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The convective Stefan problem: shaping under natural convection
No full textWhat is the shape formed by a body that is melting or dissolving into an ambient fluid? We present a theoretical analysis of the dynamics of melting or dissolving bodies in the common situation where the transfer of heat or solute at the surface creates a thin thermal or solutal convective boundary layer along its surface. By conducting a general analysis of a mathematical model describing the shape evolution of such bodies (Pegler & Davies Wykes, J. Fluid Mech., vol. 900, 2020, A35), we reveal new phenomena relating to the emergence of fundamental similarity solutions, asymptotic transitions, tip structure and the conditions for the development of sharp versus blunted tips. A universal regime diagram is developed showing asymptotic transitions between two different classes of similarity solutions. With t time, the tip of initially rectangular bodies is found to descend as t4/3 at early times, but transitions to the considerable faster power of t4 at long times, for example. Surprisingly, the tips of certain shapes, including initially rectangular bodies, sharpen continuously, whilst those of others, including initially conic bodies, blunt for all times. For the former case, the tip curvature grows rapidly as t12, forming a needle-like shape. More general initial shapes can produce multiple transitions between sharpening and blunting. These results provide foundational understanding of buoyancy-driven fluid sculpting that underlies numerous natural and industrial applications
RDLS-SS-DWT v. 0.9
No full textThis fileset contains the implementation of RDLS-DWT and SS-DWT in JPEG 2000 (RDLS-SS-DWT v. 0.9), which was used in a research described in: R. Starosolski, “Application of reversible denoising and lifting steps to DWT in lossless JPEG 2000 for improved bitrates,” Signal Processing: Image Communication, Vol. 39, Part A, pp. 249-63, DOI: 10.1016/j.image.2015.09.013, 2015 and R. Starosolski, “Skipping selected steps of DWT computation in lossless JPEG 2000 for improved bitrates,” submitted. This software is intended for research purposes only; it is provided "as is"; author makes no warranty of any kind, either express or implied, with respect to this software. <br
The convective Stefan problem: shaping under natural convection
No full textWhat is the shape formed by a body that is melting or dissolving into an ambient fluid? We present a theoretical analysis of the dynamics of melting or dissolving bodies in the common situation where the transfer of heat or solute at the surface creates a thin thermal or solutal convective boundary layer along its surface. By conducting a general analysis of a mathematical model describing the shape evolution of such bodies (Pegler & Davies Wykes, J. Fluid Mech., vol. 900, 2020, A35), we reveal new phenomena relating to the emergence of fundamental similarity solutions, asymptotic transitions, tip structure and the conditions for the development of sharp versus blunted tips. A universal regime diagram is developed showing asymptotic transitions between two different classes of similarity solutions. With time, the tip of initially rectangular bodies is found to descend as at early times, but transitions to the considerable faster power of at long times, for example. Surprisingly, the tips of certain shapes, including initially rectangular bodies, sharpen continuously, whilst those of others, including initially conic bodies, blunt for all times. For the former case, the tip curvature grows rapidly as, forming a needle-like shape. More general initial shapes can produce multiple transitions between sharpening and blunting. These results provide foundational understanding of buoyancy-driven fluid sculpting that underlies numerous natural and industrial applications
SS Northland Echo
No full textPhotograph - A view of the steamboat, SS Northland Echo on the Athabasca River. Athabasca, Albert
SS Athabasca River - 02
No full textPhotograph - A view of the SS Athabasca River paddle steamer on the river, Athabasca, Albert
The dynamics of confined extensional flows
No full textI present a theoretical and experimental study of floating viscous fluid films introduced into a channel of finite length, motivated by the flow of glacial ice shelves. The dynamics are characterized by a mixture of viscous extensional stresses, transverse shear stresses and a driving buoyancy force. A theory based on a width-integrated model is developed and investigated using analytical, asymptotic and numerical methods. With fluid introduced at a constant rate, the flow is found to approach a steady state with two possible asymptotic forms depending on the length of the channel. For channel lengths less than half the width, the flow is similar to a purely extensional one-dimensional flow, characterized by concave surface profiles and being insensitive to the position of the channel exit (or calving front). Greater lengths result in a more complex asymptotic structure in which the flow adjusts over a short distance towards a prevailing flow of universal dimensionless form. In complete contrast to the extensional regime, the prevailing flow is controlled by the position of the channel exit. Data from a new laboratory experiment involving particle velocimetry of a floating fluid film compares well with the predicted along-channel velocity. Motivated by glaciological application, the analysis is generalized to power-law rheologies and the results used to classify the flow regimes of a selection of ice shelves. The prediction for the frontal speed is in good agreement with geophysical data, indicating that the universal profile predicted by the theory is common in nature
RIC-HSCT for MF/SS
