Vertically Aligned Hybrid Core/Shell Semiconductor Nanowires for Photonics Applications

A family of 1D organic/inorganic core/shell materials formed by an inner organic nanowire (ONW) conformally covered with an inorganic wide band gap semiconductor (ZnO or TiO₂) layer is presented. The developed procedure is a two‐steps vacuum methodology involving the formation of supported single crystal small‐molecule nanowires by physical vapor deposition and plasma enhance chemical vapor deposition (PECVD) of the inorganic shell. Critical characteristics of the last technique are the possibilities of low temperature and remote configuration deposition. Additionally, an initial step has to be included in order to create nucleation centers for the growth of the ONWs. The procedure and its general character in terms of the variability in organic core and inorganic shells composition and the applicability of the technique to different substrates are presented. The formation of the inorganic shell with no damage of the organic core single‐crystalline structure is demonstrated by high resolution transmission electron microscopy. The vertical alignment of the hybrid nanostructure is achieved thanks to the interaction of the 1D organic nanostructured surfaces and the glow discharge during the deposition of the inorganic shell by PECVD. The optical properties of these core/shell NWs are studied by fluorescence spectroscopy and microscopy, and their application as nanoscale waveguides in the 550–750 nm range addressed.     

Hair mercury levels in relation to fish consumption in a community of the Moroccan Mediterranean coast

Coastal populations with high seafood consumption in the Mediterranean have a significant exposure to dietary methylmercury, and areas where environmental mercury pollution is an issue due to industrial activities are of special concern. The study was undertaken with the aim of assessing methylmercury exposure through fish consumption in a community of north Morocco and characterizing the relevant health risk. Concentrations of total mercury were determined in human hair, a biomarker of methylmercury exposure, and in locally consumed fish by cold vapour atomic absorption spectrophotometry. Based on consumption frequencies reported by the 108 subjects included in the study the weekly intake of methylmercury was estimated and biomarker data were evaluated in relation to the estimated intake and the sociodemographic characteristics of the population. Multiple regression analysis was employed for the interpretation of hair mercury data in relation to fish consumption frequency, gender and the age of individuals. Mercury concentrations in hair ranged from 0.22 to 9.56 µg g^-1 (geometric mean = 1.79 µg g^-1) and were closely related to fish intake. Fisherman and their families consumed fish three to five times per week and were the most exposed population subgroup. A high proportion of women of child-bearing age (50%) had relatively high levels of mercury in their hair (3.08-7.88 µg g^-1).     

Can a Single Atom Serve as the Active Site in Some Heterogeneous Catalysts?

We examine a number of distinct situations relating to heterogeneous catalysts where either a single atom (or ion), or a very small cluster of atoms functions as the locus of chemical turnover in various distinct kinds of conversion. There is little doubt that individual ions at certain crystallographic sites in nanoporous solids can indeed act as single-site catalysts. The situation concerning nanoclusters of pure metal (or bimetallic entities) is rather more ambiguous. What was hitherto thought to be an effective catalyst made up of a small cluster of Pt supported on ??-Al₂O₃ (for hydrogenation) now seems to be a single atom of Pt attached to a 5-coordinated Al^III ion. And in the case of Au or Pt on other supports, there is evidence that a single Pt atom, positively charged, but surrounded by alkali-metal ions, is a powerful catalyst for the water?Cgas shift (CO + H₂O ?? H₂ + CO₂) reaction. We also report interesting results concerning the mobility of CeO₂ support material.     

Introducing a Novel Flexible Conjunction System to Pressure Control in Water Distribution Networks

Pressure management is one of the most significant water demand management methods to reduce leakage in water distribution networks. Leak as an adverse event is directly related to the pressure. Therefore, reducing extra network pressure decreases leakage in water distribution networks. The pressure reducing valves have some disadvantage. For example, they break down quickly. Therefore, in this study, a novel system named Pressure Reducing Flexible Storage (PRFS) was introduced that hasn’t these disadvantages and it could consider a good alternative for pressure reducing valves in water distribution networks. In this system, a spherical tank containing a flexible rubber cover was installed at the network node. By increasing the pressure in the conjunction, the foam was compressed and reduced the pressure. In this study, the presented system was simultaneously modeled by using Flow-3D and ABAQUS softwares, and pressure decrement was estimated in the conjunction. The results show that the proposed system can decrease the pressure in the conjunctions of water distribution network by about 18%. Therefore, it could be considered as a good alternative for pressure reducing valves in water distribution networks.     

