This paper reports on the study of the strategy use of Chinese English majors in vocabulary learning; the individual differences between effective and less effective learners in employing vocabulary learning strategies and the relationship between their strategies and their outcome in English learning. In this research, 118 junior English majors inChineseUniversitywere investigated. The participants were asked to take a vocabulary test and complete a vocabulary-learning questionnaire.   The data collected was analyzed using the SPSS (the Statistical Package for Social Science) and the result indicates that there are significant differences between effective and less effective learners. Effective learners use strategies more frequently and flexibly, while less effective learners turn out to be rote learners. They employ repetition strategy more often and they rely more on their mother tongue, Chinese, in vocabulary learning. Thus the translation strategy was extensively used among them. The result also shows that seven strategies, namely applied, categorization, self-monitoring, cooperation, media, elaboration and dictionary strategy are positively correlated with the vocabulary test scores and the Test for English Majors (Grade 4) scores. The above findings have certain implication for both learners and teachers.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Corn is one of the crops that produce more in the world; it has a wise geographic distribution. It happens because of the big genetic variability present, including in creole cultivates which they are normally produced in small properties. The main goals of this study were to evaluate the growing and the relation between the seeds labile, grown plants and of the Amarelão creole cultivates, Lombo Baio and Oito carreiras as well as the maternal half-brothers progenies from these cultivates. The experiment happened in Santa Maria, RS in the agricultural year of 2012/2013, in block delineations aimlessly with four repetitions and portions constituted by two lines of five meters to the creole cultivates and a lattice delineation with constituted portions one line of five meters with a space of 0,2m and between lines of 0,9m. For an analysis of the growing plants was accomplished five evaluations of the plant height and leaves numbers by plant and the growing curves were adjusted by logistic model because of the thermal sum accumulated. To analyze the canonical correlation were evaluated: mass, length, width, and seeds thickness; plant height, ear insertion height, thatch diameter and leaves number by plant for grown plants, grain weights, row numbers and grain numbers by rows to the production. The logistic model was adequate to the growing curve adjusts to progenies of maternal half-brothers and corn creole cultivates. Amarelão creole cultivates, Lombo baio and Oito carreiras present the highest plant and the biggest number of leaves by plant in comparison to concerning progenies of maternal half-brothers. The most important canonical correlations were gotten between labile groups of the grown plant and production. The labile plant height and thatch diameter were the most favorable the grain production. / O milho é uma das culturas mais produzidas no mundo, com ampla distribuição geográfica. Isso se deve a grande variabilidade genética presente, inclusive em cultivares crioulas, normalmente produzidas em pequenas propriedades. Os objetivos do estudo foram avaliar o crescimento e a relação entre variáveis de sementes, plantas adultas e de produção das cultivares: crioulas Amarelão, Lombo Baio e Oito Carreiras, bem como, de progênies de meios-irmãos maternos destas cultivares. O experimento foi conduzido em Santa Maria, RS, no ano agrícola 2012/2013, em delineamento blocos ao acaso com quatro repetições e parcelas constituídas por duas fileiras de cinco metros e espaçamento entre plantas de 0,2 m e entre fileiras de 0,9 m para as cultivares crioulas e, delineamento em látice com parcelas constituídas de uma fileira de cinco metros e espaçamento entre plantas de 0,2 m e entre fileiras de 0,9 m para as progênies. Para análise de crescimento das plantas, foram realizadas cinco avaliações de altura de planta e número de folhas por planta, com as curvas de crescimento sendo ajustadas pelo modelo logístico em função da soma térmica acumulada. Para análise das correlações canônicas foram avaliadas: massa, comprimento, largura e espessura das sementes, altura de planta, altura de inserção da espiga, diâmetro do colmo e número de folhas por planta para plantas adultas e peso de grãos, número de fileiras e grãos por fileira para a produção. O modelo logístico foi adequado para o ajuste das curvas de crescimento para progênies de meios-irmãos maternos e cultivares crioulas de milho. As cultivares crioulas: Amarelão, Lombo Baio e Oito Carreiras apresentaram maior altura de plantas e maior número de folhas por planta em comparação às respectivas progênies de meios-irmãos maternos. As correlações canônicas mais importantes foram obtidas entre os grupos de variáveis de planta adulta e de produção. As variáveis altura de planta e diâmetro do colmo as que mais favorecem a produção de grãos.

