Polymerization shrinkage and porosity profile of dual cure dental resin cements with different adhesion to dentin mechanisms

This research aims to probe the porosity profile and polymerization shrinkage of two different dual cure resin cements with different dentin bonding systems. The self‐adhesive resin cement RelyX U200 (named RU) and the conventional Allcem Core (named AC) were analyzed by x‐ray microtomography (μCT) and Scanning Electron Microscopy (SEM). Each cement was divided into two groups (n = 5): dual‐cured (RUD and ACD) and self‐cured (RUC and ACC). μCT demonstrated that the method of polymerization does not influence the porosity profile but the polymerization shrinkage. Fewer concentration of pores was observed for the conventional resin cement (AC), independently the method used for curing the sample. In addition, SEM showed that AC has more uniform surface and smaller particle size. The method of polymerization influenced the polymerization shrinkage, since no contraction for both RUC and ACC was observed, in contrast with results from dual‐cured samples. For RUD and ACD the polymerization shrinkage was greater in the lower third of the sample and minor in the upper third. This mechanical behavior is attributed to the polymerization toward the light. µCT showed to be a reliable technique to probe porosity and contraction due to polymerization of dental cements.     

An insight into spray pulsed reactor through mathematical modeling of catalytic dehydrogenation of cyclohexane

A mathematical model has been developed to study the impact of nozzle-catalyst distance and bulk gas temperature on the conversion and hydrogen evolution rate in a spray pulse reactor. The effects of reactor configuration and operating parameters on conversion and evolution rate were predicted with more than 90% accuracy. Reactor optimization and sensitivity analysis were carried out and an optimal design of nozzle-catalyst distance 5 cm and bulk gas temperature of 50 °C were proposed. The optimized design was predicted to increase the conversion from approximately 32–74%. The model could be in general used for designing any endothermic heterogeneous catalytic reaction in a spray pulse reactor.     

Influence of DLC coating thickness on tribological characteristics under sliding rolling contact condition

Diamond-like-carbon (DLC) coating of thickness 3 and 10 μm were developed with and without radical nitriding pretreatment on steel rollers and spur gear pair. The friction coefficient and wear amount were evaluated under sliding rolling contact condition in vacuum and under oil lubrication. Delamination of coatings was observed at the interface of the substrate. The wear resistance of coatings improved with the thickness of the coating. In vacuum both the roller and the gear pair of 10 μm coating thickness with radical nitriding showed identical wear behavior. The radical nitriding seemed to enhance the life of DLC coatings.     

A power quality monitoring system: a case study in DSP-basedsolutions for electric power industry

The purpose of this study is to develop and implement a power quality monitoring system that will enable power quality engineers to conduct diagnostic testing in the field. The study is limited to the implementation of hardware and software required to process the analog signals received. A real-time monitoring system that can be used to perform automated power quality testing is described. The system is centered on a digital signal processor (DSP) interfaced to a personal computer (PC). The test signal is input to the system through the A/D board. The signal is analyzed in real-time in the DSP, and the results are transferred to the PC through the communication interface. The PC presents the results and interacts with the user. This system can be used to perform onsite power quality studies     

Novel 1,3,4-oxadiazole derivatives as efficient sensitizers for dye-sensitized solar cells: A combined experimental and computational study

We have synthesized and characterized donor–π–spacer–acceptor type molecules in which 1,3,4-oxadiazoles are π-spacers, triphenylamines are the donors and cyanoacetic acid are the acceptors for use as sensitizers in dye-sensitized solar cells (DSSCs). Detailed absorption, emission, electrochemical, photoelectrochemical and computational studies have been carried out on five novel derivatives. The dyes have an absorption range of 377–388 nm, and an emission in the range of 494–540 nm. There is a large charge transfer from the donor side to the acceptor side on excitation. The propeller shape of the triphenylamine and the bulky substituents on it help in reducing the dye-aggregation on TiO₂ surface. The dyes exhibited good overall conversion efficiency (2.79–3.21%). Plane wave calculations indicate that the dye has a reasonably strong binding to the TiO₂ surface and the generated DOS picture shows an overlap of the molecular orbitals of the dye and the TiO₂ bands. We conclude that the dyes have a promising role as sensitizers in DSSC.     

Solution combustion synthesis of layered LiNi0.5Mn0.5O2 and its characterization as cathode material for lithium-ion cells

LiNi_0.5Mn_0.5O₂, a promising cathode material for lithium-ion batteries, is synthesized by a novel solution-combustion procedure using acenaphthene as a fuel. The powder X-ray diffraction (XRD) pattern of the product shows a hexagonal cell with a = 2.8955 Å and c = 14.1484 Å. Electron microscopy investigations indicate that the particles are of sub-micrometer size. The product delivers an initial discharge capacity of 161 mAh g⁻¹ between 2.5 and 4.6 V at a 0.1 C rate and could be subjected to more than 50 cycles. The electrochemical activity is corroborated with cyclic voltammetric (CV) and electrochemical impedance data. The preparative procedure presents advantages such as a low cation mixing, sub-micron particles and phase purity.     

Chemical and Physical Sensing by Organic Field‐Effect Transistors and Related Devices

Organic semiconductor films are susceptible to noncovalent interactions, trapping and doping, photoexcitation, and dimensional deformation. While these effects can be detrimental to the performance of conventional circuits, they can be harnessed, especially in field‐effect architectures, to detect chemical and physical stimuli. This Review summarizes recent advances in the use of organic electronic materials for the detection of environmental chemicals, pressure, and light. The material features that are responsible for the transduction of the input signals to electronic information are discussed in detail.     

Performance evaluation of a multi-product system under CONWIP control

Analytical models of multi-product manufacturing systems operating under CONWIP control are composed of closed queuing networks with synchronization stations. Under general assumptions, these queuing networks are hard to analyze exactly and therefore approximation methods must be used for performance evaluation. This research proposes a new approach based on parametric decomposition. Two-moment approximations are used to estimate the performance measures at individual stations. Subsequently, the traffic process parameters at the different stations are linked using stochastic transformation equations. The resulting set of non-linear equations is solved using an iterative algorithm to obtain estimates of key performance measures such as throughput, and mean queue lengths. Numerical studies indicate that the proposed method is computationally efficient and yields fairly accurate results when compared to simulation.     

Photoluminescence characterization of the effects of rapid thermal annealing on AlGaAs/GaAs modulation-doped quantum wells

In this study, we describe the effects of rapid thermal annealing on the electrical and optical properties of modulation-doped quantum wells (MDQWs). The sheet carrier concentration in MDQW structures which have been annealed in contact with a piece of GaAs tends to decrease with increasing annealing time due to Si auto-compensation in the doped AlGaAs regions. The high energy cut-off point of 4.2 K PL spectra, which occurs at the Fermi energy, and the 77 K PL linewidth are accurate measures of sheet carrier density. These two parameters track variations in carrier density produced by annealing. Photoluminescence spectra also provide additional insight into annealing-induced changes such as Si migration, which causes a degradation in the mobility of the two-dimensional electron gas.