η (eta) nitride, Cr3Ni2SiN, is a precipitate found in high temperature austenitic stainless steel and is not yet included in Thermo-Calc steel database TCFE7. The aim of this thesis is to collect thermodynamic data to enable the addition of η nitride in the databases. Three laboratory melts with varying levels of silicon, chromium and nickel have been aged at 700-1000 °C for 75 h, 300 h and 1200 h and examined by Light Optical Microscopy, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, Wavelength Dispersive Spectroscopy, Electron Backscattered Diffraction and X-ray Powder Diffraction. η nitride is in the studied alloys an equilibrium phase stabilized with nitrogen. Presence of η nitride was confirmed by Energy Dispersive Spectroscopy and X-ray Powder Diffraction. It was found to precipitate in four different ways, at primary grain boundaries, intragranularly, as a "skeleton-like" precipitate and as a border around the occurring Cr2N precipitates. The area fraction of η nitrides increases with longer aging times and is favored by silicon and nickel. The composition of η nitride is not changing regardless of material composition, aging temperature and aging time. The composition of η nitride in all three materials are 8.7-9.7 wt.% silicon, 47-54 wt.% chromium, 1.4-4.1 wt.% iron and 33-36 wt.% nickel. The nitrogen content 2 determined by Wavelength Dispersive Spectroscopy is 2.8-3.2 wt.%. No complete equilibrium was achieved and together with incomplete mixing of the alloying elements during melting, the microstructure is difficult to evaluate. Other precipitates found are Cr2N, π nitride, σ phase and two unidentified phases, M and N. Of these phases at least Cr2N is not an equilibrium phase as it dissolves during aging. Further aging to achieve complete equilibrium is necessary.

Cette thèse a pour but d'étudier le transport de charges photogénérées dans des matériaux hybrides composés de polymères π-conjugués et de nanocristaux de semi-conducteurs, conçus pour des applications en opto-électronique. La synthèse chimique permet d'obtenir des nanocristaux de CdSe à l'échelle du gramme ayant une faible polydispersité et des formes contrôlées (sphériques, branchées). Les ligands de surface des nanocristaux de CdSe sont échangés par de petites molécules (pyridine, éthanedithiol, phénylènediamine, butylamine, benzènedithiol) afin d'augmenter leur conductivité. L'échange de ligands modifie les niveaux énergétiques des nanocristaux, comme le montrent des études optiques et électrochimiques. Le poly(3-hexylthiophène) déposé sous forme de couches minces présente différents degrés de couplage intermoléculaire et de désordre énergétique selon la méthode de dépôt et le solvant utilisé. Dans les films hybrides, des mesures de diffraction de rayons X en incidence rasante montrent que la structuration cristalline de la matrice organique est modifiée par la présence des nanocristaux. Les mesures de Temps-de-Vol dans les couches hybrides montrent que les mobilités des trous et des électrons varient avec le contenu en nanocristaux, ainsi qu'avec leur forme et leurs ligands. De faibles fractions de nanocristaux provoquent une amélioration de la mobilité des trous, tandis que de plus grandes fractions la détériorent. Les mobilités électroniques sont soumises à une fraction-seuil, assimilable à un seuil de percolation. La fraction optimale de nanocristaux, du point de vue des mobilités des trous et des électrons, est de 36% en volume pour les nanocristaux sphériques avec les ligands de synthèse. Enfin, les simulations Monte-Carlo des courants transitoires photogénérés, dans un échantillon de poly(3-hexylthiophène) et dans un hybride, montrent d'une part que la distribution énergétique du poly(3-hexylthiophène) domine l'allure des courants simulés et d'autre part que les nanocristaux peuvent être assimilés à des sites difficilement accessibles du réseau cubique.

