O ácido caproico é derivado da cadeia petroquímica e, tem diversas aplicações na indústria química. No entanto, este ácido pode ser produzido de forma mais ambientalmente adequada, a partir da fermentação anaeróbia. O objetivo dessa pesquisa foi investigar condições operacionais para a formação anaeróbia de ácido caproico a partir de produtos e subprodutos da indústria sucroalcooleira. Utilizou-se um reator anaeróbio de manta de lodo e fluxo ascendente (UASB - Upflow Anerobic Sludge Blanked), com volume útil de 13,8 L, alimentado com substratos simples (etanol e ácido acético) ou com substrato complexo (fermentado alcoólico de melaço de cana). Durante a operação do reator UASB, a COV variou de 2,0 a 5,5 gDQO.L-1.d-1 em pH ácido (5,3). A taxa de produção volumétrica de ácido caproico a partir de substrato simples (1,0 gC6.L-1.d-1) em reator UASB foi superior àquela com substrato complexo (0,2 gC6.L-1.d-1). Em pH de aproximadamente 5,3, a produção de ácido caproico ficou limitada a um valor de aproximadamente 2,8 gC6. L-1 devido a maior presença de ácidos não dissociados. Utilizando fermentado de melaço de cana contendo etanol (150 mM de etanol), é possível atingir uma produção de até 4,0 gC6. L-1 em pH com adição clorofórmio como inibidor seletivo para organismos metanogênicos. A presença de ácido acético acelera a formação de ácido butírico, resultando no acúmulo deste devido à ausência de etanol como doador de elétrons. Dessa forma, a formação de ácido caproico a partir de fermentado de melaço de cana não necessita da adição externa de ácido acético. É necessária extração seletiva do ácido caproico, evitando o acumulo indesejado. / Caproic acid is derived from the petrochemical production chain and has many applications in the chemical industry. However, this acid can be produced in a more environmental friendly technological route, using the anaerobic fermentation. The objective of this research was to investigate the operational conditions for anaerobic caproic acid formation using the products and by-products of the sugarcane industry. We used an upflow anaerobic sludge blanket and upflow (UASB - Upflow Sludge anerobic Blanked), with a working volume of 13.8 L, fed with simple substrates (ethanol and acetic acid) or complex substrate (undistilled fermented molasses). During the UASB reactor operation, OLR ranged from 2.0 to 5.5 gDQO.L-1.d-1 at acid pH (5.3). The volumetric production rate of caproic acid from simple substrates (1.0 gC6.L-1.d-1) in UASB reactor was superior to that from complex substrate (0.2 gC6.L-1.d-1). At pH of approximately 5.3, caproic acid production was limited to a value of approximately 2.8 gC6.L-1 due to the greater presence of non-dissociated acids. Using fermented sugar cane molasses containing ethanol (150 mM ethanol), can be achieved a production of up to 4.0 gC6.L-1 in pH by adding chloroform as a selective inhibitor for methanogenic organisms. The presence of acetic acid accelerates the formation of butyric acid, resulting in the accumulation of this due to the absence of ethanol as an electron donor. Thus, the formation of caproic acid from fermented molasses does not require the external addition of acetic acid. It is necessary selective extraction of caproic acid, preventing unwanted accumulation.

