Computation of optimized arrays for 3-D electrical imaging surveys

3-D electrical resistivity surveys and inversion models are required to accurately resolve structures in areas with very complex geology where 2-D models might suffer from artefacts. Many 3-D surveys use a grid where the number of electrodes along one direction (x) is much greater than in the perpendicular direction (y). Frequently, due to limitations in the number of independent electrodes in the multi-electrode system, the surveys use a roll-along system with a small number of parallel survey lines aligned along the x-direction. The ‘Compare R' array optimization method previously used for 2-D surveys is adapted for such 3-D surveys. Offset versions of the inline arrays used in 2-D surveys are included in the number of possible arrays (the comprehensive data set) to improve the sensitivity to structures in between the lines. The array geometric factor and its relative error are used to filter out potentially unstable arrays in the construction of the comprehensive data set. Comparisons of the conventional (consisting of dipole-dipole and Wenner-Schlumberger arrays) and optimized arrays are made using a synthetic model and experimental measurements in a tank. The tests show that structures located between the lines are better resolved with the optimized arrays. The optimized arrays also have significantly better depth resolution compared to the conventional array

Jointly reconstructing ground motion and resistivity for ERT-based slope stability monitoring

Electrical resistivity tomography (ERT) is increasingly being used to investigate unstable slopes and monitor the hydrogeological processes within. But movement of electrodes or incorrect placement of electrodes with respect to an assumed model can introduce significant resistivity artefacts into the reconstruction. In this work, we demonstrate a joint resistivity and electrode movement reconstruction algorithm within an iterative Gauss–Newton framework. We apply this to ERT monitoring data from an active slow-moving landslide in the UK. Results show fewer resistivity artefacts and suggest that electrode movement and resistivity can be reconstructed at the same time under certain conditions. A new 2.5-D formulation for the electrode position Jacobian is developed and is shown to give accurate numerical solutions when compared to the adjoint method on 3-D models. On large finite element meshes, the calculation time of the newly developed approach was also proven to be orders of magnitude faster than the 3-D adjoint method and addressed modelling errors in the 2-D perturbation and adjoint electrode position Jacobian

Adaptive time-lapse optimized survey design for electrical resistivity tomography monitoring

Adaptive optimal experimental design methods use previous data and results to guide the choice and design of future experiments. This paper describes the formulation of an adaptive survey design technique to produce optimal resistivity imaging surveys for time-lapse geoelectrical monitoring experiments. These survey designs are time-dependent and, compared to dipole–dipole or static optimized surveys that do not change over time, focus a greater degree of the image resolution on regions of the subsurface that are actively changing. The adaptive optimization method is validated using a controlled laboratory monitoring experiment comprising a well-defined cylindrical target moving along a trajectory that changes its depth and lateral position. The algorithm is implemented on a standard PC in conjunction with a modified automated multichannel resistivity imaging system. Data acquisition using the adaptive survey designs requires no more time or power than with comparable standard surveys, and the algorithm processing takes place while the system batteries recharge. The results show that adaptively designed optimal surveys yield a quantitative increase in image quality over and above that produced by using standard dipole–dipole or static (time–independent) optimized surveys

537Microparticles and exosomes differentially impact on endothelial cell function in coronary artery disease

Background and Purpose: Microparticles (MPs) and exosomes are released by cells using different mechanisms. Thus, quantitative as well as qualitative changes of both particle populations, MPs and exosomes, in patients with coronary artery disease (CAD) might reflect an altered activation status of the endothelium, platelets and leukocytes. Moreover, they might exert differential effects on the target organs, such as the endothelium. Yet, alterations in both populations have not been studied side-by-side so far. The aim of the study was to compare the impact of MPs and exosomes from healthy subjects and CAD patients on endothelial cell (EC) functional characteristics. Methods: MPs and exosomes were isolated by stepwise filtration and ultracentrifugation from citrate-plasma and verified by electron microscopy and dynamic light scattering. MP and exosome fractions, as well as the vehicle (PBS), were added to human arterial ECs and EC apoptosis, number, size, capacity for in vitro-reendothelialisation after scratching, expression of adhesion molecules ICAM-1 and VCAM-1 were assessed. In parallel, platelet-, endothelial- and leukocyte-derived MPs were quantified. In a separate sub-study, the same parameters were assessed in plasma of CAD patients undergoing standard medical rehabilitation or an exercise-based cardiac rehabilitation programme. Results: MPs of healthy, but not of CAD patients supported in vitro re-endothelialisation, while exosomes had no influence. Exercise, but not standard rehabilitation improved CAD MP capacity to support in vitro rehabilitation. This was negatively correlated to the number of leukocyte- and endothelial-derived MPs, but not total or platelet MPs. EC number was negatively affected by exposure to CAD MPs. ANCOVA analysis identified disease, but not the particle type as influencing factor. Instead, apoptotic cell death was influenced by particle type, but not by the disease, and was not altered in rehabilitation. Similarly, ICAM-1 and VCAM-1 expression were enhanced on ECs after incubation with exosomes, but not with MPs, with no effect of disease or rehabilitation. Conclusion: MPs and exosomes differentially affect endothelial cell function and underlie differential modulation in disease and rehabilitation. Those findings might in the future help to optimize and monitor cardiovascular therap

