Gold Spherical and Flake Assemblies Fabrication Through Calcination of Gold Nanoparticles Incorporated Poly(acrylonitrile) Nanofibers

Journal of Cluster Science - This work reports on the outcome of the calcination of gold nanoparticles incorporated polyacrylonitrile nanofibers in air which results in the formation of gold...     

Highly functionalized pyrazolines from symmetric and asymmetric 1,2-disulfonylhydrazines: a combination of experimental and DFT perspectives

Chemistry of Heterocyclic Compounds - In this work, new pyrazole derivatives were prepared by one-pot three-component reaction emloying symmetric and asymmetric 1,2-disulfonyl-hydrazines,...     

Horizon structure of rotating Bardeen black hole and particle acceleration

We investigate the horizon structure and ergosphere in a rotating Bardeen regular black hole, which has an additional parameter (g) due to the magnetic charge, apart from the mass (M) and the rotation parameter (a). Interestingly, for each value of the parameter g, there exists a critical rotation parameter (\(a=a_{E}\)), which corresponds to an extremal black hole with degenerate horizons, while for \(a<a_{E}\) it describes a non-extremal black hole with two horizons, and no black hole for \(a>a_{E}\). We find that the extremal value \(a_E\) is also influenced by the parameter g, and so is the ergosphere. While the value of \(a_E\) remarkably decreases when compared with the Kerr black hole, the ergosphere becomes thicker with the increase in g. We also study the collision of two equal mass particles near the horizon of this black hole, and explicitly show the effect of the parameter g. The center-of-mass energy (\(E_\mathrm{CM}\)) not only depend on the rotation parameter a, but also on the parameter g. It is demonstrated that the \(E_\mathrm{CM}\) could be arbitrarily high in the extremal cases when one of the colliding particles has a critical angular momentum, thereby suggesting that the rotating Bardeen regular black hole can act as a particle accelerator.     

Effect of self-fields on the electron cyclotron maser instability in a dielectric loaded waveguide

The influence of self-fields on the cyclotron maser instability in a hollow electron beam propagating parallel to a uniform axial magnetic field B ₀ ê _z in a dielectric loaded waveguide is investigated. The theoretical analysis is carried out within the framework of linearized Vlasov-Maxwell equations. It is assumed that the beam is thin with the radial thickness much smaller than the beam radius. A new dispersion relation for azimuthally symmetric electromagnetic perturbation is derived and analyzed numerically. The influence of self-fields on the cyclotron maser instability in a dielectric loaded waveguide for different dielectric medium is studied. It is found that unlike the hollow waveguide the growth rate is increased by increasing self-fields. The instability band width decreases due to the increasing self-fields. The maximum growth rate increases gradually as self-fields increase as regards a different dielectric medium.     

Heat transfer and rheological properties of transformer oil-oxidized MWCNT nanofluid

Power transformers play a key role in power and electrical industries and thus boosting their efficiency is necessary. In this study, the effect of oxidized multi-walled carbon nanotubes on transformer oil thermophysical properties was experimentally investigated. The maximum amount of carbon nanotubes was chosen up to 0.01 mass% to assure the maximum purity of transformer oil. Heat transfer characteristics of transformer oil and nanofluids in two cases of free and forced convection were studied. Breakdown voltage, flash point, pour point, density, electrical and thermal conductivities, viscosity and shear stress, as eight important quality parameters, were determined. According to the experimental results, the Breakdown voltage decreased through concentration increasing. Electrical conductivity is not changed considerable with increasing concentration and temperature. Thermal conductivity of nanofluids and transformer oil changed with increasing temperature and concentration. Furthermore, at all concentrations and temperatures, the viscosity of the nanofluids was lower than that of transformer oil.     

