Dynamics of electromagnetic waves in Kerr geometry

Here we are interested to study the spin-1 particle i.e., electro-magnetic wave in curved space-time, say around black hole. After separating the equations into radial and angular parts, writing them according to the black hole geometry, say, Kerr black hole we solve them analytically. Finally we produce complete solution of the spin-1 particles around a rotating black hole namely in Kerr geometry. Obviously there is coupling between spin of the electro-magnetic wave and that of black hole when particles propagate in that space-time. So the solution will be depending on that coupling strength. This solution may be useful to study different other problems where the analytical results are needed. Also the results may be useful in some astrophysical contexts.Comment: 15 Latex pages, 4 Figures; Accepted for publication in Classical and Quantum Gravit

Dynamic elastic properties and magnetic susceptibility across the austenite-martensite transformation in site-disordered ferromagnetic Ni-Fe-Al alloy

Besides permitting an accurate determination of the ferromagnetic-to-paramagnetic phase transition temperature and the characteristic temperatures for the beginning and end of the growth of martensite (austenite) phase at the expense of austenite (martensite) phase while cooling (heating), the results of an extensive ac susceptibility, sound velocity and internal friction investigation of the thermoelastic martensitic transformation in melt-quenched (site-disordered) Ni55Fe20Al25 alloy provide a clear experimental evidence for the following. Irreversible thermoelastic changes (thermal hysteresis) occur in the austenite phase in the premartensitic regime. In the heating cycle, the system retains the "memory" of the initiation and subsequent growth of the martensitic phase (at the expense of the parent austenite phase) that had taken place during the cooling cycle in the austenite-martensite phase coexistence region. We report and discuss these novel findings in this communication.Comment: 5 figure

Behaviour of spin-1/2 particle around a charged black hole

Dirac equation is separable in curved space-time and its solution was found for both spherically and axially symmetric geometry. But most of the works were done without considering the charge of the black hole. Here we consider the spherically symmetric charged black hole background namely Reissner-Nordstrom black hole. Due to presence of the charge of black-hole charge-charge interaction will be important for the cases of incoming charged particle (e.g. electron, proton etc.). Therefore both gravitational and electromagnetic gauge fields should be introduced. Naturally behaviour of the particle will be changed from that in Schwarzschild geometry. We compare both the solutions. In the case of Reissner-Nordstrom black hole there is a possibility of super-radiance unlike Schwarzschild case. We also check this branch of the solution.Comment: 8 Latex pages and 4 Figures; RevTex.style; Accepted for Publication in Classical and Quantum Gravit

Linear and Nonlinear Optical Properties of Graphene Quantum Dots: A Computational Study

Due to the advantage of tunability via size, shape, doping and relatively low level of loss and high extent of spatial confinement, graphene quantum dots (GQDs) are emerging as an effective way to control light by molecular engineering. The collective excitation in GQDs shows both high energy plasmon frequency along with frequencies in the terahertz (THz) region making these systems powerful materials for photonic technologies. Here, we report a systematic study of the linear and nonlinear optical properties of large varieties of GQDs (400 systems) in size and topology utilizing the strengths of both semiempirical and first-principles methods. Our detailed study shows how the spectral shift and trends in the optical nonlinearity of GQDs depends on their structure, size and shape. Among the circular, triangular, stripe, and random shaped GQDs, we find that GQDs with inequivalent sublattice atoms always possess lower HOMO-LUMO gap, broadband absorption and high nonlinear optical coefficients. Also, we find that for majority of the GQDs with interesting linear and nonlinear optical properties have zigzag edges, although reverse is not always true. We strongly believe that our findings can act as guidelines to design GQDs in optical parametric oscillators, higher harmonic generators and optical modulators.Comment: 21 pages, 11 figures, 4 table

Geochemistry of Kauai shield-stage lavas: Implications for the chemical evolution of the Hawaiian plume

We measured He, Sr, Nd, Pb, and Os isotope ratios and major and trace element concentrations in stratigraphically and paleomagnetically controlled shield-stage lavas from Kauai, Hawaii. The range of 3He/4He ratios (17–28 RA) from Kauai is similar to that reported from Loihi and thus challenges the prevailing notion that high 3He/4He ratios are restricted to the preshield stage of Hawaiian magmatism. 3He/4He ratios vary erratically with stratigraphic position, and chronostratigraphic control from paleomagnetic data indicates very rapid changes in the 3He/4He ratios (up to 8 RA in ~102 years). These variations in helium isotopic ratios are correlated with variations in radiogenic isotope ratios, suggesting rapid changes in melt composition supplying the magma reservoir. A three-component mixing model, previously proposed for Hawaiian shield lavas, does not adequately explain the isotopic data in Kauai shield lavas. The addition of a depleted-mantle (DM) component with the isotopic characteristics similar to posterosional basalts explains the isotopic variability in Kauai shield lavas. The DM component is most apparent in lavas from the Kauai shield and is present in varying proportion in other Hawaiian shield volcanoes. Shield lavas from Kauai sample a high 3He/4He end-member (Loihi component), but while lavas from western Kauai have a larger contribution from the Kea component (high 206Pb/204Pb, anomalously low 207Pb/204Pb relative to 206Pb/204Pb), lavas from eastern Kauai have a larger proportion of an enriched (Koolau) component. The systematic isotopic differences between eastern and western Kauai reflect a gradual migration of the locus of volcanism from west to east, or alternatively east and west Kauai are two distinct shield volcanoes. In the latter case, the two shield volcanoes have maintained distinct magma supply sources and plumbing systems. Our new geochemical data from Kauai are consistent with the existence of a single high 3He/4He reservoir in the Hawaiian plume and suggest that the proportion of the different mantle components in the plume have changed significantly in the past 5 Myr. The long-term evolution of the Hawaiian plume and the temporal variability recorded in Kauai lavas require more complex geochemical heterogeneities than suggested by radially zoned plume models. These complexities may arise from heterogeneities in the thermal boundary layer and through variable entrainment of ambient mantle by the upwelling plume