Στην παρούσα εργασία διερευνήθηκαν οι προσδιοριστικοί παράγοντες του βαθμού αποφοίτησης των πτυχιούχων των τμημάτων Οικονομικής Επιστήμης στην Ελλάδα. Τα στοιχεία που χρησιμοποιήθηκαν για τους σκοπούς της ανάλυσης προέρχονται από τα δευτερογενή δημοσιευμένα στοιχεία της Ελληνικής Στατιστικής Αρχής και αφορούν απόφοιτους σε επίπεδο πανεπιστημιακού τμήματος για τα έτη 2001-2007. Ως δείκτες επίδοσης χρησιμοποιήθηκε το ποσοστό των αποφοίτων με βαθμό πτυχίου " Άριστα", "Λίαν Καλώς" και "Καλώς". Στην εμπειρική ανάλυση χρησιμοποιήθηκαν υποδείγματα τύπου "fractional logit" επειδή η προς εξέταση μεταβλητή εμφανίζεται σε ποσοστά. Με βάση προγενέστερες μελέτες, κυρίως σε διεθνές επίπεδο, ως ερμηνευτικές μεταβλητές χρησιμοποιήσαμε το βαθμό εισαγωγής στα τμήματα Οικονομικής Επιστήμης που εξετάζουμε, την παλαιότητα των τμημάτων, το ποσοστό των φοιτητών που φοιτούν στον τόπο μόνιμης κατοικίας τους, την πληθυσμιακή πυκνότητα των νομών όπου είναι εγκατεστημένα τα τμήματα, τους δείκτες ερευνητικής επάρκειας των μελών ΔΕΠ και την αναλογία μελών ΔΕΠ σε κάθε βαθμίδα προς το σύνολό τους. Ακόμα συμπεριλάβαμε το έτος αποφοίτησης, αλλά και την αναλογία εγγεγραμμένων φοιτητών στα πλαίσια του κανονικού ορίου φοίτησης (συνολικά και μόνο τις γυναίκες) και φοιτητών πέραν του κανονικού ορίου φοίτησης προς το σύνολο των εγγεγραμμένων φοιτητών αντίστοιχα. Σε γενικές γραμμές σύμφωνα με τα ευρήματα της παρούσας ανάλυσης ο βαθμός αποφοίτησης των πτυχιούχων των τμημάτων Οικονομικής Επιστήμης δεν διαμορφώνεται με τον ίδιο τρόπο αλλά φαίνεται να διαφέρει συστηματικά μεταξύ των τμημάτων. Ειδικότερα, ο βαθμός εισαγωγής αποτελεί βασικό προσδιοριστικό παράγοντα του βαθμού επίδοσης, αποτέλεσμα που συμβαδίζει με τη διεθνή εμπειρική ένδειξη. Περαιτέρω, εμφανίζεται σημαντική η αναλογία μελών ΔΕΠ σε κάθε βαθμίδα προς το σύνολό τους αλλά και το έτος αποφοίτησης. / In this study we investigated the determinants of degree performance of graduates of Economic Departments in Greece.

abstract: For synthetic aperture radar (SAR) image formation processing, the chirp scaling algorithm (CSA) has gained considerable attention mainly because of its excellent target focusing ability, optimized processing steps, and ease of implementation. In particular, unlike the range Doppler and range migration algorithms, the CSA is easy to implement since it does not require interpolation, and it can be used on both stripmap and spotlight SAR systems. Another transform that can be used to enhance the processing of SAR image formation is the fractional Fourier transform (FRFT). This transform has been recently introduced to the signal processing community, and it has shown many promising applications in the realm of SAR signal processing, specifically because of its close association to the Wigner distribution and ambiguity function. The objective of this work is to improve the application of the FRFT in order to enhance the implementation of the CSA for SAR processing. This will be achieved by processing real phase-history data from the RADARSAT-1 satellite, a multi-mode SAR platform operating in the C-band, providing imagery with resolution between 8 and 100 meters at incidence angles of 10 through 59 degrees. The phase-history data will be processed into imagery using the conventional chirp scaling algorithm. The results will then be compared using a new implementation of the CSA based on the use of the FRFT, combined with traditional SAR focusing techniques, to enhance the algorithm's focusing ability, thereby increasing the peak-to-sidelobe ratio of the focused targets. The FRFT can also be used to provide focusing enhancements at extended ranges. / Dissertation/Thesis / M.S. Electrical Engineering 2011

