• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 133
  • 87
  • 44
  • 13
  • 9
  • 4
  • 3
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 320
  • 106
  • 73
  • 54
  • 50
  • 47
  • 44
  • 38
  • 31
  • 26
  • 24
  • 23
  • 22
  • 21
  • 19
  • 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.
31

Química em fluxo como alternativa ao processo batelada na reação da 2,4-Tiazolidinadiona com p-Metoxibenzaldeído / Flow chemistry as an alternative to the batch process in the reaction of 2,4-thiazolidinedione with p-methoxybenzaldehyde

Rodrigo de Oliveira Vieira 28 June 2018 (has links)
A utilização de microrreatores nas indústrias químico-farmacêuticas possibilita uma série de vantagens devido a seu tamanho reduzido comparado aos reatores batelada. Neste trabalho foi feita a transposição da reação da 2,4-tiazolidinadiona com p-metoxibenzaldeído do batelada para o processo em fluxo em microrreator capilar. Adicionalmente, são apresentados estudos de solventes com metanol, etanol e n-propanol, que são mais utilizados por essas indústrias. O etanol apresentou os melhores resultados em termos de rendimento da reação. No processo batelada foi obtido um rendimento de 100% em 480 min utilizando piperidina (0,053 M) como base e concentração equimolar dos reagentes (0,066 M), enquanto que para a reação com pirrolidina o rendimento foi de 100% em 50 min. Com a transposição para o processo em fluxo, o etanol também foi o melhor solvente, alcançando 100% de rendimento (T =140°C, tempo médio de residência: 12 min, base pirrolidina). Também foi feito um estudo de bases que promovessem a reação, sendo estas a morfolina, feniletilamina, propargilamina, piperidina, diaminoetano, piperazina e pirrolidina. No processo em fluxo, a pirrolidina (0,033 M) teve os melhores resultados em termos de conversão, rendimento e velocidade inicial para todas as temperaturas (65, 78, 98, 120, 140 e 160°C) e tempos médios de residência (2, 4, 8, 16, 20, 30, 50 e 70 min) estudados nos três solventes mencionados. O mesmo foi observado no processo batelada, com a qual foi obtido conversão e rendimentos máximos para cada solvente em tempos menores do que na reação com a piperidina. Foram também estimados quantos microrreatores associados em paralelo são necessários para equivaler à produção no processo batelada e constatou-se que um único microrreator produz mais que 1 reator em batelada operando por 8h com o mesmo meio reacional, ao se utilizar etanol (tempo médio de residência 2 min, T =140°C) mostrando assim, que o microrreator pode ser utilizado como alternativa de processo para essa síntese e que a Tecnologia de Microrreatores (TMR) pode ser melhor difundida na indústria. / The use of microreactors in the chemical-pharmaceutical industries offers several advantages due to their reduced size compared to batch reactors. In this work, the reaction of the 2,4-thiazolidinedione with p-methoxybenzaldehyde from the batch was transposed to the flow process in a capillary microreactor. In addition, solvent studies are presented with methanol, ethanol and n-propanol, which are most used by these industries. Ethanol had the best results in terms of reaction yield. In the batch process a yield of 100% in 480 min was obtained using piperidine (0.053 M) as base and equimolar concentration of the reactants (0.066 M), while for the reaction with pyrrolidine the yield was 100% in 50 min. With the transposition to the flow process, ethanol was also the best solvent, achieving 100% yield (T = 140°C, mean residence time: 12 min, pyrrolidine base). A base study was also carried out to promote the reaction, being morpholine, phenylethylamine, propargylamine, piperidine, diaminoethane, piperazine and pyrrolidine. In the flow-through process, pyrrolidine (0.033 M) had the best results in terms of conversion, yield and initial velocity at all temperatures (65, 78, 98, 120, 140 and 160°C) and average residence times (2 , 4, 8, 16, 20, 30, 50 and 70 min) studied in the three solvents mentioned. The same was observed in the batch process, with which conversion and maximum yields were obtained for each solvent at times shorter than in the reaction with piperidine. It was also estimated how many microreactors associated in parallel are required to match the production in the batch process and it was found that a single micro-reactor produces more than 1 batch reactor operating for 8h with the same reaction medium, when using ethanol (mean residence time 2 min, T = 140°C) thus showing that the micro-reactor can be used as a process alternative for this synthesis and that Microreactor Technology (TMR) may be better disseminated in the industry.
32

Application of storm transposition to the Middle Cedar Watershed : a reanalysis of the 2008 Cedar Rapids Flood

