The inspection of bridge decks is a routine application of the GPR method. Pavement thickness, depth of reinforcement, concrete damage and the position of tendons are some of the issues that are ...addressed with GPR. However, in most cases a verification of radar results is either not possible or restricted to a few points. A detailed comparison between radar results and reality for bridge decks is not only of scientific interest but could also improve the acceptance of GPR in this field of work. In an ongoing research project sponsored by the Swiss Federal Roads Authority, bridges designated for demolition are inspected with EMPA's mobile GPR unit. Radar results are reported before the bridge is taken down. After demolition radar results are verified through a comparison with actual bridge parts. The project aims at the evaluation of the accuracy of radar results on bridge decks, the identification of possible pitfalls and a possible improvement of the method and the way it is applied. Work on four bridges of different types and sizes has been completed by now. It is planned to investigate one or two further bridges during the project. The comparison between radar results and reality proves that GPR inspections provide results with an accuracy and reliability that is sufficient for many applications in civil engineering.
In recent years, innovative strategies such as inverse-scattering or data fusion have been suggested for the processing of GPR datasets in complex scenarios. In this framework, high-resolution ...concrete inspections are a challenge regarding the treatment of radar data because of the size of the datasets and the complex structures involved. In addition, the achievable depth of inspection is in many cases restricted to unacceptable limits because of the material properties of concrete and the "masking effect" of the upper layers of rebar. Thus, the application of innovative approaches to high-resolution concrete data seems to suggest itself. In this framework, this work deals with the processing of a high-resolution, dataset acquired on a concrete retaining wall via an inverse scattering technique. In particular, we show how the adoption of a strategy based on signal processing techniques and an inverse scattering approach is able to provide the mapping of the two layers of rebar.
The assessment of ageing concrete structures is a major technical challenge faced by the Civil Engineers of today. Concrete bridges are exposed to corrosion from the spreading of de-icing salts on ...roads during winter. Corrosion is problematic because it reduces the reinforcement's load carrying capacity and a long-term consequence can be structural failure. This paper describes an experiment that consisted in exposing a concrete specimen to a controlled wetting-drying cycle using a saline solution. This setup enabled the concentration of chlorides to be distributed in gradients inside the specimen. A novel methodology to estimate material properties, based on ground penetrating radar (GPR) full-waveform inversion, was used to process GPR traces. In this paper, each reflection present in the trace was regarded independently. This procedure was applied to a dataset acquired with bistatic off-ground GPR antennas. Measurements were carried out above the test specimen at regular time lapses. This allowed monitoring of the electromagnetic parameters of the top and bottom concrete specimen surfaces during the wetting-drying cycle.
Results from Pt model catalyst surfaces have demonstrated that surface defects, in particular surface concavities, can improve the oxygen reduction reaction (ORR) kinetics. It is, however, a ...challenging task to synthesize nanostructured catalysts with such defective surfaces. Hence, we present a one-step and upscalable top-down approach to produce a Pt/C catalyst (with ∼3 nm Pt nanoparticle diameter). Using high-resolution transmission electron microscopy and tomography, electrochemical techniques, high-energy X-ray measurements, and positron annihilation spectroscopy, we provide evidence of a high density of surface defects (including surface concavities). The ORR activity of the developed catalyst exceeds that of a commercial Pt/C catalyst, at least 2.7 times in terms of specific activity (∼1.62 mA/cm2 Pt at 0.9 V vs the reversible hydrogen electrode) and at least 1.7 times in terms of mass activity (∼712 mA/mgPt), which can be correlated to the enhanced amount of surface defects. In addition, the technique used here reduces the complexity of the synthesis (and therefore production costs) in comparison to state of the art bottom-up techniques.
The Octaray (Biosense Webster) is a novel, multispline mapping catheter with 48 closely spaced microelectrodes enabling high-resolution electroanatomical mapping.
This study sought to report the ...initial clinical mapping experience with this novel catheter in a variety of cardiac arrhythmias and to compare the mapping performance with the 5-spline Pentaray.
Fifty consecutive procedures among 46 patients were retrospectively analyzed regarding safety, efficacy, and acute procedural success defined as termination or noninducibility of clinical tachycardia, conduction block across an ablation line, or pulmonary vein isolation. In addition, another 10 patients with sustained atrial tachycardia mapped with the 5-spline catheter (2-5-2 spacing) or the novel 8-spline catheter (2-2-2-2-2 spacing) were analyzed.
Left atrial and ventricular mapping by either transseptal (n = 41) or retroaortic (n = 2) access was feasible without any complications related to the multispline design of the novel catheter. The acute procedural success rate was 94%. In sustained atrial tachycardia compared with the 5-spline catheter, the novel 8-spline catheter recorded more electrograms per map (3,628 ± 714 vs 11,350 ± 1,203; P < 0.001) in a shorter mapping time (13 ± 2 vs 9 ± 1 minutes; P = 0.08) resulting in a higher point density (18 ± 4 vs 59 ± 10 electrograms/cm
; P < 0.01) and point acquisition rate (308 ± 69 vs 1,332 ± 208 electrograms/min.; P < 0.01).
In this initial experience, mapping with the novel catheter was safe and efficient with a high electroanatomical resolution. In sustained atrial tachycardia the novel 8-spline catheter demonstrated a marked increase in point density and mapping speed compared with those of the 5-spline catheter. These initial results should be validated in a larger multicenter cohort with longer follow-up.
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