Le déploiement à grande échelle de l’internet des objets nécessite le développement de systèmes de radiocommunication plus économes en énergie, dont le circuit de génération de fréquences est connu pour être particulièrement énergivore. L’objectif de ce travail de thèse est donc d’une part de développer une synthèse de fréquences très faible consommation et d’autre part de démontrer les performances de la technologie FDSOI pour des applications analogiques et radiofréquences. Dans le premier chapitre sont présentées les spécifications du standard choisi -le BLE-, les spécificités de la technologie FDSOI et l'état de l’art des architectures de transmetteurs radiofréquences à faible consommation. Nous avons retenue de cette comparaison l'architecture à division par phases. Le deuxième chapitre présente les résultats de trois types de modélisation système de l’architecture ; 1 - le fonctionnement de ses composants et les points clés à respecter pour son implémentation, 2 - le comportement en bruit de phase pour la définition des spécifications, et 3 - l’impact de l’architecture sur la génération de raies spectrales parasites. Cette étude nous a permis de fixer le cahier des charges du VCRO développé au chapitre suivant. Le troisième chapitre est consacré à la conception, la réalisation et le test de 4 topologies de VCROs en technologie FDSOI 28nm et d'un circuit de test. Les premiers résultats de mesure sont encourageants mais nécessitent d’être complétés par des mesures avec PLL fractionnaire intégrée. En effet, la sensibilité des circuits à la tension d’alimentation (pushing de l’ordre de 5 GHz/V) a rendu les mesures du bruit de phase très délicates. / The large-scale deployment of IoT requires the development of more efficient energy radio systems, within which the frequency generation circuit is known to be particularly energy-consuming. The objective of this thesis is firstly to develop a very low consumption frequency synthesis and secondly to demonstrate the performance of the FDSOI technology for analog and RF applications.In the first chapter are the specifications of the chosen standard -the BLE-, the specifications of the FDSOI technology and state of the art of low power radio frequency synthesizers architecture. We have chosen from this comparison the Fractional Phase Divider architecture. The second chapter presents the results of three types of system simulations of the PLL; 1 - the operation of its components and the key points to be respected for its implementation, 2 - the phase noise behavior for the definition of specifications, and 3 - the impact of architecture on the generation of spurious. This study allowed us to set the specifications of VCROs developed in the next chapter. The third chapter is dedicated to the design, implementation and testing of four topologies of VCROs and a test circuit in FDSOI 28nm technology. The first measurement results are encouraging but they need to be complemented by an integrated fractional PLL measurement. Indeed, the sensitivity of the circuits to the supply voltage (pushing of about 5 GHz/V) made measurements of phase noise very delicate. The measured consumption is less than 0.8 mA and the surface of the circuits is of the order of 600 µm².In the fourth and final chapter we present the implementation at circuit-level of a phase synchronization PLL.

The first chapter considers the asymptotic validity of bootstrap methods in a linear trend model with a change in slope at an unknown time. Perron and Zhu (2005) analyzed the consistency, rate of convergence, and limiting distributions of the parameter estimates in this model. I provide theoretical results for the asymptotic validity of bootstrap methods related to forming confidence intervals for the break date. I consider two bootstrap schemes, the residual (for white noise errors) and the sieve bootstrap (for correlated errors). Simulation experiments confirm that confidence intervals obtained using bootstrap methods perform well in terms of exact coverage rate. The second chapter extends Perron and Zhu's (2005) analysis to cover more general fractionally integrated errors with memory parameter d in the interval (-0.5,1.5). My theoretical results uncover some interesting features. For example, with a concurrent level shift allowed, the rate of convergence of the estimate of the break date is the same for all values of d in the interval (-0.5,0.5), a feature linked to the contamination induced by allowing a level shift. In all other cases, the rate of convergence is decreasing as d increases. I also provide results about the spurious break issue. The third chapter considers constructing confidence intervals for the break date in linear regressions. I compare the performance of various procedures in terms of the exact coverage rates and lengths: Bai's (1997) based on the asymptotic distribution with shrinking shifts, Elliott and Müller's (EM) (2007) based on inverting a test locally invariant to the magnitude of the change, Eo and Morley's (2013) based on inverting a likelihood ratio test, and various bootstrap procedures. In terms of coverage rates, EM's approach is the best but with a high cost in terms of length. With serially correlated errors and a change in intercept or in the coefficient of a regressor with a high signal-to-noise ratio, or when a lagged dependent variable is present, the length approaches the whole sample as the magnitude of the change increases. This drawback is not present for the other methods. Theoretical results are provided to explain the drawbacks of EM's method.

