Dinuclear Five‐Coordinate Copper(II) Complexes with Chelating Diphosphonic Acid Ligands: Hydrothermal Synthesis,Structure, and Thermal Properties

The synthesis of two new diphosphonic acid ligands,[ethane‐1, 2‐diylbis(azanediyl)]bis[(4‐chlorophenyl)methylene]diphosphonic acid (L₁P), [ethane‐1, 2‐diylbis(azanediyl)]bis[(4‐bromophenyl)methylene]diphosphonic acid (L₂P), and their corresponding copper complexes, Cu₂(L₁P)₂ ( 1 ) and Cu₂(L₂P)₂ ( 2 ) are described herein. Complex 2 was structurally characterized with X‐ray single crystal diffraction. The structure of 2 consists of five‐coordinatecopper(II) ions with a distorted square pyramidal arrangement doubly bridged by OPO from phosphonate groups. The Cu–Cu distance is 4.7810(2) Å. The crystal packing is determined by interdinuclear hydrogen bonds, which lead to one‐dimensional chains. The results of thermogravimetric investigations (TG‐DTA), UV/Vis diffuse reflectance, infrared and (¹H and ¹³C) NMR spectroscopy, as well as elemental analyses of compounds 1 and 2 are also presented.     

Nonequilibrium spin transport through a diluted magnetic semiconductor quantum dot system with noncollinear magnetization

The spin-dependent transport through a diluted magnetic semiconductor quantum dot (QD) which is coupled via magnetic tunnel junctions to two ferromagnetic leads is studied theoretically. A noncollinear system is considered, where the QD is magnetized at an arbitrary angle with respect to the leads’ magnetization. The tunneling current is calculated in the coherent regime via the Keldysh nonequilibrium Green’s function (NEGF) formalism, incorporating the electron–electron interaction in the QD. We provide the first analytical solution for the Green’s function of the noncollinear DMS quantum dot system, solved via the equation of motion method under Hartree–Fock approximation. The transport characteristics (charge and spin currents, and tunnel magnetoresistance (TMR)) are evaluated for different voltage regimes. The interplay between spin-dependent tunneling and single-charge effects results in three distinct voltage regimes in the spin and charge current characteristics. The voltage range in which the QD is singly occupied corresponds to the maximum spin current and greatest sensitivity of the spin current to the QD magnetization orientation. The QD device also shows transport features suitable for sensor applications, i.e., a large charge current coupled with a high TMR ratio.     

Analytical solutions of the boundary layer flow of power-law fluid over a power-law stretching surface

This article discusses analytical solutions for a nonlinear problem arising in the boundary layer flow of power-law fluid over a power-law stretching surface. Using perturbation method analytical solution is presented for linear stretching surface. This solution covers large range of shear thinning and shear thickening fluids and matches excellently with the numerical solution. Furthermore, some new exact solutions are found for particular combination of m (power-law stretching index) and n (power-law fluid index). This leads to generalize the case of linear stretching to nonlinear stretching surface. The effects of fluid index n on the boundary layer thickness and the skin friction for nonlinear stretching surface is analyzed and discussed. It is observed that the boundary layer thickness and the skin friction coefficient increase as non-linear parameter n decreases. This study gives a new dimension to obtain analytical solutions asymptotically for highly nonlinear problems which to the best of our knowledge has not been examined so far.     

Spin-Hall effect of collimated electrons in zinc-blende semiconductors

We describe an intrinsic spin-Hall effect (SHE) in n-type bulk zinc-blende semiconductors with a topological origin. When a collimated flux of electrons is injected into a zinc-blende semiconductor with Dresselhaus spin–orbit interaction, a nontrivial gauge structure appears in the momentum space of the electrons. The Berry curvature of this gauge field and the corresponding Lorentz force in -space results in a finite SHE. The value of the spin-Hall current is found to be highly dependent on the degree of electron collimation, which may be varied by means of gate electrodes. Therefore, the system may potentially be useful as an electronically controllable source of pure spin-current for spintronic applications.     

Uniform copper nanoparticles as an inexpensive and efficient catalyst for synthesis of novel β-carbonyl-1, 2, 3-triazoles in water medium

Copper nanoparticles as an efficient, inexpensive catalyst were prepared via ball milling for synthesis of β-carbonyl 1, 2, 3-triazoles from azido alcohol by click reaction in water. An extensive range of raw materials such as sodium azide, phenacyl bromide, epichlorohydrin, and terminal alkynes were used. Complete reduction of CuO in presence of NaBH₄ was done via ball milling with a ball-to-powder weight ratio of 50:1 under air atmosphere at room temperature. The final copper nanoparticles (Cu NPs) were characterized by SEM, EDX, XRD and FT-IR. The Cu NPs catalyzed one-pot three component synthesis of β-carbonyl 1, 2, 3-triazoles at room temperature with short reaction time and high product yields. The catalyst could be easily recovered and reused in several successive runs.

