Detecting long-range correlation with detrended fluctuation analysis: Application to BWR stability

The aim of this paper is to explore the application of detrended fluctuation analysis (DFA) to study boiling water reactor stability. DFA is a scaling method commonly used for detecting long-range correlations in non-stationary time series. This method is based on the random walk theory and was applied to neutronic power signal of Forsmark stability benchmark. Our results shows that the scaling properties breakdown during unstable oscillations.     

Synthetic gas production by dry reforming of methane over Ni/Al2O3–ZrO2 catalysts: High H2/CO ratio

Alumina prepared by the sol-gel method, was impregnated with zirconia (5, 15 and 30 wt.%). Subsequently, the resulting Al₂O₃–ZrO₂ supports were impregnated with 15% Ni to obtain the Ni/Al₂O₃–ZrO₂ catalysts. The obtained catalysts were characterized by BET, SEM, XRD, H₂-TPR and TPD- CO₂. The catalytic activity was studied by means of dry reforming of methane (DRM) for syngas production. The catalysts displayed different physicochemical properties and trends of their catalytic activity as a function of the ZrO₂ content in the mixed oxide supports. For instance, ZrO₂ (5 wt %) in the catalyst, led to enhanced concentration of the medium strength basic sites and increased specific surface area, yielding thus the best performance in the DRM, with low carbon deposition after 36 h of reaction, compared with the other catalysts. This indicates that during the DRM reaction, this catalyst can provide more surface oxygen to prevent carbon deposits that could deactivate the catalyst.     

Nominal energy optimisation method of constrained battery packs through the iteration of the series‐parallel topology

The design of a battery pack commonly deals with high performance goals and challenging constraints in terms of cost, volume or weight. One of the most crucial variables to maximise is the nominal energy, which depends on the number of discrete battery cells that can be allocated and their individual technical specifications. This work proposes a systematic method to optimise the nominal energy of a constrained battery pack from the perspective of the series‐parallel topology. A mathematical and graphical characterisation is presented on how the main battery's variables are related to a topology bounded to discretisation procedures. It was theoretically found that the effects of rounding the values of the topology may lead to a considerable loss of potential nominal energy, a risk that increases linearly with the number of series. The behaviour of the battery is assessed under nominal conditions and under the event of a cell failure. The theoretical analysis suggests that the detrimental effects due to an open‐circuit increase as the number of series increases, while it is the opposite in the case of a shorted cell. The method is satisfactorily implemented in the development of two different battery packs for solar competition cars with limiting regulations. The candidate topologies outperformed the nominal energy of topologies defined without the method in up to 5%. It was also found that selecting an energy‐maximising topology is not always the most convenient choice, because other variables may be of interest and are dependent on the topology as well. The method is of great use to guide the topology definition process in early theoretical stages, which is usually a compromise between allocating as much cells as possible within constraints, and approaching other performance goals such as a given nominal voltage or capacity. Copyright © 2017 John Wiley & Sons, Ltd.     

Two‐ and Three‐Terminal Resistive Switches: Nanometer‐Scale Memristors and Memistors

The logical relationship between two previously defined “memory resistors” is revealed by constructing and experimentally demonstrating a three‐terminal memistor equivalent circuit using two two‐terminal memristors. A technique is then presented, using nanoimprint lithography in combination with angle evaporation, to fabricate a single nanoscale device with a footprint of 4F², where F is the minimum lithographic feature size, that can be operated as either a two‐terminal lateral memristor or a three‐terminal memistor inside a crossbar structure. These devices exhibit repeatable bipolar nonvolatile switching behavior with up to 10³ ON/OFF conductance ratios, as well as the desired three‐terminal behavior.     

Lognormal switching times for titanium dioxide bipolar memristors: origin and resolution

We measured the switching time statistics for a TiO(2) memristor and found that they followed a lognormal distribution, which is a potentially serious problem for computer memory and data storage applications. We examined the underlying physical phenomena that determine the switching statistics and proposed a simple analytical model for the distribution based on the drift/diffusion equation and previously measured nonlinear drift behavior. We designed a closed-loop switching protocol that dramatically narrows the time distribution, which can significantly improve memory circuit performance and reliability.     

