Accounting for covariate information in the scale component of spatio-temporal mixing models

Spatio-temporal processes in the environmental science are usually assumed to follow a Gaussian process, possibly after some transformation. Gaussian processes might not be appropriate to handle the presence of outlying observations. Our proposal is based on the idea of modelling the process as a scale mixture between a Gaussian and log-Gaussian process. And the novelty is to allow the scale process to vary as a function of covariates. The resultant model has a nonstationary covariance structure in space. Moreover, the resultant kurtosis varies with location, allowing the time series at each location to have different distributions with different tail behaviour. Inference procedure is performed under the Bayesian framework. The analysis of an artificial dataset illustrates how this proposal is able to capture heterogeneity in space caused by dependence on some spatial covariate or by a transformation of the process of interest. Furthermore, an application to maximum temperature data observed in the Spanish Basque country illustrates the effects of altitude in the variability of the process and how our proposed model identifies this dependence through parameters which can be interpreted as regression coefficients in the variance model

Microstructural analysis of fresh-cut red bell pepper (Capsicum annuum L.) for postharvest quality optimization

The main objective of this work was to evaluate the microstructure of fresh-cut red bell pepper (Capsicum annuum L.) after cutting, when maintained (for 0,4 and 7 d) under refrigerated storage (2°C). In order to assess the microstructure of the product, scanning electron microscopy (SEM) was applied; however, to improve this technique, preparation procedures and quantitative image analysis were specifically developed. Since sample preparation affects deeply image quality, three sample preparation procedures (viz. freezing by immersion in liquid nitrogen and subsequent storage at -80°C, freezing by storage at -80 °C and subsequent freeze-drying, and freezing by immersion in liquid nitrogen and subsequent freezedrying) were tested. One could also test (with success) a methodology of quantitative image analysis via a panel – a large number of people (N=25) rated the degree of cellular destruction, using a continuous scale (from 1- no cellular destruction to 9-extreme cellular destruction). Statistical analysis of the experimental data revealed that frozen samples exhibited higher cellular destruction than via the other two procedures; no statistically significant differences were observed between these two other procedures. Red bell pepper samples stored for 4 and 7 d presented (as expected) higher degree of cellular destruction than initial day samples. This work allowed one to develop appropriate preparation procedures of sample and quantitative image analysis – that will permit the application of this microscopy technique in future work in this area

In situ electrochemical characterization of a microbial fuel cell biocathode running on wastewater

Funding Information: FCT?Funda??o para a Ci?ncia e a Tecnologia, Portugal (Grant number grant No. FRH/BP D/33864/2009). This work was supported by the Associate Laboratory for Green Chemistry (LAQV) which is financed by national funds from FCT/MCTES (UIDB/50006/2020 and UIDP/50006/2020). Acknowledgments: S.V.R. acknowledges the financial support from FCT (Portuguese Foundation for Science and Technology) for Postdoctoral Research grant No. FRH/BPD/33864/2009. This work was supported by the Associate Laboratory for Green Chemistry?LAQV which is financed by national funds from FCT/MCTES (UIDB/50006/2020 and UIDP/50006/2020).The electrochemical features of microbial fuel cells’ biocathodes, running on wastewater, were evaluated by cyclic voltammetry. Ex situ and in situ electrochemical assays were performed and the redox processes associated with the presence of microorganisms and/or biofilms were attained. Different controls using sterile media (abiotic cathode microbial fuel cell) and membranes covering the electrodes were performed to evaluate the source of the electrochemistry response (surface biofilms vs. biotic electrolyte). The bacteria presence, in particular when biofilms are allowed to develop, was related with the enhanced active redox processes associated with an improved catalytic activity, namely for oxygen reduction, when compared with the results attained for an abiotic microbial fuel cell cathode. The microbial main composition was also attained and is in agreement with other reported studies. The current study aims contributing to the establishment of the advantages of using biocathodes rather than abiotic, whose conditions are frequently harder to control and to contribute to a better understanding of the bioelectrochemical processes occurring on the biotic chambers and the electrode surfaces.publishersversionpublishe

Toxicity of cadmium and zinc on two microalgae, Scenedesmus obliquus and Desmodesmus pleiomorphus, from Northern Portugal

Aquatic environments often contain toxic heavy metals that may enter the food web via uptake by microalgae and eventually cause severe poisoning problems at higher trophic levels. The effects of Cd and Zn cations upon growth of two native green microalgal species, Scenedesmus obliquus and Desmodesmus pleiomorphus (previously isolated from a polluted site in Northern Portugal), were accordingly evaluated. Growth inhibition of the microalgal cells was determined following exposure for 96 h to several initial concentrations of aqueous solutions of either of those two metals. At the higher end of Cd and Zn experimental concentration ranges, a significant reduction in cell density was observed in the cultures; EC50 values, calculated after fitting a Weibull model to the experimental data, were 0.058 and 1.92 mg L−1 for Cd and 16.99 and 4.87 mg L−1 for Zn in the case of S. obliquus and D. pleiomorphus, respectively. One observed that S. obliquus can tolerate higher Zn concentrations than D. pleiomorphus, but the reverse holds regarding exposure to Cd

