Encircling the dark: constraining dark energy via cosmic density in spheres

The recently published analytic probability density function for the mildly non-linear cosmic density field within spherical cells is used to build a simple but accurate maximum likelihood estimate for the redshift evolution of the variance of the density, which, as expected, is shown to have smaller relative error than the sample variance. This estimator provides a competitive probe for the equation of state of dark energy, reaching a few percent accuracy on wp and wa for a Euclid-like survey. The corresponding likelihood function can take into account the configuration of the cells via their relative separations. A code to compute one-cell density probability density functions for arbitrary initial power spectrum, top-hat smoothing and various spherical collapse dynamics is made available online so as to provide straightforward means of testing the effect of alternative dark energy models and initial power-spectra on the low-redshift matter distribution.Comment: 7 pages, replaced to match the MNRAS accepted versio

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

Landslide characterization using P- and S-wave seismic refraction tomography: the importance of elastic moduli

In the broad spectrum of natural hazards, landslides in particular are capable of changing the landscape and causing significant human and economic losses. Detailed site investigations form an important component in the landslide risk mitigation and disaster risk reduction process. These investigations usually rely on surface ob- servations, discrete sampling of the subsurface, and laboratory testing to examine properties that are deemed representative of entire slopes. Often this requires extensive interpolations and results in large uncertainties. To compliment and extend these approaches, we present a study from an active landslide in a Lias Group clay slope, North Yorkshire, UK, examining combined P- and S-wave seismic refraction tomography (SRT) as a means of providing subsurface volumetric imaging of geotechnical proxies. The distributions of seismic wave velocities determined fromSRT at the study site indicated zones with higher porosity and fissure density that are interpreted to represent the extent and depth of mass movements and weathered bedrock zones. Distinguishing the lithological units was facilitated by deriving the Poisson's ratio fromthe SRT data as saturated clay and partially saturated sandy silts showed distinctively different Poisson's ra- tios. Shear and Young's moduli derived from the SRT data revealed the weak nature of the materials in active parts of the landslide (i.e. 25 kPa and 100 kPa respectively). The SRT results are consistent with intrusive (i.e. cone penetration tests), laboratory, and additional geoelectrical data from this site. This study shows that SRT forms a cost-effective method that can significantly reduce uncertainties in the conceptual ground model of geotechnical and hydrological conditions that govern landslide dynamics

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

Measurement and modelling of moisture—electrical resistivity relationship of fine-grained unsaturated soils and electrical anisotropy

A methodology for developing resistivity-moisture content relationships of materials associated with a clayey landslide is presented. Key elements of the methodology include sample selection and preparation, laboratory measurement of resistivity with changing moisture content, and the derivation of models describing the relationship between resistivity and moisture content. Laboratory resistivity measurements show that the techniques utilised (samples and square array) have considerable potential as a means of electropetrophysical calibration of engineering soils and weak rock. Experimental electrical resistivity results show a hierarchy of values dependent on sample lithology, with silty clay exhibiting the lowest resistivities, followed by siltstones and sands, which return the highest resistivities. In addition, finer grained samples show a greater degree of anisotropy between measurement orientations than coarser grained samples. However, suitability of results in light of issues such as sample cracking and electrical conduction must be identified and accounted for if the results are to be accurately up-scaled to inverted model resistivity results. The existence of directional anisotropy makes model calibration curve selection more difficult due to variability in the range of measured laboratory resistances. The use of larger measurement array size means that experimental data will be more representative of bulk lithological properties. In addition, use of electrodes with a relatively high surface area (wide diameter) help maintain low contact resistances and repeat measurement error, relative to narrow electrodes. Variation exists between the fit of experimental data and petrophysical models. Model fit is best for clay-dominated samples but fits less well for sand-dominated samples. Waxman–Smits equation is appropriately applied in this investigation as all samples have considerable clay mineral content, as is shown in non-negligible CEC results. The incorporation of pressure plate suction measurements on samples, allows suction dissipation to be quantified and evaluated alongside moisture content and electrical resistivity

Piperacillin-Tazobactam versus Other Antibacterial Agents for Treatment of Bloodstream Infections Due to AmpC β-Lactamase-Producing Enterobacteriaceae

