Thermal properties and kinetics of new-generation posterior bulk fill composite cured light-emitting diodes

In this study, the thermal behavior in terms of glass transition (T _g), degradation, and thermal stability of four commercial new-generation posterior bulk fill composites (Surefill SDR, Dentsply; Quixfill, Dentsply; Xtrabase, Voco; and Xtrafill, Voco) activated by light-emitting diodes (LEDs) was analyzed by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The activation energies (E _a) for the decomposition of the dental resins were calculated based on the Kissinger and Doyle kinetic models from the peaks of the endothermic curves obtained when the specimens were heated at four different temperatures (5, 10, 15, and 20 °C min^?1) during DSC. The results show that the Xtrabase composite displayed the highest T _g (120 °C at a 5 °C min^?1 heating rate) and E _a (157.64 kJ mol^?1) values associated with thermal degradation from the main chain of the polymer.     

Preparation and characterization of activated carbon from pine cone by microwave-induced ZnCl2 activation and its effects on the adsorption of methylene blue

In this work, activated carbon prepared from pine cone (PCAC) with ZnCl₂ as an activation agent under microwave radiation was investigated. The activation step was performed at the microwave input power of 400 W and radiation time of 5 min. The properties of activated carbon were characterized by N₂ adsorption Brunauer–Emmett–Teller (BET), scanning electron microscopy and Fourier transform infrared spectroscopy. Results showed that the BET surface area, Langmuir surface area, and total pore volume of PCAC were 939, 1,486 m²/g and 0.172 cm³/g, respectively. Adsorption capacity was demonstrated by the iodine numbers. The adsorptive property of PCAC was tested using methylene blue dye. Equilibrium data was best fitted by the Langmuir isotherm model, showing a monolayer adsorption capacity of 60.97 mg/g. The pseudo-first- and pseudo-second-order kinetic models were examined to evaluate the kinetic data, and the rate constants were calculated. Adsorption of the dyes followed pseudo-first order kinetics. Thermodynamic parameters such as free energy, enthalpy and entropy of dye adsorption were obtained.     

The Effect of Enantiomer Elution Order on the Determination of Minor Enantiomeric Impurity in Ketoprofen and Enantiomeric Purity Evaluation of Commercially Available Dexketoprofen Formulations

In a recent study, opposite enantiomer elution order was observed for ketoprofen enantiomers on two amylose-phenylcarbamate-based chiral columns with the same chemical composition of the chiral selector but in one case with coated while in the other with an immobilized chiral selector. In the present study, the influence of this uncommon effect on method validation parameters for the determination of minor enantiomeric impurity in dexketoprofen was studied. The validated methods with two alternative elution orders for enantiomers were applied for the evaluation of enantiomeric impurity in six marketed dexketoprofen formulations from various vendors. In most of these formulations except one the content of enantiomeric impurity exceeded 0.1% (w/w).     

Natural Melanin Nanoparticle‐decorated Screen‐printed Carbon Electrode: Performance Test for Amperometric Determination of Hexavalent Chromium as Model Trace

A biosensor was prepared with natural melanin nanoparticles (MNP) decorated on a screen‐printed carbon electrode (SPCE). Hexavalent chromium was selected as a well‐known heavy metal ion to be detected for testing the performance of novel biosensor. Natural MNP was extracted from cuttlefish (Sepia officinalis) ink. Surface decoration of SPCEs with MNP was performed by two different methods. The first one was layer‐by‐layer assembly (LBL‐A) for different cycle times(n). In the second one, plasma treatment of SPCE incorporated with evaporation‐induced self‐assembly (EI‐SA) techniques including different incubation times in MNP solutions. The performance of both modified SPCEs were tested for amperometric detection of Cr(VI) in various water samples, and peak reduction of Cr(VI) was determined at 0.33 V. Amperometric results showed wide linear ranges of 0.1–2 μM and 0.1–5 μM of Cr(VI) for SPCEs modified with 14n‐LBL‐A and 12h‐EI‐SA, respectively. The sensitivities of SPCEs modified with 14n‐LBL‐A and 12h‐EI‐SA techniques were 0.27 μA μM^?1 and 0.52 μA μM^?1, respectively. In addition, both modified SPCEs selectively detected Cr(VI) in a model aqueous system composed of certain other heavy metals and minerals, and tap and lake water samples. The LOD and LOQ values for 12h‐EI‐SA were 0.03 μM and 0.1 μM, respectively. This showed that MNP‐modified‐SPCEs generated via EI‐SA techniques have the potential to be an alternative to conventional detection methods such as ICP‐MS.     