Ce mémoire s'articule autour de deux aspects complémentaires des processus qui accompagnent le transfert d'électron. Le cœur de ce projet concerne la valorisation de l'électrochimie moléculaire comme technique d'activation dans deux directions : activation de processus mécaniques ou de mouvements moléculaires dans des architectures commutables pour lesquelles un transfert d'électron fournit l'impulsion tout en permettant le contrôle et la lecture de l'état d'un système dynamique, et activation de processus chimiques pour lesquels l'électrochimie est exploitée en ingénierie moléculaire pour élaborer des molécules complexes et proposer une alternative efficace aux méthodes classiques de la synthèse organique. Le fil conducteur « activation électrochimique » est déroulé autour deux grandes classes de composés : les -dimères de dérivés du viologène et les macrocycles conjugués à base de pyrrole. Dans la première partie de ce mémoire, nous présenterons nos résultats en matière de systèmes moléculaires commutables dont les mouvements intramoléculaires et les propriétés sont activés et contrôlés par simple transfert d'électron tandis que la deuxième partie est centrée sur l'ingénierie électrochimique de porphyrines étendues.

L'état supraconducteur étant un condensat de paires de Cooper constitué d'électrons de moments et de spins opposés, il peut être fortement influencé par des effets de spin. Au cours de cette thèse, nous étudions l'effet d'un fort champ d'échange et d'un effet spin-orbite de type Rashba sur les propriétés supraconductrices. Dans une première partie, on étudie les effets associés à l'interaction entre supraconductivité et fort champ d'échange, se caractérisant par une transition de phase vers un état supraconducteur inhomogène découvert par Fulde, Ferrell, Larkin et Ovchinnikov (FFLO). On étudie tout particulièrement les fluctuations supraconductrices à l'approche de la transition de phase. On montre que ces fluctuations peuvent servir de révélateur à cette phase. Notamment, la capacité calorifique et la paraconductivité divergent de façon caractéristique à la transition vers un état modulé. On décrit également comment les effets paramagnétiques modifient les fluctuations de l'aimantation, annulant la réponse diamagnétique ou produisant des oscillations entre réponse para- et dia-magnétique. La seconde partie est dévolue aux jonctions supraconducteur-ferromagnétique (S/F). Dans les jonctions Josephson S/F/S, le champ d'échange donne lieu à des oscillations du courant critique en fonction de la longueur de la jonction, charactérisées par une alternance des états 0 et π. On prédit une transition entre les états 0 et π induite par la température, même dans la limite ballistique. Dans cette limite ballistique, on montre également que le courant de Josephson s'atténu sous la forme de lois de puissance en fonction de la longueur de la jonction, alors que le cas diffusif présente une atténuation exponentielle. On étudie ensuite la seconde harmonique de la relation courant-phase en présence d'une faible quantité d'impuretés. La dernière partie traite des effets de proximité lorsque les deux effets paramagnétique et spin-orbite sont présents dans une jonction Josephson. On montre que l'association d'une interaction Rashba et d'un champ d'échange induit un couplage direct entre les ordres magnétique et supraconducteur. En particulier, ce couplage permet de générer toute la dynamique magnétique par l'application d'une simple tension électrique.

