Interface characteristics in an {\alpha}+{\beta} titanium alloy

The alpha/beta interface in Ti-6Al-2Sn-4Zr-6Mo (Ti-6246) is investigated via centre of symmetry analysis, both as-grown and after 10% cold work. Semi-coherent interface steps are observed at a spacing of 4.5 +/-1.13 atoms in the as-grown condition, in good agreement with theory prediction (4.37 atoms). Lattice accommodation is observed, with elongation along [-1 2 -1 0]alpha and contraction along [1 0 -1 0]alpha . Deformed alpha exhibited larger, less coherent steps with slip bands lying in {110}beta. This indicates dislocation pile-up at the grain boundary, a precursor to globularisation, offering insight into the effect of deformation processing on the interface, which is important for titanium alloy processing route design.Comment: Revised after revie

Precipitate dissolution during deformation induced twin thickening in a CoNi-base superalloy subject to creep

The tensile creep performance of a polycrystalline Co/Ni-base superalloy with a multimodal γ ′ distribution has been examined at 800 ∘C and 300 MPa. The rupture life of the alloy is comparable to that of RR1000 tested under similar conditions. Microstructural examination of the alloy after testing revealed the presence of continuous γ ′ precipitates and M 23C 6 carbides along the grain boundaries. Intragranularly, coarsening of the secondary γ ′ precipitates occurred at the expense of the fine tertiary γ ′. Long planar deformation bands, free of γ ′, were also observed to traverse individual grains. Examination of the deformation bands confirmed that they were microtwins. Long sections of the microtwins examined were depleted of γ ′ stabilising elements across their entire width, suggesting that certain alloy compositions are susceptible to precipitate dissolution during twin thickening. A mechanism for the dissolution of the precipitates is suggested based on the Kolbe reordering mechanism

Interface characteristics in an α+β titanium alloy

The α/β interface in Ti-6Al-2Sn-4Zr-6Mo (Ti-6246) was investigated via center of symmetry analysis, both as-grown and after 10% cold work. Semicoherent interface steps are observed at a spacing of 4.5±1.13 atoms in the as-grown condition, in good agreement with theory. Lattice accommodation is observed, with elongation along [1210]α and contraction along [1010]α. Deformed α exhibited larger, less coherent steps with slip bands lying in {110}β. This indicates dislocation pile-up at the grain boundary, a precursor to globularization during heat treatment. Atom probe tomography measurements of secondary α plates in the fully heat-treated condition showed a Zr excess at the interface, which was localized into regular structures indicative of Zr association with interface defects, such as dislocations. Such chemo-mechanical stabilization of the interface defects would both inhibit plate growth during elevated temperature service and the interaction of interface defects with gliding dislocations during deformation

The Kinetics of Primary Alpha Plate Growth in Titanium Alloys

The kinetics of primary alpha-Ti colony/Widmanstatten plate growth from the beta are examined, comparing model to experiment. The plate growth velocity depends sensitively both on the diffusivity D(T) of the rate-limiting species and on the supersaturation around the growing plate. These result in a maxima in growth velocity around 40 K below the transus, once sufficient supersaturation is available to drive plate growth. In Ti-6246, the plate growth velocity was found to be around 0.32 um min-1 at 850 oC, which was in good agreement with the model prediction of 0.36 um min-1 . The solute field around the growing plates, and the plate thickness, was found to be quite variable, due to the intergrowth of plates and soft impingement. This solute field was found to extend to up to 30 nm, and the interface concentration in the beta was found to be around 6.4 at.% Mo. It was found that increasing O content will have minimal effect on the plate lengths expected during continuous cooling; in contrast, Mo approximately doubles the plate lengths obtained for every 2 wt.% Mo reduction. Alloys using V as the beta stabiliser instead of Mo are expected to have much faster plate growth kinetics at nominally equivalent V contents. These findings will provide a useful tool for the integrated design of alloys and process routes to achieve tailored microstructures.Comment: Revised version resubmitted to journa

