Dielectric behavior and PTCR effect in nanocrystallite PMN ferroelectric ceramics

The ac behavior of a nanocrystallite lead magnesium niobate (PMN) ceramic sample was studied over a wide range of temperatures and frequencies. The results revealed a diffuse phase transition and very high dielectric constant at lower frequencies. The high value of the dielectric constant at lower frequencies is shown to be due to barrier layer formation. A positive temperature coefficient of resistivity (PTCR) was observed in the temperature dependence of the ceramic resistivity. The results are explained on the basis of the Heywang and Jonker models. The Schottky barrier formed at grain boundary regions acts as a trap for the electrons available from oxygen vacancies in the ceramics. This provides PTCR characteristics from the transition temperature to about 208°C.     

Magic Labelings of Type (a, b, c) of Families of Wheels

In this paper, firstly, we study magic labeling of type (1, 1, 1) for wheels and subdivided wheels. Secondly, we prove that a wheel admits a magic labeling of type (0, 1, 1). We also prove that any odd wheel admits a magic labeling of type (0, 1, 0). At the last, we find the magic labeling of type (1, 1, 0) for subdivided wheels.     

Radiation-induced thermoluminescence characteristics of feldspar upon different heat and microwave treatments

Feldspar minerals are well-known markers for thermoluminescence (TL)-based identification of irradiated foodstuff because of their high TL sensitivity and characteristic TL glow curves. Post-irradiation processing, particularly heating, may affect luminescence properties. In the present study, the effect of boiling, roasting, and microwave treatments on TL properties of irradiated (0, 5, and 10 kGy) feldspar was investigated. The TL glow peak faded (TL peak maxima shift towards higher temperature) upon boiling or roasting, which was mainly dependent upon treatment temperature and time. This effect was most apparent in the roasted samples. Liquid samples showed more changes in TL characteristics than solid samples upon microwave treatment; however, the effect was less prominent compared to those of roasting and boiling. TL ratios could not confirm the TL results when boiled and roasted samples were treated at ≥100 °C, whereas the microwave treatment showed a negligible effect on the TL ratio.     

Pregnane derivatives from Potentilla evestita

A new pregnane derivative, 2,6beta,7beta-trihydroxy-4-methyl-19-norpregna-1,3,5(10)-trien-17-one, has been isolated from the ethyl acetate soluble fraction of Potentilla evestita along with a pregnane derivative, 11alpha,17alpha,21-trihydroxypregna-4,16(22)-diene-3,20-dione, that is reported for the first time as a natural product. Their structures were elucidated with the aid of 1H and 13C NMR spectra and by COSY, HMQC, HMBC and NOESY experiments.     

Two new 3-C-carboxylated flavones from the rhizomes of Caragana conferta

Confertins A (1) and B (2), new 3-C-carboxylated flavones, have been isolated from the ethyl acetate soluble fraction of the rhizomes of Caragana conferta. Their structures have been assigned on the basis of spectroscopic studies.     

Two new guaianolides from Amberboa ramosa

Two new sesquiterpene lactones named amberbins A (1) and B (2), have been isolated from the ethyl acetate soluble fraction of Amberboa ramosa, together with jaseocidine (3), crysoeriol (4) and 3beta,8alpha-dihydroxy-11alpha-methyl-1alphaH,5alphaH,6betaH, 7alphaH,11betaH-guai-10(14), 4(15)-dien-6,12-olide (5). The structures of the isolated compounds have been elucidated on the basis of their spectroscopic data.     

LMI-based robust adaptive synchronization of FitzHugh-Nagumo neurons with unknown parameters under uncertain external electrical stimulation

This Letter addresses a nonlinear robust adaptive control that utilizes linear matrix inequalities for asymptotic synchronization of two coupled chaotic FitzHugh-Nagumo neurons under unknown parameters and uncertain stimulation current amplitudes and phase shifts. Synchronization of chaotic neurons using the proposed control method through numerical simulation is demonstrated.     

Zn in ionic liquid: an efficient reaction media for the synthesis of diorganyl chalcogenides and chalcogenoesters

A straightforward and efficient methodology is described to synthesize structurally diverse diorganyl selenides, sulfides, seleno- and thioesters by using commercially available Zn dust in ionic liquid. Excellent yields were achieved under neutral conditions at room temperature in a short time. The solvent/ionic liquid is reusable and exhibited higher performance as compared with organic solvents.