Optimization of fabrication conditions of MgB2/Fe superconducting tapes using response surface methodology

We have optimized fabrication conditions of MgB₂/Fe superconducting monofilament tapes fabricated using ex-situ powder-in-tube method without any intermediate annealing. Influences of three effective parameters (annealing temperature, annealing time and argon (Ar) gas atmosphere pressure during the heat treatments) on the transport critical current densities (J_c) were investigated. The samples were characterized using X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectrometer, optical microscope, critical transition temperature and J_c measurements. Response surface methodology was used to optimize the conditions for the maximum J_c of the samples and to understand the significance and interaction of the factors affecting J_c. 3-level-3-factor central composite design was employed to evaluate the effects of the fabrication conditions parameters such as annealing temperatures (850–950?°C), annealing times (30–120?min.) and Ar pressures (1–5 bars) on J_c of the samples. Based on the analysis of ridge max, the optimum fabrication conditions were as follows: annealing temperature 948?°C, annealing time 58?min. and Ar pressure 3 bars.     

Low-Loss Optical Waveguides for the Near Ultra-Violet and Visible Spectral Regions with Al(2)O(3) Thin Films from Atomic Layer Deposition

In this work, we report low-loss single-mode integrated optical waveguides in the near ultra-violet and visible spectral regions with aluminum oxide (Al₂O₃) films using an atomic layer deposition (ALD) process. Alumina films were deposited on glass and fused silica substrates by the ALD process at substrate/chamber temperatures of 200 °C and 300 °C. Transmission spectra and waveguide measurements were performed in our alumina films with thicknesses in the range of 210-380 nm for the optical characterization. Those measurements allowed us to determine the optical constants (n_w and k_w), propagation loss, and thickness of the alumina films. The experimental results from the applied techniques show good agreement and demonstrate a low-loss optical waveguide. Our alumina thin-film waveguides are well transparent in the whole visible spectral region and also in an important region of the UV; the measured propagation loss is below 4 dB/cm down to a wavelength as short as 250 nm. The low propagation loss of these alumina guiding films, in particular in the near ultra-violet region which lacks materials with high optical performance, is extremely useful for several integrated optic applications.     

Enhancement of hydrogen storage capacity of multi-walled carbon nanotubes with palladium doping prepared through supercritical CO2 deposition method

Pd doped Multi-Walled Carbon Nanotubes were prepared via supercritical carbon dioxide deposition method in order to enhance the hydrogen uptake capacity of carbon nanotubes at ambient conditions. A new bipyridyl precursor that enables reduction at moderate conditions was used during preparation of the sample. Both XRD analyses and TEM images confirmed that average Pd nanoparticle size distribution was around 10 nm. Hydrogen adsorption and desorption experiments at room temperature with very low pressures (0–0.133 bar) were conducted together with temperature programmed desorption (TPD) and reduction (TPR) experiments on undoped and doped materials to understand the complete hydrogen uptake profile of the materials. TPD experiments showed that Pd nanoparticles increased the hydrogen desorption activity at moderate temperatures around at 38 °C while for undoped materials it was determined around at 600 °C. Moreover, a drastic enhancement of hydrogen storage was recorded from 44 μmol/g sample for undoped material to 737 μmol/g sample for doped material through adsorption/desorption isotherms at room temperature. This enhancement, also verified by TPR, was attributed to spillover effect.     

Causality between energy consumption and GDP in the U.S.: evidence from wavelet analysis

This study investigates the dynamic causal relationship between energy consumption and economic growth in the U.S. at different time scales. The main novelty of the study is that this paper complements the existing studies on the nexus between energy consumption and economic growth by employing the wavelet transformation to obtain different time scales in order to investigate causality between energy consumption and economic growth. This method is first developed by Ramsey and Lampart. Their approach consists of first decomposing the series into time scales by wavelet filters and testing causality of each time scale with the pertinent time scale of the other series separately. The data span from 1973q1 to 2012q1 on a quarterly basis. The main empirical insight is that the causal relationship is stronger at finer time scales, whereas the relationship is less and less apparent at longer time horizons. The results indicate that energy consumption causes economic growth, while the reverse is not true at the original frequency of the data. At the very finest scale the same result arises. However, at coarser scales feedback is observed. In particular, at intermediate time scales the evidence indicates that energy consumption causes economic growth, while the reverse is also true. These empirical findings are expected to be of high importance in terms of the effective design and implementation of energy and environmental policies, especially when a number of countries in the pursuit of high economic growth targets do not pay any serious attention on environmental issues.     

