Η λυοφιλοποίηση θεωρείται ιδανική μέθοδος για βραχύχρονη ή/ και μακρόχρονη αποθήκευση λιποσωμάτων. Στόχος αυτής της μελέτης ήταν να ευρεθούν οι ποσότητες κρυοπροστατευτικού που μπορεί να αυξήσουν τη συγκράτηση πρωτεϊνικών μορίων σε λιποσώματα τα οποία είναι ασταθή (δηλ. χάνουν μεγάλο τμήμα της εγκλωβισμένης πρωτεΐνης) μετά από λυοφιλοποίηση. Η μέθοδος παρασκευής των λιποσωμάτων που χρησιμοποιήθηκε ήταν η DRV μέθοδος. Είναι η πλέον κατάλληλη στην περίπτωση εγκλωβισμού πρωτεϊνικών μορίων καθώς επιτυγχάνει υψηλά ποσοστά εγκλωβισμού και επίσης χρησιμοποιεί ήπιες συνθήκες οπότε προστατεύεται η τριτοταγής δομή των πρωτεϊνών. Η διαδικασία βασίζεται στην αφυδάτωση μίγματος “άδειων” SUV (μικρών μονοστοιβαδιακών) λιποσωμάτων παρουσία του διαλύματος πρωτεΐνης που πρόκειται να εγκλωβιστεί. Μετά από ελεγχόμενη επανενυδάτωση της ξηρής κόνης σχηματίζονται τα DRV λιποσώματα. (από τις λέξεις dried-rehydrated vesicles που μεταφράζονται ως αφυδατωμένα-επανενυδατωμένα σωματίδια). Ως υλικά για την παρασκευή των λιποσωμάτων χρησιμοποιήθηκαν τα εξής: Φωσφατιδυλοχολίνη αυγού (egg PC), διστεαροϋλο-γλυκεροφωσφατιδυλοχολίνη (DSPC), διπαλμιτοϋλο-γλυκεροφωσφατιδυλοχολίνη (DPPC), διμυριστοϋλο-γλυκεροφωσφατιδυλοχολίνη (DΜPC), φωσφατιδυλογλυκερόλη (PG) και χοληστερόλη (CHOL). Παρασκευάστηκαν με τη μέθοδο DRV λιποσώματα διαφόρων λιποσωμικών συστάσεων προκειμένου να μελετηθεί η ικανότητα εγκλωβισμού για κάθε λιποσωμική σύσταση και να επιλεγούν αυτές που είναι πλέον ασταθείς για περαιτέρω μελέτη. Ως πρωτεΐνη μοντέλο χρησιμοποιήθηκε η αλβουμίνη βόειου ορού (BSA). Μελετήθηκε η επίδραση της λυοφιλοποίησης σε διάφορα DRV λιποσώματα παρουσία ή/ και απουσία κρυοπροστατευτικού παράγοντα (τρεαλόζη). Σε κάποιες περιπτώσεις προστέθηκε τρεαλόζη εντός των λιποσωμάτων κατά την αρχική παρασκευή των DRV (στο στάδιο της ανασύστασης). Επίσης, προκειμένου να αποκτήσουμε περαιτέρω πληροφορίες για τα λιποσώματα που μελετούσαμε, πραγματοποιήθηκε προσδιορισμός του μεγέθους των ορισμένων λιποσωμικών σειρών και μορφολογική μελέτη με ηλεκτρονικό μικροσκόπιο σάρωσης. Στη συνέχεια, με βάση τα αρχικά αποτελέσματα με την αλβουμίνη, επιλέχθηκαν ορισμένες λιποσωμικές συστάσεις προκειμένου να μελετηθεί η σταθερότητα λιποσωμάτων που εγκλωβίζουν ένα βιοδραστικό μόριο, το t-PA (ιστικού τύπου ενεργοποιητή πλασμινογόνου) σε ξηρή μορφή. Η μελέτη πραγματοποιήθηκε με δείκτη τη διατήρηση της ενεργότητας του μορίου μετά από FD και προσθήκη ή όχι τρεαλόζης. Απώτερος σκοπός αυτής της εργασίας είναι η δυνατότητα παρασκευής σταθερών t-PA- λιποσωμικών μορφών σε ξηρή μορφή προκειμένου να μελετηθεί η δράση τους στη θεραπεία θρομβώσεων του αμφιβληστροειδούς. Τα βασικά συμπεράσματα της μελέτης είναι τα εξής: Σχετικά με αποτελέσματα πειραμάτων με BSA: * Τα PC:PG:CHOL DRV λιποσώματα σταθεροποιούνται ικανοποιητικά αν πριν τη λυοφιλοποίηση προσθέσουμε αναλογία treh/lipid=5/1 στη λιποσωμική διασπορά. * Η καλύτερη σταθεροποίηση επιτυγχάνεται με παρουσία σακχάρου στο εσωτερικό και εξωτερικό των λιποσωμάτων * Πιθανή αλληλεπίδραση λαμβάνει χώρα μεταξύ των PC λιποσωμάτων και της αλβουμίνης, δίνοντας ψευδή υψηλά τελικά ποσοστά συγκράτησης μετά τη λυοφιλοποίηση Σχετικά με αποτελέσματα πειραμάτων με t-PA * Τα αποτελούμενα από DSPC DRV λιποσώματα