Chandra View of Pulsar Wind Nebula Tori

The results from a systematic study of eleven pulsar wind nebulae with a torus structure observed with the Chandra X-ray observatory are presented. A significant observational correlation is found between the radius of the tori, r, and the spin-down luminosity of the pulsars, Edot. A logarithmic linear fit between the two parameters yields log r = (0.57 +- 0.22) log Edot -22.3 +- 8.0 with a correlation coefficient of 0.82, where the units of r and Edot are pc and ergs s^-1, respectively. The value obtained for the Edot dependency of r is consistent with a square root law, which is theoretically expected. This is the first observational evidence of this dependency, and provides a useful tool to estimate the spin-down energies of pulsars without direct detections of pulsation. Applications of this dependency to some other samples are also shown.Comment: 8 pages, 2 figures, ApJ in pres

Stability of fluid flow in a Brinkman porous medium - a numerical study

The stability of fluid flow in a horizontal layer of Brinkman porous medium with fluid viscosity different from effective viscosity is investigated. A modified Orr-Sommerfeld equation is derived and solved numerically using the Chebyshev collocation method. The critical Reynolds number Rec, the critical wave number αc and the critical wave speed cc are computed for various values of porous parameter and ratio of viscosities. Based on these parameters, the stability characteristics of the system are discussed in detail. Streamlines are presented for selected values of parameters at their critical state.postprin

Stability of fluid flow in a Brinkman porous medium-A numerical study

The stability of fluid flow in a horizontal layer of Brinkman porous medium with fluid viscosity different from effective viscosity is investigated. A modified Orr-Sommerfeld equation is derived and solved numerically using the Chebyshev collocation method. The critical Reynolds number Re-c, the critical wave number alpha(c) and the critical wave speed c(c) are computed for various values of porous parameter and ratio of viscosities. Based on these parameters, the stability characteristics of the system are discussed in detail. Streamlines are presented for selected values of parameters at their critical state

PREVENTION OF DNA SUGAR, HUMAN PERIPHERAL LYMPHOCYTES AND ERYTHROCYTES DAMAGES FROM FREE RADICAL INDUCED OXIDATION BY NATURAL ANTIOXIDANTS

Objective: The present study focused on the identification of particular extract which shows signification protection of DNA sugar against excessive oxidation. Methods: The different extracts (water, alcohol, alcohol: water, and hexane) of Agathi seeds (Sesbania grandiflora Linn) were evaluated using various antioxidant and other relevant assays like DNA sugar protection and antioxidant activities. Results: The alcohol: water (1:1) extract of S. grandiflora Linn seeds showed the highest antioxidant and free radical scavenging activity. It inhibited membrane lipid peroxidation by 55% at 50 μg/ml, scavenged approximately 69% of hydroxyl and 1,1-diphenyl-2-picrylhydrazayl radicals at 2–3 fold lower concentrations compared to the other extracts. In addition, the alcohol: water extract inhibited ferrous sulfate: ascorbate-induced sugar oxidation of DNA and also showed non-toxic nature against lymphocytes. Conclusion: These results establish the antioxidant potential of the extract, which could be used as natural antioxidant source

Wild edible fruit tree resources of Arunachal Pradesh, North East India

The paper reports on the survey of wild edible fruit trees covering 49 sites from 17 districts of Arunachal Pradesh, India. A total of 52 wild edible fruits species representing 33 families was reported, out of which 10 had medicinal uses. The highest number of wild edible fruits belonged to family Moraceae (9 spp.) followed by Anacardiaceae (4 spp.) and Actinidiaceae (3 spp.). More than half the fruits (66.67%) are available during the monsoon season, i.e. between June and October. Dilenia indica, Castanopsis indica, Canarium strictum, Terminalia citrina, Phoebe cooperiana, Phyllanthus emblica and Artocarpus intergifolia are the commonly traded fruits. This is perhaps the only extensive survey which has so far been carried out on wild edible fruit tree resources covering all the districts of Arunachal Pradesh. In the present era where there is global interest on bioresource documentation, this study is significant for securing intellectual property right and preventing biopiracy

Electron-Beam Driven Relaxation Oscillations in Ferroelectric Nanodisks

Using a combination of computational simulations, atomic-scale resolution imaging and phenomenological modelling, we examine the underlying mechanism for nanodomain restructuring in lead zirconate titanate (PZT) nanodisks driven by electron beams. The observed subhertz nanodomain dynamics are identified with relaxation oscillations where the charging/discharging cycle time is determined by saturation of charge traps and nanodomain wall creep. These results are unusual in that they indicate very slow athermal dynamics in nanoscale systems.Comment: 5 pages, 2 figure

Nonequilibrium Keldysh Formalism for Interacting Leads -- Application to Quantum Dot Transport Driven by Spin Bias

The conductance through a mesoscopic system of interacting electrons coupled to two adjacent leads is conventionally derived via the Keldysh nonequilibrium Green's function technique, in the limit of noninteracting leads [see Y. Meir \emph{et al.}, Phys. Rev. Lett. \textbf{68}, 2512 (1991)]. We extend the standard formalism to cater for a quantum dot system with Coulombic interactions between the quantum dot and the leads. The general current expression is obtained by considering the equation of motion of the time-ordered Green's function of the system. The nonequilibrium effects of the interacting leads are then incorporated by determining the contour-ordered Green's function over the Keldysh loop and applying Langreth's theorem. The dot-lead interactions significantly increase the height of the Kondo peaks in density of states of the quantum dot. This translates into two Kondo peaks in the spin differential conductance when the magnitude of the spin bias equals that of the Zeeman splitting. There also exists a plateau in the charge differential conductance due to the combined effect of spin bias and the Zeeman splitting. The low-bias conductance plateau with sharp edges is also a characteristic of the Kondo effect. The conductance plateau disappears for the case of asymmetric dot-lead interaction.Comment: 11 pages, 3 figures, accepted by Annals of Physic