Rheology of vitreous humour and pharmacological substitutes used in the treatment of vitreoretinal pathologies

Vitreoretinal pathologies are the second leading cause of blindness worldwide. They can be caused by age-related changes in vitreous humour (VH) or as a consequence of some diseases that lead to rheological, biochemical and structural rearrangements. So far, the most effective treatment for these diseases is the injection of a VH substitute in the vitreous cavity. These substances can be used intra- operatively to push a detached retina into its normal position, to restore the volume of the vitreous cavity, and to help surgeons in membrane dissection. The major vitreous substitutes commercially available are silicone oils and perfluorocarbon liquids, but currently there is little information about the rheological properties of these fluids, that are intimately linked to their functionality. The aim of this work is to compare the rheological properties of the VH and five commercial vitreous substitutes currently used in vitreoretinal surgeries. Six fluids were analysed: VH extracted from New Zealand white rabbit specimen, three silicone oils (RS-Oil1000 and RS-Oil5000, Alchimia and Siluron 2000, Fluoron), two perfluorocarbon liquids (HPF8 and HPF10, Alchimia) and a mixture of silicone oil with perfluorocarbon (Densiron68, Fluoron). Extensional measurements were performed with a capillary break-up extensional rheometer (Haake CaBER1, ThermoElectron) and an in-house extensional rheometer. The steady shear and small amplitude oscillatory shear measurements (SAOS) were performed with a hybrid rheometer (DHR-2, TA Instruments). Our results show that VH substitutes used for same purpose exhibit significantly different rheological properties between them and when compared with the VH. Vitreous humour shows viscoelastic behaviour and all the pharmacological fluids tested display a Newtonian-like behaviour in steady shear flow with viscosities varying from 0.49 mPa s to 4.57 Pa s, at 37°C

The Space of the Photograph

This paper discusses critically the notions of ‘space’ and ‘representation’, both essential elements of the architectural photograph. The analysis is underpinned by the notion, first championed by the philosopher Henri Lefebvre, that space is produced and not merely found. It asks the question of what type of space do photographs produce when their subject is architecture, architectural photography being the genre par excellence concerned with the representation of space. The paper proposes to discuss this question in relation to the space of the office, arguing that this is a defining space of modernity and which is far from disappearing. Through the exam of photographs of offices by Ezra Stoller, Jacqueline Hassink and Lynne Cohen, the paper proposes a critique of the objective mode characteristic of architectural photography, offering a detailed analysis of the visual codes through which it produces its meanings and arguing that it is profoundly implicated in the production of corporate and, by extension, capitalist space

Rheological behaviour of vitreous humour

The vitreous humour (VH) is a complex biofluid that occupies a large portion of the eyeball between the lens and the retina, and exhibits non-Newtonian rheological properties that are key for its function in the eye. It is often possible to distinguish two different phases in VH, known as liquid and gel phases (Sebag, 1987). In this work, we present a detailed rheological characterisation of the two phases of the VH under shear and extensional flow conditions. Healthy New Zealand rabbit eyes were used to measure the surface tension and the shear and extensional rheological properties of VH in different phase conformations and at different times after dissection. The results show that VH liquid phase exhibits a surface tension of 47.8 mN/m, a shear thinning behaviour reaching a viscosity plateau around 10-3 Pa.s for shear rates above 1000 s-1, and an average relaxation time of 9.7 ms in extensional flow. Interestingly, both VH phases present higher storage modulus than loss modulus and the measurements performed with VH gel phase 4±1 hours after dissection exhibit the highest moduli values. The compliance measurements for the gel phase show a viscoelastic gel behaviour and that compliance values decrease substantially with time after dissection. Our results show that the two VH phases exhibit viscoelastic behaviour, but with distinct rheological characteristics, consistent with a gel phase mostly composed of collagen entangled by hyaluronan and a second phase mainly composed of hyaluronan in aqueous solution

Modelling irregularly spaced time series under preferential sampling

Irregularly spaced time series are commonly encountered in the analysis of time series. A particular case is that in which the collection procedure over time depends also on the observed values. In such situations, there is stochastic dependence between the process being modeled and the times at which the observations are made. Ignoring this dependence can lead to biased estimates and misleading inferences. In this paper, we introduce the concept of preferential sampling in the temporal dimension and we propose a model to make inference and prediction. The methodology is illustrated using artificial data as well a real data set.The authors acknowledge Foundation FCT (Fundacao para a Ciencia e Tecnologia) for funding through Individual Scholarship PhD PD/BD/105743/2014, Centre of Mathematics of Minho University and Center for Research & Development in Mathematics and Applications of Aveiro University within project UID/MAT/04106/2019

The omnichannel strategy in Portuguese companies: an overview

The consumer's profile and behaviour have undergone drastic changes in recent years, as a result of rapid technological developments associated with the proliferation of the Internet, which have boosted the growth of e-commerce. Retail needed to adopt new strategies to respond to new consumer demands leading to the development of omnichannel. The omnichannel strategy is centred on the consumer and aims to offer him/her a unique, consistent, and quality experience, through any contact point and wherever the consumer wants. However, most Portuguese retailers still opt for a multichannel strategy, where the physical shop and the online shop operate independently from each other. Although there are already some successful cases in Portugal, it can be considered that the use of omnichannel is still at an early stage. More publicity is needed so that retailers are aware of the concept and above all recognise the advantages of this new strategy. Before disclosure it is important to understand why companies work with both online and offline channels and do not opt for an omnichannel strategy. This study aims to analyse Portuguese companies that have not yet adopted an omnichannel strategy, to understand the barriers that make them unwilling to adopt this strategy. To this end, a quantitative research was carried out through the application of surveys to companies in different districts of Portugal to understand their position in relation to omnichannel and the reasons for not moving to this structure. The results obtained made it possible to describe the importance of omnichannel as a commercial and distribution strategy and analyse the reasons why its use by companies in Portugal is still extremely low. The lack of knowledge about the structure and management issues emerged as the biggest barriers.691D-6753-BE59 | Manuel José Serra da Fonsecainfo:eu-repo/semantics/publishedVersio