Muitas respostas moduladas pela luz durante o desenvolvimento das plantas também são reguladas por hormônios vegetais, levando à hipótese da interação entre ambos os fatores. Uma ferramenta valiosa para testar tal interação seria o uso de mutantes fotomorfogenéticos e hormonais, bem como duplos mutantes combinando ambos. Em tomateiro, embora sejam disponíveis mutantes com alterações na biossíntese de fotorreceptores e/ou na transdução do sinal da luz, bem como mutantes no metabolismo e/ou sensibilidade hormonal, esses estão presentes em cultivares diferentes, o que pode limitar seu uso de modo integrado e a construção de duplos mutantes. No presente trabalho, foram introgredidas em uma única cultivar de tomateiro, Micro-Tom (cv. MT), dezenove mutações afetando a biossíntese ou a resposta a fitocromo, bem como aos hormônios auxina (AUX), citocinina (CK), giberelina (GA), ácido abscísico (ABA), etileno (ET) e brassinoesteróides (BR). Tomando-se vantagem de tal coleção, duas respostas notadamente controladas tanto pela luz quanto por hormônios foram estudadas: alongamento e acúmulo de antocianinas em hipocótilos. Para tal, foram utilizadas as seguintes abordagens: i) tratamentos exógenos de diferentes classes hormonais em mutantes fotomorfogenéticos, ii) observação de hipocótilos de mutantes hormonais crescidos na luz e no escuro, iii) observação de duplos mutantes combinando mutações hormonais e fotomorfogenéticas. Assim, o acúmulo de antocianinas foi promovido pela CK e ABA e inibido pela GA, concordando com a redução no mutante deficiente em ABA (notabilis ou not) e no mutante hipersensível à GA (procera ou pro). Apesar do mutante com baixa sensibilidade à AUX (diageotropica ou dgt) acumular exageradamente antocianinas, a aplicação exógena não evidenciou o papel da AUX, sendo, porém, coerente com a sugestão de que esse mutante possui um balanço AUX/CK voltado para CK. Tanto a aplicação exógena quanto a avaliação nos mutantes epinastic (epi), super produção de ET, e Never ripe (Nr), baixa sensibilidade ao ET, sugerem uma função limitada desse hormônio na biossíntese de antocianinas. Na luz e no escuro, AUX, CK, ABA e ET exógenos resultaram na inibição do alongamento do hipocótilo, sendo coerente com a promoção em dgt (luz), promoção em sit (luz), inibição em epi (luz e escuro). Por outro lado, GA promoveu o alongamento corroborando a promoção em pro. Contrariando o efeito exógeno da CK, brt reduziu o alongamento na luz e no escuro. No escuro, o único mutante que apresentou alongamento do hipocótilo superior a MT foi o mutante deficiente na biossíntese do phy (aurea ou au). A utilização de duplos mutantes combinando phy- e alterações hormonais mostrou uma interação aditiva (au epi, au Nr, au dgt e au sit), sinergística (au pro) e epinástica (au brt) no acúmulo de antocianinas e alongamento do hipocótilo na luz, porém nessa última resposta, au dgt e au sit indicaram uma interação sinergística. Juntos, esses resultados indicam que, embora phy possui vias distintas da AUX, ET, ABA e GA no controle do acúmulo de antocianinas e alongamento do hipocótilo, parece que esse fotorreceptor partilha vias comuns com CK em ambas as respostas. / Many responses regulated by light during plant development are also regulated by plant hormones, suggesting an interaction between these factors. One important approach to test this hypothesis is the use of photomorphogenic and hormonal mutants and double mutant analysis. Mutants with altered photoreceptor biosynthesis, light signal transduction, hormonal metabolism and hormonal sensitivity are available in tomato. However, since they are in different cultivars, this can be a limitation for their use in a comprehensive study, as well as, for the construction of double mutants. In this work we performed the introgression of nineteen mutations in a single cultivar of tomato, Micro- Tom (cv. MT). These mutations affect biosynthesis or response to phytochrome (phy), auxin (AUX), cytokinin (CK), gibberellin (GA), abscisic acid (ABA), ethylene (ET) and brassinosteroid (BR). Using this collection of hormone mutants, we studied two responses which are controlled by light and hormones: elongation and anthocyanin accumulation in hypocotyls. For this purpose, we used three approaches: i) hormonal treatment in the photomorphogenic mutants, ii) measurement of hypocotyl lengths from hormonal mutants grown under light and dark conditions and iii) double mutant (photomorphogenic-hormonal) analysis. Anthocyanin accumulation was promoted by CK and ABA and inhibited by GA. This is in accordance with the reduction of anthocyanin accumulation in the ABA deficient mutant (not) and in the GA hypersensitive mutant (pro). Although the diageotropica (dgt), auxin-insensitive mutant, showed a high anthocyanin accumulation, the addition of auxin did not supported a role for this hormone in anthocyanin accumulation. On the other