Unsteady flow of a thixotropic fluid in a slowly varying pipe

We analyse the unsteady axisymmetric flow of a thixotropic or antithixotropic fluid in a slowly varying cylindrical pipe. We derive general perturbation solutions in regimes of small Deborah numbers, in which thixotropic or antithixotropic effects enter as perturbations to generalised Newtonian flow. We present results for the viscous Moore–Mewis–Wagner model and the viscoplastic Houška model, and we use these results to elucidate what can be predicted in general about the behaviour of thixotropic and antithixotropic fluids in lubrication flow. The range of behaviour we identify casts doubt on the efficacy of model reduction approaches that postulate a generic cross-pipe flow structure

Thixotropic pumping in a cylindrical pipe

We consider the flow of a thixotropic fluid in a uniform cylindrical pipe, driven by an oscillating pressure gradient or a body force. For a variety of rheological models, solutions can be obtained by integrating ordinary rather than partial differential equations: we illustrate this approach for the thixo-viscoplastic Houška model and the thixo-viscous simplified Moore-Mewis-Wagner model. We present asymptotic results in the limits of small and large Deborah numbers, and numerical results for intermediate Deborah numbers. Under asymmetrical "sawtooth" forcing, thixotropy leads to the net transport of fluid along the pipe, even when there would be no net transport of the corresponding generalised-Newtonian fluid. We propose the name "thixotropic pumping" for this novel transport mechanism

Slowly varying pipe flow of thixotropic fluids

In this thesis we study lubrication flows of thixotropic and antithixotropic fluids in two flow problems: unsteady flow in a slowly varying 3D pipe, and oscillating flow in a uniform cylindrical pipe. We consider two fluid models which exhibit interesting non-Newtonian behaviour: the viscous Moore-Mewis-Wagner (MMW)model, and the viscoplastic Houška model.In Chapters 2-6 we study unsteady thixotropic flow in a slowly varying pipe, in a particular regime in which the thixotropic effects are considered 'weak', with the aim of determining whether we may describe generally the qualitative behaviour of thixotropic fluids in such flows. Previous work by Pritchard et al. [Journalof Non-Newtonian Fluid Mechanics, 238: 140-157, 2016] in the related problem of steady 2D channel flow suggests that such a description may be available.After obtaining the governing equations for this problem, we perform a detailed analysis of the flow for the MMW and Houška models, and determine all of the possible behaviours of these models. This analysis shows that the results and physical interpretations of Pritchard et al. are insightful but not complete. We also study the application of an off-the-shelf finite element program to determine the suitability of such programs for studying slowly varying thixotropic flows.In Chapter 7 we study the similar but simpler problem of unsteady thixotropic pipe flow driven by an oscillating pressure gradient. This problem is simpler than the problem considered in Chapters 2-6, which allows us to explore a wider range of thixotropic behaviours, in which the thixotropic effects range from 'weak' to'strong'. We are able to describe the full range of thixotropic behaviour using a combination of analytical and numerical methods.In this thesis we study lubrication flows of thixotropic and antithixotropic fluids in two flow problems: unsteady flow in a slowly varying 3D pipe, and oscillating flow in a uniform cylindrical pipe. We consider two fluid models which exhibit interesting non-Newtonian behaviour: the viscous Moore-Mewis-Wagner (MMW)model, and the viscoplastic Houška model.In Chapters 2-6 we study unsteady thixotropic flow in a slowly varying pipe, in a particular regime in which the thixotropic effects are considered 'weak', with the aim of determining whether we may describe generally the qualitative behaviour of thixotropic fluids in such flows. Previous work by Pritchard et al. [Journalof Non-Newtonian Fluid Mechanics, 238: 140-157, 2016] in the related problem of steady 2D channel flow suggests that such a description may be available.After obtaining the governing equations for this problem, we perform a detailed analysis of the flow for the MMW and Houška models, and determine all of the possible behaviours of these models. This analysis shows that the results and physical interpretations of Pritchard et al. are insightful but not complete. We also study the application of an off-the-shelf finite element program to determine the suitability of such programs for studying slowly varying thixotropic flows.In Chapter 7 we study the similar but simpler problem of unsteady thixotropic pipe flow driven by an oscillating pressure gradient. This problem is simpler than the problem considered in Chapters 2-6, which allows us to explore a wider range of thixotropic behaviours, in which the thixotropic effects range from 'weak' to'strong'. We are able to describe the full range of thixotropic behaviour using a combination of analytical and numerical methods

Memory B cell reconstitution following allogeneic haematopoietic stem cell transplantation is an EBV-associated transformation event

Allogeneic stem cell transplantation (allo-HSCT) provides a unique opportunity to track Epstein-Barr virus (EBV) infection in the context of the reconstituting B-cell system. Although many allo-HSCT recipients maintain low or undetectable levels of EBV DNA posttransplant, a significant proportion exhibit elevated and rapidly increasing EBV loads which, if left untreated, may lead to potentially fatal EBV-associated posttransplant lymphoproliferative disease. Intriguingly, this high-level EBV reactivation typically arises in the first 3 months posttransplant, at a time when the peripheral blood contains low numbers of CD27(+) memory cells which are the site of EBV persistence in healthy immunocompetent donors. To investigate this apparent paradox, we prospectively monitored EBV levels and B-cell reconstitution in a cohort of allo-HSCT patients for up to 12 months posttransplant. In patients with low or undetectable levels of EBV, the circulating B-cell pool consisted predominantly of transitional and naive cells, with a marked deficiency of CD27(+) memory cells which lasted >12 months. However, among patients with high EBV loads, there was a significant increase in both the proportion and number of CD27(+) memory B cells. Analysis of sorted CD27(+) memory B cells from these patients revealed that this population was preferentially infected with EBV, expressed EBV latent transcripts associated with B-cell growth transformation, had a plasmablastic phenotype, and frequently expressed the proliferation marker Ki-67. These findings suggest that high-level EBV reactivation following allo-HSCT may drive the expansion of latently infected CD27(+) B lymphoblasts in the peripheral blood

Memory B-cell reconstitution following allogeneic hematopoietic stem cell transplantation is an EBV-associated transformation event

Allogeneic stem cell transplantation (allo-HSCT) provides a unique opportunity to track Epstein-Barr virus (EBV) infection in the context of the reconstituting B cell system. While many allo-HSCT recipients maintain low or undetectable levels of EBV DNA post-transplant, a significant proportion exhibit elevated and rapidly increasing EBV loads which, if left untreated, may lead to potentially fatal EBV-associated post-transplant lymphoproliferative disease. Intriguingly this high level EBV reactivation typically arises in the first three months post-transplant, at a time when the peripheral blood contains low numbers of CD27(+) memory cells which are the site of EBV persistence in healthy immunocompetent donors. To investigate this apparent paradox, we prospectively monitored EBV levels and B cell reconstitution in a cohort of allo-HSCT patients for up to 12 months post-transplant. In patients with low or undetectable levels of EBV, the circulating B cell pool consisted predominantly of transitional and naïve cells, with a marked deficiency of CD27(+) memory cells which lasted more than twelve months. However, amongst patients with high EBV loads, there was a significant increase in both the proportion and number of CD27(+) memory B cells. Analysis of sorted CD27(+) memory B cells from these patients revealed that this population was preferentially infected with EBV, expressed EBV latent transcripts associated with B cell growth transformation, had a plasmablastic phenotype and frequently expressed the proliferation marker Ki-67. These findings suggest that high level EBV reactivation following allo-HSCT may drive the expansion of latently infected CD27(+) B lymphoblasts in the peripheral blood.</p