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京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20945号 / 理博第4397号 / 新制||理||1632(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 大須賀 篤弘, 教授 依光 英樹, 教授 丸岡 啓二 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Το π–κυμένιο (p–ισοπρόπυλο τολουόλιο) είναι ένα πολύ σημαντικό προϊόν με μεγάλο εμπορικό ενδιαφέρον, καθώς αποτελεί κύριο συστατικό πολλών καλλυντικών, αρωμάτων, φαρμακευτικών προϊόντων, καθώς και την πρώτη ύλη για την παραγωγή της p–κρεσόλης. Η τρέχουσα διαδικασία παραγωγής του π–κυμενίου είναι η κατά Friedel–Crafts αλκυλίωση του τολουολίου με προπυλένιο ή προπανόλη–2, η οποία χρησιμοποιεί μεγάλες ποσότητες επιβλαβών οξέων, προκαλώντας πολλά προβλήματα χειρισμού στους εργαζόμενους με αυτό, προβλήματα διάβρωσης και προβλήματα διάθεσης των παραγόμενων αποβλήτων. Τα τελευταία χρόνια, η Πράσινη Χημεία έχει παρουσιασθεί ως η νέα προσέγγιση της Χημείας για την πρόληψη της μόλυνσης του περιβάλλοντος, καθώς και του σχεδιασμού χημικών προϊόντων και διεργασιών που είναι περισσότερο φιλικά προς το περιβάλλον. Η κατάλυση αποτελεί μία από τις κύριες αρχές, αλλά ταυτόχρονα και εργαλείο της Πράσινης Χημείας. Πιο συγκεκριμένα η ετερογενής κατάλυση, που εξυπηρετεί τους στόχους της Πράσινης Χημείας, λόγω της εξάλειψης της ανάγκης διαχωρισμού του παραγόμενου προϊόντος από τον καταλύτη. Επίσης, μία άλλη βασική παράμετρος της Πράσινης Χημείας είναι η χρήση της βιομάζας, ως ανανεώσιμη πρώτη ύλη, με σκοπό την παραγωγή ενέργειας και χημικών προϊόντων. Στην παρούσα εργασία, μελετάται η δυνατότητα καταλυτικής παραγωγής π–κυμενίου, βασιζόμενη στις αρχές της Πράσινης Χημείας. Για το σκοπό αυτό χρησιμοποιείται ως αντιδρών το α–λεμονένιο, ένα μονοτερπένιο το οποίο αποτελεί ανανεώσιμη πρώτη ύλη, καθώς είναι παραπροϊόν της βιομηχανίας χυμών λεμονιού και πορτοκαλιού, καθώς και της βιομηχανίας χάρτου και πολτού. Πιο αναλυτικά, μελετήθηκε η καταλυτική συμπεριφορά οξειδίων με μεγάλη ειδική επιφάνεια, όπως η SiO2, το MCM–41, ο ζεόλιθος NaY, η γ–Al2O3 και δύο δείγματα TiO2, με διαφορετικές ειδικές επιφάνειες, στην αντίδραση μετατροπής του λεμονενίου προς π–κυμένιο. Επίσης, ερευνήθηκε η επίδραση στη διεργασία τόσο της θερμοκρασίας της αντίδρασης, όσο και της σύστασης της ατμόσφαιρας κάτω από την οποία διεξαγόταν η αντίδραση. Τα πειράματα διεξήχθησαν σε αντιδραστήρα σταθερής κλίνης – ατμοσφαιρικής πίεσης, ενώ για την ανάλυση των λαμβανόμενων προϊόντων χρησιμοποιήθηκε αέριος χρωματογράφος – φασματογράφος μάζας (GC–MS). Από τους καταλύτες που μελετήθηκαν ο πιο αποτελεσματικός αποδείχθηκε η τιτάνια με τη σχετικά μεγάλη ειδική επιφάνεια ακολουθούμενη από την τιτάνια με την χαμηλότερη ειδική επιφάνεια, τον ζεόλιθο NaY και τη γ–Al2O3. Τόσο η σίλικα όσο και το MCM–41 παρουσίασαν μάλλον αμελητέα δραστικότητα. Επίσης, παρατηρήθηκε ότι η απόδοση σε π–κυμένιο αυξανόταν γενικά με τη θερμοκρασία, ενώ δεν επηρεαζόταν πρακτικά από την ατμόσφαιρα που διεξαγόταν η αντίδραση. Τέλος, στους 300 οC και χρησιμοποιώντας την τιτάνια με τη σχετικά μεγάλη ειδική επιφάνεια ως καταλύτη επιτεύχθηκε 90% απόδοση για το π–κυμένιο και 100% μετατροπή για το λεμονένιο. Η αυξημένη απόδοση της τιτάνιας αποδόθηκε σε επιτυχή συγκερασμό ανάμεσα στη σχετικά μεγάλη οξύτητα Brönsted και στη σχετικά εύκολη μεταβολή του λόγου Ti(IV)/Ti(III) κατά τη διάρκεια της αντίδρασης. Τα κινητικά αποτελέσματα επέτρεψαν να γραφεί ένα κινητικό σχήμα για τη διεργασία. / P–cymene is a very important product with great commercial interest because of its use as a main ingredient of cosmetics, perfumes and pharmaceutical products as well as raw material for the production of p–cresol. Current production is achieved by using the Friedel–Crafts reaction of toluene with propylene or propanol–2 which uses large quantities of harmful acids which, in turn, leads to industrial accidents, corrosion problems and the general difficulty of handling toxic wastes. A new concept of chemistry has been developed for confronting environmental problems. Green Chemistry is related to products and processes that are environmentally friendly. One of the basic tools of Green Chemistry is catalysis, mainly