παραμένουν πολύ σταθερά διατηρώντας την ενεργότητα του t-PA μετά τη λυοφιλοποίηση και χωρίς την προσθήκη κρυοπροστατευτικού. * Τα ασταθή PC:PG:CHOL και PC λιποσώματα σταθεροποιούνται ικανοποιητικά με προσθήκη τρεαλόζης πριν το FD. / Lyophilization is considered to be an ideal technique for both short-term and long-term storage of liposomes. The objective of this study was to investigate the stability of liposomes encapsulating protein molecules and the effect of freeze-drying (FD) on the stability of dehydrated-rehydrated vesicles (DRV) with and without cryoprotective agents (CPA). Τhe liposomes were prepared by the DRV method. This is considered to be the most appropriate in the cases that entrapment of proteins is desired, since it gives liposomes with high encapsulation efficiencies and by using mild conditions it protects the tertiary structure of proteins retaining thus their biological activity. The procedure followed here was based on dehydration of a mixture of “empty” SUV liposomes and the protein solution (BSA) which is to be entrapped, followed by controlled rehydration of the dry powder. The materials used for the preparation of the liposomes were: Egg-PC (phosphatidylcholine), distearoyloglycerophosphatidylcholine(DSPC), (DPPC) dipalmitoylglycerophosphatidylcholine, (DΜPC) dimyristoylglycerophosphatidylcholine, PG (phosphatidylglycerol) and CHOL (cholesterol). Liposomes of various lipid compositions were prepared so that the most unstable liposome compositions are found and available for further study. BSA was used as a protein model in these experiments. Furthermore, the influence of lyophilization for liposomes of various compositions was studied using trehalose as a cryoprotective agent. In some experiments, the dissacharide was added during the reconstitution of DRV. In order to have some more information about the liposomes under investigation, we conducted particle size determination (zetasizer) and morphological study by SEM (scanning electron microscopy. Eventually, based on the primary results with albumin, the stability of liposomes bearing a bioactive protein was studied. The protein used here was t-PA (tissue type plasminogen activator). We investigated the influence of FD on the stability of liposomes with or without the addition of a cryoprotective agent (trehalose) as a function of bioactivity retention. A long-term objective of our studies is to prepare stable after FD liposomal- tPA-formulations that may be active for therapy of ocular thrombosis cases. The mail conclusions of this study were: Concerning the results obtained with BSA: * PC:PG:CHOL DRV liposomes are adequately stabilized when trehalose in mass ratio treh/PC=5/1 is added in the liposomal dispersion * Maximum retention of BSA is achieved when trehalose is added on both sides of liposomal membrane. * There is a possible interaction between BSA and PC liposomes, which results in false estimation of BSA retention after FD. Concerning the results obtained with t-PA: * DSPC DRV liposomes are very stable after FD and they preserve t-PA activity even in absence of cryoprotectant. * Unstable PC:PG:CHOL and PC liposomes can be adequately stabilized by trehalose.

