Investigation on Acoustic Versus Functional Characteristics of Porous Asphalt

The theoretical background, standards, and contract requirements of pavement friction courses involve functional (e.g., permeability) and acoustic (e.g., resistivity) characteristics. Unfortunately, their relationship is partly unknown and uncertain. This affects the comprehensiveness and soundness of the mix design of asphalt pavements. Based on the issues above, the goals of this study were confined into the following ones: 1) to investigate the relationship between acoustic and functional properties of porous asphalts; 2) to investigate, through one-layer (1L) and two-layer (2L) models, the effectiveness of the estimates of acoustic input data through mixture volumetric- and permeability-related characteristics. Volumetric and acoustic tests were performed and simulations were carried out. Equations and strategies to support a comprehensive approach were derived. Results demonstrate that even if the measured resistivity is very important, permeability-based estimates of resistivity well explain acoustic spectra. Furthermore, the distance between observed and estimated peaks of the absorption spectrum emerges as the best error function.

Uncertainty of the 2D Resistivity Survey on the Subsurface Cavities

We examined the uncertainty of the two-dimensional (2D) resistivity method using conceptual cavity models. The experimental cavity study was conducted to validate numerical model results. Spatial resolution and sensitivity to resistivity perturbations were also assessed using checkerboard tests. Conceptual models were simulated to generate synthetic resistivity data for dipole-dipole (DD), pole-dipole (PD), Wenner–Schlumberger (WS), and pole-pole (PP) arrays. The synthetically measured resistivity data were inverted to obtain the geoelectric models. The highest anomaly effect (1.46) and variance (24,400 Ω·m) in resistivity data were recovered by the DD array, whereas the PP array obtained the lowest anomaly effect (0.60) and variance (2401 Ω·m) for the shallowest target cavity set at 2.2 m depth. The anomaly effect and variance showed direct dependency on the quality of the inverted models. The DD array provided the highest model resolution that shows relatively distinct anomaly geometries. In contrast, the PD and WS arrays recovered good resolutions, but it is challenging to determine the correct anomaly geometries with them. The PP array reproduced the lowest resolution with less precise anomaly geometries. Moreover, all the tested arrays showed high sensitivity to the resistivity contrasts at shallow depth. The DD and WS arrays displayed the higher sensitivity to the resistivity perturbations compared to the PD and PP arrays. The inverted models showed a reduction in sensitivity, model resolution, and accuracy at deeper depths, creating ambiguity in resistivity model interpretations. Despite these uncertainties, our modeling specified that two-dimensional resistivity imaging is a potential technique to study subsurface cavities. We inferred that the DD array is the most appropriate for cavity surveys. The PD and WS arrays are adequate, while the PP array is the least suitable for cavity studies.

Uncertainties Analysis of Electrical Resistivity Tomography

<p>We examined the uncertainty of the resistivity method in cavity studies using a synthetic cavity model set at six-different depths. Conceptual models were simulated to generate synthetic resistivity data for dipole-dipole, pole-dipole, Wenner-Schlumberger, and pole-pole arrays. The 2D geoelectric models were recovered from the inversion of the synthetically measured resistivity data. The highest anomaly effect (1.46) and variance (24400) in resistivity data were recovered by dipole-dipole array, while the pole-pole array obtained the lowest anomaly effect (0.60) and variance (2401) for the target cavity T<sub>1</sub>. The anomaly effect and variance were linearly associated with the quality of the inverted models. The steeper anomaly gradient of resistivity indicated more distinct cavity boundaries, while the gentler gradient prevents the inference of the cavity boundaries. The recovered model zone above the depth of investigation index of 0.1 has shown relatively higher sensitivity. Modeling for dipole-dipole array provided the highest model resolution and anomaly gradient that shows a relatively distinct geometry of the cavity anomalies. On the contrary, the pole-dipole and Wenner-Schlumberger arrays recovered good model resolutions and moderate anomaly gradient but determining the anomaly geometries is relatively challenging. Whereas, the pole-pole array depicted the lowest model resolution and anomaly gradient with less clear geometry of the cavity anomalies. At deeper depths, the inverted models showed a reduction in model resolutions, overestimation in anomaly sizes, and deviation in anomaly positions, which can create ambiguity in resistivity model interpretations. Despite these uncertainties, our modeling specified that the 2D resistivity imaging is a potential technique to study subsurface cavities.</p>