Brenner, Iris 01 May 2019 (has links)
On June 13, 2008, after many days of rain, the Cedar River flooded the city of Cedar Rapids. With a peak discharge of 139,987 cfs and at 19.12 feet above flood stage, the 2008 flood of Cedar Rapids was the largest flood in the city’s historic record. As rivers rose, the city had received forecasts of an incoming flood as early as June 8. Then, on June 12, it began to rain in Cedar Rapids. Finally, on June 13, 2008, the Middle Cedar crested at 31.12 feet. This thesis project modeled a variety of rainfall patterns on June 12, 2008, to determine the effect of varying rainfall intensity and location on the magnitude of the 2008 flood of Cedar Rapids. Using a method known as Stochastic Storm Transposition (SST), I overwrote precipitation data in a hydrologic model of the Middle Cedar Watershed with rainfall data extracted from specific storm events that occurred in the Upper Midwest. We used a physically-based, semi-distributed hydrologic model known as GHOST (Generic Hydrologic Overland-Subsurface Toolkit) developed by Marcela Politano at the University of Iowa. Traditionally, hydrologic modeling for watersheds has used design storms to create rainfall inputs in flood modeling. These design storms have uniform rainfall timing and accumulation patterns across a watershed and are determined by designated equations for a geographic region. In large watersheds such as the Middle Cedar (2,400 square miles), design storms are not physically realistic because of their uniformity. Additionally, design storms fail to capture unique storm patterns such as high intensity periods or the movement of a storm across a watershed. By implementing SST into GHOST, we used physically realistic storm events that have unique rainfall patterns and intensities within a designated return period. SST extracts rainfall data from real storm events and transposes the storm patterns onto watersheds to provide physically realistic rainfall data for hydrologic modeling. A tool called RainyDay, developed by Professor Daniel Wright at the University of Wisconsin, provided the storm transpositions used in this research. We assigned the storm transpositions return periods created by RainyDay, corresponding to their average transposed rainfall across the Middle Cedar Watershed. Replacing the June 12 rainfall with RainyDay’s two-year transposed storm events (average rain accumulation 1.8 inches) resulted in modeled flood peaks larger than the unaltered June 12 flood peak. Storm transpositions of 5-, 10-, and 2,000-year return periods showed even larger peaks, illustrating the potential for floods much larger than the 2008 flood. In addition to the analysis of flood magnitude in 2008, we modeled a set of storm transposition scenarios for a variety of soil-moisture conditions. The increased discharge levels in scenarios with high soil moisture emphasize the importance of initial conditions in flooding scenarios. Finally, we modeled the effect that two-year RainyDay storms would have had on the 2016 flood of Cedar Rapids had they occurred on the day before the peak. The two-year transpositions showed that with an impending flood crest smaller than the 2008 crest, several two-year RainyDay scenarios would have resulted in floods nearly equal in magnitude to the 2008 flood event. Our manipulation of the rainfall in the Middle Cedar Watershed on June 12, 2008, using the GHOST model provided the opportunity to re-examine the influence that a specific day of rainfall had on the 2008 flood of Cedar Rapids. The potential for higher flooding under conditions of repeated rainfall and high soil moisture illustrates the susceptibility of the Middle Cedar Watershed to future flood events under similar conditions. Applying SST in hydrologic modeling also provided an opportunity to model a variety of rainfall scenarios and to better understand watershed responses to nuanced and physically realistic rainfall patterns.
33

Nature du savoir et formulation des définitions dans les cours de mathématiques du secondaire

Defrance, Anne 13 February 2010 (has links)
Quelle est la nature des mathématiques enseignées dans les classes de l’enseignement secondaire? Dans quelle mesure l’enseignement des compétences n’handicape-t-il pas l’accès à des mathématiques telles qu’en rêvent les enseignants ? Ce qu’on enseigne a les caractéristiques d’un texte, d’une forme scripturale qui présente des différences avec la forme orale d’une société qui ne connaît pas l’écriture. Il apparaît que la formulation des définitions présente un outil performant pour cette analyse. Les investigations empiriques dévoilent, à travers quatre tensions, les difficultés qu’ont les enseignants à faire entrer leurs élèves dans l’apprentissage d’une théorie mathématique. L’analyse des différentes manières de valider ce qu’ils enseignent conduit à montrer dans quelle situation problématique se trouve l’enseignement des mathématiques aujourd’hui. Un remède serait l’apprentissage de la compétence idiomatique. What is the nature of the Mathematics which are taught in secondary education classes (pupils from 12 to 18 years old)? How far does it impair learning mathematics like teachers dream them ? The taught matter shows the features of a text, of a scriptural form showing up differences with the oral form of a society without writing. The formulation of definitions appears to be a powerful tool to perform this analysis. Empirical investigations reveal through four tensions, how hardly the teachers bring their pupils into the learning of a mathematical theory. The analysis of the various ways to validate what they teach leads to show in what serious difficulties is today the teaching of mathematics. A remedy could be the learning of idiomatic competence.
34

