Discrete/finite element modelling of rock cutting with a TBM disc cutter

The final publication is available at Springer via http://dx.doi.org/10.1007/s00603-016-1133-7This paper presents advanced computer simulation of rock cutting process typical for excavation works in civil engineering. Theoretical formulation of the hybrid discrete/finite element model has been presented. The discrete and finite element methods have been used in different subdomains of a rock sample according to expected material behaviour, the part which is fractured and damaged during cutting is discretized with the discrete elements while the other part is treated as a continuous body and it is modelled using the finite element method. In this way, an optimum model is created, enabling a proper representation of the physical phenomena during cutting and efficient numerical computation. The model has been applied to simulation of the laboratory test of rock cutting with a single TBM (tunnel boring machine) disc cutter. The micromechanical parameters have been determined using the dimensionless relationships between micro- and macroscopic parameters. A number of numerical simulations of the LCM test in the unrelieved and relieved cutting modes have been performed. Numerical results have been compared with available data from in-situ measurements in a real TBM as well as with the theoretical predictions showing quite a good agreement. The numerical model has provided a new insight into the cutting mechanism enabling us to investigate the stress and pressure distribution at the tool–rock interaction. Sensitivity analysis of rock cutting performed for different parameters including disc geometry, cutting velocity, disc penetration and spacing has shown that the presented numerical model is a suitable tool for the design and optimization of rock cutting process.Peer ReviewedPostprint (published version

Modelling and simulation of the effect of blast loading on structures using an adaptive blending of discrete and finite element methods

We present a new computational model for predicting the effect of blast loading on structures. The model is based in the adaptive coupling of the finite element method (FEM) and the discrete element method (DEM) for the accurate reproduction of multifracturing and failure of structures under blast loading. In the paper we briefly describe the basis of the coupled DEM/FEM technology and demonstrate its efficiency in its application to the study of the effect of blast loading on a masonry wall, a masonry tunnel and a double curvature dam.Postprint (published version

Genomic stability in Arabidopsis thaliana transgenic plants obtained by floral dip

. The occurrence of DNA modification is an undesired phenomenon accompanying plant cell transformation. The event has been correlated with the stress imposed by the presently utilised transformation procedures, all depending on plant differentiation from in vitro cell culture, but other causes have not been excluded. In this work, transgenic Arabidopsis thaliana plants have been produced by an approach that does not require cell dedifferentiation, being based on in planta Agrobacterium-mediated gene transfer by flower infiltration, which is followed by recovery and selection of transgenic progeny. Genomic DNA changes in transgenic and control plants have been investigated by AFLP and RAMP analysis. Results show no statistically relevant genomic modifications in transgenic plants, as compared with control untreated plants. Variations were observed in callus-derived A. thaliana plants, thus supporting the conclusion that somaclonal variation is essentially correlated with the stress imposed by the in vitro cell culture, rather than with the integration of a foreign gene

Advances in the development of the discrete element method for excavation processes

