Analysis of Pseudo-Lyapunov Exponents of Solar Convection Using State-of-the-Art Observations

The solar photosphere and the outer layer of the Sun’s interior are characterized by convective motions, which display a chaotic and turbulent character. In this work, we evaluated the pseudo-Lyapunov exponents of the overshooting convective motions observed on the Sun’s surface by using a method employed in the literature to estimate those exponents, as well as another technique deduced from their definition. We analyzed observations taken with state-of-the-art instruments at ground- and space-based telescopes, and we particularly benefited from the spectro-polarimetric data acquired with the Interferometric Bidimensional Spectrometer, the Crisp Imaging SpectroPolarimeter, and the Helioseismic and Magnetic Imager. Following previous studies in the literature, we computed maps of four quantities which were representative of the physical properties of solar plasma in each observation, and estimated the pseudo-Lyapunov exponents from the residuals between the values of the quantities computed at any point in the map and the mean of values over the whole map. In contrast to previous results reported in the literature, we found that the computed exponents hold negative values, which are typical of a dissipative regime, for all the quantities derived from our observations. The values of the estimated exponents increase with the spatial resolution of the data and are almost unaffected by small concentrations of magnetic field. Finally, we showed that similar results were also achieved by estimating the exponents from residuals between the values at each point in maps derived from observations taken at different times. The latter estimation technique better accounts for the definition of these exponents than the method employed in previous studies.     

Electrochemical and microstructural investigations on an as-cast and solution-annealed Al–Mg–Sn–Ga alloy as anode material in sodium chloride solution

In this research, the electrochemical properties of a stir cast Al-0.65Mg-0.15Sn-0.05Ga (wt.%) alloy as an anode material in 3 wt.% NaCl solution was examined by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The corrosion behavior of the material was also evaluated using self-corrosion rate, hydrogen evolution, open circuit and closed circuit potentials, and anode efficiency measurements. In addition, the microstructure of the material was studied using scanning electron microscopy (SEM) and the intermetallic particles were analyzed by energy dispersive spectrometer (EDS). The results showed that tin inclusions were formed within the grains and along the grain boundaries and the dissolution of aluminum substrate was occurred preferentially around these particles leading to form round pits. The dissolution of alloy was accompanied by hydrogen gas evolution from cathodic tin particles. Polarization measurements showed active behavior with considerably negative corrosion potential value without any passive region. The obtained impedance results showed an increase in the impedance values due to the coverage of anode surface by reaction products during immersion. A sample of the alloy which was subjected to homogenizing annealing at 570 °C showed more active behavior by providing more negative open and closed circuit potential values and improved anode efficiencies at higher impressed currents, but evolved higher amounts of hydrogen compared to the as-cast anode.

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Graphical abstract This paper aims at evaluating the electrochemical and microstructural characteristics of an as-cast and solution-annealed Al-0.65Mg-0.15Sn-0.05Ga alloy anode which was fabricated by stir casting. The polarization and EIS results indicate negative corrosion potential and OCP values without passive region. The activity and anodic efficiency of the solution-annealed anode was higher in high impressed current densities but evolves more hydrogen

     

Synthesis of new aromatic polyamides containing α-amino phosphonate with high thermal stability and low heat release rate

The new aromatic polyamides containing α-amino phosphonate were synthesized from phosphorus-based dicarboxylic acid 4 and various aromatic diamines by direct polycondensation reaction. Dicarboxylic acid 4 was successfully synthesized from trimethyl phosphite, 4-aminobenzoic acid and terephthaldehyde via a three-component reaction. The polymerization reaction produced the polyamides 6a–f with high yield and desirable inherent viscosities. The thermal properties of the all samples were investigated by thermo-gravimetric analysis (TGA). The TGA results in N₂ exhibited the 10% mass loss temperatures (T₁₀) in the ranges of 324–345 °C, while the T₁₀ resulted from thermo-oxidative degradation were higher than those. The main data obtained by microscale combustion calorimetry revealed acceptable combustion properties such as very low peak of heat release rate for the synthesized polyamides 6a–f. The all of the results indicated that these polyamides can be potentially utilized as additive for improvement of thermal resistance and combustion behavior of thermoplastic materials.

