Porous electrodes supported on ion-exchange membranes as electrochemical detectors for supercritical fluid chromatography

A conveniently assembled electrochemical cell, exploiting a porous electrode supported on a moist perfluorinated ion-exchange polymer, is proposed for profitable electrochemical detection in supercritical fluid chromatography. It consists of a porous Pt working electrode, contacted by the mobile phase from the chromatographic column, which is chemically deposited onto one side of a Nafion membrane. The rear uncoated side of this membrane, acting as a solid polymer electrolyte, is contacted by an electrolyte solution (1 M NaCl) contained in an internal compartment equipped with a Pt counter electrode and a Ag/AgCl, Cl(-) 1 M reference electrode. Ferrocene, eluted with supercritical carbon dioxide through a Spherisorb column installed in a supercritical fluid chromatographic system, was used as electroactive prototype analyte to test the performance of this detector, which turned out to be quite better than that provided by a conventional on-line UV absorbance detector. The recorded peaks were characterized by both a good reproducibility (4.5%) and a linear dependence of their height and area, which extended over a wide concentration range ( approximately 3 orders of magnitude). Moreover, they were not interfered by possible solvent front, unlike peaks recorded by the UV detector. The detection limit, estimated for a signal-to-noise ratio of 3 (4.2 x 10(-11) mol), was lower by approximately 1 order of magnitude than that found for the UV detector. Finally, the long-term stability of this detector was satisfactory in that only a approximately 6% decrease in the current responses was observed after a rather long period (2 months) of continuous use.     

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.     

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.     

Poled Polyaniline Coated Piezo Composite Using Low Electric Field and Reduced Poling Time： A Functional Material

Composite films were prepared by two different routes： lead zirconate titanate （PZT） particles coated with polyaniline （PAni） dispersed in a polymeric matrix of polyvinylidene fluoride （PVDF）; and PZT particles and PAni powder dispersed separately in the polymer matrix. The electrical conductivity of the particles was controlled by the protonation and de-protonation of PAni in solution with controlled pH. The results indicate that the percolation threshold of the composite made of PZT coated with a conductive layer （PZT-PAni） is in the range of 20 vol.% to 30 vol.% of PZT-PAni. The PZT-PAni/PVDF composite redoped in solution with pH 3.7 showed the best results in terms of longitudinal piezoelectric coefficient （d33） in samples containing 30 vol.% of ceramic particles due to the equilibrium between conduction and poling effects on the composite. The poling process of the composite sample required just 5 MV/m electric field applied during 15 min. Furthermore, the composite was used as sensor in structural health monitoring （SHM）, showing the possibility to propose it as a functional material.     

Cellulose‐Based Microparticles for Magnetically Controlled Optical Modulation and Sensing

Responsive materials with birefringent optical properties have been exploited for the manipulation of light in several modern electronic devices. While electrical fields are often utilized to achieve optical modulation, magnetic stimuli may offer an enticing complementary approach for controlling and manipulating light remotely. Here, the synthesis and characterization of magnetically responsive birefringent microparticles with unusual magneto‐optical properties are reported. These functional microparticles are prepared via a microfluidic emulsification process, in which water‐based droplets are generated in a flow‐focusing device and stretched into anisotropic shapes before conversion into particles via photopolymerization. Birefringence properties are achieved by aligning cellulose nanocrystals within the microparticles during droplet stretching, whereas magnetic responsiveness results from the addition of superparamagnetic nanoparticles to the initial droplet template. When suspended in a fluid, the microparticles can be controllably manipulated via an external magnetic field to result in unique magneto‐optical coupling effects. Using a remotely actuated magnetic field coupled to a polarized optical microscope, these microparticles can be employed to convert magnetic into optical signals or to estimate the viscosity of the suspending fluid through magnetically driven microrheology.     

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.