Controlled source electromagnetic measurements offshore the Maltese Islands: Implications for offshore freshened groundwater in a carbonate shelf

<p>Carbonate lithologies host considerable quantities of the Earth’s freshwater resources and partially supply a significant amount of the global population with drinkable water.  Although they comprise substantial amounts of the coastlines, it is not known if these carbonate lithologies can sustain freshened groundwater offshore, and if this can help meet future water demands in coastal regions. To date, predicting volumes of freshened groundwater within marine carbonates has been challenging. Here, we integrate controlled source electromagnetic profiles with seismic reflection and core log data to derive a lithological model for the eastern carbonate margin of the Maltese Islands, one of the most water-starved countries in the world. Electrical resistivity models are used to guide lithological inference where seismic data provide limited information due to the superimposed seafloor multiple. We show that resistivity values within the Upper Coralline and Globigerina Limestone formations exceed the measured resistivity of seawater-saturated core log samples by at least a factor of four. This could be indicative of offshore freshened groundwater that occupies the pore space of the low permeability limestone along the eastern Maltese shelf. To validate this observation without further ground-truthing data, we use extensive forward modelling to show that a similar resistivity footprint can be achieved by localized interbedded low-porosity or highly cemented units. However, the spatial extent of such units across the entire eastern Maltese margin is geologically improbable. This points to the occurrence of offshore freshened groundwater that was likely emplaced during the last sea-level lowstand.</p>

Sand injectite mapping using a resistivity-velocity transform function

Lack of resolution in the distribution of sand injectites in hydrocarbon fields is common and makes it difficult to predict drilling challenges and plan for optimum production. A practical workflow was developed that enables the distinction of shale and sand bodies by using a combination of low-resolution seismic data and high-resolution resistivity log data. Measured resistivity logs were used to predict synthetic velocity logs, which accurately match shale velocities and over- or underestimate velocities of other rock types. The synthetic velocity logs were spatially distributed in a 3D cube in order to predict synthetic velocities in between and away from the well locations. The 3D cube was representative of a field. It covered the interval from the seabed to below the reservoir. The spatial distribution was based on a geostatistical approach guided by measured seismic interval velocities. A residual velocity cube was calculated from the measured and synthetic velocities. The residual velocity cube produced near-zero velocities for shaly materials and velocity over- or underestimates for other rock types. Interpretation of the residual velocity cube required the identification of strong stratigraphic markers. The markers were removed from the residual cube by setting their specific layer velocities to 0 m/s. The final information stored in the residual velocity cube was then related to the over- or underestimated velocities in sand bodies.

Seeding, Plating and Electrical Characterization of Gold Nanowires Formed on Self-Assembled DNA Nanotubes

Self-assembly nanofabrication is increasingly appealing in complex nanostructures, as it requires fewer materials and has potential to reduce feature sizes. The use of DNA to control nanoscale and microscale features is promising but not fully developed. In this work, we study self-assembled DNA nanotubes to fabricate gold nanowires for use as interconnects in future nanoelectronic devices. We evaluate two approaches for seeding, gold and palladium, both using gold electroless plating to connect the seeds. These gold nanowires are characterized electrically utilizing electron beam induced deposition of tungsten and four-point probe techniques. Measured resistivity values for 15 successfully studied wires are between 9.3 × 10−6 and 1.2 × 10−3 Ωm. Our work yields new insights into reproducible formation and characterization of metal nanowires on DNA nanotubes, making them promising templates for future nanowires in complex electronic circuitry.