Ce travail de thèse porte sur l’étude expérimentale des polaritons de microcavité dans des microstructures de semiconducteurs III-V. Il présente un volet fondamental sur les propriétés de cohérence et de polarisation des lasers à polaritons, et un volet plus applicatif dédié à la démonstration de principe de nouveaux dispositifs tout optique à polaritons.Dans la première partie, nous utilisons une caméra streak en mode « single shot » pour mesurer des corrélations de photons du second ordre avec une résolution à la picoseconde. Cette technique nous permet de mesurer la statistique d’émission de lasers à polaritons. Nous analysons ainsi la dynamique à l’échelle picoseconde de l’établissement de la cohérence spontanée et de la polarisation du mode, à l’allumage du laser. Nous mettons en évidence une initialisation stochastique de la polarisation, suivie d’une précession autour d’un champ magnétique effectif présent dans la cavité. Le rôle de la dimensionnalité de la cavité est discuté, et un modèle théorique permet une meilleure compréhension de ces mesures. La deuxième partie est dédiée à la réalisation de dispositifs à polaritons, dont le contrôle est tout optique. Ces dispositifs sont essentiellement constitués d’un résonateur 0D couplés à des guides 1D d’entrée et de sortie. Nous démontrons le fonctionnement d’un « router » à polaritons, et observons une bistabilité optique du résonateur 0D pilotée à distance. Ce dernier effet est l’ingrédient de base d’une mémoire optique, et nous montrons des résultats préliminaires concernant l’implémentation de portes logiques tout optiques AND, OR et XOR. / This PhD thesis is dedicated to the experimental study of microcavity polaritons in III-V semiconductor microstructures. It consists in a fundamental part focusing on the coherence and polarization properties of polariton lasers, and in a more applied second part which concerns the proof of principle of new all-optical polariton devices.In the first part, we use a streak camera in the single shot regime to measure second order photon correlations with a picosecond resolution. This technique allows measuring the emission statistics of polariton lasers and analyzing at the picosecond scale the dynamics of the establishment of the spontaneous coherence and polarization of the mode during the laser initialization. We show a stochastic initialization of the polarization followed by a precession around an effective magnetic field inside the cavity. The influence of the system dimension is discussed and a theoretical model allows us to better understand these measurements. The second part is dedicated to the realization of polariton devices with an all-optical control. These devices are constituted of a 0D resonator coupled to 1D input and output waveguides. We demonstrate the operation of a polariton router and a remotely controlled optical bistability. This last effect is the core ingredient of an optical memory and we show preliminary results on the implementation of all-optical AND, OR and XOR logic gates.