In vivo induction of AmpC beta-lactamases produces high-level resistance to many beta-lactam antibiotics in Enterobacteriaceae, often resulting in the need to use carbapenems or cefepime (FEP). The clinical effectiveness of piperacillin-tazobactam (TZP), a weak inducer of AmpC beta-lactamases, is poorly understood. Here, we conducted a case-control study of adult inpatients with bloodstream infections (BSIs) due to Enterobacter, Serratia, or Citrobacter species from 2009 to 2015 to assess outcomes following treatment with TZP compared to FEP or meropenem (MEM). We collected clinical data and screened all isolates for the presence of ampC alleles by PCR. Primary study outcomes were 30-day mortality and persistent bacteremia at \u3e/=72 h from the time of treatment initiation. Of 493 patients with bacteremia, 165 patients met the inclusion criteria, of which 88 were treated with TZP and 77 with FEP or MEM. To minimize differences between covariates, we carried out propensity score matching, which yielded 41 matched pairs. Groups only differed by age, with patients in the TZP group significantly older (P = 0.012). There were no significant differences in 30-day mortality, persistent bacteremia, 7-day mortality, or treatment escalation between the two treatment groups, including in the propensity score-matched cohort. PCR amplification and sequencing of ampC genes revealed the presence of ampC in isolates with cefoxitin MICs below 16 mug/ml, in particular in Serratia spp., and demonstrated that these alleles were highly genetically diverse. Taken together, TZP may be a valuable treatment option for BSIs due to AmpC beta-lactamase-producing Enterobacteriaceae, diminishing the need for broader-spectrum agents. Future studies are needed to validate these findings

Investigation of suspected gulls in the Jurassic limestone strata of the Cotswold Hills, Gloucestershire, England using electrical resistivity tomography

An electrical resistivity tomography survey has clearly indicated the presence of substantial vertical zones of contrasting material beneath a set of conspicuous linear surface hollows that cut across a spur forming part of the Cotswold Hills escarpment in Gloucestershire. These zones are compared with nearby quarry exposures and are inferred to be gulls – graben-like structures at least 80 m deep filled with collapsed blocks of bedrock with intervening air-filled spaces, lying within areas of relatively undisrupted gently dipping strata, and which under some circumstances would present a significant geohazard. Our results confirm the great potential of this non-invasive and rapid survey technique for investigating such phenomena, and provide an exemplar for comparison with surveys elsewhere, to assist identification of similar features

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

Reprocessed height time series for GPS stations

Precise weekly positions of 403 Global Positioning System (GPS) stations located worldwide are obtained by reprocessing GPS data of these stations for the time span from 4 January 1998 until 29 December 2007. The processing algorithms and models used as well as the solution and results obtained are presented. Vertical velocities of 266 GPS stations having a tracking history longer than 2.5 yr are computed; 107 of them are GPS stations located at tide gauges (TIGA observing stations). The vertical velocities calculated in this study are compared with the estimates from the co-located tide gauges and other GPS solutions. The formal errors of the estimated vertical velocities are 0.01–0.80 mm yr−1. The vertical velocities of our solution agree within 1 mm yr−1 with those of the recent solutions (ULR5 and ULR3) of the Université de La Rochelle for about 67–75 per cent of the common stations. Examples of typical behaviour of station height changes are given and interpreted. The derived height time series and vertical motions of continuous GPS at tide gauges stations can be used for correcting the vertical land motion in tide gauge records of sea level changes

Limitations and considerations for electrical resistivity and induced polarization imaging of riverbed sediments:Observations from laboratory, field, and synthetic experiments

Characterization of riverbed sediments is important for understanding groundwater (GW) and surface water (SW) interactions, and their consequent implications for ecological and environmental health. There have been numerous studies using geoelectrical methods for GW-SW interaction studies; however, most applications have not focused on obtaining quantitative information. For instance, although numerous laboratory studies highlight the relationship between geoelectrical properties and relevant parameters (e.g. specific surface area, hydraulic conductivity, and cation exchange capacity), such relationships are not commonly applied to field-scale studies. Furthermore, in addition to the spatial resolution obstacles typically present when applying petrophysical models to field data, geoelectrical data from aquatic environments have complications arising from the presence of a conductive water column overlying a resistive bed. Inadequate consideration of these complications may further preclude the reliable use of such petrophysical models. In this work, laboratory measurements, synthetic modeling, and field measurements were conducted in a third-order river where the riverbed comprises alluvial gravel and underlying red sand. A strong relationship (R2 = 0.72) between imaginary conductivity and specific surface area was observed, and laboratory results were comparable to previous studies. It was demonstrated through synthetic modeling that river stage and channel width, regularization across the river-riverbed interface, and incorrect constraints of both the river conductivity and river stage can have varying influence on inverted geoelectrical images. Reliable geoelectrical images require a priori definition of river stage and conductivity, however inversion constraints using incorrect a priori values result in misleading artifacts. The conductivity image obtained from the field data in this work appeared to reflect the geoelectrical structure anticipated from the laboratory data; however, the phase angle image did not. Although this study focused on riverbed characterization, findings here demonstrate common pitfalls of inversion of aquatic-based geoelectrical data. Primarily, they highlight that synthetic modeling ought to be used to alleviate any uncertainty in the interpretation of geoelectrical models before predictions about GW-SW interactions can be made