heterogeneous catalysis, because it allows the easy separation of the catalysts used from the final product. Moreover, following the principles of the Green Chemistry, biomass should be used in the production of renewable energy and chemical products. The present Thesis deals with the catalytic production of p–cymene based on the principles of Green Chemistry. In particular, we use a–limonene, by–product of the juice of orange and lemon industry as well as the paper industry, to produce p–cymene. A number of oxides with large specific surface area, such as SiO2, MCM–41, zeolite NaY, γ–Al2O3 and two samples of TiO2, were studied as catalysts. The effect of the reaction temperature and the composition of the atmosphere were also studied. All experiments were conducted on a fixed bed micro–reactor operating under atmospheric pressure coupled with an on–line Gas Chromatograph–Mass Spectrometer (GC – MS). The titania with the relatively high specific surface area was proved to be the most efficient catalyst among those studied. The following activity series has been obtained: «high surface area titania > small surface area titania > zeolite NaY > γ–Al2O3 > MCM–41 > SiO2». Negligible activity is exhibited by MCM–41 and SiO2. The percentage yield for p–cymene increases with temperature whereas is practically independent from the carrier gas. Very high percentage yield for p–cymene was obtained at 300οC over the high specific surface area titania (~90%). Complete transformation of a–limonene was obtained over the above catalyst at the same temperature. The very high activity obtained over this catalyst was attributed to good compromise between high acidity and easy transformation of the ratio Ti(IV)/Ti(III) during reaction. The kinetic results allow the clarification of the reaction scheme.

Modern software systems, in particular distributed ones, are everywhere around us and are at the basis of our everyday activities. Hence, guaranteeing their correctness, consistency and safety is of paramount importance. Their complexity makes the verification of such properties a very challenging task. It is natural to expect that these systems are reliable and above all usable. i) In order to be reliable, compositional models of software systems need to account for consistent dynamic reconfiguration, i.e., changing at runtime the communication patterns of a program. ii) In order to be useful, compositional models of software systems need to account for interaction, which can be seen as communication patterns among components which collaborate together to achieve a common task. The aim of the Ph.D. was to develop powerful techniques based on formal methods for the verification of correctness, consistency and safety properties related to dynamic reconfiguration and communication in complex distributed systems. In particular, static analysis techniques based on types and type systems appeared to be an adequate methodology, considering their success in guaranteeing not only basic safety properties, but also more sophisticated ones like, deadlock or livelock freedom in a concurrent setting. The main contributions of this dissertation are twofold. i) On the components side: we design types and a type system for a concurrent object-oriented calculus to statically ensure consistency of dynamic reconfigurations related to modifications of communication patterns in a program during execution time. ii) On the communication side: we study advanced safety properties related to communication in complex distributed systems like deadlock-freedom, livelock-freedom and progress. Most importantly, we exploit an encoding of types and terms of a typical distributed language, session π-calculus, into the standard typed π-calculus, in order to understand the expressive power of concurrent calculi with structured communication primitives and how they stand with respect to the standard typed concurrent calculi, namely (variants) of typed π-calculus. Then, we show how to derive in the session π-calculus basic properties, like type safety or complex ones, like progress, by encoding.

