On Deformed Riemannian Extensions Associated with Twin Norden Metrics

The main purpose of this paper is to study the deformed Riemannian extension▽g +VG··in the cotangent bundle, where G is a twin Norden metric on the base manifold.     

The composite Milstein methods for the numerical solution of Stratonovich stochastic differential equations

In this paper, we present two composite Milstein methods for the strong solution of Stratonovich stochastic differential equations driven by d-dimensional Wiener processes. The composite Milstein methods are a combination of semi-implicit and implicit Milstein methods. The criterion for choosing either the implicit or the semi-implicit method at each step of the numerical solution is given. The stability and convergence properties of the proposed methods are analyzed for the linear test equation. It is shown that the proposed methods converge to the exact solution in Stratonovich sense. In addition, the stability properties of our methods are found to be superior to those of the Milstein and the composite Euler methods. The convergence properties for the nonlinear case are shown numerically to be the same as the linear case. Hence, the proposed methods are a good candidate for the solution of stiff SDEs.     

Recent trends in the chemistry of Sandmeyer reaction: a review

Metal-catalyzed reactions play a vital part to construct a variety of pharmaceutically important scaffolds from past few decades. To carry out these reactions under mild conditions with low-cost easily available precursors, various new methodologies have been reported day by day. Sandmeyer reaction is one of these, first discovered by Sandmeyer in 1884. It is a well-known reaction mainly used for the conversion of an aryl amine to an aryl halide in the presence of Cu(I) halide via formation of diazonium salt intermediate. This reaction can be processed with or without copper catalysts for the formation of C–X (X?=?Cl, Br, I, etc.), C-CF₃/CF₂, C–CN, C–S, etc., linkages. As a result, corresponding aryl halides, trifluoromethylated compounds, aryl nitriles and aryl thioethers can be obtained which are effectively used for the construction of biologically active compounds. This review article discloses various literature reports about Sandmeyer-related transformations developed during 2000–2021 which give different ideas to synthetic chemists about further development of new and efficient protocols for Sandmeyer reaction.

Graphical abstract

An updated compilation of new approaches for Sandmeyer reaction is described in this review to construct a variety of carbon-halogen, carbon-phosphorous, carbon-sulfur, carbon-boron etc. linkages.

     

Fabrication and characterization of nanocrystalline Al,Co:ZnO thin films by a sol–gel dip coating

The consequence of annealing on the micro-structural and electrochemical characteristics of Al doped CoZnO thin films deposited by sol–gel dip coating technique are studied. X-ray diffraction indicates that films have a hexagonal wurtzite structure oriented towards the (100). Optical properties of films are recorded by transmission curves utilising a UV–VIS spectrophotometer. The investigation of the optical transmission spectra indicates that the band gap of the films decrease from 3.99 eV to minimum 3.83 eV upon annealing. All films show room temperature ferromagnetism whose magnetization increases with annealing. Dip coated films possess polycrystalline nanosized grains with porous morphology.     

Intramolecular BSSE and dispersion affect the structure of a dipeptide conformer

B3LYP and MP2 calculations with the commonly-used 6-31+G(d) basis set predict qualitatively different structures for the Tyr–Gly conformer book1, which is the most stable conformer identified in a previous study. The structures differ mainly in the ψ_tyr Ramachandran angle (138° in the B3LYP structure and 120° in the MP2 structure). The causes for the discrepant structures are attributed to missing dispersion in the B3LYP calculations and large intramolecular BSSE in the MP2 calculations. The correct ψ_tyr value is estimated to be 130°. The MP2/6-31+G(d) profile identified an additional conformer, not present on the B3LYP surface, with a ψ_tyr value of 96° and a more folded structure. This minimum is, however, likely an artefact of large intramolecular BSSE values. We recommend the use of basis sets of at least quadruple-zeta quality in density functional theory (DFT), DFTaugmented with an empirical dispersion term (DFT-D) and second-order Møller-Plesset perturbation theory (MP2 ) calculations in cases where intramolecular BSSE is expected to be large.     

Entanglement dynamics of spatially close bipartite atomic systems in thermal environment

We investigate the entanglement dynamics in a bipartite atomic system subjected to thermal environment with arbitrary initial pure entangled states. We consider the atoms close together and study the effect of temperature of the reservoir and the interatomic distance on the evolution of entanglement for both initially entangled and unentangled states. We find that we can have long time entanglement even in thermal environment.     

Two-Dimensional SnSe2/CNTs Hybrid Nanostructures as Anode Materials for High-Performance Lithium-Ion Batteries

Tin diselenide (SnSe₂), as an anode material, has outstanding potential for use in advanced lithium-ion batteries. However, like other tin-based anodes, SnSe₂ suffers from poor cycle life and low rate capability due to large volume expansion during the repeated Li⁺ insertion/de-insertion process. This work reports an effective and easy strategy to combine SnSe₂ and carbon nanotubes (CNTs) to form a SnSe₂/CNTs hybrid nanostructure. The synthesized SnSe₂ has a regular hexagonal shape with a typical 2D nanostructure and the carbon nanotubes combine well with the SnSe₂ nanosheets. The hybrid nanostructure can significantly reduce the serious damage to electrodes that occurs during electrochemical cycling processes. Remarkably, the SnSe₂/CNTs electrode exhibits a high reversible specific capacity of 457.6 mA h g⁻¹ at 0.1 C and 210.3 mA h g⁻¹ after 100 cycles. At a cycling rate of 0.5 C, the SnSe₂/CNTs electrode can still achieve a high value of 176.5 mA h g⁻¹, whereas a value of 45.8 mA h g⁻¹ is achieved for the pure SnSe₂ electrode. The enhanced electrochemical performance of the SnSe₂/CNTs electrode demonstrates its great potential for use in lithium-ion batteries. Thus, this work reports a facile approach to the synthesis of SnSe₂/CNTs as a promising anode material for lithium-ion batteries.     

Electromechanical Fields and Their Influence on the Internal Quantum Efficiency of GaN-Based Light-Emitting Diodes

The effect of electromechanical fields, i.e., polarization fields, on the efficiency droop of GaN-based light-emitting diodes is presented using both experimental and numerical analyses.The role of incorporating such polarization charge density in device performance is numerically investigated and further compared with the experimental results of internal quantum efficiency of three different devices in consideration.