Perfluorooctanesulfonate and related fluorochemicals in human blood from several countries

Perfluorooctanesulfonyl fluoride based compounds have been used in a wide variety of consumer products, such as carpets, upholstery, and textiles. These compounds degrade to perfluorooctanesulfonate (PFOS), a persistent metabolite that accumulates in tissues of humans and wildlife. Previous studies have reported the occurrence of PFOS, perfluorohexanesulfonate (PFHxS), perfluorooctanoate (PFOA), and perfluorooctanesulfonamide (PFOSA) in human sera collected from the United States. In this study, concentrations of PFOS, PFHxS, PFOA, and PFOSA were measured in 473 human blood/serum/plasma samples collected from the United States, Colombia, Brazil, Belgium, Italy, Poland, India, Malaysia, and Korea. Among the four perfluorochemicals measured, PFOS was the predominant compound found in blood. Concentrations of PFOS were the highest in the samples collected from the United States and Poland (>30 ng/mL); moderate in Korea, Belgium, Malaysia, Brazil, Italy, and Colombia (3 to 29 ng/mL); and lowest in India (<3 ng/mL). PFOA was the next most abundant perfluorochemical in blood samples, although the frequency of occurrence of this compound was relatively low. No age- or gender-related differences in the concentrations of PFOS and PFOA were found in serum samples. The degree of association between the concentrations of four perfluorochemicals varied, depending on the origin of the samples. These results suggested the existence of sources with varying levels and compositions of perfluorochemicals, and differences in exposure patterns to these chemicals, in various countries. In addition to the four target fluorochemicals measured, qualitative analysis of selected blood samples showed the presence of other perfluorochemicals such as perfluorodecanesulfonate (PFDS), perfluoroheptanoic acid (PFHpA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluorododecanoic acid (PFDoA), and perfluoroundecanoic acid (PFUnDA) in serum samples, at concentrations approximately 5- to 10-fold lower than the concentration of PFOS. Further studies should focus on identifying sources and pathways of human exposure to perfluorochemicals.     

Global pollution monitoring of polybrominated diphenyl ethers using skipjack tuna as a bioindicator

To elucidate the global distribution of polybrominated diphenyl ethers (PBDEs), these chemicals were determined in the muscle of skipjack tuna (Katsuwonus pelamis) collected from offshore waters of various regions in the world (Japan, Taiwan, Philippines, Indonesia, Seychelles, and Brazil, and the Japan Sea, East China Sea, South China Sea, Indian Ocean, and North Pacific Ocean). PBDEs were detected in almost all the skipjack tuna collected from the locations surveyed (from < 0.1 to 53 ng/g of lipid), indicating widespread contamination by these compounds in the marine environment. Residue levels of PBDEs in these samples from the northern hemisphere seem to be higher than those from the southern hemisphere, which is plausibly due to larger usage of these compounds in the northern hemisphere. Higher concentrations of PBDEs were detected in the samples from waters around the East China Sea (up to 53 ng/g of lipid). Developing countries around the East China Sea are supposedly the "hot spots" releasing these chemicals into the marine environment. With regard to the composition of PBDE congeners, the percentage contribution by lower brominated congeners (BDE15, -28, and -47) showed an increasing trend with increasing latitude. On the other hand, higher brominated congeners (BDE153, -154, and -183) showed a reverse trend. These patterns suggest that lower brominated congeners of PBDEs (di-, tri-, and tetra-BDEs) were preferentially transported from pollution sources to northern colder regions through the atmosphere. PBDEs may have a high potency to cause global pollution like PCBs.     

Development of cereal bar with pineapple skin

The cereal bars are multi-component products consisting of cereals, dried fruit and syrup binder and may be added to the consumable parts of fruits and vegetables which usually are not exploited and have high nutritional value, thereby reducing food waste. It was developed a jam with pineapple skin, which it was utilized in 13.5% in the cereal bar formulation. The cereal bar was sensorial evaluated and had its centesimal and mineral composition determined. The new product achieved average of 8.3 for global impression using 9 points hedonic scale, 91% of acceptance rate and 67% of purchase intent. In this first use of pineapple skin jam as food ingredient it can be concluded that its aggregation in the cereal bar formula is feasible, making an accepted product with fibers, proteins and minerals, as an alternative to traditional cereal bars.