DSpace Community:
http://hdl.handle.net/2381/445
2016-08-31T04:19:12Z
2016-08-31T04:19:12Z
hp-Version discontinuous Galerkin methods for advection-diffusion-reaction problems on polytopic meshes
Cangiani, Andrea
Dong, Zhaonan
Georgoulis, Emmanuil H.
Houston, Paul
http://hdl.handle.net/2381/38016
2016-08-31T02:18:46Z
2016-08-30T15:11:03Z
Title: hp-Version discontinuous Galerkin methods for advection-diffusion-reaction problems on polytopic meshes
Authors: Cangiani, Andrea; Dong, Zhaonan; Georgoulis, Emmanuil H.; Houston, Paul
Abstract: We consider the hp-version interior penalty discontinuous Galerkin finite element method (DGFEM) for the numerical approximation of the advection-diffusion-reaction equation on general computational meshes consisting of polygonal/polyhedral (polytopic) elements. In particular, new hp-version a priori error bounds are derived based on a specific choice of the interior penalty parameter which allows for edge/face-degeneration. The proposed method employs elemental polynomial bases of total degree p (đ«p-basis) defined in the physical coordinate system, without requiring the mapping from a given reference or canonical frame. Numerical experiments highlighting the performance of the proposed DGFEM are presented. In particular, we study the competitiveness of the p-version DGFEM employing a đ«p-basis on both polytopic and tensor-product elements with a (standard) DGFEM employing a (mapped) đŹp-basis. Moreover, a computational example is also presented which demonstrates the performance of the proposed hp-version DGFEM on general agglomerated meshes.
2016-08-30T15:11:03Z
The convective instability of the BEK system of rotating boundary-layer flows over rough disks
AlveroÄlu, Burhan
http://hdl.handle.net/2381/37977
2016-08-17T02:26:40Z
2016-08-16T11:54:44Z
Title: The convective instability of the BEK system of rotating boundary-layer flows over rough disks
Authors: AlveroÄlu, Burhan
Abstract: A numerical study investigating the effects of surface roughness on the stability properties of the BEK system of flows is introduced. The BEK system of flows occur in many engineering applications such as turbo-machinery and rotor-stator devices, therefore they have great practical importance. Recent studies have been concerned with the effects of surface roughness on the von KĂĄrmĂĄn flow. The aim of this thesis is to investigate whether distributed surface roughness could be used as a passive drag reduction technique for the broader BEK system of flows. If it can, what is âthe right sort of roughness?" To answer these questions, a linear stability analysis is performed using the Chebyshev collocation method to investigate the effect of particular types of distributed surface roughness, both anisotropic and isotropic, on the convective instability characteristics of the inviscid Type I (cross-flow) instability and the viscous Type II instability. The results reveal that all roughness types lead to a stabilisation of the Type I mode in all flows within the BEK family, with the exception of azimuthally-anisotropic roughness (radial grooves) within the BĆdewadt flow which causes a mildly destabilising effect. In the case of the Type II mode, the results reveal the destabilising effect of radially-anisotropic roughness (concentric grooves) on all the boundary layers, whereas both azimuthally-anisotropic and isotropic roughness have a stabilising effect on the mode for Ekman and von KĂĄrmĂĄn flows. Moreover, an energy analysis is performed to investigate the underlying physical mechanisms behind the effects of rough surfaces on the BEK system. The conclusion is that isotropic surface roughness is the most effective type of the distributed surface roughness and can be recommended as a passive-drag reduction mechanism for the entire BEK system of flows.
2016-08-16T11:54:44Z
Mathematical Modelling of Oxygen - Plankton System under the Climate Change
Sekerci Firat, Yadigar
http://hdl.handle.net/2381/37971
2016-08-17T02:26:05Z
2016-08-16T10:51:51Z
Title: Mathematical Modelling of Oxygen - Plankton System under the Climate Change
Authors: Sekerci Firat, Yadigar
Abstract: Oxygen production due to phytoplankton photosynthesis is an important phenomenon keeping in mind the underlying dynamics of marine ecosystems. However, despite its crucial importance, not only for marine but also for terrestrial ecosystems, the coupled oxygen-plankton dynamics have been overlooked.
This dissertation aims to provide insight into an oxygen-plankton system using mathematical modelling. We firstly develop a âbaselineâ oxygen-phytoplankton model which is then further developed through the addition of biologically relevant factors such as plankton respiration and the predator effect of zooplankton. The properties of the model have been studied both in the nonspatial case, which corresponds to a well mixed system with a spatially uniform distribution of species, and in the spatially explicit extension, by taking into account the transport of oxygen and movement of plankton by turbulent diffusion.
Since the purpose of this work is to reveal the oxygen dynamics, the effect of global warming is considered taken into consideration and modelled by various oxygen production rates and phytoplankton growth functions in Chapters 5 and 6. It is shown that sustainable oxygen production is only possible in an intermediate range of the production rate. If the oxygen production rate becomes sufficiently low or high, in the course of time, the systemâs dynamics shows abrupt changes resulting in plankton extinction and oxygen depletion. We show that the spatial systemâs sustainability range is larger that of the corresponding nonspatial system. We show that oxygen production by phytoplankton can stop suddenly if the water temperature exceeds a certain critical threshold. Correspondingly, this dissertation reveals the scenarios of extinction which can potentially lead to an ecological disaster.
2016-08-16T10:51:51Z
The Fundamental Groupoid and the Geometry of Monoids
Pirashvili, Ilia
http://hdl.handle.net/2381/37837
2016-07-14T02:19:15Z
2016-07-13T15:42:29Z
Title: The Fundamental Groupoid and the Geometry of Monoids
Authors: Pirashvili, Ilia
Abstract: This thesis is divided in two equal parts. We start the first part by studying the Kato-spectrum of a commutative monoid M, denoted by KSpec(M). We show that the functor M â KSpec(M) is representable and discuss a few consequences of this fact. In particular, when M is additionally finitely generated, we give an efficient way of calculating it explicitly.
We then move on to study the cohomology theory of monoid schemes in general and apply it to vector- and particularly, line bundles. The isomorphism class of the latter is the Picard group. We show that under some assumptions on our monoid scheme X, if k is an integral domain (resp. PID), then the induced map Pic(X) â Pic(Xk) from X to its realisation is a monomorphism (resp. isomorphism).
We then focus on the Pic functor and show that it respects finite products. Finally, we generalise several important constructions and notions such as cancellative monoids, smoothness and Cartier divisors, and prove important results for them.
The main results of the second part can be summed up in fewer words. We prove that for good topological spaces X the assignment U â IIâ(U) is the terminal object of the 2-category of costacks. Here U is an open subset of X and IIâ(U) denotes the fundamental groupoid of U. This result translates to the Ă©tale fundamental groupoid as well, though the proof there is completely different and involves studying and generalising Galois categories.
2016-07-13T15:42:29Z
Betting Markets: Defining odds restrictions, exploring market inefficiencies and measuring bookmaker solvency
Cortis, Dominic
http://hdl.handle.net/2381/37783
2016-06-18T03:13:56Z
2016-06-17T10:02:32Z
Title: Betting Markets: Defining odds restrictions, exploring market inefficiencies and measuring bookmaker solvency
Authors: Cortis, Dominic
Abstract: Betting markets have been of great interest to researchers as they represent a simpler set-up of financial markets. With an estimated Gross Gambling Revenue of 45bn yearly on betting on outcomes alone (excluding other gambling markets such as Casino, Poker and Lottery), these markets deserve attention on their own merit.
This thesis provides simple mathematical derivation of a number of key statements in setting odds. It estimates the expected bookmaker profit as a function of wagers placed and bookmaker margin. Moreover it shows that odds set by bookmakers should have implied probabilities that add up to at least one. Bookmakers do not require the exact probability of an outcome to have positive expected profits. They can increase profitability by having more accurate odds and offering more multiples/accumulators. Bookmakers can lower variation in payouts by maintaining the ratio of wagers and implied probability per outcome.
While bookmakers face significant regulatory pressures as well as increased taxes and levies, there is no standard industry model that can be applied to evaluate the minimum reserves for a bookmaker. Hence a bookmaker may be under/over-reserving funds required to conduct business. A solvency regime for bookmakers is presented in this work.
