Predicting the movements of permanently installed electrodes on an active landslide using time-lapse geoelectrical resistivity data only

If electrodes move during geoelectrical resistivity monitoring and their new positions are not incorporated in the inversion, then the resulting tomographic images exhibit artefacts that can obscure genuine time-lapse resistivity changes in the subsurface. The effects of electrode movements on time-lapse resistivity tomography are investigated using a simple analytical model and real data. The correspondence between the model and the data is sufficiently good to be able to predict the effects of electrode movements with reasonable accuracy. For the linear electrode arrays and 2D inversions under consideration, the data are much more sensitive to longitudinal than transverse or vertical movements. Consequently the model can be used to invert the longitudinal offsets of the electrodes from their known baseline positions using only the time-lapse ratios of the apparent resistivity data. The example datasets are taken from a permanently installed electrode array on an active lobe of a landslide. Using two sets with different levels of noise and subsurface resistivity changes, it is found that the electrode positions can be recovered to an accuracy of 4 % of the baseline electrode spacing. This is sufficient to correct the artefacts in the resistivity images, and provides for the possibility of monitoring the movement of the landslide and its internal hydraulic processes simultaneously using electrical resistivity tomography only

Non-invasive characterisation of road subgrade with towed-array capacitive resistivity imaging

A towed-array Capacitive Resistivity Imaging (CRI) system has been used in a controlled experiment to acquire multi-channel high-resolution ERT data on an asphalt road. Results from a CRI survey on a purpose-built trial road are discussed and compared to corresponding GPR profile data. It is demonstrated that CRI is particularly effective for the assessment of road subgrade condition. The technique is found to be sensitive to variations in moisture content and porosity in the subgrade layer, which can be used to distinguish areas of structural weakness in roadbeds. We conclude that CRI can be a valuable tool in pavement engineering as it provides complementary information to existing non-destructive testing techniques

Characterising sand and gravel deposits using electrical resistivity tomography (ERT) : case histories from England and Wales

Electrical Resistivity Tomography (ERT) is a rapidly developing geophysical imaging technique that is now widely used to visualise subsurface geological structure, groundwater and lithological variations. It is being increasingly used in environmental and engineering site investigations, but despite its suitability and potential benefits, ERT has yet to be routinely applied by the minerals industry to sand and gravel deposit assessment and quarry planning. The principal advantages of ERT for this application are that it is a cost-effective non-invasive method, which can provide 2D or 3D spatial models of the subsurface throughout the full region of interest. This complements intrusive sampling methods, which typically provide information only at discrete locations. Provided that suitable resistivity contrasts are present, ERT has the potential to reveal mineral and overburden thickness and quality variations within the body of the deposit. Here we present a number of case studies from the UK illustrating the use of 2D and 3D ERT for sand and gravel deposit investigation in a variety of geological settings. We use these case studies to evaluate the performance of ERT, and to illustrate good practice in the application of ERT to deposit investigation. We propose an integrated approach to site investigation and quarry planning incorporating both conventional intrusive methods and ERT

Fourier, Gauss, Fraunhofer, Porod and the Shape from Moments Problem

We show how the Fourier transform of a shape in any number of dimensions can be simplified using Gauss's law and evaluated explicitly for polygons in two dimensions, polyhedra three dimensions, etc. We also show how this combination of Fourier and Gauss can be related to numerous classical problems in physics and mathematics. Examples include Fraunhofer diffraction patterns, Porods law, Hopfs Umlaufsatz, the isoperimetric inequality and Didos problem. We also use this approach to provide an alternative derivation of Davis's extension of the Motzkin-Schoenberg formula to polygons in the complex plane.Comment: 21 pages, no figure

Detection of abandoned mineshafts using towed-array capacitive resistivity and real-time kinematic GPS navigation

The UK has a long history of mining but it was not until 1875 that the accurate mapping of mine workings and the submission of abandonment plans became a legal requirement. Where mineshafts are indicated on plans, they may be mislocated due to poor or inaccurate surveying. Consequently, the redevelopment of derelict land in the built environment frequently encounters potential geohazards, such as old adits, bell pits and shafts. These mining relics pose a serious risk to health and safety. This paper demonstrates how the combination of modem geophysical survey techniques with state-of-the-art satellite-based positioning may assist in the detection of such features. Recent advances in these fields offer the possibility of using towed-array resistivity instruments in conjunction with highly accurate (sub-decimetre) real-time kinematic global positioning systems (RTKGPS). Here we describe the use of multi-offset towed-array capacitive resistivity (CR) with GPS navigation for mapping resistivity over a known mineshaft in the historic mining area of Bonsall Leys in Derbyshire, UK

