Magma flow through elastic-walled dikes

A convection–diffusion model for the averaged flow of a viscous, incompressible magma through an elastic medium is considered. The magma flows through a dike from a magma reservoir to the Earth’s surface; only changes in dike width and velocity over large vertical length scales relative to the characteristic dike width are considered. The model emerges when nonlinear inertia terms in the momentum equation are neglected in a viscous, low-speed approximation of a magma flow model coupled to the elastic response of the rock.\ud Stationary- and traveling-wave solutions are presented in which a Dirichlet condition is used at the magma chamber; and either a (i) free-boundary condition, (ii) Dirichlet condition, or (iii) choked-flow condition is used at the moving free or fixed-top boundary. A choked-flow boundary condition, generally used in the coupled elastic wave and magma flow model, is also used in the convection–diffusion model. The validity of this choked-flow condition is illustrated by comparing stationary flow solutions of the convection–diffusion and coupled elastic wave and magma flow model for parameter values estimated for the Tolbachik volcano region in Kamchatka, Russia. These free- and fixed-boundary solutions are subsequently explored in a conservative, local discontinuous Galerkin finite-element discretization. This method is advantageous for the accurate implementation of the choked flow and free-boundary conditions. It uses a mixed Eulerian–Lagrangian finite element with special infinite curvature basis function near the free boundary and ensures positivity of the mean aperture subject to a time-step restriction. We illustrate the model further by simulating magma flow through host rock of variable density, and magma flow that is quasi-periodic due to the growth and collapse of a lava dome

Instrumentation to measure mars' atmospheric composition, using a soft-landed probe

Instrumentation for analysis of Mars atmosphere after soft landin

Abductive reasoning in neural-symbolic learning systems

Abduction is or subsumes a process of inference. It entertains possible hypotheses and it chooses hypotheses for further scrutiny. There is a large literature on various aspects of non-symbolic, subconscious abduction. There is also a very active research community working on the symbolic (logical) characterisation of abduction, which typically treats it as a form of hypothetico-deductive reasoning. In this paper we start to bridge the gap between the symbolic and sub-symbolic approaches to abduction. We are interested in benefiting from developments made by each community. In particular, we are interested in the ability of non-symbolic systems (neural networks) to learn from experience using efficient algorithms and to perform massively parallel computations of alternative abductive explanations. At the same time, we would like to benefit from the rigour and semantic clarity of symbolic logic. We present two approaches to dealing with abduction in neural networks. One of them uses Connectionist Modal Logic and a translation of Horn clauses into modal clauses to come up with a neural network ensemble that computes abductive explanations in a top-down fashion. The other combines neural-symbolic systems and abductive logic programming and proposes a neural architecture which performs a more systematic, bottom-up computation of alternative abductive explanations. Both approaches employ standard neural network architectures which are already known to be highly effective in practical learning applications. Differently from previous work in the area, our aim is to promote the integration of reasoning and learning in a way that the neural network provides the machinery for cognitive computation, inductive learning and hypothetical reasoning, while logic provides the rigour and explanation capability to the systems, facilitating the interaction with the outside world. Although it is left as future work to determine whether the structure of one of the proposed approaches is more amenable to learning than the other, we hope to have contributed to the development of the area by approaching it from the perspective of symbolic and sub-symbolic integration

Decompression of magma into repository tunnels

It is nontrivial to find and design safe repository sites for nuclear waste. It appears common sense to drill tunnels as repository sites in a mountain in remote and relatively dry regions. However, erosion of the waste canisters by naturally abundant chemicals in the mountains water cycle remains a problem. Other problems may be caused by geophysical phenomenon like volcanic eruptions. Yucca Mountain is a location which has been proposed as storage site. We investigate the consequences of evolving magma flows in the repository systems, because the probability of magmatic activity at Yucca Mountain is too high to neglect an investigation of volcanic effects

The decompression of basaltic magma into a sub-surface repository

We examine the ascent of volatile-rich basaltic magma through a vertical dike that intersects a horizontal tunnel of comparable cross-sectional area to the dike and located 300 $m$ below the surface and initially filled with air at atmospheric pressure. This process is a simplified representation of some aspects of the possible interaction of a basaltic fissure eruption with a man-made tunnel, as part of a risk assessment for the proposed high level waste repository at Yucca Mountain, Nevada, U.S.A. We study the decompression and flow that develops following breakthrough into the tunnel using a one-dimensional model averaged over the prescribed dike and tunnel geometry. The main volatile phase in the basaltic magma is water and this is exsolved from the melt as the mixture decompresses. We neglect any motion of the vapor bubbles relative to the mixture and use a parameterization of the bulk viscous resistance. The model predicts that for 2 $wt$% water, the magma-gas mixture decompresses rapidly into the tunnel, and generates a pressure jump in the air, which travels at a speed of order 500 $m/s$. Two end-members references simulations are investigated: one in which the dike-drift nozzle (about $20\,m^2$) opens instantly and is relatively smooth, and another one in which the dike-drift nozzle is opened from a small area ($< 1\,m^2$) to its steady opening (of about $20\,m^2$) in a minute. In either case the tunnel is eventually filled with high-pressure magma at about its initial dike-tip pressure within a few minutes. In the faster case the pressure jump is reflected and amplified by a factor of 20 - 45 thereby producing a high pressure region at the end of the tunnel away from the dike. In the slower case, the tunnel fills more gradually in about two minutes. Further flow behavior is investigated in a parameter study. The results suggest that this pressurization of the tunnel could lead to rock fracture and magma breakthrough to the Earth's surface

Long-term survival for a cohort of adults with cerebral palsy

The aim of this study was to investigate long-term survival and examine causes of death in adult patients with cerebral palsy (CP). A 1940–1950 birth cohort based on paediatric case referral allows for long-term survival follow-up. Survival is analyzed by birth characteristics and severity of disability from age 20 years (and age 2y for a subset of the data). Survival outcome compared with that expected in the general population based on English life tables. The main cohort consisted of 341 individuals, with 193 males and 148 females. Conditional on surviving to age 20 years, almost 85% of the cohort survived to age 50 years (a comparable estimate for the general population is 96%). Very few deaths were attributed to CP for those people dying over 20 years of age. Females survived better than males. However, females faced a greater increase in risk relative to the general population than did males. We conclude that survival outlook is good though lower than in the general population. The relative risk of death compared with the UK population decreases with age, although it shows some indication of rising again after age 50 years. Many more deaths were caused by diseases of the respiratory system among those dying in their 20s and 30s than would be expected in the general population. Many fewer deaths than expected in this age group are caused by injuries and accidents. For those people who die in their 40s and 50s, an increase in deaths due to diseases of the circulatory system and neoplasms is observed. More deaths than expected in this age group are due to diseases of the nervous system