hand, this could be due to a low auxin-tocytokinin ratio presented by dgt. Data from mutants with altered metabolism and sensitivity of ethylene, epinastic (epi) and Never ripe (Nr) respectively, and from plants treated with this hormone suggest a limited role of ethylene in the anthocyanin biosynthesis. Exogenous AUX, CK, ABA and ET inhibited the hypocotyl elongation. This is coherent with the promotion of hypocotyl elongation in dgt and sit mutants under light conditions and inhibition of hypocotyl elongation in the epi mutant in the light and dark. On the other hand, GA promoted the hypocotyl elongation corroborating the same effect seen in pro. The brt mutant showed a reduced hypocotyl elongation in light and dark conditions, which contradicts the effect of exogenous cytokinin. The phytochromedeficient aurea (au) mutant was the only one to show an enhanced hypocotyl elongation in the dark compared to the wild type (MT). The combination between photomorphogenic and hormonal mutants (double mutants) showed additive (au epi, au Nr, au dgt e au sit), synergistic (au pro) and epistatic (au brt) interactions considering the anthocyanin accumulation and hypocotyl elongation. Synergistic interaction was observed in the elongation hypocotyl of the au dgt and au sit double mutants. These results indicate that phy and CK may share some signaling/metabolic pathways in the control of anthocyanin accumulation and hypocotyl elongation. On the other hand, our data do not support an interaction between phy and the hormones AUX, ET, ABA and GA in the control of hypocotyls elongation or anthocyanin accumulation.

O ácido caproico é derivado da cadeia petroquímica e, tem diversas aplicações na indústria química. No entanto, este ácido pode ser produzido de forma mais ambientalmente adequada, a partir da fermentação anaeróbia. O objetivo dessa pesquisa foi investigar condições operacionais para a formação anaeróbia de ácido caproico a partir de produtos e subprodutos da indústria sucroalcooleira. Utilizou-se um reator anaeróbio de manta de lodo e fluxo ascendente (UASB - Upflow Anerobic Sludge Blanked), com volume útil de 13,8 L, alimentado com substratos simples (etanol e ácido acético) ou com substrato complexo (fermentado alcoólico de melaço de cana). Durante a operação do reator UASB, a COV variou de 2,0 a 5,5 gDQO.L-1.d-1 em pH ácido (5,3). A taxa de produção volumétrica de ácido caproico a partir de substrato simples (1,0 gC6.L-1.d-1) em reator UASB foi superior àquela com substrato complexo (0,2 gC6.L-1.d-1). Em pH de aproximadamente 5,3, a produção de ácido caproico ficou limitada a um valor de aproximadamente 2,8 gC6. L-1 devido a maior presença de ácidos não dissociados. Utilizando fermentado de melaço de cana contendo etanol (150 mM de etanol), é possível atingir uma produção de até 4,0 gC6. L-1 em pH com adição clorofórmio como inibidor seletivo para organismos metanogênicos. A presença de ácido acético acelera a formação de ácido butírico, resultando no acúmulo deste devido à ausência de etanol como doador de elétrons. Dessa forma, a formação de ácido caproico a partir de fermentado de melaço de cana não necessita da adição externa de ácido acético. É necessária extração seletiva do ácido caproico, evitando o acumulo indesejado. / Caproic acid is derived from the petrochemical production chain and has many applications in the chemical industry. However, this acid can be produced in a more environmental friendly technological route, using the anaerobic fermentation. The objective of this research was to investigate the operational conditions for anaerobic caproic acid formation using the products and by-products of the sugarcane industry. We used an upflow anaerobic sludge blanket and upflow (UASB - Upflow Sludge anerobic Blanked), with a working volume of 13.8 L, fed with simple substrates (ethanol and acetic acid) or complex substrate (undistilled fermented molasses). During the UASB reactor operation, OLR ranged from 2.0 to 5.5 gDQO.L-1.d-1 at acid pH (5.3). The volumetric production rate of caproic acid from simple substrates (1.0 gC6.L-1.d-1) in UASB reactor was superior to that from complex substrate (0.2 gC6.L-1.d-1). At pH of approximately 5.3, caproic acid production was limited to a value of approximately 2.8 gC6.L-1 due to the greater presence of non-dissociated acids. Using fermented sugar cane molasses containing ethanol (150 mM ethanol), can be achieved a production of up to 4.0 gC6.L-1 in pH by adding chloroform as a selective inhibitor for methanogenic organisms. The presence of acetic acid accelerates the formation of butyric acid, resulting in the accumulation of this due to the absence of ethanol as an electron donor. Thus, the formation of caproic acid from fermented molasses does not require the external addition of acetic acid. It is necessary selective extraction of caproic acid, preventing unwanted accumulation.

