Olga Panagiotopoulou

Bio: Olga Panagiotopoulou is an academic researcher from Monash University. The author has contributed to research in topics: Medicine & Finite element method. The author has an hindex of 13, co-authored 34 publications receiving 611 citations. Previous affiliations of Olga Panagiotopoulou include Discovery Institute & University of Hull.

What makes an accurate and reliable subject-specific finite element model? A case study of an elephant femur (Retraction of vol 9, pg 351, 2012)

Abstract: Finite element modelling is well entrenched in comparative vertebrate biomechanics as a tool to assess the mechanical design of skeletal structures and to better comprehend the complex interaction of their form–function relationships. But what makes a reliable subject-specific finite element model? To approach this question, we here present a set of convergence and sensitivity analyses and a validation study as an example, for finite element analysis (FEA) in general, of ways to ensure a reliable model. We detail how choices of element size, type and material properties in FEA influence the results of simulations. We also present an empirical model for estimating heterogeneous material properties throughout an elephant femur (but of broad applicability to FEA). We then use an ex vivo experimental validation test of a cadaveric femur to check our FEA results and find that the heterogeneous model matches the experimental results extremely well, and far better than the homogeneous model. We emphasize how considering heterogeneous material properties in FEA may be critical, so this should become standard practice in comparative FEA studies along with convergence analyses, consideration of element size, type and experimental validation. These steps may be required to obtain accurate models and derive reliable conclusions from them.

Finite element analysis (FEA): applying an engineering method to functional morphology in anthropology and human biology.

Abstract: A fundamental research question for morphologists is how morphological variation in the skeleton relates to function. Traditional approaches have advanced our understanding of form-function relationships considerably but have limitations. Strain gauges can only record strains on a surface, and the geometry of the structure can limit where they can be bonded. Theoretical approaches, such as geometric abstractions, work well on problems with simple geometries and material properties but biological structures typically have neither of these. Finite element analysis (FEA) is a method that overcomes these problems by reducing a complex geometry into a finite number of elements with simple geometries. In addition, FEA allows strain to be modelled across the entire surface of the structure and throughout the internal structure. With advances in the processing power of computers, FEA has become more accessible and as such is becoming an increasingly popular tool to address questions about form-function relationships in development and evolution, as well as human biology generally. This paper provides an introduction to FEA including a review of the sequence of steps needed for the generation of biologically accurate finite element models that can be used for the testing of biological and functional morphology hypotheses.

The mechanical function of the periodontal ligament in the macaque mandible: a validation and sensitivity study using finite element analysis

Abstract: Whilst the periodontal ligament (PDL) acts as an attachment tissue between bone and tooth, hypotheses regarding the role of the PDL as a hydrodynamic damping mechanism during intraoral food processing have highlighted its potential importance in finite element (FE) analysis. Although experimental and constitutive models have correlated the mechanical function of the PDL tissue with its anisotropic, heterogeneous, viscoelastic and non-linear elastic nature, in many FE simulations the PDL is either present or absent, and when present is variably modelled. In addition, the small space the PDL occupies and the inability to visualize the PDL tissue using μCT scans poses issues during FE model construction and so protocols for the PDL thickness also vary. In this paper we initially test and validate the sensitivity of an FE model of a macaque mandible to variations in the Young's modulus and the thickness of the PDL tissue. We then tested the validity of the FE models by carrying out experimental strain measurements on the same mandible in the laboratory using laser speckle interferometry. These strain measurements matched the FE predictions very closely, providing confidence that material properties and PDL thickness were suitably defined. The FE strain results across the mandible are generally insensitive to the absence and variably modelled PDL tissue. Differences are only found in the alveolar region adjacent to the socket of the loaded tooth. The results indicate that the effect of the PDL on strain distribution and/or absorption is restricted locally to the alveolar bone surrounding the teeth and does not affect other regions of the mandible.

Statistical parametric mapping of the regional distribution and ontogenetic scaling of foot pressures during walking in Asian elephants (Elephas maximus)

Abstract: Foot pressure distributions during locomotion have causal links with the anatomical and structural configurations of the foot tissues and the mechanics of locomotion. Elephant feet have five toes bound in a flexible pad of fibrous tissue (digital cushion). Does this specialized foot design control peak foot pressures in such giant animals? And how does body size, such as during ontogenetic growth, influence foot pressures? We addressed these questions by studying foot pressure distributions in elephant feet and their correlation with body mass and centre of pressure trajectories, using statistical parametric mapping (SPM), a neuro-imaging technology. Our results show a positive correlation between body mass and peak pressures, with the highest pressures dominated by the distal ends of the lateral toes (digits 3, 4 and 5). We also demonstrate that pressure reduction in the elephant digital cushion is a complex interaction of its viscoelastic tissue structure and its centre of pressure trajectories, because there is a tendency to avoid rear ‘heel’ contact as an elephant grows. Using SPM, we present a complete map of pressure distributions in elephant feet during ontogeny by performing statistical analysis at the pixel level across the entire plantar/palmar surface. We hope that our study will build confidence in the potential clinical and scaling applications of mammalian foot pressures, given our findings in support of a link between regional peak pressures and pathogenesis in elephant feet.

Evolution and development of shape: integrating quantitative approaches

Abstract: Morphological traits have long been a focus of evolutionary developmental biology ('evo-devo'), but new methods for quantifying shape variation are opening unprecedented possibilities for investigating the developmental basis of evolutionary change. Morphometric analyses are revealing that development mediates complex interactions between genetic and environmental factors affecting shape. Evolution results from changes in those interactions, as natural selection favours shapes that more effectively perform some fitness-related functions. Quantitative studies of shape can characterize developmental and genetic effects and discover their relative importance. They integrate evo-devo and related disciplines into a coherent understanding of evolutionary processes from populations to large-scale evolutionary radiations.

Review of Research.

Abstract: According to WHO, the permissible limit of arsenic till 1993 was 0.05 mg. /L of drinking water. In 1993, WHO modified the maximum level and brought it down to 0.01 mg./L. According to the report of School of Environment Studies of Jadavpur University (1992-1993), West Bengal has 6 districts, affected by arsenic contamination of ground water. The present paper attempts to find out the vulnerability and impact of arsenic on human being. A detailed survey was conducted at Dahapara village of Murshidabad district to assess the present condition of the area giving emphasis on the identification of sources of arsenic pollution.

Does Bitcoin hedge global uncertainty? Evidence from wavelet-based quantile-in-quantile regressions

Abstract: In this study, we analyse whether Bitcoin can hedge uncertainty using daily data for the period of 17th March, 2011, to 7th October, 2016. Global uncertainty is measured by the first principal component of the VIXs of 14 developed and developing equity markets. We first use wavelets to decompose Bitcoin returns into various frequencies, i.e., investment horizons. Then, we apply standard OLS regressions and observe that uncertainty negatively affects raw Bitcoin return and its longer-term movements. However, given the heavy tails of the variables, we rely on quantile methods and reveal much more nuanced and interesting results. Quantile regressions indicate that Bitcoin does act as a hedge against uncertainty, that is, it reacts positively to uncertainty at both higher quantiles and shorter frequency movements of Bitcoin returns. Finally, when we use quantile-on-quantile regressions, we observe that hedging is observed at shorter investment horizons, and at both lower and upper ends of Bitcoin returns and global uncertainty.