Spectral and surface investigations of Ca2V2O7:Eu3+ nanophosphors prepared by citrate-gel combustion method: a potential red-emitting phosphor for near-UV light-emitting diodes

In the present work, red-emitting Ca₂V₂O₇:xEu³⁺ (x = 0.5–6.0 mol%) nanophosphors, in the form of powders, were synthesized by the citrate-gel combustion method using metal nitrates as precursors and citric acid as fuel. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy, photoluminescence (PL) and cathodoluminescence (CL) spectroscopy were used to study the structure, morphology and spectral properties of the samples. The chemical compositions and electronic states of the powders were analyzed with X-ray photoelectron spectroscopy. The average crystallite sizes estimated using the XRD data were found to be in the range of 30–45 nm, and were cross verified by TEM. The lattice parameters determined by the POWD program were approximated as a = 7.242 Å, b = 6.674 Å, c = 6.932 Å and V = 291.24 Å³, respectively. Under UV (395 nm) (PL) and electron (CL) excitation, the nanophosphors show characteristic emission from the Eu³⁺ ion (⁵D₀ → ⁷F_j, j = 1–5) with the main peaks at 612 and 616 nm. The maximum emission intensity was recorded from the sample with an Eu³⁺ concentration of 4 mol% and a critical energy distance of 19.084 Å between the donor and the acceptor. Above this concentration, there was a reduction in the intensity due to dipole–dipole induced concentration quenching effects. The potential applications of this phosphor as a high color-purity phosphor in light-emitting diodes are evaluated.     

Effect of substrate temperature on the growth of pulsed-laser deposited ZnO nanostructures

We report on the growth of highly c-axis-oriented ZnO nanostructures by pulsed laser deposition technique without using any catalyst. The full-width-at-half-maximum of (002) peak decreased with an increase in substrate temperature. However, a dip at 150 °C is attributed to the contribution from both the small- and large-size particles. FE-SEM images show that the increase in substrate temperature results in the formation of larger particles. Photoluminescence emission is observed both from near band edge as well as defect-related states for all the nanostructures. The presence of E ₂(low) and E ₂(high) Raman mode intensity and respective increase in the intensity with substrate temperature indicates better crystallinity. Both PL and Raman spectra indicate that A ₁(LO) mode may arise due to the defect related to interstitial zinc.     

Nanoscale flexoelectric energy harvesting

One of the most tantalizing applications of piezoelectricity is to harvest energy from ambient mechanical vibrations for powering micro and nano devices. However, piezoelectricity is restricted only to certain materials and is severely compromised at high temperatures. In this article, we examine in detail, the possibility of using the phenomenon of flexoelectricity for energy harvesting. The flexoelectric effect is universally present in all dielectrics and exhibits a strong scaling with size. Using a simple beam-based paradigmatical design, we theoretically and computationally examine flexoelectric energy harvesting under harmonic mechanical excitation. We find that the output power density and conversion efficiency increase significantly when the beam thickness reduces from micro to nanoscale and flexoelectricity-based energy harvesting can be a viable alternative to piezoelectrics. Specifically, the conversion efficiency in flexoelectric transduction at sub-micron thickness levels is observed to increase by two orders of magnitude as the thickness is reduced by an order of magnitude. The flexoelectric energy harvester works even for a single layer beam with a symmetric cross section which is not possible in piezoelectric energy harvesting. Our results also pave the way for exploration of high temperature energy harvesting since unlike piezoelectricity, flexoelectricity persists well beyond the Curie temperatures of the high electromechanical coupling ferroelectrics that are often used.     

Mössbauer and electronic spectral studies of iron(III) complexes of oximes

The hydroxo-bridge complexes of the type [Fe(2)(ligand-H)(4)(OH)(2)] with bidentate nitrogen-oxygen donor ligands, viz. 2-hydroxynaphthaldehydeoxime [hnoH(2)], 2-hydroxyacetphenoneoxime [haoH(2)], salicylaldooxime [SalH(2)], 2-hydroxypropiophenoneoxime [hnoH(2)] have been prepared. All the complexes have been characterized by elemental analysis, magnetic moments, electronic and M?ssbauer spectral studies. M?ssbauer parameters of the complexes clearly suggest high spin configuration of Fe(III) showing lower magnetic moment to that of the spin only value, i.e. 5.92 BM. It may be due to the antiferromagnetic interaction between Fe(III) centers.     