Synthèses de précurseurs carbonylés γ, δ - insaturés via un réarrangement de Claisen [3,3] : vers une nouvelle voie de synthèses d'acides aminés non naturels

Rahem, Neel 04 1900 (has links) (PDF)
Les composés carbonylés y, δ - insaturés constituent des groupes fonctionnels important présents dans plusieurs produits naturels possédant des activités biologiques diverses. Quelques méthodes de préparation de composés carbonylés y, δ - insaturés obtenues par des réactions type réarrangement [3,3] sont rapportées dans la littérature. Cependant, à notre connaissance il n'existe aucun exemple de réarrangement de Claisen [3,3] sur des composés type B-allyloxyénamides. Pourquoi s'intéresser aux composés carbonylés y, δ - insaturés? Parce que l'on peut obtenir des acides aminés non naturels par oxydation et hydrolyse de ces derniers. Les composés carbonylés y, δ - insaturés sont obtenus par un réarrangement de Claisen [3,3], de composés type B-allyloxyénamides. Ces derniers ont pu être synthétisés dans le cadre de travaux préliminaires dans notre laboratoire, par couplage cuivré entre des alcools allyliques et des B-iodoénamides. En outre, les B-iodoénamides ont été synthétisés grâce à une méthodologie de couplage cuivré, entre un amide et du (E)-diiodoéthène. Cette méthodologie a été développée et optimisée dans notre laboratoire, et cela dans le cadre d'une étude précédant celle-ci. Nous avons optimisé la synthèse des B-allyloxyénamides, et ainsi nous avons pu décrire une méthode générale permettant l'obtention de ces derniers, avec des rendements allants de bons à excellents. Nous avons également développé une méthodologie permettant la synthèse de composés carbonylés y, δ - insaturés, en effectuant un réarrangement de Claisen [3,3] des B-allyloxyénamides. Nous avons montré via cette étude, que l'on pouvait obtenir de manière diastéréosélective, des composés carbonylés y, δ - insaturés, avec de bons rendements, et cela notamment par l'emploi des micro-ondes. Ce travail a permis de confirmer la viabilité globale de la stratégie de synthèse conçue pour préparer de façon diastéréosélective des composés très prisés par l'industrie pharmaceutique, tels que les acides aminés. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : acides aminés, couplage, cuivre, réarrangement de Claisen, micro-ondes
35

Left ventricular contractile reserve and stiffness of the neoaorta after arterial switch operation for complete transposition of thegreat arteries: a stress echocardiographystudy

Chen, Hay-son, Robin., 陳羲舜. January 2012 (has links)
published_or_final_version / Paediatrics and Adolescent Medicine / Master / Master of Medical Sciences
36

A Metric for Orthographic Similarity: Theory and Implications

Gorbunova, Anastasia A. January 2007 (has links)
Letter position plays an important role in lexical access. But are some positions more important than the others? Findings from numerous studies support the notion that in lexical access, initial letters produce strongest activation, which weakens towards the end of the word. In order to create a metric for computing the activation produced by each letter position in a correctly spelled word versus a word in which some or all letters are transposed, the formula for calculating a word's orthographic match coefficient (OMC) was developed and tested. Utilizing the masked priming paradigm and a lexical decision task, Experiments 1-5 test the accuracy and reliability of the OMC predictions, and look at neighborhood density in conjunction with different types of letter movement. Results from these experiments provide empirical support for the OMC as a reliable predictor of priming that involves transposed letters, and offer insight into possible mechanisms of word recognition.
37

Comment traduire les syntagmes participiaux et infinitivaux français en suédois? : Étude contrastive de deux textes français non-littéraires et de leurs traductions suédoises.

