Highly Photostable Near-Infrared Fluorescent pH Indicators and Sensors Based on BF(2)-Chelated Tetraarylazadipyrromethene Dyes

In this study, a series of new BF(2)-chelated tetraarylazadipyrromethane dyes are synthesized and are shown to be suitable for the preparation of on/off photoinduced electron transfer modulated fluorescent sensors. The new indicators are noncovalently entrapped in polyurethane hydrogel D4 and feature absorption maxima in the range 660-710 nm and fluorescence emission maxima at 680-740 nm. Indicators have high molar absorption coefficients of ～80?000 M(-1) cm(-1), good quantum yields (up to 20%), excellent photostability and low cross-sensitivity to the ionic strength. pK(a) values of indicators are determined from absorbance and fluorescence measurements and range from 7 to 11, depending on the substitution pattern of electron-donating and -withdrawing functionalities. Therefore, the new indicators are suitable for exploitation and adaptation in a diverse range of analytical applications. Apparent pK(a) values in sensor films derived from fluorescence data show 0.5-1 pH units lower values in comparison with those derived from the absorption data due to F?rster resonance energy transfer from protonated to deprotonated form. A dual-lifetime referenced sensor is prepared, and application for monitoring of pH in corals is demonstrated.     

High-performance and cost-effective membrane electrode assemblies for advanced proton exchange membrane water electrolyzers: Long-term durability assessment

Improved activity and durability performance of a two-cell (86 cm²) proton exchange membrane water electrolyzer (PEMWE) stack is reported for the first time. Both membrane electrode assemblies (MEAs) contain one order of magnitude lower platinum group metal (PGM) loadings compared to the state-of-the-art PEMWEs and incorporate novel Pt recombination layers. The high-performance and cost-effective MEAs are fabricated by the unique reactive spray deposition technology (RSDT). This advanced methodology allows for one-step fabrication of MEAs and ensures precise control and distribution of the catalyst composition and loading. The RSDT-fabricated MEAs contain only 0.2 and 0.3 mg_PGM cm^?2 loading in the cathode and anode electrodes, respectively, and demonstrate excellent activity and durability for over 3000 h of operation at industrially-relevant operating conditions without showing significant loss in performance. This novel work shows that a significant cost reduction for PEMWEs is achieved while maintaining excellent durability, high catalysts activities, and low hydrogen cross-over.     

Application of Design of Experiments and Multilayer Perceptron Neural Network in Optimization of the Spray-Drying Process

The aim of this study was to investigate the effect of changing spray-drying parameters on the production of a naratriptan/maltodextrin/lactose composite, as well as to evaluate the application of design of experiments and multilayer perceptron (MLP) neural network in studying the spray-drying process. The system was spray dried as an aqueous solution using a Büchi 290-Mini Spray Dryer (Büchi Laboratoriums-Technik AG, Switzerland). A 2^4?1 factorial design study was undertaken to select the spray-drying processing variables that significantly affect the production yield, outlet air temperature, and residual moisture content. The process parameters studied were inlet air temperature, pump speed, aspirator setting (drying air flow rate), and feed concentration. After performing this screening study, three process parameters, pump speed, inlet air temperature, and feed concentration, were selected for further analysis, applying a central composite design and artificial neural network. Overall, the parameter that had the greatest influence on each investigated response was pump speed. It significantly influenced yield, moisture content, and particle size. Interaction between inlet air temperature and feed concentration was the only statistically significant interaction that influenced the moisture content. Particle size was mostly influenced by feed concentration as well as by a pump speed. A multilayer perceptron was the type of artificial neural network applied. The selected MLP structure had three layers: the first layer had three input units, the second layer had three hidden units, and the third layer had four output units. The selected MLP was trained through 10,000 epochs. Design of experiments using response surface methodology allows insight into interactions between variables, and an artificial neural network provides better prediction potential, enabling simultaneously determination of several outputs. Design of experiments and artificial neural network proved to be useful tool for optimization of the spray-drying process, where a design space for achieving the best process yields and optimum particle characteristics was established. There is a possibility that this conclusion can be drawn for other maltodextrin/lactose systems with other drug substances or for other similar spray-dried systems (the feedstock type is a carbohydrate-based aqueous solution). In future work, this will be tested with other materials.     

