Integer quantum Hall effect in Kekulé-patterned graphene

Y-shaped Kekulébond textures in a honeycomb lattice on a graphene-copper superlattice have recently been experimentally revealed.In this paper,the effects of such a bond modulation on the transport coefficients of Kekulé-patterned graphene are investigated in the presence of a perpendicular magnetic field.Analytical expressions are derived for the Hall and longitudinal conductivities using the Kubo formula.It is found that the Y-shaped Kekulébond texture lifts the valley degeneracy of all Landau levels except that of the zero mode,leading to additional plateaus in the Hall conductivity accompanied by a split of the corresponding peaks in the longitudinal conductivity.Consequently,the Hall conductivity is quantized as±ne²/h for n=2,4,6,8,10,...,excluding some plateaus that disappear due to the complete overlap of the Landau levels of different cones.These results also suggest that DC Hall conductivity measurements will allow us to determine the Kekulébond texture amplitude.     

Investigation of energy performance in a U-shaped evacuated solar tube collector using oxide added nanoparticles through the emitter,absorber and transmittal environments via discrete ordinates radiation method

Journal of Thermal Analysis and Calorimetry - This work is a three-dimensional numerical study of a U-shaped evacuated tube solar collector employing different types of oxide nanofluids including...     

The structural and magnetic properties of one-step mechanochemical route synthesized La0.8Pb0.2MnO3 manganites

Mechanochemical route has been used to produce La_0.8Pb_0.2MnO₃ (LPMO) nanocrystalline samples from oxide precursors. The samples were characterized using X-ray diffraction, scanning electron microscope and AC susceptibility measurements. The results showed that it is possible to produce LPMO perovskite powders after 10 h of ball milling. The crystallite size and microstrain were estimated using Williamson-Hall equation. The results showed that the crystallite size and microstrain increase initially and then decrease by the increase of milling time. By decreasing particle size the dislocation density (strain) increases and reaches to a saturation point at a particular particle size, further particle size reduction takes place through gliding motion along grain boundaries, which leads to a reduction of the strain. The dynamic properties of 15 h ball-milled sample were investigated by AC susceptibility using the Neel-Brown and Vogel-Fulcher law for superparamagnetism. The frequency dependence of blocking temperature is well described by the Vogel-Fulcher law, and fitting the experimental data with Neel-Brown law gives unphysical value for relaxation time.     

Synthesis of sulfonamides and sulfonic esters via reaction of amines and phenols with thiols using H2O2–POCl3 system

Phosphorus oxychloride efficiently promoted the synthesis of sulfonamides and sulfonic esters from thiols with hydrogen peroxide in the presence of Amberlite IRA-400 (OH^?). This method has been applied to a variety of substrates including nucleophilic and sterically hindered amines, and also phenols with excellent yields of sulfonamides and sulfonic esters. In most cases these reactions are highly selective, simple, and clean, affording products in excellent yields and high purity.     

A needle trap device packed with MIL-100(Fe) metal organic frameworks for efficient headspace sampling and analysis of urinary BTEXs

The aim of this study was to develop a new method for the determination of benzene, toluene, ethylbenzene and xylene isomers (BTEXs) in urine samples. In this method, MIL-100(Fe)@Fe₃O₄@SiO₂ metal–organic framework was synthesized, characterized and packed inside a needle trap device (NTD) as a sorbent for headspace extraction of unmetabolized BTEXs from urine samples followed by gas chromatography (GC) analysis. The GC device was equipped with a flame ionization detector (FID). The results showed that the optimal extraction time, extraction temperature and salt content were 60 min, 30°C and 5%, respectively. Also, the optimal desorption time and temperature were determined to be 1 min and 250°C, respectively. The limits of detection and quantification of the analytes of interest were in the ranges 0.0001–0.0005 and 0.0003–0.0014 μg ml⁻¹, respectively. The intra- and inter-day repeatability were <7.6%. The accuracy of the measurements in urine samples was in the range 7.1–11.4%. The results also demonstrated that the proposed NTD offered various advantages such as having high sensitivity and being inexpensive, reusable, user friendly, environmentally friendly and compatible for use with the GC device. Therefore, it can be efficiently used as a MIL–NTD for the extraction and analysis of unmetabolized BTEXs from urine samples.     