Un matériau adaptatif ou « intelligent » est capable de modifier spontanément ses propriétés physico-chimiques en réponse à un stimulus (température, pH, etc.). Les surfaces sensibles à un stimulus mécanique constituent une nouvelle catégorie de matériaux adaptatifs capables de montrer des changements de propriétés de surface sous l'effet d'une contrainte mécanique. Dans ce contexte, ces travaux se concentrent sur l'adsorption d'objets biologiques tels que des protéines sur un support élastique. L'objectif étant de contrôler cette adsorption en fonction du taux d'étirement du substrat. Les élastomères de silicone (PDMS), de par leur élasticité et leur faible toxicité, constituent des supports de choix pour l'élaboration de telles surfaces. Ces matériaux polymère sont largement utilisés dans le domaine médical et en microfluidique.La première étape d'élaboration consiste à rendre la surface du support de PDMS chimiquement réactive. Pour des temps de traitement courts, la polymérisation plasma de l'anhydride maléique permet d'introduire des groupements réactifs à la surface du PDMS, tout en conservant ses propriétés élastiques à l'échelle locale.Les substrats de PDMS traités présentent des propriétés acide-base de surface qui sont caractéristiques des groupements diacide du film polymère plasma. Le degré d'ionisation et les propriétés d'adhésion de ces surfaces sont étudiés en fonction du pH. L'évolution de ces propriétés sous élongation atteste de l'effet de dilution des groupements réactifs de surface.Le support étirable et réactif est ensuite fonctionnalisé avec des systèmes constitués de polymères et de récepteurs spécifiques. D'une part, les chaînes de poly(éthylèneglycol) (Peg) présentent des propriétés de résistance à l'adsorption de protéines. D'autre part, la biotine est un récepteur capable de se lier spécifiquement à une protéine, la streptavidine. En combinant le greffage covalent des Pegs et de la biotine sur le substrat de PDMS, on obtient une surface bi-fonctionnelle. L'objectif est de masquer la biotine avec les Pegs lorsque le substrat est à l'état relaxé, puis de promouvoir l'adsorption spécifique de la streptavidine sous élongation, afin d'obtenir un système de reconnaissance moléculaire sensible à un stimulus mécanique. / Surface responsive materials have the property to show response mechanisms triggered by external stimuli (temperature, pH, etc.). Mechanically responsive surfaces are a new kind of stimuli-responsive materials, which surface properties change in response to mechanical stress. This work focuses on the controlled adsorption of biological objects such as proteins on an elastic substrate. The goal is to control adsorption as a function of the elongation of the substrate. In elaborating mechanically responsive materials, silicone elastomers (PDMS) constitute interesting substrates because of their high flexibility and low toxicity. These polymers are widely used in biomedical devices and in microfluidics.The first step of elaboration consists in making the PDMS substrate chemically reactive. For low treatment time, plasma polymerization of maleic anhydride leads to the introduction of reactive groups on PDMS surface, while maintaining elastic properties at local scale.Treated PDMS substrates show acide-base properties which are characteristic of the diacid groups from the plasma polymer thin film. The degree of ionization and the adhesion properties of the surface are studied as a function of pH. The evolution of these properties under elongation attests from the dilution effect of surface reactive groups.The stretchable and reactive substrate is then functionalized with systems made of polymers and specific receptors. Poly(ethyleneglycol) (Peg) chains are well known to resist to protein adsorption, whereas biotin receptors bind specifically streptavidinproteins. A bi-functional surface is obtained by combining covalent grafting of Pegs and biotine on the PDMS substrate. The goal is to mask biotin with Peg chains in the relaxed state, while promoting specific binding of streptavidin under elongation of the substrate. This material may constitute a molecular recognition system that responds to a mechanical stimulus.