Proteins are large biomolecules consisting of one or more long chains of amino acid residues. They perform a vast array of functions within living organisms. In this thesis, we present analyses of different secondary structural elements (SSEs) in proteins and various methods developed for the same purpose. Using only the geometric parameters, a program for identification of SSEs has been developed, which is more sensitive to the local structural variations. An understanding of the factors that determine the length, geometry as well as location of a particular SSE in the protein is essential to fully appreciate their respective roles in protein structures. The comparative analysis of the geometry of α-helices identified by different programs showed that STRIDE assigned α-helices are more kinked. Conformation of Pro residues in α-helices has also been studied in detail. Several interesting conclusions are drawn from the comprehensive study of π-helices and PolyProline-II (PPII) helices. In the subsequent paragraphs, a brief summary of each chapter is provided. The Introduction (Chapter 1) summarizes the relevant literature, which includes both experimental as well as theoretical studies explaining the structural and functional importance of SSEs in proteins and lays down a suitable background for the subsequent chapters in the thesis. The major questions addressed and the main goals of this thesis are described to set a suitable stage for the detailed discussions. The methodologies involved are discussed in Chapter 2. These include protocol used for preparing non-redundant datasets of protein structures, various statistical methods used to test the significance of position-wise amino acid propensities and different programs used during the course of present investigations. SSEs play an important role in the folding of proteins. However, identification of these SSEs in proteins is a common yet important concern in structural biology. Chapter 3 details a new method ASSP (Assignment of Secondary Structure in Proteins), which uses only the path traversed by the Cα atoms of the consecutive residues. The algorithm is based on the premise that the protein structure can be divided into continuous or uniform stretches, which can be defined in terms of helical parameters and depending on their values, the stretches can be classified into different SSEs, viz. α, 310, π, extended β-strands and PPII and other left handed helices. The methodology was validated using an unbiased clustering of these parameters for a protein dataset containing 1008 protein chains, which advocate that there are seven well defined clusters associated with different SSEs. Apart from α-helices and extended β-strands, 310 and π-helices were also found to occur in considerable numbers. Various analyses demonstrated that the ASSP was able to discriminate the non α-helical segments from flanking α-helices, which were often identified as a part of α-helix by other algorithms. The standalone version of the program for the Linux as well as Windows operating systems is freely downloadable and the web server version is also available at http://nucleix.mbu.iisc.ernet.in/assp/index.html. Among all SSEs in proteins, α-helices are relatively well defined. However, a precise quantitative estimate of their geometrical features and identification of terminal residues is difficult. In Chapter 4, a set of major changes/ updates, implemented in the algorithm of in-house program for analysis of geometry of helices in proteins (HELANAL), has been discussed in detail. It defines the helix parameters based on the path traced by Cα atoms alone and classifies the geometry of the helices into linear, curved, kinked and unassigned type, by fitting the least square 3D line and sphere to the local helix origin points (LHOP). The geometry assigned using HELANAL-Plus is independent of the orientation of the helix in 3D space and also does not depend on the database from which it is taken. The program is made available as a webserver as well as standalone and the helices can be viewed in the JmolApplet along with the best fit helix axis, which makes HELANAL-Plus useful for analysing the inter helix interaction and packing. The utility of the webserver has been increased by incorporating the use of SSE assignment programs like ASSP, DSSP or STRIDE. Pro kinked helices and correlation with the UP and DOWN conformation of Pro were studied in more detail. HELANAL-Plus is available at http://nucleix.mbu.iisc.ernet.in/helanalplus/index.html. Linux/Unix and windows compatible executables are also available for download. The analyses of kinks in a dataset of helices indicated a correlation with the large radius of the cylinder encompassing the residue at