The magnetic properties across the martensitic transition in the Co38Ni34Al28 alloy

The magnetic properties of the Co₃₈Ni₃₄Al₂₈ alloy have been studied. The alloy exhibits a first order austenite-martensite phase transition in the temperature region between 155 and 247 K. A strain of 0.07% is produced across this phase transition. The Arrott plots obtained from the isothermal magnetic field dependence of magnetization indicate the presence of spontaneous magnetization both in the austenite and martensite phases, confirming the ferromagnetic character of the alloy up to room temperature. The temperature dependence of the high field magnetization indicates the presence of spin wave excitations, spin wave excitation gap and spin wave-spin wave interactions in the martensite phase. The magnetic anisotropy energy constant for the Co₃₈Ni₃₄Al₂₈ alloy is estimated both with the help of the standard law of approach to saturation of magnetization, and also from the field dependence of magnetization using the field for technical saturation of magnetization. The temperature dependences of these energy terms are compared. The estimated values of the magnetic anisotropy constant seem to be in agreement with the magnitude of the spin wave excitation gap estimated from the temperature dependence of high field magnetization.     

A compact plasmonic tunable filter using elasto-optic effects

We report on the theoretical concept of the design of a compact plasmonic tunable filter made of a metal–dielectric–metal waveguide and using elasto-optic effects. The proposed device is designed in a nanoring resonator structure and numerically studied by means of 3D-FEM simulations. We obtained an optimized nanoring resonator that has a radius R=390 nm and resonances at the telecommunication wavelength of 1.58 μm. Simulations using elasto-optic material as the dielectric layer and top and bottom Ag layers as electrodes indicate that the output can be tuned in the telecommunication wavelength range with an applied field. Further, using the proposed device, optical switching phenomenon is also found to be possible. This tunable ring resonator filter with ultra-small radii is considered valuable for photonic integrated systems.     

ISTBC: A spectrally efficient distributed transmission scheme using incremental redundancy with space–time block coding

Cooperative communication is a promising paradigm that could address many of the challenges encountered in the development of future mobile communication systems. With multiple wirelessly communicating devices that cooperate with each other, a network of wireless nodes with virtual antenna arrays is created. This emulates a MIMO system and mimics most of its benefits. However bandwidth efficiency is a major issue in cooperative communication. Incremental-redundancy based techniques can be employed in cooperating nodes to minimize the bandwidth penalty but lacks error protection capability against unreliable decoding. Motivated by such shortcomings, a technique that combines the concept of incremental redundancy with space–time block coding (STBC) is proposed in this paper. The proposed scheme retains spatial diversity and bandwidth efficiency advantage offered by normal incremental redundancy based systems, in addition to offering guard against error propagation due to imperfect decoding at the relay. The theoretical framework is also developed to provide an understanding on the fundamental performance characteristics of the system. Two parameters such as Error Propagation Quotient (EPQ) and Spectral Efficiency Gain (SEG) are proposed to gauge the benefits offered by the proposed technique.     

EPR and Optical Absorption Study of Cu<Superscript>2+</Superscript> Ions Doped in Potassium Hexaaquazinc (II) Sulphate (PHZS) Single Crystals

Single-crystal electron paramagnetic resonance (EPR) studies at X-band have been done on Cu²⁺-doped potassium hexaaquazinc (II) sulphate (PHZS) at room temperature. The spin Hamiltonian parameters g, A and their direction cosines are evaluated using standard diagonalization procedure with the help of a computer program. The EPR spectrum is simulated using EasySpin program to justify the calculations. The ground-state wave function of the Cu²⁺ ion in this lattice is also determined, which is predominantly |x ² − y ²〉. The optical absorption spectrum of Cu²⁺ ions doped in PHZS single crystal at room temperature is also recorded and four main d–d transition bands in visible region are assigned. With the help of assigned bands, the crystal-field parameters (Dq, Ds and Dt) are evaluated. Finally, with the optical and EPR data, the nature of bonding in the complex is discussed.     

Synthesis, structural and optical characterization of nanocrystalline ZnS:Cu embedded in silica matrix

The synthesis of Cu doped ZnS nanoparticles inside the pore of an inorganic silica gel matrix is presented. The synthesized nanoparticles were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). X-ray diffraction pattern reveals the crystalline wurtzite phase of ZnS. The existence of silica gel in modeling morphologies of the nanoparticles was characterized using Fourier transform infrared (FTIR) spectrometer. Thickness of the silica shell was also calculated. UV- absorption spectrum shows the appearance of an absorption peak at 273 nm which confirms the blue shift as compared to that of bulk ZnS. The photoluminescence (PL) emission spectrum of the sample showed a broad band in the range 465-510 nm due to the transition from the conduction band edge of ZnS nanocrystals to the acceptor like t₂ state of Cu.     

Molecular structure,vibrational spectra and potential energy distribution of protopine using <Emphasis Type="Italic">ab initio</Emphasis> and density functional theory

This work is devoted to theoretical study on molecular structure of protopine. The equilibrium geometry, harmonic vibrational frequencies and infrared intensities were calculated by ab initio Hartree-Fock and density functional B3LYP methods with the 6-31G(d) basis set and were interpreted in terms of potential energy distribution (PED) analysis. The internal coordinates were optimized repeatedly for many times to maximize the PED contributions. A detailed interpretation of the infrared spectra of protopine is reported. The calculations are in agreement with experiment. The thermodynamic functions of the title compound were also performed at HF/6-31G(d) and B3LYP/6-31G(d) level of theory. The FT-IR spectra of protopine were recorded in solid phase.     

Microwave-assisted synthesis of 1,8-naphthalic anhydride and fluorescent probes based on its derivatives

Abstract  

Efficient synthesis of fluorescent probes based on 1,8-naphthalic anhydride from acenaphthene with the help of microwave irradiation is described. Application of microwave dielectric heating helped improve the yield of the products (>85%) and also reduced the formation of undesired side-products.     

A facile approach towards synthesis of verbalactone and biologically active δ-lactones using d-glucose

A general synthetic approach has been developed for the asymmetric synthesis of chiral δ-lactones and verbalactone using d-glucose. The key intermediate used in this approach was α-diazoketone.