RNA polymerase II (Pol II) is the enzyme responsible for the synthesis of all mRNAs in eukaryotic cells. As the central component of the eukaryotic transcription machinery, Pol II is the final target of regulatory pathways. While the role for different Pol II associated proteins, co-activators and general transcription factors (GTFs) in regulation of transcription in response to different stimuli is well studied, a similar role for some subunits of the core Pol II is only now being recognized. The studies reported in this thesis address the role of the fourth largest subunit of Pol II, Rpb4, in transcription and stress response using Saccharomyces cerevisiae as the model system. Rpb4 is closely associated with another smaller subunit, Rpb7 and forms a dissociable complex (Edwards et al., 1991). The rpb4 null mutant is viable but is unable to survive at extreme temperatures (>34ºC and <12ºC) (Woychik and Young, 1989). This mutant has also been shown to be defective in activated transcription and unable to respond properly in several stress conditions (Pillai et al., 2001; Sampath and Sadhale, 2005). In spite of wealth of available information, the exact role of Rpb4 remains poorly understood. In the present work, we have used genetic, molecular and biochemical approaches to understand the role of Rpb4 as described in four different parts below: i) Studies on Genetic and Functional Interactions of Rpb4 with SAGA/TFIID Complex to Confer Promoter- Specific Transcriptional Control To carry out transcription, Pol II has to depend on several general transcription factors, mediators, activators, and co-activators and chromatin remodeling complexes. In the present study, we tried to understand the genetic and functional relationship of Rpb4 with some of the components of transcription machinery, which will provide some insight into the role of Rpb4 during transcription. Our microarray analysis of rpb4∆ strain suggests that down regulated genes show significant overlap with genes regulated by the SAGA complex, a complex functionally related to TFIID and involved in regulation of the stress dependent genes. The analysis of combination of double deletion mutants of either the SAGA complex subunits or the TFIID complex with rpb4∆ showed that both these double mutants are extremely slow growing and show synthetic growth phenotype. Further studies, including microarray analysis of these double mutants and ChIP (chromatin immunoprecipitation) of Rpb4 and SAGA complex, suggested that Rpb4 functions together with SAGA complex to regulate the expression of stress dependent genes. ii) Study of Genome Wide Recruitment of Rpb4 and Evidence for its Role in Transcription Elongation Biochemical studies have shown that Rpb4 associates sub-stoichiometrically with the core RNA polymerase during log phase but whether recruitment of Rpb4 is promoter context dependent or occurs only at specific stage of transcription remains largely unknown. Having discovered that Rpb4 can recruit on both TFIID and SAGA dominated promoters, it was important to study the genome wide role of Rpb4. Using ChIP on chip experiments, we have carried out a systematic assessment of genome wide binding of Rpb4 as compared to the core Pol II subunit, Rpb3. Our analysis showed that Rpb4 is recruited on coding regions of most transcriptionally active genes similar to the core Pol II subunit Rpb3 albeit to a lesser extent. This extent of Rpb4 recruitment increased on the coding regions of long genes pointing towards a role of Rpb4 in transcription elongation of long genes. Further studies showing transcription defect of long and GC rich genes, 6-azauracil sensitivity and defective PUR5 gene expression in rpb4∆ mutant supported the in vivo evidence of the role of Rpb4 in transcription elongation. iii) Genome Wide Expression Profiling and RNA Polymerase II Recruitment in rpb4∆ Mutant in Non-Stress