Two dimensional configurational-force-driven crack propagation using the discontinuous Galerkin method with rp-adaptivity

This paper presents a quasi-static configurational force (CF) brittle fracture propagation method, [1], using the discontinuous Galerkin (dG) symmetric interior penalty (SIP) method, [2]. The method is derived from the first law of thermodynamics with consideration of the Griffith fracture criterion [1]. The criterion is evaluated by finding the difference between the power applied to the domain and the rate of internal energy change at every point in the domain. If a node within the element mesh satisfies the criterion, a crack will propagate in the CF direction. Around the crack tip the advantage of element specific degrees of freedom in dG methods enables simple p-adaptivity to determine the CF in the spatial domain. In the material domain r-adaptivity is implemented, where the CF direction is used to align element edges, which are then split to propagate the crack

An open-source Julia code for geotechnical MPM

There is considerable interest in the Material Point Method (MPM) in the computational geotechnics community since it can model problems involving large deformations, e.g. landslides, collapses etc. without being too far from the standard finite element method, which can struggle with large deformation problems. The open-source code AMPLE developed at Durham University in recent years is a compact set of MATLAB functions that “address the severe learning curve for researchers wishing to understand, and start using, the MPM”. It is well known that MATLAB can be very slow hence limiting its utility for major studies of large problems, so here we introduce an MPM code with the same aims as AMPLE but written in the relatively new language Julia, specifically for fast runtimes. We highlight areas where MATLAB code constructs are inefficient if just transferred to Julia and show that to unlock large speed gains with Julia, one needs to code in a different way and we demonstrate this on a geotechnical problem. While this paper is concerned with the MPM, the advice regarding coding using Julia is transferable to other computational geotechnics methods and tools

An investigation into the methods for modelling pre-existing cracks in phase field problems

Phase field (PF) models are an increasingly popular method of numerically modelling fracture problems. While research has focused on the practical applications and computational efficiency of PF methods, little discussion exists around the merits of different methods of prescribing initial cracks in PF fracture problems. This paper presents a comparison of three methods for modelling pre-existing cracks, through Dirichlet-type PF boundary conditions, an initial strain history term, and through physical discontinuities in the mesh. The comparison is made using the load-displacement responses for a common tensile benchmark fracture problem

“And by Publishing, to Preserve:” Envisioning Indigenous Futures in Anishinaabe Historical Writing, 1814–1893

This dissertation bridges intellectual history, biography, and ethnohistory to reveal how nineteenth-century Anishinaabeg used historical writing to historicize their past, speak to their colonial present, and offer future visions of a transformed colonial society. Historical writing was a key site of colonial struggle in which settler histories attempted to eliminate the Indigenous past and replace it with their own conception of the ‘Indian.’ Between 1814-1893, a remarkable body of Anishinaabe historical writing in English was produced by at least ten different writers, all of whom worked from the stories and knowledge of elders, family members, and knowledge keepers. Through a focus on the lives and writings of Jane Johnston Schoolcraft (Bamewawagezhikaquay), George Copway (Kahgegagahbowh), and Francis Assiginack, this dissertation analyzes expressions of Anishinaabe historical consciousness and the settler-colonial myths and ideas they engaged with. Their writings contended that elements of Anishinaabe ways of living and knowing were not only valid, but invaluable and had to be preserved in the face of permanent loss. In addition to producing immediate political and social change in Canada and the United States, these writers also sought to shape the development of future society. While their future visions called for Indigenous adoption of Euro-Canadian and Euro-American technology and religion, they also presented Anishinaabe knowledge as a gift that could potentially facilitate spiritual and moral renewal in settler society. Historical writing was a foundational aspect of this ‘envisioning process.’ By asserting an Anishinaabe understanding of history through this trans-cultural approach, these writers were able to challenge the historical and theological foundations of settler colonialism, argue for the value and historicity of Indigenous peoples, and posit visions of a settler colonial future that would transform both Indigenous and settler society

Hydropyrolysis: implications for radiocarbon pre-treatment and characterization of Black Carbon