Furthermore a model is proposed to forecast soccer results â this focuses on goal differences in contrast to traditional models that predict outcome or goals scored per team.
Significant investigations are made on the inefficiencies of betting markets. The likelihood of Brazil reaching different stages of the 2014 World Cup, as perceived by odds, is compared to events on and outside the pitch to imply bias. An analysis of over 136,000 odds for European soccer matches shows evidence of the longshot bias. Finally this work investigates how it is possible to profit from market inefficiencies on betting exchanges during short tournaments by using a Monte Carlo simulation method as a quasi-arbitrage model.
2016-06-17T10:02:32Z
kNN predictability analysis of stock and share closing prices
Shi, Yanshan
http://hdl.handle.net/2381/37772
2016-06-17T02:17:44Z
2016-06-16T09:25:00Z
Title: kNN predictability analysis of stock and share closing prices
Authors: Shi, Yanshan
Abstract: The k nearest neighbor rule or the kNN rule is a nonparametric algorithm that search for the k nearest neighbors of a query set in another set of points. In this thesis, application of the kNN rule in predictability analysis of stock and share returns is proposed. The first experiment tests the possibility of prediction for âsuccessâ (or âwinnerâ) components of four stock and shares market indices in a selected time period [1]. We have developed a method of labeling the component with either âwinnerâ or âloserâ. We analyze the existence of information on the winnerâloser separation in the initial fragments of the daily closing prices logâreturns time series. The LeaveâOneâOut CrossâValidation with the kNN algorithm is applied on the daily logâreturns of components. Two distance measurements are used in our experiment, a correlation distance, and its proximity. By analyzing the error, for the HANGSENG and the DAX index, there are clear signs of possibility to evaluate the probability of longâterm success. The correlation distance matrix histograms and 2âD/3âD elastic maps generated from the ViDaExpert show that the âwinnerâ components are closer to each other and âwinnerâ/âloserâ components are separable on elastic maps for the HANGSENG and the DAX index while for the negative possibility indices, there is no sign of separation.
In the second experiment, for a selected time interval, daily logâreturn time series is split into âhistoryâ, âpresentâ and âfutureâ parts. The kNN rule is used to search for nearest neighbors of âpresentâ from a set. This set is created by using the sliding window strategy. The nearest neighbors are considered as the predicted âfutureâ part. We then use ideas from dynamical systems and to regenerate âfutureâ part closing prices from nearest neighbors logâreturns. Different subâexperiments are created in terms of the difference in generation of âhistoryâ part, different market indices, and different distance measurements. This approach of modeling or forecasting works for both the ergodic dynamic systems and the random processes.
The Lorenz attractor with noise is used to generate data and the data are used in the kNN experiment with the Euclidean distance. The sliding window strategy is applied in both test and training set. The kNN rule is used to find the k nearest neighbors and the next âwindowâ is used as the prediction. The error analysis of the relative mean squared error RMSE shows that k = 1 can give the best prediction and when k â 100, the average RMSE values converge. The average standard deviation values converge when k â 100. The solution Z(t) is predicted quite accurate using the kNN experiment.
2016-06-16T09:25:00Z
Kriging meta-model assisted calibration of computational fluid dynamics models
Kajero, Olumayowa T.
Thorpe, Rex B.
Chen, Tao
Wang, Bo
Yao, Yuan
http://hdl.handle.net/2381/37745
2016-06-15T02:16:02Z
2016-06-14T11:09:22Z
Title: Kriging meta-model assisted calibration of computational fluid dynamics models
Authors: Kajero, Olumayowa T.; Thorpe, Rex B.; Chen, Tao; Wang, Bo; Yao, Yuan
Abstract: Computational fluid dynamics (CFD) is a simulation technique widely used in chemical and process engineering applications. However, computation has become a bottleneck when calibration of CFD models with experimental data (also known as model parameter estimation) is needed. In this research, the kriging meta-modelling approach (also termed Gaussian process) was coupled with expected improvement (EI) to address this challenge. A new EI measure was developed for the sum of squared errors (SSE) which conforms to a generalised chi-square distribution and hence existing normal distribution-based EI measures are not applicable. The new EI measure is to suggest the CFD model parameter to simulate with, hence minimising SSE and improving match between simulation and experiments. The usefulness of the developed method was demonstrated through a case study of a single-phase flow in both a straight-type and a convergent-divergent-type annular jet pump, where a single model parameter was calibrated with experimental data.
Description: The file associated with this record is under a 12-month embargo from publication in accordance with the publisher's self-archiving policy. The full text may be available through the publisher links provided above.
2016-06-14T11:09:22Z
Delay driven spatiotemporal chaos in single species population dynamics models
Petrovskiy, Sergei
Jankovic, Masha
Banerjee, Malay
http://hdl.handle.net/2381/37594
2016-05-19T02:07:51Z
2016-05-18T12:05:18Z
Title: Delay driven spatiotemporal chaos in single species population dynamics models
Authors: Petrovskiy, Sergei; Jankovic, Masha; Banerjee, Malay
Abstract: Questions surrounding the prevalence of complex population dynamics form one of the central themes in ecology. Limit cycles and spatiotemporal chaos are examples that have been widely recognised theoretically, although their importance and applicability to natural populations remains debatable. The ecological processes underlying such dynamics are thought to be numerous, though there seems to be consent as to delayed density dependence being one of the main driving forces. Indeed, time delay is a common feature of many ecological systems and can significantly influence population dynamics. In general, time delays may arise from inter- and intra-specific trophic interactions or population structure, however in the context of single species populations they are linked to more intrinsic biological phenomena such as gestation or resource regeneration. In this paper, we consider theoretically the spatiotemporal dynamics of a single species population using two different mathematical formulations. Firstly, we revisit the diffusive logistic equation in which the per capita growth is a function of some specified delayed argument. We then modify the model by incorporating a spatial convolution which results in a biologically more viable integro-differential model. Using the combination of analytical and numerical techniques, we investigate the effect of time delay on pattern formation. In particular, we show that for sufficiently large values of time delay the systemâs dynamics are indicative to spatiotemporal chaos. The chaotic dynamics arising in the wake of a travelling population front can be preceded by either a plateau corresponding to dynamical stabilisation of the unstable equilibrium or by periodic oscillations.
2016-05-18T12:05:18Z
How animals move along? Exactly solvable model of superdiffusive spread resulting from animal's decision making
Petrovskiy, Sergei V.
Tilles, Paulo F. C.
http://hdl.handle.net/2381/37591
2016-05-19T02:07:45Z
2016-05-18T11:50:36Z
Title: How animals move along? Exactly solvable model of superdiffusive spread resulting from animal's decision making
Authors: Petrovskiy, Sergei V.; Tilles, Paulo F. C.
Abstract: Patterns of individual animal movement have been a focus of considerable attention recently. Of particular interest is a question how different macroscopic properties of animal dispersal result from the stochastic processes occurring on the microscale of the individual behavior. In this paper, we perform a comprehensive analytical study of a model where the animal changes the movement velocity as a result of its behavioral response to environmental stochasticity. The stochasticity is assumed to manifest itself through certain signals, and the animal modifies its velocity as a response to the signals. We consider two different cases, i.e. where the change in the velocity is or is not correlated to its current value. We show that in both cases the early, transient stage of the animal movement is super-diffusive, i.e. ballistic. The large-time asymptotic behavior appears to be diffusive in the uncorrelated case but super-ballistic in the correlated case. We also calculate analytically the dispersal kernel of the movement and show that, whilst it converge to a normal distribution in the large-time limit, it possesses a fatter tail during the transient stage, i.e. at early and intermediate time. Since the transients are known to be highly relevant in ecology, our findings may indicate that the fat tails and superdiffusive spread that are sometimes observed in the movement data may be a feature of the transitional dynamics rather than an inherent property of the animal movement.
Description: Copyright Â© the authors, 2015. After embargo this version will be an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License (http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
2016-05-18T11:50:36Z
Towards roughness-based drag reduction in cross-flow dominated flows
Garrett, Sephen J.
Cooper, A. J.
Ozkan, M.
Thomas, P. J.
http://hdl.handle.net/2381/37570
2016-05-18T02:08:20Z
2016-05-17T09:01:51Z
Title: Towards roughness-based drag reduction in cross-flow dominated flows
Authors: Garrett, Sephen J.; Cooper, A. J.; Ozkan, M.; Thomas, P. J.
