Rethinking the Land: An Exhibition of Ulster Maps

The author curates a touring exhibition of Northern Ireland cartography, called Mapping Alternative Ulster. The project emerged from a dissatisfaction with how Northern Ireland is represented in maps, and one example is given. To counter them, he sought independent cartographers making original maps. The curator discusses the criteria he applied when selecting work for the show. He wanted maps with politics, although not the region’s traditional sectarian politics. All the selected maps constitute arguments, critiquing problems in the lived environment or drawing attention to valuable things that may be at risk. The latter sections of the article discuss five of the contributors and looks at their work in detail. In the conclusion, the impact of the exhibition is assessed by examining visitor comments. The paper is illustrated.     

Coupled analysis of floating production systems

Fully coupled global analysis of Floating Production Systems, including the vessel, the mooring system and the riser system is described. Design of the system can be a daunting task, involving more than 1000 load cases for global analysis. The primary driver for the mooring system and for the riser system is motion of the vessel. Vessel motions are driven by environmental forces, but are restrained by forces from the mooring and riser systems. Numerical models and procedures that provide accurate and efficient global modeling of the Floating Production System are presented. Both Time Domain and Frequency Domain procedures are included. The accuracy and efficiency of the procedures are illustrated in an example: a large semi with 16 mooring lines and 20 risers. The procedures provide the accuracy and efficiency for use of fully coupled analysis in design of Floating Production Systems from concept selection to final design, installation and operation.     

The effects on water mass formation of surface mixed layer timedependence and entrainment fluxes

An air-sea buoyancy flux out of the ocean between the surface outcroppings of different isopycnals must be balanced by a convergence of advective and diffusive fluxes of buoyancy across those isopycnals (Walin, 1982; Tziperman, 1986; Garrett et al., 1995). For steady conditions, the diapycnal diffusive flux due to vertical mixing in the surface mixed layer is very small, so that the advective buoyancy flux dominates (Speer, 1993; Garrett et al., 1995). The associated advective buoyancy flux can then be used to estimate the volume flux of water out of the base of the surface mixed layer. The resulting thermodynamic algorithm provides a valuable estimate of water mass formation in the ocean.In contrast, for the time-dependent real ocean with horizontal and vertical gradients of the horizontal buoyancy gradient, diurnal and seasonal mixed layer deepening and entrainment in the presence of a buoyancy jump at the base of the mixed layer contributes to the annual volume flux out of the base of the deepest (wintertime) mixed layer. The mismatch between the predictions of the ideal algorithm and measured rates of water mass formation (Speer, 1997) may thus be partly due to mixed layer processes rather than diapycnal mixing in the thermocline.     

Sensitivity of tidal marshes as recorders of major megathrust earthquakes: constraints from the 25 December 2016 Mw 7.6 Chiloé earthquake,Chile

We present evidence of land-level change resulting from the 2016 M_w 7.6 Chiloé earthquake from tidal wetlands along the southern coastline of Isla de Chiloé, Chile, to test criteria for the detection of low-level, <0.1 m, coseismic land-level change. In order to record coseismic land-level change in tidal wetland sediments, both the creation and preservation thresholds must be exceeded. High-resolution diatom analyses of sediment blocks at two tidal marshes reveal that the 2016 earthquake exceeded the creation threshold and a statistically significant change in diatom assemblage is recorded. In contrast, the preservation threshold was not exceeded and the record of coseismic land-level motion is not preserved at any location visited. After nine months, interseismic and coseismic changes are statistically indistinguishable. The most sensitive part of the tidal wetland is not consistent between research locations, possibly as a result of changes in sedimentation after the earthquake. We compare records of change from great earthquakes in Alaska with the record from the Chiloé earthquake to explore the detection limit. We propose that coastal palaeoseismological records are highly likely to underestimate the frequency of major (M_w 7–8) earthquakes, with important implications for recurrence intervals and assessment of future seismic hazards.     

On the initial streakness of a dispersing tracer in two- and three-dimensional turbulence

If a spot of tracer is released into a turbulent flow, the peak concentration at some subsequent time will initially be much greater than that implied by a solution for the ensemble average concentration at fixed points. For two-dimensional turbulence three areas may be defined: (1) an area A_d related to the ensemble average concentration field; (2) an area A_p defined in terms of the relative dispersion of particles seeded into the patch after a short initial diffusion time; and (3) the area A_t occupied by tracer. It is argued that A_d grows linearly with time, whereas A_p and A_t grow exponentially; A_p faster than A_t. Thus, the concentration field is significantly streaky, even within the particle domain, until A_t becomes comparable with A_d. The time taken for this to occur is estimated; after this time, fluctuations about the ensemble average concentration field should not be greater than those given by a simple mixing length argument. In three-dimensional turbulence the volume V_t of the tracer domain grows much more rapidly than the volume V_p of the particle domain if the merging of streaks is ignored. However, V_t cannot be greater than V_p so streaks must merge and V_p can be used to provide a rough estimate of peak concentration, or concentration variance.     

PKS 1117+146: a new large compact symmetric object

We present 23-GHz MERLIN observations of the high-luminosity radio galaxy PKS 1117+146. The radio image obtained from these data shows, for the first time, a central weak component (designated C) that we identify as the core of the radio galaxy, and two outer components (designated N and S) which are the hotspots of the extended lobes observed at lower frequencies. Extended emission in components C and S is an indication of a possible jet connecting the core to the strongest component. The overall optical and radio properties of PKS 1117+146 are consistent with the source being classified as a compact symmetric object (CSO). We discuss this hypothesis, which would make PKS 1117+146 the largest CSO known so far.     

Optimal composite sample size selection, applications in geochemistry and remote sensing

Nearly all the data in exploration geochemistry and remote sensing represent composites. However, composites may arise implicitly or be created explicitly. Bearing in mind that a common exploration task is the classification of data as being above or below some predetermined threshold the size of the composite may be critical to the recognition of a relatively rare, subcomposite, anomalous event. Two approaches are developed, based on statistical, and cost-analytical considerations. The statistical model allows for spatial correlation in the data, of importance when sampling is undertaken continuously along a drill core or flight line. Tables are presented for optimal composite sample size selection based on both models. The procedure is illustrated by an example taken from a drilling program. In general, the cost-analytical model leads to smaller composites than the statistical model. When spatial independence may be assumed the cost-optimal composite sizes are almost always smaller than those suggested by the statistical approach.     

An analytical simulation of the geosynchronous plasma environment

A procedure for analytically simulating the parameters necessary to characterize the geosynchronous plasma is developed in terms of the daily A_p index and local time. Although based on a limited set of ATS-5 data, the simulation adequately models the simultaneous variations in the warm plasma (50 eV–50 keV) electron and ion populations during injection events. Developed primarily to estimate the varying potentials expected on a shadowed, electrically isolated surface, the simulation can also be employed in a variety of cases where knowledge of the general characteristics of the geosynchronous plasma is necessary.     

Magnesium in continental runoff

A mass balance for Mg in continental runoff has been constructed. The sources of runoff Mg in this model are cyclic salts, carbonate rock and silicate rock weathering. The calculations indicate that the Mg concentration reported for average continental runoff is anomalously high. The anomaly may be due to recent disturbances in the weathering regimes of calcite, dolomite and silicates, or to unreliable Mg concentrations reported in older analyses.