Les théories de champ moyen quantique représentent une base robuste pour la description de la dynamique de nombreux systèmes physiques, des noyaux aux systèmes moléculaires et aux agrégats. Cependant, le traitement incomplet des corrélations électroniques au niveau du champ moyen empêche de donner une description propre de la dynamique, en particulier la dynamique dans les régimes dissipatifs. La dissipation est intrinsèquement liée à la thermalisation qui représente le phénomène cible à d'écrire dans ce travail. Nous avons exploré un schéma purement quantique en terme des matrices densités et qui consiste en l'inclusion des corrélations de type collisions, responsables de la thermalisation dans les systèmes quantiques finis. Ceci est fait en traitant les corrélations entre deux particules avec la théorie des perturbations dépendantes du temps tout au long d'un intervalle de temps. Ceci permet de créer un ensemble d'états de type champ moyen pur pour les différentes configurations. Ces états sont traités stochastiquement dans la dynamique et fournissent en moyenne un état corrélé. Nous proposons dans ce travail une reformulation de cette théorie en terme des fonctions d'ondes où les corrélations sont traitées comme des transitions multiples de type particule-trou, limitées aux transitions deux-particules-deux-trous dans notre cas. On applique le schéma obtenu à un modèle unidimensionnel simulant de petites molécules. La capacité de cette théorie à introduire les effets dissipatifs dans le cadre du champ moyen est illustrée à travers plusieurs observables tels que les matrices à un et deux corps, les nombres d'occupation et l'entropie à un corps / Quantum mean field theories represent a robust basis for the description of many dynamical situations from nuclei to molecular systems and clusters. However, the missing of electronic correlations on top of mean field prevents them to give a proper description of the dynamics, in particular dissipative dynamics. Dissipation is intrinsically linked to thermalization which represents the target phenomenon to be described in this thesis. We thus explore a fully quantum mechanical strategy proposed in terms of density matrices in the case of nuclear collisions and which consists in the inclusion of collisional correlations responsible of thermalization in quantum finite systems. This is done by treating two body correlations in time dependent perturbation theory along a certain time span that allows to create an ensemble of pure mean field states for different configurations. These states are used into the dynamics, stochastically, providing in the average one correlated state. We propose in this work a reformulation of this theory in term of wave functions where correlations are translated into multiple particle-hole transitions, restricted to two-particles-two-holes transitions in our case. We apply the obtained scheme to a one dimensional model simulating small molecules. The ability of this theory to include dissipative effects on top of mean field is illustrated through several observables such as the one and two body density matrices, the occupation numbers and the one body entropy.

An important characteristic of influenza A is its ability to escape host immunity through antigenic drift. A novel influenza A strain that causes a pandemic confers full immunity to infected individuals, yet because of antigenic drift, these individuals have decreased immunity to drifted strains. We compute the required decrease in immunity so that a recurrence is possible. Models for influenza A must make assumptions on the host contact structure on which the disease spreads. By computing the reproduction number, we show that the classical random mixing assumption predicts an unrealistically large decrease of immunity before a recurrence is possible. We improve over the classical random mixing assumption by incorporating a contact network structure. A complication of contact networks is correlations induced by the initial pandemic. Thus, we provide a novel analytic derivation of such correlations and show that contact networks may require a dramatically smaller drop in immunity before recurrence. Hence, the key new insight is that on contact networks the establishment of a new strain is possible for much higher immunity levels of previously infected individuals than predicted by the commonly used random mixing assumption. This suggests that stable contacts like classmates, coworkers and family members are a crucial path for the spread of influenza in human population. / Graduate

No description available.

Pengar har under en lång tid spelat en central roll i människans samhälle och dagens samhälle präglas av allt mer handel. Utifrån detta har nya betalningsmetoder utvecklats. En förändring i konsumentbeteendet har bidragit till att allt fler individer väljer elektroniska betalningstjänster. En relativt ny innovation är kryptovalutan bitcoin som erbjuder betalning mellan köpare och säljare utan inblandning av en tredje part. Ett flertal studier har gjorts med syftet att fastställa om bitcoin är en valuta eller en tillgång, något som visat sig vara svårt. Något som varit tydligare är att bitcoins värdeförändringar inte tycks vara korrelerad med andra investeringsalternativ. I en studie av Brière et al. (2015) drogs slutsatsen att bitcoin är en intressant tillgång för en investerare tack vare bitcoins låga korrelationskoefficient med andra tillgångar. Denna studie grundar sig i de teoretiska utgångspunkterna om Famas (1970) hypotes om den effektiva marknaden, Markowitz (1952) moderna portföljteori och Rogers (2003) teori om spridning av innovationer. Med detta som utgångspunkt är syftet med denna studie att undersöka hur korrelationskoefficienten mellan bitcoin och traditionella investeringstillgångar som aktier, valutor och råvaror ser ut idag samt hur dessa har förändrats över tid. Med hjälp av Famas (1970) teori om effektiva marknader och Rogers (2003) teori om spridning av innovationer kommer en diskussion om huruvida bitcoins egenskaper som investering i den moderna portföljen har förändrats i takt med att bitcoin blivit mer använd, både som betalningsmedel och investeringsalternativ. För att besvara dessa frågor undersöks korrelationskoefficienterna mellan bitcoin och elva andra tillgångar i kombination med en analys av en deskriptiv statistik. Med en undersökningsperiod som sträcker sig från 18 augusti 2011 till 17 mars 2017. Denna period har även delats upp i mindre tidsperioder för att utifrån detta analysera om det skett några förändringar i korrelationen mellan bitcoin och de traditionella tillgångarna i studien. Resultatet visade att bitcoin inte är korrelerad med andra traditionella tillgångar, oavsett vilken tidsperiod som undersöks. Det visade sig att bitcoin i förhållande till andra tillgångar är en riskfylld investering på grund av bland annat en hög volatilitet. Dock kompenseras detta av bitcoins höga årlig avkastning. Av resultatet framgår det även att volatiliteten för bitcoin har minskat med tiden och att kryptovalutan inte är lika riskfylld idag jämfört med tidigare.