Fredriksson, Carina January 2011 (has links)
There are many aspects to consider when translating French texts into Swedish. The purpose of the present study is to examine French non-finite constructions, namely participle and infinitive phrases, and to compare them with their Swedish translations. Thus, the method is contrastive. The analysis is based on 213 phrases collected from two non-literary French texts – one economical text and one medical text – and their Swedish translations. The different interpretations have been divided into categories to study the transpositions that have been made, i.e. in what way the two languages differ from each other in this context. The structural differences but also similarities have been illustrated and, to a certain degree, it has been found, according to the hypothesis, that the examined French non-finite constructions often correspond to Swedish main or subordinate clauses, or even other constructions, such as other phrases. On the other hand, it has also been noted that the French infinitive phrase, in most cases, has been translated by an infinitive phrase, which means that no transposition has been made. The Swedish interpretations illustrated in this study are not to be regarded as proof of the occurrence of structural differences and similarities ; the intention is to show how the French constructions in question can be translated into Swedish, and to demonstrate certain tendencies of the two languages respectively.
38

Regulation of maize Ac-Ds transposition by replication and DNA methylation

Ros, Francesca. Unknown Date (has links) (PDF)
University, Diss., 2001--München.
39

Specifika metod interpretace evropského unijního práva a proces transpozice směrnic / Specifics regarding methods of interpretation of the EU law and process of EU directives transposition

Hosnedl, Daniel January 2020 (has links)
Specifics regarding methods of interpretation of the EU law and process of EU directives transposition Abstract This thesis is dedicated to the problematics regarding specifics of the European Union law interpretation methods. While majority of publications dealing with law interpretation adopts the perspective of judges and courts, and thus deals with the interpretations they render, this study adopts the viewpoint of a Czech legislator, who is facing a challenging task of transposing directives into the Czech legal order. In order for the transposition to be conducted properly, a thorough interpretation of the respective directive must precede. There is six standard and non- standard methods of interpretation at the legislator's disposal, including linguistic, logical, systematic, historical, theological and comparative one. Do these methods, however, prove to be fully applicable in case of the interpretation of the EU directives? Possibly, what would be the EU law norms interpretation specifics? This study represents an analysis of the given topic from the perspective of a legal theory and is structured into three main sections. The first section provides a brief definition of the legal interpretation as such and presents an overview of both historical and contemporary approaches towards the...
40

Transposon Tagging in Strawberry and Potato and Characterization of Representative Strawberry Mutants

Lu, Nan 25 September 2013 (has links)
Strawberry and potato are both important crop species in the world providing various nutritional values. The cultivated strawberry, Fragaria ananassa, is a fruit crop with a complex genome (2n=8x=56) whereas the diploid woodland strawberry, Fragaria vesca, has a smaller genome (2n=2x=14, 240 Mb) and lots of other qualities that make it a good model for genetic and genomic study, such as high yield of seeds and efficient transformation. Potato (Solanum tuberosum, 2n=4x=48) is an important vegetable crop in the world and is highly heterozygous. The successful sequencing of the homozygous doubled monoploid clone of potato provides good insight into the study of important genes in this species in improving the pest resistance and improving yield. One approach to characterize gene function in a model system is having large populations of T-DNA insertional or transposon tagged mutants. The idea of using AcDs construct to create transposon tagged mutant populations has also been applied in many species. Here we transformed two species, Fragaria vesca and a monoploid potato, Solanum phureja 1-3-516, which is the progenitor of the sequenced doubled monoploid clone, with the same AcDs construct, Ac-DsATag-Bar_gosGFP, to generate mutant collection, compare the marker gene performance and transposition efficiency, as well as characterizing phenotypic mutants with genes of interest. Transposants were found to reinsert to unlinked sites from the launch pad site in the strawberry genome, whereas in potato transposants tended to locate locally from the launch pad position when using the same construct. One transposon based activation tagging strawberry mutant, with its insertion in the promoter region of gene of interest in strawberry from the Ac-DsATag-Bar_gosGFP population was studied. In a segregating T2 population, expression level of the candidate gene, epidermis-specific secreted glycoprotein EP1 precursor, was 670 fold higher in petioles of homozygotes than in wild type plants, suggesting the function of this gene involved in maintaining mechanical strength of petioles. Since the often-used transposase gene was cloned from the monocot species maize, the efficiency of obtaining germinal transposants was many times lower than expected in order to saturate the genome for diploid species. In order to improve the chance of getting unique transposants, we attempted to codon optimize the transposase gene, as well as switching to microspore specific promoters that had been well characterized to control timing of expression of the transposase gene. Transposants were found in both T0 primary regenerates and anther culture derived potatoes using both the pAcDs-AtSCP and pAcDs-AmDEFH125 constructs. Sequencing of the empty donor site revealed that excision occurred in different cells during anther culture. A strawberry mutant with sugar transport deficiency due to T-DNA insertion near a sucrose transporter-2 gene showing stunted phenotype with increased level of anthocyanin was also characterized. The concentrations of sucrose, glucose, and fructose were significantly greater in source leaves of the mutant than wild type plants, suggesting these compounds might be substrates of this gene in transporting to sink leaves and roots. / Ph. D.

Page generated in 0.1049 seconds