Comparability: manufacturing, characterization and controls, report of a UK Regenerative Medicine Platform Pluripotent Stem Cell Platform Workshop, Trinity Hall, Cambridge, 14–15 September 2015

This paper summarizes the proceedings of a workshop held at Trinity Hall, Cambridge to discuss comparability and includes additional information and references to related information added subsequently to the workshop. Comparability is the need to demonstrate equivalence of product after a process change; a recent publication states that this ‘may be difficult for cell-based medicinal products’. Therefore a well-managed change process is required which needs access to good science and regulatory advice and developers are encouraged to seek help early. The workshop shared current thinking and best practice and allowed the definition of key research questions. The intent of this report is to summarize the key issues and the consensus reached on each of these by the expert delegates

Developing adenoviral hammerhead ribozyme and siRNA delivery systems to study neuronal gene function

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Αναλογιστικά μοντέλα για την εκτίμηση κινδύνων ζημιών

Loss reserving is one of the most critical actuarial procedures in non-life insurance. This procedure projects losses to their ultimate value and estimates the total reserves. The actual amount of the insurers' liability is initially unknown until all claims are finally settled. Inappropriate actuarial methods may lead to misestimation of the total reserve, which has a significant impact on the insurers' solvency. Each reserving method gives a different estimate for the required reserves which means that the appropriate method will be selected according to the judgement of the actuary. In non-life insurance, the insurer should have reserves, for his future obligations concerning with incurred but not reported claims and incurred but not enough reported. In this thesis, we present new methods for estimating the ultimate claims and the total reserves, according to insurance regulations and the market's needs. Using the data in a log-linear way, robust estimators are applied to the chain ladder procedure. We incorporate robust random coefficients regression models and robust cross-section models for the estimation of the total reserves. These models provide a solution to the problem of outlier claims, which have an effect to the pattern of outstanding claims and lead to misreserving. We present an application of the recursive Kalman filter algorithm, in order to estimate the reserves of an insurance company. A robustified version of this Kalman filter algorithm is also provided.Using quantile regression, which offers a more thorough description of the distribution than the classical least squares estimation, we construct methods for loss reserves estimation. In addition, we propose a loss reserving method for a non-life insurance portfolio consisting by several correlated run-off sub-portfolios that can be embedded within the quantile regression model for longitudinal data.Our numerical results indicate that our proposed loss reserving methods provide more reliable results than the existing ones.Η Αποθεματοποίηση ζημιών είναι μία από τις πιο σημαντικές διαδικασίες στις ασφαλίσεις κατά ζημιών. Η διαδικασία αυτή εκτιμά την τελική τιμή των ζημιών καθώς και τα αποθέματα. Το πραγματικό ποσό που ευθύνονται να πληρώσουν οι ασφαλιστικές εταιρίες είναι αρχικά άγνωστο μέχρι να διευθετηθούν οι ζημιές. Μη κατάλληλες αναλογιστικές μέθοδοι αποθεματοποίησης μπορούν να οδηγήσουν σε λανθασμένη εκτίμηση των αποθεμάτων, το οποίο έχει σημαντική επίδραση στη φερεγγυότητα μίας ασφαλιστικής εταιρίας. Κάθε μέθοδος αποθεματοποίησης δίνει διαφορετική εκτίμηση για τα απαιτούμενα αποθέματα, το οποίο σημαίνει ότι η κατάλληλη μέθοδος θα επιλεγεί σύμφωνα με την κρίση του αναλογιστή. Στις ασφαλίσεις κατά ζημιών ο ασφαλιστής θα πρέπει να δημιουργήσει αποθέματα ώστε να μπορεί να καλύψει τις μελλοντικές του υποχρεώσεις που βασίζονται σε ζημιές που έγιναν και δεν έχουν αναφερθεί ή έγιναν και δεν έχουν αποθεματοποιηθεί αρκετά. Σε αυτή τη διατριβή παρουσιάζουμε νέες μεθόδους για την εκτίμηση των τελικών ζημιών και αποθεμάτων που βασίζονται στο νομοθετικό πλαίσιο και στις ανάγκες της αγοράς. Μία κλάση ανθεκτικών εκτιμητών εφαρμόζεται με μορφή λογαριθμογραμμικών μοντέλων. Ενσωματώνουμε ανθεκτική παλινδρόμηση με τυχαίους παράγοντες και cross-section μοντέλα για την εκτίμηση των τελικών αποθεμάτων. Αυτά τα μοντέλα δίνουν λύση στο πρόβλημα των ακραίων ζημιών, οι οποίες επηρεάζουν το μοτίβο πληρωμών και οδηγούν σε λάθος αποθεματοποίηση. Παρουσιάζουμε μία εφαρμογή του Φίλτρου Κάλμαν με αλγορίθμους χώρου καταστάσεων, με σκοπό να εκτιμηθούν τα αποθέματα από μία ασφαλιστική εταιρία. Επίσης, δίνεται ο ανθεκτικός αλγόριθμος του Φίλτρου Κάλμαν. Χρησιμοποιώντας παλινδρόμηση ποσοστημορίων, η οποία παρέχει ολοκληρωμένη εικόνα της κατανομής σε σχέση με την κλασσική παλινδρόμηση, κατασκευάζουμε μεθόδους για την εκτίμηση των αποθεμάτων. Επιπλέον, προτείνουμε μέσω παλινδρόμησης ποσοστημορίων μία μέθοδο αποθεματοποίησης η οποία συνδυάζει διάφορα συσχετισμένα χαρτοφυλάκια, ως διαχρονικά δεδομένα. Τα αριθμητικά αποτελέσματα υποδηλώνουν ότι οι προτεινόμενες μέθοδοι παρέχουν πιο αξιόπιστα αποτελέσματα από τις υπάρχουσες μεθόδους αποθεματοποίησης