Abstract: Recent theoretical results are presented from our ongoing study investigating the distinct convective instability properties of the boundary-layer flow over rough rotating disks. In this study, radial anisotropic surface roughness (concentric grooves) is modelled using the partial-slip approach of MiklavÄiÄ & Wang (2004) and the surface-geometry approach of Yoon et. Al (2007). An energy analysis reveals that for both instability modes, the main contributors to the energy balance are the energy production by the Reynolds stresses and conventional viscous dissipation. For the Type I mode, energy dissipation increases and the Reynolds-stress energy production decreases with roughness under both models. This suggests a clear stabilising effect of the anisotropic roughness on the Type I mode. For the Type II mode, the Reynolds-stress energy production increases with roughness under both models. However, the energy dissipation of the Type II mode decreases with the roughness under the surface-geometry model and increases under the partial-slip model. This sensitivity to the precise form of the anisotropic roughness suggests that maximising dissipation by an appropriately designed roughness can theoretically lead to an overall beneficial stabilisation of both the Type I and Type II modes. This is a potential route to overall boundary-layer-transition delay and drag reduction in cross-flow dominated flows.
Description: This paper is under embargo as it has been submitted for publication to European Journal of Mechanics - B/Fluids. If accepted the file associated with this record is embargoed until 24 months after the date of publication.
2016-05-17T09:01:51Z
An energy analysis of convective instabilities of the BĂ¶dewadt and Ekman boundary layers over rough surfaces
Alveroglu, B.
Segalini, A.
Garrett, Stephen J.
http://hdl.handle.net/2381/37569
2016-05-18T02:08:13Z
2016-05-17T08:48:49Z
Title: An energy analysis of convective instabilities of the BĂ¶dewadt and Ekman boundary layers over rough surfaces
Authors: Alveroglu, B.; Segalini, A.; Garrett, Stephen J.
Abstract: An energy balance equation for the three-dimensional BĂ¶dewadt and Ekman layers of the so called âBEK family" of rotating boundary-layer flows is derived. A Chebyshev discretisation method is used to solve the equations and investigate the effect of surface roughness on the physical mechanisms of transition. All roughness types lead to a stabilization of the Type I (cross-flow) instability mode for both flows, with the exception of azimuthally-anisotropic roughness (radial grooves) within the BĂ¶dewadt layer which is destabilising. In the case of the viscous Type II instability mode, the results predict a destabilisation effect of radially-anisotropic roughness (concentric grooves) on both flows, whereas both azimuthally-anisotropic roughness and isotropic roughness have a stabilisation effect. The results presented here confirm the results of our prior linear stability analyses.
Description: This paper is under embargo as it has been submitted for publication to European Journal of Mechanics - B/Fluids. If accepted the file associated with this record is embargoed until 24 months after the date of publication.
2016-05-17T08:48:49Z
On a fixed point theorem of GreguĆĄ
Fisher, Brian
Sessa, S.
http://hdl.handle.net/2381/37550
2016-05-14T03:33:26Z
2016-05-13T14:33:57Z
Title: On a fixed point theorem of GreguĆĄ
Authors: Fisher, Brian; Sessa, S.
Abstract: We consider two selfmaps T and I of a closed convex subset C of a Banach space X which are weakly commuting in X, i.e.
âTIxâITxââ€âIxâTxââââforâââanyâââxâââinâââX,
and satisfy the inequality
âTxâTyââ€aâIxâIyâ+(1âa)max{âTxâIxâ,âTyâIyâ}
for all x, y in C, where 0<a<1. It is proved that if I is linear and non-expansive in C and such that IC contains TC, then T and I have a unique common fixed point in C.
2016-05-13T14:33:57Z
On common fixed points of weakly commuting mappings and set-valued mappings
Sessa, S.
Fisher, B.
http://hdl.handle.net/2381/37549
2016-05-14T03:29:59Z
2016-05-13T14:30:09Z
Title: On common fixed points of weakly commuting mappings and set-valued mappings
Authors: Sessa, S.; Fisher, B.
Abstract: Our main theorem establishes the uniqueness of the common fixed point of two set-valued mappings and of two single-valued mappings defined on a complete metric space, under a contractive condition and a weak commutativity concept. This improves a theorem of the second author.
2016-05-13T14:30:09Z
On a fixed point theorem of Pathak
Fisher, Brian
http://hdl.handle.net/2381/37548
2016-05-14T03:30:41Z
2016-05-13T14:25:52Z
Title: On a fixed point theorem of Pathak
Authors: Fisher, Brian
Abstract: It is shown that the continuity of the mapping in Pathak's fixed point theorem for normed spaces is not necessary.
2016-05-13T14:25:52Z
Common fixed point theorems for compatible mappings
TaĆ, K.
Telci, M.
Fisher, Brian
http://hdl.handle.net/2381/37547
2016-05-14T03:35:55Z
2016-05-13T14:22:20Z
Title: Common fixed point theorems for compatible mappings
Authors: TaĆ, K.; Telci, M.; Fisher, Brian
Abstract: By using a compatibility condition due to Jungck we establish some common fixed point theorems for four mappings on complete and compact metric spaces These results also generalize a theorem of Sharma and Sahu.
2016-05-13T14:22:20Z
Coincidence theorems for nonlinear hybrid contractions
Cho, Y. J.
Fisher, B.
Genga, G. S.
http://hdl.handle.net/2381/37546
2016-05-14T03:32:25Z
2016-05-13T14:18:00Z
Title: Coincidence theorems for nonlinear hybrid contractions
Authors: Cho, Y. J.; Fisher, B.; Genga, G. S.
Abstract: In this paper, we give some common fixed point theorems for single-valued mappings and multi-valued mappings satisfying a rational inequality. Our theorems generalize some results of B. Fisher, M. L. Diviccaro et al. and V. Popa.
2016-05-13T14:18:00Z
Related fixed point theorems on two complete and compact metric spaces
Namdeo, R. K.
Tiwari, N. K.
Fisher, B.
TaĆ, K.
http://hdl.handle.net/2381/37544
2016-05-14T03:31:08Z
2016-05-13T14:12:57Z
Title: Related fixed point theorems on two complete and compact metric spaces
Authors: Namdeo, R. K.; Tiwari, N. K.; Fisher, B.; TaĆ, K.
Abstract: A new related fixed point theorem on two complete metric spaces is obtained. A generalization is given for two compact metric spaces.
2016-05-13T14:12:57Z
A note on commutativity of nonassociative rings
Khan, M. S. S.
http://hdl.handle.net/2381/37543
2016-05-14T03:35:09Z
2016-05-13T14:06:58Z
Title: A note on commutativity of nonassociative rings
Authors: Khan, M. S. S.
Abstract: A theorem on commutativity of nonassociate ring is given.
2016-05-13T14:06:58Z
A Generalization of PreĆĄiÄ Type Mappings in Metric-Like Spaces
Shukla, S.
Fisher, Brian
http://hdl.handle.net/2381/37541
2016-05-14T03:34:31Z
2016-05-13T13:19:06Z
Title: A Generalization of PreĆĄiÄ Type Mappings in Metric-Like Spaces
Authors: Shukla, S.; Fisher, Brian
Abstract: We generalize the result of PreĆĄiÄ in metric-like spaces by proving some common fixed point theorems for PreĆĄiÄ type mappings in metric-like spaces. An example is given which shows that the generalization is proper.
2016-05-13T13:19:06Z
Phacoemulsification Surgery in Eyes with Neovascular Age-Related Macular Degeneration
Grixti, A.
Papavasileiou, E.
Cortis, Dominic
Kumar, B. V.
Prasad, S.
http://hdl.handle.net/2381/37538
2016-05-14T03:27:38Z
2016-05-13T11:32:13Z
Title: Phacoemulsification Surgery in Eyes with Neovascular Age-Related Macular Degeneration
Authors: Grixti, A.; Papavasileiou, E.; Cortis, Dominic; Kumar, B. V.; Prasad, S.
