BaV3O8: A possible Majumdar-Ghosh system with S=1/2

BaV3O8 contains both magnetic V4+(S=1/2) ions and non-magnetic V5+(S=0) ions. The V4+ ions are arranged in a coupled Majumdar-Ghosh chain like network. Our magnetic susceptibility chi(T) data fit well with the Curie-Weiss formula in the temperature range of 80-300K and it yields a Curie constant C=0.39cm3K/mole-V4+ and an antiferromagnetic Weiss temperature theta=-26K. The chi(T) curve shows a broad maximum at T~25K indicative of short-range order (SRO) and an anomaly corresponding to long-range order (LRO) at TN~6K. The value of the frustration index (f=mod[theta/TN]~5) suggests that the system is moderately frustrated. Above the LRO temperature the experimental magnetic susceptibility data match well with the coupled Majumdar-Ghosh chain model with the ratio of the nnn (next-nearest neighbor) to nn (nearest neighbor) magnetic coupling alpha=2 and Jnnn/kB=40K. In a mean-field approach when considering the inter-chain interactions, we obtain the total inter-chain coupling to be about 16K. The LRO anomaly at TN is also observe in the specific heat Cp(T) data and is not sensitive to an applied magnetic field up to 90kOe. A 51V NMR signal corresponding to the non-magnetic vanadium was observed. Anomalies at 6K were observed in the variation with temperature of the 51V NMR linewidth and in the spin-lattice relaxation rate 1/T1, indicating that they are sensitive to the LRO onset and fluctuations at the magnetic V sites. The existence of two components (one short and another long) is observed in the spin-spin relaxation rate 1/T2 data in the vicinity of TN. The shorter component seems to be intimately connected with the magnetically ordered state. We suggest that both magnetically ordered and non-long range ordered (non-LRO) regions coexist in this compound below the long range ordering temperature.Comment: Accepted in Phys. Rev.

Comparative GC-MS study of Schizonepeta multifida essential oil from Khakassia Republic shows potentials for nutraceuticals, flavor, and conservation

Schizonepeta multifida (L.) Briq. (Lamiaceae) is among the widely used botanicals in Siberian traditional and modern health and personal care practices, shelf life extension of agricultural produce, antimicrobial, and insect repellent. We investigated the variations or differences in the chemical composition of essential oils in wild accessions harvested from two distinct geographical regions, 'habitat-1' and 'habitat-2', in the Republic of Khakassia, Siberia. The oils were obtained by subjecting the aboveground parts of the plant to hydro-distillation, with subsequent assessment of the chemical composition using GC-FID and GC-MS analyses. The oil composition varied quite a lot according the number of components (61 in samples from 'habitat-1', 45 in sample from 'habitat-2'), the dominant components (pulegone 33.36 %, limonene 20.95 %, cis-beta-ocimene 9.96 % and isomenthone 5.31 % from 'habitat-1', limonene 27.98 %, cis-beta-ocimene 14.42 %, pulegone 14.20 %, beta-myrcene 11.95 %, and terpinolene 6.33 % from 'habitat-2'). In light of the continued overharvesting resulting in genetic erosion, further studies are warranted to establish in-situ and ex-situ conservation strategies of all populations representing different chemotypes/ecotypes and identifying promising genetic lines for sustainable cultivation as a source of renewable raw material for the oil

Phytochemical, microbiological, and technological studies in the field of obtaining a hydroalcoholic extract with antimicrobial activity from the liquorice root

Phytochemical composition and antimicrobial activity of hydroalcoholic extracts from the liquorice root with the use of different concentrations of ethanol have been studied. The optimal range of ethanol concentration of 65±15% v/v has been found. The dependency between the integral index of antimicrobial activity of the extract and concentration of glycyram and licuroside has been foun

Preheating in Derivatively-Coupled Inflation Models

We study preheating in theories where the inflaton couples derivatively to scalar and gauge fields. Such couplings may dominate in natural models of inflation, in which the flatness of the inflaton potential is related to an approximate shift symmetry of the inflaton. We compare our results with previously studied models with non-derivative couplings. For sufficiently heavy scalar matter, parametric resonance is ineffective in reheating the universe, because the couplings of the inflaton to matter are very weak. If scalar matter fields are light, derivative couplings lead to a mild long-wavelength instability that drives matter fields to non-zero expectation values. In this case however, long-wavelength fluctuations of the light scalar are produced during inflation, leading to a host of cosmological problems. In contrast, axion-like couplings of the inflaton to a gauge field do not lead to production of long-wavelength fluctuations during inflation. However, again because of the weakness of the couplings to the inflaton, parametric resonance is not effective in producing gauge field quanta.Comment: 10 pages, 9 figure

Quantum Dew

We consider phase separation in nonequilibrium Bose gas with an attractive interaction between the particles. Using numerical integrations on a lattice, we show that the system evolves into a state that contains drops of Bose-Einstein condensate suspended in uncondensed gas. When the initial gas is sufficiently rarefied, the rate of formation of this quantum dew scales with the initial density as expected for a process governed by two-particle collisions.Comment: 4 pages, revtex, 5 figure