Using GIS to Model Incidence, Prevalence and Spread of Non-legal Drug Use

Current methods for estimating the incidence and prevalence of non‐legal drug use tend to be retrospective and are not capable of forecasting spatial characteristics. This paper details the development of a GIS model for forecasting and displaying spatio‐temporal trends in non‐legal drug use. It builds upon a current model that estimates levels of drug use, using GIS to develop and visualise the spatial dimension and to predict levels of use for unknown locations using radial basis functions with a thin spline interpolator. The model is calibrated against known data for the onset and spread of heroin use. Results of validation and cross validation of the interpolated surfaces give some confidence to the accuracy of the method. It provides a first stage in a process to develop more complex models that might be used to examine the introduction of new drug use practices, socio‐economic characteristics of different drug use habits, harm reduction measures or to further examine the role of space in the spread of drug use.     

Volcanic features of the North Rockall Trough: application of visualisation techniques on 3D seismic reflection data

Understanding the volcanic processes operating during continental break-up is hampered by the subsequent burial of the majority of the volcanic pile beneath thick sedimentary sequences currently located in bathymetrically deep offshore regions. Although portions of these volcanic systems are currently exposed on land, a full understanding of the volcanic structure, the eruptive styles and their evolution is not possible as these localities have been partially eroded. Furthermore, as the onshore exposure represents a volumetrically minor part of the entire system, the documented eruptive styles may not be representative. The increasing availability of 3D seismic reflection data has the potential to significantly enhance our understanding of break-up related volcanism, as it allows direct access to detailed information from the buried volcanic succession. However, conventional seismic interpretation methodologies cannot determine lava flow morphologies, and as a result, eruptive styles and their evolution are still largely based on extrapolation from the accessible onshore outcrop data. New 3D seismic volume visualisation techniques allow the buried basalt morphologies to be examined for the first time in a manner similar to outcrop, aerial photographic or satellite-based observations. Applying this new approach for 3D seismic data to the North Rockall Trough, U.K. Atlantic margin, demonstrates that a range of volcanic features indicative of eruptive style can be determined. The data reveal a complex terrain containing lava flows originating from discrete volcanic centres, contemporaneous normal faults, linear fissures a few kilometres long, radial fissures and inflation ridges. Lava flow morphologies that are indicative of tube-fed inflated sheetflows, intracanyon flows and elongate subaerial flows that enter water downslope to produce a large hyaloclastite delta are observed.Electronic Supplementary Material Supplementary material is available in the online version of this article at .Editorial responsibility: J. Stix     

Late Pleistocene and Holocene depositional systems and the palaeogeography of the Dogger Bank, North Sea

3D seismic data from the Dogger Bank, North Sea, allow the mapping of Late Pleistocene and Holocene depositional systems in unprecedented detail. The data demonstrate that glacial processes resulted in the development of incised tunnel valley systems during the Weichselian and that these were subsequently modified by fluvial processes in a pro-glacial setting. Subsequently, the Dogger Bank formed an emergent plain during the Holocene with a complex meandering river system, associated tributary or distributary channels and lakes, dominating the region. Prior to the sea level rising sufficiently to submerge the Dogger Bank around 7500 yr ago, the meandering river system was replaced by a dendritic channel network of potential fluvial, estuarine or intertidal origin. As the Holocene depositional features bear no systematic relationship to the bathymetry this study demonstrates that previously published bathymetry-based models for the Holocene palaeogeographic development of the North Sea require modification.     

A Comparison of the Sequential Gaussian and Markov-Bayes Simulation Methods for Small Samples

We compared the performance of sequential Gaussian simulation (sGs) and Markov-Bayes simulation (MBs) using relatively small samples taken from synthetic datasets. A moderate correlation (approximately r = 0.70) existed between a continuous primary variable and a continuous secondary variable. Given the small sample sizes, our objective was to determine whether MBs, with its ability to incorporate the secondary information, would prove superior to SgS. A split-split-plot computer experiment was conducted to compare the two simulation methods over a variety of primary and secondary sample sizes as well as spatial correlations. Using average mean square prediction error as a measure of local performance, sGs and MBs were roughly equivalent for random fields with short ranges (2 m). As range increased (15 m) the average mean square prediction error for sGs was less than or equal to that for MBs, even when number of noncollocated secondary observations was twice the number of collocated observations. Median variance within nonoverlapping subregions was used as a measure of the local heterogeneity or surface texture of the image. In most situations sGs images more faithfully reflected the true local heterogeneity, while MBs was more erratic, sometimes oversmoothing and sometimes undersmoothing.     