abstract: Memories play an integral role in today's advanced ICs. Technology scaling has enabled high density designs at the price paid for impact due to variability and reliability. It is imperative to have accurate methods to measure and extract the variability in the SRAM cell to produce accurate reliability projections for future technologies. This work presents a novel test measurement and extraction technique which is non-invasive to the actual operation of the SRAM memory array. The salient features of this work include i) A single ended SRAM test structure with no disturbance to SRAM operations ii) a convenient test procedure that only requires quasi-static control of external voltages iii) non-iterative method that extracts the VTH variation of each transistor from eight independent switch point measurements. With the present day technology scaling, in addition to the variability with the process, there is also the impact of other aging mechanisms which become dominant. The various aging mechanisms like Negative Bias Temperature Instability (NBTI), Channel Hot Carrier (CHC) and Time Dependent Dielectric Breakdown (TDDB) are critical in the present day nano-scale technology nodes. In this work, we focus on the impact of NBTI due to aging in the SRAM cell and have used Trapping/De-Trapping theory based log(t) model to explain the shift in threshold voltage VTH. The aging section focuses on the following i) Impact of Statistical aging in PMOS device due to NBTI dominates the temporal shift of SRAM cell ii) Besides static variations , shifting in VTH demands increased guard-banding margins in design stage iii) Aging statistics remain constant during the shift, presenting a secondary effect in aging prediction. iv) We have investigated to see if the aging mechanism can be used as a compensation technique to reduce mismatch due to process variations. Finally, the entire test setup has been tested in SPICE and also validated with silicon and the results are presented. The method also facilitates the study of design metrics such as static, read and write noise margins and also the data retention voltage and thus help designers to improve the cell stability of SRAM. / Dissertation/Thesis / M.S. Electrical Engineering 2013

A hybrid model reduction for use with the automated multilevel substructuring (AMLS) method is presented for frequency response analysis of complex structures. Structure responses to harmonic excitations and quasi-static responses to dominant damping forces are included in a reduced approximation subspace. Both types of responses greatly increase the efficiency of the subspace for solving the frequency response problem (FRP) for systems with high modal density and structural damping, and provide a good preparation for future frequency-dependent problems. A distilled subspace assumed to provide accurate frequency responses is generated from the finite element (FE) models by using the AMLS method. Then, the hybrid model reduction method is used to reduce the distilled subspace into a small new subspace. Three types of vectors are used to construct this subspace. The first type is distilled subspace dynamic response vectors (DRVs), which are exact solutions in the distilled subspace at certain chosen frequencies, called the DRV frequencies. The second type is modal DRVs, which are inexpensive approximate solutions calculated in an eigenspace. The third type is damping deformation vectors (DDVs), which provide information about response of the structure to damping effects. As exact responses, the distilled subspace DRVs eliminate frequency response errors at the DRV frequencies, and improve the accuracy at nearby frequencies as well. A small number of DRV frequencies are chosen carefully to offer maximum benefit with minimal computational cost. The modal DRVs are approximated very inexpensively from a suitable eigenspace. Only the diagonal entries in the modal coefficient matrices are used, along with low-rank updates that improve the accuracy of the modal DRVs and are applied using the Sherman-Morrison-Woodbury formula. Because of their low cost, a large number of modal DRVs constitute the major part of the reduced subspace. A small number of DDVs represent response to provide damping with minimal computational cost. The dimension of the final subspace is minimized by removing any redundancy through a special implementation of the QR factorization. This method results in a much smaller new subspace than the one from traditional modal truncation while achieving the same FRP accuracy. Such an efficiency also establishes a good foundation for future application in frequency-dependent problems. / text

Extended plasticity mechanisms (EPM) allow a metal to undergo extended plastic deformation without failure. These mechanisms are responsible for the extended plastic deformation characteristic of hot working processes. In this thesis it is shown that electron backscatter diffraction (EBSD) is capable of detecting EPM artifacts in the final microstructure of AISI 304L stainless steel (304L). Results also indicate that dislocation cells form in hot worked AISI 304L stainless steel. Additionally, in this study EBSD data collection and analysis is used with a design of experiments approach to model the presence of EPM artifacts in the final microstructure of friction stir welded 304L. Texture analysis of the welded material reveals a dominant shear deformation texture and a lack of the rotated cube texture. The shear deformation texture is characteristic of dynamic recovery (DRV) and continuous dynamic recrystallization (CDRX), while the rotated cube texture is characteristic of discontinuous dynamic recrystallization (DDRX). The texture analysis results indicate that dynamic recovery (DRV) and continuous dynamic recrystallization (CDRX) play a role in the final microstructure of the welded material, while DDRX does not. Design of experiments was used to find the relationships between the fraction of cell boundaries and spindle speed, travel speed, location in the stir zone, and tool temperature. The regression analyses reported that predicted fraction of cell boundaries were relatively high (approximately 0.70 or more) and changed by less that 20% in the stir zone and 10% in the TMAZ. The relatively high predictions indicate that in FSW 304L DRV dominates and limited CDRX occurs. The small changes in predictions across the experimental space indicate that the effects, while statistically significant, are not practically significant. Finally, an alternate tool temperature basis was developed, which provides a valid method for selecting welds which should have constant tool temperature.

