Laser irradiation effects on the surface,structural and mechanical properties of Al–Cu alloy 2024

Laser irradiation effects on surface, structural and mechanical properties of Al–Cu–Mg alloy (Al–Cu alloy 2024) have been investigated. The specimens were irradiated for various fluences ranging from 3.8 to 5.5 J/cm² using an Excimer (KrF) laser (248 nm, 18 ns, 30 Hz) under vacuum environment. The surface and structural modifications of the irradiated targets have been investigated by scanning electron microscope (SEM) and X-ray diffractometer (XRD), respectively. SEM analysis reveals the formation of micro-sized craters along the growth of periodic surface structures (ripples) at their peripheries. The size of the craters initially increases and then decreases by increasing the laser fluence. XRD analysis shows an anomalous trend in the peak intensity and crystallite size of the specimen irradiated for various fluences. A universal tensile testing machine and Vickers microhardness tester were employed in order to investigate the mechanical properties of the irradiated targets. The changes in yield strength, ultimate tensile strength and microhardness were found to be anomalous with increasing laser fluences. The changes in the surface and structural properties of Al–Cu alloy 2024 after laser irradiation have been associated with the changes in mechanical properties.     

A highly selective fluorescent chemosensor for guanosine-5'-triphosphate via excimer formation in aqueous solution of physiological pH

A new water-soluble and fluorescent imidazolium-anthracene cyclophane 1 effectively recognizes and differentiates the biologically important GTP and ATP in 100% aqueous solution of physiological pH 7.4. Fluorescence, (1)H-NMR spectra and ab initio calculations demonstrate that excimer formation and fluorescence enhancement occur upon GTP and ATP binding, respectively, through (C-H)(+)···A(-) hydrogen bond interactions.     

Hole mediated coupling in Sr2Nb2O7 for visible light photocatalysis

The band gap reduction and effective utilization of visible solar light are possible by introducing the anionic hole-hole mediated coupling in Sr(2)Nb(2)O(7). By using the first principles calculations, we have investigated the mono- and co-anionic doping (S, N and C) in layered perovskite Sr(2)Nb(2)O(7) for the visible-light photocatalysis. Our electronic structure and optical absorption study shows that the mono- (N and S) and co-anionic doped (N-N and C-S) Sr(2)Nb(2)O(7) systems are promising materials for the visible light photocatalysis. The calculated binding energies show that if the hole-hole mediated coupling could be introduced, the co-doped systems would be more stable than their respective mono-doped systems. Optical absorption curves indicate that doping S, (N-N) and (C-S) in Sr(2)Nb(2)O(7) can harvest a longer wavelength of the visible light spectrum as compared to the pure Sr(2)Nb(2)O(7) for efficient photocatalysis.     

Critical micelle concentration and self-aggregation of hexadecyltrimethylammonium bromide in aqueous glycine and glycylglycine solutions at different temperatures

Conductivities, densities and ultrasonic speeds measurements of hexadecyltrimethylammonium bromide (HTAB) in aqueous solutions of glycine (Gly) and glycylglycine (Gly-Gly) have been made at various temperatures. The critical micelle concentration (CMC), the degree of ionization (??) of the micelles, standard free energy, enthalpy, and entropy of the micellization process (??G _m ^° , ??H _m ^° , and ??S _m ^° ) for the present systems were estimated at different temperatures. The CMC values of HTAB in aqueous Gly and Gly-Gly were also evaluated by density and ultrasonic speed measurements. Apparent molar volumes, (V _?), apparent molar volumes at infinite dilution, (V _? ^° ), apparent molar compressibilities, (K _?), of HTAB in the pre- and post-micellar regions, and volume change on micellization (??V _? ^m ) were also estimated. Large positive values of T??S _m ^° and small negative values of ??H _m ^° suggest that micellization process is driven primarily by entropy increase. The increase in ??V _? ^m and K _? with rise in temperature is indicative of less compact micellar structure of HTAB in presence of amino acid additives. These data suggest that amino acids are solubilised probably in the palisade layer of the micelle.     

Effect of thermal stresses on chip-free diode laser cutting of glass

In laser cleaving of brittle materials using controlled fracture technique, thermal stresses are used to induce a crack and the material is separated along the cutting path by extending this crack. In this study, a glass sheet is stressed thermally using a 808-940 nm diode laser radiation. One of the problems in laser cutting of glass with controlled fracture technique is the cut deviation at the leading and the trailing edges of the glass sheet. In order to avoid this damage it is necessary to understand the stress distributions which control crack propagation. A study is conducted here to analyse the cut deviation problem of glass by examining the stress fields during diode laser cutting of soda-lime glass sheets. Optical microscope photographs of the breaking surface are obtained to examine the surface quality and cut path deviation while the latter is explained from the results of the stress fields which are obtained from a finite element simulation.     