Time-lapse monitoring of climate effects on earthworks using surface waves

The UK’s transportation network is supported by critical geotechnical assets (cuttings/embankments/dams) that require sustainable, cost-effective management, while maintaining an appropriate service level to meet social, economic, and environmental needs. Recent effects of extreme weather on these geotechnical assets have highlighted their vulnerability to climate variations. We have assessed the potential of surface wave data to portray the climate-related variations in mechanical properties of a clay-filled railway embankment. Seismic data were acquired bimonthly from July 2013 to November 2014 along the crest of a heritage railway embankment in southwest England. For each acquisition, the collected data were first processed to obtain a set of Rayleigh-wave dispersion and attenuation curves, referenced to the same spatial locations. These data were then analyzed to identify a coherent trend in their spatial and temporal variability. The relevance of the observed temporal variations was also verified with respect to the experimental data uncertainties. Finally, the surface wave dispersion data sets were inverted to reconstruct a time-lapse model of S-wave velocity for the embankment structure, using a least-squares laterally constrained inversion scheme. A key point of the inversion process was constituted by the estimation of a suitable initial model and the selection of adequate levels of spatial regularization. The initial model and the strength of spatial smoothing were then kept constant throughout the processing of all available data sets to ensure homogeneity of the procedure and comparability among the obtained V S VS sections. A continuous and coherent temporal pattern of surface wave data, and consequently of the reconstructed V S VS models, was identified. This pattern is related to the seasonal distribution of precipitation and soil water content measured on site

Time-lapse monitoring of fluid-induced geophysical property variations within an unstable earthwork using P-wave refraction

A significant portion of the UK’s transportation system relies on a network of geotechnical earthworks (cuttings and embankments) that were constructed more than 100 years ago, whose stability is affected by the change in precipitation patterns experienced over the past few decades. The vulnerability of these structures requires a reliable, cost- and time-effective monitoring of their geomechanical condition. We have assessed the potential application of P-wave refraction for tracking the seasonal variations of seismic properties within an aged clay-filled railway embankment, located in southwest England. Seismic data were acquired repeatedly along the crest of the earthwork at regular time intervals, for a total period of 16 months. P-wave first-break times were picked from all available recorded traces, to obtain a set of hodocrones referenced to the same spatial locations, for various dates along the surveyed period of time. Traveltimes extracted from each acquisition were then compared to track the pattern of their temporal variability. The relevance of such variations over time was compared with the data experimental uncertainty. The multiple set of hodocrones was subsequently inverted using a tomographic approach, to retrieve a time-lapse model of VP for the embankment structure. To directly compare the reconstructed VP sections, identical initial models and spatial regularization were used for the inversion of all available data sets. A consistent temporal trend for P-wave traveltimes, and consequently for the reconstructed VP models, was identified. This pattern could be related to the seasonal distribution of precipitation and soil-water content measured on site

Assessing climate effects on railway earthworks Using MASW

Many parts of the UK’s rail network were constructed in the mid‐19th century long before the advent of modern construction standards. Historic levels of low investment, poor maintenance strategies and the deleterious effects of climate change have resulted in critical elements of the rail network being at significant risk of failure. The majority of failures which have occurred over recent years have been triggered by extreme weather events. Advance assessment and remediation of earthworks is, however, significantly less costly than dealing with failures reactively. It is therefore crucial that appropriate approaches for assessment of the stability of earthworks are developed, so that repair work can be better targeted and failures avoided wherever possible. This extended abstract briefly discusses some preliminary results from an ongoing geophysical research project being carried out in order to study the impact of climate or seasonal weather variations on the stability of a century old railway embankment on the Gloucestershire Warwickshire steam railway line in Southern England

Dark Force Detection in Low Energy e-p Collisions

We study the prospects for detecting a light boson X with mass m_X < 100 MeV at a low energy electron-proton collider. We focus on the case where X dominantly decays to e+ e- as motivated by recent "dark force" models. In order to evade direct and indirect constraints, X must have small couplings to the standard model (alpha_X 10 MeV). By comparing the signal and background cross sections for the e- p e+ e- final state, we conclude that dark force detection requires an integrated luminosity of around 1 inverse attobarn, achievable with a forthcoming JLab proposal.Comment: 38 pages, 19 figures; v2, references adde

The Schro¨\ddot{o}dinger-Poisson equations as the large-N limit of the Newtonian N-body system: applications to the large scale dark matter dynamics

In this paper it is argued how the dynamics of the classical Newtonian N-body system can be described in terms of the Schr$\ddot{o}$dinger-Poisson equations in the large $N$ limit. This result is based on the stochastic quantization introduced by Nelson, and on the Calogero conjecture. According to the Calogero conjecture, the emerging effective Planck constant is computed in terms of the parameters of the N-body system as $\hbar \sim M^{5/3} G^{1/2} (N/)^{1/6}$, where is $G$ the gravitational constant, $N$ and $M$ are the number and the mass of the bodies, and $$ is their average density. The relevance of this result in the context of large scale structure formation is discussed. In particular, this finding gives a further argument in support of the validity of the Schr$\ddot{o}$dinger method as numerical double of the N-body simulations of dark matter dynamics at large cosmological scales.Comment: Accepted for publication in the Euro. Phys. J.