Der Hochwasserschutz stellt für die gegenwärtige Gesellschaft eine Thematik von zunehmender Aktualität dar, besonders unter Berücksichtigung der Verschärfung der extremen meteorologischen Ereignisse infolge des Klimawandels einerseits und der Vergrößerung des Schadenpotenzials in den Auengebieten andererseits. Zu den möglichen Schutzmaßnahmen im Flussmittellauf zählt die in ökologischer Hinsicht sehr effektive Deichrückverlegung (DRV). Um ihre Wirksamkeit bei der Dämpfung der Hochwasserspitzen zu untersuchen, wird eine Parameterstudie mit einem eindimensionalen hydronumerischen Modell (MIKE11) durchgeführt. Dabei wird besonderes Augenmerk auf die Hüllkurve der sich einstellenden Wassertiefe gerichtet, sowohl oberhalb als auch innerhalb bzw. unterhalb des DRV-Abschnitts. Zunächst wird der Effekt einer Flussaufweitung bei stationärer Strömung theoretisch analysiert. Ausgehend von den Strömungseigenschaften und vom Breitenverhältnis wird eine Bestimmungsgleichung für die effektive Mindestlänge LAeff einer Aufweitung abgeleitet, ab der eine Wasserspiegelabsenkung stromauf hervorgerufen wird. Die darauffolgenden Untersuchungen beschreiben die Auswirkungen einer solchen Maßnahme bei instationärem Abfluss auf zwei ausgewählte synthetische Hochwasserwellen unter jeweils vier verschiedenen Ansätzen zur Erfassung einer Aufweitung. Die Beiträge zur Retention vom Hauptgerinne und von der Querschnittsvergrößerung werden getrennt berücksichtigt. Darüber hinaus werden Überlegungen über das Verhalten von Hochwasserwellen mit gleichem Abflussscheitel aber unterschiedlicher Fülle beim Durchlaufen der Flussaufweitung angestellt. Der Gültigkeitsbereich des stationären Ansatzes für die eindimensionale numerische Simulation einer DRV wird mithilfe eines Kriteriums definiert, das auf einer für die Abminderung des Wassertiefenscheitels im Hauptgerinne semi-empirisch abgeleiteten Formel und auf einer Abschätzung der Retention in der DRV basiert. Die Anwendung des o. g. Kriteriums auf die betrachteten Hochwasserereignisse zeigt, dass eine stationäre Betrachtungsweise lediglich für extrem flache Hochwasserwellen (ab einer Anstiegszeit von einigen Tagen) gerechtfertigt ist. Durch die Ergebnisauswertung von 960 Kombinationen der geometrischen bzw. hydrodynamischen Parameter bei einer DRV im Hochwasserfall konnte der Zusammenhang zwischen den einzelnen Kenngrößen (Länge und Breite der DRV, Rauheit im Hauptgerinne bzw. im Vorland, Hochwasserganglinie) und der Auswirkung der DRV auf Wasserstand und Durchfluss hergestellt werden. Während oberhalb einer DRV mit einer Länge größer LAeff immer mit einer Wasserspiegelabsenkung zu rechnen ist, profitieren die Unterlieger von dieser Schutzmaßnahme nur bei kleineren Hochwasserereignissen oder bei Deichrückverlegungen mit erheblicher Ausdehnung. Dank einer gezielten Auswahl der Ausgangsgeometrie lassen sich die numerischen Ergebnisse auch auf den Elbabschnitt bei Dresden als Anhaltswerte übertragen. / Flood protection is a topic of increasing urgency in today’s society considering two main factors. Firstly, the growth in damage potential on the riparian zones and secondly, the increase in extreme meteorological events due to climate change. Among the possible flood protection measures for a river’s middle reach, dike relocation (DRV) is especially effective from an ecological point of view. To investigate its effectiveness in flood peak attenuation, a parametric study is performed using a one-dimensional hydro-numerical model (MIKE11). Special attention is given to the envelope of the resulting water depths upstream, downstream and within the DRV stretch. Initially, the effects of river enlargement under steady flow conditions are analysed theoretically. Key hydraulic parameters and the width ratio are used in deriving an equation to determine the minimum effective length LAeff of an enlargement that will reduce the upstream water depth. An investigation of an enlargement in unsteady flow conditions is then made, focussing on two specific synthetic flood waves with four different models for the enlargement. The contributions to discharge retention from the main channel and the cross section expansion are successfully separately examinated. Considerations are then made for the behaviour of flood waves passing the river enlargement with the same