The effect of material thickness,laser power and cutting speed on cut path deviation in high-power diode laser chip-free cutting of glass

In the laser cleaving of brittle materials, using controlled fracture technique, thermal stresses are used to induce the crack and the material is separated along the cutting path by extending the crack. One of the problems in laser cutting of glass with this technique is the cut path deviation at the leading and the trailing edges of the glass sheet. Previous work has shown this deviation to be partly due to the high magnitudes of thermal stresses generated near the edges of the sheet. This paper reports on the experimental results of the effects of glass thickness, laser power and the cutting speed on cut path deviation in diode laser cutting of glass. Finite element modelling of the cutting process has also been used to simulate the transient effects of the moving beam and predict thermal fields and stress distributions. These predictions are validated against the experimental data and are used to explain the process mechanisms. It is shown that an increase in the thickness of the glass sheet for the same power and cutting speed or an increase in the cutting speed with constant power and a given sheet thickness results in smaller cut path deviations at the leading and trailing edges of the glass sheet.     

Polypropylene/carbon nanotube magnetic composites obtained using carbon nanotubes from sawdust

Magnetic polypropylene (PP) nanocomposites with different loadings (from 0.5 to 20 wt %) of carbon nanotubes with iron (CNT‐Fe) were fabricated using the melt‐mixing method. The carbon nanotubes were synthesized by pyrolysis of sawdust from the furniture industry. The morphological characterization shows homogenous dispersion of the filler in the polymer matrix. The addition of only 0.5 wt % CNT‐Fe already results in ferromagnetic behavior in the diamagnetic polymer matrix. The thermal properties were investigated using thermogravimetric analysis and differential scanning calorimetry. The results show an increase in the maximum degradation, crystallization, and melting temperatures of the nanocomposites compared with neat PP. The nanocomposites showed improvement in terms of mechanical and oxygen permeability properties. A very significant result of the work is the high remnant magnetization and coercivity values of the nanocomposites at room temperature whereas most of the works on similar systems show magnetic properties only at very low temperatures.     

Measurement of the absolute branching fraction of Ds+ --> tau+ nutau decay

Using a sample of tagged D(s)(+) decays collected near the D(s)(*+/-)D(s)(-/+) peak production energy in e(+)e(-) collisions with the CLEO-c detector, we study the leptonic decay D(s)(+)-->tau(+)nu(tau) via the decay channel tau(+)-->e(+)nu(e)nu(tau). We measure B(D(s)(+)-->tau(+)nu(tau))=(6.17+/-0.71+/-0.34)%, where the first error is statistical and the second systematic. Combining this result with our measurements of D(s)(+)-->mu(+)nu(mu) and D(s)(+)-->tau(+)nu(tau) (via tau(+)-->pi(+)nu(tau)), we determine f(D(s))=(274+/-10+/-5) MeV.     

Binder-Free Fabrication of Prussian Blue Analogues Based Electrocatalyst for Enhanced Electrocatalytic Water Oxidation

Developing a cost-effective, efficient, and stable oxygen evolution reaction (OER) catalyst is of great importance for sustainable energy conversion and storage. In this study, we report a facile one-step fabrication of cationic surfactant-assisted Prussian blue analogues (PBAs) M_x[Fe(CN)₅CH₃C₆H₄NH₂]∙yC₁₉H₃₄NBr abbreviated as SF[Fe-Tol-M] (where SF = N-tridecyl-3-methylpyridinium bromide and M = Mn, Co and Ni) as efficient heterogeneous OER electrocatalysts. The electrocatalysts have been characterized by Fourier transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX) analysis, and X-ray photoelectron spectroscopy (XPS). In the presence of cationic surfactant (SF), PBAs-based electrodes showed enhanced redox current, high surface area and robust stability compared to the recently reported PBAs. SF[Fe-Tol-Co] hybrid catalyst shows superior electrochemical OER activity with a much lower over-potential (610 mV) to attain the current density of 10 mA cm⁻² with the Tafel slope value of 103 mV·dec⁻¹ than that for SF[Fe-Tol-Ni] and SF[Fe-Tol-Mn]. Moreover, the electrochemical impedance spectroscopy (EIS) unveiled that SF[Fe-Tol-Co] exhibits smaller charge transfer resistance, which results in a faster kinetics towards OER. Furthermore, SF[Fe-Tol-Co] offered excellent stability for continues oxygen production over extended reaction time. This work provides a surface assisted facile electrode fabrication approach for developing binder-free OER electrocatalysts for efficient water oxidation.