A colorimetric assay for measuring cell-free and cell-bound cholesterol oxidase

Cholesterol oxidase (cholesterol:oxygen oxidoreductase, EC 1.1.3.6) catalyzes the conversion of sterol Δ⁵-3β-alcohol to the corresponding Δ⁴-3-ketone with the reduction of oxygen to hydrogen peroxide.Rhodococcus species GK 1, a soil isolated microbe, produces an extracellular and a membrane-bound cholesterol oxidase; the latter is bound to the outer surface of the microbial cell membrane. A simple and sensitive assay is described to measure the two enzyme types; no enzyme extraction is needed for measuring the membrane-bound cholesterol oxidase. In this assay, hydrogen peroxide is reduced by the chromogen 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) in the presence of horseradish peroxidase, and the increased absorbance is followed continuously at 600 nm (ε_m = 1.82×10⁴ M⁻¹·cm⁻¹ at pH 7.0 and 30°C). The standardized assay medium contained 46.9 mM sodium-potassium phosphate buffer pH 7.0, 0.16% Triton X-100, 312.5 μM ABTS, 50 μg peroxidase (12.5 units at 25°C), 6.25% isopropanol, 306.3 μM cholesterol or other sterols (kept in solution with isopropanol), and cholesterol oxidase. Oxidation of one molecule of cholesterol by cholesterol oxidase gives one molecule of hydrogen peroxide which reacts with two molecules of ABTS. The method is reproducible and the results correlate well with those obtained by measuring the absorbance of Δ⁴-cholest-3-one at 240 nm (ε_m = 1.40×10⁴ M⁻¹·cm⁻¹ at pH 7.0 and 30°C) and by the method of Allainet al. (Clin. Chem. 20, 470–475, 1974). In terms of efficiency, simplicity, and time saved, this coupled assay is expected to be a useful method for monitoring microbial production of cholesterol oxidase on an industrial scale, and for determining cholesterol or other sterols in biological fluids.     

Dynamics of Polar Surfaces on Ceria Nanoparticles Observed In Situ with Single‐Atom Resolution

Atomic hopping processes on ceria nanoparticle surfaces are observed by in situ phase contrast high‐resolution electron microscopy with an aberration‐corrected imaging lens. It is shown that single‐atom resolution is possible, and single‐atom dynamics for cerium are observable. Discrete changes in contrast and discrete positional changes of contrast maxima can be safely interpreted as visual fingerprints of atomic displacements. Both single‐atom movements and spontaneous sequential relocations of entire atomic rows are observed. Exclusive occurence of the effect on {100} type facets indicates polar dipole field mediated atomic rearrangements, while {111} facets are found to be stable. Molecular modelling confirms that the relocations follow genuine pathways involving partially occupied oxygen‐terminated surfaces, by means of temperature induced fluctuations. A series of images tracks the detailed atomic motions over a time of 120 s and quantifies the ratio of reversible atom hopping versus atom ablation.     

MRT letter: full-tilt electron tomography with a piezo-actuated rotary drive

Piezoelectric nanoactuation, which is rapidly becoming established as state-of-the-art positioning control in transmission electron microscopy (TEM), is extended here to include a rotational degree of freedom. A piezoelectric goniometer with both translational and rotary drive action has been designed with high level of miniaturization to fit into a standard TEM specimen holder shaft without compromising any of the performance of the default TEM goniometer and without any modifications to the TEM. Enhanced functionality of such a goniometer-in-goniometer is outlined and experimental results for electron tomography of nanostructures over a full tilt range of views, without any missing angles, are demonstrated.     

Polycondensation of new optically active diacid with diisocyanates in the presence of tetrabutylammonium bromide as a green media under microwave heating

Ionic liquids (IL)s have been recognized as ‘green’ alternatives to the organic solvents in a range of synthesis, catalysis and electrochemistry due to their unique chemical and physical properties. In this investigation, (2S)-5-(3-phenyl-2-phthalimidylpropanoylamino)isophthalic acid was prepared in three steps. The step-growth polymerization reaction of this novel diacid with various aromatic and aliphatic diisocyanates such as 4,4′-methylene bis(4-phenylisocyanate) (8a), toluylene-2,4-diisocyanate (8b), hexamethylene diisocyanate (8c) and isophorone diisocyanate (8d) were carried out in the presence of tetrabutylammonium bromide (TBAB) as a molten ionic liquid under microwave irradiation conditions and was compared with polymerization in traditional solvent like N-methyl-2-pyrrolidone (NMP). This process is safe and green since toxic and volatile organic solvent such as NMP was eliminated. The resulting new polymers were obtained in good yields with inherent viscosities ranging between 0.25 and 0.46 dL g⁻¹ and were characterized with FT-IR, ¹H-NMR, elemental and thermogravimetric analysis techniques.