peak discharge but different volumes. A criterion for the validity range of the steady flow approach of the one-dimensional, numerical simulation of a DRV is then defined. This is based on a semi-empirically derived formula for water level attenuation in the main channel, and an estimate of discharge retention in the DRV. The application of this criterion to the observed flood events shows that the steady flow assumption is only valid for extremely flat flood waves (with time to peak of a few days or more). An analysis of the results from 960 combinations of geometric and hydraulic parameters for the DRV during a flood event is then made. This allowed to derive the relation between individual characteristics (length and width of the DRV, roughness in the main channel and flood plain, flood hydrograph) and the effect of the DRV on water level and discharge. Whilst one can always expect a decrease in the water level upstream of a DRV with length greater than LAeff , the riverside dwellings downstream would only benefit in small scale flood events or with a dike relocation of extensive dimensions. Thanks to the purposefully selected initial geometry, the numerical results can now provide reference values for Dresden’s reach of the river Elbe. / La difesa dalle piene rappresenta per la società odierna una tematica di crescente attualità se si considera in particolare da una parte la crescita del potenziale di danno nelle zone di pertinenza fluviale e dall’altra l’acuirsi di eventi meteorologici estremi dovuto al cambiamento climatico in atto. Tra i possibili interventi di protezione dalle piene nei fiumi di pianura si colloca l’espansione golenale, misura che risulta oltretutto assai efficace dal punto di vista ecologico. Al fine di indagarne anche l’efficacia nei confronti della laminazione del colmo di piena si effettua uno studio parametrico con un programma di modellazione idrodinamica monodimensionale (MIKE11), ponendo particolare attenzione all’inviluppo dei tiranti nel tratto dell’espansione, nonché nei tratti confinanti rispettivamente a monte e a valle della stessa. Dapprima si analizza dal punto di vista teorico l’effetto di un allargamento fluviale in moto stazionario. A partire dalle condizioni idrauliche della corrente e dal rapporto di restringimento si ricava una formula per la lunghezza minima efficace LAeff dell’allargamento, a partire dalla quale si genera un abbassamento del pelo libero nel tratto di monte. Nella successiva analisi di un allargamento in moto vario se ne studia l’effetto su due onde di piena sintetiche e per quattro differenti schematizzazioni dell’allargamento, considerando separatamente i contributi alla laminazione dovuti all’alveo principale e all’allargamento della sezione. Ciò consente tra l’altro di trarre conclusioni sul comportamento di onde di piena aventi la stessa portata al colmo ma differente volume al passare per l’allargamento. Per mezzo di un criterio basato su una formula semiempirica della riduzione del tirante al colmo per l’alveo principale e su una stima della laminazione all’interno dell’espansione golenale, sviluppate nell’ambito di questo lavoro, é possibile definire il campo di validità dell’approccio stazionario alla simulazione monodimensionale di un’espansione golenale. L’applicazione di tale criterio agli eventi di piena presi in considerazione rivela che l’approccio stazionario si giustifica solo per onde di piena estremamente piatte (tempo di crescita a partire da alcuni giorni). Attraverso l’analisi dei risultati di 960 combinazioni dei parametri geometrico-idraulici di un’espansione golenale al passaggio di un’onda di piena si è potuto ricavare il rapporto tra le singole grandezze significative (lunghezza e larghezza dell’espansione golenale, scabrezza dell’alveo e della golena, idrogramma dell’onda di piena) e l’effetto dell’espansione sui tiranti e sulle portate. Se a monte di un’espansione golenale di lunghezza superiore a LAeff si presenta sempre una abbassamento del pelo libero, a valle della stessa si può trarre profitto da un simile intervento solo nel caso di onde di piena modeste o per espansioni golenali di dimensioni notevoli. Una scelta mirata della geometria iniziale consente di estendere i risultati numerici, quali valori indicativi, al tratto del fiume Elba all’altezza di Dresda.

