Ice-melt rates in liquid-filled cavities during explosive subglacial eruptions

Subglacial eruptions are often associated with rapid penetration of overlying ice and release of large flow rates of water as jökulhlaups. Observations of recent subglacial eruptions indicate rapid syn-eruptive ice melting within liquid-filled subglacial cavities, but quantitative descriptions of possible heat transfer processes need to be developed. Calculations of heat flux from the ice cavity fluid to the melting ice surface indicate that up to 0.6 MW m−2 may be obtained for fluids undergoing single-phase free convection, similar to minimum estimates of heat flux inferred from observations of recent eruptions. Our model of boiling two-phase free convection in subglacial cavities indicates that much greater heat fluxes, in the range 3–5 MW m−2, can be obtained in the vent region of the cavity and may be increased further by momentum transfer from the eruption jet. Rapid magma-water heat transfer from fragmented magma is needed to sustain these heat fluxes. Similar heat fluxes are anticipated for forced convection of subcooled cavity water induced by momentum transfer from an eruption jet. These heat fluxes approach those required to explain jökulhlaup flow rates and rapid ice penetration rates by melting in some, but not all recent eruptions

Automorphisms of Partially Commutative Groups II: Combinatorial Subgroups

We define several "standard" subgroups of the automorphism group Aut(G) of a partially commutative (right-angled Artin) group and use these standard subgroups to describe decompositions of Aut(G). If C is the commutation graph of G, we show how Aut(G) decomposes in terms of the connected components of C: obtaining a particularly clear decomposition theorem in the special case where C has no isolated vertices. If C has no vertices of a type we call dominated then we give a semi-direct decompostion of Aut(G) into a subgroup of locally conjugating automorphisms by the subgroup stabilising a certain lattice of "admissible subsets" of the vertices of C. We then characterise those graphs for which Aut(G) is a product (not necessarily semi-direct) of two such subgroups.Comment: 7 figures, 63 pages. Notation and definitions clarified and typos corrected. 2 new figures added. Appendix containing details of presentation and proof of a theorem adde

Ice-melt rates during volcanic eruptions within water-drained, low pressure subglacial cavities

Subglacial volcanism generates proximal and distal hazards including large-scale flooding and increased levels of explosivity. Direct observation of subglacial volcanic processes is infeasible; therefore, we model heat transfer mechanisms during subglacial eruptions under conditions where cavities have become depressurized by connection to the atmosphere.We consider basaltic eruptions in a water-drained, low-pressure subglacial cavity, including the case when an eruption jet develops. Such drained cavities may develop on sloping terrain, where ice may be relatively shallow and where gravity drainage of meltwater will be promoted. We quantify, for the first time, the heat fluxes to the ice cavity surface that result from steam condensation during free convection at atmospheric pressure and from direct and indirect radiative heat transfer from an eruption jet. Our calculations indicate that the direct radiative heat flux from a lava fountain (a “dry” end-member eruption jet) to ice is c. 25 kW m-2 and is a minor component. The dominant heat transfer mechanism involves free convection of steam within the cavity; we estimate the resulting condensation heat flux to be c. 250 kW m-2. Absorption of radiation froma lava fountain by steamenhances convection, but the increase in condensing heat flux is modest at c. 25 kW m-2. Overall, heat fluxes to the ice cavity surface are likely to be no greater than c. 300 kW m-2. These are comparable with heat fluxes obtained by single phase convection of water in a subglacial cavity but much less than those obtained by two-phase convection

Ice-melt rates by steam condensation during explosive subglacial eruptions

Subglacial volcanism melts cavities in the overlying ice. These cavities may be flooded with meltwater or they may be fully or partially drained. We quantify, for the first time, heat transfer rates by condensation of steam on the walls and roof of a fully or partially drained subglacial eruption cavity. Our calculations indicate that heat fluxes of up to 1 MW m−2 may be obtained when the bulk vapor in the cavity is in free convection. This is considerably smaller than heat fluxes inferred from ice penetration rates in recent subglacial eruptions. Forcing of the convection by momentum transfer from an eruption jet may allow heat fluxes of up to 2 MW m−2, consistent with values inferred for the Gjálp 1996 subglacial eruption. Vapor-dominated cavities in which vapor-liquid equilibrium is maintained have thermal dynamic responses that are an order of magnitude faster than the equivalent flooded cavities