Abstract: Purpose. To evaluate the visual outcomes and effect of phacoemulsification surgery on the progression of neovascular age-related macular degeneration (AMD). Methods. Retrospective, noncomparative, and interventional case series. Thirty eyes from 29 subjects with neovascular AMD treated with intravitreal antivascular endothelial growth factor (VEGF) injections who underwent phacoemulsification and had a postsurgery follow-up of 6 months were included. LogMAR best corrected visual acuity (BCVA) was assessed preoperatively; 1 month, 3 months, and 6 months postoperatively; and finally at the last visit. The frequency of anti-VEGF therapy, calculated as the number of intravitreal injections per month, and central macular thickness (CMT) before and after cataract surgery were determined. Results. Median (range) logMAR BCVA was 0.69 (0.16 to 1.32) preoperatively; 0.55 (â0.04 to 1.32) at 1 month, 0.52 (â0.1 to 1.32) at 3 months, and 0.50 (0.0 to 1.32) at 6 months postoperatively; and 0.6 (0.0 to 1.4) at final visit (P=0.0011). There was no difference in the frequency of anti-VEGF injections between the immediate 6 months before and after phacoemulsification, which was equal to 0.1667 injections per month (P=0.6377). Median CMT measured 203âÎŒm preoperatively, which temporarily increased to 238âÎŒm at 1 month after surgery (P=0.0093) and then spontaneously returned to baseline, measuring 212.5âÎŒm at 3 months postoperatively (P=0.3811). Conclusion. Phacoemulsification surgery significantly improved vision in patients with neovascular AMD, with no increased need for anti-VEGF injections to keep the macula dry postoperatively.
2016-05-13T11:32:13Z
Stability modes in vortex structure formation: Canonical examples for rotating components
Gostelow, J. Paul
Garrett, Stephen J.
Rona, Aldo
Adebayo, David S.
http://hdl.handle.net/2381/37476
2016-05-05T02:09:18Z
2016-05-04T14:50:44Z
Title: Stability modes in vortex structure formation: Canonical examples for rotating components
Authors: Gostelow, J. Paul; Garrett, Stephen J.; Rona, Aldo; Adebayo, David S.
Abstract: Three rather different physical cases have been studied. All represent very practical geometries for which the modal behavior of vortex structures is not completely understood. The work on these problems is ongoing with the objective of obtaining physical confirmation, enhanced understanding and predictive capability for the vortex structures encountered in rotating machines.
2016-05-04T14:50:44Z
Cohomology of tiling spaces: beyond primitive substitutions
Rust, Daniel George
http://hdl.handle.net/2381/37469
2016-04-30T02:28:11Z
2016-04-29T13:40:19Z
Title: Cohomology of tiling spaces: beyond primitive substitutions
Authors: Rust, Daniel George
Abstract: This thesis explores the combinatorial and topological properties of tiling spaces
associated to 1-dimensional symbolic systems of aperiodic type and their associated
algebraic invariants. We develop a framework for studying systems which are more
general than primitive substitutions, naturally partitioned into two instances: in the
first instance we allow systems associated to sequences of substitutions of primitive
type from a finite family of substitutions (called mixed substitutions); in the second
instance we concentrate on systems associated to a single substitution, but where
we entirely remove the condition of primitivity.
We generalise the notion of a Barge-Diamond complex, in the one-dimensional case,
to any mixed system of symbolic substitutions. This gives a way of describing
the associated tiling space as an inverse limit of complexes. We give an effective
method for calculating the Cech cohomology of the tiling space via an exact sequence
relating the associated sequence of substitution matrices and certain subcomplexes
appearing in the approximants. As an application, we show that there exists a
system of substitutions on two letters which exhibit an uncountable collection of
minimal tiling spaces with distinct isomorphism classes of Cech cohomology.
In considering non-primitive substitutions, we naturally divide this set of substitutions
into two cases: the minimal substitutions and the non-minimal substitutions.
We provide a detailed method for replacing any non-primitive but minimal substitution
with a topologically conjugate primitive substitution, and a more simple
method for replacing the substitution with a primitive substitution whose tiling
space is orbit equivalent. We show that an Anderson-Putnam complex with a collaring
of some appropriately large radius suffices to provide a model of the tiling
space as an inverse limit with a single map. We apply these methods to effectively
calculate the Cech cohomology of any substitution which does not admit a periodic
point in its subshift. Using its set of closed invariant subspaces, we provide a pair
of invariants which are each strictly finer than the usual Cech cohomology for a
substitution tiling space.
2016-04-29T13:40:19Z
Tiling spaces, codimension one attractors and shape
Clark, Alexander
Hunton, J.
http://hdl.handle.net/2381/37346
2016-04-19T02:15:49Z
2016-04-18T11:58:33Z
Title: Tiling spaces, codimension one attractors and shape
Authors: Clark, Alexander; Hunton, J.
Abstract: We establish a close relationship between, on the one hand, expanding, codimension one attractors of diffeomorphisms on closed manifolds (examples of so-called strange attractors), and, on the other, spaces which arise in the study of aperiodic tilings. We show that every such orientable attractor is homeomorphic to a tiling space of either a substitution or a projection tiling, depending on its dimension. We also demonstrate that such an attractor is shape equivalent to a (d+1)-dimensional torus with a finite number of points removed, or, in the nonorientable case, to a space with a two-to-one covering by such a torus-less-points. This puts considerable constraints on the topology of codimension one attractors, and constraints on which manifolds tiling spaces may be embedded in. In the process we develop a new invariant for aperiodic tilings, which, for 1-dimensional tilings is in many cases finer than the cohomological or K-theoretic invariants studied to date.
2016-04-18T11:58:33Z
From Ambiguity Aversion to a Generalized Expected Utility. Modeling Preferences in a Quantum Probabilistic Framework
Aerts, D.
Sozzo, Sandro
http://hdl.handle.net/2381/37265
2016-04-13T02:22:20Z
2016-04-12T11:41:18Z
Title: From Ambiguity Aversion to a Generalized Expected Utility. Modeling Preferences in a Quantum Probabilistic Framework
Authors: Aerts, D.; Sozzo, Sandro
Abstract: Ambiguity and ambiguity aversion have been widely studied in decision theory and economics both at a theoretical and an experimental level. After Ellsberg's seminal studies challenging subjective expected utility theory (SEUT), several (mainly normative) approaches have been put forward to reproduce ambiguity aversion and Ellsberg-type preferences. However, Machina and other authors have pointed out some fundamental difficulties of these generalizations of SEUT to cope with some variants of Ellsberg's thought experiments, which has recently been experimentally confirmed. Starting from our quantum modeling approach to human cognition, we develop here a general probabilistic framework to model human decisions under uncertainty. We show that our quantum theoretical model faithfully represents different sets of data collected on both the Ellsberg and the Machina paradox situations, and is flexible enough to describe different subjective attitudes with respect to ambiguity. Our approach opens the way toward a quantum-based generalization of expected utility theory (QEUT), where subjective probabilities depend on the state of the conceptual entity at play and its interaction with the decision-maker, while preferences between acts are determined by the maximization of this 'state-dependent expected utility'.
Description: The file associated with this record is under a 24-month embargo from publication in accordance with the publisher's self-archiving policy. The full text may be available through the publisher links provided above.
2016-04-12T11:41:18Z
A classification of the point spectrum of constant length substitution tiling spaces and general fixed point theorems for tilings
Abuzaid, Dina Asaad
http://hdl.handle.net/2381/37027
2016-03-12T04:27:12Z
2016-03-11T16:11:58Z
Title: A classification of the point spectrum of constant length substitution tiling spaces and general fixed point theorems for tilings
Authors: Abuzaid, Dina Asaad
Abstract: We examine the point spectrum of the various tiling spaces that result from
different choices of tile lengths for substitution of constant length on a two or a three letter
alphabet. In some cases we establish insensitivity to changes in length. In a wide range
of cases, we establish that the typical choice of length leads to trivial point spectrum.
We also consider a problem related to tilings of the integers and their connection to fixed
point theorems. Using this connection, we prove a generalization of the Banach Contraction
Principle.
2016-03-11T16:11:58Z
The centrifugal instability of the boundary-layer flow over a slender rotating cone in an enforced axial free stream
Hussain, Z.
Garrett, Stephen J.
Stephen, S. O.