Although the austenitic stainless steels 304 and 321 are often treated nominally as equivalents in their hot rolling characteristics, the question remains whether any subtle differences between the two allow further optimisation of their respective hot rolling schedules. The hot workability of these two types of austenitic stainless steels was compared through single-hit Gleeble simulated thermomechanical processing between 800℃ and 􀀄􀀅00℃ while the strain rate was varied between 0.00􀀄s􀀈􀀉 and 5s􀀈􀀉. It was found that the constants for the hyperbolic sinh equation for hot working of AISI 321 steel are Q = 465 kJ/mol, 􀀖􀀗 = 􀀘.􀀙6 􀀚 􀀄0􀀉􀀛 􀀜􀀝􀀞􀀈􀀉􀀟􀀈􀀉, 􀀠 = 0.00􀀘 􀀜􀀝􀀞􀀈􀀉 and 􀀡 = 6.􀀄 while for 304 steel the constants are Q = 446 kJ/mol, 􀀖􀀗 = 􀀅.􀀄4 􀀚 􀀄0􀀉􀀛 􀀜􀀝􀀞􀀈􀀉􀀟􀀈􀀉, 􀀠 = 0.008 􀀜􀀝􀀞􀀈􀀉and 􀀡 = 6.􀀄. It is shown that the occurrence of dynamic recrystallisation starts when the Zener-Hollomon parameter 􀀢 􀀣 6.4 􀀚 􀀄0􀀉􀀛s􀀈􀀉 for both steels but that the differences in the values of Q and A3 (the structure factor) between the two steels does lead to consistently lower steady state stresses for the steel 321 than is found in the steel 304 at the same Z values. This may, therefore, offer some scope for further optimisation of the hot rolling schedules and in particular in the mill loads of these two respective steels. A modelled constitutive equation derived from hot working tests to predict hot rolling mill loads is proposed and validated against industrial hot rolling data for AISI 321 stainless steel. Good correlation is found between the predicted Mean Flow Stress, the Zener-Hollomon Z parameter and actual industrial mill load values from mill logs if allowances are made for differences in Von Mises plane strain conversion, friction and front or back end tension. The multipass hot working behaviour of this steel was simulated through Gleeble thermomechanical compression testing with the deformation temperature varying between 1200℃ down to 800℃ and the strain rate between 0.001s-1 and 5s-1. At strain rates greater than 0.05s-1, dynamic recovery as a softening mechanism was dominant, increasing the dynamic recrystallisation to dynamic recovery transition temperature DRTT to higher temperatures. This implies that through extrapolation to typical industrial strain rates of about 60s-1,most likely no dynamic recrystallisation in plant hot rolling occurs in this steel but only dynamic recovery. Grain refinement by DRX is, therefore, unlikely in this steel under plant hot rolling conditions. Finally, mill load modelling using the hot working constitutive constants of the near-equivalent 304 instead of those specifically determined for 321, introduces measurable differences in the predicted mill loads. The use of alloy-specific hot working constants even for near-equivalent steels is, therefore, recommended. / Thesis (PhD)--University of Pretoria, 2014. / lk2014 / Materials Science and Metallurgical Engineering / PhD / unrestricted

Der Hochwasserschutz stellt für die gegenwärtige Gesellschaft eine Thematik von zunehmender Aktualität dar, besonders unter Berücksichtigung der Verschärfung der extremen meteorologischen Ereignisse infolge des Klimawandels einerseits und der Vergrößerung des Schadenpotenzials in den Auengebieten andererseits. Zu den möglichen Schutzmaßnahmen im Flussmittellauf zählt die in ökologischer Hinsicht sehr effektive Deichrückverlegung (DRV). Um ihre Wirksamkeit bei der Dämpfung der Hochwasserspitzen zu untersuchen, wird eine Parameterstudie mit einem eindimensionalen hydronumerischen Modell (MIKE11) durchgeführt. Dabei wird besonderes Augenmerk auf die Hüllkurve der sich einstellenden Wassertiefe gerichtet, sowohl oberhalb als auch innerhalb bzw. unterhalb des DRV-Abschnitts. Zunächst wird der Effekt einer Flussaufweitung bei stationärer Strömung theoretisch analysiert. Ausgehend von den Strömungseigenschaften und vom Breitenverhältnis wird eine Bestimmungsgleichung für die effektive Mindestlänge LAeff einer Aufweitung abgeleitet, ab der eine Wasserspiegelabsenkung stromauf hervorgerufen wird. Die darauffolgenden Untersuchungen beschreiben die Auswirkungen einer solchen Maßnahme bei instationärem Abfluss auf zwei ausgewählte synthetische Hochwasserwellen unter jeweils vier verschiedenen Ansätzen zur Erfassung einer Aufweitung. Die Beiträge zur Retention vom Hauptgerinne und von der