Modelling of granular materials, soils and rocks has been a challenging topic of investigation for decades. Classical continuum mechanics has been used to idealize soils and rocks, and numerical solution techniques such as finite element method (FEM) has been used to model these materials. Considering the idealization of the material, continuum mechanics allows the analysis of phenomena with discontinuous nature such as fracture in rock or soil via damage models. However, in more complex processes like rock milling or crushing, this kind of models are usually not suitable. Discrete models are more appropriate for problems with multiple discontinuities and particulate materials. The discrete element method (DEM) has been gaining popularity in analysis of granular materials, soils and rocks. Many aspects of this method still require more profound investigation. This thesis presents new developments of the discrete element method improving effi ciency and accuracy of modelling of rock-like materials, especially in excavation processes. All the numerical algorithms has been implemented in an in-house software, which was then used to run numerical examples. The basic formulation of DEM with linear elastic-perfectly brittle contact model is presented. The main di erence with other models found in the literature is the consideration of global sti ness and strength parameters that are constants in the whole model. The result of a simulations is strongly related with the con guration of the particle assembly used. Particle assemblies should be su ciently compact and ensure the isotropy to reproduce the physical properties of the modelled material. This thesis presents a novel technique for the generation of highly dense particle assemblies in arbitrary geometries, satisfying all the requirements for accurate discrete element simulations. One of the key issues in the use of the DEM is the estimation of the contact model parameters. A methodology is proposed for the estimation of the contact model parameters yielding required macroscopic properties of the material. The relationships between the contact model parameters and the mechanical properties of brittle materials, as well as the influence of the particles assembly con guration on the macroscopic properties, are analysed. A major di culty in the application of the DEM to real engineering problems is the high computational cost in simulation involving a large number of particles. The most common way to solve this is the use of parallel computing techniques, where multiple processors are used. As an alternative, a coupling scheme between DEM and the finite element method (FEM) is proposed in the thesis. Within the hybrid DEM/FEM model, DEM is only used in the region of the domain where it provides an advantage over a continuum-based approach, as the FEM. The coupling is dynamically adapted, starting with the whole domain discretized with FEM. During the simulation, in the regions where a high stress level are found, a change of modelling method from continuum FEM to the discrete DEM is employed. Finally, all the developments are applied to the simulation of a real excavation process. An analysis of the rock cutting process with TBM disc cutters is performed, where DEM and the DEM/FEM coupling technique presents an important advantage over other simulation techniques.La modelación de materiales granulares, terrenos y rocas ha sido un desafío para la investigación por décadas. La mecánica del continuo clásica ha sido utilizada para idealizar terrenos y rocas, y técnicas numéricas de solución, como el método de los elementos finitos (FEM), han sido usadas para modelar estos materiales. Considerando la idealización del material, la mecánica del continuo permite el análisis de fenómenos de naturaleza discontinua como la fractura en rocas y terreno mediante modelos de daño. Sin embargo, en procesos mas complejos como la molienda o trituración de roca, este tipo de modelos no suelen ser adecuados. Los modelos discretos son mas apropiados para problemas con múltiples discontinuidades y material particulado. El método de los elementos discretos (DEM) ha ido ganando popularidad en el análisis de materiales granulares, terrenos y rocas. Sin embargo, muchos aspectos de este método todavía requieren una investigación mas profunda. Esta tesis presenta nuevos desarrollos del método de los elementos discretos para mejorar su eficiencia y precisión en el modelado de materiales como roca, especialmente para procesos de excavación. Todos los algoritmos numéricos se han implementado en el programa propio, que ha sido utilizado para probar distintos ejemplos. La formulación básica del DEM, con un modelo lineal de contacto elástico perfectamente frágil ha sido utilizado en el presente trabajo. La principal diferencia con otros modelos de la literatura es la consideración de que los parámetros de rigidez y fuerzas máximas son valores globales y constantes en todo el modelo. El resultado de la simulación está fuertemente relacionado con la configuración del ensamblaje de partículas utilizado. El ensamblaje de partículas debe ser suficientemente compacto y asegurar la isotropía de las propiedades físicas del material modelado. La tesis presenta una nueva técnica para la generación de ensamblajes de partículas de alta densidad para geometrías arbitrarias, satisfaciendo todos los requisitos para una simulación con elementos discretos correcta. Uno de los temas clave en el uso del DEM es la estimación de los parámetros del modelo de contacto. Se propone una metodología para la estimación de los parámetros del modelo de contacto siguiendo las propiedades macroscópicas requeridas en el material Las relaciones entre los parámetros del modelo y las propiedades mecánicas de materiales frágiles, así como su la influencia de la configuración del ensamblaje de partículas son analizadas. Una gran dificultad en la aplicación del DEM en problemas reales de ingeniería es el alto costo computacional de simulaciones que consideran un gran número de partículas. La solución mas común para resolver esto es el uso de técnicas de computación paralela, donde se utiliza un gran número de procesadores. Como vía alternativa, un esquema acoplado entre el DEM y el FEM expuesto en la tesis. Con el modelo híbrido DEM/FEM, el DEM es usado solo en las partes del dominio donde presenta ventajas sobre el enfoque continuo del FEM. El acoplamiento puede ser adaptado dinámicamente, comenzando con todo el dominio discretizado con FEM, y durante la simulación, en las regiones donde se encuentran altos niveles de tensión, se emplea un cambio del método de simulación de continuo (FEM) a discreto (DEM). Finalmente, todos los desarrollos son aplicados a la simulación de un proceso excavación real. Se realiza un estudio del proceso de corte de roca con discos costadores, utilizados en tuneladoras, donde el DEM y la técnica de acoplamiento presentan una importante ventaja sobre otras técnicas de simulación

Advances in the development of the discrete element method for excavation processes

This work presents new developments of the discrete element method improving e ciency and accuracy of modelling of rock-like materials, especially in excavation processes.Postprint (published version

Macroevolutionary diversification of glands for chemical communication in squamate reptiles