Deformation behaviour of beta phase with similar chemical composition in beta and alpha+beta titanium alloys

Twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) in β titanium alloys have been attracting significant interest, since they offer the possibility to provide work hardening and thus, ductility. Here a quaternary Ti-Al-Cr-Mo metastable β alloy has been designed with an excellent combination of strength ductility that exploits the TWIP and TRIP effects. Its engineering yield strength, tensile strength and total elongation are 737 MPa, 999 MPa and 24%, respectively. In order to increase the yield strength but retain ductility, an attempt has been carried to design an α+β alloy with a bimodal microstructure. The composition of the β phase in the α+β alloy was tuned to provide deformation twinning of the β phase. The content of the major α and β stabilising elements, i.e. Al, Cr and Mo, in the β phase of the α+β alloy was similar to the β alloy, but the deformation twinning was not observed in the β phase. It is suggested that this may be due to over-stabilisation of the β phase and/or to the different stress/strain and dislocation distributions in the α+β alloy caused by the presence of β phase

Deformation behaviour of beta phase with similar chemical composition in beta and alpha+beta titanium alloys

Twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) in β titanium alloys have been attracting significant interest, since they offer the possibility to provide work hardening and thus, ductility. Here a quaternary Ti-Al-Cr-Mo metastable β alloy has been designed with an excellent combination of strength ductility that exploits the TWIP and TRIP effects. Its engineering yield strength, tensile strength and total elongation are 737 MPa, 999 MPa and 24%, respectively. In order to increase the yield strength but retain ductility, an attempt has been carried to design an α+β alloy with a bimodal microstructure. The composition of the β phase in the α+β alloy was tuned to provide deformation twinning of the β phase. The content of the major α and β stabilising elements, i.e. Al, Cr and Mo, in the β phase of the α+β alloy was similar to the β alloy, but the deformation twinning was not observed in the β phase. It is suggested that this may be due to over-stabilisation of the β phase and/or to the different stress/strain and dislocation distributions in the α+β alloy caused by the presence of β phase