which the kink has been observed and many a time ASSP identified that as a π-helix. The detailed analysis of π-helices was limited due to the low frequency of identification by different algorithms. ASSP identified 659 π-helices in 3582 protein chains, solved at resolution ≤ 2.5Å and validated by molprobity. Chapter 5 reports the detailed study of the functional and structural roles of π-helices along with the position-wise amino acid propensity within and around them. These helices were found to range from 5 to 18 residues in length with the average twist and rise being 85.2°±7.2° and 1.28ű0.31Å respectively. The investigation of π-helices illustrated that they occur mostly in conjunction with α-helices. The majority of π-helices, with flanking α-helices at both termini, were found to be conserved across a large number of structures within a protein family and induce local distortions in the neighbouring α-helices. The presence of a π-helical fragment leads to appropriate orientation as well as positioning of the constituent residues and hence facilitate favourable interactions and also help in proper folding of the protein chain. The comprehensive analyses of position-wise amino acid propensity within and around π-helices showed their unique preferences, which are different from those of α-helices. Additionally and most importantly, the study also brought to light the influence of π-helices on the residue preference in preceding or succeeding α-helices and vice-versa. Study of another important SSE in proteins (Chapter 6), PPII helices, was inspired by their large number of occurrence and initiated with the aim of understanding their structural and functional roles. These helices are defined as an extended, flexible left-handed helix without intra-helical H-bonds and found to occur very frequently. ASSP identifies 3597 PPII helices in 3582 protein chains. Though PPII helices occur on a much smaller scale than α-helices and β-strands, their sheer number is still more than that of π-helices. The analyses of PPII-helices revealed that almost 50% of the total helices do not contain Pro residues and show a preference for polar residues. PPII-helices were found in conjunction with major SSEs and they often connect them. These helices range from 3 to 13 residues in length with the average twist and rise being -121.2°±9.2° and 3.0ű0.1Å respectively. The analysis of various non-bonded interactions revealed the frequent presence of C-H…N and C-H…O non-bonded interactions. The analysis of the amino acid preference within and around PPII-helices showed the avoidance of aromatic residues within the helix, while preference of Gly, Asn and Asp residues in the flanking region. Detailed analyses of various functional and structural roles mediated by PPII-helices have also been carried out. Identification and analysis of non-bonded interactions within a molecule and with the surrounding molecules are an essential part of structural studies. Given the importance of these interactions, we have developed a new algorithm named MolBridge and Chapter 7 provides the detailed description about it. MolBridge is an easy to use algorithm based purely on geometric criteria that can identify all possible non-bonded interactions, such as hydrogen bond, halogen bond, cation…π, π…π and van der Waals, in small molecules as well as biomolecules. Various features available in the webserver make it more user-friendly and interactive. The Unix/Linux version of the program is freely downloadable and the web server version is available at http://nucleix.mbu.iisc.ernet.in/molbridge/index.php. The overall conclusion from the current investigation and the possible future directions are presented in Chapter 8. Our findings suggest that the path traversed by Cα atoms is enough for the identification of SSEs. We believe that the various algorithms (ASSP, HELANAL-Plus and MolBridge) developed can provide a better understanding of the finer nuances of protein secondary structures. ASSP can make an important contribution in the better understanding of comparatively less frequent structural motifs and identification of novel SSEs. The most comprehensive study of π-helices gives in-depth insight about it. The analysis of interspersed π-helices gives a comprehensive understanding of the local deformations and variations in the helical segments. Apart from studies embodied in the thesis, author has been involved in few other studies, which are provided as appendix: Appendix A describes a program RNAHelix, which can regenerate duplexes from the dinucleotide step and base pair parameters for a given double helical DNA or RNA sequence. It can be used to generate/ regenerate the duplexes with the non-canonical base pairing as well.