Electronic and optical properties of defect chalcopyrite HgAl2Se4

The structural, electronic and optical properties of HgAl₂Se₄ are investigated using the full potential linear augmented plane wave method based on density functional theory. The calculated structural parameters using LDA are in excellent agreement with the available experimental result. The obtained energy band gap (2.24 eV) using EV-GGA approximation is in excellent agreement with experimental data (2.20 eV). Variation in the energy band gap as a function of the unit cell lattice parameter has been studied. The optical properties show a considerable anisotropy, which makes this compound very useful for various linear–nonlinear optical devices.     

Effect of laser radiation on optical properties of disk shaped quantum dot in magnetic fields

The optical absorption coefficients and changes in the refractive index in GaAs/AlGaAs, disk shaped quantum dots (DSQD) with simultaneously applied laser and magnetic field are studied in detail. The use of the density matrix formalism is made to study the variations in linear and non-linear polarizability with the frequency of the electric field. It is found that the absorption coefficient and the refractive index changes depend not only on the optical wave but also on the strength of the static magnetic field.     

A-optimal designs for an additive cubic model

Chan et al. (1998a) obtained A-optimal designs for an additive quadratic mixture model for q≥3 mixture components. In this paper, we obtain the A-optimal designs for an additive cubic model for q≥3 mixture components using the class of symmetric weighted centroid designs based on barycentres of various depths. We observe that barycentres of depths 0 and 2 are possible support points for an A-optimal design. We have also given the optimal weights of A-optimal designs for 3≤q≤17.     

Bio-energetic impairment in human calf muscle in thyroid disorders: a P MRS study

Mitochondrial metabolism particularly oxidative phosphorylation is greatly influenced by thyroid hormones. Earlier studies have described neuromuscular symptoms as well as impaired muscle metabolism in hypothyroid and hyperthyroid patients. In this study, we intend to look in to the muscle bioenergetics including phosphocreatine recovery kinetics based oxidative metabolism in thyroid dysfunction using in vivo ³¹P nuclear magnetic resonance spectroscopy (MRS). ³¹P MRS was carried out at resting state on 32 hypothyroid, 10 hyperthyroid patients and 25 control subjects. Nine out of 32 hypothyroid patients and 17 out of 25 control subjects under went exercise protocol for oxidative metabolism study and performed plantar flexion exercise while lying supine in 1.5 T magnetic resonance scanner using custom built exercise device. MRS measurements of inorganic phosphate (Pi), phosphocreatine (PCr), phosphodiesters (PDE) and adenosine triphosphate (ATP) of the calf muscle were acquired during rest, exercise and recovery phase. PCr recovery rate constant (k_PCr) and oxidative capacity were calculated by monoexponential fit of PCr versus time (t) at the beginning of recovery. During resting condition in hypothyroid patients, PCr/Pi ratio was reduced whereas PDE/ATP and Pi/ATP were increased. However, in case of hyperthyroidism, an increased PCr/Pi ratio and reduced PDE/ATP and Pi/ATP were observed. The results confirmed differential energy status of the muscle due to increased or decreased levels of thyroid hormone. Our results also demonstrate reduced oxidative metabolism in hypothyroid patients based on PCr recovery kinetics. PCr recovery kinetics study after exercise revealed decreased PCr recovery rate constant (k_PCr) in hypothyroid patients compared to controls that resulted in decrease in oxidative capacity of muscle by 50% in hypothyroids. These findings are consistent with a defect of high energy phosphate mitochondrial metabolism in thyroid dysfunction.     

Phonon dispersion and specific heat in ω-helical poly-N ∊(p-bromobenzoyl-l-ornithine)

Poly-N ^?(p-bromobenzoyl-l-ornithine) (PBrBO) is one of the few biopolymers existing in the rare ω-helical (fourfold) conformation. It can be obtained from the α form through an irreversible heat treatment. A study of its normal modes and dispersive behavior shows several interesting features such as “crossing over,” “repulsion with character exchange,” and Von Hove type “singularities” which lead to a fuller interpretation of its IR spectra. The existence of alternately different side-chain conformations, which makes the phonon problem too large to solve directly, has been taken into account by considering the vibrations of the PBrBO chains with two independent conformations. Detailed study of skeletal, amide, and side-chain modes is reported, and the results have been used for the calculation of specific heat via density of states.     

Conformation and phonon dispersion in trans-1,4-polybutadiene

Phonon dispersion studies for trans-l,4-polybutadiene (TPBD) are reported. The change in profile of the dispersion curves as a function of the ═CH─CH₂─ dihedral angle φ has been obtained in order to find the geometry of the polymer that gives the best interpretation of the spectra. It is found for φ = 71°. The regions of high density of states obtained from the dispersion curves for an isolated chain have been used to explain the features of the spectra. Some of these, which were earlier attributed to interchain interactions, in fact arise due to intrachain interactions. Prominent features of the dispersion curves are discussed and heat capacity, derived therefrom, is reported. Calculations have also been performed for unsaturated C-deuterated and fully deuterated TPBD samples to check the validity of the force field and assignments.     

Effect of uniaxial pressure on the Raman spectra of fluoro perovskites containing manganese with sodium or potassium

ABSTRACT

Perovskite structured mixed metal fluorides containing manganese/sodium or potassium have been synthesized in pure form by a greener precipitation route and characterized by high-resolution powder X-ray diffraction and Raman spectroscopy techniques. While all the reflections in the powder X-ray diffraction pattern of potassium manganese fluoride could be indexed in cubic symmetry with a = 4.1889 Å, sodium manganese fluoride showed reflections at positions typical of orthorhombic symmetry (Pnma space group) with a = 5.751, b = 8.008, and c = 5.548 Å. Potassium manganese fluoride in powder form showed bands at 209, 291, 386, 558, 621, and 733 cm^?1 in the Raman spectrum at room temperature. All these bands disappeared and second-order band at 1151 and 1298 cm^?1 emerged when the powders were compacted under pressure ranging between 1 and 4 tons (uniaxial). A similar change was noticed for sodium manganese fluoride in which bands at 1099, 1149, 1203, and 1286 cm^?1 were observed for the compacted samples. The response of the vibrational modes of these compounds to uniaxial pressure revealed the existence of large structural disorder in them. Additionally, the need for the extreme care to collect and interpret Raman data of polycrystalline samples of these systems has been illustrated through this study.     

Pyrazole‐4‐carboxylic Acids from Vanadium‐catalyzed Chemical Transformation of Pyrazole‐4‐carbaldehydes

The conversion of aldehydes into carboxylic acids using oxidizing agents is a common protocol in transformation chemistry. An efficient oxidation strategy of transformation of pyrazole‐4‐aldehydes to the corresponding acids using vanadium catalysts in the presence of 30% H₂O₂ as an oxidant is described. The catalytic technology was successfully applied to a range of various 4‐formylpyrazoles, and plausible mechanism is also discussed.