Mode boundaries of automated metro and semi-rapid rail in urban transit

The research question that we pose is to what extent, and under what circumstances, full automation in metro lines defines transit mode boundaries with respect to semirapid transit. The modeling approach that we follow is based on micro-economic appraisal. Automation, beside changing the investment and operation and maintenance cost profiles of metro lines, can improve some aspects of the user experience. The low marginal cost of frequency possible with automated metro may unlock both users' benefits via reduced waiting times and crowding, and operator's savings via shorter trains and smaller platforms and stations. We show how structurally different under several configurations are the user's travel time components. In particular, we highlight the critical role that different demand and alignment patterns play in the mode comparison

Cancer risk in socially marginalised women: An exploratory study

Background: Cancer is a leading cause of premature death in women worldwide, and is associated with socio-economic disadvantage. Yet many interventions designed to reduce risk and improve health fail to reach the most marginalised with the greatest needs. Our study focused on socially marginalised women at two women's centres that provide support and training to women in the judicial system or who have experienced domestic abuse. Methods: This qualitative study was framed within a sociological rather than behavioural perspective involving thirty participants in individual interviews and focus groups. It sought to understand perceptions of, and vulnerability to, cancer; decision making (including screening); cancer symptom awareness and views on health promoting activities within the context of the women's social circumstances. Findings: Women's experiences of social adversity profoundly shaped their practices, aspirations and attitudes towards risk, health and healthcare. We found that behaviours, such as unhealthy eating and smoking need to be understood in the context of inherently risky lives. They were a coping mechanism whilst living in extreme adverse circumstances, navigating complex everyday lives and structural failings. Long term experiences of neglect, harm and violence, often by people they should be able to trust, led to low self-esteem and influenced their perceptions of risk and self-care. This was reinforced by negative experiences of navigating state services and a lack of control and agency over their own lives. Conclusion: Women in this study were at high risk of cancer, but it would be better to understand these risk factors as markers of distress and duress. Without appreciating the wider determinants of health and systemic disadvantage of marginalised groups, and addressing these with a structural rather than an individual response, we risk increasing cancer inequities by failing those who are in the greatest nee

Applying an Attentional Set to Perceived and Remembered Features

Previous research has examined our ability to attend selectively to particular features of perceptual objects, as well as our ability to switch from attending to one type of feature to another. This is usually done in the context of anticipatory attentional-set control, comparing the neural mechanisms involved as participants prepare to attend to the same stimulus feature as on the previous trial (“task-stay” trials) with those required as participants prepare to attend to a different stimulus feature to that previously attended (“task-switch” trials). We wanted to establish how participants maintain or switch attentional set retrospectively, as they attend to features of objects held in visual short-term memory (VSTM). We found that switching, relative to maintaining attentional set retrospectively, was associated with a performance cost, which can be reduced over time. This control process was mirrored by a large parietal and frontal amplitude difference in the event-related brain potentials (ERPs) and significant differences in global field power (GFP) between switch and stay trials. However, when taking into account the switch/stay GFP differences, thereby controlling for this difference in amplitude, we could not distinguish these trial types topographically. By contrast, we found clear topographic differences between preparing an anticipatory feature-based attentional set versus applying it retrospectively within VSTM. These complementary topographical and amplitude analyses suggested that anticipatory and retrospective set control recruited a qualitatively different configuration of underlying neural generators. In contrast, switch/stay differences were largely quantitative, with them differing primarily in terms of amplitude rather than topography

Supporting participatory livestock feed improvement using the Feed Assessment Tool (FEAST)

Livestock production is central to the livelihoods of smallholder farmers in low- and middle-income countries, but livestock are often poorly fed which limits their potential for reducing poverty. Efforts to improve livestock nutrition are often driven by supply-push thinking and fail to engage meaningfully with farmers and the realities they face. The Feed Assessment Tool (FEAST) was developed as a way of involving farmers more closely in decision making on livestock feed improvement. FEAST is a participatory tool which uses focus group discussions and individual farmer interviews to develop a broad overview of the livestock farming system. FEAST has been applied in many countries in the last 10 years. Examples of intensive use come from the Accelerated Value Chain Development Project in Kenya and the Rwanda Dairy Development Project in Rwanda. In both cases the tool was used to inform feed options with strong input from farmers. Although the primary purpose of FEAST is to support improved feed strategies at farm level, the data collected through the FEAST app and published in FEAST reports are a rich information resource that can be useful for developing broader system-level understanding of livestock feed issues. FEAST data can be uploaded into a global data repository where they are available for researchers. These data are also used to generate visualizations of key feed metrics further extending the use of secondary data. FEAST is an example of a participatory tool that moves decision making in the direction of farmers, while providing insights to researchers working across farming systems. Its widespread use across many countries is an indication that it fills a gap in in the livestock feed development space. Its novelty lies in bridging the knowledge gap (both ways) between livestock researchers and small-scale livestock keepers