Understanding the Central Location of a Hexagonal Hole in a B36 Cluster

The most stable form of a B₃₆ cluster has a central hexagonal hole. Such an interesting finding has led to the possible synthesis of a 2D boron sheet by employing the B₃₆ cluster as the building unit. Herein, a DFT study to investigate the reason for the central location of the hexagonal hole in the B₃₆ cluster is presented. The results show that the B₃₆ cluster with a central hexagonal hole is highly thermodynamically and kinetically stable. More importantly, such high stability is further understood through chemical bonding analysis.     

<Emphasis Type="Italic">Areca catechu</Emphasis> Assisted Synthesis of Silver Nanoparticles and its Electrocatalytic Activity on Glucose Oxidation

In this work, a facile biogenic route for the synthesis of silver nanoparticles (AgNPs) is reported. The aqueous extract of Areca catechu (A. catechu) nuts are used as reducing source. The synthesized AgNPs characterized by UV–Visible (UV–Vis) spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM) with energy dispersive spectrum (EDS) analysis. The formations of AgNPs are identified from the appearance of yellow color and the surface plasmon resonance absorbance peak between 407 and 437 nm. The FT-IR results exposed that the active biomolecules of A. catechu are responsible for capping of AgNPs. The synthesized AgNPs are distorted spherical shape with 45 nm of size, identified from the HR-TEM. In application, the electrocatalytic activity of AgNPs is analyzed towards glucose oxidation using cyclic voltammetry. The results showed that A. catechu derived AgNPs act as good electrocatalyst than bare bulk silver and glassy carbon electrodes.     

General functional response and recruitment in a predator–prey system with capture on both species

This work provides a mathematical model for a predator‐prey system with general functional response and recruitment, which also includes capture on both species, and analyzes its qualitative dynamics. The model is formulated considering a population growth based on a general form of recruitment and predator functional response, as well as the capture on both prey and predators at a rate proportional to their populations. In this sense, it is proved that the dynamics and bifurcations are determined by a two‐dimensional threshold parameter. Finally, numerical simulations are performed using some ecological observations on two real species, which validate the theoretical results obtained. Copyright © 2014 John Wiley & Sons, Ltd.     

Expanding the synthesis of Stöber spheres: towards the synthesis of nano-magnesium oxide and nano-zinc oxide

In order to synthesise Stöber spheres of different diameters, fixed amounts of ethanol, ammonia and water were used with varying amounts of tetraethyl orthosilicate. This simple method was further applied to the synthesis of nano-ZnO and nano-MgO from their respective precursors, zinc methoxide and magnesium ethoxide. The spherical nano-SiO₂, nano-ZnO and nano-MgO synthesised in this way were characterised by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. Preliminary investigations found that nano-ZnO and nano-MgO showed good catalytic activity in the trans-esterification reaction that converts vegetable oil to biodiesel.     

Application of microcolumnion chromatography using octadecylsilica immobilized with bovine serum albumin as stationary phase for the determination of inorganic anions

Microcolumn ion chromatography of inorganic anions has been studied using octadecylsilica immobilized with bovine serum albumin as a stationary phase. The analytes were monitored with a conductivity detector. The detection limits for chloride, nitrate and thiocyanate at S/N = 3 were 0.8, 1.0 and 3.0 μmol L^–1, respectively. The present system was applied to the determination of inorganic anions in tap water and serum samples. Received: 29 May 1996 / Accepted: 12 August 1996     

Comparative study of copper(II) and cadmium(II) salts as catalytic reagents in the determination of mercury by continuous-microflow cold vapour atomic absorption spectrometry

A continuous-microflow method with cold vapour atomic absorption spectrometric detection was used for the determination of mercury. A comparison of copper(II) and cadmium(II) salts as catalytic reagents is described in detail It was found that in the presence of at least 80 mg 1^?1 of copper(II) salt a similar signal was obtained for both inorganic mercury [mercury(II) chloride]and organic mercury [methylmercury(II) chloride]. With a cadmium(II) salt at least 100 mg 1^?1 were required.     

Computer simulations in the study of gold nanowires: the effect of impurities

Suspended gold nanowires have recently been made in an ultra-high vacuum ambient and were imaged by electron microscopy. Two puzzles were presented: one atom thick wires are produced and some of the atomic distances between these atoms before their breaking were too large. Simulations using realistic molecular dynamics method were able to unveil some processes to explain the mechanisms of formation, evolution, and breaking of these atomically thin Au nanowires under stress. The calculations showed how defects induce the formation of constrictions that eventually will form the one-atom chains. Atomically thin chains, five atoms long were obtained, before breaking. The results were in excellent agreement with experimental results except for the large Au-Au distances. In fact no theoretical calculation of pure gold nanowires have been able to produce such large distances. Light impurities that cannot be imaged in these experiments may be responsible for these large Au-Au distances. Using ab initio total energy calculations based on the density functional theory, we have studied the effect of H, C, O, N, B, S, CH, CH₂, and H₂ impurities on the nanowire’s electronic and structural properties, in particular how they affect the rupture of the nanowire. We find that the impurities tend to locally increase the nanowire’s strength, in such a way that its rupture always occurs at an Au-Au bond and never at an Au-X bond (X being an impurity). In particular, oxygen seems to form very stable bonds that may be used to pull longer Au chains. Regarding the observed large Au-Au bond lengths, it was found, based on quasi-static calculations, that the best candidate to explain the large distances is H. However, some particular experimental conditions may lead to different results. PACS 68.65.-k; 68.37.Lp; 71.15.Pd     

Methodology for analysis of displacement using digital holography

Digital holography is applied to make microdisplacement determination of a steel bar and an aluminum sheet. The displacement of aluminum sheet is made under immersion conditions in water and air. An experimental installation is presented for digital hologram registration with plane reference beam, using a CCD camera as detector. The “HOLODIG” computing system was developed for digital reconstruction of the image using the direct method, the intensity and phase image and interferograms were obtained. Taking into account the phase interferogram and making the unwrapping, the phase was determined for every point of the study surface. As examples of method application, the displacement of a square section steel bar, tested in air, and an aluminum sheet, tested in air and submerged in water, was determined. Experimental values of the displacement obtained agree with the applied ones. In the case of aluminum plate submerged in water, the magnitude of the measured displacement is proportional to water refraction index.     

Hot electron production using the Texas Petawatt Laser irradiating thick gold targets

We present data for relativistic hot electron production by the Texas Petawatt Laser irradiating solid Au targets with thickness between 1 and 4 mm. The experiment was performed at the short focus target chamber TC1 in July 2011, with intensities on the order of several ×10¹⁹ W/cm² and laser energies around 50 J. We discuss the design of an electron-positron magnetic spectrometer to record the lepton energy spectra ejected from the Au targets and present a deconvolution algorithm to extract the lepton energy spectra. We measured hot electron spectra out to ～50 MeV, which show a narrow peak around 10–20 MeV, plus high energy exponential tail. The hot electron spectral shapes appear significantly different from those reported for other PW lasers.