and Stress Conditions Structural studies have suggested a role of Rpb4/Rpb7 sub-complex in recruitment of different factors involved in transcription (Armache et al., 2003; Bushnell and Kornberg, 2003). Though only few studies have supported this aspect of Rpb4/Rpb7 sub-complex, more research needs to be directed to explore this role of Rpb4/Rpb7 sub-complex. To study if Rpb4 has any role in recruitment of Pol II under different growth conditions, we have studied genome wide recruitment of Pol II in the presence and absence of Rpb4 during growth in normal rich medium as well as under stress conditions like heat shock and stationary phase where Rpb4 is shown to be indispensable for survival. Our analysis showed that absence of Rpb4 results in overall reduced recruitment of Pol II in moderate condition but this reduction was more pronounced during heat shock condition. During stationary phase where overall recruitment of Pol II also goes down in wild type cells, absence of Rpb4 did not lead to further decrease in overall recruitment. Interestingly, increased expression levels of many genes in the absence of Rpb4 did not show concomitant increase in the recruitment of Pol II, suggesting that Rpb4 might regulate these genes at a post-transcriptional step. iv) Role of Rpb4 in Pseudohyphal Growth The budding yeast S. cerevisiae can initiate distinct developmental programs depending on the presence of various nutrients. In response to nitrogen starvation, diploid yeast undergoes a dimorphic transition to filamentous pseudohyphal growth, which is regulated through cAMP-PKA and MAP kinase pathways. Previous work from our group has shown that rpb4∆ strain shows predisposed pseudohyphal morphology (Pillai et al., 2003), but how Rpb4 regulates this differentiation program is yet to be established. In the present study, we found that disruption of Rpb4 leads to enhanced pseudohyphal growth, which is independent of nutritional status. We observed that the rpb4∆/ rpb4∆ cells exhibit pseudohyphae even in the absence of a functional MAP kinase and cAMP-PKA pathways. Genome wide expression profile showed that several downstream genes of RAM signaling pathway were down regulated in rpb4∆ cells. Our detailed genetic analysis further supported the hypothesis that down regulation of RAM pathway might be leading to the pseudohyphal morphogenesis in rpb4∆ cells.

Le résonateur étudié s'insère dans un projet industriel porté par NXP Semiconductors. L'objectif est la réalisation d'un résonateur MEMS RF intégrable en vue de remplacer le quartz dans certaines applications. La compatibilité du procédé de fabrication avec les technologies utilisées par la société et le faible coût de production représentent les principaux enjeux du projet. Le résonateur TFEAR (Thin Film Elongation Acoustic Resonator) est un barreau, constitué d'une superposition de couches minces de type Métal/AlN/Métal. Les propriétés piézoélectriques du nitrure d'aluminium (AlN) sont ainsi exploitées : l'application d'un champ électrique alternatif, parallèle à l'épaisseur du barreau, entraîne une propagation d'ondes acoustiques suivant sa longueur. Les dimensions des résonateurs fabriqués correspondent à des fréquences de résonance comprises entre 10MHz et 50MHz. Cette thèse s'intéresse la modélisation et à la caractérisation électrique du résonateur TFEAR. Les modèles théoriques sont développés par simulations numériques 3D et par calculs analytiques 1D. Le comportement électrique du TFEAR est décrit par un schéma équivalent, dont les éléments sont exprimés en fonction des paramètres physiques et des pertes des matériaux le constituant. Un facteur de qualité de 2250 sur un TFEAR résonant à 25,79MHz et dont la résistance motionnelle est de 2,1 kOhms a été relevé. Ces mesures ont été complétées par la caractérisation des paramètres physiques de la couche piézoélectrique. Par exemple, des valeurs de coefficient piézoélectrique d33f atteignant 2,6 pm/V ont été relevées (pour un maximum théorique de 3,93 pm/V)

