The energetics of melting fertile heterogeneities within the depleted mantle

To explore the consequences of mantle heterogeneity for primary melt production, we develop a mathematical model of energy conservation for an upwelling, melting body of recycled oceanic crust embedded in the depleted upper mantle. We consider the end‐member geometric cases of spherical blobs and tabular veins. The model predicts that thermal diffusion into the heterogeneity can cause a factor‐of‐ two increase in the degree of melting for bodies with minimum dimension smaller than ∼1 km, yielding melt fractions between 50 and 80%. The role of diffusion is quantified by an appropriately defined Peclet number, which represents the balance of diffusion‐driven and adiabatic melting. At intermediate Peclet number, we show that melting a heterogeneity can cool the ambient mantle by up to ∼20 K (spherical) or ∼60 K (tabular) within a distance of two times the characteristic size of the body. At small Peclet number, where heterogeneities are expected to be in thermal equilibrium with the ambient mantle, we calculate the energetic effect of pyroxenite melting on the surrounding peridotite; we find that each 5% of recycled oceanic crust diminishes the peridotite degree of melting by 1–2%. Injection of the magma from highly molten bodies of recycled oceanic crust into a melting region of depleted upper mantle may nucleate reactive‐dissolution channels that remain chemically isolated from the surrounding peridotite

Textural equilibrium melt geometries around tetrakaidecahedral grains.

In textural equilibrium, partially molten materials minimize the total surface energy bound up in grain boundaries and grain-melt interfaces. Here, numerical calculations of such textural equilibrium geometries are presented for a space-filling tessellation of grains with a tetrakaidecahedral (truncated octahedral) unit cell. Two parameters determine the nature of the geometries: the porosity and the dihedral angle. A variety of distinct melt topologies occur for different combinations of these two parameters, and the boundaries between different topologies have been determined. For small dihedral angles, wetting of grain boundaries occurs once the porosity has exceeded 11%. An exhaustive account is given of the main properties of the geometries: their energy, pressure, mean curvature, contiguity and areas on cross sections and faces. Their effective permeabilities have been calculated, and demonstrate a transition between a quadratic variation with porosity at low porosities to a cubic variation at high porosities

Alien Registration- Rudge, John T. (Medway, Penobscot County)

https://digitalmaine.com/alien_docs/8084/thumbnail.jp

Psychotropes: Models of Authorship, Psychopathology, and Molecular Politics in Aldous Huxley and Philip K. Dick

Among the so-called “anti-psychiatrists” of the 1960s and ‘70s, it was Félix Guattari who first identified that psychiatry had undergone a “molecular revolution.” It was in fact in a book titled Molecular Revolutions, published in 1984, that Guattari proposed that psychotherapy had become, in the de¬cades following the Second World War, far less personal and increasingly alienating. The newly “molecular” practices of psychiatry, Guattari mourned, had served only to fundamentally distance both patients and practitioners from their own minds; they had largely restricted our access, he suggested, to human subjectivity and consciousness. This thesis resumes Guattari’s work on the “molecular” model of the subject. Extending on Guattari’s various “schizoanalytic metamodels” of hu¬man consciousness and ontology, it rigorously meditates on a simple ques¬tion: Should we now accept the likely finding that there is no neat, singular, reductive, utilitarian, or unifying “model” for thinking about the human subject, and more specifically the human “author”? Part 1 of this thesis carefully examines a range of psychoanalytic, psychi¬atric, philosophical, and biomedical models of the human. It studies and re¬formulates each of them in turn and, all the while, returns to a fundamental position: that no single model, nor combination of them, will suffice. What part 1 seeks to demonstrate, then, is that envisioning these models as differ¬ent attempts to “know” the human is fruitless—a futile game. Instead, these models should be understood in much the same way as literary critics treat literary commonplaces or topoi; they are akin, I argue, to what Deleuze and Guattari called “images of thought.” In my terminology, they are “psycho¬tropes”: images with their own particular symbolic and mythical functions. Having thus developed a range of theoretical footholds in part 1, part 2 of the thesis—beginning in chapter 4—will put into practice the work of this first part. It will do so by examining various representations of authorship by two authors in particular: Aldous Huxley and Philip K. Dick. This part will thus demonstrate how these author figures function as “psychoactive scriv¬eners”: they are fictionalising philosophers who both produce and quarrel with an array of paradigmatic psychotropes, disputing those of others and inventing their own to substitute for them. More than this, however, the second part offers a range of detailed and original readings of these authors’s psychobiographies; it argues that even individual authors such as Huxley and Dick can be seen as “psychotropic.” It offers, that is, a series of broad-ranging and speculative explanations for the ideas and themes that appear in their works—explanations rooted in the theoretical work of the first part. Finally, this thesis concludes by reaffirming the importance of these authors’s narcoliteratures—both for present-day and future literary studies, and beyond. For while Huxley and Dick allow us to countenance afresh the range of failures in the history and philosophy of science, they also prom¬ise to instruct us—and instruct science—about the ways in which we might move beyond our received mimetic models of the human