O planeamento de experiências no aperfeiçoamento de metaheuristicas

Dissertação de Mestrado em Estatística, Matemática e Computação apresentada à Universidade AbertaOs problemas de otimização combinatória têm, nas últimas décadas despertado um grande interesse por parte dos investigadores, quer pela sua aplicação prática, quer pela sua dificuldade. A área do ajuste dos parâmetros duma metaheurística tem crescido bastante, com um número cada vez maior de publicações. O facto da maioria dos problemas clássicos já terem sido resolvidos com as metaheurísticas existentes direciona a comunidade científica da área a trabalhar para que os modelos e técnicas existentes gerem cada vez melhores resultados. No 1º Capítulo é feita uma introdução ao Planeamento de Experiências e Metaheurísticas e explicada a motivação para a abordagem deste tema. No Capítulo 2 realiza-se uma apresentação dos Planos Fatoriais de base dois, importantes na definição dos parâmetros estatisticamente significativos e no Capítulo 3 dos Planos Fatoriais Fracionados que são essenciais quando o número de parâmetros aumenta. O Capítulo 4 tem como objetivo fazer uma breve caraterização das técnicas de Metodologia de Superfície de Resposta importantes na definição posterior das funções de desirability, utilizadas na resolução de problemas de otimização com múltiplas respostas. No Capítulo 5 define-se alguns conceitos básicos sobre o ajuste de parâmetros de metaheurísticas, realiza-se uma revisão de literatura e são apresentados quatro exemplos de metodologias adotadas. O Capítulo 6 é reservado para a apresentação de uma proposta de metodologia de ajuste dos parâmetros de metaheurísticas que faz uso das funções desirability e é apresentada uma aplicação dessa metodologia. No Capítulo 7 são feitas algumas considerações finais e registadas perspetivas futuras de trabalho.In last years researchers have been increased their interest in the combinatorial optimization problems, due to their practical implementation and to its difficulty. The area of fine-tuning parameters of a metaheuristic has grown, with a growing number of publications. The fact that most of the classic problems have already been solved with the existing metaheuristics directs the research community to work on improving the existing models and techniques, so that they generate increasingly better results. The Chapter 1 is an introduction to the Design of experiments and metaheuristics and is explained the motivation for tackling this issue. In Chapter 2 is made a presentation of the Factorial Designs base 2 important in the definition of witch parameters are statistically significant and in Chapter 3 Fractional Factorial Design base 2, essential when the number of parameters increases. Chapter 4 aims to make a brief characterization of the techniques of Response Surface Methodology, important in the later definition of desirability functions, used in solving optimization problems with multiple responses. In Chapter 5 are defined out some basics about fine tuning parameters of metaheuristics, is carried out a literature review and are presented four examples of methodologies adopted. Chapter 6 is reserved for the presentation of a proposed methodology for setting the parameters of metaheuristics which makes use of desirability functions, and presents an application of this methodology. In chapter 7 some concluding remarks are made and recorded future work prospects

Rheological behaviour and flow dynamics of Vitreous Humour substitutes used in eye surgery during saccadic eye movements

This work discusses the rheology of several vitreous humour (VH) substitutes used in eye surgery (perfluorocarbons and silicone oils) and their flow behaviour when subjected to saccadic eye movements. Shear rheology experiments revealed that all fluids tested exhibit a constant shear viscosity, while extensional rheological experiments showed that Siluron 2000 is the only fluid tested that exhibits a measurable elasticity. To characterise the dynamics during saccadic eye movements, numerical simulations of all the VH substitutes under study were performed with the open source software OpenFOAM and compared with Vitreous Humour flow dynamics to assess their potential mechanical performance. Minor differences were found between the numerical results of a viscoelastic fluid reproducing the rheology of Siluron 2000 and a Newtonian model. Perfluorocarbon (PFLC) shows a distinct flow behaviour relative to Silicone Oils (SiO). None of the pharmacological fluids tested can adequately mimic the rheological and consequently the flow behaviour of VH gel phase (Silva et al., 2020).Comment: 16 figure

Flow dynamics of vitreous humour during saccadic eye movements

In this work, we reveal the flow dynamics of Vitreous Humour (VH) gel and liquid phases during saccadic movements of the eye, considering the biofluids viscoelastic character as well as realistic eye chamber geometry and taking into account the saccade profile. We quantify the differences in the flow dynamics of VH gel and liquid phases using viscoelastic rheological models that are able to model the VH shear rheology, considering different amplitudes of saccadic movements (10 ∘, 20 ∘, 30 ∘ and 40 ∘). For this purpose, the computational fluid dynamics (CFD) open source software OpenFOAM® was used. The results portray a distinct flow behaviour for the VH gel and liquid phases, with inertial effects being more significant for the VH liquid phase. Moreover, the Wall Shear Stress (WSS) values produced by the VH gel phase are more than twice of those generated by the VH liquid phase. Results also show that for different amplitudes of eye movement both the velocity magnitude in the vitreous cavity and the shear stresses on the cavity walls rise with increasing saccadic movement displacement