En la levadura S. cerevisiae, un incremento de la osmolaridad extracelular activa la vía de Hog1, lo que produce una compleja respuesta adaptativa. Entre las respuestas adaptativas que Hog1 coordina, está un importante cambio en el partón de expresión génica. La tesis presentada se centra en la respuesta a nivel de regulación génica, y en ella se ponen de manifiesto nuevos mecanismos por los cuales Hog1 regula la transcripción para inducir genes necesarios para la adaptación celular en respuesta a estrés osmótico. Este trabajo demuestra que Hog1 controla la iniciación y la elongación de la transcripción, interacciona con la RNA polimerasa elongando, y es reclutado en toda la región codificante de los genes que se inducen por estrés osmótico a traves del 3'UTR. Asimismo, Hog1 recluta el complejo remodelador de cromatina RSC para promover un dramático cambio en el posicionamiento de nucleosomas, permitiendo una correcta inducción de la expresión génica. / In the yeast S.cerevisiae, an increase in extra cellular osmolarity activates the Hog1 Pathway, which produces a very complex adaptive response. Among these adaptive responses coordinated by Hog1, there is an important change in the gene expression pattern. The presented Thesis focuses on the response triggered at the genomic level, showing novel mechanisms by which Hog1 regulates transcription to efficiently and properly induce a subset of genes critical for the cellular adaptation to osmotic stress. This work demonstrates that Hog1 promotes and regulates transcription not only at the initiation level, as was previously described, but it also interacts with the RNA Polymerase while elongating, and travels along the coding regions of genes induced upon osmotic stress through recognition of the 3'UTR. Furthermore, Hog1 recruits a chromatin-remodeling complex known as RSC to promote a dramatic change in nucleosome positioning of target genes, allowing a proper induction of the transcription

In this work, ultrafine-grained (UFG) Al-5wt%Zn alloy was produced by equal channel angular extrusion (ECAE). The microstructure evolution during ECAE and the mechanical properties of the UFG Al-Zn alloy were investigated. In order to identify the effect of Zn in the Al-Zn alloy, pure aluminum (4N, 99.99%) was also studied for comparison. The grains of the Al-Zn alloy could be refined effectively by increasing the ECAE passes. However, as the ECAE passes increased, the microhardness increased initially but maintained constant after 4 ECAE passes. The dislocation density within grain interior was decreased gradually with increasing ECAE passes. After being processed to twelve ECAE passes, the UFG Al-Zn alloy exhibited 53.7% of the grain boundaries being high angle grain boundaries (HAGBs). The UFG Al-5wt%Zn alloy exhibits superior tensile strength and elongation as compared with pure aluminum fabricated by the same ECAE process. Experimental results indicated that adding Zn in aluminum alloy could provide solid-solution strengthening and considerable enhancement in tensile ductility which might be related to an improved post-uniform elongation (PUE). The strain rate sensitivity (SRS) of the UFG Al-Zn alloy also increased with increasing the ECAE passes, which might be related to the fine grain size and the contribution of grain boundary sliding. The activation volume of the UFG Al-Zn alloy was in the range of 32b3~76b3, and the pure aluminum was in the range of 57b3~122b3. Because of the small value of the activation volume, it is suggested that the controlling mechanism for dislocation glide in the UFG Al-Zn alloy might be related to the generation and absorption of dislocations in grain boundary, as well as the interaction between dislocations and solute Zn atoms in the grain boundary.