Inhibitory effect of Turkish Rosmarinus officinalis L. on acetylcholinesterase and butyrylcholinesterase enzymes

In the current study, we have tested acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activity of the petroleum ether, ethyl acetate, chloroform, and methanol extracts, rosmarinic acid as well as the essential oil obtained from Rosmarinus officinalis L. growing in Turkey by a spectrophotometric method of Ellman using ELISA microplate-reader at 0.2, 0.5, and 1.0 mg/mL concentrations. In addition, quantification of rosmarinic acid, a common phenolic acid found in rosemary, was carried out by reversed-phase HPLC in the methanolic extract of the plant, which was found to have 12.21 ± 0.95% (122.1 ± 9.5 mg/g extract) of rosmarinic acid. Rosmarinic acid was also tested for its AChE and BChE inhibitory effect and found to cause 85.8% of inhibition against AChE at only 1.0 mg/mL. Besides, the essential oil was analyzed by GC–MS technique, which was shown to be dominated by 1,8-cineol (44.42%) and followed by α-pinene (12.57%).     

Synthesis of aniline—thiophene copolymer on β-PbO<Subscript>2</Subscript> electrode in acetonitrile

Electrochemical copolymerization of aniline and thiophene was investigated on -PbO₂ electrode in acetonitrile. Optimum experimental conditions were determined forcopolymerization. Copolymer films synthesized on -PbO₂ electrode were analyzed bycyclic voltammetry, dry conductivity measurements, FT-IR spectroscopy, elemental analysisand thermal methods.     

Synthesis and characterization of perfluorinated acrylate–methyl methacrylate copolymers

A novel perfluorinated acrylic monomer 3,5‐bis(perfluorobenzyloxy)benzyl acrylate (FM) with perfluorinated aromatic units was synthesized with 3,5‐bis(perfluorobenzyl)oxybenzyl alcohol, acryloyl chloride, and triethylamine. Copolymers of FM monomer with methyl methacrylate (MMA) were prepared via free‐radical polymerization at 80°C in toluene with 2,2′‐azobisisobutyronitrile as the initiator. The obtained copolymers were characterized by ¹H‐NMR and gel permeation chromatography. The monomer reactivity ratios for the monomer pair were calculated with the extended Kelen–Tüdos method. The reactivity ratios were found to be r₁ = 0.38 for FM, r₂ = 1.11 for MMA, and r₁r₂ < 1 for the pair FM–MMA. This shows that the system proceeded as random copolymerization. The thermal behavior of the copolymers was investigated by thermogravimetric analysis and differential scanning calorimetry (DSC). The copolymers had only one glass‐transition temperature, which changed from 46 to 78°C depending on the copolymer composition. Melting endotherms were not observed in the DSC traces; this indicated that all of the copolymers were completely amorphous. Copolymer films were prepared by spin coating, and contact angle measurements of water and ethylene glycol on the films indicated a high degree of hydrophobicity. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Aqueous polymerization of acrylamide initiated by 4,4′-azobis (4-cyano pentanol) and chain extension of polyacrylamide by means of ceric ion redox systems

Summary The polymerization of acrylamide (AA) initiated by 4,4-azobis (4 cyanopentanol) (ACP) was investigated in aqueous solution at 60°C. The molecular weight and the conversion depend on polymerization duration and initiator concentration. Polymerization of AA initiated by ACP yields polyacrylamide (PAA) with hydroxyl terminal groups. Redox polymerization of AA initiated by hydroxyl terminated PAA in conjuction with Ce(IV) provided increase in the molecular weight of the initial polymer.