Esta dissertação desenvolve uma proposta de ensino com alunos do 6º ano de uma escola privada de Porto Alegre, tratando da aprendizagem do conceito de número fracionário através de seu significado "medida". A proposta foi desenvolvida com base nas etapas da Engenharia Didática, uma metodologia de pesquisa que contempla experiências em sala de aula acompanhadas de análises a priori e a posteriori . Na análise das aprendizagens foi usada a Teoria dos Campos Conceituais de Vergnaud, a qual proporcionou embasamento teórico para observar o processo de aprendizagem vivenciado pelos alunos. Os resultados obtidos ao longo do gradual processo de construção de uma régua numerada indicam que os alunos compreenderam os números fracionário no seu significado "medida" e também validam a seqüência didática que foi implementada em sala de aula. / This work presents a teaching experience with students from 6th grade at a private school in Porto Alegre and it aims to provoke the understanding of the fractional numbers concept through its meaning of "measure". The Didactic Engineering was used as a research methodology, grounded on classroom experiences and supported by a priori and a posterior analysis that can validate the teaching experiment. To carry out the analysis of student's learning, this study relied on the Conceptual Fields Theory of Vergnaud, which provides the theoretical framework for the identification of knowledge that students put into action during the activities. The results point to students understanding of the fractional number concept through a sequence involving didactic meaning "measure" of fractional numbers and also certify the teaching sequence applied in the classroom.

O glicerol é gerado em grandes quantidades durante a produção de biodiesel e tem se tornado um substrato potencialmente atrativo para a produção bacteriana de produtos de valor agregado, tais como 1,3-Propanodiol (1,3-PD), etanol, hidrogênio e outros. O presente trabalho teve como objetivo a produção de hidrogênio, 1,3-PD e etanol utilizando glicerol residual obtido da síntese do biodiesel. A primeira parte do trabalho visou à produção de hidrogênio utilizando glicerol residual. Nesta etapa, o consórcio microbiano ambiental foi submetido a diferentes tratamentos (ácido, básico, choque térmico, congelamento e descongelamento e dessecação). Os resultados mostraram que a maior produção de hidrogênio ocorreu com o consórcio tratado com dessecação e choque térmico, com produções de 34,2 % mol e 27,3 % mol, respectivamente. A otimização da produção de hidrogênio foi realizada utilizando planejamento experimental e alcançou uma produção máxima de 45 % mol. A próxima etapa do projeto foi isolar as bactérias presentes no consórcio microbiano ambiental. Experimentos em biorreatores foram realizados utilizando glicerol puro e glicerol residual e os resultados mostraram que houve a completa degradação do glicerol pelas bactérias do consórcio e também a produção de 1,3-PD, hidrogênio e ácidos. Nesta etapa, 32 bactérias foram isoladas e testadas para a produção de bioprodutos em experimentos em aerobiose e anaerobiose. Quatro bactérias foram selecionadas e o seqüenciamento do gene foi identificado por 16S rRNA identificou três dos isolados como Klebsiella pneumoniae e um isolado como Pantoea agglomerans. Dentre as quatro bactérias, uma cepa, nomeada como K. pneumoniae BLh-1, foi selecionada para os trabalhos posteriores. Para otimização das condições de cultivo, utilizou-se a seleção de variáveis através do delineamento experimental Plackett Burman (P-B) avaliando a produção de 1,3-PD. Sete variáveis foram estatisticamente significativas e um novo planejamento fracionário 27-3 foi realizado com a finalidade de otimizar o meio de produção. Experimentos em biorreatores mostraram que a produção em bioreator com pH controlado com o meio otimizado no planejamento alcançou uma produção máxima de 23,80 g/L de 1,3-PD com produção de 12,30 g/L de etanol. Os ensaios com alimentação de glicerol residual mostraram que altas taxas de alimentação causam acúmulo de glicerol e diminuem a produtividade de 1,3-PD e etanol. Os estudos utilizando fluorescência 2D e modelo quimiométrico foram aplicados para avaliar as mudanças metabólicas nos cultivos aeróbios e anaeróbios. Os resultados mostraram que houve diferença nas regiões de NADH e riboflavinas ambas associadas ao metabolismo do microorganismo. / Glycerol is generated in large amounts during biodiesel production and it is becoming a potentially attractive substrate for bacterial production for value-added products such as 1,3-propanediol (1,3-PD), ethanol, hydrogen, among others. This work aimed at studying the production of hydrogen, 1,3-PD and ethanol using the raw glycerol obtained by biodiesel synthesis. The first steps were to produce hydrogen using raw glycerol. At this step, the environmental microbial consortium was submitted to different pretreatments (acid, base, heat shock, dry heat and desiccation, freezing and thawing). The results showed that dry heat and desiccation had the higher hydrogen production followed by heat shock with production of 34.2 % mol and 27.3 % mol, respectively.The optimization of hydrogen production was performed using experimental design and had a maximum hydrogen production of 45 % mol. The next spet of this project was to isolate the bacteria present in an environmental microbial consortium. Experiments in bioreactors with the microbial consortium using raw and pure glycerol were carried out and the results showed that there was a complete glycerol degradation by microbial bacteria with productions of 1,3-PD, hydrogen and acids. In this step, 32 bacteria were isolated and tested separately for by-products production under aerobic and anaerobic conditions. Four bacteria were selected and sequence gene realized by 16 S rRNA, three of them were identified as Klebsiella pneumoniae and one isolate identified as Pantoea agglomerans. Among the four bacteria, the strain K. pneumoniae BLh-1 were selected for further experiments. Plackett Burman (P-B) experimental procedure was used for assessing the production of 1,3-PD. Seven variables were statistically significant and a new 27-3 fractional design was conducted with the aim of optimizing culture conditions. Bioreactors experiments using the optimized culture conditions showed that production in bioreactor with controlled pH reached a maximal 1,3-PD production of 23.80 g/L with 12.30 g/L of ethanol. The fed-batch experiments showed that high feeding rates caused glycerol to accumulated in the medium and the1,3-PD and ethanol productivity decreased. The 2D fluorescence metodology was applied in order to study the anaerobic-aerobic changes on K. pneumoniae metabolism. The results showed a significant difference on NADH and riboflavin fluorescence that are fluorescence regions associated to metabolism.