Effect of Doping on the Electrical Characteristics of ZnSe

The effect of sulfur, iron, and chromium doping on the electrical characteristics of ZnSe single crystals was studied. The crystals, grown by the physical vapor transport method (PVT) at NASA Marshall Space Flight Center, were characterized by measuring electrical resistivity, capacitance, and dielectric constant using LCR meter. The morphology was studied by scanning electron microscopy to determine the crystallinity and micro defects. The measured resistivity and dielectric constant showed tunability as the function of frequency in the range of 100 Hz to 100,000 Hz, indicating the suitability of doped material for tuning devices. Besides, for the range from 50 mV to 1000mV, there was no difference in values for the studied frequency range, indicating no degradation or breakdown in the material. All doped ZnSe crystals with sulfur, iron, and chromium showed a similar trend as the function of frequency. Cr-ZnSe showed very high resistivity and lower dielectric constant compared to S-ZnSe and Fe-ZnSe crystals.

Analysis of landslide area of Tulung subdistrict, Ponorogo, Indonesia in 2017 using resistivity method

PurposeResearch has been conducted to analyze the landslide in Banaran area, Ponorogo Regency. The landslides occurred on April 1, 2017. This study was conducted to know the subsurface conditions in the Banaran area to analyze the disaster mitigation efforts. The mitigation efforts are made to reduce the risk from landslides and possible landslides.Design/methodology/approachThe method used is the geo-electric resistivity method of Wenner–Schlumberger configuration. The research was conducted in three villages namely Banaran Village, Bekirang Village and Mendak Village.FindingsThere are 12 resistivity measuring points with a track length of 410 m and a space of 10 m. The measured resistivity range is between 1.42 Ω.m and 67.500 Ω.m. The resistivity data and the local geological maps interpreted that the rocks in the Banaran area consist of clay, tuff lapilli, volcanic breccia and andesite lava. The landslide area begins at a depth of 8–35 m below the surface which is interpreted as tuff. Also, the thickness of the landslide material and the slope is = 400 which supports the occurrence of a more prominent landslide. The results of the parameter scoring of the landslide-prone areas indicated that the research area is very vulnerable to a landslide. The results of the interpretation indicate that the geo-electric resistivity method can provide a good overview for conducting landslide analysis, that is field slippage and potential material thickness occurrence landslide.Originality/valueThis article is very specific as it attempts to discover how prone Banaran are is to landslide.

Direct localised measurement of electrical resistivity profile in rat and embryonic chick retinas using a microprobe

We report an alternative technique to perform a direct and local measurement of electrical resistivities in a layered retinal tissue. Information on resistivity changes along the depth in a retina is important for modelling retinal stimulation by retinal prostheses. Existing techniques for resistivity-depth profiling have the drawbacks of a complicated experimental setup, a less localised resistivity probing and/or lower stability for measurements. We employed a flexible microprobe to measure local resistivity with bipolar impedance spectroscopy at various depths in isolated rat and chick embryo retinas for the first time. Small electrode spacing permitted high resolution measurements and the probe flexibility contributed to stable resistivity profiling. The resistivity was directly calculated based on the resistive part of the impedance measured with the Peak Resistance Frequency (PRF) methodology. The resistivity-depth profiles for both rat and chick embryo models are in accordance with previous mammalian and avian studies in literature. We demonstrate that the measured resistivity at each depth has its own PRF signature. Resistivity profiles obtained with our setup provide the basis for the construction of an electric model of the retina. This model can be used to predict variations in parameters related to retinal stimulation and especially in the design and optimisation of efficient retinal implants.

Investigations on the detectability of water intruding into bridge deck sealings by electrical resistivity measurements

In the context of a current joint research project a monitoring system to detect leakages in bridges is implemented by using a textile reinforced concrete interlayer which consists of two carbon meshes with a spacing of 15 mm and a new developed mortar. Between the two carbon meshes the resistivity is measured with alternating current. If a leakage in the bridge deck sealing occurs and water gets into the interlayer a drop in the measured resistivity occurs and the leakage is detected. In this case repair measures can be carried out in an early stage or a preventive cathodic protection can be switched on. To assess which sizes of leakages are detectable under which boundary conditions, laboratory tests and tests on a 100 m2 outdoor demonstrator were carried out. Therefore leakages were artificially produced and the changes in the measured resistivity values were observed under different climatic conditions. Impacts such as the form of the leakages or the position of the leakages in the measuring field were varied.