Attitudes to and Understanding of Risk of Acquisition of HIV Over Time: Design and Methods for an Internet-based Prospective Cohort Study Among UK Men Who Have Sex With Men (the AURAH2 Study)

Background: The annual number of new HIV infections among men who have sex with men (MSM) has risen in the UK and, of those HIV positive, the proportion undiagnosed is high. The prospective AURAH2 study aims to assess factors associated with HIV acquisition among MSM in the UK, and to investigate changes over time within individuals in sexual behaviour and HIV-testing practices. / Methods/Design: AURAH2 is a prospective study among MSM without diagnosed HIV, aiming to recruit up to 1000 sexually active MSM attending sexual health clinics in London and Brighton. Participants complete an initial paper-based questionnaire, followed by four monthly online follow-up questionnaires collecting socio-demographic, health and behavioural data, including sexual behaviour, recreational and other drug use, HIV testing practices and Pre-Exposure Prophylaxis use, over a planned three year period. / Discussion: The results from AURAH2 study will provide an important insight into established and emerging risk behaviours that may be associated with acquisition of HIV in MSM, in the UK, changes over time within individuals in sexual behaviour, and inform on HIV testing practices. This data will be crucial to inform future HIV prevention strategies

Surfaces roughness effects on the transmission of Gaussian beams by anisotropic parallel plates

Influence of the plate surfaces roughness in precise ellipsometry experiments is studied. The realistic case of a Gaussian laser beam crossing a uniaxial platelet is considered. Expression for the transmittance is determined using the first order perturbation theory. In this frame, it is shown that interference takes place between the specular transmitted beam and the scattered field. This effect is due to the angular distribution of the Gaussian beam and is of first order in the roughness over wavelength ratio. As an application, a numerical simulation of the effects of quartz roughness surfaces at normal incidence is provided. The interference term is found to be strongly connected to the random nature of the surface roughness.Comment: 18 pages, Journal of Physics D: Applied Physics, volume 36, issue 21, pages 2697 - 270

Writing Russia's future: paradigms, drivers, and scenarios

The development of prediction and forecasting in the social sciences over the past century and more is closely linked with developments in Russia. The Soviet collapse undermined confidence in predictive capabilities, and scenario planning emerged as the dominant future-oriented methodology in area studies, including the study of Russia. Scenarists anticipate multiple futures rather than predicting one. The approach is too rarely critiqued. Building on an account of Russia-related forecasting in the twentieth century, analysis of two decades of scenarios reveals uniform accounts which downplay the insights of experts and of social science theory alike

Monitoring international migration flows in Europe. Towards a statistical data base combining data from different sources

The paper reviews techniques developed in demography, geography and statistics that are useful for bridging the gap between available data on international migration flows and the information required for policy making and research. The basic idea of the paper is as follows: to establish a coherent and consistent data base that contains sufficiently detailed, up-to-date and accurate information, data from several sources should be combined. That raises issues of definition and measurement, and of how to combine data from different origins properly. The issues may be tackled more easily if the statistics that are being compiled are viewed as different outcomes or manifestations of underlying stochastic processes governing migration. The link between the processes and their outcomes is described by models, the parameters of which must be estimated from the available data. That may be done within the context of socio-demographic accounting. The paper discusses the experience of the U.S. Bureau of the Census in combining migration data from several sources. It also summarizes the many efforts in Europe to establish a coherent and consistent data base on international migration. The paper was written at IIASA. It is part of the Migration Estimation Study, which is a collaborative IIASA-University of Groningen project, funded by the Netherlands Organization for Scientific Research (NWO). The project aims at developing techniques to obtain improved estimates of international migration flows by country of origin and country of destination

Colouration in amphibians as a reflection of nutritional status : the case of tree frogs in Costa Rica

Colouration has been considered a cue for mating success in many species; ornaments in males often are related to carotenoid mobilization towards feathers and/or skin and can signal general health and nutrition status. However, there are several factors that can also link with status, such as physiological blood parameters and body condition, but there is not substantial evidence which supports the existence of these relationships and interactions in anurans. This study evaluated how body score and blood values interact with colouration in free-range Agalychnis callidryas and Agalychnis annae males. We found significant associations between body condition and plasmatic proteins and haematocrit, as well as between body condition and colour values from the chromaticity diagram. We also demonstrated that there is a significant relation between the glucose and plasmatic protein values that were reflected in the ventral colours of the animals, and haematocrit inversely affected most of those colour values. Significant differences were found between species as well as between populations of A. callidryas, suggesting that despite colour variation, there are also biochemical differences within animals from the same species located in different regions. These data provide information on underlying factors for colouration of male tree frogs in nature, provide insights about the dynamics of several nutrients in the amphibian model and how this could affect the reproductive output of the animals