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Scarlett Gehle
This paper presents a bifurcation analysis of a thick-wall cylinder which is loaded with increasing radial internal or external pressure. Material behaviour is modelled by large strain elastoplastic deformation theory of the Drucker-Prager solid. Stability analysis is carried out along the primary equilibrium path to examine possible emergence of bifurcations that may lead to different failure modes. The model is used to investigate the effect of bifurcation modes on the initiation of a tensile fracture and to interpret the experimental results obtained from fracturing tests on thick-wall cylinders
Fracturing experiments were performed in thickwall cylinders of Jurassic shale in order to investigate the effect of plastic yielding and the range of validity of breakdown equation (1). The first attempt to interpret the experimental results was based on a Mohr-Coulomb elastoplastic analysis of an internally pressurized cylinder (Papanastasiou et al. 1995). We found that when initiation of a tensile fracture occurs in the elastic regime, the breakdown pressure can be estimated from equation (1). When tensile failure occurs after plastic yielding, classical elastoplasticity predicts a breakdown pressure greater than the one predicted by equation (1). In addition, for high confining pressures, a tensile state of stress cannot be achieved directly during pressurization of the wellbore according to classical elastoplasticity. In contrast to the classical theory, significant lower values of breakdown pressure were observed in the experiments. Due to the inadequacy of the classical elastoplastic procedure to describe the low initiation pressures, we revisited the subject examining in this study possible emergence of bifurcations along the primary equilibrium path which may lead to different failure modes, like shear banding (Papanastasiou and Vardoulakis 1992). Lower initiation pressure can occur if a shear failure mechanism develops and the fluid penetrates the shear fracture which will further propagate in a tensile mode.
The paper is organized as follows: Firstly we present in section 2 the elastoplastic solution for the primary path of a pressurized thick-wall cylinder. Section 3 deals with the formulation of the bifurcation problem. Computational results are presented and compared with the experimental data in section 4. Finally, we outline the main conclusions in the last section.
We have recently described a rare example of plastid loss in Hematodinium sp., a parasitic deep-branching dinoflagellate within the apicomplexan-dinoflagellate radiation (Figure 1).7 This is the second only clear case of plastid loss to date, the other being from the apicomplexan Cryptosporidium.8 Key to the successful loss of a plastid in Hematodinium was the retention of some of the host cell-based metabolic pathways in place of plastid ones, thus providing host cell independence. In turn, presence of these host pathways, as alternatives to the plastid pathways found in Plasmodium, demonstrated that the common ancestor of apicomplexans and dinoflagellates must have still contained redundant metabolic pathways. Differential rationalisation of this redundancy evidently then occurred in the radiating lineages. By surveying molecular data for pathway presence from across extant apicomplexan and dinoflagellate taxa, a compilation of pathways present in the common ancestor can be made (Figure 1).6,7,9-11 This shows that redundant host and plastid pathways were present for fatty acid synthesis (type I and type II FAS) and tetrapyrrole synthesis (plastid-based C5 [glutamate] pathway and cytosol/mitochondrion-based C4 [Shemin] pathway). Furthermore, redundancy in IPP synthesis for isoprenoids must have been present before apicomplexans and dinoflagellates diverged because, while both lineages now exclusively use the plastid DOXP pathway, the sister Alveolata lineage, ciliates, retains the host mevalonate pathway (Figure 1).12 Our studies of Hematodinium also reveal the presence of a distinctive plastid-type diaminopimelate lysine biosynthetic pathway.7,13,14 This pathway occurs in plastids of red algae and other lineages with red algal-derived plastids (e.g. ochrophytes, haptophytes),7 suggesting that it was most likely present also in the original red plastid of the common ancestor of apicomplexans and dinoflagellates. This pathway is now only present in deep-branching dinoflagellates (Perkinsus, Oxyrrhis and Hematodinium),7 and in all cases it is predicted to be relocated to the cytosol. This implies further differential evolution of a plastid function after apicomplexan-dinoflagellate divergence (Figure 1).
Schematic phylogeny of alveolates (black) with inferred metabolic pathway presence, loss and redundancy indicated (colored lines). Plastid-derived pathways are shown right of phylogeny branches, host-derived pathways (located in the cytosol or mitochondrion) are shown to the left, and pathway loss is indicated by lines ending in dashes. The point of greatest inferred metabolic pathway redundancy is indicated by circles. Formation of a single chimeric tetrapyrrole pathway in apicomplexans is indicated by the merger of the plastid and cytosol/mitochondrial pathways to an undulating line. Inferred relocation of the diaminopimelate lysine pathway from the plastid to cytosol is shown by right to left switching (the number of relocations is unknown). Question marks indicate unconfirmed presence of type I fatty acid synthase in dinoflagellates and colpodellids where distinction from polyketide synthases is difficult from current incomplete gene sequence data. M, mevalonate; D, DOXP; I, type I; II, type II.
Whereas, the Cambridge Public Schools participate in the Journey into Education and Teaching Program, known as JET, to provide a pathway at little cost for paraprofessionals to get their bachelor's degrees and Massachusetts teacher licensures; and
Whereas the Massachusetts boards of Elementary and Secondary Education and Higher Education jointly launched an initiative in 2018 to establish an Early College designation for districts specifically attempting to recruit underrepresented students, to allow cohort-based models that provide high-need and low-income students with the opportunity to complete college level academic coursework on a clearly articulated pathway while simultaneously gaining exposure to a variety of career opportunities; and
Whereas: The Cambridge School Committee's "primary responsibility is to establish those purposes, programs, and procedures that will best produce the educational achievement needed by our students"; and
Whereas: CAROL will be sorely missed by all she touched and loved; now therefore be it RESOLVED: That the Cambridge School Committee go on record extending its deepest sympathy to the family of CAROL CORREIA at this time of such personal loss; and be it further
In summer 2009, Emily started the research for her required Cambridge honors thesis. Because her topic was "The Origins of the American High School" and because she was studying in England, she had difficulty getting her hands on the primary documents and research items she needed. So she packed up and headed to Washington, D.C., where she spent two weeks immersed in her topic at the Library of Congress.
I was a community nurse for many years delivering nursing care to people in their own homes and care homes. During this time, I developed a special interest in palliative and end-of-life care, particularly for those with long term conditions and dementia. I saw a need at the time to bridge the gap between primary care and specialist and palliative services. So, whilst working as a district nursing sister, I completed a Masters in palliative care at Warwick University with the aim of improving support and care for those wanting to die at home.
Given the interacting and evolving nature of sustainability challenges, along with the technological, organizational, and political strategies needed to address them, we view this report as an initial step in what must be an ongoing and continuously developing effort. Below, we outline five elements of a pathway by which MIT can formalize and build upon current efforts to address the challenges posed by sustainability and become a leader in this crucial arena. The Pathway to Sustainability Leadership calls upon MIT to become:
Our professional and dedicated teachers ensure a respectful learning environment where students can reach their academic potential through our customized academic pathway and be inspired by each other. Our caring teachers understand the importance of encouraging students to apply their critical thinking and analysis skills in order to experience an ongoing and in-depth inquiry about their learning. They give high-achieving students more opportunities to be engaged and challenged with the curriculum. Our educators provide their students with opportunities to engage in different ways of learning, seek out information related to the interest of the students, and provide them with time and resources to explore these interests. With our enriched curriculum, we help students in their personal/character development, uncover their hidden talents, and inspire a love for learning. We promote our students to embrace collaboration, communication, innovation, and computer technologies to keep up with the ever-changing landscape of education.
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