Querschnittsvergrößerung werden getrennt berücksichtigt. Darüber hinaus werden Überlegungen über das Verhalten von Hochwasserwellen mit gleichem Abflussscheitel aber unterschiedlicher Fülle beim Durchlaufen der Flussaufweitung angestellt. Der Gültigkeitsbereich des stationären Ansatzes für die eindimensionale numerische Simulation einer DRV wird mithilfe eines Kriteriums definiert, das auf einer für die Abminderung des Wassertiefenscheitels im Hauptgerinne semi-empirisch abgeleiteten Formel und auf einer Abschätzung der Retention in der DRV basiert. Die Anwendung des o. g. Kriteriums auf die betrachteten Hochwasserereignisse zeigt, dass eine stationäre Betrachtungsweise lediglich für extrem flache Hochwasserwellen (ab einer Anstiegszeit von einigen Tagen) gerechtfertigt ist. Durch die Ergebnisauswertung von 960 Kombinationen der geometrischen bzw. hydrodynamischen Parameter bei einer DRV im Hochwasserfall konnte der Zusammenhang zwischen den einzelnen Kenngrößen (Länge und Breite der DRV, Rauheit im Hauptgerinne bzw. im Vorland, Hochwasserganglinie) und der Auswirkung der DRV auf Wasserstand und Durchfluss hergestellt werden. Während oberhalb einer DRV mit einer Länge größer LAeff immer mit einer Wasserspiegelabsenkung zu rechnen ist, profitieren die Unterlieger von dieser Schutzmaßnahme nur bei kleineren Hochwasserereignissen oder bei Deichrückverlegungen mit erheblicher Ausdehnung. Dank einer gezielten Auswahl der Ausgangsgeometrie lassen sich die numerischen Ergebnisse auch auf den Elbabschnitt bei Dresden als Anhaltswerte übertragen. / Flood protection is a topic of increasing urgency in today’s society considering two main factors. Firstly, the growth in damage potential on the riparian zones and secondly, the increase in extreme meteorological events due to climate change. Among the possible flood protection measures for a river’s middle reach, dike relocation (DRV) is especially effective from an ecological point of view. To investigate its effectiveness in flood peak attenuation, a parametric study is performed using a one-dimensional hydro-numerical model (MIKE11). Special attention is given to the envelope of the resulting water depths upstream, downstream and within the DRV stretch. Initially, the effects of river enlargement under steady flow conditions are analysed theoretically. Key hydraulic parameters and the width ratio are used in deriving an equation to determine the minimum effective length LAeff of an enlargement that will reduce the upstream water depth. An investigation of an enlargement in unsteady flow conditions is then made, focussing on two specific synthetic flood waves with four different models for the enlargement. The contributions to discharge retention from the main channel and the cross section expansion are successfully separately examinated. Considerations are then made for the behaviour of flood waves passing the river enlargement with the same peak discharge but different volumes. A criterion for the validity range of the steady flow approach of the one-dimensional, numerical simulation of a DRV is then defined. This is based on a semi-empirically derived formula for water level attenuation in the main channel, and an estimate of discharge retention in the DRV. The application of this criterion to the observed flood events shows that the steady flow assumption is only valid for extremely flat flood waves (with time to peak of a few days or more). An analysis of the results from 960 combinations of geometric and hydraulic parameters for the DRV during a flood event is then made. This allowed to derive the relation between individual characteristics (length and width of the DRV, roughness in the main channel and flood plain, flood hydrograph) and the effect of the DRV on water level and discharge. Whilst one can always expect a decrease in the water level upstream of a DRV with length greater than LAeff , the riverside dwellings downstream would only benefit in small scale flood events or with a dike relocation of extensive dimensions. Thanks to the purposefully selected initial geometry, the numerical results can now provide reference values for Dresden’s reach of the river Elbe. / La difesa dalle piene rappresenta per la società odierna una tematica di crescente attualità se si considera in particolare da una parte la crescita del potenziale di