Enantioselective Synthesis of Boron‐Substituted Quaternary Carbon Stereogenic Centers through NHC‐Catalyzed Conjugate Additions of (Pinacolato)boron Units to Enones

The first examples of Lewis base catalyzed enantioselective boryl conjugate additions (BCAs) that generate products containing boron‐substituted quaternary carbon stereogenic centers are disclosed. Reactions are performed in the presence of 1.0–5.0 mol % of a readily accessible chiral accessible N‐heterocyclic carbene (NHC) and commercially available bis(pinacolato)diboron; cyclic or linear α,β‐unsaturated ketones can be used and rigorous exclusion of air or moisture is not necessary. The desired products are obtained in 63–95 % yield and 91:9 to >99:1 enantiomeric ratio (e.r.). The special utility of the NHC‐catalyzed approach is demonstrated in the context of an enantioselective synthesis of natural product antifungal (?)‐crassinervic acid.     

Modulable and Highly Diastereoselective Carbometalations of Cyclopropenes

The copper‐catalyzed carbomagnesiation reaction of cyclopropenyl esters 1 leads to various substituted cyclopropanes species 3 in good yields with very high diastereoselectivities. The reaction proceeds through a syn‐chelated carbomagnesiation reaction and could be extended to various cyclopropenylmethyl ester derivatives 5 . The potential of this approach was illustrated by the preparation of two consecutive all‐carbon quaternary stereocenters. However, the carbometalation reaction needs to be performed at temperature ranging from ?35 to ?20 °C to avoid subsequent fragmentation reaction into stereodefined β,γ‐nonconjugated unsaturated esters 4 . Alternatively, the carbocupration reaction with organocopper species could also be performed to leads to configurationally stable cyclopropyl copper species 2[Cu] . Additionally, when the Lewis acid character of the copper center is decreased (i.e., RCuCNLi), the reaction proceed with an anti‐selectivity. The diastereodivergent behavior of these organometallic species is of synthetic interest, since both diastereomers syn‐ 3 and anti‐ 3 can be obtained, at will, from the same precursor cyclopropenyl esters 1 .     

Aqueous-Mediated green synthesis of novel spiro[indole-quinazoline] derivatives using kit-6 mesoporous silica coated Fe3O4 nanoparticles as catalyst

In this work, a series of eight new spiro[3,4′]1,3-dihydro-2H-indol-2-one-2′-amino-4′,6′,7′,8′-tetrahydro-2′,5’(1’H,3’H)-quinazoline-diones were successfully synthesized through a three-component reaction of 1H-indole-2,3-diones (isatins), guanidine nitrate, and 1,3-cyclohexanediones, by use of Kit-6 mesoporous silica coated Fe₃O₄ nanoparticles (Fe₃O₄@SiO₂@KIT-6) as a highly efficient magnetically separable nanocatalyst in aqueous media at 60°C. Several notable features of thiseco-friendly protocol are high yields of products, short reaction times, operational simplicity, and the use of easily available and recyclable catalyst.     

Water treatment: functional nanomaterials and applications from adsorption to photodegradation

Global efforts for engineering desired materials which are able to treat the water sources still are ongoing in the bench level methods. Considering adsorbent and photocatalytic materials as the main reliable candidates still are encountering with struggles because of many challenges that restrict their large-scale application. This review comprehensively considered the recent advanced materials water treatment methods which involve to magnetic, activated carbon, carbon nanotubes (CNTs), graphene (G), graphene oxide (GO), (Graphene) quantum dots, carbon nanorods, carbon nano-onions, and reduced graphene oxide (RGO), zeolite, silica and clay-based nanomaterials. The adsorption and photocatalytic properties of these nanomaterials introduced them as highly potent option for heavy metal ions and organic dyes removal and photocatalytic degradation. High specific surface area in conjugation with presenting higher kinetics of adsorption and decomposition are the main characteristics of these materials which make them appropriate to treat wastewater even in ultralow concentration of the pollutants. Considering the mechanistic aspects of the adsorption and photocatalytic decomposition process, challenges and opportunities were other subjects that have been highlighted for the discussed nanomaterials. In term of the adsorption approaches, the mechanism of adsorptions and their influence on the maximum adsorption capacity were discussed and also for photocatalyst approach the radical active spices and their role in kinetic and efficiency of the organic pollutant decomposition were provided a deep discussion.     

Numerical simulation of natural gas/diesel dual-fuel engine for investigation of performance and emission

Journal of Thermal Analysis and Calorimetry - Due to global concerns about the emissions, limited hydrocarbon fuel resources and high fuel prices, a lot of researches have been done to improve the...