Griffiths, Paul Travis
http://hdl.handle.net/2381/36986
2016-06-22T01:45:07Z
2016-03-07T11:36:56Z
Title: The centrifugal instability of the boundary-layer flow over a slender rotating cone in an enforced axial free stream
Authors: Hussain, Z.; Garrett, Stephen J.; Stephen, S. O.; Griffiths, Paul Travis
Abstract: In this study, a new centrifugal instability mode, which dominates within the boundary-layer flow over a slender rotating cone in still fluid, is used for the first time to model the problem within an enforced oncoming axial flow. The resulting problem necessitates an updated similarity solution to represent the basic flow more accurately than previous studies in the literature. The new mean flow field is subsequently perturbed, leading to disturbance equations that are solved via numerical and short-wavelength asymptotic approaches, yielding favourable comparisons with existing experiments. Essentially, the boundary-layer flow undergoes competition between the streamwise flow component, due to the oncoming flow, and the rotational flow component, due to effect of the spinning cone surface, which can be described mathematically in terms of a control parameter, namely the ratio of streamwise to axial flow. For a slender cone rotating in a sufficiently strong axial flow, the instability mode breaks down into GĂ¶rtler-type counter-rotating spiral vortices, governed by an underlying centrifugal mechanism, which is consistent with experimental and theoretical studies for a slender rotating cone in otherwise still fluid.
Description: The file associated with this record is under a 6-month embargo from publication in accordance with the publisher's self-archiving policy. The full text may be available through the publisher links provided above.
2016-03-07T11:36:56Z
The neutral curve for stationary disturbances in rotating disk flow for power-law fluids
Griffiths, P. T.
Garrett, Stephen John
Stephen, S. O.
http://hdl.handle.net/2381/36985
2016-03-08T03:19:26Z
2016-03-07T11:32:29Z
Title: The neutral curve for stationary disturbances in rotating disk flow for power-law fluids
Authors: Griffiths, P. T.; Garrett, Stephen John; Stephen, S. O.
Abstract: This paper is concerned with the convective instabilities associated with the boundary-layer flow due to a rotating disk. Shear-thinning fluids that adhere to the power-law relationship are considered. The neutral curves are computed using a sixth-order system of linear stability equations which include the effects of streamline curvature, Coriolis force and the non-Newtonian viscosity model. Akin to previous Newtonian studies it is found that the neutral curves have two critical values, these are associated with the type I upper-branch (cross-flow) and type II lower-branch (streamline curvature) modes. Our results indicate that an increase in shear-thinning has a stabilising effect on both the type I and II modes, in terms of the critical Reynolds number and growth rate. Favourable agreement is obtained between existing asymptotic predictions and the numerical results presented here.
Description: The file associated with this record is under a 24-month embargo from publication in accordance with the publisher's self-archiving policy. The full text may be available through the publisher links provided above.
2016-03-07T11:32:29Z
Stability of the boundary layer on a rotating disk for power-law fluids
Griffiths, P. T.
Stephen, S. O.
Bassom, A. P.
Garrett, Stephen John
http://hdl.handle.net/2381/36963
2016-03-04T03:22:45Z
2016-03-03T11:51:44Z
Title: Stability of the boundary layer on a rotating disk for power-law fluids
Authors: Griffiths, P. T.; Stephen, S. O.; Bassom, A. P.; Garrett, Stephen John
Abstract: The stability of the flow due to a rotating disk is considered for non-Newtonian fluids, specifically shear-thinning fluids that satisfy the power-law (Ostwald-de Waele) relationship. In this case the basic flow is not an exact solution of the NavierâStokes equations, however, in the limit of large Reynolds number the flow inside the three-dimensional boundary layer can be determined via a similarity solution. An asymptotic analysis is presented in the limit of large Reynolds number. It is shown that the stationary spiral instabilities observed experimentally in the Newtonian case can be described for shear-thinning fluids by a linear stability analysis. Predictions for the wavenumber and wave angle of the disturbances suggest that shear-thinning fluids may have a stabilising effect on the flow.
2016-03-03T11:51:44Z
Global linear stability of the boundary-layer flow over a rotating sphere
Barrow, A.
Garrett, Stephen J.
Peake, N.
http://hdl.handle.net/2381/36889
2016-02-26T03:26:22Z
2016-02-25T13:44:07Z
Title: Global linear stability of the boundary-layer flow over a rotating sphere
Authors: Barrow, A.; Garrett, Stephen J.; Peake, N.
Abstract: We consider the linear global stability of the boundary-layer flow over a rotating sphere. Our results suggest that a self-excited linear global mode can exist when the sphere rotates sufficiently fast, with properties fixed by the flow at latitudes between approximately 55Â°â65Â° from the pole (depending on the rotation rate). A neutral curve for global linear instabilities is presented with critical Reynolds number consistent with existing experimentally measured values for the appearance of turbulence. The existence of an unstable linear global mode is in contrast to the literature on the rotating disk, where it is expected that nonlinearity is required to prompt the transition to turbulence. Despite both being susceptible to local absolute instabilities, we conclude that the transition mechanism for the rotating-sphere flow may be different to that for the rotating disk.
2016-02-25T13:44:07Z
The centrifugal instability of the boundary-layer flow over a slender rotating cone in an enforced axial free-stream
Hussain, Z.
Garrett, Stephen J.
Stephen, S. O.
Griffiths, Paul T.
http://hdl.handle.net/2381/36888
2016-06-26T01:45:07Z
2016-02-25T13:41:12Z
Title: The centrifugal instability of the boundary-layer flow over a slender rotating cone in an enforced axial free-stream
Authors: Hussain, Z.; Garrett, Stephen J.; Stephen, S. O.; Griffiths, Paul T.
Abstract: In this study, a new centrifugal instability mode, which dominates within the boundary-layer flow over a slender rotating cone in still fluid, is used for the first time to model the problem within an enforced oncoming axial flow. The resulting problem necessitates an updated similarity solution to represent the basic flow more accurately than previous studies in the literature. The new mean flow field is subsequently perturbed, leading to disturbance equations that are solved via numerical and short-wavelength asymptotic approaches, yielding favourable comparisons with existing experiments. Essentially, the boundary-layer flow undergoes competition between the streamwise flow component, due to the oncoming flow, and the rotational flow component, due to effect of the spinning cone surface, which can be described mathematically in terms of a control parameter, namely the ratio of streamwise to axial flow. For a slender cone rotating in a sufficiently strong axial flow, the instability mode breaks down into GĂ¶rtler-type counter-rotating spiral vortices, governed by an underlying centrifugal mechanism, which is consistent with experimental and theoretical studies for a slender rotating cone in otherwise still fluid.
Description: The file associated with this record is under a 6-month embargo from publication in accordance with the publisher's self-archiving policy. The full text may be available through the publisher links provided above.
2016-02-25T13:41:12Z
The effect of surface roughness on the convective instability of the BEK family of boundary-layer flows
Alveroglu, Burhan
Segalini, A.
Garrett, Stephen J.
http://hdl.handle.net/2381/36887
2016-02-26T03:26:38Z
2016-02-25T13:34:13Z
Title: The effect of surface roughness on the convective instability of the BEK family of boundary-layer flows
Authors: Alveroglu, Burhan; Segalini, A.; Garrett, Stephen J.
Abstract: A Chebyshev polynomial discretisation method is used to investigate the effect of both anisotropic (radially and azimuthally) and isotropic surface roughnesses on the convective instability of the BEK family of rotating boundary-layer flows. The mean-flow profiles for the velocity components are obtained by modelling surface roughness with a partial-slip approach. A linear stability analysis is then performed to investigate the effect of roughness on the convective instability characteristics of the inviscid Type I (cross-flow) instability and the viscous Type II instability. It is revealed that all roughness types lead to a stabilisation of the Type I mode in all flows within the BEK family, with the exception of azimuthally-anisotropic roughness (radial grooves) within the BĂ¶dewadt layer which causes a mildly destabilising effect. In the case of the Type II mode, the results reveal the destabilising effect of radially-anisotropic roughness (concentric grooves) on all the boundary layers, whereas both azimuthally-anisotropic and isotropic roughnesses have a stabilising effect on the mode for Ekman and von KĂĄrmĂĄn layers. Complementary results are also presented by considering the effects of roughness on the growth rates of each instability mode within the Ekman layer.
Description: The file associated with this record is under a 24-month embargo from publication in accordance with the publisher's self-archiving policy. The full text may be available through the publisher links provided above.
2016-02-25T13:34:13Z
The effect of anisotropic and isotropic roughness on the convective stability of the rotating disk boundary layer
Cooper, A. J.
