Ultra-trace determination of silver in water samples by electrothermal atomic absorption spectrometry after preconcentration with a ligand-less cloud point extraction methodology

A very simple and ligand-less cloud point extraction (CPE) methodology for the preconcentration of ultra-trace amounts of silver as a prior step to its determination by electrothermal atomic absorption spectrometry (ETAAS) has been developed. The method is based on the extraction of silver at pH 9 by using non-ionic surfactant polyethyleneglycolmono-p-nonylphenylether (PONPE 7.5) without adding any chelating agent. Several important variables that affect the CPE efficiency and ETAAS signal were investigated and optimized. The preconcentration of 15 ml sample solution allowed us to achieve an enhancement factor of 60. The calibration graph using the preconcentration system was linear in the range of 5-100 ngl(-1) with a correlation coefficient of 0.9991. The lower limit of detection (3s) obtained in the optimal conditions was 1.2 ngl(-1). The relative standard deviation (R.S.D.) for eight replicate determinations at 30 ngl(-1) Ag level was 4.2%. The proposed method was successfully applied to the ultra-trace determination of silver in water samples.     

Charge storage in double layers of thermally grown silicon dioxideand APCVD silicon nitride

Experimental results on charge storage and discharge in double layers of silicon dioxide and silicon nitride will be reported and discussed. SiO₂ with a thickness of 300 nm was thermally grown on silicon wafers, while cover layers of Si₃N₄ with thicknesses of 50, 100, and 150 nm were deposited chemically at atmospheric pressure. The samples were charged by the point-to-grid corona method. At room temperature, the measured surface potential V was stable during a period of almost three years. Isothermal measurements under different environmental conditions showed an improved charge retention compared to a single layer grown silicon dioxide. After ~3 h at 300°C, the observed voltage drop was <10% for the double layers and ~60% for bare SiO₂. Similar results were obtained under a humid condition of 95%RH and 60°C. Besides, thermally stimulated current (TSC) was measured in setup with a temperature ramp of 200°C/h. For the double layers, a current peak with a maximum temperature at ~500°C was observed. The measured current in the range of 300 to 400°C, the location of current maxima observed in thermally grown silicon dioxide or APCVD silicon nitride, was negligible. In addition to improved electret properties the internal stress in the investigated double layers can be adjusted by a proper thickness ratio of oxide layer to nitride layer. Therefore double layers of silicon dioxide and nitride seem to be promising materials for integrated sensors and actuators based on the electret effect     

Power-Electronics-Based Solutions for Plug-in Hybrid Electric Vehicle Energy Storage and Management Systems

Batteries, ultracapacitors (UCs), and fuel cells are widely being proposed for electric vehicles (EVs) and plug-in hybrid EVs (PHEVs) as an electric power source or an energy storage unit. In general, the design of an intelligent control strategy for coordinated power distribution is a critical issue for UC-supported PHEV power systems. Implementation of several control methods has been presented in the past, with the goal of improving battery life and overall vehicle efficiency. It is clear that the control objectives vary with respect to vehicle velocity, power demand, and state of charge of both the batteries and UCs. Hence, an optimal control strategy design is the most critical aspect of an all-electric/plug-in hybrid electric vehicle operational characteristic. Although much effort has been made to improve the life of PHEV energy storage systems (ESSs), including research on energy storage device chemistries, this paper, on the contrary, highlights the fact that the fundamental problem lies within the design of power-electronics-based energy-management converters and the development of smarter control algorithms. This paper initially discusses battery and UC characteristics and then goes on to provide a detailed comparison of various proposed control strategies and proposes the use of precise power electronic converter topologies. Finally, this paper summarizes the benefits of the various techniques and suggests the most viable solutions for on-board power management, more specific to PHEVs with multiple/hybrid ESSs.      

The mechanism of voltage decay in corona-charged layers of silicondioxide during UV irradiation

The charge stability in thermally grown silicon dioxide layers during irradiation with monochromatic ultraviolet light has been investigated. The samples were charged by a constant-voltage corona method. A Xenon arc lamp in combination with a monochromator was used to generate mono-energetic photons. The surface potential was measured as a function of the photon energy, the irradiation intensity, the charge polarity and the substrate doping. In order to interpret the experimental results, different theoretical models were developed which consider the possibility of photo-ionization of trapped charges, multiphoton excitation in the dielectric, and injection of hot carriers from the substrate into the oxide layer. The discussion of the parameters derived from each model leads to the conclusion that electron injection from the substrate is most probably responsible for the voltage decay     

A liquid film motor

It is well known that electro-hydrodynamical effects in freely suspended liquid films can force liquids to flow. Here, we report a purely electrically driven rotation in water and some other liquid suspended films with full control on the velocity and the chirality of the rotating vortices. The device, which is called “film motor”, consists of a quasi two-dimensional electrolysis cell in an external in-plane electric field, crossing the mean electrolysis current density. If either the external field or the electrolysis voltage exceeds some threshold (while the other does not vanish), the liquid film begins to rotate. The device works perfectly with both DC and AC fields.     