Stand-off Raman spectroscopic detection of minerals on planetary surfaces

We have designed and developed two breadboard versions of stand-off Raman spectroscopic systems for landers based on a 5-in. Maksutov-Cassegrain telescope and a small (4-in. diameter) Newtonian telescope receiver. These systems are capable of measuring the Raman spectra of minerals located at a distance of 4.5-66 m from the telescope. Both continuous wave (CW) Ar-ion and frequency doubled Nd:YAG (532 nm) pulsed (20 Hz) lasers are used as excitation sources for measuring remote Raman spectra of rocks and minerals. We have also made complementary measurements on the same rock samples with a micro-Raman system in 180 and 135 degrees geometry for evaluating the system performance and for estimating effect of grain size and laser-induced heating on the spectra of minerals using alpha-quartz as a model mineral. A field portable remote pulsed Raman spectroscopic system based on the 5-in. telescope and an f/2.2 spectrograph has been developed and tested. We have also demonstrated a prototype of a combined Raman and laser-induced breakdown spectroscopy (LIBS) system, capable of providing major element composition and mineralogical information on both biogenic and inorganic minerals at a distance of 10 m from the receiver.     

Molecular dynamics and structure-based virtual screening and identification of natural compounds as Wnt signaling modulators: possible therapeutics for Alzheimer’s disease

Molecular Diversity - Wnt signaling pathway is an evolutionarily conserved pathway responsible for neurogenesis, axon outgrowth, neuronal polarity, synapse formation, and maintenance....     

Optimal harvesting of a two species competition model with imprecise biological parameters

In this paper a two competing species harvesting model with imprecise biological parameters has been developed. We have developed a method to handle these imprecise parameters and discuss the dynamical behaviour of the model. We have discussed the existence of various equilibrium points and stability of the system at these equilibrium points. Also the bionomic equilibrium of the harvesting model has been analysed. Next the equilibrium solution of the control problem has been derived, and then dynamical optimization of the harvest policy is carried out taking combined harvesting effort as a dynamic variable by invoking Pontryagin’s Maximum Principle. Our important analytical findings are illustrated through computer simulation using MATLAB followed by discussions and conclusions.     

Heat transfer augmentation of a car radiator using nanofluids

The car radiator heat transfer enhancement by using TiO₂ and SiO₂ nanoparticles dispersed in water as a base fluid was studied experimentally. The test rig is setup as a car radiator with tubes and container. The range of Reynolds number and volume fraction are (250–1,750) and (1.0–2.5 %) respectively. Results showed that the heat transfer increases with increasing of nanofluid volume fraction. The experimental data is agreed with other investigator.     

Evaluation of antidiabetic and antioxidant potential of lupeol in experimental hyperglycaemia

Oxidative stress, produced under diabetic conditions, is a possible cause of various forms of tissue damage. The concentrations of antioxidant enzymes in cases of diabetes are significantly decreased, with a concomitant increase in lipid peroxidation. In this study, lupeol, a phytoconstituent from Solanum xanthocarpum, is shown to suppress the progression of diabetes after 21 days. Lupeol treatment caused decreases in glycated haemoglobin, serum glucose and nitric oxide, with a concomitant increase in serum insulin level. Furthermore, treatment with lupeol also increased antioxidant levels, with a decrease in the level of thiobarbituric acid-reactive oxygen species.     

Synthesis of chiral helical 1,3-oxazines

A series of novel 1,3-oxazines were prepared to construct a helical framework. The 1,3-oxazine attached to the phenanthrene unit showed a small bite angle θ (～12°), while the units attached to [4]helicene showed a larger θ (～35°) and exhibited helical isomers at ambient conditions. The diastereomers of the third type of helicene-like bis-oxazine attached to binaphthyl were easily separable and showed good thermal stability. All four diastereomers of bis-helicene were synthesized, and their absolute configuration was established.