Harris, J. H.
Garrett, Stephen John
Oezkan, M.
Thomas, P. J.
http://hdl.handle.net/2381/36886
2016-02-26T03:26:38Z
2016-02-25T13:28:22Z
Title: The effect of anisotropic and isotropic roughness on the convective stability of the rotating disk boundary layer
Authors: Cooper, A. J.; Harris, J. H.; Garrett, Stephen John; Oezkan, M.; Thomas, P. J.
Abstract: A theoretical study investigating the effects of both anisotropic and isotropic surface roughness on the convective stability of the boundary-layer flow over a rotating disk is described. Surface roughness is modelled using a partial-slip approach, which yields steady-flow profiles for the relevant velocity components of the boundary-layer flow which are a departure from the classic von KĂĄrmĂĄn solution for a smooth disk. These are then subjected to a linear stability analysis to reveal how roughness affects the stability characteristics of the inviscid Type I (or cross-flow) instability and the viscous Type II instability that arise in the rotating disk boundary layer. Stationary modes are studied and both anisotropic (concentric grooves and radial grooves) and isotropic (general) roughness are shown to have a stabilizing effect on the Type I instability. For the viscous Type II instability, it was found that a disk with concentric grooves has a strongly destabilizing effect, whereas a disk with radial grooves or general isotropic roughness has a stabilizing effect on this mode. In order to extract possible underlying physical mechanisms behind the effects of roughness, and in order to reconfirm the results of the linear stability analysis, an integral energy equation for three-dimensional disturbances to the undisturbed three-dimensional boundary-layer flow is used. For anisotropic roughness, the stabilizing effect on the Type I mode is brought about by reductions in energy production in the boundary layer, whilst the destabilizing effect of concentric grooves on the Type II mode results from a reduction in energy dissipation. For isotropic roughness, both modes are stabilized by combinations of reduced energy production and increased dissipation.
2016-02-25T13:28:22Z
On the stability of von KĂĄrmĂĄn rotating-disk boundary layers with radial anisotropic surface roughness
Garrett, Stephen J.
Cooper, A. J.
Harris, J. H.
Ozkan, M.
Segalini, A.
Thomas, P. J.
http://hdl.handle.net/2381/36885
2016-03-02T03:26:01Z
2016-02-25T13:21:15Z
Title: On the stability of von KĂĄrmĂĄn rotating-disk boundary layers with radial anisotropic surface roughness
Authors: Garrett, Stephen J.; Cooper, A. J.; Harris, J. H.; Ozkan, M.; Segalini, A.; Thomas, P. J.
Abstract: We summarise results of a theoretical study investigating the distinct convective instability properties of steady boundary-layer flow over rough rotating disks. A generic roughness pattern of concentric circles with sinusoidal surface undulations in the radial direction is considered. The goal is to compare predictions obtained by means of two alternative, and fundamentally different, modelling approaches for surface roughness for the first time. The motivating rationale is to identify commonalities and isolate results that might potentially represent artefacts associated with the particular methodologies underlying one of the two modelling approaches. The most significant result of practical relevance obtained is that both approaches predict overall stabilising effects on type I instability mode of rotating disk flow. This mode leads to transition of the rotating-disk boundary layer and, more generally, the transition of boundary-layers with a cross-flow profile. Stabilisation of the type 1 mode means that it may be possible to exploit surface roughness for laminar-flow control in boundary layers with a cross-flow component. However, we also find differences between the two sets of model predictions, some subtle and some substantial. These will represent criteria for establishing which of the two alternative approaches is more suitable to correctly describe experimental data when these become available.
2016-02-25T13:21:15Z
Global linear stability of the boundary-layer flow over a rotating sphere
Barrow, A.
Garrett, Stephen John
Peake, N.
http://hdl.handle.net/2381/36884
2016-02-26T03:28:14Z
2016-02-25T13:07:28Z
Title: Global linear stability of the boundary-layer flow over a rotating sphere
Authors: Barrow, A.; Garrett, Stephen John; Peake, N.
Abstract: We consider the linear global stability of the boundary-layer flow over a rotating sphere. Our results suggest that a self-excited linear global mode can exist when the sphere rotates sufficiently fast, with properties fixed by the flow at latitudes between approximately 55Â°-65Â° from the pole (depending on the rotation rate). A neutral curve for global linear instabilities is presented with critical Reynolds number consistent with existing experimentally measured values for the appearance of turbulence. The existence of an unstable linear global mode is in contrast to the literature on the rotating disk, where it is expected that nonlinearity is required to prompt the transition to turbulence. Despite both being susceptible to local absolute instabilities, we conclude that the transition mechanism for the rotating-sphere flow may be different to that for the rotating disk.
2016-02-25T13:07:28Z
On Streamwise Vortices in Large Eddy Simulations of Initially Laminar Plane Mixing Layers
McMullan, William Andrew
Garrett, Stephen J.
http://hdl.handle.net/2381/36790
2016-02-19T03:24:45Z
2016-02-18T12:27:41Z
Title: On Streamwise Vortices in Large Eddy Simulations of Initially Laminar Plane Mixing Layers
Authors: McMullan, William Andrew; Garrett, Stephen J.
Abstract: x
Description: The file associated with this record is under a 24-month embargo from publication in accordance with the publisher's self-archiving policy. The full text may be available through the publisher links provided above.
2016-02-18T12:27:41Z
Multiscale principal component analysis
Akinduko, Ayodeji Akinwumi
http://hdl.handle.net/2381/36616
2016-02-10T03:35:14Z
2016-02-09T10:10:00Z
Title: Multiscale principal component analysis
Authors: Akinduko, Ayodeji Akinwumi
Abstract: The problem of approximating multidimensional data with objects of lower dimension is a classical problem in complexity reduction. It is important that data approximation capture the structure(s) and dynamics of the data, however distortion to data by many methods during approximation implies that some geometric structure(s) of the data may not be preserved during data approximation. For methods that model the manifold of the data, the quality of approximation depends crucially on the initialization of the method. The first part of this thesis investigates the effect of initialization on manifold modelling methods. Using Self Organising Maps (SOM) as a case study, we compared the quality of learning of manifold methods for two popular initialization methods; random initialization and principal component initialization. To further understand the dynamics of manifold learning, datasets were further classified into linear, quasilinear and nonlinear.
The second part of this thesis focuses on revealing geometric structure(s) in high dimension data using an extension of Principal Component Analysis (PCA). Feature extraction using (PCA) favours direction with large variance which could obfuscate other interesting geometric structure(s) that could be present in the data. To reveal these intrinsic structures, we analysed the local PCA structures of the dataset. An equivalent definition of PCA is that it seeks subspaces that maximize the sum of pairwise distances of data projection; extending this definition we define localization in term of scale as maximizing the sum of weighted squared pairwise distances between data projections for various distributions of weights (scales). Since for complex data various regions of the dataspace could have different PCA structures, we also define localization with regards to dataspace. The resulting local PCA structures were represented by the projection matrix corresponding to the subspaces and analysed to reveal some structures in the data at various localizations.
2016-02-09T10:10:00Z
Out-of-band and adjacent-channel interference reduction by analog nonlinear filters
Nikitin, A. V.
Davidchack, Ruslan L.
Smith, J. E.
http://hdl.handle.net/2381/36471
2016-02-02T03:14:45Z
2016-02-01T09:58:41Z
Title: Out-of-band and adjacent-channel interference reduction by analog nonlinear filters
Authors: Nikitin, A. V.; Davidchack, Ruslan L.; Smith, J. E.
Abstract: In a perfect world, we would have âbrick wallâ filters, no-distortion amplifiers and mixers, and well-coordinated spectrum operations. The real world, however, is prone to various types of unintentional and intentional interference of technogenic (man-made) origin that can disrupt critical communication systems. In this paper, we introduce a methodology for mitigating technogenic interference in communication channels by analog nonlinear filters, with an emphasis on the mitigation of out-of-band and adjacent-channel interference.
Interference induced in a communications receiver by external transmitters can be viewed as wide-band non-Gaussian noise affecting a narrower-band signal of interest. This noise may contain a strong component within the receiver passband, which may dominate over the thermal noise. While the total wide-band interference seen by the receiver may or may not be impulsive, we demonstrate that the interfering component due to power emitted by the transmitter into the receiver channel is likely to appear impulsive under a wide range of conditions. We give an example of mechanisms of impulsive interference in digital communication systems resulting from the nonsmooth nature of any physically realizable modulation scheme for transmission of a digital (discontinuous) message.