     

Pistacia integerrima gall extract mediated green synthesis of gold nanoparticles and their biological activities

This paper reports a rapid, facile and one-pot synthesis of environmentally safe gold nanoparticles capped and stabilized with galls extract of Pistacia integerrima. The aqueous gold ions when exposed to P. integerrima galls extract were rapidly reduced as evident from abrupt color change to ruby red, suggesting the biosynthesis of gold nanoparticles (Au-NPs) which were further characterized by UV–Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). Their stability was evaluated against varying pH and different volumes of sodium chloride (NaCl) as well as at a range of temperature (20–80 °C). Au-NPs were tested for enzyme inhibition, antibacterial, antifungal, antinociceptive, muscle relaxant and sedative activities. The UV–Vis spectra of the gold nanoparticles gave surface plasmon resonance at 540 nm while the SEM analysis revealed the particle size in the range of 20–200 nm. FTIR spectra confirmed the involvement of amines, amide groups and alcohols in capping and reduction of gold nanoparticles. Au-NPs showed remarkable stability in different NaCl and pH solutions as well as at elevated temperature. Au-NPs have good antifungal activity and possessed antinociceptive and muscle relaxant properties as observed from their zone of inhibition and significant attenuation of acetic acid induced writhing and reduction of time spent on the rota rod respectively. These results concluded that the gall extract of P. integerrima is a very good bioreductant for the synthesis of gold nanoparticles that have potential for various biomedical and pharmaceutical applications.     

Dynamical analysis of a new multistable chaotic system with hidden attractor: Antimonotonicity,coexisting multiple attractors,and offset boosting

Analyzing chaotic systems with coexisting and hidden attractors has been receiving much attention recently. In this article, we analyze a four dimensional chaotic system which has a plane as the equilibrium points. Also this system is of the group of systems that have coexisting attractors. First, the system is introduced and then stability analysis, bifurcation diagram and Largest Lyapunov exponent of this system are presented as methods to analyze the multistability of the system. These methods reveal that in some ranges of the parameter, this chaotic system has three different types of coexisting attractors, chaotic, stable node and limit cycle. Some interesting dynamics properties such as reversals of period doubling bifurcation and offset boosting are also presented.     

A new 4D chaotic system with hidden attractor and its engineering applications: Analog circuit design and field programmable gate array implementation

Nowadays, designing chaotic systems with hidden attractor is one of the most interesting topics in nonlinear dynamics and chaos. In this paper, a new 4D chaotic system is proposed. This new chaotic system has no equilibria, and so it belongs to the category of systems with hidden attractors. Dynamical features of this system are investigated with the help of its state-space portraits, bifurcation diagram, Lyapunov exponents diagram, and basin of attraction. Also a hardware realisation of this system is proposed by using field programmable gate arrays (FPGA). In addition, an electronic circuit design for the chaotic system is introduced.     

Effect of Brownian motion on flow and heat transfer of nanofluids over a backward-facing step with and without adiabatic square cylinder

A mathematical model to predict large enhancement of thermal conductivity of nanofluids by considering the Brownian motion is proposed. The effect of the Brownian motion on the flow and heat transfer characteristics is examined. The computations were done for various types of nanoparticles such as CuO, Al₂O₃, and ZnO dispersed in a base fluid (water), volume fraction of nanoparticles ? in the range of 1 % to 6 % at a fixed Reynolds number Re = 450 and nanoparticle diameter d_np = 30 nm. Our results demonstrate that Brownian motion could be an important factor that enhances the thermal conductivity of nanofluids. Nanofluid of Al₂O₃ is observed to have the highest Nusselt number Nu among other nanofluids types, while nanofluid of ZnO nanoparticles has the lowest Nu. Effects of the square cylinder on heat transfer characteristics are significant with considering Brownian motion. Enhancement in the maximum value of Nu of 29 % and 26 % are obtained at the lower and the upper walls of the channel, respectively, by considering the Brownian effects, with square cylinder, compared with that in the case without considering the Brownian motion. On the other hand, results show a marked improvement in heat transfer compared to the base fluid, this improvement is more pronounced on the upper wall for higher ?.