Wave Propagation in 1-D Spiral geometry

In this article, we investigate the wave equation in spiral geometry and study the modes of vibrations of a one-dimensional (1-D) string in spiral shape. Here we show that the problem of wave propagation along a spiral can be reduced to Bessel differential equation and hence, very closely related to the problem of radial waves of two-dimensional (2-D) vibrating membrane in circular geometry

Possible use of self-calibration to reduce systematic uncertainties in determining distance-redshift relation via gravitational radiation from merging binaries

By observing mergers of compact objects, future gravity wave experiments would measure the luminosity distance to a large number of sources to a high precision but not their redshifts. Given the directional sensitivity of an experiment, a fraction of such sources (gold plated -- GP) can be identified optically as single objects in the direction of the source. We show that if an approximate distance-redshift relation is known then it is possible to statistically resolve those sources that have multiple galaxies in the beam. We study the feasibility of using gold plated sources to iteratively resolve the unresolved sources, obtain the self-calibrated best possible distance-redshift relation and provide an analytical expression for the accuracy achievable. We derive lower limit on the total number of sources that is needed to achieve this accuracy through self-calibration. We show that this limit depends exponentially on the beam width and give estimates for various experimental parameters representative of future gravitational wave experiments DECIGO and BBO.Comment: 6 pages, 2 figures, accepted for publication in PR

Synthesis and characterization of ultrafine hydroxyapatite (HAp) powder coating on stainless steel substrate by electrophoretic deposition.

In recent years, synthesis and characterization of ultrafine hydroxyapatite (HAp) powder coating on stainless steel substrate by electrophoretic deposition gives an active area of research due to their enhanced applicability in the medical field. This makes them very attractive as prosthetic replacements. Ultrafine HAp powder was obtained by milling elemental calcium phosphate mineral. The HAp powder was dispersed into isopropyl alcohol by ultrasonication and magnetic stirring. The HAp powder was deposited by electrophoretic deposition (EPD) using lead as anode and stainless steel substrate as cathode. Powder was coated on stainless steel substrate at a voltage of 60 volt and time was varying from 15 minutes to 1.5 hours. It was observed that HAp powder deposited at 60 volt for 45 minute gives the best coating. In another set of experiment, coating time was 45 minutes having periodic time of 10 minutes with gap of 2 minutes. It was also observed that there is lack of adherence of powder particles with the substrate. To improve adherence of particles with substrate a surfactant sodium dodecyl sulfate (SDS or NaDS) (C12H25SO4Na) was added during EPD process and subsequently sintering was performed at 8000C for 2 hours in open atmosphere. X-ray diffraction (XRD) shows the peaks of HAp after deposition. It was observed from XRD spectra that XRD patterns of HAp powder that was prepared by planetary milling and HAp powder was deposited on stainless steel substrate by EPD at 60 volts for 15 minutes. Here the some peaks of HAp are visible in the coated substrate along with peaks of stainless steel. The intensity of HAp peaks in the coated substrate is lesser than pure HAp powder. This is due to the presence of large peak of stainless steel along with HAp. It was observed from SEM analysis that HAp deposited on stainless steel substrate at 1 hour shows smooth and good adherence where as for deposition of 1.5 hours shows discontinuous and non-adherence deposition. As the time of deposition is increased there may be formation of thick layer which may generate cracks

Cosmology with decaying tachyon matter

We investigate the case of a homogeneous tachyon field coupled to gravity in a spatially flat Friedman-Robertson-Walker spacetime. Assuming the field evolution to be exponentially decaying with time we solve the field equations and show that, under certain conditions, the scale factor represents an accelerating universe, following a phase of decelerated expansion. We make use of a model of dark energy (with p=-\rho) and dark matter (p=0) where a single scalar field (tachyon) governs the dynamics of both the dark components. We show that this model fits the current supernova data as well as the canonical \LambdaCDM model. We give the bounds on the parameters allowed by the current data.Comment: 14 pages, 6 figures, v2, Discussions and references addede

Methane and carbon dioxide adsorption on edge-functionalized graphene: A comparative DFT study

With a view towards optimizing gas storage and separation in crystalline and disordered nanoporous carbon-based materials, we use ab initio density functional theory calculations to explore the effect of chemical functionalization on gas binding to exposed edges within model carbon nanostructures. We test the geometry, energetics, and charge distribution of in-plane and out-of-plane binding of CO2 and CH4 to model zigzag graphene nanoribbons edge-functionalized with COOH, OH, NH2, H2PO3, NO2, and CH3. Although different choices for the exchange-correlation functional lead to a spread of values for the binding energy, trends across the functional groups are largely preserved for each choice, as are the final orientations of the adsorbed gas molecules. We find binding of CO2 to exceed that of CH4 by roughly a factor of two. However, the two gases follow very similar trends with changes in the attached functional group, despite different molecular symmetries. Our results indicate that the presence of NH2, H2PO3, NO2, and COOH functional groups can significantly enhance gas binding with respect to a hydrogen-passivated edge, making the edges potentially viable binding sites in materials with high concentrations of edge carbons. To first order, in-plane binding strength correlates with the larger permanent and induced dipole moments on these groups. Implications for tailoring carbon structures for increased gas uptake and improved CO2/CH4 selectivity are discussed.Comment: 12 pages, 7 figure