We show that impulsive interference can be effectively mitigated by nonlinear differential limiters (NDLs). An NDL can be configured to behave linearly when the input signal does not contain outliers. When outliers are encountered, the nonlinear response of the NDL limits the magnitude of the respective outliers in the output signal. The signal quality is improved in excess of that achievable by the respective linear filter, increasing the capacity of a communications channel. The behavior of an NDL, and its degree of nonlinearity, is controlled by a single parameter in a manner that enables significantly better overall suppression of the noise-containing impulsive components compared to the respective linear filter. Adaptive configurations of NDLs are similarly controlled by a single parameter and are suitable for improving quality of nonstationary signals under time-varying noise conditions. NDLs are designed to be fully compatible with existing linear devices and systems and to be used as an enhancement, or as a low-cost alternative, to the state-of-art interference mitigation methods.
2016-02-01T09:58:41Z
Asymptotic variance of stationary reversible and normal Markov processes
Deligiannidis, G.
Peligrad, M.
Utev, Sergey
http://hdl.handle.net/2381/36413
2016-01-28T03:09:24Z
2016-01-27T10:37:50Z
Title: Asymptotic variance of stationary reversible and normal Markov processes
Authors: Deligiannidis, G.; Peligrad, M.; Utev, Sergey
Abstract: We obtain necessary and sufficient conditions for the regular variation of the variance of partial sums of functionals of discrete and continuous-time stationary Markov processes with normal transition operators. We also construct a class of Metropolis-Hastings algorithms which satisfy a central limit theorem and invariance principle when the variance is not linear in n.
2016-01-27T10:37:50Z
The HELP inequality for Hamiltonian systems
Brown, B. M.
Evans, W. D.
Marletta, M.
http://hdl.handle.net/2381/36295
2016-01-16T03:15:05Z
2016-01-15T15:52:52Z
Title: The HELP inequality for Hamiltonian systems
Authors: Brown, B. M.; Evans, W. D.; Marletta, M.
Abstract: We extend the HardyâEverittâLittlewoodâPolya inequality, hitherto established for 2nth order formally selfadjoint ordinary differential equations, to a wide class of linear Hamiltonian systems. The method follows Dias (Ph.D. thesis, Cardiff: University of Wales, 1994) but without the Hilbert space setting which he uses.
2016-01-15T15:52:52Z
Regularized semiclassical limits: linear flows with infinite Lyapunov exponents
Athanassoulis, Agisilaos
Kyza, I.
Katsaounis, T.
http://hdl.handle.net/2381/36266
2016-01-13T03:10:37Z
2016-01-12T12:48:18Z
Title: Regularized semiclassical limits: linear flows with infinite Lyapunov exponents
Authors: Athanassoulis, Agisilaos; Kyza, I.; Katsaounis, T.
Abstract: Semiclassical asymptotics for Schrodinger equations with non-smooth potentials give rise to ill-posed formal semiclassical limits. These problems have attracted a lot of attention in the last few years, as a proxy for the treatment of eigenvalue crossings, i.e. general systems. It has recently been shown that the semiclassical limit for conical singularities is in fact well-posed, as long as the Wigner measure (WM) stays away from singular saddle points. In this work we develop a family of refined semiclassical estimates, and use them to derive regularized transport equations for saddle points with infinite Lyapunov exponents, extending the aforementioned recent results. In the process we answer a related question posed by P. L. Lions and T. Paul in 1993. If we consider more singular potentials, our rigorous estimates break down. To investigate whether conical saddle points, such as -|x|, admit a regularized transport asymptotic approximation, we employ a numerical solver based on posterior error controal. Thus rigorous uppen bounds for the asymptotic error on concrete problems are generated. In particular, specific phenomena which render invalid any regularized transport for -|x| are identified and quantified. In that sense our rigorous results are sharp. Finally, we use our findings to formulate a precise conjecture for the condition under which conical saddle points admit a regularized transport solution for the WM.
Description: The file associated with this record is under a permanent embargo while publication is In Press in accordance with the publisher's self-archiving policy. The full text may be available through the publisher links provided above.
2016-01-12T12:48:18Z
On the XFEL SchrĂ¶dinger Equation: Highly Oscillatory Magnetic Potentials and Time Averaging
Athanassoulis, Agisilaos
Antonelli, P.
Markowich, P. A.
Hajaiej, H.
http://hdl.handle.net/2381/36247
2016-01-12T03:09:29Z
2016-01-11T11:41:27Z
Title: On the XFEL SchrĂ¶dinger Equation: Highly Oscillatory Magnetic Potentials and Time Averaging
Authors: Athanassoulis, Agisilaos; Antonelli, P.; Markowich, P. A.; Hajaiej, H.
Abstract: We analyse a nonlinear SchrĂ¶dinger equation for the time-evolution of the wave function of an electron beam, interacting selfconsistently through a HartreeâFock nonlinearity and through the repulsive Coulomb interaction of an atomic nucleus. The electrons are supposed to move under the action of a time dependent, rapidly periodically oscillating electromagnetic potential. This can be considered a simplified effective single particle model for an X-ray free electron laser. We prove the existence and uniqueness for the Cauchy problem and the convergence of wave-functions to corresponding solutions of a SchrĂ¶dinger equation with a time-averaged Coulomb potential in the high frequency limit for the oscillations of the electromagnetic potential.
2016-01-11T11:41:27Z
Numerical Simulations of X-Ray Free Electron Lasers (XFEL)
Athanassoulis, Agisilaos
Markowich, P. A.
Antonelli, P.
Huang, Z.
http://hdl.handle.net/2381/36243
2016-01-12T03:09:53Z
2016-01-11T10:48:23Z
Title: Numerical Simulations of X-Ray Free Electron Lasers (XFEL)
Authors: Athanassoulis, Agisilaos; Markowich, P. A.; Antonelli, P.; Huang, Z.
Abstract: We study a nonlinear SchrĂ¶dinger equation which arises as an effective single particle model in X-ray free electron lasers (XFEL). This equation appears as a first principles model for the beam-matter interactions that would take place in an XFEL molecular imaging experiment in [A. Fratalocchi and G. Ruocco, Phys. Rev. Lett., 106 (2011), 105504]. Since XFEL are more powerful by several orders of magnitude than more conventional lasers, the systematic investigation of many of the standard assumptions and approximations has attracted increased attention. In this model the electrons move under a rapidly oscillating electromagnetic field, and the convergence of the problem to an effective time-averaged one is examined. We use an operator splitting pseudospectral method to investigate numerically the behavior of the model versus that of its time-averaged version in complex situations, namely the energy subcritical/mass supercritical case and in the presence of a periodic lattice. We find the time-averaged model to be an effective approximation, even close to blowup, for fast enough oscillations of the external field. This work extends previous analytical results for simpler cases [P. Antonelli, A. Athanassoulis, H. Hajaiej, and P. Markowich, Arch. Ration. Mech. Anal., 211 (2014), pp. 711--732].
2016-01-11T10:48:23Z
Synergy effect of cooperative investment
Grechuk, Bogdan
Zabarankin, M.
http://hdl.handle.net/2381/36189
2016-01-07T03:09:07Z
2016-01-06T12:56:39Z
Title: Synergy effect of cooperative investment
Authors: Grechuk, Bogdan; Zabarankin, M.
Abstract: Cooperative investment consists of two problems: finding an optimal cooperative investment strategy and fairly dividing investment outcome among participating agents. In general, the two problems cannot be solved separately. It is known that when agentsâ preferences are represented by mean-deviation functionals, sharing of optimal portfolio creates instruments that, on the one hand, satisfy individual risk preferences but, on the other hand, are not replicable on an incomplete market, so that each agent is strictly better off in participating in cooperative investment than investing alone. This synergy effect is shown to hold when agentsâ acceptance sets are represented by cash-invariant utility functions in the case of multiperiod investment with an arbitrary feasible investment set. In this case, a set of all Pareto-optimal allocations is characterized, and an equilibrium-based method for selecting a âfairâ Pareto-optimal allocation is suggested. It is also shown that if exists, the âfairâ allocation belongs to the core of the corresponding cooperative game. The equilibrium-based method is then extended to the case of arbitrary utility functions. The obtained results are demonstrated in a multiperiod cooperative investment problem with investors imposing drawdown constraints on investment strategies.