A presente pesquisa investiga a aquisição do conceito de número racional na sua representação fracionária. O estudo justifica-se devido ao alto índice de dificuldades apresentadas pelos alunos na compreensão do conceito de número racional, que faz parte do pensamento multiplicativo. Apontamos a conexão entre os números fracionários e o raciocínio multiplicativo, destacando que as frações são números produzidos por divisões que resultam sempre em partes iguais. Nosso objetivo de pesquisa é comparar as estratégias cognitivas utilizadas por alunos com bom desempenho em Matemática com as estratégias cognitivas utilizadas por alunos que apresentam baixo desempenho escolar em Matemática, durante o processo de aquisição dos diferentes significados dos números fracionários: parte-todo, quociente e operador multiplicativo. Descrevemos as estratégias cognitivas utilizadas por cinqüenta alunos, de 4ª à 8ª séries do Ensino Fundamental, de uma escola privada da cidade de Porto Alegre. Verificamos a desconexão entre a compreensão dos alunos sobre a divisão e a aprendizagem de frações e a relacionamos à tendência metodológica de ensinar o conceito de número fracionário enfatizando somente o significado parte-todo. Constatamos que existem semelhanças na utilização das estratégias pelos alunos dos dois grupos. Percebemos que, embora as estratégias sejam comuns, os resultados mostram diferenças na recuperação automática de fatos na memória, que afetam a resolução de problemas mais complexos. A pesquisa aponta a necessidade de explorar a aquisição dos números fracionários em várias situações e em diferentes contextos, repensando o ensino de fração na escola. Tal ensino deve levar em consideração os conhecimentos informais, valorizar as diferentes estratégias utilizadas pelos alunos, promover interações entre eles para observar suas estratégias, proporcionar diversidade de ensino e reflexão das estratégias utilizadas, possibilitando um avanço no sentido de estratégias mais eficientes e econômicas. / The present research investigates the acquisition of the concept of rational number in its fractional representation. This study is justified due to the high degree of difficulty presented by students in understanding the concept of rational number, which is part of the multiplicative thought, observing that fractions are numbers produced by divisions which always result in equal parts. The objective of this research is to compare the cognitive strategies used by two groups of students: one with high performances in Math and the other one with low performance, during the process of learning different meanings of fractional numbers such as: whole-part, quotient’ and multiplicative operator. Cognitive strategies of fifty 4th to 8th Elementary School students from a private school in Porto Alegre were studied. A disconnection between the students’ understanding of division and their learning about fractions was verified. There is a tendency of teaching students the fractional number concept only emphasizing the meaning of the whole-part. Results of the research suggest that both groups of students used similar strategies and although strategies were alike, the results showed differences in the automatic retrieval of facts in the memory which affects solving higher complexity problems. The research shows the need of exploring the acquisition of fractional numbers in different situations and contexts, rethinking the teaching of fractions in schools. Such teaching should take into consideration informal knowledge, emphasize different strategies used by students, promote interaction between students in order to observe their strategies, and stimulate diversity in teaching and reflection on strategies used by students. Thus, more efficient and economical strategies would be possible.