Conventional ‘well-stirred’ extrapolation methodology using intrinsic metabolic clearance data from rat liver microsomes poorly predicts in vivo clearance for approximately half of drug discovery compounds. The aim of this present study was to gain a more detailed understanding of the hepatobiliary disposition pathways which influence drug clearance. A set of 77 new chemical entities (NCEs), demonstrating a range of physicochemical properties and in vitro-in vivo clearance correlations (IVIVC), were employed to explore relationships between hepatobiliary disposition pathways in rat and physicochemical, structural and molecular properties of the NCEs. Primary rat hepatocytes with >80% cell viability were successfully isolated from male Han Wistar rats and used to establish in vitro models of drug uptake and biliary efflux. Preliminary studies with cultured primary rat hepatocytes indicated that uptake of d8-taurocholic acid and pitavastatin was time, concentration and temperature dependent. Initial studies with sandwich cultured primary rat hepatocytes demonstrated that cellular accumulation and biliary efflux of [3H]-Taurocholic acid was time and concentration dependent. These in vitro rat hepatocyte models were then used to investigate drug uptake and biliary efflux for all NCEs. In general, NCEs with high (passive) permeability showed better IVIVC and a lower incidence of active uptake and biliary efflux compared to NCEs with lower permeability, suggesting permeability is a key property influencing hepatobiliary drug disposition in rat. Preliminary in silico models analysing structural and molecular descriptors of substrates of active transport in rat hepatocytes were developed and indicated modest potential to highlight clearance pathways beyond hepatic metabolism but further follow up work with larger, more diverse compound sets is warranted to gain confidence in these models. Extended clearance models were investigated to estimate the effect of hepatic transporters on clearance and to predict the overall hepatic clearance of the NCEs. None of these models resulted in a 1 to 1 correlation but in general, improvements in clearance predictions were made when drug transport processes were accounted for. In vivo excretion studies using bile duct cannulated rats demonstrated that NCEs with high permeability and good IVIVC were not directly eliminated in bile or urine as unchanged drug, whereas NCEs with lower permeability and poor IVIVC (> 3-fold under predicted) were all directly eliminated unchanged indicating key drivers of clearance beyond metabolism. In conclusion these investigations confirmed a role for hepatic transporters in clearance but the complex nature of active transport mechanisms and a lack of robust in vitro tools create challenges in the quantitative prediction of hepatobiliary clearance. However, one of the key findings from this research, which is highly applicable in early drug discovery, was to identify the existence of disposition permeability relationships. These can be anticipated by observing physicochemical parameters of NCEs in conjunction with conventional IVIVC, since NCEs that are not highly permeable, possess some hydrophobic characteristics, and which are poor substrates of cytochrome P450 enzymes are more likely to be good substrates of transporters and be directly eliminated in bile and/or urine. The present study focused on exploring hepatobiliary disposition pathways using rat as the investigative species. Whilst there is no guarantee that pathways relevant to rat will be similar to other preclinical species or even humans, an early diagnosis of dominant clearance pathways can guide a more efficient use of the ADME-PK toolbox.