Charcoal is the result of natural and anthropogenic burning events, when biomass is exposed to elevated temperatures under conditions of restricted oxygen. This process produces a range of materials, collectively known as pyrogenic carbon, the most inert fraction of which is known as Black Carbon (BC). BC degrades extremely slowly, and is resistant to diagenetic alteration involving the addition of exogenous carbon making it a useful target substance for radiocarbon dating particularly of more ancient samples, where contamination issues are critical. We present results of tests using a new method for the quantification and isolation of BC, known as hydropyrolysis (hypy). Results show controlled reductive removal of non-BC organic components in charcoal samples, including lignocellulosic and humic material. The process is reproducible and rapid, making hypy a promising new approach not only for isolation of purified BC for 14C measurement but also in quantification of different labile and resistant sample C fractions

National strategy for the prevention and management of transfusion-associated hepatitis

The screening of potential blood donors for the hepatitis B (HBV) and C (HCV) viruses has decreased the risk of transfusion-associated hepatitis, There remains. however, a lack of consensus on a number of issues including methods for screening of blood donors and the management of donors found to have markers of hepatitis virus infection. This document outlines the recommendations of a large group of interested individuals including blood transfusion service managers, primary care health authorities, epidemiologists, Virologists, pathologists, gastroenterologists and hepatologists drawn from both the public and the private sector

A revised age, structural model and origin for the North Pennine Orefield in the Alston Block, northern England: intrusion (Whin Sill)-related base metal (Cu–Pb–Zn–F) mineralization

Mineralization and associated fluid migration events in the c. 1500 km2 North Pennine Orefield (NPO) are known to be associated with tectonic activity, but the age of these tectonic events and origins of the base metal sulfide mineralization remain unresolved. New fieldwork in the Alston Block shows that mineralization post-dates a weakly developed phase of north–south shortening consistent with far-field Variscan basin inversion during the late Carboniferous. New observations of field relationships, coupled with microstructural observations and stress inversion analyses, together with Re–Os sulfide geochronology show that the vein-hosted mineralization (apart from barium minerals) was synchronous with a phase of north–south extension and east–west shortening coeval with emplacement of the Whin Sill (c. 297–294 Ma). Thus the development of the NPO was related to an early Permian regional phase of transtensional deformation, mantle-sourced hydrothermal mineralization and magmatism in northern Britain. Previously proposed Mississippi Valley Type models, or alternatives relating mineralization to the influx of Mesozoic brines, can no longer be applied to the development of the NPO in the Alston Block. Our findings also mean that existing models for equivalent base metal sulfide fields worldwide (e.g. Zn–Pb districts of Silesia, Poland and Tennessee, USA) may need to be reassessed

Cone Penetration Tests (CPTs) in layered soils: a Material Point approach

Cone Penetration Tests (CPTs) can be used to determine in-situ soil properties and represent a practical choice for site investigation offshore, especially for linear infrastructure, such as offshore wind export cables. Information gained from CPTs is key for predicting soil-structure interaction behaviour, for example when predicting the tow forces involved in seabed ploughing, as the CPT provides an analogue to the process. The numerical modelling of CPTs is challenging due to the significant distortion in the soil displaced by the penetrating cone. This means that solving this sort of problem using finite elements, although not impossible, is numerically tiresome in terms of remeshing and mapping of state variables. Therefore, in this paper we adopt the Material Point Method (MPM) to develop a CPT prediction tool in layered soils. This MPM is combined with a novel non-matching mesh frictional boundary to represent the penetrometer. The developed tool will be used to understand the response of layered soils commonly found offshore as a step towards predicting the interaction of ploughs and anchors with the seabed

An open-source Julia code for geotechnical MPM

There is considerable interest in the Material Point Method (MPM) in the computational geotechnics community since it can model problems involving large deformations, e.g. landslides, collapses etc. without being too far from the standard finite element method, which can struggle with large deformation problems. The open-source code AMPLE developed at Durham University in recent years is a compact set of MATLAB functions that “address the severe learning curve for researchers wishing to understand, and start using, the MPM”. It is well known that MATLAB can be very slow hence limiting its utility for major studies of large problems, so here we introduce an MPM code with the same aims as AMPLE but written in the relatively new language Julia, specifically for fast runtimes. We highlight areas where MATLAB code constructs are inefficient if just transferred to Julia and show that to unlock large speed gains with Julia, one needs to code in a different way and we demonstrate this on a geotechnical problem. While this paper is concerned with the MPM, the advice regarding coding using Julia is transferable to other computational geotechnics methods and tools