Fractional Chern insulators (FCIs) are strongly correlated, topological phases of matter that may exist on a lattice in the presence of broken time-reversal symmetry. This thesis explores the link between FCI states and the quantum Hall effect of the continuum in the context of the Hofstadter model, using a combination of nonperturbative, perturbative and numerical methods. We draw links to experimental realisations of topological phases, and go on to consider a novel way of generating general FCI states using strong interactions on a lattice. We begin by considering the Hofstadter model at weak field, where we use a semiclassical analysis to obtain nonperturbative expressions for the band structure and Berry curvature of the single-particle eigenstates. We use this calculation to justify a perturbative approximation, an approach that we extend to the case when the amount of flux per plaquette is close to a rational fraction with a small denominator. We find that eigenstates of the system are single- or multicomponent wavefunctions that connect smoothly to the Landau levels of the continuum. The perturbative corrections to these are higher Landau level contributions that break rotational invariance and allow the perturbed states to adopt the symmetry of the lattice. In the presence of interactions, this approach allows for the calculation of generalised Haldane pseudopotentials, and in turn, the many-body properties of the system. The method is sufficiently general that it can apply to a wide variety of lattices, interactions, and magnetic field strengths. We present numerical simulations of the Hofstadter model relevant to its recent experimental realisation using optical lattices, noting the additional complications that arise in the presence of an external trap. Finally, we show that even if a noninteracting system is topologically trivial, it is possible to stabilise an FCI state by introducing strong interactions that break time-reversal symmetry. We show that this method may also be used to create a (time-reversal symmetric) fractional topological insulator, and provide numerical evidence to support our argument.

Geographic research on the Corn Belt and other regional landscapes of the central U.S. has not to date identified quantitatively the climatic, edaphic, topographic, and economic characteristics that determine rural land cover, and that therefore govern land cover change. Using the USDA/NASS Cropland Data Layer, this study identifies these characteristics using Multivariable Fractional Polynomials within a logistic regression framework. It maps the suitability distribution for corn, soybeans, spring and winter wheat, cotton, grassland, and forest land covers that dominate the central U.S., at a 56m resolution across 16 central U.S. states. The non-linear logistic regression models are successful in identifying determinants of land cover with relative operating characteristic (ROC) scores that range from 0.769 for soybeans to 0.888 for forest, with a combined corn/soybean model achieving an ROC of 0.871. For corn and soybean models, when prior land cover of a pixel is added, predictability and ROC scores increase substantially (0.07-0.10), indicating a strong temporal feedback in land cover dynamics. This process also aids in the delineation of fields from pixels. Adding neighboring land covers, however, improves predictability and ROC scores only slightly (0.014-0.019), indicating a weak spatial feedback mechanism. By including annual crop prices within the logit models, economically marginal cropland that comes into crop production only when prices are high is identified in a spatially-explicit manner. This capacity improves further analyses of economic and environmental impacts of policies that affect crop prices. The sustainability of current rural land use trends in the central U.S. is highly dependent on the ability to adapt to changing climatic conditions of the 21st century. As the climate begins to shift towards longer growing seasons, more erratic rainfall patterns, and overall warmer temperatures, there is potential for major impacts on seven major land covers of the central U.S. Suitability landscapes of individual land covers (corn, soybeans, spring and winter wheat, cotton, grasslands, and forests) were utilized to determine the influence of climate change on these landscapes. Twenty-seven climate change projection scenarios based on three global climate models, three representative concentration pathways, and three time periods were applied to the land cover suitability maps utilizing raster regression. The area now identified as the Corn Belt is projected to see a dramatic shift in the suitable climate with a potential for a 30 percent increase in summer growing degree days. While the area where conditions are suitable for corn, soybeans and spring wheat are all expected to decrease, winter wheat has the potential to increase in suitable area. In order to maintain current geographic patterns of crop production, corn would need to be adapted to higher temperatures.

In this work, we establish the Lyapunov-type inequalities for the fractional boundary value problems with Hilfer derivative for different boundary conditions. We apply this inequality to fractional eigenvalue problems and prove one of the important results of real zeros of certain Mittag-Leffler functions and improve the bound of the eigenvalue using the Cauchy-Schwarz inequality and Semi-maximum norm. We extend it for higher order cases.