danno nelle zone di pertinenza fluviale e dall’altra l’acuirsi di eventi meteorologici estremi dovuto al cambiamento climatico in atto. Tra i possibili interventi di protezione dalle piene nei fiumi di pianura si colloca l’espansione golenale, misura che risulta oltretutto assai efficace dal punto di vista ecologico. Al fine di indagarne anche l’efficacia nei confronti della laminazione del colmo di piena si effettua uno studio parametrico con un programma di modellazione idrodinamica monodimensionale (MIKE11), ponendo particolare attenzione all’inviluppo dei tiranti nel tratto dell’espansione, nonché nei tratti confinanti rispettivamente a monte e a valle della stessa. Dapprima si analizza dal punto di vista teorico l’effetto di un allargamento fluviale in moto stazionario. A partire dalle condizioni idrauliche della corrente e dal rapporto di restringimento si ricava una formula per la lunghezza minima efficace LAeff dell’allargamento, a partire dalla quale si genera un abbassamento del pelo libero nel tratto di monte. Nella successiva analisi di un allargamento in moto vario se ne studia l’effetto su due onde di piena sintetiche e per quattro differenti schematizzazioni dell’allargamento, considerando separatamente i contributi alla laminazione dovuti all’alveo principale e all’allargamento della sezione. Ciò consente tra l’altro di trarre conclusioni sul comportamento di onde di piena aventi la stessa portata al colmo ma differente volume al passare per l’allargamento. Per mezzo di un criterio basato su una formula semiempirica della riduzione del tirante al colmo per l’alveo principale e su una stima della laminazione all’interno dell’espansione golenale, sviluppate nell’ambito di questo lavoro, é possibile definire il campo di validità dell’approccio stazionario alla simulazione monodimensionale di un’espansione golenale. L’applicazione di tale criterio agli eventi di piena presi in considerazione rivela che l’approccio stazionario si giustifica solo per onde di piena estremamente piatte (tempo di crescita a partire da alcuni giorni). Attraverso l’analisi dei risultati di 960 combinazioni dei parametri geometrico-idraulici di un’espansione golenale al passaggio di un’onda di piena si è potuto ricavare il rapporto tra le singole grandezze significative (lunghezza e larghezza dell’espansione golenale, scabrezza dell’alveo e della golena, idrogramma dell’onda di piena) e l’effetto dell’espansione sui tiranti e sulle portate. Se a monte di un’espansione golenale di lunghezza superiore a LAeff si presenta sempre una abbassamento del pelo libero, a valle della stessa si può trarre profitto da un simile intervento solo nel caso di onde di piena modeste o per espansioni golenali di dimensioni notevoli. Una scelta mirata della geometria iniziale consente di estendere i risultati numerici, quali valori indicativi, al tratto del fiume Elba all’altezza di Dresda.

The current study focus on investigating a relationship between processing variables and microstructure evolution mechanism in 304L stainless steel subjected to hot torsion. The Gleeble 3800 with Mobile Torsion Unit (MTU) is utilized in the current study to conduct hot torsion test of 304L stainless steel. Samples are rotated at 1100℃ in the shear strain rate range of 0.02s-1 to 4.70s-1 and the shear strain range of 0.5 to 4. Orientation imaging microscopy (OIM) technique is used to collect and analyze the microstructure. At low strains (≤1) and strain rate (0.02s-1), average grain size remains relatively constant, but the lengths of DSs and LABs increase within grains. These are characteristics of the dynamic recovery (DRV). With increasing strain and strain rate, the lengths of DSs, LABs and HABs increase, accompanied by the decrease of average grain size. Subgrains with HAB segments are observed. These are characteristics of continuous dynamic recrystallization (CDRX). At strain rates greater than or equal to 0.94s-1, the fraction of deformation texture is about 3 times higher than that of rotated cube texture. The average grain size increases relative to that at a strain rate of 0.20s-1, accompanied by the increase of twin length per area. This indicates that grain growth take place after CDRX. Sigma phase is not observed in the current study due to the lack of static recrystallization (SRX) and the higher cooling rate.