Groundwater recharge in the Victoria Nile basin of east Africa: support for the soil moisture balance approach using stable isotope tracers and flow modelling

Across equatorial Africa, increasing demand for groundwater has raised concerns about resource sustainability and has highlighted the need for reliable estimates of groundwater recharge. Recharge investigations in this environment are typically inhibited by a shortage of good quality meteorological and hydrogeological records. Moreover, when recharge studies are attempted they tend to rely on a single technique and frequently lack corroborating evidence to substantiate recharge predictions. In recent studies undertaken in the Aroca catchment of the Victoria Nile basin in central Uganda, the timing and magnitude of recharge determined by a soil moisture balance approach are supported by stable isotope data and groundwater flow modelling. The soil moisture balance study reveals that recharge averages in the order of 200 mm year⁻¹ and is more dependent on the number of heavy (more than 10 turn day⁻¹) rainfall events than the total annual volume of rainfall. Stable isotope data suggest independently that recharge occurs during the heaviest rains of the monsoons, and further establish that recharge stems entirely from the direct infiltration of rainfall, an assumption implicit in the soil moisture balance approach. Deforestation over the last 30 years is shown to have more than doubled the recharge estimate. Aquifer flow modelling supports the recharge estimates but demonstrates that the vast majority (over 99%) of recharging waters must be transmitted by the aquifer in the regolith rather the underlying bedrock fractures which have traditionally been developed for rural water supplies.     

Evidence for a poleward meridional flow on the sun

We define for observational study two subsets of all polar zone filaments, which we call polemost filaments and polar filament bands. The behavior of the mean latitude of both the polemost filaments and the polar filament bands is examined and compared with the evolution of the polar magnetic field over an activity cycle as recently distilled by Howard and LaBonte (1981) from the past 13 years of Mt. Wilson full-disk magnetograms. The magnetic data reveal that the polar magnetic fields are built up and maintained by the episodic arrival of discrete f-polarity regions that originate in active region latitudes and subsequently drift to the poles. After leaving the active-region latitudes, these unipolar f-polarity regions do not spread equatorward even though there is less net flux equatorward; this indicates that the f-polarity regions are carried poleward by a meridional flow, rather than by diffusion. The polar zone filaments are an independent tracer which confirms both the episodic polar field formation and the meridional flow. We find:

1. The mean latitude of the polemost filaments tracks the boundary of the polar field cap and undergoes an equatorward dip during each arrival of additional polar field.
2. Polar filament bands track the boundary latitudes of the unipolar regions, drifting poleward with the regions at about 10 m s^-1.
3. The Mt. Wilson magnetic data, combined with a simple model calculation, show that the filament drift expected from diffusion alone would be slower than observed, and in some cases would be equatorward rather than poleward.
4. The observation that filaments drift poleward along with the magnetic regions shows that fields of both polarities are carried by the meridional flow, as would be expected, rather than only the f-polarity flux which dominates the strength. This leads to the prediction that in the mid-latitudes during intervals between the passage of f-polarity regions, both polarities are present in nearly equal amounts. This prediction is confirmed by the magnetic data.

     

Late Silurian (Ludlow–Přídolí) microfossils and sedimentation in the Welsh Basin near Clun,Shropshire

The base of the Clun Forest Formation at Clun, Shropshire, has previously been taken to correlate with the base of the Downton Castle Sandstone Formation (Přídolí Series, upper Silurian) on the basis of brachiopod, bivalve, gastropod and ostracod faunas. The detailed distribution of microfossils (acritarchs, chitinozoans, conodonts and ostracods) is documented at Nantyrhynau Quarry, Clun, Shropshire, to test this correlation. Three new species of chitinozoans, Eisenackitina clunensis, Eisenackitina kerria and Angochitina paucispinosa, are described from the quarry. Macrofossil and ostracod distributions suggest that the correlation is correct. However, a typical Ludlow acritarch flora is present throughout the section and suggests that the basal part of the Clun Forest Formation is Ludlow in age. The mixture of characteristic Ludlow and Přídolí microfossils at Nantyrhynau Quarry may be the result of differing environmental conditions between the Ludlow (shelf) and Clun (basinal) areas at this time. Alternatively, the strata exposed at Nantyrhynau Quarry may represent a period towards the end of the Ludlow Series when there are no strata represented in corresponding shelf sections due to non-deposition or erosion. © 1997 John Wiley & Sons, Ltd.