Ag@Ni Core–Shell Nanowire Network for Robust Transparent Electrodes Against Oxidation and Sulfurization

Silver nanowire (Ag NW) based transparent electrodes are inherently unstable to moist and chemically reactive environment. A remarkable stability improvement of the Ag NW network film against oxidizing and sulfurizing environment by local electrodeposition of Ni along Ag NWs is reported. The optical transmittance and electrical resistance of the Ni deposited Ag NW network film can be easily controlled by adjusting the morphology and thickness of the Ni shell layer. The electrical conductivity of the Ag NW network film is increased by the Ni coating via welding between Ag NWs as well as additional conductive area for the electron transport by electrodeposited Ni layer. Moreover, the chemical resistance of Ag NWs against oxidation and sulfurization can be dramatically enhanced by the Ni shell layer electrodeposited along the Ag NWs, which provides the physical barrier against chemical reaction and diffusion as well as the cathodic protection from galvanic corrosion.     

Rotational regimes of freely suspended liquid crystal films under electric current in presence of an external electric field

The electrohydrodynamic (EHD) vortices produced by an electric current in freely suspended liquid crystal (LC) films of N-(4-methoxybenzylidene)-4-butylaniline (MBBA), convert to a pure rotation in the presence of external electric field ( $\it{E}_{{\rm ext}}$ ) perpendicular to the current direction. Here, the direction and strength of the rotation are precisely under control by our self-made device called ??liquid-film motor??. In this paper, we present experimental observations of the EHD fluid flow when external electric field varies from zero to a value in which pure rotation on the liquid crystal (LC) film is observed. We also show experimentally that the presence of external electric field causes a great decrease in the current produced by the voltage V _J required for observing EHD vortices in freely suspended films of MBBA. The LC films begin to rotate when E _ext V _J reaches a threshold value. This threshold is investigated experimentally as a function of voltage V _J and the external electrical field $\it{E}_{{\rm ext}}$ .     

Robust Acoustical Gas Leak Detection in the Presence of Correlated,Uncorrelated and Impulsive Noises,Using Wavelet-Based Optimized Residual Complexity

Leak detection based on acoustic emission needs robust time delay estimation in the presence of various types of noise. Considering several aspects of leakage signal and noise, the present work introduces wavelet based optimized residual complexity (WORC), in order to minimize the probability of false alarms in the presence of correlated, uncorrelated, and impulsive noise. The proposed method utilizes two approaches simultaneously. First, it optimizes residual complexity “for robustness against both correlated and uncorrelated noise”, then it employs wavelet basis in order to reduce the complexity of mixture of correlated and impulsive noise. In order to compare the resolution and percentage of false alarms of WORC with those of optimized residual complexity and cross correlation, we used both experimental and simulated leakage signals of a gas pipe. The results demonstrate the superiority of WORC in term of robustness in the presence of correlated, uncorrelated, and impulsive noise.     

Silicon-based inorganic electrets for application in micromachineddevices

Layers of SiO₂ and Si₃N₄ have good mechanical properties for application in micro-machined electret capacitor microphones. These materials are investigated as single or double layers in terms of chargeability and long-term charge stability. The main emphasis is put on the miniaturization of electret layers. The lateral dimensions of the electrets are reduced to 2 mm and the charge decay characteristics under different environmental conditions are described. According to the experimental data, multilayer samples of silicon dioxide and nitride possess good chargeability and higher charge stability compared to the well investigated single layers. Typically, the double layers loose ~10% of their surface potential when annealed for 200 min at 300°C and show a peak of the thermally stimulated current at 430°C. It can also be shown that the miniaturization of samples does not necessarily cause a faster charge decay     

Dual stimuli responsive neutral/cationic polymers/clay nanocomposite hydrogels

In this work, a thermodynamic-based equilibrium-swelling model was proposed to predict the swelling process of neutral/cationic polymers-clay nanocomposite hydrogels sensitive to dual stimuli temperature and pH. Indeed, the new swelling model can estimate the effect of the rigid clay nanoparticles component on swelling behavior of blend nanocomposite hydrogels. The mixing term in model was developed based on lattice theory by considering the effects of solvent-polymers, solvent-clay, and polymer-clay interaction parameters. The influence of the ionic groups of the clay layers and cationic polymer on the swelling was also taken into account in the proposed model. The model was verified by preparation of polyvinyl alcohol/chitosan/montmorillonite intelligent nanocomposite hydrogel by tripolyphosphate crosslinking method followed by freezing–thawing process. It was found that it could give good prediction for the equilibrium swelling of polymer-clay nanocomposite hydrogels in the case of phantom network, especially where the swelling temperature and clay loading level are high and the pH of swelling medium is low. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48797.