     

Copper(II) Oxide Nanoparticles Impregnated on Melamine‐Modified UiO‐66‐NH2 Metal–Organic Framework for C–N Cross‐Coupling Reaction and Synthesis of 2‐Substituted Benzimidazoles

A zirconium‐based metal–organic framework, UiO‐66‐NH₂, modified by melamine (Mlm) was used as a support for CuO nanoparticles (NPs). Melamine offered a platform for uniform and homogeneous distribution of NPs on the surface of the frameworks and made a strong bonding to the NPs to avoid undesirable leaching. UiO‐66‐NH₂‐Mlm/CuO NPs were used for the Buchwald–Hartwig C–N cross‐coupling reaction to synthesize arylated anilines from phenyl iodide, bromide, and chloride and primary and secondary amines in DMF at 110°C. The catalyst was also employed for the synthesis of 2‐substituted benzimidazole derivatives from various aromatic aldehydes and o‐phenylenediamine in the absence of an oxidant in EtOH at room temperature. The catalyst was recyclable and reusable for several times and exhibited good stability (examined by BET, XRD, and SEM–EDX) in reaction conditions.     

Effect of TiO2 nanoparticles on structure and properties of high density polyethylene membranes prepared by thermally induced phase separation method

Polyethylene/TiO₂ membranes were fabricated via thermally induced phase separation (TIPS) method. A set of characterization tests including FE‐SEM, EDX, XRD, DSC, TGA, DMA, mechanical test and relative pure water flux for characterization of membranes were carried out to investigate the effect of TiO₂ nanoparticles on membrane properties. The results of EDX, XRD and TGA analyses confirmed the presence of TiO₂ nanoparticles in the polymer matrix. The results of DSC analysis revealed that the melting point as well as the crystallinity of the membranes increased slightly with increasing TiO₂ content. However, the glass transition temperature of the membranes was not affected by the presence of particles. Addition of nanoparticles also increased storage modulus, loss modulus and tensile strength at break of the membranes due to the stiffness improvement effect of inorganic TiO₂. Finally, it was observed that incorporation of the nanoparticles improved pure water flux of the membranes. Copyright © 2015 John Wiley & Sons, Ltd.     

Thermal performance of a helical shell and tube heat exchanger without fin,with circular fins,and with V-shaped circular fins applying on the coil

Journal of Thermal Analysis and Calorimetry - This numerical study analyzes the thermal performance of a helical shell and tube heat exchanger without a fin, with circular fins, and with cut...     

Physical and optical properties of organo-modified silica nanoparticles prepared by sol–gel

A comparative study on the physical and optical properties of silica nanoparticles prepared by sol–gel has been carried out. Post-modification of as-synthesized silica nanoparticles produced organo-functionalized silica nanoparticles slightly increased in size (~20%) and relatively high aggregation. However, in situ method produced sixfold bigger functionalized particles with good dispersion and less aggregation. Higher organic content was observed for in situ modified nanosilica, leading to a higher surface hydrophobicity that improved compatibility and dispersion in preparation of silica-polymer nanocomposite. Furthermore, in situ and post-modified nanosilica demonstrated a distinct optical activity, photoluminescence and UV compared to the unmodified nanoparticles.     

Generalized norm preserving maps between subsets of continuous functions

Positivity - Let X and Y be locally compact Hausdorff spaces. In this paper we study surjections $$T: A \longrightarrow B$$ between certain subsets A and B of $$C_0(X)$$ and $$C_0(Y)$$ ,...     

Theoretical Investigation of Tunable Goos-Hänchen Shifts in a Four-Level Quantum System

Goos-Hänchen (GH) shifts in the reflected and transmitted light have been discussed in a cavity with four-level quantum system. It is realized that the refraction index of intracavity medium can be negative by manipulating the external coherent laser fields. For the negative refraction index of intracavity medium, the GH shifts of reflected and transmitted light beams have been analyzed in a parametric condition. It is found that due to modulation of laser signals and relative phase between applied fields, large and tunable GH shifts in reflected and transmitted light beams can be obtained.