This PhD work has been dedicated to the improvement of the modelling of air condensers of both round tube and fins (RTPFs) and Minichannel technologies. The calculation platform employed is IMST-ART. This is a dedicated software for the design of refrigeration, air-conditioning and heat pump equipment following the vapor compression cycle. The model implemented in IMST-ART for condensers and evaporators is the combination of a segment-by-segment approach with the numerical method SEWTLE (Semi Explicit method for Wall Temperature Linked Equations) for the solution of the resulting system of equations. The target of the first part of this thesis was the comparative analysis of the empirical correlations aimed at the evaluation of the heat transfer coefficients and pressure drop in both the air and refrigerant sides of a condenser. The Literature review pointed out the presence of many studies concerning the condensation modelling. Therefore, after selecting the most interesting to compare, the first objective of this first part of the PhD became the identification of a suitable methodology for defining the best combination of correlations for the estimation of the thermo-hydraulic performance of the condensers. After an in-depth analysis of different possibilities, a well-defined methodology was identified as the best for the purpose. In the thesis, it was successfully applied to the identification of the best set of correlations for the heat transfer coefficients and friction factors for both the round-tube and minichannel condensers. The second part of the PhD was targeted to the improvement of the condensation modelling. In particular, the attention was focused on the analysis of the phenomena taking place at the beginning of the condensation process, when the superheated vapor finds the wall of the condenser being at a temperature lower than the refrigerant saturation temperature, i.e. convective condensation superheated vapor zone (CSH zone). It is well known that, in this zone, the condensation starts with some kind of droplet/thin film condensation on the walls. Afterwards, the bulk of the refrigerant flow reaches the saturation temperature and the condensation occurs at saturated conditions. Hence, the PhD thesis has been dedicated to the implementation in the general model for condensers (in IMST-ART software) of this CSH zone, which it was found to have an important effect on the prediction of the wall temperatures distribution in the tested air condensers. Two different numerical solutions were implemented and compared, i.e. Temperature and Enthalpy approaches, and validated against experimental results. Prediction results are very similar, thus the Enthalpy approach was selected because it required lower computational time. The final part of thesis was oriented towards the study of the effect of airflow maldistribution on the performance of air condensers. An innovative experimental methodology for generating and measuring any uneven air velocity profile at the inlet of a heat exchanger was first developed in a dedicated wind tunnel and then applied for the analysis of the performance degradation of one sample of condenser of each RTPFs and Minichannel technologies. Three different velocity profiles were produced and tested along a wide set of operating conditions, including different refrigerant charges and hence subcoolings. The experimental results showed that, although differences in wall temperature distribution were significant, the effect of air maldistribution on the performance of the two tested condensers was small. The improved model was validated against the experimental results and also showed little effect on condenser performance. Finally, the agreement between the results of the simulation and the experimental results was very satisfactory. / Este trabajo de doctorado se ha dedicado a la mejora del modelado de condensadores de aire, con tecnología de tubos y aletas o minicanales. La plataforma de software empleada es IMST-ART, que es un software dedicado a asistir el diseño de equipos de refrigeración, aire acondicionado y bomba de calor, basados en el ciclo de compresión de vapor. El modelo de IMST-ART para condensadores y evaporadores se basa en una aproximación segmento a segmento combinada con el método numérico SEWTLE (Semi Explicit method for Wall Temperature Linked Equations) para la solución del sistema de ecuaciones resultante. El objetivo de la primera parte de esta tesis fue el análisis comparativo de las correlaciones empíricas destinadas a evaluar los coeficientes de transferencia de calor y la caída de presión para condensadores de aire, tanto para el lado del aire como para el del refrigerante. La revisión de la Literatura mostró la existencia de numerosos estudios sobre el modelado de la condensación en este tipo de