Phosphorus-containing block copolymer templates can control the size and shape of gold nanostructures

Amphiphilic block copolymers containing phosphine moieties in the main chain are employed as macromolecular ligands for gold(I). The sequential living anionic copolymerization of isoprene (I) and the phosphaalkene, MesP CPh2 (Mes = 2,4,6-trimethylphenyl) affords the block copolymer [PI]404-b-[MesP-CPh2]32 (1a). The incorporation of gold(I) moieties into this functional copolymer is accomplished by treating 1 with THT.AuCl (THT = tetrahydrothiophene) which affords [PI]404-b-[MesP(AuCl)-CPh2]32 (2a). Remarkably, dissolution of gold-functionalized 2 in n-heptane, a block-selective solvent for isoprene, affords spherical micelles with gold(I)-rich cores. Micelles were examined by transmission electron microscopy (TEM) and dynamic light scattering (DLS). We also prepared two additional copolymers with longer phosphine blocks and shorter PI segments: [PI]222-b-[MesP(AuCl)-CPh2]77 (2b) and [PI]164-b-[MesP(AuCl)-CPh2]85 (2c). When assembled in isoprene-selective solvents, 2b forms wormlike structures and 2c, with the longest phosphine block, forms fascinating micron sized intertwined wormlike structures. This represents a new method to control the shape and size of gold(I) nanostructures.     

Delineating the first few seconds of supramolecular self-assembly of mesostructured titanium oxide thin films through time-resolved small angle X-ray scattering

The early stages of evaporation induced self-assembly of titanium oxide mesophases from a precursor solution containing TiCl4 and the Pluronic triblock copolymer F-127 in HCl-water-ethanol solution have been studied using time-resolved SAXS techniques. Two experimental protocols were used to conduct these experiments. In one of these, the precursor solution was pumped around a closed loop as solvent was allowed to evaporate at a constant humidity-controlled rate. In the second protocol, a film of precursor solution was measured periodically as it dried completely to a residue under a stream of dry air. This permitted the detailed monitoring of changes in solution chemistry as a function of the elimination of volatile components followed by the actual drying process itself. The SAXS data were modeled in terms of two Guinier radii for soft nanoparticles while a broad Gaussian feature in the scatter profiles was accounted for by particle-article scattering interference due to close packing. For the initial precursor solution, one Guinier radius was found to be about 17 angstroms while the other ranged from 4 to 11 angstroms. Changing the rate of evaporation affected the two radii differently with a more pronounced effect on the smaller particle size range. Analysis gave an interparticle distance in the range 55-80 angstroms for the initial precursor solution which decreased steadily at both of the humidities investigated as evaporation proceeded and the particle packing increased. These results represent the first attempts to monitor in a precise fashion the growth of nano building blocks during the initial stages of the self-assembly process of a titanium oxide mesophase.     

Comparing stage-scenario with nodal formulation for multistage stochastic problems

To solve real life problems under uncertainty in Economics, Finance, Energy, Transportation and Logistics, the use of stochastic optimization is widely accepted and appreciated. However, the nature of stochastic programming leads to a conflict between adaptability to reality and tractability. To formulate a multistage stochastic model, two types of formulations are typically adopted: the so-called stage-scenario formulation named also formulation with explicit non-anticipativity constraints and the so-called nodal formulation named also formulation with implicit non-anticipativity constraints. Both of them have advantages and disadvantages. This work aims at helping the scholars and practitioners to understand the two types of notation and, in particular, to reformulate with the nodal formulation a model that was originally defined with the stage-scenario formulation presenting this implementation in the algebraic language GAMS. In addition, this work presents an empirical analysis applying the two formulations both without any further decomposition to perform a fair comparison. In this way, we show that the difficulties to implement the model with the nodal formulation are somehow reworded making the problem tractable without any decomposition algorithm. Still, we remark that in some other applications the stage-scenario formulation could be more helpful to understand the structure of the problem since it allows to relax the non-anticipativity constraints.

