Search

The paper deals with a theoretical study of electrokinetic flow of a rheological Herschel-Bulkley fluid through a cylindrical tube of variable cross-section. The concern of this study is to analyze combined pressure-driven and electroosmotic flow of Herschel-Bulkley fluid. The wall potential is considered to vary slowly and periodically along the axis of the tube. With reference to flow in the micro-vessels, the problem has been solved using the lubrication theory. The Helmholtz-Smoluchowski (HS) slip boundary condition has been employed in this study. Volumetric flow rate $Q$ is found to be significantly affected by the yield stress parameter $\nu$ only if an applied pressure force is active. The linear superposition of flow components separately due to the hydrodynamic and electric force occurs only for a strictly uniform tube. This linear relationship fails if non-uniformity appears in either tube radius or in distribution of the electrokinetic slip boundary condition. Moreover, converging/diverging nature of the mean tube radius plays a crucial role on the fluid transport. For the benefit of readers, along with the original contribution, some applications of external electrical stimulation (ES) in the human body and HS slip velocity, studied in the past by previous researchers have been discussed in the paper., Comment: 44 pages and 28 figures

In this note we provide an important and significant observation in ring theory related to weakly tripotent rings. We provide counterexamples for the structure theorem for commutative weakly tripotent rings appeared in arXiv (2017) and Bull. Korean Math. Soc.(2018)., Comment: 4 pages. This is a completely revised and corrected version of the article

In this note we provide some results related to the Koethe conjecture and exhibit that the condition R satisfies the Koethe conjecture given in [2, theorem 2.6 ] is superfluous at least under certain conditions described in this note., Comment: 4 pages. This is slightly revised version of the article

We have systematically studied the magnetic properties of chromium chalcogene compounds FeCr$_2$Se$_{4-x}$Te$_x$. The FeCr2Se4 undergoes antiferromagnetic ordering below 222 K. Substitution of tellurium lowers the antiferromagnetic ordering temperature and leads to short range ferromagnetic cluster behavior towards the tellurium end. Change over from antiferromagnetic to ferrimagnetic like behavior is also reflected in the corresponding transformation from semiconducting to metallic transport behavior. There is a large variation in the Curie-Weiss temperature, effective magnetic moment and ordering temperature (TN / TC) with Te substitution. The electronic band structure calculations suggest antiferromagnetic and ferrimagnetic ground state for the FeCr2Se4 and FeCr2Te4 respectively., Comment: 7 pages, 8 figures

One of the popular models for the low/hard state of Black Hole Binaries is that the standard accretion disk is truncated and the hot inner region produces via Comptonization, the hard X-ray flux. This is supported by the value of the high energy photon index, which is often found to be small $\sim$ 1.7 ($<$ 2) implying that the hot medium is seed photons starved. On the other hand, the suggestive presence of a broad relativistic Fe line during the hard state would suggest that the accretion disk is not truncated but extends all the way to the inner most stable circle orbit. In such a case, it is a puzzle why the hot medium would remain photon starved. The broad Fe line should be accompanied by a broad smeared reflection hump at $\sim$ 30 keV and it may be that this additional component makes the spectrum hard and the intrinsic photon index is larger, i.e. $>$ 2. This would mean that the medium is not photon deficient, reconciling the presence of a broad Fe line in the observed hard state. To test this hypothesis, we have analyzed the RXTE observations of GX 339-4 from the four outbursts during 2002-2011 and identify the observations when the system was in the hard state and showed a broad Fe line. We have then attempted to fit these observations with models, which include smeared reflection to understand whether the intrinsic photon index can indeed be large. We find that, while for some observations the inclusion of reflection does increase the photon index, there are hard state observations with broad Fe line that have photon indices less than 2., Comment: 12pages, 5figues, submitted to RAA

We present optical imaging and spectroscopic studies of the Fanaroff \& Riley class I (FR I) radio galaxy CTD 086 based on Hubble Space Telescope (HST) and Sloan Digital Sky Survey (SDSS) observations. We use isophote shape analysis to show that there is no stellar disk component within CTD 086 and further that the morphological class of the galaxy is most likely E2. Optical spectroscopy of this galaxy reveals the presence of narrow emission lines only, and thus it qualifies to be termed as a narrow-line radio galaxy (type 2 AGN). We also extract stellar kinematics from the absorption-line spectra of CTD 086 using Penalized Pixel-Fitting method and derive the black hole mass MBH to be equal to (8.8\pm2.4)\times10^{7} Msun., Comment: No. of Pages 14, Figures 5, No of table 2 and Accepted for publication in Astrophysics and Space Science

In this note we find the least order of a noncommutative even square ring and we note that it is a nil ring having characteristic four. In order to prove the main result given in this note we mainly use suitable examples., Comment: 3 pages, This is slightly improved version of the earlier version

We have examined the electronic structure evolution in transition metal dichalcogenides MX$_2$, where M=Mo,W and X=S,Se and Te. These are generally referred to as van der Waals heterostructures on the one hand, yet one has band gap changes as large as 0.6 eV with thickness in some instances. This does not seem to be consistent with a description where the dominant interactions are van der Waals interactions. Mapping onto a tight binding model allows us to quantify the electronic structure changes which are found to be dictated solely by interlayer hopping interactions. Different environments that an atom encounters could change the Madelung potential and therefore the onsite energies. This could happen while going from monolayer to bilayer as well as in cases where the stackings are different from what is found in 2H structures. These effects are quantitatively found to be negligible, enabling us to quantify the thickness dependent electronic structure changes as arising from interlayer interactions alone.

We present a multi-wavelength study of a nearby radio loud elliptical galaxy NGC708, selected from the Bologna B2 sample of radio galaxies. We obtained optical broad band and narrow images from IGO 2m telescope (Pune, India). We supplement the multi-wavelength coverage of the observation by using X-ray data from Chandra, infrared data from 2MASS, Spitzer and WISE and optical image from DSS and HST. In order to investigate properties of interstellar medium, we have generated unsharp-masked, color, residual, quotient, dust extinction, H_alph emission maps. From the derived maps it is evident that cool gas, dust, warm ionized H_alpha and hot X-ray gas are spatially associated with each other. We investigate the inner and outer photometric and kinematic properties of the galaxy using surface brightness profiles. From X-ray 2d beta model, unsharp masking, surface brightness profiles techniques, it is evident that pair of X-ray cavities are present in this system and which are ~5.6 Kpc away from the central X-ray source., Comment: 2 Pages, 1 Figure, 1 Table. From interstellar clouds to star-forming galaxies: universal Processes:Proceedings IAU Symposium No. 315, 2015