intercambiadores. Por lo tanto, después de la selección de las correlaciones más interesantes a comparar, el primer objetivo de esta primera parte de la tesis resultó el encontrar la metodología más adecuada para la identificación de cuáles eran las correlaciones que mejor estimaban el comportamiento termo-hidráulico de los condensadores. Después de un análisis en profundidad de diferentes posibilidades, se encontró la metodología claramente más adecuada y se pasó a aplicarla a la identificación del mejor conjunto de correlaciones para los coeficientes de transferencia de calor y factores de fricción para condensadores de aire. La segunda parte del doctorado se dirigió a la mejora del modelado del comienzo del proceso de condensación cuando el vapor sobrecalentado encuentra la pared del condensador a una temperatura que está por debajo de la temperatura de saturación del refrigerante en lo que se puede denominar como condensación convectiva en la zona de vapor sobrecalentado (zona CSH). Es bien sabido que la condensación comienza en esta zona con algún tipo de condensación de gotas/película delgada sobre las paredes antes de que el núcleo del flujo de refrigerante alcance la temperatura de saturación y la condensación se produzca en condiciones saturadas. La segunda parte del doctorado se ha dedicado a la implementación en el modelo general de condensadores (en el software IMST-ART) de esta zona CSH, que se encontró que tenía un efecto importante en la predicción de la distribución de las temperaturas de la pared en los condensadores de aire ensayados. Se implementaron y compararon dos soluciones numéricas diferentes, denominados aproximación de temperatura y aproximación de entalpía respectivamente, y se validaron por comparación con resultados experimentales. La predicción resultó ser muy similar con ambas aproximaciones por lo que finalmente se seleccionó la aproximación de entalpía por ser considerablemente más rápida. La parte final de la tesis se orientó hacia el estudio del efecto de la mala distribución del flujo de aire en el rendimiento de los condensadores de aire. Para este fin se desarrolló una metodología experimental innovadora capaz de generar y medir cualquier perfil de velocidad de aire no uniforme a la entrada de un intercambiador de calor. El desarrollo se llevó a cabo primero en un túnel de viento específicamente dedicado a este propósito y luego se aplicó para el análisis de la degradación de las prestaciones de dos muestras de condensador de cada una de las tecnologías estudiades: RTPFs y Minicanal. Mediante la metodología desarrollado se generaron tres perfiles de velocidad diferentes que se ensayaron a lo largo de un amplio conjunto de condiciones de funcionamiento, incluyendo diferentes cargas de refrigerante y, por tanto, grados de subenfriamiento en el refrigerante. Los resultados experimentales mostraron que el efecto de la mala distrib / Aquest treball de doctorat s'ha dedicat a la millora de la modelització de condensadors d'aire, amb tecnologia de tubs i aletes o minicanals. La plataforma de software emprada és IMST-ART, que és un software dedicat a assistir el disseny d'equips de refrigeració, aire condicionat i bomba de calor, basats en el cicle de compressió de vapor. El model de IMST-ART per condensadors i evaporadors es basa en una aproximació segment a segment combinada amb el mètode numèric SEWTLE (Semi Explicit method for Wall Temperature Linked Equations) per a la solució del sistema d'equacions resultant. L'objectiu de la primera part d'aquesta tesi va ser l'anàlisi comparativa de les correlacions empíriques destinades a avaluar els coeficients de transferència de calor i la caiguda de pressió per condensadors d'aire, tant per al costat de l'aire com per al del refrigerant. La revisió de la Literatura va mostrar l'existència de nombrosos estudis sobre la modelització de la condensació en aquest tipus d'intercanviadors. Per tant, després de la selecció de les correlacions més interessants a comparar, el primer objectiu d'aquesta primera part de la tesi va resultar el trobar la metodologia més adequada per a la identificació de quines eren les correlacions que millor estimaven el comportament termo-hidràulic dels condensadors. Després d'una anàlisi en profunditat de diferents possibilitats, es va trobar la metodologia clarament més adequada i es va passar a aplicar-la a la identificació del millor conjunt de correlacions per als coeficients de transferència de calor i factors de fricció per condensadors d'aire. La segona part del doctorat es va dirigir a la millora de la modelització del començament del procés de condensació quan el vapor sobreescalfat troba la paret del condensador a una temperatura que està per sota de la temperatura de saturació del refrigerant, en el que es pot denominar com condensació convectiva a