No full textAdvanced-stage mycosis fungoides and Sezary syndrome (MF/SS) have a poor prognosis. Allogeneic hematopoietic stem cell transplantation (HSCT), particularly using a reduced-intensity conditioning (RIC) regimen, is a promising treatment for advanced-stage MF/SS. We performed RIC-HSCT in nine patients with advanced MF/SS. With a median follow-up period of 954days after HSCT, the estimated 3-year overall survival was 85.7% (95% confidence interval, 33.4-97.9%) with no non-relapse mortality. Five patients relapsed after RIC-HSCT; however, in four patients whose relapse was detected only from the skin, persistent complete response was achieved in one patient, and the disease was manageable in other three patients by the tapering of immunosuppressants and donor lymphocyte infusion, suggesting that graft-versus-lymphoma effect and "down-staging" effect from advanced stage to early stage by HSCT improve the prognosis of advanced-stage MF/SS. These results suggest that RIC-HSCT is an effective treatment for advanced MF/SS
Marine ice sheet dynamics: the impacts of ice-shelf buttressing
No full textMarine ice sheets are continent-scale glacial masses that lie partially submerged in the ocean, as applies to significant regions of Antarctica and Greenland. Such ice sheets have the potential to destabilise under a buoyancy-driven instability mechanism, with considerable implications for future sea level. This paper and its companion present a theoretical analysis of marine ice sheet dynamics under the effect of a potentially dominant control of the buttressing force generated by lateral stresses on the downstream floating component of the ice sheet (the ice shelf). The analysis reveals critical conditions under which ice-shelf buttressing suppresses the buoyancy-driven collapse of an ice sheet and elucidates the implications of lateral stresses on grounding-line control and overall ice-sheet structure. Integrations of a suitably simplified quasi-two-dimensional model are conducted, yielding analytical results that provide a quick assessment of steady-state balances for a given ice-sheet configuration. An analytical balance equation describing the spectrum of marine ice sheet flow regimes spanning zero to strong ice-shelf buttressing is developed. It is determined that the dynamics across this spectrum exhibits markedly different flow regimes and structural characteristics. For sufficient buttressing, the grounding line occurs near to where a lateral-drag controlled section of the ice shelf meets the bedrock, implying an independent control of the grounding line by the ice shelf. The role of basal stresses is relegated to controlling only the thickness of the ice sheet upstream of the grounding line, with no significant control of the grounding line itself. It is further demonstrated that lateral stresses are responsible for inducing additional secondary contacts between the ice shelf and the bedrock downstream of the grounding line, resulting in a rich variety of additional steady states. These inducements generate a further stabilising mechanism that can fully suppress grounding-line retreat and eliminate otherwise irreparable hysteresis effects. The results provide a conceptual framework for numerical and observational interpretation of marine ice sheet dynamics, and clarifies the manner in which ice shelves can control grounding-line positions independently. It is thus indicated that a full resolution of the fine details of the flow of ice shelves and the processes controlling their erosion and disintegration is necessary for the confident forecasting of possible ice-sheet collapse over the course of the next few centuries
Suppression of marine ice sheet instability
No full textA long-standing open question in glaciology concerns the propensity for ice sheets that lie predominantly submerged in the ocean (marine ice sheets) to destabilise under buoyancy. This paper addresses the processes by which a buoyancy-driven mechanism for the retreat and ultimate collapse of such ice sheets – the marine ice sheet instability – is suppressed by lateral stresses acting on its floating component (the ice shelf). The key results are to demonstrate the transition between a mode of stable (easily reversible) retreat along a stable steady-state branch created by ice-shelf buttressing to tipped (almost irreversible) retreat across a critical parametric threshold. The conditions for triggering tipped retreat can be controlled by the calving position and other properties of the ice-shelf profile and can be largely independent of basal stress, in contrast to principles established from studies of unbuttressed grounding-line dynamics. The stability and recovery conditions introduced by lateral stresses are analysed by developing a method of constructing grounding-line stability (bifurcation) diagrams, which provide a rapid assessment of the steady-state positions, their natures and the conditions for secondary grounding, giving clear visualisations of global stabilisation conditions. A further result is to reveal the possibility of a third structural component of a marine ice sheet that lies intermediate to the fully grounded and floating components. The region forms an extended grounding area in which the ice sheet lies very close to flotation, and there is no clearly distinguished grounding line. The formation of this region generates an upsurge in buttressing that provides the most feasible mechanism for reversal of a tipped grounding line. The results of this paper provide conceptual insight into the phenomena controlling the stability of the West Antarctic Ice Sheet, the collapse of which has the potential to dominate future contributions to global sea-level rise
SS Northland Sun at Mirror Landing, AB
No full textPhotograph - The paddle-wheeler, SS Northland Sun, docked at shore in Mirror Landing, Albert
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