Direct determination of Cu and Fe in jet fuel by electrothermal atomic absorption spectrometry with injection of sample as detergent emulsions

AbstractThis paper reports the development of a method for the determination of copper and iron in jet fuels employing the electrothermal atomic absorption spectrometry (ETAAS). In order to allow the direct determination of the analytes, the samples were injected into the graphite furnace as detergent emulsions in order to avoid their volatilization during analysis. The results obtained in this work indicated that a stable emulsion can be formed by mixing 1mL of a 7% m/v Triton X-100 solution containing 10% v/v HNO3 with 4mL of jet fuel. The injection of emulsions provided integrated absorbance signals with suitable sensitivity and precision for 300min at least. The addition of chemical modifier was not necessary because background values were always very low, allowing the use of pyrolysis temperature around 1000°C for both analytes. Both Triton X-100 and HNO3 concentrations in the solution used to form the emulsion had remarkable influence on the sensitivity as well as the heating rate employed in the drying step. Under the best conditions established in the present work, limits of detection of 0.50 and 0.46μgL−1 were observed for copper when oil-based and aqueous standards were added to the emulsions for calibration, respectively. For iron, the limits of detection were 0.88 and 0.90μgL−1 for oil-based and aqueous standards, respectively. The method was applied in the determination of Cu and Fe in five samples of jet fuels and a recovery test was performed, producing recovery percentages between 95% and 105%

Bioelectricity generation using long-term operated biocathode: RFLP based microbial diversity analysis

FRH/BPD/33864/2009 UIDB/50006/2020 UIDP/50006/2020In the present work, power generation and substrate removal efficiencies of long-term operated microbial fuel cells, containing abiotic cathodes and biocathodes, were evaluated for 220 days. Among the two microbial fuel cell (MFC) types, the one containing biocathode showed higher power density (54 mW/m2), current density (122 mA/m2) coulombic efficiency (33%), and substrate removal efficiency (94%) than the abiotic cathode containing MFC. Voltammetric analysis also witnessed higher and sustainable electron discharge for the MFC with biocathode, when compared with the abiotic cathode MFC. Over the tested period, both MFC have shown a cell voltage drop, after 150 and 165, days, for the MFC with biocathode and abiotic cathodes, respectively. Polymerase chain reaction (PCR) based restriction fragment length polymorphism (RFLP) analysis identified 281 clones. Bacteria belonging to Acinetobacter, Acidovorax, Pseudomonas and Burkholderia were observed in the abiotic cathode MFC. Bacteria belonging to Geobacter, Cupriavidus and Acidobacteria were observed in the biocathode MFC. Almost similar types of archaea (Methanosarcinales, Methanolinea, Nitrososphaera and Methanomicrobiales) were observed in both MFCs.publishersversionpublishe

Effect of drill speed on the strain distribution during drilling of bovine and human bones

Drilling is an operation commonly required in orthopaedic surgery for insertion of screws and internal fixation of bone fractures. Induced damage is one of the undesired effects of drilling mainly due to the use of inadequate drilling parameters. During the recent years, scientists have been trying to describe the relationship between drilling parameters and bone injury. However, no studies have examined the level of strain generated in the bone during the drilling process. This paper focuses on the analysis of different drill speeds during drilling of fresh bovine femora and human cadaveric tibiae. The main contribution of this work is to determine how differences in applied drill speeds affect the strain of cortical tissue near the drilling site and the drill bit temperature. Strains were measured in ex-vivo material during the osteotomy preparation with three drill speeds (520, 900 and 1370 r.p.m.). Additionally, a thermographic camera was used to measure the drill bit temperature. As the drilling operations are blind in nature with unknown depth, the osteotomies were performed using a drill press machine without control of the feed rate or depth. Drill bit geometry was kept constant with 4 mm of diameter, point angle 120⁰ and helix angle 30⁰. The tests were conducted at room temperature without applying cooling at the drilling zone. Bone strains near to the drilling sites were recorded with high accuracy using linear strain gages mounted around the diaphyseal cortex. It was noted that the bone strain and drill bit temperature increased with an increasing drill speed. Human and bovine bone samples presented significantly different levels of strain and temperature. Both strain and temperature were higher when drilling bovine femora than when drilling human cadaveric tibiae