     

CuO based catalysts on modified acidic silica supports tested in the de-NOx reduction

A series of dispersed CuO catalysts supported on modified silica supports with Al2O3 (SA), TiO2 (ST), and ZrO2 (SZ) were prepared optimising the adsorption method of copper deposition assisted by ultrasound treatment, already reported in a previous paper (S. Bennici, A. Gervasini, V. Ragaini, Ultrason. Sonochem. 10 (2003) 61). The obtained catalysts were characterized in their bulk (atomic absorption, X-ray diffraction, temperature programmed reduction) and surface (N2 adsorption, X-ray photoelectron spectroscopy, scanning electron microscopy) properties. The morphology of the finished materials was not deeply modified compared with that of the relevant supports. The employed complemented techniques evidenced a well dispersed CuO phase with a copper-support interaction on the most acidic supports (SA and SZ). The catalyst performances were studied in the reaction of selective catalytic reduction of NOx with ethene in oxidizing atmosphere in a flow apparatus under variable times (0.360-0.072 s) and temperatures (200-450 degrees C). The catalysts prepared on the most acidic supports (SA and SZ) were the most active and selective towards N2 formation. They showed a particular interesting activity in the reaction of NO2 reduction besides that of NO reduction.     

Accidental exposure to UV radiation produced by germicidal lamp: case report and risk assessment

Ultraviolet radiation is known to cause both benefits and harmful effects on humans. The adverse effects mainly involve two target organs, skin and eye, and can be further divided into short- and long-term effects. The present case report describes an accidental exposure of two health-care workers to ultraviolet radiation produced by a germicidal lamp in a hospital pharmacy. The germicidal lamp presented a spectrum with an intense UV-C component as well as a modest UV-B contribution. Overexposure to UV-C radiation was over 100 times as large as the ICNIRP exposure limits. A few hours after the exposure, the two subjects reported symptoms of acute UV injury and both of them continued having significant clinical signs for over 2 years. In this study, we describe acute and potentially irreversible effects caused by high UV exposure. In addition, we present the results of risk assessment by occupational exposure to germicidal lamps.     

Drop deformation in microconfined shear flow

The deformation and breakup of a drop in an immiscible equiviscous liquid undergoing unbounded shear flow has been extensively investigated in the literature, starting from the pioneering work of Taylor. In this Letter, we address the case of microconfined shear flow, a problem which is relevant for microfluidics and emulsion processing applications. The main effects of confinement include complex oscillating transients and drop stabilization against breakup. In particular, very elongated drop shapes are observed, which would be unstable in the unbounded case and can be explained in terms of wall-induced distortion of the shear flow field. We show that wall effects can be exploited to obtain nearly monodisperse emulsions in microconfined shear flow.     

Raman spectroscopy of magneto-phonon resonances in graphene and graphite

The magneto-phonon resonance or MPR occurs in semiconductor materials when the energy spacing between Landau levels is continuously tuned to cross the energy of an optical phonon mode. MPRs have been largely explored in bulk semiconductors, in two-dimensional systems and in quantum dots. Recently there has been significant interest in the MPR interactions of the Dirac fermion magneto-excitons in graphene, and a rich splitting and anti-crossing phenomena of the even parity $E_{2g}$ long wavelength optical phonon mode have been theoretically proposed and experimentally observed. The MPR has been found to crucially depend on disorder in the graphene layer. This is a feature that creates new venues for the study of interplays between disorder and interactions in the atomic layers. We review here the fundamentals of MRP in graphene and the experimental Raman scattering works that have led to the observation of these phenomena in graphene and graphite.     

Mechanically assisted solid state synthesis of Mg2SnO4

Simultaneous TG?CDSC measurements have been used to study the solid state reaction in the system SnC₂O₄?C4MgCO₃·Mg(OH)₂·xH₂O (Sn:Mg?=?0.5). The results obtained with physically prepared mixture and with mixture mechanically activated by high-energy milling are compared. Synthesis of the compound Mg₂SnO₄ has been attempted starting from both type of mixture: Mg₂SnO₄ forms by annealing the activated mixture at temperatures between 850 and 1,000?°C while it can hardly be obtained from physical mixtures even by thermal treatment at temperature as high as 1,300?C1,350?°C. Mg₂SnO₄ prepared by annealing the activated mixture has been characterized by diffuse reflectance FT-IR spectroscopy, modulated temperature differential scanning calorimetry, scanning electron microscopy, and specific surface area measurements (B.E.T. method).