Exergoeconomic analysis of a thermochemical copper–chlorine cycle for hydrogen production using specific exergy cost (SPECO) method

The manner is investigated in which exergy-related parameters can be used to minimize the cost of a copper–chlorine (Cu–Cl) thermochemical cycle for hydrogen production. The iterative optimization technique presented requires a minimum of available data and provides effective assistance in optimizing thermal systems, particularly in dealing with complex systems and/or cases where conventional optimization techniques cannot be applied. The principles of thermoeconomics, as embodied in the specific exergy cost (SPECO) method, are used here to determine changes in the design parameters of the cycle that improve the cost effectiveness of the overall system. The methodology provides a reasonable approach for improving the cost effectiveness of the Cu–Cl cycle, despite the fact that it is still in development. It is found that the cost rate of exergy destruction varies between $1 and $15 per kilogram of hydrogen and the exergoeconomic factor between 0.5 and 0.02 as the cost of hydrogen rises from $20 to $140 per GJ of hydrogen energy. The hydrogen cost is inversely related to the exergoeconomic factor, plant capacity and exergy efficiency. The results are expected to assist ongoing efforts to increase the economic viability and to reduce product costs of potential commercial versions of this process. The impact of the results are anticipated to be significant since thermochemical water splitting with a copper–chlorine cycle is a promising process that could be linked with nuclear reactors to produce hydrogen with no greenhouse gases emissions, and thereby help mitigate numerous energy and environment concerns.     

Cloud point extraction procedure for flame atomic absorption spectrometric determination of lead(II) in sediment and water samples

The conditions for cloud point extraction of lead(II) from aqueous solutions were investigated and optimized. The procedure is based on the separation of Pb(II) – brillant cresyl blue (BCB) complexes into the micellar media by adding the surfactant Triton X-114. After phase separation, the surfactant-rich phase was dissolved with 1 mol L⁻¹ HNO₃ in ethanol and diluted with 1 mol L⁻¹ HNO₃ solution before lead was determined by flame atomic absorption spectrometry. Optimization of the pH, ligand and surfactant quantities, incubation time, temperature, viscosity, sample volume, and interfering ions was performed. The effects of the matrix ions were also examined. The detection limits for three times the standard deviations of the blank for lead were 7.5 μg L⁻¹ for water samples and 0.33 μg g⁻¹ for sediment samples. The validity of cloud point extraction was checked by employing certified reference samples of Lake Sediment IAEA-SL-1 and Sewage Sludge BCR-CRM 144R. The procedure was applied to natural waters and sediment samples with satisfactory results (recoveries >95%, relative standard deviations <6.4%).     

Oxygen assisted laser cutting mechanism—a laminar boundary layer approach including the combustion process

The present study examines the combined effects of chemical reactions taking place between a gas jet and molten metal, the cooling effect of the jet and the evaporation of metal, during a CO₂ laser cutting process. A laminar boundary layer approach was used to develop a theoretical model for the oxygen gas jet laser cutting mechanism. An experiment was carried out to monitor the keyhole formation using a video recorder and detect the light emitted from the entrance and exist surfaces of the workpiece using a fibre-optic probe during the cutting process. The experimental study was extended to employ two different workpiece materials (stainless steel and mild steel) at two thicknesses, and varying oxygen assisting gas pressures. It is found that the theoretical model developed in the present study is valid for a cutting speed of about 30 mm s⁻¹ and all jet velocities up to sonic, since the effect of shock is excluded in the model.     

Resonant non-linear waves—III. Elastic continuum with quadratic non-linearity

The paper derives the relevant non-linear integro-differential evolution equation by the method due to Collins expanding on a procedure by Keller. The quadratically non-linear case is not a trivial variation over the cubically non-linear case that was presented in preceding papers. As expected a different scaling and ordering of terms is needed and the first order perturbation solution provides no information on resonance. Nevertheless, although obtained by much longer calculations, the final equation for the present case is of identical form, with differences only in numerical coefficients, with the cubic case that was presented and solved earlier.