Η ΒΥΠ διαθέτει αντίτυπο της διατριβής σε έντυπη μορφή στο βιβλιοστάσιο διδακτορικών διατριβών που βρίσκεται στο ισόγειο του κτιρίου της. / Στα βακτήρια, η μεγάλη ριβοσωματική υπομονάδα αποτελείται από δύο είδη RNA, το 23S και το 5S rRNA, καθώς και 33 πρωτεΐνες. Ο σχηματισμός του πεπτιδικού δεσμού και η απελευθέρωση της πεπτιδικής αλυσίδας επιτελούνται στη μεγάλη υπομονάδα, όπου εδράζεται το καταλυτικό κέντρο της πεπτιδυλοτρανσφεράσης (PTase). Εκτός αυτού, η μεγάλη υπομονάδα περιλαμβάνει το κέντρο προσδέσεως των μεταφραστικών παραγόντων, το οποίο πυροδοτεί τη GTPase δραστηριότητα των G-πρωτεϊνικών παραγόντων, που εμπλέκονται στη μετατόπιση των υποστρωμάτων και άλλες ριβοσωματικές λειτουργίες. Έχει υποτεθεί ότι το 5S rRNA παίζει ουσιώδη ρόλο στη συγκρότηση του κέντρου της PTase και στη μετάδοση σημάτων μεταξύ του καταλυτικού κέντρου και των ριβοσωματικών συστατικών που διεκπεραιώνουν τη μετατόπιση των υποστρωμάτων. Το ιοντικό περιβάλλον φαίνεται να επηρεάζει καθοριστικά τη διαμόρφωση του 5S rRNA. Για παράδειγμα, έχει βρεθεί ότι οι πολυαμίνες δεσμεύονται εκλεκτικά στο 5S rRNA και επηρεάζουν τη δραστικότητα του έναντι του διμεθυλο-θεϊκού, ενός αντιδραστηρίου-ιχνηθέτη της τριτοταγούς δομής του RNA. Αρχικά ελέγξαμε αν υπάρχουν εξειδικευμένες θέσεις πρόσδεσης των πολυαμινών στο 5S rRNA. Στη συνέχεια, με σκοπό να ελέγξουμε αν η πρόσδεση των πολυαμινών επηρεάζει τη λειτουργία του 5S rRNA, 70S ριβοσώματα προγραμματισμένα με πολύ-ουριδυλικό σχηματίσθηκαν από 50S υπομονάδες, ολικά ή εκλεκτικά φωτοσημασμένες με ένα φωτοδραστικό ανάλογο της σπερμίνης και από 30S ακατέργαστες υπομονάδες. Αυτά τα ριβοσώματα είχαν την ικανότητα να δεσμεύουν AcPhe-tRNA ελαφρώς ισχυρότερα, σε σύγκριση με ριβοσώματα συγκροτημένα από φυσικά συστατικά, μη περιέχοντα πολυαμίνες. Το γεγονός αυτό υποδηλώνει ότι η πρόσδεση πολυαμινών στο 5S rRNA επηρεάζει, σε μικρό βαθμό, τη λειτουργία του παράγοντα επιμήκυνσης EF-Tu. Συζευγμένα, όμως, τα εν λόγω ριβοσώματα με tRNAPhe στην Ε-θέση και AcPhe-tRNAστην Ρ-θέση, επέδειξαν ισχυρότερη καταλυτική δραστικότητα και αυξημένη ικανότητα για μετατόπιση των υποστρωμάτων. Τα αποτελέσματα αυτά εισηγούνται σημαντική εμπλοκή των πολυαμινών στο λειτουργικό ρόλο του 5S rRNA κατά την κατάλυση και μετατόπιση των υποστρωμάτων. / In bacteria, the large ribosomal subunit comprises two RNA species, 23S and 5S rRNA, and 33 proteins. Peptide bond formation and peptide release are catalyzed by the large subunit, where the peptidyltransferase (PTase) center is located. In addition to this center, which triggers the GTPase activities of G-protein factors involved in translocation and other ribosomal functions. It has been hypothesized that 5S rRNA plays essential role in assembling the PTase center and mediating signal transmissions between this center and the translocation machinery. Furthermore, the ionic environment seems to affect the conformation of 5S rRNA. For instance, polyamines have been found to bind specifically to 5S rRNA and influence the 5S rRNA reactivity towards dimethyl-sulfate (DMS), a chemical probe of RNA tertiary structure. Initially we examined whether there are specific sites for binding of polyamines. To test whether the binding of polyamines influence the function of 5S rRNA poly(U)-programmed 70S ribosomes were reconstituted from 50S subunits, totally or specifically photolabelled in their 5S rRNA with a photoreactive analogue of spermine, and native 30S subunits. These ribosomes were found to enzymatically bind AcPhe-tRNA better than ribosomes reconstituted from native components. This means, that furnishing 5S rRNA with spermine slightly influences the elongation factor EF-Tu function. However, equipped with tRNAPhe at the A-site and AcPhe-tRNA at the P-site, these ribosomes exhibited higher catalytic activity and enhanced tRNA translocation efficiency. These results suggest an essential impact of polyamines on the functional role of 5S rRNA in catalysis and translocation of translation substrates.

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