The Theoretical and Experimental Studies on Oxidation of Straight Chain Amino Acids in Moderately Concentrated Sulfuric Acid Medium

The kinetics of the permanganic oxidation process of some straight chain amino acids in moderately concentrated sulfuric acid medium have been investigated using a spectrophotometric technique. Conclusive evidences have proven autocatalytic activity of Mn(II) for these reactions. It is determined that even and odd effects of the number carbon atom in a carbon chain are annihilated when it's the number of carbon atoms is increased more than of three in a noncatalytic oxidation pathway. Thus, rate constants belonging to glycine, l ‐α‐amino‐n‐butyric acid, l ‐norleucine, and l ‐α‐amino‐n‐heptanoic acid satisfy Taft's equation involving the induction factor in the noncatalytic pathway, whereas l ‐α‐amino‐n‐heptanoic acid has an odd number of carbon atom in its chain carbon. On the other hand, in the catalytic pathway, rate constants satisfy Taft' equation including inductive and steric factors, when rate constants belonging to amino acids with an even number of carbon atoms are separated from those with an odd number of carbon atoms. The oxidation process of amino acids in the noncatalytic pathway and those with the even number of carbon atoms in the carbon chain in the catalytic pathway speeds up by an increase in the length of chain that is accompanied with an increase in the carbon chain's electron‐donating characteristic. On the other hand, an increase in the length of the carbon chain is accompanied with more steric hindrance, which counteracts its electron‐donating character, thereby decreasing reaction rate in the catalytic pathway. Finally, amino acid–Mn(II) complexes were studied using a density functional theory method. Results obtained show that such a complex is less stable than reactants, namely it is formed in an endothermic reaction. The number and strength of hydrogen bonding belonging to amino acid is more than those of the amino acid–Mn(II) complex. Besides, it has been illustrated that natural bond orbital analysis and molecular orbital calculations satisfy the findings.     

Mechanism and Parameters Controlling the Decomposition Kinetics of Na2SiF6 Powder to SiF4

Sodium hexafluorosilicate (Na₂SiF₆) powder has been used as a silicon source for formation of Si₃N₄ coatings by the hybrid precursor system‐chemical vapor deposition (HYSY‐CVD) route. The quantitative effect of processing time, temperature, gas flow rate, and process atmosphere (N₂ and N₂:5% NH₃) upon the fractional weight loss during the decomposition of Na₂SiF₆ was studied using a standard L₉ Taguchi experimental design and analysis of variance. The decomposition kinetics of Na₂SiF₆(s) was studied theoretically and experimentally in the temperature range of 550–650ºC by applying the shrinking core model. It was found that regardless of atmosphere type, the reaction order is n ≈ 0.12 and that a two‐stage mixed mechanism consisting of chemical reaction and boundary layer gas transfer controls the decomposition rate. The determined fractional weight loss during Na₂SiF₆ decomposition in nitrogen atmosphere is about 1.05–1.5 orders of magnitude greater than that in N₂:NH₃. The gas flow rate affects the dissociation activation energy, being of 121, 109, and 94 kJ/mol in N₂ and of 140, 120, and 115 kJ/mol in N₂:NH₃, for the flow rates of 20, 60, and 100 cm³/min, respectively, in both atmosphere types. A good agreement is observed by comparing experimental weight loss data with model predictions.     

Synthesis,characterization and application of graphene palladium porphyrin as a nanocatalyst for the coupling reactions such as: Suzuki‐Miyaura and Mizoroki‐Heck

The palladium(II)‐coordinated 5,10,15,20‐tetrakis‐(4‐hexyloxyphenyl)‐porphyrin as a macrocyclic palladium complex was covalently grafted to the surface of graphene oxide (denoted as GO‐CPTMS@Pd‐TKHPP). GO‐CPTMS@Pd‐TKHPP was characterized using microscopic and spectroscopic techniques for confirmation of functionalization. The synthesized catalyst was checked in the Suzuki‐Miyaura and the Mizoroki‐Heck coupling reactions. The catalyst is very easy to handle, environmentally safe and economical. Also, this catalytic system shows high catalytic activity and the yields of the products are excellent. Moreover, the suggested catalyst was reusable for five runs with no significant decrease in catalytic activity.