Redox and pH microenvironments within Shewanella oneidensis MR-1 biofilms reveal an electron transfer mechanism

The goal of this research was to quantify the variations in redox potential and pH in Shewanella oneidensis MR-1 biofilms respiring on electrodes. We grew S. oneidensis MR-1 on a graphite electrode, which was used to accept electrons for microbial respiration. We modified well-known redox and pH microelectrodes with a built-in reference electrode so that they could operate near polarized surfaces and quantified the redox potential and pH profiles in these biofilms. In addition, we used a ferri-/ferrocyanide redox system in which electrons were only transferred by mediated electron transfer to explain the observed redox potential profiles in biofilms. We found that regardless of the polarization potential of the biofilm electrode, the redox potential decreased toward the bottom of the biofilm. In a fully redox-mediated control system (ferri-/ferrocyanide redox system), the redox potential increased toward the bottom when the electrode was the electron acceptor. The opposite behavior of redox profiles in biofilms and the redox-controlled system is explained by S. oneidensis MR-1 biofilms not being redox-controlled when they respire on electrodes. The lack of a significant variation in pH implies that there is no proton transfer limitation in S. oneidensis MR-1 biofilms and that redox potential profiles are not caused by pH.     

Landfill site selection utilizing TOPSIS methodology and clay liner geotechnical characterization: a case study for Ankara,Turkey

The purpose of this study was to select alternative landfill sites for Ankara based on the growing trends of Ankara toward the Gölba?? municipality, and to eventually select the best alternative through the use of decision-making tools. Geographic information systems (GIS) and multi-criteria decision analyses were employed to perform landfill site selection. Several criteria, including geology, slope, proximity to roads, availability and proximity of landfill containment material, settlement, suitability for agriculture, vegetation cover, erosion, and lineament system were gathered in a GIS environment. A weight value was assigned to each criterion by applying the pairwise comparison method and the analytical hierarchy method. An ideal point method, namely, the Technique for Order Preference by Similarity to the Ideal Solution (TOPSIS) was applied to choose the best alternative landfill site. The geotechnical properties of “Ankara clay”, which shows widespread distribution in Ankara, were reviewed and assessed for the clay's suitability as a single, compacted clay liner and as a component of a geomembrane-compacted clay composite liner for the alternative landfill site selected. The HELP model was employed in order to determine the cumulative, mean leachate head and cumulative, unitized expected leakage rate amounts through the landfill. Four different profiles, from the least conservative to the most conservative, were created and analyzed.     

Evaluation of biofilm image thresholding methods

To evaluate biomass distribution in heterogeneous biofilms from their microscope images, it is often necessary to perform image thresholding by converting the gray-scale images to binary images consisting of a foreground of biomass material and a background of interstitial space. The selection of the gray-scale intensity used for thresholding is arbitrary but under the control of the operator, which may produce unacceptable levels of variability among operators. The quality of numerical information extracted from the images is diminished by such variability, and it is desirable to find a method that improves the reproducibility of thresholding operations. Automatic methods of thresholding provide this reproducibility, but often at the expense of accuracy, as they consistently set thresholds that differ significantly from what human operators would choose. The performance of five automatic image thresholding algorithms was tested in this study: (1) local entropy; (2) joint entropy; (3) relative entropy; (4) Renyi's entropy; and (5) iterative selection. Only the iterative selection method was satisfactory in that it was consistently setting the threshold level near that set manually. The extraction of feature information from biofilm images benefits from automatic thresholding and can be extended to other fields, such as medical imaging.     

Electrochemical synthesis of Pd particles on poly(vinylferrocenium)

Electrochemical synthesis of Pd particles on poly(vinylferrocenium) (PVF⁺) support was described. K₂PdCl₄ was used as the metal particle precursor. Pd particles were incorporated into the polymer matrix electrochemically either by cyclic voltammetric scans (between +1.0 V and −0.8 V vs. SCE) or by reduction at constant potential (at −0.8 V vs. SCE) from aqueous solution of K₂PdCl₄. Scanning electron microscopy (SEM) studies showed that the Pd particles were well dispersed in the polymer matrix. Experimental parameters such as polymer film thickness, number of cycles during cyclic voltammetric scans in K₂PdCl₄ and electrolysis time in K₂PdCl₄ were studied. The Pd/PVF⁺ system showed catalytic activity towards hydrazine oxidation and appreciable results were obtained when compared with the related studies.     

Particle filter-based aerial tracking for moving targets

This paper considers the problem of tracking a moving target with a radio transmitter using an aerial robot in an online manner. The aerial robot is equipped with a low-cost directional antenna and Software Defined Radio receiver to obtain the signal emitted by the target. The aerial robot rotates around itself and collects a predefined number of signal recordings from each direction to determine the bearing angle to the target in which the received signal strength is maximized. The measurement uncertainty is assumed to be bounded and represented by two triangular areas divided by a bisector. To localize and track the target, a particle filter-based approach is proposed. In this approach, we integrate the discrete and bounded measurement model with the particle filter in such a way that the particles' weights are updated based on a novel method which considers the measurement wedge and the particle locations with respect to this wedge along with a logistic function. We also incorporate the doubling strategy into the particle filter to determine the next measurement locations and avoid arbitrarily large number of measurements. We choose wildlife monitoring as a use case scenario in which a radio transmitter is put on the animal under consideration to allow wildlife researchers to track it. Since each animal has its own motion behavior, we consider different motion models for the target, which are used in modeling animal movements in wildlife studies. Therefore, the proposed approach is validated using a target moving with varying velocity and acceleration. We verified the tracking performance of the approach through a series of extensive simulations. We compared the proposed approach with the optimal offline strategy in terms of the empirical competitive ratio of the total distance traveled and the tracking distance. We also developed a low-cost hardware platform and software infrastructure for the proposed tracking system. Using this platform, we conducted field experiments for the stationary and moving targets.