Chemical communication plays a central role in social, sexual and ecological interactions among animals. However, the macroevolutionary diversification of traits responsible for chemical signaling remains fundamentally unknown. Most research investigating evolutionary diversification of glands responsible for the production of chemical signals has focused on arthropods, while its study among vertebrates remains neglected. Using a global-scale dataset covering > 80% (7,904 species) of the living diversity of lizards and snakes (squamates), we investigate rates, trajectories and phylogenetic patterns of diversification of their follicular glands for chemical communication. We observed these glands in 13.66% of species, that their expression has varying phylogenetic signal among lineages, and that the crown squamate ancestor lacked follicular glands, which therefore originated and diversified subsequently during their evolutionary history. Additionally, our findings challenge the longstanding view that within squamates the Iguania are visually oriented while Scleroglossa are chemically-oriented, given that Iguania doubles Scleroglossa in the frequency of glands. Our phylogenetic analyses identified stabilizing selection as the best model describing follicular gland diversification, and revealed high rates of disparity. We provide the first global-scale analysis investigating the diversification of one of the main forms of communication among reptiles, presenting a macroevolutionary angle to questions traditionally explored at microevolutionary scale

Middle ear microbiome differences in indigenous Filipinos with chronic otitis media due to a duplication in the A2ML1 gene

Middle ear microbial profiles of indigenous Filipinos with chronic otitis media. All panels compare carriers with non-carriers of the A2ML1 duplication variant. Panel description: (A) ι-diversity by observed OTUs; (B) ι-diversity by the Shannon diversity index; (C) β-diversity from unweighted UniFrac principal coordinate analysis; (D) β-diversity from weighted UniFrac principal coordinate analysis. (PDF 1019 kb

High-throughput 18K SNP array to assess genetic variability of the main grapevine cultivars from Sicily

The viticulture of Sicily, for its vocation, is one of the most important and ancient forms in Italy. Autochthonous grapevine cultivars, many of which known throughout the world, have always been cultivated in the island from many centuries. With the aim to preserve this large grapevine diversity, previous studies have already started to assess the genetic variability among the Sicilian cultivars by using morphological and microsatellite markers. In this study, simple sequence repeat (SSR) were utilized to verify the true-to-typeness of a large clone collection (101) belonging to 21 biotypes of the most 10 cultivated Sicilian cultivars. Afterwards, 42 Organization Internationale de la Vigne et du Vin (OIV) descriptors and a high-throughput single nucleotide polymorphism (SNP) genotyping array (Vitis18kSNP) were applied to assess genetic variability among cultivars and biotypes of the same cultivar. Ampelographic traits and high-throughput SNP genotyping platforms provided an accuracy estimation of genetic diversity in the Sicilian germplasm, showing the relationships among cultivars by cluster and multivariate analyses. The large SNP panel defined sub-clusters unable to discern among biotypes, previously classified by ampelographic analysis, belonging to each cultivar. These results suggested that a very large number of SNP did not cover the genome regions harboring few morphological traits. Genetic structure of the collection revealed a clear optimum number of groups for K = 3, clustering in the same group a significant portion of family-related genotypes. Parentage analysis highlighted significant relationships among Sicilian grape cultivars and Sangiovese, as already reported, but also the first evidences of the relationships between Nero d’Avola and both Inzolia and Catarratto. Finally, a small panel of highly informative markers (12 SNPs) allowed us to isolate a private profile for each Sicilian cultivar, providing a new tool for cultivar identification

Mild cognitive impairment is associated with poor physical function but not bone structure or density in late adulthood:Findings from the Hertfordshire Cohort Study

Mini Abstract This study investigated the association between mild cognitive impairment (MCI) and physical function and bone health in older adults. MCI was associated with poor physical performance but not bone mineral density or bone microarchitecture. Abstract Purpose: Cross-sectional study to investigate the association between mild cognitive impairment (MCI) and physical performance, and bone health, in a community-dwelling cohort of older adults. Methods: Cognitive function of 222 men and 221 women (mean age 75.5 and 75.8 years in men and women, respectively) was assessed by the Strawbridge questionnaire and Mini Mental State Exam (MMSE). Participants underwent dual-energy x-ray absorptiometry (DXA), peripheral-quantitative computed tomography (pQCT) and high-resolution peripheral-quantitative computed tomography (HR-pQCT) scans to assess their bone density, strength and microarchitecture. Their physical function was assessed and a physical performance (PP) score was recorded. Results: 11.8% of women and 8.1% of men in the study were cognitive impaired on the MMSE (score<24). 24% of women were deemed cognitively impaired on the Strawbridge questionnaire, compared to 22.3% of men. Cognitive impairment on the Strawbridge questionnaire was associated with poorer physical performance score in men but not women in the unadjusted analysis. MMSE <24 was strongly associated with the risk of low physical performance in men (OR 12.9, 95% CI 1.67, 99.8, p=0.01) Higher MMSE score was associated with better physical performance in both sexes. Poorer cognitive function, whether assessed by the Strawbridge questionnaire, or by MMSE score, was not associated with bone density, shape or microarchitecture, in either sex. Conclusion: MCI in older adults was associated with poor physical performance, but not bone density, shape or microarchitecture