous tastes. It finds that failing to account for dynamics (i.e. storability) results in overestimated reduction in consumption and failing to account for persistent heterogeneous preferences (i.e. differentiation) results in overestimated reduction in consumption and underestimated welfare loss. The model and method developed here are readily applicable to many studies involving storable goods, such as firms' optimal pricing behavior and anti-trust policies analyses.</p><p>The third and last chapter focuses on the incidence of soda taxes by studying the pass-through level of these taxes. It lays out a framework for thinking about the determinants of the pass-through level. More specifically, it builds theoretical models that examine the pass-through under more complex supply structures with multiple manufactures and retailers. In addition to providing some intuition behind theoretical predictions of the models, this chapter also presents empirical results found in the data along with their implications.</p> / Dissertation
129

Dynamic and Static Characteristics of a Rocker-Pivot, Tilting-Pad Bearing with 50% and 60% Offsets.

Kulhanek, Chris David 2010 December 1900 (has links)
Static performance and rotordynamic coefficients are provided for a rocker-pivot, tilting-pad journal bearing with 50 and 60 percent offset pads in a load-between-pad configuration. The bearing uses leading-edge-groove lubrication and has the following characteristics: 5-pads, 101.6 mm (4.0 in) nominal diameter, .0814 - .0837 mm (.0032 - .0033 in) radial bearing clearance, .25 to .27 preload, 60.325 mm (2.375 in) axial pad length. Operating conditions included loads from 0 to 3101 kPa (450 psi) and speeds from 7 to 16 krpm. Dynamic tests were conducted over a range of frequencies to obtain complex dynamic stiffness coefficients as functions of excitation frequency. For most test conditions, the direct real dynamic stiffnesses were well fitted with a quadratic function with respect to frequency. This curve fit allowed for the stiffness frequency dependency to be captured by including an added mass matrix [M] to a conventional [K][C] model, producing a frequency independent [K][C][M] model. The direct imaginary dynamic stiffness coefficients increased linearly with frequency, producing frequency independent direct damping coefficients. Compared to the 50 percent offset, the 60 percent offset configuration’s direct stiffness coefficients were larger at light unit loads. At high loads, the 50 percent offset configuration had a larger direct stiffness in the loaded direction. Negative direct added-mass coefficients were regularly obtained for both offsets, especially in the unloaded direction. Added-mass magnitudes were below 32 kg for all test cases. No appreciable difference was measured in direct damping coefficients for both pivot offset. A bulk-flow Navier-Stokes CFD code provided rotordynamic coefficient predictions. The following stiffness and damping prediction trends were observed for both 50 and 60 percent offsets. The direct stiffness coefficients were modeled well at light loads and became increasingly over-predicted with increasing unit load. Stiffness orthotropy was measured at zero and light load conditions that was not predicted. Direct damping predictions in the loaded direction increased significantly with unit load while the experimental direct damping coefficients remained constant with load. The direct damping coefficients were reasonably modeled only at the highest test speed of 16 krpm. Experimental cross-coupled stiffness coefficients were larger than predicted for both offsets, but were of the same sign and considerably smaller than the direct coefficients.
130

Theory versus experiment of the rotordynamic and leakage characteristics of smooth annular bushing oil seals

Culotta, Vittorio G. 17 February 2005 (has links)
This thesis provides a comparison of experimental rotordynamic coefficients for laminar, smooth bushing oil seals to theoretical predictions from XLLubeGT and XLAnSeal. The experimental results come from a new test rig developed at the Turbomachinery Laboratory at Texas A&M University. The two software programs were developed to predict the static and dynamic characteristics of seals. XLLubeGT is a Reynolds equation based program while XLAnSeal is based on a bulk-flow Navier- Stokes model that includes temporal and convective acceleration terms. XLAnSeal was used to predict the added-mass terms of the seals since XLLubeGT assumes those terms to be zero or negligible. The data used for input into the two seals code was the actual measured conditions from the test rig. As part of the input parameters, inlet inertia effects and thermal gradients along the seal were included. Both XLLubeGT and XLAnSeal have the capability to analyze straight bore seals with different inlet and outlet clearances – essentially a tapered seal – but seal expansion caused by the radial differential pressure across the seal bushing was not included. Theoretical and experimentally determined dynamic characteristics include stiffness, damping, inertia terms and Whirl Frequency Ratio (WFR). Seal static characteristics are also reported. They include: leakage, shaft center line loci and Reynolds numbers. Test conditions include three shaft speeds: 4000, 7000 and 10,000 rpm, three test pressures: 21, 45 and 69 bar [300, 650, and 1000 psi] and multiple eccentricities from 0.0 to 0.7. The results for the dynamic characteristics show good correlation of the experimental data to the theoretical values up to an eccentricity of about 0.5. At higher eccentricities, the theory generally under-predicts the dynamic characteristics. Inertia terms are greatly under-predicted. The results for the static characteristics also show good correlation to the experimental data, but they also have a tendency to be under-predicted at higher eccentricities.

Page generated in 0.0745 seconds