la zona de vapor sobreescalfat (zona CSH). És ben sabut que la condensació comença en aquesta zona amb algun tipus de condensació de gotes/pel·lícula sobre les parets abans que el nucli del flux de refrigerant arribi a la temperatura de saturació i la condensació es produeixi en condicions saturades. La segona part del doctorat s'ha dedicat a la implementació en el model general de condensadors (en el programari IMST-ART) d'aquesta zona CSH, que es va trobar que tenia un efecte important en la predicció de la distribució de les temperatures de la paret en els condensadors d'aire assajats. Es van implementar i van comparar dues solucions numèriques diferents, denominades aproximació de temperatura i aproximació d'entalpia respectivament, i es van validar per comparació amb resultats experimentals. La predicció va resultar ser molt semblant amb les dues aproximacions pel que finalment es va seleccionar l'aproximació d'entalpia per ser considerablement més ràpida. La part final de la tesi es va orientar cap a l'estudi de l'efecte de la mala distribució del flux d'aire en el rendiment dels condensadors d'aire. Amb aquesta finalitat es va desenvolupar una metodologia experimental innovadora capaç de generar i mesurar qualsevol perfil de velocitat d'aire no uniforme a l'entrada d'un intercanviador de calor. El desenvolupament es va dur a terme primer en un túnel de vent específicament dedicat a aquest propòsit i després es va aplicar per a l'anàlisi de la degradació de les prestacions de dues mostres de condensador de cadascuna de les tecnologies estudiades: RTPFs i Minicanal. Mitjançant la metodologia desenvolupada es van generar tres perfils de velocitat diferents que es van assajar al llarg d'un ampli conjunt de condicions de funcionament, incloent càrregues diferents de refrigerant i, per tant, graus de subrefredament en el refrigerant. Els resultats experimentals van mostrar que l'efecte de la mala distribució de l'aire en les prestacions dels dos condensadors provats va / Pisano, A. (2017). Analysis of the condensation process and air maldistribution in finned tube and minichannel condensers [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/86182 / TESIS

<p>Despite worldwide interest in a number of applications involving cryogenic fluids that are crucial to future space exploration, there is presently a lack of a large, reliable cryogenic pool boiling critical heat flux (CHF) database that can be used for assessment of accuracy of available predictive tools - model and correlations – or development of new tools. This shortcoming is a primary motivation for the present study, prompting compilation of a new consolidated cryogenic pool boiling CHF database from world literature. The database is used to assess accuracy of previous models and correlations, which are segregated according to ability to predict key operating parameters, such as pressure, surface orientation, and subcooling. A new correlation is constructed which shows very good predictive accuracy, evidenced by a mean absolute error of 16.95%, based on Earth gravity data which comprise a large fraction of the consolidated database. Using a limited subset of datapoints for three cryogens and a reduced gravity range of 0 to 0.7466, the new correlation is further modified with a reduced gravity multiplier to tackle reduced gravity conditions. The modified correlation has a mean absolute error of 17.47%, slightly higher than for Earth gravity alone. Overall, the new correlations are proven far more accurate than all prior models and correlations and therefore constitute new powerful tools for design of cryogenic space systems. It is shown CHF is very sensitive to pressure, increasing with increasing pressure up to maximum before decreasing appreciably toward critical pressure. CHF is also shown to be strongly influenced by surface orientation, being highest for horizontal surfaces and decreasing monotonically with increasing orientation angle, and increasing fairly linearly with increased subcooling.</p><p>Additionally, CHF models and correlations are assessed using amassed quenching CHF data that showed overpredictions of data. A new correlation is formulated which includes the effects of surface material and heater thickness to achieve high predictive accuracy for complied quenching CHF database. The new correlation has a mean absolute error and root mean square error of 10.79% and 16.12%, respectively, based on a compiled database. Analysis of complied quenching data showed that CHF is sensitive to the surface material, increasing with increasing thermal conductivity but, the influence of surface material becomes weak with increasing thermal conductivity. CHF is also strongly influenced by heater thickness, increasing with increased heater thickness till it reaches the asymptotic thickness. </p>