Bonding of novel self-glazed zirconia dental ceramics

ABSTRACT

Bonding behaviours of a novel self-glazed zirconia dental material were investigated. The effect of a preformed porous nanoceramic bonding surface and the different cleansing methods on saliva-contaminated bonding surfaces was assessed in this in vitro study. Cleaning procedures commonly used in dental offices were tested. All specimens demonstrated adhesive fracture patterns except for airborne particle abrasion group, which resulted in mixed-type fracture pattern and the highest bonding force values. No statistically significant differences in bonding force values were found between self-glazed zirconia with and without a preformed porous nanoceramic bonding surface when bonded with the self-adhesive resin cement (RelyX? Unicem 2). Scanning electron micrographs revealed no interaction between the bonding surface and the resin cement after priming. Mechanical retention is the predominant bonding mechanism between the bonding surface and the luting resin cement.     

Cooperative multicast for maximum network lifetime

We consider cooperative data multicast in a wireless network with the objective to maximize the network lifetime. We present the maximum lifetime accumulative broadcast (MLAB) algorithm that specifies the nodes' order of transmission and transmit power levels. We prove that the solution found by MLAB is optimal but not necessarily unique. The power levels found by the algorithm ensure that the lifetimes of the active relays are the same, causing them to fail simultaneously. For the same battery levels at all the nodes, the optimum transmit powers become the same. The simplicity of the solution is made possible by allowing the nodes that are out of the transmission range of a transmitter to collect the energy of unreliably received overheard signals. As a message is forwarded through the network, nodes will have multiple opportunities to reliably receive the message by collecting energy during each retransmission. We refer to this cooperative strategy as accumulative multicast. Cooperative multicast not only increases the multicast energy-efficiency by allowing for more energy radiated in the network to be collected, but also facilitates load balancing by relaxing the constraint that a relay has to transmit with power sufficient to reach its most disadvantaged child. When the message is to be delivered to all network nodes this cooperative strategy becomes accumulative broadcast (Maric and Yates, 2002). Simulation results demonstrate that cooperative broadcast significantly increased network lifetime compared with conventional broadcast. We also present the distributed MLAB algorithm for accumulative broadcast that determines the transmit power levels locally at the nodes.     

A Novel Approach to Modeling and Simulation of NTC Thick-Film Segmented Thermistors for Sensor Applications

This paper describes the design, modeling, simulation, and fabrication of thick-film segmented thermistors. These thermistors were printed on alumina using negative temperature coefficient 3K3 paste, composed of nanometer powder. Their room temperature resistance was measured versus the number of segments and electrode surface value for the fixed layer thickness and electrode spacing. After that, very large thermistors were printed to serve as both the powerful self-heaters and the heat loss sensors in the thermistor volume air flow meter and anemometer. For an application in AC bridges, impedance Z(f) and insertion loss S21 [dB] of the same largest segmented thermistor were measured using network analyzer HP8752A. Impedance modeling was performed using simple equivalent electrical circuit with circuit parameters estimated by fitting procedure (traditional approach), as well as using a commercial electromagnetic simulation program microwave office (MWO, novel approach). This was followed by the modeling of electrical current distribution over a number of segments done within the MWO. The results obtained from simulations and measurements were mutually compared.     

Biology of TiO2-oligonucleotide nanocomposites

Emerging areas of nanotechnology hold the promise of overcoming the limitations of existing technologies for intracellular manipulation. These new developments provide approaches for the creation of chemical-biological hybrid nanocomposites that can be introduced into cells and subsequently used to initiate intracellular processes or biochemical reactions. Such nanocomposites would advance medical biotechnology, just as they are improving microarray technology and imaging in biology and medicine, and introducing new possibilities in chemistry and material sciences. Here we describe the behaviour of 45-A nanoparticles of titanium dioxide semiconductor combined with oligonucleotide DNA into nanocomposites in vivo and in vitro. These nanocomposites not only retain the intrinsic photocatalytic capacity of TiO2 and the bioactivity of the oligonucleotide DNA (covalently attached to the TiO2 nanoparticle), but also possess the chemically and biologically unique new property of a light-inducible nucleic acid endonuclease, which could become a new tool for gene therapy.