A crystallographic approach to symmetry-breaking in fluid layers

Symmetry-breaking bifurcations, where a flow state with a certain symmetry undergoes a transition to state with a different symmetry, are ubiquitous in fluid mechanics. Much can be understood about the nature of these transitions from symmetry alone, using the theory of groups and their representations. Here we show how the extensive databases on groups in crystallography can be exploited to yield insights into fluid-dynamical problems. In particular, we demonstrate the application of the crystallographic layer groups to problems in fluid layers, using thermal convection as an example. Crystallographic notation provides a concise and unambiguous description of the symmetries involved, and we advocate its broader use by the fluid dynamics community.Comment: 27 pages, 9 figures, 3 supplementary table

Rate of Melt Ascent beneath Iceland from the Magmatic Response to Deglaciation

Observations of the time lag between the last deglaciation and a surge in volcanic activity in Iceland constrain the average melt ascent velocity to be $\geq50$ $\mathrm{m/yr}$. Although existing theoretical work has explained why the surge in eruption rates increased $5$-$30$ fold from the steady-state rates during the last deglaciation, they cannot account for large variations of Rare Earth Element (REE) concentrations in the Icelandic lavas. Lavas erupted during the last deglaciation are depleted in REEs by up to $70\%$; whereas, existing models, which assume instantaneous melt transport, can only produce at most $20\%$ depletion. Here, we develop a numerical model with finite melt ascent velocity and show that the variations of REEs are strongly dependent on the melt ascent velocity. When the average melt ascent velocity is $100$ $\mathrm{m/yr}$, the variation of $\mathrm{La}$ calculated by our model is comparable to that of the observations. In contrast, when the melt ascent velocity is $1,000$ $\mathrm{m/yr}$ or above, the model variation of $\mathrm{La}$ becomes significantly lower than observed, which explains why previous models with instantaneous melt transport did not reproduce the large variations. We provide the first model that takes account of the diachronous response of volcanism to deglaciation. We show by comparing our model calculations of the relative volumes of different eruption types (subglacial, finiglacial and postglacial) and the timing of the bursts in volcanic eruptions with the observations across different volcanic zones that the Icelandic average melt ascent velocity during the last deglaciation is likely to be $\sim100$ $\mathrm{m/yr}$

The most problematic symptoms of prion disease - an analysis of carer experiences

Objectives: Prion diseases are rare dementias that most commonly occur sporadically, but can be inherited or acquired, and for which there is no cure. We sought to understand which prion disease symptoms are most problematic for carers, to inform the development of outcome measures. Design: Self-completed questionnaire with follow-up of a subset of participants by structured interview. Setting: A nested study in the UK National Prion Monitoring Cohort, a longitudinal observational study. Participants and measurements: 71 carers, of people with different prion diseases with a wide range of disease severity, identified 236 of their four most problematic symptoms by questionnaire which were grouped into ten domains. Structured interviews were then done to qualitatively explore these experiences. Eleven family carers of people with prion disease were selected, including those representative of a range of demographics and disease subtypes and those who cared for people with prion disease, living or recently deceased. Interviews were transcribed and formally studied. Results: The six most problematic symptom domains were: mobility and coordination; mood and behavior; personal care and continence; eating and swallowing; communication; and cognition and memory. The prevalence of these symptoms varied significantly by disease stage and type. A formal analysis of structured interviews to explore these domains is reported. Conclusions: We make suggestions about how healthcare professionals can focus their support for people with prion disease. Clinical trials that aim to generate evidence regarding therapies that might confer meaningful benefits to carers should consider including outcome measures that monitor the symptomatic domains we have identified as problematic

A mechanism for mode selection in melt band instabilities

The deformation of partially molten mantle in tectonic environments can lead to exotic structures, which potentially affect both melt and plate-boundary focussing. Examples of such structures are found in laboratory deformation experiments on partially molten rocks. Simple-shear and torsion experiments demonstrate the formation of concentrated melt bands at angles of around 20° to the shear plane. The melt bands form in the experiments with widths of a few to tens of microns, and a band spacing roughly an order of magnitude larger. Existing compaction theories, however, cannot predict this band width structure, let alone any mode selection, since they infer the fastest growing instability to occur for wavelengths or bands of vanishing width. Here, we propose that surface tension in the mixture, especially on a diffuse interface in the limit of sharp melt-fraction gradients, can mitigate the instability at vanishing wavelength and thus permit mode selection for finite-width bands. Indeed, the expected weak capillary forces on the diffuse interface lead to predicted mode selection at the melt-band widths observed in the experiments

Melt-band instabilities with two-phase damage

Deformation experiments on partially molten rocks in simple shear form melt bands at 20° to the shear plane instead of at the expected 45° principal compressive stress direction. These melt bands may play an important role in melt focusing in mid-ocean ridges. Such shallow bands are known to form for two-phase media under shear if strongly non-Newtonian power-law creep is employed for the solid phase, or anisotropy imposed. However laboratory experiments show that shallow bands occur regardless of creep mechanism, even in diffusion creep, which is nominally Newtonian. Here we propose that a couple of forms of two-phase damage allow for shallow melt bands even in diffusion creep