Chemical constituents, antioxidant and antimocrobial activity of essential oil of Pogostemon paniculatus (Willd.)

The essential oil extracted from the leaves of Pogostemon paniculatus (Willd.) Benth. (Lamiaceae), was analysed by gas chromatography-mass spectrometry (GC-MS). Nineteen compounds constituting 85.36% of the total oil were identified in the oil. Patchouli alcohol (30.65%), α-guaiene (10.67%), β-guaiene (9.09%), caryophyllene (8.64%), eicosene (5.27%) were the major constituents present. The essential oil was analysed for antimicrobial activity by disc diffusion assay and minimum inhibition concentration against six bacteria and three fungi. Results showed inhibitory activity against some of the tested microorganisms. The essential oil was also tested for the DPPH free-radical scavenging activity and had an inhibitory concentration (IC(50)) value of 18.5?μg?mL(-1).     

Quantum phase transition from superparamagnetic to quantum superparamagnetic state in ultrasmall Cd(1-x)Cr(II)(x)Se quantum dots?

Despite a long history of success in formation of transition-metal-doped quantum dots (QDs), the origin of magnetism in diluted magnetic semiconductors (DMSs) is yet a controversial issue. Cr(II)-doped II-VI DMSs are half-metallic, resulting in high-temperature ferromagnetism. The magnetic properties reflect a strong p-d exchange interaction between the spin-up Cr(II) t(2g) level and the Se 4p. In this study, ultrasmall (~3.1 nm) Cr(II)-doped CdSe DMSQDs are shown to exhibit room-temperature ferromagnetism, as expected from theoretical arguments. Surprisingly, a low-temperature phase transition is observed at 20 K that is believed to reflect the onset of long-range ordering of the single-domain DMSQD.     

Synthesis,characterization and studies of radiative properties on Eu3+-doped ZnAl2O4

Eu³⁺-doped ZnAl₂O₄ phosphors were successfully synthesized in air atmosphere at 900 °C. The phosphors were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermally stimulated luminescence (TSL) and photoluminescence (PL) techniques. The average particle size of the system as determined from SEM was found to be 100–150 nm (for samples annealed at 900 °C). PL spectra of the doped phosphors showed emission peaks corresponding to Eu³⁺ ions. Lifetime studies revealed Eu³⁺ ions to be in two different sites. The asymmetric ratio (I₆₁₆/I₅₉₂) was observed to be about 3.75. This suggested that Eu³⁺ ion entered the host mainly substituting Al³⁺ site distorting the local environment and is partly located on surface of the phosphors. A prominent glow peak at 430 K was observed in the TSL of γ-irradiated Eu³⁺-doped ZnAl₂O₄ phosphors. Trap parameters for this peak have been determined and the probable mechanism for the glow peak is proposed. CIE chromaticity coordinates for the system were evaluated. It was observed that, the system could be employed as a potential red emitting phosphor. Commercial utility of the phosphor was investigated by comparing it with commercial red phosphor. The PL intensity of the as prepared phosphors was 63% of that of the commercial phosphor. Apart from this, various radiative properties such as the Judd–Ofelt intensity parameters, spontaneous emission probabilities, luminescence branching ratios, radiative lifetimes and quantum efficiency were evaluated for the system.     

Dependence of surface distribution of self-assembled InSb nanodots on surface morphology and spacer layer thickness

Self-assembled InSb nanodots (NDs) were grown on a GaSb (1 0 0) substrate using metal-organic vapour phase epitaxy (MOVPE). The effects of etching depth of the substrate and thickness of the GaSb buffer layer on the density and size distribution of single and double layer dots were studied for detector applications. The etch depth of the substrate was varied up to 30 μm. In this particular study, the dots were grown at 450 °C and the GaSb spacer thickness was varied between 50 nm and 200 nm. The optimum substrate etch depth was found to be 30 μm while the best spacer thickness was found to be 200 nm.     

Effect of Pb additive on crystallization kinetics of Se80In20 glassy matrix

The crystallization kinetics of bulk Se₈₀In_20−xPb_x (x=0, 5, 10 and 15) chalcogenide glasses have been studied using a differential scanning calorimeter (DSC) with different heating rates (5, 10, 15 and 20 K/min) under non-isothermal conditions. Various kinetic parameters of crystallization, such as crystallization temperature T_c, peak crystallization temperature T_p, activation energy for crystallization E_c and order parameters n, m have been determined to study nucleation and growth during crystallization. The reaction rate constant K and pre-exponential factor K₀ also have been determined. The composition dependence of these parameters may be explained on the basis of modification of chemical bonds present in the Se–In system due to addition of Pb content.     

Synthesis and luminescence investigation of RE (Eu, Tb and Ce)-doped lithium silicate (Li2SiO3)

Synthesis and photoluminescence (PL) investigations of lithium metasilicate doped with Eu³⁺, Tb³⁺ and Ce³⁺ were carried out. PL spectra of Eu-doped sample showed peaks corresponding to the ⁵D₀→⁷F_j (j=1, 2, 3 and 4) transitions under ultraviolet excitation. Strong red emission coming from the hypersensitive ⁵D₀→⁷F₂ transition of Eu³⁺ ion suggested the presence of the dopant ion in structurally disordered environment. Tb³⁺-doped silicate sample showed blue-green emission corresponding to the ⁵D₄→⁷F_j (j=6, 5 and 4) transitions. Ce-doped sample under excitation from UV, showed a broad emission band in the region 350-370 nm with shoulders around 410 nm. The fluorescence lifetimes of Eu³⁺ and Tb³⁺ ions were found out to be 790 and 600 μs, respectively. For Ce³⁺, the lifetime was of the order of 45 ns. PL spectra of the europium- and terbium-doped samples were compared with commercial red (Y₂O₃:Eu³⁺) and green (LaPO₄:Tb³⁺) phosphors, respectively. It was found that the emission from the doped silicate sample was 37% of the commercial phosphor in case of the Tb-doped sample and 8% of the commercial phosphor in case of the Eu-doped sample.     

利用DSP智能电机控制提高能量效率

目前,工业用电的三分之二为电机所消耗,而在居民用电中这一比例亦高达四分之一,有鉴于此,电机的效率问题继续受到更大的关注.标准的电机应用完全能以更高的能量效率运行,就电能到机械能的转换而言,大多数电机的效率较低.这意味着它们浪费了大量的能量,以发热的形式散失掉,而未能变换为有用的机械能.     

Magnetization plateaus and sublattice ordering in easy-axis kagome lattice antiferromagnets

We study kagome lattice antiferromagnets where the effects of easy-axis single-ion anisotropy (D) dominates over the Heisenberg exchange J. For S> or =3/2, virtual quantum fluctuations help lift the extensive classical degeneracy. We demonstrate the presence of a one-third magnetization plateau for a broad range of magnetic fields J3/D2 < or = B < or = JS along the easy axis. The fully equilibrated system at low temperature on this plateau develops an unusual nematic order that breaks sublattice rotation symmetry but not translation symmetry; however, extremely slow dynamics associated with this ordering is expected to lead to glassy freezing of the system on intermediate time scales.