Dental Resin Monomer Enables Unique NbO2/Carbon Lithium‐Ion Battery Negative Electrode with Exceptional Performance

Niobium dioxide (NbO₂) features a high theoretical capacity and an outstanding electron conductivity, which makes it a promising alternative to the commercial graphite negative electrode. However, studies on NbO₂ based lithium‐ion battery negative electrodes have been rarely reported. In the present work, NbO₂ nanoparticles homogeneously embedded in a carbon matrix are synthesized through calcination using a dental resin monomer (bisphenol A glycidyl dimethacrylate, Bis‐GMA) as the solvent and a carbon source and niobium ethoxide (NbETO) as the precursor. It is revealed that a low Bis‐GMA/NbETO mass ratio (from 1:1 to 1:2) enables the conversion of Nb (V) to Nb (IV) due to increased porosity induced by an alcoholysis reaction between the NbETO and Bis‐GMA. The as‐prepared NbO₂/carbon nanohybrid delivers a reversible capacity of 225 mAh g^?1 after 500 cycles at a 1 C rate with a Coulombic efficiency of more than 99.4% in the cycles. Various experimental and theoretical approaches including solid state nuclear magnetic resonance, ex situ X‐ray diffraction, differential electrochemical mass spectrometry, and density functional theory are utilized to understand the fundamental lithiation/delithiation mechanisms of the NbO₂/carbon nanohybrid. The results suggest that the NbO₂/carbon nanohybrid bearing high capacity, long cycle life, and low gas evolution is promising for lithium storage applications.     

Determining the effect of trace elements on biohydrogen production from fruit and vegetable wastes

Trace elements are one of the important parameters for dark fermentative H₂ production because they work as co-factors in H₂ formation biochemistry. Lack or excess of trace element and its concentrations could be an important reason for the low yield of H₂ production. In this study, the effects of 11 different trace elements (Fe, Ni, Zn, Co, Cu, Mn, Al, B, Se, Mo and W) were tested at two levels in terms of biohydrogen production from Fruit and Vegetable Wastes (FVW) with Biochemical Hydrogen Potential (BHP) Tests using Plackett-Burman statistical design. 1.1–2.8 times enhancement of biohydrogen production was determined with its addition. The most effective trace elements were found as Zn and Ni. In order to reveal the resident microbial flora, Denaturing Gradient Gel Electrophoresis (DGGE) analysis was carried out on all BHP effluent samples. Results of DGGE analysis, four microbial sequences evaluated as Clostridium sp., Clostridium baratii, Uncultured bacterium, Uncultured Streptococcus sp., and their similarity rates were 99%, 100%, 89%, 98%, respectively.     

Catalytic dehydrogenation of calcium borohydride by using hydrogel catalyst

The aim of this study was to investigate dehydrogenation of calcium borohydride (Ca(BH₄)₂) in the presence of a catalyst. Co ion-loaded poly(acrylamide-co-acrylic acid) (p(AAm-co-AAc)-Co) hydrogel was taken as a catalyst for this dehydrogenation procedure. Dehydrogenation reactions were performed under three different reaction temperatures, so the rate order and activation energy of the reaction were determined by using experimental results. The amount of hydrogen production increased with temperature and yields of the dehydrogenation reactions were determined as 46.5, 76.0 and 98.5% for 25, 35 and 45 °C, respectively. The activation energy of the dehydrogenation of Ca(BH₄)₂ was found as 71.39 kJ/mol according to zero order reaction kinetic. In addition, in order to determine reusability of p(AAm-co-AAc)-Co hydrogel, the same catalyst system was used in ten consecutive runs for the hydrolysis of Ca(BH₄)₂. This catalyst system was used ten times without any structural defect of the catalyst. On the other hand, the conversion ratio decreased from 98.5% to 83.5%.     

Multilayered optical OFDM for high spectral efficiency in visible light communication system

Photonic Network Communications - This paper presents two new schemes for improving the spectral efficiency of an optical orthogonal frequency-division multiplexing-based visible light...     

Channel estimation based on neural network in space time block coded MIMO–OFDM system

In this study, we propose feed-forward multilayered perceptron (MLP) neural network trained with the Levenberg–Marquardt algorithm to estimate channel parameters in MIMO–OFDM systems. Bit error rate (BER) and mean square error (MSE) performances of least square (LS) and least mean square error (LMS) algorithms are also compared to our proposed neural network to evaluate the performances. Neural network channel estimator has got much better performance than LS and LMS algorithms. Furthermore it doesn?t need channel statistics and sending pilot tones, contrary to classical algorithms.     

Mechanical properties of soft liner–poly(methyl methacrylate)‐based denture material

In this study, the mechanical properties of two different permanent soft lining materials and their bonding to poly(methyl methacrylate) (PMMA) were compared. Both of the soft liners were heat‐cured commercial materials. The polymerization was carried out by conventional methods suggested by manufacturer, and the curing was done at the temperature of boiling water for 5, 15, 25, and 35 min. The sample groups were tested in the computer‐aided tensile‐testing machine at a rate of 2 mm/min. The slow rate helps the collection of more and more reliable data. At this time, the stress–strain curves were used to calculate ultimate tensile strength, elastic modulus, resilience, and toughness. The measurements were carried for PMMA, Molloplast B, Flexor, and a combination of PMMA/soft liner. After introducing the soft lining material on PMMA of the same thickness, the new material structure was more elastic than the original PMMA. Flexor showed adhesive failure at studied curing periods, but Molloplast B gave larger tear strength values and cohesive rather than adhesive failure at the 25‐min and 35‐min curing times. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 467–474, 2002     

Elastic/plastic contact of surfaces considering ellipsoidal asperities of work-hardening multi-phase materials

The importance of the plasticity index for defining the degree of elastic and plastic deformation of surface asperities is described. Some experimental validation of the argument is provided and the method is extended to cover the case of ellipsoidal asperity contacts and the effect of work-hardening for a general asperity height probability distribution. It is also shown how the model may be applied to study the behaviour of multi-phase composites. The arguments are based on Hertzian contacts without tractions but may be used with reasonable confidence for contacts where the coefficient of friction is less than 0.1.