A Mechanistic Investigation of the Kinetic Resolution of Secondary Aromatic Alcohols Using a Ferrocene‐Based Planar Chiral 4‐(Dimethylamino)pyridine Catalyst

A detailed computational and kinetic analysis of the acetylation of 1‐phenylethanol with acetic anhydride catalyzed by planar chiral 4‐(dimethylamino)pyridine (DMAP) catalyst (?)‐ 1 is presented. The study includes a computational investigation of the potential‐energy surface including the acylation and stereoselective transition states at the DFT level of theory. Experimentally, the kinetic study shows that the reaction proceeds in a first‐order manner in catalyst, whereas both substrates, acetic anhydride and 1‐phenylethanol, show fractional order, which is in accordance with steady‐state conditions. The fractional order depends on an equilibrium between the free catalyst and the acetylated catalyst.     

Effect of moisture content on the 222Rn mass exhalation rates for different grain-size samples of red brick and cement mortar used in Qena city,Egypt

Journal of Radioanalytical and Nuclear Chemistry - Four different grain size fractions (0.2–0.5, 0.5–1, 1–1.8, 1.8–2 mm) of red brick and cement mortar samples at...     

Active dielectric metasurface based on phase‐change medium

We propose all‐dielectric metasurfaces that can be actively re‐configured using the phase‐change material Ge₂Sb₂Te₅ (GST) alloy. With selectively controlled phase transitions on the composing GST elements, metasurfaces can be tailored to exhibit varied functionalities. Using phase‐change GST rod as the basic building block, we have modelled metamolecules with tunable optical response when phase change occurs on select constituent GST rods. Tunable gradient metasurfaces can be realized with variable supercell period consisting of different patterns of the GST rods in their amorphous and crystalline states. Simulation results indicate a range of functions can be delivered, including multilevel signal modulating, near‐field coupling of GST rods, and anomalous reflection angle controlling. This work opens up a new space in exploring active meta‐devices with broader applications that cannot be achieved in their passive counterparts with permanent properties once fabricated.

     

A novel chaos control strategy for discrete-time Brusselator models

This article deals with the dynamical analysis of discrete-time Brusselator models. Euler’s forward and nonstandard difference schemes are implemented for discretization of Brusselator system. We investigate the local dynamics related to equilibria of both discrete-time models. Furthermore, with the help of bifurcation theory and center manifold theorem, explicit parametric conditions for directions and existence of flip and Hopf bifurcations are investigated. A novel chaos control method is implemented in order to control chaos in discrete-time Brusselator models under the influence of flip and Hopf bifurcations. Numerical simulations are provided to illustrate theoretical discussion and effectiveness of newly introduced chaos control strategy.     

The Effect of Added Salts and Organics on the Cloud Point of TX‐114

Herein we report the effect of additives (salts and organics) on the cloud point (CP) of nonionic surfactant Triton X‐114 (TX‐114) aqueous solutions. CP showed a concentration dependent variation in the absence of any added compound. Addition of quaternary ammonium (or phosphonium) bromides to 0.8 mM TX‐114 solutions increased the CP. It was found that long chain alcohols and amines decreased the CP of 0.8 mM TX‐114 +80 mM Bu₄AmB aqueous system, while it either remained constant or increased in the presence of short chain additives. The effect of first group additives (long chain) can be explained by considering that these additives solubilize in interfacial region and assist in micellar growth. Short chain additives remain in aqueous phase and affect the micelle hydration by affecting the solvent. Pentylamine behaved differently than pentanol: pentylamine increased the CP (like short chain additives) while pentanol decreased the CP. In pentylamine, the hydrophilicity of NH₂ group and its dissociation into NH₃ ⁺ dominates over the hydrophobicity of its alkyl chain. Aliphatic hydrocarbons first decreased and then increased the CP. The overall behavior depended upon the chain length of the hydrocarbon. With decane, the CP decreasing region disappeared completely.     

Phase‐preserved macroscopic visible‐light carpet cloaking beyond two dimensions

Transformation optics, a recent geometrical design strategy of light manipulation with both ray trajectories and optical phase controlled simultaneously, promises an invisibility cloaking device that can render a macroscopic object invisible even to a scientific instrument measuring optical phase. Recent “carpet” cloaks have extended their cloaking capability to broadband frequency ranges and macroscopic scales, but they only demonstrated the recovery of ray trajectories after passing through the cloaks, while whether the optical phase would reveal their existence still remains unverified. In this paper, a phase‐preserved macroscopic visible‐light carpet cloak is demonstrated in a geometrical construction beyond two dimensions. As an extension of previous two‐dimensional (2D) macroscopic carpet cloaks, this almost‐three‐dimensional carpet cloak exhibits three‐dimensional (3D) invisibility for illumination near its center (i.e. with a limited field of view), and its ideal wide‐angle invisibility performance is preserved in multiple 2D planes intersecting in the 3D space. Optical path length is measured with a broadband pulsed‐laser interferometer, which provides unique experimental evidence on the geometrical nature of transformation optics.

     

Aggregates of iron in ytterbium films

Films of ytterbium doped with iron (0.3?C1.6 at.% Fe) have been prepared by co-deposition of atomic beams of the elements onto Kapton substrates under high vacuum. Iron is immiscible in ytterbium and various iron species are expected to occur. XRD reveals a mixture of fcc and hcp ytterbium. The Mössbauer spectra are interpreted with contributions from monomeric iron on interstitial sites, two types of neighboring substitutional iron aggregates and two types of clusters formed upon diffusion. The present data supplement earlier data obtained for 0.5 and 5 at.% Fe. There is no systematic correlation of cluster formation with increasing iron concentration. There are indications that clusters are formed more easily for thin films. We conclude that cluster formation occurs mainly on the film surface and is limited by the slow diffusion from inside films.     

A facile synthesis of novel 1,4-benzoxazepin-2-one derivatives

An efficient and simple synthesis of 1,4-benzoxazepin-2-one derivatives has been achieved via the reaction of isoquinoline, activated acetylenes, and 1-(6-hydroxy-2-isopropenyl-1-benzofuran-yl)-1-ethanone in water without using any catalyst. This one-pot reaction occurs in high yields under mild conditions.     

Synthesis,Characterization, and Magnetic Behavior of Cobalt-Ferrite Nanoparticles under Variant Temperature Conditions

Physics of the Solid State - Wet chemical method was applied for the synthesis of cobalt-ferrite nanoparticles. The physicochemical properties were investigated by number of analytical techniques....