Description: The file associated with this record is under a 12-month embargo from publication in accordance with the publisher's self-archiving policy, available at http://www.springer.com/gp/open-access/authors-rights/self-archiving-policy/2124. The full text may be available through the publisher links provided above.
2016-01-06T12:56:39Z
Related fixed points for set-valued mappings on two uniform spaces
TĂŒrkoÄlu, D.
Fisher, Brian
http://hdl.handle.net/2381/36151
2016-01-06T03:09:34Z
2016-01-05T10:28:25Z
Title: Related fixed points for set-valued mappings on two uniform spaces
Authors: TĂŒrkoÄlu, D.; Fisher, Brian
Abstract: Some related fixed point theorems for set-valued mappings on two complete and compact uniform spaces are proved.
Description: 2000 Mathematics Subject Classification: 54H25, 47H10.
2016-01-05T10:28:25Z
On the Fresnel integrals and the convolution
KiliĂ§man, A.
Fisher, Brian
http://hdl.handle.net/2381/36144
2016-01-05T03:12:31Z
2016-01-04T15:10:01Z
Title: On the Fresnel integrals and the convolution
Authors: KiliĂ§man, A.; Fisher, Brian
Abstract: The Fresnel cosine integral C(x), the Fresnel sine integral S(x), and the associated functions C+(x), Câ(x), S+(x), and Sâ(x) are defined as locally summable functions on the real line. Some convolutions and neutrix convolutions of the Fresnel cosine integral and its associated functions with x+r and xr are evaluated.
Description: 2000 Mathematics Subject Classification: 33B10, 46F10
2016-01-04T15:10:01Z
On the sine integral and the convolution
Fisher, Brian
Al-Sirehy, F.
http://hdl.handle.net/2381/36143
2016-01-05T03:12:29Z
2016-01-04T14:57:48Z
Title: On the sine integral and the convolution
Authors: Fisher, Brian; Al-Sirehy, F.
Abstract: The sine integral Si(Î»x) and the cosine integral Ci(Î»x) and their associated functions Si+(Î»x), Siâ(Î»x), Ci+(Î»x), Ciâ(Î»x) are defined as locally summable functions on the real line. Some convolutions of these functions and sin(ÎŒx), sin+(ÎŒx), and sinâ(ÎŒx) are found.
Description: 2000 Mathematics Subject Classification: 33B10, 46F10.
2016-01-04T14:57:48Z
Inverse portfolio problem with coherent risk measures
Grechuk, Bogdan
Zabarankin, M.
http://hdl.handle.net/2381/36136
2015-12-24T03:08:14Z
2015-12-23T13:36:29Z
Title: Inverse portfolio problem with coherent risk measures
Authors: Grechuk, Bogdan; Zabarankin, M.
Abstract: In general, a portfolio problem minimizes risk (or negative utility) of a portfolio of financial assets with respect to portfolio weights subject to a budget constraint. The inverse portfolio problem then arises when an investor assumes that his/her risk preferences have a numerical representation in the form of a certain class of functionals, e.g. in the form of expected utility, coherent risk measure or mean-deviation functional, and aims to identify such a functional, whose minimization results in a portfolio, e.g. a market index, that he/she is most satisfied with. In this work, the portfolio risk is determined by a coherent risk measure, and the rate of return of investorâs preferred portfolio is assumed to be known. The inverse portfolio problem then recovers investorâs coherent risk measure either through finding a convex set of feasible probability measures (risk envelope) or in the form of either mixed CVaR or negative Yaariâs dual utility. It is solved in single-period and multi-period formulations and is demonstrated in a case study with the FTSE 100 index.
2015-12-23T13:36:29Z
Implementing Automotive Telematics for Insurance Covers of Fleets
Azzopardi, M.
Cortis, Dominic
http://hdl.handle.net/2381/36130
2015-12-23T03:05:28Z
2015-12-22T16:43:17Z
Title: Implementing Automotive Telematics for Insurance Covers of Fleets
Authors: Azzopardi, M.; Cortis, Dominic
Abstract: The advantages of Usage-Based Insurance for automotive covers over conventional rating methods have been discussed in literature for over four decades. Notwithstanding their adoption in insurance markets has been slow. This paper seeks to establish the viability of introducing fleet Telematics-Based Insurance by investigating the perceptions of insurance operators, tracking service providers and corporate fleet owners. At its core, the study involves a SWOT-analysis to appraise Telematics-Based Insurance against conventional premium rating systems. Twenty five key stakeholders in Malta, a country with an insurance industry that represents others in microcosm, were interviewed to develop our analysis. We assert that local insurers have interests in such insurance schemes as enhanced fleet management and monitoring translate into an improved insurance risk. The findings presented here have implications for all stakeholders as we argue that telematics enhance fleet management, TBI improves risk management for insurers and adoption of this technology is dependent on telematics providers increasing the perceived control by insurers over managing this technology.
2015-12-22T16:43:17Z
Phacoemulsification Surgery in Eyes with Neovascular Age-Related Macular Degeneration
Grixti, A.
Papavasileiou, E.
Cortis, Dominic
Kumar, B. V.
Prasad, S.
http://hdl.handle.net/2381/36118
2015-12-23T03:05:25Z
2015-12-22T14:47:21Z
Title: Phacoemulsification Surgery in Eyes with Neovascular Age-Related Macular Degeneration
Authors: Grixti, A.; Papavasileiou, E.; Cortis, Dominic; Kumar, B. V.; Prasad, S.
Abstract: Purpose. To evaluate the visual outcomes and effect of phacoemulsification surgery on the progression of neovascular agerelated
macular degeneration (AMD). Methods. Retrospective, noncomparative, and interventional case series. Thirty eyes from 29
subjects with neovascular AMD treated with intravitreal antivascular endothelial growth factor (VEGF) injections who underwent
phacoemulsification and had a postsurgery follow-up of 6 months were included. LogMAR best corrected visual acuity (BCVA)
was assessed preoperatively; 1 month, 3 months, and 6 months postoperatively; and finally at the last visit. The frequency of antiVEGF
therapy, calculated as the number of intravitreal injections per month, and central macular thickness (CMT) before and
after cataract surgery were determined. Results. Median (range) logMAR BCVA was 0.69 (0.16 to 1.32) preoperatively; 0.55 (â0.04
to 1.32) at 1 month, 0.52 (â0.1 to 1.32) at 3 months, and 0.50 (0.0 to 1.32) at 6 months postoperatively; and 0.6 (0.0 to 1.4) at final
visit (đ = 0.0011). There was no difference in the frequency of anti-VEGF injections between the immediate 6 months before
and after phacoemulsification, which was equal to 0.1667 injections per month (đ = 0.6377). Median CMT measured 203 đm
preoperatively, which temporarily increased to 238 đm at 1 month after surgery (đ = 0.0093) and then spontaneously returned
to baseline, measuring 212.5 đm at 3 months postoperatively (đ = 0.3811). Conclusion. Phacoemulsification surgery significantly
improved vision in patients with neovascular AMD, with no increased need for anti-VEGF injections to keep the macula dry
postoperatively
2015-12-22T14:47:21Z
Atiyah sequences, connections and characteristic forms for principal bundles over groupoids and stacks
Biswas, Indranil
Neumann, Frank
http://hdl.handle.net/2381/36102
2015-12-19T03:18:59Z
2015-12-18T12:05:34Z
Title: Atiyah sequences, connections and characteristic forms for principal bundles over groupoids and stacks
Authors: Biswas, Indranil; Neumann, Frank
Abstract: We construct connections and characteristic forms for principal bundles over groupoids and stacks in the differentiable, holomorphic and algebraic category using Atiyah exact sequences associated with transversal tangential distributions.; Nous construisons les connexions et formes caractĂ©ristiques pour les fibrĂ©s principaux sur
les groupoĂŻdes et les champs dans la catĂ©gorie diffĂ©rentiable, holomorphe et algĂ©brique Ă
lâaide des suites dâAtiyah associĂ©es aux distributions transversales tangentielles.
2015-12-18T12:05:34Z